GB1587612A - Isoclavulanic acid derivatives - Google Patents

Description

(54) ISOCLAVULANIC ACID DERIVATIVES (71) We, BEECHAM GROUP LIMITED, a British Company, of Beecham House, Great West Road, Brentford, Middlesex, 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 p-lactam containing compounds, to their preparation and to compositions containing them.

Belgium Patent No. 827926 discloses inter alia clavulanic acid and its salts and esters which substance clavulanic acid has the formula (I):

Clavulanic acid and its salts and esters are able to inhibit p-lactamases from a range of bacteria and owing to this useful property are able to enhance the effectiveness of penicillins and cephalosporins against many gram-positive and gram-negative bacteria. It has now been discovered that certain derivatives of clavulanic acid also possess useful anti-bacterial and p-lactamase inhibitory activity.

Accordingly, the present invention provides an ether of the formula (II):

wherein R is a hydrogen atom or R is an alkyl group of 1--4 carbon atoms or a phenyl group or one of the aforementioned groups substituted by a carboxylic acid group or a salt or C14 alkyl ester thereof or an amino group or an acid addition salt thereof or R is a carboxylic acid group or a salt or C14 alkyl ester thereof, or a salt or ester thereof formed at the 3-position carboxyl group.

Suitably R is a hydrogen atom.

Suitably R is an alkyl group of 14 carbon atoms or a phenyl group or one of the aforementioned groups substituted by a carboxylic acid group or a salt or C alkyl ester thereof or an amino group or an acid addition salt thereof or R is a carboxylic acid group or a salt or C14 alkyl ester thereof.

A favoured value for R is the hydrogen atom.

A further favoured value for R is the methyl group.

Suitably the compound of the formula (II) is in the form of an acid or a pharmaceutically acceptable salt such as the sodium, potassium, calcium, magnesium, substituted ammonium or lithium salt.

Particularly suitable compounds of this invention include the sodium and potassium salts formed at the 3-position carboxyl group of the compounds of formula (II).

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

wherein R is as defined in relation to formula (II) 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 As 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 OAG where A6 is an alkyl group.

Benzyl esters formed at the 3-position carboxyl group of the compounds of the formula (II) are particularly useful hydrogenolysable esters. p-Methoxybenzyl and p-nitrobenzyl esters are also useful for this purpose.

The present invention also provides pharmaceutical compositions which comprise a compound of this invention and a pharmaceutically acceptable carrier.

The compositions of the invention include those in a form adapted for oral, topical or parenteral use and may be used for the treatment of infection in mammals including humans.

Suitable forms of the compositions of this invention include tablets, capsules, creams, syrups, suspensions, solutions, reconstitutable powders and sterile forms suitable for injection or infusion. Such compositions may contain conventional pharmaceutically acceptable materials such as diluents, binders, colours, flavours, preservatives and disintegrants in accordance with conventional pharmaceutical practice in the manner well understood by those skilled in the art of formulating antibiotics.

Injectable or infusable compositions of salts formed at the 3-position carboxyl group of a compound of the formula (II) are particularly suitable as high tissue levels of a compound of the formula (II) can occur after administration by injection or infusion. Thus, one preferred composition of this invention comprises a salt formed at the 3-position carboxyl group of a compound of the formula (II) in sterile form.

Unit dose compositions comprising a compound of the formula (II) or a salt or ester thereof adapted for oral administration form a further preferred composition of this invention.

Under certain conditions, the effectiveness of oral compositions of a compound of the formula (II) and its salts and esters can be improved if such compositions contain a buffering agent or an enteric coating agent such that the compounds of the invention do not have prolonged contact with highly acidic gastric juice. Such buffered or enterically coated compositions may be prepared in accordance with conventional pharmaceutical practice.

The compound of the formula (II) or its salt or ester may be present in the composition as sole therapeutic agent or it may be present together with other therapeutic agents such as a penicillin or cephalosporin. Suitable penicillins or cephalosporins for inclusion in such synergistic compositions include not only those known to be highly susceptible to p-lactamases but also those which have a good degree of intrinsic resistance to p-lactamases. Thus, suitable antibiotics for inclusion in the compositions of this invention include benzyl penicillin, phenoxymethylpenicillin, carbenicillin, propicillin, ampicillin, amoxycillin, epicillin, ticarcillin, cyclacillin, cephaloridine, cephalothin, cefazolin, cephalexin, cephacetrile, cephamandole, cephapirin, cephradine, cephaloglycine, and other well known penicillins and cephalosporins such as hetacillin, metampicillin, the acetoxymethyl, pivaloyloxymethyl or phthalidyl esters of benzylpenicillin or ampicillin or the phenyl, tolyl or indanyl esters of carbenicillin or ticarcillin.

