Synthesis and X-ray structures of unexpected 2-O-(5-deoxy-1,2-O- isopropylidene-α-D-glucofuranos-5-yloxy)quinoxalines

Article abstract of DOI:10.1002/poc.1486

Reaction of 3-methyl-2(1H)-quinoxalinone (4) and 2(1H)-quinoxalinone (5) with 5,6-anhydro-1,2-O-isopropylidene-α-D-glucofuranose 6 gives the unexpected O-glucoquinoxalines derivatives by the intermediary novel intramolecular rearrangement of 5,6-anhydro-1,2-O-isopropylidene-α-D- glucofuranose to the corresponding 3,6-anhydro form. The obtained O-glucoquinoxalines 7,8 were identified by NMR spectroscopy. The X-ray crystal structures have been determined at room temperature. Moreover, a solid-solid phase transition has been detected at 198.9 K for O-glucoquinoxalines 7 and the structure of the low-temperature phase has been solved at 188K.

Full text of DOI:10.1002/poc.1486

Research Article
Received: 26 June 2008,
Revised: 22 September 2008,
Accepted: 23 October 2008,
Published online in Wiley InterScience: 15 January 2009
(www.interscience.wiley.com) DOI 10.1002/poc.1486
Synthesis and X-ray structures of unexpected
2-O-(5-deoxy-1,2-O-isopropylidene-a-
D-glucofuranos-5-yloxy)quinoxalines
a
a
b
*
Chakir Jarmoumi , Brahim Lakhrissi , Denise Mondieig ,
b
c
c
d
d
´
´
Philippe Negrier , J. M. Leger , S. Massip , Zhor Lazar , Bouziane Benali ,
Mohamed Massouie and El Mokhtar Essassie
Reaction of 3-methyl-2(1H)-quinoxalinone (4) and 2(1H)-quinoxalinone (5) with 5,6-anhydro-1,2-O-isopropylidene-
a-D-glucofuranose 6 gives the unexpected O-glucoquinoxalines derivatives by the intermediary novel intramolecular
rearrangement of 5,6-anhydro-1,2-O-isopropylidene-a-D-glucofuranose to the corresponding 3,6-anhydro form.
The obtained O-glucoquinoxalines 7,8 were identified by NMR spectroscopy. The X-ray crystal structures have
been determined at room temperature. Moreover, a solid–solid phase transition has been detected at 198.9 K for
O-glucoquinoxalines 7 and the structure of the low-temperature phase has been solved at 188 K. Copyright ß 2009
John Wiley & Sons, Ltd.
Supporting information may be found in the online version of this article.
Keywords: Quinoxalinones; glucosyl-quinoxalines; synthesis; X-ray structure; phase transition; water solubility.
hereafter compound 7 and compound 8, respectively, for brevity).
Then we provide the results of thermal analysis performed from
INTRODUCTION
The quinoxaline derivatives show very interesting biological
properties (antibacterial,[1] antiviral, anticancer,[2] antifungal,
antihelmintic, antileish-manial,[3] anti-HIV[4]) and their contri-
bution to medicinal chemistry is far reaching.[5] Many drug
candidates bearing quinoxaline core structures are in clinical
trials in antiviral,[1] anticancer, antibacterial,[2] and central nervous
system (CNS) therapeutic areas. Among them, XK469 (1) and
173 K up to the melting temperature, which suggests a solid–solid
phase transition for compound 7. Finally, we report on the three
crystalline structures at 188 and 293 K for the compound 7 and at
293 K for compound 8.
the chloroquinoxaline sulfonamide (CQS)
2 were known
as antineoplastic quinoxaline topoisomerase II inhibitors
(Scheme 1).
XK469 is an analog of the herbicide Assure1 synthesized by
DuPont Company, which possesses antitumor activity, especially
against murine solid tumors and human xenografts.[6,7] CQS is
a structural analog of sulfoquinoxaline, a compound used to
control coccidiosis in poultry, rabbit, sheep, and cattle. CQS was
selected for clinical development based on good activity against
human tumor cells in the human tumor colony-forming assay[8]
and subsequently has shown activity against murine and human
solid tumors.[9]
´
Correspondence to: D. Mondieig, Centre de Physique Moleculaire Optique et
*
´
Hertzienne, Universite Bordeaux1, 351 cours de la liberation, Talence, France.
