Synthetic analogues of mycobacterial arabinogalactan linkage-disaccharide part II: Synthesis and preliminary screening of lipophilic O-alkyl glycosides

Article abstract of DOI:10.1016/j.carres.2011.08.027

Lipophilic analogues of the linkage-disaccharide found in the mycobacterial cell wall were synthesized and the synthetic analogues when biologically evaluated showed promising antimycobacterial property with MIC value in the range 3.13-12.50 μg/mL against

Full text of DOI:10.1016/j.carres.2011.08.027

Carbohydrate Research 346 (2011) 2401–2405
Contents lists available at SciVerse ScienceDirect
Carbohydrate Research
journal homepage: www.elsevier.com/locate/carres
Synthetic analogues of mycobacterial arabinogalactan linkage-disaccharide
part II: synthesis and preliminary screening of lipophilic O-alkyl glycosides q
G. Mugunthan a, Dharmarajan Sriram b, Perumal Yogeeswari b, K.P. Ravindranathan Kartha a,
⇑
a Department of Medicinal Chemistry, National Institute of Pharmaceutical Education and Research, S.A.S. Nagar, Punjab 160062, India
b Medicinal Chemistry & Antimycobacterial Research Laboratory, Pharmacy Group, Birla Institute of Technology and Science, Hyderabad 500078, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 July 2011
Received in revised form 17 August 2011
Accepted 25 August 2011
Available online 1 September 2011
Lipophilic analogues of the linkage-disaccharide found in the mycobacterial cell wall were synthesized
and the synthetic analogues when biologically evaluated showed promising antimycobacterial property
with MIC value in the range 3.13–12.50
l
g/mL against Mycobacterium tuberculosis H37Rv.
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
TB
Mycobacterium tuberculosis
Cell wall
Linkage-disaccharide
Antimycobacterial agents
1. Introduction
through a b-(1?4) linkage and the GlcNAc residue is linked to
the OH-6 of the muramyl moiety of the peptidoglycan through
In spite of the recent WHO fact sheet on the trend in the incidence
of TB worldwide that suggests that we are on target globally in
achieving the 2015 millennium development goal of decreasing
the incidence rate of TB, it remains to be one of the leading causes
of mortality, wiping off almost 4700 lives per day in 2009 alone.2
The major hurdle in tackling the TB is latency and drug resistance.
Alarmingly, extensively drug resistant strains (XDR-TB) have been
reported from 58 countries,2 which are resistant to the available
second line drugs as well, and thus the demand for better drugs with
novel modes of action is therefore clearly evident. The complex cell
wall architecture holds the key to a successful chemotherapy for the
mycobacterial infection, and is evident from the mode of action of
the drugs like ethambutol,3 isoniazid,4 and pyrazinamide5 currently
in use. An array of enzymatic processes involved in the biosynthesis
of the cell wall components of Mycobacterium tuberculosis (M.tb) can
be potential targets for selective chemotherapy.
a phosphate bridge (Fig. 1). The enzymes involved in the
biosynthesis of this linkage-disaccharide can possibly be targeted
selectively, since rhamnose is not found in humans.
With this perspective, McNeil and co-workers developed a
microtiter plate-based screen for the inhibitors of the enzymes
involved in the biosynthesis of L-rhamnose from a-D-glucose-1-
phosphate and identified some rhodanine-based molecules as
inhibitors.8 Similarly, Davis and co-workers synthesized a set of
a- and b-homonojirimycin analogues of L-rhamnose and tested
them for rhamnosyltransferase inhibition directly on the isolated
mycobacterial membrane and led to the identification of some
active compounds.9 Likewise, Reynolds and co-workers10 reported
some octyl b-
galactosyl transferase inhibitors having MIC values in the range >
g/mL. Similarly, Hultin and co-workers reported some
D-Galf-(1?4)-a-L-Rhap analogues as potential
12.8 6 128
l
linkage-disaccharide analogues11,12 with modification at the C-1
(GlcNAc unit) and C-40 (Rhap unit) of the disaccharide; and three
of the reported molecules showed moderate Galf transferase
inhibitory activity. In both of the above reports the disaccharides
in the completely or partially protected form were found to be more
active than the completely deprotected compounds, possibly
because of the more lipophilic nature of the protected sugars leading
to enhanced bioavailability under in vitro condition.
