Microwave-assisted synthesis of dinucleoside analogues containing a thiazolidin-4-one linkage via one-pot tandem Staudinger/aza-Wittig/cyclization

Article abstract of DOI:10.1039/c1ob05675a

Dinucleosides containing a thiazolidin-4-one linkage were prepared by one-pot tandem Staudinger/aza-Wittig/intermolecular cyclization under microwave irradiation and their structures were confirmed. Preliminary examination of HIV-RT inhibition showed that

Full text of DOI:10.1039/c1ob05675a

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PAPER
Microwave-assisted synthesis of dinucleoside analogues containing a
thiazolidin-4-one linkage via one-pot tandem
Staudinger/aza-Wittig/cyclization†
Fengjuan Shen,a,b Xiaoliu Li,*a Xiaoyuan Zhang,a Qingmei Yin,a Zhanbin Qin,a Hua Chen,a Jinchao Zhanga
and Zhaipu Mac
Received 29th April 2011, Accepted 16th May 2011
DOI: 10.1039/c1ob05675a
Dinucleosides containing a thiazolidin-4-one linkage were prepared by one-pot tandem
Staudinger/aza-Wittig/intermolecular cyclization under microwave irradiation and their structures
were confirmed. Preliminary examination of HIV-RT inhibition showed that the dinucleosides
containing (R)-thiazolidin-4-one linkage are significantly more active than those containing
(S)-thiazolidin-4-one linkage.
Introduction
Dinucleoside analogues have been demonstrated as possible
therapeutic agents for DNA repair or mutation in functional
genomics.1 The dinucleoside tetraphosphate has been applied as
an excellent chain-terminating substrate for resistant RT,2 and the
modified dinucleosides having purine and pyrimidine heterocyclic
bases have been used as inhibitors of de novo RNA polymerases for
treatment or prevention of viral infections.3 However, dinucleoside
analogues have very limited applications as therapeutic agents
because of their high toxicity, low stability to nucleases and
poor cell penetration. To overcome these problems, chemical
modifications at the sugar ring, the internucleotidic linkage and the
base have been under development.4 Especially, efforts in linking
the dinucleosides with the different functional groups, illustrated
in Fig. 1, shows an enduring interest in this area.5 These functional
groups are likely to make the dinucleasides resistant to nucleases,
be membrane permeable, and to increase the binding affinity. On
the other hand, the heterocycle bridged dinucleosides and their
biological activity have received less attention.6
Fig. 1 Dinucleoside analogues with different linkages.
The thiazolidin-4-one ring is a core substructure in various syn-
thetic pharmaceuticals that are associated with diverse biological
activities such as antibacterial, antifungal, anticancer, antiviral,
anti-inflammatory, analgesic, and calcium antagonistic.7
Conventionally, the thiazolidin-4-one derivatives can be synthe-
sized by multi component condensation using aldehydes, amines
and mercaptoacetic acid through key imine intermediates,8 which
can be readily prepared in situ from azides and aldehydes by
a Staudinger/aza-Wittig reaction9 (Scheme 1). Following this
synthetic strategy, we have developed a convenient pathway to
access to glycoside derivatives and disaccharides containing a
thiazolidin-4-one moiety from azido sugars and aromatic (or
sugar) aldehydes.10 In order to get backbone modified nucleoside
analogues as therapeutic agents for HIV, we have synthesized
a series of dinucleosides containing a novel thiazolidin-4-one
linkage from the azido nucleoside to the nucleoside aldehyde
(Scheme 2) using this methodology and checked the effect
of the configurations of the thiazolidin-4-one on inhibitory
activity.
aKey Laboratory of Chemical Biology of Hebei Province, College of
Chemistry and Environmental Science, Hebei University, Baoding, Hebei,
China. E-mail: lixl@hbu.edu.cn; Fax: 86 0312 5971116; Tel: 86 0312
5971116
bCollege of Science, Hebei University of Science & Technology, Shijiazhuang,
Hebei, China. E-mail: shenfjliu@126.com
cCollege of Life Sciences, Hebei University, Baoding, Hebei, 071002, China
† CCDC reference number 786926. For crystallographic data in CIF or
other electronic format see DOI: 10.1039/c1ob05675a
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Table 1 Synthesis of novel dinucleosides linked by thiazolidin-4-one
aYield (%)
aYield (%)
3
4
3 + 4
Ratio of 3/4
5
6
aa
ab
ba
bb
18.2
14.4
5.8
53.9
47.9
40.2
36.6
72.1
62.3
46.0
43.9
1 : 3.0
1 : 3.3
1 : 6.9
1 : 5.0
76.8
78.6
85.2
74.7
76.4
75.3
84.1
74.2
Scheme 1 One-pot tandem Staudinger/aza-Wittig reactions and three–
component synthesis of thiazolidin-4-one derivatives.
7.3
a Isolated yield.
Results and discussion
On the basis of our successful synthesis of the thiazolidin-4-one
derivatives containing a sugar moiety,10 our synthetic plan is shown
in Scheme 2.
The key azido nucleosides 1 were obtained from 5-methyl
uridine according to a procedure described preciously11(Scheme
3). The 2¢,3¢-isopropylidene-5-methyl uridine and 2¢,3¢-
isopropylidene-uridine were oxidized, using the Dess–Martin
reagent, to the aldehydes 2a and 2b in high yield (Scheme 3). The
initial attempt to carry out a Staudinger/aza-Wittig reaction at
room temperature by stirring the mixture of azido nucleoside 1a,
triphenylphosphane (Ph3P), and nucleoside aldehyde 2a failed
to yield the imine intermediate. After careful examination for
the reaction conditions, the tandem reactions were found to
proceed smoothly under microwave irradiation and afforded the
thiazolidin-4-one linked dinucleoside analogues 3aa and 4aa. In
this study, the synthesis of dinucleoside analogues was carried
out by a one-pot tandem Staudinger/aza-Wittig/intermolecular
cyclization under microwave irradiation. Thus, the mixture of
azido nucleoside 1 and triphenylphosphane (Ph3P) in dry THF
was irradiated with microwave radiation for 5 min to generate
an iminophosphorane, then the nucleoside aldehyde 2 was added
and the reaction mixture was irradiated for another 10 min
to form the key imine intermediate, followed by the addition
of mercaptoacetic acid and microwave irradiation reaction for
10 min to afford the corresponding dinucleoside analogues
containing a thiazolidin-4-one linkage 3aa–3bb and 4aa–4bb as
shown in Scheme 2. Usually, the thiazolidin-4-one derivatives
were obtained as a mixture of (R,S)-diastereomers in nearly equal
concentrations affording an unresolvable mixture of both isomers.
The ratios of the diastereomers were not equal for dinucleosides
containing a thiazolidin-4-one linkage, and the two diastereomers
were separated, as shown in Table 1. It was found that the yields
Scheme 3 The synthesis of the raw materials.
of dinucleosides from 1a were higher than those from 1b, and the
isomer 4, which has been determined to be of R-configuration at
the new generated chiral carbon (C-2) on the thiazolidin-4-one,
was the dominant product in both diastereomers. The removal of
the protecting isopropylidene of 3 and 4 was effectively carried
out in TFA–H2O (90%) at room temperature and provided the
corresponding products 5 and 6 in good yields, respectively
(Table 1).
