and 1.27 mM and 0.27 mM for oxygen (concentrations of pure O2
gas and air at room temperature, respectively). An energy transfer
reaction from (R or S)-KP–a-Ch to NP was used to calculate
the triplet state lifetimes of these dyads. These experiments were
carried out using dichloromethane solutions of the (R or S)-KP–
a-Ch dyads (0.5 mM and 2 mM–20 mm).
19.0, 20.7, 22.6, 22.8, 23.8, 24.2, 26.0, 28.0, 28.2, 31.7, 31.8, 33.6,
35.7, 36.0, 36.1, 36.9, 39.5, 39.6, 42.0, 42.2, 50.0, 56.0, 56.5, 71.9,
122.5, 126.0, 128.3, 129.1, 132.1, 134.6, 137.7, 138.0, 142.0, 153.1,
171.7, 187.7. HRMS (FAB) C41H56O3S m/z calcd: 628.39502 [M+];
found 628.39624.
Compound 5. 1H NMR (300 MHz, CDCl3) d = 0.64 (s, 3H),
0.86 (d, J = 6.5 Hz, 6H), 0.88 (d, J = 6.5 Hz, 3H), 0.96 (s, 3H),
1.60 (d, J = 7.2 Hz, 3H), 0.90–2.02 (complex signal, 26 H), 2.15
(broad d, J = 15.0 Hz, 1H), 2.40 (broad d, J = 15.0 Hz, 1H), 3.99
(q, J = 7.2 Hz, 1H), 4.97 (m, 1H), 5.08 (broad d, J = 4.8 Hz,
1H), 7.00 (d, J = 3.6 Hz, 1H), 7.47–7.57 (m, 4H), 7.84 (d, J =
6.9 Hz, 2H); 13C NMR (75 MHz, CDCl3) d = 11.8, 18.6, 18.7,
18.8, 20.7, 22.5, 22.8, 23.7, 24.1, 26.1, 28.0, 28.1, 31.6, 31.8, 33.6,
35.7, 36.0, 36.1, 36.8, 39.5, 39.6, 41.8, 42.2, 50.0, 56.0, 56.5, 71.8,
122.5, 125.9, 128.3, 129.0, 132.1, 134.5, 137.7, 138.0, 142.0, 153.1,
171.6, 187.6. HRMS (FAB) C41H56O3S m/z calcd: 628.39502 [M+];
found 628.39381.
Singlet oxygen measurements
The luminescence (1270 nm) from singlet oxygen was detected by
means of an Oriel 71614 germanium photodiode (5 mm2) coupled
to the laser photolysis cell in right-angle geometry. An excimer
laser (LEXTRA50 Lambda Physik) was used for the excitation at
308 nm (laser excitation at 5 low-pulse energies for each molecule).
A 5 mm thick (5 cm diameter) 1050 nm cut-off silicon filter and a
1270 nm interference filter were placed between the diode and the
cell. The photodiode output current was amplified and fed into
a TDS-640A Tektronix oscilloscope via a Co-linear 150 MHz,
20 dB amplifier. The output signal from the oscilloscope was
transferred to a personal computer for study. Thus, the singlet
oxygen quantum yield (UD) of the dyads was determined in
dichloromethane solutions using the same absorbance value (0.30)
at 308 nm for each compound. A singlet oxygen quantum yield
(UD) of 0.95 for perinaphthenone in dichloromethane was used as
standard.23
3b-Cholesteryl 2-(5-benzoylthienyl)propanoate (TPA–b-Ch, 6)
To a solution of racemic 2-(5-benzoylthien-2-yl)propanoyl chlo-
ride (ca. 100 mg, 0.36 mmol) in CH2Cl2 (15 mL), b-cholesterol
(150 mg, 0.39 mmol) in CH2Cl2 (3 mL) was added dropwise, and
the mixture was heated under reflux for 7 h. The reaction mixture
was cooled to room temperature and then it was washed with
water (3 × 10 mol) and brine (10 mol). The organic phase was dried
over Na2SO4, evaporated and purified by column chromatography
(eluent: hexane–dichloromethane–ethyl acetate 90 : 5 : 5 v/v/v) to
give the corresponding ester TPA–b-Ch (189 mg, 0.30 mmol, 83%).
