Stereospecific synthesis of C-arabinofuranosides and carba-disaccharide analogues of Motif C of cell wall AG complex of Mtb

Article abstract of DOI:10.1016/j.tetlet.2012.09.015

A simple strategy for the synthesis of α- and β-C- arabinofuranosides featuring a furan ring transposition reaction has been developed. A novel double furan ring transposition reaction has proposed and executed for the synthesis of the carba-disaccharide

Full text of DOI:10.1016/j.tetlet.2012.09.015

Tetrahedron Letters 53 (2012) 6347–6350
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Tetrahedron Letters
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Stereospecific synthesis of C-arabinofuranosides and carba-disaccharide
analogues of Motif C of cell wall AG complex of Mtb
⇑
Rahul S. Patil, Ketan M. Ahire, C. V. Ramana
CSIR-National Chemical Laboratory, Dr Homi Bhabha Road, Pune 411 008, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A simple strategy for the synthesis of a- and b-C-arabinofuranosides featuring a furan ring transposition
Received 13 August 2012
Revised 4 September 2012
Accepted 5 September 2012
Available online 20 September 2012
reaction has been developed. A novel double furan ring transposition reaction has proposed and executed
for the synthesis of the carba-disaccharide analogue of Motif C of the cell wall AG complex of Mtb.
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
C-Glycosides
Carba-disaccharide
Cell wall AG complex
Ring transposition
Arabinose
Carbohydrates, either in their native form or conjugated with
the proteins (glycoconjugate, glycoprotein or proteoglycan) and
lipids (glycolipid) play a major role in various biological processes
such as inflammation, intercellular and host-pathogen recogni-
tions, to name a few.1 The processing of these complex oligosac-
charides and glycoconjugates in biological systems is managed
by two classes of enzymes namely glycosidases and glycosyl trans-
ferases.2 The mimicking of the substrates of these enzymes is an
important aspect in the development of carbohydrate based
drugs.3 In this context, the C-glycosides or the carba-disaccharides
where the O-glycosidic linkage has been replaced by a C-glycosidic
bond, have been recognized for their superior physiological stabil-
ity without substantial conformational change.4,5 This hypothesis
has grown in importance as recent progress in C-glycoside biolog-
ical screening shows enhanced activity over their O-glycoside
counterparts.6
recently documented a stereoselective synthesis of allyl- and prop-
argyl C-b-arabinofuranosides10 featuring a diastereoselective Bar-
bier reaction of aldehyde, O-mesylation and subsequent furan
ring transposition followed by hydrolysis/reduction. Founded upon
the key furan ring transposition, herein we document a general
strategy for the stereospecific synthesis of
a- or b-C-arabinofur-
anosides (1 and 2). A novel double furan ring transposition reaction
of C2-symmetric dimesylate 9 to access the known carba-disaccha-
ride analogue of Motif C 3 and its diastereomer 4 is also presented.
A schematic representation of the key ring transposition reac-
tion and a general strategy for stereospecific synthesis of C-arabino-
furanosides and for the carba-disaccharides is given in Figure 1. The
intended strategy involves the use of an oxirane between C(5)–C(6)
of the hexofuranose as a handle for the introduction of aglycon and
also to prefix the anomeric configuration. The two epimeric oxir-
anes 5 and 6 have been selected as the suitable precursors for the
The arabinofuranosyl transferases (AraTs) involved in the cell
wall synthesis of Mycobacterium tuberculosis (Mtb) have been rec-
ognized as promising target for the development of new anti-
tubercular drugs.7 Inspired by the fact that all the AraTs isolated
synthesis of a- and b-configured C-arabinofuranosides 1 and 2
respectively, and for the synthesis of the Motif C carba-disaccharide
analogue 3 and the related disaccharide 4. The dec-9-enyl unit has
been selected as an aglycon by taking into account the fact that the
long chain O-arabinofuranosides have been established as good
substrates for the AraTs.11 For carba-disaccharides 3 and 4, homo-
dimerization of suitable 6-deoxy-hex-6-enofuranoside has been
planned for the synthesis of corresponding dimesylates.
so far use a common substrate b-D-arabinofuranosyl-1-monophos-
phoryldecaprenol (Fig. 1, b-DPA), there have been several reports
on the synthesis of diverse C-arabinofuranoside derivatives as b-
DPA mimics.8 Furthermore, the carba-disaccharide analogues of
Motif C of the Mtb cell wall AG complex have also revealed them-
selves to be promising substrates for AraTs.9 In this regard, we have
The synthesis of
a-C-arabinofuranoside 1 was started through
the preparation of the oxirane 512 from the known diol 10 (Scheme
1). Selective benzoylation of C(6)–OH in diol 10 and mesylation of
C(5)–OH in resulting benzoate 11 gave the compound 12 which
upon treatment with lithium hydroxide in THF:MeOH provided
⇑
Corresponding author. Tel.: +91 20 2590 2577; fax: +91 20 2590 2629.
