Synthesis, characterisation and crystal structures of Schiff bases from the reaction of 4,6-O-ethylidene-β-D-glucopyranosylamine with substituted salicylaldehydes

Article abstract of DOI:10.1016/S0008-6215(01)00201-4

Multiple chemical modifications were carried out on D-glucose to result in the corresponding Schiff bases. Such modifications performed on D-glucose not only helped in increasing the solubility of the products in nonaqueous solvents, but also restricted the anomerisation of the saccharide moiety in solution. NMR study of the products revealed the presence of the β-anomeric form of the saccharide moiety in Me₂SO solution. All the compounds were characterised by analytical and spectral methods. The literature is devoid of any crystal structures of saccharide-Schiff base combinations of the type reported in this paper. The crystal structures of these molecules exhibited a tridentate, ONO binding core. These studies further revealed that the compounds in the solid state were in the β-D-pyranose form with the ⁴C₁ chair conformation. The compounds exhibited interesting lattice structures assisted through weak interactions of the type O-H···O and C-H···O. The lattice structure of one of these compounds exhibited channels filled with chloroform molecules.

Full text of DOI:10.1016/S0008-6215(01)00201-4

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Carbohydrate Research 335 (2001) 33–43
Synthesis, characterisation and crystal structures of
Schiff bases from the reaction of
4,6-O-ethylidene-b-
D
-glucopyranosylamine with
substituted salicylaldehydes
Ajay K. Sah,a Chebrolu P. Rao,a,* Pauli K. Saarenketo,b Erkki Kolehmainen,b
Kari Rissanenb
aBioinorganic Laboratory, Department of Chemistry, Indian Institute of Technology Bombay, Powai,
Mumbai 400 076, India
bDepartment of Chemistry, Uni6ersity of Jy6askyla, Jy6askyla Fin 40351, Finland
Received 26 May 2001; accepted 9 July 2001
Abstract
Multiple chemical modifications were carried out on
D-glucose to result in the corresponding Schiff bases. Such
modifications performed on -glucose not only helped in increasing the solubility of the products in nonaqueous
D
solvents, but also restricted the anomerisation of the saccharide moiety in solution. NMR study of the products
revealed the presence of the b-anomeric form of the saccharide moiety in Me2SO solution. All the compounds were
characterised by analytical and spectral methods. The literature is devoid of any crystal structures of saccharide–
Schiff base combinations of the type reported in this paper. The crystal structures of these molecules exhibited a
tridentate, ONO binding core. These studies further revealed that the compounds in the solid state were in the
4
b-D
-pyranose form with the C1 chair conformation. The compounds exhibited interesting lattice structures assisted
through weak interactions of the type OꢀH···O and CꢀH···O. The lattice structure of one of these compounds
exhibited channels filled with chloroform molecules. © 2001 Elsevier Science Ltd. All rights reserved.
Keywords: 4,6-O-Ethylidene-b-D-glucopyranosylamine; Saccharide–Schiff bases; Single crystal XRD; Channel structure; Triden-
tate binding core; FAB mass spectrometry
1. Introduction
are considered as active-site-directed reversible
inhibitors of glycosidase, and some of these
compounds have been proposed as oral anti-
diabetic agents.2–4 Several glycosylamines are
known in the literature, but as far as the
glycosylamine derived Schiff base molecules
are concerned, the literature is scarce. Al-
though Schiff base molecules are potential
ligands for the metal–ion binding, it is sur-
prising to note that the inorganic chemists
have not much explored the potential of the
saccharide-based Schiff bases. This may be
attributed to the problem of the rearrange-
It is well known that under mild conditions,
aldoses react with primary or secondary
amines to form glycosylamines where the hy-
droxyl group on C-1 is replaced by the amine
in order to result in C-1ꢀNRR% via condensa-
tion. The glycosylamines are of biological and
pharmaceutical importance.1 Many of these
* Corresponding author. Tel.: +91-22-5783245; fax: +91-
22-5723480.
E-mail address: cprao@chem.iitb.ac.in (C.P. Rao).
0008-6215/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0008-6215(01)00201-4

34
A.K. Sah et al. / Carbohydrate Research 335 (2001) 33–43
Table 1
Summary of crystallographic data and structural parameters
for 1 and 2
1
2
Empirical formula
Molecular weight
T (K)
C17H22Cl3NO7 C15H18BrNO6
458.71
173(2)
388.21
173(2)
Crystal system
Space group
monoclinic
P21
monoclinic
P21
Cell constants
,
a (A)
11.898(1)
6.295(1)
14.718(1)
101.06(1)
1081.9(2)
2
8.439(1)
5.601(1)
16.456(1)
92.01(1)
777.34(17)
2
,
b (A)
,
c (A)
i (°)
V (A )
3
,
Z
Dcalcd (Mg m−3
)
1.408
1.659
Total Reflections
Unique reflections
6384
3543
4544
3011
[Rint=0.0424] [Rint=0.0340]
Fig. 1. (a) Molecular structure of 1 and (b) its stereoview
showing 50% probability thermal ellipsoids using ORTEP. The
dashed line enclosure shown in (a) represents the ONO bind-
ing core.
