New Trends in Alkaloid Synthesis and Biosynthesis

Modem Alkaloids Stmcture, Isolation, Synthesis and Biology. Edited by E. Eattorusso and O. Taglialatela-Scafati Copyright 2008 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 978-3-527-31521-5 

Synthesis of Alkaloids by Transition Metal-mediated Oxidative Cyclization 

Activation of the acetylene by coordination of the triple bond to the silver cation enables a 5-endo-dig cydization via nucleophilic attack of the amine [14]. Protonation of the resulting vinyl silver complex leads to an iminium ion. Subsequent p-hydride elimination affords metallic silver and a pyrrylium ion which aromatizes by proton loss to the pyrrole. For trimethylsilyl-substituted homopropargylamines (R = SiMes), the resulting pyrrole (R = SiMe3) undergoes protodesilylation to the 1,2-disubstituted pyrrole. 

The hexahydropyrrolo[2,l-a]isoquinoline alkaloid crispine A was isolated in 2002 from Carduus crispus ]15]. Extracts of this plant have been applied in Chinese folk medicine for the treatment of colds, stomach ache, and rheumatism moreover they inhibit the growth of several human cancer cell lines. The useful biological activities induced a strong interest over the last few years in the synthesis of this alkaloid [7,16]. 

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