Branched-chain fluoro nitro D- and L-sugars from glucose

Article abstract of DOI:10.1016/S0957-4166(99)00156-1

Mixed crystals of methyl 3-deoxy-3-C-methyl-3-nitro-α-D- and β-L- glucopyranosides (1:1), easily available from D-glucose by means of the Baer reaction, were completely characterised by X-ray diffraction analysis. These diastereomeric components, separation of which could be achieved through their 4,6-O-benzylidene derivatives, were selectively fluorinated at position 6 by treatment with DAST and stereoselectively transformed into phenyl 3- deoxy-3-C-methyl-3-nitro-1-thio-β-D-glucopyranoside and phenyl 3-deoxy-3-C- methyl-3-nitro-1-thio-β-L-glucopyranoside, respectively. Fluorination with DAST of each pure enantiomer afforded, depending on the conditions, the corresponding enantiomeric phenyl 3,6-dideoxy-6-fluoro-3-C-methyl-3-nitro-1- thio-β-D- and β-L-glucopyranosides or the respective rearranged 2,3,6- trideoxy-6-fluoro-3-C-methyl-3-nitro-2-phenylthio-α-D- and α-L- mannopyranosyl fluorides. This route constitutes a simple method for obtaining fair-to-good yields of 6-fluorinated branched-chain D- and L-sugar derivatives, potentially useful as glycosyl donors, starting from D-glucose.

Full text of DOI:10.1016/S0957-4166(99)00156-1

Pergamon
Tetrahedron: Asymmetry 10 (1999) 1751–1764
Branched-chain fluoro nitro D- and L-sugars from glucose
Ana T. Carmona,a Pastora Borrachero,a Francisca Cabrera-Escribano,a,∗ Mp Jesús Diánez,b
Mp Dolores Estrada,b Amparo López-Castro,b Rafael Ojeda,a Manuel Gómez-Guillén a and
Simeón Pérez-Garrido b
aDepartamento de Química Orgánica ‘Profesor García González’, Facultad de Química, Universidad de Sevilla, Apartado de
Correos No. 553, E-41071 Seville, Spain
bInstituto de Ciencias de Materiales de Sevilla and Departamento de Física de la Materia Condensada, C.S.I.C.-Universidad
de Sevilla, Apartado de Correos No. 1065, E-41080 Seville, Spain
Received 12 April 1999; accepted 22 April 1999
Abstract
Mixed crystals of methyl 3-deoxy-3-C-methyl-3-nitro-α-D- and β-L-glucopyranosides (1:1), easily available
from D-glucose by means of the Baer reaction, were completely characterised by X-ray diffraction analysis.
These diastereomeric components, separation of which could be achieved through their 4,6-O-benzylidene de-
rivatives, were selectively fluorinated at position 6 by treatment with DAST and stereoselectively transformed
into phenyl 3-deoxy-3-C-methyl-3-nitro-1-thio-β-D-glucopyranoside and phenyl 3-deoxy-3-C-methyl-3-nitro-1-
thio-β-L-glucopyranoside, respectively. Fluorination with DAST of each pure enantiomer afforded, depending on
the conditions, the corresponding enantiomeric phenyl 3,6-dideoxy-6-fluoro-3-C-methyl-3-nitro-1-thio-β-D- and
β-L-glucopyranosides or the respective rearranged 2,3,6-trideoxy-6-fluoro-3-C-methyl-3-nitro-2-phenylthio-α-D-
and α-L-mannopyranosyl fluorides. This route constitutes a simple method for obtaining fair-to-good yields of
6-fluorinated branched-chain D- and L-sugar derivatives, potentially useful as glycosyl donors, starting from D-
glucose. © 1999 Elsevier Science Ltd. All rights reserved.
1. Introduction
Diverse branched-chain nitro sugars are constituents of glycosidic antibiotics.1 D-Rubranitrose 1 and
L-evernitrose 2, the sugar moieties of rubradirin and everninomicin, respectively, are representative
examples of the D- and L-series of sugars, for which various syntheses have been reported.2,3 There has
been an increased interest in fluoro sugars in the last two decades.4–7 This may be attributed in part to the
observation that the glycosidic bond of pharmacologically active glycosides and nucleosides is reinforced
by the introduction of a fluorine atom at certain positions of the sugar moiety, a feature that consequently
∗
Corresponding author. Tel: +34 95 4557150; fax: +34 95 4624960; e-mail: fcabrera@cica.es
0957-4166/99/$ - see front matter © 1999 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(99)00156-1

