GB1595176A

GB1595176A - Clavulanic acid ethers

Info

Publication number: GB1595176A
Application number: GB50444/76A
Authority: GB
Original assignee: Beecham Group PLC
Current assignee: Beecham Group PLC
Priority date: 1976-12-03
Filing date: 1976-12-03
Publication date: 1981-08-12
Also published as: AU3118977A; JPS5392796A; FR2411194A1; NL7713220A; SE7713710L; BE861325A; AU515916B2; FR2372837B1; FR2372837A1; DE2752701A1; IE46100L; DK540177A; IE46100B1; FR2411194B1; CH637395A5

Abstract

Esters of compounds of the formula I, in which X and R<1> to R<3> have the meanings given in Claim 1, are obtained by reacting an ester of clavulanic acid with a compound of the formula V, in which Y is a readily displaceable radical. The corresponding free carboxylic acids, or their salts, are obtained by cleaving the esters by hydrolysis or hydrogenolysis. The compounds increase the antibacterial effect of penicillins and cephalosporins. They can be used in synergistic drug preparations. <IMAGE>

Description

(54) CLAVULANIC ACID ETHERS (71) We, BEECHAM GROUP LIMITED of Beecham House, Great West Road, Brentford, Middlesex, England, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to new ethers of clavulanic acid, to pharmaceutical compositions containing them and to a process for their preparation.

In Belgian Patent No. 847045 corresponding to British Patent Specification No. 1565209 it was disclosed that ethers of clavulanic acid could be prepared by the reaction of a corresponding ester of clavulanic acid with an etherifying agent such as a diazo compound.

It has now been found that certain classes of ethers can be prepared in good yield by a facile reaction. These new ethers form part of this invention.

Accordingly, the present invention provides the compounds of the formula (I):

and salts and esters thereof wherein X is an oxygen or sulphur atom.

When used herein the term "lower" means that the group contains not mdre than 6 carbon atoms and more suitably not more than 4 carbon atoms.

The preferred value for X is the oxygen atom.

Thus certain favoured compounds of this invention are those of the formula (11):

and salts and esters thereof wherein R is as defined in relation to formula (I).

Suitable values for R include the methyl, ethyl, n-propyl, iso-propyl, n-butyl iso-butyl, sec-butyl and tert-butyl groups; more suitable values for R are the methyl, ethyl and propyl groups; and especially suitable values for R are the methyl and ethyl groups, and a preferred value for R is the methyl group.

The compounds of the formula (I) are suitably in the form of a salt such as the lithium,.

sodium, potassium, calcium magnesium, ammonium or substituted ammonium salt such as the methylamine, dimethylamine, trimethylamine, pyrrolidine, or other such lower alkylamine, di-lower alkylamine, tri-lower alkylamine or heterocyclic amine salts.

Particularly suitable salts include the lithium, sodium, potassium and calcium salts.

Preferred salts include the lithium, sodium and potassium salts.

Suitable esters of the compounds of the formula (II) include those of the formulae (III) and (IV):

wherein X and R are as defined in relation to formula (I) and 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; 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 where 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.

Particularly suitable values for the O-CH2-XR' moieties in the compounds of this invention include those of the following sub-formulae (a) and (b): -O-CH2OCH3 (a) -O-CH2OC2Hs (b) A preferred value for the OCH2-XR' moiety in the compounds of this invention is that of the preceding sub-formula (a). Thus compounds of this invention worthy of mention include 9-0-methoxymethylclavulanic acid; lithium 9-0-methoxymethylclavulanate; sodium 9-0-methoxymethylclavulanate; potassium 9-0-methoxymethylclavulanate; calcium 9-0 methoxymethylclavulanate; magnesium 9-0-methoxymethylclavulanate; and other salts of 9-0-methoxymethylclavulanic acid such as those with ammonia or with pharmaceutically acceptable amines.

It is believed that the organisms most readily treated by the compounds of this invention are Staphylococcus, Proteus, Klebsiella and Escherichia coli. Particularly good blood levels are achieved after oral administration of the compounds.

The present invention also provides pharmaceutical compositions which comprise a compound of the formula (I) as hereinbefore defined or a salt or ester thereof and a pharmaceutically acceptable carrier.

