Chemical functionalization of oligodeoxynucleotides with multiple boronic acids for the polyvalent binding of saccharides

Diastereoselective Synthesis of the Borylated d-Galactose Monosaccharide 3-Boronic-3-Deoxy-d-Galactose and Biological Evaluation in Glycosidase Inhibition and in Cancer for Boron Neutron Capture Therapy (BNCT)

Drug leads with a high Fsp³ index are more likely to possess desirable properties for progression in the drug development pipeline. This paper describes the development of an efficient two-step protocol to completely diastereoselectively access a diethanolamine (DEA) boronate ester derivative of monosaccharide d-galactose from the starting material 1,2:5,6-di-O-isopropylidene-α-d-glucofuranose. This intermediate, in turn, is used to access 3-boronic-3deoxy-d-galactose for boron neutron capture therapy (BNCT) applications. The hydroboration/borane trapping protocol was robustly optimized with BH₃.THF in 1,4-dioxane, followed by in-situ conversion of the inorganic borane intermediate to the organic boron product by the addition of DEA. This second step occurs instantaneously, with the immediate formation of a white precipitate. This protocol allows expedited and greener access to a new class of BNCT agents with an Fsp³ index = 1 and a desirable toxicity profile. Furthermore, presented is the first detailed NMR analysis of the borylated free monosaccharide target compound during the processes of mutarotation and borarotation.

Surface Engineered PLGA Nanoparticle for Threshold Responsive Glucose Monitoring and "Self-Programmed" Insulin Delivery

We have developed a reversible, biocompatible, "self-programmed" PLGA [poly(lactic-co-glycolic acid)] nanoparticle-based optical biosensor capable of sensing and continuous monitoring of glucose above the physiologically relevant threshold value (100-125 mg/dL) as well as "on-demand" insulin delivery via an "On-Off" technique. We have carefully surface engineered the PLGA nanoparticle using amino dextran-fluorescein (A-DexFl) and amino-phenyl boronic acid (A-PBA) to exploit the binding affinity of boronic acids with that of cis-1,2 diols of dextran/glucose. Initially, the dextran chains wrap the nanoparticle surface due to its high affinity toward A-PBA (K_b = 6.1 × 10⁶ M^-1). The close proximity of the fluorophores with that of A-PBA quenches the fluorescence, resulting in an "Off" state. On the addition of glucose, it competes with A-DexFl to bind with A-PBA. Above a certain threshold concentration of glucose, the binding affinity overcomes (K_b = 6.3 × 10⁷ M^-1) the dextran-A-PBA binding. This opens-up the wrapped A-DexFl chains from the nanoparticle surface and results in an increased distance between the fluorophore and A-PBA, triggering the "On" state. The activation of the On-Off state can be finely tuned in the desired range of physiologically relevant glucose concentrations by varying the ligand ratios on the PLGA surface. The nanoparticle core has also been used as an insulin reservoir to trigger the drug release in the "On" state. We have obtained ∼53% encapsulation efficiency and ∼20% loading efficiency for insulin loading. Once the glucose concentration falls beyond the detection range, the dextran chains collapse on the nanoparticle surface with a suspension in drug release. The process is solely controlled by the competition and multivalent binding affinity between glucose, A-DexFl, and A-PBA, which allows it to be "self-programmed" and "self-regulated" with continuous monitoring up to 8-10 cycles over a 72 h time period. A sustained drug release has been found with ∼70% of released drug over a period of 72 h, although this release is insignificant in the absence of glucose. Several control experiments have been performed to optimize the sensor design.

Nanogel receptors for high isoelectric point protein detection: influence of electrostatic and covalent polymer-protein interactions

An aldehyde acrylate-based functional monomer was incorporated into poly(N-isopropylacrylamide-co-methacrylic acid) nanogels for use as protein receptors. The aldehyde component forms dynamic imines with surface exposed lysine residues, while carboxylic acid/carboxylate moieties form electrostatic interactions with high isoelectric point proteins. Together, these interactions effect protein adsorption and recognition.

The challenges of glycan recognition with natural and artificial receptors

Glycans - simple or complex carbohydrates - play key roles as recognition determinants and modulators of numerous physiological and pathological processes. Thus, many biotechnological, diagnostic and therapeutic opportunities abound for molecular recognition entities that can bind glycans with high selectivity and affinity. This review begins with an overview of the current biologically and synthetically derived glycan-binding scaffolds that include antibodies, lectins, aptamers and boronic acid-based entities. It is followed by a more detailed discussion on various aspects of their generation, structure and recognition properties. It serves as the basis for highlighting recent key developments and technical challenges that must be overcome in order to fully deal with the specific recognition of a highly diverse and complex range of glycan structures.

