GB2122603A - 7-Ä???-(substituted-thio)-acylamidoÜ-cephalosporanic acids - Google Patents

Abstract

7-Ä???-(substituted-thio)-acylamido-cephalosporanic acids of formula (A): <IMAGE> wherein R is a hydrogen atom or a substituted or unsubstituted carboxylic acid group, are prepared by the following reaction sequence: <IMAGE> Compounds (A) in which R is COOR% and R% is H, benzyl, Na, K or C1-4alkylamino are novel.

Description

SPECIFICATION Process for the preparation of 7-((substituted-thio)-acyIamido]-cephaIosporanic acids and products obtained This invention relates to a new process for the preparation of 7-(a-(substituted-thio)-acylamido]- cephalosporanic acids of the formula (A) TAKE IN HERE

wherein R may represent either a substituted or an unsubstituted carboxylic group or a hydrogen atom.

Compounds of formula (A) comprise also non toxic pharmaceutically acceptable salts thereof. The main scope of the present invention is to provide a new process for the preparation of cephapirin (formula A in which R = H) a valuable antibacterial agent useful in the treatment of infectious diseases caused by gram-positive and gram-negative bacteria. There are already known a few methods for the preparation of cephapirin, and namely: - Japan pat. publ. 26107/69 to FUJISAWA published on 1 sot November 1969. The process consists essentially in the reaction between 7-aminocephalosporanic acid or a salt thereof with (4-pyridylthio)-acetic acid in the presence of dicyclohexyl-carbodiimide as condensing agent. Unfortunately the yield is very low and no industrially rentable exploitation can be achieved.

- U.S. 3,422,100 to BRISTOL MYERS issued on 14th January 1969. The process consists essentially in the reaction between 7-ami-nocephalosporanic acid with bromoacetyl bromide and in the subsequent reaction of the intermediate 7-(a-bromo-acetamido)-cephalosporanic acid (as sodium salt) thus formed with 4-mercaptopyridine. Also according to this method the yields are rather poor as the crude cephapirin contains by-products which must be removed by complicated purification procedures.

It has now been surprisingly found a new process for the preparation of cephapirin which not only represents a remarkable improvement with respect of the methods of the "prior art", but it enables also the preparation of new compounds A in which R = -COOR' wherein R' may be hydrogen or -CH2 - C6H or Na-, K-, or lower alkylamine.

In fact a further object of the present invention is to provide this new class of compounds which are the intermediates for the manufacture of cephapirin, and at the same time useful end-products "per se" as antibacterials endowed with delayed release action in animals and humans in need of such treatment.

The process of the present invention can be represented by the following reaction scheme:

wherein M represents a lower alkylamine rest or an atom of an alkaline metal such as sodium or potassium.

It will be appreciated that certain of compounds IV and V of the present invention existin different optically active forms. The various stereoisomeric forms as well as the racemic mixtures are within the scope of this invention.

As it appears from the reaction scheme the process of the present invention consists essentially of three steps. 7-aminocephalosporanic acid as sodium or potassium salt dissolved in water, is reacted with an equimolar amount of bromomalonic acid monobenzyl ester monobromide (I) dissolved in a suitable water miscible solvent such as acetone in the presence of a slight excess of sodium or potassium bicarbonate as hydrogen bromide acceptor. The reaction is firstly carried out in the cols, 0 .-5C, and it may be completed at room temperature.

The solvent is then removed by distillation at 200+300C "in vacuo", the reaction mixture is diluted with water and thoroughly extracted with a water immiscible solvent such as ethyl ether or ethyl acetate, in order to remove traces of unreacted bromomalonic acid derivative (I), which can be recovered from the ethyl acetate extracts.

The aqueous, slightly alkaline reaction mixture in a separatory funnel is covered with a layer of ethyl acetate and under vigorous stirring is cautiously acidified to pH 2t3 with a dilute mineral acid such as sulfuric or phosphoric acid. Ethyl acetate extraction of the aqueous acidic layer is repeated two or three times. The combined ethyl acetate extracts are washed twice with water and then dried over anhydrous sodium sulfate. Upon filtration the ethyl acetate solution is treated with a solution of sodium or potassium 2-ethyl-hexanoate in n. butanol. The oily mass which forms is scratched to promote crystallization.

The resulting crystals are collected, washed with acetone, and dried "in vacuo" to give a sodium or potassium salt of 7-(2,-bromo-malonamido-3'-benzylester)-cephalosporanic acid (Ill).

To a water solution of this compound (III) 1 equivalent of sodium or potassium bicarbonate is added and the mixture is treated with 1 equivalent of 4-mercaptopyridine at room temperature and under vigorous stirring. When carbon dioxide evolution is over the reaction mixture is adjusted to pH2 with dilute phosphoric acid and thoroughly extracted with ethyl acetate. The ethyl acetate layer is discarded.

