Stereoselective synthesis of N-glycosyl amino acids by traceless Staudinger ligation of unprotected glycosyl azides

Article abstract of DOI:10.1002/ejoc.200900692

The stereoconservative Staudinger ligation of unprotected α- and β-glycosyl azides with 2-(diphenylphosphanyl)-4fluorophenyl esters to afford α- and β-N-glycosyl amino acids is described. The ligation method works reliably well for unprotected β-azides of

Full text of DOI:10.1002/ejoc.200900692

FULL PAPER
DOI: 10.1002/ejoc.200900692
Stereoselective Synthesis of N-Glycosyl Amino Acids by Traceless Staudinger
Ligation of Unprotected Glycosyl Azides
Filippo Nisic,[a] Manuel Andreini,[a] and Anna Bernardi*[a]
Keywords: Carbohydrates / Synthetic methods / Glycoconjugates / Glycopeptides / Amino acids
The stereoconservative Staudinger ligation of unprotected
α- and β-glycosyl azides with 2-(diphenylphosphanyl)-4-
fluorophenyl esters to afford α- and β-N-glycosyl amino acids
is described. The ligation method works reliably well for un-
protected β-azides of the gluco, galacto and fuco series.
Lower yields (ca. 50%) were obtained with a β-glucosyl-N-
acetyl azide. The reaction of an α-glucosyl azide also led to
major improvements compared with the use of non-fluori-
nated phosphanes. All the N-glycosyl amino acid products
can be isolated and byproducts removed from the crude reac-
tion mixtures by simple water extraction.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
Introduction
The synthesis of neo-glycoconjugates has gained increas-
ing attention in the past 10 years.[1] Our laboratory has re-
cently shown that the traceless Staudinger ligation[2] of gly-
cosyl azides with functionalized phosphanes 1 allows the
stereoselective synthesis of both α- and β-glycosyl amides
(Scheme 1).[3,4] With α-glycosyl azides, the stereoselectivity
of the process depends critically on the sugar protecting
groups: the unprotected monosaccharide (2a: R = H) or its
O-benzyl ether (2b: R = Bn) can be transformed into the
corresponding amides with retention of configuration at the
anomeric carbon atom, whereas the O-acetyl derivative (2c:
R = Ac) completely isomerizes to give the epimeric β-
amides. In contrast, β-glycosyl azides 3 can be transformed
into the corresponding amides with retention of configura-
tion, irrespective of the nature of the R group (R = Bn, Ac,
H).
Ligation of the unprotected α- and β-glucosyl azides[4] 2a
and 3a was particularly remarkable because in both cases it
occurred stereoconservatively and allowed simple isolation
of the resulting glucosyl amides from the phosphane oxide
byproduct by water extraction. The anomeric ratios of the
products were consistently good and the yields moderate-
to-good for most of the alkyl chains RЈ, particularly under
MW irradiation. The only notable exception was presented
by the aspartic and glutamic acid derivatives 1a and 1b
(Scheme 2), which gave poor yields of the corresponding
Scheme 1. Traceless Staudinger ligation of glycosyl azides with
functionalized phosphane 1.
glucosyl amino acids for both the α and β series. This is
particularly disappointing because these amides are impor-
tant glycoconjugates, mimicking the conserved core of nat-
ural N-asparagine-linked glycopeptides and glycopro-
teins.[5,6]
Herein we present novel functionalized phosphanes 4
(Scheme 4) that were designed to improve the Staudinger
ligation of glycosyl azides with amino acids. We show that
indeed monofluorophosphanes 4 improve the yields of
amino acid transfer in comparison with the non-fluorinated
analogues 1 and afford the corresponding N-glycosyl amino
acids in a synthetically practical manner.
[a] Università degli Studi di Milano, Dipartimento di Chimica Or-
ganica e Industriale and CISI,
Via Venezian 21, 20133 Milano, Italy
Fax: +39-02-503-14072
E-mail: anna.bernardi@unimi.it
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.200900692.
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N-Glycosyl Amino Acids by Traceless Staudinger Ligation
Fluorophenyl esters are well known to act as good acti-
vating groups in acyclic nucleophilic substitution reactions.
Thus, we replaced phosphanes 1 with the corresponding
monofluoro derivatives 4 (Scheme 4), which could be ob-
tained in high yields from the known phosphane 7[7] by re-
action with the appropriate amino acids and condensing
agents (Scheme 4). The functionalized phosphanes 4a–e
were synthesized to examine the Staudinger ligation of the
aspartic and glutamic acid side-chains (4a and 4b, respec-
tively) as well as the reactions of simple α- and β-amino
acids such as β-alanine 4c, glycine 4d and proline 4e. Opti-
mal yields were obtained by using either N-[3-(dimeth-
ylamino)propyl]-NЈ-ethylcarbodiimide (EDC) (4a and 4b)
or DCC (4c–e) as the condensing agent. The ligation rea-
gents could be isolated by simple filtration through a silica
gel plug. Analytical samples were purified by flash
chromatography. In general, and like the parent non-fluori-
nated compounds, phosphanes 4a–e were found to be air-
stable compounds that could be handled under standard
conditions with minimal precautions.
Scheme 2. Phosphanes 1a,b give poor yields of N-glycosyl amino
acids.
Results and Discussion
The Staudinger ligation of phosphanes 1 can be envis-
aged as taking place in two steps, as depicted in Scheme 3
for the reaction of 1a with α-glucosyl azide 2a. In the first
The initial experiments were performed by treating the
step, nucleophilic addition of the phosphane to the γ nitro- unprotected α- and β-glucosyl azides 2a and 3a with
gen of the azide followed by nitrogen extrusion leads to the 2 equiv. of phosphane in DMA/DMPU (98:2) at 40 °C for
iminophosphorane 5. In the second step, 5 undergoes an 18 h. After completion of the reaction, the crude mixtures
intramolecular reaction in which the acyl chain is transfer- were stirred with water for an additional 2 h, then diluted
red from the phenolic activated ester to the iminophos- with water and extracted with CH2Cl2 to eliminate the
phorane nitrogen and an amide bond is generated. Our pre- phosphane byproducts. The aqueous layers were analyzed
1
vious observations indicated that the poor amide yields ob- by H NMR (typically in D2O) and the product ratios es-
tained for the reaction of glucosyl azides with phosphanes tablished on the basis of the integration of the anomeric
1a and 1b were caused by inefficient acyl chain transfer in protons. Typical reaction crudes contained both the ex-
the iminophosphorane 5.[3,4] Hence, improving the leaving pected α- or β-pyranosyl amides 8 or 10 and variable
group ability of the activated ester should result in higher amounts of the corresponding furanosyl amides
yields for this difficult transfer step.
9
(Scheme 5). As we have previously shown,[4] the latter are
Scheme 3. Two-step mechanism for the Staudinger ligation.
Scheme 4. Synthesis of the fluorinated phosphanes 4a–e.