E-mail: d.mondieig@cpmoh.u-bordeaux1.fr
´
a
b
c
C. Jarmoumi, B. Lakhrissi
Laboratoire de Chimie d’Agroressources et Genie des procedes, Faculte des
´
´ ´
´
´
sciences, Universite IbnTofa¨ıl-Kenitra, Maroc
´
´
D. Mondieig, P. Negrier
Centre de Physique Moleculaire Optique et Hertzienne, Universite Bordeaux1,
´
´
´
351 cours de la liberation, Talence, France
In order to increase the biological activity of various
heterocyclic compounds, we have previously linked them on
monosaccharide moiety.[10,11]
´
J. M. Leger, S. Massip
Laboratoire de Pharmacochimie, EA 4138 Universite Victor Segalen Bordeaux
´
´
2, 146 rue Leo Saignat, Bordeaux, France
The aim of this study was to synthesize glucosyl-quinoxalinones
of the type 3, in which O-2 grafts to a partially protected
glucofuranosyl moiety (Scheme 2). In this paper, we firstly
present the synthesis of the 2-O-(5-deoxy-1,2-O-isopropylidene-a-
D-glucofuranos-5-yloxy)-quinoxaline 7 and 2-O-(5-deoxy-1,2-O-
d
e
Z. Lazar, B. Benali
Laboratoire d’Opto-electronique et de Physico-Chimie des Materiaux,
´
Departement de Physique, Faculte des Sciences, Kenitra, Maroc
´
´
´
´
M. Massoui, E. M. Essassi
Laboratoire de Chimie Heterocyclique, Faculte des Sciences-Universite
Mohammed V, Rabat, Maroc
´ ´
´
´
isopropylidene-a-D-glucofuranos-5-yloxy)-quinoxaline
8 (called
J. Phys. Org. Chem. 2009, 22 585–592
Copyright ß 2009 John Wiley & Sons, Ltd.

C. JARMOUMI ET AL.
EXPERIMENTAL
Synthesis of compounds 7 and 8
The starting material, 3-methyl-2(1H)-quinoxalinone 4 was
prepared by condensing ethyl pyruvate with diaminobenzene
in hydrochloric acid.[12] The 2(1H)-quinoxalinone 5 was prepared
by condensing diaminobenzene with glyoxylic acid in
n-butanol.[13] Refluxing of quinoxalinones 4, 5 with 6[11] for
24 h in the presence of K2CO3 and Bu4NBr in DMF gives the
unexpected O-glucoquinoxaline compounds 7 (66% yield) and 8
(68% yield).
For the synthesis of 5,6-anhydro-1,2-O-isopropylidene-
a-D-glucofuranose 6, glucosidic precursor was synthesized
according to the literature.[14,15] The product was isolated as a
Scheme 1. Example of quinoxaline derivatives
Scheme 2. Synthesis of 2-O-(5-deoxy-1,2-O-isopropylidene-a-D-glucofuranos-5-yloxy)-quinoxalines 7, 8
Table 1. Crystal structures refinement information and crystallographic data for compounds 7 and 8
Compound
7
7
8
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
Z
C18H20N2O5
344.36
188
C18H20N2O5
344.36
293
Monoclinic
C 2
4
25.626(9)
6.663(9)
10.526(4)
98.08(9)
1779(3)
C17H18N2O5
330.34
293
Monoclinic
P 21
Monoclinic
C 2
12
30.724 (2)
6.5850(4)
28.937(2)
117.029(2
5215.1(5)
1.316
2
˚
a (A)
8.4407(10)
5.5912(8)
17.104(2)
95.462(8)
803.5(2)
1.365
˚
b (A)
˚
c (A)
b(8)
Volume (A )
d (g cmꢀ3
3
˚
)
1.286
0.15 ꢁ 0.15 ꢁ 0.20
Crystal size (mm)
Rall
0.18 ꢁ 0.15 ꢁ 0.15
0.20 ꢁ 0.15 ꢁ 0.10
0.0918
0.805
0.0509
0.786
0.0383
0.848
m (Cu Ka) (mmꢀ1
2umax (8)
)
117.9
6942
130.3
2651
142.9
2975
No. of reflections used
No. of parameters
687
1.020
230
1.075
221
1.099
Goodness of fit on F2
Final R indices [I > 2s(I)]
Max. and min. transmission
F(000)
R1 ¼ 0.0831, wR2 ¼ 0.2334
0.8888 and 0.8556
2184
R1 ¼ 0.0437, wR2 ¼ 0.1196
0.8912 and 0.8586
728
R1 ¼ 0.0340, wR2 ¼ 0.0939
0.9200 and 0.8160
348
ꢀ3
˚
(D/r)max (A
)
0.338
ꢀ0.374
0.128
ꢀ0.125
0.178
ꢀ0.131
ꢀ3
˚
(D/r)min (A
)
CCDC deposition number
668042
668041
668043
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Copyright ß 2009 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2009, 22 585–592

SYNTHESIS OF QUINOXALINES
Figure 1. ORTEP plot (with the ellipsoids drawn at the 50% probability level) of 7 at 293 K. This figure is available in colour online at www.inters-
cience.wiley.com/journal/poc
white solid with 96% yield, mp 130–132 8C, [a]2D5 ꢀ9.38 (c 1.4,
CHCl3); 1H NMR (300 MHz, CDCl3): d 5.88 (d, 1H, J1,2 ¼ 3.6 Hz, H-1),
4.43 (d, 1H, J1,2 ¼ 3.6 Hz, J2,3 ¼ 0.0 Hz, H-2), 4.18 (d, 1H, 2.3 Hz, H-3),
3.82 (dd, 1H, J3,4 ¼ 2.3 Hz, J4,5 ¼ 5.3 Hz, H-4), 3.27 (m, 1H, H-5), 2.88
(dd, 1H, J5,6a ¼ 4.2 Hz, J6a,6b ¼ 4.8 Hz, H-6a), 2.76 (dd, 1H,
H-6b),1.37, 1.22 (2s, 6H, CH3iso); 13C NMR (75 MHz, CDCl3): d
110.4 (Ciso), 104.0 (C-1), 84.1 (C-3), 79.2 (C-4), 48.5 (C-5), 45.3 (C-6),
25.7, 25.1 (CH3iso).
For the synthesis of 2-O-(5-deoxy-1,2-O-isopropylidene-a-
D-glucofuranos-5-yloxy)-3-methylquinoxaline 7, 5,6-anhydro-
1,2-O-isopropylidene-a-D-glucofuranose 6 (0.70 g, 3.50 mmol)
was added to a solution of quinoxalinone 4 (0.459 g, 2.92 mmol),
K2CO3 (0.48 g, 4.20 mmol) and Bu4NBr (0.2 g, 0.6 mmol) in DMF
(50 ml). The solution was heated to 1108C for 24 h and the
reaction was followed by TLC (eluant hexane-acetone: 9:1, v/v).
After cooling, the mixture was filtrated and the filtrate was
neutralized with saturated NH4Cl aqueous solution and extracted
with toluene. The combined organic extracts were washed with a
saturated NaCl aqueous solution. After drying over MgSO4,
filtration and evaporation of the solvent, column chromatog-
raphy on silica gel (9.5:0.5 hexane-acetone) yielded 7(68%) as a
white crystal, mp 134 8C; 1H NMR (300 MHz, CDCl3): d glucose
5.96 (d, lH, J1,2 ¼ 3.5 Hz, H-l), 4.94 (t, lH, J4,3 ¼ J4,5 ¼ 3.7 Hz, H-4),
4.58,4.47 (2d, 2H, H-2,3), 4.08–4.02 (ddd, lH, J5,6 ¼ 7.0 Hz,
J6a,6b ¼ 8.5 Hz, H-5), 1.52, 1.36 (2s, 6H, Me2C), quinoxalinone
7.28–7.95 (m, 4H, H-Ar), 13C NMR (75 MHz, CDCl3): d glucose112.89
(Ciso), 106.92 (C-1), 84.53 (C-3), 83.28 (C-2), 86.73 (C-4), 78.89 (C-5),
73.58 (C-6), 27.71–27.01 (CH3iso), quinoxalinone 127.30, 127.47,
128.44, 129.48, 139.23, 140.76 (C-5, C-6, C-7, C-8, C-9, C-10), 20.66
(CH3).
