Mycestericins A, B, C, D and E were isolated from the culture broth of Mycelia sterilia ATCC 20349 along with thermozymocidin (=myriocin). Their structures were elucidated on the basis of spectroscopic studies and chemical evidence. The acetate of mycestericin C was identical with the acetate of 6,7-dihydromyriocin. Mycestericins suppressed the proliferation of lymphocytesin the mouseallogeneic mixed lymphocytereaction, with a potency similar to that of myriocin.We have very recently reported2)3) that a metabolite of Isaria Sinclairii (ATCC 24400) showed potent immunosuppressiveactivity. Its activities in the mouseallogeneic mixed lymphocyteand mouseallogeneic cytotoxic T lymphocyte assays were 10 times and 100 times those of cyclosporin A (CsA), respectively. The metabolite was identical with myriocin4'5) (1, Fig. 1) and thermozymocidin6), which are produced by Myriococcum albomyces (ATCC16425) and Mycelia sterilia (ATCC20349), respectively. Reduction of the ketone at C-14 of 1 to a methylene increased the activity 10-fold7). Therefore, it seemed possible that tf Present address:
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