Synthesis of docosasaccharide arabinan motif of mycobacterial cell wall

DOI: 10.1021/ja109932t

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Journal of the American Chemical Society p. 2275 - 2291 (2011)

Update date:2022-07-29

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Authors:

Ishiwata, Akihiro

Ito, Yukishige

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Article abstract of DOI:10.1021/ja109932t

Mycobacterial arabinan is a common constituent of both arabinogalactan (AG) and lipoarabinomannan (LAM). In this study, synthesis of β-Araf containing common arabinan docosasaccharide motif (22 Araf monomer units) of mycobacterial cell wall was achieved. Our synthetic strategy toward arabinan involves (1) the stereoselective β-arabinofuranosylation using both 3,5-O-TIPDS-protected and NAP-protected arabinofuranosyl donors for straightforward intermolecular glycosylation and intramolecular aglycon delivery (IAD), respectively, and (2) the convergent fragment coupling with branched fragments at the linear sequence using thioglycoside donor obtained from the corresponding acetonide at the reducing terminal of each fragment through a three-step procedure. Because the acetonide at the reducing terminal of all fragments would be converted to thioglycoside as the glycosyl donor, and mainly Bn ether protections were used, our strategy will be readily applicable to the synthesis of more complex arabinan, arabinogalactan, and arabinomycolate derived from mycobacterial CWS.

Full text of DOI:10.1021/ja109932t

ARTICLE

pubs.acs.org/JACS

Synthesis of Docosasaccharide Arabinan Motif of Mycobacterial

Cell Wall

Akihiro Ishiwata*^,†and Yukishige Ito*^,†,‡

^†RIKEN Advanced Science Institute, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan

^‡ERATO Glycotrilogy Project, Japan Science and Technology Agancy (JST), 2-1 Hirosawa, Wako, Saitama 351-0198, Japan

S Supporting Information

ABSTRACT: Mycobacterial arabinan is a common constituent

of both arabinogalactan (AG) and lipoarabinomannan (LAM).

In this study, synthesis of β-Araf containing common arabinan

docosasaccharide motif (22 Araf monomer units) of mycobac-

terial cell wall was achieved. Our synthetic strategy toward

arabinan involves (1) the stereoselective β-arabinofuranosylation

using both 3,5-O-TIPDS-protected and NAP-protected arabino-

furanosyl donors for straightforward intermolecular glycosylation

and intramolecular aglycon delivery (IAD), respectively, and (2)

theconvergentfragmentcouplingwithbranchedfragmentsatthe

linear sequence using thioglycoside donor obtained from the corresponding acetonide at the reducing terminal of each fragment through

a three-step procedure. Because the acetonide at the reducing terminal of all fragments would be converted to thioglycoside as the

glycosyl donor, and mainly Bn ether protections were used, our strategy will be readily applicable to the synthesis of more complex

arabinan, arabinogalactan, and arabinomycolate derived from mycobacterial CWS.

’ INTRODUCTION

heterogeneous, long chain functionalized fatty acid. Further com-

plexity has been found, which is produced by substitutions at the

Mycobacterial arabinan is a common constituent of both

arabinogalactan (AG) and lipoarabinomannan (LAM). They

are attracting exceptionally broad attention among furanoside-

containing glycans¹originated from bacteria,²fungi,³and para-

sites,⁴which play key roles in their infectivity and pathogenicity.

Biosynthetic steps of these glycans catalyzed by mycobacterial

arabinofuranosyl transferases (ArafTs)⁵are promising therapeu-

tic targets⁶against Mycobacterium tuberculosis, a causative agent

of tuberculosis, which remains rampant and is a growing threat

worldwide due to the emergence of strains that have multidrug

resistance (MDR).⁷On the other hand, adjuvants derived from

the cell wall skeleton (CWS) of mycobacteria, such as Bacillus

Calmette-Guꢀerin (BCG-CWS) from M. bovis, are known to be

potent activators of innate immunity.^8,9Although BCG-CWS-

initiated immunity has been proposed to involve the activation of

macrophages via Toll-like receptor (TLR) 2,¹⁰its structural basis

has been elusive, due to the extreme complexity of BCG-CWS.

Structural architecture of mycobacterial CWS is unique, being

composed of mycolic acid (MA), ^D-arabinan, D-galactan, linker

disaccharide (R-Rhap-(1f3)-R-GlcNAc), and peptidoglycan

(PG)^5,11(Figure 1). Recent eﬀorts¹²have been extended to

draw the ﬁner picture of mycobacterial cell wall, in which

hentriacontaarabinan (31 araninofuranoside (Araf) monomer

units),^12econsisting of an [R-Araf-(1f5)-R-Araf]_nrepeat, is

linked to the inner complex and is capped by a branched motif.

The latter contains terminal β-Araf residues, each of which is

linked to the 2-position of penultimate R-Araf. β-Araf residues are

O-acylated at their C-5 positions by mycolic acid, a structurally

12a

2-O-position of inner 3,5-branched-Araf by GalNH₂or succi-

nate ester.^12eOn the other hand, galactan portions are composed

of β-Galf-(1f5)-β-Galf repeating units, which are linked by

β-(1f6)-linkages and contain three arabinans.^12b

In this study, we achieved the stereoselective synthesis of β-

Araf containing common arabinan docosasaccharide motif (22

monomer units, Araf₂₂) of mycobacterial arabinogaractan. Our

synthesis features the extensive use of branched thioglycosides as

key components for fragment coupling reactions. As the target

contains problematic β-Arafs, several approaches developed in

this group to stereoselectively construct this type of linkage were

tested for their suitability to the current purpose.

’ RESULTS AND DISCUSSION

With the exception of homopolymerization, the synthesis of

structurally deﬁned oligosaccharide over 20 residues is a signiﬁcant

challenge in synthetic carbohydrate chemistry. In 1993, Ogawa

et al.¹³achieved the synthesis of polylactosamine pentacosasacchar-

ide using trisaccharyl ﬂuoride donor with decasaccharide pentaol as

the key reaction. More recently, Fraser-Reid et al.¹⁴reported the

synthesis of mannose-capped arabinomannan fragment, in its pro-

tected form, using octacosasaccharide derived trichloroacetimidate,

which in turn was synthesized from hexasaccharyl trichloroacetimi-

dates and pentasaccharide, and dodecasaccharide acceptor. As for the

Received: November 5, 2010

Published: February 2, 2011

2011 American Chemical Society

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Figure 1. Structure of mycobacterial cell wall glycoconjugate.

synthesis of mycobacterial arabinans, Lowary et al.¹⁵reported the

synthesis of docosasaccharide (Araf₂₂) using two pentasaccharyl

trichloroacetimidates as donors and dodecasaccharide as an acceptor,

which in turn was synthesized from heptasaccharyl trichloroacetimi-

date and pentasaccharide fragment. While all of these examples relied

upon fragment couplings at branching sites, our approach was

designed to conduct all fragment couplings at linear sequences so

as to maximize the reactivity of reaction sites.¹⁶It also features the use

of thioglycosides¹⁷as branched oligosaccharide donors. Although the

synthesis of linear thioglycoside could be synthesized by orthogonal

strategy,¹⁸preparation of thiglycosides of complex and branched

glycans is less straightforward. We achieved this task in a uniﬁed man-

ner by using 1,2-acetonide as the common precursors (vide infra).

Mycobacterial arabinan contains, in its nonreducing end, β-

Arafs, which are further decorated by mycolic acid esters.

Stereocontrolled formation of β-Araf is intrinsically problematic,

because of its 1,2-cis, nonaxial nature. To solve this, several

innovative methods have been developed. Of particular note

were approaches based on S_N2-type displacement of R-triﬂates

derived from 2,3-anhydro-modiﬁed and carboxybenzyl (CB)-

substituted donors, which were developed by Lowary¹⁹and by

Kim,²⁰respectively. Alternatively, certain cyclic protections have

given promising results by virtue of their abilities to bring con-

formational constrain to arabinofuranosyl donors. For instance,

bicyclic donors,^21-253,5-O-di-t-butylsilylene (DTBS)-protected

donors in particular, reported by Boons²¹and others,^22-25were

shown to give substantial β-selectivity, while our study indicated

that the introduction of 3,5-O-tetra-i-propyldisiloxanylidene

(TIPDS)-protection was optimum for this purpose.²²

(Araf₈) diol acceptor (4) so that fragment couplings can be

conducted to make linkage at nonbranched Ara residue. The

synthesis of heptasaccharide (Araf₇) fragment (3) was to involve

stereoselective introduction of two β-Araf residues by using our

TIPDS- or NAP-protected donors (Araf₁, 5-7)^22,27to penta-

saccharide (Araf₅) diol (8). On the other hand, as precursors of

the octasaccharide (Araf₈) acceptor (4), pentasaccharide (Araf₅)

donor (9) and trisaccharide (Araf₃) acceptor (11) were assumed.

According to this scheme, all branches are created before

fragment condensation, at the stage of the synthesis of penta-

saccharides (Araf₅) fragments (8, 10) from trisaccharide (Araf₃)

diol acceptors (12, 13). Reducing end terminus of acceptors

(e.g., 3, 4, 8, 10, 11-13) was masked with 1,2-O-acetonide,

which has a dual beneﬁt as follows. First, our general protocol

enabled high-yield conversion of 1,2-O-acetonides (3, 10) to

thioglycosides (2, 9) in a uniﬁed manner. Second, acetonide

group (4, 8, 11-13) served as a marker, the presence of which

was easily seen with ¹H NMR, thereby facilitating the isolation of

successfully assembled product.

In our convergent strategy, fragment couplings that employed

NIS-AgOTf²⁹mediated activation of 4-methylphenyl thiogly-

coside instead of using glycosyl imidate^14,15or ﬂuoride¹³for

fragment condensation. The use of benzyl ether for global

protection will allow us to approach mycolated arabinans.³⁰

However, acyl protections were introduced to the 2-position of

thioglycoside moieties to secure stereocontrolled formation of

the R-Araf linkages. As typiﬁed in Scheme 1, protective groups of

glycosylation product, such as silyl and acyl groups, were ex-

changed to benzyl ether (e.g., 19), except reducing terminal

acetonide and selected hydroxy groups that were going to be

liberated for further glycosylation.

To realize more complete selectivity in β-Araf formation,

approaches based on intramolecular aglycon delivery (IAD) have

been investigated. They employed 2-O-p-methoxybenzyl (PMB)²⁶

or 2-O-(2-naphthyl)methyl (NAP)²⁷equipped donor.²⁸Our study

also addressed the possibility to deploy 5-O-NAP group as a tether.

Our synthetic plan toward target arabinan 1 was based on the

canonical disconnection depicted in Figure 2. It employed two

identical heptasaccharide (Araf₇) donors (2) and octasaccharide

According to this plan, our study commenced with the syn-

thesis of Araf₃fragment 11 from common disaccharide (Araf₂)

intermediate 19,³¹which was prepared from monosaccharide

(Araf₁) units 14³²and 15²²as depicted in Scheme 1. The

disaccharide 19 was then glycosylated with 15 to give 20, which

was converted to 11 that will be used as the reducing end

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Figure 2. Retrosynthetic analysis of docosasaccharide arabinan motif.

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Scheme 1. Synthesis of Pentasaccharide Fragments^a

^aReagents and conditions: (a) 15, N-iodosuccinimide, AgOTf, MS4 Å, CH₂Cl₂, 0 °C; (b) NaOMe, MeOH; (c) BnBr, NaH, DMF, 0 °C;

(d) TBAF, THF, 91% in four steps from 14 (19), 94% in four steps from 19 (11), 84% in three steps from 24 (13); (e) 23, N-iodosuccinimide,

AgOTf, MS4 Å, CH₂Cl₂, 0 °C, 93%; (f) TBAF, THF, 91%; (g) 15, N-iodosuccinimide, AgOTf, MS4 Å, CH₂Cl₂, 0 °C, 96%; (h) NaOMe, MeOH;

(i) BnBr, NaH, DMF, 0 °C, 83% in two steps; (j) TBAF, THF, 93%; (k) 30, MeOTf, DTBMP, MS4 Å, CH₂Cl₂, room temperature; (l) Et₃N,

MeOH, H₂O, 93% in two steps.

trisaccharide component. On the other hand, reaction with 3,5-

O-TIDPS-protected donor 23³³gave 24, which in turn was

converted to Araf₃diols 12³¹and 13.³¹Thus, double glycosyla-

tion of 12 with 2 equiv of 15 produced branching to give 27,

which was followed by protective group manipulation to provide

10 and 29. Another branched Araf₅fragment 8 was prepared

from the diol 13 and a glycosyl donor 30,²²completing the

synthesis of all small fragments, including reducing-end trisac-

charide and branched pentasaccharide frameworks.

Synthesis of Octasaccharide Fragment: Conversion of 1,2-

Acetonide to Thioglycoside and Model Fragment Couplings.

Our syntheticplan required a general accessto thioglycosides form

1,2-O-acetonides (e.g., 9 from 10; Scheme 2). Initial attempts

for direct conversion of acetonide 10 to thioglycoside by using

CH₃C₆H₄SH-BF₃OEt₂conditions³⁴turned out to be fruitless.

We next explored the utility of 1,2-diol 32, obtained by acidic

hydrolysis³⁵of acetonide 10, as a precursor of thioglycoside.

However, treatment of diacetate derived from 32 with

CH₃C₆H₄SH-BF₃OEt₂met with limited success, giving very

low yield of the desired product 9. On the other hand, to our

delight, treatment of 32 with (CH₃C₆H₄S)₂-n-Bu₃P³⁶afforded

the desired Araf₅thioglycoside 33, which was immediately acety-

lated to give 9. Subsequently, the latter was used as the Araf₅donor

9 and coupled with the Araf₃acceptor 11 to give Araf₈product 34,

which was converted to Araf₈acceptor 4 through three steps.

To conﬁrm the adequacy of our approach to construct the

tetra-branched structure of the target arabinan, an attempt was

made to simultaneously introduce two Araf₅fragments to 29.

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Scheme 2. Synthesis of Octasaccharide Fragment and Heptadecasaccharide^a

^aReagents and conditions: (a) dioxane-70% AcOH aqueous-10% HCl aqueous (10:10:1), 50 °C; (b) (TolS)₂, n-Bu₃P, CH₂Cl₂; (c) Ac₂O,

pyridine, DMAP, 71% in three steps; (d) 11, N-iodosuccinimide, AgOTf, MS4 Å, CH₂Cl₂, -30 to -10 °C, 73%; (e) NaOMe, MeOH, 0 °C; (f)

BnBr, NaH, DMF, 0 °C; (g) TBAF, THF, 83% in three steps; (h) 29, N-iodosuccinimide, AgOTf, MS4 Å, CH₂Cl₂, 0 °C, 73%.

In fact, the use of 9 as the Araf₅donor gave the pentadecasac-

charide (Araf₁₅) 37 in good yield.¹⁶The presence of two acetates,

two TBDPS groups, and an acetonide, all of which were evident

from 1D ¹H NMR, provided strong support of the structure, which

was rigorously conﬁrmed by ¹³C and HMQC NMR measurements.

Synthesis of Heptasaccharide Fragment Having 1,2-cis-β

Linkages. Synthesis of the Araf₇fragment entailed the intro-

duction of two β-Araf residues. As the most straightforward

approach, double glycosylation of Araf₅acceptor 8 was first

conducted by using arabinofuranosyl donors specialized for β-

Araf formation (Scheme 3). Because our previous study revealed

the suitability of the 3,5-O-TIDPS-protected thioglyoside 5²²for

β-Araf linkage formation, this donor was a priori selected for this

purpose. As expected, the desired β,β-isomer 38 was obtained as

the major isomer (β,β-isomer:other isomers = 10.8:1). Stereo-

Although the use of 5 as a donor realized the introduction of β-

Araf residues in a practically useful selectivity, to achieve β-Araf

formation in a completely selective manner, approaches based on

intramolecular aglycon delivery were examined.²⁸In fact, we

previously reported that the NAP-mediated IAD was eﬀective for

exclusive formation of the β-Araf glycosides. For instance, the

two-step reaction ((1) DDQ, (2) MeOTf, DTBMP) between

the thioglycoside 6²⁷and acceptor 44^27,37gave the β-glycoside

47 in 77% yield through mixed acetal 46a (Table 1, entry 1).²⁷

When this reaction was applied to the double glycosylation of 8

using 6 as the donor, the desired β,β-heptasaccharide hexaacetate

53 was obtained as a single isomer in 60% yield from 8, after

acidic workup and reprotection (Scheme 4). This result clearly

indicated the advantage of using NAP ether as a tether, because a

similar transformation with PMB ether-mediated IAD gave only

low yield (23%) of doubly glycosylated product.²⁶

chemistry of newly formed linkages was confirmed by their ¹³

NMR signals, which appeared at 98.8 and 98.9 ppm.²²Although

isomer separation at this stage was not practical, removal of

TIPDS groups from 38 enabled facile separation of the isomers,

and stereochemically homogeneous diol 39 was isolated in 87%

yield from 8. Subsequent introduction of a TBDPS group to

primary alcohols and benzylation of secondary alcohols gave

Araf₇fragment 3. Further conversion to thioglycoside 2 was

conducted with the aforementioned three-step protocol that

includes acidic hydrolysis, thioglycoside formation using (CH₃-

C₆H₄S)₂-n-Bu₃P, and acetylation.

