Facile synthesis of N-glycosyl amides using a N-glycosyl-2,4-dinitrobenzenesulfonamide and thioacids

Article abstract of DOI:10.1016/j.carres.2009.07.002

N-Glucosyl-2,4-dinitrobenzenesulfonamide was prepared from N-acetyl-d-glucosamine and 2,4-dinitrobenzenesulfonyl chloride. Amidation of several thioacids using the N-glucosylsulfonamide donor proceeded smoothly to give the desired N-glucosylamides in good

Full text of DOI:10.1016/j.carres.2009.07.002

Carbohydrate Research 344 (2009) 2048–2050
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Carbohydrate Research
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Facile synthesis of N-glycosyl amides using a
N-glycosyl-2,4-dinitrobenzenesulfonamide and thioacids
*
Rommel S. Talan, Aditya K. Sanki, Steven J. Sucheck
Department of Chemistry, The University of Toledo, 2801 W. Bancroft Street, Toledo, OH 43606, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
N-Glucosyl-2,4-dinitrobenzenesulfonamide was prepared from N-acetyl-D-glucosamine and 2,4-dini-
Received 8 June 2009
Accepted 3 July 2009
Available online 12 July 2009
trobenzenesulfonyl chloride. Amidation of several thioacids using the N-glucosylsulfonamide donor pro-
ceeded smoothly to give the desired N-glucosylamides in good to high yields. The amidation reactions
were carried out at room temperature, under mild conditions, and were completed in a very short time.
Published by Elsevier Ltd.
Keywords:
N-Glycosyl amide
N-Linked glycopeptides
N-Glycosylsulfonamide
N-Glycosyl asparagines
Convergent assembly
Amino thioacid
Initially introduced as a protecting group for the controlled
alkylation of primary amines to secondary amines,1 the 2,4-dini-
trobenzenesulfonyl group as a sulfonamide derivative 1 (Scheme
1) was adapted to facilitate the formation of amides 3 with thioac-
ids.2 The reaction proceeds with the ipso attack of the thioacid to
the sulfonamide to give a Meisenheimer-type complex 2. The sul-
fonated amine traps the nearby thioacid upon decomposition of
the Meisenheimer-type complex. This chemistry quickly proved
to be applicable to the coupling of amino thioacids, peptide frag-
ments, and neoglycoconjugates.3,4 In these studies, we sought to
determine whether or not an N-glycosylsulfonamide, has the po-
tential to react with thioacids to provide b-configured glycosyl
amides. The N-glycosylsulfonamide depicted in Figure 1 contains
trobenzenesulfonyl chloride provided the glycosyl donor 6. Con-
densation of the glycosyl donor with a simple thioacid, thioacetic
acid, in the presence of cesium carbonate and anhydrous DMF
afforded the N-b-glucosylacetamide 9 in respectable yield of 65%.
Employing the same reaction conditions with thiobenzoic acid
O
NO
NO
2
O
O
O
2
O
1
1
3
S
S
R
R
S
R
SH
N
N
2
2
R
R
CsCO
DMF
3
NO
NO
2
3
2
R
O
2
1
the 2-acetamido-2-deoxy-b-D-glucopyranosyl unit that in N-linked
glycopeptides/proteins is frequently found attached to an aspara-
gine residue.5 N-Glucosylsulfonamides of this type may lend them-
selves to the convergent assembly of N-linked glycopeptides/
proteins6 considering that the 2,4-dinitrobenzenesulfonyl-thioacid
ligation is relatively unaffected by the steric bulk of the reacting
fragments.3 In this paper, we wish to communicate the use of a
N-glucosylsulfonamide (Fig. 1) as glycosyl donor to access N-
glycosyl amides.
O
- SO
NO
2
2
1
R
HS
3
R
N
+
2
R
NO
2
3
Scheme 1. Mechanism of amide formation.
The 2-acetamido-3,4,6-O-acetyl-2-deoxy-b-D-glucopyranosyl-
amine 6 was obtained after a series of functional group manipula-
tions at the anomeric carbon following literature procedures
(Scheme 2).7–9 Sulfonation of the glycosyl amine with 2,4-dini-
OAc
NO
2
H
O
AcO
AcO
N
S
AcNH
O
O
NO
2
* Corresponding author. Tel.: +1 419 530 1504; fax: +1 419 530 1990.
