Rate-dependent inverse-addition β-selective mannosylation and contiguous sequential glycosylation involving β-mannosidic bond formation

Article abstract of DOI:10.1002/asia.200900765

The β-selectivity of mannosy-lation has been found to be dependent on the addition rate of the mannosyl trichloroacetimidate donor in an inverse-addition (I-A) procedure. This rate dependent I-A procedure can improve the selectivity of direct β-mannosylat

Full text of DOI:10.1002/asia.200900765

FULL PAPERS
DOI: 10.1002/asia.200900765
Rate-Dependent Inverse-Addition b-Selective Mannosylation and
Contiguous Sequential Glycosylation Involving b-Mannosidic Bond
Formation
Shih-Sheng Chang, Che-Hao Shih, Kwun-Cheng Lai, and Kwok-Kong Tony Mong*[a]
Dedicated to Professor Tse-Lok Chan at CUHK on the occasion of his 70th birthday
Abstract: The b-selectivity of mannosy-
lation has been found to be dependent
on the addition rate of the mannosyl
trichloroacetimidate donor in an in-
verse-addition (I-A) procedure. This
rate dependent I-A procedure can im-
prove the selectivity of direct b-manno-
sylation and is applicable to orthogonal
glycosylations of thioglycoside accept-
ors. Further elaboration of this novel
procedure enables the development of
the contiguous sequential glycosylation
strategy, which streamlines the prepa-
ration of oligosaccharides invoking b-
mannosidic bond formation. The syn-
thetic utility of the contiguous glycosy-
lation strategy was demonstrated by
the preparation of the trisaccharide
core of human N-linked glycoproteins
and the trisaccharide repeating unit of
the O-specific polysaccharide found in
the cellular capsule of Salmonelle bac-
teria.
Keywords: glycosylation
· inverse
addition · mannosylation · oligosac-
charides · b-selectivity
Introduction
such a solid-phase process would be prohibitively expensive.
Moreover, particular solid-phase b-selective mannosylations
suffer from drawbacks stemming from their innate chemis-
try. For example, the acetal linkage connecting the mannosyl
donor and the support is cleaved in the intramolecular agly-
con delivery (IAD) mannosylations.[5a] On some occasions,
the b-selectivities of solid-supported mannosylation de-
creased to some extent.[5b]
Regarding the frontiers in solution-phase synthesis, the in-
corporation of b-selective mannosylation to sequential gly-
coyslation is well-recognized as a challenging task despite
the recent advances in glycosylation technologies.[3] Reports
concerning the use of contiguous sequential glycosylation
that invoke b-mannosidic bond formation remain scarce. In
most scenarios, a disaccharide bearing a b-mannosidic bond
is prepared first, which upon chromatographic purification
and modification of the anomeric function is engaged in
subsequent glycosylation.[6–10] This stepwise process is
lengthy and inefficient. Given the frequent occurrence of
The chemical synthesis of oligosaccharides is labor intensive
because it demands the preparation of monosaccharide
building blocks and the coupling of these building blocks in
a stereospecific manner.[1] Although various technologies
have been developed to expedite these processes,[2–4] there
remain no universal methods applicable to all oligosacchar-
ide structures. This is best illustrated by the synthesis of oli-
gosaccharides involving b-mannosidic bond formation. In
past decades, a few reports in the literature have investigat-
ed the construction of the b-mannosidic bond on solid sup-
port or the use of solid-phase synthesizers for the prepara-
tion of these oligosaccharide targets.[5] However, in the
solid-phase synthesis, a large excess of glycosyl substrate is
required to achieve quantitative conversion. Since glycosyl
substrates are generally prepared by multiple-step synthesis,
[a] S.-S. Chang, C.-H. Shih, K.-C. Lai, K.-K. T. Mong
Department of Applied Chemistry
National Chiao Tung University
Taiwan, ROC
oligosaccharides with
a b-mannosidic linkage and the
demand of homogeneous samples for interdisciplinary stud-
ies, developing a straightforward synthetic strategy for such
oligosaccharide targets is an urgent and necessary task.[11]
In the light of the discussion above, this paper reports for
the first time a rate-dependent inverse-addition b-mannosy-
lation with the use of an easily available mannosyl tri-
1001, Ta Hsueh Road, Hsinchu, Taiwan, 300 (Taiwan)
Fax : (+886)3572-3764
E-mail: tmong@mail.nctu.edu.tw
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.200900765.
1152
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Chem. Asian J. 2010, 5, 1152 – 1162

ACHTUNGTRENNUNGchloroacetimidate donor and its elaboration to orthogonal
glycosylations. This orthogonal glycosylation method is fur-
ther exploited in the development of the contiguous sequen-
tial glycosylation strategy, which has been found to be useful
for the preparation of the trisaccharide core of human N-
linked glycoproteins[12] and the repeating unit of the O-spe-
cific polysaccharide found in Salmonella anatum.[13]
Results and Discussion
Rate-dependent inverse-addition b-selective mannosylation:
In a project relating to the synthesis of oligosaccharides of
human N-linked glycoproteins, the synthesis of a trisacchar-
ide, namely, Man-b
quired.[12] This trisaccharide is composed of three monosac-
charides that are joined by Man-b
(1!4)-GlcNAc and
GlcNAc-b
hindered positions, the chemical constructions of these gly-
cosidic linkages are difficult. Though numerous attempts
that have targeted the preparation of this structure have
been reported, there is still the lack of a straightforward gly-
cosylation strategy.[14,15] To tackle this challenge, an efficient
N
R
Scheme 1. The inverse-addition (I-A) protocol for the glycosylation of
GlcNAc acceptor 2 with mannopyranosyl trichloroacetimidate 1. PMB=
p-methoxy benzyl; Troc=trichloroethoxycarbonyl.
AHCTUNGTRENNUNG
G
Concerning the glycosylation procedure in Man-b
N
GlcNAc glycosidic bond formation, both inverse addi-
tion[16b,17d] and conventional procedures have been exploite-
d.[16e,17h,i,l] In the conventional procedure, TMSOTf promoter
is added to a mixture of mannosyl donor and GlcNAc ac-
ceptor. In the I-A procedure, mannosyl donor is added to a
mixture of TMSOTf promoter and GlcNAc acceptor. A
search in the literature reveals that the I-A procedure is pri-
marily designed for suppression of undesired side reactions
in glycosylations when highly reactive glycosyl trichoroaceti-
midate donor is employed.[25] We speculated that the
manner of donor addition might have some bearing on the
b-selectivity of mannosylation. To attest this speculation,
both the conventional and I-A procedures were used for gly-
cosylations of GlcNAc acceptor 2 with mannsoyl trichoro-
acetimidate 1 (Scheme 1, Table 1). For the donor addition
rate used in the I-A procedure, 0.25m of mannosyl donor 1
was added to 50 mm of glycosyl acceptor 2 in CH2Cl2 over a
period of 5, 15, or 30 min, which was corresponded to the
donor addition rates of 0.2, 0.07, or 0.035 mLminꢀ1.[26]
glycosylation method for the formation of the Man-b
N
GlcNAc glycosidic bond is required. In this regard, we
sought to use the direct b-selective mannosylation approach
rather than the indirect one because the former approach
does not involve additional synthetic steps.[16–18] Among dif-
ferent mannosyl donors that have been explored in b-man-
nosylations, the mannosyl trichloroacetimidate donor is pre-
ferred because the imidate donor can be activated by a cata-
lytic amount of Lewis acid, such as trimethylsilyl trifluoro-
methanesulfonate (TMSOTf).[19] This catalytic reaction is
beneficial to the development of a sequential glycosylation
strategy as it presumably results in a less complex reaction
mixture.[20] Thus, 4,6-O-benzylidene mannosyl trichloroaceti-
midate 1 was prepared (Scheme 1).[17b,d,e,21] For the GlcNAc
acceptor, 2-deoxy-2-trichloroethoxycarbonyl thioglucopyra-
noside 2 was selected for its simpler preparation. The C-2
carbamate protecting function in 2 would guide the forma-
The conventional glycosylation of GlcNAc acceptor 2
with 1 produced the expected disaccharide 3 in 48% yield
with a 1:2 a/b-anomeric ratio along with approximately
20% aglycon transfer product 4 (Table 1, entry 1).[27] Grate-
tion of the GlcNAc-b
G
neighboring-group participation.[22,23,24] Furthermore, the
anomeric thioacetal function of 2 is stable to the activation
conditions for the mannosyl donor; if needed, this thioacetal
function can be readily activated by a suitable thiophilic re-
agent.[22]
Table 1. Glycosylations of GlcNAc acceptor 2 with mannosyl trichloro-
acetimidate 1 by the conventional and inverse-addition procedures.
Entry Addition rate of 0.25m
Yield 3 a/b
[%]
Yield 4 Yield 5
of 1 [mLminꢀ1
]
ratio[a] of [%]
[%]
3
Abstract in Chinese:
1
2
3
4
conventional
0.20[b]
0.07
48
65
47
40
1:2
20
5
0
5
1:9.5
1:5.2
1:4.5
5
10
10
10
0.035
[a] a/b-Anomeric ratios were determined by HPLC analysis (Hitachi
HPLC system: L-2300 pump, L-2400 UV-detector; Mightysil normal
phase Si 4.6-250 column; mobile phase: CH2Cl2/hexane/EtOAc gradient
from 10:75:15 to 10:70:20 at a flow rate of 0.8 mLminꢀ1). [b] This partic-
ular reaction was repeated twice for validation.