Our eﬀort was then extended to 5-O-NAP ether-protected

Araf donors such as 43^31,38and 7.³¹Although similar “long-

distance” intramolecular aglycon delivery has been reported for

the formation of simple glucopyranoside and ribofuranoside,³⁹

its application to complex glycan synthesis has not been explored.

This option seemed particularly attractive, because C-5 OH will

be liberated as the IAD from 7/43 proceeds, thereby enabling

site-selective introduction of mycolic acid without additional

protective group manipulation. Accordingly, as a model, we

conducted the reaction between 43 and 44 under our standard

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Scheme 3. Stereoselective Synthesis of Heptasaccharide Fragment Using 3,5-O-TIDPS-Protected Thioglyoside 5^a

^aReagents and conditions: (a) 5, N-iodosuccinimide, AgOTf, MS4 Å, CH₂Cl₂, -40 °C, (ββ:other isomers = 8.46:1); (b) TBAF, THF, 87%, ββ:

other isomers; (c) TBDPSCl, imidazole, DMF, 0 °C to room temperature; (d) BnBr, NaH, DMF, 0 °C, 84% in two steps; (e) dioxane-70% AcOH

aqueous-10% HCl aqueous (10:10:1), 50 °C; (f) (TolS)₂, n-Bu₃P, CH₂Cl₂; (g) Ac₂O, pyridine, DMAP, 76% in three steps.

IAD conditions. Formation of the mixed acetal proceeded quite

smoothly, giving 82% yield of 46b. It was followed by thioglyco-

side activation by MeOTf-DTBMP in CH₂Cl₂to give the IAD

product 48, which was isolated as 49 after acidic workup followed

by acetylation (Table 1, entry 2). However, somewhat to our

disappointment, the yield was only modest (34%), and the

product was a mixture of isomers, in which the desired β-isomer

predominated in a ratio of 6.67:1 (entry 2). Corresponding p-

methylphenyl (Tol) thioglycoside 7 required slightly higher

temperature (40 °C) for activation, giving the same product in

46% yield in somewhat lower selectivity (β:R = 4.24:1) (entry 3).

Further screening clariﬁed that the selectivity was enhanced

when the IAD was conducted under dilute conditions, suggesting

that the intramolecular pathway was competing with IAD. At 1

mM concentration, nearly exclusive formation of the β-isomer

was observed, although the yield was still modest (entry 4). As an

activator, a combination of NIS-AgOTf turned out to be more

eﬀective. The IAD product was obtained as 50, which had a O-(2-

naphthyl)-(succinimido)methyl group at 5-position of the β-Araf

moiety. Formation of this unexpected product, which was caused

presumably by quenching the immediate cationic species by

succinimide, was not consequential. Treatment of 50 with

(CH₂NH₂)₂in MeOH⁴⁰liberated the 5-OH to provide 48 in

58% overall yield from 44 (entry 5). A similar reaction with p-

methylphenyl thioglycoside 7 was signiﬁcantly more eﬀective,

giving 72% yield of 48 (entry 6). The disaccharide acceptor 45³¹also

aﬀorded the β-glycoside 51, which corresponds to the nonreducing

end trisaccharide of arabinan, with high selectivity (entry 7).

as the sole stereoisomer, after treatment of initially formed

5-O-(2-naphthyl)-(succinimido)methyl group of the product

with (CH₂NH₂)₂in MeOH. Subsequent silylation gave 3, which

was identical to the same compound obtained by intermolecular

glycosylation (Scheme 3). However, the overall yield of 55 from

8 was rather low (25% overall), indicating that the approach

based on 5-O-NAP needs further improvement to be competitive

with other approaches using 5 or 6.

Assembly of Docosasaccharide Arabinan Motif. To com-

plete the total framework of the target Araf₂₂, double glycosyla-

tion of Araf₈acceptor 4 with Araf₇donor 2 was carried out

through activation by NIS-AgOTf at -40 °C (Scheme 5).

Progress of the reaction was monitored by MALDI-TOF mass,

which indicated the first accumulation of the Araf₁₅product and

subsequent formation of Araf₂₂that was complete after 3 days.

Purification by gel filtration chromatography afforded 56.

Although the calculated yield (96%) may not be accurate due

to the minuteness of the reaction scale (theoretical yield, 7.9 mg),

nearly quantitative formation of Araf₂₂56 was evident from

MALDI-TOF-MS. After isolation, Nano ESI FT-ICR mass

spectrum (R = 90 000, fwhm, at m/z 2500) was acquired, which

was in full agreement with the structure.³¹While the presence of

38 Bn ethers obscured NMR peaks of anomric protons, the

structure of 56 was supported by the presence of two acetates,

four TBDPS groups, and an acetonide group. Furthermore,

extensive assignment of peaks was made at this stage using

various techniques (600 MHz, H, ¹³C, DQF-COSY, TOCSY,

HSQC, HSQC-TOCSY, HMBC) giving nearly complete assign-

ment of peaks. The anomeric peak of reducing arabinofuranose

residue protected by 1,2-acetonide was clearly distinct from other

anomeric peaks, appearing at 5.88 ppm. Signals of anomeric

With these results in hand, double IAD of 8 using the 5-O-

NAP-protected thioglycoside 7 as a donor was conducted in a

manner similar to that described for 48, giving the β,β-isomer 55

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Table 1. NAP Ether-Mediated IAD Approaches for Stereoselective Synthesis of β-Arabinofuranosides

entry

activator

conc./mM

temp

product (%)

R; β

MeOTf-DTBMP

AgOTf-NIS^d

room temperature

40 °C

47^b(77^c)

49 (34)

49 (46)

49 (34)

48^e(58)

48^e(72)

51^e(65^c)

43^a

7^a

1:6.67

1:4.24

1:>20

room temperature

-30 °C

AgOTf-NIS^d

AgOTf-NIS

^aYields of MA formation: 82% (43 þ 44), 82% (6 þ 44). ^bAcidic workup and acetylation were carried out after IAD. ^cMultistep yield from

acceptor. ^dIn the presence of 1.7 equiv of DTBMP. ^eRemoval of (2-naphthyl)-succinimidomethyl group was carried out by the treatment of a

crude mixture of IAD reaction with (CH₂NH₂)₂in n-butanol.

peaks derived from nonreducing terminal β-linked Araf residues

appeared at ca. 100 ppm in ¹³C NMR spectra. The anomeric

peaks of three branches were also found as broad singlets in ¹H

NMR spectra. Detailed assignment of connectivity of each

residue was made by using HMBC spectra, although several

simple R(1f5) linkages were obscured by extensive overlap-

ping. Subsequently, deprotection was conducted in a standard

donor obtained from the corresponding acetonide at the reducing

terminal of each fragment through a three-step procedure. Our

synthetic scheme involves eight glycosylations from monosacchar-

ide acceptor 14 including two fragment couplings with acceptors

(4 and 11) and four double glycosylations with diol acceptors (4, 8,

12, and 13), as well as one β-arabinofuranosylation with 8.

Although the use of 5 as a donor realized the introduction of β-

Araf residues in a practically useful selectivity, β-Araf formation

using 2-O- and 5-O-NAP ether protected donors (6, 7) through

intramolecular aglycon delivery was achieved with complete

stereoselectivity. We also observed that double glycosylation of

5 or 6 with diol acceptor 8 aﬀorded the desired β,β-isomer

stereoselectively in good yield through inter- and intramolecular

glycosylation pathway, respectively.

Conversion of acetonide at the reducing terminal of each

fragment to corresponding thioglycoside is one of the key steps

of our strategy for fragment couplings, which was achieved by a

three-step procedure including acetonide hydrolysis, chemose-

lective thioglycosylation using (CH₃C₆H₄S)₂-n-Bu₃P, and acet-

ylation of the resulting hydroxyl group. Subsequent fragment

couplings between fragments (2 þ 4 and 9 þ 11) at the linear

sequence were achieved successfully to aﬀord larger motifs

fashion to afford free Araf₂₂1 ([M þ Na]^þcalcd for 1: C₁₁₃H₁₈₂

O₈₉Na, 2985.96, found 2985.63). Extensive assignment of H

(800 MHz) and ¹³C (125 MHz) NMR peaks was made as in the

case for protected Araf₂₂56, which clearly indicated the presence

of 22 Araf residues with correct stereochemistry.⁴¹

’ CONCLUSION

Our study achieved the synthesis of arabinan docosasacchar-

ide motif of mycobacterial CWS, which features (1) the stereo-

selective β-arabinofuranosylation using both 3,5-O-TIPDS-

protected or NAP-equipped arabinofuranosyl donor for inter-

molecular glycosylation and intramolecular aglycon delivery

(IAD), respectively, and (2) the convergent fragment coupling

withbranched fragments atthelinearsequenceusing thioglycoside

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Scheme 4. Double IAD Approaches for Stereoselective Synthesis of Heptasaccharide Fragment^a

^aReagents and conditions: (a) (i) 6, DDQ, MS4 Å, (CH₂Cl)₂, 82%; (ii) MeOTf, DTBMP, MS4 Å, (CH₂Cl)₂; (iii) AcOH, H₂O, 80 °C; (iv) TBAF,

THF; (v) Ac₂O, pyridine, DMAP, 73% from mixed acetal 52a; (b) (i) 7, DDQ, MS4 Å, (CH₂Cl)₂, 74%; (ii) N-iodosuccinimide, AgOTf, -40-

0 °C; (iii) (CH₂NH₂)₂, n-BuOH, 34% from mixed acetal 52b; (c) TBDPSCl, imidazole, DMF, 89%.

Scheme 5. Synthesis of Docosasaccharide Arabinan Motif^a

^aReagents and conditions: (a) N-iodosuccinimide, AgOTf, -40 to 0 °C, 97%; (b) TBAF, THF; (c) Et₃N-MeOH-H₂O; (d) H₂, Pd(OH)₂,

EtOAc-MeOH-H₂O, 48% in three steps.

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(56, 34) in good yield. Because the acetonide at the reducing

terminal of all fragments would be converted to thioglycoside as

the glycosyl donor, and mainly Bn ether protections were used,

our strategy will be directly applicable to the synthesis of

arabinogalactans and arabinomycolates of further complexity.

104.9, 105.6, 105.6, 106.0, 106.3, 112.8, 127.61, 127.63, 127.7, 127.78,

127.84, 128.3, 128.36, 128.44, 128.5, 129.65, 129.72, 129.8, 133.13,

133.18, 133.37, 135.58, 135.60, 165.3, 169.6 (ꢀ2), 169.95, 170.04. ESI-

TOF MS: [M þ Na]^þcalcd for C₉₆H₁₁₂O₂₆Si₂Na, 1759.69, found

1759.33. HRMS ESI-TOF: [M þ Na]^þcalcd for C₉₆H₁₁₂O₂₆Si₂Na,

1759.6870, found 1759.6831.

2,3-Di-O-benzyl-5-O-t-butyldiphenylsilyl-R-^D-arabinofuranosyl^(d/e)

’ EXPERIMENTAL SECTION

(1f5)-(2,3-di-O-benzyl-5-O-t-butyldiphenylsilyl-R-^D-arabinofuranosyl^(d/e))-

(1f3)-2-O-benzyl-R-^D-arabinofuranosyl^(c)-(1f5)-2,3-di-O-benzyl-R-D-

arabinofuranosyl^(b)-(1f5)-3-O-benzyl-1,2-O-isopropylidene-R-D-ara-

binofuranose^(a)(10). To a solution of 27 (3.28 g, 1.89 mmol) in

MeOH (100 mL) was added 1 M solution of NaOMe in MeOH (0.40

mL) at 0 °C. After being stirred for 2 h at the same temperature, and for 1

h at room temperature at the same temperature, the reaction was

quenched by Amberlyst H^þresin, filtered, and concentrated in vacuo

to give a crude deacylated compound 28. To a solution of crude 28 in dry

DMF (20 mL) were added NaH (528 mg, 13.2 mmol) and BnBr (1.23

mL, 7.19 mmol) at 0 °C, and the mixture was stirred for 2 h, during

which time temperature was going up to room temperature. The

reaction was quenched by triethylamine and brine, extracted with

CHCl₃, dried over Na₂SO₄, and evaporated in vacuo. The residue was

purified by flash column chromatography using gradient solvent system

(hexane/ethyl acetate = 20/1 to 10/1 to 5/1 to 3/1 to 1/1) to give the

title compound 10 (2.99 g, 83% in two steps). 10: [R]²⁶_D59.0 (c 1.00,

CHCl₃). ¹H NMR (CDCl₃, 400 MHz): δ 1.15 (s, TBDPS, 9H), 1.16 (s,

TBDPS, 9H), 1.45 (s, acetonide, 3H), 1.64 (s, acetonide, 3H), 3.70 (dd,

J = 10.8, 7.2 Hz, C5-H^a, 1H), 3.84 (dd, J = 12.0, 2.8 Hz, C5-H^b, 1H),

General Procedure. All reactions sensitive to air and/or moisture

were carried out under argon atmosphere with anhydrous solvents.

Substrates of glycosylations were dried by azeotoropic removal with

toluene. Column chromatography was performed on silica gel 60N,

100-210 mesh (Kanto Kagaku Co., Ltd.). Preparative TLC was

performed on silica gel 60 F₂₅₄, 0.5 mm (E. Merck). Gel filtration was

performed on Bio beads SX-3 or Sephadex LH-20 (Pharmacia). Optical

rotations (deg; deg mL/g dm) were measured with a JASCO DIP 370

polarimeter. H NMR spectra were recorded at 400 MHz on a JEOL

ECX 400, at 600 MHz on ECA 600 (RIKEN Advanced Science

Institute), and at 800 MHz on ECA 800 (NMR facility at RIKEN

Yokohama Institute) spectrometers, and chemical shifts are referred to

internal residual solvent signals, 7.24 ppm (CDCl₃) or 2.23 ppm for

internal acetone (D₂O). ¹³C NMR spectra were recorded on the same

instruments, and chemical shifts are referred to internal CDCl₃(77.0

ppm) or 31.1 ppm for internal acetone (D₂O). MALDI-TOF mass

spectra were recorded on a SHIMADZU Kompact MALDI AXIMA-

CFR spectrometer with 2,5-dihydroxybenzoic acid as the matrix. ESI-

TOF mass spectra were recorded on a JEOL AccuTOF JMS-T700LCK

with CF₃CO₂Na as the internal standard. Fourier transform ion

cyclotron resonance (FT-ICR) mass spectra was recorded on a Bruker

Daltonics Bio APEX II 70e FT Mass Spectrometer (RIKEN Advanced

Science Institute). All other reagents were purchased from Wako Pure

Chemical Industries Ltd., Kanto Chemicals Co. Inc., Tokyo Chemical

Industry Co., Ltd., and Aldrich Chemical Co.

3.87-3.98 (m, C5-H^c, C5-H₂, C5-H₂, 1H), 4.00-4.05 (m,

C5-H^a, C5-H^b, 2H), 4.08 (dd, J = 12.0, 4.8 Hz, C5-H^c, 1H),

4.16-4.34 (m, C3-H^a, C2-H^b, C3-H^b, C4-H^b, C2-H^c, C4-H^c,

C2-H^d, C3-H^d, C4-H^d, C2-H^e, C3-H^e, C4-H^e, 12H), 4.33-4.39

(m, C4-H^a, 1H), 4.46 (dd, J = 6.8, 3.2 Hz, C3-H^c, 1H), 4.49-4.74

(m, Bn, 16H), 4.77 (d, J = 3.6 Hz, C2-H^a, 1H), 5.15 (s, C1-H^b, 1H),

5.28 (s, C1-H^c, 1H), 5.320 (s, C1-H^d, 1H), 5.324 (s, C1-H^e, 1H),

6.01 (d, J = 3.6 Hz, C1-H^a, 1H), 7.00-7.64 (m, Ar, 60H). ¹³C NMR

(CDCl₃, 100 MHz): δ 19.1, 19.2, 26.3, 26.67, 26.72, 27.1, 63.1, 63.3,

65.4, 65.9, 66.7, 71.47, 71.53, 71.57, 71.69, 71.74, 71.9, 72.0, 72.3, 80.0,

80.2, 81.1, 81.7, 82.2, 82.7 (ꢀ2), 82.8, 82.9, 83.1, 85.2, 87.8, 88.3, 88.5

(ꢀ2), 105.2, 105.5, 106.1, 106.3, 106.5, 112.7, 127.3, 127.47, 127.51,

127.56, 127.62, 127.8, 128.11, 128.14, 128.19, 128.23, 128.27, 128.35,

129.44, 129.5, 133.1, 133.3, 133.4, 135.45, 135.49, 135.53, 135.55,

137.2, 137.36, 137.42, 137.6, 137.8, 137.9, 137.1. ESI-TOF MS: [M þ

Na]^þcalcd for C₁₁₆H₁₃₀O₂₁Si₂Na, 1937.85, found 1937.44. HRMS

ESI-TOF: [M þ Na]^þcalcd for C₁₁₆H₁₃₀O₂₁Si₂Na, 1937.8541, found

1937.8533.