The structure of 4ba was confirmed to be of R configuration
at C-2 by X-ray crystallography12 (Fig. 2). Accordingly, its
diastereomer 3ba should have an S-configuration at C-2. Based
on the crystallographic structure of 4ba and the comparison of
the chemical shifts of H-2 and C-2 of compounds 3 and 4, the
structures of the other compounds of 3 and 4 could be tentatively
determined. As shown in Table 2, the chemical shifts of H-2 and
C-2 of 3 appeared more downfield than those of 4, implying that
the C-2 configurations in each 3 and 4 would be the same and
assigned as S and R, respectively. Consequently, the deprotected
Scheme 2 The tandem reactions for the synthesis of 5 and 6.
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Table 2 The chemical shifts of H-2 and C-2 of compounds 3, 4, 5, and 6
d of H-2 (ppm) d of C-2 (ppm)
3(S)
4(R)
5(S)
6(R)
3(S)
4(R)
5(S)
6(R)
aa
ab
ba
bb
4.97
4.92
5.03
5.02
4.88
4.89
4.73
4.74
5.07
5.02
5.17
4.92
4.87
4.88
4.82
4.81
62.3
62.5
64.9
63.5
60.1
59.9
61.8
61.9
49.1
45.8
35.9
34.1
59.8
46.2
37.7
37.8
Fig. 2 Perspective view of compound 4ba.
Fig. 3 In silico simulation of compounds 5ba or 6ba docking to the
RNase H domain of HIV-1 RT. (A) Binding mode of 5ba at the active
site of HIV-RT. (B) Binding mode of 6ba at the active site of HIV-RT.
Compounds are presented as stick models with carbon in grey, oxygen
in red, nitrogen in blue, sulfur in yellow. Amino acid residues forming
hydrogen bonds with compounds 6ba or 5ba are depicted by black dashed
lines. Figures were generated by DS 2.5.
products 5 and 6 should keep the same S and R forms at C-2,
respectively.
The biological activities of the target compounds (5 and 6) were
preliminary evaluated for HIV-RT inhibitory activities. The HIV-
RT inhibition was measured with a HIV-RT kit13 using AZT as the
comparison. As shown in Table 3, compounds 6aa, 6ab, and 6ba
have a good HIV-RT inhibitory activity, even better than that of
the positive control AZT, and compounds 5aa, 5ab, and 5ba have
a moderate anti-HIV-RT activity. Comparing the inhibition of 6
with the R configuration at C-2 with that of the diastereoisomer
5 with an S configuration, it was suggested that the configuration
of the C-2 effects the inhibition against HIV-RT.
To understand the difference in the anti-HIV-RT activity
between the configuration of (R) and (S), molecular modeling
studies using the crystal structure of HIV-1 RT (PDB code:
1RTD) were conducted by replacing TTP with 5ba and 6ba.
The best position of each inhibitor was found with a Monte
Carlo simulation and molecular mechanic optimization using a
CHARMM (Chemistry at Harvard Macromolecular Mechanics)
force field. According to the results of molecular docking, the
azido function on AZT formed two H-bonds, one with Ala72 and
another with Try115, and the hydroxyl of 6ba formed two H-bonds
with the amide backbone of Asp185 (the amino acid constituting
the dNTP-binding site), whereas the function on 5ba formed no
H-bonds at all, which may partially explain the (R) configuration
showing a better anti-HIV-RT activity than the (S) form (Fig. 3).
Conclusion
In conclusion, novel dinucleoside analogues containing
thiazolidin-4-one have been synthesized by a convenient one-
pot tandem Staudinger/aza-Wittig/cyclization, starting from nu-
cleoside azides, nucleoside aldehydes, and mercaptoacetic acid,
under microwave irradiation. Preliminary examination of the
HIV-RT inhibition showed that the dinucleosides containing (R)-
thiazolidin-4-one linkages 6 are significantly more active than
those containing (S)-thiazolidin-4-on linkages 5, even better than
that of the positive control AZT. Further synthesis and biological
study of new dinucleosides is underway in this laboratory.
Experimental
Synthesis
General methods. Melting points were determined with a
SGW@ X-4 micro melting point apparatus and are uncorrected.
Optical rotations were determined on a SGW@-1 automatic
polarimeter. 1H NMR and 13C NMR spectra were recorded with
a Bruker AVANCE 600 (600 MHz) NMR spectrometer, and
chemical shifts are reported in parts per million relative to tetram-
ethylsilane or a residual solvent peak (DMSO-d6: 1H: d 2.50, 13C:
d 39.52). Mass spectra (MS) and high resolution mass spectra
(HRMS) were recorded using negative electrospray ionization
(ESI-) on a FTICR-MS (Ionspec 7.0T) mass spectrometer. X-ray
crystallographic measurements were made on a Bruker SMART
CCD diffractometer. The optical densities for examining the
Table 3 HIV-RT kit assay for compounds (5) and (6)
Compounds (S)
IC50 (mM)
Compounds (R)
IC50 (mM)
5aa
5ab
5ba
5bb
AZT
35.7
26.3
45.3
>100
21.4
6aa
6ab
6ba
6bb
10.3
12.9
6.5
>100
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activity of HIV-RT inhibition was measured on a BioRad Model
3550 microplate spectrophotometer. Anticancer activity was eval-
uated using MTT assay. The microwave assisted reaction was
carried out on a CEM DISCOVER S-Class Chemical Synthesis
System in a 10 mL (or 35 mL) seamless pressure vial. Thin-layer
chromatography (TLC) was performed on precoated plates (Qing-
dao GF254) with detection by UV light or with phosphomolybdic
acid in EtOH–H2O followed by heating. Column chromatography
was performed using SiO2 (Qingdao 200–300 mesh or 300-400
mesh). All other commercial reagents were used as received.
113.14, 111.69, 111.36, 98.67, 92.34, 91.01, 83.98, 83.83, 83.12,
81.54, 60.11, 45.21, 31.50, 27.13, 26.90, 26.04, 25.34, 12.25, 12.22;
HR-ESI-MS: calcd for [M - H]-C28H36N5O11S, 649.2053; found,
649.2045.
