Total Synthesis and Stereochemical Revision of Biemamides B and D

The first expedient asymmetric synthesis of both enantiomers of 5,6-dihydrouracil-type marine natural products biemamides B and D was achieved from chiral 1-(alpha-methylbenzyl)aziridine-2-carboxylate. The key steps involved in the synthetic route are regio- and stereoselective aziridine ring opening via azide followed by a base-induced cyclization reaction. After comparison of ECD and optical rotation data of both synthetic enantiomers, the absolute configuration of natural biemamides B and D at the C5 position has been assigned as (-)-(5S), which is an enantiomer to the originally proposed structure (-)-(5R).