E-mail address: Steve.Sucheck@Utoledo.edu (S.J. Sucheck).
Figure 1. N-glucosylsulfonamide.
0008-6215/$ - see front matter Published by Elsevier Ltd.
doi:10.1016/j.carres.2009.07.002

R. S. Talan et al. / Carbohydrate Research 344 (2009) 2048–2050
2049
Pyridine and DMF were dried over 3 Å and 4 Å molecular sieves,
respectively. Crude products were purified by flash column chro-
matography on silica gel (230–400 mesh) using commercial sol-
vents as received. Analytical thin layer chromatography (TLC,
Silica Gel 60, F254) was performed in the specified developing sol-
vents and visualized under UV or charring in the presence of 5%
H2SO4/MeOH or cerium ammonium molybdate. 1H spectra were
taken on either a 400 or a 600 MHz spectrometer and 13C NMR
spectra were obtained on either 100 or 150 MHz spectrometer in
CDCl3 with the residual CHCl3 signal as internal reference (CDCl3:
1H NMR at d 7.27, 13C NMR at d 77.23). 1H–1H gCOSY was per-
formed on a 600 MHz spectrometer. Low resolution mass spectra
were obtained on an electrospray ionization mass spectrometer
operated in the positive ion mode and high resolution mass spectra
were determined on a TOF mass spectrometer.
OAc
O
NO
2
O
O
S
Cl
AcO
AcO
NH
2
AcNH
pyridine
NO
2
46%a
5
4
OAc
O
NO
2
H
AcO
AcO
N
S
AcNH
O
O
NO
2
6
OAc
O
CsCO , DMF
3
O
AcO
NH
O
AcO
AcNH
HS
R
1.2. N-(2-Acetamido-3,4,6-tri-O-acetyl-2-deoxy-b-D-
R
glucopyranosyl)-2,4-dinitrobenzenesulfonamide (6)
9
R = CH (65%)
3
7 R = CH
3
8 R = C H
10 R = C H (85%)
6 5
6
5
The crude glucosylamine 4, obtained from glucosylazide (0.11 g,
0.29 mmol) following literature procedure,9 was reacted with 2,4-
dinitrobenzenesulfonyl chloride (0.12 g, 0.44 mmol) in anhydrous
pyridine (4 mL) at room temperature under N2 atmosphere. The
reaction was monitored by TLC and appeared complete within
3 h. After completion of the reaction, EtOAc (50 mL) was added
and the diluted mixture was washed with water, saturated aque-
ous sodium bicarbonate, and brine. The organic phase was dried
(anhydrous Na2SO4) and filtered, and the filtrate was concentrated
under reduced pressure. The crude material was purified by silica
gel column chromatography (7.5 ꢀ 3.0 cm) using EtOAc–hexanes
(3:2) to generate N-glucosylsulfonamide 6 as a yellow fluffy solid:
yield 46% (0.078 g, in two steps); 1H NMR (600 MHz, CDCl3): d 1.99
(s, 3H, CH3CO), 2.03 (s, 3H, CH3CO), 2.04 (s, 3H, CH3CO), 2.07 (s, 3H,
CH3CO), 3.67 (m, 1H, H-5), 3.83 (dd, 1H, J = 4.2, 12.6 Hz, H-6), 4.07
(dd, 1H, J = 1.8, 12.6 Hz, H-60), 4.16 (dd, 1H, J = 9.6, 19.2 Hz, H-2),
4.88 (t, 1H, J = 9.0 Hz, H-1), 5.00 (t, 1H, J = 9.6 Hz, H-4), 5.13 (t,
1H, J = 9.6 Hz, H-3), 6.51 (d, 1H, J = 7.8 Hz, NHAc), 7.74 (d, 1H,
J = 7.2 Hz, NHSO2Ar), 8.36 (d, 1H, J = 9.0 Hz, aromatic), 8.51 (dd,
1H, J = 1.8, 8.4 Hz, aromatic), 8.65 (d, 1H, J = 1.8 Hz, aromatic);
13C NMR (100.56 MHz, CDCl3): d 20.8 (CH3CO), 20.9 (CH3CO),
20.93 (CH3CO), 23.3 (CH3CO), 53.4 (C-2), 61.4 (C-6), 68.0, 72.5,
73.7, 84.9 (C-1), 120.6, 127.1, 132.5, 140.8, 148.0, 149.9 (six aro-
matic carbons), 169.5 (C@O), 170.3 (C@O), 171.9 (C@O), 173.1
(C@O); mass spectrum (HRMS): m/z = 577.1098 [M+H]+
(C20H25N4O14S requires 577.1088).
