Modification of guanine with photolabile N-hydroxypyridine-2(1H)-thione: Monomer synthesis, oligonucleotide elaboration, and photochemical studies

Article abstract of DOI:10.1002/hlca.200690220

The photochemistry of N-hydroxypyridine-2(1H)-thione (NHPT), inserted as a photolabile modifier at the 6-position of 2′-deoxyguanosine or guanosine, has been evaluated. In particular, 6-[(1-oxidopyridin-2-yl)sulfanyl]- (1a) and 6-[(pyridin-2-yl)sulfanyl]-

Full text of DOI:10.1002/hlca.200690220

Helvetica Chimica Acta – Vol. 89 (2006)
2371
Modification of Guanine with Photolabile N-Hydroxypyridine-2(1H)-thione:
Monomer Synthesis,Oligonucleotide Elaboration,and Photochemical Studies
by Despoina Vrantzaa), Panagiotis Kaloudisa), Leondios Leondiadisa)1), Thanasis Gimisis*a), Georgios
C. Vougioukalakisb), Michael Orfanopoulosb), Didier Gasparuttoc),Jean Cadet c), Susana Encinasd),
Cecilia Parisd), and Miguel A. Miranda*d)
a) Organic Chemistry Laboratory, Department of Chemistry, University of Athens, 15771 Athens, Greece
(phone: +30-2107-274-928; fax: +30-2107-274-761; e-mail: gimisis@chem.uoa.gr)
b) Department of Chemistry, University of Crete, Heraklion, Greece
c) Laboratoire ꢀLØsions des Acides NuclØiquesꢁ, SCIB/LAN, CEA, Grenoble, France
d) Instituto de Tecnología Química, Universidad PolitØcnica de Valencia, Valencia, Spain
Dedicated to the memory of Professor Hanns Fischer
The photochemistry of N-hydroxypyridine-2(1H)-thione (NHPT), inserted as a photolabile modifier
at the 6-position of 2’-deoxyguanosine or guanosine, has been evaluated. In particular, 6-[(1-oxidopyri-
din-2-yl)sulfanyl]- (1a) and 6-[(pyridin-2-yl)sulfanyl]-2’,6-dideoxyguanosine (2a), novel photolabile
derivatives of the natural nucleosides, were synthesized and characterized. The observed photolysis prod-
ucts of 1a in organic solvents could only be rationalized by assuming a rapid equilibrium with the corre-
sponding 6-[(2-thioxopyridin-1(2H)-yl)oxy] analogue 3a (Scheme 5). Transient spectroscopy of 1a indi-
cated a strong triplet-excited state suitable for triplet ! triplet energy transfer or singlet-oxygen gener-
ation. The NHPT function was stable enough for (slightly modified) automated solid-phase oligonucleo-
tide synthesis. The utility of the above compounds is discussed, as well as their potential use in photosen-
sitization of reactive oxygen species in DNA.
1. Introduction. – The oxidation chemistry of the guanine base in DNA is rich [1],
and numerous product lesions need to be examined for their mutagenic potential, with
implications in the mechanisms involved in many human conditions including aging and
cancer [2]. The generation of synthetic lesions for the study of their mutagenicity pro-
file can be accomplished through two different lines of research. In the first approach,
stable lesions are independently synthesized and subsequently inserted into oligonu-
cleotides. Alternatively, stable or unstable lesions can be generated in oligonucleotides
by inserting a stable modification capable of chemoselectively generating the lesion
under study. Light is the ideal ꢀreagentꢁ for such in situ transformations, and light-sen-
sitive tert-butyl ketones have already been inserted in various positions of the sugar
moiety for the generation of reactive sugar-radical intermediates [3–6]. Purine-base
radicals, particularly guanine, possessing the lowest reduction potential [7], as well as
pyrimidine triplet-excited states, leading to pyrimidine dimers [8], are also important
intermediates in DNA chemistry. To date, the generation of these reactive species in
1
)
Present address: Mass Spectrometry & Dioxin Analysis Laboratory, NCSR ꢀDemokritosꢁ, 15310
Athens, Greece.
ꢂ 2006 Verlag Helvetica Chimica Acta AG, Zürich

2372
Helvetica Chimica Acta – Vol. 89 (2006)
isolated monomers or within DNA has been effected in the presence of one-electron
oxidants and photosensitizers.
The purpose of this study was to evaluate N-hydroxypyridine-2(1H)-thione
(NHPT) as a photolabile modifier introduced as (1-oxidopyridin-2-yl)sulfanyl moiety
at the 6-position of 2’-deoxyguanosine. The synthetically targeted compounds are
shown in Fig. 1. The amphiphilicity and rich photochemistry of this group [9] could pro-
vide a handle for the generation of reactive intermediates such as triplets, radicals, and
reactive-oxygen species in the vicinity of the DNA double helix. The photochemistry of
both ꢀpyridine-2-thioneoxycarbonylꢁ (PTOC) imidate esters [10] and pyridine-N-oxides
[11] is well-established, and the particular case of photo-deoxygenation has been
reported to generate reactive species [12] that could be used in the study of oxidative
DNA damage.
Fig. 1. Structures of target compounds
Compounds 1, 2, and 3 have not been previously reported. The structure of 3 could
be considered reminiscent of PTOC imidate esters, the synthesis and photochemistry of
which have been extensively studied by Newcomb and co-workers [10][13]. The major
difference of the proposed derivative was the aromaticity of the imidate moiety and, as
such, these structures were unknown. A small number of heteroaromatic ꢀ2-thiopyri-
dine-N-oxidesꢁ (=pyridine-2-thiol 1-oxides), structurally related to compound 1, with
the S-function ortho (or a) to a heterocyclic N-atom, has been reported [14–19].
Although the related products exhibited interesting properties, mainly herbicidal, fun-
gicidal, antimicrobial, and even anticancer actions, the photochemical properties of
these compounds have not been studied. In all the above cases, the method of choice
for the insertion of the (1-oxidopyridin-2-yl)sulfanyl function a to a heterocyclic N-
atom was the reaction of NHPT with the corresponding chloroimidate.
On the other hand, it has been known [20] that 6-arylsulfonyl derivatives of 2’-
deoxy
nucleophiles. In a recent improvement of this methodology, activation of 6-mesityl-
2’-deoxyguanosine derivatives with DABCO (=1,4-diazabicyclo[2.2.2]octane) allowed
guanosine can be used for the functionalization of the 6-position with various
AHCTREUNG
for the addition of various O- and N-nucleophiles [21].
2. Results and Discussion. – 2.1. Monomer Synthesis. The synthesis of the 6-deoxy-6-
[(1-oxidopyridin-2-yl)sulfanyl]- and of the corresponding 2’,6-dideoxy-guanosine deriv-

