Abstract: Novel carbapenem compounds of the formula: ##STR1## in which R.sup.1 is carboxy or protected carboxy,R.sup.2 is hydroxy(lower)alkyl or protected hydroxy(lower)alkyl,R.sup.3 is hydrogen or lower alkyl,R.sup.4 is unsaturated bicyclic heterocyclic group which may be substituted by suitable substituent(s),R.sup.5 is hydrogen or imino-protective group, andA is lower alkylene,or pharmaceutically acceptable salts thereof.Processes for their preparation and pharmaceutical compositions for the treatment of infectious diseases are also disclosed.

Abstract: Novel amino acid derivatives of the formula ##STR1## wherein R.sup.1 is a protecting group removable under reducing or acid conditions, and R.sup.2 and R.sup.5 are hydrogen or carboxylic protecting groups, are useful as intermediates in preparing stereospecific carbapenam/carbapenem derivatives. R.sup.1 is removed under reducing conditions to form a pyrrolidine derivative, which is further cyclized from the R.sup.5 =H compound to form a .beta.-lactam ring. Stereospecificity at the 6-position is achieved by treatment with lithium diisopropylamide (LDA) and quenching at different temperatures. Compound (I) can be prepared by treating R.sup.1 -protected R.sup.3 -pyrrolidone carboxylic acid R.sup.2 -ester with a lithium enolate of the formula R.sup.4 CHLiCO.sub.2 R.sup.5. The lithium enolate can be formed from R.sup.4 CH.sub.2 CO.sub.2 R.sup.5 by treatment with LDA.

Abstract: Compound I ##STR1## is obtained by reaction of compound II with compound III

Abstract: The present invention provides a process for preparing a 2-exo-methylenepenam derivative represented by the formula (2), the process being characterized by reacting an allenyl .beta.-lactum compound represented by the formula (1) with a metallic reducing agent, in which R.sup.1, R.sup.2, R.sup.3 and X are defined in the specification.

Abstract: An efficient, multistep process for the synthesis of certain 6-(1-hydroxyethyl) 2-substituted penem antibiotics from 2-[4R-(triphenylmethylthio)-3S-(1R-(dimethyl-t-butylsilyloxy)ethyl)-2-azet idon-1-yl]acetic acid esters.

Abstract: Antimicrobial quinolonyl lactam esters comprising a lactam-containing moiety linked, by an ester group, to the 3-carboxy group of a quinolone moiety. These compounds are of the formula: ##STR1## wherein (1) R.sup.3, R.sup.4, and R.sup.5, together with bonds "a" and "b", form certain lactam-containing moieties similar to those known in the art to have antimicrobial activity; and(2) A.sup.2, A.sup.2, A.sup.3, R.sup.7, R.sup.8, and R.sup.9 form any of a variety of quinolone or naphthyridine structures similar to those known in the art to have antimicrobial activity.

Abstract: Antibacterial compounds of the formula ##STR1## in which R.sub.1 is a cyclic or secondary acyclic amino group which independently has antibacterial activity:R.sub.2 is hydrogen, lower alkoxy, lower alkylthio or formamido;R.sub.3 is hydrogen or an organic group bonded through carbon, oxygen, sulfur or nitrogen;R.sub.4 is an electronegative acidic group; or R.sub.3 and R.sub.4 together form a heterocycle; andR.sub.5 is a hydrogen or lower alkyl, except when R.sub.3 and R.sub.4 form a heterocycle, in which case R.sub.5 is hydrogen only; and methods of using same.

Abstract: The invention relates to an improved process for the preparation of compounds of formula ##STR1## or salts thereof, starting from compounds of formulae ##STR2## via compounds of formulae ##STR3## in which compounds R.sub.1 is hydrogen or lower alkyl, R.sub.2 is an organic radical which may carry a functional group which may be protected by a customary protective group R.sub.2 .degree., R.sub.3 is hydrogen or a customary carboxyl protective group R.sub.3 .degree., W is a group which can be replaced by a thiocarboxylic acid radical of formula III, and Z is oxygen or sulfur.

