Synthesis and photophysical properties of novel cyclonucleosides-substituent effects on fluorescence emission

Article abstract of DOI:10.1016/j.tet.2008.05.098

An intramolecular [3+2]-cycloaddition between an azide and a disubstituted alkyne afforded a number of novel adenosine-derived cyclonucleosides, which exhibited fluorescence in the visible range. The synthesis and photophysical properties of these potenti

Full text of DOI:10.1016/j.tet.2008.05.098

Tetrahedron 64 (2008) 7151–7158
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis and photophysical properties of novel cyclonucleosidesdsubstituent
effects on fluorescence emission
y
*
Gavin O’Mahony , Eleonor Ehrman, Morten Grøtli
Department of Chemistry, Medicinal Chemistry, University of Gothenburg, Kemiva¨gen 10, 41296 Go¨teborg, Sweden
a r t i c l e i n f o
a b s t r a c t
Article history:
An intramolecular [3þ2]-cycloaddition between an azide and a disubstituted alkyne afforded a number
of novel adenosine-derived cyclonucleosides, which exhibited fluorescence in the visible range. The
synthesis and photophysical properties of these potential fluorescent probes are described.
Ó 2008 Elsevier Ltd. All rights reserved.
Received 15 February 2008
Received in revised form 8 May 2008
Accepted 22 May 2008
Available online 24 May 2008
Keywords:
Fluorescent nucleosides
Cyclonucleosides
Sonogashira
Cycloaddition
1. Introduction
different structures, including coumarin,4 naphthalene,5 BODIPY,6
thioxanthone,7
imidazol[1,2-a]pyridine8
and
pyrimidopyr-
Fluorescent nucleotides have found a plethora of applications in
life science including their use in signal transduction research of G-
proteins and kinases, as probes for nucleoside-utilising proteins or
for labelling of DNA through incorporation by polymerases.1
We have previously reported the preparation of some novel
fluorescent adenosine-based nucleosides (‘fluorosides’) possessing
a bridging 1,2,3-triazole moiety between the purine base and the
ribose.2 These nucleosides can be regarded as fluorescent derivatives
of 8-methanocyclo-adenosine derivative 1, a micromolar inhibitor of
Brugia malayi (a tropical nematode parasite) asparaginyl tRNA syn-
thetase,3 and could be useful to explore the structure, dynamics and
recognition of ligands by the asparaginyl tRNA synthetase (Fig. 1).
It is well established that the substituents in a fluorescent or-
ganic compound significantly influence its absorption and emis-
sion maxima, and quantum yields. Studies of the substituent
effects on fluorophores have been conducted on a variety of
imidoindole,9 and showed that their fluorescence properties could
be successfully modulated by the introduction of appropriate
substituents.
In this paper, we report the complete synthesis and photo-
physical properties of a number of fluorosides.10 We also analysed
the relationship between their fluorescence properties and their
substituents.
In our previous communication,2 we reported the synthesis of
a small number of compounds of structure 2 as well as the fluo-
rescence properties of compound 2a (Scheme 1). In this paper, we
R
N
N
NH2
8
5'
O
1'
4'
3'
N
N
N
[3+2]
O
HO
NH2
N
8
PGO
PGO
2'
2'
N
N
HO
N
N
R
N3
N
4
2
N
O
N
O
S
O
H2N
N
NH2
N
H
O
Sonogashira
N
O
NH2
O
HO
1
PG = protecting group
a R = H
Br
8
N
Figure 1.
O
NH2
N
PGO
PGO
N
N
OH
* Corresponding author. Tel.: þ46 (0) 31 7722905; fax: þ46 (0) 31 7723840.
E-mail address: grotli@chem.gu.se (M. Grøtli).
3
y
Scheme 1. Retrosynthesis of compound 2.
Present address: AstraZeneca R&D Mo¨lndal, 431 83 Mo¨lndal, Sweden.
0040-4020/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2008.05.098

7152
G. O’Mahony et al. / Tetrahedron 64 (2008) 7151–7158
report the synthesis of a number of analogues of 2, with variation of
the substituent at the 4-position of the 1,2,3-triazole moiety. The
effect of such substitutions on the fluorescence properties of the
resulting nucleosides is also investigated.
Thegeneralsyntheticstrategy(Scheme1)wasinessencethesame
as that previously utilised by us. A Sonogashira reaction11 between
a suitably protected 8-bromoadenosine derivative 3 and various
terminal alkynes installed the 8-alkynyl group of cyclisation pre-
cursor 4.2,12 The alkynes were chosen to give products with electron-
withdrawing and electron-donating substituents on the final
1,2,3-triazole ring. This ring was to be formed by a thermal Huisgen
[3þ2]-cycloaddition between the disubstituted alkyne and the
20-azide.
Introduction of the 20-azide was achieved by nucleophilic dis-
placement of the 20-O-triflate of compounds 7. As reported in
our initial communication, this displacement occurred at room
temperature for R¼TMS due to initial cleavage of the TMS group
followed by nucleophilic displacement of the 20-O-triflate. The 20-
azide 8 could not be isolated as it underwent in situ [3þ2]-cyclo-
addition with the alkyne to give the desired 1,2,3-triazole. For
alkyne substituents other than R¼H, the initial nucleophilic sub-
stitution is significantly more difficult due to steric hindrance about
the 20-position. The azide anion must approach the 20-position of 7
from the same side of the sugar ring as the purine base. Bulky
substituents on the alkyne shield this face of the sugar ring, thus
slowing the rate of nucleophilic displacement. For R¼TBDMS (7k),
a 30% yield of the cyclised product (10k) was obtained after 120 h at
room temperature.
The displacement and subsequent cyclisation were more satis-
factorily performed by using 10 equiv of sodium azide and using
microwave heating (150 ꢀC for 15 min). However, these conditions
were largely incompatible with the silyl protecting group. In ad-
dition to the 30,50-O-TIPDS-protected cycloaddition products, some
cleavage of the TIPDS protecting group occurred, with mono-
cleavage at both the 30- and 50-positions being observed as well as
complete TIPDS cleavage to give the highly polar deprotected nu-
cleosides 2. These complex crude reaction mixtures were treated
with ammonium fluoride in methanol to completely remove the
silyl groups.18 The highly polar deprotected products were difficult
to isolate, so the crude deprotection mixture was treated with
acetic anhydride in pyridine to acetylate the 30- and 50-hydroxyl
functionalities affording diacetylated nucleosides 9. These acetate-
protected compounds could be isolated and purified by column
chromatography, affording pure compounds 9 in modest yield (17–
34%) calculated from the crude triflates 7 (Scheme 2).
2. Results and discussion
2.1. Synthesis
8-Bromoadenosine was synthesised using a literature pro-
cedure.13 Following a modified literature procedure,14 simultaneous
protection of its 30- and 50-hydroxyl groups was achieved with
TIPDSCl2 (1,3-dichloro-1,1,3,3-tetraisopropyldisiloxane) affording
known compound 5. This aryl bromide was the substrate for the
Sonogashira reaction, which was used to install the 8-alkynyl
substituents.
The Sonogashira reactions of
5 were performed using
Pd(PPh3)2Cl2 as the palladium source. Attempts to perform the
cross-coupling at room temperature led to rather low conversion of
5 due to competing homocoupling of the alkyne. In addition, the
cross-coupled products 6 and starting material 5 effectively co-
eluted on flash chromatography, leading to poor recovery of pure
product. Performing the cross-coupling using microwave heating
(120 ꢀC,12.5 min) with 4 equiv of the alkyne,10 mol % Pd(PPh3)2Cl2,
20 mol % CuI and 4 equiv of triethylamine in THF led to complete
conversion of 5 to the cross-coupled products 6b–l. The coupling
proceeded smoothly in all cases, providing the desired coupled
products in good yields (73–88%) after flash chromatography. The
coupling of 5 with tert-butyl-ethynyl-dimethylsilane proceeded
smoothly at room temperature. Propiolate derivative 6m was pre-
pared indirectly using 3,3,3-triethoxypropyne (prepared by sodium
hydroxide-mediated hydrolysis15 of trimethyl-triethoxyprop-1-
ynyl-silane16) as the coupling partner to give compound 6l. Use of
ethyl propiolate as the coupling partner gave none of the desired
cross-coupled product with 5, instead addition of the 20-hydroxy to
The 30- and 50-O-acetyl esters were cleaved by treating 9 with
ammonia in methanol at room temperature overnight. Concen-
tration under reduced pressure and drying under vacuum afforded
the analytically pure deprotected nucleosides 2.
