IE50650B1 - Method for producing penicillanic acid derivatives - Google Patents

Abstract

Compounds of the formula I in which R1 stands for hydrogen, alkyl, alkoxy, halogen, or trifluoromethyl, and R2 stands for a carboxy group or for a protected carboxy group, in particular an esterified carboxy group; or, if appropriate, a salt thereof, are obtained by oxidising the corresponding penicillanic acid derivatives or their sulfoxides with hydrogen peroxide in the presence of a tungsten or molybdenum catalyst. This process eliminates secondary degradative oxidative side reactions and simplifies the isolation and purification of the product, thus providing high yields and thereby being particularly suited for large scale production. The compounds of formula I, depending upon the meanings of R1 and R2, are of value as beta -lactamase inhibitors and/or antibiotics, and/or as intermediates in the production of antibiotics and/or beta -lactamase inhibitors.

Description

The present invention relates to a nev and improved method for producing a compound of the formula I in which R^ stands for hydrogen, alkyl, alkoxy, h.alogen, or trifluoromethyl, and Rg stands for a carboxy group or for a protected carboxy group, in particular an esterified carboxy group; or a salt thereof in case Rg is a carboxy group or Rg contains a basic or acidic group.

Depending upon the meanings of and Rg, the compounds of formula I are of value as β-lactamase inhibitors and/or antibiotics, and/or as intermediates in the production of antibiotics and/or β-lactamase inhibitors.

R^ may preferably represent a member selected from the group consisting of hydrogen, chlorine and bromine.

When Rg stands for an esterified carboxy group, it may both represent an ester group which is easily hydrolyzable either spontaneously or under the influence of esterases, or an ester group which can be cleaved by hydrogenolysis. Vhen Rg represents an a-haloalkyl ester group, the compound of formula I is a useful intermediate. The easily hydrolysable esters are well known types of esters, e.g. acyloxyalkyl esters, such as 506S0 alkanoyloxyalkyl eaters, e.g. acetoxymethyl and pivaloyloxymethyl eaters and the corresponding 1-acetoxyethyl and 1-pivaloyloxyethyl esters, alkoxyearbonyloxyalkyl esters, e.g. metboxycarbonyloxymethyl and 1-ethoxy5 carbonyloxyethyl esters, lactonyl esters, e.g. phthalidyl esters, or lover alkoxymethyl and acylaminomethyl esters. Examples of other useful esters are the lover alkyl esters, the benzyl esters, the haloalkyl esters, e.g. the chloromethyl esters, and the cyanomethyl esters.

The salts of the compounds of formula I may be formed by any basic or acidic group present in R2 reacting vith suitable acids or bases, respectively. In case the compounds of formula I are to be used as β-lactamase inhibitors or antibiotics, the salt-forming acid or base should be pharmaceutically acceptable and non-toxic, vhereas in case the compound of formula I is an intermediate, then any acid or base vhich is suitable vith a viev to the use of the intermediate may be applied in the salt formation.

The salts of the compounds of formula I are thus in addition to their inner salts (zvitterions), salts formed vith non-toxic pharmaceutically acceptable acids such as hydrochloric acid, phosphoric acid, nitric acid, p-toluenesulphonic acid, acetic acid, propionic acid, citric acid, tartaric acid, maleic acid, etc·, but any pharmaceutically acceptable, non-toxic inorganic or organic acids can be used as veil.

Also included in the invention are salts with pharmaceutically acceptable, non-toxic, inorganic or organic bases, e.g. alkali metal salts and alkaline earth metal salts, for example sodium, potassium, magnesium or calcium salts, as well as salts with ammonia or suitable nontoxic amines, such as lower alkyl amines, for example triethylamine, hydroxy-lower alkylamines, for example 2-hydroxyethylamine, bis-(2-hydroxyethyl)-amine or tris-(2-hydroxyethyl)-amine , cycloalkylamines, for example dicyclohexylamine, or benzylamines, for example Ν,N'-dibenzyl-ethylenediamine, and dibenzylamine, without these examples being limiting the invention.

Thus, for instance other antibiotics with acid or basic character can be used as components of such salts of the compounds of formula I.

