Heteroyohimbinoid type oxindole alkaloids from Mitragyna parvifolia

The leaves of the plant Mitragyna parvifolia have afforded two alkaloids, 16,17-dihydro-17β-hydroxy isomitraphylline (1) and 16,17-dihydro-17β-hydroxy mitraphylline (2), together with two known alkaloids, isomitraphylline (3) and mitraphylline (4). The structures of 1 and 2 were elucidated using 1D and 2D NMR spectral methods, including 1H-1HCOSY, DEPT, HSQC, and HMBC. Mitraphylline was the main alkaloid constituent.