Most suitably the compound of the formula (I) in the composition of this invention will be in the form of a pharmaceutically acceptable salt or in-vivo hydrolysable ester.

Preferably the compound of the formula (I) in the composition of this invention will be a pharmaceutically acceptable salt of a compound of the formula (II).

The composition of this invention may be presented orally or parenterally or in other convenient form. Generally the composition will be adapted for oral administration to humans or for administration by injection to humans. Veterinary compositions may also be prepared.

Normally the composition of this invention will be in unit dosage form containing from about 20 mg to 250 mg, for example about 50 or 100 mg, of the active ingredient.

Such compositions will usually be administered from 2 to 6 times daily, for example 3 or 4 times daily, so that the daily dose is from about 60 mg to 1000 mg, more usually from about 200 mg to about 1000 mg.

Desirably the composition of this invention will also comprise a penicillin or cephalosporin. Most suitably the ratio of compound of this invention to penicillin or cephalosporin is from 1:10 to 10:1, more usually 2:1 to 1:5, for example 1:1 to 1:3 (by weight).

Suitable penicillins and cephalosporins for inclusion in such compositions include those named in Belgian Specification No. 827926.

Particularly suitable penicillins for inclusion in the compositions of this invention include ampicillin, amoxycillin and their pro-drugs such as their in-vivo hydrolysable esters.

Preferred penicillins for inclusion in the compositions of this invention include ampicillin trihydrate and amoxycillin trihydrate, particularly amoxycillin trihydrate. Other preferred penicillins include the pharmaceutically acceptable salts of amoxycillin.

Penicillins suitable for inclusion in orally administrable compositions of this invention include benzylpenicillin, phenoxymethylpenicillin, propicillin, amoxycillin, ampicillin, epicillin, cyclacillin and their salts and in-vivo hydrolysable esters and aldehyde and ketone adducts of those penicillins containing a 6-a-aminoacylamido side chain and their salts.

Suitable penicillin in-vivo hydrolysable esters include the acetoxymethyl, pivaloyloxy methyl, a-ethoxycarbonyloxyethyl and phthalidyl esters of ampicillin or amoxycillin or the 1phenyl, tolyl and indanyl a-esters of carbenicillin and ticarcillin and salts thereof. Suitable aldehyde and ketone adducts of penicillins containing a 6-a-aminoacylamido side chain include the formaldehyde and acetone adducts metampicillin and hetacillin and their salts.

Suitable penicillins for inclusion in injectably or infusably administrable compositions include the acceptable salts of benzylpenicillin, phenoxymethylpenicillin, carbenicillin, propicillin, ampicillin, amoxycillin, epicillin, ticarcillin and cyclacillin.

Cephalosporins suitable for inclusion in orally administrable compositions of this invention include cephalexin, cephradine, cephaloglycine. and their salts and in-vivo hydrolysable esters and aldehyde and ketone adducts of those cephalosporins containing a 7-a-aminoacylamido side chain and their salts. Suitable cephalosporins for inclusion in the injectable or infusable compositions of this invention include the salts of cephaloridine, cephalothin, cefazolin, cephalexin, cephacetrile, cephamandole, cephapirin, cephradine and cephaloglycine.

In a further aspect the present invention provides a process for the preparation of a compound of the formula (I) or a salt or ester thereof which comprises the reaction of an ester of clavulanic acid with a compound of the formula (V): Y -CH2 - XR (V) wherein X, and R' are as defined in relation to formula (I) and Y is a readily displaceable atom or group; and thereafter if desired converting the thus produced ester into the free acid or a salt or other ester thereof.

Suitable values for Y include I, Br, Cl, OSO2CH3, OSO2C6H4CHB or other similar atoms or groups readily displaced by a nucleophile.

Particularly suitable moieties Y include bromine and chlorine atoms.

The etherification reaction will normally be effected in the presence of a base of low nucleophilicity such as 2, 4, 6-collidine, potassium carbonate, sodium bicarbonate or 2,6-lutidine.

The etherification will normally take place at a non-extreme temperature such as -20" to 30"C, for example about 0 to 200C.

The solvent used for the reaction may comprise dichloromethane, chloroform, dimethylformamide or tetrahydrofuran: In another process aspect this invention also 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 of clavulanic acid with a compound of the formula (VI): R5 - O - CH2 -OR (VI) wherein R is as defined in relation to formula (I) and R5 is a tertiary alkyl group of 4 - 6 carbon atoms; and thereafter if desired converting the thus produced ester into the free acid or a salt or other ester thereof.

