GB2166435A - 2-modified penams, their preparation and their use - Google Patents

Abstract

<IMAGE> Penams IV (N=0, 1 or 2, R=H or a carboxy protecting group, R1=H, alkyl, alkoxy, cycloalkyl or optionally protected hydroxyalkyl, especially 1-hydroxyethyl, R3 and Y are certain defined organic groups or R3=H) have antibacterial activity. They may be prepared by cyclising an azetidinone II <IMAGE> (E is a leaving group) and are further useful in the preparation of known antibacterial penems I <IMAGE>

Description

SPECIFICATION Penams, their preparation and their use The invention relates to penams, to a process for the preparation and to a process for their conversion to known penams having antibacterial activity.

The invention provides penams having the general formula IV

wherein n is 0, 1 or 2, R represents a hydrogen atom, a lower alkyl group, a 2,2,2-trichloroethyl, acetonyl, allyl, benzyl, p-nitrobenzyl, p-methoxybenzyl, phenyl, o-nitrophenyl, diphenylmethyl or 1-phenoxyethyl group, or a residue known to be hydrolysed in vivo and having favourable pharmacokinetic properties, R, represents a hydrogen atom, a lower alkyl group, a lower alkoxy group, a lower cycloalkyl group or a free or protected hydroxyalkyl group, R3 represents a hydrogen atom or a lower alkyl, aralkyl, aryl, heterocyclyl, lower alkenyl, lower alkynyl or lower cycloalkyl group, each group being optionally substituted by a halogen atom or a hydroxy, mercapto, alkylthio, lower alkyl, lower alkoxy, cyano, carboxy, nitro, amino, lower aminoalkyl or lower haloalkyl group, and Y represents (a) a hydroxymethyl group,

wherein Z represents an oxygen or atom and R3 is as above defined,

wherein Z is as above defined and each of R4 and R5 independently represents a hydrogen atom, a lower alkyl, carbamoyl, lower alkanoyl, formyl or lower alkoxycarbonyl group or an amindino group optionally substituted by a lower alkyl group,

wherein R3 is as above defined and R6 represents a hydrogen atom or a lower alkyl, carbamoyl, lower alkanoyl, formyl, hydroxy, lower alkoxy or aryloxy group, (e) a cyano group, or (f) -CH2-X wherein X represents (i) NO2 as such or as its nitronates of formula

wherein R7 represents a sodium, potassium, lithium or hydrogen atom or a lower alkyl, aryl, lower alkenyl, lower alkynyl, lower cycloalkyl, heterocyclyl, lower alkanoyl, formyl or carbamoyl group, tii) -NR4Rs wherein R4 and R5 are as above defined.

wherein R3 and Z are as above defined,

wherein R4, R5 and Z are as above defined, (v) S(O)nRS wherein n and R3 are as above defined, (vi) a cyano group, (vii) a heterocyclylthio group, or (viii) -ORa wherein R8 represents a lower alkyl, carbomoyl, alkanoyl, lower cycloalkylcarbonyl or arylcarbonyl group.

In this Specification the term 'lower' is used in relation to the simple radicals 'alkyl', 'alkoxy', 'alkenyl', 'alkynyl' or 'alkanoyl' to limit the radical concerned to one containing not more than 6 carbon atoms. In relation to complex radicals incorporating those simple radicals, it is used to limit those simple radicals as aforesaid. Thus 'lower alkoxycarbonyl' can contain up to 7 carbon atoms (up to 6 for lower alkoxy plus 1 for carbonyl) and 'lower aminoalkyl' can contain up to 6 carbon atoms. The term 'lower cycloalkyl' is used to mean cycloalkyl having from 4 to 6 carbon atoms. Correspondingly a lower cycloalkylcarbonyl group can contain from 5 to 7 carbon atoms. The term 'a halogen atom' means a fluorine chlorine, bromine or iodine atom, and the term 'halo' is to be interpreted correspondingly.The term 'aryl' is used to means a phenyl group optionally substituted by one or more lower alkyl groups and/or lower alkoxy groups and/or halogen atoms. Examples include p-tolyl, o-tolyl, m-tolyl, p-chlorophenyl and o-methoxyphenyl. The term 'aralkyl' is used to mean a lower alkyl group substituted by one or more aryl groups as above defined. Examples include benzyl, phenethyl and diphenylmethyl. The term 'heterocyclyl' is used to means a radical derived from a compound having a ring composed of carbon atoms and from 1 to 4 other atoms, the free valency of the radical being borne by one of the ring atoms, the ring optionally being substituted by up to 3 lower alkyl groups.Examples include pyridyl, furanyl, thienyl, thiazolyl, imidazolyl, tetrazolyl, 2-methylpyridyl, 3-methylthienyl and 1-methyltetrazolyl. All possible positional isomers are included, for example 'pyridyl' includes 2-pyridyl, 3-pyridyl and 4-pyridyl. The meanings given above for 'aryl' and 'heterocyclyl' are retained in complex radicals such as aryloxy and heteroclylthio.

