GB2042508A

GB2042508A - 3-alkoxy penem derivatives

Info

Publication number: GB2042508A
Application number: GB7937756A
Authority: GB
Original assignee: Beecham Group PLC
Current assignee: Beecham Group PLC
Priority date: 1979-02-14
Filing date: 1979-10-31
Publication date: 1980-09-24
Also published as: GB2042508B

Abstract

The compounds of the formula (II): <IMAGE> and their salts and cleavable esters wherein R1 is an optionally substituted alkyl group are anti-bacterially effective compounds. Their preparation and use is described.

Description

SPECIFICATION p-lactam antibacterial agents, their use in pharmaceutical compositions, processes for their preparation and intermediates for use in such processes Belgian Patent No. 866845 and European Published Application No. 0,û0,636A disclosed that the compounds of the formula (I):

where R was inter alia an optionally substituted alkyl group possessed antibacterial activity. Belgian Patent No. 866845 also disclosed that the compounds of the formula (I) wherein R is inter alia alkylthio, aralkyithio or arylthio also possessed antibacterial activity. No disclosure was made of compounds containing other than a carbon, sulphur or hydrogen atom attached to the 2-position carbon atom nor was any process described which could lead to the preparation of such compounds.It has now been found that it is possible to prepare compounds of the formula (I) wherein the 2-position substituent is linked via an oxygen atom.

Such compounds have been found to possess antibacterial activity.

Accordingly the present invention provides the compounds of the formula (ill):

and salts and cleavable esters thereof wherein R1 is an optionally substituted alkyl group.

It is believed that the compounds of the formula (11) or their salts are the antibacterially active species and that biologically cleavable esters thereof act as pro-drugs. Thus in one favoured aspect this invention provides the compounds of the formula (ll) wherein R1 is as hereinbefore defined and pharmaceutically acceptable salts thereof. Non-pharmaceutically acceptable salts of the compounds of the formula (II) also form part of this invention since they may be used as chemical intermediates, for example in the preparation of pharmaceutically acceptable salts by ion-exchange. Thus suitable salts of the compounds of the formula (II) include the lithium, sodium, potassium, calcium and magnesium salts and salts of nitrogenous bases.

Particularly suitable salts of this invention include the sodium and potassium salts. Antibacterially active esters of the compounds of the formula (II) are believed to be those cleavable by in-vivo hydrolysis to the compounds of the formula (II) or their salt. Such esters may be identified by administration to a test animal such as a rat or a mouse by intravenous administration and thereafter examining the test animal's body fluids for the presence of the compound of the formula (II) or its salt.

Suitable esters of this type include those of the part formulae (a) and (b): -co-o-cHA1-o-CQ-A2 (a)

wherein A1 is a hydrogen atom or a methyl group, A2 is an alkyl or alkoxyl group of 1 * 4 carbon atoms or a phenyl group, A3 is a hydrogen atom or a methyl or methoxyl group, and A4 is a hydrogen atom or a methyl or methoxyl group. Other esters of the compounds of the formula (II) of interest are those cleavable by chemical methods as described hereinafter.

Suitable optionally substituted alkyl groups for R1 are those which contain up to 12 carbon atoms and which optionally also contain up to 4 heteroatoms selected from oxygen, nitrogen, sulphur or chlorine and bromine atoms.

Apt groups of the formula R1 include alkyl groups of up to 4 carbon atoms; alkenyl groups of up to 4 carbon atoms; alkyl groups of up to 4 carbon atoms substituted other than on the a-carbon atom by an amino or acetylamino group; alkyl group of up to 4 carbon atoms substituted by an alkoxycarbonyl group wherein the alkoxyl part contains up to 4 carbon atoms; alkenyl groups of up to 4 carbon atoms substituted other than on the a-carbon atom by an acetylamino groups; alkenyl groups of up to 4 carbori atoms substituted by an alkoxycarbonyl group wherein the alkoxyl part contains up to 4 carbon atoms; a benzyl group; or a benzyl group substituted by a methyl, amino, alkoxycarbonyl wherein the alkoxy part contains up to 4 carbon atoms, acetamido or methoxyl group, or by a chlorine or bromine atom.

