Convergent Synthesis of Branched β-Glucan Tridecasaccharides Ready for Conjugation

SYNTHESIS

0

3

9

-

7

8

1

4

3

7

-

2

1

0

X

Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart

2021, 53, A–N

paper

A

en

X. Zhou et al.

Paper

Synthesis

Convergent Synthesis of Branched -Glucan Tridecasaccharides

Ready for Conjugation

Xin Zhou^a

TBSO

O

[4+9] glycosylation

O

H

O

BzO

HO

STol

Qing Long^a

Dongwei Li^a

Jingru Gao^a

Qikai Sun^a

Shaozi Sun^a

Yong Su^a

Peng Wang^a

Wenjie Peng*^b

Ming Li*^a,c

BzO

O

HO

OBz

OH

O

4

HO

+

O

HO

OR

O

Ph

O

H

O

OH

O

OH

4

[4+5]

STol

[1+4]

HO

glycosylation

OBz

glycosylation

1a R = CH₂CH₂NH₂; 1b R = CH₂CH₂N₃

convergent synthesis based on catalytic glycosylation of glycosyl trichloroacetimidates

in 4.7% and 3.9% overall yield and in the longest linear sequence of 16 and 17 steps

gram-scale access to the nonasaccharide main chain

installation of the tetrasaccharide branch via orthoester rearrangement

^aKey Laboratory of Marine Medicine, Chinese Ministry of Education,

School of Medicine and Pharmacy, Ocean University of China, Qingdao

266003, P. R. of China

lmsnouc@ouc.edu.cn

^bLaboratory of Systems Biomedicine, Chinese Ministry of Education,

Shanghai Center for Systems Biomedicine, Shanghai Jiao Tong

University, Shanghai 200240, P. R. of China

wenjiep@sjtu.edu.cn

^cLaboratory for Marine Drugs and Bioproducts, Pilot National Laboratory

for Marine Science and Technology, Qingdao 266237, P. R. of China

Corresponding Authors

Received: 19.02.2021

Accepted after revision: 16.03.2021

Published online: 16.03.2021

prevention and treatment of mycotic infections and can-

cers.⁴

The heterogeneity of isolates from natural sources re-

sults in difficulties in acquiring pure homogeneous glyco-

forms of -1,3-glucans, thus complicating the establish-

ment of structure–activity relationships. To overcome these

obstacles, much effort has been devoted to the chemical

synthesis and biological evaluation of -1,3-glucan frag-

ments and derivatives with a rigorously defined structure

and a high degree of purity.⁵Among these precedents, im-

pressive achievements are the automated assembly of a do-

deca- and tridecasaccharide^6,7and the one-pot synthesis of

6-O-branched tridecasaccharides based on the preactiva-

tion of thioglycosides.⁸Regioselective glycosylation featur-

ing step economy was successfully applied in the synthesis

of a linear tridecasaccharide⁹and branched heptadecasac-

charide.^10,11Chromatography-free synthesis of a -1,6-

hexaglucan¹²and -1,3-glucan¹³laminarihexaose was

achieved relying on hydrophobic tag assisted, liquid-phase

ionic liquid supported synthesis technologies. Gold-cata-

lyzed glycosylation of o-alkynylbenzoates represents a mild

method to construct various glycosidic linkages.¹⁴The reac-

tion was employed to assemble hexadeca- and tetradecasa-

ccharides of glucans.¹⁵Very recently, Crich and co-workers

described the synthesis of 1,5-dithia- and thioether-linked

carbocyclic mimics as -1,3-glucan oligomers.¹⁶Biological

activities of the synthesized -1,3-glucan oligomers and de-

rivatives have been evaluated including binding affinity to

dectin-1,^{6,7,10,11,14–17}the possibility as antibody epitopes,⁷

and the ability to stimulate phagocytosis and pinocytosis,¹⁶

DOI: 10.1055/a-1440-9386; Art ID: ss-2021-g0073-op

Abstract Structurally defined and pure oligosaccharides correspond-

ing to -glucans have attracted great attention because of their poten-

tial properties as immunostimulating agents and as antigens of vaccine

candidates. We herein describe a convergent synthesis of ready-to-con-

jugate tridecasaccharides composed of a -1,3-glucan nonasaccharide

backbone and a -1,6-glucan tetrasaccharide branch. The assembly was

achieved by employing trichloroacetimidate glycosylations and features

the gram-scale preparation of the nonasaccharide backbone and instal-

lation of the tetrasaccharide branch involving orthoester rearrange-

ment to the glycoside.

Key words -glucans, glycosyl trichloroacetimidates, oligosaccharide

synthesis, orthoester rearrangement, convergent synthesis

-D-Glucans are fundamental structural members of

the cell wall or reserve polysaccharides of yeasts, algae, and

high plants. They are composed of a -1,3-glucan backbone

decorated frequently with branches consisting of -1,3- or

-1,6-linked short glucans that are usually attached to C6-

OHs of glucosyl units of the main chain.¹-Glucans have

been shown to possess anti-inflammatory, anticancer, anti-

microbial, and antidiabetic activities, among others.²The

immunostimulating properties of -glucans have been ap-

plied to enhance the natural immune system and to relieve

the side effects resulting from chemotherapy.³The absence

of -1,3-glucans in mammals makes such glucans and

structurally related oligosaccharides promising antigens of

carbohydrate–protein conjugate vaccine candidates for the

Georg Thieme Verlag KG, Rüdigerstraße 14, 70469 Stuttgart, Germany

B

X. Zhou et al.

Paper

Synthesis

[4+9] glycosylation via

orthoester rearrangement

O

HO

H

O

OH

4

OH

O

HO

OR

O

H

4

OH

4

1a R = CH₂CH₂NH₂

1b R = CH₂CH₂N₃

O

BzO

O

HO

BnO

TBS

Ph

O

Ph

O

+

OBz BzO

O

N₃

Lev

3

BzO

OBz

4

BzO

OTCAI

2

3

TBSO

BzO

O

TBSO

BnO

LevO

O

BzO

Ph

O

Ph

3

O

R

OBz

O

R

+

O

Lev

BzO

OBz

BzO

OTCAI

4 R = β-STol

5 R = α-OTCAI

9

R = β-STol

10 R = α-OTCAI

8

TBSO

BzO

Ph

O

Ph

O

Ph

O

BzO

O

R

STol

LevO

HO

OBz

11 R = β-STol

12 R = α-OTCAI

OBz

13

6 R = β-STol

7 R = α-OTCAI

Scheme 1 Strategy for the synthesis of tridecasaccharides 1a and 1b

which show potential applications in carbohydrate-based

medicines. In addition, the conjugate of 2-aminoethyl -

glucan tridecasaccharide 1a (Scheme 1) with keyhole lim-

pet hemocyanin (KLH) has been shown to be a promising

antifungal vaccine candidate.¹⁸Herein, we describe the as-

sembly of 1a and its azido congener 1b (Scheme 1). Either

the amino or azido group could serve as a handle to couple

with functional devices through amide bond formation or

click chemistry, thus giving access to chemical probes for

use in biological studies.

Synthetic Plan. The Schmidt glycosylation has been

recognized as one of the most popular reactions to con-

struct various glycosidic bonds because of the easy prepa-

ration of glycosyl trichloroacetimidates and high-yielding

coupling with nucleophiles under mild conditions with cat-

alytic Lewis acids such as trimethylsilyl trifluoromethane-

sulfonate (TMSOTf) and boron trifluoride etherate

(BF₃·OEt₂) as the promoters.¹⁹As such, we wanted to assem-

ble the target molecules following a convergent strategy

based on the Schmidt glycosylation.

thermore, in order to ensure the formation of 1,2-trans--

glucosidic bonds by means of anchimeric assistance, benzo-

yl was selected as the protecting group at C2-OH of glucosyl

units.

With these considerations in mind, the target molecules

1a and 1b could be disconnected into -1,6-linked tetrasac-

charide 2 as the branch and -1,3-connected linear nona-

saccharide 3 as the backbone (Scheme 1). Tetrasaccharide 2

could be prepared by the coupling of disaccharide trichloro-

acetimidate (TCAI) 5 with thioglycoside 4, both of which

could originate from thioglucoside 6 and glucosyl TCAI do-

nor 7. The bulky tert-butyldimethylsilyl (TBS) was selected

as the protecting group of C6-OH of 6 in recognition of its

reliability and proven record in highly preferential installa-

tion at primary hydroxy groups over secondary ones and

orthogonal removal in the presence of benzoates for ensu-

ing sugar chain extension at this position. 4,6-O-Ben-

zylidene acetal as the C4- and C6-OHs of glucosyl building

blocks has witnessed successes in several syntheses of -

1,3-glucans.^{6,8–11,13,15,20}Accordingly, the nonasaccharide 3

could be divided into the monosaccharide TCAI donor 8 and

the tetrasaccharide fragments 9 and 10. Building block 8 is

characterized by the C6 TBS ether and C3 levulinoyl (Lev)

ester that mark the branching and the elongating sites. Di-

saccharides 11 and 12 en route to tetrasaccharides 9 and 10

could be traced to readily available 4,6-O-benzylidene-pro-

tected thioglucoside 13, with Lev and benzoyl differentiat-

ing C3- and C2-OH. Thioglycoside 13 also could serve as the

Structurally, tridecasaccharides 1a and 1b are composed

of a -1,3-nonaglucan backbone and a -1,6-tetraglucan

branch appended to C6-OH of the central glucosyl unit of

the backbone. Since a primary hydroxy group such as C6-

OH of glucose is generally more accessible than a secondary

hydroxy group such as C3-OH, we aimed to reach the target

by assembling the -1,3-glucan nonasaccharide backbone

prior to the introduction of -1,6-glucan branching. Fur-

C

X. Zhou et al.

Paper

Synthesis

OTBS

O

OTBS

O

BzO

O

BzO

i) NBS, acetone/H₂O

O

14, TMSOTf

BzO

O

BzO

STol

OBz

ii) CCl₃CN, DBU

DCM, 0 °C

73% over 2 steps

DCM, 0 °C

93%

BzO

OBz

OTCAI

6

7

4

OH

O

α/β = 9.5:1

BzO

STol

OBz

14

OTBS

O

BzO

i) NBS, acetone/H₂O

O

BzO

O

OTCAI

ii) CCl₃CN, DBU

DCM, 0 °C

92% over 2 steps

OBz

5

O

BzO

α/β = 1:1

O

TBS

O

BzO

TMSOTf

O

R

OBz

DCM, 0 °C

84%

3

BzO

OBz

OH

O

16 R = β-STol

i) NBS, acetone/H₂O

ii) CCl₃CN, DBU

DCM, 0 °C

BzO

TBAF, AcOH

THF, 89%

O

BzO

O

OBz

82% over 2 steps

STol

2 R = α-OTCAI

15

OBz

Scheme 2 Synthesis of -1,6-glucan tetrasaccharide building block 2

precursor to orthogonally protected TCAI donor 8 which

entails protecting group manipulations to decorate C6-OH

with a TBS group.

warrant comments. Monitoring the reaction process by

thin-layer chromatography revealed conversion of kineti-

cally formed benzoate 13a into thermodynamic product 13

through migration of the benzoyl group from C3-OH to C2-

OH. Separation of the desired product 13 from regioisomer

13a with very close polarity could be readily achieved by

crystallization in toluene; however, it was crucial to remove

the silver species and dibenzoate 13b using flash chroma-

tography on a short silica gel column prior to the crystalli-

zation because their presence resulted in decomposition or

difficulty in the isolation of 13. Following this procedure,

7.0 g of 13 could be obtained in 61% yield in one batch, set-

ting a solid foundation for the assembly of nonasaccharide

3.

Synthesis of -1,6-Glucan Tetrasaccharide 2. Our

study toward convergent synthesis of -1,6-glucan tetram-

er 2 (Scheme 2) commenced with the preparation of gluco-

syl TCAI donor 7, which would be employed as the glyco-

sylating agent. Thus, treatment of thioglycoside 6²¹with N-

bromosuccinimide in aqueous acetone followed by 1,8-di-

azabicyclo[5.4.0]undec-7-ene (DBU)-catalyzed addition of

the resulting hemiacetal to trichloroacetonitrile afforded 7

in 73% yield over two steps. TMSOTf-catalyzed orthogonal

glycosylation of acceptor alcohol 14,²¹readily prepared by

selective removal of the TBS group at position C6 of thiogly-

coside 6, with TCAI donor 7 smoothly provided the desired

disaccharide 4 in 93% yield. With disaccharide 4 in hand, we

then converted the disaccharide into TCAI donor 5 and ac-

ceptor alcohol 15 by anomeric functional group manipula-

tions and selective cleavage of the TBS ether with AcOH-

buffered tetrabutylammonium fluoride in 92% and 89%

yield, respectively. 1,6-Linked -tetraglucan 16 was stereo-

selectively achieved in 84% yield by coupling 5 with 15.

Conversion of thioglycoside 16 into the corresponding TCAI

donor 2 was accomplished in 82% yield over two steps.

Synthesis of -1,3-Glucan Nonasaccharide 3. Accord-

ing to our synthetic plan, we assembled -1,3-glucan nona-

saccharide backbone 3 following a [4+(1+4)] strategy. Thus,

the synthesis proceeded from preparation of the key mono-

saccharide building block 13 bearing a benzoyl protecting

group at C2-OH (Scheme 3). Motivated by the protocol of Ye

and Chang, whose groups independently described Ag₂O-

mediated site-selective benzoylation of sugars,^22,23we em-

ployed the reaction to selectively protect benzylidene-pro-

tected thioglucoside 17.²²The desired 2-O-benzoylthioglu-

coside 13 was obtained, accompanied by 3-O-benzoyl iso-

mer 13a and 2,3-di-O-benzoylglucoside 13b as the

unwanted products. Several features of the transformation

O

Ph

O

Ph

O

Ag₂O, BzCl

CHCl₃, 0 °C

O

STol

R²O

STol

HO

OR¹

OH

13 R¹= Bz, R²= H

17

(7.0 g, 61%)

13a R¹= H, R²= Bz (7%)

13b R¹= R²= Bz (9%)

OH

O

13

Bu₂BOTf, BH₃THF

TBSCl, DMAP

BnO

HO

STol

DCM, 28 °C, 71%

pyridine, 50 °C

97%

OBz

18

OTBS

i) NIS, TFA, DCM/H₂O

O

BnO

STol

RO

LevO

ii) CCl₃CN, DBU, DCM

67% over 2 steps

OBz

BzO

OTCAI

8

19 R = H

levulinic acid

DCC, DMAP

DCM, 98%

α/β = 20:1

20 R = Lev

Scheme 3 Synthesis of monosaccharide TCAI donor 8

With sufficient 13 in hand, we turned our attention to

the synthesis of mono- and tetrasaccharide TCAI donors 8

and 10, two key intermediates to reach nonasaccharide 3.

As shown in Scheme 3, regioselective reductive ring open-

ing of the benzylidene acetal on 13 using the combination

of borane–tetrahydrofuran complex (BH₃·THF)/dibutylboryl

trifluoromethanesulfonate (Bu₂BOTf)²⁴delivered 71% of 4-

D

X. Zhou et al.

Paper

Synthesis

O-benzyl ether 18 with C3- and C6-OH free. Silylation at

C6-OH with TBSCl (→ 19) and then levulinoylation at C3-

OH using N,N′-dicyclohexylcarbodiimide-mediated esterifi-

cation afforded orthogonally protected thioglycoside 20. Fi-

nally, the expected TCAI donor 8 was obtained in a satisfac-

tory yield by a two-step reaction sequence involving N-io-

dosuccinimide-mediated hydrolysis of 20 and addition of

the resulting hemiacetal to trichloroacetonitrile in the pres-

ence of DBU.