Scheme 2. N-Glucosyl amides from sulfonamide 6 (yield over two steps from
glucosylazide to glucosyl amine to glucosylsulfonamide).
OAc
SH
6, DMF
O
CsCO
AcO
NH
O
3
O
OBn
O
AcO
AcNH
70%
OBn
BocHN
O
BocHN
11
12
Scheme 3. N-Glycosylation of aspartic acid.
gave a high yield of 85% of the corresponding N-b-glucosylbenza-
mide 10. In both examples, the reaction was performed at room
temperature and was complete in 30 min, indicating the relative
ease with which this reaction could be carried out.
Encouraged by these results, we immediately turned our atten-
tion to the synthesis of N-(b-D-glucosyl)asparagine derivative 12
(Scheme 3). The requisite aspartic acid 11 with a thioacid-modified
side chain was prepared following a five-step protocol reported in
the literature.3,10 Reaction of the N-glucosylsulfonamide with thio-
acid 11 under similar conditions as the previous examples gave an
isolated yield of 69% of the desired N-(b-D-glucosyl)asparagine
derivative 12. The observed yield was comparable with other
methods such as the Staudinger ligation reaction involving glyco-
syl azides.11,12,6b The preservation of the b-configuration in the
product is a valuable feature of this method in light of the fact that
it is a crucial aspect of convergent N-linked glycopeptide synthesis.
In summary, we have demonstrated that N-glucosylsulfona-
mide 12 is an efficient and convenient glycosylating agent of thio-
acids that is able to introduce the desired b-glycosidic linkage as
shown by the preparation of several N-glucosylamides. The
reaction proceeds at room temperature under mild conditions in
1.3. General procedure for N-glycopeptide synthesis
To a suspension of cesium carbonate (2 equiv) in anhydrous
DMF in a 50-mL round-bottomed flask was added appropriate thio-
acid (2 equiv). The mixture was stirred for 10 min at room temper-
ature under N2 atmosphere before addition of sulfonamide starting
material (1 equiv). The resulting solution (approximately 0.2 M,
red in color) was stirred further for a given time until judged com-
plete by TLC. After completion of the reaction, the reaction mixture
was diluted with EtOAc (60 mL), and washed with saturated aque-
ous NH4Cl (2 ꢀ 30 mL), followed by brine. The organic phase was
dried (anhydrous Na2SO4), filtered, and the filtrate concentrated
under reduced pressure to afford a crude material. The crude mate-
rial was purified by silica gel flash column chromatography to fur-
nish the desired product.
relatively short time. This method for forming the N-(b-D-
glycosyl)asparagine linkage is expected to have applications
for the convergent synthesis of homogeneous N-linked glycopep-
tides/proteins.
1. Experimental
1.1. General
1.3.1. N-(2-Acetamido-3,4,6-tri-O-acetyl-2-deoxy-b-D-
glucopyranosyl)acetamide (9)
Aspartic acid and other fine chemicals were purchased from
commercial suppliers and were used without further purification.
Glucosylsulfonamide 6 (0.039 g, 0.068 mmol) was converted to
9 (0.017 g, 0.044 mmol) as a glassy yellow solid following the

2050
R. S. Talan et al. / Carbohydrate Research 344 (2009) 2048–2050
general procedure described earlier with a reaction time of 30 min.
