PENEM DERIVATIVES

Abstract: New antibacterial agents are compounds of formula wherein R is hydrogen atom or C₁-C₄ alkyl group optionally substituted from halogen atom or hydroxy group optionally protected, A is Z, ZOCO or ZCO residue, wherein Z is phenylene, naphthylene, heterocyclediyl, C₁-C₇ alkylene, C₂-C₄ alkenylene, alkynylene, , C₃-C₈ cyclo­ alkylene, aralkylene radical optionally substituted, and Q (+) represents a group , wherein R₁, R₂ and R₃ are each either: (i) optionally substituted alkyl, aralkyl or aryl radical or (ii) R₁ is as defined above under (i) and R₂, R₃, taken together, represent an optionally substituted or fused heterocyclic radical or (iii) R₁, R₂, R₃ taken together, represent an optionally substituted azonia-bicyclo or tricyclo radical or (iv) R₁, R₂, R₃, taken together, represent an optionally substituted or fused pyridinium, pyrazinium, pyrazolium or pyridazinium radical, and the pharmaceutically or veterinarily acceptable salts thereof. The compounds are prepared by reacting the amine NR, R² R³ with the corresponding penem substituted in the s positions by A-HC₂-L group where A is as defined above and L is a leaving group.

Description: The present invention relates to new penem compounds, to processes for their preparation, and to pharmaceutical and veterinary compositions containing them. Compounds of the invention are quaternary ammonium carboxylates of the following formula (I) and their pharmaceutically or veterinarily acceptable salts wherein R is hydrogen or a C₁-C₄ alkyl group either unsubstituted or substituted by one or more substituents chosen from a free or protected hydroxy group and halogen atom; A is a Z , Z-O-CO- or -Z-CO- residue, wherein Z represents (a) an optionally substituted phenylene or naph­ thylene group, (b) an optionally substituted heterocyclediyl radical wherein the hetero ring is mono or bicyclic, saturated or unsaturated containing at least one heteroatom selected from oxygen, sulphur and nitrogen; (c) an optionally substituted linear or branched C₁-C₇ alkylene radical; (d) a C₂-C₄ alkenylene or alkynylene group or a group of formula ; (e) an optionally substituted C₃-C₈ cyclo­ alkylene ring or (f) an aralkylene radical of formula wherein n is 1, 2 or 3, and Q(+) represents a group, wherein (i) R₁, R₂, R₃ are each independently an optionally substituted alkyl, aralkyl or aryl radical; or (ii) R₁ is as defined above under (i) and R₂, R₃ taken together with the nitrogen atom represent an optionally substituted heterocyclic or fused heterocyclic radical; or (iii) R₁, R₂, R₃, taken together with the nitrogen atom, repre­ sent an optionally substituted azoniabicyclo or azonia­ tricyclo radical; or (iv) R₁, R₂, R₃, taken together with nitrogen atom, represent an optionally substituted pyridinium, pyrazinium, pyrazo­ lium, or pyridazinium radical, such radicals being optio­ nally fused with one phenyl ring or with a 5-7 membered, saturated or unsaturated cycloaliphatic or heterocyclic ring. The present invention includes all the possible geometrical and optical isomers of the compounds of formula (I), either in the form of isomeric mixtures or in the form of the individual separated isomers. Preferably, the compounds of formula (I) have a (5R,6S) configuration. The preferred R group is an (α-hydroxy)ethyl radical and this radical preferably has a (1R) configuration, i.e. a R configuration at the α-carbon atom of the ethyl group. As already said also the pharmaceutically or veterinarily acceptable salts of the compounds of formula (I) are included within the scope of the invention. The said salts may be salts with acids, either inorganic acids such as, e.g. acetic, citric, tartaric, fumaric or methanesulphonic acid, and salts with bases, either inorganic bases such as, e.g. alkali or alkaline-earth metal hydroxides, in particular sodium and potassium hydroxides, or organic bases such as, e.g., triethylamine, pyridine, benzylamine or collidine, including aminoacids such as, e.g., lysine or procaine. The invention includes also internal salts, i.e. zwitterions. In the present specification, the term "halogen" preferably encompasses fluorine and chlorine atom, but also iodine and bromine atoms. The alkyl groups, including the aliphatic moieties of the alkoxy, alkylthio and alkanoyl groups, may be branched or straight chain. Preferably, the alkyl and aralkyl radicals under definition (i) for Q are optionally substituted C₁-C₄nd alkyl and C₇-C₁₁ aralkyl radicals. In the definitions of Z, R₁, R₂, R₃, the substituents for the mentioned alkyl, aralkyl, aryl, azoniabicyclo, azoniatricyclo, pyridinium, pyrazinium, pyrazolium, pyridazinium, cycloalkylene, alkylene, phenylene, naphthylene and heterocyclediyl radicals are preferably selected from : (a) halogen; (b) hydroxy; (c) C₁-C₄ alkoxy; (d) C₁-C₄ alkylthio; (e) a group wherein each of R₄ and R₅ is, independently, hydrogen or C₁-C₄ alkyl; (f) sulfo; (g) -CO₂R₄ wherein R₄ is as defined above; (h) -C≡N; (1) dimethyl-formamidino; (j) a group wherein R₄ and R₅ are as defined above; (k) hydroxycarbamoyl or carbamoyloxy; (l) a hydroximinomethyl (HO-N=CH-) or methoximinomethyl (CH₃O-N=CH-), hydroximino (α-methyl)methyl group; (m) a formamido or acetamido group; (n) a formyloxy or acetoxy group; (o) a C₁-C₄ alkanoyl group; (p) an aryl group; (q) a saturated or unsaturated heterocyclic ring; (r) a nitro group; (s) a mesyloxy group; (t) an oxo group; and (u) a C₁-C₄ alkyl group either unsubstituted or substituted by a substituent chosen from (a) to (t) above. A C₁-C₄ alkyl group is, preferably, methyl or ethyl. A heterocyclediyl radical is, preferably, a furanediyl, a 1,3 thiadiazolediyl, thiophenediyl or pyridinediyl. A C₁-C₇ alkylene radical is preferably methylene, ethylene, propylene or buthylene group. A C₃-C₈ cycloalkylene ring is, preferably, cyclobutylene, cyclopentylene or cyclohexylene. A C₂-C₄ alkenylene group is, preferably, a 1,2-ethenylene. A C₂-C₄ alkynylene group is, preferably, ethynylene. The term "aryl" encompasses, preferably, phenyl and naphthyl groups. The heterocyclic rings may be saturated or unsaturated, may have from 4 to 7 members and may contain from 1 to 4 hetero­ atoms selected from oxygen, nitrogen and sulphur atom. A C₁-C₄ alkoxy group is preferably, methoxy or ethoxy. A C₁-C₄ alkylthio group is, preferably, methylthio or ethylthio. A C₁-C₄ alkanoyl group is, preferably, acetyl or propionyl. A protected hydroxy group may be a hydroxy group protected by a protecting group chosen, for instance, from an optionally substituted, especially halo-substituted, acyl group, e.g., acetyl, monochloroacetyl, dichloroacetyl, trifluoroacetyl, benzoyl or p-bromophenacyl; a triarylmethyl group, in particular triphenylmethyl; a silyl group, in particular trimethylsilyl, dimethyl-tert-butylsilyl,diphenyl-tert-butyl silyl; or also a group such as tert-butoxy carbonyl, p-nitro-benzyloxycarbonyl, 2,2,2-trichloroethoxycarbonyl, allyloxycarbonyl, benzyl, and pyranyl. Preferred protecting groups of the hydroxy function are p-nitro-­ benzyloxycarbonyl; dimethyl-tert-butyl-silyl; diphenyl-tert­ -butyl-silyl; trimethyl silyl; allyloxy-carbonyl; benzyl; p-bromo-phenacyl; triphenylmethyl and pyranyl. Preferred classes of compounds under this invention include compounds of formula (I) wherein : R is an (α-hydroxy)ethyl group; Z is one of the following residues: (c') methylene, ethylene, n-propylene or tetramethylene group (d') 1,2 ethenediyl group (f') para, meta or ortho Q (+) is , wherein (i') R₁, R₂, R₃ are each independently methyl, ethyl, n-propyl, i -propyl, dimethylaminomethyl, cyanomethyl, cyanoethyl, carbamoylmethyl, 2-hydroxyethyl, 2-chloroethyl, carboxymethyl, ethoxycarbonylmethyl, carboxyethyl, 2­ -methyl-2-cyanoethyl, 3-oxobutyl or dimethylformimidino group ; or (ii') R₁ is as defined above under (i'), still preferably methyl, ethyl, chloroethyl, cyanomethyl, cyanoethyl, hydroxyethyl or aminoethyl, and R₂, R₃, taken together with the nitrogen atom, represent one of the following heterocyclyl ammonium radicals in said heterocyclic ring, when substituted, the substituents being one or more, preferably one or two, equal or different and selected from the group (a), (b), (e), (g), (h), (i), (q), (t) and (u) as defined above; or (iii') R₁, R₂, R₃, taken together with the nitrogen atom, represent one of the following radicals wherein the quinuclidine ring may be sustituted by an oxo , hydroxy or methoxy group; or (iv') R₁, R₂, R₃, taken together with the nitrogen atom, represent one of the following radicals wherein R₆, R₇ are independently hydrogen atom, C₁-C₄ alkyl, optionally substituted from cyano, hydroxy, sulfo, hydroxyimino group; methylsulphonyl, carbamoyl, hydroxy, methylthio, methoxy, formamido, formyl, hydroxycarbamoyl or amino group and the pharmaceutically or veterinarily acceptable salts thereof. Specific examples of preferred compounds of the invention are listed in the