58(P-15) 超遠隔異種核相関NMR法とその応用(ポスター発表の部)

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Determination of molecular structure by heteronuclear long-range C-H correlation methods such as HMBC and COLOC has a substantial problem in which a carbon bearing no proton within three bond cannot be detected. The structure elucidation of highly hydrogen deficient compounds might thus be problematic since the carbon network of those molecules could not be completely followed by information from indirect ^<2,3>J_<CH>. For the structure elucidation of such molecules, utilization of long-range ^<13>C-^<13>C coupling is a necessity. In this study we present a BIRD DEPT long-range C-C relay in which C-C relay part of the previously proposed H-C-C relay sequence was tuned for long-range C-C coupling to detect the super long-range H/C correlations via four bonds, ^1H-^<13>C-X-X-^<13>C. BIRD pulse efficiently reduced large unwanted signals arising from single ^<13>C isotopomers. The spectral editing in the DEPT part gave CH, CH_2, and CH_3 subspectra, which enabled not only simplification of the spectra but also elimination of unnecessary magnetization transfer from other protonated carbons in single ^<13>C isotopomers. This one-dimensional method was applied for the structure elucidation of a highly substituted fused heteroaromatic, khellin, the connectivity of which could not be determined by conventional HMBC. The necessary super long-range correlations were available by only 15μmol of the compound in 90μL solvent in 15 hr. In addition, by the method it is possible to determine accurate values of long-range ^<13>C-^<13>C coupling constants, which depend on their dihedral angle similar to the corresponding H/H couplings. Hence, discrimination of E/Z isomers by homoallyl J_<CC> values could be done. Furthermore, a two-dimensional version of the method was constructed by an insertion of an additional delay followed by t_1 in place of the long-range C-C evolution. An application of this 2D super long-range H-C-C relay for a ^<13>C-enriched natural macrolide was also presented.
天然有機化合物討論会の論文
2001-09-01

58(P-15) 超遠隔異種核相関NMR法とその応用(ポスター発表の部)

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