Examples of residues known to be hydrolysed in vivo and having favourable pharmacokimetic properties are acetoxymethyl, pivaloyloxymethyl and phthalidyl groups and groups of the formulae

wherein R2 represents an alkyl group having from 1 to 5 carbon atoms or an aryl group.

Rl preferably represents a free or protected lower hydroxyalkyl group, especially a free or protected 1hydroxyethyl group, the protecting group (PG) preferably being a p-nitrobenzyloxycarbonyl, dimethyl-tbutylsilyl, diphenyl-t-butylsilyl, 2,2,2-trichloroethoxycarbonyl, trimethylsilyl, benzyl, p-bromophenacyl, triphenylmethyl or pyranyl group.

Y preferably represents (a') a hydroxymethyl group,

wherein R2 is as defined above

wherein each of R'4 and R'5 independently represents a hydrogen atom or a lower alkyl, lower alkanoyl, formyl or carbamoyl group,

wherein R3 and R6 are as defined above, (e') a cyano group, or (f') -CH2-X' wherein X' represents (i') NO2 as such or as its nitronates of formula

wherein R7 is as above defined, (ii') -NR'4R's wherein R'4 and R's are as above defined,

wherein R2 is as above defined,

wherein R'4 and R's are as above defined, (v') -S(O)nR3 wherein n and R3 are as above defined, or (viii') -ORS wherein Ra is as above defined.

More preferably Y represents (a") a hydroxymethyl group,

wherein R2 is as above defined, (f") -CH2-X" wherein X" represents (i") -NO2 as such or as its nitronates of the formula

are as above defined, (ii") -NR'4R's wherein R'4 and R's are as above defined,

wherein R3 is as above defined, or (viii") -OR8 wherein R8 is as above defined.

The invention further provides a method for the preparation of a penam IV as herein defined, the method comprising cyclising an azetidinone having the general formula II

wherein R, R, and R2 are as above defined and E represents an electron withdrawing group selected from heterocyclylthio, methyl, nitro and cyano groups and groups of the formulae

and S(O)nR3 wherein R2, R4, R8, Z and n are as above defined, the cyclisation being effected in tetrahydro furan, hexane or toluene in the presenece of a base at a temperature of from -100 to 0 C to obtain a penam having the general formula Ill

wherein E, R, R1, R2 and n are as above defined and, if necessary, converting the group CH2E in the penam Ill into a group Y.

The base used for the cyclisation step is preferably an organometallic compound such as n-butyl lithium, t-butyl lithium, methyl lithium, phenyl lithium or those of the formulae LiN[Si(CH3)3]2 or LiN[CH(CH2)2]2.

The conversions of the group CH2E in the penam Ill to a group Y may be performed by well known methods. For example, the penams IV (Y=CH2NR4R8) may be obtained from the penams Ill (E=NO2) by reduction, for example with hydrogen over a palladium-on-charcoal catalyst, followed by alkylation or acylation. The penams IV (Y=CHO) may be obtained from the penams Ill (E=NO2) by basic treatment, optional quenching with an alkylating agent such as methyl iodide, and subsequent ozonisation. Penams IV (Y=CH2OH) may be obtained from penams Ill (E=NO2) by the above route to the penams IV (Y=CHO) followed by reduction. The route to the penams IV

also passes through the penams IV (Y=CHO), after which oxidation and other well known reactions give the desired compounds.

The azetidinones II used in the method of the invention may be prepared from the azetidinones of the general formula V

wherein R, is as above defined and L represents a leaving group, such as an acetoxy or benzoyloxy group. These are known compounds or may be prepared from known compounds by known proceedures. The azetidinone V is condensed with a dipotassium salt of the general formula

wherein E is as above defined. These dipotassium salts are either known themselves [Ber. 52, 542 (1919)] or may be prepared by procedures analogous to the preparation of the known salts. Alkylation of the condensate gives a compound of the general formula VI

wherein R1, R2, E and n are as above defined.The introduction of a 1-substituent of the formula CH2COOR wherein R is as above defined to the azetidinones VI to give the azetidinones II may be performed using well known methods.

The penams IV wherein all O-protecting groups and, optionally, all N-protecting groups have been removed and replaced with hydrogen atoms exhibit anti-bacterial activity. Accordingly the invention provides a pharmaceutical composition comprising an O-deprotected and, optionally, N-protected penam IV as above defined in admixture with a pharmaceutically acceptabie diluent or carrier. The dosage to be administered is dependent upon the age and weight of the animal species being treated, the mode of administration, and the type and severity of bacterial infection being prevented or reduced. Typically, the dosage administered per day will be in the range of 100 to 5000 mg, with 500 to 1000 mg being preferred. For oral administration, the penams may be formulated as tablets, capsules, elixirs or the like.