following table : The compounds of formula (I) can be prepared by a process comprising reacting a compound of formula (II) wherein R₁, R₂, R₃ are as defined above, with a penem intermediate of formula (III) wherein R and A are as defined above, Z' is a carboxy protecting group, and L is a leaving group susceptible of nucleophilic displacement by the amine of formula (II), and then removing the protecting groups therein present and, if desired, separating a mixture of isomers into the single isomers. The leaving group L in the compound of formula (III) may be, for example, a sulphonyloxy group -OSO₂R', wherein R' is a substituted or unsubstituted alkyl or aryl group; or a halogen atom such as iodine, bromine, chlorine. A particularly preferred sulphonyloxy group is trifluoro­ methanesulphonyloxy, -OSO₂CF₃. A particularly preferred halogen atom is iodine. A carboxy protecting group Z' may be any group which, together with the -CO₂- moiety, forms an esterified carboxy group. Examples of carboxy protecting groups are, in particular, C₁-C₆ alkyl groups, for instance methyl, ethyl or tert-butyl; halo-substituted C₁-C₆ alkyl groups, for example 2,2,2-tri­ chloroethyl; C₂-C₄ alkenyl groups, for example allyl; optionally substituted aryl groups, for example phenyl and p-nitro-phenyl; optionally substituted aryl C₁-C₆ alkyl groups, for example benzyl, p-nitro-benzyl and p-methoxy­ -benzyl; aryloxy-C₁-C₆ alkyl groups, for example phenoxy­ -ethyl; or groups such as benzhydryl, o -nitro-benzyhydryl, acetonyl, trimethylsilyl, diphenyl-tert-butyl-silyl, and dimethyl-tert-butyl-silyl, or groups such as pivaloyloxy methyl or phthalidyl. Particularly preferred carboxy protecting groups are allyl, p -nitrobenzyl, trimethylsilyl, dimethyl-tert-butyl-silyl, and trichloroethyl. When in the compound of formula (III) R is a C₁-C₃ alkyl group substituted by hydroxy, the hydroxy is preferably protected, and a particularly preferred protecting group is dimethyl-tert-butyl-silyl. The reaction between a compound of formula (II) and a compound of formula (III), may be performed in a suitable organic, preferably aprotic, solvent which may be, for instance, tetra­ hydrofuran, dimethylformamide, acetone or a halogenated hydro­ carbon such as, e.g., dichloromethane. The reaction temperature may, preferably, vary between about -100°C and about +40°C, preferably between -70°C and + 15°C. A compound of formula (III) wherein L is a sulphonyloxy group may be prepared reacting, according to known and conventional procedures, a carbinol precursor of formula (IV) wherein R, A and Z' are as defined above, with the appropriate sulphonyl anhydride or sulphonyl halide, preferably triflic anhydride, or triflic chloride, in the presence of a non-­ nucleophilic acid acceptor which may be, for instance, an inorganic base such as, e.g., calcium or lithium carbonate or calcium oxide, or an organic base such as, e.g., 2,6-lutidine or also the same compound of formula (II) to be reacted in the subsequent step. Indeed, according to a preferred procedure of the invention the compound of formula (IV) is made to react with the suitable sulphonyl anhydride or sulphonyl halide in the presence of an excess, usually an amount equal to or greater than 2 molar equivalents, of the desired compound of formula (II): in this situation the compound of formula (III) is not even isolated from the reaction mixture because it reacts in situ with the compound of formula (II). The hereabove said preferred procedure is preferably carried out using dry dichloromethane as solvent at temperatures from about -70°C to +25°C. When a compound of formula (II) is reacted with a compound of formula (III) wherein L is halogen, the presence of a silver salt particularly if soluble in the media, e.g. AgClO₄, may be beneficial. A compound of formula (III) wherein L is halogen, may be prepared from the corresponding carbinol precursor of formula (IV) according to a modified Mitsunobu reaction, according to which this carbinol is allowed to react with an organic amine hydro­ halide, such as, for instance, methoxyamine hydrochloride, pyridine hydrochloride, pyridine hydrobromide and the preformed complex obtained from diethylazodicarboxylate and triphenyl­ phosphine, said reaction being carried out, e.g., in tetra­ hydrofuran or methylene chloride, preferably around room temperature. Alternatively, in the above modified Mitsunobu reaction a zinc halide, such as zinc chloride, zinc bromide and zinc iodide, can be sustituted for the organic amine hydrohalide, under conditions substantially similar to those reported in J. Org. Chem. , 1984, 49 , 3027. Alternatively, a compound of formula (III) wherein L is halogen may be obtained from the carbinol of formula (IV) according to the more conventional procedures, entailing reaction with inorganic acid halides such as SOCl₂, PCl₅, PCl₃, PBr₃, POCl₃, POBr₃ and the like. An additional methodology well-known in the literature, namely the reaction with PPh₃ in CCl₄, can be exploited for the pre­ paration of compounds of formula (III) wherein L is chloride. A compound of formula (III) wherein L is iodine can be prepared by a halide exchange reaction from a compound of formula (III), wherein L is chlorine or bromine and sodium iodide, this reaction being preferably carried out in acetone at tempera­ tures ranging from 0°C to + 60°C (reflux temperature). Some intermediates of formula (III), preferably when L is chlo­ rine, and the intermediates of formula (IV), either as such or as their protected derivatives, are known compounds or can be prepared from known compounds by following known gene­ ral methodolgies. These include, for example, A) thermal cyclisation of a compound of formula (V) wherein R, A, Z' are as defined above, X represents sulphur or oxygen, and W is free or protected OH, or halogen, preferably chlorine, according to the method described, for example, in J. Am. Chem. Soc. , 1978, 100 , 8214 and Chem. Pharm. Bull. , 1981, 29 , 3158; B) thermal cyclization of a compound of formula (VI) wherein R, X, A, Z' are as defined above, and W' is free or protected OH; said cyclisation being performed in the presence of an organic phosphite, preferably trimethyl or triethyl phosphite, according to the method described, for example in Chem. Pharm. Bull. , 1983, 31 , 768 and Tetrahedron Lett. , 1984, 25 , 2395; C) reaction of a compound of formula (VII) wherein R, X, Z, Z' are as defined above, with a carboxylic acid of formula (VIII), or an activated derivative thereof wherein W is as defined above, according to the method described, for example, in our British Patent Application No. 2,118,181A. In particular, method C may be used to obtain intermediates of formula (III) and (IV) wherein -A- represents a group ; method B may be used to obtain compounds of formula (IV) and method A may be used to obtain intermediates of the formula (III) or (IV). Removal of the protecting groups can be effected by known per se procedures; e.g. silyl groups can be removed under mild acidic conditions, or by fluoride ions, e.g. with tetrabutylammonium fluoride; p-nitrobenzyl groups can be removed by reduction, e.g. by catalytic hydrogenation, or with metals, such as Fe and Zn; allyl carboxylates can be cleaved by transallylation with an organic acid or a salt thereof, such as acetic acid, 2-ethylhexanoic acid or their sodium and potassium salts, this reaction being catalyzed by a triphenylphosphine-palladium complex, preferably by tetra­ kis-triphenylphosphine-Pd°. The optional salification of an obtained compound and the separation of a mixture of isomers into the single isomers may be carried out following known and conventional proce­ dures. Compounds of formula (II), (V), (VI), (VII), (VIII) are known compounds or can be prepared from known compounds according to known methods. The compounds of formula (I) provided by the present invention are potent, broad spectrum antibacterial agents. In comparison with other penem compounds, e.g. the sodium salts derived from penems of formula (IV), or compounds of formula (I) wherein Q is an amine instead of quaternary ammonium, they usually show markedly increased in vitro activity against both Gram-positive and Gram-negative strains. Moreover, in comparison with other penem compounds, they show unusually prolonged plasma levels and, when tested in vivo after parenteral administration, they displayed a very high degree of therapeutic effectiveness in treating infections caused by both Gram-positive and Gram-negative bacteria, their toxicity being on the other hand quite negligible. Table I shows the in vitro activity of a typical compound of formula (I), the compound 5 of the previous examples, in comparison with a classical penem of relevance, FCE 21420 ( J. Antibiotics , 1982, 35 , 1248) and the third generation cephalosporin Cefotaxime. Table II shows "in vivo" the activity of compound 5. Owing to their high