Synthesis of 2′-deoxy-5-(methylselenyl)cytidine and Se-DNAs for structural and functional studies

Article abstract of DOI:10.1002/asia.201100898

It's not in your DNA: We report here the synthesis of a novel 5-methyl deoxycytidine analog and its phosphoramidite modified with selenium at the C-5 position (^SeC). Incorporation of ^SeC into DNA does not cause structural perturbations, as shown by X-ray crystallography and in agreement with UV melting data. The Se modification provides a useful strategy for biochemical and structural investigations on 5-methylation of cytidine.

Full text of DOI:10.1002/asia.201100898

COMMUNICATION
DOI: 10.1002/asia.201100898
Synthesis of 2’-Deoxy-5-(methylselenyl)cytidine and Se-DNAs for Structural
and Functional Studies
Wen Zhang, Jia Sheng, Abdalla E. Hassan, and Zhen Huang*[a]
Introduction
will likely provide novel insight into the methylation of cyto-
sine and offers a stable and useful derivatization for nucleic
acid X-ray crystallography, as selenium-derivatized nucleic
acids (SeNA) can facilitate crystallization and phasing.[12]
Herein we report the synthesis of SeC, its phosphoramidite,
and SeC-DNAs, and biophysical and structural studies of the
Se-modified DNA.
5-Methylcytosine (m5C), which is being recognized as the
fifth nucleobase of genomic DNA, has attracted tremendous
research interest since its first discovery over six decades
ago.[1] m5C is generated through methylation of cytosine in
both prokaryotes and eukaryotes by DNA cytosine methyl-
transferases (DNMTs). Although its occurrence is minor in
mammalian and plant genomic DNA (about 1–6%),[1a,2] 5-
methylcytosine carries additional inheritable information be-
sides its regular function as cytosine in genomic DNA. The
cytosine 5-methylation is a key epigenetic event in vivo for
maintaining genome integrity[3] and regulating gene expres-
sion.[4] It is also known that m5C often exists in repetitive
DNA elements, such as CpG islands,[5] and that m5C in
transposons is able to reduce the damage and stability
threat to the host genome.[6] Furthermore, cytosine methyla-
tion is essential for X-chromosome inactivation, resulting in
silencing of gene expression in females.[7] As most of the
monoallelic expression of imprinted genes also depends on
m5C, the methylation in CpG islands normally causes asym-
metric expression from only one of two identical alleles.[8] In
some somatic cells, m5C in promoters often contributes to
the regulation of gene expression by influencing the interac-
tions between transcriptional regulators and cognate
DNA.[9] Moreover, hypermethylation of cytosine may acti-
vate oncogenes, cause silencing of tumor suppressor genes,
and contribute to tumorigenesis, thereby playing a critical
role in the etiology of human cancers.[5,9–10]
Results and Discussion
The synthesis (Scheme 1) of 2’-deoxy-5-(methylselenyl)cyti-
dine started from the protected deoxyuridine (1), and the 5-
seleno-thymidine analog (2) was synthesized by following
our previous report.[11b] To convert the thymidine analog
into the cytidine derivative, 2 was activated by the triisopro-
pylbenzenesulfonyl (TIPS) group, followed by ammonium
treatment. Initially, we attempted to isolate the TIPS-acti-
vated thymidine; however, unlike the corresponding purine
analogue, the TIPS-activated thymidine derivative is unsta-
ble and decomposed during silica gel chromatography. Final-
ly, we developed a one-pot reaction to synthesize the 5-Me-
Considering the fact that such a minor chemical modifica-
tion at the C-5 position of cytosine can cause tremendous
functional alterations, we decided to investigate the effect of
a modification in which a selenium atom is inserted between
the 5-methyl group and the pyrimidine. On the basis of our
previous research, selenium can afford nucleic acids with
many unique properties for structural and functional stud-
ies.[11] Thus, by tailoring the electron density and steric
effect at the C-5 position of m5C, the selenium modification
[a] W. Zhang, J. Sheng, A. E. Hassan, Z. Huang
Department of Chemistry
Scheme 1. Synthesis of 2’-deoxy-5-(methylselenyl)cytidine phosphorami-
dite and incorporation of the modified base into oligonucleotides.
a) TIPS-Cl, DIEA, DMAP, acetonitrile, RT, 16 h; b) conc. NH3·H2O, RT,
1 h; c) Bz-Cl, pyridine; RT, 1 h (54% combined yield); d) TBAF, acetic
acid, THF, 08C!RT, 16 h (91%); e) 2-cyanoethyl N,N-diisopropylchloro-
phosphoramidite, DIEA, CH2Cl2, RT, 2 h (85%); f) solid-phase synthesis.
