Shuangancistrotectorines A-E, dimeric naphthylisoquinoline alkaloids with three chiral biaryl axes from the Chinese plant Ancistrocladus tectorius

Five novel dimeric naphthylisoquinoline alkaloids, shuangancistrotectorines A (3 a), B (3 b), C (4), D (5 a), and E (5 b), have been isolated from the twigs of the Chinese plant Ancistrocladus tectorius. Their absolute stereostructures were determined by spectroscopic and chiroptical methods in combination with quantum chemical CD calculations. In contrast to all other known dimeric naphthylisoquinoline alkaloids, in which the central binaphthalene axis is 6',6''-coupled and thus not rotationally hindered, the dimers described here are linked via the sterically more hindered 3',3''- or 1',1''-positions of the naphthalene units. They are thus the first such dimers-and even the very first natural products at all-that have three consecutive stereogenic axes. Hence, including the stereogenic centers, they have up to seven stereogenic units in total. Some of the compounds, in particular shuangancistrotectorines A, B, and D (3 a, 3 b, and 5 a) exhibit very good, and specific, antiplasmodial activities