Influence of the Linking Bridge on the Photoreactivity of Benzophenone-Thymine Conjugates

Article abstract of DOI:10.1021/acs.joc.0c02088

Benzophenone (BP) is present in a variety of bioactive molecules. This chromophore is able to photosensitize DNA damage, where one of the most relevant BP/DNA interactions occurs with thymine (Thy). In view of the complex photoreactivity previously observed for dyads containing BP covalently linked to thymidine, the aim of this work is to investigate whether appropriate changes in the nature of the spacer could modulate the intramolecular BP/Thy photoreactivity, resulting in an enhanced selectivity. Accordingly, the photobehavior of a series of dyads derived from BP and Thy, separated by linear linkers of different length, has been investigated by steady-state photolysis, as well as femtosecond and nanosecond transient absorption spectroscopy. Irradiation of the dyads led to photoproducts arising from formal hydrogen abstraction or Paterno-Büchi (PB) photoreaction, with a chemoselectivity that was clearly dependent on the nature of the linking bridge; moreover, the PB process occurred with complete regio- and stereoselectivity. The overall photoreactivity increased with the length of the spacer and correlated well with the rate constants estimated from the BP triplet lifetimes. A reaction mechanism explaining these results is proposed, where the key features are the strain associated with the reactive conformations and the participation of triplet exciplexes.

Full text of DOI:10.1021/acs.joc.0c02088

pubs.acs.org/joc
Article
Influence of the Linking Bridge on the Photoreactivity of
Benzophenone−Thymine Conjugates
́
Alejandro Blasco-Brusola, Ignacio Vaya,* and Miguel A. Miranda*
Cite This: https://dx.doi.org/10.1021/acs.joc.0c02088
Read Online
sı
*
Metrics & More
Article Recommendations
Supporting Information
ACCESS
ABSTRACT: Benzophenone (BP) is present in a variety of bioactive molecules. This
chromophore is able to photosensitize DNA damage, where one of the most relevant BP/
DNA interactions occurs with thymine (Thy). In view of the complex photoreactivity
previously observed for dyads containing BP covalently linked to thymidine, the aim of this
work is to investigate whether appropriate changes in the nature of the spacer could
modulate the intramolecular BP/Thy photoreactivity, resulting in an enhanced selectivity.
Accordingly, the photobehavior of a series of dyads derived from BP and Thy, separated by
linear linkers of different length, has been investigated by steady-state photolysis, as well as
femtosecond and nanosecond transient absorption spectroscopy. Irradiation of the dyads led to photoproducts arising from formal
hydrogen abstraction or Paterno−Buchi (PB) photoreaction, with a chemoselectivity that was clearly dependent on the nature of the
̈
linking bridge; moreover, the PB process occurred with complete regio- and stereoselectivity. The overall photoreactivity increased
with the length of the spacer and correlated well with the rate constants estimated from the BP triplet lifetimes. A reaction
mechanism explaining these results is proposed, where the key features are the strain associated with the reactive conformations and
the participation of triplet exciplexes.
chromophore itself is known to elicit DNA damage by
photosensitization.24,25 Interestingly, this scaffold is present
in a variety of drugs, which exhibit a broad range of biological
activities such as anticancer, anti-inflammatory, antimicrobial,
and antiviral.26
INTRODUCTION
■
The interaction of solar UV light with DNA can give rise to
chemical modifications in its structure that may result in cell
death and eventually in the appearance of cancer.1,2 Direct
photoinduced damage is mainly associated with the formation
of cyclobutane pyrimidine dimers (CPDs) and to a lesser
extent pyrimidine (6-4) pyrimidone photoproducts ((6-
4)PPs), which are highly mutagenic;3−7 in addition, oxidative
DNA lesions can also be formed in lower yields.8 Formally,
CPDs are generated through a [2 + 2] cycloaddition between
two adjacent nucleobases, while the (6-4)PPs arise from a
One of the most relevant interactions in the DNA
photosensitization by BP derivatives occurs between the BP
chromophore and the thymine (Thy) nucleobase. A simplified
mechanism explaining these interactions is shown in Scheme 1.
Absorption of UVA light by BP rapidly generates its excited
triplet state (3BP*), which can mediate formation of 3Thy* by
triplet−triplet energy transfer (TTET), either directly or
̀
Paterno−Buchi (PB) photochemical reaction to form an
̈
3
3
oxetane intermediate, which rapidly evolves through ring
opening and isomerization to afford the (6-4)PPs as photo-
products.9,10 Both lesions, CPDs and (6-4)PPs, can be
efficiently repaired by two mechanisms: in humans, the
nucleotide excision repair predominates, while in other
organisms (i.e., bacteria and plants), the photolyase-mediated
mechanism reverses the damage through a photoinduced
electron-transfer process.11−15
through a triplet exciplex [BP···Thy]*. Subsequently, Thy*
or 3[BP···Thy]* may react with another thymine moiety,
leading ultimately to CPDs as formal [2 + 2] cycloadducts.27
Alternatively, 3[BP···Thy]* can also evolve to oxetane
derivatives. Exciplexes of this type have recently been detected
in BP-Thy conjugates.28 Finally, an electron-transfer process
may also occur, albeit to a lesser extent, producing oxidative
damage.29
Photoinduced damage to DNA can occur not only upon
direct absorption of UVB light but also through photo-
sensitization.3,16 In this case, excitation of an exogenous or
endogenous photosensitizer (PS) at comparatively longer
wavelengths leads, after intersystem crossing, to reactive
long-lived triplet excited states. In this context, some
nonsteroidal anti-inflammatory drugs (NSAIDs) photosensi-
tize DNA damage upon absorption of UVA light.17 A typical
example is ketoprofen (KP),18−23 whose photobehavior can be
attributed to its benzophenone (BP) substructure, as the BP
Bichromophoric systems composed of a nucleobase (or
nucleoside) covalently linked to a photosensitizer (or a
Received: August 30, 2020
https://dx.doi.org/10.1021/acs.joc.0c02088
© XXXX American Chemical Society
J. Org. Chem. XXXX, XXX, XXX−XXX
A

The Journal of Organic Chemistry
pubs.acs.org/joc
Article
Scheme 1. Simplified Mechanism Showing the Excited-State Interactions between BP and Thy, which may Finally Result in the
Formation of Some Photoproducts Inducing Damage to DNA
photoactive drug) have been previously used as models to
investigate the excited-state interactions underlying photo-
sensitized DNA damage.30−32 In particular, the photoreactivity
of two dyads containing KP covalently linked to thymidine at
positions 5′ or 3′ of the sugar moiety has been previously
investigated.33 The behavior of both regioisomers was found to
be strongly influenced by the relative spatial arrangement
(cisoid or transoid) of the KP and Thy units. Photolysis of the
cisoid isomer gave rise to four oxetanes plus two additional
photoproducts arising from a formal intramolecular hydrogen
abstraction; on the contrary, irradiation of the transoid isomer
by a linear chain composed of four, six, or ten linking atoms. In
the cisoid dyad D7, which we have reinvestigated for
comparison, the BP and Thy units are separated by the
sugar moiety, where the cisoid arrangement of BP and Thy can
increase the number of reactive conformations with respect to
the linear linkers.