◦
Compound 3ab. White solid, 14%; mp: 162.5–164 C; [a]D22
-24.1 (c 1, CHCl3); 1H NMR (600 MHz, CDCl3): d 10.55 (s, 1H,
NH), 10.45 (s, 1H, NH), 7.33 (d, J = 7.8 Hz, 1H, CH-6 (U)),
7.05 (s, 1H, CH-6 (T)), 5.87 (d, J = 7.8 Hz, 1H, CH-5 (U)), 5.59
(d, J = 1.8 Hz, 1H, CH-1¢ (nucleoside2)), 5.32 (d, J = 1.8 Hz,
1H, CH-1¢ (nucleoside1)), 5.10 (dd, J = 1.8, 6.6 Hz, 1H, CH-2¢
(nucleoside1)), 5.02 (dd, J = 2.4, 6.6 Hz, 1H, CH-2¢ (nucleoside2)),
4.92 (dd, J = 1.2, 7.8 Hz, CH-2 (thiazolidin-4-one)), 4.75 (q, J =
4.2, 7.2 Hz, CH-3¢ (nucleoside2)), 4.64 (q, J = 4.8, 6 Hz, 1H, CH-3¢
(nucleoside1)), 4.41 (m, 1H, CH-4¢ (nucleoside1)), 4.29 (q, J = 3.6,
7.8 Hz, 1H, CH-4¢ (nucleoside2)), 3.97 (dd, J = 3.6, 14.4 Hz, 1H,
CH2-5 (thiazolidin-4-one)), 3.68 (dd, J = 1.2, 15.6 Hz, 1H, CH2-
5¢ (nucleoside1)), 3.47–3.43 (m, 2H, CH2-5¢ (nucleoside1), CH2-5
(thiazolidin-4-one)), 1.92 (s, 3H, CH3 (T)), 1.59 (s, 3H, CH3), 1.53
(s, 3H, CH3), 1.34 (s, 3H, CH3), 1.30 (s, 3H, CH3); 13C NMR (125
MHz, CDCl3): d 171.42, 165.02, 164.55, 149.96, 149.92,143.07,
140.04, 114.94, 114.58, 110.78, 102.88, 96.72, 95.79, 90.96, 84.24,
83.90, 83.75, 82.52, 81.10, 62.51, 47.47, 31.64, 27.17, 27.00, 25.36,
25.09, 12.24; HR-ESI-MS: calcd for [M - H]- C27H34N5O11S,
635.1799; found, 635.1810.
General procedure for the synthesis of compounds 3 and 4
A solution of nucleoside azide 1 (1 mmol), triphenylphosphane
(Ph3P 1.2 mmol) was irradiated (80 ◦C, 150 W, 5 min), then
aldehyde 2 (1.2 mmol) was added and the mixture was irradiated
with microwave radiation for 10 min, followed by addition of
mercaptoacetic acid and irradiated at 80 ◦C for 10 min. The
reaction mixture was cooled to room temperature and then
submitted to silica gel column chromatography to afford the
corresponding products 3 and 4, respectively.
◦
Compound 3aa. White solid, 18%; mp: 176.7–178.4 C; [a]D30
1
-12.0 (c 1, CHCl3); H NMR (600 MHz, CDCl3): d 10.39 (s,
1H, NH (T)), 10.36 (s, 1H, NH (T)), 7.15 (d, J = 1.2 Hz, 1H,
CH-6 (T)), 7.08 (d, J = 1.2 Hz, 1H, CH-6 (T)), 5.62 (d, J =
2.4 Hz, 1H, CH-1¢ (nucleoside2)), 5.38 (d, J = 1.8 Hz, 1H, CH-1¢
(nucleoside1)), 5.10 (dd, J = 1.8, 6.6 Hz, 1H, CH-2¢ (nucleoside1)),
5.02 (dd, J = 2.4, 6.6 Hz, 1H, CH-2¢ (nucleoside2)), 4.97 (dd,
J = 1.2, 7.8 Hz, 1H, CH-2 (thiazolidin-4-one)), 4.75 (q, J = 3.6,
6.6 Hz, 1H, CH-3¢ (nucleoside2)), 4.67 (dd, J = 4.8, 6.6 Hz, 1H,
CH-3¢ (nucleoside1)), 4.41 (m, 1H, CH-4¢ (nucleoside1)), 4.32 (q,
J = 4.2, 7.8 Hz, 1H, CH-4¢ (nucleoside2)), 3.99 (dd, J = 4.8, 14.4 Hz,
1H, CH2-5¢ (nucleoside1)), 3.68 (dd, J = 1.2, 15.6 Hz, 1H, CH2-
5¢ (thiazolidin-4-one)), 3.51–3.47 (m, 2H, CH2-5¢ (thiazolidin-4-
one), CH2-5¢ (nucleoside1)), 1.94 (d, J = 0.6 Hz, 3H, CH3-5), 1.92
(d, J = 0.6 Hz, 3H, CH3-5), 1.59 (s, 3H, CH3), 1.53 (s, 3H, CH3),
1.34 (s, 3H, CH3), 1.31 (s, 3H, CH3); 13C NMR (125 MHz, CDCl3):
d 171.55, 164.95, 164.76, 150.28, 150.04, 139.82, 138.62, 114.96,
114.57, 111.45, 110.89, 96.47, 95.13, 90.08, 84.29, 83.90, 83.61,
82.63, 81.76, 62.32, 47.11, 31.62, 27.13, 26.99, 25.33, 25.12, 12.34,
12.22; HR-ESI-MS: calcd for [M - H]- C28H36N5O11S, 649.2053;
found 649.2043.
Compound 4ab. White solid, 47.9%; mp: 201.5–202.8 ◦C; [a]D30
109.8 (c 0.1, CHCl3); 1H NMR (600 MHz, CDCl3): d 10.24 (s, 1H,
NH), 9.75 (s, 1H, NH), 7.25 (d, J = 8.4 Hz, 1H, CH-6 (U)), 7.11
(d, J = 0.6 Hz, 1H, CH-6 (T)), 5.78 (dd, J = 1.8, 8.4 Hz, 1H, CH-5
(U)), 5.69 (d, J = 1.8 Hz, 1H, CH-1¢ (nucleoside2)), 5.40 (s, 1H,
CH-1¢ (nucleoside1)), 5.25 (d, J = 6 Hz, 1H, CH-2¢ (nucleoside2)),
5.19 (dd, J = 4.2, 6 Hz, 1H, CH-3¢ (nucleoside2)), 5.06 (dd, J =
2.4, 6.6 Hz, 1H, CH-2¢ (nucleoside1)), 4.89 (dd, J = 1.2, 9.6 Hz,
CH-2 (thiazolidin-4-one)), 4.84 (q, J = 3.6, 6.6 Hz, 1H, CH-3¢
(nucleoside1)), 4.68 (q, J = 4.2, 9.6 Hz, 1H, CH-4¢ (nucleoside2)),
4.26–4.22 (m, 2H, CH-4¢ (nucleoside1), CH2-5¢ (nucleoside1)), 3.73
(d, J = 15.6 Hz, 1H, CH2-5 (thiazolidin-4-one)), 3.68 (d, J =
10.8 Hz, 1H, CH2-5¢ (nucleoside1)), 3.43 (d, J = 15.6 Hz, 1H,
CH2-5 (thiazolidin-4-one)), 1.93 (s, 3H, CH3), 1.56 (s, 3H, CH3),
1.45 (s, 3H, CH3), 1.35 (s, 6H, CH3); 13C NMR (125 MHz, CDCl3):
d 172.51, 164.24, 164.08, 151.10, 150.47, 144.53, 138.04, 114.51,
113.27, 111.59, 102.91, 98.81, 93.12, 91.18, 84.31, 83.98, 83.03,
81.79, 59.94, 53.44, 45.37, 31.54, 27.13, 26.06, 25.32, 24.41, 12.26;
HR-ESI-MS: calcd for [M - H]-C27H34N5O11S, 635.1799; found,
635.1806.
