Stereospecific deuteration in the synthesis of methyl α-(4-2H)- cellobioside

Full text of DOI:10.1021/jo982256h

J . Org. Chem. 1999, 64, 4199-4200
4199
dride [NaBH(OAc)3] is known to be a mild reducing agent
which can selectively reduce aldehydes in the presence
of ketones.8,9 In the presence of an alcohol (ROH), NaBH-
(OR)(OAc)2 is formed which can carry out reduction of
ketones.10-12
Ster eosp ecific Deu ter a tion in th e Syn th esis
of Meth yl r-(4-2H)-Cellobiosid e
Peter So¨derman and Go¨ran Widmalm*
Department of Organic Chemistry, Arrhenius Laboratory,
Stockholm University, S-106 91 Stockholm, Sweden
Treatment of the 4-ulose derivative 4 with [NaB2H-
(OAc)3], generated in situ from sodium borodeuteride and
deuterated acetic acid, led to an intermediate in which
the reducing agent is attached at O-6, from where an
intramolecular reduction with high stereoselectivity can
take place. This resulted in 5 as the sole product (isolated
in 84% yield from 3), having the gluco configuration as
determined by comparison to the nondeuterated analogue
of 5. The extent of deuteration was >98% as calculated
by integration of the remaining H-4 signal in the 1H NMR
spectrum. Activation of diol 5 with dibutyltin oxide in
methanol, followed by addition of benzoyl chloride at -10
°C, gave the regioselectively benzoylated derivative 6
which was isolated in 90% yield. A silver trifluoromethane-
sulfonate (AgOTf) mediated coupling13,14 of 2,3,4,6-tetra-
O-benzoyl-â-D-glucopyranosyl bromide15 with 6 produced
disaccharide 7 in 91% yield. Subsequent deprotection by
hydrogenolysis (H2, Pd-catalytic) followed by debenzoyl-
ation with methanolic sodium methoxide gave after gel
permeation chromatography the title compound 1 in 88%
yield (Scheme 1). The stereospecific intramolecular re-
duction using NaB2H(OAc)3 followed by a glycosylation
reaction resulted in a site-specifically deuterated methyl
R-cellobioside, which is presently being used for further
conformational studies of carbohydrate flexibility and
dynamics using NMR spectroscopy.
Received November 12, 1998
Isotopic labeling of compounds is of great help in areas
that investigate, for example, reaction mechanisms and
biosynthesis and also in structural investigations of
3
biomolecules. Unstable isotopes such as H, 11C, and 14C
are important in biochemical studies as well as in
medicine. The use of stable isotopes combined with mass
spectrometry offers great advantages in handling and
storage of compounds that are used in these studies. In
NMR investigations of large biomolecules such as pro-
teins, isotope enrichment with 13C and 15N is commonly
performed to alleviate spectral overlap by resorting to
higher dimensional NMR spectroscopy.1 The use of
fractional deuteration in these studies has recently found
2
application for even larger structures.2 If H instead of
1H is present, certain relaxation pathways can be elimi-
nated. This is of interest, in particular, when a problem
is difficult to solve, even with existing NMR methodology.
We have previously synthesized a site-specific deuterium-
substituted methyl â-D-glucan decasaccharide and a
methyl â-cellobioside analogue thereof.3 Recently, we
published a conformational study of methyl R-cellobioside
using ab initio, molecular mechanics and NMR methods.4
To continue the detailed analysis of carbohydrate con-
formation and dynamics, we have performed a stereo-
specific synthesis of a deuterated methyl R-cellobioside,
which we here report.
Exp er im en ta l Section
Gen er a l. Concentrations were performed under reduced
pressure at temperatures < 40 °C (bath). Optical rotations were
determined at the sodium D line and measured at 22 °C for
solutions in chloroform or water. [R]D values are given in units
of 10-1 deg cm2 g-1. NMR spectra were recorded at 30 °C for
solutions in CDCl3 and DMSO-d6 or at 27 °C in D2O. High-
resolution fast atom bombardment mass spectrometry (HR-
FABMS) was performed in the positive mode at a resolution of
10 000 using triethyleneglycol or 3-nitrobenzylalcohol as a
matrix.
Meth yl 2,3-Di-O-ben zyl-r-D-(4-2H)-glu cop yr a n osid e (5).