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Table 2. Conventional and I-A mannosylations of glycosyl acceptors 7, 8, and 9 with mannosyl trichloroaceti-
midate 6.
fully, this aglycon transfer prod-
uct was reduced when the I-A
mannosylation procedure was
applied (column 4). More sig-
nificantly, a higher b-selectivity
was observed in the I-A man-
nosylations, and such selectivity
was found to be dependent on
the addition rate of mannosyl
donor 1. For instance, at the
Entry Donor addition rate of Acceptor Product (yield [%]) a/b ratio[a] Reported a/b ratios
0.25m of 6 [mLminꢀ1
]
in the literature
1
2
3
4
5
6
7
8
conventional
0.26
0.07
conventional
0.46
0.14
7
7
7
8
8
8
9
8
10 (88)
10 (90)
10 (85)
11 (85)
11 (92)
11 (87)
12 (87)
11 (50)
1:2
1:10
1:8
for 10, 1:9 to 1:16[17c,g,k]
1:2
for 11, 1:2 to 1:5.0[17a,d,j,k]
for 12, 1:10[17k]
1:2.3
1:2.3
1:>15[b]
2:1[c]
0.26
conventional
donor
addition
rate
of
0.2 mLminꢀ1, the disaccharide 3
was produced in 65% yield
with a 1:9.5 a/b-anomeric ratio
(entry 2), but this selectivity de-
clined to some degree at slower
[a] a/b-Anomeric ratios were determined by HPLC analysis. [b] In practice, no a-anomer was detected on the
base of NMR spectroscopy, and the ratio of 1:>15 was a conservative minimum. [c] BF3·Et2O (1 molequiv
with respect to the donor) was used for activation of 6.
donor 6 was employed instead of 1 for the reason of its sim-
donor additions (0.07 and 0.035 mLminꢀ1; Table 1, entries 3
and 4). A minor drawback of the present I-A mannosyla-
tions was the formation of approximately 5–10% N-(b-man-
nosyl) trichloroacetamide 5 (column 5).[28] One possible so-
lution to eliminate amide product formation is to use the
mannosyl (N-phenyl) trifluoroacetimidate donor.[17h,i,l] How-
ever, the synthesis of such a mannosyl donor requires the
use of unstable N-phenyl trifluoroacetimidoyl chloride,
which is not commercially available.[29] Nevertheless, the
amide byproduct 5 does not interfere with the development
of a sequential glycosylation strategy. Thus, this study select-
ed the easily accessible mannosyl trichloroacetimidate as the
donor for subsequent glycosylations after the trade-off be-
tween the preparatory convenience and optimization of the
glycosylation yield.
pler preparation. For the glycosylation of acceptor 7 with
mannosyl donor 6, the I-A procedure furnished a higher b-
selectivity than that given by the conventional procedure
(Table 2, entries 1–3). However, the improvement of b-selec-
tivity was less pronounced in the glycosylations of diisopro-
pylidene acetal protected galactopyranosyl acceptor 8 (en-
tries 4–6). A search in literature revealed that the b-manno-
sylations of the galactopyranosyl acceptor 8 often result in
modest b-selectivities to other glycosyl acceptors.[17k,31] This
peculiar result may be due to a mismatched interaction be-
tween the mannosyl donor 6 and galactopyranosyl acceptor
8 in the transition state leading to b-anomer formation.[32]
Another possible explanation is the erosion in selectivity of
b-mannosylation when a highly reactive acceptor is employ-
ed.[17d,j,k] To clarify the exact cause, methyl 2,3,4-tri-O benzyl
glucopyranoside 9, which bears a C-6 hydroxyl function, was
prepared and used as a reactive acceptor for glycosylation
with mannosyl donor 6. Remarkably, the glycosylation pro-
duced the desired disaccharide 12 with excellent b-selectivi-
ty (entry 7). The experimental result is in line with the ex-
planation of mismatching interactions.
Guided by the results of the foregoing glycosylations, we
extended the scope of this study to mannosylations of glyco-
syl acceptors 7, 8, and 9 with mannosyl trichloroacetimidate
donor 6 (Table 2).[30] It should be noted that the mannosyl
Since TMSOTf and BF3·Et2O are widely used as promot-
ers for the activation of trichloroacetimidate donors, it is
reasonable to question if BF3·Et2O could also be used in the
present mannosylation context.[33] To answer this quest, the
glycosylation of acceptor 8 with donor 6 was repeated with
the conventional procedure by using BF3·Et2O as the pro-
moter. In sharp contrast, this change of promoter reversed
the selectivity of mannosylation and a 2:1 a/b-anomeric mix-
ture of 11 was obtained (Table 2, entry 8). It should be
noted that the loss of b-selectivity in the absence of triflate-
based promoters has also been reported by other studie-
s.[16e,17k,34] A possible explanation is that when TMSOTf was
used, the counter anion of the mannosyl oxocarbenium ion
was the triflate anion and thus the two ions quickly coupled
to generate the covalent a-mannosyl triflate. This a-manno-
syl triflate would follow an SN2-like pathway and produce
the b-mannoside. On the other hand, when BF3·OEt2 was
used, the mannosyl oxocarbenium ion would directly react
with the acceptor to give the a-mannoside as the major
product.[35]
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b-Mannosidic Bond Formation
Orthogonal b-mannosylation: After establishing the rate-de-
pendent I-A mannosylation procedure, we proceeded to
apply the procedure to orthogonal glycosylations. Thus, thio-
glycosides 13–17a were synthesized and used as glycosyl ac-
ceptors for glycosylation with mannosyl donor 6 (Table 3).[36]
The synthesis of 17a employed a modified procedure,
which, therefore, deserved some elaboration (Scheme 2).
Scheme 2. Reagents and conditions: a) i)azido-sulfonyl imidazolium chlo-
ride, Et3N, cat. CuSO4, MeOH, RT; ii)Ac2O, py. CH2Cl2, RT; iii)thiocre-
sol, BF3·Et2O, CH2Cl2, RT, 2 days, 60% 3 steps; b) i)Na (s), MeOH/
CH2Cl2, RT, 90%; ii)C6H5CHACHTNUTRGNEUNG(OMe)2, cat. TsOH, CH3CN; iii)benzyl bro-
mide, NaH, DMF, 08C–RT; 84% over 2 steps; c) Et3SiH, TFA, CH2Cl2,
ꢀ158C, 80%. py=pyridine.
thioglycosides 17a and 17b could be separated by standard
chromatography.
With thioglycoside acceptors 13–17a and mannosyl donor
6 in hand, the stage was set for studying the orthogonal gly-
cosylations. With the exception of thioglycoside 15, all the
examined glycosylations furnished the expected disaccharide
thioglycosides 18, 19, 21, and 22 in 60–90% yields with ex-
cellent b-selectivities (1:>15 a/b). In practice, no a-anomers
were isolated by chromatographic purification (Table 3, en-
tries 1, 2, 4, and 5). To our delight, the aglycon transfer side
reaction was not significant, which may probably be attribut-
ed to the relatively mild promoting conditions used. Howev-
er for the glycosylation of deoxy thioglycoside 15, aglycon
transfer-product 20 was obtained in the majority. This pecu-
liar phenomenon can be explained by the higher reactivity
of the deoxy glycosyl substrate, which accelerates the agly-
con transfer reaction (Table 3, entry 3).[20d,27] Nevertheless,
the adverse reaction was rectified by using a bulky thioace-
tal function in the thioglycoside acceptor, which was illus-
trated by the glycosylation of thioglycoside 16 (Table 3,
entry 4).
Glucosamine hydrogen chloride was first converted to the
glucosamine azido derivative by a recently reported diazo
transfer reaction.[37] Acetylation and thioglycosidation of the
crude azido derivative produced the peracetyl GlcNAc thio-
glycoside 23. Followed by standard protecting-group manip-
ulations, the GlcNAc thioglycoside 23 was converted to a-
and b-thioglycosides 17a and 17b via intermediate 24. The
Since disaccharides 3, 18,[9c] 19,[9a] 21, and 22 are potential
glycosyl donors, it is necessary to confirm their structures
for future applications. Thus, all these disaccharides were
rigorously characterized by NMR spectroscopy and selected
characteristic data are depicted in Table 4. The b-configura-
tions of the mannosidic linkages in disaccharides 3, 18, 19,
21, and 22 are evidenced by 1) the 13C chemical shifts of C-
1’, which lie between d=98.1 and 102.4 ppm (Table 4,
Table 3. Results of orthogonal b-mannosylations with the rate dependent
I-A procedure.
1
column 3), 2) the H chemical shifts of H-1’, which lie be-
1
tween d=4.08 and 5.06 ppm (column 5), and 3) the JCH cou-
Entry Thioglycoside
acceptor
Glycosylation product
(yield [%])
Yield 20 a/b
[%]
ratio[a]
pling constants, which span from 153 to 159 Hz
(column 3).[38]
1
2
3
4
5
13
14
15
16
18 (75)
19 (70)
–
21 (90)
22 (60)
<5
<5
80
–
<5
1:>15
1:>15
–
[b]
Development of contiguous sequential glycosylation: En-
couraged by the results of the orthogonal glycosylations, this
1:>15
17a
1:>15[c]
study resumed the synthesis of the Man-b
G
[a] No a-anomers were detected based on NMR spectroscopy of the
crude chromatography products and ratios of 1:>15 were based on con-
servative estimate. [b] Predominant formation of a-thiomannopyranoside
was observed. [c] This particular glycosylation has been repeated twice
for validation.
(1!4)-GlcNAc trisaccharide (Schemes 3 and 4). As a model
study, a stepwise glycosylation approach was examined to
test the suitability of the GlcNAc glycoside 25 as an accept-
or. The GlcNAc glycoside 25 was prepared from glycosyla-
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K.-K. T. Mong et al.
