Synthesis of a tetrasaccharide glycosyl glycerol. Precursor to glycolipids of Meiothermus taiwanensis ATCC BAA-400

Article abstract of DOI:10.1021/jo070629l

(Chemical Equation Presented) Synthesis of a tetrasaccharide glycosyl glycerol, the core structure of glycoglycerolipid from Meiothermus taiwanensis ATCC BAA-400, was described. A one-pot glycosylation with three components was employed as a key step.

Full text of DOI:10.1021/jo070629l

intermediates.3 There are three approaches reported in the
literature: the first one uses glycosyl donors with orthoganol
glycosyl leaving groups;4 the second one relies on diverse
protected glycosyl leaving groups,5 e.g. different thiol aglycons;6
the third one is an optimer method developed by Wong and
co-workers, which activates (armed and disarmed) thioglycosyl
donors in a sequential manner because the activation of a
thioglycoside apparently depends on their protecting groups.3c
Our approach toward the tetrasaccharide derivative (2), described
herein, was based on a three-component one-pot strategy.
Different glycosyl leaving groups were used in order to achieve
better chemoselectivity. We chose 2,2,2-trichloroethyoxycar-
bonyl as an amine protecting group and isopropylidene to protect
glycerol hydroxyls for further lipidation.
Synthesis of a Tetrasaccharide Glycosyl Glycerol.
Precursor to Glycolipids of Meiothermus
taiwanensis ATCC BAA-400
Chien-Tai Ren,† Yu-Hsuan Tsai,† Yu-Liang Yang,†
Wei Zou,‡ and Shih-Hsiung Wu*,†
Institute of Biological Chemistry, Academia Sinica,
Taipei 115, Taiwan, and Institute for Biological Sciences,
National Research Council of Canada, 100 Sussex DriVe,
Ottawa, Ontario, Canada K1A 0R
shwu@gate.sinica.edu.tw
A retrosynthetic analysis of glycoglycerolipid (1) is depicted
in Scheme 1. The key synthetic consideration is control of
anomeric stereochemistry during the respective glycosylation
reactions with or without the participation of the protecting
group at O-2. Furthermore, it was envisaged that all hydroxyl
groups in saccharides would be protected as benzyl ethers before
installation of the fatty acids. This strategy has the advantage
that a final global deprotection step by catalytic hydrogenation
would allow access to the deprotected glycoglycerolipids. On
the basis of these considerations, three building blocks 3-5 were
designed to incorporate a descending order of reactivity toward
activation (Scheme 2). Building blocks 3 and 5 were further
bisected into building blocks 6 and 7, 8 and 9, respectively.
Thioglycoside 10 was prepared from galactose pentaacetate.7
Followed by regioselective 6-O-tritylation, O-benzylation, and
subsequent removal of 6-O-trityl group, compound 10 was
converted to compound 7 as both donor and acceptor.8
Compound 12 (R:â ) 1:1) was also synthesized from compound
10 in three steps: (i) O-benzylation, (ii) treatment with NBS in
aqueous acetone, and (iii) anomeric acetylation.9 Conversion
of compound 12 into glycosyl iodide 6 by treatment with
trimethylsilyl iodide in dichloromethane at 0 °C was im-
ReceiVed April 3, 2007
Synthesis of a tetrasaccharide glycosyl glycerol, the core
structure of glycoglycerolipid from Meiothermus taiwanensis
ATCC BAA-400, was described. A one-pot glycosylation
with three components was employed as a key step.
Glycoconjugates, including glycolipids, play an important role
in modulating biological functions in many species.1 Recently,
we isolated a glycolipid (1) from thermophilic bacteria, M.
taiwanensis ATCC BAA-400,2 and preliminary biological
studies in our laboratory suggest the glycolipid may be a
potential immunomodulator. Although we are still investigating
the biological functions of the glycolipid, we are also interested
to understand the different roles played by the sugar moiety
and lipids. Therefore, we decided to first synthesize the
tetrasaccharide core (2) with the intention to derivatize it by
adding various lipids in order to study the structure-function
relationship.
(3) (a) Raghavan, S.; Kahne, D. J. Am. Chem. Soc. 1993, 115, 1580. (b)
Ley, S. V.; Priepke, H. W. M. Angew. Chem., Int. Ed. 1994, 33, 2292. (c)
Zhang, Z.; Ollmann, I. R.; Ye, X.-S.; Wischnat, R.; Baasov, T.; Wong,
C.-H. J. Am. Chem. Soc. 1999, 121, 734.
