Rogersonins C-F, 9 H -Imidazo[2,1- i ]purine-Incorporating Adenine-Polyketide Hybrids from an Ophiocordyceps -Associated Clonostachys rogersoniana .

Rogersonins C-F ( 1 - 4 ), four unprecedented adenine-polyketide hybrids featuring a rare 9 H -imidazo[2,1- i ]purine (1, N 6 -ethenoadenine) moiety, were isolated from an Ophiocordyceps -associated fungus, Clonostachys rogersoniana . Their structures were elucidated primarily by NMR experiments. The absolute configurations of 1 - 4 were assigned by a combination of the modified Mosher method, chemical degradation, electronic circular dichroism (ECD) calculations, and X-ray crystallography using Cu Kα radiation. Compound 3 downregulated the expression of PD-L1 protein in MDA-MB-231 and A549 cells, but did not show detectable effect on mRNA transcription of the PD-L1-encoding gene CD274 .