Synthesis and spectral properties of 1,3,4-oxadiazol-2-yl-coumarines containing 3,7,12-threehydroxycholic fragment

Abstract

1,3,4-oxadiazol-2-yl-coumarins containing 3,7,12-threehydroxycholic fragment (cholic acid residue) are promising as fluorescent labels in biochemical studies. A new method for the synthesis of 1,3,4-oxadiazol-2-yl-coumarines containing 3,7,12-threehydroxycholic fragment at position 5 of the 1,3,4-oxadiazole cycle is proposed. It is based on the recyclization of 2-iminocoumarin-3-carboxamides. As a result a systematic series of identified derivatives has been obtained. The structures of synthesized compounds have been proven by the data of ¹H NMR-spectroscopy and mass-spectrometry. A series of 3-(5-(3-(3,7,12-threehydroxy-10,13- dimetilgeksadekagidro-1H-cyclopenta[a]phenanthrene-17-yl)butyl)-1,3,4-oxadiazol-2-yl)-2H-coumarin-2-ones have been synthesized and their spectral properties investigated to explore the possibility of using them as fluorescent labels. It was found that all compounds show fluorescence emission in the 420–510 nm range (quantum yields range from 0,02 to 0,58) which greatly depends on the position and donor strength of the coumarin core substituents.