2,3,4,6-tetra- O -acetyl-D-gluconic acid: Crystal structure and application in the synthesis of N -(D-gluconyl) derivatives of D-glucosamine

Article abstract of DOI:10.1080/07328303.2013.872790

2,3,4,6-tetra-O-Acetyl-D-gluconic acid was synthesized and coupled with 1,3,4, 6-tetra-O-acetyl-2-amino-2-deoxy-β-D-glucopyranose and diosgenyl 3,4,6-tri-O-acetyl-2-amino-2-deoxy-β-D-glucopyranoside to afford N-gluconyl derivatives of diosgenyl 2-amino-2-deoxy-D-glucopyranoside using the methods of solution-phase peptide synthesis. Both coupling reactions suffered from acetyl O→N migration, which caused the N-acetyl derivatives to be formed together with the N-(D-gluconyl) derivatives of D-glucosamine. Additionally, single-crystal X-ray diffraction and high-resolution NMR spectral data for 2,3,4,6-tetra-O-acetyl-D-gluconic acid were analyzed to reveal that this acyclic carbohydrate has adopted the ₂G^- conformation instead of a typical zigzag conformation. The planarity and cis geometry of the acetoxyl groups are demonstrated.

Full text of DOI:10.1080/07328303.2013.872790

This article was downloaded by: [York University Libraries]
On: 16 November 2014, At: 14:19
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered
office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Journal of Carbohydrate Chemistry
Publication details, including instructions for authors and
subscription information:
http://www.tandfonline.com/loi/lcar20
2,3,4,6-tetra-O-Acetyl-D-Gluconic Acid:
Crystal Structure and Application in the
Synthesis of N-(D-gluconyl) Derivatives of
D-Glucosamine
Monika Norkowska a , Henryk Myszka a , Magdalena Cyman a , Daria
Grzywacz a , Damian Trzybiński a , Artur Sikorski a & Beata Liberek a
a Faculty of Chemistry, University of Gdańsk, Wita Stwosza 63,
PL-80-308 Gdańsk , Poland
Published online: 24 Feb 2014.
To cite this article: Monika Norkowska , Henryk Myszka , Magdalena Cyman , Daria Grzywacz , Damian
Trzybiński , Artur Sikorski & Beata Liberek (2014) 2,3,4,6-tetra-O-Acetyl-D-Gluconic Acid: Crystal
Structure and Application in the Synthesis of N-(D-gluconyl) Derivatives of D-Glucosamine, Journal of
Carbohydrate Chemistry, 33:1, 33-47, DOI: 10.1080/07328303.2013.872790
To link to this article: http://dx.doi.org/10.1080/07328303.2013.872790
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the
“Content”) contained in the publications on our platform. However, Taylor & Francis,
our agents, and our licensors make no representations or warranties whatsoever as to
the accuracy, completeness, or suitability for any purpose of the Content. Any opinions
and views expressed in this publication are the opinions and views of the authors,
and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content
should not be relied upon and should be independently verified with primary sources
of information. Taylor and Francis shall not be liable for any losses, actions, claims,
proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or
howsoever caused arising directly or indirectly in connection with, in relation to or arising
out of the use of the Content.
This article may be used for research, teaching, and private study purposes. Any
substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,
systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &
Conditions of access and use can be found at http://www.tandfonline.com/page/terms-
and-conditions

Journal of Carbohydrate Chemistry, 33:33–47, 2014
ꢀ
C
Copyright Taylor & Francis Group, LLC
ISSN: 0732-8303 print / 1532-2327 online
DOI: 10.1080/07328303.2013.872790
2,3,4,6-tetra-O-Acetyl-D-
Gluconic Acid: Crystal
Structure and Application in
the Synthesis of N-(D-gluconyl)
Derivatives of D-Glucosamine
Monika Norkowska, Henryk Myszka, Magdalena Cyman, Daria
Grzywacz, Damian Trzybin´ski, Artur Sikorski, and Beata Liberek
Faculty of Chemistry, University of Gdan´sk, Wita Stwosza 63, PL-80-308 Gdan´sk,
Poland
2,3,4,6-tetra-O-Acetyl-D-gluconic acid was synthesized and coupled with 1,3,4,
6-tetra-O-acetyl-2-amino-2-deoxy-β-D-glucopyranose and diosgenyl 3,4,6-tri-O-acetyl-
2-amino-2-deoxy-β-D-glucopyranoside to afford N-gluconyl derivatives of diosgenyl
2-amino-2-deoxy-D-glucopyranoside using the methods of solution-phase peptide syn-
thesis. Both coupling reactions suffered from acetyl O→N migration, which caused
the N-acetyl derivatives to be formed together with the N-(D-gluconyl) derivatives
of D-glucosamine. Additionally, single-crystal X-ray diffraction and high-resolution
NMR spectral data for 2,3,4,6-tetra-O-acetyl-D-gluconic acid were analyzed to reveal
that this acyclic carbohydrate has adopted the 2G− conformation instead of a typi-
cal zigzag conformation. The planarity and cis geometry of the acetoxyl groups are
demonstrated.
Keywords D-Glucosamine; D-Gluconic acid; X-ray critical structure; Conformation;
Mesomeric effect
INTRODUCTION
Our research is aimed to synthesize and study N-substituted derivatives
of diosgenyl 2-amino-2-deoxy-β-D-glucopyranoside 2, a synthetic steroid
saponin. Naturally occurring diosgenyl glycosides are widely distributed in
plants and marine organisms.[1–3] The biological activities of these glycosides
Received September 24, 2013; accepted December 3, 2013.
Address correspondence to Beata Liberek, Faculty of Chemistry, University of Gdan´sk,
Wita Stwosza 63, PL-80-308 Gdan´sk, Poland. E-mail: beata.liberek@ug.edu.pl
33