Georgia State University
Atlanta, Georgia 30303 (USA)
E-mail: Huang@gsu.edu
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201100898.
476
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2012, 7, 476 – 479

Table 2. Thermal stability of SeC-DNAs.
Se-deoxycytidine without purification of the intermediate.
After protection of the exocyclic amino group and deprotec-
tion of the 3’-hydroxy group, the resulting compound 4 was
converted into the phosphoramidite 5 in high yield. The cy-
tosine derivative was then incorporated into oligonucleo-
tides (6, SeC-DNA) by solid-phase synthesis. It was found
that the selenium functionality is stable under the synthetic
conditions (including strong base, fluoride treatment, I2 oxi-
dation, and strong acid treatments) and purification.
The modified oligonucleotides were purified by high-per-
formance liquid chromatography (HPLC). Typical HPLC
profiles of a synthesized oligonucleotide carrying the modi-
fied base are shown in the Supporting Information. Accord-
ing to HPLC analysis of a crude SeC-DNA (5’-DMTr-T-SeC-
T-3’), the coupling yield of 5 was higher than 95%. All SeC-
DNAs synthesized were characterized and analyzed by mass
spectrometry (MS) and HPLC (Table 1 and Figures S11–S16
in the Supporting Information).
Entry
DNA duplexes
Tm [8C]
1
5’-ATGGTGCTC-3’
3’-TACCACGAG-5’
40.3ꢀ1.0
2
3
4
5
6
7
8
5’-ATGGTGSeCTC-3’
3’-TACCACGAG-5’
40.3ꢀ1.0
36.5ꢀ1.0
36.3ꢀ1.0
44.9ꢀ1.0
43.6ꢀ1.0
27.5ꢀ1.0
27.8ꢀ1.0
5’-CTCCCATCC-3’
3’-GAGGGTAGG-5’
5’-CTCCSeCATCC-3’
3’-GAGGGTAGG-5’
5’-CTTCTTGTCCG-3’
3’-GAAGAACAGGC-5’
5’-CTTSeCTTGTCCG-3’
3’-GAAGAACAGGC-5’
5’-GTGTACAC-3’
(self-complementary)
5’-GdU2’-SeGTASeCAC-3ꢂ
Table 1. Mass spectrometry data of SeC-DNAs.
(self-complementary)
Entry
SeC-DNA
5’-GdU2’-SeGTASeCAC-3’
Measured (calcd.) m/z
[M]+: 2581.6 (2581.5)
1
C79H101N30O46P7Se2
2
3
4
5’-ATGGTGSeCTC-3’
C89H114N32O54P8Se
[M+H]+: 2823.7 (2823.8)
ACHTUNGTRENNUNG
5’-CTCCSeCATCC-3’
C85H113N27O53P8Se
[M+H]+: 2688.6 (2688.7)
ACHTUNGTRENNUNG
5’-CTTSeCTTGTCCG-3’
[M+H]+: 3368.3 (3368.6)
ACHTUNGTRENNUNG
C107H140N32O69P10Se
We also carried out UV melting experiments to study the
thermostability of DNA duplexes carrying the modified
base, comparing them with the corresponding native ones.
The melting temperatures (Tm) are listed in Table 2 and the
original profiles are provided in the Supporting Information.
Our experimental results indicate that the SeC-DNA duplex-
es are as stable as the corresponding native duplexes, thus
suggesting that the Se functionality at C-5 of cytidine causes
no significant perturbation.
To further understand the effect of the Se modification,
we carried out a structural study of a self-complementary
SeC-DNA (Figure 1). For reasons yet unknown, the crystalli-
zation of the SeC-DNA was facilitated by the incorporation
of 2’-Me-Se-dU into the oligonucleotide. With the assistance
of the 2’-Se functionality, the SeC-DNA crystallized within
two weeks. SeC-DNA crystals were observed in 20 out of 24
diversified reagents (Nucleic Acid Mini Screen kit, Hamp-
ton Research). By contrast, the corresponding native DNA
required more than two months for crystallization under the
different conditions.[11g] The crystal structure of the SeC-
DNA was determined at 1.80 ꢁ resolution. Superimposition
of this structure with the structure of the corresponding
native DNA reveals that these two structures are virtually
Figure 1. SeC-DNA crystal structure. a) Superimposed structures of native
DNA (GTGTACAC in gray; PDB ID: 1DNS) and the corresponding
SeC-DNA (GdU2’ꢁSeGTASeCAC in color; PDB ID: 3IJN, with Se atoms
shown in gold). b) Structural model and electron density map of the
SeC:G base pair. c) Superimposed structures of native C:G (gray) and
SeC:G base pairs.
identical (Figure 1). The structural characterization result is
consistent with the obtained thermostability data.
