Abstract: A cephalosporin derivative of formula (I): ##STR1## wherein X is an --OCOCH.sub.3 group or an -S-Het group in which Het is a 5- or 6-membered heterocyclic ring containing one to four hetero atoms selected from the group consisting of nitrogen, oxygen and sulfur atoms, which may be substituted with one or more substituents, and the non-toxic pharmaceutically acceptable salts thereof which are useful as an antimicrobial material and which are prepared by the reaction of a compound of formula (II): ##STR2## or a reactive derivative thereof, with a compound of formula (III): ##STR3## wherein X is as defined above, or a derivative thereof.

Abstract: A penicillin of the formula: ##STR1## (i.e. 6-[D-2-(3-hydroxypyridazine-4-carbonamido)-2-(p-hydroxyphenyl)acetamido]pe nicillanic acid), which is valuable as an antibacterial agent, a nutritional supplement in animal feeds and a therapeutic agent in poultry and mammals including man and is especially useful in the treatment of infectious diseases caused by Gram-positive and Gram-negative bacteria.

Abstract: A penicillin of the formula: ##STR1## wherein ##STR2## is a six-membered heteroaromatic ring containing 1 or 2 nitrogen atoms as the hetero atom, Y is hydrogen, lower alkanoyl or lower alkoxycarbonyl, R.sub.1 and R.sub.2 are each hydrogen, lower alkyl, lower alkanoyl, benzoyl, lower alkylmercapto, hydroxyl, mercapto, hydroxy(lower)alkyl, halogen or cyano or R.sub.1 and R.sub.2 may link together to form a lower alkylene chain which may be substituted with an oxo group, and Z is phenyl, hydroxyphenyl, lower alkyl, cyclohexadienyl, thienyl or isothiazolyl, which is prepared by reacting a compound of the formula: ##STR3## wherein Z is as defined above or its derivative with a carboxylic acid of the formula: ##STR4## wherein ##STR5## and R.sub.

Abstract: Penicillins of the formula: ##STR1## wherein R is an unsubstituted phenyl group or a substituted phenyl group having one or more hydroxyl groups or a cyclohexadienyl group and A represents a monocyclic or polycyclic nitrogen-containing heterocyclic aromatic ring, which are useful as antimicrobial agents having a broad antimicrobial spectrum against gram-positive and gram-negative bacteria including Pseudomonas and can be produced advantageously from the phenacyl ester of 6-aminopenicillanic acid through a series of steps.

Abstract: Novel penicillins of the formula: ##STR1## wherein the ring A is a benzene ring or a 5 or 6-membered heteroaromatic ring containing one or two nitrogen atoms as the hetero atom, on which one or more of lower alkyl, lower alkoxy, lower alkylthio, lower haloalkyl, lower alkylenedioxy halogen, hydroxyl, nitro, free or protected amino, lower alkylamino, di(lower)alkylamino and lower alkanoylamino may be present, Z is a nitrogen atom or a methylene group, X is an oxygen atom or a sulfur atom, Y is a hydrogen atom, a lower alkoxycarbonyl group or a lower alkanoyl group, R.sub.1 is a free or protected hydroxyl group and R.sub.2 and R.sub.3 are each a hydrogen atom or a halogen atom, and their non-toxic pharmaceutically acceptable salts, and their preparation.

Abstract: Novel penicillins of the formula ##SPC1##Wherein ##EQU1## represents a substituted or unsubstituted benzene or nitrogen atom-containing heteroaromatic ring which may be substituted, ##EQU2## represents a pyridine, pyrazine or pyridazine ring, X represents an oxygen or sulfur atom, Y represents a hydrogen atom or a loer alkoxycarbonyl or lower alkanoyl group, and R.sub.1, R.sub.2 and R.sub.3 are each a hydrogen or halogen atom or a nitro, lower alkylamino, di(lower)alkylamino, aine, lower alkoxycarbonylamino, lower alkanoylamino, amino(lower)alkyl, lower alkyl, lower alkoxy, hydroxyl, sulfamoyl, trifluoromethyl, lower alkylthio or lower alkylsulfonyl group, excluding the cases where all of R.sub.1, R.sub.2 and R.sub.3 are hydrogen atoms and where R.sub.1 is a hydroxyl group and R.sub.2 and R.sub.

Abstract: Novel penicillins of the formula: ##SPC1##Wherein the ring A is a benzene ring or a 5 or 6-membered heteroaromatic ring containing one or two nitrogen atoms as the hetero atom, on which one or more of lower alkyl, lower alkoxy, lower alkylthio, lower haloalkyl, lower alkylenedioxy, halogen, hydroxyl, nitro, free or protected amino, lower alkylamino, di(lower)alkylamino and lower alkanoylamino may be present, Z is a nitrogen atom or a methylene group, X is an oxygen atom or a sulfur atom, Y is a hydrogen atom, a lower alkoxycarbonyl group or a lower alkanoyl group, R.sub.1 is a free or protected hydroxyl group and R.sub.2 and R.sub.3 are each a hydrogen atom or a halogen atom, and their non-toxic pharmaceutically acceptable salts, and their preparation.

Abstract: Penicillins of the formula: ##SPC1##Wherein R is an unsubstituted phenyl group or a substituted phenyl group having one or more hydroxyl groups or a cyclohexadienyl group and A represents a monocyclic or polycyclic nitrogen-containing heterocyclic aromatic ring, which are useful as antimicrobial agents having a broad antimicrobial spectrum against gram-positive and gram-negative bacteria including Pseudomonas and can be produced advantageously from the phenacyl ester of 6-aminopenicillanic acid through a series of steps.