The elementary composition, functional groups, and some reactions of piptanthine (C₂₀H₃₅N₃, m.p. 142–143°C), an alkaloid of Piptanthus nanus, were described by Eisner and s'orm, who suggested its possible relationship to Ormosia alkaloids. Karle and Karle determined the structure and stereochemistry of ormosanine (formulation I) via X-ray crystallography. We found that prolonged treatment of ormosanine with platinum in acetic acid under a hydrogen atmosphere yields a compound identical to piptanthine (confirmed by infrared and NMR spectroscopy, thin-layer chromatography, and comparison with an authentic sample), demonstrating piptanthine is an epimer of ormosanine at C₁₁ and possesses structure II. Homoxy-ormosanine (the urea derivative of ormosanine) was converted to homoxypiptanthine under similar conditions, indicating involvement of the tertiary nitrogen. Bohlmann bands analysis (showing stable conformation VI for piptanthine/homoxypiptanthine vs. variable conformations for ormosanine/homoxy-ormosanine) supports an irreversible configurational change at C₁₁. This discovery revises two recently reported configurational assignments: (1) the isomer obtained from panamine reduction is piptanthine (revealing panamine and natural piptanthine belong to antipodal series), and (2) the catalytic dehydrogenation product of ormosanine/panamine has piptanthine stereochemistry at C₁₁ (with an α-hydrogen at C₁₁).