Max/min transmission
factors
Parameters
Final R (I\2|(I))
Rw
0.9008 and
0.8514
262
0.5937 and
0.5586
217
0.0657
0.1521
0.0290
0.0623
Table 2
Atomic coordinates (×104) for 1
x
y
z
C(2)
C(3)
C(5)
C(6)
C(7)
C(8)
C(9)
C(10)
C(12)
C(14)
C(15)
C(16)
C(18)
C(21)
C(22)
C(24)
N(11)
O(1)
7524(4)
7926(4)
9213(5)
7542(4)
6730(5)
6322(4)
6718(4)
6290(4)
6223(4)
4925(4)
4362(4)
5228(4)
5728(4)
3028(4)
2497(4)
4038(4)
6639(3)
7928(3)
8704(3)
5341(3)
4685(3)
6627(3)
3859(3)
3552(3)
9826(5)
11099(1)
8995(2)
10135(3)
7801(8)
5969(8)
3027(9)
5511(8)
6843(8)
8604(8)
9117(7)
11027(8)
13324(7)
16211(7)
15539(7)
14504(8)
12600(7)
18323(8)
20168(8)
17315(8)
11498(6)
8175(5)
4814(6)
14374(5)
13868(5)
11645(6)
17356(5)
19042(5)
5934(10)
4685(3)
4160(6)
8326(5)
4124(3)
4649(3)
4809(4)
5449(4)
5743(4)
5249(3)
4427(3)
3899(3)
2619(3)
2478(3)
1503(3)
1030(3)
1623(3)
1450(3)
880(3)
2922(3)
3158(3)
3344(2)
4283(2)
3002(2)
127(2)
Scheme 1. Glycosylamine-based Schiff base compounds. (i)
3-Methoxysalicylaldehyde; (ii) 5-bromosalicylaldehyde; (iii) 5-
nitrosalicylaldehyde.
O(4)
O(13)
O(17)
O(19)
O(20)
O(23)
C(30)
Cl(31)
Cl(32)
Cl(33)
1260(2)
994(2)
2339(2)
2508(4)
3058(1)
1750(2)
2065(4)
Scheme 2. Resonance stabilisation in Schiff base 3.

A.K. Sah et al. / Carbohydrate Research 335 (2001) 33–43
35
ment of the glycosylamines in solution via the
formation of imonium ion intermediates, re-
sulting in mutarotation, hydrolysis, transgly-
cosylation, or Amadori rearrangements.5 To
our knowledge, the structurally characterised
complex of C-1 amine based Schiff base ligand
is the tetranuclear copper complex reported
ethylidene-b- -glucopyranosylamine. All the
D
products were characterised based on FTIR,
UV–Vis, NMR, FAB mass spectrometry, mi-
croanalysis and single-crystal X-ray diffrac-
tion studies.
for 1-amino-1-deoxy-
D
-sorbitol based Schiff
2. Experimental
base ligand in the literature.6 Therefore, herein
we report the synthesis and characterisation of
the Schiff base molecules derived from 4,6-O-
D
-Glucose was procured from Aldrich
Chemical Co. (USA) and 3-methoxysalicyl-
Table 3
2
3
,
Anisotropic displacement parameters (A ×10 ) for 1
U11 U22
U33
18(2)
U23
1(2)
U13
−2(2)
U12
2(2)
C(2)
26(3)
19(3)
C(3)
C(5)
C(6)
C(7)
C(8)
C(9)
C(10)
C(12)
C(14)
C(15)
C(16)
C(18)
C(21)
C(22)
C(24)
N(11)
O(1)
20(2)
38(3)
27(3)
33(3)
28(3)
25(2)
12(2)
20(2)
20(2)
21(2)
24(2)
22(3)
19(2)
30(3)
31(3)
24(2)
34(2)
32(2)
30(2)
29(2)
31(2)
24(2)
31(2)
36(3)
34(1)
92(2)
101(2)
17(3)
21(3)
22(3)
30(3)
24(3)
13(3)
20(3)
19(3)
17(2)
11(2)
18(3)
17(2)
19(3)
24(3)
21(3)
19(2)
24(2)
23(2)
16(2)
23(2)
26(2)
17(2)
18(2)
55(4)
81(1)
165(3)
116(2)
28(3)
57(4)
34(3)
24(3)
22(3)
19(2)
25(3)
18(2)
14(2)
19(2)
16(2)
20(2)
21(2)
24(3)
20(3)
18(2)
25(2)
37(2)
17(2)
14(2)
21(2)
19(2)
22(2)
54(4)
78(1)
89(2)
322(5)
3(2)
7(3)
16(2)
10(2)
1(2)
2(2)
−2(2)
1(2)
5(2)
4(2)
−4(2)
−2(2)
0(2)
6(2)
1(2)
1(2)
8(2)
9(2)
0(1)
−3(1)
−4(2)
1(1)
−3(1)
4(3)
5(1)
−55(2)
138(3)
−3(2)
−1(3)
−3(2)
3(2)
4(2)
−3(2)
5(2)
0(2)
0(2)
4(2)
5(2)
4(2)
5(2)
−1(2)
6(2)
0(2)
10(2)
4(2)
6(1)
2(1)
4(2)
3(2)
10(2)
−1(2)
−12(2)
−1(2)
−2(2)
1(2)
5(2)
4(2)
2(2)
−6(2)
2(2)
0(2)
11(2)
4(2)
3(2)
10(2)
10(2)
5(1)
3(1)
9(2)
3(1)
7(2)
7(3)
O(4)
O(13)
O(17)
O(19)
O(20)
O(23)
C(30)
Cl(31)
Cl(32)
Cl(33)
4(1)
0(1)
8(3)
7(1)
10(1)
12(2)
48(2)
−24(1)
119(3)
The anisotropic displacement factor exponent takes the form: −2y2[h2a*2U11+…+2hka×b×U12].