The preparation of tetrasaccharide TCAI donor 10 is out-

lined in Scheme 4. Thioglycoside 13 evolved into TCAI do-

nor 22 in overall 84% yield involving levulinoylation of C3-

OH (→ 21) and subsequent conversion of thioglycoside into

the corresponding TCAI donor 22. With the building blocks

22 and 13 secured, TMSOTf-catalyzed chemoselective acti-

vation coupling efficiently furnished disaccharide thiogly-

coside 11 in 83% yield and in significant quantities (5.65 g

scale). Next, 11 was split and transformed in parallel to di-

saccharide TCAI donor 12 and acceptor alcohol 23 as fol-

lows. As usual, TCAI donor 12 was obtained in 79% yield

through N-iodosuccinimide-mediated hydrolysis of thiogly-

coside followed by reaction with trichloroacetonitrile.

Selective removal of Lev using hydrazine-mediated amino-

lysis²⁵in the presence of AcOH allowed for the preparation

of 23 in almost quantitative yield. Coupling of 12 and 23 at

–40 °C by the action of TMSOTf (0.1 equiv) exclusively gave

-linked tetrasaccharide 9, which was further converted

into the corresponding TCAI donor 10 (4.2 g scale) in 70%

yield over two steps.

Cleavage of the Lev group uneventfully resulted in acceptor

alcohol 25 in 87% yield. Unexpectedly, sugar chain exten-

sion at C3-OH of 25 using monosaccharide donor 8 is not

trivial. The initial reaction promoted by TMSOTf as the con-

ventional catalyst resulted in a complicated mixture. To our

delight, after evaluating various Lewis acids, we found that

a switch of the activator from TMSOTf to TBSOTf yielded the

desired pentasaccharide 26 in 83% yield at –40 °C. TBSOTf

has proven to be a superior catalyst to TMSOTf for glyco-

sylations of TCAI donors with substrates difficult to glyco-

sylate.²⁶Iterative coupling of TCAI 10 with 27, prepared by

removing Lev from compound 26, under the promotion of

TBSOTf (0.2 equiv) smoothly furnished nonasaccharide 28

(2.25 g scale) in excellent 84% yield. Deprotection of the TBS

ether with pyridinium poly(hydrofluoride) (pyridine·nHF)

in acetonitrile efficiently liberated C6-OH of the central glu-

cose unit and left the eight benzylidene acetals untouched.

As such, the gram-scale synthesis of 1,3-linked nonasaccha-

ride 3 (1.08 g scale) was achieved in 86% yield, ready for

next installation of the -(1,6)-glucan tetrasaccharide

branch.

Synthesis of -Glucan Tridecasaccharides 1a and 1b.

With -1,6-glucan tetrasaccharide TCAI donor 2 and -1,3-

glucan nonasaccharide acceptor alcohol 3 in hand, the as-

sembly of tridecasaccharide 30 was performed. We first

evaluated the possibility of the coupling of 2 with 3 cata-

lyzed by TMSOTf or TBSOTf. We were, however, unrewarded

and hydrolysis of 2 was found to take place as the major

side reaction. These unwanted results might originate from

the unmatched reactivity of 2 with 3 due to steric hin-

drance of the acceptor alcohol. Inspired by the reports using

silver triflate (AgOTf) as a mild activator in the Schmidt gly-

cosylation reaction,²⁷we opted to apply this catalyst to the

coupling between 2 and 3. The reaction promoted by AgOTf

resulted in a clean transformation in toluene in the pres-

ence of 5 Å molecular sieves. The isolated product was,

With TCAI donors 8 and 10 available, we set out to as-

semble the nonasaccharide following the [4+(1+4)] strate-

gy. As shown in Scheme 5, TMSOTf-promoted glycosylation

of TCAI donor 10 with 2-azidoethanol at 0 °C furnished -

1,3-glucan tetramer 24 in 90% yield. It should be pointed

out that attempts to couple tetrasaccharide thioglycoside 9

with 2-azidoethanol produced 24 in a lower yield of 61%.

O

i) NIS, TFA, DCM/H₂O

0 to 28 °C

Ph

levulinic acid

DCC, DMAP

Ph

O

STol

LevO

STol

HO

LevO

BzO

OBz

ii) CCl₃CN, DBU, DCM

28 °C, 88% over 2 steps

DCM, 26 °C, 96%

OTCAI

22

21

13

α/β = 20:1

O

i) NIS, TFA, DCM/H₂O

0–26 °C

Ph

O

LevO

ii) CCl₃CN, DBU, DCM

26 °C

79% over 2 steps

OBz

12

BzO

OTCAI

Ph

O

Ph

13, TMSOTf

O

TMSOTf

O

STol

LevO

DCM, –40 °C

83%

OBz

DCM, –40 °C

85%

Ph

O

NH₂NH₂·H₂O, AcOH

DCM, 26 °C, 98%

11

O

STol

HO

OBz

23

O

Ph

2

Ph

O

Ph

O

R

O

LevO

BzO

OBz

9 R = β-STol

10 R = OTCAI, α/β = 8.3:1

i) NIS, TFA, DCM/H₂O, 0–27 °C

ii) DBU, CCl₃CN, DCM, 27 °C

4.2 g scale, 70% over 2 steps

Scheme 4 Synthesis of -1,3-glucan tetrasaccharide building blocks 9 and 10

E

X. Zhou et al.

Paper

Synthesis

ry carbon signal in the ¹³C NMR spectrum appeared at 121.3

ppm, data diagnostic of an orthoester quaternary carbon.

Although circuitous, protic acid promoted rearrange-

ment of orthoesters has proven to be an efficient method to

gain access to glycosides.²⁸Gratifyingly, treatment of or-

thoester 29 with TfOH, generated in situ by reacting AgOTf

and ^tBuCl, afforded tridecasaccharide 30 in 71% yield. How-

ever, attempts to directly reach 30 by treating acceptor al-

cohol 3 with TCAI donor 2 in the presence of TfOH failed.

With fully protected 30 in hand, synthesis of tridecasac-

charides 1a and 1b was carried out as shown in Scheme 6.

After desilylation of 30 with pyridine·nHF resulted in tride-

casaccharide 31, we initially tended to employ lithium-me-

diated Birch reduction in liquid ammonia to globally re-

move all protecting groups, including the eight benzylidene

acetals, one benzyl group, 21 benzoyl groups, and one Lev,

along with concomitant reduction of the azido substituent.

Unfortunately, the reaction was messy and ESI-MS analysis

of the crude reaction mixture did not show a peak corre-

sponding to the anticipated oligosaccharide. Next, we

turned to a stepwise manner to deprotect 31 involving a

three-step sequence of reactions, composed of removal of

the benzylidene acetals with a mixture of MeOH and DCM

in the presence of p-toluenesulfonic acid hydrate at 40 °C,

hydrolysis of the esters using LiOH·H₂O as the base in aque-

ous MeOH, and then palladium-catalyzed hydrogenolysis of

the benzyl group along with hydrogenation of the azido

group, which provided the desired target molecule 1a in

overall 66% yield. Reversal of the manipulation order of ace-

tal and ester hydrolysis is not suggested because the ben-

zylidene-protected polyalcohol arising from saponification

was found to be very poorly soluble in either pure MeOH or

aqueous MeOH. Amine 1a was transformed to azide 1b in

10

2-azidoethanol

TMSOTf, DCM, 0 °C

90%

O

Ph

O

Ph

O

N₃

O

RO

BzO

OBz

2

24 R = Lev

25 R = H

NH₂NH₂H₂O, AcOH

DCM, 30 °C, 87%

8, TBSOTf

DCM, –40 °C

83%

Ph

3

O

Ph

O

TBSO

BnO

RO

O

N₃

O

BzO

26 R = Lev

27 R = H

NH₂NH₂H₂O, AcOH

DCM, 30 °C, 95%

10, TBSOTf

DCM, –40 °C

84%

RO

O

Ph

O

BnO

O

N₃

Lev

BzO

4

BzO

4

BzO

28 R = TBS

R = H

pyridine nHF, MeCN, 30 °C

1.08 g, 86%

3

Scheme 5 Synthesis of -1,3-glucan nonasaccharide backbone 3

however, determined to be orthoester 29 (Scheme 6) rather

than the expected glycoside. The structure of 29 was evi-

dent from the ¹H and ¹³C NMR spectroscopic data. The ano-

meric proton associated with the newly formed glycosidic

bond was found to resonate at 5.77 ppm as a doublet with a

coupling constant of ³J_H1–H2= 4.9 Hz, implying the presence

of an -configured glycosidic bond. In addition, a quaterna-

O

TBS

O

BzO

OBz

O

BzO

3

2, AgOTf

3

Ph

O

toluene, 32 °C

77%

O

Ph

O

BnO

O

4

O

N₃

O

Lev

OBz

4

29 (498 mg)

AgOTf, ^tBuCl

toluene, 18 °C

293 mg, 71%

O

R⁶

R³O

O

R³O

O

4

OR¹

R¹O

R⁴O

R¹O

O

R²

R⁵

R³O

4

30 R¹–R¹= CHPh, R²= Lev, R³= Bz, R⁴= Bn, R⁵= N₃, R⁶= TBS

31 R¹–R¹= CHPh, R²= Lev, R³= Bz, R⁴= Bn, R⁵= N₃, R⁶= H

pyridine nHF, MeCN

89% (278 mg)

i) TsOH H₂O, DCM/MeOH, 40 °C

ii) LiOH H₂O, MeOH/H₂O, 40 °C

iii) Pd/C, H₂, H₂O, 40 °C, 66%

1a R¹

1b R¹

=

R²

=

R³

=

R⁴= R⁶= H, R⁵= NH₂

R⁴= R⁶= H, R⁵= N₃

ImSN₃·HCl, CuSO₄·5H₂O, K₂CO₃

MeOH/H₂O, 23 °C, 83% (38 mg)

Scheme 6 Synthesis of branched -glucan tridecasaccharides 1a and 1b

F

X. Zhou et al.

Paper

Synthesis

83% yield using imidazole-1-sulfonyl azide hydrochloride

(ImSN₃·HCl)²⁹as diazo transfer agent in the presence of Cu-

SO₄·5 H₂O and K₂CO₃in MeOH/H₂O.

by silica gel column chromatography (petroleum ether/EtOAc, 7:1) to

afford 7 (2.3 g, 3.07 mmol, 73% over 2 steps, / = 9.5:1) as a slightly

yellow foam.

[]_D¹⁵+0.88 (c 1.75, CHCl₃).

¹H NMR (500 MHz, CDCl₃):  = 7.96 (d, J = 7.8 Hz, 4 H), 7.87 (d, J = 7.5

Hz, 2 H), 7.50 (t, J = 6.7 Hz, 2 H), 7.45–7.27 (m, 5 H), 7.29 (t, J = 7.6 Hz,

2 H), 6.84 (d, J = 3.2 Hz, 1 H), 6.23 (t, J = 10.0 Hz, 1 H), 5.73 (t, J = 10.0

Hz, 1 H), 5.55 (dd, J = 10.2, 3.4 Hz, 1 H), 4.35 (d, J = 10.1 Hz, 1 H), 3.91–

3.81 (m, 2 H), 0.86 (s, 9 H), 0.00 (s, 6 H).

¹³C NMR (101 MHz, CDCl₃):  = 165.9, 165.6, 165.2, 160.7, 133.6,

133.4, 133.3, 130.0, 129.94, 129.86, 129.23, 129.18, 128.8, 128.5,

128.4, 93.5, 91.0, 73.6, 71.1, 70.6, 68.6, 62.2, 25.9, 18.4, –5.32, –5.33.

In conclusion, we have developed an efficient conver-

gent synthesis of branched -glucan tridecasaccharides

bearing a 2-amino- or 2-azidoethyl linker. The synthesis

takes advantage of Lewis acid catalyzed Schmidt glycosyla-

tion and features the preparation of a -1,3-nonasaccharide

backbone on a gram scale and the installation of a -1,6-

tetrasaccharide branch relying on TfOH-catalyzed rear-

rangement of an orthoester intermediate to the corre-

sponding glycoside. The ready availability of tridecasaccha-

rides sets a solid foundation for conjugation to biological

devices for use in biological studies.

HRMS (ESI): m/z [M + NH₄]⁺calcd for C₃₅H₄₂Cl₃N₂O₉Si: 767.1720;

found: 767.1704.

p-Tolylthio (2,3,4-Tri-O-benzoyl-6-O-tert-butyldimethylsilyl--D-

glucopyranosyl)-(1→6)-2,3,4-tri-O-benzoyl--D-glucopyranoside

All reactions were carried out under argon with magnetic stirring un-

less otherwise indicated. All commercially obtained reagents were

used as received, except where specified otherwise. NBS, NIS,

TMSOTf, TBSOTf, AgOTf, BH₃·THF, TBSCl, DMAP, DCC, NH₂NH₂·H₂O,

and p-TsOH·H₂O were purchased from Energy Chemical; trichloroace-

tonitrile, DBU, TBAF, levulinic acid, pyridine·nHF, and CuSO₄·5 H₂O

were purchased from Macklin Biochemical; Bu₂BOTf, ^tBuCl, and

LiOH·H₂O were purchased from Aladdin; Pd/C was purchased from

Sigma-Aldrich and used without further purification. Anhydrous

DCM and toluene were obtained by passing commercially available

pre-dried, oxygen-free formulations through activated alumina col-

umns. Pyridine was refluxed over CaH₂and distilled before use. Ace-

tone and MeOH were used without further purification. Flash column

chromatography was performed on Silica Gel H (300–400 mesh, Qing-

dao, China). Analytical TLC was performed on SiliCycle SiliaPlate

glass-backed plates coated with silica gel (60 mesh pore size, F-254

indicator) and visualized by exposure to UV light and/or staining with

8% H₂SO₄in MeOH. Optical rotations were determined with a JASCO

P-1020 digital polarimeter. NMR spectra were recorded on an Agilent

DD2 400 or 500 MHz NMR spectrometer and calibrated by using re-

sidual undeuterated chloroform (_H= 7.26 ppm) and CDCl₃(_C= 77.16

ppm) as internal references. The following abbreviations are used to

designate multiplicities: s = singlet, d = doublet, t = triplet, q = quartet,

m = multiplet, brs = broad singlet. High-resolution mass spectra were

obtained using a Thermo LTQ Orbitrap XL high resolution mass

spectrometer.

(4)

A mixture of trichloroacetimidate 7 (2.0 g, 2.67 mmol, 1.0 equiv) and

acceptor 14 (1.84 g, 3.07 mmol, 1.15 equiv) in anhydrous DCM (50

mL) was stirred for 30 min in the presence of activated 5 Å molecular

sieves (5.0 g). Then the mixture was cooled to 0 °C followed by addi-

tion of TMSOTf (49 L, 0.27 mmol, 0.1 equiv). After being stirred for 4

h at 0 °C, the reaction mixture was filtered through a Celite pad, and

the filtrate was sequentially washed with saturated aqueous NaHCO₃

and brine. The collected organic layers were dried over Na₂SO₄. The

solid was filtered off, and the filtrate was concentrated. The residue

was purified by silica gel chromatography (petroleum

ether/DCM/EtOAc, 8:1:1) to afford 4 (2.94 g, 2.48 mmol, 93%) as a

white foam.

[]_D¹⁵+0.07 (c 3.25, CHCl₃).

¹H NMR (500 MHz, CDCl₃):  = 7.95–7.91 (m, 6 H), 7.85 (d, 7.4 Hz, 4

H), 7.74 (d, J = 7.4 Hz, 2 H), 7.55–7.45 (m, 4 H), 7.45–7.22 (m, 16 H),

7.17 (d, J = 7.8 Hz, 2 H), 5.83 (t, J = 9.6 Hz, 1 H), 5.77 (t, J = 9.5 Hz, 1 H),

5.52–5.42 (m, 2 H), 5.34 (t, J = 9.7 Hz, 1 H), 5.27 (t, J = 9.7 Hz, 1 H), 4.97

(d, J = 7.9 Hz, 1 H), 4.80 (d, J = 9.9 Hz, 1 H), 4.06–3.97 (m, 2 H), 3.92–

3.88 (m, 1 H), 3.85–3.73 (m, 3 H), 2.37 (s, 3 H), 0.83 (s, 9 H), –0.04 (d,

J = 6.7 Hz, 6 H).