Naturally if the penicillin or cephalosporin present in the composition is not suitable for oral administration then the composition will be adapted for parenteral administration.

When present in a pharmaceutical composition together with a p-lactam antibiotic, the weight ratio of a compound of the formula (II) or its salt or ester present to other p-lactam antibiotic present may be from, over a wide range of ratios, for example 10:1 to 1:10, and advantageously may be from 5:1 to 1:2, for example, 3:1, 2:1, 1:2 or 1:3.

The total quantity of antibacterial agents present in any unit dosage form will normally be between 50 and 1500 mg and will usually be between 100 and 1000 mg.

Compositions of this invention may be used for the treatment of infections of inter alia, the respiratory tract, the urinary tract and soft tissues in humans.

Compositions of this invention may also be used to treat infections of domestic animals such as mastitis in cattle.

Particularly favoured compositions of this invention will contain from 150--1000 mg of amoxycillin, ampicillin or a salt thereof and from 50--500 mg of a salt formed at the 3-position carboxyl group of a compound of the formula (II) and more suitably from 200-500 mg of amoxycillin, ampicillin or a salt thereof and from 50-250 mg of a salt formed at the 3-position carboxyl group of a compound of the formula (II).

A preferred method of preparing esters formed at the 3-position carboxyl group of the compound of the formula (II) comprises the reaction of the corresponding ester of isoclavulanic acid with a compound of the formula (V):~ N2-CH-R (V) wherein R is as defined in relation to formula (II) in the presence of a Lewis acid.

The preferred Lewis acid catalyst is boron trifluoride or its equivalent such as a boron trifluoride etherate, for example, BF3.O(C2Hs)2.

The preceding reaction normally takes place in a solvent inert under the reaction conditions such as chloroform, dichloromethane, tetrahydrofuran or dioxane.

Most suitably the reaction takes place at a depressed or non-elevated temperature, for example -809 to +300C, and preferably at a depressed temperature, for example -30" to +100C. We have found a convenient suitable temperature for carrying out the reaction to be about 0 C.

Esters formed at the 3-position carboxyl group of the compound of the formula (II) may also be prepared by the reaction of the corresponding ester of isoclavulanic acid with a compound of the formula (VII): X-CH2-R (VII) wherein X is I, Br, or Cl and R is as defined in relation to formula (II), in the presence of a source of silver ions.

The preferred source of silver ions is silver oxide. Generally, about 1--2 equivalents are employed based on the isoclavulanic acid ester.

This reaction is normally carried out in an inert medium at a non-extreme temperature.

Suitable solvents include hydrocarbon solvents such as benzene and toluene, and other conventional solvents such as ethyl acetate, tetrahydrofuran and acetone.

The reaction is best effected at a temperature of from about 10 to about l00 C, for example, 30"--80"C.

Esters formed at the 3-position carboxyl group of the compound of the formula (II) may be prepared by the reaction of a salt of isoclavulanic acid with a compound of the formula (VIII): (RCH2)2Oeny (VIII) wherein R is as defined in relation to formula (II) and Y is BF4, PF5.

Preferably yo is Be48.

Generally, at least 2 equivalents, for example, 2-5 equivalents, of the compound of the formula (VIII) is used, based on the salt of isoclavulanic acid.

The reaction will take place in an inert, dry organic solvent, such as dichloromethane, chloroform, carbon tetrachloride, or other haloalkane or non-hydroxylic solvent.

The reaction is normally carried out at a temperature of from 600 to +40"C, for example, at from -400 to + 100C. It is often convenient to start the reaction at a low temperature and allow the reaction mixture to increase in temperature during the course of the reaction until ambient or slightly depressed temperature is reached.

Preferably, the reaction takes place in the presence of a base. Suitable bases include carbonates and bicarbonates such as sodium carbonate, sodium bicarbonate, potassium carbonate, lithium carbonate, calcium carbonate and magnesium carbonate. The base should be anhydrous and preferably insoluble in the solvent used for the reaction, and in such circumstances, may be present in excess.