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A. T. Carmona et al. / Tetrahedron: Asymmetry 10 (1999) 1751–1764
enhances their therapeutic effect.8,9 Biologically active fluoro sugar derivatives of both D-series10 and
L-series, for example 2-deoxy-2,2-difluoro-L-ribofuranosyl adenine,11 have been synthesised. The utility
of glycosyl fluorides as glycosyl donors in the synthesis of glycosides, oligosaccharides and nucleosides
is well established.7,12,13 Moreover, when a phenylthio group is located at the 2 position of this glycosyl
donor, a good stereocontrol in the formation of the glycoside bond can be achieved,14 with subsequent
reductive desulphuration of the product affording the corresponding 2-deoxy-glycosidic compound.14
On the other hand, phenyl 1-thioglycosides are quite versatile intermediates in oligosaccharide synthesis
because of their possible usage as glycosyl donors, as well as glycosyl acceptors, particularly in the
Nicolaou two-stage procedure for glycoside bond formation.13 In this paper we propose the synthesis
of 6-fluorinated branched-chain nitro sugars having a fluorine atom or a phenylthio group at the
anomeric position, or rearranged 2-phenylthio-glycosyl fluorides, which might be used as synthons for
pharmaceuticals of enhanced activity. The proposed methodology for obtaining this kind of compound
involves the selective fluorination of nitro sugars having several free OH groups by diethylaminosulphur
trifluoride (DAST),4,15 which in most cases occurs with inversion of configuration (SN2 mechanism).
Taking advantage of the easy access to sugars of D- or L-configurations starting from D-glucose by means
of the Baer reaction,16 the synthesis of new D- and L-branched-chain fluoro nitro monosaccharides was
carried out, and is reported herein.
2. Results and discussion
Complete characterisation of the crystalline product obtained in the Baer reaction of dialdehyde 3
with nitroethane (Scheme 1) was achieved. Baer had concluded16 that this product was an equimolecular
mixture of an α-D- and a β-L-gluco-(or allo-)hexopyranosides, but no configurational assignment for
C-3 was made. We could carry out the X-ray diffraction analysis of the crystals, thus elucidating
the absolute configuration of the nitro-substituted centre (C-3). A perspective PLATON17 view of the
asymmetric unit enclosing one molecule of each of the two isomers, methyl 3-deoxy-3-C-methyl-3-
nitro-α-D-gluco-hexopyranoside 4 and methyl 3-deoxy-3-C-methyl-3-nitro-β-L-gluco-hexopyranoside
5, is given in Fig. 1, where the atomic numbering scheme is also shown. The crystal cohesion is governed
by intra- and intermolecular H-bonds (Fig. 2), the two molecules being connected by a complex system
of H-bonds forming a three-dimensional network which stabilises the crystal structure. To separate the
mixture, it was treated with benzaldehyde–zinc chloride to afford a mixture of the respective 4,6-O-
benzylidene derivatives 6 and 7, which could be separated by column chromatography to yield 36% of
6 and 35% of 7; alternatively, the use of benzaldehyde dimethylacetal in N,N-dimethylformamide led,
after chromatography, to 42% of 6 and 47% of 7. Separate treatment of 6 and 7 with p-toluenesulphonic
acid in methanol–dioxane quantitatively yielded the respective deprotected methyl glycosides 4 and
5. From these two pairs of separated branched-chain nitro sugars we carried out diverse parallel
transformations focused on the preparation of novel fluoro and phenylthio-fluoro derivatives belonging
to the D- or L-series of monosaccharides. First, 4 and 5 were separately treated with the DAST reagent in
dichloromethane at −35°C; under these conditions, the reaction proceeded regioselectively on position 6,
to give only the respective 6-monofluoro derivative in good yield (77% of 8 and 64% of 9, respectively,
after column chromatography), which is a model for more complex branched-chain glycosides with

A. T. Carmona et al. / Tetrahedron: Asymmetry 10 (1999) 1751–1764
1753
enhanced resistance to chemical and enzymatic cleavage. Application of the method of Hanessian and
Guindon18 for preparing phenyl 1-thioglycosides to each pure benzylidene compound (6, 7) provoked
its debenzylidenation and stereoselectively led, after a first purification by column chromatography, to a
1:4 α/β mixture of the branched-chain phenyl 1-thioglycosides 10 and 11 (67% from 6) or 12 and 13
(64% from 7). The mixtures were resolved by preparative thin-layer chromatography on silica gel. The
pure β enantiomers 11 and 13 were then separately allowed to react with DAST to give monofluoro and
difluoro sugars having the phenylthio group at position 1 or 2. Thus, starting from 11, treatment at −30°C
for 3 h [(A) conditions] yielded 42% of the 6-deoxy-6-fluoro-1-thio-β-D-gluco-hexopyranosyl derivative
14 and 11% of unreacted 11, while the rearranged 1,6-di- and 1-monofluoro-2-phenylthio-α-D-manno-
hexopyranosyl derivatives 16 and 18 were obtained in 60% and 10% yields, respectively, by treatment
of 11 first at −35°C and then allowing the reaction mixture to rise to room temperature for 90 min [(B)
conditions]. Starting from 13, under (A) conditions the 6-fluoro-1-thio sugar 15, enantiomer of 14, was
isolated in 68% yield, whereas under (B) conditions the reaction led to the 1,6-difluoro sugar 17 (58%)
and the sugar fluoride 19 (15%), enantiomers of 16 and 18, respectively.
With regard to the characterisation of the new compounds, the elemental analyses and/or the high-
resolution mass spectra were in agreement with the respective molecular formulae; all the compounds
were optically active and the characteristic IR bands confirmed the presence of the nitro group and other
functional groups in each particular case. The assignment of anomeric configuration was straightforward
for the gluco-configured compounds (4–15); thus, the 1H NMR spectra of all the α-D-gluco-isomers (4, 6,
8, and 10) and the α-L-gluco-isomer 12 showed H-1/H-2 coupling constants of lower value (4.3–6.3 Hz)
than those of their respective β-L-gluco-isomers (5, 7, 9, 13) and the β-D-gluco-isomer 11 (7.5–10.0
Hz), as expected. The presence of one fluorine atom at C-6 of the methyl glycosides 8 and 9 was
1
evidenced by the following data: (i) the H–19F coupling constant values, measured on the H-6 and
H-60 signals (each of them ddd), are 47.3 and 47.6 Hz, in agreement with a geminal-fluorine atom;19 (ii)
the C-6 signal in the 13C NMR spectrum is a doublet, the high values of the coupling constant (172.2
1
and 176 Hz) corresponding19 to a J (13C–19F). Also in agreement with that expected, the anomeric
proton of the enantiomeric phenyl 6-fluoro-1-thio-β-D- and -β-L-gluco-pyranosides 14 and 15 gave rise
to a doublet showing the value 9.9 Hz for the H-1/H-2 coupling. For these enantiomers 14 and 15, the
1H–19F coupling constant values (47.5 and 47.2 Hz), measured on the H-6 and H-60 signals (each of
1
them ddd), as well as the high value (176 Hz) of the coupling constant J (13C–19F), measured at the
C-6 signal, evidenced the fluorine substituent at this position; moreover, their preferred conformation in
chloroformic solution is that which has the fluorine atom and the H-5 in the anti-periplanar disposition, as
shown by the corresponding coupling constant value (24.8 Hz), in the range 21–30 Hz observed for other
pyranose derivatives.19 The α-anomeric configuration was assigned for the D- and L-manno-pyranosyl
1
fluorides 16–19, also on the basis of H–19F or 13C–19F coupling constants;19 thus, the presence of
one fluorine atom at position 1 is shown by the coupling constant (233.8, 233.4 Hz) observed for C-1,
1
and by the anomeric proton signal, which is now a double doublet with a high-value H–19F geminal-
coupling constant (53.2, 53.3 Hz). The low-value H-1/H-2 coupling constant (1.3 Hz) agrees with a trans-
diequatorial relationship, corroborated by the absence of splitting of the C-3 signal [3J (13C–19F)≈0 Hz],
indicative of a syn-relationship between C-3 and F around the C-2/C-1 bond. Interestingly, the methyl
5
4
proton signal and the methyl carbon signal appear as doublets with J (1H–19F) 2.3 and J (13C–19F)
7.8–7.6 Hz, respectively, similar to those found for a related compound also showing the 1-fluoro-3-
methyl-syn-diaxial pattern.20 NOE experiments (1D NOESY), carried out for 17, showed contacts of the
methyl group with H-2 and H-5, but not with H-1, a fact congruent only with the α-anomer. The second
fluorine atom of 16 and 17 is located at C-6, as shown by the splitting of the H-6 and H-60 signals (each