A suspension of diol 35 (1.1 g, 2.94 mmol) and dibutyltin oxide
(739 mg, 2.97 mmol) and 3 Å molecular sieves in anhydrous
toluene were refluxed for 3 h. The solvent was evaporated under
reduced pressure and the material further dried under vacuum
for 1 h. The crude stannylene derivative was dissolved in dry
chloroform (10 mL). The mixture was stirred at room temper-
ature under a nitrogen atmosphere for 10 min, whereafter 1,3-
dibromo-5,5-dimethylhydantoin (424 mg, 1.48 mmol) was added.
After 15 min TLC (toluene-acetone 3:1) showed complete
conversion of the starting material and the reaction mixture was
diluted with chloroform (10 mL) and washed with sodium
The synthesis of â-D-Glcp-(1f4)-R-D-(4-2H)-Glcp-OMe
(1) started from 2 by the removal of the 4,6-benzylidene
group with 90% trifluoroacetic acid to give 3.5 A slightly
modified oxidation of the diol 3, based on the method
described by David and Thieffry,6 was achieved by
activation with dibutyltin oxide in toluene followed by
regioselective oxidation with 1,3-dibromo-5,5-dimethyl-
hydantoin7 in chloroform, which is faster in 3 than for
the derivative having the gluco-configuration. This led
to methyl 2,3-di-O-benzyl-R-D-xylo-hexopyranosid-4-ulose
(4), which after flash chromatography was isolated in
92% yield. Reduction of the latter compound or its O-6-
protected analogue with NaBH4 leads to a 9:1 mixture
of the galacto:gluco isomers. To convert the galacto
derivative to the desired gluco isomer, inversion of the
configuration at C-4 must be achieved. However, a
strategy based on a stereoselective intramolecular reduc-
2
tion with H, followed by regioselective protection of O-6,
would give the 4-deuterated gluco derivative 6, in a
convenient and efficient way. Sodium triacetoxyborohy-
(8) Gribble, G. W.; Ferguson, D. C. J . Chem. Soc., Chem. Commun.
1975, 535.
(1) McIntosh, L. P.; Dahlquist, F. W. Q. Rev. Biophys. 1990, 23, 1.
(2) Yamazaki, T.; Lee, W.; Arrowsmith, C. H.; Muhandiram, D. R.;
Kay, L. E. J . Am. Chem. Soc. 1994, 116, 11655.
(3) Ha¨llgren, C.; Widmalm, G. J . Carbohydr. Chem. 1993, 12, 309.
(4) Hardy, B. J .; Gutierrez, A.; Lesiak, K.; Seidl, E.; Widmalm, G.
J . Phys. Chem. 1996, 100, 9187.
(5) Bernotas, R. C. Tetrahedron Lett. 1990, 31, 469.
(6) David, S.; Thieffry, A. J . Chem. Soc., Perkin Trans. 1 1979, 1568.
(7) So¨derman, P.; Widmalm, G. Carbohydr. Res. 1999, in press.
(9) Nutaitis, C. F.; Gribble, G. W. Tetrahedron Lett. 1983, 24, 4287.
(10) Saksena, A. K.; Mangiaracina, P. Tetrahedron Lett. 1983, 24,
273.
(11) Robins, M. J .; Samano, V.; J ohnson, M. D. J . Org. Chem. 1990,
55, 410.
(12) McDevitt, R. E.; Fraser-Reid, B. J . Org. Chem. 1994, 59, 3250.
(13) Kronzer, F. J .; Schuerch, C. Carbohydr. Res. 1973, 27, 379.
(14) Hanessian, S.; Banoub, J . Carbohydr. Res. 1977, 53, C13.
(15) Fletcher, H. G.; J r. Methods Carbohydr. Chem. 1963, 2, 226.
10.1021/jo982256h CCC: $18.00 © 1999 American Chemical Society
Published on Web 04/24/1999

4200 J . Org. Chem., Vol. 64, No. 11, 1999
Notes
Sch em e 1a
aReaction conditions: (a) 90% TFA aqueous, CHCl3, 25 °C, see also ref 5; (b) Bu2SnO, toluene, 3 h, reflux; 1,3-dibromo-5,5-
dimethylhydantoin, 15 min, 25 °C; (c) NaB2H(OAc)3, 1 h, 0 °C; (d) Bu2SnO, methanol, 3 h, reflux; CH2Cl2, benzoyl chloride, -10 °C; (e)
Bz4GlcBr, AgOTf, CH2Cl2, -30 °C; (f) H2-Pd/C, EtOAc, 100 psi, 15 h; NaOMe/MeOH, 30 min, 25 °C.
