Synthesis Of Glucosides Research Articles

Stereoselective Synthesis of C-Aryl-α-Glycosides by Reductive C(sp2)–C(sp3) Cross-Coupling Reaction

Abstract C-Aryl glycosides have attracted considerable interest as biologically active natural products and as O-aryl glycoside mimetics in drug discovery. Here, we describe a straightforward synthesis of C-aryl glycosides by photoredox/Ni dual-catalyzed reductive cross-coupling between glycosyl bromides and aryl bromides. This methodology enables a highly α-stereoselective synthesis of C-aryl glucosides, galactosides, and mannosides.

Total synthesis of nepodin and torachrysone glucosides: Evidence for naturally occurring l-glucosides

The first concise synthesis of nepodin-1-O-β-d-glucopyranoside (D-1) and its l-glucopyranoside (L-1), as well as torachrysone-1-O-β-d-glucopyranoside (D-2) and its l-glucopyranoside (L-2), was achieved via Fries rearrangement and selective glycosylation. Spectral data, particularly the specific rotation signs of the synthetic l-glucosides, correlated with those of natural products previously isolated from Rumex dentatus. This confirms the presence of naturally occurring l-glucosides, L-1 and L-2, identified through synthetic approaches.

Mutability landscape guided engineering of a promiscuous microbial glycosyltransferase for regioselective synthesis of salidroside and icariside D2

Microbial glycosyltransferases efficiently synthesize glucosides and have garnered increasing interest. However, limited regioselectivity has impeded their broad application, particularly in the pharmaceutical industry. In this study, the UDP-glycosyltransferase YjiC from Bacillus licheniformis (BlYjiC) was engineered to achieve the bidirectional regioselective glycosylation of tyrosol and its derivatives. Initially, site-directed saturation mutagenesis was performed on two newly identified substrate-binding cavities in the acceptor pocket of BlYjiC to provide a comprehensive blueprint of the interplay between mutations and function (mutability landscape). Iterative saturation mutagenesis was performed, guided by the mutability landscape. Two highly regioselective mutants M6 (M112L/I325Y/L70R/Q136E/I67E/M77R) and M2’ (M112D/I62L) were generated, exhibiting >99 % regioselectivity toward the alcoholic and phenolic hydroxyl of tyrosol, respectively, compared with the wild-type (product mixture: 51:49 %). Both mutants exhibited excellent regioselectivity toward several dihydroxy phenolic substrates, offering valuable biocatalysts for the regioselective synthesis of glucosides. Their application was confirmed in a short synthesis of salidroside (3.6 g/L) and icariside D2 (2.4 g/L), which exhibited near-perfect regioselectivity. This study provides valuable insights into future protein engineering of similar enzymes and opens new avenues for their practical applications.

Preparation of porous sulfated zirconia with deep eutectic solvents for improved catalytic efficiency in the synthesis of biodegradable alkyl glucosides

In this study, a deep eutectic solvent (DES) system, comprising choline chloride and urea, was employed to synthesize sulfated zirconia (SZ) solid acid catalysts. The characteristics and efficacy of the SZ catalysts synthesized using this DES system were meticulously evaluated using a suite of analytical techniques, including nitrogen sorption, X-ray diffraction (XRD), pyridine adsorption infrared spectroscopy (Py-IR), X-ray photoelectron spectroscopy (XPS), and ammonia temperature-programmed desorption (NH3-TPD). The research also focused on analyzing the distinctive role and characteristics of the DES in the preparation of SZ. When compared with conventional aqueous phase precipitation methods, the SZ catalysts synthesized in the DES environment exhibited enhanced properties, such as an increased specific surface area, a higher density of acidic sites, and a larger proportion of potent acid centers. These improvements led to augmented catalytic activity in the reaction between alkyl alcohols and glucose. Moreover, the SZ catalysts prepared with DES demonstrated superior reaction stability and reusability, which can be attributed to the well-dispersed strong acid centers. The study uncovered that the components of the DES significantly contribute as microporous templating agents during the formation of SZ, assisting in the stabilization of the defect sites in the zirconia precursor. These components eventually evolved into prominently exposed surface strong acid centers during the stages of acidification and calcination, enhancing mass transfer efficiency and the acidic catalytic properties of the catalysts.

