title: Toward intrinsically colored peptides: Synthesis and investigation of the spectral properties of methylated azatryptophans in tryptophan-cage mutants.
abstract: Tryptophan has been taken as the basic scaffold for a chromophore whose indole residue can be further functionalized by the introduction of endocyclic nitrogen atoms or by N-methylation. When compared with exocyclic modifications, modifying tryptophan in an endocyclic fashion (through atomic substitution) should not perturb the steric profile of the amino acid side chain to such a large extent as that of an exocyclic modification, while simultaneously modulating the polarity, hydrogen-bonding ability, and spectral properties of the amino acid. Of particular interest is that the spectral properties can be tailored such that the chromophore can be monitored at wavelengths that exceed natural protein fluorescence. Ideally, the optimum excitation wavelength should be between 300 and 350 nm, and the emission wavelength should be ≥500 nm such that no cross-excitation/fluorescence occurs. Here, we report the synthesis of amino acid labels that exhibit large red shifts in their fluorescence profiles and their use in peptides.
authors.affiliation: Department of Chemistry, Berlin Institute of Technology, Müller-Breslau-Straße 10, 10623, Berlin, Germany.
authors.forename: Benjamin P
authors.initials: BP
authors.lastname: Noichl
authors.affiliation: Department of Chemistry, Berlin Institute of Technology, Müller-Breslau-Straße 10, 10623, Berlin, Germany.
authors.forename: Patrick M
authors.initials: PM
authors.lastname: Durkin
authors.affiliation: Department of Chemistry, Berlin Institute of Technology, Müller-Breslau-Straße 10, 10623, Berlin, Germany.
authors.forename: Nediljko
authors.initials: N
authors.lastname: Budisa
mesh_terms: D001372:Aza Compounds / Q000737:chemistry*; D003116:Color; D005456:Fluorescent Dyes / Q000737:chemistry; D008745:Methylation; D009154:Mutation; D010455:Peptides / Q000737:chemistry*; D014364:Tryptophan / Q000737:chemistry* / Q000235:genetics
chemical_list: D001372:Aza Compounds; D005456:Fluorescent Dyes; D010455:Peptides; D014364:Tryptophan
keywords: azatryptophan; chromophore; fluorescence; heteroannulation reaction; tryptophan analogs