Synthesis of thymidine dimers from 5′-O-aminothymidine

Article abstract of DOI:10.1055/s-0031-1289759

The synthesis of modified oligonucleotides is of great importance for various therapeutic and diagnostic applications. The facile secondary structure formation of N-oxyamide-linked peptide analogues and the high nucleophilicity of the aminooxy function prompted us to prepare O-amino nucleoside derived dinucleosides. Herein, the efficient synthesis of three novel thymidine dimers with N-oxyamide, oxime and oxyamine linkages via a convergent approach from a common 5-O-aminothymidine is reported. Georg Thieme Verlag Stuttgart · New York.

Full text of DOI:10.1055/s-0031-1289759

1718▌
PAPER
paper
Synthesis of Thymidine Dimers from 5′-O-Aminothymidine
Synthesis of Thymidine Dimers
Sandrine Peyrat, Juan Xie*
PPSM, ENS Cachan, Institut d’Alembert, CNRS, UMR 8531, 61 av. Président Wilson, 94235 Cachan cedex, France
Fax +33(1)47402454; E-mail: joanne.xie@ens-cachan.fr
Received: 20.02.2012; Accepted after revision: 28.03.2012
philicity, reacts readily with aldehydes or carboxylic
acids, resulting in the formation of a highly stable oxime
or N-oxyamide linkage. Aminooxy-functionalized
nucleosides11,17 and oligonucleotides18 have been reported
Abstract: The synthesis of modified oligonucleotides is of great
importance for various therapeutic and diagnostic applications. The
facile secondary structure formation of N-oxyamide-linked peptide
analogues and the high nucleophilicity of the aminooxy function
prompted us to prepare O-amino nucleoside derived dinucleosides. in the development of methylene(methylimino)-linked
Herein, the efficient synthesis of three novel thymidine dimers with
N-oxyamide, oxime and oxyamine linkages via a convergent ap-
proach from a common 5′-O-aminothymidine is reported.
oligonucleotide mimics, in prodrug design and in immo-
bilization in the fabrication of microarrays. A N-oxy-
amide-linked thymidine dimer M (Figure 1) has been
incorporated into a DNA oligomer which annealed to
Key words: dinucleosides, O-amino nucleoside, thymidine, N-
oxyamide, oxime, oxyamine
complementary DNA with nearly the same affinity as the
natural sequence.15 These results prompted us to prepare
novel O-amino nucleoside derived dinucleosides. Latter-
ly, we19 and others20 have developed glycoaminooxy
acids as a new class of sugar building blocks, with inter-
Modified oligonucleotides (ONs) are being investigated
for various therapeutic and diagnostic applications be-
cause of their capability to cause selective inhibition of
gene expression by binding to the target DNA/RNA se-
quences through mechanisms such as anti-gene, anti-
sense, RNA interference, or to restore gene function by
sterically blocking the access of cellular machinery to pre-
mRNA and mRNA.1,2 The availability of synthetic ONs
has led to major advances in molecular biology; however,
limited clinical success has been achieved with ONs,
mainly due to their instability toward nucleases, lack of
target specificity, and poor cellular uptake and targeted
delivery. Therefore, the development of novel synthetic
ONs with appropriate modifications and improved prop-
erties is of great importance. Nonionic analogues of nu-
cleic acids are promising for the treatment of viral
diseases and cancer since nonionic phosphate mimics
could increase cellular permeability and resistance to ex-
tra- and intracellular nucleases. A number of phosphodi-
ester replacements have been reported, including amide,3
thioacetamide,4 triazole,5 amine,6 formacetal,7 thioform-
acetal,7b,8 dimethylenesulfone,9 N-acylsulfamide,10 oxy-
amine or methylene(methylimino),11 amino acid,12 C=C
double bond,13 and silyl,14 as well as oxyamide15 ana-
logues (Figure 1). These three- to six-atom-linked dinu-
cleosides have been incorporated into standard
oligonucleotides, with the ability to anneal to complemen-
tary DNA/RNA.
O
O
O
B
O
B
B
B
O
O
O
n
O
NH
N
O
O
N
N
S
HN
HN
B
B
B
B
O
O
O
O
O
O
O
O
n = 1, 2
D
A
B
C
O
O
O
O
B
B
B
B
O
O
O
O
O
O
O
O
R
N
O
S
S
O
O
O
X
HN
B
B
B
B
O
O
O
O
O
O
O
O
R = H, Me
E (X = O), F (X = S)
H
I
G
O
O
O
O
B
B
B
B
Recently, it has been demonstrated that O-aminopeptides
can easily form intramolecular hydrogen bonds with turn
and helice structures, and a new family of foldamers has
been developed from α-, β- and γ-aminooxy acids.16 Fur-
thermore, the aminooxy group, thanks to its high nucleo-
O
O
O
O
O
O
O
NH
O
i-Pr Si i-Pr
HN
B
O
R
O
B
B
HN
O
B
O
O
O
O
O
O
O
SYNTHESIS 2012, 44, 1718–1724
Advanced online publication: 09.05.2012
J
K
L
M
0
0
3
9
-
7
8
8
1
1
4
3
7
-
2
1
0
X
DOI: 10.1055/s-0031-1289759; Art ID: SS-2012-Z0178-OP
© Georg Thieme Verlag Stuttgart · New York
Figure 1 Structures of nonionic dinucleoside analogues

PAPER
Synthesis of Thymidine Dimers
1719
esting secondary structures for their oligomers.20 Ribonu-
cleoside aminooxy acids have also been prepared through
N-glycosylation of glycoaminooxy acids.21 As part of a
continuing program on the synthesis of modified nucleo-
sides and oligonucleotides, we decided to synthesize thy-
midine dimers 1–3 with N-oxyamide, oxime and
oxyamine linkages (Scheme 1).
BrCH2CO2Et
R1O
T
R1O
T
NaH, THF or DMF
O
O
or BrCH2CO2Na
O
OH
CO2R2
NaH, DMSO
R1 = DMT, 9
R1 = Tr, 10
R2 = Et or H
R1 = TBS, 11
O
NBz
1. BSA (2 equiv), MeCN, reflux
9
DMTO
O
N
2. BzCl (1 equiv), Et3N (2 equiv)
3. TBAF (2 equiv)
O
DMTO
DMTO
DMTO
T
T
T
O
O
O
62%
OH
12
O
O
O
BrCH2CO2Et
NaH, THF or DMF
NH
O
NH
O
O
N
O
T
T
DMTO
T(Bz)
T
NaH (2.5 equiv)
BrCH2CH=CH2 (2.5 equiv)
O
O
O
O
O
THF, sonication
90%
OTBS
OTBS
3
2
1
OTBS
O
O
CO2Et
T
DMTO
DMTO
O
T
1. OsO4 (cat.), NMO
2. NaIO4, pH 7
DMTO
DMTO
or
T
H2N O
T
O
T
O
O
O
100%
+
1–3
O
O
O
6
13
OTBS
CO2H
CHO
4
5
6
1. TEMPO, BAIB
MeCN–H2O
64%
T
2. MeI, NaHCO3
Cs2CO3, DMF
Scheme 1 Structures and retrosynthesis of novel thymidine dinucle-
osides 1–3
DMTO
HO2C
T
DMTO
O
O
LiOH, MeOH
90%
Thymidine dinucleosides 1–3 are accessible from 5′-O-
aminothymidine 4 and thymidine carboxylic acid 5 or al-
dehyde 6. We first prepared the common 5′-O-amino nu-
cleoside 4. To introduce the aminooxy function,
commercial thymidine was reacted with N-hy-
droxyphthalimide using the Mitsunobu reaction.11c Slow
addition of diisopropyl azodicarboxylate (1 drop every 10
seconds) allowed us to increase the yield of 7 to 86%
(Scheme 2). The 3′-hydroxy group was then protected
with the tert-butyldimethylsilyl (TBS) group. Hydrazinol-
ysis led to the 5′-O-aminothymidine 4.
