Synthesis of N-methyl-d-ribopyranuronamide nucleosides

Article abstract of DOI:10.1016/j.tet.2008.08.027

The synthesis of N-methyl-d-ribopyranuronamide nucleosides is described. The key route is the rearrangement of a 1,2-O-isopropylidene protected furanose sugar with a carboxamide function in the 4-position to a ribopyranuronamide ring. The Lewis acid catalyzed condensation of adenine and thymine nucleobases with the per-O-acetylated N-methyl-d-ribopyranuronamide sugar is used to give the target nucleosides as a mixture of the α and β anomers. The mixture was separated and the final compounds were obtained by deacetylation in basic conditions.

Full text of DOI:10.1016/j.tet.2008.08.027

Tetrahedron 64 (2008) 10062–10067
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis of N-methyl-
D-ribopyranuronamide nucleosides
*
Shiqiong Yang, Roger Busson, Piet Herdewijn
Laboratory for Medicinal Chemistry, Rega Institute for Medical Research, Catholic University of Leuven, Minderbroedersstraat 10, B-3000 Leuven, Belgium
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 9 July 2008
Received in revised form 5 August 2008
Accepted 9 August 2008
Available online 13 August 2008
The synthesis of N-methyl-D-ribopyranuronamide nucleosides is described. The key route is the
rearrangement of a 1,2-O-isopropylidene protected furanose sugar with a carboxamide function in the
4-position to a ribopyranuronamide ring. The Lewis acid catalyzed condensation of adenine and thymine
nucleobases with the per-O-acetylated N-methyl-
nucleosides as a mixture of the and anomers. The mixture was separated and the final compounds
were obtained by deacetylation in basic conditions.
D-ribopyranuronamide sugar is used to give the target
a
b
Keywords:
Ribopyranuronamide
Nucleosides
Ó 2008 Elsevier Ltd. All rights reserved.
Nucleobase
1. Introduction
In this paper, we describe the synthesis of this class of nucleo-
side analogues (1a, 1b and 2a, 2b) with an adenine and thymine
base and in which the sugar moiety of the nucleoside is replaced by
an N-methyl-D-ribopyranuronamide ring (Fig. 1). These compounds
have been evaluated for their potential antiviral activity and have
been found to be inactive.
Modification of the sugar moiety of nucleosides has given
a plethora of biological active compounds.1 Many modified nucleo-
sides exhibiting remarkable antiviral and anticancer properties
have been discovered in this way.2 The biological activity of these
nucleoside analogues is highly related to their substrate specificity
for cellular and viral kinase and, as triphosphate, for cellular and
viral polymerases.3,4
2. Results and discussion
In the series of azasugar nucleosides, D- and L-nucleoside ana-
Thefournucleosides1a,1band2a, 2bweresynthesizedfrom3-O-
acetyl-1,2:5,6-di-O-isopropylidene-a-D-allofuranose (3) (Scheme 1).
logues with a pyrrolidine,5 pyridine, piperidine7,8 and five-, six-,
seven-membered lactam9–12 ring have been synthesized and bio-
logically evaluated. These nucleoside analogues are characterized
by the presence of one nitrogen atom in the sugar ring moiety.
Replacement of the oxygen atom of a furanose nucleoside by an
amide function would deliver us ribopyranuronamide nucleosides.
The amide resonance would give the nucleosides with a restricted
conformational flexibility as is seen with cyclohexenyl
nucleosides.13
6
The synthesis of the starting material 3 has been described
previously.16,17 We followed the literature procedure and obtained
compound 3 starting from 1,2:5,6-di-O-isopropylidene-a-D-gluco-
furanose by inversion of configuration in the 3-position and
Few attempts have been described before to synthesize pyr-
anuronamide nucleosides.14,15 In 1987, Timoshchuk14 described the
synthesis of the N-unsubstituted-
moiety by the rearrangement of the
a
-
D
-xylopyranuronamide sugar
-xylopyranuronamide in
a-D
BF3$Et2O and acetic anhydride. However, they failed to introduce
the base moiety using fluorouracil as example. In 2005, Van Rom-
paey et al.15 isolated the acetyl-protected 4-azido 6-oxopiperidinyl
nucleoside with the 6-chloropurine base, as unexpected compound
during a sugar–base condensation reaction.
* Corresponding author. Tel.: þ32 16 337387; fax: þ32 16 337340.
E-mail address: piet.herdewijn@rega.kuleuven.be (P. Herdewijn).
Figure 1. Structures of 1a, 1b and 2a, 2b.
