4,21-Dehydrogeissoschizine, an intermediate in heteroyohimbine alkaloid biosynthesis

4,21-Dehydrogeissoschizine (5) was proven to be a metabolic intermediate in the enzymatic synthesis of cathenamine (6) and its transformation products ajmalicine (7), 19-epiajmalicine (8), and tetrahydroalstonine (9); the enzyme catalysing the synthesis of (6) from (5) was identified and named cathenamine synthase.