5-Deoxy glycofuranosides by carboxyl group assisted photoinduced electron-transfer deoxygenation

Article abstract of DOI:10.1016/j.tet.2007.12.005

In connection with the development of practical methods for the synthesis of deoxy sugars, a photoinduced electron-transfer (PET) reaction using 9-methylcarbazole (MCZ) as photosensitizer was applied to a 2-O-(3-trifluoromethyl)benzoylated derivative of d

Full text of DOI:10.1016/j.tet.2007.12.005

Available online at www.sciencedirect.com
Tetrahedron 64 (2008) 1703e1710
www.elsevier.com/locate/tet
5-Deoxy glycofuranosides by carboxyl group assisted photoinduced
electron-transfer deoxygenation
*
Andrea Bordoni, Rosa M. de Lederkremer, Carla Marino
CIHIDECAR (CONICET), Departamento de Qu´ımica Orga´nica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires,
Pabello´n II, Ciudad Universitaria, 1428 Buenos Aires, Argentina
Received 28 November 2007; accepted 4 December 2007
Available online 8 December 2007
Abstract
In connection with the development of practical methods for the synthesis of deoxy sugars, a photoinduced electron-transfer (PET) reaction
using 9-methylcarbazole (MCZ) as photosensitizer was applied to a 2-O-(3-trifluoromethyl)benzoylated derivative of D-galacturonic acid. The
carboxylic group efficiently assists a-deoxygenation, the required irradiation time being significantly shorter than that in the absence of it. The
photochemical reaction was also used for the deoxygenation of D-glucurono-6,3-lactone derivatives, providing in both cases the convenient
routes for the synthesis of 5-deoxy-hexofuranosides and intermediate compounds for the synthesis of natural products, avoiding the use of metal
hydrides.
Ó 2007 Elsevier Ltd. All rights reserved.
Keywords: PET deoxygenatin; Deoxy sugars; Galactofuranosides; Glucofuranosides
1. Introduction
reduction of hydroxyl groups was previously used for the
deoxygenation of different ester derivatives under diverse con-
ditions.9e13 Saito et al. described that the 3-trifluoromethyl-
benzoyl group was an efficient group for this reaction.11 In
all the applications, several hours of irradiation were required
for conversion of the starting material into the corresponding
deoxygenated photoproducts. Following Rizzo’s protocol,13
we observed that the reaction conditions necessary for the
deoxygenation of 2-O-(3-trifluoromethyl)benzoyl derivatives of
aldono-1,4-lactones were extremely mild compared, for exam-
ple, with those required for the synthesis of 2-deoxyribonucleo-
sides13 (Table 1, entries 1 and 2). The effectiveness of this
reaction on lactone derivatives was attributed to the stabiliza-
tion of the intermediate radical by the carbonyl group.6 The
PET deoxygenation was optimized for different derivatives of
D-galactono- and D-glucono-1,4-lactones, confirming the selec-
tivity for the reduction at the a-carbonyl position. The unique
reactivity of aldonolactones allows for 9-methylcarbazole
(MCZ) to turn over, so it can be used in 10 mol %.14
The glycobiology of galactofuranose is a topic of great
interest, since galactofuranosyl residues are constituents of
infectious microorganisms, but are absent in mammal glyco-
conjugates. The enzymes involved in the metabolism of
the sugar are good targets for the development of antimicro-
bial agents.1e3 As part of an ongoing project for the synthesis
of compounds useful for the characterization of the en-
zymes,4,5 we have developed strategies for the synthesis of
galactofuranosides deoxygenated at C-2, 3, and 6 and we
showed that these hydroxyls are necessary for the interaction
with exo b-D-galactofuranosidase from Penicillium felluta-
num.6e8 The synthesis of 2-deoxy-D-lyxo-hexofuranosides
(‘2-deoxy-galactofuranosides’) was performed via a photoin-
duced electron-transfer (PET) reaction on 2-O-(3-trifluorome-
thyl)benzoyl-D-galactono-1,4-lactone using 9-methylcarbazole
(MCZ) as photosensitizer (Table 1, entry 1).3 The PET
The importance of the HO-5 of galactofuranosides in the
interaction with exo b-D-galactofuranosidase has not been
reported. Therefore, we pursued the design of a methodology
* Corresponding author. Tel.: þ54 11 45763352; fax: þ54 11 45763346.
E-mail address: cmarino@qo.fcen.uba.ar (C. Marino).
0040-4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.12.005

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A. Bordoni et al. / Tetrahedron 64 (2008) 1703e1710
Table 1
Photoinduced deoxygenation of hydroxyl groups derivatized as 3-(trifluoromethyl)benzoates
Entry
Compound
Product
Time
Conversiona (%)
Yieldb (%)
O
H
O
O
OH
O
O
1
3 min
100
7314
OCOC6H4(3-CF3)
OH
CH2OH
OH
CH2OH
O
O
NH
NH
BzOH2C
N
O
O
BzOH2C
N
O
O
2
12e15 h
d
50e7013
O
C
O
BzO
BzO
CF3
OCH3
O
O
OH
OCH3
O
OH
OH
OH
O
H
H
3
3 min
60
42
CO2CH3
CO2CH3
F3C
4
4
4
3
4
5
3
3
6 min
8 min
90
100
66
25
O
O
O
O
H
H
OCH3
O
O
OCH3
O
O
CF3
6
6 min
100
90
OH
10
OH
9
O
O
O
H
H
O
O
O
O
O
CF3
O
O
7
8
3 min
6 min
78
46
90
O
O
13
13
14
14
100
O
O
O
H
H
O
O
O
O
OH
O
OH
CF3
9
3 min
6 min
85
27
56
OH
17
17
OH
16
16
10
100
The reaction was performed with a 450 W medium-pressure lamp (lexc >300 nm), at 25 ꢀC, in 9:1 2-PrOHeH2O in the presence of MCZ (0.075 mmol) and
Mg(ClO4)2 (0.3 mM).
a
Conversion was determined by NMR spectroscopy.
Yields refer to the isolated pure products after column chromatography.
b
for the deoxygenation of C-5 in galactofuranosides and in
general, for the synthesis of 5-deoxy-glycofuranosides.