O
MeO2C
O
14
5
Scheme 3 Synthesis of thymidine carboxylic acid and aldehyde deriv-
atives 5 and 6
ppm.22 Treatment of thymidine 9 with sodium bromoace-
tate under Greenberg’s conditions23 also gave the N-alkyl-
ation product. We then decided to protect the N3 position
of the thymidine with a benzoyl group, by temporary si-
lylation of the 3′-hydroxy using N,O-bis(trimethylsi-
lyl)acetamide (BSA), followed by benzoylation and
desilylation. This one-pot procedure allowed us to rapidly
obtain the protected intermediate 12;24 however, reaction
of 12 with sodium hydride and ethyl bromoacetate ap-
peared to be very slow and incomplete. As a consequence,
the O-allylthymidine 13 was chosen as the intermediate
for the preparation of both the carboxylic acid and alde-
hyde derivatives 5 and 6. Thus, reaction of thymidine 9
with allyl bromide under ultrasonic conditions gave the
desired product 13 in 90% yield.25 Oxidative cleavage of
the allyl group allowed the formation of the aldehyde 6 in
quantitative yield. Radical oxidation (TEMPO, BAIB) led
to the corresponding carboxylic acid derivative which was
not pure enough to be engaged in further reactions. As pu-
rification was not easy because of the polarity of this com-
pound and the acid sensitivity of the dimethoxytrityl
(DMT) group, the obtained intermediate was converted
into the pure methyl ester 14 in 64% yield (from aldehyde
6). Addition of cesium carbonate (0.5 equiv) was expedi-
ent for completion of the esterification. The subsequent
saponification gave the carboxylic acid derivative 5 in
90% yield.
HO
PhthN-OH
Ph3P, DIAD
PhthN O
T
T
O
O
DMF
0 °C to r.t.
86%
OH
OH
7
TBSCl
DMF, r.t.
imidazole 95%
H2N O
PhthN O
T
NH2NH2
MeOH
T
O
O
100%
OTBS
OTBS
4
8
Scheme 2 Synthesis of 5′-O-aminothymidine 4
To synthesize the thymidine carboxylic acid 5, we first en-
visaged an O-alkylation with ethyl bromoacetate (Scheme
3); however, this reaction failed to give the O-alkylated
product with dimethoxytrityl-, trityl- or TBS-protected
thymidines 9–11, whatever the quantity of reagents, the
nature of the solvent (THF or DMF) and the reaction time.
N-Alkylation mainly occurred in all tested conditions, as
proved by the 13C NMR signal of N–CH2 at 42.5 to 43.1
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2012, 44, 1718–1724

1720
S. Peyrat, J. Xie
PAPER
min at 300 °C. NMR spectra were recorded in acetone-d6 or CD3OD
on a JEOL DX 400 spectrometer. Optical rotations were measured
using a Jasco P-2000 polarimeter. High-resolution mass spectra
(HRMS) were recorded on an MA1212 instrument using standard
conditions (ESI, 70 eV).
Thymidine carboxylic acid 5 was then reacted with 5′-O-
aminothymidine 4 with EDC/HOAt as coupling reagents
to afford the N-oxyamide-linked dimer 1 in 94% yield
(Scheme 4). It is to be noted that replacement of HOAt by
HOBt led to the formation of several unidentified prod-
ucts. Formation of the oxime bond usually necessitated
acidic conditions. Due to the presence of the very acid-
sensitive DMT group in the aldehyde 6, we firstly tried the
condensation reaction in a mixture of acetate buffer (pH
5) and tetrahydrofuran (2:1); however, no reaction
occurred because of poor solubility. Fortunately, the reac-
tion worked smoothly in anhydrous N,N-dimethyl-
formamide or tetrahydrofuran, in the presence of acetic
acid. The best yield was obtained with 1.5% acetic acid in
tetrahydrofuran, leading to the desired oxime 2 as a mix-
ture of E/Z-isomers (3:2) in 84% yield. Desilylation of 2
gave the dimer 15 in 99% yield. Reduction of oxime 2
with sodium cyanoborohydride in the presence of 2.5%
acetic acid in tetrahydrofuran led to the oxyamine-linked
thymidine dimer 3 in 66% yield (Scheme 4).
5′-O-Phthalimidothymidine (7)11c
To a soln of thymidine (5.09 g, 21.0 mmol) in anhyd DMF (55 mL)
under argon at 0 °C were added Ph3P (7.04 g, 26.9 mmol) and
PhthNOH (4.46 g, 27.3 mmol), followed by the slow addition (1
drop/10 s) of a soln of DIAD (6.10 mL, 30.9 mmol) in anhyd DMF
(10 mL). The mixture was stirred at r.t. for 15 h, then concentrated.
The residue was dissolved in CH2Cl2 (50 mL) and poured into a
mixture of H2O–ice (250 mL); then, the resulting mixture was
stirred for 30 min. Filtration of the formed precipitate afforded 7 as
a white solid; yield: 7.01 g (86%); mp 222 °C.
Rf = 0.50 (CH2Cl2–MeOH, 9:1).
1H NMR (400 MHz, acetone-d6): δ = 1.86 (d, J = 0.9 Hz, 3 H,
T
CH3 ), 2.19 (ddd, J = 5.5, 8.3, 14.2 Hz, 1 H, H-2′a), 2.25 (ddd,
J = 2.3, 6.0, 14.2 Hz, 1 H, H-2′b), 4.21–4.24 (m, 1 H, H-4′), 4.46
(dd, J = 3.0, 10.1 Hz, 1 H, H-5′a), 4.50 (dd, J = 4.6, 10.1 Hz, 1 H,
H-5′b), 4.62–4.65 (m, 1 H, H-3′), 5.14 (d, J = 4.1 Hz, 1 H, OH), 6.39
(dd, J = 6.0, 8.3 Hz, 1 H, H-1′), 7.74 (d, J = 0.9 Hz, 1 H, H-6), 7.90
(s, 4 H, Phth), 10.68 (s, 1 H, NH).
T
13C NMR (100 MHz, acetone-d6): δ = 12.4 (CH3 ), 40.3 (C-2′), 72.1
DMTO
T
O
(C-3′), 78.6 (C-5′), 85.5 (C-1′, C-4′), 110.9 (C-5), 123.9 (Phth),
129.8 (Cq), 135.4 (Phth), 136.3 (C-6), 151.3, 163.8 (C-2, C-4, CO
Phth).
