Note: Descriptions are shown in the official language in which they were submitted.
WO 95/00492 ~ PCTIE194/00263
ENANTIOMERS OF 4-(5-FLUORO-2,3-OIHYDRO-lH-INDEN-2-YL)-lH-IMIOAZOLE
The invention provides new optical isomers of 4-(5-fluoro-2,3-dihydro-
1H-inden-2-yl)-1H-imidazole and pharmaceutically acceptable salts thereof,
their use and preparation. Both optical isomers are potent in the treatment of
5 coy";li~/e disorders, although somewhat different pharmacological profiles maybe ascl ibed to them. The (-)-enantiomer is the preferred one of the two
enantiomers because it has a wider therapeutic window than the (+)-
enantiomer. lt is a very powerful antagonist of a2-adrenoceptors without any
a1-agonism whereas the (+)-enantiomer is a moderate antagonist of a2-
1 o adrenoceptors and a full a1-agonist. Both enantiomers have good peroral
bioavailability.
Valuable a2-adrenoceptor antagonist have been disclosed earlier e.g. in
the El~ropean patent publicalio"s No. 183492, 247764 and 372954. PCT
patent publication No. 91/18886 disclQses the use of some indan-imid~uls
1 5 derivatives, especi~lly atipamezole, in the treatment of age-related memory
impairment and other coy"ili~/e disorder~. lnler-,alional patent applicdlic;n No.
PCT/1-192/00349 desc,il,~s a group of new long-acting 4(5)-substituted indan-
imidazole derivatives which are useful in the treatment of coy"ili~re d;sorder~.One of these indan-imidazole derivatives is the racemate of 4-(5-fluoro-2,3-
20 dihydro-1H-inden-2-yl)-1H-imidazole which has an asymmetric carbon atom in
the position 2 of the indan ring:
~NH
The optically active enantiomers of 4-(5-fluoro-2,3-dihydro-1 H-inden-2-
yl)-1 H-imidazole may be prepared e.g. by conversion of racemic 4-(5-fluoro-2,3-
25 dihydro-1H-inden-2-yl)-1H-imidazole into a mixture of diastereoisomers and
separating these by fractional cryst~ tion. Since 4-(5-fluoro-2,3-dihydro-1H-
inden-2-yl)-1 H-imidazole is a base, it may be converted into diastereoisomer
salt mixture by reaction with an optically active acid, preferably with L-(+)- or D-
(-)-taltaric acid. The diastereoisomers may be separated by repeated
3 o cryst;~lli7~tion e.g. from water.
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Once the diastereoisomers have been separated the acid addition salts
may be converted back to the free bases by making their aqueous solutions
alkaline with a base (e.g. sodium hydroxide) and by extracting the liberated
base into an appropriate organic solvent.
The (-)- and (+)-enantiomers of 4-(5-fluoro-2,3-dihydro-1 H-indsn-2-yl)-
1 H-imidazole react with organic or inorganic acids to form the corresponding
acid addition salts, which have the same therapeutic activities as the bases.
They can thus form many pharmaceutically useful acid addition salts such as
cl,lo,ides, bromides, sulfat~s",il,ales, phosphates, sulfonates, formates,
10 tartrates, m~le~tes, citrates, ben~o~tes, salicylates and ascorbates.
The racemate of 4-(5-fluoro-2,3-dihydro-1H-inden-2-yl)-1H-imidazole
may be prepared e.g. by llilldlil)g 4-(2,3-dihydro-1H-inden-2-yl)-1H-imid~olc
hydrochloride with a strong nilldlil)5~ agent such as ureanitrate in the presence
of sulfuric acid and thereafter reducing the nitro compound to the corresponding15 amino compound e.g by catalytic hydrogenation using PtO2 or Pd/C as
catalysts. The amino substituted compound is further converted to the
corresponding diazonium fluoroborate with sodium nitrite in fluoboric acid at
lowered temperature. The diazonium fluoroborate is then decomposed
thermally to yield the racemate of 4-(5-fluoro-2,3-dihydro-1 H-inden-2-yl)-1 H-
2 o imidazole.
