Characterization of lyso-galactolipids, C-2 and C-3 O-acyl trigalactosylglycerol isomers, obtained from the lichenized fungus Dictyonema glabratum

A mixture of two lyse isomers of a galactolipid was obtained from Dictyonem a glabratum. Aqueous hydrolysis gave rise to galactose and glycerol in a 3. 1 molar ratio. ESI-MS spectroscopy gave. in the positive-ion mode, a pseudo molecular ion at mlz 839 and daughter ions with mlz 677, 600, 515 and 353, suggesting three galactosyl units linked to a glycerol moiety, substituted by one O-acyl group. 1D and 1D NMR experiments were used to characterize th e glycolipid, and HMQC examination showed three anomeric signals, correspon ding to two alpha -Galp, and one beta -Galp residue liked to glycerol. The glycolipid structure was shown to be O-alpha -D-Galp-(1-->6)-O-alpha -D-Gal p-(1-->6)-O-beta -D-Galp-(1<->1)-2- and -3-monoacyl-D-glycerol, the latter structures not having been previously found in nature. The fatty acid compo sition was determined by GC-MS of derived methyl esters: that of palmitic a cid C-16:0 was the most abundant, although the presence of C-12:0, C-14:0, C-16:1 and C-18:0 esters was observed. (C) 2001 Federation of European Micr obiological Societies. Published by Elsevier Science B.V. All rights reserv ed.