RATIONALLY DESIGNED DIPEPTOID ANALOGS OF CCK - ACID MIMICS OF THE POTENT AND SELECTIVE NONPEPTIDE CCK-B RECEPTOR ANTAGONIST CI-988

This paper outlines the synthesis of selected acid mimics of the non-peptide CCK-B selective antagonist CI-988, 1. CCK-B and CCK-A binding affinities of these analogues are described and their CCK-B affinity and selectivity rationalized by consideration of the pK(a) values, charge distribution, and geometry of the respective acid mimics. Several of the compounds have CCK-B binding affinities similar to the parent carboxylic acid 1 (CCK-B, IC50 = 1.7 nM; pK(a) = 5.6) and span a pK(a) range of <1 (sulfonic acid 27) to >9.5 (5-thio-1,2,4-triazole 24). Among the more active compounds synthesized are tricyclo[3.3.1.1(3,7)]dec-2-yl [R-(R*,R*)]-[2-[[2-[[(3-hydroxy-5-isoxazolyl)acetyl]-amino]-2-phenylethyl]amino]-1-(1H-indol-3-ylmethyl)-1-methyl-2-oxoethyl]carbamate (15), tricyclo[3.3.1.1(3,7)]dec-2-yl [R-(R*,R*)]-[1-(1H-indol-3-ylmethyl)-1-methyl-2-oxo-2-[[2-[(1-oxo-3-sulfopropyl)amino]-2-phenylethyl]amino]-ethyl]carbamate, monosodium salt (27), and tricyclo[3.3.1.1(3,7)]dec-2-yl [R-(R*,R*)]-[1-(1H-indol-3-ylmethyl)-1-methyl-2-oxo-2-[[2-1[(1H-1,2,4-triazol-5-ylsulfinyl)acetyl]amino]-2-phenylethyl]amino]ethyl]carbamic acid (34) which have CCK-B binding affinities of IC50 = 2.6,1.3, and 1.7 nM, CCK-A/-B ratios of 650,780, and 550 and pK(a) values of 6.5, <1, and 7.0, respectively.