R1 groups worthy of mention include the methyl, ethyl, n-propyl, ss-aminoethyl and ss-acetamidoethyl groups.

The present invention also provides a pharmaceutical composition which comprises a compound of the formula (II) or a pharmaceutically acceptable salt or in-vivo hydrolysable ester thereof and a pharmaceutically acceptable carrier.

Most suitably the composition of this invention comprises a compound of the formula (II) or a pharmaceutically acceptable salt thereof. It is particularly suitable that the compositions of this invention comprises a sodium or potassium salt of a compound of the formula (II).

The compositions of this invention may be in a form suitable for injection or for oral administration such as tablets or capsules. In general such compositions are in unit dose form and contain from 50 mg to 1000 mg and more usually from 100 mg to 500 mg. Such compositions may be administered once or more times per day so that the daily dose for a 70 kg adult is in the range of 500 mg to 2500 mg.

The compositions of this invention may be formulated in the manner of known antibiotics such as ampicillin. Thus for example an injectable solution may be prepared by dissolving 100 mgs of a sodium salt of a compound of the formula (II), for example that where R1 is a methyl group, in sterile water for injection BP. Alternatively, such a compound may be formulated into a tablet or capsule in standard manner with such excipients as lubricant, disintegrant, filler, binder or the like, for example magnesium stearate, microcrystalline cellulose, sodium starch glycollate, polyvinylpyrrolidone, polyvinylpolypyrrolidone or the like.

The compositions of this invention may also comprise a penicillin or cephalosporin if desired. Amoxycillin, for example as the trihydrate or sodium salt, is particularly apt for use in such mixed compositions.

In a process aspect this invention provides a process for the preparation of an ester of a compound of the formula (II) as hereinbefore defined which process comprises the ring closing elimination of the elements of triphenylphosphinesulphide from a cleavable ester of a compound of the formula (III):

wherein R1 is a group Rz as defined in relation to formula (II) in which any amino group present has been protected, and thereafter removing the protecting group from any amino group present and cleaving the ester if desired to yield the compound of the formula (II) or its salt.

The elimination of the triphenylphosphinesulphide is brought about by heating the monocyclic compound in an inert solvent such as xylene, for example at 140"C. The desired ester may be obtained by evaporation of the solvent and may thereafter be purified chromatographically, for example over silica gel eluting with ethyl acetate/petroleum ether.

A particularly suitable cleavable ester for use in this process is the p-nitrobenzyl ester which maybe cleaved to yield the corresponding acid by catalytic hydrogenation. A suitable catalyst is palladium, for example 5% palladium on charcoal. In general an atmospheric pressure of hydrogen is suitable. The reaction may be carried out in a conventional solvent such as aqueous dioxan or the like.

Once formed the acid of the formula (II) may be converted into a salt in conventional manner, for example by neutralisation with a lithium, sodium, potassium, calcium or magnesium hydroxide, carbonate or bicarbonate or by treatment with one equivalent of a nitrogenous base.

The esters of the compounds of the formula (III) may be prepared as outlined in Scheme 1 hereinafter.

Thus the ester of a compound of the formula (III) may be prepared by the reaction of a corresponding ester of a compound oftheformula (IV):

wherein R1 is as defined in relation to formula (Ill) with thionyl chloride and then with triphenylphosphine.

The chlorination normally takes place at a depressed temperature such as -20" whereas the phosphonylation takes place at an elevated temperature such as 60"C. Both reactions take place in an aprotic medium such as tetrahydrofuran or dioxane. In the first step one equivalent of a tertiary organic base such as lutidine should be present and thereafter a further equivalent may be used if desired.

The ester of the compound of the formula (IV) may be prepared by the reaction of the corresponding ester of g lyoxylic acid with a compound of the formula (V):

wherein R1 is as defined in relation to formula (IV).

