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Logo of nihpaAbout Author manuscriptsSubmit a manuscriptHHS Public Access; Author Manuscript; Accepted for publication in peer reviewed journal;
 
J Org Chem. Author manuscript; available in PMC 2010 October 16.
Published in final edited form as:
PMCID: PMC2765671
NIHMSID: NIHMS147196

Chemical Synthesis of a Hyaluronic Acid Decasaccharide

Abstract

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The chemical synthesis of a hyaluronic acid decasaccharide using the pre-activation based chemoselective glycosylation strategy is described. Assembly of large oligosaccharides is generally challenging due to the increased difficulties in both glycosylation and deprotection. Indeed, the same building blocks previously employed for hyaluronic acid hexasaccharide syntheses failed to yield the desired decasaccharide. After extensive experimentation, the decasaccharide backbone was successfully constructed with an overall yield of 37% from disaccharide building blocks. The trichloroacetyl group was used as the nitrogen protective group for the glucosamine units and the addition of TMSOTf was found to be crucial to suppress the formation of trichloromethyl oxazoline side-product and enable high glycosylation yield. For deprotections, the combination of a mild basic condition and the monitoring methodology using 1H-NMR allowed the removal of all base-labile protective groups, which facilitated the generation of the fully deprotected HA decasaccharide.

Introduction

Hyaluronic acid (HA), a component of the extracellular matrix and a member of the glycosaminoglycan family, contains linear tandem disaccharide repeats of D-glucuronic acid and 2-deoxy-2-N-acetyl-D-glucose [β-D-GlcpA-(1→3)-β-D-GlcpNAc-(1→4)-].1 HA can interact with a wide variety of cell surface receptors, including the lymphatic vessel endothelial receptor, CD44, TNF simulated gene-6 and HA receptor for endocytosis.24 The biological activities of HA can be length dependent.5 For example, HA polymers have been found to be anti-angiogenic, while its oligomers promote angiogenesis.6,7 HA is the major ligand of CD44, a transmembrane protein involved in cell-cell, cell-matrix interactions and signal transduction.3 Evidence is accumulating suggesting that the size of HA fragments recognized by CD44 provides a physiologically important switch between its adhesion and signaling functions.8 Binding of HA polymers to CD44 usually leads to cell adhesion9,10 rather than activation. In contrast, recognition of HA fragments instead of the polymer leads to CD44 signaling, which is involved in diseases such as cancer and inflammation.1114 CD44 requires at least a HA hexasaccharide sequence for binding, and only a decasaccharide or higher can effectively compete with polymeric HA.15 Therefore, access to synthetic HA with variable length and sequence can greatly facilitate the establishment of its structure–activity relationship.5

HA can be synthesized via either enzymatic or chemical methods.16 Based on the understanding of HA biosynthetic and catabolism pathways, innovative studies have been carried out utilizing HA synthases or hyaluronidases to acquire synthetic HA.1719 While impressive synthetic efficiency has been achieved, the inherent substrate specificities of enzymes limit the structural diversity of HA analogs that can be generated. Chemical synthesis can thus complement the enzymatic approaches to create greater varieties of HA structures.

Chemical syntheses of HA oligomers have been performed with the majority of studies focusing on di- and hexa-saccharides.16,2025 The longest HA oligosaccharides chemically assembled to date are an HA octasaccharide26 and heptasaccharide.27 Previously, our group has developed a synthetic strategy to acquire HA oligosaccharides ranging from di- to hexa-saccharides.21 With the fascinating biological activities of longer HA oligosaccharides, we became interested in pursuing their chemical synthesis, which is not a trivial extension of shorter oligomers because elongation of the sugar sequences can create significant new challenges in both glycosylation and deprotection. Herein, we report our results on overcoming the obstacles for chemical synthesis of an HA decasaccharide.

Results and Discussion

The design of a successful route to HA oligosaccharides must take into account three factors: 1) stereochemical control in glycosylation; 2) introduction of the glucuronic acid; and 3) protective groups for the glucosamine nitrogen moieties. In our previous hexasaccharide synthesis, we used two key building blocks 1 and 2, which led to high yield of hexasaccharide 3 in one pot (Scheme 1).21 The benzoyl (Bz) and phthalimido (Phth) groups were crucial to facilitate the formation of 1,2-trans glycosidic linkages. Due to its high inherent reactivities,28 glucoside building block 1 was utilized as a glucuronic acid surrogate.21 The p-methoxybenzyl (PMB) groups in 3 masking the glucoside 6-O-position were selectively removed by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) oxidation and the resulting triol was successfully oxidized and deprotected producing HA hexasaccharide. Following the success of hexasaccharide synthesis, our initial attempt towards HA decasaccharide hinged upon the usage of monosaccharides 1 and 2, from which decasaccharide 4 was assembled. However, removal of the five PMB groups in 4 turned out to be very problematic (Scheme 2a). The previously employed DDQ oxidation21 decomposed the oligosaccharide. Cerium ammonium nitrate (CAN) oxidation29 or the combination of p-tolyl sulfonamide and triflic acid30 also failed to lead to the desired penta-ol. To circumvent this problem, the 6-hydroxyl group liberation and oxidation state adjustment were performed on disaccharide 6 (Scheme 2b). DDQ mediated PMB removal followed by primary hydroxyl oxidation and benzyl ester formation produced disaccharide 7 containing the glucuronic acid moiety. Condensations of the resulting disaccharides afforded decasaccharide 8 with the glucuronic acids already installed, which set the stage for deprotection. Although it has been shown previously that Phth groups could be deprotected in molecules containing carboxylic esters,21,25,31 despite repeated trials and screening of a variety of reagents and reaction conditions, the conditions required to remove all five Phth groups in 7 turned out to be incompatible with the five carboxylic ester moieties present and vice versa. This prompted us to abandon the Phth group and utilize the trichloroacetyl (TCA) group26,27 as an alternative protective group for nitrogen.

Scheme 1Scheme 1
Previous Synthesis of HA Hexasaccharide 3.

Based on these considerations, a new retrosynthetic route towards HA decasaccharide 9 is designed (Scheme 3). The fully protected decasaccharide 10 will be assembled from disaccharides 11, 12 and 13, which in turn will be derived from monosaccharide building blocks 1, 14 and 15.

Scheme 3
Retrosynthetic Scheme towards HA Decasaccharide 9.

Glucoside donor 1 was prepared according to a literature procedure21 and the syntheses of glucosamine building blocks 14 and 15 were outlined in Scheme 4. Peracetylated N-trichloroacetyl-glucosamine 1626 was transformed into the corresponding 1-β-p-tolyl thioglycoside 17 and the 1-β-methoxy derivative 18. Compound 17 was then deacetylated and protected with a benzylidene group to afford 14, whereas compound 18 was protected by benzylidene to give 15.

Scheme 4
Syntheses of Monosaccharide Building Blocks 14 and 15.

With the monosaccharides in hand, disaccharide synthesis was performed. Pre-activation of glucoside donor 1 by the reagent combination of silver triflate (AgOTf) and p-toluenesulfenyl chloride (p-TolSCl)21,32 at − 78 °C was performed followed by the addition of acceptor 14 and a bulky base 2, 4, 6-tri-tert-butyl pyrimidine (TTBP)33 leading to disaccharide 19 in 80% yield. The primary hydroxyl group in 19 was liberated by treatment with DDQ and oxidized by pyridinium dichromate (PDC) in dimethylformamide (DMF) to afford its carboxylic acid derivative, which was protected as a benzyl ester (disaccharide 11) in 65% yield for the three steps. Subsequent removal of the TBS group led to the disaccharide acceptor 12 bearing a free secondary hydroxyl group (Scheme 5a). Disaccharide 13 was constructed through a similar sequence from 1 and 15 in an overall yield of 48% for the five steps (Scheme 5b).

Scheme 5
Assembly of Disaccharide Building Blocks.

Following the same glycosylation protocol as used in the preparation of disaccharide 19, coupling of disaccharide donor 11 with acceptor 12 was attempted (Scheme 6a). However, no desired tetrasaccharide was obtained with full recovery of acceptor 12. Oxazoline derivative 20 (3JH1–H2 = 8.0 Hz34,35) was isolated from the reaction in quantitative yield with the possible mechanism for its formation depicted in Scheme 6b. Neighboring group participation by the TCA group through attachment of its carbonyl oxygen to the oxacarbenium ion forms the oxazolinium ion intermediate 22, which can react with an acceptor to afford the expected 1,2-trans-glycoside 23 (pathway a, Scheme 6b). Alternatively, deprotonation of the oxazolinium ion produces the stable trichloro-oxazoline 24 (pathway b). Following this mechanism, the failure of glycosylation could be attributed to the addition of TTBP,27 which is used to scavenge the triflic acid accumulated upon productive glycosylation. Therefore, a 2nd generation glycosylation protocol was adopted by omitting TTBP from the reaction. Following this protocol, 11 (1 equiv) was condensed with 12 (1 equiv) to produce tetrasaccharide 25 in 55% yield with 40% oxazoline by-product 20 (Table 1, entry 2). The next condensation of tetrasaccharide donor 25 (1 equiv) with disaccharide acceptor 13 gave hexasaccharide 26 in 40% yield and oxazoline 27 (50% yield). Subsequent cleavage of TBS group in 26 gave the hexasaccharide acceptor 28 in 90% yield. Disappointingly, the final coupling of 25 (1.25 equiv) and 28 (1 equiv) only gave decasaccharide 10 in 10% yield, with the majority of 25 converted to oxazoline 27 (85% yield, Table 1, entry 2). The substantial increase of the amounts of oxazoline side products is presumably because with the increasing sizes of the glycosyl donor and acceptor, the compounds become less reactive towards glycosylation (Scheme 6b, pathway a), which in turn favors the competing reaction of oxazoline formation even in the absence of base (Scheme 6b, pathway b).

