Note: Descriptions are shown in the official language in which they were submitted.
WO91/02711 PCT/~S90/04~2'
-l- 2 ~
7,7-DIMETHYLNORBORNANE DERIVATIVES
BACKGROUND AND SUMMARY
This invention relates to novel nor~ornane derivatives
and processes for their preparation and conversion o~ such
derivatives to high intensity artificial sweeteners. In
addition, this invention also relates to novel catalysts for
the preparation of fenchyl alcohol and alpha-fenchene.
The novel norbornane derivatives of this invention are
more speci~ically represented by formula (I) as follows:
I~-`Y (~
wh e r e i n Y i s -CHO,
.
C H o r ~<QN H
wherein R is hydrogen or a lower alkyl group of one to three :
carbons and wherein R' is hydrogen or a lower alkyl group of
one to three carbons. The compounds of f ormula (I) are very
useful as intermediates for the production of high intensity
sweQteners, particularly L-aspartyl-3-(7,7-dimethylnorbornyl)-
L-alanine derivatives of the following formula:
.. : : . . . : - .
';~' ~ ~ '. ' ' . . ' ' .
.: .
W091/02~11 PCT/US~/W722
6 ~4
/
~ ~C 11 - H - C - C 11 - C r 2 ~ C O O ~ ( l V )
:'
wherein R is a lower alkyl group of one to three carbons.
Such high intensity sweeteners are described in U.S. Patent
~o. 4,788,069.
In U.S. Patent No. 4,78~,069 the preparation of sweetener
(IV) involves the synthesis of the amino acid I-2 and the
amino ester I-3, the later being prepared from the former via
esterification with methanolic hydrochloric acid.
~ ~ C - ~U~ 1 -2 , R
.,
Tws methods are di3clo~ed for the preparation of I-2 and
related bicyclic amino acids. In the first, alpha-fenchene is
converted to the corresponding 7,7-dimethylnorbornyl-2-
methanol u~ing diborane and hydrogen peroxide. This
intermediate is then converted to the tosylate and condensed
with sodium dimethylmalonate to give a norbornyl malonic acid
diester. To finally arrive at amino acid I-2, three
:,
. ~ . , . " . . . . . .
- . , ~ , .
wos~ l PCT/US~/~722
3206~01~
additional steps, bromination, hydrolysis and amination, are
required. The overall process known in the art is very
expensive and give~ only low yields of the I-2. In the second
method, alpha-fenchene is treated with 9-
bcrabicyclo~3.3.1]nonane and the resulting hydroboration
product condensed with methyl-N-(diphenylmethylene)-2-
acetoxyglycinate to give an adduct which can be hydrolyzed to
I-3 with dilute acid. This method, although much simpler than
the first, involves the use of very expensive reagents and
would not be economical on an industrial scale.
The present invention overcomes the disadvantageR of the
prior art by converting alpha-fenchene directly to the novel
aldehyde I-1 either via reductive carbonylation or via the
Vilsmeier reaction and catalytic hydrogenation. See Reaction
Schemes A and B. The novel norbornyl aldehyde I-l can b~
readily converted to amino acid I-2 via I-4 (the Strecker
reaction) or via I-5 (the hydantoin procedure~. In both cases
yields are high and reagent costs low.
The present invention provides a process for ~aXing 3-
(2R-exo-7,7-dimethylnorbornyl)-L-alanine lower alXyl esters
represented by the following formula:
. . _ , , :.
[~ / ;H C-CH -Cll 2-COOII ( I V ) ~ `'
wherein R represents a lower alkyl group of 1 to 3 carbon
atoms comprising the steps of: (a) rearranging (-)-~n~-2-
.,' . , ~- : . .:
:: . . - , . - :
.. . . .
: : :
.
~ '' . ` . . .
WO91~02~1l PCT/US~/~722
~ 4-
pinanol to form (+)-alpha-fenchyl alcohol; (b) dehydrating
(+)-alpha-fenchyl alcohol to form (+)-alpha-fenchene;
(c) converting the (+)-alpha-fenchene to 2R-exo-7,7-
dimethylnor~ornyl acetaldehyde; (d) converting 2R-exo-7,7-
dimethylnorbornyl acetaldehyde to 3-(2R-exo-7,7-
dimethylnorbornyl)-D,L-alanine (e) resolving 3-(2R-exo-7,7-
dimethylnorbornyl)-D,L- alanine to produce 3~(2R-exo-7,7-
dimethylnorbornyl)-L- alanine; and (f) esterifying 3-(2R-exo-
7,7-dimethylnor- bornyl)-L-alanineto form 3-(2R-exo-7,7-
dimethylnorbor- nyl)-L-alanine lower alkyl ester. In the
above process step (d) may comprise converting the
acetaldehyde to an aminonitrile and hydrolyzing the nitrile to
form 3-(2R-exo-7,7-dimethylnorbornyl)-D,L-alanine.
Alternatively, in the above process step (d) may comprise
converting the acetaldehyde to a hydantoin and hydrolyzing the
hydantoin to for~ 3-(2R-exo-7,7-dimethyl- norbornyl)-D,L-
alanine. In the above process the step of resolving ~ay occur
after the step of esterifying.
In step (a) (+)-alpha-fenchyl alcohol is produced by
reacting (-)-trans-2-pinanol with a catalyst selected from the
group of aluminum phosphate, niobium oxide and nickel sulfate.
General methods of producing alpha-fenchyl alcohol
include, for example, (1) the Wagner-Meerwein type
rearrangement reaction of alpha- or ~eta-pinene with mineral
acids or organic acids [G. G. Henderson et al., J. Chem. Soc.,
125, 107-13 (1924)], (2) the reduction of fenchone with
various reducing agents, for example metallic sodium and
alcohol tW. Huckel et al., Chem. Ber. 90, 2025 (1957); P.
Teisseire et al., ~echerches, 19, 232 (1974)] and (3) the
rearrangement o~ n~-2-pinanol with perchloric acid or
acetic anhydride t~. Indyk et al., J. Chem. Soc. Perkin II,
:'
?
- :
O9l/02,lI pCT/~S~/~7~7
_5_ 2 0 ~ S 0 ~ ~
3113 (1974), W. D. Burrows et al., J. Am. Chem. Soc. 81, 245
(1959)~.
In the Wagner-Meerwein type reaction in method (1), the
selectivity of alpha-fenchyl alcohol or alpha-fenchyl alcohol
derivative is 10% or less, and it is dif~icult for this method
to give alpha-fenchyl alcohol at a high selectivity. In
method (2), the production of fenchone itssl~ is complex [G.
~uchbauer et al~, Liebigs. Ann. Chem., 2093 tl981)]. Method
(3) is not economically feasible because it requires acetic
anhydride or a large amount of solvent and the product i
obtained as alpha- fenchyl acetate.
The present invention overcomes the problems of the prior
art and provides an economical industrial method of producing
alpha-fenchyl alcohol from trans-2-pinanol as a starting
material.
In step (b) above, (+)-alpha-fenchyl alcohol is converted
to (+)-alpha-fenchene by heating in the presence of a
specially prepared aluminum oxide catalyst disclosed herein.
one prior process for producing alpha-fenchene comprises
solvolyzing fenchyl tosylate with acetic acid in the presence
of an excess of sodium acetate thereby giving alpha fenchene
in a selectivity of 90% [W. Hueckel et al., Liebigs Ann. Chem.
664, 31 (1963)]. However, this process is economically and
industrially disadvantageous because tosylation of -fenchyl
alchol requires a large amount of pyridine and a long period
of reaction ~me and the solvolysis requires a large amount of
acetic acic As a method of dehydrating and rearranging
fenchyl alcohol to alpha-fenchene, the use of potassium
sulfate [W. ~ueckel et al., Liebigs Ann. Chem., 687~ 40
(1965)], the use of aluminum phosphate tD. Tishchenko et al.,
Zhur. Obshchei Khim., ~, 1824-29 (1952)], and the use of
kaolin or zinc chloride [E. Pulkkinen, Suomen Kemistilehti,
- .
. :, : . . :-:- . -
, :
WO 91/0271 I j~,~,, P/~/I~Sgo/04722
6--
~Q~, 239 (1957)] are known. In all o~ these methods, theselectivity and yields of alpha-fenchene are about 20 to 30%,
and are not industrially satisfactory.
The present invention overcomes the above disadvantages
of the prior art and provides a co,~ ercial process utilizin~ a
solid acid catalyst and heat to convert renchyl alcohol to
alpha-fenchene with high selectivity and high yield.
The present invention also discloses a process for
purifying (+)-alpha-fenchyl alcohoI, which comprises
crystallizing alpha-fenchyl alcohol in a hydrocarbon solvent
at low temperatures.
In steps (c) through (f) described above the intermediate
(+)-alpha-fenchene is converted to amino acid ester I-3 via
the novel intermediates I-l, I-4, and I-5 using procedures
described in the literature. See Reaction Schemes A and B and
the specification below.
The present invention also provides a proces~ for
producing alpha-L-aspartyl-3-(2R-exo-7,7-dimethylnor~or- nyl)-
L-alanine lower alkyl ester represented by the following
formula:
- .
\~ '~
~\\C H -11 H - C - C H - C H 2 - C O O H ( I V ) ~:
wherein R is a lower alkyl group of one to three carbon
atoms comprising the steps of: (a) coupling 3-(2R-exo-7,7-
,: : :: ~ - . .
WO91/02~11 PCT/~S~/~722
2~.)014
dimethylnorbornyl)-L-alanine lower alkyl ester with an N-
protected aspartic acid anhydride to produce an N-protected-
(alpha/beta~-L-aspartyl-3-(2R-exo-7,7-dimethylnorbornyl)-L-
alanine lower alkylester; (b) deprotecting the N-protected-
(alpha/beta)-L-aspartyl-3-(2R-exo-7,7-di~ethylnorbornyl)L-
alaninelower alkyl ester to produce a mixture of alpha and
beta-L-aspartyl-3-(2R-exo-7,7-dimethylnorbornyl)-L-alanine
lower alkyl estçrs; and (c) separating the alpha-L-aspartyl-
3-(2R-exo-7,7-dimethylnorbornyl)-L-alanine lower alkyl ester
from the mixture. The step of deprotecting may occur after
the step of separating. An N-protected aspartic acid havin~ a
beta-ester protecting group may be utilized for the N-
protected aspartic acid anhydride.
~ he present invention also discloses a process for
producing an optically active 3-(2R-exo-7,7-dlmethylnor-
bornyl)-L-alanine or its lower alkyl ester, which comprises
treating an N-acyl-3-(2R-exo-7,7-dimethyl~or- bornyl)-D,L-
alanine or its lower alkyl ester with an acylase in an aqueous
medium, and recovering the resulting 3-(2R-exo-7,7-
dimethylnorbornyl)-L-alanine or its lower alkyl ester.
In the present invention, the term "lower" used to
qualify a group or a compound includes methyl, ethyl, n-
propyl, and isopropyl groups.
An advantage o~ the present invention is to provide the
novel 7,7-dimethylnorbornane derivatives of-formula (I) which
are use~ul as synthesis intermediates for the preparation of
L-aspartyl-3-(2R-exo-7,7-dimethylnorbornyl)-L-alanine
derivativ~ of formula (IV), particularly the compound of
formula (IV-l, R-CH3), which are useful as sweeteners having
high sweetening power.
Another advantage of the present invention is to provide
a process for producing the L-aspartyl-3-(7,7-
:~ '
. .
: , , ., - ::
- . : .
.
091~0271~ 4 PCT/US~/~722
--8--
dimethyl~orbornyl)-L-alanine derivatives of formula (IV)
useful as sweeteners from the novel 7,7-dimethylnorbor- nane
derivatives of ~ormula (I).
Another advantag~ of the present invention is to provide
novel catalysts use~ul in the preparation of fenchyl alcohol
and alpha-fenchene.
