Glucosyl Donor Research Articles

Potential Prebiotic Effects of Artemisia capillaris-Derived Transglycosylated Product.

This study investigated the impact of a transglycosylated product (ACOD) catalyzed by Leuconostoc mesenteroides MKSR dextransucrase using sucrose as a glucosyl donor and both maltose and Artemisia capillaris as acceptors on gut microbiota through fecal fermentation. ACOD promoted the growth of probiotics such as Lactiplantibacillus plantarum, Lacticaseibacillus casei, Lacticaseibacillus rhamnosus GG, and Leuconostoc mesenteroides MKSR, while inhibiting the growth of pathogenic bacteria such as Escherichia coli, E. coli O157:H7, Enterococcus faecalis, Listeria monocytogenes, Staphylococcus aureus, Shigella flexneri, Streptococcus mutans, Pseudomonas aeruginosa, and Bacillus cereus during independent cultivation. Fecal fermentation for 24 h revealed that ACOD significantly increased the production of short-chain fatty acids (SCFAs) compared to the blank and fructoooligosaccharide (FOS) groups. Specifically, ACOD led to a 4.5-fold increase in acetic acid production compared to FOSs and a 3.3-fold increase in propionic acid production. Both the ACOD and FOS groups exhibited higher levels of butyric acid than the blank. Notably, ACOD significantly modulated the composition of the gut microbiota by increasing the relative abundances of Lactobacillus and decreasing Escherichia/Shigella and Salmonella. In contrast, FOSs remarkably promoted the growth of Salmonella. These findings suggest that ACOD is a potential candidate for prebiotics that improve the intestinal environment by being actively used by beneficial bacteria.

The influence of acceptor acidity on hydrogen bond mediated aglycone delivery (HAD) through the picoloyl protecting group

AbstractThe outcome of glycosylation reactions heavily relies on the specific protecting group patterns employed on both the donor and acceptor molecules. The picoloyl (Pico) protecting group stands out as it can steer the stereoselectivity in a glycosylation reaction through hydrogen bond‐mediated aglycone delivery (HAD). This provides syn‐stereoselectivity, with respect to the stereochemistry of the Pico group, by forming a hydrogen bond between the incoming acceptor and the picoloyl ring nitrogen. We here probe how acceptor acidity influences the stereodirecting effect of the picoloyl protecting group. A set of 3‐O‐functionalized glucosyl and mannosyl donors, each bearing different protecting groups (picolinate, nicotinate, isonicotinate, and benzoate), were synthesized for systematic evaluation. For the 3‐O‐picoloyl‐glucose series, the picoloyl group exhibited minimal influence on stereoselectivity, with only weak nucleophiles showing a modest shift in selectivity for the 3‐O‐Pico protected glucosyl donor in comparison to the other C‐3‐acyl glucosides. In contrast, in the 3‐O‐picoloyl‐mannose series a much stronger β‐directing effect was observed, wherein more acidic acceptors led to increased β‐selectivity. The results provide insights into the complex interplay of acceptor acidity and glycosylation stereoselectivity mediated by the picoloyl protecting group.

Anomeric Triflates versus Dioxanium Ions: Different Product-Forming Intermediates from 3-Acyl Benzylidene Mannosyl and Glucosyl Donors.

Minimal structural differences in the structure of glycosyl donors can have a tremendous impact on their reactivity and the stereochemical outcome of their glycosylation reactions. Here, we used a combination of systematic glycosylation reactions, the characterization of potential reactive intermediates, and in-depth computational studies to study the disparate behavior of glycosylation systems involving benzylidene glucosyl and mannosyl donors. While these systems have been studied extensively, no satisfactory explanations are available for the differences observed between the 3-O-benzyl/benzoyl mannose and glucose donor systems. The potential energy surfaces of the different reaction pathways available for these donors provide an explanation for the contrasting behavior of seemingly very similar systems. Evidence has been provided for the intermediacy of benzylidene mannosyl 1,3-dioxanium ions, while the formation of the analogous 1,3-glucosyl dioxanium ions is thwarted by a prohibitively strong flagpole interaction of the C-2-O-benzyl group with the C-5 proton in moving toward the transition state, in which the glucose ring adopts a B2,5-conformation. This study provides an explanation for the intermediacy of 1,3-dioxanium ions in the mannosyl system and an answer to why these do not form from analogous glucosyl donors.

Zinc(ii)-mediated stereoselective construction of 1,2-cis 2-azido-2-deoxy glycosidic linkage: assembly of Acinetobacter baumannii K48 capsular pentasaccharide derivative.

