Lemnalemnanes A–C, Three Rare Rearranged Sesquiterpenoids from the Soft Corals <i>Paralemnalia thyrsoides</i> and <i>Lemnalia</i> sp.

Abstract

Three novel sesquiterpenoids, lemnalemnanes A-C (<b>1</b>-<b>3</b>), were obtained from marine soft corals <i>Paralemnalia thyrsoides</i> and <i>Lemnalia</i> sp. Their structures were determined by 1D/2D NMR spectroscopy, HRESIMS, single-crystal X-ray diffraction analysis (Cu Kα), Mosher's method, and ECD quantum chemistry calculations. Lemnalemnane A (<b>1</b>) possessed an intriguing basket-like structure with a spiro[bicyclo[3.3.1]nonane-furan core, while lemnalemnanes B (<b>2</b>) and C (<b>3</b>) exhibited unusual 6/6/5 and 6/5/5 carbon skeletons, respectively. In the proposed biosynthesis pathway, <b>1</b>-<b>3</b> were suspected to originate from the same precursor, 4-<i>O</i>-deacetylparalemnolin D (<b>4</b>), a compound coisolated from both aforementioned species. Furthermore, lemnalemnane C (<b>3</b>) exhibited strong <i>in vivo</i> promoting-angiogenesis activity.