GB2218093A - Cephalosporin carbamoylation - Google Patents

Description

4 1. 1 J is CHEMICAL PROCESS This invention relates to improvements in or

relating to cephalosporins. More particularly it relates to processes for the preparation of the oral antibiotic cefuroxime axetil.

Cefuroxime exetil the 1-acetoxyethyl ester of (6R,7R)-3carbemoyloxymethyl7-E(Z)-2-(fur-2-yl)-2-methoxyiminoacetamidoleeph -3-em-4-carboxylic acid (cefuroxime) is described in British Patent Specification No. 1571683. Cefuroxime axetil is a particularly valuable cephalosporin since it may be administered orally. The compound has been shown to possess good antibiotic activity, following oral administration, against a broad spectrum of gram-positive and gramnegative bacteria and has high stability to p-lactamases.

Cephalosporin esters may conventionally be prepared by the acylation of an appropriate 7-aminocephalosporin with a compound serving to introduce a preformed 7-substituent, or by esterification of the 4-carboxyl group of the corresponding cephalosporin 4-carboxylic acid, for example by reaction with a haloester to introduce the desired esterifying group. These general processes are described in British Patent Specification No. 1571683 for the preparation of cefuroxime axetil.

We have now devised a process for the preparation of cefuroxime exetil and protected derivatives thereof in which the carbamoyl group on the 3substituent of the cephalosporin nucleus is introduced as the last major chemical step in the synthesis, by a carbamoylation reaction.

According to one aspect of the invention, therefore, we provide a process for the preparation of compounds of general formula (I) H H Z C - CONH 0 N ---N CH OCONHR OCH3 0 2 CO0CHOCOCH 3 1 Uh3 (1) fi - 2 (wherein R represents a hydrogen atom or a labile substi- Ituent group, is 5 or S-3. 0 and the dotted line indicates that the compound is a ceph-2-em or ceph-3-em compound) which comprises reacting a compound of formula lkII) H H Z C CONH 0 N OCH3 0 // 'D \ '71 - CH20H 0 1 COO HOCOCH3 CH3 (I I) (wherein Z and the dotted line are as defined above) with a carbamoylating agent serving to introduce in one or more steps a carbamoyloxymnethyl or N-substituted carbamoyloxymethyl group at the 3- position.

Carbamoylation of 3-hydroxymethyl compounds of formula (II) may be effected by conventional methods using suitable acylating (i.e. carbamoylating) agents. Suitable carbamoylating agents include isocyanates of formula RaNCO (wherein Ra is a labile substituent group) which give a compound containing a 3-position substituent having the formula -CH20.CONHRa (wherein Ra has the above defined meaning).

A labile substituent group R or Ra present in the compounds of formula (1) or intermediates thereof is conveniently a group which may be readily removed at an appropriate stage in the reaction sequence, for example an acyl group (especially a lower alkanoyl group such as acetyl, a halosubstituted lower alkanoyl group such as mono-, di- or trichloreacetyl, a chlorosulphonyl or bromosulphonyl group, a dihalophosponyl group such as a dichlorophosphonyl group, or a halogenated alkoxycerbonyl group such as 2,2,2-trichlopoethoxy carbonyl).

The carbamoylation reaction,may desirably be effected in the presence of a solvent or solvent mixture selected from hydrocarbons (e.g. aromatic hydrocarbons such as benzene and toluene), halogenated hydrocarbons (e.g. dichloromethane), amides (e.g. formamide or dimethylformemide), esters (e. g. ethyl acetate), ethers (e.g. cyclic ethers such as tetrahydrofuran and dioxan), ketones (e.g. acetone), Q 1 1 r sulphoxides (e.g. dimethylsulphoxide) and mixtures of two or more of these solvents. The reaction may conveniently be carried out at a temperature of between -800C and the boiling temperature of the reaction mixture, for example up to 1000C, preferably between -200 and +300C.