◦
Compound 4aa. White solid, 54%; mp: 164.1–165.9 C; [a]D31
1
81.4 (c 1, CHCl3); H NMR (600 MHz, CDCl3): d 10.15 (s, 1H,
NH(T)), 9.66 (s, 1H, NH(T)), 7.10 (d, J = 1.2 Hz, 1H, CH-6(T)),
7.03 (d, J = 0.6 Hz, 1H, CH-6(T)), 5.74 (d, J = 2.4 Hz, 1H,
CH-1¢ (nucleoside1)), 5.33 (s, 1H, CH-1¢ (nucleoside2)), 5.23 (d,
J = 6.6 Hz, 1H, CH-2¢ (nucleoside2)), 5.18 (dd, J = 3.6, 6 Hz,
1H, CH-3¢ (nucleoside2)), 5.01 (dd, J = 2.4, 6.6 Hz, 1H, CH-2¢
(nucleoside1)), 4.88 (dd, J = 1.2, 9.6 Hz, 1H, CH-2 (thiazolidin-4-
one)), 4.79 (q, J = 3.6, 6.6 Hz, 1H, CH-3¢ (nucleoside1)), 4.68 (q,
J = 3.6, 9.6 Hz, 1H, CH-4¢ (nucleoside2)), 4.276 (m, 1H, CH-4¢
(nucleoside1)), 4.24 (m, 1H, CH2-5 (thiazolidin-4-one)), 3.73 (d,
J = 15.6 Hz, 1H, CH2-5¢ (nucleoside1)), 3.69 (dd, J = 3.6, 14.4 Hz,
1H, CH2-5¢ (thiazolidin-4-one)), 3.41 (d, J = 15.6 Hz, 1H, CH2-5¢
(nucleoside1)), 1.93 (s, 6H, two CH3), 1.43 (s, 6H, two CH3), 1.34
(s, 3H, CH3), 1.33 (s, 3H, CH3); 13C NMR (125 MHz, CDCl3)
d 172.59, 164.71, 164.24, 150.28, 150.53, 140.48, 137.59, 114.62,
Compound 3ba. White solid, 5.8%; mp: 173.5–174.4 ◦C; [a]D15
-19.8 (c 1, DMSO); 1H NMR (600 MHz, CD3OD): d 7.67 (d, J =
0.6 Hz, 1H, CH-6 (T)), 7.53 (d, J = 1.2 Hz, 1H, CH-6(T)), 6.33
(q, J = 5.4, 7.2 Hz, 1H, CH-1¢ (nucleoside1)), 5.77 (d, J = 1.8 Hz,
1H, CH-1¢ (nucleoside2)), 5.16 (dd, J = 1.8, 6 Hz, 1H, CH-2¢
(nucleoside2)), 5.03 (dd, J = 1.2, 9 Hz, 1H, CH-2 (thiazolidin-
4-one)), 4.85 (q, J = 3.6, 6.6 Hz, 1H, CH-3¢ (nucleoside2)), 4.37
(m, 2H, CH-3¢ (nucleoside1), CH-4¢ (nucleoside2)), 4.30 (m, 1H,
CH-4¢ (nucleoside1)), 3.83 (dd, J = 1.2, 15.6 Hz, 1H, CH2-5¢
(nucleoside1)), 3.79 (dd, J = 3, 12 Hz, 1H, CH2-5 (thiazolidin-
4-one)), 3.64 (dd, J = 3, 12 Hz, 1H, CH2-5 (thiazolidin-4-one)),
3.46 (d, J = 16.2 Hz, 1H, CH2-5¢ (nucleoside1)), 2.89 (m, 1H,
CH2-2¢ (nucleoside1)), 2.17 (m, 1H, CH2-2¢ (nucleoside1)), 1.90 (d,
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J = 1.2 Hz, 3H, CH3 (T)), 1.86 (d, J = 1.2 Hz, 3H, CH3 (T)), 1.56
(s, 3H, CH3), 1.37 (s, 3H, CH3); 13C NMR (125 MHz, CD3OD):
d 174.05, 166.46, 166.37, 152.26, 152.10, 141.03, 138.42, 115.45,
112.11, 111.36, 97.27, 92.92, 87.28, 85.26, 84.07, 82.40, 64.92,
62.56, 58.32, 36.70, 32.72, 27.24, 25.24, 12.49, 12.27; HR-ESI-MS:
calcd for [M - H]- C25H32N5O10S, 593.1791; found, 593.1785.
CH2-2¢ (nucleoside1)), 2.19 (m, 1H, CH2-2¢ (nucleoside1)), 1.77 (s,
3H, CH3 (T)), 1.47 (s, 3H, CH3), 1.31 (s, 3H, CH3); 13C NMR
(125 MHz, DMSO-d6): d 172.42, 164.21, 164.00, 151.41, 150.86,
144.95, 136.93, 112.65, 109.86, 102.00, 95.88, 89.35, 85.21, 84.20,
82.69, 82.64, 61.86, 61.54, 56.89, 38.12, 31.70, 26.47, 24.72, 12.71;
HR-ESI-MS: calcd for [M - H]- C24H30N5O10S, 579.1634; found,
579.1648.
Compound 4ba. White solid, 40.2%; mp: 241.1–241.9 ◦C; [a]D21
1
76.7 (c 1, DMSO); H NMR (600 MHz, DMSO-d6): d 11.41 (s,
General procedure for deprotection of compounds 3 and 4
1H, NH (T)), 11.25 (s, 1H, NH (T)), 7.75 (d, J = 1.2 Hz, 1H, CH-6
(T)), 7.55 (d, J = 1.2 Hz, 1H, CH-6 (T)), 6.39 (t, J = 4.8, 14.4 Hz,
1H, CH-1¢ (nucleoside1)), 5.69 (s, 1H, CH-1¢ (nucleoside2), 5.22
(d, J = 6 Hz, 1H, CH-2¢ (nucleoside2)), 5.05 (dd, J = 4.2, 6 Hz,
1H, CH-3¢ (nucleoside2)), 4.93 (s, 1H, OH), 4.73 (dd, J = 1.2,
9 Hz, 1H, CH-2 (thiazolidin-4-one)), 4.60 (q, J = 3.6, 9 Hz, 1H,
CH-4¢ (nucleoside2)), 4.38 (m, 1H, CH-3¢ (nucleoside1)), 4.27 (m,
1H, CH-4¢ (nucleoside1)), 3.79 (dd, J = 1.8, 15.6 Hz, 1H, CH2-5¢
(nucleoside1)), 3.53–3.46 (m, 2H, CH2-5 (thiazolidin-4-one)), 3.41
(d, J = 15.6 Hz, 1H, CH2-5¢ (nucleoside1)), 2.32 (m, 1H, CH2-2¢
(nucleoside1)), 2.20 (m, 1H, CH2-2¢ (nucleoside1)), 1.77 (d, J =
0.6 Hz, 3H, CH3 (T)), 1.77 (d, J = 1.2 Hz, 3H, CH3 (T)), 1.47 (s,
3H, CH3), 1.30 (s, 3H, CH3); 13C NMR (125 MHz, DMSO-d6):
d 172.41, 164.61, 164.20, 151.39, 150.85, 140.67, 136.93, 112.63,
109.87, 109.68, 95.65, 89.16, 85.13, 84.06, 82.76, 82.48, 61.84,
61.46, 56.79, 37.96, 31.67, 26.50, 24.76, 12.68, 12.40; HR-ESI-MS:
calcd for [M - H]- C25H32N5O10S, 593.1791; found, 593.1794.