Table 1
The Effects of Additives on Glycosylation Product Distribution

In order to suppress the amount of oxazoline, exogenous triflic acid (~ 0.4 equiv.) was introduced to the reaction mixture after the donor activation to shift the equilibrium from oxazoline 24 to the oxazolinium ion 22 (Scheme 6b). Following this 3rd generation procedure, although the reaction of 11 and 12 was not affected, the yields for 25 with 13 and 28 were enhanced to 60% and 40% respectively (Table 1, entry 3). The acid sensitive benzylidene moieties were found to be stable under this condition. To further improve on the glycosylation, Lewis acid trimethylsilyl triflate (TMSOTf) was examined as an alternative to TfOH. Based on this protocol, significant enhancements were observed for all three reactions (Table 1, entry 4), with the yield of decasaccharide 10 reaching 77%, which enabled us to acquire over 200 mg of this decasaccharide. These results suggest that the addition of TMSOTf successfully suppressed the formation of trichloro-oxazoline by-products.

Deprotection of large complex oligosaccharides could be very challenging due to the presence of multiple protective groups, as observed in our attempts on decasaccharides 4 and 8. To deprotect decasaccharide 10, its TBS group was removed first by hydrogen fluoride (HF) in pyridine to give 29 in 79% yield. This was followed by a mild basic condition (20 equivalents of KOH added in 10 portions to a solution of 29 over 2 days20) in order to cleave all ten carboxylic esters and five trichloroacetamides (Scheme 7). Harsh basic conditions should be avoided to prevent epimerization of the glucuronic acids. The progress of the hydrolysis turned out to be difficult to monitor by TLC for two reasons. First, the liberated amino groups gave no ninhydrin test presumably due to steric hindrance. Secondly, the compounds with free carboxylic acid and amino groups became zwitterionic, which streaked on TLC. Mass spectrometry analysis of the crude reaction mixture did not yield much information resulting from signal suppression by the presence of salts. NMR analysis of the reaction mixture turned out to be most informative. The cluster of peaks around 8.0 ppm in 1H-NMR assigned to the ortho-hydrogens of benzoyl groups, merged into a doublet like pattern over time signifying the cleavage of benzoyl esters to benzoate salt. Another characteristic of the NMR is that the set of four doublets around 7.0 ppm, representing the amide protons of trichloroacetamide groups in 29, became smaller and eventually disappeared as the reaction proceeded. The rate of trichloroacetamide cleavage was much slower compared with that of the benzoates. When the crude NMR spectra did not show much change after week 5, the reaction was stopped. The reaction mixture was N-acetylated followed by hydrogenation and size exclusion chromatography to produce the fully deprotected HA decasaccharide 9 in 35% yield from 29. NMR analysis indicated all the glycosyl linkages were β, confirming no epimerizations occurred despite the prolonged reaction time.

Conclusions

We report here the first chemical synthesis of a fully deprotected HA decasaccharide. Our pre-activation based thioglycoside strategy with p-TolSCl/AgOTf as the promoter was successfully applied for efficient construction of the decasaccharide backbones. However, considerable difficulties were encountered in deprotection, with the selection of nitrogen protective group turned out to be crucial. While removal of all five Phth was found to be incompatible with the carboxylic esters present in the decasaccharide, TCA could be removed together with the esters under a mild basic condition. The TCA associated oxazoline formation side reaction during glycosylation was suppressed by addition of TMSOTf to the reaction mixture. Our experience highlights the challenges associated with assembly of large oligosaccharides, as the conditions employed for synthesis of shorter counterparts may not be directly translatable and each synthesis needs individual optimization and development. We believe our strategy on the HA decasaccharide assembly can open up possibilities to chemical synthesis of longer HA oligomers and facilitate the structure-activity relationship studies of this important class of molecules.

Experimental Section

General procedure for deprotection of p-methoxybenzyl (PMB) group

PMB-protected compound (1 mmol) and DDQ (1.3 equiv.) were dissolved in a solvent mixture of dichloromethane (CH2Cl2) and a saturated aqueous solution of NaHCO3 (v/v 19:1), which was kept in dark. The reaction mixture is stirred for two hours from 0°C to room temperature. Then a 2nd portion of DDQ (0.5 equiv) was added to the reaction mixture, and a 3rd portion of DDQ (0.5 equiv) could be added 15 minutes after the addition of the 2nd portion to further push the reaction to completion. When most starting material disappeared, the reaction mixture was diluted with CH2Cl2 and washed repeatedly with a saturated aqueous solution of NaHCO3 until the organic layer become colorless. The organic layer was concentrated, and the resultant residue was purified by silica gel chromatography to give the desired compound.

General procedure for oxidation of alcohols to carboxylic acids

After a mixture of alcohol (1 mmol) and MS-4A (5 g) in anhydrous DMF was stirred at room temperature for two hours, a solution of PDC (6 mmol) in DMF was added dropwise to the reaction. The reaction mixture was stirred at room temperature until TLC indicated completion of the reaction, which typically required overnight. The reaction was diluted with ethyl acetate and filtrated to remove the insoluble PDC. The filtrate was washed with brine to remove DMF. The crude product was then purified by silica gel chromatography with ethyl acetate/ CH2Cl2 / methanol solvent systems.

General procedure for benzyl ester formation

The carboxylic acid containing compound was dissolved in CH2Cl2 (5 mL) and treated with phenyldiazomethane solution in diethyl ether (~2 equiv.)21,36 for 2–3 hours until the disappearance of all the starting material. The crude product was purified by silica gel chromatography.

General procedure for removal of tert-butyldimethylsilyl (TBS) groups

The TBS-protected compound (0.5 mmol) was dissolved in pyridine (4 mL) in a plastic flask followed by the addition of 65–70% HF·pyridine solution (2 mL) at 0 °C. The solution was stirred for 24 hours until TLC indicated completion of the reaction. The reaction mixture was diluted with ethyl acetate (50 mL) and washed with 10% aqueous CuSO4 solution (20 mL). The aqueous phase was extracted with ethyl acetate (30 mL) twice and the combined organic layers were washed with a saturated aqueous solution of NaHCO3 to remove HF. The crude product was purified by silica gel chromatography.

p-Tolyl 4,6-O-benzylidene-2-deoxy-2-trichloroacetamido-β-D-glucopyranoside (14)

After D-glucosamine hydrochloride (10.78 g, 50 mmol) and sodium methoxide (50 ml 1M NaOMe/ MeOH, 50 mmol) in methanol were stirred at room temperature under N2 protection for 45 minutes, trichloroacetyl chloride (5.61 ml, 50 mmol) and triethylamine (6.95 ml, 50 mmol) were added. After overnight when ESI-MS indicated that D-glucosamine hydrochloride has completely disappeared, methanol was removed by a rotary evaporator and the flask was placed under high vacuum for two hours. Acetic anhydride and pyridine (150 ml, v/v 1:2) were then added and reaction mixture was stirred for two days. The mixture was concentrated, and the resulting residue was diluted with ethyl acetate and washed with a saturated aqueous solution of NaHCO3, 10% HCl, water, and brine. The organic phase was dried over Na2SO4, filtered, and concentrated. After recrystallization, 1,3,4,6-tetra-O-acetyl-2-deoxy-2-trichloroacetamido-D-glucopyranoside (16) was obtained as a white solid (16.26 g, 33 mmol, 66% for two steps). Boron trifluoride dimethyl etherate (7.75 ml, 89 mmol) was added to a solution of 16 (4.93 g, 10 mmol) and p-toluenethiol (1.99 g, 16 mmol) in dry CH2Cl2 (200 ml). The reaction mixture was stirred at room temperature under N2 protection overnight, diluted with CH2Cl2 (300 ml), washed with saturated NaHCO3, dried over Na2SO4, filtered, and concentrated. Recrystallization afforded p-tolyl 3,4,6-tri-O-acetyl-2-deoxy-2-trichloroacetamido-1-thio-β-D-glucopyranoside (17) as a white solid (5.01 g, 9 mmol, 90%). 17 (5.01 g, 9.0 mmol) was dissolved in mixed solvent of CH2Cl2 and methanol (v/v = 1/1, 200 ml). Sodium methoxide (2.7 ml 1M NaOMe/ MeOH, 2.7 mmol) in methanol was added, and the mixture was stirred at room temperature under N2 protection for two hours, neutralized with Amberlite IR-120, concentrated and dried under vacuum. Benzaldehyde dimethyl acetal (1.52 ml, 10.8 mmol) was added to a solution of resulting residue and camphorsulfonic acid (0.94 g, 4.05 mmol) in anhydrous toluene (200 ml). The reaction mixture was stirred under N2 protection at 80°C for one hour. When TLC showed around 70% conversion of starting material to product, the reaction flask was placed on a high vacuum rotary evaporator to further push the reaction to completion. When toluene was completely removed by the high vacuum rotary evaporator, the reaction mixture was neutralized with triethylamine in CH2Cl2. The mixture was diluted with CH2Cl2 (300 mL) and washed with saturated NaHCO3, dried over Na2SO4, filtered, and concentrated. Recrystallization afforded 14 as a white solid (3.27 g, 6.3 mmol, 70% for two steps), the structure of which was confirmed by comparison of NMR spectra.21

Methyl 4,6-O-benzylidene-2-deoxy-2-trichloroacetamido-β-D-glucopyranoside (15)

Compound 16 (4.93 g, 10 mmol) was dissolved in HBr in acetic acid (30 mL, 33% w/w, 173.6 mmol). After six hours, the mixture was diluted with CH2Cl2 (240 mL) and poured onto crushed ice in saturated NaHCO3 (600 mL). The organic phase was separated and washed again with saturated NaHCO3 until the pH reached 7, which was then dried over Na2SO4, filtered, and concentrated. The resulting crude residue was mixed with Ag2CO3 (2.76 g, 10 mmol), CaSO4 (2.72 g, 20 mmol) and anhydrous methanol (100 ml). The mixture was stirred at room temperature under N2 protection for one day until TLC showed one major product, on which all three acetyl groups has already been cleaved because of the basic reaction condition. The mixture was concentrated and purified by silica column with CH2Cl2/ MeOH system. Methyl 2-deoxy-2-trichloroacetamido-β-D-glucopyranoside (18) was afforded (2.70 g, 8.0 mmol, 80% for two steps). 18 (2.70 g, 8.0 mmol) was mixed with camphorsulfonic acid (0.84 g, 3.6 mmol), benzaldehyde dimethyl acetal (1.35 ml, 9.6 mmol) in anhydrous toluene (200 ml). The reaction mixture was stirred under N2 protection at 80 °C for one hour. When TLC showed around 70% conversion of starting material to product, the reaction flask was placed on a high vacuum rotary evaporator to further push the reaction to completion. When toluene was completely removed by the high vacuum rotary evaporator, the reaction mixture was neutralized with triethylamine in CH2Cl2. The mixture was diluted with CH2Cl2 (300 mL) and washed with saturated NaHCO3, dried over Na2SO4, filtered, and concentrated. Recrystallization afforded 15 as a white solid (2.39 g, 5.6 mmol 70%). [α]D 20 −29.3 ° (c 0.5, CH2Cl2); 1H NMR (500 MHz, CDCl3): δ = 3.46–3.59 (m, 6 H, −OCH3, H-2, H-4, H-5), 3.80–3.84 (m, 1 H, H-6), 4.38−4.42 (m, 2 H, H-3, H-6), 4.87 (d, 1 H, J = 8.0 Hz, H-1), 5.57 (s, 1 H, CHPh), 6.93 (d, 1 H, J = 7.0 Hz, NH), 7.38−7.51 (m, 5 H, CHarom); 13C NMR (125 MHz, CDCl3): δ = 57.8 (−OCH3), 59.8 (C-2), 66,4 (C-5), 68,8 (C-6), 69.8 (C-3), 81.8 (C-4), 92.5 (CCl3), 101,2 (C-1), 102,2 (CHPh), 126.5 –129.6 (Carom), 137.12 (Cq Carom), 162.6 (C=O TCA); HRMS [M + Na]+: m/z: calcd for C16H18Cl3NNaO6 448.0097, found 448.0088.