EDC, HOAt, DMF
94%
4 + 5
O
CONH
O
T
O
3′-O-(tert-Butyldimethylsilyl)-5′-O-phthalimidothymidine (8)
To a suspension of 7 (498 mg, 1.29 mmol) in anhyd DMF (2.5 mL)
under argon was added imidazole (229 mg, 3.37 mmol) followed by
the dropwise addition of a soln of TBSCl (252 mg, 1.67 mmol) in
anhyd DMF (2.5 mL). The mixture was stirred at r.t. for 15 h, then
concentrated. Purification by flash column chromatography
(EtOAc–petroleum ether, 1:1) afforded 8 as a white solid; yield: 610
mg (95%); mp 201 °C.
1
OTBS
DMTO
T
O
1.5% AcOH in THF
84%
O
4 + 6
O
N
T
O
2
OTBS
66%
TBAF, THF
99%
[α]D22 +97.4 (c 0.80, acetone).
2.5% AcOH in THF
NaBH3CN
Rf = 0.61 (EtOAc–petroleum ether, 7:3).
1H NMR (400 MHz, acetone-d6): δ = 0.19 (s, 6 H, 2 × CH3TBS), 0.94
DMTO
T
DMTO
T
O
T
(s, 9 H, t-BuTBS), 1.86 (d, J = 0.9 Hz, 3 H, CH3 ), 2.26 (ddd, J = 2.7,
O
6.0, 13.7 Hz, 1 H, H-2′a), 2.32 (ddd, J = 6.0, 8.3, 13.7 Hz, 1 H, H-
2′b), 4.23–4.24 (m, 1 H, H-4′), 4.48 (dd, J = 3.0, 10.3 Hz, 1 H, H-
5′a), 4.53 (dd, J = 3.9, 10.3 Hz, 1 H, H-5′b), 4.86–4.88 (m, 1 H, H-
3′), 6.37 (dd, J = 6.2, 8.1 Hz, 1 H, H-1′), 7.74 (d, J = 0.9 Hz, 1 H, H-
6), 7.90 (s, 4 H, Phth), 10.04 (s, 1 H, NH).
O
O
O
N
T
O
N
T
H
O
O
15
OH
3
OTBS
T
13C NMR (100 MHz, acetone-d6): δ = –4.7 (CH3TBS), 14.4 (CH3 ),
18.5 (Cq, t-BuTBS), 26.1 (t-BuTBS), 41.0 (C-2′), 73.6 (C-3′), 78.2 (C-
5′), 85.7 (C-4′), 85.9 (C-1′), 111.1 (C-5), 124.0 (Phth), 130.0 (Cq),
135.6 (Phth), 136.4 (C-6), 151.2 (C-2), 163.8 (Cq), 164.2 (C-4),
170.9 (Cq).
Scheme 4 Synthesis of thymidine dimers 1–3
In summary, this paper describes the efficient synthesis of
three novel thymidine dimers with N-oxyamide, oxime
and oxyamine linkages via a convergent approach from
the 5′-O-aminothymidine 4. This methodology should be
applicable to the synthesis of other O-amino nucleoside
derived dinucleosides. These dinucleosides are ready to
be incorporated into natural oligonucleotide sequences to
study their annealing properties with complementary
DNA or RNA.
HRMS (ESI): m/z [M + Na]+ calcd for C24H31N3NaO7Si: 524.1829;
found: 524.1823.
5′-O-Amino-3′-O-(tert-butyldimethylsilyl)thymidine (4)
To a suspension of 8 (250 mg, 0.50 mmol) in MeOH (2 mL) was
added NH2NH2·H2O (75 μL, 1.55 mmol). The suspension became
clear; this was followed by the formation of a precipitate after 2 h.
Et2O (10 mL) was then added. The mixture was washed with sat. aq
NaHCO3 (10 mL). The aqueous layer was extracted with Et2O
(3 × 20 mL), and the combined organic layers were dried over
MgSO4, filtered and concentrated. The crude product 4 (white solid;
195 mg, 100%) was pure enough for further reactions.
All air-sensitive reactions were carried out under argon. Column
chromatography was performed on E. Merck silica gel 60 (230–400
mesh). Analytical thin-layer chromatography was performed on E.
Merck aluminum precoated plates of silica gel 60 F-254 with detec-
tion by UV and by spraying with 6 N H2SO4 and heating for ca. 2
Mp 98 °C; [α]D22 –0.86 (c 0.90, MeOH).
Rf = 0.39 (EtOAc–petroleum ether, 1:1).
Synthesis 2012, 44, 1718–1724
© Georg Thieme Verlag Stuttgart · New York

PAPER
Synthesis of Thymidine Dimers
1721
1H NMR (400 MHz, acetone-d6): δ = 0.12 (s, 6 H, 2 × CH3TBS), 0.91
ture was poured into sat. aq NaHCO3 (20 mL) and extracted with
EtOAc (3 × 20 mL). The combined organic layers were then
washed with brine (30 mL), dried over MgSO4, filtered and concen-
trated. Purification by flash column chromatography (EtOAc–pe-
troleum ether, 1:1, + 1% Et3N) afforded 13 as a white solid; yield:
954 mg (90%); mp 85 °C.
T
(s, 9 H, t-BuTBS), 1.80 (d, J = 1.3 Hz, 3 H, CH3 ), 2.22–2.25 (m, 2
H, H-2′a, H-2′b), 4.07–4.10 (m, 1 H, H-4′), 4.18 (dd, J = 3.6, 12.0
Hz, 1 H, H-5′a), 4.23 (dd, J = 4.5, 12.0 Hz, 1 H, H-5′b), 4.60–4.62
(m, 1 H, H-3′), 6.28–6.31 (m, 1 H, H-1′), 7.49 (d, J = 1.3 Hz, 1 H,
H-6), 9.94 (s, 2 H, ONH2), 10.06 (s, 1 H, NH).
T
13C NMR (100 MHz, acetone-d6): δ = –4.7 (CH3TBS), 12.6 (CH3 ),
[α]D22 +16.2 (c 0.90, acetone).
18.5 (Cq, t-BuTBS), 26.1 (t-BuTBS), 40.8 (C-2′), 73.6 (C-3′), 73.7 (C-
5′), 85.5 (C-1′), 86.7 (C-4′), 110.7 (C-5), 136.3 (C-6), 151.2 (C-2),
164.2 (C-4).
Rf = 0.44 (EtOAc–petroleum ether, 7:3).