¹³C NMR (126 MHz, CDCl₃):  = 165.9, 165.8, 165.40, 165.37, 165.2,

165.1, 138.9, 134.1, 133.6, 133.4, 133.26, 133.22, 133.20, 129.96,

129.95, 129.92, 129.85, 129.78, 129.5, 129.4, 129.3, 129.1, 128.9,

128.8, 128.50, 128.47, 128.40, 128.36, 128.32, 127.7, 101.2, 86.1, 78.4,

75.4, 74.3, 73.5, 72.1, 70.6, 69.69, 69.65, 68.4, 62.7, 25.9, 21.3, 18.4,

–5.26, –5.29.

2,3,4-Tri-O-benzoyl-6-O-tert-butyldimethylsilyl--D-glucopyrano-

HRMS (ESI): m/z [M + NH₄]⁺calcd for C₆₇H₇₀NO₁₆SSi: 1204.4179;

syl Trichloroacetimidate (7)

found: 1204.4158.

NBS (1.50 g, 8.42 mmol, 2.0 equiv) was added to a solution of tolyl

glycoside 6 (3.0 g, 4.21 mmol, 1.0 equiv) in a mixture of acetone/H₂O

(30 mL, 9:1 v/v) at 0 °C. The reaction was allowed to proceed under

stirring for 2 h at rt and quenched with Et₃N, and the mixture was

concentrated. The residue was dissolved in DCM (30 mL) and washed

with 20% (w/w) aqueous Na₂S₂O₃(30 mL). The aqueous layer was re-

extracted with DCM (2 × 30 mL) and the combined organic layers

were dried and concentrated; the crude hemiacetal was used in the

next step without further purification. Trichloroacetonitrile (2.11 mL,

21.05 mmol, 5.0 equiv) was added to a solution of the hemiacetal in

anhydrous DCM (30 mL) stirred at rt under N₂. DBU (315 L, 2.11

mmol, 0.5 equiv) was then added slowly, and the mixture was stirred

at 0 °C for 12 h. The reaction mixture was concentrated, and purified

(2,3,4-Tri-O-benzoyl-6-O-tert-butyldimethylsilyl--D-glucopyra-

nosyl)-(1→6)-2,3,4-tri-O-benzoyl-D-glucopyranosyl Trichloroace-

timidate (5)

Following the procedure for 7, treatment of 4 (2.0 g, 1.69 mmol, 1.0

equiv) with NBS (601 mg, 3.38 mmol, 2.0 equiv) in acetone/H₂O (30

mL, 9:1 v/v) at 0 °C afforded the crude hemiacetal, which was treated

with trichloroacetonitrile (847 L, 8.45 mmol, 5.0 equiv) and DBU

(126 L, 0.85 mmol, 0.5 equiv) at 0 °C to afford 5 (1.9 g, 1.55 mmol,

92% over 2 steps, / = 1:1) as a white foam after purification by silica

gel column chromatography (petroleum ether/EtOAc, 4:1).

G

X. Zhou et al.

Paper

Synthesis

¹H NMR (500 MHz, CDCl₃):  = 8.62 (s, 1 H), 8.31 (s, 1 H), 8.01 (d, J =

7.8 Hz, 2 H), 7.97 (d, J = 7.9 Hz, 2 H), 7.94–7.86 (m, 12 H), 7.83–7.76

(m, 8 H), 7.52–7.18 (m, 36 H), 6.68 (d, J = 3.0 Hz, 1 H), 6.21–6.14 (m, 1

H), 6.08 (d, J = 7.9 Hz, 1 H), 5.90–5.80 (m, 3 H), 5.70 (t, J = 8.6 Hz, 1 H),

5.57–5.38 (m, 7 H), 5.06 (d, J = 7.8 Hz, 1 H), 4.92 (d, J = 7.5 Hz, 1 H),

4.46 (dd, J = 10.2, 5.4 Hz, 1 H), 4.25–4.18 (m, 1 H), 4.17–4.05 (m, 3 H),

3.94 (dd, J = 11.7, 7.5 Hz, 1 H), 3.85–3.75 (m, 6 H), 0.82 (d, J = 3.6 Hz,

18 H), –0.04 (d, J = 8.9 Hz, 12 H).

¹³C NMR (126 MHz, CDCl₃):  = 166.02, 165.98, 165.7, 165.41, 165.37,

165.32, 165.24, 165.22, 165.14, 164.9, 164.3, 163.8, 160.7, 160.3,

133.7, 133.60, 133.57, 133.45, 133.43, 133.38, 133.33, 133.26, 133.25,

133.23, 133.1, 130.1, 130.02, 129.95, 129.87, 129.82, 129.78, 129.57,

129.55, 129.25, 129.23, 129.04, 129.03, 129.01, 128.97, 128.70,

128.68, 128.64, 128.54, 128.49, 128.46, 128.41, 128.39, 128.35,

128.26, 100.9, 100.6, 95.8, 92.9, 75.5, 75.4, 73.43, 73.39, 72.8, 72.1,

71.99, 71.97, 71.91, 70.84, 70.82, 70.2, 69.7, 69.5, 69.2, 68.7, 67.6,

67.5, 62.7, 62.6, 29.8, 25.88, 25.86, 18.4, –5.29, –5.30, –5.32, –5.35.

¹H NMR (500 MHz, CDCl₃):  = 8.06–7.94 (m, 6 H), 7.94–7.85 (m, 12

H), 7.83 (d, J = 7.7 Hz, 4 H), 7.71 (d, J = 7.6 Hz, 2 H), 7.57–7.14 (m, 38

H), 7.10 (d, J = 7.7 Hz, 2 H), 6.08 (t, J = 9.7 Hz, 1 H), 5.92–5.81 (m, 3 H),

5.58 (t, J = 9.7 Hz, 1 H), 5.55–5.45 (m, 3 H), 5.45–5.39 (m, 1 H), 5.38–

5.23 (m, 3 H), 4.99 (t, J = 9.0 Hz, 2 H), 4.93 (d, J = 7.9 Hz, 1 H), 4.72 (d,

J = 7.8 Hz, 1 H), 4.12–3.96 (m, 5 H), 3.91–3.74 (m, 6 H), 3.45–3.36 (m,

1 H), 2.33 (s, 3 H), 0.83 (s, 9 H), –0.06 (s, 6 H).

¹³C NMR (126 MHz, CDCl₃):  = 165.9, 165.77, 165.73, 165.71, 165.5,

165.25, 165.22, 165.19, 165.18, 165.06, 165.02, 138.9, 133.98, 133.5,

133.4, 133.20, 133.17, 133.16, 133.08, 132.97, 130.1, 130.00, 129.95,

129.93, 129.91, 129.83, 129.79, 129.70, 129.54, 129.52, 129.48,

129.42, 129.21, 129.14, 129.10, 129.05, 128.98, 128.88, 128.87,

128.83, 128.7, 128.5, 128.43, 128.36, 128.27, 128.25, 128.1, 101.7,

100.93, 100.91, 86.9, 78.6, 75.4, 74.2, 73.9, 73.1, 72.97, 72.90, 72.5,

72.1, 71.96, 70.8, 70.6, 69.9, 69.8, 69.7, 69.2, 68.3, 68.1, 62.9, 60.4,

25.9, 21.2, 18.3, –5.3, –5.4.

HRMS (ESI): m/z [M + NH₄]⁺calcd for C₁₂₁H₁₁₄NO₃₂SSi: 2153.6887;

found: 2153.6838.

HRMS (ESI): m/z [M + NH₄]⁺calcd for C₆₂H₆₄Cl₃N₂O₁₇Si: 1241.3034;

found: 1241.3042.

(2,3,4-Tri-O-benzoyl-6-O-tert-butyldimethylsilyl--D-glucopyra-

nosyl)-(1→6)-(2,3,4-tri-O-benzoyl--D-glucopyranosyl)-(1→6)-

(2,3,4-tri-O-benzoyl--D-glucopyranosyl)-(1→6)-2,3,4-tri-O-ben-

zoyl--D-glucopyranosyl Trichloroacetimidate (2)

p-Tolylthio (2,3,4-Tri-O-benzoyl--D-glucopyranosyl)-(1→6)-2,3,4-

tri-O-benzoyl--D-glucopyranoside (15)

To a stirred solution of 4 (3.5 g, 2.95 mmol, 1.0 equiv) in AcOH (675

L, 11.80 mmol, 4.0 equiv) and THF (44 mL) was added TBAF (1 M in

THF, 5.9 mL, 5.9 mmol, 2.0 equiv). After the mixture was stirred at rt

for 12 h, DCM (50 mL) and saturated aqueous NaHCO₃(50 mL) were

successively added. The organic phase was separated and washed

with brine (50 mL), dried over anhydrous Na₂SO₄, and concentrated.

The residue was purified by silica gel column chromatography (petro-

leum ether/DCM/EtOAc, 6:3:1) to afford 15 (2.81 g, 2.62 mmol, 89%)

as a white foam.

Following the procedure for 7, treatment of 16 (1.0 g, 0.47 mmol, 1.0

equiv) with NBS (167 mg, 0.94 mmol, 2.0 equiv) in acetone/H₂O (11

mL, 9:1 v/v) at 0 °C afforded the crude hemiacetal, which was treated

with trichloroacetonitrile (235 L, 2.35 mmol, 5.0 equiv) and DBU (35

L, 0.235 mmol, 0.5 equiv) at 0 °C to afford 2 (837 mg, 0.39 mmol, 82%

over 2 steps) as a white foam after purification by silica gel column

chromatography (petroleum ether/DCM/EtOAc, 8:4:1).

[]_D²⁴–8.9 (c 1.0, CHCl₃).

[]_D¹⁵–0.15 (c 1.55, CHCl₃).

¹H NMR (500 MHz, CDCl₃):  = 8.48 (s, 1 H), 8.03 (d, J = 7.4 Hz, 2 H),

8.01–7.92 (m, 8 H), 7.91–7.84 (m, 8 H), 7.82 (d, J = 7.4 Hz, 2 H), 7.78

(d, J = 7.3 Hz, 2 H), 7.73 (d, J = 7.4 Hz, 2 H), 7.57–7.14 (m, 34 H), 7.05 (t,

J = 7.8 Hz, 2 H), 6.82 (d, J = 3.5 Hz, 1 H), 6.28 (t, J = 9.9 Hz, 1 H), 6.07 (t,

J = 9.7 Hz, 1 H), 5.93 (t, J = 9.6 Hz, 1 H), 5.82–5.7 (m, 2 H), 5.65 (dd, J =

10.2, 3.5 Hz, 1 H), 5.55 (t, J = 9.7 Hz, 1 H), 5.49 (dd, J = 9.7, 8.0 Hz, 1 H),

5.41 (dd, J = 9.6, 8.0 Hz, 1 H), 5.37–5.25 (m, 3 H), 5.04 (d, J = 7.8 Hz, 1

H), 4.81 (d, J = 7.8 Hz, 2 H), 4.49–4.42 (m, 1 H), 4.15–4.07 (m, 3 H),

4.02–3.98 (m, 1 H), 3.88–3.73 (m, 5 H), 3.72–3.65 (m, 1 H), 3.50 (dd,

J = 11.6, 5.7 Hz, 1 H), 0.83 (s, 9 H), –0.04 (s, 6 H).

¹³C NMR (126 MHz, CDCl₃):  = 165.9, 165.77, 165.74, 165.68, 165.4,

165.31, 165.30, 165.26, 165.21, 165.16, 165.08, 165.07, 160.4, 133.6,

133.5, 133.38, 133.35, 133.18, 133.11, 132.98, 130.1, 130.0, 129.91,

129.88, 129.80, 129.77, 129.74, 129.63, 129.57, 129.51, 129.15,

129.07, 129.06, 128.97, 128.92, 128.87, 128.83, 128.81, 128.76,

128.62, 128.57, 128.48, 128.44, 128.36, 128.30, 128.27, 128.23,

128.17, 101.3, 100.75, 100.71, 93.2, 77.4, 77.2, 75.2, 74.0, 73.96, 73.2,

72.95, 72.8, 72.4, 72.3, 72.0, 71.9, 70.9, 69.99, 69.6, 69.5, 69.2, 68.6,

67.9, 67.3, 62.8, 25.8, 18.3, –5.3, –5.4.

¹H NMR (400 MHz, CDCl₃):  = 7.96–7.90 (m, 8 H), 7.82 (d, J = 7.7 Hz, 2

H), 7.76 (d, J = 7.7 Hz, 2 H), 7.57–7.46 (m, 5 H), 7.45–7.33 (m, 12 H),

7.32–7.22 (m, 3 H), 7.15 (d, J = 7.9 Hz, 2 H), 5.87 (t, J = 9.7 Hz, 1 H),

5.79 (t, J = 9.5 Hz, 1 H), 5.45–5.27 (m, 4 H), 4.97 (d, J = 7.9 Hz, 1 H),

4.83 (d, J = 10.0 Hz, 1 H), 4.06 (d, J = 10.2 Hz, 1 H), 4.03–3.91 (m, 2 H),

3.82–3.72 (m, 2 H), 3.62 (d, J = 12.6 Hz, 1 H), 2.83 (brs, 1 H), 2.36 (s, 3

H).

¹³C NMR (101 MHz, CDCl₃):  = 165.97, 165.87, 165.85, 165.81, 165.2,

165.1, 139.0, 134.2, 133.75, 133.70, 133.38, 133.33, 133.32, 133.28,

130.05, 130.02, 129.97, 129.84, 129.40, 129.38, 128.99, 128.93,

128.91, 128.74, 128.65, 128.60, 128.48, 128.41, 128.35, 127.5, 100.7,

86.2, 77.9, 74.8, 74.2, 72.97, 71.7, 70.6, 70.1, 69.5, 68.1, 61.4, 21.4.

HRMS (ESI): m/z [M + NH₄]⁺calcd for C₆₁H₅₆NO₁₆S: 1090.3314; found:

1090.3284.

p-Tolylthio (2,3,4-Tri-O-benzoyl-6-O-tert-butyldimethylsilyl--D-

glucopyranosyl)-(1→6)-(2,3,4-tri-O-benzoyl--D-glucopyranosyl)-

(1→6)-(2,3,4-tri-O-benzoyl--D-glucopyranosyl)-(1→6)-2,3,4-tri-

O-benzoyl--D-glucopyranoside (16)

HRMS (ESI): m/z [M + NH₄]⁺calcd for C₁₁₆H₁₀₈Cl₃N₂O₃₃Si: 2189.5664;

found: 2189.5633.

Following the procedure for 4, trichloroacetimidate 5 (1.04 g, 0.85

mmol, 1.0 equiv) and acceptor alcohol 15 (1.03 g, 0.96 mmol, 1.13

equiv) were treated with TMSOTf (15 L, 0.085 mmol, 0.1 equiv) in

anhydrous DCM (17 mL) to afford 16 (1.52 g, 0.71 mmol, 84%) as a

white foam after purification by silica gel column chromatography

(petroleum ether/DCM/EtOAc, 6:3:1).

p-Tolylthio 2-O-Benzoyl-4,6-O-benzylidene--D-glucopyranoside

(13), p-Tolylthio 3-O-Benzoyl-4,6-O-benzylidene--D-glucopyra-

noside (13a), and p-Tolylthio 2,3-Di-O-benzoyl-4,6-O-benzylidene-

-D-glucopyranoside (13b)

To a stirred solution of 17 (9.0 g, 24.0 mmol, 1.0 equiv) in CHCl₃(350

mL) were added freshly prepared Ag₂O (8.34 g, 36.0 mmol, 1.5 equiv),

BzCl (3.7 mL, 31.2 mmol, 1.3 equiv) at –20 °C. After the reaction mix-

[]_D¹⁵–0.86 (c 1.0, CHCl₃).

