New nucleoside-based polymeric supports for the solid phase synthesis of ribose-modified nucleoside analogues

Article abstract of DOI:10.1055/s-2004-830864

New solid supports, linking protected pyrimidine and purine nucleoside derivatives through the nucleobase, have been prepared. The support, incorporating a suitable derivative of 2′-azido, 2′-deoxyuridine, allowed the simple and efficient solid-phase synthesis of ribose-modified nucleoside and nucleic acid analogues, particularly of aminoacyl derivatives of 2′-deoxy, 2′-amino-uridine, following methodologies well established in peptide and oligonucleotide chemistry.

Full text of DOI:10.1055/s-2004-830864

LETTER
1975
New Nucleoside-Based Polymeric Supports for the Solid Phase Synthesis of
Ribose-Modified Nucleoside Analogues
Solid
P
hase Syn
o
thesis of
R
ib
r
ose-Mo
e
difie
d
N
ucl
n
e
oside
A
nalo
z
gues o De Napoli, Giovanni Di Fabio,* Jennifer D’Onofrio, Daniela Montesarchio
Dipartimento di Chimica Organica e Biochimica, Università degli Studi di Napoli ‘Federico II’, Complesso Universitario
di Monte S. Angelo, via Cynthia, 80126 Napoli, Italy
Fax +39(081)674393; E-mail: difabio@unina.it
Received 25 May 2004
can be successfully realized in a short time, provided that
Abstract: New solid supports, linking protected pyrimidine and
a few synthetic problems are solved. As a basic require-
ment, an appropriate linker has to be incorporated in the
solid support, stable enough under the reaction conditions
purine nucleoside derivatives through the nucleobase, have been
prepared. The support, incorporating a suitable derivative of 2¢-azi-
do, 2¢-deoxyuridine, allowed the simple and efficient solid-phase
synthesis of ribose-modified nucleoside and nucleic acid analogues, used throughout the synthesis, and labile enough to be
particularly of aminoacyl derivatives of 2¢-deoxy, 2¢-amino-uridine,
following methodologies well established in peptide and oligonu-
cleotide chemistry.
neatly cleaved from the solid support without affecting the
integrity of the desired products. Only recently has the
combinatorial approach been profitably extended to the
synthesis of nucleic acid-based (NABTM) libraries,5 allow-
ing the rapid and efficient preparation of a high number of
short nucleic acids fragments to be tested in their antiviral
activity. Notably, Epple and coworkers6 described a li-
brary of more than 25000 members of nucleoside ana-
logues, obtained in milligram quantities, prepared from
uridine- or 6-chloroinosine-based solid supports. In their
strategy the starting nucleosides are anchored onto the
polymer through an acetal linkage blocking the 2¢- and 3¢-
OH of the ribose moiety, which can be cleaved under very
mild acidic conditions, thus allowing an enormous variety
of modifications on the nucleobase or on the 5¢-position.
Key words: combinatorial chemistry, Mitsunobu reaction, nucleo-
sides, nucleotides, solid phase synthesis
The development of a broad array of reactions in the solid
phase1 increase the scope and potential of combinatorial
chemistry,2 allowing the synthesis of large libraries of
compounds endowed with a series of molecular diversity
motifs. Various combinatorial approaches have been suc-
cessfully adopted for the generation of a wide range of oli-
gomeric and small molecule libraries for biological
screenings. Small molecule libraries are generally de-
signed around a single core scaffold, which is typically a
polyfunctional and biomedically interesting molecule.3
We recently described an efficient solid phase strategy for
the synthesis of various 5¢,3¢-derivatized thymidine ana-
logues by using supports linking the thymidine residue
through the nucleobase, so that all the ribosidic functions
are susceptible to selective modifications in the solid
phase. To this purpose, ad hoc selected thymidine deriva-
tives were attached to a TentaGel® resin functionalized
with a b-hydroxyethyl-thioether linker. After the desired
manipulations of the ribosidic functions, oxidation of the
thioether function of the linker to sulfone, followed by a
simple ammonia cleavage, allowed the release of the tar-
get compounds in highly pure form.7
In this context, nucleosides can be regarded as valuable
scaffolds to be incorporated into polymeric supports for
combinatorial libraries, containing various functional
groups that can be selectively and differently manipulat-
ed. In addition, in the last decades a plethora of biological
properties have been found in nucleosides, either naturally
occurring or not; their use in pharmaceutics and/or in di-
agnostics actively stimulates the preparation of novel,
more efficient and less toxic related compounds.4 Howev-
er, the chemical diversity of the usual constituents of nu-
cleic acids is rather limited in terms of number of the
starting structures, of types of accessible reactions, and of
sites which can be combinatorialized on the nucleoside
skeleton. These issues intrinsically prevent the generation
of a large diverse nucleoside library. In order to conspic-
uously expand the repertoire of topological variations on
nucleoside and oligonucleotide analogues, a valid strategy
is the replacement of natural nucleosides with modified or
non-nucleotide moieties.