1H NMR (400 MHz, acetone-d6): δ = 1.47 (d, J = 1.4 Hz, 3 H,
T
CH3 ), 2.35 (ddd, J = 5.5, 7.8, 13.5 Hz, 1 H, H-2′a), 2.41 (ddd,
5′-O-(Dimethoxytrityl)thymidine (9)26
J = 2.5, 6.0, 13.5 Hz, 1 H, H-2′b), 3.39 (d, J = 3.7 Hz, 2 H, OCH2),
3.79 (s, 6 H, 2 × OCH3DMT), 4.02 (dd, J = 5.5, 13.3 Hz, 1 H, H-5′a),
4.07 (dd, J = 5.5, 13.3 Hz, 1 H, H-5′b), 4.12–4.14 (m, 1 H, H-4′),
4.37–4.39 (m, 1 H, H-3′), 5.14 (m, 1 H, =CH2allyl), 5.26 (m, 1 H,
=CH2allyl), 5.85–5.98 (m, 1 H, =CHallyl), 6.31 (dd, J = 6.0, 7.8 Hz, 1
H, H-1′), 6.89–6.93 (m, 4 H, H-Ar), 7.24–7.39 (m, 7 H, H-Ar),
7.47–7.50 (m, 2 H, H-Ar), 7.61 (d, J = 1.4 Hz, 1 H, H-6), 10.00 (s,
1 H, NH).
To a soln of thymidine (4.96 g, 20.5 mmol) in anhyd pyridine (100
mL) under argon was added Et3N (5.8 mL, 41.3 mmol) and DMTCl
(7.7 g, 22.7 mmol). The mixture was stirred at refux for 1.5 h, then
concentrated. The residue was taken up in EtOAc (100 mL), washed
with sat. aq NaHCO3 (2 × 50 mL) and brine (50 mL), dried over
MgSO4, filtered and concentrated. Purification by flash column
chromatography (CH2Cl2–MeOH–Et3N, 98:1:1) afforded 9 as a
white solid; yield: 9.15 g (82%); mp 89 °C.
T
13C NMR (100 MHz, acetone-d6): δ = 12.2 (CH3 ), 38.2 (C-2′), 55.5
(OCH3DMT), 64.8 (CH2allyl), 70.6 (C-5′), 79.9 (C-3′), 84.6 (C-4′),
85.3 (C-1′), 87.5 (Cq), 111.0 (C-5), 114.0, 116.9, 127.7, 128.7,
129.0 and 131.0 (6 × C-Ar), 135.8 (CHallyl), 136.5 (C-6), 145.9 (Cq),
151.2 (C-2), 159.7 (Cq), 164.2 (C-4).
Rf = 0.31 (CH2Cl2–MeOH, 9:1).
1H NMR (400 MHz, acetone-d6): δ = 1.46 (d, J = 1.4 Hz, 3 H,
T
CH3 ), 2.30 (ddd, J = 2.8, 6.0, 13.8 Hz, 1 H, H-2′a), 2.38 (ddd,
J = 6.1, 7.8, 13.8 Hz, 1 H, H-2′b), 3.37 (d, J = 3.6 Hz, 2 H, H-5′a,
H-5′b), 3.79 (s, 6 H, 2 × OCH3DMT), 4.01–4.07 (m, 1 H, H-4′), 4.51
(d, J = 4.1 Hz, 1 H, OH), 4.58–4.62 (m, 1 H, H-3′), 6.38 (dd, J = 6.0,
7.8 Hz, 1 H, H-1′), 6.88–6.92 (m, 4 H, H-Ar), 7.23–7.38 (m, 7 H, H-
Ar), 7.48–7.50 (m, 2 H, H-Ar), 7.63 (d, J = 1.4 Hz, 1 H, H-6), 10.01
(s, 1 H, NH).
5′-O-(Dimethoxytrityl)-3′-O-(formylmethyl)thymidine (6)25c
To a soln of 13 (1.63 g, 2.79 mmol) in a mixture of acetone–H2O
(3:1, 12 mL) were added NMO (0.65 g, 5.58 mmol) and a soln of
4% OsO4 in t-BuOH (900 μL). The mixture was stirred at r.t. for 2
h, then treated with Na2S2O5 (0.98 g) and stirred for 30 min. H2O
(50 mL) was then added. The aqueous layer was extracted with EtO-
Ac (3 × 50 mL). The combined organic layers were washed with
brine (100 mL), dried over MgSO4, filtered and concentrated. The
residue was dissolved in a mixture of acetone–phosphate buffer pH
7 (3:1, 22 mL), and NaIO4 (1.50 g, 7.02 mmol) was added. The mix-
ture was stirred at r.t. for 2 h, then filtered, and the precipitate was
washed with EtOAc (50 mL). The separated aqueous layer was ex-
tracted with EtOAc (2 × 50 mL) and then the combined organic lay-
ers were washed with brine (100 mL), dried over MgSO4, filtered
and concentrated. The crude product 6 (beige solid; 1.64 g, 100%)
was pure enough for further reactions.
T
13C NMR (100 MHz, acetone-d6): δ = 12.1 (CH3 ), 41.1 (C-2′), 55.5
(OCH3DMT), 64.8 (C-5′), 72.5 (C-3′), 79.2 (Cq), 85.1 (C-1′), 87.1 (C-
4′), 110.9 (C-5), 113.9, 127.7, 128.7, 129.0 and 131.0 (5 × C-Ar),
136.4 (C-6), 145.9 (Cq), 151.2 (C-2), 159.7 (Cq), 164.2 (C-4).
3-N-Benzoyl-5′-O-(dimethoxytrityl)thymidine (12)24
To a soln of 9 (508 mg, 0.93 mmol) in anhyd MeCN (15 mL) under
argon was added BSA (455 μL, 1.84 mmol). The mixture was
stirred at reflux for 45 min, then cooled to r.t. Et3N (255 μL, 1.83
mmol) and BzCl (130 μL, 1.20 mmol) were added and the mixture
was stirred for 15 h. TBAF (740 mg, 2.83 mmol) was introduced
and the reaction mixture was stirred for 1 h, then concentrated. The
residue was taken up in EtOAc (20 mL), washed with sat. aq
NaHCO3 (2 × 10 mL) and brine (20 mL), dried over MgSO4, fil-
tered and concentrated. Purification by flash column chromatogra-
phy (petroleum ether–EtOAc, 1:1) afforded 12 as a white solid;
yield: 375 mg (62%); mp 92 °C.
Mp 123 °C; [α]D22 +3.61 (c 0.80, acetone).
Rf = 0.55 (CH2Cl2–MeOH, 9:1).
1H NMR (400 MHz, acetone-d6): δ = 1.45 (d, J = 0.9 Hz, 3 H,
T
CH3 ), 2.39 (ddd, J = 6.0, 8.5, 14.2 Hz, 1 H, H-2′a), 2.50 (ddd,
J = 2.3, 6.0, 14.2 Hz, 1 H, H-2′b), 3.41–3.43 (m, 2 H, H-5′a, H-5′b),
3.79 (s, 6 H, 2 × OCH3DMT), 4.20–4.22 (m, 1 H, H-4′), 4.27 (s, 2 H,
OCH2), 4.46–4.48 (m, 1 H, H-3′), 6.33 (dd, J = 6.0, 8.5 Hz, 1 H, H-
1′), 6.90–6.92 (m, 4 H, H-Ar), 7.25–7.37 (m, 7 H, H-Ar), 7.48–7.50
(m, 2 H, H-Ar), 7.60 (d, J = 0.9 Hz, 1 H, H-6), 9.64 (s, 1 H, CHO),
10.01 (s, 1 H, NH).