H

X. Zhou et al.

Paper

Synthesis

ture was stirred for 8 h at 0 °C, the mixture was filtered through a

small pad of Celite, and washed with DCM. The collected filtrate was

concentrated and the residue was purified by flash chromatography

on a silica gel column (petroleum ether/DCM/EtOAc, 6:3:1) to give

13b (1.25 g, 2.16 mmol, 9%) and a mixture of 13 and 13a. Pure 13 (7.0

g, 14.64 mmol, 61%) was isolated by recrystallization from toluene

and analytically pure 13a (0.8 g, 1.68 mmol, 7%) was separated from

the mother liquid.

13: ¹H NMR (500 MHz, CDCl₃):  = 8.11 (d, J = 7.6 Hz, 2 H), 7.61 (t, J =

7.4 Hz, 1 H), 7.48 (t, J = 7.6 Hz, 4 H), 7.41–7.32 (m, 5 H), 7.11 (d, J = 7.8

Hz, 2 H), 5.55 (s, 1 H), 5.12 (t, J = 9.4 Hz, 1 H), 4.83 (d, J = 10.0 Hz, 1 H),

4.41 (dd, J = 10.5, 4.7 Hz, 1 H), 4.03 (t, J = 8.8 Hz, 1 H), 3.81 (t, J = 10.1

Hz, 1 H), 3.63–3.51 (m, 2 H), 2.89 (s, 1 H), 2.35 (s, 3 H).

p-Tolylthio 2-O-Benzoyl-4-O-benzyl-6-O-tert-butyldimethylsilyl-

-D-glucopyranoside (19)

To a solution of 18 (3.40 g, 7.07 mmol, 1.0 equiv) in anhydrous pyri-

dine (68 mL) were added TBSCl (1.60 g, 10.6 mmol, 1.5 equiv) and

DMAP (87 mg, 0.71 mmol, 0.1 equiv). The resulting mixture was

stirred for 4 h at 50 °C. At this stage the solution was concentrated in

vacuo, and the resultant solid was dissolved in DCM, and sequentially

washed with 1 M HCl and brine. The aqueous layer was extracted

with DCM and the combined organic layers were dried over Na₂SO₄.

The solid was filtered off and the filtrate was concentrated. The

obtained residue was purified by silica gel column chromatography

(petroleum ether/EtOAc, 5:1) to afford 19 (4.08 g, 6.86 mmol, 97%) as

a white foam.

[]_D¹⁹–33.0 (c 1.1, CHCl₃).

13a: []_D²³–113.6 (c 0.667, CHCl₃).

¹H NMR (500 MHz, CDCl₃):  = 8.09 (d, J = 7.3 Hz, 2 H), 7.60 (t, J = 7.4

Hz, 1 H), 7.47 (t, J = 7.8 Hz, 2 H), 7.40–7.33 (m, 6 H), 7.32–7.27 (m, 1

H), 7.07 (d, J = 7.9 Hz, 2 H), 4.94 (t, J = 9.5 Hz, 1 H), 4.84 (d, J = 11.2 Hz,

1 H), 4.78–4.70 (m, 2 H), 4.00–3.87 (m, 3 H), 3.64 (t, J = 9.3 Hz, 1 H),

3.44–3.37 (m, 1 H), 2.65 (brs, 1 H), 2.33 (s, 3 H), 0.96 (s, 9 H), 0.14 (s, 6

H).

¹³C NMR (126 MHz, CDCl₃):  = 166.4, 138.4, 138.3, 133.7, 133.5,

130.1, 129.8, 129.7, 128.7, 128.56, 128.53, 128.2, 128.1, 85.8, 80.2,

77.8, 77.4, 75.1, 73.5, 62.3, 26.1, 21.3, 18.5, –4.9, –5.2.

¹H NMR (400 MHz, CDCl₃):  = 8.07 (d, J = 7.2 Hz, 2 H), 7.56 (t, J = 7.4

Hz, 1 H), 7.51–7.38 (m, 6 H), 7.34–7.28 (m, 3 H), 7.17 (d, J = 7.9 Hz, 2

H), 5.59–5.46 (m, 2 H), 4.72 (d, J = 9.7 Hz, 1 H), 4.42 (dd, J = 10.5, 4.9

Hz, 1 H), 3.80 (m, 2 H), 3.73–3.57 (m, 2 H), 3.00 (d, J = 3.1 Hz, 1 H),

2.38 (s, 3 H).

¹³C NMR (101 MHz, CDCl₃):  = 166.7, 138.9, 136.8, 133.9, 133.3,

130.0, 129.6, 129.1, 128.4, 128.2, 127.3, 126.1, 101.5, 89.4, 78.4, 75.6,

71.7, 70.9, 68.6, 21.3.

HRMS (ESI): m/z [M + NH₄]⁺calcd for C₂₇H₃₀NO₆S: 496.1788; found:

496.1783.

HRMS (ESI): m/z [M + NH₄]⁺calcd for C₃₃H₄₆NO₆SSi: 612.2810; found:

612.2825.

13b: ¹H NMR (400 MHz, CDCl₃):  = 7.97 (d, J = 7.2 Hz, 4 H), 7.51 (m, 2

H), 7.45–7.29 (m, 11 H), 7.13 (d, J = 7.9 Hz, 2 H), 5.80 (t, J = 9.5 Hz, 1

H), 5.54 (s, 1 H), 5.46 (t, J = 9.6 Hz, 1 H), 4.98 (d, J = 10.0 Hz, 1 H), 4.47

(dd, J = 10.5, 4.8 Hz, 1 H), 3.89 (m, 2 H), 3.74 (m, 1 H), 2.36 (s, 3 H). The

data are indentical with the reported.³⁰

p-Tolylthio 2-O-Benzoyl-4-O-benzyl-6-O-tert-butyldimethylsilyl-

3-O-levulinoyl--D-glucopyranoside (20)

A solution of 19 (4.17 g, 7.01 mmol, 1.0 equiv) and levulinic acid (1.22

g, 10.5 mmol, 1.5 equiv) in DCM (60 mL) was treated with DMAP (86

mg, 0.70 mmol, 0.1 equiv) and DCC (2.60 g, 12.6 mmol, 1.8 equiv) at 0

°C. The solution was allowed to stir at rt for 3 h. A white precipitate

slowly formed, and the solution turned slightly pink. After complete

conversion of the starting material, the mixture was filtered through

a Celite pad and the filtrate was evaporated in vacuo. The residue was

purified by silica gel column chromatography (petroleum ether/EtOAc,

4:1) to afford 20 (4.76 g, 6.87 mmol, 98%) as a colorless oil.

p-Tolylthio 2-O-Benzoyl-4-O-benzyl--D-glucopyranoside (18)

A solution of BH₃·THF (1 M, 100 mL, 100 mmol, 10.0 equiv) was added

to a 250 mL dry flask containing 13 (4.79 g, 10 mmol, 1.0 equiv) at 0

°C. After the resulting solution was stirred for 5 min, a solution of

Bu₂BOTf (1 M in DCM, 5 mL, 5 mmol, 0.5 equiv) was then added to the

clear solution slowly. After being stirred for 2 h at 28 °C, the starting

material had disappeared (TLC monitoring). Et₃N (1.4 mL, 10 mmol,

1.0 equiv) was added to quench the reaction, then MeOH was slowly

added until the evolution of H₂had ceased while cooling in an ice

bath. The reaction mixture was concentrated in vacuo. The residue

was purified by silica gel column chromatography (petroleum

ether/EtOAc, 3:1) to afford 18 (3.40 g, 7.07 mmol, 71%) as a white

foam.

[]_D¹⁹–10.2 (c 1.23, CHCl₃).

¹H NMR (500 MHz, CDCl₃):  = 8.02 (d, J = 7.3 Hz, 2 H), 7.58 (t, J = 7.4

Hz, 1 H), 7.45 (t, J = 7.7 Hz, 2 H), 7.39–7.24 (m, 7 H), 7.07 (d, J = 8.0 Hz,

2 H), 5.41 (t, J = 9.4 Hz, 1 H), 5.08 (t, J = 9.7 Hz, 1 H), 4.75 (d, J = 10.0

Hz, 1 H), 4.69–4.62 (m, 2 H), 3.98–3.85 (m, 2 H), 3.79 (t, J = 9.5 Hz, 1

H), 3.47–3.43 (m, 1 H), 2.52–2.25 (m, 7 H), 1.99 (s, 3 H), 0.96 (s, 9 H),

0.15 (s, 3 H), 0.12 (s, 3 H).

[]_D¹⁹–15.0 (c 0.95, CHCl₃).

¹³C NMR (126 MHz, CDCl₃):  = 205.9, 172.0, 165.4, 138.4, 138.1,

133.7, 133.4, 130.1, 129.71, 129.68, 128.55, 128.54, 128.46, 128.1,

127.96, 86.1, 80.4, 76.5, 75.4, 74.8, 71.2, 62.1, 37.9, 29.7, 28.1, 26.1,

21.3, 18.5, –4.9, –5.2.

HRMS (ESI): m/z [M + NH₄]⁺calcd for C₃₈H₅₂NO₈SSi: 710.3177; found:

710.3194.

¹H NMR (400 MHz, CDCl₃):  = 8.09 (d, J = 7.1 Hz, 2 H), 7.60 (t, J = 7.5

Hz, 1 H), 7.48 (t, J = 7.7 Hz, 2 H), 7.38–7.28 (m, 7 H), 7.09 (d, J = 8.0 Hz,

2 H), 4.98 (t, J = 10.0 Hz, 1 H), 4.85 (d, J = 11.3 Hz, 1 H), 4.79–4.71 (m, 2

H), 3.99–3.90 (m, 2 H), 3.79–3.70 (m, 1 H), 3.56 (t, J = 9.2 Hz, 1 H),

3.49–3.43 (m, 1 H), 2.78 (d, J = 3.3 Hz, 1 H), 2.33 (s, 3 H), 2.07 (brs, 1

H).

¹³C NMR (101 MHz, CDCl₃):  = 166.5, 138.7, 138.0, 133.6, 133.5,

130.2, 129.9, 129.6, 128.7, 128.6, 128.3, 128.2, 85.9, 79.4, 77.8, 77.4,

75.1, 73.6, 62.2, 21.3.

2-O-Benzoyl-4-O-benzyl-6-O-tert-butyldimethylsilyl-3-O-levuli-

noyl--D-glucopyranosyl Trichloroacetimidate (8)

HRMS (ESI): m/z [M + NH₄]⁺calcd for C₂₇H₃₂NO₆S: 498.1945; found:

498.1960.

NIS (3.11 g, 13.83 mmol, 2.0 equiv) and TFA (565 L, 7.60 mmol, 1.1

equiv) were added to a solution of 20 (4.79 g, 6.91 mmol, 1.0 equiv) in

a mixture of DCM/H₂O (66 mL, 10:1 v/v) at 0 °C. The reaction was al-

lowed to proceed under stirring for 2 h at rt and quenched with Et₃N.

The mixture was concentrated, and then the residue was dissolved in

DCM (50 mL) and washed with 20% (w/w) aqueous Na₂S₂O₃(50 mL)

I

X. Zhou et al.

Paper

Synthesis

and saturated aqueous NaHCO₃(50 mL). The organic layer was sepa-

rated and the aqueous layer was reextracted with DCM (2 × 50 mL).

The combined organic layers were dried over anhydrous Na₂SO₄and

concentrated. The resultant hemiacetal was treated with trichloro-

acetonitrile (3.47 mL, 34.6 mmol, 5.0 equiv) in anhydrous DCM (50

mL) in the presence of DBU (517 L, 3.46 mmol, 0.5 equiv). After be-

ing stirred at rt for 12 h, the reaction mixture was concentrated. The

residue was purified by silica gel column chromatography (petroleum

ether/EtOAc, 6:1) to afford 8 (3.39 g, 4.64 mmol, 67% over 2 steps,

/ = 20:1) as a white foam.

¹H NMR (500 MHz, CDCl₃):  = 8.58 (s, 1 H), 8.01 (d, J = 7.2 Hz, 2 H),

7.57 (t, J = 7.4 Hz, 1 H), 7.52–7.46 (m, 2 H), 7.44–7.33 (m, 5 H), 6.69 (d,

J = 3.8 Hz, 1 H), 5.89 (t, J = 9.9 Hz, 1 H), 5.59 (s, 1 H), 5.38 (dd, J = 9.9,

3.8 Hz, 1 H), 4.40 (dd, J = 10.4, 4.9 Hz, 1 H), 4.22–4.17 (m, 1 H), 3.91–

3.81 (m, 2 H), 2.68–2.46 (m, 4 H), 1.99 (s, 3 H).

¹³C NMR (126 MHz, CDCl₃):  = 205.7, 171.8, 165.2, 138.7, 136.7,

133.7, 133.4, 130.0, 129.7, 129.3, 129.1, 128.5, 128.2, 127.8, 126.1,

101.4, 87.1, 78.2, 73.0, 71.1, 70.8, 68.5, 37.9, 28.0, 21.2.

HRMS (ESI): m/z [M + NH₄]⁺calcd for C₂₇H₃₀Cl₃N₂O₉: 631.1011; found:

631.1012.

[]_D¹⁹+82.8 (c 0.94, CHCl₃).

¹H NMR (500 MHz, CDCl₃):  = 8.47 (s, 1 H), 7.97 (d, J = 8.2 Hz, 2 H),

7.55 (t, J = 7.4 Hz, 1 H), 7.41 (t, J = 7.8 Hz, 2 H), 7.37–7.32 (m, 4 H),

7.32–7.27 (m, 1 H), 6.66 (d, J = 3.5 Hz, 1 H), 5.85 (t, J = 9.5 Hz, 1 H),

5.22 (dd, J = 10.2, 3.6 Hz, 1 H), 4.73 (s, 2 H), 4.05–3.93 (m, 3 H), 3.89

(d, J = 11.1 Hz, 1 H), 2.58–2.50 (m, 2 H), 2.43–2.33 (m, 2 H), 2.00 (s, 3

H), 0.95 (s, 9 H), 0.12 (s, 6 H).

¹³C NMR (126 MHz, CDCl₃):  = 205.8, 171.98, 165.7, 160.8, 138.0,

133.5, 130.1, 129.1, 128.59, 128.53, 128.3, 128.0, 93.8, 75.09, 75.06,

74.5, 72.1, 71.3, 61.5, 37.9, 29.7, 28.1, 26.1, 18.5, –4.9, –5.2.

p-Tolylthio (2-O-Benzoyl-4,6-O-benzylidene-3-O-levulinoyl--D-

glucopyranosyl)-(1→3)-2-O-benzoyl-4,6-O-benzylidene--D-glu-

copyranoside (11)

Following the procedure for 4, trichloroacetimidate 22 (5.4 g, 8.78

mmol, 1.2 equiv) and 13 (3.5 g, 7.32 mmol, 1.0 equiv) were treated

with TMSOTf (132 L, 0.73 mmol, 0.1 equiv) in anhydrous DCM (120

mL) at –40 °C to afford 11 (5.65 g, 6.07 mmol, 83%) as a white foam

after purification by silica gel column chromatography (petroleum

ether/EtOAc, 3:1).

HRMS (ESI): m/z [M + NH₄]⁺calcd for C₃₃H₄₆Cl₃N₂O₉Si: 747.2033;

[]_D¹⁹+16.1 (c 1.59, CHCl₃).

found: 747.2046.

¹H NMR (500 MHz, CDCl₃):  = 7.77 (d, J = 7.6 Hz, 2 H), 7.62–7.46 (m, 6

H), 7.43–7.31 (m, 10 H), 7.30–7.21 (m, 4 H), 7.05 (d, J = 7.8 Hz, 2 H),

5.58 (s, 1 H), 5.34–5.16 (m, 4 H), 4.92 (d, J = 7.0 Hz, 1 H), 4.75 (d, J =

10.0 Hz, 1 H), 4.39 (dd, J = 10.4, 4.6 Hz, 1 H), 4.26–4.12 (m, 2 H), 3.88–

3.75 (m, 3 H), 3.68 (t, J = 10.2 Hz, 1 H), 3.59–3.53 (m, 1 H), 3.46–3.39

(m, 1 H), 2.53–2.26 (m, 7 H), 1.94 (s, 3 H).