In an effort to render more general this approach attaching
to polymeric supports also other nucleosides through the
base, including ribo- and less usual nucleosides, we have
investigated the possibility to obtain solid supports func-
tionalized with uridine, inosine and 2¢-deoxyguanosine
derivatives, by exploiting the reactivity of the imidic or
amidic function of the nucleobase moieties. Our synthetic
strategy is based on the Mitsunobu condensation reaction
between suitably protected pyrimidine and purine nucleo-
sides 2, 3, 6 or 7 (Scheme 1) and previously described
support 1.7 The nucleoside derivatives were reacted with
resin 1 in the presence of PPh3 and DEAD as condensing
agents in THF–CH2Cl2 1:1 (v/v) at room temperature for
5 h. The loading yields, determined by quantitation of the
DMT cation released from weighed samples of supports
In principle, by exploiting combinatorial solid phase strat-
egies, a large number of structurally diverse analogues
SYNLETT 2004, No. 11, pp 1975–1979
0
6
.0
9
.2
0
0
4
Advanced online publication: 04.08.2004
DOI: 10.1055/s-2004-830864; Art ID: G18504ST
© Georg Thieme Verlag Stuttgart · New York

1976
L. De Napoli et al.
LETTER
4, 5, 8, 9, respectively, upon treatment with 2% dichloro- aqueous ammonia treatment. The reaction of 8 with 2 M
acetic acid (DCA) in dichloromethane solution, were al- NH3 in MeOH (60 °C, 18 h) released only 45% of the
ways above 90%, except in the case of 2¢-deoxyguanosine loaded nucleoside. After DMT removal, this eluate con-
derivative 7, which gave sensibly lower incorporation tained exclusively inosine, generated by preferential at-
yields (15%).
tack of NH3, in the case of a less concentrated solution, to
the CH2 in b to the sulfur atom of the linker in 8. This hy-
pothesis was confirmed by the Kaiser test performed on
the resin after the detachment, which was found to be pos-
itive. Conversely, when the MCPBA oxidation was per-
formed on resin 8, a successive basic treatment allowed
the quantitative detachment of the nucleoside from sup-
port 10. In this case, exclusively inosine was released by
reaction with 0.5 M NaOH (60 °C, 18 h).
S
O
O
HN
N
N
O
O
S
DMTO
N
DMTO
OH
O
O
1
PPh3 – DEAD
THF/CH2Cl2
Y
X
Y
X
2 X = OAc, Y = OAc
4 X = OAc, Y = OAc
93%
3 X = N3, Y = OTBDMS
5 X = N3, Y = OTBDMS 90%
X
O
Z
N
N
N
N
N
N
S
OH
N
O
N
N
DMTO
HO
N
O
b, c
O
R
R
N
N
N
N
AcO
OAc
HO
OH
N
N
S
DMTO
DMTO
OH
O
O
11 Z = NH2
12 Z = OH
8
X = S
10 X = SO2
1
a
PPh3 – DEAD
THF/CH2Cl2
Y
X
Y
X
Scheme 2 Reagents and conditions: a: 0.5 M MCPBA, CH2Cl2, r.t.,
1 h; b: 1% DCA, CH2Cl2, r.t., 10 min.; c: 17 M NH4OH, 60 °C, 18 h
or 0.5 M NaOH, 60 °C, 18 h (see text).