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A. T. Carmona et al. / Tetrahedron: Asymmetry 10 (1999) 1751–1764
Scheme 1.
of them ddd) and the C-6 one (d), and the corresponding coupling constant values, as in the case of 8, 9,
14 and 15.
The formation of compounds 16–19 can be considered a new case of the known 1,2-rearrangement
that occurs in the fluorination of related sugars,14,20,21 and therefore may be explained in terms of a
mechanism similar to that proposed by other authors.22,23

A. T. Carmona et al. / Tetrahedron: Asymmetry 10 (1999) 1751–1764
1755
Figure 1. A PLATON view of the unit cell of the mixed crystal of 4 and 5 along the z-axis
Figure 2. A perspective PLUTON drawing of the packing arrangement viewed along the y-axis, with dashed lines indicating
H-bonds

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A. T. Carmona et al. / Tetrahedron: Asymmetry 10 (1999) 1751–1764
2.1. X-Ray structure analysis of 1:1 mixed crystals of 4+5
A perspective PLATON view17 of the asymmetric unit (two molecules: 4 and 5) in the solid
state, showing the relative configuration and the atomic numbering scheme, is given in Fig. 1.
Bond lengths and torsion angles are shown in Table 1. The pyranose endocyclic bond lengths
O5–C1=1.409(3) Å and O5–C5=1.429(3) Å, and O50–C10=1.419(3) Å and O50–C50=1.429(3) Å shows
the characteristic anomeric effects. The two α-D- and β-L-pyranose rings show chair conformations,
1
4C1 and C4, respectively, with Cremer and Pople24 parameters: θ=172(1)°, Q=0.57(2) Å, ϕ=−23(2)°,
and θ0=7(1)°, Q0=0.60(2) Å, ϕ0=−0.36(2)°, and Nardelli25 asymmetry parameters: ∆Cs[C1]=0.014,
∆C2[C1–O5]=0.008, and ∆Cs[C10]=0.024, ∆C2[C10–O50]=0.036, respectively. For the α-D-pyranose
molecule, the substituents O1 and C31 are in axial positions and the O2, N3, O4, and C6 in equatorial
positions. For the β-L-molecule, the substituents O10, O20, N30, O40, and C60 are in equatorial and the
C310 in axial position. The crystal cohesion is governed by intra- and intermolecular H-bonds (Fig. 2
and Table 2). The α-D- and β-L-molecules are linked to each other by two oxygen–oxygen H-bonds;
moreover, they are connected by a complicated system of H-bonds forming a three-dimensional network
which stabilises the crystal structure.
3. Conclusion
In conclusion, the described chemical transformations constitute a convenient route to 6-fluorinated
branched-chain D- and L-sugar derivatives starting from D-glucose. In particular, the methyl glycosides 6
and 7, the phenyl 1-thioglycosides 14 and 15, and the glycosyl fluorides 16 and 17 (the latter two carrying
a phenylthio group at C-2), were prepared in fair-to-good yields. It is noteworthy that the application
of the Hanessian and Guindon procedure to the methyl glycosides 6 (α-D) and 7 (β-L) preferentially
afforded, in both cases, the β-anomer [D (11) and L (13)], thus opening access to enantiomeric pairs
of derivatives (14/15, 16/17, 18/19). These findings are expected to enhance the availability of fluoro
nitro branched-chain sugars, directly useful as synthons for pharmaceuticals through stereocontrolled
glycosidation processes.
Extension of this methodology and its application to the synthesis of oligosaccharides and nucleosides
of potential biological activity, especially 2-deoxy glycosides structurally related to compounds 1 and 2,
are in progress.
4. Experimental
4.1. General
TLC was performed on silica gel 60 plates (DC-Alufolien F254, E. Merck, or Alugram Sil G/UV254
,
Macherey–Nagel), and preparative TLC on Kieselgel 60 F254 DC-Platten 105715 HR, with detection
by UV light (254 nm) or by charring with H2SO4. Silica gel 60 (E. Merck) was used for column
chromatography. Solutions were concentrated under diminished pressure at <40°C. Optical rotations
were measured with a Perkin–Elmer 241 MC polarimeter. IR spectra (films or films on KBr discs)
1
were recorded with an FTIR Bomem Michelson MB-120 spectrophotometer. H NMR spectra (500
or 300 MHz) and 13C NMR spectra (125.7 or 75.5 MHz) were recorded with a Bruker AMX-500
or a Bruker AMX-300 spectrometer. Assignments were confirmed by decoupling and/or homonuclear

A. T. Carmona et al. / Tetrahedron: Asymmetry 10 (1999) 1751–1764
1757
Table 1
Bond distances (Å) and torsion angles (°) for 4+5

