CA1191853A - Intermediates for use in production of cephalosporin antibiotics - Google Patents

Abstract

Abstract A novel syn-isomer is described of the formula II

which is useful in the production of known 2-oximino-acetamido-3-cephem-4-carboxylic derivatives. A method of producing the above isomer is also described.

Description

Novel intermediates for use in ~_duction of ~halosporin antibi_ lcs This invention relates to novel intermediates for the production of known 2-oximinoacetamido-3-cephem-4-carboxylic derivatives and is a divisional of Canadian applicat:ion Seri2l1 No. 374,191, filed March 30, 1981.
That application describes a process for the production of ~yn-isomers of formula I, ~ORl N

R -C-CO-NH ~ S~ I
~ N ~ CH2R4 in which Rl is hydrogen, alkyl, phenalkyl, carbalk-oxyalkyl, acyl or carboxyalkyl, R2 :is hydrogen, pivaloyloxymethyl or a carboxy protecting group, R3 :is a 5-membered oxygen- or sulphur-containing heterocyclic ring, which may be substituted by amino or azido, and R4 is hydrogen, acetoxy, carbamoyloxy of -S-Y, in which Y is a heterocyclic ring which may be substituted.

~¢~

- 2 - 970-9688 The compounds of formula I represent a known class of valuable cephalosporin antibiotics disclosed for example in W. German DOS 2,223,375; 2,556,736;
2,702,501; 2,707,565; 2,715,385; 2,992,036; as well as numerous other patent and other publications. This class of antibiotics is characterised by the presence of an oximino group in the 7-acylamido side-chain attached to the cephalosporin nucleus. It is known that this oximino group may have the syn of anti con-figuration but that the syn isomers are preferred.

The heterocyclj.c ring in R3 contains, asindicated, one or more oxygen and/or sulphur atoms as heteroatom(s). It may, however, additionally con-tain one or more nitrogen hetero atoms. Suitable heterocyclic rings inclucle furyl, thienyl, thiazolyl, thiadiazolyl, oxazolyl and oxadiazolyl. The hetero-cyclic ring may as indicated be unsubstituted or sub-stituted by amino or azido, preferably amino. Prefer-ably the heterocyclic ring of R3is thiazolyl and this is preferably substituted by amino.

A particular preferred group of ~ isomers is that of formula Ia,

- 3 - 970-9688 ORl 2 ~ \ ~ -C-CONH ~ S ~ Ia N N ~--~CH2~4 O~R2 Rl~ R2 and R4 are as defined above In ~hese structures 9 the radical R4 can be hydrogen. Ik may also be carba~oyloxy. I~ is, how-e~er, prleferably, acetoxy or -S-Y. Su~table het~ro-cycllc g:roups which Y may represent are well-known, for example from the numerous publications referred to above. ~Preferred Iheterocyclic rings include thiad~az-olyl, diazolyl, tr;iazolyl, tetra~olyl, thiazolyl, thiatriazolyl, oxa~olyl, oxadia~olyl, triazolylpyridyl, purinyl, pyridyl, pyrimidinyl, pyridaæinyl, pyrazolyl or tr.iazi.nyl. Thec;e heterocyclic rings may be unsub-stituted or substituted, for example up to three times.
Suitable substituents include Cl_4alkyl, Cl 4alkoxy, halogen, trihalo-Cl 4 alkyl, hydroxy, oxo, mercapto, amino, carboxyl, carbamoyl, di-(Cl 4)alkylamino, carboxymethyl, carb,amoylmethyl, sulphomethyl and methoxycarbonylamino. Heterocyclic moieties indlcated in the pr.ior art to be particularly prefPrred include tetrazoly.L, in partl.cular l-rnethyl-l~-tetra~ol-5-yl, 2l) and triazilnyl, in pa~ticular 1,2,5,6-tetrahydro-2-

- 4 - 9~0~9688 methyl-5,6-dioxo-as-triazin-3-yl, 2,5-dihydro-6-hydroxy-2-methyl-5-oxo-as-triazin-3-yl or 1,4,5,6-tetrahydro-~-lnethyl-5,6--dioxo-as-triazin-3-yl. Pref-erably R~ is acetoxy, l-meth~l-lH-tetrazol-5-yl, or 2,5-dihydro-6--hydroxy-2-methyl-5-oxo-as-triazin-3-yl.

