Efficient and selective enzymatic acylation reaction: Separation of furanosyl and pyranosyl nucleosides

Article abstract of DOI:10.1021/jo800731u

(Chemical Equation Presented) Candida antarctica lipase-B (CAL-B) immobilized on lewatite selectively acylated the primary hydroxyl group of the furanosyl nucleoside in a mixture of 1-(α-D-arabinofuranosyl)thymine and 1-(α-D-arabinopyranosyl)thymine. This selective biocatalytic acylation of furanosyl nucleoside has enabled us an easy separation of arabinofuranosyl thymine from an inseparable mixture with arabinopyranosyl thymine. The primary hydroxyl selective acylation methodology of arabinonucleoside has also been successfully used for the separation of 1-(β-D-xylofuranosyl)thymine and 1-(β-D-xylopyranosyl)thymine from a mixture of the two, which demonstrate the generality of the enzymatic methodology for separation of furanosyl and pyranosyl nucleosides.

Full text of DOI:10.1021/jo800731u

antitumor,4 antihepatitis B virus,5,6 antimycobacterial,7 and
cytostatic agents.8
Efficient and Selective Enzymatic Acylation
Reaction: Separation of Furanosyl and Pyranosyl
Nucleosides
Arabinonucleosides with pyranosyl configuration have been
used as nucleoside monomers in the synthesis of oligonucle-
otides for the evaluation of their importance in etiology of
nucleic acid structure.9 In one of our research programs we
aimed to synthesize R-D-arabinofuranosyl nucleosides but all
our efforts of condensation of tetraacetylated arabinose with
thymine led to the formation of an inseparable mixture of R-D-
arabinofuranosyl and R-D-arabinopyranosyl nucleosides in vary-
ing proportions depending on the temperature of the reaction.
Imbach and co-workers10 have generalized Guthrie-Smith11
methodology for the synthesis of tetraacetate of five-membered
aldofuranose sugars. They synthesized R- and ꢀ-anomers of
tetra-O-acetyl-D-aldopentofuranosides starting from D-ribose,
D-arabinose, D-xylose, and D-lyxose by their methanolysis,
acetylation, and acetolysis protocol with an overall yield of
∼70%.
Jyotirmoy Maity,† Gaurav Shakya,† Sunil K. Singh,†
Vasulinga T. Ravikumar,‡ Virinder S. Parmar,† and
Ashok K. Prasad*,†
Bioorganic Laboratory, Department of Chemistry,
UniVersity of Delhi, Delhi-110 007, India, and Isis
Pharmaceuticals Inc., 2292 Faraday AVenue,
Carlsbad, California 92008
ashokenzyme@yahoo.com
ReceiVed April 3, 2008
Contrary to this, Bristow and Lythgoe12 pointed out that the
preparative procedure for 1,2,3,5-tetra-O-acetylribofuranosyl
starting from D-ribose cannot be applied in its entirety to other
pentoses such as D-arabinose and D-xylose, possibly because
of the existence of the sugar mainly in one cyclic form over
the other at equilibrium in solution.
Further, during the synthesis of R- and ꢀ-D-xylofuranosyl
nucleosides of the five naturally occurring bases, Imbach and
co-workers13 have also reported the existence of furanosyl sugar
tetraacetate and the corresponding nucleosides with pyranose
forms and found it very difficult to separate them on a
preparative scale in contrast to their earlier report.10 Thus far,
no methodology exists for the efficient separation of mixtures
of furanosyl and pyranosyl nucleosides.
