First synthesis of β-D-galf(1-4)GlcNAc, a structural unit attached O-glycosidically in glycoproteins of Trypanosoma cruzi

Full text of DOI:10.1021/jo951934m

1886
J . Org. Chem. 1996, 61, 1886-1889
furanose disaccharides16,17 and in the characterization of
F ir st Syn th esis of â-D-Ga lf(1-4)GlcNAc, a
Str u ctu r a l Un it Atta ch ed O-Glycosid ica lly
in Glycop r otein s of Tr ypa n osom a cr u zi
galactofuranose-containing glycoconjugates from T. cruzi.8,9
This, together with the fact that the synthesis of â-D-
Galf(1-4)-D-GlcNAc (8) was not previously reported,
prompted us to synthesize the disaccharide. The corre-
sponding alditol â-D-Galf(1-4)-D-GlcNAc-ol (9) was also
Carola Gallo-Rodriguez, Oscar Varela, and
Rosa M. de Lederkremer*
1
prepared, and its H and 13C NMR chemical shifts were
compared with the data reported for the oligosaccharide
alditols obtained by reductive â-elimination of the T. cruzi
glycoproteins.4
Departamento de Qu´ımica Orga´nica, Facultad de Ciencias
Exactas y Naturales, Universidad de Buenos Aires, Ciudad
Universitaria, Pabello´n II, 1428 Buenos Aires, Argentina
Received October 31, 1995
Resu lts a n d Discu ssion
For the synthesis of the target disaccharide 8 a
partially protected derivative of 2-acetamido-2-deoxy-D-
glucose (N-acetyl-D-glucosamine) having HO-4 free was
required. Such an intermediate (3) was successfully
prepared by selective benzoylation of benzyl 2-acetamido-
2-deoxy-R-D-glucopyranoside18 (1). Acylation with dif-
In tr od u ction
The glycobiology of galactofuranose is a topic of in-
creasing interest. This monosaccharide is a constituent
of polysaccharides and glycoconjugates from infectious
bacteria,1,2 protozoa,3,4 and fungi,5-7 while the mammal
host does not biosynthesize glycoconjugates containing
Galf. In particular, galactofuranose is a component of
glycoinositol phospholipids, with anchor characteristics,
isolated from Trypanosoma cruzi8,9 and Leishmania
species.10,11 Also, recently, O-linked oligosaccharides of
different size, all attached by the unit â-D-Galf(1-4)-
GlcNAc, have been released by â-elimination from gly-
coproteins of T. cruzi.4 This is a unique type of linkage,
and the presence of Galf could be related to the antige-
nicity of the glycoprotein.12 The disaccharide is further
branched by different numbers of â-Galp units turning
the sugar chain in an acceptor of sialic acid, in a trans-
sialidase reaction previously characterized in T. cruzi.13,14
Interestingly, the presence of â-D-Galf units in the sialic
acid acceptor glycoproteins of T. cruzi epimastigote forms
is dependent on the strain. Thus, in the Y strain the
O-linked oligosaccharides do not contain â-galactofura-
nosyl units.15
ferent reagents, under a variety of conditions, of pyra-
nosides having the gluco configuration have indicated19
a lower reactivity for HO-4. In our laboratory, N-
benzoylimidazole has been successfully employed for the
regioselective benzoylation of all the HO-groups, except
HO-4, of methyl R-D-glucopyranoside.20 For this reason,
compound 1 was benzoylated with N-benzoylimidazole
(2.4 mol per mol of 1) in refluxing acetonitrile. The
resulting mixture was chromatographed to give the
desired 3,6-di-O-benzoyl derivative 3 in ∼70% yield. The
perbenzoate 2 was isolated in low yield (9.4%). The
structure of 3 was established by comparison of its
spectral data with those for 2. Thus, the H-4 signal in 2
appeared shifted downfield in ∼1.9 ppm, with respect to
the same signal in 3, and the signals for H-3 and H-5
were shifted downfield less than 0.5 ppm, indicating that
HO-4 was the free hydroxyl group of 3. This result was
confirmed by the 13C NMR spectra of 2 and 3 (Table 1).
