Improved synthesis and characterization of 1,3,4,6-tetra-O-acetyl-2-(N-acetylacetamido)-2-deoxy-β-D-glucopyranose

Article abstract of DOI:10.1016/S0008-6215(01)00180-X

A method from the 1960s to synthesize the N,N-diacetyl derivative of peracetylated β-D-glucosamine was improved by assistance of molecular sieves. The melting point of the title compound was revised and the structure determined by means of X-ray diffraction.

Full text of DOI:10.1016/S0008-6215(01)00180-X

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Carbohydrate Research 334 (2001) 337–341
Note
Improved synthesis and characterization of
1,3,4,6-tetra-O-acetyl-2-(N-acetylacetamido)-2-
deoxy-b-
D-glucopyranose
Mona Suihko,* Markku Ahlgre´n, Paula Aulaskari, Juha Rouvinen
Department of Chemistry, Uni6ersity of Joensuu, PO Box 111, FIN-80101 Joensuu, Finland
Received 29 March 2001; accepted 23 June 2001
Abstract
A method from the 1960s to synthesize the N,N-diacetyl derivative of peracetylated b-
D
-glucosamine was improved
by assistance of molecular sieves. The melting point of the title compound was revised and the structure determined
by means of X-ray diffraction. © 2001 Elsevier Science Ltd. All rights reserved.
Keywords: Glucosamine; Peracetylated N-acetylacetamido derivatives; Molecular sieves in acetylation; Crystal structure
the stereocontrol for acetylated b-products.
Hence, it is essential to acetylate the hydroxyl
and amido groups in separate stages. For
N,N-diacetylation, isopropenyl acetate (IPA),
including a trace of p-toluenesulfonic acid
(TsOH) monohydrate as a catalyst, was dis-
covered in the 1960s to be a promising
reagent, especially for synthesizing peracety-
lated 2-acetylacetamido derivatives of gluco-,
manno-, and galactopyranose.4–8 In the
present study, this method was applied start-
ing from 2-acetamido-,3,4,6-tetra-O-acetyl-2-
1. Introduction
Glucosamine is a common constituent of
natural glycoconjugates. Prior to synthetic
glycosylation, the neighboring amino group
and the leaving group must be adapted. For b
linkages, the neighboring N-diacetyl group,
introduced after placement of a methylthio
group at C-1 as a leaving group has given
encouraging results.1 The present study intro-
duces an intermediate for an alternative route
toward this kind of donor.
The methods for acetylation of amines or
amides are traditionally the same as for the
hydroxyl groups, acetic anhydride being one
of the most popular reagents. Nevertheless,
the mutarotation of the sugar, the thermody-
namic stability of the peracetylated a anomer,2
and the anomeric effect3 tend to complicate
deoxy-b-
D
-glucose (1) and compared to the
acetic anhydride method starting from 2-acet-
amido-1,3,4,6-tetra-O-acetyl-2-deoxy-b-
cose (2).
D
-glu-
,
Rauhut and Tseng have found that 3–5 A
molecular sieves are effective adsorbents of
acidic byproducts in a series of amide prepara-
tions.9 In the present N-acetylation study, the
,
effect of 3 A sieves, added to the isopropenyl
* Corresponding author. Fax: +358-13-2513390.
E-mail address: mona.suihko@joensuu.fi (M. Suihko).
acetate solvent, was tested. The N,N-diacetyl
0008-6215/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0008-6215(01)00180-X

338
M. Suihko et al. / Carbohydrate Research 334 (2001) 337–341
9
,
Fletcher, but with the addition of 3 A molec-
ular sieves. The reaction mixture referred to
consists of the starting material and refluxing
isopropenyl acetate as a solvolytic acetylating
reagent, including a trace of the protonic cata-
lyst, p-toluenesulfonic acid (TsOH) monohy-
drate. The addition of the sieves to the
reaction mixture raised the yield of the title
compound 3 from 13 to 32% (entry b) to
76–98% (Table 1).