0040-4020/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2008.08.027

S.-Q. Yang et al. / Tetrahedron 64 (2008) 10062–10067
10063
Scheme 1. Reagents: (a) 75% AcOH; (b) KIO4, CH3OH/H2O; (c) KMnO4, 50% AcOH; (d) EDAC, DMAP, CH3OH; (e) CH3NH2, THF; (f) BF3$Et2O, acetic anhydride; (g) silylated thymine or
N6-benzoyladenine, SnCl4, CH3CN; (h) saturated NH3 in CH3OH.
followed by acetylation.18–20 Removal of the 5,6-O-isopropylidene
protection group was carried out under mild acidic conditions (75%
acetic acid). Without purification, the obtained diol was oxidized to
an aldehyde intermediate and further to the carboxylic acid 4.21 The
methylamide group of 6 was introduced by esterification of the
carboxylic acid 4 to yield compound 5 followed by reaction with
methylamine under pressure.22,23
Having the key N-methyl-D-ribopyranuronamide sugar moiety
in hand, final conversion to the target nucleosides was attempted
using silylated thymine and N6-benzoyladenine in the presence of
SnCl4.24–26 The nucleosidation reactions led, in both cases, to
moderate yield of the adenine and thymine nucleoside analogues.
The reaction did not proceed exclusively via the neighboring group
effect of the 20-OAc group to give preponderant -anomers.26 The
b
The critical reaction in this synthetic scheme is the rearrange-
desired nucleosides were obtained as a mixture of diastereoisomers
(10a, 10b and 11a, 11b). The final compounds 1a, 1b and 2a, 2b were
obtained by deprotection using saturated ammonia in methanol.24
Preparative TLC or column chromatographic purification followed
by HPLC was used to purify the acetyl-protected nucleoside pre-
cursors and the final products.
ment of the furanose ring to the N-methyl-
D
-ribopyranuronamide
-ribofur-
ring starting from N-methyl-1,2-O-isopropylidene-a-D
anuronamide (6) in a reproducible way.14 This rearrangement was
accomplished using BF3$Et2O followed by acetylation using acetic
anhydride to obtain N-methyl-1,2,3,4-tetra-O-acetyl-D-ribopyr-
anuronamides (7a and 7b). However, these compounds easily
undergo elimination reaction in the presence of Lewis acid. Thin
layer chromatographic analysis of the reaction indicated that four
products are formed. The two more mobile compounds were sep-
arated by column chromatography, and shown by 1H NMR to be the
desired products, 7a and 7b. The anomeric configuration of the
compounds 7a and 7b was deduced from the 1H NMR coupling
constants and confirmed where appropriate by Noediff experi-
The structure of compounds 1a,1b was unambiguously assigned
using a combination of NMR techniques (H,H-COSY, H,C-HSQC, and
H,C-HMBC). Compound 1b shows a large 1H NMR coupling con-
stant (J¼8.0 Hz), which is typical for a trans di-axial relationship
between H-10 and H-20. This implies a
b-configuration. Compound
1a is then the
a-anomer having a slightly distorted half-chair
conformation and resulting in an increased coupling constant be-
tween H-20 and H-30 (J2 ,3 ¼5.5 Hz), and the disappearance of the
long-range H-10/H-30 W-coupling. Noediff at H-10 gave a significant
signal increase only for H-20, and thus confirms the C-10 confor-
0
0
ments. In this way, compound 7b was shown to be the a-anomer
mainly on the basis of the small long-range coupling of 1.3 Hz
between H-10 and H-30, pointing to a W-coupling path between
these two protons. This can happen only when both protons are
equatorial and thus cis-oriented, and therefore only possible in the
mation and at the same time the a-configuration of 1a. In the same
way, we characterized compounds 2a and 2b and also the protected
derivatives 10a,10b, and 11a,11b, since they all showed very similar
1H-couplings as in 1a and 1b. Compound 1a is the more mobile one
on TLC of the two diastereoisomers. Normally we had expected that
the presence of the 20-O-acetyl group would direct sugar–base
0
0
a
-anomer. The rather high coupling constant J2 ,3 ¼7.9 Hz in the
other isomer 7a, which has thus the -configuration, can be ratio-
b
nalized by the adoption of a more boat-like conformation of this
six-membered lactam ring. This also explains the absence of a large
condensation reaction in the direction of the
termediate 12 (Fig. 2). Apparently, this is not the sole mechanism as
a considerable amount of the -anomer is formed. The N-Me group
b-anomer via in-
0
0
J1 ,2 coupling between these two trans-oriented protons.
The less mobile material consisted of two aromatic compounds
8 and 9. They were separated by column chromatography. Both
compounds are more likely originated by the elimination reaction
of 7a and 7b. Compound 8 is the less stable compound and is
deacetylated easily to 9. Compound 9 is the less mobile and more
stable component of the mixture.
a
may participate in the reaction mechanism analogous to the con-
densation reaction of N-methyloxycarbonyl protected pyrrolidine
and nucleobase via the formation of an iminium ion (13).26 The
infrared absorption of compound 7a (1694 cmꢀ1) is situated at
somewhat higher wavelength than that of N-methyl-a-piperidone

10064
S.-Q. Yang et al. / Tetrahedron 64 (2008) 10062–10067
(Bruker Daltonics, Bremen, Germany). Tuning in positive electro-
spray mode to resolution of 95,000 (at m/z 400) and calibration
(from m/z 100 to 1500) were performed using poly-DL-alanine
(Sigma–Aldrich, St. Louis, MO). Spray voltage was set to 4000 V,
capillary temperature 240 ꢁC. Samples were infused in a water/
acetonitrile (1:1) mixture with a flow rate of 180 mL/h; 32 scans of
512k datapoints were acquired and averaged. For the acquisition
and processing, software ApexControl 1.0 and DataAnalysis 3.4
(Bruker Daltonics, Bremen, Germany) were used, respectively.