The first synthesis of 5-deoxyhexoses was developed by
Wolfrom et al. which involved the anti-Markovnikov hydra-
tion of a 5,6-alkene derivative.15 Since that report, the same
approach has been followed by several authors, and the condi-
tions for the key step have been improved.16,17 A three-step
sequence involving the reduction of a 5,6-O-benzylidene
derivative was used for the deoxygenation of glucofuranose,
but the reaction was not regioselective, and some of the 6-de-
oxy sugar was obtained.17
We now report the successful application of the PET
deoxygenation on derivatives of D-galacturonic acid and D-glu-
cofuranosidurono-6,3-lactone for the synthesis of 5-deoxy-gal-
acto and glucofuranosides.
2. Results and discussion
One of the obvious approaches to 5-deoxy-L-arabino-hexo-
furanosides would be the reduction of a compound conve-
niently derivatized at C-5. With this aim and taking
advantage of the different reactivities of the hydroxyl groups

A. Bordoni et al. / Tetrahedron 64 (2008) 1703e1710
1705
in aldohexono-1,4-lactones, we treated 2,6-di-O-benzoyl-D-
galactono-1,4-lactone18 with 1.2 equiv of tosylchloride (4-tol-
uenesulfonylchloride) in pyridineeCHCl2 at 0 ꢀC, expecting
that the exocyclic 5-hydroxyl would be selectively substituted.
Unfortunately, regioselective sulfonation was not achieved.
On the basis of the effectiveness of the photoinduced elec-
tron-transfer (PET) a-deoxygenation of aldonolactones,6,14 we
thought to extend it to the synthesis of 5-deoxy-galactofurano-
syl derivatives. This strategy would require a derivative
oxidized at C-6. Thus, we envisioned commercial D-galactur-
onic acid (1) as a convenient starting material, considering
that the carboxylic group could probably facilitate the PET de-
oxygenation at the vicinal position by stabilization of the inter-
mediate radical. We subsequently investigated the reactions
that would lead to appropriate derivatives for the PET reaction.
The preparation of methyl (methyl a-D-galactopiranosid)uro-
nate from 1 by treatment with methanol in the presence of
a cation-exchange resin (Hþ form) under reflux was earlier de-
scribed. The authors pointed out that the same reaction under
room temperature for 8 h led to the methyl D-galacturonate.19
In our case, treatment of 1 with methanol in the presence of
Amberlite IR-120H cation resin was performed at 35 ꢀC for
48 h. Methyl uronate was formed during the early stages of
the reaction, but after keeping the reaction for 48 h, mainly
the glycosylated b-furanosic derivative 2 was obtained. Pyra-
nose glycosides were not detected by 13C NMR spectroscopy.
Conditions for the stereospecific glycofuranosylation of uronic
acids with long chain alcohols were also described.20 A stereo-
specific three-step procedure for the preparation of 2 from
D-Gal was reported,21 but the procedure optimized here for the
preparation of 2 from D-galacturonic acid is certainly easier.
Subsequent reduction of the ester group constitutes a direct
strategy for accessing galactofuranosides.
from 4.50 ppm in 222 to 5.53 ppm in 3, and the signal for C-
5 was shifted from 70.0 to 72.3 ppm. Signals corresponding
to C-4 and C-6 were shielded in comparison to those of com-
pound 2, as a result of the b-effect.
With compound 3 in hand, conditions for the PET deoxy-
genation could be studied. The photochemical reaction was
carried out by irradiation with a Heraeus TQ, medium-pres-
sure Hg lamp of 450 W in the presence of 9-methylcarbazole
(MCZ) at 10 mol % as photosensitizer, and 2-PrOHewater
(9:1) as solvent. We have previously observed that photolysis
of 2-O-(3-trifluoromethyl)benzoyl-D-galactono (Table 1, entry
1) and D-glucono-1,4-lactone derivatives under these condi-
tions for 3 min led to total conversion to the corresponding
2-deoxy-aldonolactones.14 Compound 3 was irradiated for dif-
ferent times in order to find the optimal conditions (Table 1,
entries 3e5). On the basis of the 13C NMR spectrum of the
crude mixture complete disappearance of the starting material
occurred after 8 min of irradiation, however, the recovery of
the deoxygenated product was low. The best yield of 4 was ob-
tained with 6 min of irradiation to give the desired product in
66% yield although some of the starting material was still
present in the crude reaction mixture. This result shows that
the carboxylate ester group is also effective for assisting the
deoxygenation at the vicinal position, in comparison with
the derivatives without a carbonyl group, which required sev-
eral hours of irradiation (Table 1, entry 2).13 As in the case of
aldonolactone derivatives,14 the reactivity enhanced by the
carboxylate ester group allows for MCZ to turn over, so it
can be used in sub-molar quantity.
1
Complex signals were observed in the H NMR spectrum
of 4, as a result of long range couplings. Nevertheless, the
presence of two double doublets at high field (2.86 and
2.72 ppm) with a large Jgem (16.0 Hz) and the signal corre-
sponding to the deoxy function (C-5) at 38.57 ppm in the
13C NMR spectrum confirmed the identity of 4. The signal
corresponding to C-6 was shifted from 168.1 ppm in 3 to
172.3 ppm in 4, as a result of the C-5 deoxygenation, as we
previously observed.6,14
The next step was the reduction of the carboxylic ester of 4
to afford methyl glycoside 5. Reduction of carboxylic esters
with NaBH4 is usually slow,23 but in the case of 2 we observed
that it could be performed by the use of an excess of reagent in
methanol at room temperature. This fact could be attributed to
the presence of an a-heteroatom, as it has been observed in
aldonolactones.23 Compound 4 could not be reduced under simi-
lar conditions, confirming the influence of HO at the vicinal
position. Although a powerful reducing agent could be used,
we were interested in using NaBH4 with the aim to extend
the methodology to the use of NaB3H4, and thus introduce
a tritium label for sensitive biological assays.4 By using the
I2eNaBH4 system,24 reduction of the carboxylic group of 6
was successfully achieved to afford glycoside 5. Compound
5 was thus obtained in four steps from commercial D-galactur-
onic acid, and the physical properties were in agreement with
those reported.16 The synthetic sequence now described is
shorter and more efficient in terms of yield. The NMR spectra
of 5 are now completely assigned. Complex signals for H-5,
We considered that compound 2 could be selectively esteri-
fied at C-5 owing to the enhanced reactivity of the HO vicinal
to the carboxyl group, similar to the regioselectivity observed
in aldonolactones.6,14,18 In fact, treatment of 2 with 1.2 equiv
of 3-(trifluoromethyl)benzoyl chloride led to derivative 3
(Scheme 1), in 68% yield. The structure of 3 was confirmed
on the basis of the NMR data. The signal of H-5 was shifted
HO
OCH3
O
COOH
O
O
OH
OCH3
O
OH
a
b
OH
OH
HO
OH
OH
1
OH
CO2CH3
2
O
CO2CH3
3
F3C
OH
OCH3
OCH3
O
OH
O
OH
O
OH
d
e
c
OH
OH
OH
H
H
H
H
H
H
CO2CH3
CH2OH
CH2OH
4
5
6
Scheme 1. Synthesis of methyl 5-deoxy-a-L-arabino-hexofuranoside (5) and
5-deoxy-L-arabino-hexofuranose (6). (a) Amberlite IR-120H, MeOH; (b)
(3-CF3)C4H6COCl, CH2Cl2epyridine; (c) hn, MCZ, Mg(ClO4)2; (d) NaBH4e
I2, THF; (e) 40 mM TFA, 100 ꢀC.