Abstract: Novel beta lactam compounds having potent elastrase inhibition activity are disclosed. These compounds are characterized by the general structural formulae I, II, and III: ##STR1## These compounds are further characterized such that X and Y are each --S-- or --CH.sub.2 --, with at least one of X and Y being --S--, or alternatively, X is --SO-- or --SO.sub.2 -- and Y is --CH.sub.2 --; R.sup.1 is hydrogen, tri(lower alkyl)silyl, --COOR" or --CONHR"', wherein R" and R"' are each lower alkyl or phenyl(lower alkyl), and may be the same or different; R.sup.3 is hydrogen, lower alkyl or (lower alkyl)oxy; one of B and D is (lower alkyl)oxycarbonyl, (lower alkenyl)oxycarbonyl, allyloxycarbonyl or phenyl(lower alkyl)oxycarbonyl; and the other of B and D is hydrogen or lower alkyl.The compounds are useful as anti-inflammatory agents, particularly in the treatment of adult respiratory distress syndrome and rheumatoid arthritis.

Abstract: A regeneratable polymer-supported Pd(O) catalytic deblocking process using a regeneratable polymer-supported Pd(O) catalyst in a biphasic system deblocks various allyl-protected ester, carbonates, carbamates and cinnamyl esters.

Abstract: Novel penem compounds of the formula, ##STR1## wherein R is hydrogen or allyl, and A is an aliphatic 5- or 6-membered heterocyclic group having one or two oxygens in the ring and their pharmaceutically acceptable salts are produced from the compounds of the formula, ##STR2## wherein A is the same as above and respective R.sup.1 and R.sup.2 are protective groups for hydroxyl and carboxyl groups, through several steps. The compounds and their salts are useful as antibacterial agents.

Abstract: 6-substituted penem esters of formula (I): ##STR1## wherein R.sub.1 is halogen or a C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy, phenyl, phenoxy, benzyl or sulphonyloxy group; R.sub.2 is a C.sub.1 -C.sub.4 alkyl, benzyl diphenylmethyl ##STR2## group where A is C.sub.1 -C.sub.4 alkyl, benzyl, p-nitrobenzyl or p-methoxybenzyl; and R.sub.3 is an organic radical, are elastase inhibitors and thereby useful antiinflammatory and antidegenerative agents.

Abstract: A compound selected from the group consisting of a compound of the formula ##STR1## wherein R.sub.1 and R.sub.2 are individually selected from the group consisting of hydrogen, alkyl and hydroxyalkyl of 1 to 5 carbon atoms and amino, n is an integer from 1 to 3, X and X.sub.1 are individually selected from the group consisting of hydrogen and alkyl of 1 to 3 carbon atoms or taken together with the carbon atom to which they are attached are ##STR2## Y is --O-- or --S--, R.sub.3 is alkyl of 1 to 3 carbon atoms or aryl of 6 to 8 carbon atoms, ##STR3## is selected from the group consisting of ##STR4## R.sub.4 and R.sub.5 are individually aryl unsubstituted or substituted with at least one member of the group consisting of halogen, --NO.sub.2 and alkyl and alkoxy of 1 to 3 carbon atoms and non-toxic, pharmaceutically acceptable salts thereof with acids and bases having cyclooxygenase inhibiting and antibiotic acitvity.

Abstract: New derivatives of penem and pharmacutically acceptable salt thereof are herein disclosed; these compounds being useful as an antibacterial agent which has an extremely wide antibacterial spectrum, exhibits a high sensitivity to bacteria resistant to conventional penicillins and cephalosporin antibiotics and is excellent in its physico-chemical stability, solubility to water and biological stability, in particular, stability to decomposition by enzyme such as dehydropeptidase I in kidney, .beta.-lactamase; these derivatives of penem being able to be prepared by reacting 2-substituted sulfinyl derivative of penem with a thiol compound and then optionally removing protective group(s) and further alkylating the reaction product or vice versa.

Abstract: This invention provides a method of producing a .beta.-lactam derivative represented by the formula (I): ##STR1## said method consisting essentially of the step of reacting a .beta.-lactam derivative represented by the formula (II): ##STR2## with a phenol in a reaction system which consists essentially of said .beta.-lactam derivative of formula (II) and said phenol.

Abstract: There is disclosed a compound represented by the formula ##STR1## where P is a hydroxy protecting group.

Abstract: Penem derivatives of the formula ##STR1## having R.sup.1 equal to 3-oxocyclobutyl and R.sup.2 equal to H or an ester-forming group, pharmaceutical preparations active against bacterial infections and which contain penem derivatives of this type, processes for the preparation of the penem derivatives and the pharmaceutical preparations, and use of the penem derivatives for the control of bacterial infections are described.

