pH-Dependent Photoinduced Interconversion of Furocoumaric and Furocoumarinic Acids

Abstract

Photo-controlled or photo-regulated molecules, especially biologically active and operating in physiological conditions, are in steady demand. Herein, furocoumaric and furocoumarinic acids being (Z/E)-isomers relative to each other were obtained in two stages starting from psoralen: the alkaline solvolysis of psoralen led to furocoumaric acid, which was further Z → E photoisomerized (365 nm) to furocoumarinic acid. The kinetics of Z → E photoisomerization was monitored by HPLC and UV-vis spectrophotometry. Photophysical characteristics in the aqueous phase for both acids, as well as the reversibility of (Z/E) photoisomerization process, were also assessed. Furocoumarinic acid was found to be visibly fluorescent at pH 2.0–12.0, with the maxima of fluorescence emission spectra being pH-dependent. The reverse E → Z photoisomerization predicted by quantum chemistry calculations as energetically favorable for the monoanionic form of furocoumarinic acid was proved in the experiment while being complicated by pyrone ring closure back to psoralen in acidic and neutral conditions. The preparative synthesis of furocoumarinic acid outlined in this work is particularly valuable in view of a wide range of pharmacological effects previously predicted for this compound.

Efficient Synthesis of Fluorescent Coumarins and Phosphorous-Containing Coumarin-Type Heterocycles via Palladium Catalyzed Cross-Coupling Reactions

“…This statement was based on the NMR spectra where the characteristic signals for the protons at position C-4 for neither the 5 , 3a, or 7 were found. This might be due to opening of the lactone ring in the presence of ethanol/base as it was previously reported [ 42 , 43 , 49 , 50 , 51 , 52 ].…”

Twice as Nice: The Duff Formylation of Umbelliferone Revised

“…The chosen acidic pH value corresponded to a pH range where 7-OH groups of both 8-FUmb and 6-FUmb were fully protonated. The alkaline conditions were mild enough to deprotonate the 7-OH groups affording anionic form of both umbelliferones, but not too alkaline to induce a solvolytic pyrone ring opening [29].…”