Is an acyl group at O-3 in glucosyl donors able to control α-stereoselectivity of glycosylation? the role of conformational mobility and the protecting group at O-6

Article abstract of DOI:10.1016/j.carres.2013.11.016

The stereodirecting effect of a 3-O-acetyl protecting group, which is potentially capable of the remote anchimeric participation, and other protecting groups in 2-O-benzyl glucosyl donors with flexible and rigid conformations has been investigated. To this aim, an array of N-phenyltrifluoroacetimidoyl and sulfoxide donors bearing either 3-O-acetyl or 3-O-benzyl groups in combination with 4,6-di-O-benzyl, 6-O-acyl-4-O-benzyl, or 4,6-O-benzylidene protecting groups was prepared. The conformationally flexible 3-O-acetylated glucosyl donor protected at other positions with O-benzyl groups demonstrated very low or no α-stereoselectivity upon glycosylation of primary or secondary acceptors. On the contrary, 3,6-di-O-acylated glucosyl donors proved to be highly α-stereoselective as well as the donor having a single potentially participating acetyl group at O-6. The 3,6-di-O-acylated donor was shown to be the best α-glucosylating block for the primary acceptor, whereas the best α-selectivity of glycosylation of the secondary acceptor was achieved with the 6-O-acylated donor. Glycosylation of the secondary acceptor with the conformationally constrained 3-O-acetyl-4,6-O-benzylidene-protected donor displayed under standard conditions (-35 C) even lower α-selectivity as compared to the 3-O-benzyl analogue. However, increasing the reaction temperature essentially raised the α-stereoselectivities of glycosylation with both 3-O-acetyl and 3-O-benzyl donors and made them almost equal. The stereodirecting effects of protecting groups observed for N- phenyltrifluoroacetimidoyl donors were also generally proven for sulfoxide donors.2013 Elsevier Ltd. All rights reserved.

Full text of DOI:10.1016/j.carres.2013.11.016

Accepted Manuscript
Is an Acyl Group at O-3 in Glucosyl Donors Able to Control α-Stereoselectivity
of Glycosylation? The Role of Conformational Mobility and the Protecting
Group at O-6
Bozhena S. Komarova, Maria V. Orekhova, Yury E. Tsvetkov, Nikolay E.
Nifantiev
PII:
S0008-6215(13)00411-4
DOI:
http://dx.doi.org/10.1016/j.carres.2013.11.016
CAR 6614
Reference:
To appear in:
Carbohydrate Research
Received Date:
Revised Date:
Accepted Date:
9 October 2013
21 November 2013
23 November 2013
Please cite this article as: Komarova, B.S., Orekhova, M.V., Tsvetkov, Y.E., Nifantiev, N.E., Is an Acyl Group at
O-3 in Glucosyl Donors Able to Control α-Stereoselectivity of Glycosylation? The Role of Conformational Mobility
and the Protecting Group at O-6, Carbohydrate Research (2013), doi: http://dx.doi.org/10.1016/j.carres.
2
013.11.016
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Is an Acyl Group at O-3 in Glucosyl Donors Able to Control α-
Stereoselectivity of Glycosylation? The Role of Conformational
Mobility and the Protecting Group at O-6
*
Bozhena S. Komarova, Maria V. Orekhova, Yury E. Tsvetkov, Nikolay E. Nifantiev
Laboratory of Glycoconjugate Chemistry, N.D. Zelinsky Institute of Organic Chemistry, Russian
Academy of Sciences, Leninsky Prospect 47, 119991 Moscow, Russia
Abstract
The stereodirecting effect of a 3-O-acetyl protecting group, which is potentially capable
of the remote anchimeric participation, and other protecting groups in 2-O-benzyl glucosyl
donors with flexible and rigid conformations has been investigated. To this aim, an array of N-
phenyltrifluoroacetimidoyl and sulfoxide donors bearing either 3-O-acetyl or 3-O-benzyl groups
in combination with 4,6-di-O-benzyl, 6-O-acyl-4-O-benzyl or 4,6-O-benzylidene protecting
groups was prepared. The conformationally flexible 3-O-acetylated glucosyl donor protected at
other positions with O-benzyl groups demonstrated very low or no α-stereoselectivity upon
glycosylation of primary or secondary acceptors. On the contrary, 3,6-di-O-acylated glucosyl
donors proved to be highly α-stereoselective as well as the donor having a single potentially
participating acetyl group at O-6. The 3,6-di-O-acylated donor was shown to be the best α-
glucosylating block for the primary acceptor, whereas the best α-selectivity of glycosylation of
the secondary acceptor was achieved with the 6-O-acylated donor. Glycosylation of the
*
Corresponding author. Tel./fax: +7 499 135 8784.
E-mail address: nen@ioc.ac.ru (N.E. Nifantiev)

secondary acceptor with the conformationally constrained 3-O-acetyl-4,6-O-benzylidene-
protected donor displayed under standard conditions (–35 °C) even lower α-selectivity as
compared to the 3-O-benzyl analogue. However, increasing the reaction temperature essentially
raised the α-stereoselectivities of glycosylation with both 3-O-acetyl and 3-O-benzyl donors and
made them almost equal. The stereodirecting effects of protecting groups observed for N-
phenyltrifluoroacetimidoyl donors were also generally proven for sulfoxide donors.
Keywords: Glycosylation; Remote anchimeric participation; α-Stereodirecting effect; 3-
O-acetyl group; Glucosyl N-phenyltrifluoroacetimidate; Glucosyl sulfoxide
1. Introduction
Each of the protecting groups in pyranosyl donors has a considerable influence on
1
-10
stereoselectivity of glycosylations.
Investigation of the stereocontrolling properties of the
1
protecting groups provides deeper insight into the mechanism of glycosylation and can give
1
1
2
rise to new technics for the synthesis of challenging 1,2-cis-glycosides. One of the most
intriguing types of stereocontrolling groups is non-vicinal or remote acyl groups, that is, the acyl
groups at O-3, O-4 or O-6 of glycosyl donors with a non-participating alkyl group at O-2 or
azide at C-2. The impact of such O-acyl groups may be explained in terms of the remote
1
3
anchimeric participation. Usually the presence of a non-vicinal potentially participating acyl
group in the donor favors the formation of a glycosylation product with the trans-
1
stereoselectivity relatively to the remote acyl group. The notion to govern the selectivity of
3
glycosylations by non-vicinal acyl protecting groups was successfully applied in our group for
1
the synthesis of linear and branched fucoidans, and oligosaccharides related to glycoforms I
4
1
5-17
and II of LPS of Pseudomonas aeruginosa.
Glucosyl N-phenyltrifluoroacetimidates
possessing α-stereodirecting acyl groups at O-3 and O-6 were employed in the latter syntheses
based on the assumption that the combined effects of both acyl groups would provide the highest

1
α-selectivity. But however attractive the remote anchimeric participation might be for the
7
rationalization of the stereodirecting effect of non-vicinal acyl groups, it is still not proven and
1
8,19
provokes a plenty of questions.
One of them is why the degree of the stereodirecting effect of
a certain acyl group is different for different pyranoses. For example, an acyl group at O-3 in
1
4,15
glucose affected very slightly the stereoselectivity of glycosylation,
while the same 3-O-acyl
2
0
group in fucose provides almost complete α-selectivity. Moreover, 3-O-acyl groups in
mannose demonstrated a powerful α-directing effect, which switches the inherent β-selectivity
21
of 4,6-O-benzylidene-protected mannosyl donors to the complete α-selectivity on replacement
2
2,23
of a single benzyl protecting group at O-3 by an acetyl one.
In principle, the 4,6-O-
benzylidene group should disfavor in this case the plausible anchimeric assistance but in reality
it does not impede the α-selectivity of mannosylation. This fact complicates even more an
adequate explanation of the α-stereocontrolling effect of 3-O-acyl groups. In this communication
we attempted to estimate the limits of the α-directing effect of the 3-O-acetyl group in
conformationally rigid and flexible glucose donors bearing various protecting groups at O-4 and
O-6 and define how stereocontrolling properties of the 3-O-acetyl substituent correlate with the
presence of the 4,6-O-benzylidene group. Another goal of this investigation was a search for
optimal glucosyl donors and conditions for α-(1→3)- and α-(1→6)-glucosylation for further
application in the synthesis of oligosaccharides related to fungal α-glucans.
2. Results and discussion
2
.1. Preparation of glycosyl donors and acceptors
Primary and secondary alcohols, when coupled with the same glycosyl donor, often
produce anomeric mixtures with different α:β ratios. On the other hand, as already mentioned
above, we intended to find an optimal protecting group pattern in donor and acceptor molecules,
which would facilitate a blockwise synthesis of α-(1→3)- and α-(1→6)-glucans. This protecting
group pattern in glycosyl acceptors had to provide easy replacement of the anomeric protection

by a leaving group and a possibility to glycosylate the hydroxy group at either C-3 or C-6.
Therefore, primary alcohol 13 and secondary alcohols 16 and 30 derived from ethylthio or p-
methoxyphenyl glucosides were used as the model glycosyl acceptors.
Application of partially acylated donors in
a
combination with the N-
phenyltrifluoracetimidoyl leaving group always resulted in our hand in good to excellent yields
1
5-17
of 1,2-cis-glycosides.
On the other hand, glycosyl sulfoxides are widely used in the recent
2
4-32
oligosaccharide synthesis.
For these reasons, the present investigation of stereocontrolling
properties of protecting groups was performed using both types of the leaving groups.
Application of two different glycosylation protocols would allow us to differentiate the effect of
the way of activation and the stereocontrol of protecting groups.
Preparation of the principal trifluoracetimidoyl donor 6 with the sole acetyl group at O-3
3
took advantage of the availability of methyl 2,4,6-tri-O-benzyl-α-glucoside 1 (Scheme 1). Its
3
3
3,34
acetylated derivative 2
was subjected to acidic hydrolysis in the presence of HCl. Since this
procedure led to partial 3-O-deacetylation, the reaction products was acetylated again to provide
3
an anomeric mixture of 1,3-di-O-acetylated glucose. Regioselective removal of the anomeric
5
3
6
acetyl group with hydrazine acetate in DMF afforded hemiacetal 3 in overall yield 21% for
four steps. For the transformation of hemiacetals into N-phenyltrifluoroacetimidoyl donors and,
in particular, for the preparation of the donor 6, 1-OH derivatives were treated with N-
3
7
2 3
phenyltrifluoroacetimidoyl chloride (PTAIC) in acetone in the presence of solid K CO .
16,38
Perbenzylated donor 4 and 6-acetate 5 were prepared as described.