Abstract: Beta-lactamase inhibiting compounds of the formula ##STR1## or a pharmaceutically acceptable acid addition or carboxylate salt thereof; where n is zero, 1 or 2; X.sub.3 is H or Br, R.sup.1 is H, the residue of certain carboxy-protecting groups or the residue of an ester group readily hydrolyzable in vivo; one of R.sup.12 and R.sup.13 is H and the other is vinyl, certain aryl, alkylthio, alkylsulfonyl or certain heterocyclyl, aminomethyl, thiocarboxyamido or amidino groups; one of R.sup.2 and R.sup.3 is H and the other is as disclosed for the other of R.sup.12 and R.sup.13, or is Cl or CH.sub.2 OH, and R.sup.18 is H or certain acyl groups; intermediates useful in their production, methods for their preparation and use, and pharmaceutical compositions containing them.

Abstract: Diastereomeric 5R,6S-6-(1R-hydroxyethyl)-2-(1S-oxo-3R-thiolanylthio)-2-penem-3-carboxylic acid and 5R,6S-6-(1R-hydroxyethyl)-2-(1R-oxo-3S-thiolanylthio )-2-penem-3-carboxylic acid, and pharmaceutically-acceptable salts and in vivo hydrolyzable esters thereof, useful as systemic antibacterial agents; and intermediates and processes which are useful in the said synthesis of said diastereoisomers.

Abstract: The present invention relates to a method for producing novel 4-[1-oxoalkyl]-2,5-oxazolidinediones, (4-1 OOD), and their use in a stereoselective method of producing beta-lactam-containing compounds which include several biologically active compounds such as the well-known families of pencillin and cephalosporin antibiotics. The method of the present invention involves generally the reaction of the above-described 4-[1-oxoalkyl]-2,5-oxazolidinediones so produced with a thiol amine having a geometry amenable to forming the precursor of the desired beta-lactam-containing compound or, in one scheme, forming the beta-lactam-containing compound itelf directly. This is done either by direct reaction of the 4-1 ODD with a thiol amine (which by one pathway proceeds directly to the beta-lactam-containing compound) or by first converting the 4-1 OOD to its 2-[1-oxoalkyl]-2-amino acid form before its reaction with the thiol amine; and then forming the beta lactam by action of cyanogen).

Abstract: A penem compound represented by the general formula: ##STR1## (wherein R denotes hydrogen or allyl group, A denotes oxygen atom or methylene group and B denotes methylene, ethylene or carbonyl group) or a pharmacologically acceptable salt is produced through several processes.The compound exhibits stronger activities against wide variety of gram-positive and gram-negative bacteria as compared with known penem compounds.

Abstract: Disclosed are 6- and 4-substituted-1-azabicyclo[3.2.0]heptan-3,7-dione-2-carboxylic acid esters and salts (I) which are useful in the preparation of 6-, 1- and 2-substituted carbapenem antibiotics. ##STR1## wherein R.sup.5 is a pharmaceutically acceptable ester moiety or a removable protecting group or an alkali or alkaline earth metal cation such as sodium or potassium and wherein R.sup.1, R.sup.2, Rhu 3 and R.sup.4 are, inter alia, independently selected from the group consisting of hydrogen, alkyl, aryl and aralkyl. Another embodiment disclosed is a group of compounds having the formula ##STR2## where X is a leaving group.

Abstract: An efficient, multistep process for the synthesis of certain 6-(1-hydroxyethyl) 2-substituted penem antibiotics from 2-[4R-(triphenylmethylthio)-3S-(1R-(dimethyl-t-butylsilyloxy)ethyl)-2-azet idon-1 yl]acetic acid ester.

Abstract: (1R,5S,6S)-6-[(R)-1-hydroxyethyl]-1-methyl-2-[(1,2-diiminomethyl)-4-pyrazol idinyl-thio-carbapenem-3-carboxylic acid is provided as an intermediate, which is converted into (1R,5S,6S)-2-[(6,7-dihydro-5H-pyrazolo[1,2-a][1,2,4]triazolium-6-yl]thio-6 -[R-1-hydroxyethyl]-1-methyl-carbapenem-3-carboxylate. This compound is an antibacterial agent, which also may be in the form of the corresponding acid or pharmaceutically acceptable salt, in which case there is included an anionic group balancing the traizolinium positive charge. As such as anionic group may be mentioned, for example, the chloride, acatate or carbonate. As the salt may be mentioned the alkali metal salts, for example, sodium.

