N-[4-(methylsulfonylamino)benzyl]thiourea analogues as vanilloid receptor antagonists: analysis of structure-activity relationships for the "C-Region".

We recently reported that N-(4-t-butylbenzyl)-N'-[4-(methylsulfonylamino)benzyl] thiourea (2) was a high affinity antagonist of the vanilloid receptor with a binding affinity of K(i)=63 nM and an antagonism of K(i)=53.9 nM in rat VR1 heterologously expressed in Chinese hamster ovary (CHO) cells (Mol. Pharmacol. 2002, 62, 947-956). In an effort to further improve binding affinity and antagonistic potency, we have modified the C-region of the lead 4-t-butylbenzyl group with diverse surrogates, such as araalkyl, alkyl, 4-alkynylbenzyl, indanyl, 3,3-diarylpropyl, 4-alkoxybenzyl, 4-substituted piperazine and piperidine. The lipophilic surrogates, arylalkyl and alkyl, conferred modest decreases in binding affinities and antagonistic potencies; the groups having heteroatoms resulted in dramatic decreases. Our findings indicate that 4-t-butylbenzyl is one of the most favorable groups for high receptor binding and potent antagonism to VR1 in this structural series.