Disordered hydrogen bonding in N-(1-deoxy-β-d-fructopyranos-1-yl)-N-allylaniline

Article abstract of DOI:10.1016/j.carres.2009.02.017

We report on a ¹³C NMR and a single-crystal X-ray diffraction study of N-(1-deoxy-β-d-fructopyranos-1-yl)-N-allylaniline (d-fructose-N-allylaniline). In solution, an equilibrium of α-pyranose, β-pyranose, α-furanose, β-furanose, and acyclic ket

Full text of DOI:10.1016/j.carres.2009.02.017

Carbohydrate Research 344 (2009) 948–951
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Note
Disordered hydrogen bonding in
N-(1-deoxy-b-D-fructopyranos-1-yl)-N-allylaniline
b
a
Valeri V. Mossine a, , Charles L. Barnes , Thomas P. Mawhinney
*
a Department of Biochemistry, University of Missouri, Columbia, MO 65211, USA
b Department of Chemistry, University of Missouri, Columbia, MO 65211, USA
a r t i c l e i n f o
a b s t r a c t
We report on a 13C NMR and a single-crystal X-ray diffraction study of N-(1-deoxy-b-
yl)-N-allylaniline ( -fructose-N-allylaniline). In solution, an equilibrium of -pyranose, b-pyranose, a-
D-fructopyranos-1-
Article history:
Received 22 January 2009
Received in revised form 18 February 2009
Accepted 19 February 2009
Available online 25 February 2009
D
a
furanose, b-furanose, and acyclic keto tautomers of the carbohydrate was detected in the following
respective proportions: 2.2%, 47.4%, 4.5%, 33.6%, and 12.3%. In the crystalline state, the compound exists
exclusively as the b-pyranose form, in the normal 2C5 chair conformation. Bond lengths and valence
angles compare well with the average values from a number of b-fructopyranose derivatives. The struc-
ture displays two unusual features for this class of compounds. First, the molecule assumes an eclipsed
conformation around the C1–C2 bond, apparently stabilized by an intramolecular O2–HÁÁÁN hydrogen
bond. Second, the O3, O4, and O5 hydroxyl groups are involved in an intermolecular hydrogen bonding,
which forms 12-membered homodromic cycles. In the cycles, each determined hydrogen atom site is half
occupied, possibly due to the ÁÁÁH–OÁÁÁH–OÁÁÁ ꢀ ÁÁÁO–HÁÁÁO–HÁÁÁ flip-flop type disorder.
Keywords:
Amadori compound
Crystal structure
Flip-flop hydrogen bonding
D-Fructose-N-allylaniline
Ó 2009 Elsevier Ltd. All rights reserved.
N-Derivatives of 1-amino-1-deoxy-D-fructose, also referred to
acyclic keto tautomer of N-(1-deoxy-D-fructos-1-yl)amines in
as fructosamines or Amadori rearrangement products or com-
pounds, belong to a family of key intermediates in the Maillard
reaction.1 As products of the nonenzymatic modification of amino
aqueous solutions did not exceed 2% and generally were around
or below 1%.8,9 Apparently, the hydrophobic amino substituents,
which are in close proximity to the carbonyl group, contribute to
a significant increase in the acyclic keto tautomer proportion,
while the hydrated keto form is not detectable. A similar phenom-
enon was previously observed in 1- and 3-deoxyhexoketose deriv-
acids, proteins, or other biologically relevant amines with D-glu-
cose, these compounds are of a significant interest for the food
and health sciences due to their impact on the nutritional and
organoleptic quality of processed foods,2,3 as well as their diagnos-
tic use in clinics.4,5
A therapeutic potential has been recently demonstrated for
some Amadori compounds which may inhibit tumorigenesis
in vivo through blockage of tumor-associated lectins, interaction
with other anti-tumor agents or antioxidant activity.6,7 As a part
of the structural identification of potential candidates for the bio-
logical studies, we have performed an X-ray diffraction study of
atives.10
D-Fructose-N-allylaniline crystallized exclusively in the b-
pyranose form, as evidenced by solid-state 13C NMR data (Table 1)
and the following X-ray diffraction study.