As observed for other partially benzoylated derivatives
of sugars21 the benzoylation of a given hydroxyl group
causes a small displacement for the R-carbon atom but a
larger upfield shift for the â-carbon. Thus, the C-4 signal
of 2 (identified by a heteronuclear 2D-COSY experiment)
appears 0.4 ppm downfield with respect to the C-4 signal
of 3, whereas the resonances of C-3 and C-5 in the
spectrum of 2 were shifted upfield (2.9 and 1.5 ppm,
respectively) compared to the same signals in 3. These
displacements were expected to occur on benzoylation of
the free hydroxyl group of 3, if such a group was located
on C-4.
The synthetic galactofuranose-containing oligosaccha-
rides could be useful for the identification of strains of
T. cruzi as well as for studies on the inhibition of the
biosynthesis of these unique O-linked chains. Our
laboratory has been involved in the synthesis of galacto-
(1) McNeil, M.; Wallner, S. J .; Hunter, S. W.; Brennan, P. J .
Carbohydr. Res. 1987, 166, 299.
(2) Richards, J . C.; Perry, M. B.; Carlo, D. T. Can. J . Biochem. Cell.
Biol. 1983, 61, 178.
(3) Lederkremer, R. M.; Colli, W. Glycobiology 1995, 5, 547.
(4) Previato, J . O.; J ones, C.; Gonc¸alves, L. P. B.; Wait, R.; Travassos,
L. R.; Mendonc¸a-Previato, L. Biochem. J . 1994, 301, 151.
(5) Latge´, J . P.; Kobayashi, H.; Debeaupuis, J . P.; Diaquin, M.;
Sarfati, J .; Wieruszeski, J . M.; Parra, E.; Bouchara, J . P.; Fournet, B.
Infect. Immun. 1994, 62, 5424.
(6) Unkefer, C. J .; Gander, J . J . Biol. Chem. 1990, 265, 685.
(7) Mendonc¸a-Previato, L.; Gorin, P. A. J .; Travassos, L. R. Infect.
Immun. 1980, 29, 934.
(8) Lederkremer, R. M.; Lima, C.; Ramirez, M. I.; Ferguson, M. A.
J .; Homans, S. W.; Thomas-Oates, J . J . Biol. Chem. 1991, 266, 23670.
(9) Lederkremer, R. M.; Lima, C.; Ramirez, M. I.; Gonc¸alves, M. F.;
Colli, W. Eur. J . Biochem. 1993, 218, 929.
(10) McConville, M. J .; Homans, S. W.; Thomas-Oates, J . E.; Dell,
A.; Bacic, A. J . Biol. Chem. 1990, 265, 7385.
(11) McConville, M. J .; Collidge, T. A. C.; Ferguson, M. A. J .;
Schneider, P. J . Biol. Chem. 1993, 268, 15595.
(12) De Arruda, M. V.; Colli, W.; Zingales, B. Eur. J . Biochem. 1989,
182, 413.
(13) Ferrero-Garcia, M. A.; Trombetta, S. E.; Sanches, D. O.; Reglero,
A.; Frasch, A. C. C.; Parodi, A. J . Eur. J . Biochem. 1993, 213, 765.
(14) Vandekerckhove, F.; Schenkman, S.; Carvalho, L. P.; Tomlin-
son, S.; Kiso, M.;Toshida, M.; Hasegawa, A.; Nussenzweig, V. Glyco-
biology 1993, 2, 541.
(15) Previato, J . O.; J ones, C.; Xavier, M. T.; Wait, R.; Travassos,
L. R.; Parodi, A. J .; Mendonc¸a-Previato, L. J . Biol. Chem. 1995, 270,
7241.
