Cantharanthus roseus

Wu ML, Deng JF, Wu JC, et al. Severe bone marrow depression induced by the anticancer herb Cantharanthus roseus. J Toxicol Clin Toxicol 2005 43 667-671. 

According to Samuelsson (1992) over 100 alkaloids have been isolated from Cantharanthus roseus—the rose or Madagascar periwinkle, a popular garden plant—including some with hypo-glycaemic properties. However, the alkaloids occur naturally in very small quantities. Vinblastine and vincristine are antineoplastic, used as chemotherapy treatment in childhood leukaemia and Hodgkin s disease. They are dimeric indole alkaloids. 

For the syntheses of alkaloids of Cantharanthus roseus, such as vindoline, the preferred C(5) substiment on the 1,3,4-oxadiazole is an ester, because it not only activates the oxadiazole, but also remains in the final product. Consistent with the inverse-electron-demand [4 + 2] cycloaddition. 

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