Magnusson Olafur Th, Frey Perry A
Department of Biochemistry, University of Wisconsin-Madison, 1710 University Avenue, 53705, USA.
Bioorg Chem. 2002 Feb;30(1):53-61. doi: 10.1006/bioo.2001.1223.
S-3',4'-anhydroadenosyl-l-methionine is an analogue of the S-adenosyl-l-methionine coenzyme. Here we report on a rapid solvent exchange of the methylene protons at the 5'-position of this analogue. The rate of H/D exchange was measured by nuclear magnetic resonance spectroscopy under buffered conditions in deuterium oxide. The reaction is specific base catalyzed and displays a second-order rate constant of 2 x 10(4) M(-1) s(-1), which corresponds to a rate enhancement of 10(12) compared to solvent exchange of alpha-methylene protons in acyclic, aliphatic sulfonium ions. No other carbon bonded hydrogens in the molecule exchange with solvent under the experimental conditions. Allylic stabilization of a carbanionic-like transition state for the solvent exchange process can account for these results. Solvent exchange under these mild conditions provides a simple way to prepare a 5'-2H-labeled form of the coenzyme analogue.
