Stereodivergent syntheses of the first bis(cyclobutane) β-dipeptides

The efficient synthesis of methyl 2-benzyloxycarbonylamino-(1S,2R)-cyclobutane-1-carboxylate starting from 2-methoxycarbonyl-(1R,2S)-cyclobutane-1-carboxylic acid is described. This β-amino acid derivative is antipodal with respect to the (1R,2S)-compound that was previously synthesized in our laboratory from the same chiral hemi ester. In turn, these enantiomeric β-amino acids have been self-condensed and coupled with one another to provide, respectively, enantiomeric and diastereomeric bis(cyclobutane) β-dipeptides. These products are the first reported β-amino acid oligomers containing two directly linked cyclobutane residues. © 2002 Elsevier Science Ltd. All rights reserved.