Scheme 1. Preparation of donor 6 and the structure of donors 4 and 5.
The synthesis of 4,6-O-benzylidene-protected donors 18, 19, 3,6-di-O-acylated donors
3
0, 21, and acceptors 13 and 16 was performed starting from the known diol 7 as outlined in
9
2
4
Scheme 2. The key step was stannylene-mediated monobenzylation of 7, which proceeded with
0
moderate regioselectivity and provided 2-O-benzyl and 3-O-benzyl ethers 10 and 8 in 58 and
39% yield respectively. Transformation of 8 and 10 into glucosyl donors included introduction
of necessary protecting groups into proper positions, removal of the anomeric p-methoxyphenyl
4
group with CAN and acylation with PTAIC. Thus, benzylation of 8 gave 2,3-di-O-benzyl ether
1
9, which was converted into donor 18.

Scheme 2. Synthesis of 4,6-O-benzylidene-protected glucosyl donors 18, 19, 3,6-di-O-acylated
donors 20,21, and acceptors 13 and 16 from diol 7.
Similarly, compound 10 was acetylated with the formation of 11, from which 3-O-
acetylated donor 19 was obtained. Regioselective reductive opening of the acetal ring in 10 with
4
2
3
BH ⋅THF provided 3,6-diol 14; the latter was transformed into diacetate 15 and then – into 3,6-
di-O-acetylated donor 20. Selective benzoylation of the primary OH group in 14 provided
monobenzoate 16, which was used as a model secondary glycosyl acceptor and also as a starting
compound for the preparation, via 3-acetate 17, of donor 21. Model primary acceptor 13 was
synthesized from 10 by benzoylation followed by reductive opening of the 4,6-O-benzylidene
group in 12.
Variously protected sulfoxide donors 26-29 were prepared from the known ethyl
4
3
44
45
thioglucoside precursors 22, 23, 24 and 25 by oxidation with mCPBA as shown on
46
Scheme 3.
Scheme 3. Synthesis of sulfoxide donors 26-29.
2.2. Glucosylation reactions
The ratio of anomers in disaccharide mixtures produced in glycosylation reactions given
in Table 1 was measured by means of analytical HPLC. In all cases, each of the anomers was
isolated and their structure was unambiguously proved by NMR techniques.
The first series of glucosylation reactions was made with N-phenyltrifluoracetimidoyl
1
5-17
donors. Our experience
of application of such donors showed that they are preferentially

activated with methyl triflate. Probably, its way of action is similar to N-methylation of a C=N
4
7
bond.
Coupling of perbenzylated glucosyl donor 4 with secondary acceptor 30 led to
disaccharide mixture 31 with an α:β ratio of 1.5:1, while glycosylation of primary acceptor 13
produced an α,β-mixture of disaccharides 35 in a ratio of 1:3 (Table 1, entries 1 and 5).
Glycosylation of 30 with 3-O-acetylated donor 6 provided almost the same stereoselectivity of
the formation of 32 as perbenzylated donor 4 (cf. entries 2 and 1). Similarly, only a negligible
decrease of the proportion of the β-product was observed when primary acceptor 13 was
glycosylated with 3-O-acetylated donor 6 instead of 4 (cf. entries 6 and 5). Thus, the single 3-O-
acetyl group in N-phenyltrifluoroacetimidate 6 does not affect the stereoselectivity of
glycosylation relatively to stereochemistry inherent to perbenzylated glucosyl donor 4.
These results contradict published examples of α-directing properties of acyl groups at O-
3
proved by comparative glycosylation with fully alkylated and 3-O-acylated donors of different
3
,20,22,23,48-50
48
configurations
including those closely related to glucose, such as 6-deoxyglucose,
4
9
50
xylose and glucuronic acid. Apparently, the negligible stereochemical effect of the 3-O-acetyl
group in 6 as compared to the noticeable α-directing influence of that group in works cited above
evidenced that the degree of the stereochemical effect of the 3-O-acyl group depends not only on
the structure of the glycosyl donor but also on the structure of the glycosyl acceptor and reaction
conditions.
The results of glycosylation with donor 6 clearly indicated that it is insufficiently α-
stereoselective for the practical use in the synthesis of α-glucooligosaccharides. Therefore, then
we studied 3,6-di-O-acetylated donor 20 assuming that the combined effect of two participating
acetyl groups would essentially increase the α-stereoselectivity of glycosylation. 6-O-Acetylated
donor 5 was also studied to estimate the contribution of the substituents at O-3 and O-6 to
increasing the α-stereoselectivity.

Indeed, glycosylation of secondary acceptor 30 with donor 20 resulted in the considerable
increase of the proportion of α-33 as compared to glycosylation with 3-monoacetate 6 (cf.
entries 2 and 3). Unexpectedly, 6-monoacetate 5 provided even higher α-stereoselectivity than
3,6-diacetate 20 (entries 3 and 4). From these results one might conclude that the 3-O-acetyl
group does not contribute to the α-stereoselectivity and, moreover, can even reduce it. However,
an opposite picture was observed on glycosylation of primary acceptor 13: both 3,6-diacetate 20
and 6-monoacetate 5 provided considerably higher proportions of corresponding α-anomers than
3
-acetate 6 (cf. entries 5 and 7, 8), but glycosylation with 3,6-diacetate 20 was more α-
stereoselective than that with 6-monoacetate 5. This indicated that the contribution of the acyl
substituents at O-3 and O-6 to the overall α-stereoselectivity can vary depending on the structure
of the glycosyl acceptor. As for the synthetic utility of the donors, both 5 and 20 demonstrated
sufficiently high α-stereoselectivity of glycosylation and can used in the synthesis of α-(1→3)-
and α-(1→6)-glucooligosaccharides. 3,6-Di-O-acylated donor 21, which showed high efficiency
and α-stereoselectivity on glycosylation of monocyclic secondary acceptor 16 (entry 9), can also
be included in the group of glycosyl donors with a high synthetic potential.
Then we studied α-stereodirecting effect of the acetyl group at O-3 in conformationally
5
1-55
rigid 4,6-O-benzylidene-protected donors. It is generally accepted
that the 4,6-O-benzylidene
group in glucose donors facilitates the formation of α-linked glucosylation products. This feature
was confirmed by practical application of such donors in several syntheses of oligosaccharides
5
6-59
containing α-glucosyl residues.
However, the stereoselectivity of these glycosylation
5
reactions can depend on the leaving group type and the promoter system.
2
52,53
To the best of our
knowledge, only one example of direct comparison of stereochemical results of glycosylation
with conformationally free tetrabenzyl- and rigid 4,6-O-benzylidene-protected donors has been
5
2
described so far. Therefore, the stereochemistry of MeOTf-promoted glycosylation with 4,6-O-
benzylidene-protected imidate 18 in comparison with that of tetrabenzyl counterpart 4 was
initially studied. It turned out that the reaction of 18 with the secondary acceptor 30 was only

slightly more α-selective (α:β = 2.2:1, entry 10) than glycosylation with 4 (α:β = 1.5:1, entry 1),
whereas the reaction with primary acceptor 13 changed its stereochemistry to the opposite one
upon replacement of 4 (α:β = 1:3.3, entry 5) by 18 (α:β = 5.2:1, entry 15). Thus, again, the
stereochemical impact of the certain structural element in the glycosyl donor is strongly
dependent on the glycosyl acceptor.
3
-O-Acetyl group in the 4,6-O-benzylidene-protected donor 19 did not improved the α-
stereoselectivity of glycosylation of acceptor 30 relatively to 2,3-dibenzyl 18 but, on the
contrary, worsened it (α:β = 2.2:1 → 1:1.4, entries 10, 11). Probably, it indicates that the rigid
4,6-O-benzylidene-protected donor cannot change its conformation in such a way as to enable
carbonyl oxygen of the 3-O-acetyl group to reach positively charged anomeric carbon. The
change of stereochemistry in favor of β-41 may be explained by the electron-withdrawing
influence of the acetyl group similar to that of fluorine in the 2-O-benzyl-3-fluoro-3-
6
deoxyglucosyl donor, which provided a noticeable increase of the β-anomer proportion (α:β =
0
1
:1.8) as compared to the 2,3-di-O-benzyl- donor (α:β = 3.2:1).
The MeOTf-promoted coupling of the donors 18 and 19 with the acceptor 30 was used to
study the effect of the reaction temperature on the stereoselectivity. When the reaction was
carried out at room temperature, the α:β ratio (3.8:1, entry 13) was somewhat higher than at –50
°
C. The same α:β ratio was observed on glycosylation of 30 with 3-O-acetylated 19 (entry 14).
The use of silver triflate as the reaction promoter only slightly affected the stereoselectivity of
the coupling of 19 with 30 (entry 12). These results indicated that the presence of the acetyl
group at the position 3 of the donor again did not improve the α-stereoselectivity, whereas
increasing the reaction temperature facilitated the formation of α-anomers. However, it should
be noted that the yields of the disaccharides 41 and 42 at room temperature were markedly lower
than under standard glycosylation conditions (–35 °C).
In order to rule out anomerization of the β-glycoside bond as a possible reason of the
higher α-stereoselectivity at room temperature, a blank experiment was carried out (Scheme 4).

2 2
Disaccharide β-41 was treated with 1 equiv. of TfOH in CH Cl in the presence of mol. sieve
AW-300 (Scheme 4). No formation of α-41 was observed within 4 hours, thus indicating that the
temperature-dependent stereoselectivity did not relate to anomerization. The dependence of the
6
1,62
stereochemical outcome of glycosylation on the temperature is known.
Most likely, this
phenomenon is a consequence of changes in the conformation of intermediate oxacarbenium
62
ions occurring on increasing the temperature.

