Stereoisomer differentiation for the analgesic drug nefopam hydrochloride using modeling studies of serotonin uptake area

Solid-state stereochemistry and activity of 3-methylnefopam diastereomers: manipulation of eight-membered ring conformations in analogues of the non-narcotic analgesic drug

The solid-state structures of (+/-)-(1R,3S,5S)/(1S,3R,5R)- and (+)/(-)-(1R,3R,5R)/(1S,3S,5S)-3-methylnefopam hydrochloride, epimeric 3-methyl derivatives of the non-narcotic analgesic drug, were determined by single-crystal X-ray diffraction analyses. (+/-)-(1R,3S,5S)/(1S,3R,5S)-3-Methylnefopam hydrochloride gave crystals belonging to the monoclinic space group P2(1)/c, and at ambient temperature, a = 7.993(2), b = 34.376(4), c = 11.785(2) A, beta = 93.06 degrees, V = 3234(2) A3, Z = 8, R(F = 0.070, and Rw(F) = 0.053. (+)/(-)-(1R,3R,5R)/(1S,3S,5S)-3-Methylnefopam hydrochloride gave chiral crystals belonging to the orthorhombic space group P2(1)2(1)2(1), and at 92 K, a = 9.261(2), b = 10.280(2), c = 16.668(4) A, V = 1587(1) A3, Z = 4, R(F) = 0.034, and Rw(F) = 0.035. The two molecules in the asymmetric unit of the (1R,3S,5S)/(1S,3R,5R)-racemic modification had twist-chair-(flattened chair) [TCfC] conformational geometries for the eight-membered ring. Both molecules are virtually identical as shown by a root mean squares fit of 0.077 A in the superimposition of all nonhydrogen atoms in both molecules. The (+)/(-)-(1R,3R,5R)/(1S,3S,5S)-epimers were found in the same boat-(flattened chair) [BfC] conformation previously noted for crystalline nefopam hydrochloride. The TCfC and BfC eight-membered ring conformations of the two 3-methylnefopam diastereomers differ in the -N+H(CH3)CH2CH-fragment chair or boat arrangement vis-a-vis the adjacent flattened region. In both 3-methyl diastereomers, the C(3)-methyl group was disposed in an equatorial orientation, the phenyl group resided in an exo-position, and the -OCH(Ph)-o-C6H4- fragment occupied the flattened region of the eight-membered ring.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of pyrroloisoquinoline enantiomers ((+)- and (-)-McN-5652-Z) on behavioral and pharmacological serotonergic mechanisms in rats

A behavioral syndrome consisting of 5-hydroxytryptamine (5-HT)-dependent behaviors (e.g. forepaw treading, retropulsion and splayed hindlimbs) as well as hyperthermia occurred after bilateral injection of the (6S, 10bR)-(+)-enantiomer of McN-5652-Z into the cerebral ventricles in pargyline-treated rats. Both the behavioral syndrome and hyperthermia produced by (+)-McN-5652-Z were counteracted by parachlorophenylalanine or ketanserin. The (6R, 10bS)-(-)-enantiomer of McN-5652-Z influenced neither behavior nor body temperature. The enantiomers of McN-5652-Z differed also in their ability to inhibit ex vivo binding of paroxetine in rat frontal cortex and hypothalamus, in vitro uptake of 5-HT in rat blood platelets, and 5-HT-induced contraction of rat vascular smooth muscle, with (+)-McN-5652-Z being most active. No difference was observed between the effects of (+)- and (-)-McN-5652-Z on 5-HT metabolism by rat brain monoamine oxidase. Molecular models of N-protonated enantiomers having a cis B,C-ring juncture and a B-ring chair conformation were differentiated using a hypothetical model of the 5-HT uptake area. The findings indicate that the enantiomers of McN-5652-Z are useful tools for studying the stereoselectivity of behavioral and pharmacological effects exerted by serotonergic neurotransmission.

Differential scanning calorimetry study of the interaction of antidepressant drugs, noradrenaline, and 5-hydroxytryptamine with a membrane model

Differential scanning calorimetry was used to study the interaction of a membrane model with two neuromediators [noradrenaline and 5-hydroxytryptamine (Serotonin)] and four antidepressant drugs (imipramine, indalpine, citalopram, and milnacipran), known to be uptake inhibitors of these neuromediators. The study was carried out on dipalmitoyl phosphatidylcholine liposomes, a bilayer phospholipid system taken as a simplified model of biological membranes. Analysis of the thermograms led us to classify the molecules according to their lipophilic action, as in the conventional measurement of the water-octanol partition coefficient, and also enabled us to precisely determine their location along the phospholipid bilayer. A hypothesis based on this localization is put forward concerning the competitive, or otherwise, character of the blocking of uptake of the neuromediators. The extreme cases of interaction and localization of imipramine and milnacipran, a new antidepressant, relative to the bilayer are also analyzed in terms of side effects.