During the synthesis of R-D-arabinofuranosyl thymine from
D-arabinose following literature procedure,10 we obtained an
anomeric mixture of 1,2,3,5-tetra-O-acetylarabinofuranoside
(6a,b)10 and 1,2,3,4-tetra-O-acetylarabinopyranoside (7a,b). The
Vorbruggen’s coupling14 of thymine with the anomeric mixtures
of furanosides 6a,b and pyranosides 7a,b afforded a mixture
of 1-(2′,3′,5′-tri-O-acetyl-R-D-arabinofuranosyl)thymine (8)15
and 1-(2′,3′,4′-tri-O-acetyl-R-D-arabinopyranosyl)thymine (9),
Candida antarctica lipase-B (CAL-B) immobilized on le-
watite selectively acylated the primary hydroxyl group of
the furanosyl nucleoside in a mixture of 1-(R-D-arabinofura-
nosyl)thymine and 1-(R-D-arabinopyranosyl)thymine. This
selective biocatalytic acylation of furanosyl nucleoside has
enabled us an easy separation of arabinofuranosyl thymine
from an inseparable mixture with arabinopyranosyl thymine.
The primary hydroxyl selective acylation methodology of
arabinonucleoside has also been successfully used for the
separation of 1-(ꢀ-D-xylofuranosyl)thymine and 1-(ꢀ-D-
xylopyranosyl)thymine from a mixture of the two, which
demonstrate the generality of the enzymatic methodology
for separation of furanosyl and pyranosyl nucleosides.
(4) Ohtawa, M.; Ichikawa, S.; Teishikata, Y.; Fujimuro, M.; Yokosawa, H.;
Matsuda, A. J. Med. Chem. 2007, 50, 2007–2010.
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Revankar, G. R. J. Med. Chem. 1995, 38, 3957–3966.
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Modified nucleosides of arabinofuranosyl moiety have at-
tracted much attention as antiviral,1 anticancer,2 antimicrobial,3
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Balzarini, J.; Knaus, E. E. J. Med. Chem. 2007, 50, 2851–2857.
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135–142.
† University of Delhi.
‡ Isis Pharmaceuticals Inc.
(11) Guthrie, R. D.; Smith, S. C. Chem. Ind. 1968, 547–548.
(12) (a) Bristow, N. W.; Lythgoe, B. J. Chem. Soc. 1949, 2306–2309. (b)
Chang, P.; Lythgoe, B. J. Chem. Soc. 1950, 1992–1993.
(13) Gosselin, G.; Bergogne, M. C.; Rudder, J.; De Clercq, E.; Imbach, J. L.
J. Med. Chem. 1986, 29, 203–213.
(1) Pankiewicz, K. W.; Nawrot, B.; Gadler, H.; Price, R. W.; Watanabe, K. A.
J. Med. Chem. 1987, 30, 2314–2316.
(2) Miura, S.; Yoshimura, Y.; Endo, M.; Satoh, H.; Machida, H.; Sasaki, T.
Cancer Lett. 1999, 144, 177–182.
(3) Bosco, M.; Bisseret, P.; Constant, P.; Eustache, J. Tetrahedron Lett. 2007,
48, 153–157.
(14) Niedbella, U.; Vorbruggen, H. J. Org. Chem. 1974, 39, 3654–3660.
(15) Danishefsky, S.; Chow, K. J. Org. Chem. 1990, 55, 4211–4214.
10.1021/jo800731u CCC: $40.75
Published on Web 06/17/2008
2008 American Chemical Society
J. Org. Chem. 2008, 73, 5629–5632 5629

SCHEME 1. Procedure for the Synthesis of 10 and 11
SCHEME 3. Separation of 10/ 11 and 21/ 22 by
CAL-B-Catalyzed Selective Acylation Reaction
SCHEME 2. Procedure for the Synthesis of 21 and 22
of nucleosides from their anomeric mixtures24 and for the
resolution of ꢀ-D/L-2′-deoxynucleosides.25 Herein for the first
time, a lipase-catalyzed selective acylation methodology has
been developed for the separation of furanosyl and pyranosyl
nucleosides from their mixture.