RESULTS AND DISCUSSION
■
The synthesis of the selected dyads is described in detail in the
Supporting Information. For D7, the reported synthesis33
involves covalent KP linking to the 5′ position of the sugar
through an ester bond; by contrast, for the linear dyads D4,
D6, and D10 (see Scheme 2), a thy-derived alkanoic acid of
variable length is conjugated with the BP derivative 4-
benzoylbenzylamine (BPN) through an amide bond.
3
resulted only in slow polymerization. Accordingly, the KP*
triplet excited state was markedly shorter-lived in the cisoid
isomer, in line with its higher reactivity. In this context, recent
theoretical calculations on ligand/DNA interactions have
found that photosensitized DNA damage depends on the
relative orientation of the chromophore interacting with Thy.34
In view of the rich photoreactivity observed for the dyads
containing KP covalently linked to thymidine at position 5′ of
the sugar, which leads to complex photoproduct mixtures, it
appeared interesting to investigate whether appropriate
changes in the nature of the spacer could modulate the
intramolecular BP/Thy photoreactivity, resulting in an
enhanced chemo-, regio-, and/or stereoselectivity. Therefore,
with the general goal of getting a better understanding of
ligand/DNA interactions, a series of photosensitizer-nucleo-
base dyads have been designed in the present work (Figure 1)
and submitted to a systematic study of their photochemical
and photophysical properties, including careful identification of
the photoproducts obtained by steady-state photolysis and
transient spectroscopic characterization of the reactive triplet
excited states in the nanosecond and femtosecond timescales.
In dyads D4, D6, and D10, both chromophores are separated
The photoreactivity of the obtained dyads was first
investigated by means of steady-state photolysis and transient
absorption spectroscopy. Thus, isoabsorptive solutions (A =
0.05, concentration ca. 20 μM) of the three new compounds
were irradiated in deaerated acetonitrile in a multilamp
photoreactor emitting at λmax = 350 nm. The course of the
reaction was followed by monitoring the decrease of the UV
absorption at 254 nm (Figure 2), which is mainly associated
with the diaryl ketone (see Figure S1 in the Supporting
Information).
A progressive disappearance of the absorption at ca. 254 nm
was observed for the dyads, whereas the reference compound
BPN was nearly unreactive under the same conditions (see also
Figure S11 in the Supporting Information). The photo-
chemical reactivity followed the order D4 < D6 < D10 ≈ D7.
For product studies, higher concentrations of the dyads (2.6
mM) were used. Irradiation of D4 gave rise only to
unidentified polymeric materials. By contrast, D6 and D10
led to the formation of well-defined photoproducts that were
separated and purified by semipreparative high-performance
1
liquid chromatography (HPLC) and characterized by H- and
13C NMR, as well as high-resolution mass spectrometry
(HRMS) (see details in the Supporting Information). Thus,
photolysis of D6 resulted not only in polymerization but also
in the formation of photoproduct PP-D6 (see Scheme 3) in
very low yields (∼3%) after HPLC purification, which may
arise from a direct H-atom abstraction or through an electron-
transfer process followed by proton transfer, to afford formal
hydrogen abstraction chemistry. The intermediate radical pair
contains a thy-derived radical at the C5-methyl group, which
under aerobic conditions would be trapped by oxygen, to give
a 5-formyluracil. Thus, this chemistry would be connected with
the oxidative damage to DNA.35 However, it should be noted
Figure 1. Chemical structure of the investigated dyads.
B
https://dx.doi.org/10.1021/acs.joc.0c02088
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
pubs.acs.org/joc
Article
Scheme 2. Schematic Representation of the Synthesis of D4, D6, and D10
that oxidation of Thy in the biomolecule is less favored than
that of the guanine nucleobase, which has the lowest oxidation
potential and would be a better electron donor than Thy
toward the excited BP moiety.21 Conversely, the main
photoproduct resulting from irradiation of D10 was an oxetane
(Ox-D10), ca. 20% yield after HPLC purification, which
̀
clearly arises from a Paterno−Buchi reaction between the
̈
excited carbonyl of BP and the C5C6 double bond of Thy.
The regio- and stereochemistry of Ox-D10 were unambigu-
ously established by X-ray crystallography (see Figure 3). The
photoproducts arising from irradiation of D7, namely, Ox-D7a,
Ox-D7b, Ox-D7c, Ox-D7d, PP-D7a, and PP-D7b, have been
previously characterized;33 higher yields were observed for the
oxetane formation, while photoproducts PP-D7a and PP-D7b
were obtained in lower yields.
Figure 2. Photochemical reactivity of BPN (black), D4 (green), D6
(red), D7 (blue), and D10 (magenta) followed by the decrease in the
absorbance of the carbonyl band at 254 nm against the irradiation
time. Irradiations were performed in deaerated acetonitrile (∼20 μM)
using a multilamp photoreactor (λmax = 350 nm) through quartz cells.
C
https://dx.doi.org/10.1021/acs.joc.0c02088
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
pubs.acs.org/joc
Article
Scheme 3. Simplified Mechanism for the Photoproduct Formation upon Steady-State Photolysis of D6, D7, and D10
Figure 4. Femtosecond transient absorption spectra from 0.5 to 40 ps
for BPN (A), D4 (B), D6 (C), and D10 (D) upon excitation at 280
nm in MeCN. The insets show the kinetic traces at 340 nm (gray)
and 530 nm: BPN (black), D4 (red), D6 (green), and D10
(magenta).
Figure 3. Structure of Ox-D10 in the crystalline state: C blue, H
white, O red, and N violet. The thermal ellipsoids are drawn at the
50% probability level.
excited state of the benzophenone chromophore has been
completely formed. Therefore, nanosecond laser flash
photolysis (LFP) experiments were performed upon excitation
at 355 nm with the aim of investigating the transient species at
longer times. Thus, photolysis of BPN gave rise to its triplet−
triplet absorption band with the maxima centered at ca. 320
and 530 nm. A similar trend was observed for the dyads (see
Figure S12 in the Supporting Information).
To characterize the excited states involved in the photo-
chemical reactivity of each dyad and to elucidate the
mechanistic pathways leading to the isolated photoproducts,
transient absorption experiments were performed on D4, D6,
and D10, using BPN as a reference compound. Measurements
in the femtosecond time scale were conducted upon excitation
at 280 nm in MeCN; control experiments demonstrated that,
under the employed conditions, the degree of photo-
decomposition of the four compounds was lower than 5%.
As expected, the photobehavior of BPN at the really early
times after excitation was very similar to that displayed by
BP,28,36 but with different kinetics. Hence, the triplet excited
state of BPN displayed a maximum at ca. 530 nm; it was
formed within ca. 5.5 ps through intersystem crossing (ISC)
concomitantly with the disappearance of the band centered at
340 nm, associated with the singlet−singlet absorption.