1706
A. Bordoni et al. / Tetrahedron 64 (2008) 1703e1710
1
50, 6, and 60 were observed in the H NMR spectrum. Signals
corresponding to H-5 and 50 were shielded from 2.86/2.72 to
1.96/1.87 ppm as a result of the reduction of the methoxycar-
bonyl group and appeared as complex multiplets (dddd). Also
H-4 was shielded. The reduction was confirmed by the appear-
ance of a complex signal centered at 3.72 ppm corresponding
signal corresponding to C-6, from 178.0 ppm in 8 to
170.1 ppm in 9 observed in the 13C NMR spectrum, was
also an indicative of the substitution at C-5.
Photolysis of compound 9 afforded 10 (Table 1, entry 6).
The presence of two double doublets at high fields (2.82 and
1
2.54 ppm) with a large Jgem in the H NMR spectrum and
1
to H-6 and 60 in the H NMR spectrum and the signal corre-
sponding to C-6 in the 13C NMR spectra, which was shifted
from 174.3 ppm in 4 to 59.0 ppm in 5.
the signal corresponding to the deoxy function (37.01 ppm,
C-5) in the 13C NMR spectrum were diagnostic signals for
the deoxygenation. The deprotection of C-6 was similar to
the effect observed in other a-deoxygenations.6,14
Although reduction of aldonolactones is usually achieved
with NaBH4, reduction of 10 failed presumably due to the ab-
sence of a heteroatom at C-a to the carboxylic group.23 Using
the NaBH4eI2 method,24 methyl 5-deoxy glucofuranoside
(11) was efficiently obtained.
Glycoside 5 was hydrolyzed by treatment with dilute TFA,
affording 5-deoxy-D-galactose (6, 5-deoxy-L-arabino-hexose).
Compounds 4e6 were analyzed by high performance anion-
exchange chromatography with pulse amperometric detection
(HPAECePAD) and the conditions for good resolution were
established (see Section 3). Thus, this analytical method
could be useful for studies on the substrateeinhibitor
properties of 5-deoxy-galactofuranoside with respect to b-D-
galactofuranosidase.
Based on the results obtained with the PET deoxygenation
of derivatives of D-galacturonic acid, we studied the reaction
with derivatives of D-glucurono-6,3-lactone (7) with the aim
to obtain 5-deoxygenated derivatives of D-glucose. Deoxygen-
ated derivatives of glucose are important for the characteriza-
tion of glucosidases and glucose-isomerases.17 Recently, the
synthesis of 4-deoxypyranosides from 7 has been reported.25
Treatment of 7 with Amberlite IR-120H in methanol at
room temperature led to b-methyl glycoside 8 in good yield
(Scheme 2). Although, some of the a-anomer was detected
With the purpose to study the PET deoxygenation in the
presence of different protective groups, we developed the reac-
tion sequences depicted in Schemes 3 and 4, starting from ace-
tonide 12.26 The free hydroxyl group of 12 was converted to
its (3-trifluoromethyl)benzoyl ester 13, as described for the
preparation of 9. Photochemical deoxygenation was more effi-
cient in this case and compound 13 afforded 14 in 90% yield
after 6 min of irradiation (Table 1, entries 6 and 7). The ab-
sence of free hydroxyls in product 14 facilitated the work up
of the reaction, compared with the other derivatives. Com-
pound 14 was previously obtained by the Barton deoxygen-
ation method applied to the phenylthiocarbonate derivative
of 1227 and used as intermediate for the synthesis of halichon-
drins28 and (þ)-cardiobutanolide.29
1
by H NMR, pure b-anomer was obtained by crystallization
from chloroform. A similar procedure, but under reflux, was
earlier reported to afford the methyl glycoside as an anomeric
mixture.19
By reduction of 14 with NaBH4eI2,24 compound 15 was
obtained. The synthesis of 15 was previously reported.16,27
On the other hand, deisopropylidenation of 13 afforded 16.
PET deoxygenation and subsequent reduction with NaBH4eI2
of 16 was a good route to 2-deoxy-L-xylo-hexitol (18, ‘5-de-
oxy-D-glucitol’, Scheme 4). During the work up of the deoxy-
genation reaction of 16 partial glycosylation with the solvent
(2-PrOH) occurred, lowering the yield of compound 17 (Table
1, entries 9 and 10). The 13C NMR spectrum of the glycosy-
lated product showed the signals corresponding to C-1 at
109.3 ppm and those of the aglycone at 69.1, 22.7, and
20.7 ppm. We concluded that compounds 9 and 13 would be
O
O
O
O
HO
HO
O
OCH3
OCH3
O
O
O
O
a
OH
O
b
O
CF3
OH
OH
OH
7
9
8
O
O
CH2OH
H
H
H
OCH3
OCH3
O
OH
d
c
H
O
OH
OH
11
10
O
O
O
Scheme 2. Synthesis of methyl 5-deoxy-b-D-xylo-hexofuranoside (11). (a)
Amberlite IR-120H, MeOH; (b) (3-CF3)C6H4COCl, CH2Cl2epyridine, 0 ꢀC;
(c) hn, MCZ, Mg(ClO4)2; (d) NaBH4eI2, THF.