M. Norkowska et al.
34
are manifold: anti-inflammatory, antibacterial, antiparasitic, antifungal, and
antitumor,[4,5,6,7] making them attractive targets for synthetic and biological
studies. For example, a number of synthetic analogs of diosgenyl glycosides
have recently been synthesized and subjected to SAR studies.[8,9]
As we have demonstrated previously, diosgenyl 2-amino-2-deoxy-β-D-
glucopyranoside 2 showed promising antitumor and antimicrobial activi-
ties.[10,11] Unfortunately, its solubility in water is relatively poor. The presence
of a free amino group in 2 provides the opportunity for further derivatization
12
]
to discover new analogs with improved solubility and cytotoxic activity.[ For
this purpose, the N-gluconyl analog of 2 and related structures were designed
and synthesized.
Here, the synthesis of N-gluconyl derivatives of 2-amino-2-deoxy-D-
glucopyranose and its diosgenyl glycoside is presented. Coupling of 2-amino-
2-deoxy-D-glucopyranose and its diosgenyl glycoside with D-gluconic acid
required the acetylated forms of all the substrates. Therefore, 2,3,4,6-tetra-
O-acetyl-D-gluconic acid was synthesized. In the second part of this ar-
ticle, the crystal structure of 2,3,4,6-tetra-O-acetyl-D-gluconic acid is pre-
sented. Crystal data enabled us to disclose the conformation of the D-gluconic
acid chain, orientation of the acetoxyl groups, and intra- and intermolecu-
lar interactions in the crystal lattice of 2,3,4,6-tetra-O-acetyl-D-gluconic acid
monohydrate.
RESULTS AND DISCUSSION
Syntheses
1,3,4,6-tetra-O-Acetyl-D-glucosamine hydrochloride 1,[10] diosgenyl 2-
amino-2-deoxy-β-D-gluco-pyranoside 2,[10] or its per-O-acetylated analog 4 was
used to couple with sodium D-gluconate 5, D-gluconic acid 6, or its 2,3,4,6-
tetra-O-acetyl derivative 7 by the method of solution-phase peptide synthesis
(Sch. 1). Even though coupling of 1,3,4,6-tetra-O-acetyl-D-glucosamine
hydrochloride 1 with sodium L-lactate in the presence of dicyclohexylcar-
bodiimide (DCC) and 1-hydroxybenzotriazole (HOBt) proceeded smoothly
(unpublished data), the analogous reaction of 1 with commercially available
sodium D-gluconate 5 failed to proceed efficiently. Similarly, the coupling
of diosgenyl 2-amino-2-deoxy-D-gluco-pyranoside 2 with D-gluconic acid 6,
prepared from 5 upon treatment with Dowex H+, in the presence of diiso-
propylcarbodiimide (DIC) and HOBt was unsuccessful. We therefore decided
to use the acetylated form of D-gluconic acid 7.
It is known that direct acetylation of D-gluconic acid 6 yields a com-
plicated mixture of products. Thus, we employed the procedure where D-
glucono-δ-lactone was acetylated to give 2,3,4,6-tetra-O-acetyl-D-gluconic acid

2,3,4,6-tetra-O-Acetyl-D-gluconic acid
35
13
7 monohydrate.[ ] Coupling of 1,3,4,6-tetra-O-acetyl-D-glucosamine hydrochlo-
ride 1 with 2,3,4,6-tetra-O-acetyl-D-gluconic acid 7 in presence of DCC, HOBt,
and Et3N was successful, which led to two products: 1,3,4,6-tetra-O-acetyl-
N-(2ꢁ,3ꢁ,4ꢁ,6ꢁ-tetra-O-acetyl-D-gluconyl)-2-amino-2-deoxy-β-D-glucopyranose 8
(28%) and 1,3,4,6-tetra-O-acetyl-2-acetamido-2-deoxy-β-D-glucopyranose 9
(42%). The latter was formed from acetyl O→N migration. Coupling of 1,3,4,6-
tetra-O-acetyl-D-glucosamine hydrochloride 1 with 2,3,4,6-tetra-O-acetyl-D-
gluconic acid 7 was also conducted in the presence of DIC and HOBt, giving
the same products 8 and 9 with similar yields. Complete O-deacetylation of 8
with sodium methylate gave 2-amino-2-deoxy-N-(D-gluconyl)-D-glucopyranose
1
10 (85%) as a mixture of α and β anomers (α:β = 1.2:1.0), as identified by H
NMR.
Scheme 1: Coupling of 2-amino-2-deoxy-D-glucopyranose derivatives with 2,3,4,6-tetra-O-
D-gluconic acid.
An attempt was also made to couple 2,3,4,6-tetra-O-acetyl-D-gluconic
acid 7 with diosgenyl 2-amino-2-deoxy-D-gluco-pyranoside 2 in the pres-
ence of DIC and HOBt. Unfortunately, no desired reaction was observed.
Therefore, we synthesized diosgenyl 3,4,6-tri-O-acetyl-2-amino-2-deoxy-D-
gluco-pyranoside 4, which was less hydrophilic than 2, from the previ-
ously reported diosgenyl 3,4,6-tri-O-acetyl-2-deoxy-2-(2,2,2-trichloro-ethoxy-
14
]
carbonyl-amino)–β-D-gluco-pyranoside (3).[ Coupling of 4 with 7 in the
presence of DIC and HOBt yielded diosgenyl 3,4,6-tri-O-acetyl-N-(2ꢁ,3ꢁ,4ꢁ,6ꢁ-
tetra-O-acetyl-D-gluconyl)-2-amino-2-deoxy-β-D-glucopyranoside 11 (17%), as
well as diosgenyl 3,4,6-tri-O-acetyl-2-acetamido-2-deoxy-β-D-glucopyranoside
12 (34%). The result again demonstrated that the use of acetylated D-
glucosamine and D-gluconic acid derivatives caused acetyl O→N migration to
occur.

M. Norkowska et al.
36
Table 1: Crystal data and structure refinement for 7 monohydrate
Empirical formula
Formula weight
Temperature (K)
C14H20O11·H2O
382.32
295(2)
Wavelength (Å)
0.71073
Monoclinic
P21
Crystal system
Space group
Unit cell dimensions
a (Å)
b (Å)
7.1732(4)
15.2991(8)
c (Å)
8.2095(4)
β (º)
94.976(5)
V (Å3)
Z
897.54(8)
2
Dcalcd (Mg m−3
)
1.415
0.126
Absorption coefficient (mm−1
Absorption correction type
F(000)
)
“multiscan”
404
Crystal size (mm)
ꢀ Range for data collection (a˚ )
Limiting indices
0.40 × 0.15 × 0.05
3.62–25.05
−5 ≤ h ≤ 8, −17 ≤ k ≤ 18, −9 ≤ l ≤ 9
22208 / 3118 [Rint = 0.0269]
99.7
Reflections collected/unique
Completeness 2ꢀ = 25.05a˚ (%)
Refinement method
Full-matrix least-squares on F2
3118 / 4 / 247
1.040
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I>2σ(I)]
R1 = 0.0450
wR2 = 0.1078
R1 = 0.0515
R indices (all data)
wR2 = 0.1153
−0.10(12)
Absolute structure parameter
Extinction coefficient
0.046(5)
Largest diff. peak and hole (a Å−3
)
0.278 and −0.265
The Crystal Structure of 7 Monohydrate
A single crystal of 2,3,4,6-tetra-O-acetyl-D-gluconic acid 7 was obtained
and then subjected to X-ray analysis. The crystallographic data, data collec-
tion, and structure refinement are summarized in Table 1. The coordinates of
atoms and their isotropic temperature factors are set out in Table 2, and selec-
tion of the crystal’s important geometric parameters is given in Table 3. The
hydrogen bonds and short contacts are summarized in Table 4.
The X-ray crystal structure of 2,3,4,6-tetra-O-acetyl-D-gluconic acid 7
(Fig. 1) showed that it contained one molecule of water. The occluded water
molecule created three hydrogen bonds (Fig. 2), which stabilized the crystal
structure. These are H-bonds between the water hydrogen and the oxygen of
the sugar 5-OH group, between the water hydrogen and the O7 carbonyl oxy-
gen of the 2-OAc group, and between the water oxygen and the H11 hydrogen of

