Quantum chemical model study of the acyl migration in 2′(3′)‐formylnucleosides

Abstract

AbstractThis work reports a density functional study of the mechanism of acyl migration between vicinal OH groups in monoformylated cis‐tetrahydrofuran‐3,4‐diol as a model system for the acyl migration in amino‐acylated tRNA. In addition, migration toward the ionized hydroxyl group was modeled, which simulates the process in the presence of basic reagents. The polarized continuum model (PCM) for four solvents evaluated the solvent effect on the reaction energetics. The computational results suggest that the stepwise mechanism via an orthoester intermediate is preferred by 45–48 kJ/mol over the concerted mechanism where migration of the formyl group, and the proton from the vicinal OH group occurs simultaneously via a four‐atom transition state. The conformational constrains of the THF ring could increase the energy of the transition states by ∼24 and 37 kJ/mol for the stepwise and concerted reaction paths, respectively. The calculated lowest activation energy of the reaction both in vacuum and in solvents is rather high, at 188 and 172–182 kJ/mol, respectively. These results suggest that in real systems, the process is most likely catalyzed by preliminary deprotonation of the vicinal OH group. In this case, the formyl group migration proceeds spontaneously, and the intermediate formed is 15–30 kJ/mol more stable than the initial anion of the monoformylated diol. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006