The preceding condensation is normally carried out under conditions which remove water, for example in benzene under reflux using a water separator.

The compound of the formula (V) may be prepared by the reaction of 4-acetoxyazetidin-2-one with a compound of the formula (VI): K.S.CS.OR'j (Vl) wherein R1 is as defined in relation to formula (V).

The reaction is normally carried out in a two phase system of methylene chloride/water at an approximately ambient temperature such as 15 - 20 .

The compounds of the formulae (IV) - (V) are useful intermediates and as such form a part of this invention.

(R* is a group such that CO2R* is a cleavable ester) The processes of this invention generally lead to the preparation of compounds of racemic at C-5. It is believed that the more active isomer is that of the formula (VII):

and salts and cleavable esters thereof wherein R1 is as defined in relation to formula (II).

When used herein the term "alkyl" includes straight chain alkyl, branched chain alkyl and cycloalkyl.

Additionally when used herein alkenyl or aralkyl groups (for example the allyl or benzyl groups) are regarded as alkyl substituted by alkenyl or aryl (for example methyl substituted by vinyl or by phenyl).

In the following illustrative examples all column chromatography was carried out using Merck Silica gel 60 (7729). Petroleum ether means petroleum ether b.p. 60- 80 . PNB means p-nitrobenzyl.

EXAMPLE 1 4-Ethoxythiocarbonylthioazetidin-2-one

To a stirred solution of acetoxy-azetidinone (e1) (130 mg) in dichloromethane (10 ml) was added at room temperature, a solution of potassium ethyl xanthate (180 mg) in water (10 ml). After 15 mins stirring the organic layer was separated, washed with water, dried (MgSO4) and evaporated to give the desired ethoxythiocarbonylthioazetidinone (e2) as a white solid in theoretical yield (190 mg).This was recrystallised from ethyl acetate - petroleum ether to give white needles (120 mg, 63%) mp. 117 . (Found: C,37:69; H, 4.80; N, 7.13; S, 33.50. C6HgNO2S2 requires C,37.70; H, 4.71; N, 7.33; S,33.51 %). ssmax (EtOH) 276 (Em = 11,000) vmax (CHCI3) 3420,3250 (b) 1780 cm-l. 6ppm (CDCI3) 1.47 (3H, t, J = 7 Hz), 2.98 (1 H, ddd, J, 15,3, 1 Hz), 3.51 (1H, ddd, J, 15, 5, 2Hz), 4.69 (2H, q, J, 7 Hz), 5.40(1H, dd, J, 5, 3 Hz), 7.07(1H, b.s, exch D20).

EXAMPLE 2 1-(1-p-Nitrobenzyloxycarbonyl- 1-hydroxymethyl)-4-ethoxythiocarbonylthioazetidin-2-one

The azetidinone (e2) (1.6 g) was refluxed overnight with p-nitrobenzyl glyoxylate (2.7 g, 1.5 eq) in benzene (100 ml) with constant removal of water. The mixture was concentrated and chromatographed on silicagel to give the desired hydroxyester (e3), (2.4g,72%) as a gum, a mixture of diastereoisomers vmax (CHCI3) 3520, 3400(b), 1780, 1755 (sh)cm ppm (CDCI3),1.30 (3H, t, J, 7Hz), 3.04 and 3.07 (1H, 2dd, J, 15,3Hz), 3.56(1 H, dd J, 15, 5 Hz), 4.16 (1 H, b.s, exch D2O,) 4.63 (2H, q, J, 7 Hz) 5.28 and 5.34 (2s), 5.55 (b.s, sharpens with D2O), 5.65 and 5.71 (2 dd J 5,3 Hz), together 4H, 7.53 (2H, d, J, 9Hz), 8.2 (2H, d, J, 9Hz).