The compounds according to the invention may be administeredenterally or par~"lerally. In the treatment of cognitive disorders the preferable
daily dosage is from 0.1 to 10 mg/kg, especi^'ly preferably from 0.2 to 1 mg/kg.
The acute toxicity (LDso) for both enanliG~Iafs is about 100 mg/kg in mice
2 5 (p.o.) and about 50 mg/kg in rat.
The pharmaceutical carriers which are typically employed with the
compound of the invention may be solid or liquid and are selected with ths
planned manner of admil,i~ lion in mind. Choosing ths auxiliary ingredients
for the formulation is routine for those of ordinary skill in the art.
3 o 1. The oc-adrenoceptor selectivity in vitro
oc2-Antagonism was determined by means of isolated, electrically
stimulated prostatic portion of rat vas de~re~ Is preparation (Virtanen et al, Arch.
Int. Pharmacodyn et Ther., 297, 190-204, 1989). In this model, a2-agonist
(detomidine) blocks electrically stimulated muscular contractions and the effect
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~ WO 95/00492 PCT/E'194/00263
of the a2-antagonist is seen by administering it prior to the agonist and by
deter")ining its PA2 value. The known a2-antagonist atipamezole was used as
a reference substance.
To obtain information also on the selectivity of the antagonist between a1- and
5 a2-receptors, its ability to inhibit or stimulate a1-receptors was determined by
means of isolated epididymal portion of rat vas deferens. To determine a1-
antagonism, muscular contraction was induced by phenylephrine and the PA2
value of the studied compound was determined as above. a1-Agonist effect is
presented as the PD2 value (negative logarithm of the molar conce~ lion of
10 the col~"~ound producing 50 percent of maximal contraction). The results are
given in Table 1.
T~hle 1. The selectivity of racemic 4-(~-fluoro-2,3-dihydro-1 H-inden-2-yl)-
1 H-innidazole and its enantiomers in comparison with atipamezole
Compound a2-Antagonisma1-Antagonism a1-Agonism
(PA2Vs (pA2 vs phenyl- (pD2)
detomidine) ephrine)
(-)-enantiomer 9.1 6.7 no sffect
(+)-enantiomer 7.9 not tested 6.0
full agonist
racemate 8.0 not tested 5.~
partial agonist
Atipamezole 8.0 5.0 no effect
2. Effects on memory
The effect of the (-)-enantiomer on learning and memory in linear arm
maze task in rats was studied. The linear arm maze is a modified version of
radial arm maze, which is a generally used memory test in rats. The (-)-
enantiomer hydrochloride (0.1 mg/kg s.c.) was dissolved in distilled watsr.
2 o Water was also used as control. All injections were made in a volume of 1 ml/kg.
Apparatus: The maze was a wooden plafform in a shape of two crosses
one after another. The stem (starting arm) was 90 cm long and 12 cm wide. Ths
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WO 95/00492 ~ ~ PCT/1;194/00263
five other arms (goal arms) were 50 cm long and 12 cm wide. Four goal arms
were situated perpendicularly to the stem and to the fifth arm which located
opposite to the stem. On either side of the stem and the arms were edges, 2.0
cm high. At the end of each goal arm a hole 1 cm deep and 3 cm in diameter,
5 served as a food cup. The starting platform (20 x 20 cm) was separated from the
stem by a guillotine door. The door was 12 cm high and 7 cm wide. The door
frame was 20 cm high and 20 cm wide. The maze was elevated 31 cm above
the floor, in a low-lighted test room which contained other objects as well as the
test apparatus. The holes at the end of the goal arms were baited with three
10 pellets of prize food (45 mg pellets Bio Serve Inc.).
