Summers M F, Powell C, Egan W, Byrd R A, Wilson W D, Zon G
Nucleic Acids Res. 1986 Sep 25;14(18):7421-36. doi: 10.1093/nar/14.18.7421.
1H NMR chemical shift assignments for the title compounds were made for all but a few H5' and H5" signals using two-dimensional nuclear Overhauser effect (2D-NOE) data, which was also used for the first time to assign absolute configuration at phosphorus. The chemical shifts were, in general, similar to those reported [Broido, M.S., et al. (1985) Eur. J. Biochem. 150, 117-128] for the B-like conformation of the unmodified, parent duplex, [d(GGAATTCC)]2. Differences in chemical shifts for corresponding protons were mostly localized to the AA(Et)TT region, and showed some stereochemical dependence. Unambiguous assignment of the phosphotriester 31P signals was achieved in a novel way using selective insensitive nucleus enhancement by polarization transfer (selective INEPT) NMR. The Rp-Rp duplex melted ca. 11 degrees C lower than either the Sp-Sp or parent duplexes, as evidenced by Tm and variable temperature 1H/31P NMR measurements. The 2D-NOE data for the Rp-Rp duplex suggested possible steric interactions between the ethyl group and the H3' of the flanking A residue. At low ionic strength, the Sp-Sp and parent duplexes had similar stability but at high ionic strength the Sp-Sp duplex was less stable.
利用二维核Overhauser效应（2D - NOE）数据对标题化合物的1H NMR化学位移进行了归属，除了少数几个H5'和H5"信号外，所有信号均已归属。该数据还首次用于确定磷原子的绝对构型。一般来说，化学位移与报道的[Broido, M.S., 等人 (1985) Eur. J. Biochem. 150, 117 - 128]未修饰的亲本双链体[d(GGAATTCC)]2的B型构象相似。相应质子化学位移的差异大多局限于AA(Et)TT区域，并表现出一定的立体化学依赖性。使用选择性极化转移增强非灵敏核（选择性INEPT）NMR以一种新颖的方式实现了磷酸三酯31P信号的明确归属。通过熔点（Tm）和变温1H/31P NMR测量证明，Rp - Rp双链体的熔点比Sp - Sp双链体或亲本双链体低约11℃。Rp - Rp双链体的2D - NOE数据表明乙基与侧翼A残基的H3'之间可能存在空间相互作用。在低离子强度下，Sp - Sp双链体和亲本双链体具有相似的稳定性，但在高离子强度下，Sp - Sp双链体稳定性较差。