Helvetica Chimica Acta – Vol. 89 (2006)
2373
Scheme 1
atives 1 is presented in Scheme 12). The O6-[(2,4,6-trimethylphenyl)sulfonyl] deriva-
tives 4 were synthesized according to the above-mentioned methodology for the 2’-
deoxy analogue [20][22]. By introducing NHPT through DABCO-induced activation
[21], compounds 1a and 1b were formed in 55 and 51% yield, respectively, together
with the readily separable nucleoside side products 5a (34%) and 5b (30%), respec-
tively.
In accordance with the aforementioned literature data, the spectroscopic data of the
major reaction products 1a or 1b were in agreement with the proposed structure. The
longest-wavelength absorption (lmax) in the UV/VIS spectrum was centered at 325 nm.
At the same time, there was no 13C-NMR absorption at d(C)>160 ppm, indicating the
lack of a thiocarbonyl function. The isolated compounds were off-white solids that were
relatively stable to visible light, although they slowly developed a grey coloration while
stored at low temperature. Product 1a was readily deprotected in the presence of tet-
rabutylammonium fluoride (TBAF) in THF, and the water-soluble derivative 1c was
isolated in good yield. It is interesting that the NHPT function, although stable
under these conditions, was readily replaced by MeOH when exposed to NH4F in boil-
ing MeOH.
A significant effort went into the characterization of the side product 5a, as it was
possible that it had arisen from O-nucleophilic attack of the ambident NHPT nucleo-
1
phile. However, ESI-MS as well as H- and 13C-NMR spectroscopy indicated that
DABCO is covalently bonded in 5a. Specifically, the [M+H]+ peak at m/z 717.1 and
fragments at 373.3 ([base+DABCO+NHPT+H]+) and 246.2 ([base+DABCO]+)
2
)
For systematic compound names, see the Exper. Part.

2374
Helvetica Chimica Acta – Vol. 89 (2006)
were observed. At the same time, one of the three ethylene groups was differentiated
by both 1H- and 13C-NMR, one methylene appearing at high field (d(C) 28.3). Product
5a was stable under the reaction conditions and did not transform to 1a when it was re-
subjected to the same reaction conditions. The above evidence led to the conclusion
that 5a,b result from S-nucleophilic attack of NHPT at the a-C-atom of the positively
charged DABCOÀpurine intermediate, followed by an SN2 addition and opening of the
ethylene DABCO bridge. Such SN2 displacements have not been previously observed
when DABCO was used as an activator of the C(6) position of purines [23][24], but
have been reported for analogous reactions activated by Me
ACHTREUNG
imply that S-nucleophiles induce this side reaction in the trialkyl
AHCTREUNG
vation of the (trimethylphenyl)sulfonyl leaving group in related reactions.
In order to avoid the above side reaction in the synthesis of the 6-(pyridin-2-ylsul-
fanyl) derivatives 2 (Scheme 2), these compounds were synthesized directly by treating
1a with ꢀ2-thiopyridineꢁ (=pyridine-2(1H)-thione) in benzene. The substitution prod-
uct 2a was finally transformed to the water-soluble derivative 4c by short exposure to
TBAF in THF.
Scheme 2
2.2. Monomer Stability. Insertion of the above modified guanosines in synthetic oli-
gonucleotides requires that they are stable under the standard condition used in auto-
mated oligonucleotide synthesis on solid support. Compound 1c was indefinitely stable
in D2O at neutral pH, and its solutions showed no appreciable change (in spectroscopic
G
terms) for at least two months when stored at room temperature. It was also stable at
808 in the dark for at least 24 h, as well as in 80% AcOH at room temperature. How-
ever, compound 1c was less stable in 0.1M I2 in THF (>90% recovery after 1 h), and
similarly sensitive to 25% aq. NH4OH solution (>90% recovery after 2.5 h). Finally,
it decomposed relatively fast under more-basic conditions. Therefore, this type of
chemical modification could be inserted in synthetic oligonucleotides, but certain pre-
cautions had to be taken, especially with regards to base treatment.
2.3. Phosphoramidite Synthesis. For the above reasons, we proceeded in the prepa-
ration of the corresponding phosphoramidite (Scheme 3) by applying phenoxyacetic
(Pac) protection for the guanine 2-amino function [26][27]. Pac Protection of the 2-
t
amino function of 1a, followed by removal of the Bu(Me2)Si (TBDMS) ethers of the
sugar functions gave 6c. The latter was then ꢀdimethoxytritylatedꢁ at 5’-position and
ꢀphosphitylatedꢁ at 3’-position to provide the phosphoramidite 7a, suitable for oligonu-
cleotide synthesis.

Helvetica Chimica Acta – Vol. 89 (2006)
2375
Scheme 3
2.4. Solid-Phase Synthesis of Oligonucleotides. The synthesis of all oligonucleotides
(3-, 5-, 9-, and 15-mers) was performed on a 1-mmol scale using phosphoramidite
chemistry on an Applied Biosystems 392 automated nucleic-acids synthesizer. The
Pac-protection system for the nucleobase amino functions was used with regard to
the high lability of the modified nucleoside under alkaline deprotection conditions.
The synthesis was performed on controlled-pore-glass (CPG) support following the
standard protocol, with the exception of three modifications: first, the duration of cou-
pling of the modified nucleoside phosphoramidite was extended to 5 min instead of 30 s
for normal nucleosides. Under the latter conditions, an adduct coupling efficiency up to
80–90% was achieved. Moreover, the capping step was carried out with a solution of
phenoxyacetic anhydride ((Pac)2O) in THF to prevent possible transacylation reac-
G
tions. The oxidation step was subsequently performed with a 20-mM I2 solution to pre-
vent possible oxidizing degradation of the modified nucleoside during solid-phase
assembly. Upon completion of the synthesis, the base-labile protecting groups of the
oligodeoxyribonucleotides were removed by treatment with concentrated aqueous
NH3 (32%) at room temperature for 4 h. Solvents were removed by evaporation
under vacuum. The crude oligomers were then purified by reverse-phase HPLC.
2.5. Monomer Photolysis in Organic Solvents. Irradiation of a 10-mM solution of 1a
in anhydrous toluene under Ar atmosphere in the presence of an excess of tert-butyl-
thiol (20 equiv.) at 208 led to complete disappearance of the starting material within
20 min of photolysis. There was a single nucleosidic product isolated in 95% yield,
which was identified as the TBDMS-protected 2’-deoxyguanosine 8a (Scheme 4).
Two other nonnucleosidic side products were identified as 2,2’-dipyridinyl disulfide
(=2,2’-disulfanediyldipyridine; 9), by comparison with a commercial sample, and as
ꢀtert-butyl-2-pyridinyldisulfideꢁ (=2-[(tert-butyl)disulfanyl]pyridine) by comparison
with literature data [28].
Similarly, irradiation of 1b gave a near quantitative yield of protected guanosine 8b
together with the above two side products. When the photolysis of 1a was performed in
the presence of less-efficient hydrogen donors compared to tBuSH, such as Bu3
ACHTREUNG
(Me3
A
ACHTREUNG
When no hydrogen donor was used, 8a was isolated in 60% yield, together with a sec-
ond nucleoside component in 15% yield. ESI-MS indicated a loss of 16 amu in the new

