利用~1H-NMR模拟谱研究二核苷酸A2′P(CH_3)5′A的构象性质

CONFORMATION ANALYSIS OF DINUCLEOTIDES A2'P(CH_3)5'A BY H-NMR SIMULATED SPECTRUM

根据Altona等人的方法,在利用~1H-NMR模拟谱确定18℃、40℃、70℃三种温度下有关质子化学位移及偶合常数基础上,分析了A2′P(CH_3)5′A的两种非对映异构体(a)和(b)的构象状态。它们与A2′P(OH)5′A相比发现:(1)在18℃时两个核糖环是S型构象占主要成分,但随温度升高有的核糖环趋向于转化成N型构象;(2)磷酸骨架的扭角ε′和β分别改变±2°及±12°;(3)A2′P(CH_3)5′A(a)和(b)的两个核糖环均属部分重叠,并且前者的重叠程度小于后者;(4)随着温度升高,A2′P(CH_3)5′A(a)比A2′P(CH_3)5′A(b)有着更强的去堆积效应。

According to Altonas' method, the chemical shifts and the coupling constants of the relevant protons for two stereoisomers a and b, of A2/P(CHs)5/A were determined by means of simulated spectra of ID 1H-NMR at 18℃, 40℃ and 70℃ respectively. By comparing with known compound A2'P(OH) 5'A,it was shown that two ribose rings of a and b adopt predominantly S conformation at 18℃, but with elevation of temperature, the N conformation of some ribose ring increaed: the torsional angles e' and β of the phosphate backbone were estimated to have a change of +2° and ±12°respectively; two ribose rings of both A2'P(CH3)5'A (a) and (b) were partially overlapped and the degree of overlapping of (a) was smaller than that of the (b) : with increasing of temperature, the adenine moiety of A2'P(CH3)5'A (a) showed a stronger tendency to unstack than A2'P(CH3)5'A (b) .