New Cembranoid Diterpenes from Sarcophyton trocheliophorum

Aims: To isolate the unpolar bioactive diterpenes in pure forms from the soft coral Sarcophyton trocheliophorum, collected from Red Sea at the Egyptian coasts, and to identify their structures using diverse spectroscopic means (NMR [1D&2D] and MS). Additionally, to study the antimicrobial and cytotoxicity of the isolated compounds compared with the main crude extract of the soft coral.
Study Design: Collection of the soft coral, Sarcophyton trocheliophorum from Red Sea at coast of Hurgada, east Egypt, its homogenization, maceration in suitable organic solvent for extraction of the desired bioactive compounds and their purification by a series of different chromatographic techniques, identification of the compounds by mass spectrometry and NMR (1D&2D) spectroscopy, and then determination of the antimicrobial and cytotoxicity for them compared with their original crude extract.
Place and Duration of Study: Institute of Organic and Biomolecular Chemistry, University of Göttingen, Germany; and Chemistry of Natural Compounds Department, National Research Centre, Egypt, between August, 2008 and December, 2010.
Methodology: The soft coral Sarcophyton trocheliophorum was homogenized in a blender, macerated with chloroform-methanol, and the chloroform layer was concentrated in vacuo; while aqueous methanol solution was re-extracted with n-butanol, and the latter was concentrated to dryness. The resultant whole crude extract was fractionated using several subsequent column chromatographies on silica gel, and the fast fractions containing the unpolar components were purified by different column chromatographies (silica gel, Sephadex column and preparative TLC) to deliver the desired diterpenes in pure form. Structures of the afforded diterpenes were identified by mass spectrometry (ESI and HRESI-MS), NMR analysis (1H,13C NMR, and 2D NMR) and by comparison with reference data. The antimicrobial activity was determined by disc diffusion assay, while the cytotoxicity was determined using brine shrimp assay.
Results: Two new unpolar diterpenes, cis-cembrene C (1) and cis-cembrenene C (2) were isolated along with (+)-sarcophine (3), (+)-sarcophytoxide (4) and (-)-sarcophytoxide (5), from the chloroform-soluble extract of soft coral Sarcophyton trocheliophorum, collected from Red Sea. Four additional unpolar sesquiterpenes; ß-elemene (6), caryophyllene (7), alloaromadendrene (8) and 1-methyl-4-(5-methyl-1-methylene-hex-4-enyl)-cyclohexene; bisabolene (9) were identifed by GC-MS analysis. Structures of the new diterpenes 1-2 were identified by spectroscopic data (1H, 13C, 1H-1H COSY, HMQC, HMBC, HREI-MS and HRESI-MS) interpretation and comparison with related structures. The antimicrobial and cytotoxic activities of compounds 1-5 were evaluated in comparison with the original soft coral crude extract.
Conclusion: The soft coral Sarcophyton trocheliophorum is a prolific source for production of numerous bioactive compounds with diverse structures and biological activities which can be exploited for their commercial production.