Table 4
Selected torsion angles (°) for 1
N(11)ꢀC(12)ꢀO(13)ꢀC(14)
O(13)ꢀC(12)ꢀC(18)ꢀO(19)
O(17)ꢀC(16)ꢀC(18)ꢀC(12)
O(20)ꢀC(15)ꢀC(16)ꢀC(18)
C(24)ꢀC(14)ꢀC(15)ꢀC(16)
C(9)ꢀC(10)ꢀN(11)ꢀC(12)
179.4(4)
178.0(4)
−175.5(3)
179.5(3)
178.1(4)
178.8(4)
N(11)ꢀC(12)ꢀC(18)ꢀC(16)
C(15)ꢀC(16)ꢀC(18)ꢀO(19)
C(14)ꢀC(15)ꢀC(16)ꢀO(17)
O(13)ꢀC(14)ꢀC(15)ꢀO(20)
C(24)ꢀC(14)ꢀO(13)ꢀC(12)
C(2)ꢀC(9)ꢀC(10)ꢀN(11)
177.7(4)
−175.0(4)
179.4(4)
175.4(3)
−177.8(4)
0.5(6)

36
A.K. Sah et al. / Carbohydrate Research 335 (2001) 33–43
Table 5
were recorded at room temperature. Short
labels, such as, ‘Sac’, ‘Prot’ and ‘Ar’ are used
in the NMR spectral assignments in order to
refer to the saccharide, protection and aro-
matic groups, respectively.
Cremer–Pople puckering parameters and asymmetry parame-
ters
1
2
,
Q (A)
0.603
2.2
0.595
8.9
N-(2-Hydroxy-3-methoxybenzylidene)-4,6-
q (°)
O-ethylidene-i-
To a suspension of 4,6-O-ethylidene-b-
D
-glucopyranosylamine (1).—
ƒ (°)
278.07
286.36
D
-
DCs (C-1, C-4) (°)
DCs (C-2, C-5) (°)
DCs (C-3, O-5) (°)
0
0
0
0
0
0
glucopyranosylamine (EGNH2, 5.12 g, 24.97
mmol) in EtOH (40 mL), 3-methoxysalicy-
laldehyde (3.82 g, 25.11 mmol) was added,
and the reaction mixture was allowed to reflux
for 2.5 h, which resulted in a clear orange
solution. The reaction mixture was allowed to
cool to rt, and the solvent was evaporated to
result in a pasty mass. This was further dis-
solved in CH2Cl2 (10 mL), and excess
petroleum ether was added to precipitate the
product. The product was isolated through
filtration, and the filtrate was concentrated
and kept at −20 °C to result in a second crop
of solid. Yield 8.08 g (93%): mp 130–132 °C.
UV–Vis [umax; nm (m; L cm−1 mol−1)]: 267
(21667), 334 (4408), 419 (86). 1H NMR
(Me2SO-d6, 300 MHz, ppm): 13.01 (1 H, s,
ArOH), 8.57 (1 H, s, HCꢁN), 7.09 (2 H, m,
ArH), 6.85 (1 H, t, J 7.9 Hz, ArH), 5.54 (1 H,
d, J 5.9 Hz, SacOH), 5.35 (1 H, d, J 5.5 Hz,
SacOH), 4.75 (1 H, q, J 4.9 Hz, ProtCH), 4.56
(1 H, d, J 8.4 Hz, SacH-1), 4.06 (1 H, m,
SacH-5), 3.79 (3 H, s, ArCH3), 3.0–3.6 (5 H,
Fig. 2. H-bonding pattern observed in 1. The filled circles
denote oxygen atoms, circles bisected with one line denote
nitrogen atoms and circles with cross denote chlorine atoms.
Dotted lines represent H-bonds.
aldehyde from Lancaster Synthesis Ltd (UK).
4,6-O-Ethylidene-
ethylidene-b-
D
-glucopyranose,7
4,6-O-
13
m, Sac), 1.25 (3 H, d, J 5.1 Hz, ProtCH3). C
D
-glucopyranosylamine8
(EG-
NMR (Me2SO-d6, 126 MHz, ppm): 165.4,
150.6, 147.8, 123.7, 118.3, 118.2, 115.4, 98.6,
95.2, 80.1, 74.7, 73.3, 67.9, 67.2, 55.8, 20.3.
FABMS: m/z 340 (M+H+, 100%). Anal.
Calcd for C16H22NO7.5: C, 55.16; H, 6.22; N,
4.02. Found C, 55.40; H, 6.56; N, 4.16. Single
crystals suitable for X-ray diffraction studies
were grown by slow diffusion of CHCl3 into a
concentrated solution of the compound in
MeOH at rt.
