Regioselective nitration of Nα,N1-bis(trifluoroacetyl)-l-tryptophan methyl ester: Efficient synthesis of 2-nitro and 6-nitro-N-trifluoroacetyl-l-tryptophan methyl ester

Nitration of Nα,N1-bis(trifluoroacetyl)-l-tryptophan methyl ester with HNO3 in acetic anhydride at 0 °C provides Nα-trifluoroacetyl-2-nitro-l-tryptophan methyl ester in 67% yield, whereas nitration in trifluoroacetic acid at 0 °C gives Nα-trifluoroacetyl-6-nitro-l-tryptophan methyl ester in 69% yield.