MIDCHAIN HYDROXY LONG-CHAIN FATTY-ACIDS IN MICROALGAE FROM THE GENUS NANNOCHLOROPSIS

Extractable and bound lipids of four species of microalgae from the ge nus Nannochloropsis have been examined by capillary GC-mass spectromet ry. In addition to previously described unusual C-28-C-34 alkyl diols and n-alcohols, small quantities of compounds identified as C-28-C-34 monohydroxy fatty acids were detected both in free and bound form. For each carbon chain-length member of the series, a single positional is omer predominated, which was identified as the omega 18-isomer from ch aracteristic mass spectral fragment ions. The position of the hydroxyl group at omega 18 rather than at a constant position relative to the carboxylic acid group indicates that the series results from chain-elo ngation (or perhaps chain-shortening) of a particular hydroxy fatty ac id, rather than hydroxylation of a range of fatty acids. Furthermore, two dihydroxy fatty acids, identified as 15,16-dihydroxydotriacontanoi c and 16,17-dihydroxytritriacontanoic acids, were also found in the pr oducts from acid hydrolysis of the cell residue. Possible biosynthetic correlations between these hydroxy and dihydroxy fatty acids and the long-chains diols also produced by these algae are discussed. Our data suggest that hydroxy acids may be precursors of the diols via reducti on of the acid group. However, another pathway must be invoked in orde r to explain the formation of some diol isomers. (C) 1997 Elsevier Sci ence Ltd.