A Synthetic Route to 3‐(Heteroaryl)‐7‐hydroxycoumarins Designed for Biosensing Applications

Abstract

A straightforward method to synthesize 3‐(2‐benzimidazolyl)‐7‐hydroxycoumarins, based on the condensation reaction of 7‐acetoxy‐3‐formylcoumarin with various C‐ and/or N‐substituted ortho‐phenylenediamine derivatives is presented. This unusual approach proved particularly effective for introducing different hydrophilic groups (carboxylic or sulfonic acids or trimethylalkylammonium moieties) onto the heteroaryl scaffold, leading to cyan‐green emitting coumarins that were both water‐soluble and strongly fluorescent under physiological conditions. The further extension of this condensation reaction to bis(2‐aminophenyl)diselenide enabled the first synthesis of 3‐(2‐benzoselenazolyl)‐7‐hydroxycoumarin. The potential utility of these new 7‐hydroxycoumarins was demonstrated through the synthesis and spectroscopic and analyte‐responsive behavior of fluorogenic probes suitable for sensing biologically relevant thiols and urokinase, a protease that plays a key role in cancer invasion and metastasis.

Dual enzyme-responsive “turn-on” fluorescence sensing systems based on in situ formation of 7-hydroxy-2-iminocoumarin scaffolds

“…21,22 Furthermore, bis--O--protected 2,4--dihydroxycinnamonitrile derivatives should be easily synthesised from cheap commercial starting materials (i. e., 2,4--dihydroxybenzaldehyde and malonitrile or benzothiazole--2--acetonitrile) and through a Knoevenagel--type condensation reaction. Indeed, 7-hydroxycoumarin derivatives are often more fluorescent than their 7--amino counterparts, particularly at physiological pH, and the facile functionalization of their C--3 position with an electron--withdrawing group (typically, a cyano group) or an heteroaryl substituent (e.g., 2--benzothiazolyl or 2-benzimidazolyl moiety) is an asset to red--shift their absorption/emission maxima, and to facilitate fluorescence detection in complex biological media.…”

New 3‐(Heteroaryl)‐2‐iminocoumarin‐based Borate Complexes: Synthesis, Photophysical Properties, and Rational Functionalization for Biosensing/Biolabeling Applications

“…Despite its lower reactivity,t his reagent was preferred over the more effective uronium-based coupling agent TSTU (2-succinimido-1,1,3,3-tetramethyluronium tetrafluoroborate) because the latter is known to readily react with the 7-OH group of 7-hydroxycoumarin derivatives. [13] BSA was labeled after overnight incubation with either a1 5-or 30-foldm olar excess of the NHS ester in phosphate buffer (pH 7.0 or pH 7.7) at 4 8C. The "Borico"-conjugated proteinsB SA-8 were washed with an ultra-centrifugal filter device (30 kDa cut-off) to remove most of the excess of free unbound" 7-hydroxy-Borico" dye.…”

“…[9][10][11] Interestingly, pertinent studies concerning their solubilization in water and site-specific introduction of ab ioconjugatable handle within their core structure have recently been published. [12,13] Furthermore, the appended N-aryl moiety introduced through the transimination step could be exploited both to introduce further chemical diversity into the targeted fluorescent "Borico" scaffold and to increaset he stability of its BF 2 -chelate moiety. In this article, we report the practical implementation of this synthetic strategy for the preparation of such "7-hydroxyBorico"d erivatives, the 3-heteroaryl substituent of which is either ab enzothiazole or ab enzimidazole moiety (Scheme 2).…”

“…Ha nd 13 CNMR spectra were recorded on aB ruker DPX 300 spectrometer (Bruker,W issembourg, France). Chemical shifts are expressed in parts per million (ppm) using the residual solvent peak for calibration.…”

Coumarin heterocyclic derivatives: chemical synthesis and biological activity

“…99 As suggested by other authors, 100 this additive may favor the in situ formation of the more reactive bisulte adduct 115. This approach proved particularly effective for introducing different hydrophilic groups, leading to coumarins that were both water-soluble and strongly uorescent under physiological conditions.…”