The carbamoylating agent is desirably used in excess (for example at least 1.1 moles relative to the compound of formula (II)). The carbamoylation may be assisted by the presence of a base, e.g. a tertiary organic base such as a tri-(lower alkyl)amine (e.g. triethylamine) although such assistance may not be necessary in the case of more active isocyanates, e.g. compounds when R is a strongly electron-withdrawing group such as chlorosulphonyl or trichloroacetyl.

Another useful carbamoylating agent is cyanic acid, which is conveniently generated in sit, for example, from an alkali metal is cyanate such as sodium cyanate, the reaction being facilitated by the presence of an acid, e.g. a strong organic acid such as trifluoroacetic acid. Cyanic acid effectively corresponds to the isocyanate compounds mentioned above wherein Ra is hydrogen and therefore converts compounds of formula (II) directly to their 3-carbamoyloxymethyl analogues.

Alternatively, carbamoylation may be effected by reaction of the compound of formula (II) with phosgene, or carbonyldiimidazole followed by ammonia or an appropriately activated form thereof, optionally in an aqueous or non-aqueous reaction medium. The carbamoylating agent may thus be phosgene, or carbonyldiimidazole, and ammonia which are reacted successively.

The carbamoylation reaction may be followed where desired by conversion of the compound of formula (I) initially obtained into a different compound of formula (I), for example by means of one or more of the following reactions:- (i) reduction of a compound wherein Z is -,,, 0 to a compound wherein Z is S; conversion of a A2-isomer into a A3_ isomer; removal of any carbamoyl substituents.

The reactions may be effected by conventional methods, and in any convenient order.

Thus, if desired, a A2-cephalosporin obtained in accordance with the process of the invention may be converted into the corresponding A3-derivative by, for example, treatment of the A2ester with a base, such as pyridine or triethylamine.

A ceph-2-em reaction product may also be oxidised to yield corresponding ceph3-em 1-oxide, for example by reaction with a peracid, e.g. peracetic or m-chloroperbenzoic acid; the resulting sulphoxide may subsequently be reduced as described hereinafter to yield the corresponding ceph-3-em sulphide.

Where a compound of formula (I) is obtained in which Z is 5 + 0 this may, if desired, be converted into the corresponding sulphide by, for example, reduction of the corresponding acyloxysulphonium or alkoxysulphonium salt prepared in situ by reaction with e.g. acetyl chloride in the case of an acetoxysulphonium salt, reduction being effected by, for example, sodium dithionite or by iodide ion as in a solution of potassium iodide in a solvent e.g. acetic acid, acetone, tetrahydrofuran, dioxan, dimethylformamide or dimethylacetemide. The reaction may be effected at temperature from -200 to +500C.

Any labile substituent group R present in the compound of formula (I) may be removed, if desired, by any appropriate methods known in the art. Labile groups such as chlorosulphonyl, dichlorophosphonyl and trichloroacetyl may generally be cleaved by acid or base catalysed hydrolysis and halogenated groups such as 2,2,2-trichloroethoxycarbonyl may also be cleaved reductively, while groups such as chloroacetyl may also be cleaved by treatment with thioamides such as thiourea. For example a trichloroacetyl group may be cleaved by treatment with sodium formate in water optionally containing a water miscible solvent such as methanol or alternatively the group may be removed by treatment with silica in an organic solvent such as methylene chloride.

It should be noted that it may be convenient to retain the labile substituent or even introduce such a group during transformations of intermediate 3-carbamoYloxymethyl compounds in order to minimise unwanted side reactions involving the carbamoyloxymethyl group. Hence as a further feature of the invention we provide a process for the preparation of a compound of formula (I) in which R is hydrogen by removal of the labile substituent from an equivalent compound of formula (I) in which R is a 1 is labile substituent. The labile substituent group may be removed by use of the methods described above.

The reaction product may be separated from the reaction mixture, which may contain, for example, unchanged cephalosporin starting material and other substances, by a variety of processes including solvent extraction, recrystallisation, ionophoresis, column chromatography, high pressure liquid chromatography, ion-exchange chromatography or chromatography on macroreticular resins.