Interestingly, a similar trend with analogous kinetics was
detected for D4, D6, and D10 (see Figure 4). This suggests
that the photoreactivity of all dyads occurs once the triplet
A more detailed analysis of the LFP spectra revealed
marginal absorption between 350 and 420 nm, only for D10.
This band is difficult to visualize due to overlap with that of
320 nm; however, it can be clearly observed by subtracting the
3BPN* spectrum from that of the corresponding dyad (inset in
Figure 5A). The weak absorption band found for D10 displays
a maximum at ∼360 nm, analogous to that of 3Thy*.37 Indeed,
a very similar band was previously detected for related thy−
benzophenone conjugates, and it was associated with the
3
formation of Thy* by triplet−triplet energy transfer (TTET)
38
3
from BP*. Moreover, the involvement of triplet exciplexes
D
https://dx.doi.org/10.1021/acs.joc.0c02088
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
pubs.acs.org/joc
Article
Table 1. Photophysical Data (Triplet Lifetimes and
Intramolecular Quenching Rate Constants) Obtained for
the Investigated Dyads and their Reference Compounds
τ (3BP*)/μs
kQ/s‑1
BPN
1.5
1.0
0.8
0.05
1.3
a
D4
D6
3.3 × 105
5.8 × 105
1.9 × 107
a
a
D10
KP
D7
Figure 5. LFP spectra recorded at the very beginning after the laser
pulse (A) and decay traces at 530 nm (B) for BPN (black), D4
(green), D6 (red), and D10 (magenta). The inset in (A) shows the
transient absorption spectra obtained by subtraction of the BPN*
spectrum from that of the corresponding dyad. All measurements
b
0.03
3.3 × 107
a
b
Determined as (1/τdyad − 1/τBPN). Determined as (1/τD7 − 1/τKP).
3
mM, the intermolecular reaction rates would be ca. 106 s−1.
Accordingly, polymerization competes with the intramolecular
reaction for D4 and to a lesser extent for D6; conversely, the
intramolecular process is much faster and prevails in the case of
D10.
were performed in deaerated MeCN at λexc = 355 nm.
arising from the photocleavage of oxetanes composed of BP
and dimethylthymine (DMT) has been recently proposed. The
signature of these exciplexes (3[BP···DMT]*) is the appear-
ance of an absorption band at ca. 400 nm, whose formation
depends on the oxetane regiochemistry.28 Therefore, by
analogy, the weak absorption detected for D10 could also be
associated with a triplet exciplex between the benzophenone
and thymine units.
Having established that the photobehavior of the linear
dyads is highly influenced by the distance between the BP and
Thy moieties, the photophysical properties of D7 were
reinvestigated. It has been reported that steady-state irradiation
of D7 gives mainly rise to the formation of oxetanes, along
with minor amounts of photoproducts arising from a formal
intramolecular hydrogen abstraction process.33 Accordingly, a
fast deactivation of the triplet excited state of KP was
evidenced for D7, which was attributed to its high reactivity
due to the strong intramolecular interaction between the KP
and Thy units. To get a deeper insight into the photophysical
properties of D7, femtosecond transient absorption measure-
ments (λexc = 280 nm) were performed using KP as a
reference. As expected, the triplet excited state of KP, with λmax
= 530 nm,40,41 was formed within ca. 9.5 ps. The same was true
for D7 (see Figure S13 in the Supporting Information),
suggesting that its photoreactions occur once 3KP* is
completely formed. Consequently, the photophysical proper-
ties of D7 were reinvestigated in longer timescales by means of
LFP.
Interestingly, D10 is the only linear dyad that generates an
oxetane upon absorption of UVA light. This must be related
with the length of the spacer compared to D4 and D6, which
may allow reaching the appropriate conformational arrange-
ment between the two chromophores enabling closer
interaction between the carbonyl group of BP and the C5
C6 double bond of Thy, thus favoring the formation of a triplet
exciplex (3[BP···Thy]*). This species would later evolve
toward the formation of the oxetane (see Scheme 3). In this
context, the shorter interchromophoric distance in D4 and D6
might be associated with a higher strain to reach the proper
3
conformational arrangement to form [BP···Thy]*. Indeed, a
significant degree of polymerization was observed for both
dyads, although in the case of D6 the (sterically less
demanding) hydrogen abstraction product PP-D6 was
obtained in low yields.
Excitation of D7 at 355 nm resulted in the formation of
3KP* with a maximum at 530 nm (see Figure 6). In agreement
Analysis of the triplet decay traces at 530 nm evidenced a
clear intramolecular quenching for all dyads (see Figure 5B).
This quenching was not associated to triplet−triplet
annihilation since the results obtained at different laser
intensities were very similar. The decays followed in all cases
a first-order exponential law; the reference compound BPN
showed a triplet lifetime of 1.5 μs, which was markedly
shortened in D10 (∼0,05 μs) in line with its highest
photochemical reactivity. By contrast, D4 was the dyad with
the longest lifetime, ca. 1.0 μs, which agrees well with its lowest
reactivity. Accordingly, D6 exhibited an intermediate triplet
lifetime (∼0,8 μs), shorter than D4 but longer than D10, in
line with its photoreactivity. Thus, a good correlation was
found between the results obtained in the steady-state
photolysis and the laser flash photolysis experiments.
Figure 6. LFP spectra recorded at the very beginning after the laser
pulse (A) and decay traces at 530 nm (B) for KP (black) and D7
(blue) after excitation at 355 nm in deaerated MeCN.
The triplet lifetimes obtained by LFP for all dyads and for
the reference compounds BPN and KP are summarized in
Table 1, together with the intramolecular quenching rate
constants (kQ), calculated by subtraction of the reciprocal
lifetimes. Thus, the kQ values for the dyads were in the order of
105−107 s−1, whereas the reported intermolecular photo-
with a previous report,33 the triplet lifetime of KP in the dyad
was strongly quenched (∼30 ns) compared to the isolated
chromophore (1.3 μs), in line with its high photochemical
reactivity. Interestingly, the transient absorption spectrum of
D7 clearly showed a band with maximum ca. 370 nm, very
similar to that observed for D10. Again, this band could be
associated with a triplet exciplex between KP and Thy, which
would evolve toward the formation of the oxetanes.
3
reaction rate constant between BP* and DMT is 3.5 × 108
M−1 s−1.39 Taking into account that the concentration of the
dyads employed in the product studies was in the order of 2.6
E
https://dx.doi.org/10.1021/acs.joc.0c02088
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
pubs.acs.org/joc
Article
1H NMR (400 MHz, CD3OD) δ 7.76−7.47 (m, 9H), 7.43 (s, 1H),
4.52 (s, 2H), 4.48 (s, 2H), 2.16 (s, 3H), 1.92 (s, 3H); 13C{1H} NMR
(100 MHz, CD3OD) δ 196.9, 168.4, 164.7, 151.9, 143.5, 140.4, 137.5,
136.3, 132.4, 130.0, 129.5, 128.1, 127.0, 108.9, 50.9, 42.5, 26.9, 11.5;
HRMS (ESI): m/z calcd for (MH+) C22H22N3O4: 392.1610, found:
392.1613.
