title: Synthesis of tricyclic 1,3-oxazin-4-ones and kinetic analysis of cholesterol esterase and acetylcholinesterase inhibition.
abstract: A series of thieno[1,3]oxazin-4-ones and thieno[1,3]thiazin-4-ones were synthesized and investigated as inhibitors of the alpha/beta hydrolases cholesterol esterase (CEase) and acetylcholinesterase (AChE). The introduction of a cycloaliphatic five- or six-membered ring fused at the thiophene was favorable for CEase inhibition. Such compounds were analyzed as true alternate substrate inhibitors. 6,7-Dihydro-2-(dimethylamino)-4H,5H-cyclopenta[4,5]thieno[2,3-d][1,3]oxazin-4-one (33) exhibited a K(i) value of 630 nM and excelled in its low susceptibility to CEase-catalyzed degradation. Compound 33 and its analogues did not inhibit AChE. The introduction of a tetrahydropyrido ring with bulky hydrophobic substituents at the basic nitrogen provided inhibitors of AChE which were completely inactive toward CEase. 7-Benzyl-5,6,7,8-tetrahydro-2-(N-3,4-dimethoxybenzyl-N-methylamino)-4H-pyrido[4',3':4,5]thieno[2,3-d][1,3]oxazin-4-one (21) had the IC(50) value of 330 nM for AChE inhibition. A residual enzymatic activity at an infinite inhibitor concentration and thus a catalytically active ternary enzyme-substrate-inhibitor complex was concluded. To specify kinetic parameters of inhibition, a new method was derived to characterize selected thieno[1,3]oxazin-4-ones as hyperbolic mixed-type inhibitors of AChE.
authors.affiliation: Pharmaceutical Institute, University of Bonn, Kreuzbergweg 26, D-53115 Bonn, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Pietsch
authors.forename: Michael
authors.initials: M
authors.lastname: Gütschow
mesh_terms: D000110:Acetylcholinesterase / Q000378:metabolism; D000818:Animals; D002417:Cattle; D002800:Cholinesterase Inhibitors / Q000138:chemical synthesis* / Q000494:pharmacology; D004593:Electrophorus; D004791:Enzyme Inhibitors / Q000138:chemical synthesis / Q000494:pharmacology; D006575:Heterocyclic Compounds, 3-Ring / Q000138:chemical synthesis* / Q000494:pharmacology; D007700:Kinetics; D010078:Oxazines / Q000138:chemical synthesis* / Q000494:pharmacology; D002787:Sterol Esterase / Q000037:antagonists & inhibitors*; D013329:Structure-Activity Relationship
chemical_list: D002800:Cholinesterase Inhibitors; D004791:Enzyme Inhibitors; D006575:Heterocyclic Compounds, 3-Ring; D010078:Oxazines; D002787:Sterol Esterase; D000110:Acetylcholinesterase