Boronic Derivatization of Monoacylglycerol and Monitoring in Biofluids

Monoacylglycerols (MAGs) are active mediators involved in multiple biological processes closely related to the pathological development of diabetes, obesity, and cancers. Sensitive and unambiguous detection of MAGs is thus essential; however, previous methods are both indirect and labor-intensive. Herein, we developed a straightforward approach by derivatization of MAGs with 3-nitrophenylboronic acid (3-NPB) for sensitive and selective analysis in cell lysates, tissues, and serums by mass spectrometry (MS). Reaction occurring between boronic acid and cis-diol moiety of MAGs blocked the formation of multiple adduct ions and tuned MAGs to negatively charged carrying species. In addition, the characteristic isotopic distribution of boron specialized the presence of modified MAGs in MS and led to distinctive identification. To eliminate endogenous interferences, we further introduced isotopic labeled d₄-NPB equivalently premixed with d₀-NPB to perform MAG derivatization, which resulted in rapid identification of modified MAGs in biofluids by displaying doublet peak characteristics. A comparative quantification approach was thereafter evoluted to reveal the amount variation of MAGs by d₀-NPB and d₄-NPB separately derivatized in different pathological tissue and serum samples. The presently developed NPB-based derivatization approach is expected to be essential in the metabolic study of MAG-related diseases.

Glucose-Responsive Trehalose Hydrogel for Insulin Stabilization and Delivery

Effective delivery of therapeutic proteins is important for many biomedical applications. Yet, the stabilization of proteins during delivery and long-term storage remains a significant challenge. Herein, a trehalose-based hydrogel is reported that stabilizes insulin to elevated temperatures prior to glucose-triggered release. The hydrogel is synthesized using a polymer with trehalose side chains and a phenylboronic acid end-functionalized 8-arm poly(ethylene glycol) (PEG). The hydroxyls of the trehalose side chains form boronate ester linkages with the PEG boronic acid cross-linker to yield hydrogels without any further modification of the original trehalose polymer. Dissolution of the hydrogel is triggered upon addition of glucose as a stronger binder to boronic acid (Kb = 2.57 vs 0.48 m-1 for trehalose), allowing the insulin that is entrapped during gelation to be released in a glucose-responsive manner. Moreover, the trehalose hydrogel stabilizes the insulin as determined by immunobinding after heating up to 90 °C. After 30 min heating, 74% of insulin is detected by enzyme-linked immunosorbent assay in the presence of the trehalose hydrogel, whereas only 2% is detected without any additives.

Hydrogen peroxide-triggered gene silencing in mammalian cells through boronated antisense oligonucleotides

Hydrogen peroxide (H2O2) is a reactive oxygen species (ROS) involved in various diseases, including neurodegeneration, diabetes, and cancer. Here, we introduce a new approach to use H2O2 to modulate specific gene expression in mammalian cells. H2O2-responsive nucleoside analogues, in which the Watson-Crick faces of the nucleobases are caged by arylboronate moieties, were synthesized. One of these analogues, boronated thymidine (dTB ), was incorporated into oligodeoxynucleotides (ODNs) using an automated DNA synthesizer. The hybridization ability of this boronated ODN to complementary RNA was clearly switched in the off-to-on direction upon H2O2 addition. Furthermore, we demonstrated H2O2-triggered gene silencing in mammalian cells using antisense oligonucleotides (ASOs) modified with dTB . Our approach can be used for the regulation of any gene of interest by the sequence design of boronated ASOs and will contribute to the development of targeted disease therapeutics.

Oligonucleotide-Based Systems for Input-Controlled and Non-Covalently Regulated Protein-Binding

Supramolecular chemists continuously take inspiration from complex biological systems to develop functional molecules involved in molecular recognition and self-assembly. In this regard, "smart" synthetic molecules that emulate allosteric proteins are both exciting and challenging, since many allosteric proteins can be considered as molecular switches that bind to other protein targets in a non-covalent fashion, and importantly, are capable of having their output activity controlled by prior binding to input molecules. This review discusses the foundations and passage toward the development of non-covalently operated oligonucleotide-based systems with protein-binding capacity that can be precisely regulated in an input-controlled manner.

Carbohydrate biomarker recognition using synthetic lectin mimics

Carbohydrate biomarkers play very important roles in a wide range of biological and pathological processes. Compounds that can specifically recognize a carbohydrate biomarker are useful for targeted delivery of imaging agents and for development of new diagnostics. Furthermore, such compounds could also be candidates for the development of therapeutic agents. A tremendous amount of active work on synthetic lectin mimics has been reported in recent years. Amongst all the synthetic lectins, boronic-acid-based lectins (boronolectins) have shown great promise. Along this line, four classes of boronolectins including peptide-, nucleic-acid-, polymer-, and small-molecule-based ones are discussed with a focus on the design principles and recent advances. We hope that by presenting the potentials of this field, this review will stimulate more research in this area.