6 R = H, X = OAc, Y = OAc
7 R = NHi-Bu, X = H, Y = OAc
8 R = H, X = OAc, Y = OAc
9 R = NHi-Bu, X = H, Y = OAc 15%
95%
Scheme 1 Reagents and conditions: PPh3–DEAD in THF–CH2Cl2
1:1 (v/v), r.t., 5 h.
On the basis of the obtained results, we focused our atten-
tion on support 5, which contains three functional groups
in its ribose moiety susceptible to different manipulation.
In fact, the DMT and TBDMS are two well known orthog-
onally removable hydroxyl protecting groups, which can
easily be exploited for the selective formation of phospho-
ester or glycosidic bonds. In addition, the presence of an
azido group in the 2¢-position, as a masked form of an
amino group, can be a useful entry to the functionalization
of the sugar with a variety of carboxylic acid-containing
molecules, upon formation of stable amide linkages by
adopting highly efficient solid phase peptide synthetic
protocols. In this respect, support 5 can be especially use-
ful to generate a library of aminoacyl- or peptidyl-deriva-
tives of uridine, as new hybrid molecules the biological
potential of which is still largely unexplored.8 To test the
feasibility of the here described synthetic scheme for the
preparation of 2¢-aminoacyl-uridine analogues and short
oligomers containing this scaffold, we first synthesized
aminoacyl derivatives of uridine 13–16 (Scheme 3). Suc-
cessively, di- and trinucleotide hybrids having a 5¢-3¢ or a
3¢-3¢ phosphodiester bond (17–20, Scheme 3) were pre-
pared. In the first experiments, 5 was exploited to produce
a set of 2¢-N-aminoacyl analogues of uridine (route A in
Scheme 3).9 To this purpose, the azido function in 5 was
reduced to amine by treatment with PBu3 in H2O–THF10
and successively coupled with the chosen Fmoc-protected
aminoacid in the presence of HATU–HOBt in DMF at
room temperature for 2 hours. The coupling yields, mea-
sured by quantitative Fmoc test (20% piperidine in DMF)
on weighed samples of the dried supports, were always in
As a general procedure, after the desired manipulations of
the ribosidic functions, the detachment from the resin in-
volves the following steps: i) oxidation of the thioether
function of the functionalized support with a MCPBA so-
lution (0.5 M in CH2Cl2, r.t., 1 h); ii) removal of the DMT
group from the 5¢-OH with 1% DCA in CH2Cl2; iii) treat-
ment with concentrated aqueous ammonia solution
(60 °C, 18 h). To test the efficiency of this procedure on
the obtained functionalized supports, this sequence of re-
actions was first studied on supports 4 and 5. In repeated
experiments, the quantitative release exclusively of uri-
dine and of 2¢-amino-2¢-deoxyuridine, respectively, was
1
observed, the identity of which was confirmed by H
NMR analysis of the isolated compounds and by HPLC
comparison with authentic samples.
When support 8 was directly treated with a concentrated
aqueous ammonia solution (17 M, 60 °C, 18 h), only a
partial release of the nucleosidic material from the support
was achieved (40%), as checked by quantitation of the
DMT group still present on 8 after the detachment proce-
dure. HPLC analysis of the eluate from support 8, first
treated with DCA and then with ammonia, showed the
presence of 11 and 12 (Scheme 2) in 2:1 ratio, identified
as adenosine and inosine, respectively, on the basis of the
1H NMR and ESI-MS data of the isolated compounds and
by comparison with authentic samples. This result con-
firmed the high reactivity of C-6 of the purine towards nu-
cleophilic displacement by NH3 and/or OH– during the
Synlett 2004, No. 11, 1975–1979 © Thieme Stuttgart · New York

LETTER
Solid Phase Synthesis of Ribose-Modified Nucleoside Analogues
1977
the range 85–95%. After Fmoc removal and acetylation of with 5¢-DMT-2¢-deoxycytidine-3¢-phosphoramidite, ac-
the liberated amino groups, complete oxidation of the cording to a classical solid phase phosphoramidite proto-
thioether function to sulfone was obtained by treatment col. After deprotection of the 5¢-OH groups, complete
with a MCPBA solution (0.5 M in CH2Cl2, 1 h, r.t.). DMT detachment from the support was achieved by treatment
and TBDMS protecting groups were respectively re- with a concentrated aqueous ammonia solution (60 °C, 18
moved by acidic (1% DCA in CH2Cl2 solution) and fluo- h), giving the desired 3¢-3¢ phosphodiester linked dinucle-
ride ions (Et3N·3HF, r.t., overnight) treatments. The otide 17.
following concentrated aqueous ammonia solution treat-
ment (60 °C, 18 h) released 2¢-N-aminoacyl uridine ana-
logues 13–16 in very pure form.
