Fluorescent Probes for Zinc Ions
FULL PAPER
spectra were obtained by means of a JEOL AccuTof spectrometer, and
EI spectra by using a JEOL JMS600H spectrometer. Spectrophotometric
and fluorimetric titrations were conducted by using a Varian Cary 100
Bio UV–visible spectrophotometer and a Varian Cary Eclipse fluores-
cence spectrophotometer, respectively.
155.79, 149.18, 143.06, 137.00, 126.71, 123.02, 122.53, 119.78, 60.01,
53.70 ppm; MS (ESI): m/z: calcd [M+Na+]: 346.1; found: 346.1.
Compound 12b: This was prepared by deprotecting 11b by the proce-
dure described above for the preparation of 12a. 1H NMR (300 MHz,
CDCl3): d=9.98 (s, 1H), 8.53 (d, J=4.2 Hz, 2H), 7.82 (d, J=6.6 Hz,
2H), 7.67 (t, J=7.8 Hz, 2H), 7.60–7.54 (m, 4H), 7.18–7.14 (m, 2H), 3.82
(s, 4H), 3.78 ppm (s, 2H); 13C NMR (75 MHz, CDCl3): d=191.97, 159.22,
149.11, 146.59, 136.56, 135.50, 129.86, 129.32, 122.92, 122.18, 60.17,
58.25 ppm; HRMS (ESI): m/z: calcd [M+Na+]: 340.1426; found:
340.1421.
Compound 9: 5-Bromomethyl-5’-methyl-2,2’-bipyridyl[63] (0.28 mmol,
75 mg) was dissolved in triethyl phosphite (2 mL). The mixture was
heated at 1258Cfor 4 h. Excess of triethyl phosphite was removed under
high vacuum in a fume hood. The crude product was analyzed by TLC
(silica, MeOH/CH2Cl2 0.2 mL/4 mL, Rf =0.35). Compound 9 was isolated
1
by silica chromatography using 0–4% MeOH in CH2Cl2 (93%). H NMR
Compound 3a: Note: The reaction flask was protected from ambient
light by aluminum foil; work-up and purification were carried out under
illumination of red light bulbs. NaH (60% in mineral oil, 26 mg,
0.66 mmol) was added to a solution of 12a (70 mg, 0.2 mmol) in anhy-
drous dimethoxyethane (0.5 mL) in the reaction flask. The suspension
was stirred for 8 min while the reaction mixture changed color to brown.
The flask was cooled in an ice bath (08C) and the solution of 9 (69 mg,
0.22 mmol) in anhydrous dimethoxyethane (0.5 mL) was added dropwise.
After the mixture had been stirred overnight, icy brine was added to
quench the reaction. The reaction mixture was partitioned between
CH2Cl2 and basic brine (pH 11). The organic layer was dried over
Na2SO4, then the solvent was removed under vacuum. The residue was
chromatographed on alumina gel with 10% EtOAc in CH2Cl2. The isolat-
ed product (66 mg, 60%) was precipitated from a CH2Cl2 solution by ad-
dition of hexanes to afford pure trans-3a (22 mg, 20%). 1H NMR
(300 MHz, CDCl3): d=8.71 (s, 1H), 8.54 (d, J=4.2 Hz, 2H), 8.51 (s, 1H),
8.34 (d, J=8.4 Hz, 2H), 8.29 (d, J=8.4 Hz, 1H), 7.91 (d, J=8.4 Hz, 1H),
7.73–7.62 (m, 5H,), 7.30 (d, J=16.2 Hz, 1H), 7.20–7.18 (m, 2H), 6.97–
6.88 (m, 3H), 3.89 (s, 6H), 2.41 ppm (s, 3H); 13C NMR (75 MHz, CDCl3):
d=159.7, 155.2, 153.6, 150.0, 149.3, 148.0, 143.5, 142.1, 137.7, 136.8, 133.4,
133.2, 127.9, 127.1, 126.9, 124.3, 124.0, 123.0, 122.3, 120.9, 120.7, 60.0,
53.6, 18.6 ppm; HRMS (ESI): m/z: calcd [M+Na+]: 512.1885; found:
512.1887.
