Three tetrapeptides incorporating a 14-membered (Ri+1, Si+2) cycloisodityrosine at the i + 1 and i + 2 positions were designed and synthesized. Conformational anal. by 1H NMR and CD spectra as well as mol. modeling indicated that they all adopt a beta -turn conformation. While the CD spectrum of peptide I is characteristic of the typical type-II beta -turn (max. at .apprx.200 nm and a min. at .apprx.220 nm), that of peptide II (atropisomer of I) is opposite in sign to the expected spectrum of the type-II beta -turn. [on SciFinder (R)]