All our attempts to separate the mixture of arabinofuranosyl
and arabinopyranosyl thymine 10 and 11, and xylofuranosyl
and xylopyranosyl thymine 21 and 22 by silica gel column
chromatography failed. In the present study we have used
Candida antarctica lipase-B (CAL-B)26 for the separation of
the furanosyl and the pyranosyl nucleosides of D-arabinose and
D-xylose sugars. The CAL-B-catalyzed acylation of the furano
and the pyrano nucleoside mixture of the two sugars was studied
in different organic solvents, i.e., DCM, DIPE, THF, dioxane,
and acetonitrile. The lipase in acetonitrile was found to be the
best system for the efficient and selective acylation reaction of
furano and pyrano nucleoside mixtures. CAL-B in acetonitrile
selectively acylated the primary hydroxyl group in furano
nucleosides of both sugars; since there is no primary hydroxyl
group in pyrano nucleoside, it remained unreacted during the
biocatalytic acylation reaction. There was an appreciable dif-
ference between the polarity of 5′-O-acylated furanonucleoside
and pyranonucleoside, thus they were easily separated by
column chromatography over silica gel.
In a typical reaction, the mixture of R-D-arabinofuranosyl and
pyranosyl thymine 10 and 11, or ꢀ-D-xylofuranosyl and pyra-
nosyl thymine 21 and 22 and acetic anhydride 23 in acetonitrile
were incubated with CAL-B (substrate-enzyme ratio, ∼1:0.5,
w/w) at 40-42 °C and the progress of the reaction was
monitored on TLC (Scheme 3). On completion of the reaction,
the enzyme was filtered off and the solvent removed under
reduced pressure. The residue thus obtained was purified by
which on treatment with half-saturated methanolic ammonia
gave a mixture of 1-(R-D-arabinofuranosyl)thymine (10)16,17 and
1-(R-D-arabinopyranosyl)thymine (11)8 in the ratio of 7.2:1
(Scheme 1).
The extension of study on D-xylose also led to the formation
of 1,2,3,5-tetra-O-acetylxylofuranoside (17a,b)10 and 1,2,3,4-
tetra-O-acetylxylopyranoside (18a,b), which on Vorbruggen’s
coupling14 with thymine followed by treatment of the resulting
1-(2′,3′,5′-tri-O-acetyl-ꢀ-D-xylofuranosyl)thymine (19)15 and
1-(2′,3′,4′-tri-O-actyl-ꢀ-D-xylopyranosyl)thymine (20) with half-
saturated methanolic ammonia afforded 1-(ꢀ-D-xylofurano-
syl)thymine (21)18,19 and 1-(ꢀ-D-xylopyranosyl)thymine (22)19,20
in the ratio of 1.4:1 (Scheme 2).
The potential of enzymes in nucleoside chemistry21 is well
recognized for selective acylation of different functional groups
of similar reactivity present in the molecule. Some of the lipases
have been found to selectively acylate/deacylate primary hy-
droxyl over secondary hydroxyl group(s) of sugars22 and
nucleosides.23 Earlier, lipases have been used for the separation
(22) (a) Prasad, A. K.; Sorensen, M. D.; Parmar, V. S.; Wengel, J.
Tetrahedron Lett. 1995, 36, 6163–6166. (b) Prasad, A. K.; Wengel, J.
Nucleosides, Nucleotides Nucleic Acids 1996, 15, 1347–1359. (c) Prasad, A. K.;
Kalra, N.; Yadav, Y.; Kumar, R.; Sharma, S. K.; Patkar, S.; Lange, L.; Wengel,
J.; Parmar, V. S. Chem. Commun. 2007, 2616–2617. (d) Prasad, A. K.; Kalra,
N.; Yadav, Y.; Singh, S. K.; Sharma, S. K.; Patkar, S.; Lange, L.; Olsen, C. E.;
Wengel, J.; Parmar, V. S. Org. Biomol. Chem. 2007, 5, 3524–3530.
(23) (a) Moris, F.; Gotor, V. Tetrahedron 1993, 49, 10089–10098. (b)
Ciuffreda, P.; Casati, P.; Santaniello, E. Bioorg. Med. Chem. Lett. 1999, 9, 1577–
1582.
(16) Adams, A. D.; Petrie, C. R.; Meyer, R. B. Nucleic Acids Res. 1991, 19,
3647–3651.