In summary the present inventio~ discloses compounds
repre~ented by the following formula:
I~Y ( 1
w h ~ r e i n Y i s - C H O ,
.
NH2 NHCR'~ r
C N C O O R H N~
wherein R is hydrogen or a lower alkyl group of one to three
car~ons and wherein R' is hydrogen or a lower al~yl group of
one to three carbons. The present invention discloses 2R-
exo-7,7-dimethylnorbornyl acetaldehyde, 3-(2R-exo-7,7-
dimethylnorbornyl)-2-aminopropionitrile and 3-(2R-exo-7,7-
dimethylnorbornyl)alanine hydantoin. A compound compri~ing N-
acyl-3-(2R-exo-7,7-dimethylnorbor- nyl)-D,L-alanine, wherein
acyl is acetyl, propionyl, butyryl or chloroacetyl is
disclosed in the present invention. ~pecifically, N-acetyl-
,
WO91/02~11 PCT/~'S~/~722
20~:~014
_9_
3-(2R-exo-7,7-dimethyl-norbornyl)-D,L-alanine and N-
chloroacotyl-3-(2R-exo-7,7- dlmethylnorbornyl)-D,L-alanine are
disclosed.
A fenchyl alcohol dehydration catalyst selected ~rom the
group consisting of calcined aluminum oxide is disclosed;
specifically, the dehydration catalyst comprising calcined
aluminum oxide having Hammett acidity function of -5.6cHS-
3.0 is described. Finally, there is also disclosed a catalyst
for producing alpha-fenchyl alcohol from trans-2-pinanol,
selected from the group aluminum phosphate, niobium oxide and
nickel sulfate.
DESCRIPTION OF THE PREFERRED EM3ODIMENTS
The compounds of formula (I) in accordance with this
invention [the compounds of formulae (I-l), (I-2) and (I-33 in
the following reaction scheme] may be produced by a synthetic
route summarized in the following reaction Scheme A.
~ . ., .: , : .. . . . -
WO 91/02~ PCr/US90/~47~2
--10--
Re~ç~t ion Scheme A
_ ,
OH _ _ ~
l~orncrl20110n OH l~m~rlZO~lon
1rcnr-2-pino~ol -~-nchol
Vil~rnoior roogcn~ ~ ~
-lonchono doh~dro (1-l)
( 1-1 ) ~=
~N ~
~0; /a~OH)2
t 5 t o r i f i c a t i o n ~, ~N R 2
( 1-2)
'''
: :- . :, . : :.
- :: . ... .
~ ;- :. . ::
.
WO9l/02/ll PCT/~S~/~22
206;,~14
In the abcve Reaction Scheme A, alpha-fenchyl alcohol is
prepared in a high conversion and at a high ~electivity by
heating tr~n~-2-pinanol to a temperature of 60 to 150C in the
presence of one or more catalysts selected from aluminum
phosphate, nio~ium oxide and nic~el sul~ate.
This method will be doscribed below in detail. ~ns-2-
pinanol used as a starting material in this method can usually
be obtained by subjectin~ nopinone (obtained by oxidation of
beta-pinene with ozone or potassium permanganate) to Grignard
reaction with a methyl magnesium halide tW. Huckel et al.,
Liebigs, Ann. Chem., 625, 12, (1959)], or by catalytically
reducing alpha- or beta-pinene to form pinane, oxidizing it
with oxygen and reducing it further ~S. G. Traynor et al.,
J. Org. Chem., 45, 900 (1980).
Aluminu~ phosphate used as the catalyst in this invention
can be obtained by hydrolyzing hydrous aluminum nitrate,
hydrous aluminum sulfate, hydrous aluminum chloride or sodium
aluminate with an aqueous solution o~ ~ nonmetallic alkali,
i.e. ammonia or urea, adding an equivalent weight of ortho-
phosphoric acid to the re~ulting aluminum hydroxids to permit
precipitation, and calcining the resulting hydrous aluminum
phosphate at a temperature of 300 to 800C, preferably 300C,
for about 3 hours.
Niobium oxide used as the catalyst in the method of this
invention may contain water. Niobium oxide and its hydrate
(so-called niobic acid) may generally be produced by
precipitation from a solution of a niobium compound such as
niobium chloride or niobiuo oxalate by the action of an
alkali. U~ually, the resulting precipitate contains a
considerable amount of water, but it can be dehydrated almost
completely by heating to more than 200C. Niobic acid
: , : ::: .:. . : . . .
:. ; . : :: :
. . .
.
WO91/02711 PCT/~S~W72'
6~ 4 -12-
obtained by precipitation Erom solution can be used as such or
after calcination at soooc or below, as niobium oxide.
Nickel sulfate as another catalyst can be prepared by
calcination of a commercially available nickel sul~ate
hydrate.
The treatment of trans-2-pinanol in the presence of the
catalyst may be carried out at a temperature of 60 to 150C,
preferably 65 to ~5C.
The suitable amount of the catalyst used is about l to
10% by weight based on the ~n~-2-pinanol. The reaction in
this invention is usually performed without solvent. In view
of the separation of the desired compound from the reaction
products, the conversion o~ trans-2-pinanol is preferably at
least 90%.
After the reaction, tha reaction mixture is filtered to
remove the catalyst, and the residue distilled in a customary
manner. Alternatively, the reaction mixture may be directly
distilled without separation of the catalyst.
The starting trans-2-pinanol includes a (~)-form and a (-
)-form, and its optical purity can be determlned by its
specific rotation. The present inventors condensed trans-2-
pinanol with N-carbobenzyloxy-(D)- or (L)-alanoyl chloride in
the presence of pyridine, removed the N-protecting group from
the reaction product, and measured its optical purity by gas
chromatography ~the gas chromatographic column is, for
example, a PEG-HT capillary, 0.25 mm. in diameter, 25 m. in
length; made ~y Gasukuro Kogyo Co., Ltd.,). Alpha-fenchyl
alcohol obtained by the method of this invention also includes
a (+)-form and a (-)-form. The use of either the (+)-form or
(-)-form of ~rans-2-pinanol can give either one of theise
forms. For example, if the method of this invention is
carried out by using t-)-trans-2-pinanol obtained by the
,~, "
. . . ~ : ~ , . . . .
~() (!1~)!~1 I PCr/l:S90/W/2Z
2 0 6 ,~
method of the above-cited Liebigs Ann. Chem., 62S, 12, (1959)
as the starting material, (+)-alpha-fenchyl alcohol is
obtained without racemization.
The method of this invention can economically give alpha-
f~nchyl alcohol useful as a material for a perfume or as a
sweetener intermediate as described below.
In the above Reaction Scheme A, fenchyl alcohol is heated
in the presence of a ~olid acid catalyst to per~orm a
dehydration and isomerization reaction simultaneously to
selectively produce alpha-fenchene.
It has now been found in accordanc~ with this invention
that aluminum oxide is especially suitable as the solid acid
catalyst used in this reaction. Especially suitable is
aluminum oxide prspared by hydrolyzing hydrous aluminum
nitrate, hydrous aluminum sulfate, hydrous aluminum chloride
or sodium aluminate with an aqueous solution of a non-metallic
alkali such as ammonia or urea and calcining the resulting
aluminum hydroxide. More specifically, thi~ aluminum oxide is
obtained by dispersing a lOS by weight aqueous solution of
aluminum nitrate hydrate in 28% aqueous ammonia at room
temperature to hydrolyze it, separating and recovering the
resulting aluminum hydroxide precipitate by filtration in a
customary manner, and calcining the resulting aluminu~
hydroxide at a te~perature range of from about 400 to 600C,
preferably about 500C, for about 3 hours. The acid strength
of the aluminum oxide prepared under these conditions,
expressed by the Ham~ett acidity function, is -5.6<~os-3Ø
It is a solid acid o~ a medium acidity.
For the conversion to fenchene the solid acid can
generally be used in an amount of 0.1 to 19%, preferably 1 to
5~, based on the weight of the starting fenchyl alcohol.
..... ~ .~ ~- , . . .
: ~ , . , {
,, .
- ~: ,. .
.: . . . ~ . .
'~ ' , . . , : ' ~ . -
PCT/~'S~/~72'
-14-
The reaction temperature is usually in a range from about
150 to 250C, particularly 195 to 2000C. If the reaction
temperature is too low, the rate o~ the reaction becomes slow.
The reaction time varies with the ~enchyl alcohol used, but
usually a period of time ranging from about 1 to 24 hours
suffices.
The presence of water in the reaction system in the above
reaction is undesirable, and it is preferred to carry out the
reaction in a reactor equipped with a water removing device
such as the Dean-Stark device. Usually, the reaction can be
carried out without using a solvent.
After the reaction, the reaction mixture is distilled
with or without prior separation of the catalyst, and as
required, rectified in a rectification column.
The starting fenchyl alcohol may be either alpha-fenchyl
alcohol or beta-fenchyl alcohol. Alphafenchyl alcohol can be
obtained commercially or prepared from trans-2-pinanol as
described above. Beta-fenchyl alcohol can be obtained in a
high purity by catalytically reducing fenchone, converting the
resulting mixture of alpha- and beta-fenchyl alcohols into
their crystalline p-nitrobenzoates, recrystallizing
repeatedly, and hydrolyzing the purified product.
Alternatively, a mixture of alpha-fenchyl alcohol and beta-
fenchyl alcohol may be obtained by epimerizing alpha-fenchyl
alcohol under hydrogen pressure in the presence of a copper-
chromiu~ catalyst.
In the production of L-aspartyl-3-(2R-exo-7,7-
dimethylnorbornyl~-L-alanine methyl ester of formula (IV-1,
R=CH3) in particular, the use of (+)-alpha-fenchyl alcohol as
the starting material is preferred. ~he (+)-alpha-fenchyl
alcohol may be isolated and purified in a high optical purity
of, for exa~ple, about 94~ e.e. by crystallizing commercial
.. . .
, . .- . . - ~
, . , . . - ~ , . , . -
~.-- .. .. . - ~ . . , : .
\~)9lJ0~~ll PCT/~S~/W722
2~6~
--15--
alpha-fenchyl alcohol in a hydrocarbon type organic sol-ent at
low temperatures.
The commercially available alpha-fenchyl alcohol is
generally a mixture of the (+)-alpha-isomer and the (-)-alpha-
isomer in a weight ratio of from 80:20 to 70:30.
C.ystallization of the commercial alpha-fenchyl alcohol in an
aliphatic hydrocarbon solvent such as n-pentane, n-hexane,
isohexane, n-heptane, n-octane and isooctane ~preferably n-
heptane or n-octane) gives the (+)-alpha-isomer of high
purity, for example an optical purity of 94 S e.e. or more.
The crystallization treatment can be carried out by
dissolving the alpha-fenchyl alcohol in the solvent at roo~
temperature or at a slightly elevated temperature and cooling
the solution to a temperature of about -10 to -60C,
preferably -35 to -60C.
A product having a sufficient optical purity may be
obtained by one crystallization, but by repeating the
crystallization two or three times, a product of a very high
optical purity can be obtained.
The optical purity of the purified (+)-alpha- fenchyl
alcohol can be determined by its specific rotation. The
present inventors measured the optical purity of the alpha-
fenchyl alcohols by gas chromatography of their L-alanine or
D-alanine esters (the col o may be, for example, PEG-HT
capillary, 0.25 mm in diameter and 25 m in length, made by
Gasukuro ~ogyo K. R.). ~he sample wa prep~red by condensing
alpha-fenchyl alcohol with N-carbobenzyloxy-(D) or (L)-alanine
using a dehydrating agent such as dicyclohexylcarbodiimide
(DCC) or l-ethyl-3- (3-dimethylamino- propyl)carbodiimide
hydrochloride in the presence of N,N-dimethylaminopyridine, or
by condensing alpha- fenchyl alcohol with N-butoxycarbonyl-
(D) or (L)-aianine using the above dehydrating agent.
..... . ... . . .
: ,, '' ~ , ~ ,
:: - . , .
WO9l/02,lI PCT/~'S~/~722
~Q~ -16-
The amino protecting groups are then removed by
hydrogenation (the N-carbobenzyloxy group) or acid treatment
(the N-t-butoxycarbonyl group) prior to G.C. analysis.
In the above dehydration-isomerization reaction o~
fenchyl alcohol to alpha-fenchene, the rate of the reaction of
beta-fenchyl alcohol is faster than that o~ its alpha-epimer.
The reaction with beta-fenchyl alcohol generally comes to
completion within 3 hours, and alpha-fenchene forms with a
selectivity of about 80~. On the other hand, when alpha-
fenchyl alcohol is used as the starting material, the
selectivity for alpha-fenchene after 16 hours is about 59%.
When a mixture of alpha- and beta-fenchyl alcohols (alpha/beta
s 6/4) is used, the selectivity for alpha-fenchene i~
increased to 65~.
The alpha-fenchene so obtained is subjected to the
Vilsmeier reaction to form 7,7-dimethyl-2-~ormyl-
methylenenorbornane. Stereoselective reduction~ of this
product yields 2R-exo-7,7-dimethylnorbornyl acetaldehyde (I-
1) .
Tha Vilsmeier reaction of alpha-fenchene can be carried
out by a known method described, for example, in C. Jutz et
al., Chem. Ber. 100, 1536 (1967). For example, alpha-
fenchene is added to the Vilsmeier reagent prepared at room
temperature from phosgene or thionyl chloride and an N,N-
disubstituted formamide such ac N-methylformanilide;
preferably from phosphoru3 oxychloride and more than one
equivalent of N,N-dimethylformamide. The mixture i8 reacted
at a temperature of 50 to gooc to give dehydro~ 1) as an E-
/Z- mixture.
The resulting 7,7-dimethyl-2-formylmethylenenorbornane
[dehydro-(I-1)] is reduced to give 2R-exo-7,7-dimethyl-
norbornyl acetaldehyde of for~ula (I-1). Reduction of
~,. . . : : ;i .;, . . .
.: .^~ .: . ,
. . . . . . . .
~09l/02~ll PCT/US~/W~22
2 ~
dehydro~ 1) may be carried out by a catalytic hydrogenation
method using hydrogen in the presence of a noble metal
catalyst such as palladium on carbon. As a result, the
compound of formula (I-l) can be obtained with an exo-
selectivity of as high as or greater than about 95S.
As an alternative, alpha-fenchene may be directly
converted to 7,7-dimethylnorbornyl-2-acetaldehyde of formula
(I-l) by oxo reaction using various rhodium complex catalysts.
According to this method, the selectivity of the exo-form of
formula (I-l) is somewhat inferior to that in the method which
goes through dehydro-(I-l).
The oxo reaction of alpha-fenchene may be carried out in
the same way as an ordinary oxo reaction described, for
example, in W. Himmele et al., Tetrahedron Letters, 907, 1976
and J. Hagen and K. Bruns, U.S. Patent No. 4,334,100. For
example, alpha-fenchene is hydroformylated with a gaseous
mixture of carbon monoxide and hydrogen a~ a temperature of
about 30 to about 150C under a gas pressure of about ~5 to
about 150 kg/cm2 in the presence of a rhodium complex
catalyst, for example a rhodium carbonyl complex such as
Rh6(CO)16, RhCl(CO)(pph3)2 (pph3 stand for
triphenylphosphine), RhH(CO)(pph3)3, [Rh(COD)X~2 ~COD stands
for cyclooctadienyl and X i5 halogen, acetate) or
Rh(COD)(acac) (acac stands for acetyl acetonate).
The resulting 2R-exo-7,7-dimethylnorbprnyl acetaldehyde
of formula (I-1) is then reacted wi~h ammonia or ammonium
chlorido and hydrogen cyanide or an alkali cyanide in
accordance with Strecker'samino acid synthesis method [see,
for example, J.P. Green~tein & M. Winitz, "Chemistry of the
Amino Acids," Vol. I, pg. 698-700 (1961); R. Gardry, Can. J.
Res., ~, 301 (1946)]. The resulting 3~(2R-exo-7,7-
dimethylnorbornyl) -2-amino propionitrile (I-4) is hydrolyzed
~.
; -
091/0271l 6~4 PCT/US~/~22
-18-
under acidic conditions created by a mineral acid such as
hydrochloric acid, hydrobromic acid or hydriodic acid to give
3-(2R-exo-7,7-dimethylnorbornyl)-D,L-alanine of formula (I-
2).
The Strecker reaction can be conducted in alcoholic or
mixed alcoholic-aqueous solution using ammonia gas or ammonium
hydroxide solution. The cyanide can be supplied as the Li, Na
or K salt, the more soluble Li and Na salts being preferred.
Reaction temperatures of 0 to 30OC may be employed, the time
being adjusted accordingly. After removal of the solvent by
evaporation the residue is treated with a strong base (such as
NaOH, KOH or Na2CO3) and the aminonitrile extracted with
ether, toluene, or any suitable organic solvent which does n~t
react with the amino function.
Hydrolysis of the resulting 3-(2R-exo-7,7-dimethyl-
norbornyl~-2-amino propionitrile is best achieved by refluxing
in approximately 10 ~ HCl solution for 18 hours. ~Lower acid
concentrations may be used, but longer reaction times are
required. Shorter reaction times may be achieved by heating
at elevated temperatures in an autoclave. Other acids may
also be employed such as hydrobromic or sulfuric.
Hydrochloric i5 particularly useful in that the product can be
obtained as the hydrochloride by direct crystallization from
the cooled, concentrated reaction mixture.
An alternative method for producing the amino acid of
formula (I-2) involves preparation of an intermediate
hydantoin. In this procedure, the 2R-exo-7,7-dimethyl-
norbornyl acetaldehyde of formula (I-l) i~ reacted with an
alkali metal cyanide and ammonium carbonate. ~8~cherer-Berg
reaction - SQe H. R. Henze and R. J. Speer, J. Am. Chem. Soc.,
64, 522-3 (1942) and E. Wade, Chem. Rev., 46, 441-4, (`1950)].
,~.. .. .. ~ . ..... . .
, . . : .. -
: ~ : . . . ~ ' . - ' . .:
~91102~11 PCT/~S~/~722
-19- 20~ 14
The resultinq hydantoin (I-5) is then hydrolyzed with a strong
aqueous base [NaOH, ~a(0~)2] to afford the amino acid (I-2).
In a typical procedure, one mole of the aldehyde is
heated at 50-70C for 8-24 hours with 2-5 moles of (NH4)2C03
and l.l moles of NaCN in an aqueous ethanolic solution. The
mixture is cooled, concentrated and acidi~ied to pH ~~ 5 to
precipitate the product (I-5) as a white solid.
Hydrolysis of (I-5) to the amino acid (I-2) is then
achieved by refluxing in 1.5 M Ba(OH)2 solution for 72 hours.
The 3-(2R-exo-7,7-dimethylnorbornyl)alanine of formula
(I-2) produced as above is generally obtained as a mixture of
the D-form and L-form. The mixture must, therefore, be
optically r solved and the L-form suitable a a sweetener
intermediate recovered.
Optical resolution may be carried out before or after the
compound of formula (I-2) is esterified.
Esterification of the compound of formula (I-2) can be
carried out by reacting it with a lower aikanol having from
one to three carbon atoms.
For example, esterification of (1-2) with methanol is
readily achieved by heating a solution of the amino acid in
methanolic hydrogen chloride solution for 18 hours at reflux.
Evaporation of the solvent af~ords the amino ester
hydrochloride. The free base (I-3, R'CH3) is then obtained by
neutrali~ing an aqueous solution of the hydrochloride with a
suitabl~ base (~OH, NaOH, Na2CO3) and extracting the product
into ether, toluene or other organic solvents which are not
base-sensitive. Evaporation of the extract gives the pure
amino e~ter (I-3, R - CH3).
Optical resolution of 3-(2R-exo-7,7-dimethylnorbor- nyl)-
D,L-alanine (I-2) or its lower alkyl ester (I-3) may be
..... . -
: . ,, ; ,
.
, ~
6 PCT/~S~/W722
-20-
carried out by known methods such as using D-tartaric acid or
an enzyme.
(1) Optical resolution with D-tartaric acid is
practiced on the 3-(2R-exo-7,7-dimethylnorbornyl)-D,L-alanine
lower alXyl ester by heating a one to one mixture of D-
tartaric acid and the amino ester in methanol until the D-
ta.taric acid goes into solution. The solution is then cooled
to induce crystallization. Two further recrystallizations
gives matçrial of >95% ee.
If possible, the alcohol used for the crystallizations
should be the same as that represented by the R group of (I-
3) so that trans-esterification is avoided.
(2) Optical resolution by the enzy~e method.
The compound of formula (I-2 or I-3) is N-acylated ~for
example, N-acetylated or N-chloroacetylated) in a known manner
and acylase is caused to act on the acylated compound in an
aqueous medium. A~ a re~ult, the L-for~ of N-acyl~3-(2R-exo-
7,7-dimethylnorbornyl)-D,L-alanine or its ester i8 selectively
deacetylated to give 3-(2R-exo-7,7-dimethylnorbornyl)-L-
alanine or its ester.
The acylase that can be used in the enzyme reaction may
be of any type which has the ability to hydrolyze the L-form
of an N-acylamino acid selectively tsee for example
I. Chibata, et al., in K. ~osbach, ed., Methods in Enzvmo}ocv,
Vol. 44, 746-59, (1976)]. It may be originated from an animal
source, a plant source or a microorganism source. Since the
acyla~e reaction $s qenerally carried out in weak alkalinity,
the acylase preferably has an optimal pH in the range of from
about 6 to 9. ~he acylase may be obtained by culturing a
microorganism, for example a mold of the genus Aspergillus or
Penicillium, a bacterium of the genus Pseudomonas, or an
actinomyces of the genus Streptomyces, and recovering the
.
,. . ~ ,
: . . .
~ . , .: . . . -
:- ~ ~ ;. : . . ' - :
:: . . . : . . : ,
: . :
,
w091/02~1I PCT/~S~/W722
2~ 01~
-21-
acylase from the culture. For example, Acylase I (Sigma
Chemical company) and Acylase "Amano" (Amano Pharmaceutical
Co., Ltd.; derived from As~erqill~s welleus~ are co~mercially
available.
Deacylation of the N-acyl-3-(2R-exo-7,7-dimethylnor-
bornyl)-D,L-alanine (I-6) or its ester using such an acylase
may be carried out in the same way as in an ordinary enzy~e
reaction. For exampl~, the N-acyl compound is dissolved or
dispersed in an aqueous medium. ~he pH of the medium is
adjusted to the optimal pH of the acylase with an alXali such
as sodium hydroxide or sodium carbonate. If desired, an
enzyme stabilizer such as cobalt chloride hexahydrate is added
so that the cobalt ion concentration becomes 10-6 to 1o~2M.
The reaction is carried out at a temperature range of from
about 35 to 40C for several hours to more than 10 hours.
After the reaction, the pH of the reaction mixture is
adjusted to an acidic pH, for example about 1 to about 2, and
the unreacted N-acyl-3-(2R-exo-7,7-dimethylnorbor- nyl)alanine
or its ester is separated and recovered usinq a solvent such
as ethyl acetate, methylene chloride or chloroform. In the
case of the acid (I-2) the aqueous layer is adjusted to a pH
range of from about 3 to 5 with aqueous ammonia. The desired
3-(2R-exo-7,7-di~ethylnor- bornyl)-L-alanine precipitates as
crystals. ~he crystals are separated and purified by a
customary method, for example by treat~ent with activated
car~on in hot water. White purified 3-(2R-exo-7,7-
dimethylnorbornyl)-L-alanine can thus be recovered. In the
case of the ester (I-3, R=CH3) the aqueous layer is adjusted
to pH 8-9 (instead of 3-5) and the product isolated by
extraction with a solvent such as ethyl acetate, chloroform or
methylene chloride. Evaporation of the solvent gives 3-(2R-
.~, . ~, . . .
