The isolation of three naphthylisoquinoline alkaloids from the leaves of Ancistrocladus guineensis is described. Their complete structures were established by spectroscopic, chiroptical and degradative methods. Thus, two hitherto unknown 5,8'-coupled naphthylisoquinolines, named ancistroguineines A and B, were isolated, constituting the first example of a pair of 3-epimeric naphthylisoquinoline alkaloids. Moreover, ancistrotectorine, a 7,3'-coupled alkaloid previously known only from the South-East Asian species Ancistrocladus tectorius, was isolated. Its absolute stereostructure was confirmed by oxidative degradation and by comparison of experimental and calculated CD spectra. (C) 1997 Elsevier Science Ltd.