2,3,4,6-tetra-O-Acetyl-D-gluconic acid
37
Table 2: Atomic coordinates (×104) and equivalent isotropic displacement
parameters (Å2 × 103) for 7 monohydrate
Atom
x
Y
z
Ueq
O-1W
C-1
593(4)
9362(4)
10757(3)
8635(3)
7959(4)
5283(3)
5991(4)
7120(2)
5927(4)
2694(3)
3975(4)
4515(3)
3934(4)
9291(4)
9234(5)
4815(5)
4919(5)
8662(3)
8407(4)
4960(4)
5032(5)
8920(3)
9981(6)
4248(6)
9433(5)
5680(8)
2502(2)
1421(2)
1766(2)
891(1)
3440(3)
9898(3)
9479(2)
7183(2)
8761(3)
10086(2)
8526(3)
8558(2)
7611(3)
6643(2)
7411(3)
4835(2)
6416(3)
6658(3)
7437(3)
10997(4)
10555(3)
6393(3)
7797(3)
4333(3)
3911(4)
11418(2)
5031(4)
12606(4)
8953(4)
2353(5)
78(1)
39(1)
57(1)
44(1)
37(1)
37(1)
34(1)
37(1)
33(1)
47(1)
36(1)
45(1)
43(1)
47(1)
88(1)
48(1)
87(1)
59(1)
41(1)
78(1)
50(1)
54(1)
61(1)
63(1)
61(1)
81(1)
O-1
O-2
C-2
926(2)
O-3
C-3
1503(1)
1331(2)
2799(1)
2192(2)
1986(1)
2602(2)
3213(1)
3426(2)
124(2)
O-4
C-4
O-5
C-5
O-6
C-6
C-7
O-7
C-8
−532(2)
824(2)
O-8
O-9
C-9
84(2)
3167(2)
3259(2)
4622(2)
3878(2)
1408(2)
217(2)
O-10
C-10
O-11
C-11
C-12
C-13
C-14
1108(2)
3866(2)
3571(3)
Ueq is defined as one-third of the trace of the orthogonalized Uij tensor.
the carboxyl group (Table 4). The crystal structure of 2,3,4,6-tetra-O-acetyl-D-
gluconic acid monohydrate was also stabilized by the intermolecular hydrogen
bond between carbonyl O1 and the hydrogen of the 5-OH group. Additionally,
several C H···O contacts consolidated the crystal structure (Table 4).
Most acyclic carbohydrate derivatives in the solid state adopt a conforma-
tion having the carbon atoms in an extended, planar zigzag arrangement, un-
less there are parallel 1,3-steric interactions, written in abbreviated form as
15
]
O//O interactions (Fig. 3).[ The presence of O//O interactions may cause the
carbon chain to twist in such a manner as to give a local gauche relationships
between carbon atoms in their chains; these have been termed sickle conform-
16
]
ers.[ Nomenclature for gauche (sickle) conformations was developed by Hor-
17
]
ton and Wander.[ According to their nomenclature of gauche conformations,
a 2G− conformation is obtained from the planar zigzag conformation by a 120◦
clockwise rotation of the remote atom along the C2-C3 bond (Fig. 3). Analo-
gously, a G+ conformation is obtained from the planar zigzag conformation
2
by a 120◦ counter-clockwise rotation of the remote atom along the C2-C3 bond.

M. Norkowska et al.
38
Table 3: Selected bond lengths (Å), valence angles (◦), and torsion angles (◦) for 7
monohydrate
Bond lengths
(Å)
O-2—C-7
1.348(3)
1.423(3)
1.340(3)
1.442(3)
1.355(3)
1.444(3)
1.426(3)
1.340(4)
1.435(3)
1.193(4)
1.194(4)
1.191(3)
1.193(4)
(◦)
O-2—C-2
O-3—C-8
O-3—C-3
O-4—C-9
O-4—C-4
O-5—C-5
O-6—C-10
O-6—C-6
C-7—O-7
C-8—O-8
C-9—O-9
C-10—O-10
Valence angles
C-7—O-2—C-2
O-2—C-2—C-1
C-8—O-3—C-3
O-3—C-3—C-2
C-9—O-4—C-4
O-4—C-4—C-3
C-10—O-6—C-6
O-7—C-7—O-2
O-8—C-8—O-3
O-9—C-9—O-4
O-10—C-10—O-6
Torsion angles
C-1—C-2—C-3—C-4
C-2—C-3—C-4—C-5
C-3—C-4—C-5—C-6
C-4—C-5—C-6—O-6
C-2—O-2—C-7—O-7
C-3—O-3—C-8—O-8
C-4—O-4—C-9—O-9
C-6—O-6—C-10—O-10
118.7(2)
108.6(2)
118.6(2)
110.7(2)
118.76(19)
107.54(19)
117.1(2)
122.1(3)
122.8(3)
123.6(3)
122.6(3)
(◦)
67.9(3)
−178.8(2)
−176.6(2)
59.5(3)
3.9(5)
−1.8(5)
−3.0(4)
−2.7(5)
Chain twisting generally results in an oxygen atom extending the chain rather
than a hydrogen atom. With reference to the terminal hydroxymethyl group,
all rotamers are observed, but the preferred one has the oxygen atom extend-
ing the chain.[15]
The crystal data of 2,3,4,6-tetra-O-acetyl-D-gluconic acid 7 monohydrate
presented here corroborate the above-mentioned general rules concerning the
conformation of the acyclic carbohydrate derivatives. Clearly, 2,3,4,6-tetra-O-
acetyl-D-gluconic acid 7 adopts the 2G− conformation in order to avoid the 1,3-
parallel interactions between the 2-OAc and 4-OAc groups (Figs. 1 and 3). The
2G− conformation is demonstrated by the C1-C2-C3-C4 torsion angle of 67.9◦
(Table 3). Interestingly, 7 does not twist to replace the O//O interactions by
the O//H interactions (the G+ conformation). Instead, it twists to replace the
2

