The structure of kopsine, an alkaloid from Kopsia fruticosa, proposed by previous workers was incompatible with its published ultraviolet and infrared spectra, prompting a re-investigation. This study fractionated the alkaloids of K. fruticosa and isolated three crystalline bases: the previously known kopsine and two new isomeric alkaloids, fruticosamine and fruticosine. All three alkaloids have the molecular formula C₂₂H₂₄N₂O₄, correcting the earlier proposed formula for kopsine (C₂₂H₂₆N₂O₂), with the molecular weight rigorously confirmed by mass spectrometry. The properties (melting point, specific rotation, basicity, chromatographic behavior), functional groups, and interrelationships of these alkaloids were investigated using countercurrent distribution for separation, and spectroscopic (ultraviolet, infrared, nuclear magnetic resonance, mass spectrometry) and chemical analyses (hydrolysis, borohydride reduction, platinum-catalyzed hydrogenation, acetylation, methiodide formation). Key findings include: kopsine is a monoacid base containing an O-methyl group, cyclopentanone, methoxycarbonylindoline system, tertiary nitrogen, and hydroxyl group; fruticosamine and fruticosine also possess the methoxycarbonylindoline system, with fruticosamine readily converting to fruticosine under acidic or basic conditions; fruticosine has a hindered carbonyl group and a secondary hydroxyl group. The study confirms and extends prior observations, provides new structural evidence for these alkaloids, and notes ongoing work toward complete structure elucidation.