NH2) and 5-bromosalicylaldehyde were syn-
thesised as per the reported procedures,9 and
all other chemicals were procured from local
sources. All the solvents were purified and
dried immediately before use. Elemental anal-
ysis was carried out on a Carlo–Erba elemen-
tal analyser, and FTIR spectra were recorded
on a Nicolet Impact 400 instrument in KBr
matrix. Absorption spectra were measured on
a Shimadzu UV2101PC spectrophotometer.
1H NMR spectra were recorded on Bruker
Avance DRX 500 or Varian XL-300 spec-
trometer in Me2SO-d6. The FAB mass spectra
were recorded on a JEOL SX 102/DA-600
mass spectrometer/data system using argon/
xenon (6 kV, 10 mA) as the FAB gas and
m-nitrobenzyl alcohol as the matrix. The ac-
celerating voltage was 10 kV, and the spectra
N-(5-Bromo-2-hydroxybenzylidene)-4,6-O-
ethylidene-i-
D
-glucopyranosylamine
(2).—
This compound was prepared by a procedure
similar to that adopted for 1, but by using
EGNH2 (2.77 g, 13.51 mmol) and 5-bromosal-
icylaldehyde (2.77 g, 13.78 mmol) in MeOH
(40 mL). Yield 4.36 g (83%): mp 171–72 °C.
UV–Vis [umax; nm (m; L cm−1 mol−1)]: 261
(15620), 330 (7154), 414 (61). 1H NMR

A.K. Sah et al. / Carbohydrate Research 335 (2001) 33–43
37
(Me2SO-d6, 300 MHz, ppm): 12.91 (1 H, s,
ArOH), 8.57 (1 H, s, HCꢁN), 7.80 (1 H, d, J
2.6 Hz, ArH), 7.50 (1 H, dd, J 2.6, 8.8 Hz,
ArH), 6.89 (1 H, d, J 8.8 Hz, ArH), 5.57 (1 H,
d, J 5.7 Hz, SacOH), 5.37 (1 H, d, J 5.5 Hz,
SacOH), 4.75 (1 H, q, J 5.0 Hz, ProtCH), 4.58
(1 H, d, J 8.2 Hz, SacH-1), 4.06 (1 H, m,
SacH-5), 3.0–3.5 (5 H, m, Sac), 1.25 (3 H, d,
J 4.9 Hz, ProtCH3). 13C NMR (Me2SO-d6, 126
MHz, ppm): 163.3, 159.3, 135.2, 133.8, 120.3,
118.9, 109.5, 98.5, 95.0, 80.0, 74.6, 73.2, 67.8,
67.2, 20.2. FABMS m/z 388 (M+, 100%).
Anal. Calcd for C15H18BrNO6: C, 46.41; H,
4.67; N, 3.61. Found C, 46.72; H, 4.76; N,
3.31. Single crystals suitable for X-ray diffrac-
tion studies were grown by slow evaporation
of a concentrated solution in MeOH at rt.
N-(2-Hydroxy-5-nitrobenzylidene)-4,6-O-
ethylidene-i-
D
-glucopyranosylamine
(3).—
This compound was prepared by adopting the
procedure given for 1 but using EGNH2 (0.41
g, 2.00 mmol) and 5-nitrosalicylaldehyde (0.34
Fig. 3. Packing diagram of 1 showing channels filled with chloroform molecules. The filled circles denote oxygen atoms, circles
bisected with one line denote nitrogen atoms and circles with cross denote chlorine atoms. Dotted lines represent H-bonds.
Table 6
Hydrogen bond data in the case of 1
,
,
,
DꢀH···A
d(DꢀH) (A)
d(H···A) (A)
d(D···A) (A)
B(DHA) (°)
Symmetry
O(1)ꢀH(1)···N(11)
O(17)ꢀH(17)···O(20)
O(19)ꢀH(19)···O(17)
C(7)ꢀH(7a)···O(23)
C(30)ꢀH(30)···O(1)
C(30)ꢀH(30)···O(4)
0.838(10)
0.839(10)
0.837(10)
0.950(12)
1.000(12)
1.000(12)
1.814(3)
1.964(2)
2.128(3)
2.543(6)
2.245(5)
2.367(5)
2.577(5)
2.779(5)
2.905(5)
3.398(8)
3.110(7)
3.232(7)
150.5(5)
163.5(6)
154.3(6)
149.8(8)
144.0(7)
144.3(7)
1−x, −1/2+y, −z
1−x, −1/2+y, −z
1−x, −3/2+y, 1−z
1−x, 1/2+y, 1−z
1−x, 1/2+y, 1−z

38
A.K. Sah et al. / Carbohydrate Research 335 (2001) 33–43
L cm−1 mol−1)]: 261 (21049), 321 (15647),
1
414 (4843). H NMR (Me2SO-d6, 300 MHz,
ppm): 8.80 (1 H, s, HCꢁN), 8.62 (1 H, d, J 2.9
Hz, ArH), 8.21 (1 H, dd, J 2.9, 9.3 Hz, ArH),
7.03 (1 H, d, J 9.5 Hz, ArH), 5.68 (1 H, d, J
5.5 Hz, SacOH), 5.43 (1 H, d, J 5.5 Hz,
SacOH), 4.76 (1 H, q, J 4.9 Hz, ProtCH), 4.69
(1 H, d, J 8.4 Hz, SacH-1), 4.07 (1 H, m,
SacH-5), 3.00–3.60 (5 H, m, Sac), 1.25 (3 H,
d, J 5.1 Hz, ProtCH3). 13C NMR (Me2SO-d6,
126 MHz, ppm): 167.9, 163.6, 138.5, 128.8,
128.4, 118.6, 117.3, 98.6, 93.6, 79.9, 74.5, 73.0,
67.9, 67.2, 20.2. FABMS m/z 355 (M−H+,
100%). Anal. Calcd for C15H20N2O8: C, 50.56;
H, 5.66; N, 7.86; Found C, 50.53; H, 5.14; N,
7.86.
