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Asymmetric Total Synthesis of Gracilamine and Determination of Its Absolute Configuration
- Zuo, Xiao-Dong, Guo, Shu-Min, Yang, Rui, Xie, Jian-Hua, Zhou, Qi-Lin
- Organic letters 2017 v.19 no.19 pp. 5240-5243
- Amaryllidaceae, alkaloids, biomimetics, chemical structure, cycloaddition reactions, hydrogenation, oxidation
- (+)-Gracilamine, a biologically attractive and structurally unique pentacyclic Amaryllidaceae alkaloid, was biomimetically synthesized in 11 linear steps in 9.9% overall yield from the known racemic oxocrinine. The synthesis features an asymmetric hydrogenation, a ring-opening/benzylic oxidation/cyclization sequence, and a biomimetic intramolecular cycloaddition. This total synthesis not only allows the assignment of its absolute configuration, but also provides experimental support for the hypothesis that naturally occurring (+)-gracilamine is biogenetically derived from the crinine-type alkaloid (+)-epivittatine.