PROCESS FOR THE PREPARATION OF CLAVULANIC ACID ESTERS

TRADUCTION NON-DISPONIBLE

English Abstract

Abstract of the Disclosure
A process for the preparation of a compound of the formula
(1):
<IMG> (I)
or a salt or ester thereof wherein R is a methyl or ethyl group which
process comprises the reaction of clavulanic acid or a salt or ester
thereof with an oxonium salt of the formula (II):
R3O? X.THETA. (II)
wherein R is a methyl or ethyl group and X.THETA. is an anion and thereafter
if desired performing one or both of the following reactions: (a) con-
verting the thus formed ester into the acid or salt and (b) converting
the thus formed acid or salt into an alternative ester or alternative
salt. The compounds of formula (I) have utility as additives to enhance
the effectiveness of penicillins and cephalosporius. The novel process is
generally convenient, safer and often higher yielding than known processes.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for the preparation of a compound of
the formula (I):
(I)
<IMG>
or a pharmaceutically acceptable salt or pharmaceutically
acceptable ester thereof wherein R is a methyl or ethyl
group which process comprises the reaction of clavulanic acid
or a salt or ester thereof with an oxonium salt of the formula
(II):
R3O.THETA. X.THETA. (II)
wherein R is a methyl or ethyl group and X.THETA. is an
anion and thereafter if desired performing one or
both of the following reactions: (a) converting the
thus formed ester into the acid or pharmaceutically acceptable
salt and (b) converting the thus formed acid or pharmaceutically
acceptable salt into an alternative pharmaceutically acceptable
ester or alternative pharmaceutically acceptable salt.
37

2. A process is claimed in Claim 1 wherein X.THETA.
is BF4.THETA..
3. A process as claimed in Claim 1 wherein X.THETA.
is PF6.THETA..
4. A process as claimed in Claim 1 wherein X.THETA.
is 2,4,6-trinitrobenzenesulphonate.
5. A process as claimed in Claim 1 wherein the
oxonium salt of the formula (II) is trimethyloxonium
tetrafluoroborate.
6. A process as claimed in Claim 1 wherein the
oxonium salt of the formula (II) is triethyloxonium
tetrafluoroborate.
7. A process as claimed in Claim 1 which
employs a hydrolysable ester of clavulanic acid.
8. A process as claimed in Claim 1:
which employs a hydrogenolysable ester of clavulanic
acid.
9. A process as claimed in Claim 1 which
employs an ester of clavulanic acid of the formula (III):
38

<IMG>
(III)
wherein A1 is an alkyl group of 1-8 carbon atoms
optionally substituted by halogen or a group of
the formula OA4, OCOA4, SA4 or SO2A4 wherein A4
is a hydrocarbon group of up to 6 carbon atoms.
10. A process as claimed in Claim 1 which
employs an ester of clavulanic acid of the formula
(III) as shown in claim 7 wherein A1 is an alkenyl or
alkynyl group of up to 4 carbon atoms.
11. A process as claimed in Claim 1 which
employs an ester of clavulanic of the formula (III)
as shown in claim 9 wherein A1 is a group such that
the compound is an acetoxymethyl, .alpha.-acetoxyethyl,
pivaloyloxymethyl, phthalidyl, ethoxycarbonyloxymethyl
or .alpha.-ethoxycarbonyloxyethyl ester.
39

12. A process as claimed in Claim 1 which
employs an ester of clavulanic acid of the formula (V):
(V)
<IMG>
A2 is a hydrogen atom, an alkyl group of up to 4
carbon atoms or a phenyl group optionally substituted
by halogen or by a group A5 or OA5 above A5 is an alkyl
group of up to 6 carbon atoms; and A3 is a phenyl
group optionally substituted by halogen or by a group
A5 or OA5 where A5 is an alkyl group of up to 6
carbon atoms.
13. A process as claimed in claim 9 wherein A1 is
an alkyl group of up to 4 carbon atoms optionally
substituted by a group of the formula OA4 or OCOA4
where A4 is an alkyl group of up to 4 carbon atoms.
14. A process as claimed in claim 9 wherein A1 is
a methyl group.

15. A process as claimed in claim 9 wherein A1 is
an ethyl group.
16. A process as claimed in Claim 1l which
employs an ester of the formula (V) as shown in
claim 12 wherein A2 is as defined in claim 12 and A3
is a nitrophenyl group.
17. A process as claimed in claim 12 wherein
A2 is hydrogen.
18. A process as claimed in claim 12 wherein CHA2A3
is benzyl.
19. A process as claimed in claim 12 wherein CHA2A3 is
p-methoxybenzyl.
20. A process as claimed in claim 12 wherein CHA2A3
is p-bromobenzyl.
21. A process as claimed in claim 12 wherein CHA2A3
is p-nitrobenzyl.
22. A process as claimed in Claim 1 which
employs a salt of clavulanic acid.
23. A process as claimed in claim 22 wherein the
salt is an alkali metal salt.
41

24. A process as claimed in claim 22 wherein
the salt is an alkaline earth metal salt.
25. A process as claimed in claim 22 wherein
the salt is of a nitrogenous base.
26. A process as claimed in claim 23 wherein the
salt is the lithium salt.
27. A process as claimed in claim 23 wherein the
salt is the sodium salt.
28. A process as claimed in claim 23 wherein the
salt is the potassium salt.
29. A process as claimed in claim 25 wherein
the base is tetramethylguanidine.
30. A process as claimed in Claim 22
wherein the salt is employed in finely divided
form.
31. A process as claimed in Claim 22
wherein the salt employed has been prepared by
freeze-drying.
32. A process as claimed in claim 27 wherein the
sodium salt employed has been prepared by dehydrating
sodium clavulanate tetrahydrate.
42

33. A process as claimed in Claim 1 carried
out at a temperature of from -60° to 60°C.
34. A process as claimed in claim 33 wherein the
temperature is from -40° to 30°C.
35. A process as claimed in claim 33 wherein the
temperature is from -30° to 20°C.
36. A process as claimed in claim 33 wherein the initial
temperature is from -30° to 0°C.
37. A process as claimed in claim 33 wherein the
final temperature is 10 to 20°C.
38. A process as claimed in Claim 1
wherein the solvent is a haloalkane.
39. A process as in Claim 38 wherein the haloalkane
is dichloromethane.
40. A process as claimed in Claim 38 wherein the
solvent is chloroform.
41. A process as claimed in Claim 1
wherein the solvent is nitromethane.
42. A process as claimed in Claim 1
wherein the reaction is performed in the presence of
a base.
43

43. A process as claimed in Claim 42 wherein
the base is an insoluble base present to a large
excess.
44. A process as claimed in Claims 42 or 43
wherein the base is an alkali metal carbonate or
bicarbonate.
45. A process as claimed in Claims 41 or 42
wherein the base is an alkaline earth metal
carbonate or bicarbonate.
46. A process as claimed in Claims 41 or 42 wherein
the base is an alkaline earth metal oxide or
hydroxide.
47. A process as claimed in Claim 42 wherein
the base is sodium carbonate.
48. A process as claimed in Claim 43 wherein the
base is sodium bicarbonate.
49. A process as claimed in Claim 42 or 43 wherein the
base is lithium carbonate.
50. A process as claimed in Claim 42 wherein the
base is potassium carbonate.
44

51. A process as claimed in Claim 43 wherein the
base is potassium bicarbonate.
52. A process as claimed in Claim 42 wherein the
base is calcium carbonate.
53. A process as claimed in Claim 43 wherein the
base is calcium bicarbonate.
54. A process as claimed in Claim 42 or 43 wherein the
base is magnesium carbonate or magnesium bicarbonate.
55. A process as claimed in Claim 1
wherein an ester of the ether is obtained from the
reaction mixture by washing with water to remove ionic
materials and thereafter evaporating the organic
phase.
56. A process as claimed in Claim 1
wherein the initially produced ester of the compound of formula (1)
is converted to a salt by hydrolysis.
57. A process as claimed in Claim 56 wherein the
hydrolysis is effected by the addition of an alkali
metal base.

