Structural elucidation of two new polypropionates from the marine slug Paromoionchis tumidus by spectroscopic analyses and DFT calculations

Tumiduspyrones A and B (1‒2), two new C17 and C18 polypropionates, and three known compounds (3‒5) were isolated from the sea slug Paromoionchis tumidus. Their structures and the absolute configurations of 1 and 2 were elucidated by spectroscopic analyses and quantum chemical calculations of the ECD and NMR data. The stereochemistry of compound 1 was also established based on the single-crystal X-ray diffraction method. In antimicrobial assays, only (E)-4-(1H-indol-3-yl)but‑3-en-2-one (3) showed moderate activity, whereas remaining compounds were weakly active.