A multiplicity of neolemnane-type sesquiterpenoids from the soft coral Lemnalia sp.

Terpenoids are a large class of structurally diverse secondary metabolites that have attracted the attention of chemists and pharmacologists due to their unique skeletal structures and wide range of biological activities. Octocorals are major contributors to the diversity of terpenoids in the ocean, and soft corals are one of the representative species of octocorals. An investigation into the chemical composition of a soft coral identified as Lemnalia sp., yielded six previously undescribed neolemnane-type sesquiterpenoids (1-6) and twelve known ones (7-18). The elucidation of their structures drew on spectroscopic data, while the assignment of absolute configurations was accomplished by means of X-ray crystallography, TDDFT-ECD calculations, and biogenetic clues. Neolemnane-type sesquiterpenoids have a relatively conserved 6/8 bicyclic skeleton, and the novelty of compounds 1-6 relate to the alteration of the cis/trans geometry around the Δ2,3 olefin, or the different oxidative substituents or configurational changes at the C-4, C-5, and C-10 positions.