2,3-Di-O-acetyl-5-O-t-butyldiphenylsilyl-R-^D-arabinofuranosyl^(d/e)

(1f5)-(2,3-di-O-acetyl-5-O-t-butyldiphenylsilyl-R-^D-arabinofuranosyl^(d/e))-

(1f3)-2-O-benzoyl-R-^D-arabinofuranosyl^(c)-(1f5)-2,3-di-O-benzyl-

R-^D-arabinofuranosyl^(b)-(1f5)-3-O-benzyl-1,2-O-isopropylidene-

R-^D-arabinofuranose^(a)(27). To a mixture of 12³¹(2.02 g, 2.44 mmol)

and 15²²(2.97 mg, 5.13 mmol) in dry CH₂Cl₂(100 mL) was added MS4

Å (15 g, freshly dried) at room temperature. After the mixture was cooled

to 0 °C, NIS (1.92 g, 8.27 mmol) and AgOTf (125 mg, 486 μmol) were

added to the mixture. After being stirred for 3 h at the same temperature,

the reaction was quenchedbytriethylamine, followed byfiltration through

Celite pad and washing of pad with CHCl₃. The combined solutions were

washed with 20% aqueous Na₂S₂O₃, saturated aqueous NaHCO₃, and

brine, dried over Na₂SO₄, and concentrated in vacuo. The residue was

purified by flash column chromatography using gradient solvent system

(hexane/ethyl acetate = 20/1 to 10/1 to 5/1 to 2/1) to give the title

compound 27 (4.08 g, 96%). 27: [R]²⁶_D65.2 (c 1.00, CHCl₃). ¹H NMR

(CDCl₃, 400 MHz): δ 1.00 (s, TBDPS, 9H), 1.02 (s, TBDPS, 9H), 1.32

(s, acetonide, 3H), 1.49 (s, acetonide, 3H), 1.76 (s, Ac, 3H), 1.91 (s, Ac,

3H), 1.93 (s, Ac, 3H), 1.95 (s, Ac, 3H), 3.57 (dd, J = 10.0, 6.8 Hz, C5-H^a,

2,3-Di-O-benzyl-R-^D-arabinofuranosyl^(d/e)-(1f5)-(2,3-di-O-benzyl-R-

D-arabinofuranosyl^(d/e))-(1f3)-2-O-benzyl-R-D-arabinofuranosyl^(c)

(1f5)-2,3-di-O-benzyl-R-^D-arabinofuranosyl^(b)-(1f5)-3-O-benzyl-1,2-

O-isopropylidene-R-^D-arabinofuranose^(a)(29). To a solution of 10

(243.0 mg, 127 mmol) in dry THF (3 mL) was added 1 M solution of

TBAF in THF (3.75 mL, 3.75 mmol) at room temperature. After being

stirred for 4 h at the same temperature, the mixture was concentrated in

vacuo. The residue was purified by flash column chromatography using

gradient solvent system (hexane/ethyl acetate = 20/1 to 10/1to 5/1to 1/1

1H), 3.63-3.83 (m, C5-H^b, C5-H^c, C5-H₂, C5-H₂, 6H), 3.84-

3.93 (m, C5-H^a, C5-H^b, C5-H^c, 3H), 3.99-4.10 (m, C3-H^a, C2-

H^b, C3-H^b, C4-H^d, C4-H^e, 5H), 4.12-4.18 (m, C4-H^b, 1H),

4.19-4.26 (m, C4-H^a, C4-H^c, 1H), 4.29-4.35 (m, C3-H^c, Bn, 2H),

4.42-4.59 (m, Bn, 6H), 4.64 (d, J = 4.0 Hz, C2-H^a, 1H), 5.03 (s,

C1-H^b, 1H), 5.09 (d, J = 1.6 Hz, C2-H^e, 1H), 5.11 (s, C1-H^e, 1H),

5.16 (d, J = 2.0 Hz, C2-H^d, 1H), 5.20-5.25 (m, C3-H^d, C3-H^e, 2H),

5.25 (s, C1-H^c, 1H), 5.39 (d, J = 1.6 Hz, C2-H^c, 1H), 5.40 (s, C1-H^d,

1H), 5.88 (d, J = 4.0 Hz, C1-H^a, 1H), 7.10-8.08 (m, Ar, 40H). ¹³C

NMR (CDCl₃, 100 MHz): δ 19.2, 19.3, 20.4, 20.6, 20.7 (ꢀ2), 20.8, 26.4,

26.7, 27.2, 62.8 (ꢀ2), 65.4, 65.8, 66.9, 71.6, 71.9, 72.3, 76.8 (ꢀ2), 80.0,

80.4, 81.7 (ꢀ2), 81.8, 81.9, 82.2, 82.8, 82.9, 83.19, 83.22, 83.3, 85.3, 88.2,

to 1/2 to 1/5) to give the title compound 29 (170.6 mg, 93%). 29: [R]²⁷

67.6 (c 1.00, CHCl₃). ¹H NMR (CDCl₃, 400 MHz): δ 1.32 (s, acetonide,

3H), 1.50 (s, acetonide, 3H), 3.52-3.59 (m, C5-H^a, C5-H^e, 2H),

3.60-3.81 (m, C5-H^c, C5-H^b, C5-H₂, C3-H^e, C5-H^e, 6H),

3.84-3.94 (m, C5-H^a, C5-H^b, C5-H^c, C3-H^d, 4H), 3.99-4.11 (m,

C3-H^a, C2-H^b, C3-H^b, C2-H^c, C4-H^c, C2-H^d, C2-H^e, C4-H^e,

8H), 4.12-4.18 (m, C4-H^b, 1H), 4.19-4.26 (m, C4-H^a, C4-H^d,

1H), 4.29-4.35 (m, C3-H^c, Bn, 2H), 4.40-4.60 (m, Bn, 15H), 4.65

(d, J = 4.0 Hz, C2-H^a, 1H), 5.01 (s, C1-H^b, 1H), 5.10 (s, C1-H^e, 1H),

5.13 (s, C1-H^c, C1-H^d, 2H), 5.88 (d, J = 4.0 Hz, C1-H^a, 1H), 7.10-7.40

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ARTICLE

(m, Ar, 40H). ¹³C NMR (CDCl₃, 100 MHz): δ 26.4, 27.2,

62.7 (ꢀ2), 64.7, 66.0, 66.9, 71.7, 71.8, 71.9, 72.0, 72.1 (ꢀ2), 72.2, 72.3,

79.6, 80.3, 80.6, 81.8, 82.3, 82.8, 82.9 (ꢀ2), 83.0, 83.3, 85.2, 87.4, 88.4, 88.5,

88.6, 105.6, 105.9, 106.1 (ꢀ2), 106.2, 112.8, 127.69, 127.72, 127.78,

127.89, 128.16, 128.23, 128.35, 128.41, 137.23, 137.30, 137.35, 137.39,

137.44, 137.61, 137.65, 137.82. ESI-TOF MS: [M þ Na]^þcalcd for

C₈₄H₉₄O₂₁Na, 1461.62, found 1461.30. HRMS ESI-TOF: [M þ Na]^þ

calcd for C₈₄H₉₄O₂₁Na, 1461.6185, found 1461.6152.

temperature, and the mixture was stirred for 1 h, during which time the

temperature was going up to room temperature. After being concentrated

in vacuo, the residue was purified by flash column chromatography using

gradient solvent system (hexane/ethyl acetate = 50/1 to 30/1 to 10/1 to

5/1 to 3/1 to 2/1) to give the title compound 9 (120.9 mg, 71% in three

steps) as a mixture of anomers. 9 (R-isomer), H NMR (CDCl₃, 400

MHz): δ 0.99 (s, TBDPS, 9H), 1.00 (s, TBDPS, 9H), 1.45 (s, acetonide,

3H), 1.92 (s, Ac, 3H), 2.28 (s, Me, 3H), 3.60-3.98 (m, C5-H₂,

3,5-Di-O-benzyl-R-^D-arabinofuranosyl^(d)-(1f5)-(3,5-di-O-benzyl-R-

D-arabinofuranosyl^(e))-(1f3)-2-O-benzyl-R-D-arabinofuranosyl^(c)-(1f5)-

2,3-di-O-benzyl-R-^D-arabinofuranosyl^(b)-(1f5)-3-O-benzyl-1,2-O-

isopropylidene-R-^D-arabinofuranose^(a)(8). To a mixture of 13³¹(408 mg,

0.500 mmol, acceptor), 30²²(527 mg, 1.10 mmol, acceptor), and DTBMP

(513 mg, 2.50 mmol) in dry CH₂Cl₂(10 mL) was added MS4 Å (1.5 g,

freshly dried) at room temperature. Next, MeOTf (283 mL, 2.50 mmol) was

addedtothemixture. Afterbeingstirredfor24hatthesametemperature, the

reaction was quenched by triethylamine, followed by filtration through Celite

pad and washing of pad with CHCl₃. The combined solutions were washed

with saturated aqueous NaHCO₃and brine, dried over Na₂SO₄, and

concentrated in vacuo. To the crude mixture (31) in MeOH (10 mL) were

added TEA (2 mL) and H₂O (1 mL) at room temperature. After being

stirred for 2 d at the same temperature and concentrated in vacuo, the residue

was purified by flash column chromatography using gradient solvent system

(hexane/ethyl acetate = 20/1 to 10/1 to 5/1 to 2/1 to 1/1 to 1/2) to give

deacylated compound 8 (670 mg, 93% in two steps). 8: [R]²⁵_D103.88 (c

1.03, CHCl₃). ¹HNMR(CDCl₃, 400 MHz): δ1.33 (s, acetonide, 3H), 1.50

(s, acetonide, 3H), 3.26 (d, J = 9.2 Hz, C2-OH^e, 1H), 3.30 (d, J = 9.2 Hz,

C2-OH^d, 1H), 3.41-3.46 (m, C5-H^d, C5-H^e, 2H), 3.53-3.60 (m,

C5-H^a, C5-H^d, C5-H^e, 3H), 3.63 (dd, J = 11.2, 3.2 Hz, C5-H^b, 1H),

3.69 (dd, J = 12.0, 3.2 Hz, C5-H^c, 1H), 3.80-3.90 (m, C5-H^a, C5-H^b,

C3-H^d, C3-H^e, 4H), 3.93 (dd, J = 12.0, 3.6 Hz, C5-H^c, 1H), 4.00-4.07

(m, C3-H^a, C2-H^c, C2-H^b, C3-H^b, 4H), 4.08-4.18 (m, C4-H^b,

C4-H^c, C2-H^d, C2-H^e, 4H), 4.20-4.25 (m, C4-H^a, C4-H^e, 2H),

4.25-4.29 (m, C4-H^d, 1H), 4.33 (dd, J = 6.8, 4.0 Hz, C3-H^c, 1H),

4.20-4.25 (m, Bn, 16H), 4.65 (d, J=4.0Hz, C2-H^a, 1H), 5.00(s, C1-H^b,

1H), 5.05 (s, C1-H^d, 1H), 5.06 (s, C1-H^e, 1H), 5.11 (s, C1-H^c, 1H),

5.89 (d, J = 4.0 Hz, C1-H^a, 1H), 7.20-7.40 (m, Ar, 50H). ¹³C NMR

(CDCl₃, 100 MHz): δ 26.4 (acetonide), 27.2 (acetonide), 65.4 (C5^b), 65.9

(C5^c), 66.9 (C5^a), 69.6 (C5^d/e), 69.7 (C5^d/e), 71.66 (Bn), 71.73 (Bn), 71.8

(ꢀ2, Bn), 72.1 (Bn), 72.3 (Bn), 73.6 (ꢀ2, Bn), 78.36 (C2^d/e), 78.42

(C2^d/e), 79.0 (C3^c), 80.2 (C4^b), 80.9 (C4^c), 82.3 (C4^d), 82.8 (C3^a), 82.9

(C4^a), 83.0 (C4^e), 83.2 (C3^b), 84.5 (C3^d), 84.8 (C3^e), 85.2 (C2^a), 87.5

(C2^c), 88.6 (C2^b), 105.6 (C1^a), 106.1 (C1^c), 106.2 (C1^b), 107.5 (C1^e),

109.2 (C1^d), 112.9 (acetonide), 127.6, 127.7, 127.8, 127.86, 127.90,

127.93, 128.0, 128.3, 128.42, 128.45, 128.53, 137.25, 137.31, 137.4, 137.5,

137.85, 137.89. MALDI-TOF MS: [M þ Na]^þcalcd for C₈₄H₉₄O₂₁Na,

1461.62, found 1461.93. HRMS ESI-TOF: [M þ Na]^þcalcd for

C₈₄H₉₄O₂₁Na, 1461.6185, found 1461.6187.

C5-H₂, C5-H₂, C5-H₂, C5-H₂, 10H), 3.98-4.18 (m, C3-H^a,

C2-H^b, C3-H^b, C4-H^b, C2-H^c, C4-H^c, C2-H^d, C3-H^d, C4-H^d,

C2-H^e, C3-H^e, C4-H^e, 12H), 4.30 (dd, J = 7.6, 3.2 Hz, C3-H^c, 1H),

4.33-4.75 (m, C4-H^a, Bn, 17H), 5.03 (s, C1-H^b, 1H), 5.11 (s, C1-H^c,

1H), 5.147 (s, C1-H^d/e, 1H), 5.154 (s, C1-H^d/e, 1H), 5.28 (t, J = 2.0

Hz, C2-H^a, 1H), 5.45 (s, C1R-H^a, 1H), 7.00-7.64 (m, Ar, 64H). β-

isomer: 5.41 (dd, J = 4.8, 2.8 Hz, C2β-H^a, 0.93H), 5.52 (d, J = 4.8 Hz,

C1β-H^a, 0.93H). Selected ¹³C NMR (CDCl₃, 100 MHz): δ 91.3 (C1^a),

105.3, 106.4, 106.5, 106.6. MALDI-TOF MS: [M þ Na]^þcalcd for

₁₂₂H₁₃₄O₂₁SSi₂Na, 2045.86, found 2045.39. HRMS ESI-TOF: [M þ

Na]^þcalcd for C₁₂₂H₁₃₄O₂₁SSi₂Na, 2045.8575, found 2045.8600.

2,3-Di-O-benzyl-5-O-t-butyldiphenylsilyl-R-^D-arabinofuranosyl^(f1/2)

(1f5)-(2,3-di-O-benzyl-5-O-t-butyldiphenylsilyl-R-^D-arabinofuranosyl^(f1/2))-

(1f3)-2-O-benzyl-R-^D-arabinofuranosyl^(e)-(1f5)-2,3-di-O-benzyl-R-D-

arabinofuranosyl^(d)-(1f5)-2-O-acetyl-3-O-benzyl-R-D-arabinofuranosyl^(c)-

(1f5)-2,3-di-O-benzyl-R-^D-arabinofuranosyl^(b1/2)-(1f5)-2,3-di-O-

benzyl-R-^D-arabinofuranosyl^(b1/2)-(1f5)-3-O-benzyl-1,2-O-isopropy-

lidene-R-^D-arabinofuranose^(a)(34). To a mixture of Araf₃acceptor

11³¹(14.4 mg, 15.9 μmol) and Araf₅donor 9 (35.3 mg, 17.4 μmol) in

dry CH₂Cl₂(2 mL) was added MS4 Å (250 mg, freshly dried) at room

temperature. After the mixture was cooled to -30 °C, NIS (6.1 mg,

27.1 μmol) and AgOTf (1.0 mg, 3.9 μmol) were added to the mixture.

After being stirred for 24 h at the same temperature and 3 h at -10 °C,

the reaction was quenched by triethylamine and followed by filtration

through Celite pad and washing of pad with CHCl₃. The combined

solutions were washed with 20% aqueous Na₂S₂O₃, saturated aqueous

NaHCO₃, and brine, dried over Na₂SO₄, and concentrated in vacuo.

