Chemo- and enzyme-catalyzed reactions revealing a common temperature-dependent dynamic solvent effect on enantioselectivity

The enantiomeric ratio E of enzyme-catalyzed (Candida antarctica lipase and lipase PS) and chemocatalyzed (L-proline-based diamines) acylation reactions of 1-(naphthalen-2-yl)ethanol, 2-phenylpropanol, and 2-benzylpropane-1,3-diol is dependent on solvent and temperature. Plots of In E vs. 1/T showed the presence of inversion temperatures (T-inv). The T-inv values for the bio-catalyzed and the cherno-catalyzed reactions are fairly in agreement, and correspond as well to the T-NMR values obtained by variable-temperature C-13-NMR experiments on the substrates in the same solvent of the resolution. This result demonstrates that clustering effects in the substrate solvation manage the chemical and the enzymatic enantioselectivity, and, moreover, that the solute-solvent cluster is always the real reacting species in solution for chemical as well as for enzymatic reactions.