Direct amidation of aldoses and decarboxylative amidation of α-keto acids: An efficient conjugation method for unprotected carbohydrate molecules

Article abstract of DOI:10.1021/jo802338k

With use of iodine as an appropriate oxidant, unprotected and unmodified aldoses undergo oxidative amidation with a variety of functionalized amines, a-amino esters, and peptides, whereas KDO, sialic acid, and other a-keto acids proceed with oxidative dec

Full text of DOI:10.1021/jo802338k

Direct Amidation of Aldoses and Decarboxylative Amidation of
r-Keto Acids: An Efficient Conjugation Method for Unprotected
Carbohydrate Molecules
Chia-Ching Cho,† Jia-Nan Liu,† Chung-Hsun Chien,† Jiun-Jie Shie,‡ Ying-Chu Chen,† and
Jim-Min Fang*,†,‡
Department of Chemistry, National Taiwan UniVersity, Taipei 106, Taiwan, and The Genomics Research
Center, Academia Sinica, Taipei, 11529, Taiwan
jmfang@ntu.edu.tw
ReceiVed October 21, 2008
With use of iodine as an appropriate oxidant, unprotected and unmodified aldoses undergo oxidative
amidation with a variety of functionalized amines, R-amino esters, and peptides, whereas KDO, sialic
acid, and other R-keto acids proceed with oxidative decarboxylation followed by in situ amidation.
Glycoside bond and many other functional groups are inert under such mild reaction conditions. This
reaction protocol for direct ligation of carbohydrate molecules looks promising in the development of a
general and efficient synthesis of glycoconjugates.
Introduction
complex.9 In another approach, the oxidants of t-BuOOH10,11
and Oxone (potassium peroxymonosulfate)12 have been utilized
in the metal-free amidation of aldehydes and alcohols. Though
most aromatic aldehydes are effectively converted to aromatic
amides with the above-mentioned methods,3-12 direct amidation
of aliphatic aldehydes may be problematic due to enolization
and other side reactions.
En route to study the scope and limitation of aldehyde
substrates in direct amidation, we have previously found that
aldosesaresuccessfullyconvertedtoaldonamidesinammonia-water
using iodine as the oxidant.13 Compain and co-workers have
also reported that iodine is an appropriate oxidant for direct
amidation of protected aldoses, e.g. 2,3,4,6-tetra-O-benzylglu-
copyranose, with functionalized amines, e.g., ethanolamine, in
the presence of K2CO3.14 The free hydroxyl group at the C-5
Amides are an important functional group widely found in
natural products, pharmaceuticals, and polymers. Besides the
conventional methods of amide formation by the coupling
reactions between carboxylic acids and amines,1 direct methods
for oxidative amidation of aldehydes2 have been explored. Direct
amidation of aldehydes have been achieved by using Nickel
peroxide3 and transition metal catalysts, e.g., Pd(OAc)2,4 CuI,5
RuH2(PPh3)4,6 [Rh(COD)2]BF4,7 and [Cp*RhCl2]2,6,8 in com-
bination with oxidants. Aliphatic alcohols also undergo direct
amidation with primary amines by catalysis of a ruthenium
† National Taiwan University.
‡ Academia Sinica.
(1) Smith, M. B. Compendium of Organic Synthetic Methods; Wiley: New
York, 2001; Vol. 9, pp 100-116.
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10.1021/jo802338k CCC: $40.75
Published on Web 01/21/2009
2009 American Chemical Society
J. Org. Chem. 2009, 74, 1549–1556 1549

Cho et al.
TABLE 1. Iodine-Promoted Oxidative Amidation of Aldoses with
Primary Aminesa
position of the aldose substrate is essential for the oxidative
amidation reaction, supporting that only aldose in the hemiacetal
form can give the aldonamide product.13,14 However, they were
unable to convert unprotected aldoses to the desired aldonamide
products according to their reaction protocol, i.e., premixing
the aldose and amine substrates for 1 h in tert-butyl alcohol
followed by addition of I2/K2CO3 and reflux at 90 °C.
We report herein the use of iodine to promote the direct
amidation reaction of unprotected and unmodified carbohydrate
molecules with a variety of primary amines, including bifunc-
tional amines and peptides. Glycoconjugation with amide
linkage has been reported,15,16 in addition to other methods17
using reductive amination, oxime linkage, and thiazolidine
formation. It is noted that immobilization of carbohydrate
molecules renders wide applications in glycochemistry and
glycobiology,15-17 even though the cyclic structure of hemi-
acetal at the reducing end of saccharides is opened.
Conventional methods for the synthesis of glycoconjugates
via amide bond formation usually require prior isolation of
aldonic acids or aldonolactones.15,16 Lo¨nngren and co-workers
have reported the coupling reaction of aldonic acids with
proteinaceous amines by using an activating agent.15 They have
also shown that the neoglycoproteins prepared from di- and
trisaccharide acids still hold reasonable binding affinity toward
lectins.15 In comparison, our method is simple and attractive
because linkage of aldoses with amines is irreversibly driven
by oxidation with iodine to form a robust amide bond in a one-
pot operation. An aldose that exists in the cyclic hemiacetal
form can be oxidized by iodine in the basic conditions to give
an intermediate aldonolactone,13,14 which reacts in situ with
amine to give the aldonamide product.
entry
aldoses
amines
products
yield,b
%
1
2
3
4
5
6
7
8
D-glucose
D-glucose
D-glucose
D-glucose
D-glucose
D-glucose
D-glucose
D-glucose
D-arabinose
D-xylose
D-galactose
D-mannose
D-GlcNAc
D-GlcA
D-cellobiose
D-lactose
ethylamine
1a
98
85
80
92
84
85
77
98
74
85
86
75
80
61
94
95
92
93
93
93
91
ethylamine
hexylamine
cetylamine
benzylamine
allylamine
1aAcc
1bAcc
1cAcc
1dAcc
1eAcc
1fAcc
1gAcc
2dAcc
3aAcc
4aAcc
5bAcc
6bAcc
7b
ethanolamine
1,6-diaminohexane
benzylamine
ethylamine
ethylamine
hexylamine
hexylamine
hexylamine
ethylamine
ethylamine
cetylamine
ethylamine
cetylamine
ethylamine
cetylamine
9
10
11
12
13
14
15
16
17
18
19
20
21
8aAcc
9aAcc
9cAcc
10aAcc
10cAcc
11aAcc
11cAcc
D-lactose
D-maltose
D-maltose
D-maltotriose
D-maltotriose
a Aldose (1 mmol) was stirred with iodine (2 mmol) and amine (4
mmol) in aqueous or methanolic solution at room temperature for 6-13
h. A smaller amount of amine (1 mmol) was used when the reaction
was performed in the presence of K2CO3 (2 mmol). b The isolated yield
is based on aldose. c The peracetate derivative of aldonamide.
TABLE 2. Iodine-Promoted Oxidative Amidation of Aldoses with
Amino Esters and Peptidesa
entry
aldoses
amines
products
yield,b
%
1
2
3
4
5
6
7
8
D-glucose
D-glucose
D-glucose
D-glucose
D-glucose
D-glucose
D-glucose
D-glucose
D-glucose
D-glucose
D-glucose
D-glucose
D-glucose
D-arabinose
D-xylose
gly(OMe)
gly(OMe)
12
96
94
70
55
62
47
42
54
78
40
91
80
87
90
91
84
70
74
82
66
12Acc
13Acc
14Acc
L-val(OMe)
L-ser(OMe)
L-tyr(OMe)
L-met(OMe)
L-cys(OMe)
L-his(OMe)
L-lys(OMe)
L-pro(OMe)
gly-gly(OMe)
gly-L-val(OMe)
gly-gly-gly(OMe)
gly(OMe)
gly(OMe)
gly(OMe)
gly(OMe)
gly(OMe)
gly(OMe)
L-lys-D-ala-D-ala
Results and Discussion
15Acc d
,
16Acc d
,
To establish the protocol for direct amidation, we first
investigated the iodine-promoted reactions of D-glucose with
aliphatic primary amines (Table 1). A methanolic solution of
D-glucose was stirred with ethylamine hydrochloride salt (1
equiv) and I2 (1.2 equiv) in the presence of K2CO3 at room
temperature for 6 h to give a quantitative yield of N-ethyl
gluconamide (1a). Alternatively, a direct amidation of D-glucose
was furnished by using aqueous ethylamine (1 mL of 70 wt %
solution) and iodine. Excess amine was applied to neutralize
the released HI molecules. The hydroxyl groups in saccharides
were inert in this amidation reaction, though primary alcohol
can be oxidized by I2/K2CO3 at elevated temperature (60 °C).18
17Acc d
,
18Acc d
,
9
19Acc
20Acc
21Acc
22Acc
23Acc
24Acc
25Acc
26Acc
27Acc
28Acc
29Acc
30e
10
11
12
13
14
15
16
17
18
19
20
D-galactose
D-mannose
D-lactose
D-maltose
D-maltose
a Two-step procedure: A mixture of aldose (1 mmol), iodine (1.2
mmol), K2CO3 (1.5 mmol), and molecular sieves in MeOH solution was
stirred at room temperature for 3 h, followed by addition of a methyl
ester of R-amino acid (or peptide as the hydrochloric salt, 1-2 mmol)
and K2CO3 (1.5 mmol). The amidation completed in 12-16 h at 40 °C.
b The isolated yield is based on aldose. c The peracetate derivative of
aldonamide. d Only 1.0 mmol of iodine was used. e The reaction was
performed with maltose (0.2 mmol), I2 (0.2 mmol), peptide (0.1 mmol),
and K2CO3 (0.5 mmol). The yield of 30 (as the CF3CO2H salt) is based
on peptide.