A particularly suitable group R5 is the t-butyl group.

Most suitably the reaction utilizes an excess of the compound of the formula (VI).

Generally at least 1 molar excess and preferably 2 - 5 molar excess of the compound of the formula (VI) is employed. If the compound of the formula (VI) utilized is a volatile liquid it may be used as a solvent.

The present invention also provides a process for the preparation of the compounds of the formula (I) or a salt thereof which process comprises the de-esterification of a corresponding ester of a compound of the formula (I).

Such de-esterification processes may involve hydrolysis or hydrogenolysis. Thus, for example an ester may be subjected to mild base hydrolysis to yield a salt of the compound of the formula (I) or alternatively a hydrogenolysable ester may be catalytically hydrogenated to yield the free acid or, if a base is present or added later, a salt. More specifically a lower alkyl ester such as a methyl ester may be hydrolysed at pH 7-10 by the slow addition of equivalent of base or a benzyl, methoxybenzyl, nitrobenzyl or like ester may be hydrogenated in the presence of a transition metal catalyst such as palladium on charcoal optionally in the presence of a base such as NaHCO3, Na2CO3, KHCO3, K2CO3, Li2CO3 or the like.

This invention also provides a process for the preparation of esters of the compounds of the formula (I) which process comprises the esterification of the compound of the formula (I) or a salt thereof.

Thus a compound of the formula (I) may be reacted with a diazo compound or a salt of the compound of the formula (I) may be reacted with a reactive halocompound or the like.

The following Examples illustrate the invention: EXAMPLE 1 Benzyl 9-O-methoxymethylclavulanate

Benzyl clavulanate (e 1) (2.89 g, 0.01 mole), chlorodimethyl ether (1.6 ml, 1.7 g) and 2, 4, 6-collidine (1.3 ml) were dissolved in dichloromethane (20 ml) at 5"C with stirring. After 1 hr at 10 tIc showed that the benzyl clavulanate had disappeared almost completely. Water (50 ml) was added and the mixture shaken and separated (aqueous solution was strongly acidic) 3% aqueous sodium bicarbonate solution (50 ml) was added to the dichloromethane layer. The organic phase was separated, dried (Na2SO4), filtered, treated with silica (5 g), filtered, evaporated to low volume and subjected to column chromatography on silica gel using ethyl acetate and cyclohexane as eluents. The product was isolated as a pale yellow oil (1 g). Vmax (film) 1803, 1753, 1700 cm-l (C=C); 6(CDCl3) 3.01 (1H, bd, J 17 Hz 6-B-CH) 3.33 (3H, s, OCH3) 3.50 (1H, dd, J 3 and 17 Hz, 6-a-CH) 4.14 (2H, bd, J 7Hz, CHCH2O) 4.57 (3H, s, CH3O) 4.86 (1H, bdt, J 7 and 1.5 Hz, CH=) 5.10 (lH, d, J 1.5) Hz) 5.69 (IH, bd, J 3 Hz, 5-CH) 7.36 5(5H, s, C6H5) EXAMPLE 2 Lithium 9-O-methoxymethylclavulanate

Benzyl O-methoxymethylclavulanate (e2) (0.7 g) in tetrahydrofuran (7 ml) containing ,water (0.5 ml) was hydrogenated over 10% palladised charcoal (0.2 g) for 1 hr. to yield a solution of (e3). The catalyst was removed by filtration, and the filtrate added to water (10 ml), neutralised with 1 M lithium hydroxide solution to pH 7.0, and evaporated to dryness, to give colourless crystals, which were triturated with acetone, filtered, washed with ether and air-dried, to yield 0.45 g of the title compound (e4).

vmax (Nujol mull) 1785, 1705, 1617 cm-l; aD2O) 2.98 (1H, d, J 17Hz, 6(3-CH), 3.43 (1H, dd, J 17 and 3Hz, 6a-CH), 4.07 (2H, d, J 8Hz, 9-CH2), 4.5 (under HOD, OCH2O), 4.79 (1H, t, J 8Hz, 8-CH=), 4.83 (1H, s, 3-CH), 5.61 (1H, d, J 3Hz, 5-CH).