EXAMPLE 3 1-r1-p-Nitrobenzyloxycarbonyl- 1-triphenylphosphoranylidenemethyl)-4-ethoxythiocarbonylthioazetidin-2- one

The hydroxyester (e3) (1.3g) in tetrahydrofuran (30 ml) at -15 was treated first with lutidine (0.52 g) followed by thionyl chloride (0.36 ml) dissolved in tetrahydrofuran (10 ml). After 1/2 hr. the mixture was allowed to reach r.t. Toluene (.5ml) was added and the mixture was filtered and evaporated in vacto give the chloride as a gum.

The crude chloride was heated with dioxan (50 ml) and triphenylphosphine (1.3 g) at 50 overnight. Solvent was removed in vac and the residue was partitioned between ethyl acetate and aqueous sodium hydrogen carbonate solution. The ethyl acetate layer was separated and washed successively with N/10 hydrochloric acid, sodium hydrogen carbonate solution, and brine.

The solution was then dried (MgSO4) and evaporated in vac, and the residue chromatographed on silicagel, eluting with ethyl acetate/petroleum ether.

The phosphorane (e4) was isolated as a pale cream amorphous solid (1.15 g, 50%) vmax (CHCI3) 1755, 1625, 1610cm1.

EXAMPLE 4 p-Nitrobenzyl 2-ethoxypenem-3-carboxylate

The phosphorane (e4) (1.7g) was refluxed 10 hr in xylene (500 ml) then the solution was concentrated and chromatographed on silicagel, eluting with ethyl acetate/petroleum ether. The desired penem ester (e5) (95 mg, 10%) was separated and unchanged phosphorane (1.5g) was recovered.The recovered phosphorane was treated as before to give a further portion (52 mg, 5.5%) of the desired penem ester (e5) Xmax (EtOH) 308, 271 hm, vmax. (CHCl3) 1800,1705cm-1. 5ppm (CDCl3) 1.42 (3H, t, J, 9 Hz), 3.40 (1H, dd, J, 16, 2 Hz), 3.80 (1 H, dd, J, 16,4Hz), 4.24 (dq, J, 9.2Hz, 5.17 and 5.43 (2H, AB q, J, 12Hz), 5.63 (1 (1H, dd, J 4,2Hz), 7.55 and 8.15 (4H, 2 d, J 8 Hz).

EXAMPLE 5 2-Ethoxypenem-3-carboxylic acid

p-Nitrobenzyl 2-ethoxypenem-3-carboxylate (e5) (52 mg) in dioxan (4 ml) and water (1 ml) was hydrogenated over 5% palladised charcoal (50 mg) at atmospheric pressure/room temperature for 11/2 hr. A further portion (45 mg) of catalyst was added and hydrogenation continued for a further 1 hr. Sodium hydrogen carbonate (12 mg in 1.2 ml water) was then added and the mixture was filtered (Kieselguhr). The filtrate was evaporated to low bulk in vacuo, the residue was dissolved in water (20 ml) and washed with 2 x 20 ml ethyl acetate, adding a little brine to break the emulsion. The aqueous layer was evaporated to low bulk and chromatographed on 'Bio Gel P2' eluting with water and collecting fractions with u.v. absorbance at 306 nm.

These combined fractions were acidified (pH 2.5) with citric acid and extracted with 2 x 10 ml ethyl acetate.

The ethyl acetate layers were combined, washed with a little water, dried (MgSO4) and evaporated in vacuo to give the penem acid as an amorphous cream solid (5.7 mg, 18%) Amax (EtoH) 306 nm (Em = 4000) Vmax lCHCl3l31OO-2800, 1795, 1730, 1670, 1670cm1.