Enzymatic Synthesis of α-Glucosyl-Baicalin through Transglucosylation via Cyclodextrin Glucanotransferase in Water.

Baicalin is a biologically active flavone glucuronide with poor water solubility that can be enhanced via glucosylation. In this study, the transglucosylation of baicalin was successfully achieved with CGTases from Thermoanaerobacter sp. and Bacillus macerans using α-cyclodextrin as a glucosyl donor. The synthesis of baicalin glucosides was optimized with CGTase from Thermoanaerobacter sp. Enzymatically modified baicalin derivatives were α-glucosylated with 1 to 17 glucose moieties. The two main glucosides were identified as Baicalein-7-O-α-D-Glucuronidyl-(1→4')-O-α-D-Glucopyranoside (BG1) and Baicalein-7-O-α-D-Glucuronidyl-(1→4')-O-α-D-Maltoside (BG2), thereby confirming recent findings reporting that glucuronyl groups are acceptors of this CGTase. Optimized conditions allowed for the attainment of yields above 85% (with a total glucoside content higher than 30 mM). BG1 and BG2 were purified via centrifugal partition chromatography after an enrichment through deglucosylation with amyloglucosidase. Transglucosylation increased the water solubility of BG1 by a factor of 188 in comparison to that of baicalin (molar concentrations), while the same value for BG2 was increased by a factor of 320. Finally, BG1 and BG2 were evaluated using antioxidant and anti-glycation assays. Both glucosides presented antioxidant and anti-glycation properties in the same order of magnitude as that of baicalin, thereby indicating their potential biological activity.

Enzymatic synthesis, characterization and molecular docking of a new functionalized polyphenol: Resveratrol-3,4′-⍺-diglucoside

Transglucosylation of resveratrol by the Q345F variant of sucrose phosphorylase from Bifidobacterium adolescentis (BaSP) was extensively studied during the last decade. Indeed, Q345F is able to catalyze the synthesis of resveratrol-3-O-⍺-D-glucoside (RES-3) with yield up to 97% using a cost-effective glucosyl donor, sucrose (Kraus et al., Chemical Communications, 53(90), 12182–12184 (2017)). Despite the fact that two further products were detectable in low amounts after glucoside synthesis, they were never identified. Here, we isolated and fully characterized one of those two minor products: resveratrol-3,4′-O-⍺-D-diglucoside (RES-3,4′). This original compound had never been described before. Using bioinformatics models, we successfully explained the formation of this diglucosylated product. Indeed, with RES-3 as acceptor substrate, Q345F is able to transfer a glucosyl moiety in position 4′-OH, what had been reported as impossible in the literature. The low yield observed is due to the steric hindrance into the catalytic site between RES-3 and residues Tyr132 and Tyr344. Nevertheless, the substrate orientation in the active site is favored by stabilizing interactions. Ring A of RES-3 bearing the diol moiety is stabilized by hydrogen bonds with residues Asp50, Arg135, Asn347 and Arg399. Hydroxyl group OH-4′ shares hydrogen bonds with the catalytic residues Asp192 and Glu232. Multiple hydrophobic contacts complete the stabilization of the substrate to favor the glucosylation at position 4′. Understanding of the mechanisms allowing the glucosylation at position 4′ of resveratrol will help the development of enzymatic tools to target and control the enzymatic synthesis of original ⍺-glucosylated polyphenols with high added value and better biodisponibility.

Strategy for the Synthesis of C-Aryl Glucosides as Sodium Glucose Cotransporter 2 Inhibitors

Strategy for the Synthesis of C-Aryl Glucosides as Sodium Glucose Cotransporter 2 Inhibitors

Engineering of Cyclodextrin Glycosyltransferase through a Size/Polarity Guided Triple-Code Strategy with Enhanced α-Glycosyl Hesperidin Synthesis Ability.