1H NMR (300 MHz, CDCl3) d = 0.67 (s, 3H), 0.84 (d, J = 6.6 Hz,
6H), 0.90 (d, J = 6.6 Hz, 3H), 1.01 (s, 3H), 1.60 (d, J = 7.2 Hz,
3H), 0.90–2.05 (complex signal, 26 H), 2.32 (m, 2H), 3.99 (q, J =
7.2 Hz, 1H), 4.66 (m, 1H), 5.37 (m, 1H), 7.02 (d, J = 3.9 Hz, 1H),
7.45–7.57 (m, 4H), 7.83 (d, J = 6.9 Hz, 2H); 13C NMR (75 MHz,
CDCl3) d = 11.7, 18.7, 19.2, 19.3, 21.0, 22.5, 22.8, 23.8, 24.3, 28.0,
28.2, 31.8, 31.9, 35.8, 36.2, 36.6, 36.9, 37.8, 38.0, 39.5, 39.7, 41.9,
42.3, 50.0, 56.1, 56.7, 75.1, 122.8, 125.8, 128.3, 129.1, 132.1, 134.8,
138.0, 139.3, 142.2, 152.9, 171.8, 188.0. HRMS (FAB) C41H56O3S
m/z calcd: 628.39502 [M+]; found 628.39293.
Synthesis of the dyads 4 and 5
To
a cold solution of racemic 2-(5-benzoylthiophen-2-yl)-
propanoic acid (100 mg, 0.38 mmol) in CH2Cl2 (1.5 mL),
dicyclohexylcarbodiimide (DCC, 136 mg, 0.66 mmol) was added
portionwise, and the mixture was stirred at 0 ◦C for 30 min.
Then, a solution of a-cholesterol (131 mg, 0.34 mmol) and 4-
dimethylaminopyridine (DMAP, 4 mg, 0.033 mmol) in CH2Cl2
(1.2 mL) was added, and stirring was continued for 8 h at the same
temperature. The reaction mixture was filtered through a pad of
R
Celiteꢀ, brine (5 mL) added to the filtrate, and the mixture was
extracted with CH2Cl2 (3 × 5 mL). The combined organic layers
were washed with water, the organic phase was dried over Na2SO4
and evaporated and further purified by column chromatography
(eluent: hexane–dichloromethane–ethyl acetate 90 : 5 : 5 v/v/v) to
yield a diastereomeric mixture of the corresponding esters. After
crystallization of the above mixture from hexane–ethyl acetate
(1 : 1 v/v), one of the stereoisomers precipitated as a white solid
(88 mg, 0,14 mmol, 41%, 4); the other isomer was obtained by
elimination of the solvent from the filtered solutions as a colorless
oil (79 mg, 0,12 mmol, 37%, 5). Alternative synthesis of the
corresponding ester from enantiomerically pure (S)-TPA obtained
by chiral HPLC separation of the racemic mixture was used for
stereochemical assignment.
Steady-state photolysis of the dyads 1, 2, 4 and 5
Deaerated dichloromethane (20 mL) solutions of (S)- or (R)-KP–
a-Ch dyads and (S)- or (R)-TPA–a-Ch dyads (100 mg, 0.16 mmol)
were irradiated through Pyrex with a 400 W medium pressure
mercury lamp. Reactions were monitored by TLC and NMR, and
only KP derived dyads (1 and 2) were found to be reactive. After
4 hours, the reaction mixtures were concentrated under reduced
pressure and submitted to silica gel column chromatography, using
hexane–ethyl acetate–dichloromethane (eluent: 70 : 20 : 10 v/v/v).
This afforded the pure photoproducts 8–10.13
Data for (R)-TPA–a-Ch (4) and (S)-TPA–a-Ch (5)
Compound 4. 1H NMR (300 MHz, CDCl3) d = 0.64 (s, 3H),
0.86 (d, J = 6.5 Hz, 6H), 0.88 (d, J = 6.5 Hz, 3H), 0.97 (s, 3H),
1.61 (d, J = 7.2 Hz, 3H), 0.90–1.99 (complex signal, 26 H), 2.20
(broad d, J = 15.0 Hz, 1H), 2.45 (broad d, J = 15.0 Hz, 1H), 3.99
(q, J = 7.2 Hz, 1H), 4.97 (m, 1H), 5.19 (broad d, J = 5.1 Hz,
1H), 7.00 (d, J = 3.9 Hz, 1H), 7.48–7.58 (m, 4H), 7.84 (d, J =
7.2 Hz, 2H); 13C NMR (75 MHz, CDCl3) d = 11.8, 18.7, 18.8,
Acknowledgements
Financial support from the Spanish Government (Grant
CTQ2004–03811 and CTQ2007–67010), Generalitat Valenciana
(GV06/099), Vicerrectorado de Investigacio´n Desarrollo e Inno-
vacio´n de la UPV (PAID-06–06) and Juan de la Cierva contract
to I. A., are gratefully acknowledged.
866 | Org. Biomol. Chem., 2008, 6, 860–867
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The Royal Society of Chemistry 2008
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