Synthesis, NMR, and conformational studies of cyclic oligo-(1-→6)- β-D-Glucosamines

Article abstract of DOI:10.1002/ejoc.200901275

The first synthesis of a series of homologous cyclic oligo(l-→6)- β-D-glucosamines consisting of two to seven residues and representing a new type of functionalized cyclic oligosaccharides is reported. Remarkably high yields of the studied macrocyclizatio

Full text of DOI:10.1002/ejoc.200901275

FULL PAPER
DOI: 10.1002/ejoc.200901275
Synthesis, NMR, and Conformational Studies of Cyclic
Oligo-(1Ǟ6)-β- -Glucosamines
D
Marina L. Gening,[a] Denis V. Titov,[a,b] Alexey A. Grachev,[a] Alexey G. Gerbst,[a]
Olga N. Yudina,[a] Alexander S. Shashkov,[a] Alexander O. Chizhov,[a] Yury E. Tsvetkov,[a]
and Nikolay E. Nifantiev*[a]
Dedicated to Professor Klaus Bock on the occasion of his 65th birthday
Keywords: Carbohydrates / Oligosaccharides / Conformation analysis / Macrocycles
The first synthesis of a series of homologous cyclic oligo-
(1Ǟ6)-β- -glucosamines consisting of two to seven residues
studies, the described linear (1Ǟ6)-β-linked oligoglucos-
amines exist in a right-handed helix-like conformation, in
D
and representing a new type of functionalized cyclic oligo- which the glycosyl donor and acceptor moieties are pre-
saccharides is reported. Remarkably high yields of the
studied macrocyclization reaction irrespective of the length
of the acyclic precursors were observed. In the case of com-
pounds constituted of four to seven glucosamine units α-
stereoisomers formed as side products despite the presence
of a strongly participating 2-N-phthaloyl group to control β-
arranged in a way that facilitates intramolecular glycosyl-
ation from the α-side. Prepared cyclo-oligoglucosamines dif-
fer in their conformational flexibilities, as illustrated by their
spectral characteristics and calculated asphericity distribut-
ions. Moreover, the obtained compounds do not possess a
distinct hydrophobic cavity, which is in contrast to the well-
glycosylation. Both phenomena may be accounted for by known cyclodextrins. All these characteristics provide an ex-
conformational features of the linear bifunctional precursors.
According to computer modeling and NMR conformational
cellent basis for the use of these novel cyclic oligosaccharides
as scaffolds for the construction of biomolecular conjugates.
The preparation of cyclo-oligosaccharides by intramolec-
ular glycosylation of bifunctional oligosaccharide blocks is
more complicated, as the number of available conforma-
tions is restricted due to specific properties of the glycoside
linkage. As a result of the limited conformational space, the
cyclization occurs efficiently only at a certain length of the
linear oligosaccharide precursors. For instance, malto-
oligosaccharides are properly preorganized for ring closure
when the number of -glucopyranose units is six, seven, or
eight.[1] This preorganization explains the efficiency of the
enzymatic production of α-, β-, and γ-cyclodextrins. An-
other illustration is the chemical synthesis of cyclic (1Ǟ4)-
α--mannopyranosides, where the observed yield for the
macrocyclization of penta- and hexasaccharides was 8 and
92%, respectively.[3–5]
Despite considerable research activity in the field of syn-
thetic cyclic oligosaccharides, there have been no examples
to date of these compounds with -glucosamine units and
only a few discrete examples of cycles with (1Ǟ6)-glycoside
linkages.[6–9] The work described here was initiated by our
recent observation[10] that cyclization of bifunctional disac-
charide 1 and trisaccharide 2 (Scheme 1) resulted in the al-
most quantitative formation of corresponding cyclic prod-
ucts 3 and 4, and surprisingly, the formation of linear oligo-
mers was not detected. This is in contrast with previous
Introduction
The synthesis of carbohydrate macrocycles is a challeng-
ing task.[1] In general, cyclizations to form large rings re-
quire the formation of a cyclic transition state from acyclic
precursors that can adopt numerous conformations. The
probability of attaining the cyclic transition state decreases
dramatically with elongation of the linear chain. This re-
sults from significant loss of entropy due to coiling of the
extended acyclic precursors. For example, the relative reac-
tion rate for the formation of an eight-membered lactone is
six orders of magnitude lower than that for a five-mem-
bered one.[2] Larger bifunctional precursors more readily
undergo intermolecular condensation instead of macro-
cyclization, and therefore, high dilution or other special
techniques are necessary for the effective formation of cyclic
products.
[a] N. D. Zelinsky Institute of Organic Chemistry RAS
Leninsky prospect 47, 119991 Moscow, Russia
Fax: +7-499-135-87-84
E-mail: nen@ioc.ac.ru
[b] Higher Chemical College RAS
Miusskaya sq. 9, 125047 Moscow, Russia
Fax: +7-499-978-85-27
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.200901275.
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N. E. Nifantiev et al.
FULL PAPER
examples of cyclo-oligomerization involving small oligosac-
charide blocks.[11–15] Here we report on the cyclization of
oligo-(1Ǟ6)-β--glucosamine derivatives containing up to
seven monosaccharide units and the synthesis of the corre-
sponding cyclic oligosaccharides. A variety of modern tech-
niques was employed to reveal structural characteristics of
all synthesized oligosaccharides and to study the conforma-
tional basis for the stereochemistry of cycloglycosylation.
Scheme 1. Cyclization of oligosaccharides 1 and 2. Reagents and
conditions: (a) NIS, TfOH, CH2Cl2, 4 Å MS, –15 °C, 90–95%.
Results and Discussion
Scheme 2. Synthesis of linear precursors 7–10. Reagents and condi-
tions: (a) Br2, CH2Cl2; (b) 1, HgBr2, Hg(CN)2, MeCN, 3 Å MS;
(c) HCl/MeOH; (d) 6, HgBr2, Hg(CN)2, MeCN, 3 Å MS.
Synthesis of Cyclic Oligo-(1Ǟ6)-β-D-Glucosamines
A series of homologous bifunctional blocks 7–10 were
used as the precursors of target cyclic oligoglucosamines.
Compounds 7–10 were prepared by using a convergent ap- minal glycosyl donor and acceptor moieties. It was notice-
proach (Scheme 2). Thus, disaccharide thioglycoside 5[16] able that the intramolecular glycosylation of compounds 7,
was converted into bromide 6,[16] which was used as a key 8, and 10 resulted in the formation of symmetric cycles 11β,
glycosylating agent for chain elongation. Its coupling with 13β, and 14β as major products along with minor amounts
di- and trisaccharide glycosyl acceptors 1[10] and 2[10] and of (1Ǟ6)-α-linked cycles 11α, 13α, and 14α (Scheme 3)
subsequent selective O-deacetylation produced correspond- which were obtained in individual state. Cyclization of 9
ing thioglycosides 7 and 9 bearing a free OH group at the afforded 12β almost exclusively; corresponding α-linked
terminal “nonreducing” GlcN unit. Repetition of the same cycle 12α apparently also formed, but its very low yield
procedures with the obtained products afforded hexasac- (Ͻ3%) did not allow its isolation and unambiguous charac-
charide 8 and heptasaccharide 10 in good yields.
terization.
