Synthesis and diastereoselective catalytic hydrogenation of optically active cyclobutyl α,β-dehydro-α-dipeptides

Optically active cyclobutyl (Z)-α,β-dehydro-α-dipeptides have been efficiently synthesized through the coupling of conveniently protected glycine or (S)-phenylalanine residues with a (Z)-dehydro-α-amino acid derivative prepared, in turn, from (-)-verbenone as a chiral precursor. The alternative use of (R,R)- and (S,S)-Et-duphos-Rh as the hydrogenation catalyst led to the stereoselective production of both diastereomeric saturated dipeptides in each case. Thus, the chirality of the catalyst employed has been shown to be the factor governing the configuration of the newly created stereogenic centre. Regarding structural features, both NMR and CD data establish a marked conformational bias for both the unsaturated and the saturated peptides synthesized herein. © 2003 Elsevier Ltd. All rights reserved.