Scheme 1. Methods used for the acetylation of the acetamido-
or amino group of peracetylated glucosamine. (a) Isopropenyl
acetate, TsOH monohydrate, molecular sieves, 94 °C; (b)
isopropenyl acetate, TsOH monohydrate, 94 °C; (c) Ac2O,
NaOAc, 140 °C.
The method of Bergmann and Zervas for
N-monoacetylation of 2 with refluxing acetic
anhydride and NaOAc during 2 min worked
also for N,N-diacetylation prolonging the re-
action time (Scheme 1, entry c).10 Production
of the monoacetylated compound 1 as one of
the byproducts indicates that the ionic form of
the amino group requires a refluxing period of
more than 1–2 h in order to yield the purely
diacetylated amino product. The reaction con-
ditions and the results of the three procedures
are summarized in Table 2.
Table 1
Influence of the molecular sieves on the yield of the title
compound using isopropenyl acetate as an acetylating reagent
and TsOH monohydrate as a catalyst
Entry Molecular Column eluent
Yield Mp (°C)
(%) a
,
sieves (A)
a
b
3
5:2 CHCl3–Me2CO 98
5:1 CHCl3–Me2CO 32
1:1 C6H6–Et2O 56
111–113 b
c
Ref. 4
84–85 d
When examining the influence of anomeric
orientation on the melting point of peracety-
a From column chromatography, pure according to 1H
NMR.
lated carbohydrates in the
D
-series that the
b Recrystallized from diethyl ether.
c Not recrystallized.
melting point is usually observed to be higher
for the b form.6,11 In this respect, the melting
points for the N-acetylacetamido compounds
published by Inch and Fletcher: 111–112 °C
for the a anomer and 84–85 °C for the b
anomer,4 seem contradictory. In the present
study, a melting point of 111–113 °C was
found for the b anomer, the structure of which
was confirmed by X-ray crystallographic data.
1,3,4,6 - Tetra - O - acetyl - 2 - (N - acetylaceta-
d Recrystallized from diethyl ether–heptane.
derivative 3, which was obtained in nearly
quantitative yield by this method, was charac-
terized by X-ray diffraction in addition to
general spectroscopic methods and melting
point measurement.
2. Results and discussion
mido)-2-deoxy-b- -glucopyranose (3) crystal-
D
lizes in the monoclinic space group P21. The
asymmetric unit contains two independent
molecules, in which the 6-membered sugar
Three procedures were used to synthesize
the N-acetylacetamido derivative of peracety-
lated b-GlcNAc. The best result was obtained
by starting from 1 (Scheme 1, entry a) follow-
ing the method developed by Inch and
4
ring adopts the C1 chair conformation com-
mon for
D
-aldohexopyranoses (Fig. 1). In
both molecules, the corresponding bond
Table 2
Comparison of the methods used for synthesizing the title compound 3
Entry Starting compound Reagents Temperature (°C)/time (h)
Yield of 3 (%)
Other products
a
b
c
1
1
2
IPA, TsOH·H2O, MS
IPA, TsOH·H2O
Ac2O, NaOAc
94/12
94/12
140/1
98
32
43
4, 5 (traces)
4, 5
1, 4, 5
IPA, isopropenyl acetate; TsOH, p-toluenesulfonic acid; MS, molecular sieves.

M. Suihko et al. / Carbohydrate Research 334 (2001) 337–341
339
The yield-enhancing effect of the sieves is
presumably based on their ability to absorb
the eliminating amino proton during the reac-
tion. Absence of the sieves facilitates depar-
ture of the anomeric acetyl group, giving rise
to the byproducts 4 and 5 (3,4,6-tri-O-acetyl-
2-(N-acetylacetamido)-1,5-anhydro-2-deoxy-
D
-arabino-hex-1-enitol).