thiosulfate and water. The organic phase was dried and con-
centrated in vacuo. Flash column chromatography (silica gel,
toluene-EtOAc 6:1 and 2:1) gave methyl 2,3-di-O-benzyl-R-D-
xylo-hexopyranosid-4-ulose (4) (1.01 g, 92%): [R]D +75° (c 1.5,
Meth yl 2,3,4,6-Tetr a-O-ben zoyl-â-D-glu copyr an osyl-(1f4)-
2,3-di-O-ben zyl-6-O-ben zoyl-r-D-(4-2H)-glu copyr an oside (7).
Compound 6 (600 mg, 1.25 mmol) and 2,3,4,6-tetra-O-benzoyl-
â-D-glucopyranosyl bromide (1.07 g, 1.68 mmol) were mixed
together with sym-collidine and 4 Å molecular sieves (2 g) in
CH2Cl2 (30 mL) and cooled to -30 °C. AgOTf (460 mg, 1.79
mmol) was added under stirring, and the temperature was kept
at -30 °C until the reaction was complete as indicated by TLC
(toluene-EtOAc 5:1). The reaction was quenched with triethyl-
amine (1 mL), filtered through Celite, and concentrated. The
crude residue was purified by flash column chromatography
(silica gel, toluene-EtOAc 8:1) to give 7 (1.20 g, 91%): [R]D +49°
(c 1.1, CHCl3); 1H NMR (CDCl3) δ 3.30 (s), 3.48 (1H, dd, J )
3.7, 9.6 Hz), 3.84 (1H, m), 3.86 (1H, m), 4.01 (1H, d, J ) 9.6
Hz), 4.25, 4.35, 4.40, 4.51 (4H, dd), 4.54 (1H, d), 4.58, 4.72, 4.94,
5.08 (4H, d, J ≈ 12 Hz), 5.09 (1H, d, J ) 8 Hz), 5.57 (1H, dd, J
) 8, 10 Hz,), 5.63, 5.79 (2H, dd, J ≈ 10 Hz), 7.17-7.93; 13C NMR
(CDCl3) δ 55.2, 62.7, 62.8, 68.1, 69.5, 72.2, 72.3, 73.0, 73.4, 75.2,
79.4, 79.7, 97.8, 101.1, 125.3, 127.1-133.6, 138.0, 139.0, 165.0-
165.9; HR-FABMS [M + Na]+ m/z calcd for C62H55O16DNa
1080.3529, found 1080.3511.
1
CHCl3); H NMR (CDCl3) δ 3.48 (s), 3.79 (1H, dd, J ) 3.5, 10.0
Hz), 3.88 (2H), 4.13 (1H, dd, J ≈ 5 Hz), 4.45 (1H, d, J ) 10.0
Hz), 4.78 (1H, d, J ) 3.5 Hz), 4.66, 4.69, 4.86, 4.95 (4H, d, J ≈
12 Hz), 7.25-7.44; 13C NMR (CDCl3) δ 56.1, 60.6, 72.8, 73.9,
74.5, 80.0, 82.5, 98.5, 127.9-128.5, 137.6, 137.7, 203.9.
Sodium borodeuteride (330 mg, 7.88 mmol) was added to
acetic acid-d (10 mL) cooled to 0 °C. After 30 min methyl 2,3-
di-O-benzyl-R-D-xylo-hexopyranosid-4-ulose (0.98 g, 2.63 mmol)
was added under vigorous stirring and the reaction mixture was
allowed to attain room temperature. Stirring was continued for
1 h or until TLC (toluene-acetone 1:1) showed complete reaction,
and the mixture was concentrated in vacuo. Purification by flash
column chromatography (silica gel, toluene-acetone 1:1) pro-
vided 5 as the sole product (916 mg, 93%): [R]D +26° (c 1.0,
1
CHCl3); H NMR (CDCl3) δ 3.38 (s), 3.50 (1H, dd, J ) 3.6, 9.6
Hz), 3.62 (1H, dd, J ≈ 4 Hz), 3.74 (1H, dd, J ) 4.6, 12 Hz), 3.79
(1H, d, J ) 9.6 Hz), 3.81 (1H, dd, J ) 3.8, 12 Hz), 4.61 (1H, d,
J ) 3.6 Hz), 4.66, 4.77 (2H, d, J ) 12.1 Hz), 4.70, 5.03 (2H, d, J
) 11.6 Hz), 7.26-7.38; 13C NMR (CDCl3) δ 55.2, 62.3, 69.9 (t),
70.7, 73.1, 75.4, 79.8, 81.3, 98.2, 125.3, 127.9-129.0, 138.0, 138.7;
HR-FABMS [M + Na]+ m/z calcd for C21H25O6DNa 398.1690,
found 398.1676.