According to prior art, some of the compounds of formula I have been prepared by oxidation of a compound of formula II or formula III: in which and R2 have the above meanings, or a salt thereof as defined above. 506S0 According to German patent application, laid-opennumber 2,824,535 and European patent application No. 2927, publ. July 11, 1979, thia oxidation can be carried through, using a number of oxidising agents known in the technique for oxidizing sulphides or sulphoxides to sulphones, but according to the said prior art, the oxidation is with advantage performed using metal permanganates, such as alkali metal permanganates and earth alkalimatal permanganates, or by using organic peroxycarboxylic acids, like 3-chloroperbenzoic acid and peracetic acid. These methods, however, tend to give problems, in particular when applied in a large scale, in form of lover yields and/or technical difficulties like filtration problems.

It has also been described to oxidize simple organic sulphides into ths corresponding sulphones by using hydrogen peroxide in the presence of a suitable catalyst (j, Org, Chem., Vol, 28 (l9<»3), P· 1140-42). However, when applied to penam-derivatives, this method has previously only led to sulphoxides. Thus, US patent No. 3,993,646 describee a method for converting compounds of formula II to compounds of formula III by subjecting the first mentioned to an oxidation process using peracids, salts of peracids, or hydrogen peroxide as oxidizing agent, in the presence of a compound containing a metal of group Vb or VTb of the Periodic Table.

It has now surprisingly been shown that it is possible to oxidize certain penicillanic acid derivatives or their sulfoxides to the corresponding sulphones without destroying the lactam ring by using the mild oxidizing agent, hydrogen peroxide, provided a tungsten or molybdenum catalyst is present. This process eliminates secondary degradative oxidative side reactions and simplifies the isolation and purification of the product, thus providing high yields and thereby being particular suited for large scale production.

According to the present invention the oxidation is generally performed by dissolving the starting material of formula II or III or a salt thereof in water, or, if insoluble in water, in a suitable organic solvent.

The catalyst is dissolved in water or a suitable organic solvent, the two solutions are mixed, and hydrogen peroxide is added to the mixture either in one portion or gradually, with efficient stirring, preferably keeping the reaction temperature about or below room temperature, more preferably from 20°C. to 30°C.

Even in case that the starting material of formula II or III has limited solubility in water, it is possible, with good stirring, to carry the present method through in aqueous medium with a satisfactory result. In case of extreme insolubility of the starting material, water-miscible solvents, such as an alkanol or dioxane, may be added. Vaterimmiscible solvents may be applied as well, provided 50680 a phase transfer catalyst, s.g. a quaternary ammonium salt, such as tetrabutylammonium bromide, is added.

Bxamplss of suitable organic reaction madia include, but are not limited to tha following» alkanols, s.g. methanol, ethanol, propanol, Isopropanol, tart-butanol, dioxane, dialkyl ethers, lover alkyl esters of lover fatty acids, unsubetituted or substituted aliphatic and aromatic hydrocarbons, tetrahydrofuran, dimethylformamide, and haxamftbylphospboric acid triamide.

Ixamplea of preferred organic reaction media are ethanol, isopropanol, methylene chloride and tetrahydrofuran.

The need for an efficient cooling ‘may be particularly appropriate during the conversion of the sulphide into the sulphoxide be'cause the reaction rate is high, and ths reaction is exothermic, vhereas the conversion from sulphoxide to sulphone needs heating or a longer reaction time at ambient temperatures.

The present method is of specific interest also in the preparation of certain esters of formula Σ, in parti20 cular the important intermediates of formula Zas Za COOCH-X I 506B0 in which has the above meanings, R^ is a hydrogen atom, or a lower alkyl, aryl or aralkyl radical, preferably hydrogen, methyl, phenyl or benzyl, and X stands for a halogen atom, preferably chlorine. The compounds of formula Ia thus include compounds of formula I in which Rj may be a hydrogen or bromine atom and Rg is -COOCHgCl. The compounds of formula Ia are important intermediates in the production of di-esters of the formula IV: in which R^ and R^ have the above meanings, and R^COrepresents the acyl radical of a penicillin, or an amidinopenicillanoyl radical.

The compounds of formula la can be prepared 15 according to the following reaction scheme: 0=C_ NV 'COOM + Ia *)_ = oxidation according to the present invention 80650 in which reaction scheme R^, R^ and X have the above meanings, M stands for a cation, such as Na+, K+, an ammonium ion, a trialkylemmonium ion or a tetraalkylammonium ion, e.g. a tetrabutylammonium ion, and T stands for a bromine or iodine atom or for an alkylsulphonyloxy, halosulphonyloxy, a-halo-alkoxysulphonyloxy, or arylsulphonyloxy radical.

