The development of the active analog approach to computer-assisted drug design offers an opportunity to increase the efficiency of designing new drug candidates by predicting the biologically active conformation of peptide ligands, but the accuracy of such molecular modeling predictions needs verification. TRH was chosen as an ideal test case for probing the effectiveness of this approach due to its important role in regulating functions of the anterior pituitary gland and the nervous system, its six rotatable bonds, and the existence of extensive activity data for its analogs. Conformationally restricted analogs of [Phe2]TRH (analog 3) were designed to probe the pyroglutamate region. A spirocyclic building block was synthesized via electrochemical functionalization and subsequent alkylation of a pyroglutamate derivative, and two routes (one using an amino alcohol and another using direct reductive amination with a dipeptide) were explored for the synthesis of analog 3. TRH analog 3 was tested for its ability to bind (Ki) and activate (EC50 for inositol phosphate formation) TRH receptors and compared to unrestricted [Phe2]TRH. Results revealed that the affinity and potency of restricted analog 3 were only 3-fold lower than that of unrestricted [Phe2]TRH, with similar maximal extents of stimulation of inositol phosphate formation. This indicates that restricting the pyroglutamate region of [Phe2]TRH with a spirocyclic bridge does not significantly interfere with binding or activation. The approach of using electrolysis to introduce bridges into the pyroglutamate region of TRH analogs may provide a means for "mapping" the conformational requirements of the TRH receptor. Work aimed at verifying these conclusions by constructing a conformationally restricted TRH analog analogous to 3 (with His instead of Phe) is underway.