Syn isomers of cephalosporins having .alpha.-hydroximino- or .alpha.-acyloxyiminoacylamido groups at position-7

A compound selected from the group consisting of a cephalosporin antibiotic of the formula ##STR35## wherein R is thienyl;

• furyl or pyridyl;
• R.sup.a is H or ##STR36## wherein R.sup.c is C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 chloroalkyl, C.sub.1 -C.sub.4 alkoxy, phenyl, nitrophenyl, C.sub.1 -C.sub.4 alkylamino or C.sub.1 -C.sub.4 chloroalkylamino;
• and,
• Y is ##STR37## in which n is zero or an integer from 1 to 5 and R.sup.d, which when n is from 2-5 may be the same or different, is lower alkyl;
• phenyl;
• phenyl lower alkyl;
• C.sub.1 -C.sub.3 alkoxymethyl;
• acetoxymethyl;
• formyl;
• carbamoyl;
• acetoxy;
• C.sub.1 -C.sub.3 alkoxy;
• phenoxy, benzyloxy;
• C.sub.1 -C.sub.2 alkylthio;
• cyano;
• hydroxy;
• N-monoloweralkylcarbamoyl;
• N,N-diloweralkylcarbamoyl;
• N-(hydroxyloweralkyl) carbamoyl;
• or carbamoylloweralkyl or;
• ii. azido;
• and a physiologically acceptable salt thereof, said cephalosporin antibiotic being in the form of a syn isomer free of the corresponding anti isomer to the extent of at least 75% based on the total weight of said antibiotic.