Polyoxygenated Steroids from the Sponge Clathria gombawuiensis

Six new polyoxygenated steroids (1–6) along with clathriol (7) were isolated from the Korean marine sponge Clathria gombawuiensis. Based upon the results of combined spectroscopic analyses, the structures of gombasterols A–F (1–6) were elucidated to be those of highly oxygenated steroids possessing a 3β,4α,6α,7β-tetrahydroxy or equivalent (7β-sodium O-sulfonato for 3) substitution pattern and a C-15 keto group as common structural motifs. The relative and absolute configurations of these steroids, including the rare 14β configuration of 1–4, were determined by a combination of NOESY, J-based analyses, the 2-methoxy-2-(trifluoromethyl)­phenylacetic acid (MTPA) method, and X-ray crystallographic analysis. The absolute configuration of 7 was also assigned by these methods. These compounds moderately enhanced 2-deoxy-2-[(7-nitro-2,1,3-benzoxadiazol-4-yl)­amino]-d-glucose (2-NBDG) uptake in differentiated 3T3-L1 adipocytes and phosphorylation of AMP-activated protein kinase (AMPK) and acetyl-CoA carboxylase (ACC) in differentiated mouse C2C12 skeletal myoblasts.