3 Teucrin P1の立体配座解析 : 単離可能な安定及び不安定立体配座異性体の構造解析

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Teucrin P1 1 isolating by Popa', Mollov', and Piozzi's groups showed specific rotations of [α]_D +22.4, 6.6, and -13°, respectively. Piozzi's group reported X-ray study on its absolute stereochemistry and conformations which retained a boat form on B ring. However, we found that the boat form was an unstable conformation than the chair form by about 1 Kcal/mol with molecular mechanics. Then we attempted to derive a conformational isomer 4 (B ring: chair) from 1 and to analyze its conformation by CD and NMR spectra. The isomer 4 was given as needles by treatment with LDA/HMPA-THF followed by purification on pTLC and recrystallization from ether-acetone, and showed CD spectra (Fig. 3, 6) and [α]_D +2.93°different from 1. However, the isomer 4 reproduced 1 by recrystallization from EtOAc-hexane. These facts show that the B ring of 1 retaines the boat form as the stable conformation by solvation. Teucrin P1 1 attained to equilibrium with 4 content of ca. 30% after 5 days in CHCl_3 at 0℃. On the other hand, it is very significant that the isomer 4 decrease to about 75% content after 84 hrs in CHCl_3 at 25℃ (Fig. 8). It was unexpected that NMR spectra (2DJ, 2DNOE, and differece NOE spectra) of 4 were almost identical to those of 1. Differences on the spectra between 1 and 4 were shown only by coupling patterns of higher orders for the signals at 2.88 (C・7 Hβ) and 2.20-2.30 (C・7 Hα, C・8 H) ppm (Fig. 10). Now we propose that Teucrin P1 presents with the chair conformation in both native plants, and the conformation changes in the process of the extraction and recrystallization.
天然有機化合物討論会の論文
1983-09-15

3 Teucrin P1の立体配座解析 : 単離可能な安定及び不安定立体配座異性体の構造解析

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