Stereoselective synthesis of α-C-glycosides of N-acetylgalactosamine

Article abstract of DOI:10.1016/S0957-4166(99)00480-2

Attempts to synthesise α-C-glycosides of N-acetylgalactosamine by selective deprotection at C-2' of allyl α-C-galactoside 1 and subsequent amination failed, but opened the way to α-C-talopyranosides. The synthesis of α-C-glycosides of N-acetylgalactosamin

Full text of DOI:10.1016/S0957-4166(99)00480-2

TETRAHEDRON:
ASYMMETRY
Pergamon
Tetrahedron: Asymmetry 11 (2000) 295–303
Stereoselective synthesis of α-C-glycosides of
N-acetylgalactosamine
Laura Cipolla,a,∗ Barbara La Ferla,b Luigi Lay,b Francesco Peri a and Francesco Nicotra a,∗
aDipartimento di Biotecnologie e Bioscienze, Università degli Studi di Milano-Bicocca, Via L. Emanueli 12, 20126 Milano,
Italy
bDipartimento di Chimica Organica ed Industriale, Università degli Studi di Milano, and Centro di Studio per le Sostanze
Naturali del CNR, Via Venezian 21, 20133 Milano, Italy
Received 15 October 1999; accepted 1 November 1999
Abstract
Attempts to synthesise α-C-glycosides of N-acetylgalactosamine by selective deprotection at C-20 of allyl α-C-
galactoside 1 and subsequent amination failed, but opened the way to α-C-talopyranosides. The synthesis of α-C-
glycosides of N-acetylgalactosamine was performed from allyl α-C-glucopyranoside 9, which was regioselectively
deprotected, stereoselectively aminated at C-20, and finally epimerised at C-40. © 2000 Elsevier Science Ltd. All
rights reserved.
1. Introduction
The carbohydrate moieties of glycoproteins are known to influence the properties of the parent
protein in many diverse ways. First of all, glycosylation not only affects the physical properties of
proteins (i.e. folding and conformation) but also influences their biological functions.1 For example,
glycosylation provides protection against proteolysis, influences uptake of serum proteins by the liver,
affects intracellular transport of enzymes to lysosomes, determines human blood groups, and regulates
leukocyte trafficking to sites of inflammation. In addition, the glycosidic part of glycoproteins is
responsible for many intercellular cell surface recognition phenomena.2,3 In this context, of fundamental
biological and pharmaceutical importance are, for example, the aberrant glycosylation patterns of
glycoproteins in cancer,4 the carbohydrate-mediated cell adhesion involved in hematogenous metastasis
of cancer5 and the carbohydrate-based inflammatory response mechanism.6
Among the fundamental saccharidic units in biologically relevant glycoproteins, N-acetyl α-
D-galactosamine plays important roles. Mucin glycoproteins are represented by the common
∗
Corresponding authors. Tel: +39-02-64483457; fax: +39-02-64483565; e-mail: francesco.nicotra@unimib.it
0957-4166/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(99)00480-2
tetasy 3116

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GalNAcα1→O-serine or threonine core structure (Tn antigen) found in MUC1–MUC4 and are
the most important surface O-linked glycoproteins of epithelial cells and of the mucous.7 The Tn
structure in normal cells is cryptic since it is further glycosylated to construct complex O-linked glycans
on mucin-type glycoproteins, whereas in most human carcinomas this structure is exposed at the cell
surface, due to incomplete synthesis of saccharidic chains.4 The Tn epitope is expressed in over 70% of
human epithelial cancers such as lung, colon, stomach and breast carcinomas, the increased expression
being correlated with tumour aggressiveness.8,9 Hence, Tn containing glycoconjugates can be promising
as synthetic cancer vaccines.10
The main drawback in using O-glycoconjugate-based therapeutic approaches is the inherent lack of
in vivo stability of such compounds, since native O-glycopeptides are easily degraded in both acidic
and basic media, and in biological systems by enzymes. Therefore, access to hydrolytically stable
saccharidic residues is of great interest. A solution to this problem lies in C-glycosides,11,12 in which the
interglycosidic oxygen is replaced with a methylene group. The C-glycosidic linkage provides hydrolytic
stability to glycopeptides without greatly affecting their structure.
