A series of N(1)-arylsulfonyl-3-(pyrrolidin-3-yl)-1H-indole and N(1)-arylsulfonyl-3-(4-chloro-2,5-dihydro-1H-pyrrol-3-yl)-1H-indole derivatives (tryptamine derivatives with rigidized side chain) have been prepared and tested for their binding affinity to 5-HT(6) receptor. Several compounds displayed potent binding affinity for the 5-HT(6) receptor when tested in in vitro binding assay. The primary SAR indicates that rigidification of dimethylamino alkyl chain at C(3) of indole carbon maintains the binding affinity to 5-HT(6)R. The lead compound N(1)-benzenesulfonyl-3-(4-chloro-1-methyl-2,5-dihydro-1H-pyrrol-3-yl)-1H-indole, 10a (K(b)=0.1 nM) has shown excellent in vitro affinity and was active in animal models of cognition like NORT and water maze.
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