Likewise, they may be admixed with animal feed. They may also be applied topically in the form of ointments, both hydrophilic and hydrophobic, in the form of lotions which may be aqueous, non-aqueous or of the emulsion type, or in the form of creams. They may be utilized in liquid form such as solutions, suspensions and the like for otic and optic use and may also be administered parenterally via intramuscular injection.

The penams IV are also useful as starting materials for the preparation of penams of the general formula I

wherein R, R, and Y are as above defined. The penems I wherein Y has any of the values (b) to (f) defined above are known antibacterial agents, active against both Gram-positive and Gram-negative bacteria (EP 2210 and 3960, GB 2043639 and 2042515). The penams I wherein Y represents a hydroxymethyl group are useful intermediates for the preparation of other penems (GB 2111496 and 2118181). The process whereby the penems I may be obtained from the penams iV comprises oxidising and treating with a tertiary amine or an alkali metal carbonate a penam IV in an inert solvent at a temperature of 0 to 130"C.

The penems I so prepared may optionally be converted into other penems I wherein Y is different by conversions such as those described above.

Suitable inert solvents are any organic or inorganic solvents in which the starting compound and reagent are soluble, and which will not interfere with the process under the reaction conditions thereof, so there are produced a minimum of competing side reactions. Inert solvents which may be used in the process include aromatic hydrocarbons such as benzene and toluene, aliphatic ethers such as diethyl ether and dipropyl ether, cyclic ethers such as dioxan and tetrahydrofuran, and, preferably, halogenated hydrocarbons such as dichloromethane and chloroform.

The oxidation may be carried out using conventional oxidisation agents, such as peracids (for example m-chloroperbenzoic acid or peracetic acid) or ozone. The teriary amine is preferably triethylamine or diisopropylethylamine and the alkali metal carbonate is preferably sodium bicarbonate.

In the most preferred embodiments, the invention provides the penam IV in which R represents a pnitrobenzyl group, R, represents a 1-(t-butyidimethylsilyloxy)-ethyl group, R2 represents a methyl group, Y represents a formyl group and n is 0 and its preparation and use according to the following reaction scheme:

The azetidinone II' [Il:R, = CH3CH(OH) protected by a t-butyldimethylsilyl group, R = p-nitrobenzyl, R2 = CH2, E = NO2::configuration 3S, 4R, 5R], dissolved in tetrahydrofuran, is added to a solution containing about 2 molar equivalents of LiN[Si(CH3)3]2 at -78 C. After 10 minutes, the obtained compound III' is isolated and purified by chromotography on silica gel and crystallization from diisorpropyl ether. The compound IV' is obtained by treating the compound Ill' with LiN[Si(CH3)3]2 in tetrahydrofuran at -78 C for 10 minutes, followed by addition of methyl iodide and subsequent ozonization. The penam IV', dissolved in chloroform, is treated at 0 C with about 1.05 molar equivalents of m-chloroperbenzoic acid in chloroform.

After 10 minutes, excess sodium bicarbonate is added and the desired penem (I'A) is isolated and purified by chromatography on silica gel. The conversion of compound (I'A) to compound (I'a) is carried out by reaction with L-selectride in tetrahydrofuran at -78 C.

The compounds I and IV discussed above possess several centres of chirality. The processes of the invention provide compounds having the configuration of C8 of the absolute stereochemistry R. The 6substituents may have either a or ss orientation, a orientation being preferred.

The following Examples illustrate the invention.

Preparation A 3S-(1R4-butyldimeth ylsllyloxyeth yl)-4R-( 1-methylthio-2-nitro-vin ylthio)-azetidin-2-one A solution of 1.1 g (4.95 mM) of dipotassium 2-nitro-ethylene-1,1-dithiolate in 5 ml of ethanol and 5 ml of water was dropped into a cooled (0 C) and stirred solution of 1.44 g (5 mM) of 4-acetoxy-3R-(1 R-tbutyl-dimethyl-silyloxyethyl)-azetidin-2-one in 20 ml of ethanol and 5 ml of water. The mixture was then stirred for a further 10 minutes and dimethylsulphate was added at 0 C. The solution was then stirred for 1 hour at room temperature and again cooled. 50 ml of water was added and the suspension was stirred for 30 minutes at 0 C. The solid was collected by filtration, washed with small portions of cold aqueous ethanol, collected and dissolved in diethyl ether.The ethereal solution was dried over anhydrous magnesium sulphate, decolourized with charcoal, filtered and evaporated. The solid residue was then crystallized from chloroform:hexanes to give the title compound as a yellowish-white solid, 1.25 g (66%).

m.p. 144 - 146"C with decomposition.