Despite the biological relevance of the Tn antigen, only a couple of examples of the synthesis of α-
C-glycoside analogues of N-acetylgalactosamine have been reported,13,14 both suffering from the use of
the expensive tri-O-benzylgalactal as starting material. Here we describe a convenient procedure for the
synthesis of α-C-glycosidic analogues of N-acetylgalactosamine, suitably functionalised for the synthesis
of neoglycoconjugates by chemoselective ligation,15 and eventually having the free hydroxyl group at C-
30 which can be galactosylated in order to obtain T antigen analogues.
2. Results and discussion
The synthetic strategy adopted for our synthesis of an α-C-glycosidic analogue of N-
acetylgalactosamine takes advantage of our observations that polybenzylated allyl C-glucosides
can be selectively deprotected at C-20 and then aminated.16 We first studied the exploitation of
this procedure on galactoderivative 1 (Scheme 1). Treatment of 1-(20,30,40,60-tetra-O-benzyl-α-D-
galactopyranosyl)-2-propene 117 with iodine afforded the cyclic iodoether 2, in agreement with what
was observed for glucose derivatives.16 Subsequent ring opening with zinc and acetic acid afforded
compound 3 (91% from 1) in which the 20-OH was selectively deprotected. In order to convert the free
hydroxyl group into an acetamido function, compound 3 was oxidised with PCC in dichloromethane
to the corresponding ketone 4 (93%), which was then transformed into two diastereomeric oximes 5
(MeONH2·HCl, pH 4.5, quantitative yield). Reduction of compound 5 with LiAlH4 afforded mainly
the elimination product 6, obtained in 40% yield, together with a multitude of unidentified by-products.
The undesired outcome of this reaction can be explained in the light of the steric hindrance on both the
α-face, caused by the allylic appendage, and the β-face, due to the axial benzyloxy group in position
40. The basicity of the aluminium hydride causes first β-elimination, and secondly reduction of the
oxime. The net result of the reaction is the formation of 6. In order to avoid the elimination reaction,
different reducing agents which could operate in acidic conditions were used: zinc in acetic acid,18
sodium cyanoborohydride in the presence of Lewis acids,19 sodium borohydride in acetic acid,20 sodium
borohydride in the presence, respectively, of cerium trichloride21 and nickel dichloride,22 and catalytic
hydrogenation. In either case no reaction occurred. Since every attempt to reduce the oxime 5 failed, we
tried reductive amination of ketone 4 with benzylamine and sodium triacetoxyborohydride as reducing
agent.23 However, the desired amine was obtained only in traces, while the main product derived from
the reduction of ketone 4 was the allyl C-talopyranoside 7 (Fig. 1). Compound 7 is the only product

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297
if the reduction is performed with sodium borohydride at −20°C (97% yield); the alcohol was then
converted into the corresponding triflate 8 (Fig. 1), but every attempt to displace the triflate with an azido
group failed. In summary, selective deprotection at position 20 by iodination/reductive elimination can
be efficiently extended to allyl C-glycosides of galactose, and gives access to C-talopyranosides.
Scheme 1. Reagents and conditions: (a) I2, CH2Cl2; (b) Zn, AcOH, THF:MeOH 1:1, 91% over two steps; (c) PCC, CH2Cl2,
m.s. 4 Å, 93%; (d) NH2OMe, pH=4.5, quantitative; (e) LiAlH4, THF, 40%
Fig. 1.
However, following this approach, it was impossible to obtain C-glycosides of N-acetylgalactosamine.