(15) Lo¨nngren, J.; Goldstein, I. J.; Niederhuber, J. E. Arch. Biochem. Biophys.
1976, 175, 661–669.
(16) (a) Fujimoto, K.; Miyata, T.; Aoyama, Y. J. Am. Chem. Soc. 2000, 122,
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B. Y.; Montgomery, R. Carbohyd. Res. 2005, 340, 2698–2705. (e) Kida, T.;
Tanaka, T.; Nakatsuji, Y.; Akashi, M. Chem. Lett. 2006, 35, 112–113. (f) El
Ashry, E. S. H.; Awad, L. F.; Hamid, H. A.; Atta, A. I. J. Carbohydr. Chem.
2007, 26, 329–338. (g) Morimoto, N.; Ogino, N.; Narita, T.; Kitamura, S.;
Akiyoshi, K. J. Am. Chem. Soc. 2007, 129, 458–459. (h) Kim, K.; Matsuura,
K.; Kimizuka, N. Bioorg. Med. Chem. 2007, 15, 4311–4317.
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Biochem. Biophys. 1974, 163, 426–428. (c) Halkes, K. M.; Souza, A. C. de;
Maljaars, C. E. P.; Gerwig, G. J.; Kamerling, J. P. Eur. J. Org. Chem. 2005,
3650–3659. (d) Nishimura, S.-I.; Niikura, K.; Kurogochi, M.; Matsushita, T.;
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Jensen, K. J. Carbohyd. Res. 2006, 341, 1209–1234.
The gluconamide was then subjected to acetylation to give 1aAc
for full characterization (mp, [R], IR, HRMS, 1H and 13C NMR).
The iodine-promoted amidation of glucose with other aliphatic
and bifunctional amines was also carried out smoothly by similar
procedures.
It appeared that the CdC double bond, phenyl, hydroxyl, and
ester groups were inert under the reaction conditions. The double
(18) (a) Moria, N.; Togo, H. Tetrahedron 2005, 61, 5915–5925. (b) Shie,
J.-J.; Fang, J.-M. J. Org. Chem. 2007, 72, 3141–3144.
1550 J. Org. Chem. Vol. 74, No. 4, 2009

Amidation of Aldoses and R-Keto Acids
amidation with 1,6-hexanediamine yielded a bis-gluconamide
(entry 8, Table 1). Furthermore, a series of unmodified
monosaccharides were treated with iodine/amines to give the
corresponding aldonamides in good yields. The iodine-promoted
amidation of glucuronic acid (entry 14, Table 1) occurred
selectively at the C-1 aldehyde group without interference with
the C-6 carboxylic group, distinguishing itself from the con-
ventional amidation reaction of saccharide acids.17 The oxidative
amidation of di- and trisaccharides also proceeded smoothly with
retention of the glycoside bonds. The result promises an
extension of this reaction protocol to polysaccharides. The
neoglycolipids (e.g., 9c, 10c, and 11c) prepared as such can be
immobilized on a styrene-coated microtiter plate for binding
studies.19
gluconolactone.14,15 Similar reactions of D-glucose with other
representative R-amino esters by the one-pot two-step procedure
afforded aldonamides 13Ac-20Ac after subsequent acetylation
(entries 3-10, Table 2). No racemerization occurred during the
1
amide formation as evidence of the H NMR analyses. The
reaction with lysine occurred preferably at the ε-amino group
(more nucleophilic than the R-amino group) to give 19Ac as
indicated by the 2D NMR spectra (COSY, HMQC, and HMBC),
which showed correlations of the C-1 amide carbon (δC 166.0)
with H-2 (δH 5.24), H-3 (δH 5.66), and the two ε-protons (δH
3.23). Noteworthily, iodine has been consumed before addition
of R-amino ester by this one-pot two-step procedure, therefore,
conjugation of aldoses with tyrosine, methionine, and histidine
was achieved without complication by the side reactions at the
phenol, thioether, and imidazole sites. Formation of 20Ac
offered an example for the iodine-promoted amidation of aldose
with a secondary amine (proline in entry 10, Table 2).
The amidation of aldoses with less nucleophilic amines, such
as R-amino esters, was better performed by a one-pot two-step
procedure, i.e., an aldose was first oxidized by I2/K2CO3, and
then R-amino ester (as the hydrochloric salt) was added along
with K2CO3 to furnish the amidation. By this means, a high
yield of gluconamide 12 was obtained, and further characterized
by its peracetylation derivative 12Ac (Table 2). The yield of
gluconamide decreased when aldose and glycine methyl ester
were stirred together with I2/K2CO3 in methanol, and a side
product of methyl gluconate (∼ 10%) was also obtained
presumably by a competitive methanolysis of the intermediate
In the reaction with cysteine methyl ester (entry 7, Table 2),
the gluconolactone intermediate might first react with the more
nucleophilic thiolate group to form a thioester, which was then
attacked by the adjacent amino group to give the amide product
17 (Scheme 1). Excess iodine should be avoided; otherwise, a
side product of disulfide compound might be obtained by an
oxidative coupling of 17 with cys(OMe).
(19) Huang, G.-L.; Zhang, H.-C.; Wang, P.-G. Bioorg. Med. Chem. Lett.
2006, 16, 2031–2033.
J. Org. Chem. Vol. 74, No. 4, 2009 1551

Cho et al.
SCHEME 2. Iodine-Promoted Decarboxylative Amidation
SCHEME 1. Iodine-Promoted Oxidative Amidation of
Aldoses with L-Cysteine Methyl Ester
of r-Keto Acids
This reaction protocol was also successfully applied to ligation
of glucose with di- and tripeptides to give the corresponding
peracetates 21Ac, 22Ac, and 23Ac in high yields (entries 11,
12, and 13, Table 2). The oxidative amidation reactions of other
mono- and disaccharides with glycine methyl ester were
similarly carried out (entries 14-19, Table 2). The amidation
reaction of maltose with a tripeptide Lys-D-Ala-D-Ala (0.1 equiv)
afforded the desired product 30 (as the CF3CO2H salt) in 66%
isolated yield. In summary of the results shown in Table 2,
glycine and lysine worked well in the oxidative amidation of
aldoses with the protocol of one-pot two-step procedure.
However, the oxidative amidation with other amino esters was
less efficient due to other competitive reactions, in particular,
the nucleophilic attack of solvent (MeOH) on the intermediate
aldonolactone.
We also utilized the iodine-promoted amidation reaction to
link D-lactose with poly-L-lysine and bovine serum albumin.
Even though the conjugation efficiency is not optimized in this
preliminary study, our reaction protocol looks promising and
will be useful for the development of a general one-pot synthesis
of carbohydrate-protein conjugates.
The aerobic metabolism of pyruvate to acetyl CoA involves
a sequence of decarboxylation, oxidation, and thioester bond
formation. By inspiration of this natural course, we explored
an iodine-promoted method for decarboxylative amidation of
R-keto acids in mild reaction conditions. Bode and co-workers
have demonstrated the decarboxylative condensation of phe-
nylpyruvic acid and peptide keto acids with N-alkylhydroxy-
lamines at 40 °C to give the amide products.20 In our hand,
phenylglyoxylic acid reacted with iodine and RNH2 (R ) Et
and C6H13) at room temperature in aqueous solution to give the
corresponding N-alkyl benzoates 31a and 31b in 74% and 91%
yields (Scheme 2). Though the mechanism in the iodine-
promoted degradative amidation of R-keto acids is not rigorously
determined, we speculate that the reaction involves an inter-
mediate of iodinated hemiaminal such as A, by analogy to that
described previously.20
respectively in 73%, 61%, and 74% yields after acetylation. In
contrast, R-hydroxy acids, e.g., quinic acid, were inert to I2/
EtNH2 under similar conditions. Therefore, this iodine-promoted
decarboxylative amidation is unique to R-keto acids. In com-
parison, the conventional conjugation method for unmodified
(poly)sialic acid and KDO relies on reductive amination.21,22
However, reductive amination of the ketone group is much less
effective than that on aldoses. The reductive amination of ketone
is further complicated by generation of a new stereocenter.
We also attempted the iodine-promoted decarboxylative
amidation reaction of disialic acid (Neu5Ac-R2,8-Neu5Ac) in
aqueous ethylamine (70 wt % solution). The product showed
the exact mass at m/z 598.2451 [M - H]- (calculated 598.2459
for C23H40N3O15) consistent with the desired glyconamide
product. The diagnostic proton signals at δ 3.22-3.18 and
2.39-2.37 were attributable to the amide bond formation
(compared with the glyconamide from sialic acid in the
Supporting Information). However, we are so far unable to
purify or derivatize this glyconamide product for unambiguous
structural elucidation.
Conclusion
We have explored a direct, simple, and efficient one-pot
protocol for ligation of aldoses and R-keto acids with a variety
of amines using iodine as an appropriate oxidant. Because many
The iodine-promoted decarboxylative amidation reactions of
2-keto-L-gulonic acid/ethylamine, sialic acid/hexylamine, and
KDO/ethylamine were similarly carried out to give L-xylona-
mide peracetate 32Ac, octanamide 33Ac, and heptanamide 34Ac
(21) (a) Jennings, H. J. AdV. Carbohydr. Chem. Biochem. 1993, 41, 155–
208. (b) Mieszala, M.; Kogan, G.; Jennings, H. J. Carbohydr. Res. 2003, 338,
167–175.
(22) (a) Reddy, V. B.; Bartoszewicz, Z.; Rebois, R. V. Cell. Signalling 1996,
8, 35–41. (b) Grimmecke, H. D.; Brade, H. Glycoconj. J. 1998, 15, 555–562.
(23) (a) Mieszala, M.; Kogan, G.; Jennings, H. J. Carbohydr. Res. 2003,
338, 167–175. (b) Seid, R. C., Jr.; Sadoff, J. C. J. Biol. Chem. 1981, 256, 7305–
7310.
(20) Bode, J. W.; Fox, R. M.; Baucom, K. D. Angew. Chem., Int. Ed. 2006,
45, 1248–1252.
1552 J. Org. Chem. Vol. 74, No. 4, 2009

Amidation of Aldoses and R-Keto Acids
According to the general procedure for oxidative amidation of
aldose, an aqueous solution of D-glucose (180 mg, 1.0 mmol) was
stirred with EtNH2 (1 mL of 70% aqueous solution) and I2 (508
mg, 2.0 mmol) at room temperature for 6 h to give a crude product,
which was subsequently treated with Ac2O in pyridine to give
peracetate 1aAc (368 mg, 85% yield from glucose). C18H27NO11;
other functional groups, including the hydroxyl groups and
glycoside bonds in carbohydrate molecules, are inert under such
mild reaction conditions, the present protocol may be developed
as a general method for conjugation of polysaccharides with
functional amines without prior protection and modification of
the substrates. The iodine-promoted amidation of aldoses was
successfully applied to couple with R-amino esters, especially
in high yields with glycine and lysine, by using the one-pot
two-step procedure. However, competitive methanolysis of the
intermediate aldonolactone might interfere with the amidation
with less nucleophilic R-amino esters. We will attempt to find
an improved solvent system to circumvent this problem.
Extension of the novel decarboxylative amidation method for
conjugation of polysialic acid23a and the KDO-terminated
lipopolysaccharides (the lipid A-free LPS)23b will also be
explored in due course.
white solid, mp 189.7-190.7 °C; [R]25 +19.81 (c 0.6, EtOAc);
D
IR Vmax (neat) 3368, 1751, 1671 cm-1; 1H NMR (CDCl3, 400 MHz)
δ 6.08 (1 H, s), 5.68 (1 H, t, J ) 4.8 Hz), 5.45 (1 H, dd, J ) 6.4,
5.6 Hz), 5.30 (1 H, d, J ) 5.6 Hz), 5.06-5.02 (1 H, m), 4.32 (1 H,
dd, J ) 12.4, 4.4 Hz), 4.14 (1 H, dd, J ) 12.4, 5.6 Hz), 3.37-3.25
(2 H, m), 2.22 (3 H, s), 2.13 (3 H, s), 2.11 (3 H, s), 2.07 (6 H, s),
1.15 (3 H, t, J ) 7.2 Hz); 13C NMR (CDCl3, 100 MHz) δ 169.8,
169.1 (2×), 168.9, 168.4, 165.1, 71.6, 69.3, 69.0, 68.6, 61.5, 34.6,
21.0 (4×), 20.7, 14.9; MS (ESI) calcd for C18H28NO11 434, found
m/z 434 [M + H]+; HRMS (ESI) calcd for C18H27NO11Na 456.1476,
found m/z 456.1471 [M + Na]+.
N-Allyl 2,3,4,5,6-O-pentaacetyl-D-gluconamide (1eAc). According
to the general procedure for oxidative amidation of aldose, an
aqueous solution of D-glucose (180 mg, 1.0 mmol) was stirred with
allylamine (228 mg, 4 mmol) and I2 (508 mg, 2.0 mmol) at room
temperature for 8 h to give a crude product of N-allyl gluconamide,
which was subsequently treated with Ac2O in pyridine to give
compound 1eAc (379 mg, 85% yield). C19H27NO11; white solid,
mp 160.0-161.5 °C; [R]25D +10.18 (c 0.3, EtOAc); IR Vmax (neat)
3265, 1750, 1659 cm-1; 1H NMR (CDCl3, 400 MHz) δ 6.19 (1 H,
br), 5.83-5.73 (1 H, m), 5.67 (1 H, t, J ) 5.6 Hz), 5.44 (1 H, t, J
) 5.6 Hz), 5.32 (1 H, d, J ) 4.8 Hz), 5.20-5.12 (2 H, m),
5.04-5.00 (1 H, m), 4.30 (1 H, dd, J ) 12, 4.4 Hz), 4.11 (1 H, dd,
J ) 12, 5.2 Hz), 3.94-3.80 (2 H, m), 2.20 (3 H, s), 2.10 (3 H, s),
2.08 (3 H, s), 2.04 (6 H, s); 13C NMR (CDCl3, 100 MHz) δ 169.8,
169.1 (2×), 168.9, 168.4, 165.2, 132.9, 116.4, 71.6, 69.3, 69.0,
68.6, 61.5, 41.9, 21.1 (2×), 21.0 (2×), 20.8; HRMS calcd for
C19H28NO11 446.1657, found m/z 446.1625 [M + H]+.
Experimental Section
General Procedure for the Iodine-Promoted Amidation of
Carbohydrate Molecules with Primary Amines. A mixture of
aldose (or R-keto acid, 1.0 mmol), amine (4 mmol), and iodine
(508 mg, 2.0 mmol) in 5 mL of water (or aqueous MeOH solution)
was stirred at room temperature for 6-10 h until the aldose (or
R-keto acid) was completely consumed as indicated by TLC
analysis. A smaller amount of amine (1.0 mmol) was used when
the reaction was conducted in the presence of K2CO3 (276 mg, 2
mmol). The reaction was quenched by addition of Na2S2O3 (2 mL
of saturated aqueous solution). The mixture was concentrated under
reduced pressure to give a crude product of aldonamide.
The crude product was treated with acetic anhydride (2 mL) and
pyridine (2 mL) at 0-25 °C for 8 h, then the mixture was partitioned
between 1 M HCl (30 mL) and CH2Cl2 (50 mL). The organic phase
was collected, washed with brine (30 mL), and concentrated under
reduced pressure. The residue was purified on a silica gel column
by elution with gradients of EtOAc/hexane to afford the desired
product of aldonamide peracetate.
General Procedure for Oxidative Amidation of Aldoses
with the Methyl Esters of r-Amino Acid and Peptides. To a
stirred solution of aldose (1.0 mmol), K2CO3 (207 mg, 1.5 mmol),
and activated molecular sieves in MeOH (10 mL) was added iodine
(305 mg, 1.2 mmol) at room temperature under argon for 3 h until
aldose was completely consumed as indicated by TLC analysis.
Then R-amino acid methyl ester (1.0-2.0 mmol, as the hydrochloric
salt) and K2CO3 (207 mg, 1.5 mmol) were added, and the mixture
was stirred at 40 °C under argon for 12-16 h until the product of
the first step was completely consumed as indicated by TLC
analysis. The reaction was quenched by addition of Na2S2O3 (2
mL of saturated aqueous solution), and the mixture was concentrated
under reduced pressure to give a crude product of glycol-conjugate,
which was subsequently treated with acetic anhydride (2 mL) and
pyridine (2 mL) to afford the corresponding peracetate.
N,N′-Hexylene Bis(2,3,4,5,6-pentaacetoxyhexamide) (1gAc). Ac-
cording to the general procedure for oxidative amidation of aldose,
a methanolic solution of D-glucose (180 mg, 1.0 mmol) was stirred
with 1,6-diaminohexane (232 mg, 2.0 mmol) and I2 (508 mg, 2.0
mmol) at room temperature for 10 h to give a crude product, which
was subsequently treated with Ac2O in pyridine to give compound
1gAc (440 mg, 98% yield). C38H56N2O22; white foam; [R]25D +27.40
1
(c 1.5, CH2Cl2); IR Vmax (neat) 3375, 1751, 1677 cm-1; H NMR
(CDCl3, 400 MHz) δ 6.26 (2 H, t, J ) 5.2 Hz), 5.67 (2 H, t, J )
5.6 Hz), 5.44 (2 H, dd, J ) 6.4, 5.2 Hz), 5.28 (2 H, d, J ) 5.6 Hz),
5.06-5.02 (2 H, m), 4.32 (2 H, dd, J ) 12, 4.0 Hz), 4.13 (2 H, dd,
J ) 12, 5.6 Hz), 3.27-3.21 (4 H, m), 2.21 (6 H, s), 2.12 (6 H, s),
2.10 (6 H, s), 2.06 (12 H, s), 1.49 (4H, br m), 1.30 (4 H, br m); 13
C
NMR (CDCl3, 100 MHz) δ 170.3 (2×), 169.5 (4×), 169.4 (2×),
168.9 (2×), 165.8 (2×), 71.6 (2×), 69.3 (2×), 68.9 (2×), 68.6 (2×),
61.4 (2×), 38.8 (2×), 29.1 (2×), 25.6 (2×), 20.7 (8×), 20.4 (2×);
HRMS (ESI) calcd for C38H57N2O22 893.3397, found m/z 893.3391
[M + H]+.
N-Hexadecyl 2,2′,2′′,3,3′,3′′,4′′,5,6,6′,6′′-O-Undecaacetylmaltot-
rionamide (11cAc). According to the general procedure for oxidative
amidation of aldose, an methanoic solution of D-maltotriose (504
mg, 1.0 mmol) was stirred with cetylamine (964 mg, 4 mmol) and
I2 (508 mg, 2.0 mmol) at room temperature for 10 h to give a crude
product, which was subsequently treated with Ac2O in pyridine to
give compound 11cAc (1.10 g, 91% yield). C56H87NO27; white
N-Ethyl Gluconamide (1a) and N-Ethyl 2,3,4,5,6-O-Pentaacetyl-
D-gluconamide (1aAc). A methanolic solution of D-glucose (180
mg, 1.0 mmol) was stirred with ethylamine hydrochloride salt (81.5
mg, 1.0 mmol), I2 (300 mg, 1.2 mmol), and potassium carbonate
(276.0 mg, 2.0 mmol) at room temperature for 6 h. The mixture
was filtered, and the filtrate was treated with resin (Dowex 8WX-
100, acid form). The supernatant was decanted and concentrated
under reduced pressure. The residue was washed with Et2O to give
a quantitative yield of practically pure amide 1a. C8H17NO6; IR
foam, [R]25 +78.11 (c 1.06, EtOAc); IR Vmax (neat) 3637, 3270,
D
1754, 1672, 1639 cm-1; 1H NMR (CDCl3, 400 MHz) δ 6.21 (1 H,
t, J ) 5.6 Hz), 5.53-5.36 (5 H, m), 5.24 (1H, d, J ) 3.6 Hz),
5.17-5.15 (1 H, m), 5.07 (1 H, t, J ) 10.4 Hz), 4.87 (2 H, dd, J
) 10.4, 3.6 Hz), 4.65 (1 H, dd, J ) 12.0, 2.4 Hz), 4.48 (1 H, d, J
) 12.0 Hz), 4.28-3.94 (8 H, m), 3.21 (2 H, m), 2.17 (3 H, s), 2.15
(3 H, s), 2.11 (3 H, s), 2.10 (6 H, s), 2.09 (3 H, s), 2.08 (3 H, s),
2.05 (3 H, s), 2.03 (3 H, s), 2.01 (6 H, s), 1.44 (2 H, br m), 1.25
(26 H, br m), 0.88 (3 H, t, J ) 6 Hz); 13C NMR (CDCl3, 100 MHz)
δ 170.7, 170.3 (2×), 170.2, 169.9, 169.7, 169.5 (2×), 169.4, 169.2,
νmax (neat) 3369, 2933, 1644 cm-1; H NMR (D2O, 400 MHz) δ
1
4.54 (1 H, d, J ) 3.6 Hz), 4.30 (1 H, t, J ) 3.2 Hz), 4.06-3.97 (3
H, m), 3.89 (1 H, dd, J ) 11.6, 5.6 Hz), 3.49 (2 H, q, J ) 7.2 Hz),
1.36 (3 H, t, J ) 7.2 Hz); 13C NMR (D2O, 100 MHz) δ 173.8,
73.7, 72.4, 71.5, 70.6, 63.1, 34.9, 14.7; HRMS calcd for
C8H17NO6Na 246.0948, found m/z 246.0948 [M + Na]+.
J. Org. Chem. Vol. 74, No. 4, 2009 1553

Cho et al.
169.0, 166.2, 97.6, 95.5, 77.1, 72.6, 71.8, 71.3, 70.9, 70.8, 70.5,
69.9, 69.3, 68.8, 68.3, 67.9, 62.5, 62.4, 61.3, 53.4, 39.8, 39.5, 31.9,
29.7 (2×), 29.6 (2×), 29.4, 29.3 (2×), 26.9, 26.8, 23.3, 22.7, 21.0,
20.9 (2×), 20.8, 20.7 (6×), 20.6, 14.2; MS calcd for C56H88NO27
1206, found m/z 1206 [M + H]+; HRMS calcd for C56H88NO27
1206.5538, found m/z 1206.5537 [M + H]+.
19.2, 17.6 (2×); HRMS (ESI) calcd C22H33NO13Na 542.1844, found
m/z 542.1836 [M + Na]+.
N-(2,3,4,5,6-O-Pentaacetyl-D-gluconyl)-O-acetyl-L-serine Meth-
yl Ester (14Ac). According to the general procedure for oxidative
amidation of aldose, a methanolic solution of D-glucose (180 mg,
1.0 mmol) was stirred with K2CO3 (207 mg, 1.5 mmol) and I2 (305
mg, 1.2 mmol) in the presence of activated molecular sieves at
room temperature under argon for 3 h. Then the HCl salt of L-serine
methyl ester (311 mg, 2.0 mmol) and K2CO3 (207 mg, 1.5 mmol)
were added, and the mixture was stirred at 40 °C under argon for
16 h. The mixture was concentrated by rotary evaporation to give
a crude product, which was subsequently treated with Ac2O in
pyridine and purified by flash chromatography (silica gel; EtOAc/
hexane, 1:1) to give compound 14Ac (300 mg, 55% yield).
C22H31NO15; yellow foam; [R]25D +28.08 (c 3.9, CH2Cl2); IR Vmax
(neat) 3360, 1747, 1694 cm-1; 1H NMR (CDCl3, 400 MHz) δ 6.87
(1 H, d, J ) 7.6 Hz), 5.70 (1 H, dd, J ) 5.8, 4.6 Hz), 5.45 (1 H,
t, J ) 5.8 Hz), 5.38 (1 H, d, J ) 4.4 Hz), 5.01 (1 H, dd, J ) 10.6,
5.0 Hz), 4.80-4.76 (1 H, m), 4.48 (1 H, dd, J ) 11.8, 4.8 Hz),
4.33-4.29 (2 H, m), 4.14 (1 H, dd, J ) 11.8, 5.2 Hz), 3.76 (3 H,
s), 2.26 (3 H, s), 2.10 (6 H, s), 2.09 (3 H, s), 2.05 (3 H, s), 2.04 (3
H, s); 13C NMR (CDCl3, 100 MHz) δ 170.6, 170.0, 169.3 (2×),
169.2, 168.9, 168.5, 166.0, 71.7, 69.4, 68.5 (2×), 62.9, 61.1, 52.7,
51.8, 20.6 (2×), 20.5 (2×), 20.4, 20.3; HRMS (ESI) calcd for
C22H32NO15 550.1766, found m/z 550.1765 [M + H]+.
