This article is part of a series on Indolizidines and quinolizidines: natural products and beyond, edited by Prof Joseph P Michael, University of Witwatersrand.

Editorial

Indolizidines and quinolizidines: natural products and beyond

Joseph P Michael

Molecular Sciences Institute, School of Chemistry, University of the Witwatersrand, PO Wits 2050, South Africa

Beilstein Journal of Organic Chemistry 2007, 3:27doi:10.1186/1860-5397-3-27

Published:	26 September 2007

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First paragraph (this article has no abstract)

Alkaloids occur in such astonishing profusion in nature that one tends to forget that they are assembled from a relatively small number of structural motifs. Among the motifs that are most frequently encountered are bicyclic systems containing bridgehead nitrogen, especially 1-azabicyclo[4.3.0]nonanes and 1-azabicyclo[4.4.0]decanes or their unsaturated analogues – the indolizidines and quinolizidines to which this Thematic Series is devoted. These two azabicyclic systems may occur in the natural products either in isolation (the so-called 'simple izidine' alkaloids) or, more commonly, embedded within fused polycyclic arrays. Just how widespread they are was pointed out over two decades ago in a review in which it was estimated that between 25% and 30% of all alkaloids possess structures incorporating one or other of these motifs. [1] As might be expected of systems that are so pervasive, their natural sources are extremely diverse: they occur in organisms as widely different as bacteria, fungi, higher plants, invertebrates and vertebrates; and both terrestrial and marine sources are represented. For example, two of the best-known and most widely investigated groups of 'simple izidine' alkaloids are the plant-derived polyhydroxylated indolizidines that function as potent glycosidase inhibitors, [2-4] and the alkylindolizidines and analogues sequestered from dietary sources in the skins of amphibians. [5,6] It is thus hardly surprising that both the structural elucidation and the total synthesis of these and related alkaloids continue to attract the attention of eminent chemists, as borne out by the seemingly inexhaustible flow of publications in prominent journals. [7] Several general reviews on these alkaloids have also appeared in recent years. [8-11]

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