We then decided to take advantage of the possibility to epimerise selectively the C-40 of N-
acetylglucosamino derivatives.24,25 This new strategy uses glucose as a cheap starting material,
which can be easily converted into α-C-glucoside 9.26 Compound 9 was transformed into the α-C-
glucoside of glucosamine 10, according to the selective debenzylation–amination procedure,11 and then
acetylated, affording compound 11 (Scheme 2). It is noteworthy that 11 is obtained from 9 in 51% overall
yield over six steps. Interestingly, 1H NMR coupling constants show a 1C4 conformation for compound
11, probably due to hydrogen bonding between the NH functionality and the oxygen in position 40. In
order to epimerise C-40, compound 11 must be converted into a suitable protected derivative, having
the hydroxyl group in position 40 deprotected. Compound 11 was then debenzylated with ethanethiol
in the presence of boron trifluoride etherate, affording 12, in quantitative yield (Scheme 2). The triol
12 was selectively protected as the t-butylcarbonyl ester at positions 30 and 60, affording 13 in 82%
yield. The epimerisation was effected taking advantage of acyl migration in basic media, preferring
an axial configuration to an equatorial one.27 The migration/epimerisation reaction was all but trivial;
many different conditions were tried for the optimisation of this one pot reaction previously reported
on the parent O-glycoside.25 The optimal conditions are as follows: compound 13 was converted
into the corresponding triflate by adding triflic anhydride (2.5 equiv.) portionwise to a solution of the

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alcohol in a 2:1 mixture of pyridine:dichloromethane at 0°C. After the complete consumption of the
starting material 13, water was added to the reaction mixture, affording the α-C-glycosidic analogue
of N-acetylgalactosamine 14 in 84% yield. Deprotection of 14 under Zemplén conditions (NaOMe in
MeOH) afforded compound 15 in 87% yield; the allylic appendage was then functionalised by reaction
with Na2PdCl4 in water (80% yield) giving methyl ketone 16.
Scheme 2. Reagents and conditions: (a) see Ref. 16; (b) Ac2O, Py, CH2Cl2, 83%; (c) EtSH, BF3·OEt2, quantitative; (d) PivCl,
Py, −20°C, 82%; (e) (i) Tf2O, Py:CH2Cl2 2:1, 0°C; (ii) H2O, rt, 84%; (f) NaOMe, MeOH, 87%; (g) Na2PdCl4, H2O, 60°C,
80%
In conclusion, the procedure herein described for the synthesis of a Tn antigen analogue exploits
selective amination at C-20 of an allyl C-glucoside, easily available from glucose, and epimerisation at C-
40 of the obtained N-acetylglucosamine derivative. The allylic appendage of compound 14 can be further
functionalised as ketone 16, suitable for the synthesis of neoglycoconjugates, and the free hydroxyl group
at C-30 can be galactosylated to T antigen analogues.
3. Experimental
3.1. General remarks
1H NMR and 13C NMR spectra were recorded using a Bruker AC 300 or a Varian XL 200 instrument
using CDCl3 as solvent unless otherwise stated. Chemical shifts are reported in ppm downfield from TMS
as an internal standard. Reported assignments of the 1H NMR spectra were based on 2D proton–proton
shift-correlation spectra. Signals of the aromatic carbons in the 13C NMR spectra are not reported. [α]D
values were measured at 20°C and are given in units of 10−1 deg cm2 g−1. Chromatographic purifications
were performed by the flash procedure using Merck silica gel 60 (230–400 mesh). TLC was performed
on Merck silica gel 60 F254 plates and visualised by spraying with a solution prepared with concentrated
H2SO4 (5 mL), MeOH (45 mL) and water (45 mL), and then heating to 110°C for 5 min. All solvents
were dried prior to use.
3.2. 1-(30,40,60-Tri-O-benzyl-α-D-galactopyranosyl)-2-propene 3
Under argon atmosphere, iodine (3.86 g, 15.22 mmol) was added to a solution of 1 (4.30 g, 7.61 mmol)
in dry CH2Cl2 (20 mL) at 0°C. After 30 min the reaction was complete; aqueous Na2S2O3 was added

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299
and the mixture stirred until the organic phase became colourless. The organic layer was washed with
water, then dried over Na2SO4, filtered and concentrated to dryness. The crude cyclic iodoether 2 (5.00
g, yellowish oil) was dissolved in a 1:1 mixture of Et2O:MeOH (40 mL), and Zn (4.90 g, 76.1 mmol) and
glacial AcOH (0.87 mL) were added. After 30 min the reaction mixture was filtered over a Celite pad and
the solvent evaporated. The residue was dissolved in CH2Cl2, and the organic phase washed sequentially
with 5% HCl and water. The organic layer was dried over Na2SO4, filtered and concentrated to dryness.