Meth yl â-D-Glu cop yr a n osyl-(1f4)-r-D-(4-2H)-glu cop yr a -
n osid e (1). Compound 7 (900 mg, 0.85 mmol) was dissolved in
EtOAc (10 mL), and a catalytic amount of 10% Pd/carbon was
added. Hydrogenolysis was performed under an H2 atmosphere
at a pressure of 100 psi. After 15 h the mixture was filtered
through Celite, the solvent was evaporated, and the residue was
dissolved in CH2Cl2 (20 mL). Methanolic sodium methoxide (0.1
M, 5 mL) was added, and the reaction mixture was stirred at
room temperature for 30 min. The mixture was filtered through
a column of Dowex-50(H+), the solvent was evaporated, and the
product was purified by gel filtration chromatography (Bio-Gel
P-2, pyridinium acetate buffer, pH 5.4) to yield 1 (265 mg,
Meth yl 2,3-Di-O-ben zyl-6-O-ben zoyl-r-D-(4-2H)-glu cop y-
r a n osid e (6). Compound 5 (860 mg, 2.29 mmol) and dibutyltin
oxide (628 mg, 2.52 mmol) were mixed together in MeOH (25
mL) and refluxed for 3 h. The solvent was removed under
reduced pressure. The crude stannylene derivative was dissolved
in CH2Cl2 (20 mL) and cooled to -10 °C. Benzoyl chloride (0.27
mL, 2.34 mmol) was added and stirring continued at -10 °C
until TLC (toluene-EtOAc 1:1) indicated complete reaction. The
mixture was brought up to 0 °C and quenched with water (5
mL). The phases were separated, and the organic phase was
washed with saturated aqueous NaHCO3 (2 × 10 mL) and water
(10 mL), dried (Na2SO4), filtered, and concentrated under
reduced pressure. Flash column chromatography (silica gel,
toluene-EtOAc 3:1) gave 6 (989 mg, 90%): [R]D +25° (c 1.0,
1
88%): [R]D +82° (c 0.9, H2O); H NMR (D2O) 3.29 (1H, dd, J )
7.9, 9.2 Hz), 3.39 (1H, dd, J ≈ 9.4 Hz), 3.39 (s), 3.46 (1H, ddd),
3.48 (1H, dd, J ≈ 9.1 Hz), 3.58 (1H, dd, J ) 3.9, 9.8 Hz), 3.70
(1H, dd, J ) 5.9, 12 Hz), 3.74 (1H), 3.75 (1H, d, J ≈ 9 Hz), 3.82
(1H, dd, J ) 4.8, 12 Hz), 3.89, 3.90 (2H, dd, J ) 2.3, 12 Hz),
4.48 (1H, d, J ) 7.9 Hz), 4.78 (1H, d, J ) 3.9 Hz); HR-FABMS
[M + Na]+ m/z calcd for C13H23O11DNa 380.1279, found 380.1286.
1
CHCl3); H NMR (CDCl3) δ 3.40 (s), 3.53 (1H, dd, J ) 3.5, 9.6
Hz), 3.83 (1H, d, J ) 9.6 Hz), 3.88 (1H), 4.51 (1H, dd, J ) 2.1,
12.1 Hz), 4.62 (1H, dd, J ) 4.9, 12.1 Hz), 4.65 (1H, d, J ) 3.5
Hz), 4.67, 4.76, 4.78, 5.01 (4H, d, J ≈ 12 Hz), 7.28-8.03; 13C
NMR (CDCl3) δ 55.2, 63.7, 69.4, 69.7 (t), 73.1, 75.6, 79.6, 81.1,
98.0, 125.3, 127.9-130.2, 133.0, 133.5, 137.9, 138.5, 166.7; HR-
FABMS [M + Na]+ m/z calcd for C28H29O7DNa 502.1952, found
502.1956.
Ack n ow led gm en t. This work was supported by a
grant from the Swedish Natural Science Research
Council.
J O982256H