A regio- and stereo-controlled approach to triazoloquinoxalinyl C-nucleosides

Article abstract of DOI:10.1016/j.carres.2010.08.010

The synthesis of a new series of acyclic triazoloquinoxalinyl C-nucleosides and their transformation to their cyclic analogs are described following protection, activation, and deprotection with subsequent intramolecular nucleophilic substitution protocol. The antibacterial potency of the new compounds was determined using an inhibition zone diameter test. The results show that 3a and 2b exhibit good activity against Escherichia coli and Candida albicans. On the other hand, the cyclic mesylated C-nucleoside 13 showed activity against the Gram-positive bacteria (Staphylococcus aureus) and antifungal activity against C. albicans.

Full text of DOI:10.1016/j.carres.2010.08.010

Carbohydrate Research 345 (2010) 2474–2484
Contents lists available at ScienceDirect
Carbohydrate Research
journal homepage: www.elsevier.com/locate/carres
A regio- and stereo-controlled approach to triazoloquinoxalinyl C-nucleosides
Adel Amer a, , Mohammed Salah Ayoup a, Sherine Nabil Khattab a, Seham Yassen Hassan a,
⇑
Vratislav Langer b, Samir Senior a, Abdel Moneim El Massry a
a Department of Chemistry, Faculty of Science, PO Box 426 Ibrahimia, Alexandria University, Egypt
b Department of Chemical and Biological Engineering, Chalmers University of Technology, SE-41296 Gothenburg, Sweden
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 12 June 2010
Received in revised form 6 August 2010
Accepted 16 August 2010
Available online 9 October 2010
The synthesis of a new series of acyclic triazoloquinoxalinyl C-nucleosides and their transformation to
their cyclic analogs are described following protection, activation, and deprotection with subsequent
intramolecular nucleophilic substitution protocol. The antibacterial potency of the new compounds
was determined using an inhibition zone diameter test. The results show that 3a and 2b exhibit good
activity against Escherichia coli and Candida albicans. On the other hand, the cyclic mesylated C-nucleoside
13 showed activity against the Gram-positive bacteria (Staphylococcus aureus) and antifungal activity
against C. albicans.
Keywords:
Acyclic triazoloquinoxalinyl C-nucleosides
Cyclic triazoloquinoxalinyl C-nucleosides
Antimicrobial activity
Ó 2010 Elsevier Ltd. All rights reserved.
Tautomerism
1. Introduction
could easily attack to form the ring.16,17 The latter route showed
that such transformations occurred with stereoselectivity to afford
Modified nucleobases, nucleosides and nucleotides are impor-
tant in the process of regulation and are used broadly in chemistry,
biochemistry, and pharmacology as probes of biological mecha-
nisms. C-Nucleosides are a subtype of these compounds that are
of great interest owing to their potential biological activity
together with their higher stabilities than that of the correspond-
ing N-nucleosides. These findings prompted extensive research in
recent years1–13 in the area of modified nucleosides.
The reported synthetic strategies for the C-nucleosides could be
classified into three routes:14 (1) direct attachment of a pre-formed
aglycon unit to an appropriate carbohydrate moiety, for example,
coupling of ribofuranose derivatives or 1,4-ribonolactones with
organometallic reagents and Heck-type coupling; (2) introduction
of a functional group at the anomeric position of a sugar derivative,
followed by the construction of a heterocyclic base; (3) nucleo-
philic addition to the aldehydic carbonyl of the open-chain form
of sugars, followed by elimination to build up heterocyclic rings.
The latter approach was used widely leading to heteroarylpolyols
that lack the vital elements of the structure of a potential anti-viral
nucleoside I (Fig. 1).
the nucleoside skeleton I (Fig. 2).
We have envisioned that this approach, which involved protec-
tion, activation then deprotection followed by cyclization could
Base with potential for
hydrogen bonding sites
Hydroxymethyl group
with potential for
phosphorylation
a
b
c
HO
O
d
Figure 1.
CHOH
CHOH
Transformation of polyols to the furanose ring was reported via
two different methods, namely: (1) dehydrative cyclization under
acidic conditions;15 (2) intramolecular nucleophilic substitution
reaction by activating one center while another hydroxyl group
protection
activation
i) deprotection
ii) cyclization
I
CHOH
CHOH
CH2OH
C-nucleoside
⇑
Corresponding author. Tel.: +20 122219463; fax: +20 33911794.
E-mail address: aamer@sci.alex.edu.eg (A. Amer).
Figure 2.
0008-6215/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2010.08.010

A. Amer et al. / Carbohydrate Research 345 (2010) 2474–2484
2475
indeed comprise a general route. Herein we report our findings to-
ward this goal utilizing 2-hydrazino-3-benzylquinoxaline (1) as
the heterobase builder because of its involvement in several bio-
logical activities.18
considering solvent effects (DMSO). In the gas phase, the syn form
showed one of type N–Hꢀ ꢀ ꢀO (2.045 Å), four of type O–Hꢀ ꢀ ꢀO (all
above 2 Å) and one of type O–Hꢀ ꢀ ꢀN (2.178 Å) H-bonds, while the
anti form possesses three of type O–Hꢀ ꢀ ꢀO (only one of them is
above 2 Å), and one of type O–Hꢀ ꢀ ꢀN (1.929 Å) (Fig. 4). The pres-
ence of more H-bond types in the syn isomer increases the repul-
sion energy and also increases the H-bond energy. In case of the
anti isomer, the lower number of H-bonds decreases the repulsion
energy while increases its energy, because the H-bonds formed
cause a decrease in distances between the atoms. In DMSO as a
solvent, the anti form shows low solute–solvent repulsion energy
that has a higher cavitation energy but the overall non-electrostatic
energy is lower than that of the syn isomer by 0.35 kcal/mol. The
solvation energy of the anti form is lower than that of the syn form
by 0.68 kcal/mol.
2. Results and discussion
2.1. Chemistry
Treatment of 1 with D-glucose, D-galactose, and D-mannose in
EtOH leads to the formation of their corresponding hydrazones
2a–c (Scheme 1). Compounds 2a–c were found to exist in their ex-
pected ring and chain tautomeric forms, A–F in dimethyl sulfoxide
solution as evident from their NMR spectra (see Section 3).19 Sig-
nals were assigned using a variety of NMR experiments including
1D and 2D (namely, DQF-COSY and HMQC).
As a prototype, compound 2b showed the presence of the open
forms to cyclic forms in 7:3 ratios (Fig. 3). In the proton spectra two
well-resolved doublets at 7.87 and 7.79 ppm for H-10 (anti:
syn = 3:1) were found to correlate to signals at 4.60 and
4.46 ppm of the H-20 hydrogen of the sugar moiety. Heteronuclear
correlations between these protons of the H–C@N and the carbons
at 162.18 and 151.66 ppm were observed. The presence of the cyc-
lic forms C–F was evident from the 13C NMR spectrum which dis-
played signals at 94.96, 94.50, 92.54, and 92.49 ppm. In addition,
the exchangeable signals of the NHs were seen at 10.98, 10.43,
10.21, 10.08, and 9.53 ppm.
In order to determine which of the open forms is more abun-
dant , an NOE experiment was performed by irradiation of the most
intense NH signal. The result showed no enhancement of any of the
sugar moiety protons indicating that it is of the anti form.
