Polyhydroxylated tropane alkaloids

A series of polyhydroxylated tropane alkaloids have been isolated from the leaves of Solanum tuberosum and from both a sphingid moth and an ithomiine butterfly, the larvae of which feed on Solanum species (Nash et al., 1993). These alkaloids are potent glycosidase inhibitors, in a manner similar to certain hydrox3q)yrrolidine and indolizidine alkaloids see Chapter 30). 

Tropane alkaloids are still of significant interest for the pharmaceutical industry, as well as for pharmacology, toxicology, and phytochemistry, which is evident from the number of articles on the topic which have been published since our previous review [15]. Thus, this chapter will essentially cover the evolution of analytical methods for this class of compounds over the past few years. Calystegines and other polyhydroxylated compounds will not be further discussed herein as they have been thoroughly reviewed by Drager [14, 24]. 

Moreover, recently the boronic acid Mannich reaction, mostly referred to as Petasis reaction [163,164], has evolved as a powerful entry to polyhydroxylated pyrrolizidine, indol-izidine, and tropane alkaloids, among others [165, 166]. For example, Pyne and coworkers disclosed a short total synthesis of calystegine (270) starting from (-)-o-lyxose in 4.7% overall yield (Scheme 11.55), which involved, besides a ring-closing metathesis, the Petasis reaction as key step [167]. In a similar fashion, castanospermine (86) was prepared in 14 steps from (-)-L-xylose in 1.5% overall yield (Scheme 11.55) [168]. 

Because they exhibit various fascinating biological activities [1], polyhydroxylated alkaloids that mimic sugar structure arouse a growing interest in the last few years. Naturally occurring iminosugars are classified in five structural families polyhydroxylated pyrrolidines, piperidines, indolizidines, nor-tropanes, and pyrrolizidines (fused pyrrolidines with N at the bridgehead) alkaloids [2]. The pyrrolizidine skeleton with a hydroxyl substituent at C-3 is relatively rare in Nature and appears to be restricted to specific families, while piperidine and pyrrolidine skeleton are conunon in many species. 

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