Carbon-13 nuclear magnetic resonance spectra of vitamins D and related compounds.

1. The natural abundance carbon-13 nmr of vitamins D (D2 and D3) and several isomers (5, 6-trans-vitamin D2, isotachysterol2 and isovitamin D2) have been completely assigned by employing off-resonance noise-decoupling, acetylation shifts, and lanthanide-induced shifts experiments. The last two techniques were especially useful for the present study. 2. Carbon-13 nmr spectral characteristics of the three main conjugated triene moieties (SE-Z-SZ, SE-E-SZ, or SE-E-SE), involved in the molecules of vitamin D and its isomers, were revealed. Thus, the striking dependence of the shieldings on molecular geometries and high sensitivity of the resonances to the environments of conjugated systems were surveyed. 3. Conformational preferences in solutions of the hydroxyl groups in vitamins D2 and D3 as well as 5, 6-trans-vitamin D2 were conveniently determined.