Compounds of the formula (II) in the form of a salt may be prepared from esters of formula (II) by very mild basic hydrolysis, for example by hydrolysis in an aqueous solution maintained at pH7 to 9 by the addition of base.

Acids and salts formed at the 3-position carboxyl group of the compounds of the formula (II) may be prepared from corresponding hydrogenolysable esters of compounds of formula (II) by hydrogenation using an ambient pressure of hydrogen in the presence of a transition metal catalyst.

Palladium, for example 10% palladium on charcoal, has proved a particularly useful catalyst. We have found that a suitable ratio for the weight of 10% palladium on charcoal used to the weight of hydrogenolysable ester of the compound of the formula (II) used is 1:3.

The hydrogenation reaction preferably occurs in a solution in a solvent which consists of or contains tetrahydrofuran.

If a base such as sodium hydrogen carbonate or potassium hydrogen carbonate is included in the reaction mixture then the resulting compound is in the form of a salt. If no such base is included the product is in the form of the free acid.

Acids within formula (II) may be prepared by the careful acidification of the corresponding sodium salt.

Those compounds of the formula (II) which contain a relatively reactive moiety such as an amino, carboxylic acid or hydroxyl group may be prepared by the previously described processes if the moiety is protected during the condensation reaction.

Suitable protecting groups include benzyloxycarbonyl derivatives for amino or hydroxyl groups and benzyl esters for the carboxyl group. Such protecting groups may be removed by hydrogenation in conventional manner.

The esters formed at the 3-position carboxyl group of the compounds of the formula (II) may also be prepared by isomerisation of a corresponding ester of a compound of the formula (VI):

wherein R is as defined in relation to formula (II).

From one aspect the isomerisation reaction comprises contacting an ester of a compound of the formula (VI) with a transition metal catalyst in the presence of hydrogen. Suitable catalysts include palladium on charcoal. Normally the ratio of the weight (including support) of catalyst to the weight of the ester of the compound of the formula (VI) present will be about 1:2.5 to 1:3. This reaction is normally carried out at a temperature of about -5"C to 40"C, for example 0 C to +20"C. Suitable solvents include lower alkanols such as ethanol, low boiling halohydrocarbons such as dichloromethane or chloroform and ethers such as tetrahydrofuran.

A more favourable method of isomerisation of the ester of the compound of the formula (VI) comprises ultra-violet irradiation. This reaction is normally carried out in a degassed organic solvent such as benzene, carbon tetrachloride or acetonitrile under an inert atmosphere such as argon or nitrogen at a temperature of -20"C to +800 C, for example 0 C to 300 C. A photosensitizer such as dibenzyl, iodine, acetophenone or benzophenone may be included if desired.

Wide or narrow spectrum uv may be employed. Hanovia (Registered Trade Mark) low and medium pressure mercury lamps employing water-cooling silica or glass jackets have given satisfactory results.

The following Examples illustrate the invention: Example 1.

Benzyl 9-O-(benzyloxycarbonylmethyl)isoclavulanate

(a) From Photolysis A solution of benzyl 9-O-(benzyloxycarbonylmethyl)clavulanate (0.3 g) in benzene (400 ml) was irradiated with a Hanovia 2 x 45 W low pressure mercury lamp under nitrogen at room temperature for 3 hours. The solution was evaporated to dryness and the oily mixture was separated by preparative high pressure liquid chromatography (h.p.l.c.) (j" x 8+" 5y LiChrosorb) (Registered Trade Mark) into benzyl 9-O-(benzyloxycarbonylmethyl)isoclavulanate (0.05 g), [a]D +27.6 (CHCl3; C, 1.0), VmaX (liquid film) 1800, 1755, 1750, 1695, 1190, 1120 and 1020cam~'; SH(CDCL3): 7.27 (10H, s, ArH), 5.60 (1H, d, J=2.5Hz, 5--CH), 5.23 (lH, m, 3--CH), 5.20 (lH, m, 8--CH), 5.12 (2H, s, CH2Ph), 5.10 (2H, s, CH2Ph), 4.20--3.75 (2H, m, 9-CH2), 3.90 (2H, s, -O-C112-CO2-), 3.40 (1H, dd, J=17Hz, 2.5 Hz, 6a --CH) and 2.95 (Ih, d, J = 17Hz, 6/3-CH, m/e (relative intensity), 437 (0.5, M+), 409 (3.5), 395 (3), 368 (9), 346 (17), 327 (27), 304 (22), 260 (48), 219 (53), 166 (87) and 91 (100) (Found: C, 66.25; H, 5.45; N, 3.05% C24H23NO, requires C, 65.9; H, 5.3; N, 3.2%) and the starting material (0.l5g).

