Structurally diverse diketopiperazine alkaloids from the marine-derived fungus Aspergillus versicolor SCSIO 41016

Abstract

Ten new diketopiperazine alkaloids (DAs, 1–10) along with two known congeners (11–12) were characterized from the marine sponge-derived fungus Aspergillus versicolor SCSIO 41016. Their structures including absolute configurations were determined by spectroscopic analyses, quantum chemical calculations, and X-ray diffraction analysis. Pyranamides A–D (1–4) were obtained as rare 1-oxa-8,10-diazaspiro[5.5]undecane containing diketopiperazine alkaloids, while secopyranamide C (5) was obtained as a tetrahydropyran-ring cleavage derivative. Plausible biosynthetic pathways of 1–12 were postulated. Compounds 7 and 12 exhibited weak cytotoxic activities against ACHN, OS-RC-2, and 786-O cells.