Concise synthesis of the vasorelaxant alkaloids schwarzinicines A and B

Abstract

A concise synthesis of the 1,4-diarylbutanoid-phenethylamine alkaloids, schwarzinicines A (<b>1</b>) and B (<b>2</b>), recently isolated from <i>Ficus schwarzii</i>, is reported. Key steps include a Claisen condensation to assemble the 1,4-diaryl-2-butanone intermediate, followed by a reductive amination to furnish the core skeleton of the target compounds. The overall synthetic yields of <b>1</b> and <b>2</b> were 9.1% and 3.5%, respectively. Synthetic (-)-<b>1</b>, (+)-<b>1</b> and (±)-<b>1</b> exhibited comparable vasorelaxation as natural schwarzinicine A on rat isolated aortic rings, suggesting that the observed vasorelaxant effects were not influenced by the chirality at C-2.