For the synthesis of 18, the 2¢-azido function of support 5
was first reduced to free amine; this was coupled with
Fmoc-Lys(Fmoc)-OH in the presence of HATU–HOBt in
DMF and the unreacted amino groups then capped by
treatment with Ac2O–pyridine. The successive reactions
O
HN
performed in the solid phase are essentially those de-
O
scribed above for 17 (c–g, route B in Scheme 3).12 3¢-5¢
phosphodiester-linked dinucleotide 19 (route C in
Scheme 3)13 was obtained from support 5 by the follow-
ing reactions: i) reduction of the 2¢-azido function; ii) cou-
pling with Fmoc-Lys(Fmoc)-OH; iii) DMT removal; iv)
capping; v) oxidation of the thioether function on the sup-
port; vi) TBDMS removal; vii) standard automated cou-
pling with 3¢-DMT-thymidine-5¢-phosphoramidite, with
final DMT removal from the 3¢-OH group; viii) Fmoc re-
moval; ix) final detachment by aqueous ammonia treat-
ment. Support 5 was then employed in the synthesis of
hybrid trinucleotide 20 (route D in Scheme 3),14 prepared
essentially as described above for 19. In all cases, the
crude detached materials were analyzed and then purified
by RP HPLC. The identity of isolated 13–20 was ascer-
tained on the basis of 1H NMR and ESI-MS data
(Table 1).15 31P NMR experiments confirmed 17–19 to be
dinucleotides and 20 as a trinucleotide. In a typical exper-
iment, starting from 60 mg of support 5 (0.18 mequiv/g,
0.11 mmol), 60 OD (ca. 2 mg, 18% overall yield) of pure
trinucleotide 20 were isolated after HPLC.
HO
N
O
HO HN
R
U
13 R = Ac -Leu-
14 R = Ac -Phe-
15 R = Ac -Val-
HO
HO
O
16 R = Ac -Lys(Ac)-
O
P
HN R
O
B
O
O
HO
B
17 R = Ac, B = C; 18 R = Lys, B = T
U
HO
A
O
O
NH2
C
O
P
NH
NH2
HO
O
T
O
19
O
HO
Table 1 Analytical Data of Products 13–20
A
HO
HO
5
O
O
Product
tRa (min)
ESI-MS (m/z)
O
P
Found
Calcd for M
398.18
13
14
14.51
13.02
399.27 [M + H]+;
421.21 [M + Na]+
U
20
O
O
NH2
455.25 [M + Na]+;
471.23 [M + K]+
432.16
D
O
HN
NH2
HO
O
P
O
O
385.38 [M + H]+
384.16
455.20
T
15
16
13.07
11.50
O
456.44 [M + H]+;
478.42 [M + Na]+
HO
17
18
19
20
10.76
10.01
10.80
15.20
573.10 [M – H]–
674.54 [M – H]–
674.47 [M – H]–
574.11
675.23
675.23
988.28
Scheme 3 Reagents and conditions: for A, B, C, D see ref. 9, 12–14,
respectively.
To generate 3¢-3¢ linked dinucleotide 17, the azido func-
tion in 5 was reduced to amine and successively capped by
reaction with Ac2O–pyridine (1:1, v/v, r.t., 30 min). The
thioether function of the support was then oxidized (0.5 M
MCPBA in CH2Cl2, r.t., 1 h),11 the 3¢-OH function depro-
tected by treatment with Et3N·3HF (r.t., overnight) and the
support then subjected to a standard automated coupling
987.52 [M – H]–;
493.46 [M – 2H]2–
a Analytical column Nucleosil RP8 (Macherey-Nagel, 250 × 4.6 mm,
5 mm); linear gradient from 0% to 100% B in 30 min, flow rate 0.8
mL/min, of eluent A = H2O in B = MeCN; detection at l = 260 nm.