p-Tolyl O-(2-O-benzoyl-3-O-benzyl-4-O-tert-butyldimethylsilyl-6-O-p-methoxybenzyl-β-D-glucopyranosyl)-(1→3)-4,6-O-benzylidene-2-deoxy-1-thio-2-trichloroacetamido-β-Dglucopyranoside (19)

The mixture of donor 1 (715 mg, 1 mmol) and freshly activated MS-4A (800 mg) in diethyl ether (20 mL) was stirred in a dry ice–isopropanol bath for one hour, followed by the addition of AgOTf (771 mg, 3 mmol) in diethyl ether (10 mL). After five minutes, orange colored p-TolSCl (157 µL, 1 mmol) was added via a micro-syringe. Since the reaction temperature was lower than the freezing point of p-TolSCl, p-TolSCl was added directly into the reaction mixture to prevent it from freezing on the flask wall. The characteristic yellow color of p-TolSCl in the reaction solution dissipated rapidly within a few seconds indicating depletion of p-TolSCl. The temperature at which pre-activation was performed was not crucial as long as it did not exceed −50 °C. After the donor was completely consumed according to TLC analysis (about 5 minutes at −78 °C), a solution of acceptor 14 (467 mg, 0.9 mmol) and TTBP (248 mg, 1 mmol) in a mixture solvent of CH2Cl2 and acetonitrile (v/v 19:1, 3 mL) was then added dropwise within ten minutes to the reaction mixture (acetonitrile was necessary as acceptors 14 were not freely soluble in CH2Cl2). The reaction mixture was warmed to −10 °C under stirring in 2 hours. Triethylamine (0.5 mL) was then added and the mixture was diluted with CH2Cl2 (100 mL) and filtered over Celite. The Celite was further washed with CH2Cl2 until no organic compounds were observed in the filtrate by TLC. All CH2Cl2 solutions were combined and washed twice with a saturated aqueous solution of NaHCO3 (100 mL) and twice with water (100 mL). The organic layer was concentrated and the crude product was purified by silica gel chromatography. Typical conditions for chromatography are silica gel / product ~ 2000 by weight with a flow rate of approximate 5 mL/min and a solvent gradient of Rf ~ 0.1 – 0.3 in the ethyl acetate/ CH2Cl2/hexanes solvent systems. 19 (800 mg, 0.72 mmol, 80%) was afforded as white solid. [α]D 20 +22.2 ° (c 0.5, CH2Cl2); 1H NMR (500 MHz, CDCl3): δ = −0.08 (s, 3 H, SiCH3), −0.05 (s, 3 H, SiCH3), 0.79 (s, 9 H, SiC(CH3)3), 2.35 (s, 3 H, PhCH3), 3.35–3.43 (m, 3 H, H-5’, H-6’, H-2), 3.49 (ddd, 1 H, J = 4.5 Hz, 5.0 Hz, 9.0 Hz, H-5), 3.56–3.68 (m, 4 H, H-3’, H-4’, H-6, H-6’), 3.72 (t, 1 H, J = 9.0 Hz, H-4), 3.80 (s, 3 H, CH3 PMB), 4.27 (dd, 1 H, J = 5.0 Hz, 10.5 Hz, H-6), 4.34 (d, 1 H, J = 12.0 Hz, CH2PMP), 4.54 (d, 1 H, J = 11.0 Hz, CH2Ph), 4.58 (d, 1 H, J = 11.0 Hz, CH2Ph), 4.63 (d, 1 H, J = 12.0 Hz, CH2PMP), 4.66 (t, 1 H, J = 9.0 Hz, H-3 ),4.93 (d, 1 H, J = 8.0 Hz, H-1’), 5.20 (t, 1 H, J = 8.0 Hz, H-2’), 5.32 (s, 1 H, CHPh), 5.44 (d, 1 H, J = 10.5 Hz, H-1), 6.89 (d, 1 H, J = 8.5 Hz, NH), 7.04–7.11 (m, 7 H, CHarom), 7.20–7.42 (m, 14 H, CHarom), 7.82–7.84 (m, 2 H, CHarom Bz); 13C NMR (125 MHz, CDCl3): δ = −4.5 (SiCH3), −3.6(SiCH3), 18.1 (SiC(CH3)3), 21.4 (PhCH3), 26.0 (x3, SiC(CH3)3), 55.5 (PhOCH3), 57.6 (C-5’), 68.7 (C-6), 69.1 (C-6’), 70.9 (C-5), 71.7 (C-4’), 73.3, (CH2PMP), 74.4 (C-2’), 75.0 (CH2Ph), 76.0 (C-3), 77.4 (C-2), 78.8 (C-4), 83.5 (C-3’), 85.4 (C-1), 92.5 (CCl3), 98.0 (C-1’), 101.3 (CHPh), 114.0 (Carom-2 PhOCH3), 126.4–130.2 (CHarom), 133.3, 133.8 (x2), 137.3, 137.9, 139.0 (Cq SPhCH3, Cq CHPh, Cq Bn, Cq Bz, Carom-4 PhOCH3), 159.6 (Carom-1 PhOCH3), 161.7, 165.3 (C=O TCA, C=O Bz); HRMS [M + Na]+: m/z: calcd for C56H64Cl3NNaO12SSi 1130.2882, found 1130.2845.

p-Tolyl O-(benzyl 2-O-benzoyl-3-O-benzyl-4-O-tert-butyldimethylsilyl-β-Dglucopyranosyluronate)-(1→3)-4,6-O-benzylidene-2-deoxy-1-thio-2-trichloroacetamido-β-D-glucopyranoside (11)

19 was converted to 11 in three steps (65% for three steps) following the general procedures for deprotection of PMB, oxidation of alcohol to carboxylic acid and benzyl ester formation. [α]D 20 +10.2 ° (c 0.5, CH2Cl2); 1H NMR (500 MHz, CDCl3): δ = −0.16 (s, 3 H, SiCH3), −0.13 (s, 3 H, SiCH3), 0.74 (s, 9 H, SiC(CH3)3), 2.36 (s, 3 H, PhCH3), 3.30 (ddd, 1 H, J = 7.5 Hz, 9.0 Hz, 10.5 Hz, H-2), 3.49–3.55 (m, 2 H, H-3’, H-5), 3.65–3.70 (m, 2 H, H-6, H-4), 3.83 (d, J = 6.5 Hz, H-5’), 4.13 (t, J = 6.5 Hz, H-4’), 4.32 (dd, 1 H, J = 5.0 Hz, 10.0 Hz, H-6), 4.54 (t, 1 H, J = 9.0 Hz, H-3),4.59 (d, 1 H, J = 11.5 Hz, −CH2Ph ), 4.65 (d, 1 H, J = 11.5 Hz, −CH2Ph), 5.03 (d, 1 H, J = 7.0 Hz, H-1’), 5.13 (d, 1 H, J = 10.5 Hz, −COOCH2Ph ), 5.17 (d, 1 H, J = 10.5 Hz, −COOCH2Ph ), 5.18 (dd, 1 H, J = 6.0 Hz, 7.0 Hz, H-2’), 5.29 (d, 1 H, J = 10.5 Hz, H-1), 5.32 (s, 1 H, CHPh), 6.96 (d, 1 H, J = 7.5 Hz, NH), 7.10–7.18 (m, 7 H, CHarom), 7.26–7.38 (m, 14 H, CHarom), 7.51–7.54 (m, 1 H, CHarom), 7.88–7.89 (m, 2 H, CHarom Bz); 13C NMR (125 MHz, CDCl3): δ = −5.0 (SiCH3), −4.3 (SiCH3), 18.0 (SiC(CH3)3), 21.4 (PhCH3), 25.9 (x3, SiC(CH3)3), 57.5 (C-2), 67.4 (COOCH2Ph), 68.8 (C-6), 70.8 (C-5), 71.4 (C-4’), 73.7 (OCH2Ph), 74.4 (C-2’), 76.5 (C-3), 77.6 (C-5’), 80.2 (C-4), 81.3 (C-3’), 84.6 (C-1), 92.2 (CCl3), 99.0 (C-1’), 101.8 (CHPh), 126.5–130.2 (CHarom), 133.5, 134.2, 135.3, 137.3, 137.9, 139.2 (Cq STol, Cq CHPh, Cq OBn, Cq Bz, Cq COOBn), 161.8, 165.4, 168.6 (C=O TCA, C=O COOBn, C=O Bz); HRMS [M + Na]+ calcd for C55H60Cl3NNaO12SSi 1114.2563, found 1114.2560.

p-Tolyl O-(benzyl 2-O-benzoyl-3-O-benzyl-β-D-glucopyranosyluronate)-(1→3)-4,6-O-benzylidene-2-deoxy-1-thio-2-trichloroacetamido-β-D-glucopyranoside (12)