In 1990, Brennan and co-workers established the nature of the
linkage6 between the mAG complex and the peptidoglycan of the
mycobacterial cell wall and consequently elucidated its
biosynthetic origin.7 The linkage unit was identified to be
a-L-Rhap-(1?3)-D-GlcNAc-(1?P), wherein the OH-4 of the
rhamnose moiety is linked to the Galf unit of the arabinogalactan
As a part of the ongoing antimycobacterial drug discovery project
we planned to synthesize and investigate the possibility of using
linkage-disaccharide analogues as potential antimycobacterial
q
See Ref. 1.
⇑
Corresponding author. Tel.: +91 (0) 172 2214682 86; fax: +91 (0) 172 2214692.
E-mail address: rkartha@niper.ac.in (K.P.R. Kartha).
0008-6215/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2011.08.027

2402
G. Mugunthan et al. / Carbohydrate Research 346 (2011) 2401–2405
alcohol in the presence of F3BꢀOEt2 in anhydrous CH3CN, followed
HO
HO
by benzylidene acetal protection of the OH-4 and OH-6 using
benzaldehyde dimethyl acetal in the presence of p-TsOH to get
the acceptor 314 with OH-3 free as shown in Scheme 1.
O
O
O
O
AcHN
P
O
O
O
O
The acceptor was subjected to glycosylation with tri-O-acetyl-
O
a-L
-rhamnopyranosyl bromide (4, readily prepared and used as
O
HO
O
OH
OH
O
such) to get the 1?3 -linked disaccharide 5 (Scheme 2). For the
a
O
O
glycosylation reaction Helferich condition using Hg(CN)2 in
anhydrous CH3CN worked well (yields 60%), but AgOTf in the pres-
ence of N,N,N0,N0-tetramethyl urea (TMU)15 was found to be supe-
rior in terms of yield (P60%).
OH
NHAc
HO
O
Galf residue of AG
MurNGly residue
of peptidoglycan
NH
In order to facilitate the radical addition of thiol to the allyl
group of disaccharides 5, the benzylidene protection in 5 was
hydrolytically removed and the 4,6-diol obtained was acetylated
to get the disaccharide derivative 6. Compound 6 (Scheme 2) was
Figure 1. Linkage-disaccharide found in the cell wall of M.tb.
subjected to radical addition16 initially with
a set of four
agents. Even though many carbohydrate derivatives act as effective
enzyme inhibitors, they perform poorly in the whole cell assay
against M.tb probably because of the waxy lipophilic cell wall
architecture that acts as a formidable barrier. Synthesis of lipophilic
sugar derivatives can be one of the possible solutions for this. Initial
attempts to synthesize lipophilic analogues containing 1-deoxy
GlcNHCOR moiety, led to highly unstable molecules.13 As an
alternate therefore we went on to synthesize some of the relatively
different thiols by using AIBN as the radical initiator to get the
corresponding lipophilic disaccharides 7a–d (Scheme 2).
Based on the previous reports of better inhibitory activity
of protected sugars as against partially or completely unprotected
ones, the synthesized lipophilic disaccharides along with
disaccharides 5 and 6 were screened in vitro against M.tb H37Rv
and the results are summarized in Table 1.
more stable analogues, lipophilic
herein and were screened against M.tb for the evaluation of their
a-O-glycosides, reported
The disaccharides were found to be active against M.tb H37Rv as
expected, the one containing the acetylated thioglycerol moiety
antimycobacterial activity.
