Configurational and conformational analysis of highly oxygenated pyrrolizidines: definitive identification of same naturally occurring 7a-epi-alexines

被引：51

作者：

Wormald, MR

Nash, RJ

Hrnciar, P

White, JD

Molyneux, RJ

Fleet, GWJ

机构：

[1] Univ Oxford, Dept Biochem, Oxford Glycobiol Inst, Oxford OX1 3QU, England

[2] Inst Grassland & Environm Res, Aberystwyth SY23 3EB, Dyfed, Wales

[3] Oregon State Univ, Dept Chem, Corvallis, OR 97331 USA

[4] USDA ARS, Western Reg Res Ctr, Berkeley, CA 94710 USA

[5] Univ Oxford, Dyson Perrins Lab, Oxford OX1 3QY, England

来源：

TETRAHEDRON-ASYMMETRY | 1998年 / 9卷 / 14期

关键词：

D O I：

10.1016/S0957-4166(98)00254-7

中图分类号：

O61 [无机化学];

学科分类号：

070301 ; 081704 ;

摘要：

The NMR spectra of a number of naturally occurring alexines (tetrahydroxylated pyrrolizidine alkaloids) are analyzed and the consequences of changes in the configuration on the conformation of these bicyclic systems discussed. Unambiguous syntheses of australine (7-epi-alexine) and of 7,7a-epi-alexine have now unequivocally established the structures of two natural products isolated from Castanospermum australe which were insecure due to erroneous NMR data. Chemical shift parameters are unreliable as a method of comparing different samples of identical compounds; however,H-1-H-1 three bond coupling constants ((3)J(HH)) provide easy direct comparison between samples and allow assignments of both the relative configurations for the ring protons and the conformation of the pyrrolizidine framework. (C) 1998 Elsevier Science Ltd. All rights reserved.

引用

页码：2549 / 2558

页数：10

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