In these structures, Rlmay be hydrogen. It may also be C] 4alkyl preferably Cl 2alkyl, in partic-ular methyl. Suitable pnenalkyl groups include phen-Cl 4-alkyl, particularly benzyl. Rl may also be carb--alkoxyalkyl, for example carb~Cl_2)alkoxy(C1 4)alkyl,in particular carb(Cl ~)alkoxymethyl, e.g. carbethoxy-methyl. Suitable acyl radicals include C2 5alkanyol or, Cl ~alkoxycarbonyl. Rl rnay also be carboxyalkyl, in particular carboxy-Cl_4a:Lkyl, e.g. carboxymethyl.

As is well known in the cephalosporin field, the compound~ may be in theform of free acids (R2 = H) or of salts, f~r example alkali or al~aline earth metal salts, preferably alkali metal salts, such as sodium salts. Alternatively, tile compounds may be in the form of esters, e.g. the pivaloyloxymethyl ester.
(R2 = pivaloyloxymethyl). Other carboxy protecting groups which R2 may represent are well-known and include acetoxyrnethyl, :L-acetoxyethyl, l-ethoxycarbonyl-oxyethyl, 5-indanoyl or, preferably, hexanoylmethyl, phthalidyl, carbethoxymethoxymethyl or 3-carbethoxy~

- 5 - 970-96~8 l-acetonyl.

Particulnrly preferred compounds are ~y~
lsomers havin~ the formula Ib, ~ OCH3 }3~N~ C-CONH ~ ~ Ib OOi~

in which R4 ls acetoxy, l-methyl-lH-tetrazol-S-yl, or 2,5-dihydro-6-hydroxy-2-methyL-5-oxo-as-triazin-3-yl, and salts thereof.

The compounds of formula Ib are the products known as Cefotax1m (R4 = acetoxy), SCE-1365 (R4 = 1-methyl~ tetrazol-5-yl) and Ceftrlaxone (Rol3-9904) (R4 - 2,5-dlhydro-6-hydroxy-2-~ethyl-5-oxo-as-triazin-3-yl~, in the form c)f sodium salts (Cefotaxim and SCE-1365) or the disodium salt (Ceftriaxone).

As indicated, the compounds of formula I are generally known, ancl various methods for thelr produc-tion have been proposed. One such method involves acylatlon of the corresponding 7-aminocephalosporanic acid derivative, which may be protected, wlth a reactive deriva~ive of the acid of formula A, f~

- 6 - 970-9688 N-O~l R --C-COOH A

in which Rl and R3 are as defined above.

The various reactive derivatives that have been proposed include activated esters. For the prod-uc~ion of the ~y~-isomers of formula I the reactive S derivatives of the acid of formula A should also be in _y~-isomeric formin as high a purity as possible, and the ~y~-configuration should as far as possible be unaffected by the subsequent steps, in particular the acylation step. Various reactive derivatives that have previous:Ly been proposed, in particular activated esters, suffer from the disadvantage that the ~y~-configurationissomewhat unstable during production or use thus le!ading to increased formation of the anti-isomer and consequential reduction of the yields of the lS desired syn-isomers.