(16) Marino, C.; Varela, O.; Lederkremer, R. M. Carbohydr. Res.
1989, 190, 65.
(17) Lederkremer, R. M.; Marino, C.; Varela, O. Carbohydr. Res.
1990, 200, 227.
(18) Kuhn, R.; Baer, H. H. Ann. 1958, 611, 236.
(19) Haines, A. H. Adv. Carbohydr. Chem. Biochem. 1976, 33, 11.
(20) Varela, O.; Cicero, D.; Lederkremer, R. M. J . Org. Chem. 1989,
54, 1884.
(21) Bock, K.; Pedersen, C. Adv. Carbohydr. Chem. Biochem. 1983,
41, 27.
0022-3263/96/1961-1886$12.00/0 © 1996 American Chemical Society

Notes
J . Org. Chem., Vol. 61, No. 5, 1996 1887
Ta ble 1. 13C NMR (50.3 MHz) Ch em ica l Sh ifts for Com p ou n d s 1-3 a n d 5-10
δc (ppm)
C-4
compd
C-1
C-2
C-3
C-5
C-6
CH2Ph
1a
2b
3b
96.7
96.7
96.8
96.7
107.0
91.7
106.9
96.6
108.7
91.5 (R); 95.8 (â)
108.6
61.8
109.0
54.5
52.3
51.6
52.2
82.3
52.6
82.2
54.5
81.9
54.9
81.9
53.6
82.1
47.9
80.9
71.7
71.7
74.6
72.3
77.1
72.1
77.1
71.8*
78.3
71.3*
78.5
69.4
77.2
70.4#
75.9*
70.9*
69.3
68.9
74.7
82.7
74.8
82.7
77.0
83.6
77.0
83.5
78.8
83.8
75.4*
81.6
72.9
68.4
69.9
69.5
70.1
69.0
70.1
71.3*
70.6*
71.3*
70.0*
72.1*
71.4*
69.5#
69.8#
61.4
62.9
63.4
62.7
63.4
62.7
63.4
60.8
63.6
60.9
63.6
62.9
63.8
62.3
62.7
70.5*
70.2
70.7
70.0
5b GlcNAc
Galf
6b GlcNAc
Galf
7a GlcNAc
Galf
70.2
8a GlcNAc
Galf
9a GlcNAc-ol
Galf
10b GlcNAc-ol
Galf
61.6
106.9
a
b
Recorded in D2O. Recorded in CDCl3. c Signals marked with or # may be interchanged.
*
Sch em e 1a
The condensation of 3 with penta-O-benzoyl-D-galacto-
furanose22 (4) was performed employing tin(IV) chloride
as catalyst (Scheme 1). In previous work from this
laboratory,16,17 we have demonstrated the utility of this
Lewis acid to activate the anomeric center of peracylated
glycofuranose derivatives, leading to the formation of a
glycosidic linkage having the 1,2-trans configuration. The
high stereoselectivity for the glycosylation may be at-
tributed to the participation of the C-2 substituent to
stabilize the positive charge on C-1, generated by the
remotion of the anomeric substituent by the Lewis acid.
The resulting acyloxonium ion (or an orthoester inter-
mediate23 ) blocks one of the sides of C-1 and induces the
attack of the HO-donor moiety from the unblocked side,
leading to the 1,2-trans glycoside. This procedure has
the additional advantage that the precursor of the
nonreducing end of the disaccharide is a per-O-acylated
furanose and not a rather unstable glycofuranosyl ha-
lide,24 usually employed as glycosyl donor. As expected,
the tin(IV) chloride-catalyzed condensation of 3 and 4
afforded stereoselectively the disaccharide 5 in 85% yield.
The anomeric configuration for the furanose unit was
established as â by the small value for J 1′,2′ (<1 Hz),
indicative of a trans relationship between H-1 and H-2.
Also, the C-1′ resonance appeared at low field, with a δ
value (107.0 ppm) similar to that observed for the
anomeric carbon of â-galactofuranosides,16,17 confirming
the â-configuration for C-1′.
