Cangumycins A-F, six new angucyclinone analogues with immunosuppressive activity from Streptomyces

Cangumycins A-F ( 1-6 ), six new angucyclinone analogues, together with two known ones ( 7 and 8 ), were isolated from the fermentation broth of a soil-derived Streptomyces sp. KIB-M10. Structures of these compounds were elucidated via a joint use of spectroscopic analyses and single-crystal X-ray diffractions. Among them, cangumycins E ( 5 ) and F ( 6 ) share a C-ring cleaved backbone, and cangumycins B ( 2 ) and E ( 5 ) exhibit potent immunosuppressive activity (IC₅₀ 8.1 and 2.7 μmol·L^-1, respectively) against human T cell proliferation at a non-cytotoxic concentration.