11 was converted to 12 following the general procedure for TBS removal (90%). [α]D 20 +5.5 ° (c 1.0, CH2Cl2); 1H NMR (500 MHz, CDCl3): δ = 2.36 (s, 3 H, PhCH3), 3.02 (s, 1 H, OH), 3.30 (ddd, 1 H, J = 7.0 Hz, 9.0 Hz, 10.5 Hz,H-2), 3.52 (ddd, 1 H, J = 4.0 Hz, 4.5 Hz, 9.0 Hz, H-5), 3.55–3.60 (m, 3 H, H-3’, H-5’, H-6), 3.70 (t, 1 H, J = 9.0 Hz, H-4), 4.03 (t, 1 H, J = 9.0 Hz, H-4’), 4.27 (dd, 1 H, J = 4.0 Hz, 10.0 Hz, H-6), 4.59 (t, 1 H, J = 9.0 Hz, H-3 ),4.62 (d, 1H, J = 11.5 Hz, −CH2Ph ), 4.72 (d, 1 H, J = 11.5 Hz, −CH2Ph ), 4.86 (d, 1 H, J = 8.0 Hz, H-1’), 5.15 (d, 1 H, J = 11.5 Hz, −COOCH2Ph ), 5.17 (t, 1 H, J = 8.0 Hz, H-2’), 5.26 (d, 1 H, J = 11.5 Hz, −COOCH2Ph ), 5.32 (s, 1 H, CHPh), 5.37 (d, 1 H, J = 10.5 Hz, H-1), 7.05 (d, 1 H, J = 7.0 Hz, NH), 7.08–7.18 (m, 7 H, CHarom), 7.30–7.45 (m, 14 H, CHarom), 7.54–7.57 (m, 1 H, CHarom), 7.92–7.94 (m, 2 H, CHarom Bz); 13C NMR (125 MHz, CDCl3): δ = 21.4 (PhCH3), 57.4 (C-2), 68.1 (COOCH2Ph), 68.7 (C-6), 70.7 (C-5), 72.2 (C-4’), 73.2 (C-2’), 74.0 (OCH2Ph), 74.7 (C-3), 76.9 (C-5’), 80.1 (C-4), 81.0 (C-3’), 84.4 (C-1), 92.1 (CCl3), 99.6 (C-1’), 101.4 (CHPh), 126.3–130.2 (CHarom), 133.6, 134.1, 134.8, 137.3, 137.8, 139.2 (Cq STol, Cq CHPh, Cq OBn, Cq Bz, Cq COOBn), 161.8, 165.3, 169.3 (C=O TCA, C=O COOBn, C=O Bz); HRMS [M + Na]+: m/z: calcd for C49H46Cl3NNaO12S 1000.1699, found 1000.1706.

Methyl O-(benzyl 2-O-benzoyl-3-O-benzyl-β-D-glucopyranosyluronate)-(1→3)-4,6-O-benzylidene-2-deoxy-2-trichloroacetamido-β-D-glucopyranoside (13)

The mixture of donor 1 (715 mg, 1 mmol), acceptor 15 (427 mg, 1 mmol) and freshly activated MS-4A (800 mg) in a mixture solvent of CH2Cl2 and acetonitrile (v/v 40:1, 20 mL) was stirred for one hour at −78 °C, followed by the addition of AgOTf (771 mg, 3 mmol) in diethyl ether (10 mL). After five minutes, p-TolSCl (157 µL, 1 mmol) was added via a syringe to activate the donor. The yellow color of the reaction disappears quickly and TLC analysis showed the donor was completely consumed. A solution of TTBP (248 mg, 1 mmol) in dichloromethane (1 mL) was then added dropwise to the reaction mixture. The reaction mixture was warmed to −10 °C under stirring in 2 hours, followed by the same workup and purification procedures described above for the synthesis of 19. The resulting disaccharide was subjected to deprotection of PMB, oxidation of alcohol to carboxylic acid, benzyl ester formation and TBS removal reactions following the general procedures to afford 13 (426 mg, 0.48 mmol, 48% for five steps) as white solid. [α]D 20 +8.2 ° (c 0.5, CH2Cl2); 1H NMR (500 MHz, CDCl3): δ = 3.00 (d, 1 H, J = 2.5 Hz, OH), 3.30 (ddd, 1 H, J = 7.0 Hz, 8.0 Hz, 9.5 Hz, H-2), 3.48–3.50 (m, 4 H, −OCH3, H-5), 3.57–3.60 (m, 3 H, H-3’, H-5’, H-6), 3.76 (t, 1 H, J = 9.0 Hz, H-4), 4.03 (ddd, 1 H, J = 2.5 Hz, 9.0 Hz, 9.0 Hz, H-4’), 4.26 (dd, 1 H, J = 5.0 Hz, 10.5 Hz, H-6), 4.59 (dd, 1 H, J = 9.0 Hz, 9.5 Hz, H-3 ),4.63 (d, 1 H, J = 11.5 Hz, −CH2Ph ), 4.73 (d, 1 H, J = 11.5 Hz, −CH2Ph ), 4.88 (d, 1 H, J = 7.5 Hz, H-1’), 4.99 (d, 1 H, J = 8.0 Hz, H-1), 5.14 (d, 1 H, J = 12.0 Hz, −COOCH2Ph ), 5.20 (dd, 1 H, J = 7.5 Hz, 9.5 Hz, H-2’), 5.26 (d, 1 H, J = 12.0 Hz, −COOCH2Ph ), 5.36 (s, 1 H, CHPh), 7.05 (d, 1 H, J = 7.0 Hz, NH), 7.08–7.09 (m, 3 H, CHarom), 7.27–7.40 (m, 14 H, CHarom), 7.54–7.57 (m, 1 H, CHarom), 7.92–7.94 (m, 2 H, CHarom Bz); 13C NMR (125 MHz, CDCl3): δ = 57.8 (−OCH3) 59.3 (C-2), 66.3 (C-5), 68.0 (COOCH2Ph), 68.8 (C-6), 72.3 (C-4’), 73.2 (C-2’), 74.0 (C-5’), 74.7 (OCH2Ph), 76.2 (C-3), 80.3 (C-4), 81.1 (C-3’), 92.1 (CCl3), 99.7 (C-1), 100.0 (C-1’), 101.4 (CHPh), 126.2–130.2 (CHarom), 133.5, 134.9, 137.4, 138.0 (Cq CHPh, Cq OBn, Cq Bz, Cq COOBn), 162.3, 165.3, 169.3 (C=O TCA, C=O COOBn, C=O Bz); HRMS [M + Na]+: m/z: calcd for C43H42Cl3NNaO13 908.1619, found 908.1616.

2-Trichloromethyl O-(benzyl 2-O-benzoyl-3-O-benzyl-4-O-tert-butyldimethylsilyl-β-D-glucopyranosyluronate)-(1→3)-4,6-O-benzylidene-1,2-dideoxy-α-D-glucopyrano-[2,1-d]-2-oxazoline (20)

[α]D 20 +54.1 ° (c 1.0, CH2Cl2); 1H NMR (500 MHz, CDCl3): δ = −0.06 (s, 3 H, SiCH3), −0.05 (s, 3 H, SiCH3), 0.81 (s, 9 H, SiC(CH3)3), 3.53 (dd, 1 H, J = 5.0 Hz, 10.0 Hz, H-6), 3.61 (t, 1 H, J = 10.0 Hz, H-5), 3.68 (t, 1 H, J = 7.5 Hz, H-3’), 3.91 (dd, 1 H, J = 7.5 Hz, 10.0 Hz, H-4), 4.01 (d, 1 H, J = 8.0 Hz, H-5’),4.15–4.18 (m, 2 H, H-3, H-4’), 4.22 (dd, 1 H, J = 5.0 Hz, 8.0 Hz, H-2), 4.34 (dd, 1 H, J = 5.0 Hz, 10.0 Hz, H-6), 4.66 (d, 1 H, J = 12.5 Hz, CH2Ph ), 4.69 (d, 1 H, J = 12.5 Hz, CH2Ph ), 5.02 (d, 1 H, J =7.5 Hz, H-1’), 5.11 (d, 1 H, J = 12.0 Hz, COOCH2Ph), 5.15 (d, 1 H, J = 12.0 Hz, COOCH2Ph), 5.38 (t, 1 H, J = 7.5 Hz, H-2’), 5.39 (s, 1 H, CHPh), 6.08 (d, 1 H, J = 8.0 Hz, H-1), 7.13–7.17 (m, 4 H, CHarom), 7.31–7.43 (m, 13 H, CHarom), 7.53–7.70 (m, 1 H, CHarom), 8.00–8.10 (m, 2 H, CHarom Bz); 13C NMR (125 MHz, CDCl3): δ = −4.9 (SiCH3), −4.0 (SiCH3), 18.1 (SiC(CH3)3), 26.1 (x3, SiC(CH3)3), 63.4 (C-5), 67.5 (COOCH2Ph), 68.7 (C-6), 69.0 (C-2), 72.1 (C-4’), 74.1 (C-2’), 74.6 (OCH2Ph), 77.4 (C-5’), 78.7 (C-4), 80.3 (C-3), 82.3 (C-3’), 101.1 (C-1’), 101.5 (CHPh), 105.3 (C-1), 110.0 (CCl3), 125.5–128.7 (CHarom), 133.5, 135.2, 137.1, 137.8 (Cq CHPh, Cq OBn, Cq Bz, Cq COOBn), 162.5, 165.5, 168.2 (C=N, C=O COOBn, C=O Bz); HRMS [M + Na]+: m/z: calcd for C48H52Cl3NNaO12Si 990.2222, found 990.2231.

p-Tolyl O-(benzyl 2-O-benzoyl-3-O-benzyl-4-O-tert-butyldimethylsilyl-β-D-glucopyranosyluronate)-(1→3)-O-(4,6-O-benzylidene-2-deoxy-2-trichloroacetamido-β-D-glucopyranosyl)-(1→4)-O-(benzyl 2-O-benzoyl-3-O-benzyl-β-D-glucopyranosyluronate)-(1→3)-4,6-O-benzylidene-2-deoxy-1-thio-2-trichloroacetamido-β-D-glucopyranoside (25)

