Influence of the benzyloxycarbonyl protective group on glycosylation with mannopyranosyl donors

Article abstract of DOI:10.1080/07328300600859759

The perbenzyloxycarbonylation of D-mannose, D-glucose, and D-galactose was achieved in high yield. In the mannose series, the selective removal of the anomeric benzyloxycarbonyl group followed by the activation of the anomeric position furnished, dependin

Full text of DOI:10.1080/07328300600859759

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Influence of the Benzyloxycarbonyl
Protective Group on Glycosylation with
Mannopyranosyl Donors
Alain Morère a , Fouzi Mouffouk a , Simon Leiris a , Alain Leydet a &
Jean‐Louis Montero a
a Laboratoire de Chimie Biomoléculaire, UMR CNRS 5032, Université
Montpellier II – ENSCM., France
Published online: 22 Sep 2006.
To cite this article: Alain Morère , Fouzi Mouffouk , Simon Leiris , Alain Leydet & Jean‐Louis Montero (2006)
Influence of the Benzyloxycarbonyl Protective Group on Glycosylation with Mannopyranosyl Donors, Journal of
Carbohydrate Chemistry, 25:6, 451-459, DOI: 10.1080/07328300600859759
To link to this article: http://dx.doi.org/10.1080/07328300600859759
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Journal of Carbohydrate Chemistry, 25:451–459, 2006
Copyright # Taylor & Francis Group, LLC
ISSN: 0732-8303 print 1532-2327 online
DOI: 10.1080/07328300600859759
Influence of the
Benzyloxycarbonyl
Protective Group on
Glycosylation with
Mannopyranosyl Donors
`
Alain Morere, Fouzi Mouffouk, Simon Leiris, Alain Leydet, and
Jean-Louis Montero
´
´
Laboratoire de Chimie Biomoleculaire, UMR CNRS 5032, Universite Montpellier II –
ENSCM., France
The perbenzyloxycarbonylation of D-mannose, D-glucose, and D-galactose was achieved
in high yield. In the mannose series, the selective removal of the anomeric benzyloxycar-
bonyl group followed by the activation of the anomeric position furnished, depending on
the activation conditions, either a bromo glycosyl donor or a trichloroacetimidate donor.
The trichloroacetimidate donor, protected by benzyloxycarbonyl groups, was used
successfully for the synthesis of a disaccharide.
Keywords Benzyloxycarbonyl, Protective group, Glycosylation
INTRODUCTION
Sugars fully protected by esters (e.g., Ac, Bz) play a very important role in
carbohydrate synthesis. They are commonly used for the preparation of
Received December 28, 2005; accepted May 30, 2006.
`
´
Address correspondence to Alain Morere, Laboratoire de Chimie Biomoleculaire, UMR
´
CNRS 5032, Universite Montpellier II – ENSCM., 8, rue de 1’Ecole Normale, 34296,
Montpellier cedex 05, France. E-mail: morere@univ-montp2.fr
451

`
A. Morere et al.
452
glycosyl donors employed, for instance, in oligosaccharide synthesis. Peracy-
lated saccharides are easily prepared and because of their importance most
of these protected sugars are commercially available. However, neither
acetates nor benzoates can be removed under hydrogenolysis conditions.
Therefore, we attempted to protect all hydroxyl groups of several D-hexoses
by hydrogenolabile benzyl carbonate in order to determine if such
perbenzyloxycarbonylated saccharides could be used in saccharidic synthesis.
The benzyloxycarbonyl group (Cbz) has been reported to be useful in carbo-
hydrate synthesis, not only for N-protection of amino sugars,[1] but also to
protect alcohols. For instance, a selective monobenzyloxycarbonylation of a
primary alcohol was made in the presence of a lipase.[2] On the other hand,
the benzyloxycarbonylation at all of the secondary positions on 6-O-(4-methox-
y)tritylated glycopyranosides was achieved in high yield by use of CbzCl and
DMAP.[3,4] Recently, the Cbz group was shown to be an efficient tool for high-
yielding regioselective monobenzyloxycarbonylation of secondary alcohols in
glycopyranoside series.[5] Moreover, when compared to benzyl ethers, benzyl
carbonates are not only removed more readily,[6] but also allow hydroxyl
group protection under softer conditions than those employed for benzylation
reactions.
RESULTS AND DISCUSSION
Before studying the influence of the Cbz group on glycosylation reaction, we
had to prepare perbenzyloxycarbonylated monosaccharides. Unfortunately,
methods generally used for peracylation of saccharides[7] were unsuccessfully
applied to the perbenzyloxycarbonylation of D-glucose, D-mannose, and
D-galactose. Blocking experiments with CbzCl in basic medium favored the
formation of cyclic carbonates,[8] and procedure using pyridine as solvent and
CbzCl as acylating reagent did not afford the expected perprotected sugars
4–6, even in the presence of a catalytic amount of DMAP. Therefore,
pyridine was replaced by DMF, which is a very good solvent for sugars, and
DMAP was used as the base. Under such conditions, the reaction proceeds
very smoothly and quickly. Indeed, it was complete within 15 min after
addition of CbzCl to the mixture of sugar and DMAP dissolved in DMF. The
perbenzyloxycarbonylated monosaccharides 4, 5, and 6 were obtained in
90%, 95%, and 90% starting from 1, 2, and 3, respectively. It is worth
pointing out that only b-anomers were obtained in the D-gluco (5) and
D-galactopyranose (6) series. More surprisingly, the b-anomer was also
mainly obtained in the D-mannopyranose (4) series (Sch. 1). The stereo-
chemistry at the anomeric center of the manno perbenzyloxycarbonylated
derivative 4 was confirmed by the magnitude of the coupling constant
between the anomeric carbon and its directly attached hydrogen. Indeed, in
1
4a the JC1-H1 is 178 Hz while in 4b the 1JC1-H1 is smaller, 163 Hz.

