Molecule of the Month “Gx” (2,6,10-trimethyl-7-(3-methylbutyl)-dodecane)

Rarely noted in petroleum geochemistry, this C₂₀ highly branched isoprenoid (HBI) alkane usually co-elutes with (and is thus obscured by) the more common and usually more abundant pristane. 

Sometimes referred to as “Gx”, it was first reported in the mid 1970s, its structure was identified in 1982 (Yon et al., 1982), but its biological source remained unknown.  Much later, in the 1990s, suitable precursors were found in diatoms for this and other (C₂₅ and C₃₀) highly branched isoprenoids.  As diatoms evolved in the Jurassic, highly branched isoprenoids have significant potential as age diagnostic biomarkers, although coelution of the C₂₀ HBI with pristane makes identification problematic.  It is also worth noting of course that when present this coelution can also lead to an over-estimation of the abundance of pristane.

Reference:

Yon D.A., Maxwell J.R. & Ryback G. (1982). 2,6,10-Trimethyl-7-(3-methylbutyl)-dodecane, a novel sedimentary biological marker compound. Tetrahedron Letters23, 2143-2146.