The capsular polysaccharide (CPS) is a major virulence factor of the pathogenic Acinetobacter baumannii and a promising target for vaccine development. However, the synthesis of the 1,2-cis-2-amino-2-deoxyglycoside core of CPS remains challenging to date. Here we develop a highly α-selective ZnI2-mediated 1,2-cis 2-azido-2-deoxy chemical glycosylation strategy using 2-azido-2-deoxy glucosyl donors equipped with various 4,6-O-tethered groups. Among them the tetraisopropyldisiloxane (TIPDS)-protected 2-azido-2-deoxy-d-glucosyl donor afforded predominantly α-glycoside (α : β = >20 : 1) in maximum yield. This novel approach applies to a wide acceptor substrate scope, including various aliphatic alcohols, sugar alcohols, and natural products. We demonstrated the versatility and effectiveness of this strategy by the synthesis of A. baumannii K48 capsular pentasaccharide repeating fragments, employing the developed reaction as the key step for constructing the 1,2-cis 2-azido-2-deoxy glycosidic linkage. The reaction mechanism was explored with combined experimental variable-temperature NMR (VT-NMR) studies and mass spectroscopy (MS) analysis, and theoretical density functional theory calculations, which suggested the formation of covalent α-C1GlcN-iodide intermediate in equilibrium with separated oxocarbenium-counter ion pair, followed by an SN1-like α-nucleophilic attack most likely from separated ion pairs by the ZnI2-activated acceptor complex under the influence of the 2-azido gauche effect.

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.

Expression, purification, characterization and glycoside production potential of rice β-d-glucan glucohydrolase I (OsExoI)

β-d-Glucan glucohydrolases from glycoside hydrolase family 3 (GH3) act to break-down β-glucans, which is critical to growth and cell wall remodeling in plants. To investigate the function and application of the rice GH3 β-d-glucan glucohydrolases OsExoI, we produced the protein from a codon-optimized cDNA in the heterogenous expression host Pichia pastoris. After purification from the medium, OsExoI was found to be heterogeneously glycosylated and could be separated into pools with different glycosylation levels and specific activities by size exclusion chromatography (SEC). The total glycosylated protein pool had specific activity similar to that of protein from which N-linked carbohydrate had been removed with endoglycosidase H. Purified enzyme hydrolyzed β-1,3- and 1,4- linked oligosaccharides, polysaccharides, and synthetic p-nitrophenyl-β-d-glucopyranoside. The deglycosylated OsExoI had catalytic efficiency (kcat/Km) slightly higher than pooled glycosylated OsExoI, although their overall biochemical properties were similar. OsExoI also exhibits transglycosylation activity using pNP-β-d-glucopyranoside, oligosaccharides, or polysaccharides as glucosyl donor to glycosylate a variety of alcohols. These results suggest that the OsExoI can be applied to alkyl glycoside production using natural polysaccharides or oligosaccharides released during biomass degradation as a source of glucosyl moieties.

Transglycosylation of Stevioside by a Commercial β-Glucanase with Fungal Extracted β-Glucans as Donors

Alternative sweeteners, such as steviol glucosides from the plant Stevia rebaudiana Bertoni, are becoming increasingly popular for the design of next-generation foodstuffs. However, the bitter aftertaste of native steviol glucosides is one of the main reasons behind consumer reluctance towards stevia-containing products. Biocatalysis could be a sustainable solution to this problem, through addition of glucosyl moieties to the molecule. Glycoside hydrolases are enzymes performing transglycosylation reactions, and they can be exploited for such modifications. In the present work, the commercial β-glucanase Finizym 250L® was employed for the transglycosylation of stevioside. After optimization of several reaction parameters, the maximal reaction yield obtained was 19%, with barley β-glucan as the glycosyl donor. With the aim to develop a sustainable process, β-glucan extracts from different fungal sources were prepared. Pulsed Electric Field pretreatment of mycelial biomass resulted in extracts with higher β-glucan content. The extracts were tested as alternative glucosyl donors, reaching up to 15.5% conversion yield, from Pleurotus-extracted β-glucan. Overall, in the present work a novel enzymatic process for the modification of stevioside is proposed, with concomitant valorization of β-glucans extracted from fungal biomass, potentially generated as a byproduct from other applications, in concert with the principles of circular economy.Graphical

Producing 2-O-α-D-glucopyranosyl-L-ascorbic acid by modified cyclodextrin glucosyltransferase and isoamylase