HO
O
O
O
(3-CF3)C4H6COCl
CH2Cl2/Py
O
O
CF3
O
O
O
O
On the basis of the selectivity observed in the substitution
of the HO vicinal to the carbonyl group in lactones,6,14 we
supposed that 8 could be selectively esterified at C-5. In
fact, treatment of 8 with 1.2 equiv of (3-trifluoromethyl)ben-
zoyl chloride led to derivative 9 in good yield (Scheme 2).
12
13
CH2OH
O
H
H
H
O
O
OH
NaBH4/I2
THF
hυ
H
O
1
MCZ, Mg(ClO4)2
The H NMR spectrum of 9 clearly confirmed the regioselec-
O
O
O
O
tivity of the benzoylation. The signal at 4.47 ppm, assigned to
H-2, showed coupling with the hydroxyl group (d 2.56 ppm,
J2,HO¼4.94 Hz). On deuteration this signal disappeared and
the H-2 signal collapsed into a singlet. The shielding of the
14
15
Scheme 3. Synthesis of 1,2-di-O-isopropylidene-5-deoxy-D-xylo-hexo-
furanose (15).

A. Bordoni et al. / Tetrahedron 64 (2008) 1703e1710
1707
O
3.2. General procedure for PET deoxygenation
O
O
O
In a custom-made Pyrex reaction vessel equipped with
a cold finger, a solution containing 0.75 mmol of the substrate,
Mg(ClO4)2 (33 mg, 0.3 mM), and 9-methylcarbazole (13 mg,
0.075 mmol) in 500 mL of 10% deionized watere2-propanol
was degassed by bubbling UHP Ar through the solution for
30 min. The solution was photolyzed with a 450 W medium-
pressure lamp (lexc >300 nm), while the temperature was
maintained at 25 ꢀC with a circulating water bath. After irra-
diation for the times indicated in Table 1, the solvent was
removed under reduced pressure and the residue was treated
as described in each case.
HOAc(aq), H2SO4 (cat)
75 °C
hυ
O
OH
13
CF3
MCZ, Mg(ClO4)2
OH
16
O
OH
H
O
OH
H
NaBH4/I2
THF
O
OH
HO
OH OH
OH
17
18
Scheme 4. Synthesis of 2-deoxy-L-xylo-hexitol (18).
more convenient than 16 as starting material for 5-deoxy
glucose derivatives.
3.2.1. Methyl (methyl b-D-galactofuranosid)uronate (2)
A suspension of D-galacturonic acid (1.00 g, 5.15 mmol) in
MeOH (20.0 mL) with 1.0 g of Amberlite IR-120H was stirred
at 35 ꢀC for 48 h. TLC examination showed a main product
with Rf 0.48 (EtOAc, twice development) and a lower moving
product (Rf 0.36). After filtration and removal of the solvent
under diminished pressure, the residue (1.11 g) was purified
by column chromatography (EtOAcetoluene, 49:1). Fractions
of Rf 0.48 afforded syrup 2b (0.71 g, 62%), [a]D ꢁ125 (c 1,
methanol), lit.22 [a]D ꢁ112 (c 1.38, methanol). 1H NMR
(500 MHz, D2O) d 4.89 (d, J¼1.9 Hz, 1H, H-1), 4.50 (d, J¼
2.7 Hz, 1H, H-5), 4.29 (dd, J¼2.7, 6.5 Hz, 1H, H-4), 4.18
(dd, J¼3.9, 6.5 Hz, 1H, H-3), 4.03 (dd, J¼1.9, 3.9 Hz, 1H,
H-2), 3.81 (s, 3H, OCH3), 3.38 (s, 3H, CO2CH3). 13C NMR
(50.3 MHz, D2O) d 174.2 (C-6), 109.0 (C-1), 84.1, 81.0 (C-
2, 4), 76.3 (C-3), 70.0 (C-5), 55.6, 53.5 (2OCH3). Fractions
of Rf 0.36 afforded methyl (methyl a-D-galactofuranosid)uro-
nate (0.31 g, 28%) with physical and spectroscopic data iden-
tical to those reported in the literature.22
The development of specific deoxygenation methods for
carbohydrates is important as they are useful not only for en-
zymatic characterization, but also for the synthesis of natural
products from carbohydrate precursors as chiral templa-
tes.27e29 On the other hand, avoiding the use of metal hydrides
is desirable from the environmental point of view.30 For 5-de-
oxy sugars, several methods have been reported, all of them
involving several steps to afford the appropriate furanosic de-
rivative for the deoxygenation step.17 We investigated here the
efficiency of the PET deoxygenation on D-galacturonic acid
and D-glucofuranosidurono-6,3-lactone derivatives, showing
the effectiveness of the carboxylate ester group for the reduc-
tion of the vicinal position, and we used this reaction as the
key step for the synthesis of 5-deoxy-D-galacto and glucofur-
anosides. The straightforward access to furanosyl precursors
from uronic acids by the resin catalyzed glycosylation, com-
bined with the regioselectivity on the acylation of glycuronic
acids, and the easiness of the deoxygenation, significantly
shorten the pathway to 5-deoxy sugars.