For the synthesis of 2-O-(5-deoxy-1,2-O-isopropylidene-
a-D-glucofuranos-5-yloxy)-quinoxaline 8, 5,6-anhydro-1,2-O-
isopropylidene-a-D-glucofuranose 6 (0.70 g, 3.50 mmol) was
added to a solution of quinoxalinone 5 (0.60 g, 4.20 mmol),
K2CO3 (0.48 g, 4.20 mmol) and Bu4NBr (0.2 g, 0.6 mmol) in DMF
(50 ml). The solution was heated to 110 8C for 24 h and the
Figure 2. ORTEP plot (with the ellipsoids drawn at the 50% probability level) of 8 at 293 K. This figure is available in colour online at www.
interscience.wiley.com/journal/poc
J. Phys. Org. Chem. 2009, 22 585–592
Copyright ß 2009 John Wiley & Sons, Ltd.
www.interscience.wiley.com/journal/poc

C. JARMOUMI ET AL.
reaction was followed by TLC (eluant hexane-ether: 9:1, v/v). After
cooling, the mixture was filtrated and the filtrate was neutralized
with saturated NH4Cl aqueous solution and extracted with
toluene. The combined organic extracts were washed with a
saturated NaCl aqueous solution. After drying over MgSO4,
filtration and evaporation of the solvent, column chromatog-
raphy on silica gel (9.5:0.5 hexane-acetone) yielded 8 (68%) as a
white crystal, mp 137 8C; 1H NMR (300 MHz, CDCl3): d glucose
5.97 (d, lH, J1,2 ¼ 3.5 Hz, H-l), 4.94 (t, lH, J4,3 ¼ J4,5 ¼ 3.7 Hz, H-4),
4.58,4.47 (2d, 2H, H-2,3), 4.08–4.02 (ddd, lH, J5,6 ¼ 7.0 Hz,
J6a,6b ¼ 8.5 Hz, H-5), 1.52, 1.43 (2s, 6H, Me2C), quinoxalinone
7.27–8.03 (m, 4H, H-Ar), 8.50 (s, 1H, CH); 13C NMR (75 MHz, CDCl3):
d glucose 112.91 (Ciso), 106.92 (C-1), 73.60 (C-3), 84.61 (C-2), 86.16
(C-4), 78.81 (C-5), 73.38 (C-6), 27.05–27.74 ppm (CH3iso),
quinoxalinone 127.47, 127.87, 129.38, 139.64, 140.27 (C-5, C-6,
C-7, C-8, C-9, C-10).
Figure 3. DSC thermogram for 7 showing the solid–solid transition:
(a) heating and (b) cooling
Thermal analysis
Table 2. Melting temperature and enthalpy changes for
compounds 7 and 8
Temperatures as well as enthalpy changes were determined
using a PerkinElmer DSC-7 instrument equipped with the cooling
accessory allowing temperature rising from 110 to 950 K. Heating
rate of 2 K minꢀ1 was used. Samples (about 4 mg) were put into
aluminum pans and weighed before and after each experiment
to control the eventual mass loss. At least four measurements
were performed on each compound. The uncertainty on the
Compound
7
8
Temperature (K)
Enthalpy (kJ molꢀ1
371.4 ꢂ 0.4
20.4 ꢂ 0.3
393.2 ꢂ 0.4
29.5 ꢂ 0.4
)
Figure 4. ORTEP plot (with the ellipsoids drawn at the 50% probability level) of the three molecules forming the asymmetric unit of compound 7 at
188 K.
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Copyright ß 2009 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2009, 22 585–592

SYNTHESIS OF QUINOXALINES
temperatures and enthalpies were determined using the
Student’s method with a 95% threshold of reliability. To this
value the systematic error related to the calibration of the
apparatus was added, which was set at ꢂ0.2 K for the
temperatures and ꢂ1% for the enthalpies.
X-ray diffraction measurements
High-quality powder X-ray diffraction measurements were
performed with an Inel CPS 120 powder diffractometer. It was
equipped with an Oxford Cryosystems N2 cryostream to provide
isothermal experiments at different temperatures. The Inel CPS
120 works with the Debye–Scherrer transmission geometry and
the diffracted beams are collected on a 1208 curved counter by
gas ionization (argon þ C2H6). Cu Ka radiation was selected as the
incident beam. Samples are introduced in 0.5 mm diameter
Lindemann glass capillaries. The latter rotates around its axis in
order to minimize preferential orientations of the crystallites. The
time of acquisition was set to 6 h in order to obtain reflections
with exploitable intensities.
