Nonpeptide somatostatin agonists with sst4 selectivity:: Synthesis and structure-activity relationships of thioureas

Utilizing NNC 26-9100 (11) as a structural lead, a variety of nonpeptide derivatives of somatostatin were synthesized and evaluated for sst(2) and sst(4) receptor binding affinity. A novel thiourea scaffold was utilized to attach (1) a heteroaromatic nucleus to mimic the Trp(8) residue, (2) a nonheteroaromatic nucleus to mimic Phe(7), and (3) a primary amine or other basic group to mimic the Lys(9) residue of somatostatin. Displacement studies were carried out using membranes from cell lines expressing ssts [BHK cells (sst(4)) and HEK 293 cells (sst(2))] utilizing [I-125]Tyr(11)-SRIF as the radioligand. Several thioureas (11, 38, 39, 41, and 42) and the urea 66 exhibited K-i values of less than 100 nM. The thioureas 11 (K-i = 6 nM) and 41 (K-i = 16 nM) and the urea 66 (K-i = 14 nM) are believed to be the most potent nonpeptide sst(4) agonists known. Since the thiourea 11 and the urea 66 exhibit high ssts selectivity, these novel nonpeptide derivatives may be useful tools for studying the sst(4) receptor. Studies are currently in progress to evaluate the therapeutic potential of NNC 26-9100 (11) in the treatment of glaucoma.