Enantioselective total syntheses of cyclopropane amino acids: Natural products and protein methanologs

The syntheses of (-)-allo-coronamic acid, (-)-allo-norcoronamic acid, (-)-(Z)-2,3-methanohomoserine, (-)-(Z)-2,3-methanomethionine, and (2S,3R)-Cbz-cyclo-Asp-OMe have been achieved in 45-68% overall yields from suitable intermediates derived from homochiral aminopentenoates which were obtained, in turn, from D-glyceraldehyde. The key synthetic step involves the quantitative and highly diastereoselective cyclopropanation of such precursors. The factors dealing with the control of stereoselectivity are highlighted and the main features in side-chain functionalization to the respective target molecules are discussed.