Synthesis of furan 4′-thio-C-nucleosides, their methylsulfonium and sulfoxide derivatives. Evaluation as glycosidase inhibitors

Article abstract of DOI:10.1016/S0040-4020(03)00339-9

A series of furan C-nucleosides having a sulfur atom in the sugar ring were synthesised. The α and β anomers of 3-ethoxycarbonyl-2-methyl-5-(4′-thio-D-erythrofuranosyl)furans 10 and 11 were obtained by acid treatment of (4′-S-acetyl-4′-thio-D-arabino-tetritol-1-yl)furan 9. Oxidation of 10 with m-chloroperbenzoic acid gave sulfoxide 12 as one epimer at the sulfur atom whereas 11 was transformed into sulfoxide 13 as an epimeric mixture. S-Methylation of 10 and 11 with methyl triflate led to sulfonium salts 14 and 15. The prepared compounds were found to be moderate inhibitors of α-L-fucosidase.

Full text of DOI:10.1016/S0040-4020(03)00339-9

Tetrahedron 59 (2003) 2801–2809
Synthesis of furan 40-thio-C-nucleosides, their methylsulfonium
and sulfoxide derivatives. Evaluation as glycosidase inhibitors
a
Vıctor Ulgar, Oscar Lopez, Ines Maya, Jose G. Fernandez-Bolan˜os and Mikael Bols
a,b
a
a
b
,
´
*
´
´
´
´
´
a
´ ´ ´
Departamento de Quımica Organica, Facultad de Quımica, Universidad de Sevilla, Apartado de Correos 553, E-41071 Sevilla, Spain
bDepartment of Chemistry, Aarhus University, DK-8000 Aarhus C, Denmark
Received 13 January 2003; revised 20 February 2003; accepted 4 March 2003
Abstract—A series of furan C-nucleosides having a sulfur atom in the sugar ring were synthesised. The a and b ano0mers of
3-ethoxycarbonyl-2-methyl-5-(40-thio-D-erythrofuranosyl)furans 10 and 11 were obtained by acid treatment of (40-S-acetyl-4 -thio-D-
arabino-tetritol-1-yl)furan 9. Oxidation of 10 with m-chloroperbenzoic acid gave sulfoxide 12 as one epimer at the sulfur atom whereas 11
was transformed into sulfoxide 13 as an epimeric mixture. S-Methylation of 10 and 11 with methyl triflate led to sulfonium salts 14 and 15.
The prepared compounds were found to be moderate inhibitors of a-L-fucosidase. q 2003 Elsevier Science Ltd. All rights reserved.
1. Introduction
analogues in order to study the influence of the heteroatom
and the positive charge in their inhibitory properties. Some
sugar analogues having divalent sulfur in the ring have
shown activity as glycosidase inhibitors, and that activity
could be modified after oxidation or alkylation.21,28,29 In
this paper we report the synthesis of 10 and 11 as the sulfur
analogues of 5 and 6, their sulfoxides, and the methyl
sulfonium ion derivatives, and evaluate their activity against
several glycosidases. Compounds 10 and 11 can be
considered as 40-thio-C-nucleosides, many of which exhibit
antitumor and antiviral properties.29–31
Glycosidase enzymes acting on cell-surface carbohydrates
are involved in processes such as viral infection and tumor
metastasis.1 Synthetic and naturally occurring inhibitors of
glycosidases2 – 7 have already demonstrated promising
therapeutic possibilities in controlling viral infections
including HIV,8 hepatitis,9 and influenza,10 tumor cells11
or carbohydrate-mediated metabolic disorders such as
diabetes12 and Gaucher disease.13
Recently, potent a-glucosidase inhibitors salacinol 114 and
kotalanol 215 (Fig. 1) have been isolated from Salacia
reticulata WIGHT14,15 and S. oblonga and S. chinensis,16
traditionally used in the Ayurvedic system of India and Sri
Lanka for the treatment of diabetes. The sulfonium structure
of these compounds has stimulated different groups to carry
out the synthesis of salacinol17,18 and other carbohydrate-
based cyclic sulfonium compounds19–21(e.g. 320 and 421) as
a new class of glycosidase inhibitors. Heteroanalogues of
salacinol having nitrogen22 or selenium23 instead of sulfur
have also been reported. Previous to salacinol few examples
of synthetic sugar-derived cyclic24 and bicyclic25 sulfonium
compounds were known.
2. Results and discussion
32
´
Lopez Aparicio et al. have previously described the
synthesis of 40-thio-D-erythrofuranosyl-furans 10 and 11 as
a non-resolved 1:6 a and b mixture by treatment of 5-(40-S-
tert-butyl-40-thio-D-arabino-tetritol-1-yl)-3-ethoxycar-
bonyl-2-methylfuran with conc. hydrochloric acid at rt.