FULL PAPERS
1
Table 4. Selected NMR spectroscopic chemical shifts and JCH coupling constants of the disaccharide thiogly-
cosides 3, 18, 19, 21, and 22.
GlcNAc acceptor 2 was glyco-
sylated with mannosyl donor 1
by the rate-dependent I-A pro-
1
1
Entry Disaccharide thiogly- d [ppm] and JCH [Hz]
d [ppm] and JCH [Hz]
of C-1’
d [ppm] of
H-1
d [ppm] of
H-1’
coside
of C-1
cedure to furnish Man-b
N
1
2
3
4
5
6
a-anomer 3
b-anomer 3
18
19
21
22
86.5, 158.4
87.3, 158.4
86.6, 164
86.1, 167
84.9, 165
87.5, 167
100.7, 167
102.4, 159
100.8, 153
98.1, 158
100.4, 158
101.1, 157
4.58
–
5.47
5.56
5.47
5.49
5.01
4.52
4.65
4.08[b]
5.06
4.36
GlcNAc disaccharide 3. The
crude thioglycoside 3 obtained
upon standard workup was
used directly as a donor for gly-
cosylation of GlcNAc glycoside
25 to produce trisaccharide 26.
Subsequent removal of the ben-
zylidene acetal function of 26
[a]
[a] H-1 anomeric proton of the b-anomer of 3 was obscured by the benzylic protons, but its presence was clear-
ly implicated by noting the cross-peak in the H–13C HMQC spectrum. [b] This upfield anomeric H signal was
1
1
1
confirmed by the H–13C HMQC spectrum.
Scheme 3. Synthesis of GlcNAc glycoside 25 by the low substrate concen-
tration b-selective glycosylation.
Scheme 5. Reagents and conditions: a) cat. TMSOTf, CH2Cl2, 4 ꢁ MS,
ꢀ508C, addition of 0.25m of 1 at 0.2 mLminꢀ1; b) cat. TMSOTf, NIS,
CH2Cl2, 4 ꢁ MS, 08C–RT, 16 h; c) 90% AcOH/H2O, 70 8C, 1 h, 40%
over a to c.
produced the target trisaccharide 27 in 40% yield as the
sole isolable isomer.
The synthetic utility of the foregoing contiguous sequen-
tial glycosylation was further exploited in the preparation of
Man-b
N
U
thesis of this trisaccharide target employed a stepwise glyco-
sylation approach.[7,39] We envisaged that the application of
the contiguous glycosylation strategy should simplify the
synthetic endeavor (Scheme 6). Thus, thiorhamopyranoside
16 was glycosylated with mannosyl trichloroacetimidate 6 to
produce disaccharide thioglycoside 19. The crude disacchar-
ide 19 obtained from standard workup was directly coupled
with the galactopyranoside acceptor 28 to furnish the de-
Scheme 4. Stepwise synthesis of the protected trisaccharide core of N-
linked glycoproteins 26 and 27.
tion of 3-chloropropanol with GlcNAc thioglycoside 17 by
the low substrate concentration b-selective glycosylation
(Scheme 3).[36c] Subsequent glycosylation of the GlcNAc gly-
coside 25 with the b-anomer of disaccharide thioglycoside 3
produced the expected trisaccharide 26 (Scheme 4). To sim-
plify the purification process, the benzylidene acetal func-
tion in trisaccharide 26 was removed to give trisaccharide
diol 27. The b-configurations of the anomeric centers in 27
are evidenced by 1) the 13C chemical shifts at d=102.5,
1
101.2, and 101.1 ppm and 2) the corresponding JCH coupling
constants of 158.2, 158.6, and 160.8 Hz.[38]
After proving the utility of GlcNAc glycoside 25 as an ac-
ceptor, the stage was mature for developing the contiguous
sequential glycosylation strategy, which skipped the need for
isolating the disaccharide intermediate 3 (Scheme 5). Thus,
Scheme 6. Reagents and conditions: a) cat. TMSOTf, CH2Cl2, 4 ꢁ MS,
ꢀ508C, 10 min, addition of 0.25m of 6 at 0.4 mLminꢀ1; b) cat. TMSOTf,
NIS, CH2Cl2, 4 ꢁ MS, ꢀ20 to 08C, 30 min; 70% over a and b.
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b-Mannosidic Bond Formation
sired trisaccharide 29 as the single isolable isomer in a high
70% yield.[40] The configurations of the anomeric centers in
trisaccharide 29 are evidenced by 1) the 13C chemical shifts
at d=104.0, 100.6, and 100.5 ppm and 2) the corresponding
1JCH coupling constants of 156.5, 157.5, and 167.9 Hz.[38]
or was added to the reaction mixture several minutes after
the donor was completely activated by the promoter.17a,17e It
is believed that such a preactivation approach allows the
quantitative conversion of the oxocarbenium ion to the a-
mannosyl triflate before charging the acceptor to the reac-
tion mixture. Thus, both the present rate-dependent I-A ap-
proach and previous preactivation approach enhance the b-
selectivity by avoiding the accumulation of the mannosyl ox-
ocarbenium ions. Regarding the decline of b-selectivity in
slower donor additions, we are unable to give an explana-
tion at the present stage and further investigations along
this line are being undertaken.
Mechanistic discussion: Based on experimental observations
and literature review, we propose a mechanistic model to ac-
count for the observations in this study (Scheme 7).[16b,17,41,42]
At first, the mannosyl trichloroacetimidate is activated by
TMSOTf to produce free oxocarbenium and triflate ions.
Conclusions
This study describes for the first time the rate-dependent in-
verse-addition procedure. This procedure improves the se-
lectivity of direct b-mannosylations with the use of an easily
accessible mannosyl trichloroacetimidate donor. Further
elaboration of this procedure leads to the incorporation of
b-mannosidic bond formation to a contiguous sequential gly-
cosylation strategy, which streamlines the preparation of oli-
gosaccharides bearing b-mannosidic linkages. The synthetic
utility of this glycosylation strategy was demonstrated by the
synthesis of the trisaccharide core of human N-linked glyco-
proteins and the trisaccharide repeating units of O-specific
polysaccharide in the cellular capsule of Salmonella bacte-
ria. Owing to the frequent occurrence of natural oligosac-
charides with b-mannosidic linkages and their biological
relevance, the proposed method should prove useful in their
preparation.
Experimental Section
Scheme 7. Proposed mechanism for the rate-dependent I-A b-selective
mannosylation.
General: Chemicals employed in this study were purchased as ACS read-
ent grande from loval commercial vendors and used without further pu-
rification. CH2Cl2 (Mallinckrodt), MeOH, and CH3CN (J. T. Baker) were
distilled over calcium hydride before use. Addition rates of mannosyl
donor were controlled by KSD 101 syringe pump. Chemical reactions
were monitored by thin layer chromatography (TLC) on a silca gel F-254
plate (Merck). Compounds on the TLC plate were visualized with UV il-
lumination (254 nm) and/or by staining with p-anisaldehyde staining re-
These ions are coupled to each other and generate a series
of glycosyl intermediates, namely, closed-contact ion pairs
(CCIPs), solvent-separated ion pairs (SSIPs), and a-manno-
syl triflate, which are engaged in a complex equilibrium net-
work. Each of these intermediates can react with the nucleo-
philic acceptor to furnish the glycosylation product through
either the SN1- or SN2-like pathway. The former reaction
pathway leads to the formation of a- and b-anomers, where-
as the latter pathway furnishes the b-anomeric product.
When these coupling reactions are complete, a proton is re-
leased and recycled to activate other trichloroacetimidate
donors. It is reasoned that the optimized rate-dependent I-A
protocol results in a low concentration of free oxocarbenium
ions. Under these conditions, the SN1-like reaction pathway
is suppressed, thus reducing the formation of the undesired
a-anomer.
agent. Optical rotations of new compounds were acquired using
a
JASCO DIP-1000 polarimeter at RT. Chromatographic purification was
performed on either 70–230 or 230–400 mesh size silca gel (Merck). Elu-
tion of 230–499 mesh size silica gel was achieved by medium pressure
liquid chromatography (MPLC) (Buchi 688 pump). 1H NMR spectra
were recorded by 300 or 500 MHz spectrometers (13C NMR spectra by 75
or 125 MHz spectrometers), which are either configured in the Bruker or
Varian console as specified. Chemical shifts are calibrated against the re-
sidual 1H resonance signal and 13C resonance signal of the deuterated sol-
vent used. Coupling constants measured in hertz (Hz) were derived from
the difference of chemical shifts in the 1H NMR spectra. a/b-Anomeric
ratiosAnomeric ratios of glycosylation products were determined either
by HPLC or NMR analysis of the isolated products. HPLC analysis was
performed by 1) Hitachi L-2130 gradient pump and L-2400 UV/Vis de-
tector; and 2) Mightysil Si 260-4.6 normal phase column.
Rate-dependent inverse-addition procedure for disaccharide 3 and its
side products 4 and 5: A mixture of GlcNAc thioglycoside 2[23] (100 mg,
0.17 mmol) and activated 4 ꢁ molecular sieves (MS; AW300) (500 mg) in
In hindsight, in earlier 4,6-O-benzylidene-directed b-man-
nosylations, the b-selectivity was enhanced when the accept-
Chem. Asian J. 2010, 5, 1152 – 1162
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
1157

K.-K. T. Mong et al.
FULL PAPERS
CH2Cl2 (3.5 mL) was stirred at ꢀ508C for 10 min under N2, followed by
the addition of TMSOTf (5.0 mL, 0.026 mmol). A solution of mannosyl
trichloroacetimidate 1 (158 mg, 0.25 mmol) in CH2Cl2 (1 mL, 0.25m) was
added at 0.20, 0.07, or 0.035 mLminꢀ1 (by KDS100 syringe pump) to the
reaction mixture. Upon completion of the reaction as judged by TLC, (Rf
of 3=0.22; EtOAc/hexane 1:4), a few drops of Et3N were added to
quench the reaction, which was followed by the removal of the MS by fil-
tration over Celite. The resulting filtrate was concentrated for purifica-
tion by MPLC over 230–400 mesh silica gel (EtOAc/hexane 1:4) to fur-
nish tolyl 2-O-benzyl-4,6-O-benzylidene-3-O-p-methoxy-benzyl-b-d-man-
nopyranosyl-(1!4)-3-O-acetyl-6-O-benzyl-2-deoxy-2-trichloroethoxycar-
bonyl-1-thio-b- d-glucopyranoside (3) (118 mg, 65%, a/b 1:9.5), tolyl 2-
O-benzyl-4,6-O-benzylidene-3-O-p-methoxybenzyl-1-thio-a-d-mannopyr-
anoside (4) as a colorless syrup (6 mg, 5%), and N-(2-O-benzyl-4,6-O-
benzylidene-3-O-p-methoxybenzyl-1-b-d-mannopyranosyl) trichloroace-
tamide (5) as a colorless syrup (10 mg, 10%). The a/b-anomeric ratio of
3 was determined by HPLC analysis (Hitachi HPLC system: L-2300
pump, L-2400 UV-detector and Mightysil Si 60 250–4.6 normal phase
column; mobile phase: CH2Cl2/hexane/EtOAc, elution gradient from
10:75:15 to 10:70:20 at a flow rate of 0.8 mLminꢀ1).
For the b-anomer of 3: Rf =0.22 (EtOAc/hexane 1:4); [a]2D7 =ꢀ30.7 (c=
0.63 in CHCl3); 1H NMR (500 MHz, CDCl3): d=7.50 (d, J=7.2 Hz, 2H;
ArH), 7.44 (d, J=7.8 Hz, 2H; ArH), 7.42–7.22 (m, 15H; ArH), 7.09 (d,
J=7.9 Hz, 2H; ArH), 6.86 (d, J=8.3 Hz, 2H; ArH), 5.58 (s, 1H; benzyli-
dene-CH), 5.35 (d, J=9.3 Hz, 1H), 5.17 (t, J=9.5 Hz, 1H), 4.84 (d, J=
12.0 Hz, 1H), 4.79–4.62 (m, 5H), 4.56 (dd, J=22.9, 11.9 Hz, 2H), 4.42 (d,
J=12.0 Hz, 2H; PhCH2, H-1’), 4.28 (dd, J=10.1, 4.5 Hz, 1H), 4.09 (t, J=
9.5 Hz, 1H), 3.89 (t, J=9.2 Hz, 1H), 3.84–3.77 (m, 4H), 3.72 (d, J=
9.8 Hz, 1H), 3.67 (d, J=8.4 Hz, 2H), 3.54 (d, J=10.9 Hz, 1H), 3.44 (d,
J=7.1 Hz, 1H), 3.18 (d, J=4.2 Hz, 1), 2.33 (s, 3H; ArCH3), 2.01 ppm (s,
3H; CH3C=O); 13C NMR (125 MHz, CDCl3): d=171.3 (C=O), 159.5-
(0.15 equiv to acceptor). A solution of mannosyl trichloroacetimidate 6
in CH2Cl2 (1.5 equiv, 0.25m) was added at the designated addition rate
(0.26, 0.07 for 7; 0.46, 0.14 for 8; 0.26 for 9, 13, and 14; 0.40 for 16; and
0.24 mLmimꢀ1 for 17a). The progress of the reaction was monitored by
TLC with EtOAc/hexane or EtOAc/CH2Cl2/hexane mixture as the devel-
oping solvent. Upon complete consumption of the glycosyl acceptor, a
few drops of Et3N were added to quench the reaction, which was then
followed by filtration over Celite. The resulting filtrate was concentrated
for standard chromatography or MPLC purification to furnish disacchar-
ide 10 (from glycosylation of 7), 11 (from glycosylation of 8), 12 (from
glycosylation of 9), 18 (from glycosylation of 13), 19 (from glycosylation
of 14), 21 (from glycosylation of 16), or 22 (from glycosylation of 17a).
a/b-Anomeric ratios of the glycosylation products were determined by
either HPLC analysis (HPLC system: Hitachi L-2300 pump, L-2400 UV-
detector, and Mightysil Si 60 250–4.6 normal phase column; mobile
phase for elution: hexane/CH2Cl2/EtOAc mixture gradient from 75:10:15
to 70:10:20 at a flow rate of 0.8 mLminꢀ1) (for disaccharides 10–12) or
NMR spectroscopy of the isolated products (for disaccharides 18, 19, 21,
and 22).
Methyl 2,3-di-O-benzyl-4,6-O-benzylidene-b-d-mannopyranosyl-(1!4)-
2,3,6-tri-O-benzyl-1-a-d-glucopyranoside (10): Disaccharide 10 was pre-
pared from glucopyranoside acceptor 7 (100 mg, 0.216 mmol) and man-
nosyl trichloroacetimidate 6 (192 mg, 0.324 mmol) according to the gen-
eral I-A procedure at a donor addition rate of 0.26 mLminꢀ1. The crude
disaccharide 10 was purified by MPLC over silica gel (230–400 mesh)
(EtOAc/hexane 1:3) to furnish the b-anomer of disaccharide 10 as an
amber-colored syrup (170 mg, 90%, a/b 1:10 based on HPLC analysis).
For the b-anomer of disaccharide 10: Rf =0.30 (EtOAc/hexane 1:3);
1H NMR (300 MHz, CDCl3): d=7.50 (dt, J=8.0, 4.3 Hz, 4H; ArH),
7.46–7.23 (m, 26H; ArH), 5.55 (s, 1H; benzylidene-CH), 5.08 (d, J=
10.7 Hz, 1H; PhCH2), 4.87–4.73 (m, 5H), 4.72–4.57 (m, 5H), 4.39 (s,
1H), 4.31 (d, J=12.1 Hz, 1H), 4.15–4.03 (m, 2H), 3.96–3.84 (m, 2H),
3.67 (d, J=2.9 Hz, 1H), 3.62 (dd, J=8.0, 4.8 Hz, 1H), 3.58–3.52 (m, 1H),
3.49 (dd, J=11.1, 2.7 Hz, 1H), 3.43 (s, 3H; OCH3), 3.36 (dd, J=10.0,
2.9 Hz, 2H), 3.08–3.01 ppm (m, 1H); 13C NMR (75 MHz, CDCl3): d=
139.8, 139.0, 138.9, 138.7, 138.0, 137.9, 129.2, 128.9, 128.8, 128.7, 128.6,
128.5, 128.4, 128.2, 128.1, 127.96, 127.91, 127.7, 127.6, 126.5, 101.9 (benzyl-
idene-CH), 101.7 (C-1’), 98.8 (C-1), 80.6, 79.3, 79.1, 78.6, 78.0, 77.6, 75.7,
75.4, 74.0, 73.9, 72.9, 70.0, 68.9, 68.7, 67.6, 55.7 ppm (OCH3).[17c,g,k]
ACHTUNGTRENNUNG(ArOCH3), 154.6 (carbamate-C=O), 138.8, 138.7, 138.0, 137.8, 134.0,
130.8, 130.1, 129.5, 129.3, 128.9, 128.9, 128.6, 128.5, 128.4, 128.2, 128.0,
126.4, 114.1, 102.4 (1JCH =158.6 Hz; C-1’), 101.8 (benzylidene-CH), 95.9
(CCl3), 87.3 (1JCH =158.4 Hz; C-1), 79.1, 78.9, 78.0, 77.7, 76.9, 76.3, 75.1,
74.9, 74.4, 73.9, 72.6, 68.9, 68.8, 67.8, 55.6, 55.3, 21.6 (CH3), 21.4 ppm
(CH3); HRMS-ESI: m/z: calcd for C53H56Cl3NO13SNa: 1074.2436; found:
1074.2430 [M+Na]+. The crude NMR (including 1H-, 13C-, HMQC-, and
gated decoupling 13C NMR) spectra of a-anomer of 3 are provided in the
Supporting Information.