(17) Jorgensen, P. T.; Pedersen, E. B.; Nielsen, C. Synthesis 1992, 1299–
1306.
(18) (a) Gosselin, G.; Imbach, J. L. Tetrahedron Lett. 1981, 22, 4699–4702.
(b) Gosselin, G.; Imbach, J. L. J. Heterocycl. Chem. 1982, 19, 597–602.
(19) Fox, J. J.; Yung, N.; Davoll, J.; Brown, G. B. J. Am. Chem. Soc. 1956,
78, 2117–2122.
(24) (a) Damkjaer, D. L.; Petersen, M.; Wengel, J. Nucleosides Nucleotides
1994, 13, 1801–1807. (b) Garcia, J.; Diaz-Rodriguez, A.; Fernandez, S.; Sanghvi,
Y.; Ferrero, M.; Gotor, V. J. Org. Chem. 2006, 71, 9765–9771.
(25) Garcia, J.; Fernandez, S.; Ferrero, M.; Sanghvi, Y.; Gotor, V. Org. Lett.
2004, 6, 3759–3762.
(20) Wagner, T.; Huynh, H. K.; Krishnamurthy, R.; Eschenmoser, A. HelV.
Chim. Acta 2002, 85, 399–416.
(21) (a) Prasad, A. K.; Trikha, S.; Parmar, V. S. Bioorg. Chem. 1999, 27,
135–154. (b) Ferrero, M.; Gotor, V. Chem. ReV. 2000, 100, 4319–4347.
(26) The lipase CAL-B immobilized on lewatite has been obtained from
Novozymes A/S (Copenhagen, Denmark).
5630 J. Org. Chem. Vol. 73, No. 14, 2008

TABLE 1. CAL-B-Catalyzed Regioselective Acylation of a
Mixture of r-D-Arabinofuranosyl and Pyranosyl Thymine in
Acetonitrile, Using Different Acylating Agents at 40-42 °Ca
and/or spectral data with those reported in the literature. All
these reactions, when performed under identical conditions but
without addition of CAL-B, did not yield any product.
substrate
acylating agent reaction time product yieldb (%)
In summary, it has been established that CAL-B selectively
and efficiently catalyzes the butanoylation of the primary
hydroxyl group in R-D-arabinofuranosyl thymine and ꢀ-D-
xylofuranosyl thymine over the secondary hydroxyl groups in
the molecule. It has also been demontrated for the first time
that the primary hydroxyl group selectivity of CAL-B can
efficiently be used for the separation of furanosyl and pyranosyl
nucleoside mixtures of different pentoses, which is otherwise
very difficult to achieve on preparative scale. This enzymatic
methodology of separation of mixtures of arabinofuranosyl/
pyranosyl thymine and xylofuranosyl/pyranosyl thymine may
find applications in the preparation of pure derivatized furano
nucleotides to be used for the synthesis of oligonucleotides on
DNA synthesizer and for other useful applications.
mixture of
furanoside 10 and
pyranoside 11
23
24
25
26
27
28
6 days
2.5 h
45 min
4 h
1.5 h
6 days
29
30
31
32
29
33
40
92
97
82
95
64
a All these reactions did not yield any product when performed in the
absence of CAL-B. b The yields reported are based on the consideration
of furanonucleosides as 100% in the mixture.
