Synthesis of new branched-chain amino sugars

Article abstract of DOI:10.1016/S0008-6215(02)00527-X

1,3-Dipolar cycloaddition of methylideneaniline N-oxide to sugar enones is described. The addition occurred exclusively from the side opposite to the aglycone affording the corresponding alkyl α-D-lyxo-hexopyranosid-(2,3:5′,4′)-phenylisoxazolidin-4- ulose

Full text of DOI:10.1016/S0008-6215(02)00527-X

Carbohydrate Research 338 (2003) 673–680
www.elsevier.com/locate/carres
Note
Synthesis of new branched-chain amino sugars
Joa˜o R. de Freitas Filho,a Rajendra M. Srivastava,a,* Waldenberg J.P. da Silva,a
Louis Cottier,b Denis Sinoub
aDepartamento de Qu´ımica Fundamental, Uni6ersidade Federal de Pernambuco Cidade Uni6ersita´ria, CCEN, 50.740-540, Recife, PE, Brazil
bLaboratoire de Synthe`se Asymetrique, associe au CNRS, CPE Lyon, Uni6ersite´ Claude Bernard Lyon 1, 43, boule6ard du 11 no6embre 1918,
F-69622 Villeurbanne, France
Received 27 December 2001; received in revised form 6 November 2002; accepted 10 December 2002
Abstract
1,3-Dipolar cycloaddition of methylideneaniline N-oxide to sugar enones is described. The addition occurred exclusively from
the side opposite to the aglycone affording the corresponding alkyl a-
D
-lyxo-hexopyranosid-(2,3:5%,4%)-phenylisoxazolidin-4-uloses.
-talopyranoside,
Hydrogenation of these compounds readily yielded the corresponding alkyl 3-deoxy-3-N-phenylaminomethyl-a-
D
1
that were readily transformed to the acetates. The structure and conformation of the bicyclic compounds were determined by H
NMR studies and semi-empirical molecular orbital calculations employing the AM1 method. © 2003 Elsevier Science Ltd. All
rights reserved.
Keywords: Amino sugars; Cycloaddition; Nitrone
1. Introduction
alization of sugar molecules.14 In fact, NꢀO bond in
this bicyclic system can readily be cleaved to yield the
branched-chain amino sugars. We describe herein a
novel and potentially adaptable methodology for the
synthesis of isoxazolidino–pyranosidulose system
which can readily be transformed to branched-chain
amino sugars.
Amino sugars are constituents of many biologically
active compounds, such as antibiotics,1,2 and biopoly-
mers.3 It is known that the relative stereochemistry of
the functional groups in natural and unnatural amino
sugars plays an important role on the activity profile of
the anthracycline.4 So there has been a great interest in
the development of efficient syntheses of these target
molecules.
We then focused our attention to the synthesis of
amino sugars in a rather simple manner. It has been
shown that carbohydrate molecules possessing the
enone functionality are the preferred precursors for the
synthesis of branched-chain and rare sugars.5–10
As 1,3-dipolar cycloaddition of nitrones has been
used as a route to amino sugars,11–13 the addition of
methylideneaniline N-oxide (or simply referred as a
nitrone) to a,b-unsaturated carbonyl compounds
derived from sugars has been examined to a limited
extent and therefore opens a new way for the function-
2. Results and discussion
The synthetic route to these amino sugars is described
in Scheme 1. The starting unsaturated glycosides 1a–d
were prepared by allowing 3,4,6-tri-O-acetyl-1,5-anhy-
dro-2-deoxy-D-arabino-hex-1-enitol(tri-O-acetyl-D-glu-
cal) to react with an appropriate alcohol in the presence
of montmorillonite K-10 catalyst.15,16 This simple pro-
cedure provided only a anomers of 1a–d. Deacetylation
of alkyl 4,6-di-O-acetyl-2,3-dideoxy-a-D-erythro-hex-2-
enopyranosides (1a–d), according to the method of
Fraser-Reid et al.5 furnished compounds 2a–d, which
in turn were subjected to allylic oxidation at C-4 with
activated MnO2 to afford enones 3a–d. The enones are
important precursors for amino and other sugars. Ad-
dition of methylideneaniline N-oxide17 to 3a–d gave a
* Corresponding author. Tel.: +55-81-32718440; fax: +
55-81-32718442
E-mail address: rms@npd.ufpe.br (R.M. Srivastava).
0008-6215/03/$ - see front matter © 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0008-6215(02)00527-X

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J.R. de Freitas Filho et al. / Carbohydrate Research 338 (2003) 673–680
it to be H-2. This large J value clearly supports a cis
relationship between H-2 and H-3. Another interesting
feature supporting the lyxo configuration is that H-3
appeared at a lower field (l 3.40 ppm) than expected
(approx l 2.50 Hz); this is demonstrative that the
oxygen atom at C-1 and H-3 are axial and this could
cause the anisotropic effect and result in a downfield
shift for H-3. Alternatively, the molecular model of the
ribo configuration gives a dihedral angle of ꢀ60° or
less between H-1 and H-2, giving a J1,2 value of about
3.0 Hz or more; this has not been observed. Also, H-3
will not experience the anisotropic effect of the C-1
oxygen atom in the ribo configuration. We therefore
infer that the configuration was lyxo and not ribo in 4b,
and the same was true for other compounds 4a, c, and
d of this series. In spite of our best efforts, it was not
possible to detect and isolate the compounds having the
ribo configuration. Similar results have been observed
before in the cycloaddition of nitrones to a a,b-unsatu-
rated sugar lactone.14
cycloadduct 4a–d in moderate yields. The addition of
the nitrone to C-2ꢀC-3 double bond in 3a–d occurred
from the opposite site of the aglycone to afford isoxa-
zolidines 4a–d exclusively via the transition state shown
in Scheme 2.
The structures and configurations of products 4a–d
have been deduced through their 1H NMR spectra.
Compound 4b has been chosen for examination by 300
1
MHz H NMR spectroscopy in order to deduce the
configuration and conformation of this bicyclic com-
pound. The signal for H-1 appeared as a broad singlet
at l 5.18 ppm. According to the molecular model, the
lyxo configuration gives a dihedral angle of about 100°
between the two hydrogens H-1 and H-2. This means
that there should be a small coupling between the two
protons referred just now. This fact became apparent
when we irradiated H-1, which caused the proton at l
4.35 ppm to become a sharp doublet (J 8.40 Hz) and
there was a loss of 51.0 Hz or less coupling indicating
Scheme 1. Reagents and conditions: (a) MeOH–water–Et3N, r.t.; (b) MnO2, CHCl2, r.t.; (c) methylideneaniline N-oxide; (d)
Ac2O, C5H5N, r.t. for 5b; ClSiMe2t-Bu, DMF, imidazole, 0 °C for 6b; (e) H2 (101 kPa) PtO2, EtOAc, r.t.; (f) Ac2O, C5H5N, r.t.