58. A process as claimed in Claims 56 or 57
wherein the base is an hydroxide.
59. A process as claimed in any of Claims 56 or 57
wherein the base is a lithium base.
60. A process as claimed in any of Claims 56 or 57
wherein the base is a sodium base.
61. A process as claimed in any of Claims 56 or 57
wherein the base is a potassium base.
62. A process as claimed in Claims 56 or 57 wherein the
base is lithium hydroxide.
63. A process as claimed in Claims 56 or 57 wherein the
base is sodium hydroxide.
64. A process as claimed in Claims 56 or 57 wherein the
base is potassium hydroxide.
65. A process as claimed in Claim 56 wherein the
hydrolysis is effected by the addition of an alkaline
earth metal base.
66. A process as claimed in Claims 56 or 57 wherein the
initially produced base is a lithium salt and is converted
into a sodium, potassium, calcium or magnesium salt.
46

67. A process as claimed in Claim 1 wherein the initially
produced ester of the compound of the formula (I) is con-
verted to the free acid by hydrogenolysis of a hydrogenoly-
sable ester.
68. A process as claimed in Claim 1
wherein the initially produced hydrogenolysable
ester is converted to the salt by hydrogenolysis in
the presence of a base.
69. A process as in Claim 67 wherein the acid is
converted to a salt by reaction with a base.
70. A process as claimed in Claims 68 or 69 wherein
the base is a lithium, sodium, potassium calcium
or magnesium carbonate, bicarbonate or hydroxide.
71. A process as claimed in Claims 68 or 69 wherein the
base is lithium, sodium or potassium carbonate
or sodium bicarbonate.
72. A process as claimed in Claims 68 or 69 wherein the
base is lithium hydroxide.
73. A process as claimed in Claim 1 wherein the ester of
clavulanic acid is prepared in-situ.
47

74. A process as claimed in Claim 9 wherein A' is a methyl
or ethyl group and wherein the ester of clavulanic acid is
produced by the reaction of a salt of clavulanic acid and an
oxonium salt of the formula (II).
75. A process as claimed in claim 74 wherein the compound
of the formula (II) is trimethyloxonium tetrafluoroborate or
triethyloxonium tetrafluoroborate and the ester of clavulanic
acid is produced by the reaction of a salt of clavulanic acid
and an oxonium salt of the formula (II).
76. A process as claimed in Claim 74 or 75
wherein the salt of clavulanic is the lithium salt.
77. A process as claimed in Claims 74 or 75
wherein the salt of clavulanic acid is the sodium
salt.
78. A process as claimed in Claims 74 or 75
wherein the salt of clavulanic acid is the
potassium salt.
79. A process for the preparation of methyl 9-0-
methylclavulanate which process comprises the
reaction of a salt of clavulanic acid with a
trimethyloxonium salt.
48

80. A process for the preparation of ethyl 9-0-
ethylclavulanate which process comprises the
reaction of a salt of clavulanic acid with a
triethyloxonium salt.
81. A process as claimed in Claims 79 or 80
wherein the oxonium salt is the tetrafluoroborate.
82. A process as claimed in Claims 79 or 80 carried out
at a temperature selected from -60° to 60°C, -40° to 30°C
-30° to 20°C, -30° to 0° C and 10 to 20°C.
83. A process as claimed in Claims 79 or 80 carried out
at a temperature of from -50° to 20°C.
84. A process as claimed in Claims 79 or 80 wherein the
solvent is selected from dichloromethane, chloroform and
nitromethane.
85. A process for the preparation of a pharmaceutically
acceptable salt of 9-0-methylclavulanate which comprises
the base hydrolysis of methyl 9-0-methylclavulanate pre-
pared by a process as claimed in Claim 79.
49

86. A process for the preparation of a pharmaceutically
acceptable salt of 9-0-ethylclavulanate which comprises the
base hydrolysis of ethyl 9-0-ethylclavulanate prepared by a
process as claimed in Claim 80.
87. A process as claimed in Claims 85 or 86
wherein the hydrolysis employs an alkali base metal or an
alkaline earth metal base.
88. A process as claimed in Claims 85 or 86 wherein
the hydrolysis is effected by lithium hydroxide.
89. A process as claimed in Claims 85 or 86 wherein the
initially produced lithium salt is converted into
a sodium, potassium calcium or magnesium salt.
90. A process as claimed in Claims 85 or 86 wherein the
convertion effected by contacting a solution of the
lithium salt with a cation exchange resin in the
form of the sodium, potassium, calcium or magnesium
salt and thereafter eluting the desired salt from
the resin.

91. A process as claimed in Claim 1 for the preparation
of the sodium, potassium, calcium or magnesium salt of 9-0-
methylclavulanic acid which process comprises contacting a
solution of the lithium salt of 9-0-methylclavulanic acid
with a cation exchange resin in the form of a sodium, pot-
assium, calcium or magnesium salt and thereafter eluting the
desired salt from the resin.
92. A process as claimed in Claim 1 for the preparation
of the sodium, potassium, calcium or magnesium salt of 9-0-
ethylclavulanic acid which process comprises contacting a
solution of the lithium salt of 9-0-ethylclavulanic acid
with a cation exchange resin in the form of a sodium, pot-
assium, calcium or magnesium salt and thereafter eluting the
desired salt from the resin.
93. A process as claimed in Claims 91 or 92 wherein the
elution solvent is water or water in admixture with amiscible
organic solvent.
94. A process as claimed in Claims 91 or 92 wherein the
elution solvent is water.
95. A process as claimed in claim 1 for the preparation
of 9-0-methylclavulanic acid or 9-0-ethylclavulanic acid
which comprises the acidification of a salt of 9-0-methyl-
clavulanic acid or of 9-0-ethylclavulanic acid prepared as
claimed in Claim 1.
96. Compounds of the formula (I) as set forth and defined
in Claim 1 and their pharmaceutically acceptable salts and
esters whenever prepared by the process of Claim 1 or an
obvious chemical equivalent thereof.
51

97. Methyl 9-0-methylclavulanate whenever prepared by the
process of Claim 79 or an obvious chemical equivalent thereof.
98. Ethyl 9-0-ethylclavulanate whenever prepared by the
process of Claim 80 or an obvious chemical equivalent thereof.
99. Pharmaceutically acceptable salts of 9-0-methylclavulanic
acid whenever prepared by the process of Claim 85 or an obvious
chemical equivalent thereof.
100. Pharmaceutically acceptable salts of 9-0-ethylclavulanic
acid whenever prepared by the process of Claim 86 or an obvious
chemical equivalent thereof.
101. The sodium, potassium, calcium or magnesium salts of
9-0-methylclavulanic acid whenever prepared by the process
of Claim 91 or an obvious chemical equivalent thereof.
102. The sodium, potassium, calcium or magnesium salts of
9-0-ethylclavulanic acid whenever prepared by the process of
Claim 92 or an obvious chemical equivalent thereof.
103. 9-0-methylclavulanic acid and 9-0-ethylclavulanic acid
whenever prepared by the process of Claim 95 or an obvious
chemical equivalent thereof.
104. A process for the preparation of ethyl 9-0-ethylclavul-
anate which comprises reacting anhydrous sodium carbonate,
potassium clavulanate with triethyloxonium tetrafluoroborate
in dry dichloromethane and isolating the desired ester.
105. A process as claimed in Claim 104 wherein the ester is
converted into the acid or a pharmaceutically acceptable
salt and when required the thus formed acid or pharmaceutically
52

