NMR spectral assignment of 2 alpha- and 3 beta-methylhopanes and evidence for boat conformation in D ring of 17 alpha(H),21 alpha(H)-hopanes

作者：Kildahl Andersen Geir^*; Nytoft Hans Peter; Johansen Jon Eigill

来源：Magnetic Resonance in Chemistry, 2010, 48(12): 951-954.

DOI：10.1002/mrc.2688

• (1)H NMR
• (13)C NMR
• methyl hopane
• triterpane
• biomarker
• revised assignment
• boat conformation

The full (1)H and (13)C NMR chemical shift assignment of 2 alpha-methyl-17 alpha(H),21 beta(H)-hopane is presented. This compound is formed in mature sediments from biogenic sources of 2 beta-methyl-17 beta(H),21 beta(H)-hopanoids, which include several cyanobacteria. In addition, full (1)H and (13)C NMR chemical shift data of all four 17,21 isomers of 3 beta-methylhopane have been assigned. The thermodynamically most stable 3 beta-configuration corresponds to that found in bacterial sources. The data presented here suggest minor corrections to the (13)C chemical assignments reported earlier for 17 alpha(H)-hopanes. Moreover, spectral evidence indicates an unexpected ring-D boat conformation of 17 alpha(H),21 alpha(H)-hopanes, which may serve to explain the steric strain reported for this isomer.

• 出版日期2010-12