In addition, quantum chemical calculations were carried out
with the GAUSSIAN 98 suite of programs and were in agreement with
the experimental observations. Full geometry optimizations were
carried out using the DFT level (B3LYP/6-31G**) of theory and with
a PCM (B3LYP/6-31G*) SCRF model to consider the solvent to
assess the relative stability of the anti–syn isomeric species. Com-
puted energies are illustrated in Table 1 and indicate the stability
of the anti isomer over the syn one by 0.00120641 au (0.757034
kcal/mol) due to the presence of strong hydrogen bonding in
the gas phase as well as by 0.00167216 au (1.049297 kcal/mol)
Annulation reactions of 2 to their corresponding triazoloquin-
oxalines 3 were achieved by treatment of 2 with methanolic bro-
mine in good yield. The protection of 3a with acetone in the
presence of elemental iodine afforded a mixture of (1S)-1-C-
(4-benzyl-1,2,4-triazolo[4,3-a]quinoxalin-1-yl)-2,3:4,5-di-O-isopro-
pylidene-
D-arabinitol (4) and (1S)-1-C-(4-benzyl-1,2,4-triazolo[4,
3-a]quinoxalin-1-yl)-1,2:4,5-di-O-isopropylidene-
D-arabinitol (5)
(Scheme 2). They were separated by crystallization from ethanol
followed by silica gel plate chromatography using a mixture of
8:1 n-hexane–ethyl acetate as the eluent. The protection was car-
ried out by using acetone–iodine or acetone–FeCl3 and afforded
compounds 4 and 5 in 3:2 and 2:1 ratios, respectively. Further-
more, the structure of 5 was secured by X-ray crystallography
(see Table 2 and Fig. 5).
On the other hand, protection of the polyols of 3b using
acetone–H2SO4,20 acetone–FeCl3,21 acetone–iodine,22 acetone–
DMF–p-TSA,23 and acetone–benzene–H2SO4 afforded only the
24
mono-O-isopropylidene 6. Repeating this reaction using 2,2-dime-
thoxypropane–DMF–p-TSA25 afforded the mono- 6 and the di-O-
isopropylidene 7 (Scheme 3). Even though their structures can
easily be inferred from their spectroscopic and analytical data,
the structure of 6 was secured by X-ray diffraction analysis of a
suitable crystal of its acetylated product 8 (see Table 2 and Fig. 6).
Similarly, protection of 3c using dimethoxypropane led to the
formation of the di-O-isopropylidene derivative 9 (Fig. 7) in good
yield while acetone–H2SO4 and acetone–iodine gave reaction mix-
tures that were extremely difficult to work with.
Ph
Ph
H
O
N
N
R
HCl/EtOH
H
NNH
N
N
NH
NH2
R
2
1
a) R=
b) R=
c) R=
HO
OH
OH
HO
HO
HO
HO
OH
OH
OH
OH
OH
OH
OH
OH
Scheme 1.

2476
A. Amer et al. / Carbohydrate Research 345 (2010) 2474–2484
Ar
HN
N
H
H
Ar
N
N
H
OH
OH
open forms
HO
HO
HO
HO
Anti
syn
OH
OH
OH
OH
B
A
Ar
NH
HN
O
O
OH
OH
furanose
HN
OH
OH
OH
OH
OH
OH
HN
Ar
C
D
β−
α−
Ar
OH
HO
NH
O
HO
HN
O
pyranose
HO
HO
OH
OH
HN
HN
HO
Ar
F
E
Ph
N
Ar =
N
Figure 3. Isomeric structures of compound 2b.
Table 1
established by an NOE experiment that showed no correlation
between H-10 and H-40 (see Scheme 4).
Calculated relative energies of 2b anti–syn isomers
Mesylation of 6 afforded the tri-O-mesylated derivative 12,
which upon treatment with 4% HCl gave the cyclic compound 13
in good yield (Scheme 5). Its structure was unambiguously
Isomer
anti
syn
Vacuum
DMSO
ꢁ1409.79532 au
ꢁ1409.380808 au
ꢁ1409.794114 au
ꢁ1409.379136 au
assigned by 2D NMR experiments (see Section 3) and the
a-ano-
meric configuration of 13 was clearly established by an NOE corre-
Transformation of 4 to its O-mesyl derivative 10 employed
treatment with methanesulfonyl chloride in pyridine and stirring
at 0 °C for 3 h. Deprotection of the isopropylidene groups of 10
using 4% HCl in 1,2-dimethoxyethane (DME) under gentle refluxing
conditions afforded the desired cyclic C-nucleoside 11 in 74% yield
(Scheme 4). The selective C-40–C-10 cycloetherification was con-
firmed by the 13C NMR spectroscopy that showed the resonance
lation between H-10 and H-40. The anomeric proton H-10 for 13 was
0
0
shown as a doublet at d 5.89 having a coupling constant of J1 ,2
7.6 Hz.15c
On the other hand, one-pot OH activation, O-deisopropylidena-
tion of 9, followed by intramolecular substitution, led to the
formation of 1-(b-D-arabinofuranosyl)-4-benzyl-1,2,4-triazolo[4,3-a]
quinoxaline 14 (Scheme 6). The chemical shift of the anomeric
for C-40 at d 84.27, and the
a-anomeric configuration of 11 was
proton of 14 having a cis arrangement of H-10 and H-20 was shown

A. Amer et al. / Carbohydrate Research 345 (2010) 2474–2484
2477
Figure 4. Full geometry optimizations using the DFT level with a PCM (B3LYP/6-31G*) SCRF model for 2b syn and anti forms.
Ph
N
NH
N
Ar'
N
OH
OH
Br2−MeOH
HO
HO
OH
OH
OH
OH
OH
OH
2a
3a
acetone−iodine
Ar'
Ar'
O
OH
O
O
OH
O
O
O
Ph
N
N
O
O
N
N
Ar' =
4
5
Scheme 2.
0
0
at d 5.96 as a doublet (J1 ,2 5.35 Hz) more downfield than that for
ATCC8739, Pseudomonas (P. aeruginosa) ATCC 9027 as Gram-
negative bacteria, Staphylococcus aureus ATCC 6583P as an example
of Gram-positive bacteria, and Candida albicans ATCC 2091 as a
yeast-like fungus. The inhibition zone (IZ) and minimal inhibitory
zone (MIC) results are given in Table 3. It is apparent from the
data listed in Table 3 that 3a and 2b exhibit good activity against
E. coli and C. albicans. On the other hand, the cyclic mesylated
C-nucleoside 13 showed activity against the Gram-positive bacte-
ria (S. aureus) and antifungal activity against C. albicans.
11 (d 5.34 as a doublet of J1 ,2 6.8 Hz), in accord15c with the b con-
0
0
figuration of 14 and the
a configuration of 11.
2.2. Biology
Four test organisms representing different groups of microor-
ganisms were used to evaluate the bioactivity of the designed
products. The utilized test organisms were: Escherichia coli

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A. Amer et al. / Carbohydrate Research 345 (2010) 2474–2484
Table 2
Crystal data and structure refinement for compounds 5 and 8
Compound 5
27H30N4O5
490.55
153(2)
0.71073
Triclinic
P1
Compound 8
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
C
C30H32N4O8
576.6
153(2)
0.71073
Monoclinic
P21
Space group
Unit cell dimensions
a = 8.2475(11) Å
a
= 110.886(2)°
a = 12.2818(8) Å a = 90°
b = 9.4606(12) Å b = 105.975(2)°
b = 9.3225(11) Å b = 100.153(1)°
c = 9.5750(12) Å
611.13(14)
1
1.333
0.093
260
c
= 105.837(3)°
c = 7.3035(5) Å c = 90°
1454.63(16)
2
1.316
0.097
608
Volume (Å3)
Z
Density (calculated) (Mg/m3)
Absorption coefficient (mmꢁ1
F(0 0 0)
)
Crystal size (mm3)
1.06 ꢂ 0.46 ꢂ 0.38
0.77 ꢂ 0.68 ꢂ 0.54
Theta range for data collection
Index ranges
Reflections collected
2.50–33.03°
2.11–30.54°
ꢁ12 6 h 6 12, ꢁ14 6 k 6 14, ꢁ14 6 l 6 14
10,948
ꢁ17 6 h 6 17, ꢁ13 6 k 6 13, ꢁ18 6 l 6 18
24,130
Independent reflections
Completeness to theta = 31.00°
Absorption correction
4248 [R(int) = 0.0576]
99.3%
Multi-scan
4687 [R(int) = 0.0451]
99.5%
Multi-scan
Max. and min. transmission
Refinement method
0.9654 and 0.9076
Full-matrix least-squares on F2
4248/3/330
0.9496 and 0.9293
Full-matrix least-squares on F2
4687/1/384
Data/restraints/parameters
Goodness-of-fit on F2
1.000
0.997
Final R indices [I > 2sigma(I)]
R indices (all data)
R1 = 0.0466, wR2 = 0.1031
R1 = 0.0719, wR2 = 0.1160
0.378 and ꢁ0.232
R1 = 0.0456, wR2 = 0.1125
R1 = 0.0659, wR2 = 0.1241
0.650 and ꢁ0.259
Largest diff. peak and hole (e Åꢁ3
)
using aluminum-backed E. Merck Silica Gel 60 F254 plates, with
UV 254 nm. Separation by plate chromatography was performed
using 20 ꢂ 20 cm, 2000
lm TLC plates, using suitable solvent sys-
tems with spots being visualized by a Spectroline UV Lamp (254
or 366 nm).