The esterification process V—A VII is performed in a suitable solvent, e.g. dimethylformamide, acetone or hexa10 methylpbosphoric acid triamide, for sufficient time and at an adequate temperature with a view to accomplish the desired conversion, usually at a temperature from 0°C to 6o°C.

The compounds of formula Ia may also be produced by first subjecting a compound of fbrmula V to the oxidation process of the present invention and thereafter esterifying the sulphone obtained to give the desired compound of formula Xa. However, it is preferred when preparing the compounds of formula Ia, to first perform the esterification process and thereafter the oxidation process of the invention. Both methods for preparing the compounds of formula Ia are within the scope of the invention.

Some of the compounds of formula VII are new.

A particular exaaple of a valuable intermediate is the hitherto unknown compound of formula VII in which R^ and stand for hydrogen, and X is chlorine.

The catalyst used in the oxidation process of the invention is appropriately in the fora of a salt. If the reaction medium is aqueous, an alkalimetal salt may be the preferred form, whereas in an organic reaction medium, it may bo appropriate to use the catalyst in the form of a salt with an organic cation, e.g.-φη the form of a quaternary ammonium salt, such as a tetrabutylammonium aalt.

The invention will be further illustrated by the following, non-limiting examples.

£X£B£l£_l_ Chloromethvl 1.1-dioxopenicillanate A. Tetrabutylammonium penicillanate To a cooled (+5°c) «elution of tetrabutylaemonium hydrogeasulphat· (35*7 g, 0.103 sol·) in water (80 ml), dichloromethane (100 ml) was added, followed by 30% •odium hydroxide to bring the pH to about 3. Potassium penicillanate (2k g, 0.1 mole) was added, and pH adjusted to 7 with 30% sodium hydroxide. The organic layer was separated, and the aqueous phase was extracted thrice with 25 al portions of dichloromethane. The combined extracts were dried, and the solvent removed in vacuo to give the title compound as a yellow-brown oil (k$ g), B. Chloromethvl penicillanate Tetrabutylammonium penicillanate (65 g) was dissolved in chloroiodomethane (100 ml) and left for 20 hours at ambient temperature. Excess of chloroiodomethane was removed at reduced pressure, first at 10 mm Hg, finally at 0.1 mm Hg. Tbe semi-crystalline residue was treated with ethyl acetate (200 ml), and separated tetrabutylaamonium iodide was filtered off and washed with ethyl acetate. The filtrate was evaporated ir. vacuo, and the brown residue was chromatographed on silica gel (hexaneethyl acetate (U:l)) to give the title compound as a faintly yellow oil. The IR spectrum (chloroform) showed a strong band at 17^5-17®5 cm The NMR spectrum (CDCl^) showed peaks at £ = 1.55 (s), 1.8? (a), 3.10 (dd, J=l6, J=2), 3.62 (dd, J=l6, J=4), 4.50 (s), 5.30 (dd, Je2, J=4), 5.65 d, J=6.5), 5.88 (d, Jw6.5).

C. Chloromethvl 1,1-dioxopenicillanate To a stirred solution of chloromethyl penicillanate (12.5 g, 0.05 aole) in 96% ethanol (50 ml), sodium tungstate (lOO mg) dissolved in water (0.5 ml) was lO added. Hydrogen peroxide (30$, 11 ml) was added in one portion. No immediate heat was evolved, but after a few minutes an exothermic reaction set in. The temperature was kept below 30°C by cooling in ace-water, and the mixture was left at ambient temperature for 20 hours.

The crystalline mass was cooled to 0°C, and the crystals were filtered off, washed and dried, and recrystallized from ethyl acetate-hexane to give the title compound with a melting point of 95-96°C. The IH spectrum (chloroform) showed strong bands at 1805, 1780, 1330 and 1120 cn'^ Example 2 1,1-Dioxopenicillanic acid To a cooled (lO°C), stirred solution of potassium penicillanate (12 g, 0.05 mole) and sodium tungstate (lOO mg) In water (50 ml), 30^ hydrogen peroxide (ll ml) was added portionwise. During addition of the first five ml,, heat was evolved and the temperature was kept below 30°C by cooling in ice-water. The mixture was left, at room temperature for 20 hours, and excess of hydrogen peroxide was destroyed with sodium bisulphite. The mixture was saturated with sodium chloride, and pH was adjusted to 1,5 with concentrated hydrochloric acid under ethyl acetate (50 ml). The layers were separated, and the aqueous phase was extracted twice with 25 ml portions of ethyl acetate. The combined extracts were dried, and the solvent stripped in vacuo. The crystalline residue was washed with hexane to yield the title compound as colourless crystals with a melting point of 15^°C (decomp.).