Purification of the crude product by flash chromatography (8:2, petroleum ether:EtOAc) afforded 3.29
g of 3 (91% yield) as a colourless oil. [α]D=+63.5 (c 1, CHCl3); 1H NMR (300 MHz) δ 7.40–7.20 (m,
15H), 5.89–5.75 (m, 1H), 5.12 (d, 1H, J=19.2 Hz), 5.06 (d, 1H, J=10.2 Hz), 4.74, 4.58 (ABq, 2H, J=11.3
Hz), 4.71, 4.56 (ABq, 2H, J=11.7 Hz), 4.57, 4.49 (Abq, 2H, J=12.0 Hz), 4.10–4.00 (m, 4H), 3.83 (dd,
1H, J=10.2, 6.3 Hz), 3.70 (dd, 1H, J=10.2, 4.7 Hz), 3.69–3.67 (m, 1H), 2.45–2.37 (m, 2H), 2.08 (bd, 1H,
J=3.5 Hz); 13C NMR (75.43 MHz) δ 134.77 (d), 116.80 (t), 78.33 (d), 73.30 (d), 73.18 (t), 73.06 (t),
73.04 (t), 72.37 (d), 71.51 (d), 68.62 (d), 67.23 (t), 31.49 (t). Anal. calcd for C30H34O5: C, 75.92%; H,
7.22%. Found: C, 76.01%; H, 7.18%.
3.3. 1-(30,40,60-Tri-O-benzyl-α-D-lyxo-hexulopyranosyl)-2-propene 4
Alcohol 3 (200 mg, 0.42 mmol) was dissolved in dry CH2Cl2 (10 mL), under argon atmosphere.
Activated powdered molecular sieves (4 Å, 500 mg) and PCC (136 mg, 0.64 mmol) were added to the
solution. After 40 min the reaction mixture was filtered over a Celite pad and the filtrate concentrated.
The residue was purified by flash chromatography (8.5:1.5, petroleum ether:EtOAc), affording 4 (184
mg, 93%) as a white solid. Mp 36–38°C; [α]D=+34.2 (c 0.5, CHCl3); 1H NMR (300 MHz) δ 7.45–7.20
(m, 15H), 5.92–5.73 (m, 1H), 5.11 (d, 1H, J=18.0 Hz), 5.06 (d, 1H, J=10.3 Hz), 4.96–4.90 (m, 2H),
4.54–4.49 (m, 5H), 4.33–4.28 (m, 2H), 4.21 (dd, 1H, J=7.6, 4.3 Hz), 3.63 (bd, 2H, J=5.8 Hz), 2.59–2.52
(m, 1H), 2.41 (dt, 1H, J=14.7, 7.6 Hz); 13C NMR (54.29 MHz) δ 208.28 (s), 133.14 (d), 117.79 (t),
82.37 (d), 78.79 (d), 76.31 (d), 75.58 (d), 73.48 (t), 72.84 (t), 72.38 (t), 67.53 (t), 34.70 (t). Anal. calcd
for C30H32O5: C, 76.25%; H, 6.83%. Found: C, 76.07%; H, 6.79%.
3.4. 1-(30,40,60-Tri-O-benzyl-α-D-lyxo-hexulopyranosyl)-2-propene methyloxime 5
Ketone 4 (5.0 g, 10.6 mmol) dissolved in a 1:1 THF:MeOH mixture (30 mL) was stirred overnight with
a buffer solution (50 mL) prepared by dissolving NH2OMe·HCl (5.0 g, 59.9 mmol) and AcONa·3H2O
(10.0 g, 74.2 mmol) in water (the pH was adjusted to 4.5 with AcOH). The reaction mixture was stirred
overnight. The solution was then diluted with EtOAc and the organic layer washed sequentially with
satd NaHCO3 and water to neutrality. The crude was purified by flash chromatography (9:1, petroleum
ether:EtOAc) affording two products corresponding to the diastereomeric oximes 5 as an amorphous
white solid. The two isomers interconvert quite rapidly. The spectral data given below correspond to the
major isomer. 1H NMR (300 MHz) δ 7.45–7.20 (m, 15H), 5.81–5.71 (m, 1H), 5.26 (dd, 1H, J=8.1, 6.1
Hz), 5.07 (d, 1H, J=16.0 Hz), 5.05 (d, 1H, J=11.1 Hz), 4.99, 4.68 (ABq, 2H, J=11.9 Hz), 4.96, 4.62
(ABq, 2H, J=12.1 Hz), 4.42, 4.34 (ABq, 2H, J=11.8 Hz), 4.25 (d, 1H, J=2.3 Hz), 3.98 (bd, 1H, J=2.3
Hz), 3.92 (s, 3H), 3.88 (t, 1H, J=6.3 Hz), 3.49 (d, 2H, J=6.3 Hz), 2.45 (dt, 1H, J=14.4, 8.1 Hz), 2.18
(dt, 1H, J=14.4, 6.1 Hz); 13C NMR (54.29 MHz) δ 154.45 (s), 133.42 (d), 117.35 (t), 76.31 (d), 75.66
(d), 74.01 (t), 73.38 (t), 72.37 (t), 71.94 (d), 69.49 (d), 69.11 (t), 61.99 (q), 34.31 (t). Anal. calcd for
C31H35NO5: C, 74.23%; H, 7.03%; N, 2.79%. Found: C, 74.45%; H, 6.92%; N, 2.94%.
