Abstract
Four new hasubanan alkaloids, stephamiersine (1), epistephamiersine (2), oxostephamiersine (3) and stephasunoline (4) were isolated together with seven known and three unidentified alkaloids from Stephania japonica MIERS (Menispermaceae). Among these new alkaloids, 1 and 2 were found to be epimeric isomers with respect to the C-7 methoxyl group. Permanganate oxidation of 1 gave 3, and borohydride reduction of 1 and 2 gave the highly stereoselective products, dihydrostephamiersine (6) and dihydroepistephamiersine (5). On mild treatment of 5 with hydrochloric acid gave 4. Acetolyses of 1, 2, 5 and 6 gave the phenanthrene derivatives, 7, 8 and 9, respectively. Further, both 1 and 2 were converted to the conjugated carbonyl compound (14) which was obtained from dihydro-16-oxohasubanonine (17a) (17b). On the other hand, the stereochemistry of 1, 2, 3 and 4 was elucidated by nuclear magnetic resonance (NMR) spectroscopic studies as follows : the C-7 methoxyl group of 1 has the α-axial and that of 2 and 4 has the β-equatorial configuration, and the hydroxyl group of 4 has the β-axial one. On the basis of the above chemical correlation coupled with the spectral arguments, the constitution of the new alkaloids was represented as drawn in the formulas, 1, 2, 3 and 4.
