The discovery of potent, orally bioavailable pyrazolo and triazolopyrimidine CXCR2 receptor antagonists.

A hit-to-lead optimisation programme was carried out on the Novartis archive screening hit, pyrazolopyrimidine 2-methyl-5-((phenylthio)methyl)pyrazolo[1,5-a]pyrimidin-7-ol 1, resulting in the discovery of CXCR2 receptor antagonist 2-benzyl-5-(((2,3-difluorophenyl)thio)methyl)-[1,2,4]triazolo[1,5-a]pyrimidin-7-ol 14. The SAR was investigated by systematic variation of the pendant thiol, alkyl and pyrimidinol groups. Replacement of the pyrazolopyrimidine core with a triazolo alternative led to a dual series of antagonists with favourable biological and pharmacokinetic properties.