Influence of Benzyloxycarbonyl Protective Group
453
Scheme 1
This anomeric selectivity could be explained by an anomeric O-acylation
reaction.[9] In this reaction, the anomeric alcoholate reacts on the acylating
reactant and the stereochemistry is controlled by the increased nucleophilicity
of the equatorial oxygen atom. Therefore, the kinetic control of the anomery
favors the formation of b-anomers.
In order to determine the influence of the benzyloxycarbonyl protective
group on the glycosylation reaction, we had to first selectively deprotect then
activate the anomeric position of a perbenzyloxycarbonylated monosaccharide.
For this study, we chose the mannose series because of the interest we have in
the synthesis of analogs of the mannose 6-phosphate recognition marker and to
their binding affinity for the mannose 6-phosphate/insulin-like growth factor
II receptor (M6P/IGF2R).[10] We have to emphasize that the benzyl carbonate
can be removed either by hydrogenolysis or under aminolysis conditions, as we
demonstrated it recently.[6] Therefore, starting from the a,b-anomeric mixture
of the perbenzyloxycarbonylated mannopyranose 4, the anomeric benzyloxy-
carbonyl group was selectively removed by using hydrazinium acetate.[11] Gen-
erally, the solvent used in this reaction is DMF. In our case, the best results
were obtained by using acetonitrile to give the tetrabenzyloxycarbonylated
mannopyranose 7 in 90% yield (Sch. 2).
The next step consisted of an activation of the hemiacetal into a stable
glycosyl donor. Among the numerous glycosylation procedures described in
the literature, we focused on the Koenigs-Knorr reaction[12] and on the
Scheme 2

`
A. Morere et al.
454
trichloroacetimidate method.[13] The activation step during the Koenigs-Knorr
method is the replacement of the anomeric hydroxyl group by a bromine atom.
The bromine was introduced at the anomeric position of 7 according to the soft
BiBr3/Me3SiBr procedure.[14] The glycosyl donor 8, obtained in 80% yield, was
directly used after purification by flash chromatography. Following the same
BiBr3/Me3SiBr procedure, an attempt of direct incorporation of the bromine
at the anomeric position of the perbenzyloxycarbonylated mannopyranose 4
failed to give compound 8. The glycosylation reaction was promoted by
addition of silver triflate[15] into a mixture of the glycosyl donor 8 and methyl
2,3,4-tri-O-acetyl-a-D-mannopyranoside 9 as the acceptor. However, the for-
mation of the expected disaccharide was not observed even at low temperature.
Under these conditions, the methyl 2,3,4-tri-O-acetyl-6-O-benzyl-a-D-manno-
pyranoside 10 was the only isolated product (60%). This is a consequence of
the participating feature of the Cbz group. Indeed, during the Koenigs-Knorr
reaction the oxycarbenium intermediate is stabilized by the Cbz group at
position 2 and the positive charge is partially delocalized on the carbonyl of
this Cbz group. We suppose that this delocalization leads to the cleavage of
the C-O bond of the benzyloxy group and that the benzylium intermediate
thus generated is trapped by the glycosyl acceptor, leading in this way to the
benzyl ether derivative 10. Moreover, the formation of 10 was accompanied
by the liberation, from the mannosyl donor 8, of the 1,2-cyclic carbonate,
which was only detected, among other byproducts, by FABMS analysis of the
crude reaction mixture.
The trichloroacetimidate method, which is certainly one of the most
applicable procedures for glycoside bond formation, was also studied. The
glycosyl donor 11 was prepared in 95% yield by reaction of 7 with trichloroace-
tonitrile in the presence of NaH (Sch. 3). TMSOTf-promoted glycosylation of 11
and 9 gave disaccharide 12 in 65% yield.
In conclusion, we have shown that the benzyloxycarbonyl protective group
can be used for the peracylation of D-hexoses. We have also demonstrated that
an anomeric benzyl carbonate can be selectively removed by using
Scheme 3

