A new alkaloid, 4‐hydroxy‐5‐methoxycanthin‐6‐one (1), has been isolated from Picrasma quassioides (Simaroubaceae), and its structure has been determined by high‐field 1H‐ and 13C‐NMR, 13C,1H‐HETCOR, 1H,1H‐2D‐COSY, and NOE‐difference spectra. Previous data, interpreted by other workers as being from this compound, is instead tentatively reassigned to another new alkaloid structure, 4‐hydroxy‐3‐methylcanthine‐5,6‐dione (2). Copyright © 1992 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim