A theoretical study on the elimination reaction of acrylonitrile from 2′-O-cyanoethylated nucleosides by Bu4NF

The elimination reaction of acrylonitrile from 2'-O-cyanoethylated nucleosides by Bu4NF was studied computationally. The transition structures for the reaction of 3-methoxypropionitrile with Me4NF were located at the MP2, B3LYP, and B3LYP-SCRF(Dipole) levels with 6-31 + G* basis set. The alpha-hydrogen of the cyano group was removed via a proton transfer from the alpha-carbon to the oxygen with a syn-periplanar arrangement rather than the deprotonation reaction with F-. In the presence of an excess amount of Me4NF, the activation energy decreased by the coordination of Me4N+ to the cyano group. The reaction of 3-methoxypropionitrile with Bu4NF and 2'-O-cyanoethylated uridine with Me4NF also occurred via a proton transfer mechanism with lower activation energies. The reactivity tendency corresponds to the amount of the negative charge on the oxygen atom and part of the reason for the faster elimination with F- rather than with DBU concerns entropy. The experimental results are well explained by these calculations. (C) 2018 Elsevier Ltd. All rights reserved.