(b) From Benzyl Isoclavulanate Boron trifluoride etherate (1 drop) was added to a solution of benzyl isoclavulanate (ca. 3 mg) in methylene chloride (1 ml) at -300C. Benzyl diazoacetate (2 drops) was added to the reaction mixture at -300C which was then stirred at -300C for 1 hour. This was washed with aqueous sodium bicarbonate and filtered through anhydrous magnesium sulphate to give a mixture of benzyl isoclavulanate and 9-O-(benzyloxycarbonylmethyl)isoclavulanate identified by t.l.c. and h.p.l.c.

comparisons with authentic samples.

Example 2.

Benzyl 9-O-(ethoxycarbonylmethyl)isoclavulanate

Boron trifluoride etherate (2 drops) was added to a solution of benzyl isoclavulanate (0.1 g) in methylene chloride (25 ml) at -30 C. Ethyl diazoacetate (0.2 ml) was added to the reaction mixture at -300C which was then stirred at -30 to -10 C for 1 hour. This was washed with aqueous sodium bicarbonate (2 x 25 ml), dried, and evaporated to give a mixture which was chromatographed over silica gel (20 g). Elution of the column with chloroform gave benzyl 9-O-(ethoxycarbonylmethyl)isoclavulanate (0.056 g), [a], +33.0 (CHCl3; c, 1.0), Vmax (liquid film) 1805, 1750, 1695, 1205, 1175, 1140, 1120 and 1020 cm-1, #H(CDCl3): 7.29 (5H, s, ArH), 5.61 (1H, d, J = 2.5Hz, 5-CH), 5.28(1H, m 3-CH), 5.20(1H, m, 8-CH), 5.13(2H, s, CH,Ph), 4.16 (2H, g, J= 7Hz, -CO2CH2CH3), 4.30-3.77 (2H, m, 9-CH2), 3.88 (2H, s, -OCH2CO2), 3.41 (1H, dd, J = 18Hz, J' = 2.5 Hz, 6a-CH), 2.97 (1 H, d, J = 18Hz, 6-CH), and 1.26 (3H, t, J 7Hz, -CO2CH2CH3), m/e (relative intensity) 347 (21), 333 (19), 306 (80), 284 (80), 272 (61), 256 (55), 242 (80), 230 (50), 198 (38), 157 (53) and 91 (100) (Found: C, 61.1; H, 5.7; N, 3.55% C19H2tNO7 requires C, 60.8; H, 5.65; N, 3.75%), and the starting material (0.04 g).

Example 3.

Sodium 9-O-ethoxycarbonylmethylisoclavulanate

A mixture of benzyl 9-O-ethoxycarbonylmethylisoclavulanate (22.5 mg) and sodium bicarbonate (5 mg) in tetrahydrofuran-water (5:1, 6 ml) was hydrogenated at room temperature and pressure in the presence of 10% palladium-charcoal (7.5 mg) for 15 minutes. The mixture was then filtered and the solvent evaporated to give the title compound (0.015 g), Vm,,x (KBr) 1785, 1745, 1685, 1620, 1385, 1320, 1300, 1225, 1200, 1100 and 1020 cm-, AH(D2O): 5.70 (1H, d, J= 3Hz, 5-CH), 5.09 (1H, m, 3-CH), 5.08 (1H, m, 8-CH), 4.34.04 (2H, m, 9-CH2), 4.20 (2H, g, J= 8Hz, -OCH2CH3), 4.10 (2H, s, -OCH2CO2-), 3.55 (lH, dd, J 17Hz, J' = 3Hz, 6α-CH), 3.03 (1H, d, J= 18Hz, 6 -CH), and 1.22 (3H, t, J= 8Hz, -OCH2CH3).

Example 4.

