Diterpene content of the alga Dictyota ciliolata from a Moroccan lagoon
Graphical abstract
Chemical analysis of the brown alga Dictyota ciliolata led to the isolation and characterization of two new xenicane type compounds 1 and 2.
Introduction
Brown algae of the genus Dictyota are a rich source of diterpenes with different carbon frameworks including xenicane, dolabellane and prenylated guaiane skeletons (Blunt et al., 2009). Among these, xenicanes are an intriguing group of bioactive molecules that occur also in gorgonians and soft corals (Blunt et al., 2009). Several Dictyota diterpenes exhibit interesting biological activities including cytotoxic, antiviral, ichtyotoxic and antifouling properties (Duran et al., 1997, Sun et al., 1983, Pereira et al., 2004, Schmitt et al., 1998, Viano et al., 2009). Xenicanes, in particular, have been reported to be significantly cytotoxic against a number of human cancer cell lines (Cheng et al., 2006, Shen et al., 2005, El-Gamal et al., 2005).
As part of our ongoing investigation on bioactive compounds from marine sources we have analyzed the diterpene content of the brown alga Dictyota ciliolata, Kutzing, 1859, collected from Oualidia lagoon (Morocco). Previous chemical and ecological studies on the same species from distinct geographical areas have resulted in the finding of an unusual sulfonoglycolipid (Bourne et al., 1999) as well as of typical Dictyota diterpenes including dictyodial, pachydictyol A and dictyol B acetate (Cronin et al., 1995, Schmitt et al., 1998). The possible involvement of these diterpenes in the defensive mechanisms of D. ciliolata has been also suggested (Cronin and Hay, 1996, Schmitt et al., 1998).
Here we describe the structure elucidation and the biological activity of two new xenicane diterpenes, ciliolatale (1) and 17-acetoxy-dictyodial (2), isolated from the lipophilic extract of D. ciliolata along with dictyodial (Finer et al., 1979), and the guaiane homologs, dictyol C (Danise et al., 1977) and dictyol H (Alvarado and Gerwick, 1985). The previously reported pachydictyol A and dictyol B acetate were not detected in the sample analyzed in the present work.
Section snippets
Results and discussion
The Et2O soluble fraction of the Me2CO extract of D. ciliolata was analyzed by TLC chromatography (light petroleum ether/Et2O in different ratio) and showed the presence of chlorophyll and lipids mainly along with a series of spots, at Rf 0.60–0.55 and 0.30–0.23 (light petroleum ether/Et2O, 1:1). The extract was then purified on a silica-gel column (petroleum light ether with increasing amount of Et2O as eluent) to obtain two fractions containing the two groups of metabolites evidenced by TLC.
General experimental procedures
Optical rotations were measured on a Jasco DIP 370 digital polarimeter; IR spectra were measured on a Biorad FTS 155 FTIR spectrophotometer; 1D and 2D NMR spectra were recorded on a Bruker 400 AMX (400.13 MHz) in CDCl3 (δ values are reported referred to CHCl3 at 7.26 ppm) and in C6D6 (δ values are reported referred to C6H6 at 7.16 ppm) and 13C NMR were recorded on a 300 AMX Bruker (75.47 MHz) (δ values are reported to CDCl3, 77.0 ppm and to C6D6, 128 ppm); HRESIMS were carried out on a Micromass
Acknowledgements
The NMR spectra were recorded at the ICB NMR Service, the staff of which is gratefully acknowledged. Particular thanks are due to Mrs. Dominique Melck for NOE experiments. The authors are also grateful to Mr. C. Iodice for spectrophotometric measurements and to Mr. R. Turco for preparing the structures and tables. Dr. Maria Cristina Buia (Laboratorio di Ecologia Funzionale ed Evolutiva, Stazione Zoologica Anton Dohrn, Naples) is kindly acknowledged for taxonomic identification of the alga. This
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