The crude product was purified by silica gel flash column chroma-
tography (6 ꢀ 3 cm) using MeOH–CHCl3 (1:19): yield 65%; Rf = 0.5
(1:9 MeOH–CHCl3); 1H NMR (600 MHz, CDCl3): d 1.96 (s, 3H,
CH3CO), 1.98 (s, 3H, CH3CO), 2.05 (s, 3H, CH3CO), 2.07 (s, 3H,
CH3CO), 2.09 (s, 3H, CH3CO), 3.77 (m, 1H, H-5), 4.08 (dd, 1H,
J = 1.8, 12.6 Hz, H-6), 4.13 (dd, 1H, J = 10.2, 18.6 Hz, H-2), 4.29
(dd, 1H, J = 4.8, 12.6 Hz, H-60), 5.04–5.13 (m, 3H, H-1, H-3 and H-
4), 6.16 (d, 1H, J = 8.4 Hz, NHAcC-2), 7.02 (d, 1H, J = 8.4 Hz, NHAcC-
1); 13C NMR (150 MHz, CDCl3): d 20.8 (CH3CO), 20.9 (CH3CO),
21.0 (CH3CO), 23.4 (CH3CO), 23.6 (CH3CO), 53.6, 61.9, 67.9, 73.2,
73.6, 80.5 (C-1), 169.5 (C@O), 171.0 (C@O), 171.2 (C@O), 172.2
(C@O), 172.3 (C@O). This compound was reported in the
literature.12
2.07 (s, 3H, CH3CO), 2.08 (s, 3H, CH3CO), 2.67 (dd, 1H, J = 4.2,
16.2 Hz, Asp-b-CH), 2.94 (dd, 1H, J = 4.2, 16.2 Hz, Asp-b-CH),
3.72–3.75 (m, 1H, H-5), 4.06 (dd, 1H, J = 1.8, 12.0 Hz, H-60), 4.08–
4.13 (m, 1H, H-2), 4.31 (dd, 1H, J = 4.2, 12.0 Hz, H-6), 4.56–4.57
(m, 1H, Asp-
a-CH), 5.01–5.04 (t, 2H, J = 8.4 Hz, H-1, H-4), 5.12–
5.20 (m, 3H, H-3, OCH2Ph), 5.55 (d, 1H, J = 8.4 Hz, Asp-
a-NH),
5.96 (d, 1H, J = 7.8 Hz, NHAcC-2), 7.04 (d, 1H, J = 8.4 Hz, NHAcC-1),
7.33–7.37 (m, 5H, aromatic); 13C NMR (150 MHz, CDCl3): 20.8
(CH3CO), 20.9 (CH3CO), 20.9 (CH3CO), 23.3 (CH3CO), 28.5
(C(CH3)3), 38.4 (Asp-b-CH2), 50.3 (Asp-a-CH), 53.6, 61.9, 67.6,
67.7, 73.0, 73.8, 80.3, 80.5 (C-1), 128.4, 128.5, 128.7, 135.5, 155.7
(C@O), 169.5 (C@O), 170.9 (C@O), 170.9 (C@O), 171.3 (C@O),
172.2 (C@O), 172.4 (C@O); mass spectrum (ESI-MS): m/z = 674.3
[M+Na]+ (C30H41N3Na O13 requires 674.3). The 1H NMR and 13C
NMR were identical to the reported compound.12
1.3.2. N-(2-Acetamido-3,4,6-tri-O-acetyl-2-deoxy-b-D-
glucopyranosyl)benzamide (10)
Acknowledgments
Glucosylsulfonamide 6 (0.030 g, 0.052 mmol) was converted to
10 (0.020 g, 0.044 mmol) as an amorphous off white cotton-like so-
lid, following the general procedure described earlier with a reac-
tion time of 30 min. The crude product was purified by silica gel
flash column chromatography (6 ꢀ 3 cm) using MeOH–CHCl3
(1:19): yield 85%; Rf = 0.62 (1:9 MeOH/CHCl3); 1H NMR
(600 MHz, CDCl3): d 1.92 (s, 3H, CH3CO), 2.07 (s, 3H, CH3CO),
2.09 (s, 3H, CH3CO), 2.11 (s, 3H, CH3CO), 3.86 (m, 1H, H-5), 4.12
(dd, 1H, J = 1.8, 12.0 Hz, H-6), 4.28 (dd, 1H, J = 10.2, 18.6 Hz, H-2),
4.35 (dd, 1H, J = 4.2, 12.6 Hz, H-60), 5.14 (t, 1H, J = 9.6 Hz, H-3),
5.20 (t, 1H, J = 9.6 Hz, H-4), 5.28 (dd, 1H, J = 8.4, 9.6 Hz, H-1), 6.18
(d, 1H, J = 7.8 Hz, NHAc), 7.44 (t, 2H, J = 7.2 Hz, aromatic), 7.52 (t,
1H, J = 7.2 Hz, aromatic), 7.82 (d, 2H, J = 7.8 Hz, aromatic), 7.84
(d, 1 H, J = 8.4 Hz, NHCOPh); 13C NMR (100 MHz, CDCl3): d 20.9
(CH3CO), 21.0 (CH3CO), 23.4 (CH3CO), 29.9 (CH3CO), 53.8 (C-2),
61.9 (C-6), 67.8, 73.2, 73.7, 81.4 (C-1), 127.6, 128.9, 132.5, 132.9,
167.7 (C@O), 169.5 (C@O), 170.9 (C@O), 172.4 (C@O), 172.6
(C@O); mass spectrum (HRMS): m/z = 473.1545 [M+Na]+
(C21H26N2NaO9 requires 473.1536). This compound was reported
in the literature.12
This work was supported in part by grants from The University
of Toledo deArce Memorial Endowment Fund, Elsa U. Pardee Foun-
dation, and The Ohio Cancer Research Associates.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.carres.2009.07.002.