2376
Helvetica Chimica Acta – Vol. 89 (2006)
Scheme 4
product when compared with 1a. The new product was identified as 2a by comparison
with an authentic sample (Scheme 4). The same product was also observed (together
with 8a) when other additives, sources of Sn-radical intermediates (e.g., ditin and allyl-
tin compounds) were used (Table). In all cases, both products, 8a and 2a, were isolated
in comparable amounts, with the highest yield of 2a obtained by initiation at 808 in the
presence of allyl(tributyl)tin and AIBN (=2,2’-azobis[2-methylpropanenitrile]).
Table. Product Distribution upon Photolysis or Radical-Induced Cleavage of 1a in the Presence of Various
Additives (for details, see Exper. Part)
Entry
Additive
Initiation
8a [%]
2a [%]
1
2
3
4
5
6
7
8
None
hv
hv
60
95
95
90
85
47
45
30
15
–
–
–
5
40
45
65
tBuSH
tBuSH
AIBNa), 808
Bu
A
hv
hv
hv
hv
(Me
A
U
Me
Bu3
U
G
CH2=CHCH2
G
AIBN, 808
a) AIBN=2,2’-Azobis[2-methylpropanenitrile].
The above results are remarkable, since it is the first time that pyridine-N-oxides are
reported to behave like pyridine-2-thiones quantitatively providing the corresponding
reduction product in the presence of hydrogen donors. The observed products can only
be rationalized by assuming an equilibrium between 2’,6-dideoxy-6-[(1-oxidopyridin-2-
yl)sulfanyl]guanosine (1a) and 2’-deoxy-6-[(2-thioxopyridin-1(2H)-yl)oxy]guanosine
(3a), as outlined in Scheme 5. This would correspond to a [1,4]-sigmatropic rearrange-
ment of a pyridine-N-oxide to a pyridine-2-thione. The reverse [1,4]-sigmatropic rear-
rangement was reported by Hay and Beckwith [29], and more recently also by Hartung
et al. [30] for related O-alkyl pyridine-2-thiones to be an irreversible process rendering

Helvetica Chimica Acta – Vol. 89 (2006)
2377
photolytically inactive pyridine-N-oxides. This is the first report that this rearrange-
ment appears to be reversible and that pyridine-N-oxides behave photolytically as pyr-
idine-2-thiones. We propose that this reversibility is due to the resonance stabilization
of the ipso intermediate 10 by the aromatic purine ring (Scheme 5).
Scheme 5. Proposed Equilibrium between Pyridine-N-oxides 1 and pyridine-2-thiones 3
Fig. 2. HPLC Profile for the photolysis of 1c in H2O
2.6. Photolysis in Aqueous Solutions. The Photolysis of 1c in H2O was followed by
HPLC (Fig. 2). The starting HPLC signal disappeared at least one order of magnitude
more slowly than in the case of 1a in organic solvents. The only product observed in
small conversion was 2’-deoxyguanosine (8c; Scheme 6). At longer times of continuous
irradiation, 2’,6-dideoxy-6-[(pyridin-2-yl)sulfanyl]guanosine (2c) appeared, together
with a new product characterized by LC/MS ([M+H+] signal at m/z 261.3) as the prod-
uct of N-glycosidic bond cleavage of 1c. This product (11) did not appear, when aque-
ous phosphate buffer (pH 7.2) was used; as expected in this case, the consumption of
the starting material was even slower than in the previous experiment. More impor-
tantly, there was no 18O incorporation into 8c, which was isolated and characterized
by ESI-MS after 5 h of irradiation of 1c in H218O solution. This indicated that, as
observed in the absence of irradiation (vide supra), no hydrolysis takes place under
these conditions. There were no differences observed in the product distribution in
the presence or absence of molecular oxygen (O2).

2378
Helvetica Chimica Acta – Vol. 89 (2006)
Scheme 6
As observed in the 3D HPLC plot shown in Fig. 2, there is a built up of 8c coupled
with the disappearance of 1c at lower than 40% conversion. Eventually, 8c reaches a
plateau and starts decomposing concurrently with the further consumption of 1c and
the formation of both 2c and a significant amount of the acid-catalyzed product of gly-
cosidic bond cleavage (11), after extensive continuous photolysis.
Preliminary photolysis experiments were also performed on the prepared oligonu-
cleotides with short UV-C treatment, followed by HPLC and ESI-MS analyses. Again,
in the case of oligonucleotides, reversion to the unmodified oligonucleotide was the
major event observed. A few other degradation and rearrangement products were
also detected. The identification and characterization of these products is currently
in progress.
2.7. Comparison of Photoreaction Efficiency under Different Conditions. The course
of the photolysis was monitored by following the decrease of the UV/VIS absorption
band at lmax 325 nm. The data are shown in Fig. 3. Approximate values of the photolysis
quantum yields f can be estimated from the slopes of the straight lines obtained when
the absorbance at 325 nm is plotted against irradiation time, after correction for the rel-
ative number of absorbed photons. In agreement with the product studies reported
above, the value for H2O (f=0.015) was clearly lower than in MeCN (f=0.03). More-
over, the reaction efficiency was duplicated (f=0.07) when a thiol was present in the
organic medium. A solution of benzophenone in i-PrOH was used as actinometer, as its
photoreduction quantum yield is well-established (f=1.96) [31].
2.8. Transient Spectroscopy. Laser flash photolysis of 1 and 2 was performed upon
excitation at 308 nm in MeCN/H2O 4 :1 under an anaerobic atmosphere. In the case
of compounds 1, a weak signal was generated, with a maximum at ca. 420 nm; the
same transient was also formed when 1 was photolyzed in MeOH, MeCN, or benzene.
By contrast, compounds 2 gave rise to the same type of transient, albeit with a much
higher absorbance. The signal displayed two maxima at ca. 390 and 435 nm (Fig.
4,a), and its lifetime was 10 ms. In all cases (for 1 and 2), the transient species were
À1
quenched by O2 (Fig. 4,b), with a quenching rate kq of 2”109 sÀ1
M
.
To assign the signals obtained for 1 and 2, different model compounds were also
photolyzed (Scheme 7). Thus, 2,2’-dithiodipyridine (9) was irradiated under the same
conditions, giving rise to the known pyridin-2-ylsulfanyl radical [9], whose spectro-
scopic features (lmax 480 nm, no quenching by O2) were very different from those of
the transients obtained for 1 or 2. Likewise, photolysis of the known ꢀ2,2’-dithiodi(pyr-

Helvetica Chimica Acta – Vol. 89 (2006)
2379
Fig. 3. Plot of the relative UV/VIS absorbance (in %) at 325 nm vs. irradiation time for 1c in water
~
&
*
(
), and for 1a in MeCN in the absence ( ) and presence ( ) of dodecane-1-thiol (20 equiv.)
Fig. 4. a) Change in UV/VIS absorbance of a solution of 2 in anaerobic MeCN/H2O 1 ms after the
laser pulse. A similar transient spectrum, though much weaker, was obtained for 1. b) Decay of the
UV/VIS signal at 420 nm of 2 under anaerobic atmosphere (N2) (solid curve) and under aerobic condi-
tions (O2) (dashed curve).
idine-N-oxide)ꢁ (=2,2’-disulfanediylbis(pyridine) 1,1’-dioxide; 12) led to the (1-oxido-
pyridin-2-yl)sulfanyl radical [9], which also showed a significantly different UV/VIS
spectrum (lmax 340 nm, no quenching by O2).
Hence, the transients observed for compounds 1 and 2 were very similar and were
tentatively assigned to a triplet-excited state. Confirmation of this assignment was ach-
ieved by using well-known triplet quenchers such as biphenyl and naphthalene [32].
Only the latter was found to be an efficient quencher of the transient, though, with a
À1
rate constant of 2”109
M
sÀ1. This value was estimated from the Stern–Volmer plot

2380
Helvetica Chimica Acta – Vol. 89 (2006)
Scheme 7. Laser-Flash Photolysis of Model Compounds 9 and 12. The reactions were performed
under anaerobic conditions in MeCN/H2O 4 :1.
Fig. 5. Stern–Volmer plot for the triplet-lifetime quenching of 2 in MeCN/H2O 4 :1 in the presence of
increasing concentrations of naphthalene
obtained by monitoring the triplet decay at 460 nm in the presence of increasing
amounts of naphthalene (Fig. 5). As biphenyl was unable to act as a quencher, the trip-
let energy of 1 and 2 must be in the range of 63–65 kcal/mol.
Thus, the same type of transients are detected for compounds 1 and 2. However, the
observation that the triplet signal is much weaker in the case of 1 can be attributed to
the occurrence of other photophysical processes that should be competing with inter-
system crossing (ISC) to the triplet state. One such process might well be deoxygena-
tion of the N-oxide moiety, with generation of atomic oxygen, as previously reported
[12]. This would be in agreement with the formation of the deoxygenated products 2
upon prolonged photolysis of 1.
It should be noted that no evidence for the 2’-deoxyguanosine neutral radical (the
likely precursor of 8) was obtained in these laser-flash-photolysis experiments. How-
ever, this is not surprising, as the quantum yield of the reaction leading to 8 is very
low, since the photoactive species 3 is only a minor compound in the equilibrium
shown in Scheme 5.