¹³C NMR (126 MHz, CDCl₃):  = 205.8, 171.8, 164.9, 164.7, 138.6,

137.1, 136.9, 133.4, 133.1, 132.9, 129.9, 129.8, 129.14, 129.07, 128.47,

128.41, 128.25, 128.21, 126.20, 126.14, 101.6, 101.3, 100.7, 87.6, 79.6,

79.3, 77.9, 72.96, 72.1, 70.8, 68.6, 66.2, 37.9, 29.6, 28.0, 21.2.

p-Tolylthio 2-O-Benzoyl-4,6-O-benzylidene-3-O-levulinoyl--D-

glucopyranoside (21)

Following the procedure for 20, 13 (9.0 g, 18.8 mmol, 1.0 equiv) and

levulinic acid (3.28 g, 28.2 mmol, 1.5 equiv) were treated with DCC

(6.97 g, 33.8 mmol, 1.8 equiv) and DMAP (230 mg, 1.88 mmol, 0.1

equiv) in anhydrous DCM (20 mL) to afford 21 (10.4 g, 18.1 mmol,

96%) as a white foam after purification by silica gel column chroma-

tography (petroleum ether/DCM/EtOAc, 6:3:1).

[]_D²⁴–12.3 (c 1.1, CHCl₃).

HRMS (ESI): m/z [M + NH₄]⁺calcd for C₅₂H₅₄NO₁₄S: 948.3260; found:

¹H NMR (400 MHz, CDCl₃):  = 8.05 (d, J = 7.1 Hz, 2 H), 7.60 (t, J = 7.4

Hz, 1 H), 7.52–7.41 (m, 4 H), 7.39–7.31 (m, 5 H), 7.11 (d, J = 8.0 Hz, 2

H), 5.57–5.46 (m, 2 H), 5.26 (t, J = 9.5 Hz, 1 H), 4.88 (d, J = 10.0 Hz, 1

H), 4.42 (dd, J = 10.5, 4.9 Hz, 1 H), 3.83 (t, J = 10.2 Hz, 1 H), 3.74 (t, J =

9.5 Hz, 1 H), 3.68–3.59 (m, 1 H), 2.58–2.41 (m, 4 H), 2.34 (s, 3 H), 1.98

(s, 3 H).

¹³C NMR (126 MHz, CDCl₃):  = 205.8, 171.9, 165.3, 138.9, 136.9,

133.9, 133.5, 130.1, 129.9, 129.5, 129.2, 128.6, 128.3, 127.96, 126.3,

101.6, 87.2, 78.3, 73.1, 71.2, 70.9, 68.6, 38.0, 29.6, 28.1, 21.3.

948.3279.

(2-O-Benzoyl-4,6-O-benzylidene-3-O-levulinoyl--D-glucopyrano-

syl)-(1→3)-2-O-benzoyl-4,6-O-benzylidene--D-glucopyranosyl

Trichloroacetimidate (12)

Following the procedure for 8, treatment of 11 (2.8 g, 3.0 mmol, 1.0

equiv) with NIS (1.69 g, 7.5 mmol, 2.5 equiv) and TFA (245 L, 3.3

mmol, 1.1 equiv) in DCM/H₂O (66 mL, 10:1 v/v) at 0 °C afforded the

crude hemiacetal, which was treated with trichloroacetonitrile (1.5

mL, 15.0 mmol, 5.0 equiv) and DBU (224 L, 1.5 mmol, 0.5 equiv) at rt

to afford 12 (2.30 g, 2.37 mmol, 79% over 2 steps) as a white foam af-

ter purification by silica gel column chromatography (DCM/EtOAc,

30:1).

HRMS (ESI): m/z [M + NH₄]⁺calcd for C₃₂H₃₆NO₈S: 594.2156; found:

594.2173.

2-O-Benzoyl-4,6-O-benzylidene-3-O-levulinoyl--D-glucopyrano-

syl Trichloroacetimidate (22)

[]_D¹⁹+46.2 (c 0.99, CHCl₃).

Following the procedure for 8, treatment of 21 (4.20 g, 7.28 mmol, 1.0

equiv) with NIS (4.09 g, 18.2 mmol, 2.5 equiv) and TFA (595 L, 8.01

mmol, 1.1 equiv) in DCM/H₂O (154 mL, 9:1 v/v) at 0 °C afforded crude

the hemiacetal, which was treated with trichloroacetonitrile (3.65

mL, 36.4 mmol, 5 equiv) and DBU (544 L, 3.64 mmol, 0.5 equiv) at rt

to afford 22 (3.94 g, 6.41 mmol, 88% over 2 steps, / = 20:1) as a

white foam after purification by silica gel column chromatography

(petroleum ether/DCM/EtOAc, 6:3:1).

¹H NMR (500 MHz, CDCl₃):  = 8.50 (s, 1 H), 7.72 (d, J = 7.6 Hz, 2 H),

7.61–7.51 (m, 5 H), 7.49–7.28 (m, 11 H), 7.18 (t, J = 7.7 Hz, 2 H), 6.55

(d, J = 3.9 Hz, 1 H), 5.64 (s, 1 H), 5.42–5.34 (m, 2 H), 5.31–5.22 (m, 2

H), 5.05 (d, J = 7.2 Hz, 1 H), 4.48 (t, J = 9.4 Hz, 1 H), 4.39–4.31 (m, 2 H),

4.12–4.06 (m, 1 H), 3.92–3.73 (m, 4 H), 3.65–3.57 (m, 1 H), 2.53–2.33

(m, 4 H), 1.94 (s, 3 H).

¹³C NMR (126 MHz, CDCl₃):  = 205.8, 171.9, 165.0, 160.7, 137.0,

136.9, 133.5, 133.1, 129.81, 129.75, 129.4, 129.2, 128.9, 128.6, 128.47,

128.38, 128.32, 128.30, 126.28, 126.15, 101.51, 101.46, 101.36, 93.6,

79.1, 78.1, 76.0, 72.98, 72.3, 72.1, 68.7, 68.6, 66.5, 65.3, 37.97, 29.6,

28.1.

[]_D¹⁹+38.8 (c 0.33, CHCl₃).

HRMS (ESI): m/z [M + NH₄]⁺calcd for C₄₇H₄₈N₂O₁₅Cl₃: 985.2115;

found: 985.2113.

J

X. Zhou et al.

Paper

Synthesis

p-Tolylthio (2-O-Benzoyl-4,6-O-benzylidene--D-glucopyranosyl)-

(1→3)-2-O-benzoyl-4,6-O-benzylidene--D-glucopyranoside (23)

(2-O-Benzoyl-4,6-O-benzylidene-3-O-levulinoyl--D-glucopyrano-

syl)-(1→3)-(2-O-benzoyl-4,6-O-benzylidene--D-glucopyranosyl)-

(1→3)-(2-O-benzoyl-4,6-O-benzylidene--D-glucopyranosyl)-

(1→3)-2-O-benzoyl-4,6-O-benzylidene-D-glucopyranosyl Trichlo-

roacetimidate (10)

Compound 11 (2.5 g, 2.68 mmol, 1.0 equiv) was dissolved in DCM (40

mL), followed by addition of AcOH (15.3 mL, 268 mmol, 100.0 equiv)

and NH₂NH₂·H₂O (650 L, 13.4 mmol, 5.0 equiv). The resulting reac-

tion mixture was stirred at rt for 3 h and quenched with acetone. The

mixture was diluted with DCM and washed with saturated aqueous

NaHCO₃. The collected organic layer was dried over Na₂SO₄and con-

centrated. The residue was purified by silica gel column chromatogra-

phy (petroleum ether/DCM/EtOAc, 9:2:2, to DCM/EtOAc, 30:1) to af-

ford 23 (2.19 g, 2.63 mmol, 98%) as a white foam.

Following the procedure for 8, treatment of 9 (5.8 g, 3.54 mmol, 1.0

equiv) with NIS (1.59 g, 7.07 mmol, 2.0 equiv) and TFA (289 L, 3.89

mmol, 1.1 equiv) in DCM/H₂O (77 mL, 10:1 v/v) at 0 °C afforded the

hemiacetal, which was treated with trichloroacetonitrile (1.77 mL,

17.7 mmol, 5.0 equiv) and DBU (265 L, 1.77 mmol, 0.5 equiv) at rt to

afford 10 (4.19 g, 2.50 mmol, 70% over 2 steps, / = 8.3:1) as a white

foam after purification by silica gel column chromatography (petro-

leum ether/DCM/EtOAc, 5:2:2).

[]_D²⁴–6.0 (c 1.1, CHCl₃).

¹H NMR (500 MHz, CDCl₃):  = 7.83 (d, J = 7.6 Hz, 2 H), 7.68 (d, J = 7.6

Hz, 2 H), 7.58–7.48 (m, 4 H), 7.44–7.24 (m, 14 H), 7.06 (d, J = 7.9 Hz, 2

H), 5.56 (s, 1 H), 5.31 (s, 1 H), 5.24 (t, J = 9.3 Hz, 1 H), 5.07 (t, J = 7.4 Hz,

1 H), 4.91 (d, J = 7.0 Hz, 1 H), 4.78 (d, J = 9.9 Hz, 1 H), 4.39 (dd, J = 10.5,

4.8 Hz, 1 H), 4.23 (t, J = 8.9 Hz, 1 H), 4.15 (dd, J = 10.4, 4.9 Hz, 1 H),

3.88–3.73 (m, 3 H), 3.66 (t, J = 9.6 Hz, 2 H), 3.61–3.55 (m, 1 H), 3.38–

3.32 (m, 1 H), 2.64 (brs, 1 H), 2.32 (s, 3 H).

¹³C NMR (126 MHz, CDCl₃):  = 165.6, 164.8, 138.6, 137.2, 137.0,

133.6, 133.2, 133.1, 129.91, 129.90, 129.8, 129.6, 129.46, 129.36,

129.30, 128.44, 128.43, 128.36, 128.28, 126.3, 126.2, 101.71, 101.67,

100.4, 87.5, 80.5, 79.4, 79.2, 75.5, 72.7, 72.4, 70.8, 68.71, 68.68, 66.1,

21.3.

[]_D²⁴+35.6 (c 1.1, CHCl₃).

¹H NMR (500 MHz, CDCl₃):  = 8.48 (s, 1 H), 7.83 (d, J = 7.7 Hz, 2 H),

7.80–7.66 (m, 6 H), 7.63–7.57 (m, 3 H), 7.53–7.22 (m, 28 H), 7.15 (t, J =

7.4 Hz, 1 H), 6.43 (d, J = 3.2 Hz, 1 H), 5.58 (s, 1 H), 5.39–5.32 (m, 2 H),

5.27–5.23 (m, 2 H), 5.19 (s, 1 H), 5.06 (d, J = 6.5 Hz, 1 H), 5.02–4.98 (m,

2 H), 4.88 (s, 1 H), 4.57–4.50 (m, 2 H), 4.41 (t, J = 9.5 Hz, 1 H), 4.32 (dd,

J = 10.4, 4.9 Hz, 1 H), 4.23–4.17 (m, 3 H), 4.02–3.87 (m, 4 H), 3.80–3.43

(m, 9 H), 3.35–3.22 (m, 1 H), 2.53–2.36 (m, 4 H), 1.95 (s, 3 H).

¹³C NMR (126 MHz, CDCl₃):  = 205.9, 171.8, 165.1, 164.9, 164.7,

164.5, 160.7, 137.36, 137.30, 137.0, 136.9, 133.55, 133.52, 133.4,

133.2, 129.9, 129.82, 129.74, 129.65, 129.48, 129.47, 129.27, 129.19,

129.07, 128.9, 128.78, 128.74, 128.51, 128.47, 128.43, 128.40, 128.26,

128.22, 128.02, 126.6, 126.25, 126.22, 126.1, 102.2, 101.3, 101.1,

100.8, 99.9, 98.1, 97.4, 93.5, 78.9, 78.3, 78.2, 78.0, 77.3, 75.1, 73.5,

72.97, 72.94, 72.8, 72.1, 71.1, 68.8, 68.7, 68.64, 68.55, 66.2, 66.0, 65.4,

65.3, 60.5, 37.97, 29.6, 28.1.

HRMS (ESI): m/z [M + NH₄]⁺calcd for C₄₇H₄₈NO₁₂S: 850.2892; found:

850.2907.

p-Tolylthio (2-O-Benzoyl-4,6-O-benzylidene-3-O-levulinoyl--D-

glucopyranosyl)-(1→3)-(2-O-benzoyl-4,6-O-benzylidene--D-glu-

copyranosyl)-(1→3)-(2-O-benzoyl-4,6-O-benzylidene--D-gluco-

pyranosyl)-(1→3)-2-O-benzoyl-4,6-O-benzylidene--D-

glucopyranoside (9)

HRMS (ESI): m/z [M + Na]⁺calcd for C₈₇H₈₀³⁷ClCl₂NNaO₂₇: 1700.3846;

found: 1700.3830.

2-Azidoethyl (2-O-Benzoyl-4,6-O-benzylidene-3-O-levulinoyl--D-

glucopyranosyl)-(1→3)-(2-O-benzoyl-4,6-O-benzylidene--D-glu-

copyranosyl)-(1→3)-(2-O-benzoyl-4,6-O-benzylidene--D-gluco-

pyranosyl)-(1→3)-2-O-benzoyl-4,6-O-benzylidene--D-gluco-

pyranoside (24)

Following the procedure for 4, trichloroacetimidate 12 (1.39 g, 1.43

mmol, 1.1 equiv) and alcohol 23 (1.08 g, 1.3 mmol, 1.0 equiv) were

treated with TMSOTf (24 L, 0.13 mmol, 0.1 equiv) in anhydrous DCM

(24 mL) at –40 °C to afford 9 (1.82 g, 1.11 mmol, 85%) as a white foam

after purification by silica gel column chromatography (DCM/EtOAc,

15:1).

Following the procedure for 4, trichloroacetimidate 10 (1.81 g, 1.08

mmol, 1.0 equiv) and 2-azidoethanol (563 mg, 6.47 mmol, 6.0 equiv)

were treated with TMSOTf (39 L, 0.216 mmol, 0.2 equiv) in anhy-

drous DCM (40 mL) to afford 24 (1.55 g, 0.97 mmol, 90%) as a white

foam after purification by silica gel column chromatography (petro-

leum ether/DCM/EtOAc, 2:1:1).

[]_D¹⁹+36.1 (c 0.97, CHCl₃).

¹H NMR (500 MHz, CDCl₃):  = 7.88 (d, J = 7.8 Hz, 2 H), 7.77 (d, J = 7.7

Hz, 4 H), 7.65 (d, J = 7.8 Hz, 2 H), 7.60 (t, J = 7.3 Hz, 1 H), 7.56–7.20 (m,

32 H), 7.14 (t, J = 7.3 Hz, 1 H), 7.07 (d, J = 7.9 Hz, 2 H), 5.48 (s, 1 H),

5.42–5.34 (m, 2 H), 5.27–5.21 (m, 2 H), 5.14 (s, 1 H), 5.03 (t, J = 7.6 Hz,

2 H), 4.85–4.81 (m, 2 H), 4.76 (t, J = 9.3 Hz, 1 H), 4.66 (d, J = 10.1 Hz, 1

H), 4.51 (s, 1 H), 4.33 (dd, J = 10.4, 4.8 Hz, 1 H), 4.24–4.16 (m, 2 H),

4.15–4.05 (m, 3 H), 3.96–3.88 (m, 2 H), 3.81–3.54 (m, 6 H), 3.54–3.38

(m, 4 H), 3.13 (t, J = 9.4 Hz, 1 H), 2.57–2.36 (m, 4 H), 2.32 (s, 3 H), 1.97

(s, 3 H).

