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Identification of a novel undecamethylhenicosane and three oxygenated precursors in a Maoming Basin shale, China
Organic Geochemistry ( IF 3 ) Pub Date : 2020-03-01 , DOI: 10.1016/j.orggeochem.2020.103974 Jing Liao , Hong Lu , Qiao Feng , Youping Zhou , Quan Shi , Ping'an Peng , Guoying Sheng
Organic Geochemistry ( IF 3 ) Pub Date : 2020-03-01 , DOI: 10.1016/j.orggeochem.2020.103974 Jing Liao , Hong Lu , Qiao Feng , Youping Zhou , Quan Shi , Ping'an Peng , Guoying Sheng
Abstract Further to our recent identification of a C33 botryococcane, a C33 botryococcan-24-one and two C31 botryococcanes (2,3,6,7,10,12,15,16,19,20-decamethylhenicosanes: C31 DMHs) with a methyl group β-positioned to the sole quaternary carbon in the skeleton in a sediment sample from the Maoming Basin, we report the NMR-based structural identification of a new C32 botryococcane (2,3,6,7,10,10,12,15,16,19,20-undecamethylhenicosane: C32 UMH), and MS-based structural identification of a C32 botryococcanal (C32 UMH-al) and two C31 epimeric botryococcanols (C31 DMH-ols) in the same sediment sample after trimethylsilylation. These three oxygenated botryococcanoids are speculated to possess the same β-positioned methyl group (to the sole quaternary carbon). We propose that the C32 UMH-al and two epimeric C31 DMH-ols are degradation products of the C C double bond in the ethenyl group connected to the sole quaternary carbon in their biological precursor C33 botryococcene with a unique β-positioned methyl group (to the quaternary carbon), and are geochemical precursors for the C32 UMH and previously identified C31 DMHs, respectively. Since it is known that abiotic degradation (photo-mediated or autoxidation) preferentially acts on the internal double bond while sedimentary bacteria preferentially degrade the terminal double bond, our finding of a degraded terminal C24-25 double bond and an intact internal double bond (at C11-12) is indicative of bacterially mediated degradation. A detailed bacterially mediated degradation pathway is proposed to explain the formation of C31–C33 botryococcanes and their oxygenated derivatives.
更新日期：2020-03-01
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