The minimum inhibitory concentration of this compound to inhibit the growth of the following bacteria are: Fgiml ORGANISM AGAR1 BROTH2 Citrobacterfreundii E8 12.5 Enterobacter cloacae N1 12.5 Escherichia coli 0111 12.5 16 Escherichia coli JT39 12.5 31 Klebsiella aerogenes A 6.2 16 Proteus mirabilis C977 25 31 Proteus morganii 1580 50 Proteus rettgeri WM16 50 Proteus vulgaris WO91 25 Pseudomonas aeruginosa A 50 125 Salmonellatyphimurium CT10 12.5 Serratia marcescens US20 25 Shigella sonnei MB 11967 25 Bacillus subtilis A 3.1 Staphylococcus aureus Oxford 1.6 4.0 Staphylococcus aureus Russell 3.1 16 Staphylococcus aureus 1517 50 Streptococcus faecalis 1 > 50 Streptococcus pneumoniae CN33 60.1 Streptococcus pyogenes CN10 0.4 C. albicans 1.6 1. DST agar + 10% horse blood inoculum 0.001 ml of a 10-2 dilution for G + ve 2. Microtitre using Nutrient broth bacteria ora 10-4 dilution for G-ve organisms EXAMPLE 6 4(2-p-Nitrobenzyloxycarhonylaminoethoxy)thiocarbonylthioazetidin-2-one

p-Nitrobenzyl 2-hydroxyethylcarbamate (6.1 g) in tetrahydrofuran (200 ml) at -60'was treated with a 1.6 molar solution of n-butyl lithium in hexane (15.9 ml) and then allowed to reach room temperature. Carbon disulphide (10 ml) was added and the mixture was stirred for 30 min and then evaporated to dryness at room temperature.The yellowish residue was stirred with dichloromethane (200 ml), acetoxyazetidinone (3.3 g) and water (100 ml) for 30 min, then the dichloromethane layer was separated, and evaporated. The residue was partitioned between ethyl acetate and dilute aqueous citric acid solution and the ethyl acetate layer was separated, dried (MgS04) and evaporated.The residue was chromatographed on silica gel, eluting with ethyl acetate to give the desired azetidinone (e7) (2.73g, 27%) as an amorphous cream solid. Vmax (CHCl3) 3450, 3420, 1780, 1725 cm-l bppm 2.93 (1H, dd, J 16,2 Hz) 3.5 (dd,J16,5 Hz) 3.5 - 3.85 (m) together 3H, 4.3 - 4.9 (2H, m) 5.23 (s) 5.36 (dd, J 5, 3 Hz) together 3H, 5.72 (1 H, b.t., J 6Hz, slow exch. with D2O) 7.4 (b.s. exch. D2O) 7.52 (d, J 9 Hz) together 3H, 8.25 (2H, d, J 9 Hz Ar).

EXAMPLE 7 ,-( l-p-Nitrobenzyloxycarbonyl- l-hydroxymethyl)-4-(2-p-nitrobenzyloxycarbonylaminoethoxy)thiocarbonyl.

thioazetidin-2-one

The azetidinone (e7) (2.85 g) was refluxed for 48 hr. with p-nitrobenzylglyoxylate (3.4 g) in benzene (200 ml) with constant removal of water. The mixture was concentrated and chromatographed on silica gel to give the hydroxy ester (e8) as a gum, a mixture of diastereoisomers (3.54 g, 80%). Vmax (CHCI3) 3510, 3450, 3350(b), 1780, 1755, 1720 cm-'.

EXAMPLE 8 l-(l-p-Nitrobenzyloxycarbonyl- 1-triphenylphosphorarylidenemethyl)-4-(2-p-nitrobenzyloxycarbonylamino- ethoxy)thiocarbonylthioazetidin-2-one

The hydroxy ester (e8) (3.54 g) in tetrahydrofuran (100 ml) at -15" was treated first with lutidine (1.28 g) followed by thionyl chloride (0.88 ml) diluted with tetrahydrofuran (10 ml). After 30 min. the mixture was allowed to reach room temperature. Toluene (20 ml) was added and the mixture was filtered and evaporated to give the chloride as a gum, Vmax (CHCI3) 1785, 1750, 1725 cm-1.

The chloride was then heated with triphenylphosphine (2.34 g) and lutidine (0.96 g) in dioxan (100 ml) at 60 overnight. The reaction mixture was worked up as in Example 3 to give chromatographically purified phosphorane (e9) (2.86g 57%) as a white amorphous solid Vmax (CHCI3) 3450, 1750,1720, 1620, 1600 cm-1.