The structures of the β- and α-isomers of cyclic products
Then, cyclization of bifunctional (1Ǟ6)-β--glucosamine
oligomers 7–10 constituted of four to seven monosaccha- 11–14 were deduced from their NMR and mass spectro-
ride units was investigated. Regardless of the length of the scopic data. The NMR spectra of products 11β–14β con-
linear precursor, N-iodosuccimide (NIS)-trifluoromethane- tained only the signals of one monosaccharide repeating
sulfonic acid (TfOH) promoted activation of 7–10 afforded unit due to their symmetry and confirmed that all glucosa-
corresponding cyclic products 11–14 in good yields mine residues have the β-configuration. It was not possible
(Scheme 3). Practically no products of linear oligomeriza- to determine the anomeric configuration of the α-units in
tion were detected, even at concentrations up to 10 times 11α, 13α, and 14α from the corresponding J1,2 values as a
1
higher than those described for the cyclization of other lin- result of peak overlap in the H NMR spectra. Their α-
ear oligosaccharides.[6–9] Strong prevalence of intramolecu- configuration was confirmed on the basis of a characteristic
lar glycosylation over linear chain elongation may be ex- downfield shift of the signals for H-3, which appeared at
plained by the conformational preorganization of the pre- 6.9–7.3 ppm. The cyclic nature of compounds 11α, 13α, and
cursors in a shape providing spatial proximity of the ter- 14α was confirmed by the presence of a correlation cross-
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Studies of Cyclic Oligo-(1Ǟ6)-β--Glucosamines
Scheme 3. Cyclization of oligosaccharides 7–10. Reagents and conditions: (a) NIS, TfOH, CH2Cl2, 4 Å MS, –15 °C.
peak between H-1 of the α-residue with H-6 of another glu- cle. At the beginning, we obtained experimental values of
cosamine residue in the ROESY spectra. The absence of the transglycosidic constants for the molecule in CD2Cl2 solu-
signals for non-glycosylated C-6 in the 13C NMR spectra, tion at 268 K (Table 1) because these conditions are close
which are typically observed in the range of 60–62 ppm, to those used for cyclization of tetrasaccharide 7. However,
also supported the cyclic structure of these compounds.
we could not determine in this case some constant values
of interest (Table 1) due to the overlap of the signals. There-
fore, the values of transglycosidic constants were addition-
ally measured for compound 7 in CDCl3 solution at 303 K
(Table 2). The comparison of the constants for CD2Cl2 and
CDCl3 has shown that the corresponding values are close
to each other (usually the difference does not exceed 1 Hz),
thus revealing the conformational similarity of 7 in these
two solvents.
Conformational Analysis of Linear Tetrasaccharide 7
The formation of the α-products upon the cyclization of
bifunctional blocks 7–10 was unexpected because they con-
tain a strongly participating N-phthaloyl blocking group at
C-2 that provides stereospecific β-glycosylation, especially
if a primary OH group is involved. To the best of our
knowledge, only one example of α-glycoside bond forma-
tion upon glycosylation with the glycosyl donors having the
participating N-phthaloyl group has been described so far
without any explanation of the observed stereochemical
outcome.[17] We supposed that the α-linked cycles formed as
a result of conformational features of the linear precursors,
which were illustrated by the example of tetrasaccharide 7.
The spatial structure of (1Ǟ6)-linked pyranosides (such as
compound 7) is primarily described by the dihedral angles
φ, ψ, and ω around the bridges between the monosaccha-
ride residues (Figure 1). Conformations of pyranoside rings
change slightly and are considered to have little influence
on the conformation of the whole saccharide molecule.[18]
The values of these dihedral angles are related with the ex-
perimentally measured coupling constant values JH,H and
JC,H around the glycosidic linkages through the Karplus
equation[19,20] (Figure 1). Hence, we performed the analysis
of the values of JH,H and JC,H calculated from molecular
dynamics (MD) simulations and experimental ones. The
Figure 1. Dihedral angles and the Karplus equations for the cou-
3
[19]
3
[20]
pling constants JC,H
and JH,H describing the conformation
of the (1Ǟ6)-linkage.
3
experimental values of JH,H were measured from the
Analysis of the conformers obtained from MD simula-
1H NMR spectra and the values of long-range coupling tions for tetrasaccharide 7 shows that the conformations of
3
constants JC,H were determined by employing 2D J- the C1–O6 bonds are most rigid. For these bonds the typi-
HMBC[21,22] NMR techniques. The detailed description of cal values of the φ angles are in the range from +20° to
the NMR technique for the measurement of transglycosidic +50°, which is in accordance with the exoanomeric effect.
coupling constants in oligosaccharides is given in our pre- Rotation around the O6–C6 bond (angles ψR and ψS, Fig-
vious work[23] and in the Experimental Section of this arti- ure 1) results in two conformers with ψR and ψS angles of
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Table 1. Experimental (CD2Cl2, 268 K) and calculated (in paren- mation. Calculated average values of constants show ac-
theses) values of transglycosidic 3J coupling constants [Hz] for
compound 7.
ceptable[19] coincidence with experimental ones (Table 1),
which also confirms that the studied tetrasaccharide gen-
erally has a helical shape, whereas unfolded conformers are
present in minor quantity. Hence, compound 7 in its prefer-
ential conformation represents one turn of a right-handed
spiral (Scheme 4), in which C-1 of the glycosylating unit (A)
and 6-OH of the glycosyl acceptor residue (D) are spatially
prearranged in a way favoring α-glycosylation (I) to give
11α. However, the anchimeric participation of the phthaloyl
group impedes the immediate formation of α-linked cycle
11α and also stabilizes glycosyl cationic intermediate II,
which becomes stable enough to survive until reorganiza-
tion to conformation III favoring β-attack. The observed
stereochemical outcome of the cyclization of tetrasaccha-
ride 7 is apparently a result of the competition between
these two processes. Similar conformational α-stereocontrol
could be also expected for longer bifunctional blocks 8–10
in which the terminal residues are situated on adjacent
turns of the right-handed helical structure. The spectra of
protected saccharides 8–10 are rather complicated, and
hence, the accurate measurement of coupling constants
and, subsequently, the determination of torsion angles in
them are impossible. On the other hand, the data obtained
from molecular dynamics simulations suggest that the pref-
erable orientation around the C5–C6 bond in the structures
with the β(1Ǟ6)-glycoside linkage is characterized by ω an-
gle values of –60°, thus leading to a helical shape of the
molecules. Presumably, the conformational reorganization
of oligosaccharides 8–10 to adopt a conformation suitable
for the intramolecular glycosylation proceeds through inter-
Bond[a]
Jφ
JψR
JψS
JH-5,H-6R
JH-5,H-6S
BǞA
CǞB
DǞC
2.5 (3.3)
2.5 (3.3)
3.3 (3.2)
nd[b] (2.5) 2.3 (2.6) nd[b] (4.5) 2.0 (2.2)
nd[b] (2.9) 2.5 (2.4) nd[b] (4.4) 2.9 (2.5)
nd[b] (2.5) 2.7 (2.5)
4.9 (4.6)
3.3 (2.5)
[a] Unit labels are shown in Scheme 4. [b] Not determined due to
peak overlap.
Table 2. Experimental values of transglycosidic 3J coupling con-
stants [Hz] for compound 7 (CDCl3, 303 K).
Bond[a]
Jφ
JψR
JψS
JH-5,H-6R JH-5,H-6S
BǞA
CǞB
DǞC
3.6
3.5
3.5
2.8
3.3
3.1
2.8
3.0
2.8
5.5
4.6
4.8
2.4
3.9
4.0
[a] Unit labels are shown in Scheme 4.
(–20°, 50°) and (–60°, 20°), respectively. Although transi-
tions between these conformers slightly change the shape of
the saccharide chain, the helical conformation is generally
maintained. Unfolded conformers appear due to the rota-
tion around the C6–C5 bond. Two main rotamers are ob-
served for this bond with O5–C5–C6–O6 angles ω of about
–60° and +60°, respectively; the latter rotamer is responsible
for the occurrence of unfolded conformations (not shown).
