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

Rogersonins C–F (<b>1</b>–<b>4</b>), four unprecedented adenine-polyketide hybrids featuring a rare 9<i>H</i>-imidazo­[2,1-<i>i</i>]­purine (1,<i>N</i>⁶-ethenoadenine) moiety, were isolated from an <i>Ophiocordyceps</i>-associated fungus, <i>Clonostachys rogersoniana</i>. Their structures were elucidated primarily by NMR experiments. The absolute configurations of <b>1</b>–<b>4</b> 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 <b>3</b> 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 <i>CD274</i>.