2.2. Photophysical properties
The 30,50-di-O-acetyl derivatives 9 were used to measure the UV
absorption and fluorescence emission spectra, due to the in-
solubility of the fully deprotected nucleosides 2. The 30,50-O-TIPDS
protected nucleoside 10b was also sufficiently soluble in organic
solvents to allow analysis of its photophysical characteristics. As
they are electronically isolated from each other, it was assumed that
the nature of the 30- and 50-O protecting groups had no effect on the
absorption or emission wavelengths of the chromophore.
The compounds showed, in general, two absorption bands:
a higher energy transition centred between approximately 240–
260 nm (not shown in Table 1 or Fig. 2) and a higher energy tran-
sition with maxima in the range 308–338 nm. With respect to the
lower energy transition, the nature of the substituent R had an
effect on the UV absorption maxima of compounds 9 and 10. A
the triple bond occurred in a conjugate fashion, affording an a,b-
unsaturated ester. 3,3,3-Triethoxypropyne proved to be less re-
active in the Sonogashira reaction than any of the other alkynes
used, with 20 min of microwave heating to 120 ꢀC required to force
the reaction to completion. An attempt to hydrolyse the orthoester
moiety of 6l using an acidic ion-exchange resin17 (Dowex 50-WX2-
400) in benzene gave a mixture of products by TLC. The use of
trifluoroacetic acid in a 1:1 mixture of ethanol and THF afforded the
desired carboxylic ester 6m in good yield (86%).
Triflation of the 20-hydroxyl group of compounds 6 was per-
formed with trifluoromethanesulfonyl chloride and DMAP in
dichloromethane. Triflates 7b and 7k were used directly in the
subsequent nucleophilic substitution reaction, without recording
their crude NMR spectra. The crude 20-O-triflates 7, despite being
stable to column chromatography, were sufficiently pure to be used
without purification. Attempted triflation of propiolate 6m gave
a very messy reaction, with none of the desired 20-O-trilfate
obtained after careful chromatography of the complex crude mix-
ture. Attempted 20-O-triflation of compounds 6h and 6j failed to
give the desired products, due the presence of unprotected amino
and hydroxyl groups, respectively, which competed with the 20-
hydroxyl group.
substituent, which cannot participate in
p
-conjugation (R¼n-butyl,
10b) had a minimal effect on lmax compared to the parent com-
pound (R¼H, lmax¼307 nm2). A
p-conjugating substituent, e.g.,
a phenyl ring (R¼Ph, 9c) shifted lmax to a longer wavelength. The
presence of electron-donating or electron-withdrawing sub-
stituents in the 4-position of the phenyl ring had only a small effect
on lmax, showing that the extent of conjugation in the chromo-
phore plays a larger role in determining lmax. This is further borne
out by the observation that the presence of a substituted naphthyl
group (9i) gave the highest value for lmax (338 nm).
Excitation at the lower energy band led to fluorescence emission
with maxima in the range 378–455 nm (i.e., in the visible range),
with the value of lem dependant on the triazole substituent, R. A

G. O’Mahony et al. / Tetrahedron 64 (2008) 7151–7158
7153
R
Br
N
N
O
N
NH2
N
O
O
O
NH2
NH2
N
Refs 13 and 14
N
O
i
Si
HO
N
N
Si
O
N
OH
N
O
N
N
Si
HO
OH
O
OH
O
Si
5
6b-k, 6l
6m
ii
iii
R
R
N
N
NH2
N
N
O
O
O
NH2
NH2
N
N
N
R'O
O
O
Si
O
v
iv
N
Si
N
N
N
N
N
N
O
N3
OTf
R'O
O
O
Si
Si
R
N
8
7
R' = Ac
R' = H
9
2
vi
N
OMe
Si(Me)2t-Bu
k
b
c
N
g
h
NH2
C(OEt)3
CO2Et
O
l
N
O
N
Si
m
O
N
N
NH2
10b,k
O
Si
R
CH3
CF3
F
N
d
e
OMe
i
HO
j
f
Scheme 2. (i) RC^CH, Pd(PPh3)2Cl2, NEt3, THF, 120 ꢀC, microwave, 12 min; (ii) TFA, 75% aqueous EtOH, rt, 1.5 h, 86% (for 6l); (iii) trifluoromethanesulfonyl chloride, DMAP, CH2Cl2,
0 ꢀC, 1 h; (iv) NaN3, DMF, 150 ꢀC, microwave, 15 min then rt, see Section 4 for reaction times; (v) (a) NH4F, MeOH, reflux, 5 h then rt, overnight, (b) acetic anhydride, pyridine, rt,
overnight; (vi) NH3, MeOH, rt, overnight.
non-conjugating alkyl substituent (R¼n-butyl, 10b) gave both the
lowest lem and the lowest fluorescence intensity. With respect to
the phenyl-substituted triazoles (9c–e,g), the effect of the p-sub-
stituent on the Stokes shift was unpredictable, with electron-
withdrawing (–CF3, 9e) and electron-donating (–OCH3, 9g)
substituents giving almost identical Stokes shifts in methanol. It
appears that the extent of conjugation in the chromophore plays
a greater role in determining the Stokes shift (i.e., a greater degree
of conjugation led to a longer lem). However, it must be pointed out
that alkyl-substituted triazole 10b exhibited a greater Stokes shift
than either 9c (R¼Ph) or 9d (R¼4-Me–Ph), making such general-
isations of apparently limited utility.
fluorescence spectra of the compounds in methanol (hydrogen
bonding possible) and acetonitrile (non-hydrogen bonding sol-
vent). The absorption maxima were largely insensitive to solvent
changes, with the same values obtained for lmax in either methanol
or acetonitrile. However, in each case, as can be seen from Table 1,
lem was shifted to a shorter wavelength when the emission spectra
0.12
10b
9c
0.1
9d
9e
The influence of hydrogen bonding on the fluorescence prop-
erties of compounds 9 was investigated by measuring the UV and
9g
0.08
9i
0.06
Table 1
Photophysical properties of compounds 9c,d,e,g,i and 10b
a
0.04
0.02
0
Compound
lmax
lem
Stokes shift lem
Stokes shift
(nm) (MeOH) (MeOH)
(MeCN) (MeCN)
(nm)
(nm)
(nm)
(nm)
10b, R¼n-Bu
308
324
326
326
332
385
395
390
415
419
455
77
71
64
89
87
117
378
387
383
395
415
449
70
63
57
69
83
9c, R¼Ph
9d, R¼4-Me–Ph
9e, R¼4-CF3–Ph
9g, R¼4-OMe–Ph
300
320
340
Wavelength (nm)
360
380
400
9i, R¼4-OMe–naphth-6-yl 338
111
Conditions for absorption and emission spectra: 5ꢁ10ꢂ6 M in methanol or
Figure 2. UV absorbance spectra (5ꢁ10ꢂ6 M) of compounds 9c,d,e,g,i and 10b in
a
acetonitrile. Identical values were obtained for lmax in both solvents.
methanol.

7154
18000
G. O’Mahony et al. / Tetrahedron 64 (2008) 7151–7158
10b MeOH
9c MeOH
9c MeCN
9d MeOH
9d MeCN
9e MeOH
9g MeOH
9g MeCN
9i MeOH
was performed using Merck Geduran Si 60 (0.063–0.200 mm) silica
gel. Thin layer chromatography (TLC) was performed using Merck
Silica Gel 60 F254 aluminium-backed plates and visualised using UV
light (254 and/or 366 nm) and potassium permanganate dip. The
solvents used to determine Rf values are the same as used for
chromatographic purification, unless otherwise stated. Microwave
heating was performed using a Biotage Initiator microwave, with
a fixed hold time at the desired reaction temperature (wattage
was automatically varied to maintain the desired temperature).