2,3-Di-O-benzyl-4,6-O-benzylidene-b-d-mannopyranosyl-(1!6)-1,2:3,4-
di-O-isopropylidene-a-d-galactopyranose (11): Disaccharide 11 was pre-
pared from galactopyranosyl acceptor 8 (100 mg, 0.385 mmol) and man-
nosyl trichloroacetimidate 6 (342 mg, 0.578 mmol) according to the gen-
eral I-A procedure at a donor addition rate of 0.46 mLminꢀ1. The crude
reaction product was purified by MPLC over 230–400 mesh silica gel
(EtOAc/hexane 1:4). The disaccharide 11 was obtained as an amber-col-
ored syrup (250 mg, 90%, a/b 1:2.3 based on HPLC analysis). For the b-
anomer of disaccharide 11, Rf =0.35 (EtOAc/hexane 1:4); 1H NMR
(300 MHz, CDCl3): d=7.56–7.47 (m, 5H; ArH), 7.45–7.28 (m, 10H;
ArH), 5.63 (s, 1H; benzylidene-CH), 5.61 (d, J=5.0 Hz, 1H; H-1), 5.02
(d, J=12.1 Hz, 1H; PhCH2), 4.91 (d, J=12.1 Hz, 1H; PhCH2), 4.68–4.53
(m, 4H), 4.38–4.32 (m, 2H), 4.29–4.15 (m, 3H), 4.12–4.08 (m, 1H), 4.07
(d, J=3.1 Hz, 1H), 3.94 (t, J=10.3 Hz, 1H), 3.67 (dd, J=10.7, 8.2 Hz,
1H), 3.59 (dd, J=9.9, 3.1 Hz, 1H), 3.39–3.31 (dt, J=9, 3 Hz, 1H), 1.53 (s,
3H; CH3), 1.48 (s, 3H; CH3), 1.36 ppm (d, J=3.6 Hz, 6H; 2ꢂCH3);
13C NMR (75 MHz, CDCl3): d=138.6, 138.5, 137.9, 129.3, 129.2, 128.7,
128.66, 128.61, 128.0, 127.9, 126.4, 109.9 (quaternary-C), 109.2 (quaterna-
ry-C), 103.2 (C-1’), 101.8 (benzylidene-CH), 96.7 (C-1), 78.8, 77.6, 75.5,
75.1, 72.5, 71.9, 71.1, 70.8, 70.4, 68.9, 68.3, 67.9, 26.4 (CH3), 26.3 (CH3),
25.4 (CH3), 24.7 ppm (CH3).[17a,d,j,k]
For side-product 4: Rf =0.75 (EtOAc/hexane 1:4); 1H NMR (300 MHz,
CDCl3): d=7.63 (dd, J=7.6, 1.8 Hz, 2H; ArH), 7.54–7.37 (m, 12H;
ArH), 7.19 (d, J=8.1 Hz, 2H; ArH), 7.01–6.93 (m, 2H; ArH), 5.73 (s,
1H; benzylidene-CH), 5.54 (d, J=0.9 Hz, 1H; H-1), 4.88–4.77 (m, 3H),
4.68 (d, J=11.8 Hz, 1H), 4.45–4.27 (m, 3H), 4.14–4.04 (m, 2H), 4.02–3.91
(m, 1H), 3.87 (s, 3H; OCH3), 2.41 ppm (s, 3H; ArCH3); 13C NMR
(75 MHz, CDCl3): d=159.7 (ArOCH3), 138.4, 138.3, 138.1, 132.8, 130.9,
130.4, 130.3, 129.8, 129.3, 128.9, 128.6, 128.5, 128.3, 126.6, 114.2, 101.9
(benzylidene-CH), 87.9 (C-1), 79.5, 78.4, 76.2, 73.4, 73.1, 69.0, 65.9, 55.7
(ArOCH3), 21.6 ppm (CH3); HRMS-ESI: m/z: calcd for C35H37O6SNa:
608.2209; found: 608.2203 [M+Na]+.
For side-product 5: Rf =0.65 (EtOAc/hexane 1:4); [a]2D7 =+17.3 (c=0.75
in CHCl3); 1H NMR (300 MHz, CDCl3): d=7.60–7.48 (m, 3H; ArH),
7.48–7.30 (m, 10H; ArH), 6.98–6.89 (m, 2H; ArH), 5.67 (s, 1H; benzyli-
dene-CH), 5.22 (dd, J=9.2, 1.35 Hz, 1H; H-1), 5.15 (d, J=11.5 Hz, 1H),
4.93 (d, J=11.7 Hz, 1H), 4.75 (d, J=11.4 Hz, 2H), 4.36 (dd, J=10.4,
4.9 Hz, 1H), 4.22 (t, J=9.6 Hz, 1H), 3.97–3.90 (m, 1H), 3.89–3.79 (m,
5H), 3.52 ppm (td, J=9.8, 4.9 Hz, 1H); 13C NMR (75 MHz, CDCl3): d=
161.7 (C=O), 159.8 (ArOCH3), 137.7, 137.6, 130.4, 129.9, 129.4, 129.3,
128.9, 128.6, 126.4, 114.3, 101.9 (benzylidene-CH), 92.3 (CCl3), 79.4
(1JCH =160.7 Hz), 78.98, 77.9, 77.4, 77.0, 76.7, 75.9, 73.9, 69.4, 68.7,
55.7 ppm (ArOCH3); HRMS-FAB: m/z: calcd for C30H30NO7Cl3:
621.1088; found: 621.1085 [M]+.
Methyl
2,3-di-O-benzyl-4,6-benzylidene-b-d-mannopyranosyl-(1!6)-
2,3,4-tri -O-benzyl-a-d-glucopyranoside (12): Disaccharide 12 was pre-
pared from galactopyranosyl acceptor 9 (100 mg, 0.215 mmol) and man-
nosyl trichloroacetimidate 6 (191 mg, 0.324 mmol) according to the gen-
eral I-A procedure at a donor addition rate of 0.26 mLminꢀ1. Purification
of 12 was achieved by standard column chromatography (hexane/CH2Cl2/
EtOAc 3:1:0.5) and 12 was obtained as white glassy substance (135 mg,
68%, a/b 1:>15 based on NMR spectroscopy). For the b-anomer of di-
Rate-dependent inverse-addition (I-A) procedure for the synthesis of 10–
12, 18, 19, 21, and 22: A suspension of O-glycoside acceptor (7, 8, or 9)
(1 equiv, 100 mg) or thioglycoside acceptor (13, 14, 16, or 17a) (1 equiv,
100 mg) and activated 4 ꢁ MS (AW300) in CH2Cl2 was stirred at ꢀ508C
for 10 min under N2, which was followed by the addition of TMSOTf
1158
www.chemasianj.org
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2010, 5, 1152 – 1162

b-Mannosidic Bond Formation
A
dene-CH), 5.47 (s, 1H; H-1), 5.06 (s, 1H; H-1’), 4.95 (q, J=12.2 Hz, 2H;
PhCH2), 4.72 (q, J=12.6 Hz, 2H; PhCH2), 4.44 (d, J=5.3 Hz, 1H), 4.27
(ddd, J=15.4, 11.8, 5.3 Hz, 3H), 4.10–3.94 (m, 3H), 3.73 (ddd, J=12.9,
9.9, 5.4 Hz, 2H), 3.37 (dt, J=9.8, 4.9 Hz, 1H), 2.60 (s, 6H; ArCH3), 1.53
(s, 3H; CH3), 1.40 (s, 3H; CH3), 1.30 ppm (d, J=6.2 Hz, 3H; CH3);
13C NMR (75 MHz, CDCl3): d=143.4, 139.0, 138.8, 138.0, 131.9, 129.3,
129.2, 128.9, 128.8, 128.7, 128.6, 128.5, 128.3, 128.2, 128.1, 128.04, 128.00,
(300 MHz, CDCl3): d=7.52–7.49 (m, 2H; ArH), 7.32–7.14 (m, 30H;
ArH), 5.59 (s, 1H; benzylidene-CH), 5.03 (d, J=12 Hz, 1H), 4.91 (d, J=
12 Hz, 1H), 4.86–4.71 (m, 4H), 4.67 (d, J=12 Hz, 1H), 4.62–4.59 (m,
2H), 4.54 (d, J=12 Hz, 1H), 4.28–4.17 (m, 2H), 4.14–3.98 (m, 3H), 3.90
(t, J=12 Hz, 1H), 3.77–3.73 (m, 2H), 3.53–3.42 (m, 4H), 3.34 (s, 1H;
OCH3), 3.28–3.18 ppm (m, 1H); 13C NMR (75 MHz, CDCl3): d=139.0,
138.5, 138.2, 137.7, 128.6, 128.4, 128.2, 127.9, 126.2, 102.1 (C-1’), 101.6
(benzylidene-CH), 98.0 (C-1), 77.2, 75.8, 74.9, 74.8, 73.5, 72.8, 69.8, 68.8,
68.3, 67.7, 55.4 ppm.[17k]
127.9, 126.4, 109.9 (quaternary-C), 101.8 (benzylidene-CH), 100.4 (1JCH
=
158.2 Hz; C-1’), 84.9 (1JCH =164.6 Hz; C-1), 79.1, 78.5, 78.4, 78.2, 78.1,
76.8, 75.3, 72.6, 69.0, 68.1, 67.4, 28.2, 27.0, 22.6, 18.0 ppm; HRMS-ESI:
m/z: calcd for C44H50O9SNa: 777.3073; found: 777.3068 [M+Na]+.