Rf = 0.61 (EtOAc–petroleum ether, 7:3).
1H NMR (400 MHz, acetone-d6): δ = 1.51 (d, J = 1.4 Hz, 3 H,
T
CH3 ), 2.38 (ddd, J = 3.3, 6.4, 13.5 Hz, 1 H, H-2′a), 2.48 (ddd,
J = 6.2, 7.3, 13.5 Hz, 1 H, H-2′b), 3.41 (d, J = 3.2 Hz, 2 H, H-5′a,
H-5′b), 3.80 (s, 6 H, 2 × OCH3DMT), 4.07–4.10 (m, 1 H, H-4′), 4.53
(s, 1 H, OH), 4.63–4.65 (m, 1 H, H-3′), 6.34 (dd, J = 6.4, 7.3 Hz, 1
H, H-1′), 6.90–6.94 (m, 4 H, H-Ar), 7.25–7.29 (m, 1 H, H-Ar),
7.33–7.40 (m, 7 H, H-Ar), 7.50–7.60 (m, 4 H, H-Ar), 7.73–7.77 (m,
2 H, H-Ar), 7.82 (d, J = 1.4 Hz, 1 H, H-6).
T
13C NMR (100 MHz, acetone-d6): δ = 12.2 (CH3 ), 38.0 (C-2′), 55.5
(OCH3DMT), 64.8 (C-5′), 75.4 (OCH2), 81.7 (C-3′), 84.7 (C-4′), 87.5
(Cq), 87.6 (C-1′), 111.1 (C-5), 114.0, 127.8, 128.8, 129.0 and 131.0
(5 × C-Ar), 136.4 (C-6), 145.9 (Cq), 151.3 (C-2), 159.6 (Cq), 164.2
(C-4), 200.6 (CHO).
T
13C NMR (100 MHz, acetone-d6): δ = 12.1 (CH3 ), 41.3 (C-2′), 55.5
(OCH3DMT), 64.6 (C-5′), 72.3 (C-3′), 85.8 (C-1′), 87.4 (C-4′), 110.9
(C-5), 114.0, 127.8, 128.7, 129.0, 130.1, 131.0 and 131.1 (7 × C-
Ar), 132.9 (Cq), 135.8 (C-6), 136.4 (C-Ar), 136.6 (Cq), 137.0 (Cq),
143.9 (Cq), 145.9 (Cq), 150.1 (C-2), 159.7 (Cq), 163.5 (C-4), 170.3
(Cq).
5′-O-(Dimethoxytrityl)-3′-O-(methoxycarbonylmethyl)thymi-
dine (14)
To a soln of 6 (492 mg, 0.84 mmol) in a mixture of MeCN–H2O
(1:1, 8 mL) were added BAIB (547 mg, 1.70 mmol) and TEMPO
(27 mg, 0.17 mmol). The mixture was stirred at r.t. for 2 h, then di-
luted with EtOAc (15 mL) and washed with brine (15 mL). The
aqueous layer was extracted with EtOAc (2 × 15 mL). The com-
bined organic layers were dried over MgSO4, filtered and concen-
trated. The crude product was then engaged in ester formation.
3′-O-Allyl-5′-O-(dimethoxytrityl)thymidine (13)25c
To a suspension of 60% NaH (182 mg, 4.55 mmol) in anhyd THF
(10 mL) under argon at 0 °C was added 9 (988 mg, 1.82 mmol). Af-
ter sonication for 20 min, allyl bromide (400 μL, 4.62 mmol) was
added and the reaction mixture was stirred at r.t. for 3 h. The mix-
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2012, 44, 1718–1724

1722
S. Peyrat, J. Xie
PAPER
To a soln of the acid derivative (500 mg, 0.84 mmol) in anhyd DMF
(5 mL) under argon were added NaHCO3 (222 mg, 2.64 mmol) and
MeI (85 μL, 1.36 mmol). The mixture was stirred at r.t. for 15 h,
then Cs2CO3 (143 mg, 0.43 mmol) was added to complete the reac-
tion. The mixture was stirred for 24 h, then concentrated, and the
residue was diluted with EtOAc (20 mL). The organic layer was
washed with sat. aq NaHCO3 (20 mL) and brine (20 mL), and then
dried over MgSO4, filtered and concentrated. Purification by flash
column chromatography (CH2Cl2–MeOH–Et3N, 99:0:1, then
98:1:1) afforded 14 as an oil; yield: 345 mg (64%).
4.05–4.07 (m, 1 H, H-4′B), 4.10–4.15 (m, 4 H, H-5′aB, H-5′bB,
OCH2), 4.22–4.24 (m, 1 H, H-4′A), 4.48–4.49 (m, 1 H, H-3′A), 4.71–
4.73 (m, 1 H, H-3′B), 5.58 (s, 1 H, CO–NH–O), 6.31–6.36 (m, 2 H,
H-1′A, H-1′B), 6.89–6.93 (m, 4 H, H-Ar), 7.23–7.27 (m, 1 H, H-Ar),
7.32–7.38 (m, 6 H, H-Ar), 7.47–7.51 (m, 2 H, H-Ar), 7.61 (d,
J = 1.4 Hz, 1 H, H-6A), 7.85 (d, J = 0.9 Hz, 1 H, H-6B), 10.0 (s, 2 H,
NHA, NHB).
T
13C NMR (100 MHz, acetone-d6): δ = –4.6 (CH3TBS), 12.2 (CH3 A),
T
12.4 (CH3 B), 18.5 (Cq, t-BuTBS), 26.1 (CH3, t-BuTBS), 37.8 (C-2′A),
41.2 (C-2′B), 55.5 (OCH3DMT), 64.9 (C-5′A), 68.8 (OCH2), 73.8 (C-
3′B), 76.6 (C-5′B), 82.2 (C-3′A), 84.4 (C-4′A), 85.1, 85.7 (C-1′A, C-
1′B), 86.2 (C-4′B), 87.6 (Cq), 111.1 (C-5A, C-5B), 114.0, 127.7,
128.7, 129.0 and 131.0 (5 × C-Ar), 136.3, 136.9 (C-6A, C-6B), 145.8
(Cq), 151.2 (C-2A, C-2B), 159.7 (Cq), 164.1, 164.3 (C-4A, C-4B),
166.5 (Cq).
[α]D22 +18.6 (c 1.6, acetone).
Rf = 0.48 (EtOAc–petroleum ether, 7:3).
