Rogersonins C–F, 9H‑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 9H-imidazo­[2,1-i]­purine (1,N⁶-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.