OPTICAL ACTIVITY OF SIMPLE CYCLIC AMIDES IN SOLUTION

The cyclic dipeptide, L‐alanylglycyl anhydride, has been studied by optical rotatory dispersion; both L‐alanylglycyl anhydride and the lactam, L‐3‐aminopyrrolidin‐2‐one, have been studied by circular dichroism. In hydroxylic solvents the circular dichroism spectra of 3‐aminopyrrolidin‐2‐one can be attributed to an n–π* transition near 220 mμ and a π–π* transition near 190 mμ. In these solvents the optical activity of L‐alanylglycyl anhydride can be explained as being due to contributions of n–π* transitions and a split π–π* transition. In acetonitrile, however, the circular dichroism spectrum of 3‐aminopyrrolidin‐2‐one shows an additional apparent minimum near 200 mμ. The CD spectrum of the dipeptide is also quite distinctive in this solvent. The possible nature of the band at 200 mμ and the implications of these findings are discussed. Copyright © 1969 John Wiley & Sons, Inc.