Precoated aluminum sheets (MN ALUGRAM SIL G/UV254 20ꢂ20 cm)
were used for TLC; the spots were examined with UV light. Pre-
parative TLC was performed on 20ꢂ40 cm plate coated with MN-
Silica Gel P/UV 254. Column chromatography was performed on
ICN silica gel 63–200, 60 Å. Analytical HPLC was performed on
waters 600E-2487 system using Alltima HP C18 column
(4.6ꢂ250 mm) at the flow rate of 1 mL/min by a gradient elution of
acetonitrile and water. Preparative HPLC was performed on waters
Figure 2. Possible intermediates of condensation reaction.
(1669 cmꢀ1), which may indicate lesser amide resonance.27–29 This
suggests that the lone pair electrons on the nitrogen atom of the
cyclic amide (7a and 7b) can be involved in the mechanism of
sugar–base condensation reaction.
In order to overcome the formation of
condensation reaction, we tried different condensation conditions.
By using SnCl230 as the catalyst, also a mixture of
and anomers
a-nucleoside during the
a
b
was formed. The condensation reaction was not successful using
TMS–OTf as catalyst (no nucleosides were formed).
Additionally, we also attempted to introduce the base moiety to
the N-unsubstituted-D-ribopyranuronamide sugar moiety, which
was obtained from compound 5 by ammonolysis and further
rearrangement.14 By using silylated thymine catalyzed with SnCl4,
we found that the N-unsubstituted sugar moiety was unstable, and
the corresponding nucleoside could not be obtained.
We have also attempted to synthesize the 30-OMe analogue
starting from 3-O-methylated 1,2:5,6-di-O-isopropylidene-D-allo-
1525-2487 system using Prep C18 5
m
m column 19ꢂ150 mm at the
flow rate of 16 mL/min by a gradient elution of acetonitrile and
water. Elemental analyses were performed at the Department of
Chemistry, K.U. Leuven. For sake of clarity of the NMR signal as-
signment, sugar protons and carbons are numbered with a prime,
and signals of base protons and carbons are given without prime.
4.2. 3-O-Acetyl-1,2-O-isopropylidene-a-D-5-ribofuronic
acid (4)
furanose and following a similar reaction sequence.31 The yield of
the key rearrangement, however, was only about 10%. More side
product 8 and 9 were obtained. Methylation of the 3-OH group
gives rise to an easier elimination reaction in contrast to what was
expected.
No antiviral activity has been found when the compounds 1a, 1b
and 2a, 2b were evaluated against Parainfluenza-3-virus, Reovirus-
1, Sindbis virus, Coxsackie virus B4, Punta Toro virus, Feline Corona
virus, Feline Herpes virus, Herpes simplex virus-1, Herpes simplex
virus-2, Vaccinia virus, Vesicular stomatitis virus, Respiratory syn-
cytial virus, Influenza virus A, Influenza virus B. No cytotoxicity was
detected in MDCK cells (Madin Darby Canine Kidney cells), HeLa
cells, CRFK cells (Crandell-Rees Feline Kidney cells), and Vero cells.
Compound 3 (4.43 g, 14.65 mmol) was dissolved in 75% acetic
acid (37 mL) at room temperature and stirred for 2 days. Solvents
were removed in vacuo. The residue obtained was dissolved in
methanol (30 mL) and water (45 mL) was added. Then KIO4 (3.69 g,
16.04 mmol) was added portionwise to the solution, while cooling
by ice bath and vigorously stirring. After 5 h, the reaction mixture
was diluted with methanol (50 mL), and then the inorganic salts
were filtered and washed with ethanol. The filtrate was evaporated.
The syrup obtained was dissolved in 50% acetic acid (70 mL) and the
solutionwas cooled to 10 ꢁC. KMnO4 (4.74 g, 29.99 mmol) was added
in small portions while stirring. After 6 h, sodium sulfite was added
tothe solution until MnO2 disappears, and the pH of the solutionwas
adjusted to 2 with concentrated hydrochloric acid. The solution was
extracted with CH2Cl2 (80 mLꢂ4), the extracts were washed with
water, dried over Na2SO4, filtered, and evaporated to afford com-
3. Conclusions
pound 4 (3.08 g, 85.4%) as a syrup.1H NMR (300 MHz, MeOD):
d 5.92
(d, 1H, J¼3.6 Hz, H-10), 5.01 (dd, 1H, J1¼4.8 Hz, J2¼8.7 Hz, H-30), 4.84
We reported the synthesis of N-methyl-D-ribopyranuronamide
(m,1H, H-20), 4.50 (d,1H, J¼8.8 Hz, H-40), 2.11 (s, 3H, Me),1.53 (s, 3H,
nucleosides 1a, 1b and 2a, 2b by a rearrangement of a furanose
sugar with a carboxamide function in the 4-position to a ribopyr-
anuronamide ring followed by condensation with adenine and
thymine nucleobases, catalyzed by SnCl4. The compound without
the N-methyl group on the ribopyranuronamide sugar moiety
proved to be less stable during the condensation reaction. No
antiviral activity and toxicity was found for the four deprotected
nucleosides 1a, 1b and 2a, 2b.