(4) (a) Kanie, O.; Ito, Y.; Ogawa, T. J. Am. Chem. Soc. 1994, 116, 12073.
(b) Yamada, H.; Harada, T.; Miyazaki, H.; Takahashi, T. Tetrahedron Lett.
1994, 35, 3979. (c) Grice, P.; Ley, S. V.; ietruszka, J.; Priepke, H. W. M.;
Walther, E. P. E. Synlett 1995, 781.
(5) (a) Fraser-Reid, B.; Udodong, U. E.; Wu, Z.; Ottosson, H.; Merritt,
J. R.; Rao, C. S.; Roberts, C. Synlett 1992, 927. (b) Yamada, H.; Harada,
T.; Takahashi, T. J. Am. Chem. Soc. 1994, 116, 7919. (c) Chenault, H. K.;
Castro, A. Tetrahedron Lett. 1994, 35, 9145.
(6) (a) Zuurmond, H. M.; v. d. Laan, S. C.; van der Marel, G. A.; v.
Boom, J. H. Carbohydr. Res. 1991, 215, c1. (b) Choudhury, A. K.;
Mukherjee, I.; Mukhopadhyay, B.; Roy, N. J. Carbohydr. Chem. 1999, 18,
361. (c) Boons, G. J.; Guertsen, R.; Holmes, D. Tetrahedron Lett. 1995,
31, 6325.
Numerous methods are available for the synthesis of oli-
gosaccharides. One-pot synthesis is an attractive one, which
achieves multiple glycosylations without purification of the
(7) (a) Nicolaou, K. C.; Winssinger, N.; Pastor, J.; DeRoose, F. J. Am.
Chem. Soc. 1997, 119, 449. (b) Janczuk, A. J.; Zhang, W.; Andreana, P.
R.; Warrick, J.; Wang P. G. Carbohydr. Res. 2002, 337, 1247. (c) Cheng,
M. S.; Wang, Q. L.; Tian, Q.; Song, H. Y.; Liu, Y. X.; Li, Q.; Xu, X.;
Miao, H. D.; Yao, X. S.; Yang, Z. J. Org. Chem. 2003, 68, 3658.
(8) (a) Kakarla, R.; Ghosh, M.; Anderson, J. A.; Dulina, R. G.; Sofia,
M. J. Tetrahedron Lett. 1999, 40, 5. (b) Ziegler, T.; Dettmann, R.;
Ariffadhillah Zettl, U. J. Carbohydr. Chem. 1999, 18, 1079.
(9) (a) Ohlsson, J.; Magnusson, G. Carbohydr. Res. 2000, 329, 49. (b)
Marco-Contelles, J.; Gallego, P.; Rodriguez-Fernandez, M.; Khiar, N.;
Destabel, C. J. Org. Chem. 1997, 62, 7397. (c) Dondoni, A.; Mariotti, G.;
Marra, A. J. Org. Chem. 2002, 67, 4475.
* Author to whom correspondence should be addressed. Phone: 886-2-2785-
5696 ext. 7121. Fax: 886-2-26539142.
† Academia Sinica.
‡ National Research Council of Canada.
(1) (a) Varki, A.; Cunnings, R.; Esko, J.; Freeze, H.; Hart, G.; Marth, J.
Essentials of Glycobiology; Cold Spring Harbor Laboratory Press: New
York, 1999. (b) Ernst, B.; Hart, G. W.; Sinay, P. Carbohydrates in Chemistry
and Biology; Wiley-VCH: Weinheim, 2000; Vols. 3 and 4.
(2) Yang, F. L.; Lu, C. P.; Chen, C. S.; Chen, M. Y.; Hsiao, H. L.; Su,
Y.; Tsay, S. S.; Zou, W.; Wu, S. H. Eur. J. Biochem. 2004, 271, 4545.
10.1021/jo070629l CCC: $37.00 © 2007 American Chemical Society
Published on Web 06/19/2007
J. Org. Chem. 2007, 72, 5427-5430
5427

SCHEME 1. Retrosynthesis of Glycerolated Tetrasaccharide (1)
SCHEME 2. Synthesis of Building Block 3
SCHEME 3. Synthesis of Building Block 4
mediately followed by coupling with alcohol 7 under the
conditions in a previous report10 to obtain disaccharide 13 in
excellent yield with desired anomeric configuration.