Hesperidin, a flavonoid enriched in citrus peel, can be enzymatically glycosylated using CGTase with significantly improved water solubility. However, the reaction catalyzed by wild-type CGTase is rather inefficient, reflected in the poor production rate and yield. By focusing on the aglycon attacking step, seven residues were selected for mutagenesis in order to improve the transglycosylation efficiency. Due to the lack of high-throughput screening technology regarding to the studied reaction, we developed a size/polarity guided triple-code strategy in order to reduce the library size. The selected residues were replaced by three rationally chosen amino acids with either changed size or polarity, leading to an extremely condensed library with only 32 mutants to be screened. Twenty-five percent of the constructed mutants were proved to be positive, suggesting the high quality of the constructed library. Specific transglycosylation activity of the best mutant Y217F was assayed to be 935.7 U/g, and its kcat/KmA is 6.43 times greater than that of the wild type. Homology modeling and docking computation suggest the source of notably enhanced catalytic efficiency is resulted from the combination of ligand transfer and binding effect. IMPORTANCE Size/polarity guided triple-code strategy, a novel semirational mutagenesis strategy, was developed in this study and employed to engineer the aglycon attacking site of CGTase. Screening pressure was set as improved hesperidin glucoside synthesis ability, and eight positive mutants were obtained by screening only 32 mutants. The high quality of the designed library confirms the effectiveness of the developed strategy is potentially valuable to future mutagenesis studies. Mechanisms of positive effect were explained. The best mutant exhibits 6.43 times enhanced kcat/KmA value and confirmed to be a superior whole-cell catalyst with potential application value in synthesizing hesperidin glucosides.

Chemical synthesis and tyrosinase inhibitory activity of resorcinol alkyl glucosides, hydroxyalkyl resorcinols, and alkyl resorcinols

To develop novel tyrosinase inhibitors, resorcinol alkyl glucosides 7–12 were synthesized via the Wittig and/or Horner-Wadsworth-Emmons reactions with Koenigs-Knorr glycosylation as the key step. Half maximal inhibitory concentrations (IC50) of 35.9–0.39 µM were observed for 7–12 for the tyrosinase-catalyzed oxidation. Tyrosinase inhibitory activity of hydroxyalkyl resorcinols 13–18 and alkyl resorcinols 19–24 were also evaluated to investigate the effect of sugar in their structures. As a result, the IC50s of 13–18 and 19–24 were 9.27–0.32 µM and 1.58–0.53 µM, respectively. Most of the derivatives became more potent with the increasing length of the alkyl chain. The gap in the activities between the C2 and C3 analogs was decreased in the order: resorcinol alkyl glucosides>hydroxyalkyl resorcinols>alkyl resorcinols. It indicates that the sugar and hydroxy groups interfered in the functions when they were adjacent to the resorcinol ring. C14 analog 22 (IC50 = 0.81 µM) with the poor water solubility showed slightly weak activity compared with the C10 analog 21 (IC50 = 0.53 µM). Thus, the modification of a prescribed distance, at least, the C3 alkyl spacer, between the resorcinol ring and sugar or hydroxy group is a requisite to effectively design a potent, hydrophilic tyrosinase inhibitor.

Regulation of cyanogenic glucosides in wild and domesticated Eusorghum taxa.

Domesticated sorghum (Sorghum bicolor [L.] Moench subsp. bicolor) diverts significant amounts of nitrogen away from primary metabolism to the synthesis of cyanogenic glucosides (CNglc) - specialized metabolites that release toxic hydrogen cyanide (HCN). Our aim was to identify the point in the genus Sorghum Moench at which plants gained the ability to maintain hazardous concentrations of cyanogenic glucosides in their leaves into maturity (HCN potential >0.4 mg g-1 ). This ability occurs in domesticated sorghum (in the subgenus Eusorghum), but not in wild taxa in other Sorghum subgenera. Eight accessions from the subgenus Eusorghum were grown in a common garden: an improved sorghum line, five sorghum landraces, the crop's wild progenitor (S. bicolor subsp. verticilliflorum [Steud.] de Wet ex Wiersema & J. Dahlb.) and wild Sorghum propinquum (Kunth) Hitchc. HCN potential was measured in plants (n = 80) at the three-leaf stage and at 6 weeks old. All study accessions, including the wild taxa, had hazardous CNglc concentrations in the leaves at both the three-leaf stage (mean HCN potentials > = 2.5 mg g-1 ) and at 6 weeks old (mean HCN potentials > = 0.68 mg g-1 ), greatly contrasting the much lower mature leaf HCN potentials previously found in wild Sorghum taxa outside subgenus Eusorghum (generally <= 0.01 mg g-1 ). Our results suggest that the ability to maintain hazardous leaf HCN potentials into maturity might have arisen during the divergence of Eusorghum from other Sorghum subgenera, rather than during the speciation or domestication of S. bicolor, and highlights the value of utilizing Sorghum taxa outside Eusorghum in efforts to improve the crop safety of sorghum.