The residue was purified by gel filtration (Bio beads SX-3, toluene/ethyl

acetate = 1/1) to give the title compound Araf₈34 (33.1 mg, 73%). 34:

[R]²³_D64.4 (c 1.0, CHCl₃). ¹H NMR (CDCl₃, 400 MHz): δ 0.98 (s,

TBDPS, 9H), 0.99 (s, TBDPS, 9H), 1.31 (s, acetonide, 3H), 1.49 (s,

acetonide, 3H), 1.86 (s, Ac, 3H), 3.50-3.93 (m, C5-H₂, C5-H_{2 f2}

C5-H₂^b2, C3-H^c, C5-H₂, C5-H₂, C5-H₂, C5-H₂^f1, C5-H₂

17H), 3.99-4.07 (m, C3-H^a, C2-H^b1, C3-H^b1, C4-H^b1, C2-H^b2,

C3-H^b2, C4-H^b2, C4-H^c, C2-H^d, C3-H^d, C4-H^d, C2-H^e,

C4-H^e, C2-H^f1, C3-H^f1, C4-H^f1, C2-H^f2, C3-H^f2, C4-H^f2,

19H), 4.19 (ddd, J = 6.8, 4.8, 3.6 Hz, C4-H^a), 4.26 (dd, J = 7.6, 4.0

Hz, C3-H^e), 4.26-4.58 (m, Bn, 25H), 4.63 (d, J = 4.0 Hz, C2-H^a),

4.70 (d, J = 12.4 Hz, Bn), 5.00 (s, C1-H^b/d, 2H), 5.08 (s, C1-H^c, 1H),

5.10 (s, C1-H^b/d, C1-H^e, 2H), 5.13 (d, J = 0.8 Hz, C1-H^f, 1H), 5.14

(s, C1-H^f, 1H), 5.15 (d, J = 1.2 Hz, C2-H^c, 1H), 5.87 (d, J = 4.0 Hz,

C1-H^a, 1H), 7.15-7.70 (m, Ar, 85H). ¹³C NMR (CDCl₃, 100 MHz):

δ 19.2 (s), 19.3 (s), 20.8 (q), 26.4 (q), 26.75 (x3, q), 26.8075 (ꢀ3, q),

27.2 (q), 63.2 (t), 63.4 (t), 65.4 (t), 65.6 (t), 65.8 (t), 65.9 (t), 66.0 (t),

66.8 (t), 71.58 (t), 71.67 (ꢀ2, t), 71.77 (ꢀ2, t), 71.86 (t), 71.93 (t),

71.99 (t, ꢀ2), 72.15 (t), 72.21 (t), 72.32 (t, ꢀ2), 80.1 (d), 80.3 (d, ꢀ2),

80.4 (d), 80.6 (d), 81.2 (d), 81.4 (d), 81.8 (d), 82.1 (d), 82.3 (d), 82.80

(ꢀ2, d), 82.88 (d, ꢀ2), 82.97 (d), 83.1 (d), 83.2 (d), 83.3 (d), 85.4 (d),

87.9 (d), 88.0 (d), 88.36 (d), 88.46 (d), 88.54 (d), 88.59 (d), 88.63 (d),

105.3, (d), 105.6 (d), 106.1 (d), 106.2 (d), 106.4 (d, ꢀ2), 106.5 (d),

106.6 (d), 112.9 (s), 127.41, 127.55, 127.60, 127,67, 127.70, 127.9,

128.0, 128.21, 128.24, 128.28, 128.32, 128.37, 128.46, 129.52, 129.6,

133.2, 133.40, 133.43, 133.5, 135.56, 135.60, 135.63, 135.7, 137.3,

137.46, 137.50, 137.54, 137.65, 137.67, 137.8, 137.90, 137.92, 138.0,

138.1, 138.2, 169.7. MALDI-TOF MS: [M þ Na]^þcalcd for

C₁₆₈H₁₈₆O₃₄Si₂Na, 2826.23, found 2826.00. HRMS ESI-TOF:

4-Methylphenyl 2,3-Di-O-benzyl-5-O-t-butyldiphenylsilyl-R-^D-ara-

binofuranosyl^(d/e)-(1f5)-(2,3-di-O-benzyl-5-O-t-butyldiphenylsilyl-R-D-

arabinofuranosyl^(d/e))-(1f3)-2-O-benzyl-R-D-arabinofuranosyl^(c)-(1f5)-

2,3-di-O-benzyl-R-^D-arabinofuranosyl^(b)-(1f5)-2-O-acetyl-3-O-benzyl-

1-thio-^D-arabinofuranoside^(a)(9). A solution of 10 (162 mg, 845 μmol)

in dioxane (2.0 mL), 10% aqueous HCl (0.2 mL), and 70% aqueous

AcOH (2.0 mL) was stirred at 50 °C for 2 h. After being cooled to room

temperature, the reaction was quenched with saturated aqueous NaH-

CO₃, extracted with CHCl₃, washed with brine, dried over Na₂SO₄, and

concentrated in vacuo with azeotropic removal of H₂O with toluene. The

residue was used without further purification. To a solution of the crude

hemiacetal 32 and ditolyldisulfide (312 mg, 1.27 mmol) in dry THF (2.0

mL) was added n-Bu₃P (317 μL, 1.23 mmol) at 0 °C under Ar

atmosphere. After being stirred for 2 h at the same temperature, the

mixture was concentrated in vacuo. To the mixture (33) in pyridine (3.0

mL) were added Ac₂O (1.0 mL) and DMAP (5.0 mg) at room

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[M þ Na]^þcalcd for C₁₆₈H₁₈₆O₃₄Si₂Na, 2826.2262, found 2826.

2299.

Celite pad and washing of pad with CHCl₃. The combined solutions were

washed with 20% aqueous Na₂S₂O₃, saturated aqueous NaHCO₃, and

brine, dried over Na₂SO₄, and concentrated in vacuo. The residue was

purified by gel filtration (Bio beads SX-3, toluene/ethyl acetate = 1/1) and

PTLC (hexane/EtOAc = 2:1) to give the title compound Araf₁₅37 (20.9

mg, 73%). 37: [R]²⁵_D60.0 (c 0.43, CHCl₃). ¹H NMR(CDCl₃, 400 MHz):

δ0.99(s, TBDPSꢀ2, 18H),1.00(s, TBDPSꢀ2, 18H),1.32(s, acetonide,

3H), 1.49 (s, acetonide, 3H), 1.83 (s, Ac, 3H), 1.85 (s, Ac, 3H), 3.49-3.94

2,3-Di-O-benzyl-R-^D-arabinofuranosyl^(d1/2)-(1f5)-(2,3-di-O-benzyl-

R-^D-arabinofuranosyl^(d1/2))-(1f3)-2-O-benzyl-R-D-arabinofuranosyl^(c)-

(1f5)-2,3-di-O-benzyl-R-^D-arabinofuranosyl^(b)-(1f5)-2,3-di-O-benzyl-

R-^D-arabinofuranosyl^(b)-(1f5)-2,3-di-O-benzyl-R-D-arabinofuranosyl^(b)

(1f5)-2,3-di-O-benzyl-R-^D-arabinofuranosyl^(b)-(1f5)-3-O-benzyl-1,2-

O-isopropylidene-R-^D-arabinofuranose^(a)(4). To a solution of 34 (52.7

mg, 18.8 μmol) in MeOH (2 mL)-THF (1 mL) was added 1 M NaOMe

in MeOH (0.1 mL, 0.1 mmol) at 0 °C. After being stirred for 30 min at the

same temperature, the reaction was quenched by Amberlyst H^þresin,

filtered, and concentrated in vacuo to give deacylated compound 35. After

azeotoropic removal of MeOH with toluene, to a solution of 35 in dry

DMF (1 mL) were added NaH (1.1 mg, 27.5 μmol) and BnBr (2.5 μL,

21.0 μmol) at 0 °C, and the mixture was stirred for 2 h, during which time

the temperature was going up to room temperature. The reaction was

quenched by triethylamine and brine, extracted with CHCl₃, washed with

brine, driedover Na₂SO₄, and evaporatedinvacuo togivea crude mixture,

which was used without further purification. To a solution of crude 36 in

dry THF (1 mL) was added 1 M solution of TBAF in THF (50 μL, 50

mmol) at room temperature. After being stirred overnight at the same

temperature, the mixture was concentrated in vacuo. The residue was

purified by PTLC (toluene/ethyl acetate = 3/1) to give the title com-

pound 4 (37.0 mg, 83% in three steps). 4: [R]²³_D18.1 (c 0.31, CHCl₃).

¹H NMR (CDCl₃, 400 MHz): δ 1.32 (s, acetonide, 3H), 1.49 (s, ace-

(m, C5-H₂, C5-H₂^b1, C5-H₂^b2, C5-H₂^b3, C5-H₂^c1, C5-H₂

C5-H₂

, C5-H₂, C5-H₂, ,

C3-H^e1, C5-H₂C3-H^e2,

C5-H₂^e2, C5-H₂^f1, C5-H₂^f2, C5-H₂^f3, C5-H₂^f4, 32H), 3.95-4.17

(m, C3-H^a, C2-H^b1, C3-H^b1, C4-H^b1, C2-H^b2, C3-H^b2, C4-H^b2,

C2-H^b3, C3-H^b3, C4-H^b3, C2-H^c1, C4-H^c1, C2-H^c2, C4-H^c2,

C2-H₂^c3, C4-H₂^c3, C2-H^d1, C3-H^d1, C4-H^d1, C2-H^d2, C3-H^d2,

C4-H^d2, C4-H^e1, C4-H^e2, C2-H^f1, C4-H^f1, C2-H^f2, C4-H^f2,

C2-H^f3, C4-H^f3, C2-H^f4, C4-H^f4, C3-H^f1/2/3/4, C3-H^f1/2/3/4

C3-H^f1/2/3/4, 35H), 4.16-4.23 (m, C4-H^a, C3-H^f1/2/3/4, 2H), 4.24

(dd, J = 7.2, 3.2 Hz, C3-H^c1, 1H), 4.28 (dd, J = 6.8, 3.6 Hz, C3-H^c2,

C3-H^c3, 2H), 4.31-4.60 (m, Bn, 30H), 4.64 (d, J = 4.0 Hz, C2-H^a, 1H),

4.69 (d, J = 12.4 Hz, Bn, 1H), 4.70 (d, J = 12.4 Hz, Bn, 1H), 4.97 (s,

C1-H^b1/2/3, 1H), 4.99 (s, C1-H^b1/2/3, 1H), 5.00 (s, C1-H^b1/2/3, 1H),

5.08 (s, C1-H^c1, C1-H^e1/2, 2H), 5.10 (s, C1-H^c2, C1-H^c3, C1-H^e1/2

3H), 5.15-5.18 (s ꢀ8, C1-H^d1, C1-H^d2, C2-H^e1, C2-H^e2, C1-H^f1,

C1-H^f2, C1-H^f3, C1-H^f4, 3H), 5.88 (d, J = 4.0 Hz, C1-H^a, 1H),

7.13-7.80 (m, Ar, 200H). ¹³C NMR (CDCl₃, 100 MHz): δ 19.2, 19.3,

20.77, 20.78, 26.4, 26.7, 26.8, 27.2, 63.2 (ꢀ2), 63.4 (ꢀ2), 65.1, 65.2, 65.3

(ꢀ2), 65.5, 65.9 (ꢀ2), 66.0 (ꢀ2), 66.1, 66.9, 71.56 (ꢀ2), 71.66 (ꢀ4),

71.77 (ꢀ4), 71.86 (ꢀ2), 71.90 (ꢀ2), 71.98 (ꢀ2), 72.06 (ꢀ2), 72.11,

72.17, 72.23, 72.3 (ꢀ2), 72.4, 79.8, 79.9, 80.1 (ꢀ2), 80.22, 80.28, 80.32,

80.39, 81.18 (ꢀ2), 81.20 (ꢀ2), 82.15, 82.21, 82.3 (ꢀ2), 82.7, 82.8 (ꢀ4),

82.9, 83.0 (ꢀ3), 83.1 (ꢀ2), 83.2 (ꢀ2), 83.3, 85.3, 87.8, 87.9 (ꢀ2), 88.0,

88.5 (ꢀ3), 88.58 (ꢀ3), 88.64 (ꢀ3), 105.0, 105.3 (ꢀ2), 105.6, 105.00,

106.1, 106.2, 106.4 (ꢀ5), 106.6 (ꢀ3), (acetonide), 127.4, 127.55, 127.59,

127.65, 127.70, 127.86, 127.90, 127.94, 128.21, 128.23, 128.27, 128.32,

128.5, 129.5, 129.6, 133.2, 133.39, 133.42, 133.50, 135.55, 135.60, 135.63,

135.7, 137.3, 137.4, 137.5, 137.6, 137.90, 137.93, 138.06, 138.14, 138.2,

169.62, 169.64. MALDI-TOF MS: [M þ Na]^þcalcd for C₃₁₄H₃₄₆O₆₃N-

aSi₄, 5259.28, found 5259.36. ESI-TOF: [M þ 2Na]^2þcalcd for

[C₃₁₄H₃₄₆O₆₃Na₂Si₄]/2, 2641.14, found 2641.62.

tonide, 3H), 3.50-3.92 (m, C5-H₂, C5-H₂^b1, C5-H₂^b2, C5-H₂

C5-H₂^b4, C5-H₂, C3-H^d1, C5-H₂^d1, C3-H^d2, C5-H₂^d2, 18H),

3.99-4.17 (m, C3-H^a, C2-H^b1, C3-H^b1, C4-H^b1, C2-H^b2, C3-

H^b2, C4-H^b2, C2-H^b3, C3-H^b3, C4-H^b3, C2-H^b4, C3-H^b4,

C4-H^b4, C2-H^c, C4-H^c, C2-H^d1, C4-H^d1, C2-H^d2, 18H),

4.18-4.25 (m, C4-H^a, C4-H^d2, 2H), 4.31 (dd, J = 6.0, 4.0 Hz,

C3-H^c, 1H), 4.30-4.59 (m, Bn, 28H), 4.66 (d, J = 4.0 Hz, C2-H^a,

1H), 5.01 (s, C1-H^c, 1H), 5.10 (s, C1-H^b1, C1-H^b2, C1-H^d1, 3H),

5.12 (s, C1-H^b3, 1H), 5.13 (s, C1-H^b4, 1H), 5.11 (s, C1-H^d2, C1-H^e,

2H), 5.89 (d, J = 4.0 Hz, C1-H^a, 1H), 7.16-7.33 (m, Ar, 70H). ¹³C

NMR (CDCl₃, 100 MHz): δ 26.4 (q), 27.2 (q), 62.7 (t), 62.8 (t), 64.7(t),

65.84 (t), 65.88 (t), 65.95 (t), 65.99 (t), 66.8 (t), 71.7 (t), 71.9 (t, ꢀ4),

72.0 (t, ꢀ3), 72.2 (t), 72.25 (t, ꢀ4), 72.34 (t), 79.6 (d), 80.1 (d), 80.38

(d), 80.42 (d), 80.5 (d), 80.6 (d), 81.8 (d), 82.3 (d), 82.8 (d), 82.9 (d,

ꢀ3), 83.0 (d), 83.18 (d, ꢀ2), 83.24 (d), 85.3 (d), 87.4 (d), 88.3 (d, ꢀ3),

88.4 (d), 88.54 (d), 88.56 (d), 105.6 (d), 106.0 (d), 106.1 (d, ꢀ2), 106.3

(d), 106.5 (d, ꢀ3), 112.9 (s), 127.6, 127.7, 127.8, 127.86, 127.92, 128.0,

128.35, 128.39, 128.5, 137.25, 137.34, 137.48, 137.51, 137.61, 137.63,

2-O-Benzyl-3,5-O-(tetraisopropylsiloxane-1,3-diyl)-β-^D-arabinofur-

anosyl^(f/g)-(1f2)-3,5-di-O-benzyl-R-D-arabinofuranosyl^(d/e)-(1f5)-

[2-O-benzyl-3,5-O-(tetraisopropylsiloxane-1,3-diyl)-β-^D-arabinofura-

nosyl^(f/g)-(1f2)-3,5-di-O-benzyl-R-D-arabinofuranosyl^(d/e)]-(1f3)-2-O-

benzyl-R-^D-arabinofuranosyl^(c)-(1f5)-2,3-di-O-benzyl-R-D-arabino-

furanosyl^(b)-(1f5)-3-O-benzyl-1,2-O-isopropylidene-R-D-arabinofur-

anose^(a)(38). To a mixture of Araf₅acceptor 8 (230 mg, 160 μmol) and

TIPDS-protected Araf donor 5²¹(235 mg, 400 μmol) in dry CH₂Cl₂

(4 mL) was added MS4 Å (500 mg, freshly dried) at room tempera-

ture. After being cooled to -40 °C, NIS (126 mg, 560 μmol) and

AgOTf (20.5 mg, 7.98 μmol) were added to the mixture. After being

stirred for 4 h at the same temperature, the reaction was quenched by

triethylamine, followed by filtration through Celite pad and washing of

pad with CHCl₃. The combined solutions were washed with 20%

aqueous Na₂S₂O₃, saturated aqueous NaHCO₃, and brine, dried over

Na₂SO₄, and concentrated in vacuo. The residue was purified by gel

filtration (Bio beads SX-3, toluene/ethyl acetate = 1/1) to give the title

compound Araf₇38 (R:β = 8.46:1). 38 (major β,β-isomer), ¹H NMR

(CDCl₃, 400 MHz): δ 0.80-1.05 (s, TIPDS, 28H), 1.25 (s, acetonide,

3H), 1.41 (s, acetonide, 3H), 3.40-3.53 (m, C5-H^a, C5-H^b,

137.7, 137.9, 138.0. MALDI-TOF MS: [M þ Na]^þcalcd for C₁₄₁H₁₅₄

O₃₃Na, 2398.03, found 2398.88. HRMS ESI-TOF: [M þ Na]^þcalcd for

C₁₄₁H₁₅₄O₃₃Na, 2398.0270, found 2398.0271.