¹³C NMR (126 MHz, CDCl₃):  = 205.9, 171.8, 165.1, 164.97, 164.67,

164.64, 138.4, 137.40, 137.39, 137.2, 137.0, 133.7, 133.39, 133.31,

133.28, 132.8, 129.96, 129.93, 129.81, 129.76, 129.57, 129.54, 129.51,

129.48, 129.28, 129.18, 129.12, 129.10, 128.91, 128.87, 128.59,

128.51, 128.45, 128.38, 128.27, 128.0, 126.6, 126.3, 126.2, 102.1,

101.4, 101.1, 100.7, 99.8, 97.8, 97.3, 88.0, 78.9, 78.6, 78.3, 77.9, 77.3,

75.3, 74.9, 73.3, 73.0, 72.9, 72.8, 72.1, 70.8, 68.8, 68.7, 68.6, 66.3,

65.97, 65.4, 38.1, 29.6, 28.1, 21.2.

[]_D²⁴+13.2 (c 1.1, CHCl₃).

¹H NMR (500 MHz, CDCl₃):  = 7.88 (d, J = 7.7 Hz, 2 H), 7.78 (d, J = 7.9

Hz, 4 H), 7.67 (d, J = 7.7 Hz, 2 H), 7.61–7.16 (m, 32 H), 5.51 (s, 1 H),

5.42–5.37 (m, 2 H), 5.28 (t, J = 8.1 Hz, 1 H), 5.21 (t, J = 6.0 Hz, 1 H),

5.10–4.99 (m, 3 H), 4.88–4.86 (d, J = 8.0 Hz, 3 H), 4.68 (s, 1 H), 4.55 (d,

J = 7.6 Hz, 1 H), 4.34 (dd, J = 10.2, 4.6 Hz, 1 H), 4.26–4.07 (m, 5 H), 3.95

(t, J = 8.2 Hz, 2 H), 3.89–3.83 (m, 1 H), 3.81–3.43 (m, 11 H), 3.31–3.22

(m, 3 H), 2.58–2.36 (m, 4 H), 1.97 (s, 3 H).

¹³C NMR (126 MHz, CDCl₃):  = 205.9, 171.7, 165.1, 164.7, 164.62,

164.56, 137.3, 137.2, 136.96, 133.4, 133.20, 133.18, 129.9, 129.8,

129.74, 129.70, 129.48, 129.41, 129.38, 129.2, 129.10, 129.09, 129.04,

128.96, 128.7, 128.6, 128.43, 128.38, 128.32, 128.21, 128.18, 128.0,

126.5, 126.28, 126.22, 126.1, 101.9, 101.33, 101.31, 100.98, 100.92,

99.5, 98.1, 97.3, 78.7, 78.6, 78.3, 77.7, 77.5, 77.4, 74.8, 74.5, 73.9, 73.2,

72.8, 72.7, 72.1, 68.76, 68.73, 68.6, 67.9, 66.6, 66.2, 65.8, 65.5, 50.7,

37.98, 29.6, 28.1.

HRMS (ESI): m/z [M + Na]⁺calcd for C₉₂H₈₆NaO₂₆S: 1661.5020; found:

1661.5022.

K

X. Zhou et al.

Paper

Synthesis

HRMS (ESI): m/z [M + Na]⁺calcd for C₈₇H₈₃N₃NaO₂₇: 1624.5106;

H), 3.16 (t, J = 9.3 Hz, 1 H), 3.02 (t, J = 8.8 Hz, 1 H), 2.52–2.47 (m, 2 H),

found: 1624.5095.

2.40–2.27 (m, 2 H), 2.01 (s, 3 H), 0.87 (s, 9 H), 0.01 (s, 3 H), –0.05 (s, 3

H).

¹³C NMR (126 MHz, CDCl₃):  = 206.0, 171.8, 165.3, 164.8, 164.7,

164.6, 164.5, 138.2, 137.33, 137.27, 137.21, 133.96, 133.49, 133.44,

133.2, 129.88, 129.87, 129.69, 129.65, 129.46, 129.40, 129.24, 129.18,

129.06, 129.01, 128.80, 128.74, 128.71, 128.5, 128.44, 128.40, 128.36,

128.31, 128.2, 128.1, 128.0, 127.8, 127.7, 126.6, 126.4, 126.3, 102.2,

101.6, 101.2, 100.88, 100.82, 97.9, 97.3, 96.9, 96.7, 78.6, 78.2, 78.1,

77.5, 76.1, 75.7, 75.4, 75.2, 74.6, 74.5, 74.3, 73.99, 73.7, 73.5, 72.6,

72.4, 72.1, 68.9, 68.7, 68.59, 68.55, 67.9, 66.5, 65.7, 65.4, 65.1, 61.6,

50.7, 37.9, 29.6, 28.1, 25.9, 18.3, –4.7, –5.6.

2-Azidoethyl (2-O-Benzoyl-4,6-O-benzylidene--D-glucopyrano-

syl)-(1→3)-(2-O-benzoyl-4,6-O-benzylidene--D-glucopyranosyl)-

(1→3)-(2-O-benzoyl-4,6-O-benzylidene--D-glucopyranosyl)-

(1→3)-2-O-benzoyl-4,6-O-benzylidene--D-glucopyranoside (25)

Following the procedure for 23, tetrasaccharide 24 (3.01 g, 1.88

mmol, 1.0 equiv) was treated with NH₂NH₂·H₂O (455 L, 9.39 mmol,

5.0 equiv) and AcOH (10.7 mL, 188 mmol, 100 equiv) in DCM (50 mL)

to afford 25 (2.45 g, 1.63 mmol, 87%) as a white foam after purifica-

tion by silica gel column chromatography (petroleum

ether/DCM/EtOAc, 5:2:2).

HRMS (ESI): m/z [M + NH₄]⁺calcd for C₁₁₃H₁₂₁N₄O₃₃Si: 2089.7677;

found: 2089.7622.

[]_D²⁴+4.4 (c 1.2, CHCl₃).

¹H NMR (400 MHz, CDCl₃):  = 7.91 (d, J = 7.3 Hz, 2 H), 7.86 (d, J = 7.2

Hz, 2 H), 7.79 (d, J = 7.3 Hz, 2 H), 7.66 (d, J = 7.3 Hz, 2 H), 7.58–7.48 (m,

5 H), 7.47–7.43 (m, 3 H), 7.42–7.31 (m, 19 H), 7.31–7.17 (m, 5 H), 5.54

(s, 1 H), 5.42 (s, 1 H), 5.22–5.13 (m, 2 H), 5.05 (d, J = 7.4 Hz, 1 H), 4.99

(d, J = 5.3 Hz, 1 H), 4.93 (t, J = 8.1 Hz, 1 H), 4.89–4.79 (m, 3 H), 4.76 (s,

1 H), 4.56 (d, J = 7.6 Hz, 1 H), 4.34 (dd, J = 10.4, 4.8 Hz, 1 H), 4.20 (dd,

J = 10.4, 4.9 Hz, 1 H), 4.17–4.05 (m, 4 H), 4.01–3.91 (m, 3 H), 3.90–3.87

(m, 1 H), 3.76–3.64 (m, 3 H), 3.62–3.35 (m, 9 H), 3.32–3.20 (m, 2 H),

2.63 (brs, 1 H).

¹³C NMR (101 MHz, CDCl₃):  = 165.9, 164.68, 164.65, 164.61, 137.31,

137.24, 137.1, 137.0, 133.6, 133.4, 133.2, 133.1, 129.9, 129.8, 129.72,

129.68, 129.44, 129.41, 129.36, 129.30, 129.25, 129.1, 129.04, 128.95,

128.66, 128.59, 128.40, 128.37, 128.32, 128.29, 128.1, 126.4, 126.33,

126.31, 126.1, 101.9, 101.8, 101.3, 101.2, 100.8, 98.8, 98.4, 97.1, 80.8,

78.7, 78.3, 77.5, 77.3, 77.1, 76.9, 75.1, 74.9, 74.4, 73.8, 73.5, 72.7, 72.5,

68.70, 68.66, 68.64, 67.9, 66.6, 66.0, 65.6, 50.7.

2-Azidoethyl (4-O-Benzyl-2-O-benzoyl-6-O-tert-butyldimethyl-

silyl--D-glucopyranosyl)-(1→3)-(2-O-benzoyl-4,6-O-benzylidene-

-D-glucopyranosyl)-(1→3)-(2-O-benzoyl-4,6-O-benzylidene--D-

glucopyranosyl)-(1→3)-(2-O-benzoyl-4,6-O-benzylidene--D-glu-

copyranosyl)-(1→3)-2-O-benzoyl-4,6-O-benzylidene--D-gluco-

pyranoside (27)

Following the procedure for 23, pentasaccharide 26 (3.81 g, 1.84

mmol, 1.0 equiv) was treated with NH₂NH₂·H₂O (446 L, 9.2 mmol,

5.0 equiv) in AcOH (10.5 mL, 184 mmol, 100 equiv) and DCM (50 mL)

at 30 °C to afford 27 (3.45 g, 1.75 mmol, 95%) as a white foam after

purification by silica gel column chromatography (petroleum

ether/DCM/EtOAc, 2:1:1).

[]_D²⁴+99.9 (c 0.9, CHCl₃).

¹H NMR (500 MHz, CDCl₃):  = 8.11 (d, J = 7.7 Hz, 2 H), 7.93 (d, J = 7.8

Hz, 4 H), 7.81 (d, J = 7.9 Hz, 2 H), 7.71 (d, J = 7.9 Hz, 2 H), 7.64 (d, J = 7.7

Hz, 2 H), 7.56–7.43 (m, 10 H), 7.43–7.22 (m, 27 H), 7.17 (t, J = 7.3 Hz, 1

H), 5.54 (s, 1 H), 5.19 (s, 1 H), 5.15–5.03 (m, 3 H), 5.01–4.73 (m, 9 H),

4.70 (s, 1 H), 4.61–4.52 (m, 2 H), 4.34 (dd, J = 10.1, 4.5 Hz, 1 H), 4.25–

4.03 (m, 7 H), 3.98–3.93 (m, 1 H), 3.92–3.82 (m, 4 H), 3.78 (d, J = 11.5

Hz, 1 H), 3.72–3.62 (m, 3 H), 3.61–3.21 (m, 10 H), 3.15 (t, J = 9.4 Hz, 1

H), 2.96 (t, J = 9.0 Hz, 1 H), 0.85 (s, 9 H), –0.01 (s, 3 H), –0.07 (s, 3 H).

¹³C NMR (126 MHz, CDCl₃):  = 166.3, 165.0, 164.8, 164.7, 164.6,

138.5, 137.4, 137.30, 137.23, 134.13, 133.56, 133.49, 133.2, 129.99,

129.94, 129.73, 129.71, 129.6, 129.5, 129.4, 129.3, 129.2, 129.09,

129.07, 128.89, 128.80, 128.66, 128.57, 128.51, 128.47, 128.45,

128.35, 128.25, 128.10, 128.06, 127.9, 127.8, 126.6, 126.5, 126.4,

126.3, 102.2, 101.8, 101.3, 100.86, 100.79, 97.9, 97.1, 96.84, 96.79,

78.6, 78.2, 77.94, 77.91, 77.6, 75.7, 75.4, 74.9, 74.7, 74.6, 74.2, 74.1,

73.99, 73.5, 72.6, 72.2, 68.88, 68.80, 68.62, 68.56, 67.98, 66.6, 65.8,

65.4, 65.2, 61.98, 50.7, 25.9, 18.3, –4.7, –5.6.

HRMS (ESI): m/z [M + NH₄]⁺calcd for C₈₂H₈₁N₄O₂₅: 1521.5184; found:

1521.5186.

2-Azidoethyl (4-O-Benzyl-2-O-benzoyl-6-O-tert-butyldimethylsi-

lyl-3-O-levulinoyl--D-glucopyranosyl)-(1→3)-(2-O-benzoyl-4,6-

O-benzylidene--D-glucopyranosyl)-(1→3)-(2-O-benzoyl-4,6-O-

benzylidene--D-glucopyranosyl)-(1→3)-(2-O-benzoyl-4,6-O-ben-

zylidene--D-glucopyranosyl)-(1→3)-2-O-benzoyl-4,6-O-ben-

zylidene--D-glucopyranoside (26)

A mixture of trichloroacetimidate 8 (1.45 g, 1.98 mmol, 1.5 equiv) and

tetrasaccharide 25 (1.99 g, 1.32 mmol, 1.0 equiv) in anhydrous DCM

(50 mL) was stirred for 30 min in the presence of freshly activated 5 Å

molecular sieves (2.5 g). Then the mixture was cooled to –40 °C fol-

lowed by addition of TBSOTf (61 L, 0.264 mmol, 0.2 equiv). After be-

ing stirred for 2 h at –40 °C, the reaction mixture was filtered through

a Celite pad, and the filtrate was sequentially washed with saturated

aqueous NaHCO₃and brine. The collected organic layers were dried

over Na₂SO₄. The solid was filtered off, and the filtrate was concen-

trated. The residue was purified by silica gel chromatography (tolu-

ene/EtOAc, 6:1) to afford 26 (2.28 g, 1.10 mmol, 83%) as a white foam.

HRMS (ESI): m/z [M + NH₄]⁺calcd for C₁₀₈H₁₁₅N₄O₃₁Si: 1991.7309;

found: 1991.7260.

2-Azidoethyl (2-O-Benzoyl-4,6-O-benzylidene-3-O-levulinoyl--D-

glucopyranosyl)-(1→3)-(2-O-benzoyl-4,6-O-benzylidene--D-glu-

copyranosyl)-(1→3)-(2-O-benzoyl-4,6-O-benzylidene--D-gluco-

pyranosyl)-(1→3)-(2-O-benzoyl-4,6-O-benzylidene--D-gluco-pyr-

anosyl)-(1→3)-(4-O-benzyl-2-O-benzoyl-6-O-tert-butyldimethyl-

silyl--D-glucopyranosyl)-(1→3)-(2-O-benzoyl-4,6-O-benzylidene-

-D-glucopyranosyl)-(1→3)-(2-O-benzoyl-4,6-O-benzylidene--D-

glucopyranosyl)-(1→3)-(2-O-benzoyl-4,6-O-benzylidene--D-glu-

copyranosyl)-(1→3)-2-O-benzoyl-4,6-O-benzylidene--D-gluco-

pyranoside (28)

[]_D²⁴+29.7 (c 1.1, CHCl₃).

¹H NMR (500 MHz, CDCl₃):  = 7.99–7.87 (m, 6 H), 7.79 (d, J = 7.7 Hz, 2

H), 7.69 (d, J = 7.7 Hz, 2 H), 7.64 (d, J = 7.6 Hz, 2 H), 7.55–7.23 (m, 37

H), 7.16 (t, J = 7.4 Hz, 1 H), 5.54 (s, 1 H), 5.39 (t, J = 9.4 Hz, 1 H), 5.22–

5.09 (m, 3 H), 5.04–4.95 (m, 2 H), 4.95–4.84 (m, 4 H), 4.81 (t, J = 6.8

Hz, 1 H), 4.71–4.60 (m, 4 H), 4.55 (d, J = 7.7 Hz, 1 H), 4.33 (dd, J = 10.4,

4.7 Hz, 1 H), 4.21–4.02 (m, 7 H), 3.93 (dd, J = 8.2, 3.9 Hz, 1 H), 3.90–

3.66 (m, 6 H), 3.65–3.58 (m, 1 H), 3.58–3.34 (m, 8 H), 3.32–3.22 (m, 2

Following the procedure for 26, trichloroacetimidate 10 (1.66 g, 0.99

mmol, 1.3 equiv) and pentasaccharide 27 (1.50 g, 0.76 mmol, 1.0

L

X. Zhou et al.

Paper

Synthesis

equiv) were treated with TBSOTf (35 L, 0.15 mmol, 0.2 equiv) in an-

hydrous DCM (20 mL) at –40 °C to afford 28 (2.25 g, 0.64 mmol, 84%)

as a white foam after purification by silica gel column chromatogra-

phy (petroleum ether/DCM/EtOAc, 5:2:2).

