| abstract |
(<sub>57</sub>) A cephalosporin derivative of the formula I:in which X is S, O, CH<sub>2</sub> or SO,represents one of C-7 acyl groups known in the cephalos porin art, R3 is hydrogen or methoxy, R4 is hydrogen, optionally substituted alkyl or allyl, and R5 is an aromatic heterocyclic ring system which is linked via carbon, and which contains a quaternised nitrogen atom. |