2,3,4,6-tetra-O-Acetyl-D-gluconic acid
39
Table 4: Hydrogen bonds and short contacts (∗) for 7 monohydrate with distances
. . .
. . .
(d): d(D A) < R(D) + R(A) + 0.50Å; d(H A) < R(H) + R(A) − 0.12 Å, and angle (<)
<D-H A > 100.0◦
. . .
. . .
d(H A)
. . .
. . .
<D—H A
D—H
A
D(D-H)
d(D
A
O-1W—H-1W
O-1W—H-2W
O-5—H-5
O-7a
O-5
0.84(3)
0.84(3)
0.82
2.32(3)
2.20(3)
2.06
3.097(4)
3.020(3)
2.833(3)
2.579(3)
2.678(4)
3.024(4)
2.825(3)
2.874(3)
2.723(4)
3.514(4)
3.326(5)
153(5)
165(5)
157
O-1b
O-1Wc
O-7
O-11—H-11
0.82
1.78
166
∗C-2—H-2
0.98
2.23
106
∗C-2—H-2
O-8
0.98
2.50
113
∗C-4—H-4
O-2
0.98
2.49
100
∗C-4—H-4
O-6
0.98
2.51
102
∗C-4—H-4
O-9
0.98
2.31
105
C-11—H-11B
C-14—H-14A
O-9iv
O-8i
0.96
2.57
167
0.96
2.47
148
Symmetry codes: a –x + 1, y + 1/2, –z + 1; b x – 1, y, z; c x + 1, y, z + 1, z; (iv) –x + 2, y – 1/2, –z + 1.
O//O interactions by the C//O interactions (the G− conformation). It may be
2
due to the fact that 1,3-diaxial interactions in the case of the planar carboxyl
group are not as strong as in the case of the other groups (e.g., hydroxymethyl
18
]
group).[
Figure 1: Structure of 7 monohydrate showing 25% probability displacements for ellipsoids.

M. Norkowska et al.
40
Figure 2: Molecular packing of 7 monohydrate (view along c-axis).
Contrary to the presented results, Ko¨ll et al. demonstrated that 1,3-
parallel O//O arrangements in planar zigzag chains of 2,3,4,5,6-penta-O-acetyl-
19
D-gluconic acid and its ester derivatives are tolerated.[ ] This means that steric
1,3-parallel interactions between 2-OAc and 4-OAc are not very strong and
other factors (e.g., crystal packing or intermolecular hydrogen bonds) can eas-
ily change the conformational preferences of aldonic acids. Importantly, our
-
the G conformation
2
+
the
HO
G
conformation
the zigzag conformation
H
2
(adopted in the crystal)
a)
H
H
HO
H
HO
H
H
OAc
OAc
OAc
O
1C-OH
AcO
6
2
C
H
6
C
2
C
AcO
6
C
2
C
C
4
C
C
C
4
C
C
3
C
4
C
OAc
H
5
3
5
5
3
C
C
1
AcO 1C-OH
O
H
H
AcO
H
H
H
OAc
OAc
H
AcO
H
H
H
OAc C-OH
O
H
O//O 1,3-parallel interactions
C1
O//H 1,3-parallel interactions
OAc
C//O 1,3-parallel interactions
H
H
H
H
OAc
OAc
OAc
C1
o
120
o
120
b)
C2
C4
C2
C4
C2
C4
C1
H
AcO
H
OAc
Figure 3: (a) Considered conformations of 2,3,4,6-tetra-O-acetyl-D-gluconic acid 7. (b)
Newman projections along the C2-C3 bond showing the interconversion of the zigzag
conformation into the 2G− and 2G+ conformations.

2,3,4,6-tetra-O-Acetyl-D-gluconic acid
41
data are in accordance with Ko¨ll’s statement that gluconic acid derivatives
are prone to adopt the zigzag conformation in the solid state unless these are
monohydrates. It seems that to be in the form of monohydrate, D-gluconic
acid derivative needs at least one unprotected hydroxyl group. Such kind of
group is present in 2,3,4,6-tetra-O-acetyl-D-gluconic acid 7 (5-OH). Typically,
D-gluconic acid derivatives, found in the crystals in a sickle conformation, in
almost all cases have unprotected hydroxy groups.[19]
With reference to the C5-C6 bond rotations, 2,3,4,6-tetra-O-acetyl-D-
gluconic acid 7 adopts the conformation with the hydrogen atom instead of
the O6 oxygen atom extending the chain. This is demonstrated by the C4-C5-
C6-O6 torsion angle of 59.5◦ (Table 3). Thus, the carbon zigzag chain of the
presented gluconic acid from both sides is extended by the hydrogen atoms,
not by the respective oxygen atoms. In this way, the molecule is probably bet-
ter packed in the crystal.
20
]
In our previous crystallographic[ and theoretical studies,[18,21] we have
consistently demonstrated that the acetoxyl groups were planar starting from
the respective pyranose carbon atom. Here, we have been able to demonstrate
that the acetoxyl groups are also planar in acyclic compounds. The planarity
of the acetoxyl group is required due to the mesomeric effect, which causes
the delocalization of the noncarbonyl oxygen lone pair of electrons onto the
carbonyl oxygen atom. Such delocalization stabilizes the compound and in-
creases the CO-O rotational barrier. On the other hand, the mesomeric ef-
fect requires the noncarbonyl oxygen atom to be sp2 hybridized. Indeed, in
2,3,4,6-tetra-O-acetyl-D-gluconic acid 7 monohydrate, the respective C7-O2-
C2, C8-O3-C3, C9-O4-C4, and C10-O6-C6 valence angles of 118.7◦, 118.6◦,
118.76◦, and 117.1◦ (Table 3) are better suited to sp2 than to sp3 hybridiza-
tion of the noncarbonyl oxygen atoms. Comparison of the O-C (carbonyl) and
O-C (noncarbonyl) bond lengths additionally points to the action of the me-
someric effect. The former bonds (O2-C7, O3-C8, O4-C9, and O6-C10, Ta-
ble 3) are shorter than the latter bonds (O2-C2, O3-C3, O4-C4, and O6-C6,
˚
Table 3) by 0.075–0.102 A.
Being planar, the acetoxyl group may adopt two orientations with regard
to the Ac-O bond rotation, in which the carbonyl oxygen is oriented trans
or cis to the respective sugar carbon atom (Fig. 4). Our studies of peracety-
lated glycals using DFT calculations have indicated that the trans orientation
of the acetoxyl group is unfavorable, due to both electronic and steric inter-
actions.[18] This work has demonstrated that in acyclic compounds, too, the
acetoxyl group prefers the cis over the trans orientation. Thus, the C2-O2-
C7-O7 (3.9◦), C3-O3-C8-O8 (−1.8◦), C4-O4-C9-O9 (−3.0◦), and C6-O6-C10-O10
(−2.7◦) torsion angles (Table 3) confirm that the acetoxy groups are almost pla-
nar and cis oriented in the crystal lattice of 2,3,4,6-tetra-O-acetyl-D-gluconic
acid 7 monohydrate. Besides the previously discussed steric and electronic fac-
tors, X-ray analysis presented here also reveals that the cis orientation of