Table 1. Stereochemical results of glucosylation with variously protected donors bearing an acetyl at O-3.
Entry
Donor
Acceptor
Conditions
Coupling product
α:β Ratio (yield)
2 2
MeOTf, CH Cl ,
1
2
4 R = R = Bn
1
2
31 R = R = Bn
1
2
3
AW-300,
1.5:1 (90%)
1.4:1 (98%)
5.3:1 (89%)
17:1 (77%)
1
6 R = Bn, R = Ac
2
1
2
32 R = Bn, R = Ac
-35 → -15 °C
1
20 R = R = Ac
2
1
33 R = R = Ac
2
1
5 R = Ac, R = Bn
2
1
2
34 R = Ac, R = Bn
4
MeOTf, CH
AW-300,
35 → -15 °C
2 2
Cl ,
1
4 R = R = Bn
2
1
35 R = R = Bn
2
5
6
7
8
1:3.3 (99%)
1:2.3 (94%)
11.2:1 (93%)
4:1 (97%)
-
1
6 R = Bn, R = Ac
2
1
36 R = Bn, R = Ac
2
1
20 R = R = Ac
2
1
2
37 R = R = Ac
1
5 R = Ac, R = Bn
2
1
38 R = Ac, R = Bn
2
MeOTf, CH
AW-300,
35 → -15 °C
2 2
Cl ,
9
16.4:1 (93%)
-
MeOTf, CH
AW-300,
50 → -15 °C,
2 2
Cl ,
-

2
.2:1 (95%)
1
1
0
1
18 R = Bn
19 R = Ac
40 R = Bn
41 R = Ac
1:1.4 (92%)
3:1 (71%)
AgOTf, CH
AW-300,
0 °C
MeOTf, CH
AW-300,
0 °C
2 2
Cl ,
1
2
19 R = Ac
41 R = Ac
2
1
1
3
4
18 R = Bn
19 R = Ac
2
Cl
2
,
40 R = Bn
41 R = Ac
3.8:1 (78%)
3.8:1 (64%)
2
2 2
MeOTf, CH Cl ,
AW-300,
-35 → 20 °С
1
1
5
6
18 R = Bn
19 R = Ac
42 R = Bn
43 R = Ac
5.2:1 (96%)
5.9:1 (96%)
MeOTf, CH
AW-300,
0 °С
2 2
Cl ,
2
MeOTf,
AW-300,
1
19a R = OC(=NPh)CF
2
, R = H
1
1
7
8
3
1:1.2 (91%)
1:1.5 (91%)
-35 →-15 °С
1
19b R = H, R = OC(=NPh)CF
2
3
Tf
2
O, DTBMP,
CH Cl
78 → 0°C
2
2
,
-
1
9
22 R = Bn
31 R = Bn
1.8:1 (63%)

2
0
25 R = Ac
33 R = Ac
6.8:1 (59%)
Tf
2
O, DTBMP,
CH Cl
78 → 0 °C
2
2
,
-
2
2
1
2
22 R = Bn
25 R = Ac
35 R = Bn
37 R = Ac
1.1:1 (79%)
5.9:1 (92%)
Tf
2
O, DTBMP,
CH Cl
78 → 0 °C
2
2
,
-
2
2
3
4
27 R = Bn
28 R = Ac
40 R = Bn
41 R = Ac
1:1.9 (45%)
No formation of 41
Tf
2
O, DTBMP,
CH Cl
78 → 0 °C
2
2
,
-
2
2
5
6
27 R = Bn
28 R = Ac
42 R = Bn
43 R = Ac
2.3:1 (88%)
No formation of 43

Scheme 4. An attempt at anomerization of the disaccharide β-41.
Finally, the role of the initial anomeric configuration was estimated by comparison of
glycosylation of 30 with the α and β-anomers of the donor 19. The reaction with the β-donor
19b resulted in an insignificantly higher proportion of the β-isomer (entry 18) than the reaction
with the α-donor 19a (entry 17).
The study of the influence of the 4,6-O-benzylidene protecting group on the
stereoselectivity of glycosylation was primarily carried out using glycosyl sulfoxides or
2
4,25
63
thioglycosides activated with Tf
2
O
or 1-benzenesulfinylpiperidine/Tf
2
O
respectively. In
both cases, in situ generated glycosyl trifluormethanesulfonates are believed to be the reactive
2
1,23,64,65
species defining stereochemistry of products.
It is not obvious, whether a similar
intermediate glycosyl trifluoromethanesulfonate is formed and can determine the stereochemical
outcome, if glycosylation is made with a 3,6-di-O-acylated donor. Therefore, it was interesting to
ascertain, whether the stereochemical results observed for trifluoroacetimidoyl donors can be
reproduced with sulfoxide donors promoted with Tf
α-Stereoselectivity of Tf O-promoted glycosyaltion of the secondary acceptor 30 with the
tetrabenzyl sulfoxide 22 (α:β = 1.8:1, entry 19) and the 3,6-di-O-acetyl sulfoxide 25 (α:β =
2
O.
2
6
.8:1, entry 20) was slightly higher than that for trifluoroacetimidoyl donors 4 (α:β = 1.5:1, entry
) and 20 (α:β = 5.3:1, entry 3). However, the yields of glycosylation with sulfoxides were
1
essentially lower than the yields achieved with the corresponding trifluoroacetimidates.
Glycosylation of the primary acceptor 13 with the sulfoxide donors 22 and 25 was
somewhat contradictory: tetrabenzyl sulfoxide 22 produced a higher proportion of α-35 (α:β =

1
.1:1, entry 21) as compared to the corresponding trifluoracetimidate 4, whereas 3,6-di-O-acetyl
sulfoxide 25 appeared to be less α-stereselective (α:β = 5.9:1, entry 22) than the imidate 20.
,6-O-Benzylidene-2,3-di-O-benzyl sulfoxide 27 demonstrated lower α-selectivity upon
4
glycosylation of both primary and secondary acceptors 13 and 30 (entries 25 and 23) than the
trifluoracetimidate 18 (entries 10 and 15). Moreover, glycosylation with 27 provided lower
yields of the corresponding disaccharides especially for the secondary acceptor 30. It is
noteworthy that no formation of disaccharides 41 and 43 (entries 24 and 26) was detected when
the 3-O-acetylated sulfoxide 28 was coupled with the acceptors 30 and 13.
To summarize, the stereochemical results of glycosylation with the sulfoxide donors 22,
25, and 27 resembled, with minor deviations, those with the corresponding N-
phenyltrifluoroacetimidoyl donors 4, 20, and 18, thus indicating the generality of stereodirecting
effects of protecting groups, in particular remote acyl groups, in different glycosyl donors
regardless of the leaving group type and activation protocol.
2.3. Conclusions
The effect of 3-O- and 6-O-acyl protecting groups on stereochemistry of glucosylation of
primary and secondary glucose acceptor with conformationally flexible monocyclic and
conformationally rigid 4,6-O-benzylidene-protected glucosyl N-phenyltrifluoroacetimidates and
glucosyl sulfoxides has been investigated. The results obtained were sometimes contradictory
(
for example, a certain group in the glucosyl donor exerted an opposite stereochemical effect
depending on the structure of the acceptor) and could not be rationalized in terms of a single
concept, for example, the concept of the remote anchimeric assistance. Nevertheless, some
important particular conclusions could be drawn. Thus, it has been found that, contrary to
previous observations (see refs. 14-18, 20, 40, 50 and ref. 13 for a review), in studied cases a
single 3-O-acetyl group in mono- and bicyclic glucosyl donors did not cause any appreciable α-
directing effect but in one case even changed the stereoselectivity towards the β-anomer. The

latter fact may be attributed to the electron-withdrawing effect of the acetyl group (by analogy
with fluorine in 3-fluoro-3-deoxydonors) or mismatched interaction of the donor and acceptor in
6
glycosylation reaction or other phenomena. On the other hand, the 3-O-acetyl group is able to
6
increase the α-stereoselectivity of 3,6-di-O-acylated donors as compared to the donor with a
single 6-O-acetyl group. The latter donor also demonstrated good α-stereoselectivity on
glycosylation of the primary and especially the secondary acceptor.
α-Stereoselectivity of glycosylation with rigid 4,6-O-benzylidene-protected glucosyl
donors turned out to be temperature-dependent and rose on increasing the reaction temperature
irrespectively of the protecting group type at O-3.
From the synthetic standpoint, 6-O-acetyl and 3,6-di-O-acyl donors proved the most
effective and α-stereoselective donors for the practical synthesis of α-(1→3)- and α-(1→6)-
linked oligosaccharides.
3
Experimental Section
.1 General methods
3
All glycosylation reactions were carried out under dry Ar. Molecular sieves for
glycosylation reactions were activated prior to application at 180 ºC in vacuum of an oil pump
during 2 h. Dichloromethane was successively distilled from diethanolamine, P , and CaH
under Ar. For glycosylation reactions, dichloromethane was freshly redistilled from CaH . THF
was distilled from sodium benzophenone ketyl. DMF was distilled under reduced pressure (17
mm Hg) from phthalic anhydride and then from CaH . Pyridine was dried by distillation from
. Analytical thin-layer chromatography (TLC) was performed on Silica Gel 60 F254
aluminium sheets (Merck), and visualization was accomplished using UV light or by charring at
150 ºC with 10% (v/v) H PO in ethanol. Column chromatography was performed on Silica Gel
2
O
5
2
2
2
2 5
P O
~
3
4
6
0, 40–63 µm (Merck). Analytical HPLC was carried out on a Supelcosil LC-SI column (5 µm,
50×4.6 mm) at a flow rate of 0.8 mL/min with a K-2301 refractive index detector (Knauer)
2

