The present disclosure provides methods for preparing β-substituted tryptophan compounds. The methods include: combining i) an unsubstituted indole or a substituted indole, ii) a β-substituted serine, and iii) a tryptophan synthase β-subunit (i.e., a TrpB); and maintaining the resulting mixture under conditions sufficient to form the β-substituted tryptophan. The TrpB contains at least one amino acid mutation which promotes formation of an amino-acrylate intermediate. New TrpB variants and new β-substituted tryptophan analogs are also described.