Where a compound of formula (I) is obtained as a mixture of isomers, the syn isomer may be obtained by conventional methods, such as crystallisation or chromatography. Also, the product may be recovered in a mixture with an approximately 1:1 mole ratio of R and S isomers of the esterifying group, for example, as described in UK Patent Specification No. 2145409.

A compound of formula (II) may be prepared, for example, by esterification of a compound of formula (III) 11 11 0 -C - \ / 11 0 N OCH, 0 H H Z CONH 20H UUUM (III) (wherein Z and the dotted line are as defined above) or a salt thereof, e. g. an alkali metal salt (such as the sodium or potassium salt) or an onium salt, e.g. an ammonium salt (such as a quaternary ammonium salt) with an appropriate haloester, for example, 1-acetoxyethyl bromide.

The reaction is conveniently effected in an inert solvent, for example, an N,N-disubstituted amide such as N,N-dimethylformamide, N, Ndimethylacetamide; a ketone such as acetone; a sulphoxide such as dimethylsulphoxide; a halogenated hydrocarbon such as dichloromethane; or a nitrile such as acetonitrile. The reaction may be carried out at a temperature in the range -500 to +1500, e.g. -100 to +500C, conveniently between -100 and room temperature.

i The esterification is generally carried out in the presence of an agent serving to generate an anion from the 4-carboxyl function, for example, a base such as an alkali metal carbonate (e.g. sodium or potassium carbonate).

A compound of formula (III) may be prepared, for example, by conventional acylation methods as described in British Patent Specification No. 1474520. A compound of formula I where R is a labile substituent group may be prepared by a carbamoylation reaction as described above or alternatively a conventional acylation process may be used, for example, as described in British Patent Specification No. 1571683.

The invention is exemplified by the following. All temperatures are in degrees Celsius. The term "dried" refers to drying over sodium sulphate or magnesium sulphate. Petrol refers to petroleum ether b.p. 40-600C.

Intermediate 1 Potassium (6R97R)-7-[(Z)-2-(fur-2-yl)-2-methoxyiminoacetemidol-3hydroxymethyleeph-3-em-4-carboxylate A solution of (6R,7R) 7-[(Z)-2-(fur-2-yl)-2-methoxyiminoacetamidol-3hydroxymethyleeph-3-em-4-carboxylic acid (10.04g) in ethanol (150 ml) at about 400 was clarified by filtering through Kieselguhr. The filtrate was treated dropwise with a 0-5M solution of potassium acetate (52.6ml) over 20 minutes. The crystallising mixture was cooled to 40 during 1.5 hour and was filtered. The solid was washed with ethanol (3 x 40 ml), ether (2 x 40 ml) and was dried at about 1 mm Hg and 200 over phosphorus pentoxide for 20 hours to give the title compound (11.11g); X (ethanol) 275 nm (El 446) max 1 Intermediate 2 (6R,7R)-7-(2-Thienylacetamido)-3-(trichloroacetylearbamoyloxyinethyl) ceph-3-em-4-carboxylic acid Trichloroacetylisocyanate (4.3m1) was added rapidly to a stirred suspension of (6R,7R)-3-hydroxymethyl-7-(2-thienylacetamido)ceph-3- 0 is em-4-carboxylic acid (10.62 g) at 60 in ethyl acetate (70 ml). The reaction mixture was stirred at 50 for 40 minutes. Petrol was added dropwise during 15 minutes. The mixture was stirred for 30 minutes, filtered and the solid was washed with petrol and dried to give the title compound as a solid (16.48 [a] 22 + 730 (c 1.2 in Me2So) D - Intermediate 3 (R and 5)-1-Acetoxyethyl (6R,7R)-7-(2-thienylacetamido)-3- (trichloro acetylcarbamoyloxymethyl)ceph-3-em-4-carboxylate.