The deprotection of 3 and 4 was carried out effectively in TFA–
H2O (90%) at room temperature for 1 h and provided the
corresponding products 5 and 6 in good yields.
Compound 5aa. White solid, 77%; mp: 270 ◦C (decomposi-
tion); [a]2D1 -11.5 (c 1, DMSO); 1H NMR (600 MHz, DMSO-d6):
d 11.40 (s, 1H, NH (T)), 11.35 (s, 1H, NH (T)), 7.58 (s, 1H, CH-
6 (T)), 7.49 (s, 1H, CH-6 (T)), 5.83 (d, J = 7.2 Hz, 1H, CH-1¢
(Nucleoside2)), 5.82 (d, J = 6.6 Hz, 1H, CH-1¢ (Nucleoside1)), 5.49
(d, J = 6 Hz, 1H, OH), 5.38 (d, J = 5.4 Hz, 1H, OH), 5.31 (d,
J = 4.8 Hz, 1H, OH), 5.23 (d, J = 4.8 Hz, 1H, OH), 5.07 (dd,
J = 1.2, 6 Hz, 1H, CH-2 (thiazolidin-4-one)), 4.25 (m, 3H, CH-2¢
(nucleoside2), CH-2¢ (nucleoside1), CH-4¢ (nucleoside2)), 4.03 (m,
1H, CH-4¢ (nucleoside1)), 3.96 (m, 2H, CH-3¢ (nucleoside2), CH-5
(thiazolidin-4-one)), 3.87 (m, 1H, CH-3¢ (nucleoside1)), 3.74 (d, J =
15.6 Hz, 1H, CH2-5¢ (nucleoside1)), 3.50 (d, J = 15.6 Hz, 1H, CH2-
5¢ (nucleoside1)), 3.40 (dd, J = 7.2, 14.4 Hz, 1H, CH2-5 (thiazolidin-
4-one)), 1.77 (s, 3H, CH3), 1.75 (s, 3H, CH3); 1H NMR (600 MHz,
DMSO-d6, D2O): d 7.53 (s, 1H, CH-6(T)), 7.46 (s, 1H, CH-6(T)),
5.80 (d, J = 6.6 Hz, 1H, CH-1¢ (nucleoside2)), 5.70 (d, J = 6.6 Hz,
1H, CH-1¢ (nucleoside1)), 5.03 (d, J = 6 Hz, 1H, CH-2 (thiazolidin-
4-one)), 4.23 (m, 3H, CH-2¢ (nucleoside2), CH-2¢ (nucleoside1),
CH-4¢ (nucleoside2)), 4.01 (m, 1H, CH-4¢ (nucleoside1)), 3.97 (q,
J = 3.6, 5.4 Hz, 1H, CH-3¢ (nucleoside2)), 3.93 (dd, J = 4.8, 14.4 Hz,
1H, CH2-5 (thiazolidin-4-one)), 3.86 (t, J = 4.2 Hz, 1H, CH-3¢
(nucleoside1)), 3.70 (covered by H2O, s, 1H, CH2-5¢ (nucleoside1)),
3.48 (d, J = 9.6 Hz, 1H, CH2-5¢ (nucleoside1)), 3.40 (q, J = 7.8,
14.4 Hz, 1H, CH2-5 (thiazolidin-4-one)), 1.76 (s, 3H, CH3), 1.75
(s, 3H, CH3); 13C NMR (125 MHz, DMSO-d6): d 171.48, 164.16,
164.02, 151.29, 137.26, 136.48, 110.60, 110.34, 88.45, 87.79, 85.56,
82.03, 72.17, 71.85, 71.73, 70.25, 61.78, 49.07, 46.33, 31.38, 12.49,
12.33; HR-ESI-MS: calcd for [M - H]- C28H36N5O11S, 569.1427;
found, 569.1435.
Compound 3bb. White solid, 7.3%; mp: 168.4–169.6 ◦C; [a]D27
1
-7.9 (c 1, DMSO); H NMR (600 MHz, CD3OD): d 7.70 (dd,
J = 1.2, 7.8 Hz, 1H, CH-6 (U)), 7.66 (d, J = 1.2 Hz, 1H, CH-6
(T)), 6.31 (t, J = 7.2, 12.6 Hz, 1H, CH-1¢ (nucleoside1)), 5.79 (s,
1H, CH-1¢ (nucleoside2)), 5.73 (dd, J = 1.2, 7.8 Hz, 1H, CH-5
(U)), 5.18 (dd, J = 1.8, 6.6 Hz, 1H, CH-2¢ (nucleoside1)), 5.02 (dd,
J = 1.2, 8.4 Hz, 1H, CH-2 (thiazolidin-4-one)), 4.85 (q, J = 3.6,
6.6 Hz, 1H, CH-3¢ (nucleoside2)), 4.38 (m, 2H, CH-3¢ (nucleoside1),
CH-4¢ (nucleoside2)), 4.29 (m, 1H, CH-4¢ (nucleoside1)), 3.83 (d,
J = 16.2 Hz, 1H, CH2-5¢ (nucleoside1)), 3.80 (dd, J = 3, 12.6 Hz,
1H, CH2-5 (thiazolidin-4-one)), 3.65 (dd, J = 3, 12 Hz, 1H,
CH2-5 (thiazolidin-4-one)), 3.45 (d, J = 15.6 Hz, 1H, CH2-5¢
(nucleoside1)), 2.92 (m, 1H, CH2-2¢ (nucleoside1)), 2.20 (m, 1H,
CH2-2¢ (nucleoside1)), 1.87 (s, 3H, CH3(T)), 1.56 (s, 3H, CH3),
1.37 (s, 3H, CH3); 13C NMR (125 MHz, CD3OD): d 172.61,
165.01, 164.68, 150.75, 150.67, 143.99, 137.10, 114.07, 109.98,
101.94, 96.10, 91.77, 85.96, 83.88, 82.69, 80.82, 63.49, 61.09, 56.89,
35.07, 31.35, 25.85, 23.87, 11.13; HR-ESI-MS: calcd for [M - H]-
C24H30N5O10S, 579.1634; found, 579.1645.