Example 3 Chloromethyl 1,1-dioxopenicillanate To a stirred solution of chloromethyl penicillanate (2.5 g, 0.01 mole) in ether (25 ml), 30?i hydrogen peroxide (2.5 al) aad eodi.ua tungstate (40 mg) in water (0.25 ml) wore added. The mixture was stirred for 2 days at ambient temperature, whereafter the ether was removed in vacuo, asd the separated eryetals were filtered off, washed with water followed by cold propanol-2 to give the' title compound aa colourless crystals with a melting point of p6-97°C.

Example 4 Chloromethvl 1,l-dioxonenicillanate χθ To a stirred solution of chloromethyl penicillanate (2.5 Si 0.01 mole) and tetrabutyiammonium bromide (0.5 g) in dichloromethane (25 ml), 30^ hydrogen peroxide (2.5 ml) and sodium tungstate (40 mg) in water (0.25 ml) were added. The temperature was kept below 30°C by cooling 15 in water. After stirring for 2 cays at ambient temperature , dichloromethane was removed in vacuo, and the rosiduo was extracted with ether. The ether phase was evaporated in vacuo, and the residue was chromatographed on silica gel (hexane-ethyl acetate (3:2)) to give the title compound as colourless crystals with a melting point of 96-97°C. soeso Example 5 Chloromethvl 1.1-dioxopenicillanate To a stirred solution of chlorocethyl penicillanate (2.5 g, 0.01 aole) in propanol-2 (25 al), 30^ hydrogen peroxide (2.5 nl) and aodiua tungstate (40 ng) in vater (0.25 al) vere added. The temperature vas kept below 30°C and then left at ambient temperature for 2k hours. After cooling to 0°C, the crystals were filtered off and washed vith cold propanol-2 to give the title compound as colourless crystals vith a melting point of 96-976C.

Example 6 1-Chloroethyl 1,1-dloxopenicillar.ate A. Chloroethyl penicillanate By following the procedure of Example IB, but replacing chloroiodomethane with 1,1-chloroiodoethane, the title compound vas obtained as an oily substance vhich vas used in the next step without further purification. Β. 1-Chlo roe thyl 1, l-dioxspenicillar.a te By following the procedure of Example 1C, but replacing chloromethyl penicillanate vith the ehloroethyl penicillanate prepared according to step A of this Example, the title compound vas obtained as a crystalline mixture of the two diastereoisomers.

Example 7 6c-Bromo-l.1-dioxopenicillanic acid To a solution of δα-bromopenicillanic acid (4.3 g, 0,015 M) in ethanol (15 ml), 0,5 M aqueous sodium tung5 state (1.5 ml) was added, followed by 30# hydrogen peroxide (/ ml). After about 5 minutes, the temperature rose gradually to 50°C, and the mixture was kept at this temperature for two hours. After cooling in ice, excess of hydrogen peroxide was destroyed with sodium bisulphite, and the mixture was taken to dryness in vacuo. The residue was extracted with ether (50 ml), and the extract evaporated in vacuo. The residue was crystallized from ether-diisopropyl ether to give the title compound as colourless crystals, melting point: 124-126°C.

The NMR-spectrum (CD^OD) showed peaks at 5 = 1.48 (s), 1.59 (s), 4.48 (s), 5.10 (d, J=2Hz, 5.35 (d, J=2Hz).

Example 8 1,1-Dioxopenicillanoyloxvmethvl phenoxvmethvlpenicillanate To a solution of chloromethyl penicillanate 1,1-dioxide (l.4l g, 5 mmol) in dimethylformamide (25 ml) was added potassium phenoxymethylpenicillanate (1.94 g, 5 mmol), and the mixture was stirred at room temperature for 18 hours. After dilution with ethyl acetate (100 ml), the mixture was washed with water (4 x 25 ml), dried, and evaporated soeso in v>cu£. Th· residual oil was purified hy dry column chromatography on silica gel (ethyl acetate-petroleum •tbar, 8«2), to yield the desired compound ae e slightly yellowish foaa.

Example 9 1,l-Pioxopenjcillanovloxymethvl 6-(D-g-amino-a-phenylacetamido)penicillanate. hydrochloride By following the procedure of Example 8, hut replacing potassium pbenoxymethylpenicillanate with potassium 6-(D-a-aminophsnylacetamido)penicillanate, the title compound was obtained as a colourless foam.

