Pandaca calcarea

Pandoline and pandine have again been encountered, in Pandaca calcarea, P. debrayi, and in P. caducifolia, which contains other bases of the pseudoaspido-spermidine group, namely, (-l-)-20/ -pseudovincadifformine (203), (+)-... 

The structure of pandoline (37), isolated from Pandaca calcarea and P. debrayi, has been established as (37) and confirmed by chemical interrelationship with catharanthine. Here again the structure assignments relied heavily on n.m.r. evidence comparisons of the data (p. 190) on (37) with those for the aspidosperma alkaloid vincadifTormine (31) will illustrate this point. Thus, for example, the chemical shift of C-20, being 49 p.p.m. downfield from its position in (31), showed this to be the hydroxy-bearing carbon that this carbon was also shown to be quaternary confirmed the presence of the ethyl at this same position. 

The first of these was a novel hexacyclic alkaloid, pandine, obtained from three Pandaca species, P. calcarea, P. debrayi (99), and P. caduci-folia Mgt. (99, 102). Pandine had IR and UV spectra typical of a / -anilinoacrylate but an atypical mass spectrum showing no products arising from a simple retro-Diels-Alder reaction and 5, 6-fission sequence. 

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