Pyrazine derivatives with extended conjugation and methods of using the same in optical applications

An optical diagnostic agent having Formula 1

• or pharmaceutically acceptable salt thereof, wherein:
• X is -Ar-Y, —C(R4)═C(R5)-Ar-Y, —C≡C-Ar-Y, —N═N-Ar-Y, —CO-Ar-Y, —N(R6)-Ar-Y, —O-Ar-Y, —S-Ar-Y, —SO-Ar-Y, —SO2-Ar-Y, —C(R4)═C(R5)—Y, or —C≡C—Y;
• Ar is phenyl, naphthyl, biphenyl, pyridyl, pyridazyl, pyrimidinyl, pyrazinyl, pyrrolyl, furanyl, thiopheneyl, pyrazolyl, imidazolyl, oxazolyl, thiazolyl, triazinyl, triazolyl or thiadiazolyl;
• with the proviso that if Ar is phenyl, pyrrolyl, or thiopheneyl, then at least one of R1, R2, and R3 is other than hydrogen;
• each Y is independently hydrogen, C1-C10 alkyl, halo, haloalkyl, —CN, —CO2R7, —CONR8R9, —COR10, —NO2, —SOR11, —SO2R12, —SO2OR13, —PO3R14R15, —OR16, —SR17, —NR18R19, —N(R20)COR21, —P(R22)3, —CO(AA)j, or —CONH(PS)k;
• each of, R1, R2 and R3 is independently hydrogen, C1-C10 alkyl, halo, haloalkyl, —CN, —CO2R7, —CONR8R9, —COR10, —NO2, —SOR11, —SO2R12, —SO2OR13, —PO3R14R15, —OR16, —SR17, —NR18R19, —N(R20)COR21, —P(R22)3, —CO(AA)j, —CONH(PS)k, or X;
• with the proviso that no more than one of R1, R2 and R3 is a —CN group and at least one of R1, R2 and R3 comprises a substituted or unsubstituted amino group;
• (AA)j is a polypeptide chain comprising the same or different amino acids linked together by peptide bonds, wherein j is an integer from 1 to 50;
• (PS)k is a sulfated or non-sulfated polysaccharide chain comprising the same or different monosaccharide units connected together by glycosidic linkages, wherein k is an integer from 1 to 50;
• each of R4 to R22 is independently —H, C1-C10 alkyl, —(CH2)aOR23, —CH2(CHOH)aR24, —CH2(CHOH)aCO2H, —(CHCO2H)aCO2H, —(CH2)aNR25R26, —CH[(CH2)bNH2]aCO2H, —CH[(CH2)bNH2]aCH2OH, —CH2(CHNH2)aCH2NR27R28, —(CH2CH2O)cR29, or —(CH2)dCO(CH2CH2O)cR30;
• each of R23 to R30 is independently —H or —CH3;
• each of a, b, and d is independently an integer from 1 to 10;
• and
• c is an integer from 1 to 100.