[aj = + 215.3 (c=1.55, CHCI2) IR (CHO3 film) cm-1:3300, 1770, 1525 NMR (90 MHz, CDCI3) 8 (ppm) 0.08 (3H,s), 0.09 (3H,s) 0.88 (9H,s), 1.25 (3H, d J=6.5 Hz), 2.62 (3H,s), 3.28 (1H,dd, J=2.6 and 3Hz), 4.3 (1H, m), 5.44 (1H,d, J=2.6 Hz), 6.84 (1H, br s), 7.05 (1H,s) Mass Spectrum:CI:379 (M+1), 228 (M-150) C,4H2sN204Si requires:C 44.41, H 6.92, N 7.40, S 16.94 found C 44.53, H 7.00, N 7.32, S 16.61 Preparation B 1-(p-NitrobenzyloxyCarbonylmethyl)-3S-{1R-t-butyldimethyl-silyloxwethyl)-4R-rl-methylthio-2-nitro-vinyl- thio)-azetidin-2-one 2g of calcium carbonate, 1.2 g of p-nitrobenzyloxyoxalyl chloride and 0.8 ml of N,N-diisopropyl-ethylamine were added in sequence to a solution of 1.519 (4 mM) of 3S-(1R-t-butyidimethylsilyloxyethyl)-4R- (1-methylthio-2-nitro-vinylthio)-azetidin-2-one in 50 ml of dry dichloromethane at 0 C. The mixture was filtered through celite, washed twice with cold water, dried and evaporated in vacuo.The residue was taken up in toluene and purified on a short column of silanized silica gel eluting with toluene containing 0.5% by volume of ethyl acetate to give 1.7 g of 1-(p-nitrobenzyloxyoxalyl)-3S-(1 R-t-butyidimethylsilyloxy- ethyl)-4R-(1 -methylthio-2-nitro-vinylthio)-azetidin-2-one as a yellow syrup.

1R (CHCl2film) cm-1: 1820, 1760,1720, 1530.

NMR (CDCI,)G (ppm): 0.1 (6H, s), 0.9 (9H, s), 1.35 (3H,d, J=6.0 Hz), 2.6 (3H, s), 3.5 (1H, dd), 4.4 (1H, m), 5.3 (2H, s), 6.2 (1H, d, J=3.5 Hz), 7.1 (1H, s), 7.6 (2H, d), 8.25 (2H, d).

The above syrup (1.7 g) was dissolved in 20 ml of chloroform and treated with 0.77 ml (6.5 mM) of trimethylphosphite at room temperature under argon. The solution was then stirred for 36 hours at room temperature. The crude product was then purified by column chromatography yielding 1.55 g of 1-[1-(p nitrobenzyloxy-carbonyl)4rimethylphosphoranylidenemethylj-35-(1 R-t-butyidimethylsilyloxyethyl)-4R-( 1- methylth io-2-nitro-vinylthio)-azetidin-2-one.

IR (CHCI2 film) cm-1: 1770, 1650, 1530.

A solution of the last named compound in 50 ml of tetrahydrofuran and 10 ml of water was stirred at room temperature for 1 hour with a catalytic amount of p-toluenesulphonic acid. The solution was then poured into a mixture of 1% by weight aqueous sodium bicarbonate and ethyl acetate. The organic phase was separated, washed twice with brine, dried and evaporated. The crude residue was purified by column chromatography to give the title compound as a yellow oil (0.82 g).

IR (CHCI2, film) cm-1: 1780, 1760 (sh), 1530.

NMR 3 (ppm): 0.07 (3H, s), 0.09 (3H, s), 0.88 (9H, s), 1.28 (3H, d, J=6.0Hz), 2.48 (3H, s), 3.25 (1H, dd, J=2.5, 4Hz), 3.90, 4.09, 4.23, 4.45 (ABq, 2H, J=19Hz), 4.35 (1H, m) 5.25 (2H, s), 5.78 (1H, d, J=2.5Hz), 7.0 (1H, s), 7.55 (2H, d, J=8Hz), 8.25 (2H, d, J=8Hz).

Mass spectral data: Cl: 572 (M+1), 514 (M-C4H8), 421 (M-150) Example 1 p-Nitrobenzyl (5R)-6S-( lR-t-b utyldimeth ylsilyloxyeth VI)- 2-meth ylthio-2-nitrometh yl-penam-3-carb oxylate 1 ml of a 1.6 M solution of n-butyl lithium in n-hexane was added dropwise under stirring to a solution of 0.337 ml (1.60 mM) of hexamethyldisilazane in 10 ml of dry TMF at 0 C under argon. The resulting colourless solution was stirred for 30 minutes at 0 C, and then cooled to -78 C. A solution of 430 mg (0.75 mM) of 1 -(p-nitrobenzyloxycarbonylmethyl)-3S-(1 R-t-butyldimethyl-silyloxyethyl)-4R-( 1 -methylthio-2nitro-vinylthio)-azetidin-2-one in 5 ml of TMF was added over a period of 2 minutes.The resulting dark red solution was stirred at -78 C for 10 minutes and quenched with water containing acetic acid. The mixture was allowed to warm to room temperature and then partitioned between ethyl acetate and water. The organic phase was washed twice with salted water, dried, evaporated in vacuo and purified by column chromatography to give the title compound as a waxy solid. It was then crystallized from diisopropyl ether.