Instead of this method we prepared the mixture of 10 and 11
by selective tosylation of 7,33 followed by nucleophilic
displacement with potassium thioacetate and treatment of 9
with 10% trifluoroacetic acid in refluxing 1:1 ethanol–water
(Scheme 1). This gave a mixture of 10 and 11 (76%) in a 2:3
The finding that the new type of imino-C-nucleosides 526
and 627 (Fig. 2) are strong and selective glycosidase
inhibitors against b-D-galactosidase and a-L-fucosidase,
respectively, has promted us to prepare their sulfur
1
a/b ratio, as deduced by H NMR. Repeated chromato-
graphy on silica gel of this mixture allowed the separation of
10 (29%) and 11 (39%).
The formation of these 40-thio-C-nucleosides 10 and 11
involves the hydrolysis of the thioacetate group and the
nucleophilic attack of the thiol group on the stabilised
carbocation in C-10 as described for the synthesis of 40-thio-
D-erythrofuranosyl-imidazoles (Fig. 3).34
Keywords: C-nucleoside; 40-thio-nucleoside; sulfoxide; sulfonium salt;
glycosidase inhibitor; furan.
*
Corresponding author. Tel.: þ34-95-4557151; fax: þ34-95-4624960;
e-mail: bolanos@us.es
0040–4020/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0040-4020(03)00339-9

2802
V. Ulgar et al. / Tetrahedron 59 (2003) 2801–2809
Figure 1.
The anomeric configuration of 10 and 11 was confirmed by
the optical rotation values, the a anomer dextrorotatory and
the b anomer being strongly levorotatory, in agreement wit0h
the reported data for 1132 and for the a and b anomers of 4 -
thio-D-erythrofuranosyl-imidazoles.34 The conformational
analysis of the thiofuranosyl ring of 10, based on the
relationship of the vicinal coupling constants with the
pseudorotational parameters,35,36 indicates that the a
anomer exhibits a strong preference for the N conformations
E2, 3T2 and 3E (not shown), which occupy the northern part
of the pseudorotational circle. These conformations are in
sulfoxide 13 in a 95% yield after purification. The 1H NMR
spectrum of 13 revealed a 2:3 mixture of stereoisomers,
which could not be resolved by chromatography. The
vicinal coupling constants for sulfoxides 12 and 13 indicate
that the conformation of the thiofuranosyl ring is not
modified by S-oxidation. The R configuration for the only
isomer of 12 is deduced from the deshielding effect
(0.63 ppm) of the S-O group on the H-30 (Fig. 4). This is
similar to the syn-axial effect found for thiane oxides that
implies a deshielding of the axial b-hydrogens in axial
sulfoxides.21,37 The proposed configuration for 12 implies
that the oxygen is added exclusively on the opposite face to
the three substituents on the thiolane ring. This is in
accordance with the reported steric approach control in
oxidations of cis-3,4-dihydroxythiolanes with peroxycar-
boxylic acids.38
0
accordance with the high values (9.8 and 6.9 Hz) for J3 ,4
0
(Table 1). On the contrary, the b anomer 11 populates
preferentially the S conformations 2E, 2T3 and E3, according
0
to the high value (7.2 Hz) for J1 ,2 and the small values (4.8
0
0
0
and 3.8 Hz) for J3 ,4 . Similar conformational behaviour was
found for the a and b anomers of 40-thio-C-nucleosides
derived from imidazol.34
For sulfoxide 13, the R configuration of the sulfur atom of
the minor isomer 13a could be deduced by the deshielding
effect of the oxygen attached to the ring sulfur on H-20
In order to test how a positive charge on the sulfur atom of
10 and 11 would affect their activity as glycosidase
inhibitors, we prepared the sulfoxides 12 and 13. Oxidation
of 10 with an equimolecular amount of m-chloroperbenzoic
acid at 2788C in EtOAc gave sulfoxide 12 in a 93% yield
2
(0.55 ppm), which is a pseudoaxial orientation in the E
conformation. This deshielding effect on H-20 is absent in
the major isomer 13b,0according to the trans disposition of
the S–O group to H-2 .
1
after chromatography (Scheme 2). H NMR of 12 showed
signals only for one stereoisomer. On the other hand,
treatment of the b isomer 11 with 1 equiv. of MCPBA gave
Reaction of 10 and 11 with methyl triflate in nitromethane
afforded the sulfonium salts 14 and 15, respectively, in
almost quantitative yields (Scheme 2), as mixtures of
stereoisomers which showed the same chromatographic
mobility. 1H NMR of 14 and 15 in D2O showed signals for
the two possible stereoisomers. The conformational
behaviour of the thiofuranosyl ring of these sulfonium
salts was found to be almost the same as for the parent
thiolanes 10 and 11, as deduced from the analysis of the
vicinal coupling constants. Interestingly, the preferred
conformations of the prepared thiolanes, their sulfoxides
and sulfonium salts derivatives are strongly dependent on
the anomeric configuration; however, they seem to be
almost independent of the configuration of the sulfur atom.
Figure 2.

