Helmer B, Schnoes H K, DeLuca H F
Arch Biochem Biophys. 1985 Sep;241(2):608-15. doi: 10.1016/0003-9861(85)90587-9.
Using proton NMR, the solution conformation of the A ring of vitamin D3 and its analogs has been studied by application of the Karplus relation to the observed coupling constants. The A-ring conformations of vitamins D3, D2, and 25-hydroxyvitamin D3 were found to be solvent dependent, with a clear preference for an equatorial hydroxyl group in polar solvents such as methanol and dimethyl sulfoxide. Conversion of the hydroxyl group to an acetate did not affect solution conformation appreciably, but the corresponding t-butyl-dimethylsilyl ether derivative of vitamin D3 showed a strong preference for the 3 beta-equatorial conformer. The A-ring conformation of the active hormone, 1,25-dihydroxyvitamin D3, which has two hydroxyl groups competing for the equatorial position, was found not to be solvent-dependent.
利用质子核磁共振，通过将卡尔普斯关系式应用于观测到的耦合常数，对维生素D3及其类似物的A环溶液构象进行了研究。发现维生素D3、D2和25-羟基维生素D3的A环构象取决于溶剂，在甲醇和二甲基亚砜等极性溶剂中，明显倾向于赤道羟基。将羟基转化为乙酸酯对溶液构象没有明显影响，但维生素D3相应的叔丁基二甲基甲硅烷基醚衍生物强烈倾向于3β-赤道构象体。活性激素1,25-二羟基维生素D3有两个羟基竞争赤道位置，其A环构象不依赖于溶剂。