Yield 0.22 g (51%) mp 103-105"C [ X]D = + 216.9 (c=0.775 CHO2) IR (CHO3, film) cm-: 1780, 1750, 1560, 1525 NMR (60, 90, 400 MHz, CDCI3) 8 (ppm): 0.01 (6H, s), 0.09 (9H, s), 1.26 (3H, d, J=6.3 Hz), 2.33 (3H, s), 3.39 (1H, dd, J=1.8 and 4.5 Hz), 4.15 (1H, s), 4.28 (1H, m), 4.79, 4.82, 5.47, 5.50 (2H, ABq, J=13.4 Hz), 5.20 (1H, d, J=1.8 Hz), 5.29, 5.32, 5.36, 5.39 (2H ABq, J=13Hz), 7.65 (2H, d, J=9Hz), 8.25 (2H, d, J=9Hz).

Mass Spectrum: DCI-HN3: 572 (M+1), 514 (M-C4H8), 372 (M-199) C23H22N208S2Si requires C 48.31, H 5.82, N 7.35, S 11.22 found: C 48.13, H 5.75, N 7.25, S 10.89 Example 2 p-Nitrobenzyl (5R)-GS-( lR-t-h utyldimeth ylsllyloxyeth yl)-2-m eth ylthio-2-form yl-p enam-3-carb oxylate Method A A solution of the penam prepared in Example 1 was added, at -78 C over a period of 1 minute under argon, to a solution of lithium hexamethyldisilylazide in 5 ml of TMF (prepared as described in Example 1 from 0.032 ml of hexamethyldisilazane and 0.095 ml of 1.6M solution of n-butyl lithium in n-hexane). The dark yellow mixture was stirred for 10 minutes at -780C and 0.2 ml of methyl iodide was added.After a further 10 minutes the mixture was ozonized for 15 minutes (monitoring the progress by TLC). The excess ozone was purged with argon and then 0.2 ml of dimethylsulphide was added together with a few drops of acetic acid (in order to maintain the pH at about 6). The reaction mixture was allowed to warm to 08C and then poured immediately into a mixture of aqueous sodium chloride solution and diethyl ether. The ethereal phase was washed twice with aqueous sodium chloride solution, dried over anhydrous magnesium sulphate, evaporated in vacuo in the cold and purified by passing it rapidly through a column of silanized silica gel (eluting with toluene:hexane 7:3 by volume) to give the title compound as a colourless oil (45 mg).

IR (CHCI2, film) cm-1: 1785, 1750, 1725, 1525 NMR (60, 90, 400 MHz, CDCI3) 8 (ppm): 0.05 (3H, s), 0.07 (3H, s), 0.86 (9H, s), 1.23 (3H, d, J=6.3Hz), 2.17 (3H, s), 3.40 (1H, dd, J=1.8 and 4.1 Hz), 4.19 (1H, s), 4.25 (1H, m), 5.21 (1H, d, J=1.8 Hz), 5.23, 5.26, 5.36, 5.39 (2H, ABq, J=13Hz), 7.56 (2H, d, J=9Hz), 8.21 (2H, d, J=9Hz), 9.21 (1H, s).

Mass Spectrum DCI, isobutane: 483 (M-C4H8), 341 (M-199).

Method B A solution of 430 mg (0.75 mM) of 1 -(p-nitrobenzyloxy-carbonylmethyl)-3S-( 1 R-t-butyldi methylsilyloxy- ethyl)-4R-(1-methylthio-2-nitro-vinylthio)-azetidin-2-one in 5 ml of TMF was added, over a period of 2 minutes to a solution of lithium hexamethyldisilyazide in 10 ml of TMF (prepared as described in Example 1 from 0.337 ml of hexamethyldisilazane and 1 ml of a 1.6M solution of n-butyl lithium in n-hexane.

The resulting solution was stirred for 10 minutes at -78 C and 0.4 ml of methyl iodide was added. After a further 10 minutes the mixture was ozonized for 15 minutes. After work-up as described in.method A the title compound was obtained (0.11 g). Its chemical and physical properties were identical to those of the same compound prepared by method A.

Example 3 p-Nitrobenzyl (5R)-6S- (lR-t-b utyldimeth ylsllyloxyethyl)-2-form yl-p en em -3-ca rb oxylate A solution of 21.6 mg of 85% m-chloroperoxybenzoic acid (0.105 mM) in 1.5 ml of chloroform was added to a stirred and cooled (0 C) solution of 54 mg of p-nitrobenzyl (5R)-6S-(1 R-t-butyldimethylsilyloxy- ethyl)-2-methylthio-2-formyl-penam-3-carboxylate (0.1 mM) in 3 ml of chloroform. After 10 minutes the solution was vigorously stirred with a solution of sodium bicarbonate at 0 C. The aqueous phase was separated and the organic phase was stirred vigorously for 30 minutes at room temperature with water.