V. Ulgar et al. / Tetrahedron 59 (2003) 2801–2809
2803
Scheme 1. Reagents and conditions: (i) TsCl, Py, 2158C, 2 h; (ii) KSAc, DMF, rt, 3 h; (iii) 10% TFA, 1:1 EtOH/H2O, reflux, 1 h.
The stereochemistry of the ring sulfur atom of the methyl
sulfonium salts 14 and 15 was determined by NOE
correlation experiments involving the SMe groups (Fig. 5).
In the case of 14, the R and S stereoisomers could be clearly
distinguished by the strong NOE effect observed between
H-10 and the SMe group for the R isomer (14a), which is
absent for the S isomer. Similarly, for 15 a strong NOE was
found between the SMe group and the anomeric proton in
the S isomer (15b).
of b anomer. After 6 h at rt the signals for the b anomer
increased up to 35% in a ca. 1:1 R/S ratio. The faster
anomerization for the a anomers 14 compared with that for
the b anomers 15 could be explained in terms of steric
hindrance between the furan on C-10 and the OH on C-20.
The shielding effect of the SMe group on protons H-40 that
are in a cis arrangement is observed by comparison of the
1
Table 1. 1H NMR data (d in ppm, J in Hz) for compounds 10–15
The H NMR of 15 in D2O just dissolved showed a R/S
mixture in a 2:5 ratio; 3 h after it showed these epimers in an
1:1.2 ratio and signals for the a anomer in a ca. 3%. The
higher proportion of the S isomer before equilibration could
be explained in terms of steric interaction between the
methyl group and the bulky substituent on C-10 during the
formation of the sulfonium salt. The equilibration observed
would involve the opening of the thiolanium ring to give a
stabilised carbocation on C-10 and a neutral thioether group,
whose sulfur is able to attack C-10 to form the other
stereoisomer in the sulfur atom. A slow anomerization took
place, as after 6 h at rt only 5% of a anomer was detected.
For a anomer 14 just dissolved in D2O a ca. 1:1 R/S mixture
ratio was observed together with 10% of both stereoisomers
Compound
H-10
H-20
H-30
H-4a0
H-4b0
H-4
10a
4.54
4.36
4.22
4.44
4.42
5.33
5.40
5.36
5.17
4.20
4.23
4.53
4.78
4.30
4.71
4.72
4.97
4.81
4.28
4.35
4.91
4.57
4.48
4.92
4.65
4.80
4.77
3.02
3.16
3.36
3.75
3.53
3.73
4.04
3.88
3.96
2.93
2.81
3.04
2.91
2.89
3.68
3.38
3.68
3.46
6.61
6.50
6.81
6.82
6.74
6.96
7.27
7.13
6.95
11a
12a
13a (R isomer)a
13b (S isomer)a
14a (R isomer)b
14b (S isomer)b
15a (R isomer)b
15b (S isomer)b
0
J1 ,2
0
0
J2 ,3
0
0
J3 ,4a
0
0
J3 ,4b
0
0
J4a ,4b
0
10a
3.8
7.2
3.5
10.4
10.0
3.0
3.0
9.8
3.3
3.5
3.0
3.6
3.2
3.0
3.1
3.1
3.0
9.8
4.8
9.9
2.1
4.3
7.4
7.3
2.0
3.6
6.9
3.8
7.1
4.7
1.9
9.6
9.9
3.8
1.2
9.5
11.1
13.7
14.3
14.8
13.2
12.4
13.4
14.4
11a
12a
13a (R isomer)a
13b (S isomer)a
14a (R isomer)b
14b (S isomer)b
15a (R isomer)b
15b (S isomer)b
9.8
a
CD3OD, 300 MHz.
D2O, 500 MHz.
b
Figure 3.

2804
V. Ulgar et al. / Tetrahedron 59 (2003) 2801–2809
Scheme 2. Reagents and conditions: (i) MCPBA (1 equiv.), EtOAc, 2788C, 20 min; (ii) MeOTf, MeNO2, 08C, 2 h.
chemical shift of H-40a in 14a (3.73 ppm) and in 14b
(4.04 ppm). Similarly, H-40b is shielded in 14b (3.38 ppm)
compared to that proton in 14a (3.68 ppm). The SMe group
also provokes a deshielding effect (ca. 0.3 ppm) on the cis-
arranged H-30 as observed by comparison of that proton in
14a (4.92 ppm) and in 14b (4.65 ppm). For the sulfonium
salts of b configuration, 15a and 15b, it was confirmed by
NOE experiments that the cis-arranged H-40 to H-30 is that
anomers C-10 is more shielded (5.5 ppm) for the R isomer
15a. It is noteworthy that in sulfoxides 13a and 13b the
oxygen on the sulfur0 atom exhibits the same effect as
the methyl group, C-1 being shielded (9.5 ppm) when the
oxygen and the heterocycle are cis-arranged.