The mixture of donor 11 (37 mg, 33.9 µmol) and freshly activated MS-4A (300 mg) in diethyl ether (2.0 mL) was stirred for one hour at −78°C, followed by the addition of AgOTf (26 mg, 101.7 µmol) in diethyl ether (1.0 mL). After five minutes, p-TolSCl (5.3 µL, 33.9 µmol) was added via a micro-syringe to activate the donor. The characteristic yellow color of p-TolSCl in the reaction solution dissipated rapidly within a few seconds indicating depletion of p-TolSCl and TLC analysis showed the donor was completely consumed. A solution of acceptor 12 (30 mg, 30.5 µmol) in a mixture solvent of CH2Cl2 and acetonitrile (v/v 19:1, 0.7 mL) was then added dropwise to the reaction mixture. After five minutes, TMSOTf (2 µL, 11.0 µmol) was added via micro-syringe. The reaction mixture was warmed to −10 °C under stirring in 2 hours followed by the same workup and purification procedures described above for the synthesis of 19. 25 (54 mg, 27.8 µmol, 82%) was afforded as white solid. [α]D 20 +2.9 ° (c 0.5, CH2Cl2); 1H NMR (500 MHz, CDCl3): δ = −0.14 (s, 3 H, SiCH3), −0.11 (s, 3 H, SiCH3), 0.78 (s, 9 H, SiC(CH3)3), 2.31 (s, 3 H, PhCH3), 3.09 (ddd, 1 H, J = 5.0 Hz, 5.0 Hz, 10.0 Hz, H-5”), 3.17–3.22 (m, 1 H, H-6”), 3.44–3.50 (m, 2 H, H-2, H-5), 3.53 (dd, 1 H, J = 9.5 Hz, 10.0 Hz, H-3), 3.55 (t, 1 H, J = 7.0 Hz, H-3’ ”), 3.58–3.61 (m, 2 H, H-4”, H-6), 3.64 (t, 1 H, J = 8.0 Hz, H-3’), 3.72 (t, 1 H, J = 9.0 Hz, H-2”), 3.81 (dd, 1 H, J = 9.0 Hz, 9.5 Hz H-4), 3.86 (d, 1 H, J = 7.0 Hz, H-5’ ”), 3.87 (d, 1 H, J = 8.0 Hz, H-5’), 4.02 (dd, 1 H, J = 5.0 Hz, 10.5 Hz, H-6”), 4.17 (t, 1 H, J = 7.0 Hz, H-4’ ”), 4.20 (t, 1 H, J = 8.0 Hz, H-4’ ), 4.29 (dd, 1 H, J = 5.0 Hz, 10.5 Hz, H-6 ), 4.41 (t, 1 H, J = 9.0 Hz, H-3” ), 4.53 (d, 1 H, J = 11.5 Hz, −CH2Ph ), 4.61 (d, 1 H, J = 9.0 Hz, H-1”), 4.61 (d, 1 H, J = 11.5 Hz, −CH2Ph ), 4.68 (d, 1 H, J = 11.5 Hz, −CH2Ph ), 4.74 (d, 1 H, J = 11.5 Hz, −CH2Ph ), 4.97 (d, 1 H, J = 10.0 Hz, −COOCH2Ph ), 5.00 (s, 1 H, CHPh ), 5.00 (d, 1 H, J = 7.0 Hz, H-1’ ”), 5.06 (t, 1 H, J = 8.0 Hz, H-2’), 5.12 (d, 1 H, J = 7.5 Hz, H-1), 5.12 (d, 1 H, J = 10.0 Hz, −COOCH2Ph), 5.16 (d, 1 H, J = 10.0 Hz, −COOCH2Ph), 5.17 (d, 1 H, J = 8.0 Hz, H-1’ ), 5.19 (d, 1 H, J = 11.5 Hz, −COOCH2Ph ), 5.20 (t, 1 H, J = 7.0 Hz, H-2’ ”), 5.32 (s, 1 H, CHPh), 6.49 (d, 1 H, J = 9.0 Hz, NH), 7.08 (d, 1 H, J = 7.5 Hz, NH”), 7.10–7.20 (m, 13 H, CHarom), 7.26–7.42 (m, 25 H, CHarom), 7.53–7.58 (m, 2 H, CHarom), 7.89–7.91 (m, 2 H, CHarom Bz), 7.95–7.97 (m, 2 H, CHarom Bz); 13C NMR (125 MHz, CDCl3): δ = −5.0 (SiCH3), −4.2 (SiCH3), 18.1 (SiC(CH3)3), 21.4 (PhCH3), 26.0 (x3, SiC(CH3)3), 56.8 (C-2), 57.6 (C-2”), 66.4 (C-5”), 67.4 (COOCH2Ph), 68.4 (COOCH2Ph),68.0 (C-6), 68.0 (C-6”), 70.8 (C-5), 71.4 (C-4’ ”), 73.7 (OCH2Ph), 74.6 (OCH2Ph), 74.6 (C-2’ ”), 75.0 (C-2’), 75.0 (C-5’), 75.8 (C-4), 77.0 (C-3”), 77.3 (C-4’), 77.8 (C-5’ ”), 78.5 (C-3’), 79.8 (C-4”), 80.2 (C-3), 81.4 (C-3’ ”), 85.6 (C-1), 92.4 (CCl3), 92.7 (CCl3), 99.3 (CHPh), 100.0, 100.0 (C-1”, C-1’ ”), 101.0 (CHPh), 101.7 (C-1’), 126.2–130.1 (CHarom), 133.5, 133.5, 134.1, 135.4, 135.4, 137.4, 137.4, 138.0, 138.4, 138.4 (Cq STol, Cq CHPh x2, Cq OBn x2, Cq Bz x2, Cq COOBn x2), 161.7, 165.0, 165.3, 165.7, 168.5, 169.1 (C=O TCA x2, C=O COOBn x2, C=O Bz x2); HRMS [M + H]+: m/z: calcd for C97H99Cl6N2O24SSi 1949.4191, found 1949.4142.

Methyl O-(benzyl 2-O-benzoyl-3-O-benzyl-4-O-tert-butyldimethylsilyl-β-D-glucopyranosyluronate)-(1→3)-O-(4,6-O-benzylidene-2-deoxy-2-trichloroacetamido-β-D-glucopyranosyl)-(1→4)-O-(benzyl 2-O-benzoyl-3-O-benzyl-β-D-glucopyranosyluronate)-(1→3)-O-(4,6-O-benzylidene-2-deoxy-2-trichloroacetamido-β-D-glucopyranosyl)-(1→4)-O-(benzyl 2-O-benzoyl-3-O-benzyl-β-D-glucopyranosyluronate)-(1→3)-4,6-O-benzylidene-2-deoxy-2-trichloroacetamido-β-D-glucopyranoside (26)

After a mixture of donor 25 (33.4 mg, 17.14 µmol), acceptor 13 (15.2 mg, 17.14 µmol) and MS-AW-300 (200 mg) in a mixture solvent of CH2Cl2 and acetonitrile (v/v 19:1, 2 mL) was stirred at −78 °C for one hour, AgOTf (13 mg, 51.4 µmol) in diethyl ether (0.7 mL) was added. When the temperature of the reaction mixture reduced to −78 °C, p-TolSCl (17.14 µmol, 2.46 µL) was added via a micro-syringe. After five minutes when the yellowish color disappears, TMSOTf (0.75 µL, 4.13 µmol) was added via micro-syringe. The reaction mixture was warmed to −10 °C under stirring in 2 hours, followed by the same workup and purification procedures described above for the synthesis of 19. 26 (33 mg, 12 µmol, 71%) was afforded as white solid. [α]D 20 −1.7 ° (c 0.5, CH2Cl2); 1H NMR (500 MHz, CDCl3): δ = −0.14 (s, 3 H, SiCH3), −0.10 (s, 3 H, SiCH3), 0.78 (s, 9 H, SiC(CH3)3), 3.00 (dd, 1 H, J = 4.5 Hz, 9.5 Hz, H-6a/c/e), 3.13 (ddd, 1 H, J = 4.5 Hz, 5.0 Hz, 9.5 Hz, H-5a/c/e), 3.15 (dd, 1 H, J = 4.5 Hz, 9.5 Hz, H-6a/c/e), 3.18–3.23 (m, 1 H, H-5 a/c/e), 3.42–3.48 (m, 3 H, H-5a/c/e, H-6a/c/e, H-2a/c/e), 3.50 (s, 3 H, OCH3), 3.52–3.61 (m, 3 H, H-3a/c/e, H-3b/d/f x2), 3.61–3.70 (m, 3 H, H-3a/c/e, H-3b/d/f, H-4a/c/e), 3.72–3.78 (m, 2 H, H-2a/c/e x2), 3.81 (dd, 1 H, J = 9.0 Hz, 9.5 Hz, H-4a/c), 3.81 (dd, 1 H, J = 9.0 Hz, 9.5 Hz, H-4a/c), 3.85 (d, 1 H, J = 6.5 Hz, H-5b/d/f), 3.86 (d, 1 H, J = 8.5 Hz, H-5b/d/f), 3.90 (d, 1 H, J = 8.5 Hz, H-5b/d/f), 4.02 (dd, 1 H, J = 4.5 Hz, 10.0 Hz, H-6a/c/e), 4.04 (dd, 1 H, J = 4.5 Hz, 10.5 Hz, H-6a/c/e), 4.17 (t, 1 H, J = 6.5 Hz, H-4b/d/f), 4.19 (t, 1 H, J = 8.5 Hz, H-4b/d/f), 4.25 (t, 1 H, J = 8.5 Hz, H-4b/d/f), 4.29 (dd, 1 H, J = 5.5 Hz, 10.5 Hz, H-6a/c/e), 4.47 (dd, 1 H, J = 9.0 Hz, 9.5 Hz, H-3a/c/e), 4.52 (d, 1 H, J = 8.0 Hz, H-1c/e), 4.56 (d, 1 H, J = 11.5 Hz, −CH2Ph ), 4.57 (d, 1 H, J = 12.0 Hz, −CH2Ph ), 4.62 (d, 1 H, J = 11.5 Hz, −CH2Ph ), 4.68 (d, 1 H, J = 12.0 Hz, −CH2Ph ), 4.72 (d, 1 H, J = 8.0 Hz, H-1c/e), 4.75 (d, 1 H, J = 11.5 Hz, −CH2Ph ), 4.78 (d, 1 H, J = 11.5 Hz, −CH2Ph ), 4.84 (d, 1 H, J = 8.5 Hz, H-1a),4.94 (d, 1 H, J = 6.0 Hz, H-1b/d/f), 4.97 (d, 1 H, J = 6.5 Hz, H-1b/d/f), 4.99 (d, 1 H, J = 7.0 Hz, H-1b/d/f), 5.01 (d, 1 H, J = 12.0 Hz, −COOCH2Ph), 5.04 (d, 1 H, J = 12.0 Hz, −COOCH2Ph), 5.07 (dd, 1 H, J = 6.0 Hz, 8.0 Hz, H-2b/d/f), 5.11 (d, 1 H, J = 12.0 Hz, −COOCH2Ph ), 5.12 (dd, 1 H, J = 6.5 Hz, 8.5 Hz, H-2b/d/f), 5.14 (s, 1 H, CHPh), 5.18 (d, 1 H, J = 12.0 Hz, −COOCH2Ph), 5.19 (s, 1 H, CHPh), 5.20 (d, 1 H, J = 12.0 Hz, −COOCH2Ph), 5.21 (d, 1 H, J = 12.0 Hz, −COOCH2Ph), 5.21 (dd, 1 H, J = 6.0 Hz, 7.0 Hz, H-2b/d/f), 5.32 (s, 1 H, CHPh), 6.48 (d, 1 H, J = 8.5 Hz, NH), 6.60 (d, 1 H, J = 8.5 Hz, NH), 6.99 (d, 1 H, J = 8.0 Hz, NH), 7.13–7.60 (m, 54 H, CHarom), 7.89–7.98 (m, 6 H, CHarom Bz); 13C NMR (125 MHz, CDCl3): δ = −5.0 (SiCH3), −4.2 (SiCH3), 18.1 (SiC(C 3)3), 26.0 (x3, SiC(CH3)3), 57.2 (C-2a/c/e), 57.5 (C-2a/c/e), 57.7 (OCH3), 58.8 (C-2a/c/e), 66.3, 66.4, 66.4 (C-5a/c/e, C-6a/c/e, C-5a/c/e), 67.4 (COOCH2Ph ), 68.0 (COOCH2Ph ), 68.1 (COOCH2Ph ), 68.3, 68.6, 68.7 (C-6a/c/e, C-6a/c/e, C-5a/c/e), 71.4 (C-4f), 73.7 (OCH2Ph), 74.3 (C-2b/d/f), 74.7 (OCH2Ph), 74.7 (OCH2Ph), 74.7 (x2, C-5b/d/f x2), 75.0 (C-2b/d/f), 75.1 (C-2b/d/f), 76.0 (C-3a/c/e), 76.8 (C-4a/c/e), 77.0 (C-4a/c/e), 77.5 (C-4b/d), 77.6 (C-4b/d), 77.8 (C-5b/d/f), 78.8 (C-3b/d/f), 79.0 (C-3b/d/f), 80.0 (x2, C-3a/c/e x2), 82.2 (C-4a/c/e), 81.5 (C-3b/d/f), 92.4 (CCl3), 92.6 (CCl3), 92.7 (CCl3), 99.3 (C-1b/d/f), 99.9 (C-1b/d/f), 100.0 (C-1c/e), 100.1 (C-1c/e), 100.3 (C-1b/d/f), 100.8 (C-1a), 100.9 (CHPh), 101.1 (CHPh), 101.7 (CHPh), 126.3–130.4 (CHarom), 133.4, 133.5, 133.6, 135.0 (x2), 135.4, 137.4, 137.5, 137.5, 137.9, 138.3, 138.5 (Cq CHPh x3, Cq OBn x3, Cq Bz x3, Cq COOBn x3), 161.6, 162.0, 162.3, 165.3, 165.6, 165.6, 168.6, 169.0, 169.1 (C=O TCA x3, C=O COOBn x3, C=O Bz x3); HRMS [M + Na]+: m/z: calcd for C133H132Cl9N3NaO37Si 2734.5383, found 2734.5469.

