Synthesis of alpha, beta-unsaturated gamma-amino esters with unprecedented high (E)-stereoselectivity and their conformational analysis in peptides

Mild, efficient and racemization-free synthesis of N-protected alpha, beta-unsaturated gamma-amino esters with unprecedented high E- stereoselectivity is described. This method is found to be compatible with Boc-, Fmoc- and other side chain protecting groups. The crystal conformations of the vinylogous gamma-amino esters in monomers and in homo- and mixed dipeptides are studied. Further, the vinylogous homo-dipeptide showed a beta-sheet conformation, while mixed alpha- and alpha,beta-unsaturated gamma-hybrid dipeptide adapted an irregular structure in single crystals.