1H NMR (400 MHz, acetone-d6): δ = 1.46 (d, J = 0.9 Hz, 3 H,
T
CH3 ), 2.37 (ddd, J = 5.9, 8.3, 13.9 Hz, 1 H, H-2′a), 2.49 (ddd,
J = 2.3, 6.0, 13.9 Hz, 1 H, H-2′b), 3.40 (dd, J = 3.7, 10.6 Hz, 1 H,
H-5′a), 3.44 (dd, J = 3.7, 10.6 Hz, 1 H, H-5′b), 3.67 (s, 3 H,
COOCH3), 3.79 (s, 6 H, 2 × OCH3DMT), 4.17–4.20 (m, 1 H, H-4′),
4.22 (s, 2 H, OCH2), 4.50–4.52 (m, 1 H, H-3′), 6.32 (dd, J = 6.0, 8.3
Hz, 1 H, H-1′), 6.89–6.93 (m, 4 H, H-Ar), 7.23–7.38 (m, 7 H, H-Ar),
7.47–7.50 (m, 2 H, H-Ar), 7.59 (d, J = 0.9 Hz, 1 H, H-6), 10.03 (s,
1 H, NH).
HRMS (ESI): m/z [M + Na]+ calcd for C49H61N5NaO13Si:
978.3927; found: 978.3894.
Oxime Dinucleoside 2
To a soln of 6 (162 mg, 0.28 mmol) and 4 (105 mg, 0.28 mmol) in
anhyd THF (10 mL) under argon was added AcOH (150 μL). The
mixture was stirred at r.t. for 20 h, then neutralized with sat. aq
NaHCO3 (10 mL) and extracted with EtOAc (3 × 15 mL). The com-
bined organic layers were washed with brine (15 mL), dried over
MgSO4, filtered and concentrated. Purification by flash column
chromatography (CH2Cl2–MeOH–Et3N, 98:1:1) afforded 2 as a
white solid; yield: 220 mg (84%); mp 135 °C.
T
13C NMR (100 MHz, acetone-d6): δ = 12.1 (CH3 ), 38.0 (C-2′), 51.9
(COOCH3), 55.5 (OCH3DMT), 64.8 (C-5′), 66.9 (OCH2), 81.5 (C-3′),
84.7 (C-4′), 85.1 (C-1′), 87.5 (Cq), 111.0 (C-5), 114.0, 127.7, 128.7,
129.0 and 131.0 (5 × C-Ar), 136.3 (C-6), 136.6 (Cq), 145.9 (Cq),
151.2 (C-2), 159.7 (Cq), 164.1 (C-4), 171.2 (COOCH3).
HRMS (ESI): m/z [M + Na]+ calcd for C34H36N2NaO9: 639.2319;
Rf = 0.42 (CH2Cl2–MeOH, 9.5:0.5).
1H NMR (400 MHz, acetone-d6): δ = 0.11 (s, 6 H, 2 × CH3TBS), 0.91
found: 639.2303.
T
(s, 9 H, t-BuTBS), 1.29 (d, J = 1.4 Hz, 3 H, CH3 A), 1.79 (d, J = 0.9
3′-O-(Carboxymethyl)-5′-O-(dimethoxytrityl)thymidine (5)23
To a soln of 14 (200 mg, 0.32 mmol) in MeOH (2 mL) was added
LiOH (12 mg, 0.50 mmol). The reaction mixture was stirred at r.t.
for 36 h, then quenched with sat. aq NH4Cl (10 mL) and extracted
with EtOAc (3 × 10 mL). The combined organic layers were dried
over MgSO4, filtered and concentrated. The crude product 5 (oil;
176 mg, 90%) was pure enough for further reactions.
T
Hz, 3 H, CH3 B), 2.19–2.33 (m, 2 H, H-2′aB, H-2′bB), 2.35–2.50 (m,
2 H, H-2′aA, H-2′bA), 3.37–3.44 (m, 2 H, H-5′aA, H-5′bA), 3.79 (s, 6
H, 2 × OCH3DMT), 4.04–4.08 (m, 1 H, H-4′B), 4.13–4.16 (m, 1 H, H-
4′A), 4.17–4.20 [t, J = 5.0 Hz, 1.2 H, OCH2CH=N–O (E)], 4.24–
4.31 (m, 2 H, H-5′aB, H-5′bB), 4.38–4.41 [dd, J = 3.4, 8.0 Hz, 0.8 H,
OCH2CH=N–O (Z)], 4.43–4.46 (m, 1 H, H-3′A), 4.54–4.58 (m, 1 H,
H-3′B), 6.25–6.32 (m, 2 H, H-1′A, H-1′B), 6.89–6.95 [m, 4.4 H, H-Ar,
CH=N–O (Z)], 7.23–7.27 (m, 1 H, H-Ar), 7.31–7.36 (m, 6 H, H-
Ar), 7.47–7.51 (m, 3 H, H-Ar, H-6B), 7.59–7.61 [m, 1.6 H, H-6A,
CH=N–O (E)], 10.0 (s, 2 H, NHA, NHB).
[α]D22 +11.9 (c 1.50, MeOH).
Rf = 0.13 (CH2Cl2–MeOH, 9:1).
1H NMR (400 MHz, CD3OD): δ = 1.36 (d, J = 1.4 Hz, 3 H, CH3 ),
2.27–2.34 (m, 1 H, H-2′a), 2.50–2.54 (m, 1 H, H-2′b), 3.37–3.43 (m,
2 H, H-5′a, H-5′b), 3.77 (s, 6 H, 2 × OCH3DMT), 3.93 (s, 2 H, OCH2),
4.21–4.25 (m, 1 H, H-4′), 4.38–4.41 (m, 1 H, H-3′), 6.31–6.34 (m,
1 H, H-1′), 6.85–6.87 (m, 4 H, H-Ar), 7.28–7.31 (m, 7 H, H-Ar),
7.41–7.43 (m, 2 H, H-Ar), 7.68 (d, J = 1.4 Hz, 1 H, H-6).
T
T
13C NMR (100 MHz, acetone-d6): δ = –4.7 (CH3TBS), 12.2 (CH3 A),
T
12.7 (CH3 B), 18.5 (Cq, t-BuTBS), 26.2 (CH3, t-BuTBS), 37.9 (C-2′A),
40.6 (C-2′B), 55.5 (OCH3DMT), 64.3 [OCH2CH=N–O (Z)], 64.8 (C-
5′A), 66.7 [OCH2CH=N–O (E)], 73.4 (C-3′B), 74.5 (C-5′B), 75.0
(Cq), 81.0 (C-3′A), 84.5 (C-4′A), 85.2, 85.5 (C-1′A, C-1′B), 86.1 (C-
4′B), 87.5 (Cq), 110.0, 110.8 (C-5A, C-5B), 114.0, 127.7, 128.7,
129.0 and 131.0 (5 × C-Ar), 136.2, 136.4 (C-6A, C-6B), 145.8 (Cq),
148.6 (Cq), 151.2 (C-2A, C-2B), 159.7 (Cq), 164.1 (C-4A, C-4B).
3′-O-(N-Carbonylmethyl)-5′-O-(dimethoxytrityl)thymidylyl-
(3′→5′)-5′-O-amino-3′-O-(tert-butyldimethylsilyl)thymidine (1)
To a soln of 5 (51 mg, 0.085 mmol) in anhyd DMF (1 mL) at 0 °C
under argon were added HOAt (15 mg, 0.11 mmol) and EDC (11
mg, 0.10 mmol). The mixture was stirred for 10 min, then 4 (32 mg,
0.085 mmol) was added. The reaction was complete after stirring
for 1 night at r.t. The mixture was diluted with EtOAc (10 mL) and
washed with sat. aq NaHCO3 (10 mL). The aqueous layer was ex-
tracted with EtOAc (2 × 10 mL). The combined organic layers were
washed with brine (20 mL), dried over MgSO4, filtered and concen-
trated. Purification by flash column chromatography (CH2Cl2–
MeOH–Et3N, 99:0:1, then 98:1:1) afforded 1 as a white solid; yield:
76 mg (94%); mp 137 °C.