The NME-spectrum (ΰ^Ο) shoved signals at ί * 1.38 (s, 6H{ 2-CH3), 1.46 (s, 3H; 2-Cfij), 1.58 (s, 3H} 2-0^), 3.56 M, 2Hj 60-H and 6β-Η), 4.60 (s, IH} 3-H), 4.63 (s, 1Η» 15 3-H), 5.03 (m, 1H> 5-H), 5.27 (s, IH; CH-NTI2), 5.53 (s, 2H; -H and 6-H), 5,97 (be, IHj 0Cg20), and 7.53 (s, 5H; arom. CH) ppm.

Tetramethylsilane was used as external reference.

Example 10 1.1-Dioxopenicillanic acid Λ stirred solution of penicillanic acid morpholine salt (288 g, 1 mole) in water (l l) was acidified to pH 3.4 with hydrochloric acid, whereafter sodium tungstate (12.5 g) was added. Hydrogen peroxide (3096-, 330 ml, 3·3 moles) was added portionwise over about k hours, the tern0 perature being kept below 25 C. After standing over night at 5°C, excess of hydrogen peroxide was destroyed with sodium bisulphite. Sodiua chloride (300 g) was added, and pH was adjusted to 1,1 with hydrochloric acid, whereafter the mixture was extracted thrice with 1 1 portions of ethyl acetate. After drying, the organic phase was concen trated to about 1 1 in vacuo. whereafter heptane (3 l) waa added. After standing over night at 5°C, the crystals were collected and washed with heptane to yield the title compound as faintly yellow crystals with melting point: 148-15O°C.

Example 11 Potassium 1,1-dioxopenicillanate A solution of 1,1-dioxopenicillanic acid (23.3 g, 0,1 mole) in ethanol (99%, 100 ml) was wanned to about 0 C on the steam bath. A solution of potassium acetate (lO g) in warm ethanol (99%, 60 ml) was added, and crys20 tallisation was induced by scratching. After standing for about 10 minutes, the crystals were filtered off and washed with ethanol and ether to give the title compound as colourless crystals.

Exanple 12 6g-Chloropenicillanic acid 1.1-dioxide By substituting 6a-chloropenicillanic acid for the 6g-bromopeaicillanie aeid in the procedure of Example 7, 6g-chloropenicillanie aeid 1,1-dioxide vas obtained as crystals fron diisopropyl ether, melting points 134-137°C.

The NMR-speetrum (CDCl/) shoved signals at ά » 1.50 (a, 3H·, 2-CH3), 1.64 (s, 3H{ 2-Cg3), 4.46 (s, IH; >g), 4.70 (d, Jal.5Hz, 1H{ 6-H), and 5.18 (d, J«1.5Hz, IB» -H) ppm. Tetramethylsilane vas used as internal reference.

A crystalline potassium salt of the above conpound vas obtained by addition of an equimolar amount of 0.8 M potassium 2-etbylhexanoate in acetone to a stirred solution of 6a-chloropenicillanic acid 1,1-dioxide in acetone. gxamgie, -U Pivaloyloxymethyl 1,l-dloxopenicillanate A. Pivalovloxymethvl penicillanate To a stirred suspension of potassium penicillanate (12 g, 0.05 mole) in DMF (50 ml), chloromethvl pivalate (7.5 ml) vas added. After stirring for 24 hours, ether (lOO ml) vas added, and the mixture vas washed twice with water (lOO + 50 ml). The organic layer vas dried and taken to dryness in vacuo. giving tbe title compound as a faintly yellow oil.

The IR-spectrua (CHCl^) showed a strong broad band centered at 1765 cm”1.

B. Pivaloyloxvmethvl 1,1-dioxooeni cillanate To a stirred solution of A (3.14 S, 0.01 mole) in ethaaol (96$, 25 ml) hydrogen peroxide (30^6, 2.2 ml) was added, followed by 0.5 M aqueous sodium tungstate (l ml).

Th© temperature rose to about 35°C in the course of 10 minutes. After stirring for 20 hours, water (50 ml) was added, and ethanol was removed in vacuo. The separated oil was extracted with ethyl acetate which was dried and evaporated to dryness. The residue crystallized from ether to give the title compound as colourless crystals with melting point: 103“104°C The NMR-spectrum (CDCl^) showed peaks at 6 = 1.27 (s), 1.47 (s), 1.62 (a), 3.52 (m), 4.4?(s), 4.70(a), 5.73 (d, Jn6Hg, 5.98 (d, Je6 Hz).

