Oligosaccharide Sensing in Aqueous Media by Porphyrin–Curdlan Conjugates: A Prêt‐á‐Porter Rather Than Haute‐Couture Approach

Abstract

Saccharide sensing in aqueous media is an intriguing but challenging goal in current chemistry. Herein we report the oligosaccharide-sensing behavior of newly synthesized porphyrin-curdlan conjugates, which are random coils in DMSO but become globules in aqueous solutions to induce circular dichroism (ICD) in the biologically accessible spectral region due to the conformational fixation of porphyrin reporters. The magnitude of ICD was significantly varied specifically in the presence of acarbose, a drug for type-2 diabetes, enabling us to detect the aminosaccharide at concentrations down to 200 μm. This result demonstrates that the prêt-á-porter approach, using less-defined reporter-curdlan conjugates, is more advantageous than the traditional haute-couture approach with highly sophisticated hosts in particular in oligosaccharide sensing.

Helical polysaccharides

“…Molecular recognition and catalysis are two of the main fields that could benefit from these new materials. One step in this direction has recently been made; helical polysaccharides were recently applied for molecular recognition of drugs in aqueous solution . In addition, the application of polysaccharides in photochirogenesis has been reported, in which the polysaccharide helical structure, intrinsically chiral, is exploited to achieve stereocontrol .…”

Oligosaccharide Sensing in Aqueous Media Using Porphyrin–Curdlan Conjugates: An Allosteric Signal-Amplification System

“…For a better understanding of the acarbose sensing behavior in aqueous media by using the Por-Cur sensors, H 2 Por-Cur 3.6 ( 1 ) and AlPor-Cur 8.9 ( 2 ) (Figure d) were designed as the different porphyrin DS for comparison reasons with the previous data obtained from H 2 Por-Cur 5.2 and AlPor-Cur 3.3 . The synthetic routes for all of the porphyrin reporters and Cur conjugates reported in the present study were summarized in Scheme .…”

“…Using Nature’s sophisticated technique, ,− ,,,, spreading a highly ordered multiple hydrogen-bonding and CH−π interaction network in a supramolecular architecture seems quite promising. In order to construct such a “smart” oligosaccharide sensor, we focus on polysaccharide curdlan (Cur; Figure a) as an adjustable hydrogen-bonding recognition moiety for oligosaccharides. ,− , …”

“…Acarbose, an inhibitor of α-glucosidase releasing glucose from higher carbohydrates, is a world-famous drug to treat type-2 diabetes and obesity; hence for preventing side effects, highly selective and sensitive sensing of acarbose in blood, i.e., an aqueous medium, is one of the most significant landmarks in medical practice . Recently, we have constructed more sensitive acarbose Cur sensors by replacing the DABz reporter with porphyrin chromophores (Figure d; two of the top) . The random coil of the modified Cur sensors in DMSO reversibly converts to a globule upon addition of water (Figure f, top), and therefore the acarbose molecule is included in the globule to form an expanded globule Cur-saccharide coaggregation during the random coil-to-globule conversion (Figure f, bottom).…”

“…Since conformational changes of the attached chromophores in the Cur globule transform into CD signals, we expected a more sensitive readout of the complexation-induced structural changes through exciton couplings by using porphyrin chromophores possessing a characteristic Soret band, rather than the DABz reporter. Eventually, the limit of detection (LOD) was greatly improved from 10 mM for DABz-Cur, to 5 mM for H 2 Por-Cur 5.2 , and to 0.2 mM for AlPor-Cur 3.3 . , …”