turned out to be the best with an MIC value of 3.13
to the MIC of one of the positive controls used (Ethambutol MIC
1.56 g/mL) followed by the disaccharide with cyclopentyl moiety
with an MIC of 6.25 g/mL. The disaccharide bearing an adamantyl
group on the aglycon moiety exhibited moderate inhibition with
an MIC value of 12.5 g/mL whereas the disaccharide bearing a
dodecyl group turned out to be inactive (MIC >25 g/mL). From
lg/mL, close
2. Results and discussion
l
l
The
prepared using an appropriately protected
a suitable -rhamnosyl donor. Commercial 2-acetamido-2-deoxy-
-glucopyranose (1) was converted to allyl 2-acetamido-2-deoxy-
-glucopyranoside (2), by Fisher type glycosylation using allyl
a-O-allyl glycoside of the linkage-disaccharide was
l
D-GlcNAc acceptor and
L
l
the above results it is quite evident that an increase in lipophilicity
beyond an optimum level can lead to a decrease in the activity and
D
a-D
OH
OH
O
Ph
O
O
O
a
O
b
HO
HO
HO
HO
HO
NH
NH
NH
3
O
OH
O
2
1
O
O
O
Scheme 1. Synthesis of GlcNAc acceptor. Reagents and conditions: (a) Allyl alcohol, F3BꢀOEt2, CH3CN, reflux, 60–70%; (b) benzaldehyde dimethylacetal, p-TsOH, DMF, 70–75%.
Br
Ph
O
O
Ph
O
O
O
a
O
O
O
HO
AcO
NH
NH
AcO
O
O
4
O
OAc
AcO
3
O
O
5
AcO
OAc
b
OAc
OAc
O
S
AcO
O
R
O
O
AcO
O
c
O
NH
O
NH
AcO
O
O
AcO
AcO
7a-d
6
OAc
O
AcO
OAc
Scheme 2. Glycosylation followed by radical addition. Reagents and conditions: (a) AgOTf, TMU, MeCN, >60%; (b) (i) AcOH, catalytic TFA, H2O, (ii) Ac2O, pyridine, 90%; (c)
RSH, AIBN, 70 °C, 3–4 h, 70–80%.

G. Mugunthan et al. / Carbohydrate Research 346 (2011) 2401–2405
2403
Table 1
different mono- and disaccharides that can facilitate a more
detailed SAR study.
In vitro assay results against M.tb H37Rv
Entry Molecule
MIC
(
lg/mL)
3. Experimental
OAc
OAc
3.1. Materials and methods
OAc
O
S
S
S
S
AcO
O
1.
3.13
All reagents and chemicals were purchased from Sigma–Aldrich
and were used without further purification. TLC analyses were
performed on 0.2 mm Merck pre-coated silica gel 60 F254
aluminium sheets and the spots were visualized under UV lamp
and/or by immersion in an ethanolic solution of sulfuric acid (5%,
v/v) followed by heating. Final purifications were performed using
silica gel 200–400 mesh size. Melting points were determined on a
Büchi melting point (B-540) apparatus and are uncorrected.
NH
O
O
AcO
AcO
AcO
O
O
O
O
7a
AcO
AcO
AcO
OAc
OAc
O
AcO
O
O
2.
3.
4.
6.25
NH
O
Specific rotations were recorded on
a Rudolph Autopol IV
7b
OAc
Polarimeter at 20 °C. NMR spectra were recorded on a Bruker
Avance DPX (400 MHz) spectrometer. 1H NMR and 13C NMR
spectra were referenced to the internal standard tetramethylsilane,
in the respective deuterated solvents. Coupling constants (J) are
reported in Hertz. IR spectra were recorded on a Nicolet FT-IR
Impact 410 instrument either as thin film (neat) or as KBr pellet.
High resolution mass spectra (HRMS) were recorded on a Bruker
Maxis spectrometer.
