Kinetics of the hydrolysis of guanosine 5'-phospho-2-methylimidazolide.
We have studied the hydrolysis of guanosine 5'-phospho-2-methylimidazolide, 2-MeImpG, in aqueous buffered solutions of various pH's at 75 degrees C and 37 degrees C. At 75 degrees C and pH < or = 1.0, two kinetic processes were observed spectrophotometrically: the first and more rapid one is attributed to the hydrolysis of the phosphoimidazolide P-N bond; the second and much slower one, to the cleavage of the glycosidic bond. At 37 degrees C, pH 2.0, the spectrophotometrically determined rate constant of P-N bond hydrolysis was confirmed by using high pressure liquid chromatography, HPLC. With the latter technique it was possible to separate reactants and products and also to extend the pH-rate profile into the neutral region where rates are slower and, therefore, difficult to measure spectrophotometrically. The pH-rate profiles at both temperatures exhibit similar behavior. At pH < 2 the pseudo-first-order rate constant increases with decreasing pH; in the region 2 < pH < 7 there is a plateau followed by a decrease for pH > 7. These data are consistent with a reactivity order zwitterion > anion for P-N bond hydrolysis. It is noteworthy that P-N bond hydrolysis in phosphoimidazolides is very slow compared to other phosphoramidates. This may be one of the reasons why this compound showed extraordinary ability in forming long oligomers under template-directed conditions.
Kanavarioti
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NASA/Ames Research Center, Moffett Field, CA 94035, USA.
D019418:Evolution, Chemical; D019143:Evolution, Molecular; D006157:Guanosine Monophosphate / Q000031:analogs & derivatives* / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007700:Kinetics; D009584:Nitrogen; D009841:Oligonucleotides / Q000138:chemical synthesis; D010758:Phosphorus; D013056:Spectrophotometry, Ultraviolet; D013696:Temperature
D009841:Oligonucleotides; D010758:Phosphorus; C036896:guanosine 5'-phospho-2-methylimidazolide; D006157:Guanosine Monophosphate; D009584:Nitrogen