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Two New Isoprenoidal Ketones Related to Botryococcus braunii in The Chinese Maoming Basin
Organic Geochemistry ( IF 3 ) Pub Date : 2020-01-01 , DOI: 10.1016/j.orggeochem.2019.103946 Jing Liao , Xiangyun Zhang , Hong Lu , Youping Zhou , Quan Shi , Ping'an Peng , Guoying Sheng
Organic Geochemistry ( IF 3 ) Pub Date : 2020-01-01 , DOI: 10.1016/j.orggeochem.2019.103946 Jing Liao , Xiangyun Zhang , Hong Lu , Youping Zhou , Quan Shi , Ping'an Peng , Guoying Sheng
Abstract We report the spectroscopy-based (NMR, HRMS, IR) reassignment of the structures of two previously mis-identified saturated methyl ketones (formerly C15 ketone: 5,9-dimethyl-6-isopropyl-2-decanone and C18 ketone: 4,9,11-trimethyl-6-isopropyl-2-dodecanone) in the Maoming oil shale to: 5,6,9,10-tetramethylundecan-2-one and 4,7,8,11,12-pentamethyltridecan-2-one, respectively. A diagenetic pathway is proposed to explain the isotopic and structural closeness between these two methyl ketones and recently identified saturated C31 alcohols, C32 aldehydes and C33 ketones (all with a unique methyl group β to the sole quaternary carbon in their skeletons) obtained from the same Maoming Basin sediments. The pathway involves, firstly, epoxidation, hydration, oxidation and double decarboxylation of the C33 botryococcene to C31 botryococcene. Subsequent photo- or autoxidation of the internal double bond around the quaternary carbon in the C31 botryococcene in an oxic environment leads to the formation of a C31 hydroperoxy-alkene. A heterolytic (Hock-type) or homolytic cleavage of the hydroperoxy-alkene around the quaternary carbon then gives rise to the C15 and C18 unsaturated methyl ketones, respectively. The so-formed unsaturated ketones are then geochemically stabilized by hydrogenation in an anoxic environment.
更新日期：2020-01-01
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