Enzymatic Synthesis of Alkyl Glucosides byβ‐Glucosidases in a 2‐in‐1 Deep Eutectic Solvent System

AbstractAlkyl glycosides are biodegradable surfactants with excellent physico‐chemical properties. Although their wide‐range application is considered ecofriendly, their synthesis is not due to the need for toxic organic solvents and corrosive acids as catalysts. Moreover, chemical synthesis results in complex mixtures rather than defined compounds. To overcome both disadvantages as well as the limited solubility of sugars in organic solvents, a highly selective enzymatic synthesis was set up with aβ‐glucosidase condensing D‐glucose and different fatty alcohols in a deep eutectic solvent.

Enzymatic Synthesis of Novel Vitexin Glucosides.

Vitexin is a C-glucoside flavone that exhibits a wide range of pharmaceutical activities. However, the poor solubility of vitexin limits its applications. To resolve this limitation, two glycoside hydrolases (GHs) and four glycosyltransferases (GTs) were assayed for glycosylation activity toward vitexin. The results showed that BtGT_16345 from the Bacillus thuringiensis GA A07 strain possessed the highest glycosylation activity, catalyzing the conversion of vitexin into new compounds, vitexin-4′-O-β-glucoside (1) and vitexin-5-O-β-glucoside (2), which showed greater aqueous solubility than vitexin. To our knowledge, this is the first report of vitexin glycosylation. Based on the multiple bioactivities of vitexin, the two highly soluble vitexin derivatives might have high potential for pharmacological usage in the future.

Optimized enzymatic synthesis of digestive resistant anomalous isoquercitrin glucosides using amylosucrase and response surface methodology.

Diverse flavonoid glycosides are present in the plant kingdom. Advanced technologies have been utilized to synthesize glycosyl flavonoids which exhibit good physicochemical characteristics. Previously, novel isoquercitrin (IQ) mono-, di-, and tri-glucosides (IQ-G1', IQ-G2', and IQ-G3'; atypical IQ-Gs (IQ-Gap)) were synthesized through the reaction of amylosucrase. Here, the regio-selective transglycosylation yields were predicted using response surface methodology for three variables (glucose donor (sucrose; 100-1500mM), glucose acceptor (IQ; 100-400µM), and pH (5.0-8.8)) using 1 unit/mL of enzyme at 45°C; then, the optima were verified according to the experimental responses. Acidity (pH 5.0) was a major contributor for IQ-G1' production (> 50%), and high sucrose concentration (1500mM) limited IQ-G3' production (< 15%). Low sucrose concentration (100mM) at pH 7.0 promoted higher glycosyl IQ production (> 30%). Time-course production of IQ-Gap showed an exponential growth with different rates. IQ-Gap was stable under the simulated intestinal conditions compared with typical IQ-Gs. Digestive stable IQ-Gap can be effectively synthesized by modulating reaction conditions; thereby, atypical glycosyl products may contribute to the elucidation of nutraceutical potential of flavonoid glycosides. KEY POINTS: •Predictions of RSM were validated for the regio-selective IQ-Gap production. • Time course changes of IQ-Gap indicate non-processive glycosylation of DGAS. • IQ-Gap exceed typical IQ-G in digestive stability at simulated intestinal condition.

First total syntheses of four natural bioactive glucosides

The efficient total syntheses of four biologically interesting natural glucosides Ethylconiferin, Butylconiferin, 2’-Butoxyethylconiferin and Balajaponin B, have been achieved for the first time starting from commercially available Vanilline via concise reaction sequence of 8–10 steps with the overall yield of 26–41%. This work definitely laid the foundation for the further pharmacological study of this kind of natural compounds. Meanwhile, currently developed approach could be used as a general synthetic strategy for the syntheses of other monolignol glucosides and their derivatives, and provides an opportunity for further study of the structure-activity relationship of this kind of glucosides.