Tolyl 2,3-di-O-benzyl-4,6-O-benzylidene-b-d-mannopyranosyl-(1!2)-3-
O-benzyl-4,6-O-benzylidene-1-thio-a-d-mannopyranoside (18): Disac-
charide 18 was prepared from thio-a-d-mannopyranosyl acceptor 13
Tolyl 2,3-di-O-benzyl-4,6-O-benzylidene-1-b-d-mannopyranosyl-(1!4)-2-
azido-3,6-di-O-benzyl-2-deoxy-1-thio-a-d-glucopyranoside (22): Disac-
charide 22 was prepared from 2-azido-2-deoxy thio-a-d-glucopyranoside
17a (100 mg, 0.20 mmol) and mannosyl trichloroacetimidate 6 (180 mg,
0.30 mmol) according to the general I-A procedure at a donor addition
rate of 0.24 mLminꢀ1. Disaccharide 22 was purified by MPLC over 230–
400 mesh silica gel (EtOAc/hexane 1:8). The b-anomer of disaccharide 22
was furnished as a colorless syrup (120 mg, 65%, a/b 1:>15). For disac-
charide thioglycoside 22: Rf =0.25 (EtOAc/CH2Cl2/hexane 0.5:1:4);
[a]2D7 =+20.84 (c=0.5 in CHCl3); 1H NMR (500 MHz, CDCl3): d=7.50–
7.18 (m, 32H; ArH), 7.11 (d, J=7.5 Hz, 2H; ArH), 5.51 (s, 1H; benzyli-
dene-CH), 5.49 (s, 1H; H-1), 5.16 (d, J=10 Hz, 1H; PhCH2), 4.90 (d, J=
11.5 Hz, 1H; PhCH2), 4.81(d, J=12 Hz, 1H), 4.76 (d, J=12.5 Hz, 1H),
4.62 (d, J=6.5 Hz, 1H), 4.58 (d, J=12 Hz, 1H), 4.36 (s, 1H; H-1’), 4.26
(d, J=12 Hz, 1H), 4.21 (d, J=10 Hz, 1H), 4.07 (t, J=10 Hz, 1H), 4.03–
3.99 (m, 2H), 3.90–3.88 (m, 1H), 3.70 (d, J=2.5 Hz, 1H), 3.67 (t, J=
5.5 Hz, 1H), 3.54–3.49 (m, 2H), 3.39 (t, J=5.5 Hz, 1H), 3.33 (dd, J=6.5,
10 Hz, 1H), 3.03 (dt, J=5, 9.5 Hz, 1H), 2.312 ppm (s, 3H; ArCH3);
13C NMR (125 MHz, CDCl3): d=138.5, 138.4, 137.8, 137.6, 137.3, 132.3,
129.8, 129.7, 128.9, 128.8, 128.5, 128.3, 128.2, 128.1, 128.0, 127.7, 127.6,
127.5, 127.4, 127.3, 126.1, 101.3 (benzylidene-CH), 101.1 (1JCH =157 Hz;
C-1’), 87.5 (1JCH =167 Hz; C-1), 79.8, 78.6, 78.2, 77.2, 77.0, 76.7, 75.2, 75.0,
73.5, 72.6, 71.3, 68.3, 68.1, 67.2, 63.2, 21.1 ppm (ArCH3); HRMS-ESI:
m/z: calcd for C54H55N3O9SNa: 944.3551; found: 944.3546 [M+Na]+.
(100 mg, 0.216 mmol) and mannosyl trichloroacetimidate
0.325 mmol) according to the general I-A procedure at a donor addition
rate of 0.26 mLminꢀ1. Disaccharide 18 was purified by MPLC over 230–
400 mesh silica gel (EtOAc/hexane 1:4). The b-anomer of disaccharide 18
was obtained as an amber-colored syrup (145 mg, 75%, a/b 1:>15, based
on NMR spectroscopy). For disaccharide 18: Rf =0.29 (EtOAc/hexane/
CH2Cl2 1:4); 1H NMR (500 MHz, CDCl3): d=7.58–7.33 (m, 27H; ArH),
7.18 (d, J=8 Hz, 2H; ArH), 5.64 (s, 1H; benzylidene-CH), 5.55 (s, 1H;
benzylidene-CH), 5.47 (d, J=0.5 Hz, 1H; H-1), 5.08 (d, J=12.5 Hz, 1H;
PhCH2), 4.99 (d, J=12.5 Hz, 1H; PhCH2), 4.85 (d, J=12 Hz, 1H), 4.80
(d, J=12 Hz, 1H), 4.73 (d, J=12 Hz, 1H), 4.651 (d, J=12 Hz, 1H), 4.649
(s, 1H; H-1’), 4.56–4.54 (m, 1H), 4.39 (dt, J=5, 1.5 Hz, 1H), 4.31–4.27
(m, 3H), 4.21 (t, J=10 Hz, 1H), 4.01 (dd, J=3.5, 11 Hz; 1H), 3.99 (d, J=
3 Hz, 1H), 3.91 (t, J=10.5 Hz, 1H), 3.82 (t, J=10.2 Hz, 1H), 3.62 (dd,
J=13.5, 3.5 Hz, 1H), 3.31 (m, 1H), 2.33 ppm (s, 1H; ArCH3); 13C NMR
(125 MHz, CDCl3): d=138.4, 138.3, 137.4, 132.4, 129.9, 129.6, 128.5,
128.4, 128.3, 128.2, 128.1, 127.9, 127.7, 127.6, 127.5, 127.4, 127.3, 126.1,
101.6 (benzylidene-CH), 101.3 (benzylidene-CH), 100.8 (1JCH =153 Hz;
C-1’), 86.6 (1JCH =164 Hz; C-1), 78.6, 78.5, 77.9, 77.4, 77.2, 77.0, 76.7, 76.0,
74.7, 74.6, 74.2, 72.3, 71.4, 71.03, 68.5, 68.4, 67.7, 76.5, 65.3, 21.1 ppm
(ArCH3).[9c]
Tolyl 2,3-di-O-benzyl-4,6-O-benzylidene-b-d-mannopyranosyl-(1!3)-2-
O-benzyl-4,6-O-benzylidene-1-thio-a-d-mannopyranoside (19): Disac-
charide 19 was prepared from thio-a-d-mannopyranosyl acceptor 14
Synthesis of tolyl 2-azido-3,4,6-tri-O-acetyl-2-deoxy-1-thio-d-glucopyra-
noside (23): CuSO4 (17 mg, 0.07 mmol) was added to a mixture of glucos-
amine hydrogen chloride salt (1.5 g, 6.9 mmol), Et3N (2.8 mL, 21 mmol),
and azido sulfonylimidazolium chloride (1.8 g, 9 mmol) in MeOH
(35 mL) that was stirred at RT.[37] The progress of reaction was monitored
by TLC (Rf =0.45, CH2Cl2/MeOH 3.5:1). After stirring for 1–2 h, the re-
action solvent was removed by a rotary evaporator. The crude residue
was redissolved in pyridine (6.5 mL) and Ac2O (5.4 mL, 57 mmol) was
then added. The resulting mixture was stirred for 10 h at RT and then ex-
cessive pyridine was removed in vacuo to give the crude peracetyl gluco-
amine derivative. This derivative was diluted with EtOAc, washed with
0.1m HCl (25 mLꢂ3), H2O (25 mLꢂ1), and saturated NaCl (25 mLꢂ1),
dried (MgSO4), filtered, and concentrated for thioglycosidation. The
crude peracetyl glucosamine derivative (2.1 g, 5.8 mmol) obtained from
the preceding step was dissolved in CH2Cl2 and then thiocresol (1.5 g,
12 mmol) and BF3·Et2O (1.6 g, 13.2 mmol) were added. The resulting
mixture was stirred at RT under N2 for 2 days and the progress of the re-
action was monitored by TLC (Rf =0.4, hexane/EtOAc 2:1). The reaction
mixture was diluted with CH2Cl2, washed with 1.0m NaOH (25 mLꢂ3),
HCl (25 mLꢂ1), and saturated NaCl (25 mLꢂ1), and then dried
(MgSO4), filtered, and concentrated for standard chromatographic purifi-
cation (hexane/EtOAc 3:1) to furnish 2-azido-2-deoxy-d-thioglucopyra-
noside 23 as a colorless oily syrup (1.8 g, 60% over three steps, a/b
2:1).[36c]
(100 mg, 0.216 mmol) and mannosyl trichloroacetimidate
0.325 mmol) according to the general I-A procedure at a donor addition
rate of 0.26 mLminꢀ1. Disaccharide 19 was purified by MPLC over 230–
400 mesh silica gel (EtOAc/hexane 4:1). The b-anomer of disaccharide
19 was furnished as a colorless syrup (135 mg, 70%, a/b 1:>15). For dis-
accharide 19: Rf =0.28 (EtOAc/CH2Cl2/hexane 0.5:1:4); 1H NMR
(300 MHz, CDCl3): d=7.50–7.14 (m, 24H; ArH), 5.64 (s, 1H; benzyli-
dene-CH), 5.56 (d, J=1.0 Hz, 1H; H-1), 5.53 (s, 1H; benzylidene-CH),
4.96 (d, J=12.0 Hz, 1H; PhCH2), 4.78 (s, 1H; PhCH2), 4.701 (s, 1H;
PhCH2), 4.695 (s, 1H), 4.62 (d, J=12.0 Hz, 1H; PhCH2), 4.46–4.35 (m,
2H), 4.34–4.18 (m, 4H), 4.12 (t, J=9 Hz, 1H), 4.08 (s, 1H; H-1’), 4.05–
4.03 (m, 1H), 3.88 (dt, J=9.0, 5.4 Hz, 2H), 3.75 (d, J=3.3 Hz, 1H), 3.32
(dd, J=9.7, 3.3 Hz, 1H), 2.97 (dt, J=4.8, 9.0 Hz, 1H), 2.36 ppm (s, 3H;
ArCH3); 13C NMR (125 MHz, CDCl3): d=138.7, 138.6, 138.2, 137.7,
137.4, 137.1, 132.4, 130.0, 129.8, 128.9, 128.8, 128.5, 128.33, 128.30, 128.2,
128.1, 128.03, 128.99, 127.54, 127.48, 127.42, 127.3, 126.2, 126.1, 101.8
(benzylidene-CH), 101.3 (benzylidene-CH), 98.1 (1JCH =158 Hz; C-1’),
86.1 (1JCH =167 Hz; C-1), 78.5, 77.4, 77.3, 77.2, 76.1, 75.2, 74.7, 72.3. 72.0,
71.8, 68.5, 67.7, 65.4, 21.1 ppm (ArCH3); HRMS-ESI: m/z: calcd for
C54H54O10SNa: 917.3330; found: 917.3327 [M+Na]+.[9a]
2,6-Dimethylphenyl
pyranosyl-(1!4)-2,3-di-O-isopropylidene-1-thio-a-l-rhamnopyranoside
(21): Disaccharide 21 was prepared from thio-a-l-rhamnopyranosyl ac-
ceptor 16 (100 mg, 0.31 mmol) and mannosyl trichloroacetimidate
ACHTUNGTRENNUNG
Synthesis of tolyl 2-azido-3-O-benzyl-4,6-O-benzylidene-2-deoxy-1-thio-
d-glucopyranoside (24): 2-Azido-2-deoxy thioglucopyranoside 23 (2.3 g,
5.2 mmol) was dissolved in CH2Cl2/MeOH 1:2 (ca. 9 mL), followed by
the addition of slumps of freshly cut Na metal (~10 mg). The reaction
mixture was stirred at RT for 3 h and then diluted with MeOH (3 mL)
before being neutralized with IR-120 (H+). After the removal of the
resin by filtration, the filtrate was concentrated and the residue was dried
in vacuo for few hours to give the crude deacetylated 2-azido-2-deoxy
thioglucopyranoside as a white glassy solid (1.45 g, 90%). The deacetylat-
(274 mg, 0.46 mmol) according to the general I-A procedure at a donor
addition rate of 0.26 mLminꢀ1. Disaccharide 21 was purified by MPLC
over 230–400 mesh silica gel (EtOAc/hexane 1:8). The b-anomer of disac-
charide 21 was furnished as a colorless syrup (210 mg, 90%, a/b 1:>15).