Overall, the photoreactivity of the investigated dyads has
evidenced remarkable differences due to the interchromo-
phoric distance between BP and Thy and also to the
conformational arrangement provided by the spacer.
CONCLUSIONS
The synthesis of the intermediate Thy-1 has been explained
elsewhere.42 Briefly, to a solution of 6.35 g (50 mmol) of thymine in
100 mL of dimethylformamide (DMF), 15.5 g of Na2CO3 was added.
Then, 8.6 mL (70 mmol) of ethyl 4-bromobutyrate was added and
left stirring at 125 °C using a reaction block for 6h. After this time, the
crude product was cooled down to room temperature and left stirring
for 2 days. DMF was removed under reduced pressure and, after
addition of 50 mL of water, the unreacted thymine precipitated, which
was removed by filtration. The dissolved product was extracted with
dichloromethane, washed with brine (×2), and dried with MgSO4.
The solvent was removed under reduced pressure and the residue was
subsequently dissolved in 100 mL of NaOH 2 M and stirred under
reflux for 2 h. Then, the solution was acidified with HCl 4 M to pH 1
and the final product was purified by recrystallization. The
intermediate Thy-1 was obtained as a white solid (4.8 g, 45% yield).
Synthesis of N-(4-benzoylbenzyl)-4-(5-methyl-2,4-dioxo-3,4-di-
hydropyrimidin-1(2H)-yl)butanamide (Int-D6). To a solution
containing 1.7 g of thymine-1-butanoic acid (8.0 mmol), 2.1 g of
EDC (11.0 mmol), and 1.18 g of hydroxybenzotriazole (HOBt, 8.7
mmol) in anhydrous DMF, a solution of 1.8 g of BPN (7.3 mmol) in
DMF was added dropwise. The mixture was stirred for 2 h at 0 °C
using an ice bath. The DMF was removed under reduced pressure,
and the crude product was dissolved in dichloromethane and washed
with NaHCO3 1 M (×3), HCl 1 M (×3), and brine (×3). The final
product Int-D6 was purified by recrystallization with methanol as a
white solid (1.86 g, 60% yield).
■
The photobehavior of a series of dyads composed of
benzophenone and thymine separated by spacers of different
lengths has been investigated in the present work by means of
steady-state photolysis and transient absorption spectroscopy.
In general, the photoreactivity of the dyads can be satisfactorily
correlated with their photophysical properties. Ultrafast
spectroscopy reveals that, in all cases, the photochemical
reactions occur once the triplet excited state of the BP
chromophore has been fully populated after a few picoseconds.
In this context, nanosecond laser flash photolysis demonstrates
that D10 and D7 have the shortest triplet lifetimes, due to a
faster intramolecular quenching, in line with their higher
photoreactivity. Interestingly, a transient absorption band with
maximum centered at ca. 370 nm is detected for both D10 and
D7 upon laser flash photolysis, which can be attributed to the
formation of a triplet exciplex that might finally evolve toward
the formation of oxetanes. In conclusion, the obtained results
suggest that not only the interchromophoric distance between
benzophenone and thymine but also the conformational
arrangement enhanced by the degree of flexibility of the
spacer play a significant role in the photobehavior of the
investigated dyads.
1H NMR (400 MHz, CD3OD) δ 7.78−7.45 (m, 9H), 7.41 (s, 1H),
4.46 (s, 2H), 3.78 (t, J = 7.2 Hz, 2H), 2.33 (t, J = 7.2 Hz, 2H), 2.05
(m, 2H), 1.87 (s, 3H); 13C{1H} NMR (100 MHz, DMSO-d6) δ
195.4, 171.4, 164.3, 150.9, 144.7, 141.4, 137.1, 135.5, 132.6, 129.8,
129.5, 128.5, 127.1, 108.4, 46.8, 41.8, 32.1, 24.6, 11.9; HRMS (ESI):
m/z calcd for (MH+) C23H24N3O4: 406.1760, found: 406.1764.
Synthesis of N-(4-benzoylbenzyl)-4-(3,5-dimethyl-2,4-dioxo-3,4-
dihydropyrimidin-1(2H)-yl)butanamide (dyad D6). To a solution of
135 mg of Int-D6 (0.3 mmol) in 4 mL of NaOH (2.5 M), 100 μL of
SO2(OMe)2 (1 mmol) was added dropwise. The mixture was stirred
overnight at room temperature. The crude product was extracted with
ethyl acetate (×3), washed with 1 M NaHCO3, dried with anhydrous
MgSO4, filtered, and concentrated under reduced pressure. The final
product was purified by precipitation in dichloromethane/hexane to
get D6 as a white solid (118 mg, 85% yield).
EXPERIMENTAL SECTION
■
Chemicals and Reagents. Thymine (Thy) and 4-benzoylbenzyl-
amine (BPN) hydrochloride were purchased from Achemblock. Ethyl
8-bromooctanoate was purchased from Fluorochem. Thymine-1-
acetic acid, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC),
ethyl 4-bromobutyrate, 1-hydroxybenzotriazole (HOBt), dimethyl
sulfate, sodium carbonate, and potassium carbonate were purchased
from Sigma-Aldrich. Sodium hydroxide (NaOH), hydrochloric acid
solution (HCl), acetonitrile (MeCN) spectroscopic grade, dimethyl-
formamide (DMF), dichloromethane (DCM), methanol (MeOH),
ethyl acetate, and magnesium sulfate anhydrous were purchased from
Scharlab.
Synthesis of the Dyads. Synthesis of N-(4-benzoylbenzyl)-2-(5-
methyl-2,4-dioxo-3,4-dihydropyrimidin-1(2H)-yl)acetamide (Int-
D4). To a solution of 74.5 mg of thymine-1-acetic acid (0.4 mmol)
in MeCN, 100 mg (0.4 mmol) of 4-benzoylbenzylamine hydro-
chloride (BPN) and 180 mg of EDC (0.94 mmol) were added. The
mixture was stirred at room temperature overnight. The organic
solvent was removed under reduced pressure and the crude product
was purified by column chromatography (SiO2, CH2Cl2/MeOH,
95:5). The intermediate Int-D4 was obtained as a colorless solid (105
mg, 70% yield).
1H NMR (400 MHz, CD3OD) δ 7.75−7.44 (m, 9H), 7.42 (s, 1H),
4.45 (s, 2H), 3.81 (t, J = 7.2 Hz, 2H), 3.29 (s, 3H), 2.32 (t, J = 7.2 Hz,
2H), 2.02 (m, 2H), 1.89 (s, 3H); 13C{1H} NMR (100 MHz,
CD3OD) δ 196.8, 173.4, 164.6, 151.8, 143.9, 139.8, 137.5, 136.3,
132.4, 130.0, 129.5, 128.1, 127.1, 108.9, 48.5, 42.4, 32.1, 26.9, 24.6,
11.5; Yield: 85%. HRMS (ESI): m/z calcd for (MH+) C24H26N3O4:
420.1923, found: 420.1927.