Infrared spectra (IR) were recorded on a Perkin–Elmer 1600 ser-
ies Fourier-transform instrument as KBr pellets. 1H and 13C NMR
spectra were recorded on JOEL 500-MHz spectrometers at ambient
temperature using tetramethylsilane (TMS) as the internal refer-
ence. Mass spectra were recorded on a JOEL JMS AX-500 spectrom-
eter in the electron impact (EI) mode at 70 eV. X-ray diffraction
data were collected using a Siemens SMART CCD diffractometer
with Mo K
a radiation (k = 0.71073 Å, graphite monochromator).
The crystals were cooled to 153(2) K by a flow of nitrogen gas using
the LT-2A device. A full sphere of reciprocal space was scanned by
0.3 ° steps in
x with a crystal-to-detector distance of 3.97 cm. Ele-
mental analyses were carried out by the University of Cairo Micro-
analytical Laboratories.
3.2. General procedures for the preparation of
benzylquinoxalin-2-yl)hydrazones (2)
D-sugar (3-
To a solution of the hydrazine 1 (1.25 g, 5.0 mmol) in EtOH
(25 mL), the corresponding sugar (2.50 mmol) was added, followed
by one drop of 33% HCl. The reaction mixture was heated under
reflux on a boiling water bath for 1 h, then left to cool to room tem-
perature. The solid that separated was filtered off, washed with
EtOH, and dried.
Figure 5. Numbering scheme with atomic displacement ellipsoids drawn at 50%
probability level of compound 5.
3. Experimental
3.2.1.
This compound was obtained as deep-red crystals, (0.6 g, 58%);
mp 204–205 °C; Rf 0.7 (7:3 EtOAc–n-hexane). IR (KBr) m 3310 (NH,
D-Glucose (3-benzylquinoxalin-2-yl)hydrazone (2a)
3.1. General methods
OH), and 1665 cmꢁ1 (C@N); 1H NMR (DMSO-d6, 500 MHz): d 2.4–
3.38 (br s, 9H, H-20, 30, 40, 2H-50, 4OH-20, 30, 40, 50), 4.34–5.7 (m,
4H, 2H-14, OH-10, H-10) 6.9–7.8 (m, 9H, H-7, 8, 9, 10, 16, 17, 18,
19, 20), 8.8 (m, 1H, H-13 of HC@N), 11.69, 11.37, 10.95, 10.83,
10.46, 10.23, 10.08, 9.01, 8.82, and 8.48 (different singlet, H0 of
Melting points were obtained in open capillary tubes by using a
MEL-Temp II melting point apparatus and are uncorrected. Column
chromatography was performed by using silica gel obtained from
E. Merck (EM-9385, Mesh 230–400 ASTM). TLC was performed

A. Amer et al. / Carbohydrate Research 345 (2010) 2474–2484
2479
Ar'
Ar'
OAc
OH
AcO
HO
O
Ac2O
acetone/H2SO4
or
or
O
pyridine
acetone/FeCl3
acetone/iodine
O
O
OAc
OH
Ar'
8
6
OH
HO
HO
Ar'
O
OH
OH
O
O
2,2-dimethoxypropane
/DMF/p-TSA
+ 6
3b
O
Ph
N
OH
N
7
N
Ar' =
N
Scheme 3.
m
3299 (NH, OH), 1665 cmꢁ1 (C@N); 1H NMR (DMSO-d6,
500 MHz): anti form: d 3.51–3.63 (m, 3H, H-40, H-6a0 , H-6b0 ), 3.70–
3.73 (m, 1H, H-50), 4.07 (br s, 2H, PhCH2), 4.18 (d, 1H, JOH4 ,4
0
0
6.9 Hz, OH-40, exchangeable with D2O), 4.24 (d, 1H, JOH5 ,5 6.9 Hz,
0
0
OH-50, exchangeable with D2O), 4.36 (d, 1H, JOH2 ,2 6.1 Hz, OH-20,
exchangeable with D2O), 4.45 (m, 1H, OH-60, exchangeable with
D2O), 4.54 (d, 1H, J 6.1 Hz, H-30), 4.60 (br s, 1H, H-20), 5.02 (d, 1H,
OH-30, exchangeable with D2O), 7.15 (t, 1H, J 7.6 Hz, Ph-H), 7.22–
7.25 (m, 3H, Ph-H), 7.31–7.40 (m, 4H, quin-H6, quin-H7, quin-H8,
0
0
0
0
Ph-H) 7.48 (d, 1H, J9,8 7.6 Hz, quin-H9), 7.88 (d, 1H, J1 ,2 3.8 Hz,
H-10), 10.98 (s, 1H, N–H, exchangeable with D2O), 13C NMR
(DMSO-d6, 125.7 MHz):
d
39.76 (PhCH2), 63.63 (C-40), 69.61
(C-300), 70.34 (C-60), 71.27 (C-50), 72.00 (C-20), 126.79, 128.75,
129.73, 132.37, 132.67, 138.35, 145.86, 146.87, 148.04, 151.66,
159.5 aromatic carbons for the major isomer,162.18 (C-10). syn
Form: d 3.36–3.40 (m, 2H, H-30, H-50), 3.55–3.40 (m, 2H, H-60a,
H-60b), 3.88–3.90 (m, 1H, OH-50, exchangeable with D2O), 4.07 (br
s, 2H, PhCH2), 4.24 (d, 1H, JOH4 ,4 6.9 Hz, OH-40, exchangeable with
D2O), 4.45–4.53 (m, 2H, H-20, OH-60, exchangeable with D2O), 4.53–
4.89 (m, 2H, H-40, OH-30, exchangeable with D2O), 5.11 (d, 1H,
0
0
JOH2 ,2 6.1 Hz, OH-20, exchangeable with D2O), 7.04 (t, 1H, J
7.6 Hz, Ph-H), 7.22–7.25 (m, 3H, Ph-H), 7.31–7.40 (m, 4H, quin-
H6, quin-H7, quin-H8, Ph-H), 7.68 (d, 1H, J9,8 7.6 Hz, quin-H9), 7.79
0
0
(d, 1H, J1 ,2 6.9 Hz, H-10), 10.43 (s, 1H, N–H, exchangeable with
D2O), 13C NMR (DMSO-d6, 125.7 MHz): d aromatic carbons for
the major isomer, 151.66 (C-10). Anal. Calcd for C21H24N4O5: C,
61.15; H, 5.87; N, 13.58. Found: C, 61.41; H, 6.07; N, 13.77.
0
0
Figure 6. Numbering scheme with atomic displacement ellipsoids drawn at 50%
probability level for compound 8.
NH group, exchangeable with D2O). 13C NMR (DMSO-d6,
125.7 MHz): d 61.16, 70.22, 74.84, 76.42, 76.46, 116.70, 118.61,
129.13, 129.27, 129.53, 136.58, 137.78, 142.85, 147.59, 150.94,
153.46, and 153.88. Anal. Calcd for C21H24N4O5: C, 61.15; H, 5.87;
N, 13.58. Found: C, 61.43; H, 6.03; N, 13.09.