antibacterial activity the compounds of the invention are thus useful, for example, in the treatment of respiratory tract infections, for example, bronchitis, bronchopneumonia, pleuritis, hepatobiliary and abdominal infections, septicemia; urinary tract infections, for example, pyelonephritis, cystitis; obstetrical and gynecological infections, for instance, cervicitis, endometritis; ear, nose and throat infections, for instance otitis, sinusitis, parotitis. The compounds of the invention may be administered, either to humans or to animals, in a variety of dosage forms, e.g., orally in the form of tablets, capsules, drops or syrups; rectally in the form of suppositories; parenterally, e.g., intravenously or intramuscularly (as solutions or suspen­ sions), with intravenous administration being preferred in emergency situation; by inhalation in the form of areosols or solutions for nebulizers; intravaginally in the form, e.g., of pessaries; or topically in the form of lotions, creams and ointments. The pharmaceutical or veterinary compositions containing the compounds of formula (I), which are also within the scope of the invention, may be prepared in a conventional way by employing the conventional carriers or diluents used for, e.g., cephalosporins. Conventional carriers or diluents are, for example, water, gelatine, lactose, starches, magnesium stearate, talc, vegetable oils, cellulose and the like. Daily doses in the range of about 0.5 to about 100 mg per kg of body weight may be used, in various animal species, the exact dose depending on the age, weight and condition of the subject to be treated and on the frequency and route of administration. A preferred way of administration of the compounds of the invention is the parenteral one: in this case the compounds may be administered, for example to adult humans, in an amount ranging from about 250 mg to about 1000 mg pro dose , preferably about 500 mg pro dose , 1-4 times a day, dissolved in a suitable solvent, such as, for example, sterile water or lidocaine hydrochloride solution for in­ tramuscolar injections, and sterile water, physiological saline solution, dextrose solution or the conventional in­ travenous fluids or electrolytes, for intravenous injec­ tions. Furthermore, the compounds of the invention may be used as antibacterial agents in a prophylactic manner, e.g., in cleaning or as surface disinfecting compositions, for example, at a concentration of about 0.2 to 1% by weight of such compounds admixed with, suspended or dissolved in conventional inert dry or aqueous carriers for application by washing or spraying. They are also useful as nutritional supplements in animal feeds. The following examples illustrate but do not limit the present invention. EXAMPLE 1 (5R,6S)-6-[(1R)-hydroxyethyl]-2-[4-(N-methylpyrrolidiniomethyl)-­ phenyl]-penem-3-carboxylate (Compound 1) A solution of (3S)-[(1R)-tert-butyldimethylsilyloxyethyl]­ -(4R)-[4-( tert -butyldiphenylsilyloxymethyl)-phenyl] acetyl-­ thio-1-[α-triphenylphosphoranylidene)allyloxycarbonylmethyl]­ azetidin-2-one (1.6 g) in dry distilled tetrahydrofuran (16 ml) is treated with acetic acid (0.95 ml) and tetrabutylammonium fluoride trihydrate (1.25 g). After 6 hours stirring at room temperature, the solvent was removed in vacuo and the residue was partioned between diluted aq. NaHCO₃ and ethyl acetate. The residue from the organic layer was purified by SiO₂ chroma­ tography to afford (3 S )-[(1 R )-tert-butyldimethylsilyloxyethyl]-­ (4R)-[4-(hydroxymethyl)phenyl]-acetylthio-1-[(α-triphenyl­ phosphoranylidene)allyloxy-carbonylmethyl]azetidin-2-one (1.0 g) as a foam. A solution of this material in toluene (30 ml) was refluxed for 7 hours; the solvent was then removed and the residue passed through a SiO₂ column (EtOAc - cyclohexane as eluants). There was obtained allyl (5 R , 6 S )-6-[(1R)- tert -butyldimethyl­ silyloxyethyl]-2-[4-(hydroxymethyl)phenyl]penem-3-carboxylate (375 mg) as waxy solid; IR : ν max (CH₂Cl₂) 1790, 1710 cm⁻¹; NMR (60 MHz, CDCl₃ + D₂O) = δ 0.08 (6H, s, SiMe₂), 0.88 (9H, s, SiBu t ), 1.28 (3H, d, J = 6Hz, CH ₃-CH), 3.68 (1H, dd, J = 1.5 and 6Hz, H-6), 4.2 (1H, m; CH₃ CH ) , 4.5-4.7 (4H, m, Ar CH ₂ + CO₂ CH ₂) , 5.2 and 5.35 (2H, each m, =CH₂), 5.65 (1H, d, J = 1.5 Hz, H-5), 5.9 (1H, m,CH₂ CH =CH₂), 7-7.5 (4H, m, Ar) ppm. A solution of the above intermediate (225 mg) in dry ethanol-free dichloromethane (10 ml), cooled at -50°C under argon, was treated in sequence with N-methylpyrrolidine (0.25 ml) and trifluoromethanesulphonic anhydride (0.125 ml). The reaction mixture was let rise to -20°C and after 20 minutes quenched with 0.1 M aqueous HCl. The organic layer was separated, washed with brine, dried and evaporated to give a residue which was triturated in ethyl acetate -ethyl ether mixtures, thus obtaining allyl (5 R ,6 S )-6-[(1R)-tert­ -butyldimethylsilyloxyethyl]-2-[4-(N-methylpyrrolidiniomethyl)­ phenyl]penem-3-carboxylate, as a powder (150 mg) ; IR: ν max (CHCl₃ film) 1785, 1710 cm⁻¹. This material was taken up in tetrahydrofuran (9 ml) and acetic acid (0.18 ml) and tetrabutylammonium fluoride trihy­ drate (0.3 g) were added. The clear solution was let stand for 30 hours at room temperature, then concentrated and passed through a silica gel column packed with CH₂Cl₂. The ammonium salts were eluted by a gradient of MeCN in CH₂Cl₂; then the product was eluted out by aqueous MeCN. The product-containing fractions were salted (NaCl) and the separated aqueous phase extracted twice with fresh MeCN. The MeCN phase and the MeCN extracts were collected, dried (MgSO₄) and evaporated to obtain salts (Cl⁻, acetate) of allyl (5 R ,6 S )-6-[(1R)-hydroxyethyl]-2-[4-(N-methyl-N-pyrro­ lidioniomethyl)phenyl]penem-3-carboxylate (90 mg); IR : ν max (film) 3400-3200, 1785, 1710 cm⁻¹. The above product (90 mg) in a 1:1 tetrahydrofuran-dichloro­ methane mixture (6 ml) was treated, in sequence, with acetic acid (0.03 ml), triphenylphosphine (9 mg) and tetrakis (tri­ phenylphosphine) Pd(O) (9 mg). After 10 minutes stirring, the addition of HOAc, PPh₃o­ and the catalyst was repeated and, after further 15 minutes, the solvents were removed in vacuo. The residue was dissolved in demineralized water and purified by reverse-phase chroma­ tography (LiChroprep RP-18 Merck), eluting first with water, therewith a gradient in MeCN (from 95:5 to 1:1), and finally with H₂O-MeCN-EtOH (4:6:1). The appropriate fractions (TLC on SiO₂, i-PrOH/H₂O/HOAc 5:1:1, slow-running spot) were combined and freeze-dried to obtain 40 mg of the title product; IR : ν max (KBr) 3400, 1770, 1620 cm⁻¹; NMR (200 MHz, D₂O) : δ 1.31 (3H, d, J = 6.3 Hz, CH ₃CH), 2.23 (4H, m, , 2.95 (3H, s, CH₃), 3.3-3.7 (4H, ), 4.00 (1H, dd, J = 1.6 and 6.0 Hz, H-6), 4.27 (1H, dq, J = 6.0 and 6.3 Hz, CH₃- CH ), 4.51 (2H, s, CH₂), 5.80 (1H, d, J = 1.6 Hz, H-5), 7.53 (4H, s, Ph) ppm, UV = λ max (H₂O) : 250 and 330 nm. EXAMPLE 2 (5R,6S)-6-[(1R)-hydroxyethyl]-2-[4-(pyridiniomethyl)phenyl]­ penem-3-carboxylate (Compound 5) A solution of allyl (5 R ,6 S )-6-[(1R)- tert -butyldimethylsilyloxy­ ethyl]-2-[4-(hydroxymethyl)phenyl]penem-3-carboxylate (300 mg) obtained as described in Example 1, in dry, ethanol-free dichloromethane (16 ml) was treated with pyridine (1.4 ml) and trifluoromethanesulphonic anhydride (0.8 ml) at -40°C under nitrogen. After 30 minutes, 0.1M aqueous HCl (10 ml) was added, the organic layer was separated, washed with a further amount of 0.1N HCl, dried and evaporated. The resulting residue (410 mg) was dissolved in tetrahydro­ furan (20 ml) and stirred for 24 hours at room temperature in the presence of acetic acid (1 ml) and tetrabutylammonium fluoride trihydrate (1.6 g). Removal of the solvent and purif­ cation by silica gel chromatography (CH₂Cl₂, then CH₂Cl₂-MeCN, then MeCN-H₂O) afforded the allyl ester of the title compound (250 mg); IR : ν max (KBr) : 3400, 1780, 1705 cm⁻¹; UV : λ max (EtOH) 256 and 336 um. This material was dissolved in a 1:1 tetrahydrofuran-dichloro­ methane mixture and stirred under argon in the presence of acetic acid (0.25 ml), PPh₃ (25 mg) and tetrakis (triphenyl­ phosphine) Pd(O) (25 mg). More catalyst was added at ten minutes intervals (4x25 mg), until the reaction was judged complete by TLC (C₆H₆-EtOAc­ -HOAc-H₂O 9:9:15:5). After evaporation in vacuo, the residue was dissolved in water and purified by reverse-phase chromatography. Freeze-drying of the last eluted fractions afforded the title compound (100 mg); IR : ν max (KBr) 3400, 1770, 1600 cm⁻¹, NMR (200 MHz, D₂O) : δ 1.29 (3H, d, J = 6.4 Hz, CH ₃CH), 3.94 (1H, dd, J = 1.6 and 6.0 Hz, H-6), 4.24 (1H, dq, J = 6.0 and 6.4 Hz, CH₃ CH ), 5.74 (1H, d, J = 1.6 Hz, H-5), 5.80 (2H, s, CH₂), 7.43 (4H, m, Ph), 8.05 (2H, dd, J = 6.5 and 7.7 Hz, ), 8.55 (1H, t, J=7.7 Hz, 8.90 (2H, d, J = 6.5 Hz, ) ppm; UV : λ max (H₂O) : 254 and 330 nm. EXAMPLE 3 (5R,6S)-6-[(1R)-hydroxyethyl]-2-[2-(pyridiniomethyl)phenyl] penem-3-carboxylate (Compound 14) A