For the structure at 293 K of compound 7, X-ray crystal
measurements were performed with an Enraf-Nonius CAD4 using
the ‘Enraf–Nonius SDP’ program system. The two other crystals
have been measured with an R-Axis Rapid-S diffractometer
equipped with a rotating anode X-ray tube. The X-ray wavelength
˚
was that for Cu Ka (l ¼ 1.54180 A). The structures were solved by
direct methods and refined by full-matrix least-squares using
SHELXS-97 software. Meanwhile, all of the non-hydrogen atoms
were refined anisotropically. The H-atoms were allowed to ride on
the parent atoms in the model. Additional details of structure
determination are summarized in Table 1.
Figure 5. (a) Powder diffraction patterns at various temperatures for 7.
Black and red lines correspond to the low- and high-temperature phases,
respectively. (b) Zoom between 15 and 25-, arrows point out some
differences between the patterns of the two phases. This figure is
available in colour online at www.interscience.wiley.com/journal/poc
Figure 6. Structures of compound 7: (a) High-temperature form with three unit cells (the pink dotted line indicates approximately the unit cell of the
low-temperature form). (b) Low-temperature form (the three different molecules forming the asymmetric unit are indicated with the numbers , and ).
,
J. Phys. Org. Chem. 2009, 22 585–592
Copyright ß 2009 John Wiley & Sons, Ltd.
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C. JARMOUMI ET AL.
RESULTS
The chemical structures of the compounds 7 and 8 were deduced
from their 1H and 13C NMR and confirmed by X-ray analysis
(Figs. 1 and 2).
1H NMR data of compounds 7, 8 clearly showed the presence
of d H-1 at 5.96 ppm (d, 1H, J1,2 ¼ 3.6 Hz), d H-5 at 4.02–4.08 ppm
(m, 1H) and aromatic protons at 7.27–8.05 ppm (m, 4H).
13C NMR data of these compounds confirm their structures
without ambiguity. In particular we observed the disappearance
of the carbonyl signal and the appearance of C(5)-O signal at
78.9 ppm.
One of the most significant results of this work was the
revelation of an intramolecular rearrangement of 5,6-anhydro-
1,2-O-isopropylidene-a-D-glucofuranose in the corresponding
3,6-anhydro form.[16,17]
Figure 7. Structure of compound 7 at 188 K. (a) Displacement of mol-
ecule
(in yellow) with regard to molecule . (b) Displacement of
molecule (in yellow) with respect to molecule . This figure is available
in colour online at www.interscience.wiley.com/journal/poc
The optical rotatory power of these compounds has been
measured and found to be equal to zero indicating that the
powders are racemic mixtures.
Table 3. Most affected intramolecular distances, angles, and torsion by the solid–solid transition (for the structure at 188 K the labels
of the atoms of molecule 1 are the same as those of the molecule at 293 K, the labels of molecule 2 and 3 are added to 30 and 60,
respectively)
At 293 K
Molecule 1 at 188 K
Molecule 2 at 188 K
Molecule 3 at 188 K
˚
Intramolecular distances (A)
C(1)-C(6)
C(5)-C(6)
C(6)-N(7)
C(19)-O(23)
C(19)-C(20)
C(22)-O(23)
1.412(4)
1.397(4)
1.372(4)
1.386(4)
1.514(4)
1.419(5)
1.386(7)
1.432(6)
1.394(6)
1.411(5)
1.532(7)
1.426(6)
1.386(6)
1.426(5)
1.386(6)
1.411(5)
1.536(7)
1.420(7)
1.398(6)
1.420(5)
1.397(6)
1.416(5)
1.532(6)
1.444(5)
Intramolecular angles (8)