Compound 6: Oximes 5 (1.4 g, 2.8 mmol) were dissolved in dry THF (10 mL), the solution cooled to
0°C, and LiAlH4 was added (5.5 mL of a 1 M solution in THF). After 24 h the reaction was quenched

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by adding EtOAc, the organic layer washed with water, dried over Na2SO4 and concentrated to dryness.
Purification by flash chromatography afforded 6 (510 mg, 50% yield) as an amorphous solid. 1H NMR
(300 MHz, C6D6) δ 7.37–7.03 (m, 10H), 6.02–5.83 (m, 1H), 5.16 (d, 1H, J=17.2 Hz), 5.07 (d, 1H, J=10.3
Hz), 4.63–4.57 (m, 1H), 4.52–4.38 (m, 5H), 3.76 (dt, 1H, J=7.0, 2.1 Hz), 3.52 (dd, 1H, J=9.9, 6.7 Hz),
3.33 (dd, 1H, J=9.9, 5.0 Hz), 2.90 (d, 1H, J=2.5 Hz), 2.59 (dt, 1H, J=14.1, 7.0 Hz), 2.47 (dt, 1H, J=14.1,
7.0 Hz), 1.03 (bs, 2H); 13C NMR (75.43 MHz) δ 157.47 (s), 134.74 (d), 117.00 (t), 93.81 (d), 73.30 (t),
72.24 (2d), 71.19 (t), 69.09 (t), 50.04 (d), 35.38 (t). Anal. calcd for C23H27NO3: C, 75.58%; H, 7.45%;
N, 3.83%. Found: C, 74.45%; H, 7.62%; N, 3.94%.
3.5. 1-(30,40,60-Tri-O-benzyl-α-D-talopyranosyl)-2-propene 7
To a solution of ketone 4 (100 mg, 0.21 mmol) in 96% EtOH (0.5 mL) cooled to –20°C, NaBH4
(16 mg, 0.42 mmol) was added. After 15 min the reaction was quenched with a 5% aqueous solution of
NaOH and diluted with EtOAc. The organic layer was washed with water, dried over Na2SO4, filtered and
evaporated under reduced pressure. Purification by flash chromatography (9:1, petroleum ether:EtOAc)
1
afforded 97 mg of 7 as a colourless oil (97% yield). [α]D=+17.6 (c 1, CHCl3); H NMR (300 MHz,
C6D6) δ 7.30–7.12 (m, 15H), 5.91–5.82 (m, 1H), 5.06 (d, 1H, J=17.5 Hz), 5.03 (d, 1H, J=9.8 Hz), 4.62,
4.40 (ABq, 2H, J=11.4 Hz), 4.56, 4.51 (ABq, 2H, J=11.6 Hz), 4.42, 4.35 (ABq, 2H, J=11.0 Hz), 4.03
(bdd, 1H, J=9.6, 5.6 Hz), 3.97–3.90 (m, 1H), 3.89–3.82 (m, 3H), 3.63 (bd, 1H, J=2.8 Hz), 3.53–3.51 (m,
2H), 2.22 (t, 2H, J=6.5 Hz); 13C NMR (54.29 MHz) δ 134.24 (d), 117.14 (t), 76.37 (d), 75.74 (d), 74.69
(d), 74.00 (t), 73.36 (t), 72.05 (d), 71.45 (t), 69.09 (d), 67.75 (t), 34.38 (t). Anal. calcd for C30H34O5: C,
75.92%; H, 7.22%. Found: C, 75.84%; H, 7.11%.
