Configurational analysis of cubebins and bicubebin from Aristolochia lagesiana and Aristolochia pubescens

(8S,8′R,9S)-, (8R,8′R,9R)-, and (8R,8′R,9S)-cubebins, together with (8R,8′R,8″R,8‴R,9R,9″S) bicubebin, were isolated from Aristolochia lagesiana and Aristolochia pubescens. Their structures were determined by spectroscopic methods, including 1H and 13C NMR spectroscopy at low temperatures, and by chemical transformations.