Compound 6aa. White solid, 76%; mp: >300 ◦C; [a]D20 55.5 (c
1, DMSO); 1H NMR (600 MHz, DMSO-d6): d 11.32 (s, 2H, NH
(T)), 7.62 (d, J = 0.6 Hz, 1H, CH-6 (T)), 7.42 (d, J = 0.6 Hz, 1H,
CH-6 (T)), 5.95 (d, J = 7.8 Hz, 1H, CH-1¢ (nucleoside2)), 5.76
(d, J = 5.4 Hz, 1H, CH-1¢ (nucleoside1)), 4.89 (dd, J = 0.6, 9 Hz,
1H, CH-2 (thiazolidin-4-one)), 4.60 (dd, J = 3, 9.6 Hz, 1H, CH-4¢
(nucleoside2)), 4.33 (q, J = 4.2, 7.8 Hz, 1H, CH-2¢ (nucleoside2)),
4.16 (t, J = 3.6, 7.2 Hz, 1H, CH-3¢ (nucleoside2)), 4.08 (m,
1H, CH-4¢ (nucleoside1)), 3.99 (t, J = 5.4, 10.8 Hz, 1H, CH-2¢
(nucleoside1)), 3.99 (t, J = 8.4, 14.4 Hz, 1H, CH2-5 (thiazolidin-
4-one)), 3.90 (q, J = 4.8, 9 Hz, 1H, CH-3¢ (nucleoside1)), 3.68 (d,
J = 15.6 Hz, 1H, CH2-5¢ (nucleoside1)), 3.51 (dd, J = 3.6, 14.4 Hz,
1H, CH2-5 (thiazolidin-4-one)), 3.46 (d, J = 15.6 Hz, 1H, CH2-5¢
(nucleoside1)), 1.81 (s, 6H, CH3); 13C NMR (125 MHz, DMSO-
d6): d 12.42, 12.50, 31.42, 46.27, 59.82, 71.45, 72.57, 73.20, 73.95,
80.48, 86.70, 88.04, 89.14, 110.23, 110.41, 136.42, 137.39, 151.19,
Compound 4bb. White solid, 36.6%; mp: 202.5–203.8 ◦C; [a]D28
1
53.5 (c 1, DMSO); H NMR (600 MHz, DMSO-d6): d 11.44 (d,
J = 6 Hz, 1H, NH (U)), 11.44 (s, 1H, NH (T)), 7.76 (d, J =
0.6 Hz, 1H, CH-6 (T)), 7.71 (d, J = 8.4 Hz, 1H, CH-6 (U)), 6.41
(t, J = 7.2, 14.4 Hz, 1H, CH-1¢ (nucleoside1)), 5.74 (s, 1H, CH-1¢
(nucleoside2)), 5.61 (dd, J = 2.4, 8.4 Hz, 1H, CH-5 (U)), 5.22 (d,
J = 6 Hz, 1H, CH-2¢ (nucleoside2)), 5.04 (dd, J = 4.2, 11.4 Hz,
1H, CH-3¢ (nucleoside2)), 4.96 (s, 1H, OH), 4.74 (dd, J = 1.2,
9 Hz, 1H, CH-2 (thiazolidin-4-one)), 4.62 (q, J = 4.2, 9.6 Hz, 1H,
CH-4¢ (nucleoside2)), 4.39 (m, 1H, CH-3¢ (nucleoside1)), 4.29 (m,
1H, CH-4¢ (nucleoside1)), 3.80 (dd, J = 1.8, 15.6 Hz, 1H, CH2-5¢
(nucleoside1)), 3.55 (q, J = 11.4, 39 Hz, 2H, CH2-5 (thiazolidin-4-
one)), 3.41 (d, J = 15.6 Hz, 1H, CH2-5¢ (nucleoside1)), 2.33 (m, 1H,
5770 | Org. Biomol. Chem., 2011, 9, 5766–5772
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151.31, 164.17, 164.20, 172.16; HR-ESI-MS: calcd for [M - H]-
C28H36N5O11S, 569.1427; found, 569.1433.
70.56, 63.46, 61.49, 57.07, 35.87, 32.11, 12.67, 12.40; HR-ESI-MS:
calcd for [M - H]- C22H28N5O10S, 553.1478; found, 553.1480.
◦
Compound 6ba. White solid, 84%; mp: 206.9–207.7 C; [a]D22
Compound 5ab. White solid, 79%; mp: 214–215 ◦C; [a]D21 -58.8
(c 1, DMSO); H NMR (600 MHz, DMSO-d6): d 11.38 (s, 2H,
6.15 (c 1, DMSO); 1H NMR (600 MHz, DMSO-d6): d 11.28
(s, 1H, NH (T)), 11.22 (s, 1H, NH (T)), 7.73 (d, J = 1.2 Hz,
1H, CH-6 (T)), 7.64 (d, J = 1.2 Hz, 1H, CH-6 (T)), 6.36 (t,
J = 7.2, 14.4 Hz, 1H, CH-1¢ (nucleoside1)), 5.97 (d, J = 7.8 Hz,
1H, CH-1¢ (nucleoside2)), 5.53 (s, 2H, OH), 4.82 (dd, J = 1.8,
9 Hz, 1H, CH-2 (thiazolidin-4-one)), 4.59 (dd, J = 3, 9 Hz,
1H, CH-4¢ (nucleoside2)), 4.34–4.29 (m, 3H, CH-3¢ (nucleoside1),
CH-2¢ (nucleoside2),CH-3¢ (nucleoside2)), 4.16 (m, 1H, CH-4¢
(nucleoside1)), 3.68 (dd, J = 1.8, 15.6 Hz, 1H, CH2-5 (thiazolidin-
4-one)), 3.54–3.42 (m, 2H, CH2-5¢ (nucleoside1)), 3.44 (d, J =
15.6 Hz, 1H, CH2-5 (thiazolidin-4-one)), 2.32 (m, 1H, CH2-2¢
(nucleoside1)), 2.18 (m, 1H, CH2-2¢ (nucleoside1)), 1.80 (d, J =
0.6 Hz, 3H, CH3(T)), 1.75 (d, J = 0.6 Hz, 3H, CH3 (T)); 13C NMR
(125 MHz, DMSO-d6): d 172.22, 164.29, 164.20, 151.36, 150.82,
137.26, 136.96, 110.37, 109.78, 88.90, 86.02, 85.05, 82.32, 74.09,
72.69, 62.02, 61.94, 56.81, 37.66, 31.67, 12.61, 12.46; HR-ESI-MS:
calcd for [M - H]- C22H28N5O10S, 553.1478; found, 553.1483.