X-ray crystallography.—Standard proce-
dures were used for mounting the crystals.
The diffraction data were collected on a Non-
ius–Kappa CCD machine in the ƒ scan+ꢀ
scan mode using Mo Ka radiation. Empirical
absorption correction was applied on the data.
The structures were solved using SHELXS97
and refined using SHELXL97 program pack-
ages.10 The diagrams were generated using
ORTEP311 and PLATON99.12 Full-matrix least-
squares refinement on F2 with anisotropic
thermal parameters for all nonhydrogen
atoms was used. The hydrogen positions of
the ꢀOH groups were picked up from the
difference Fourier and were refined with con-
straints on OꢀH bond length and temperature
factor. All the other hydrogen atoms were
geometrically fixed and were treated as riding
atoms with fixed thermal parameters. The hy-
drogen atom data is given under supplemen-
tary data. Other details of data collection and
structure refinement are provided in Table 1.
Fig. 4. (a) Molecular structure of 2 and (b) its stereoview
showing 50% probability thermal ellipsoids using ORTEP. The
dashed line enclosure shown in (a) represents the ONO bind-
ing core.
Table 7
Atomic coordinates (×104) for 2
x
y
z
C(2)
C(3)
C(4)
C(5)
C(7)
C(8)
C(9)
C(11)
C(13)
C(14)
C(15)
C(17)
C(20)
C(21)
C(23)
Br(6)
N(10)
O(1)
O(12)
O(16)
O(18)
O(19)
O(22)
7325(3)
8189(3)
8228(3)
7409(3)
6505(3)
6453(3)
5448(3)
4315(3)
1715(2)
2311(3)
3822(3)
5027(3)
−297(3)
−1451(3)
116(3)
7491(1)
5412(3)
7334(2)
2840(2)
4479(2)
6327(2)
1152(2)
−913(2)
1699(5)
826(8)
6230(2)
5590(2)
4857(2)
4766(2)
5384(2)
6125(2)
6762(2)
8046(2)
8193(1)
8562(2)
9065(2)
8516(2)
8629(2)
9197(2)
7757(2)
3774(1)
7451(1)
6935(1)
7627(1)
9381(1)
9012(1)
9071(1)
8333(1)
2032(5)
4160(5)
5046(5)
3826(5)
4723(5)
4550(5)
5961(6)
8297(5)
7834(4)
6689(4)
9658(5)
10720(7)
6373(5)
5876(1)
3684(4)
464(4)
3. Results and discussion
4,6-O-Ethylidene-b- -glucopyranosylamine
D
5149(3)
9985(3)
5823(5)
9298(3)
7442(3)
was condensed with substituted salicylalde-
hydes to give the corresponding Schiff base
products as given in Scheme 1. The molecular
weights of these products were obtained from
the molecular-ion peaks in their respective
FAB mass spectra. XRD study of the Schiff
base molecules revealed the presence of an
interesting ONO tridentate core suitable for
g, 2.03 mmol) in EtOH (10 mL). Yield 0.29 g
(40%): mp 169–171 °C. UV–Vis [umax; nm (m;

A.K. Sah et al. / Carbohydrate Research 335 (2001) 33–43
39
binding. Ours is the first crystallographic char-
acterisation of Schiff bases derived from a
glycosylamine.
wCꢁN at 1632, 1627 and 1628 cm−1, respec-
tively, supporting the formation of the imine
centre. Fingerprint regions of the spectra were
also compared. In the spectrum of the Schiff
base derived from 5-nitrosalicylaldehyde, 3,
FTIR studies.—In the FTIR spectra of the
glycosylamine-based Schiff base molecules 1, 2
and 3, a few strong characteristic bands for
saccharides wCꢀO were observed in the range
900–1160 cm−1 along with the characteristic
peaks of aromatic wCꢁC in the range 1500–
1600 cm−1, revealing the presence of both the
saccharide and the aromatic moiety in it;
hence, the desired product. These compounds
asymmetric wNꢁO was observed at 1520 cm−1
,
and the corresponding symmetric stretch was
found at 1335 cm−1. Thus, FTIR spectra
supported the formation of the desired
products.