2,3-Di-O-benzyl-5-O-t-butyldiphenylsilyl-R-^D-arabinofuranosyl^(f)-

(1f5)-(2,3-di-O-benzyl-5-O-t-butyldiphenylsilyl-R-^D-arabinofuranosyl^(f))-

(1f3)-2-O-benzyl-R-^D-arabinofuranosyl^(c)-(1f5)-2,3-di-O-benzyl-R-D-

arabinofuranosyl^(b)-(1f5)-2-O-acetyl-3-O-benzyl-R-D-arabinofuranosyl^(e)-

(1f5)-2,3-di-O-benzyl-R-^D-arabinofuranosyl^(d)-(1f5)-[2,3-di-O-benzyl-

5-O-t-butyldiphenylsilyl-R-^D-arabinofuranosyl^(f)-(1f5)-(2,3-di-O-benzyl-

5-O-t-butyldiphenylsilyl-R-^D-arabinofuranosyl^(f))-(1f3)-2-O-benzyl-R-D-

arabinofuranosyl^(c)-(1f5)-2,3-di-O-benzyl-R-D-arabinofuranosyl^(b)

(1f5)-2-O-acetyl-3-O-benzyl-R-^D-arabinofuranosyl^(e)-(1f5)-2,3-di-

O-benzyl-R-^D-arabinofuranosyl^(d)]-(1f3)-2-O-benzyl-R-D-arabinofura-

nosyl^(c)-(1f5)-2,3-di-O-benzyl-R-D-arabinofuranosyl^(b)-(1f5)-3-O-be-

nzyl-1,2-O-isopropylidene-R-^D-arabinofuranose^(a)(37). To a mixture of

Araf₅acceptor 29 (7.6 mg, 5.28 μmol) and Araf₅donor 9 (23.8 mg, 11.8

μmol) in dry CH₂Cl₂(2 mL) was added MS4 Å (250 mg, freshly dried) at

room temperature. After the mixture was cooled to -30 °C, NIS (4.2 mg,

18.1 μmol) and AgOTf (1.0 mg, 3.9 μmol) were added to the mixture.

After being stirred for 6 h at the same temperature and 24 h at -10 °C, the

reaction was quenched by triethylamine and followed by filtration through

C5-H₂, C5-H₂, 6H), 3.70-3.90 (m, C5-H^a, C5-H^b, C5-H^c,

C2-H^f, C4-H^f, C5-H₂, C2-H^g, C4-H^g, C5-H₂, 11H),

3.93-4.00 (m, C3-H^d, C3-H^e, C5-H^c, C2-H^b, C3-H^b, 5H),

4.00-4.40 (m, C3-H^a, C2-H^c, 2H), 4.06-4.20 (m, C4-H^a,

C4-H^b, C4-H^c, C4-H^e, 4H), 4.24-4.31 (m, C3-H^c, C2-H^d,

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C4-H^d, C2-H^e, 4H), 4.38-4.51 (m, C3-H^f, C3-H^g, Bn, 20H),

4.53-4.56 (m, C2-H^a, Bn, 3H), 4.94 (d, J = 4.8 Hz, C1b-H^f/g, 1H),

5.08 (d, J = 4.4 Hz, C1β-H^f/g, 1H), 4.88 (s, C1-H^b, 1H), 4.96 (s,

C1-H^c, 1H), 5.00 (s, C1-H^d, C1-H^e, 2H), 5.80 (d, J = 4.0 Hz,

C1-H^a, 1H), 7.00-7.64 (m, Ar, 50H). ¹³C NMR (CDCl₃, 100 MHz):

δ 12.4 (TIPDS), 12.7 (TIPDS), 13.2 (TIPDS), 13.3 (TIPDS), 16.97

(TIPDS), 17.03 (TIPDS), 17.30 (TIPDS), 17.36 (TIPDS), 17.45

(TIPDS), 26.4 (acetonide), 27.2 (acetonide), 65.2 (C5^c), 65.5 (C5^d),

66.2 (C5^f/g), 66.3 (C5^f/g), 66.7 (C5^a), 69.6 (C5^d/e), 69.8 (C5^d/e), 71.6

(ꢀ2, Bn), 71.7 (Bn), 71.9 (Bn), 72.0 (Bn), 72.23 (ꢀ2, Bn), 72.3 (Bn),

73.1 (ꢀ2, Bn), 79.98 (C3^c), 80.28 (C4^d/e), 80.44 (C4^d/e), 80.8 (ꢀ2,

C4^b, C4^c), 81.37 (C4^g/f), 81.51 (C4^g/f), 81.61 (ꢀ2, C3^f, C3^g), 82.68

(C3^a), 82.78 (C4^a), 83.07 (C3^b), 83.89 (ꢀ2, C3^d, C3^e), 84.13 (C2^f/g),

84.23 (C2^f/g), 85.23 (C2^a), 85.82 (C2^d/e), 85.74 (C2^d/e), 88.32

(C2^b/c), 88.46 (C5^b/c), 98.77 (C1^g), 98.88 (C1^f), 105.32 (C1^b),

105.47 (C1^a), 106.04 (C1^e), 106.17 (C1^d), 106.55 (C1^c), 112.78

(acetonide), 127.37, 127.49, 127.53, 127.57, 127.60, 127.66, 127.78,

127.86, 128.1, 128.19, 128.23, 128.3, 128.4, 137.25, 137.39, 137.42,

137.5, 137.62, 137.67, 137.78, 137.84, 137.9, 138.0, 138.1. MALDI-

TOF MS: [M þ Na]^þcalcd for C₁₃₂H₁₇₄O₃₁NaSi₄, 2390.10, found

2390.02.

ofuranosyl^(c)-(1f5)-2,3-di-O-benzyl-R-D-arabinofuranosyl^(b)-(1f5)-

3-O-benzyl-1,2-O-isopropylidene-R-^D-arabinofuranose^(a)(3). To a solution

of tetraol 39 (242 mg, 0.128 mmol) and imidazole (43.5 mg, 0.639 mmol) in

dry DMF (2 mL) was added TBDPSCl (74.9 mL, 0.282 mmol) at 0 °C. After

the mixture was stirred for 18 h at room temperature, further imidazole (22.0

mg, 0.323 mmol) and TBDPSCl (37.5 μL, 0.141 mmol) were added to the

reaction mixture. After being stirred for 6 h at room temperature, the reaction

was quenched by saturated aqueous NaHCO₃and extracted with CHCl₃. The

combined organic phase was washed with brine, dried over Na₂SO₄, and

concentrated in vacuo. The residue was purified by flash column chromatog-

raphy using gradient solvent system (hexane/ethyl acetate = 100/1 to 50/1 to

25/1 to 10/1 to 5/1 to 2/1 to 1/1) to give diol 40. To a solution of diol 40 in

dry DMF (2 mL) were added NaH (18.6 mg) and BnBr (40.5 mL, 43.3

mmol) at 0 °C. After being stirred for 2 h at room temperature, the reaction

was quenched by triethylamine and brine, and extracted with CHCl₃. The

combined organic phase was washed with brine, dried over Na₂SO₄, and

concentrated in vacuo. The residue was purified by flash column chromatog-

raphy using gradient solvent system (hexane/ethyl acetate = 100/1 to 50/1 to

25/1 to 10/1 to 5/1 to 1/1) to give the title compound 3(0.273g, 84%intwo

steps). 3: [R]²³_D10.2 (c 1.00, CHCl₃). ¹H NMR (CDCl₃, 400 MHz): δ 1.03

(s, TBDPS, 9H), 1.34 (s, acetonide, 3H), 1.51 (s, acetonide, 3H), 3.43-3.52

(m, C5-H₂^d, C5-H₂^e, 4H), 3.54 (dd, J = 10.4, 6.8 Hz, C5-H^a, 1H), 3.61

(dd, J = 12.0, 3.2 Hz, C5-H^b, 1H), 3.72 (dd, J = 12.0, 2.8 Hz, C5-H^c, 1H),

3.77-3.90 (m, C5-H^a, C5-H^b, C3-H^d, C3-H^e, C5-H₂^f, C5-H₂^g, 8H),

3.93-4.17 (m, C3-H^a, C2-H^b, C3-H^b, C4-H^b, C2-H^c, C4-H^c,

C5-H^c, C4-H^d, C2-H^f, C3-H^f, C4-H^f, C2-H^g, C3-H^g, C4-H^g,

Bn, 16H), 4.17-4.23 (m, C4-H^a, 1H), 4.23-4.26 (m, C2-H^d, C4-H^e,

2H), 4.27-4.32 (m, C3-H^c, C2-H^e, 2H), 4.34-4.62 (m, Bn, 22H), 4.66

(d, J = 4.0 Hz, C2-H^a, 1H), 4.94 (d, J = 4.4 Hz, C1β-H^f, 1H), 4.97 (s,

C1-H^b, 1H), 5.06 (s, C1-H^c, 1H), 5.08 (d, J = 4.4 Hz, C1β-H^g, 1H), 5.11

(s, C1-H^d, C1-H^e, 2H), 5.89 (d, J = 4.0 Hz, C1-H^a, 1H), 7.00-7.64 (m,

Ar, 80H). ¹³CNMR(CDCl₃, 100MHz):δ19.1 (ꢀ2, tBu), 26.4(acetonide),

26.8 (ꢀ2, tBu), 27.2 (acetonide), 65.3 (C5^c), 65.7 (C5^b), 66.1 (C5^f/C5^g),

66.2 (C5^f/C5^g), 66.8 (C5^a), 69.9 (C5^d), 70.1 (C5^e), 71.6 (Bn), 71.7 (Bn),

72.0 (ꢀ3, Bn), 72.16 (ꢀ3, Bn), 72.25 (Bn), 72.32 (Bn), 73.07 (Bn), 73.11

(Bn), 79.9 (C3^c), 80.41 (C4^b/C4^c), 80.44 (C4^b/C4^c), 81.4 (C4^e), 81.8 (ꢀ3,

C4^d, C4^f, C4^g), 81.9 (C3^e), 82.8 (C2^c), 82.9 (C3^a), 83.2 (C4^a), 84.0 (C2^f/

C4^f/C2^g/C4^g), 84.1 (C2^f/C4^f/C2^g/C4^g), 84.2 (ꢀ2, C2^f/C4^f/C2^g/C4^g),

84.52 (C2^f/C4^f/C2^g/C4^g), 84.5 (C3^e), 84.7 (C3^d), 85.3 (C2^a), 85.4 (C2^e),

85.7 (C2^d), 88.4 (C2^b), 100.2 (C1^f), 100.6 (C1^g), 105.2 (C1^d), 105.5 (C1^a),

106.2 (C1^c), 106.2 (C1^b), 106.4 (C1^e), 112.9 (acetonide), 127.26, 127.30,

127.34, 127.37, 127.49, 127.53, 127.62, 127.73, 127.83, 127.90, 127.97, 128.04,

128.21, 128.24, 128.26, 128.28, 128.36, 128.44, 129.71, 133.06, 133.15, 133.19,

135.5, 137.3, 137.5, 137.64, 137.70, 137.73, 137.89, 137.93, 138.0, 138.2, 138.3.

HMBC δ_H4.94 (C1-H^f) f δ_C85.4 (C2^d), 4.98 (C1-H^b) f δ_C66.8

(C5^a), δ_H5.06 (C1-H^c) f δ_C65.7 (C5^b), δ_H5.08 (C1-H^g) f δ_C85.7

(C2^e), δ_H5.11 (C1-H^d) f δ_C65.3 (C5^c), δ_H5.11 (C1-H^e) f δ_C79.9

(C3^c). MALDI-TOFMS: [Mþ Na]^þcalcd for C₁₅₄H₁₇₀O₂₉NaSi₂, 2562.13,

found 2561.99. HRMS ESI-TOF: [M þ Na]^þcalcd for C₁₅₄H₁₇₀O₂₉NaSi₂,

2562.1264, found 2562.1268.

2-O-Benzyl-β-^D-arabinofuranosyl^(f/g)-(1f2)-3,5-di-O-benzyl-R-D-

arabinofuranosyl^(d/e)-(1f5)-[2-O-benzyl-β-D-arabinofuranosyl^(f/g)-(1f2)-

3,5-di-O-benzyl-R-^D-arabinofuranosyl^(d/e)]-(1f3)-2-O-benzyl-R-D-

arabinofuranosyl^(c)-(1f5)-2,3-di-O-benzyl-R-D-arabinofuranosyl^(b)-(1f5)-

3-O-benzyl-1,2-O-isopropylidene-R-^D-arabinofuranose^(a)(39). To a

solution of 38 in dry THF (5 mL) was added 1 M solution of TBAF in

THF (1.0 mL, 1.0 mmol) at room temperature. After being stirred for

18 h at the same temperature, the mixture was concentrated in vacuo.

The residue was purified by flash column chromatography using

gradient solvent system (hexane/ethyl acetate = 20/1 to 5/1 to 2/1

to 1/1 to 1/2 to 1/5) to give the pure β,β-compound 39 (262.5 mg,

87% in two steps from 8 and 5). 39: [R]²⁷_D21.8 (c 1.00, CHCl₃). ¹H

NMR (CDCl₃, 400 MHz): δ 1.34 (s, acetonide, 3H), 1.50 (s,

acetonide, 3H), 2.50-2.80 (br m, OH, 4H), 3.47-3.64 (m, C5-H^a,

C5-H^b, C5-H₂, C5-H₂, C5-H₂, C5-H₂, 10H), 3.72-3.90 (m,

C5-H^a, C5-H^b, C5-H^c, C2-H^f, C4-H^f, C2-H^g, C4-H^g, 10H),

3.96 (dd, J = 12.4, 4.0 Hz, C5-H^c), 4.00-4.06 (m, C3-H^a, C2-H^b,

C3-H^b, C2-H^c, C3-H^c, 5H), 4.09 (dd, J = 6.8, 4.0 Hz, C3-H^e, 1H),

4.10-4.19 (m, C3-H^d, C4-H^d, C4-H^b, C4-H^c, 4H), 4.20-4.15

(m, C4-H^a, C4-H^e, 2H), 4.28-4.36 (m, C2-H^d, C2-H^e, C3-H^f,

C3-H^g, 4H), 4.41-4.63 (m, Bnꢀ10, 20H), 4.66 (d, J = 4.0 Hz,

C2-H^a, 1H), 4.977 (d, J = 4.4 Hz, C1-H^f/g, 1H), 4.983 (s, C1-H^b,

1H), 5.03 (d, J = 4.4 Hz, C1-H^f/g, 1H), 5.07 (s, C1-H^c, 1H), 5.12 (s,

C1-H^e, 1H), 5.14 (s, C1-H^d, 1H), 5.90 (d, J = 4.0 Hz, C1-H^a, 1H),

7.16-7.40 (m, Ar, 50H). ¹³C NMR (CDCl₃, 100 MHz): δ 26.3

(acetonide), 27.1 (acetonide), 62.6 (C5^f/g), 62.7 (C5^f/g), 65.5 (C5^c),

65.7 (C5^b), 66.8 (C5^a), 69.2 (C5^d/e), 69.3 (C5^d/e), 71.57 (Bn), 71.61

(Bn), 71.93 (Bn), 71.99 (Bn), 72.06 (Bn), 72.31 (Bn), 72.38 (Bn),

73.20 (ꢀ2, Bn), 73.25 (Bn), 79.9 (C3^c), 80.2 (C4^b), 80.5 (C4^e), 80.77

(C4^c), 81.1 (C4^d), 81.86 (C5^f/g), 81.88 (C5^f/g), 82.7 (C3^a), 82.87

(C3^b/d/e), 82.90 (C3^b/d/e), 82.94 (C3^b/d/e), 83.3 (C4^a), 84.1 (ꢀ2, C2^f,

C2^g), 85.1 (C2^a), 85.6 (ꢀ2, C2^d/e, C2^f/g), 85.7 (ꢀ2, C2^d/e, C2^f/g),

88.3 (C2^b), 88.4 (C2^c), 99.3 (ꢀ2, C1^f, C1^g), 105.2 (C1^d), 105.5 (C1^a),

106.07 (C1^e), 106.16 (C1^c), 106.24 (C1^b), 112.81 (acetonide), 127.55,

127.60, 127.63, 127.66, 127.71, 127.77, 127.99, 128.15, 128.23, 128.29,

128.38, 128.42, 128.46, 128.96, 137.24, 137.34, 137.52, 137.54, 137.77,

137.80, 137.85, 137.90. MALDI-TOF MS: [M þ Na]^þcalcd for

C₁₀₈H₁₂₂O₂₉Na, 1905.80, found 1905.51. HRMS ESI-TOF: [M þ

Na]^þcalcd for C₁₀₈H₁₂₂O₂₉Na, 1905.7970, found 1905.7954.