A solution of intermediate 2 (218 g) in dimethylformamide (1500 ml) was stirred under nitrogen with potassium carbonate (27.6 g) at less than 200 for 1 hour. The solution was cooled to 30 and stirred with (R,S)-1acetoxyethyl bromide (80 ml added in 3 portions at hourly intervals) for a total of 3 hours at 30. The mixture was poured into ice-cold 2Mhydrochloric acid (5 1) and extracted with ethyl acetate (3 x 2.5 1). The organic layers were combined and washed with cold 2M-hydrochloric acid (2 x 2.5 1), cold water (2.5 1), cold 3% sodium bicarbonate solution (2 x 2. 5 1), and water (2.5 1). The organic layer was dried and evaporated to a gum, which was stirred with petrol (b.p. 60-800, 1 1) containing a little ethyl acetate to give the title compound as a solid (175 g); 6 (MC13) 91 (1H, broad s), 7.9 to 6.6 OH, m), 5.9 (1H, m), 5.4 to 4.8 (3H, m), 3.8 (2H, s), 3.6 (2H, m), 2.02 (3H s) and 1.5 (3H, d).

Intermediate 4 (R and S)-1-Acetoxyethyl (6R,7R)-7-amino-3(trichloroacetylearbamoyl,oxymethyl)eeph-3-em-4-carboxylate hydrochloride salt Phosphorus pentachloride (41.73 9) was stirred in dichloromethene (400 ml) until the solution was almost clear. This was cooled in an ice bath and treated dropwise with pyridine (16.1 ml). When the temperature of the mixture was 50 Intermediate 3 (62.85 g) was added and the mixture was stirred at less than 100 for 2 hours. This solution was added to a stirred solution of methanol (70 ml) in dichloromethane (170 ml) over 30 minutes at -40 to -300.After 1 minutes the solution was warmed to -100 and stirred with water (200 ml). The mixture was stirred without cooling for 30 minutes and separated. The aqueous layer was extracted with dichloromethane (2 x 100 ml) and the organic layers were combined and evaporated to a gum, which was triturated with ether to give the title compound as a solid (40.3 g); 6 (DMSO-d6) 6.9 (1H1m), 5.3 (2H,m), 5.1 (2H,m), 3.8 (2H,m), 2.04 (3H,s) and 1.5 (3H,d).

Intermediate 5 (R and 5)-1-Acetoxyethyl (6R97R)-7-amino-3(trichloroacetylearbamoyl oxymethyl)ceph-3-em-4-carboxylic acid A solution of Intermediate 4 (40 g) in dichloromethane (250 ml) was shaken with a solution of sodium bicarbonate (6.82 g) in water (100 ml). The organic phase was separated and washed with dilute sodium bicarbonate solution, water and dried. Following charcoal treatment the solvent was removed to give the title compound as a foam (31.3 g); 6 6.9 and 6.7 (1H, m), 4.92 (2H, broad s) 5.0 and 4.6 (2H), 3.9 to 3.4 (2H), 2.00 (3H,s) and 1.42 (3H9d) Example 1 (R and S)-1-Acetoxyethyl (6R,7R)-3-Carbamoyloxymethyl-7[(Z)-2(fur-2-yl)-2-methoxyiminoacetemidoleeph -3-em-4-carboxylete A suspension of the product of Intermediate 1 (2.159) in dimethylformamide (100 ml) was stirred with (R,S)-1-acetoxyethyl bromide (1.169) under nitrogen at and then at between -10 and 00 for 45 minutes. The solution was cooled to -100 and stirred with chlorosulphonyl isocyanate (1.0m1) for 5 minutes at -100, then at 00 for 30 minutes. The solution was poured into a mixture of ice (200 g) M hydrochloric acid (200m1), and ethyl acetate, which was stirred for 90 minutes. The mixture was separated and the aqueous layer was extracted with ethyl acetate. The organic layers were combined, washed with 2M-hydrochloric acid, water (2x), saturated sodium bicarbonate solution (2x), and water and was stirred with sodium thiosulphate solution. The organic layer was separated and washed with water (2x) and brine (2x) and was dried and evaporated. A solution of this gum in ethyl acetate (30 ml) was added to petrol (500 ml) to give a white solid (869 mg). Part of this solid (797 mg) was chromatographed on silica (40 g) eluting initially with dichloromethane-ethyl acetate (4d) and then with dichloromethane-ethyl acetate (3:1). Appropriate fractions were combined and evaporated to yield a gum which was dissolved in ethyl acetate and added to petrol to give the title compound as a solid (93 mg) which was identical to an authentic sample of cefuroxime axetil by HPLC.