A new synthetic biology approach for the production of curcumin and its glucoside in Atropa belladonna hairy roots

Curcumin has ignited global interest as an elite drugable molecule, owing to its time-honoured pharmacological activities against diverse human ailments. Limited natural accessibility and poor oral bioavailability caused major hurdles in the curcumin-based drug development process. We report the first successful testimony of curcumin and its glucoside synthesis in Atropa belladonna hairy roots (HR) through metabolic engineering. Re-routing the inherent biosynthetic precursors of the phenylpropanoid pathway of A. belladonna by heterologous expression of key curcumin biosynthetic pathway genes (i.e., Diketide-CoA synthase-DCS and Curcumin synthase-CURS3) and glucosyltransferase gene (CaUGT2) resulted in the production of curcumin and its glucoside in HR clones. Under shake-flask cultivation, the PGD2-HR1clone bearing DCS/ CURS3 genes showed the maximum curcumin yield (180.62 ± 4.7 μg/g DW), while the highest content of curcumin monoglucoside (32.63 ± 2.27 μg/g DW) along with curcumin (67.89 ± 2.56 μg/g DW) were noted in the PGD3-HR3 clone co-expressing DCS/CURS3 and CaUGT2 genes. Bioreactor up-scaling showed yield improvements in the PGD2-HR1 (2.3 fold curcumin) and the PGD3-HR3 clone (0.9 and 1.65 folds of curcumin-monoglucoside and curcumin respectively). These findings proved the advantageous use of HR cultures as the production source for curcumin and its glucoside, which remained unexplored so far.

β-glucosidase from Streptomyces griseus: Ester hydrolysis and alkyl glucoside synthesis in the presence of Deep Eutectic Solvents

Deep Eutectic Solvents (DES) are ionic liquid analogs that have attracted considerable attention as green solvents for biocatalytic transformations. The use of DES as part of a ‘solvent engineering’ approach to enhance enzyme stability holds great promise since they are biodegradable, relatively inexpensive and environmentally safe media for enzyme reactions. However, the behaviour of specific enzymes in such solvents is complex; some enzymes are inhibited in DES, while others appear to be activated.Glucosidases are among the most widely used enzymes for commercial chemoenzymatic synthesis. In particular, their application in the synthesis of biodegradable alkyl glucosides by reverse hydrolysis is of great interest. Previous work in this laboratory identified Streptomyces griseus glucosidase (Sgβgl) as an interesting enzyme for biotechnological applications. In this study, we examined its behaviour in the presence of DES as a co-solvent using choline chloride as hydrogen bond donor and using glycerol, glucose and urea as hydrogen bond acceptors. We show that Sgβgl activity depends on both the nature of DES components, and their ratio in the eutectic mixture, as well as the water content of the reaction medium. A choline chloride/glycerol DES mixture at a level of 40% (v/v) caused activation of Sgβgl and increased its optimum temperature from 70 to 80 ​°C: it also led to a striking increase in its thermostability, doubling its half-life at 60 ​°C and almost tripling its half-life at 80 ​°C.The synthesis of alkyl glucosides was explored using DES as a co-solvent. In the presence of DES, Sgβgl catalysed the formation of a range of alkyl glucosides. The presence of DES resulted in enhanced product yield, which was observed to increase with increasing temperature, up to 60 ​°C.These studies show that the application of DES at relatively low % (v/v) levels can dramatically effect enzyme activity and stability. Specifically, enhanced thermostability can significantly increase the operating range for glucosidases for biocatalytic applications. Solvent engineering offers a simple and effective way to enhance glucosidase stability and will be useful as an alternative and/or adjunct to more complex methods such as immobilisation or protein engineering.

Synthesis of eugenol-derived glucosides and evaluation of their ability in inhibiting the angiotensin converting enzyme

We report here a series of glucosides which are active as inhibitors of the angiotensin converting enzyme (ACE). They are structurally related to the natural compound eugenol and exhibited significant inhibition values. Their syntheses were expeditious and we could obtain informative docking plots of them complexed to this enzyme. A glucoside derived from eugenol, carrying a carboxylic group in the aglycone, was the most active of them (with an IC50 of 0.4 mM) and showed good binding energies in docking studies with ACE. Moreover, computational prediction of toxicity risks, physicochemical properties and drug score show that the glucoside derivative of eugenol is a suitable compound for optimisation studies aimed at finding new drug candidates.