Helvetica Chimica Acta – Vol. 89 (2006)
2381
3. Conclusions. – We have synthesized and characterized novel photolabile 6-[(1-
oxidopyridin-2-yl)sulfanyl]-substituted 6-deoxy- and 2’,6-dideoxyguanosines of type
1. The observed photolysis products can only be rationalized by assuming a rapid equi-
librium of these compounds with the corresponding 6-[(2-thioxopyridin-1(2H)-yl)oxy]
analogues 3 (Scheme 5) in organic solvents. In the presence of hydrogen donors, a rad-
ical-chain mechanism can account for the fast formation of the products. In their
absence, the photochemistry observed is mainly homolysis of the NÀO bond present
in both the prevalent pyridine-N-oxide and its reversible pyridine-2-thione isomer.
Triplet formation was the primary photochemical event observed by transient spectro-
scopy. A higher absorbance was exhibited by compounds 2 when compared with com-
pounds 1. The energy of the triplet-excited state is suitable for triplet ! triplet energy
transfer or singlet-oxygen generation, but not high enough for the generation of thy-
mine dimers within DNA.
We thank Prof. M. Newcomb and Dr. C. Chatgilialoglu for useful discussions. HR-MS experiments
from the laboratory of Prof. Thomas Carell is appreciated. Financial support from the ꢀPlatoꢁ and ꢀKapo-
distriasꢁ programs is kindly acknowledged. This work was supported, in part, by the European Commun-
ityꢀs Marie Curie Research Training Network (contract MRTN-CT-2003-505086 [CLUSTOXDNA]). The
project was co-funded by the European Social Fund and National Resources (EPEAEK II, PYTHAGO-
RAS II).
Experimental Part
General. For reactions conducted under inert atmosphere, flasks were flame-dried and purged with
anh. Ar gas until cool. Thin-layer (TLC) and column chromatography (CC) were performed on silica gel
F254 and silica gel 60 (SDS, 230–400 mesh; ASTM), resp. UV/VIS Spectra: Varian Cary-50 apparatus; lmax
À1
in nm (e in M cmÀ1). IR Spectra: Perkin-Elmer 841 or 1760X FT-IR spectrometers, in CHCl3 soln.; in
1
cmÀ1. H- and 13C-NMR Spectra: Varian Mercury-200, Bruker MSL-300 or AMX-500 spectrometers; d
in ppm rel. to residual solvent signals, J in Hz.
Mass Spectrometry. Electrospray-ionization mass-spectrometry (ESI-MS) analyses of the nucleoside
derivatives, together with those of the modified oligonucleotides, were conducted on either a Finnigan
AQA quadrupole, a ThermoFinnigan LCQ Ion Trap, or a Finnigan LTQ-FT apparatus; values in m/z.
Samples were prepared at a concentration of 10 mM in MeCN/H2O 1:1 (v/v) containing either 0.1% of
HCOOH (pos. mode) or 1% of Et3N (neg. mode), and introduced into the ESI source with a syringe
A
pump at a flow rate of 10 ml/min. MALDI Mass spectra were obtained with a Bruker Biflex time-of-flight
mass spectrometer equipped with a 337-nm N2 laser and a pulsed-delay source extraction. The matrix was
prepared by dissolving 3-hydroxypicolinic acid/picolinic acid 4 :1 (w/w) in 50% aq. MeCN containing a
small amount of Dowex-50W (50X8-200; Sigma) cation-exchange resin. Then, 1 ml of an aq. soln. of the
sample was added to 1 ml of the dissolved matrix, and the resulting soln. was stirred. The sample was sub-
sequently placed on top of the target plate and allowed to dry by itself. The mass spectra were calibrated
with the aid of myoglobin (1 pmol/ml; m/z 16,952) using the same assay conditions as described for the
oligonucleotides.
UV-A Irradiation of Monomers. Typically, monomer-photolysis experiments were performed with a
variable-intensity Xe-arc lamp (1000 W; ORIEL6269) equipped with a UV-A filter. 10 mM Solns. were
prepared and irradiated in Pyrex glass vials with a local light intensity of 4.5 mW/cm2. Reactions in
org. solvent (toluene) were followed by TLC and NMR spectroscopy, whereas those performed in aq.
solns. were followed by RP-HPLC and LC coupled with ESI-MS.
Determination of Photolysis Quantum Yields. Solutions (A350 =0.1) of 1a or 1c in MeCN and in H2O,
resp., were irradiated at 350 nm with a low-pressure Hg lamp emitting mainly at 350 nm (Gaussian dis-
tribution) under N2. The UV/VIS absorption at 325 nm was measured after different irradiation times in

