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

Abstract

A biologically inert photolabile precursor of carbamoylcholine has been synthesized; it is photolyzed to carbamolycholine, a well-characterized acetycholine analogue, with a half-time of 40μs at pH 7.0 and a quantum yield of 0.8. The compound, N-(α-carboxy-2-nitrobenzyl) carbamoylcholine, was sunthesized 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 thier ability to activate the nicotinic acetycholine receptor. BC₃H1 musle cells containing those receptors and a cell-flow method were used in the biological assay. The approach described may be useful in the preparation and characterization of other photolabile precursors of neutransmitters 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.