N-Gluconylglycine Methyl Ester (12) and N-(2,3,4,5,6-O-Pen-
taacetylgluconyl)glycine Methyl Ester (12Ac). According to the
general procedure for oxidative amidation of aldose, a methanolic
solution of D-glucose (180 mg, 1.0 mmol) was stirred with K2CO3
(207 mg, 1.5 mmol) and I2 (305 mg, 1.2 mmol) in the presence of
activated molecular sieves at room temperature under argon for
3 h. Then the HCl salt of glycine methyl ester (251 mg, 2.0 mmol)
and K2CO3 (207 mg, 1.5 mmol) were added, and the mixture was
stirred at 40 °C under argon for 12 h. The mixture was filtrated,
and subsequently purified by flash chromatography (RP-18; water)
to give the title compound (256 mg, 96% yield). C9H17NO8; yellow
solid (hygroscopic); [R]25 +45.97 (c 2.6, MeOH); IR Vmax (neat)
D
3362, 1739, 1658 cm-1; 1H NMR (D2O, 400 MHz) δ 4.37 (1 H, d,
J ) 4 Hz), 4.13-4.01 (3 H, m), 3.83-3.80 (1 H, m), 3.77-3.72
(5 H, m), 3.66-3.62 (1 H, m); 13C NMR (D2O, 100 MHz) δ 175.0,
171.9, 73.4, 72.6, 71.2, 70.6, 62.8, 53.0, 41.1; HRMS (ESI) calcd
for C9H17NO8K 306.0585, found m/z 306.0580 [M + K]+.
According to the general procedure for oxidative amidation of
aldose, a methanolic solution of D-glucose (180 mg, 1.0 mmol)
was stirred with K2CO3 (207 mg, 1.5 mmol) and I2 (305 mg, 1.2
mmol) in the presence of activated molecular sieves at room
temperature under argon for 3 h. Then the HCl salt of glycine
methyl ester (251 mg, 2.0 mmol) and K2CO3 (207 mg, 1.5 mmol)
were added, and the mixture was stirred at 40 °C under argon for
12 h. The mixture was concentrated by rotary evaporation to give
a crude product, which was subsequently treated with Ac2O in
pyridine and purified by flash chromatography (silica gel; EtOAc/
hexane, 2:1) to give compound 12Ac (448 mg, 94% yield).
N-(2,3,4,5,6-O-Pentaacetyl-D-gluconyl)-L-tyrosine Methyl Ester
(15Ac). According to the general procedure for oxidative amidation
of aldose, a methanolic solution of D-glucose (180 mg, 1.0 mmol)
was stirred with K2CO3 (207 mg, 1.5 mmol) and I2 (254 mg, 1.0
mmol) in the presence of activated molecular sieves at room
temperature under argon for 3 h. Then the HCl salt of L-tyrosine
methyl ester (463 mg, 2.0 mmol) and K2CO3 (207 mg, 1.5 mmol)
were added, and the mixture was stirred at 40 °C under argon for
14 h. The mixture was concentrated by rotary evaporation to give
a crude product, which was subsequently treated with Ac2O in
pyridine and purified by flash chromatography (silica gel; EtOAc/
MeOH/Et3N, 98:1:1) to give compound 15Ac (388 mg, 62% yield).
Alternatively, a methanolic solution of D-glucose (180 mg, 1.0
mmol) was stirred with the HCl salt of glycine methyl ester (500
mg, 4.0 mmol) and I2 (508 mg, 2.0 mmol) in the presence of K2CO3
(552 mg, 4.0 mmol) at room temperature for 10 h to give a crude
product, which was subsequently treated with Ac2O in pyridine to
give compound 12Ac (225 mg, 50% yield). C19H27NO13; pale
C28H35NO15; yellow solid, mp 121.3-122.5 °C; [R]25 +22.98 (c
D
1
2.4, CH2Cl2); IR Vmax (neat) 3344, 1749, 1688 cm-1; H NMR
(CDCl3, 400 MHz) δ 7.03-6.98 (4 H, m), 6.37 (1 H, d, J ) 8.0
Hz), 5.64 (1 H, dd, J ) 5.6, 3.6 Hz), 5.43 (1 H, d, J ) 6.0 Hz),
5.41 (1 H, t, J ) 2.4 Hz), 5.02-4.98 (1 H, m), 4.87-4.83 (1 H,
m), 4.29 (1 H, dd, J ) 12.1, 4.4 Hz), 4.13 (1 H, dd, J ) 12.1, 5.4
Hz), 3.75 (3 H, s), 3.14 (1 H, dd, J ) 14.1, 5.0 Hz), 3.07 (1 H, dd,
J ) 14.1, 6.0 Hz), 2.29 (3 H, s), 2.12 (3 H, s), 2.11 (3 H, s), 2.08
(3 H, s), 2.04 (3 H, s), 2.02 (3 H, s); 13C NMR (CDCl3, 100 MHz)
δ 170.8, 170.3, 169.6, 169.4, 169.3, 169.1, 169.0, 165.8, 149.7,
132.6, 130.1 (2×), 121.7 (2×), 72.0, 69.6, 68.8, 68.7, 61.3, 52.6,
52.5, 36.8, 21.2, 20.82, 20.78, 20.74, 20.65, 20.5; HRMS (ESI)
calcd for C28H35NO15Na 648.1899, found m/z 648.1904 [M + Na]+.
N-(2,3,4,5,6-O-Pentaacetyl-D-gluconyl)-L-methionine Methyl Es-
ter (16Ac). According to the general procedure for oxidative
amidation of aldose, a methanolic solution of D-glucose (180 mg,
1.0 mmol) was stirred with K2CO3 (207 mg, 1.5 mmol) and I2 (254
mg, 1.0 mmol) in the presence of activated molecular sieves at
room temperature under argon for 3 h. Then the HCl salt of
L-methionine methyl ester (400 mg, 2.0 mmol) and K2CO3 (207
mg, 1.5 mmol) were added, and the mixture was stirred at 40 °C
under argon for 17 h. The mixture was concentrated by rotary
evaporation to give a crude product, which was subsequently treated
with Ac2O in pyridine and purified by flash chromatography (silica
gel; EtOAc/hexane, 1:1) to give compound 16Ac (259 mg, 47%
yellow solid, mp 175.3-177.5 °C; [R]25 +6.86 (c 0.3, EtOAc);
D
IR Vmax (neat) 3361, 1750, 1681 cm-1; 1H NMR (CDCl3, 400 MHz)
δ 6.63 (1 H, br s), 5.68 (1 H, t, J ) 4.8 Hz), 5.48 (1 H, dd, J )
6.4, 4.8 Hz), 5.38 (1 H, d, J ) 5.2 Hz), 5.07-5.03 (1 H, m), 4.32
(1 H, dd, J ) 12.4, 4.4 Hz), 4.16-4.08 (2 H, m), 3.97 (1 H, dd, J
) 18, 4.8 Hz), 3.77 (3 H, s), 2.24 (3 H, s), 2.13 (3 H, s), 2.11 (3
H, s), 2.10 (3 H, s), 2.06 (3 H, s); 13C NMR (CDCl3, 100 MHz) δ
170.4, 169.7, 169.6, 169.4 (2×), 169.2, 166.2, 71.6, 69.4, 68.6,
68.6, 61.4, 52.5, 41.0, 20.9, 20.8 (3×), 20.6; HRMS (ESI) calcd
C19H28NO13 478.1555, found m/z 478.1536 [M + H]+.
N-(2,3,4,5,6-O-Pentaacetylgluconyl)-L-valine Methyl Ester (13Ac).