In order to remove the benzyl group on C-1 of 5,
hydrogenolysis was attempted under a variety of condi-
tions, but in all the cases, the reaction was extremely
slow. The best results were obtained when palladium
hydroxide followed by 10% Pd/C were employed as
catalysts and the hydrogenation was performed at at-
mospheric pressure for 10 days. Regardless, only partial
hydrogenolysis occurred, compound 6 was isolated by
column chromatography in 77% yield, and unreacted 5
(11%) was also recovered. Furthermore, the alkaline
O-debenzoylation of 6 was unsuccessful, as several
decomposition products were detected. Alternatively,
O-debenzoylation of 5 with sodium methoxide in metha-
nol afforded the crystalline disaccharide glycoside 7 in
97% yield. As observed for 5, hydrogenation of 7 also
a
Reagents: (i) SnCl4, Cl2CH2, 20 h, 0 °C to rt; (ii) H2 (1 atm),
catalyst, 10 days; (iii) NaOMe, MeOH; (iv) NH4CO2H, 10% Pd/C,
MeOH, reflux, 1 h; (v) NaBH4, 9:1 MeOH-H2O, 16 h; (vi) Ac2O,
C5H5N.
led to incomplete reaction. However, heterogeneous
catalytic transfer hydrogenolysis25 provided a highly
efficient means for the removal of the O-benzyl group.
(22) D’Accorso, N. B.; Thiel, I. M. E.; Schu¨ller, M. Carbohydr. Res.
1983, 124, 177.
(23) Hanessian, S.; Banoub, J . Carbohydr. Res. 1977, 59, 261.
(24) Haynes, L. J .; Newth, F. H. Adv. Carbohydr. Chem. 1955, 10,
207.
(25) Beaupere, D.; Boutbaiba, I.; Demailly, G.; Uzan, R. Carbohydr.
Res. 1988, 180, 152.

1888 J . Org. Chem., Vol. 61, No. 5, 1996
Notes
0.93 mmol). After 10 min of stirring at 0 °C, a solution of 3
(0.30 g, 0.578 mmol) in dry dichloromethane (5 mL) was slowly
Treatment of 7 with ammonium formate and 10% Pd/C,
in refluxing methanol for 1 h, afforded syrupy 8 in 98%
yield. Compound 8 was obtained in crystalline form by
slow crystallization from methanol. The disaccharide 8
constitutes the intact linkage unit between the threonine
or serine residues of the protein and oligosaccharides of
Galp in the 38/43 kDa glycoproteins of T. cruzi. The 13C
NMR spectrum of 8 showed the resonance for the
anomeric carbons of Galf (108.6 ppm) and GlcNAc (91.5
ppm and 95.8 ppm, for the R and â anomers, respec-
tively).
Sodium borohydride reduction of 8 afforded the crys-
talline alditol Galf-â-(1-4)GlcNAc-ol (9), which showed
in its 13C NMR spectrum the diagnostic signals (C-
anomeric 109.0 ppm, C-1 and C-4 of GlcNAc-ol 61.8 and
78.8) almost identical to those reported for the “disac-
charide alditol” isolated from the glycoprotein of T. cruzi.4
Thus, the present study confirms by synthesis the
structure of the naturally occurring and biologically
interesting disaccharide Galf-â-(1-4)-GlcNAc (8). As the
synthetic route here described led to 8 in a high overall
yield (56.5%), a considerable amount of the compound
was available for the complete determination of its
physical and spectral properties.
added, and the stirring was continued for 20
h at room
temperature. The mixture was diluted with Cl2CH2 (40 mL) and
poured into saturated aqueous NaHCO3 with vigorous stirring.