Influence of Benzyloxycarbonyl Protective Group
455
hydrazinium acetate and that the resulting hemiacetal can be activated as a
glycosyl bromide or as a trichloroacetimidate donor. The later activation
allowed the formation of a disaccharide in 65% yield, showing that a glycosyl
donor containing benzyl carbonates can be used successfully in disaccharide
synthesis. Based on the trichloroacetimidate method, work is under progress
to study (1) the outcome of the glycosylation when involving a secondary
hydroxyl group of a protected acceptor and (2) the coupling stereoselectivity
when gluco- or galacto-perbenzyloxycarbonylated derivatives are used as
glycosyl donors.
EXPERIMENTAL
General Experimental
Analytical TLC was performed using aluminum-coated TLC plates 60-F254
(Merck). Plates were developed with (1) UV light (254 nm) and (2) immersion in
a 10% H2SO4/EtOH solution followed by charring. Silica gel column chromato-
graphy was performed with silica gel 60A (Carlo Erba). Optical rotations were
measured at the sodium D-line with a Perkin-Elmer-241 polarimeter. Fast
atom bombardment (FAB) mass spectra were recorded on a Jeol JMS-DX300
spectrometer in positive (FAB þ ) mode and using either 3-nitrobenzylic
1
alcohol (NBA) or glycerol/thioglycerol (1:1) mixture (G/T). H NMR spectra
were recorded on a Bru¨ker DRX 400 (400 MHz) at 258C. Chemical shifts (d)
are given in ppm and referenced using residual solvent signal (7.24 ppm
for CHCl3). The following abbreviations were used to explain the signal
multiplicities or characteristics:
s (singlet), d (doublet), dd (double
doublet), ddd (double double doublet), t (triplet), dt (double triplet), and m
(multiplet). 13C NMR spectra were recorded on an Avance Bru¨ker 400
(100.6 MHz). Chemical shifts (d) are reported in ppm and referenced to
CDCl3 (77.0 ppm).
General procedure for the perbenzyloxycarbonylation. To a solution of
D-hexose (1 g; 5.5 mmol) in DMF (30 mL), the DMAP (8.13 g; 66 mmol) was
added. After 10 min under stirring, the CbzCl (9.5 mL, 66 mmol) was added
dropwise at rt. After addition, the reaction mixture was stirred at rt for
15 min, then diluted by Et2O, and salts were removed by filtration. The
filtrate was washed twice with water, dried (Na2SO4), and then evaporated
under reduced pressure. The residue was purified by column chromatography
on silica gel (hexane-EtOAc, 7:3).
1,2,3,4,6-Penta-O-benzyloxycarbonyl-a-D-mannopyranose (4). Following
the general procedure, the anomers of 4 (4.24 g, 90%; a/b 1:4) were obtained as
white powders and were separated during the chromatography.