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F. Nisic, M. Andreini, A. Bernardi
FULL PAPER
Scheme 5. Synthesis of α- and β-glucosyl amino acids 8a–d and 10a–e.
formed by ring-opening/ring-closure of the intermediate with the use of non-fluorinated phosphanes, although it af-
iminophosphoranes.[8] Free glucose (equilibrium anomeric forded the corresponding α-amides 8a–d in modest yields
mixtures) is also formed by hydrolysis of the same interme- in comparison with the β anomer. As an example, the as-
diates. The glucosyl amides were purified by flash partic acid side-chain was transferred giving a yield of 55%
chromatography on silica gel (4:1 CHCl3/MeOH) and fully with phosphane 4a (entry 6) as opposed to the 35% yield
characterized as their acetylated counterparts.
obtained with the non-fluorinated phosphane 1a. Ligation
The phosphanes 4 afforded major improvements in the of the α-azide was generally accompanied by ring contrac-
Staudinger ligation of 2a and 3a with amino acids. The re- tion and sizeable quantities of the glucofuranosyl amides 9
actions with β-glucosyl azide 3a (Table 1, entries 1–5) gave were formed (Table 1, entries 6–9). Strict control of anhy-
good-to-excellent yields of the corresponding pyranosyl drous conditions was found to minimize the formation of
amides 10a–e, which were essentially pure after water ex- ring-contraction byproducts. In our previous studies with
traction. The 1H NMR spectra of the reaction crudes phosphanes 1, the use of MW irradiation proved beneficial
showed no trace of the anomeric α-pyranosyl epimer and for reducing the amount of furanose formation,[4] but this
very minor quantities (Յ3%) of a byproduct to which the was not the case with phosphanes 4 as MW irradiation
furanosyl amide structure 9 was tentatively assigned; α-, β- (50 °C, 50 min) gave lower yields of the desired pyranosyl
and γ-amino acids were transferred with equal efficiency. amides and more byproducts.
The aspartic acid amide 10a (Table 1, entry 1) was the most
To probe the scope of the fluorinated phosphanes 4,
difficult to obtain, but could still be isolated in 77% yield, other β-unprotected glycosyl azides were tested in the
as opposed to the yield of 32% obtained under the same Staudinger ligation (Scheme 6, Table 2). The reactions of
conditions with phosphane 1a.[4]
phosphanes 4a–e with β-galactosyl azide 11, β-fucosyl azide
The reactions of α-glucosyl azide 2a (Table 1, entries 6– 12 and β-glucosyl-N-acetyl azide 13 were performed and
9) with 4a–d also led to major improvements compared afforded the corresponding glycosyl amides 14–16 in good
Table 1. Synthesis of α- and β-glucosyl amino acids 8 and 10 by ligation of α- and β-glucosyl azides 2a and 3a with 4a–e.
Entry
Phosphane
Azide
Product
Isolated yield[a] [%]
α/β Ratio[b]
Pyr/fur[c]
1
2
3
4
5
6
7
8
9
4a
4b
4c
4d
4e
4a
4b
4c
4d
3a
3a
3a
3a
3a
2a
2a
2a
2a
10a
10b
10c
10d
10e
8a
77
87
85
75
70
56
59
Յ1:99
Յ1:99
Յ1:99
Յ1:99
Յ1:99
98:2
98:2
98:2
98:2
98:2[d]
98:2[d]
98:2[d]
97:3[d]
98:2[d]
85:15[e]
87:13[e]
90:10[e]
67:33[e]
8b
8c
8d
60
36 (12)[f]
[a] Yields based on glucopyranosyl amide. [b] Ratio of the anomeric proton signals of the α- and β-pyranosyl amides 8 and 10 in the
1
1
crude H NMR spectrum. [c] Ratio of the anomeric proton signals in the crude H NMR spectrum. [d] Ratio of 10/9. [e] Ratio of 8/9
ratio. [f] Isolated yield of furanosyl amide 9d.
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N-Glycosyl Amino Acids by Traceless Staudinger Ligation
Scheme 6. Synthesis of amides 14–16 with 4a–e.
Table 2. Synthesis of amides 14–16 with 4a–e.
Entry
Phosphane
Azide
Product
Isolated yield[a] [%]
Furanose[b] [%]
1
2
3
4
5
6
7
8
9
4a
4b
4c
4d
4a
4b
4c
4d
4e
4a
4b
4c
11
11
11
11
12
12
12
12
12
13
13
13
14a
14b
14c
14d
15a
15b
15c
15d
15e
16a
16b
16c
74
70
71
–
5
10
5
9
9
13
6
–
–
–
73
60[c]
68[c]
70[c]
75[c]
87[c]
56
10
11
12
54
60
–
1
[a] Yields based on β-pyranosyl amide. [b] Estimated by integration of the anomeric proton signals in the H NMR spectra of the crude
reaction mixtures. [c] Around 10% of hydrolysis product (fucose) was also observed.
yields. 1H NMR analysis of the crude reaction mixtures
showed no trace of the anomeric α-pyranosyl epimer. Vari-
Conclusions
able quantities (5–13%) of the isomeric furanosyl amides
The results reported herein show that unprotected α- and
were formed, depending both on the nature of the azide β-glycosyl azides can be stereoselectively ligated to α-, β-
and the amino acid transferred (see Table 2). In all cases, and γ-amino acids by traceless Staudinger ligation using
this byproduct could be separated from the pyranose isomer phosphanes 4. All the N-glycosyl amino acid products
by flash chromatography. With the β-galactosyl azide 11, β- could be isolated from the crude reaction mixtures by sim-
and γ-amino acids were transferred with an average yield ple water extraction and were further purified by flash
of 70% (Table 2, entries 1–4). Similar results were obtained chromatography on silica gel.
with β-fucosyl azide 12 (Table 2, entries 5–9). β-Glucosyl-
The starting phosphane 7 is not commercially available,
N-acetyl azide 13 was found to be less reactive and the cor- but it can be easily prepared on the gram scale by following
responding amides were formed in an average yield of 55% the reported procedure.[7] It is stable to air at room tempera-
(Table 2, entries 10–12).[9] Comparison with the yields ob- ture for weeks and can be handled with no special pre-
tained with the corresponding β-glucosyl azide 3a (Table 1), cautions. Acylation followed by silica gel filtration affords
which on average are higher by 30%, suggests a deactivating the ligation agents 4, which can be used without further
role of the acetamido group in 13.
purification. The stereoselective synthesis of the required
Eur. J. Org. Chem. 2009, 5744–5751
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5747

F. Nisic, M. Andreini, A. Bernardi
FULL PAPER
azide precursors has been reviewed.[3] A recently developed
methodology also allows the direct conversion of unprotec-
ted sugars to glycosyl azides,[12–14] often stereoselectively.
The ligation method described herein works reliably well
for unprotected β-azides of the gluco, galacto and fuco
series. Lower yields (ca. 50%) were obtained with β-gluco-
syl-N-acetyl and α-glycosyl azides. Only one method for the
synthesis of β--2-deoxy-2-N-acetylglucopyranosyl-aspara-
gine from unprotected N-acetylglucosamine has been de-
scribed.[15]
1-Methyl 5-[2-(Diphenylphosphanyl)-4-fluorophenyl] N-(Benzyloxy-
carbonyl)-L-aspartate (4a): A solution of o-(diphenylphosphanyl)-
p-fluorophenol (7; 253 mg, 0.85 mmol, 1 equiv.), the commercially
available 1-methyl N-(benzyloxycarbonyl)--aspartate (380 mg,
1.02 mmol, 1.2 equiv.) and 4-(dimethylamino)pyridine (10.4 mg,
0.085 mmol, 0.1 equiv.) in dry CH2Cl2 (8.5 mL, 0.1 ) were added,
at room temperature and under nitrogen, to a suspension of N-[3-
(dimethylamino)propyl]-NЈ-ethylcarbodiimide
hydrochloride
(EDC) (228 mg, 1.19 mmol, 1.4 equiv.) and dry N,N-diisopropyl-
ethylamine (203.7 µL, 1.19 mmol, 1.4 equiv.) in dry CH2Cl2. The
mixture was stirred at room temp. for 2 h, monitoring by TLC (7:3
There are only a handful of methods that can be used to hexane/AcOEt). The reaction mixture was diluted with CH2Cl2 and
synthesize α-N-glycosyl amides,[3,4,10,11] among them,
the traceless Staudinger ligation of α-glycosyl azides with
extracted with 5% aqueous HCl and water. The organic layer was
dried with Na2SO4 and concentrated. The crude product was puri-
fied by flash chromatography using 6:4 hexane/AcOEt as the eluent
functionalized phosphanes was found to perform poorly
to afford 4a (404 mg, 0.72 mmol) in 85% yield. 1H NMR
with amino acids. The fluorophenylphosphanes 4 described
(400 MHz, CDCl3, 25 °C): δ = 7.48–7.27 (m, 15 H, Ar-H), 7.12–
herein overcome most of the limitations previously de-
7.02 (m, 2 H, 2-H, 3-H), 6.55 (m, 1 H, 1-H), 5.70 (d, JNH-CH
=
scribed and allow the synthesis of α-N-glucosyl amino acids
in reasonable yields and in a synthetically practical
manner.