3.6. 1-(20-Acetamido-30,40,60-tri-O-benzyl-20-deoxy-α-D-glucopyranosyl)-2-propene 11
To a solution of amine 1016 (1.0 g, 2.11 mmol) in dry CH2Cl2 (15 mL), dry pyridine (680 µL, 8.44
mmol) and acetic anhydride (398 µL, 4.22 mmol) were added. After 1 h the solution was washed
sequentially with 5% aqueous HCl and water. The organic layer was dried over Na2SO4, filtered and
concentrated to dryness. The residue was purified by flash chromatography (6:4, petroleum ether:EtOAc),
affording 900 mg of 11 as a white solid (83% yield). Mp 115–117°C; [α]D=+4.4 (c 1, CHCl3); 1H NMR
(300 MHz) δ 7.45–7.28 (m, 15H, Ph-H), 6.51 (d, 1H, J=9.8 Hz, NH), 5.86–5.75 (m, 1H, H-2), 5.08 (d,
1H, J=17.9 Hz, H-3a), 5.04 (d, 1H, J=10.8 Hz, H-3b), 4.62, 4.49 (ABq, 2H, J=11.8 Hz, PhCH2O), 4.58,
4.43 (ABq, 2H, J=11.3 Hz, PhCH2O), 4.52 (bs, 2H, PhCH2O), 4.25 (t, 1H, J=7.0 Hz, H-50), 4.20 (bdt,
1H, J=9.8, 1.6 Hz, H-20), 3.95 (dt, 1H, J=7.3, 1.6 Hz, H-10), 3.85 (dd, 1H, J=9.9, 7.0 Hz, H-60a), 3.75
(dd, 1H, J=9.9, 7.0 Hz, H-60b), 3.70 (t, 1H, J=3.0 Hz, H-30), 3.58 (bs, 1H, H-40), 2.32–2.10 (m, 2H,
H-1), 1.83 (s, 3H, CH3CO); 13C NMR (54.29 MHz, C6D6) δ 169.53 (s), 135.81 (d), 117.93 (t), 76.26
(d), 75.74 (d), 74.65 (d), 74.18 (t), 72.96 (t), 72.56 (t), 69.45 (t), 69.34 (d), 49.30 (d), 37.30 (t), 23.64 (q).
Anal. calcd for C32H37NO5: C, 74.54%; H, 7.23%; N, 2.72%. Found: C, 75.64%; H, 7.15%; N, 2.69%.
3.7. 1-(20-Acetamido-20-deoxy-α-D-glucopyranosyl)-2-propene 12
Compound 11 (2.3 g, 4.46 mmol) was dissolved in ethanethiol (22 mL) and BF3·OEt2 (13 mL) was
added dropwise. After 24 h the reaction mixture was neutralised by adding Et3N (10 mL) and the solvent
evaporated. Purification by flash chromatography (8:2, CH2Cl2:EtOH) afforded 12 as a white solid in
quantitative yield. Mp 176–178°C; [α]D=+108.4 (c 1, MeOH); 1H NMR (300 MHz, MeOD) δ 7.95 (d,
1H, J=5.5 Hz, NH), 5.92–5.73 (m, 1H, H-2), 5.21 (dd, 1H, J=16.3, 2.2 Hz, H-3a), 5.13 (d, 1H, J=9.0

L. Cipolla et al. / Tetrahedron: Asymmetry 11 (2000) 295–303
301
Hz, H-3b), 4.10 (dt, 1H, J=10.1, 5.5 Hz, H-10), 3.94 (bdt, 1H, J=10.0, 5.5 Hz, H-20), 3.75 (dd, 1H,
J=11.9, 2.8 Hz, H-60a), 3.67 (dd, 1H, J=11.9, 6.8 Hz, H-60b), 3.62 (t, 1H, J=10.0 Hz, H-30), 3.50–3.44
(m, 1H, H-50), 3.35 (t, 1H, J=10.0 Hz, H-40), 2.54–2.41 (m, 1H, H-1), 2.28–2.16 (m, 1H, H-1), 1.98 (s,
3H, CH3CO); 13C NMR (75.43 MHz, D2O) δ 175.13 (s), 135.15 (d), 118.35 (t), 73.94 (d), 73.52 (d),
71.55 (d), 71.45 (d), 61.74 (t), 54.23 (d), 30.82 (t), 22.75 (q). Anal. calcd for C11H19NO5: C, 53.87%; H,
7.81%; N, 5.71%. Found: C, 53.75%; H, 7.95%; N, 5.89%.