2382
Helvetica Chimica Acta – Vol. 89 (2006)
the range 0–30 min. A soln. of benzophenone in i-PrOH was used as actinometer. In this case, the
decrease of the C=O absorption at 254 nm was followed after the irradiation times. Conversions were
kept below 10% throughout the measurements.
UV-C Irradiation of Precursor-Containing Modified Oligodeoxyribonucleotides. Typically, an aq.
soln. (2 ml) of compound containing the precursor moiety (1 AU260/ml) was exposed during 5 min to
16 black-light lamps (lmax 260 nm) of a Rayonet photochemical reactor. The resulting mixture was ana-
lyzed on a Hypersil ODS column (5 mm, 250 mm”4.6 mm i.d.) with a gradient of MeCN/10 mM triethy-
lacetate ammonium (pH 7) at a flow rate of 1 ml/min (detection at 260 nm). The collected samples were
analyzed by ESI-MS (neg. mode).
Nanosecond Laser-Flash Photolysis. For excitation at 308 nm, an excimer laser with a Xe/HCl/Ne
mixture was used. The single pulses were ca. 17 ns in duration, and the energy was 200 mJ output at
the source. For both systems, a pulsed Oriel-Lo255 Xe lamp was employed as the detecting light source.
The laser-flash-photolysis apparatus consisted of the pulsed laser, the Xe lamp, an Oriel-77200 mono-
chromator, and an Oriel photomultiplier-tube (PMT) system made up of a 77348 side-on PMT tube, a
70680 PMT housing, and a 70705 PMT power supply. The output signal from the oscilloscope (Tektronix
TDS-640A) was transferred to a personal computer. Concentrations of 1 and 2 were ca. 2”10À5 M, which
ensured an absorbance of ca. 0.4 in the laser cell at the excitation wavelengths. When different quenchers
were added to the soln. of 2, their concentrations oscillated from equimolar to 50 times for the case of
biphenyl, and up to ten times for naphthalene.
9-{2-Deoxy-3,5-bis-O-[(1,1-dimethylethyl)(dimethyl)silyl]-b-D-erythro-pentofuranosyl}-6-{[(2,4,6-tri-
methylphenyl)sulfonyl]oxy}-9H-purin-2-amine (4b). Prepared according to [22] for the 2’-deoxy ana-
logue. TLC (AcOEt/hexane 15 :85): Rf 0.25. 1H-NMR: (200 MHz, CDCl3): À0.22, À0.04 (2s, 3 H,
t
MeSi); 0.09, 0.12 (2s, 6 H, MeSi); 0.79, 0.92, 0.94 (3s, 9 H, Bu); 2.30 (s, 3 H, Me); 2.75 (s, 6 H, 2 Me);
3.75 (dd, J4’ =2.6, J5’ =11.4, HÀC(5’’)); 3.95 (dd, J4’ =2.6, J5’’ =11.4, HÀC(5’)); 4.08 (dd, J3’ =5.0,
J5’ =2.6, HÀC(4’)); 4.25 (dd, J2’ =5.0, J4’ =5.0, HÀC(3’)); 4.46 (dd, J1’ =J3’ =5.0, HÀC(2’)); 4.79 (br. s, 2
H, HÀC(2)); 5.88 (d, J2’ =5.0, HÀC(1’)); 6.97 (s, 2 arom. H); 8.06 (s, HÀC(8)). 13C-NMR (50 MHz,
CDCl3): À5.37, À5.06, À4.75, À4,64, 4.38 (MeSi); 17.9, 18.1, 18.5 (tBuSi); 21.1 (Me); 22.8 (Me); 25.6,
25.8, 26.1 (tBuSi); 62.4 (C(5’)); 71.8 (C(3’)); 76.0 (C(2’)); 85.3 (C(4’)); 87.9 (C(1)’); 117.7 (C(5)); 131.6
(2 arom. m-C); 132.3 (C(8)); 140.3 (2 arom. o-C); 140.4 (arom. o-C); 142.5 (CS); 143.8 (arom. p-C);
153.1 (C(6)); 155.8 (C(4)); 158.3 (C(2)).
9-{2-Deoxy-3,5-bis-O-[(1,1-dimethylethyl)(dimethyl)silyl]-b-D-erythro-pentofuranosyl}-6-[(1-oxido-
pyridin-2-yl)sulfanyl]-9H-purin-2-amine (1a) and 9-[(2R,4S,5R)-4-{[(1,1-dimethylethyl)(dimethyl)silyl]-
oxy}-5-({[(1,1-dimethylethyl)(dimethyl)silyl]oxy}methyl)tetrahydrofuran-2-yl]-6-(4-{2-[(1-oxidopyridin-
2-yl)sulfanyl]ethyl}piperazin-1-yl)-9H-purin-2-amine (5a). A soln. of 4a [22] (905 mg, 1.33 mmol),
DABCO (299 mg, 2.67 mmol)3), 4-Š molecular sieves (427 mg), and N-hydroxypyridine-2(1H)-thione
(NHPT; 850 mg, 6.68 mmol) in anh. 1,2-dimethoxyethane (DME; 14.5 ml) was stirred for 30 min
under Ar gas at r.t. Then, DBU (0.62 ml, 4.14 mmol) was added, and the mixture was stirred at r.t. for
an additional 24 h. The molecular sieves were filtered off, washed with AcOEt, and the filtrate was
evaporated to dryness. The residue was purified by CC (SiO2; 1.5–3.5% MeOH in CHCl3) to afford
1a (438 mg, 55%) as a yellowish solid, together with 5a (324 mg, 34%) as a colorless solid.
Data of 1a. TLC (CH2Cl2/MeOH 95 :5): Rf 0.49. UV (CHCl3): 281 (13,727), 325 (14,500). UV
(MeCN): 281 (12,076), 324 (12,803). IR (CHCl3): 1599, 1561, 1471, 1420, 1400, 1362, 1254, 1222, 1109,
1
1030, 940, 883, 778, 706. H-NMR (500 MHz, CDCl3): 0.06, 0.07 (2s, 3 H, MeSi); 0.10 (s, 6 H, MeSi);
0.89, 0.90 (2s, 9 H, tBu); 2.30–2.42 (m, HÀC(2’)); 2.51–2.63 (m, HÀC(2’’)); 3.74 (dd, J5’’ =11.2,
J4’ =3.1, HÀC(5’)); 3.80 (dd, J5’ =11.2, J4’ =4.2, HÀC(5’’)); 3.98 (dd, J3’ =6.6, J5’ =3.1, HÀC(4’)); 4.58
(ddd, J4’ =6.6, J2’ =3.3, HÀC(3’)); 5.26 (s, 2 H, HÀC(2)); 6.31 (dd, J2’ =6.9, J2’’ =6.8, HÀC(1’)); 7.15
(dd, 2 H, HÀC(4,5) of SPy); 7.74 (dd, HÀC(3) of SPy); 7.98 (s, HÀC(8)); 8.29 (dd, HÀC(6) of SPy).
13C-NMR (125 MHz, CDCl3): À5.60, À5.48, À4.89, À4.76 (MeSi); 17.8, 18.2 (tBu); 25.6, 25.8 (tBuSi);
3
)
Dried by heating over P2O5 under vacuum at 568 for 2 h before use.