The aqueous phase was discarded and the organic phase was dried over anhydrous magnesium sulphate, filtered, washed carefully with chloroform and evaporated repeatedly in vacuo. The crude residue was purified by column chromatography eluting with a graduated mixture of ethyl acetate and hexanes to give the title compound as an amorphous solid (26 mg).

IR (CHO2, film) cm-1: 1790, 1715, 1660, 1520.

NMR (CDC13) 8 (ppm): 0.04 (3H, s), 0.08 (3H, s), 0.83 (9H, s), 1.25 (3H, d, J=6.3 Hz), 3.91 (1H, dd, J=2.0 and 3.3 Hz), 4.27 (1H, m), 5.30, 5.33, 5.45, 5.49 (2H, ABq, J=13Hz), 5.68 (1H, d, J=2.0Hz), 7.63 (2H, d, J=9Hz), 8.23 (2H, d, J=9Hz), 10.42 (1H, s).

Mass Spectrum DCI-isobutane: 435 (M-C4H8), 293 (M-199).

UV (CHCl2) À max (nm): 265, 390.

Example 4 p-Nitrobenzyl (5R)-6S-( lR-t-butyldimeth ylsllyioxyeth yl)-2-nitrometh yl-p en em -3-carb ox yla te A solution of 21.5 mg of 85% m-chloroperoxybenzoic acid (0.105 mM) in 1.5 ml of chloroform was added to a stireed and cooled (OC) solution of 57.1 mg of p-nitrobenzyl (5R)-6S-(1R-t-butyldimethylsily- loxyethyl)-2-methylthio-2-nitromethyl-penam-3-carboxylate (0.1 mM) in 3 ml of chloroform. After 10 minutes the solution was vigorously stirred with a solution of sodium bicarbonate at 0 C. The aqueous phase was separated and the organic phase was washed at room temperature with water. The collected organic phase was dried over an hydros magnesium sulphate, filtered, and evaporated in vacuo yielding a yellowish oil (20 mg).

IR (CHO3) cm-1: 1795, 1715 UV (CHCl2) A max nm: 264, 334 NMR (CDCI3) 3 ppm: 0.01 (3H, s), 0.09 (3H, s), 0.9 (9H, s), 1.32 (3H, d, J=6 Hz), 3.95 (1H, dd, J=1.9 and 3.8 Hz), 4.3 (1H, m), 5.28, 5.35, 5.48 and 5.55 (2H, ABq, J=13.8 Hz), 5.39, 5.47, 6.10 and 6.17 (2H, ABq, J=15Hz), 5.86 (1H, d, J=1.9Hz), 7.6 (2H, d, J=9Hz), 8.23 (2H, d, J=9Hz).

Mass Spectrai data (FD): 523 (M), 466 (M-C4H8).

Example 5 p-Nitrohenzyl (SRI-GS-(IR-t-b utyldimeth ylsilyloxyethyl-2-hydroxymeth yl-penem-3-caroxylate 0.1 ml of 1M L-selectride solution (0.1 mM) was added dropwise, under argon and with stirring, to a solution of 49 mg of p-nitrobenzyl (5R)-6S-( 1 R-t-butyldimethyl-silyloxyethyl)-2-formyl-penem-3-carboxy- late (0.1 mM) in 10 ml of tetrahydrofuran at -78 C. The solution was stirred for 5 minutes at -78 C and then quenched with 1 ml of ammonium chloride solution at -78"C. The reaction mixture was warmed to room temperature and then partitioned between ethyl acetate and water.The aqueous phase was extracted twice with ethyl acetate and the combined organic extracts were washed twice with sodium chloride solution, dried over anhydrous sodium sulphate, filtered, and evaporated in vacuo. The crude product was then purified by column chromatography yielding the title compound as an amorphous solid (31 mg).

UV (CHCl2) X max: 265, 324.

IR (CHO2, film) cm-1: 3400 (br), 1790, 1710, 1525.

NMR (400 MHz, CDCI3) 8 (ppm): 0.04 (3H, s), 0.08 (3H, s), 0.82 (2H, s), 1.25 (3H, d, J=6.3Hz), 3.32 (1H, brt, J=7.0 Hz), 3.77 (1H, dd, J=1.7 and 3.8Hz), 4.26 (1H, m), 4.71 (2H, br m), 5.21, 5.25, 5.41, 5.44 (2H, ABq, J=13.7Hz), 5.64 (1H, d, J=1.7Hz), 7.62 (2H, d, J=8.7Hz), 8.23 (2H, d, J=8.7 Hz).