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A. T. Carmona et al. / Tetrahedron: Asymmetry 10 (1999) 1751–1764
Table 2
Hydrogen-bonding geometry
2D COSY, 1D NOESY, and heteronuclear 2D correlated (HETCOR) experiments. HR-EI mass spectra
(70 eV) were measured with a Kratos MS-80RFA instrument, with an ionising current of 100 mA, an
accelerating voltage of 4 kV, and a resolution of 10 000 (10% valley definition). Fast-atom bombardment
mass spectrometry (FABMS) was performed on the same instrument; ions were produced by a beam of
xenon atoms (6–7 keV) using a matrix consisting of m-nitrobenzyl alcohol or thioglycerol and NaI as salt.
FAB-HRMS was performed on a VG Autospec spectrometer (Fisons Instruments) (30 keV). Desorption
chemical ionisation (DCI) HRMS (methane) was performed on an AutospecQ instrument (Micromass).
4.2. Preparation of mixed crystals of methyl 3-deoxy-3-C-methyl-3-nitro-α-D-glucopyranoside 4 and
methyl 3-deoxy-3-C-methyl-3-nitro-β-L-glucopyranoside 516
Nitroethane (2.7 mL, 3.00 g, 0.04 mol) and abs. methanol (37.5 mL) were added to a sample of crude
dialdehyde 3 obtained by quantitative oxidation of methyl α-D-glucopyranoside (7.74 g, 0.04 mol).26
After 3 was totally dissolved, 1.3 M methanolic NaOMe (29 mL) was gradually added, the mixture was
kept at room temperature for 3 h and water (50 mL) was then added. Sodium ions were exchanged by
shaking the mixture with Amberlite IR-120 H resin until pH≈5. The resin was filtered off and washed
with distilled water. The filtrate and washings were joined and concentrated at reduced pressure, and the
residue was coevaporated with abs. ethanol (3×20 mL). Addition of a final amount of abs. ethanol (25
mL) to the dry residue and cooling at 5°C afforded, after 1 h, a crystalline product, X-ray crystallographic

A. T. Carmona et al. / Tetrahedron: Asymmetry 10 (1999) 1751–1764
1759
analysis of which evidenced that it consisted of mixed crystals formed by a 1:1 mixture of 4 and 5 (1.46
g, 15%); mp 183–185°C, [α]30 +73.4 (c 1.45, H2O). Anal. calcd for C8H15NO7: C, 40.52; H, 6.37; N,
D
5.91. Found: C, 40.28; H, 6.11; N, 6.07; lit.16, mp 191–193°C, [α]23 +79.3 (c 1.45, H2O). The residue
D
1
obtained (7.28 g) by evaporation of the mother liquor contained α-D-isomer 4 (50% by H NMR) and
minor amounts of other diastereomers.
4.3. Methyl 4,6-O-benzylidene-3-deoxy-3-C-methyl-3-nitro-α-D-glucopyranoside 6 and methyl 4,6-O-
benzylidene-3-deoxy-3-C-methyl-3-nitro-β-L-glucopyranoside 7
(a) Dry zinc chloride (0.97 g, 7.11 mmol) was added to a solution of mixed crystals of 4 and 5 (1.00 g,
4.22 mmol) in freshly distilled benzaldehyde (6 mL, 6.27 g, 59.10 mmol). The solution was kept at room
temperature for 24 h and then poured into ice-water. After separation of the two layers, the organic phase
was washed with water. Hexane was added to the organic phase to afford, after cooling and scratching, a
solid which was filtered and washed with hexane portions to eliminate the excess of benzaldehyde. The
solid was subjected to column chromatography (1:2, ether:hexane) to give, separately, 6 (0.488 g, 36%)
and 7 (0.486 g, 35%).
(b) Benzaldehyde dimethylacetal (475 µL, 3.16 mmol) and p-toluenesulphonic acid (3 mg) were added
to a solution of mixed crystals of 4 and 5 (0.50 g, 2.11 mmol) in N,N-dimethylformamide (3 mL). The
solution was kept at room temperature and reduced pressure for 8 h in order to eliminate the MeOH
evolved. It was necessary to replace the benzaldehyde dimethylacetal partially evaporated during the
process. The reaction mixture was then neutralised with saturated aqueous sodium hydrogencarbonate
and concentrated at reduced pressure. The residue was treated with dichloromethane (3×10 mL) and
the extract was concentrated to a colourless syrup, which was subjected to column chromatography
(same system) to give, separately, 6 (0.291 g, 42%) and 7 (0.321 g, 47%). Compound 6: mp 162–164°C;
RF=0.35 in 2:1 ether:hexane; [α]20 +84 (c 1, CH2Cl2); IR (film) νmax 3507 (OH), 1545 and 1394 cm−1
D
1
(NO2); H NMR (500 MHz, CDCl3): δ 7.40–7.33 (m, 5H, Ph), 5.53 (s, 1H, CH–Ph), 4.85 (d, 1H,
0
J
J
1,2=4.4, H-1), 4.45 (dd, 1H, J2,OH=11.0, H-2), 4.36 (dd, 1H, J5,6=5.5, J6,6 =9.5, H-6), 4.33 (dd, 1H,
4,5=9.1, H-4), 3.79 (m, 2H, H-5 and H-60), 3.46 (s, 3H, MeO), 2.48 (d, 1H, HO-2), and 1.79 (s, 3H,
Me-3); 13C NMR (75.5 MHz, CDCl3): δ 136.4, 129.1, 128.1 and 126.0 (Ph), 101.3 (CH–Ph), 99.3 (C-1),
92.9 (C-3), 79.8 (C-4), 72.1 (C-2), 68.9 (C-6), 60.8 (C-5), 56.1 (MeO), and 11.3 (Me-3); FABMS: m/z
348 (100, [M+Na]+). Anal. calcd for C15H19NO7: C, 55.38; H, 5.89; N, 4.30. Found: C, 55.16; H, 6.13;
N, 4.54. Compound 7: mp 154–156°C; RF=0.46 in 2:1 ether:hexane; [α]25 +69 (c 0.75, CH2Cl2); IR
D
(film) νmax 3437 (OH), 1563 and 1388 cm−1 (NO2); 1H NMR (300 MHz, CDCl3): δ 7.44–7.33 (m, 5H,
0
Ph), 5.53 (s, 1H, CH–Ph), 4.42 (dd, 1H, J5,6=5.0, J6,6 =10.6, H-6), 4.36 (d, 1H, J1,2=7.5, H-1), 4.30 (d,
0
0
1H, J4,5=9.5, H-4), 4.20 (dd, 1H, H-2), 3.83 (dd, 1H, J5,6 ≈10.0, H-6 ), 3.61 (ddd, 1H, H-5), 3.59 (s,
3H, MeO), 2.56 (brs, 1H, HO-2), and 1.77 (s, 3H, Me-3); 13C NMR (75.5 MHz, CDCl3): δ 136.2, 129.2,
128.2 and 125.9 (Ph), 102.8 (C-1), 101.4 (CH–Ph), 91.9 (C-3), 80.4 (C-4), 74.0 (C-2), 68.8 (C-6), 65.7
(C-5), 57.6 (MeO), and 10.3 (Me-3); FABMS: m/z 348 (100, [M+Na]+). Anal. calcd for C15H19NO7: C,
55.38; H, 5.89; N, 4.30. Found: C, 55.35; H, 6.06; N, 4.17.
4.4. Methyl 3-deoxy-3-C-methyl-3-nitro-α-D-glucopyranoside 4
p-Toluenesulphonic acid (19 mg, 0.1 mmol) was added to a solution of 6 (0.325 g, 1 mmol) in 1:1
methanol:dioxane (10 mL). The mixture was heated at 60°C for 2 h and then at 85°C for 1 h, neutralised
with Et3N and concentrated at reduced pressure. Treatment of the residue with hexane gave a white
solid which was collected and washed thoroughly with hexane to yield the title product 4: 0.237 g, 99%;