Synlett 2004, No. 11, 1975–1979 © Thieme Stuttgart · New York

1978
L. De Napoli et al.
LETTER
MCPBA, CH2Cl2, r.t., 1 h; f: Et3N·3HF, THF, r.t., 18 h; g:
1% DCA, CH2Cl2, r.t., 10 min; h: 17 M NH4OH, 60 °C, 18 h.
(10) Silva, D. J.; Wang, H.; Allanson, N. M.; Jain, R. K.; Sofia,
M. J. J. Org. Chem. 1999, 64, 5926.
(11) In the synthesis of short oligomers 17–20, better crudes were
obtained if the oxidation of the support was carried out
before the coupling with the phosphoramidite building
block.
In conclusion, we have described the synthesis of new nu-
cleoside-based solid supports (4, 5 and 8, 9) in which the
nucleosides are anchored onto the solid support through
the base, so that all the ribosidic functions are susceptible
to selective manipulation to introduce the required diver-
sity into the carbohydrate subunit. Particularly, support 5
can be a useful entry to high diversity nucleic acid-based
libraries (NAB). In fact, not only does this support contain
an intact nucleoside skeleton, but also the simultaneous
presence of a masked amino function (i.e. the 2¢-azido
group) and orthogonally removable protecting groups
(DMT and TBDMS), respectively at the 5¢ and 3¢-OH of
the ribose moiety, allows a versatile tridirectional elonga-
tion and/or derivatization of the hybrid biomolecules.
Starting from support 5, incorporating a 2¢-amino-2¢-
deoxyuridine scaffold, we devised a facile synthetic strat-
egy to obtain different nucleoside or short oligonucleotide
hybrids of uridine (as 13–20), following simple and well-
established peptide and oligonucleotide chemistry. Fur-
ther studies are currently in progress to extend the Mit-
sunobu reaction to anchor other nucleosides on high
loading polystyrene based resin, allowing higher amounts
of the desired products in the series of ribose-modified nu-
cleoside analogues.
(12) Reagents and conditions for route B: a: 0.35 M Bu3P, THF–
H2O–EtOH (4.5:1.4:6), r.t., 5 h; b: Ac2O–pyridine (1:1, v/v),
r.t., 30 min; c: 0.5 M MCPBA, CH2Cl2, r.t., 1 h; d:
Et3N·3HF, THF, r.t., 18 h; e: coupling with DMT-
phosphoramidite (5¢-DMT-dC-3¢-phosphoramidite for 17;
5¢-DMT-T-3¢-phosphoramidite for 18); f: 1% DCA, CH2Cl2,
r.t., 10 min; g: 17 M NH4OH, 60 °C, 18 h.
(13) Reagents and conditions for route C: a: 0.35 M Bu3P, THF–
H2O–EtOH (4.5:1.4:6), r.t., 5 h; b: HATU, HOBt, DIPEA,
Fmoc-a.a.-OH, DMF, r.t., 1 h.; c: 1% DCA, CH2Cl2, r.t., 10
min; d: Ac2O–pyridine (1:1, v/v), r.t., 30 min; e: 0.5 M
MCPBA, CH2Cl2, r.t., 1 h; f: Et3N·3HF, THF, r.t., 18 h; g:
coupling with 3¢-DMT-T-5¢-phosphoramidite; h: 1% DCA,
CH2Cl2, r.t., 10 min; i: 20% piperidine/DMF, r.t., 5 min; l:
17 M NH4OH, 60 °C, 18 h.
(14) Reagents and conditions for route D: a: 0.35 M Bu3P, THF–
H2O–EtOH (4.5:1.4:6), r.t., 5 h; b: HATU, HOBt, DIPEA,
Fmoc-a.a.-OH, DMF, r.t., 1 h.; c: Ac2O–pyridine (1:1, v/v),
r.t., 30 min; d: 0.5 M MCPBA, CH2Cl2, r.t., 1 h; e 1% DCA,
CH2Cl2, r.t., 10 min; f: coupling with 5¢-DMT-dA-3¢-
phosphoramidite; g: 1% DCA, CH2Cl2, r.t., 10 min; h:
Ac2O–pyridine (1:1, v/v), r.t., 30 min; i: Et3N·3HF, THF, r.t.,
18 h; l: coupling with 3¢-DMT-T-5¢-phosphoramidite; m:
1% DCA, CH2Cl2, r.t., 10 min; n: 20% piperidine–DMF, r.t.,
5 min; o: 17 M NH4OH, 60 °C, 18 h.