A further difficulty that arises in the prod-uction of the preferred compounds of formula Ia is that in practice it is essential to protect the amino su~stituent in the thia~olyl ring of the side-chain prior to the acylation step. Otherwise competing reactions canoccur leading to greatly reduced yields of the final products. The introduction, however, of ~~

suitable protecting groups prior to the acylation step, and thei~ subsequent removal is in general accompanied by redueed yield and purity of the desired final product and not insubstantial addition reaction time, energy, effort and cost.
Applicatîon Serial No. 374,191 provides a method by which the desired syn-isomers may be obtained in high purity and yield; in particular, the syn-isomers of formula Ia may be obtained in high purity and yield without the necessity to protect the amino substituent in the thiazolyl ring of the side~chain.
More parti.cularly, it provides a process for the production of syn-isomers of formula I and salts thereof, eomprising reaeting a ~y~-isomer of formula II, ~ORl N
R3-C-CO-S-C Het I II

in whieh Rl is as defined above, R3 is a 5--membered oxygen- or sulphur-eontaining heteroeyelie ring, which may be substituted by amino, protected amino, or azido, and -C Het~ represents a 5- or 6-membered heterocyclic ring, which may contain in addition to the nitrogen atom, one or two further hetero atoms, seLected S from oxygen, nltrogen and sulphur, and which may be substituted or fused to a benzene ring which may itself be sub-stituted~
with a compound of formula III.

R5-NE~- ~ S~ III

~ N ~ CH2R4 10in whlch R2 and R4 are as defined above, and R5 is hydrogen or an amino protecting group, where required, disprotecting the resulting product, and, where required, converting a resulting product in which E~2 is hydrogen into a salt thereof or vice versa.

The process is suitably carried out in an inert organic solvent, such as a chlorinated hydro-carbon, e.g. methylene dichloride, or an ether, e~g.
ethyl acetate,or in a mixture of such solvents with water. The reaction temperature is suitably from -40 to ~60C, in particular -15 to +25C, espcially 0'to - 9 ~ 97~-9688 20C, and the reaction time may typically vary from 1/2 to 48 hours. The reactants of formula II or III may conveniently be employed in stoichiometric quantitLes.
Alternatively, an excess of up to 25~ of the compound of formula II is conveniently employed.

As indicated, the production of compounds in which R2 is hydrogen (as well as salts thereof), the carboxyllc acid group in the starting material of formula II, is conveniently protected. Suitable protec-ting ~roups are well known and include not only thosereferred t:o above as possible significances for R2, but also sily:L ester protecting groups, in particular the trimethylsilyl protectlng groups, which may ~or example be introduced by reaction of the free acid with N,O-bis-trimethylsilylacetamide.

The 7-amino group of the starting material of formula III may, as indicated, also be protected. Again, suitable protecting groups are well-known and include for exarnple the trimethylsilyl group, which may for example be introduced simultaneously when protecting the carboxylic acid group.

~ en R3 in the desired product contains an amino substituent in the heterocyclic ring, the corres-ponding startlng material of formula II may ha~e this r~

~ 10 ~ 970-9688 amino subst:ituent in free or in protected form. As dls-cussed, in general protection is not necessary. IE
protection :is nevertheless desired, this may be accom-plished in conventional manner, suitable protecting S groups being well-known.

Af,ter reaction of the compounds of formula II
and III, any subsequent disprotection steps rnay be effected in conventional manner. Likewise, inter-conversion of the free acid (R2 = H~ and salts thereof may be accomplished in well-known manner.

The resultlng products may be isolated and purified usiny conventional techniques.

The process of the invention thus employs as reactive derivatives of the acid of formula A, hetero-cyclic thioesters. It has been surprisingly foundthat these esters may be prepared and employed with virtually complete control of the geometry of the --C=N- syn-configuration. Furthermore, it has surprisingly been found that,when there is an amino group in the heterocycli.c ring of these esters, the esters are not self-reacting. Accordingly, protection of this amino group in the subsequent acylation is not essential (although oE course not ruled out if for any reason desired).