TABLE 2. CAL-B-Catalyzed Regioselective Acylation of a
Mixture of ꢀ-D-Xylofuranosyl and Pyranosyl Thymine in
Acetonitrile, Using Different Acylating Agents at 40-42 °Ca
substrate
acylating agent reaction time product yieldb (%)
mixture of
furanoside 21 and
pyranoside 22
23
24
25
26
27
28
6 days
3 h
1 h
8 h
2 h
34
35
36
37
34
38
25
93
96
82
92
30
Experimental Section
General Procedure for the Enzymatic Acylation Reaction
on the Mixture of 10 and 11/21 and 22. To a mixture of 1-(R-
D-arabinofuranosyl)thymine (10) and 1-(R-D-arabinopyranosyl) thy-
mine (11)/1-(ꢀ-D-xylofuranosyl) thymine (21) and 1-(ꢀ-D-xylopy-
ranosyl)thymine (22) (0.39 g, 1.5 mmol) and dry acetonitrile (25
mL), appropriate acid anhydride/vinyl acylate (1.05/0.7 equiv) was
added, followed by CAL-B (200 mg). The reaction mixture was
stirred in an incubator shaker at 40-42 °C and the progress of the
reaction was monitored by TLC. Solubility of the reaction mixture
increases with progress of the reaction. On completion, the reaction
was stopped by filtering off the enzyme and the solvent was
evaporated to dryness under reduced pressure. The crude product
thus obtained was purified by column chromatography to afford
5′-O-acylated arabinofuranosyl thymine 29-33/ 5′-O-acylated
xylofuranosyl thymine 34-38 in 40-97%/25-96% yields (calcu-
lated by considering furanonucleoside as 100% in the mixture).
The unreacted arabinopyranosyl thymine 11/xylopyranosyl thymine
22 was recovered from the mixture in 60-85%/95-97% yields.
1-(5′-O-Acetyl-r-D-arabinofuranosyl)thymine (29). 29 was
obtained as a colorless oil (0.16 g) in 40% yield (when acetic
anhydride was used as acetylating agent)/(0.38 g) in 95% yield
(when vinyl acetate was used as acetylating agent). Rf 0.45 (10%
6 days
a All these reactions did not yield any product when performed in the
absence of CAL-B. b The yields reported are based on the consideration
of furanonucleosides as 100% in the mixture.
column chromatography to afford 5′-O-acetylated arabino and
xylofuranosyl thymine 29 and 34 in 40% and 25% yields,
respectively together with unreacted, recovered arabino and
xylopyranosyl thymine 11 and 22 (Tables 1 and 2).
To find an efficient acylating agent, we carried out CAL-B-
catalyzed acylation of a mixture of arabinofuranosyl/pyranosyl
thymine 10/11 and xylofuranosyl/pyranosyl thymine 21/22 with
different acid anhydrides 24-26 and two active esters, i.e., vinyl
acetate 27 and vinyl benzoate 28. The results compiled in Tables
1 and 2 clearly indicated that CAL-B most efficiently transfers
the butanoyl group from butanoic anhydride to the primary
hydroxyl group of R-D-arabinofuranosyl thymine 10 or ꢀ-D-
xylofuranosyl thymine 21 when the mixtures of nucleosides 10/
11 or 21/22 and butanoic anhydride were incubated with the
lipase in acetonitrile at 40-42 °C. The efficiency of the acyl
group transfer potential of the lipase decreases, both on
descending or ascending the anhydrides from butanoic anhydride
in the homologous series. Even the active ester, vinyl benzoate,
was far from competing with the butanoic anhydride for the
CAL-B-catalyzed benzoyl transfer reactions on nucleoside
mixtures under study (Tables 1 and 2). In contrast to acetic
anhydride, vinyl acetate was found to be a much better
acetylating agent for the acetylation of both R-D-arabinofura-
nosyl thymine 10 and ꢀ-D-xylofuranosyl thymine 21 in the
presence of CAL-B. Thus incubation of mixtures of nucleosides
10/11 or 21/22 with vinyl acetate leads to the formation of 29
and 34 in almost quantitative yields in 1.5 and 2.0 h,
respectively; whereas the conversion was only 40% and 25%
during the acetylation of the mixtures with acetic anhydride,
that too in 6 days. However, butanoic anhydride was found to
be a still better acylating agent than vinyl acetate. All the
compounds prepared herein were unambiguously identified on
the basis of their spectral (1H, 13C, 1H-1H COSY, NOE NMR,
IR, and high-resolution mass spectral) data analysis. The
structures of known compounds 6a,b, 8, 10, 11, 17a,b, 19, 21,
and 22 were further confirmed by the comparison of the physical
methanol in chloroform, v/v); [R]32 +43.6 (c 0.1, MeOH); IR
D
(KBr) νmax 3416, 1720, 1698, 1474, 1372, 1265, 1046, and 783
1
cm-1; H NMR (300 MHz, CDCl3 + DMSO-d6) δ 1.64 (s, 3H),
1.88 (s, 3H), 3.75 (q, J ) 4.5 Hz, 1H), 3.90-4.01 (m, 3H),
4.12-4.13 (m, 1H), 5.42 (d, J ) 4.1 Hz, 1H), 5.57 (d, J ) 4.7 Hz,
1H), 5.61 (d, J ) 4.5 Hz, 1H), 7.39 (s, 1H), and 11.09 (s, 1H); 13
C
NMR (75.5 MHz, CDCl3 + DMSO-d6) δ 12.4, 20.9, 64.2, 75.7,
79.3, 83.0, 90.1, 109.5, 137.2, 150.9, 164.2, and 170.3; HRMS m/e
calcd for C12H16N2O7 + Na (M + Na)+ 323.0850, found 323.0837.