The aqueous layer was extracted with Cl2CH2 (2 × 30 mL), and
the combined organic solutions were washed with water until
pH 7, dried (MgSO4), filtered, and concentrated. TLC monitoring
of the residue showed a main product having Rf 0.50 (solvent
A). This product was isolated by column chromatography (9:1
toluene-EtOAc and then 5:1 toluene-EtOAc), affording com-
pound 5 (0.54 g, 85%) as a foamy solid: [R]D +63° (c 0.9, CHCl3);
1H NMR (200 MHz, CDCl3) δ 8.15-7.10 (m, 35H), 5.80 (d, 1H,
J ) 9.6 Hz, NH), 5.70-5.60 (m, 2H), 5.60 (d, 1H, J ) 4.8 Hz),
5.46 (s, 1H), 5.36 (d, 1H, J ) 0.9 Hz), 5.01 (d, 1H, J ) 3.7 Hz),
4.87 (d, 1H, J ) 13.1 Hz), 4.81 (d, 1H, J ) 11.9 Hz), 4.64 (d, 1H,
J ) 13.1 Hz), 4.58 (d, 1H, J ) 11.9 Hz), 4.70-4.45 (m,1H), 4.40-
4.20 (m, 5H), 1.76 (s, 3H). Anal. Calcd for C63H55NO17: C, 68.91;
H, 5.05; N, 1.28. Found: C, 69.00; H, 5.19; N, 1.32.
2-Aceta m id o-3,6-d i-O-ben zoyl-2-d eoxy-4-O-(2,3,5,6-tetr a -
O-ben zoyl-â-D-ga la ctofu r a n osyl)-r,â-D-glu cop yr a n ose (6).
A suspension of 10% Pd(OH)2/C (0.10 g) in EtOAc (2 mL) was
hydrogenated at 15 psi (1 atm) for 1 h, and then a solution of
compound 5 (0.70 g, 0.64 mmol) in EtOAc (7 mL) was added.
The mixture was hydrogenated for 3 days at atmospheric
pressure. The catalyst was filtered, and 10% Pd/C (0.10 g) was
added to the filtrate. Further hydrogenation (1 atm) for 7
additional days afforded, after filtration and concentration, a
syrup which was purified by column chromatography (1:1
toluene-EtOAc). The starting material 5 (0.08 g, 11%) was first
eluted (Rf 0.75, solvent B). The next fraction from the column
afforded compound 6 (0.497 g, 77%) as an R,â mixture (Rf 0.31
and 0.19, solvent B) that was recrystallized from 9:1 EtOH-
water: mp 199-202 °C, [R]D +46.3° (c 0.9, CHCl3). Anal. Calcd
for C56H49NO17: C, 66.73; H, 4.90; N, 1.39. Found: C, 66.98;
H, 5.17; N, 1.23.
Ben zyl 2-Aceta m id o-2-d eoxy-4-O-â-D-ga la ctofu r a n osyl-
r-D-glu cop yr a n osid e (7). To a suspension of 5 (1.7 g, 1.55
mmol) in anhydrous methanol cooled at 0 °C was added 0.55 M
sodium methoxide in methanol (18.6 mL). After being stirred
for 1 h at 0 °C, the reaction mixture was warmed to room
temperature. The stirring was maintained for an additional
hour, and then water (1 mL) was added. The solution was
passed through a column (1.5 cm × 6 cm) containing BioRad
AG 50W-X12 (H+) resin. The solvent was removed under
vacuum, and the remaining methyl benzoate was eliminated by
five successive coevaporations with water to afford 7 as a
crystalline white solid (0.71 g, 97%), Rf 0.68, solvent C. After
recrystallization from 2:1 EtOAc-methanol it had: mp 196.5-
197.5 °C; [R]D +58° (c 1, H2O); 1H NMR (200 MHz, D2O)
anomeric region δ 5.03 (bs, 1H), 4.88 (d, 1H, J ) 2.8 Hz). Anal.
Calcd for C21H31NO11‚H2O: C, 51.32; H, 6.77; N, 2.85. Found:
C, 51.77; H, 7.17; N, 2.90.
