L-Glutamate semialdehyde (L-GSA) is an intermediate in biosynthetic pathways including those leading to the carbapenem antibiotics. We describe studies on asymmetric deuteration or hydrogenation of appropriate didehydro-amino acid precursors for the stereoselective synthesis of C-2-and/or C-3-[2H]-labelled L-GSA suitable for use in mechanistic studies. Regioselective deuterium incorporation into the 5-position of L-GSA was achieved using a ...