4-Methylphenyl 2,3-Di-O-benzyl-5-O-t-butyldiphenylsilyl-β-^D-ara-

binofuranosyl^(f/g)-(1f2)-3,5-di-O-benzyl-R-D-arabinofuranosyl^(d/e)-(1f5)-

[2,3-di-O-benzyl-5-O-t-butyldiphenylsilyl-β-^D-arabinofuranosyl^(f/g)

(1f2)-3,5-di-O-benzyl-R-^D-arabinofuranosyl^(d/e)]-(1f3)-2-O-benzyl-

R-^D-arabinofuranosyl^(c)-(1f5)-2,3-di-O-benzyl-R-D-arabinofuranosyl^(b)

(1f5)-2-O-acetyl-3-O-benzyl-1-thio-^D-arabinofuranoside^(a)(2). A

solution of acetonide 3 (10.5 mg, 4.13 μmol) in dioxane (2 mL), 10%

aqueous HCl (0.2 mL), and 70% aqueous AcOH (2.0 mL) was stirred at

50 °C for 3 h. After the mixture was cooled to room temperature and

quenched with saturated aqueous NaHCO₃, the residue was extracted

with AcOEt, and the combined organic phase was washed with brine and

dried over Na₂SO₄. After concentration in vacuo and azeotropic removal

of H₂O with toluene, the residue was used without further purification.

To a solution of the crude hemiacetal 41 and ditolyldisulfide (16.0 mg,

2,3-Di-O-benzyl-5-O-t-butyldiphenylsilyl-β-^D-arabinofuranosyl^(f/g)

(1f2)-3,5-di-O-benzyl-R-^D-arabinofuranosyl^(d/e)-(1f5)-[2,3-di-O-

benzyl-5-O-t-butyldiphenylsilyl-β-^D-arabinofuranosyl^(f/g)-(1f2)-3,5-

di-O-benzyl-R-^D-arabinofuranosyl^(d/e)]-(1f3)-2-O-benzyl-R-D-arabin-

2286

dx.doi.org/10.1021/ja109932t |J. Am. Chem. Soc. 2011, 133, 2275–2291

Journal of the American Chemical Society

ARTICLE

64.9 μmol) in CH₂Cl₂(1.0 mL) was added n-Bu₃P (16.0 μL, 64.1 μmol)

at 0 °C under Ar atmosphere. After being stirred for 24 h at room

temperature, the mixture was concentrated in vacuo to give crude 42

(MALDI-TOF MS: [M þ Na]^þcalcd for C₁₅₈H₁₇₂O₂₈SSi₂Na, 2628.12,

found 2628.59. HRMS ESI-TOF: [M þ Na]^þcalcd for C₁₅₈H₁₇₂O₂₈S-

Si₂Na, 2628.1192, found 2628.1163). To the mixture in pyridine (2.0 mL)

were added Ac₂O (0.5 mL) and DMAP (10 mg) at room temperature.

After the mixture was stirred for 24 h at the same temperature, to the

mixture was added ice water. The residue was extracted with AcOEt, and

the combined organic phase was washed with H₂O, aqueous saturated

KHSO₄, H₂O, aqueous saturated NaHCO₃, and brine, and dried over

Na₂SO₄, then concentrated in vacuo. The residue was purified by PTLC

(hexane/ethyl acetate = 4/1) to give the title compound 2 (8.3 mg, 76% in

72.4 (Bn), 72.5 (Bn), 78.7 (C4^b), 81.4 (C4^a), 82.2 (C3^b), 83.6 (C3^a), 84.1

(C2^b), 86.5 (C2^a), 100.5 (C1^b), 104.7 (C1^a), 127.7, 127.8, 128.0, 128.4,

128.5, 137.3, 137.7, 170.6. ESI-TOF MS: [M þ Na]^þcalcd for

C₄₇H₂₉D₂₁O₁₀Na, 818.46, found 818.39. HRMS ESI-TOF: [M þ Na]^þ

calcd for C₄₇H₂₉D₂₁O₁₀Na, 818.4620, found 818.4585.

General Procedure for IAD Using NIS-AgOTf as the

Activator. 2,3-Di-O-benzyl-β-D-arabinofuranosyl^(c)-(1f2)-3,5-di-O-

benzyl-r-^D-arabinofuranosyl^(b)-(1f5)-3-O-benzyl-1,2-O-isopropylidene-

r-^D-arabinofuranose^(a)(51). To a mixture of acceptor 45³¹(25.2 mg,

41.0 μmol), 5-O-NAP-protected donor 7³¹(26.0 mg, 45.1 μmol), and

dried powdered MS4 Å (250 mg) in dry (CH₂Cl)₂(2.0 mL) was added

DDQ (6.5 mg, 49.8 μmol) at room temperature under Ar atmosphere.

The mixture was stirred for 18 h at the same temperature, quenched with

aqueous ascorbate buffer, and filtered through Celite. The filtrate was

extracted with CHCl₃, and washed with saturated aqueous NaHCO₃and

brine. A combined organic layer was dried over Na₂SO₄and evaporated

in vacuo. The crude product was purified by gel filtration (SX-3,

EtOAc-toluene = 1:1) to give a crude mixed acetal. To the crude mixed

acetal and MS4 Å (1.5 g) in dry CH₂Cl₂(20.0 mL) were added NIS (16.2

mg, 71.9 μmol) and AgOTf (1.1 mg, 4.3 μmol) at -30 °C under Ar

atmosphere. The mixture was stirred for 12 h at the same temperature.

The reaction mixture was quenched with triethylamine, diluted with

EtOAc, and filtered through Celite. The filtrate was washed with 20%

aqueous Na₂S₂O₃, saturated aqueous NaHCO₃, and brine. The washed

organic layer was dried over Na₂SO₄and evaporated in vacuo to give the

crude product including the diastereomeric mixture of (2-naphthyl)-

(succinimido)methyl ether (HRMS ESI-TOF: [M þ Na]^þcalcd for

C₆₈H₇₁O₁₅NNa, 1164.4721, found 1164.4672). The crude mixture in

(CH₂NH₂)₂(0.25 mL) and n-BuOH (3.0 mL) was stirred at 80 °C for 3

d, then evaporated in vacuo. The crude product was purified by gel

filtration chromatography (SX-3, EtOAc-toluene = 1:1) to give the

three steps). 2 (R-isomer), H NMR (CDCl₃, 400 MHz): δ 0.97 (s,

TBDPS ꢀ2, 18H), 1.89 (s, Ac, 3H), 2.26 (s, Me, 3H), 3.39-3.46 (m,

C5-H₂, C5-H₂, 4H), 3.52-3.58 (m, C5-H^a, C5-H^b, 2H),

3.63-3.81 (m, C5-H^a, C5-H^b, C5-H^c, C3-H^d, C3-H^e, C5-H₂,

C5-H₂, 9H), 3.88-4.13 (m, C2-H^b, C3-H^b, C4-H^b, C2-H^c,

C4-H^c, C5-H^c, C4-H^e, C2-H^f, C3-H^f, C4-H^f, C2-H^g, C3-H^g,

C4-H^g, Bn, 15H), 4.16-4.22 (m, C4-H^d, C2-H^e, 2H), 4.22-4.27 (m,

C3-H^c, C2-H^d, 5H), 4.28-4.66 (m, C4-H^a, Bn, 23H), 5.06 (d, J = 4.4

Hz, C1-H^f/g, 1H), 5.06 (s, C1-H^c, 1H), 5.06 (m, C1-H^b, C1-H^f/g

2H), 5.06 (s, C1-H^d, C1-H^e, 2H), 5.25 (t, J = 1.2 Hz, C1R-H^a, 1H),

5.42(s, C1R-H^a, 1H), 6.96-7.60 (m, Ar, 84H);β-isomer, 5.38 (dd, J=4.8,

2.0 Hz,C2β-H^a, 0.43H), 5.49 (d, J =4.8Hz, C1β-H^a, 0.43H). ¹³CNMR

(CDCl₃, 100 MHz): δ 91.3 (C1^a), 100.2, (ꢀ2, C1^f, C1^g), 105.2 (C1^d/e),

106.2 (C1^c), 106.4 (C1^b), 106.5 (C1^d/e). MALDI-TOF MS: [M þ Na]^þ

calcd for C₁₆₀H₁₇₄O₂₉SSi₂Na, 2670.13, found 2670.05. HRMS ESI-TOF:

[M þ Na]^þcalcd for C₁₆₀H₁₇₄O₂₉SSi₂Na, 2670.1298, found 2670.1314.

5-O-Acetyl-2,3-di-O-benzyl-β-^D-arabinofuranosyl^(b)-(1f2)-3,5-di-

O-[D₇]benzyl-R-D-arabinofuranoside^(a)(49). To a mixture of acceptor

44³¹(21.0 mg, 47.6 μmol), 5-O-NAP-protected donor 43³¹(26.2 mg, 52.3

μmol), and dried powdered MS4 Å (250 mg) in dry (CH₂Cl)₂(2.0 mL)

was added DDQ (10.3 mg, 49.8 μmol) at room temperature under Ar

atmosphere. The mixture was stirred for 18 h at the same temperature,

quenched with aqueous ascorbate buffer,²⁴and filtered through Celite. The

filtrate was extracted with CHCl₃, and washed with saturated aqueous

NaHCO₃and brine. A combined organic layer was dried over Na₂SO₄and

evaporated in vacuo. The crude product was purified by gel filtration

chromatography (SX-3, EtOAc-toluene = 1:1) to give mixed acetal 46a

(36.9 mg, 82%) as the mixture of diastereomers. To the mixed acetal (20.0 mg,

21.3 μmol), DTBMP (17.5 mg, 85.2 μmol), and MS4 Å (1.5 g) in dry

(CH₂Cl)₂(21.3 mL) was added MeOTf (8.2 μL, 72.6 mmol) at room

temperature under Ar atmosphere. The mixture was stirred for 3 d at the

same temperature. The reaction mixture was quenched with triethylamine,

diluted with EtOAc, and filtered through Celite. The filtrate was washed

with saturated aqueous NaHCO₃and brine. The washed organic layer was

dried over Na₂SO₄and evaporated in vacuo to give the crude product. To

the crude mixture in CH₂Cl₂(2.0 mL) was added TFA (0.2 mL) at 0 °C,

and the mixture was stirred for 30 min at the same temperature. After

evapolation, the resultant mixture was treated with Ac₂O (0.5 mL) in

pyridine (1.0 mL) for 12 h at room temperature, and then evaporated in

vacuo. The crude product was purified by gel filtration chromatography

(SX-3, EtOAc-toluene = 1:1) to give the product 49 (6.0 mg, 34% from

mixed acetal, β). 49: [R]²⁷_D1.77 (c 0.68, CHCl₃). ¹H NMR (CDCl₃, 400

MHz): δ 1.92 (s, Ac, 3H), 3.56 (dd, J = 11.2, 6.4 Hz, C5-H^a, 1H), 3.60

(dd, J = 11.2, 4.0 Hz, C5-H^a, 1H), 3.96-4.13 (m, C2-H^b, C3-H^a,

C3-H^b, C4-H^b, C5-H^b, 5H), 4.15-4.22 (m, C5-H^b1H), 4.24-4.28

(m, C4-H^a, 1H), 4.34 (d, J = 2.4, Hz, C2-H^a), 4.00-4.06 (m, C3-H^a,

C2-H^b, C3-H^b, C2-H^c, 4H), 4.32-4.57 (m, Bn ꢀ11, 22H), 4.61 (d, J

= 4.0 Hz, C2-H^a, 1H), 4.39 (d, J = 12.0 Hz, Bn, 1H), 4.45 (d, J = 12.0 Hz,

Bn, 1H), 4.56 (d, J = 12.0 Hz, Bn, 1H), 4.67 (d, J = 12.0 Hz, Bn, 1H), 4.96

(d, J = 4.4 Hz, C1-H^b, 1H), 5.05 (s, C1-H^a, 1H), 7.22-7.35 (m, Ar,

10H). ¹³C NMR (CDCl₃, 100 MHz): δ20.7 (Ac), 66.0 (C5^b), 69.8 (C5^a),

product 51 (24.2 mg, 65% from 45, ββ). 51: [R]²⁵-2.80 (c 0.50,

CHCl₃). ¹H NMR (CDCl₃, 400 MHz): δ 1.31(s, acetonide, 3H), 1.49 (s,

acetonide, 3H), 2.25-2.37 (br m, OH, 1H), 3.47-3.60 (m, C5-H^a,

C5-H₂, C5-H₂, 5H), 3.87 (dd, J = 10.8, 5.6 Hz, C5-H^a, 1H),

3.93-3.98 (m, C4-H^c, 1H), 4.02-4.06 (m, C3-H^a, C2-H^c, 2H),

4.09-4.17 (m, C3-H^b, C4-H^b, 2H), 4.18-4.27 (m, C4-H^a, C2-H^b,

C3-H^c, 3H), 4.42-4.58 (m, Bn, 8H), 4.60 (d, J = 12.0 Hz, Bn, 1H), 4.63

(d, J = 4.0 Hz, C2-H^a, 1H), 4.70 (d, J = 12.0 Hz, Bn, 1H), 4.66 (d, J =

12.0Hz, Bn, 1H), 5.00 (s, C1-H^b, 1H), 5.01 (d, J = 4.0Hz, C1-H^c, 1H),

5.87 (d, J = 4.0 Hz, C1-H^a, 1H), 7.23-7.345 (m, Ar, 25H). ¹³C NMR

(CDCl₃, 100 MHz): δ 26.4 (acetonide), 27.2 (acetonide), 63.4 (C5^c),

66.9 (C5^a), 69.3 (C5^b), 71.7 (Bn), 72.2 (Bn), 72.5 (Bn), 72.7 (Bn), 73.4

(Bn), 80.4 (C4^a), 80.9 (C4^b), 82.8 (C4^c), 82.81 (C3^a), 82.83 (C3^c), 83.1

(C3^b), 84.0 (C2^c), 85.3 (C2^a), 86.3 (C2^b), 100.2 (C1^c), 105.6 (C1^a),

106.0 (C1^b), 112.9 (acetonide), 127.66, 127.71, 127.80, 127.84, 128.0,

128.32, 128.37, 128.43, 128.45, 128.51, 137.3, 137.5, 137.8, 137.9, 138.0.

ESI-TOF MS: [M þ Na]^þcalcd for C₅₃H₆₀O₁₃Na, 927.39, found

927.32. HRMS ESI-TOF: [M þ Na]^þcalcd for C₅₃H₆₀O₁₃Na,

927.3932, found 927.3911.

[D₇]Benzyl 2,3-Di-O-benzyl-β-D-arabinofuranosyl^(b)-(1f2)-3,5-di-

O-[D₇]benzyl-R-D-arabinofuranoside^(a)(48). This compound 48 was

synthesized from 44³¹according to the general procedure for IAD using

NIS-AgOTf as the activator synthesis (82% for mixed acetal formation

with 6 and 72% from mixed acetal 46b, R:β = 1:>20) (58% from mixed

acetal 46a, R:β = 1:>20). 48: [R]²⁷1.18 (c 0.38, CHCl₃). H NMR

(CDCl₃, 400 MHz): δ 2.22-2.37 (br m, OH, 1H), 3.45-3.67 (m,

C5-H₂, C5-H₂, 4H), 3.95 (ddd, J = 6.8, 4.8, 3.2 Hz, C4-H^b, 1H), 4.01

(dd, J = 7.6, 4.4 Hz, C2-H^b, 1H), 4.10 (dd, J = 7.6, 4.4 Hz, C3-H^a, 1H),

4.16-4.28 (m, C3-H^b, C4-H^a, 2H), 4.31 (dd, J = 4.0, 1.6 Hz, C2-H^a,

1H), 4.40 (d, J = 12.0 Hz, Bn, 1H), 4.45 (d, J = 12.0 Hz, Bn, 1H), 4.55 (d,

J = 12.0 Hz, Bn, 1H), 4.68 (d, J = 12.0 Hz, Bn, 1H), 4.96 (d,

J = 4.4 Hz, C1-H^b, 1H), 5.05 (d, J = 1.6 Hz, C1-H^a, 1H), 7.21-7.35

(m, Ar, 10H). ¹³C NMR (CDCl₃, 100 MHz): δ 63.3 (C5^b), 69.4 (C5^a),

2287

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72.4 (Bn), 72.6 (Bn), 80.5 (C3^b), 80.9 (C4^a), 82.0 (C4^b), 83.1 (C3^a), 83.9

(C2^b), 86.5 (C2^a), 100.2 (C1^b), 104.7 (C1^a), 127.7, 128.0, 128.4, 128.5,

137.4, 138.0. ESI-TOF MS: [M þ Na]^þcalcd for C₄₅H₂₇D₂₁O₉Na,

776.45, found 776.39. HRMS ESI-TOF: [M þ Na]^þcalcd for C₄₇H₂₉-

D₂₁O₁₀Na, 776.4478, found 776.4514.