For disaccharide 21: Rf =0.35 (EtOAc/hexane 1:8); [a]2D7 =ꢀ140.4 (c=
0.77 in CHCl3); 1H NMR (300 MHz, CDCl3): d=7.54 (m, 4H; ArH),
7.47–7.29 (m, 12H; ArH), 7.24–7.11 (m, 2H; ArH), 5.67 (s, 1H; benzyli-
Chem. Asian J. 2010, 5, 1152 – 1162
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
1159

K.-K. T. Mong et al.
FULL PAPERS
ed 2-azido-2-deoxy thioglucopyranoside from the preceding step (1 g,
3.2 mmol) was suspended in dried CH3CN (10 mL), followed by the addi-
tion of p-toluenylsulfonic acid monohydrate (61 mg, 0.32 mmol) and ben-
zaldehyde dimethyl acetal (0.72 mL, 4.8 mmol). The reaction mixture was
stirred at RT for 4 h and the progress of reaction was monitored by TLC
(hexane/CH2Cl2/EtOAc 3:1:1; the Rf values of the a- and b-anomers=0.4
and 0.45). After completion of the reaction, a few drops of Et3N were
added and the solvent was reduced by a rotary evaporator. The crude
product from the preceding procedure was purified by standard chroma-
tographic purification (hexane/CH2Cl2/EtOAc 3:1:1) and the resulting
product was used as a substrate for benzylation. The anomeric mixture of
the benzylidene derivative from the preceding step (0.9 g, 2.3 mmol) was
dissolved in dried DMF (5 mL) and stirred at 08C under N2, to which
60% NaH (0.3 g, 4.4 mmol) and benzyl bromide (BnBr) (0.5 mL,
4.4 mmol) were added. The mixture was stirred from 08C to RT for 2 h
and the reaction was then quenched by the addition of MeOH (2 mL).
The resulting mixture was diluted with H2O (20 mL) and the product was
extracted with Et2O (15 mLꢂ3). The pooled ether solution was washed
with 0.1m HCl (50 mLꢂ2) and saturated NaCl (50 mLꢂ1), dried
(MgSO4), and then concentrated for standard chromatographic purifica-
tion (hexane/CH2Cl2/EtOAc 3:1:0.3) to give 24 as a white glassy solid
(0.95 g, 84% over two steps, a/b 2:1). For the a-anomer of 24: Rf =0.31
(EtOAc/hexane/CH2Cl2 1:4:1); 1H NMR (300 MHz, CDCl3): d=7.52–
7.31 (m, 12H; ArH), 7.13 (d, J=7.8 Hz, 2H; ArH), 5.60 (s, 1H; benzyli-
dene-CH), 5.49 (d, J=2.4 Hz, 1H; H-1), 4.89 (dd, J=11, 45 Hz, 2H;
PhCH2), 4.44 (dt, J=5, 11 Hz, 1H), 4.23 (dd, J=5, 10 Hz, 1H), 4.01–3.92
(m, 2H), 3.80–3.73 (m, 2H), 2.34 ppm (s, 3H; ArCH3); 13C NMR
(75 MHz, CDCl3): d=138.0, 133.5, 130.4, 129.5, 129.3, 128.8, 128.7, 128.6,
128.4, 126.4, 101.8 (benzylidene-CH), 88.5 (C-1), 83.1, 78.2, 77.8, 77.4,
77.0, 69.0, 64.0, 63.9, 21.6 ppm (ArCH3).
mixture was stirred from 08C to RT for 16 h. Upon completion of the
glycosylation, the reaction was quenched by the addition of a few drops
of saturated NaHCO3 and small pieces of solid Na2S2O3, and was then
stirred at RT for ca. 30 min. The resulting solution was filtered over
Celite to remove the MS, and the filtrate was concentrated to furnish
crude trisaccharide 26 (the crude 1H NMR spectrum of 26 is given in the
Supporting Information for reference). Crude trisaccharide 26 was dis-
solved in 90% aqueous acetic acid (1.0 mL) and the resulting mixture
was stirred at 708C for 1 h. Upon complete removal of the acetal func-
tion as implicated by TLC examination, the reaction mixture was concen-
trated for MPLC purification over 230–400 mesh silica gel (EtOAc/
hexane 1:1+1% MeOH) to furnish trisaccharide diol 27 as a colorless
syrup (188 mg, 70% over two steps).
By the contiguous sequential glycosylation approach:
A mixture of
GlcNAc thioglycoside 2 (100 mg, 0.17 mmol) and 4 ꢁ MS (AW300)
(300 mg) in CH2Cl2 (3.5 mL, 50 mm) was stirred at ꢀ508C for 10 min
under N2, followed by the addition of TMSOTf (5.0 mL, 0.025 mmol). In
the meantime, a solution of 0.25m of mannosyl trichloroacetimidate 1
(160 mg, 0.25 mmol) in CH2Cl2 (1.0 mL) was prepared and added to the
reaction mixture of 2 and TMSOTf at 0.2 mLminꢀ1 by a syringe pump
(KSD 100). Upon completion of the glycosylation, the reaction was
quenched with few drops of Et3N, and the mixture was filtered over
Celite. The resulting filtrate was washed with water (20 mLꢂ1) and brine
(20 mLꢂ1), dried (MgSO4), filtered, and concentrated to give crude dis-
accharide 3. After drying in vacuo for couple of hours, disaccharide 3 was
dissolved in CH2Cl2 (4.0 mL) and GlcNAc thioglycoside 25 (100 mg,
0.20 mmol) and 4 ꢁ molecular sieves (AW300) (500 mg) were added and
the mixture was stirred under N2 at ꢀ208C for 10 min. Then, the result-
ing mixture was treated with NIS (45 mg, 0.20 mmol) and TMSOTf
(3.0 mL, 0.017 mmol). The resulting mixture was stirred from 08C to RT
for 16 h under N2. Upon completion of the glycosylation, the reaction
was quenched and worked up as described previously to give crude tri-
saccharide 26. The crude trisaccharide 26 was dissolved in 90% aqueous
acetic acid (1.0 mL) and stirred at 708C for 1 h. After completion of
acetal deprotection, the reaction mixture was concentrated for purifica-
tion by MPLC over 230–400 mesh silica gel (EtOAc/hexane 1:1+1%
MeOH) to furnish target trisaccharide diol 27 (90 mg, 40% over three
steps). For trisaccharide diol 27: Rf =0.30 (EtOAc/hexane 1:1+1%
MeOH); [a]2D7 =ꢀ45.9 (c=0.20 in CHCl3); 1H NMR (300 MHz, CDCl3):
d=7.52–7.22 (m, 17H; ArH), 6.94–6.82 (m, 2H; ArH), 5.02 (d, J=
11.6 Hz, 1H; PhCH2), 4.90–4.54 (m, 6H), 4.46–4.11 (m, 8H), 3.90 (ddd,
J=19.8, 11.3, 6.9 Hz, 4H), 3.81 (s, 3H; OCH3), 3.78–3.59 (m, 4H), 3.56
(t, J=6.7 Hz, 3H), 3.43–3.23 (m, 4H), 3.19 (dd, J=6.3, 3.0 Hz, 1H), 3.07
(dd, J=9.4, 2.8 Hz, 1H), 2.04 (s, 3H; CH3C=O), 1.86–1.74 (m, 4H; CH2),
1.72–1.59 (m, 2H; CH2), 1.55–1.38 ppm (m, 4H; CH2); 13C NMR
(75 MHz, CDCl3): d=171.0 (C=O), 159.8 (ArOCH3), 154.5 (carbamate-
C=O), 139.1, 138.9, 138.0, 137.6, 129.9, 129.7, 129.6, 129.4, 129.3, 128.9,
128.7, 128.6, 128.55, 128.52, 128.3, 128.2, 128.1, 128.05, 128.0, 127.7, 114.3,
102.5 (1JCH =158.2 Hz), 101.2 (1JCH =158.6 Hz), 101.1 (1JCH =160.8 Hz),
96.0 (CCl3), 81.6, 81.4, 77.6, 76.4, 75.7, 75.5, 74.9, 74.8, 74.6, 74.5, 74.1,
74.0, 73.8, 73.0, 71.1, 70.4, 69.3, 67.6, 67.5, 66.5, 63.4, 56.7, 55.7, 45.4
(CH2Cl), 32.9, 29.7, 26.9, 25.6, 21.2 ppm; HRMS-ESI: m/z: calcd for
C65H79Cl4N4O18Na: 1366.4041; found: 1366.4036 [M+Na]+.