:
.
WO ~1/02~ PCT/I S90/04~22
-22-
exo- 7,7-di~ethylnorbornyl)-L-alanine methyl ester as a
liquid.
The purified 3-~2R-exo-7,7-dimethylnor~ornyl)-L- alanine
or its ester has an optical purity, determined by gas
chromatography using a specially worked capillary (G-800
column made by Chemical Inspection & Testing Institute) after
N-trifluoroacetylation and as required esterification, of
substantially 100%.
~ he unreacted N-acyl-3-(2R-exo-7,7-dimethyl- norbornyl)-
D-alanine or its ester ~ay be converted to 3-(2R-exo-7,7-
dimethylnorbornyl)-L-alanine or its ester by a Xnown method,
for example, by treating it with acetic anhydride to racemize
it, and subjecting the racemate again to the acylase reaction.
The N-acyl derivative of (I-2) used in the above
enzymatic resolution procedure can in principle also bQ
prepared by the direct amido carbonylation of either alpha-
fenchene or the 7,7-dimethylnorbornyl-2-acetalde- hy~de
O
(I-l) using CO/H2, R-C-NH2 and a catalyst. ~The amido-
carbonylation reaction -- see I. Ojima, J. Mol. Catal., 37,
25-44 (1986); P. Magnus and M. Slater, Tet. Let., 28, 2829
(1987~; K. Izawa, Svn Ora. Chem. J~., 46, 218 (1988) and
Japanese Patent No. 61/236760.
Typical condition require the alkene (or aldehyde), a
combined cobalt-rhodium catalyst, carbon monoxide, acetamide,
hydrogen (500-2000 p5i) and a temperature of 80-150C for 1-
10 hours.
A third method of resolving the amino acid of Formula (I-
2) can also ~e envisioned, which involves treating the
hydantoin (I-5) with a microbial enzyme capable o~ selective
hydrolysis of the hydantoin ring to afford the L-amino acid.
Although most hydantoinase enzymes give the D-amino acid as
.. .
::. : - : .
.:: . : : . . -
,: .
. .
. , -, . ~
WO 9 1 /027 1 I Pcl /us9o/w722
2 o ~ 4
-23-
the only product, the enzyme isolated from ~3C~ brevis has
been found to give the desired L-isomer in the case of valine
hydantoin. [(See A. Yamashiro et al., Aaric. ~iol. Chem., 52,
2851-2856 and 2857-2863, (1988).]
Treatment of hydantoin (I-5) with the enzyme and reaction
conditions described by Yamashiro et al., hould give 3-(2R-
exo-7,7-dimethylnorbornyl)-L-alanine (I-2).
The compound of formula (1-2 or 1-3) produced as above is
useful as an intermediate for production of the compound of
formula (IV) which is useful as a non-nutritive sweetener.
The sweetener compound of formula (IV) can be produced from
the compound of formula (I-3) by a synthesis route summarized
in the following Reaction Scheme B.
. . .
:.... . , :. , . . ., :
:-, . .. , . .. , : , .
: . ... . : : .
: . .. . . :~:
WO 91/02711 Pcr/~sso/o4722
6~ 4 -24-
Reaction Scheme ~
_ _ ~ `
\/
,NH2 +
COOR l-H
~1-3) (Il) NH-Z
(l-form) ~ .
~\CH-NH-C-CH2-CH i ~\CH-NH-C-CH-CHl-COOH
COOR COOH (111 olpho) -:~
(111 b-t~)
~limln3tlon o~ tho ,
omino prot~cting group : -
/ \CH-NH-C-CH-CHl-COOH
COOR ( V )
- _ _ _ __ ~.
: . :, . . ~ . . -.: . .
~, ' ~ ' " '"- ~ ' ' : ' :'
:: ..
~ )91/02~1l PCT/US90/~722
20~3014
-25-
In the above scheme, Z represents a protective group
for the amino function. (See M. Bodansky, "Principles of
Peptide Syntnesis," Springer-Verlag, Berlin, (1984)
pp. 90-102) and R is as defined above. Typical examples
of Z include the allyloxy carbonyl [I. Ninomi et al, Tet.
Let., 26, 2449 (1985); O. Dangles et al., J. Ora. Chem.,
52, 4984-93 (1987)], the formyl (U.S. Patent No~.:
4,684,745, 3,879,372 and 3,933,781), the t-butoxycarbo-
nyl, tD. T. Witiak et al., J. ~ed. Che~. 14, 24-30
t1971)]; and the carbobenzyloxy (U.S. Patent
No. 4,508,912; EP 22730~; July 1, 1987). The latter is
particularly useful in that it can be readily removed by
catalytic hydrogenation.
In the Reaction Scheme B, the compound of formula
(I-3,L-form) is reacted with an N-protected-L-aspartic
acid anhydride in a non-protic solvent to yield the
desired alpha-(~-protected-L-aspartyl)-3-(2R-exo-7,7-
dimethylnorbornyl)-L-alanine alkyl ester (I~I alpha). In
addition, a small (10-20%) amount of the beta-(N-
protected-L-aspartyl)-3-(2R-exo-7,7- dimethylnorbornyl)-
L-alanine alkyl ester (III beta) is also produced. The
amount of by-product (III beta) formed in the reaction
can be controlIed by variations of the reaction
conditions as shown in Table 5 for Z = carbobenzyloxy
(=CBZ).
Si~ilar solvent effects on the coupling of (II)
(Z=CBZ) with phenylalanine methyi ester have been
observed by Yang and Su tJ. Ora. Chç~, ~, 5186-91
(1986)] and T. Yukawa et al, EP 227301~.
The undesired (III beta) can be separated from
~III alpha) by partitioning between a suitable organic
solvent and an aaueous buffer of the proper pH. In
WO 91/0271 I PCI/I.'S90/04722
previous reports of this type of separation tw.
J. LeQuesne and G. T. '~oung, J. Chem. Soc., 24-28 (1952)
and W. D. John and G. T. Young, J. Chem. Soc. 2870
(1954) ], alpha/beta-N carbobenzyloxyaspartylglycine
m e t h y 1 e s t e r , a 1 p h a / ~ e t a - N -
carbobenzyloxyaspartyltyrosine methyl ester, alpha/beta-
N-carbobenzyloxyaspartylglutamic acid diethyl ester, and
alpha/beta-N-carbobenzyloxyaspar- tyl-valine were
separated by extraction of ethyl acetate solutions with
aqueous sodium carbonate (concentration and pH
unspecified).
In a further example alpha and beta-NCBZ-
aspartylphenylalanine methyl esters were separated by
extraction of the beta- isomer from ethyl acetate using
buffer of about pH 6-7 ~ t ~ S ~ Patent No. 3,808,190). No
indication of the purity of the separated isomers was
given.
We have folmd in the case of (III alpha) and
(III beta) (Z=CBZ) that the pH of the aqueous pha~e mu t
be carefully controll~d (See Table 6)o In addition, the
choice of organic phase is also important. Good
separation is achieved with ether and toluene, only
modest partitioning with ethyl acetate and no separation
at all with hexane or butanol.
on a preparative scale, the extraction of a 1%
toluene solution of the crude coupling mixture
(III alpha/beta, alpha/beta~5/1, Z~CBZ) with three
portions of p~ 6.5, 0.1 ~ phosphate buffer gives
(III alpha) in 50-70% yield and a purity of 93-98%. The
remaining (III beta) is removed during crystallization of
(IV).
.~ '.:
' .: -
WO 91/0271 ~ PCl/US90/1)4722
2 ~
-27-
Removal of the CBZ group from (III alpha) is readily
achieved by hydrogenation at 2-3 kg./cm.2 using palladium
on charcoal as catalyst in a methanol solution. ~he
catalyst is removed by filtration through celite and the
filtrate evaporated to give crude (IV). Sweetener (IV)
is purified by crystallization ~rom chloroform-hexane.
In addition we have also ~ound that pure (IV) can be
obtained from the original (III alpha-III beta) mixture
(- 9/1, III alpha/III beta) by hydrogenation as mentioned
and repeated crystallization from methanol-water as shown
in Table 7. Tha procedure is most effective when the
(III alpha)/(III beta) ratio from the coupling reaction
is high (III alpha/III beta >8/1).
A similar separation of alpha-N-aspartylphenylala-
nine methyl ester fro~ the beta- isomer by
crystallization from water or water-alcohol mixtures has
been described previously in U.S. Patent No. 3,786,039.
An alternate coupling procedure which avoids the
above formation o~ a product mixture of alpha- and beta-
dipeptides involves performing the reaction using (I-3,
R=CH3) and a diprotected aspartic acid derivative (V~
;
.......... ,.. ~ ~ . : ;
Wo 9l/02711 PCT/US~/W122
-28-
_
N H Y ( V )
X O O C/ C O O H
where X = benzyl or t-butyl and Y = carbobenzyloxy or t-
butoxycarbonyl. (t-BOC) [M. Bsdansky, "Principles o~
Peptide Synthesis,~ Springer-Verlag, Berlin, 70-79 and
90-102 (1984)~ The coupling reaction may be carried out
by first converting the ~ree carboxyl of the aspartic
acid moiety to an activat-d leaving group by treatment
with i.e. p-nitrophenol/DCC, N-hydroxy~uccinimide/DCC,
isobutylchoroformate/N-methylmorpholine, or the like,
followed by the addition of (I-3, R~CH3). Alternatively,
it may be performed using DCC in organic solvents at a
temperature range of from about -20 to 30C. ~See
M. Bodansky, loc. cit., pg. 9-58; U.S. Patent No.
4,788,069 and J. W. Tsang et al., J. Med Chem, 27, 1663-
1668 (1984).] The resulting intermediates may then be
converted to (IV) by deprotection employing catalytic
hydrogenation under standard hydrogenation conditions
(Pd/C, MeOH, H~ pressure 10-50 psig) for Y 3 CBZ and X ~
benzyl. In the cas- where Y ~ t-~OC and X ~ t-butyl, the
deprotection may be carried out in organic solvents
w09l/o'7ll PCT/~'S~/~2~
2o~t~vl 4
-29-
employing strang acids [HCl, trifluoracetic acid (TFA) or
the like] with ~IV) being obtained ~ollowing
neutralization of the resultant salt.
The following examples illustrate the present
invention more specifically.
EXAMPLE 1
Conversion of trans-2-pinanol to alpha-~enchyl
alcohol.
PreDaration of Catalvs~s
Catalysts A, B and C used in the following Runs were
prepared as follows:
Catalyst A
Commercial reagent, aluminum nitrate nonahydrate
[Al(NO)3 9H20] (a product o~ Junsei Chemical Co., Ltd.),
150 g., was dissolved in 800 ml. of water, and 27 ml. of
8S% phosphoric aoid (a product of Nacalai Te~gue, Inc.)
was added to the solution, and while the mixture was
being stirred at room temperature 240 ml. of 10 % aqueous
ammonia was slowly added dropwise to adjust its pH to 7.
The resulting precipitate was left to stand overnight,
filtered, thoroughly washed with water, and dried at 60C
for 24 hours to give 65 g. of product. It was powdered
in a mortar to give a powder having a size sma~ler than
40 mesh.
Catalvst B
Hydrous niobium hydroxide (Nb205-xH20, a product o~
Companhia Brasileira de Metalurgia E Mineraç~o) was
pulverized to a size smaller than 40 mesh.
