Analysis of cholinesterase inactivation and reactivation by systematic structural modification and enantiomeric selectivity.
We show here with a congeneric series of Rp- and Sp-alkoxymethyl phosphonothiolates of known absolute stereochemistry that chiral selectivity in their reaction with acetylcholinesterase can be described in terms of discrete orientational and steric requirements. Stereoselectivity depends on acyl pocket dimensions, which govern leaving group orientation and a productive association of the phosphonyl oxygen in the oxyanion hole. Overall geometry is consistent with a pentavalent intermediate where the attacking serine and leaving group are at apical positions. Oxime reactivation of the phosphonylated enzyme occurs through a similar associative intermediate presumably forming an oxime phosphonate. The oximes of differing structure show distinct angles of attacking the phosphate where the attack angles and access to the phosphorus are constrained in the sterically impacted gorge. Hence, efficacy of oxime reactivation is dependent on both oxime and conjugated phosphonate structures.
Taylor
P
P
Department of Pharmacology, University of California, San Diego, La Jolla 92093-0636, USA.
Wong
L
L
Radić
Z
Z
Tsigelny
I
I
Brüggemann
R
R
Hosea
N A
NA
Berman
H A
HA
D000818:Animals; D001665:Binding Sites; D002800:Cholinesterase Inhibitors / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D002802:Cholinesterases / Q000737:chemistry / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D004793:Enzyme Reactivators / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D006801:Humans; D008958:Models, Molecular; D010755:Organophosphates / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D011487:Protein Conformation; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D013816:Thermodynamics
D002800:Cholinesterase Inhibitors; D004793:Enzyme Reactivators; D010755:Organophosphates; D002802:Cholinesterases