RESUMO
18α(H)-, 18ß(H)-oleanane and lupane are angiosperm-derived biomarkers that are used as age indicators for the Late Cretaceous onwards when the first proliferation of angiosperms occurred. In addition, the 18α(H)-/18ß(H)-oleanane ratio is employed as a thermal maturity parameter of crude oil. However, evidence has shown that accurate quantification of these compounds has been impeded by inadequate chromatographic separation by traditional one-dimensional gas chromatography. In this study, we present the separation of 18α(H)-, 18ß(H)-oleanane and lupane with comprehensive two-dimensional gas chromatography (GC×GC). Furthermore, it was observed that 18ß(H)-oleanane elutes earlier than 18α(H)-oleanane in second dimension (polarity) which we attribute to steric hindrance effects. Two GC conditions have been developed in order to achieve baseline separation of the triterpenoids of interest in complex mixtures such as sediment extracts and crude oils.
Assuntos
Cromatografia Gasosa/métodos , Magnoliopsida/química , Ácido Oleanólico/análogos & derivados , Triterpenos/química , Isomerismo , Estrutura Molecular , Ácido Oleanólico/química , Ácido Oleanólico/isolamento & purificação , Petróleo/análiseRESUMO
A modular approach for the synthesis of molecular rods based on oligospiroketals has been developed. The strategy relies on different terminal and intermediate segments, which are joined by ketal formation between ketones and diols. For this purpose it was necessary to develop a new ketalization method to circumvent some problems related with the established methods. The terminal segments are either derived from 4-piperidinone or from 4-oxocyclohexane carboxylic acid whereas the intermediate segments rest on pentaerythritol and cyclohexane-1,4-dione. A series of trispiro (14-18), hexaspiro (19) and nonaspiro (20) compounds have been prepared and characterized. From these we realized that it is imperative to use solubility enhancing groups if more than seven rings are joined.
