Benzilylcholine mustard

An example of an irreversible antagonist with a very long action (usually many hours) is phenoxybenzamine, which blocks a-adrenoceptors and, less potently, H,-histamine and muscarinic receptors. Its structure is shown below. Also illustrated is benzilylcholine mustard, a highly active and selective irreversible blocker of muscarinic receptors. 

Even though the muscarinic receptor, which is present in postganglionic parasympathetic synapses, is much more stereospecific and structure-specific than its nicotinic counterpart, only since the 1980s have any molecular studies been undertaken to explore similarities and differences between the two classes of AChR. It has been labeled with the affinity label pH] propyl-benzilylcholine-mustard (4.5). 

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