3.2.2. Methyl (methyl 5-O-(3-trifluoromethyl)benzoyl-
3. Experimental section
b-D-galactofuranosid)uronate (3)
To a solution of 2 (0.50 g, 2.25 mmol) in CH2Cl2 (10.0 mL)
containing pyridine (5 mL), cooled at 0 ꢀC, 3-(trifluorome-
thyl)benzoyl chloride (0.39 mL, 2.64 mmol) diluted in
CH2Cl2 (5.0 mL) was added in three aliquots for 1.5 h. After
1 h of stirring at 0 ꢀC, TLC analysis showed a main product
of Rf 0.63 (EtOAcetoluene, 9:1) and a minor amount of the
starting material. The solution was diluted with CH2Cl2 and
washed with HCl (5%), water, satd NaHCO3, and water, dried
(Na2SO4), and concentrated. The syrup obtained was purified
by column chromatography (tolueneeEtOAc, 3:2). Evapora-
tion of the corresponding fractions afforded 3 (0.70 g, 68%),
3.1. General
Thin layer chromatography (TLC) was performed on
0.2 mm Silica Gel 60 F254 (Merck) aluminum supported
plates. Detection was effected by exposure to UV light and
by spraying 10% (v/v) H2SO4 in EtOH and charring. Column
chromatography was performed on Silica Gel 60 (200e400
mesh, Merck). NMR spectra were recorded with a Bruker
AC 200 spectrometer at 200 MHz (1H) and 50.3 MHz (13C)
or with a Bruker AM 500 spectrometer at 500 MHz (1H)
and 125.8 MHz (13C). Assignments were supported by
COSY and HSQC experiments. High resolution mass spectra
(HRMS) were recorded on an Agilent LCTOF with Windows
XP based OS and APCI/ESI ionization high resolution mass
spectrometer analyzer, with Opus V3.1 and DEC 3000 Alpha
Station. Melting points were determined with a FishereJohns
apparatus and are uncorrected. Optical rotations were mea-
sured at 25 ꢀC with a PerkineElmer 343 polarimeter, with
a path length of 1 dm.
1
which gave [a]D ꢁ66 (c 1, CH3OH). H NMR (500 MHz,
CDCl3) d 8.37e7.58 (4H, CHAr), 5.53 (d, J¼4.2 Hz, 1H, H-
5), 4.92 (s, 1H, H-1), 4.48 (apparent t, J¼4.5 Hz, 1H, H-4),
4.11 (m, 2H, H-2, 3), 3.79 (s, 3H, CO2CH3), 3.36 (s, 3H,
OCH3). 13C NMR (125 MHz, D2O) d 168.1 (C-6), 164.8
(COAr), 133.1e122.5 (6C, CAr), 108.6 (C-1), 83.1 (C-4),
81.1 (C-2), 77.7 (C-3), 72.3 (C-5), 55.2 (OCH3), 53.0
(CO2CH3). Anal. Calcd for C16H17F3O8: C, 48.74; H, 4.35.
Found: C, 49.01; H, 4.48.

1708
A. Bordoni et al. / Tetrahedron 64 (2008) 1703e1710
3.2.3. Methyl (methyl 5-deoxy-b-L-arabino-hexofuranosid)-
uronate (4)
140e141 ꢀC, [a]D ꢁ52 (c 1.1, water), lit.19 mp 139 ꢀC, [a]D
ꢁ56 (c 1.4, water). 13C NMR (50 MHz, D2O) d 178.0 (C-6),
110.0 (C-1), 84.0 (C-3), 78.6 (C-4), 76.8 (C-2), 69.6 (C-5),
55.9 (OCH3).
Compound 4 was obtained by photolysis of 3 (0.29 g,
0.75 mmol) as described in Section 3.2. After evaporation of
the solvent, the residue was partitioned between water and
CH2Cl2. TLC examination of the aqueous layer showed the
deoxygented product (Rf 0.47, EtOAcetoluene, 9:1) and faster
moving components (Rf 0.95) corresponding to 9-methylcarb-
azole and a photoproduct of 9-methylcarbazole. After evapo-
ration under reduced pressure the syrup obtained was purified
by column chromatography (EtOAcetoluene, 97:3) to afford
0.102 g (66%) of 4, Rf 0.40 (EtOAcetoluene, 9:1), [a]D ꢁ68
(c 1, CHCl3). 1H NMR (500 MHz, D2O) d 4.89 (d, J¼
0.5 Hz, 1H, H-1), 4.30 (m, 1H, H-4), 4.04 (m, 1H, H-2),
3.89 (ddd, J¼4.4, 5.3, 0.4 Hz, 1H, H-3), 3.73 (CO2CH3),
3.36 (OCH3), 2.86 (dd, J¼4.4, 16.0 Hz, 1H, H-5), 2.72 (dd,
J¼8.7, 16.0 Hz, 1H, H-50). 13C NMR (125 MHz, D2O)
d 174.3 (C-6), 109.1 (C-1), 81.4 (C-4), 80.5 (C-2), 80.2 (C-
3), 55.4 (CO2CH3), 53.2 (OCH3), 38.6 (C-5). HRMS (ESI/
APCI) calcd for C8H18NO6: [MþNH4]þ 224.1929, found:
224.2234.
3.2.6. Methyl 5-O-(3-trifluoromethyl)benzoyl-
b-D-glucofuranosidurono-6,3-lactone (9)
To a solution of 8 (0.75 g, 3.96 mmol) in CH2Cl2 (7.0 mL)
containing pyridine (7.0 mL), cooled at 0 ꢀC, 3-(trifluorome-
thyl)benzoyl chloride (0.70 mL, 4.64 mmol) was added in
three aliquots for 1.5 h. The solution was stirred for an addi-
tional 0.5 h at 0 ꢀC and then for 1 h at room temperature.
TLC analysis of the syrup showed a main product with Rf
0.33 (tolueneeEtOAc, 7:3). The solution was diluted with
CH2Cl2 and washed with HCl (5%), water, satd NaHCO3,
and water, dried (NaSO4), and concentrated. The syrup ob-
tained was purified by column chromatography (toluenee
EtOAc, 4:1). Evaporation of the corresponding fractions af-
forded compound 9 (1.07 g, 75%), which gave [a]D þ33
1
(c 1, CHCl3). H NMR (200 MHz, CDCl3) d 8.44e7.68 (m,
4H, CHAr), 5.52 (d, J¼6.8 Hz, 1H, H-5), 5.34 (dd, J¼4.9,
6.8 Hz, 1H, H-4), 5.02 (d, J¼4.9 Hz, 1H, H-3), 4.98 (s, 1H,
H-1), 4.47 (d, J¼4.94 Hz, 1H, H-2), 3.38 (s, 3H, OCH3),
2.56 (d, 1H, OH). 13C NMR (50 MHz, CDCl3) d 170.1 (C-
6), 163.9 (COAr), 133.8e127.2 (6C, Ar), 109.7 (C-1), 83.8
(C-3), 77.5 (C-4), 75.5 (C-2), 70.0 (C-5), 55.7 (OCH3).
