This invention relates to a process for preparing optically active .alpha.-amino acid substrates which are used to make potent lethal factor (LF) inhibitors for the treatment of anthrax. This invention further relates to a process for synthesis of potent LF-inhibitors for the treatment of anthrax. Specifically, the invention concerns a novel, high-yielding and highly enantioselective asymmetric hydrogenation reaction of a tetrasubstituted ene-sulfonamide acid or ester.