Benzyl 9-O-methylisoclavulanate

Boron trifluoride etherate (2 drops) was added to a solution of benzyl isoclavulanate (0.07 g) in methylene chloride (10 ml) at -40 C. Diazomethane (~20 equiv.) was added to the reaction mixture at -40 C, which was then stirred at 400 to -100C for 1 hour. The solution was washed with aqueous sodium bicarbonate (2 x 10 ml), dried and evaporated to give a mixture which was fractionated on silica gel. Elution with ethyl acetate/cyclohexane (1:2) gave the required product as a colourless oil (0.04g). [α]D20= +56.2 (C= 1.0, CHCl3); Vmax (CHCl3) 1800, 1745, 1690 cm-'; b(CDCI3) 2.96 (lH, d, J 17Hz, 6 -CH), 3.13 (3H, s, OCH3), 3.4 (lH, dd, J17 and 3Hz, 6a-CH), 3.77 (2H, m, CH2OCH3), 5.12 (2H,s, CH2C6H5), 5.17 (methine triplet 8-CH), (partially obscured), 5.21 (1H, d, J 1.5Hz, 5-CH), 5.59 (1 H, d, J 3Hz, 5-CH), 7.27 (5H, s, C8Hs); Analysis found: C63.36; H 5.76; N 4.73%; C,6H,7NOs requires C 63.36, H 5.65, N 4.26%.

Starting material (0.02 g) was also recovered.

Benzyl 9-O-ethylisoclavulanate may be similarly prepared by substituting an equivalent amount of diazoethane for the diazomethane.

Example 5.

Lithium 9-O-methylisoclavulanate

Benzyl 9-O-methylisoclavulanate (0.04 g) in tetrahydrofuran (10 ml) was hydrogenated at room temperature and pressure in the presence of 10% palladised charcoal (20 mg). The mixture was filtered and the filtrate titrated with I M aqueous lithium hydroxide to pH8. The solution was evaporated to give the salt as a white powder (0.015 g). Vmax (KBr) 1783 1683, 1600 cm-'; b(D2O) (acetonitrile standard at 2.0) 3.03 (1H, d, J 17.5Hz, 6,BCH), 3.25 (3H, s, 0CH3), 3.52 (1H, dd, J 17.5 and 3.5Hz, 6--CH), 4.0 (2H, m, :CHCH2), 5.06 (1H, bs, 3--CH), 5.14 (lH, bt, J 8Hz, :CHCH2), 5.69 (1H, d, J 3Hz, 5-CH).

Example 6.

Benzyl 9-O-methylisoclavulanate

A solution of benzyl isoclavulanate (72 mg) in methylene chloride (5 ml) was treated successively with anhydrous sodium carbonate (132 mg) and a solution of trimethyloxonium tetrafluoroborate (111 mg) in methylene chloride (5 ml) at -30 C.

The reaction mixture was allowed to warm slowly (-1 hr) to room temperature and stirred for a further 2 hrs. (t.l.c. showed the absence of starting material).

Water (5 ml) was added, the organic phase separated, dried over magnesium sulphate and evaporated to an oil. Fast chromatography on silica gel, eluting with ethyl acetate/cyclohexane (1:1), gave the product as a colourless oil (60 mg).

Ir.: identical with authentic sample.

Example 7.

Benzyl 9-O-methylisoclavulanate

Benzyl isoclavulanate (400 mg), calcium oxide (0.65 g), silver oxide (0.65 g) and methyl iodide (1.7 ml) were refluxed in benzene (5 ml) for 0.75 hr. The solution was filtered and the filtrate evaporated to dryness. Chromatography on silica gel using n-hexane/ethyl acetate (2:1) as the eluting solvent gave the product (spectral characteristics were identical with authentic samples) as a colourless oil (66 mg) and starting material (64 mg).

Synergistic Activity The minimum inhibitory concentration (MIC) of ampicillin in the presence of compounds of the formula (A) was determined for a range of bacteria. The results are shown below.

MIC of Ampicillin in the presence of Inhibitor.