`
A. Morere et al.
456
4a: [a]D ¼ þ228 (c 1, CHCl3). Rf ¼ 0.58 (CH2Cl2: hexane, 8:2). 1H NMR (CDCl3)
d 4.15 (ddd, 1H, J5,4 ¼ 7.2 Hz, J5,6a ¼ 5.2 Hz, J5,6b ¼ 3.0 Hz, H-5), 4.28 (dd, 1H,
J6a,6b ¼ 11.9 Hz, H-6a), 4.39 (dd, 1H, H-6b), 4.79–5.60 (m, 13H, H-2, H-3, H-4,
5PhCH2), 6.13 (d, 1H, J1,2 ¼ 1.8 Hz, H-1), 7.33–7.41 (m, 25H, 5 C6H5). 13C
NMR (CDCl3) d ¼ 154.7, 154.1, 154.0, 153.9, 152.4, 135.0, 134.8, 134.7, 134.5,
134.3, 128.9, 128.8, 128.7, 128.6, 128.5, 128.4, 128.3, 128.2, 93.5, 72.3, 71.4,
70.7, 70.6, 70.4, 70.3, 70.0, 69.6, 65.8. FABMS (m/z): 873 (M þ Na)þ, 851
(M þ H)þ.
4b: [a]D ¼ 2118 (c 1, CHCl3). Rf ¼ 0.43 (CH2Cl2: hexane, 8 : 2). 1H NMR
(CDCl3) d 3.94 (dt, 1H, J5,4 ¼ 9.5 Hz, J5,6a ¼ J5,6b ¼ 4.9 Hz, H-5), 4.38–4.46
(m, 2H, H-6a, H-6b), 5.06–5.37 (m, 12H, H-3, H-4, 5 Ph-CH2), 5.57 (dd, 1H,
J2,1 ¼ 1.1 Hz, J2,3 ¼ 3.1 Hz, H-2), 5.83 (d, 1H, H-1), 7.27–7.40 (m, 25H,
5C6H5). 13C NMR (CDCl3) d ¼ 154.6, 153.9, 153.8, 152.9, 135.0, 134.7, 134.6,
134.4, 128.8, 128.7, 128.6, 128.5, 128.4, 128.3, 128.1, 93.0, 74.1, 72.6, 71.3,
70.7, 70.5, 70.4, 70.0, 69.7, 65.8. FABMS (m/z): 873 (M þ Na)þ, 851 (M þ H)þ.
Anal. Calcd. for C46H42O16 (850.82): C, 64.94; H, 4.98. Found: C, 64.78;
H, 4.92.
1,2,3,4,6-Penta-O-benzyloxycarbonyl-b-D-glucopyranose (5). Following
the general procedure, 5 (4.43 g, 95%) was obtained as a white powder.
1
[a]D ¼ 2418 (c 1, CHCl3). Rf ¼ 0.45 (CH2Cl2: hexane, 8:2). H NMR (CDCl3)
d ¼ 3.96 (td, 1H, J5,4 ¼ 9.8 Hz, J5,6a ¼ J5,6b ¼ 3.9 Hz, H-5), 4.35–4.43 (m, 2H,
H-6a, H-6b), 5.03–5.23 (m, 13H, H-2, H-3, H-4, 5 Ph-CH2), 5.69 (d, 1H,
J1,2 ¼ 8 Hz, H-1), 7.28–7.41 (m, 25H, 5 C6H5). FABMS (m/z): 873 (M þ Na)þ,
851 (M þ H)þ.
Anal. Calcd. for C46H42O16 (850.82): C, 64.94; H, 4.98. Found: C, 64.83;
H, 4.94.
1,2,3,4,6-Penta-O-benzyloxycarbonyl-b-D-galactopyranose (6). Follow-
ing the general procedure, 6 (4.21 g, 90%) was obtained as a white powder.
1
[a]D ¼ 2328 (c 1, CHCl3). Rf ¼ 0.49 (CH2Cl2: hexane, 8:2). H NMR (CDCl3) d
4.07–4.13 (m, 1H, H-5), 4.29–4.32 (m, 2H, H-6a, H-6b), 4.96 (dd, 1H,
J3,4 ¼ 3.3 Hz, J3,2 ¼ 10.3 Hz, H-3), 5.12–5.20 (m, 10H, 5 Ph-CH2), 5.24 (dd,
1H, J2,1 ¼ 8.2 Hz, H-2), 5.46 (dd, 1H, J4,5 ¼ 1 Hz, H-4), 5.61 (d, 1H, H-1),
7.27–7.41 (m, 25H, 5 C6H5). FABMS (m/z): 873 (M þ Na)þ.
Anal. Calcd. for C46H42O16 (850.82): C, 64.94; H, 4.98. Found: C, 64.75;
H, 5.03.
2,3,4,6-Tetra-O-benzyloxycarbonyl-D-mannopyranose (7). To a solution
of the perbenzyloxycarbonyl derivative 4 (1 g, 1.2 mmol) in dry acetonitrile
(10 mL) was added the hydrazinium acetate (0.25 g, 2.7 mmol). The reaction
mixture was refluxed under stirring for 1 h and then diluted with CH2Cl2.
The solution was washed with water, dried (Na2SO4), and concentrated.