In this study, site saturation mutagenesis was performed on the - 3 (R44, D86, S90, and D192) and - 6 subsite (Y163, G175, G176, and N189) of Bacillus stearothermophilus NO2 cyclodextrin glucosyltransferase to enhance its specificity for the donor substrate maltodextrin for 2-O-α-D-glucopyranosyl-L-ascorbic acid (AA-2G) preparation. The AA-2G yields produced by the mutants S90D, G176H, and S90D/G176H were 181, 171, and 185g/L, respectively. Our previous study found that the mutant K228R/M230L also increased the AA-2G yield. Therefore, the mutants S90D, G176H, S90D/G176H, and K228R/M230L were further used to generate combinatorial mutants. Among these mutants, the highest AA-2G yield (217g/L) was produced by S90D/K228R/M230L with 500g/L maltodextrin as the glucosyl donor, which was 56g/L higher than that produced by wild-type CGTase. In addition, AA-2G was prepared by adding isoamylase to hydrolyze α-1,6 glucosidic linkages in maltodextrin that could not be utilized by CGTase to improve the utilization rate of maltodextrin. The addition of isoamylase reduced the concentration of maltodextrin from 500 to 350g/L, while the AA-2G yield remained high (208g/L). The preparation of AA-2G by complexing isoamylase with mutant S90D/K228R/M230L reduced the maltodextrin concentration by 150g/L, while the AA-2G yield increased by 47g/L than preparation with wild-type CGTase alone, which laid a foundation for the large-scale preparation of AA-2G. KEY POINTS: • Mutants exhibited improved maltodextrin specificity. • Mutant S90D/K228R/M230L produced high yield of AA-2G with maltodextrin as substrate. • AA-2G was first synthesized by a combination of isoamylase and CGTase.

Mapping the effect of configuration and protecting group pattern on glycosyl acceptor reactivity.

The reactivity of the acceptor alcohol can have a tremendous influence on the outcome of a glycosylation reaction, both in terms of yield and stereoselectivity. Through a systematic survey of 67 acceptor alcohols in glycosylation reactions with two glucosyl donors we here reveal how the reactivity of a carbohydrate acceptor depends on its configuration and substitution pattern. The study shows how the functional groups flanking the acceptor alcohol influence the reactivity of the alcohol and show that both the nature and relative orientation play an essential role. The empiric acceptor reactivity guidelines revealed here will aid in the rational optimization of glycosylation reactions and be an important tool in the assembly of oligosaccharides.

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.

A Facile Synthesis of Thiazole Derivatives bearing Imidazole Moiety, Schiff Bases and their O-Glucosides

A unique approach for the synthesis of new thiazole O-glycosides is presented in this work. 2-Amino-4-hydroxy-phenyl-1,3-thiazole-5-carboxaldehyde (3a) was reacted with phenyl glyoxal and benzil to form 4-(4-hydroxy-phenyl)-5-(4-phenyl-1H-imidazol-2-yl)-thiazol-2-amine (4a) and 4-(4-hydroxy-phenyl)-5-(4,5-diphenyl-1H-imidazol-2-yl)-thiazol-2-amine (4b), respectively. A series of substituted Schiff bases of 4a and 4b were synthesized reacting with various aryl aldehyde to form 2-(imino substituted benzal)-4-(4-hydroxy-phenyl)-5-(4-phenyl-1H-imidazol-2-yl)-thiazoles (5a-e) and 2-(imino substituted benzal)-4-(4-hydroxy-phenyl)-5-(4,5-diphenyl-1H-imidazol-2-yl)-thiazoles (5f-j). Glucosylation of compounds (5a-j) have been done by using acetobromoglucose as glucosyl donor to afford 2-(imino substituted benzal)-4-(2,3,4,6-tetra-O-acetyl-p-O-β-D-glucosidoxyphenyl)-5-(4-phenyl- 1H-imidazol-2-yl)-thiazoles (6a-e) and 2-(imino substituted benzal)-4-(2,3,4,6-tetra-O-acetyl-p-O-β- D-glucosidoxyphenyl)-5-(4,5-diphenyl-1H-imidazol-2-yl)-thiazoles (6f-j) further on deacetylation to produce 2-(imino substituted benzal)-4-(p-O-β-D-glucosidoxyphenyl)-5-(4-phenyl-1H-imidazol-2-yl)- thiazoles and 2-(imino substituted benzal)-4-(p-O-β-D-glucosidoxyphenyl)-5-(4,5-diphenyl-1Himidazole- 2-yl)-thiazoles (7f-j). The synthesized compounds were characterized by elemental analyses, FTIR, 1H & 13C NMR and electron mass spectra (EI-MS) techniques and then screened for their in vitro antimicrobial activity.

