Synthesis and characterization of anaerobic degradation biomarkers of n-alkanes via hydroxylation/carboxylation pathways.

Metabolite profiling is a powerful method in research on anaerobic biodegradation of hydrocarbons. Hydroxylation and carboxylation are proposed pathways in anaerobic degradation but very little direct evidence is available about metabolites and signature biomarkers. 2-Acetylalkanoic acid is a potential signature metabolite because of its unique and specific structure among possible intermediates. A procedure for the synthesis of four homologues with various carbon chain lengths was proposed and the characteristics of 2-acetyl- alkanoic acid esters were investigated using four derivatization processes, namely methyl, ethyl, n-butyl and trimethylsilyl esterification. Four intermediate fragments observed were at m/z 73 + 14n, 87 + 14n, 102 + 14n (n = 1, 2 and 4 for methyl, ethyl and n-butyl ester, respectively) and [M - 42]+ for three of the derivatization methods. For silylation, characteristic ions were observed at m/z 73, 117, [M - 42](+) and [M - 55](+). These are basic and significant data for the future identification of potential intermediates of the hydroxylation and carboxylation pathways in hydrocarbon degradation.