Synthesis and structure-activity relationships of new carbonyl guanidine derivatives as novel dual 5-HT₂B and 5-HT₇ receptor antagonists. Part 2.

We previously reported that the novel dual 5-HT₂B and 5-HT7 receptor antagonist N-(9-hydroxy-9H-fluorene-2-carbonyl)guanidine (4) exerted a suppressing effect on 5-HT-induced dural protein extravasation in guinea pigs. To develop a synthetic strategy, we performed docking studies of lead compound 4 bound to 5-HT₂B and 5-HT₇ receptors, and observed that the carbonyl guanidine group forms a tight interaction network with an active center Asp (D135:5-HT2B, D162:5-HT₇), Tyr (Y370:5-HT₂B, Y374:5-HT₇) and aromatic residue (W131:5-HT2B, F158:5-HT₇). Based on molecular modeling results, we optimized the substituents at the 5- to 8-position and 9-position of the fluorene ring and identified N-(diaminomethylene)-9-hydroxy-9-methyl-9H-fluorene-2-carboxamide (24a) exhibits potent affinity for 5-HT₂B (Ki=4.3 nM) and 5-HT7 receptor (Ki=4.3 nM) with high selectivity over 5-HT₂A, 5-HT₂C, α₁, D₂ and M₁ receptors. Compound 24a reversed the hypothermic effect of 5-carboxamidotryptamine (5-CT) in mice and also showed a suppressing effect on 5-HT-induced dural protein extravasation in guinea pigs when orally administered at 30 mg/kg. Compound 24a is therefore a promising candidate for a novel class of anti-migraine agent without any adverse effects.