8.6 Hz, 1 H, NH), 5.18 (d, J = 6 Hz, 2 H, CH2-O), 4.61 (q,
JCH-CH2 = 4.4 Hz, 1 H, CH), 3.72 (s, 3 H, O-CH3), 3.01 (dd, J =
4.6, J = 17.2 Hz, 1 H, Ha, CH2), 2.75 (dd, J = 4.2, 17.2 Hz, 1 H,
Hb, CH2) ppm. 13C NMR (100 MHz, CDCl3, 25 °C): δ = 170.9,
169.2, 161.8, 159.4 (COCbz), 134.2, 134.1, 133.9, 133.8, 129.7, 129.6,
The elaboration of unprotected carbohydrates has re-
ceived considerable attention in recent years.[16–18] Unpro-
tected glycosyl amino acid can be used directly for the lin- 129.0, 128.9, 128.7, 128.6, 128.4, 128.3, 128.1 (5 CAr), 123.9, 123.8,
120.2, 120, 116.9, 116.6, 67.2 (CH2-O), 52.9 (O-CH3), 50.3 (CH),
ear synthesis of glycopeptides (direct insertion of the gly-
cosyl amino acid into a growing peptide chain).[15,19] Meth-
ods of glycopeptide synthesis that do not involve protected
sugars do not require further manipulation of the sugar,
which can lead to racemization of the amino acid.[20]
Beyond affording N-glycosylated Asn and Gln building
blocks, the functionalized phosphanes described herein
could also be used to achieve traceless ligation of glycosyl
azides to glycine, proline and the non-proteinogenic amino
acid β-Ala. The resulting compounds are not meant to be
incorporated into N-glycopeptide sequences, but can be
used for the bioconjugation of carbohydrates to aglycons
using chemically stable bonds and for the design of carbo-
36.5 (CH2) ppm. 31P NMR:
δ = =
–15.3 ppm [oxide 31P
+26.7 ppm]. MS (ESI): m/z = 582.2 [M + Na]+. Rf = 0.61 (6:4
hexane/AcOEt).
1-Methyl 5-[2-(Diphenylphosphanyl)-4-fluorophenyl] N-(Benzyloxy-
carbonyl)-L-glutamate (4b): A solution of o-(diphenylphosphanyl)-
p-fluorophenol (7; 324 mg, 1.09 mmol, 1 equiv.), the commercially
available 1-methyl N-(benzyloxycarbonyl)--glutamate (386 mg,
1.31 mmol, 1.2 equiv.) and 4-(dimethylamino)pyridine (13.5 mg,
0.11 mmol, 0.1 equiv.) in dry CH2Cl2 (0.1 ) were added, at room
temperature and under nitrogen, to a suspension of N-[3-(dimeth-
ylamino)propyl]-NЈ-ethylcarbodiimide hydrochloride (293.3 mg,
1.53 mmol, 1.4 equiv.) and dry N,N-diisopropylethylamine (262 µL,
1.53 mmol, 1.4 equiv.) in dry CH2Cl2. The mixture was stirred at
hydrate mimics which may resist in vivo to hydrolytic en- room temp. for 2 h, monitoring by TLC (8:2 hexane/AcOEt). The
zymes.[21,22]
reaction mixture was diluted with CH2Cl2 and extracted with 5%
aqueous HCl and water. The organic layer was dried with Na2SO4
and concentrated. The crude product was purified by flash
chromatography using 6:4 hexane/AcOEt as the eluent to afford 4b
(531 mg, 0.93 mmol) in 85% yield. 1H NMR (400 MHz, CDCl3,
25 °C): δ = 7.40–7.27 (m, 15 H, Ph), 7.09 (m, 1 H, 2-H), 7.00 (m,
1 H, 3-H), 6.47 (m, 1 H, 1-H), 5.34 (d, JNH-CH = 7.9 Hz, 1 H, NH),
5.11 (d, J = 3.8 Hz, 2 H, CH2-O), 4.35 (m, 1 H, CH), 3.74 (s, 3 H,
O-CH3), 2.28 (m, 2 H, CH2-CO), 2.01 (m, 1 H, Ha, CH2-CH), 1.80
(m, 1 H, Hb, CH2-CH) ppm. 13C NMR (100 MHz, CDCl3, 25 °C):
δ = 170.8, 161.9, 159.4 (COCbz), 134.4, 134.4, 134.2, 134.2, 129.8,
129.2, 129.1, 128.9, 128.6, 128.5 (5 CAr), 124.3, 124.2, 120.2, 119.9,
116.9, 116.7, 67.5 (CH2-O), 53.5 (CH), 52.8 (O-CH3), 30.3 (CH2-
CO), 27.6 (CH2) ppm. 31P NMR: δ = –14.2 ppm [oxide 31P =
+26.8 ppm]. MS (ESI): m/z = 596.3 [M + Na]+. Rf = 0.56 (6:4
hexane/AcOEt).
Experimental Section
General: Solvents were dried by standard procedures: dichloro-
methane, methanol, N,N-diisopropylethylamine and triethylamine
were dried with calcium hydride; N,N-dimethylacetamide (DMA),
1,3-dimethyltetrahydro-2(1H)-pyrimidinone (DMPU), chloroform
and pyridine were dried with activated molecular sieves. Reactions
requiring anhydrous conditions were performed under nitrogen.
1H, 13C and 31P NMR spectra were recorded at 400 MHz with a
Bruker AVANCE-400 instrument. Chemical shifts (δ) for the 1H
and 13C NMR spectra are expressed in ppm relative to internal
Me4Si as standard. Signal multiplicities are abbreviated as follows:
s, singlet; br. s, broad singlet; d, doublet; t, triplet; q, quartet; m,
multiplet. Mass spectra were obtained with a Bruker ion-trap Es-
quire 3000 (ESI ionization) or Autospec Fission spectrometer (FAB
ionization) and FT-ICR Mass Spectrometer APEX II & Xmass 4.7
Magnet software (Bruker Daltonics). Thin-layer chromatography
(TLC) was carried out on precoated Merck F254 silica gel plates.