Divergent Synthesis of Natural Benzyl Salicylate and Benzyl Gentisate Glucosides.

Herein is reported the first total synthesis of benzyl salicylate and benzyl gentisate glucosides present in various plant species, in particular the Salix genus, such as Populus balsamifera and P. trichocarpa. The method permits the synthesis of several natural phenolic acid derivatives and their glucosides starting from salicylic or gentisic acid. The divergent approach afforded access to three different acetylated glucosides from a common synthetic intermediate. The key step in the total synthesis of naturally occurring glycosides-the selective deacetylation of the sugar moiety-was achieved in the presence of a labile benzyl ester group by employing mild deacetylation conditions. The protocol permitted synthesis of trichocarpine (4 steps, 40% overall yield), isotrichocarpine (3 steps, 51% overall yield), trichoside (6 steps, 40% overall yield), and deoxytrichocarpine (3 steps, 42% overall yield) for the first time (>95% purity). Also, the optimized mild deacetylation conditions allowed synthesis of 2-O-acetylated derivatives of all four glycosides (5-17% overall yield, 90-95% purity), which are rare plant metabolites.

The first synthesis of peracetyl glycosyl aurone derivatives and aurone glucosides

Aurones, a sub-class of the flavonoids with proven therapeutic importance, also exist in variously glycosylated forms. Although a large number of glycosylated aurone derivatives have been isolated from plant sources, no syntheses have been reported yet. Inspired from this gap, here we report the first synthesis of peracetylated glycosyl derivatives of synthetic aurones. The direct O-glycosylation was achieved by reacting 6-hydroxy aurones with 2, 3, 4, 6-tetra-O-acetyl-α-D glucopyranosyl bromide in the presence of a phase transfer catalyst tetrabutylammonium bromide (TBAB). The successful synthesis of aurone glycosides (33 examples) in 60–92% yield will benefit the synthesis of combinatorial libraries of glycosylated aurones for their biological study and comparison with non-glycosylated aurones.

Synthesis of Butyl-β-D-Galactoside in the Ternary System: Acetone/1-Butanol/Aqueous Solution.

The enzymatic synthesis of short-tailed alkyl glucosides is generally carried out in an aqueous-organic biphasic reaction medium with a rather low fatty alcohol concentration in the aqueous phase (where the synthesis occurs). Thus, hydrolytic reactions have a significant impact on the synthesis performance. Given this background, the use of acetone as cosolvent was studied for the synthesis of butyl-β-galactoside with Aspergillus oryzae β-galactosidase. The liquid–liquid equilibrium of the reaction mixture components (acetone/1-butanol/aqueous solution) was determined and the single- and two-phase regions were defined at 30, 40, and 50°C. It was observed that the liquid–liquid equilibrium of the ternary system acetone/1-butanol/water differs significantly from the one obtained using an aqueous solution (50 mM McIlvaine buffer pH 4.5; 5 g L–1) instead of water. This is mainly because of the salting-out effect of the buffer; nevertheless, the presence of lactose also altered the equilibrium. Having this in mind, the effects of temperature (30 and 50°C) and reaction mixture composition were assessed. Three general conditions were evaluated: single-phase ternary system (30% acetone), two-phase ternary system (10% acetone) and two-phase binary system (0% acetone). Acetone had a deleterious effect on enzyme stability at 50°C, leading to low reaction yields. However, no enzyme deactivation was detected at 30°C. Moreover, a reaction yield of 0.98 mol mol–1 was attained in the 30/50/20% (w/w) mixture of acetone/1-butanol/aqueous solution. This very high yield can be explained by the huge increase in the concentration of 1-butanol and the reduction of water activity. The synthesis was carried out using also the β-galactosidase immobilized in glyoxal-agarose and amino-glyoxal-agarose, and by aggregation and crosslinking. In the case of agarose-derived catalysts, two average particle diameters were assessed to evaluate the presence of internal mass transfer limitations. Best yield (0.88 mol mol–1) was obtained with glyoxal-agarose derivatives and the particle size had non-effect on yield. The chemical structure of butyl-β-galactoside was determined by NMR and FT-IR.