128.45, 128.41, 128.37, 128.33, 128.28, 128.26, 128.21, 128.18, 128.0,

127.8, 126.54, 126.45, 126.43, 126.39, 126.38, 126.25, 126.15, 102.05,

101.5, 101.38, 101.35, 101.26, 101.22, 100.9, 99.24, 99.17, 98.4, 97.7,

97.6, 97.5, 96.99, 79.0, 78.80, 78.77, 78.41, 78.38, 78.13, 78.05, 77.7,

77.6, 77.4, 75.6, 75.4, 75.11, 75.10, 75.0, 74.97, 74.8, 74.5, 74.38,

74.35, 73.9, 73.68, 73.67, 73.65, 73.42, 73.35, 73.2, 73.07, 73.05, 72.62,

72.59, 72.1, 68.79, 68.72, 68.68, 68.0, 66.6, 66.4, 66.3, 65.70, 65.68,

65.65, 65.59, 62.2, 50.8, 38.0, 29.6, 28.1.

[]_D¹⁹+61.7 (c 0.9, CHCl₃).

¹H NMR (500 MHz, CDCl₃):  = 7.91–7.73 (m, 10 H), 7.71–7.66 (m, 4

H), 7.62–7.56 (m, 6 H), 7.55–7.15 (m, 70 H), 5.51 (s, 1 H), 5.42–5.35

(m, 2 H), 5.30 (s, 1 H), 5.26 (t, J = 8.1 Hz, 1 H), 5.11 (t, J = 5.4 Hz, 1 H),

5.07–5.03 (m, 2 H), 4.99 (s, 1 H), 4.96–4.75 (m, 14 H), 4.73–4.65 (m, 3

H), 4.54 (d, J = 7.8 Hz, 2 H), 4.32 (dd, J = 10.1, 4.4 Hz, 1 H), 4.30–3.83

(m, 18 H), 3.81–3.61 (m, 7 H), 3.59–3.22 (m, 21 H), 3.13 (t, J = 9.4 Hz, 1

H), 3.02 (t, J = 8.8 Hz, 1 H), 2.56–2.38 (m, 4 H), 1.97 (s, 3 H), 0.80 (s, 9

H), –0.07 (s, 3 H), –0.11 (s, 3 H).

¹³C NMR (126 MHz, CDCl₃):  = 205.9, 171.7, 165.1, 164.72, 164.68,

164.65, 164.51, 164.49, 138.8, 137.4, 137.3, 137.25, 137.20, 136.89,

133.88, 133.46, 133.37, 133.18, 133.11, 129.85, 129.82, 129.74,

129.69, 129.64, 129.59, 129.52, 129.44, 129.32, 129.28, 128.98,

128.96, 128.8, 128.7, 128.57, 128.54, 128.42, 128.39, 128.36, 128.30,

128.28, 128.23, 128.16, 128.07, 128.04, 127.8, 127.5, 126.50, 126.49,

126.32, 126.29, 126.16, 126.05, 102.1, 101.7, 101.4, 101.3, 101.22,

101.15, 100.84, 100.79, 99.5, 99.0, 98.5, 97.95, 97.4, 97.1, 96.9, 96.3,

79.6, 78.7, 78.5, 78.31, 78.27, 78.1, 77.58, 77.51, 77.27, 77.22, 75.6,

75.5, 74.9, 74.7, 74.3, 74.2, 73.95, 73.65, 73.62, 73.54, 73.47, 72.7,

72.5, 72.0, 68.75, 68.68, 68.58, 67.9, 66.5, 66.24, 66.17, 65.8, 65.61,

65.56, 65.4, 65.2, 62.8, 50.7, 37.9, 29.5, 28.0, 25.9, 18.3, –5.0, –5.4.

HRMS (ESI): m/z [M + NH₄]⁺calcd for C₁₈₇H₁₇₉N₄O₅₇: 3392.1226;

found: 3392.1195.

2-Azidoethyl (2-O-Benzoyl-4,6-O-benzylidene-3-O-levulinoyl--D-

glucopyranosyl)-(1→3)-(2-O-benzoyl-4,6-O-benzylidene--D-glu-

copyranosyl)-(1→3)-(2-O-benzoyl-4,6-O-benzylidene--D-gluco-

pyranosyl)-(1→3)-(2-O-benzoyl-4,6-O-benzylidene--D-gluco-

pyranosyl)-(1→3)-{4-O-benzyl-2-O-benzoyl-6-O-[(2,3,4-tri-O-ben-

zoyl-6-O-tert-butyldimethylsilyl--D-glucopyranosyl)-(1→6)-

(2,3,4-tri-O-benzoyl--D-glucopyranosyl)-(1→6)-(2,3,4-tri-O-ben-

zoyl--D-glucopyranosyl)-(1→6)-(3,4-di-O-benzoyl-1,2-O--D-glu-

copyranosyl Orthobenzoate]--D-glucopyranosyl}-(1→3)-(2-O-

benzoyl-4,6-O-benzylidene--D-glucopyranosyl)-(1→3)-(2-O-ben-

zoyl-4,6-O-benzylidene--D-glucopyranosyl)-(1→3)-(2-O-benzoyl-

4,6-O-benzylidene--D-glucopyranosyl)-(1→3)-2-O-benzoyl-4,6-

O-benzylidene--D-glucopyranoside (29)

Trichloroacetimidate 2 (391 mg, 0.18 mmol, 1.5 equiv) and nonasac-

charide 3 (403 mg, 0.12 mmol, 1.0 equiv) were dissolved in anhydrous

toluene (15 mL). The mixture was stirred for 15 min at rt in the pres-

ence of flame-activated 5 Å molecular sieves (1.8 g). At this point,

AgOTf (154 mg, 0.60 mmol, 5.0 equiv) was added. After being stirred

for 3 h at 32 °C with the exclusion of light, the reaction was quenched

with Et₃N. The solid was filtered off, and the filtrate was concentrat-

ed. The resulting residue was purified by silica gel column chromatog-

raphy (petroleum ether/DCM/EtOAc, 7:2:1 to 2:1:1) to afford 29 (498

mg, 92.4 mol, 77%) as a white foam.

HRMS (ESI): m/z [M + NH₄]⁺calcd for C₁₉₃H₁₉₃N₄O₅₇Si: 3506.2090;

found: 3506.2053.

2-Azidoethyl (2-O-Benzoyl-4,6-O-benzylidene-3-O-levulinoyl--D-

glucopyranosyl)-(1→3)-(2-O-benzoyl-4,6-O-benzylidene--D-glu-

copyranosyl)-(1→3)-(2-O-benzoyl-4,6-O-benzylidene--D-gluco-

pyranosyl)-(1→3)-(2-O-benzoyl-4,6-O-benzylidene--D-gluco-

pyranosyl)-(1→3)-(4-O-benzyl-2-O-benzoyl--D-glucopyranosyl)-

(1→3)-(2-O-benzoyl-4,6-O-benzylidene--D-glucopyranosyl)-

(1→3)-2-O-benzoyl-4,6-O-benzylidene--D-glucopyranoside (3)

[]_D²⁴+20.1 (c 1.1, CHCl₃).

¹H NMR (400 MHz, CDCl₃):  = 8.03–7.84 (m, 20 H), 7.80–7.70 (m, 18

H), 7.69–6.93 (m, 112 H), 6.04 (t, J = 9.7 Hz, 1 H), 5.81 (t, J = 9.5 Hz, 1

H), 5.77 (d, J = 4.9 Hz, 1 H), 5.75–5.71 (m, 1 H)', 5.57–5.20 (m, 12 H),

5.18–5.08 (m, 2 H), 5.03 (d, J = 7.7 Hz, 2 H), 4.96–4.88 (m, 7 H), 4.88–

4.69 (m, 12 H), 4.67–4.61 (m, 2 H), 4.59–4.48 (m, 3 H), 4.34 (dd, J =

10.2, 4.6 Hz, 1 H), 4.25–4.08 (m, 7 H), 4.06–3.65 (m, 23 H), 3.64–3.16

(m, 29 H), 3.06 (s, 1 H), 2.57–2.30 (m, 4 H), 1.96 (s, 3 H), 0.83 (s, 9 H),

–0.04 (s, 6 H).

¹³C NMR (126 MHz, CDCl₃):  = 205.95, 171.8, 165.9, 165.8, 165.6,

165.43, 165.40, 165.37, 165.32, 165.16, 165.12, 164.98, 164.84,

164.79, 164.71, 164.65, 164.64, 164.49, 138.5, 137.44, 137.39, 137.33,

137.28, 137.0, 135.1, 133.8, 133.6, 133.54, 133.50, 133.4, 133.3,

133.22, 133.17, 133.15, 133.09, 133.04, 133.03, 132.84, 132.82, 130.2,

130.1, 130.03, 129.98, 129.91, 129.84, 129.80, 129.75, 129.6, 129.51,

129.46, 129.42, 129.35, 129.26, 129.19, 129.16, 129.08, 129.01, 128.8,

128.63, 128.59, 128.50, 128.45, 128.41, 128.34, 128.30, 128.26,

128.21, 128.18, 128.0, 127.9, 127.6, 126.9, 126.65, 126.57, 126.49,

126.43, 126.40, 126.3, 126.2, 121.3, 102.1, 101.93, 101.90, 101.6,

101.4, 101.3, 101.2, 100.96, 100.92, 99.2, 98.5, 98.4, 97.6, 97.5, 97.4,

96.9, 95.9, 79.21, 79.20, 79.05, 78.8, 78.44, 78.40, 78.3, 78.2, 77.67,

77.63, 77.36, 75.32, 75.28, 75.09, 75.02, 75.01, 74.99, 74.8, 74.44,

74.35, 73.96, 73.81, 73.78, 73.6, 73.5, 73.29, 73.23, 73.19, 73.05, 72.75,

72.66, 72.62, 72.5, 72.3, 72.1, 71.98, 71.64, 70.58, 69.7, 69.4, 69.1,

68.8, 68.7, 68.5, 68.3, 68.0, 67.7, 66.6, 66.4, 66.3, 65.7, 65.6, 65.5, 64.5,

62.9, 50.8, 38.1, 29.6, 28.1, 25.9, 18.4, –5.23, –5.29.

Pyridine·nHF (255 L, 7.45 mmol, 20.0 equiv) was added to a solution

of nonasaccharide 28 (1.3 g, 0.372 mmol, 1.0 equiv) in MeCN (20 mL)

at 0 °C. The reaction was allowed to proceed under stirring for 2 h at

rt. The mixture was poured into H₂O and the aqueous phase was ex-

tracted with DCM. The combined organic layers were washed with

saturated aqueous NaHCO₃and dried over Na₂SO₄, filtered, and con-

centrated. The residue was purified by silica gel column chromatogra-

phy (petroleum ether/DCM/EtOAc, 3:2:2) to afford 3 (1.08 g, 0.32

mmol, 86%) as a white foam.

[]_D¹⁹+24.9 (c 1.21, CHCl₃).

¹H NMR (500 MHz, CDCl₃):  = 7.86 (d, J = 7.6 Hz, 2 H), 7.77 (d, J = 7.0

Hz, 4 H), 7.72–7.55 (m, 14 H), 7.56–7.19 (m, 70 H), 5.52 (s, 1 H), 5.41–

5.34 (m, 2 H), 5.28–5.23 (m, 2 H), 5.11 (t, J = 5.4 Hz, 1 H), 5.04 (d, J =

7.5 Hz, 1 H), 4.96–4.70 (m, 20 H), 4.55 (d, J = 7.5 Hz, 1 H), 4.34 (dd, J =

10.2, 4.6 Hz, 1 H), 4.26 (dd, J = 9.9, 4.2 Hz, 1 H), 4.23–4.06 (m, 8 H),

4.06–3.99 (m, 2 H), 3.98–3.84 (m, 7 H), 3.76–3.63 (m, 4 H), 3.60–3.34

(m, 22 H), 3.34–3.21 (m, 4 H), 2.56–2.35 (m, 4 H), 1.96 (s, 3 H).

¹³C NMR (126 MHz, CDCl₃):  = 205.97, 171.8, 165.1, 164.78, 164.74,

164.72, 164.69, 164.63, 164.62, 164.59, 164.50, 138.4, 137.38, 137.36,

137.34, 137.28, 137.27, 137.23, 136.99, 133.63, 133.57, 133.55,

133.53, 133.45, 133.27, 133.22, 133.21, 129.91, 129.86, 129.79,

129.73, 129.6, 129.5, 129.4, 129.3, 129.20, 129.17, 129.16, 129.14,

129.13, 129.08, 128.73, 128.68, 128.65, 128.62, 128.56, 128.49,

M

X. Zhou et al.

Paper

Synthesis

HRMS (ESI): m/z [M + NH₄]⁺calcd for C₃₀₁H₂₈₁N₄O₈₉Si: 5402.7349;

found: 5402.7302.

copyranosyl}-(1→3)-(2-O-benzoyl-4,6-O-benzylidene--D-gluco-

pyranosyl)-(1→3)-(2-O-benzoyl-4,6-O-benzylidene--D-gluco-

pyranosyl)-(1→3)-(2-O-benzoyl-4,6-O-benzylidene--D-glucopy-

ranosyl)-(1→3)-2-O-benzoyl-4,6-O-benzylidene--D-glucopyrano-

side (31)

2-Azidoethyl (2-O-Benzoyl-4,6-O-benzylidene-3-O-levulinoyl--D-

glucopyranosyl)-(1→3)-(2-O-benzoyl-4,6-O-benzylidene--D-glu-

copyranosyl)-(1→3)-(2-O-benzoyl-4,6-O-benzylidene--D-gluco-

pyranosyl)-(1→3)-(2-O-benzoyl-4,6-O-benzylidene--D-gluco-

pyranosyl)-(1→3)-{4-O-benzyl-2-O-benzoyl-6-O-[(2,3,4-tri-O-ben-

zoyl-6-O-tert-butyldimethylsilyl--D-glucopyranosyl)-(1→6)-

(2,3,4-tri-O-benzoyl--D-glucopyranosyl)-(1→6)-(2,3,4-tri-O-ben-

zoyl--D-glucopyranosyl)-(1→6)-(2,3,4-tri-O-benzoyl--D-gluco-

pyranosyl)]-(1→6)--D-glucopyranosyl}-(1→3)-(2-O-benzoyl-4,6-

O-benzylidene--D-glucopyranosyl)-(1→3)-(2-O-benzoyl-4,6-O-

benzylidene--D-glucopyranosyl)-(1→3)-(2-O-benzoyl-4,6-O-ben-

zylidene--D-glucopyranosyl)-(1→3)-2-O-benzoyl-4,6-O-ben-

zylidene--D-glucopyranoside (30)

Following the procedure for 3, treatment of 30 (320 mg, 59.4 mol,

1.0 equiv) with pyridine·nHF (41 L, 1.2 mmol, 20.2 equiv) in MeCN

(4 mL) afforded 31 (278 mg, 52.7 mol, 89%) as a white foam after pu-

rification by silica gel column chromatography (petroleum

ether/DCM/EtOAc, 2:1:1).

[]_D²⁴–0.5 (c 1.1, CHCl₃).

¹H NMR (500 MHz, CDCl₃):  = 8.00 (d, J = 7.8 Hz, 2 H), 7.93 (d, J = 8.5

Hz, 12 H), 7.83 (d, J = 7.6 Hz, 12 H), 7.77 (d, J = 7.8 Hz, 2 H), 7.69 (d, J =

7.7 Hz, 2 H), 7.67–7.12 (m, 120 H), 5.97 (t, J = 9.7 Hz, 1 H), 5.87 (t, J =

9.5 Hz, 1 H), 5.73 (t, J = 9.6 Hz, 2 H), 5.57 (s, 1 H), 5.47–5.22 (m, 11 H),

5.18 (t, J = 9.8 Hz, 1 H), 5.10 (t, J = 5.4 Hz, 1 H), 5.06 (d, J = 7.5 Hz, 1 H),

5.03–4.56 (m, 23 H), 4.51 (t, J = 6.9 Hz, 2 H), 4.42–4.33 (m, 1 H), 4.25–

4.07 (m, 9 H), 4.02 (t, J = 9.2 Hz, 3 H), 3.96–3.83 (m, 11 H), 3.81–3.21

(m, 36 H), 3.13 (t, J = 8.1 Hz, 1 H), 3.03 (s, 1 H), 2.56–2.37 (m, 4 H),

1.95 (s, 3 H).