Flash chromatography (FC) was carried out on Macherey–Nagel
N-(Benzyloxycarbonyl)-β-alanine 2-(Diphenylphosphanyl)-4-fluoro-
phenyl Ester (4c): A solution of o-(diphenylphosphanyl)-p-fluoro-
phenol (7; 283.3 mg, 0.96 mmol, 1 equiv.), the protected amino
acid N-(benzyloxycarbonyl)--β-alanine (257.1 mg, 1.15 mmol,
1.2 equiv.) and 4-(dimethylamino)pyridine (11.7 mg, 0.096 mmol,
0.1 equiv.) in dry CH2Cl2 (9.6 mL, 0.1 ) was added, at room tem-
silica gel 60 (230–400 mesh). Compounds 8a,b,[4] 10a,b,[4] 10d[23] perature and under argon, to a solution of N,NЈ-dicyclohexylcar-
and 16a[24] have been previously described.
bodiimide (277.3 mg, 1.34 mmol, 1.4 equiv.) in dry CH2Cl2. The
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N-Glycosyl Amino Acids by Traceless Staudinger Ligation
mixture was stirred at room temperature for 2 h, monitoring by (1 equiv.) in 98:2 N,N-dimethylacetamide/DMPU. The solution was
TLC (7:3 hexane/AcOEt). The reaction mixture was filtered and
washed with CH2Cl2. The crude product was purified by flash
chromatography using 7:3 hexane/AcOEt as the eluent to afford 4c
(460 mg, 0.88 mmol) in 92% yield. 1H NMR (400 MHz, CDCl3,
25 °C): δ = 7.42–7.27 (m, 15 H, Ph), 7.15–7.05 (m, 2 H, 2-H, 3-H),
6.52 (m, 1 H, 1-H), 5.27 (m, 1 H, NH), 5.12 (s, 2 H, CH2-O), 3.48
(q, JCH2-NH = 12 Hz, 2 H, CH2-NH), 2.50 (t, JCH2-CH2 = 6 Hz, 2
H, CH2-CO) ppm. 13C NMR (100 MHz, CDCl3, 25 °C): δ = 170.8,
161.9, 159.5 (COCbz), 156.5, 134.8, 134.7, 134.4, 134.2, 132.1, 132,
129.8, 129.3, 129.2, 128.8, 128.5, 128.4 (5 CAr), 124.3, 124.2, 120.4,
120.2, 117.1, 116.8, 67 (CH2-O), 36.6 (CH2), 34.8 (CH2CO) ppm.
31P NMR: δ = –15.2 ppm [oxide 31P NMR: δ = +27.9 ppm]. MS
(ESI): m/z = 524.2 [M + Na]+. Rf = 0.42 (7:3 hexane/AcOEt).
stirred for 16 h at 40 °C, then water was added and the mixture
was stirred for an additional 2 h at the same temperature. The sol-
vent was evaporated under reduced pressure and the residue was
diluted with water and extracted with CH2Cl2. The water layer was
evaporated under reduced pressure and the crude was purified as
indicated below for each compound. The reactions were performed
on the 0.1–1 mmol scale. Yields are reported in Tables 1 and 2.
N-(N-Benzyloxycarbonyl-β-alanyl)-α-D-glucopyranosylamine (8c):
The compound was purified by flash chromatography (80:20:2
CHCl3/MeOH/H2O, Rf = 0.38). [α]2D5 = +46.4 (c = 1, MeOH). H
1
NMR (400 MHz, D2O, 25 °C): δ = 7.41–7.33 (m, 5 H, Ph), 5.52
(d, J1,2 = 5.4 Hz, 1 H, 1-H) 5.05 (s, 2 H, CH2-O), 3.78–3.58 (m, 4
H, 2-H, 6-H, 6Ј-H), 3.50–3.27 (m, 4 H, CH2), 2.53–2.48 (m, 2 H,
CH2) ppm. 13C NMR (100 MHz, D2O, 25 °C): δ = 175.9, 158.2
(COCbz), 136.4 (Cipso), 128.8, 128.5, 127.7 (5 Ar), 76.6 (C-1), 73.0,
72.6, 69.3, 69.2, 66.9 (CH2-O), 60.4 (C-6), 38.1 (CH2), 36.1
(CH2) ppm.
N-(Benzyloxycarbonyl)glycine
2-(Diphenylphosphanyl)-4-fluoro-
phenyl Ester (4d): A solution of o-(diphenylphosphanyl)-p-fluo-
rophenol (7; 158.3 mg, 0.53 mmol, 1 equiv.), the protected amino
acid N-(benzyloxycarbonyl)--glycine (134 mg, 0.64 mmol,
1.2 equiv.) and 4-(dimethylamino)pyridine (6.5 mg, 0.053 mmol,
0.1 equiv.) in dry CH2Cl2 (5.3 mL, 0.1 ) was added, at room tem-
perature and under argon, to a solution of N,NЈ-dicyclohexylcar-
bodiimide (152.7 mg, 0.74 mmol, 1.4 equiv.) in dry CH2Cl2. The
mixture was stirred at room temperature for 2 h, monitoring by
TLC (7:3 hexane/AcOEt). The reaction mixture was filtered and
washed with CH2Cl2. The crude product was purified by flash
chromatography using 7:3 hexane/AcOEt as the eluent to afford 4d
N-(N-Benzyloxycarbonylglycyl)-α-D-glucopyranosylamine (8d): The
compound was purified by flash chromatography (80:20:2CHCl3/
1
MeOH/H2O, Rf = 0.23). [α]2D5 = +16.3 (c = 0.5, MeOH). H NMR
(400 MHz, D2O, 25 °C): δ = 7.43–7.29 (m, 5 H, Ph), 5.53 (d, J1,2
= 5.6 Hz, 1 H, 1-H), 5.09 (s, 2 H, CH2-O), 3.89 (br. s, 2 H, CH2),
3.87–3.34 (m, 6 H, 2-H, 3-H, 4-H, 5-H, 6-H, 6Ј-H) ppm. 13C NMR
(100 MHz, D2O, 25 °C): δ = 170.3, 128.8, 128.4, 127.8 (5 CAr),
79.4 (C-1), 76.7, 72.7, 72.4, 69.4, 67.3 (CH2-O), 60.6 (C-6), 43.4
(CH2) ppm.
1
(232.5 mg, 0.48 mmol) in 90% yield. H NMR (400 MHz, CDCl3,
25 °C): δ = 7.48–7.30 (m, 15 H, Ph), 7.15 (m, 1 H, 2-H), 7.11 (m,
1 H, 3-H), 6.53 (m, 1 H, 1-H), 5.12 (s, 2 H, CH2-O), 4.99 (m, 1 H,
NH), 3.85 (d, JNH-CH2 = 5.2 Hz, 2 H, CH2) ppm. 13C NMR
(100 MHz, CDCl3, 25 °C): δ = 168.4, 159.6 (COCbz), 156.4, 162.1,
136.4 (Cipso), 134.8, 134.7, 134.4, 134.2, 129.9, 129.2, 129.1, 128.9,
128.6, 128.4 (5 CAr), 124.2, 124.1, 120.4, 120.3, 120.1, 120.1, 117,
116.8, 67.5 (CH2-O), 42.8 (CH2) ppm. 31P NMR: δ = –14.0 ppm.
[oxide 31P NMR: δ = +27.5 ppm]. MS (ESI): m/z = 510.4 [M +
Na]+. Rf = 0.51 (7:3 hexane/AcOEt).