16 by lithium aluminum hydride, (iv) N-protection with 2,2,2-
trichloroethoxycarbonyl carbamate to 17, and (v) removal of
6-O-TBDMS of 17 with p-toluenesulfonic acid in methanol.
Synthesis of building block 4 was achieved from phenyl
2-azido-1-selenyl-D-galactopyranoside11 in five steps (Scheme
3), which included (i) a regioselective silylation with tert-
butyldimethylsilyl chloride (TBDMSCl) to 6-O-protected 15,
(ii) O-benzylation to 16, (iii) reduction of the azido group in
Initially, we attempted coupling thioglycoside 13 with alcohol
4 without success because of the decomposition of 4 under the
reaction conditions. Consequently, thioglycoside 13 was con-
verted to glycosyl phosphite 3 by treatment of 13 with NBS
followed by reaction with diethyl chlorophosphite. It is known
that glycosyl phosphite as a glycosyl donor generally results in
excellent 1,2-trans-selectivity, even when there is no participat-
ing group at the 2-position.12
(10) Du, W.; Gervay-Hague, J. Org. Lett. 2005, 7, 2063-2065.
(11) Czernecki, S.; Randriamandimby, D. Tetrahedron Lett. 1993, 34,
7915.
5428 J. Org. Chem., Vol. 72, No. 14, 2007

SCHEME 4. Synthesis of Building Block 5
SCHEME 5. Synthesis of Glycerolated Tetrasaccharide (2)
Glycosyl donor 8 was synthesized from the starting material
via intermediate 3,4,6-tri-O-benzyl-1-thio-â-D-glucopyranose13
by 2-O-protection with the 4-methoxybenzyl group. With 8 in
hand, we investigated its coupling with 9. Under acidic coupling
conditions, we observed acid-catalyzed isopropylidene migration
which resulted in glycoside products with undesired C-2′
racemization. Therefore, the glycosylation reaction has to be
carried out under neutral conditions. It has been reported that
2,4,6-tri-tert-butylpyrimidine (TTBP) is recommended in cases
where the glycosylation reactions are acid sensitive.14 Thus, in
the presence of excess TTBP, coupling of 8 with 9 was
successfully performed using N-iodosuccinimide and a catalytic
amount of trimethylsilyl trifluoromethanesulfonate acid (TM-
SOTf) in dichloromethane to give an inseparable anomeric
mixture (1:1) of glycosides in 78% yield (Scheme 4). Fortu-
nately, after the mixture was treated with 2,3-dichloro-5,6-
dicyano-1,4-benzoquinone (DDQ) to remove the 2-O-PMB
protecting group, building block 5 was obtained in 43% after
silica gel chromatographic separation.
With all building blocks available, we carried out one-pot
glycosylation with three components as outlined in Scheme 5
to obtain a fully protected tetrasaccharide glycosyl glycerol (2).
A trisaccharide intermediate was formed from glycosyl phos-
phite (3) and selenoglycoside (4) by glycosylation activated by
trimethylsilyl trifluoromethanesulfonate acid, which could actu-
ally be isolated in 65% yield as an anomeric mixture (â:R )
6:1). Subsequent addition of acceptor 5 and N-iodosuccinimide
allowed the second glycosylation to produce 2. Purification by
silica gel column chromatography provided 2 in 46% overall
yield.
This intermediate would provide an easy entry to the native
glycoglycerolipid and its analogues to investigate their immu-
nomodulation activities.