MIC ( g/ml) Conc. of Inhibitor Staph. Klebsiella Proteus A' R ( g/ml) Russell E 70 C889 - - 0 500 1000 2000 CH2C6Hs H 5.0 > 100 > 100 > 500 20.0 12.5 50 62.5 Li H 1.0 12.5 - 5.0 0.8 3.1 8.0 - - 0 500 250 2000 CH2C6Hs CO2C2Hs 5.0 6.0 62 > 500 20.0 1.6 15 500 - - 0 500 500 > 2000 Na CO2C2Hs 1.0 6.2 50 > 500 5.0 0.08 6.2 62 20.0 0.01 3.1 8.0 WHAT WE CLAIM IS:1. A compound of the formula (II):

wherein R is a hydrogen atom, or R is an alkyl group of 1-4 carbon atoms or a phenyl group or one of the aforementioned groups substituted by a carboxylic acid group or a salt or C14 alkyl ester thereof or an amino group or an acid addition salt thereof, or R is a carboxylic acid group or a salt or C14 alkyl ester thereof; or a salt or ester thereof formed at the 3-position carboxyl group.

2. A compound as claimed in claim 1 wherein R is a hydrogen atom.

3. A compound as claimed in claim 1 wherein R is an alkyl group of 1-4 carbon atoms or a phenyl group or one of the aforementioned groups substituted by a carboxylic acid group or a salt or C14 alkyl ester thereof or an amino group or an acid addition salt thereof, or R is a carboxylic acid group or a salt or C14 alkyl ester thereof.

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

Claims (38)

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

   MIC of Ampicillin in the presence of Inhibitor.

   MIC ( g/ml) Conc. of Inhibitor Staph. Klebsiella Proteus A' R ( g/ml) Russell E 70 C889 - - 0 500 1000 2000 CH2C6Hs H 5.0 > 100 > 100 > 500 20.0 12.5 50 62.5 Li H 1.0 12.5 - 5.0 0.8 3.1 8.0 - - 0 500 250 2000 CH2C6Hs CO2C2Hs 5.0 6.0 62 > 500 20.0 1.6 15 500 - - 0 500 500 > 2000 Na CO2C2Hs 1.0 6.2 50 > 500 5.0 0.08 6.2 62 20.0 0.01 3.1 8.0 WHAT WE CLAIM IS:1. A compound of the formula (II):

   wherein R is a hydrogen atom, or R is an alkyl group of 1-4 carbon atoms or a phenyl group or one of the aforementioned groups substituted by a carboxylic acid group or a salt or C14 alkyl ester thereof or an amino group or an acid addition salt thereof, or R is a carboxylic acid group or a salt or C14 alkyl ester thereof; or a salt or ester thereof formed at the 3-position carboxyl group.
2. 2. A compound as claimed in claim 1 wherein R is a hydrogen atom.
3. 3. A compound as claimed in claim 1 wherein R is an alkyl group of 1-4 carbon atoms or a phenyl group or one of the aforementioned groups substituted by a carboxylic acid group or a salt or C14 alkyl ester thereof or an amino group or an acid addition salt thereof, or R is a carboxylic acid group or a salt or C14 alkyl ester thereof.
4. 4. A compound as claimed in claim I wherein R is a methyl group.
5. 5. A compound as claimed in any one of claims 1--4 wherein the compound is in the form of an acid or a pharmaceutically acceptable salt.
6. 6. A compound as claimed in any one of claims 1--4 wherein the compound is in the form of a sodium, potassium, calcium, magnesium, lithium or substituted ammonium salt.
7. 7. A compound as claimed in any one of claims l wherein the compound is in the form of the sodium or potassium salt.
8. 8. An ester of the formula (III) or (IV):