mixture of potassium 2-hydroxymethylbenzoate (9.45 g) and chloroacetone (5 ml) in dry dimethylformamide (100 ml) was stirred for 3 hours at room temperature. Ethyl acetate and brine were then added and the organic layer, after further washing with water, was dried and evaporated to obtain acetonyl 2-hydroxymethylbenzoate (10 g) as a white powder. A solution of this material (1 g) in dimethylformamide (20 ml) was stirred for 3 hours in the presence of tert-butyldiphenyl­ silylchloride (2.32 ml) and imidazole (0.864 g). The reaction mixture was partitioned between ethyl acetate and aqueous HCl; the dried organic phase was evaporated and the residue triturated in n-hexane to yield acetonyl 2-(tert­ -butyldiphenylsilyloxymethyl)benzoate (0.94 g) as a white solid; IR : ν max (CHCl₃) 1740 sh, 1725 cm⁻¹; NMR (60 MHZ, CDCl₃) δ 1.15 (9H, s, SiBu t ), 2.15 (3H, s, CH₃), 4.70 (2H, s, CH₂CO), 5.20 (2H, s, Ph CH ₂O), 7.2-8.2 (14H, m, Ar) ppm. To this compound (0.78 g) dissolved in acetonitrile (25 ml), a solution of N/10 NaOH was added (26.3 ml). The resul­ ting mixture was concentrated in vacuo to half of its volume and ethyl acetate was added. The mixture was acidified with diluted HCl under stirring, the organic layer was separated, then washed twice with brine, dried and evaporated. The solid residue was triturated in n -hexane and filtered thus obtaining 2-(tert-butyldiphenylsilyloxymethyl)-benzoic acid (0.54 g) as a white solid; m.p. 130-132°C. This product, dissolved in dry, ethanol-free di­ chloromethane (30 ml), was stirred for 6 hours at room temperature in the presence of thionyl chloride (0.5 ml). The reaction mixture was evaporated in vacuo from benzene (twice), thus obtaining 2-(tert-butyldiphenylsilyloxymethyl) benzoyl chloride, which was immediately used as such in the following step. A solution of silver (3S)-[(1R)-tert-butyldimethylsilyloxy­ ethyl]-1-[(α-triphenylphosphoranylidene)allyloxycarbonylmethyl]­ -2-oxoazetidinyl-4-thiolate (0.7 g) in dry dichloromethane (25 ml) was allowed to react with the above acyl chloride (0.55 g) and pyridine (0.08 ml) for 30 minutes at room tem­ perature. After addition of Celite and charcoal, the mixture was stirred for a further 10 minutes, filtered through Celite and sequentially washed with 4% aq. HCl, brine, aq. NaHCO₃. Flash-chromatography afforded (3S)-[(1R)-tert-­ butyldimethylsilyloxyethyl]-(4R)-[2-(tert-butyldiphenylsilyl­ oxymethyl)phenyl]acetylthio-1-[(α-triphenylphosphoranylidene) allyloxycarbonylmethyl]azetidin-2-one (0.8 g) as a foam; IR : ν max (CHCl₃) 1740, 1660, 1610 cm⁻¹. This intermediate was dissolved in dry xylene and refluxed for 7 hours in the presence of a catalytic amount of hydro­ quinone (20 mg). The cooled reaction mixture was passed through a SiO₂ column, thereby obtaining allyl (5R,6S)-6-­ [(1R)-tert-butyldimethylsilyloxyethyl]-2-[2-(tert-butyldiphenyl­ silyloxymethyl)phenyl]penem-3-carboxylate (0.4 g); IR : ν max (film) 1790, 1710 cm⁻¹; NMR (60MH z , CDCl₃) : δ 0.06 (6H, s, SiMe₂), 0.8 (9H, s, SiBu t ), 1.1 (9H, s, SiBu t ), 1.25 (3H, d, J = 6.5 H z , CH ₃CH), 3.6 (1H, dd, J = 1.5 and 4.5 H z , H-6), 4.3 (1H, m, CH₃ CH ), 4.5 (2H, d, CH ₂CH=CH₂), 4.7 (2H, s, Ar CH ₂O), 4.9 (2H, m, CH= CH ₂), 5.5 (1H, d, J = 1.5 Hz, H-6), 5.7 (1H, m, CH₂- CH =CH₂), 7.1-7.7 (14H, m, Ar) ppm. To a solution of this material (400 mg) in dry tetrahydrofuran (20 ml), acetic acid (0.7 ml) and tetrabutylammonium fluoride trihydrate (500 mg) were added. The mixture was stirred for 5 hours, the solvent was removed in vacuo and the residue purified by flash-chromatography (EtOAc-cyclohexane mixtures) to obtain allyl (5R,6S)-6-[(1R)-tert-butyldimethylsilyloxy­ ethyl]-2-[2-(hydroxymethyl)phenyl]penem 3-carboxylate as a white foam (250 mg); IR : ν max (film) : 3400, 1790, 1705 cm⁻¹; NMR (60 MHz, CDCl₃) : δ 0.05 (6H, s, SiMe₂), 0.9 (9H, s, SiBu t ), 1.25 (3H, d, CH ₃CH), 2.3 (1H, br s, OH), 3.8 (1H, dd, J=1.8 and 5 Hz, H-6), 4.3 (1H, m, CH₃ CH ), 4.52 (2H, d, J=5 Hz, CH ₂CH=CH₂), 4.65 (2H, s, ArCH₂), 5.2 (2H, m, CH₂= CH ₂), 5.5-5.9 (1H, m, CH₂- CH -CH₂), 5.85 (1H, d, J=1.8 Hz, H-5), 7.2-7.8 (4H, m, Ar) ppm. Pydridine (0.1 ml) and trifluoromethanesulphonic anhydride (0.1 ml) were added to a solution of the above intermediate (100 mg) in dry CH₂Cl₂ (2 ml) at -60°C under nitrogen. After 15 minutes stirring at -40°C, the reaction mixture was quenched with 4% HCl and brine. The organic layer was separated, washed twice with brine and evaporated to leave a residue which was triturated with ethyl ether, thus obtaining allyl (5R,6S)-6-[(1R)-tert-butyldimethyl­ silyloxyethyl]-2-[2-(pyridiniomethyl)pehnyl]penem-3-carboxylate, chloride salt, as a white crystalline solid; IR : ν max (KBr) 1795, 1705 cm⁻¹; NMR (200 MHz, acetone d₆, 45°C) : δ 0.11 (6H, s, SiMe₂), 0.91 (9H, s, SiBu t ), 1.28 (3H, d, J=6.4 Hz, CH ₃CH), 4.07 (1H, m, H-6), 4.3-4.4 (3H, m, O CH ₂CH=CH₂ and CH₃ CH ), 5.10 and 5.18 (each 1H, m, CH= CH ₂), 5.68 (1H, m, CH₂ CH =CH₂), 5.95 (1H, d, J=1.7Hz, H-5), 6.10 (2H, m, PhCH₂N⁺), 7.4-7.8 (4H, m, Ph), 8.19 (2H, dd, J=5.7 and 7.8 Hz, ), 8.72 (1H, t, J=7.8 Hz, , and 9.05 (2H, d, J=5.7 Hz, ) ppm. Sequential treatment of this product with tetrabutylammonium fluoride and finally with HOAc/PPh₃/(PPh₃)₄Pd under the same identical conditions indicated in Example 2 afforded a sample (25 mg) of the title compound; IR : ν max (KBr) 3400, 1765, 1590 cm⁻¹; UV = λ max (H₂O) 330 nm. EXAMPLE 4 Operating as described in the previous examples, the following compounds were analogously prepared : (5R,6S)-6-[(1R)-hydroxyethyl]-2-[4-(N-methylpiperidiniomethyl)­ phenyl]penem-3-carboxylate (2) ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[4-(N,N,N-trimethylammonio­ methyl)phenyl]-3-carboxylate (3) ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[4-(N,N,N-triethylammoniomethyl)­ phenyl]penem-3-carboxylate (4) ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(6,7-dihydro-5 H -cyclopenta­ [b]-pyridinio)methyl]phenyl}penem-3-carboxylate (6); (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(4-carbamoylpyridinio)methyl]­ phenyl}penem-3-carboxylate (7) ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(5-ethyl-2-methylpyridinio) methyl]phenyl}penem-3-carboxylate (8) ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[4-(quinoliniomethyl)phenyl]­ penem-3-carboxylate (9) ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[4-(quinuclidiniomethyl)-phenyl]­ penem-3-carboxylate (10) ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(1-methylmorpholinio)methyl]­ phenyl}penem-3-carboxylate (11) ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(1-methylpiperazinio)methyl]­ phenyl}penem-3-carboxylate (12); (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(1,4-dimethylpiperazinio)­ methyl]phenyl}penem-3-carboxylate (13) ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[2-(isoquinuclidiniomethyl)phenyl]­ penem-3-carboxylate (15) ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-{2-[(3-cyanomethylpyridinio)­ methyl]phenyl}penem-3-carboxylate (16) ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[2-(pyraziniomethyl)phenyl]­ penem-3-carboxylate (17) ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[2-(N,N,N-trimethylammonio­ methyl)phenyl]penem-3-carboxylate (18) ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[2-(N,N,N-triethylammonio­ methyl)-phenyl]-penem-3-carboxylate (19) ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[2-(N-methylpyrrolidiniomethyl)­ phenyl]penem-3-carboxylate (20) ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[2-(N-methylpiperidiniomethyl)­ phenyl]-penem-3-carboxylate (21) ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[3-(pyridiniomethyl)phenyl]­ penem-3-carboxylate (22) ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[3-(N-methylpyrrolidiniomethyl)­ phenyl]penem-3-carboxylate (23) ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[3-(N,N,N-trimethylammonio­ methyl)phenyl]-penem-3-carboxylate (24) ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[( E )-2-(pyridiniomethyl)ethenyl]­ penem-3-carboxylate (38) ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[( Z )-2-(pyridiniomethyl)ethenyl]­ penem-3-carboxylate (39) ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[( Z )-2-(N-methylpyrrolidinio­ methyl)-phenyl]penem-3-carboxylate (40) ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[5-(N-methylpyrrolidiniomethyl)­ thien-2-yl]-ethenyl-3-carboxylate (28) ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[4-(pyridinioacetyl)-phenyl]­ penem-3-carboxylate (44) ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[3-(pyridinioacetyl)phenyl]­ penem-3-carboxylate (45) ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[4-(2-oxo-3-pyridiniopropyl)­ phenyl]-penem-3-carboxylate (46) ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(3-methylthiopyridinio)­ methyl]phenyl}penem-3-carboxylate (47) ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-{3-[(4-methylthiopyridinio)­ methyl]phenyl}penem-3-carboxylate (48) and (5R,6S)-6-[(1R)-hydroxyethyl]-2-{3-[(4-methoxypyridinio)methyl]­ phenyl}penem-3-carboxylate (49). EXAMPLE 5 (5R,6S)-6-[(1R)-hydroxyethyl]-2-[(N-methylpyrrolidinio)­ acetoxymethyl]penem-3-carboxylate (Compound 41) A solution of allyl (5R,6S)-6-[(1R)- tert -butyldimethylsilyloxy­ ethyl]-2-(hydroxymethyl)penem-3-carboxylate (480 mg) in dry dichloromethane (15 ml) was sequentially treated with tri­ phenylphosphine (790 mg), tert -butyldiphenylsilyloxyacetic acid (420 mg) and diethyl azodicarboxylate (0.475 ml). A mild exotermic reaction took place and rapidly subsided. The solvent was removed and the residue was purified by silica gel chromatography, thus obtaining allyl(5R,6S)-6-[(1R)- tert -­ butyldimethylsilyloxyethyl]-2-[(tert-butyldiphenylsilyloxy)­ acetoxymethyl]penem-3-carboxylate (700 mg); IR : ν max (CHCl₃) : 1780, 1740, 1710 cm⁻¹. This material was dissolved in a tetrahydrofuran solution (30 ml) of tetrabutylammonium fluoride trihydrate (630 mg) and acetic acid (0.92 ml). After 1 hour standing at room tempera­ ture, the solvent was removed and the residue purified by silica gel chromatography to obtain allyl (5R,6S)-6-[(1R)-­ tert -butyldimethylsilyloxyethyl]-2-[(hydroxymethyl)acetoxy-­ methyl]penem-3-carboxylate as a yellowish oil (250 mg) ; IR = ν max (CHCl₃) : 1785, 1745, 1705 cm⁻¹; NMR (60MHz, CDCl₂) : δ 0.1 (6H, s, SiMe2), 0.9 (9H, s, SiBu t ), 1.25 (3H, d, J = 6Hz, CH ₃.CH), 3.70 (1H, dd, J= 1.5 and 4.5 Hz, H-6), 4.2 (3H, m, CO CH ₂O + CH₃ CH ), 4.75 (2H, m, CO₂ CH ₂), 5.2 and 5.4 (2H, each m, =CH₂), 5.35 (2H, ABq, J=15 Hz, 2- CH ₂O), 5.6 (1H, d, J = 1.5 Hz, H-5), 5.8-6.2 (1H, m, CH -CH₂) ppm The above intermediate (200 mg) was dissolved in dry CH₂Cl₂ (10 ml) and the cooled solution (-70°C, nitrogen atmosphere) was treated in sequence with N-methylpyrrolidine (0.22 ml) and trifluoromethanesulphonic anhydride (0.17 ml). After 10 minutes, the reaction mixture was diluted with more CH₂Cl₂, washed with 4% aq. HCl, then with water, dried and evaporated. The oily residue was stirred for 20 hours in a tetrahydrofuran solution (8 ml) containing acetic acid (0.5 ml) and tetra­ butylammonium fluoride trihydrate (470 mg). The solvent was then removed and the residue loaded on a SiO₂ column packed in dichloromethane. Sequential elution with CH₂Cl₂, CH₂Cl₂-EtOH 1:1, EtOH-MeCN gave some impurities, while the desired salts of allyl (5R,6S)-6-[(1R)-hydroxyethyl] -2-[(N-methylpyrrolidinio)acetoxymethyl]-penem-3-carboxylate were collected by eluting with 35% aq. MeCN. The product-containing fractions were collected, saturated with NaCl and extracted with MeCN. The organic extracts were dried and evaporated; the residue was taken up in dry CH₂Cl₂ (10 ml) containing HOAc (0.2 ml), and triphenylphosphine (50 mg) followed by tetrakis (triphenyl­ phosphine) Pd(O) (40 mg) were added. After 30 minutes stirring at room temperature, the catalyst was filtered off and after removal of the solvent, the crude product was dissolved in water and purified by reverse-phase chromatography (LiChroprep RP-18 Merck, water). The title product was eluted out with H₂O-MeCN and freeze­ -dried; white powder, 40 mg; IR : ν max (KBr) 3400, 1765, 1610 cm⁻¹; UV = λ max (H₂O) 258 and 308 nm; NMR (200 MHz, D₂O) = δ 1.29 (3H, d, J=6.4 Hz, CH ₃CH), 2.24 (4H, 3.27 (3H, s, ⁺NCH₃), 3.6-3.9 (4H, ), 3.93 (1H, dd, J = 1.4 and 5.9 Hz, H-6), 4.24 (1H, dq, J = 5.9 and 6.4 Hz), CH₃- CH ), 4.45 (2H, s, CH₂), 5.22 and 5.63 (2H, ABq, J = 14.0 Hz, 2- CH ₂), 5.68 (1H, d, J = 1.4 Hz, H-5) ppm. EXAMPLE 6 Operating as described in the former example, there were obtained : (5R,6S)-6-[(1R)-hydroxyethyl]-2-[2-(pyridinioacetoxy)ethyl]­ penem-3-carboxylate (42) ; and (5R,6S)-6-[(1R)-hydroxyethyl]-2-{2-[(N-methylpyrrolidinio)­ acetoxy]ethyl}penem-3-carboxylate (43). EXAMPLE 7 (5R,6S)-6-[(1R)-hydroxyethyl]-2-[3-(N-methylpyrrolidinio)­ propyl]-penem-3-carboxylate (Compound 31) PROCEDURE A - To a solution of allyl (5R,6S)-6-[(1R)- tert -­ butyl-dimethylsilyloxyethyl]-2-(3-hydroxypropyl)penem-3­ -carboxylate (400 mg) in dry ethanol-free dichloromethane (15 ml, cooled at -30°C under nitrogen, N-methylpyrrolidine (0.47 ml) and trifluoromethane sulphonic anhydride (0.36 ml) were added in sequence. The bath was removed and the reaction mixture was kept at room temperature until most of the starting material had disappeared (TLC monitoring). More dichloro­ methane and 0.1M aqueous HCl were added under stirring and the separated organic phase was washed with brine, dried and evaporated to afford an oily residue, mainly consisting of salts (chloride, triflate) of allyl (5R,6S)-6-[(1R)-tert-­ butyldimethylsilyloxyethyl]-2-[3-(N-methylpyrrolidinio)propyl]­ penem-3-carboxylate. Without purification, this material was added to a solution of tetrabutylammonium fluoride trihydrate (1.8 g) in tetra­ hydrofuran (15 ml) and acetic acid (1 ml), and the desilylation monitored by TLC. When the reaction was completed, the solvent was removed in vacuo and the residue was purified by flash-­ chromatography (CHCl₂-MeCN and then MeCN-H₂O). The obtained product (0.27 g), the allyl ester of the title compound, was stirred for 30 minutes under nitrogen in a mixture of triphenylphosphine (50 mg) and tetrakis (triphenyl­ phosphine) palladium (50 mg) in dichloromethane-tetrahydro­ furan (7 ml + 7 ml) and acetic acid (0.5 ml). The catalyst was filtered off and the solution, after removal of the solvent, was passed through a column packed with LiChroprep RP-18 Merck by eluting with water and then with 10% MeCN in H₂O. Freeze-drying of the relevant fractions afforded the title product (70- mg); IR : ν max (KBr) 3400, 1765, 1605 cm⁻¹; UV = λ max (H₂O) 304 nm. PROCEDURE B - Allyl (5R,6S)-6-[(1R)-tert-butyldimethylsilyl­ oxyethyl]-2-(3-chloropropyl)penem-3-carboxylate (270 mg) and sodium iodide were refluxed under argon in dry acetone until the reaction was judged complete by TLC. Most of the solvent was then removed in vacuo and the residue was partitioned between ethyl acetate and water. The dried organic layer was concentrated to give a residue which was purified by short-path flash-chromatography, thereby obtaining allyl (5R,6S)-6-[(1R)-tert-butyldimethylsilyl­ oxyethyl]-2-(3-iodopropyl)penem-3-carboxylate as a syrup (220 mg); IR : ν max (film) 1790, 1710 and 1580 cm⁻¹. To a solution of the above material in dry tetrahydrofuran (30 ml), N-methylpyrrolidine (0.1 ml) and silver perchlorate (165 mg) were added. The reaction mixture was stirred for 6 hours at 0°C and then left rise to room temperature in a nitrogen atmosphere in the dark. The solvent was removed and the residue was partitioned between dichloromethane and 0.1N HCl at 5°C. The organic layer was collected, filtered and evaporated to leave a residue consisting of salts (mainly chloride) of allyl (5R,6S)-6-[(1R)-tert-butyldimethylsilyloxy­ ethyl]-2-[3-(N-methylpyrrolidinio)propyl]penem-3-carboxylate. This intermediate was processed through the desilylation and deallylation steps as described above under Procedure A, thus obtaining an identical sample of the title compound. EXAMPLE 8 Operating as described in the previous example, there were obtained : (5R,6S)-6-[(1R)-hydroxyethyl]-2-[1-(pyridiniomethyl)cyclo­ pentyl]penem-3-carboxylate (25); (5R,6S)-6-[(1R)-hydroxyethyl]-2-[1-(N-methylpyrrolidinio­ methyl-cyclopentyl]penem-3-carboxylate (26); (5R,6S)-6-[(1R)-hydroxyethyl]-2-[1-(N,N,N-triethylammonio­ methyl)cyclopentyl]penem-3-carboxylate (27); (5R,6S)-6-[(1R)-hydroxyethyl]-2-[3-(N,N,N-trimethylammonio­ methyl)cyclobutyl]penem-3-carboxylate (36); (5R,6S)-6-[(1R)-hydroxyethyl]-2-[3-(pyridiniomethyl)cyclo­ pentyl]penem-3-carboxylate (37); (5R,6S)-6-[(1R)-hydroxyethyl]-2-(3-pyridiniopropyl)penem-3­ -carboxylate (29); (5R,6S)-6-[(1R)-hydroxyethyl]-2-[3-(3-cyanomethylpyridinio)­ propyl]penem-3-carboxylate (30); (5R,6S)-6-[(1R)-hydroxyethyl]-2-[3-(N,N,N-trimethylammonio)­ propyl]penem-3-carboxylate (32); (5R,6S)-6-[(1R)-hydroxyethyl]-2-[4-(3-cyanomethylpyridinio)­ butyl]penem-3-carboxylate (33); (5R,6S)-6-[(1R)-hydroxyethyl]-2-(4-pyridiniobutyl)-penem-3­ -carboxylate (34); and (5R,6S)-6-[(1R)-hydroxyethyl]-2-[4-(N-methylpyrrolidinio)­ butyl]penem-3-carboxylate (35). EXAMPLE 9 (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4[(3,5-dimethylpyridinio)­ methyl]phenyl}penem-3-carboxylate (compound 54) Operating as in Example 2, but employing 3,5-dimethylpyridine instead of pyridine, the title compound was obtained (700 mg) ; UV (H₂O) λ max 328, 268 nm; NMR (200 MHz, D₂O) δ ppm 1.30 (3H, d, J=6.2 Hz), 2.47 (6H, s), 3.93 (1H, d, J=1.6 and 5.8 Hz), 4.25 (1H, dq, J=5.8 and 6.2 Hz), 5.68 (2H, s), 5.73 (1H, d, J=1.6 Hz), 7.3-7.4 (4H, m), 8.19 (1H, m), 8.55 (2H, m). EXAMPLE 10 (5R,6S)-6-[(1R)-tert-butyldimethylsilyloxyethyl]-2-[4-(bromo­ methyl)phenyl]penem-3-carboxylate Step A) - A solution of (3S)-[(1R)-tert-butyldimethylsilyloxy­ ethyl]-(4R)-triphenylmethylthio-1-(1-allyloxycarbonyl-1-tri­ phenylphosphoranylidenemethyl)azetidin-2-one (5 g) and imidazole (0.75 g) in methanol (15 ml) was added to a stirred suspension of powdered silver nitrate (1.97 g) in the same solvent (20 ml) under nitrogen in the dark. After 15 minutes, dichloromethane (250 ml) was added; the organic layer was washed with water (2x200 ml), dried (Na₂SO₄) and evaporated to give 4.7 g of crude silver (3S)-[(1R)-tert-butyldimethylsilyloxyethyl]-1­ -(1-allyloxycarbonyl-1-triphenylphosphoranylidenemethyl)-2-oxo­ azetidinyl-4-thiolate as a brown foam. Step B) - A solution of α-bromotoluic acid (1.08 g) in dry benzene (10 ml) was stirred for 2 h with thionyl chloride (0.73 ml) and dry DMF (five drops). The reaction mixture was evaporated to dryness, taken up in toluene and evaporated again. The crude product was crystallized from n-hexane (10 ml, charcoal) thereby obtaining pure α-bromotoluic acid chloride (0.95 g) as white leaflets. This product was added to a solution of the silver thiolate from the step A) above (2.2 g) in dry dichloromethane. After 25 minutes stirring, the precipitated AgCl was filtered off and the organic solution was washed with brine and with aqueous NaHCO₃. The residue resulting from removal of the solvent was purified by SiO₂ chromatography, thereby obtaining (3S)-[(1R)-tert-­ butyldimethylsilyloxyethyl]-(4R)-[4(bromomethyl)phenyl]thio-1-­ (1-allyloxycarbonyl-1-triphenylphosphoranylidenemethyl)azetidin­ -2-one (2 g) as a foam; IR (CHCl₃) ν max 1750, 1660, 1605 cm⁻¹. Step C) - The product from step B) above was dissolved in dry toluene and heated in an oil bath (100°C) for 12 hours under nitrogen and in the presence of a catalytic amount of hydro­ quinone. Silica gel chromatography (cyclohexane-ethyl acetate) afforded the title product (1.3 g) as white leaflets; IR (CHCl₃) ν max 1785, 1705 cm⁻¹; NMR (90 MHz, CDCl₃) δ ppm 0.05 and 0.12 (each 3H, s), 0.82 (9H, s), 1.20 (3H, d, J = 6.5 Hz), 3.66 (1H, dd, J = 1.5 and 4.5 Hz), 4.2 (1H, m), 4.35 (2H, s), 4.45 (2H, m), 5.0-5.2 (2H, m), 5.60 (1H, d, J = 1.5 Hz), 5.5-5.9 (1H, m), 7.35 (4H, m). EXAMPLE 11 Allyl (5R,6S)-6-[(1R)-hydroxyethyl]-2-[4-(bromomethyl)phenyl]­ penem-3-carboxylate Step A) - Aqueous 2N HCl (80.3 ml) was added to a solution of (3S)-[(1R)-tert-butylidimethylsilyloxyethyl]-(4R)-triphenyl-­ methylthio-1-(1-allyloxycarbonyl-1-triphenylphosphoranylidene­ methyl)azetidin-2-one (34.62 g) in THF (346 ml). After standing overnight, most of the solvent was removed in vacuo and the resulting mixture was partitioned between EtOAc and brine. The organic layer was washed twice with aq. NaHCO₃of dried and evaporated, thereby obtaining crude (3S)-[(1R)­ -hydroxyehtyl]-(4R)-triphenylmethylthio-1-(1-allyloxycarbonyl­ -1-triphenylphosphoranylidenemethyl)azetidin-2-one as a foam in quantitative yield. Step B) - A saturated solution of AgNO₃ (8.5 g) in methanol (333 ml) under nitrogen and in the dark was treated at 20°C with a solution of the material of step A) above and imidazole (2.7 g) in methanol (100 ml). After 5 minutes most of the solvent was removed in vacuo and the residue was taken up in EtOAc. The organic layer was washed with water (3 x), dried (MgSO₄), concentrated to 150 ml and treated under stirring with ethyl ether (300 ml). After further 10 minutes stirring, the precipi­ tated silver (3S)-[(1R)-hydroxyethyl]-1-(1-allyloxycarbonyl-1­ -triphenylphosphoranylidenemethyl)-2-oxoazetidinyl-4-thiolate was collected as a white powder in quantitative yield (24.5 g) ; IR (CHCl₃) ν max 1740, 1615 cm⁻¹. Step C) - The material from step B) above (24 g) was reacted with α-bromotoluic acid chloride (11.7 g) as described in Example 10, Step B). Work-up and chormatography afforded (3S)-[(1R)-hydroxyethyl]-­ (4R)-[4-(bromomethyl)-phenyl]thio-1-(1-allyloxycarbonyl-1-tri­ phenylphosphoranylidenemethyl)-azetidin-2-one (20.6 g) as a foam; IR (CHCl₃) ν max 1750, 1660, 1605 cm⁻¹. Step D) - The material from step C) above was heated for 10 hours in a toluene solution at 90°C under nitrogen and in the presence of hydroquinone. Silica gel chromatography afforded first some allyl 5-[4-(bromo­ methyl)phenyl]-1,3-thiazole-4-carboxylate, and then the title product (8.65 g), as white needles (from ethyl ether) ; m.p. 121 - 122°C. NMR (200 MHz, CDCl₃) 1.36 (3H, d, J = 6.3 Hz), 3.81 (1H, dd, J = 1.5 and 6.6 Hz), 4.27 (1H, dq, J = 6.3 and 6.6 Hz), 4.47 (2H, s), 4.57 (2H, m), 5.14 (1H, d, J = 10.0 Hz), 5.15 (1H, d, J = 17.0 Hz), 5.7 - 5.9 (1H, m), 5.71 (1H, d, J = 1.5 Hz), 7.4 - 7.5 (4H, m). EXAMPLE 12 (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(3-hydroxypyridinio)methyl]­ phenyl}penem-3-carboxylate (compound 55) A mixture of allyl (5R,6S)-6-[(1R)tertbutyldimethylsilyloxyethyl]­ -2-[4-(bromomethyl)-phenyl]-penem-3-carboxylate (110 mg) and 3-(tertbutyldimethylsilyloxy)pyridine (125 mg) in DMF (2 ml) was stirred overnight at room temperature. The solvent was then evaporated in vacuo , ether was added and the suspension was stirred for 1 hour at room temperature. The yellowish solid was then collected yielding 100 mg of allyl (5R,6S)-6-[(1R)-tertbutyldimethylsilyloxyethyl]-2-{4[3-hydroxy­ pyridinio)methyl]phenyl}penem-3-carboxylate, bromide salt; NMR (90 MHz, CDCl₃) δ ppm 0.12 (6H, s), 0.82 (9H, s), 1.20 (3H, d, J = 6.0 Hz), 3.70 (1H, dd, J = 1.6 and 5.0 Hz), 4.18 (1H, dd, J = 5.0 and 6.0 Hz), 4.45 (2H, m), 5.02 (1H, d, J = 10.0 Hz), 5.14 (1H, d, J = 17.0 Hz), 5.61 (1H, d, J = 1.6 Hz), 5.5-5.7 (1H, m), 5.82 (2H, s), 7.50 (4H, s), 7.4-7.7 (1H, m), 7.8-8.0 (1H, m), 8.2-8.4 (1H, m), 8.68 (1H, m) 9.26 (1H, br s). This compound was dissolved in dry TMF and stirred overnight in the presence of acetic acid (100 ml) and tetrabutylammonium fluoride trihydrate (125 mg). The reaction mixutre was then evaporated in vacuo and partially purified on silica gel eluting with acetonitrile/water mixtures. The resulting solution was then evaporated in vacuo to yield allyl (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4[(3-hydroxypyridinio) methyl]phenyl}penem-3-carboxylate, bromide salt, as a yellow oil (80 mg). This product was then dissolved in THF/CH₂Cl₂. Acetic acid (0.8 ml), triphenylphosphine (80 mg) and (Ph₃P)₄Pd (30 mg) were then sequentially added. The reaction, performed as indicated in previous examples, afforded 20 mg of the title compound; IR : ν max (KBr) 3400, 1770, 1600 cm⁻¹ UV : λ max (H₂O) 326, 250 nm. EXAMPLE 13 (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(4-ethansulfonate-1-pyridi­ nio)methyl]phenyl}penem-3-carboxylic acid (compound 55/a). A mixture of allyl (5R,6S)-6-[(1R)-hydroxyethyl]-2-[4-(bromo­ methyl)phenyl]penem-3-carboxylate (100 mg) and sodium 4-pyridine­ ethanesulfonate (145 mg) in dry DMF was stirred for 48 hours at room temperature. The mixture was then evaporated in vacuo and the residue purified by reverse phase chromatography to yield, after feeze-driing, 40 mg of allyl (5R,6S)-6-[(1R)-hydroxy-ethyl]-2-{4-[(4-ethane­ sulfonate-1-pyridinio)methyl]phenyl}penem-3-carboxylate. IR (KBr) : 3400, 1790, 1710 cm⁻¹ UV (H₂O/10% CH₃CN) : 336 nm NMR (200 MH z , D₂O) δ ppm 1.30 (3H, d, J=6.4 H z ), 3.34 (4H, m), 4.05 (1H, dd, J = 1.5 and 5.6 H z ), 4.26 (1H, dq, J = 5.6 and 6.4 Hz), 5.04 (1H, d, J = 16.2 H z ), 5.6-5.8 (1H, m), 5.78 (2H, s), 5.80 (1H, d, J = 1.5 Hz), 7.46-7.54 (4H, ABq, J = 8.4 Hz), 7.98 (2H, d, J = 6.7 Hz), 8.77 (2H, d, J = 6.7 Hz). Treatment of this product with HOAc/Ph₃P / (Ph₃P)₄Pd under the same identical conditions indicated in Example 2 afforded a sample (20 mg) of the title compound. IR (KBr) : 3400, 1775, 1700 cm⁻¹ UV (H₂O) : 330, 252 nm NMR (200 MHz, D₂O, t = 45°C) δ ppm 1.56 (3H, d, J = 6.5 Hz), 3.60 (4H, m), 4.27 (1H, dd, J = 1.5 and 5.8 Hz), 4.51 (1H, dq, J = 5.8 and 6.5 Hz), 6.02 (2H, s), 6.05 (1H, d, J = 1.5 Hz), 7.69 - 7.79 (4H, ABq, J = 8.3 Hz), 8.24 (2H, d, J = 6.8 Hz), 9.00 (2H, d, J = 6.8 Hz). EXAMPLE 14 By following the experimental procedure described in the above Example 13 and replacing sodium 4-pyridineethansulphonate with 3-hydroxymethylpyridine, 2-(2-hydroxyethyl)pyridine, 8-hydroxyquinoline, 8-hydroxyisoqui­ noline, 3-formylaminopyridine, isonicotinohydroxamic acid, 3-py­ ridinecarboxaldehyde, 3-pyridinealdoxime, 4-acetylpyridine oxime, 3-aminopyridine, pyrazine, 1-methyl-1,2,3-triazole, 1-methylpyra­ zole, thieno[2,3-c]pyridine, furo[2,3-c]pyridine, furo[3,2-c]py­ ridine, thieno[3,2-c]pyridine, thieno[2,3-b]pyridine, furo[2,3-b] pyridine, thieno[3,4-c]pyridine, and thiazolo[4,5-c]pyridine, there were obtained, respectively, (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(3-hydroxymethyl-1-pyridinio)­ methyl]phenyl} penem-3-carboxylate (Compound 56); (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(2-hydroxyethyl-1-pyridinio)­ methyl]phenyl} penem-3-carboxylate (Compound 57); (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-(8-hydroxy-1-quinolinio)methyl phenyl} penem-3-carboxylate (Compound 58); (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-(8-hydroxy-2-isoquinolinio)­ methyl]phenyl} penem-3-carboxylate (Compound 59); (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-(3-formylamino-1-pyridinio)­ methyl]phenyl} penem-3-carboxylate (Compound 60); (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4[(4-hydroxyaminocarbonyl-1-­ pyridinio)methyl]phenyl} penem-3-carboxylate (Compound 61); (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(3-formyl-1-pyridinio)methyl]­ phenyl} penem-3-carboxylate (Compound 62); (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(3-hydroxyiminomethyl-1-pyri­ dinio)methyl]phenyl} penem-3-carboxylate (Compound 63); (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-{4-[(1-hydroxyiminoethyl)-1-­ pyridinio]methyl}phenyl} penem-3-carboxylate (Compound 64); (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4[(3-amino-1-pyridinio)methyl]phe­ nyl} penem-3-carboxylate (Compound 65); (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(1-pyrazinio)methyl]phenyl}­ penem-3-carboxylate (Compound 66); (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(1-methyl-1-triazolio)methyl]­ phenyl} penem-3-carboxylate (Compound 67); (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(2-methyl-1-pyrazolio)methyl]­ phenyl} penem-3-carboxylate (Compound 68); (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(thieno[2,3-c]pyridinio)methyl]­ phenyl} penem-3-carboxylate (Compound 69); (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(furo[2,3-c]pyridinio)methyl]­ phenyl} penem-3-carboxylate (Compound 70); (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(furo[3,2-c]pyridinio)methyl]­ phenyl} penem-3-carboxylate (Compound 71); (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(thieno[3,2-c]pyridinio)methyl]­ phenyl} penem-3-carboxylate (Compound 72); (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(thieno[2,3-b]pyridinio)methyl]­ phenyl} penem-3-carboxylate (Compound 73); (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-(furo[2,3-b]pyridinio)methyl]phe­ nyl} penem-3-carboxylate (Compound 74); (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(thieno[3,4-c]pyridinio)methyl]­ phenyl} penem-3-carboxylate (Compound 75); and (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(thiazolo[4,5-c]pyridinio)methyl]­ phenyl} penem-3-carboxylate (Compound 76).

Claims: 1. A compound of the following formula I wherein R is hydrogen or a C₁-C₄ alkyl group either unsubstituted or substituted by one or more substituents chosen from a free or protected hydroxy group and halogen atom; A is a Z, Z-O-CO- or -Z-CO- residue, wherein Z represents (a) an optionally substituted phenylene or naph­ thylene group, (b) an optionally substituted heterocyclediyl radical wherein the hetero ring is mono or bicyclic, saturated or unsaturated containing at least one heteroatom selected from the group of oxygen, sulphur and nitrogen; (c) an optionally substituted linear or branched C₁-C₇ alkylene radical; (d) a C₂-C₄ alkenylene or alkynylene group or a group of formula : (e) an optionally substituted C₃-C₈ cyclo­ alkylene ring or (f) an aralkylene radical of formula wherein n is 1, 2 or 3, and Q(+) represents a group, wherein (i) R₁, R₂, R₃, are each independently an optionally substituted alkyl, aralkyl or aryl radical; or (ii) R₁ is as defined above under (i) and R₂, R₃ taken together with the nitrogen atom represent an optionally substituted heterocyclic or fused heterocyclic radical; or (iii) R₁, R₂, R₃, taken together with the nitrogen atom, repre­ sent an optionally substituted azoniabicyclo or azonia­ tricyclo radical; or (iv) R₁, R₂, R₃, taken together with nitrogen atom, represent an optionally substituted pyridinium, pyrazinium, pyrazo­ lium, or pyridazinium radical, such radicals being optio­ nally fused with one phenyl ring or with a 5-7 membered, saturated or unsaturated cycloaliphatic or heterocyclic ring, or a pharmaceutically acceptable salt thereof. 2. A compound of the formula (I) as defined in claim 1 wherein R is an (α-hydroxy)ethyl group. 3. A compound according to claim 1 or claim 2 wherein Z is a group of the formula 4. A compound according to any one of claims 1 to 3, wherein R₁, R₂, R₃ are each independently methyl, ethyl, n-propyl, i-propyl, dimethylaminomethyl, cyanomethyl, cyanoethyl, carbamoylmethyl, 2-hydroxyethyl, 2-chloroethyl, carboxymethyl, ethoxycarbonyl­ methyl, carboxyethyl, 2-methyl-2-cyanoethyl, 3-oxobutyl or dimethylformamidino group 5. A compound according to claim 4 which is chosen from (5R,6S)-6-[(1R)-hydroxyethyl]-2-[4-(N,N,N-trimethylammonio­ methyl)phenyl]-3-carboxylate; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[4-(N,N,N-triethylammoniomethyl)­ phenyl]penem-3-carboxylate ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[2-(N,N,N-trimethylammonio­ methyl)phenyl]penem-3-carboxylate; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[2-(N,N,N-triethylammonio­ methyl)-phenyl]-penem-3-carboxylate and (5R,6S)-6-[(1R)-hydroxyethyl]-2-[3-(N,N,N-trimethylammonio­ methyl)phenyl]-penem-3-carboxylate . 6. A compound according to any one of claims 1 to 3, wherein R₁, R₂ and R₃ taken together with the nitrogen atom, represent one of the following radicals wherein R₆, R₇ are independently hydrogen atom, C₁-C₄ alkyl, optionally substituted from cyano, hydroxy, sulfo, hydroxyimino group; methylsulphonyl, carbamoyl, hydroxy, methylthio, methoxy, formamido, formyl, hydroxycarbamoyl or amino group. 7. A compound according to claim 6, which is selected from (5R, 6S)-6-[(1R)-hydroxyethyl]-2-[4-(pyridiniomethyl)-­ phenyl]penem-3-carboxylate; (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(6,7-dihydro-5H-cyclopenta­ [b]-pyridinio)methyl]phenyl}penem-3-carboxylate ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(4-carbamoylpyridinio)methyl]­ phenyl}penem-3-carboxylate ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(5-ethyl-2-methylpyridinio)­ methyl]phenyl}penem-3-carboxylate ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[4-(quinoliniomethyl)phenyl]­ penem-3-carboxylate ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[2-(pyridiniomethyl)phenyl]­ penem-3-carboxylate; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[2-(isoquinuclidiniomethyl)phenyl]­ penem-3-carboxylate ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-{2-[(3-cyanomethylpyridinio)­ methyl]phenyl} penem-3-carboxylate ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[2-(pyraziniomethyl)phenyl]­ penem-3-carboxylate ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[3-(pyridiniomethyl)phenyl]­ penem-3-carboxylate ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[4-(pyridinioacetyl)-phenyl]­ penem-3-carboxylate ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[3-(pyridinioacetyl)phenyl]­ penem-3-carboxylate ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(3-methylthiopyridinio)­ methyl]phenyl}penem-3-carboxylate; (5R,6S)-6-[(1R)-hydroxyethyl]-2-{3-[(4-methylthiopyridinio)­ methyl]phenyl}penem-3-carboxylate; (5R,6S)-6-[(1R)-hydroxyethyl]-2-{3-[(4-methoxypyridinio)methyl]­ phenyl}penem-3-carboxylate; (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4[(3,5-demethylpyridinio)­ methyl]phenyl}penem-3-carboxylate; (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[3-hydroxypyridinio)methyl]­ phenyl}penem-3-carboxylate; (5R,6S)-6-[1(R)-hydroxyethyl]-2-{4-[(4-ethansulfonate-1-pyridinio)­ methyl]phenyl}penem-3-carboxylic acid; (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(3-hydroxymethyl-1-pyridinio)­ methyl]phenyl} penem-3-carboxylate; (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(2-hydroxyethyl-1-pyridinio)­ methyl]phenyl} penem-3-carboxylate ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-(8-hydroxy-1-quinolinio)methyl phenyl} penem-3-carboxylate ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-(8-hydroxy-2-isoquinolinio)­ methyl]phenyl} penem-3-carboxylate ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-(3-formylamino-1-pyridinio)­ methyl]phenyl} penem-3-carboxylate ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(4-hydroxyaminocarbonyl-1-­ pyridinio)methyl]phenyl} penem-3-carboxylate ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(3-formyl-1-pyridinio)methyl]­ phenyl} penem-3-carboxylate ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(3-hydroxyiminomethyl-1-pyri­ dinio)methyl]phenyl} penem-3-carboxylate ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-{4-[(1-hydroxyiminoethyl)-1-­ pyridinio]methyl}phenyl} penem-3-carboxylate ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(3-amino-1-pyridinio)methyl]phe­ nyl} penem-3-carboxylate ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(1-pyrazinio)methyl]phenyl}-­ penem-3-carboxylate ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(2-methyl-1-pyrazolio)methyl]­ phenyl} penem-3-carboxylate; (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(thieno[2,3-c]pyridinio)methyl]­ phenyl} penem-3-carboxylate ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(furo[2,3-c]pyridinio)methyl]­ phenyl} penem-3-carboxylate ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(furo[3,2-c]pyridinio)methyl]­ phenyl} penem-3-carboxylate ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(thieno[3,2-c]pyridinio)methyl]­ phenyl} penem-3-carboxylate; (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(thieno[2,3-b]pyridinio)methyl]]­ phenyl} penem-3-carboxylate ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-(furo[2,3-b]pyridinio)methyl]phe­ nyl} penem-3-carboxylate ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(thieno[3,4-c]pyridinio)methyl]­ phenyl} penem-3-carboxylate and (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(thiazolo[4,5-c]pyridinio)methyl] phenyl} penem-3-carboxylate. 