Benzene-di-N-octylcarbamates as conformationally constrained phospholipase A2 inhibitors

Comparison of active sites of butyrylcholinesterase and acetylcholinesterase based on inhibition by geometric isomers of benzene-di-N-substituted carbamates

We have reported that benzene-1,2-, 1,3-, and 1,4-di-N-substituted carbamates (1-15) are characterized as the conformationally constrained inhibitors of acetylcholinesterase and mimic gauche, eclipsed, and anti-conformations of acetylcholine, respectively (J Biochem Mol Toxicol 2007;21:348-353). We further report the inhibition of butyrylcholinesterase by these inhibitors. Carbamates 1-15 are also characterized as the pseudosubstrate inhibitors of butyrylcholinesterase as in the acetylcholinesterase catalysis. Benzene-1,4-di-N-n-hexylcarbamate (12) and benzene-1,4-di-N-n-octylcarbamate (13) are the two most potent inhibitors of butyrylcholinesterase among inhibitors 1-15. These two para compounds, with the angle of 180 degrees between two C(benzene)--O bonds, mimic the preferable anti C--O/C--N conformers for the choline ethylene backbone of butyrylcholine during the butyrylcholinesterase catalysis. The second n-hexylcarbamyl or n-octylcarbamyl moiety of inhibitors 12 and 13 is proposed to bind tightly to the peripheral anionic site of butyrylcholinesterase from molecular modeling. Butyrylcholinesterase prefers para-carbamates to ortho- and meta-carbamates, whereas acetylcholinesterase prefers para- and meta-carbamates to ortho-carbamates. This result implies that the anionic site of butyrylcholinesterase is relatively smaller than that of acetylcholinesterase because meta-carbamates, which may bind to the anionic sites of both enzymes, are not potent inhibitors of butyrylcholinesterase.

QSAR for phospholipase A2 inhibitions by 1-acyloxy-3-N-n-octylcarbamyl-benzenes

1-Acyloxy-3-N-n-octylcarbamyl-benzenes are potent reversible competitive inhibitors of Naja mocambique mocambique phospholipase A2 with the Ki values from 9.6 to 119 microM. The pKi values are correlated to both Taft substituent constant sigma* and Hansch hydrophobicity constant pi. The pre-steady state inhibition studies indicate that the pK(S) values for the first inhibition step are linearly correlated to sigma* alone with the rho* of -0.09 for this correlation. Thus, the first inhibition step may involve the insertion of the inhibitor to hepta-coordinated Ca2+ ion of the enzyme to form the octa-coordinated Ca2+ ion of the enzyme. The log(k2/k(-2)) values for the second inhibition step are linearly correlated to pi alone, and the psi value for this correlation is 0.13. Therefore, the second step inhibition step may involve the van der Waals' interaction between the acyl group of the inhibitor and Tyr 69 of the enzyme.