Acetoxvmethvl 6a-methoxv-1,1-dicxcpenicillanate A. Acetoxvmethvl 6g-methoxv-penicillanate To a stirred suspension of acetoxymethyl 6-aminopenicillanate 4-toluenesulphonic acid salt (4.6l g, 0.01 mole) in a cold (0-3°C) mixture of dichloromethane (400 ml) and water (400 ml), sodium nitrite (3-45 Si θ·05 mole) and 4=toluenesulphonic acid (1.90 g, 0.01 mole) were added.

The latter was added in three equal portions at inten’als of 5 minutes. After stirring at 0-3°C for a further 20 minutes, the organic layer was separated, dried, and con21 Soeso centrated to about 40 ml in vacuo. Methanol (2 al) and boron trifluoride etherate (0.2 ml) vere added under stirring, whereby an immediate evolution of nitrogen occurred. After stirring for 5 minutes, aqueous potassium bicarbonate (0.2 M, 10 ml) was added. The organic layer was separated, washed vith saturated aqueous sodium chloride (2x5 ml), dried, and evaporated in vacuo.

The residual oil vas purified by chromatography on silica gel (ethyl acetate-hexane (3:7)) to afford the pure title compound as a faintly yellov oil.

The NMR spectrum (CDCl^) shoved signals at & a 1.46 (s), 1.55 (»), 2.11 (s), 3.51 (s), 4.50 (s), 4.57 (d, J-1.5 Ha), 5.29 (d, J«1.5 Ha), and 5.78 (s).

B. Acetoxvmethvl 6a-methoxy-l.1-dioxopenicillanate To a stirred solution of A (0,72 g, 0.0024 mols) in tetrahydrofuran (6 ml), hydrogen peroxide (30$, 0.52 ml) vas added, folloved by aqueous sodium tungstate (0.5 M, 0.24 ml). The temperature rose to 36°C in the course of 5 minutes. After stirring for 20 hours, vater (20 ml) vas added, and tetrahydrofuran vas removed in vacuo. The residue vas worked up through ethyl acetate to give a yellowish oil, which vas purified by chromatograpy on silica gel (ether) to yield an oil, vhich crystallized from ether to give the title compound as colourless crystals vith melting point 88-9O°C.

The NMR-spectrum showed signals at & «1.41 (s), 1.56 (s), 2.14 (,), 3.57 (s), (d> 5 .02 (d, J«1.5 Hz), and 5.72-5.91 (ABq, J=5.8 Hz).

Claims (10)

CLAIMS Method for producing a compound of the formula I in which R^ stands for hydrogen, alkyl, alkoxy, halogen, or trifluoromethyl, and R^ s ta «ds for a carboxy group or for a protected carboxy group; or a salt thereof in case Rj is a carboxy group or contains a basic or acidic group, in which method a compound of the formula II or III

1··. o=c? j) ’m ill in which R^ and R^ have the above meanings, or a salt thereof as defined above, is subjected to an oxidation process using hydrogen peroxide as oxidizing agent in the presence of a tungsten or molybdenum catalyst.

2. A «etbod according to claia 1, in which the oxidation process is carried out in a suitable solvent at a. tenperature between the boiling point of the solvent used, and a temperature about or below room temperature.

3. 5 3. A Method according to claim 2, in which the temperature is fro· 20°C. to 30°C. A. A method according to claia 1, 2 or 3, in which the catalyst is used in the fora of a salt. 5. A method according to any one of claims 1 to 4, in which 10 represents hydrogen and Rj is a carboxy group.

4. 6. A aethod according to any one of claims 1 to 4, in which R^ represents bromine and R? is a carboxy group,

5. 7. A method according to claim 5 or 6, in which a salt of a compound of formula 1 is formed. 15

6. 8. A method according to any one of claims 1 to 4, in which R 2 is an esterified carboxy group.

7. 9. A method according to any one of claims 1 to 4, in uhich R^ represents hydrogen and R 2 is -COOCH^Cl.

8. 10. A aethod according to aoy one of claims 1 to 4, in which R^ 20 represents bromine and Rj is -COOCHjCl.

9. 11. A method of producing a compound of the formula I defined in claim 1 substantially as hereinbefore described in any one of the foregoing Examples 1 to 7, 10 and 12 to 14.

10. 12. A compound of the formula I defined in claim 1 whenever produced 25 by the method claimed in any preceding claim.