Stereoselective synthesis of the 3,6-branched Fuzi α-glucans up to 15-mer via a one-pot and convergent glycosylation strategy

A family of the 3,6-branched Fuzi α-glucans including the pentasaccharide repeating unit as well as its di- and trimers were efficiently achieved via a one-pot and convergent glycosylation strategy. All the protected α-glucans up to 15-mer were assembled with high yields and excellent α-stereoselectivity, which was secured by the synergistic α-directing effects of the TolSCl/AgOTf promotion system and the steric β-facial shielding of bulky saccharide residues linked at the 6-O-position of glucosyl donors. Moreover, the 3,6-branched architecture of glycosyl donor was revealed to be more favorable for the α-selective glucosidation of primary hydroxyl group, especially in the case of large oligosaccharide acceptor. The structurally well-defined synthetic α-glucans would be useful for various biological studies.

α-Selective Glucosylation Can Be Achieved with 6-O-para-Nitrobenzoyl Protection.

A systematic study of the effect of various 6-O-acyl groups on anomeric selectivity in glucosylations with thioglycoside donors was conducted. All eight different esters were found to induce moderate-to-high α-selectivity in glucosylation with l-menthol with the best being 6-O-p-nitrobenzoyl. The effect appears to be general across various glucosyl acceptors, glucosyl donor types, and modes of activation. No evidence was found in favor of distal participation.

Stereocontrolling Effect of a Single Triisopropylsilyl Group in 1,2‐cis‐Glucosylation

AbstractGlycosylation with phenyl 3,4,6‐tri‐O‐benzoyl‐2‐O‐triisopropylsilyl (TIPS)‐1‐thio‐β‐d‐glucopyranoside is highly 1,2‐cis‐stereoselective, while the use of 2,3‐di‐O‐TIPS glucosyl donor with benzoyl groups at O‐4 and O‐6 results in the loss of α‐stereoselectivity (α/β=3 : 1). Complete α‐stereocontrol with 2‐O‐TIPS substituted glucosyl donors could only be achieved in glucosylation of weak nucleophiles. In this case, the glucosylation seems to proceed along the SN1‐like pathway via the 4H3 conformer of glycosyl cation stabilized by the bulky TIPS group at O‐2.

Preparation and characterization of a novel 3D polymer support for the immobilization of cyclodextrin glucanotransferase and efficient biocatalytic synthesis of α-arbutin

In macropores of a melamine sponge epoxy resin was cured in ethanol solution. The produced polymer gel could uniformly deposit on the surface of melamine in either porous or nonporous morphology. The composite sponge with porous coating can be used as a large-sized and well-mass transferred support for the immobilization of cyclodextrin glucosyltransferase (CGTase, from Thermoanaerobacter sp.) through the method of adsorption and crosslinking, and a column reactor was made for the preparation of α-arbutin in a sealed circulation way. The porosity and specific surface area were 91.6 % and 46 m2/g, respectively. The loading amount and the specific activity of immobilized CGTase under the optimal immobilization conditions were 42 mg/gsupport and 651 U/gsupport, respectively. 5 mg/ml maltodextrin and 10 mM hydroquinone were used as a glucosyl donor and acceptor for the biosynthesis of α-arbutin, respectively. Under optimized conditions, the α-arbutin yield reached 61 % within 24 h at 40 °C. After 10 cycles, the immobilized CGTase retained 33 % of the α-arbutin yield.

Enzymatic Synthesis of Maltitol and Its Inhibitory Effect on the Growth of Streptococcus mutans DMST 18777.

This study aimed to synthesize maltitol using recombinant CGTase from Bacillus circulans A11 with β-cyclodextrin (β-CD) and sorbitol as a glucosyl donor and acceptor, respectively, and assess its antibacterial activity. Optimal conditions for producing the highest yield, 25.0% (w/w), were incubation of 1% (w/v) β-CD and sorbitol with 400 U/mL of CGTase in 20 mM phosphate buffer at pH 6.0 and 50 °C for 72 h. Subsequently, maltitol underwent large-scale production and was purified by HPLC. By mass spectrometry, the molecular weight of the synthesized maltitol was 379.08 daltons, corresponding exactly to that of standard maltitol. The relative sweetness of synthesized and standard maltitol was ~90% of that of sucrose. Spot assay on the agar plate showed that maltitol inhibited the growth of Streptococcus mutans DMST 18777 cells. In addition, the MIC and MBC values of synthesized and standard maltitol against S. mutans were also determined as 20 and 40 mg/mL, respectively. These results show that the synthesized maltitol can be produced at high yields and has the potential to be used as an anticariogenic agent in products such as toothpaste.

