Abstract
Seven new polyoxygenated steroids (1–7) were isolated together with seven known analogues (8–14) from the South China Sea soft coral, Sarcophyton sp. The structures of the new compounds were identified on the basis of extensive spectroscopic analysis and comparison with reported data. All the steroids are characterized with 3β,5α,6β-hydroxy moiety, displaying carbon skeletons of cholestane, ergostane, gorgostane and 23,24-dimethyl cholestane. In the in vitro bioassay, metabolites exhibited different levels of antimicrobial activity against bacterial species Escherichia coli and Bacillus megaterium, and fungal species Microbotryum violaceum and Septoria tritici. No inhibition was detected towards microalga Chlorella fusca. Preliminary structure-activity analysis suggests that the 11α-acetoxy group may increase both antibacterial and antifungal activities. The terminal-double bond and the cyclopropane moiety at the side chain may also contribute to the bioactivity.
Highlights
Soft corals are thought to produce various bioactive metabolites that chemically defend themselves from attack [1,2,3]
Purification of the Et2O extract, by repeated column chromatography on silica and Sephadex LH-20 and followed by reversed-phase semi-preparative HPLC, yielded the pure compounds shown in 1–14 (Figure 1)
Chemical investigation of the soft coral Sarcophyton sp. from the South China Sea led to the isolation and structural elucidation of fourteen polyoxygenated steroids (1–14) with 3β,5α,6β-hydroxy moiety, demonstrating an excellent example of chemical diversity
Summary
Soft corals are thought to produce various bioactive metabolites that chemically defend themselves from attack [1,2,3]. The soft coral Sarcophyton species (order Alcyonacea, family Alcyoniidae) are prolific in the South China Sea and are dominant in many coral reef areas [4]. In the course of our ongoing screening for bioactive secondary metabolites from marine sources [7,8,9,10,11], we have made a collection of Sarcophyton sp. Chemical investigation on the Et2O-soluble fraction of the acetone extract from Sarcophyton sp. Resulted in the isolation of fourteen steroids (1–14, Figure 1) with 3β,5β,6β-hydroxy moiety. We describe the isolation, structural elucidation and bioactivity of these new metabolites
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