In conclusion, it can be stated that molecu-
lar sieves are useful IPA, preventing the for-
mation of byproducts in N-acetylation of
peracetylated GlcNAc. In the acetic anhydride
method starting from the ionic amine hydro-
chloride, a prolonged reaction time is recom-
mended. Keeping the temperature high is a
requirement for stereocontrol of the b product
in both of the methods.
Fig. 1. Crystal structure of the compound 3.
lengths are equal and quite comparable to
3. Experimental
those found in 1,3,4,6-tetra-O-acetyl-2-
(N - acetylacetamido) - 2 - deoxy - b - - galacto-
D
General methods.—All solvents were freshly
distilled and the starting compounds were
dried in vacuo prior to use. Silica gel 60
70–230 mesh was used for column chro-
matography. Melting points were measured
on a GWB Gallenkamp melting-point appara-
tus and are uncorrected. TLC was performed
on SiO2 60 F254 and plates were sprayed with
10% H2SO4 in EtOH. Specific rotations were
measured on a JASCO DIP-1000 digital po-
larimeter. Infrared spectra were obtained on a
Nicolet Avatar 320 FT-IR spectrometer.
NMR spectra were produced by a Bruker
Avance 250 MHz spectrometer. Chemical
shifts are reported in l (ppm) with reference
pyranose.12 The bonding of the additional N-
1
acetyl group is evident in the H NMR spec-
trum of 3 by the downfield shift of the H-1
doublet 6.55 ppm and by two singlets at 2.39
and 2.36 ppm. The large coupling constant of
the H-1 doublet, 8.2 Hz, indicates retention of
the b-anomeric orientation.
Observation of the elimination product 5 as
a component of every product mixture sup-
ports the observation made by Fletcher’s
group, that 2-acetylamido-pyranoses with the
trans arrangement at C-1 and C-2 have the
tendency to undergo 1,2-elimination.6,8 They
found that prolonging the N-acetylation time
of peracetylated b-GalNAc using isopropenyl
acetate favored formation of the elimination
product (lyxo derivative) at the cost of the
b-anomeric N,N-diacetyl product, whose yield
was best after 1 h of refluxing.6 In the present
to internal CHCl3 (1H NMR: 7.27, C NMR:
13
77.0 ppm) and coupling constants are in Hz.
Mass spectra were obtained on a MALDI-
TOF Proflex mass spectrometer (Bruker Dal-
tonics, Billerica, MA, USA). Elemental
analyses were obtained on an EA 1110
CHNS-O (CE Instruments). Crystal data were
obtained by means of a Nonius Kappa-CCD
diffractometer using Mo Ka radiation (u=
1
study, H NMR monitoring of the reaction of
the peracetylated b-GlcNAc in isopropenyl
acetate after 1 h of refluxing showed that half
of the starting compound 1 was cleanly con-
verted into the title compound 3. This finding
suggests that as little as a few hours of reflux-
ing is sufficient for satisfactory results. Never-
theless, as evidenced by the yield of 98% after
12 h of refluxing, the prolonged reaction time
,
0.71073 A). DENZO and SCALEPACK programs
were used for cell refinement and data reduc-
tion.13 The structure was solved by direct-
methods
with
SHELXS97.14
Structure
refinement was carried out with SHELXL97.15
All hydrogen atoms were placed in idealized
positions.
,
did no harm in the presence of 3 A molecular
sieves.