The ORTEP view of the molecule and numbering of atoms are
shown in Figure 1. The molecule of
conjugate of 1-deoxy- -fructose and N-allylaniline via its amino
group. The b-
D-fructose-N-allylaniline is a
D
D
-pyranose ring of the crystalline Amadori compound
exists in the 2C5 chair conformation, with puckering parameters11
of Q = 0.5689 Å, h = 177.36°, and u = 277.87°. This conformation
corresponds to the energy minimum for b-fructopyranose12 and
was experimentally established as the major or the only structure
N-(1-deoxy-D-fructos-1-yl)-N-allylaniline
(D-fructose-N-allylani-
line) and noticed an unusual hydrogen bonding pattern which ex-
ists in the crystal structure of this compound.
D-Fructose-N-allylaniline tautomerizes in aqueous solution, as
in both solution equilibria8,13 and crystalline state of
D
-fruc-
-fructose-amino acids16–19 and other 1-ami-
-fructose derivatives.20
Bond distances and valence angles (Table 2) in the carbohydrate
part of -fructose-N-allylaniline compare well to the corresponding
values for b- -fructosamine derivatives and
-fructose,14,15 other
expected, with b-pyranose as a predominant anomeric form (Table
1). It is followed by the b-furanose form, which amounts to one-
tose,14,15 a number of
no-1-deoxy-
D
D
third of the tautomeric population in the equilibrium. Both
a-fura-
nose and -pyranose tautomers are present as minor forms. Nota-
a
D
bly, there is an unusually high (12%) proportion of the acyclic keto
D
D
tautomer. Previously reported estimates for the population of the
to the average values for a number of crystalline pyranose struc-
tures.12,21 One noticeable difference is the elongated C1–C2 bond.
The endocyclic torsions (Table 2) do not differ significantly from
the ‘standard’ pyranoside torsions21 with C–C–C–C(ring) at 53-
* Corresponding author. Tel.: +1 573 882 2608; fax: +1 573 884 4631.
E-mail address: MossineV@missouri.edu (V.V. Mossine).
0008-6215/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2009.02.017

V. V. Mossine et al. / Carbohydrate Research 344 (2009) 948–951
949
Table 1
ing effect of the intramolecular hydrogen bond between the two
atoms (Fig. 1). Short intramolecular contacts between the anomer-
ic hydroxy group and the amino group are the most common fea-
ture of the H-bonding network in crystalline Amadori compounds.
As a rule, in ketosamine derivatives with an uncharged amino
group, the anomeric hydroxyl acts a sole donor for the amine nitro-
gen acceptor.20,22 When the amino group is protonated and
Chemical shifts of the carbohydrate portion in 13C NMR spectra (ppm relative TSPS or
glycine standards) and tautomeric composition of N-(1-deoxy-D-fructos-1-yl)-N-
allylaniline in D2O–pyridine solution and in solid state at 25 °C
Carbon
Tautomers in solution
Cryst
b-pyr
a-pyr
b-pyr
a-fur
b-fur
keto
C1
C2
C3
C4
C5
C6
57.00
58.54
56.60
57.62
60.36
52.33
101.52 102.11 108.95 105.76 214.91 97.12
charged, such as in D-fructose–amino acid zwitterions, the ammo-
72.44
73.99
66.29
62.04
72.02
72.91
71.90
65.80
84.40
80.37
85.83
64.34
79.72
77.42
83.90
65.02
79.00
75.15
73.40
65.8
71.47
71.6
70.61
64.25
nium group donates its hydrogen(s) to multicentered heteroatom
short contacts, which may involve the anomeric O2, the ring O6,
and/or endocyclic O3 as acceptors.16–19 However, in all 1-amino-
1-deoxy-b-D-fructopyranose structures reported to date, the rele-
Relative % of tautomer in 2.2
equilibrium
47.4
4.5
33.6
12.3
100
vant configuration was closer to the staggered, regardless of the
mutual disposition of the O2 and N1 atoms and the type of intra-
molecular hydrogen bonding. Hence, the crystal packing forces
may have also contributed to such an unusual structure in N-(1-
deoxy-b-D-fructopyranos-1-yl)-N-allylaniline.
