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Rapid way to fluorescent cholic-based chemosensor precursors
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1  National Pharmacy University, Kharkiv, Ukraine

Abstract: Fluorescent cholic acid derivatives are used as well in biological investigations as in chemical. As nature products their derivatives can be used in research of hepatotoxicity, cell transport system and distribution of the drugs in organisms. Cholic acid-based fluorescent sensors are used to detection different organic and inorganic compounds such as drugs, toxins, amino acids and heavy metals. \'Fluorophore–spacer–receptor\' motif is an effective way of designing of plurality of chemosensors and has used in the last two decades. Coumarines containing electron donating groups are natural non-toxic compounds that have good fluorescent parameters. It is also known that rearrangement of imino-coumarines is the easy way to fluorescent coumarine derivatives. Hence, in present work fluorescent receptor precursors bearing coumarine fluorophore on C24 of cholic acid were designed and synthesized in 3 steps. The condensation of 2-imino-coumarine-3-carboxamides with cholic hydrazide in acetic acid with following recyclization in diphenyl ether formed the corresponding 1,3,4-oxadiazol-2-yl-coumarin derivatives in moderate to good yields. Structures of synthesized 7 examples fluorescent cholic-based derivatives were confirmed by NMR H1 and MS. The UV-absorption and fluorescent spectrum of the newly synthesized compounds was measured in acetonitrile and ethanol solutions. It is shown that wave length of emitted irradiation is in the range from 420 to 510nm and quantum yield is in the range from 0,02 to 0,58. Either wave length or quantum yields depend on donation value and position of substitution group in coumarine fragment. Sensor-precursors that are developed in this way are very flexible to modifications. On the one hand, it\'s possible to modify easily the coumarine fragment in order to change the wavelength of fluorescence and color, respectively, on the other hand, by the introduction of various substituents on the hydroxyl groups in cholic fragment it\'s allowed to control the response level from attaching guest-substances.
Keywords: fluorescent chemosensors, cholic acid, coumarine