Anal. Calcd for C15H13F3O7: C, 49.73; H, 3.62. Found: C,
50.03; H, 3.59.
3.2.4. Methyl 5-deoxy-a-L-arabino-hexofuranoside (5)
To a suspension of NaBH4 (0.126 g, 3.34 mmol) in dry
THF (6.7 mL) at 0 ꢀC under argon atmosphere, a solution of
I2 (0.34 g, 1.34 mmol) in THF (3.2 mL) was added slowly
for 1 h. A solution of 4 (0.08 g, 0.38 mmol) in THF
(2.0 mL) was then added and the mixture was vigorously
stirred under reflux for 1.5 h. Then 5% HCl (2 mL) was care-
fully added and the mixture was partitioned with CHCl3eH2O.
The aqueous layer was washed with CHCl3 (3ꢂ15 mL) in or-
der to remove iodine and deionized by elution with water
through a column of IWTÒ TMD-8, mixed bed ion-exchange
resin (1.0ꢂ6.0 cm). Evaporation of the solvent under reduced
pressure and co-evaporation with methanol (3ꢂ5 mL) afforded
5 (0.051 g, 76%), [a]D ꢁ141 (c 1, CH3OH), lit.16 [a]D ꢁ137 (c
3.2.7. Methyl 5-deoxy-b-D-xylo-hexofuranosidurono-6,
3-lactone (10)
Compound 10 was obtained by photolysis of 9 (0.35 g,
0.85 mmol) as described above. After irradiation for 6.5 min,
the solvent was removed under reduced pressure and the syrup
obtained was purified by column chromatography (toluenee
EtOAc, 2:1). Evaporation of fractions with Rf 0.45 (EtOAc) af-
forded compound 10 (0.16 g, 97%), [a]D ꢁ53 (c 1, CHCl3). 1H
NMR (500 MHz, CDCl3) d 5.13 (dd, J¼5.2, 7.9 Hz, 1H, H-4),
4.94 (s, 1H, H-1), 4.88 (d, J¼5.2 Hz, 1H, H-3), 4.40 (s, 1H, H-
2), 3.35 (s, 3H, OCH3), 2.82 (dd, J¼7.9, 18.9 Hz, 1H, H-5),
2.64 (d, J¼18.9 Hz, 1H, H-50). 13C NMR (125 MHz, CDCl3)
d 175.9 (C-6), 109.4 (C-1), 86.4 (C-3), 77.6 (C-4), 77.1 (C-2),
55.3 (OCH3), 37.0 (C-5). HRMS (ESI/APCI) calcd for
(C7H14NO5): [MþNH4]þ 192.0866, found: 192.0867.
1
1, methanol). H NMR (500 MHz, D2O) d 4.89 (d, J¼1.4 Hz,
1H, H-1), 4.03 (m, 2H, H-2, 3), 3.83 (ddd, J¼0.5, 3.4, 7.1 Hz,
1H, H-4), 3.75 (ddd, J¼5.7, 6.9, 11.1 Hz, 1H, H-6), 3.71 (ddd,
J¼6.4, 7.4, 11.1 Hz, 1H, H-60), 3.39 (OCH3), 1.96 (dddd,
J¼4.8, 7.2, 9.3, 14.2 Hz, 1H, H-5), 1.87 (dddd, J¼5.7, 6.3,
8.3, 14.2 Hz, 1H, H-50). 13C NMR (125 MHz, D2O) d 108.7
(C-1), 81.6, 81.3 (C-2, 3), 80.8 (C-4), 59.0 (C-6), 55.4 (OCH3),
35.8 (C-5).
5-Deoxy-L-arabino-hexose (6) for HPAEC was obtained by
hydrolysis of 5 with 40 mM TFA (100 mL) at 100 ꢀC for 1 h,
[a]D ꢁ16 (c 1, water), lit.16 [a]D ꢁ18 (c 1, water).
3.2.8. Methyl 5-deoxy-b-D-xylo-hexofuranoside (11)
Compound 11 was obtained from 10 (0.10 g, 0.57 mmol)
by reduction as described for the preparation of 5 with
0.11 g (2.93 mmol) of NaBH4 and 0.23 g (0.91 mmol) of I2
in THF (4.0 mL). Compound 11 (0.073 g, 72%) gave [a]D
ꢁ69 (c 1, CH3OH). 1H NMR (500 MHz, D2O) d 4.85 (s,
1H, H-1), 4.37 (ddd, J¼4.5, 5.7, 8.1 Hz, 1H, H-4), 4.12 (d,
J¼1.6 Hz, 1H, H-2), 4.10 (dd, J¼1.6, 4.5 Hz, 1H, H-3), 3.75
(m, 1H, H-6), 3.73 (m, 1H, H-60), 3.37 (s, 3H, OCH3), 1.89
(m, 2H, H-5, 50). 13C NMR (125 MHz, D2O) d 109.2 (C-1),
80.5 (C-2, 4), 75.9 (C-3), 59.5 (C-6), 55.9 (OCH3), 32.5 (C-
3.2.5. Methyl b-D-glucofuranosidurono-6,3-lactone (8)
A suspension of D-glucuronic-6,3-lactone (7, 2.00 g,
1.14 mmol) in MeOH (15.0 mL) with Amberlite IR-120H cat-
ion resin (1.25 g) was stirred at 35 ꢀC until TLC examination
showed complete conversion of the starting material into a sin-
gle faster moving product (24 h). The resin was filtered and the
filtrate was evaporated under vacuum. NMR examination
showed the b/a anomeric mixture in a 4:1 ratio. Recrystalliza-
tion from CHCl3 afforded the b-anomer 8 (1.54 g, 71%), mp

A. Bordoni et al. / Tetrahedron 64 (2008) 1703e1710
1709
5). Anal. Calcd for C7H14O5: C, 47.18; H, 7.92. Found: C,
47.25; H 7.82.