According to the general procedure for oxidative amidation of
aldose, a methanolic solution of D-glucose (180 mg, 1.0 mmol)
was stirred with the HCl salt of L-valine methyl ester (671 mg, 4.0
mmol) and I2 (508 mg, 2.0 mmol) in the presence of K2CO3 (552
mg, 4.0 mmol) at room temperature for 10 h to give a crude product,
which was subsequently treated with Ac2O in pyridine to give
compound 13Ac (364 mg, 70% yield). C22H33NO13; white solid,
mp 130.5-132.0 °C; [R]25D +29.43 (c 0.5, CH2Cl2); IR Vmax (neat)
3297, 1757, 1668 cm-1; 1H NMR (CDCl3, 400 MHz) δ 6.47 (1 H,
d, J ) 8.8 Hz), 5.68 (1 H, dd, J ) 5.6, 4.4 Hz), 5.46 (1 H, t, J )
5.6 Hz), 5.37 (1 H, d, J ) 4.4 Hz), 5.02 (1 H, dd, J ) 10.4, 5.2
Hz), 4.52 (1 H, dd, J ) 8.8, 4.4 Hz), 4.31 (1 H, dd, J ) 12, 4.4
Hz), 4.16 (1 H, dd, J ) 12, 5.6 Hz), 3.73 (3 H, s), 2.25 (3 H, s),
2.23-2.12 (1 H, m), 2.11 (6 H, s), 2.07 (3 H, s), 2.05 (3 H, s),
0.91 (3 H, d, J ) 6.8 Hz), 0.86 (3 H, d, J ) 6.8 Hz); 13C NMR
(CDCl3, 100 MHz) δ 171.1, 169.8, 169.1 (2 ×), 168.9, 168.6, 165.6,
72.3, 72.2, 69.6, 68.7, 61.4, 56.9, 52.4, 31.4, 21.1 (2×), 20.9, 20.8,
yield). C22H33NO13S; white foam; [R]25 +26.72 (c 1.5, CH2Cl2);
D
IR Vmax (neat) 3358, 1749, 1687 cm-1; 1H NMR (CDCl3, 400 MHz)
δ 6.85 (1 H, d, J ) 7.6 Hz), 5.68 (1 H, t, J ) 4.8 Hz), 5.44 (1 H,
t, J ) 5.6 Hz), 5.34 (1 H, d, J ) 4.4 Hz), 5.02 (1 H, dd, J ) 9.6,
5.6 Hz), 4.69-4.64 (1 H, m), 4.30 (1 H, dd, J ) 12.1, 4.2 Hz),
4.14 (1 H, dd, J ) 12.1, 5.6 Hz), 3.74 (3 H, s), 2.48 (2 H, t, J )
7.2 Hz), 2.23 (3 H, s), 2.20-2.12 (1 H, m), 2.10 (6 H, s), 2.08 (3
1554 J. Org. Chem. Vol. 74, No. 4, 2009

Amidation of Aldoses and R-Keto Acids
H, s), 2.07 (3 H, s), 2.04 (3 H, s), 2.02-1.95 (1 H, m); 13C NMR
(CDCl3, 100 MHz) δ 171.4, 170.3, 169.52, 169.45, 169.4, 169.0,
165.9, 71.8, 69.4, 68.64, 68.59, 61.2, 52.6, 51.5, 30.8, 29.8, 20.74,
20.68 (3×), 20.4, 15.4; HRMS (ESI) calcd for C22H33NO13SNa
574.1565, found m/z 574.1538 [M + Na]+.
give compound 19Ac (372 mg, 63% yield). C25H38N2O14; white
foam; [R]25 +26.37 (c 0.4, CH2Cl2); IR Vmax (neat) 3316, 1751,
D
1663 cm-1; 1H NMR (CDCl3, 400 MHz) δ 6.33-6.31 (2 H, br s),
5.66 (1 H, t, J ) 5.2 Hz), 5.43 (1 H, dd, J ) 6.2, 5.4 Hz), 5.24 (1
H, d, J ) 5.2 Hz), 5.05-5.01 (1 H, m), 4.57-4.52 (1 H, m), 4.32
(1 H, dd, J ) 12.4, 3.6 Hz), 4.11 (1 H, dd, J ) 12.4, 5.6 Hz), 3.73
(3 H, s), 3.23 (2 H, dd, J ) 12.8, 6.4 Hz), 2.20 (3 H, s), 2.10 (3 H,
s), 2.08 (3 H, s), 2.05 (3 H, s), 2.04 (3 H, s), 2.03 (3 H, s),
1.84-1.77 (1 H, m), 1.72-1.65 (1 H, m), 1.54-1.47 (2 H, m),
1.37-1.26 (2 H, m); 13C NMR (CDCl3, 100 MHz) δ 172.6, 170.5,
170.0 (2×), 169.6 (2×), 169.2, 166.0, 71.6, 69.4, 69.0, 68.8, 61.6,
52.4, 51.9, 38.8, 31.7, 28.8, 23.0, 22.2, 20.8 (2×), 20.7 (2×), 20.5;
HRMS (ESI) calcd for C25H39N2O14 591.2396, found m/z 591.2378
[M + H]+.
N-(2,3,4,5,6-O-Pentaacetyl-D-gluconyl)-S-acetyl-L-cysteine Meth-
yl Ester (17Ac). According to the general procedure for oxidative
amidation of aldose, a methanolic solution of D-glucose (90 mg,
0.5 mmol) was stirred with K2CO3 (138 mg, 1.0 mmol) and I2 (127
mg, 0.5 mmol) at 70 °C under argon for 20 min. Then the HCl salt
of L-cysteine methyl ester (103 mg, 0.6 mmol) was added, and the
mixture was stirred at 70 °C under argon for 5 h to complete the
amidation as shown by TLC analysis. The mixture was concentrated
by rotary evaporation to give a crude product, which was
subsequently treated with Ac2O in pyridine and purified by flash
chromatography (silica gel; EtOAc/hexane, 1:1) to give compound
N-(2,3,4,5,6-O-Pentaacetylgluconyl)-L-proline Methyl Ester (20Ac).
According to the general procedure for oxidative amidation of
aldose, a methanolic solution of D-glucose (180 mg, 1.0 mmol)
was stirred with K2CO3 (207 mg, 1.5 mmol) and I2 (254 mg, 1.0
mmol) in the presence of activated molecular sieves at room
temperature under argon for 3 h. Then the HCl salt of L-proline
methyl ester (325 mg, 2.0 mmol) and K2CO3 (207 mg, 1.5 mmol)
were added, and the mixture was stirred at room temperature under
argon for 48 h. The mixture was concentrated by rotary evaporation
to give a crude product, which was subsequently treated with Ac2O
in pyridine and purified by flash chromatography (silica gel; EtOAc/
hexane, 2:1) to give compound 20Ac (207 mg, 40% yield).
C22H31NO13; yellow foam; [R]25D +15.64 (c 1.7, CH2Cl2); IR Vmax
(neat) 1748, 1661 cm-1; 1H NMR (CDCl3, 400 MHz) δ 5.75 (1 H,
dd, J ) 7.0, 3.4 Hz), 5.43 (1 H, d, J ) 7.2 Hz), 5.39 (1 H, dd, J
) 8.0, 3.2 Hz), 5.06-5.02 (1 H, m), 4.44 (1 H, dd, J ) 8.6, 3.8
Hz), 4.24 (1 H, dd, J ) 12.5, 3.0 Hz), 4.12 (1 H, dd, J ) 12.5, 5.2
Hz), 3.81-3.76 (1 H, m), 3.71 (3 H, s), 3.47-3.41 (1 H, m),
2.20-2.15 (2 H, m), 2.14 (3 H, s), 2.13 (3 H, s), 2.07 (3 H, s),
2.06 (3 H, s), 2.05 (3 H, s), 2.04-1.97 (2 H, m); 13C NMR (CDCl3,
100 MHz) δ 171.5, 170.1, 169.4, 169.3, 169.08, 169.05, 164.0,
69.4, 68.5, 68.4, 68.1, 61.3, 59.1, 52.0, 46.7, 28.6, 24.7, 20.63 (2×),
20.55, 20.32, 20.26; HRMS (ESI) calcd for C22H31NO13Na 540.1688,
found m/z 540.1690 [M + Na]+.
N-(2,3,4,5,6-O-Pentaacetyl-D-gluconyl)glycyl-L-valine Methyl Es-
ter (21Ac). According to the general procedure for oxidative
amidation of aldose, a methanolic solution of D-glucose (180 mg,
1.0 mmol) was stirred with K2CO3 (207 mg, 1.5 mmol) and I2 (305
mg, 1.2 mmol) in the presence of activated molecular sieves at
room temperature under argon for 3 h. Then the HCl salt of glycyl-
L-valine methyl ester (449 mg, 2.0 mmol) and K2CO3 (207 mg,
1.5 mmol) were added, and the mixture was stirred at 40 °C under
argon for 16 h. The mixture was concentrated by rotary evaporation
to give a crude product, which was subsequently treated with Ac2O
in pyridine and purified by flash chromatography (silica gel; EtOAc/
hexane, 2:1) to give compound 21Ac (461 mg, 80% yield).
