Klyflaccilides A and B, Diterpenoids with 6/5/8/3 Fused Tetracyclic Carbon Skeleton from the Hainan Soft Coral <i>Klyxum flaccidum</i>

Abstract

Two novel polyoxygenated diterpenoids, klyflaccilides A (<b>1</b>) and B (<b>2</b>), featuring an uncommon 6/5/8/3 tetracyclic ring system, were isolated from the Hainan soft coral <i>Klyxum flaccidum</i>. Their structures were established by extensive spectroscopic analysis, X-ray diffraction analysis, and/or a quantum chemical computation method. A plausible biosynthetic relationship of <b>1</b> and <b>2</b> with their potential precursor <b>3</b> was further proposed. Compounds <b>1</b> and <b>3</b> exhibited moderate anti-inflammatory activity by the inhibition of LPS-induced TNF-α protein release.