OAc
O
AcO
O
12.5
NH
O
O
7c
OAc
OAc
O
AcO
O
O
11
3.2. Agar dilution method
>12.5
NH
O
AcO
AcO
Tenfold serial dilutions of each test compound/drug were
incorporated into Middlebrook 7H11 agar medium with OADC
7d
AcO
OAc
Growth Supplement (Drug concentration from 12.5
lg/mL to
Ph
O
O
0.78 g/mL). Inoculum of M.tb H37Rv was prepared from fresh
l
O
O
Middlebrook 7H11 agar slants with OADC Growth Supplement
was adjusted to 1 mg/mL (wet weight) in Tween 80 (0.05%) saline
diluted to 10–2 to give a concentration of approximately 107 cfu/
5.
6.25
NH
O
O
O
O
5
mL. A 5 lL amount of bacterial suspension was spotted into
AcO
OAc
7H11 agar tubes containing 10-fold serial dilutions of drugs per
mL. The tubes were incubated at 37 °C and final readings were re-
corded after 28 days. The minimum inhibitory concentration (MIC)
is defined as the minimum concentration of the compound re-
quired to give the complete inhibition of bacterial growth.
OAc
O
AcO
O
O
12.5
6.
7.
NH
AcO
3.2.1. Allyl 20,30,40-tri-O-acetyl-
acetamido-4,6-O-benzylidine-2-deoxy-
a-L
-rhamnopyranosyl-(1?3)-2-
-glucopyranoside (5)
6
O
AcO
OAc
a
-D
Ethambutol
Isoniazid
Rifampicin
1.56
0.05
0.10
The acceptor (3, 0.7 g, 2 mmol) was co-dissolved with silver
triflate (4 mmol) and N,N,N0,N0-tetramethylurea (20 mmol) in
anhydrous CH2Cl2–DMF (9:1, 10 mL) maintained under an inert
atmosphere. The reaction mixture was cooled to ꢁ40 °C and donor
4 (4 mmol) in anhydrous CH2Cl2 (10 mL) was added slowly to the
reaction mixture. The reaction mixture was then brought to room
temperature over a period of 12 h. After the completion of the
reaction, the mixture was filtered through a Celite-bed and was
then concentrated under reduced pressure. The crude reaction
mixture was chromatographed to get the pure disaccharide 5
(0.75 g, 62%).
MIC—Minimum concentration required for complete inhibition.
thus it appears that a moderate degree of lipophilicity is sufficient
for the activity and that lipophilicity is not the only factor in
imparting the activity. Another interesting thing observed was that
both of the starting disaccharides 5 and 6 were found to be
reasonably active with MIC values 6.25 and 12.5
tively. This observation was supported by the literature precedence
of trisaccharide OCT359 [allyl O-(2,3,4,6-tetra-O-acetyl-
-galactopyranosyl)-(1?6)-O-(2,3,4-tri-O-acetyl- -galactopy-
ranosyl)-(1?6)-O-2,3,4-tri-O-acetyl-b- -glucopyranoside] being
active against M.tb H37Rv with an MIC value of 3.13
g/mL.17 In
the latter, the allylic aglycon residue and the acetate protection
present in the molecule were reported to be essential for activity.
These observations suggest a definitive role for the aglycon in
imparting the desired bioactivity.