Nα-(Benzyloxycarbonyl)-Nγ-(β-
D-glucopyranosyl)-L-asparagine O-
Methyl Ester (10a): The compound was purified by flash
chromatography (80:20:2 CHCl3/MeOH/H2O, Rf = 0.43). [α]2D5
=
1
–0.6 (c = 1, MeOH). H NMR (400 MHz, D2O, 25 °C): δ = 7.45–
7.35 (m, 5 H, Ph), 5.10 (s, 2 H, CH2-O), 4.96 (d, J1,2 = 9.2 Hz, 1
H, 1-H), 4.65 (t, J = 6.4 Hz, 1 H, CH-N), 3.88 (dd, J6,6Ј = 12.4,
J5,6 = 2.4 Hz, 1 H, 6-H), 3.80–3.69 (m, 4 H, 6Ј-H, O-CH3), 3.60–
3.51 (m, 2 H, 4-H, 5-H), 3.46–3.37 (m, 2 H, 3-H, 2-H), 2.95–2.89
(m, 2 H, CH2) ppm. 13C NMR (100 MHz, D2O, 25 °C): δ = 173.4,
173.1, 157.7 (COCbz), 136.2 (Cipso), 128.8, 128.4, 127.6 (5 CAr), 79.2
(C-1), 77.5 (C-5), 76.4 (C-4), 71.7 (C-2), 69.2 (C-3), 67.2 (CH2-O),
53.1 (O-CH3), 50.6 (CH), 37.1 (CH2) ppm. MS (FAB): m/z = 465
[M + Na]+.
N-(tert-Butoxycarbonyl)-L-proline 2-(Diphenylphosphanyl)-4-fluoro-
phenyl Ester (4e): A solution of o-(diphenylphosphanyl)-p-fluoro-
phenol (7; 119.6 mg, 0.40 mmol, 1 equiv.), the protected amino acid
N-Boc--proline (103.3 mg, 0.48 mmol, 1.2 equiv.) and 4-(dimeth-
ylamino)pyridine (4.9 mg, 0.04 mmol, 0.1 equiv.) in dry CH2Cl2
(4 mL, 0.1 ) was added, at room temperature and under argon,
Nα-(Benzyloxycarbonyl)-Nδ-(β-
D-glucopyranosyl)-L-glutamine
O-
Methyl Ester (10b): The compound was purified by flash
chromatography (80:20:2 CHCl3/MeOH/H2O, Rf = 0.47). [α]2D5
–10 (c = 1, MeOH). H NMR (400 MHz, D2O, 25 °C): δ = 7.49–
7.38 (m, 5 H, Ph), 5.14 (s, 2 H, CH2-O), 4.95 (d, J1,2 = 9.2 Hz, 1
H, 1-H), 4.25 (m, 1 H, CH-N), 3.86 (dd, J5,6 = 2, J6,6’ = 12.4 Hz,
=
to
a
solution of N,NЈ-dicyclohexylcarbodiimide (115.5 mg,
1
0.56 mmol, 1.4 equiv.) in dry CH2Cl2. The mixture was stirred at
room temperature for 2 h, monitoring by TLC (8:2 hexane/AcOEt).
The reaction mixture was filtered and washed with CH2Cl2. The
crude product was purified by flash chromatography using 8:2
hexane/AcOEt as the eluent to afford 4e (185.3 mg, 0.37 mmol) in
1 H, 6-H), 3.72 (s, 3 H, O-CH3), 3.67 (dd, J5,6Ј = 5.2, J6,6Ј
=
12.4 Hz, 1 H, 6Ј-H), 3.54–3.47 (m, 2 H, 4-H, 5-H), 3.44–3.35 (m,
2 H, 3-H, 2-H), 2.44 (t, J = 7.6 Hz, 2 H, CH2-CO), 2.27–2.18 (m,
1 H, Ha, CH2-CH), 2.04–1.95 (m, 1 H, Hb, CH2-CH) ppm. 13C
NMR (100 MHz, D2O, 25 °C): δ = 176.2, 174.2, 158 (COCbz), 136.3
(Cipso), 128.8, 128.4, 127.6 (5 CAr), 79.2 (C-1), 77.5 (C-5), 76.4 (C-
4), 71.8 (C-2), 69.2 (C-3), 67.2 (CH2-O), 60.5 (C-6), 53.5 (CH), 52.9
(O-CH3), 31.7 (CH2-CO), 26.2 (CH2) ppm. MS (FAB): m/z = 479
[M + Na]+.
1
94% yield. H NMR (400 MHz, CDCl3, 25 °C): δ = 7.30–7.25 (m,
5 H, Ar), 7.24–7.09 (m, 5 H, Ar), 7.06–6.92 (m, 2 H, 2-H, 3-H),
6.36 (m, 1 H, 1-H), 4.24 (m, 1 H, CH), 3.26 (t, JHc,Hd = 6.8 Hz, 1
H, Hc, CH2), 3.18 (t, JHc,Hd = 6.8 Hz, 1 H, Hd, CH2), 2.03–1.95
(m, 1 H, Ha), 1.78–1.62 (m, 3 H, Hb, CH2), 1.39–1.36 (2 s, 9 H,
Boc) ppm. 13C NMR (100 MHz, CDCl3, 25 °C): δ = 171.2, 161.9,
159.4, 154.8, 153.9, 148.9, 135.1, 134.4, 134.2, 133.9, 132.1, 129.7,
129, 124.3, 123.5, 119.9, 117.2, 116.9, 80.4, 80.1, 59.4, 46.8, 30.6,
29.6, 28.8 (Boc), 24.9, 23.8 ppm. 31P NMR: δ = –15.5, –15.8 ppm.
[oxide 31P NMR: δ = +27.7, 28.0 ppm]. MS (ESI): m/z = 516.2 [M
+ Na]+. Rf = 0.43 (8:2 hexane/AcOEt).
N-(N-Benzyloxycarbonyl-β-alanyl)-β-D-glucopyranosylamine (10c):
The compound was purified by flash chromatography (80:20:2
1
CHCl3/MeOH/H2O, Rf = 0.34). [α]2D5 = +3.5 (c = 0.7, MeOH). H
NMR (400 MHz, D2O, 25 °C): δ = 7.50–7.38 (m, 5 H, Ph), 5.11 (s,
General Procedure for the Stereoselective Ligation of Glycosyl
Azides in DMA/DMPU Mixtures: The phosphane (2 equiv.) was
added, at room temperature, to a 0.1  solution of the azide
2 H, CH2-O), 4.97 (d, J1,2 = 8.8 Hz, 1 H, 1-H), 3.88 (d, J6,6’ =
12.4 Hz, 1 H, 6-H), 3.72 (dd, J6,6Ј = 12.4, J5,6Ј = 5.2 Hz, 1 H, 6Ј-
H), 3.60–3.30 (m, 6 H, 5-H, 4-H, 2-H, 3-H, CH2-NHCbz), 2.54 (t,
Eur. J. Org. Chem. 2009, 5744–5751
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
5749

F. Nisic, M. Andreini, A. Bernardi
FULL PAPER
J = 6.4 Hz, 2 H, CH2) ppm. 13C NMR (100 MHz, D2O, 25 °C): δ CHCl3/MeOH/H2O, Rf = 0.35). 1H NMR (400 MHz, MeOD,
= 175.3, 158.2 (COCbz), 136.4 (Cipso), 128.8, 128.3, 127.6 (5 CAr), 25 °C): δ = 7.42–7.28 (m, 5 H, Ph), 5.14 (s, 2 H, CH2-O), 4.92 (d,
79.2 (C-1), 77.5 (C-5), 76.4 (C-4), 71.7 (C-2), 69.2 (C-3), 66.9 (CH2- J1,2 = 8.8 Hz, 1 H, 1-H), 3.95–3.83 (m, 3 H, 5-H, CH2), 3.78–3.70
O), 60.5 (C-6), 36.7 (CH2), 35.8 (CH2) ppm. MS (FAB): m/z = 407
(m, 2 H), 3.60–3.58 (m, 2 H, 2-H, 6-H), 3.55–3.52 (dd, J5,6Ј = 3.2,
J6,6’ = 9.6 Hz, 1 H, 6Ј-H) ppm. 13C NMR (100 MHz, MeOD,
25 °C): δ = 172.9, 159.1 (COCbz), 138.1 (Cipso), 129.5, 129.0, 128.9
(5 CAr), 81.6 (C-1), 78.3, 75.7, 71.4, 70.4, 67.9 (CH2-O), 62.6 (C-
6), 46.1 (CH2) ppm.