M. Norkowska et al.
42
Figure 4: Newman projections along the Ac-O bond showing planarity and two possible
conformations of the acetoxy group (R = sugar residue).
the acetoxyl groups enable the carbonyl oxygen atoms to interact preferen-
tially with the chain hydrogen atoms. These intramolecular C-H. . . O interac-
tions, namely, C2-H2. . . O7, C2-H2. . . O8, and C4-H4. . . O9, are illustrated in
Table 4.
To conclude, coupling 2,3,4,6-tetra-O-acetyl-D-gluconic acid 7 with 1,3,4,
6-tetra-O-acetyl-D-glucosamine 1 or diosgenyl 3,4,6-tri-O-acetyl-2-amino-2-
deoxy-β-D-gluco-pyranoside 4 by the methods of solution-phase peptide syn-
thesis was proved to be not very efficient. Not only the desired N-(D-gluconyl)
derivatives but also the N-acetyl derivatives of D-glucosamine as side prod-
ucts were formed, demonstrating that acetyl O→N migration occurred readily
under the condition. The crystal structure of 2,3,4,6-tetra-O-acetyl-D-gluconic
acid 7 mono-hydra-te gave some very interesting results. It was shown that
this acyclic carbohydrate adopted the 2G− conformation instead of the ex-
tended zigzag conformation. In this way, 7 could avoid the 1,3-parallel inter-
actions between 2-OAc and 4-OAc groups. Based on the crystal data, we also
found that the acetoxyl groups in this linear compound are planar starting
from the respective chain carbon. Being planar, the acetoxyl groups adopt the
cis orientation.
EXPERIMENTAL
General Methods
Melting points were uncorrected. IR spectra were recorded as a Nujol mull
1
with a Bruker IFS 66 spectro-pho-to-meter, and the H and 13C NMR spectra
(CDCl3, DMSO or D2O, internal Me4Si) were recorded on a Varian Mercury
400 (400/100 MHz) instrument; positive-ion mode MALDI-TOF mass spectra
were obtained on a Bruker Biflex III spectrometer. Thin-layer chromatography
(TLC) was performed on E. Merck Kieselgel 60 F-254 plates using the following
eluent systems (v/v): A, 1:3 CHCl3-MeOH, or B, 1:6 toluene-AcOEt; and column
chro-ma–tography was performed on MN Kieselgel 60 (<0.08 mm) with the
eluent system B.

2,3,4,6-tetra-O-Acetyl-D-gluconic acid
43
Diosgenyl 3,4,6-tri-O-acetyl-2-amino-2-deoxy-D-gluco-
pyranoside 4
Previously obtained diosgenyl 3,4,6-tri-O-acetyl-2-deoxy-2-(2,2,2-trichloro-
ethoxy-carbonyl-amino)–β-D-gluco-pyranoside 9[14] (373.4 mg, 0.427 mmol)
was dissolved in glacial acetic acid (10 mL), followed by addition of Zn-Cu dust
(3 g). The mixture was stirred at rt and detected by TLC (solvent B). After
24 h, the Zn-Cu dust was filtered off and the filtrate was diluted with CH2Cl2,
washed with saturated NaHCO3, and dried over MgSO4. Concentration under
reduced pressure gave 11 (210.3 mg, 70%, white powder): Rf 0.47 (solvent B);
IR: ν 3392 (N H), 2950, 2905, 2870 (C H), 1749 (ester C O), 1243 cm−1 (ester
C O); MALDI TOF-MS: m/z 702.9 (M)+, 724.7 (M+Na)+, 740.7 (M+K)+.
2,3,4,6-tetra-O-Acetyl-D-gluconic acid 7
Compound 7 (71%) was synthesized according to the literature proce-
dure.[13] Literature mp, 110–113◦C,[13] observed, 113–117◦C; Rf 0.87 (solvent
A); IR: ν 3445 (O H,), 2964 (C H), 1746 (ester C O), 1715 (acid C O),
1
1234 cm−1 (ester C O); H NMR (400 MHz, DMSO): δ 5.59 (dd, J3,4 5.2 Hz,
H3), 5.55 (bd, 1 H, J5,OH = 5.2 Hz, OH), 5.09 (d, 1 H, J2,3 = 3.6 Hz, H2), 5.08
(dd, 1H, J4,5 = 7.2 Hz, H4), 3.93 (d, 2 H, J5,6 = 5.2 Hz, 2 × H6), 3.75 (m, 1
H, H5), 2.07 (s, 3 H, OAc), 2.00 (s, 3 H, OAc), 1.98 (s, 6 H, 2 × OAc); 13C NMR
(100 MHz, DMSO): δ 170.88 (acid C O), 170.20, 170.14, 169.78, 168.74 (4 × es-
ter C O), 71.86, 71.75 (C2, C4), 69.68 (C3), 67.49 (C5), 65.36 (C6), 21.27, 21.21,
21.00 (4 × ester CH3); MALDI TOF-MS: m/z 365.0 (M+H)+, 387.1 (M+Na)+,
403.1 (M+K)+.
1,3,4,6-tetra-O-Acetyl-N-(2ꢀ,3ꢀ,4ꢀ,6ꢀ-tetra-O-acetyl-D-gluconyl)-2-
amino-2-deoxy-β-D-glucopyranose 8 and 1,3,4,6-tetra-O-
acetyl-2-acetamido-2-deoxy-β-D-glucopyranose 9
1,3,4,6-tetra-O-Acetyl-D-glucosamine hydrochloride 1[10] (301.6 mg,
0.785 mmol) and Et3N (0.109 mL, 0.785 mmol) were dissolved in dry CH2Cl2
(7 mL). Next, 2,3,4,6-tetra-O-acetyl-D-gluconic acid 7 (341.9 mg, 0.942 mmol),
HOBt (106 mg, 0.785 mmol), DCC (161.7 mg, 0.785 mmol), and anhydrous
DMF (3 mL) were added. The mixture was stirred at rt and detected by TLC
(solvent A). After 120 h, the reaction mixture was diluted with CH2Cl2; washed
with water, 1 M aq. HCl, brine, and saturated NaHCO3; and then dried over
MgSO4. Concentration under reduced pressure led to the crude product, which
was chromatographed (solvent B) to yield first 8 (155 mg, 28%, syrup) and then
9 (120.3 mg, 42%, syrup). 8: Rf 0.41 (solvent B); IR: ν 3356, 3469 (O H, N H),
2959, 3023 (C H), 1753 (ester C O), 1538 (amide II), 1225 cm−1 (ester C O);
1H NMR (400 MHz, CDCl3): δ 6.56 (d, 1 H, NH), 5.74 (d, 1 H, J1,2 = 8.8 Hz, H1),
5.61 (dd, 1 H, J3 ,4 = 2.4 Hz, H3ꢁ), 5.20 (t, 1 H, J3,4 = 10.0 Hz, H3), 5.08 (t, 1 H,
ꢁ
ꢁ

