2,3-Methanoamino acids resemble protein amino acids. The only difference between these groups of compounds is that the former have one additional carbon which spans the α- and β atoms (Fig. 1 ). This cyclopropane ring constraint of 2,3-methanoamino acids allows four side chain orientations; different conformations are therefore favored when stereoisomeric cyclopropane amino acids are incorporated into peptide sequences. Peptidomimetics containing 2,3-methanoamino acids are also more hindered, and this imparts proteolytic stability ( 1 – 4 ). Overall, both these factors (i.e., the conformational constraints and enhanced proteolytic stabilities, make 2,3-methanoamino acids excellent probes for medicinal chemistry and biophysical experiments.) Fig. 1. Leu and the four stereoisomers of cyclo-Leu.