NMR studies.—NMR Spectra of 1, 2 and 3
were recorded in Me2SO-d6 and were com-
pared with the spectra of the corresponding
saccharide and amine counterparts. Positions
of all the exchangeable proton signals were
identified by D2O exchange experiments. In
exhibited wphenolic
in the range 3427–3510
OH
cm−1, and wsaccharide OH around 3439, 3397 and
3275 cm−1, for 1, 2 and 3, respectively. Prod-
ucts 1, 2 and 3 showed characteristic peaks for
Table 8
2
3
,
Anisotropic displacement parameters (A ×10 ) for 2
U11
U22
U33
U23
1(1)
U13
2(1)
U12
4(1)
C(2)
C(3)
C(4)
C(5)
C(7)
C(8)
C(9)
C(11)
C(13)
C(14)
C(15)
C(17)
C(20)
C(21)
C(23)
Br(6)
N(10)
O(1)
O(12)
O(16)
O(18)
O(19)
O(22)
21(1)
25(1)
23(1)
21(1)
21(1)
16(1)
20(1)
15(1)
14(1)
13(1)
15(1)
12(1)
16(1)
19(1)
15(1)
37(1)
17(1)
39(1)
13(1)
18(1)
10(1)
13(1)
14(1)
26(2)
30(1)
31(2)
31(2)
23(1)
24(1)
24(1)
25(2)
19(1)
22(1)
20(1)
24(1)
23(1)
35(2)
31(2)
45(1)
25(1)
37(2)
28(1)
28(1)
33(1)
28(1)
27(1)
28(2)
35(1)
31(2)
20(1)
25(1)
23(1)
26(2)
19(1)
20(1)
18(1)
13(1)
15(1)
25(2)
42(2)
21(1)
22(1)
23(1)
32(1)
20(1)
22(1)
22(1)
19(1)
26(1)
−2(2)
−7(1)
1(1)
−1(1)
−2(1)
−4(1)
1(1)
−1(2)
0(1)
−1(1)
2(1)
8(1)
11(1)
4(1)
4(1)
3(1)
3(1)
4(1)
5(1)
2(1)
0(1)
2(1)
0(1)
1(1)
2(1)
8(1)
5(1)
13(1)
2(1)
3(1)
2(1)
1(1)
4(1)
9(2)
2(1)
0(1)
5(1)
1(1)
2(1)
3(1)
2(2)
−1(1)
−1(1)
0(1)
3(1)
6(2)
−2(1)
9(1)
2(1)
18(1)
2(1)
−6(1)
0(1)
0(1)
−16(2)
−3(1)
4(1)
−5(1)
8(1)
−6(1)
−8(1)
4(1)
−4(1)
−4(1)
3(1)
−1(1)
The anisotropic displacement factor exponent takes the form: −2y2[h2a*2U11+…+2hka×b×U12].
Table 9
Selected torsion angles (°) for 2
N(10)ꢀC(11)ꢀO(12)ꢀC(13)
O(12)ꢀC(11)ꢀC(17)ꢀO(18)
O(16)ꢀC(15)ꢀC(17)ꢀC(11)
O(19)ꢀC(14)ꢀC(15)ꢀC(17)
C(23)ꢀC(13)ꢀO(12)ꢀC(11)
C(8)ꢀC(9)ꢀN(10)ꢀC(11)
178.8(2)
170.6(2)
−171.3(2)
178.2(2)
−174.8(2)
−176.0(2)
N(10)ꢀC(11)ꢀC(17)ꢀC(15)
C(14)ꢀC(15)ꢀC(17)ꢀO(18)
C(13)ꢀC(14)ꢀC(15)ꢀO(16)
O(12)ꢀC(13)ꢀC(14)ꢀO(19)
C(23)ꢀC(13)ꢀC(14)ꢀC(15)
C(2)ꢀC(8)ꢀC(9)ꢀN(10)
172.6(2)
−168.8(2)
176.3(2)
174.2(2)
174.5(2)
4.5(4)

40
A.K. Sah et al. / Carbohydrate Research 335 (2001) 33–43
the case of 1 and 2, three exchangeable pro-
tons corresponding to the phenolic ꢀOH, and
the C-2 and C-3 OHs of the saccharide moiety
were observed, whereas 3 exhibited only two
such signals, corresponding to the saccharide
ꢀOH groups, but not the phenolic ꢀOH. This
observation may be attributed to the fact that
the phenoxo ion is resonance stabilised in the
presence of the nitro group as shown in
Scheme 2. The spectra clearly revealed the
presence of the saccharide moiety in a single
anomeric form in solution. Based on the
chemical shifts (4.56–4.69 ppm) and the J
values (8.2–8.4 Hz) observed for H-1, the
presence of the b anomeric form of the sac-
charide moiety was identified in all the three
products reported in this paper.13
Fig. 5. H-bonding pattern observed in 2. The filled circles
denote oxygen atoms, circles bisected with one line denote
nitrogen atoms and circles with cross denote bromine atoms.
Dotted lines represent H-bonds.
Fig. 6. Packing diagram of 2 showing anti-parallel b-sheet type structure. The filled circles denote oxygen atoms, circles bisected
with one line denote nitrogen atoms and circles with cross denote chlorine atoms. Dotted lines represent H-bonds.