M. Norkowska et al.
44
J4,5 = 9.6 Hz, H4), 5.01 (dd, 1 H, J4 ,5 = 8.4 Hz, H4ꢁ), 5.00 (d, 1H, J2 ,3 = 6.8 Hz,
ꢁ
ꢁ
ꢁ
ꢁ
H2ꢁ), 4.27 (q, 1 H, J2,3 = 10.0 Hz, J2,NH = 9.2 Hz, H2), 4.25 (dd, 1 H, J6A,6B
=
12.4 Hz, H6A), 4.11 (dd, 1 H, H6B), 4.09 (d, 2 H, 2 × H6ꢁ), 3.83 (ddd, 1 H,
J5,6A = 2.4, J5,6B = 4.8 Hz, H5), 3.79 (m, 1H, J5 ,OH = 6.0 Hz, H5ꢁ), 3.29
ꢁ
(d, 1H, OH), 2.12–2.01 (8 s, 8 H, 8 × OAc); 13C NMR (100 MHz, CDCl3):
δ 171,67–169.53 (8 × ester C O), 166.92 (amide C O), 92.26 (C1), 73.01
(C5), 72.62 (C3), 72.58 (C2ꢁ), 71.02 (C4ꢁ), 69.57 (C3ꢁ), 68.41 (C5ꢁ), 68.34 (C4),
65.10 (C6ꢁ), 61.96 (C6), 53.06 (C2), 21.07–20.64 (8 × ester CH3); MALDI
TOF-MS: m/z 716.2 (M+Na)+, 732.2 (M+K)+. 9: Rf 0.25 (solvent B); IR: ν 3330
(N H), 2850, 2928 (C H), 1748 (ester C O), 1666 (amide I), 1536 (amide II),
1
1224 cm−1 (ester C O); H NMR (400 MHz, CDCl3): δ 5.69 (d, 1 H, J1,2
=
8.8 Hz, H1), 5.61 (d, 1 H, J2,NH = 9.2 Hz, NH), 5.13 (m, 2 H, J4,5 = 9.6 Hz,
H3, H4), 4.30 (m, 1 H, H2), 4.26 (dd, 1 H, J6A,6B = 12.4, J5,6A = 4.8 Hz, H6A),
4.12 (dd, 1H, J5,6B = 2.4 Hz, H6B), 3.79 (m, 1 H, H5), 2.11 (s, 3 H, OAc), 2.08
(s, 3 H, OAc), 2.04 (s, 3 H, OAc), 2.03 (s, 3 H, OAc), 1.93 (s, 3 H, NAc); MALDI
TOF-MS: m/z 412.1 (M+Na)+, 428.1 (M+K)+.
2-Amino-2-deoxy-N-(D-gluconyl)-D-glucopyranose 10
O-Deacetylation of 8 (30.6 mg, 0.044 mmol) was achieved with 0.1 N Me-
ONa in MeOH (0.442 mL) to give 10 (α:β ∼ 1:1) (13.3 mg, 85%, white powder).
IR: ν 3389, 3307 (O H, N H), 2929 (C H), 1647 (amide I), 1553 cm−1 (amide
II); 1H NMR (400 MHz, D2O): δ 5.17 (d, 1 H, J1,2 = 3.6 Hz, H1α), 4.73 (d, 1 H,
J1,2 = 8.0 Hz, H1β), 4.30 (d, 1 H, J3 ,4 = 4.4 Hz, 2 × H-3ꢁ), 4.05 (bs, 2 H, J2 ,3
=
ꢁ
ꢁ
ꢁ
ꢁ
6.0 Hz, 2 × H2ꢁ), 3.88 (dd, 1 H, J2,3 = 10.0 Hz, H2α), 3.70 (m, 1 H, H2β); MALDI
TOF-MS: m/z 357.2 (M)+, 379.2 [(M-1)+Na)]+.
Diosgenyl 3,4,6-tri-O-acetyl-N-(2ꢀ,3ꢀ,4ꢀ,6ꢀ-tetra-O-acetyl-D-
gluconyl)-2-amino-2-deoxy-β-D-glucopyranoside 11 and
diosgenyl 3,4,6-tri-O-acetyl-2-acetamido-2-deoxy-β-D-
glucopyranoside 12
Diosgenyl
3,4,6-tri-O-acetyl-2-amino-2-deoxy-D-gluco-pyranoside
4
(205.3 mg, 0.293 mmol) was dissolved in dry CH2Cl2 (10 mL). Next, 2,3,4,6-
tetra-O-acetyl-D-gluconic acid 7 (213.3 mg, 0.586 mmol), HOBt (39.6 mg,
0.293 mmol), DIC (0.0456 mL, 0.293 mmol), and anhydrous DMF (1 mL) were
added. The mixture was stirred at rt and detected by TLC (solvent A and
B). After 24 h, the reaction mixture was concentrated and chromatographed
(solvent B) to yield first 11 (44.6 mg, 27%, syrup) and then 12 (39.2 mg, 34%).
11: Rf 0.67 (solvent B); IR: ν 3477, 3351 (O H, N H), 2950, 2872 (C H), 1749
(ester C O), 1687 (amide I), 1538 (amide II), 1227 cm−1 (ester C O). 1H NMR
ꢁ
ꢁ
(400 MHz, CDCl3): δ 6.25 (d, 1 H, J2,NH = 8.4 Hz, NH), 5.69 (dd, 1 H, J3 ,4
=
2.4 Hz, H3ꢁ), 5.38 (dd, 1 H, J3,4, J4,5 = 9.2, 10.4 Hz, H4), 5.28 (d, 1 H, J5 ,OH
=
ꢁ

