Lecanicilliums A-F, Thiodiketopiperazine-class Alkaloids from the mangrove sediment-derived fungus Lecanicillium kalimantanense

Six new thiodiketopiperazine-class alkaloids, lecanicilliums A-F (1-6), were isolated from the mangrove sediment-derived fungus Lecanicillium kalimantanense SCSIO41702, together with 13 known analogous (7-19). Compound 1 contained an unprecedented 6/5/6/5/7/6 cyclic system. Their structures were elucidated by spectroscopic analysis, and the absolute configurations were further determined by quantum chemical calculations electronic circular dichroism (ECD) spectra. Biologically, 5, 7 and 16 displayed significant cytotoxicity against human lung adenocarcinoma cell line H1975 with IC50 values of 7.2~16.9 μM, and 5 showed antibacterial activity against five pathogens. Their structure-activity relationship is also discussed.