HRMS (ESI): m/z [M + H]+ calcd for C49H62N5O12Si: 940.4164;
found: 940.4151; m/z [M + Na]+ calcd for C49H61N5NaO12Si:
962.3984; found: 962.3972.
5′-O-(Dimethoxytrityl)-3′-O-(N-ethyl)thymidylyl-(3′→5′)-5′-O-
amino-3′-O-(tert-butyldimethylsilyl)thymidine (3)
To a soln of dinucleoside 2 (52 mg, 0.055 mmol) in anhyd THF (1
mL) under argon were added AcOH (25 μL) and NaBH3CN (10 mg,
0.17 mmol). The mixture was stirred at r.t. for 24 h, then NaBH3CN
(10 mg, 0.17 mmol) was added again. The mixture was stirred for
48 h, then diluted with EtOAc (10 mL) and washed with sat. aq
NaHCO3 (10 mL). The aqueous layer was extracted with EtOAc
(2 × 10 mL). The combined organic layers were washed with brine
(15 mL), dried over MgSO4, filtered and concentrated. Purification
by flash column chromatography (CH2Cl2–MeOH–Et3N, 98:1:1)
afforded 3 as a white solid; yield: 34 mg (66%); mp 106 °C.
[α]D22 +19.8 (c 1.10, acetone).
Rf = 0.36 (CH2Cl2–MeOH, 9.5:0.5).
1H NMR (400 MHz, acetone-d6): δ = 0.13 (s, 6 H, 2 × CH3TBS), 0.92
(s, 9 H, t-BuTBS), 1.45 (d, J = 1.4 Hz, 3 H, CH3 A), 1.84 (d, J = 0.9
T
T
Hz, 3 H, CH3 B), 2.14–2.26 (m, 2 H, H-2′aB, H-2′bB), 2.34–2.42 (m,
[α]D22 +18.8 (c 0.7, acetone).
2 H, H-2′aA, H-2′bA), 3.39 (dd, J = 3.4, 10.7 Hz, 1 H, H-5′aA), 3.45
(dd, J = 3.4, 10.3 Hz, 1 H, H-5′bA), 3.79 (s, 6 H, 2 × OCH3DMT),
Rf = 0.45 (CH2Cl2–MeOH, 9.5:0.5).
Synthesis 2012, 44, 1718–1724
© Georg Thieme Verlag Stuttgart · New York

PAPER
Synthesis of Thymidine Dimers
1723
1H NMR (400 MHz, acetone-d6): δ = 0.11 (s, 6 H, 2 × CH3TBS), 0.91
(3) (a) Mesmaeker, A.; Waldner, A.; Lebreton, J.; Hoffmann,
P.; Fritsch, V.; Wolf, R. M.; Freier, S. M. Angew. Chem., Int.
Ed. Engl. 1994, 33, 226. (b) De Mesmaeker, A.; Lesueur, C.;
Bevierre, M.-O.; Waldner, A.; Fritsch, V.; Wolf, R. M.
Angew. Chem., Int. Ed. Engl. 1996, 35, 2790. (c) Rozners,
E.; Katkevica, D.; Bizdena, E.; Strömberg, R. J. Am. Chem.
Soc. 2003, 125, 12125.
(4) (a) Gogoi, K.; Gunjal, A. D.; Kumar, V. A. Chem. Commun.
2006, 2373. (b) Gogoi, K.; Gunjal, A. D.; Phalgune, U. D.;
Kumar, V. A. Org. Lett. 2007, 9, 2697. (c) Gokhale, S. S.;
Gogoi, K.; Kumar, V. A. J. Org. Chem. 2010, 75, 7431.
(5) (a) Freier, S. M.; Altmann, K.-H. Nucleic Acids Res. 1997,
25, 4429. (b) Isobe, H.; Fujino, T.; Yamazaki, N.; Guillot-
Nieckowski, M.; Nakamura, E. Org. Lett. 2008, 10, 3729.
(c) Lucas, R.; Zerrouki, R.; Granet, R.; Krausz, P.;
Champavier, Y. Tetrahedron 2008, 64, 5467. (d) El-
Sagheer, A. H.; Brown, T. J. Am. Chem. Soc. 2009, 131,
3958.
T
(s, 9 H, t-BuTBS), 1.46 (d, J = 0.9 Hz, 3 H, CH3 A), 1.80 (d, J = 0.9
T
Hz, 3 H, CH3 B), 2.15–2.28 (m, 2 H, H-2′aB, H-2′bB), 2.32–2.46 (m,
2 H, H-2′aA, H-2′bA), 3.09–3.13 (m, 2 H, OCH2CH2NH–O), 3.36–
3.43 (m, 2 H, H-5′aA, H-5′bA), 3.62–3.71 (m, 2 H, OCH2CH2NH–
O), 3.79 (s, 6 H, 2 × OCH3DMT), 3.81–3.92 (m, 2 H, H-5′aB, H-5′bB),
3.99–4.02 (m, 1 H, H-4′B), 4.13–4.15 (m, 1 H, H-4′A), 4.33–4.35 (m,
1 H, H-3′A), 4.50–4.53 (m, 1 H, H-3′B), 6.26–6.31 (m, 2 H, H-1′A, H-
1′B), 6.43–6.46 (t, 1 H, CH2NH–O), 6.89–6.93 (m, 4 H, H-Ar),
7.23–7.27 (m, 1 H, H-Ar), 7.32–7.38 (m, 6 H, H-Ar), 7.48–7.50 (m,
2 H, H-Ar), 7.56 (d, J = 0.9 Hz, 1 H, H-6), 7.60 (d, J = 0.9 Hz, 1 H,
H-6), 9.94 (s, 1 H, NHA), 9.97 (s, 1 H, NHB).
T
13C NMR (100 MHz, acetone-d6): δ = –4.6 (CH3TBS), 12.2 (CH3 A),
T
12.6 (CH3 B), 18.5 (Cq, t-BuTBS), 26.1 (CH3, t-BuTBS), 38.0 (C-2′),
40.9 (C-2′), 52.2 (OCH2CH2NH–O), 55.5 (OCH3DMT), 64.9 (C-5′A),
66.7 (OCH2CH2NH–O), 73.7 (C-3′B), 74.4 (C-5′B), 81.0 (C-3′A),
84.5 (C-4′A), 85.2, 85.5 (C-1′A, C-1′B), 86.4 (C-4′B), 87.5 (Cq),
110.8, 111.0 (C-5A, C-5B), 114.0, 127.7, 128.7, 129.0 and 131.0 (5
× C-Ar), 136.3, 136.5 (C-6A, C-6B), 145.8 (Cq), 151.2 (C-2A, C-2B),
159.7 (Cq), 164.2 (C-4A, C-4B).
