Synthesis of 10, 11-Dihydroxydihydroquinidine N-oxide, a New Metabolite of Quinidine. Preparation and ¹H-nmr Spectroscopy of the Metabolites of Quinine and Quinidine and Conformational Analysis via 2D COSY NMR Spectroscopy

The first synthesis of 10,11-dihydroxydihydroquinidine N-oxide [7b], a recently isolated metabolite of quinidine, was accomplished in three steps from 1b. The related congener 7a in the quinine series was also prepared, as well as two other analogues 3a and 4a. In addition, the previously reported human metabolites 2a, 5a, and 6a of quinine [1a] and those 2b, 3b, 4b, 5b, and 6b of quinidine [1b] were synthesized. The chemical shift and coupling constants for all of the metabolites of quinine and quinidine were assigned via 2D COSY 1H-nmr spectroscopy. Moreover, the conformations of these metabolites in solution were found to parallel those of the parent alkaloids, quinine [1a] and quinidine [1b], respectively.