   wherein R is as defined in any one of claims 14 and A' 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 OA6 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 A6 is an alkyl group.
9. 9. The benzyl ester formed at the 3-position carboxyl group of a compound of the formula (II) as defined in claim 1.
10. 10. The p-methoxybenzyl or p-nitrobenzyl ester formed at the 3-position carboxyl group of a compound of the formula (II) as defined in claim 1.
11. 11. A pharmaceutical composition comprising a compound as claimed in any one of claims 1--10 and a pharmaceutically acceptable carrier.
12. 12. A salt formed at the 3-position carboxyl group of a compound of the formula (II) in sterile form.
13. 13. A composition as claimed in claim 11 in unit dose form adapted for oral administration.
14. 14. A composition as claimed in claim 13 comprising a buffering agent or an enteric coating agent.
15. 15. A composition as claimed in any one of claims 11 to 14 comprising a penicillin or cephalosporin.
16. 16. A composition as claimed in claim 15 wherein the ratio of the compound of the formula (II) or its salt or ester to the other p-lactam antibiotic is from 10:1 to 1:10 by weight.
17. 17. A composition as claimed in claim 15 wherein the ratio of the compound of the formula (II) or its salt or ester to the other p-alctam antibiotic is from 5:1 to 1:2 by weight.
18. 18. A composition as claimed in any one of claims 11 to 17 wherein the total quantity of antibacterial agents present is from 50 to 1500 mg.
19. 19. A composition as claimed in claim 18 wherein the total quantity of antibacterial agents present is from 100 to 1000 mg.
20. 20. A composition as claimed in claim 15 or claim 16 comprising from 150 to 1000 mg of amoxycillin, ampicillin or a salt thereof and from 50 to 500 mg of a salt formed at the 3-position carboxyl group of a compound of the formula (II).
21. 21. A composition as claimed in claim 20 comprising from 200 to 500 mg of amoxycillin, ampicillin or a salt thereof and from 50 to 250 mg of a salt formed at the 3-position carboxyl group of a compound of the formula (it).
22. 22. A process for the preparation of esters formed at the 3-position carboxyl group of the compound of the formula (II) as defined in claim 1 which process comprises the reaction of the corresponding ester of isoclavulanic acid with a compound of the formula (V): N2-CH-R (V) wherein R is as defined in relation to formula (II) in the presence of a Lewis acid.
23. 23. A process for the preparation of esters formed at the 3-position carboxyl group of the compound of the formula (II) as defined in claim 1 which process comprises the reaction of the corresponding ester of isoclavulanic acid with a compound of the formula (VII): X-CH2-R (VII) wherein X is I, Br or Cl and R is as defined in relation to formula (II), in the presence of a source of silver ions.
24. 24. A process for the preparation of esters formed at the 3-position carboxyl group of the compound of the formula (II) as defined in claim 1 which process comprises the reaction of a salt of isoclavulanic acid with a compound of the formula (VIII): (RCH2)3os ey (VIII) wherein R is as defined in relation to formula (II) and Y is BF4 or PF6.
25. 25. A process for the preparation of the compound of the formula (II) as defined in claim 1 in the form of a salt which process comprises the hydrolysis in an aqueous solution at pH7 to 9 of a corresponding ester by the addition of base.
26. 26. A process for the preparation of acids of the formula (II) as defined in claim 1 and salts thereof formed at the 3-position carboxyl group, which process comprises the hydrogenation of a corresponding hydrogenolysable ester of a compound of the formula (II) using an ambient pressure of hydrogen in the presence of a transition metal catalyst.
27. 27. A process for the preparation of acids of the formula (II) as defined in claim 1, which process comprises the acidification of the corresponding sodium salt.
28. 28. A process for the preparation of esters formed at the 3-position carboxyl group of compounds of the formula (II) as defined in claim 1, which process comprises the isomerisation of a corresponding ester of a compound of the formula (VI):

    wherein R is as defined in relation to formula (II).
29. 29. A process as claimed in claim 28, which process comprises contacting an ester of a compound of the formula (VI) as defined in claim 28 with a transition metal catalyst in the presence of hydrogen.
30. 30. A process as claimed in claim 28 which process comprises the ultraviolet irradiation of an ester of a compound of the formula (VI) as defined in claim 28.
31. 31. An ester formed at the 3-position carboxyl group of a compound of the formula (II) as defined in claim 1 when prepared by the process claimed in claim 22.
32. 32. An ester formed at the 3-position carboxyl group of a compound of the formula (II) as defined in claim 1 when prepared by the process claimed in claim 23.
33. 33. An ester formed at the 3-position carboxyl group of a compound of the formula (II) as defined in claim 1 when prepared by the process claimed in claim 24.
34. 34. A salt of a compound of the formula (II) as defined in claim 1 when prepared by the process claimed in claim 25.
35. 35. A compound of the formula (II) as defined in claim 1 or salt thereof when prepared by the process claimed in claim 26.
36. 36. An acid of the formula (II) as defined in claim 1 when prepared by the process claimed in claim 27.
37. 37. An ester formed at the 3-position carboxyl group of a compound of the formula (II) as defined in claim I when prepared by the process of any one of claims 28-30.
38. 38. A compound of the formula (II) as defined in claim 1 or a salt or ester thereof formed at the 3-position carboxyl group when prepared substantially as described in any of Examples 1--7 herein.