We have tested compounds 10–15 for their inhibitory
activities against several glycosidases and the results are
shown in Table 3. The strong inhibitory activity found for
the imino-C-nucleoside analogue of a configuration 5
against b-galactosidase (Aspergillus oryzae, Ki¼6.6 mM)26
contrasts with the absence of activity of the thio analogue 10
and its sulfoxide 12 and sulfonium derivatives 14. These
40-thionucleosides in the E2 conformation have the sub-
stituents on the thio sugar ring with an orientation
resembling the C-3–C-5 moiety of D-galactose (Fig. 6), as
has been suggested for 526 and several polihydroxylated
pyrrolidines.39 However the lack of inhibitory activity for
10, 12 and 14 compared to the strong activity of the
pyrrolidine isoster 5 may be due to the difference in the
geometry of the two rings in terms of puckering and bond
lengths,28a and the ability of 5 to become protonated at the
nitrogen atom in order to mimic oxocarbenium cation C
and, thus, to interact strongly with a carboxylate group at the
enzyme active site.40,41 In contrast, nitrogen analogues of
salacinol 1 have shown less inhibitory activity than the
natural sulfonium analogue.22
0
0
with the higher J3 ,4 (3.6 and 3.8 Hz). The shielding effect of
the SMe group on the cis-arranged H-40 makes this proton
the most shielded proton on C-40 for 15a and 15b.
The SMe group provokes a shielding effect on C-10 when the
met0hyl group is in a cis arrangement to the heterocycle on
C-1 (Table 2). Thus, for the a anomers C-10 is more
shielded (6.3 ppm) for the S isomer 14b, whereas for the b
On the other hand, despite the strong activity determined for
compound 6 against a-fucosidase (bovine epididymis,
Ki¼9 mM; human placenta, Ki¼15 mM),27 its counterpart
11 showed only a weak inhibition against a-fucosidase. This
activity was found to be improved with positive charge on
the sulfur atom, although it was slightly better with the
Figure 4. One of the preferred conformations for 12 (E2) and 13 (2E).

V. Ulgar et al. / Tetrahedron 59 (2003) 2801–2809
2805
Figure 5. NOE correlations observed for14 and15 in one of their preferred conformations.
partial positive charge in sulfoxide 13, than in sulfonium 15.
These 40-thionucleosides of b-configuration have the
hydroxy groups in the E3 conformation with the same
orientation as those groups on C-3 and C-4 for L-fucose
(Fig. 6). The analogues of a configuration were also weak
inhibitors, showing that a-fucosidase does not discriminate
the anomeric configuration of these nucleoside analogues.
Table 2. 13C NMR (d in ppm) for compounds 10–15
Compound
C-10
C-20
C-30
C-40
S–Me
10a
45.53
46.18
72.94
61.92
71.44
61.83
55.52
54.29
59.81
75.72
80.17
76.50
76.82
76.13
76.15c
75.64c
76.63
78.29
77.68
75.37
74.95
72.80
74.34
74.33
74.83
72.73
73.99
33.68
34.22
55.57
60.57
56.61
43.49
45.49
48.50
45.95
–
–
–
–
11a
12a
13a (R isomer)a
13b (S isomer)a
14a (R isomer)b
14b (S isomer)b
15a (R isomer)b
15b (S isomer)b
–
27.20
26.02
23.34
29.89
In contrast, the compounds of a configuration 10, 12, 14
were not recognised by the a-glucosidase from baker yeast,
and an improvement of the inhibitory activity against
b-glucosidase from almonds was related to the charge on
the sulfur atom, sulfide 10 being non-active, and sulfonium
14 (Ki¼250 mM) the most active of them. The compounds
of b configuration 11, 13 and 15 also exhibited a weak
a
CD3OD, 75.5 MHz.
D2O, 125.7 MHz.
Assignments may have to be reversed.
b
c
Table 3. Inhibition constants (Ki) in mM
Enzyme
10
11
13
14
15
12
b-Galactosidase (Aspergillus oryzae) NI
NI
NI
NI
NI
NI
a-L-Fucosidase (bovine kidney)
a-Glucosidase (baker yeast)
b-Glucosidase (almonds)
452
853
1350
674
1220
NI
5500
348
496
771
500
NI
250
663
NI
1050
NIa
NI
a
NI: no inhibition.

2806
V. Ulgar et al. / Tetrahedron 59 (2003) 2801–2809
Figure 6. Comparison of the nucleosides analogues 5, 10, 12 and 14 in the E2 conformation, and 6, 11, 13 and 15 in the E3 conformation with the oxocarbenium
cations from D-galactose C and L-fucose D.
activity against the a and b-glucosidases studied, except for
the sulfonium 15, which turned out to be non-active against
the a-glucosidase tested.