1
NH (T)), 7.62 (d, J = 8.4 Hz, 1H, CH-6 (U)), 7.59 (s, 1H, CH-
6 (T)), 5.81 (d, J = 6.6 Hz, 1H, CH-1¢ (nucleoside2)), 5.72 (d,
J = 6 Hz, 1H, CH-1¢ (nucleoside1)), 5.70 (d, J = 8.4 Hz, 1H,
CH-4 (U)), 5.56 (d, J = 6 Hz, 1H, OH), 5.41 (d, J = 6 Hz, 1H,
OH), 5.33 (d, J = 5.4 Hz, 1H, OH), 5.28 (d, J = 4.8 Hz, 1H,
OH), 5.02 (dd, J = 1.2, 5.4 Hz, 1H, CH-2 (thiazolidin-4-one)),
4.30 (q, J = 3.6, 4.8 Hz, 1H, CH-2¢ (nucleoside2)), 4.25 (q, J = 6,
12 Hz, 1H, CH-2¢ (nucleoside1)), 4.19 (q, J = 6, 12 Hz, 1H, CH-3¢
(nucleoside1)), 4.15 (q, J = 5.4, 10.2 Hz, 1H, CH-4¢ (nucleoside2)),
3.99 (m, 1H, CH-4¢ (nucleoside1)), 3.94 (dd, J = 4.2, 14.4 Hz,
1H, CH2-5¢ (nucleoside1)), 3.87 (q, J = 4.8, 9 Hz, 1H, CH-3¢
(nucleoside2)), 3.71 (d, J = 15.6 Hz, 1H, CH2-5 (thiazolidin-4-
one)), 3.51 (d, J = 15.6 Hz, 1H, CH2-5 (thiazolidin-4-one)), 3.41
(d, J = 9 Hz, 1H, CH2-5¢ (nucleoside1)), 1.78 (s, 3H, CH3); 13C
NMR (125 MHz, DMSO-d6): d 170.84, 163.69, 162.85, 150.76,
150.72, 140.57, 136.89, 109.87, 102.49, 88.46, 87.48, 84.38, 81.78,
72.02, 71.43, 71.13, 69.28, 61.57, 45.84, 30.83, 11.84; HR-ESI-MS:
calcd for [M - H]- C21H26N5O11S, 555.1271; found, 555.1263.
◦
Compound 5bb. White solid, 75%; mp: 194.7–196.2 C; [a]D28
1
-94.0 (c 1, DMSO); H NMR (600 MHz, D2O): d 7.67 (d, J =
7.8 Hz, 1H, CH-6 (U)), 7.52 (s, 1H, CH-6 (T)), 6.20 (t, J = 5.4,
12.6 Hz, 1H, CH-1¢), 5.81 (d, J = 7.8 Hz, 1H, CH-5 (U)), 5.77 (d,
J = 6.6 Hz, 1H, CH-1¢ (nucleoside2)), 4.92 (dd, J = 1.8, 7.2 Hz, 1H,
CH-2 (thiazolidin-4-one)), 4.42–4.37 (m, 2H, CH-4¢ (nucleoside1),
CH-2¢ (nucleoside2)), 4.23–4.18 (m, 3H, CH-3¢ (nucleoside1), CH-
4¢ (Nucleoside2), CH-3¢ (Nucleoside2)), 3.78–3.74 (m, 2H, CH2-
5¢ (nucleoside1), CH2-5 (thiazolidin-4-one)), 3.68 (dd, J = 4.2,
12.6 Hz, CH2-5 (thiazolidin-4-one)), 3.49 (d, J = 16.2 Hz, 1H,
CH2-5¢ (nucleoside1)), 2.86 (m, 1H, CH2-2¢ (nucleoside1)), 2.25
(m, 1H, CH2-2¢ (nucleoside1)), 1.75 (s, 3H, CH3); 13C NMR (125
MHz, D2O): d 174.10, 166.31, 165.80, 151.60, 151.38, 142.31,
137.71, 111.13, 102.73, 89.66, 86.09, 85.88, 80.35, 72.19, 70.03,
64.06, 60.97, 56.53, 34.09, 32.14, 11.55; HR-ESI-MS: calcd for [M
- H]-C21H26N5O10S, 539.1321; found, 539.1333.
Compound 6ab. White solid, 75%; mp: 215 ◦C; [a]D20 44.2 (c 1,
DMSO); 1H NMR (600 MHz, DMSO-d6): d 11.31 (s, 2H, NH (T),
NH (U)), 7.78 (d, J = 7.8 Hz, 1H, CH-6 (U)), 7.42 (d, J = 1.2 Hz,
1H, CH-6 (T)), 5.93 (d, J = 7.8 Hz, 1H, CH-1¢ (nucleoside2)), 5.76
(d, J = 5.4 Hz, 1H, CH-1¢ (nucleoside1)), 5.68 (d, J = 7.8 Hz, 1H,
CH-5 (U)), 5.59 (d, J = 6 Hz, 1H, OH), 5.56 (d, J = 4.8 Hz, 1H,
OH), 5.47 (d, J = 6 Hz, 1H, OH), 5.22 (d, J = 5.4 Hz, 1H, OH), 4.88
(dd, J = 1.2, 9.6 Hz, 1H, CH-2 (thiazolidin-4-one)), 4.60 (dd, J = 3,
9.6 Hz, 1H, CH-4¢ (nucleoside2)), 4.33 (q, J = 7.8, 10.2 Hz, 1H, CH-
2¢ (nucleoside2)), 4.17–4.12 (m, 1H, CH-3¢ (nucleoside2)), 4.08–
4.05 (m, 1H, CH-4¢ (nucleoside1)), 3.99 (q, J = 6, 11.4 Hz, 1H, CH-
2¢ (nucleoside1)), 3.94–3.87 (m, 2H, CH-3¢ (nucleoside1), CH2-5¢
(nucleoside1)), 3.68 (d, J = 15.6 Hz, 1H, CH2-5¢ (nucleoside1)), 3.50
(dd, J = 3.6, 14.4 Hz, 1H, CH2-5 (thiazolidin-4-one)), 3.45 (d, J =
16.2 Hz, 1H, CH2-5 (thiazolidin-4-one)), 1.81 (d, 1.2 Hz, 3H, CH3);
13C NMR (125 MHz, DMSO-d6): d 172.15, 164.18, 163.54, 151.23,
151.19, 142.15, 136.44, 110.24, 102.65, 89.66, 88.07, 86.80, 80.48,
74.12, 73.19, 72.59, 71.46, 59.79, 46.23, 31.39, 12.41; HR-ESI-MS:
calcd for [M - H]- C21H26N5O11S, 555.1271; found, 555.1266.
◦
Compound 6bb. White solid, 74%; mp: 228.4–229.7 C; [a]D27
20.6 (c 1, DMSO); 1H NMR (600 MHz, DMSO-d6): d 11.33
(d, J = 1.2 Hz, 1H, NH (U)), 11.24 (s, 1H, NH (T)), 7.82 (d,
J = 8.4 Hz, 1H, CH-6 (U)), 7.75 (s, 1H, CH-6 (T)), 6.36 (t, J =
5.4, 12.6 Hz, 1H, CH-1¢ (nucleoside1)), 5.97 (d, J = 7.8 Hz, 1H,
CH-1¢ (nucleoside2)), 5.67 (d, J = 8.4 Hz, 1H, CH-5 (U)), 4.81
(d, J = 9 Hz, 1H, CH-2 (thiazolidin-4-one)), 4.60 (dd, J = 2.4,
9 Hz, 1H, CH-4¢ (nucleoside2)), 4.35 (m, 2H, CH-3¢ (nucleoside1),
CH-2¢ (nucleoside2)), 4.29 (m, 1H, CH-4¢ (nucleoside1)), 4.17
(m, 1H, CH-3¢ (nucleoside2)), 3.68 (dd, J = 1.2, 15.6 Hz, 1H,
CH2-5¢ (nucleoside1)), 3.54 (m, 3H, CH2-5¢ (nucleoside1), CH2-
5 (thiazolidin-4-one)), 2.30 (m, 2H, CH2-2¢ (nucleoside1)), 1.75
(s, 3H, CH3 (T)); 13C NMR (125 MHz, DMSO-d6): d 172.26,
164.22, 163.64, 151.29, 150.83, 141.99, 136.98, 109.80, 102.65,
89.25, 86.03, 85.04, 82.36, 74.29, 72.62, 61.93, 56.86, 37.79, 31.68,
12.62; HR-ESI-MS: calcd for [M - H]- C21H26N5O10S, 539.1321;
found, 539.1336.
