1982
J Fluoresc (2011) 21:1979–1986
N-((3-(2-(3-((1-phenylethylamino)methyl)-9-butyl-9H-carbazol
-6-yl)ethynyl)phenyl)methyl)-1-phenylethanamine (S, S-6
or R, R-6)
(m, 2H), 1.59 (d, 6H, J=7.2 Hz), 1.34-1.43 (m, 2H), 0.95
(t, 3H, J=7.2 Hz). 13C NMR (100 MHz, CDCl3/CD3OD) δ
141.9, 141.6, 140.5, 140.3, 137.8, 136.2, 132.7, 131.4,
130.4, 130.0, 129.3, 129.2, 129.1, 128.8, 128.5, 128.4,
128.0, 127.8, 127.7, 127.4, 127.2, 124.1, 123.9, 122.8,
121.8, 113.3, 109.0, 108.9, 91.0, 87.6, 54.0, 53.6, 43.2, 31.3,
29.5, 20.7, 15.7, 14.0. ESI-HRMS ([C58H61B2N3O4 + 2H]2+):
calcd 443.7503, found 443.7483.
5 (150.0 mg, 0.4 mmol) and S-1-phenylethylamine
(288.0 mg, 3.2 mmol) were dissolved in ethanol/THF
(3:2, V/V). The mixture was refluxed with stirring for 6 h
under N2. The solvent was removed under reduced
pressure, the residue was dissolved in 10 mL of MeOH/
THF, NaBH3CN (252.0 mg, 4.0 mmol) was added in
several portions and the mixture was stirred for 1 h at room
temperature. The solvent was removed and the residue was
taken up with dichloromethane (DCM), the organic phase
was washed with brine and dried over Na2SO4, DCM was
removed and the residue was purified with column
chromatography (silica gel, DCM/MeOH, 20:1, v/v). A
light yellow oil of S,S-6 was obtained in quantitative yield.
1H NMR (400 MHz, CDCl3) δ 8.17 (s, 1H), 8.00 (s, 1H),
7.53 (s, 1H), 7.46-7.50 (m, 6H), 7.40-7.43 (m, 7H), 7.28-
7.30 (m, 2H), 7.14-7.17 (m, 2H), 4.13-4.17 (q, 1H), 4.09
(t, 2H, J=7.6 Hz), 4.01 (d, 1H, J=6.8 Hz), 3.85-3.96
(m, 2H), 3.60-3.68 (m, 2H), 1.70-1.76 (m, 2H), 1.66 (d, 3H,
J=6.8 Hz), 1.58 (d, 3H, J=6.8 Hz), 1.30-1.38 (m, 2H),
0.91 (t, 3H, J=7.6 Hz). ESI-HRMS ([C42H43N3 + H]+):
calcd 590.3535, found 590.3518.
R,R-1 was prepared with the same method of S,S-1.
24.0 mg of yellow powder (R,R-1) was obtained, yield:
1
11.7 %. m.p. 118.9-119.4 °C. H NMR (400 MHz, CDCl3/
CD3OD) δ 8.25 (s, 1H), 7.86 (s,1H), 7.81 (s, 2H), 7.61
(d, 1H, J=8.4 Hz), 7.40-7.45 (m, 6H), 7.33-7.39 (m, 12H),
7.17-7.28 (m, 5H), 4.30 (t, 2H, J=7.2 Hz), 3.93-4.16
(m, 5H), 3.61-3.71 (m, 5H), 1.81-1.89 (m, 2H), 1.60 (d, 6H,
J=7.2 Hz), 1.37-1.42 (m, 2H), 0.95 (t, 3H, J=7.2 Hz). 13C
NMR (100 MHz, CDCl3/CD3OD) δ 142.0, 141.6, 140.7,
140.4, 137.1, 136.5, 132.9, 131.6, 130.5, 130.1, 129.7,
129.6, 129.4, 129.0, 128.6, 128.5, 128.0, 127.8, 127.7,
127.5, 127.2, 124.2, 124.0, 122.5, 122.0, 113.5, 109.0,
108.9, 91.1, 87.7, 54.0, 53.7, 43.3, 31.3, 29.9, 20.7, 16.1,
14.0. ESI-HRMS ([C58H61B2N3O4 + 2H]2+): calcd
443.7503, found 443.7501.
