Paraflexinols A−G, rare flexibilane-based diterpenoids from the soft coral Paralemnalia thyrsoides

Seven undescribed diterpenoids paraflexinols A–G (1–7), possessing a fifteen-membered macrocyclic ring, have been isolated from the ethyl acetate extract of the soft coral Paralemnalia thyrosides. The structures of 1–7 have been established by the detailed spectroscopic analysis, including 2D NMR spectroscopy, while their absolute configurations were determined using a modified Mosher's method for 1–3, 6, and 7. For over four decades after the first discovery of the ancestor of these compounds flexibilene (8) from the soft coral Sinularia flexibilis until the current report, no flexibilane-based diterpenoids had been isolated or identified. This study provides detailed NMR data for metabolites of this type for the first time.