◦
Compound 5ba. White solid, 85%; mp: 206.5–207 C; [a]D21
-46.5 (c 1, DMSO); 1H NMR (600 MHz, DMSO-d6): d 11.35 (s,
2H, NH (T)), 7.80 (s, 1H, CH-6 (T)), 7.45 (s, 1H, CH-6 (T)), 6.32 (t,
J = 0.6, 13.8 Hz, 1H, CH-1¢ (nucleoside1)), 5.86 (d, J = 7.2 Hz, 1H,
CH-1¢ (nucleoside2)), 5.17 (d, J = 7.2 Hz, 1H, CH-2 (thiazolidin-
4-one)), 4.32 (t, J = 6, 13.2 Hz, 1H, CH-2¢ (nucleoside2)), 4.28 (m,
1H, CH-3¢ (nucleoside1)), 4.16 (m, 1H, CH-4¢ (nucleoside1)), 4.12
(dd, J = 3, 7.2 Hz, 1H, CH-4¢ (nucleoside2)), 3.97 (q, J = 3, 6 Hz,
1H, CH2-3¢ (nucleoside2)), 3.77 (dd, J = 1.8, 16.2 Hz, 1H, CH2-5
(thiazolidin-4-one)), 3.58–3.58 (d, 2H, CH2-5¢ (nucleoside1)), 3.46
(d, J = 15.6 Hz, 1H, CH2-5 (thiazolidin-4-one)), 2.60 (m, 1H, CH2-
2¢ (nucleoside1)), 1.95 (m, 1H, CH2-2¢ (nucleoside1), 1.84 (d, J =
1.2 Hz, 3H, CH3 (T)), 1.74 (d, J = 1.2 Hz, 3H, CH3(T)); 13C NMR
(125 MHz, DMSO-d6): d 171.55, 164.15 (two), 151.47, 150.79,
136.62, 136.20, 110.55, 110.15, 87.42, 86.30, 84.21, 81.25, 72.04,
X-ray crystallographic measurement of single crystal of 4ba
The single crystal of the compound 4ba was obtained by recrys-
tallization from the solution of H2O–MeOH–THF and applied
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on a Bruker Axssmart apexII Mo diffractometer for analysis.
The intensity data were collected on a Bruker SMART CCD
diffractometer with graphite-monochromated Mo-Ka radiation
Basic Research 973 Pre-research Program of China
(2010CB534913), and the program of Science and Technology
(S & T) of Hebei (09276418D-13) is gratefully acknowledged.
˚
(l = 0.71073 A) using the q/2w scan technique from a single-
crystal of 0.68 mm ¥ 0.16 mm ¥ 0.15 mm, and a semi-empirical
absorption correction was applied for all complexes. The crystal
system was orthorhombic, and the space group was P212121. The
structures were solved by direct methods and refined by full-matrix
least-squares on F2. The absolute structure parameter was -0.13
(13). All non-hydrogen atoms were refined anisotropically. The
crystallographic structure is shown in Fig. 1.
Notes and references
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Y. Turpin, J. Bok, I. Rosenberg and M. Petrova´-Endova´, Nucleic Acids
Res., 2001, 29, 5182; (d) A. Grajkowski, J. Pedras-Vasconcelos, V. Wang,
C. Aus´ın, S. Hess, D. Verthelyi and S. L. Beaucage, Nucleic Acids Res.,
2005, 33, 3550.
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2 (a) Q. W. Han, S. G. Sarafianos, E. Arnold, M. A. Parniak, B. L. Gaffney
and R. A. Jones, Org. Lett., 2007, 9, 5243; (b) S. Dharmasena, Z.
Pongracz, E. Arnold, S. G. Sarafianos and M. A. Parniak, Biochemistry,
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HIV-RT kit assay. The HIV-RT inhibition assay was per-
formed by using an RT assay kit (Roche), and the procedure
for assaying RT inhibition was performed as described in the
kit protocol. Briefly, the reaction mixture consists of a template–
primer complex, 2¢-deoxy-nucleotide-5¢-triphosphates (dNTPs)
and reverse transcriptase (RT) enzyme in the lysis buffer with
◦
or without inhibitors. After 1 h incubation at 37 C the reaction
mixture was transferred to a streptavidin-coated microtitre plate
(MTP). The biotin labeled dNTPs that are incorporated in the
template due to the activity of RT were bound to streptavidin.
The unbound dNTPs were washed using wash buffer and
antidigoxigenin-peroxidase (DIG-POD) was added in MTP. The
DIG-labeled dNTPs incorporated in the template was bound
to anti-DIG-POD antibody. The unbound anti-DIG-POD was
washed and the peroxide substrate (ABST) was added to the MTP.
A colored reaction product was produced during the cleavage of
the substrate catalyses by a peroxide enzyme. The absorbance of
the sample was determined at OD 405 nm using a microtiter
plate ELISA reader. The resulting color intensity is directly
proportional to the actual RT activity. The percentage inhibitory
activity of RT inhibitors was calculated by comparing to a sample
that does not contain an inhibitor. The percentage inhibition was
calculated by formula as given below:
% Inhibition = 100 - [(OD 405 nm with inhibitor/OD 405 nm
without inhibitor) ¥ 100]
.
Dock modeling
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Qin, Q. M. Yin and J. C. Zhang, Eur. J. Org. Chem., 2009, 35,
6100.
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http://www.orgsyn.org/orgsyn/pdfs/v77p0141.pdf.
12 CCDC (786926) contains the supplementary crystallographic
data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
data_request@ccdc.cam.ac.uk, or by contacting The Cambridge Crys-
tallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK;
fax: +44 1223 336033.
An X-ray structure of HIV-1 RT was downloaded from the
Protein Data Bank (PDB code 1RTD). This structure contains
a DNA template, primer, dTTP containing two Mg2+ ions, and
two Mg2+ ions in the RNase H active site in addition to the
p66 and p51 domains. Molecular docking of a ligand into the
dNTP-binding site of HIV-1 RT was carried out using discovery
studio 2.5 (software from Accelrys, USA) and libdock was
used.
Acknowledgements
13 Reverse Transcriptase Assay, Colorimetric kit, Roche Diagnostics
GmbH, Roche Applied Science, Sandhofer strasse 116, D-68305
Mannheim, Germany.
The financial support from the National Natural Science Foun-
dations of China (NSFC) (20672027 and 20972039), the National
5772 | Org. Biomol. Chem., 2011, 9, 5766–5772
This journal is
The Royal Society of Chemistry 2011
©