Acknowledgment
We acknowledge MIUR, CNR and Regione Campania for grants in
support of this investigation. We also thank C.I.M.C.F., Università
degli Studi di Napoli ‘Federico II’, for the NMR and MS facilities.
(15) Selected data for compound 13: 1H NMR (500 MHz, D2O):
d = 7.78 (1 H, d, J = 7.5 Hz, H-6), 6.06 (1 H, d, J = 8.0 Hz,
H-1¢), 5.89 (1 H, d, J = 7.5 Hz, H-5), 4.60 (1 H, m, H-2¢),
4.33–4.22 (2 H, overlapped signals, H-3¢ and CH a Leu),
4.20 (1 H, m, H-4¢), 3.85 (2 H, m, H2-5¢), 2.00 (3 H, s, acetyl
protons), 1.60–1.57 (3 H, overlapped signals, CH and CH2
Leu), 0.90 and 0.86 (3 H each, 2 d, CH3 Leu). Compound 14:
1H NMR (500 MHz, D2O): d = 7.86 (1 H, d, J = 8.0 Hz, H-
6), 7.42–7.26 (5 H, complex signals, aromatic protons), 6.01
(1 H, d, J = 7.0 Hz, H-1¢), 5.93 (1 H, d, J = 8.0 Hz, H-5); H-
2¢ signal is buried under the residual HDO signal; 4.21 (1 H,
dd, J = 2.5 and 2.0 Hz, CH a of Phe), 4.16 (1 H, m, H-4¢),
3.93–3.84 (2 H, m, H2-5¢), 3.81 (1 H, m, H-3¢), 3.73 (2 H, m,
CH2 of Phe), 1.97 (3 H, s, acetyl protons). Compound 15: 1H
NMR (500 MHz, D2O): d = 7.75 (1 H, d, J = 8.0 Hz, H-6),
6.07 (1 H, d, J = 8.0 Hz, H-1¢), 5.89 (1 H, d, J = 8.0 Hz, H-
5), 4.72–4.64 (1 H, m, H-2¢), 4.34 (1 H, dd, J = 5.5 and 2.5
Hz, H-3¢), 4.20 (1 H, m, H-4¢), 4.12 (1 H, d, J = 6.5 Hz, CH
a Val), 3.85 (2 H, m, H2-5¢), 2.18–2.12 [1 H, m, CH(CH3)2],
1.83 (3 H, s, acetyl protons), 0.92 and 0.89 [3 H each, 2 d,
J = 7.0 Hz, CH(CH3)2]. Compound 16: 1H NMR (500 MHz,
D2O): d = 7.85 (1 H, d, J = 8.5 Hz, H-6), 6.05 (1 H, d, J = 8.5
Hz, H-1¢), 5.92 (1 H, d, J = 8.5 Hz, H-5), 4.65 (1 H, m, H-2¢),
4.35 (1 H, m, H-3¢), 4.30 (1 H, m, CH a Lys), 4.25 (1 H, m,
H-4¢), 3.85 (2 H, m, H2-5¢), 3.25 (2 H, t, CH2 e Lys), 2.08 and
2.04 (3 H each, 2 s, acetyl protons), 1.75 (2 H, m, CH2 b
Lys), 1.55 (2 H, m, CH2 d Lys), 1.35 (2 H, m, CH2 g Lys).
Compound 17: 1H NMR (500 MHz, D2O), significant
signals: d = 7.86 (1 H, d, J = 7.5 Hz, H-6 U), 7.78 (1 H, d,
J = 7.5 Hz, H-6 C), 6.31 (1 H, dd, J = 6.5 and 7.0 Hz, H-1¢ C),
6.14 (1 H, d, J = 7.5 Hz, H-5 C), 6.07 (1 H, d, J = 7.5 Hz,
H-5 U), 5.88 (1 H, d, J = 8.0 Hz, H-1¢ U), 3.89–3.76 (4 H,
overlapped signals, H2-5¢ U and C), 2.62–2.30 (2 H, m, H-2¢
C), 2.15 (1 H, m, H-2¢ U), 1.93 (3 H, s, acetyl protons).
