Synthesis and pharmacological evaluation of optically pure, novel carbonyl guanidine derivatives as dual 5-HT sub(2B) and 5-HT sub(7) receptor antagonists

A series of 9-disubstituted N-(9H-fluorene-2-carbonyl)guanidine derivatives have been discovered as potent and orally active dual 5-HT sub(2B) and 5-HT sub(7) receptor antagonists. Upon screening several compounds, N-(diaminomethylene)-4',5'-dihydro-3'H-spiro[f luorene-9,2'-furan]-2-carboxamide (17) exhibited potent affinity for both 5-HT sub(2B) (K sub(i) = 5.1 nM) and 5-HT sub(7) (K sub(i) = 1.7 nM) receptors with high selectivity over 5-HT sub(2A), 5-HT sub(2C), alpha sub(1), D sub(2) and M sub(1) receptors. Optical resolution of the intermediate carboxylic acid 16 via the formation of diastereomeric salts using chiral alkaloids gave the optically pure compounds (R)-17 and (S)-17. Both enantiomers suppressed 5-HT-induced dural protein extravasation in guinea pigs in a dose-dependent manner and the amount of leaked protein was suppressed to near normal levels when orally administrated at 10 mg/kg. (R)-17 and (S)-17 were therefore selected as candidates for human clinical trials.