3.8. 1-(20-Acetamido-20-deoxy-30,60-di-O-pivaloyl-α-D-glucopyranosyl)-2-propene 13
Triol 12 (1.0 g, 4.07 mmol) was dissolved in a 2:1 mixture of dry pyridine:CH2Cl2 (21 mL), and the
solution cooled to –20°C; pivaloyl chloride (1 mL, 8.15 mmol) was added portionwise and the reaction
mixture allowed to warm to 0°C. After 7 h the organic phase was washed sequentially with 5% aqueous
HCl and water. The organic layer was dried over Na2SO4, filtered and evaporated. The crude was purified
by flash chromatography (98:2, CH2Cl2:EtOH). Compound 13 was obtained as an amorphous white solid
1
(1.37 g, 82% yield). [α]D=+16.6 (c 0.5, CHCl3); H NMR (300 MHz) δ 6.12 (d, 1H, NH, J=8.2 Hz),
5.81–5.70 (m, 1H, H-2), 5.11 (dd, 1H, H-3a, J=16.9, 1.3 Hz), 5.07 (d, 1H, H-3b, J=9.4 Hz), 5.01 (t, 1H,
H-30, J=8.0 Hz), 4.47 (dd, 1H, H-60a, J=11.9, 5.9 Hz), 4.25–4.12 (m, 3H, H-10, H-20, H-60b), 3.76 (ddd,
1H, H-50, J=8.0, 5.9, 2.5 Hz), 3.52 (t, 1H, H-40, J=8.0 Hz), 3.30 (bs, 1H, OH), 2.52–2.20 (m, 2H, H-1),
1.93 (s, 3H, CH3CO), 1.32–1.15 (m, 18H, (CH3)3C-); 13C NMR (54.29 MHz) δ 179.41 (s), 178.93 (s),
169.99 (s), 133.70 (d), 117.26 (t), 72.61 (d), 72.08 (d), 71.41 (d), 68.27 (d), 62.79 (t), 50.72 (d), 38.88
(s), 38.78 (s), 31.72 (t), 27.44–26.41 (m), 23.00 (q). Anal. calcd for C21H35NO7: C, 61.00%; H, 8.53%;
N, 3.39%. Found: C, 59.94%; H, 8.65%; N, 3.49%.
3.9. 1-(20-Acetamido-20-deoxy-40,60-di-O-pivaloyl-α-D-galactopyranosyl)-2-propene 14
Gluco derivative 13 (62 mg, 0.15 mmol) was dissolved in a 2:1 pyridine:CH2Cl2 mixture (1 mL) and
the solution cooled to 0°C. Triflic anhydride (62 µL, 0.37 mmol) was added portionwise until complete
consumption of the starting material; water (148 µL, 8.2 mmol) was then added, and the reaction mixture
was allowed to stir overnight at room temperature. The reaction was diluted with CH2Cl2, the organic
layer washed sequentially with 5% aqueous HCl and water, dried over Na2SO4, filtered and evaporated
under reduced pressure. Purification by flash chromatography (1:1, petroleum ether:EtOAc+0.2% EtOH)
afforded 52 mg of 14 as a yellowish oil (84% yield). [α]D=+50.1 (c 1, CHCl3); 1H NMR (300 MHz) δ
5.99 (d, 1H, NH, J=7.7 Hz), 5.81–5.69 (m, 1H, H-2), 5.13 (d, 1H, H-40, J=3.9 Hz), 5.10 (d, 1H, H-3a,
J=15.5 Hz), 5.05 (d, 1H, H-3b, J=9.5 Hz), 4.62 (bt, 1H, H-60a, J=9.7 Hz), 4.36 (ddd, 1H, H-10, J=8.9,
5.0, 3.3 Hz), 4.16 (dt, 1H, H-20, J=7.7, 3.3 Hz), 4.11 (dd, 1H, H-50, J=9.7, 4.4 Hz), 4.03 (dd, 1H, H-60b,
J=9.7, 4.4 Hz), 4.01 (dd, 1H, H-30, J=7.7, 3.9 Hz), 2.36–2.15 (m, 3H, H-1, OH), 2.01 (s, 3H, CH3CO),
1.33–1.13 (m, 18H, (CH3)3C-); 13C NMR (54.29 MHz) δ 178.04 (s), 170.91 (2s), 133.83 (d), 117.27 (t),
70.70 (d), 68.50 (d), 68.18 (d), 67.58 (d), 60.74 (t), 52.07 (d), 39.01 (s), 38.63 (s), 33.01 (t), 27.04 (6q),
23.04 (q). Anal. calcd for C21H35NO7: C, 61.00%; H, 8.53%; N, 3.39%. Found: C, 60.13%; H, 8.68%;
N, 3.64%.
