Four New Polyhydroxysteroids From the South China Sea Cryptomonad Rhodomonas sp.

To date, metabolites of cryptomonads from the South China Sea have not been investigated. Herein, four new highly-oxidized steroids, named rhodomonasterols A-D (1-4), of which compounds 1, 2, and 4 possess a long-conjugated carbon chain, were obtained from the South China Sea cryptomonad Rhodomonas sp. The structures and absolute configurations of these steroids were unambiguously established by high-resolution electrospray ionization mass spectrometry, nuclear magnetic resonance spectroscopy, and single-crystal X-ray diffraction analyses (Cu-Kα). Notably, compounds 1 and 4 exhibited inhibitory activities against the production of nitric oxide (NO) in lipopolysaccharide-induced BV2 cells at the concentration of 10.0 µM. The two steroids inhibited the expression of inducible NO synthase, thereby displaying anti-inflammatory effects.