The intermolecular hydrogen bonding scheme in the crystalline
D-fructose-N-allylaniline is relatively simple, as compared to that
in other Amadori compounds. It is represented by only one cyclic
pattern of short heteroatom contacts involving O3, O4, and O5 hy-
droxyl groups, all of which act as both donors and acceptors of the
hydrogen bonding (Fig. 2). A unique feature of this H-bonding pat-
tern is that each hydrogen atom position is only partially, one-half,
occupied (Table 3). Such a situation would be possible in case of a
superposition of two arrays of nonequivalent homodromic cycles,
as shown in Figure 3, since O–HÁÁÁH–O contacts in the cycles would
be unlikely due to an overlapping of the hydrogen van-der-Waals
radii. These alternative patterns must be of a similar energy, due
to an equal occupancy for the alternative hydrogen sites, and prob-
ably in a fast equilibrium, as evidenced by an absence of any signif-
icant shift in the hydroxyl atom positions (Table 4). This
phenomenon has previously been observed in crystalline cyclodex-
trin complexes,23 and has been attributed to a type of temperature-
Figure 1. Atomic numbering and thermal ellipsoids (50% probability) for molecular
conformations of N-(1-deoxy-b-D-fructopyranos-1-yl)-N-allylaniline. Intramolecu-
lar hydrogen bonds are shown as dotted lines.
Table 2
Selected bond distances (Å) and angles (°) in crystalline N-(1-deoxy-b-D-fructopyr-
anos-1-yl)-N-allylaniline
Bond distances
C1–C2
C4–C5
O6–C2
C1–N1
C2–O2
N1–C7
C14–C15
Valence angles
C1–N1–C7
C1–N1–C13
C7–N1–C13
N1–C1–C2
O2–C2–C1
C1–C2–O6
C2–C3–O3
C4–C5–O5
C6–O6–C2
1.554(3)
1.523(2)
1.430(2)
1.461(2)
1.401(2)
1.403(2)
1.306(3)
119.6(1)
113.5(1)
120.2(2)
113.6(2)
112.7(2)
106.0(1)
109.4(1)
109.8(2)
113.4(1)
Endocyclic torsion angles
C2–C3–C4–C5
+56.2(2)
C5–C6–O6–C2
À59.1(2)
Exocyclic torsion angles
N1–C1–C2–C3
N1–C1–C2–O2
N1–C1–C2–O6
C1–C2–C3–C4
O2–C2–C3–O3
O4–C4–C5–C6
O5–C5–C6–O6
À126.9(2)
À6.1(2)
Other torsions
C2–C1–N1–C7
C2–C1–N1–C13
C1–N1–C7–C8
C1–N1–C13–C14
N1–C13–C14–C15
À117.3(2)
+91.4(2)
+37.8(2)
+65.2(2)
À122.1(2)
+115.6(2)
À174.0(1)
À62.0(2)
À176.4(2)
À66.6(2)
54°, C-C–C–O(ring)—at 55–56°, and C–C–O–C at 59–60°. The exo-
cyclic angles around the ring bonds are close to the ‘ideal’ 180°
as well.
One obviously outstanding feature of D-fructose-N-allylaniline
structure is found in the nearly eclipsed (by 6°) conformation
around the C1–C2 bond. The anomeric oxygen O2 and amino N1
are in the (À)syn-periplanar disposition, possibly due to a stabiliz-
Figure 2. Crystal packing and intermolecular hydrogen bonding in N-(1-deoxy-b-
D-fructopyranos-1-yl)-N-allylaniline. Hydrogen atoms are not shown for clarity.