340
M. Suihko et al. / Carbohydrate Research 334 (2001) 337–341
OAc), 2.089 (s, 3 H, OAc), 2.01 (s, 3 H, OAc);
1,3,4,6-Tetra-O-acetyl-2-(N-acetylaceta-
mido)-2-deoxy-i- -glucopyranose (3) from 1-
D
13C NMR (CDCl3), characteristic peaks: l
147.5 (d, J 189.9, C-1), 112.8 (s, C-2), 77.2 (d,
J 210.8, C-3); MS: Calcd for C16H21NO9 [M+
H] 372.13. Found m/z 372.64.
acetamido-1,3,4,6-tetra-O-acetyl-2-deoxy-i- -
D
glucose (1).—(a) A solution of 111 (210 mg,
0.54 mmol) in isopropenyl acetate (8 mL,
71.91 mmol) containing TsOH monohydrate
From 1,3,4,6-tetra-O-acetyl-2-amino-2-de-
,
(0.8 mg, 0.004 mmol) and 3 A molecular
oxy- -glucose hydrochloride (2). (c) Com-
D
pound 210 (3.45 g, 8.99 mmol) was added to a
refluxing suspension of Ac2O (36 mL, 381
mmol) and NaOAc (1.12 g, 13.7 mmol) and
boiled for 1 h. The mixture was concentrated
and poured into ice–water to produce 3 (0.81
g, 23%) as a white precipitate. An additional
fraction (0.70 g, 43% total yield) of the
product was obtained by extracting the water
filtrate with CHCl3, water and brine, and
chromatographed as in (a). Byproducts
proved to be 5, 4, and 1 (in order of elution).
Crystallographic summary.—C18H25NO11,
Mr =431.39, monoclinic, P21, Z=4, a=
sieves (38 mg) was boiled under reflux for 12
h. The sieves were removed and the mixture
was concentrated in vacuo and chro-
matographed (5:2 CHCl3–Me2CO) to remove
the catalyst, giving foamy 3 (225 mg, 98%),
1
which was pure according to H NMR. Re-
crystallization (Et2O) yielded colorless crys-
tals; mp 111–113 °C (the structure confirmed
by X-ray crystallographic data), lit. 84-85 °C
for the b anomer, 111–112 °C for the a
anomer;4 [h]D20 +8.90° (c 2.06, CHCl3), lit.
+9°;4 Rf 0.62 (5:2 CHCl3–Me2CO); IR (KBr):
w 1756 (OAc), 1719 and 1691 cm−1 (NAc2),
lit. 1770, 1755 and 1720 cm−1 (Nujol);4 1H
NMR (CDCl3): l 6.55 (d, 1 H, J1,2 8.2, H-1),
5.91 (dd, 1 H, J2,3 9.5, J3,4 9.0, H-3), 5.14 (dd,
1 H, J4,5 9.5, H-4), 4.39 (dd, 1 H, J5,6a 4.4,
J6a,6b 12.5, H-6a), 4.09 (dd, 1 H, J5,6b 1.8,
H-6b), 3.97 (m, 1 H, H-5), 3.90 (dd, 1 H,
H-2), 2.39, 2.36 (2s, 6 H, NAc2), 2.11 (2s, 6 H,
OAc2), 2.05, 2.02 (s, 6 H, OAc2), lit. similar
,
8.2286(1), b=13.2314(2), c=19.4224(3) A,
i=94.159(1)°, V=2109.06(5) A3, Dcalcd
=
,
3
1.359 g/cm , Mo Ka radiation, u=0.71073 A,
v=0.11 mm−1, F(000)=912, T=150 K,
conventional R(F)=0.0281 for 8321 observed
reflections [Fo ]4|(Fo)], wR(F2)=0.0661 for
all 8898 unique data, goodness-of-fit=1.056,
largest difference peak/hole=0.201/−0.163
e/A3.