Nucleoside numbering is used throughout.
16000
14000
12000
10000
8000
6000
4000
2000
0
4.2. General procedure (A) for Sonogashira reactions of 30,50-
O-TIPDS-8-bromoadenosine 5 using microwave heating
A
solution of 30,50-O-TIPDS-8-bromoadenosine
5 (500 mg,
0.85 mmol), Pd(PPh3)2Cl2 (60 mg, 0.085 mmol), CuI (32 mg,
0.17 mmol) and triethylamine (344 mg, 3.40 mmol) in THF (10 mL)
was placed in a sealed 25 mL microwave vial. The appropriate
terminal alkyne (4 equiv) was then added and the mixture heated
to 120 ꢀC for 12.5 min (fixed hold time on). The solvents were re-
moved under reduced pressure and the residue dissolved in CHCl3
(100 mL) and the solution washed with 1 M aqueous HCl (50 mL),
water (50 mL) and brine (50 mL), dried over MgSO4 and concen-
trated under reduced pressure affording the crude product, which
was purified by column chromatography (19:1 CH2Cl2/MeOH).
360
400
440
480
520
Wavelength (nm)
560
600
Figure 3. Fluorescence emission spectra (5ꢁ10ꢂ6 M) of compounds 9c,d,e,g,i and 10b
in methanol (smooth lines) and acetonitrile (dotted lines). For each compound lex
-
¼
lmax (see Table 1).
were recorded in acetonitrile compared to the values obtained in
methanol. In other words, a larger Stokes shift is observed when the
compounds are analysed in a solvent that is a hydrogen bond donor.
Compound 9e (R¼4-CF3–Ph) exhibited an anomalously large dif-
ference in Stokes shift on changing from methanol to acetonitrile,
with a difference of 20 nm between the two solvents (the median
difference in Stokes shift exhibited by the other compounds being
7 nm).
Fluorescence emission intensity was also affected by the solvent,
but not in a predictable way, with 9c and 9g emitting more intense
fluorescence in acetonitrile, while the opposite was true for com-
pound 9d (Fig. 3).
4.2.1. 30,50-O-TIPDS-8-(hex-1-ynyl)-adenosine 6b
Yield: 366 mg (73%), pale grey foam. Rf 0.5 (9:1 CHCl2/MeOH);
20
[a
]
ꢂ40.4 (c 0.1, CHCl3); nmax (KBr)/cmꢂ1 3416, 3178, 2239 (C^C),
D
1646, 1599, 1464, 1329, 1298, 1137, 1088, 1037, 885, 694. dH
(400 MHz, CDCl3) 8.22 (1H, s), 6.13 (1H, s), 5.93 (2H, br s), 5.58–5.53
(1H, m), 4.81 (1H, d, J¼5.9 Hz), 4.05–3.99 (3H, m), 3.36 (1H, br s),
2.51 (2H, t, J¼7.3 Hz), 1.65 (2H, quin, J¼7.3 Hz), 1.48 (2H, sext,
J¼7.3 Hz), 1.26–1.00 (28H, m), 0.94 (3H, t, J¼7.3 Hz); dC (100 MHz,
CDCl3) 155.2, 153.3, 148.9, 135.6, 119.6, 99.1, 89.9, 82.3, 74.7, 72.1,
69.5, 62.9, 30.0, 22.2, 19.3, 17.54, 17.48, 17.44, 17.38, 17.3, 17.2, 17.12,
17.09, 13.6, 13.3, 13.2, 12.8, 12.7; MS (FAB) m/z (%)¼590 (68), 216
(100); HRMS-FAB: m/z [MþHþ] calcd for C28H47N5O5Si2: 590.3193,
found: 590.3189. Anal. Calcd for C28H47N5O5Si2: C, 57.01; H, 8.03; N,
11.87. Found: C, 56.89; H, 7.97; N, 11.81.
3. Conclusion
We have synthesised a series of adenosine-based nucleosides
possessing
a bridging 1,5-disubstituted 1,2,3-triazole moiety
between the purine base and the ribose. The 4-substituent of the
1,2,3-triazole ring was easily varied, through the use of various
terminal alkynes in a Sonogashira cross-coupling reaction. Bulky
substituents on the alkynes slowed down both the nucleophilic
displacement of the 20-O-triflates as well as the cycloaddition
reaction. The final compounds of general structure 2 and 10 were
found to be fluorescent with emission centred at around 400 nm
and with a Stokes shift of the order of 57–111 nm. Analysis of the
solvatochromic behaviour of these nucleosides showed that lem
was shifted to a shorter wavelength when the emission was
recorded in acetonitrile compared with methanol. Fluorescence
emission intensity was also affected by the solvent, but not in
a predictable way.
4.2.2. 30,50-O-TIPDS-8-(phenylethynyl)-adenosine 6c
20
Yield: 385 mg (74%), yellow glass. Rf 0.5 (9:1 CHCl2/MeOH); [a]
D
ꢂ46.0 (c 0.09, CHCl3); nmax (KBr)/cmꢂ1 3417, 3171, 2218 (C^C),1653,
1598, 1465, 1328, 1299, 1136, 1090, 1036, 885, 756, 691. dH
(400 MHz, CDCl3) 8.23 (1H, s), 7.66–7.63 (2H, m), 7.47–7.36 (3H, m),
6.24 (1H, s), 5.68 (2H, br s), 5.56 (1H, t, J¼6.1 Hz), 4.87–4.84 (1H, m),
4.09–4.01 (3H, m), 3.31 (1H, br s), 1.19–1.02 (28H, m); dC (100 MHz,
CDCl3) 155.5, 153.6, 149.0, 135.1, 132.3, 130.1, 128.6, 120.5, 120.0,
96.2, 90.1, 82.5, 77.6, 74.6, 72.1, 62.9, 17.6, 17.5, 17.44, 17.39, 17.3, 17.2,
17.14, 17.12, 17.09, 13.3, 13.2, 12.78, 12.75. Anal. Calcd for
C30H43N5O5Si2: C, 59.08; H, 7.11; N, 11.48. Found: C, 58.94; H, 7.05;
N, 11.41.
4. Experimental
4.1. General
4.2.3. 30,50-O-TIPDS-8-(p-tolylethynyl)-adenosine 6d
20
Yield: 456 mg (86%), yellow solid. Rf 0.5 (9:1 CHCl2/MeOH); [a]
D
ꢂ47.1 (c 0.09, CHCl3); nmax (KBr)/cmꢂ1 3414, 3172, 2216 (C^C),
1646, 1598, 1464, 1329, 1298, 1134, 1089, 1036, 885, 698. dH
(400 MHz, CDCl3) 8.19 (1H, s), 7.46 (2H, d, J¼8.1 Hz), 7.13 (2H, d,
J¼8.1 Hz), 6.58 (2H, br s), 6.22 (1H, s), 5.53 (1H, t, J¼5.9 Hz), 4.84
(1H, d, J¼5.9 Hz), 4.09–3.99 (3H, m), 3.57 (1H, br s), 2.35 (3H, s),
1.18–0.97 (28H, m); dC (100 MHz, CDCl3) 155.5, 153.5, 149.0, 140.6,
135.3, 132.2, 129.4, 119.9, 117.4, 96.6, 90.0, 82.4, 77.4, 74.6, 72.2, 63.0,
21.8, 17.6, 17.50, 17.46, 17.4, 17.3, 17.2, 17.12, 17.09, 13.3, 13.2, 12.78,
12.76. MS (FAB) m/z (%)¼624 (36), 250 (100); HRMS-FAB: m/z
[MþHþ] calcd for C31H45N5O5Si2: 624.3037, found: 624.3030.