Synthesis of 8-(5-methyl-2,4-dioxo-3,4-dihydropyrimidin-1(2H)-
yl)octanoic acid (Thy-2). To a solution of 6.35 g of thymine (50
mmol) in DMF (100 mL), 7.5 g of Na2CO3 (50 mmol) and 14.8 mL
of ethyl 8-bromooctanoate (70 mmol) were added. The temperature
was risen using a reaction block until the solution was clear, and the
mixture was stirred for 6 h. Then, it was cooled down and left stirring
for 2 days at room temperature. The DMF was removed under
reduced pressure, and the crude product was dissolved in water (50
mL). The product was extracted with dichloromethane, washed with
brine (×3), and dried with anhydrous MgSO4. The solvent was
removed under reduced pressure, subsequently dissolved in 50 mL of
NaOH (2.5 M), and stirred under reflux, using a reaction block, for 2
h. Then, the mixture was cooled down to room temperature. The
solution was acidified with HCl (4 M) to pH 1, and the precipitate
was purified by silica gel chromatography using a mixture of ethyl
1H NMR (400 MHz, CD3OD) δ 7.78−7.47 (m, 9H), 7.41 (s, 1H),
4.52 (s, 2H), 4.48 (s, 2H), 1.89 (s, 3H); 13C{1H} NMR (100 MHz,
CD3OD) δ 196.9, 168.5, 165.6, 151.8, 143.5, 142.3, 137.5, 136.1,
133.1, 130.0, 129.5, 128.2, 127.1, 109.9, 49.9, 42.7, 10.9; HRMS
(electrospray ionization (ESI)): m/z calcd for (MH+) C21H20N3O4:
378.1457, found: 378.1454.
Synthesis of N-(4-benzoylbenzyl)-2-(3,5-dimethyl-2,4-dioxo-3,4-
dihydropyrimidin-1(2H)-yl)acetamide (dyad D4). To a solution of
Int-D4 (22.8 mg, 0.06 mmol) in 4 mL of NaOH (2.5 M) in pure
water, 30 μL of dimethyl sulfate (0.2 mmol) was added dropwise. The
mixture was stirred at room temperature overnight. The crude
product was extracted with ethyl acetate, dried with anhydrous
MgSO4, filtered, and concentrated under reduced pressure. The final
product D4 was obtained as a colorless solid (20 mg, 83% yield).
F
https://dx.doi.org/10.1021/acs.joc.0c02088
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
pubs.acs.org/joc
Article
acetate/methanol/acetic acid (8:2:0.1). The intermediate Thy-2 was
obtained as a white solid (10 g, 75% yield).
atmosphere through quartz cells. For photoproduct studies, higher
concentrations of the dyads (2.6 mM) were used; irradiations were
performed through Pyrex for 3 h.
1H NMR (400 MHz, CD3OD) δ 7.44 (s, 1H), 3.71 (t, J = 7.6 Hz,
2H), 2.22 (t, J = 7.6 Hz, 2H), 1.87 (s, 3H), 1.67-1.60 (m, 4H), 1.36
(m, 6H); 13C{1H} NMR (100 MHz, CD3OD) δ 176.1, 166.6, 151.6,
141.9, 109.7, 48.0, 34.7, 28.8, 28.5, 25.9, 25.0, 20.7, 10.8; HRMS
(ESI): m/z calcd for (MH+) C13H21N2O4: 269.1512, found:
269.1501.
Analytical Instrumentation. A semipreparative JASCO HPLC
system (PU-2080 Plus pump, DG-2080-54 line degasser, and LG-
2080-04 gradient unit) connected to a JASCO (UV-1575) detector
was used to separate and purify the different photoproducts, using an
isocratic flux (2 mL/min) of MeCN as an eluent and a SEA18
Teknokroma column, 5 μm (25 cm × 1 cm).
Synthesis of N-(4-benzoylbenzyl)-8-(5-methyl-2,4-dioxo-3,4-di-
hydropyrimidin-1(2H)-yl)octanamide (Int-D10). To a solution of
Thy-2 (0.73 g, 2.7 mmol) in DMF, 0.78 g of EDC (4.1 mmol) and
0.44 g of HOBt (3.3 mmol) were added; the mixture was kept at 0 °C
using an ice bath for 15 min. Then, a solution of BPN (0.74 g, 3.0
mmol) in DMF was added dropwise. The mixture was stirred at 0 °C
for 2 h. Then, DMF was removed under reduced pressure and the
crude product was dissolved in ethyl acetate and washed with 1 M
NaHCO3, HCl 1 M, and brine. The final product Int-D10 was
purified by recrystallization and obtained as a white solid (563 mg,
45% yield).
Spectroscopic Techniques. The 1H- and 13C-NMR spectra were
recorded at 400 and 100 MHz, respectively, using a Bruker AVANCE
III instrument; chemical shifts are reported in ppm.
High-resolution mass spectrometry (HRMS) was performed in an
ultra-performance liquid chromatography (UPLC) ACQUITY system
(Waters Corp.) with a conditioned autosampler at 4 °C. The
separation was accomplished on an ACQUITY UPLC BEH C18
column (50 mm × 2.1 mm i.d., 1.7 μm), which was maintained at 40
°C. The analysis was performed using acetonitrile and water (60:40 v/
v containing 0.01% formic acid) as the mobile phase with a flow rate
of 0.5 mL/min, and the injection volume was 5 μL. The Waters
ACQUITY XevoQToF spectrometer (Waters Corp.) was connected
to the UPLC system via an electrospray ionization (ESI) interface.
This source was operated in positive ionization mode with the
capillary voltage at 1.5 kV at 100 °C and the temperature of the
desolvation was 300 °C. The cone and desolvation gas flows were 40
and 800 L/h, respectively. The collision gas flow and collision energy
applied were 0.2 mL/min and 12 V, respectively. All data collected in
Centroid mode were acquired using Masslynx software (Waters
Corp.). Leucine-enkephalin was used at a concentration of 500 pg/μL
as the lock mass generating an [M + H]+ ion (m/z 556.2771) and
fragment at m/z 120.0813 and flow rate of 50 μL/min to ensure
accuracy during the MS analysis.
The steady-state absorption spectra were recorded using a JASCO
V-760 spectrophotometer. Laser flash photolysis (LFP) measure-
ments were performed using a pulsed Nd:YAG L52137 V LOTIS TII
at the excitation wavelength of 355 nm. The single pulses were of ca.
10 ns duration, and the energy was ∼12 mJ/pulse. The laser flash
photolysis system consisted of the pulsed laser, a 77250 Oriel
monochromator, and an oscilloscope DP04054 Tektronix. The output
signal from the oscilloscope was transferred to a personal computer.
