Calditol tetraether lipids of the archaebacterium Sulfolobus solfataricus. Biosynthetic studies.

Lipids from the archaebacterium Sulfolobus solfataricus are based on 72-membered macrocyclic tetraethers made up from two C40 diol units differently cyclized and either two glycerol moieties or one glycerol moiety and a unique branched-chain nonitol named calditol (glycerodialkylnonitol tetraethers, GDNTs). To elucidate the biosynthesis of calditol and related tetraethers, labelled precursors, [U-14C,1(3)-3H]glycerol, [U-14C,2-3H]glycerol, D-[1-14C,6-3H]glucose, D-[6-14C,1-3H]glucose, D-[1-14C,2-3H]glucose, D-[1-14C,6-3H]fructose and D-[1-14C]galactose, were fed to S. solfataricus. Without regard to stereochemistry or phosphorylation, incorporation experiments provided evidence that the biosynthesis of calditol occurs via an aldolic condensation between dihydroxyacetone and fructose, through a 2-oxo derivative of calditol as an intermediate. The latter is in turn reduced and then alkylated to yield the GDNTs. The biogenetic origins of both glycerol and C40 isoprenoid moieties of GDNTs are also discussed.