Solvents were dried using standard procedures. 1H NMR spectra
were recorded at 400 MHz and 13C NMR spectra recorded at
100 MHz in the solvents specified using a Jeol ECX spectrometer.
Spectra were referenced to residual non-deuterated solvent (1H
NMR: CDCl3 7.26 ppm, DMSO-d6 2.55 ppm and 13C NMR: CDCl3
77.2 ppm, DMSO-d6 39.5 ppm). Mass spectra were run using the
FAB (p-nitrobenzyl alcohol) method. IR spectra were recorded as
KBr disks. Fluorescence and UV spectra were obtained using a Mo-
lecular Devices SpectraMax M2 plate reader. Flash chromatography

G. O’Mahony et al. / Tetrahedron 64 (2008) 7151–7158
7155
4.2.4. 30,50-O-TIPDS-8-(p-trifluoromethylphenylethynyl)-
adenosine 6e
(C^C), 1636, 1602, 1468, 1330, 1297, 1135, 1089, 1035, 886, 859, 693.
dH (400 MHz, CDCl3) 8.24 (1H, s), 8.12 (1H, s), 7.76 (1H, d, J¼5.0 Hz),
7.74 (1H, d, J¼5.0 Hz), 7.62 (1H, dd, J¼8.9, 1.6 Hz), 7.20 (1H, dd,
J¼8.9, 2.4 Hz), 7.14 (1H, d, J¼2.4 Hz), 6.30 (1H, d, J¼1.1 Hz), 5.63 (2H,
br s), 5.56 (1H, t, J¼6.0 Hz), 4.89–4.87 (1H, m), 4.09–4.05 (3H, m),
3.95 (3H, s), 3.33 (1H, br s), 1.17–1.02 (28H, m); dC (100 MHz, CDCl3)
159.1,155.4,153.5,149.1,135.4, 135.1,132.9,132.0,129.7,128.7, 128.2,
127.2, 120.1, 119.9, 115.2, 105.9, 97.1, 90.1, 82.5, 74.7, 72.2, 63.0, 55.5,
17.6, 17.49, 17.45, 17.4, 17.30, 17.27, 17.14, 17.11, 13.3, 13.2, 17.79, 17.77;
MS (FAB) m/z (%)¼690 (44), 316 (100); HRMS-FAB: m/z [MþHþ]
calcd for C35H47N5O6Si2: 690.3143, found: 690.3129. Anal. Calcd for
Yield: 461 mg (80%), yellow foam. Rf 0.5 (9:1 CHCl2/MeOH);
20
[
a]
ꢂ48.4 (c 0.09, CHCl3); nmax (KBr)/cmꢂ1 3330, 3178, 2226
D
(C^C), 1646, 1465, 1323, 1297, 1132, 1090, 1067, 1037, 885, 843, 696.
dH (400 MHz, CDCl3) 8.26 (1H, s), 7.77 (2H, d, J¼8.0 Hz), 7.67 (2H, d,
J¼8.0 Hz), 6.21 (1H, s), 5.62 (2H, br s), 5.57 (1H, t, J¼6.3 Hz), 4.88–
4.86 (1H, m), 4.08–4.02 (3H, m), 3.31 (1H, br s), 1.24–1.03 (28H, m);
dC (100 MHz, CDCl3) 155.5, 153.9, 149.1, 134.5, 132.6, 131.7 (q,
J¼33 Hz), 128.6, 125.6 (q, J¼4 Hz), 124.2, 123.7 (q, J¼251 Hz), 94.3,
90.1, 82.5, 79.6, 74.6, 72.0, 62.8, 17.53, 17.45, 17.43, 17.36, 17.3, 17.2,
17.11, 17.07, 13.3, 13.2, 12.78, 12.75; MS (FAB) m/z (%)¼678 (52), 304
(100); HRMS-FAB: m/z [MþHþ] calcd for C31H42F3N5O5Si2:
678.2754, found: 678.2752. Anal. Calcd for C31H42F3N5O5Si2: C,
54.93; H, 6.25; N, 10.33. Found: C, 55.08; H, 6.21; N, 10.30.
C35H47N5O6Si2: C, 60.93; H, 6.87; N, 10.15. Found: C, 60.93; H, 6.76;
N, 10.06.
4.2.9. 30,50-O-TIPDS-8-(cycloxexan-1-ol-1-ethynyl)-adenosine 6j
Yield: 427 mg (80%), grey foam. Rf 0.5 (9:1 CHCl2/MeOH); [
20
a
]
D
4.2.5. 30,50-O-TIPDS-8-(p-fluorophenylethynyl)-adenosine 6f
ꢂ36.5 (c 0.09, CHCl3); nmax (KBr)/cmꢂ1 3378, 3210, 2234 (C^C),
1643, 1598, 1464, 1330, 1136, 1081, 1037, 885, 862, 697. dH (400 MHz,
CDCl3) 8.19 (1H, s), 6.11 (1H, s), 5.91 (2H, br s), 5.50 (1H, t, J¼6.2 Hz),
4.83 (1H, d, J¼6.2 Hz), 4.20 (1H, br s), 4.08–3.97 (3H, m), 3.33 (1H,
s), 2.14–2.01 (2H, m), 1.82–1.49 (6H, m), 1.38–0.90 (30H, m); dC
(100 MHz, CDCl3) 155.3, 153.6, 148.9, 134.5, 119.3, 101.6, 90.0, 82.4,
74.5, 72.4, 72.0, 68.8, 62.8, 39.8, 39.6, 39.3, 25.1, 23.1, 17.54, 17.46,
17.42, 17.38, 17.25, 17.10, 17.06, 13.3, 13.2, 12.76, 12.73; MS (FAB) m/z
(%)¼632 (52), 258 (100); HRMS-FAB: m/z [MþHþ] calcd for
Yield: 402 mg (76%), yellow foam. Rf 0.5 (9:1 CHCl2/MeOH);
20
[
a]
ꢂ38.4 (c 0.1, CHCl3); nmax (KBr)/cmꢂ1 3414, 3172, 2220 (C^C),
D
1645, 1598, 1465, 1329, 1297, 1130, 1091, 1037, 885, 837, 695. dH
(400 MHz, CDCl3) 8.24 (1H, s), 7.65 (2H, ddt, J¼9.5, 5.1, 2.6 Hz), 7.14–
7.08 (2H, m), 6.21 (1H, d, J¼1.1 Hz), 5.61 (2H, br s), 5.57 (1H, t,
J¼6.2 Hz), 4.87–4.84 (1H, m), 4.08–4.00 (3H, m), 3.31 (1H, d,
J¼1.1 Hz), 1.22–1.02 (28H, m); dC (100 MHz, CDCl3) 164.9, 162.4,
155.4,153.7, 149.1, 135.0, 134.5 (d, J¼9 Hz), 120.2 (d, J¼210 Hz), 116.7
(d, J¼3 Hz), 116.1 (d, J¼22 Hz), 95.1, 90.1, 82.5, 74.7, 72.1, 62.9, 17.54,
17.48, 17.44, 17.38, 17.3, 17.2, 1712, 17.09, 13.3, 13.2, 12.78, 12.76; MS
(FAB) m/z (%)¼628 (45), 254 (100); HRMS-FAB: m/z [MþHþ] calcd
for C30H42FN5O5Si2: 628.2786, found: 628.2779. Anal. Calcd for
C
C
30H49N5O6Si2: 632.3200, found: 632.3292. Anal. Calcd for
30H49N5O6Si2: C, 57.02; H, 7.82; N,11.08. Found: C, 57.12; H, 7.75; N,
10.88.
C
30H42FN5O5Si2: C, 57.39; H, 6.74; N, 11.15. Found: C, 57.28; H, 6.67;
4.2.10. 30,50-O-TIPDS-8-([tert-butyldimethylsilyl]ethynyl)-
adenosine 6k
N, 11.08.
