Indeed, in conventional homogeneous processes, the generation of the free amino acid esters implies the concomitant generation of at least 1 equiv of inorganic salt. Various R-amino acids, i.e., D-phenylglycine, L-phenylalanine, D,L- homophenylalanine, and D-p-hydroxyphenylglycine, reacted with alcohols over H-USY (SAR ) 5), giving the corresponding esters (Table 18, entry 4).153 To explain the partial racemization observed, the au- thors showed that the amino acid ester undergoes thermal racemization, even in refluxing methanol.