C24H36N2O14; yellow foam; [R]25D +25.55 (c 3.7, CH2Cl2); IR Vmax
(neat) 3366, 1748, 1677 cm-1; 1H NMR (CDCl3, 400 MHz) δ 6.93
(1 H, br s), 6.62 (1 H, br s), 5.66 (1 H, t, J ) 4.8 Hz), 5.45 (1 H,
dd, J ) 6.6, 4.6 Hz), 5.30 (1 H, d, J ) 4.8 Hz), 5.08-5.04 (1 H,
m), 4.50 (1 H, dd, J ) 8.8, 5.2 Hz), 4.30 (1 H, dd, J ) 12.4, 3.8
Hz), 4.13 (1 H, dd, J ) 12.4, 5.4 Hz), 4.01 (1 H, dd, J ) 16.8, 5.6
Hz), 3.94 (1 H, dd, J ) 16.8, 5.2 Hz), 3.74 (3 H, s), 2.21 (3 H, s),
2.19-2.12 (1 H, m), 2.11 (3 H, s), 2.08 (3 H, s), 2.07 (3 H, s),
2.05 (3 H, s), 0.94 (3 H, d, J ) 6.4 Hz), 0.91 (3 H, d, J ) 6.8 Hz);
13C NMR (CDCl3, 100 MHz) δ 171.6, 169.9, 169.3, 169.2 (2×),
168.7, 168.0, 166.3, 71.6, 69.1, 68.5, 68.3, 61.1, 57.2, 51.8, 42.3,
30.6, 20.4, 20.3 (3×), 20.1, 18.7, 17.6; HRMS (ESI) calcd for
C24H36N2O14Na 599.2059, found m/z 599.2052 [M + Na]+.
N-Maltonyl-L-lysyl-D-alanyl-D-alanine Trifluoroacetic Salt (30).
According to the general procedure for oxidative amidation of
aldose, a methanolic solution of D-maltose monohydrate (72 mg,
0.2 mmol) was stirred with K2CO3 (42 mg, 0.3 mmol) and I2 (62
mg, 0.2 mmol) at room temperature under argon for 3 h. Then the
TFA salt of L-lysyl-D-alanyl-D-alanine (50 mg, 0.1 mmol) and
17Ac (120 mg, 42% yield). C22H31NO14S; white foam; [R]25
D
+13.33 (c 2.2, EtOAc); IR Vmax (neat) 3363, 1750, 1691 cm-1; 1H
NMR (CDCl3, 400 MHz) δ 6.82 (1 H, d, J ) 8.0 Hz), 5.71 (1 H,
dd, J ) 6.0, 3.6 Hz), 5.46-5.43 (2 H, m), 5.01-4.97 (1 H, m),
4.72-4.67 (1 H, m), 4.31 (1 H, dd, J ) 12.1, 4.8 Hz), 4.14 (1 H,
dd, J ) 12.1, 5.4 Hz), 3.73 (3 H, s), 3.35 (1 H, dd, J ) 14.5, 8.8
Hz), 3.21 (1 H, dd, J ) 14.5, 3.4 Hz), 2.35 (3 H, s), 2.30 (3 H, s),
2.11 (3 H, s), 2.09 (6 H, s), 2.03 (3 H, s); 13C NMR (CDCl3, 100
MHz) δ 196.4, 170.2, 169.6, 169.5, 169.4, 169.3, 169.0, 166.4,
71.7, 69.7, 68.9, 68.7, 61.1, 52.76, 52.75, 30.4, 30.0, 20.8, 20.74,
20.72 (2×), 20.5; HRMS (ESI) calcd for C22H31NO14SNa 588.1357,
found m/z 588.1328 [M + Na]+.
N-(2,3,4,5,6-O-Pentaacetyl-D-gluconyl)-L-histidine Methyl Ester
(18Ac). According to the general procedure for oxidative amidation
of aldose, a methanolic solution of D-glucose (180 mg, 1.0 mmol)
was stirred with K2CO3 (207 mg, 1.5 mmol) and I2 (254 mg, 1.0
mmol) in the presence of activated molecular sieves at room
temperature under argon for 3 h. Then the HCl salt of L-histidine
methyl ester (484 mg, 2.0 mmol) and K2CO3 (414 mg, 3.0 mmol)
were added, and the mixture was stirred at 40 °C under argon for
14 h. The mixture was concentrated by rotary evaporation to give
a crude product, which was subsequently treated with Ac2O in
pyridine and purified by flash chromatography (silica gel; EtOAc/
MeOH/Et3N, 98:1:1) to give compound 18Ac (302 mg, 54% yield).
C23H31N3O13; yellow foam; [R]25D +31.83 (c 3.9, CH2Cl2); IR Vmax
(neat) 3348, 1745, 1678 cm-1; 1H NMR (CDCl3, 400 MHz) δ 8.24
(1 H, br), 7.51 (1 H, s), 6.77 (1 H, s), 5.77 (1 H, dd, J ) 6.2, 3.8
Hz), 5.49 (1 H, t, J ) 5.6 Hz), 5.45 (1 H, d, J ) 3.2 Hz), 5.03 (1
H, dd, J ) 10.4, 5.2 Hz), 4.74-4.70 (1 H, m), 4.32 (1 H, dd, J )
12.0, 4.8 Hz), 4.17 (1 H, dd, J ) 12.0, 5.6 Hz), 3.64 (3 H, s), 3.12
(1 H, dd, J ) 14.9, 5.2 Hz), 2.99 (1 H, dd, J ) 14.9, 4.6 Hz), 2.32
(3 H, s), 2.11 (3 H, s), 2.10 (3 H, s), 2.05 (3 H, s), 2.04 (3 H, s);
13C NMR (CDCl3, 100 MHz) δ 170.4, 170.1, 169.6, 169.42, 169.36,
169.2, 166.2, 135.0, 134.5, 114.4, 72.0, 69.7, 68.6 (2×), 61.0, 52.2,
52.0, 28.4, 20.60, 20.55, 20.51, 20.49, 20.3; HRMS (ESI) calcd
for C23H32N3O13 558.1930, found m/z 558.1927 [M + H]+.
Nr-Acetyl-Nε-(2,3,4,5,6-O-pentaacetylgluconyl)-L-lysine Meth-
yl Ester (19Ac). According to the general procedure for oxidative
amidation of aldose, a methanolic solution of D-glucose (180 mg,
1.0 mmol) was stirred with K2CO3 (207 mg, 1.5 mmol) and I2 (305
mg, 1.2 mmol) in the presence of activated molecular sieves at
room temperature under argon for 3 h. Then the HCl salt of L-lysine
methyl ester (466 mg, 2.0 mmol) and K2CO3 (414 mg, 3.0 mmol)
were added, and the mixture was stirred at 40 °C under argon for
14 h. The mixture was concentrated by rotary evaporation to give
a crude product, which was subsequently treated with Ac2O in
pyridine and purified by flash chromatography (silica gel; EtOAc)
to give compound 19Ac (460 mg, 78% yield).
Alternatively, a methanolic solution of D-glucose (180 mg, 1.0
mmol) was stirred with the HCl salt of L-lysine methyl ester (933
mg, 4.0 mmol) and I2 (508 mg, 2.0 mmol) in the presence of K2CO3
(1.11 g, 8.0 mmol) at room temperature for 14 h to give a crude
product, which was subsequently treated with Ac2O in pyridine to
J. Org. Chem. Vol. 74, No. 4, 2009 1555

Cho et al.
K2CO3 (62 mg, 0.2 mmol) were added, and the mixture was stirred
at 40 °C under argon for 16 h. The mixture was filtrated, and
subsequently purified by gel filtration (Sephadex G-10; 10%
aqueous AcOH). The filtrate was concentrated under reduced
pressure, and the residue was treated with trifluoroacetic acid. After
the excess trifluoroacetic acid was removed under reduced pressure,
the desired product 30 (49 mg, 0.66 mmol) was obtained in 66%
3.36-3.25 (2 H, m), 2.21 (3 H, s), 2.09 (3 H, s), 2.08 (3 H, s),
2.06 (3 H, s), 1.14 (3 H, t, J ) 7.2 Hz); 13C NMR (CDCl3, 100
MHz) δ 170.2, 169.6, 169.1, 168.9, 165.5, 71.7, 69.6, 69.2, 61.7,
34.4, 20.8, 20.7 (2×), 20.5, 14.7; HRMS calcd for C15H23NO9Na
384.1265, found m/z 384.1269 [M + Na]+.
N-Hexyl (3S,4R,5R,6S,7R)-4-Acetamido-3,5,6,7,8-pentaacetoxy-
octanamide (33Ac). According to the general procedure for decar-
boxylative amidation of R-keto acid, an aqueous solution of sialic
acid (309 mg, 1.0 mmol) was stirred with hexylamine (404 mg,
4.0 mmol) and I2 (508 mg, 2.0 mmol) at room temperature for 10 h
yield. C24H44N4O15 · CF3CO2H; white solid (hygroscopic); [R]25
D
1
+23.83 (c 1.5, H2O); IR Vmax (KBr) 3429, 1681 cm-1; H NMR
(D2O, 400 MHz) δ 5.16 (1 H, d, J ) 3.6 Hz), 4.35 (1 H, d, J ) 7.2
Hz), 4.32 (1 H, d, J ) 2.4 Hz), 4.20 (1 H, dd, J ) 6.4, 2.4 Hz),
4.16-4.09 (2 H, m), 3.99-3.65 (9 H, m), 3.59 (1 H, dd, J ) 9.8,
3.8 Hz), 3.45 (1 H, t, J ) 9.4 Hz), 3.30-3.25 (2 H, m), 1.86-1.80
(2 H, m), 1.62-1.52 (2 H, m), 1.41 (3 H, d, J ) 7.6 Hz), 1.39-1.37
(2 H, m), 1.34 (3 H, d, J ) 7.2 Hz); 13C NMR (D2O, 100 MHz) δ
177.1, 174.4, 174.1, 169.8, 163.2, 162.9, 118.0, 115.1, 100.7, 82.2,
73.2, 72.7, 72.5, 72.1, 72.0, 71.9, 69.6, 62.4, 60.6, 53.4, 50.0, 49.5,
38.9, 30.8, 28.4, 21.8, 17.1, 16.6; HRMS (ESI) calcd for
C24H45N4O15 629.2881, found m/z 629.2878 [M - CF3CO2]+.