(300 MHz, CDCl3): d=8.55 (s, 1H), 8.49 (s, 1H), 8.30 (d, J=8.4 Hz, 1H),
8.25 (d, J=7.8 Hz, 1H), 7.77 (dd, J=2.4, 8.4 Hz, 1H), 7.61 (dd, J=1.8,
8.4 Hz, 1H), 4.06 (m, 4H), 3.18 (d, J=21.6 Hz, 2H), 2.38 (s, 3H),
1.26 ppm (t, J=7.2 Hz, 6H).
Compound 10a: A round-bottomed flask charged with 2,5-thiophenedi-
carboxaldehyde (5.0 mmol, 701 mg) and ethylene glycol (5.0 mmol,
279 mL) in benzene (25 mL) was equipped with a Dean–Stark distilling
receiver (5.0 mL). A catalytic amount of toluenesulfonic acid (TsOH)
was added and the reaction mixture was stirred for 5 h under reflux. The
reaction mixture was cooled to room temperature, then the solvent was
removed and the residue was partitioned between CH2Cl2 and NaHCO3
(0.1m). The organic portion was separated and dried over Na2SO4 before
the solvent was removed under vacuum. The crude product was chroma-
tographed (silica, hexanes/CH2Cl2 1:1–1:9 v/v) to afford 10a (87%).
1H NMR (300 MHz, CDCl3): d =9.91 (s, 1H), 7.68 (d, J=3.6 Hz, 1H),
7.25 (d, J=3.6 Hz, 1H), 6.15 (s, 1H), 4.12 (m, 2H), 4.08 ppm (m, 2H);
13CNMR (75 MHz, CDCl 3): d=183.35, 152.48, 143.94, 136.24, 126.82,
99.74, 65.54 ppm; HRMS (EI): m/z: calcd [M+]: 184.0194; found:
184.0192.
Compound 10b: This was prepared by mono-protection of terephthalal-
dehyde with ethylene glycol, by the procedure described above for the
1
preparation of 10a. Yield 67%; H NMR (300 MHz, CDCl3): d=10.04 (s,
1H), 7.90 (d, J=8.4 Hz, 2H), 7.65 (d, J=8.4 Hz, 2H), 5.88 (s, 1H), 4.16–
4.04 ppm (m, 4H).
Compound 3b: Compound 3b was prepared by Horner–Wadworth–
Emmons reaction between 12b and 9 by the same procedure as for 3a
above. The isolated product (49.6 mg, 73%) was precipitated from a
CH2Cl2 solution by addition of hexanes to afford pure trans-3b (31.8 mg,
49%). 1H NMR (300 MHz, CDCl3): d=8.74 (d, J=1.8 Hz, 1H), 8.55–
8.51 (m, 3H), 8.36 (d, J=8.4 Hz, 1H), 8.30 (d, J=8.4 Hz, 1H), 7.96 (dd,
J=2.4, 8.4 Hz, 1H), 7.72–7.59 (m, 5H), 7.52 (d, J=8.4 Hz, 2H), 7.44 (d,
J=8.4 Hz, 2H), 7.24–7.08 (m, 4H), 3.83 (s, 4H), 3.72 (s, 2H), 2.40 ppm
(s, 3H); 13CNMR (75 MHz, CDCl 3): d=159.91, 155.27, 153.61, 149.85,
149.21, 148.19, 139.47, 137.59, 136.58, 135.87, 133.48, 132.94, 130.68,
129.51, 126.85, 124.70, 123.02, 122.15, 120.82, 120.73, 60.23, 58.46,
18.54 ppm; HRMS (ESI): m/z: calcd [M+Na+]: 506.2321; found:
506.2312.
Compound 11a: Di(2-picolyl)amine (128 mg, 1.07 mmol) was added
dropwise to an anhydrous 1,2-dichloroethane (4 mL) solution of 10a
(198 mg, 1.07 mmol). The mixture was stirred overnight before NaBH-
(OAc)3 (642 mg, 3.22 mmol) was added. The mixture was stirred for an-
other 2 h, then the solvent was removed under vacuum. The residue was
washed with basic brine (pH 11) and extracted with CH2Cl2 (325 mL).