We also observed that SeC and G form a base pair similar
to the native C:G pair (Figure 1B and 1C), with hydrogen
bond lengths of 2.7–2.8 ꢁ. The furanose ring is puckered in
the 3’-endo conformation, and the 5-Se atom is pointed to
the major groove of the duplex. Moreover, the weak 5-CH3/
p interaction between the thymine and its neighboring base
was disrupted by the insertion of selenium. However, the 5-
Se atom on the cytosine allows better electron delocaliza-
tion and may contribute to the stacking interaction, thereby
Chem. Asian J. 2012, 7, 476 – 479
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477

Z. Huang et al.
COMMUNICATION
1H, NH2), 6.86–7.48 (m, 13H, arom. H), 8.30 ppm (s, 1H, H-6).
compensating the duplex destabilization by the disruption of
the 5-CH3/p interaction. The collected diffraction data,
phasing, and refinement statistics of the Se-DNA structure
(3IJN) are included in the Supporting Information (Ta-
bles S1 and S2).
13C NMR (100 MHz, DMSO-d6): d=ꢁ4.86 and ꢁ4.69 [Si
ACHTUGNTRNEN(UNG CH3)2], 7.31
(SeCH3), 17.96 [SiCACHTUNTRGENNUG(CH3)], 25.74 [SiCACHTUGNTERN(NUNG CH3)], 41.74 (C-2’), 55.26 (OMe),
62.88 (C-5’), 72.23 (C-3’), 85.55 (C-4’), 87.05 (arom. C), 87.16 (C-1’),
103.45 (C-5), 113.23 (arom. C), 126.94 (arom. C), 128.15 (arom. C),
130.11 (arom. C), 135.50 (arom. C), 141.74 (C-6), 144.41 (arom. C),
149.89 (C-2), 155.46 (arom. C), 158.66 (C-4), 161.46 (arom. C),
165.55 ppm (arom. C). HR-MS (ESI-TOF, possitive ion mode): calcd for
C37H47N3O6SeSi [M+H]+: 738.2478, found 738.2468.
Conclusions
4-N-Benzoyl-5-methylseleno-3’-tert-butyldimethylsilyl-5’-O-(4,4-
dimethoxytrityl)-2’-deoxycytidine (3)
In summary, we have successfully synthesized the novel SeC-
phosphoramidite and incorporated the nucleoside into DNA
for biophysical and structural studies. Our experimental re-
sults indicate that the Se functionality at the C-5 position of
cytidine does not perturb the DNA duplex structure; the
thermostability and structure of Se-DNA in its duplex form
is highly similar to the corresponding native DNA. We
expext that our study on 5-methylcytosine with the selenium
modification will encourage further investigation on m5C, its
epigenetic mechanism, and methyltransferase inhibitor
design. Furthermore, the synthesis reported herein offers a
useful derivatization strategy for nucleic acid X-ray crystal-
lography.