'. '-' ' ,, - '' .' . , - :
.: . . . .
WO 91/0271 I PCT/I,'S90/W7'2
-30-
Catalvst C
Nickel sulfate hexahydrate (NiSo4-6H2o, a product of
Nacalai Tesque, Inc.) was calcined at 250C or 350C for
3 hours to reduce its size to smaller than 40 mesh.
RUN 1
Catalyst A was calcined at 300C for 3 hours, and
used in this example.
A four-necked flask equipped with a stirrer, a
thermometer and a reflux condenser was charged with 35 g.
(0.227 mole) of trans-2-pinanol (a product of Glidco
Organics) and 2.0 g. of the catalyst, and with stirring,
it was reacted at 75C for 16 hours. The reaction
product was coarsely distilled to give 29.1 g. of an oily
product. Gas chromatographic analysis showed that the
conversion was 98.2 S, and the selectivity of alpha-
fenchyl alcohol was 48.1 %. The reaction product was
rectified to give 15.3 g. (theoretical yield 42.9 ~;
purity 98.3 %) of alpha-fenchyl alcohol.
RU~ 2
A four-necked flaak equipped with a stirrer, a
thermometer and a reflux condenser was charged with 35 g.
(0.227 mole) of trans-2-pinanol (a product of Glidco
Organics) and 2.0 g. of catalyst B, and it was reacted at
75C for 63 hours. The reaction mixture was treated a~
in Example 1 and analyzed by gas chromatography. The
conversion was 99.3 %, and the selectivity of alpha-
fenchyl alcohol was 52.3 %.
RUN 3
Catalyst C was calcined at 250C for 3 hours, and
used in this example.
A four-necked flask equipped with a stirrer, a
thermometer and a re~lux condenser was charged with 35 g.
. ~ ~ . ....... . . . .............................. - . ,
.
, , : ... ,,.,., . :. . .
. . ~ .
WO 91/0271 I PC~ S90/0~722
-31- 205~V14
t0.227 mole) o~ trans-2-pinanol (a product of Glidco
Or~anics) and 2.0 g. of the catalyst, and it was reacted
at 75C for 20 hours. The conversion was 51.0 ~, and the
selectivity of alpha-fenchyl alcohol was 40.6 %.
RUNS 4-16
As in Runs 1 to 3, alpha-fenchyl alcohol was
producsd from trans-2-pinanol using catalyst A, B or C
prepared as abo~e at the calcination temperatures and
reaction temperatures indicated in Table 1. The results
are shown in Table 1. In the examples, gas
chromatographic analysis was carried out using a Shimadzu
GC-9A (made by Shimadzu Seisakusho Ltd.) with a PEG-HT
capillary 0.25mm. in diameter X 25m. in length (made by
Gasukuro Kagyo Co., Ltd.). The column temperature was
100C.
! ' . . ' .
''' ' ' .. ' ~" ~ , ' : '
:` ~ ' ' ~,. . ' . '
WO91/02711 PCT/US~/~22
2 a 6~ 4 -32-
_
Calci- Reaction
nation conditions Con- Selectivity
tempera- version of ~-fenchyl
Run Cata- ture (%)alcohol
lyst (C) (%)
~emper- Time
ature (hr)
(C)
_
1 300 75 16 98.248.1
2 _ 75 63 99.352.3
3 C 250 75 20 51.0 40.6
_ _ _
4 300 110 6 100 41.2
n 500 110 6 lOQ 36.0
_ . _
6 n 800 110 3 100 35.0
7 _ 110 18 99.3 45.4
8 ~ 200 75 18 97 . 8 46.1
9 ~ 200 110 4 100 34.2
- 300 75 22 99.4 43.2
11 n 400 75 22 99.4 42.7
_ _
12 500 75 19 98.5 41.7 :- .
13 n 600 75 20 34.1 40.0
.
14 C 2S0 110 18 100 24.8
350 75 18 23.9 34.4
16 3S0 110 15 97.3 20.3
- : . , .:
.
.
,
.
`
WO9l/02~11 PCT/US90/~72~
2 0 ~
Example 2. Purification of (+)-alpha-fenchyl alcohol
Commercial alpha-fenchyl alcohol
(~]23D-+10.0(c-5, ethanol), mp. 43.2c; 709.2 g) was
dissolved in ~55 g. of n-heptane, and the solution wa~ cooled
to about -33C. The crystals that precipitated were separated
by filtration to gi~e 493.6 g. of a first
crop of crystals ([~]2~'+11.6, mp. 45.2)
The residue (228.9 g.) left after evaporation of the
filtrate was dissolved in 160 g. of n-heptane and the solution
was cooled to -50C. The precipitate was filtered giving
128.6 g. of a second crop of crystals
([~]2~=+10.2, mp. 43.2C). These
crystals were of the same quality aR the starting mat¢rial.
They were again dissolved in 64 g. of n-heptane, and the
solution was cooled to about -33C. The crystals that
precipitated were separated by filtration to obtain 94.0 g. of
the crystals
([~]23=+11.5, mp. 45.1C~. These crystals were
combined with the first crystals (total 587.6 g.) and
dissolved in 411 g. of n-heptane. The solution was cooled to
about -35C. The crystals that precipitated were separated by
filtration to obtain 416.1 g. of second crystals ([~]a~=+11.9,
mp. 45.7C). The second
D
crop of crystals (416.2 g.) was dissolvQd in 310 g. of n-
heptano, and the solution was cooled to -31C. The crystals
that precipitated were separated by filtration to obtain 218.9
g. of third crystal3
([~2~,+l2.2o~ mp. 46.4C)
: ::
': : . . .. .
:.:: ~ ,: . - ~ : .
: ~ - - .. -
WO91102~11
PCTtUS~/W,2
9 ~ 5 ~ ~
The mother liquors of the second crystals and third
crystals were combined, and the solvent was reco~ered to
yield 298.7 g. of crystals ([~]23=+9.84O). The resulting
crystals were subjected to three cycles of crystallization in
the same way as above to give 84.2 g. of fourth crystal~
([~]23=+l2.2, mp. 46.1C). The third crystals and
fourth crystals were combined to obtain 363.2 g. of the
desired t+)-alpha-fenchyl alcohol in a yield of 5l.2 %.
The optical purities of the resulting crystals were
measured by the method described below. The results are
tabulated below.
Ta~le,2
optical
Specific purity
rota,,~iQ~ (,% e-e- L
Starting +lO.0 81
material
First crystals +ll.6 89.9
Second crystals +ll.6 92.l
Third crystals +12.2 94.8
Fourth crystals +12.1 94.6
Mea~ur,ement of ~he O~ti~al P4~ity
N-carbobenzyloxy-L-alanine (0.31 g.; 1.4 m~, O.Ol g.
(O.1 mM) of N,N-d$methylaminopyridine (DMAP) and 0.2 g. (l.28
mM) of fenchyl alcohol were dissolved in 2 ml. of methyl~ne
chloride. In a stream of nitrogen under cooling, 0.27 g. (1.4
mM) of l-ethyl-3-(3-di- methylaminopropyl~carbodiimid-
hydrochlorid~ (WSC) was added to the solution, and reacted for
about 30 minutes. The temperature was returned to room
,i- ,
. .
~O9l/02~1l PCT/~'S~/~722
2 0 ~
temperature, and the reaction was carried out for about 1
hour. Methylene chloride was added to the reaction solution
to adjust the total amount of the reaction mixture to 10 ml.
It was washed with a 10% aqueous solution of citric acid, a 4%
aqueous solution of sodium carbonate and a saturated aqueous
solution of sodium chloride, and dried over anhydrous
magnesium sulfate. The solvent was evaporated at less than
40OC. ~he residue was dissolved in 5 ml. of methanol and
reduced with hydrogen under atmospheric pressure in the
presence of 20 mg. of palladium black. The solution was
analyzed by gas chromatography under the following conditions.
Column: PEG-HT, 0.25 mm. in diameter and
25 m. in length
Introduction temperature: about 200C.
Column temperature: a range from about 100 -200C,
3oC/min.
Retention time: a range of about 11-12 min.
Separation coefficient: 1.02
EXAMPLE 3
Preparation of alpha-fenchene from fenchyl alcohol
1. Preparation of aluminum oxide catalysts ;~
(a) Catalyst A
Two hundred grams of aluminum nitrate nonahydrate
[Al(N03)3~9H20; reagent first class produced by Junsei Chemical
Co., Ltd.~ was dissolved in 2 liters of water. The solution
was slowly added dropwise with stirring to 500 g. of 28%
agueous ammonia. After standing, the resulting aluminum
hydroxide was aged overnight, filtered, washed with water, and
dried at 60C for 24 hours to give 43 of aluminu~
hydroxide. It was powdered in a mortar anc calcinQd in an
, , ,. : . , - . :
: . -: : .. .-: -
. ~. - -- -
: .: ~,- . : : - -
, :, :: . , - ' -: , : . . :- , : - : ~ -
W0~l/0271l PCT/~S~/W~22
~e5~ 4
-36-
electric furnace at 5000C for 3 hours to give 28.4 g. of
aluminum oxide as a white powder. The Hammett acidity
function H~ of this product was -5.6<H S-3Ø
o
(b) Catalyst B
Two hundred grams of aluminum sulfate 14- to
18-hydrate tA12(S0~)3-14-18 H20; r~agent first cla~s produced
by Junsei Chemical Co., Ltd.~ was dissolved in 2 liters o~
water. Aqueous ammonia (10% by weight) W2S added dropwise to
the solution until the solution reached pH 8. The resulting
aluminum hydroxide was fully washed with a large amount of
water, and dried at about 60C for 24 hours. The dried
product was powdered in a mortar and then calcined in an
electric furnace at 5000C for 3 hours to give 70 g. o~
aluminum oxide as a white powder. The Hammett acidity
function Ho of the
product was -5.6<Hos-3Ø
(c) Catalyst C
Two hundred grams of aluminum chloride hexa- hydrate
[AlC13.6H20; reagent first class produced by Junsei Chemical
Co., Ltd.] was dissolved in 2 liters of water, and then
treated as in the preparation of catalyst B to give 62 g. of
aluminum oxide. The Hammett
acidity function of this product was -5.6<H S-3Ø
(d) Catalyst D
Two hundred grams of sodium aluminate [NaA102 xH20;
reagent first class produced by Nakarai Tesque Co., Ltd.]
wa~ dissolved in 2 liters of water. With stirring, the
solution was added to an aqueous solution of hydrochloric
acid (250 g/3 liters) to adjust the solution to about
pH 8. The precipitate was ~eparated by filtration, dried
.
:: , ,: :- : - . .
osl/o2~1l PCT/~'S~/W72
_37_ 2 0 S i 0 1 ~
at 60C for 12 hours, and washed five times with 500 ml.
of 14% aqueous ammonia. The washed product was dried at
60C for 24 hour~, powdered in a mortar, and calcined in
an electric furnace at 500C for 3 hours to give 115 g. o~
aluminum oxide as a white powder. The Hammett acidity
function of this
product was -5.6~H~<-3Ø
2. Production of (+)-alpha-fenchene
(a) A three-nec~ed flask equipped with a Dean-
Stark device, a stirrer, a thermometer and a reflux
condenser was charged with 100 g. (0.65 mole, purity
98.7%) of alpha-fenchyl alcohol and 5 g. (5% by weight) o~
catalyst A, and with stirring, the mixture was heated at a
temperature range ~rom ab~ut 195 to 200C for 10 hours.
The reaction mixture was then coarsely distilled to give
95.8 g. of an oily product. Gas chro~atographic analysis
showed the oily product to consist of 72% o~ fenchene
isomers (in which alpha-fenchene accounted for 59%~ and
28% of unreacted fenchyl alcohol. Rectification of the
oily product gave 34.4 g. of (+)-alpha-fenchene (yield
54.1%; purity 98.7%; Run No.l).