2-Trichloromethyl O-(benzyl 2-O-benzoyl-3-O-benzyl-4-O-tert-butyldimethylsilyl-β-D-glucopyranosyluronate)-(1→3)-O-(4,6-O-benzylidene-2-deoxy-2-trichloroacetamido-β-D-glucopyranosyl)-(1→4)-O-(benzyl 2-O-benzoyl-3-O-benzyl-β-D-glucopyranosyluronate)-(1→3)-4,6-O-benzylidene-1,2-dideoxy-α-D-glucopyrano-[2,1-d]-2-oxazoline (27)

[α]D 20 +19.3 ° (c 0.5, CH2Cl2); 1H NMR (500 MHz, CDCl3): δ = −0.15 (s, 3 H, SiCH3), −0.12 (s, 3 H, SiCH3), 0.77 (s, 9 H, SiC(CH3)3), 3.02 (ddd, 1 H, J = 4.5 Hz, 5.0 Hz, 9.5 Hz, H-5”), 3.26–3.31 (m, 1 H, H-6”), 3.44–3.48 (m, 2 H, H-6, H-5), 3.55 (t, 1 H, J = 7.0 Hz, H-3’ ”), 3.63 (t, 1 H, J = 9.5 Hz, H-4”), 3.73-3.68 (m, 2 H, H-3’, H-2”), 3.82–3.91 (m, 4 H, H-3, H-4, H-5’, H-5’ ”), 4.04 (dd, 1 H, J = 5.0 Hz, 11.0 Hz, H-6”), 4.13–4.23 (m, 4 H, H-2, H-3’’, H-4’, H-4’’’), 4.28–4.29 (m, 1 H, H-6), 4.55 (d, 1 H, J = 8.0 Hz, H-1”), 4.57 (d, 1 H, J = 11.5 Hz, −CH2Ph), 4.60 (d, 1 H, J = 11.5 Hz, −CH2Ph ), 4.67 (d, 1 H, J = 11.5 Hz, −CH2Ph ), 4.77 (d, 1 H, J = 11.5 Hz, −CH2Ph ), 4.89 (d, 1 H, J = 7.5 Hz, H-1’ ”), 4.95 (d, 1 H, J = 12.0 Hz, −COOCH2Ph), 5.02 (d, 1 H, J = 7.0 Hz, H-1’), 5.15 (d, 1 H, J = 12.0 Hz, −COOCH2Ph ), 5.17 (s, 1 H, CHPh), 5.19 (d, 1 H, J = 12.0 Hz, −COOCH2Ph), 5.20 (d, 1 H, J = 12.0 Hz, −COOCH2Ph ), 5.20 (t, 1 H, J = 7.0 Hz, H-2’ ), 5.24 (dd, 1 H, J = 7.5 Hz, 8.5 Hz, H-2’ ”), 5.34 (s, 1 H, CHPh), 6.09 (d, 1 H, J = 7.5 Hz, H-1), 6.58 (d, 1 H, J = 8.5 Hz, NH”), 7.10–7.18 (m, 10 H, CHarom), 7.29–7.45 (m, 22 H, CHarom), 7.59–7.52 (m, 2 H, CHarom), 7.95–8.00 (m, 4 H, CHarom Bz); 13C NMR (125 MHz, CDCl3): δ = −5.0 (SiCH3), −4.2 (SiCH3), 18.1 (SiC(CH3)3), 26.0 (x3, SiC(CH3)3), 57.6 (C-2’’), 63.4 (C-5), 66.4 (C-5’’), 67.4 (COOCH2Ph ), 67.8 (COOCH2Ph ), 68.6 (C-6), 68.6 (C-6”), 68.9 (C-2), 71.4 (C-4’ ”), 73.1 (C-2’ ”), 73.7 (OCH2Ph), 74.7 (C-2’), 74.8 (OCH2Ph), 75.2 (C-5), 76.7 (C-4”), 77.1 (C-3”), 77.8 (C-5’ ”), 78.5 (C-4), 79.9 (C-3’), 80.1 (C-4’), 80.2 (C-3), 81.4 (C-3’ ”), 92.6 (CCl3, TCA), 99.2 (C-1’), 99.4 (C-1”), 101.0 (C-1’ ”), 101.3 (CHPh), 101.7 (CHPh), 110.0 (N=C-CCl3), 105.2 (C-1), 126.2–130.1 (CHarom), 133.4x2, 135.1, 135.4, 137.1, 137.4, 138.0, 138.2 (Cq CHPh x2, Cq OBn x2, Cq Bz x2, Cq COOBn x2), 161.8, 162.5, 165.3, 165.4, 168.2, 168.5 (C=N-CCl3, C=O TCA, C=O COOBn x2, C=O Bz x2); HRMS [M + Na]+: m/z: calcd for C90H90Cl6N2NaO24Si 1843.3682, found 1843.3724.

Methyl O-(benzyl 2-O-benzoyl-3-O-benzyl-β-D-glucopyranosyluronate)-(1→3)-O-(4,6-O-benzylidene-2-deoxy-2-trichloroacetamido-β-D-glucopyranosyl)-(1→4)-O-(benzyl 2-O-benzoyl-3-O-benzyl-β-D-glucopyranosyluronate)-(1→3)-O-(4,6-O-benzylidene-2-deoxy-2-trichloroacetamido-β-D-glucopyranosyl)-(1→4)-O-(benzyl 2-O-benzoyl-3-O-benzyl-β-D-glucopyranosyluronate)-(1→3)-4,6-O-benzylidene-2-deoxy-2-trichloroaceta mido-β-D-glucopyranoside (28)