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A. T. Carmona et al. / Tetrahedron: Asymmetry 10 (1999) 1751–1764
RF=0.27 (ether); mp 156–158°C; [α]28 +124 (c 1.0, methanol); IR (film) νmax 3325 (OH), 1553 and
D
1418 cm−1 (NO2); 1H NMR (500 MHz, CD3OD): δ 4.74 (d, 1H, J1,2=4.3, H-1), 4.28 (d, 1H, H-2), 4.19
0
0
0
(d, 1H, J4,5=10.1, H-4), 3.81 (dd, 1H, J5,6=2.4, J6,6 =12.0, H-6), 3.71 (dd, 1H, J5,6 =5.1, H-6 ), 3.53 (ddd,
1H, H-5), 3.40 (s, 3H, MeO), and 1.66 (s, 3H, Me-3); 13C NMR (125.7 MHz, CD3OD): δ 101.0 (C-1),
98.2 (C-3), 73.3 (C-2), 71.9 (C-5), 71.7 (C-4), 62.5 (C-6), 56.1 (OMe) and 11.8 (Me-3); CIHRMS: m/z
238.0928 (calcd for C8H15NO7 [M++1]: 238.0927).
4.5. Methyl 3-deoxy-3-C-methyl-3-nitro-β-L-glucopyranoside 5
Treatment of compound 7 (0.325 g, 1 mmol) as indicated above for compound 6 gave the title product
5: 0.235 g, 99%; RF=0.38 (ether); mp 102–104°C; [α]23 +13 (c 1.0, methanol); IR (film) νmax 3341
D
(OH), 1553 and 1410 cm−1 (NO2); 1H NMR (500 MHz, CD3OD): δ 4.31 (d, 1H, J1,2=8.0, H-1), 4.15 (d,
0
0
1H, J4,5=10.0, H-4), 3.94 (d, 1H, H-2), 3.86 (dd, 1H, J5,6=2.1, J6,6 =12.0, H-6), 3.68 (dd, 1H, J5,6 =5.1,
H-60), 3.53 (s, 3H, MeO), 3.42 (ddd, 1H, H-5), and 1.60 (s, 3H, Me-3); 13C NMR (125.7 MHz, CD3OD):
δ 103.7 (C-1), 97.5 (C-3), 76.9 (C-5), 72.0 (C-2), 68.1 (C-4), 62.7 (C-6), 57.3 (OMe) and 10.3 (Me-3);
CIHRMS: m/z 238.0933 (calcd for C8H15NO7 [M++1]: 238.0927).
4.6. Methyl 3,6-dideoxy-6-fluoro-3-C-methyl-3-nitro-α-D-glucopyranoside 8
A suspension of compound 4 (0.80 g, 3.36 mmol) in dry dichloromethane (13.6 mL), cooled at −35°C
under argon, was treated with DAST (2.5 mL, 20 mmol). The cooling bath was removed and the mixture
was kept stirring at room temperature for 1.5 h. The mixture was cooled to −10°C, quenched via addition
of methanol (6.8 mL), and then concentrated at reduced pressure. Column chromatography of the residue
(2:1, hexane:ethyl acetate) afforded 8 as a syrup: 0.62 g, 77%; RF=0.25 (same system); [α]23 +10.1
D
1
(c 0.9, methanol); IR (film) νmax 3436 (OH), 1553 and 1347 (NO2), 1045 (CF) cm−1; H NMR (500
0
MHz, CD3OD): δ 4.75 (d, 1H, J1,2=4.3, H-1), 4.64 (ddd, 1H, J6,F=47.3, J6,6 =10.3, J5,6=3.8, H-6), 4.59
(ddd, 1H, J6 ,F=47.9, J5,6=1.7, H-60), 4.28 (d, 1H, H-2), 4.24 (d, 1H, J4,5=10.4, H-4), 3.66 (dddd, 1H,
0
J
5,F=26.5, H-5), 3.40 (s, 3H, MeO), and 1.68 (s, 3H, Me-3); 13C NMR (125.7 MHz, CD3OD): δ 101.1
(s, C-1), 98.0 (s, C-3), 83.3 (d, JC-6,F=172.2, C-6), 73.2 (s, C-2), 70.6 (d, JC-5,F=24.5, C-5), 70.5 (s, C-4),
56.2 (s, MeO), and 11.7 (s, Me-3). FABMS: m/z 262 (58, [M+Na]+); EIHRMS: m/z 208.0608 (calcd for
C8H14FNO6−OMe: 208.0621). Anal. calcd for C8H14FNO6: C, 40.16; H, 5.90; N, 5.85. Found: C, 40.32;
H, 5.85; N, 5.80.
4.7. Methyl 3,6-dideoxy-6-fluoro-3-C-methyl-3-nitro-β-L-glucopyranoside 9
Compound 5 (0.284 g, 1.2 mmol), dissolved in dichloromethane (5 mL) at −35°C, was treated with
DAST (900 µL, 7.15 mmol) as indicated for the preparation of 6. The mixture was processed as stated
above, and the residue was subjected to column chromatography (4:1, hexane:ethyl acetate) to give 9:
183 mg, 64%; RF=0.21 (2:1, hexane:ethyl acetate); [α]25 +14.0 (c 1, methanol); IR (film) νmax 3412
D
(OH), 1553 and 1355 (NO2), 1045 (CF) cm−1; 1H NMR (500 MHz, CD3OD): δ 4.80 (dd, 2H, J6,F=47.6,
J
5,6=2.4, H-6 and H-60), 4.54 (d, 1H, J1,2=8.0, H-1), 4.39 (d, 1H, J4,5=10.1, H-4), 4.12 (d, 1H, H-2), 3.80
(ddt, 1H, J5,F=25.6, H-5), 3.71 (s, 3H, MeO), and 1.79 (s, 3H, Me-3); 13C NMR (125.7 MHz, CD3OD): δ
103.7 (s, C-1), 97.2 (s, C-3), 83.2 (d, JC-6,F=176.0, C-6), 75.4 (d, JC-5,F=25.1, C-5), 74.8 (s, C-2), 70.9 (d,
J
C-4,F=7.5, C-4), 57.3 (s, MeO), and 10.1 (s, Me-3). FABHRMS: m/z 262.0686 (93, [M+Na]+; calcd for
C8H14FNO6+Na: 262.0703). CIHRMS: m/z 238.0724 ([M−1]+; calcd for C8H14FNO6−H: 238.0730);