Abstract: Compounds of the formula ##STR1## in which R.sub.1 is lower alkyl substituted by hydroxy or by protected hydroxy, R.sub.2 represents carboxy or functionally modified carboxy, R.sub.3 is hydrogen, amino, mono- or di-substituted amino, carbamoyl, hydroxy, protected hydroxy, carbamoyloxy, lower alkoxy, halogen, lower alkanoyl, sulphamoyl or heteroarylthio, each of R.sub.4 and R.sub.5, independently of the other, represents hydrogen, lower alkyl, hydroxy, protected hydroxy, lower alkoxy, halogen, amino, protected amino, lower alkanoylamino or carbamoyl, or R.sub.4 and R.sub.5 together represent methylenedioxy, Y represents a group of the formula --O--, --S-- or --NR.sub.6 --, R.sub.6 is hydrogen or lower alkyl, A.sub.1 represents lower alkylene or unsubstituted or substituted phenylene and A.sub.2 represents a direct bond or lower alkylene, and salts of such compounds, have antibacterial activity. The compounds of the formula I are manufactured by processes that are known per se.

Abstract: New derivatives of penem and pharmaceutically acceptable salt thereof are herein disclosed; these compounds being useful as an antibacterial agent which has an extremely wide antibacterial spectrum, exhibits a high sensitivity to bacteria resistant to conventional penicillins and cephalosporing antibiotics and is excellent in its physico-chemical stability, solubility to water and biological stability, in particular, stability to decomposition by enzyme such as dehydropeptidase I in kidney, .beta.-lactamase; these derivatives of penem being able to be prepared by reacting 2-substituted sulfinyl derivative of penem with a thiol compound and then optionally removing protective group(s) and further alkylating the reaction product or vice versa.

Abstract: The invention relates to an improved process for the preparation of compounds of formula ##STR1## or salts thereof, starting from compounds of formulae ##STR2## via compounds of formulae ##STR3## in which compounds R.sub.1 is hydrogen or lower alkyl, R.sub.2 is an organic radical which may carry a functional group which may be protected by a customary protective group R.sub.2.sup.o, R.sub.3 is hydrogen or a customary carboxyl protective group R.sub.3.sup.o, W is a group which can be replaced by a thiocarboxylic acid radical of formula III, and Z is oxygen or sulfur.

Abstract: A process for producing the compound [2S-(2.alpha.,3.beta.,5.alpha.)]-3-methyl-7-oxo-3-(1H-1,2,3-triazol-1-yl-m ethyl)-4-thia-1-azabicyclo[3 2 0]-heptane-2-carboxylic acid, (4-nitrophenyl)methyl ester, 4,4-dioxide, which comprises reacting a solution of azidopenamsulfone, 4-methoxyphenol and vinylpropionate with a solution of bis(trimethylsilyl)acetamide and 4-methoxyphenol is toluene at 80.degree.-100.degree. C. for 18-30 hours followed by filtering the resulting solution and cooling the filtrate to 0.degree.-10.degree. C.

Abstract: 6-substituted penem esters of formula (I): ##STR1## wherein R.sub.1 is halogen or a C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy, phenyl, phenoxy, benzyl, or sulphonyloxy group; R.sub.2 is a C.sub.1 -C.sub.4 alkyl, benzyl diphenylmethyl ##STR2## group where A is C.sub.1 -C.sub.4 is C.sub.1 -C.sub.4 alkyl, benzyl, p-nitrobenzyl or p-methoxybenzyl; and R.sub.3 is an organic radical, are elastase inhibitors and thereby useful antiinflammatory and antidegenerative agents.

Abstract: A substantially (.gtoreq.95%) optically pure (5R,6S,1'R) penem of formula ##STR1## and the pharmaceutically acceptable salts and the ester prodrugs thereof, are endowed with antibacterial activity.