Experimentally observed coupling constants are presum-
ably averages over the ensemble of all these conformers, as
the observed experimental values of the pairs of JH-5,H-6R
/
JH-5,H-6S constants cannot be attributed to a single confor-
Scheme 4. Preferential conformation of tetrasaccharide 7 and possible intermediates explaining the stereochemical result of cyclization.
Reagents and conditions: (a) NIS, TfOH, CH2Cl2, 4 Å MS, –15 °C.
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Studies of Cyclic Oligo-(1Ǟ6)-β--Glucosamines
mediate conformations, which also favor α-bond formation. were isolated as acetic acid salts. Further N-acetylation re-
The formation of α-linked cycles 11α–14α can be regarded sulted in the formation of corresponding N-acetylated de-
as a specific case of “tethered” glycosylation (for a recent rivatives 21–26 (Figure 2). The structures of the thus ob-
review see ref.[24]).
tained cyclic oligosaccharides were confirmed by mass spec-
1
trometry and H and 13C NMR spectroscopy (Tables 3 and
4, Figure 3). The NMR spectra were acquired at a tempera-
ture of 303–310 K. For each compound, the temperature
was chosen so as to exclude the overlap of the solvent signal
(HOD) with the anomeric proton signal of the cyclic glu-
Synthesis of Unprotected Cyclic Oligo-(1Ǟ6)-β-D-
Glucosamines 15–26
The one-step deprotection of cyclic oligosaccharides by
hydrazinolysis provided a series of free amines 15–20, which
1
cosamines in the H NMR spectrum.
Figure 2. Final set of synthesized deprotected cyclic oligosaccharides. 1H NMR spectra of compounds (a) 20 (303 K), (b) 19 (303 K),
(c) 18 (310 K), (d) 17 (307 K), (e) 16 (307 K), and (f) 15 (303 K).
1
Table 3. H NMR spectroscopic data for cyclic oligosaccharides 15–26 (D2O, 500.13 or 600.13 MHz, 303–310 K).
Chemical shift [δ, ppm]
Coupling constants [J, Hz]
H-1
H-2
H-3
H-4
H-5
H-6R
H-6S
1,2
2,3
3,4
4,5
5,6R
5,6S
6R,6S
15
16
17
18
19
20
21
22
23
24
25
26
4,95
4.52
4.74
4.74
4.73
4.79
4.68
4.60
4.57
4.59
4.54
4.58
3,33
2.73
3.03
3.04
3.02
3.06
3.94
3.64
3.67
3.67
3.63
3.70
3,72
3.56
3.67
3.65
3.64
3.67
3.62
3.49
3.53
3.55
3.59
3.57
4,17
3.47
3.72
3.58
3.55
3.60
4.32
3.46
3.52
3.46
3.40
3.47
3,85
3.42
3.60
3.61
3.68
3.66
3.72
3.48
3.51
3.53
3.54
3.57
4,12
4.18
4.07
4.03
3.97
3.96
4.17
4.09
3.94
3.90
3.77
3.82
3,73
3.97
4.14
4.13
4.21
4.20
3.61
3.90
4.02
4.07
4.10
4.13
Յ2[b]
8.1
8.5
8.4
8.4
5.7
8.9
8.8
8.7
8.8
9.0
5.7
9.6
nd[a]
10.1
8.4
8.6
9.8
9.1
9.2
10.2
10.0
9.1
9.8
9.1
9.5
9.4
9.4
9.1
9.9
nd[a]
nd[a]
9.4
9.1
9.4
Յ2.0[b]
3.9
Յ2[b]
Յ2[b]
Յ2[b]
Յ2[b]
Յ2[b]
Յ2[b]
Յ2[b]
Յ2[b]
Յ2[b]
Յ2[b]
Յ2[b]
Յ2[b]
12.8
12.2
11.0
11.3
11.5
11.5
12.8
12.5
11.4
11.0
11.1
10.5
2.5[
4.0
4.9
8.4
3.7
Յ2[b]
8.4
9.9
Յ2.0[b]
4.1
nd[a]
nd[a]
9.0
8.6
8.3
8.0
8.4
2.3
4.9
6.0
5.2
9.1
9.2
[a] Not determined due to peak overlap. [b] The small value of the coupling constant could not be measured exactly because of line
1
broadening of the signals in the H NMR spectra.
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N. E. Nifantiev et al.
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Table 4. 13C NMR chemical shifts [δ, ppm] for cyclic oligosaccha- crease in the cycle size from two to seven units is ac-
rides 15–26 (D2O, 125.75 or 150.90 MHz, 303–310 K).
companied by changes in the localization of the signals and
coupling constants values (Figure 3). It is also noticeable
C-1
C-2
C-3
C-4
C-5
C-6
that in the case of disaccharides 15 and 21 the coupling
15
16
17
18
19
20
21
22
23
24
25
26
100.1
102.4
100.2
100.9
100.8
100.8
103.3
101.4
102.3
102.8
102.6
102.7
60.1
57.4
56.6
56.9
56.8
56.8
59.9
57.0
56.7
56.8
56.9
56.8
71.8
75.7
73.1
73.4
73.5
73.2
74.3
75.2
75.0
74.8
74.7
74.9
67.6
70.5
69.8
70.6
70.8
70.8
67.9
70.6
70.5
71.0
71.3
71.3
79.4
76.0
75.7
76.2
75.7
75.9
78.1
75.8
75.9
76.2
75.7
75.9
70.0
69.3
69.4
69.8
69.5
69.5
71.3
69.7
69.5
69.9
70.2
69.8
3
constants JH,H within the glucosamine residues (Table 3)
4
have atypical values for the glucopyranose in the C1 con-
formation. This fact could be explained by conformational
distortions of the pyranose rings in disaccharide cycles 15
and 21 due to steric hindrance. Similar distortion was al-
ready observed for cyclogentiobioside.[7,8]
To investigate the conformational properties of cyclic
oligoglucosamines 15–26, we performed analysis of the ex-
3
perimental values of transglycosidic constants JH,H and
3JC,H (Table 5). The experimental constants for small cycles
changed significantly upon enlargement of the molecules.
On the contrary, the constants for the cycles with five and
more monosaccharide residues in the molecules coincided
within the series of free oligoglucosamines 18–20 (in the
form of ammonium salts) and the series of N-acetylated
derivatives 24–26. The spectral characteristics of these large
cycles (Tables 3 and 4) are similar to those for internal units
of the large linear oligoglucosamines described before.[16]
Table 5. Experimental transglycosidic coupling constants 3JC,H and
3JH,H [Hz] for cycles 15–26.
Jφ
JψR
JψS
JH-5,H-6R
JH-5,H-6S
15
16
17
18
19
20
21
22
23
24
25
26
4.3
3.8
4.9
3.8
3.9
3.8
3.4
3.7
4.9
4.4
3.5
3.9
2.2
3.2
2.3
2.7
3.9
3.5
2.3
2.7
2.5
3.6
3.7
3.5
6.0
5.2
2.4
2.8
2.5
3.2
6.4
6.1
3.5
2.8
2.4
2.8
Յ2.0[a]
3.9
2.5
4.0
4.9
Յ2[a]
Յ2[a]
Յ2[a]
Յ2[a]
Յ2[a]
Յ2[a]
Յ2[a]
Յ2[a]
Յ2[a]
Յ2[a]
Յ2[a]
Յ2[a]
3.7
Յ2.0[a]
4.1
2.3
4.9
6.0
5.2
[a] The small value of the coupling constant could not be measured
exactly because of line broadening of the signals in the 1H NMR
spectra.