Me), 1.34 (s, 3H, Me); 13C NMR (75 MHz, MeOD):
d 172.61 (COOH),
171.43 (Me–CO), 114.74 (isopropylidene–C), 106.39 (C-10), 79.13 (C-
40), 77.33 (C-20), 75.49 (C-30), 27.01 (Me), 26.86 (Me), 20.36 (Me);
HRMS for C10H14O7 (MþNa)þ calcd: 269.0637, found: 269.0630.
4.3. Methyl 3-O-acetyl-1,2-O-isopropylidene-a-D-
ribofuranuronate (5)
4. Experimental
4.1. General
N-Ethyl-N0-(3-dimethylaminopropyl)-carbodiimide hydrochlo-
ride (EDAC, 722 mg, 3.77 mmol) and DMAP (18 mg, 0.15 mmol)
were added to a solution of compound 4 (370 mg, 1.50 mmol) in
MeOH (11 mL), and the reaction mixture was stirred for 24 h at
room temperature. After the solvent was removed by rotary
evaporation, the residue was dissolved in dichloromethane
(70 mL), washed with water (60 mL) and brine (60 mL), dried over
anhydrous Na2SO4, filtered, and concentrated to dryness. The res-
idue was purified by column chromatography (n-hexane/EtOAc,
3:1) to yield compound 5 (300 mg, 76.9%) as a colorless syrup. 1H
For all reactions, analytical grade solvents were used. All mois-
ture-sensitive reactions were carried out in oven-dried glassware
(135 ꢁC). Anhydrous CH3CN was refluxed over calcium hydride and
distilled. A Bruker Avance II 500 MHz spectrometer and a Bruker
Avance 300 MHz apparatus were used for 1H NMR and 13C NMR.
Accurate mass spectra were recorded on a Fourier transform ion-
cyclotron resonance (FTICR) mass spectrometer, apex-Qe (Bruker
Daltonics, Bremen, Germany) with a passively shielded 9.4 T
superconducting magnet equipped with an Apollo 2 CombiSource
NMR (300 MHz, CDCl3):
d
5.79 (d, 1H, J¼3.6 Hz, H-10), 4.85 (dd, 1H,
J1¼4.7 Hz, J2¼8.7 Hz, H-30), 4.68 (dd, 1H, J1¼3.7 Hz, J2¼4.7 Hz, H-20),
4.40 (d, 1H, J¼8.8 Hz, H-40), 3.62 (s, 3H, Me), 1.99 (s, 3H, Me), 1.40 (s,

S.-Q. Yang et al. / Tetrahedron 64 (2008) 10062–10067
10065
3H, Me), 1.20 (s, 3H, Me); 13C NMR (75 MHz, CDCl3):
d
169.74
compound 9 (100 mg, 14.1%) as a white solid. Data for 8: 1H NMR
(300 MHz, CDCl3)
7.16 (d, 1H, J¼2.9 Hz, H-6), 7.01 (d, 1H, J¼2.9 Hz,
H-4), 3.46 (s, 3H, N–Me), 2.21 (s, 3H, Me), 2.15 (s, 3H, Me); 13C NMR
(75 MHz, CDCl3) 169.11, 168.27, 156.50 (C-2), 140.92 (C-3), 131.22
(–COOMe), 169.31 (Me–CO), 113.60 (isopropylidene–C), 104.69 (C-
10), 77.50 (C-40), 75.90 (C-20), 73.89 (C-30), 52.44 (COO–Me), 26.57
(Me), 26.52 (Me), 20.36 (Me); HRMS for C11H16O7 (MþNa)þ calcd:
283.0794, found: 283.0788.
d
d
(C-5), 127.49 (C-6), 126.14 (C-4), 38.04 (N–Me), 20.83 (Me), 20.70
(Me); HRMS for
C
10H11NO5 (MþH)þ calcd: 226.0710, found:
4.4. N-Methyl-1,2-O-isopropylidene-
a
-D
-ribofur-
226.0708. Data for 9: 1H NMR (300 MHz, CDCl3)
d 7.04 (br, 1H, 5-
anuronamide (6)
OH), 6.83 (d, 1H, J¼2.7 Hz, H-6), 6.68 (d, 1H, J¼2.7 Hz, H-4), 3.59 (s,
3H, N–Me), 2.25 (s, 3H, Me); 13C NMR (75 MHz, CDCl3)
d
169.36,
A solution of compound 5 (310 mg, 1.19 mmol) and 2 M methyl-
amine inTHF (7 mL) was heatedfor 24 h at 55 ꢁC in a sealed tube. The
reaction mixture was concentrated to dryness, and the residue was
purified by column chromatography (n-hexane/EtOAc/MeOH,
5:5:1) to yield 6 (250 mg, 96.6%). 1H NMR (300 MHz, DMSO-d6):
157.7 (C-2), 146.40 (C-3), 133.77 (C-5), 119.72 (C-6), 111.00 (C-4),
37.68 (N–Me), 20.94 (Me); HRMS for C8H9NO4 (MþH)þ calcd:
184.0604, found: 184.0603. Elemental analysis found, %: C 52.04; H
5.20; N 6.92. Calculated, %: C 52.46; H 4.95; N 7.65.