950
V. V. Mossine et al. / Carbohydrate Research 344 (2009) 948–951
Table 4
dependent, dynamic H-bonding disorder termed flip-flop hydrogen
bonding.24 It is assumed that the conformational change such as
the one shown in Figure 3, is achieved by a concerted rotation of
the hydroxyl groups from one H-bonded position into the other:
Atomic coordinates (Â104) and equivalent isotropic displacement parameters
(A2 Â 103) for N-(1-deoxy-b-D-fructopyranos-1-yl)-N-allylaniline
x
y
z
U(eq)
N1
C1
O2
C2
O3
C3
O4
C4
O5
C5
O6
C6
C7
C8
C9
C10
6414(1)
6091(1)
6503(1)
6170(1)
5493(1)
5683(1)
5292(1)
5747(1)
5606(1)
5961(1)
6345(1)
6425(1)
6755(1)
7000(1)
7358(1)
7484(1)
7244(1)
6882(1)
6201(1)
5752(1)
5325(1)
5744
6850(2)
7598(2)
9964(2)
9388(2)
9963(2)
10,266(2)
12,824(2)
12,001(2)
11,805(2)
12,243(2)
9656(2)
11,280(3)
5725(2)
5918(2)
4863(3)
3602(3)
3399(3)
4432(2)
6755(2)
5730(3)
6229(3)
7397
9635(2)
8032(3)
9406(2)
7844(3)
10,231(2)
8119(3)
7908(3)
7702(3)
3820(3)
5440(3)
5684(2)
5203(3)
8951(3)
6960(3)
6314(3)
7621(4)
9580(4)
10,236(3)
11,819(3)
11,957(3)
12,631(4)
8436
25(1)
26(1)
29(1)
23(1)
30(1)
23(1)
36(1)
25(1)
38(1)
28(1)
28(1)
31(1)
25(1)
29(1)
37(1)
41(1)
39(1)
30(1)
27(1)
32(1)
40(1)
31
H
H
O
O
O
O
H
H
Besides cyclodextrins, such disorder has been observed in crys-
talline phenols,25 calixarenes,26 or ice. We are not aware of its con-
firmed presence in previously reported crystal structures of any
fructosamine or other monosaccharide derivatives, although it
would be reasonably expected to be found among the networks
with homodromic hydrogen bonding patterns.
1. Experimental
1.1. N-(1-Deoxy-b-D-fructopyranos-1-yl)-N-allylaniline (D-
fructose-N-allylaniline)
C11
C12
C13
C14
A suspension of 3.6 g of D-glucose in a solution of 3.8 mL N-ally-
C15
laniline, 0.5 mL of HOAc and 8 mL of 2-propanol was stirred in a
H(1A)
H(1B)
H(3)
H(4)
H(5)
H(6A)
H(6B)
H(8)
H(9)
H(10)
H(11)
H(12)
H(13A)
H(13B)
H(14)
H(15A)
H(15B)
H(2O)
H(3OA)
H(3OB)
H(4OA)
H(4OB)
H(5OA)
H(5OB)
6146
7115
6589
31
Table 3
5442
9850
7019
28
Hydrogen-bonding in N-(1-deoxy-b-D-fructopyranos-1-yl)-N-allylaniline
5986
12,425
8803
30
6044
13,372
5251
34
D–HÁÁÁA
Occupancy
DÁÁÁA (Å)
D–H (Å)
HÁÁÁA (Å)
\ (D–HÁÁÁA) (°)
6547
11,381
3693
37
6682
11,696
6199
37
O2–HÁÁÁN1
1
2.683
2.688
2.723
2.790
3.030
2.723
2.790
2.795
0.81(3)
0.73(4)
0.76(5)
0.74(6)
0.78(6)
0.74(6)
0.73(5)
0.73(5)
2.16
1.96
2.02
2.09
2.27
2.06
2.19
2.53
123
171
154
157
164
149
141
104
O3–HAÁÁÁO3a
O3–HBÁÁÁO5b
O4–HAÁÁÁO5c
O4–HBÁÁÁO4a
O5–HAÁÁÁO3d
O5–HBÁÁÁO4c
O5–HBÁÁÁO4
½
½
½
½
½
½
½
6920
6779
6047
35
7518
5006
4959
44
7731
2888
7178
49
7328
2539
10,487
47
6718
4262
11,577
36
6111
7821
12,298
33
6454
6355
12,845
33
5781
4667
11,534
38
Suspected H-bonding contacts
5287
7287
13,063
47
C1–H1ÁÁÁO3
1
1
2.932
3.379
0.99
0.95
2.55
2.53
103
149
5053
5535
12,689
47
C15–H1ÁÁÁO4e
6677(11)
5224(14)
5615(15)
5100(20)
5193(19)
5649(16)
5391(16)
9230(40)
10,040(50)
10,430(60)
12,380(80)
12,760(80)
11,130(60)
12,310(60)
9700(50)
10,190(60)
11,140(80)
7300(90)
9100(100)
3090(80)
3880(70)
57(9)
9(9)
19(11)
47(17)
51(17)
24(12)
17(11)
Intramolecular syndiaxial contacts
C3–HÁÁÁO5
C4–HÁÁÁO2
C6–H1ÁÁÁO2
1
1
1
2.953
2.883
2.820
1.00
1.00
0.99
2.62
2.56
2.52
99
99
97
Symmetry codes: aÀx + 1, y, Àz + 2; bx, y, z + 1; cÀx + 1, y, Àz + 1; dx, y, zÀ1; eÀx + 1,
y À 1, Àz + 2.
