Studies on Neurokinin Antagonists. 4. Synthesis and Structure-Activity Relationships of Novel Dipeptide Substance P Antagonists: N2-[(4R)-4-Hydroxy-1-[(1-methyl-1H-indol-3-yl)carbonyl]-L-prolyl]-N-methyl-N-(phenylmethyl)-3-(2-naphthyl)-L-alaninamide and Its Related Compounds

As an extension of our studied on discovering a novel substance P (SP) antagonist, we modified the previously reported dipeptide, 2 -[N 2 -(1H-indol-3-ylcarbonyl)-L-lysyl]-N-methyl-N-(phenylmethyl)-L-phenylalaninamide (2b). The lysine part in 2b was first optimized to a (2S,4R)-hydroxyproline derivatives (3h), which is 2-fold more potent than 2b in [ 3 H]SP bindin assay using guinea pig lung membranes. Next we modified the 1H-indol-3-ylcarbonyl part in 3h. Introduction of a methyl group at the indole nitrogen enhanced the oral activity, while retaining the binding activity. Finally, we modified the phenylalanine part to culminate in the most potent compound 7k (FK888), which is a potent SP antagonist with NK1 selectivity as well as oral activity