This compound was prepared by stirring overnight at room
temperature, using the same amounts of reagents as for the mi-
4.2.6. 30,50-O-TIPDS-8-(p-methoxyphenylethynyl)-adenosine 6g
Yield: 476 mg (88%), yellow solid. Rf 0.5 (9:1 CHCl2/MeOH); [
20
a
]
crowave method. Yield: 239 mg (43%), yellow foam. Rf 0.6 (9:1
D
20
ꢂ38.7 (c 0.09, CHCl3); nmax (KBr)/cmꢂ1 3321, 3174, 2214 (C^C),
1645, 1602, 1465, 1329, 1296, 1252, 1135, 1090, 1035, 885, 832, 694.
dH (400 MHz, CDCl3) 8.23 (1H, s), 7.60 (2H, dt, J¼9.3, 2.3 Hz), 6.92
(2H, dt, J¼9.3, 2.3 Hz), 6.24 (1H, d, J¼1.1 Hz), 5.60 (2H, br s), 5.56
(1H, t, J¼6.1 Hz), 4.86–4.83 (1H, m), 4.09–4.01 (3H, m), 3.86 (3H, s),
3.30 (1H, d, J¼1.1 Hz), 1.19–1.02 (28H, m); dC (100 MHz, CDCl3)
161.0, 155.4, 153.4, 149.0, 135.5, 134.0, 120.0, 114.3, 112.4, 96.7, 90.0,
82.4, 76.7, 74.7, 72.2, 63.0, 55.4, 17.6, 17.49, 17.45, 17.4, 17.3, 17.14,
17.12, 17.09, 13.3, 13.2, 12.77, 12.75; MS (FAB) m/z (%)¼640 (52), 266
(100); HRMS-FAB: m/z [MþHþ] calcd for C31H45N5O6Si2: 640.2986,
found: 640.2989. Anal. Calcd for C31H45N5O6Si2: C, 58.19; H, 7.09; N,
10.94. Found: C, 58.28; H, 7.04; N, 10.86.
CHCl2/MeOH); [
a]
ꢂ36.6 (c 0.07, CHCl3); nmax (KBr)/cmꢂ1 3414,
D
3177, 2167 (C^C), 1644, 1596, 1466, 1327, 1135, 1091, 1037, 885, 826,
695. dH (400 MHz, CDCl3) 8.21 (1H, s), 6.15 (1H, d, J¼1.1 Hz), 5.74
(2H, br s), 5.50 (1H, t, J¼6.4 Hz), 4.83 (1H, d, J¼6.4 Hz), 4.09–4.00
(3H, m), 3.29 (1H, d, J¼1.5 Hz), 1.17–0.99 (37H, m), 0.25 (6H, s); dC
(100 MHz, CDCl3) 155.3, 153.8, 140.0, 134.9, 119.8, 103.0, 92.7, 90.1,
82.5, 74.5, 72.2, 63.0, 26.2, 17.6, 17.5, 17.44, 17.39, 17.3, 17.12, 17.09,
16.8, 13.3, 13.2, 12.79,12.75, ꢂ4.9; HRMS-FAB: m/z [MþHþ] calcd for
C
C
30H53N5O5Si3: 648.3432, found: 648.3471. Anal. Calcd for
30H53N5O5Si3: C, 55.6; H, 8.2; N, 10.8. Found: C, 55.5; H, 8.3; N,
10.4.
4.2.11. 30,50-O-TIPDS-8-(triethoxyprop-1-ynyl)-adenosine 6l
4.2.7. 30,50-O-TIPDS-8-(m-aminophenylethynyl)-adenosine 6h
This reaction was heated in the microwave to 150 ꢀC for 20 min
20
Yield: 389 mg (73%), yellow solid. Rf 0.5 (9:1 CHCl2/MeOH); [
a
]
(fixed hold time on) to force the reaction to completion. Yield:
D
ꢂ40.2 (c 0.09, CHCl3); nmax (KBr)/cmꢂ1 3373, 3172, 2216 (C^C),
1638, 1599, 1576, 1464, 1329, 1299, 1130, 1089, 1036, 885, 692. dH
(400 MHz, CDCl3) 8.21 (1H, s), 7.14 (1H, t, J¼7.7 Hz), 7.00 (1H, d,
J¼7.7 Hz), 6.89 (1H, s), 6.71 (1H, d, J¼7.7 Hz), 6.22 (1H, s), 6.07 (2H,
br s), 5.54 (1H, t, J¼6.0 Hz), 4.86 (1H, d, J¼6.0 Hz), 4.12–3.99 (3H, m),
3.78 (2H, br s), 3.43 (1H, br s), 1.19–1.01 (28H, m); dC (100 MHz,
CDCl3) 155.3, 153.6, 149.1, 146.6, 135.4, 129.6, 122.7, 121.1, 120.1,
118.1, 117.1, 96.7, 90.0, 82.5, 77.0, 62.9, 17.6, 17.49, 17.45, 17.4, 17.3,
17.14, 17.1, 13.3, 13.2, 12.79, 12.76; MS (FAB) m/z (%)¼625 (28), 251
(100); HRMS-FAB: m/z [MþHþ] calcd for C30H44N6O5Si2: 625.2990,
found: 625.2988. Anal. Calcd for C30H44N6O5Si2: C, 57.66; H, 7.10; N,
13.45. Found: C, 57.83; H, 7.06; N, 13.37.
121 mg (47%), brown glass. Rf 0.4 (9:1 CHCl2/MeOH); [
a
]
ꢂ41.3 (c
20
D
0.07, CHCl3); nmax (KBr)/cmꢂ1 3444, 1646, 1464, 1131, 1088, 1037,
884, 697. dH (400 MHz, CDCl3) 8.21 (1H, s), 6.09 (1H, d, J¼1.5 Hz),
5.95 (2H, br s), 5.46 (1H, t, J¼5.9 Hz), 4.86 (1H, dt, J¼5.9, 1.5 Hz),
4.06–3.99 (3H, m), 3.79 (6H, q, J¼7.2 Hz), 3.26 (1H, d, J¼1.5 Hz), 1.28
(9H, t, J¼7.2 Hz), 1.15–1.00 (28H, m); dC (100 MHz, CDCl3) 155.5,
154.0,149.1,133.6,120.0,109.2, 90.6, 90.0, 82.5, 77.3, 74.4, 72.0, 62.8,
59.6, 17.5, 17.44, 17.42, 17.38, 17.3, 17.11, 17.07, 14.9, 13.3, 13.2, 12.77,
12.74. HRMS-FAB: m/z [MþHþ] calcd for C31H53N5O8Si2: 680.3511,
found: 680.3541.
4.2.12. 30,50-O-TIPDS-8-(carboethoxyethynyl)-adenosine 6m
A solution of 30,50-O-TIPDS-8-(triethoxyprop-1-ynyl)-adenosine
6l (122 mg, 0.16 mmol) and trifluoroacetic acid (2 drops) in 75%
aqueous ethanol (20 mL) and THF (5 mL) was stirred at room
temperature for 1.5 h. The mixture was concentrated to dryness
and the residue azeotroped with ethanol (3ꢁ10 mL) to remove
4.2.8. 30,50-O-TIPDS-8-(2-methoxynaphthyl-6-ethynyl)-
adenosine 6i
Yield: 440 mg (76%), pale brown powder. Rf 0.5 (9:1 CHCl2/
20
MeOH); [
a
]
ꢂ34.7 (c 0.09, CHCl3); nmax (KBr)/cmꢂ1 3446, 2212
D

7156
G. O’Mahony et al. / Tetrahedron 64 (2008) 7151–7158
water. The dried residue was purified by column chromatography
(19:1 CHCl2/MeOH) affording 80 mg (86%) 6m as a pale brown
J¼13.2, 2.9 Hz), 4.05–4.01 (2H, m), 1.21–1.03 (28H, m), 1.02 (9H, s),
0.25 (6H, s).
20
foam. Rf 0.5 (9:1 CHCl2/MeOH); [
a]
ꢂ36.9 (c 0.09, CHCl3); nmax
D
(KBr)/cmꢂ1 3447, 2230 (C^C), 1717 (C]O), 1638, 1460, 1325, 1248,
1136, 1088, 1037, 884, 697. dH (400 MHz, CDCl3) 8.25 (1H, s), 6.17
(2H, br s), 6.10 (1H, d, J¼1.5 Hz), 5.44 (1H, t, J¼6.0 Hz), 4.87 (1H, dt,
J¼6.0, 1.5 Hz), 4.34 (2H, q, J¼7.2 Hz), 4.07–3.98 (3H, m), 3.36 (1H, d,
J¼1.5 Hz), 1.14–1.02 (28H, m); dC (100 MHz, CDCl3) 155.9, 154.8,
152.5, 149.2, 132.0, 128.5, 89.9, 85.5, 82.7, 74.4, 73.1, 71.8, 63.0, 62.6,
17.53, 17.45, 17.44, 17.37, 17.3, 17.11, 17.06, 14.1, 13.3, 13.2, 12.78, 12.74;
MS (FAB) m/z (%)¼606 (30), 232 (100); HRMS-FAB: m/z [MþHþ]
calcd for C27H43N5O7Si2: 606.2779, found: 606.2780.