The organic portions were dried over K2CO3, and then concentrated
under vacuum. Compound 11a (163 mg, yield 41%) was isolated by alu-
mina chromatography (CH2Cl2/EtOAc, 10:1–2:1 v/v); 1H NMR
(300 MHz, CDCl3): d=8.52 (d, J=4.8 Hz, 2H), 7.72–7.65 (m, 4H), 7.18–
7.14 (m, 2H), 7.01 (d, J=3.0 Hz, 1H), 6.86 (d, J=3.6 Hz, 1H), 6.05 (s,
1H), 4.19–4.00 (m, 4H), 3.85 ppm (s, 6H); 13C NMR (75 MHz, CDCl3):
d=159.67, 149.18, 144.55, 140.89, 136.78, 126.21, 125.62, 122.94, 122.26,
100.70, 65.42, 59.95, 53.48 ppm; HRMS (ESI): m/z: calcd [M+Na+]:
390.1252; found: 390.1250.
Example of fluorescence titration procedure: An MeCN solution of 3a
(6.0mm), zinc trifuloromethanesulfonate [Zn(OTf)2] (48.1mm), diisopropyl-
G
ethylamine (DIPEA) (6.0mm), and tetrabutylammonium perchlorate
(TBAP) (5.0mm) was titrated into a semi-micro quartz fluorimeter cuv-
ette (Starnaꢂ) containing an MeCN solution of 3a (840 mL, 6.0mm),
DIPEA (6.0mm), and TBAP (5.0mm) at 258C. The samples were excited
at l=375 nm and emission spectra were collected (Figure 4).
Compound 11b: Compound 11b was prepared by reductive amination
between 10b and di(2-picolyl)amine, by the procedure described above
for the preparation of 11a. Yield 82%; 1H NMR (300 MHz, CDCl3): d=
8.51 (d, J=4.2 Hz, 2H), 7.66 (t, J=7.8 Hz, 2H), 7.57 (d, J=7.8 Hz, 2H),
7.44 (s, 4H), 7.16–7.12 (m, 2H), 5.79 (s, 1H), 4.13–4.02 (m, 4H), 3.79 (s,
4H), 3.69 ppm (s, 2H); 13C NMR (75 MHz, CDCl3): d=159.27, 148.61,
139.77, 136.49, 136.02, 128.44, 126.19, 122.40, 121.61, 103.21, 64.88, 59.55,
57.83 ppm; HRMS (ESI): m/z: calcd [M+Na+]: 384.1688; found:
384.1695.
Crystal structure determination
Complex [Zn(6)Cl2]: Complex [Zn(6)Cl2] was prepared by mixing an
MeCN solution of ZnCl2 (0.1m, 0.2 mL) with a CH2Cl2 solution of 6
(0.02m, 1.0 mL). Solvent was removed on a rotary evaporator and the
crude product was washed with diethyl ether before being dried under
vacuum, then redissolved in MeCN to ꢀ0.02m. The solution was filtered
through a Pasteur pipette plugged with glass fiber. Crystals were grown
as large, colorless prisms by diffusing diethyl ether into the filtered
MeCN solution of [Zn(6)Cl2]. A crystal of [Zn(6)Cl2] was mounted on a
nylon loop and centered in the beam of 0.71073 D X-rays. They were in-
dexed and found to be monoclinic. Data set were taken out to about 288
2q. Frame data were obtained on a Bruker SMART APEX diffractome-
ter at T=153 K by using a detector distance of 5 cm. The number of
frames taken was 2400 with 20 second collection time followed by a final
50 frames to check on decomposition. The data sets had high redundancy
Compound 12a: Compound 11a (173 mg, 0.47 mmol) was dissolved in a
mixed solvent (14 mL) of 37% HCl/H2O/THF (1:6:7 by vol.). The solu-
tion was stirred overnight before being partitioned between basic brine
(pH 11) and CH2Cl2 (325 mL). The organic portions were dried over
K2CO3, then concentrated under vacuum. The residue was chromato-
graphed (alumina; CH2Cl2/EtOAc 10:1 to 2:1 v/v) to afford 12a (130 mg,
86%); 1H NMR (300 MHz, CDCl3): d=9.85 (s, 1H), 8.52 (d, J=4.2 Hz,
2H), 7.73–7.62 (m, 5H), 7.19–7.17 (m, 2H), 7.06 (d, J=3.6 Hz, 1H), 3.94
(s, 2H), 3.86 ppm (s, 4H); 13C NMR (75 MHz, CDCl3): d=183.22, 159.00,
Chem. Eur. J. 2008, 14, 2894 – 2903
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2901