5,6,8-Trisubstituted indolizidines

Indolizidine and quinolizidine alkaloids found in amphibians and ants were studied by Daly and co-workers who classified them in two different classes, A and B, Fig. (1) [2,15-17]. The former include 3,5- and 5,8-disubstituted indolizidines, 5,6,8-trisubstituted indolizidines and 1,4- and 4,6-disubstituted quinolizidines that can be derived from straight-chain carbon precursors. The latter contain one or more isoprene units, and include pumiliotoxins (PTX-A), allopumiliotoxins (a//o-PTX-A or... 

The isolation and characterisation from a Panamian population of Dendrobates pumilio Schimdt of indoiizidine 223A [25], formerly identified as 1,4-dipropyl quinolizidine [5], established a new type of class A alkaloids the 5,6,8-trisubstituted indolizidines. 

Fig. (10). 5,6,8-Trisubstituted indolizidines 223A, 237L, 2S1M and 267J [25]...

The 5,6,8-trisubstituted indolizidine alkaloids form another class of amphibian skin alkaloids that has grown enormously since the first member of this group was reported in 1997. At present approximately 70 such alkaloids have been tentatively or positively identified.As has so often happened with minor or trace components of the skin extracts, very few of them have been characterized completely, and the relative configurations are almost entirely unknown other than for a few in which strong or weak Bohlmann bands in the FTIR spectra imply cis- or iram-relationships respectively between the hydrogen atoms on C-5 and C-8a. 

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