Helvetica Chimica Acta – Vol. 89 (2006)
2383
40.7 (C(2’)); 62.6 (C(5’)); 71.8 (C(3’)); 83.5 (C(1’)); 87.6 (C(4’)); 123.3 (C(5) of SPy); 124.8 (C(4) of SPy);
127.5 (C(5)); 128.3 (C(3) of SPy); 138.9 (C(6) of SPy); 139.7 (C(8)); 145.9 (C(4)); 152.1 (C(2)); 155.3 (SC
of SPy); 159.2 (C(6)). HR-ESI-MS (pos.): 605.2749 ([M+H]+, C27
C
G
G
A
t
CDCl3): 0.06, 0.09 (2s, 6 H, MeSi); 0.90 (s, 18 H, Bu); 1.66 (br. s, 1 H, SH); 2.26–2.37 (m, HÀC(2’));
2.48–2.55 (m, HÀC(2’’)); 2.61 (dd, J=5.1, 4.6, 4 H, N(CH2)2); 2.79 (dd, J=7.9, 6.3, NCH2); 3.08 (dd,
J=7.7, 6.3, SCH2) 3.67–3.82 (m, HÀC(5’), HÀC(5’’)); 3.95 (dd, J3’ =6.9, J5’ =4.1, HÀC(4’)); 4.24 (br. s,
4 H, N6(CH2)2); 4.53–4.56 (m, HÀC(3’)); 4.58 (s, 2 H, HÀC(2)); 6.30 (dd, J2’ =7.1, J2’’ =5.9, HÀC(1’));
7.04 (dd, J=6.8, 6.4, HÀC(5) of SPy); 7.05 (dd, J=6.8, 3.0, HÀC(3) of SPy); 7.20 (d, J=3.0, HÀC(4)
SPy); 7.70 (s, HÀC(8)); 8.26 (d, J=6.4, HÀC(6) of SPy). 13C-NMR (125 MHz, CDCl3): À5.3, À5.1,
À4.6, À4.5 (MeSi); 18.2, 18.6, 26.0, 26.2 (tBuSi); 28.3 (SCH2); 40.8 (C(2’)); 44.9 (N6(CH2)2); 53.3
(N(CH2)2); 56.4 (NCH2); 63.1 (C(5’)); 72.3 (C(3’)); 83.4 (C(1’)); 87.8 (C(4’)); 115.4 (C(4)); 120.6 (C(5)
of SPy); 121.7 (C(3) of SPy); 125.9 (C(4) of SPy); 134.3 (C(8)); 139.0 (C(6) of SPy); 152.6 (C(6));
153.0 (C(2) of SPy); 154.2 (C(5)); 159.4 (C(2)).
6-[(1-Oxidopyridin-2-yl)sulfanyl]-9-{2,3,5-tris-O-[(1,1-dimethylethyl)(dimethyl)silyl]-b-D-ribofura-
nosyl}-9H-purin-2-amine (1b). Prepared in analogy to 1a, and purified by CC (SiO2; 1.5–3.5% MeOH in
CHCl3) to yield 60 mg (51%) of 1b, together with 44 mg (30%) of 5b, which was not further character-
ized.
Data of 1b. Yellowish solid. TLC (SiO2; CHCl3/MeOH 9 :1): Rf 0.40. 1H-NMR (200 MHz, CDCl3):
À0.02, 0.10, 0.11 (3s, 6 H, MeSi); 0.82, 0.92, 0.93 (3s, 9 H, t-Bu); 3.76 (dd, J5’’ =11.3, J4’ =2.8, HÀC(5’));
3.96 (dd, J5’ =11.3, J4’ =3.5, HÀC(5’’)); 4.10 (dd, J3’ =4.8, J5’ =3.5, HÀC(4’)); 4.27 (dd, J4’ =4.8, J2’ =4.3,
HÀC(3’)); 4.48 (dd, J1’ =4.7, J3’ =4.3, HÀC(2’)); 5.92 (d, J2’ =4.7, HÀC(1’)); 5.06 (br. s, HÀC(2)); 7.19
(dd, HÀC(4,5) of SPy); 7.73 (dd, HÀC(3) of SPy); 8.09 (s, HÀC(8)); 8.33 (dd, HÀC(6) of SPy).
9-(2-Deoxy-b-D-erythro-pentofuranosyl)-6-[(1-oxidopyridin-2-yl)sulfanyl]-9H-purin-2-amine (1c).
To a soln. of 2a (765 mg, 1.26 mmol) in anh. THF (15 ml) were added activated 4-Š molecular sieves
(250 mg) and a 1M soln. of TBAF in THF (2.77 ml, 2.77 mmol). The mixture was stirred for 1 h at r.t.
under Ar gas, filtered, and washed with MeOH (20 ml). The filtrate was evaporated to dryness, and
the residue was purified by CC (SiO2; CH2Cl2/MeOH 91:9) to afford 7 mg (78%) of 1c. TLC (SiO2;
CHCl3/MeOH 9 :1): Rf 0.23 . UV (H2O): 253 (13,750), 325 (7,002). UV (MeCN): 224 (18,540), 324 (6,
750). 1H-NMR (500 MHz, CD3
G
J3’ =1.2, HÀC(2’’)); 3.75 (dd, J5’’ =12.1, J4’ =3.8, HÀC(5’)); 3.83 (dd, J5’ =12.1, J4’ =3.4, HÀC(5’’)); 4.03
(dd, J3’ =6.6, J5’ =3.4, HÀC(4’)); 4.58 (ddd, J4’ =6.6, J2’ =2.9, HÀC(3’)); 6.37 (dd, J2’ =6.9, J2’’ =6.8, HÀ
C(1’)); 7.45 (ddd, J=7.7, 6.3, 1.9, HÀC(5) of SPy); 7.50 (ddd, J=8.1, 7.7, 1.1, HÀC(4) of SPy); 8.00
(dd, J=8.1, 1.9, HÀC(3) of SPy); 8.24 (s, HÀC(8)); 8.41 (dd, J=6.3, 1.1, HÀC(6) of SPy). 13C-NMR
(125 MHz, CD3OD): 40.1 (C(2’)); 62.4 (C(5’)); 71.8 (C(3’)); 85.2 (C(1’)); 88.5 (C(4’)); 124.8 (C(5) of
G
SPy); 126.6 (C(5)); 128.4 (C(4) of SPy); 129.8 (C(3) of SPy); 139.6 (C(6) of SPy); 141.6 (C(8)); 146.3
(C(4)); 152.3 (C(2)); 155.0 (CS of SPy); 160.3 (C(6)). HR-ESI-MS (pos.): 377.1014 ([M+H]+, C15
H17N6-
4S+; calc. 377.1027).
9-{2-Deoxy-3,5-bis-O-[(1,1-dimethylethyl)(dimethyl)silyl]-b-D-erythro-pentofuranosyl}-6-(pyridin-2-
A
ACHTREUNG
A
ACHTREUNG
ylsulfanyl)-9H-purin-2-amine (2a). To a soln. of 1a (15 mg, 0.025 mmol) in anh. benzene (1 ml) was added
pyridine-2(1H)-thione (2.8 mg, 0.025 mmol), and the mixture was stirred at r.t. for 72 h. The solvent was
evaporated under vacuum, and the residue was purified by CC (SiO2; 3–5% MeOH in CHCl3) to afford
12 mg (80%) of 2a. TLC (SiO2; CHCl3/MeOH 95 :5): Rf 0.33. 1H-NMR (200 MHz, CDCl3): 0.07, 0.10 (2s,
t
6 H, MeSi); 0.90, 0.91 (2s, 9 H, Bu); 2.29–2.41 (m, HÀC(2’)); 2.52–2.65 (m, HÀC(2’’)); 3.74 (dd,
J
5’’ =11.6, J4’ =3.6, HÀC(5’)); 3.81 (dd, J5’ =11.6, J4 =4.5, HÀC(5’’)); 3.98 (dd, J3’ =6.8, J5’ =3.6, HÀ
C(4’)); 4.58 (ddd, J4’ =6.8, J2’ =3.6, HÀC(3’)); 4.92 (s, 2 H, HÀC(2)); 6.31 (dd, J2’ =7.0, J2’’ =6.2, HÀ
C(1’)); 7.22–7.25 (m, HÀC(5) of SPy); 7.62–7.76 (m, HÀC(3,4) of SPy); 7.96 (s, HÀC(8)); 8.59 (d,
HÀC(6) of SPy). 13C-NMR (50 MHz, CDCl3): À5.49, À5.37, À4.79, À4.69 (MeSi); 18.0, 18.4, 25.7,
25.9 (tBuSi); 40.8 (C(2’)); 62.8 (C(5’)); 72.0 (C(3’)); 83.6 (C(1’)); 87.8 (C(4’)); 122.7 (C(5) of SPy);
129.4 (C(3) of SPy); 136.7 (C(4) of SPy); 139.2 (C(4,8)); 150.1 (C(6) of SPy); 151.3 (C(2)); 153.1 (SSC
of SPy); 159.0 (C(6)). HR-ESI-MS: 611.2612 ([M+Na]+, C27
H44
G
U
E
9-(2-Deoxy-b-D-erythro-pentofuranosyl)-6-(pyridin-2-ylsulfanyl)-9H-purin-2-amine (2c). To a soln.
of 2a (15 mg, 0.025 mmol) in anh. THF (0.5 ml) were added activated 4-Š molecular sieves (50 mg)