Mass spectral data: Ci: 495 (M+1), 437 (M-C4H8), 295 (m-199) [(Y]D (c=1,CHCl2) = + 33.5 Example 6 p-Nitrobenzyl 15RJ-6S-(IR-hydroxyethyl)-2-hydroxymethyl-penem-3-carboxylate 1.47 ml of acetic acid (24 mmol) and 2.27 g of tetrabutylammonium fluoride (7.2 mmol) were added to a solution of 1.2 g of p-nitrobenzyl (5R)-6S-(1R-t-butyldimethylsilyloxyethyl)-2-hydroxymethyl-penem-3- carboxylate (2.4 mmol) in 50 ml of tetrahydrofuran. The resulting mixture was stirred at room temperature for 16 hours. The solution was then evaporated in vacuo and the residue was chromatographed on silica gel eluting with ethyl acetate:cyclohexane mixtures to give the title product as a light yellow solid (775 mg, 85%).

UV (EtOH) X max: 264, 322.

NMR (Acetone) 8 ppm (60 MHz): 1.45 (3H, d, J=6.5 Hz), 3.67 (1H, dd, J=1.5, 6.0 Hz), 4.10 (1H, m), 4.72 (2H, s), 5.32 (2H, ABq, J=14 Hz, separation of inner lines 8 Hz), 5.59 (1H, d, J=1.5 Hz), 7.69 (2H, d, J=7 Hz), 8.18 (2H, d, J=7 Hz) Example 7 Sodium {5R)-6S-{lR-hydroxyethyl-2-hydroxymethyl-penam-3-carboxylate A solution of 450 mg of p-nitrobenzyl (5R)-6S-(1R-hydroxyethyl)-2-hydroxymethyl-penem-3-carboxylate (1.2 mmol) in 25 ml of ethyl acetate containing 100 mg of sodium bicarbonate (1.2 mmol) was hydrogenated over 450 mg of 5% palladium-on-carbon under normal pressure for 1 hour. A further 750 mg of 5% palladium-on-carbon was then added and the hydrogenation was continued for 1 hour. The mixture was then filtered and the organic phase was discarded. The aqueous phase was concentrated in vacuo to give a brownish oil which was purified on a reverse phase column eluting with water. The title product was obtained as an amorphous solid (210 mg, 62.1%).

UV (H2O) À max: 259, 306 nm NMR (D2O) 3 ppm (90MHz): 1.30 (3H, d, J=7Hz), 3.88 (1H, dd, J=1 and 6.3 Hz), 4.23 (1H, m), 4.63 (2H, ABq, J=14.5 Hz, separation of inner lines=4 Hz), 5.62 (1H, d, J=1 Hz) Example 8 Sodium (5R)-6S- (iR-h ydroxyeth yl)-2-m eth ylthio-2-form yl-penam-3-carh oxylate Starting from p-n itrobenzyl (5R)-6S-(1 R-t-butyidimethyl-silyloxyethyl)-2-methylthio-2-formyl-pena m-3carboxylate, prepared in Example 2, and operating as described in Examples 5 and 6, the title compound was obtained.

Claims (17)

1. A penam having the general formula IV

wherein n is 0, 1 or 2, R represents a hydrogen atom, a lower alkyl group, a 2,2,2-trichloroethyl, acetonyl, allyl, benzyl, p-nitrobenzyl, p-methoxybenzyl, phenyl, o-nitrophenyl, diphenylmethyl or 1-phenoxyethyl group, or a residue known to be hydrolysed in vivo and having favourable pharmacokinetic properties, R1 represents a hydrogen atom, a lower alkyl group, a lower alkoxy group, a lower cycloalkyl group or a free or protected hydroxyalkyl group, R2 represents a hydrogen atom or a lower alkyl, aralkyl, aryl, heterocyclyl, lower alkenyl, lower alkynyl or lower cycloalkyl group, each group being optionally substituted by a halogen atom or a hydroxy, mercapto, alkylthio, lower alkyl, lower alkoxy, cyano, carboxy, nitro, amino, lower aminoalkyl or lower haloalkyl group, and Y represents (a) a hydroxymethyl group,

wherein Z represents an oxygen or atom and R2 is as above defined,

wherein Z is as above defined and each of R4 and R8 independently represents a hydrogen atom, a lower alkyl, carbamoyl, lower alkanoyl, formyl or lower alkoxycarbonyl group or an amindino group optionally substituted by a lower alkyl group,

wherein R2 is as above defined and R8 represents a hydrogen atom or a lower alkyl, carbamoyl, lower alkanoyl, formyl, hydroxy, lower alkoxy or aryloxy group, (e) a cyano group, or (f) -CH2-X wherein X represents (i) NO2 as such or as its nitronates of formula

wherein R7 represents a sodium, potassium, lithium or hydrogen atom or a lower alkyl, aryl, lower alkenyl, lower alkynyl, lower cycloalkyl, heterocyclyl, lower alkanoyl, formyl or carbamoyl group, (ii) -NR4Rs wherein R4 and R8 are as above defined.

wherein R2 and Z are as above defined,

wherein R4, R8 and Z are as above defined, (v) S(O),1R3 wherein n and R2 are as above defined, (vi) a cyano group, (vii) a heterocyclylthio group, or (viii)-OR8 wherein R8 represents a lower alkyl, carbomoyl, alkanoyl, lower cycloalkylcarbonyl or arylcarbonyl group.