acceptable salt is converted into an alternative pharmaceut-
ically acceptable ester or alternative pharmaceutically accept-
able salt.
106. A process as claimed in Claim 104 wherein tetramethyl-
guanidinuim clavulanate is reacted with triethyloxonium tetra-
fluoroborate.
107. A process as claimed in Claim 105 wherein tetramethyl-
guanidinuim clavulanate is reacted with triethyloxonium tetra-
fluroborate.
108. A process as claimed in Claim 104 wherein a catalytic
amount of crown ether is added to the dry dichloromethane
solution of reactants before the oxonium salt is added.
109. Ethyl 9-0-ethylclavulanate whenever prepared by the
process of Claim 104 or an obvious chemical equivalent thereof.
110. Pharmaceutically acceptable salts, pharmaceutically
acceptable esters and the acid form of ethyl 9-0-ethylclav-
ulanate whenever prepared by the process of Claim 105 or an
obvious chemical equivalent thereof.
111. Ethyl 9-0-ethylclavulanate whenever prepared by the
process of Claim 106 or 107 or an obvious chemical equivalent
thereof.
112. Ethyl 9-0-ethylclavulanate whenever prepared by the
process of Claim 108 or an-obvious chemical equivalent thereof.
113. A process for the preparation of lithium 9-0-ethyl-
clavulanate which comprises treating ethyl 9-0-ethylclavulanate
with lithium hydroxide solution and isolating the desired salt.
53

114. Lithium 9-0-ethylclavulanate whenever prepared by
the process of Claim 113 or an obvious chemical equivalent
thereof.
115. A process for the preparation of sodium 9-0-ethyl-
clavulanate which comprises treating lithium 9-0-ethyl-
clavulanate with a cation exchange resin to obtain the de-
sired sodium salt and isolating said salt.
116. Sodium 9-0-ethylclavulanate whenever prepared by the
process of Claim 115 or an obvious chemical equivalent thereof.
117. A process for the preparation of ethyl 9-0-ethylclavu-
lanate which comprises reacting anhydrous sodium carbonate,
dehydated sodium clavulanate and triethyloxonium tetrafluoro-
borate in dry methanol-free methylene chloride and in the
presence of a catalytic amount of crown ether and isolating
the desired ester.
118. Ethyl 9-0-ethylclavulanate whenever prepared by the
process of Claim 117 or an obvious chemical equivalent thereof.
119. A process for the preparation of ethyl 9-0-ethylclav-
ulanate which comprises reacting a solution of lithium
clavulanate and anhydrous sodium carbonate in dry methylene
chloride and a trace of crown ether with a solution of tri-
ethyloxonium tetrafluoroborate in dry methylene chloride and
isolating the desired ester.
120. Ethyl 9-0-ethylclavulanate whenever prepared by the
process of Claim 119 or an obvious chemical equivalent thereof.
121. A process for the preparation of ethyl 9-0-ethyl-
54

ethylclavulanate which comprises reacting a solution of
magnesium clavulanate and anhydrous sodium carbonate in dry
methylene chloride and a trace of crown ether with a solution
of triethyloxonium tetrafluoroborate in dry methylene chloride
and isolating the desired ester.
122. Ethyl 9-0-ethylclavulanate whenever prepared by the
process of Claim 121 or an obvious chemical equivalent thereof.
123. A process for the preparation of methyl 9-0-methyl
clavulanate and its lithium salt which comprises reacting
a suspension of potassium clavulanate and anhydrous sodium
carbonate in dry methylene chloride and 18-crown-6 with a
suspension of trimethyl-oxonium tetrafluoroborate in dry
methylene chloride and isolating the desired ester and when
required hydrolyzing the ester with lithium hydroxide to obtain
the lithium salt.
124. Methyl 9-0-methylclavulanate and its lithium salt when-
ever prepared by the process of Claim 123 or an obvious
chemical equivalent thereof.
125. A process for the preparation of methyl 9-0-methyl-
clavulanate and its potassium salt which comprises reacting
potassium clavulanate and anhydrous sodium carbonate in the
presence of crown ether and dried methylene chloride with
trimethyloxonium tetrafluoroborate to obtain an isolation
of the desired ester and when required hydrolyzing the ester
to obtain the potassium salt.
126. Methyl 9-0-methylclavulanate and its potassium salt
whenever prepared by the process of Claim 125 or an obvious
chemical equivalent thereof.

127. A process for the preparation of methyl 9-0-methyl-
clavulanate which comprises reacting dehydrated sodium clavu-
lanate and anhydrous sodium carbonate with trimethyloxonium
tetrafluoroborate in the presence of dried methylene chloride
containing crown ether to obtain the ester and isolating said
ester.
128. Methyl 9-0-methylclavulanate whenever prepared by the
process of Claim 127 or an obvious chemical equivalent thereof.
129. A process for the preparation of methyl 9-0-methyl-
clavulanate which comprises adding dry methylene chloride
containing crown ether to lithium clavulanate, anhydrous
sodium carbonate and trimethyloxonium tetrafluoroborate and
isolating the desired ester.
130. Methyl 9-0-methylclavulanate whenever prepared by the
process of Claim 129 or an obvious chemical equivalent thereof.
131. A process for the preparation of methyl 9-0-methyl-
clavulanate which comprises adding dry methylene chloride
containing crown ether to magnesium clavulanate, magesium
oxide and trimethyloxonium tetrafluoroborate and isolating
the desired ester.
132. Methyl 9-0-methylclavulanate whenever prepared by the
process of Claim 131 or an obvious chemical equivalent thereof.
133. A process for the preparation of methyl 9-0-methyl-
clavulanate which comprises adding dry nitromethane contain-
ing crown ether to potassium clavulanate, anhydrous sodium
carbonate and trimethyloxonium tetrafluoroborate and isolating
the desired ester.
56

134. Methyl 9-0-methylclavulanate whenever prepared by the
process of Claim 133 or an obvious chemical equivalent thereof.
135. A process for the preparation of benzyl 9-0-methyl-
clavulanate which comprises reacting trimethyloxonium tetra-
fluoroborate in dry dichloromethane and anhydrous sodium car-
bonate with benzyl clavulanate and isolating the desired ester.
136. Benzyl 9-0-methylclavulanate whenever prepared by the
process of Claim 135 or an obvious chemical equivalent thereof.
137. A process for the preparation of p-methoxybenzyl 9-0-
ethylclavulanate which comprises reacting a solution of p-
methoxybenzyl clavulanate in dichloromethane with anhydrous
sodium carbonate and a solution of triethyloxonium tetra-
fluoroborate in dichloromethane and isolating the desired ester.
138. A process as claimed in Claim 137 wherein the ester is
hydrogenated to obtain 9-0-ethylclavulanic acid which is
then treated with lithium hydroxide or sodium hydroxide to
obtain the lithium and sodium salts, respectively.
139. p-Methoxybenzyl 9-0-ethylclavulanate whenever prepared
by the process of Claim 137 or an obvious chemical equivalent
thereof.
140. Lithium and sodium 9-0-ethylclavulanate whenever pre-
pared by the process of Claim 138 or an obvious chemical
equivalent thereof.
141. A process for the preparation of ethyl 9-0-ethylclavu-
lanate which comprises reacting dehydrated sodium clavulanate
anydrous sodium carbonate and a trace of crown ether in dry,
57

