Total Synthesis of (+)-Perophoramidine and Determination of the Absolute Configuration

Abstract

The first asymmetric total synthesis of (+)-perophoramidine has been achieved in 17 steps with ∼11% overall yield. The key step relies on an asymmetric biomimetic Diels-Alder reaction between the in situ-generated chiral diene T-24 and the substituted tryptamine 23 to assemble the core structure 27a in a highly efficient way. An acid-catalyzed thermodynamic equilibrium results in C═N double-bond migration of the amidine moiety in 37, which guarantees a regioselective methylation on N(1) at the end of the synthesis. The absolute configuration of (+)-perophoramidine was determined by X-ray crystallographic analysis of the chiral intermediate 32 and comparison of the rotation of synthetic (+)-perophoramidine with that of the natural product.