2. A penam according to claim in which 1 R1 represents a free or protected lower hydroxyalkyl group.

3. A penam according to claim 1 or claim 2 in which R1 represents a 1-hydroxyethyi group, free or protected by p-nitrobenzyloxyca rbonyl, dimethyl-t-butylsilyl, diphenyl-t-butylsilyl, 2,2,2-trichloroethoxycarbonyl, trimethylsilyl, benzyl, p-bromophenacyl, triphenylmethyi or pyranyl group.

4. A penam according to any preceding claim in which Y represents (a') a hydroxymethyl group

wherein R2 is as defined above

wherein each of R'4 and R'5 independently represents a hydrogen atom or a lower alkyl, lower alkanoyl, formyl or carbonoyl group,

wherein R2 and R8 are as defined above, (e') a cyano group, or (f') -CH2-X' wherein X' represents (i') NO2 as such or as its nitronates of formula

wherein R7 is as above defined, (ii') -NR'4R'5 wherein R'4 and R'5 are as above defined,

wherein R2 is as above defined,

wherein R'4 and R'5 are as above defined, (v') -S(O)nR3 wherein n and R2 are as above defined, and (viii') -OR8 wherein R8 is as above defined.

5. A penam according to any preceding claim in which Y represents (a") a hydroxymethyl group,

wherein R2 is as above defined, or (f") -CH2-X" wherein X" represents (i") -NO2 as such or as its nitronates of the formula

are as above defined, (ii") -NR'4R'5 wherein R'4 and R'5 are as above defined,

wherein R2 is as above defined, or (viii") -OR8 wherein R8 is as above defined.

6. p-N itrobenzyl (5R)-6S-(1 R-t-butyidimethylsilyloxy-ethyl)-2-methylthio-2-nitromethyl-penam-3-car- boxylate.

7. p-N itrobenzyl (5R)-6S-(1 R-t-butyldimethylsilyloxy ethyl)-2-methylthio-2-formyl-pena m-3-carboxylate.

8. A method for the preparation of a penam according to claim 1, the method comprising cyclising an azetidinone having the general formula II

wherein R, R, and R2 are as defined in claim 1 and E represents an electron withdrawing group selected from heterocyclthio, methyl, nitro and cyano groups and groups of the formulae

and S(O),1R2 wherein R2, R4, R5, Z and n are as defined in claim 1, the cyclisation being effected in tetrahydrofuran, hexane or toluene in the presence of a base at a temperature of from -100 C to 0 C to obtain a penam having the general formula Ill

wherein E is as defined in this claim and, R, R1, R2 and n are as defined in claim 1 and, if necessary, converting the group CH2E in the penam ill into a group Y.

9. A method according to claim 8 in which the base is n-butyl-lithium, methyl lithium, phenyl lithium, lithium hexamethyldisilylazide or lithium diisopropylazide.

10. A method for the preparation of a penam having the general formula I

wherein R, R1 and Y are as defined in claim 1, the method comprising oxidising and treating with a tertiary amine or an alkali metal carbonate a penam IV in an inert solvent at a temperature of 0 to 1300C.

11. A method according to claim 10 in which the solvent is dichloromethane or chloroform.

12. A method according to claim 10 or claim 11 in which the oxidisation agent is m-chloroperbenzoic acid, peracetic acid or ozone.

13. A method according to any of claims 10 to 12 in which the tertiary amine is triethylamine or diisopropylethylamine.

14. A method according to any of claims 10 to 13 in which the alkali metal carbonate is sodium bicarbonate.

15. A method for the preparation of a penem having the general formula I as defined in claim 10, the method comprising proceeding according to claim 8 or claim 9 from an azetidinone II to a penam IV and proceeding according to any of claims 10 to 14 from the penam IV to the penam 1.

16. A method according to claim 15 in which the azetidinone II in which R represents a carboxy protecting group, R1 represents a protected 1-hydroxyethyl group, E represents a nitro group, R2 represents a methyl group and n is O is cyclised to give a penem Ill, the nitromethyl group in the penam Ill is converted to a formyl group and the resultant penam IV is oxidised and treated with a tertiary amine or an alkali metal carbonate to give a 2-formyl-6-(protected 1-hydroxyethyl)-penam-3-carboxylate which is reduced to give 2-hydroxymethyl-6-(protected 1 -hydroxyethyl )-penem-3-carboxylate.

17. A pharmaceutical composition comprising an O-deprotected and optionally N-deprotected penam according to claim 1 in admixture with a pharmaceuticaily acceptable diluent or carrier.