5-Methylseleno-3’-tert-butyldimethylsilyl-5’-O-(4,4-dimethoxytrityl)-2’-de-
oxycytidine (300 mg, MW 751.3, 0.4 mmol) was placed in a flask and
dried under high vacuum for 1 h before anhydrous pyridine (10 mL) was
added. Subsequently, benzoyl chloride (0.03 mL, 0.6 mmol, 1.5 equiv) was
added dropwise, and the reaction mixture was stirred for 1 h at room
temperature. After the reaction was completed (monitored by TLC, 30%
ethyl acetate in n-hexane, Rf =0.5), the crude product was extracted with
brine and EtOAc. The organic phase was removed and the aqueous
phase was extracted thrice with EtOAc. The combined organic phase was
dried over anhydrous MgSO4, filtered, and the organic solvents were
evaporated under reduced pressure. The residue was purified by column
chromatography on silica gel (10–50% EtOAc in n-hexane) to afford 3
as
a
yellow–green solid (287 mg, 84% yield). 1H NMR (400 MHz,
(CH3)2], 0.86 (s, 9H, tert-butyl),
DMSO-d6): d=0.09 and 0.04 [2x s, 6H, SiAHCUTNGTRENNUNG
2.02 (s, 3H, SeCH3), 2.18–2.20 and 2.43–2.52 (2x m, 2H, H-2’), 3.29–3.33
and 3.43–3.46 (2x m, 2H, H-5’), 3.81 (s, 6H, 2x OMe), 4.05–4.08 (m, 1H,
H-3’), 4.41–4.45 (m, 1H, H-4’), 6.30–6.34 (t, J=6.4 Hz, 1H, H-1’), 6.86–
7.56 (m, 18H, arom. H), 7.88 (s, 1H, NH), 8.32 ppm (s, 1H, H-6).
Experimental Section
13C NMR (100 MHz, DMSO-d6): d=ꢁ4.89 and ꢁ4.69 [Si
ACHTUGNTRNEN(UNG CH3)2], 1.03
(SeCH3), 17.95 [SiCACHTUNTRGENNUG(CH3)], 25.73 [SiCACHTUGNTERN(NUNG CH3)], 41.86 (C-2’), 55.26 (OMe),
Materials
63.05 (C-5’), 72.41 (C-3’), 86.30 (C-4’), 86.77 (C-5), 87.24 (C-1’), 113.27
(arom. C), 127.07 (arom. C), 128.13 (arom. C), 128.27 (arom. C), 129.38
(arom. C), 130.09 (arom. C), 132.67 (arom. C), 133.68 (C-6), 135.51
(NHCO), 144.41 (arom. C), 144.36 (C-2), 158.69 ppm (C-4). HR-MS
(ESI-TOF, negative ion mode): calcd for C44H51N3O7SeSi [MꢁH]ꢁ:
840.2583, found, 840.2570.
Unless stated otherwise, reagents and chemicals were purchased from
Sigma, Fluka, or Aldrich. Phosphoramidites used in the solid-phase syn-
thesis of oligonucleotides were obtained from Glen Research. THF, di-
chloromethane, and acetonitrile were distilled under argon. Solid starting
materials were dried under high vacuum before use. All reactions were
performed under argon. Thin layer chromatography (TLC) was per-
formed on analytical Merck 60 F254 plates (0.25 mm thickness) and vi-
sualized under UV light. Flash column chromatography was performed
using Fluka silica gel 60 (mesh size 0.040–0.063 mm) with a silica gel/
crude compound weight ratio of approximately 30:1. 1H and 13C NMR
spectra were recorded on a Bruker-400 (400 MHz) spectrometer. Chemi-
cal shifts are reported in ppm relative to tetramethylsilane and coupling
constants are in Hz. High-resolution mass spectra were recorded at Geor-
gia State University.
4-N-Benzoyl-5-methylseleno-5’-O-(4,4-dimethoxytrityl)-2’-deoxycytidine
(4)
4-N-Benzoyl-5-methylseleno-3’-tert-butyldimethylsilyl-5’-O-(4,4-dime-
thoxytrityl)-2’-deoxycytidine (3, 280 mg, MW 855.3, 0.33 mmol) was
placed in a flask, dried under high vacuum, and dissolved in anhydrous
THF (3 mL). The solution was placed in an ice–water bath under dry
argon. Next, tetrabutylammonium fluoride (0.44 mL of a 1m solution in
THF, 1.2 equiv) and acetic acid (0.03 mL, 1.2 equiv) were injected drop-
wise simultaneously to maintain the pH value at 7. After stirring over-
night, the reaction was completed (monitored by TLC, 3% MeOH in
CH2Cl2, Rf =0.35). The crude product was extracted with EtOAc and
brine (3x), and the combined organic layer was dried over anhydrous
MgSO4, filtered, and concentrated. The residue was purified by column
chromatography on silica gel (5% MeOH in CH2Cl2) to afford 4 as a
white solid (225 mg, 91% yield). 1H NMR (400 MHz, DMSO-d6): d=
2.04 (s, 3H, SeCH3), 2.21–2.26 and 2.69–2.76 (2x m, 2H, H-2’), 3.34–3.47
(2x m, 2H, H-5’), 3.79 (s, 6H, 2x OMe), 4.15–4.17 (m, 1H, H-3’), 4.46–
4.48 (m, 1H, H-4’), 6.14–6.17 (t, J=6.4 Hz, 1H, H-1’), 6.84–7.79 (m, 18H,
arom-H), 8.48 ppm (s, 1H, H-6). 13C NMR (100 MHz, DMSO-d6): d=
11.02 (SeCH3), 41.99 (C-2’), 55.27 (OMe), 63.11 (C-5’), 72.41 (C-3’), 86.67
(C-4’), 86.94 (arom. C), 87.87 (C-1’), 102.39 (C-5), 113.31 (arom-C),
127.07 (arom. C), 128.04 (arom. C), 128.07 (arom. C), 128.29 (arom. C),
129.68 (arom. C), 129.45 (arom. C), 130.00 (arom. C), 130.92 (arom. C),
132.70 (arom. C), 134.22 (arom. C), 135.47 (NHCO), 144.41 (arom. C),
144.32 (C-2), 150.83 (C-6), 158.69 (C-4), 172.28 ppm (arom. C). HR-MS
(ESI-TOF, possitive ion mode): calcd for C38H38N3O7Se: [M+H]+:
728.1797, found, 728.1898.
