Structure-activity relations for anticholinergic 2(1-aryl(or cyclohexyl)-1-hydroxy-1-phenyl)methyl-1,3-dioxolans

Anticholinergic substances: A single consistent conformation

An interactive computer-graphics analysis of 24 antagonists of acetylcholine at peripheral autonomic post-ganglionic (muscarinic) nervous junctions and at similar junctions in the central nervous system, the crystal structures of which are known, has led to the determination of a single, consistent, energetically favorable conformation for all 24 substances, although their observed crystal structure conformations vary widely. The absolute configuration and the single, consistent (ideal) conformation of the chemical groups required for maximum anticholinergic activity are described quantitatively.

Pentatomic cyclic antagonists and muscarinic receptors: a 30-year review

This work is a sequel to and completes the review, that recently appeared in this journal, of pentatomic cyclic muscarinic agonists. It reports the results of structure-activity relationship (SAR) studies of pentatomic cyclic antagonists on muscarinic receptors and compares these results with some recent advances in molecular biology and quantitative structure-activity relationship (QSAR) studies.

Antimuscarinic effects of (R)- and (S)- oxyphencyclimine hydrochloride

The (R)-(+)- and (S)-(-)-enantiomers of the anticholinergic compound, oxyphencyclimine, were synthesized from (R)-(-)- and (S)-(+)-2-cyclohexyl-2-hydroxy-2-phenylethanoic acid, respectively. The potencies of the enantiomers were compared using a cholinergic receptor binding assay. The (R)-(+)-enantiomer inhibited binding 29 times more potently than the (S)-(-)-enantiomer.

Stimulation of acetylcholine synthesis by blockade of presynaptic muscarinic inhibitory autoreceptors: observations in rat and human brain preparations and comparison with the effect of choline

The central presynaptic muscarinic inhibitory autoreceptor has been monitored by measuring the effects of muscarinic agents on acetylcholine (ACh) synthesis by rat and human neocortical tissue prisms. Quinuclidinyl benzilate (QNB), the antimuscarinic which of 20 tested caused the most marked stimulation of ACh synthesis in rat, significantly increased ACh synthesis in human prisms over a range or concentrations of 0.1 microM-10 microM. This data provides the first evidence that human brain contains presynaptic muscarinic receptors. However, the most marked effect of QNB was to increase synthesis to only 112% of control (value without drug) which was much less than in rat (to 140% of control). ACh synthesis is reduced to 50% of control in neocortex from Alzheimer patients so none of the antimuscarinics tested seem to be potentially capable of appreciably reversing this deficit. A high concentration of choline (10 mM) stimulated synthesis in rat prisms to about the same extent as QNB. Moreover, the ACh precursor was at least as effective in stimulating synthesis in human prisms (including those from a patient with Alzheimer's disease). This suggests that an elevated intracellular concentration of choline is likely to be much more effective than an antimuscarinic agent in stimulating synthesis in Alzheimer brain.

Evidence for the pharmacological similarity between the central presynaptic muscarinic autoreceptor and postsynaptic muscarinic receptors

Twenty antagonist substances with varying potencies for central and peripheral postsynaptic muscarinic receptors have been examined for effects on the central presynaptic muscarinic autoreceptor. This has been monitored by measuring the stimulating effects of the substances on acetylcholine synthesis by rat neocortical tissue prisms. Dose-response curves for selected agents showed that maximal stimulation of synthesis was to 136-140% of the value without an antagonist. At a concentration of 1 microM, 17 of the substances caused a significant increase in synthesis, whilst at 0.01 microM significant stimulation occurred with only atropine, dexetimide, N-methyl-piperdin-4-yl (R)-2-cyclohexyl-2-hydroxyl-2-phenylacetate, quinuclidinyl benzilate (QNB) and scopolamine. Linear regression analysis between synthesis values obtained with the substances and published data for the effects on either cholinoceptor-agonist induced contraction of guinea-pig ileum or the binding of [3H]-QNB to rat forebrain membranes gave correlation coefficients of r = 0.84 (P less than 0.01), and r = 0.75 (P less than 0.02) respectively. The results provide no indication of a pharmacological difference between the central presynaptic muscarinic autoreceptor and central and peripheral postsynaptic muscarinic receptors.

The significance of differences in the potency of enantiomers of anti-acetylcholine drugs

The anti-acetylcholine potencies of the dimethylaminoethyl and N/-methyl piperidin-4-yl esters of R and S 2-cyclohexyl-2-hydroxy-2-phenylacetic acid and their quaternary derivatives have been measured by in vitro and in vivo procedures. The R-enantiomer of dimethylaminoethyl-2-cyclohexyl-2-hydroxy-2-phenylacetate was approximately 100 times more active than the corresponding S-enantiomer both in vivo and in vitro. In contrast, the differences in potencies of the enantiomers of the other compounds were smaller in vivo than in vitro and moreover, the in vivo differences in potency decreased as the potency of the racemates increased. The relevance of these results to general studies of enantiomeric differences is discussed.