Indole Alkaloids from a Soil-Derived Clonostachys rosea

Clonorosins A (1) and B (2), two novel indole alkaloids featuring unprecedented 6/5/6/6/5 and 6/5/5 cores, together with seven known indole-linked 2,5-diketopiperazine alkaloids (3-9), were isolated from the soil-derived fungus Clonostachys rosea YRS-06. The new structures were proposed through HR-MS, NMR, and ECD spectroscopic data. They were established by comparing the calculated NMR, ECD, and specific rotation data with the experimental. To assist in determining the absolute configuration of the chiral carbon in the side chain of 2,5-diketopiperazine derivatives, flexible analogues 3i-3iv were synthesized and analyzed. 1 was active against Fusarium oxysporum with an MIC value of 50 mu g/mL. 7 and 8 showed excellent activity against human HeLa and HepG2 cells with IC50 values of 0.12-0.60 mu M.

Automated summary

Clonorosins A and B, two novel indole alkaloids with unprecedented core structures, were isolated from the fungus Clonostachys rosea YRS-06, along with seven known indole-linked 2,5-diketopiperazine alkaloids. The new structures were proposed and established through spectroscopic data analysis. Compound 1 showed antifungal activity, while compounds 7 and 8 exhibited excellent activity against human cancer cells.