3-ethoxycarbonyl-2-methyl-5-(D-arabino-tetritol-1-yl)furan
733 (0.60 g, 2.19 mmol) in pyridine (4 mL) at 2158C was
added a solution of p-toluenesulfonyl chloride (0.83 g,
4.38 mmol) in dry pyridine (4 mL). After 2 h water was
added (three drops) and the solution was concentrated to
dryness and co-concentrated several times with toluene/
ethanol to afford crude 8. The residue was purified by
column chromatography (30:1 CH2Cl2/MeOH) to afford 8
as a syrup (0.72 g, 77%). Rf 0.65 (10:1 EtOAc/Et2O);
[a]2D7¼23.28 (c 1.0, CHCl3); IR: nmax 3468, 1704, 1363,
In conclusion, the results show that 40-thio-D-erythro-
furanosyl-furans of a and b configuration, their sulfoxides
and methyl sulfonium salts are weak inhibitors against
a-fucosidase from bovine kidney, and not active at all
against the b-galactosidase tested. This is in contrast with
the activity exhibited by the analogues having a nitrogen in
the furanosyl ring that are strong and selective inhibitors of
these enzymes. The positive charge on the sulfur atom of
these nucleosides analogues does not seem to be relevant for
their inhibitory properties.
1
1180, 1093, 822 cm21; H NMR (300 MHz, CD3OD): d
7.79 (m, 2H, Ar), 7.42 (m, 2H, Ar), 6.54 (s, 1H, H-4), 4.81
0
0
0
(d, 1H, J1 ,2 ¼2.6 Hz, H-1 ), 4.25 (q, 2H, J¼7.1 Hz,
0
0
0
0
CH2CH3), 4.24 (dd, 1H, J3 ,4a ¼2.5 Hz, 0 J4a ,4b ¼10.0 Hz,
H-4a0), 4.05 (dd, 1H, J3 ,4b ¼6.2 Hz, H-4b ), 3.85 (ddd, 1H,
0
0
0
0
0
0
J2 ,3 ¼8.3 Hz, H-3 ), 3.68 (dd, 1H, H-2 ), 2.51 (s, 3H, CH3
furan), 2.44 (s, 3H, CH3 Ar), 1.32 (t, 3H, CH2CH3); 13C
NMR (75.5 MHz, CD3OD): d 165.67 (CO), 159.62 (C-2),
155.11 (C-5), 146.41, 134.25, 131.00, 129.10 (Ar), 115.11
(C-3), 108.54 (C-4), 73.64 (C-40), 73.48 (C-20), 70.12 (C-30),
67.44 (C-10), 61.26 (CH2CH3), 21.56 (CH3 Ar), 14.64
(CH2CH3), 13.76 (CH3 furan); FABMS: m/z 451 [100,
(MþNa)þ]; HRFABMS calcd for C19H24NaO9S (MþNa)þ
451.1039, found 451.1029.
3. Experimental
3.1. General
Nitromethane was dried over anhydrous CaCl2 and then
˚
distilled over 4 A molecular sieves. Pyridine was refluxed
over potassium hydroxide and then distilled. Optical
rotations were measured with a Perkin–Elmer 241 polari-
meter, and IR spectra (KBr disks) were obtained with an
FT-IR Bomem MB-120 spectrophotometer. H (300 and
3.1.2. 5-(40-S-Acetyl-40-thio-D-arabino-tetritol-1-yl)-3-
1
500 MHz) and 13C (75.5 and 125.7 MHz) NMR spectra
were recorded on Bruker AMX-300 and AMX-500
spectrometers for solutions in D2O (internal DOH at
4.75 ppm and internal 1,4-dioxane at 67.4 ppm as reference)
and CD3OD (internal CD2HOD at 3.30 ppm and internal
13CD3OD at 49.0 ppm as reference). The assignments of 1H
and 13C signals were confirmed by homonuclear COSY and
heteronuclear 2D correlated spectra, respectively. Mass
spectra were recorded on Kratos MS 80 RFA and
Micromass AutoSpeQ mass spectrometers. TLC was
performed on aluminium pre-coated sheets (E. Merck Silica
Gel 60 F254); spots were visualized by UV light, by charring
with 10% H2SO4 in EtOH and by CEMOL (1% ceric sulfate
and 1.5% ammonium molybdate in 10% aqueous H2SO4).
Column chromatography was performed using E. Merck
Silica Gel 60 (40–63 mm).
ethoxycarbonyl-2-methylfuran 9.