Scheme 2. Transition state in the addition of nitrone to 3a–d.

J.R. de Freitas Filho et al. / Carbohydrate Research 338 (2003) 673–680
675
ing an a anomeric configuration. The proton signal of
H-4 appeared at l 3.65 ppm as a broad singlet. Since,
the J value between H-4 and H-5 is small (J 3.0 Hz), it
is inferred that the OH group at C-4 is axial indicating
a talo configuration for 7b–d. Moreover, the two-di-
1
mensional H–1H NMR spectrum clearly showed that
H-4 (l 3.65 ppm) is coupled with H-5 at l 3.74 and H-3
1
at l 2.13 ppm. H NMR spectra of 7c–d agreed also
with these structures. Acetylation of 7b–d yielded com-
1
pounds 8b–d; for example the H NMR spectrum of
compound 8b exhibited a broad singlet at l 5.03 ppm
for H-2, 4.88 ppm for H-1, and 4.70 ppm for H-4,
characteristics of the talo configuration.
In order to confirm the configurations and conforma-
tions of 4a–d, we performed the semi-empirical molecu-
lar orbital calculations for 4b and b% using the AM1
method. The enthalpy of formation of 4b and b% are
−146.17 and −143.85 kcal/mol. The torsion angles
H-2ꢀC-2ꢀC-1ꢀH-1 and O-12ꢀC-1ꢀO-11ꢀC-5 in 4b are
−102.2 and 70.1° indicating that the anomeric proton
is equatorial and that H-1 and H-2 have a torsion angle
of approx 100°. The calculations also show that C-1,
C-2, C-3, C-4 and C-5 of the pyranose system are
somewhat planar and the ring oxygen atom is above the
plane. The isoxazolidine ring has a slight deviation
from the planarity since the dihedral angle O-9ꢀN-8ꢀC-
7ꢀC-3 is −8.7° only. This is in agreement with
Fig. 1. Structure and more stable conformation of 4b ob-
tained using the AM1 method.
the cyclopentyl a-D-lyxo-hexopyranosid-(2,3:5%,4%)-2%-
phenylisoxazolidin-4-ulose structure assigned to 4b.
The same method was applied to the other isomer
4b% cyclopentyl a-D-ribo-hexopyranosid-(2,3:5%,4%)-2%-
phenylisoxazolidin-4-ulose (not isolated). The structures
of these two diastereoisomers are given in Figs. 1 and 2,
respectively.
In conclusion, we have synthesized three new
branched-chain amino sugars in excellent yields by a
1,3-dipolar cycloaddition of methylideneaniline N-ox-
ide to enones 3a–d, followed by hydrogenation. The
structures as well conformations of these compounds
Fig. 2. Structure and more stable conformation of 4b% ob-
tained using the AM1 method.
1
were determined from H NMR spectra in conjunction
Since compounds 4a–d were not crystalline, it was
not possible to collect crystallographic data for deter-
mining their configurations. So, we prepared the O-ace-
tyl and O-tert-butyldimethylsilyl derivatives 5b and 6b
from 4b with the hope to get crystals. Although we got
effectively fine crystals, they were not suitable for X-ray
analysis.
with molecular orbital calculations.
3. Experimental
3.1. General methods
Hydrogenation of compounds 4b–d using PtO2 as a
catalyst under 1.5 atmosphere of hydrogen resulted in
simultaneous cleavage of the NꢀO bond of the isoxazo-
lidine system and the reduction of the CꢁO bond to
provide 7b–d. The structures of 3-deoxy-N-pheny-
Melting points were determined with a Digital Melting
Point Apparatus, series IA-9100, Electrothermal Ltd.,
England. IR spectra were recorded as KBr films on a
Brucker IFFS66 series Fourier transform spectrophoto-
1
meter. The 300 MHz H NMR spectra were recorded
laminomethyl-a- -talopyranoside (7b–d) were deduced
D
with a Varian Unity Plus spectrophotometer or a
Brucker DRX 300 using CDCl3 as solvent and Me4Si as
an internal standard. Elemental analyses were per-
formed in our Department. Optical rotations were mea-
1
from the H NMR spectra. For example, the anomeric
proton of compound 7b presented a small coupling
constant (approx 1.3 Hz) between H-1 and H-2 suggest-

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J.R. de Freitas Filho et al. / Carbohydrate Research 338 (2003) 673–680
1
sured with a Perkin–Elmer 141 and 241 polarimeters at
the Universite´ Claude Bernard Lyon 1, Villeurbanne
(France), and at the University of Sa˜o Carlos, S.P.
(Brazil). Thin layer chromatography (TLC) was carried
out on plates coated with Silica Gel 60 (E. Merck) and
the plates were exposed in a chamber containing iodine
vapors which revealed the spots.
0.97, CHCl3); IR (KBr): 3396 cm−1 (w OH); H NMR
(300 MHz, CDCl3): l 5.95 (d, 1 H, J3,2 9.9 Hz, H-3),
5.79 (dd, 1 H, J2,3 9.9, J2,4 2.1 Hz, H-2), 5.05 (bs, 1 H,
H-1), 4.23 (bd, 1 H, J4,5 9.0 Hz, H-4), 3.87 (m, 2 H,
H-6, H-6%), 3.75 (dt, 1 H, J5,4 9.0, J5,6 4.2 Hz, H-5), 3.89
(dd, 1 H, J 6.9, J 10.5 Hz, OCH2), 3.53 (dd, 1 H, J 7.5,
J 10.5 Hz, OCH2), 1.90 and 1.75 (2 bs, exchangeable, 2
H, 2 OH), 1.09 (m, 1 H, CH), 0.57–0.23 (m, 4 H, CH2).
Anal. Calcd for C10H16O4 (200.23): C, 59.98; H, 8.05.
Found: C, 59.70; H, 7.90.