Experimental Section
6-O-(2,3,4,6-Tetra-O-benzyl-r-D-galactopyranosyl)-2,3,4-tri-
O-benzyl-â-d-galactopyranose (14). To a solution of compound
13 (650 mg, 0.61 mmol) in 90% acetone aqueous solution (10 mL)
was added NBS (370 mg, 2.08 mmol) in small portions, and the
resulting solution was stirred for 30 min at room temperature. The
solvent was evaporated at room temperature until turbidity devel-
oped. The residue was dissolved in ethyl acetate and washed with
water and brine. The organic layer was dried over Na2SO4, filtered,
and evaporated in vacuo. The product was isolated by silica gel
column chromatography to give compound 14 (492 mg, 82.9%) as
20
a 3:1 anomeric mixture. [R]D +43.6 (c 1.22, CHCl3). Rf ) 0.33
(hexane/EtOAc, 2:1, v/v). Characteristic 1H NMR (400 MHz,
CDCl3) for R: δ 5.24 (d, 1 H, J ) 3.4 Hz, H1), 4.83 (d, 1 H, J )
5.1 Hz, H1′); for â: 4.80 (d, 1 H, J ) 3.1 Hz, H1′), 4.62 (d, 1 H,
J ) 9.6, H1). Characteristic 13C NMR (100 MHz, CDCl3) for R:
δ 98.4 (C1′), 91.6 (C1); for â: 98.2 (C1′), 97.7 (C1). HR-ESIMS
[M + H]+ calculated for C61H64O11H 973.4527, found 973.4521.
Building Block 3. To a solution of lactol 14 (508 mg, 0.522
mmol) and Et3N (0.20 mL, 1.43 mmol) at -78 °C was added diethyl
chlorophosphite (0.10 mL, 0.70 mmol). The resulting mixture was
stirred at -78 °C for 1 h, poured into saturated aqueous NaHCO3,
and extracted with CH2Cl2. The organic layer was dried over
anhydrous Na2SO4, filtered, and concentrated. The residue was
purified by flash silica gel column chromoatography (10-30%
gradient of EtOAc in hexane with 2% Et3N) to yield compound 3
(349 mg, 61.2%, 1:1 anomeric mixture) as white amophous. Rf )
1
0.30 (hexane/EtOAc, 3:1, v/v). H NMR (400 MHz, CDCl3): δ
We synthesized a tetrasaccharide glycosyl glycerol, which
represents the core structure of a glycoglycerolipid (1) of M.
taiwanensis, by one-pot glycosylation in an acceptable yield.
7.39-7.23 (35 H, Ph), 6.10 (d, anomeric position), 4.91-3.51,
1.57-1.25 (CH3).
Phenyl 3,4-Di-O-benzyl-6-O-(tert-butyl-dimethyl-silyl)-1-se-
lanyl-2-(2,2,2-trichloroethoxycarbonylamine)-â-D-galactopyra-
noside (17). To a solution of 16 (1.1 g, 1.72 mmol) in dry ether
(30 mL) at 0 °C was added LiAlH4 (132 mg, 3.48 mmol). After 1
h, water (1.0 mL) was added to quench excess reagent. The resulting
solution was filtered and concentrated. The concentrated residue
was dissolved in 1,4-dioxane (3.0 mL) and 1 N NaHCO3 (3.0 mL),
and a solution of succinimidyl 2,2,2-trichloroethyl carbonate (600
mg, 2.06 mmol) in 1,4-dioxane (2.0 mL) was added. The resulting
mixture was stirred at room temperature for 1 h. The solvent was
(12) (a) Kondo, H.; Aoki, S.; Ichikawa, Y.; Halcomb, R. L.; Ritzen, H.;
Wong, C.-H. J. Org. Chem. 1994, 59, 864. (b) Martin, T. J.; Schmidt, R.
R. Tetrahedron Lett. 1993, 34, 1765. (c) Hashimoto, S.; Umeo, K.; Sano,
A.; Watanabe, N.; Nakajima, N.; Ikegami, S. Tetrahedron. Lett. 1995, 36,
2251. (d) Sim, M. M.; Kondo, H.; Wong, C.-H. J. Am. Chem. Soc. 1993,
115, 2260.
(13) Ennis, S. C.; Cumpstey, I.; Fairbanks, A. J.; Butters, T. D.; Mackeen,
M.; Wormald, M. R. Tetrahedron 2002, 58, 9403.
(14) Crich, D.; Smith, M. J. Am. Chem. Soc. 2001, 123, 9015.