U(eq) is defined as 1/3 of the trace of the orthogonalized Uij tensor.
Figure 3. Proposed hydrogen bonding scheme in the crystal structure of N-(1-deoxy-b-D-fructopyranos-1-yl)-N-allylaniline. The homodromic cycles are formed by
intermolecular hydrogen bonds and linked in pairs by the intramolecular H-bonds. There is a fast equilibrium between the hydroxyl groups orientations, resulting in a
statistical one-half occupancy of the hydrogen atom positions on the electron density maps.

V. V. Mossine et al. / Carbohydrate Research 344 (2009) 948–951
951
Table 5
CCDC 717417. Copies of this information may be obtained free of
charge from the Director, Cambridge Crystallographic Data Centre,
12 Union Road, Cambridge, CB2 1EZ, UK. (fax: +44-1223-336033, e-
mail: deposit@ccdc.cam.ac.uk or via: www.ccdc.cam.ac.uk).
Crystal data, structure determination and refinement data for N-(1-deoxy-b-D-
fructopyranos-1-yl)-N-allylaniline
Empirical formula
Formula weight
C12H19NO6
273.28
Crystal system, space group
Monoclinic, C2
Unit cell dimensions
a(Å)
b(Å)
c(Å)
Acknowledgments
27.142(4)
8.567(1)
6.1331(9)
90.523(2)
1426.0(4)
4
The authors thank Drs. Wei Wycoff and Shaokai Jiang for their
assistance with acquiring NMR spectra. This work was supported,
in part, by the University of Missouri Experiment Station Chemis-
try Laboratories.
b(°)
U(Å3)
Z
Crystal size (mm)
0.50 Â 0.25 Â 0.25
Dcalc (cmÀ3
)
1.273
l
(cmÀ1
F(0 0 0)
)
1.02
584
References
Radiation Mo K
(Å)
Diffractometer
Temperature (K)
Data collection range (°)
Limiting indices
a, graphite monochromator k = 0.71073
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Enraf–Nonius CAD4
173
2
1.50 < h < 27.12
À34 6 h 6 34, À10 6 k 6 10,
À7 6 l 6 7
No. of observed/unique data
Completeness to h = 27.12°
Absorption correction
Max/min transmission
Refinement method
5130/1670 [Rint = 0.0240]
99.5%
Semi-empirical from equivalents
0.97/0.78
Full-matrix least-squares on F2
1/218
No. of restraints/parameters
R indices (all data)
R1 = 0.0309, wR2 = 0.0751
R1 = 0.0277, wR2 = 0.0725
1.036
Final R indices [I > 2
r(I)]
Goodness of fit on F2
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(10)
Largest difference in peak and hole (e ÅÀ3
)
0.206 and À0.128
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cap-closed vial at 87 °C for 14 h. Completion of the reaction was
confirmed by TLC. The dark amber solution was diluted with 50
mL of Et2O and left at 4 °C. Within a week, the crystalline title com-
pound was separated as light-amber prisms, mp 120–121 °C. See
Table 1 for NMR data. Anal. Calcd for C15H21NO5: C, 61.0; H, 7.17;
N, 4.74. Found: C, 60.7; H, 7.08; N, 4.77.
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1.2. Single-crystal X-ray diffraction study
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and polarization effects, but not for absorption. Non-hydrogen
atoms were refined with anisotropic thermal parameters. Hydroxyl
hydrogen atoms were located in difference Fourier maps and were
refined with fixed isotropic thermal parameters. The remaining H-
atoms were placed at calculated positions. Positional and thermal
parameters are listed in Table 4.
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Complete crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic Data Centre,