E-mail address: vr.chepuri@ncl.res.in (C.V. Ramana).
0040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2012.09.015

6348
R. S. Patil et al. / Tetrahedron Letters 53 (2012) 6347–6350
HO
OH
HO
OH
P
O
OH
O
O
O
O
O
OH
HO
O
HO
8
O
O
β-D-arabinofuranosyl-1-mono-phosphodecaprenol (β-DPA)
Motif C
R
OH
6
HO
H+
OMs
1
H+
OH
O
O
5
OMe
1
O
5
O
R
O
1
5
furan ring
transposition
(FRT)
NaBH4
R
6
6
HO
OMe
OMe
HO
1
7 (R = dec-9-enyl)
8 (R = dec-9-enyl)
HO
2 x [H+]
MeO
OH
OMs
O
O
OH
O
O
O
O
O
O
O
NaBH4
HO
OMe
OH
OMs
HO
3
9
HO
OH
HO
HO
O
O
O
OH
O
O
O
O
O
OH
O
7
HO
OMe
HO
HO
OH
OH
1
5
3
HO
HO
OH
OH
O
O
O
OH
O
OH
7
OMe
HO
2
6
4
Figure 1. Structure of b-DPA and Motif C analogues, the key ring transposition reaction and proposed C-arabinofuranosides 1 and 2, and the Motif C carba-disaccharide
analogues 3 and 4.
O
OMs
OH
MsCl, Et3N
LiOH:H2O
O
O
O
O
O
O
O
O
BzO
O
RO
CH2Cl2, 0°C, 1h
94%
THF:MeOH
65%
OMe
MgBr
OMe
OMe
10
5
12
(R = H)
BzCl, Et3N
DCM, 0°C, 3h
74 %
11
(R = Bz)
8
71%
CuCN, Et2O
-10 °C to rt, 7h
OMe
HO
OH
O
OH
OR
a. TFA/H2O, 4h
HO
p-TSA, MeOH
Δ, 48 h
O
O
O
MeO
O
9
b. NaBH4, i-PrOH
9
9
OMe
HO
2h, rt
88%
1
7
13
(R = H)
77%
MsCl, Et3N
CH2Cl2, 0°C, 2h
8 (R = Ms)
96%
MgBr
8
OMe
HO
OH
O
OR
a. TFA/H2O, 5h
p-TSA, MeOH
Δ, 48h
O
O
O
O
O
O
9
MeO
O
b. NaBH4, i-PrOH
CuCN, Et2O
9
OMe
2h, rt
OMe
OH
-10 °C to rt, 6h
78%
6
16
83%
72%
14
(R = H)
MsCl, Et3N
CH2Cl2, 0°C, 1h
95%
15 (R = Ms)
O
HO
9
HO
2
Scheme 1. Stereospecific synthesis of 10-undecenyl C-arabinofuranosides 1 and 2.

R. S. Patil et al. / Tetrahedron Letters 53 (2012) 6347–6350
6349
the oxirane 5. The oxirane 5 was treated with the 10-decenylmag-
nesium bromide in the presence of CuCN to afford the alcohol 13 in
71% yield. Subsequently, the mesylation of 5–OH group in com-
pound 13 followed by acid mediated ring transposition10,13 of the
resulting mesylate 8 in methanol provided the dimethoxyacetal
7. The acetal 7 on acid hydrolysis and reduction with NaBH4 gave
derived from the one carbon extension of the oxirane 5 by treat-
ment with dimethyl sulphoxonium ylide.
The synthesis of carba-disaccharide 3 commenced with Mios-
kowski one carbon homologation17 of oxirane 5 (Scheme 2). Treat-
ment of 5 with in situ generated trimethylsulfoxonium ylide
(TMSOI) gave the allyl alcohol 17 in good yield. The homo dimer-
ization of 17 with Grubb 2nd generation catalyst (GII) was facile.
