Studies of the thyrotropin-releasing factor. II. Conformations of TRF and some analogs

The conformation of the thyrotropin-releasing factor (TRF) and four analogs have been studied by the CNDO/2 molecular orbital method. The N^δ-protonated tautomer of TRF is predicted to be the more stable of the two tautomeric forms; however, it is postulated that the N^ε-tautomer possesses the most active minimum-energy conformation. The peptide backbone for the five compounds remains nearly constant. The conformations predicted from model fragments are very near to those found for the full compound.