77 新Mosher法による直線形海洋天然物のコンフォメーション解析(ポスター発表の部)

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In order to elucidate the absolute configuration of 17-OH of the compounds A (7), isolated from the brown alga Zonaria diesingiana, the dimethyl ether (9) was converted to the (+) and (-)-MTPA esters (10). The Δδ values were assigned to most of the protons. Examination of the arrangement of positive and negative Δδ values led to the R-configuration at C-17. Interestingly, the signs of the Δδ are inverted from negative into positive for the protons close to the aryl terminus. This is interpretable by assuming the round-shape conformation (Fig. 2), in which the aryl moiety is located at the right-hand side of the MTPA plane. The NOESY spectrum exhibited the NOE between 18-H_2 and one of the aryl protons, which consequently verified the proposed round-shape conformation of 10 (see 10b). The Δδ values observed for the protons remote from the MTPA moiety of 10 are so small (<0.002ppm). Therefore, enhancement of the anisotropic effect was intended by replacing the phenyl group of mandelic acid with (1) 1-naphthyl (1NMA: 12), (2) 2-naphthyl (2NMA; 13), and (3) 9-anthranyl (ATMA; 14) groups. The 1NMA and 2NMA esters of 9 (17, 18, respectively) revealed 3 to 5 times greater Δδ values of the protons than those of 10.
天然有機化合物討論会の論文
1992-09-10