A solution of 8
(2.34 g, 5.45 mmol) and potassium thioacetate (1.24 g,
10.90 mmol) in N,N-dimethylformamide (20 mL) was kept
at rt for 3 h. Water (80 mL) was added and the compound
was extracted with ethyl acetate (4£50 mL). The organic
layer was washed with brine (2£50 mL), dried (MgSO4),
concentrated and the residue was purified by column
chromatography (5:1 Et2O/hexane) to afford 9 as a syrup
(1.38 g, 76%). Rf 0.60 (10:1 EtOAc/Et2O); [a]2D6¼0.08 (c
0.8, CHCl3); IR: nmax 3419, 1704, 1424, 1226, 1093,
1
784 cm21; H NMR (300 MHz, CD3OD): d 6.57 (s, 1H,
0
0
0
H-4), 4.85 (d, 1H, J1 ,2 ¼2.9 Hz, H-1 ), 4.25 (q, 2H,
0
0
0
0
J¼7.1 Hz, CH2CH3), 3.76 (td, 1H, J2 ,3 ¼7.8 Hz, J3 ,4a
¼
0
0
0
0
3.2 Hz, J3 ,4b ¼7.8 Hz, H-3 ), 3.64 (dd, 1H, H-2 )0, 3.42 (dd,
0
0
0
1H, J4a ,4b ¼13.8 Hz, H-4a ), 2.97 (dd, 1H, H-4b ), 2.53 (s,
3H, CH3 furan), 2.32 (s, 3H, SAc), 1.32 (t, 3H, CH2CH3);
13C NMR (75.5 MHz, CD3OD): d 197.67 (SCOCH3),
165.60 (CO), 159.61 (C-2), 155.27 (C-5), 115.18 (C-3),
108.55 (C-4), 76.08 (C-20), 71.21 (C-30), 67.72 (C-10), 61.26
3.1.1. 3-Ethoxycarbonyl-2-methyl-5-(40-O-p-toluene-
sulfonyl-D-arabino-tetritol-1-yl)furan 8. To a solution of

V. Ulgar et al. / Tetrahedron 59 (2003) 2801–2809
2807
(CH2CH3), 34.41 (C-40), 30.45 (SCOCH3), 14.64
(CH2CH3), 13.76 (CH3 furan); FABMS: m/z 355 [100,
(MþNa)þ]; HRFABMS calcd for C14H20NaO7S (MþNa)þ
355.0827, found 355.0827.
chromatography (20:1 CH2Cl2/MeOH) to afford 13 (24 mg,
95%). The 1H NMR of 13 showed a mixture of
stereoisomers R (13a) and S (13b) in a 2:3 ratio. Rf 0.30
(10:1 CH2Cl2/MeOH); [a]2D5¼2201.88 (c 1.1, CHCl3); IR:
1
nmax 3261, 1720, 1418, 1228, 1093, 1013 cm21; H NMR
3.1.3. 3-Ethoxycarbonyl-2-methyl-5-(40-thio-a-D-
erythrofuranosyl)furan 10 and 3-ethoxycarbonyl-2-
(300 MHz, CD3OD) for 13a: Table 1 and d 4.27 (q, 2H,
J¼7.1 Hz, CH2CH3), 2.57 (s, 3H, CH3 furan), 1.33 (t, 3H,
CH2CH3); for 13b: d 6.74 (s, 1H, H-4), 4.27 (q, 2H,
J¼7.1 Hz, CH2CH3), 2.57 (s, 3H, CH3 furan), 1.33 (t, 3H,
CH2CH3); 13C NMR (75.5 MHz, CD3OD) for 13a: Table 2
and d 165.20 (CO), 161.67 (C-2), 145.38 (C-5), 115.91
(C-3), 113.89 (C-4), 61.40 (CH2CH3), 14.63 (CH2CH3),
13.88 (CH3 furan); for 13b: d 165.08 (CO), 161.35 (C-2),
147.74 (C-5), 115.91 (C-3), 111.56 (C-4), 61.47 (CH2CH3),
14.63 (CH2CH3), 13.88 (CH3 furan). CIMS: m/z 289 [68,
(MþH)þ], 253 [100, (MþH22H2O)þ]; HRCIMS calcd for
C12H17O6S (MþH)þ 289.0746, found 289.0741.
methyl-5-(40-thio-b-D-erythrofuranosyl)furan 11.
A
solution of 9 (0.96 g, 2.88 mmol) in 1:1 ethanol/water
(16 mL) containing trifluoroacetic acid (1.6 mL) was boiled
under reflux for 1 h. The solution was co-concentrated with
1
ethanol (3£5 mL). The H NMR of the residue showed a
mixture of the a and b anomers in a 2:3 ratio. Purification by
column chromatography (5:1 EtOAc/Et2O) gave a mixture
of 10 and 11 (0.60 g, 76%), which were separated by
column chromatography followed by preparative TLC of
the non-resolved fractions (40:1 CH2Cl2/MeOH). Eluated
first was 10 as a white solid (0.23 g, 29%). Rf 0.25 (40:1
CH2Cl2/MeOH); [a]2D5¼þ32.88 (c 1.4, CHCl3); IR: nmax
3.1.6. (2S,3R,4S)-2-(3-Ethoxycarbonyl-2-methylfuran-5-
yl)-3,4-dihydroxy-1-methylthiolanium triflate 14. To a
solution of 10 (42 mg, 0.16 mmol) in dry MeNO2 (1 mL) at
08C under argon was added methyl triflate (23 mL,
0.21 mmol). After 2 h the solution was concentrated to
1
3428, 1712, 1585, 1418, 1236, 1093, 783 cm21; H NMR
(300 MHz, CD3OD): Table 1 and d 4.24 (q, 2H, J¼7.1 Hz,
CH2CH3), 2.51 (s, 3H, CH3 furan), 1.32 (t, 3H, CH2CH3);
13C NMR (75.5 MHz, CD3OD): Table 2 and d 165.67 (CO),
159.85 (C-2), 151.89 (C-5), 115.24 (C-3), 110.60 (C-4),
61.23 (CH2CH3), 14.64 (CH2CH3), 13.77 (CH3 furan);
CIMS: m/z 273 [64, (MþH)þ]; HRCIMS calcd for
C12H17O5S (MþH)þ 273.0797, found 273.0784. Eluted
second was 11 as a syrup (0.30, 39%). Rf 0.22 (40:1
CH2Cl2/MeOH); [a]D25¼2160.88 (c 1.0, CHCl3), lit.32
[a]1D5¼21678 (c 1.0, CHCl3); IR: nmax 3396, 1720, 1236,
1093, 783 cm21; 1H NMR (300 MHz, CD3OD): Table 1 and
d 4.24 (q, 2H, J¼7.1 Hz, CH2CH3), 2.52 (s, 3H, CH3 furan),
1.32 (t, 3H, CH2CH3); 13C NMR (75.5 MHz, CD3OD): d
165.46 (CO), 160.10 (C-2), 153.13 (C-5), 115.23 (C-3),
109.01 (C-4), 61.29 (CH2CH3), 14.63 (CH2CH3), 13.79
(CH3 furan); CIMS: m/z 273 [100, (MþH)þ]; HRCIMS
calcd for C12H17O5S (MþH)þ 273.0797, found 273.0790.