A.K. Sah et al. / Carbohydrate Research 335 (2001) 33–43
41
Table 10
Hydrogen bond data in the case of 2
,
,
,
DꢀH···A
d(DꢀH) (A)
d(H···A) (A)
d(D···A) (A)
B(DHA) (°)
Symmetry
O(1)ꢀH(1A)···N(10)
O(16)ꢀH(16A)···O(18)
O(18)ꢀH(18A)···O(22)
C(11)ꢀH(11)···O(16)
0.834 (10)
0.836 (10)
0.836 (10)
1.000 (12)
1.860 (20)
1.984 (13)
1.938 (11)
2.403 (23)
2.588 (3)
2.793 (2)
2.771 (3)
3.371 (4)
145.0 (4)
162.6 (3)
174.8 (4)
162.8 (5)
1−x, 1/2+y, −z
−1+x, y, z
x, −1+y, z
4
UV–Vis studies.—UV–Vis spectra of all
the compounds were measured in Me2SO us-
ing 10−2 as well as 10−4 M solutions, and the
corresponding data is provided in Section 2.
Schiff base compounds exhibited three bands
in the range 261–420 nm. For both com-
pounds 1 and 2, very weak bands at 419 nm
(m=86 L cm−1 mol−1) and 414 nm (m=61 L
cm−1 mol−1), respectively, were found. The
same band for 3 was found to be very strong
at 414 nm (m=4843 L cm−1 mol−1). This may
be attributed to the fact that the ꢀNO2 group
is a chromophore, and in the solution, the
phenolic ꢀOH (an auxochrome) is deproto-
nated due to the presence of the nitro group,
which enhances the molar absorptivity. De-
protonation of the phenolic ꢀOH in the
Me2SO solution was also supported by NMR
spectra. The red shift observed in the case of
the methoxy derivative with respect to its
other analogues may be attributed to the pres-
ence of the ꢀOMe group, which acts as an
auxochrome.14
Single crystal X-ray studies.—In the case of
1 and 2, the molecules crystallised in a mono-
clinic lattice. One chloroform molecule was
associated with compound 1, but no such
association with a solvent molecule was ob-
served in the case of 2.
Molecular structure of 1.—The molecular
structure of 1 revealed the pyranose form of
the saccharide moiety, with the 4- and 6-
positions as being protected by an ethylidene
group, and the C-1 being modified through
Schiff base formation. An ORTEP view of the
molecule is shown in Fig. 1(a). Atomic coordi-
nates and the temperature parameters are
given in Tables 2 and 3, respectively. The
bond lengths and bond angles in the structure
are quite normal and hence this information is
given in Section 5. A stereoview of this
molecule, Fig. 1(b), supports the presence of
the saccharide in the C1 conformation along
with its b anomeric form, which was also
indicated by the NMR study. The stereoview
further reveals the chair conformation of both
of the 5-membered rings, resulting from the
saccharide moiety and its protection at the 4-
and 6- positions. The presence of the b-
anomeric form of the saccharide moiety is also
understood based on the torsion angles, i.e.,
N(11)ꢀC(12)ꢀO(13)ꢀC(14)=179.4°(4)
and
N(11)ꢀC(12)ꢀC(18)ꢀC(16)=177.7°(4). Analy-
sis of the torsion angles (Table 4) revealed the
trans-orientation of the saccharide moiety and
aromatic rings with respect to the CꢁN bond
[C(9)ꢀC(10)ꢀN(11)ꢀC(12)=178.8°(4)], and the
cis-orientation of the phenolic ꢀOH group and
imine nitrogens [C(2)ꢀC(9)ꢀC(10)ꢀN(11)=
0.5°(6)]. This structure favours the formation
of an interesting ONO tridentate binding core
comprised of the phenolic ꢀOH, the imine
nitrogen, and the saccharide 2-OH group as
shown by an enclosure in Fig. 1(a). Cremer–
Pople parameters15 as well as asymmetry
parameters16 for 1 and 2, obtained using the
program PLATON99, are given in Table 5.
Lattice structure of 1.—The lattice structure
of this molecule exhibited a six-atom in-
tramolecular hydrogen bonding interaction
between the phenolic ꢀOH and the imine ni-
trogen. In the lattice, while the 2-OH and
3-OH of the saccharide moiety of each ligand
acts as a hydrogen donor towards another
molecule, 3-OH and 4-O acts as a hydrogen
acceptor towards a third molecule. Thus, in
the lattice, each molecule is linked with two
other molecules through four intermolecular
OꢀH···O interactions. In addition, the
molecule also exhibited three weak CꢀH···O
type interactions, viz., Cl3CꢀH···Ophenolic
,
Cl3CꢀH···Omethoxy and ArꢀCꢀH···OꢀC-6(sac).
