Highly diastereo- and enantioselective synthesis of syn-β-substituted tryptophans via asymmetric Michael addition of a chiral equivalent of nucleophilic glycine and sulfonylindoles.

The asymmetric synthesis of syn-β-substituted tryptophan derivatives was carried out by the Michael addition of chiral equivalent of nucleophilic glycine with sulfonylindoles, and high diastereo- and enantioselectivities were achieved. The resulting adducts were readily converted to syn-β-substituted tryptophans in 96% yield, indicating that the proposed method is a highly efficient route to chiral syn-β-substituted tryptophans.