O(12)-C(13)-C(14)
O(12)-C(13)-C(17)
O(18)-C(17)-C(13)
Torsions (8)
112.0(2)
104.6(2)
107.7(2)
103.5(4)
112.2(4)
103.8(4)
105.2(4)
112.5(3)
104.6(3)
111.8(4)
103.4(3)
104.5(3)
C(9)-O(12)-C(13)-C(14)
C(9)-O(12)-C(13)-C(17)
C(13)-C(14)-O(15)-C(16)
C(14)-O(15)-C(16)-C(20)
C(14)-O(15)-C(16)-C(17)
O(15)-C(16)-C(17)-O(18)
C(20)-C(16)-C(17)-O(18)
O(15)-C(16)-C(17)-C(13)
C(20)-C(16)-C(17)-C(13)
O(12)-C(13)-C(17)-O(18)
C(14)-C(13)-C(17)-O(18)
C(16)-C(17)-O(18)-C(19)
C(13)-C(17)-O(18)-C(19)
C(17)-O(18)-C(19)-O(23)
C(17)-O(18)-C(19)-C(20)
O(15)-C(16)-C(20)-O(21)
O(18)-C(19)-O(23)-C(22)
C(20)-C(19)-O(23)-C(22)
O(21)-C(22)-O(23)-C(19)
C(24)-C(22)-O(23)-C(19)
C(25)-C(22)-O(23)-C(19)
76.2(3)
ꢀ174.0(2)
13.6(3)
118.7(3)
6.7(3)
89.2(3)
ꢀ28.5(3)
ꢀ23.9(3)
ꢀ142.0(2)
162.5(2)
ꢀ80.6(3)
28.5(3)
79.6(5)
ꢀ170.0(3)
6.3
125.8(4)
14.6(4)
83.5(4)
ꢀ33.1(4)
ꢀ29.6(4)
ꢀ146.0(3)
165.9(3)
ꢀ77.1(4)
34.6(4)
74.2(5)
ꢀ175.1(3)
17.4(5)
117.3(4)
4.2(4)
88.9(4)
ꢀ29.3(4)
ꢀ24.0(4)
ꢀ142.2(4)
164.9(4)
ꢀ77.3(4)
31(4)
80.5(5)
ꢀ171.0(3)
13.7(5)
119.3(4)
7.3(5)
87.7(4)
ꢀ29.2(4)
ꢀ25.2(4)
ꢀ142(3)
165.5(3)
ꢀ78.5(4)
30.4(5)
138.9(3)
98.2(3)
144.0(3)
92.2(4)
140.0(4)
94(4)
140.7(3)
94.4(4)
ꢀ16.3(4)
153.1(2)
ꢀ130.0(3)
ꢀ13.5(4)
27.5(4)
ꢀ22.0(4)
156.8(4)
ꢀ133(4)
ꢀ17.2(4)
31.3(4)
ꢀ19.6(4)
150.6(4)
ꢀ133.6(4)
ꢀ18.2(5)
31.5(5)
ꢀ18.8(4)
152.7(4)
ꢀ135(4)
ꢀ20.4(4)
35.6(4)
ꢀ90.6(3)
ꢀ87.2(4)
ꢀ88.0(4)
ꢀ83.8(4)
144.5(3)
147.8(4)
148.5(4)
151.1(4)
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Copyright ß 2009 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2009, 22 585–592

SYNTHESIS OF QUINOXALINES
A first order solid–solid phase transition has been detected by
means of thermal analysis for the compound 7 at 198.9 ꢂ 0.4 K
with an enthalpy variation of 0.35 ꢂ 0.06 kJ ꢃ molꢀ1 (Fig. 3). The
melting temperature and enthalpy measured for the two
compounds are gathered in Table 2.
The crystallographic data for compounds 7 and 8 at room
temperature are given in Table 1 together with those for
compounds 7 at 188 K. The ORTEP representations of theses
structures are shown in Figs. 1,2 and 4, respectively.
The phase transition has also been observed with X-ray powder
diffraction. Figure 5a gathers powder diffractograms recorded
between 143 and 298 K. A zoom in the 2u domain between
15 and 258 permits to reveal that supplementary reflexions
appear at low temperature. The diffactograms obtained at
various temperature are in agreement with the cell parameters
obtained from single crystal data for both phases. The low-
and high-temperature solid phases of 2-O-(5-deoxy-1,2-
O-isopropylidene-a-D-glucofuranos-5-yloxy)-3-methyl quinoxa-
line 7 crystallize in the C2 monoclinic system, that may explain
the similarity of the powder diffractograms. Their structures are
however different as pointed out in Fig. 5b. The asymetric unit of
the low-temperature phase contains three independent mol-
ecules (Fig. 4). As a consequence, its crystallographic cell has
approximately a triple volume.
Figure 6 illustrates the modification of cell parameters from
high to low temperature form: three unit cells of the high-
temperature form are shown in Fig. 6a, the pink dotted line
indicates approximatively the unit cell of the low temperature
form; Fig. 6b shows the unit cell of the low-temperature phase.