One of the main problems during the study of free oligo-
glucosamines 15–20 relates to the susceptibility of their am-
monium salts to partial hydrolysis in water solution with
the formation of free oligoglucosamines. We carried out
molecular dynamics (MD) simulations for their fully pro-
tonated derivatives (NH3+ forms). Theoretical simulation of
compounds 15–26 by using MD revealed that di-, tri-, and
tetrasaccharides existed mostly in symmetrical ring-shaped
conformations. Larger cycles tended to adopt more compli-
cated shapes and the existence in conformations similar to
that of 23 was unlikely for them. Row a in Figure 4 is com-
posed of wireframe drawings that are superimpositions of
Figure 3. 1H NMR spectra of compounds (a) 20 (303 K), (b) 19
(303 K), (c) 18 (310 K), (d) 17 (307 K), (e) 16 (307 K), and (f) 15
(303 K)..
NMR Spectroscopy and Theoretical Conformational
Studies of Cyclic Oligo-(1Ǟ6)-β-D-glucosamines 15–26
The NMR spectra of all β-cycles contained the signals different shape representatives found in MD trajectories for
of one monosaccharide repeating unit, thus revealing the these molecules. It demonstrates the increasing flexibility of
equivalence of all units within the cycle (Figure 3, Tables 3 glycosidic linkages in the studied cycles upon their enlarge-
and 4, and Supporting Information). Changes in the 1H ment. After geometry optimizations of the structures gener-
NMR spectra within the series of 15–20 and 21–26 reflect ated during the MD simulations, global minima were found
the changes in their conformational strain. Indeed, the in- for each molecule. Those for saccharides containing four to
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Studies of Cyclic Oligo-(1Ǟ6)-β--Glucosamines
Figure 4. Superimpositions of eight different shapes found for cycles 23–26 during MD simulations (a); global minima for conformations
of compounds 23–26 in the stick model (b) and schematic representations (c).
seven monosaccharide units are shown in Figure 4 (rows b are similar and resemble those of long chain linear oligo-
and c) as a stick model and a schematic representation, (1Ǟ6)-β--glucosamines.[16] It is also noteworthy that the
respectively.
distribution curves for oligoglucosamines 15–20 and corre-
The asphericity parameters were calculated[25] for the
conformations obtained from MD simulations. The formula
used for the calculation of asphericity was A3/36πV2, where
A is the molecule surface and V is the molecule volume.
The higher value of this parameter indicates the greater de-
viation of the molecular shape from an “ideal sphere”. As
the areas under the curves are all normalized to the same
value, the width of the distribution curve may be correlated
to the number of conformational states available for the
molecule. Thus, the broader curves are interpreted as show-
ing a greater number of conformational states for the mole-
cule. Figure 5 represents the asphericity distributions for
oligoglucosamines 15–20 (ammonium salts) and their N-
acetylated derivatives 21–26, respectively. The disaccharides
(both 15 and 21) are unsurprisingly the most rigid ones;
tri- and tetramers have moderate flexibilities, whereas cycles
with a number of residues in the molecule of five and higher
seem to adopt a wider range of possible conformations,
which is reflected in the broadness of their asphericity dis-
tributions. In the case of cyclic penta-, hexa-, and heptasac-
charides 18–20 and 24–26 (Figure 5), the distribution curves
even look multicentered. This means that cycles with five
and more residues in the molecule may undergo various
conformational transformations like their linear counter-
parts. This conclusion is also supported by the results ob-
tained from analysis of the coupling constant values, which
showed that the conformational properties of the disaccha-
Figure 5. Asphericity distributions for (a) cyclic oligoglucosamines
15–20 (as ammonium acetate salts) and (b) oligo-N-acetylglucos-
ride fragments in cyclic penta-, hexa-, and heptasaccharides amines 21–26.
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N. E. Nifantiev et al.
FULL PAPER
the case of free oligosaccharides. TLC was performed on silica gel
60 F254 plates (E. Merck) and visualization was accomplished by
using UV light or by charring with 10% H3PO4 in EtOH. Column
chromatography was carried out on silica gel 60 (40–63 µm, E.
Merck). Gel-permeation chromatography of protected oligosaccha-
rides was performed with Bio-Beads SX-3 (13ϫ450 mm) and Bio-
Beads SX-1 (18ϫ500) (Bio-Rad Laboratories) columns in toluene.
Gel-permeation chromatography of free oligosaccharides was per-
formed on a column of TSK HW-40 (S) gel (25ϫ800 mm) in 0.1 
AcOH. All reactions involving air- or moisture-sensitive reagents
were carried out by using dry solvents under an atmosphere of dry
argon.
sponding N-acetylated derivatives 21–26 are similar to each
other.
The calculation of the hydrophobicity and hydrophilicity
distribution[26] exemplified by tetramer 23 (Figure 6) has
shown that, unlike the well-known cyclodextrins, cyclo-
oligo-(1Ǟ6)-β--glucosamines lack the distinct hydro-
phobic cavity.
Special NMR Experiments: The values of long-range coupling con-
3
stants JC,H were measured by employing a 2D J-HMBC[21,22] ex-
periment, which was performed in the constant-time version.[21]
The spectral widths were about 2.5 ppm for 1H region and 50 ppm
for 13C region and did not include resonances of acetyl groups in
the case of oligosaccharides 21–26. The data were collected in the
echo/antiecho mode. For echo selection the two sinusoidal field
gradients in a ratio of 5:–3 are applied, and for antiecho selection
the ratio was –3:5. The length of gradients was 1 ms, and the recov-
ery time was 100 µs. The spectra were acquired with 60–100 t1 in-
crements and 40–500 scans per increment. A total of 512 points
were collected during the acquisition time t2. The HMBC prepara-
tion delay ∆ for the reliable measurement of a coupling constants
should be taken at least 60% of inversion values of smallest cou-
pling of interest (∆ = 0.6/JC,Hmin).[22] Smaller values of ∆ lead to
Figure 6. Distribution of the hydrophilic (red) and hydrophobic
(blue) areas in molecules of tetrasaccharide 23 (outer diameter is
1.16 nm) and β-cyclodextrin (outer diameter is 1.44 nm).
the overestimation of J because of the antiphase character of the
Conclusions
min
peaks. ∆ = 300 ms was used that corresponds to JC,H
= 2.0 Hz.
n
In this paper we have discussed the remarkable ability of
oligo-(1Ǟ6)-β--glucosamine derivatives 7–10 to undergo
The upscaling coefficient k for determination of JC,H from the
spectra[21] was 30–60. The relaxation delay was 1 s. The third-order
intramolecular glycosylation with the formation of a new low-pass J-filter[22] was made on suppression of one bond constants
(1JC,H) in the range from 125 Hz to 180 Hz. Sinusoidal field gradi-
family of functionalized cyclic oligosaccharides. As a result
of their structure and molecular architectonics, these com-
pounds may be regarded as convenient scaffolds for the de-
sign of conjugates with defined valency, symmetry, and flex-
ibility. The absence of a distinct hydrophobic cavity pre-
cludes the possibility of the formation of inclusion com-
plexes like in cyclodextrins. This may be an advantage for
the use of described cyclo-oligoglucosamines as covalent
ent sequence with the ratio +7:–4:–2:–1 was applied during low-
pass J-filter. The forward linear prediction to 1024 points was used
in F1 that corresponds to resolution 5–6 Hz, and zero-filling to
1024 points was used in F2. The processing was performed with π/
2 shifted sine square function in both dimensions. The values of
1
3JH,H were measured from the H NMR spectra.
