¹H NMR structural analysis of isomeric tetrazole‐substituted spirostan steroids: Shielding effects and conformational study

Abstract

The structures of two pairs of tetrazole-substituted spirostan steroids were characterized by the use of one-and twadimensional 'H NMR measurements. The conformation of the seven-membered spirostan ring A of the steroid was determined by analysis of proton spin coupling Constants and confirmed by 1D and 2D NOE experiments showing interactions between the methyl group and ring protons. The conformation of the tetrazole-substituted ring A was found to he the same for the four isomers, allowing them to be differentiated by the analysis of the effect of tetrazole-ring isornerization on the chemical shifts of neighbouring protons.

Application of high‐resolution, two‐dimensional 1H and 13C nuclear magnetic resonance techniques to the characterization of lipid oxidation products in autoxidized linoleoyl/linolenoylglycerols

“…However, the recent availability of spectrometers of operating frequencies ≥600 MHz has led to a synchronous increase in the development and application of both homonuclear and heteronuclear two-dimensional NMR methods in order to resolve the many overlapping multiplet resonances (many with higher-order coupling patterns) now detectable in very high field 1 H NMR spectra acquired on complex multicomponent samples. Indeed, the battery of such two-dimensional techniques employable facilitates the establishment of the molecular structures of specified organic compounds (15)(16)(17)(18)(19). Proton-proton and protoncarbon scalar couplings readily determine groups of resonances arising from individual components, and the unambiguous structural information derived therefrom is, in general, not obtainable from alternative analytical techniques.…”