The ~ isomers o formula II are novel and represent the present invention. The nature of the / ~
-C~et, ring therein is not critical, the preferred compounds being determined by such factors as ease S of formation and availability of starting materials.
Preferably, however, this signifies 2-pyridyl, or, especially, 2-benzthiazolyl. It may also be pyrimi-dinyl, triazolyl or thiazolyl, however. The preferred compounds of formula II correspond to the preferred end products, namely syn isomers of formula IIa and IIb, ~ORl 2 ~ ~ C-CO-S C / ` IIa N __ 2 ~ \ ~ C-CO-S-C Het ~ N--' IIb in which Rl and C ~ ~ are as defined above.
~ N
In accordance with the invention, the syn-isomers of formula II may be prepared by esterification of a isomer of formula IV, ~ORl N IV
l 11 R -C-COOH
in which Rl and R3 are as defined above.
The esterification may for example be accom-- 12 - 970-96~8 plished by reaction wl-th a compound of formula V, ~Het C-S-S-C Het I V
`N~Y ~N-\
in which the two groups ~let C are the same and `~
are as defined above.
The reaction is suitably effected in the presence of a tri-(lower alkyl~- or tri(aryl) phosphine or phosphite, in particular triphenylphosphine. The reaction temperature may for example be from -30 to ~50C, in particular -20 to +25C, preferably -5 to ~5C. The reaction is sultably effected in an inert, non-hydroxy-containing-, organic solvent, for example a chlorinated hydrocarbon, such as methylene chloride.
Where a compound of formula II in which R3 is a pro~
tected-amino-substituted heterocycle is desired, the amino protecting group may of course be introduced prior to or subsequent to the esterification reaction.

The syn-isomers of formula I are as indicated in general known antibiotics. In particular they are in-dicated for use as antibacterial agents as indicated in vitroin the series dilution test,ata concentration for example of 0.01 to S0 ~g/ml, and ln vlvo in the mouse at a dosage of for example from 0.1 to 100 mg/kg of animal body weight, against a wide variety of stralns, such as Staphy]ococcus aureus, Streptococcus pyogenes, Streptococcus faecalls, E. coli, Proteus vulgarix, Proteus mirabilis, Proteus morganii, Shigella dysent-eria, Shigella sonnei, Shigella flexneri, Alcaligenes faecalis, Klebsiella aerogenes, Klebsiella penumoniae, Serrata marcescens, Salmonella Heidelberg, Salmonella typhinuriurn, Salmonella enteritidis and Neuseria gonorrhoae.

The compounds are therefore useful as bact-erially active antibio~ics. For this usage, the dosage will of course vary depending on the compound employed, mode of administration and treatment desired.
Howev~r, in general, satisfactory results are obtained when administered at a daily dosage of from 1 to 6 g conveniently given in divided dosages of from about 0.25 to about 3 g of the compound two to four times daily, or in sustained release form.

The compounds in which R2 is hydrogen may be employed in free acid form or in the form of their physiologically acceptable salts, which salt forms have ~ 9~0-9688 the same order of activity as the free aci.d forms.
Suitable salt forms include alkall metal and alkaline earth metal salt ~Q~S~in particular alkali metal, such as sodium salt forms. The compounds may be admixed with conventîonal pharmaceutically acceptable diluents and carriers and optionally other excipients and admin-istered in such forms as capsules or injectable prep-arations.

The followlng Examples in which all temper~
atures are in degrees Centigrade, illustrate the i.nvention.

EXAMPI.E 1: 7-t[2-(2-~ninothiazol-4-yl)-2-syn-methox-imlno]acetamido~cephalosporanic acid [Cefotaxim]

2.72 g of 7-Aminocephalosporanic acid are suspended ln 50 ml of methylene dichloride. 3.5 ml of N,O-bis-(-trimethylsilyl)acetamide are added and the mixture is stirred at room temperature until a clear solution is obtained. 3.5 g of 2-(2-aminothiazol-4-yl~-2-syn-metho:cimino acetic acid 2-benthLazolyl thioester are added and the mixture is stirred for 15 hours at room temperature. The solution is then extracted with 2 cJ of ~HCO3 and 40 ml of water and the phases are separated. The aqueous phase is extracted with a mix-ture of ethyl acetate/n-butanol (8/2) at p~l 2 and before phase separation, the aqueous phase is satur-ated with (NH4)2SO4. The organic phase is washed twice with 100 ml of NaCl solution and evaporated to dryness.
The crystalline residue is shaken with 100 ml of diethyl ether, filtered and washed with ether. The title product is obtained. M.P. 20~ (decomp.). Yield 4.2 cJ;
92~ of theory ~ased on pure ~X~ isomer.