Elution of the column with dichloromethane-ethyl acetate (3:2) gave more of the title compound as a white solid (146 mg).

Example 2 (R and S)-1-Acetoxyethyl (6R,7R)-7-[fur-2-yl)-2-methoxyiminoacetamidol-3-trichloroacetylcarbamoyloxymethylceph-3-em-4-carboxylete.

Method a A suspension of the product of Intermediate 1 (2.23 9) in dimethylformamide (100 ml) at -100 under nitrogen was stirred with M,S)-1-acetoxyethyl bromide (1.201 g) for 1 hour to give a solution of (R and 5)-1-acetoxyethyl (6R,7R)-7-[(Z)-2-(fur-2-yl)-2 methoxyiminoacetamido]-3-hydroxymethyleeph-3-em-4-carboxylate.

Trichloroacetyl isocyanate (1.8 ml) was added to this solution under nitrogen at -100. The solution was stirred at -100 for 5 minutes then at about 00 for 25 minutes. It was poured into a mixture of ice (2009), 2M hydrochloric acid (200 ml), and ethyl acetate (100 ml).

This was stirred for 30 minutes and separated. The aqueous layer was extracted with ethyl acetate (2 x 100 ml), and the organic layers were combined and washed with 2M hydrochloric acid (2 x 100 ml), water (1x), saturated sodium bicarbonate solution, (diluted 1:1, 2x), sodium thiosulphate solution (1 wash, 1 stirred wash), water, and brine (2x).

The organic layer was dried and evaporated to a foam, which was dissolved in ethyl acetate (20 ml) and added to petrol (500 ml) to give the title compound as a solid (1.898g); X (ethanol) 275.5 nm (E 333).

max 6 (MC13) 7.51 (1Hgs), 7.28 (1H, d J 8Hz), 7.13 and 6.98 (1H, q J 6 Hz), 6. 89 (1H, m), 6.48 (1Hgm) 5.98 (1H,m), 5.4-4.8 (3H,m), 4.02 (3H,s), 3.80 and 3.60 (2H,m), 2.04 (3-H,s) and 1.56 (3H,d J 6Hz) Method b A solution of Intermediate 5 (1.01 g) and Q)-2(fur-2-yl)2methoxyiminoacetie acid (0.34 9) in dichloromethane (20 ml) was stirred at 200 with dicyclohexylcarbodiimide (0.45 g) for 45 minutes. Water (20 ml) was added and the mixture was stirred for 15 minutes at 200 and separated. The organic layer was chromatographed on a column of Sorbsil (10 g) made up in dichloromethane. Fractions eluted with 10% ethyl acetate in dichloromethane were combined and evaporated to a solid. This was triturated with petrol (b.p. 600-800) containing ethyl acetate to give the title compound as a solid (1.2 g).

Example 3 Method a (R and S)-1-Acetoxyethyl (6R,7R)-3-Carbamoyloxymethyl7-[(Z)-2(fur-2-xl)-2-methoxyiminoacetamidoiceph-3-em-4-carboxylate A solution of the product of Example 2a, (911 mg) in methanol (15 ml) was stirred with a solution of sodium formate (280 mg) in water (1 ml) at 200 for 2.25 hours. The solution was poured into a mixture of ethyl acetate and dilute sodium bicarbonate solution, and the aqueous layer was extracted twice more with ethyl acetate. The organic layers were combined, washed with water (2x), brine (2x) and then dried and evaporated to give a foam. A solution of this foam in ethyl acetate (10 ml) was added to petrol (400 ml) to give a solid product (520 M9).