2384
Helvetica Chimica Acta – Vol. 89 (2006)
and a 1M soln. of TBAF in THF (55 ml, 0.055 mmol). The mixture was stirred for 1 h at r.t. under Ar gas,
filtered, and washed with MeOH (2 ml). The filtrate was evaporated to dryness, and the residue was puri-
fied by CC (SiO2; CH2Cl2/MeOH 91:9) to afford 7 mg (78%) of 2c. TLC (SiO2; CH2Cl2/MeOH 9 :1): Rf
0.28. 1H-NMR (200 MHz, D2
G
C(5’), HÀC(5’’)); 4.10 (d, HÀC(4’)); 4.60 (s, HÀC(3’)); 6.31 (dd, J=7.2, 5.8, HÀC(1’)); 7.43 (dd,
J=7.0, 4.2, HÀC(5) of SPy); 7.69 (d, J=8.0, HÀC(3) of SPy); 7.85 (dd, J=8.0, 7.0, HÀC(4) of SPy);
8.13 (s, HÀC(8)); 8.47 (d, J=4.2, HÀC(6) of SPy). HR-ESI-MS: 361.1064 ([M+H]+, C15
calc. 361.1083).
9-{2-Deoxy-3,5-bis-O-[(1,1-dimethylethyl)(dimethyl)silyl]-b-D-erythro-pentofuranosyl}-6-[(1-oxido-
pyridin-2-yl)sulfanyl]-N-[(phenyloxy)acetyl]-9H-purin-2-amine (6a). To a soln. of 1-hydroxy-1H-benzo-
triazole (HOBt; 475 mg, 3.4 mmol) and Tris buffer (evaporated from anh. MeCN) in anh. MeCN/pyri-
dine 1:1 (6 ml) were added dropwise 2-phenoxyacetyl chloride (446 mg, 3.3 mmol). At the same time,
a soln. of 1a (800 mg, 1.3 mmol) in 6 ml of anh. pyridine was prepared. After 15 min, both solns. were
ice-cooled, and the soln. of 1a was added dropwise to the latter soln. The resulting mixture was stirred
for 24 h at r.t., then cooled to 58, treated with H2O (10 ml), and stirred for an additional 30 min. Then,
CHCl3 (15 ml) was added, the mixture was extracted with sat. aq. NaHCO3 (15 ml), and the org. layer
was dried (Na2SO4) and evaporated to dryness. The residue was purified by CC (SiO2; CHCl3/MeOH
1
99 :1) to afford 701 mg (73%) of 6a. TLC (SiO2; CHCl3/MeOH 95 :5): Rf 0.68 . H-NMR (200 MHz,
t
CDCl3): 0.09, 0.12 (2s, 6 H, MeSi); 0.91, 0.93 (2s, 9 H, Bu); 2.39–2.51 (m, HÀC(2’)); 2.57–2.70 (m,
HÀC(2’’)); 3.77 (dd, J=11.4, 3.0, HÀC(5’)); 3.88 (dd, J=11.4, 3.8, HÀC(5’’)); 4.02 (dd, HÀC(4’));
4.60–4.65 (m, HÀC(3’)); 4.69 (s, COCH2); 6.26 (dd, J=6.4, 6.0, HÀC(1’)); 6.96–7.39 (m, 5 arom H,
HÀC(4,5) of SPy); 8.28 (s, HÀC(8)); 8.32 (d, HÀC(3) of SPy); 8.47 (d, HÀC(6) of SPy); 8.82 (s, HÀC(3)).
9-(2-Deoxy-b-D-erythro-pentofuranosyl)-6-[(1-oxidopyridin-2-yl)sulfanyl]-N-[(phenyloxy)acetyl]-
9H-purin-2-amine (6c). To a soln. of 6a (520 mg, 0.704 mmol)4) in anh. THF (8.5 ml) were added acti-
vated 4-Š molecular sieves (150 mg) and a 1M soln. of TBAF in THF (2.11 ml, 2.11 mmol). The mixture
was stirred for 1 h at r.t. under Ar gas, filtered, and washed with MeOH (20 ml). The filtrate was evapo-
rated to dryness, and the residue was purified by CC (SiO2; CH2Cl2/MeOH 95 :5) to afford 213 mg (60%)
of 6c. TLC (SiO2; CH2Cl2/MeOH 95 :5): Rf 0.30. 1H-NMR (200 MHz,CDCl3): 2.51–2.64 (m, HÀC(2’));
2.85–2.99 (m, HÀC(2’’)); 3.76–3.79 (m, HÀC(5’), HÀC(5’’)); 4.12 (dd, J=8.8, 4.4, HÀC(4’)); 4.70–4.79
(m, HÀC(3’)); 4.79 (s, COCH2); 6.50 (dd, J=6.9, 5.9, HÀC(1’)); 6.91–7.10 (m, 3 arom. H); 7.35 (dd, 2
arom. H); 7.48 (ddd, J=7.9, 7.0, 1.7, HÀC(5) of SPy); 7.59 (dd, J=8.0, 7.9, HÀC(4) of SPy); 7.95 (d,
J=8.0, HÀC(3) of SPy); 8.36 (s, HÀC(8)); 8.37 (d, J=7.0, HÀC(6) of SPy).
9-(5-O-{Bis[4-(methyloxy)phenyl](phenyl)methyl}-2-deoxy-b-D-erythro-pentofuranosyl)-6-[(1-oxi-
dopyridin-2-yl)sulfanyl]-N-[(phenyloxy)acetyl]-9H-purin-2-amine (7c). To a soln. of 6c (100 mg, 0.20
mmol) in anh. pyridine (1.4 ml) was added dimethoxytrityl chloride5) (154 mg, 0.46 mmol), and the mix-
ture was stirred at r.t. for 24 h. MeOH (1.2 ml), CHCl3 (7.5 ml), and phosphate buffer (7.5 ml; pH 7.0)
were added, and the org. phase was separated and washed again with phosphate buffer. The org. layer
was dried (Na2SO4), and co-evaporated with toluene (3”2.5 ml). The residue was purified by CC
(SiO2; 2–5% of MeOH in CHCl3) to afford 109 mg (67%) of 7c. TLC (SiO2; CHCl3/MeOH 98 :2): Rf
1
0.55. H-NMR (200 MHz, CDCl3): 2.59–2.68 (m, HÀC(2’), HÀC(2’’)); 3.32–3.44 (dd, 2 H, HÀC(5));
3.69 (s, 2 MeO); 4.16 (d, HÀC(4’)); 4.56 (s, COCH2); 4.69 (s, HÀC(3’)); 6.46 (dd, HÀC(1’)); 6.72 (d, 5
arom H); 6.86–7.02 (m, 3 arom. H); 7.14–7.36 (m, 12 arom. H, HÀC(4,5) of SPy); 8.04 (s, HÀC(8));
8.25 (d, HÀC(3) of SPy); 8.38 (d, HÀC(6) of SPy); 8.94 (s, HÀC(3)). 13C-NMR (50 MHz, CDCl3): 40.5
(C(2’)); 55.1 (MeO); 63.9 (C(5’)); 67.6 (CÀCH2); 71.8 (C(3’)); 84.2 (C(1’)); 86.3 (C(4’)); 88.0 (CÀ
OC(5’)); 113.0 (arom. C); 114.8 (C(5=of SPy); 122.1 (C(4) of SPy); 125.3 (C(3) of SPy); 126.8, 127.0
(arom. C); 127.6 (C(6) of SPy); 127.7, 128.0, 128.9, 129.0, 129.7, 129.9 (arom. C); 135.5 (C(2)); 135.6
(C(4)); 139.1 (C(8)); 142.3 (MeOÀC), 144.4 (C(6)); 158.3 (C=O). ESI-MS: 813.5 ([M+H]+), 511.3
([MÀDMT+H]+), 395.3 ([base+H]+), 303.3 (DMT+). HR-ESI-MS (pos.): 835.2455 ([M+Na]+, C44
A
N6NaO8
U
H39N6
G
N
4
5
)
)
Dried by heating over P2O5 under vacuum at 568 for 2 h before use.
Systematic name: 1,1’-(chlorophenylmethylene)bis[4-methoxybenzene].