methanol-free methylene chloride with triethyloxonium hexa-
fluorophosphate in dry methylene chloride and isolating the
desired ether.
142. Ethyl 9-0-ethylclavulanate whenever prepared by the
process of Claim 141 or an obvious chemical equivalent thereof.
143. A process for the preparation of 9-0-methylclavulanic
acid which comprises treating lithium o-methylclavulanate
with a cation exchange resin and isolating the desired acid.
144. 9-0-Methylclavulanic acid whenever prepared by the
process of Claim 143 or an obvious chemical equivalent thereof.
145. A process for the preparation of p-nitrobenzyl 9-0-
methylclavulanate which comprises reacting p-nitrobenzyl
clavulanate, trimethyloxonium tetrafluoroborate and anhydrous
sodium carbonate in the presence of methylene chloride and
crown ether and isolating the desired ester.
146. p-Nitrobenzyl 9-0-methylclavulanate whenever prepared
by the process of Claim 145 or an obvious chemical equivalent
thereof.
147. A process as claimed in Claim 123 wherein the ester is
converted into the acid or a pharmaceutically acceptable salt
and when required the thus formed acid or pharmaceutically
acceptable salt is converted into an alternative pharmaceut-
ically acceptable ester or alternative pharmaceutically
acceptable salt.
148. Pharmaceutically acceptable salts and esters of 9-0-
methylclavulanic acid whenever prepared by the process of
Claim 147 or an obvious chemical equivalent thereof.
58

Description

~1997~3
The present invention relates to a process for the
preparation of clavulanic acid ethers.
Belgian Patent No. 847045 (and also Canadian Patent
Application No. 263,105) disclose that ethers of
clavu]anic acid and their salts and esters may be used
to enhance the effectiveness of penicillins and
cephalosporins. The process illustrated for the
preparation of such compounds involved the reaction of
a diazocompound on an ester of clavulanic acid. A generally
more convenient, safer and often higher yieldin~ process has now
discovered.
Accordingly the present inven-tion provides a process for
~i .
the preparation of a compound of the formula (I):
.
H
~ O . f~H20
0'~ --
CO2H
or a salt or ester thereof wherein R is a methyl or ethyl
group which process comprises the reaction of clavulanic
' `
~ 2 -
~,~ .
! a
. ~ . , .
` " ,'`` `~,' " ` ' ~ , :
",

acid or a salt or ester thereof with a compound of the
formula (II):
R30~ X~ (II)
` wherei~ R is a methyl or ethyl group and X~ is an anion
and thereafter if desired performing one or more of the
following reactions:. (a) convertingthe initially
formed ester into an acid or sait and (b) converting the
,~ thus formed acid or salt into an alternative ester or
alternatlve salt.
When the etherification is performed on an ester of
clavulanic acid then usually at least 1 equivalent ~for
example 1 - 5 equivalents) o~ a compound of ~he formula.
is employed per equivalent of ester of clavulanic
acid. When the etheri~ication lS per-formed on:a salt
of clavulanic acid (or on the aoid)~then usually at least
2 equivalents (for example 2 - 5 equi~valents) of a compound
- of the formula (II) is employed per equivalent of clavulanlc
acid salt.
. , .
-
Most suitably ~ is BF4 or its equivalent such as
PF6~ or 2,4,6-trinltrobenzenesulphonate.
3 -
~ '
~,"~,......
,
. .
. ' - ' , ' , , .
.. . .
, ':,' ' ,' " ' ' ' , ~ ' ~

~7f~53
The preceding reaction generally employs a salt or ester of
clavulanic acid which is the compound of the formula (III):
H CH20~
_~0~/
N ~ (III)
When clavulanic acid or its salt is employed etherification and
esterification take place so that methyl 9-O~methyl-clavulanate
or ethyl 9-0-ethylclavulanate are produced. This reaction gener-
ally proceeds via the methyl or ethyl ester intermediate formed
in-situ.
~ost suitably the compound of the formula (II) is either trimethyl-
oxonium tetrafluoroborate or tr:Lethyloxonium tetrafluoroborate.
Thus in one particularly suitable aspect this invention provides
a process for the preparation of a compound of the formula (I) or
a salt or ester thereof which process comprises the reaction of an
; ester Oe clavulanic acid with trimethyloxonium tetrafluoroborate
or ~riethyloxonium tetrafluoroborate and thereafter if desired
forming the free acid or~ salt thereof~from an ester.
:
- 4 -
~ '
.
-. .: - . : '
: . . . ~
.. . ~ .
: ' . ~' ' ' ~:: `
: : . . ' ' ' . ' : . .
':
. .
, '

- ~0~653
The ester of clavulanic acid is preferably one ~7hich is hydroly-
sable or hydrogenolysable to the parent acid or its salt.
Suitable esters of clavulanic acid for use in the process of this
invention include those of the formula (IV) and also those of the
formula (V):
H H
r `1~ ~ C~l~O}I ` U~O}I
O
CO2A C02-CH-A
(IV) (V)
where A is an alkyl group of 1 - 8 carbon atoms optionally sub-
stituted by haogen or a group of the formula OA , OCOA , SA ,
. ~ 10~ 502A4 wherein A4 is a hydrocarbon group of up to 6 carbon
atoms; A ls a hydrogen atom, an alkyl group of up to 4
carbon atoms or a phenyl gro~up optionally substituted by halogen
or by~a~ grou~p A5 or oA5 ~here A5 is an alkyl ~group of~ up to 6 carbon
atoms;~ and A ~is a phenyl group~optlonally substituted~by halogen,
o~r a group A~ or OA where~A is an alkyl group. Othe:r sultable
values~fo~r~A lnclud~e~a:lkenyl or~alkynyl:~groups; of~ up~:to 4 carbon
~ .
: ~ ~ ' :, ', '. : '
:- ~ ' ' ' ' ' ' ' ` ~ : -

76~
Other suitable values for A include nitrophenyl.
Most suitably Al is an alkyl group of up to 4 carbon
atoms, for example the methyl, ethyl, n-propyl or n-butyl
groups or such a group substituted by a group of the
:Eormula oA4 or oCOA4 where A4 is an alkyl group of up
to ~ carbon atoms.
Preferably Al is either a me-thyl group or an ethyl group.
Particularly suitable values for CEIA A3 lnclude benzyl
and mono-substituted benzyl such as bromobenzyl, nitro-
benzyl, methoxybenzyl and the like in which thesubstituent is preferably in the para-position.
Other esters which may be employed include in-vivo
hydrolysable esters such as those described in ~elgian
Patent No. 827926 as~being in-vivo hydrolysable when
attached to clavulanic acid. Such esters include
acetoxymethyl, ~-acetoxyethyl, pivaloyloxymethyl, phthalidyl,
ethoxycarbonyloxymethyl, ~-ethoxycarbonyloxyethyl or the
like.
When the process of this invention employs a salt of
:
clavulanic acid~as starting material the process offers
the advantages of good overall yields of pure products
and an advantageously low number of reaction steps.
.
'
- :. . . . .. . . .
- ~ : ; ... . .. : : -
:: :
', ' . . ~
,. -: . ,, .:
,
. . ,

~q~976~3
Suitable salts of clavulanic acid used in the process of this
invention may be any convenient salt of clavulanic acid such as an
alkali metal or alkaline earth metal salt or a salt of a nitro-
genous base. Thus suitable salts of clavulanic acid for use in
this process include the lithium, sodium~ po~assium, calcium,
magnesium, barium, tetramethylguandinium or the like salt.
The reaction of the~compound of the formula (II) with a salt or
ester of clavulanic acid will take place in an inert dry organic
solvent such as dichloromethane or chloroform, or other haloalkane
or other non-hydroxylic solvent such as nitromethane. Most
suitably the solvent system is strictly non-hydroxylic.
Preferably the etherification takes place in the presence of a
base. Most suitably the base is one which is insoluble in the
reaction medium such as an alkali metal carbonate or bicarbonate
or an alkaline earth metal oxide or hydroxide or the like. Thus
suitable bases include sodium carbonate, sodium bicarbonate,
lithium carbonste, calcium carbonate, magnesium carbonate or the
llke. The base used should be snhydrous. ~
Such insolublÆ bases are preferably presÆnt in excess, for example
~20 from 1 - 5 equivalents of ba~se per equivalent of oxonium salt may
be used~
: ~ ~
~' :
-- 7 --:
~sr
.
. . .
- ', . . ' ' , - : .