Nujol is a registered trade mark.

EXAMPLE 3 Benzyl 9-O-ethoxymethylclavulanate

A mixture of benzyl clavulanate (el) (5.78 g), 2,4,6-collidine (5.8 ml) and chloromethyl ethyl ether (3.7 ml) in dichloromethane (100 ml) was stirred at room temperature for 2 h.

The reaction mixture was then washed with aqueous hydrochloric acid (2M, 100 ml), dried over anhydrous sodium carbonate - magnesium sulphate, and evaporated to dryness to give an oil which was chromatographed over silica gel (50 g). Elution of the column with cyclohexane-ethyl acetate gave the title compound (e5) (6.15 g) as an oil, [a]2" + 45.2 (c.

1.0; CHCl3), Vmax (CHCl3) 1810, 1755, 1705, 1310, 1190, and 1030 cm (CDC13) 7.28 (5Hs, ArH), 5.61 (1H, d, J = 2.5 Hz, 5-CH), 5.13 (2H, s, -CH2Ar), 5.03 (1H, broad s 3-CH), 4.78 (1H, broad t, J = 8Hz, 8-CH), 4.56 (2H, s , -OCH2O-), 4.09 (2H, broad d, J = 8Hz, 9-CH2), 3.52 (2H, g, J = 7.5 Hz. - OCH2CH3), 3.41 (1H, dd, J = 17Hz, J = 2.5Hz.

6a-CH), 2.99 (1H, d, J = 17Hz, 6 -CH), and 1.18 (3H, t, J = 7.5Hz, OCH2CH3) (Found: C, 62.2; H, 6.15; N, 3.8%.

C,8H2lNO6 requires C, 62.25; H, 6.1; N, 4.05%).

EXAMPLE 4 Lithium 9-O-ethoxymethylclavulanate

A solution of benzyl 9-O-ethoxymethylclavulanate (e5) (5.95 g) in tetrahydrofuran (80ml) and water (2 drops) was hydrogenated at room temperature and pressure in the presence of 10% palladium-charcoal (3.35%) for 0.5h. The mixture was then filtered, the filtrate diluted with water (250ml) and neutralised to pH 7.2 with aqueous lithium hydroxide (1M). The mixture was then evaporated to dryness and the residue, after trituration with ether, afforded the title compound (e6) (4.4 g), [a]D + 34.8 (c,1.0; H2O), Vrnax (KBr) 1780, 1700, 1620, 1320 and 1030 cm-', (CD2O) 5.70 (1H, d, J = 2.5 Hz, 5-CH, 4.90 (1H,s , 3-CH), 4.88 (1H, broad t, J = 8 Hz, 8 - CH), 4.68 (2H, s, -OCH2O-), 4.17 (2H, d, J = 8Hz, 9-CH2), 3.58 (2H, q, J = 8Hz, -OCH2CH3), 3.52 (1H, dd, J = -17 Hz, J':= 2.5Hz, 6a-CH), 3.04 (1H, d, J=17Hz, 6p-CH), and 1.13 (3H, t, J-= 8Hz,-OCH2CH3).

EXAMPLE 5 Benzyl 9- O-methylthiomethylclavulanate

A solution of benzyl clavulanate (el) (2.89 g, 0.1 mole) and 2, 4, 6-collidine (2 ml, 0.015 mole) in dimethoxyethane (10 ml) was added to a mixture of sodium iodide (1.5 g) and chloromethyl methyl sulphide (0.97 g, 0.01 mole) in 1,2-dimethoxyethane (20 ml) at 0 C under Argon. The mixture was stirred at 50 C for 3 h. and then at room temperature for 66 h. This was then poured into ice-water (40 ml) and extracted with ethyl acetate (3 x 40 ml).

The organic extract was washed with dilute hydrochloric acid (SM, 100 ml), brine (100 ml), dried and evaporated to give an oil which was chromatographed over silica gel (30 g).

