Alkaloid studies—XXX

The isolation and structure elucidation of three new Aspidosperma alkaloids is reported. Cylindrocarpine (II) and cylindrocarpidine (XI) are noteworthy in that they represent analogs of aspidospermine (I) in which the latter's angular ethyl group has been replaced by an angular acetic acid methyl ester function. Furthermore, cylindrocarpine (II) represents the first naturally occurring dihydroindole with a N-cinnamoyl residue. Pyrifolidine (XII) has been shown to be the antipode of O-methylaspidocarpine (XV) and thus bears an enantiomeric relationship at all four asymmetric centers to (-)-aspidospermine (I). Attention is drawn to the possible biogenetic implications of this observation.