The amino acid 2-amino-4-(2-aminoethoxy)-trans-but-3-enoic acid can be conveniently prepared via novel intermediates from a 2,2'-disubstituted diethyl ether and a dialkyl N-protected amidomalonate starting material using a multi-step process. Preferred starting materials are bis-2-chloroethyl ether and diethyl acetamidomalonate. The process, in a preferred embodiment, proceeds through the key intermediate ethyl-2-acetamido-4-[2-(2-phthalimido)ethoxy]-but-2-enoate.