5-Methylseleno-3’-tert-butyldimethylsilyl-5’-O-(4,4-dimethoxytrityl)-2’-
deoxycytidine
Diisopropylethyl amine (0.67 mL, 3.19 mmol, 5 equiv), triisopropylbenze-
nesulfonyl chloride (576 mg, 1.59 mmol, 2.5 equiv), and 4-dimethylamino-
pyridine (96 mg, 0.64 mmol, 1 equiv) were added sequentially to a solu-
tion of 5-methylseleno-3’-tert-butyldimethylsilyl-5’-O-(4,4-dimethoxytri-
tyl)-2’-deoxyuridine[1] (MW 752.2, 480 mg, 0.64 mmol) in 10 mL acetoni-
trile. The reaction mixture was stirred for 16 h and monitored by TLC
(EtOAc/n-hexane, 3:7). After completion, an excess of concentrated am-
monium hydroxide solution was added dropwise, and the reaction was
stirred for 1 h at room temperature. After the reaction was completed
(monitored by TLC, 5% MeOH in CH2Cl2, Rf =0.5), the organic solvent
and ammonium hydroxide were evaporated under reduced pressure. Sub-
sequently, the crude product was purified by column chromatography on
silica gel (1–7% MeOH in CH2Cl2). The fractions containing the product
were combined, evaporated, and dried under high vacuum overnight to
yield a yellow solid (307 mg, 64% yield). 1H NMR (400 MHz, DMSO-
d6): d=0.05 (s, 6H, SiCH3), 0.87 (s, 9H, tert-butyl), 1.95 (s, 3H, SeCH3),
2.18–2.25 and 2.58–2.62 (2x m, 2H, H-2’), 3.30–3.33 and 3.46–3.49 (2x m,
2H, H-5’), 3.84 (s, 6H, 2x OMe), 4.03–4.08 (m, 1H, H-3’), 4.42–4.46 (m,
1H, H-4’), 6.11 (s, 1H, NH2), 6.28–6.31 (t, J=5.6 Hz, 1H, H-1’), 6.50 (s,
478
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Chem. Asian J. 2012, 7, 476 – 479

Se-DNAs for Structural and Functional Studies
3’-O-(2-Cyanoethyl-N,N-diisopropylphosphoramidite)-4-N-benzoyl-5-
methylseleno-5’-O-(4,4-dimethoxytrityl)-2’-deoxycytidine (5)
lected for SAD phasing were used for the final refinement, and the struc-
ture of the SeC-DNA was solved at 1.80 ꢁ resolution. The diffraction data
were processed using HKL2000 and SHELXS. The collected data, phas-
ing, and refinement statistics of the determined SeC-DNA structure
(3IJN) are included in Tables S1 and S2 in the Supporting Information.