Synthesis of tolyl 2-azido-3,6-di-O-benzyl-6-O-benzyl-2-deoxy-d-thioglu-
copyranoside (17) (a-anomer: 17a b-anomer: 17b): A suspension of an
anomeric mixture of 24 (0.8 g, 1.64 mmol), Et3SiH (2.8 mL, 16.4 mml),
and activated 4 ꢁ MS (AW300) (1 g) in dried CH2Cl2 (6 mL) was stirred
under N2 at RT and then at ꢀ158C for 20 min, which was followed by the
addition of trifluoroacetic acid (TFA) (1.1 mL, 16 mmol). After stirring
at ꢀ158C for 2 h, the reaction mixture was diluted with CH2Cl2 (10 mL)
and washed with 0.1m NaOH (30 mLꢂ2), 0.1m HCl (30 mLꢂ1), and sa-
turated NaCl (30 mLꢂ1), dried (MgSO4), filtered, and concentrated for
standard chromatographic purification (hexane/CH2Cl2/EtOAc 4:1:1) to
produce 17 as a white amorphous solid (0.63 g, 78%, a/b 2:1).
For a-anomer: 17a: Rf =0.25 (EtOAc/hexane/CH2Cl2 1:4:1); [a]D27
=
1
+144.2 (c=0.6 in CHCl3); H NMR (300 MHz, CDCl3): d=7.42–7.34 (m,
6H; ArH), 7.32–7.28 (m, 6H; ArH), 7.04 (d, J=8.1 Hz, 2H; ArH), 5.47
(d, J=5.4 Hz, 1H; H-1), 4.87 (dd, J=11, 31 Hz, 2H; PhCH2), 4.51 (dd,
J=11.1, 27 Hz, 2H; PhCH2), 4.34 (dt, J=4, 9 Hz, 1H), 3.84 (dd, J=5,
10 Hz, 1H; H-6), 3.75–3.61 (m, 4H), 2.63 (d, J=2.6 Hz, 1H; OH),
2.30 ppm (s, 3H; ArCH3); 13C NMR (75 MHz, CDCl3): d=137.9, 137.6,
133.8, 129.8, 128.5,128.3, 128.0, 87.4 (C-1), 81.2, 75.3, 74.1, 73.4, 72.1, 70.1,
63.4, 21.0 ppm (ArCH3).
For b-anomer 17b: Rf =0.31 (EtOAc/CH2Cl2/hexane 1:1:4); [a]2D7 =ꢀ95.8
(c=1.0 in CHCl3); 1H NMR (300 MHz, CDCl3): d=7.45 (d, J=8.4 Hz,
2H; ArH), 7.35–7.27 (m, 10H; ArH), 7.06 (d, J=8.4 Hz, 2H; ArH), 4.83
(d, J=11, 35 Hz, 2H; PhCH2), 4.55 (d, J=12, 25 Hz, 2H; PhCH2), 4.35
(d, J=9.6 Hz, 1H; H-1), 3.79–3.70 (m, 2H), 3.58 (t, J=9 Hz, 1H), 3.43–
3.23 (m, 3H), 2.78 (s, 1H; OH), 2.31 ppm (s, 3H; ArCH3); 13C NMR
(75 MHz, CDCl3): d=138.6, 137.6, 134.1, 129.7, 128.5, 128.2, 127.6, 86.1
(C-1), 84.5, 78.0, 75.4, 73.7, 71.7, 70.1, 64.3, 21.1 ppm (ArCH3); HRMS-
ESI: m/z: calcd for C27H29N3O4SNa: 514.1771; found: 514.1777 [M+Na]+.
Preparation of 3-chloropropyl 2,3-di-O-benzyl-4,6-O-benzylidene-b-d-
mannopyranosyl-(1!4)-2,3-O-isopropylidene-a-l-rhamnopyranosyl-(1!
3)-2-O-benzyl-4,6-O-benzylidene-b-d-galactopyranoside (29): A mixture
of thio-l-rhamnopyranoside 16 (100 mg, 0.31 mmol) and 4 ꢁ MS-AW
(300 mg) in CH2Cl2 (6.0 mL, 50 mm) was stirred under N2 at ꢀ50 8C for
10 min, followed by the addition of TMSOTf (8.0 mL, 0.046 mmol).
Meanwhile, 0.25m of mannosyl trichloroacetimidate
6
(274 mg,
Preparation of 6-chlorohexyl 2-O-benzyl-3-O-p-methoxybenzyl-b-d-man-
nopyranosyl-(1!4)-3-O-acetyl-6-O-benzyl-2-deoxy-2-trichloroethoxycar-
bonyl-b-d-glucopyranosyl-(1!4)-3,6-di-O-benzyl-2-azido-2-deoxy-b-d-
glucopyranoside (27)
0.46 mmol) in CH2Cl2 (2.0 mL) was prepared and added to the mixture
of 16 and TMSOTf at 0.40 mLminꢀ1 by a syringe pump (KSD 100).
Upon completion of the glycosylation, the reaction was quenched by the
addition of a few drops of Et3N, and the resulting mixture was filtered
over Celite to remove the MS. The resulting filtrate was then washed
with water (20 mLꢂ1) and brine (20 mLꢂ1), dried (MgSO4), filtered,
and concentrated to yield crude disaccharide 21. Upon drying in vacuo
for couple of hours, the crude disaccharide 21 was dissolved in CH2Cl2
(6.0 mL), to which b-galactopyranoside 28 (162 mg, 0.37 mmol) and 4 ꢁ
By a stepwise approach: A mixture of the b-anomer of disaccharide 3
(310 mg, 0.30 mmol), GlcNAc acceptor 25 (100 mg, 0.20 mmol), and 4 ꢁ
MS (AW300) (500 mg) in CH2Cl2 (6.0 mL) was stirred at ꢀ208C for
10 min under N2, followed by the addition of N-iodosuccinimide (NIS)
(67 mg, 0.30 mmol) and TMSOTf (5 mL, 0.03 mmol). Then, the reaction
1160
www.chemasianj.org
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2010, 5, 1152 – 1162

b-Mannosidic Bond Formation
MS (AW300) (500 mg) were added, and the mixture was stirred under N2
for 10 min at ꢀ208C. Then, NIS (84 mg, 0.37 mmol) and TMSOTf
(6.0 mL, 0.031 mmol) were added, and the resulting mixture was stirred
from ꢀ20 to 08C for ca. 30 min. The reaction was then quenched by the
addition of a few drops of saturated NaHCO3 and small pieces of solid
Na2S2O3, followed by vigorous stirring at RT for 15 min. The resulting
mixture was filtered over Celite to remove the MS and the filtrate was
concentrated for MPLC purification over 230–400 mesh silica gel
(EtOAc/CH2Cl2/hexane 1:1:4) to furnish target trisaccharide 29 as a col-
orless syrup (272 mg, 70%). For trisaccharide 29: Rf =0.20 (EtOAc/
CH2Cl2/hexane 1:1:4); [a]2D7 =ꢀ3.33 (c=0.30 in CHCl3); 1H NMR
(300 MHz, CDCl3): d=7.54–7.19 (m, 25H; ArH), 5.71–5.48 (m, 2H), 5.25
(s, 1H; H-1”’), 5.01 (s, 1H; H-1”), 4.95–4.81 (m, 3H), 4.75–4.67 (m, 2H),
4.63 (d, J=9.1 Hz, 1H), 4.47 (d, J=7.2 Hz, 1H; H-1’), 4.35 (t, J=8.3 Hz,
2H), 4.32–4.19 (m, 3H), 4.18–4.06 (m, 3H), 4.02–3.91 (m, 3H), 3.85–3.59
(m, 7H), 3.46 (d, J=8.1 Hz, 1H), 3.33 (td, J=9.8, 4.9 Hz, 1H), 2.28–2.01
(m, 2H; CH2), 1.52 (s, 3H; CH3), 1.34 ppm (s, 6H; CH3); 13C NMR
(75 MHz, CDCl3): d=138.9, 138.8, 138.7, 138.1, 137.9, 129.5, 129.2,
128.88, 128.81, 128.7, 128.65, 128.60, 128.5, 128.4, 128.3, 128.28, 128.23,
128.1, 127.9, 127.8, 126.69, 126.65, 126.5, 126.4, 109.6 (quaternary-C),
104.0 (1JCH =156.5 Hz; C-1’), 101.8 (benzylidene-CH), 101.7 (benzyli-
dene-CH), 100.6 (1JCH =157.5 Hz; C-1”’), 100.5 (1JCH =167.9 Hz; C-1”),
81.6, 79.0, 78.5, 78.3, 78.2, 77.67, 76.65, 76.5, 76.4, 75.7, 75.2, 72.4, 69.6,
69.0, 68.0, 66.7, 66.6, 65.2, 42.2 (CH2Cl), 33.1, 28.2, 26.8, 18.2 ppm;
HRMS-ESI: m/z: calcd for C59H67ClO15Na: 1073.4066; found: 1073.4061
[M+Na]+.[7,38]
[11] a) B. G. Davis, Chem. Rev. 2002, 102, 579–602; b) S. R. Shenoy,
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4506–4507; b) D. Crich, S. Sun, J. Am. Chem. Soc. 1998, 120, 435–
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Acknowledgements
We thank the National Science Council of Taiwan for financial support
(grant no. NSC 97-2113M-009-007), Ms. C.-C. Chang of NCTU for
500 MHz NMR spectral analysis, and Mr. T.-Y. Chen for MS analysis.
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Received: December 31, 2009
Published online: March 23, 2010
1162
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