2,3,4,6-tetra-O-Acetyl-D-gluconic acid
45
3.6 Hz, OH), 5.15 (d, 1 H, J2 ,3 = 7.6 Hz, H2ꢁ), 5.01 (m, 2 H, H3, H4ꢁ), 4.86 (d,
1 H, J1,2 = 8.4 Hz, H1), 4.25 (dd, 1 H, J5,6B = 4.8 Hz, H6B), 4,12 (m, 2 H, 2 ×
H6ꢁ), 4.09 (dd, 1 H, J5,6A = 2.4, J6A,6B = 12.4 Hz, H6A), 3.83 (m, 1 H, H5ꢁ), 3.70
(m, 2 H, H2, H5), 3.14, 2.11–2.00 (7s, 21 H, 7 × OAc); diosgenyl protons: 5.28
ꢁ
ꢁ
ꢁ
(d, J6,7 = 6.0 Hz, H6), 4.40 (q, J = 7.6 Hz, H16), 3.49 (m, H3), 3.46 (dd, J25,26
=
4.0, J26,26 = 10.8 Hz, H26ꢁ), 3.36 (t, J25,26 = 10.8 Hz, H26), 1.00 (s, H19), 0.96
(d, J20,21 = 6.8 Hz, H21), 0.78 (d, J25,27 = 6.4 Hz, H27), 0.77 (s, H18); 13C NMR
(100 MHz, CDCl3): δ 171.36–169.66 (7 × ester C O), 166.70 (amide C O),
98.66 (C1), 72.22 (C2ꢁ), 72.09 (C5), 71.82 (C4), 71.05 (C3), 69.65 (C3ꢁ), 69.24
(C4ꢁ), 68.78 (C5ꢁ), 65.08 (C6ꢁ), 62.51 (C6), 55.78 (C2), 21.05–20.76 (7 × acetyl
CH3); diosgenyl carbons: 140.64 (C5), 122.03 (C6), 109.49 (C22), 81.02 (C16),
79.48 (C3), 67.07 (C26), 62.35 (C17), 56.72 (C14), 50.28 (C9), 41.83–38.72
(C4, C12, C13, C20), 37.35–37.06 (C1, C10), 32.28–31.61 (C7, C8, C15, C23),
30.51–29.03 (C2, C24, C25), 21.83 (C11), 19.53 (C19), 17.33 (C27), 16.46 (C18),
14.70 (C21); MALDI TOF-MS: m/z 1048.4 (M+H)+, 1070.3 (M+Na)+, 1086.4
(M+K)+. 12: Rf 0.59 (solvent B); IR: ν 3415, 3272 (N H), 2939, 2906, 2877
(C H), 1747 (ester C O), 1652 (amide I), 1577 (amide II), 1245 cm−1 (C O);
1H NMR (400 MHz, CDCl3): δ 5.46 (d, 1 H, J2,NH = 8.4 Hz, NH), 5.37 (dd, 1 H,
ꢁ
J4,5 = 10.4 Hz, H4), 5.03 (t, 1 H, J2,3 = J3,4 = 9.6 Hz, H3), 4.84 (d, 1 H, J1,2
=
8.4 Hz, H1), 4.25 (dd, 1 H, J5,6B = 5.2 Hz, H6B), 4.10 (dd, 1H, J5,6A = 2.8,
J6A,6B = 12.0 Hz, H6A), 3.68 (m, 2 H, H-2, H-5), 2.06, 2.02, 2.01 (3 s, 9 H, 3 ×
OAc), 1.95 (s, 3 H, NAc); diosgenyl protons: 5.34 (d, J6,7 = 6.4 Hz, H6), 4.40 (q,
J = 7.6 Hz, H16), 3.50 (m, H3), 3.47 (dd, J25,26 = 4.0, J26,26 = 10.8 Hz, H26ꢁ),
3.37 (t, J25,26 = 10.8 Hz, H26), 1.00 (s, H19), 0.96 (d, J20,21 = 7.2 Hz, H21), 0.79
(d, J25,27 = 5.2 Hz, H27), 0.78 (s, H18); MALDI TOF-MS: m/z 744.2 (M+H)+,
766.3 (M+Na)+, 782.3 (M+K)+.
ꢁ
ꢁ
Description of the Crystal Structure of 2,3,4,6-tetra-O-
Acetyl-D-gluconic Acid 7 Monohydrate
Diffraction data were collected at rt (295 K) on a Gemini R Ultra four circle
diffractometer[22] with MoKα radiation (λ = 0.71073 A). The initial phase angle
˚
determination was performed by the SHELXS-97.[23] The H atoms of the water
molecule were located on a Fourier difference map, restrained by DFIX com-
mand 0.85 for O−H distances and by DFIX 1.39 for H···H distance, and refined
as riding with Uiso(H) = 1.5Ueq(O). All other H atoms were placed geometri-
˚
cally and refined using a riding model with C−H = 0.96-0.98 A, and Uiso(H) =
˚
1.2Ueq(C) (C−H = 0.96 A and Uiso(H) = 1.5Ueq(C) in the case of the methyl H
˚
atoms) and O−H = 0.82 A and Uiso(H) = 1.5Ueq(O).
The crystal structure was refined to R1 = 0.0515 (5721 reflections) and
R1 = 0.0450 (3118 reflections with F > 2σ(F0)) by full-matrix least-squares
24
method using the SHELXL-97 program[ ] based on 247 parameters. The com-
pound structure showing the conformations and atom numbering system is

