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

✍ Scribed by Geir Kildahl-Andersen; Hans Peter Nytoft; Jon Eigill Johansen

• Publisher: John Wiley and Sons
• Year: 2010
• Tongue: English
• Weight: 92 KB
• Volume: 48
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/mrc.2688

✦ Synopsis

Abstract

The full ^1^H and ^13^C NMR chemical shift assignment of 2α‐methyl‐17α(H),21β(H)‐hopane is presented. This compound is formed in mature sediments from biogenic sources of 2β‐methyl‐17β(H),21β(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 3β‐methylhopane have been assigned. The thermodynamically most stable 3β‐configuration corresponds to that found in bacterial sources. The data presented here suggest minor corrections to the ^13^C chemical assignments reported earlier for 17α(H)‐hopanes. Moreover, spectral evidence indicates an unexpected ring‐D boat conformation of 17α(H),21α(H)‐hopanes, which may serve to explain the steric strain reported for this isomer. Copyright © 2010 John Wiley & Sons, Ltd.