Structure Elucidation and Chiral-Total Synthesis of a New Indole Alkaloid, (−)-9-Methoxymitralactonine, Isolated from Mitragyna speciosa in Malaysia

A new Corynanthe-type indole alkaloid, (−)-9-methoxymitralactonine (1), having a highly conjugated system was isolated from the young leaves of Mitragyna speciosa in Malaysia, and its structure was first deduced by spectroscopic analysis and then confirmed by chiral-total synthesis starting from optically pure epoxy-ketone and 5-methoxy-3,4-dihydro-β-carboline. The chiral HPLC analysis demonstrated that the natural 9-methoxymitralactonine contained predominantly the (−)-enantiomer over the (+)-enantiomer in the ratio of 62:38.