3.2. General procedure for the preparation of diols 2a–
d
Alkyl
4,6-di-O-acetyl-2,3-dideoxy-a-
D
-erythro-hex-2-
3.3. General procedure for the preparation of alkyl 2,3-
dideoxy-a-D-glycero-2-enopyranosid-4-uloses (3a–d)
enopyranosides (1a–d) were obtained by the method of
Toshima et al.15 The hydrolysis of 1a–d in 9:6:1
MeOH–water–Et3N (32 mL) required 3 h at room
temperature (rt) for deacetylation as determined by
TLC. Solvent evaporation under reduced pressure, fol-
lowed by chromatography on silica (1:1 C6H14–
EtOAc), gave diols 2a–d in almost quantitative yield.
The appropriate diol 2 (4.67 mmol) was dissolved in
CH2Cl2 (150 mL), activated MnO2 (4.61 g, 53 mmol)
was added, and the contents stirred at rt until the
completion of the reaction. The progress of the reaction
was monitored by TLC using 9:1 CH2Cl2–EtOAc fol-
lowed by spot viewing under UV light. Filtration and
solvent evaporation gave 3a–d analytically pure after
recrystallization from ether–C6H14.
3.2.1. Ethyl 2,3-dideoxy-a- -erythro-hex-2-enopyran-
D
oside (2a). Obtained as described above from 1a (1.25 g,
5.4 mmol) and MeOH–water–Et3N (32 mL); 1.0 g
(86%); Rf 0.12 (9:1 CH2Cl2–EtOAc). The 1H NMR
spectrum and the elemental analysis of 2a were in
agreement with the reported data.5
3.3.1. Ethyl 2,3-dideoxy-a- -glycero-hex-2-enopyran-
D
osid-4-ulose (3a). From 2a (0.82 g, 4.67 mmol); 0.53 g
(65%); mp 86–87 °C; Rf 0.36 (4:1 CHCl3–EtOAc); [h]D25
−14.5° (c 2.1, CHCl3); IR (KBr): 3457 (w OH), 1692
1
3.2.2. Cyclopentyl 2,3-dideoxy-a-
D-erythro-hex-2-enopy-
cm−1 (w CꢁO); H NMR (300 MHz, CDCl3): l 6.89
ranoside (2b). From 1b (2.0 g, 9.3 mmol); oil; 1.74 g
(dd, 1 H, J2,3 10.5, J2,1 3.6 Hz, H-2), 6.10 (d, 1 H, J3,2
10.5 Hz, H-3), 5.28 (d, 1 H, J1,2 3.6 Hz, H-1), 4.50 (t, 1
H, J5,6 4.5 Hz, H-5), 4.00–3.66 (m, 4 H, OCH2, H-6,
H-6%), 2.27 (b, exchangeable, 1 H, OH), 1.28 (t, 3 H, J
7.1 Hz, CH3). Anal. Calcd for C8H12O4 (172.18): C,
55.81; H, 7.02. Found: C, 55.52; H, 6.86.
(93%); Rf 0.16 (9:1 CH2Cl2–EtOAc); [h]2D5 +54° (c 1.0,
CHCl3); IR (KBr): 3404 cm−1 (w OH); H NMR (300
1
MHz, CDCl3): l 5.95 (d, 1 H, J3,2 10.2 Hz, H-3), 5.70
(dd, 1 H, J2,3 10.2, J2,4 2.4 Hz, H-2), 5.04 (bs, 1 H,
H-1), 4.23 (m, 1 H, OCH), 4.21 (bd, J4,5 9.3 Hz, 1 H,
H-4), 3.87 (bd, 2 H, J6,5 3.7 Hz, H-6, H-6%), 3.70 (dt, J5,4
9.4, J6,5 3.7 Hz, 1 H, H-5), 2.33 and 2.22 (bs, exchange-
able, 2 H, 2 OH), 1.83–1.51 (m, 8 H, 4 CH2). Anal.
Calcd for C11H18O4 (214.12): C, 61.70; H, 8.47. Found:
C, 61.28; H, 8.37.
3.3.2. Cyclopentyl 2,3-dideoxy-a- -glycero-hex-2-enopy-
D
ranosid-4-ulose (3b). From 2b (1.0 g, 4.67 mmol); 0.79
(76%); mp 76.4–77.0 °C; Rf 0.39 (9:1 CH2Cl2–EtOAc);
[h]2D5 −30° (c 0.92, CHCl3); IR (KBr): 3457 (w OH),
1
1692 cm−1 (w CꢁO); H NMR (300 MHz, CDCl3): l
3.2.3. Cyclohexyl 2,3-dideoxy-a-
D-erythro-hex-2-enopy-
6.85 (dd, 1 H, J2,3 10.2, J2,1 3.6 Hz, H-2), 6.09 (d, 1 H,
J3,2 10.2 Hz, H-3), 5.32 (d, 1 H, J1,2 3.6 Hz, H-1), 4.49
(dd, 1 H, J5,6 4.5, J5,6% 4.5 Hz, H-5), 4.34 (m, 1 H,
OCH), 4.01 (dd, J6,6% 11.7, J6,5 4.5 Hz, H-6), 3.91 (dd,
J6%,6 11.7, J6%,5 4.5 Hz, H-6%), 2.27 (bs, exchangeable, 1
H, OH), 1.87–1.55 (m, 8 H, 4 CH2). Anal. Calcd for
C11H18O4 (212.24): C, 62.25; H, 7.59. Found: C, 62.15;
H, 7.39.
ranoside (2c). From 1c (3.0 g, 9.6 mmol); oil; 1.62 g
(87%); Rf 0.20 (9:1 CH2Cl2–EtOAc); [h]2D5 +46° (c 3.4,
CHCl3); IR: 3100–3600 cm−1 (w OH) (Nujol); 1H
NMR (300 MHz, CDCl3): l 5.95 (ddd, 1 H, J3,2 10.2,
J3,1 1.3, J3,4 1.3 Hz, H-3), 5.73 (ddd, 1 H, J2,3 10.5, J2,4
2.4, J2,1 2.7 Hz, H-2), 5.13 (m, 1 H, H-1), 4.20 (bd, J4,5
9.0 Hz, H-4), 3.85 (d, 2 H, J6,5 3.9 Hz, H-6, H-6%), 3.75
(dt, 1 H, J5,4 9.0, J5,6 3.9 Hz, H-5), 3.62 (m, 1 H, OCH),
2.63 and 2.37 (bs, exchangeable, 2 H, 2 OH), 2.04–1.10
(m, 10 H, 5 CH2). Anal. Calcd for C12H20O4 (228.29):
C, 63.13; H, 8.83. Found: C, 63.25; H, 9.10.