6S3
It has been found that the presence of a crown-ether in the reaction
medium can increase the yield of the desired compound from the
clavulanate salt. Thus crown-ethers such as "18 crown 6",
"15 crown 5", "dicyclohexo 18 crown 6", or their equivalents may
be used.
A preferred aspect this invention provides a process for the
preparation of methyl 9-0-methylclavulanate which comprises the
reaction of a salt of clavulanic acid with trimethyloxonium
fluoroborate. ~ further preferred aspect of this invention provides
'a process for the preparat:ion ofethyl 9-0-ethylclavulanate which
comprises the reaction of a salt of clavulanic acid with triethyl-
oxonium tetrafluoroborate.
Once the etherification reaction is substantially complete (for --
example as shown by thin layer chromatorgraphy-identification by
permanganate spray) the desired compound may be obtained from thP
mixture by washing the organic phase with water to remove ionic
materials, drying the organic phase and evaporating the solvent
and thereafter if desired further purlfylng the ester/ether
chromatographically. Suitable chromatographic systems employ
stationary~phases such as silica gel, cellulose or the like and
solvents such~as ester hydrocarbon mixtures such as ethyl acetate/
cyclohexane mixtures.
:
, :
: ~ :
.
~ - 8 -
,
.

71653
Esters of the compounds of the formula (I) may be
converted -to the :~ree acid or its sal-ts by the methods
described in Belgian Patent No. 8470~5. Such methods
include the hydrogJc-!na~i.on of hydrogenolysable esters
such as the ben~.yl or p-methoxybenzyl. or ecluivalent
esters (such as the p-nitroben~yl or p-bromobenzyl
esters) optionally in the presence of a base such as
Li2C03, Na2C03, ~2CO3, NaH C03, KHCO3, or the like and
in the presence of a transition metal catalyst such as
10~ palladium on charcoal. Such methods also include
mild base hydrolysis, for example hydrolysis of the
methyl ester by the controlled addition of LiOH, NaOH
or the like aclded a-t a rate to maintain the pH (as
recorded on a pII meter) of the solution in the region
7.5 - 10 for example malntamed between such ranges as
7.5 - 9, 8 - 10 or preferably 9 - 9.5. This may be
conveniently affected using a plI-stat so that the base
is normally used in an aqueous medium. Bases which may
be employed inc].ude LlOH, NaOH, KOH, Li2C03, NaCO3,
20 ~ ~ICO3, ~K2CO3, Mg(II)2~ Ca(H)2~ or the like-
;
In a particularly Lavourecl aspect thls invention provides
a process adapted to the preparation of a salt of a
compound of~ the formula (I) which process comprises
:
.
~ 9 ~
"~
. . .
.
,

6S3
forming the methyl ester of the mc-thyl ether of
c:Lavulanic acid or the ethyl ester of the ethyl ether
of clavulanic acid as hereinbeEore described and
therea-Eter hydrolyslng the ester group to yield a
salt oI the methyl ether of clavulanic acid or a
salt of the ethyl ethex of clavulanic acid.
Generally the hydrolysis is e-ffected in an aqu~ous
solvent system such as aqueous tetrahydrofuran or
the like using a base such as one of those described
above.
A preferred salt of clavulanic acid for use in the
process of tllis invention is the sodium salt. A
further preferred salt of clavulanic acid for use
in the process of this invention is the potassium
salt. Yet another preferred salt for use in the
process of this invention is the lithium salt.
It appears that the use of a finely divided form
of the salt leads to improved yields. Such finely
divided forms include those prepared by freeze
drying a solution or by dehydratlng a hydrated salt
such as sodium clavulanate tetrahydrate.
~: :
- .
-: .
'~ ' ~' ' ''' '~
.

~7653
The etherification reaction is normally carried out
at a temperature of -80 (or more ~tsually -60) to +60 (or up to
boiling point ol the solvent although temperatures
of not more than +40 are more conventional) and more
usually at from -40 t.o 30C. Often it is convenient
to start -the reaction at a low temperature such as
-30 to 0 and to allow the reaction mixture to
gradually increase in temperature until an ambient
or slightly depressed temperature is reached such
as about 10 to 20C.
The hydrolysis is conveniently effected at roughly
ambient temperature, for example at from about 10
to about 30C, for example at 15 to 25C.
; When the reaction is complete (for example no further
base is taken up without degradation or as judged by
: tlc) the pH of the medium may be adjusted to pH 7 by,
for example, the addition of a small quantity of an
acid such as acetic acid.
,
~ - In order to obtain the desired salt the solvent may
, ~ :
: 20 be~removed for example by evaporation, and the dried
:~ : salt obtained in crystalline form by the addition of
. ;~. ; ~ an;approprlate solvent such as acetone,~acetonltrile,
'` ; '`
' '' ' `~ ' . " ``
' , '- ` . ,
` ' , ~ ~ ~ ,;

7~53
tetrahydrofuran or the like. It can be favourable
if such solvents contain moisture but large proportions
O:e water should be avoided owing to the solubility of
the e~tllers.
A particularly suitable form of this part of the
invention comprises hydrolysis of the ester to yield
the lithium salt as this salt can be produced in
highly pure form in good yield.
If other salts of the methyl or ethyl ether are
required these may conveniently be prepared from the
lithium salt, for example by dissolving the lithium
salt in water, applying thissolution to a polymeric
ca-tion exchange resin in the form of alternative salt
(for example in the sodium, potassium, calcium,
magnesium or like form) and eluting the alternative
salt therefrom.
Suitable cation exchange resins lnclude cross-lined
polystyrene-divinylbenzene co-polymers substituted
- by sulphonic acid moieties; for example Amberlite
2~0 IR-120, IR-118 or IR-122, Dowex 50X8, Zerolit 225,
: . *
;~ BioRad AG 50W-X8, Ionac C250, C255 or C258.
Normally the elution solvent is water or water in
.2 -
* All of whlch are
Trade Marks
,
.
. .
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-, . :-
: .
. . . .
. : ,
.. . , . - .
- - . . :. : : . . .. .