8. A compound according to any one of claims 1 to 3 wherein R₁ is methyl, ethyl, n-propyl, i-propyl, dimethylaminomethyl, cyanomethyl, cyanoethyl, carbamolymethyl, 2-hydroxyethyl, 2-chlorothyl, carboxymethyl, ethoxycarbonylmethyl, carboxyethyl, 2-methyl-2cycanoethyl, 3-oxobutyl or dimethyl­ formamidino group and R₂, R₃ taken together with the nitrogen atom, represent one of the following heterocyclyl ammonium radicals unsubstituted or substituted by one or more substituents selected from halogen atom, hydroxy, amino, cyano, dimethylformimidino, ethoxycarbonyl, heterocyclic ring, oxo, C₁-C₄ alkyl or alkanoyl group. 9. A compound according to claim 8, which is chosen from (5R,6S)-6-[(1R)-hydroxyethyl]-2-[4-(N-methylpyrrolidiniomethyl)­ methyl)phenyl]-penem-3-carboxylate; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[4-(N-methylpiperidiniomethyl)­ phenyl]penem-3-carboxylate ; (5R,6S)-6[(1R)-hydroxyethyl]-2-{4-[(1-methylmorpholinio)­ methyl]phenyl} penem-3-carboxylate ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(1-methylpiperazinio)­ methyl]phenyl} penem-3-carboxylate ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(1,4-dimethylpiperazinio)­ methyl]phenyl} penem-3-carboxylate ; (5R,6S)-6-[(1R)-hydroxyethyl[-2-]-(N-methylpyrrolidiniomethyl phenyl/penem-3-carboxylate ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[2-(N-methylpiperidiniomethyl)­ phenyl]-penem-3-carboxylate; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[3-(N-methylyprrolidiniomethyl)­ phenyl]penem-3-carboxylate and (5R,6S)-6-[(1R)-hydroxyethyl]-2-{4-[(1-methyl-1-triazolio)methyl]­ phenyl}-penem-3-carboxylate. 10. A compound according to any one of claims 1 to 3, wherein R₁, R₂, R₃ taken together with the nitrogen atom, represent one of the following radicals wherein the quinuclidine ring may be substituted by an oxo, hydroxy or methoxy group. 11. A compound according to claim 10 which is (5R,6S)-6­ -[(1R)-hydroxyethyl]-2-[4-(quinuclidiniomethyl)-phenyl]-penem­ -3-carboxylate. 12. A compound according to claim 1 or claim 2, wherein Z is a group of the formula : 13. A compound according to claim 12, which is chosen from (5R,6S)-6-[(1R)-hydroxyethyl]-2-[1-(pyridiniomethyl)cyclo­ pentyl]penem-3-carboxylate; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[1-(N-methylpyrrolidinio­ methyl-cyclopentyl]penem-3-carboxylate; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[1-(N,N,N-triethylammonio­ methyl)cyclopentyl]penem-3-carboxylate; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[3-(N,N,N-trimethylammonio­ methyl)cyclobutyl]penem-3-carboxylate and (5R,6S)-6-[(1R)-hydroxyethyl]-2-[3-(pyridiniomethyl)cyclo­ pentyl]penem-3-carboxylate. 14. A compound according to claim 1 or claim 2, wherein Z is a residue of the formula : 15. A compound according to claim 14, which is (5R,6S)-6­ -[(1R)-hydroxyethyl]-2-[5-(N-methylpyrrolidiniomethyl)thien­ -2-yl]penem-3-carboxylate. 16. A compound according to Claim 1 or 2, wherein Z is a methylene, ethylene, n-propylene or tetramethylene group. 17. A compound according to claim 16, which is chosen from (5R,6S)-6-[(1R)-hydroxyethyl]-2-(3-pyridiniopropyl)penem-3­ -carboxylate ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[3-(3-cyanomethylpyridinio)­ propyl]penem-3-carboxylate ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[3-(N-methylpyrrolidinio)­ propyl]-penem-3-carboxylate; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[3-(N,N,N-trimethylammonio)­ propyl]penem-3-carboxylate ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[4-(3-cycanomethylpyridinio)­ butyl]penem-3-carboxylate ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-(4-pyridiniobuytl)-penem-3­ -carboxylate; (34); (5R,6S)-6-[(1R)-hydroxyethyl]-2-[4-(N-methylpyrrolidinio)­ butyl]penem-3-carboxylate ; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[(N-methylpyrrolidinio)­ acetoxymethyl]penem-3-carboxylate; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[2-(pyridinioacetoxy)ethyl]­ penem-3-carboxylate; and (5R,6S)-6-[(1R)-hydroxyethyl]-2-{2-[(N-methylpyrrolidinio)­ acetoxy]ethyl}penem-3-carboxylate. 18. A compound according to claim 1 or claim 2, wherein Z is a 1, 2-ethenylene group. 19. A compound according to claim 18, which is chosen from (5R,6S)-6-[(1R)-hydroxyethyl]-2-[(E)-2-(pyridiniomethyl)ethenyl]­ penem-3-carboxylate; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[(Z)-2-(pyridiniomethyl)ethenyl]­ penem-3-carboxylate; (5R,6S)-6-[(1R)-hydroxyethyl]-2-[(Z)-2-(N-methylpyrrolidinio-­ methyl)-ethenyl]penem-3-carboxylate. 20. A compound according to claim 1 or claim 2, wherein Z is a group of the formula: 21. A compound according to claim 20, which is (5R,6S)-6­ -[(1R)-hydroxyethyl]-2-[4-(2-oxo-3-pyridiniopropyl)phenyl]­ -penem-3-carboxylate. 22. A process for the preparation of a compound of formula (I) wherein R is hydrogen or a C₁-C₄ alkyl group either unsubstituted or substituted by one or more substituents chosen from a free or protected hydroxy group and halogen atom; A is a Z, Z-O-CO- or -Z-CO- residue, wherein Z represents (a) an optionally substituted phenylene or naph­ thylene group, (b) an optionally substituted heterocyclediyl radical wherein the hetero ring is mono or bicyclic, saturated or unsaturated containing at least one heteroatom selected from the group of oxygen, sulphur and nitrogen; (c) an optionally substituted linear or branched C₁-C₇ alkylene radical; (d) a C₂-C₄ alkenylene or alkynylene group or a group of formula : (e) an optionally substituted C₃-C₈ cyclo­ alkylene ring or (f) an aralkylene radical of formula wherein n is 1, 2 or 3, and Q(+) represents group, wherein (i) R₁, R₂, R₃ are each independently an optionally substituted alkyl, aralkyl or aryl radical; or (ii) R₁ is as defined above under (i) and R₂, R₃ taken together with the nitrogen atom represent an optionally substituted heterocyclic or fused heterocyclic radical; or (iii) R₁, R₂, R₃, taken together with the nitrogen atom, repre­ sent an optionally substituted azoniabicyclo or azonia­ tricyclo radical; or (iv) R₁, R₂, R₃, taken together with nitrogen atom, represent an optionally substituted pyridinium, pyrazinium, pyrazo­ lium, or pyridazinium radical, such radicals being optio­ nally fused with one phenyl ring or with a 5-7 membered, saturated or unsaturated cycloaliphatic or heterocyclic ring, or a pharmaceutically acceptable salt thereof, the process comprising reacting a compound of formula (II) wherein R₁, R₂ and R₃ are as defined in claim 1, with a penem intermediate of formula (III) wherein R and A are as defined in claim 1, Z' is a carboxy protecting group, and L is a leaving group susceptible of nucleophilic displacement by the amine of formula (II), and then removing the protecting groups therein present and, if desired, converting the resulting compound into a salt thereof and/or, if desired, separating a mixture of isomers into the single isomers. 23. A process according to claim 22 wherein a compound as defined in any of claims 2 - 21 is prepared. 24. A process according to claim 22 or 23, wherein the intermediate of formula III is one prepared by reacting a carbinol precursor of formula (IV) wherein R, A and Z' are as defined in claim 22 or 23, with a sulphonyl anhydride or sulphonyl halide in the presence of an excess of the compound of formula (II) without isolating said compound of formula III from the reaction mixutre. 25. A pharmaceutical or veterinary composition containing a suitable carrier and/or diluent and, as an active principle, a compound according to any one of claims 1 to 21 or a pharmaceutically or veterinarily acceptable salt thereof. 26. A compound of formula (I) as defined in any of claims 1 to 21 or a pharmaceutically or veterinarily acceptable salt thereof, for use in a method of treatment of the human or animal body by therapy. 27. A compound or salt according to claim 26 for use as an antibacterial agent.

Inventors: ALPEGIANI, MARCO, BEDESCHI, ANGELO, BRUNA, COSTANTINO DELLA, FRANCHESCHI, GIOVANNI, PERRONE, ETTORE, ZARINI, FRANCO
Applicants: FARMITALIA CARLO ERBA S.R.L.
Application year: 1986
Main classification: C07D499
IPC codes: A61K31, C07D499, C07D519, A61P31