Helvetica Chimica Acta – Vol. 89 (2006)
2385
9-(3-O-{[Bis(1-methylethyl)amino][(2-cyanoethyl)oxy]phosphanyl}-5-O-{bis[4-(methyloxy)phenyl]-
ACHTREUNG
gas was added i-Pr2NEt (200 ml, 1.14 mmol) and 2-cyanoethyl-N,N-diisopropylchlorophosphoramidite
G
(100 ml, 0.43 mmol), and the mixture was stirred for 2 h at r.t. Then, MeOH (1 ml) was added, the org.
layer was extracted, dried (Na2SO4), and evaporated. The residue was purified by CC (SiO2; 1–2% of
MeOH in CH2Cl2/Et3
A
1
MeOH/Et3N 94 :5 :1): Rf 0.55. H-NMR (200 MHz, CDCl3): 1.11–1.42 (m, 4 Me of i-Pr); 1.24 (dd, 2
AHCTREUNG
CH of i-Pr); 2.71–2.77 (m, 2 H, HÀC(2)); 3.39–3.67 (m, 6 H, HÀC(5), CH2); 3.75 (s, 2 MeO);
4.08–4.19 (m, 3 H, COCH2, HÀC(4’)); 4.50–4.58 (m, HÀC(3’)); 6.41 (dd, HÀC(1’)); 6.73–6.87 (m, 7
arom. H); 7.01 (dd, 1 arom. H); 7.19–7.38 (m, 10 arom. H); 7.70 (dd, HÀC(5) of SPy); 7.85 (dd, HÀ
C(4) of SPy); 8.08 (d, HÀC(3) of SPy); 8.54 (s, HÀC(8)); 8.58 (d, HÀC(6) of SPy). 31P-NMR (32.4
MHz, CDCl3/H3PO4 (85%)): 150.04 (s). ESI-MS (pos.): 1073.3 ([MÀH+Na+K]+, 1052.1 ([M+K]+),
1034.9 ([M+Na]+). HR-ESI-MS: 1013.3769 ([M+H]+, C53
A
N8
G
N
REFERENCES
[1] T. Gimisis, C. Cismas¸, Eur. J. Org. Chem. 2006, 1351.
[2] K. B. Beckman, B. N. Ames, J. Biol. Chem. 1997, 272, 19633.
[3] S. Korner, A. Bryant-Friedrich, B. Giese, J. Org. Chem. 1999, 64, 1559.
[4] E. Meggers, M. E. Michel-Beyerle, B. Giese, J. Am. Chem. Soc. 1998, 120, 12950.
[5] A. Romieu, S. Bellon, D. Gasparutto, J. Cadet, Org. Lett. 2000, 2, 1085.
[6] C. Tronche, B. K. Goodman, M. M. Greenberg, Chem. Biol. 1998, 5, 263.
[7] S. Steenken, S. V. Jovanovic, J. Am. Chem. Soc. 1997, 119, 617.
[8] L. C. J. Gillet, O. D. Scharer, Chem. Rev. 2006, 106, 253.
[9] B. M. Aveline, I. E. Kochevar, R. W. Redmond, J. Am. Chem. Soc. 1996, 118, 10113.
[10] J. H. Horner, O. M. Musa, A. Bouvier, M. Newcomb, J. Am. Chem. Soc. 1998, 120, 7738.
[11] A. Albini, M. Alpegiani, Chem. Rev. 1984, 84, 43.
[12] G. Bucher, J. C. Scaiano, J. Phys. Chem. 1994, 98, 12471.
[13] J. L. Esker, M. Newcomb, J. Org. Chem. 1993, 58, 4933.
[14] M. L. Conalty, J. F. OꢁSullivan, D. Twomey, Proc. R. Irish Acad., B 1976, 76, 151.
[15] G. L. Bachman, J. W. Baker, D. P. Roman, J. Pharm. Sci. 1978, 67, 1323.
[16] V. P. Arya, K. Nagarajan, S. J. Shenoy, Indian J. Chem., B 1982, 21, 1115.
[17] J. J. DꢁAmico, D. E. Schafer, to Monsanto Co., USA, US Pat. 4,239,527, 1980, p. 6.
[18] H. Schoenowsky, H. Mildenberger, B. Sachse, to Hoechst AG, Germany, DE Pat. 3,101,889, 1982,
p. 18.
[19] R. C. Portnoy, to du Pont de Nemours, E. I. & Co., USA, US Pat. 4,497,807, 1985, p. 9.
[20] Y. Hayakawa, M. Hirose, R. Noyori, J. Org. Chem. 1993, 58, 5551.
[21] M. K. Lakshman, F. N. Ngassa, J. C. Keeler, Y. Q. V. Dinh, J. H. Hilmer, L. M. Russon, Org. Lett.
2000, 2, 927.
[22] M. K. Lakshman, P. Gunda, P. Pradhan, J. Org. Chem. 2005, 70, 10329.
[23] N. K. Lembicz, S. Grant, W. Clegg, R. J. Griffin, S. L. Heath, B. T. Golding, J. Chem. Soc., Perkin
Trans. 1 1997, 3573.
[24] N. K. Lembicz, S. Grant, W. Clegg, R. J. Griffin, S. L. Heath, B. T. Golding, J. Chem. Soc., Perkin
Trans. 1 1997, 185.
[25] J. Kiburis, J. H. Lister, J. Chem. Soc., C 1971, 1587.
[26] E. Muller, D. Gasparutto, J. Cadet, ChemBioChem 2002, 3, 534.
[27] F. Raynaud, U. Asseline, V. Roig, N. T. Thuong, Tetrahedron 1996, 52, 2047.
[28] P. Blom, A. X. Xiang, D. Kao, E. A. Theodorakis, Bioorg. Med. Chem. 1999, 7, 727.
[29] B. P. Hay, A. L. J. Beckwith, J. Org. Chem. 1989, 54, 4330.
6
)
Dried by co-evaporation with anh. pyridine (2”).

2386
Helvetica Chimica Acta – Vol. 89 (2006)
[30] J. Hartung, M. Hiller, P. Schmidt, Chem.–Eur. J. 1996, 2, 1014.
[31] W. M. Moore, M. D. Ketchum, J. Phys. Chem. 1964, 86, 214.
[32] V. Lhiaubet-Vallett, J. Trzcionka, S. Encinas, M. A. Miranda, N. Chouini-Lalanne, J. Phys. Chem., B
2004, 108, 14148.
Received May 3, 2006