1-(5′-O-Propanoyl-r-D-arabinofuranosyl)thymine (30). 30 was
obtained as a light yellow oil (0.38 g) in 92% yield. Rf 0.48 (10%
methanol in chloroform, v/v); [R]32 +33.0 (c 0.1, MeOH); IR
D
1
(KBr) νmax 3420, 1715, 1698, 1472, 1269, 1201, 1054 cm-1; H
NMR (300 MHz, CDCl3) δ 1.78 (t, J ) 7.4 Hz, 3H), 1.81 (s, 3H),
2.42 (q, J ) 7.5 Hz, 2H), 4.25 (s, 1H), 4.29-4.41 (m, 2H), 4.51
(s, 2H), 5.03, 5.50 (2 × br s, 2H), 5.83 (s, 1H), 7.36 (s, 1H), and
10.91 (s, 1H); 13C NMR (75.5 MHz, CDCl3) δ 9.4, 12.7, 27.8,
64.3, 76.3, 81.1, 85.5, 92.7, 110.2, 137.4, 151.9, 164.2, and 175.0;
HRMS m/e calcd for C13H18N2O7 + Na (M + Na)+ 337.1006, found
337.0997.
1-(5′-O-Butanoyl-r-D-arabinofuranosyl)thymine (31). 31 was
obtained as a colorless oil (0.42 g) in 97% yield. Rf 0.5 (10%
methanol in chloroform, v/v); [R]32 +31.1 (c 0.1, MeOH); IR
D
(KBr) νmax 3442, 1703, 1477, 1270, 1099, 1059, 712 cm-1; 1H NMR
(300 MHz, CDCl3) δ 0.96 (t, J ) 7.3 Hz, 3H), 1.67 (hex, J ) 7.3
J. Org. Chem. Vol. 73, No. 14, 2008 5631

Hz, 2H), 1.80 (s, 3H), 2.36 (t, J ) 7.3 Hz, 2H), 4.22 (br s, 1H),
4.32-4.37 (m, 2H), 4.65 (br s, 1H), 5.34 (s, 1H), 5.85 (s, 1H),
5.90 (br s, 1H), 6.01 (br s, 1H), 7.37 (s, 1H), and 11.12 (s, 1H);
13C NMR (75.5 MHz, CDCl3) δ 12.7, 14.0, 18.8, 36.4, 64.2, 76.3,
81.2, 85.4, 92.6, 110.2, 137.2, 152.0, 165.1, and 174.1; HRMS m/e
calcd for C14H20N2O7 + Na (M + Na)+ 351.1163, found 351.1161.