Computer Simulations: MD simulations were carried out in vacuo
with dielectric constant 81 by using MM3 force field (TINKER 4.1
program suit). Simulation time was 5 ns for each molecule. Snap-
shot structures were written every 5 ps and then used for further
analysis. The geometry optimization of the snapshots led to 1000
structures among which the lowest energy conformer was chosen
and used to represent the global minimum (Figure 4). In the case
carriers. Compounds 24–26 relate structurally to exopoly-
saccharide adhesin poly-(1Ǟ6)-β--glucosamine (PNAG)
produced by Staphylococcus aureus,[27] S. epidermidis,[28] Es-
cherichia coli,[29] Bordetella bronchiseptica,[30] Actinobacillus
pleuropneumoniae,[31] and Yersinia pestis.[32] Thus, the ob-
tained cyclo-oligosaccharides can be also regarded as po-
of linear protected precursor 7, conformational search was first
performed by using standard dihedral driving of φ and ψ angles.
Two starting conformations were used; in the first one all ω angles
were set to –60°, in the other to +60°. Two conformational maps
were thus constructed for each glycosidic linkage with one local
minimum found on each map. Six MD trajectories were then writ-
ten, each starting from a different local minimum. trans-Glycosidic
coupling constants were calculated for each structure of MD trajec-
tories according to the Karplus equation and then averaged.
tential inhibitors[33] of the biosynthesis of PNAG.
Experimental Section
General Information: NMR spectra were recorded with Bruker
DRX-500 and Bruker Avance 600 instruments. Spectra of protected
oligosaccharides were measured for solutions in CDCl3, and 1H
NMR chemical shifts were referenced to the residual signal of
CHCl3. NMR spectra of free oligosaccharides were measured for
General Procedure A
solutions in D2O by using acetone (δH = 2.225 ppm, δC
=
Glycosylation Under Helferich Conditions: To a mixture of a glyco-
syl acceptor (0.1 mmol), Hg(CN)2 (0.15 mmol), HgBr2
(0.03 mmol), and 3 Å molecular sieves (500 mg) in anhydrous
CH3CN (3 mL) and CH2Cl2 (2 mL) was added a solution of a gly-
cosyl bromide (0.15 mmol) in CH3CN (2 mL) under an argon at-
mosphere. The reaction mixture was stirred for 30 min at room
31.45 ppm) as internal standard. HRMS (ESI) were obtained with
Finnigan LTQ FT (Thermo Scientific) and MicrOTOF II (Bruker
Daltonics) instruments. Optical rotations were measured by using
a JASCO DIP-360 polarimeter at 18–22 °C in CHCl3 in the case
of the protected and partially protected derivatives and in water in
2472
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© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2010, 2465–2475

Studies of Cyclic Oligo-(1Ǟ6)-β--Glucosamines
temperature, diluted with CH2Cl2, and washed with 1  aqueous
KI, saturated aqueous NaHCO3, and brine. The organic layer was
dried with Na2SO4, filtered, and concentrated. The crude product
was subjected to gel-chromatography in toluene, and the fractions
with the highest molecular weight were collected and concentrated.
Purification by silica gel column chromatography (toluene/EtOAc)
afforded the corresponding coupling product.
anoside (8): Following general procedure A, coupling of 7 (131 mg,
0.064 mmol) and 6[16] (104 mg, 0.096 mmol) and subsequent de-
acetylation according to general procedure B. Yield: 104 mg (53%).
[α]2D0 = +7 (c = 1, CHCl3). H NMR (500 MHz, CDCl3): δ = 7.55–
1
7.95 (m, 42 H), 7.12–7.51 (m, 42 H), 6.20 (t, J = 9.8 Hz, 1 H), 6.14
(t, J = 9.8 Hz, 1 H), 6.03–6.10 (m, 4 H), 5.55 (d, J = 8.1 Hz, 1 H),
5.47 (d, J = 10.4 Hz, 1 H), 5.30–5.5.44 (m, 4 H), 5.11–5.26 (m, 5
H), 5.05 (t, J = 8.4 Hz, 1 H), 4.48 (t, J = 10.4 Hz, 1 H), 4.41 (t, J
= 8.6 Hz, 1 H), 4.19–4.31 (m, 4 H), 3.50–4.02 (m, 18 H), 2.65 (m,
2 H),1.11 (t, 3 H) ppm. 13C NMR (125 MHz, CDCl3): δ = 167.90,
167.12, 165.65, 165.56, 165.49, 165.17, 165.05, 164.86, 134.14,
133.86, 133.26, 131.10, 129.93, 129.74, 129.22, 129.11, 129.04,
128.73, 128.44, 128.22, 125.30, 123.59, 97.90 (C-1), 97.55 (C-1),
97.32 (C-1), 80.63 (C-1), 77.30, 74.16, 73.04, 72.74, 72.45, 72.28,
72.08, 70.99, 70.69, 70.31, 69.75, 67.98, 67.58, 67.03, 61.30 (C-6),
54.72, 54.60, 53.81, 23.71, 14.94 ppm. C170H132N6O48S (3058.94):
calcd. C 66.75, H 4.35, N 2.75; found C 66.68, H 4.29, N 2.75.
HRMS (ESI): calcd. for C170H132N6O48S [M + Na]+ 3079.7690;
found 3079.7685.
General Procedure B
Selective O-Deacetylation in the Presence of Benzoates: A solution
of the 6-O-acetyl derivative (0.1 mmol) in CH2Cl2 (2 mL) was di-
luted with absolute MeOH (2 mL) and then AcCl (0.1 mL,
1.4 mmol) was added under cooling with an ice bath. The mixture
was kept for 16 h at room temperature and then concentrated. The
residue was purified by silica gel column chromatography (EtOAc/
toluene) to give the product with a free terminal 6-OH group.
General Procedure C
NIS/TfOH-Promoted Intramolecular Glycosylation–Cyclization: A
mixture of the linear precursor (6 µmol), anhydrous dichlorometh-
ane (1 mL), and 4 Å molecular sieves (250 mg) was stirred under
an argon atmosphere at room temperature. After 30 min, NIS (12
µmol) and TfOH (6 µmol) were added at –15 °C. The reaction mix-
ture was stirred at –15 °C for an additional 30 min and then
quenched with pyridine (5 µL), diluted with chloroform (20 mL),
and filtered through a Celite layer. The filtrate was washed with 1 
aqueous Na2S2O3, dried (Na2SO4), and concentrated. The crude
product was purified by silica gel column chromatography (toluene/
EtOAc) to give the cyclo-oligosaccharide. The molecular weight
homogeneity and the absence of oligomerization products were es-
tablished by gel-permeation chromatography of the crude products
in toluene. The product was further purified either by silica gel
column chromatography (toluene/EtOAc) or by C-18 reverse-phase
chromatography (95% aq. CH3CN).
Ethyl 3,4-Di-O-benzoyl-2-deoxy-2-phthalimido-β-
D
-glucopyranosyl-
-glucopyranosyl-
-glucopyranosyl-
-glucopyranosyl-
(1Ǟ6)-3,4-di-O-benzoyl-2-deoxy-2-phthalimido-β-
(1Ǟ6)-3,4-di-O-benzoyl-2-deoxy-2-phthalimido-β-
(1Ǟ6)-3,4-di-O-benzoyl-2-deoxy-2-phthalimido-β-
D
D
D
(1Ǟ6)-3,4-di-O-benzoyl-2-deoxy-2-phthalimido-1-thio-β-D-glucopyr-
anoside (9): Prepared from 4[16] (106 mg, 0.069 mmol) and 6[16]
(108 mg, 0.1 mmol) according to general procedures A and B.
