Fig. 4.

Hypothetical scheme outlining a potential biosynthesis route from the C₁₅ iso fatty acid to branched GDGT 1. Intermediates are iso-diabolic acid formed by the coupling of two C₁₅ iso fatty acids as previously proposed by Jung et al. (23), a glycerol dialkyl glycerol tetraester in which iso-diabolic acid forms the backbone, and an intermediate in its conversion into branched GDGT. The latter step is based on a biosynthetic route of branched dialkyl glycerol diethers in M. xanthus proposed by Ring et al. (43).