Berberis buxifolia Lam. (Berberidaceae) has yielded the new bisbenzylisoquinolines chillanamine (3) and (-)-osornine (4), as well as the new secobisbenzylisoquinolines (-)-curacautine (10) and (-)-talcamine (11). Cleavage of (-)-O-methylosor-nine (5) with sodium in liquid ammonia led to tetrahydrobenzylisoquinolines (+)-6 and (-)-7. A close relative of (-)-osornine is the known calafatine (1), now reisolated from B. buxifolia. This alkaloid is levo- rather than dextro-rotatory, and its sodium-in-liquid-ammonia cleavage provided (+)-8 and (-)-9. Potassium permanganate oxidation of 1 gave rise to 10. Biogenetic considerations imply that two N-methylcoclaurines first combine in tail-to-tail fashion. The resulting dimer is then oxidized enzymically ortho to the diaryl ether bridge to supply the C-10 oxygenated function. O-Methylation at an appropriate stage furnishes 3. Alkaloid 3 is the likely precursor of 4 and 1. The latter suffers oxidative cleavage to(-)-curacautine, which can then be transformed into (-)-talcamine. © 1983, American Chemical Society. All rights reserved.