Data processing was performed using the MultiChrom Software. Preparative HPLC was
performed on a Supelcosil LC-SI column (5 µm, 250×21.2 mm) at a flow rate of 8 mL/min with
a K-2401 refractive index detector (Knauer). Optical rotation values were measured using a
1
13
JASCO DIP-360 polarimeter at the ambient temperature in solvents specified. H and C NMR
spectra were recorded on Bruker AMX-400, Bruker DRX-500, and Bruker Avance
spectrometers. Chemical shifts were referenced to residual solvent signals. Signal assignment in
1
13
H and C NMR spectra was made using COSY, TOCSY, and H– C HSQC techniques. High-
1
13
resolution mass spectra were acquired by electrospray ionization on a MicrOTOF II (Bruker
Daltonics) instrument.
3.2. 3-O-Acetyl-2,4,6-tri-O-benzyl-D-glucopyranose (3)
A solution of the methyl glucoside 2 (0.91 mg, 1.95 mmol) in a mixture of AcOH (13
mL) and 1 M aq. HCl (3.45 mL) was boiled under reflux for 1 h and poured into a mixture of
crushed ice and satd NaHCO . The resulting mixture was extracted with EtOAc (4 × 150 mL)
and the combined organic extracts were dried and concentrated. Toluene was evaporated twice
from the solid residue, which was then acetylated with Ac O (5 ml) in pyridine (5 mL) for 5 h.
Pyridine and acetic acid anhydride were evaporated, and toluene was twice evaporated from the
residue. After chromatographic purification on SiO (CHCl – Et O, 40:1), 1,3-di-O-acetyl-2,4,6-
3
2
2
3
2
f
tri-O-benzyl-D- glucopyranose (398 mg, 38%) was obtained as a colorless foam; R 0.62
1
petroleum ether – EtOAc, 1.8:0.5); H NMR (500 MHz, CDCl
(
3
): δ 7.47-7.12 (m, Ar), 6.38 (d,
α
β
α
J
3
3
2
1,2 = 3.5 Hz, H-1 ), 5.65 (d, J1,2 = 8.1 Hz, H-1 ), 5.48 (t, J 9.7 Hz, H-3 ), 5.28 (t, J 9.4 Hz, H-
β
α
α
α
β
2
), 4.72-4.44 (m, CH Ph), 3.91 (m, H-5 ), 3.77 (m, H-6A ), 3.74 (m, H-4 ), 3.73 (m, H-6 ),
β
.72 (m, H-4 ), 3.65 (m, H-6B ), 3.61 (m, H-5 ), 3.59 (m, H-2 ), 3.53 (t, J 9.4 Hz, H-2 ), 2.12,
α
β
α
β
1
3
.03, 1.94, 1.85 (4 s, CH
3 3
CO). C NMR (125 MHz, CDCl ): δ 169.9, 169.7, 169.3, 168.9
β
α
CO), 137.8, 137.5, (ipso-C, Ph), 129.0, 128.0, 127.9 (Ar), 94.0 (C-1 ), 89.5 (C-1 ), 78.4 (C-
(
CH
3
β
2
α
), 76.0 (C-2 ), 75.6 (C-3 ), 75.5 (C-4 , C-5 ), 75.3 (C-4 ), 74.3, 74.2, 73.6 (3 CH
β
α
β
β
2
Ph), 73.3 (C-

α
α
α
β
3
), 72.6 (C-5 ), 72.5 (CH
mg, 4.4 mmol) was added to a solution of the above 1,3-diacetate (1.53 g, 2.9 mmol) in DMF (16
mL), the mixture was stirred for 1.5 h at rt, and poured into cold aq satd NaHCO solution. The
solution was extracted with EtOAc (3 × 200 mL), the combined extracts were dried and
2 3
Ph), 67.8 (C-6 , C-6 ), 21.0, 20.9 (CH CO). Hydrazine acetate (403
3
concentrated. Chromatographic purification (CHCl
3
– Et
2
O, 20:3) of the residue provided the
1
0.59 and 0.47 (petroleum ether – EtOAc, 1.8:0.5); H NMR
hemiacetal 3 (773 mg, 55 %); R
f
α
): δ 7.38–7.10 (m, Ar), 5.50 (t, J 9.5 Hz, H-3 ) 5.28 (br. s, H-1 ), 5.21 (t, J 9.1
α
(
500 MHz, CDCl
3
β
Hz, H-3 ), 4.84 (d, PhCH
β
), 4.74 (dd, J1,2 7.5 Hz, J1,OH 5.2 Hz, H-1 ), 4.65-4.40 (m, PhCH
2
2
),
β
.30 (d, OH ), 4.08 (m, H-5 ), 3.71 (dd, J5,6A 3.5 Hz, J6A,6B 10.7 Hz, H-6A ), 3.68-3.53 (m, H-6 ,
α
α
β
4
α
α
β
β
α
β
H-6B , H-4 , H-4 , H-5 ), 3.50 (dd, J2,1 3.4 Hz, J2,3 9.7 Hz, H-2 ), 3.29 (dd, J2,3 9.4 Hz, H-2 ),
1
CO). C NMR (125 MHz, CDCl
3
1
.91, 1.87 (2 s, CH
3
3
): δ 170.0 (CH
3
CO), 138.2, 137.9, 137.7,
β
37.5 (ipso-C, Ph), 128.5, 128.4, 128.3, 128.1, 128.0, 127.9, 127.8, 127.6 (Ar), 97.4 (C-1 ), 90.8
1
α
β
α
β
α
β
β
C-1 ), 80.0 (C-2 ), 77.5 (C-2 ), 76.2 (C-4 ), 76.0 (C-4 ), 75.5 (C-3 ), 74.4 (C-5 ), 74.2, 73.8,
(
α
Ph), 73.3 (C-3 ), 72.6 (CH
α
β
α
7
3.5 (3 CH
2
2 3
Ph), 69.9 (C-5 ), 68.5 (C-6 ), 68.2 (C-6 ), 21.0 (CH CO).
32 7
Anal. Calcd. for C29H O
: C, 70.71; H, 6.55. Found: C, 70.72; H, 6.62.
3
.3. O-(3-O-Acetyl-2,4,6-tri-O-benzyl-D-glucopyranosyl) N-phenyltrifluoroacetimidate (6)
N-Phenyltrifluoroacetimidoyl chloride (PTAIC) (50 µL, 0.31 mmol) and K CO (45 mg,
.31 mmol) were added to a solution of the hemiacetal 3 (104 mg, 0.21 mmol) in acetone (4.4
2
3
0
mL), and the mixture was intensively stirred until TLC showed the absence of the starting
material. The mixture was filtered through a Celite layer, the solvent was evaporated under
reduced pressure and the residue was purified by column chromatography to give the donor 6
(
f
132 mg, 94%) as an amorphous solid, R 0.69 (petroleum ether – EtOAc, 2:1). Data for α-
1
anomer: H NMR (500 MHz, CDCl
3
): δ 7.60–6.71 (m, 20H, Ar), 6.55 (br. s, 1H, H-1), 5.57 (t,
), 4.01 (m, 1H, H-5), 3.82–3.65 (m, 4H, H-2, H-
CO). C NMR (125 MHz, CDCl ): δ 169.7 (CO), 143.5 (ipso-C,
1
4
H, J 9.7 Hz, H-3), 4.71–4.50 (m, 6H, 3 PhCH
2
1
3
, H-6A, H-6B), 1.96 (s, CH
3
3

NPh), 137.7, 137.5 (ipso-C, Bn), 129.5, 128.7, 128.4, 128.0, 127.9, 127.6 (Ar), 125.7, 124.2,
119.3 (NPh), 92.9 (C-1), 76.4 (C-2), 75.4 (C-4), 73.1 (C-3), 72.8 (C-5), 67.8 (C-6), 21.0
1
(
CH
3
CO). Data for β-anomer: H NMR (500 MHz, CDCl
3
): δ 7.40–6.70 (m, Ar), 5.69 (br s, H-
), 3.80–3.70 (m, H-4, H-6A, H-6B), 2.29 (s, CH CO).
): δ 169.8 (CO), 143.3 (ipso-C, NPh), 137.8, 137.7 (ipso-C, Ph),
29.6, 128.9, 128.4, 128.0, 127.9, 127.6 (Ar), 125.8, 124.3, 119.3 (NPh), 97.2 (C-1), 78.1 (C-2),
5.2-75.3 (C-3, C-4, C-5), 67.8 (C-6), 21.9 (CH CO). Anal. Calcd. for C37 NO : C, 66.96;
1
), 5.22 (m, H-3), 4.82–4.50 (m, PhCH
2
3
1
3
C NMR (125 MHz, CDCl
3
1
7
3
H
36
F
3
8
H, 5.47; N, 2.11. Found: C, 66.89; H, 5.49; N, 2.13.
3.4. p-Methoxyphenyl 3-O-benzyl-4,6-O-benzylidene-β-D-glucopyranoside (8) and p-
methoxyphenyl 2-O-benzyl-4,6-O-benzylidene-β-D-glucopyranoside (10)
A mixture of the diol 7 (6.38 g, 17.06 mmol) and dibutyltin oxide (4.25 g, 17.06 mmol)
in toluene (480 mL) was boiled under refluxed with aseotropic removal of water for 6 h. The
solvent was evaporated and benzyl bromide (100 mL) was added. The resulting mixture was
stirred at 80-90 °C until TLC indicated that the starting material had disappeared. Benzyl
bromide was removed in vacuum of an oil pump and benzyl ethers 10 (4.61 g, 58%) and 8 (3.02
g, 38.6%) were isolated from the residue by column chromatography (petroleum ether – CH
2
Cl
2
–
acetone, 2:1:0.1→1.5:1:0.1). Data for 10: white crystals, mp 150–153 °C; [α]
D
+4.5 (c 1,
1
CHCl
Ph), 7.05 (d, 2H, J 9.1 Hz, C
.07 (d, 1H, Jgem 11.3 Hz, PhCH
dd, 1H, J6A,5 5.0 Hz, J6A,6B 10.5 Hz, H-6A), 3.95 (t, 1H, J 9.4 Hz, H-3), 3.84 (t, 1H, J 10.7 Hz,
3
); R
f
0.52 (CHCl
3
– acetone, 50:1); H NMR (600 MHz, CDCl
3
): δ 7.52–7.28 (m, 10H, 2
OCH ), 5.58 (s, 1H, PhCH),
A), 5.05 (d, 1H, J1,2 7.9 Hz, H-1), 4.88 (d, 1H, PhCH B), 4.39
6
H
4
OCH
3
), 6.88 (d, 2H, J 9.0 Hz, C
6
H
4
3
5
2
2
(
1
3
H-6B), 3.82 (s, 3H, CH
3
O), 3.67-3.62 (m, 2H, H-2, H-4), 3.55 (m, 1H, H-5). C NMR (150.9
OCH ), 114.7
), 73.3 (C-3), 68.7
MHz, CDCl
3
): δ 129.2, 128.5, 128.3, 128.2, 128.0, 126.3 (Ar), 118.5 (C
6
H
4
3
(
C
6
H
4
OCH ), 102.3 (C-1), 101.8 (PhCH), 81.7 (C-2), 80.2 (C-4), 75.0 (PhCH
3
2

