Abstract
Several species of red algae (Rhodophyta) from the coastal regions of Madagascar have been investigated for their natural products. The most abundant compound was cholesterol (5) in combination with a series of oxidized congeners. The brominated indoles 1–3 along with the sesquiterpene debilone (4) have been isolated from Laurencia complanata. For the first time, debilone (4) has been obtained from a marine plant. From the methanol extract of Calloseris sp., we have achieved the second isolation of the unusual A-ring contracted steroids (−)-2-ethoxycarbonyl-2β-hydroxy-A-nor-cholest-5-en-4-one (9) and phorbasterone B (10). The crude extracts of Laurencia complanata exhibited antimicrobial activity against Bacillus cereus, Staphylococcus aureus, Streptococcus pneumoniae, and Candida albicans.
Highlights
Marine organisms may comprise over 80% of the world’s plant and animal species and offer an enormous source of novel and potentially biologically active compounds [1]
Dried samples of Laurencia complanata were extracted with methanol
In his early work on the sterols of marine algae, Patterson reported that cholesterol (5) is the major sterol in most of the red algae (Rhodophyta) [20]
Summary
Marine organisms may comprise over 80% of the world’s plant and animal species and offer an enormous source of novel and potentially biologically active compounds [1]. About 9% of biomedical compounds from marine sources are found in algae [1]. Madagascar, the fourth largest island in the world with a coastline of almost 5000 km, accommodates a wealth of marine organisms in its coastal region. Only few representatives of red algae from Madagascar have been studied for their bioactive compounds. For the red alga Gelidium madagascariense, Mollion identified an agar polymer in which the methylated fraction contains predominantly 6-O-methyl galactose and traces of 4-O-methyl galactose [4].
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