Regioselective nitration of N(alpha),N(1)-bis(trifluoroacetyl)-L-tryptophan methyl ester: efficient synthesis of 2-nitro and 6-nitro-N-trifluoroacetyl-L-tryptophan methyl ester.

Nitration of N(alpha),N(1)-bis(trifluoroacetyl)-l-tryptophan methyl ester with HNO(3) in acetic anhydride at 0 degrees C provides N(alpha)-trifluoroacetyl-2-nitro-l-tryptophan methyl ester in 67% yield, whereas nitration in trifluoroacetic acid at 0 degrees C gives N(alpha)-trifluoroacetyl-6-nitro-l-tryptophan methyl ester in 69% yield.