Based on these observations, therefore the work is being
extended to generating a larger library of the linkage-disaccharide
analogues with moderate lipophilicity as well as allyl glycosides of
lg/mL, respec-
a
Colourless solid; mp 165.5–166.5 °C; [a]
+0.8 (c 1, CHCl3); 1H
D
a
-
D
a-D
NMR (400 MHz, CDCl3) d 7.49 (m, 2H, Ar-H), 7.33–7.31 (m, 3H,
Ar-H), 7.93–7.83 (m, 1H, –CH2–CH@CH2), 5.68 (d, J = 10 Hz,
1H, –CONH–), 5.55 (s, 1H, Ph-CH), 5.32–5.24 (m, 3H, H-10,
–CH2–CH@CH2), 4.98 (dd, J = 1.8 Hz, J = 3.4 Hz, 1H, H-20),
4.95–4.90 (m, 2H, H-30, H-40), 4.78 (d, J = 3.6 Hz, 1H, H-1),
4.47–4.41 (m, J = 3.6 Hz, J = 10 Hz, 1H, H-2), 4.27 (dd, J = 4.6 Hz,
J = 10 Hz, 1H, H-4), 4.18, 3.97 (2 ꢂ m, 2H, –CH2–CH@CH2),
4.10–4.03 (m, J = 6.2 Hz, 1H, H-50), 3.92–3.94 (m, J = 4.6 Hz,
J = 9.3 Hz, 2H, H-6a, H-3), 3.76 (pt, J = 10.2 Hz, 1H, H-5), 3.68 (pt,
J = 9.3 Hz, 1H, H-6b), 2.09, 2.07, 1.97, 1.96 (4 ꢂ s, 12H, 3 ꢂ –COCH3,
D
l

2404
G. Mugunthan et al. / Carbohydrate Research 346 (2011) 2401–2405
–NCOCH3), 0.66 (d, J = 6.2 Hz, 3H, C-50-CH3); 13C NMR (100 MHz,
CDCl3) d 170.39, 170.12, 169.99, 169.81, 137.15, 133.18, 129.11,
128.27, 128.08, 126.40, 126.29, 118.42, 102.01, 80.24, 75.89,
71.41, 70.78, 68.89, 68.57, 68.48, 66.32, 63.24, 52.88, 23.34,
20.91, 20.73, 16.54, IR (Neat) mmax 3291, 2934, 2862, 1748, 1659,
1541, 1375, 1225, 1126, 1087, 1043, 1000, 915 cmꢁ1; HRMS: m/z
calculated for C30H39NNaO13: 644.2319. Found: 644.2327.
C-50-CH3); 13C NMR (100 MHz, CDCl3) d 170.88, 170.83, 170.75,
170.72, 170.29, 170.13, 169.55, 169.48, 99.61, 97.60, 77.24, 70.64,
70.50, 70.25, 70.12, 70.07, 69.02, 68.08, 67.43, 66.37, 63.79,
63.72, 62.15, 51.99, 32.10, 31.56, 29.22, 29.13, 29.01, 28.57,
23.17, 23.13, 21.17, 21.05, 20.97, 20.81, 20.77, 20.74, 20.66, 17.23
(R, S); IR (Neat) mmax 3444, 2936, 1744, 1652, 1372, 1226, 1125,
1045 cmꢁ1; HRMS: m/z calculated for C34H51NNaO19S: 832.2674.
Found: 832.2653.
3.2.2. Allyl 20,30,40-tri-O-acetyl-
2-acetamido-4,6-di-O-acetyl-2-deoxy-
a
-L
-rhamnopyranosyl-(1?3)-
-glucopyranoside (6)
a-
D
3.2.3.2. 3-(1-Thiocyclopentyl)propyl
rhamnopyranosyl-(1?3)-2-acetamido-4,6-di-O-acetyl-2-deoxy-
-glucopyranoside (7b). Yield 60%; colourless glassy solid;
+41.3 (c 1, CHCl3); 1H NMR (400 MHz, CDCl3) d 5.89 (d,
20,30,40-tri-O-acetyl-
a-L-
To a solution of the disaccharide (5, 0.5 g) in AcOH-H2O (9:1,
10 mL) a few drops of TFA were added and was stirred at room
temperature overnight. After the the completion of the reaction
it was concentrated under reduced pressure and was
co-evaporated with anhydrous toluene. The crude product was
then acetylated in the same pot using Ac2O (2 mL) in pyridine
(5 mL). After the completion of the reaction, the mixture was
concentrated under reduced pressure and was co-evaporated with
anhydrous toluene to dryness. The crude product was taken up in
CH2Cl2 and was extracted with ice-cold 5% aqueous HCl solution
followed by extraction with ice-cold sodium bicarbonate solution.