Elution of the column with cyclohexane-ethyl acetate afforded benzyl 9-0methylthiomethylclavulanate (e8) (0.4 g) as a colourless oil, [a]2" + 38.3 (c, 2.0; CHCl), Vmax (liquid film) 1805, 1750, 1695, 1300, 1180, and 1035 cm , (CDCl3) 7. 28 (5H, s, ArH), 5.61 (1H, d, J = 2.5Hz, 5-CH), 5.12 (2H, s, -CH2Ar), 5.03 (1H, s, 3-CH), 4.75 (1H, broad t, J = 8Hz, 8-CH, 4.49 (2H, s, -OCH2SMe), 4.10 (2H, d, J = 9-CH2), 3.42 (1H, dd, J = 17Hz, J' = 2.5Hz, 6a-CH), 2.99 (1H, d, J = 17Hz, 6 -CH), and 2.09 (3H, s, -SCH3), mle (relative intensity) 301.0968 (25, M+fflMeSH), 288.0849 (10, M±C2H5S), 272.0903 (5,M±C2HsOS), 230 (30, M±C2H5OS-C2H5OS-C2H2O), and 91 (100).

EXAMPLE 6 Lithium 9-O-methylthiomethylclavulanate

A mixture of benzyl 9-O-methylthiomethylclavulanate (0.35 g), tetrahydrofuran (15 ml), and water (15 ml) was titrated to constant pH at pH 10 with lithium hydroxide solution (1M) in a pH-stat at 240C. The addition of lithium hydroxide was stopped after 2 h. The solution was then concentrated in vacuo to 10 ml and then diluted with water (10 ml). This aqueous mixture was extracted with ethyl acetate (2 x 20 ml) and then evaporated to dryness. The residue was purified by column chromatography over cellulose (10 g). Elution of the column with butanol-water-ethanol (5:5:1, top phase) gave lithium 9-0methylthiomethylclavulanate (e9) (0.04 g), vrnax (Nujol) 1780, 1695, 1620, 1300, and 1020 cam~1, a (D2O) 5.80 (1H, d, J = 2.5Hz, 5-CH), 5.05 (1H, s, 3-CH), 4.97 (1H, broad t, J = 8Hz, 8-CH), 4.73 (2H, s, -OCH2SMe), 4.27 (2H, d, J = 8Hz, 9-CH2), 3.63 (1H, dd, J = 18Hz, J' = 2.5Hz, 6a-CH), 3.14 (1H, d, J = 18Hz, 60-CH), and 2.19 (3H, s, -SCH3).

EXAMPLE 7 Sodium 9-O-methoxymethylclavulanate

p-Methoxybenzyl O-methoxymethylclavulanate (e7) (6.0 g) was dissolved in ethanol (60 ml) in a pressure bottle. Sodium bicarbonate (1.39 g) in water (8 ml) was added. The bottle was purged with nitrogen and 10% palladium on charcoal catalyst (0.75 g, Johnston-Mathey Type 76/L) was added. The mixture was then hydrogenated at 25 psi for one hour. Thin layer chromatography (E. Merck silica gel, ethyl acetate/chloroform 50/50) (E. Merck is a registered trade mark) showed the hydrogenolysis to be complete and the mixture was filtered through Celite (Celite is a registered trade mark), and the Celite was washed with water (10 ml). The filtrate was evaporated, using a rotary evaporator, to a gum. The gum was dissolved in acetone (10 ml) and to this solution was added, with vigorous shaking, dry diethyl ether (900 ml). This gave a fine white precipitate. The suspension was chilled at 4"C for two hours and then filtered. The solid was washed with ether (2 x 100 ml) and immediately dried in a low vacuum desiccator to yield the title compound (e21) as a hydroscopic pale yellow powder (2.1 g).

m/e 649 (M+), 621, 607, 594, 549, 403,331, 289, 288, 271, 259, 200 and 169 (Found: C, 55.1; H, 5.4; N, 1.95%, C30H35NO15 requires C, 55.45; H, 5.45; N, 2.15%), followed by a mixture (7.8 g) of the title compound (e22) and a small amount of starting material.