3.3.3. Cyclohexyl 2,3-dideoxy-a- -glycero-hex-2-enopy-
D
ranosid-4-ulose (3c). From 2c (1.06 g, 4.67 mmol); 0.73
g (69%); mp 99.0–100 °C; Rf 0.42 (9:1 CH2Cl2–
EtOAc); IR (KBr): 3100–3600 (w OH), 1690 cm−1 (w
1
3.2.4. Cyclopropylmethyl 2,3-dideoxy-a-
D-erythro-hex-2-
CꢁO); H NMR (300 MHz, CDCl3): l 6.87 (dd, 1 H,
enopyranoside (2d). From 1d (1.34 g, 4.7 mmol); oil; 0.9
J2,3 10.2, J2,1 3.6 Hz, H-2), 6.11 (d, 1 H, J3,2 10.2 Hz,
H-3), 5.17 (d, 1 H, J1,2 3.6 Hz, H-1), 4.53 (dd, 1 H, J5,6
g (95%); Rf 0.17 (9:1 CH2Cl2–EtOAc); [h]2D5 +63° (c

J.R. de Freitas Filho et al. / Carbohydrate Research 338 (2003) 673–680
677
4.2, J5,6% 4.2 Hz, H-5), 4.02 (dd, J6%,6 11.8, J6%,5 4.2 Hz,
H-6%), 3.92 (dd, 2 H, J6,6% 11.8, J6,5 4.2 Hz, H-6),
3.80–3.62 (m, 1 H, OCH), 2.22 (bs, exchangeable, 1 H,
OH), 2.20–0.80 (m, 10 H, 5 CH2). Anal. Calcd for
C12H18O4 (226.26): C, 63.72; H, 7.96. Found: C, 63.42;
H, 8.07.
EtOAc); [h]2D5 +134.9° (c 0.38, CH2Cl2); IR (KBr):
1
3467 (w OH), 1670 cm−1 (w CꢁO); H NMR (300 MHz,
CDCl3): l 7.42–7.26 (m, 2 H, H-2%, H-6%, Ph-H), 7.15–
7.00 (m, 3 H, H-3%, H-4%, H-5%, PhꢀH), 5.18 (s, 1 H,
H-1), 4.35 (dd, 1 H, J2,3 8.4, J2,1 1.0 Hz, H-2), 4.32 (m,
1 H, OCH), 4.17 (ddd, J5,6 3.6, J5,6% 3.6, 1 H, J5,CH N 3.6
Hz, H-5), 3.89 (m, 2 H, H-6, H-6%), 3.80 (dd, 22 H,
3.3.4. Cyclopropylmethyl 2,3-dideoxy-a-
D
-glycero-hex-2-
JCH N,3 7.5, JCH N,5 1.2 Hz, CH2N), 3.40 (dt, 1 H, J3,2
2
enopyranosid-4-ulose (3d). From 2d (0.94 g, 4.67 mmol);
0.64 g (68%); mp 96.4–96.9 °C; Rf 0.32 (9:1 CH2Cl2–
EtOAc); [h]2D5 +18.6° (c 1.2, CHCl3); IR (KBr): 3456 (w
OH), 1692 cm−1 (w CꢁO); 1H NMR (300 MHz,
CDCl3): l 6.92 (dd, 1 H, J2,3 10.5, J2,1 3.7 Hz, H-2),
6.13 (d, 1 H, J3,2 10.5 Hz, H-3), 5.33 (d, 1 H, J1,2 3.7
Hz, H-1), 4.52 (dd, 1 H, J5,6 4.2, J5,6% 4.2 Hz, H-5), 4.03
(dd, J6,6% 11.7, J6,5 4.2 Hz, 1 H, H-6), 3.93 (dd, J6%,6 11.7,
J6%,5 4.2 Hz, 1 H, H-6%), 3.52 (m, 2 H, OCH2), 1.95 (bs,
exchangeable proton, 1 H, OH), 1.18 (m, 1 H, CH),
8.4,2J3,CH N 7.5 Hz, H-3), 2.54 (bs, exchangeable, 1 H,
2
OH), 1.79–1.58 (m, 8 H, 4 CH2); 13C NMR (75 MHz,
CDCl3): l 206.9 (C-4), 150.1 (C-1%), 129.3 (C-3%, C-5%),
123.3 (C-4%), 116.0 (C-2%, C-6%), 94.9 (C-1), 81.2 (C-5),
79.5 (C-2), 76.5 (OC), 60.7 (C-6), 55.2 (CH2N), 51.1
(C-3), 33.5 and 23.8 (2×CH2). Anal. Calcd for
C18H23NO5 (333.17): C, 64.84; H, 6.95; N, 4.20. Found:
C, 65.13; H, 6.97; N, 3.95.
3.4.3. Cyclohexyl a- -lyxo-hexopyranosid-(2,3:5%,4%)-2%-
D
0.60–0.20 (m,
C10H14O4·0.25 H2O (202.72): C, 59.25; H, 7.20. Found:
C, 59.34; H, 7.18.
4
H,
2
CH2). Anal. Calcd for
phenylisoxazolidin-4-ulose (4c). From 3c (0.68 g, 3
mmol); syrup, 0.53 g (62%); Rf 0.63 (9:1 CH2Cl2–
EtOAc); [h]2D5 +104.6° (c 0.4, CHCl3); IR (KBr): 3312
(w OH), 1693 cm−1 (w CꢁO); 1H NMR (300 MHz,
CDCl3): l 7.31–7.28 (m, 2 H, H-2%, H-6%, Ph-H), 7.07–
7.01 (m, 3 H, H-3%, H-4%, H-5%, Ph-H), 5.29 (s, 1 H,
H-1), 4.38 (dd, 1 H, J2,3 8.7, J2,1 1.2 Hz, H-2), 4.20
(bdd, 1 H, J5,6 3.6, J5,6% 3.6 Hz, H-5), 3.90 (m, 2 H, H-6,
H-6%), 3.79 (dd, 2 H, JCH N,3 7.5, JCH N,5 1.5 Hz,
CH2N), 3.69 (m, 1 H, OCH),2 3.38 (dt, 1 H2, J3,2 8.7, J3,7
7.5 Hz, H-3), 2.52 (bs, exchangeable, 1 H, OH), 1.95–
1.54 (m, 10 H, 5 CH2); 13C NMR (75 MHz, CDCl3): l
207.1 (C-4), 150.0 (C-1%), 129.4 (C-3%, C-5%), 123.4 (C-4%),
115.0 (C-2%, C-6%), 94.0 (C-1), 78.2 (C-5), 76.3 (C-2),
75.9 (OC), 62.6 (C-6), 56.5 (CH2N), 49.8 (C-3), 36.5,
25.8 and 24.3 (3×CH2). Anal. Calcd for C19H25NO5
(347.40): C, 65.68; H, 7.25; N, 4.03. Found: C, 66.02;
H, 7.32; N, 4.04.