The organic layer was then dried over anhydrous sodium
sulfate and was concentrated under reduced pressure followed
by chromatographic purification to get pure 6 (0.44 g).
a-D
[a]
D
J = 10 Hz, 1H, –CONH–), 5.13–5.06 (m, 3H, H-20, H-30, H-4) 5.00
(pt, J = 10 Hz, 1H, H-40), 4.80 (d, J = 1.7 Hz, 1H, H-10), 4.79 (d,
J = 3.6 Hz, 1H, H-1), 4.47–4.41 (m, J = 3.6 Hz, J = 10 Hz, 1H, H-2),
4.16 (dd, J = 4.8 Hz, J = 12.3 Hz, 1H, H-6a), 4.06 (dd, J = 2.3 Hz,
J = 12.3 Hz, 1H, H-6b), 3.91–3.76 (m, 4H, H-50, H-3, H-5, H-1a
(propyl)), 3.52–3.47 (m, 1H, H-1b(propyl), 3.08 (m, 1H,
–S–CH-(cyclopentyl)), 2.66–2.63 (m, 2H, –CH2–S-(propyl)), 2.14,
2 ꢂ 2.10, 2.07, 2.02, 1.95 (6 ꢂ s, 18H, 5 ꢂ –COCH3, –NCOCH3),
2.10–1.98 (m, 4H, –CH2–), 1.60–1.48 (m, 6H, –CH2–), 1.13 (d,
J = 6.2 Hz, 3H, C-50-CH3) 13C NMR (100 MHz, CDCl3) d 170.85,
170.56, 170.50, 170.14, 169.53, 169.51, 99.69, 97.64, 80.49, 70.61,
70.10, 69.93, 68.93, 68.12, 67.43, 66.99, 62.04, 51.81, 44.10,
33.80, 33.77, 29.02, 28.87, 24.78, 23.32, 21.17, 21.02, 20.82,
20.69, 17.21; IR (Neat) mmax 3398, 2952, 1747, 1652, 1371, 1224,
Yield 75%; colourless glassy solid; [a]
+43.0 (c 1, CHCl3); 1H
D
NMR (400 MHz, CDCl3) d 5.92–5.83 (m, 1H, –CH2–CH@CH2), 5.69
(d, J = 10 Hz, 1H, –CONH–), 5.32–5.24 (m, 2H, –CH2–CH@CH2),
5.13–5.07 (m, 3H, H-20, H-30 and H-4), 5.01 (pt, J = 10 Hz, 1H,
H-40), 4.85 (d, J = 3.6 Hz, 1H, H-1), 4.80 (d, J = 1.7 Hz, 1H, H-10),
4.47–4.41 (dt, J = 3.6 Hz, J = 10 Hz, J = 10.5 Hz, 1H, H-2), 4.19–4.13
(m, 2H, H-6a, –CH2–CH@CH2), 4.07–3.97 (m, 2H, H-6b,
–CH2–CH@CH2), 3.93–3.78 (m, 3H, H-50, H-5, H-3), 2.14, 2 ꢂ 2.10,
2.07, 2.02, 1.95 (6 ꢂ s, 18H, 5 ꢂ –COCH3, –NCOCH3), 1.13 (d,
J = 6.2 Hz, 3H, C-50-CH3); 13C NMR (100 MHz, CDCl3) d 170.83,
170.57, 170.13, 169.53, 133.06, 118.64, 99.71, 96.75, 80.44, 70.56,
70.09, 69.95, 68.92, 68.68, 68.13, 67.46, 62.03, 51.76, 23.31,
21.31, 21.17, 21.02, 20.82, 20.79, 20.68, 17.20; HRMS: m/z
calculated for C27H39NNaO15: 640.2212. Found: 640.2217.