d
7.97 (q, 1H, J¼4.6 Hz, NH), 5.74 (d, 1H, J¼3.4 Hz, H-10), 5.34 (d, 1H,
4.7. (2S,3S,4S)-N-Methyl-1-(N6-benzoyladenin-9-yl)-2,3,4-tri-
O-acetyl-D-ribopyranuronamides (10a and 10b)
J¼6.7 Hz, 30-OH, exchanged with D2O), 4.48 (t, 1H, J¼3.9 Hz, H-20),
4.03 (d, 1H, J¼8.9 Hz, H-40), 3.92 (m, 1H, H-30), 2.59 (d, 3H, J¼4.7 Hz,
NH–Me),1.45 (s, 3H, Me),1.27 (s, 3H, Me); 13C NMR (75 MHz, DMSO-
N6-Benzoyladenine (0.29 g,1.21 mmol), ammonia sulfate (10 mg,
0.08 mmol) and 15 mL of HMDS were added to a dried flask. The
mixturewasrefluxed overnightundernitrogen. HMDSwas removed
invacuowithexclusion ofmoisture. Totheflask withthe residuewas
added a solution of compounds 7a and 7b (410 mg, 1.19 mmol) in
12 mL of dry CH3CN and the solutionwas cooled to 0 ꢁC and followed
d6 and one drop D2O):
d 169.38 (CO), 111.96 (isopropylidene–C),
103.95 (C-10), 79.51 (C-20), 78.61 (C-30), 73.93 (C-40), 26.83 (NH–Me),
26.51 (Me), 25.34 (Me); HRMS for C9H15NO5 (MþNa)þ calcd:
240.0848, found: 240.0840. Elemental analysis found, %: C 49.37; H
7.08; N 6.30. Calculated, %: C 49.76; H 6.96; N 6.45.
by dropwise addition of SnCl4 (280 mL, 2.39 mmol), under N2. The
4.5. N-Methyl-1,2,3,4-tetra-O-acetyl-
anuronamide (7)
D
-ribopyr-
reaction mixture was stirred overnight at room temperature and
then poured into ice-cold saturated aqueous NaHCO3 solution
(20 mL). It was extracted with CH2Cl2 (60 mLꢂ3) and then NaHCO3
solution layer was concentrated to a small volume. The residue was
taken up in H2O (30 mL) and CH2Cl2 (60 mL). The combined CH2Cl2
layer was washed with water, dried over anhydrous Na2SO4, filtered,
and concentrated in vacuo. To obtain an analytical sample, the
brown crude solid product (390 mg, 62.5%) was further purified by
preparative TLC (CH2Cl2/MeOH, 12:1) and then by preparative HPLC
with 25% CH3CN inwater toyield 10a and 10b. Data for (1S,2S,3S,4S)-
To a solution of compound 6 (840 mg, 3.87 mmol) in acetic
anhydride (15 mL) was added 0.4 mL of BF3$Et2O. The reaction
mixture was stirred for 19 h and another 0.2 mL of BF3$Et2O was
added. The reaction was continued to stir for 4 h and then poured
into iced water and extracted with CH2Cl2 (60 mLꢂ3). The com-
bined extracts were washed with saturated NaHCO3 solution and
water, dried over anhydrous Na2SO4, filtered, and concentrated to
dryness. The residue was purified by column chromatography (n-
hexane/EtOAc, 2:1) to yield compounds 7a and 7b (430 mg, 32.2%)
as a syrup. A second column chromatographic purification was
needed to obtain analytical pure compounds. The compound with
isomer (a d 8.90 (s,1H, NH),
-anomer) 10a: 1H NMR (300 MHz, CDCl3)
8.81 (s,1H, H-2), 8.06 (s,1H, H-8), 8.03 (d, 2H, J¼7.2 Hz, benzoyl), 7.64
(t, 1H, J¼7.2 Hz, benzoyl), 7.55 (t, 2H, J¼7.3 Hz, benzoyl), 6.42 (d, 1H,
J¼4.7 Hz, H-10), 5.97 (d, 1H, J¼3.6 Hz, H-40), 5.73 (dd, 1H, J1¼3.6 Hz,