Boiling point: 157-158C (730 mm Hg)
(t~ '+36.27(neat)
H-NMR (~DC~3)
0.97 and 0.98 (each 3H, s),
1.20 - 1.34 (2H, m),
1.65 (lH, t),
1.79 - 1.96 (3~, m)
Z.03 (lH, d), 2.41 (lH, d)
,;, ,, ; ,
.. ' ' '. . ~ :
': " " , '' '' . ~ , ' . , ' ~ ~
: ' ' '- ' ' : ' ' : :
WO 91/02711 PCT/US90/W722
`~ 38-
4.60 and 4.81 (each lH, s)
Mass Spectrum (m/e):
136 (M+), 121, 107, 93, 79, 53,
41, 39.
(b) Catalyst A (5%) was added to a mixture of (+)-alpha-
and (+)-beta-fenchyl alcohol (alpha-/ beta--6/4). The
mixture was treated as in section (a) above to obtain an oily
product. Gas chromatographic analysis showed the product to
comprise 95% of fenchene isomers (in which (+)-alpha-fenchene
accounted for 65%) (Run No.2).
(c) Catalyst A (5% by weight) was added to (+)-beta-
fenchyl alcohol (purity 95%). ~he mixture was heated at a
temperature range of from about 195 to 200C for 3 hours with
stirring and then coarsely distilled. Gas chromatographic
analysis of the distillate showed it to comprise 98% of
fenchene isomers (in which (+)-alpha-fenchene accounted for
80%) (Run No.3).
(d) Using catalysts ~, C or D, (+)-alpha-fenchene was
produced from (+)-alpha-fenchyl alcohol~ The results are
shown in Table 3 below (Runs Nos. 4 to 6).
(e) The procedure as in (a) aboYe was repeated except
that catalyst A was replaced by commercial aluminum oxide
catalysts having a Hammett acidity
function of +l.5<HoS+3. 3 and +3.3<Ho<+4.8.
(Runs Nos. 7 and 8), a catalyst obtained by calcining
nickel sulfate hexahydrate at about 250C for 3 hours (Run
No. 9), a catalyst obtained by calcining nickel sulfate
hexahydrate at about 400C ~or about 3 hours (Run No. 10),
aluminum sulfate (Run No. 11), a catalyst obtained by
calcining aluminum phosphate at about 500C for about 3
hours (Run No.12), aluminum silicate (Run No. 13), alum
" - . ,:
:- .. . , . :::
.,- :- .
.. . . ., .. : . . :
: :: :.
: - ~ : .: ~ : - , :-
~0 91/02-1 I PCI/I S90/W7''
2 ~
-3~-
(Run No.14) or acid clay (Run No. 15). The results are
also shown in Table 3.
. - . . . ~ ;... , :
W09l/027lI PCT/US~/W72'
2n~
vu~01440
~able 3
__ Amount
of the Reaction
cata- conditions Total Alpha-
Starting lyst fen- fen-
Run Catalyst fenchyl based chene chene
No. alcohol on tha selec- selec-
fen- tivity tivity
alhycl_ Temp. Time
hol(C) (hr) (%) (%)
(wt~)
_ _
Catalyst A ~- 195-200 10 72 59
2 Catalyst A ~/B=6/4 5 195-20010 95 65
3 Catalyst A B- S 195-200 3 98 80
4 Catalyst B ~- 5 195-200 10 82 44
Catalyst C ~- 5 195-200 10 70 47
6 Catalyst D ~- 5 195-200 10 70 53
7 Active ~- 10195-200 16 20 36
alumina
. .
8 Active ~- 10195-200 16 . 4 32
alumina
_
9 NiSo~-6H2o ~- 50 195-200 4 100 2
NiS04 CHa I ~- ¦50¦195-200¦ 4 ¦ 98 ¦ 10
¦ 11 A12(SO~)3 ¦ ~ ¦ 50¦195-200l 4 1 88 1 6
12 A1106 ~- 50195-200 16 ~ 8 23
: . :: : :
:
:: :-
. .-
: :, ' -, ' `,, `
~ 91/0'71 I PCT/I~'S9~/W722
--41-- 3 t~ 1 ~
_ _ _
13 Aluminum ~- 50 195-200 6 97 . 5 O
silicate
14 Alum ~ - 5 0 19 5 - 2 0 0 16 7 7 . 4 1
lS Ac id clay . 5 19 5-2 00 7 94 . 9 4
- :, . . ~ ,- . . - ~ . -
. - - ~ .; , . . .
091/0271l Pcr~us~/~722
2 e 6~ 4 -42-
The fenchenes were analyzed ~y gas chromatography using a gas
chromatographic device ("Shimazu" GC-9A made by Shimazu
Seisakusho Co., Ltd.~ using an OV-l silica capillary column
(diameter O.25 mm., length 25 m.); made by Gasukuro Kogyo Co.,
Ltd.) at a temperature of about 700C.
EXAMPLE 4
Production of 7,7-dimethyl-2-formylmethylenenorbornane:
Fifty grams (0.368 mole) of (+)-alpha-fenchene obtained
as in Example 3 was added dropwise under a nitrogen stream at
50 to 60C over about 1 hour to a solution which had been
prepared by adding 38 ml. (0.415 mole) of POC13 to 92.5 ml.
(1.19 mole) of DMF over about 1 hour. The mixture was reacted
for 2 hours. The reaction solution was poured into 800 ml. of
a lOS aqueous solution of sodium carbonate, and extracted
twice with 300 ml. of toluene. The combined toluene extracts
were washed with water, and the solvent was evaporated.
Fractional distillation under reduced pressure gave 50.5 g.
(yield 71%) of the captioned compound.
Boiling point: 76 - aooc/l mm Hg
~H-NMR (CDC13 solvent, TMS internal
standard, ~):
E-form
0.98 and 1.08 (each 3H, s, CH3), 5.94 (lH, d,
J27.9 Hz, olefinic H) and 9.79 (lH, d, J=7.9
Hz, CHO).
Z-form
0.97 and 1.08 (each 3H, s, CH3), 5.86
(lH, d, J=8.4 Hz, olefinic H), 9.84
(lH, d, J=8.3 Hz, CHO).
,
.
wO9~/U2~1l PCT/~'S~/~722
_43- 2~S~14
Mass Spectrum (m/e):
E-form
150, 125, 109, 107, 82, 81 (base),
79, 67 and 41.
Z-form
165 (M~+1), 164 (M~), 149, 121 (base),
93, 91, 19, 77, 41 and 39.
EXAMPLE 5
Production of 2R-exo-7,7-dimethylnorbornyl acetaldehyde:
(a) A 1 liter autoclave was charged with 20 g. (0.12
mole~ of 7,7-dimethyl-2-formylmethylenenorbornane obtained as
in Example 4 above, 200 ml. of n-heptane and 0.5 q. of 5~
palladium-carbon, and the reaction was carried out at room
temperature under a hydrogen pressure of 2 ~g./cm.2. After
the reaction, the catalyst was filtered and the solvent was
evaporated. The residue was distilled under reduced pressure
to give 19.7 g. (yield 97.3%) of the captioned compound. The
exo/endo ratio of this compound wa~ found to be 98:2 by
measurement of lH-NMR.
Boiling point: 54 - 55C/0.2 mm ~g
H-NMR (CDCl3 solvent, TMS internal standard, ~):
~o-form
0.97 and 1.08 (each 3H, s, CH3), 2.60 (2H, d,
d, d, J=2.1, 9.6, 5.9 Hz; CH2CHO~) and 9.71
(lH, t, J=7.9Hz; CHO).
Endo-form
1.02 ?nd 1.08 (each 3H, s, CH3),
9.76 (lH, t, J=7.9 Hz, CHO).
~'O9l/0271l PCT/US~/W722
L~ Q ~ 4
-44-
Mass Spectrum (m/e): 166 (Ml), 151, 133, 123, 122 (base),
107, 95, 81, 79, 69, 67, 55, 41.
(b) A 200 ml. autoclave was charged with s.o g. (0.037 mole)
of (+)-alpha-fenchene obtained as in Example 3, 45.3 ~g. (0.18
mmole) of the dimer of rhodium (I) chloride-1,5-
cyclooctadiene, 95 mg. (0.36 mmole) of triphenylphospine, 0.5
ml. of triethylamine and 25 ml. of benzene, and the reaction
was carried out at 90C for 16 hours under a synthesis gas
pressure of 80 kg./cm.2 (carbon monoxide pressure 40 kg./cm.2;
hydrogen pressure 40 kg./cm.~). The solvent was evaporated,
and the residue was fractionally distilled under reduced
pressure to give 5.7 g. (yield 93.4~) of an exo/endo mixture
of 7,7-dimethylnorbornyl-2-acetaldehyde. The (2R)-exo/(2S)-
endo ratio of the product was determined to be 85:15 by lH-
NMR.
(c) 7,7-Dimethylnorbornyl-2-acetaldehyde having the (2R)-
exo/(2S)-endo ratios shown in Table 4 was obtained by carrying
out the oxo reaction as in (b) above under the conditions
shown in Table 4.
Table 4
_ Reaction
conditions Yield Exo/endo
Run Oxo reaction ratio
No. catalyst t-mp. ti=e (~)
2 [CODRhC1)2-2pph3 50 64 35 ¦ 89/11
3 Rh6(co)16 1 70 1 18 1 ~0 1 66/34
4 ¦Rh6(CO~l6-2pph3 ¦ 70 1 17 1 81 ¦ 87113
*COD = 1,5-Cyclooctadiene
.
~ ' ~ ' : ~ . - .
: '
Osl/o~-ll PCT/~'S~tW-22
_45_ 2 ~ ~ ~ 0
EXAMPLE 6
Production of 3-(2R-exo-7,7-dimethylnorbornyl) 2-D,L-
amino propionitrile:
Ammonia gas was passed through 400 ml. of methanol at 5C
for lS minutes. To the resulting solution were added 17.5 g.
(0.357 mole) of sodium cyanide, 17.8 g. ~0.333 mole) of
ammonium chloride and 52.0 g. (0.313 mole) of (2R-exo-7,7-
dimethylnorbornyl) acetaldehyde. The reaction mixt~lre was
stirred overnight at room temperature and the methanol was
evaporated under reduced pressure. To the residue was added
750 ml. of a 2% aqueous solution of sodium carbonate, and the
mixture was extrac ed with 350 ml. of ether twice. The
extracted ether layers were washed with water, and then
extracted with 300 ml. of 1 N hydrochloric acid twice. The
extracted hydrochloric acid layers were neutralized with
sodium carbonate and further extracted with 300 ml. of ether
three times. The extracts were dried over anhydrous sodium
sulfate and the solvent was evaporated to give 3-(2R-exo-7,~-
dimethylnorbornyl)-2-D,L-amino propionitrile as a pale yellow
oil in a yield of 95.5%.
lH-NMR (CD30D solvent, TMS internal standard, ~): 1.07
and 1.11 (each 3H, s, CH3) and 4.38 - 4.49
CN
(lH, m, C~< ) (as amino propionitrile hydrochloride) ;~
EXAMPLE 7
Production of 3-(2R-exo-7,7-dimethylnorbornyl)-D,L-
alanine hydrochloride:
:~:.:: . ~ . . .
:, - . . - ,, :
I I PCI / l,'S90/0472'
~Q6 ~ 46-
52.0 g. (0.271 mole) of 3-(2R-exo-7,7-dimethylnorbornyl)-
2-D,L-amino propionitrile was added to 200 ml. of water and
900 ml. of concentrated hydrochloric acid, and the mixture was
heated under reflux for 18 hours. The reaction solution was
concentrated under reduced pressure and then cooled. Amino
acid hydrochloride precipitated. It was left to stand
overnight at 5C, filtered, and washed with 600 ml. of ether
to give 63.2 g. of 3-(2R-exo-7,7-dimethylnorbornyl)-D,L-
alanine hydrochloride in a yield of 94.1%.