4.3.6. 30,50-O-TIPDS protected n-butyl-substituted triazole 10b
30,50-O-TIPDS-8-(hex-1-ynyl)-adenosine 6b (250 mg, 0.42 mmol)
was 20-O-triflated according to general procedure B, affording crude
7b as a pale yellow solid (212 mg). A mixture of this crude 7b and
sodium azide (189 mg, 2.90 mmol) in DMF (5 mL) in a sealed
microwave vial was heated to 150 ꢀC in the microwave for 15 min
(fixed hold time on) and the resulting solution stirred at room
temperature for a further 72 h affording a pale brown suspension.
The solvents were removed under reduced pressure and the resi-
due coevaporated with toluene (3ꢁ25 mL). The solid residue was
partitioned between water (50 mL) and CHCl3 (3ꢁ50 mL). The
combined organic extracts were washed with brine, dried over
MgSO4 and concentrated under reduced pressure. Purification by
4.3. General procedure (B) for 20-O-triflation of 30,50-O-TIPDS-
8-alkynyladenosines 6
column chromatography (19:1 CHCl2/MeOH) afforded 43 mg (24%)
20
Trifluoromethanesulfonyl chloride (1.2 equiv) was added at 0 ꢀC
to a solution of the 30,50-O-TIPDS-8-alkynyladenosine 6 (1 equiv)
and DMAP (3 equiv) in dry CH2Cl2 (to give a 0.1 M concentration of
the secondary alcohol) and the resulting mixture stirred at 0 ꢀC for
1 h. The reaction mixture was diluted with CHCl3 (100 mL) and
washed with 1% aqueous acetic acid (75 mL). The aqueous layer was
extracted with CHCl3 (100 mL) and the combined organic extracts
washed with saturated aqueous NaHCO3 (75 mL) and brine
(75 mL), dried over MgSO4 and concentrated under vacuum,
affording the crude product 7, which was used in subsequent re-
actions without further purification.
10b as a colourless glass. Rf 0.52 (9:1 CHCl2/MeOH); [
a
]
D
ꢂ55.0
(c 0.05, CHCl3); nmax (KBr)/cmꢂ1 3445, 1652, 1594, 1462, 1055, 885,
693. dH (400 MHz, CDCl3) 8.42 (1H, s), 6.66 (1H, d, J¼4.5 Hz), 5.84
(2H, br s), 5.45 (1H, dd, J¼4.2, 1.9 Hz), 5.11 (1H, dd, J¼4.5, 2.0 Hz),
4.22 (1H, dt, J¼9.6, 4.0 Hz), 3.99 (1H, dd, J¼11.4, 4.0 Hz), 3.45 (1H,
dd, J¼11.4, 9.6 Hz), 3.15 (2H, t, J¼7.6 Hz), 1.86 (2H, quin, J¼7.6 Hz),
1.45 (2H, sext, J¼7.6 Hz), 1.16–0.91 (31H, m); dC (100 MHz, CDCl3)
155.5, 154.2, 149.9, 147.6, 137.6, 121.6, 120.6, 85.8, 79.4, 78.6, 65.9,
63.7, 30.7, 25.4, 22.4, 17.6, 17.43, 17.38, 17.3, 17.2, 17.1, 17.0, 14.0, 13.53,
13.45, 13.2, 13.0, 12.5; MS (FAB) m/z (%)¼615 (100); HRMS-FAB: m/z
[MþHþ] calcd for C28H46N8O4Si2: 615.3259, found: 615.3245.
4.3.1. 20-O-Triflyl-30,50-O-TIPDS-8-(phenylethynyl)-adenosine 7c
768 mg (1.26 mmol) of 30,50-O-TIPDS-8-(phenylethynyl)-adeno-
sine 6c afforded 935 mg crude 7c as a pale yellow solid. dH
(400 MHz, CDCl3) 8.23 (1H, s), 7.64–7.62 (2H, m), 7.48–7.41 (3H, m),
6.36 (1H, s), 5.93 (1H, d, J¼5.1 Hz), 5.71 (1H, dd, J¼8.8, 5.1 Hz),
4.17–4.12 (1H, m), 4.08–4.03 (2H, m), 1.19–1.02 (28H, m).
4.3.7. 30,50-O-TIPDS protected tert-butyldimethylsilyl-substituted
triazole 10k
30,50-O-TIPDS-8-([tert-butyldimethylsilyl]ethynyl)-adenosine 6k
(203 mg, 0.31 mmol) was 20-O-triflated according to general pro-
cedure B, affording crude 7k as a colourless glass (232 mg). A mix-
ture this crude 7k and sodium azide (98 mg, 1.50 mmol) in DMF
(5 mL) was stirred at room temperature for 21 h affording a pale
brown suspension. The solvents were removed under reduced
pressure and the residue coevaporated with toluene (3ꢁ25 mL). The
solid residue was partitioned between water (50 mL) and CHCl3
(3ꢁ50 mL). The combined organic extracts were washed with brine,
dried over MgSO4 and concentrated under reduced pressure. Puri-
4.3.2. 20-O-Triflyl-30,50-O-TIPDS-8-(p-tolylethynyl)-adenosine 7d
415 mg (0.67 mmol) of 30,50-O-TIPDS-8-(p-tolylethynyl)-adeno-
sine 6d afforded 506 mg crude 7d as a yellow foam. dH (400 MHz,
CDCl3) 8.22 (1H, s), 7.51 (2H, d, J¼8.1 Hz), 7.23 (2H, d, J¼8.1 Hz), 6.36
(1H, s), 5.89 (1H, d, J¼5.6 Hz), 5.67 (1H, dd, J¼8.6, 5.6 Hz), 4.17–4.11
(1H, m), 4.07–4.02 (2H, m), 2.41 (3H, s), 1.19–0.99 (28H, m).
fication by column chromatography (19:1 CHCl2/MeOH) afforded
60 mg(30%) 10k as paleyellowsolid. Rf 0.65(9:1 CHCl2/MeOH);[a]
D
20
4.3.3. 20-O-Triflyl-30,50-O-TIPDS-8-(p-trifluoromethylphenyl-
ethynyl)-adenosine 7e
ꢂ87.6 (c 0.1, CHCl3); nmax (KBr)/cmꢂ1 3386, 1637, 1576, 1465, 1146,
1115,1039, 886, 841, 780, 702. dH (400 MHz, CDCl3) 8.42 (1H, s), 6.67
(1H, d, J¼4.7 Hz), 5.88 (2H, br s), 5.49 (1H, dd, J¼4.2, 2.0 Hz), 5.16 (1H,
dd, J¼4.7, 2.0 Hz), 4.24 (1H, dt, J¼9.3, 4.2 Hz), 3.98 (1H, dd, J¼11.4,
4.2 Hz), 3.42 (1H, dd, J¼11.4, 9.3 Hz),1.17–0.96 (37H, m), 0.55 (3H, s),
0.54 (3H, s); dC (100 MHz, CDCl3) 155.7, 154.2, 149.9, 144.4, 137.6,
130.7, 120.5, 85.8, 79.2, 78.8, 65.9, 63.7, 26.8, 17.9, 17.6, 17.44, 17.37,
17.31, 17.27, 17.2, 17.1, 17.04, 16.95, 13.52, 13.48, 13.2, 13.0, 12.5, ꢂ5.4,
ꢂ5.6; HRMS-FAB: m/z [MþHþ] calcd for C30H53N8O4Si3: 674.3576,
found: 674.3502.
