2,8-Diazaspiro[4.5]decan-8-yl)pyrimidin-4-amine potent CCR4 antagonists capable of inducing receptor endocytosis

A number of potent 2,8-diazaspiro[4.5]decan-8-yl)pyrimidin-4-amine CCR4 antagonists binding to the extracellular allosteric site were synthesised. (R)-N-(2,4-Dichlorobenzyl)-2-(2-(pyrrolidin-2-ylmethyl)-2,8-diazaspiro[4.5]decan-8-yl)pyrimidin-4-amine (R)-(18a) has high affinity in both the [125I]-TARC binding assay with a pKi of 8.8, and the [35S]-GTPγS functional assay with a pIC50 of 8.1, and high activity in the human whole blood actin polymerisation assay (pA2 = 6.7). The most potent antagonists were also investigated for their ability to induce endocytosis of CCR4 and were found to internalise about 60% of the cell surface receptors, a property which is not commonly shared by small molecule antagonists of chemokine receptors