The isolation and structural elucidation of a new naphthylisoquinoline alkaloid, 8-O-methyldioncophyllinol B, from Triphyophyllum peltatum (Hutch. et Dalz.) Airy Shaw (Dioncophyllaceae) is described, together with the revised structures of other 'B-type' compounds previously misidentified as dioncophylline D, dioncophyllinol D, and 8-O-methyldioncophylline D. All of the presently described structures are 7,6'-coupled and thus have to be addressed as 'B-type' naphthylisoquinoline alkaloids. This is in contrast to the initially defined 'D-type' structures, which are 7,8'-coupled as confirmed by a total synthesis of dioncophylline D. Some of these natural and synthetic naphthylisoquinolines were found to display good in vitro antiplasmodial activities.