Lactimidomycin (LTM, 1) is a macrolide antitumor antibiotic with a glutarimide side chain from Streptomyces amphibiosporus ATCC53964. To further develop LTM and related analogues as drug candidates we have (i) improved LTM production by approximately 20 fold, (ii) identified three new metabolites (2-4) possibly involved in the LTM biosynthetic pathway; (iii) found 3 to be identical with a previously