~ 7~3
admixture with an organic solvent such as methanol,
ethanol, acetone or the like. Most suitably the
elution solvent is water. The cation exchange
resin is preferably present in large excess, -for
example at least a 3-fold excess, most suitably at
least an 8-~old excess and preferably at least a 10
fold excess. In the simplest and most convenient form
of the process a solution of the lithium salt is
simply percolated through a bed of resin from which
it emerges in the form of the alternative salt. The
desired salt may then be obtained from solution by
conventional methods such as freeze-drying, evaporation,
precipitation using an organic solvent or the like.
The acids o~ the formula (I~ may be prepared from
the lithium or other salt by acidification, for example
by using an acid such as a miueral acid or a strong
acid cation exchange resin (which acts as a convenient
insoluble acid~.
~ne follo~ Examples~illustrate the invention:
' :
- 13 -
~............................ .

iS3
EXAMPLE 1
Ethyl 9-0-ethylclavulate
To a vigorously stirred suspension o~ potassium clav-
ulanate (l.52g) and anhydrous sodium carbonate (4g) in
dry dichloromethane (70 ml) cooled to -20C, was added
dropwise a solution of triethyloxonium tetrafluoroborate
(4.86g) in dry dichloromethane (40 ml). The reaction was
stirred for 3 hours at circa -20C (very slow reaction) and
then for l hour at circa 5C (ice-bath). At this time
tlc showed a moderately strong ester zone and a strong
ester-ether zone. Water (90 ml) was added, the phases
separated and the organic phase dried over sodium sulphate.
The drying agent was filtered off and the filtrate evaorated
to an orange oil. :
This was subjected to gradient elution chromatography
on silica gel using ethyl acetate and cyclohexane, graded
from l:l ratio to pure ethyl acetate. The ether-ester eluted
before the éster. Fractions con-taining these (by tlc) were
respectively combined and evaporated, to yield 44 mg of crude
ethyl clavulanate and 520 mg of ester-e~ These were
; re-chromatographed separàtely. (The ester was~ ~ ~hromatographed
20~ using the~orlginal solvent system to yield-l5~g pure ester).
The ester-ether was re-chromatographed using ethyl acetate
and cyc1Ohex~ane graded from 3:2 to 2:3 ratio,~to y~ield 375 mg
of~pure ethy~l~9-0-ethylclavulanate as a~pale yellow~oil.
.R.~fmax (fi1m) 1802,~1744 and 1699 cm~l;
~ (CDCl3?: 1.14 (3H,~t,J 7Hz, ether C~I3)~, 1.26 ~3H, t, J
14
. . . ...
: . , ~ .
-. . - .
: . : : , ..
, . . ,, . . .
, . - . , : . :: .
:, :, : . - , . . .
"~ . . :: , , .. : . , : :

~L~Ca76~3
7 Hz, ester CH3), 2.97 (lH, d, J 17Hz, 6-~-CH), 3.46 (lH, dd,
J 17 ancl 3Hz, 6-a-CH), 3.39 (2H, q, J 7Hz, 9-0-C_2), 4.01
(2H, d, J 7Hz, 9-CH2), 4.17 (2H, cl, J 7Hz, C02 CH2), 4.78
(lH, t, J 7Hz, 8-CH), 4.99 (lH, s, 3-CH), 5.63 (lH, d, J 3Hz,
5-CH).
Tetramethylguanidinium clavulanate can replace
potassium clavulanate in this reaction, but without
advantage, in spite of the solubility of the salt in
dichloromethane.
- 15 -
, ~ . ' : , , . . :
.
. , . ~

7~53
EXAMPLE 2
-
Ethyl 9-0-e-thylclavulanate
The process of Example 1 can be improved by the addition
oi a cata]ytic amount (0.17 g in this case) of crown ether
('18 crown 6') to the dichloromethane solution o the reagents
before adding the oxonium salt. In this case 1.1 g (75%)
of substantially pure ethyl O-ethylclavulanate was obtained
after the first column (based on 89% pure potassium salt
starting material).
,
:
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,
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. .
, , ,, ' .' ~ .' ' :
' ' ~ ,,:- ', ', ', ' ' ' " .
-
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7~i~i3
EXA~LE 3
Lithlum 9-0-ethylclavulanate
A solution of ethyl 9-0-ethylclavulanate (1.1 g) in
tetrahydrofuran/water (1:2, 60 ml) was maintained at pH
9.4(p~I-Stat) by the addition of lM Li OH solution until
4.0 ml had been used (about 90 min) at 22C with stirring.
One small drop of acetic acid was added to bring the pH
down to 7.0, and the solution then evaporated to an orange
gum on the rotary evaporator at ambient temperature. The
gum was dissolved in acetone (about 20 ml) and chilled
at 2-3C for 1 hour, when the lithium salt crystallized.
It was filtered off, washed with acetone (20 ml) and with
ether (20 ml) and dried in vacuo, to yield highly pure
lithium 0-ethylclavulanate as a pale yellow crystalline
solid (0.73 g).
(Overall yield from potassium clavulanate via Exa~ple 2 - 55%)
(20 using Cu K ~ radiation = 12.6, 13.3, 14.7, 17.2, 17.8,
18.7, 19.9,20.8, 21.6, 22.8, 24.6, 26.8, 27.4, 28.2 and
28.7).
,
--
- 17 -
:
,

7~53
~XAMPLE 4
-
Sodium 9-0-ethylclavulanate
A part of the product o:f Example 3 (0.25g) in water
(2 ml) was passed through a bed o~` Amerlite IR-120 (Na
form, 8 ml standard grade wet resin). The eluate was
collected and evaporated under reduced pressure at ambient
temperature. The residue was triturated under acetone-
ether, filtered off, washed with ether and dried to
: yield sodium 9~0-~thylclavulanate (0.2 g).
::
-
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- . , .. : .. ... ,, ,: : ,. - - '-.
:,: ~ , , ,- -
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-~,:

~ AIPL~ 5 7~53
_
~-thyl 9-0- e-thylcl~vulara-te
Crystalline hydrated sodium clavulanate was
dehydrated under vacuum over pho~phorus pentoxide to con.~tant
weigllt. A suspension of the dry salt (1.11 g) and anhydrous
sodiunl carbonate (2.65 g) in dry (treated with 3A molecular
sieves), methanol-free methylene chloricle (50 ml) was
treated with a crown e1;her (20 mg ol` 18 crown 6) and stirred
and cooled to -20, protected from atmospheric moisture.
A solution of triethyloxonium tetrafluoroborate (3.8 g)
in dry methylene chloride (50 ml) was added over 20 minutes
and the mixture stirred vigorously at -20 for 3 hours.
~amples were taken at intervals and examined by tlc to
; follow the reaction. The stirred reaction was then kept at
about 5 (ice/water bath) until the quantity o~ the desired
product was at a maximum (as judged by tlc against a
standard sample). Water (50 ml) was then added and the
phases stirred and then separated. The methylene chloride
solution was washed with more water (50 ml), dried over
anhydrous sodium sulphate and the drying agent removed
by ~iltration. The solvent was distilled at reduced pressure
at <20 to give crude title product as a light orange oil
(1.10 g). The crude etherlester was dissolved in a 1:1 mixture
of cyclohexane: ethylacetate (25 ml) and run onto a column
of silica gel (30 g) prepared in the same solvent mixture.
The colunm was eluted wlth 1.1 cyclohexane/ethyl acetate and
the eluent examined by tlc at 10 ml intervals. Those ~ractions
which contained the title compound were combined and the
- 19 -
.

