Two series of compounds having the general structure of C6H5CRR'COOCH2CH2NEt2 were synthesized and examined for their antispasmodic activities. These compounds were selected as structural probes for exploring the nature of muscarinic cholinergic receptor binding sites that interact with atropine-like anticholinergics. These studies indicate a rather strict size limitation for the hydrophobic region of the receptor and suggest intramolecular hydrogen bonding as a possible means to explain the observed stereoselectivity.