1
R, R-6 was prepared with same method of S,S-6. H
Results and Discussions
NMR (400 MHz, CDCl3) δ 8.17 (s, 1H), 7.95 (s, 1 H), 7.50
(s, 1H), 7.40-7.50 (m, 7H), 7.32-7.39 (m, 6H), 7.24-7.28
(m, 2H), 7.14-7.19 (m, 2H), 4.12-4.17 (q, 1H), 4.05 (t, 2H,
J=7.2 Hz), 4.00 (d, 1H, J=6.8 Hz), 3.84-3.92 (m, 2H),
3.61-3.69 (m, 2H), 1.68-1.74 (m, 2H), 1.66 (d, 3H,
J=6.8 Hz), 1.52 (d, 3H, J=6.8 Hz), 1.24-1.33 (m, 2H),
0.87 (t, 3H, J=7.2 Hz). ESI-HRMS ([C42H43N3 + 2H]2+):
calcd 295.6807, found 295.6812.
Synthesis Previously we devised chiral d-PET chemosensor
9 with unsubstituted carbazole as the fluorophore
(Scheme 1) [30]. In a later study we designed chemosensors
10–12 (Scheme 1) [31]. Interestingly, with introduce of
ethynylene subunit to the carbazole fluorophore, the d-PET
effect was switched to a-PET effect, which is probably due
to the electron-deficient feature of the ethynylene moiety.
Herein we design the bisboronic acid chemosensors based
on the scaffold of ethynylated carbazole. The binding
pocket of the new chiral chemosensor is larger than the
previous chiral bisboronic acid chemosensors [31].
The synthesis is with carbazole as the starting material
(Scheme 2), with iodination and formylation, the iodo-
aldehyde 4 was obtained. Then with Sonogashira coupling
reaction, the bis-aldehyde 5 was obtained. With reductive
amination and introduce of the binding moiety of boronic
acid moieties, the chiral chemosensor 1 (S,S-1 and R,R-1)
was obtained in moderate yields.
S, S-1 or R, R-1
S,S-6 (140.0 mg, 0.24 mmol), 2-(2-bromomethylphenyl)-
1,3,2-dioxaborinane (390.0 mg, 1.31 mmol) and K2CO3
(620.0 mg, 3.86 mmol) were mixed in acetonitrile (15 mL),
the mixture was refluxed for 10 h under N2. The mixture
was cooled and DCM was added. The organic layer was
washed with water and dried over anhydrous Na2SO4. The
solvent was removed under reduced pressure and the
residue was purified with column chromatography (Al2O3,
DCM/MeOH, 15:1, V/V). 26.0 mg of yellow powder
(S,S-1) was obtained, yield: 12.6 %. M.p. 116.5-117.2 °C.
1H NMR (400 MHz, CDCl3/CD3OD) δ 8.27 (s, 1H), 7.88
(s, 1H), 7.81 (d, 2H, J=6.0 Hz), 7.61 (d, 1H, J=8.8 Hz),
7.39-7.45 (m, 6H), 7.31-7.37 (m, 12H), 7.16-7.27 (m, 5H),
4.28 (t, 2H, J=7.2 Hz), 4.07-4.16 (m, 2H), 3.93-4.00
(m, 2H), 3.84 (d, 1H, J=13.2 Hz), 3.59-3.69 (m, 3H), 3.51
(d, 1H, J=12.4 Hz), 3.33 (d, 1H, J=13.6 Hz), 1.81-1.88
Fluorescence of the Chemosensors The excitation and the
emission spectra of S,S-1 were studied (Fig. 1). Broad
structureless excitation and emission bands were observed,
which are different from the structured excitation/emission
bands of the previously reported carbazole-based chemo-
sensor [30, 31]. Furthermore, the emission is red-shifted by
ca. 15 nm compared to a previously reported boronic acid