2-Aceta m id o-2-d eoxy-4-O-â-D-ga la ctofu r a n osyl-r,â-D-glu -
cop yr a n ose (8). To a solution of 6 (0.30 g, 0.63 mmol) in
methanol (30 mL) were added 10% Pd/C (60 mg) and ammonium
formate (0.10 g, 1.59 mmol). The mixture was heated under
reflux for 1 h in a water bath and then filtered and concentrated.
The resulting syrup was dried in vacuo at 50 °C for 10 min,
affording an amorphous solid, which was dissolved in MeOH (2
mL) and passed through a column of BioRad AG 501-X8 mixed
resin. Evaporation of the solvent under vacuum gave pure
compound 8 (0.253 g, 98%) which slowly crystallized from
MeOH: mp 191-192 °C; [R]D -48° (c 1, H2O); Rf 0.52 and 0.47
(solvent C) for the R and â anomers, respectively; 1H NMR (200
MHz, D2O) anomeric region δ 5.15 (d, J ) 2.8 Hz, R anomer),
5.05 (bs, 1H). The signal for the â anomer of GlcNAc was
overlapped with that of DHO. Anal. Calcd for C14H25NO11: C,
43.86; H, 6.57; N, 3.65. Found: C, 44.00; H, 6.45; N, 3.57.
2-Acetam ido-2-deoxy-4-O-â-D-galactofu r an osylglu citol (9).
To a solution of 8 (91.5 mg, 0.24 mmol) in 9:1 methanol-water
(10 mL) was added sodium borohydride (90.2 mg, 2.34 mmol),
and the mixture was stirred overnight at room temperature. The
solution was decationized by elution through a column of BioRad
AG 50W-X12 (H+ form) resin. The solvent was evaporated, and
the boric acid was eliminated by five successive coevaporations
with methanol and finally by ion-exchange column chromatog-
raphy on BioRad AG 501-X8 resin. Evaporation of the solvent
Exp er im en ta l Section
Gen er a l. The following solvent systems were used for
analytical thin-layer chromatography (TLC): (A) 2:1 toluene-
EtOAc, (B) 1:1 toluene-EtOAc, (C) 7:1:1 nPrOH-EtOH-H2O.
TLC was performed on 0.2 mm silica gel 60 F254 (Merck)
aluminum-supported plates. Detection was effected by exposure
to UV light or by spraying with 5% (v/v) sulfuric acid in EtOH
and charring. Column chromatography was performed on silica
gel 60 (230-400 mesh, Merck).
Ben zyl 2-Acet a m id o-3,6-d i-O-b en zoyl-2-d eoxy-r-D-glu -
cop yr a n osid e (3). To a suspension of benzyl 2-acetamido-2-
deoxy-R-D-glucopyranoside18 (1, 1.5 g, 4.8 mmol) in dry aceto-
nitrile (38 mL) was added a solution of N-benzoylimidazole (2
g, 11.5 mmol) in dry acetonitrile (10 mL). The mixture was
heated at the reflux temperature for 17 h. After cooling, water
was added (1 mL) and the solution was stirred for 0.5 h. The
solvent was evaporated in vacuo, and the syrupy residue was
washed with cold water (15 mL, twice) and then dissolved in
dichloromethane (100 mL). The solution was extracted with 5%
aqueous HCl, brine, saturated aqueous NaHCO3, and water,
dried (MgSO4), and concentrated. The resulting residue was
purified by column chromatography (2:1 hexane-EtOAc). The
fastest migrating component (Rf 0.48, solvent A) was identified
as benzyl 2-acetamido-3,4,6-tri-O-benzoyl-2-deoxy-R-D-glucopy-
ranoside (2, 0.28 g, 9.4%) which after recrystallization from
methanol gave: mp 159-160 °C; [R]D +61° (c 1, CHCl3); 1H NMR
(200 MHz, CDCl3) δ 8.15-7.25 (m, 20H), 5.91 (d, 1H, J ) 9.2
Hz, NH), 5.81-5.71 (m, 2H), 5.10 (d, 1H, J ) 3.4 Hz), 4.85 (d,
1H, J ) 11.7 Hz), 4.64-4.62 (m, 5H), 1.85 (s, 3H). Anal. Calcd
for C36H33NO9: C, 69.32; H, 5.34; N, 2.25. Found: C, 69.01; H,
5.21; N, 2.16.
