Xylaridines C and D, Unusual Thiopyranodipyridine Alkaloids from the Fungus .

Structurally unique thiopyranodipyridine alkaloids xylaridines C () and D () were isolated from the fungus . Their structures were established by comprehensive spectroscopic analysis combined with single-crystal X-ray diffraction and electron-capture detection (ECD) calculations. Compound possesses two piperidine moieties fused with a centered thiopyran ring, while compound is a dimer of . Compound was resoluted into optical pure enatiomers (+)- and (-)- by chiral HPLC. Moreover, compound was resoluted into an optically pure compound (+)- and a mixture of (-)- and meso-. Plausible biosynthetic pathways of compounds and are proposed.