Abstract: This invention relates to an improved process for the preparation of cyanoalkyl lactams by the reaction of an unsaturated nitrile with a lactam, said cyanoalkyl lactam of the formula ##STR1## wherein R is H, or methyl, R.sub.1 is H, methyl or ethyl and n is a number ranging from 2-11 and wherein each of the methylene groups may carry a lower alkyl substituent as shown. The improvement comprises: reacting said lactam with an alpha-beta unsaturated nitrile having from 3-6 carbon atoms in the presence of a catalytic amount of a diazabicycloalkene of the formula ##STR2## wherein R, R.sub.1 and n have the above meaning. Typically, acrylonitrile is reacted with .epsilon.-caprolactam in the presence of diazabicycloundecene.

Abstract: Novel .beta.-lactam compounds belonging to carbapenem or penem derivatives useful as antimicrobial agents or intermediates therefor and a process for producing these compounds are disclosed.

Abstract: An improved process for the production of penicillic acid compounds, especially chloromethyl ester of penicillin G, penicillin V or sulbactam is disclosed.

Abstract: A process for preparing azetidinones of the formula: ##STR1## wherein R.sup.1 is an amino-protecting group and R.sup.2 is alkyl or aryl, which comprises reacting compounds of the formulae (VIII) and (IX) ##STR2## wherein L is a leaving group. The product azetidinones are intermediates in the preparation of penem and carbapenem antibiotics.

Abstract: Novel .beta.-lactam compounds belonging to carbapenem or penem derivatives useful as antimicrobial agents or intermediates therefor and a process for producing these compounds are disclosed.

Abstract: Compounds of the general formula (II): ##STR1## in which N.sup.+ denotes an unsubstituted or substituted nitrogen-containing heterocyclyl ring bonded to the remainder of the molecule through a ring nitrogen atom and carrying a positive charge on said nitrogen atom;and the wavy line denotes either the E- or Z-isomeric position,are novel and are useful in the treatment of antibacterial infection in humans or animals.

Abstract: The invention provides a process for preparing a .beta.-lactam derivative represented by the formula ##STR1## the process comprising reacting a .beta.-lactam derivative represented by the following formula (II) and having a protected carboxyl group with a cresol; ##STR2## wherein R represents a benzyl group having an electron-donating group as a substituent on the phenyl ring, a diphenylmethyl group which may have an electron-donating group as a substituent on the phenyl ring or a tert-butyl group.

Abstract: Compounds of the general formula (II): ##STR1## and pharmaceutically acceptable salts and in-vivo hydrolysable esters thereof, in whichR denotes a hydrogen atom or an in vivo hydrolysable acyl group;and the wavy line denotes either the E- or Z-isometric position,are novel compounds which exhibit .beta.-lactamase inhibitory action and have antibacterial properties.

Abstract: The present invention provides a process for preparing a penicillanic acid derivative of the formula ##STR1## which comprises reacting lead with a halogenated penicillanic acid derivative of the formula ##STR2## wherein X, Y, Z and R.sup.1 are as defined in the specification. The reaction is advantageously conducted in the presence of a metal having higher ionization tendency than lead such as aluminum, iron, magnesium or a mixture thereof.

Abstract: A process for preparing a 2.beta.-substituted-methylpenicillin compound of the formula ##STR1## wherein --N Y is an optionally substituted heterocyclic group containing 2 to 4 nitrogen atoms as the hetero atom in the ring structure, and R.sub.1 is a penicillin carboxyl protecting group, the process comprising reacting an azetidinonedisulfide compound of the formula ##STR2## wherein R.sub.1 is as defined above and R is a substituted or unsubstituted heterocyclic group with a nitrogen-containing heterocyclic compound of the formula ##STR3## wherein ##STR4## is as defined above in the presence of a metal compound.

Abstract: During the preparation of 6-(substituted methylene)-2-penem compounds (which are known for their anti-bacterial and .beta.-lactamase inhibitory properties) mixtures of the E-isomer and the Z-isomer may be formed. The Z-isomer is, however generally preferred, and the present invention provides a process whereby the E-isomer may be converted into the Z-isomer by reaction with an aromatic heterocyclic thiol in the presence of a base.

Abstract: 2.alpha.-Methyl-2.beta.-(1,2,3-triazol-1-yl)methylpenam-3.alpha.-carboxylic acid derivatives are prepared by reacting a penicillanic acid sulfoxide derivative of the formula ##STR1## wherein R is a penicillin carboxyl protecting group, and R.sub.1 is hydrogen or halogen, R.sub.2 is hydrogen, lower alkyl or the like with a triazole derivative of the formula ##STR2## wherein R.sub.3 and R.sub.4 are hydrogen, trialkylsilyl, lower alkyl, lower alkoxy or the like and R.sub.5 is hydrogen or silyl substituted with 3 groups selected from the class consisting of lower alkyl, benzyl and phenyl in a solvent.