Yield: 124 mg (70%). [α]2D0 = +5 (c = 1, CHCl3). 1H NMR
(500 MHz, CDCl3): δ = 7.61–7.95 (m, 35 H), 7.15–7.60 (m, 35 H),
6.00–6.27 (m, 5 H), 5.57 (d, J = 8.4 Hz, 1 H), 5.50 (d, J = 10.5 Hz,
1 H), 5.00–5.45 (m, 8 H), 4.40–4.55 (m, 3 H), 4.21–4.35 (m, 2 H),
3.53–4.05 (m, 12 H), 3.51–3.70 (m, 3 H), 3.05 (br. s, 1 H, OH), 2.62
(m, 2 H),1.10 (t, 3 H) ppm. 13C NMR (125 MHz, CDCl3): δ =
167.88, 167.11, 165.66, 165.54, 165.17, 164.93, 134.18, 133.85,
133.38, 133.26, 133.09, 131.64, 131.19, 129.95, 129.86, 129.74,
129.17, 129.10, 129.03, 128.92, 128.84, 128.72, 128.45, 128.37,
128.21, 125.30, 123.59, 97.85 (C-1), 97.47 (C-1), 97.32 (C-1), 80.62
(CI-1), 77.27, 74.13, 72.95, 72.53, 72.20, 72.07, 70.95, 70.63, 70.39,
69.75, 67.90, 67.74, 67.62, 67.18, 61.25 (CV-6), 54.70, 54.52, 53.80,
23.71, 14.95 ppm. C142H111N5O40S (2559.48): calcd. C 66.64, H
4.37, N 2.74; found C 66.55, H 4.41, N 2.72. HRMS (ESI): calcd.
for C142H111N5O40S [M + Na]+ 2580.6424; found 2580.6418.
Ethyl 3,4-Di-O-benzoyl-2-deoxy-2-phthalimido-β-
D
-glucopyranosyl-
-glucopyranosyl-
-glucopyranosyl-
(1Ǟ6)-3,4-di-O-benzoyl-2-deoxy-2-phthalimido-β-
(1Ǟ6)-3,4-di-O-benzoyl-2-deoxy-2-phthalimido-β-
D
D
(1Ǟ6)-3,4-di-O-benzoyl-2-deoxy-2-phthalimido-1-thio-β-D-glucopyr-
anoside (7): Following general procedure A, coupling of 3[16]
(101 mg, 0.095 mmol) and 6[16] (152 mg, 0.14 mmol) followed by
deacetylation according to general procedure B. Yield: 145 mg
(74%). [α]2D0 = +8 (c = 1, CHCl3). H NMR (500 MHz, CDCl3): δ
1
Ethyl 3,4-Di-O-benzoyl-2-deoxy-2-phthalimido-β-
D
-glucopyranosyl-
-glucopyranosyl-
-glucopyranosyl-
-glucopyranosyl-
-glucopyranosyl-
-glucopyranosyl-
= 7.95–7.15 (m, 56 H), 6.25 (t, J = 10.0 Hz, 1 H), 6.18 (t, J =
10.0 Hz, 1 H), 6.07 (m, 2 H), 5.60 (d, J = 8.4 Hz, 1 H), 5.51 (d, J
= 10.5 Hz, 1 H), 5.43 (d, J = 8.4 Hz, 1 H), 5.39 (d, J = 8.4 Hz, 1
H), 5.34 (t, J = 9.7 Hz, 1 H), 5.28 (t, J = 9.6 Hz, 1 H), 5.22 (t, J =
9.6 Hz, 1 H), 5.18 (t, J = 9.6 Hz, 1 H), 4.50 (t, J = 10.4 Hz, 1 H),
4.43 (dd, J = 8.4, 10.5 Hz, 1 H), 4.33 (dd, J = 8.4, 10.5 Hz, 1 H),
4.25 (dd, J = 8.4, 10.5 Hz, 1 H), 4.03–3.97 (m, 2 H), 3.96–3.85 (m,
4 H), 3.82–3.76 (m, 3 H), 3.68–3.57 (m, 3 H) 5.05 (br. s, 1 H), 2.62
(m, 2 H), 1.15 (t, J = 8.5 Hz, 3 H) ppm. 13C NMR (125 MHz,
CDCl3): δ = 167.0, 165.6, 165.5, 165.0, 164.9, 134.1, 134.0, 133.8,
133.2, 133.1, 131.6, 131.1, 129.8, 129.7, 129.1, 129.0, 128.7, 128.6,
128.3, 128.2, 125.2, 123.6, 98.04, 97.6, 97.5, 80.9, 77.2, 74.1, 72.6,
72.4, 72.0, 70.9, 70.6, 70.0, 69.8, 67.8, 67.5, 61.2, 54.7, 54.6, 53.8,
23.8, 15.0 ppm. C114H90N4O32S (2060.01): calcd. C 66.47, H 4.40,
N 2.72; found C 66.29, H 4.50, N 2.67.
(1Ǟ6)-3,4-di-O-benzoyl-2-deoxy-2-phthalimido-β-
(1Ǟ6)-3,4-di-O-benzoyl-2-deoxy-2-phthalimido-β-
(1Ǟ6)-3,4-di-O-benzoyl-2-deoxy-2-phthalimido-β-
(1Ǟ6)-3,4-di-O-benzoyl-2-deoxy-2-phthalimido-β-
(1Ǟ6)-3,4-di-O-benzoyl-2-deoxy-2-phthalimido-β-
D
D
D
D
D
(1Ǟ6)-3,4-di-O-benzoyl-2-deoxy-2-phthalimido-1-thio-β-D-glucopyr-
anoside (10): Prepared from 9 (223 mg, 0.087 mmol) and 6[16]
(94 mg, 0.131 mmol) according to general procedures A and B.
Yield: 140 mg (45%). [α]2D0 = +10 (c = 1, CHCl3). 1H NMR
(500 MHz, CDCl3): δ = 7.57–8.05 (m, 49 H, Ar), 7.13–7.56 (m, 49
H, Ar), 6.05–6.30 (m, 7 H), 5.35–5.62 (m, 8 H), 5.05–5.33 (m, 6
H), 4.43–4.60 (m, 6 H), 4.18–4.40 (m, 8 H), 3.53–4.10 (m, 14 H),
3.23 (br. s, 1 H, OH), 2.62 (m, 2 H),1.10 (t, 3 H) ppm. 13C NMR
(125 MHz, CDCl3): δ = 165.65, 165.56, 165.27, 165.13, 165.08,
164.96, 137.91, 134.20, 133.94, 133.31, 133.17, 131.71, 131.26,
Ethyl 3,4-Di-O-benzoyl-2-deoxy-2-phthalimido-β-D-glucopyranosyl- 130.00, 129.80, 129.12, 128.86, 128.80, 128.46, 128.29, 125.37,
(1Ǟ6)-3,4-di-O-benzoyl-2-deoxy-2-phthalimido-β-
(1Ǟ6)-3,4-di-O-benzoyl-2-deoxy-2-phthalimido-β-
(1Ǟ6)-3,4-di-O-benzoyl-2-deoxy-2-phthalimido-β-
(1Ǟ6)-3,4-di-O-benzoyl-2-deoxy-2-phthalimido-β-
D
D
D
D
-glucopyranosyl-
-glucopyranosyl-
-glucopyranosyl-
-glucopyranosyl-
123.64, 98.01 (C-1), 97.55 (C-1), 97.35 (C-1), 80.71 (C-1), 77.37,
74.20, 73.15, 72.89, 72.75, 72.61, 72.29, 72.15, 71.07, 70.72, 70.35,
70.24, 69.81, 67.98, 67.58, 67.21, 61.30 (C-6), 54.80, 53.86, 29.77,
23.69 (SCH2CH3), 14.93 (SCH2CH3) ppm. C198H153N7O56S
(3558.41): calcd. C 66.83, H 4.33, N 2.76; found C 66.75, H 4.37,
(1Ǟ6)-3,4-di-O-benzoyl-2-deoxy-2-phthalimido-1-thio-β-D-glucopyr-
Eur. J. Org. Chem. 2010, 2465–2475
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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2473

N. E. Nifantiev et al.
N 2.74. HRMS (ESI): calcd. for C198H153N7O56S [M + Na]+ Cycloheptakis-(1Ǟ6)-(3,4-di-O-benzoyl-2-deoxy-2-phthalimido-β-
FULL PAPER
D-
3578.8958; found 3578.8953.