1H-NMR (CD30D solvent, TMS internal standard, ~): 1.02
and 1.11 (each 3H, s, CH3) and 4.37-4.42 (lH,
C02H
m, C~<
N
The amino acid was prepared by neutralization of the
hydrochloride and precipitation at pH 4Ø Melting point:
216-218C, IR: 3400, 2930, 1610, 1495, 1395, 1330 and 1100 cm-
1.
EXAMPLE 8
Optical resolution of 3-(2R-exo-7,7- dimethylnorbornyl)-
D,L-alanine methyl ester by the tartaric acid method:
To a solution of 36.5 g. of 3-(2R-exo-7,7 dimethyl-
norbornyl)-D,L-alanine methyl ester (prepared from 3-(2R-exo-
7,7-dimethylnorbornyl)-D,L-alanine as described in Example 15)
in 500 ml. of methanol was added a solution of 25.7 g. of D-
(-)-tartaric acid in 500 ml. of methanol. The solution was
diluted to 1800 ml. with methanol, then heated to reflux to
dissolve the precipitate which had formed. Crystallization
was obtained by allowing the hot solution to stand at about
21C overnight. Filtration, washing with 50 ml. of methanol
and drying 1~ vacuo gave 24.1 g.
WO 91tO211 I PCl t~:S90/04~22
2 a ~
--47--
The above material was recrystallized from 850 ml. of
methanol to give 13.1 g. This in turn was recrystallized from
450 ml. of methanol to afford 8.8 g. o~ 3-(2R-exo-7,7-
dimethylnorbornyl)-L-alanine methyl ester-D-tartrate salt.
Melting point: 160C (decompose)
[~]20 - + 36.4 (c = 0.5, MeOH)
D
EXAMPLE 9
Synthesis of N-acetyl-3-(2R-exo-7,7-dimethylnor~ornyl)-
D,L-alanine:
3- (2R-exo-7, 7-dimethylnorbornyl) -D, L-alanine
hydrochloride (60 g.; 0.242 mole) was dissolved in 300 ml. of
a 10% aqu~ous solution of NaOH, and then 32 g. (0.314 mole) of
acetic anhydride was added dropwise at 35 to 40C. After the
addition, they were reacted for 30 minutes. The reaction
solution was cooled to 5 to 10C, and adjusted to pH 3 with 6
N hydrochloric acid. The precipitated crude crvstals were
filtered, washed with water and driOEd. The crude crystals
were recrystallized from ethyl acetate and n-hexane to give
60 g. (yield 97.6%) of the captioned compound.
Melting point: 170 - 171C
[~]24 -~36.6 (c51, methanol)
lH-NMR (CD3D solvQnt, TMS internal standard, ô):
0.98 and 1.09 (each 3H, s, C~I3), 1.98
t3H, s, NHCOC~3) and 4.31 - 4.39 (lH, m,
C02
C~<
NHAC
,., ., , .... . . ~. , :,
.,: . . : i, : ,. : . .:
. - .:. .. : . . . . .
.:. . .: : : - : - :
W091/0271l PC~/~S90/W722
48-
EXAMPLE 10
optical resolution of N-acetyl 3-(2R-exo-7,7-
dimethylnorbornyl)-D,L-alanine:
A 4 N aqueous solution of NaOH was added to a slurry
composed of 450 ml. of water, 28.8 g. of disodium hydrogen
phoephate, 30 mg. of cobalt chloride hexahydr~te and 60 g.
(0.236 mole) of N-acetyl-3-(2R- exo-7,7-dimethylnorbornyl)-
D,L-alanine to adjust the pH to 8Ø A solution of 1.12 g. of
acylase (a product of Amano Pharmaceutical Co., Ltd.) in
12 ml. of phosphate buffer (pH 8.0~, was added and the mixtsre
stirred at 37 to 390C for 20 hours. The reaction solution was
adjusted to pH 1.4 with concentrated hydrochloric acid, and
washed with 200 ml. of ethyl acetate three times. The aqueous
layer was adjusted to pH 3.0 with aqueous ammonia. The crude
crystals that precipitated were separated by filtration. ~he
resulting crude crystals (18~3 g.) were dissolved in 800 ml.
of hot water, and treated with 1. 8 g. of activat~d carbon to
give 17.7 g. (yield 71.1%) of 3-(iR-exo-7,7-
dimethylnorbornyl)-L-alanine.
Melting point: 224 - 226C
t~]23 z+49.5 (csl, methanol)
D
lH-NMR (CD30D solvent, TMS internal standard, ~):
0.99 and 1.11 (each 3H, s, CH3) and
3.44-3.47 (lH, m, C~-C02)
Separately, the ethyl acetate washings were concentrated
to give crude crystal3 (34.9 g.). The crude crystals were
recrystallized from ethyl acetate and n-hexane to give 26.6 g.
(yield 88.7%) of N-acetyl-3-(2R-exo-7,7-dimethylnorbornyl)-D-
alanine having a specific rotation of +4.1 (c=1, methanol).
. ~ :
::~ ' . . . - . ' .
, .
O9l/0~7l1PCT/~S~/~7'~
_49_ 2 ~ 0
EXAMPLE 11
Racemization of N-acetyl-3-(2R-exo-7,7-dimethyl-
norbornyl)-D-alanine:
Ten grams (0.039 mole) of N-acetyl-3-(2R-exo-7,7-
dimethylnorbornyl)-D-alanine obtained in Example 10 was
dissolved in 50 ml. of acetic acid and 1.0 g. of acetic
anhydride, and reacted at 100C for 16 hours. After cooling,
the reaction mixture was concentrated under reduced pressure.
The resulting crude crystals were dissolved in 35 ml. of ethyl
acetate and washed with water. The ethyl acetate layer was
crystallized by adding n-hexane to give 6.8 g. of N-acetyl-3-
(2R-exo-7, 7-dimethylnor~ornyl)-D,L-alanine having a specific
rotation of +35.50 (c=l, ~ethanol).
EXAMPLE 12
Synthesis of N-chloroacetyl-3-(2R-exo-7,7-
dimethylnorbornyl)-D,L-alanine:
Ten grams (47.4 mmoles) of 3-(2R-exo-7,7-dimethyl-
norbornyl)-D,L-alanine was suspended in 120 ml. of ethyl
acetate, and 35.36 g. (47.4 mmoles) of chloroacetyl chloride
was added. The mixture was heated under reflux for 1 hour.
After cooling, the unreacted amino acid was separated by
filtration, and the ethyl acetate was evaporated. The
resulting crude crystals were recrystallized from ether and n-
hexane to give 10.1 g. (yield 63%) of the captioned compound.
... ...... ~.. .. .. . .
: - -. . : . ,: , :
: - . : ~ - -
. -.. .
WO91/02~1l PCT/US~/W722
~ Q -50-
Melting point: 149 - 150C
[~]23 = ~22.2~ (c=1, methanol)
D
lH-NMR ~CD30D solvent, TMS internal standard, ~):
0.98 and 1.09 (each 3~, s, CH3),4.07 (2H, d,
J-10.7 Hz, NHCOC~2Cl), 4.36 - 4.44 (lH, m, C~Co2)
NH--
EXAMPLE 13
Optical resolution of N-chloroacetyl-3-(2R-exo-7,7-
dimethylnorbornyl)-D,L-alanine:
A 4 ~ aqueous solution of NaOH was atded to a slurry
composed of 300 ml. of water, 24.1 g. of disodium hydragen
phosphate, 25.5 mg. of cobalt chloride hexahydrate and 50.0 9.
(0.173 mole~ of N-chloroacetyl-3-(2R-exo-7,7-
dimethylnorbornyl3-D,L- alanine to adjust the pH to 8Ø A
solution of 0.85 g. of acyla~e (a product ~ o~ Amano
Pharmaceutical Co., Ltd.) in 42.5 ml. of 0.5 ~ phosphate
buffer (pH 8.0), was added and the mixture stirred at 37 to
39C for 16 hours. The reaction soll~tion was adjusted to
pH 1.7 with concentrated hydrochloric acid, and washed with
350 ml. of ethyl a~etate twice. The aqueous layer was
adjusted to about pH 3.0 with aqueous ammonia. The crude
crystals that precipit~ted were separated by filtration. The
resulting crude cry~tals (10.3 g.) were dissolved in 800 ml.
of hot water, and treated with 1.4 g. of activated carbon to
give 10.3 g. (yield 56.3%) of 3-(2R-exo-7,7-
dimethylnorbornyl)-L-alanine.
Separately, the ethyl acetate washings were conc~ntrated,
and the residue was recrystallized from ether and n-hexane to
give 20.4 g. (yield 81.6%) of N-chloroacetyl-3-(2R-exo-7,7-
dimethylnorbornyl)-D- alanine.
~: ' ' ., . ' :'
., . , : - :
- . '- : -.
~09l/0~1l PCT/~S~0/~
-51- 2 0 ~ 5
Melting point: 150 - 153C
23 ~ +14 . 1 ( c=l, methanol)
EXAMPLE 14
Production of 3-(2R-exo-7,7-dimethylnorbornyl)-L- alanine
methyl ester:
Hydrogen chloride gas (12.S g.) was bubbled into 1 liter
of methanol, and 52.0 g. (0.210 mole) of 3-(2R- exo-7,7-
dimethylnorbornyl)-L-alanine hydrochloride was added. The
mixture was heated under reflux for 18 hours. After cooling,
the solvent was evaporated under reduced pressure. The
residue was dissolYed in 750 ml. of water, and the pH of the
solution was adjusted to about 8.5 with a 50% aqueous solution
of NaOH under cooling. The reaction mixture was extracted
with 250 ml. of ethyl acetate twice and dried over anhydrous
sodium sulfate. The solvent was evaporated to give 47.2 g.
(yield 99.9%) of 3-(2R-exo-7,7-di~ethylnorbornyl)-L-alanine
methyl ester as a pale yellow oil.
The product (45.0 g.; 0.2 mole) was dissolved in 80 ml.
of ethyl acetate and 13.2 g. (0.22 mole) of acetic acid was
added under cooling and stirring. The crystals which
precipitated were collected by filtration to give 48.8 g. of
the acetic acid salt of the above-captioned compound having a
melting point of 101 to 104C.
~ ..
EXAMPLE 15
Production of 3-(2R-exo-7,7-dimethylnorbornyl)-D, L-
alanine methyl ester:
To a solution of 12.5 g. of hydrogen chloride gas in 1
liter of methanol was added 52.0 g. of 3-(2R-exo-7,7-
dimethylnorbornyl)-D,L-alanine hydrochloride. The olution
was heated at reflux for 18 hours, then the product ~solated
:: .. -, ,,~: , . .; ~ :
;: ,, - -: . . . .. , :: .
09l/027ll PCT/USsO~W72
2 ~ ~'i ~ ~ -52-
as described in Example 14 to give the title compound
t44-~ g.) as a pale yellow oil.
[~23, (as the hydrochloride) - +29.50
(C=1.2, methanol)
EXAMPLE 16
Production of L-aspartyl-3-(2R-exo-7,7-
dimethylnorbornyl)-L-alanine methyl ester:
24.9 g. (~.1 mole) of N-carbobenzyloxy-L-aspartic
anhydride was suspended in S00 ml. of toluene, and the
suspension was cooled to 5~C. With stirring, a suspension of
28.5 g. (0.1 mole) of 3-(2R-exo-7,7- dimethylnorbornyl)-L-
alanine me~hyl ester acetate in 50 ml. of toluene was added.