Influence of Benzyloxycarbonyl Protective Group
457
The syrupy residue was purified by column chromatography on silica gel
(hexane-EtOAc, 7:3) to give 7 (0.77 g, 90%) as a viscous oil. Rf ¼ 0.43
(hexane-EtOAc, 7:3). 1H NMR (CDCl3) d 3.29 (d, 1H, JOH,1 ¼ 3.1 Hz, OH),
4.26–4.35 (m, 4H, H-1, H-5, H-6a, H-6b), 5.13–5.33 (m, 11H, H-2, H-3, H-4,
4 Ph-CH2), 7.28–7.40 (m, 20H, 4 C6H5). FABMS (m/z): 739 (M þ Na)þ.
Anal. Calcd. for C38H36O14 (716.68): C, 63.68; H, 5.06. Found: C, 63.57;
H, 5.02.
2,3,4,6-Tetra-O-benzyloxycarbonyl-a-D-mannopyranosyl bromide (8).
To a solution 7 (0.3 g, 4.18 1024 mol) in dry CH2Cl2 (15 mL) was added a cata-
lytic quantity of BiBr3 (0.02 g, 4.5 1025 mol). Then Me3SiBr (0.21 mL,
1.6 mmol) in dry CH2Cl2 (2 mL) was added dropwise under stirring at 08C.
After the addition, the reaction mixture was allowed to warm to rt, stirred
for 1 h, and then washed with water. The organic layer was dried (Na2SO4)
and evaporated. The residue was purified by flash chromatography on silica
gel (hexane-EtOAc, 7 : 3) to afford compound 8 (0.26 g, 80%) as a yellow
syrup. [a]D ¼ 2358 (c 1, CHCl3). Rf ¼ 0.77 (hexane-EtOAc, 7 : 3). 1H NMR
(CDCl3)
d
4.15–4.19 (m, 1H, H-5), 4.26 (dd, 1H, J6a,6b ¼ 12 Hz,
J6a,5 ¼ 5.1 Hz, H-6a), 4.41 (dd, 1H, J6b,5 ¼ 3 Hz, H-6b), 5.07–5.38 (m, 11H,
H-2, H-3, H-4, 4 Ph-CH2), 6.15 (d, 1H, J1,2 ¼ 1.8 Hz, H-1), 6.99–7.46
(m, 20H, 4 C6H5). FABMS (m/z): 802 (M þ Na)þ.
Methyl 2,3,4-tri-O-acetyl-6-O-benzyl-a-D-mannopyranoside (10). To a
solution of methyl 2,3,4-tri-O-acetyl-a-D-mannopyranoside 9 (0.04 g, 1.25
1024 mol), AgOTf (0.06 g, 2.5 1024 mol), and collidine (0.016 mL, 1.25 1024
mol) in dry CH2Cl2 (4 mL) was added 8 (0.2 g, 2.5 1024 mol) in dry CH2Cl2
(2 mL) under stirring at 2458C. After the addition, the reaction mixture was
allowed to warm to rt, stirred for 3 h, and then washed with water. The
organic layer was dried (Na2SO4) and evaporated. The residue was chromato-
graphed (petroleum ether-EtOAc, 7:3) to provide 10 (0.03 g, 60%) as a viscous
oil. [a]D ¼ þ438 (c 1, CHCl3). Rf ¼ 0.43 (hexane-EtOAc, 7:3). 1H NMR (CDCl3) d
1.94 (s, 3H, CH3CO2), 2.00 (s, 3H, CH3CO2), 2.17 (s, 3H, CH3CO2), 3.44 (s, 3H,
OCH3), 3.50 (d, 2H, J6,5 ¼ 4.3 Hz, H-6), 3.88–4.01 (m, 1H, H-5), 4.54 (d, 1H,
Ja,b ¼ 11.9 Hz, H-a Ph-CH2), 4.64 (d, 1H, H-b Ph-CH2), 4.75 (d, 1H,
J1,2 ¼ 1.5 Hz, H-1), 5.24 (t, 1H, J2,3 ¼ 1.5 Hz, H-2), 5.29–5.36 (m, 2H, H-3,
H-4), 7.20–7.83 (m, 5H, C6H5). FABMS (m/z): 433 (M þ Na)þ, 411 (M þ H)þ.
Anal. Calcd. for C20H26O9 (410.42): C, 58.53; H, 6.39. Found: C, 58.47;
H, 6.33.
2,3,4,6-Tetra-O-benzyloxycarbonyl-a-D-mannopyranosyl trichloroace-
timidate (11). To a solution of 7 (0.38 g, 5.3 1024 mol) in dry CH2Cl2 (10 mL)
was added the NaH (0.016 g, 6.8 1024 mol) at rt. After stirring for 10 min,
the trichloroacetonitrile (0.22 mL, 3.8 mmol) was added. The reaction