The optimized reaction condition involves the refluxing of a solu-
tion of allyl alcohol 17 in the presence of 3 mol % of GII in dichlo-
romethane for 16 h gave the dimer 18 in quantitative yield. The
resulting dimer 18 was subjected to the olefin hydrogenolysis over
Pd/C in methanol at 60 psi pressure to secure the diol 19. The dim-
esylation of diol 19 was carried out by following the Corey proce-
dure18 (mesyl chloride and triethylamine at –30 °C) to prepare the
dimesylate 9 in 87% yield. The key double ring transposition of 9
proceeded smoothly under the established conditions (refluxing
in methanol using catalytic p-TSA for 72 h) to afford the C2-sym-
metric diacetal 20 in 83% yield. Following the sequence of the ace-
tal hydrolysis with 70% aq TFA and the reduction of the
intermediate dialdehyde with sodium borohydride in isopropanol
gave the known carba-disaccharide 319 in seven steps with 37%
overall yield. The spectral and analytical data of 3 are in agreement
with the data reported by Wightman group.9c Next, starting with
the oxirane 6 and following a similar sequence of reactions em-
ployed in 3, the carba-disaccharide 420 has been prepared in an
overall yield of 41% across 7 steps.
the a
-C-arabinofuranoside 114 in 21% overall yield from 10.
Along similar lines, the synthesis of b-C-arabinofuranoside was
executed from the known oxirane 6.15 The opening of the oxirane 6
with 9-decenylmagnesium bromide was carried out in the presence
of CuCN to afford the alcohol 14. Mesylation of the alcohol 14 and the
acid mediated ring transposition of the resulting mesylate 15 in
methanol provided the dimethoxy acetal 16. Finally, the required
b-C-arabinofuranoside 216 was prepared from dimethyl acetal 16 fol-
lowing the established sequence of acetal hydrolysis and the reduc-
tion of the intermediate aldehyde in 44% overall yield from 6.
We next focused our attention towards the synthesis of the car-
ba-disaccharide Motif C analogue 3. Donodoni et al. have first doc-
umented the synthesis of parent 3 and the higher oligomers of
Motif C by the iterative Wittig reaction.9b Wightman group used
nucleophilic addition of an alkynyl anion on a sugar lactone for
the synthesis of 3.9c The Lowary group reported the synthesis of
the corresponding C(1)-O-alkyl derivatives of 3 as potential sub-
strates for the AraTs by self-dimerization of a suitable arabinose
derivative via olefin metathesis.9d Our projected strategy also in-
volves the self-dimerization of L-gulo derivative 17 which can be
OH
MeO
OH
n-BuLi, TMSOI
GII
, CH2Cl2
H2, Pd/C
O
O
O
O
O
5
O
O
CH3OH
97%
Δ, 16h
O
O
THF, -78 °C, 7h
OMe
OH
OMe
17
18
96%
83%
OMe
O
HO
MeO
OH
OH
O
OR
MeO
a. TFA/H2O, 6h
p-TSA, MeOH
O
O
O
OH
OH
O
O
O
b. NaBH4, i-PrOH
Δ, 72 h
83%
O
O
HO
OMe
OMe
HO
OMe
OR
OH
5h, rt
67% (2 steps)
HO
3
HO
19
(R = H)
MsCl, Et3N
20
CH2Cl2, -30°C, 3h
87%
9 (R = Ms)
OH
OH
O
MeO
O
O
GII
, CH2Cl2
n-BuLi, TMSOI
H2, Pd/C
O
O
O
6
O
O
O
CH3OH
94%
Δ, 18h
THF, -78 °C, 6h
OMe
OH
OMe
21
22
98%
76%
OH
OH
OMe
OR
MeO
MeO
O
MeO
HO
O
O
O
a. TFA/H2O, 7h
OH
OH
p-TSA, MeOH
O
O
O
HO
OMe
HO
OH
O
O
O
b. NaBH4
i-PrOH
Δ, 72 h
88%
OMe
OR
HO
HO
4h, rt
25
4
73% (2 steps)
23 (R = H)
MsCl, Et3N
CH2Cl2, -30 °C, 1h
92%
24 (R = Ms)
N
N
Cl
Ru
GII
Ph
Cl
P(Cy)3
Scheme 2. A double furan ring transposition and synthesis of Motif C carba-saccharide analogues 3 and 4.

6350
R. S. Patil et al. / Tetrahedron Letters 53 (2012) 6347–6350
Balasubramanian, V.; Balganesh, T.; Tyagi, S.; Grosset, J.; Riccardi, G.; Cole, S. T.
