SummaryGreen Fluorescent Protein (GFP) and homologous proteins possess a unique pathway of chromophore formation based on autocatalytic modification of their own amino acid residues. Greento-red photoconvertible fluorescent protein Kaede carries His-Tyr-Gly chromophore-forming triad.Here we describe synthesis of Kaede red chromophore (2-[(1E)-2-(5-imidazolyl)ethenyl]-4-(phydroxybenzylidene)-5-imidazolone) and its analogs that can be potentially formed by natural amino acid residues. Chromophores corresponding to the following tripeptides were obtained: His-Tyr-Gly, Trp-Tyr-Gly, Phe-Trp-Gly, Tyr-Trp-Gly, Asn-Tyr-Gly, Phe-Tyr-Gly, and Tyr-Tyr-Gly. In basic conditions they fluoresced red with relatively high quantum yield (up to 0.017 for Trp-derived compounds). The most red-shifted absorption peak at 595 nm was found for the chromophore TrpTyr-Gly in basic DMSO. Surprisingly, in basic DMF non-aromatic Asn-derived chromophore AsnTyr-Gly demonstrated the most red-shifted emission maximum at 642 nm. Thus, Asn residue may be a promising substituent, which can potentially diversify posttranslational chemistry in GFP-like proteins.