aspects of organic geochemistry of nigerian coal university of ibadan

These isoprenoid ketones could be produced from free phytol by bacteria degradation
and photosynthesized oxidation, photosynthesized oxidation of some isoprenoids
hydrocarbons and during photo degradation of α-chlorophyll (Tuo and Li, 2005).
The homologous series of alkan-2-ones is generally found with an odd carbon number
predominance and its source is likely microbial (Leif and Simoneit, 1995; Bai et al.,
2006). It has been proposed that n-alkan-2-ones are formed by microbially mediated
β-oxidation of alkanes (Simoneit et al., 1979; Cranwell et al., 1987;
Rieley et al., 1991) or from β-oxidation and decarboxylation of n-fatty acids
(Volkman et al., 1983). n-Alkan-2-ones maximizing at C25 or C27 have been reported
in higher plants,microalgae and phytoplankton(Gonzalez et al., 2003; Bai et al., 2006).
2.1.5 Sesquiterpenoids
Sesquiterpanes primarily those based on the cadinane skeleton, with their aromatic
derivatives, are found in many crude oils from inferred deltaic source rock
(Van Aarssen et al., 1990, 1992). Cadinanes (structure VI) and bisabolanes belong to
the most common sesquiterpenoids in the plant kingdom and are thus non-specific
(Otto and Wilde, 2001). Derivatives of longifolane, santalane, and himachalane were
reported from conifer species of the Pinaceae, Cupressaceae, and Podocarpaceae
(Otto and Wilde, 2001). Also, aromatic sesquiterpenoids, dihydro-ar-curcumene,
cuparene, calamene, cadina-1(10),6,8-triene and cadalene have been reported from
various origin including, higher plants, conifers, dammar resin, Dipterocarpacceae
and Cupressaceae sensu lato (Haberer et al., 2006),thereby supporting its non-
specificity. However, there are some specific sesquiterpenes like cuparene, which are
characteristic biomarkers for the conifer family Cupressaceae sensu lato including the
genera, Cupressus, Thuja and Juniperus (Grantham and Douglas, 1980; Otto and
Wilde, 2001) or sativene, a specific marker for Pinaceae (Otto and Wilde, 2001).
Sesquiterpenoids are valuable chemosystematic markers for extant conifers.
Examples include sesquiterpenoid classes of the cedrane, cuparane, valencane and
thujospane.
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