3.2.3. D-Mannose (3-benzylquinoxalin-2-yl)hydrazone (2c)
This compound was obtained as deep-yellow crystals (0.75 g;
72.8%); mp 173–174 °C; Rf 0. 62 (7:3 EtOAc–n-hexane). IR (KBr);
m
3221 (NH, OH) and 1613 cmꢁ1 (C@N); 1H NMR (DMSO-d6,
500 MHz): d 3.39–3.70 (m, 5H, H-30, H-50, H-6a0 , H-6b0 , OH-30,
exchangeable with D2O), 4.07 (br s, 2H, PhCH2), 4.26–4.28 (m,
1H, H-20), 4.31–4.43 (m, 3H, OH-40, OH-50, OH-60, exchangeable
3.2.2. D-Galactose (3-benzylquinoxalin-2-yl)hydrazone (2b)
This compound was obtained as deep-yellow crystals (0.91 g;
88.3%); mp 183–184 °C; Rf 0. 66 (7:3 EtOAc–n-hexane). IR (KBr);
with D2O), 4.49 (d, 1H, J 6.1 Hz, H-40), 5.07 (d, JOH2 ,2 5.3 Hz,
0
0

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A. Amer et al. / Carbohydrate Research 345 (2010) 2474–2484
Ph
N
N
N
N
HO
OH
O
OMs
MsCl−Py
4% HCl
4
DME
O
OH
N
N
O
O
O
N
N
Ph
10
11
Scheme 4.
Ph
added, and the volatile components were evaporated under
vacuum at 60 °C. The residue was treated with EtOH (95%,
10 mL), then left to cool at room temperature. The crude product
that precipitated was collected by filtration and washed with
EtOH.18
N
N
N
N
3.3.1. 1-(D-gluco-Pentitol-1-yl)-4-benzyl[1,2,4]triazolo[4,3-
a]quinoxaline (3a)
The crude product was recrystallized from MeOH to give color-
less crystals (0.71 g, 69.2%); mp 183–184 °C; Rf 0.6 (6:1 CHCl3–
HO
O
MeOH); IR(KBr);
m
3412 (OH), and 1643 cmꢁ1 (C@N); 1H NMR
(DMSO-d6, 500 MHz): d 3.28–3.31 (m, 2H, H-40, H-30), 3.49–3.52
(m, 2H, H-50a;b), 4.26–4.28 (m, 1H, OH -40, exchangeable with
D2O), 4.36 (m, 1H, OH-50, exchangeable with D2O), 4.42 (d, 1H,
O
O
O
JOH3 ,3 7.6 Hz, OH-30), 4.54 (s, 3H, H-20, PhCH2), 4.88 (d, 1H, J2 ,
0
0
0
6.10 Hz, OH-20, exchangeable with D2O), 5.42 (dd, 1H, J1 , OH1
0
0
OH20
6.1, J1 , 2 8.4, H-10), 6.12 (d, 1H, J1 , OH1 6.1 Hz, OH-10, exchangeable
with D2O), 7.17 (t, 1H, J 6.8 Hz, Ph-H), 7.25–7.28 (m, 2H, Ph-H),
7.45 (d, 2H, J 7.6 Hz, Ph-H), 7.65–7.74 (m, 2H, quin-H7, quin– H8),
8.02 (d, 1H, J6,7 8.4 Hz, quin-H6), 8.64 (d, 1H, J9,8 8.4 Hz, quin-H9);
13C NMR (DMSO-d6, 125.7 MHz): d 63.99, 66.84, 70.56, 70.61,
71.82, 119.30, 126.01, 127.24, 128.14, 129.02, 129.70, 129.83,
130.05, 136.46, 137.42, 144.55, 151.54, 154.09. Anal. Calcd for
0
0
0
0
9
Figure 7.
OH-20, exchangeable with D2O), 7.15 (dist. t, 1H, J 7.6 Hz, J 6.9 Hz,
Ph-H), 7.22–7.40 (m, 6H, quin-H7, quin-H8, Ph-H), 7.48 (d, 1H, J6,7
0
0
7.6 Hz, quin-H6), 7.67 (m, 1H, quin-H9), 7.96 (d, 1H, J1 ,2 3.8 Hz,
H-10), 10.92 (s, 1H, N–H, exchangeable with D2O), 13C NMR
(DMSO-d6, 125.7 MHz): d 40.0 (PhCH2, C-40), 64.37 (C-40), 70.09
(C-60), 70.94 (C-20), 71.51 (C-30), 126.80, 128.63, 129.80, 132.34,
132.66, 138.32, 145.75, 146.86, 147.99, 151.27, 159.45 aromatic
carbons for the major isomer 162.05 (C-10). Anal. Calcd for
C21H22N4O5: C, 61.45; H, 5.40; N, 13.65. Found: C, 61.40; H, 6.07;
N, 13.52.
3.3.2. 1-(D-galacto-Pentitol-1-yl)-4-benzyl[1,2,4]triazolo[4,3-
a]quinoxaline (3b)
The crude product was recrystallized from MeOH to give bright
gray crystals (0.85 g, 82.9%); mp 240–241 °C; Rf 0.63 (6:1 CHCl3–
C21H24N4O5: C, 61.15; H, 5.87; N, 13.58. Found: C, 61.06; H, 6.10;
N, 13.39.
MeOH); IR (KBr);
m ;
3249 (OH), 1603 (C@N) cmꢁ1 1H NMR
(DMSO-d6, 500 MHz): d 3.37–3.44 (m, 2H, H-50 , H-50 ), 3.69–3.72
a
b
3.3. General procedure for the preparation of: 1-(alditol-1-yl)-4-
benzyl [1,2,4]triazolo[4,3-a]quinoxaline (3)
(m, 1H, H-30), 3.77 (m, 1H, H-40), 4.1 (d, 1H, J 7.6 Hz, H-20), 4.25
(br s, 1H, OH-50, exchangeable with D2O), 4.38 (d, 1H, JOH-4 ,4
0
0
7.6 Hz, OH-40, exchangeable with D2O), 4.50–4.60 (m, 3H, OH-30,
0
0
To a solution of 2-hydrazino-3-benzylquinoxaline 1 (625 mg,
2.50 mmol) in MeOH (25 mL), the corresponding sugar (2.50
mmol) and one drop of 33% HCl was added. The reaction mixture
was heated under reflux on a boiling water bath for 1 h, left to cool
at room temperature, and then a solution of bromine (0.13 mL,
2.50 mmol) in MeOH (5.0 mL) was added drop wise with stirring,
over 2 h. A mixture of EtOH (3 mL) and pyridine (0.5 mL) was
PhCH2, exchangeable with D2O), 4.86 (d, 1H, JOH-2 ,2 5.35 Hz,
OH-20, exchangeable with D2O), 5.62 (d, 1H, J 5.35 Hz, H-10), 5.92
(d, 1H, JOH-1 ,1 6.85 Hz, OH-10, exchangeable with D2O), 7.17 (dist.
t, 1H, J 7.6 Hz, J 6.9 Hz, Ph-H), 7.28 (t, 2H, J 7.6 Hz, Ph-H), 7.43 (d,
2H, J 8.4 Hz, Ph-H), 7.64 (t, 1H, J7,6 = J7,8 7.6 Hz, quin-H7), 7.71 (t,
1H, J8,7 = J8,9 7.6 Hz, quin-H8), 8.0 (d, 1H, J6,7 7.6 Hz, quin-H6),
8.79 (d, 1H, J9,8 8.4 Hz, quin-H9); 13C NMR (DMSO-d6, 125 MHz):
0
0

A. Amer et al. / Carbohydrate Research 345 (2010) 2474–2484
2481
Ph
N
N
N
MsO
N
OH
OMs
O
MsCl−Py
4% HCl
DME
OMs
6
MsO
O
N
N
N
N
O
OMs
Ph
12
13
Scheme 5.
Ph
H-50b), 3.63–3.67 (m, 2H, H-30, OH-50, exchangeable with D2O),
3.79–3.85 (m, 2H, H-20, OH-30, exchangeable with D2O), 4.40–
4.50 (m, 2H, PhCH2), 5.45 (dist. t, 1H, J 10.7 Hz, 9.9 Hz, H-10), 5.52
N
N
(d, 1H, JOH-2 ,2 9.9 Hz, OH-20, exchangeable with D2O), 6.46 (s, 1H,
OH-10, exchangeable with D2O), 7.17 (s, 1H, Ph-H), 7.31–7.40 (m,
2H, Ph-H), 7.69–7.82 (m, 2H, quin-H7, quin-H8), 8.10 (d, 1H, J
8.4 Hz, quin-H6), 8.62–8.67 (m, 1H, quin-H9). Anal. Calcd for
0
0
N
N
N
Ph
MsO
N
4% HCl
DME
N
O
MsCl−Py
HO
C21H22N4O5: C, 61.45; H, 5.40; N, 13.65. Found: C, 61.25; H, 5.74;
N, 13.59.