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(9) Reagents and conditions for route A: a: 0.35 M Bu3P, THF–
H2O–EtOH (4.5:1.4:6), r.t., 5 h; b: HATU, HOBt, DIPEA,
Fmoc-a.a.-OH, DMF, r.t., 1 h.; c: 20% piperidine–DMF, r.t.,
5 min; d: Ac2O–pyridine (1:1, v/v), r.t., 30 min; e: 0.5 M
Synlett 2004, No. 11, 1975–1979 © Thieme Stuttgart · New York

LETTER
Solid Phase Synthesis of Ribose-Modified Nucleoside Analogues
1979
Compound 18: 1H NMR (500 MHz, D2O) significant signals
4¢ U), 4.19 (5 H, overlapped signals, H2-5¢ U, H2-5¢ T and
CH a Lys), 3.24 (2 H, m, CH2 e Lys), 2.33 (2 H, m, H2-2¢ T),
1.93 (3 H, s, CH3 T), 1.80 (2 H, m, CH2 b Lys), 1.72 (2 H, m,
CH2 d Lys), 1.18 (2 H, m, CH2 g Lys). 31P NMR (161.98
MHz, D2O): d = 1.75. Compound 20: 1H NMR (500 MHz,
D2O), significant signals at: d = 8.33 (1 H, s, H-2 A), 8.29 (1
H, s, H-8 A), 7.78 (1 H, d, J = 9.5 Hz, H-6 U), 7.53 (1 H, s,
H-6 T), 6.44 (1 H, dd, J = 7.0 and 7.5 Hz, H-1¢ A), 6.19 (1 H,
dd, J = 8.0 and 8.5 Hz, H-1¢ T), 6.11 (1 H, d, J = 11.0 Hz, H-
1¢ U), 5.80 (1 H, d, J = 9.5 Hz, H-5 U), 3.35 (2 H, m, CH2 e
Lys); H-3¢, H-2¢ U and H-3¢ A are buried under the residual
HDO signal; 2.55 (2 H, m, H2-2¢ A), 2.32 (2 H, m, H2-2¢ T),
1.84 (3 H, s, CH3 T), 1.68–1.49 (4 H, overlapped signals,
CH2 b and CH2 d Lys), 1.19 (2 H, m, CH2 g Lys). 31P NMR
(161.98 MHz, D2O): d = 2.20, 1.92.
at: d = 7.40 (1 H, d, J = 8.0 Hz, H-6 U), 7.67 (1 H, s, H-6 T),
6.35 (1 H, dd, J = 6.5 and 6.5 Hz, H-1¢ T), 6.09 (1 H, d,
J = 8.5 Hz, H-1¢ U), 5.91 (1 H, d, J = 8.0 Hz, H-5 U); H-3¢,
H-2¢ U and H-3¢ T are buried under the residual HDO signal;
4.15 (5 H, overlapped signals, H-4¢ U, H-4¢ T, CH a Lys and
H2-5¢ T), 3.85 (2 H, m, H2-5¢ U), 3.28 (2 H, m, CH2 e Lys),
2.36 (2 H, m, H2-2¢ T), 1.93 (3 H, s, CH3 T), 1.85 (2 H, m,
CH2 b Lys), 1.79 (2 H, m, CH2 d Lys), 1.22 (2 H, m, CH2 g
Lys). Compound 19: 1H NMR (500 MHz, D2O) significant
signals at: d = 7.91 (1 H, d, J = 8.0 Hz, H-6 U), 7.68 (1 H, s,
H-6 T), 6.32 (1 H, dd, J = 6.5 and 6.5 Hz, H-1¢ T), 6.10 (1 H,
d, J = 8.0 Hz, H-1¢ U), 5.94 (1 H, d, J = 8.0 Hz, H-5 U); H-
3¢, H-2¢ U and H-3¢ T are buried under the residual HDO
signal; 4.47 (2 H, overlapped signals, H-4¢ U, H-4¢ T and H-
Synlett 2004, No. 11, 1975–1979 © Thieme Stuttgart · New York