ACYL DERIVATIVES

Novel cephalosporin derivatives are disclosed of the formula: < IMG > I wherein R1 represents a hydrogen atom or a methoxy group and Y represents a 6-membered, optionally substituted heterocyclic group which contains 1,2 or 3 nitrogen atoms but which is not aromatic and is not enolisable to an aromatic group; at least one of said nitrogen atoms being substituted and at least one of said nitrogen atoms forming an amide group with an adjacent carbonyl group, and wherein the carboxyl group in the 4-position can be protected by salt formation with an inorganic or tertiary organic base. The derivatives I are useful as in-termediates in preparing cephalosporins having antibiotic activity.