The mixture was then stirrred overnight at 5C. The solution
was subjected to a countercurrent distribution-type
chromatographic device to obtain 33.5 g. (70.6 %) of N-
(carbobenzyloxy -L-aspartyl)-3-(2R-exo-7,7-dim~thylnorbornyl)- ~-
L-alanine methyl ester. In a l-liter autoclav2, 25.8 g. (54.4
mmoles) of N-(carbobenzyloxy-L-aspartyl)-3-(2R-exo- 7,7-
dimethylnorbornyl)-L-alanine methyl ester was dissolved in
400 ml. of methanol, and catalytically reduced in the presence
of 1.0 g. of 5% palladium carbon under a hydrogen pressure of
3 ~g./cm.2. After the decrease of the hydrogen pressure wa~
no longer observed, the catalyst was removed by ~iltration
through Celite. The filtrate was concentrated under reduced
pressure to give crude crystals. Recrystallization from
chloro~orm/n-hexane gave 14.4 g. (yield 77.8%) o~ the desired
L-aspartyl-3-(2R-exo-7,7-dimethylnorbornyl)-L- alanine methyl
ester.
Melting point: 148 - 148.2C
[~]23 = +30.50 (c=1, methanol)
., , .' ''' ' ' .
- , ~ ,.- . -
WO91/0271l PCT/~S~/047Z2
2os~
-53-
lH NMR (CD30D sol~ent, TMS internal standard, ~):
0.98 and 1.10 (each 3H, s, CH3), 2.53
(lH, dd, J~9.7 and 16.0 Hz, CH2CO~H),
2.78 (lH, dd, J=4.7 and 17.1 Hz, CH2C02H),
4.09 (lH, q, J-4.64 Hz, -C~CH2COaH), 4.41
(lH, q, J-5.4Hz, C~CO~Me)
NHCO
EXAMPLE 17
Production of (N-C8Z-L-aspartyl-beta-0-benzyl~-3-(2R- exo-
7,7-dimethylnorbornyl)-L-alanine methyl ester:
43 g. of the 3-(2R-exo-7,7-dimethylnorbornyl)-L- alanine
methyl ester-D-tartrate was suspended in an excess of a 5%
NaaCO3 solution and stirred vigorously at 23C ~or 30 minutes
to give the free a~ino ester. Thi~ mixture was extracted with
2 x 500 ml. of EtOAc and the combined EtOAc layers dried over
MgS0~ (anh.). The EtOAc solution was filtered, the filtrate
concentrated under reduced pressure and dried i~ vacuo to give
22.5 g. of ~ -
the amino ester as a clear oil. [c]23 ~ 61.8 (c-2.2,
dioxane).
The above 22.5 g. of amino ester was dissolved in 800 ml.
of dioxane under N~. This was followed by the addition of
35 g. o~ N-CBz-L-aspartic acid-B-benzyl ester, 24.8 g. of 1,3-
dicyclohexylcar~odiimide and 12.4 g. of N-hydroxy-5-
norbornene-2,3-dicarboximide. This mixture was then stirred
overnight, during which time a solid precipitated.
The solid 1,3-dicyclohexylurea was removed by filtration
and the filtrate concentrated under reduced pressure. The ~-
residue was taken up in 1000 ml. of ether and washed with
. . , . , ............ - .~ --
. ~ : ~,, ' . :
: . .. , : :
wosl/027ll PCT/~S~/~7~2
~ ~ S~3~ ~4 _54_
2 x l000 ml. of 5~ citric acid, 2 x l000 ml. of 7% NaHCO3 and
200 ml. of saturated NaCl solution. The ether solution was
then dried over MgSOq (anh.), filtered and the filtrate
concentrated under reduced pressure.
The residue was chromatographed on silica gel using
hexane with increasi~g amounts of EtOAc as the eluent. The
progress of the column was monitored by TLC (silica gel-40%
EtOAc/Hexane) and the appropriate fractions combined to give,
following concentration, 49.7 g. of the titled compound.
Melting point: 62-64C
t~]23 =+9 S (c=l, methanol)
H-NMR (CDCl3 solvent, TMS internal standard, ~):
0.95 and 1.05 (each 3H, s, -CH3), 3.70
(3~, s, -OCH3),
5.15 (4H, s, -CH2-Ar), 7.35 (lOH, s, Ar)
EXAMP~E 18
Production of L-aspartyl-3-(2R-exo-7,7-dimethylnorbor- nyl)-
L-alanine methyl ester:
To 8.6 g. of N-(~-benzyl-N-CBZ-L-aspartyl)-3-(2R-exo-7, 7-
dimethylnorbornyl)-L-alanine methyl ester in 200 ml. of
methanol was added 0.4 g. of 10% palladium/carbon. The
mixture was hydrogenated at 3 kg./cm.2 H2 and room te~perature
for 18 hours. The catalyst was then removed by filtration
th~ough a short pad of celite and the filtrate evaporated to
give 5.2 g. of th~ title compound as a clear gla~s. This was
crystallized from chlorofor~/hexane to afford material
comparable to that of Example 16 as determined by HPLC, IR and
3C NMR comparison.
Melting point: 144-146 C
~]23 , +29.2 ~c-l, methanol)
'
.
WO 91/02?11 2 ~ PC~'/1,'590/1}4722
--55--
D
H NMR (CD30D solvent, TMS internal standard, ~):
l.o and 1.1 (each 3H, s, -CH3)
2.75 (lH, m, -CH2-C02H)
3.7S (3H, s, -OCH3)
EXAMPLE 19
Purification of alpha-L-aspartyl-3-(2R-exo-7,7-dimethyl-
nor~ornyl)-L-alanine methyl ester:
A 60.4 g. sample of ~ L-aspartyl-3-(2R-exo-7,7-
dimethylnorbornyl)-L-alanine methyl ester (alpha/beta 390/10)
was dissolved by heating in 900 ml. of a 1:2 methanol:water
mixture. Cooling the solution afforded 51.2 g. of a white
solid (alpha/beta = 94.6/5.4). Repeated crystallization from
the same solvent mixture (15:1 vol./wt.) as shown in Table 7
gave IV (alpha/beta - 99.2/0.8).
EXAMPLE 20
Synthesis of 3-(2R-exo-7,7-dimethylnorbornyl)alanine
hydantoin: -
To a solution of 2 g. (12.2 mmole) of 2R-exo-7,7-
dimethylnorbornyl acetaldehyde in 35 ml. of 60% EtOH-H20 was
added 3.5 g. of ~N~)2C03 and the resulting slurry warmed to
55C. To this mixture was added 650 mg. (13.2 mmols) of NaCN
in 5 ~1. of H~0 and the resulting mixture heated at 60C
overnight under a reflux condenser. The condenser was removed
and the solution warmed to 90C for three hours to drive off
excess (NH~)2C03-
Upon cooling to room temperature, 10 ml. of H20 was addedand the solution extracted with 20 ml. of hexane. The agueous
phase was then acidified to pH 5 (to be carried out under a
hood) with 1 N HCl to give a white solid precipitate. This
.,
WO9l/027ll PCT/~S~/W722
2~5~4
-56-
was removed by filtration and dried in vacuo to afford 3.1 g.
of the desired product.
Melting point: 178-183C;
IR: 3280, 2950, 1720, 1420, 1315 and 1190 cm. 1
H-NMR (Pyridine-d5, TMS, ~): 9.25-9.05
O , .
(lH, m, -NH-), 4.4 - 4.15 (lH, m, -C-CH-N), 2.4-1.3
I
(llH, m, -CH2-,-CH-), 1.1-0.8 (6H, s, -CH3)
EXAMP~E 21
Hydrolysis of 3-(2R-exo-7,7-dimethylnorbornyl)alanine
hydantoin:
A mixture of 500 mg. of 3-(2R-exo-7,7-dimethylnor-
bornyl)alanine hydantoin (2.12 mmoles), 2.5 g. of barium
hydroxide and 10 ml. of H~O was heated at reflux for 72 hours.
Upon cooling 20 ml. of H20 wa~ added and th~ mixture acidified
to pH 2.0 with 1 ~ H25O~. The solid was removed by filtration
and the filtrate adjusted to pH 4.0 with 1 N NaOH.
Concentration of the solution to -_ 10 ml. and cooling to 5C
gave a white solid. After drying n vacuo the yield was -
83 ~g. (0.39 mmole, 19%) of 3-(2R-exo-7,7-dimethylnobornyl)-
D,L-alanine. Nelting point: 217-219C;, IR: 3430, 2950, 1610,
lS05, 1400, 1320 and 1100 cm~l.
; ` ' . ! . . ~ , . . .
., . ~ ' ' ' ' ' , ;
WO91102~11 PCT/~S90/W7~'
_57_ 2 ~5 V l q
~able 5
"
SolventIII~/IIIB ~ielectric Constant
Acetic Acid 4.5 6.15
Acetone 0.9 20.7 --
Acetonitrile l.3 37.5 -
Ethyl Acetate 3.6 6.02
Ethyl Ether * 7.7 (3.5) 4.34
Dioxane 2.2 2.~l
Toluene* 8.6 2.38
Butyl Acetate 4.2 5.0l
Carbon Tetrachloride * 5.0 2.24
Trichloroethylene 5.6 3.4
Tetrahydrofuran l.4
Chloroform 5.l 4.8l
Diglyme 0.27
Hexane * l.5 l.89
Dimethylformamide 0.08 37.6
Cyclopentanone l.7 18.0
Xylene * 7.6 2.27
Butyl Ether * 6.8 3.0
* N-Carbobenzyloxyaspartic anhydride was insoluble
(suspension) at 5C.
Reaction o~ one part N-carbobenzyloxy aspartic anhydride
(II) with one part 3-(2R-exo-7,7-dimethyl- norbornyl)-L-
alanine methyl ester acetic acid salt in lO0 parts solvent at
5C for 18 hours. Ratios of (III alpha)/(III beta) were
determined by peak heights on HPLC using an Altex 5u C18 column
:
. .
~ . ', . - : ~
- .
WO 91/02~1l PCT/US~/~722
2~Sv~
-58-
with 60~ acetonitrile/O.OSM KH2Po~, pH 4.0 as solvent and UV
detection at 210 nm.
Tabl* 6
III a III
pH 6.093/7 83/17
pH 6.587/13 17/83
pH 7.019/81 9/91
Partition of alpha- and beta-(N-carbobenzyloxy-L- -~ -
aspartyl)-3-(2R-exo-7,7-dimethylnorbornyl)-L-alanine
methyl ester (III ~/B) between toluene and 0.1 ~ phosphate
buffers at the pH indicated. The ratios indicate the
percent in the toluene phase over the percent in the
buffer phase. Values are for 100 mg. of compcund in
10 ml. of toluene and 10 ml. of buffer.
Table 7
A~ount of material ~ ratio
1. 1.482 89.9/10.1
2. 1.265 94.6/ 5.4
3. 1.129 97.1/ 2.9
4. 1.073 98.4/ 1.6 ~
S. 1.000 99.2/ 0.8 - ;
- - .. .. .
,, ~ . ,: .. -:, :.. :-: : . : , .
,. : :, . :, .
, : ~ .... . . . . .. .. .
WO91/02711 PCT/US~722
2 ~
-59-
Recrystallization of a mixture of ~IV alpha) and (IV beta)
from 33% methanol-water. Alpha/beta ratios were determined by
peak heights on HPLC using a unisil Q Cl8 column with 40%
acetonitrile/1% methanol/ 59S O.l ~ KH2P0~, pH-4.0 as solvent
and W detection at 220 nm. (UNISIL Q Cl8: particle size 5~m,
Gasukuto Kogyo Co. Ltd.)
While specific embodiments of the invention have been
shown and deccribed in detail to illustrate the application of
the inventive principles, the invention may be embodied
otherwise without departing from such principles.
,~ . ' ' ' , ' . . .
. ' . `~ ' .
" . "' ~ ', ` . '
' ' ,. ',. ,, , ' .. '' ~. : ~'
.: ' ', . , ~ , . , ' '
