12 複雑な化合物の構造および立体化学研究に有用なNMRの新しい測定方法 : CT-HMBC法とJ-resolved HMBC法(口頭発表の部)

抄録

We present two new NMR techniques prepared by modification of HMBC, Constanttime HMBC (CT-HMBC) and J-resolved HMBC. CT-HMBC One problem of HMBC is that J-modulation due to H-H couplings cause line broadening of the ^<13>C-signals in the F_1 axis through coupling to the relevant protons during the t_1 period. This undesirable effect together with poor separation of carbon signals of complicated molecules sometimes makes strict assignments of cross peaks difficult. In order to solve this problem, we have developed a new technique, constant CT-HMBC by incorporation of the constant time method to HMBC. This modification suppresses the line broadening of cross peaks resulting in improvement of separation of carbon signals in the F_1 axis. Its application to complicated molecules proved the usefulness of this new technique. J-resolved HMBC In the conventional HMBC spectra, the cross peaks contain information on the long-range C-H J splittings and/or H-H J splittings. However, due to the poor resolution in the F_2 or F_1 dimension, it is difficult to measure directly the long-range C-H J couplings from HMBC cross peaks. In order to solve this problem, we have incorporated the J-scaling method into HMBC and developed a new technique, J-resolved-HMBC. This modification enables to determine easily long range C-H J couplings of complicated compounds and will be useful for conformational analysis of non-cyclic systems. Advantages of this method are simple operation, high sensitivity and general applicability.