Absorbances of all solutions were adjusted at ∼0.20 at 355 nm in
MeCN. All UV and LFP measurements were done using 10 × 10
mm2 quartz cuvettes at room temperature in deaerated conditions (25
min N2 bubbling), using 30 mL of fresh solution to avoid data
acquisition from photodegraded products.
Femtosecond transient absorption experiments were performed
using a pump−probe system. The femtosecond pulses were generated
with a mode-locked Ti-Sapphire laser of a compact Libra HE (4 W
power at 4 kHz) regenerative amplifier delivering 100 fs pulses at 800
nm (1 mJ/pulse). The output of the laser was split into two parts to
generate the pump and the probe beams. Thus, tunable femtosecond
pump pulses were obtained by directing the 800 nm light into an
optical parametric amplifier. In the present case, the pump was set at
280 nm and passed through a chopper prior to focusing onto a
rotating cell (1 mm optical path) containing the samples in organic
solution. The white light used as the probe was produced after part of
the 800 nm light from the amplifier traveled through a computer-
controlled 8 ns variable optical delay line and impinged on a CaF2
rotating crystal. This white light was in turn split into two identical
portions to generate reference and probe beams that then are focused
on the rotating cell containing the sample. The pump and the probe
beams were made to coincide to interrogate the sample. The power of
the pump beam was set to 180 μW. A computer-controlled imaging
spectrometer was placed after this path to measure the probe and the
reference pulses to obtain the transient absorption decays/spectra.
The experimental data were treated and compensated by the chirp
using the ExciPro program.
1H NMR (400 MHz, CD3OD) δ 7.76−7.43 (m, 9H), 7.41 (s, 1H),
4.46 (s, 2H), 3.69 (t, J = 7.2 Hz, 2H), 2.27 (t, J = 7.2 Hz, 2H), 1.86 (s,
3H), 1.65 (m, 4H), 1.36 (m, 6H); 13C{1H} NMR (100 MHz,
CD3OD) δ 196.9, 174.9, 165.5, 151.5, 144.2, 141.8, 137.5, 136.2,
132.4, 130.0, 129.6, 128.1, 127.1, 109.7, 47.9, 42.3, 35.6, 28.7, 28.5,
28.5, 25.9, 25.4, 10.8; HRMS (ESI): m/z calcd for (MH+)
C27H32N3O4: 462.2393, found: 462.2398.
Synthesis of N-(4-benzoylbenzyl)-8-(3,5-dimethyl-2,4-dioxo-3,4-
dihydropyrimidin-1(2H)-yl)octanamide (dyad D10). To a solution
of Int-D10 (260 mg, 0.56 mmol) in 3 mL of NaOH (2.5 M), 250 μL
of SO2(OMe)2 (2.5 mmol) was added dropwise. The mixture was
stirred overnight at room temperature. The crude product was
extracted with ethyl acetate (×3), washed with 1 M NaHCO3, dried
with anhydrous MgSO4, filtered, and concentrated under reduced
pressure. The final product was purified by precipitation in
dichloromethane/hexane to get D10 as a white solid (236 mg, 89%
yield).
1H NMR (400 MHz, CDCl3) δ 7.75−7.44 (m, 9H), 6.96 (s, 1H),
4.52 (s, 2H), 3.69 (t, J = 7.2 Hz, 2H), 3.34 (s, 3H), 2.25 (t, J = 7.2 Hz,
2H), 1.93 (s, 3H), 1.68 (m, 4H), 1.35 (m, 6H); 13C{1H} NMR (100
MHz, CD3OD) δ 196.8, 174.9, 164.6, 151.7, 144.1, 139.9, 137.5,
136.2, 132.4, 130.0, 129.6, 128.1, 127.1, 112.2, 49.1, 42.4, 35.6, 28.6,
28.5, 28.4, 26.9, 25.9, 25.4, 11.5; yield: 89%. HRMS (ESI): m/z calcd
for (MH+) C28H34N3O4: 476.2549, found: 476.2546.
(Z)-3-hydroxy-13-methyl-3-phenyl-11,12,13,14-tetrahydro-6-aza-
1(5,1)-pyrimidina-4(1,4)-benzenacyclodecaphane-12,14,7-trione
1
(PP-D6). H NMR (400 MHz, CD3OD) δ 7.64−7.26 (m, 9H), 6.91
(m, 1H), 5.43 (s, 1H), 4.32 (d, J = 13.6 Hz, 1H), 4.03 (d, J = 13.6 Hz,
1H), 3.70 (m, 1H), 3.55 (d, J = 13.6 Hz,1H), 3.27 (s, 3H), 3.14 (m,
1H), 3.03 (d, J = 13.6 Hz, 1H), 2.23 (m, 1H), 1.84 (m, 1H), 1.70 (m,
1H), 1.15 (m, 1H); 13C{1H} NMR (100 MHz, CD3OD) δ 174.7,
165.5, 151.2, 147.1, 145.0, 142.4, 138.5, 128.9, 127.8, 127.3, 126.9,
126.9, 126.5, 126.4, 108.1, 78.5, 48.7, 43.1, 38.0, 32.5, 27.0, 25.9;
HRMS (ESI): m/z calcd for (MH+) C24H26N3O4: 420.1923, found:
420.1927.
14,16-dimethyl-18-phenyl-17-oxa-12,14,4-triaza-1(8,2)-bicyclo-
[4.2.0]octana-2(1,4)-benzenacyclododecaphane-13,15,5-trione
1
(Ox-D10). H NMR (400 MHz, CDCl3) δ 7.50−7.08 (m, 9H), 5.91
(m, 1H), 4.90 (dd, J1 = 8.8 Hz, J2 = 14 Hz, 1H), 4.52 (s, 1H), 3.80
(dd, J1 = 4 Hz, J2 = 14 Hz, 1H), 3.57 (m, 1H), 3.34 (s, 3H), 2.49 (m,
1H), 2.24 (m, 1H), 2.00 (m, 1H), 1.62 (s, 3H), 1.8-0.2 (m, 10H);
13C{1H} NMR (100 MHz, CDCl3) δ 172.9, 168.6, 151.7, 143.7,
140.5, 138.6, 128.7, 128.5, 128.4, 128.0, 126.0, 90.7, 75.1, 69.0, 51.7,
42.7, 36.4, 28.6, 27.9, 27.3, 26.7, 26.6, 26.3, 24.4; HRMS (ESI): m/z
calcd for (MH+) C28H34N3O4: 476.2549, found: 476.2545. CCDC
2022525.
Steady-State Photolysis. Irradiations were performed in a
multilamp Luzchem photoreactor emitting at λmax = 350 nm (14 ×
8 W lamps). Isoabsorptive solutions at 350 nm (A = 0.05,
concentration ∼ 20 μM) of the different bichromophoric systems
were irradiated at different times in acetonitrile under a N2
G
https://dx.doi.org/10.1021/acs.joc.0c02088
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
pubs.acs.org/joc
Article
(3) Cadet, J.; Mouret, S.; Ravanat, J. L.; Douki, T. Photoinduced
damage to cellular DNA: direct and photosensitized reactions.
