The discovery of 4-(3-pentylamino)-2,7-dimethyl-8-(2-methyl-4-methoxyphenyl)-pyrazolo-[1,5-α]-pyrimidine:: A corticotropin-releasing factor (hCRF1) antagonist

Structure-activity relationship studies led to the discovery of 4-(3-pentylamino)-2,7-dimethyl-8-(2-methyl-4-methoxyphenyl)-pyrazolo-[1,5-a]-pyrimidine 11-31 (DMP904), whose pharmacological profile strongly supports the hypothesis that hCRF(1) antagonists may be potent anxiolytic drugs. Compound 11-31 (hCRF(1) K-i= 1.0 +/- 0.2 nM (n = 8)) was a potent antagonist of hCRF(1)-coupled adenylate cyclase activity in HEK293 cells (IC50 = 10.0 +/- 0.01 nM versus 10 nM r/hCRF, I? = 8); alpha-helical CRF(9-41) had weaker potency (IC50 = 286 +/- 63 nM, n = 3). Analogue 11-31 had good oral activity in the rat situational anxiety test; the minimum effective dose for 11-31 was 0.3 mg/kg (po). Maximal efficacy (approximately 57% reduction in latency lime in the dark compartment) was observed at this dose. Chlordiazepoxide caused a 72% reduction in latency at 20 mg/kg (po). The literature compound 1 (CP154526-1. 30 mg/kg (po)) was inactive in this lest. Compound 11-31 did not inhibit open-field locomotor activity at 10, 30, and 100 mg/kg (po) in rats. In beagle dogs, this compound (5 mg/kg, iv, po) afforded good plasma levels. The key iv pharmacokinetic parameters were t(1/2), CL and V-d.ss values equal to 46.4 +/- 7.6 h, 0.49 +/- 0.08 L/kg/h and 23.0 +/- 4.2 L/kg, respectively. After oral dosing. the mean C-max, T-max, t(1/2) and bioavailability values were equal to 1260 +/- 290 nM, 0.75 +/- 0.25 h, 45.1 +/- 10.2 h and 33.1%, respectively. The overall rat behavioral profile of this compound suggests that it may be an anxiolytic drug with a low motor side effect Liability. (C) 2000 DuPont Pharmaceuticals Company. Published by Elsevier Science Ltd. All rights reserved.