The next fraction from the column (Rf 0.35, solvent A) afforded
compound 3 (1.70 g, 70.3%) as a foamy solid: [R]D +120° (c 1,
CHCl3); 1H NMR (200 MHz, CDCl3) δ 8.15-7.25 (m, 15H), 5.85
(d, 1H, J ) 9.6 Hz, NH), 5.39 (dd, 1H, J ) 10.7, 9.1 Hz), 4.98 (d,
1H, J ) 3.6 Hz), 4.78 (d, 1H, J ) 11.8 Hz), 4.75 (dd, 1H, J )
12.2, 4.2 Hz), 4.54 (d, 1H, J ) 11.8 Hz), 4.50 (dd, 1H, J ) 12.2,
2.1 Hz), 4.47 (ddd, 1H, J ) 10.7, 9.6, 3.6 Hz), 4.07 (ddd, 1H, J )
9.8, 4.2, 2.1 Hz), 3.85 (ddd, 1H, J ) 9.8, 9.1, 4.4 Hz), 3.38 (d,
1H, J ) 4.4 Hz, OH), 1.79 (s, 3H). Anal. Calcd for C29H29NO8:
C, 67.03; H, 5.63; N, 2.70. Found: C, 67.08; H, 5.56; N, 2.47.
Ben zyl 2-Acetam ido-3,6-di-O-ben zoyl-2-deoxy-4-O-(2,3,5,6-
t et r a -O-b en zoyl-â-D-ga la ct ofu r a n osyl)-r-D-glu cop yr a n o-
sid e (5). To an externally cooled (0 °C) solution of 1,2,3,5,6-
penta-O-benzoyl-R,â-D-galactofuranose (4, 0.61 g, 0.87 mmol) in
dry dichloromethane (5 mL) was added tin(IV) chloride (0.11 mL,

Notes
J . Org. Chem., Vol. 61, No. 5, 1996 1889
afforded compound 9 (92 mg, 100%) as a chromatographically
homogeneous (Rf 0.34, solvent C) colorless syrup, which slowly
crystallized from methanol: mp 161-162 °C; [R]D -42° (c 0.8,
H2O); 1H NMR (200 MHz, D2O) anomeric region δ 5.21 (bs, 1H).
Ack n ow led gm en t. We are indebted to the UNDP/
WORLD BANK/WHO Special Programme for Research
and Training in Tropical Diseases (TDR), CONICET
(Consejo Nacional de Investigaciones Cient´ıficas y Te´c-
nicas), and the University of Buenos Aires for financial
support and to UMYMFOR (CONICET-FCEN) for the
microanalyses. O.V. and R.M.L. are Research Members
of the National Research Council of Argentina
(CONICET).
Anal. Calcd for
C14H27NO11: C, 43.63; H, 7.06; N, 3.63.
Found: C, 43.90; H, 7.01; N, 3.77.
Compound 9 was conventionally acetylated to give syrupy 10,
whose 1H- and 13C-NMR spectra were recorded: 1H NMR (200
MHz, CDCl3) δ 5.86 (d, 1H, J ) 9.5 Hz, NH), 5.33 (dt, 1H, J )
6.8, 4.4 Hz), 5.16 (bs, 1H), 5.18-5.01 (m, 4H), 4.63 (m, 1H), 4.51
(dd, 1H, J ) 12.5, 3.2 Hz), 4.44-3.94 (m, 8H), 2.08-1.95 (9 s,
Ac).
J O951934M