26 was converted to 28 following the general procedure for TBS removal as described before (90%). [α]D 20 −3.0 ° (c 0.5, CH2Cl2); 1H NMR (500 MHz, CDCl3): δ = 3.00 (ddd, 1 H, J = 5.0 Hz, 5.0 Hz, 10.0 Hz, H-5a/c/e), 3.07 (s, 1 H, OH), 3.12–3.20 (m, 3 H, H-6a/c/e x3), 3.43–3.48 (m, 3 H, H-5a/c/ex2, H-2a/c/e), 3.50 (s, 3 H, OCH3), 3.61 (t, 2 H, J = 9.0 Hz, H-3a/c/e x2), 3.63–3.70 (m, 3 H, H-3 b/d/f x2, H-4a/c/e), 3.72–3.79 (m, 2 H, H-2a/c/e x2), 3.82 (dd, 1 H, J = 8.5 Hz, 9.0 Hz, H-4a/c/e), 3.82 (dd, 1 H, J = 8.5 Hz, 9.5 Hz, H-4a/c/e), 3.87 (d, 1 H, J = 8.5 Hz, H-5b/d), 3.90 (d, 1 H, J = 8.0 Hz, H-5b/d), 4.02 (dd, 1 H, J = 4.5 Hz, 9.5 Hz, H-6a/c/e), 4.05 (dd, 1 H, J = 4.5 Hz, 11.0 Hz, H-6a/c/e), 4.08–4.18 (m, 3H, H-3b/d/f, H-4b/d/f x2), 4.19 (dd, 1 H, J = 8.0 Hz, 8.5 Hz, H-4b/d/f), 4.25 (d, 1 H, J = 8.5 Hz, H-5b/d/f), 4.29 (dd, 1 H, J = 5.5 Hz, 10.5 Hz, H-6a/c/e), 4.48 (dd, 1 H, J = 9.0 Hz, 9.5 Hz, H-3a/c/e), 4.52 (d, 1 H, J = 8.0 Hz, H-1c/e), 4.56 (d, 1 H, J = 12.0 Hz, −CH2Ph ), 4.57 (d, 1 H, J = 12.0 Hz, −CH2Ph ), 4.66 (d, 1 H, J = 11.5 Hz, −CH2Ph ), 4.75 (d, 1 H, J = 7.5 Hz, H-1c/e), 4.75 (d, 1 H, J = 11.5 Hz, −CH2Ph ), 4.76 (d, 1 H, J = 12.0 Hz, −CH2Ph ), 4.79 (d, 1 H, J = 12.0 Hz, −CH2Ph ), 4.85 (d, 1 H, J = 8.0 Hz, H-1a), 4.85 (d, 1 H, J = 7.5 Hz, H-1b/d/f), 4.94–4.98 (m, 2 H, H-1b/d/f x2), 5.02 (d, 1 H, J = 11.5 Hz, −COOCH2Ph), 5.04 (d, 1 H, J = 12.0 Hz, −COOCH2Ph), 5.06 (dd, 1 H, J = 8.0 Hz, 8.5 Hz, H-2b/d/f), 5.10 (d, 1 H, J = 12.0 Hz, −COOCH2Ph ), 5.13 (s, 1 H, CHPh), 5.16 (d, 1 H, J = 12.0 Hz, −COOCH2Ph), 5.16 (d, 1 H, J = 12.0 Hz, −COOCH2Ph), 5.17 (dd, 1 H, J = 7.5 Hz, 8.5 Hz, H-2b/d/f), 5.19 (dd, 1 H, J = 6.5 Hz, 8.0 Hz, H-2b/d/f), 5.21 (s, 1 H, CHPh ), 5.25 (d, 1 H, J = 11.5 Hz, −COOCH2Ph), 5.32 (s, 1 H, CHPh), 6.45 (d, 1H, J = 8.5 Hz, NH), 6.63 (d, 1 H, J = 9.0 Hz, NH), 7.02 (d, 1 H, J = 7.5 Hz, NH), 7.13–7.61 (m, 54 H, CHarom), 7.90–8.04 (m, 6 H, CHarom Bz); 13C NMR (125 MHz, CDCl3): δ = 57.1 (C-2a/c/e), 57.5 (C-2a/c/e), 57.7 (OCH3), 58.8 (C-2a/c/e), 66.3, 66.4 (C-5a/c/e, C-6a/c/e), 66.4 (COOCH2Ph ), 68.0 (COOCH2Ph ), 68.1 (COOCH2Ph ), 68.1, 68.3, 68.5, 68.7 (C-6a/c/e x2, C-5a/c/e x2), 72.0 (C-4f), 73.6 (C-2b/d/f), 74.2 (C-2b/d/f), 74.3 (C-5b/d), 74.6 (OCH2Ph), 74.8 (OCH2Ph), 74.7 (OCH2Ph), 74.9 (C-5b/d), 75.2 (C-2b/d/f), 76.0 (C-3f), 76.9 (C-4a/c/e), 77.2 (C-4b/d), 77.4 (C-4b/d), 77.6 (C-5f), 78.8 (C-3a/c/e), 79.0 (C-3a/c/e), 80.1, 80.1, 80.1 x2 (C-3b/d/f x2, C-4a/c/e x2), 81.1 (C-3a/c/e), 92.4 (CCl3), 92.6 (CCl3), 92.7 (CCl3), 99.8 (C-1b/d/f), 99.9 (C-1b/d/f), 100.0 (C-1c/e), 100.0 (C-1c/e), 100.4 (C-1b/d/f), 100.8 (C-1a), 100.9 (CHPh), 101.1 (CHPh), 101.4 (CHPh), 126.1–130.3 (CHarom), 133.5, 133.6, 133.6, 134.9, 135.0, 135.1, 137.4, 137.5 x2, 138.0, 138.3, 138.5 (Cq CHPh x3, Cq OBn x3, Cq Bz x3, Cq COOBn x3), 161.7, 162.0, 162.4, 165.1, 165.6, 165.7, 169.0, 169.3, 169.3 (C=O TCA x3, C=O COOBn x3, C=O Bz x3); HRMS [M + Na]+: m/z: calcd for C127H118Cl9N3NaO37 2620.4513, found 2620.4595.

Methyl O-(benzyl 2-O-benzoyl-3-O-benzyl-4-O-tert-butyldimethylsilyl-β-D-glucopyranosyluronate)-(1→3)-O-(4,6-O-benzylidene-2-deoxy-2-trichloroacetamido-β-D-glucopyranosyl)-(1→4)-O-(benzyl 2-O-benzoyl-3-O-benzyl-β-D-glucopyranosyluronate)-(1→3)-O-(4,6-O-benzylidene-2-deoxy-2-trichloroacetamido-β-D-glucopyranosyl)-(1→4)-O-(benzyl 2-O-benzoyl-3-O-benzyl-β-D-glucopyranosyluronate)-(1→3)-O-(4,6-O-benzylidene-2-deoxy-2-trichloroacetamido-β-D-glucopyranosyl)-(1→4)-O-(benzyl 2-O-benzoyl-3-O-benzyl-β-D-glucopyranosyluronate)-(1→3)-O-(4,6-O-benzylidene-2-deoxy-2-trichloroacetamido-β-D-glucopyranosyl)-(1→4)-O-(benzyl 2-O-benzoyl-3-O-benzyl-β-D-glucopyranosyluronate)-(1→3)-4,6-O-benzylidene-2-deoxy-2-trichloroacetamido-β-D-glucopyranoside (10)