The aqueous acidic layer is then extracted with a solution of alkyl amine sulfonic acid and methyl isobutyl ketone, The combined extracts are concentrated "in vacuo" at 20"C to a reduced volume then treated with triethylamine under stirring and the reaction mixture is left overnight at room temperature to complete crystallization ofthe desired compound 7-[2'-(4-pyridylthio)-maloamido-3'-benzyl-ester]-cephalosporanic acid (IV).

This latter compound (IV) can be isolated as such and used as anti-bacterial agent or can be submitted to a catalytic hydrogenolysis to give the sodium, potassium or amine salts of the corresponding malonic acid derivative 7-[2'-(4-pyridylthio)-malonamido]-cephalosporanic acid (V), if the catalytic hydrogenolysis is carried out in the presence of an alkaline bicarbonate or in the presence of a lower alkylamine. Compound V can be easily isolated as salt, which in its turn could be employed as antibacterial agent.

If the catalytic hydrogenolysis is carried out in the presence of dilute hydrochloric acid 30 . 40 C there is a simultaneous splitting of the benzylic rest followed by decarboxylation of malonic acid to give cephapirin in good yield and high purity in one step by starting from (IV). From the reaction scheme it results evident that also the conversion Ve - VI can be easily carried out.

The following Examples illustrate the invention without limiting it: EXAMPLE 1 7-(2'-hromo-malonamido-3'-benzylester)-cephalosporanic acid (111) To a solution of 13,6 g of 7-aminocephalosporanic acid, 16,6 g of sodium bicarbonate in 100 ml of water and 50 ml of acetone cooled to 0 C with an ice bath 13,3 g of bromomalonic acid monobenzyl ester monobromide (I) dissolved in 70 ml of acetone were added with stirring. The temperature of the reaction mixture was kept at 00 - 5"C for 15 minutes, then the temperature was allowed to rise to 250C and the reaction mixture was kept under stirring for one hour.

The solvent was distilled off "in vacuo" at 20"C whereupon 100 ml of water were added and the resulting reaction mixture was transferred into a 1 liter-separatory funnel and extracted with 200 ml portions of ethyl ether and the extracts discarded. The aqueous layer was covered with 100 ml of ethyl acetate and vigorously stirred and cooled while being acidified to pH 2 - 3 with 30% phosphoric acid. After filtration the ethyl acetate extracts were washed twice with 40 ml portions of water and dried over anhydrous sodium sulfate.

The mixture was filtered and treated with a solution of 6,9 g of sodium ethylhexanoate in n. butanol.

The sodium salt of desired product crystallized.

The mixture was kept for one hour under stirring, filtered, the filter cake was washed with acetone and dried: 23,1 g of the title compound (III) as sodium salt were obtained.

EXAMPLE 2 7-[2'-r4-pyridylthio)-malonamido-3'-benzylesterl-cephalosporanic acid (IV) To a solution of 24.25 g of compound Ill obtained according to Example 1 in 130 ml of water containing 4,3 g of NaHCO3, 5,6 g of 4-mercaptopyridine were added with stirring at room temperature.

After 20 minutes, when evolution of carbon dioxide was over, the pH was adjusted to 2,2 with 30% H3PO4, the solution was extracted a few times with 50 ml portions of ethyl acetate and these extracts discarded.

The aqueous acidic layer was then extracted with a solution of 22,2 g of a long chain alkylamine sulfonic acid such as "aerosol OT" (Registered Trade Mark) and 280 ml of methyl isobutyl ketone. After separation of the two layers, the methyl isobutyl ketone layer was washed with water and dried over anhydrous sodium sulfate.

The mixture was filtered, the cake was washed with methyl isobutyl ketone, and the solution was concentrated at 20"C in vacuo to about 250 ml. and 7,1 g of triethylamine were added with stirring. The crystallized product was collected washed with methyl isobutyl ketone and ethyl ether and dried. 20,7 g of the title compound were obtained.

EXAMPLE 3 7-i2'-(4-py,idyIthio)-maIonamidoi-cephaiospoinic acid (V) as disodium salt 5,55 g of compound IV as obtained in Example 2 were dissolved in 40 ml of water containing 1,70 g of NaHCO3 and 0,5 g of catalyst 5% palladium on charcoal. The reaction mixture was hydrogenated at room temperature and under atmospheric pressure. After 2 hours, the mixture was filtered and the solution was concentrated 20"C "in vacuo" to about 12 ml and 45 ml of acetone were added. The reaction mixture was allowed to stand at +4"C overnight. The crystalline product was collected, washed with ice-cooled acetone and dried "in vacuo" to constant weight.

EXAMPLE 4 7-i-(4-pyndyitnio)-acetamidoi-cephalospornnic acid {Cepharin = compound Vl) 5,55 g of compound IV as obtained in Example 2 were dissolved in 40 ml of water containing 1,70 g of NaHCO3 and 0,5 g of catalyst 5% palladium on charcoal.

The reaction mixture was hydrogenated at room temperature and under atmospheric pressure.

