Systematic comparison of sets of C-13 NMR spectra that are potentially identical. Confirmation of the configuration of a cuticular hydrocarbon from the cane beetle antitrogus parvulus

Abstract

A systematic process is introduced to compare C-13 NMR spectra of two (or more) candidate samples of known structure to a natural product sample of unknown structure. The process is designed for the case where the spectra involved can reasonably be expected to be very similar, perhaps even identical. It is first validated by using published C-13 NMR data sets for the natural product 4,6,8,10,16,18-hexamethyldocosane. Then the stereoselective total syntheses of two candidate isomers of the related 4,6,8,10,16-pentamethyldocosane natural product are described, and the process is applied to confidently assign the configuration of the natural product as (4S,6R,8R,10S,16S). This is accomplished even though the chemical shift differences between this isomer and its (16R)-epimer are only +/- 5-10 ppb (+/- 0.005-0.01 ppm).