Synthesis of methylsulfanyl analogs of Kaede protein chromophore

5-Arylidene-1-methyl-2-[2-(methylsulfanyl)-2-phenylethenyl]-1H-imidazol-5(4H)-ones were synthesized as a result of the reaction of 5-arylidene-1-methyl-2-(methylsulfanyl)-1H-imidazol-5(4H)-ones with terminal acetylenes in the presence of a palladium catalyst and copper iodide. This reaction presents a rare example of the formation of a compound with a methylsulfanylethenyl group. A study of the optical properties of the obtained compounds showed that they are characterized by a significant bathochromic shift of spectral maxima in comparison with similar derivatives of the GFP chromophore.