Abstract
Ansamitocins are new maytansinoid antitumor antibiotics produced by an actinomycete strain No. C-15003 (N-1). The organism is characterized by coremia formation on solid media, release of the rod-shaped motile spores with peritrichous flagella in liquid media, the formation of some branched mycelia at a later stage of growth in liquid culture which break up into motile elements, lysozyme resistance, the occurrence of meso-diaminopimelic acid in the cell wall, and guanine-cytosine content of 71±1 mol %. From these results, the organism has been designated as Nocardia sp. No. C-15003 (N-1). In the fermentation fluids, activity against eukaryotic microorganisms was detected. Three of the purified materials, which have the activity against Tetrahymena pyriformis strain W and Hamigera avellanea IFO 7721, were new ansamycin antibiotics with antileukemic activities and were named ansamitocins P-3, P-3' and P-4. Ansamitocins show growth inhibitory activity against several eukaryotic microorganisms but no activity against prokaryotic microorganisms. The acyl moieties at the C-3 position of ansamitocins are essential for their antifungal activities.