Procedures: Two days prior to training, animals were placed on a food
deprivation scedule that reduces their body wcighls to 90% of initial weigl ,Is.During these days the rats were habituated to handling (three times/day), test
room and prize food. On the second day they were also habituated to the
15 unbaited maze: three to five animals from the same cage at the same time for
ten minutes. On the third day the goal arms were baited, and the teaching trial,one rat at a time, was carried out. The rat received drug or distilled water and 60
minutes later it was placed in the sla~ g plafform. After ten seconds the door
was opened and the rat was allowed to explore the maze until all the baits were
2 o found. Reentries into an arm previously visited during that session were
counted as errors. The time to find all the baits and correct choices made untilthe first mistake was recorded. At this time (teaching), every rat was allowed to
stay in the maze for at least five minutes. On the next day the proper memory
and learning testing began and continued for four days (testing days 1 to 4).
2 5 Rats were given eight trials, two per day. Inter trial interval was 50 minutes. The
drug or distilled water were admir,isle,ed 30 minutes before the first trial of the
day. Otherwise testing trials were identical to the teaching trial. There were 20
animals in both groups.
Statistical analysis: The results were expressed as mean errors/trial,
3 o mean correct choices/trial and mean time/trial (seconds).The analysis of
variance for the repe~ted measurements (ANOVA) was used to compare the
effects of the drug and the testing day on learning and memory.
The results: The effects of the (-)-enantiomer on learning and memory are
presented in the Figures 1, 2 and 3. The drug decreased the number of errors
3 5 i.e. reentries into the arms already visited during the same trial (Fig 1). The (-)-
enantiomer also increased the number of correct choices made before the first
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WO 9~/00492 2~ 5 ~ ~ 9 PCT/E'194/00263
error of the trial (Fig 2). These are thought to mean an effect on working memory
and on the ability to concentrate on the trial, respectively. The drug also tended
to decrease the time to solve the task (Fig 3).1t is co"sidered as an effect on
speed to make decisions, in this case the correct choices. The number of errors
5 and tirne decreased and the number of correct choices increased trial by trialwhich indic~tes learning also in the control group. There were no group x trial
interactions, which means that the effect of the (-)-Bl lal-liCJm er did not depend on
the trial. These results suggest that the
(-)-en~mtiomer has learning and memory enhancing effects on adult rats.
1 o 3. The preparation of the optically active isomers
Racernic 4-(5-fluoro-? :~-dihydro-1 H-inden-2-yl)-1 H-imidazole
Concentrated sulphuric acid (58 ml) was cooled to -10C and the mixture
of 4-(2,3-dihydro-1H-inden-2-yl)-1H-imidazole hydrochloride (Karjalainen, A. J.
et al lJ.S. 4,689,339; 13.8 g, 0.0625 mol) and ureanitrate (7.70 g, 0.0625 mol)
was aLdded in small pGI lions to the acid solution at -10C. After the reaction the
solution was poured onto ice. The solution was made alkaline and extracted
three times with ethyl acetate. The organic extracts were co~,lbined, dried and
evaporated to dryness. The yield 13.0 g, 91 % of
4-(2,3-dihydro-5-nitro-1 H-inden-2-yl)-1 H-imidazole.
Reduction of 4-(2,3-dihydro-5-nitro-1H-inden-2-yl)-1H-imidazole to 4-(5-
amino-2,3-dihydro-1H-inden-2-yl)-1H-imidazole was carried out by adding 1.0
g of 10% p~ di~m on carbon to 11.7 g (0.0512 mol) of 4-(2,3-dihydro-5-nitro-
1H-inden-2-yl)-1H-imidazole in 100 ml of ethanol and sh~hill~ the mixture in a
hydrogel, al,nos~here at the room temperature. When the reduction came to a
2 5 standstill the catalyst was removed. The filtrate was conce, Illaled to give 9.63 g
(94 C~o) of 4-(5-amino-2,3-dihydro-1 H-inden-2-yl)-1 H-imidazole. The product
was purified by flash chromatogfapl,y eluting with methylene chloride -
methanol (9.5:0.5).
