Novel intact glycolipids in sediments from an Antarctic lake (Ace Lake)

Two novel glycolipids, docosanyl 3-O-methyl-alpha -rhamnopyranoside and doc osanyl 3-O-methylxylopyranoside, were identified as the most abundant GC-am enable components of extracts of sediments of Ace Lake, an Antarctic meromi ctic lake. Docosanyl 3-O-methyl-alpha -rhamnopyranoside was identified by i solation and high-field two-dimensional NMR techniques. Docosanyl 3-O-methy lxylopyranoside was tentatively identified by characterisation of its sugar moiety by methanolysis and demethylation. Both glycolipids also have a min or homologue, containing a C-24 instead of a C-22 n-alkyl chain. Stable car bon isotope measurements indicate that the sugar moieties of these glycolip ids are ca. 8-9 parts per thousand enriched relative to the alkyl chains. C oncentrations increased markedly with depth reaching 2 mg/g sediment at 25 cm depth. Structurally related glycolipids occur in specialised cells of ni trogen-fixing cyanobacteria, so a cyanobacterial origin is suggested for th ese sedimentary glycolipids. (C) 2001 Elsevier Science Ltd. All rights rese rved.