3.4. General method for the preparation of 4a–d
A mixture of the phenylhydroxylamine (3 mmol) and
37% aq formaldehyde (5 mmol) in EtOH (5 mL) was
warmed to 50 °C and the appropriate enone 3a–d (3
mmol) was added. The mixture was refluxed for 1.5 h.
The progress of the reaction was monitored by TLC.
Solvent evaporation and purification of the crude
residue on silica gel column using 4:1 C6H14–AcOEt as
eluent provided 4a–d.
3.4.1. Ethyl a- -lyxo-hexopyranosid-4-(2,3:5%,4%)-2%-
D
phenylisoxazolidin-4-ulose (4a). From 3a (0.52 g, 3
mmol); syrup, 0.26 g (52%); Rf 0.61 (4:1 CHCl3–
EtOAc); [h]2D5 +54.6° (c 1, CHCl3); IR (KBr): 3450 (w
OH), 1725 cm−1 (w CꢁO); 1H NMR (300 MHz,
CDCl3): l 7.30–7.25 (m, 2 H, H-2%, H-6%, Ph-H), 7.06–
6.98 (m, 3 H, H-3%, H-4%, H-5%, PhꢀH), 5.13 (s, 1 H,
H-1), 4.42 (d, 1 H, J2,3 8.4 Hz, H-2), 4.13 (dd, 1 H, J5,6
3.3, J5,6% 3.3 Hz, H-5), 3.90 (m, 1 H, H-6), 3.79 (m, 1 H,
3.4.4.
Cyclopropylmethyl
a-D-lyxo-hexopyranosid-
(2,3:5%,4%)-2%-phenylisoxazolidin-4-ulose (4d). From 3d
(0.59 g, 3 mmol); syrup, 0.34 g (52%); Rf 0.52 (4:1
CHCl3–EtOAc); [h]2D5 +53.2° (c 0.4, CHCl3); IR
1
(KBr): 3385 (w OH), 1725 cm−1 (w CꢁO); H NMR
H-6%), 3.80 (d, 2 H, JCH N,3 7.8 Hz, CH2N), 3.70–3.64
(300 MHz, CDCl3): l 7.31–7.25 (m, 2 H, H-2%, H-6%,
Ph-H), 7.08–7.01 (m, 3 H, H-3%, H-4%, H-5%, Ph-H), 5.21
(s, 1 H, H-1), 4.46 (d, 1 H, J2,3 8.4 Hz, H-2), 4.15 (dd,
1 H, J5,6 3.6, J5,6% 3.6 Hz, H-5), 3.90–3.40 (m, 2 H, H-6,
2
(m, 2 H, OCH2), 3.39 (dt, H, J3,2 8.4, J3,CH N 7.8 Hz,
H-3), 2.67 (bs, exchangeable, 1 H, OH), 1.252 (t, 3 H, J
7.1 Hz, CH3); 13C NMR (75 MHz, CDCl3): l 206.7
(C-4), 150.0 (C-1%), 129.4 (C-3%), 123.4 (C-4%), 115.7
(C-2%), 96.9 (C-1), 77.4 (C-5), 77.0 (C-2), 76.1 (OꢀC),
64.5 (C-6), 62.7 (CH2N), 56.3 (CH2, aglycone), 51.0
(C-3), 15.1 (CH3). Anal. Calcd for C15H19NO5 (293.32):
C, 61.42; H, 6.53; N, 4.77. Found: C, 61.78; H, 6.71; N,
4.51.
H-6%), 3.81 (d, 2 H, JCH N,3 7.2 Hz, CH2N), 3.43 (m, 2
2
H, OCH2), 3.12 (dt, 1 H, J3,2 8.4, J3,CH N 7.2 Hz, H-3),
2.05 (bs, s, exchangeable, 1 H, OH), 0.920 (m, 1 H, CH),
0.60 (m, 2 H, CH2), 0.20 (m, 2 H, CH2); 13C NMR (75
MHz, CDCl3): l 205.9 (C-4), 150.3 (C-1%), 128.3 (C-3%,
C-5%), 124.3 (C-4%), 115.1 (C-2%, C-6%), 94.3 (C-1), 79.5
(C-5), 75.5 (C-2), 67.0 (C-6), 64.2 (CH2, aglycone), 63.3
(C-3), 57.4 (CH2N), 11.2 (CH), 10.9 (CH2). Anal. Calcd
for C17H21NO5 (319.36): C, 63.93; H, 6.63; N, 4.39.
Found: C, 64.13; H, 6.97; N, 3.95.
3.4.2. Cyclopentyl a- -lyxo-hexopyranosid-(2,3:5%,4%)-2%-
phenylisoxazolidin-4-ulose (4b). From 3b (0.64 g, 3
mmol); syrup, 0.68 g (76%); Rf 0.55 (4:1 CHCl3–
D

678
J.R. de Freitas Filho et al. / Carbohydrate Research 338 (2003) 673–680
3.5. General procedure for the synthesis of 7b–d
7.01 (m, 3 H, H-3%, H-4%, H-5%, Ph-H), 4.95 (bs, 1 H,
H-1), 4.14 (bs, 1 H, H-2), 3.94 (d, 2 H, J5,6 3.6 Hz, H-6,
H-6%), 3.78 (bs, 1 H, H-4), 3.76 (m, 1 H, H-5), 3.62 (dd,
The appropriate isoxazolidine 4b–d (0.75 mmol) in
EtOAc (10 mL) containing 20 mg of PtO2 was hydro-
genated at 152 kPa for 4 h. Filtration of the catalyst
followed by removal of the solvent under diminished
pressure gave a product that was promptly chro-
matographed over a silica gel column using 1:1 C6H14–
EtOAc as the eluent.
