Lemneolemnanes A–D, Four Uncommon Sesquiterpenoids from the Soft Coral Lemnalia sp.

Four undescribed sesquiterpenoids, lemneolemnanes A–D (1–4), have been isolated from the marine soft coral Lemnalia sp. The absolute configurations of the stereogenic carbons of 1–4 were determined by single-crystal X-ray crystallographic analysis. Compounds 1 and 2 are epimers at C-3 and have an unusual skeleton with a formyl group on C-6. Compound 3 possesses an uncommonly rearranged carbon skeleton, while 4 has a 6/5/5 tricyclic system. Compound 1 showed significant anti-Alzheimer’s disease (AD) activity in a humanized Caenorhabditis elegans AD pathological model.