J. Org. Chem, Vol. 72, No. 14, 2007 5429

removed under reduced pressure, and the residue was diluted with
water (10 mL), and extracted with ethyl acetate (2 × 30 mL). The
combined organic layer was dried over anhydrous Na2SO4, filtered,
and concentrated. The residue was purified by silica gel column
chromatography (10-20% gradient of EtOAc in hexane) to yield
the compound 17 (1.12 g, 82.6%) as a colorless solid. [R]D20 +97.2
(c 0.87, CHCl3). mp 131-132 °C. Rf ) 0.35 (hexane/EtOAc, 10:
86.9 (C4), 80.7 (C2), 79.2 (C5), 77.6 (C3), 75.9 (CH2Ph at C4),
74.2 (CH2Ph at C2 and C3), 73.6 (CH2Phat C6), 69.2 (C6), 55.4
(OMe). HR-ESIMS [M + H]+ calculated for C41H42O6SH 663.2780,
found 663.2775.
Building Block 5. To a mixture of 8 (6.87 g, 10.36 mmol), 9
(1.48 g, 11.2 mmol), TTBP (500 mg, 2.01 mmol), and molecular
sieves (3 Å, 8.5 g) in CH2Cl2 (60 mL) was added NIS (2.52 g,
11.2 mmol) followed by TMSOTf (0.15 mL, 0.83 mmol) at 10 °C.
The reaction was stirred at room temperature for 1 h, quenched
with Et3N (0.5 mL), diluted with CH2Cl2 (100 mL), filtered through
a pad of celite, and washed with saturated aqueous Na2S2O3 and
NaHCO3. The organic layer was dried over Na2SO4, filtered, and
concentrated. The residue was chromatographed on silica gel (10-
30% gradient of EtOAc in hexane) to afford PMB-ether (1:1
anomeric mixture, 5.54 g, 78%) as a colorless syrup. To a solution
of PMB-ether (1:1 mixture, 5.54 g, 8.09 mmol) in CH2Cl2 (70
mL) and water (3.5 mL) at 0 °C was added DDQ (2.2 g, 9.7 mmol),
and the resulting solution was allowed to warm to 25 °C and stirred
for 1 h. After the reaction was completed by TLC analysis, the
reaction was quenched by addition of saturated aqueous Na2S2O3
and saturated aqueous NaHCO3. The reaction mixture was then
extracted with CH2Cl2 (3 × 100 mL), and the combined extracts
were dried over Na2SO4 and concentrated. The crude residue was
purified by flash chromatography (20-40% gradient of EtOAc in
hexanes) to provide alcohol 5 (1.94 g, 42.5%) and alcohol 5′ (1.89
1
1, v/v). H NMR (400 MHz, CDCl3): δ 7.56-7.26 (15 H, Ph),
6.07 (d, 1 H, J ) 4.7 Hz, H1), 4.97 (d, 1 H, J ) 11.4 Hz, CH2Ph
at C4), 4.78 (d, 1 H, J ) 12.0 Hz, CH2Ph at C3), 4.77 (d, 1 H, J
) 12.1 Hz, CH2CCl3), 4.70 (d, 1 H, J ) 12.1 Hz, CH2CCl3), 4.66
(d, 1 H, J ) 11.4 Hz, CH2Ph at C4), 4.56 (d, 1 H, J ) 12.0 Hz,
CH2Ph at C3), 4.55 (m, 1 H, H2), 4.14 (m, 1 H, H5), 4.12 (br, 1
H, H4), 3.78 (t, 1 H, J ) 8.9 Hz, H6), 3.65 (t, 1 H, J ) 8.9 Hz,
H6), 3.53 (dd, 1 H, J ) 2.1, 11.0 Hz, H3), 0.92 (s, 9H, Me at
t-Bu), 0.08 (s, 3 H, SiMe2), 0.07 (s, 3 H, SiMe2). 13C NMR (100
MHz, CDCl3): δ 154.0 (CdO), 138.4, 137.4, 134.2-127.6 (Ph),
95.4 (CCl3), 89.6 (C1), 78.3 (C3), 74.7 (CH2Ph at C4), 74.6 (CH2),
74.4 (C5), 72.0 (C4), 71.5 (CH2Ph at C3), 61.2 (C6), 52.1 (C2),
25.9 (Me at t-Bu), 18.24 (CMe3), -5.4 (SiMe2), -5.5 (SiMe2). HR-
ESIMS [M + H]+ calculated for C35H44Cl3NO6SeSiH 788.1247,
found 788.1243.
Phenyl 3,4-Di-O-benzyl-1-selanyl-2-(2,2,2-trichloroethoxycar-
bonylamine)-â-D-galactopyranoside (4). To a solution of com-
pound 17 (1.12 g, 1.42 mmol) in DCM and MeOH (1:1, 10 mL)
was added p-toluenesulfonic acid monohydrate (38 g, 0.2 mmol).