9
N
OH
O
O
O
O
OH
3.4. Acetonization of 1-(alditol-1-yl)-4-benzyl[1,2,4]triazolo[4,
3-a]quinoxalines
14
Scheme 6.
3.4.1. (1S)-1-C-(4-Benzyl-1,2,4-triazolo[4,3-a]quinoxalin-1-yl)-
2,3:4,5-di-O-isopropylidene-
Benzyl-1,2,4-triazolo[4,3-a]quinoxalin-1-yl)-1,2:4,5-di-O-
isopropylidene- -arabinitol (5)
3.4.1.1. Method A. To a mixture of 1-(
benzyl[1,2,4]triazolo[4,3-a]quinoxaline (3a, 1.50 g, 3.66 mmol) in
dry acetone (60 mL) was added elemental iodine (0.25 g,
1.20 mmol) and the mixture was heated under reflux. The reaction
was monitored by TLC (9:1 CHCl3–MeOH). After the reaction was
complete, dilute aq sodium thiosulfate was added, and the excess
acetone was evaporated under vacuum. The isopropylidene deriv-
atives were extracted with CHCl3 (3 ꢂ 30 mL), and the CHCl3 ex-
tracts were combined and washed with water, then dried over
D-arabinitol (4) and (1S)-1-C-(4-
d 63.25, 66.35, 69.08, 71.55, 71.65, 119.79, 125.90, 127.34, 128.28,
129.07, 129.64, 129.68, 129.75, 136.28, 137.27, 137.31, 144.61,
153.25, 154.05. Anal. Calcd for C21H22N4O5: C, 61.45; H, 5.40; N,
13.65. Found: C, 61.64; H, 5.09; N, 13.44.
D
D
-gluco-pentitol-10-yl)-4-
3.3.3. 1-(D-manno-Pentitol-1-yl)-4-benzyl[1,2,4]triazolo[4,3-
a]quinoxaline (3c)
The crude product was recrystallized from 95% EtOH to give col-
orless crystals, (0.61 g; 59.5%); mp 199–200 °C; Rf 0.47 (6:1 CHCl3–
MeOH). IR (KBr);
m
3342 (OH), and 1627 cmꢁ1 (C@N); 1H NM0R
(DMSO-d6, 500 MHz): d 3.42–3.48 (m, 4H, H-40, OH-40, H-5a,
Table 3
In vitro antimicrobial activity of the test compounds and evaluation of their antimicrobial activity of the inhibition zone (IZ) and the minimal inhibitory concentration (MIC)
Microorganism test compounds
E. coli
S. aureus
C. albicans
MIC
P. aerugenosa
MIC
IZ
MIC
IZ
MIC
IZ
IZ
Ampicillin 10.0
Ciprofloxacin 5.0
Clotrimazole 100.0
l
g/disc
g/disc
g/disc
g/disc
18
28
—
26
20
32
35
25
39
31
25
12.5
—
—
—
—
62.5
62.5
22
30
—
30
25
14
19
8
21
13
23
13
13
12.5
25
—
—
125
—
—
40
—
17
31
34
27
39
30
—
—
12.5
—
—
38
—
—
25
—
l
l
Imipenam 10.0
l
30
20
15
17
7
19
11
21
15
15
—
1
2a
2b
2c
3a
3b
3c
11
13
62.5
—
—
62.5
62.5
31.25
62.5
—
125
—
15
15
—
62.5
—
31.25
19
15
—
15.62
62.5

2482
A. Amer et al. / Carbohydrate Research 345 (2010) 2474–2484
anhyd Na2SO4. The organic solvent was evaporated under vacuum
to give a mixture of 4 and 5 that was separated by recrystallization
from absolute EtOH to give 5 as pure colorless crystals (0.6 g, 33%);
mp 207–208 °C. The highly soluble 4 was purified and separated by
plate chromatography using eluent (8:1 EtOAc–n-hexane) to give
colorless crystals (0.9 g, 50%); mp 110–111 °C.
3.4.2.4. Method D. To a mixture of unprotected 3b (0.30 g,
0.73 mmol) and dry acetone (30 mL), FeCl3 (0.10 g) and dry DMF
(5 mL) were added. The reaction mixture was irradiated in the
microwave oven for 2 min. The product that precipitated was fil-
tered and washed with acetone to give a white solid in good yield
(0.31 g, 93%); mp 226–227 °C; Rf 0.5 (4:1 EtOAc–n-hexane); 1H
NMR (DMSO-d6, 500 MHz): d 0.80 (s, 3H, CH3), 0.96 (s, 3H, CH3),
3.4.1.2. Method B. The unprotected 3a (1.0 g, 2.43 mmol) was
treated with a mixture of dry acetone (80 mL), and two drops of
97% H2SO4. The reaction mixture was stirred overnight, then neu-
tralized by careful addition of satd aq NaHCO3 (20 mL). The reac-
tion mixture was filtered and the excess acetone was evaporated
under vacuum at 60 °C, then the product was extracted using
CHCl3 (3 ꢂ 30 mL). The combined organic layers were dried over
anhyd Na2SO4, then evaporated under vacuum at 50 °C, and the
residue was recrystallized from absolute EtOH to give a mixture
of 5 (0.6 g, 50%) and 4 (0.35 g, 29%).
3.35 (dd, 1H, JH5 a,5 b 11.4 Hz, JH5 a,4 6.4 Hz H-50a), 3.54, (dd, 1H,
0
0
0
0
0
JH5 b,5 a 11.4 Hz, JH5 b,4 2.3 Hz H-5b) 3.73 (t, 1H, J 7.6 Hz, H-40),
0
0
0
0
3.93 (br s, 1H, H-30), 4.07–4.11 (m, 1H, H-20), 4.44, 4.60 (2 d, 2H,
J 13, 64 Hz, PhCH2), 4.70 (t, 1H, JOH5 ,5 a = JOH5 ,5 b 5.35 Hz, OH-50,
0
0
0
0
exchangeable with D2O), 5.38 (t, 1H, J 6.1, 3.0 Hz, H-10), 5.54 (d,
1H, JOH2 ,2 6.15 Hz, OH-20, exchangeable with D2O), 6.48 (d, 1H,
0
0
JOH-1 ,1 6.85 Hz, OH-10, exchangeable with D2O), 7.14–7.25 (m,
3H, Ph-H), 7.41 (d, 2H, J 7.6 Hz, Ph-H), 7.60–7.68 (m, 2H, quin-H7,
quin-H8), 7.98 (d, 1H, J6,7 7.6 Hz, quin-H6), 8.78 (d, 1H, J9,8 8.4 Hz,
quin-H9). Anal. Calcd for C24H26N4O5: C, 63.99; H, 5.82; N, 12.44.
Found: C, 63.71; H, 6.02; N, 12.34.
0
0
3.4.1.3. Compound 4. 1H NMR (CDCl3, 500 MHz): d 1.30, 1.42,
1.46, 1.48 (4 s, 12H, 1:1:1:1, 2 ꢂ Me2C), 4.03–4.25 (m, 5H, H-20,
H-30, H-40, H-5a0 , H-5b0 ), 4.66–4.76 (m, 2H, CH2Ph), 4.81 (d, 1H, J
7.6 Hz, H-10), 5.63–5.73 (m, 1H, OH-10), 7.19–7.29 (m, 3H, Ph-H),
7.62–7.66 (m, 4H, Ph-H, quin-H7, quin-H8), 8.21–8.23 (m, 1H,
quin-H6), 8.43–8.45 (m, 1H, quin-H9). Anal. Calcd for C27H30N4O5:
C, 66.11; H, 6.16; N, 11.42. Found: C, 65.92; H, 5.57; N, 11.18.