A flask containing fluoboric acid (48 wt. % solution in water, 120 ml) and
9.50 g (0.0475 mol) of 4-(5-amino-2,3-dihydro-1H-inden-2-yl)-1H-imidazole
was placed in an ice-salt bath and cooled to 0 C. A solution of
3.30 g (0.0478 mol) of sodium nitrite in 10 ml of water was run in slowly while
the temperature was kept at 0 C. The mixture was stirred for an hour at 0 C
and then for an hour at the room temperature. The reaction mixture was
3 5 evaporated twice to dryness with toluene. The thermal decomposition was
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WO 95/00492 ~ PCT/E194/00263
carried out in a flask which was hsated with an electric heating mantle. When
the generation of white fumes of boron trifluoride ceased the heating was
stopped. The crude product was dissolved in methanol, the solution was filtered
and evaporated to dryness. The yield of the crude 4-(5-fluoro-2,3-dihydro-1H-
inden-2-yl)-1 H-imidazole was 9.51 g, 99 %. The product was purified by flash
chromatography (the eluent methylene chloride - methanol 9.5:0.5).
1 H NMR (300 MHz, CD30D): ~ 2.g6-3.08 (2H, m, one H-1 and one
H-3), 3.19-3.27 (2H, m, another H-1 and another H-3), 3.68 (1H, quintet, 3JHH
8.3 Hz, H-2), 6.80-6.86 (1 H, m, H-6), 6.83 (1 H, s, im-5), 6.92 (1 H, dd, 3JHF 8.9
HZ~4JHH2.4Hz~H-4)~7.16(1H~dd~3JHH8.1 HZ~4JHF5.3Hz~H-7)~ 7.59(1H,
s, im-4)
~eparation of the enantiomers
1 5 D-(-)-Tartaric acid (0.44 g, 0.00293 mol) was dissolved in 2.5 ml of water
at 60 C. The racemate of 4-(5-fluoro-2,3-dihydro-1 H-inden-2-yl)-1 H-imidazole
(1, 1.03 g, 0.00509 mol) and 178 1ll of co"ce"l,dled hydrochloric acid were
added at 60 C. The mixture was stirred at 60 C until it became a clear solution.
The solution was allowed to cool slowly. The preci,~,ilales were collected and
recrystallized five times from water to give the D-(-)-tartaric acid salt of the (-)-
enantiomer: mp 186-187 C.
The D-(-)-tartaric acid adduct of the (-)-enantiomer was dissolved in
water at 60 C and ethyl acetate was added. The solution was made alkaline
(pH 10) with diluted sodium hydroxide. The ethyl acetate phase was separated
2 5 and the water phase was extracted twice with ethyl acetate. The corl,b;nedorganic phases were washed with water. Ethyl ac~tate was evaporated to
dryness and the residue was crystallized from ethyl acetate. The product was
filtered by suction and washed with cold ethyl acetate: mp 139 C (DSC),
specific rotation at 20 C in methanol solution -3.7 (c=20 mg/ml).
3 o The (-)-enantiomer base was dissolved in ethyl acetate and filtered by
Millipore. The filtrate was made acidic (pH 1) with dry hydrochloric acid - ethyl
acetate solution and cooled to -10 C. The precipitate was filtered by suction
and washed with ethyl acetate. Recryst~ n from ethyl acetate gave th~
hydrochloride salt of (-)-4-(5-fluoro-2,3-dihydro-1H-inden-2-yl)-1H-imidazole as3 5 a white crystalline solid: mp 191 C (DSC); chromalog~aphic purity 99.8 %
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~ WO 95/00492 PCT/F194/00263
~ ~ 6 3 4 ~ ~
(HPLC); optical purity 99.9 %(HPLC); specific rotation at ambient temperature inwater solution -3.5 (c=20 mg/ml).
The (+)-enantiomer was resolved in the same way as the (-)-isomer using L-
(+)-tartaric acid as a resolving agent to give the L-(+)-tartaric acid adduct of the
(+)-enantiomer: mp 187-189 C. The base and hydrochloride salt (mp
190 C) were made as described above. The chromaloy~ hic purity of the
hydrochloride salt was 98.7 % (HPLC); optical purity 99.6 % (HPLC); specific
rotation at ambient temperature in water solution +3.2 (c=20 mg/ml).
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