Identification of Novel Indanylsulfonamide Guanylhydrazones as Potent 5-HT6 Serotonin Receptor Antagonists

Changing the N,N-(dimethylamino)ethyl side chain in the N-[3-(aminoethyl)inden-5-yl]sulfonamide 5-HT6 serotonin receptor agonists 1 by a conformationally rigid guanylhydrazone moiety at the indene 3-position led to the identification of the title indanylguanylhydrazones 6, which exhibited excellent binding affinities and an antagonistic response at the 5-HT6 receptor, with K-i and IC50 values in the nanomolar range (K-i >= 1.2 nM, IC50 >= 47 nM, and I-max <= 173%).