3.2.12. 5-O-[3-(Trifluoromethyl)benzoyl]-b-D-gluco-
furanosidurono-6,3-lactone (16b)
A solution of 13 (2.07 g, 5.33 mmol) in AcOHeH2O (4:1,
15 mL) with H2SO4 (72 mL, 1.3 mmol) was heated under re-
flux for 1.5 h. The mixture was concentrated under diminished
pressure and the syrup obtained was crystallized from water. It
was filtered and thoroughly washed. 1H NMR spectrum of this
product showed the b-anomer with traces of the a-anomer. Re-
crystallization from CHCl3 gave pure 16b (1.15 g, 87%), mp
3.2.9. 1,2-Di-O-isopropylidene-5-O-(3-trifluoromethyl)-
benzoyl-a-D-glucofuranosidurono-6,3-lactone (13)
Compound 13 was obtained by reacting 12 (1.30 g,
6.15 mmol)26 with 3-(trifluoromethyl)benzoyl chloride
(1.10 mL, 7.20 mmol) in CH2Cl2 (15.0 mL) containing pyri-
dine (7.5 mL) at 0 ꢀC for 1 h. After the work up as used for
9, the syrup was purified by column chromatography (tolue-
neeEtOAc, 95:5) and evaporation of the fractions of Rf 0.65
(hexaneeEtOAc, 3:1) gave 13 (1.97 g, 82%), mp 102e
1
162e164 ꢀC, [a]D þ64 (c 1, acetone). H NMR (500 MHz,
DMSO-d6)
d
6.74 (d, J¼4.0 Hz, 1H, OH), 5.75 (d,
J¼6.8 Hz, 1H, H-5), 5.71 (d, J¼4.0 Hz, 1H, OH), 5.18 (d,
J¼4.0 Hz, 1H, H-1), 5.04 (dd, J¼4.8, 6.8 Hz, 1H, H-4), 4.92
(d, J¼4.8, 1H, H-3), 4.07 (d, J¼4.0 Hz, 1H, H-2). 13C NMR
(50.3 MHz, DMSO-d6) d 171.3 (C-6), 163.8 (COAr), 103.6
(C-1), 85.1 (C-3), 77.5 (C-4), 75.6 (C-2), 70.8(C-5). Anal.
Calcd for C14H11F3O7: C, 48.29; H, 3.18. Found: C, 48.34;
H, 3.26.
1
103 ꢀC, [a]D þ62 (c 1, CHCl3). H NMR (200 MHz, CDCl3)
4
d 8.42e7.15 (4H, CHAr), 6.06 (dd, J¼0.5 Hz, J¼3.7 Hz, 1H,
H-1), 5.76 (d, J¼4.4 Hz, 1H, H-5), 5.20 (ddd, 4J¼0.5 Hz,
J¼2.9, 4.4 Hz, H-4), 4.97 (d, J¼2.9 Hz, 1H, H-3), 4.89 (d,
J¼3.7 Hz, 1H, H-2), 1.52, 1.36 (2s, 6H, C(CH3)2). 13C NMR
(50.3 MHz, CDCl3) d 169.2 (C-6), 165.5 (COAr), 113.6
(C(CH3)2), 107.0 (C-1), 82.6, 82.3 (C-2, 3), 77.0 (C-4), 70.6
(C-5), 26.9, 26.5 (C(CH3)2). Anal. Calcd for C17H15F3O7: C,
52.58; H, 3.89. Found: C, 52.46; H, 4.05.
3.2.13. 5-Deoxy-a,b-D-xylo-hexofuranosidurono-6,
3-lactone (17)
Compound 17 was obtained by photolysis of 16 (0.26 g,
0.75 mmol) as described in Section 3.2. After evaporation of
the solvent, the residue was partitioned between water and
CH2Cl2. The aqueous layer was concentrated and purified by
column chromatography (EtOAcetoluene, 99:1) to afford
0.078 g (65%) of 17 (Rf 0.38, 9:1 EtOAcetoluene) as a b/a
3.2.10. 1,2-Di-O-isopropylidene-5-deoxy-a-D-
xylo-hexofuranosidurono-6,3-lactone (14)
Compound 14 was obtained by photolysis of 13 (0.29 g,
0.75 mmol) as described in Section 3.2. After evaporation of
the solvent, the syrup obtained was purified by column chro-
matography (tolueneeEtOAc, 8:1). Evaporation of fractions
with Rf 0.60 (hexaneeEtOAc, 1:1) afforded compound 14
(0.09 g, 90%), mp 89e90 ꢀC, [a]D þ73 (c 1, CHCl3), lit.28
1
mixture in 5:1 ratio. H NMR (500 MHz, D2O) data for 17b
d 5.42 (s, 1H, H-1), 5.18 (dd, J¼5.3, 7.7 Hz, 1H, H-4), 4.04
(d, J¼5.3 Hz, 1H, H-3), 4.37 (s, 1H, H-2), 3.06 (dd, J¼
7.7, 19.2 Hz, 1H, H-5), 2.75 (d, J¼19.2 Hz, 1H, H-50).
Selected signals for the a-anomer d 5.50 (d, J¼4.0 Hz, 1H,
H-1), 3.01 (dd, J¼6.5, 18.9 Hz, 1H, H-5), 2.71 (d,
J¼18.9 Hz, 1H, H-50). 13C NMR (125 MHz, D2O) for 17b
d 180.1 (C-6), 102.8 (C-1), 87.8 (C-3), 78.6, 77.2 (C-2, 4),
38.1 (C-5). For 17a d 179.7 (C-6), 97.5 (C-1), 89.2 (C-3),
75.9, 75.6 (C-2, 4), 36.1 (C-5). HRMS (ESI/APCI) calcd for
(C6H4NO5): [MþNH4]þ 178.0715, found: 178.0714.
1
mp 90e92 ꢀC. H NMR (500 MHz, CDCl3) d 5.97 (d, J¼
3.8 Hz, 1H, H-1), 5.00 (dd, J¼3.3, 4.2 Hz, 1H, H-4), 4.84
(d, J¼3.8 Hz, 1H, H-2), 4.81 (d, J¼3.3 Hz, 1H, H-3), 2.75 (d,
J¼18.0 Hz, 1H, H-5), 2.70 (dd, J¼4.2, 18.0 Hz, 1H, H-50),
1.52, 1.35 (2s, 6H, C(CH3)2). 13C NMR (125 MHz, CDCl3)
d 174.2 (C-6), 112.7 (C(CH3)2), 106.2 (C-1), 85.5 (C-3), 82.4
(C-2), 77.9 (C-4), 35.8 (C-5), 26.9, 26.5 (C(CH3)2). HRMS
(ESI/APCI) calcd for (C9H16NO5): [MþNH4]þ 218.1023,
found: 218.1025.
