73(P-63) メキシコ産ヒガンバナ科植物Zephyranthes carinataのアルカロイドとそのNMRスペクトルにおける特異な挙動(ポスター発表の部)

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Hamayne (1) was isolated from Mexican medicinal plant Zephyranthes carinata, together with 13 alkaloids (2-14) including 3 novel ones (11, 13, 14). Hamayne (1) was isolated as two isomers (1a, 1b). Compounds 1a and 1b were determined to be the same planer structure as hamayne from their NMR spectra and the same absolute structure from the X-ray crystal structure analysis of their p-bromobenzoates. Compounds 1a and 1b converted into each other by alternation of pH conditions. At the same time, 1a and 1b were found to exhibit the different conformations, which was confirmed by the long range C-H coupling constants (^3J_<C-H>). J-HMBC experiments revealed that the ^3J_<C-H> of H-4b/C-10b, H-1/C-3 and H-4a/C-3 of 1a and 1b were unambiguously different from each other. The ^1H-NMR spectra of 1a and 1b showed the unusual behavior. In the ^1H-NMR spectra of the mixture of 1a and 1b, the signals appeared at the average positions of those in the respective spectra, and the signals of 1a and 1b were never separated by measuring ^1H-NMR spectra at -20℃, which suggest the equilibrium between 1a and 1b is rapid. In contrast, the fact that 1a slowly changed into 1b in CD_3OD suggest the equilibrium between them is slow and the conformation of 1b is more stable than 1a. The reason for these unusual behavior in the ^1H-NMR spectra is still unclear, and the investigation is now in progress.
天然有機化合物討論会の論文
2000-10-01