Mechanistic Study of Silyl‐Assist Effect on 1,2‐cis‐α‐Glucosylation

AbstractThe stereoselectivity of the 1,2‐cis‐α‐glucosylation reaction has been reported to be enhanced by introducing a tert‐butyldimethylsilyl (TBS) protecting group into the glucosyl donor. Herein, the origin of this silyl‐assist effect was identified using chemical experiments and density functional theory (DFT) calculations. Glucosylation reactions using various glucosyl donors with different TBS group positions showed that α‐selectivity decreased when the TBS group position was further from the anomeric position. These systematic experiments showed that the silyl‐assist effect was mainly due to electronic factors. Comparing DFT calculations of oxocarbenium intermediates derived from typical glucosyl donors showed that the introduced TBS group contributed to enhanced electron density at the anomeric position. Chemical experiments and DFT calculations showed that introducing a TBS group near the anomeric position stabilized the cationic intermediate and promoted α‐selectivity.

Synthesis of biotinylated pentasaccharide structurally related to a fragment of glucomannan from Candida utilis.

The polysaccharide mannan is the main surface antigen of the cell wall of Candida fungi, playing an important role in the pathogenesis of diseases caused by these mycopathogens. Mannan has a complex, comb-like structure and includes a variety of structural units, with their combination varying depending on the Candida species and strain. Glucomannan, a polysaccharide from Candida utilis, contains terminal α-d-glucose residues attached to oligomannoside side chains. This paper describes the first synthesis of a pentasaccharide structurally related to C. utilis glucomannan fragment, which is an α-(1→2)-linked tetramannoside terminated at the non-reducing end by an α-d-glucopyranosyl residue. The pentasaccharide was obtained as a 3-aminopropyl glycoside, which made it possible to synthesize also its biotinylated derivative, suitable for various glycobiological studies. The most complicated step in the pentasaccharide synthesis was stereoselective 1,2-cis-glycosylation to attach the α-d-glucopyranosyl residue. This was accomplished using a glucosyl donor specially developed in our laboratory, the protecting groups of which provide the necessary α-stereoselectivity. The target biotinylated pentasaccharide thus obtained will be used in the future as a model antigen for the detection of immunodeterminant epitopes of Candida mannans.

Polyglucosylation of Rutin Catalyzed by Cyclodextrin Glucanotransferase from Geobacillus sp.: Optimization and Chemical Characterization of Products

Despite the presence of a rutinosyl group at 3-OH, the aqueous solubility of the flavonoid rutin is even lower than that of its aglycon quercetin. In this work, we describe a fast, simple, and easily scalable process for polyglucosylation of rutin to enhance aqueous solubility, catalyzed by a cyclodextrin glucanotransferase (CGTase). Several reaction parameters (source of enzyme, rutin/starch weight ratio, cosolvent, pH, and temperature) were assessed to optimize the transglucosylation yield. Under the best conditions (6 mg/mL rutin, 30 mg/mL soluble starch as glucosyl donor, 20% (v/v) acetonitrile, pH 9.2, 3.3 U/mL CGTase from Geobacillus sp., 60 °C), the total glucosides reached a maximum concentration of 6 mM (60% conversion yield). The glucosylated products were chemically characterized by MALDI-TOF mass spectrometry and 2D nuclear magnetic resonance. The glucosylation takes place with an α-configuration at the 4-OH position of the β-Glc moiety. A series of maltooligosyl derivatives with 1–6 residues of glucose linked by α(1 → 4) bonds was obtained. The yield of monoglucosylated product was increased 2-fold by treatment with amyloglucosidase STA1 from S. cerevisiae.

ZnI2-Directed Stereocontrolled α-Glucosylation.

Here we report a glucosylation strategy mediated by ZnI2, a cheap and mild Lewis acid, for the highly stereoselective construction of 1,2-cis-O-glycosidic linkages using easily accessible and common 4,6-O-tethered glucosyl donors. The versatility and effectiveness of the α-glucosylation strategy were demonstrated successfully with various acceptors, including complex alcohols. This approach demonstrates the feasibility of the modular synthesis of various α-glucans with both linear and branched backbone structures.