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

Expanding the Substrate Scope of Nitrating Cytochrome P450 TxtE by Active Site Engineering of a Reductase Fusion

Aromatic nitration reactions are a cornerstone of organic chemistry, but are challenging to scale due to corrosive reagents and elevated temperatures. The cytochrome P450 TxtE nitrates the indole 4-position of l-tryptophan at room temperature using NO, O2 and NADPH, and has potential to be developed into a useful aromatic nitration biocatalyst. However, its narrow substrate scope (requiring both the α-amino acid and indole functionalities) have hindered this. Screening of an R59 mutant library of a TxtE-reductase fusion protein identified a variant (R59C) that nitrates tryptamine, which is not accepted by native TxtE. This variant exhibits a broader substrate scope than the wild type enzyme and is able to nitrate a range of tryptamine analogues, with significant alterations to the aromatic and aminoethyl moieties.

Design and synthesis of enantiopure 18 F-labelled [18 F]trifluoromethyltryptophan from 2-halotryptophan derivatives via copper(I)-mediated [18 F]trifluoromethylation and evaluation of its in vitro characterization for the serotonergic system imaging

We synthesized [¹⁸ F]trifluoromethyl-l-tryptophan ([¹⁸ F]CF₃ -l-Trp) using Cu(I)-mediated [¹⁸ F]trifluoromethylation to image serotonergic system. Radiochemical yield was 6 ± 1.5% (n = 9), and radiochemical purity was over 99%. The molar activity was 0.44 to 0.76 GBq/μmol. [¹⁸ F]CF₃ -l-Trp was stable for up to 6 hours in mouse and human sera at 37°C. Protein-binding was 0.26 ± 0.03% and 0.34 ± 0.02% in human and mouse serum at 60 minutes, respectively. In conclusion, enantiopure [¹⁸ F]CF₃ -l-Trp was synthesized as a feasible imaging agent for the serotonergic system.

Cytochrome P450–catalyzed L-tryptophan nitration in thaxtomin phytotoxin biosynthesis

Thaxtomin phytotoxins produced by plant-pathogenic Streptomyces species contain a nitro group that is essential for phytotoxicity. The N,N’-dimethyldiketopiperazine core of thaxtomins is assembled from L-phenylalanine and L-4-nitrotryptophan by a nonribosomal peptide synthetase and nitric oxide synthase-generated NO is incorporated into the nitro group, but the biosynthesis of the non-proteinogenic amino acid L-4-nitrotryptophan is unclear. Here we report that TxtE, a unique cytochrome P450, catalyzes L-tryptophan nitration using NO and O₂.