Photochem. Photobiol. 2012, 88, 1048−1065.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.joc.0c02088.
■
sı
(4) Rastogi, R. P.; Richa; Kumar, A.; Tyagi, M. B.; Sinha, R. P.
Molecular mechanisms of ultraviolet radiation-induced DNA damage
and repair. J. Nucleic Acids 2010, 2010, No. 592980.
1H- and 13C NMR spectra of the synthesized dyads and
intermediates; UV, femtosecond transient absorption,
and laser flash photolysis spectra and kinetics; and X-ray
crystallography data for Ox-D10 (PDF)
(5) Sinha, R. P.; Hader, D. P. UV-induced DNA damage and repair:
a review. Photochem. Photobiol. Sci. 2002, 1, 225−236.
(6) Chatterjee, N.; Walker, G. C. Mechanisms of DNA damage,
repair, and mutagenesis. Environ. Mol. Mutagen. 2017, 58, 235−263.
(7) Brash, D. E.; Haseltine, W. A. UV-induced mutation hotspots
occur at DNA damage hotspots. Nature 1982, 298, 189−192.
(8) Cadet, J.; Berger, M.; Douki, T.; Ravanat, J. L. Oxidative damage
to DNA: formation, measurement, and biological significance, In
Physiology Biochemistry and Pharmacology, Giessen, E. H., Ed.;
Springer: 1997; Vol. 131, pp 1−87.
Ox-D10_archive (CIF)
AUTHOR INFORMATION
Corresponding Authors
■
́
́
Ignacio Vaya − Departamento de Quımica, Instituto de
́
́
̀
Tecnologıa Quımica (UPV-CSIC), Universitat Politecnica de
(9) Taylor, J.-S.; Cohrs, M. P. DNA, light and Dewar pyrimidones:
the structure and biological significance of TpT3. J. Am. Chem. Soc.
1987, 109, 2834−2835.
̀
̀
Valencia, 46022 Valencia, Spain; orcid.org/0000-0003-
1682-9342; Email: igvapre@qim.upv.es
(10) Taylor, J.-S.; Garrett, D. S.; Cohrs, M. P. Solution-state
structure of the Dewar pyrimidone photoproduct of thymidylyl-(3′-
5′)-thymidine. Biochemistry 1988, 27, 7206−7215.
́
Miguel A. Miranda − Departamento de Quımica, Instituto de
́
́
̀
Tecnologıa Quımica (UPV-CSIC), Universitat Politecnica de
̀
̀
Valencia, 46022 Valencia, Spain; orcid.org/0000-0002-
(11) Kim, S.-T.; Malhotra, K.; Smith, C. A.; Taylor, J.-S.; Sancar, A.
Characterization of (6-4) Photoproduct DNA Photolyase. J. Biol.
Chem. 1994, 269, 8535−8540.
7717-8750; Email: mmiranda@qim.upv.es
Author
Alejandro Blasco-Brusola − Departamento de Quımica,
(12) Li, J.; Liu, Z.; Tan, C.; Guo, X.; Wang, L.; Sancar, A.; Zhong, D.
Dynamics and mechanism of repair of ultraviolet-induced (6-4)
photoproduct by photolyase. Nature 2010, 466, 887−890.
(13) Todo, T.; Ryo, H.; Yamamoto, K.; Toh, H.; Inui, T.; Ayaki, H.;
Nomura, T.; lkenaga, M. Similarity Among the Drosophila (6-
4)Photolyase, a Human Photolyase Homolog, and the DNA
Photolyase-Blue-Light Photoreceptor Family. Science 1996, 272,
109−112.
́
́
́
Instituto de Tecnologıa Quımica (UPV-CSIC), Universitat
̀
̀
̀
Politecnica de Valencia, 46022 Valencia, Spain
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.joc.0c02088
Author Contributions
(14) Todo, T.; Takemori, H.; Ryo, H.; Ihara, M.; Matsunaga, T.;
Nikaido, O.; Sato, K.; Nomura, T. A new photoreactivating enzyme
that specifically repairs ultraviolet light-induced (6-4)photoproducts.
Nature 1993, 361, 371−374.
(15) Todo, T.; Tsuji, H.; Otoshi, E.; Hitomi, K.; Kim, S.-T.; Ikenaga,
M. Characterization of a human homolog of 6-4 photolyase. Mutat.
Res., DNA Repair 1997, 384, 195−204.
(16) Epe, B.; Pflaum, M.; Boiteux, S. DNA damage induced by
photosensitizers in cellular and cell-free systems. Mutat. Res., Genet.
Toxicol. 1993, 299, 135−145.
The manuscript was written through the contributions of all
authors. All authors have given approval to the final version of
the manuscript.
Funding
́
Ministerio de Economia y Competitividad and Consellerıa
́
́
d’Educacio, Investigacio, Cultura i Esport.
Notes
The authors declare no competing financial interest.
(17) Michaud, S.; Hajj, V.; Latapie, L.; Noirot, A.; Sartor, V.; Fabre,
P. L.; Chouini-Lalanne, N. Correlations between electrochemical
behaviors and DNA photooxidative properties of non-steroidal anti-
inflammatory drugs and their photoproducts. J. Photochem. Photobiol.
B 2012, 110, 34−42.
(18) Marguery, M. C.; Chouini-Lalanne, N.; Ader, J. C.; Paillous, N.
Comparison of the DNA damage photoinduced by fenofibrate and
ketoprofen, two phototoxic drugs of parent structure. Photochem.
Photobiol. 1998, 68, 679−684.
ACKNOWLEDGMENTS
Financial support from the Spanish Government (RYC-2015-
■
́
17737 and CTQ2017-89416-R) and from the Consellerıa
́
d’Educacio Cultura i Esport (PROMETEO/2017/075 and
GRISOLIAP/2017/005) is gratefully acknowledged. The
authors would like to thank the use of RIAIDT-USC analytical
facilities for the X-ray crystallography analysis.
(19) Vinette, A. L.; McNamee, J. P.; Bellier, P. V.; McLean, J. R. N.;
Scaiano, J. C. Prompt and Delayed Nonsteroidal Anti-inflammatory
Drug-photoinduced DNA Damage in Peripheral Blood Mononuclear
Cells Measured with the Comet Assay. Photochem. Photobiol. 2003,
77, 390−396.
(20) Lhiaubet, V.; Gutierrez, F.; Penaud-Berruyer, F.; Amouyal, E.;
Daudey, J.-P.; Poteau, R.; Chouini−Lalanne, N.; Paillous, N.
Spectroscopic and theoretical studies of the excited states of fenofibric
acid and ketoprofen in relation with their photosensitizing properties.
New J. Chem. 2000, 24, 403−410.
