Abstract: The present invention involves a process for preparing protected amino acids. The process produces a di-tert-butyl amino ester or an N-protected di-tert-butyl amino ester by transesterification of an acidic amino acid or an N-protected acidic amino acid. By-products of the transesterification reaction may be recycled for use as part of the starting material. The N-protected di-tert-butyl amino ester may be hydrogenated to form a di-tert-butyl amino ester, which may subsequently form a di-tert-butyl ester hydrocholride salt.