Asymmetric Total Synthesis of Vindorosine, Vindoline, and Key Vinblastine Analogues
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- 作者：Yoshikazu Sasaki ; Daisuke Kato ; Dale L. Boger
- 刊名：Journal of the American Chemical Society
- 出版年：2010
- 出版时间：September 29, 2010
- 年：2010
- 卷：132
- 期：38
- 页码：13533-13544
- 全文大小：940K
- 年卷期：v.132,no.38(September 29, 2010)
- ISSN：1520-5126
文摘
Concise asymmetric total syntheses of vindoline (1) and vindorosine (2) are detailed based on a unique intramolecular [4 + 2]/[3 + 2] cycloaddition cascade of 1,3,4-oxadiazoles inspired by the natural product structures. A chiral substituent on the tether linking the dienophile and oxadiazole was used to control the facial selectivity of the initiating Diels−Alder reaction and set the absolute stereochemistry of the remaining six stereocenters in the cascade cycloadduct. This key reaction introduced three rings and four C−C bonds central to the pentacyclic ring system setting all six stereocenters and introducing essentially all the functionality found in the natural products in a single step. Implementation of the approach for the synthesis of 1 and 2 required the development of a ring expansion reaction to provide a 6-membered ring suitably functionalized for introduction of the Δ6,7-double bond found in the core structure of the natural products. Two unique approaches were developed that defined our use of a protected hydroxymethyl group as the substituent that controls the stereochemical course of the cycloaddition cascade. In the course of these studies, several analogues of vindoline were prepared containing deep-seated structural changes presently accessible only by total synthesis. These analogues, bearing key modifications at C6−C8, were incorporated into vinblastine analogues and used to probe the unusual importance (100-fold) and define the potential role of the vinblastine Δ6,7-double bond.