1125, 1046 cmꢁ1
; HRMS: m/z calculated for C32H49NNaO15S:
742.2721. Found: 742.2709.
3.2.3.3. 3-(1-Thioadamantyl)propyl
20,30,40-tri-O-acetyl-
a-L-
rhamnopyranosyl-(1?3)-2-acetamido-4,6-di-O-acetyl-2-deoxy-
-glucopyranoside (7c). Yield 68%; colourless glassy solid;
+40.5 (c 1, CHCl3); 1H NMR (400 MHz, CDCl3) d 5.90 (d,
a-D
[a]
D
J = 10 Hz, 1H, –CONH–), 5.13–5.06 (m, 3H, H-20, H-30, H-4) 5.00
(pt, J = 10 Hz, 1H, H-40), 4.80 (d, J = 1.7 Hz, 1H, H-10), 4.78 (d,
J = 3.6 Hz, 1H, H-1), 4.46–4.40 (m, J = 3.6 Hz, J = 10 Hz, 1H, H-2),
4.16 (dd, J = 4.4 Hz, J = 12.3 Hz, 1H, H-6a), 4.06 (dd, J = 2.3 Hz,
J = 12.3 Hz, 1H, H-6b), 3.91–3.76 (m, 4H, H-50, H-3, H-5, H-1a
(propyl)), 3.51–3.46 (m, 1H, H-1b(propyl)), 2.63–2.59 (m, 2H,
–CH2–S-(propyl)), 2.14, 2 ꢂ 2.11, 2.07, 2.02, 1.95 (6 ꢂ s, 18H,
5 ꢂ –COCH3, –NCOCH3), 1.86 (br s, 7H, –CH2–), 1.73–1.65 (m,
10H, –CH2–, and –CH–), 1.13 (d, J = 6.2 Hz, 3H, C-50-CH3) 13C
NMR (100 MHz, CDCl3) d 170.86, 170.56, 170.46, 170.15, 169.51,
169.49, 99.72, 97.61, 80.53, 70.64, 70.11, 69.94, 68.94, 68.11,
67.42, 67.01, 62.04, 51.83, 44.35, 43.53, 36.28, 29.63, 29.51,
23.37, 22.43, 21.16, 21.00, 20.83, 20.68, 17.22; IR (Neat) mmax
3.2.3. General prodecure for the radical addition of thiols to the
allyl disaccharide 6
To a solution of disaccharide 6 (1 mmol) in anhydrous dioxane
(10 mL) maintained under an inert atmosphere was added the
desired thiol (5 mol equiv) followed by addition of catalytic
2,20-azobis(2-methylpropionitrile). The reaction mixture was
stirred at 70 °C for 3–4 h. After the completion of the reaction, a
few drops of cyclohexene were added and were concentrated
under reduced pressure. The crude product was subjected to
chromatographic purification to get the pure disaccharide (7a–c).
In the case of 7d the reaction mixture was acetylated with Ac2O
in pyridine before purification.
3436, 2910, 2851, 1747, 1653, 1371, 1225, 1135, 1044 cmꢁ1
;
HRMS: m/z calculated for
C37H55NNaO15S: 808.3190. Found:
808.3175.
3.2.3.4.
rhamnopyranosyl-(1?3)-2-acetamido-4,6-di-O-acetyl-2-deoxy-
-glucopyranoside (7d). Yield 63%; colourless glassy solid;
+35.5 (c 1, CHCl3); 1H NMR (400 MHz, CDCl3) d 5.84 (d,
3-(1-Thiododecyl)propyl
20,30,40-tri-O-acetyl-
a-L-
3.2.3.1. 3-(1-Thio-2,3-di-O-acetyl glyceryl)propyl 20,30,40-tri-O-
acetyl-
2-deoxy-
Yield 68%; syrup; [
a
-
L
-rhamnopyranosyl-(1?3)-2-acetamido-4,6-di-O-acetyl-
a-D
a
-D
-glucopyranoside (7a).