A. T. Carmona et al. / Tetrahedron: Asymmetry 10 (1999) 1751–1764
1761
208.0622 (calcd for C8H14FNO6−OMe: 208.0621). Anal. calcd for C8H14FNO6: C, 40.16; H, 5.90; N,
5.85. Found: C, 40.40; H, 5.24; N, 5.97.
4.8. Phenyl 3-deoxy-3-C-methyl-3-nitro-1-thio-α-D-glucopyranoside 10 and phenyl 3-deoxy-3-C-
methyl-3-nitro-1-thio-β-D-glucopyranoside 11
Into a solution of compound 6 (0.60 g, 1.85 mmol) in freshly distilled pyridine (5.5 mL), kept
under argon atmosphere, were dropped successively hexamethyldisilazane (193 µL, 0.92 mmol) and
trimethylchlorosilane (234 µL, 1.85 mmol). After 2 h at room temperature, the mixture was diluted
with hexane (∼35 mL) and poured into a large excess of ice-water. The organic layer was separated,
washed several times with water and brine, and dried over sodium sulphate. Evaporation of the solvent
yielded the per-O-trimethylsilyl derivative, to which, without further purification, was added under
argon a solution of trimethyl(phenylthio)silane (1.75 mL, 9.26 mmol) in 1,2-dichloroethane (9 mL).
To this mixture were added zinc iodide (1.77 g, 5.55 mmol) and tetrabutylammonium iodide (0.69 g,
1.85 mmol), and the resulting suspension was heated at 60°C with stirring for 8 h. The solids were
filtered off and the filtrate was washed with saturated aqueous sodium hydrogencarbonate. The organic
phase was shaken with brine, dried over sodium sulphate, and concentrated at reduced pressure to give
a syrup which was purified by column chromatography (9:1, dichloromethane:acetone). The product
(0.39 g, 67%) was a 1:4 mixture of the anomeric thioglycosides 10 and 11, respectively. Anal. calcd
for C13H17NO6S: C, 49.51; H, 5.43; N, 4.44. Found: C, 49.75; H, 5.62; N, 4.02. Separation of the
two anomers could be achieved by preparative TLC (22:1, dichloromethane:methanol). α-Anomer 10:
RF=0.21 (20:1, dichloromethane:methanol); [α]25 +220.7 (c 0.58, CHCl3); IR (film) νmax 3444 (OH),
D
1
1545 and 1348 (NO2), 606 (CS) cm−1; H NMR (300 MHz, CDCl3): δ 7.49–7.35 (m, 5H, Ph), 5.61
(d, 1H, J1,2=6.3, H-1), 4.70 (dd, 1H, J2,OH=8.0,0H-2), 4.50 (dd, 1H, J4,5=9.8, H-4), 4.06 (dt, 1H,
0
5,6=J5,6 =3.3, H-5), 3.95 (brs, 2H, H-6, and H-6 ), 3.11 (brs, 1H, HO-4), 2.83 (d, 1H, HO-2), 1.99
J
(brs, 1H, HO-6), and 1.82 (s, 3H, Me-3); 13C NMR (75.5 MHz, CDCl3): δ 133.6, 132.3, 129.3 and 128.3
(Ph), 95.5 (C-3), 90.2 (C-1), 71.2 (C-2), 70.4 (C-5), 69.7 (C-4), 62.0 (C-6), and 12.1 (Me-3); FABMS:
m/z 338 (46, [M+Na]+); CIHRMS: m/z 315.0789 ([M+]; calcd for C13H17NO6S: 315.0776). β-Anomer
11: RF=0.43 (20:1, dichloromethane:methanol); [α]25 −39 (c 1, CHCl3); IR (film) νmax 2880 (OH), 1547
D
1
and 1340 (NO2), 574 (CS) cm−1; H NMR (500 MHz, CDCl3): δ 7.50–7.34 (m, 5H, Ph), 4.61 (d, 1H,
J
J
1,2=10.0, H-1), 4.06 (dd, 1H, J2,OH=2.7, H-2), 4.30 (dd, 1H, J4,OH=3.4, J4,5=9.7, H-4), 3.46 (dt, 1H,
0
0
0
5,6=J5,6 =3.4, H-5), 3.90 (dd, 1H, J6,6 =11.9, H-6), 3.82 (dd, 1H, H-6 ), 3.32 (brs, 1H, HO-4), 2.79 (d,
1H, HO-2), 2.33 (brs, 1H, HO-6), and 1.68 (s, 3H, Me-3); 13C NMR (125.7 MHz, CDCl3): δ 133.2,
130.8, 129.3 and 128.8 (Ph), 95.3 (C-3), 87.2 (C-1), 77.4 (C-5), 71.7 (C-2), 70.1 (C-4), 62.2 (C-6), and
9.6 (Me-3); FABMS: m/z 338 (17, [M+Na]+). CIHRMS: m/z 315.0771 ([M+]; calcd for C13H17NO6S:
315.0776).
4.9. Phenyl 3-deoxy-3-C-methyl-3-nitro-1-thio-α-L-glucopyranoside 12 and phenyl 3-deoxy-3-C-
methyl-3-nitro-1-thio-β-L-glucopyranoside 13
Treatment of compound 7 (0.80 g, 2.46 mmol), under the above conditions, with hexamethyldisilazane
(256 µL, 1.23 mmol) and trimethylchlorosilane (310 µL, 2.46 mmol), and subsequently with tri-
methyl(phenylthio)silane (2.32 mL, 12.3 mmol) gave, after a similar workup, a syrup, which was purified
by column chromatography (11:1, dichloromethane:acetone). The product (0.50 g, 64%) was a 1:4
mixture of the anomeric thioglycosides 12 and 13, respectively. FABMS: m/z 338 (48, [M+Na]+). Anal.
calcd for C13H17NO6S: C, 49.51; H, 5.43; N, 4.44. Found: C, 49.26; H, 5.34; N, 4.39. Separation of the