Abstract: An efficient, multistep process for the synthesis of 6-(1-hydroxyethyl) 2-thio-substituted penem antibiotics from 2-[4R-(triphenylmethy lthio)-3S-(1S-(dimethyl-t-butylsilyloxy)ethyl)-2-azetidon-1-yl]acetic acid esters.

Abstract: Disclosed are 2.beta.-substituted-methylpenicillanic acid compounds of the formula ##STR1## wherein n is 0, 1 or 2; and ##STR2## is monocyclic or bicyclic heterocyclic ring group which has 2 to 4 nitrogen atoms as hetero atom in its ring structure and which may be optionally substituted with alkyl, alkoxycarbonyl, phenyl, formyl or benzyloxycarbonyl optionally having alkyl, nitro or a halogen atom on the benzene ring, with the proviso that said heterocyclic ring group is not 1,2,3-triazol-1-yl; or salts or esters thereof.These compounds are useful as .beta.-lactamase inhibitor.

Abstract: There are provided compounds of formula I: ##STR1## wherein R.sup.1 is hydrogen or a C.sub.1 -C.sub.4 alkyl group either unsubstituted or substituted by one or more substituents chosen from a free or protected hydroxy or halogen atom;R.sup.2 is a free or esterified carboxy group or carboxylate anion;R.sup.3 and R.sup.4 are each independently hydrogen or organic group,X is --O--, ##STR2## --S--, Q is either(a") free or protected hydroxy, or(b") a C.sub.1 -C.sub.1 acyloxy, or(c") carbamoyloxy OCONH.sub.2, or(d") an optionally substituted heterocyclylthio group, or(e") an optionally substituted imido group, or(f") an optionally substituted quaternary ammonium group or(g") a halogen atom,A and the pharmaceutically or veterinarily acceptable salts thereof. There are provided also methods for preparing compounds of formula I. The compounds of formula I are useful as antibacterial agents.

Abstract: Process and intermediates for the conversion of 3R,4R-4-acetoxy-3-[1R-1-(silyloxy)ethyl]-2-acetidinones to antibacterial 5R,6S-6-(1R-1-hydroxyethyl)-2-(1-oxo-3-thiolanylthio)-2-penem-3-carboxylic acids, and the pharmaceutically-acceptable salts and pivaloyloxymethyl esters thereof.

Abstract: 6-(1-Carbamoyl-1-hydroxymethyl)penicillanic acid derivatives are useful as antibacterials and/or beta-lactamase inhibitors.

Abstract: 6-Halo- and 6,6-dihalo-1,1-dioxopenicillanoyloxymethyl 6-[D-2-(2-alkoxycarbonyl-1-methylvinylamino- and 1-methyl-3-oxo-1-butenylamino)-2-phenylacetamido]penicillanates and analogs; process for their conversion to sultamicillin and analogs; and process for their preparation.

Abstract: Diphenylmethyl esters of cephalosporins, and processes for synthesizing such, are described and disclosed.

Abstract: Compounds of formula ##STR1## wherein R is hydrogen atom or C.sub.1 -C.sub.4 alkyl group optionally substituted from halogen atom or hydroxy group optionally protected, A is a Z, Z--O--C--O-- or Z--C)-- residue, wherein Z is phenylene, naphthylene, heterocyclediyl, C.sub.1 -C.sub.7 alkylene, C.sub.2 -C.sub.4 alkenylene, alkynylene, ##STR2## C.sub.3 -C.sub.8 cycloalkylene, aralkylene radical optionally substituted, and O.sup.(+) represents a group +NR.sub.1 R.sub.2 R.sub.3, wherein R.sub.1, R.sub.2 and R.sub.3 are each either:(i) a optionally substituted alkyl, aralkyl or aryl radical or(ii) R.sub.1 is as defined above under (i) and R.sub.2 and R.sub.3, taken together, represent an optionally substituted or fused heterocyclic radical, or(iii) R.sub.1, R.sub.2 and R.sub.3, taken together, represent an optionally substituted azonia-bicyclo or tricyclo radical, or(iv) R.sub.1, R.sub.2 and R.sub.