(
3 28 7
C-6), 66.2 (C-5), 55.7 (CH O) Anal. Calcd. for C27H O : C, 69.81; H, 6.08. Found: C, 69.91;
H, 6.28.
D 3 f 3
Data for 8: white crystals, mp 200-205 ºC; [α] +24.3 (c 1, CHCl ); R 0.46 (CHCl –
1
acetone, 50:1); H NMR (600 MHz, CDCl
3
): δ 7.52–7.25 (m, 10H, Ar), 7.05 (d, 2H, J 9.0 Hz,
OCH ), 5.62 (s, 1H, PhCH), 5.03 (d, 1H, Jgem 11.7 Hz,
A), 4.93 (d, 1H, J1,2 7.7 Hz, H-1), 4.86 (d, 1H, PhCH B), 4.40 (dd, 1H, J6A,5 4.9 Hz, J6A,6B
0.6 Hz, H-6A), 3.88–3.82 (m, 2H, H-2, H-6B), 3.81 (s, 1H, CH
C
6
H
4
OCH
3
), 6.87 (d, 2H, J 9.0 Hz, C
6
H
4
3
PhCH
2
2
1
3
O), 3.80–3.74 (m, 2H, H-4, H-
): δ 129.0, 128.5, 128.3, 128.1, 127.9, 126.0
), 102.6 (C-1), 101.4 (PhCH), 81.2, 80.3 (C-3, C-4), 74.7
), 74.1 (C-2), 68.7 (C-6), 66.6 (C-5), 55.7 (CH O). Anal. Calcd.for C27 : C, 69.81 H,
.08. Found: C, 69.68; H, 6.29.
1
3
3
), 3.56 (m, 1H, H-5). C NMR (150.9 MHz, CDCl
3
(
(
Ar), 118.8, 114.6 (C
6
H
4
OCH
3
PhCH
2
3
28 7
H O
6
3.5. p-Methoxyphenyl 2,3-di-O-benzyl-4,6-O-benzylidene-β-D-glucopyranoside (9)
Benzyl bromide (380 µL, 3.2 mmol) and NaH (130 mg of 60% dispersion, 3.2 mmol)
were added to a solution of 8 (500 mg, 1.08 mmol) in dry DMF (15 mL). The mixture was
stirred until TLC indicated disappearance of the starting material, diluted with EtOAc and
successively washed with 1 M HCl, water, aq satd NaHCO
3
, and water. The organic layer was
dried with Na SO , the solvent was removed under reduced pressure and the residue was purified
2
4
by column chromatography (petroleum ether–EtOAc, 6:1). Dibenzyl ether 9 (549 mg, 92%) was
1
isolated as white crystals; H NMR (400 MHz, CDCl
3
): δ 7.52–7.50 (m, 2H, Ar), 7.42–7.29 (m,
), 6.88 (d, 2H, J 9.0 Hz, C OCH ), 5.61 (s, 1H,
PhCH), 5.03 (d, 1H, J1,2 7.7 Hz, H-1), 5.01 (d, 1H, Jgem 10.9 Hz, PhCH A), 4.97 (d, 1H, Jgem 11.4
Hz, PhCH A’), 4.89 (d, 1H, PhCH B), 4.85 (d, 1H, PhCH B’), 4.40 (dd, 1H, J5,6A 5.2 Hz, J6A,6B
0.6 Hz, H-6A), 3.87–3.77 (m, 7H, H-6B, H-3 or H-4, H-2, CH
1
5H, Ar), 7.03 (d, 2H, J 9.0 Hz, C
6
H
4
OCH
3
6
H
4
3
2
2
2
2
1
3
O), 3.74 (t, 1H, J 8.3 Hz, H-3 or
1
H-4), 3.53 (m, 1H, H-5). H NMR data were in accordance with those published.
68

3.6. О-(2,3-Di-О-benzyl-4,6-O-benzylidene-D-glucopyranosyl) N-phenyltrifluoroacetimidate
(
18)
Cerium(IV) ammonium nitrate (5.20 g, 9.48 mmol) was added to a solution of 9 (525 mg,
.95 mmol) in a mixture of CH CN, toluene, and water (1:1:1, 75 mL). The mixture was
intensively stirred at room temperature until TLC showed disappearance of the starting material,
diluted with EtOAc, and washed with aq satd NaHCO and water. The organic layer was dried
with Na SO , concentrated, and the residue was purified by silica gel column chromatography
0
3
3
2
4
(
(
(
petroleum ether – EtOAc, 5:1) to afford 2,3-di-О-benzyl-4,6-O-benzylidene-D-glucopyranose
1
256 mg, 60%) as a 1:1 mixture of α- and β-anomers; H NMR (CDCl3, 500 MHz): δ 7.55–7.28
α,β
α
2
ArH), 5.60 (2 s, 1H, PhCH ), 5.22 (d, 0.5H, J1,2 4.4 Hz, H-1 ), 5.00-4.75 (m, 4.5H, 2 PhCH ,
β
H-1 ), 4.38 (dd, 0.5 H, J5,6A 4.9 Hz, J6A,6B 10.4 Hz, H-6A), 4.33 (dd, 0.5 H, J5,6A 4.9 Hz, J6A,6B
α
0.3 Hz, H-6A), 4.11 (m, 0.5 H, H-5 ), 4.04 (t, 0.5 H, J 9.3 Hz, H-3 ), 3.81 (t, 1H, J 9.8 Hz, H-
α
1
α,β β
), 3.78-3.70 (m, 1H), 3.70-3.60 (m, 1H), 3.50 (m, 0.5 H, H-5 ), 3.45 (t, 0.5H J 8.2 Hz), 3.24
4
1
br. s, 0.5H, OH), 3.12 (br. s, 0.5H, OH). H NMR data were in agreement with those
(
6
7
published. The above hemiacetal (245 mg, 0.547 mmol) was dissolved in acetone (11.4 mL),
PTAIC (105 µL, 0.656 mmol) and K CO (118 mg, 0.821 mmol) were added and the reaction
2
3
mixture was intensively stirred until TLC showed the absence of the starting material. The
resulting mixture was filtered through a pad of Celite, the filtrate was concentrated under
reduced pressure, and the residue was purified by column chromatography (petroleum ether –
EtOAc, 12:1) to give 18 (319 mg, 94 %) as an α,β-mixture in a ratio of ~1:6. Pure anomers were
D 3 f
isolated for characterization purposes. Data for 18α: [α] +44.6 (c 1, CHCl ); R 0.57 (petroleum
1
ether–EtOAc, 2:1); H NMR (500 MHz, C
6
D
6
): δ 7.68– 6.81 (m, 20H, 4 Ph), 6.67 (br. s, 1H, H-
A), 4.83 (d, 1H, PhCH B), 4.77 (d, 1H,
B’), 4.29 (t, 1H, J 9.3 Hz, H-3), 4.26-4.21 (m, 2H,
H-5, H-6A), 3.68 (dd, 1H, J2,1 = 3.4 Hz, J2,3 = 9.2 Hz, H-2), 3.58 (t, 1H, J 9.3 Hz, H-4), 3.52 (t,
1
), 5.43 (s, 1H, PhCH), 5.01 (d, 1H, Jgem 11.7 Hz, PhCH
2
2
J
gem 12.0 Hz, PhCH A’), 4.67 (d, 1H, PhCH
2
2
1
3
1
6 6
H, J 10.4 Hz, H-6B). C NMR (150.9 MHz, C D ): δ 144.5, 139.8, 138.9, 138.5, 129.4, 129.0,

128.8, 128.7, 128.6, 128.5, 128.4, 128.2, 128.0, 127.0, 124.9, 120.2 (ArH), 102.2 (PhCH), 95.0
(
C-1), 82.4 (C-4), 79.5 (C-2), 79.2 (C-3), 75.8 (PhCH
2
), 74.4 (PhCH
2
), 69.2 (C-6), 66.2 (C-5).
1
0.66 (petroleum ether – EtOAc, 2:1); H-NMR (500
Data for 18β: [α]
D
+48.4 (c 1, CHCl
3
); R
f
MHz, C
gem 11.9 Hz, PhCH
Hz, H-6A), 3.82-3.73 (m, 2H, H-2, H-3), 3.62 (t 1H, J 9.2, Hz H-4), 3.52 (t, 1H, J 10.1 Hz, H-
6
D
6
): δ 7.62–6.82 (m, 20H, 4 Ph), 5.91 (br. s, 1H, H-1), 5.33 (s, 1H, PhCH), 4.99 (d, 1H,
J
2
A), 4.90 (s, 2H, PhCH ), 4.82 (d, 1H, PhCH B), 4.17 (dd, 1H, J6A,6B 10.3
2
2
1
B), 3.21 (bs, 1H, H-5). C-NMR (150.9 MHz, C
3
6
1
8
6 6
D ): δ 144.3, 138.9, 138.5, 129.4, 129.3,
28.9, 128.8, 128.6, 128.1, 126.9, 125.0, 120.0 (ArH), 102.0 (PhCH), 98.1 (C-1), 81.8 (C-4),
1.5 (C-3), 81.3 (C-2), 75.7 (PhCH
2
), 75.2 (PhCH
2
), 69.0 (C-6), 67.2 (C-5). HR ESI MS for the
NO Na: 2.2074, found: 642.2046.
+
anomeric mixture of 18 calcd for [M + Na] C35
H
32
F
3
6
3.7. О-(3-O-Acetyl-2-О-benzyl-4,6-O-benzylidene-D-glucopyranosyl) N-
phenyltrifluoroacetimidate (19)
CAN (2.12 g, 9.48 mmol) was added to a solution of compound 11 (391 mg, 0.773
mmol) in 80% aq acetonitrile (65 mL) and the mixture was intensively stirred at rt until TLC
showed disappearance of the starting material. The mixture was diluted with EtOAc and washed
3 2 4
with aq satd NaHCO and water, the organic layer was dried with Na SO and concentrated.
Purification of the residue on a silica gel column (petroleum ether – EtOAc, 3:1→2:1) provided
1
3
-O-acetyl-2-О-benzyl-4,6-O-benzylidene-D-glucopyranose (256 mg, 83%). H NMR (400
β
β
3
MHz, CDCl ): δ 7.40–7.10 (m, 10H, Ar), 5.44 (t, 1H, J 9.6 Hz H-3 ), 5.37(s, 1H, PhCH ), 5.35
α
α
s, 1H, PhCH ), 5.22 (t, 1H, J 9.3 Hz, H-3 ), 5.17 (d, J1,2 3.7 Hz, 1H, H-1 ), 4.78 (d, 1H, Jgem
α
(
α
A ), 4.75 (d, J1,2 7.7 Hz, 1H, H-1 ), 4.55-4.60 (d, 3H, PhCH
β
11.9 Hz, PhCH
2
2
), 4.52 (d, 1H,
β
B ), 4.20 (m, 2H, H-6A
α
,
β
α
α
H-6A ), 4.04 (m, 1H, H-5 ), 3.65 (t, 1H, J 10.2 Hz, H-6B ),
PhCH
2
β
.60 (t, 1H, J 10.3 Hz, H-6B ), 3.51 (dd, 1H, J2,3 9.4 Hz, H-2 ), 3.49 (t, J 9.6 Hz, 1H, H-4 ), 3.45
α
α
3
β
t, 1H, J 9.7 Hz, H-4 ), 3.39 (m, 1H, H-5 ), 3.31 (dd, 1H, J2,3 9.2 Hz, H-2 ), 1.96 (s, 3H,
β
β
(
β
α
13
3 3 3 3
CH CO ), 1.90 (s, 3H, CH CO ). C NMR (100.9 MHz, CDCl ): δ 170.10 (CH CO), 138.0,