Conjugation of D-Lactose with Polylysine. According to the
general procedure for oxidative amidation of aldose, a methanolic
solution of D-lactose monohydrate (180 mg, 0.5 mmol) was stirred
with K2CO3 (97 mg, 0.7 mmol) and I2 (153 mg, 0.6 mmol) at room
temperature under argon for 3 h. Then the HBr salt of poly-L-lysine
(20.9 kDa, Mw/Mn ) 1.24, 10 mg, 0.5 µmol, containing ap-
proximately 93 lysyl residues per poly-L-lysine molecule) and
K2CO3 (10 mg, 0.07 mmol) were added, and the mixture was stirred
at 40 °C under argon for 24 h. The mixture was concentrated under
reduced pressure. The residue was dissolved in water (10 mL) and
subjected to dialysis with cellulose ester membrane (5 kDa MWCO)
by deionized water (2 L). The dialysis was repeated 2 times with
2 L of fresh deionized water for 6 and 14 h, respectively, to give
the lactonyl-polylysine conjugate as shown by a sulfuric acid-phenol
assay.
1
to give a glyconamide product. H NMR (D2O, 400 MHz) δ 4.48
(1 H, t, J ) 6.8 Hz), 3.90 (2 H, br s), 3.80 (1 H, dd, J ) 11.6, 3.6
Hz), 3.75-3.70 (1 H, m), 3.60 (1 H, dd, J ) 11.6, 6.0 Hz), 3.45 (1
H, d, J ) 8.0 Hz), 3.16 (2 H, t, J ) 6.8 Hz, H-1′), 2.38-2.36 (2
H, m, H-2), 2.06 (3 H, s), 1.48 (2 H, t, J ) 6.8 Hz), 1.32 (6 H, br
m), 0.86 (3 H, t, J ) 6.8 Hz).
The crude product was treated with Ac2O in pyridine to give
compound 33Ac (350 mg, 61% overall yield). C26H42N2O12; yellow
foam, [R]25 -4.71 (c 1.10, CH2Cl2); IR Vmax (neat) 3289, 1750,
D
1
1652 cm-1; H NMR (CDCl3, 400 MHz) δ 6.50 (1 H, br s), 5.86
(1 H, d, J ) 10.4 Hz), 5.39 (1 H, dd, J ) 8.4, 2.0 Hz), 5.27 (1 H,
dd, J ) 10.0, 2.0 Hz), 5.08 (1 H, dd, J ) 8.8, 4.8 Hz), 5.05-5.00
(1 H, m), 4.37 (1 H, t, J ) 10.4 Hz), 4.24 (1 H, dd, J ) 12.4, 3.2
Hz), 3.99 (1 H, dd, J ) 12.8, 5.6 Hz), 3.24-3.16 (2 H, m), 2.38 (1
H, dd, J ) 13.2, 4.8 Hz), 2.29 (1 H, dd, J ) 13.2, 8.8 Hz), 2.09 (3
H, s), 2.05 (6 H, s), 2.04 (9 H, s), 1.53-1.46 (2 H, m), 1.34-1.25
(6 H, m), 0.87 (3 H, t, J ) 6.8 Hz); 13C NMR (CDCl3, 100 MHz)
δ 171.2, 170.3, 169.8, 169.6, 169.5, 169.2, 167.9, 68.7 (2×), 67.9,
67.7, 61.9, 49.5, 39.8, 38.9, 31.5, 29.3, 26.6, 23.2, 22.6, 21.0, 20.9,
20.8, 20.7 (2×), 14.1; HRMS calcd for C26H43N2O12 575.2811,
found m/z 575.2804 [M + H]+.
N-Ethyl (3R,4R,5R,6R)-3,4,5,6,7-Pentaacetoxyheptanamide (34Ac).
According to the general procedure for decarboxylative amidation
of R-keto acid, an aqueous solution of KDO (100 mg, 0.39 mmol)
was stirred with ethylamine (70% wt, 1.0 mL) and I2 (125 mg,
0.49 mmol) at room temperature for 12 h to give a crude product,
which was subsequently treated with Ac2O in pyridine to give amide
34Ac (130 mg, 74% yield). C19H29NO11; white solid, mp 149.1-151.3
°C; [R]25D +36.11 (c 0.7, CH2Cl2); IR Vmax (neat) 2924, 1743, 1649
Conjugation of D-Lactose with Bovine Serum Albumin.
According to the general procedure for oxidative amidation of
aldose, a methanolic solution of D-lactose monohydrate (180 mg,
0.5 mmol) was stirred with K2CO3 (9.3 mg, 67 µmol) and I2 (13.6
mg, 54 µmol) at room temperature under argon for 3 h. Then bovine
serum albumin (50 mg, 0.8 µmol, 66 kDa, containing 59 lysyl
residues per BSA molecule) and K2CO3 (9.3 mg, 67 µmol) were
added, and the mixture was stirred at room temperature for 24 h.
The mixture was filtered, and thoroughly rinsed with deionized
water (50 mL) to give the lactonyl-BSA conjugate. The MALDI-
TOF MS analysis of the glycoprotein indicated that approximately
4 lactosyl moieties were linked to BSA (see the Supporting
Information, Figure S1).
N-Ethyl 2,3,4,5-O-Tetraacetyl-L-xylonamide (32Ac). According
to the general procedure for decarboxylative amidation of R-keto
acid, an aqueous solution of 2-keto-L-gulonic acid (194 mg, 1.0
mmol) was stirred with EtNH2 (1 mL of 70% aqueous solution)
and I2 (508 mg, 2.0 mmol) at room temperature for 8 h to give a
crude product, which was subsequently treated with Ac2O in
1
cm-1; H NMR (CDCl3, 400 MHz) δ 5.80 (1 H, br s), 5.43 (1 H,
dd, J ) 8.8, 2.8 Hz), 5.36 (1 H, dd, J ) 7.6, 3.2 Hz), 5.30-5.24(1
H, m), 5.11-5.07 (1 H, m), 4.22 (1 H, dd, J ) 12.4, 2.8 Hz), 4.10
(1 H, dd, J ) 12.4, 5.2 Hz), 3.33-3.21 (2 H, m), 2.51 (1 H, dd, J
) 14.8, 4.8 Hz), 2.39 (1 H, dd, J ) 14.8, 7.2 Hz), 2.11 (3 H, s),
2.10 (3 H, s), 2.07 (3 H, s), 2.06 (3H, s), 2.05 (3 H, s), 1.13 (3 H,
t, J ) 7.2 Hz); 13C NMR (CDCl3, 100 MHz) δ 170.3, 170.2, 169.7
(2×), 169.5, 167.7, 70.2, 68.1, 67.8, 67.5, 61.8, 38.1, 34.6, 21.0,
20.9, 20.8 (2×), 20.7, 14.8; HRMS calcd for C19H29NO11Na
470.1633, found m/z 470.1628 [M + Na]+.
Acknowledgment. We thank the National Science Council
for financial support.
pyridine to give amide 32Ac (264 mg, 73% yield). Compound 32Ac
Supporting Information Available: Experimental proce-
dures, product characterization, and NMR spectra. This material
is available free of charge via the Internet at http://pubs.acs.org.
1
(enantiomer of 3aAc): [R]25 -11.6 (c 0.65, CH2Cl2); H NMR
D
(CDCl3, 400 MHz) δ 6.01 (1 H, br s), 5.61 (1 H, dd, J ) 5.6, 4.8
Hz), 5.33 (1 H, d, J ) 4.8 Hz), 5.30 (1 H, dd, J ) 10.4, 6.0 Hz),
4.32 (1 H, dd, J ) 12.0, 4.8 Hz), 4.04 (1 H, dd, J ) 12.0, 6.0 Hz),
JO802338K
1556 J. Org. Chem. Vol. 74, No. 4, 2009