[a]
D
a]
+34.6 (c 1, CHCl3); 1H NMR (400 MHz,
J = 10 Hz, 1H, –CONH–), 5.13–5.06 (m, 3H, H-20, H-30, H-4) 5.01
(pt, J = 10 Hz, 1H, H-40), 4.80 (d, J = 1.7 Hz, 1H, H-10), 4.79 (d,
J = 3.6 Hz, 1H, H-1), 4.45–4.39 (m, J = 3.6 Hz, J = 10 Hz, 1H, H-2),
4.16 (dd, J = 4.5 Hz, J = 12.3 Hz, 1H, H-6a), 4.07 (dd, J = 2.3 Hz,
J = 12.3 Hz, 1H, H-6b), 3.93–3.75 (m, 4H, H-50, H-3, H-5, H-1a
(propyl)), 3.53–3.47 (m, 1H, H-1b(propyl)), 2.64–2.48 (2 ꢂ m,
4H, –CH2–S–CH2–), 2.14, 2.10, 2.09, 2.07, 2.02, 1.95, (6 ꢂ s, 18H,
5 ꢂ –COCH3, –NCOCH3), 1.69 (m, 3H, –CH2–), 1.58, 1.37 (2 ꢂ m, 5H,
–CH2–), 1.25 (br s, 19H, –CH2–), 1.13 (d, J = 6.2 Hz, 3H, C-50-CH3);
0.88 (t, J = 7 Hz, 3H –CH3); 13C NMR (100 MHz, CDCl3) d 170.82,
CDCl3) d 6.24, 6.20 (2 ꢂDd, J = 10 Hz, 1H, –CONH–R, S), 5.16–5.06
(m, 4H, H-20, H-30, H-4 and H-2 of thioglycerol R, S), 5.03–4.97
(m, 1H, H-40R, S), 4.85–4.80 (m, 2H, H-1 and H-10R, S), 4.44–4.39
(m, 2H, H-2 and H-3a of thioglycerol R, S), 4.23–4.14 (m, 2H,
H-6a and H-3b of thioglycerol R, S), 4.08–4.04 (m, 1H, H-6b R, S),
3.91–3.75 (m, 4H, H-50, H-3, H-5, H-1a(propyl)R, S), 3.48–3.45
(m, 1H, H-1b(propyl) R, S), 2.64–2.48 (2 ꢂ m, 4H, –CH2–S–CH2–R,
S), 2.13, 2 ꢂ 2.10, 2.09, 2 ꢂ 2.08, 2.02, 1.94 (8 ꢂ s, 24H, 7 ꢂ –COCH3,
–NCOCH3), 1.86 (m, 2H, H-2 (propyl)), 1.13 (d, J = 6.2 Hz, 3H,

G. Mugunthan et al. / Carbohydrate Research 346 (2011) 2401–2405
2405
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170.53, 170.11, 169.51, 99.66, 97.65, 80.43, 70.62, 70.13, 69.97,
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29.62, 29.54, 29.33, 29.26, 29.08, 28.96, 28.92, 23.30, 22.67,
21.14, 20.99, 20.80, 20.66, 17.21, 14.11; IR (Neat) mmax 2925,
2854, 1749, 1657, 1541, 1371, 1226, 1135, 1075, 1046 cmꢁ1
;
HRMS: m/z calculated for
C39H65NNaO15S: 842.3973. Found:
842.3966.
8. Ma, Y.; Stern, R. J.; Scherman, M. S.; Vissa, V. D.; Yan, W.; Jones, V. C.; Zhang, F.;
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Acknowledgement
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M.G. sincerely acknowledges financial support in the form of a
Senior Research Fellowship by NIPER.
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Supplementary data
13. Mugunthan, G.; Ramakrishna, K.; Kartha, K. P. R. Trends Carbohydr. Res. 2010, 2,
20–27.
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Supplementary data associated with this article can be found, in
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References
1. For part I see Ref. 13.
2. World Health Organisation, 2010/2011 Tuberculosis global facts.
www.who.int/tb/publications/2010/factsheet_tb_2010.pdf.