Norsesquiterpenoids from the octocoral Paralemnalia thyrsoides (Ehrenberg 1834)

Three norsesquiterpenoids, pathyspirolactones A (1) and B (2), and napalilactone (3), featuring a γ-spirolactone moiety, were isolated from the cultured octocoral Paralemnalia thyrsoides. The structures of 1–3 were determined by analyzing spectroscopic data, DP4+ computation, specific optical rotation, and X-ray diffraction. In addition, we explored the absolute configurations of pathyspirolactone A (1) and its conformation of the cyclohexane ring to resolve the stereochemical confusion of those of norsesquiterpenoid compounds. Furthermore, we proved that pathyspirolactone B (2) was the first bromine-containing norsesquiterpenoid reported from octocorals.