Constituents of the Red Alga Laurencia obtusa

The genus Laurencia Lamouroux (Rhodomelaceae) includes about 140 species distributed throughout the world except in the Arctic and Antartic zones [1]. The red algae of the genus Laurencia (Rhodomelaceae) are known as a rich source of the halogenated sesquiterpenes, diterpenes and acetylenes [2,3]. Although a number studies have been done on L. obtusa, investigations are still going on this species due to high biodiversity of its constituents. In our continuing research on secondary metabolites of the alga L. obtusa Lamoroux, which has different colors in different regions of Turkey and at different times, we have obtained several halogenated sesquiterpenoids [4,5].

In this study, a sample of L. obtusa, collected from North eastern part of Aegean Sea (Bademli- Ayvalık) in Turkey and an extract was obtained by exhausting in chloroform-methanol (1:1) solvent mixture as 14g. Fractionation of the extract on a Si-gel column carried out by the elution starting petroleum ether, and gradients used were first dichloromethane, and then acetone, finally methanol with increasing amounts. The fraction, obtained by elution with the petroleum ether-dichloromethane mixture (6:4) afforded two halogenated compounds, their 1H-NMR spectra indicated that they have probably sesquiterpene skeleton. Another compound was obtained during elution with the dichloromethane-acetone solvent mixture (8:2). Structure elucidation studies are still going on using by intensive NMR and mass spectral analyses. There are a number of compounds which have not purified yet. After purification and structure elucidation studies, the pure compounds will be investigated for their potential bioactivity including cytotoxic and anti-cholinesterase activity tests.

References: [1] Rodriguez MCG et al. (1992) Bot Mar 35: 227–237

[2] Faulkner D J (1999) Nat Prod Rep16: 155–198

[3] Scheuer PJ (1989) Med Res Rev 9: 535–545

[4] Topçu et al. (2003)J Nat Prod66: 1505–1508

[5] Öztunç A et al. (2001) Tetrahedron 47: 2273–2276