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D. R.; Sucheck, S. J. Med. Res. Rev. 2010, 30, 290–326.
To conclude, a general protocol for the stereospecific synthesis
a- and b-C-arabinofuranosides has been developed. The carba-
of
disaccharide Motif C analogues of AG complex of cell wall of Mtb
have been synthesized featuring a novel double furan ring transpo-
sition reaction. This double furan ring transposition reported here-
in is the first of its kind and involves the stereo specific
rearrangement of 4 key C–O bonds in one pot. This novel double
furan ring transposition has the potential to find applications in
the synthesis of carba-disaccharides where, in general the methods
for control over the fixing of anomeric configuration in a desired
way are not available.
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T. L. Bioorg. Med. Chem. 2004, 12, 5495–5503.
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Acknowledgment
11. Lee, R. E.; Brennan, P. J.; Besra, G. S. Glycobiology 1997, 7, 1121–1128.
12. Yuasa, H.; Izukawa, Y.; Hashimoto, H. J. Carbohydr. Chem. 1989, 8, 753–763.
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12946–12954.
We thank the Ministry of Science and Technology for funding
through the Department of Science and Technology under the
Green Chemistry Program (Grant No. SR/S5/GC-20/2007). Financial
support from CSIR (New Delhi) in the form of a research fellowship
to RSP is gratefully acknowledged.
14. Characterization data of 1-
a
-
D
-Arabinofuranosyl-undec-10-ene (1). Colorless
Supplementary data
gum. Rf = 0.2 (1:9 CH3OH/CH2Cl2);
½ ꢀ
a 2D5
+29.77 (c 0.8, CHCl3); 1H NMR
(400 MHz, CDCl3): d 1.28–1.40 (br m, 14H), 1.56–1.63 (m, 2H), 2.02–2.06 (m,
2H), 3.61 (dd, J = 5.3, 11.8 Hz, 2H), 3.69 (dd, J = 3.5, 11.8 Hz, 1H), 3.71–3.74 (br
m, 2H), 3.76 (dt, J = 3.5, 5.3 Hz, 2H), 3.93 (t, J = 5.5 Hz, 1H), 4.91 (ddt, J = 1.1, 2.2,
10.2 Hz, 1H), 4.98 (br ddt, J = 1.6, 2, 17.1 Hz, 1H), 5.80 (ddt, J = 6.7, 10.2,
17.1 Hz., 1H) ppm; 13C NMR (100 MHz, CDCl3): d 26.7, 31.0, 30.2, 30.6, 30.7
(2C), 30.8, 34.7, 34.9, 63.4, 79.1, 82.7, 84.1, 84.5, 114.7, 140.1 ppm; ESI-MS
309.22 ([M+Na]+,100%), 301.28 (22%); HRMS (MALDI-TOF) (m/z) calcd for
([C16H30O4Na]+) 309.2042, found 309.2052.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.tetlet.2012.09.015.
References and notes
1. (a) Varki, A.; Cummins, R. D.; Esko J. D.; Freeze H. P.; Stanley P.; Bertozzi C. R.;
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X.; Linhardt, R. J. Curr. Top. Med. Chem. 2005, 5, 1393–1430; (f) Koester, D. C.;
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15. Hanaya, T.; Yamamoto, H. Helv. Chim. Acta. 2002, 85, 2608–2618.
16. Characterization data of b-D-Arabinofuranosyl-undec-10-ene (2). Colorless gum;
Rf = 0.3 (1:9 CH3OH/CH2Cl2); ½a D25
ꢀ
+25.9 (c 0.6, CHCl3). 1H NMR (400 MHz,
CDCl3): d 1.31–1.44 (br s, 14H), 1.61–1.66 (m, 2H), 2.01–2.07 (m, 2H), 3.63 (dd,
J = 4.8, 11.5 Hz, 1H), 3.68 (dd, J = 3.9, 11.5 Hz, 1H), 3.73 (ddd, J = 2.5, 3.7, 4.6 Hz,
1H), 3.78 (br dd, J = 0.9, 3.0 Hz, 1H), 3.91 (dt, J = 3.1, 6.9 Hz, 1H), 3.96 (br dd,
J = 1.0, 2.4 Hz, 1H), 4.91 (ddt, J = 1.2, 2.2, 10.1 Hz 1H), 4.98 (ddt, J = 1.5, 2.2,
17.1 Hz 1H), 5.81 (ddt, J = 6.8, 10.2, 17.1 Hz, 1H) ppm; 13C NMR (100 MHz,
CDCl3): d 27.4, 29.8, 30.2, 30.3, 30.7, 30.8 (2C), 31.1, 35.0, 63.7, 78.9, 80.7, 81.2,
87.4, 114.8, 140.3 ppm; ESI-MS 287.40 ([M+H]+ 2%), 309.29 ([M+Na]+, 100%),
325.37 ([M+K]+, 2%), 301.21 (11%); HRMS (MALDI-TOF) (m/z) calcd for
([C16H30O4Na]+) 309.2042, found 309.2011.