7~53
solven-t distilled at reduced pressure and <20. This gave
ethyl 9-0-ethylclavulanate as a colourless oil (640 mg,
50%). It showed -the same spectrographic characteristlcs as
the product ~rom E.Yample 1. Those ractions which were
shown by t:l.c (.-gainst a standard sample) to contain e-thyl
clavulanate were combined and the solvent removed. The
ester was obtained as a colourless oil 350 mg, (31~o).
' ' -
,, , ; -~,:,
'~ :
'
- 20 -
:. ,.
.
'
'
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~g7~53
EXAM~L~ ~
Ethyl 9-0-ethylclavulanate
Potassium clavulanate (1.19 g), anhydrous sodium
carbonate (2.Gs g) and a trace of 'crown ether' (1 drop
of 15-crown-5) were suspended in nitromethane (50 ml)
and the mixture stirred and cooled to -20 and Pro~ected
from atmospheric moisture. A solution of triethyloxonium
t~tra~]uoroborate (3.8 g) in nitromethane (50 ml)
was added over 20 minutes and the mixture stirred
vigorously at -20 for 3 hours.
The stirred reaction was then kept at about 5
: (ice/water bath) for 5 hours, after which an analysis of
the reaction mixture by tlc showed the presence of a
large zone typical of ethyl 9-0-ethylclavulanate (as
compared with a standard sample).
,
: ~ :
: ~ :
,
`: :
~ - 21 -
- . ~ . ~ : .
-:
-: :
,

7~53
E~ample 7
Ethyl 9-0-_thylclavulanate
Lithium clavulanate (1.03g), anhydrous sodium carbonate
(2.65g) and a trace of crown ether~ (1 drop of 15-crown-5)
wer0 suspended in dry methylene chloride (50ml) and the
mixture stirred and cooled ~o -20 and ~rotected from atmospheric
moisture. A solution of triekhyloxonium tetrafluoroborate
(3.8g) in dry methylene chloride (50 ml) was added over
20 minutes and the mixture stirred vigorously at -20 for
1 hour.
The stirred reaction was then kept at about 5(ice/water bath)
for 5 ho~rs, after which it was treated with water (50 ml) and
the crude ester/ether (250mg) isolated as described in
Example 5. This product was purified on a silica gel column
to give the pure title compound (130mg, 10%)~ and ethyl clavu-
~ lanate (50mg, 5%).
.,
,:
- 22 -
-.
,
: . : - .
. .'.' :' . ' ~- " . ;- .
.
. . : .
- . .: . . . .

~7653
~XAM~LE 8
Ethyl 9-0-ethylclavulanate
MaLrnesium clavulanate (0.60 g), anhydrous sodium
cabonate (1.5 g) and a trace of 'crown ether' (10 mg of
1~-crown-6) were suspended in dry methylene chloride (30 ml)
and the mixture stirred and cooled to -20 and protec-ted
from atmospheric moisture. A solution of triethyloxonium
tetrafluoroborate (2.15 g) in dry methylene chloride ( 30 ml)
was added over 15 minutes and the mixture stirred vigorously
at -20 for 1 hour.
The stirred reaction was then kept at 5 (icetwater
bath) for 2 hours, after which an analysis of the reaction
mixture by tlc showed the presence of a larger zone typical
of ethy] 9-0-ethylclavulanate and only a small zone for
ethyl clavulanate.
,
- 23 -
~,
, -
-
. ' ' ~
. . ., ~ ,:, , ..
' ' ~ ' :
,: . , . - ,

~7~3
EXAMPLE 9
9-0-m~thvl clavulanate
Potassium clavulanate (95,~ pure, 1.52 g) and anhydrous
sodium carbonate (4.0 g) were suspended in dry methylene
chloride (70 ml) in a vessel protected from moisture by
a calcium chloride drying tube. 18-Crown-~ (0.17 g) was
dissolved in the methylene chloride. The suspension was
stirred and cooled to about -20 and a suspension of trimethyl-
oxonium tetrafluoroborate (4.22 g) in dry methylene
chloride (90 ml) added slowly. The reaction mixture was
stirred at -20 for three hours and at about 0 for 1 hour.
Water (90 ml) was then added and the organic phase
separated and dried (w:ith anhydrous sodium sulphate).
The solvent was removed under vacuum and the product
purified by column chromatography on silica gel, eluting
with cyclohexane/ethyl acetate (1:1).
Evaporation of appropriate eluent fract1ons yielded
0.54 g methyl 9-0-methylclavulanate (41%) and a further
0.37 g) methy] clavulanate (29%).
The sample of methyl 9-0-methylclavulanate was
hydrolysed~ln aqueous tetrahydr~uran solution with molar
lithium hydroxide on a pH-stat at pH 9.5.
Crystalline lithium 9-0-methylclavulanate (.43 g)
was isolated by evaporation and addition o-F acetone.
:
.
- 24 -
:
: .......... . : .
: :
: . : . .. : .
' .: .... ' '. , :
' ' ~ ' ,

'76S3
X-ray powder diffractogram - reflections at
following an~rles
2H,(~opper Ka radi~tion) 11.5, 12.9, 14.2, 15.3, 17.9,
19.1, 21.0, 21.3, 22.1, 23.5, 24.1, 24.6, 25.~, 28.6,
29,~.
~` :
- ZS -
,. . , , ~ , .
.. . . . .
,:,
"' , ' . ~ ' ' ' ,, '
. . .

7~i3
EXAMPLE 10
Methyl 9-0-methylclavul~a e
Potassium clavulanate (95% pure, 4.56 g) anhydrous
sodium carbonate (12 g), crown ether (18-crown-6, 0.5 g),
trimethyloxonium tetra:Eluoroborate (12.7 g) were cooled
at -70 and stirred while dried methylene chloride (200 ml)
was added slowly. After addition of solvent the temperature
was allowed to rise slowly to 20 . Aiter three hours
stirring at room temperature tlc examination showed two
zones (rf 0.35 and 0.12) with an area ratio of approximately
10:1.
Water (250 ml) was added to the stirring re`ac-tion
mixture and the organic phase separated, dried (anhydrous - .
sodium sulphate), evaporated, and purified by column
chromatography as in Example 9. The eluent fractions
containing the desired product were evaporated to give 2.6 g
(62%) methyl 9-0-methylclavulanate (pure:by~tlc).
; 1.13 g`of~ the~above product was dissolved in aqueous
tetrahydrofuran and hydroIysed on a pH-stat at pE g.5 to
give potassium 9-0-methylclavulanate.
.
. .
~: :
_ 26 -
'~ .' :
.
-
~., ` " ' ' ' ' ` ' ~ ' ~. ' ' ` , ' ' , .
. . . - . : , .
, : ' -: ,
. .
,

6~3
E~A~LL 11
Methyl 9-0-me~ylclavul(~te
Sodium clavulanate (1.6 g, vacuum dehydrated tetra-
r) hydraC~? - 92% pure), ~nhydrous sodi-lm carbonate (4.~ g) and trimethyl-
oxonium tetrafluoroborate (4.9 g) were cooled to -70
and stirred while dried methyle~ne chloride (100 ml)
containing crown ether (about 50 mg 15-crown-5) was added
gradually. Stirring was continued while the temperature
was allowed to increase to room temperature. Progress of
the reaction was monitored by thin layer chromatography
and after three hours at room temperature the reaction
mixture was worked up as in Example 10. The yield of
methyl 9-0-methylclavulanate was 1.03 g (70%).
~ethyl clavulanate (0.22 g) was also isolated.
~(CDC13)2.99 l(H,d, J=16Hz, 6-~CH), 3.24 (3}I,s,e-ther CH3)
3.44 (lE, dd, J=16Hz and 3 ~z, 6-aCH), 3.72 (3H,
a, ester, C 3) 3.96 (2H, d, J=7Hz, 9-CH20)~, 4.7~9
(lH,t,J=7Hz, 8-CH) 5.00 (lH, bs, 3-CH), 5.63
(}H,d,J=3 Hz,~ 5-CH)
.: .
~: :
`: :
- 27 -
:::
, .. : , . ~ . . .. : .. . : : . . -
- , -
- ., . :' ... : :'. . ..
. - ,, - . . , . - .
: : . : ~
.
.
. . ' :

~37653
EXAMPLE 12
Me~yl 9-0-methylclavulanate
Dry methylene chloride (110 ml) containing crown
e-ther (about 50 mg. 15--crown-5) was added slowly to a
stirred cold (-70) mixture of crystalline lithium
clavulanate (1.0 g), anhydrous sodium carbonate (4.0 g) and
trimethyloxonium tetrafluoroborate (4.4 g). The mixture
was allowed to reach room temperature and then stirred
for a further 4 hours. After work-up and chromatography
as in Example 10 pure methyl 9-0-methylclavulanate was
isolated (0.65 g, 57% yield). NMR identical to Example 11
product.
.
. . .
'' : '
,.
'
~ - 28 -
, . , ~. .

