This chapter provides an overview of a program directed at the synthesis of amino acids (AA's) bearing a vinyl substituent in place of the usual α-proton. These quaternary amino acids are of interest, in and of themselves, as mechanism-based inhibitors of pyridoxal phosphate dependent enzymes, and also as building blocks for natural product or peptide synthesis. Importantly, these unnatural amino acids also serve as synthetic precursors for α-halovinyl AA's and α-oxiranyl AA's. Stereoselective synthetic methodology development in this area is highlighted and the initial performance of the α- (2'Z-fluoro)vinyl trigger in an amino acid decarboxylase (AADC) active site is described. Interestingly, at least for H. alvei lysine decarboxylase (LDC), inactivation with this trigger, along the α-branch, displays a marked enantio- dependence, with the L-antipode giving efficient inactivation, and its mirror image behaving as a simple substrate.