Reductive cyclization of 5-hydroxy-3-methyl-3-methoxycarbonylmethylenebenzofuran-2(3H)-one (4) gave 5-hydroxy-3a-methyl-2,3,3a,8a-tatrahydrofuro[2,3-b]
benzofuran (5) and the rearrangement product 7-hydroxy-4,5-dihydro-2,5-methano-1,3-benzodioxepine (6). Reaction of compounds 5 and 6 with different
isocyanates provided two series novel
carbamates (7-12) whose structures were confirmed by X-ray crystallography. These were assessed for
anticholinesterase action against freshly prepared human
enzyme and proved to be potent inhibitors of either acetyl- (AChE) or
butyrylcholinesterase (BChE) with specific compounds exhibiting remarkable selectivity. Because the two series of
carbamates (7-12) differ in their phenolic moieties, their respective potency and selectivity for AChE versus BChE was governed by their N-substituted groups. This same characteristic was also present in a series of
physovenine analogues (1, 13, 15, 17) and
physostigmine analogues (2, 14, 16, 18). These structure-activity relations proved valuable in elucidating the mechanisms underpinning the interaction between
carbamate-based
cholinesterase inhibitors and their
enzyme target. In addition, because
physostigmine analogues have demonstrated activity in lowering the
Alzheimer's disease protein, amyloid precursor
protein (APP), examples of the two new series of
carbamates were characterized in culture assays of quantifying cell viability and synthesis of APP.