1 H, JH,H 13.5, JCH N,3 6.3 Hz, CH2N), 3.48 (dd, 1 H,
2
JH,H 13.5, JCH N,3 8.1 Hz, CH2N), 3.36 (dd, 2 H, J 11.1,
J 6.6 Hz, OC2H2), 2.23 (m, 1 H, H-3), 2.23 (bs, 1 H,
OH), 1.05 (m, 1 H, CH), 0.51 (m, 2 H, CH2), 0.20 (m,
2 H, CH2); 13C NMR (75 MHz, CDCl3): l 149.3 (C-1%),
128.7 (C-3%, C-5%), 117.3 (C-4%), 114.1 (C-2%, C-6%), 98.7
(C-1), 79.5 (C-5), 75.5 (C-2), 67.4 (C-6), 64.5 (CH2,
aglycone), 62.8 (C-3), 46.2 (CH2N), 12.1 (CH), 10.1
(CH2). Anal. Calcd for C17H25NO5 (323.38): C, 63.14;
H, 7.79; N, 4.33. Found: C, 63.60; H, 7.97; N, 4.32.
3.5.1. Cyclopentyl 3-deoxy-3-N-phenylaminomethyl-a-D-
talopyranoside (7b). From 4b (0.25 g, 0.75 mmol);
syrup, 0.21 g (86%); Rf 0.42 ( 8.5:1:0.5 CH2Cl2–
EtOAc–MeOH); [h]D25 +84° (c 0.3, CH2Cl2); IR (KBr):
1
3467 (w OH), 1603 cm−1 (bend NꢀH); H NMR (300
3.6. General procedure for the preparation of 3-deoxy-
3-(N-acetyl-N-phenylaminomethyl)-2,4,6-tri-O-acetyl-
a-D-talopyranosides (8b–d)
MHz, CDCl3): l 7.42–7.26 (m, 2 H, H-2%, H-6%, Ph-H),
7.15–7.00 (m, 3 H, H-3%, H-4%, H-5%, Ph-H), 4.95 (d, 1
H, J1,2 1.3 Hz, H-1), 4.22 (m, 1 H, OCH), 4.12 (bs, 1 H,
H-2), 3.96 (d, J6,5 3.3 Hz, 2 H, H-6, H-6%), 3.74 (t, 1 H,
J5.6 3.0 Hz, H-5), 3.65 (bs, 1 H, H-4), 3.44 (dd, 1 H,
The appropriate compound 7b–d (0.42 mmol) was dis-
solved in dry Py (2 mL) and the solution cooled to
0 °C. Acetic anhydride (1.5 mL) was added and the
contents left under stirring overnight. A single spot was
observed on the TLC plate as detected under UV light.
Evaporation of the solvent left a syrup that was quickly
passed through a silica gel column using 7:3 C6H14–
EtOAc as the eluent in order to purify the material.
JH,H 13.5, JCH N%,3 6.3 Hz, CH2N), 3.42 (dd, 1 H, JH,H
2
13.5, JCH N,3 8.1 Hz, CH2N), 2.13 (m, 1 H, H-3), 2.13
(bs, 1 H,2OH), 1.77–1.52 (m, 8 H, 4 CH2); 13C NMR
(75 MHz, CDCl3): l 148.5 (C-1%), 129.7 (C-3%, C-5%),
117.9 (C-4%), 113.4 (C-2%, C-6%), 99.7 (C-1), 79.2 (C-5),
70.4 (OCH), 70.3 (C-2), 69.9 (C-4), 65.3 (C-6), 42.8
(CH2N), 37.4 (C-3), 33.5 and 23.9 (CH2, aglycone).
Anal. Calcd for C18H27NO5 (337.41): C, 64.07; H, 8.06;
N, 4.15. Found: C, 63.83; H, 8.42; N, 3.86.
3.6.1. Cyclopentyl 3-deoxy-2,4,6-tri-O-acetyl-3-N-ace-
tyl-phenylaminomethyl-a-D-talopyranoside (8b). From 7b
(0.14 g, 0.42 mmol); syrup, 0.12 g (82%); Rf 0.37 (4:1
CHCl3–EtOAc); [h]2D5 +42.1° (c 0.38, CH2Cl2); IR
(KBr): 1742 cm−1 (w OAc); 1H NMR (300 MHz,
CDCl3): l 7.42–7.26 (m, 2 H, H-2%, H-6%, Ph-H), 7.15–
7.00 (m, 3 H, H-3%, H-4%, H-5%, Ph-H), 5.03 (bs, 1 H,
H-2), 4.88 (bs, 1 H, H-1), 4.70 (bs, 1 H, H-4), 4.18–3.96
(m, 4 H, H-5, H-6, H-6%, OCH), 4.07 (dd, 1 H, JH,H
13.8, JCH N,3 5.7 Hz, CH2N), 3.52 (dd, 1 H, JH,H 13.8,
3.5.2. Cyclohexyl 3-deoxy-3-N-phenylaminomethyl-a-D-
talopyranoside (7c). From 4c (0.26 g, 0.75 mmol); syrup,
0.2 g (78%); Rf 0.47 ( 8.5:1:0.5 CH2Cl2–EtOAc–
MeOH); [h]2D5 +82.1° (c 0.79, CH2Cl2); IR (KBr): 3407
1
(w OH), 1603 cm−1 (bend NꢀH); H NMR (300 MHz,
CDCl3): l 7.21–7.15 (m, 2 H, H-2%, H-6%, Ph-H), 6.73–
6.66 (m, 3 H, H-3%, H-4%, H-5%, Ph-H), 5.03 (bs, 1 H, J1,2
1.5 Hz, H-1), 4.11 (bs, 1 H, H-2), 3.93 (d, 2 H, J5,6 3.6
Hz, H-6, H-6%), 3.78 (t, 1 H, J5.6 3.6 Hz, H-5), 3.67 (bs,
1 H, H-4), 3.60 (m, 1 H, OCH), 3.55 (dd, 1 H, JH,H
JCH N,3 6.26 Hz, CH2N), 2.35 (m, 1 H, H-3), 2.13 (s, 3 H,
2
Ac), 2.05 (s, 3 H, Ac), 2.02 (s, 3 H, Ac), 1.78 (s, 3 H,
NAc), 1.68–1.53 (m, 8 H, 4 CH2); 13C NMR (75 MHz,
CDCl3): l 171.3, 171.0, 170.6 (3 C, CO2), 167.3 (NCO),
148.5 (C-1%), 129.3 (C-3%, C-5%), 123.1 (C-4%), 115.4 (C-2%,
C-6%), 89.0 (C-1), 79.2 (C-5), 75.1 (OCH), 73.8 (C-2),
71.0 (C-4), 68.3 (C-6), 42.3 (CH2N), 32.8 (C-3), 31.1
and 22.3 ( CH2, aglycone), 20.1 (4×CH3). Anal. Calcd
for C26H35NO9 (505.56): C, 61.77; H, 6.98; N, 2.77.