1
1
4
6
37.3, 137.1, 137.0, 129.01, 128.7, 128.5, 128.5, 128.4, 128.3, 128.1, 128.0, 127.8, 126.25,
β
26.20 (Ar), 101.6, 101.4 (PhCH), 98.0 (C-1 ), 91.8 (C-1 ), 80.8 (C-2 ), 79.2 (C-2 ), 78.8 (C-
α
β
α
β
α
), 78.8 (C-4 ), 74.4 (PhCH
β
α
α
β
), 72.7 (C-3 ), 70.7 (C-3 ), 69.0 (C-6 ), 68.7 (C-6 ),
2
), 73.0 (PhCH
2
β
α
6.3 (C-5 ), 62.6 (C-5 ), 21.03, 20.95 (CH
3
24 7
CO). Anal. Calcd.for C22H O : C, 65.99 H, 6.04.
Found: C, 65.88; H, 6.27.
Compound 19 (124 mg, 92.5%) was obtained as an α,β-mixture in a ratio of ~1:6 from
the above hemiacetal (94 mg, 0.235 mmol) as described for preparation of 6 and purified by
silica gel column chromatography (petroleum ether – EtOAc, 12:1→10:1). Pure anomers were
D 3 f
isolated for characterization purposes. Data for 19α: syrup, [α] +70.6 (c 1, CHCl ); R 0.53
1
(
petroleum ether–EtOAc, 3:1); H NMR (400 MHz, C
6
D
6
): δ 7.65–6.78 (m, 15H, Ar), 6.70 (br. s,
A),
B), 4.29 (m, 1H, H-5), 4.19 (dd, 1H, J6A,5 5.0 Hz, J6A,6B 10.3 Hz, H-6A), 3.68
1
H, H-1), 5.63 (t, 1H, J 9.8 Hz, H-3), 5.38 (s, 1H, PhCH), 4,60 (d, Jgem 12,3 Hz, 1H, PhCH
.49 (d, 1H, PhCH
2
4
2
1
3
(
dd, 2H, J2,1 3.1 Hz, J2,3 9.7 Hz, H-2), 3.55–3.47 (m, 2H, H-4, H-6B), 1.79 (s, 3H, CH
NMR (100.9 MHz, acetone-d ): δ 129.7, 129.2, 128.9, 128.7, 128.6, 127.2, 125.2, 120.2 (Ar),
02.2 (PhCH), 94.9 (C-1), 79.2 (C-4), 77.9 (C-2), 73.9 (PhCH ), 71.0 (C-3), 68.9 (C-6), 66.4 (C-
), 20.9 (CH CO). Data for 19β: syrup, [α] +46.2 (c 1, CHCl ); R 0.67 (petroleum ether –
): δ 7.62–6.79 (m, 15H, ArH), 5.93 (br. s, 1H, H-1), 5.62
t, 1H, J 8.6 Hz, H-3), 5.30 (s, 1H, PhCH), 4.87 (d, 1H, Jgem 11.9 Hz, PhCH A), 4.74 (d, 1H,
B), 4.12 (dd, 1H, J5,6A 4.9 Hz, J6A,6B 10.3 Hz, H-6A), 3.78 (t, 1H, J 7.6 Hz, H-2), 3.60 (t,
CO).
CO), 144.1, 138.5, 138.2, 129.5, 129.4, 129.1, 128.7,
28.6, 128.4, 128.2, 127.1, 125.2, 120.0 (Ar), 102.3 (PhCH), 98.1 (C-1), 79.6 (C-2), 79.1 (C-4),
5.0 (PhCH ), 73.3 (C-3), 69.1 (C-6), 67.1 (C-5), 20.8 (CH CO). HR ESI MS calcd for [M +
NNaO 594.1710, found 594.1631. Anal. Calcd.for C30 NO : C, 63.04, H,
.94, N 2.45. Found: C, 62.93, H, 4.80, N, 2.52.
3
CO). C
6
1
5
2
3
D
3
f
1
6 6
EtOAc, 3:1); H NMR (600 MHz, C D
(
2
PhCH
2
1
H, J 9.6 Hz, H-4), 3.48 (t, 1H, J 10.2 Hz, H-6B), 3.29 (br. s, 1H, H-5), 1.78 (s, 3H, CH
3
1
3
6 6 3
C NMR (150.9 MHz, C D ): δ 169.5 (CH
1
7
2
3
+
Na] C30
H
28
F
3
7
H
28
F
3
7
4

3.8. p-Methoxyphenyl 3-O-acetyl-2-O-benzyl-4,6-O-benzylidene-β-D-glucopyranoside (11)
A solution of 10 (400 mg, 0.862 mmol) in a mixture of pyridine (0.85 mL) and acetic
anhydride (0.65 mL) was kept at rt for 5 h and concentrated. Residual pyridine and Ac
2
O were
removed by coevaporation with toluene. The residue was purified by column chromatography
(
[
petroleum ether – EtOAc, 3:1) to give pure 11 (414 mg, 95 %); white crystals, mp 165-170 °C;
1
α]
D
–7.3 (c 1, CHCl
.27 (m, 10H, Ar), 7.08 (d, 2H, J 8.9 Hz C
H, PhCH), 5.42 (t, J 9.4 Hz, 1H, H-3), 5.12 (d, J1,2 7.6 Hz, 1H, H-1), 4.99 (d, 1H, Jgem 11.7 Hz,
A), 4.79 (d, 1H, PhCH B), 4.40 (dd, 1H, J6A,5 6 Hz, J6A,6B 10.6 Hz, H-6A), 3.83 (br. t, 1H,
H-6B), 3.82 (s, 3H, CH O), 3.74 (t, 1H, J 8.3 Hz, H-2), 3.71 (t, J 9.6 Hz, 1H, H-4), 3.62 (m, 1H,
H-5), 2.03 (s, 3H, CH
3
); R
f
0.67 (toluene – EtOAc, 6:1); H NMR (600 MHz, CDCl
3
): δ 7.50–
7
1
6
H
4
OMe), 6.89 (d, 2H, J 8.9 Hz C
6
H
4
OMe), 5.51 (s,
PhCH
2
2
3
1
3
3
CO). C NMR (150.9 MHz, CDCl
29.1, 128.4, 128.2, 127.9, 126.2 (Ar), 151.0, 155.8, 118.7, 114.7 (C
01.45 (PhCH), 79.6 (C-2), 78.6 (C-4), 74.7 (PhCH ), 72.6 (C-3), 68.7 (C-6), 66.3 (C-5), 55.7
O), 20.9 (CH CO). Anal. Calcd. for C29 : C, 68.76, H, 5.97. Found: C, 68.73; H, 5.90.
3
): δ 169.8 (CH
3
CO), 137.9, 136.9,
1
1
6
H
4
OCH
3
), 103.4 (C-1),
2
(
CH
3
3
30 8
H O
3.9. p-Methoxyphenyl 3-O-benzoyl-2-O-benzyl-4,6-O-benzylidene-β-D-glucopyranoside (12)
Benzoyl chloride (500 µL, 4.3 mmol) and DMAP (132 mg, 1.08 mmol) were added to a
solution of 10 (500 mg, 1.08 mmol) in pyridine (10 mL). When TLC showed disappearance of
the starting material, the reaction was quenched by adding aq satd NaHCO . The resulting
mixture was extracted three times with CH Cl , the combined extracts were concentrated and
residual pyridine was removed by coevaporation with toluene. After column chromatography
3
2
2
(
toluene – EtOAc, 30:1), compound 12 (600 mg, 98 %) was obtained; white crystals, mp 165–
1
1
70°C; [α]
CDCl ): δ 8.02–7.10 (m, 15H, 3 Ph), 7.08 (d, 2H, J 9.1 Hz, C
OCH ), 5.68 (t, 1H, J 9.3 Hz, H-3), 5.51 (s, 1H, PhCH), 5.18 (d, 1H, J1,2 7.4 Hz, H-1), 4.92
d, 1H, Jgem 11.5 Hz, PhCH A), 4.77 (d, 1H, PhCH B), 4.42 (dd, 1H, J6A,5 5.0 Hz, J6A,6B 10.5 Hz,
D
+2.4 (c 1, CHCl
3
); R
f
0.51 (petroleum ether – EtOAc, 3:1); H NMR (600 MHz,
3
6 4 3
H OCH ), 6.89 (d, 2H, J 9.1 Hz,
C
6
H
4
3
(
2
2