J2¼6.6 Hz, H-30), 5.63 (dd,1H, J1¼4.6 Hz, J2¼6.6 Hz, H-20), 2.82 (s, 3H,
N–Me), 2.21 (s, 3H, Me), 2.18 (s, 3H, Me), 2.02 (s, 3H, Me); 13C NMR
0
0
a large J2 ,3 ¼7.9 Hz could be assigned as 7a, while the one with
0
0
0
0
a small J1 ,3 ¼1.3 Hz, J1 ,2 ¼4.4 Hz could be assigned as 7b. Data for 7a
(b
-anomer): 1H NMR (300 MHz, CDCl3)
d
6.27 (d, 1H, J¼4.0 Hz, H-
(75 MHz, CDCl3) d 169.79 (CO–acetyl), 169.06 (CO–acetyl), 168.62
10), 5.79 (d,1H, J¼4.8 Hz, H-40), 5.54 (dd,1H, J1¼4.8 Hz, J2¼7.9 Hz, H-
30), 5.39 (dd, 1H, J1¼4.0 Hz, J2¼7.9 Hz, H-20), 2.99 (s, 3H, N–Me), 2.14
(s, 6H, 2Me), 2.06 (s, 3H, Me), 2.05 (s, 3H, Me); 13C NMR (75 MHz,
(CO–acetyl), 165.56 (CO–N–Me), 164.58 (CO–NH–benzoyl), 153.43
(C-2),151.98 (C-4), 150.05 (C-6), 141.22 (C-8), 133.37 (C-benzoyl),
133.22 (C-benzoyl), 129.15 (C-benzoyl), 128.03 (C-benzoyl), 122.95
(C-5), 67.73 (C-10), 67.09 (C-30), 66.77 (C-40), 66.04 (C-20), 32.27 (N–
Me), 20.82 (Me), 20.70 (Me), 20.64 (Me); HRMS for C24H24N6O8
(MþH)þ calcd: 525.1728, found: 525.1727. Data for (1R,2S,3S,4S)-
CDCl3)
(C-40), 67.21 (C-20), 66.90 (C-30), 33.74 (N–Me), 20.81 (Me), 20.67
(Me), 20.62 (2Me); IR (film on KBr tablet, cmꢀ1): 2937 (m, nC–H
d
170.13, 169.76, 169.64, 169.55, 165.33, 79.05 (C-10), 67.46
,
CH3), 1748 (s, nC]O, OAc), 1694 (s, nC]O, CONCH3), 1372 (s, nO–C, OAc),
isomer (b d 8.94 (s, 1H,
-anomer) (10b): 1H NMR (500 MHz, CDCl3)
1215 (s, nC–O), 1047 (s, nC–N); HRMS for C14H19NO9 (MþH)þ calcd:
NH), 8.82 (s, 1H, H-2), 8.13 (s, 1H, H-8), 8.03 (d, 2H, J¼7.5 Hz, o-
benzoyl), 7.64 (t, 1H, J¼7.5 Hz, benzoyl), 7.55 (t, 2H, J¼7.6 Hz, m-
benzoyl), 6.04 (dd, 1H, J1¼2.0 Hz, J2¼8.0 Hz, H-20), 6.01 (d, 1H,
J¼2.4 Hz, H-40), 5.88 (overl. m,1H, H-30), 5.87 (d,1H, J¼8.0 Hz, H-10),
2.73 (s, 3H, N–Me), 2.23 (s, 3H, Me), 2.22 (s, 3H, Me),1.92 (s, 3H, Me);
346.1132, found: 346.1133. Data for 7b (a
-anomer): 1H NMR
0
0
0
0
0
(300 MHz, CDCl3)
d
6.32 (dd, 1H, J1 ,2 ¼4.4 Hz, J1 ,3 ¼1.30Hz, H-1 ),
0
0
0
0
0
0
5.70 (ddd, 1H, J3 ,4 ¼3.7 Hz, J3 ,2 ¼2.3 Hz, J3 ,1 ¼1.3 Hz, H-3 ), 5.56 (0d,
1H, J¼3.7 Hz, H-40), 5.43 (dd, 1H, J2 ,1 ¼4.4 Hz, J2 ,3 ¼2.3 Hz, H-2 ),
0
0
0
0
2.94 (s, 3H, N–Me), 2.15 (s, 3H, Me), 2.14 (s, 3H, Me), 2.12 (s, 3H, Me),
13C NMR (75 MHz, CDCl3)
d 169.96 (CO–acetyl), 169.70 (CO–acetyl),
2.03 (s, 3H, Me); 13C NMR (75 MHz, CDCl3)
d
170.29, 169.99, 169.56,
168.95 (CO–acetyl), 164.76 (CO–N–Me), 164.64 (CO–NH–benzoyl),
153.52 (C-2), 151.85 (C-4), 150.16 (C-6), 141.38 (C-8), 133.20 (Cp-
benzoyl), 133.18 (Ci-benzoyl), 129.10 (Co-benzoyl), 128.04 (Cm-
benzoyl), 124.82 (C-5), 70.32 (C-10), 68.69 (C-30), 68.42 (C-20), 67.12
(C-40), 31.03 (N–Me), 20.97 (Me), 20.69 (Me), 20.43 (Me); HRMS for
169.27, 165.54, 79.65 (C-10), 68.60 (C-30), 66.73 (C-40), 64.56 (C-20),
33.29 (N–Me), 20.83 (Me), 20.68 (Me), 20.54 (Me), 20.41 (Me);
HRMS for C14H19NO9 (MþH)þ calcd: 346.1132, found: 346.1138.