[M + Na]+.
N-(N-Benzyloxycarbonylglycyl)-β-
D-glucopyranosylamine
(10d):
The compound was purified by flash chromatography (80:20:2
CHCl3/MeOH/H2O, Rf = 0.32). [α]2D5 = +4.1 (c = 1, MeOH). 1H
NMR (400 MHz, D2O, 25 °C): δ = 7.45–7.30 (m, 5 H, Ph), 5.09 (s,
2 H, CH2O), 4.94 (d, J1,2 = 9.2 Hz, 1 H, 1-H), 3.88–3.77 (m, 3 H,
CH2, 6-H), 3.64 (dd, J5,6Ј = 5.2, J6,6’ = 12.4 Hz, 1 H, 6Ј-H), 3.53–
3.44 (m, 2 H, 5-H, 3-H), 3.39–3.28 (m, 2 H, 2-H, 4-H) ppm. 13C
NMR (100 MHz, D2O, 25 °C): δ = 173.4, 158.6 (COCbz), 136.2
(Cipso), 128.8, 128.2, 127.7 (5 CAr), 79.3 (C-1), 77.6, 76.4, 71.7, 68.9,
66.4 (CH2-O), 60.5 (C-6), 43.7 (CH2) ppm.
Nα-(Benzyloxycarbonyl)-Nγ-β-
D-fucopyranosyl-L-asparagine
O-
Methyl Ester (15a): The compound was purified by flash
chromatography (80:20 CHCl3/MeOH, Rf = 0.45). [α]2D5 = –0.04 (c
= 0.6, MeOH). 1H NMR (400 MHz, MeOD, 25 °C): δ = 7.41–7.31
(m, 5 H, Ph), 5.12 (s, 2 H, CH2-O), 4.60 (m, 1 H, Ha, CH-N), 3.68
(s, 3 H, O-CH3), 3.67–3.56 (m, 3 H, 2-H, 3-H, 5-H), 3.52 (d, J =
6.4 Hz, 1 H, 4-H), 2.84 (m, 2 H, CH2-CH), 1.25 (d, J5,6 = 8 Hz, 3
H, 6-H) ppm. 13C NMR (100 MHz, MeOD, 25 °C): δ = 173.5,
172.8, 158.4 (COCbz), 138.1 (Cipso), 129.5, 128.8 (5 CAr), 81.3 (C-
1), 75.9, 73.7, 73.1, 71.1, 67.1 (CH2-O), 53.0 (O-CH3), 52.0 (CH),
38.5 (CH2), 16.9 (C-6) ppm. FT-ICR MS (ESI): calcd. for
C19H26N2O9Na [M + Na]+ 449.15305; found 449.15235.
N-(N-tert-Butoxycarbonyl-L-prolyl)-β-D-glucopyranosylamine (10e):
The compound was purified by flash chromatography (80:20:2
CHCl3/MeOH/H2O, Rf = 0.36). [α]2D5 = –39.2 (c = 0.6, MeOH). 1H
NMR (400 MHz, MeOD, 25 °C): δ = 4.95 (d, J1,2 = 8.8 Hz, 1 H,
1-H), 4.26 (dd, J = 3.6, J = 8.4 Hz, 1 H, CH), 3.87 (br. dd, J6,6’
=
11.6 Hz, 1 H, 6-H), 3.75–3.68 (m, 1 H, 6Ј-H), 3.63–3.52 (m, 1 H,
Ha, CH2-CH), 3.51–3.42 (m, 2 H, 3-H, Hb, CH2-CH), 3.41–3.30
(m, 3 H, 2-H, 4-H, 5-H), 2.37–2.18 (m,1 H, Hc), 2.08–1.88 (m, 3
H, Hd, CH2), 1.50 (m, 9 H, Boc) ppm. 13C NMR (100 MHz,
MeOD, 25 °C): δ = 81.4 (C-1), 79.8, 79.1, 74.2, 71.6, 62.8 (C-6),
61.8 (CH), 48 (CH2), 32 (CH2), 28.8 (Boc), 25.1 (CH2) ppm. FT-
ICR MS (ESI): calcd. for C16H28N2O8Na [M + Na]+ 399.17379;
found 399.17314.
Nα-(Benzyloxycarbonyl)-Nδ-(β-
D-fucopyranosyl)-L-glutamine
O-
Methyl Ester (15b): The compound was purified by flash
chromatography (80:20 CHCl3/MeOH, Rf = 0.68). [α]2D5 = –23.4 (c
= 0.2, MeOH). 1H NMR (400 MHz, D2O, 25 °C): δ = 7.52–7.43
(m, 5 H, Ph), 5.18 (s, 2 H, CH2-O), 4.92 (d, J1,2 = 9.2 Hz, 1 H, 1-
H), 4.30 (m, 1 H, CH-N), 3.89–3.67 (m, 6 H, 3-H, 4-H, 5-H, O-
CH3), 3.59 (t, J2,3 = 9.2 Hz, 1 H, 2-H), 2.47 (m, 2 H, CH2-CO),
2.24 (m, 1 H, Ha, CH2-CH), 2.06 (m, 1 H, Hb, CH2-CH), 1.25 (d,
J5,6 = 6.4 Hz, 3 H, 6-H) ppm. 13C NMR (100 MHz, D2O, 25 °C):
δ = 175.8, 174.0, 157.8 (COCbz), 136.0 (Cipso), 128.6, 128.2, 127.4
(5 CAr), 79.3 (C-1), 73.3 (C-2), 72.4, 71.2, 68.9, 67.0 (CH2-O), 53.4
Nα-(Benzyloxycarbonyl)-Nγ-(β-
D-galactopyranosyl)-L-asparagine O-
Methyl Ester (14a): The compound was purified by flash
chromatography (80:20:2 CHCl3/MeOH/H2O, Rf = 0.18). 1H NMR
(400 MHz, MeOD, 25 °C): δ = 7.42–7.28 (m, 5 H, Ph), 5.11 (s, 2 (CH), 52.7 (O-CH3), 31.5 (CH2-CO), 26.0 (CH2-CH), 15.3 (C-
H, CH2-O), 4.58 (m, 1 H, CH), 3.89 (d, J = 2.4 Hz, 1 H, 4-H),
6) ppm. MS (FAB): m/z (%) = 441 (56) [M + 1]+, 463 (33) [M +
3.77–3.64 (m, 5 H, 6-H, 6Ј-H, O-CH3), 3.63–3.47 (m, 3 H, 2-H, 3- Na]+. FT-ICR MS (ESI): calcd. for C20H28N2O9Na [M + Na]+
H, 5-H), 2.89–2.78 (m, 2 H, CH2) ppm. 13C NMR (100 MHz, 463.16870; found 463.16891.
MeOD, 25 °C): δ = 129.6, 129.1, 129 (5 CAr), 81.6 (C-1), 78.4, 75.9,
N-(N-Benzyloxycarbonyl-β-alanyl)-β-L-fucopyranosyl amine (15c):
71.4, 70.6 (C-4), 67.9 (C-6), 62.7 (CH2-O), 53.1 (O-CH3), 52.1
(CH), 38.2 (CH2) ppm.