`
A. Morere et al.
458
mixture was stirred at rt for 1 h and then washed with water. The organic layer
was dried (Na2SO4) and evaporated. The residue was purified by column
chromatography on silica gel (hexane-EtOAc, 7:3) to provide 11 (0.44 g, 95%)
as a white powder. [a]D ¼ 2548 (c 1, CHCl3). Rf ¼ 0.78 (hexane-EtOAc, 7:3).
1H NMR (CDCl3) d 4.27–4.45 (m, 3H, H-5, H-6a, H-6b), 5.1–5.5 (m, 11H, 4
Ph-CH2, H-2, H-3, H-4), 6.42 (d, 1H, J1,2 ¼ 1.9 Hz, H-1), 7.28–7.43 (m, 20H,
5 C6H5), 8.90 (s, 1H, NH). FABMS (m/z): 882 (M þ Na)þ.
Anal. Calcd. for C40H36Cl3NO14 (861.07): C, 55.79; H, 4.21. Found: C: 55.68;
H, 4.16.
Methyl 2,3,4,6-tetra-O-benzyloxycarbonyl-a-D-mannopyranosyl-(1!6)-
2,3,4-tri-O-acetyl-a-D-mannopyranoside (12). To a solution of the methyl
2,3,4-tri-O-acetyl-a-D-mannopyranoside (0.07 g, 2.18 1024 mol) and trichloro-
acetimidate 11 (0.37 g, 4.3 1024 mol) in dry CH2Cl2 (5 mL) was added molecular
˚
sieves (4-A, 0.1 g). The solution was cooled at 2708C and the TMSOTf
(0.008 mL, 4.36 1025 mol) was added dropwise. After the addition, the
solution was allowed to warm to rt and stirred for 1 h. The reaction mixture
was neutralized with NaHCO3 (0.2 g) and washed with water. The organic
layer was dried (Na2SO4) and evaporated. The residue was chromatographed
(petroleum ether-EtOAc, 7:3) to afford 12 (0.14 g, 65%) as a colorless oil.
1
[a]D ¼ þ178 (c 1, CHCl3). Rf ¼ 0.43 (petroleum ether-EtOAc, 7:3). H NMR
(CDCl3) d 2.01 (s, 3H, CH3CO2), 2.03 (s, 3H, CH3CO2), 2.14 (s, 3H, CH3CO2),
3.34 (s, 3H, OCH3), 3.60 (dd, 1H, J6a,6b ¼ 10.9 Hz, J6a,5 ¼ 2.2 Hz, H6a),
3.80 (dd, 1H, J6b,5 ¼ 6.3 Hz, H-6b), 3.84–3.90 (m, 1H, H-5), 4.09–4.2 (m, 1H,
H-50), 4.25 (dd, 1H, J6 a,6 b ¼ 11.8 Hz, J6 a,5 ¼ 3.0 Hz, H-60a), 4.25 (dd, 1H,
0
0
0
J6 b,5 ¼ 5.9 Hz, H-60b), 4.68 (d, 1H, J1,2 ¼ 1.8 Hz, H-1), 4.98 (d, 1H,
0
J1 ,2 ¼ 1.4 Hz, H-10), 5.05–5.34 (m, 14H, H-2, H-3, H-4, H-20, H-30, H-40,
4Ph-CH2), 7.23–7.81 (m, 20H, 4 C6H5). FABMS (m/z): 1041 (M þ Na)þ.
Anal. Calcd for C51H54O22 (1018.96): C, 60.11; H, 5.34. Found: C, 59.85;
H, 5.37.
0
0
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[2] Pulido, R.; Gotor, V. Enzymic regioselective alkoxycarbonylation of hexoses and
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`
[3] Morere, A.; Mouffouk, F.; Chavis, C.; Montero, J.-L. The benzyloxycarbonyl protec-
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`
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