The resulting solution was stirred for 30 min. The solvent and
volatile material were removed under reduced pressure, and the
residue was dissolved in CH2Cl2 (30 mL) and washed with saturated
aqueous NaHCO3 and brine. The organic layer was dried over Na2-
SO4, filtered, and concentrated. The residue was purified by flash
silica gel column chromatography (10-30% gradient of EtOAc in
hexane) to provide compound 4 (756 mg, 78.9%) as a colorless
crystalline solid. [R]D20 +104.0 (c 0.99, CHCl3). mp 146-148 °C.
1H NMR (400 MHz, CDCl3): δ 7.40-7.23 (15 H, Ph), 6.10 (d, 1
H, J ) 4.8 Hz, H1), 5.09 (d, 1 H, J ) 7.6 Hz, NH), 4.97 (d, 1 H,
J ) 11.6 Hz, CH2Ph at C4), 4.81 (d, 1 H, J ) 11.4 Hz, CH2Ph at
C3), 4.78 (d, 1 H, J ) 12.0 Hz, CH2 at Troc), 4.68 (d, 1 H, J )
12.0 Hz, CH2 at Troc), 4.64 (d, 1 H, J ) 11.6 Hz, CH2Ph at C4),
4.59 (m, 1 H, H2), 4.55 (d, 1 H, J ) 11.4 Hz, CH2Ph at C3), 4.14
(t, 1 H, J ) 5.6 Hz, H3), 4.03 (br s, 1 H, H4), 3.78 (dd, 1 H, J )
6.6, 11.4 Hz, H6a), 3.58 (dd, 1 H, J ) 6.6, 11.4 Hz, H6b), 3.55
(dd, 1 H, J ) 2.0, 10.8 Hz, H3). 13C NMR (100 MHz, CDCl3): δ
154.3 (CdO), 138.0, 137.4, 134.6, 129.4-128.0 (Ph), 95.6 (CCl3),
89.1 (C1), 78.4 (C3), 74.8 (CH2 at Troc), 74.6 (CH2Ph at C4), 74.3
(C5), 72.1 (C4), 71.9 (CH2Ph at C3), 62.2 (C6), 52.2 (C2). HR-
ESIMS [M + H]+ calculated for C29H30Cl3NO6SeH 674.0382,
found 674.0372.
20
g, 41.4%) as a colorless syrup. 5: [R]D +70.1 (c 3.12, CHCl3).
mp 78-80 °C. 1H NMR (400 MHz, CDCl3): δ 7.40-7.14 (15 H,
Ph), 4.96 (d, 1 H, J ) 11.2 Hz, CH2Ph), 4.94 (1 H, H1), 4.85 (d,
1 H, J ) 11.2 Hz, CH2Ph), 4.84 (d, 1 H, J ) 10.8 Hz, CH2Ph),
4.63 (d, 1 H, J ) 12.4 Hz, CH2Ph), 4.52 (d, 1 H, J ) 12.4 Hz,
CH2Ph), 4.50 (d, 1 H, J ) 10.8 Hz, CH2Ph), 4.33 (quin, 1H, J )
6.0 Hz, H2′), 4.07, 3.76, 3.71, 3.56 (m, 4 H, H1′, H3′), 3.82 (m, 1
H, H5), 3.76 (m, 1H, H3), 3.74 (m, 1 H, H2), 3.71 (m, 2 H, H6),
3.63 (m, 1 H, H4), 1.44 (s, 3 H, CH3), 1.36 (s, 3 H, CH3). 13C
NMR (100 MHz, CDCl3): δ 138.9, 138.4, 138.1, 128.6-127.8 (Ph),
109.9 (C4′), 99.6 (C1), 83.5 (C3), 77.6 (C4), 75.5, 75.2 (CH2), 74.8
(C2′), 73.7 (CH2), 73.3 (C2), 71.0 (C5), 69.9, 66.7 (C1′ and C3′),
68.7 (C6), 27.0 (CH3), 25.5 (CH3). HR-ESIMS [M + H]+ calculated
for C33H40O8H 565.2801, found 565.2796.
