Pentacyclic triterpene methyl ethers in recent lacustrine sediments (Lagoa do Caçó, Brazil)

The lipid extracts of sediments collected from the Quaternary filling of a tropical lacustrine series (Lagoa do Caçó, Brazil) were investigated using gas chromatography–mass spectrometry (GC–MS). Various pentacyclic triterpene 3-methyl ethers (PTMEs) were present in the neutral fraction. Comparison of retention times and mass spectra with available standards allowed us to confirm the presence of olean-12-en-3β-ol ME (β-amyrin ME), olean-18-en-3β-ol ME (miliacin), taraxer-14-en-3β-ol ME (crusgallin), fern-9(11)-en-3β-ol ME (arundoin) and arbor-9(11)-en-3β-ol ME (cylindrin). The following other compounds could also be tentatively identified from their GC–MS characteristics: urs-12-en-3β-ol ME, bauer-7-en-3β-ol ME and fern-8-en-3β-ol ME. Other compounds such as possible 3α isomers of the PTMEs as well as di- or tri-unsaturated counterparts might be PTME diagenetic derivatives. According to previous chemotaxonomic studies, all these compounds most probably originate from Gramineae that used to colonize the savanna of Northern Brazil at the time of deposition.