(Bn), 75.7 (C3^f, C3^g), 76.4 (C2^f/g), 76.6 (C2^f/g), 78.3 (C4^f/g), 78.5

(C4^f/g), 79.7 (C4^a), 80.4 (C4^b), 80.6 (C3^a), 81.0 (C4^d), 81.4 (C4^e), 82.8

(C4^c), 82.9 (C3^c), 83.2 (C3^b), 83.8 (C3^e), 83.9 (C3^d), 85.3 (C2^a), 85.9

(C2^d), 86.2 (C2^e), 88.4 (C2^c), 88.5 (C2^b), 99.8 (C1^f/g), 99.8 (C1^f/g),

104.7 (C1^e), 105.5 (C1^a), 106.1 (C1^d), 106.2 (C1^b/c, C1^b/c), 112.8

(acetonide), 127.4, 127.5, 127.6, 127.67, 127.73, 127.75, 127.83, 127.9,

128.2, 128.3, 128.36, 128.42, 137.3, 137.5, 137.9, 137.97, 138.02, 138.06,

138.11, 170.01, 170.03 (ꢀ2), 170.07, 170.45, 170.48. MALDI-TOF MS:

[M þ Na]^þcalcd for C₁₀₆H₁₂₂O₃₅Na, 1977.77, found 1977.70.

2,3-Di-O-benzyl-β-^D-arabinofuranosyl^(f/g)-(1f2)-3,5-di-O-benzyl-R-

2,3,5-Tri-O-acetyl-β-^D-arabinofuranosyl^(f/g)-(1f2)-3,5-di-O-benzyl-

R-^D-arabinofuranosyl^(d/e)-(1f5)-[2,3,5-tri-O-acetyl-β-D-arabinofuran-

osyl^(f/g)-(1f2)-3,5-di-O-benzyl-R-D-arabinofuranosyl^(d/e)]-(1f3)-2-O-

benzyl-R-^D-arabinofuranosyl^(c)-(1f5)-2,3-di-O-benzyl-R-D-arabinofur-

anosyl^(b)-(1f5)-3-O-benzyl-1,2-O-isopropylidene-R-D-arabinofuranose^(a)

(53). To a mixture of acceptor 8 (81.2 mg, 56.4 μmol), 2-O-NAP-

protected donor 6²⁷(29.5 mg, 124 μmol), and dried powdered MS4 Å

(250 mg) in dry CH₂Cl₂(2.0 mL) was added DDQ (45.2 mg, 199

μmol) at room temperature under Ar atmosphere. The mixture was

stirred for 20 h, quenched with aqueous ascorbate buffer, and filtered

through Celite. The filtrate was extracted with CHCl₃, and washed with

saturated aqueous NaHCO₃and brine. A combined organic layer was

dried over Na₂SO₄and evaporated in vacuo. The crude product was

purified by gel filtration chromatography (SX-3, EtOAc-toluene = 1:1)

to give mixed acetal (119 mg, 82%) as the mixture of diastereomers

(MALDI-TOF MS: [M þ Na]^þcalcd for C₁₄₂H₁₈₂O₃₁Si₄Na, 2582.10,

found 2582.47). To the mixed acetals were added DTBMP (76.4 mg,

372 μmol) and MS4 Å in dry (CH₂Cl)₂(5.0 mL) at room temperature

under Ar atmosphere. Next, MeOTf (35.8 μL, 316 μmol) was added to

the mixture, and the mixture was stirred for 18 h at the same

temperature. The reaction mixture was quenched with triethylamine,

diluted with EtOAc, and filtered through Celite. The filtrate was washed

with saturated aqueous NaHCO₃and brine. The washed organic layer

was dried over Na₂SO₄and evaporated in vacuo to give the diastereo-

meric mixture of 5,5⁰-naphylidene acetal (MALDI-TOF MS: [M þ

Na]^þcalcd for C₁₂₉H₁₆₈O₃₁Si₄Na, 2348.05, found 2348.93) and

product (MALDI-TOF MS: [M þ Na]^þcalcd for C₁₁₈H₁₆₂O₃₁Si₄Na,

2210.01, found 2210.06). The mixture in THF (3.0 mL) and 70% AcOH

(3.0 mL) was stirred at 80 °C for 2 d, then evaporated in vacuo. At this

stage, the hydrolysis of TIPDS group was observed. After azeotropic

removal of acetic acid with toluene, the mixture was treated with TBAF

in THF for 18 h at room temperature. After evaporation, to the mixture

were added pyridine (2.0 mL), Ac₂O (0.5 mL), and DMAP (5.0 mg).

The mixture was stirred for 12 h at room temperature. After addition of

ice water, the residue was diluted with EtOAc, and washed with H₂O,

saturated aqueous NaHCO₃KHSO₄, H₂O, saturated aqueous NaHCO₃

and brine. The washed organic layer was dried over Na₂SO₄and

evaporated in vacuo. The crude product was purified by PTLC

(toluene-EtOAc = 3:1) to give the product 53 (65.2 mg, 73% from

mixed acetal, ββ) as the hexaacetate. 53: [R]²³_D35.4 (c 1.27, CHCl₃).

¹H NMR (CDCl₃, 400 MHz): δ 1.25 (s, acetonide, 3H), 1.42 (s,

acetonide, 3H), 1.80 (s, Ac, 3H), 1.84 (s, Ac, 3H), 1.85 (s, Ac, 3H), 1.88

(s, Ac, 3H), 2.00 (s, Ac, 3H), 2.01 (s, Ac, 3H), 3.40-3.52 (m, C5-H^c,

D-arabinofuranosyl^(d/e)-(1f5)-[2,3-di-O-benzyl-β-D-arabinofuranosyl^(f/g)

(1f2)-3,5-di-O-benzyl-R-^D-arabinofuranosyl^(d/e)]-(1f3)-2-O-benzyl-R-D-

arabinofuranosyl^(c)-(1f5)-2,3-di-O-benzyl-R-D-arabinofuranosyl^(b)-(1f5)-

3-O-benzyl-1,2-O-isopropylidene-R-^D-arabinofuranose^(a)(55). To a

mixture of diol acceptor 8 (35.5 mg, 24.7 μmol), 5-O-NAP-protected

donor 7²⁸(31.7 mg, 54.3 μmol), and dried powdered MS4 Å (250 mg)

in dry (CH₂Cl)₂(2.0 mL) was added DDQ (19.1 mg, 84.1 μmol) at

room temperature under Ar atmosphere. The mixture was stirred for 24

h at the same temperature, quenched with aqueous ascorbate buffer, and

filtered through Celite. The filtrate was extracted with CHCl₃, and

washed with saturated aqueous NaHCO₃and brine. A combined organic

layer was dried over Na₂SO₄and evaporated in vacuo. The crude

product was purified by gel filtration chromatography (SX-3,

EtOAc-toluene = 1:1) to give mixed acetal (47.4 mg, 74%) as the

mixture of diastereomers (MALDI-TOF MS: [M þ Na]^þcalcd for

C₁₅₈H₁₆₂O₂₉S₂Na, 2610.05, found 2609.98). To the mixed acetal and

MS4 Å (1.5 g) in dry (CH₂Cl)₂(8 mL) and dry CH₂Cl₂(8.0 mL) were

added NIS (14.4 mg, 62.1 μmol) and AgOTf (2.0 mg, 7.8 μmol) at -30

°C under Ar atmosphere. The mixture was stirred for 1 h at -20 °C, and

further NIS (14.4 mg, 62.1 μmol) and AgOTf (2.0 mg, 7.8 μmol) were

added to the mixture. The mixture was stirred for 3 h at -10 °C and for

18 h at 0 °C. The reaction mixture was quenched with triethylamine,

diluted with EtOAc, and filtered through Celite. The filtrate was washed

with 20% aqueous Na₂S₂O₃, saturated aqueous NaHCO₃, and brine.

The washed organic layer was dried over Na₂SO₄and evaporated in

vacuo to give the crude product including the diastereomeric mixture of

naphthyl(succinimido)methyl ether (MALDI-TOF MS: [M þ Na]^þ

calcd for C₁₅₂H₁₅₆O₃₃N₂Na, 2560.05, found 2560.26). The crude

mixture in (CH₂NH₂)₂(0.25 mL) and n-BuOH (3.0 mL) was stirred

at 80 °C for 2 d, then evaporated in vacuo. The residue in THF (2 mL)

and 70% AcOH aqueous (2 mL) was stirred at 80 °C for 24 h, then

evaporated in vacuo. The crude product was purified by PTLC

(toluene-EtOAc = 5:1) to give the product 55 (12.7 mg, 34% from

52, ββ). 55, ¹H NMR (CDCl₃, 400 MHz): δ 1.29 (s, acetonide, 3H),

1.54 (s, acetonide, 3H), 2.25-2.37 (br m, OH, 2H), 3.41-3.59 (m,

C5-H^a, C5-H^b, C5-H₂, C5-H₂, C5-H₂, C5-H₂, 10H), 3.70

(dd, J = 12.0, 4.4 Hz, C5-H^c, 1H), 3.78 (dd, J = 12.0, 4.0 Hz, C5-H^b,

1H), 3.81 (dd, J = 10.8, 5.6 Hz, C5-H^a, 1H), 3.86-4.02 (m, C3-H^a,

C2-H^b, C3-H^b, C2-H^c, C5-H^c, C2-H^f, C3-H^f, C2-H^g, C3-H^g,

9H), 4.03-4.12 (m, C4-H^b, C4-H^c, C3-H^d, C4-H^d, C3-H^e, 5H),

4.14-4.20 (m, C4-H^a, C4-H^e, C4-H^f, C4-H^g, 4H), 4.25-4.31 (m,

C3-H^c, C2-H^d, C2-H^e, 3H), 4.32-4.57 (m, Bn ꢀ11, 22H), 4.61 (d,

J = 4.0 Hz, C2-H^a, 1H), 4.64 (d, J = 12.0 Hz, Bn, 1H), 4.66 (d, J = 12.0

Hz, Bn, 1H), 4.93 (s, C1-H^b, 1H), 4.96 (d, J = 4.8 Hz, C1-H^f/g, 1H),

5.02 (s, C1-H^c, 1H), 5.05 (d, J = 4.0 Hz, C1-H^f/g, 1H), 5.08 (d, J = 1.6

Hz, C1-H^e, 1H), 5.09 (d, J = 2.0 Hz, C1-H^d, 1H), 5.85 (d, J = 4.0 Hz,

C1-H^a, 1H), 7.16-7.35 (m, Ar, 60H). ¹³C NMR (CDCl₃, 100 MHz):

δ 26.4 (q), 27.2 (q), 63.4 (t, ꢀ2), 65.56 (t), 65.60 (t), 66.8 (t), 69.3 (t),

69.5 (t), 71.6 (t), 71.8 (t), 72.0 (t), 72.1 (t, ꢀ2), 72.28 (t, ꢀ2), 72.33 (t),

72.5 (t, ꢀ2), 73.3 (t, ꢀ2), 80.0 (d), 80.2 (d), 80.57 (d), 80.64 (d), 80.8

(d), 81.2 (d), 81.8 (d), 81.9 (d, ꢀ2), 82.8 (d), 82.9 (d), 83.0 (d), 83.1

(d), 83.2 (d), 84.00 (d), 84.02 (d), 85.3 (d), 85.9 (d), 86.1 (d), 88.41

(d), 88.43 (d), 99.86 (d), 99.91 (d), 105.2 (d), 105.6 (d), 106.1 (d),

106.2 (d), 106.3 (d), 112.8 (s), 127.60, 127.63, 127.69, 127.74, 127.83,

C5-H₂, C5-H₂, 5H), 3.58 (dd, J = 12.0, 3.6 Hz, C5-H^b), 3.64 (dd, J

= 12.0, 2.0 Hz, C5-H^a), 3.76 (dd, J = 12.0, 4.4 Hz, C5-H^b), 3.78-3.83

(m, C5-H^a, C5-H^c, 2H), 3.85 (dd, J = 6.4, 2.4 Hz, C3-H^d), 3.64 (dd, J

= 6.4, 2.0 Hz, C3-H^e), 3.93-4.03 (m, C3-H^a, C2-H^b, C3-H^b,

C2-H^c, C3-H^c, C4-H^f, C5-H^f, C4-H^g, C5-H^g, 9H), 4.03-4.08

(m, C4-H^b, C4-H^e, 2H), 4.11-4.18 (m, C4-H^c, C4-H^d, 2H),

4.19-4.23 (m, C4-H^a, C2-H^e, 2H), 4.19-4.23 (m, C2-H^d, C5-H^f,

C5-H^g, 3H), 4.32-4.58 (m, C2-H^a, Bn ꢀ8, 17H), 4.83-4.88 (m,

C2-H^f, C2-H^g, 2H), 4.91 (s, C1-H^d, 1H), 4.93 (s, C1-H^c, 1H), 4.95

(s, C1-H^e, 1H), 5.06 (s, C1-H^b, 1H), 5.20-5.22 (m, C3-H^f, C3-H^g,

2H), 5.23 (d, J = 4.8 Hz, C1-H^f/g, 1H), 5.27 (d, J = 4.8 Hz, C1-H^f/g

1H), 5.80 (d, J = 4.0 Hz, C1-H^a, 1H), 7.10-7.30 (m, Ar, 40H). ¹³C

NMR (CDCl₃, 100 MHz): δ 20.2 (Ac), 20.4 (Ac), 20.6 (Ac ꢀ2), 20.7

(Ac ꢀ2), 26.4 (acetonide), 27.2 (acetonide), 65.20 (C5^a), 65.3 (C5^f/g),

65.4 (C5^f/g), 65.8 (C5^b), 66.8 (C5^c), 69.2 (C5^e), 69.6 (C5^d), 71.7 (Bn

ꢀ2), 71.9 (Bn), 71.95 (Bn), 72.04 (Bn), 72.3 (Bn), 73.20 (Bn), 73.23

2288

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127.87, 127.92, 127.93, 128.0, 128.3, 128.4, 128.5, 137.3, 137.4, 137.5,

137.8, 137.9, 137.97, 138.04, 138.09, 138.11. MALDI-TOF MS: [M þ

Na]^þcalcd for C₁₂₂H₁₃₄O₂₉Na, 2085.89, found 2085.77.

(t, ꢀ2, Bn), 79.85 (d), 79.96 (d, ꢀ2), 80.08 (d), 80.41 (d), 80.42

(d, ꢀ2), 80.45 (d), 80.46 (d), 80.50 (d, ꢀ2), 80.57 (d), 80.98 (d), 81.21

(d, ꢀ2), 81.43 (d, ꢀ2), 81.83 (d, ꢀ2), 81.86 (d, ꢀ2), 81.96 (d, ꢀ2),

81.18 (d), 81.24 (d), 82.71 (d), 82.81 (d), 82.84 (d), 82.88 (d, ꢀ2),

82.89 (d, ꢀ2), 82.92 (d), 82.99 (d), 83.15 (d), 83.16 (d), 83.26 (d),

84.02 (d, ꢀ2), 84.09 (d, ꢀ2), 84.11 (d, ꢀ2), 84.19 (d, ꢀ2), 84.56

(d, ꢀ2), 84.69 (d, ꢀ2), 85.33 (d), 85.41 (d, ꢀ2), 85.73 (d, ꢀ2), 87.72

(d), 88.31 (d), 88.34 (d, ꢀ2), 88.40 (d), 88.42 (d), 88.50 (d), 88.53 (d),

88.54 (d, ꢀ2), 88.60 (d), 100.23 (d, ꢀ2), 100.60 (d, ꢀ2), 105.01 (d),

105.23 (d, ꢀ2), 105.57 (d), 106.23 (d), 106.09 (d), 106.19 (d, ꢀ2),

106.28 (d, ꢀ2), 106.35 (d), 106.40 (d, ꢀ3), 106.52 (d), 106.54 (d),

106.57 (d), 106.65 (d), 112.89 (s, acetonide), 127.28 (d, Ar), 127.32

(d, Ar), 127.35 (d, Ar), 127.38 (d, Ar), 127.45 (d, Ar), 127.47 (d, Ar),

127.50 (d, Ar), 127.53 (d, Ar), 127.57 (d, Ar), 127.63 (d, Ar), 127.69

(d, Ar), 127.71 (d, Ar), 127.73 (d, Ar), 127.74 (d, Ar), 127.78 (d, Ar),

127.81 (d, Ar), 127.83 (d, Ar), 127.84 (d, Ar), 127.87 (d, Ar), 127.91

(d, Ar), 127.92 (d, Ar), 127.94 (d, Ar), 127.96 (d, Ar), 127.97 (d, Ar),

128.00 (d, Ar), 128.06 (d, Ar), 128.21 (d, Ar), 128.22 (d, Ar), 128.25 (d,

Ar), 128.27 (d, Ar), 128.29 (d, Ar), 128.31 (d, Ar), 128.33 (d, Ar),

128.35 (d, Ar), 128.36 (d, Ar), 128.40 (d, Ar), 128.46 (d, Ar), 129.69

(d, Ar), 129.71 (d, Ar), 129.73 (d, Ar), 129.74 (d, Ar), 133.08 (s, Ar),

133.09 (s, Ar), 133.17 (s, Ar), 133.22 (s, Ar), 135.49 (s, Ar), 135.50

(s, Ar), 135.52 (s, Ar), 135.53 (s, Ar), 137.35 (s, Ar), 137.46 (s, Ar),

137.47 (s, Ar), 137.49 (s, Ar), 137.54 (s, Ar), 137.56 (s, Ar), 137.63

(s, Ar), 137.65 (s, Ar), 137.67 (s, Ar), 137.72 (s, Ar), 137.75 (s, Ar),

137.88 (s, Ar), 137.90 (s, Ar), 137.94 (s, Ar), 137.96 (s, Ar), 138.06

(s, Ar), 138.07 (s, Ar), 138.20 (s, Ar), 138.22 (s, Ar), 138.22 (s, Ar),

138.28 (s, Ar), 169.61 (s, CdO), 169.64 (s, CdO); see also Table SI-1.