4.6. 1-Methyl-2-oxo-1,2-dihydropyridine-3,5-diyl diacetate
(8) and 5-hydroxy-1-methyl-2-oxo-1,2-dihydropyridin-3-yl
acetate (9)
C
24H24N6O8 (MþH)þ calcd: 525.1728, found: 525.1715.
4.8. (2S,3S,4S)-N-Methyl-1-(thymin-1-yl)-2,3,4-tri-O-acetyl-D-
ribopyranuronamides (11a and 11b)
After compounds 7a and 7b were obtained, the column chro-
matography was further eluted with n-hexane/EtOAc (1:1 to 2:3) to
yield compound 8 (320 mg, 36.7%) as a yellowish solid and
Thymine (0.18 g, 1.43 mmol), ammonia sulfate (20 mg,
0.15 mmol) and 4 mL of HMDS were added to a dried flask. The

10066
S.-Q. Yang et al. / Tetrahedron 64 (2008) 10062–10067
mixture was refluxed overnight under nitrogen. HMDS was re-
moved in vacuo with exclusion of moisture. To the flask with the
residue was added a solution of compounds 7a and 7b (400 mg,
1.16 mmol) in 10 mL of dry CH3CN and the solution was cooled to
4.10. (2S,3S,4S)-N-Methyl-1-(thymin-1-yl)-D-
ribopyranuronamides (2a and 2b)
A solution of the crude product obtained in the previous re-
action (compounds 11a and 11b) was dissolved in MeOH saturated
with ammonia (45 mL) and stirred at room temperature overnight.
The reaction mixture was concentrated, and the residue was puri-
fied by chromatography (n-hexane/EtOAc/MeOH, 5:5:0.5 to 5:5:1)
to yield compound 2a (50 mg, 15.1% starting from 7a and 7b) and
compound 2b (100 mg, 30.2% starting from 7a and 7b). An ana-
lytical sample was obtained by purification with preparative HPLC
0 ꢁC and followed by dropwise addition of SnCl4 (300
mL,
2.56 mmol), under N2. The reaction mixture was stirred overnight
at room temperature and then poured into ice-cold saturated
aqueous NaHCO3 solution (30 mL). It was extracted with CH2Cl2
(60 mLꢂ3) and then the NaHCO3 solution layer was concentrated to
a small volume. The residue was divided between H2O (30 mL) and
CH2Cl2 (60 mL). The combined CH2Cl2 layer was washed with wa-
ter, dried over anhydrous Na2SO4, filtered, and concentrated in
vacuo. To obtain an analytical sample, the brown crude solid
product (280 mg, 58.7%) was further purified by preparative TLC
(CH2Cl2/MeOH, 12:1) and then by preparative HPLC with 15%
CH3CN in water to yield 11a and 11b. Data for (1R,2S,3S,4S)-isomer
with 1% CH3CN in water. Data for (1R,2S,3S,4S)-isomer (
a-anomer)
11.12 (br, 1H, NH-3),
(2a): 1H NMR (500 MHz, DMSO-d6, at 60 ꢁC):
d
7.22 (q,1H, J¼1.0 Hz, H-6), 5.70 (br, 1H, 20-OH), 5.61 (d,1H, J¼3.9 Hz,
H-10), 5.45 (br, 1H, 40-OH), 5.17 (br, 1H, 30-OH), 4.13 (d, 1H, J¼3.1 Hz,
H-40), 3.94 (dd, 1H, J1¼3.9 Hz, J2¼6.7 Hz, H-20), 3.80 (dd, 1H,
J1¼3.2 Hz, J2¼6.9 Hz, H-30), 2.66 (s, 3H, N–Me), 1.77 (d, 3H, J¼1.0 Hz,
(a d 8.05 (br, 1H, NH),
-anomer) (11a): 1H NMR (300 MHz, CDCl3)
7.05 (s, 1H, H-6), 5.93 (d, 1H, J¼3.2 Hz, H-10), 5.76 (d, 1H, J¼3.5 Hz,
H-40), 5.46 (dd, 1H, J1¼3.7 Hz, J2¼7.0 Hz, H-30), 5.37 (dd, 1H,
J1¼3.1 Hz, J2¼7.0 Hz, H-20), 2.91 (s, 3H, N–Me), 2.20 (s, 3H, Me), 2.16
(s, 3H, Me), 2.01 (s, 3H, Me), 1.97 (s, 3H, Me); 13C NMR (75 MHz,
Me); 13C NMR (125 MHz, DMSO-d6):
d 170.86 (CO), 163.84 (C-4),
151.13 (C-2), 136.08 (C-6), 109.28 (C-5), 73.59 (C-10), 69.94 (C-30),
69.21 (C-20), 68.96 (C-40), 31.24 (N–Me), 12.55 (5-Me); HRMS for
