COMPLEX-FORMATION OF CYCLO(L-PHE-L-PRO)(4) WITH NORADRENALINE HYDROCHLORIDE

The C-13-NMR spectrum of cyclo(L-Phe-L-Pro), (1) and Dt-noradrenaline hydrochloride (DL-NA.HCl) in a mixture of CDCl3 and CD3OD suggested th e formation of a complex, which was demonstrated to be 1:1 from examin ation of the titration curves. The complex retained the C-2-symmetric conformation of 1 containing two cis-peptide bonds, and was linked thr ough hydrogen bonds between the carbonyl groups of the Phe(1) and Pro( 2) residues, and the ammonium moiety of NA.HCl.