After a mixture of donor 25 (33.4 mg, 17.14 µmol), acceptor 28 (25 mg, 9.62 µmol) and MS-AW-300 (200 mg) in a mixture solvent of CH2Cl2 and acetonitrile (v/v 19:1, 2 mL) was stirred at −78 °C for one hour, AgOTf (51.4 mg, 20 µmol) in diethyl ether (0.7 mL) was added. When the temperature of the reaction mixture reduces to −78 °C, p-toluene sulfenyl chloride (p-TolSCl) (17.1 µmol, 2.5 µL) was added via a micro-syringe. After five minutes when the yellowish color disappeared, TMSOTf (1.25 µL, 6.9 µmol) was added via micro-syringe. The reaction mixture was warmed to −10 °C under stirring in 2 hours, followed by the same workup and purification procedures described above for the synthesis of 19. 10 (32.6 mg, 7.37 µmol, 76.6%) was afforded as white solid. [α]D 20 −2.7 ° (c 0.5, CH2Cl2); 1H NMR (500 MHz, CDCl3): δ = −0.14 (s, 3 H, SiCH3), −0.10 (s, 3 H, SiCH3), 0.79 (s, 9 H, SiC(CH3)3), 3.01 (dd, 1 H, J = 5.0 Hz, 9.0 Hz, H-5 a/c/e/g/i), 3.03 (dd, 1 H, J = 5.0 Hz, 9.0 Hz, H-5 a/c/e/g/i), 3.05 (dd, 1 H, J = 5.0 Hz, 9.0 Hz, H-5 a/c/e/g/i), 3.12–3.22 (m, 5 H, H-5 a/c/e/g/i, H-6 a/c/e/g/i x4), 3.42–3.48 (m, 3 H, H-2 a/c/e/g/i, H-5 a/c/e/g/i, H-6a/c/e/g/i), 3.50 (s, 3 H, OCH3), 3.53 (dd, 1 H, J = 7.0 Hz, 7.5 Hz), 3.55 (dd, 1 H, J = 6.0 Hz, 7.0 Hz), 3.56 (dd, 1 H, J = 5.5 Hz, 6.0 Hz), 3.60 (dd, 2 H, J = 8.5 Hz, 10.0 Hz), 3.66 (dd, 1 H, J = 6.5 Hz, 8.5 Hz), 3.67 (t, 2 H, J = 8.0 Hz), 3.68 (dd, 2 H, J = 8.5 Hz, 9.0 Hz) (H-4 a/c/e/g/i, H-3 a/c/e/g/i x4, H-3 b/d/f/h/j x5), 3.72–3.78 (m, 4 H, H-2 a/c/e/g/i x4), 3.80 (dd, 2 H, J = 9.0 Hz, 9.5 Hz, H-4b/d/f/h/j x2), 3.81 (dd, 2 H, J = 9.0 Hz, 9.5 Hz, H-4b/d/f/h/j x2), 3.85 (d, 1 H, J = 6.5 Hz, H-5b/d/f/h/j), 3.86 (d, 1 H, J = 7.0 Hz, H-5b/d/f/h/j), 3.88 (d, 2 H, J = 9.0 Hz, H-5b/d/f/h/j x2), 3.90 (d, 1 H, J = 8.5 Hz, H-5b/d/f/h/j), 4.01–4.06 (m, 4 H, H-6 a/c/e/g/i x4), 4.14 (t, 1 H, J = 7.0 Hz, H-4b/d/f/h/j), 4.16 (t, 1 H, J = 7.0 Hz, H-4b/d/f/h/j), 4.18 (t, 1 H, J = 8.5 Hz, H-4b/d/f/h/j), 4.24 (dd, 1 H, J = 8.5 Hz, 9.0 Hz, H-4b/d/f/h/j), 4.25 (dd, 1 H, J = 8.5 Hz, 9.0 Hz, H-4b/d/f/h/j), 4.28 (dd, 1 H, J = 5.0 Hz, 10.5 Hz, H-6 a/c/e/g/i), 4.48 (dd, 1 H, J = 9.0 Hz, 9.5 Hz, H-3 a/c/e/g/i), 4.53 (d, 1 H, J = 8.0 Hz, H-1 a/c/e/g/i), 4.56 (d, 1 H, J = 11.5 Hz, −CH2Ph ), 4.56 (d, 1 H, J = 11.5 Hz, −CH2Ph ), 4.56 (d, 1 H, J = 8.5 Hz, H-1 a/c/e/g/i), 4.57 (d, 1 H, J = 11.5 Hz, −CH2Ph ), 4.62 (d, 1 H, J = 11.5 Hz, −CH2Ph ), 4.63 (d, 1 H, J = 8.0 Hz, H-1 a/c/e/g/i), 4.63 (d, 1 H, J = 11.5 Hz, −CH2Ph ), 4.69 (d, 1 H, J = 11.5 Hz, −CH2Ph), 4.75 (d, 1 H, J = 8.0 Hz, H-1 a/c/e/g/i), 4.76 (d, 1 H, J = 11.5 Hz, −CH2Ph ), 4.79 (d, 1 H, J = 11.5 Hz, −CH2Ph x3 ), 4.83 (d, 1 H, J = 8.0 Hz, H-1 a/c/e/g/i), 4.91 (t, 2 H, J = 6.0 Hz, H-2b/d/f/h/j x2), 4.95 (d, 1 H, J = 6.0 Hz, H-1b/d/f/h/j), 4.96 (d, 1 H, J = 6.0 Hz, H-1b/d/f/h/j), 5.00 (d, 1 H, J = 7.0 Hz, H-1b/d/f/h/j), 4.98 (d, 1 H, J = 11.0 Hz, −COOCH2Ph), 5.00 (d, 1 H, J = 12.0 Hz, −COOCH2Ph), 5.02 (d, 1 H, J = 11.5 Hz, −COOCH2Ph x2), 5.06 (d, 1 H, J = 8.0 Hz, H-1b/d/f/h/j), 5.06 (d, 1 H, J = 8.0 Hz, H-1b/d/f/h/j), 5.06 (d, 1 H, J = 12.0 Hz, −COOCH2Ph), 5.09 (dd, 1 H, J = 8.0 Hz, 9.0 Hz, H-2b/d/f/h/j), 5.12 (d, 1 H, J = 11.5 Hz, −COOCH2Ph ), 5.13 (s, 3 H, CHPh x3), 5.15 (d, 1 H, J = 11.5 Hz, −COOCH2Ph), 5.15 (dd, 1 H, J = 8.0 Hz, 9.0 Hz, H-2b/d/f/h/j), 5.19 (d, 1 H, J = 12.0 Hz, −COOCH2Ph ), 5.19 (s, 1 H, CHPh ), 5.20 (d, 1 H, J = 11.0 Hz, −COOCH2Ph ), 5.21 (d, 1 H, J = 12.0 Hz, −COOCH2Ph ), 5.21 (dd, 1 H, J = 7.0 Hz, 8.5 Hz, H-2b/d/f/h/j), 5.31 (s, 1H, CHPh), 6.50 (d, 1 H, J = 9.0 Hz, NH), 6.55 (d, 2 H, J = 8.0 Hz, NH x2), 6.64 (d, 1 H, J = 9.0 Hz, NH), 7.02 (d, 1 H, J = 7.5 Hz, NH), 7.10–7.58 (m, 90 H, CHarom), 7.90–7.95 (m, 10 H, CHarom Bz); 13C NMR (125 MHz, CDCl3): δ = −5.0 (SiCH3), −4.2 (SiCH3), 18.1 (SiC(C 3)3), 26.0 (x3, SiC(CH3)3), 57.1, 57.1 (x2) (C-2a/c/e/g/i x3), 57.8 (C-2a/c/e/g/i), 57.8 (OCH3), 58.7 (C-2a/c/e/g/i), 66.4, 66.3 (x2), 66.3 (x2) (C-5a/c/e/g/i x5), 67.4 (COOCH2Ph ), 68.1 (x5, COOCH2Ph x4, C-6a/c/e/g/i), 68.4 (x2, C-6a/c/e/g/i x2), 68.6 (C-6a/c/e/g/i), 68.7 (C-6a/c/e/g/i), 71.4 (C-4j), `73.7 (OCH2Ph), 74.3 (C-2b/d/f/h/j), 74.6 (C-2b/d/f/h/j), 74.7 (OCH2Ph), 74.8 (x7), 74.9 (OCH2Ph x3, C-5b/d/f/h/j x5), 75.0 (C-2b/d/f/h/j), 75.0 (C-2b/d/f/h/j), 75.2 (C-2b/d/f/h/j), 76.0 (C-3a/c/e/g/i), 77.8, 77.6, 77.4 (x2) (C-4b/d/f/h x4), 77.1 (x3), 76.9 (C-4a/c/e/g/i x4), 81.4, 83.3, 80.1 (x4), 79.0, 79.0 (x2), 78.8 (C-3b/d/f/h/j x5, C-3 a/c/e/g/i x4, C-4 a/c/e/g/i), 92.4, 92.6, 92.7, 92.8 (x2) (CCl3 x5), 99.3 (C-1b/d/f/h/j), 100.0 (C-1a/c/e/g/i), 100.0 (C-1a/c/e/g/i), 100.2 (C-1b/d/f/h/j), 100.3 (C-1a/c/e/g/i x2), 100.3 (C-1b/d/f/h/j x3), 100.8 (C-1a/c/e/g/i), 100.9 (CHPh), 100.9 (CHPh x2), 101.1 (CHPh), 101.7 (CHPh), 126.2–130.2 (CHarom), 133.5, 133.5 (x2), 133.5, 133.6, 135.0 (x2), 135.0 (x2), 135.4, 137.4, 137.5 (x2), 137.5, 137.5, 138.0, 138.3, 138.5 (x2), 138.5 (Cq CHPh x5, Cq OBn x5, Cq Bz x5, Cq COOBn x5), 161.6, 161.9 (x2), 162.0, 162.3, 165.3, 165.6, 165.6, 165.7, 165.6, 168.6, 169.1 (x2), 169.3, 169.4 (C=O TCA x5, C=O COOBn x5, C=O Bz x5); MALDI [M + Na]+: m/z: calcd for C217H208Cl15N5NaO61Si 4442.85, found 4443.15.

Methyl O-(β-D-glucopyranosyluronic acid)-(1→3)-O-(2-N-acetyl-2-deoxy-β-Dglucopyranosyl)-(1→4)-O-(β-D-glucopyranosyluronic acid)-(1→3)-O-(2-N-acetyl-2-deoxy-β-D-glucopyranosyl)-(1→4)-O-(β-D-glucopyranosyluronic acid)-(1→3)-O-(2-N-acetyl-2-deoxy-β-D-glucopyranosyl)-(1→4)-O-(β-D-glucopyranosyluronic acid)-(1→3)-O-(2-N-acetyl-2-deoxy-β-D-glucopyranosyl)-(1→4)-O-(β-D-glucopyranosyluronic acid)-(1→3)-2-N-acetyl-2-deoxy-β-D-glucopyranoside (9)

10 was converted to 29 following the general procedure for TBS removal as described before (79%). 29 (44 mg, 10 µmol) was dissolved in 2 ml THF. 0.2 M KOH aqueous solution (1 ml, 200 µmol) was added in 10 portions during two days. The reaction mixture was stirred at room temperature during which the ratio of water to THF was gradually increased for a better solubility of the reaction mixture. Reaction was checked by comparisons of the crude 1H NMR spectra which was taken by the end of each week. Reaction was stopped by the neutralization with 0.2 M acetic acid in water by the end of the fifth week when peaks around 7.0 ppm in 1H-NMR of the crude NMR indicating NHTCA groups disappeared and peaks around 8.0 peaks for ortho-hydrogens on benzoyl groups changed from several equally height peaks into two main peaks. The solvent was completely removed by high vacuum rotary evaporator, and the crude residue was dissolved in anhydrous methanol (3 ml) and cooled to 0°C. Triethylamine (7.0 µL, 50 µmol) and acetic anhydride (118 µL, 1.25 mmol) were added, and the reaction mixture was stirred for two days under N2 protection at room temperature. The reaction was stopped when TLC (acetic acid/ CH2Cl2/ methanol solvent systems) show one main product forms. The reaction solvent was removed by a rotary evaporator and silica column purification (acetic acid/ CH2Cl2/ methanol solvent systems) yielded a mixture mainly composed of 31. Pd(OH)2 (50 mg) was added to a solution of the 31 in THF (0.5 mL), methanol (0.7 mL) and acetic acid (0.5 mL). The reaction flask was evacuated using a water aspirator and filled with hydrogen. This process was repeated three times and the reaction mixture was stirred under hydrogen atmosphere for three days. The solution was filtered and concentrated, and the crude product was purified by Sephadex G-15 size exclusion chromatography to give the desired product 9 (6.6 mg, 3.5 µmol, 35% from 29 for three steps). [α]D 20 −27 ° (c 0.05, H2O); 1H NMR (500 MHz, D2O): δ = 1.90–1.92 (m, 15 H, NHCOCH3 x5), 3.20–3.26 (m, 5 H), 3.35–3.43 (m, 15 H), 3.45–3.48 (m, 5 H), 3.56–3.66 (m, 20 H), 3.70–3.82 (m, 10 H), 4.34 (d, 2 H, J = 8.5 Hz, anomeric H x2), 4.36 (d, 4 H, J = 7.0 Hz, anomeric H x4), 4.44 (d, 2 H, J = 8.5 Hz, anomeric H x2), 4.45 (d, 2 H, J = 7.5 Hz, anomeric H x2); HRMS [M-3H]3−: m/z: calcd for C71H106N5O56 641.5200, found 641.5198.

Supplementary Material

1_si_001

Acknowledgment

We are grateful for the National Institutes of Health (R01-GM-72667) and a CAREER award from the National Science Foundation (CHE0852308) for financial support of this work.

Footnotes

Supporting Information Available: General experimental procedures and selected 1H-, 13C-and 2D NMR spectra. This material is available free of charge via the Internet at http://pubs.acs.org.

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