A novel series of C-8 ester derivatives of leinamycin are described. Condensation of N-substituted amino acids or carboxylic acids containing polyether moiety with leinamycin resulted in the C-8 ester derivatives with good antitumoractivity in several experimental models. Among these derivatives, compound 4e, which has five ethylene glycol ether units in the C-8 acyl group, showed potent antitumor