Pentacyclic triterpenol methyl ethers (PTMEs), germanicol methyl ether (miliacin), 3-methoxyfern-9(11)-ene (arundoin), -amyrin methyl ether (iso-sawamilletin), and 3-methoxytaraxer-14-ene (sawamilletin or crusgallin) were characterized in surface sediments of the Cross-River system using gas chromatography-mass spectrometry (GC-MS). Triterpenol esters (mainly - and -amyrinyl acetates and hexanoates, and lupeyl acetate and hexanoate) were also found. These distinct compounds are useful for assessing diagenesis that can occur during river transport of organic detritus. Poaceae, mainly Gramineae and Elaeis guineensis higher plant species, are proposed as primary sources for the PTMEs and esters in the sediments. PTMEs are biomarkers of specific higher plant subspecies, while the triterpenol esters are indicators of early diagenetic alteration of higher plant detritus. 1. Introduction Pentacyclic triterpenoids have generally been utilized as biomarkers to trace genetic sources of organic matter in sedimentary environments, petroleum exploration, or paleoenvironmental reconstructions of biome changes that document climate change [1–4]. The oleananes, ursanes, fernanes, lupanes, and their derivatives, widely distributed mainly as the oxygenated forms in many varieties of higher plant species, belong to this class of compounds [4–10]. Their characterization in chemotaxonomic studies can provide key information of flora changes [11]. Their tendencies to also resist biodegradation and occurrence in sediments suggest the potential application as specific higher plant derived biomarkers [9, 10]. However, reports of pentacyclic triterpenol methyl ethers (PTMEs) in sedimentary environments are limited to lakes [2, 4, 12]. Other reports have assessed sedimentary input of terrestrial and/or planktonic organic matter with triterpenoid natural products (e.g., [13–15]) and biomass source tracers to smoke aerosols (e.g., burning of sugar cane [16]). Reports of triterpenoid esters in sediments are also limited, because typical extract analyses generally involved saponification as a preparative step. Plant wax analyses without hydrolysis do reveal triterpenol esters as part of the wax esters in epicuticular waxes (e.g., [17, 18]). Under aerobic conditions, the transformation of plant-derived triterpenoids often involves oxidation, dehydration, hydrolysis, decarboxylation, ring opening, and aromatization reactions [19]. For instance, in coal forming environments, higher plant triterpenoids generally undergo aromatization starting from ring A, triggered by the elimination of
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