EXAMPLE 2: 7-- [2-(2-~ninothiazol-~yl)-2=syn- ethox-~ .
imino]acetamido ce~halosporanic acid [Cefotaxim]

2.72 g of 7-~minocephalospQranic acid are suspended in 40 ml of methylene dichloride and 2.75 ml of N,O-bis-(trimethylsilyl)acetamide are added, drop-wise. The mixture is stirred until a clear solution is obtained. 2.9 g of 2-(2-aminothiazol-4-yl)-2-~
methaminoacetic acid 2-pyridyl thioester are added, the mixture is cooled to 10 D and stirred at this temper-ature for 24 hours. 2 g of KHCO3 in 40 ml of water are added and the mixture is stirred for 30 minutes and the aqueous phase i6 separated. This is layered with a mixture of n-butanol/ethyl acetate and the pH of the mixture is adjusted to 2. The organic phase is evapor-ated in vacuo and the residue is mixed with ether. The precipitated crystalline heading compound is filtered off, washed with ether and dried. ~.P. 205 (decom~.).
Yield 4.1g; 90% of theory based on pure ~y~ isomer.

EXAMPLE 3: 7-~2--(2-Aminothia ~ )-2-syn-methoximino]acetamido~3-~[(2~5-dihydro--6-_y~oxy-2-methyl-5-oxo-a,s-triazin-3-yl) thio]methyl}-3-ce~em-4-carboxylic acid Ceftriaxon 3.71 g of 7-Amino-3-(2,5-dihydro-2-methyl-6-hydroxy-5-oxo-a,s-triazin-3-yl)thiomethyl-3-cephem-4-carboxylic acid are suspended in 50 ml oE dry methylene chloride under an inert gas atmosphere. ~3 ml of N,O-bis (trimethylsllyl)acetamide are added, with stirring, and the mixture is stirred for 30 minutes when a clear solution is formed which is then cooled to +15C.
9 g of 2-(2-aminothiaz.ol-4-yl)-2-~-methoximino acetic acid 2-benzthiazolyl thioester are added and the mix-ture is stlrred for5hours a-t 15 to 20, whereupon a clear solution is forrrled. The mixture is then cooled to 0C and poured into a solution of 3 ml of methanol in 120 ml of acetonitrile, pre-cooled to 0. From the xesulting initially clear solution, a light precipitate is formed on further stirring at 0 to 5 and this is filtered off and washed with acetonitrile. After drying in vacuum at 50C, 4.7 g (85%) of substantially pure title compound are obtained, in the form of the free acid, m.p. ~120C (decomp.).

EXAMPLE 4: 7-~[2-Amunothiazol-4-yl)-2-syn-methoxirnino]-acetamido~-3-(1-methyl-lH-tetrazol-5-yl~-thiometh~1-3-cephem-4-carbox~lic acid [SCE 1365]

In manner analogous to that of any one of Examples 1 to 3, employing appropriate starting mater-ials in approximately equivalent amounts, the heading compound may be obtained.

- 1~ - 970-9688 EXAMPLE 5: 2-(2-Aminothiazol-9-yl?-2-syn~methoxlmino-acetic acid_2~yridyl thioester ~Compound II]

26 g of triphenylphosphine are dissolved in 130 ml of methylene dichloride and 22 g of 2,2-dithio-pyridine are added. The mixture is stirred at room temperature for lS minutes and then cooled to 0. lOg of finely powdered 2-(2-aminothiazol-4-yl)-2-~y~-methoximinoacetic acid are then added in portions over 1 hour. The mlxture is seeded and cooled for 3 hours at 0, whereby the heading compound crystallises out.
This is filtered and washed with cold met~len~ chloride;
m.p. 112; yield 16.4 g - 98% of theory based on pure syn isomer.