References
1. Fukuyama, T.; Cheung, M.; Jow, C.-K.; Hidai, Y.; Kan, T. Tetrahedron Lett. 1997,
38, 5831–5834.
2. Messeri, T.; Sternbach, D. D.; Tomkinson, N. C. O. Tetrahedron Lett. 1998, 39,
1669–1672.
3. Crich, D.; Sana, K.; Guo, S. Org. Lett. 2007, 9, 4423–4426.
4. Crich, D.; Bowers, A. A. Org. Lett. 2007, 9, 5323–5325.
5. Essentials of Glycobiology; Varki, A., Cumings, R., Esko, J., Freeze, H., Hart, G.,
Marth, J., Eds.; Cold Spring Harbor Laboratory Press: New York, 1999; pp 85–
100.
6. For examples of convergent synthesis of N-linked glycopeptides/proteins see:
(a) Nagorny, P.; Fasching, B.; Li, X.; Chen, G.; Aussedat, B.; Danishefsky, S. J. J.
Am. Chem. Soc. 2009, 131, 5792–5799; (b) Doores, K. J.; Mimura, Y.; Dwek, R. A.;
Rudd, P. M.; Elliot, T.; Davis, B. G. Chem. Commun. 2006, 1401–1403; (c) Cohen-
Anisfeld, S. T.; Lansbury, P. T., Jr. J. Am. Chem. Soc. 1993, 115, 10531–10537.
7. Horton, D. Org. Synth. 1973, 5, 1–4.
8. Bianchi, A.; Bernardi, A. J. Org. Chem. 2006, 71, 4565–4577.
9. Bolton, C. H.; Jeanloz, R. W. J. Org. Chem. 1963, 28, 3228–3230.
10. Vlahov, I. R.; Santhapuram, H. K. R.; Wang, Y.; Kleindl, P. J.; You, F.; Howard, S.
J.; Westrick, E.; Reddy, J. A.; Leamon, C. P. J. Org. Chem. 2007, 72, 5968–5972.
11. He, Y.; Hinklin, R. J.; Chang, J.; Kiessling, L. L. Org. Lett. 2004, 6, 4479–4482.
12. Györgydeák, Z.; Hadady, Z.; Felföldi, N.; Krakomperger, A.; Nagy, V.; Tóth, M.;
Brunyánszki, A.; Docsa, T.; Gergely, P.; Somsák, L. Bioorg. Med. Chem. 2004, 12,
4861–4870.
a
1.3.3. Benzyl N -tert-butoxycarbonyl-N-(2-acetamido-3,4,6-tri-
O-acetyl-2-deoxy-b-D-glucopyranosyl)-L-asparaginate (12)
Glucosylsulfonamide 6 (0.031 g, 0.054 mmol) was converted to
12 (0.024 g, 0.037 mmol) as an amorphous light green solid, fol-
lowing the general procedure described earlier with a reaction
time of 60 min. The crude product was purified by silica gel flash
column chromatography (10 ꢀ 2.5 cm) using hexane–CHCl3–
MeOH–acetone (60:30:5:5): yield 69%; Rf = 0.09 (60:30:5:5,
hexane–CHCl3–MeOH–acetone); 1H NMR (600 MHz, CDCl3):
1.42 (s, 9H, C(CH3)3), 1.95 (s, 3H, CH3CO), 2.05 (s, 3H, CH3CO),
d