1
give pure 14 (66 mg, 98%). The H NMR of 14 in D2O
showed a mixture of stereoisomers R (14a) and S (14b) in an
1:1 ratio. Rf 0.18 (10:1 CH2Cl2/MeOH); [a]2D0¼þ67.68 (c
1.1, H2O); IR: nmax 3364, 1704, 1434, 1259, 1093,
;
1037 cm21 1H NMR (500 MHz, D2O) for R isomer
(14a): Table 1 and d 4.29 (q, 2H, J¼7.1 Hz, CH2CH3),
3.15 (s, 3H, SMe), 2.53 (s, 3H, CH3 furan), 1.30 (t, 3H,
CH2CH3); for S isomer (14b): d 4.28 (q, 2H, J¼7.1 Hz,
CH2CH3), 2.83 (s, 3H, SMe), 2.53 (s, 3H, CH3 furan), 1.30
(t, 3H, CH2CH3); 13C NMR (125.7 MHz, D2O) for 14a and
14b: Table 2 and d 166.84, 166.77 (CO), 164.58, 163.42
(C-2), 142.42, 140.16 (C-5), 117.72 (C-4 for 14b), 115.79,
115.59 (C-3), 114.42 (C-4 for 14a), 62.90 (CH2CH3), 14.59,
14.42 (CH2CH3, CH3 furan). FABMS: m/z 723 [2,
(2M2TfO)þ], 459 [3, (MþNa)þ], 287 [100, (M2TfO)þ];
HRFABMS calcd for C14H19F3NaO8S2 (MþNa)þ
459.0371, found 459.0359.
3.1.4. 3-Ethoxycarbonyl-2-methyl-5-(40-thio-a-D-
erythrofuranosyl)furan S-oxide 12. To a solution of 10
(30 mg, 0.11 mmol) in EtOAc (2 mL) at 2788C under argon
was added a solution of m-chloroperbenzoic acid (28 mg,
0.11 mmol) in EtOAc (1 mL). After 20 min the solution was
concentrated and the crude product was purified by column
chromatography (20:1 CH2Cl2/MeOH) to afford 12 (30 mg,
93%). Rf 0.39 (20:1 CH2Cl2/MeOH); [a]2D4¼2188.98 (c 1.0,
CHCl3); IR: nmax 3357, 1704, 1521, 1236, 1093,
3.1.7. (2R,3R,4S)-2-(3-Ethoxycarbonyl-2-methylfuran-5-
yl)-3,4-dihydroxy-1-methylthiolanium triflate 15. To a
solution of 11 (36 mg, 0.13 mmol) in dry MeNO2 (1 mL) at
08C under argon was added methyl triflate (19 mL,
0.17 mmol). After 2 h the solution was concentrated to
1
give pure 15 (57 mg, quantitative). The H NMR of 15 in
1
1013 cm21; H NMR (300 MHz, CD3OD): Table 1 and d
D2O showed a mixture of stereoisomers R (15a) and S (15b)
in a 2:5 ratio; after 3 h at rt a 1:1.2 ratio was observed. Rf
0.14 (10:1 CH2Cl2/MeOH); [a]2D0¼279.68 (c 0.9, H2O); IR:
4.27 (q, 2H, J¼7.1 Hz, CH2CH3), 2.56 (s, 3H, CH3 furan),
1.33 (t, 3H, CH2CH3); 13C NMR (75.5 MHz, CD3OD):
Table 2 and d 165.24 (CO), 160.76 (C-2), 147.11 (C-5),
115.84 (C-3), 111.98 (C-4), 61.42 (CH2CH3), 14.62
(CH2CH3), 13.74 (CH3 furan); CIMS: m/z 577 [3,
(2MþH)], 289 [78, (MþH)þ], 271 [100, (MþH2H2O)þ],
253 [87, (MþH22H2O)þ]; HRCIMS calcd for C12H17O6S
(MþH)þ 289.0746, found 289.0746.