Part of this solid (462 mg) was chromatographed on silica (27g) eluting initially with dichloromethane-ethyl acetate (4:1) (fractions discarded) and then with dichloromethane-ethyl acetate (3:1). Appropriate fractions were combined, evaporated, and the residue taken up in ethyl acetate. The solution was added to petrol to give the title compound as a white solid (162 mg) which was identical to a reference sample of cefuroxime axetil by HPLC 1 1 W j k Method b A solution of the product of Example 2 (785 mg) in dichloromethane was stirred with silica (10 9) for about 15 minutes. The solvent was evaporated and the coated silica loaded onto a column of silica (40g) in dichloromethane-ethyl acetate (4:1). The column was eluted with dichloromethane-ethyl acetate (4:1 and 3:1) to give fractions which were discarded. Dichloromethane-ethyl acetate (3:2, then 1:1) eluted fractions which were combined to give the title compound as a foam (0.28 g) identical to a reference sample by HPLC.

j 1 1 QT 52-871

Claims (12)

1. CLAIMS:

   A process for the preparation of compounds of general formula (I) H H Z C - CONH 0 N \ OCH 3 0 # CH20CONHR COOCHOCOCH, 1 Lh3 (I) (wherein P, represents a hydrogen atom or a labile substituent group, Z is S or -SOand the dotted line indicates a ceph-2-em or ceph-3-em compound) which comprises reacting a compound of formula (II) H H Z C CONH 0 N //---N\ CH20H OCH 3 0 COTOCOCH3 CH3 (11) (wherein Z and the dotted line are as defined above) with a carbamoylating agent serving to introduce in one or more steps a carbamoyloxymethyl or Nsubstituted carbamoyloxymethyl group at the 3- position, followed where desired by conversion of the compound of formula (I) initially obtained into a different compound of formula (1) by.means of one or more of the following reactions:- i z 13 - (i) reduction of a compound wherein Z is -SO- to a compound wherein Z is S; 2.

   (ii) conversion of a A -isomer into a 3. A6-isomer; (iii) removal of any carbamoyl substituents.
2. 2. A process as claimed in claim 1 wherein the carbamoylating agent comprises an isocyanate of formula R aNCO, wherein Ra represents a labile substituent group; or cyanic acid.
3. 3.

   A process as claimed in claim 2 wherein the carbamoylating agent comprises a compound of formula RaNCO, in which Ra represents an acyl group.
4. 4.

   A process as claimed in claim 3 wherein the carbamoylating agent comprises chlorosulphonyl isocyanate or trichloroacetyl isocyanate.
5. 5. A process as claimed in claim 1 wherein the carbamoylating agent comprises phosgene or carbonyldiimidazole and ammonia which are reacted successively.
6. 6. A process for the preparation of compounds of general formula (I) C- m 1 6 - 0 H H Z C - CONH 11 1 1 N ----N j- CH20CONHR OCH3 0 (I) COOCHOCOCH 3 1 UM 3 (wherein R represents a hydrogen atom, Z is S or -SO- and the dotted line indicates that the compound is a ceph-2-em or ceph-3-em compound) which comprises the step of removing the labile substituent from a corresponding compound of formula (I) in which R is a labile substituent.
7. 7. A process as claimed in claim 6 wherein the labile substituent is removed by acid or base catalysed hydrolysis, reductive cleavage or treatment with a thioamide.
8. 8. A process as claimed in claim 6 or claim 7 wherein the compound of formula (I) is first prepared by a process as claimed in any of claims 1 to 5.
9. 9. A process as claimed in any of claims 1 to 5 wherein a compound of formula (II) in which Z represents S and the dotted line indicates a ceph3-em compound is reacted with the said carbamoylating agent.
10. 10. A process for the preparation of compounds of general formula (I) as defined in claim 1, substantially as herein defined in any of the Examples.
11. 11. Compounds of general formula (I) as defined in claim 1, when prepared by a process as claimed in any of the preceding claims.
12. 12. Cefuroxime axetil, when prepared by a process as claimed in claim 9.

    Published 1989 at The Patent Office, State House, 66/71 High Halborn. London WC1R 4TP. Purther copies maybe obtained from The Patent Office Sales Branch, St Mary Cray. Orpington, Rent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent, Con. 1/87 jp S!