Abd M. Ismaiel

Binding of arylpiperazines to 5-HT3 serotonin receptors: results of a structure-affinity study

The binding affinities of a series of arylpiperazine derivatives at [3H]quipazine-labeled central 5-HT3 sites were investigated. Features determined to be important for binding include the N4 piperazine nitrogen atom (but not the N1 piperazine nitrogen), and a quinolinyl group. The quinoline nitrogen atom of quipazine also contributes to affinity and its replacement by carbon reduces affinity by 20-fold. The entire quinoline nucleus is not necessary for binding, and certain monocyclic arylpiperazines, particularly those with a chloro group meta to the position of the piperazine ring (e.g. mCPP, MK-212), also bind at 5-HT3, sites; however, the affinities of these agents are at least an order of magnitude less than that of quipazine itself. Taking advantage of the fact that tertiary amines are not well tolerated at 5-HT1B sites, but that N-methyl substituents have little effect on 5-HT3 binding, we designed and synthesized a tertiary amine analog of quipazine, i.e., N-methylquipazine (NMQ). NMQ binds at 5-HT3 sites with an affinity similar to that of quipazine; however, unlike quipazine, NMQ shows very little affinity (IC50 greater than 10,000 nM) for central 5-HT1B sites.

Ketanserin and Spiperone as Templates for Novel Serotonin 5-HT2A Antagonists

The structures of ketanserin (1) and spiperone (2) were examined in detail to determine the role of various substituent groups on 5-HT(2A) receptor affinity and selectivity. It was found that the presence of the quinazoline ring of ketanserin detracts from selectivity and that various ring-opened analogs displayed ketanserin-like affinity and up to 30-fold enhanced selectivity. The triazaspirodecanone portion of spiperone is a major determinant of its 5-HT affinity and selectivity. The conformational rigidity imposed by the ring, as well as the nature of the N(1)-substituent, are important factors in controlling binding at 5-HT(2A), 5-HT(2C), 5-HT(1A), and dopamine D2 receptors. Replacement of the N(1)-phenyl ring of spiperone with a methyl group (KML-010; 48) resulted in a compound that binds at 5-HT(2A) receptors with slightly lower affinity than spiperone, but that lacked affinity (Ki >10,000 nM) for 5-HT(2C) and 5-HT(1A) receptors and binds with 400-fold reduced affinity at D2 receptors.

A preliminary behavioral investigation of PMMA, the 4-methoxy analog of methamphetamine

The controlled-substance analog N-monomethyl-1-(4-methoxyphenyl)-2-aminopropane (PMMA) may be viewed as being either the 4-methoxy analog of methamphetamine or the N-methyl analog of 1-(4-methoxyphenyl)-2-aminopropane (PMA). Because of its abuse potential, PMMA was examined with regard to (a) its stimulus properties in rats trained to discriminate either 1.0 mg/kg of (+)amphetamine or (+/-)DOM from saline, (b) its toxicity (isolated and aggregated) in mice relative to (+/-)PMA, and (c) its locomotor stimulant activity in mice relative to (+/-)amphetamine, (+/-)methamphetamine, and (+/-)PMA. Racemic PMMA produced neither DOM-like nor, unlike PMA, amphetamine-like stimulus effects. There was no significant difference between the 24-hr isolated (LD50 = 63 mg/kg) and aggregated (LD50 = 53 mg/kg) toxicity, and PMMA did not produce significant locomotor stimulation at doses of up to 30 mg/kg. The present results suggest that while PMMA may produce central effects it does not appear to behave as a simple amphetamine-like agent.