186 mg (0.27 mmol) of 30,50-O-TIPDS-8-(p-trifluoromethyl-
phenylethynyl)-adenosine 6e afforded 200 mg crude 7e as a pale
yellow solid. dH (400 MHz, CDCl3) 8.25 (1H, s), 7.75 (2H, d, J¼8.4 Hz),
7.70 (2H, d, J¼8.4 Hz), 6.34 (1H, s), 5.94 (1H, d, J¼5.2 Hz), 5.71 (1H,
dd, J¼9.4, 5.2 Hz), 4.18–4.03 (3H, m), 1.19–1.03 (28H, m).
4.3.4. 20-O-Triflyl-30,50-O-TIPDS-8-(2-methoxynaphthyl-6-ethynyl)-
adenosine 7g
218 mg (0.32 mmol) of 30,50-O-TIPDS-8-(2-methoxynaphthyl-6-
ethynyl)-adenosine 6g afforded 241 mg crude 7g as a pale yellow
solid. dH (400 MHz, CDCl3) 8.23 (1H, s), 8.09 (1H, s), 7.77–7.74 (2H,
m), 7.58 (1H, dd, J¼7.0, 1.0 Hz), 7.23–7.20 (1H, m), 7.14 (1H, d,
J¼2.6 Hz), 6.42 (1H, s), 5.94 (1H, d, J¼5.4 Hz), 5.72 (1H, d, J¼9.4,
5.4 Hz), 4.16–4.03 (3H, m), 3.95 (3H, s), 1.19–1.02 (28H, m).
4.4. General procedure (C) for the preparation of 30,50-di-O-
acetyl triazoles 9
A mixture of a 20-O-triflyl-30,50-O-TIPDS-8-alkynyl-adenosine
(1 equiv) and sodium azide (10 equiv) in DMF (5 mL) in a sealed vial
was heated to 150 ꢀC in a microwave for 15 min (fixed hold time on)
and the resulting solution stirred at room temperature for 120 h
affording a pale brown suspension. The solvent was removed under
reduced pressure and the oily residue coevaporated with toluene
(3ꢁ25 mL). The solid residue was partitioned between water
(50 mL) and CHCl3 (3ꢁ50 mL), and the combined organic extracts
washed with brine, dried over MgSO4 and concentrated under
4.3.5. 20-O-Triflyl-30,50-O-TIPDS-8-([tert-butyldimethyl-
silyl]ethynyl)-adenosine 7k
203 mg (0.31 mmol) of 30,50-O-TIPDS-8-([tert-butyldimethylsi-
lyl]ethynyl)-adenosine 6k afforded 232 mg crude 7k as a colourless
glass. dH (400 MHz, CDCl3) 8.21 (1H, s), 6.26 (1H, s), 5.94 (1H, d,
J¼5.2 Hz), 5.69 (1H, dd, J¼9.3, 5.2 Hz), 5.65 (2H, br s), 4.12 (1H, dd,

G. O’Mahony et al. / Tetrahedron 64 (2008) 7151–7158
7157
reduced pressure. The solid residue was dissolved in methanol
(20 mL) and ammonium fluoride (10 equiv, calculated with respect
to the starting triflate) was added. The mixture was refluxed for 5 h
and then stirred at room temperature overnight. The solvent was
removed under reduced pressure and the solid residue taken up in
pyridine (5 mL) and acetic anhydride (1 mL) was added. The re-
action was stirred overnight at room temperature. The volatiles
were removed under reduced pressure, the oily residue coevapo-
rated with toluene (3ꢁ25 mL) and then purified by column chro-
matography (19:1 CHCl2/MeOH).
dt, J¼9.5, 2.4 Hz), 6.80 (1H, d, J¼4.2 Hz), 6.30 (1H, d, J¼2.2 Hz), 5.96
(2H, br s), 5.24 (1H, d, J¼4.2 Hz), 4.41–4.38 (1H, m), 4.13 (1H, dd,
J¼12.1, 3.1 Hz), 4.10 (1H, dd, J¼12.1, 2.7 Hz), 3.86 (3H, s), 2.25 (3H, s),
1.62 (3H, s); dC (100 MHz, CDCl3) 170.3, 169.7, 160.6, 155.8, 154.4,
149.9, 145.9, 137.2, 129.6, 121.5, 120.5, 120.0, 114.0, 83.1, 79.6, 77.7,
62.9, 62.6, 55.4, 20.8, 20.2; UV (MeOH) lmax
(3
)¼258 (21,840), 333
(18,280); MS (FAB) m/z (%)¼507 (65); HRMS-FAB: m/z [MþHþ] calcd
for C23H22N8O6: 507.1741, found: 507.1731.
4.4.5. 30,50-Di-O-acetyl 4-methoxynaphth-6-yl triazole 9i
422 mg (0.59 mmol) of 20-O-Triflyl-30,50-O-TIPDS-8-(2-
4.4.1. 30,50-Di-O-acetyl phenyl triazole 9c
methoxynaphthyl-6-ethynyl)-adenosine 7i afforded 99 mg (30%)
20
549 mg (0.74 mmol) of 20-O-Triflyl-30,50-O-TIPDS-8-(phenyl-
9i as a yellow glass. Rf 0.49 (9:1 CHCl2/MeOH); [
a
]
þ144.6 (c 0.05,
D
ethynyl)-adenosine 7c afforded 95 mg (27%) 9c as a yellow solid. Rf
CHCl3); nmax (KBr)/cmꢂ1 1746, 1637, 1220. dH (400 MHz, CDCl3) 9.00
(1H, s), 8.46 (1H, dd, J¼8.7, 1.9 Hz), 8.39 (1H, s), 7.73 (2H, dd, J¼8.7,
2.9 Hz), 7.10 (1H, dd, J¼8.7, 2.5 Hz), 7.05 (1H, d, J¼1.9 Hz), 6.78 (1H,
d, J¼4.2 Hz), 6.29 (1H, d, J¼2.2 Hz), 6.13 (2H, br s), 5.24 (1H, d,
J¼4.2 Hz), 4.40 (1H, q, J¼2.8 Hz), 4.15–4.07 (2H, m), 3.89 (3H, s),
2.25 (3H, s), 1.59 (3H, s); dC (100 MHz, CDCl3) 170.3, 169.7, 158.5,
155.7, 154.5, 149.9, 146.2, 137.0, 135.1, 130.2, 128.7, 127.8, 127.1, 125.8,
124.2, 121.2, 120.1, 119.3, 105.8, 83.1, 79.6, 77.8, 63.0, 62.6, 55.4, 20.3,
20
0.44 (9:1 CHCl2/MeOH); [
a
]
þ102.6 (c 0.05, CHCl3). dH (400 MHz,
D
CDCl3) 8.54–8.51 (2H, m), 8.38 (1H, s), 7.50–7.45 (2H, m), 7.43–7.38
(1H, m), 6.79 (1H, d, J¼4.0 Hz), 6.33 (2H, br s), 6.29 (1H, d, J¼2.9 Hz),
5.24 (1H, d, J¼4.0 Hz), 4.39 (1H, q, J¼2.9 Hz), 4.12 (1H, dd, J¼12.3,
2.9 Hz), 4.09 (1H, dd, J¼12.3, 2.9 Hz), 2.24 (3H, s), 1.61 (3H, s); dC
(100 MHz, CDCl3) 170.3, 169.7, 155.8, 154.2, 149.9, 146.0, 137.1, 129.6,
129.0, 128.7, 128.2, 121.3, 120.1, 83.1, 79.6, 77.7, 63.0, 62.6, 20.8, 20.3;
UV (MeOH) lmax
(
3
)¼246 (19,000), 324 (16,800); MS (FAB) m/z
20.8; UV (MeOH) lmax
for C27H24N8O6: C, 58.27; H, 4.35; N, 20.13. Found: C, 58.20; H, 4.43;
N, 20.08.
(
3
)¼240 (52,340), 338 (21,160). Anal. Calcd
(%)¼477 (33); HRMS-FAB: m/z [MþHþ] calcd for C22H20N8O5:
477.1635, found: 477.1630. Anal. Calcd for C22H20N8O5: C, 55.46; H,
4.23; N, 23.52. Found: C, 55.36; H, 4.14; N, 23.41.
