The present invention relates to an oral drug delivery system, and in particular to modified amino acids and modified amino acid derivatives for use as a delivery system of sensitive agents such as bioactive peptides. The modified amino acids and derivatives can form non-covalent mixtures with active biological agents and in an alternate embodiment can releasably carry active agents. Modified amino acids can also form durg containing microspheres. These mixtures are suitable for oral administration of biologically active agents to animals. Methods for the preparation of such amino acids are also disclosed.