Abstract: The penicillins of the formulae ##STR1## in which R.sup.1 is phenyl, 2-thienyl, 3-thienyl, cyclohexyl, cyclohexen-1-yl, cyclohexa-1,4-dienyl, cyclohexa-1,4-dienylmethyl, 4-methoxycyclohexa-1,4-dienylmethyl or one of certain 4-substituted or 3,4-disubstituted phenyl moieties, and their pharmaceutically acceptable salts and physiologically hydrolyzed esters possess antibacterial activity and are particularly valuable in treating Pseudomonas infections.

Abstract: The penicillin of the formula ##STR1## and its pharmaceutically acceptable salts and physiologically hydrolyzed esters possess antibacterial activity and are particularly valuable in treating Pseudomonas infections.

Abstract: 7-[.alpha.-(4-hydroxy-1,5-naphthyridine-3-carboxamido)-.alpha.-phenyl or thienyl (and substituted phenyl) acetamido]-3-(pyridiniummethyl)-3-cephem-4-carboxylates having on the pyridine ring an acidic group which is preferably --COOH or --SO.sub.3 H and also, if desired, having one or two methylene groups together with or without a hetero atom between the pyridine ring and the acidic group were synthesized and found to have potent antibacterial activity in vitro especially against many strains of Pseudomonas aeruginosa and also high solubility in water.

Abstract: Certain 7-acylamido-3-(2-carboxyalkyl-2,3-dihydro-s-triazolo[4,3-b]pyridazin-3-on- 6-ylthiomethyl)-3-cephem-4-carboxylic acids and their salts and easily hydrolyzed esters of the 4-carboxyl group were synthesized and found to be potent antibacterial agents which exhibited good aqueous solubility. A preferred embodiment was 7-[o-(methylaminomethyl)phenylacetamido]-3-(2-carboxyalkyl-2,3-dihydro-s-t riazolo[4,3-b]pyridazin-3-on-6-ylthiomethyl)-3-cephem-4-carboxylic acid.

Abstract: Certain 7-acylamido-3-(2-carboxyalkyl-2,3-dihydro-s-triazolo[4,3-b]pyridazin-3-on- 6-ylthiomethyl)-3-cephem-4-carboxylic acids and their salts and easily hydrolyzed esters of the 4-carboxyl group were synthesized and found to be potent antibacterial agents which exhibited good aqueous solubility. A preferred embodiment was 7-[o-(methylaminomethyl)phenylacetamido]-3-(2-carboxyalkyl-2,3-dihydro-s-t riazolo[4,3-b]pyridazin-3-on-6-ylthiomethyl)-3-cephem-4-carboxylic acid.

Abstract: 7-[D-.alpha.-(4-hydroxy-1,5-naphthyridine-3-carboxyamido)-.alpha.-phenyl (and p-hydroxyphenyl) acetamido]-3-carbamoyloxymethyl-3-cephem-4-carboxylic acids were synthesized and found to have potent antibacterial activity in vitro especially against many strains of Pseudomonas aeruginosa.

Abstract: 7-(D-.alpha.-Hydroxy-2-arylacetamido)-3-(2-carboxyalkyl-2,3-dihydro-s-triaz olo[4,3-b]pyridazin-3-on-6-ylthiomethyl)-3-cephem-4-carboxylic acids and derivatives containing blocking groups on the .alpha.-hydroxy group and their nontoxic, pharmaceutically acceptable salts are valuable as antibacterial agents and are particularly valuable as therapeutic agents in poultry and in animals, including man, in the treatment of infectious diseases caused by many Gram-positive and Gram-negative bacteria. A preferred compound is 7-(D-mandelamido)-3-(2-carboxyalkyl-2,3-dihydro-s-triazolo[4,3-b]pyridazin -3-on-6-ylthiomethyl)-3-cephem-4-carboxylic acid.

Abstract: Cephalosporins in a series having the formula ##STR1## wherein R.sup.1 is alkyl containing 1-4 carbon atoms or a nontoxic pharmaceutically acceptable salt thereof, were synthesized and found to be potent antibacterial agents especially when in the form of the syn isomers essentially free of the corresonding anti isomer.

Abstract: Cephalosporins in a series having the formula ##STR1## wherein R.sup.1 is alkyl containing 1-4 carbon atoms and n is 1 or 2 or a nontoxic pharmaceutically acceptable salt thereof, were synthesized and found to be potent antibacterial agents especially when in the form of the syn isomers essentially free of the corresponding anti isomer.

Abstract: Certain 7-acylamido-3-(2-carboxyalkyl-2,3-dihydro-s-triazolo[4,3-b]pyridazin-3-on- 6-ylthiomethyl)-3-cephem-4-carboxylic acids and their salts and easily hydrolyzed esters of the 4-carboxyl group were synthesized and found to be potent antibacterial agents which exhibited good aqueous solubility. A preferred embodiment was 7-[o-(methylaminomethyl)phenylacetamido]-3-(2-carboxyalkyl-2,3-dihydro-s-t riazolo[4,3-b]pyridazin-3-on-6-ylthiomethyl)-3-cephem-4-carboxylic acid.

Abstract: 7-(D-.alpha.-Hydroxy-2-arylacetamido)-3-(tetrazolo-[4,5-b]pyridazin-6-ylthi omethyl)-3-cephem-4-carboxylic acids and their nontoxic, pharmaceutically acceptable salts are valuable as antibacterial agents and are particularly valuable as therapeutic agents in poultry and animals, including man, in the treatment of infectious diseases caused by many Gram-positive and Gram-negative bacteria.

Abstract: 7-[.alpha.-(2-Aminomethyl-1-cyclohexyl)-acetamido]-3-heterocyclic thiomethyl-3-cephem-4-carboxylic acids, and their nontoxic, pharmaceutically acceptable salts and their Schiff bases, as made by reaction of salicylaldehyde with the free amino group, are valuable as antibacterial agents and are particularly valuable as therapeutic agents in poultry and animals, including man, in the treatment of infectious diseases caused by many Gram-positive and Gram-negative bacteria.