3
H-6A), 3.88–3.65 (m, 3H, H-2, H-4, H-6B), 3.81 (s, 3H, CH O), 3.68 (m, 1H, J5,6A 4.9 Hz, H-5).
1
3
C NMR (100.6 MHz, CDCl ): δ 137.5, 136.8, 133.0, 129.9, 129.0, 128.3, 128.2, 127.7, 126.1
3
(
Ar), 118.7, 114.7 (C OCH ), 103.4 (C-1), 101.4 (PhCH), 79.3 (C-2 or C-4), 78.7 (C-2 or C-
6
H
4
3
4
2 3 32 8
), 74.5 (PhCH ), 73.2 (C-3), 68.7 (C-6), 66.3 (C-5), 55.7 (CH O). Anal. Calcd.for C34H O : C,
71.82, H, 5.67. Found: C, 71.90; H, 5.76.
3
.10. p-Methoxyphenyl 2,4-di-O-benzyl-β-D-glucopyranoside (14)
M solution of BH ·THF in THF (22.6 mL, 22.54 mmol) was added to a solution of 10
5.23 g, 11.27 mmol) in dry CH Cl (90 mL). Then TMSOTf (306 µL, 1.7 mmol) was added
1
3
(
2
2
dropwise and the mixture was stirred under argon atmosphere at rt until TLC showed
disappearance of the starting material. The reaction was quenched by adding MeOH (10 mL) and
3
Et N (5 mL), the resulting mixture was concentrated, and MeOH (3×35 mL) was evaporated
from the residue. Purification of the residue by silica gel column chromatography (toluene –
D
EtOAc, 12:1) afforded diol 14 (4.71 g, 90%) as white crystals, mp 112–113 °C; [α] +0.3 (c 1,
1
CHCl
3
); R
f
0.39 (toluene – EtOAc, 5:1); H NMR (600 MHz, CDCl
3
): δ 7.40–7.30 (m, 10H, Ar),
OMe), 5.07 (d, 1H, Jgem 11.4 Hz,
A), 4.95 (d, 1H, J1,2 7.8 Hz, H-1), 4.92 (d, 1H, Jgem 11.3 Hz, PhCH A’), 4.79 (d, 1H,
B), 4.71 (d, 1H, PhCH B’), 3.91 (ddd, 1H, J5,6A 2.9 Hz, J6A,6B 12.0 Hz, J6A,OH 6.1 Hz, H-
O), 3.75 (ddd, 1H, J5,6B 4.9 Hz,
6B,OH 7.6 Hz, H-6B), 3.56 (t, 1H, J 9.3 Hz, H-4), 3.51 (dd, 1H, J2,3 9.0 Hz, H-2), 3.48 (m, 1H, H-
7.00 (d, 2H, J 9.1 Hz, C
6
H
4
OMe), 6.86 (d, 2H, J 9.1 Hz, C
6
H
4
PhCH
PhCH
2
2
2
2
6
A), 3.84 (dt, 1H, J3,OH 2.3 Hz, J 8.9 Hz, H-3), 3.79 (s, 3H, CH
3
J
1
3
5
1
7
6
), 2.54 (d, 1H, 3-OH), 1.95 (br. t, 1H, 6-OH); C NMR (100.6 MHz, CDCl
28.6, 128.3, 128.2, 128.1 (Ar), 118.2, 114.8 (C OCH ), 102.3 (C-1), 81.3 (C-2), 77.1 (C-4),
6.7 (C-3), 75.4 (C-5), 74.8 (PhCH ), 62.2 (C-6), 55.8 (CH O). Anal. Calcd.for C27 : C,
9.51 H, 6.48. Found: C, 69.71; H, 6.63.
3
): δ 138.2, 128.7,
6
H
4
3
2
3
30 7
H O
3.11. p-Methoxyphenyl 3,6-di-O-acetyl-2,4-di-O-benzyl-β-D-glucopyranoside (15)

Acetylation of 14 (210 mg, 0.45 mmol) as described above for the preparation of 11
afforded, after column chromatography (toluene – EtOAc, 15:1), diacetate 15 (243 mg, 98%) as
white crystals, mp 117–119°C; [α]
D
+2.4 (c 1, CHCl
3
); R
f
0.36 (petroleum ether – EtOAc, 3:1);
OCH ), 6.84
), 5.33 (t, 1H, J 9.2 Hz, H-3), 4.96–4.92 (m, 2H, H-1, PhCH A),
.73 (d, 1H, Jgem 11.9 Hz, PhCH B), 4.59 (d, 1H, Jgem 11.2 Hz, PhCH A’), 4.54 (d, 1H,
B’), 4.36 (dd, 1H, J6A,6B 11.8 Hz, J6A,5 2.2 Hz, H-6A), 4.25 (dd, 1H, J6B,6A 12.0 Hz, J6B,5
3
.4 Hz, H-6B), 3.78 (s, 3H, CH O), 3.68 (m, 1H, H-5), 3.64-3.58 (m, 2H, H-2, H-4), 2.05 (s, 3H,
1
H NMR (400 MHz, CDCl
3
): δ 7.39–7.22 (m, 10H, Ar), 7.02 (d, 2H, J 9.0 Hz, C
6
H
4
3
(
d, 2H, J 9.0 Hz, C OCH
6
H
4
3
2
4
2
2
PhCH
2
5
1
3
CH
3
CO), 1.92 (s, 3H, CH
28.1, 128.0, 127.8 (Ar), 118.7, 114.6 (C
), 74.5 (PhCH ), 74.2 (PhCH ), 72.9 (C-5), 62.9 (C-6), 55.7 (CH
CO). Anal. Calcd.for C31 : C, 67.62, H, 6.22. Found: C, 67.77; H, 6.04.
3
CO). C-NMR (100.6 MHz, CDCl
OCH ), 102.8 (C-1), 78.9 (C-2), 76.1 (C-4), 75.5 (C-
O), 21.0 (CH CO), 20.8
3 3
): δ 169.8 (CH CO), 128.5, 128.4,
1
3
6
H
4
3
2
2
3
3
(
CH
3
34 9
H O
3
.12 p-Methoxyphenyl 6-O-benzoyl-2,4-di-O-benzyl-β-D-glucopyranoside (16)
Pyridine (6 mL) and benzoyl chloride (1.18 mL, 10.1 mmol) were added to a solution of
4 (3.93 g, 8.43 mmol) in dry CH Cl (100 mL) at –20 ºC. When TLC showed full conversion of
Cl , washed successively with aq
, and water. The organic layer was dried over Na SO , the
1
2
2
the starting material, the reaction mixture was diluted with CH
2
2
1
M HCl, water, aq satd NaHCO
3
2
4
solvent was removed under reduced pressure and residue was purified by column
chromatography (toluene – EtOAc, 15:1) to afford monobenzoate 16 (4.30 g, 89.5%) as white
1
crystals, mp 107–108 °C; [α]
MHz, CDCl ): δ 7.94–7.15 (m, 15H, 3 Ph), 6.91 (d, 2H, J 8.9 Hz, C
Hz, C OMe), 5.00 (d, 1H, Jgem 11.4 Hz, PhCH A), 4.84 (d, 1H, Jgem 11.2 Hz, PhCH
d, 1H, J1.2 7.8 Hz, H-1), 4.71 (d, 1H, PhCH B), 4,61 (d, 1H, PhCH B’), 4.58 (m, 1H, H-6A),
.35 (dd, 1H, J6B,6A 11.8 Hz, J6B,5 6.7 Hz, H-6B), 3.77 (t, 1H, J 8.9 Hz, H-3), 3.66 (m, 1H, H-5),
D
+6.9 (c 1, CHCl
3
); R
f
0.39 (toluene – EtOAc, 5:1); H NMR (400
3
6
H
4
OMe), 6.62 (d, 2H, J 8.9
A’), 4.79
6
H
4
2
2
(
2
2
4
3
1
3
3 3
.63 (s, 3H, CH O), 3.47 (m, 2H, H-2, H-4). C NMR (100.6 MHz, CDCl ): δ 166.2 (PhCO),

1
38.2, 137.9, 133.1, 129.8, 129.1, 128.7, 128.6, 128.4, 128.2, 128.1, 128.0, 127.9 (Ar), 118.5,
14.6 (C OCH ), 102.5 (C-1), 81.2 (C-2), 77.3 (C-4), 77.0 (C-3), 74.71 (PhCH ), 74.69
), 73.3 (C-5), 63.9 (C-6), 55.7 (CH O). Anal. Calcd. for C34 : C, 71.56, H, 6.01.
Found: C, 71.33; H, 6.28.
1
6 4
H
3
2
(
PhCH
2
3
34 8
H O
3.13. p-Methoxyphenyl 3-O-acetyl-6-O-benzoyl-2,4-di-O-benzyl-β-D-glucopyranoside (17)
Compound 16 (284 mg, 0.50 mmol) was acetylated as described for 11. After purification
by silica gel column chromatography (toluene – EtOAc, 12:1), acetate 17 (300 mg, 98%) was
1
obtained as a foam, [α]
MHz, CDCl ): δ 7.97–7.14 (m, 15H, 3 Ph), 6.91 (d, 2H, J 9.1 Hz, C
Hz, C OMe), 5.29 (t, 1H, J 9.3 Hz, H-3), 4.90–4.86 (m, 2H, H-1, PhCH
1.9 Hz, PhCH B), 4.57–4.47 (m, 3H, H-6A, PhCH A’, PhCH B’), 4,37 (dd, 1H, J6B,5 6.3 Hz,
6B,6A 11.8 Hz, H-6B), 3,74 (m, 1H, H-5), 3.65 (s, 3H, CH O), 3.62–3.53 (m, 2H, H-2, H-4), 1,84
): δ 169.9 (CH CO), 166.2 (PhCO), 138.1, 137.3,
33.2, 129.8, 128.6, 128.4, 128.2, 128.1, 127.9 (Ar), 118.9, 114.6 (C OCH ), 102.9 (C-1),
9.1 (C-2), 76.6 (C-4), 75.6 (C-3), 74.6, 74.3 (PhCH ), 73.2 (C-5), 63.5 (C-6), 55.7 (CH O), 21.1
CO). Anal. Calcd. for C34 : C, 70.58, H, 5.92. Found: C, 70.58; H, 5.74.
D
+9.2 (c 1, CHCl
3
); R
f
0.48 (toluene – EtOAc, 10:1); H NMR (400
3
6
H
4
OMe), 6.63 (d, 2H, J 9.0
A), 4.66 (d, 1H, Jgem
6
H
4
2
1
2
2
2
J
3
1
3
(
s, 3H, CH
3
CO). C NMR (100.6 MHz, CDCl
3
3
1
7
6
H
4
3
2
3
(
CH
3
34 8
H O
3.14. О-(3,6-Di-O-acetyl-2,4-di-О-benzyl-D-glucopyranosyl) N-phenyltrifluoroacetimidate
(
20)
CAN (1.00 g, 1.85 mmol) was added to a solution of 15 (203 mg, 0.369 mmol) in a
mixture of CH CN (25 mL) and water (6.3 mL) at 0 °C. After being stirred for 10 min, the
reaction mixture was diluted with EtOAc and washed with aq satd NaHCO and water. The
organic layer was dried over Na SO and the solvent was removed in vacuum. Chromatographic
3
3
2
4
purification (petroleum ether – EtOAc, 2:1) on silica gel provided 3,6-di-O-acetyl-2,4-di-О-
1
benzyl-D-glucopyranose (129 mg, 79%) as a syrupy α,β-mixture in a ratio of 1.9:1; H NMR

