A detailed analysis of the alkylation of phosphodiesters with a P-quinone m
ethide under aqueous conditions has been accomplished. The relative rates o
f phosphodiester alkylation and hydrolysis have been examined by H-1 NMR an
alysis of the reaction of 2,6-dimethyl-p-quinone methide in a buffered diet
hyl phosphate/acetonitrile solution (1:9 v/v, pH 4.0). The rate of hydrolys
is of the quinone methide was confirmed by UV analysis in 28.5% solutions o
f aqueous inorganic phosphate in acetonitrile at pH 4.0 and 7.0. Similarly,
the rate of phosphodiester alkylations by the quinone methide was also con
firmed by UV analysis in 28.5% solutions of aqueous dibenzyl, dibutyl, or d
iethyl phosphate in acetonitrile at pH 4.0 and 7.0. These kinetic studies f
urther establish that the phosphodiester alkylation reactions are acid-cata
lyzed, second-order processes. The rate constant for phosphodiester alkylat
ion was found to range from approximately 370-3700 times the rate constant
of quinone methide hydrolysis with diethyl and dibenzyl phosphate, respecti
vely (pH 4.0, 28.5% aqueous acetonitrile).