1-(5′-O-Pentanoyl-r-D-arabinofuranosyl)thymine (32). 32 was
obtained as a white solid (0.37 g) in 82% yield. Rf 0.45 (10%
1H NMR (300 MHz, CDCl3 + DMSO-d6) δ 1.51 (t, J ) 7.5 Hz,
3H), 1.88 (s, 3H), 2.39 (q, J ) 7.5 Hz, 2H), 4.11 (s, 1H), 4.22 (s,
1H), 4.33-4.42 (m, 2H), 4.50 (t, J ) 7.3 Hz, 1H), 5.02, 5.32 (2 ×
br s, 2H), 5.78 (s, 1H), 7.62 (s, 1H), and 10.32 (br s, 1H); 13C
NMR (75.5 MHz, DMSO-d6) δ 9.7, 13.2, 27.6, 63.4, 75.9, 80.9,
81.4, 91.7, 109.5, 137.7, 151.4, 164.6, and 174.3; HRMS m/e calcd
for C13H18N2O7 + Na (M + Na)+ 337.1006, found 337.1000.
1-(5′-O-Butanoyl-ꢀ-D-xylofuranosyl)thymine (36). 36 was ob-
tained as a white solid (0.28 g) in 96% yield. Rf 0.5 (10% methanol
methanol in chloroform, v/v); mp 186 °C; [R]32 +34.1 (c 0.1,
D
in chloroform, v/v); mp 69-70 °C; [R]32 +10.9 (c 0.1, MeOH);
MeOH); IR (KBr) νmax 3460, 1711, 1486, 1262, 1099, 989, and
D
1
706 cm-1; H NMR (300 MHz, CDCl3) δ 0.92 (t, J ) 7.5 Hz,
IR (KBr) νmax 3418, 1714, 1694, 1470, 1266, 1091, and 786 cm-1
;
1H NMR (300 MHz, CDCl3 + DMSO-d6) δ 0.90 (t, J ) 7.2 Hz,
3H), 1.56 (q, J ) 7.2 Hz, 2H), 1.78 (s, 3H), 2.31 (t, J ) 7.2 Hz,
2H), 3.98 (br s, 2H), 4.25-4.33 (m, 3H), 5.64 (br s, 1H), 5.71 (s,
1H), 5.80 (br s, 1H), 7.62 (s, 1H), and 11.40 (br s, 1H); 13C NMR
(75.5 MHz, CDCl3 + DMSO-d6) δ 11.6, 12.6, 17.1, 34.5, 61.7,
74.2, 79.3, 79.6, 90.0, 107.9, 136.1, 149.7, 163.0, and 171.9; HRMS
m/e calcd for C14H20N2O7 + Na (M + Na)+ 351.1163, found
351.1152.
3H), 1.35 (sep, J ) 7.5 Hz, 2H), 1.63 (p, J ) 7.5 Hz, 2H), 1.78 (s,
3H), 2.38 (t, J ) 7.5 Hz, 2H), 4.22 (br s, 1H), 4.30-4.34 (m, 3H),
4.51 (s, 2H), 5.23 (br s, 1H), 5.84 (s, 1H), 7.38 (s, 1H), and 11.10
(s, 1H); 13C NMR (75.5 MHz, CDCl3) δ 12.7, 14.1, 22.6, 27.3,
34.2, 64.2, 76.4, 81.2, 85.9, 92.9, 110.0, 137.4, 151.9, 165.1, and
174.2; HRMS m/e calcd for C15H22N2O7 + Na (M + Na)+
365.1319, found 365.1308.
1-(5′-O-Benzoyl-r-D-arabinofuranosyl)thymine (33). 33 was
obtained as a colorless oil (0.31 g) in 64% yield. Rf 0.53 (10%
1-(5′-O-Pentanoyl-ꢀ-D-xylofuranosyl)thymine (37). 37 was
methanol in chloroform, v/v); [R]32 +16.0 (c 0.1, MeOH); IR
D
obtained as a sticky white solid (0.25 g) in 82% yield. Rf 0.45 (10%
(KBr) νmax 3437, 1712, 1694, 1271, 1096, 1061, and 708 cm-1; 1H
NMR (300 MHz, CDCl3) δ 1.76 (s, 3H), 4.31 (br s, 2H), 4.49-4.62
(m, 3H), 4.66 (s, 1H), 5.33 (br s, 1H), 5.90 (s, 1H), 7.38-7.45 (m,
3H), 7.53 (d, J ) 7.4 Hz, 1H), 8.05 (d, J ) 7.4 Hz, 2H), and 11.10
(s, 1H); 13C NMR (75.5 MHz, CDCl3) δ 12.7, 64.7, 76.3, 81.2,
85.7, 92.8, 110.1, 128.9, 130.0, 130.2, 133.7, 137.3, 152.0, 165.1,
and 166.9; HRMS m/e calcd for C17H18N2O7 + Na (M + Na)+
385.1006, found 385.0997.
