Indolizidine mass spectrum

The amphibian alkaloids considered to be 3,5-disubstituted indolizidines are tabulated below. Two other bicyclic alkaloids, proposed as monosub-stituted indolizidines in an earlier review, are included. These are 167B, which was considered likely to be a 5-n-propylindolizidine, based on its mass spectrum and biosynthetic considerations, and 209D, which was considered likely to be a 5-n-hexylindolizidine. These two indolizidines have been synthesized (130,131), but efforts to compare the synthetic indolizidines to natural 167B and 209D were thwarted when the natural trace alkaloids could no longer be detected in extracts. Structures of relatively well-characterized 3,5-disubstituted indolizidines from amphibians are shown in Fig. 11. 

The comparison of the mass spectrum of indolizidine 223A with those of indolizidines 237L and 251M led to their tentative structure assignment the major peaks at m/z 180 and m/z 124 confirmed the indolizidine nucleus and the identical substituents at C-6 and C-8, while the observed molecular ions suggested, respectively, -butyl and n-pentyl side-chains at C-5 (Table 1). 

The comparison of the mass spectrum of indolizidine 223A with those of indolizidines 237L and 251M led to their tentative structure... 

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