The odd couple: The synthesis of 20,20‐difluorocatharanthine starting from naturally occurring catharanthine is reported. The fluorinated catharanthine analogue was investigated as a potential precursor to dimericVincaalkaloids of the vinflunine family. However, the biomimetic coupling of difluorocatharanthine with vindoline led to unexpected products, the formation of which was rationalized (see
Detailed investigations on one of the key steps of the superacidic fluorination of Vinca alkaloids that is the origin of C20' activation are reported. While two different pathways can be envisioned for the emergence of the transient secondary carbocationic intermediate, isotopic labeling experiments unambiguously revealed the involvement of a 1,2-hydride shift mechanism.
Synthesis of a Potent Vinblastine: Rationally Designed Added Benign Complexity
作者:Oliver Allemann、Manuela Brutsch、John C. Lukesh、Daniel M. Brody、Dale L. Boger
DOI:10.1021/jacs.6b04330
日期:2016.7.13
Many natural products, including vinblastine, have not been easily subjected to simplifications in their structures by synthetic means or modifications by late-stage semisynthetic derivatization in ways that enhance their biological potency. Herein, we detail a synthetic vinblastine that incorporates added benign complexity (ABC), which improves activity 10-fold, and is now accessible as a result of advances in the total synthesis of the natural product. The compound incorporates designed added molecular complexity but no new functional groups and maintains all existing structural and conformational features of the natural product. It constitutes a member of an analogue class presently inaccessible by semisynthetic derivatization of the natural product, by its late-stage functionalization, or by biosynthetic means. Rather, it was accessed by synthetic means, using an appropriately modified powerful penultimate single-step vindoline-catharanthine coupling strategy that proceeds with a higher diastereoselectivity than found for the natural product itself.