methanol in chloroform, v/v); [R]32 +24.9 (c 0.1, MeOH); IR
D
(KBr) νmax 3412, 1708, 1695, 1470, 1266, 1178, and 1092 cm-1
;
1H NMR (300 MHz, DMSO-d6) δ 0.86 (t, J ) 7.2 Hz, 3H), 1.26
(h, J ) 7.2 Hz, 2H), 1.51 (p, J ) 7.5 Hz, 2H), 1.76 (s, 3H), 2.32
(t, J ) 7.5 Hz, 2H), 3.97 (s, 2H), 4.22-4.24 (m, 1H), 4.30-4.32
(m, 2H), 5.65 (d, J ) 3.0, 1H), 5.69 (s, 1H), 5.82 (d, J ) 3.8 Hz,
1H), 7.61 (s, 1H), and 11.42 (br s, 1H); 13C NMR (75.5 MHz,
DMSO-d6) δ 11.6, 12.8, 20.8, 25.7, 32.4, 61.8, 74.1, 79.2, 79.5,
89.9, 107.9, 136.1, 149.8, 163.0, and 171.1; HRMS m/e calcd for
C15H22N2O7 + Na (M + Na)+ 365.1319, found 365.1311.
1-(5′-O-Acetyl-ꢀ-D-xylofuranosyl)thymine (34). 34 was ob-
tained as a sticky white solid (0.07 g) in 25% yield (when acetic
anhydride was used as acetylating agent)/(0.24 g) in 92% yield
(when vinyl acetate was used as acetylating agent). Rf 0.45 (10%
methanol in chloroform, v/v); [R]32D +3.5 (c 0.1, MeOH); IR (KBr)
Acknowledgment. We thank the Department of Biotechnol-
ogy (DBT, New Delhi) and ISIS Pharmaceuticals, USA for
financial support to this work. J.M., G.S., and S.K.S. thank the
Council of Scientific and Industrial Research (CSIR, New Delhi)
for the award of senior research fellowships.
νmax 3433, 1718, 1698, 1664, 1475, 1374, 1267, and 1054 cm-1
;
1H NMR (300 MHz, CDCl3 + DMSO-d6) δ 1.85 (s, 3H), 2.03 (s,
3H), 3.45 (2 × br s, 2H), 4.06-4.08 (m, 2H), 4.33-4.40 (m, 3H),
5.82 (s, 1H), 7.64 (s, 1H), and 11.30 (br s, 1H); 13C NMR (75.5
MHz, CDCl3 + DMSO-d6) δ 13.1, 21.3, 63.7, 76.0, 80.9, 81.6,
92.1, 109.8, 137.8, 151.3, 164.9, and 171.0; HRMS m/e calcd for
C12H16N2O7 + Na (M + Na)+ 323.0850, found 323.0842.
Supporting Information Available: Procedure for the
preparation of 10/11 and 21/22, spectral data of 11, 22 and, 38,
1
and H and 13C spectra for all compounds. This material is
1-(5′-O-Propanoyl-ꢀ-D-xylofuranosyl)thymine (35). 35 was
obtained as a sticky white solid (0.26 g) in 93% yield. Rf 0.48 (10%
methanol in chloroform, v/v); [R]32D +7.3 (c 0.1, MeOH); IR (KBr)
available free of charge via the Internet at http://pubs.acs.org.
νmax 3412, 1720, 1694, 1471, 1393, 1267, 1199, and 1086 cm-1
;
JO800731U
5632 J. Org. Chem. Vol. 73, No. 14, 2008