4.4.2. 30,50-Di-O-acetyl 4-methylphenyl triazole 9d
4.5. General procedure (D) for deprotection
396 mg (0.61 mmol) of 20-O-Triflyl-30,50-O-TIPDS-8-(4-methyl-
of 30,50-di-O-acetates
phenylethynyl)-adenosine 7d afforded 65 mg (22%) 9d as a yellow
20
solid. Rf 0.46 (9:1 CHCl2/MeOH); [
a
]
þ114.8 (c 0.05, CHCl3). dH
D
The 30,50-di-O-acetyl compounds were dissolved in 7 N ammo-
nia in methanol (5 mL) and the mixture stirred at room tempera-
ture for 20 h (after approximately 10 min, the solutions became
cloudy). The solvents were removed under reduced pressure and
the residue dried under vacuum for 20 h affording the pure product
without the need for chromatographic purification.
(400 MHz, CDCl3) 8.35 (2H, d, J¼8.0 Hz), 8.34 (1H, s), 7.21 (2H, d,
J¼8.0 Hz), 6.76 (1H, d, J¼4.2 Hz), 6.55 (2H, br s), 6.26 (1H, d,
J¼2.6 Hz), 5.23 (1H, d, J¼4.2 Hz), 4.38 (1H, q, J¼2.6 Hz), 4.10 (1H, dd,
J¼12.1, 2.6 Hz), 4.07 (1H, dd, J¼12.1, 2.6 Hz), 2.34 (3H, s), 2.23 (3H, s),
1.58 (3H, s); dC (100 MHz, CDCl3) 170.3, 169.7, 155.8, 153.9, 149.7,
146.1, 139.7, 137.1, 129.4, 128.0, 126.1, 120.9, 120.0, 83.1, 79.6, 77.7,
62.9, 62.6, 21.5, 20.8, 20.2; UV (MeOH) lmax
(
3
)¼252 (29,560), 326
4.5.1. 4-Trifluoromethylphenyl triazole 2e
(21,800); MS (FAB) m/z (%)¼491 (77); HRMS-FAB: m/z [MþHþ] calcd
44 mg (0.08 mmol) of 30,50-Di-O-acetyl 4-trifluoromethylphenyl
for
C23H22N8O5: 491.1791, found: 491.1773. Anal. Calcd for
20
triazole 9e afforded 36 mg (97%) 2e as a white solid. [
a]
þ216.4 (c
D
C
23H22N8O5: C, 56.32; H, 4.52; N, 22.8. Found: C, 56.19; H, 4.60; N,
0.03, DMSO); nmax (KBr)/cmꢂ1 3449, 3343, 1641, 1332. dH (400 MHz,
DMSO-d6) 9.13 (2H, d, J¼8.0 Hz), 8.31 (1H, s), 7.96 (2H, d, J¼8.0 Hz),
7.77 (2H, br s), 6.64 (1H, d, J¼4.8 Hz), 6.45 (1H, d, J¼5.1 Hz), 5.34
(1H, d, J¼4.8 Hz), 5.14 (1H, dd, J¼5.1, 3.2 Hz), 4.74 (1H, t, J¼5.5 Hz),
4.05–4.02 (1H, m), 3.17–3.08 (2H, m); dC (100 MHz, DMSO-d6)
156.7, 155.0, 149.3, 149.9, 142.8, 136.4, 134.0, 129.1, 128.8, 126.3,
123.2, 123.1, 119.4, 87.4, 79.8, 76.3, 60.2; HRMS-FAB: m/z [MþHþ]
calcd for C19H16F3N8O3: 462.1376, found: 462.2230.
22.72.
4.4.3. 30,50-Di-O-acetyl 4-trifluoromethylphenyl triazole 9e
200 mg (0.25 mmol) of 20-O-Triflyl-30,50-O-TIPDS-8-(4-tri-
fluoromethylphenylethynyl)-adenosine 7e afforded 46 mg (34%)
9e as a yellow solid. Rf 0.38 (9:1 CHCl2/MeOH); [
20
a
]
þ112.6 (c 0.05,
D
CHCl3); nmax (KBr)/cmꢂ1 3448, 1745, 1641, 1583, 1327, 1227, 1164,
1118, 1067, 850. dH (400 MHz, CDCl3) 8.76 (2H, d, J¼8.4 Hz), 8.45
(1H, s), 7.76 (2H, d, J¼8.4 Hz), 6.84 (1H, d, J¼4.2 Hz), 6.31 (1H, d,
J¼2.6 Hz), 6.08 (2H, br s), 5.28 (1H, d, J¼4.2 Hz), 4.42 (1H, q,
J¼3.0 Hz), 4.14 (1H, dd, J¼12.5, 3.0 Hz), 4.09 (1H, dd, J¼12.5, 3.0 Hz),
2.25 (3H, s), 1.61 (3H, s); dC (100 MHz, CDCl3) 170.2, 169.6, 155.8,
154.9, 150.0, 144.5, 136.6, 132.6, 131.2 (q, J¼32 Hz), 128.4, 126.9 (q,
J¼286 Hz), 125.6 (q, J¼4 Hz), 122.2, 120.1, 83.1, 79.5, 77.6, 63.1, 62.6,
4.5.2. 4-Methylphenyl triazole 2d
55 mg (0.11 mmol) of 30,50-Di-O-acetyl 4-methylphenyl triazole
20
9d afforded 45 mg (100%) 2d as a pale yellow solid. [
a
]
þ267.7 (c
D
0.03, DMSO); nmax (KBr)/cmꢂ1 3447, 3335, 1641. dH (400 MHz,
DMSO-d6) 8.70 (2H, d, J¼8.1 Hz), 8.29 (1H, s), 7.66 (2H, br s), 7.40
(2H, d, J¼8.1 Hz), 6.62 (1H, d, J¼4.4 Hz), 6.42 (1H, d, J¼5.2 Hz), 5.28
(1H, d, J¼4.4 Hz), 5.13 (1H, dd, J¼5.2, 2.7 Hz), 4.77 (1H, t, J¼5.5 Hz),
4.02 (1H, td, J¼5.2, 2.7 Hz), 3.12–3.04 (2H, m), 2.40 (3H, s); dC
(100 MHz, DMSO-d6) 156.0, 154.1, 149.3, 143.9, 138.3, 136.3, 129.4,
127.7, 126.7, 121.1, 118.8, 86.8, 79.2, 75.6, 65.0, 60.7, 21.1; HRMS-FAB:
m/z [MþHþ] calcd for C19H19N8O3: 408.1659, found: 408.1489.
20.8, 20.2; UV (MeOH) lmax
(
3
)¼254 (27,400), 326 (14,980); MS
(FAB) m/z (%)¼545 (48); HRMS-FAB: m/z [MþHþ] calcd for
C
23H19F3N8O5: 545.1509, found: 545.1509.
4.4.4. 30,50-Di-O-acetyl 4-methoxyphenyl triazole 9g
20-O-Triflation of 30,50-O-TIPDS-8-(p-methoxyphenylethynyl)-
adenosine 6g using general triflation procedure A afforded 566 mg
crude 20-O-triflyl-30,50-O-TIPDS-8-(4-methoxyphenylethynyl)-adeno-
sine 7g. This afforded 63 mg (17%) compound 9g as a yellow solid
Acknowledgements
20
using general procedure B. Rf 0.48 (9:1 CHCl2/MeOH); [
a]
þ88.5
D
(c 0.06, CHCl3); nmax (KBr)/cmꢂ1 3444, 1746, 1638, 1248, 1225. dH
(400 MHz, CDCl3) 8.54 (2H, dt, J¼9.5, 2.4 Hz), 8.42 (1H, s), 7.02 (2H,
We wish to acknowledge financial assistance from University of
Gothenburg and the Knut and Alice Wallenberg Foundation.

7158
G. O’Mahony et al. / Tetrahedron 64 (2008) 7151–7158
8. Tomoda, H.; Hirano, T.; Saito, S.; Mutai, T.; Araki, K. Bull. Chem. Soc. Jpn. 1999, 72,
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