Nα-(Benzyloxycarbonyl)-Nδ-(β-
D-galactopyranosyl)-L-glutamine O-
The compound was purified by flash chromatography (80:20:2
CHCl3/MeOH/H2O, Rf = 0.35). [α]2D5 = –14.1 (c = 1, MeOH). H
1
NMR (400 MHz, D2O, 25 °C): δ = 7.49–7.39 (m, 5 H, Ph), 5.11 (s,
Methyl Ester (14b): The crude compound was crystallized from
MeOH, filtered and washed with diethyl ether.1H NMR (400 MHz,
DMSO, 25 °C): δ = 7.47–7.26 (m, 5 H, Ph), 5.04 (s, 2 H, CH2-O),
4.63 (d, J1,2 = 5.2 Hz, 1 H, 1-H), 4.10–4.01 (m, 1 H, CH), 3.70–
3.67 (m, 1 H, 5-H), 3.64 (s, 3 H, O-CH3), 3.52–3.31 (m, 5 H, 2-H,
3-H, 4-H, 6-H, 6Ј-H), 2.25–2.20 (t, J = 7.6 Hz, 2 H, CH2), 2.03–
1.95 (m, 1 H, Ha, CH2-CH), 1.78–1.73 (m, 1 H, Hb, CH2-CH) ppm.
13C NMR (100 MHz, DMSO, 25 °C): δ = 172.6, 171.6, 156.1
(COCbz), 136.8 (Cipso), 128.3, 127.7, 127.1 (5 CAr), 79.9 (C-1), 76.7,
74.1, 69.7, 68.2, 65.5 (CH2-O), 60.4 (C-6), 53.5 (CH), 51.8 (O-CH3),
31.6 (CH2-CO), 26.3 (CH2) ppm.
2 H, CH2-O), 4.91 (d, J1,2 = 9.2 Hz, 1 H, 1-H), 3.85 (q, J5,6
=
6.4 Hz, 1 H, 5-H), 3.79 (d, J3,4 = 3.2 Hz, 1 H, 4-H), 3.71 (dd, J2,3
= 9.4, J3,4 = 3.2 Hz, 1 H, 3-H), 3.59 (“t”, J1,2 = 9.2, J2,3 = 9.4 Hz,
1 H, 2-H), 3.43 (t, J = 6.4 Hz, 2 H, CH2) 2.53 (m, 2 H, CH2CO),
1.24 (d, J5,6 = 6.4 Hz, 3 H, 6-H) ppm. 13C NMR (100 MHz, D2O,
25 °C): δ = 175.1, 158.2 (COCbz), 136.4 (Cipso), 128.7, 128.3, 127.7
(5 CAr), 79.4 (C-1), 73.5 (C-3), 72.5 (C-5), 71.4 (C-4), 69.1 (C-2),
66.9 (CH2-O), 36.7 (CH2), 35.7 (CH2CO), 15.6 (C-6) ppm. FT-ICR
MS (ESI): calcd. for C17H24N2O7Na [M + Na]+ 391.14757; found
391.14714.
N-(N-Benzyloxycarbonylglycyl)-β-L-fucopyranosylamine (15d): The
N-(N-Benzyloxycarbonyl-β-alanyl)-β-D-galactopyranosylamine (14c):
compound was purified by flash chromatography (80:20:2 CHCl3/
MeOH/H2O, Rf = 0.34). [α]2D5 = –12.1 (c = 1, MeOH). 1H NMR
(400 MHz, D2O, 25 °C): δ = 7.52–7.37 (m, 5 H, Ph), 5.19 (s, 2 H,
CH2-O), 4.96 (d, J1,2 = 9 Hz, 1 H, 1-H), 3.95 (d, J = 3.4 Hz, 2 H,
CH2), 3.89 (q, J5,6 = 6.4 Hz, 1 H, 5-H), 3.82 (br. d, J3,4 = 3.4 Hz,
1 H, 4-H), 3.74 (dd, J2,3 = 9.4, J3,4 = 3.4 Hz, 1 H, 3-H), 3.64 (“t”,
J1,2 = 9.2, J2,3 = 9.4 Hz, 1 H, 2-H), 1.26 (d, J5,6 = 6.4 Hz, 3 H, 6-
H) ppm. 13C NMR (100 MHz, D2O, 25 °C): δ = 173.2, 158.6
(COCbz), 136.2 (Cipso), 128.8, 128.5, 127.8 (5 CAr), 79.6 (C-1), 73.5
(C-3), 72.7 (C-5), 71.4 (C-4), 69.1 (C-2), 67.4 (CH2-O), 43.5 (CH2),
15.5 (C-6) ppm. FT-ICR MS (ESI): calcd. for C16H22N2O7Na [M
+ Na]+ 377.13192; found 377.13165.
The crude compound was crystallized from MeOH, filtered and
1
washed with diethyl ether. H NMR (400 MHz, DMSO, 25 °C): δ
= 7.46–7.29 (m, 5 H, Ph), 5.04 (s, 2 H, CH2-O), 4.70 (d, J1,2
=
8.8 Hz, 1 H, 1-H), 3.71 (d, J = 2.4 Hz, 1 H, 4-H), 3.54–3.29 (m, 5
H, 2-H, 3-H, 5-H, 6-H, 6Ј-H), 3.27–3.23 (m, 2 H, CH2), 2.41–2.28
(m, 2 H, CH2) ppm. 13C NMR (100 MHz, DMSO, 25 °C): δ =
170.6, 155.9 (COCbz), 137.2 (Cipso), 128.4, 127.8, 127.7 (5 CAr), 79.8
(C-1), 76.6, 73.9, 69.5, 68.1 (C-4), 62.2 (CH2-O), 60.4 (C-6), 36.6
(CH2), 35.5 (CH2) ppm.
N-(N-Benzyloxycarbonylglycyl)-β-
D-galactopyranosylamine (14d):
The compound was purified by flash chromatography (80:20:2
5750
www.eurjoc.org
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2009, 5744–5751

N-Glycosyl Amino Acids by Traceless Staudinger Ligation
N-(N-tert-Butoxycarbonyl- -prolyl)-β- -fucopyranosylamine (15e):
L
L
Acknowledgments
The compound was purified by flash chromatography (80:20:2
1
CHCl3/MeOH/H2O, Rf = 0.48). [α]2D5 = –49.7 (c = 1, MeOH). H
This project was supported by the University of Milano (PUR-
2008) and by the Ministero dell’Università e della Ricerca (MIUR),
Fondo per gli Investimenti della Ricerca di Base (FIRB)
(RBPR05NWWC, CHEM-PROFARMANET)
NMR (400 MHz, MeOD, 25 °C): δ = 4.21–4.13 (m, 1 H, CH), 3.70
(q, J5,6 = 6.4 Hz, 1 H, 5-H), 3.64 (s, 1 H, 4-H), 3.56–3.47 (m, 3 H,
2-H, 3-H, Ha), 3.43–3.37 (m, 1 H, Hb), 2.31–2.17 (m, 1 H, Hc,
CH2), 2.15–1.78 (m, 3 H, CH2, Hd), 1.52–1.39 (br. s, 9 H, Boc),
1.21 (d, J5,6 = 6.4 Hz, 3 H, 6-H) ppm. 13C NMR (100 MHz,
MeOD, 25 °C): δ = 176.8, 156.3 (COBoc), 81.5 (C-1), 76.3, 73.7 (C-
5), 73.4 (C-4), 71.3, 61.9 (CH), 48.0 (CH2), 32.6 (CH2), 28.8 (Boc),
24.8 (CH2), 17.1 (H-6) ppm. FT-ICR MS (ESI): calcd. for
C16H28N2O7Na [M + Na]+ 383.17887; found 383.17848.