3.2.14. 2-Deoxy-L-xylo-hexitol (18, ‘5-deoxy-b-D-glucitol’)
Compound 17 (0.10 g) was reduced with NaBH4 (0.12 g,
3.08 mmol) and I2 (0.31 g, 1.23 mmol) in THF (5.0 mL) as de-
scribed for the preparation of 4. After the work up compound
18 (0.066 g, 63%) gave Rf 0.33 (n-PrOHeNH3eH2O,
7:0.5:0.5), [a]D þ14 (c 1, CH3OH). 1H NMR (500 MHz, D2O)
d 3.81 (m, 2H, H-2, 4), 3.70 (m, 3H, H-1, 6, 60), 3.62 (dd,
J¼6.8, 11.7 Hz, 1H, H-10), 3.49 (t, J¼4.5 Hz, 1H, H-3), 1.78
(m, 2H, H-5, 50). 13C NMR (125 MHz, D2O) d 74.1 (C-4),
72.6 (C-5), 69.3 (C-3), 63.3 (C-6), 59.1 (C-1), 35.8 (C-2).
Anal. Calcd for C6H14O5: C, 43.37; H, 8.49. Found: C,
43.18; H, 8.63.
3.2.11. 1,2-Di-O-isopropylidene-5-deoxy-
D-xylo-hexofuranose (15)
Compound 14 (0.16 g, 0.80 mmol) was reduced with the
I2eNaBH4 system,24 as described for the synthesis of 5, using
0.076 g (2.0 mmol) of NaBH4 and 0.203 g (0.8 mmol) of I2 in
THF (5.0 mL). After the work up, compound 15 (0.104 g,
64%) was obtained, [a]D ꢁ10 (c 1, water), mp 91e92 ꢀC,
lit.9 [a]D ꢁ10.5 (c 1.7, chloroform), mp 93e94.5 ꢀC. 1H NMR
(500 MHz, D2O) d 5.98 (d, J¼3.9 Hz, 1H, H-1), 4.68 (d,
J¼3.9 Hz, 1H, H-2), 4.30 (apparent dt, J¼2.6, 6.8 Hz, 1H,
H-4), 4.14 (d, J¼2.6 Hz, 1H, H-3), 3.71 (m, 2H, H-6, 60), 1.88
(q, J¼6.7 Hz, 2H, H-5, 50), 1.51, 1.35 (2s, 6H, C(CH3)2). 13C
NMR (125 MHz, D2O) d 112.9 (C(CH3)2), 104.6 (C-1), 85.2
(C-2), 78.8 (C-4), 75.1 (C-3), 59.3 (C-6), 30.6 (C-5), 26.0,
25.6 (C(CH3)2).
3.2.15. HPAECePAD analysis
Analysis by HPAECePAD was performed using a Dionex
DX 300 HPLC system with pulse amperometric detection
(PAD), set at 30 nA and E1¼þ0.05 V, E2¼þ0.60 V, and
E3¼ꢁ0.60 V. The column used was a CarboPac MA-10

1710
A. Bordoni et al. / Tetrahedron 64 (2008) 1703e1710
10. Portella, C.; Deshayes, H.; Pete, J. P.; Scholler, D. Tetrahedron 1984, 40,
3635e3644.
anion-exchange analytical column (4ꢂ250 mm), equipped
with a guard column MA-10 (4ꢂ50 mm). The separations
were performed isocratically at 0.6 M NaOH, at a flow rate
of 0.4 mL minꢁ1: tr for 4¼28.8 min; tr for 5¼13.7 min, tr for
6¼24.1 min.
11. Saito, I.; Ikehira, H.; Kasatani, R.; Watanabe, M.; Matsuura, T. J. Am.
Chem. Soc. 1997, 62, 8257e8260.
12. Jutten, P.; Scharf, H.-D. J. Carbohydr. Chem. 1990, 5, 675e681.
¨
13. Park, M.; Rizzo, C. J. J. Org. Chem. 1996, 61, 6092e6093; Prudhomme,
D. R.; Wang, Z.; Rizzo, C. J. J. Org. Chem. 1997, 62, 8257e8260; Wang,
Z.; Prudhomme, D. R.; Buck, J. R.; Park, M.; Rizzo, C. J. J. Org. Chem.
2000, 65, 5969e5985.
Acknowledgements
14. Bordoni, A.; Lederkremer, R. M.; Marino, C. Carbohydr. Res. 2006, 341,
1788e1795.
´
This work was supported by grants from Fundacion An-
torchas, Universidad de Buenos Aires, Agencia Nacional de
15. Wolfrom, M. L.; Matsuda, K.; Komitsky, F., Jr.; Whiteley, T. E. J. Org.
Chem. 1963, 28, 3551e3553.
´
´
´
Promocion Cientıfica y Tecnologica and CONICET. R.M.L.
and C.M. are research members of CONICET, and A.B. was
supported by a fellowship from CONICET.
16. Szarek, W. A.; Ritchie, R. G. S.; Vyas, D. M. Carbohydr. Res. 1978, 62,
89e103.
17. Lederkremer, R. M.; Marino, C. Adv. Carbohydr. Chem. Biochem. 2007,
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Supplementary data
19. Cadotte, J. E.; Smith, F.; Spriestersbach, D. J. Am. Chem. Soc. 1952, 74,
1501e1504.
1
Copies of the H and 13C NMR spectra for all new com-
`
20. Bertho, J. N.; Ferrieres, V.; Plusquellec, D. J. Chem. Soc., Chem.
pounds. Supplementary data associated with this article can
be found in the online version, at doi:10.1016/j.tet.2007.
12.005.
`
Commun. 1995, 1391e1393; Ferrieres, V.; Bertho, J.-N.; Plusquellec, D.
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