α
(
3
600 MHz, CDCl ): δ 7.40-7.20 (m, Ar), 5.53 (t, 1.9 H, J 9.4 Hz, H-3 ), 5.29 (t, 1H, J 9.4 Hz, H-
β
3
α
), 5.25 (d, 1.9H, J1,2 3.4 Hz, H-1 ), 4.87 (d, 1H, Jgem 11.9 Hz, PhCH
β
2
), 4.83 (dd, 1H, J1,2 7.7
β
Hz, J1,OH 4.9 Hz, H-1 ), 4.67-4.64 (m, 2.9H, PhCH
α
β
α
,
2
, PhCH
2
), 4.61-4.55 (m, 3.8H, 2PhCH
2
β
α
β
PhCH
2
), 4.54-4.50 (m, 2.9H, PhCH
2 2
, PhCH ), 4.36 (dd, 1H, J6A,5 2.1Hz, J6A,6B 12.0 Hz, H-
β
A ), 4.31 (dd, 1.9H, J6A,5 2.3 Hz, J6A,6B 11.8 Hz, H-6A ), 4.20-4.15 (m, 2.9H, H-6B , H-5 ),
α
β
α
6
3
2
β
.63 (m, 1H, H-5 ), 3.57-3.49 (m, 3.8H, H-4 , H-4 , H-2 ), 3.31 (dd, J2,3 9.6 Hz, H-2 ), 3.18 (m,
β
α
α
β
α
.9H, OH , OH ), 2.07, 2.07, 1.99, 1.92 (4s, CH
β
3
CO).
Transformation of the hemiacetal (102 mg, 0.230 mmol) into donor 20 was conducted
according to the procedure described for the preparation of 6. Pure 20 (121 mg, 86%) was
isolated by column chromatography (petroleum ether – EtOAc, 10:1→8:1) as a syrupy mixture
1
of α- and β-anomers in a ratio of 2:1; H NMR (600 MHz, CDCl
3
): δ 7.40-7.10 (13H, Ar), 6.85
α
β
(
d, 2H, C(NPh)CF
3
3
), 6.25 (d, 2H, C(NPh)CF ), 6.48 (br. s, 1H, H-1 ), 5.68 (br. s, 2H, H-1 ),
α
.60 (t, 1H, J 9.6 Hz, H-3 ), 5.27 (t, 2H, J 8.5 Hz, H-3 ), 4.81 (d, 2H, Jgem 11.8 Hz, PhCH
β
β
5
2
),
α
α
β
4
.70 (d, 1H, Jgem 12.3 Hz, PhCH
2
), 4.66-4.51 (m, 9H, 3PhCH
2
, 3PhCH
2
), 4.38-4.32 (m, 3H,
α
β
H-6A , H-6A ), 4.26 (dd, 1H, J6B,5 4.4 Hz, J6B,6A 12.2 Hz, H-6B ), 4.20 (dd, 2H, J6B,5 4.5 Hz,
α
β
6B,6A 12.1 Hz, H-6B ), 4.08 (m, 1H, H-5 ), 3.77 (br. s, 2H, H-5 ), 3.68-3.55 (m, 6H, H-4 , H-4 ,
α
β
α
β
J
α
H-2 , H-2 ), 2.07, 2.05, 2.00, 1.92 (4 s, CH
β
+
3
CO). HR ESI MS calcd. for [M + Na]
C
32
H
32
F
3
NNaO : 638.1972, found: 538.1922.
8
3
.15. О-(3-O-Acetyl-6-O-benzoyl-2,4-di-О-benzyl-D-glucopyranosyl) N-
phenyltrifluoroacetimidate (21)
CAN (1.30 g, 2.37 mmol) was added to a solution of 17 (290 mg, 0.474 mmol) in a
mixture of CH CN (32 mL) and H O (8 mL) at 0 °C. After 10 min, the reaction mixture was
diluted with EtOAc and washed with aq satd NaHCO and water. The organic layer was dried
over anhydrous Na SO and the solvent was removed in vacuum. Chromatographic purification
3
2
3
2
4

(
petroleum ether – EtOAc, 3:1) on silica gel provided 3-O-acetyl-6-O-benzoyl-2,4-di-О-benzyl-
f
D-glucopyranose (186 mg, 78%) as a syrup. Data for α-anomer: R 0.19 (toluene – EtOAc, 6:1);
1
H NMR (400 MHz, CDCl
H, J1,2 3.5 Hz, H-1); 4.57–4.45 (m, 5H, H-6A, PhCH
6B,6A 13.8 Hz, H-6B), 4.20 (m, 1H, H-5), 3.55 (t, 1H, J 9.6 Hz, H-4), 3.43 (dd, 1H, J2,3 9.7 Hz,
3
): δ 7.95–7.10 (m, 15H, 3 Ph), 5.49 (t, 1H, J 9.4 Hz, H-3), 5.19 (d,
1
2
, PhCH ’), 4.40 (dd, 1H, J6B,5 2.2 Hz,
2
J
1
3
3 3 3
H-2), 1.90 (s, 3H, CH CO). C NMR (100.6 MHz, CDCl ): δ 170.0 (CH CO), 137.5, 137.3,
133.2, 130.0, 129.8, 128.6, 128.5, 128.1, 128.0, 127.9(Ar), 90.8 (C-1), 77.9 (C-2), 76.2 (C-4),
7
4.5 (PhCH
0.12 (toluene – EtOAc, 6:1); H NMR (400 MHz, CDCl
Ph), 5.22 (t, 1H, J 9.3 Hz, H-3), 4.80 (d, 1H, Jgem 11.9 Hz, PhCH
2
), 73.4 (C-3), 72.8 (PhCH
2
), 68.9 (C-5), 63.4 (C-6), 21.1 (CH
3
CO). Data for β-
1
anomer: R
f
3
): δ 7.95–7.10 (m, 15H, 3
2
A), 4.74 (d, 1H, J1,2 7.6 Hz, H-
’, H-6A), 4.41 (dd, 1H, J6B,5 2.2 Hz, J6B,6A 13.7 Hz, H-
B), 3.64 (m, 1H, H-5), 3.57 (t, 1H, J 9.1 Hz, H-4), 3.25 (dd, 1H, J2,1 1.9 Hz, J2,3 7.7 Hz, H-2),
1
6
1
1
3
2 2
), 4.60–4.47 (m, 3H, PhCH B, PhCH
1
3
.82 (s, 3H, CH
29.9, 129.8, 128.5, 128.6, 128.1, 128.0, 127.8 (Ar), 97.6 (C-1), 80.3 (C-2), 76.3 (C-4), 75.6 (C-
), 74.6 (PhCH ), 74.0 (PhCH ), 73.1 (C-5), 63.4 (C-6), 21.0 (CH CO). Anal. Calcd. for
: C, 68.76, H, 5.97. Found: C, 68.59; H, 5.86.
Transformation of the above hemiacetal (160 mg, 0.316 mmol) into donor 21 was carried
3 3
CO). C-NMR (100,6 MHz, CDCl ): δ 166.3 (PhCO), 137.5, 137.3, 133.2,
2
2
3
29 30 8
C H O
out according to the procedure described for the preparation of 6. Pure 21 (200 mg, 93.5%) was
isolated by column chromatography (petroleum ether – EtOAc, 12:1→10:1) as a syrupy α,β-
mixture. Pure anomers were isolated for characterization purposes. Data for 21α: syrup, [α]
D
1
0.21 (petroleum ether – EtOAc, 8:1); H NMR (600 MHz, CDCl
+
71.4 (c 1, CHCl
3
); R
f
3
): δ
8
.05–6.70 (m, 20H, 4 Ph), 6.49 (br. s, 1H, H-1), 5.66 (t, 1H, J 9.6 Hz, H-3), 4.71 (d, 1H, Jgem
2.3 Hz, PhCH A), 4.67–4.59 (m, 4H, 3 PhCH , H-6A), 4.53 (dd, 1H, J6B,5 4.7 Hz, J6B,6A 12.2
1
2
2
1
3
Hz, H-6B), 3.80 (m, 1H, H-5), 3.73–3.67 (m, 2H, H-2, H-4), 1.93 (s, 3H, CH
100.6 MHz, DMSO-d ): δ 169.3 (CH CO), 165.3 (PhCO), 143.0, 137.8, 137.4, 133.3, 129.1,
28.6, 128.1, 127.7, 127.6, 127.5, 127.3, 124.2, 118.8 (Ar), 93.1 (C-1), 75.8 (C-2), 75.2 (C-4),
3
CO). C NMR
(
6
3
1