Summary
Two novel glycolipids, docosanyl 3-O-methyl-alpha - rhamnopyranoside and docosanyl 3-O-methylxylopyranoside, were identified as the most abundant GC-amenable components of extracts of sediments of Ace Lake, an Antarctic meromictic lake. Docosanyl 3-O-methyl-alpha -rhamnopyranoside was identified by isolation and high-field two-dimensional NMR techniques. Docosanyl 3-O-methylxylopyranoside was tentatively identified by characterisation of its sugar moiety by methanolysis and demethylation. Both glycolipids also have a minor homologue, containing a C-24 instead of a C-22 n-alkyl chain. Stable carbon isotope measurements indicate that the sugar moieties of these glycolipids are ca. 8-9 parts per thousand enriched relative to the alkyl chains. Concentrations increased markedly with depth reaching 2 mg/g sediment at 25 cm depth. Structurally related glycolipids occur in specialised cells of nitrogen-fixing cyanobacteria, so a cyanobacterial origin is suggested for these sedimentary glycolipids.