EXAMPLE: 8 Compositions: The following may be prepared in conventional mainer utilizing dry ingredients uiider a dry atmosphere: a. Tablets of the following composition may be prepared: Sodium 9-O-methoxymethylclavulanate 150 mg Anhydrous ampicillin 300 mg Microcrystalline cellulose 600 mg Magnesium stearate 15 mg b. - Capsules of the following compositions may be prepared: Sodium 9-O-methoxymethylclavulanate 250 mg Magnesium stearate 2.5 mg Sodium starch glycollate 5.0 mg c. The following may be sealed into ampoules for reconstitution in sterile water for immediate injection: Sodium 9-O-methoxymethylclavulanate 50 mg Sodium ampicillin 250 mg EXAMPLE 9 Pharmacology: Using conventional methods the following results were obtained: a. Compound of Example 7 MIC (g/ml) of Ampicillin Conch Inhibitor Staph. Prot. Kleb E. coli (Rg/ml) Russell C 889 E 70 JT 39 20 - 1.0 - 5 - 2.0 1.6 4 1 0.3 - 1.6 125 0 125 > 2000 1000 > 2000 b. Compound of Example 4 MIC ( > g/ml) of Ampicillin Conch Inhibitor Staph. Kleb - Proteus E. coli E. coli (Rg/ml) Russell E 70 C 889 JT 39 JT 410 20 - - - - 5 0.04 3.12 1.0 2.0 125 1 0.6 3.12 15.6 4.0 0 250 500 > 2000 1000 250 e. Blood Levels obtained with Sodium Methoxymethyl clavulanate The following blood levels were found after subcutaneous administration to mice at a dose of 10 mg/kg; the result for sodium clavulanate is included for comparison: Time (mins) 20 30 45 60 pg/ml sodium ether 3.1 3.4 1.3 0.8 ,ug/ml sodium clavulanate 4.2 2.2 0.8 0.5 The following blood levels were found after oral administration to mice at a dose of 20 mg/kg; the result for sodium clavulanate is included for comparison: Time (mins) 15 30 45 60 ,ug/ml sodium ether 10.8 7.4 2.1. 1.4 Fg/ml sodium clavulanate 3.5 2.6 1.5 0.6 f. Curative effect of Sodium 9-O-Methoxymethylclavulanate and Amoxycillin The following Cud,, values were obtained in intraperitoneal Escherichia coli JT 39 infections. The test materials were administered either by sub-cutaneous administration 1 and 5 hours post infection or by oral administration 1, 3 and 5 hours post infection: Test Material CDs(, (mg/kg) of Amoxycillin (Sub-cutaneous Dosing) 2.5 mg/kg Sodium 9-O-Methoxymethyl- 6.8 clavulanate + Amoxycillin 2.5 mg/kg Sodium Clavulanate 14 + Amoxycillin 1 mg/kg Sodium 9-O-Methoxymethyl- 23.4 clavulanate + Amoxycillin 1 mg!kg Sodium Clavulanate 40 + Amoxycillin Test Material CDso (mg/kg x 3) of Amoxycillin (Oral Dosing) 20 mg/kg Sodium 9-O-Methoxymethyl- 11 clavulanate + Amoxycillin 20 mg/kg Sodium Clavulanate 9 + Amoxycillin EXAMPLE 10 9-O-methoxymethylclavulanic acid

To a solution of lithium 9-O-methoxymethylclavulante (0.43g) in water (25ml), covered with ethyl acetate (50ml) and stirred, was added Amberlite IR 120 (H+form) strong acid ion exchange resin until the pH of the aqueous layer was < 2.0 (about 20ml wet resin). The mixture was filtered, and the filtrate separated. The aqueous layer was extracted with 3 x 30ml portions of ethyl acetate. The ethyl acetate extracts were combined, dried quickly over molecular sieve (3A,30g), filtered and evaporated to an oil in a rotary evaporator under reduced pressure, to yield 0.3g of the title material.I.r.(film): v max 2500 - 3600 (very broad), 1805, 1750, 1695cm'.

n.m.r.(CDCl3), 5 : 3.00(1H,d,J 17Hz, 6- -CH), 3.33(3H,s,OCH3), 3.45 (1H,dd,J 2.5 and 17Hz, 6-a-CH), 4.13 (2H,d,J 7Hz,9-CH2), 4.58 (2H,s,OCH20), 4.88 (lH,t,J 7Hz,8-CH), 5.01 (1H,s,3-CH), 5.63 (lH,d,J 2.5Hz,5-CH).

Amberlite is a registered Trade Mark.

WHAT WE CLAIM IS: 1. A compound of the formula (I):

or a salt or ester thereof wherein X is an oxygen or sulphur atom and R' is a lower alkyl group.

