The brown macroalgae Cystoseira abies-marina as a natural source of D-(+)-mannitol

Abstract

Cystoseira abies marina is a brown macroalgae that inhabits the coast of the Canary Islands and has caught our attention by our Canary islands Industrial Development Project (DISCAN-2007), due to its potential as a natural source of high added-value products from marine origin. The literature indicated the presence in their organic extracts of high content of polyunsaturated fatty acids 16:3 and 16:4 (w- 3), monogalactosyldiacylglycerols, triacylglycerols, phospholipids, sterols (mainly fucosterol), meroter- penes, and sulfated polysaccharides of different molecular weights and sulfate contents which exhibit potent anticoagulant activity. With this background, it was decided to improve the knowledge about the natural product chemistry of this interesting seaweed. Fresh seaweed biomass of C. abies marina was submitted to Soxhlet extraction with acetone followed by concentration on a rotary evaporator. The crude extract upon evaporation afforded a dark-brown syrup. Column chromatography was carried out eluting with n-hexane/ ethyl acetate trough successive increasing amounts of the last solvent. The fractions were monitored by thin layer chromatography (TLC) and joined by similarity. Finally, two fractions were isolated according to their chromatography behaviour: one polar, and other non-polar that were analyzed and characterized. The so-called ”non-polar fraction” was found to be composed of alkanes and fatty acids as revealed by NMR spectroscopy. The ”polar fraction” (~2.2% on a wet weight) was found to be formed by D- (+)-mannitol, which was recrystallized from acetone: m.p. 165-166ºC: [α]D20ºC = + 0.32º (c= 2.185, water). The acetylated derivative crystallized in the form of transparent hexagonal crystals, and its mix melting point (with authentic mannitol acetate) gave 123-124ºC which is consistent with the literature data. The optical rotation also agreed with the literature value: [α]D20ºC = + 23.32º (c= 1.90, chloro- form). As conclusion, Cystoceira abies marina offers a great potential natural source of D-(+)-mannitol, an important monosaccharide used in the pharmaceutical industries and nutraceutical companies.