Total Synthesis of (-)-Strictosidine and Interception of Aryne Natural Product Derivatives Strictosidyne and Strictosamidyne

Monoterpene indole alkaloids are a large class of natural products derived from a single biosynthetic precursor, strictosidine. We describe a synthetic approach to strictosidine that relies on a key facially selective Diels-Alder reaction between a glucosyl-modified alkene and an enal to set the C15-C20-C21 stereotriad. DFT calculations were used to examine the origin of stereoselectivity in this key step, wherein two of 16 possible isomers are predominantly formed. These calculations suggest the presence of a glucosyl unit, also inherent in the strictosidine structure, guides diastereoselectivity, with the reactive conformation of the vinyl glycoside dienophile being controlled by an exo-anomeric effect. (-)-Strictosidine was subsequently accessed using late-stage synthetic manipulations and an enzymatic Pictet-Spengler reaction. Several new natural product analogs were also accessed, including precursors to two unusual aryne natural product derivatives termed strictosidyne and strictosamidyne. These studies provide a strategy for accessing glycosylic natural products and a new platform to access monoterpene indole alkaloids and their derivatives.

Automated summary

A synthetic approach to strictosidine relying on a facially selective Diels-Alder reaction and DFT calculations to achieve stereoselectivity is described. (-)-Strictosidine and several new natural product analogs were obtained through late-stage synthetic manipulations and an enzymatic reaction.