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 3 beta,4 alpha,6 alpha,7 beta-tetrahydroxy or equivalent (7 beta-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 14 beta 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.