In the reinvestigation of the constituents of Uncaria rhynchophylla MIQ. (Japanese name "kagikazura"), the presence of two oxindole alkaloids, corynoxeine and isocorynoxeine, was demonstrated, besides the reported rhynchophylline and isorhynchophylline.3) Furthermore, four indole alkaloids were newly isolated ; hirsutine, hirsuteine, dihydrocorynantheine, and corynantheine. A chemical structural evidence of hirsutine was obtained from its epimerization to dihydrocorynantheine with acetic acid catalysis.