Found: C, 61.81; H, 7.16; N, 2.86.
13.5, JCH N,3 6.3 Hz, CH2N), 3.42 (dd, 1 H, JH,H 13.5,
2
JCH N,3 8.1 Hz, CH2N), 2.29 (bs, 1 H, OH), 2.16 (m, 1
2
H, H-3), 1.88–1.20 (m, 10 H, 5 CH2); 13C NMR (75
MHz, CDCl3): l 152.7 (C-1%), 129.3 (C-3%, C-5%), 122.1
(C-4%), 114.2 (C-2%, C-6%), 98.8 (C-1), 75.5 (C-5), 70.4
(OCH), 69.8 (C-2), 69.6 (C-4), 64.8 (C-6), 42.6 (CH2N),
37.3 (C-3), 31.9, 24.3 and 21.4 (CH2, aglycone). Anal.
Calcd for C19H29NO5 (351.44): C, 64.93; H, 8.32; N,
3.98. Found: C, 64.84; H, 8.34; N, 3.64.
3.6.2. Cyclohexyl 3-deoxy-2,4,6-tri-O-acetyl-3-N-acetyl-
phenylaminomethyl-a-D-talopyranoside (8c). From 7c
3.5.3. Cyclopropylmethyl 3-deoxy-3-phenylaminomethyl-
a-
D
-talopyranoside (7d). From 4d (0.24g, 0.75 mmol);
(0.15 g, 0.42 mmol); syrup, 0.12 g (85%); Rf 0.40 (9:1
CH2Cl2–EtOAc); [h]2D5 +36° (c 0.5, CH2Cl2); IR
(KBr): 1745 cm−1 (w OAc); 1H NMR (300 MHz,
CDCl3): l 7.21–7.15 (m, 2 H, H-2%, H-6%, Ph-H), 6.73–
6.66 (m, 3 H, H-3%, H-4%, H-5%, Ph-H), 5.03 (bs, 1 H,
syrup, 0.18 g (75%); Rf 0.44 (8.5:1:0.5 CH2Cl2–EtOAc–
MeOH); [h]2D5 +70.2° (c 0.9, CHCl3); IR (KBr): 3383 (w
OH), 1603 cm−1 (bend NꢀH); H NMR (300 MHz,
1
CDCl3): l 7.31–7.25 (m, 2 H, H-2%, H-6%, Ph-H), 7.08–

J.R. de Freitas Filho et al. / Carbohydrate Research 338 (2003) 673–680
679
H-2), 4.88 (bs, 1 H, H-1), 4.72 (d, 1 H, J 2.4 Hz, H-4),
4.18–3.94 (m, 4 H, H-5, H-6, H-6%, OCH, CH2N), 3.56
7.9 Hz, 2 H, CH2N), 3.18 (t, J3,CH N 8.7 Hz, 1 H, H-3),
2
2.19 (s, 3 H, CH3), 1.79–1.58 (m, 8 H, 4 CH2); 13C
NMR (75 MHz, CDCl3): l 205.0 (C-4), 169.7 (CO2),
152.0 (C-1%), 129.4 (C-3%, C-5%), 128.7 (C-4%), 116.0 (C-2%,
C-6%), 96.7 (C-1), 81.3 (C-5), 78.5 (C-2), 77.0 (OCH),
59.3 (C-6), 51.1 (CH2N), 41.0 (C-3), 33.5 and 238 (CH2,
aglycone), 21.1 (CH3). Anal. Calcd for C20H25NO6
(375.22): C, 63.98; H, 6.71; N, 3.73. Found: C, 64.18;
H, 6.92; N, 3.87.
(dd, 1 H, JH,H 13.5, JCH N,3 5.7 Hz, CH2N), 2.38 (s, 1
2
H, H-3), 2.13 (s, 3 H, Ac), 2.05 (s, 3 H, Ac), 2.01 (s, 3
H, Ac) 1.78 (s, 3 H, NAc), 1.83–1.21 (m, 10 H, 5 CH2);
13C NMR (75 MHz, CDCl3): l 170.4, 170.2, 169.7 (3 C,
CO2), 166.0 (NAc), 152.7 (C-1%), 129.1 (C-3%), 121.4
(C-4%), 114.3 (C-2%), 96.9 (C-1), 76 (C-2), 74.5 (C-5), 66.4
(OCH), 65.0 (C-6), 63.7 (C-4), 41.3 (CH2N), 33.7 (C-3),
31.8, 26.0 and 24.6 (CH2, aglycone), 20.7 (4×CH3).
Anal. Calcd for C27H37NO9 (519.59): C, 62.41; H, 7.17;
N, 2.69. Found: C, 62.50; H, 7.36; N, 2.35.
3.6.5. Cyclopentyl 6-O-tert-butyldimethylsilyl-a- -lyxo-
D
hexopyranosid-(2,3:5%,4%)-2%-phenylisoxazolidin-4-ulose
(6b). Compound 4b (0.2 g, 6 mmol) was dissolved in
DMF (2 mL) and the solution cooled to 0 °C. Imida-
zole (0.13 g, 1.97 mmol) and TBDMSiCl (0.15 g, 0.46
mmol) was added. The mixture was stirred at rt for 22
h. TLC in 9:1 CH2Cl2–EtOAc showed a new product
with Rf 0.68. The mixture was extracted with petroleum
ether (3×20 mL), the organic solution was washed
with water (2×20 mL), then with a saturated aq soln
of NaCl (2×20 mL), and dried over Na2SO4. Fitration
and solvent removal under reduced pressure gave a
viscous material which was chromatographed over sil-
ica gel using initially petroleum ether (40–60 °C), fol-
lowed by petroleum ether–EtOAc (9:1) as the eluent to
give 6b (0.21 g, 78%) as a semisolid; [h]2D5 −125° (c 1,
CHCl3); IR (KBr): 1745 (w CꢁO), 1060 cm−1 (w CꢀO);
1H NMR (300 MHz, CDCl3): l 7.31–7.26 (m, 2 H,
H-2%, H-6%, Ph-H), 7.08–7.00 (m, 3 H, H-3%, H-4%, H-5%,
PhꢀH), 5.16 (s, 1 H, H-1), 4.37 (d, 1 H, J2,3 8.9 Hz,
H-2), 4.30 (m, 1 H, OCH), 4.14 (dd, 1 H, J5,6 3.6, J5,6%
2.3 Hz, H-5), 4.07 (dd, 1 H, JH,H 10.9, J6,5 3.6 Hz, H-6),
3.93 (dd, 1 H, JH,H 10.9, J6,5 2.3 Hz, H-6%), 3.90-3.8 (bd,
3.6.3. Cyclopropylmethyl 3-deoxy-2,4,6-tri-O-acetyl-N-
acetyl-N-phenylaminomethyl-a-
D-talopyranoside
(8d).