ABBREVIATIONS
■
(6-4)PPs, pyrimidine (6-4) pyrimidone photoproducts; BP,
benzophenone; BPN, 4-benzoylbenzylamine; CPD, cyclo-
butane pyrimidine dimers; DMT, dimethylthymine; ISC,
intersystem crossing; KP, ketoprofen; LFP, laser flash
photolysis; NSAIDs, nonsteroidal anti-inflammatory drugs;
̀
PB, Paterno−Buchi; PS, photosensitizer; Thy, thymine; TTET,
̈
triplet−triplet energy transfer
(21) Lhiaubet, V.; Paillous, N.; Chouini-Lalanne, N. Comparison of
DNA Damage Photoinduced by Ketoprofen, Fenofibric Acid and
Benzophenone via Electron and Energy Transfer. Photochem.
Photobiol. 2001, 74, 670−678.
(22) Cuquerella, M. C.; Lhiaubet-Vallet, V.; Cadet, J.; Miranda, M.
A. Benzophenone Photosensitized DNA Damage. Acc. Chem. Res.
2012, 45, 1558−1570.
REFERENCES
■
(1) Friedel, M. G.; Cichon, M. K.; Carell, T. DNA damage and
repair: photochemistry, In CRC Handbook of Organic Photochemistry
and Photobiology, 2nd ed.; CRC Press LLC: Boca Raton, 2004.
(2) Kraemer, K. H. Sunlight and skin cancer: another link revealed.
Proc. Natl. Acad. Sci. U.S.A. 1997, 94, 11−14.
H
https://dx.doi.org/10.1021/acs.joc.0c02088
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
pubs.acs.org/joc
Article
(23) Bignon, E.; Marazzi, M.; Besancenot, V.; Gattuso, H.; Drouot,
G.; Morell, C.; Eriksson, L. A.; Grandemange, S.; Dumont, E.;
Monari, A. Ibuprofen and ketoprofen potentiate UVA-induced cell
death by a photosensitization process. Sci. Rep. 2017, 7, No. 8885.
(42) Martens, J.; Maison, W.; Schlemminger, I.; Westerhoff, O.;
Groger, H. Preparation of Precursors for PNA monomers.
WO20000028642000.
́
(24) Bosca, F.; Miranda, M. A. Photosensitizing drugs containing the
benzophenone chromophore. J. Photochem. Photobiol. B 1998, 43, 1−
26.
(25) Rogers, J. E.; Kelly, L. A. Nucleic Acid Oxidation Mediated by
Naphthalene and Benzophenone Imide and Diimide Derivatives:
Consequences for DNA Redox Chemistry. J. Am. Chem. Soc. 1999,
121, 3854−3861.
(26) Surana, K.; Chaudhary, B.; Diwaker, M.; Sharma, S.
Benzophenone: a ubiquitous scaffold in medicinal chemistry. Med.
Chem. Commun. 2018, 9, 1803−1817.
(27) Cuquerella, M. C.; Lhiaubet-Vallet, V.; Bosca, F.; Miranda, M.
A. Photosensitised pyrimidine dimerisation in DNA. Chem. Sci. 2011,
2, 1219−1232.
(28) Blasco-Brusola, A.; Navarrete-Miguel, M.; Giussani, A.; Roca-
́
́
Sanjuan, D.; Vaya, I.; Miranda, M. A. Regiochemical memory in the
adiabatic photolysis of thymine-derived oxetanes. A combined
ultrafast spectroscopic and CASSCF/CASPT2 computational study.
Phys. Chem. Chem. Phys. 2020, 22, 20037−20042.
(29) Burrows, C. J.; Muller, J. C. Oxidative Nucleobase
Modifications Leading to Strand Scission. Chem. Rev. 1998, 98,
1109−1151.
(30) Belmadoui, N.; Climent, M. J.; Miranda, M. A. Photochemistry
of a naphthalene-thymine dyad in the presence of acetone.
Tetrahedron 2006, 62, 1372−1377.
́
(31) Bonancía, P.; Vaya, I.; Climent, M. J.; Gustavsson, T.;
Markovitsi, D.; Jimenez, M. C.; Miranda, M. A. Excited-state
interactions in diastereomeric flurbiprofen-thymine dyads. J. Phys.
Chem. A 2012, 116, 8807−8814.
(32) Encinas, S.; Climent, M. J.; Gil, S.; Abrahamsson, U. O.;
Davidsson, J.; Miranda, M. A. Singlet excited-state interactions in
naphthalene-thymine dyads. ChemPhysChem 2004, 5, 1704−1709.
(33) Belmadoui, N.; Encinas, S.; Climent, M. J.; Gil, S.; Miranda, M.
A. Intramolecular interactions in the triplet excited states of
benzophenone-thymine dyads. Chem. − Eur. J. 2006, 12, 553−561.
(34) Dumont, E.; Wibowo, M.; Roca-Sanjuan, D.; Garavelli, M.;
Assfeld, X.; Monari, A. Resolving the Benzophenone DNA-Photo-
sensitization Mechanism at QM/MM Level. J. Phys. Chem. Lett. 2015,
6, 576−580.
(35) Delatour, T.; Douki, T.; D’Ham, C.; Cadet, J. Photo-
sensitization of thymine nucleobase by benzophenone through energy
transfer, hydrogen abstraction and one-electron oxidation. J. Photo-
chem. Photobiol. B 1998, 44, 191−198.
(36) Tamai, N.; Asahi, T.; Masuhara, H. Intersystem crossing of
benzophenone by femtosecond transient grating spectroscopy. Chem.
Phys. Lett. 1992, 198, 413−418.
(37) Gut, I. G.; Wood, P. D.; Redmond, R. W. Interaction of Triplet
Photosensitizers with Nucleotides and DNA in Aqueous Solution at
Room Temperature. J. Am. Chem. Soc. 1996, 118, 2366−2373.
́
́
(38) Miro, P.; Gomez-Mendoza, M.; Sastre, G.; Cuquerella, M. C.;
Miranda, M. A.; Marín, M. L. Generation of the Thymine Triplet
State by Through-Bond Energy Transfer. Chem. − Eur. J. 2019, 25,
7004−7011.
(39) Joseph, A.; Prakash, G.; Falvey, D. E. Model studies of the (6-4)
photoproduct photolyase enzymz: laser flash photolysis experiments
confirm radical ion intermediates in the sensitized repair of thymine
oxetane adducts. J. Am. Chem. Soc. 2000, 122, 11219−11225.
(40) Martínez, L. J.; Scaiano, J. C. Transient intermediates in the
laser flash photolysis of ketoprofen in aqueous solution: unusual
photochemistry of the benzophenone chromophore. J. Am. Chem. Soc.
1997, 119, 11066−11070.
́
(41) Perez-Ruiz, R.; Groeneveld, M.; van Stokkum, I. H. M.;
Tormos, R.; Williams, R. M.; Miranda, M. A. Fast transient absorption
spectroscopy of the early events in photoexcited chiral benzophenone-
naphthalene dyads. Chem. Phys. Lett. 2006, 429, 276−281.
I
https://dx.doi.org/10.1021/acs.joc.0c02088
J. Org. Chem. XXXX, XXX, XXX−XXX