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Carbohydrate Chemistry (Ed.: G. J. Boons), Chapman & Hall,
London, 1998, pp. 243–321; N. V. Bovin, Neoglycoconjugates as
probes in glycobiology, 129, Chemical Probes in Biology, NATO
Science Series, II: Mathematics, Physics and Chemistry, Kluwer
Academic Publishers, 2003, pp. 207–225; D. P. Gamblin, E. M.
Scanlan, B. G. Davis, Chem. Rev. 2009, 109, 131–163.
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2141–2143; B. L. Nilsson, L. L. Kiessling, R. T. Raines, Org.
Lett. 2000, 2, 1939–1941.
Nα-(Benzyloxycarbonyl)-Nγ-(2-acetamido-2-deoxy-β-
syl)- -asparagine O-Methyl Ester (16a): The compound was puri-
D-glucopyrano-
L
fied by flash chromatography (80:20 CHCl3/MeOH, Rf = 0.20).
[α]2D5 = +19.2 (c = 1, MeOH). 1H NMR (400 MHz, MeOD, 25 °C):
δ = 7.39–7.31 (m, 5 H, Ph), 5.11 (s, 2 H, CH2-O), 4.96 (d, J1,2
=
[3] A. Bianchi, A. Bernardi, J. Org. Chem. 2006, 71, 4565–4577,
9.7 Hz, 1 H, 1-H), 4.60 (t, JCH-CH2 = 6.8 Hz, 1 H, CH-N), 3.85 (br.
d, J6,6’ = 11.8 Hz, 1 H, 6-H), 3.77–3.70 (m, 4 H, 2-H, O-CH3), 3.66
(dd, J5,6Ј = 3.8, J6,6Ј = 11.8 Hz, 1 H, 6Ј-H) 3.47 (m, 1 H, 3-H),
3.40–3.32 (m, 2 H, 4-H, 5-H), 2.73 (t, J = 7.2 Hz, 2 H, CH2), 1.94
(s, 3 H, NHAc) ppm. 13C NMR (100 MHz, CDCl3, 25 °C): δ =
174.6, 173.5 172.6, 129.6, 129.2, 129.0 (5 CAr), 80.4 (C-1), 79.9,
76.5 (C-3), 72.0, 67.9 (CH2-O), 62.8 (C-6), 56.2 (C-2), 53.1 (O-
CH3), 52.2 (CH), 38.7 (CH2), 23.0 (CO-CH3) ppm. MS (FAB): m/z
(%) = 484 (17) [M + 1]+, 506 (12) [M + Na]+.
and references cited therein.
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107, 1590–1613.
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a different functionalized phosphane: Y. He, R. J. Hinklin, J. Y.
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Nα-(Benzyloxycarbonyl)-Nδ-(2-acetamido-2-deoxy-β-
syl)- -glutamine O-Methyl Ester (16b): The compound was purified
by flash chromatography (80:20 CHCl3/MeOH, Rf = 0.42). [α]2D5
D-glucopyrano-
L
=
+3.5 (c = 0.6, MeOH). 1H NMR (400 MHz, MeOD, 25 °C): δ =
7.45 (m, 5 H, Ph), 5.15 (s, 2 H, CH2-O), 5.05 (d, J1,2 = 9.7 Hz, 1
H, 1-H), 4.20 (m, 1 H, CH-NH), 3.47–3.81 (m, 6 H, 2-H, 3-H, 4-
H, 5-H, 6-H, 6Ј-H), 3.75 (s, 3 H, O-CH3), 2.38 (t, J = 7.4 Hz, 2 H,
CH2-CO), 2.15–2.05 (m, 1 H, Ha, CH2-CH), 2.03–1.92 (m, 4 H,
Hb, NHAc) ppm. 13C NMR (100 MHz, MeOD, 25 °C): δ = 175.7,
174.8, 152.6 (COCbz), 136.4 (Cipso), 128.9, 128.5, 127.7 (5 CAr), 78.4
(C-1), 77.6, 74.2, 69.6, 67.3 (CH2-O), 60.6 (C-6), 54.4 (CH-NH),
53.6 (C-2), 53.0 (O-CH3), 31.8 (CH2-CO), 26.3 (CH2-CH), 22.0
(CO-CH3) ppm. MS (FAB): m/z (%) = 498 (73) [M + 1]+, 520 (77)
[M + Na]+. FT-ICR MS (ESI): calcd. for C22H31N3O10Na [M +
Na]+ 520.19017; found 520.19006.
[11] F. Damkaci, P. DeShong, J. Am. Chem. Soc. 2003, 125, 4408–
4409.
[12] R. Kumar, P. Tiwari, P. R. Maulik, A. K. Misra, Eur. J. Org.
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Chem. Commun. 2009, 3378–3379.
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B. G. Davis, Chem. Commun. 2006, 1401–1403.
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C.-C. Lee, K.-L. Chang, S.-C. Hung, Nature 2007, 446, 896–
899.
N-(N-Benzyloxycarbonyl-β-alanyl)-2-acetamido-2-deoxy-β-
pyranosylamine (16c): The compound was purified by flash
chromatography (80:20:2 CHCl3/MeOH/H2O, Rf = 0.24). [α]2D5
D-gluco-
[17] F. Cardona, B. La Ferla, J. Carbohydr. Chem. 2008, 27, 203–
213.
=
[18] T. Saloranta, C. Muller, D. Vogt, R. Leino, Chem. Eur. J. 2008,
14, 10539–10542.
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560–565; H. Kunz, Angew. Chem. Int. Ed. Engl. 1987, 26, 294–
308.
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ChemBioChem 2008, 9, 1921–1930.
[23] J. Baddiley, J. G. Buchanan, R. E. Handschumacher, J. F. Pres-
cott, J. Chem. Soc. 1956, 2818–2823.
+18.6 (c = 1, MeOH). 1H NMR (400 MHz, MeOD, 25 °C): δ =
7.31–7.24 (m, 5 H, Ph), 5.01 (s, 2 H, CH2-O), 4.91 (d, J1,2 = 9.6 Hz,
1 H, 1-H), 3.78 (d, J6,6’ = 11.6 Hz, 1 H, 6-H), 3.69 (t, J3,4 = 10 Hz,
1 H), 3.60 (dd, J5,6Ј = 2.4, J6,6Ј = 11.6 Hz, 1 H, 6Ј-H), 3.39 (m, 1
H, 3-H), 3.31–3.24 (m, 4 H, 4-H, 5-H, CH2), 2.34 (t, J = 6.7 Hz, 2
H, CH2), 1.88 (s, 3 H, NHAc) ppm. 13C NMR (100 MHz, D2O,
25 °C): δ = 173.0, 172.8, 157.2 (COCbz), 136.9 (Cipso), 128.1, 127.6,
127.4 (5 CAr), 78.9 (C-1), 78.1, 74.9 (C-3), 71.1, 66.1 (CH2-O), 61.3
(C-6), 54.8 (C-2), 37.9 (CH2), 35.8 (CH2), 21.4 (CO-CH3) ppm. MS
(FAB): m/z = 448 [M + Na]+.
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J. W. B. Moir, A. J. Fairbanks, Carbohydr. Res. 2006, 16, 1574–
1596.
Supporting Information (see also the footnote on the first page of
this article): General procedure for the acetylation of glycosyl
amino acids, characterization of the O-acetylglycosyl amino acids
and 13C NMR spectra of all new compounds.
Received: June 22, 2009
Published Online: October 5, 2009
Eur. J. Org. Chem. 2009, 5744–5751
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
5751