A new enantiomeric synthesis utilizing classical resolution provided two novel series of optically active inhibitors of cholinesterase: (-)- and (+)-O-carbamoyl phenols of tetrahydrofurobenzofuran and methanobenzodioxepine. An additional two series of (-)- and (+)-O-carbamoyl phenols of pyrroloindole and furoindole were obtained by known procedures, and their anticholinesterase actions were similarly quantified against freshly prepared human acetyl- (AChE) and butyrylcholinesterase (BChE). Both enantiomeric forms of each series demonstrated potent cholinesterase inhibitory activity (with IC(50) values as low as 10 nM for AChE and 3 nM for BChE), with the exception of the (+)-O-carbamoyl phenols of pyrroloindole, which lacked activity (IC(50) values >1 microM). Based on the biological data of these four series, a structure-activity relationship (SAR) analysis was provided by molecular volume calculations. In addition, a probable transition-state model was established according to the known X-ray structure of a transition-state complex of Torpedo californica AChE-m-(N,N,N-trimethylammonio)-2,2,2-trifluoroacetophenone (TcAChE-TMTFA). This model proved valuable in explaining the enantioselectivity and enzyme subtype selectivity of each series. These carbamates are more potent than, or similarly potent to, anticholinesterases in current clinical use, providing not only inhibitors of potential clinical relevance but also pharmacological tools to define drug-enzyme binding interactions within an enzyme crucial in the maintenance of cognition and numerous systemic physiological functions in health, aging, and disease.