For the purpose of rational modification of the TRH molecule, we were pursuing an approach that consists of two steps:(1)'obligatory'replacement of histidine with glutamine in TRH and (2) the application of conformational constraints for putative bioactive conformation I stabilized by an intramolecular hydrogen bond between C-terminal carboxamide proton and α-carbonyl of histidyl (glutaminyl), and conformation II formed by an intramolecular ...