3.4.3. (1S)-1-C-(4-Benzyl-1,2,4-triazolo[4,3-a]quinoxalin-1-yl)-
1,2:3,4-di-O isopropylidene-D-lyxitol (7)
A solution of 3b (1.0 g, 2.22 mmol) in dry DMF (50 mL) was
added in turn to p-toluenesulfonic acid (60 mg) and 2,2-dimeth-
oxypropane (DMP, 2.50 mL, 20.0 mmol), and the mixture was left
to stir for 72 h at room temperature. The reaction was monitored
by TLC which showed complete conversion of the starting material
into the product of higher mobility Rf 0.77, and a trace of com-
pound 6 (low mobility Rf 0.50) using eluent 1:8 EtOAc–n-hexane.
The excess DMP was evaporated under vacuum at 80 °C, and the
mixture was poured into cold water (100 mL). The crude product
was collected by filtration and washed with water (20 mL). The
crude product was dissolved in EtOAc to eliminate the less soluble
monoisopropylidene 6 by filtration. Column chromatography of
the residue using 1:8 EtOAc–n-hexane as the eluent afforded pure
7 (0.6 g, 54%); mp 69–70 °C. 1H NMR (CDCl3, 500 MHz): d 1.07,
1.24, 1.37, 1.46 (4s, 12H, 1:1:1:1, 2 ꢂ Me2C); 3.86–4.27 (m, 4H,
3.4.1.4. Compound 5. 1H NMR (DMSO-d6, 500 MHz): d 0.98, 1.16,
1.31, 1.53 (4 s, 12H, 1:1:1:1, 2 ꢂ Me2C), 3.39–3.46 (m, 1H, H-50 ),
b
3.76–3.80 (m, 1H, H-50a), 3.93–3.98 (m, 2H, H-40, H-30), 4.52, 4.57
(2d, 2H, J 14.5 Hz, 13.7 Hz, CH2Ph), 5.36–5.40 (m, 2H, H-20, OH-30,
exchangeable with D2O), 5.66 (d, 1H, J1 ,2 7.6 Hz, H-10), 7.16 (dist.
t, 1H, J 7.6 Hz, 6.9 Hz, Ph-H), 7.25 (t, 2H, J 7.6 Hz, Ph-H), 7.41 (d,
2H, J 7.6 Hz, Ph-H), 7.69 (dist. t, 1H, J 8.4 Hz, 6.9 Hz, quin-H7),
7.79 (dist. t, 1H, J 8.4 Hz, 6.9 Hz, quin-H8), 8.07 (d, 1H, J6,7 7.6 Hz,
quin-H6), 8.34 (d, 1H, J 7.6 Hz, quin-H7), 8.43–8.45 (m, 1H, quin-
H9). 13C NMR (DMSO-d6, 125.7 MHz): d 25.62, 27.04, 27.13,
27.20, 39.7, 39.9, 67.48, 69.85, 70.35, 75.87, 79.10, 108.98,
110.88, 117.47, 125.63, 127.24, 128.48, 128.99, 129.79, 130.15,
130.38, 136.37, 137.27, 145.04, 148.69, 154.09. Anal. Calcd for
0
0
H-50a, H-50b H-40, H-30), 4.38–4.69 (m, 3H, H-20, PhCH2), 5.57–5.64
,
(m, 1H, OH-50), 5.72 (d, 1H, J
6.15 Hz, H-10), 7.17–7.25 (m, 3H,
0
0
1 ,2
Ph-H), 7.50–7.61 (m, 4H, quin-H7, quin-H8, Ph-H), 8.10 (br s, 1H,
quin-H6), 8.42 (dd, 1H, J9,8 2.4 Hz, J9,7 7.6 Hz, quin-H9); 13C NMR
(CDCl3, 125 MHz): d 11.06, 14.18, 25.12, 25.77, 26.36, 27.16, 40.7
(CH2Ph), 65.93, 71.04, 75.42, 76.88, 77.13, (sugar part), 109.44,
111.56, 117.15, 128.62, 129.75, 130.43, 136.68, 144.99, 149.01,
154.05; Anal. Calcd for C27H30N4O5: C, 66.11; H, 6.16; N, 11.42.
Found: C, 65.89; H, 5.83; N, 11.10.
C27H30N4O5: C, 66.11; H, 6.16; N, 11.42. Found: C, 66.27; H, 6.46;
N, 11.20.
3.4.2. (1S)-1-C-(4-Benzyl-1,2,4-triazolo[4,3-a]quinoxalin-1-yl)-
3,4-O-isopropylidene-D-lyxitol (6)
3.4.2.1. Method A. The unprotected 3b (0.75 g, 1.80 mmol) was
treated with a mixture of dry acetone (60 mL), and two drops of
97% H2SO4, in the presence of 4 Å molecular sieves. The reaction
mixture was stirred for 50 h, then neutralized by careful addition
of satd aq NaHCO3 (20 mL). The crude product was collected by fil-
tration, washed with acetone, and air dried to give a white solid
(0.71 g; 85%).
3.4.4. (1R)-1-C-(4-Benzyl-1,2,4-triazolo[4,3-a]quinoxalin-1-yl)-
2,3:4,5-di-O-isopropylidene-D-arabinitol (9)
A solution of 3c (1.0 g, 2.22 mmol) in dry DMF (50 mL) was
added to p-toluenesulfonic acid (60 mg) and DMP (2.50 mL,
20.0 mmol), and the mixture was stirred for 72 h at room temper-
ature. The reaction was monitored by TLC, which showed complete
conversion of the starting material into a product of higher mobil-
ity Rf 0.8 (1:8 EtOAc–n-hexane). The excess DMP was evaporated
under vacuum at 80 °C, and the mixture was poured into cold
water (100 mL). The crude product was collected by filtration,
washed with water (20 mL), and dried. Purification by column
chromatography using 1:8 EtOAc–n-hexane afforded a foamy solid
(0.8 g, 72%); mp 92–93 °C. 1H NMR (CDCl3, 500 MHz): d 1.34, 1.35,
3.4.2.2. Method B. A mixture of unprotected 3b (0.50 g,
1.20 mmol) was treated with a mixture of dry acetone (30 mL),
dry benzene (40 mL) and 3 drops of 97% H2SO4. The reaction mix-
ture was fitted with a Dean-Stark trap and heated under reflux for
8 h, then neutralized by careful addition of satd aq NaHCO3
(20 mL). The crude product was collected by filtration, washed
with acetone, and air dried to give a white solid (0.25 g, 50%).16
1.40, 1.46 (4s, 12H, 1:1:1:1, 2 ꢂ Me2C); 3.44–3.48 (m, 2H, H-50 ,
a
3.4.2.3. Method C. Unprotected 3b (0.50 g, 1.20 mmol) was trea-
ted with a mixture of dry acetone (30 mL) and FeCl3 (0.17 g). The
reaction mixture was heated under reflux with stirring for
30 min then cooled to room temperature. The separated solid
was collected by filtration, washed with acetone, and air dried to
afford the product as a white solid (0.4 g, 72%).
H-50b); 4.08 (dd, 1H, J 4.6 Hz, J 8.4 Hz H-40), 4.17–4.24 (m, 1H, H-
30), 4.63–4.75 (m, 3H, H-20, PhCH2), 5.12 (t, 1H, J1 ,2 = J
0
0
10,OH10
7.6 Hz, H-10), 5.68 (d, 1H, J1 ,OH1 8.4 Hz, OH-10), 7.18 (dist. t, 1H, J
6.8 Hz, 8.4 Hz, Ph-H), 7.55–7.67 (m, 6H, quin-H7, quin-H8, Ph-H),
8.11 (m, 1H, quin-H6), 8.45 (d, 1H, J9,8 8.4 Hz, quin-H9), Anal. Calcd
0
0

A. Amer et al. / Carbohydrate Research 345 (2010) 2474–2484
2483
for C27H30N4O5: C, 66.11; H, 6.16; N, 11.42. Found: C, 66.31; H,
5.88; N, 11.17.
