We have performed a detailed study of the title reaction, which is the key step of one of the most realistic processes suggested for the prebiotic synthesis of amino acids. From a methodological point of view, our results confirm the reliability of the integrated computational tool formed by the B3LYP density functional model and the polarizable continuum model for the description of solvent effects, From a more chemical point of view, the reaction is quite unlikely in the gas phase due to the presence of significant reaction barriers, whereas the aqueous medium lends to a more feasible mechanism thanks to the preferential solvation of zwitterionic transition structures. Both specific and bulk solvent effects play a role in determining the overall mechanism.