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19. Characterization
data of 6,7-Diedeoxy-D-glycero-D-lyxo-D-manno-dodeca-
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D. J. Am. Chem. Soc. 2001, 123, 8602–8603; (b) Dondoni, A.; Marra, A. Chem. Rev.
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2,5:8,11-dianhydroalditol (3). Colorless solid (hygroscopic). Rf = 0.3 (2:8
CH3OH/CH2Cl2); ½a D25
ꢀ
+62.8 (c 1.25, MeOH); 1H NMR (400 MHz, MeOH-d4): d
1.75 (br m, 4H), 3.61 (ddd, J = 2.3, 5.6, 11.8 Hz, 2H), 3.69 (dt, J = 3.0, 11.8 Hz,
2H), 3.75–3.82 (m, 6H), 3.93 (ddd, J = 2.4, 5.6, 8.0 Hz, 2H); 13C NMR (100 MHz,
MeOH-d4): d 30.4 (2C), 63.3 (2C), 79.0 (2C), 82.5 (2C), 83.7 (2C), 84.5 (2C) ppm;
1H NMR (400 MHz, D2O): d 1.70 – 1.80 (m, 4H), 3.67 (dd, J = 5.9, 12.2 Hz, 2H),
3.74 (dd, J = 3.9, 12.2 Hz, 2H), 3.80–3.88 (m, 4H), 3.91 (t, J = 6.0 Hz, 2H), 4.0 (t,
J = 6.0 Hz, 2H); 13C NMR (100 MHz, D2O): d 28.7 (2C), 61.7 (2C), 77.2 (2C), 80.7
(2C), 82.1 (2C), 82.6 (2C) ppm; ESI-MS 317.01 (100%, [M+Na]+); HRMS (MALDI-
TOF) (m/z) calcd for ([C12H22O8Na]+) 317.1213, found 317.1205.
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7. (a) Wolucka, B. A. FEBS J. 2008, 275, 2691–2711; (b) Makarov, V.; Manina, G.;
Mikusova, K.; Mollmann, U.; Ryabova, O.; Saint-Joanis, B.; Dhar, N.; Pasca, M. R.;
Buroni, S.; Lucarelli, A. P.; Milano, A.; De Rossi, E.; Belanova, M.; Bobovska, A.;
Dianiskova, P.; Kordulakova, J.; Sala, C.; Fullam, E.; Schneider, P.; McKinney, J.
D.; Brodin, P.; Christophe, T.; Waddell, S.; Butcher, P.; Albrethsen, J.;
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20. Characterization data of 6,7-Diedeoxy-D-glycero-D-xylo-L-gulo-dodec-2,5:8,11-
dianhydroalditol (4). Colorless solid (hygroscopic); Rf = 0.2 (1:4 CH3OH/
CH2Cl2); ½a 2D5
ꢀ
+17.4 (c 0.5, MeOH); 1H NMR (400 MHz, MeOH-d4): d 1.67–
1.73 (m, 2H), 1.77–1.84 (m, 2H), 3.64 (dd, J = 5.0, 11.5 Hz, 2H), 3.69 (dd, J = 3.8,
11.5 Hz, 2H), 3.75 (ddd, J = 3.0, 5.0, 6.7 Hz, 2H), 3.85 (dd, J = 1.0, 3.0 Hz, 2H),
3.96 (dd, J = 1.0, 3.0 Hz, 2H), 3. 97–4. 00 (m, 2H); 13C NMR (100 MHz, MeOH-
d4): d 26.2 (2C), 63.6 (2C), 78.9 (2C), 80.5 (2C), 82.9 (2C), 87.3 (2C) ppm; ESI-MS
317.03 (100%, [M+Na]+); HRMS (MALDI-TOF) (m/z) calcd for ([C12H22O8K]+)
333.0952, found 333.0938.