All such interactions found around each
molecule in the lattice are shown in Fig. 2. In

42
A.K. Sah et al. / Carbohydrate Research 335 (2001) 33–43
neighbouring molecule, and the 3-OH acts as
donor towards the 2-OH of a different neigh-
bouring molecule. Similarly, the molecule acts
as acceptor towards two other molecules in
the lattice. Therefore, in this case every
molecule is linked with four other molecules
through OꢀH···O interactions and with one
other molecule through C-1ꢀH···OHꢀC-3 type
interactions as shown in Fig. 5. Thus, in the
lattice, the molecules are interconnected
through C-2ꢀOH···OꢀC-6 to form chains,
where the phenyl moieties protrude out of the
chain with an inclined angle with respect to
the axis of propagation of the chain. Two
such adjacent chains or strands are connected
together as in an antiparallel b-sheet through
hydrogen-bond interaction of the type C-
3ꢀOH···OꢀC-2 and C-2ꢀO···HOꢀC-3. Packing
of such dimeric chains in the lattice results in
the stacking of phenyl rings. Stacking of the
chains in the third dimension results in the
formation of channels, as shown in Fig. 6,
the lattice, dimers are formed due to the pres-
ence of two ArꢀCꢀH···OꢀC-6 interactions.
These dimers are further connected to form
chains through two OꢀH···O interactions of
the
type,
C-2ꢀOH···OꢀC-3
and
C-
3ꢀO···HOꢀC-2. The chains thus formed, stack
to result in large size rectangular type cavities
,
with dimensions 12.2 and 6.8 A, which hold
two CHCl3 molecules using two interactions
of
the
type
Cl3CꢀH···Omethoxy
and
Cl3CꢀH···Ophenoxy. These cavities can be ob-
served as channels when the stacking of
molecules in the lattice is viewed in the third
dimension as shown in Fig. 3. The metric
parameters of these interactions are given in
Table 6.
Molecular structure of 2.—The molecular
structure of 2 is shown in Fig. 4(a). Atomic
coordinates and the temperature parameters
are given in Tables 7 and 8, respectively. The
bond lengths and the bond angles in the struc-
ture are quite normal, and hence this informa-
tion is given in Section 5. Even in this case,
the stereoview shown in Fig. 4(b), revealed the
,
having dimensions of 7.4 and 4.6 A. These
channels are smaller than those observed in
case of 1. Metric parameters for weak interac-
tions are listed in Table 10.
4
saccharide moiety in the C1 conformation as
the b anomer. The saccharide and the aro-
matic moieties maintained a trans-orientation
with respect to the CꢁN bond, and this orien-
tation resulted in the formation of an ONO
tridentate core that is specially oriented for
chelation, as shown by an enclosure in Fig.
4(a). The torsion angles given in Table 9 sup-
port these features.
4. Conclusions
D
-Glucose was successfully modified into
the corresponding Schiff base molecules
through partial protection and glycosyl ami-
nation, followed by condensation with substi-
tuted salicylaldehydes. Such modifications
facilitate the solubility of the resulting Schiff
base products in nonaqueous solvents and
lock the saccharide in the b-anomeric form,
even in the solution. Such also assists in the
formation of single crystals of the products.
X-ray diffraction study of the molecules re-
veals the pyranose form of the saccharide
moiety, with the 4- and 6- positions being
protected by the ethylidene moiety. The C-
1ꢀNH2 is modified to give a Schiff base, ꢀC-
1ꢀNꢁC(H)ꢀ. The same study also reveals the
4C1 chair conformation of the saccharide moi-
ety as the b-anomeric form even in the solid
state. A stereoview of the molecules shows the
presence of an interesting ONO tridentate
chelating core. Metal–ion binding to such an
ONO core is expected to result in one six-
Lattice structure of 2.—In the lattice, this
molecule possesses one intramolecular and
five intermolecular hydrogen-bonding interac-
tions. Out of five intermolecular interactions,
four are of the OꢀH···O type and one is of the
CꢀH···O type. Like the previous case, even in
this one, the intramolecular hydrogen bonding
interactions arise due to the close proximity of
the phenolic OH and the imine nitrogens.
Between the lattice structures of 1 and 2,
major differences lie in the nature of the inter-
molecular interaction as well as the donor and
acceptor centres. In this case, the 2-OH group
acts as both the hydrogen donor and the
acceptor, whereas the 3-OH group acts only as
the hydrogen donor, and the 6-O acts as ac-
ceptor instead of the 4-O group. Thus, the
2-OH acts as donor towards the 6-O of a

A.K. Sah et al. / Carbohydrate Research 335 (2001) 33–43
43
membered and another five-membered
chelate, and work is currently in progress in
our laboratory to investigate the formation of
their possible complexes. Recently, we re-
ported the interaction of metal ions with an
anthranilic acid based glycosylamine, viz.,
Sciences of Department of Atomic Energy.
We thank RSIC, CDRI Lucknow for Mass
and RSIC, IIT Bombay for some NMR spec-
tra, and Mr Kuppinen for some experimental
help.
N-(O-carboxyphenyl)-4,6-O-ethylidene-b- -
D
glucopyranosylamine.7 The crystal lattices of 1
and 2 exhibit a number of OꢀH···O and
CꢀH···O interactions that result in interesting
structures. The lattice of 1 exhibits a channel
type structure where the channels are filled
with chloroform molecules. Moreover, the lat-
tice 2 exhibits an antiparallel b-sheet type
structure where two strands consisting of sac-
charide molecules are held together by hydro-
gen-bonding interactions, and the aromatic
moieties protrude out of these strands and are
stacked.
References
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Acknowledgements
C.P.R. acknowledges financial support from
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