(m, 1H, quin-H6), 8.16 (m, 1H, quin-H9), 13C NMR (CDCl3,
125 MHz): d 26.31, 26.57 (2 CH3), 37.64, 38.99, 39.87 (3 ꢂ CH3SO2),
40.7 (CH2Ph), 60.48, 68.35, 73.14, 77.26, 77.50, 111.35, 125, 16,
127.08, 128.5, 129.6, 130.8, 131.48, 136.36, 136.9, 140, 145.4,
146.2, 154.2, 171.2. Anal. Calcd for C27H32N4O11S3: N, 8.18. Found:
N, 8.45.
3.5. (1S)-1-C-(4-Benzyl-1,2,4-triazolo[4,3-a]quinoxalin-1-yl)-
3,4-O-isopropylidene-1,2,5-tri-O-acetyl-D-lyxitol (8)
A solution of 6 (0.50 g, 1.10 mmol) in dry pyridine (5 mL) was
treated with Ac2O (5 mL), and the mixture was stirred overnight
at room temperature. It was then poured onto crushed ice
(100 g), and the crude product was filtered, washed with water,
dried and subsequently purified by recrystallization from EtOH to
give colorless crystals (0.5 g, 79%); mp 140–141 °C; Rf 0.8 (2:1
EtOAc–n-hexane). 1H NMR (DMSO-d6, 500 MHz): d 0.97 (s, 3H,
CH3), 1.09 (s, 3H, CH3), 1.94 (s, 3H, OAc-50), 1.96 (s, 3H, OAc-20),
3.8. 1-(a-D-Arabinofuranosyl)-4-benzyl-1,2,4-triazolo[4,3-
a]quinoxaline (11)
A mixture of (1S)-1-C-(4-benzyl-1,2,4-triazolo[4,3-a]quinoxa-
lin-1-yl)-2,3:4,5-di-O-isopropylidene-1-O-methanesulfonyl-D-ara-
binitol (10, 280 mg, 0.5 mmol), 1,2-dimethoxyethane (DME,
10 mL), and HCl (4%, 0.5 mL, 0.5 mmol) was stirred under gentle re-
flux and monitored by TLC (5:1 toluene–EtOH). After 30 h the ex-
cess DME was evaporated under vacuum, and the oily residue
was treated with Et2O (5 mL) and anhyd EtOH (5 mL). The resulting
precipitate was collected by filtration and washed with Et2O (2 mL)
to afford a white solid (140 mg, 74%); mp 225–226 °C; 1H NMR
(DMSO-d6, 500 MHz): d 3.56–3.65 (m, 2H, H-50a;b), 3.73–3.76 (m,
1H, H–40), 4.08 (br s, 1H, H-30), 4.54–4.58 (m, 2H, PhCH2), 4.94
(br s, 1H, OH-50, exchangeable with D2O), 5.10 (br s, 1H, H-20),
2.1 (s, 3H, OAc-10), 3.9 (dd, 1H, J5a ,4 6.8 Hz, J5a ,5 b 11.5 Hz, H-50a),
4.0 (dist. t, 1H, J 6.1 Hz, J 7.6 Hz, H-50b), 4.17 (t, 1H, H-40), 4.25–
4.28 (m, 1H, H-30), 4.52, 4.57 (2d, 2H, J 29 Hz, J 13 Hz, PhCH2),
0
0
0
0
5.58 (t, 1H, J 6.8 Hz, 5.3 Hz, H-20), 6.87 (d, 1H, J1 ,2 5.35 Hz, H-10),
7.15 (dist. t, 1H, J 7.6 Hz, 6.9 Hz, Ph-H), 7.23 (dist. t, 2H, J 7.6 Hz,
6.9 Hz, Ph-H), 7.39 (d, 2H, J 7.6 Hz, Ph-H), 7.70–7.78 (m, 2H,
quin-H7, quin-H8), 8.1 (d, 1H, J6,7 7.6 Hz, quin-H6), 8.32 (d, 1H,
J9,7.6 Hz, quin-H9). Anal. Calcd for C30H32N4O8: C, 62.49; H, 5.59;
N, 9.72. Found: C, 62.52; H, 4.85; N, 9.76.
0
0
5.34 (d, 1H, J1 ,2 6.8 Hz, H-10), 5.48 (br s, 1H, OH-30, exchangeable
with D2O), 5.76 (br s, 1H, OH-20, exchangeable with D2O), 7.16–
7.19 (dis. t, 1H, J 5.35, 6.9 Hz, Ph-H), 7.24–7.27 (dis. t, 2H, J 6.9,
7.6 Hz, Ph-H), 7.42 (d, 2H, J 7.6 Hz Ph-H), 7.66–7.74 (m, 2H, quin-
H7, quin-H8), 8.03 (d, 1H, J6,7 7.6 Hz, quin-H6), 8.44 (d, 1H, J9,8
8.4 Hz, quin-H9); 13C NMR (DMSO-d6, 125.7 MHz): d 40.0 (CH2Ph),
61.53 (C-50), 76.03 (C-10), 76.94 (C-30), 78.73 (C-20), 84.27 (C-40),
118.50, 125.73, 127.20, 128.29, 128.99, 129.80, 130.11, 136.38,
137.43, 145.30, 149.26, 154.02 are aromatic carbons. Anal. Calcd
for C21H20N4O4, C, 64.28; H, 5.14; N, 14.28. Found: C, 64.08; H,
5.24; N, 14.24.
0
0
3.6. (1S)-1-C-(4-Benzyl-1,2,4-triazolo[4,3-a]quinoxalin-1-yl)-
2,3:4,5-di-O-isopropylidene-1-O-methanesulfonyl-D-arabinitol
(10)
To a stirred mixture of 4 (0.5 g, 1.02 mmol) and dry pyridine
(5 mL), methanesulfonyl chloride (0.10 mL, 1.25 mmol) was added
at 0 °C and the reaction mixture was stirred for 3 h, then poured
into cold water (30 mL). The product was extracted with CHCl3
(3 ꢂ 20 mL), and the organic layers were combined, dried over an-
hyd Na2SO4, and filtered. The solvent was removed under vacuum
to give a colorless solid (0.45 g, 77%); mp 100–101 °C; 1H NMR
(CDCl3, 500 MHz): d 1.09, 1.26, 1.42, 1.63 (4 s, 12H, 1:1:1:1,
3.9. 1-(a D-lyxofuranosyl)-4-
-20,50-Di-O-methanesulfonyl-
benzyl[1,2,4]triazolo[4,3-a]quinoxaline (13)
0
0
0
0
2 ꢂ Me2C), 3.13 (s, 3H, CH3SO2), 4.05 (t, 1H, J5 a,5 b 8.4 Hz, J5 a,4
8.4 Hz, H-50 ), 4.12 (dd, 1H, J5 b,5 a 9.2 Hz, J5 b,4 6.9 Hz, H-50b), 4.33–
A mixture of (1S)-1-C-(4-benzyl-1,2,4-triazolo[4,3-a]quinoxa-
lin-1-yl)-3,4-O-isopropylidene-1,2,5-tri-O-methanesulfonyl-D-lyxitol
0
0
0
0
a
4.36 (m, 1H, H-40), 4.63, 4.72 (2 d, 2 H, J 13.3 Hz, 46 Hz, PhCH2),
5.03 (t, 1H, J 3.8 Hz, 4.6 Hz, H-30), 5.66 (dd, 1H, J2 ,1 7.6 Hz, J2 ,3
(12, 0.50 g, 0.73 mmol), 1,2-dimethoxyethane (DME, 10 mL), and
HCl (4%, 0.8 mL, 0.8 mmol) was stirred under gentle reflux and
was monitored by TLC (5:1 toluene–EtOH). After 12 h the excess
DME was evaporated under vacuum, and the oily residue was trea-
ted with Et2O (5 mL) and anhyd EtOH (5 mL). The precipitate was
collected by filtration, washed with Et2O (2 mL), and recrystallized
from MeOH to afford a white solid (300 mg, 75%); mp 222–223 °C.
