Conformationally restrained carbamoylcholine homologues. Synthesis, pharmacology at neuronal nicotinic acetylcholine receptors and biostructural considerations.

Exploration of small selective ligands for the nicotinic acetylcholine receptors (nAChRs) based on acetylcholine (ACh) has led to the development of potent agonists with clear preference for the α4ß2 nAChR, the most prevalent nAChR subtype in the central nervous system. In this work we present the continuation of these efforts aimed at increasing this subtype selectivity by introduction of conformational restriction in the carbamoylcholine homologue, 3-(dimethylaminobutyl) dimethylcarbamate (DMABC). Our results highlight the importance of the N-carbamoyl substitution in α4ß2-subtype selectivity. Moreover, we have confirmed the non-linear conformation of DMABC bound to nAChRs suggested by recent crystal structures of the compound in complex with the Lymnaea stagnalis ACh binding protein.

Design, synthesis and binding affinity of acetylcholine carbamoyl analogues.

A series of acetylcholine carbamoyl analogues, cyclised at the carbamate moiety or at the cationic head or at both, were tested for binding affinity at muscarinic and neuronal nicotinic receptors (nAChRs). While no muscarinic affinity was found, submicromolar Ki values, similar to that of carbachol, were measured at α4ß2 nAChRs for the enantiomers of 5-dimethylaminomethyl- and 5-trimethylammoniomethyl-2-oxazolidinone, 2 and 2a, and for (S)-N-methylprolinol carbamate (S)-3. Methylation of oxazolidinone nitrogen of 2 and 2a and of N-methylprolinol nitrogen of (S)-3 and, even more, hybridization of cyclic carbamate substructure (oxazolidinone) with cyclic cationic head (N-methylpyrrolidine) markedly lower the nicotinic affinity. Docking results were consistent with SAR analysis highlighting the interaction capabilities of (R)-2a and (S)-3 and the negative effect of intracyclic nitrogen methylation and of double cyclisation.

Carbamoylcholine analogs as nicotinic acetylcholine receptor agonists--structural modifications of 3-(dimethylamino)butyl dimethylcarbamate (DMABC).

Compounds based on the 3-(dimethylamino)butyl dimethylcarbamate (DMABC) scaffold were synthesized and pharmacologically characterized at the alpha(4)beta(2), alpha(3)beta(4,) alpha(4)beta(4) and alpha(7) neuronal nicotinic acetylcholine receptors (nAChRs). The carbamate functionality and a small hydrophobic substituent in the C-3 position were found to be vital for the binding affinity to the nAChRs, whereas the carbamate nitrogen substituents were important for nAChR subtype selectivity. Finally, the compounds were found to be agonists at the alpha(3)beta(4) nAChR.

Carbamoylcholine homologs: synthesis and pharmacology at nicotinic acetylcholine receptors.

In a recent study, racemic 3-(N,N-dimethylamino)butyl-N,N-dimethylcarbamate (1) was shown to be a potent agonist at neuronal nicotinic acetylcholine receptors with a high selectivity for nicotinic over muscarinic acetylcholine receptors [Mol. Pharmacol. 64 (2003) 865-875]. Here we present the synthesis and pharmacological characterization of a series of analogs of, where the methyl group at C-3 has been replaced by different alkyl substituents. Ring systems have been incorporated into the carbon backbone of some of the molecules, or the amino group has been build into ring systems. Furthermore, the (+)- and (-)-enantiomers of have been separated, and X-ray crystallography has revealed that (-)-1 possesses (S)-configuration. The compounds have been characterized pharmacologically at recombinant nicotinic receptor subtypes. The structure-activity relationship study has provided valuable insight into the mode of interactions of and its analogs with neuronal nicotinic acetylcholine receptors.

An acetylcholine receptor regulatory site in BC3H1 cells: characterized by laser-pulse photolysis in the microsecond-to-millisecond time region.

When a neurotransmitter binds to its specific receptor, the protein forms transmembrane channels through which ions flow, leading to changes in transmembrane voltage that trigger signal transmission between neurons. How do inhibitors affect this process? Interesting and extensive information comes from investigations of the acetylcholine receptor, the best known of these proteins. This receptor is inhibited by cationic inhibitors, including local anesthetics, and acetylcholine at high concentrations. The accepted mechanism, elegant in its simplicity, is that these compounds enter the receptor-channel after it opens and block inorganic ion flux. This mechanism requires that the inhibitors affect only the apparent rate constant for channel closing (k'cl). An alternative mechanism invokes a specific regulatory (inhibitory) site to which inhibitors bind before the channel opens and the signal is transmitted. This mechanism requires that the inhibitors affect the apparent rate constants for both channel opening (k'op) and closing. The effect of inhibitors on k'op has not been determined previously. This report describes the use of a newly developed laser-pulse photolysis technique with a dead time of approximately 120 microseconds to determine the effect of a local anesthetic, procaine, one of the best studied cationic inhibitors of the acetylcholine receptor, on both k'op and k'cl. Both k'op and k'cl were found to decrease with increasing procaine concentration. This effect of the inhibitor of k'op cannot be explained by the open-channel-blocking mechanism but is consistent with the existence of a regulatory (inhibitory) receptor site.

Synthesis, photochemistry, and biological activity of a caged photolabile acetylcholine receptor ligand.

A biologically inert photolabile precursor of carbamoylcholine has been synthesized; it is photolyzed to carbamoylcholine, a well-characterized acetylcholine analogue, with a half-time of 40 microseconds at pH 7.0 and a quantum yield of 0.8. The compound, N-(alpha-carboxy-2-nitrobenzyl)carbamoylcholine, was synthesized from (2-nitrophenyl)glycine. The photolysis rates (of five compounds) and the biological activity (of two compounds) were determined, and both properties were found to depend on the nature of the substituents on the photolabile protecting group. Laser pulse photolysis at wavelengths between 308 and 355 nm was used to investigate the wavelength dependence, quantum yield, and rate of the photolysis reaction. Photolysis products were isolated by high-performance liquid chromatography and identified by chemical and spectroscopic analysis and by their ability to activate the nicotinic acetylcholine receptor. BC3H1 muscle cells containing those receptors and a cell-flow method were used in the biological assays. The approach described may be useful in the preparation and characterization of other photolabile precursors of neurotransmitters that contain amino groups. The importance of these rapidly photolyzed, inert precursors of neurotransmitters is in chemical kinetic investigations of the reactions involving diverse neuronal receptors; such studies have been hampered because the available techniques have an insufficient time resolution.