1762
A. T. Carmona et al. / Tetrahedron: Asymmetry 10 (1999) 1751–1764
two anomers could be achieved by preparative TLC (22:1, dichloromethane:methanol). α-Anomer 12:
[α]25 −215.5 (c 0.58, CHCl3); CIHRMS: m/z 315.0777 ([M+]; calcd for C13H17NO6S: 315.0776); this
D
product showed IR and NMR spectra identical to those of its enantiomer 10. β-Anomer 13: [α]25 +38 (c
D
1, CHCl3); CIHRMS: m/z 315.0785 ([M+]; calcd for C13H17NO6S: 315.0776); this product showed IR
and NMR spectra identical to those of its enantiomer 11.
4.10. Phenyl 3,6-dideoxy-6-fluoro-3-C-methyl-3-nitro-1-thio-β-D-glucopyranoside 14
A suspension of compound 11 (100 mg, 0.32 mmol) in dry dichloromethane (2 mL), cooled at −35°C
under argon, was treated with DAST (250 µL, 1.91 mmol). The mixture was stirred at −30°C for 3
h; then the temperature was allowed to rise to −20°C and the reaction was quenched via addition of
methanol (600 µL). After evaporation of the solvents under reduced pressure, column chromatography
of the residue (gradient 60:1 to 10:1, dichloromethane:acetone) afforded pure 14 (42 mg, 26%) [unreacted
11 (11 mg, 11%) was recovered]. Compound 14 had [α]27 −22.4 (c 1.0, CHCl3); EIHRMS: m/z 317.0727
D
(calcd for C13H16FNO5S [M+]: 317.0733); this product showed IR and NMR spectra identical to those
of its enantiomer 15.
4.11. 2,3,6-Trideoxy-6-fluoro-3-C-methyl-3-nitro-2-phenylthio-α-D-mannopyranosyl fluoride 16 and
2,3-dideoxy-3-C-methyl-3-nitro-2-phenylthio-α-D-mannopyranosyl fluoride 18
DAST (305 µL, 2.30 mmol) was added to a solution of compound 11 (120 mg, 0.38 mmol) in dry
dichloromethane (2 mL), cooled at −35°C under argon. The mixture was allowed to warm to room
temperature for 90 min and the reaction was then quenched at −10°C by adding methanol (0.75 mL).
After evaporation of the solvents, the residue was subjected to column chromatography (gradient 1:3 to
1:1, ether:hexane) to afford 73 mg (60%) of 16 and 10 mg (10%) of 18, both as syrups. Compound 16
had [α]28 −14.8 (c 0.80, CHCl3); EIHRMS: m/z 319.0688 ([M+]; calcd for C13H15F2NO4S: 319.0690);
D
this product showed identical IR and NMR spectra to those of its enantiomer 17. Compound 18 showed
IR and NMR spectra identical to those of its enantiomer 19.
4.12. Phenyl 3,6-dideoxy-6-fluoro-3-C-methyl-3-nitro-1-thio-β-L-glucopyranoside 15
A suspension of compound 13 (70 mg, 0.23 mmol) in dry dichloromethane (2 mL), cooled at −35°C
under argon, was treated with DAST (179 µL, 1.38 mmol) for 3 h under the conditions indicated above
for the preparation of 14, followed by a similar workup (460 µL of methanol used for quenching), to
afford after column chromatography (same system) 47 mg (68%) of 15 as a syrup [unreacted 13 (16
mg, 22%) was recovered]; RF=0.57 (2:1, ether:hexane); [α]27 +23.6 (c 0.55, CHCl3); IR (film) νmax
D
1551 and 1344 (NO2), 1096 (CF) cm−1; 1H NMR (500 MHz, CD3OD): δ 7.56–7.35 (m, 5H, Ph), 4.57
0
0
(d, 1H, J1,2=9.9, H-1), 4.70 (ddd, 1H, J6,F=47.5, J6,6 =10.3, J5,6=2.3, H-6), 4.67 (ddd, 1H, J6 ,F=47.2,
J
5,6=3.2, H-60), 4.31 (d, 1H, J4,5=10.0, H-4), 4.02 (d, 1H, H-2), 3.56 (dddd, 1H, J5,F=24.8, H-5), 2.64
and 2.54 (each brs, each 1H, HO-2 and HO-4), and 1.70 (s, 3H, Me-3); 13C NMR (125.7 MHz, CD3OD):
δ 133.6, 130.3, 129.2 and 128.9 (each s, Ph), 95.0 (s, C-3), 86.9 (s, C-1), 81.9 (d, JC-6,F=176.0, C-6), 76.4
(d, JC-5,F=18.4, C-5), 71.2 (s, C-2), 69.2 (d, JC-4,F=7.5, C-4), and 9.7 (s, Me-3); FABMS: m/z 340 (30,
[M+Na]+); CIHRMS: m/z 317.0740 ([M+]; calcd for C13H16FNO5S: 317.0733); EIHRMS: m/z 317.0727
([M+]; calcd for C13H16FNO5S: 317.0733).

