Department of Chemistry, Carnegie Mellon University, Pittsburgh, PA, USA.
Magn Reson Chem. 2012 Dec;50 Suppl 1:S86-91. doi: 10.1002/mrc.3895.
A new strategy to assign diastereotopic protons was developed on the basis of residual dipolar couplings (RDCs) collected in compressed poly(methyl methacrylate) (PMMA) gels. A combination of 2D J-scaled BIRD HSQC and J-scaled BIRD HMQC/HSQC NMR experiments was used to collect the RDC data. In the proposed strategy, the first experiment is used to measure (1)D(CH) for methine groups, the sum of (1)D(CHa) + (1)D(CHb) for methylene groups and the average (1)D(CH3) value for methyl groups. In turn, the small molecule alignment tensor is calculated using these D values without the a priori assignment of CH(2) diastereotopic protons. The D values of each individual CH bond (CHa and CHb) of each methylene group in the molecule are then predicted using the calculated alignment tensor and these values compared with the results from the HMQC/HSQC experiment, leading to their unambiguous assignment. This strategy is demonstrated with the alkaloid strychnine that contains five methylene groups with diastereotopic protons, and our results fully agree with the previously reported assignment using combinations of permutated assignments.
基于在压缩聚甲基丙烯酸甲酯 (PMMA) 凝胶中收集的残剩偶极耦合 (RDC)，开发了一种为非对映质子分配的新策略。使用二维 J 标度 BIRD HSQC 和 J 标度 BIRD HMQC/HSQC NMR 实验的组合来收集 RDC 数据。在所提出的策略中，第一个实验用于测量亚甲基的 (1)D(CH)、甲基亚甲基的 (1)D(CHa) + (1)D(CHb) 和甲基的平均 (1)D(CH3) 值。反过来，使用这些 D 值计算小分子对准张量，而无需预先分配 CH(2)非对映质子。然后使用计算出的对准张量预测分子中每个亚甲基组中每个 CH 键 (CHa 和 CHb) 的 D 值，并将这些值与 HMQC/HSQC 实验的结果进行比较，从而对其进行明确的分配。该策略通过含有五个具有非对映质子的亚甲基的生物碱士的宁进行了演示，我们的结果与先前使用置换分配组合报告的分配完全一致。
