Asymmetric Total Synthesis of Indole Alkaloids Containing an Indoline Spiroaminal Framework

Abstract

The total synthesis of the indole alkaloids, neoxaline, oxaline and meleagrin A, all containing a unique indoline spiroaminal framework, was accomplished through the stereoselective introduction of a reverse prenyl group to the congested benzylic carbon of furoindoline, a two-pot transformation of indoline (containing three nitrogen atoms at appropriate positions) to the featured indoline spiroaminal framework, and elimination of carbonate assisted by the adjacent imidazole moiety to construct the (E)-dehydrohistidine. The absolute stereochemistry of neoxaline was elucidated through our total synthesis. In addition, we evaluated the bioactivity, especially the anti-infectious properties, of neoxaline and oxaline, and of some synthetic intermediates.

Keywords: alkaloids; fused-ring systems; natural products; spiro compounds; total synthesis.