Tetrasaccharide 2. To a mixture of 3 (230 mg, 0.210 mmol)
and 4 (142.2 mg, 0.211 mmol) and molecular sieves (3 Å) in CH2-
Cl2 (14 mL) at -78 °C was added TMSOTf (0.02 mL, 0.01 mmol).
After the reaction was stirred for 1 h at -78 °C, TLC analysis
indicated completion. To the reaction mixture was added a solution
of 5 (122 mg, 0.216 mmol) in CH2Cl2 (4 mL) via a cannula. The
resulting solution was stirred for 30 min at -78 °C, and NIS (56
mg, 0.249 mmol) was added. The reaction was stirred for 1 h,
quenched with Et3N (0.5 mL), diluted with CH2Cl2 (50 mL), filtered
through a pad of Celite, and washed with saturated aqueous Na2S2O3
andNaHCO3. The organic layer was dried over Na2SO4, filtered,
and concentrated. The residue was chromatographed on silica gel
(10-30% gradient EtOAc in hexane) to afford 2 (198 mg, 46.3%)
as white amorphous. [R]D20 +42.6 (c 1.16, CHCl3). 1H NMR (400
MHz, d6-acetone): δ 5.18 (d, 1 H, J ) 3.4 Hz, anomeric), 4.99 (d,
1 H, J ) 2.3 Hz, anomeric), 4.88 (d, 1 H, J ) 7.6 Hz, anomeric),
4.53 (d, 1 H, J ) 7.4 Hz, anomeric), 1.35 (s, 3 H, CH3), 1.26 (s,
3 H, CH3). 13C NMR (100 MHz, d6-acetone): δ 104.5 (anomeric),
103.7 (anomeric), 99.7 (anomeric), 99.4 (anomeric). HR-ESIMS
[M + H + 2]+ calculated for C117H126Cl3NO24H2 2036.7813, found
2036.7824.
Phenyl 3,4,6-Tri-O-benzyl-2-O-(p-methoxybenzyl)-1-thio-â-
D-galactopyranoside (8). To a solution of phenyl 3,4,6-tri-O-
benzyl-1-thio-â-d-galactopyranoside (6.0 g, 11.1 mmol) in DMF
(25 mL) were added NaH (0.88 g of a 60% suspension in oil, 22.0
mmol) and 4-methoxybenzyl chloride (3.2 mL, 22.0 mmol) at 0
°C. After 4 h, the reaction mixture was diluted with CH2Cl2 (300
mL), washed with water (3 × 100 mL) and brine (100 mL), dried
over Na2SO4, filtered, and concentrated. The residue was purified
by silica gel column chromatography to yield the compound 8 (6.16
g, 84%) as a colorless solid. [R]D20 +6.2 (c 1.29, CHCl3). mp 83-
1
84 °C. H NMR (400 MHz, CDCl3): δ 7.66 (m, 2H, Ph), 7.41-
7.25 (20 H, Ph), 6.92 (d, J ) 8.8 Hz, 2H), 4.99 (d, 1 H, J ) 10.8
Hz, CH2Ph at C4), 4.92 (d, 1 H, J ) 10.8 Hz, CH2Ph at C4), 4.89
(br d, 2 H, CH2Ph at C3 and CH2 at PMB), 4.74 (d, 1 H, J ) 11.6
Hz, H1), 4.74 (d, 1 H, J ) 7.6 Hz, CH2 at PMB), 4.67 (d, 1 H, J
) 12.0 Hz, CH2Ph at C6), 4.66 (d, 1 H, J ) 10.8 Hz, CH2Ph at
C3), 4.60 (d, 1 H, J ) 12.0 Hz, CH2Ph at C6), 3.84 (s, 3 H, OMe),
3.83 (m, 2 H, H6), 3.75 (m, 1 H, H4), 3.73 (m, 1 H, H3), 3.58 (m,
1 H, H2), 3.57 (m, 1H, H5). 13C NMR (100 MHz, CDCl3): δ 159.5,
138.6, 138.4, 138.2, 134.1, 132.0, 130.4-127.6 (Ph), 87.6 (C1),
Acknowledgment. This work was supported in part by
National Science Council, Taiwan.
Supporting Information Available: General techniques and
NMR spectra of compounds 2-8 and 13-17. This material is
available free of charge via the Internet at http://pubs.acs.org.
JO070629L
5430 J. Org. Chem., Vol. 72, No. 14, 2007