2. A compound as claimed in claim 1 wherein X is an oxygen atom.

3. A compound as claimed in either of claims 1 or 2 wherein R is a methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl or tert-butyl group.

4. A compound as claimed in either of claims 1 or 2 wherein R1 is a methyl, ethyl, n-propyl or iso-propyl group.

5. A compound as claimed in either .er of claims 1 or 2 wherein R' is a methyl group.

6. A compound as claimed in either of claims 1 or 2 wherein Rl is an ethyl group.

7. A compound as claimed in claim 1 wherein OCH2XR' is OCH2OCH3.

8. A compound as claimed in claim 1 wherein OCH2XR is OCH20C2H5 9. A compound as claimed in any of claims 1 - 8 in the form of the acid.

10. A compound as claimed in any of claims 1 - 8 in the form of a salt.

11. A compound in any of claims 1 - 8 in the form of a lithium, sodium, potassium, calcium, magnesium, ammonium or substituted ammonium salt.

12. A compound as claimed in any of claims 1 - 8 in the form of a lithium salt.

13. A compound as claimed in any of claims 1 - 8 in the form of a sodium salt.

14. A compound as claimed in any of claims 1 - 8 in the form of a potassium salt.

15. A compound as claimed in any of claims 1 - 8 which is an ester wherein the ester moiety is of the sub-formula (c) or (d): CO2A' (c) CO2CHA2A3 (d)

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. EXAMPLE 10 9-O-methoxymethylclavulanic acid To a solution of lithium 9-O-methoxymethylclavulante (0.43g) in water (25ml), covered with ethyl acetate (50ml) and stirred, was added Amberlite IR 120 (H+form) strong acid ion exchange resin until the pH of the aqueous layer was < 2.0 (about 20ml wet resin). The mixture was filtered, and the filtrate separated. The aqueous layer was extracted with 3 x 30ml portions of ethyl acetate. The ethyl acetate extracts were combined, dried quickly over molecular sieve (3A,30g), filtered and evaporated to an oil in a rotary evaporator under reduced pressure, to yield 0.3g of the title material.I.r.(film): v max 2500 - 3600 (very broad), 1805, 1750, 1695cm'. n.m.r.(CDCl3), 5 : 3.00(1H,d,J 17Hz, 6-ss-CH), 3.33(3H,s,OCH3), 3.45 (1H,dd,J 2.5 and 17Hz, 6-a-CH), 4.13 (2H,d,J 7Hz,9-CH2), 4.58 (2H,s,OCH20), 4.88 (lH,t,J 7Hz,8-CH), 5.01 (1H,s,3-CH), 5.63 (lH,d,J 2.5Hz,5-CH). Amberlite is a registered Trade Mark. WHAT WE CLAIM IS:

1. A compound of the formula (I):

2. A compound as claimed in claim 1 wherein X is an oxygen atom.

7. A compound as claimed in claim 1 wherein OCH2XR' is OCH2OCH3.

8. A compound as claimed in claim 1 wherein OCH2XR is OCH20C2H5

9. A compound as claimed in any of claims 1 - 8 in the form of the acid.

10. A compound as claimed in any of claims 1 - 8 in the form of a salt.

12. A compound as claimed in any of claims 1 - 8 in the form of a lithium salt.

13. A compound as claimed in any of claims 1 - 8 in the form of a sodium salt.

wherein A' is an alkyl group of 1-8 carbon zooms 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; 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 As or OA5 where A5 is an alkyl group of up to 6 carbon atoms; and A3 is a phenyl group optionally substituted by halogen or by As or OA5 where A5 is an alkyl group.

16. A compound as claimed in any of claims 1 - 8 which is a hydrolysable ester.

17. -A compound as claimed in any of claims 1 - 8 which is a hydrogenolysable ester.

18. A compound as claimed in claim 16 wherein the ester is the methyl ester.

19. A compound as claimed in claim 17 wherein the ester is the benzyl ester.

20. A compound as claimed in claim 17 wherein the ester is a methoxybenzyl ester.

21. A compound as claimed in claim 17 wherein the ester is a nitrobenzyl ester.

22. A pharmaceutical composition which comprises a compound as claimed in ariy of claims 1 - 21 and a pharmaceutically acceptable carrier.