EXAMPLE 9 p-Nitrobenzyl 2-(2-p-nitrobenzyloxycarbonylaminoethoxyl)-penem-3-carboxylate

The phosphorane (e9) (20 g) was refluxed in xylene (1500 ml) then the solution was concentrated and chromatographed on silica gel, eluting with dichloromethane/ethyl acetate mixtures.

The ester was obtained as a white amorphous solid (300 mg 8%) Xmax (EtOH) 314 n.m. (Em 8,200) Vmax (CHCl3) 3450, 1795, 1720, 1705 cm-l, ppm (CDCl3) 3.45 (dd, J 15, 2 Hz), 3.57 (m, collapsing with D2O tot, J 5 Hz) together 3H, 3.86 (1 H, dd, J 15,4 Hz), 4.25 (2H, t, J 5 Hz) 5.20 (s) 5.2 and 5.34 (ABq J 13 Hz) together 4H, 5.67 (dd, J 4,2 Hz C5-H) and 5.75 (m, exch. D2O) together 2H, 7.46,7.56 8.75 (8 H, 3 d, J 8 Hz)

Claims

1. Acompoundoftheformula (ill):

or a salt or cleavable ester thereof wherein R1 is an optionally substituted alkyl group.

2. A compound of the formula (II) as claimed in claim 1 or a salt or cleavable ester thereof wherein R is an alkyl group of up to 4 carbon atoms; an alkenyl group of up to 4 carbon atoms; an alkyl group of up to 4 carbon atoms substituted other than on the a-carbon atom by an amino or acetylamino group; an alkyl group of up to 4 carbon atoms substituted by an alkoxycarbonyl group wherein the alkoxyl part contains up to 4 carbon atoms; an alkenyl group of up to 4 carbon atoms substituted other than on the carbon atom by an acetylamino group; an alkenyl group of up to 4 carbon atoms substituted by an alkoxycarbonyi group wherein the alkoxyl part contains up to 4 carbon atoms; a benzyl group; or a benzyl group substituted by a methyl, amino, alkoxycarbonyl wherein the alkoxy part contains up to 4 carbon atoms, acetamido or methoxyl group, or by a chlorine or bromine atom.

3. A compound of the formula (II) as claimed in claim 2 or a pharmaceutically acceptable salt thereof.

4. An ester of a compound of the formula (Il) as claimed in claim 2 wherein the ester moiety has the part formula (a) or (b): -CO-O-CHA1-o-Co-A2 (a)

wherein A1 is a hydrogen atom or a methyl group, A2 is an alkyl or alkoxyl group of 1 to 4 carbon atoms or a phenyl group, A3 is a hydrogen atom or a methyl or methoxyl group, and A4 is a hydrogen atom or a methyl or methoxyl group.

5. A compound as claimed in any of claims 2 to 4 wherein R1 is a methyl, ethyl, n-propyl, ss-aminoethyl or ss-acetamidoethyl group.

6. 2-Ethoxypenem-3-carboxylic acid or a pharmaceutically acceptable salt thereof.

7. A p-nitrobenzyl ester of a compound of the formula (II) as claimed in claim 2.

8. A pharmaceutical composition which comprises a compound as claimed in any of claims 1 to 6 and a pharmaceutically acceptable carrier therefor.

9. A process for the preparation of a salt or cleavable ester of a compound oftheformula (II) as claimed in claim 1 which process comprises the ring closing elimination of the elements oftriphenylphosphinesulphide from a cleavable ester of a compound oftheformula (ill):

wherein Rr is a group R1 as defined in relation to formula (II) in which any amino group present has been protected, and thereafter removing the protecting group from any amino group present and cleaving the ester if desired to yield the compound of the formula (II) or its salt.

10. ' The use of a compound as claimed in any of claims 1 to 6 as an antibacterial agent.