Novel 1-dethia-2-thia-cephalosporanic acid derivatives of the formula ##STR1## wherein R is selected from the group consisting of ##STR2## Ra is an organic radical, R.sub.i and R.sub.j are individually selected from the group consisting of hydrogen, aliphatic, aromatic and heterocycle or taken together with the nitrogen atom to which they are attached form an optionally substituted cycle or R.sub.b NH--, R.sub.b is optionally substituted carbocyclic or heterocyclic aryl, R.sub.1 and --COM are as defined in the specification, R.sub.4 is hydrogen or methoxy, n.sub.2 is 0, 1 or 2 and their non-toxic, pharmaceutically acceptable acid addition salts in racemic or optically active form having antibiotic activity and their preparation and novel intermediates.