3.1.5. 3-Ethoxycarbonyl-2-methyl-5-(40-thio-b-D-
erythrofuranosyl)furan S-oxide 13. To a solution of 11
(24 mg, 0.09 mmol) in EtOAc (2 mL) at 2788C under argon
was added a solution of m-chloroperbenzoic acid (22 mg,
0.09 mmol) in EtOAc (1 mL). After 20 min the solution was
concentrated and the crude product was purified by column
1
nmax 3389, 1704, 1434, 1267, 1172, 1093 cm21; H NMR
(500 MHz, D2O) for R isomer (15a): Table 1 and d 4.29 (q,
2H, J¼7.1 Hz, CH2CH3), 2.62 (s, 3H, SMe), 2.55 (s, 3H,
CH3 furan), 1.31 (t, 3H, CH2CH3); for S isomer (15b): d
4.28 (q, 2H, J¼7.1 Hz, CH2CH3), 3.27 (s, 3H, SMe), 2.53 (s,
3H, CH3 furan), 1.30 (t, 3H, CH2CH3); 13C NMR
(125.7 MHz, D2O) for R isomer (15a): Table 2 and d
166.57 (CO), 164.63 (C-2), 140.76 (C-5), 117.54 (C-4),
116.05 (C-3), 63.03 (CH2CH3), 14.64, 14.49 (CH2CH3, CH3
furan); for S isomer (15b): d 166.79 (CO), 163.86 (C-2),
143.07 (C-5), 115.74 (C-3), 114.65 (C-4), 62.96 (CH2CH3),
14.64, 14.49 (CH2CH3, CH3 furan). FABMS: m/z 723 [2,
(2M2TfO)þ], 459 [4, (MþNa)þ], 287 [100, (M2TfO)þ];

2808
V. Ulgar et al. / Tetrahedron 59 (2003) 2801–2809
HRFABMS calcd for C14H19F3NaO8S2 (MþNa)þ
K. D.; Kati, W.; Maring, C.; Kempf, D.; Hutchins, C.; Laver,
W. G. Bioorg. Med. Chem. Lett. 2002, 12, 3425–3429.
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459.0371, found 459.0360.
3.2. Enzyme kinetics
The enzyme assays were carried out as described pre-
viously.42 All assays were performed at pH 6.8 and 328C.
Steady state kinetics was performed and reaction rates were
measured after possible slow-onset inhibition was essen-
tially complete. The inhibition constants (Ki) were obtained
0
0
from the formula Ki¼[I]/(KM /KM21), where KM and KM
are Michaelis–Menten constants with and without inhibitor
0
present (Table 3). KM and KM were obtained from a Hanes
13. Dwek, R. A.; Butters, T. D.; Platt, F. M.; Zitzmann, N. Nature
Rev. Drug Discov. 2002, 1, 65–75.
plot, which was also used to ensure that inhibition was
competitive. The following KM values (without inhibitor)
were obtained using 4-nitrophenyl glycosides as substrates,
except for b-galactosidase for which 2-nitrophenyl glyco-
side was used: a-glucosidase (yeast): 0.20 mM, b-glucosi-
dase (almonds): 3.90 mM, a-fucosidase (bovine kidney):
0.34 mM, b-galactosidase (Aspergillus oryzae): 1.23 mM.
The amount of p-nitrophenol was determined colorimetri-
cally at 400 nm and the o-nitrophenol at 420 nm.
14. (a) Yoshikawa, M.; Murakami, T.; Shimada, H.; Matsuda, H.;
Yamahara, J.; Tanabe, G.; Muraoka, O. Tetrahedron Lett.
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Yoshikawa, M. Chem. Pharm. Bull. 1999, 47, 1725–1729.
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Acknowledgements
17. Yuasa, H.; Takada, J.; Hashimoto, H. Tetrahedron Lett. 2000,
41, 6615–6618.
´
We thank the Direccion General de Ensen˜anza Superior e
18. Ghavami, A.; Johnston, B. D.; Pinto, B. M. J. Org. Chem.
2001, 66, 2312–2317.
´
´
Investigacion Cientıfica (Grant No BQU 2001-3740), the
Junta de Andalucia (FQM134) and the Danish National
Research Council (THOR program) for financial support.
19. (a) Svansson, L.; Johnston, B. D.; Gu, J.-H.; Patrick, B.; Pinto,
B. M. J. Am. Chem. Soc. 2000, 122, 10769–10775.
(b) Ghavami, A.; Johnston, B. D.; Maddess, M. D.; Chinapoo,
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´
´
O. Lopez thanks the Ministerio de Educacion y Cultura for
the fellowship. This work is part of the European
Programme COSTD13, action number D13/0001/98.
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