4-N-Benzoyl-5-methylseleno-5’-O-(4,4-dimethoxytrityl)-2’-deoxycytidine
(4, 200 mg, MW 741.2, 0.27 mmol) was placed in a 25 mL round-bot-
tomed flask and dried under high vacuum. Subsequently, dry CH2Cl2
(3 mL), N,N-diisopropylethylamine (0.06 mL, 0.4 mmol, 1.5 equiv), and 2-
cyanoethyl-N,N-diisopropylchlorophosphoramidite (80 mg, 0.4 mmol,
1.5 equiv) were added sequentially. The reaction was completed after stir-
ring for 2 h at room temperature, as assessed by TLC (3% MeOH in
CH2Cl2, Rf =0.37 and 0.38, two diastereomers). The reaction was then
quenched with sat. NaHCO3, and the mixture was extracted thrice with
CH2Cl2, dried over anhydrous MgSO4, filtered, and the solvent was
evaporated. The crude product was redissolved in CH2Cl2 (3 mL), and
this solution was added dropwise to pentane (200 mL) under vigorous
stirring to yield a yellow precipitate. After removal of pentane by decant-
ation and/or filtration, the crude product was purified by column chroma-
tography on silica gel (1–5% MeOH in CH2Cl2 containing 1% triethyl-
amine) to afford 5 as a yellow solid (216 mg, 85% yield).
Acknowledgements
This work was financially supported by the Georgia Cancer Coalition
(GCC) Distinguished Cancer Clinicians and Scientists, the NIH
(GM095086), and the NSF (MCB-0824837).
Keywords: 5-methyl cytidine
·
DNA methylation
·
epigenetics · structure elucidation · X-ray diffraction
Synthesis and Purification of Modified Oligonucleotides(6)
All DNA oligonucleotides were synthesized by solid-phase synthesis
using an ABI392 DNA/RNA synthesizer at 1 mmol scale. The concentra-
tion of the Se-modified cytidine phosphoramidite (5) was identical to
that of the standard phosphoramidites (0.1m in acetonitrile). The cou-
pling reaction was carried out using a solution of 5-benzylthio-1H-tetra-
zole (5-BTT, 0.25m) in acetonitrile and a coupling time of 25 s. All oligo-
nucleotides were synthesized with DMTr-On, followed by their cleavage
from the CPG solid support (beads) and deprotection with concentrated
ammonia solution at 558C overnight. After DMTr-on purification by
HPLC, detritylation of oligonucleotides was performed by the treatment
with 3% aq. trichloroacetice acid for 5 min, followed by neutralization to
pH 7.0 with triethylamine and extraction with petroleum ether to remove
the by-product DMTr-OH. The oligonucleotides were then purified again
by HPLC. Typical HPLC profiles (DMTr-on and DMTr-off) and mass
spectra of the Se-modified oligonucleotides are shown in Figures S11–S16
in the Supporting Information.
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UV Melting Experiments
The experiments were performed using DNA duplexes (2 mm) in 10 mm
Na-phosphate buffer (pH 6.5) containing 10 mm MgCl2, 50 mm NaCl, and
0.1 mm EDTA. Samples were annealed by heating to 858C, followed by
slow cooling to room temperature. Melting experiments were carried out
by using a Cary 300 UV/Visible Spectrophotometer with a temperature
controller at a heating rate of 0.58Cminꢁ1. Typical melting curves are
shown in Figures S17–S20 in the Supporting Information.
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2008, 59, 267–280.
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Crystallization and X-ray Crystal Structure Determination
The self-complementary Se-DNA, 5’-GdU2’ꢁSeGTASeCAC-3’, crystallized
in 1–2 weeks in 20 out of 24 reagents supplied in the Nucleic Acid Mini
Screen kit (Hampton Research). The crystals grown in reagent #5 [10%
(v/v) 2-methyl-2,4-pentanediol (MPD), 40 mM Na cacodylate (pH 6.0),
12 mm spermine tetra-HCl, 80 mm KCl, and 20 mm MgCl2] were used for
diffraction data collection; the crystals diffracted well. X-ray diffraction
data were collected at beam line X29A at the National Synchrotron
Light Source (NSLS) at Brookhaven National Laboratory. Two data sets
were collected: one at the selenium K-edge (0.9795 ꢁ) for SAD phasing
and the other at 0.9795 ꢁ for the molecular replacement. The data col-
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b) W. Zhang, J. Sheng, Z. Huang, Med. Chem. Nucl. Acids 2011,
101–141; c) J. Sheng, Z. Huang, Int. J. Mol. Sci. 2008, 9, 258–271;
d) J. Sheng, Z. Huang, Chem. Biodiversity 2010, 7, 753–785.
Received: November 3, 2011
Published online: January 13, 2012
Chem. Asian J. 2012, 7, 476 – 479
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
479