15 EXAMPLE 6: 2-(2-Aminothiaæol-4-Y1)-2-syn-methoximlno . . _ . _ . _ . ~ . . _ = . _ acetio acid 2-benzothiazolyl_thioester [Compound II]

3.93 g of Triphenylphosphine and 5 g of ~is-[ben~thiazolyl-(2)]disulphide are suspended in 50 ml of methylene dicl-loride and tl-e suspension is stirred for 30 minutes at room temperature. A~ter cooling to 0, 2 g of 2-(2~aminothiazol-4-yl)-2-~y~-methoximino-acetic acid are added and the mixture is stirred for 3 to 4 hours at 0. The insolubles are filtered off and - 19 - 970-968~

washed with a little cold methylene dichloride. The solid is suspended in 25 ml of ethyl acetate and the suspension is stlrred ior 30 minutes at 0, filtered and washed wlth ethyl acetate to obtain the heading compound, m.p. 128-13() (from tetrahydrofuran/methyl-ene dichloride).

Claims (11)

Claims:

1. A process for the production of syn-isomers of formula II, II

in which R1 is hydrogen, alkyl, phenalkyl, carbalkoxyalkyl, acyl or carboxyalkyl, and R? is a 5-membered oxygen- or sulphur-containing heterocyclic ring, or such ring substituted by amino, protected amino, or azido, and represents a 5- or 6-membered heterocyclic ring, or such ring containing in addition to the nitrogen atom, one or two further hetero atoms selected from oxygen, nitrogen and sulphur, or such ring sub-stituted or fused to a benzene ring or substituted benzene ring, which comprises esterifying a syn-isomer of formula IV, (IV) in which R1 and R? are as defined above.

2. A process according to Claim 1, in which the esterification is effected by reaction with a compound of formula V, V

in which the two groups Het C are the same and are as defined in Claim 1.

3. Syn-isomers of formula II, II

in which Rl is hydrogen, alkyl, phenalkyl, carbalkoxyalkyl, acyl or carboxyalkyl, and R? is a 5-membered oxygen- or sulphur-containing heterocyclic ring, or such ring substituted by amino, protected amino, or azido, and represents a 5- or 6-membered heterocyclic ring, or such ring containing in addition to the nitrogen atom, one or two further hetero atoms selected from oxygen, nitrogen and sulphur, or such ring sub-stituted or fused to a benzene ring or substituted benzene ring, whenever produced by the process of claim 1 or an obvious chemical equivalent.

4. A process according to claim 1 wherein R? is and Rl and are as defined in Claim 1.

5. Syn-isomers of formula IIa, IIa in which Rl and are as defined in Claim 4, whenever produced by the process of Claim 4 or an obvious chemical equivalent.

6. A process according to claim 1 wherein R? is Rl is CH3 and is as defined in Claim 1

7. Syn-isomers of formula IIb, IIb in which is as defined in Claim 6, whenever produced by the process of Claim 6 or an obvious chemical equivalent.

8. A process for producing 2-(2-aminothiazol-4-yl)-2-syn-methoximinoacetic acid 2-pyridyl thioester which comprises esterifying 2-(2-aminothiazol-4-yl)-2-syn-methoximinoacetate acid with 2,2-dithiopyridine.

9. 2-(2-Aminothiazol-4-yl)-2-syn-methoximinoacetic acid 2-pyridyl thioester, whenever produced by the process of Claim 8 or an obvious chemical equivalent.

10. A process for producing 2-(2-aminothiazol-4-yl)-2-syn-methoximinoacetic acid 2-benthiazolyl thioester which comprises esterifying 2-(2-aminothiazol-4-yl)-2-syn-methoximinoacetic acid with bis-[benzthiozolyl-(2)]
disulphide.

11. 2-(2-Aminothiazol-4-yl)-2-syn-methoximinoacetic acid 2-benthiazolyl thioester, whenever produced by the process of Claim 10 or an obvious chemical equivalent.