¹³C NMR (126 MHz, CDCl₃):  = 205.9, 171.7, 165.86, 165.82, 165.77,

165.64, 165.45, 165.36, 165.30, 165.11, 164.71, 164.66, 164.58,

164.57, 164.54, 164.52, 164.35, 164.26, 164.1, 138.5, 137.47, 137.40,

137.33, 137.31, 137.27, 137.24, 136.97, 133.54, 133.52, 133.47,

133.39, 133.36, 133.35, 133.27, 133.18, 133.14, 133.09, 133.0, 130.1,

130.0, 129.90, 129.86, 129.81, 129.74, 129.67, 129.56, 129.52, 129.49,

129.47, 129.42, 129.38, 129.36, 129.34, 129.32, 129.26, 129.24,

129.19, 129.17, 129.13, 129.09, 129.08, 129.05, 129.02, 128.99, 128.8,

128.65, 128.59, 128.53, 128.49, 128.48, 128.42, 128.37, 128.31,

128.22, 128.19, 128.15, 128.13, 128.04, 127.7, 127.6, 126.50, 126.48,

126.36, 126.26, 126.22, 126.12, 101.95, 101.44, 101.41, 101.35,

101.31, 101.2, 101.1, 100.95, 100.86, 100.78, 100.77, 100.74, 99.4,

99.1, 98.7, 98.5, 98.2, 97.54, 97.50, 97.4, 96.7, 79.1, 78.9, 78.7, 78.5,

78.4, 77.9, 77.65, 77.61, 77.4, 77.3, 76.6, 75.55, 75.53, 75.09, 74.99,

74.76, 74.67, 73.88, 73.82, 73.69, 73.61, 73.3, 73.23, 73.16, 73.06,

72.98, 72.93, 72.8, 72.70, 72.69, 72.57, 72.1, 71.9, 71.8, 71.7, 70.6,

70.3, 69.4, 68.75, 68.65, 68.57, 68.49, 68.34, 68.32, 67.96, 66.5, 66.4,

66.2, 65.67, 65.62, 65.46, 65.43, 61.36, 50.7, 37.99, 29.6, 28.1.

Orthoester 29 (412 mg, 76.5 mol, 1.0 equiv) was dissolved in anhy-

drous toluene (6 mL). The mixture was stirred for 15 min at rt in the

presence of flame-activated 5 Å molecular sieves (0.6 g). At this point,

AgOTf (98 mg, 382.5 mol, 5.0 equiv) and ^tBuCl (11 L, 99.5 mol, 1.3

equiv) were added. After being stirring for 2 h at 18 °C with the exclu-

sion of light, the reaction was quenched with Et₃N. The solid was fil-

tered off, and the filtrate was concentrated. The resultant residue was

purified by silica gel column chromatography (petroleum

ether/DCM/EtOAc, 5:2:2) to afford 30 (293 mg, 54.4 mol, 71%) as a

white foam.

[]_D²⁴–4.1 (c 0.6, CHCl₃).

¹H NMR (500 MHz, CDCl₃):  = 7.99–7.75 (m, 28 H), 7.69 (d, J = 7.8 Hz,

2 H), 7.66–7.60 (m, 9 H), 7.58–7.11 (m, 111 H), 6.03 (t, J = 9.6 Hz, 1 H),

5.85 (t, J = 9.5 Hz, 1 H), 5.74 (t, J = 9.6 Hz, 2 H), 5.57 (s, 1 H), 5.51 (t, J =

9.7 Hz, 1 H), 5.47–5.36 (m, 5 H), 5.33–5.19 (m, 5 H), 5.15 (t, J = 9.7 Hz,

1 H), 5.10 (t, J = 5.4 Hz, 1 H), 5.05 (d, J = 7.4 Hz, 1 H), 4.97 (t, J = 8.6 Hz,

3 H), 4.94–4.61 (m, 18 H), 4.61–4.50 (m, 4 H), 4.36 (dd, J = 10.6, 4.8 Hz,

1 H), 4.28–4.07 (m, 9 H), 4.05–3.18 (m, 50 H), 3.09 (t, J = 8.3 Hz, 1 H),

2.58–2.37 (m, 4 H), 1.95 (s, 3 H), 0.82 (s, 9 H), –0.06 (s, 6 H).

¹³C NMR (126 MHz, CDCl₃):  = 205.96, 171.8, 165.88, 165.84, 165.7,

165.5, 165.34, 165.27, 165.26, 165.23, 165.21, 165.15, 165.11, 164.74,

164.67, 164.61, 164.55, 164.1, 138.6, 137.48, 137.42, 137.37, 137.35,

137.29, 137.0, 133.55, 133.51, 133.45, 133.43, 133.41, 133.37, 133.32,

133.24, 133.20, 133.1, 133.0, 130.13, 130.10, 129.92, 129.88, 129.85,

129.83, 129.78, 129.6, 129.51, 129.44, 129.38, 129.33, 129.29, 129.27,

129.20, 129.17, 129.14, 129.07, 128.98, 128.62, 128.57, 128.52,

128.47, 128.39, 128.36, 128.33, 128.26, 128.23, 128.18, 128.09,

127.73, 127.65, 126.5, 126.4, 126.28, 126.26, 126.15, 101.99, 101.41,

101.39, 101.27, 101.07, 101.03, 100.99, 100.90, 100.7, 99.6, 99.1, 98.7,

98.5, 98.3, 97.56, 97.45, 96.76, 79.3, 78.95, 78.7, 78.6, 78.4, 77.97,

77.66, 77.63, 77.4, 76.7, 75.6, 75.5, 75.3, 75.1, 74.99, 74.8, 74.0, 73.9,

73.7, 73.64, 73.58, 73.4, 73.26, 73.17, 73.08, 73.03, 72.9, 72.8, 72.6,

72.3, 72.1, 71.99, 71.8, 70.5, 70.4, 69.81, 69.76, 69.3, 68.8, 68.7, 68.6,

68.4, 68.3, 68.0, 66.6, 66.4, 66.3, 65.72, 65.68, 65.5, 62.9, 60.5, 50.8,

38.0, 29.8, 28.1, 25.9, 18.4, –5.3, –5.4.

HRMS (ESI): m/z [M + NH₄]⁺calcd for C₂₉₅H₂₆₇N₄O₈₉: 5288.6484;

found: 5288.6446.

2-Aminoethyl (-D-Glucopyranosyl)-(1→3)-(-D-glucopyranosyl)-

(1→3)-(-D-glucopyranosyl)-(1→3)-(-D-glucopyranosyl)-(1→3)-

{6-O-[(-D-glucopyranosyl)-(1→6)-(-D-glucopyranosyl)-(1→6)-(-

D-glucopyranosyl)-(1→6)-(-D-glucopyranosyl)]-(1→6)--D-gluco-

pyranosyl}-(1→3)-(-D-glucopyranosyl)-(1→3)-(-D-glucopyrano-

syl)-(1→3)-(-D-glucopyranosyl)-(1→3)--D-glucopyranoside (1a)

Tridecasaccharide 31 (278 mg, 52.7 mol, 1.0 equiv) was dissolved in

DCM/MeOH (24 mL, 1:2 v/v), followed by addition of p-TsOH·H₂O

(40.1 mg, 210.8 mol, 4.0 equiv). After being stirred at 40 °C for 4 h,

the reaction was quenched with Et₃N. The volatiles were removed, the

resulting residue was dissolved in MeOH/H₂O (60 mL, 1:1 v/v), and Li-

OH·H₂O (195 mg, 4.64 mmol, 88.0 equiv) was added in portions. The

mixture was heated at 40 °C for 12 h, and the solution was neutral-

ized with resin (H⁺). The solid was filtered off, and the filtrate was

concentrated. The whole amount of residue and 10% Pd/C (90 mg) in

H₂O (10 mL) was stirred under H₂atmosphere (1 atm) overnight at 40

°C. Then the solid was filtered off through a Celite pad. The filtrate

was concentrated and the residue was purified by silica gel column

chromatography (ⁱPrOH/H₂O/NH₄OH, 2:1:1) to afford 1a (75 mg, 34.6

mol, 66% over 3 steps) as a white foam.

HRMS (ESI): m/z [M + NH₄]⁺calcd for C₃₀₁H₂₈₁N₄O₈₉Si: 5402.7349;

found: 5402.7307.

2-Azidoethyl (2-O-Benzoyl-4,6-O-benzylidene-3-O-levulinoyl--D-

glucopyranosyl)-(1→3)-(2-O-benzoyl-4,6-O-benzylidene--D-glu-

copyranosyl)-(1→3)-(2-O-benzoyl-4,6-O-benzylidene--D-gluco-

pyranosyl)-(1→3)-(2-O-benzoyl-4,6-O-benzylidene--D-gluco-

pyranosyl)-(1→3)-{4-O-benzyl-2-O-benzoyl-6-O-[(2,3,4-tri-O-ben-

zoyl--D-glucopyranosyl)-(1→6)-(2,3,4-tri-O-benzoyl--D-gluco-

pyranosyl)-(1→6)-(2,3,4-tri-O-benzoyl--D-glucopyranosyl)-

(1→6)-(2,3,4-tri-O-benzoyl--D-glucopyranosyl)]-(1→6)--D-glu-

N

X. Zhou et al.

Paper

Synthesis

[]_D²⁴–4.6 (c 0.2, H₂O).

¹H NMR (500 MHz, D₂O):  = 4.91–4.70 (m, 9 H), 4.55–4.49 (m, 4 H),

(3) Legentil, L.; Paris, F.; Ballet, C.; Trouvelot, S.; Daire, X.; Vetvicka,

V.; Ferrières, V. Molecules 2015, 20, 9745.

(4) (a) Casadevall, A.; Pirofski, L. A. Trends Mol. Med. 2006, 12, 6.

(b) Wang, H.; Yang, B.; Wang, Y.; Liu, F.; Fernández-Tejada, A.;

Dong, S. Chem. Commun. 2019, 55, 253.

(5) Tsvetkov, Y. E.; Khatuntseva, E. A.; Yashunsky, D. V.; Nifantiev,

N. E. Russ. Chem. Bull. 2015, 64, 990.

(6) Weishaupt, M. W.; Matthies, S.; Seeberger, P. H. Chem. Eur. J.

2013, 19, 12497.

4.26–4.18 (m, 3 H), 4.16–4.08 (m, 1 H), 4.01–3.21 (m, 78 H).

¹³C NMR (126 MHz, D₂O):  = 102.9, 102.79, 102.71, 102.4, 101.8, 84.7,

84.12, 84.05, 83.97, 83.8, 75.9, 75.8, 75.5, 74.8, 74.45, 73.35, 73.2,

73.1, 72.95, 72.7, 69.5, 69.3, 68.7, 68.5, 67.99, 65.86, 60.6, 60.4, 39.3.

HRMS (ESI): m/z [M + H]⁺calcd for C₈₀H₁₃₈NO₆₆: 2168.7467; found:

2168.7441.

(7) Weishaupt, M. W.; Hahm, H. S.; Geissner, A.; Seeberger, P. H.

Chem. Commun. 2017, 53, 3591.

(8) Liao, G.; Burgula, S.; Zhou, Z.; Guo, Z. Eur. J. Org. Chem. 2015,

2942.

(9) Yashunsky, D. V.; Tsvetkov, Y. E.; Grachev, A. A.; Chizhov, A. O.;

Nifantiev, N. E. Carbohydr. Res. 2016, 419, 8.

(10) Tanaka, H.; Kawai, T.; Adachi, Y.; Hanashima, S.; Yamaguchi, Y.;

Ohno, N.; Takahashi, T. Bioorg. Med. Chem. 2012, 20, 3898.

(11) Tanaka, H.; Kawai, T.; Adachi, Y.; Ohno, N.; Takahashi, T. Chem.

Commun. 2010, 46, 8249.

(12) Lu, D.; Wang, S.; Yin, H.; Chu, F.; Wei, Q.; Wang, P. Synlett 2020,

31, 1163.

(13) Wang, Y.; Zhao, X.; Kong, Q.; Yao, J.; Meng, X.-B.; Li, Z.-J. Tetrahe-

dron Lett. 2017, 58, 1655.

(14) (a) Li, W.; Yu, B. Chem. Soc. Rev. 2018, 47, 7954. (b) Yu, B. Acc.

Chem. Res. 2018, 51, 507.

(15) (a) Wang, Z.; Hua, Q.; Yang, Y. Carbohydr. Res. 2019, 482,

107735. (b) Hamagami, H.; Adachi, Y.; Ohno, N.; Tanaka, H.

Asian J. Org. Chem. 2019, 8, 411.

2-Azidoethyl (-D-Glucopyranosyl)-(1→3)-(-D-glucopyranosyl)-

(1→3)-(-D-glucopyranosyl)-(1→3)-(-D-glucopyranosyl)-(1→3)-

{6-O-[(-D-glucopyranosyl)-(1→6)-(-D-glucopyranosyl)-(1→6)-(-

D-glucopyranosyl)-(1→6)-(-D-glucopyranosyl)]-(1→6)--D-gluco-

pyranosyl}-(1→3)-(-D-glucopyranosyl)-(1→3)-(-D-glucopyrano-

syl)-(1→3)-(-D-glucopyranosyl)-(1→3)--D-glucopyranoside (1b)

To a solution of 1a (46 mg, 21.2 mol, 1.0 equiv) in MeOH/H₂O (5 mL,

1:1 v/v) were added imidazole-1-sulfonyl azide hydrochloride (44.4

mg, 212 mol, 10.0 equiv), K₂CO₃(58.6 mg, 424 mol, 20.0 equiv), and

CuSO₄·5 H₂O (1.06 mg, 4.24 mol, 0.2 equiv). The reaction mixture

was stirred at rt for 10 h. Thereafter, the solvent was evaporated, and

the residue was purified by silica gel chromatography (ⁱP-

rOH/H₂O/NH₄OH, 2:1:1) to afford the white sticky solid 1b (38 mg,

17.6 mol, 83%).

[]_D²⁴–19.6 (c 0.5; H₂O/MeOH, 1:1).

¹H NMR (500 MHz, D₂O):  = 5.00–4.69 (m, 9 H), 4.57–4.49 (m, 4 H),

4.26–4.18 (m, 3 H), 4.08–4.02 (m, 1 H), 4.01–3.25 (m, 78 H).

¹³C NMR (126 MHz, D₂O):  = 102.92, 102.89, 102.80, 102.72, 102.4,

102.0, 84.7, 84.1, 83.98, 83.96, 83.8, 75.9, 75.8, 75.5, 74.8, 73.4, 73.20,

73.15, 73.06, 72.97, 72.8, 69.53, 69.48, 69.4, 69.3, 68.8, 68.7, 68.5,

68.0, 60.6, 50.4.

HRMS (ESI): m/z [M – 2 H]⁺/2 calcd for C₈₀H₁₃₃N₃O₆₆: 1095.8577;

found: 1095.8564.

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Conflict of Interest

The authors declare no conflict of interest.

Funding Information

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We are grateful for financial support from the National Natural

Science Foundation of China (Nos. 21672194 and 21977088), the

National Natural Science Foundation of China-Shandong Joint Fund

(No. U1906213), and the Natural Science Foundation of Shandong

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Article Doi

Convergent Synthesis of Branched β-Glucan Tridecasaccharides Ready for Conjugation

DOI: 10.1055/a-1440-9386

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Article abstract of DOI:10.1055/a-1440-9386

Full text of DOI:10.1055/a-1440-9386

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