M. Norkowska et al.
46
illustrated in Figure 1.[25] Molecular packing in the crystal, illustrated in Fig-
ure 2, was prepared by ORTEP-3[25] The computational material for publica-
tion was prepared using the PLATON program.[26]
FUNDING
This research was financed by the European Union within the European Re-
gional Development Fund (grant UDA-POIG.01.01.02-14-102/09-04) and by
Ministry of Science and Higher Education (grant DS/530-8451-D-382-13).
SUPPLEMENTAL MATERIALS
Full crystallographic details, excluding structural features, have been de-
posited (deposition No. CCDC 935806) with the Cambridge Crystallographic
Data Center. These data may be obtained, on request, from The Director,
CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (tel.: +44-1223-336408;
fax: +44-1223-336033; e-mail: deposit@ccdc.cam.ac.uk; http://www.ccdc.cam.
ac.uk).
REFERENCES
1. Sparg, S.G.; Light, M.E.; van Staden, J. Biological activities and distribution of
plant saponins. J. Ethnopharmacol. 2004, 94, 219–243.
2. Hostettman, K.; Maraton, A. Saponins. Cambridge University Press: New York,
1995; pp. 287–299.
3. Yu, B.; Zhang, Y.; Tang, P. Carbohydrate chemistry in the total synthesis of
saponins. Eur. J. Org. Chem. 2007, 5145–5161.
4. Tran, Q.L.; Tezuka, Y.; Banskota, A.H.; Tran, Q.K.; Saiki, I.; Kadota, S. New
spirostanol steroids and steroidal saponins from roots and rhizomes of Dracaena an-
gustifolia and their antiproliferative activity. J. Nat. Prod. 2001, 64, 1127–1132.
5. Iorizzi, M.; Lanzotti, V.; Ranalli, G.; De Marino, S.; Zollo, F. Antimicrobial
furostanol saponins from the seeds of Capsicum annuum L. Var. acuminatum. J. Agric.
Food Chem. 2002, 50, 4310–4316.
6. Raju, J.; Bird, R.P. Diosgenin, a naturally occurring furostanol saponin suppresses
3-hydroxy-3-methylglutaryl CoA reductase expression and induces apoptosis in HCT-
116 human colon carcinoma cells. Cancer Lett. 2007, 255, 194–204.
7. Dave, S.; Tarafdar, J.Ch. Stimulatory synthesis of saponin by mycorrhizal fungi in
safed musli (Chlorophytum borivilianum) tubers. Int. Res. J. Agric. Sci. Soil Sci. 2011,
1, 137–141.
8. Pe´rez-Labrada, K.; Brouard, I.; Este´vez, S.; Marrero, M.T.; Este´vez, F.; Bermejo,
J.; Rivera, D.G. New insights into the structure-cytotoxicity relationship of spirostan
saponins and related glycosides. Bioorg. Med. Chem. 2012, 20, 2690–2700.
9. Wang, B.; Chun, J.; Liu, Y.; Han, L.; Wang, Y.; Joo, E.-J.; Kim, Y.-S.; Cheng, M.
Synthesis of novel diosgenyl saponin analogues and apoptosis-inducing activity on A549
human lung adenocarcinoma. Org. Biomol. Chem. 2012, 10, 8822–8834.

2,3,4,6-tetra-O-Acetyl-D-gluconic acid
47
10. Myszka, H.; Bednarczyk, D.; Najder, M.; Kaca, W. Synthesis and induction of apop-
tosis in B cell chronic leukemia by diosgenyl 2-amino-2-deoxy-β-D-glucopyranoside hy-
drochloride and its derivatives. Carbohydr. Res. 2003, 338, 133–141.
11. Cirioni, O.; Myszka, H.; Dawgul, M.; Ghiselli, R.; Orlando, F.; Silvestri, C.;
Brescini, L.; Kamysz, W.; Guerrieri, M.; Giacometti, A. In vitro activity and in vivo
efficacy of the saponin diosgenyl 2-amino-2-deoxy-β-D-glucopyranoside hydrochloride
(HSM1) alone and in combination with daptomycin and vancomycin against Gram-
positive cocci. J. Med. Microbiol. 2011, 60, 1337–1343.
12. Kaskiw, M.J.; Tassotto, M.L.; Mok, M.; Tokar, S.L.; Pycko, R.; Th’ng, J.; Jiang,
Z.-H. Structural analogues of diosgenyl saponins: synthesis and anticancer activity.
Bioorg. Med. Chem. 2009, 17, 7670–7679.
13. Braun, C.E.; Cook, C.D. 2,3,4,5,6-Penta-O-acetyl-D-gluconic acid and 2,3,4,5,6-
penta-O-acetyl-D-gluconyl chloride. Org. Synth. Coll. 1973, 5, 887.
14. Bednarczyk, D.; Walczewska, A.; Grzywacz, D.; Sikorski, A.; Liberek, B.; Myszka,
H. Differently N-protected 3,4,6-tri-O-acetyl-2-amino-2-deoxy-D-glucopyranosyl chlo-
rides and their application in the synthesis of diosgenyl 2-amino-2-deoxy-β-D-
glucopyranoside. Carbohydr. Res. 2013, 367, 10–17.
15. Grindley, T.B. Structure and conformation of carbohydrates. In: Glycoscience:
Chemistry and Chemical Biology, B. Fraser-Reid, K. Tatsuta, J. Thiem, Eds. Springer:
Heidelberg, 2001, pp. 13–14.
16. Stoddart, J.F. Stereochemistry of Carbohydrates. J. Wiley & Sons: Toronto, 1971,
p. 94.
17. Horton, D.; Wander, J.D. Conformation of acyclic derivatives of sugars. XI. Con-
formations of the D-aldopentose diethyl and diphenyl dithioacetals in solution. J. Org.
Chem. 1974, 39, 1859–1863.
18. Nowacki, A.; Walczak, D.; Liberek, B. Fully acetylated 1,5-anhydro-2-deoxypent-
1-enitols and 1,5-anhydro-2,6-dideoxyhex-1-enitols in DFT level theory conformational
studies. Carbohydr. Res. 2012, 352, 177–185.
19. Ko¨ll, P.; Bruns, R.; Kopf, J. Crystal and molecular structures of the pen-
taacetates of D-gluconic acid and derived tert-butyl- and tert-butylperoxyesters and
the tetra-O-acetyl-1,2-O-tert-butyl-peroxyorthoacetyl derivative. Carbohydr. Res. 1998,
305, 147–154.
20. Tuwalska, D.; Sikorski, A.; Liberek, B. Synthesis and geometry of methyl (methyl
4-O-acetyl-3-azido-2,3-dideoxy-α/β-D-arabino- and α/β-D-ribo-hexopyranosid)uronates.
Carbohydr. Res. 2008, 343, 404–411.
21. Nowacki, A.; Liberek, B. Methyl 4-O-Acetyl-3-azido- and 3-azido-4-O-
methylsulfonyl-2,3,6,-trideoxy-hex-5-enopyranosides in DFT Level Theory Confor-
mational Studies. J. Phys. Chem. A. 2007, 111, 4397–4403.
22. CrysAlis CCD, Version 1.171.32.15. Oxford Diffraction Ltd., 2008.
23. Sheldrick, G.M. A short history of SHELX. Acta Cryst. 2008, A64, 112–122.
24. Sheldrick, G.M. SHELXL-97. Program for Crystal Structure Refinement. Univer-
sity of Go¨ttingen: Go¨ttingen, Germany, 1997.
25. Farrugia, L.J. ORTEP-3 for Windows - a version of ORTEP-III with a Graphical
User Interface (GUI). J. Appl. Cryst. 1997, 30, 565.
26. Spek, A.L. Structure validation in chemical crystallography. Acta Cryst. 2009,
D65, 148.