At the phase transition there are little displacements of the
molecules and relative to molecule , which are shown in Fig. 7a
and Fig. 7b. In Table 3 some intramolecular parameters (distances,
angles, and torsions) affected by the solid–solid transition
are collected. In Table 3, the first column is dedicated to
intramolecular parameters of the molecule at 293 K and the three
others to equivalent parameters of the three independent
molecules of the asymmetric unit at 188 K. For the distances, the
highest differences between the first column and the three
˚
˚
˚
others are observed for C(5)-C(6) (0.035 A, 0.029 A, and 0.023 A).
For the intramolecular angles the highest differences are
detected for O(12)-C(13)-C(14) (8.58, 6.88, 0,28). It has to be
noted that the parameter differences between the low- and
high-temperature forms are not similar for the three independent
molecules at 188 K.
Intramolecular C—HꢃꢃꢃN hydrogen bonding chelate with-
drawals appear in both forms. However, the low-temperature
form presents additional short bond lengths and among them
are three intermolecular pseudo hydrogen bonds (Table 4). For
comparison between the two forms and also between the
molecules at 188 K, we give all the equivalent distances. All the
HꢃꢃꢃA distances given in the bottom part of Table 4 are higher
˚
than 2.6 A. In Fig. 6, the shortest bonds are emphasized with blue
dashed lines.
The absolute configuration of the two crystals measured was
the same: S, S, S, R, and R for C(13), C(16), C(17), C(19), and C(20),
respectively. Although the optical rotatory power of the powder
was equal to zero, both single crystals were pure enantiomers
extracted from a conglomerate mixture.
The 2-O-(5-deoxy-1,2-O-isopropylidene-a-D-glucofuranos-5-
yloxy)quinoxaline 8 does not present phase transition between
173 K and its melting which occurs at 393.2 ꢂ 0.4 K (Table 2). It
crystallizes in a monoclinic P21 system with Z ¼ 2 molecules per
Table 4. (a) Shortest donor–Hꢃꢃꢃacceptor distances and for comparison, other equivalent distances which are not so short
˚
D–H (A)
˚
˚
D–HꢃꢃꢃA
HꢃꢃꢃA (A)
DꢃꢃꢃA (A)
D–HꢃꢃꢃA(8)
(A) Symmetry code
(a) Shortest donor–Hꢃꢃꢃacceptor distances
Compound 7 at 188 K
C20 H20 O45
C44 H44B N40
C13 H13 O21
C43 H43 O51
C34 H34 O45
1.00
0.99
1.00
1.00
0.95
2.55
2.55
2.58
2.58
2.55
3.285(5)
3.035(6)
3.509(6)
3.468(6)
3.443(6)
130.0
111.0
154.0
149.0
156.0
x, y, z
x, y, z
x, y ꢀ 1, z
x, y ꢀ 1, z
x, y ꢀ 1, z
Compound 7 at 293 K
C14 H14B N10
Compound 8 at 293 K
C24 H24A O15
(b) For comparison, other intermolecular distances which are not so short
0.97
2.58
3.050(6)
110.0
162.0
x, y, z
0.96
2.58
3.507(3)
x ꢀ 1, y, z
Compound 7 at 188 K
C50 H50 O75
C80 H80 O15
C14 H14B N10
C74 H74B N70
C73 H73 O81
C64 H64 O75
C4 H4 O51
Compound 7 at 293 K
C4 H4 O15
C20 H20 O15
C13 H13 O21
1.00
1.00
0.99
0.99
1.00
0.95
0.95
2.95
2.76
2.69
2.63
2.70
2.73
2.71
3.541(5)
3.448(5)
3.118(6)
3.095(6)
3.589(6)
3.616(6)
3.541(6)
118.5
126.6
106.7
108.1
148.7
155.3
146.9
x, y, z
x, y, z
x, y, z
x, y, z
x, y ꢀ 1, z
x, y ꢀ 1, z
x, y ꢀ 1, z
0.93
0.98
0.98
2.71
2.79
2.75
3.567(6)
3.498(5)
3.640(6)
153.1
129.2
151.8
x, y ꢀ 1, z
ꢀx, y,ꢀz þ 2
x, yꢀ1, z
J. Phys. Org. Chem. 2009, 22 585–592
Copyright ß 2009 John Wiley & Sons, Ltd.
www.interscience.wiley.com/journal/poc

C. JARMOUMI ET AL.
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8. The crystal structure of these compounds have been
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www.interscience.wiley.com/journal/poc
Copyright ß 2009 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2009, 22 585–592