23. A composition as claimed in claim 22 which comprises a pharmaceutically acceptable salt of a compound as claimed in any of claims 1 - 8.

24. A composition as claimed in claim 23 wherein the salt is as claimed in claim 14.

25. A composition as claimed in claim 23 wherein the salt is as claimed in claim - 13.

26. A composition as claimed in any of claims 22 - 25 in unit dosage form which contains from 20 to 250 mg of a compound as claimed in any of claims 1 - 21.

27. A composition as claimed in any of claims 22 - 26 which also comprises a penicillin.

28. A composition as claimed in any of claims 22 - 26 which also comprises a cephalosporin.

29. A composition as claimed in claims 27 or 28 wherein the weight ratio of a compound as claimed in any of claims 1 - 21 to a penicillin or a cephalosporin is 1:10 to 10:1.

30. A composition as claimed in claim 29 wherein the ratio is 2:1 to 1:5.

31. A composition as claimed in claim 29 wherein the ratio is 1:1 to 1:3.

32. A composition as claimed in any of claims 27 or 29 - 31 wherein the penicillin is ampicillin, amoxycillin or a pro-drug therefor.

33. A composition as claimed in any of claims 27 or 29 - 31 wherein the penicillin is ampicillin trihydrate.

34. A composition as claimed in any of claims 27 or 29 - 31 wherein the penicillin is amoxycillin trihydrate.

35. A process for the preparation of a compound of the formula (I) as defined in claim 1 or a salt or ester thereof which process comprises the reaction of an ester of clavulanic acid with a compound of the formula (V): Y-CH2-X-R' (V) wherein X and Rt are as defined in claim 1 and Y is a readily dispaceable atom or group; and thereafter, if desired, converting the thus produced ester into the free acid or a salt or other ester thereof.

36. A process as claimed in claim 35 wherein Y is I, Br, Cl, OSO2CH3 or OSO2C6H4CH3.

37. A process as claimed in claim 35 wherein Y is Br or Cl.

38. A process as claimed in any of claims 35 - 37 wherein the etherification step is carried out in the presence of a base of low nucleophilicity.

39. A process as claimed in any of claims 35 - 38 wherein the etherificaton step is carried out at -200C to 30"C.

40. A process as claimed in any of claims 35 - 39 adapted to the preparation of an ester.

41. A process for the preparation of a compound of the formula (I) as defined in claim 1 or a salt or ester thereof which process comprises the reaction of an ester of clavulanic acid with a compound of the formula (VI): R5-O-CH2-ORl (VI) wherein Rl is as defined in claim 1 and R5 is a tertiary alkyl group of 4 - 6 carbon atoms; and thereafter, if desired, converting the thus formed ester into the free acid or a salt or other ester thereof.

42. A process as claimed in claim 41 wherein R5 is a tert-butyl group.

43. A process for the preparation of a compound of the formula (I) as defined in claim 1 or a salt thereof which process comprises the de-esterification of a corresponding ester of a compound of the formula (I).

44. A process as claimed in claim 43 for the preparation of a salt of the compound of the formula (I) which process comprises the mild base hydrolysis of an ester of the compound of the formula (I).

45. A process as claimed in claim 44 wherein the ester is the methyl ester.

46. A process as claimed in claim 43 wherein the de-esterification is effected by hydrogenolysis.

47. A process as claimed in claim 46 wherein the hydrogenolysis is of a benzyl ester.

48. A process as claimed in claim 46 wherein the hydrogenolysis is of a methoxybenzyl ester.

49. A process as claimed in claim 46 wherein the hydrogenolysis is of a nitrobenzyl ester.

50. Benzyl 9-O-methoxymethylclavulanate.

51. Lithium 9-O-methoxymethylclavulanate.

52. Benzyl 9-O-ethoxymethylclavulanate.

53. Lithium 9-0-ethoxymethylclavulanate.

54. Benzyl 9-0-methylthiomethylclavulanate.

55. Lithium 9-O-methylthiomethylclavulanate.

56. 9-O-Methoxymethylclavulanic acid.

57. Sodium 9-O-methoxymethylclavulanate.

58. Potassium 9-O-methoxymethylclavulanate.

59. Calcium 9-O-methoxymethylclavulanate.