glucopyranosyl) (14): Cyclization of 10 (66 mg, 0.018mmol) accord-
ing to general procedure C afforded 14β (39 mg, 59%) and 14α
Cyclotetrakis-(1Ǟ6)-(3,4-di-O-benzoyl-2-deoxy-2-phthalimido-β-D-
(8 mg, 10%). Ratio β/α ≈ 6:1. Data for 14β: Colorless foam. [α]2D0
glucopyranosyl) (11β) and (11α): Cyclization of
7 (187 mg,
1
= +30 (c = 1, CHCl3). H NMR (600 MHz, CDCl3): δ = 7.75 (m,
0.082 mmol) according to general procedure C afforded 11β
(112 mg, 68%) and 11α (28 mg, 17%). Ratio β/α = 4:1. Data for
11β: Colorless foam. [α]2D0 = +3 (c = 1, CHCl3). 1H NMR
(500 MHz, CDCl3): δ = 7.71 (m, 4 H), 7.58 (m, 4 H), 7.37 (m, 2
H), 7.22 (m, 4 H), 6.09 (t, J3,2 = J3,4 = 9.5 Hz, 1 H, H-3), 5.77 (d,
J1,2 = 8.4 Hz, 1 H, H-1), 5.57 (t, J4,5 = 9.4 Hz, 1 H, H-4), 4.71 (dd,
1 H, H-2), 4.16–4.02 (m, 3 H, H-5, 2 H-6) ppm. 13C NMR
(125 MHz, CDCl3): δ = 167.9, 165.6, 164.6, 133.7, 132.9, 132.8,
131.7, 129.8, 129.6, 129.0, 128.7, 123.3, 98.3 (C-1), 74.6 (C-5), 71.6
(C-3), 69.6 (C-4), 68.5 (C-6), 54.3 (C-2) ppm. HRMS (ESI): calcd.
for C112H84N4O32 [M + Na]+ 2019.4966; found 2019.4961. Data
for 11α: Colorless foam. [α]2D0 = +29 (c = 0.5, CHCl3). 1H NMR
(500 MHz, CDCl3): δ = 7.98–7.20 (m, 56 H), 6.86 (br. t, J =
10.0 Hz, 1 H, H-3α), 6.33 (t, J = 10.0 Hz, 1 H), 6.25 (t, J = 10.0 Hz,
1 H), 5.99 (t, J = 10.4 Hz, 1 H), 5.85 (t, J = 10.4 Hz, 1 H), 5.71
(d, J = 8.5 Hz, 1 H), 5.62 (m, 2 H), 5.50 (t, J = 9.6 Hz, 1 H), 5.33
(m, 2 H), 5.01 (br. s, 1 H, H-1α), 4.88 (br. t, J = 9.6 Hz, 1 H), 4.82–
4.77 (m, 2 H), 4.68–4.62 (m, 2 H), 4.26–4.20 (m, 2 H), 4.17 (m, 2
H), 4.00 (m, 1 H), 3.96–3.89 (m, 3 H), 3.87–3.82 (m, 2 H), 3.73 (m,
1 H) ppm. 13C NMR (125 MHz, CDCl3): δ = 165.6, 165.46, 164.0,
134.0, 133.7, 133.6, 133.4, 133.1, 132.9, 132.7, 132.6, 131.8, 131.7,
131.4, 130.1, 129.8, 129.7, 129.4, 129.3, 129.1, 128.9, 128.4, 128.2,
128.1, 127.9, 123.6, 98.8, 98.2, 97.8, 97.5, 73.65, 73.36, 73.19, 71.58,
71.16, 70.8, 70.2, 69.3, 67.9, 67.6, 65.9, 54.6, 54.2, 53.9 ppm.
HRMS (ESI): calcd. for C112H84N4O32 [M + Na]+ 2019.4966;
found 2019.4961.
4 H), 7.62 (m, 4 H), 7.42 (m, 1 H), 7.38 (m, 1 H), 7.25 (m, 2 H),
7.19 (m, 2 H), 6.18 (t, J3,2 = J3,4 = 9.8 Hz, 1 H, H-3), 5.53 (d, J1,2
= 8.3 Hz, 1 H, H-1), 5.46 (t, J4,5 = 9.6 Hz, 1 H, H-4), 4.59 (dd, 1
H, H-2), 4.18 (d, J6a,6b = 9.8 Hz, 1 H, H-6a), 4.03 (m, 1 H, H-5),
3.89 (dd, J6b,5 = 5.0 Hz, 1 H, H-6b) ppm. 13C NMR (150 MHz,
CDCl3): δ = 167.8, 164.8, 133.7, 132.9, 132.8, 131.7, 129.8, 129.7,
129.2, 128.2, 128.1, 123.5, 97.8 (C-1), 73.4 (C-5), 71.4 (C-3), 70.1
(C-4), 67.1 (C-6), 54.6 (C-2) ppm. HRMS (ESI): calcd. for
C
196H147N7O56 [M + Na]+ 3516.8767; found 3516.8762. Data for
1
14α: H NMR (600 MHz, CDCl3) selected signals: δ = 7.17 (H-3
α-GlcN), 5.45 (H-4 α-GlcN), 5.19 (H-1 α-GlcN) 4.82 (dd, J2,1
=
2.8 Hz, J2,3 = 11.1 Hz, 1 H, H-2 α-GlcN), 4.45 (H-5 α-GlcN) ppm.
HRMS (ESI): calcd. for C196H147N7O56 [M + 2Na]2+ 1769.9327;
found 1769.9327.
Cyclobis-(1Ǟ6)-(2-amino-2-deoxy-2-β-D-glucopyranosyl) (15): Pre-
pared from 3[16] (49 mg, 0.049 mmol) according to the published
procedure for total deprotection.[16] Yield: 15 mg (95%). [α]2D0 = –22
(c = 1, H2O). HRMS (ESI): calcd. for C12H22N2O8 [M + H]+
323.1449; found 323.1447.
Cyclotris-(1Ǟ6)-(2-amino-2-deoxy-2-β-
pared from 4[16] (39 mg, 0.026 mmol) according to the published
procedure for total deprotection.[16] Yield: 12 mg (95%). [α]2D0
D-glucopyranosyl) (16): Pre-
=
–0.5 (c = 1, H2O). HRMS (ESI): calcd. for C18H33N3O12 [M +
H]+ 484.2137; found 484.2136.
Cyclopentakis-(1Ǟ6)-(3,4-di-O-benzoyl-2-deoxy-2-phthalimido-β-D-
Cyclotetrakis-(1Ǟ6)-(2-amino-2-deoxy-2-β-D-glucopyranosyl) (17):
glucopyranosyl) (12): Cyclization of 9 (96 mg, 0.038 mmol) accord-
ing to general procedure C gave pure 12β (59 mg, 63%) and an
inseparable mixture of 12β/12α (20 mg, 21%) in a ratio of ≈6:1 (1H
Prepared from 11β (65.8 mg, 0.033 mmol) according to the pub-
lished procedure for total deprotection.[16] Yield: 20 mg (94%).
[α]2D0 = –30 (c = 1, H2O). HRMS (ESI): calcd. for C24H44N4O16 [M
+ H]+ 645.2825; found 645.2826.