C
11H15N3O6 (MþNa)þ calcd: 308.0859, found: 308.0851. Data for
CDCl3)
d
170.01, 169.24, 169.00, 168.57, 165.22, 150.89, 134.08,
(1S,2S,3S,4S)-isomer (b
-anomer) (2b): 1H NMR (500 MHz, DMSO-
112.15, 71.53 (C-10), 67.53 (C-20), 67.02 (C-30), 66.77 (C-40), 33.80 (N–
Me), 20.76 (Me), 20.68 (Me), 20.62 (Me), 13.00 (5-Me); HRMS for
d6)
d
11.34 (br, 1H, NH-3), 7.62 (q, 1H, J¼1.1 Hz, H-6), 5.68 (br, 1H, H-
10), 5.60 (d, 1H, J¼5.9 Hz, 20-OH), 5.44 (d, 1H, J¼3.5 Hz, 30-OH), 4.99
(d, 1H, J¼3.2 Hz, 40-OH), 4.22 (br, 1H, H-40), 3.98 (m, 1H, H-30), 3.94
(br, 1H, H-20), 2.58 (s, 3H, N–Me), 1.79 (s, 3H, Me); 13C NMR
C
17H21N3O9 (MþNa)þ calcd: 434.1176, found: 434.1167. Data for
(1S,2S,3S,4S)-isomer (b
-anomer) (11b): 1H NMR (300 MHz, DMSO-
d6)
d
11.49 (br, 1H, NH), 7.82 (s, 1H, H-6), 6.01 (br, 1H, H-10), 5.83 (br,
(75 MHz, DMSO-d6) d 171.83 (CO), 163.80 (C-4), 151.45 (C-2), 136.15
1H), 5.65 (br, 2H), 2.68 (s, 3H, N–Me), 2.15 (s, 3H, Me), 2.07 (s, Me),
(C-6), 110.72 (C-5), 71.66 (C-30), 70.83 (C-10), 69.06 (C-40), 68.18 (C-
20), 29.49 (N–Me), 12.05 (5-Me); HRMS for C11H15N3O6 (MþNa)þ
calcd: 308.0859, found: 308.0853.
1.97 (s, 3H, Me), 1.78 (s, 3H, Me); 13C NMR (75 MHz, DMSO-d6)
d
170.62, 169.72, 169.51, 165.33, 164.22, 151.42, 136.63, 109.84, 69.00
(C-10), 67.49 (C-40), 67.22 (C-20 and C-30), 30.34 (N–Me), 20.97 (Me),
20.77 (2Me), 12.59 (5-Me); HRMS for C17H21N3O9 (MþNa)þ calcd:
434.1176, found: 434.1166.
Acknowledgements
We are grateful to Professor Jef Rozenski for the electrospray
HRMS and Chantal Biernaux for editorial help. We are also in-
debted to Luc Baudemprez for running the NMR spectra. S.-Q. Yang
is obliged to Chinese Scholarship Council for a Ph.D. fellowship. We
thank the members of the Laboratory of Virology and Chemo-
therapy, Rega Institute, for evaluating the compounds for their
antiviral activity.
4.9. (2S,3S,4S)-N-Methyl-1-(adenin-9-yl)-D-
ribopyranuronamides (1a and 1b)
A solution of the crude product obtained in the previous re-
action (compounds 10a and 10b) was dissolved in MeOH saturated
with ammonia (35 mL) and stirred at room temperature for 1 day.
The reaction mixture was concentrated, and the residue was puri-
fied by chromatography (n-hexane/EtOAc/MeOH, 5:5:0.5 to 5:5:1)
to yield compound 1a (45 mg, 12.9% starting from 7a and 7b) and
compound 1b (100 mg, 28.6% starting from 7a and 7b). An ana-
lytical sample was obtained by purification with preparative HPLC
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with 1% CH3CN in water. Data for (1S,2S,3S,4S)-isomer (
a-anomer)
(1a): 1H NMR (500 MHz, DMSO-d6)
*
d
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(b-
anomer) (1b): 1H NMR (500 MHz, DMSO-d6)
*
d 8.38 (s, 1H, H-8),
8.13 (s, 1H, H-2), 7.31 (s, 2H, NH2), 5.61 (d, 1H, J¼8.0 Hz, H-10), 5.61
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4.05 (t, 1H, J¼2.3 Hz, H-30), 2.45 (s, 3H, N–Me); 13C NMR (125 MHz,
DMSO-d6)
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140.80 (C-8), 119.30 (C-5), 72.42 (C-10), 71.80 (C-30), 69.45 (C-40),
68.60 (C-20), 29.76 (N–Me); HRMS for C11H14N6O4 (MþH)þ calcd:
295.1149, found: 295.1146.
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