MALDI-TOF MS: [M þ Na]^þcalcd for C₄₄₇H₄₈₆O₉₁Si₄Na, 7444.24,

found 7444.78. Nano ESI FT-ICR mass: see Figure SI-1.

2,3-Di-O-benzyl-5-O-t-butyldiphenylsilyl-β-^D-arabinofuranosyl-(1f2)-

3,5-di-O-benzyl-R-^D-arabinofuranosyl-(1f5)-[2,3-di-O-benzyl-5-O-t-

butyldiphenylsilyl-β-^D-arabinofuranosyl-(1f2)-3,5-di-O-benzyl-R-D-

arabinofuranosyl]-(1f3)-2-O-benzyl-R-^D-arabinofuranosyl-(1f5)-

2,3-di-O-benzyl-R-^D-arabinofuranosyl-(1f5)-3-O-benzyl-1,2-O-iso-

propylidene-R-^D-arabinofuranose (4). To the solution of diol 55 (4.1 mg,

1.99 μmol) in dry DMF (0.5 mL) were added imidazole (2.1 mg, 25.7 mmol)

and t-butyldiphenylsilyl chloride (4.0 μL, 11.4 mmol) at room temperature,

and the mixture was stirred for 24 h at the same temperature. After being

quenched by saturated aqueous NaHCO₃, the product was extracted with

CHCl₃. Combined solution was washed with brine and dried over Na₂SO₄.

After filtration followed by concentration, the residue was purified by PTLC

(hexane-EtOAc = 5:1) to give the product 4 (4.5 mg, 89%).

2,3-Di-O-benzyl-5-O-t-butyldiphenylsilyl-β-^D-arabinofuranosyl⁽ⁱ¹⁾

(1f2)-3,5-di-O-benzyl-R-^D-arabinofuranosyl^(j1)-(1f5)-[2,3-di-O-benzyl-

5-O-t-butyldiphenylsilyl-β-^D-arabinofuranosyl^(m1)-(1f2)-3,5-di-O-benzyl-

R-^D-arabinofuranosyl^(k1)]-(1f3)-2-O-benzyl-R-D-arabinofuranosyl^(l1)

(1f5)-2,3-di-O-benzyl-R-^D-arabinofuranosyl^(h1)-(1f5)-2-O-acetyl-3-

O-benzyl-R-^D-arabinofuranosyl^(g1)-(1f5)-2,3-di-O-benzyl-R-D-arabi-

nofuranosyl^(e)-(1f5)-{2,3-di-O-benzyl-5-O-t-butyldiphenylsilyl-β-D-

arabinofuranosyl^(l2)-(1f2)-3,5-di-O-benzyl-R-D-arabinofuranosyl^(j2)

(1f5)-[2,3-di-O-benzyl-5-O-t-butyldiphenylsilyl-β-^D-arabinofuranosyl^(m2)

(1f2)-3,5-di-O-benzyl-R-^D-arabinofuranosyl^(k2)]-(1f3)-2-O-benzyl-

R-^D-arabinofuranosyl^(l2)-(1f5)-2,3-di-O-benzyl-R-D-arabinofuranosyl^(h2)

(1f5)-2-O-acetyl-3-O-benzyl-R-^D-arabinofuranosyl^(g1)-(1f5)-2,3-di-

O-benzyl-R-^D-arabinofuranosyl^(f)}-(1f3)-2-O-benzyl-R-D-arabinofu-

ranosyl^(d)-(1f5)-2,3-di-O-benzyl-R-D-arabinofuranosyl^(c3)-(1f5)-2,3-

di-O-benzyl-R-^D-arabinofuranosyl^(c2)-(1f5)-2,3-di-O-benzyl-R-D-ara-

binofuranosyl^(c1)-(1f5)-2,3-di-O-benzyl-R-D-arabinofuranosyl^(b)-(1f5)-

3-O-benzyl-1,2-O-isopropylidene-R-^D-arabinofuranose^(a)(56). To a

mixture of Araf₈acceptor 4 (2.5 mg, 1.1 μmol) and Araf₇donor 2 (6.2 mg,

2.3 μmol) in dry CH₂Cl₂(2 mL) was added MS4 Å (250 mg, freshly

dried) at room temperature. After being cooled to -40 °C, NIS (1.0 mg,

4.4 μmol) and AgOTf (1.0 mg, 3.9 μmol) were added to the mixture.

After being stirred for 3 d at the same temperature and 2 h at 0 °C, the

reaction was quenched by triethylamine and followed by filtration

through Celite pad and washing of pad with CHCl₃. The combined

solutions were washed with 20% aqueous Na₂S₂O₃, saturated aqueous

NaHCO₃, and brine, dried over Na₂SO₄, and concentrated in vacuo.

The residue was purified by gel filtration (Bio beads SX-1, toluene/ethyl

acetate = 1/1) to give the title compound Araf₂₂56 (7.6 mg, 96%). 56:

[R]²⁵_D50.0 (c 0.44, CHCl₃). ¹H NMR (CDCl₃, 600 MHz): δ 0.99 (s,

tBu ꢀ4, 36H), 1.32 (s, acetonide, 3H), 1.49 (s, acetonide, 3H), 1.81 (s,

Ac, 3H), 1.82 (s, Ac, 3H), 3.40-4.59 (m, 181H), 4.64 (d, J = 4.0 Hz,

C2-H^a, 1H), 4.65 (d, J = 12.1 Hz, Bn, 1H), 4.67 (d, J = 12.1 Hz, Bn,

β-^D-Arabinofuranosyl^(i1/2)-(1f2)-R-D-arabinofuranosyl^(g1/2)-(1f5)-

[β-^D-arabinofuranosyl^(j1/2)-(1f2)-R-D-arabinofuranosyl^(h1/2)]-(1f3)-R-

D-arabinofuranosyl^(f1/2)-(1f5)-R-D-arabinofuranosyl^(c)-(1f5)-R-D-ara-

binofuranosyl^(c)-(1f5)-R-D-arabinofuranosyl^(c)-(1f5)-{β-D-arabino-

furanosyl^(i1/2)-(1f2)-R-D-arabinofuranosyl^(g1/2)-(1f5)-[β-D-arabino-

furanosyl^(j1/2)-(1f2)-R-D-arabinofuranosyl^(h1/2)]-(1f3)-R-D-arabino-

furanosyl^(f1/2)-(1f5)-R-D-arabinofuranosyl^(c)-(1f5)-R-D-arabinofurano-

syl^(c)-(1f5)-R-D-arabinofuranosyl^(e)}-(1f3)-R-D-arabinofuranosyl^(d)

(1f5)-R-^D-arabinofuranosyl^(c)-(1f5)-R-D-arabinofuranosyl^(c)-(1f5)-

R-^D-arabinofuranosyl^(c)-(1f5)-R-D-arabinofuranosyl^(b)-(1f5)-1,2-

O-isopropylidene-R-^D-arabinofuranose^(a)(1). To a solution of pro-

tected Araf₂₂56 (12.0 mg, 1.62 μmol) in dry THF (2 mL) was added

TBAF (16.2 μL, 16.2 μmol) at room temperature. After being stirred for

18 h at the same temperature, the solvent was evaporated in vacuo. The

crude mixture in MeOH (2.0 mL), triethylamine (1.0 mL), and H₂O

(0.2 mL) was stirred for 24 h at room temperature. After evaporation,

the residue was purified by PTLC (toluene/EtOAc = 3:1) to give hexaol

58 (5.3 mg, 51% in two stps). Hydrogenolysis of resulting residue 58 was

carried out in the presence of Pd(OH)₂(6.0 mg) in EtOAc-

MeOH-H₂O (4:4:1, 9.0 mL) for 6 h at room temperature. After

further addition of Pd(OH)₂(6.0 mg) to the mixture under Ar atmo-

sphere, hydrogenolysis was continued for 24 h. The mixture was filtered

through Celite, and filtrate was concentrated in vacuo. The residue was

purified by gel filtration (Sephadex LH-20, MeOH-H₂O = 1/1) to give

1H), 4.90 (d, J = 4.5 Hz, C1-H^m2, C1-H^m2, 2H), 4.94 (s, C1-H^l1/l2

1H), 4.95 (s, C1-H^l1/l2, 1H), 5.01 (s, C1-H^b2, 1H), 5.02 (s, C1-Hⁱ¹,

C1-Hⁱ², 2H), 5.04 (d, J = 4.5 Hz, C1-H^l2, C1-H^l2, 2H), 5.06 (s,

C1-H^c3, 1H), 5.07 (s, C1-H^g2, C1-H^k1, C1-H^k2, 3H), 5.08 (s,

C1-H^d, C1-H^g1, C1-H^j1, C1-H^j2, 4H), 5.09 (s, C1-H^c2, 1H), 5.10

(s, C1-H^c1, 1H), 5.13 (s, C1-H^f, 1H), 5.14 (s, C1-H^e, C2-H^g1, 2H),

5.15 (s, C2-H^g2, 1H), 5.88 (d, J = 4.0 Hz, C1-H^a, 1H), 7.69-7.60 (m,

Ar, 230H); see also Table SI-1. ¹³C NMR (CDCl₃, 125 MHz): δ 19.2 (s,

tBu), 20.7 (q, Ac), 20.8 (q, Ac), 26.4 (q, acetonide), 26.8 (q, tBu), 27.2

(q, acetonide), 65.1 (t), 65.3 (t, ꢀ2), 65.5 (t), 65.6 (t, ꢀ2), 65.8 (t),

65.86 (t, ꢀ2), 65.88 (t, ꢀ2), 66.0 (t), 66.1 (t, ꢀ2), 66.2 (t, ꢀ3), 66.8 (t),

66.9 (t, ꢀ2), 70.1 (t, ꢀ2), 71.6 (t, Bn), 71.7 (t, ꢀ2, Bn), 71.76 (t, ꢀ2,

Bn), 71.78 (t, Bn), 71.80 (t, ꢀ2, Bn), 71.84 (t, Bn), 71.9 (t, ꢀ2, Bn),

71.98 (t, ꢀ3, Bn), 72.03 (t, ꢀ2, Bn), 72.04 (t, ꢀ3, Bn), 72.1 (t, ꢀ2, Bn),

72.17 (t, ꢀ3, Bn), 72.20 (t, ꢀ3, Bn), 72.21 (t, ꢀ2, Bn), 72.24 (t, ꢀ2, Bn),

72.26 (t, ꢀ3, Bn), 72.33 (t, Bn), 72.35 (t, Bn), 73.09 (t, ꢀ2, Bn), 73.14

the title compound Araf₂₂1 (1.3 mg, 93%). 1, H NMR (D₂O, 800

MHz): δ 1.27 (s, acetonide, 3H), 1.48 (s, acetonide, 3H), 3.68-4.31 (m,

C2-5-H, 109H), 4.63 (d, J = 4.0 Hz, C2-H^a, 1H), 4.96 (s, C1-H^b,

1H), 4.97-5.00 (br s, C1-H^c, 8H), 5.02 (s, C1-H^d, C1-H^f, 3H), 5.15

(d, J = 4.0 Hz, C1β-H^j, 2H), 5.16 (d, J = 4.0 Hz, C1 β-Hⁱ, 2H), 5.178 (s,

C1-H^e, 1H), 5.1875 (s, C1-H^g, 1H), 5.1858 (s, C1-H^g, 1H), 5.256 (s,

C1-H^h, 1H), 5.258 (s, C1-H^h, 1H), 6.06 (d, J = 4.0 Hz, C1-H^a, 1H);

see also Table SI-2. ¹³C NMR (D₂O, 125 MHz): δ 25.1 (q, acetonide),

25.8 (q, acetonide), 60.6 (t), 62.99 (t), 63.04 (t), 66.3 (t), 66.5 (t), 66.7

(t), 66.8 (t), 66.9 (t), 67.2 (t), 74.17 (d), 74.23 (d), 74.76 (d), 74.81 (d),

2289

dx.doi.org/10.1021/ja109932t |J. Am. Chem. Soc. 2011, 133, 2275–2291

Journal of the American Chemical Society

ARTICLE

74.9 (d), 76.3 (d), 76.6 (d), 76.79 (d), 76.83 (d), 77.0 (d), 79.1 (d), 79.2

(d), 80.88 (d), 80.92 (d), 80.94 (d), 81.1 (d), 81.2 (d), 82.1 (d), 82.23

(d), 82.26 (d), 82.36 (d), 82.40 (d), 82.42 (d), 82.46 (d), 82.56 (d), 82.9

(d), 83.0 (d), 86.0 (d), 86.1 (d), 86.9 (d), 100.7 (d, C1^jꢀ2), 100.8 (d,

C1ⁱꢀ2), 105.5 (d, C1^a), 105.6 (d, C1^jꢀ2), 105.7 (d, C1^gꢀ2), 107.2 (d,

C1^e), 107.48 (d, C1^d, C1^fꢀ2), 107.54 (d, C1^b), 107.6 (d, C1^cꢀ8),

113.53 (s, acetonide); see also Table SI-2. MALDI-TOF MS: [M þ

Na]^þcalcd for C₁₁₃H₁₈₂O₈₉Na, 2985.96, found 2985.63.

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Supporting Information. Complete ref 36a, lists of ¹H

and ¹³C NMR data of 56 and 1, experimental procedures and

characterization data for the preparation of trisaccharides

11-13 in Scheme 1, and of substrates 7, 43-45 in Table 1,

and ¹H and ¹³C NMR spectra of all new key compounds. This

material is available free of charge via the Internet at http://

pubs.acs.org.

’ AUTHOR INFORMATION

Corresponding Author

aishiwa@riken.jp; yukito@riken.jp

(14) Fraser-Reid, B.; Jayaprakash, J. L. K. N.; Lꢀopez, J. C. Tetra-

hedron: Asymmetry 2006, 17, 2449–2463.

(15) Joe, M.; Bai, Y.; Nacario, R. C.; Lowary, T. L. J. Am. Chem. Soc.

2007, 129, 9885–9901.

’ ACKNOWLEDGMENT

We thank Dr. Hiroyuki Koshino for 600 MHz NMR,

Dr. Mayumi Yoshida and Dr. Chihiro Kurosaki for 800 MHz

NMR, and Dr. Takemichi Nakamura for nano ESI FT-ICR mass

measurements, and Ms. Akemi Takahashi and Ms. Satoko

Shirahata for technical assistance. This work was partly sup-

ported by a Grant-in-Aid for Scientiﬁc Research from the

Ministry of Education, Culture, Sports, Science, and Technology

(no. 22510243), and by an Incentive Research Grant (2009) and

Fund for Collaborative Research (2010) in RIKEN.

(16) In general, a secondary alcohol is less reactive than a primary

alcohol. Also, on the basis of our preliminary result of fragment coupling

of an Araf₇donor like 2 with 3,5-diol trisaccharide acceptor 11 giving

mainly monoglycosylated product (Araf₁₀63%) concomitant with a

desired Araf₁₇(29%), we designed so as to conduct all fragment

couplings at linear sequences.

(17) For recent examples for fragment coupling using thioglycoside

of a branched trisaccharide, see: Pragani, R.; Seeberger, P. H. J. Am.

Chem. Soc. 2011, 133, 102–107.

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(19) Callam, C. S.; Gadikota, R. R.; Krein, D. M.; Lowary, T. L. J. Am.

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