peaks;4,16 13C NMR (CDCl3):
l
173.9,
173.1(2×s NCOCH3), 170.1, 169.3, 169.2,
167.8 (4×s, OCOCH3), 90.4 (d, J 176.5, C-1),
71.9 (d, J 144.2, C-3), 69.9 (d, J 156.4, C-4),
68.3 (d, J 151.6, C-5), 61.1 (t, J 149.1, C-6),
60.6 (d, J 138.2, C-2), 27.3, 24.6 (dq, J 129.9,
NCOCH3), 20.4, 20.4, 20.2, 20.1 (qq, J 130.3
OCOCH3); MS: Calcd for C18H25NO11 [M+
Na] 454.13. Found m/z 454.14. Anal. Calcd C,
50.12; H, 5.84; N, 3.25. Found C, 50.13; H,
4. Supplementary material
Full crystallographic details, excluding
structure features, have been deposited with
the Cambridge Crystallographic Data Centre,
CCDC No. 160409. Copies of this informa-
tion can be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK (Fax: +44-1223-336033; e-
mail: deposit@ccdc.cam.ac.uk or www: http://
www.rsc.org/suppdata/).
1
5.90; N, 3.22. H NMR of the crude product
showed traces of 4 and 5.
(b) The synthesis was carried out from com-
pound 1 (100 mg, 0.26 mmol) as in (a) but
without the use of molecular sieves. The elu-
ent for the chromatography was 5:1 CHCl3–
Me2CO. The method gave 3 (35 mg, 32%) and
compounds 4 and 5 as byproducts; for 5 Rf
References
1
0.55 (5:2 CHCl3–Me2CO); H NMR (CDCl3):
1. Castro-Palomino, J. C.; Schmidt, R. R. Tetrahedron Lett.
1995, 36/38, 6871–6874.
2. Vogel Vogel’s Textbook of Practical Organic Chemistry,
4th ed.; Longman: London, 1978; pp. 447–453.
3. Ellervik, U.; Magnusson, G. J. Am. Chem. Soc. 1994,
116, 2340–2347.
l 6.60 (s, 1 H, H-1), 5.57 (d, 1 H, J3,4 5.1,
H-3), 5.26 (dd, 1 H, J4,5 6.3, H-4), 4.49 (m, 2
H, H-5, H-6a), 4.18 (d, 1 H, J6a,6b 9.0, H-6b),
2.36, 2.33 (2s, 6 H, NAc2), 2.092 (s, 3 H,

M. Suihko et al. / Carbohydrate Research 334 (2001) 337–341
341
4. Inch, T. D.; Fletcher, Jr., H. G. J. Org. Chem. 1966, 31,
1815–1820.
5. Pravdic´, N.; Franjic´-Mihalic´, I.; Danilov, B. Carbohydr.
Res. 1975, 45, 302–306.
6. Pravdic´, N.; Fletcher, Jr., H. G. Croat. Chem. Acta 1969,
41, 125–133.
11. Jones, J. K. N.; Perry, M. B.; Shelton, B.; Walton, D. J.
Can. J Chem. 1961, 39, 1005–1016.
&
12. Ruzˇic-Torosˇ, Z.; Kojic´-Prodic´, B.; Rogic´, V. Acta Crys-
tallogr., Sect. B 1980, 36, 284–388.
13. Otwinowski, Z.; Minor, W. Methods Enzymol. 1997, 276,
307–326.
7. Pravdic´, N.; Fletcher, Jr., H. G. J. Org. Chem. 1967, 32,
1806–1810.
8. Pravdic´, N.; Fletcher, Jr., H. G. J. Org. Chem. 1967, 32,
1811–1814.
9. Rauhut, M. M.; Tseng, S. S. US Patent 4288 592, 1981;
Chem. Abstr. 1981, 95, 202719p.
14. Sheldrick, G. M. SHELXS97: Program for Crystal Struc-
ture Determination; University of Go¨ttingen: Go¨ttingen,
Germany, 1997.
15. Sheldrick, G. M. SHELXL97: Program for Crystal Struc-
ture Refinement, University of Go¨ttingen: Go¨ttingen,
Germany, 1997.
10. Bergmann, M.; Zervas, L. Chem. Ber. 1931, 64, 975–
980.
16. Inch, T. D.; Plimmer, J. R.; Fletcher, Jr., H. G. J. Org.
Chem. 1966, 31, 1825–1829.
.