7~i3
EXAMPLE _
Methyl 9~0-methylclavulanate
Dry methylene chloride (80 ml) containing crown
ether (50 mg 18-crown-6) was added slowly to a stirred
cold (-70) mixture of magnesium clavulanate (0.6 g),
magnesium oxide (3.0 g) and trimethyloxonium tetra-
fluoroboræte. The r~action mixture was allowed to reach
room temperature and the progress of the reaction was
followed by tlc. After several hours at room temperature
zones corresponding to methyl clavulanate and methyl
9-0-methylclavulanate could be seen on the developed tlc
plates.
: - 29
- . .
... . . .. . :
: . . . :
-
.
.

S3
EXAMPLE 14
i`k~h~l 9-0-meth~lclavulanate
Dry nitromethane (110 ml) containing cro~vn ether
(about 20 mg 15-crown-5) was added slowly to a cooled,
stirred mixture of potassium clavulanate (1.52 g), anhydrous
sodium carbonate(4.0 g) and trimethyloxonium tetrafluoroborate
(4,5 g). The reaction mixture was allowed to warm to room
temperature and was stirred at this temperature for three
hours. Work-up and purification as in Example 10 gave
methyl 9-0-methylclavulanate (0.72 g, 51% yield) (NMR
ide~tical t7 E~ample 11 product).
:
-
: .
;
. .
~ ~ - 30 -
' ~:

~@~6~ii3
EXAMPLE 15
Benzyl 9-0-Methylclavulanate
Trimethyloxonium tetrafluoro~orate (100 g) in dry
di.chloromethane (2 l) was slurried at -30 whilst
anhydrous sodium carbonate (110 g) was added in one portion.
Benzyl clavulanate (70 g) in dry dichloromethane (11~
was added fairly rapidly keeping the temperature at -30.
The reaction then was carried out and worked up in tha
same way as described in Example 10 to yield benzyl
9-0-methylclavulanate (39.2 g).
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S3
~X~MPLE ~6
_ _
p-Methoxybenzyl 9-0-ethylclavulanate
To a solution of p-methoxybenzyl clavulanate
(9.6 g), ln dicllloromethane ~500 ml) stirred at -30C,
was aclded successlve]y anhydrous sodium carbonate (15 g, excess
and ~ solution o~ tr:iethyloxonium tetrafluoroborate 17.6 g)
in dlchloromethane (100 ml).
The mixture was stirred at abou-t -10C Ior 6 hr,
then allowed to warm to ambient temperature during ~ hr.
Water (100 ml) was added cautiously with stirring, the
organic phase separated, dried over anhydrous sodium
sulphate, and evaporated to a syrup. This was subjected
to column chromatography on silica gel, eluting
initially with 1:1, then with 2:1, ethylacetate-cyclohexane
mixtures. The fir~t eluted product was the ethyl ether
(4.9 g after evaporation of solvents) followed by recovered
p-methoxybenzyl clavulanate (4 g). me-title c~ound was a
pale yellow oil wlth the following properties.
I.r. (liquid film) 1805 (~-lactam C=O) 1750 (ester
C=0) 1700cm l(C=C); nmr (CDC13) 1.17 (3H, t, J 7Hz,
CH3CH~) 2.96 (lH, d, J 17Hz, 6-~-CH) 3.41 (2H, q, J
7Hz, CH3CH~-) 3.~7 (lH, dd, J 17 and 3Hz~ 6-~-CH) 3.79
(3H, s, OCH3) 4.03 (2H, d,~J 7Hz, -C~20) ~4.82 (lH, t,
J 7Hz, CH-) 5.04 (lH, s,~3-CH) 5.11 (2~, s, PhCH2~,
5.65 (lH, d, J 3H3, 5 - CH~ 6.9, 7.3 (4H, A2B2q, J 10~ ,
).
, ' : . . : '

~37~3
Example 17
Lithium and sodium 9-0-ethyl.clavulanate
p-Methoxybenzyl 9-0-ethylclavulanate (2.5 g) in
tetrahydrofuran (25 ml) containing water (0.1 ml) was
hydrogenated over 10% palladised charcoal (0.8 g).
After 2 hr, the absence of starting material was
demonstrated by tlc. The catalyst was removed by
filtration through a bed of finely divided silica,
the filtrate diluted with an equal volume of water to
yield a solution of 9-0-ethylclavulanic acid. This
solution was titrated to pH 7.0 with lM lithium
hydroxide solution. Evaporation of the solvents and
trituration with acetone yielded the lithium salt as
a pale cream crystalline solid (1.05 g).
The sodium salt was prepared in an identical manner
using 1~ NaOH solution; yield 0.85 g .
I.r. (nujol mull) 1785 (~-lactam C=0)
1685 ~C-C) 1615 cm (-C02-). (Both salts).
(The s~ting material for this Example is produced as
des~ i in E~1A 16).
. - 33 _
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:. ' , ~: ' . ,

EXAMPI,E l8
Ethyl 9-0-ethylclavulanate
Dehydrated sodi.um clavulanate (1.1 g), anhydrous
sodlum carbonate (Z..65 g) and a trace of 'crown ether'
(10 mg of 18-crown-6) were suspended in dry, methano:L -
:Eree methylene chloride (50 ml) and the mixture
stirred and cooled to -20~ A solution of tri-
cthyloxonium hexafluorophosphate ( 5.0g ) in dry
methylene chloride (50 ml) was added over 20 ~ninutes
and the mixture stirred vlgorously at -20 for 3 hours.
The stirred reaction mixture was then kept at about
5 for 7 hours, a:Eter which it was treated with
water (50 ml) and the ester/ether ( 250mg) isolated
as described in Example 5. This product was
: 15 purified on a silica ~el column to give the desircd ethyl
9-0-ethylclavulanate.
.
.~
, '
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i53
EXAMPLE 19
9-0-Methylclavulanic acid
A solution of Lithium 0-methyl clavulanate (0.9 g)
in water (40 ml) was covered with a layer of ethyl
acetate (150 ml) and stirred vigorously at room
temperature. Strong acid ion exchange resin (Amberlite
IR 120 (H )) (10 ml wet resin) was added. After 5 mins;
the resin was removed by decantation) and the layers
separated. The aqueous layer was extracted with a
further lO0 ml of ethyl acetate; the solvent layers
were combined, washed with water (5 ml) dried over
anhydrous calcium sulphate and iiltered~ The
solution was evaporated to crystallization under
reduced pressure then the remainder of the solvent
removed in vacuo) to leave the free 0-methylclavulanic
._
acid as a colourless crystalline solid (0.85 g).
' ~ ~
_ 35 -
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~7~53
Exa~pleZ0
P-~itrobenzyl 9-0-meth~lclavulanate
P-Nitrobenzylclavulanate (3.51 g), trimethyloxonium
tetrafluoroborate (3.15 g) and anhydrous sodiu~ carbonate
(4.0 g) were stirred and cooled to -70. To the stirred mixture
was slowly added methylene chloride (150 ml) co~taining --
approximately 100 mg of 18 "crcwn" 6 crown ether.
After the addition the reaction mixture was allcwed to wanm
up to rocm temperature and then stirred for a further three
hours. The product was isolated as descriked in Example 10
to yield p-nitrobenzyl 9-0-methylclavulanate (2.91 g) as a
white crystalline solid.
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