(6) Stork, G.; Zhang, C.; Gryaznov, S.; Schultz, R. Tetrahedron
Lett. 1995, 36, 6387.
HRMS (ESI): m/z [M + Na]+ calcd for C49H63N5NaO12Si:
964.4135; found: 964.4087.
(7) (a) Jones, R. J.; Lin, K.-Y.; Milligan, J. F.; Wadwani, S.;
Matteucci, M. D. J. Org. Chem. 1993, 58, 2983. (b) Rozners,
E.; Strömberg, R. J. Org. Chem. 1997, 62, 1846.
(c) Pitulescu, M.; Grapp, M.; Krätzner, R.; Knepel, W.;
Diederichsen, U. Eur. J. Org. Chem. 2008, 2100.
(8) Cao, X.; Matteucci, M. D. Bioorg. Med. Chem. Lett. 1994, 4,
807.
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J. Am. Chem. Soc. 1995, 117, 7249. (b) Huang, Z.; Benner,
S. A. J. Org. Chem. 2002, 67, 3996.
Oxime Dinucleoside 15
To a soln of 2 (301 mg, 0.32 mmol) in THF (3 mL) was added
TBAF (150 mg, 0.57 mmol). The mixture was stirred at r.t. for 1
night, then concentrated, diluted with EtOAc (30 mL) and washed
with sat. aq NaCl (20 mL). The organic layer was dried over
MgSO4, filtered and concentrated. Purification by flash chromatog-
raphy (CH2Cl2–MeOH–Et3N, 98:1:1, then 97:2:1) afforded 15 as a
white solid; yield: 261 mg (99%); mp 122 °C.
(10) Zhang, J.; Matteucci, M. D. Bioorg. Med. Chem. Lett. 1999,
9, 2213.
Rf = 0.33 (CH2Cl2–MeOH, 9.5:0.5).
(11) (a) Vasseur, J. J.; Debart, F.; Sanghvi, Y. S.; Cook, P. D.
J. Am. Chem. Soc. 1992, 114, 4006. (b) Morvan, F.; Sanghvi,
Y. S.; Perbost, M.; Vasseur, J. J.; Bellon, L. J. Am. Chem.
Soc. 1996, 118, 255. (c) Perbost, M.; Hoshiko, T.; Morvan,
F.; Swayze, E.; Griffey, R. H.; Sanghvi, Y. S. J. Org. Chem.
1995, 60, 5150. (d) Bhat, B.; Swayze, E. E.; Wheeler, P.;
Dimock, S.; Perbost, M.; Sanghvi, Y. S. J. Org. Chem. 1996,
61, 8186.
(12) (a) Gogoi, K.; Kumar, V. A. Chem. Commun. 2008, 706.
(b) Bagmare, S.; D’Costa, M.; Kumar, V. A. Chem.
Commun. 2009, 6646.
(13) (a) Wendeborn, S.; Wolf, R. M.; De Mesmaeker, A.
Tetrahedron Lett. 1995, 36, 6879. (b) Fargeas, V.; Ané, A.;
Dubreuil, D.; Lebreton, J. Synlett 2009, 3341.
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(b) Lv, J.-L.; Zhao, Z.-Y.; Yang, Z.-Q.; Liu, D.-S.; Fan,
Q.-H. Tetrahedron 2011, 67, 9080.
(15) Burgess, K.; Gibbs, R. A.; Metzker, M. L.; Raghavachari, R.
J. Chem. Soc., Chem. Commun. 1994, 915.
(16) (a) Yang, D.; Ng, F.-F.; Li, Z.-J.; Wu, Y.-D.; Chan, K. W.
K.; Wang, D.-P. J. Am. Chem. Soc. 1996, 118, 9794. (b) Li,
X.; Wu, Y.-D.; Yang, D. Acc. Chem. Res. 2008, 41, 1428.
(17) Ge, Y.; Wu, X.; Zhang, D.; Hu, L. Bioorg. Med. Chem. Lett.
2009, 19, 941.
(18) (a) Salo, H.; Virta, P.; Hakala, H.; Prakash, T. P.; Kawasaki,
A. M.; Manoharan, M.; Lönnberg, H. Bioconjugate Chem.
1999, 10, 815. (b) Sethi, D.; Patnaik, S.; Kumar, A.; Gandhi,
R. P.; Gupta, K. C.; Kumar, P. Bioorg. Med. Chem. 2009, 17,
5442.
1H NMR (400 MHz, acetone-d6): δ = 1.47 (d, J = 1.4 Hz, 3 H,
T
T
CH3 A), 1.81 (d, J = 1.4 Hz, 3 H, CH3 B), 2.15–2.29 (m, 2 H, H-2′aB,
H-2′bB), 2.36–2.48 (m, 2 H, H-2′aA, H-2′bA), 3.39–3.40 (m, 2 H, H-
5′aA, H-5′bA), 3.79 (s, 6 H, 2 × OCH3DMT), 4.07–4.11 (m, 1 H, H-
4′B), 4.14–4.15 (m, 1 H, H-4′A), 4.17–4.19 [t, J = 5.0 Hz, 1.2 H,
OCH2CH=N–O (E)], 4.25–4.30 (m, 2 H, H-5′aB, H-5′bB), 4.37–4.41
[m, 0.8 H, OCH2CH=N–O (Z)], 4.44–4.48 (m, 2 H, H-3′A, H-3′B),
4.58–4.59 (m, 1 H, OH), 6.28–6.34 (m, 2 H, H-1′A, H-1′B), 6.89–
6.93 [m, 4.4 H, H-Ar, CH=N–O (Z)], 7.23–7.28 (m, 1 H, H-Ar),
7.31–7.38 (m, 6 H, H-Ar), 7.44–7.50 (m, 3 H, H-Ar, H-6B), 7.57–
7.58 [m, 0.6 H, CH=N–O (E)], 7.61 (d, J = 1.4 Hz, 1 H, H-6A), 10.00
(s, 2 H, NHA, NHB).
T
T
13C NMR (100 MHz, acetone-d6): δ = 12.2 (CH3 A), 12.7 (CH3 B),
38.0 (C-2′A), 40.4 (C-2′B), 55.5 (OCH3DMT), 64.7 [OCH2CH=N–O
(Z)], 64.8 (C-5′A), 66.6 [OCH2CH=N–O (E)], 72.3 (C-3′B), 75.0 (C-
5′B), 75.1 (Cq), 81.0 (C-3′A), 84.5 (C-4′A), 85.1, 85.2 (C-1′A, C-1′B),
86.1 (C-4′B), 110.8, 111.1 (C-5A, C-5B), 114.0, 127.7, 128.7, 129.0
and 131.0 (5 × C-Ar), 136.3, 136.4 (C-6A, C-6B), 145.8 (Cq), 148.6
(Cq), 151.2 (C-2A, C-2B), 159.7 (Cq), 164.1 (C-4A, C-4B).
HRMS (ESI): m/z [M + Na]+ calcd for C43H47N5NaO12: 848.3113;
found: 848.3058.
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