Vincristine Impurity G (Formyl Leurosine)

(1aS,11S,13R,13aR)-methyl 11-((3aR,3a1R,4R,5S,5aR,10bR)-4-acetoxy-3a-ethyl-6-formyl-5-hydroxy-8-methoxy-5-(methoxycarbonyl)-3a,3a1,4,5,5a,6,11,12-octahydro-1H-indolizino[8,1-cd]carbazol-9-yl)-1a-ethyl-2,4,5,10,11,12,13,13a-octahydro-1aH-3,13-methanooxireno[2′,3′:9,10][1]azacycloundecino[5,4-b]indole-11-carboxylate