The synthesis is described of tabtoxinine-β-lactam, an amino acid produced by various Pseudomonad species and also formed on hydrolysis of tabtoxin. The key intermediate in the synthesis is 1-anisyl-6-methoxycarbonyl-3-methylene-2-piperidone, which is easily obtained by application of the α-methylenelactam rearrangement to dimethyl 1-anisyl-2,5-piperidinedicarboxylate. Epoxidation gave a mixture of cis and trans oxides which were individually treated with ammonia. From the trans epoxide, the major isomer, the corresponding 3-aminomethyl-3 hydroxy compound was isolated. Removal of the anisyl protecting group gave the amino acid, cis- 3-aminomethyl-6-carboxy-3-hydroxy-2-piperidone, identical with tabtoxinine-β-lactam. This synthesis confirms the structure of, and establishes the aminomethyl and carboxy groups as cis in, the natural amino acid.