Indolizidines distribution

Tab. 5.1 Distribution of polyhydroxylated nortropane and indolizidine alkaloids in the Convolvulaceae. 

During 1993, Daly and co-workers reviewed the alkaloids found in amphibians [5] and Takahata et al. focused on structural assignments and the synthesis of amphibian and polyhydroxylated indolizidines [6]. Wink reviewed the characterisation, natural distribution and biological activity of lupine alkaloids [7] and systematic updates on indolizidine and quinolizidine alkaloids are annually summarized by Michael [8-14]. 

A variety of quinolizidines and indolizidines may be accessed in good yields by the facile two-step process shown in Scheme 5. Although not noted in this publication, the distribution of diastereomers (where possible) most likely reflects the relative energies of the diastereomeric transition state conformations depicted in Scheme 6. The transition state conformation that orients the larger substituent (R or R ) in the less sterically encumbered equatorial position gives rise to the major diastereomer in all of the per-... 

Pyrrolizidine, quinolizidine, and indolizidine alkaloids are chemically diverse and restricted in distribution. Some similarities in structures and biosynthesis exist, but as the pathways become more clear, these three major groups of alka-... 

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