NMR spectra estimation). Data for 12β: Colorless foam. [α]2D0
+58 (c = 1, CHCl3). H NMR (600 MHz, CDCl3): δ = 7.75 (m, 4
=
1
H), 7.62 (m, 4 H), 7.42 (m, 1 H), 7.38 (m, 1 H), 7.25 (m, 2 H), 7.19
Cyclopentakis-(1Ǟ6)-(2-amino-2-deoxy-2-β-
Prepared from 12β (44.9 mg, 0.018 mmol) according the published
9.6 Hz, 1 H, H-4), 5.57 (d, J1,2 = 8.3 Hz, 1 H, H-1), 4.69 (dd, 1 H, procedure for total deprotection.[16] Yield: 14 mg (95%). [α]2D0 = –22
D-glucopyranosyl) (18):
(m, 2 H), 6.19 (t, J3,2 = J3,4 = 9.9 Hz, 1 H, H-3), 5.62 (t, J4,5
=
H-2), 4.15 (d, J6a,6b = 9.1 Hz, 1 H, H-6a), 3.97 (m, 1 H, H-5), 3.87
(c = 1, H2O). HRMS (ESI): calcd. for C30H55N5O20 [M + H]+
(dd, J6b,5 = 5.2 Hz, 1 H, H-6b) ppm. 13C NMR (150 MHz, CDCl3): 806.3513; found 806.3510.
δ = 167.8, 164.8, 133.7, 132.9, 132.8, 131.7, 129.8, 129.7, 129.2,
Cyclohexakis-(1Ǟ6)-(2-amino-2-deoxy-2-β-D-glucopyranosyl) (19):
128.2, 128.1, 123.5, 97.9 (C-1), 72.9 (C-5), 71.4 (C-3), 70.5 (C-4),
68.0 (C-6), 54.7 (C-2) ppm. HRMS (ESI): calcd. for C140H105N5O40
[M + Na]+ 2518.6233; found 2518.6228.
Prepared from 13β (39 mg, 0.013 mmol) according to the published
procedure for total deprotection.[16] Yield: 12 mg (96%). [α]2D0 = –14
(c = 1, H2O). HRMS (ESI): calcd. for C36H66N6O24 [M + 2H]2+
484.2137; found 484.2135.
Cyclohexakis-(1Ǟ6)-(3,4-di-O-benzoyl-2-deoxy-2-phthalimido-β-D-
glucopyranosyl) (13): Cyclization of 8 (72 mg, 0.023 mmol) accord-
ing to general procedure C produced 13β (48 mg, 69%) and 13α
(8 mg, 11%). Data for 13β: Colorless foam. [α]2D0 = +36 (c = 1,
Cycloheptakis-(1Ǟ6)-(2-amino-2-deoxy-2-β-D-glucopyranosyl) (20):
Prepared from 14β (121 mg, 0.035 mmol) according to the pub-
lished procedure for total deprotection.[16] Yield: 18 mg (92%).
[α]2D0 = –12 (c = 1, H2O). HRMS (ESI): calcd. for C42H77N7O28 [M
+ 2H]2+ 564.7481; found 564.7479.
1
CHCl3). H NMR (600 MHz, CDCl3): δ = 7.75 (m, 4 H), 7.62 (m,
4 H), 7.42 (m, 1 H), 7.38 (m, 1 H), 7.25 (m, 2 H), 7.19 (m, 2 H),
6.25 (t, J3,2 = J3,4 = 9.9 Hz, 1 H, H-3), 5.61 (d, J1,2 = 7.9 Hz, 1 H,
H-1), 5.54 (br. t, J4,5 = 9.1 Hz, 1 H, H-4), 4.69 (br. t, 1 H, H-2),
4.11 (d, J6a,6b = 10.0 Hz, 1 H, H-6a), 4.02 (br. m, 1 H, H-5), 3.95
(br. m, 1 H, H-6b) ppm. 13C NMR (150 MHz, CDCl3): δ = 165.6,
164.8, 133.7, 132.9, 132.8, 131.7, 129.8, 129.7, 129.2, 128.2, 128.1,
123.5, 97.5 (C-1), 73.2 (C-5), 71.4 (C-3), 70.5 (C-4), 66.8 (C-6), 54.6
(C-2) ppm. HRMS (ESI): calcd. for C168H126N6O48 [M + Na]+
Cyclobis-(1Ǟ6)-(2-acetamido-2-deoxy-2-β-
Prepared from 15 (5.7 mg, 0.0176 mmol) according to the pub-
lished procedure for N-acetylation.[16] Yield: 7 mg (98%). [α]2D0
D-glucopyranosyl) (21):
=
+29 (c = 0.5, H2O). HRMS (ESI): calcd. for C16H26N2O10 [M +
Na]+ 407.1480; found 407.1481.
3017.7500; found 3017.7495. Data for 13α: Colorless foam. 1H Cyclotris-(1Ǟ6)-(2-acetamido-2-deoxy-2-β-
NMR (600 MHz, CDCl3) selected signals: δ = 7.28 (H-3 α-GlcN), Prepared from 16 (4.9 mg, 0.01 mmol) according to the published
D-glucopyranosyl) (22):
5.64 (t, J4,3 = J4,5 = 9.5 Hz, 1 H, H-4 α-GlcN), 5.30–5.33 (br. m, 2 procedure for N-acetylation.[16] Yield: 6 mg (97%). [α]2D0 = –9 (c =
H, H-1 and H-2 α-GlcN), 4.27 (H-5 α-GlcN) ppm. HRMS (ESI):
0.5, H2O). HRMS (ESI): calcd. for C24H39N3O15 [M + Na]+
632.2273; found 632.2274.
calcd. for C168H126N6O48 [M + Na]+ 3017.7500; found 3017.7495.
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© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2010, 2465–2475

Studies of Cyclic Oligo-(1Ǟ6)-β--Glucosamines
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D-glucopyranosyl)
(23): Prepared from 17 (8.7 mg, 0.012 mmol) according to the pub-
lished procedure for N-acetylation.[16] Yield: 10 mg (98%). [α]2D0
=
–9 (c = 1, H2O). HRMS (ESI): calcd. for C32H52N4O20 [M + H]+
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Cyclopentakis-(1Ǟ6)-(2-acetamido-2-deoxy-2-β-D-glucopyranosyl)
(24): Prepared from 18 (4.9 mg, 0.0061 mmol) according to the
published procedure for N-acetylation.[16] Yield: 6 mg (97%). [α]2D0
= –10 (c = 1, H2O). HRMS (ESI): calcd. for C40H65N5O25 [M +
H]+ 1016.4041; found 1016.4029.
Cyclohexakis-(1Ǟ6)-(2-acetamido-2-deoxy-2-β-D-glucopyranosyl)
(25): Prepared from 19 (4.9 mg, 0.0051 mmol) according to the
published procedure for N-acetylation.[16] Yield: 6 mg (97%). [α]2D0
= –22 (c = 1, H2O). HRMS (ESI): calcd. for C48H78N6O30 [M +
Na]+ 1241.4655; found 1241.4660.
Cycloheptakis-(1Ǟ6)-(2-acetamido-2-deoxy-2-β-D-glucopyranosyl)
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neral procedure for N-acetylation.[16] Yield: 8 mg (98%). [α]2D0 = –22
(c = 1, H2O). HRMS (ESI): calcd. for C56H91N7O35 [M + H]+
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Acknowledgments
We are grateful for the financial support of the Russian Foundation
for Basic Research (project no. 07-03-00603), and we acknowledge
a grant from the President of the Russian Federation to Young
Scientists (MK-5970.2008.3 to A.A.G.). We thank Professor G. B.
Pier (Channing Laboratory, Brigham and Women’s Hospital, Har-
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Received: November 6, 2009
Published Online: March 17, 2010
Eur. J. Org. Chem. 2010, 2465–2475
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
2475