3.10. 1-(20-Acetamido-20-deoxy-α-D-galactopyranosyl)-2-propene 15
Galacto derivative 14 (80 mg, 0.193 mmol) was dissolved in dry MeOH (2 mL) and a catalytic amount
of sodium was added; after 45 min the reaction mixture was neutralised with Amberlite IR-120, filtered
and evaporated. Purification of the crude by crystallisation (EtOH/EtOAc) afforded 41 mg of 15 as a

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1
white solid (87% yield). Mp 215–217°C; [α]D=+129.0 (c 0.85, MeOH); H NMR (200 MHz, D2O) δ
7.99 (d, 1H, NH, J=6.4 Hz), 5.92–5.68 (m, 1H, H-2), 5.08 (dd, 1H, H-3a, J=17.1, 2.3 Hz), 5.02 (dd,
1H, H-3b, J=9.1, 2.3 Hz), 4.30–4.01 (m, 2H, H-10, H-50), 3.91 (bs, 1H, H-40), 3.83–3.65 (m, 4H, H-20,
H-30, H-60), 2.32–2.58 (m, 1H, H-1a), 2.09–2.27 (m, 1H, H-1b), 2.00 (s, 3H, CH3CO). Anal. calcd for
C11H19NO5: C, 53.86%; H, 7.80%; N, 5.71%. Found: C, 53.93%; H, 7.69%; N, 5.74%.
3.11. 1-(20-Acetamido-20-deoxy-α-D-galactopyranosyl)-propan-2-one 16
Compound 15 (24 mg, 0.098 mmol) was dissolved in water (1.5 mL), Na2PdCl4 was added and the
reaction mixture warmed to 60°C. After 30 min the suspension was filtered on a Celite pad, and the
filtrate concentrated to dryness. The crude was purified by flash chromatography (6:4, EtOAc:EtOH),
affording 20 mg of ketone 16 as a yellowish oil (80% yield). 1H NMR (300 MHz, MeOD) δ 7.99 (d, 1H,
NH, J=5.0 Hz,), 4.64 (dt, 1H, H-10, J=9.6, 5.0 Hz), 4.27 (dt, 1H, H-20, J=9.5, 5.0 Hz), 3.96 (t, 1H, H-40,
J=2.4 Hz), 3.88–3.63 (m, 4H, H-30, H-50, H-60), 2.91 (dd, 1H, H-1a, J=16.0, 9.6 Hz), 2.67 (dd, 1H, H-1b,
J=16.0, 5.0 Hz), 2.22 (s, 3H, H-3), 2.01 (s, 3H, CH3CO); 13C NMR (75.43 MHz, MeOD) δ 211.07 (s),
174.80 (s), 76.51 (d), 74.76 (d), 74.02 (d), 71.01 (d), 62.71 (t), 51.71 (d), 42.37 (t), 31.21 (q), 23.36 (q).
Anal. calcd for C11H19NO6: C, 50.57%; H, 7.32%; N, 5.38%. Found: C, 50.53%; H, 7.26%; N, 5.42%.
Acknowledgements
We gratefully acknowledge Carmelo Buda and Eleonora Forni for their contribution to the experimen-
tal results.
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