0
0
0
0
3.05 Hz, H-20), 5.70 (d, 1H, J1 ,2 7.6 Hz, H-10), 7.19 (dist. t, J 8.4 Hz,
7.6 Hz, 1H, Ph-H), 7.25–7.30 (dd, 2H, J 6.8 Hz, 15.3 Hz, Ph-H),
7.61 (d, 2H, J 7.6, Ph-H), 7.63–7.71 (m, 2H, quin-H7, quin-H8),
8.14–8.15 (m, 1H, quin-H6), 8.32 (m, 1H, quin-H9); 13C NMR (CDCl3,
125 MHz): d 25.10, 26.34, 26.67, 26,75, (2 ꢂ CMe2) 38.95, (CH3SO2),
40.79, (PhCH2), 65.68, 70.35, 75.14, 75.30, 78.79, 109.36, 111.90,
112.08, 116.78, 127.04, 128.01, 128.66, 128.80, 129.82, 145.15,
147.18, 148.71, 154.03. Anal. Calcd for C28H32N4O7S: C, 59.14; H,
5.67; N, 9.85. Found: C, 59.74; H, 5.02; N, 9.87.
0
0
1H NMR (DMSO-d6, 500 MHz):
d
3.14, 3.310 (2 S, 6H, 1:1,
2 ꢂ MeSO2), 4.44–4.47 (m, 3H, H-40, H-5a0 , H-5b), 4.49–4.59 (m,
2H, CH2Ph), 4.72 (m, 1H, H-30), 5.89 (d, 1H, J1 ,2 7.6 Hz, H-10),
0
0
6.12 (ꢃt, 1H, H-20), 6.3 (d, 1H, J3 -OH,3 7.6 Hz, OH-30, exchangeable
0
3.7. (1S)-1-C-(4-Benzyl-1,2,4-triazolo[4,3-a]quinoxalin-1-yl)-
3,4- O- isopropylidene-1,2,5-tri-O-methanesulfonyl-D-lyxitol
with D2O), 7.18 (t, 1H, J 6.9 Hz, Ph-H), 7.26 (dist. t, 2H, J 6.9 Hz,
7.6, Ph-H), 7.41 (d, 2H, J 8.4 Hz, Ph-H), 7.67–7.75 (m, 2H, quin-
H7, quin-H8), 8.04 (d, 1H, J6,77.6 Hz, quin-H6), 8.36 (d, 1H, J9,8
7.6 Hz, quin-H9). 13C NMR (DMSO-d6, 125.7 MHz): d 37.33, 38.77
(2 ꢂ CH3SO2), 40.11 (CH2Ph), 70.24 (C-30), 70.50 (C-50), 72.91 (C-
10), 79.10 (C-40), 80.80 (C-20), 118.060, 125.57, 127.22, 128.51,
129.01, 129.80, 130.10, 136.36, 137.31, 145.50, 147.69, 153.94
are aromatic carbons. EIMS: Calcd for C23H24N4O8S2, 548.1; Found
m/z 547.47. Anal. Calcd for C23H24N4O8S2: C, 50.36; H, 4.41; N,
10.21. Found: C, 50.26; H, 4.73; N, 10.09.
(12)
To a stirred mixture of 6 (0.5 g, 1.1 mmol) and dry pyridine
(5 mL), methanesulfonyl chloride (0.35 mL, 4.4 mmol) was added
at 0 °C, and the reaction mixture was stirred for 3 h. The reaction
mixture was poured into cold water (30 mL), and the product
was extracted with CHCl3 (3 ꢂ 20 mL). The organic layers were
combined, dried over anhyd Na2SO4, and filtered. The solvent
was removed in vacuum to give a colorless solid (0.6 g, 80%); mp
96–97 °C; 1H NMR (CDCl3, 500 MHz): d 1.2–1.23 (m, 6H, Me2C),
2.9–3.20 (m, 11H, H-50 , H-50 , 3 ꢂ CH3SO2), 4.22–4.31 (m, 2H, H-
3.10. 1-(b-D-Arabinofuranosyl)-4-benzyl-1,2,4-triazolo[4,3-
a]quinoxaline (14)
a
b
30, H-40), 4.43 (d, 1H, J0 11.45 Hz, H-20), 4.62, 4.68 (2d, 2H, J
13.1 Hz, J 32.1 Hz, PhCH2), 5.27 (br s,1H, H-10), 6.8 (br s, 1H, Ph-
H), 7.15–7.26 (m, 4H, Ph-H), 7.52 (d, 2H, quin-H7, quin-H8), 7.66
To a stirred mixture of (1R)-1-C-(4-benzyl-1,2,4-triazolo[4,
3-a]quinoxalin-1-yl)-2,3:4,5-di-O-isopropylidene-D-arabinitol (9,

2484
A. Amer et al. / Carbohydrate Research 345 (2010) 2474–2484
0.5 g, 1.02 mmol) and dry pyridine (5 mL), methanesulfonyl chlo-
ride (0.10 mL, 1.25 mmol) was added at 0 °C, and the reaction mix-
ture was stirred for 3 h, then poured into cold water (30 mL). The
crude product was filtered and then washed with a solution of
citric acid (5%). The mesylated crude product was refluxed gently
in DME (10 mL) and HCL (4%, 0.5 mL, 0.5 mmol) for 12 h while
monitoring by TLC (5:1 toluene–EtOH). The excess DME was evap-
orated under vacuum, and the oily residue was treated with Et2O
(5 mL) and anhyd EtOH (5 mL). The precipitate was collected by fil-
tration, washed with Et2O (2 mL), and recrystallized from EtOH to
afford a white solid (90 mg, 23%); mp 227–228 °C. 1H NMR (DMSO-
d6, 500 MHz): d 3.92–3.94 (m, 4H, PhCH2, H-50 , H-50 ), 4.10–4.13
that showed no bacterial growth. The only test compound that
showed efficacy against C. albicans was compound 13 in compari-
son to clotrimazole.
Supplementary data
Crystallographic data, excluding structure factors, have been
deposited with the Cambridge Crystallographic Data Centre. The
CCDC numbers are 781073 and 781074 for compounds 5 and 8,
respectively. Copies of the data can be obtained free of charge on
application with the Director, CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK (fax: +44-1223-336-033; e-mail: deposit@ccdc.cam.
ac.uk or via www.ccdc.cam.ac.uk/products/csd/request/).
a
b
(m, 3H, H-40, OH-20, OH-50), 4.54 (m, 1H, H-20) 5.14 (t, 1H, J
6.8 Hz, H-30), 5.40 (d, JOH3 ,3 6.8 Hz, OH-30), 5.96 (d, 1H, J1 ,2
0
0
0
0
5.35 Hz, H-10), 7.54–7.58 (m, 2H, Ph-H), 7.73– 7.77 (m, 2H, Ph-H),
7.83–7.91 (m, 1H, quin-H8), 8.02–8.06 (m, 2H, quin-H7, Ph-H),
8.10–8.15 (m, 1H, quin-H6), 8.58–8.60 (dd, 1H, J 7.6 Hz, J 4.5 Hz,
quin-H9); 13C NMR (DMSO-d6, 125.7 MHz): d 40.76 (CH2Ph),
61.87, 64.81, 77.12, 79.47, 87.09, for sugar carbons.
References
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MIC measurements27 were carried out for compounds that
showed significant inhibition zones using the twofold serial dilu-
tion technique. The compounds 1, 2a, 2b, 2c, 3a, 3b, 3c, 11, and
13 were prepared in a concentration range of 500, 250, 125, 62.5,
31.25, and 15.63 lg/mL. The microdilution susceptibility test in
Muller–Hinton broth (oxoid) and Sabouraud Liquid Medium
(oxoid) were used for the determination of antibacterial and anti-
fungal activity. The same test organisms were utilized as in Sec-
tion 3.11.1. The microorganism suspensions at 106 CFU/mL
(colony forming unit/mL) were used to inoculate the prepared test
compounds in the above-mentioned serial dilution broth. The cul-
ture tubes were incubated at 37 °C for 24–48 h. At the end of the
incubation period the growth of bacteria was observed by turbidity
measurements.27 The MIC is defined as the lowest concentration
27. Cruickshank, R.; Duguid, J. P.; Marmion, B. P.; Swam, H. A. The Practice of
Medical Microbiology, 12th ed.; Churchill Livingstone: London, 1975.