After 2 hours the mixture was filtered and the solution was cooled to 5-10"C and acidified with dilute hydrochloric acid to pH2 with stirring. Temperature was allowed to rise to 35-40"C and the reaction mixture was kept at this temperature for 1 hour. The progressive disappearance of Compound V which is converting to the desired Compound VI could also be checked by T.L.C.

The reaction mixture was then extracted with 50 ml portions of ethylacetate and the extracts discarded.

To the aqueous layer a solution of 4,45 of "aerosol OT" (Registered Trade Mark which is explained in Example 2) in 60 ml of methyl isobutyl ketone were added and the desired cephalosporin compound (IV) was extracted. The methyl isobutyl ketone extracts were combined and washed with water and dried over anhydrous sodium sulfate.

The mixture was filtered, the filtration cake was washed with methyl isobutyl ketone, the resulting solution was concentrated at 20"C "in vacuo" to about 40 mland 1,37 g of triethylamine were added and the reaction mixture was allowed to stand at room temperature overnight. The precipitated product was filtered, washed with methyl isobutyl ketone and with ethyl ether and dried.

3,8 g of 7-[a-(4-pyridylthio)-acetamido]-cephalosporanic acid were obtained: its IR and NMR spectra were identical with the same spectra of a sample of cephapirin prepared according to known methods.

EXAMPLE 5 Cephapirin (Compound VI) Comparable good results for the preparation of cephapirin could be achieved when the disodium salt of Compound V was first isolated as shown in Example 3, then dissolved in water, acidified with hydrochloric acid and then submitted to decarboxylation by gentle warming up to 35"C.

EXAMPLE 6 Cephapirin (Compound Vl) 5,55 g of compound IV as obtained in Example 2 were suspended in 50 ml of H2O and concentrated hydrochloric acid was dropwise cautiously added with cooling and stirring so as to adjust the pH to 2, whereby the product dissolved completely, 0.5 g of catalyst 5% palladium on charcoal were added. The reaction mixture was hydrogenated at room temperature and under atmospheric pressure.

After 11/2 hours the mixture was cautiously warmed up to 35-40"C and kept at this temperature for a further 30 minutes with stirring.

The mixture was then filtered, the filtration cake washed with dilute hydrochloric acid.

The resulting solution was then worked up in the same manner as described in the second part of Example 4 (extraction with "aerosol OT" etc.). 3,5 g of 7-[a-4-pyridylthio)-acetamido]-cephalosporanic acid were obtained; its IR, NMR spectra and the other characterizing parameters were identical with those of an authentic sample of cephapirin prepared according to known methods.

Claims (11)

1. A process for the preparation of 7-[a-(substituted-thio)-acylamido]-cephalosporanic acids of formula (A):

wherein R is a hydrogen atom or a substituted or unsubstituted carboxylic acid group, comprising the following reaction sequence:

2. A process as claimed in claim 1, in which R = COOR' wherein R' is a hydrogen atom, a -CH2C6H5 radical, Na-, K- or a C1-C4 alkylamino radical.

3. A process as claimed in claim 1 or 2, substantially as hereinbefore described and exemplified.

4. A compound whenever prepared by the process as claimed in any preceding claim,

5. A process for the preparation of 7-[o-(4-pyridylthio)-acetamido]-cephalosporanic acid characterised in that 7-amino-cephalosporanic acid as its sodium or potassium salt is reacted with bromomalonic acid monobenzyl ester monobromide in the presence of a slight excess of sodium or potassium bicarbonate to give 7-(2'-bromo-malonamido-3'-benzyl ester)-cephalosporanic acid (III) as its sodium or potassium salt, and that this latter compound is reacted with 4-mercaptopyridine in the presence of sodium or potassium bicarbonate to produce 7-[2'-(4-pyridylthio)-maloriamido-3'-benzyl ester]-cephalosporanic acid (IV), and that this compound, in the presence of sodium or potassium bicarbonate, is submitted to a catalytic hydrogenolysis in the presence of 5% Pd-C at room temperature and under atmospheric pressure and that without isolating the intermediate V as di-alkaline salt, this latter compound is decarboxylated at 35-40"C in the presence of dilute hydrochloric acid to give 7-[-(4-pyridylthio)-acetamido]-cephalosporanic acid, which is isolated and purified in known manner.

6. A process as claimed in claim 5, substantially as hereinbefore described and exemplified.

7. 7-[oe-(4-pyridylthio)-acetamido]-cephalosporanic acid whenever prepared by a process as claimed in claim 5 or 6.

8. A 7-[a-(substituted-thio)-acylamido]-cephalosporanic acid of formula (A):

wherein R = COOR' wherein R' is a hydrogen atom, a -CH2C6Hs radical, Na-, K- or a C1-C4 alkylamino radical.

9. A compound as claimed in claim 8, substantially as hereinbefore described and exemplified.

10. 7-[2'-(4-pyridylthio)-malonamido-3'-benzyl-ester)-cephalosporanic acid,

11. 7-[2'-(4-pyridylthio)-malonamido]-cephalosporanic acid disodium salt.