From 7d (0.14 g, 0.42 mmol); syrup, 0.11 g (83%); Rf
0.39 (4:1 CHCl3–EtOAc); [h]2D5 +38.7° (c 0.4, CHCl3);
1
IR (KBr): 1740 cm−1 (w OAc); H NMR (300 MHz,
CDCl3): l 7.31–7.25 (m, 2 H, H-2%, H-6%), 7.08–7.01
(m, 3 H, H-3%, H-4%, H-5%), 5.08 (bs, 1 H, H-2), 4.90 (bs,
1H, H-1), 4.80 (d, 1 H, J 2.7 Hz, H-4), 4.17 (m, 3 H,
H-5, H-6 and H-6%), 3.71 (dd, 2 H, J 6.0, J 10.8 Hz,
CH2O), 3.52 (dd, 1 H, JH,H 10.8, JCH N,3 8.4 Hz,
2
CH2N), 3.44 (dd, 1 H, JH,H 10.8, JCH N,3 7.2 Hz,
2
CH2N), 2.44 (m, 1 H, H-3), 2.14 (s, 3 H, Ac), 2.04 (s, 3
H, Ac), 2.02 (s, 3 H, Ac), 1.79 (s, 3 H, NAc), 1.02 (m,
1, CH), 0.52 (m, 2 H, CH2), 0.19 (m, 2 H, CH2); 13C
NMR (75 MHz, CDCl3): l 170.3, 170.0, 169.6 (3 C,
CO2), 167.1 (NAc), 147.5 (C-1%), 131.3 (C-3%, C-5%),
125.2 (C-4%), 113.4 (C-2%, C-6%), 91.2 (C-1), 79.5 (C-5),
75.5 (C-2), 67.4 (C-6), 63.7 (C-4), 63.5 (CH2, aglycone),
61.8 (C-3), 41.3 (CH2N), 16.5 (CH3), 12.3 (CH), 10.3
(CH2). Anal. Calcd for C25H33NO9·0.5 H2O (500.52): C,
59.98; H, 6.84; N, 2.79. Found: C, 59.69; H, 6.71; N,
3.08.
JCH N,3 10.9 Hz, 2 H, CH2N), 3.28 (dt, 1 H, J3,2 8.9, J3,7
2
10.9 Hz, H-3), 1.75–1.58 (m, 8 H, 4 CH2), 0.90 (s, 9 H,
CMe3), 0.09 (s, 6 H, SiCH3); 13C NMR (75 MHz,
CDCl3): l 206.5 (CꢁO), 150.4 (C-1%), 129.3 (C-3%, C-5%),
123.1 (C-4‘), 115.6 (C-2%, C-6%), 95.6 (C-1), 81.3 (C-5),
79.2 (C-2), 76.9 (O-C), 63.4 (C-6), 55.9 (CH2N), 53.2
(C-3), 33.6 (2 CH2), 23.9 (2 CH2), 26.2 (CH3)3CSi), 23.6
(CH3)3, −4.92 and −5.08 (CH3Si). Anal. Calcd for
C24H37NO5Si (447.65): C, 64.39; H, 8.33; N, 3.12.
Found: C, 64.13; H, 8.14; N, 2.93.
3.6.4. Cyclopentyl 6-O-acetyl-a- -lyxo-hexopyranosid-
D
(2,3:5%,4%)-2%-phenylisoxazolidin-4-ulose (5b). Compound
4b (0.2 g, 6 mmol) was dissolved in dry Py (10 mL) and
the solution cooled to 0 °C. Acetic anhydride (1.5 mL)
was added and the contents left under stirring
overnight. A single spot was observed by TLC (9:1
CH2Cl2–EtOAc) having a Rf value of 0.58. Evapora-
tion of the solvent left a syrup which was quickly
passed through a silica gel column using petroleum
ether (40–60 °C) as the eluent. Solvent evaporation
provided 5b as a colorless syrup (0.2 g, 87%). Recrystal-
ization from n-C6H14–EtOAc gave 5b (95 mg, 41%).
Mp 110–111 °C; [h]D25 +10.8° (c 0.5, CHCl3); IR
Acknowledgements
One of us (J.R.d.F.F.) is thankful to the Brazilian
National Research Council (CNPq) for a fellowship.
We are grateful to CAPES-COFECUB and CNPq for
financial assistance. We also thank Professor T. Brock-
som, Chemistry Department, Federal University of Sa˜o
Carlos for allowing his technician, Antoˆnio Pinto
Loureiro Filho, to measure the specific rotations of
compounds 4b–c, 7a–c and 8a–b, and to Wagner de
Mendonc¸a Faustino for his help in performing the
molecular orbital calculations.
1
(KBr): 1745 (w OAc), 1695 cm−1 (w CꢁO); H NMR
(300 MHz, CDCl3): l 7.31–7.21 (m, 2 H, H-2%, H-6%,
Ph-H), 7.08–7.00 (m, 3 H, H-3%, H-4%, H-5%, PhꢀH),
5.07 (s, 1 H, H-1), 4.63 (d, 1 H, J3,2 9.8 Hz, H-2), 4.05
(dd, 1 H, J5,6 3.8, J5,6% 2.4 Hz, H-5), 4.22 (m, 1 H,
OCH), 3.99 (dd, 1 H, J6,6% 10.9, J6,5 3.8 Hz, H-6), 3.85
(dd, 1 H, J6%,6 10.9, J6%,5 2.4 Hz, H-6%), 3.76 (b, JCH N,3
2

680
J.R. de Freitas Filho et al. / Carbohydrate Research 338 (2003) 673–680
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