A. T. Carmona et al. / Tetrahedron: Asymmetry 10 (1999) 1751–1764
1763
4.13. 2,3,6-Trideoxy-6-fluoro-3-C-methyl-3-nitro-2-phenylthio-α-L-mannopyranosyl fluoride 17 and
2,3-dideoxy-3-C-methyl-3-nitro-2-phenylthio-α-D-mannopyranosyl fluoride 19
Treatment of compound 13 (58 mg, 0.18 mmol) in dry dichloromethane (1.2 mL) with DAST (146
µL, 1.11 mmol) under the conditions stated above for the preparation of 16 and 18, followed by a similar
workup (0.40 mL of methanol used for quenching), afforded after column chromatography (same system)
34 mg (58%) of 17 and 8.5 mg (15%) of 19, both as syrups. Compound 17: RF=0.53 (1:1, ether:hexane);
[α]30 +14.9 (c 0.80, CHCl3); IR (film) νmax 3579 (OH), 1553 and 1394 (NO2), 1097 (CF) and 665 (CS)
D
cm−1; H NMR (500 MHz, CDCl3): δ 7.47–7.34 (m, 5H, Ph), 5.98 (dd, 1H, J1,F=53.2, J1,2=1.3, H-1),
1
4.82 (ddd, 1H, J6,F=46.0, J6,6 =10.3, J5,6=3.3, H-6), 4.72 (ddd, 1H, J6 ,F=45.4, J5,6=1.7, H-60), 4.67 (d,
1H, J4,5=10.2, H-4), 3.94 (dddd, 1H, J5,F=25.7, H-5), 3.73 (dd, 1H, J2,F=3.4, H-2), 2.97 (brs, 1H, HO-4),
and 1.91 (d, 3H, JMe,F=2.3, Me-3); NOE contacts (1D NOESY): Me-3, H-2, H-5; 13C NMR (125.7 MHz,
CDCl3): δ 133.2, 133.0, 129.6 and 129.2 (each s, Ph), 108.6 (d, JC-1,F=233.8, C-1), 91.8 (s, C-3), 81.3 (d,
0
0
J
C-6,F=174.7, C-6), 71.6 (d, JC-5,F=18.9, C-5), 64.3 (d, JC-4,F=7.5, C-4), 56.4 (d, JC-2,F=23.9, C-2), and
20.2 (d, JMe,F=7.8, Me-3); EIHRMS: m/z 319.0688 ([M+]; calcd for C13H15F2NO4S: 319.0690). Anal.
calcd for C13H15F2NO4S: C, 48.90; H, 4.73; N, 4.39; S, 10.04. Found: C, 49.24; H, 4.50; N, 4.78; S, 9.55.
Compound 19: RF=0.21 (2:1, ether:hexane); [α]29 +16.2 (c 0.80, CHCl3); IR (film) νmax 3542 (OH),
D
1545 and 1386 (NO2), 1085 (CF) and 653 (CS) cm−1; 1H NMR (300 MHz, CDCl3): δ 7.47–7.35 (m, 5H,
0
Ph), 5.97 (dd, 1H, J1,F=53.3, J1,2=1.3, H-1), 4.69 (d, 1H, J4,5=9.9, H-4), 3.99 (d, 2H, J5,6≈J5,6 =3.2, H-6
and H-60), 3.87 (dt, 1H, H-5), 3.73 (dd, 1H, J2,F=3.5, H-2), and 1.92 (d, 3H, JMe,F=2.3, Me-3); 13C NMR
(75.5 MHz, CDCl3): δ 133.2, 132.8, 129.5 and 129.1 (each s, Ph), 108.4 (d, JC-1,F=233.4, C-1), 91.8 (s,
C-3), 72.4 (s, C-5), 64.9 (s, C-4), 61.5 (s, C-6), 56.4 (d, JC-2,F=25.0, C-2), and 20.2 (d, JMe,F=7.6, Me-3);
EIHRMS: m/z 317.0732 ([M+]; calcd for C13H16FNO5S: 317.0733).
4.14. Crystallographic analysis for mixed crystals of 4+5†
The compound crystallised as colourless monoclinic prisms. A crystal of dimensions 0.20×0.28×0.40
mm was mounted on a CAD4 Enraf–Nonius automated diffractometer; it belonged to the monoclinic
system, space group P21. Accurate cell dimensions and crystal orientation matrix, determined by least-
squares treatment of the setting angles of 25 independent reflections in the range 2<θ<30° using
Mo-Kα radiation (λ=0.71069 Å), were a=12.713(2), b=12.557(3), and c=6.708(1) Å, β=104.07(1)°,
V=1038.7(3) Å3, dcalc=1.52 g cm−3 for Z=2, F(000)=504 and the absorption coefficient µ=0.13 mm−1.
Data (3148 reflections) were collected at room temperature, using ω/2θ scan mode to a maximum 2θ
value of 60°. The intensities of two standard reflections were measured every 100 reflections, and as
the intensities of these reflections showed less than 5% variation, corrections for decomposition were
deemed unnecessary. Intensities were corrected for Lorentz and polarisation effects, but no absorption
correction was made. A total of 2547 reflections were considered observed [I>2σ(I0)]. The structure
was solved by direct methods using SIR9227 to locate all non-hydrogen atoms. Refinement on F2
was performed using SHELXL93.28 All H-atoms were located by difference Fourier, but not refined.
The final cycle of refinements led to a final agreement factor R=0.0374, and wR(F2)=0.0918 for
w=1/[σ2(F02)+(0.0602P)2+0.0000P] where P=(F02+2Fc2)/3 for 197 variables. Atomic scattering factors
were taken from the International Tables for X-Ray Crystallography,29 maximum and minimum residual
†
Lists of the atomic coordinates, hydrogen coordinates, and thermal parameters have been deposited at the Cambridge
Crystallographic Data Centre.

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A. T. Carmona et al. / Tetrahedron: Asymmetry 10 (1999) 1751–1764
densities in the final difference map 0.30 and −0.23 eÅ−3, respectively. The geometrical analysis was
performed using PARST.30
Acknowledgements
We are grateful to the Dirección General de Enseñanza Superior, Ministerio de Educación y Cultura
of Spain (grant No. PB96-1326) and the Dirección General de Universidades e Investigación, Consejería
de Educación y Ciencia of Andalusia, for financial support.
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