5-Noranhydrovinblastine; NVB;Kw-2307;(2β,3β,4β,5α,12R,19α)-4-(Acetyloxy)-6,7-didehydro-15-[(2R,6R,8S)-4-ethyl-1,3,6,7,8,9-hexahydro-8-(methoxycarbonyl)-2,6-methano-2H-azecino[4,3-b]indol-8-yl]-3-hydroxy-16-methoxy-1-methyl-aspidospermidine-3-carboxylic ac