Inorganic Chemistry
Article
2.64 (t, J = 7.0 Hz, 2H, Ar−CH2), 1.80 (m, 2H, −CH2−), 1.44 (s, 9H,
−CH3).13C NMR (101 MHz, CDCl3) δ 171.51, 150.02, 146.34,
129.21, 123.63, 81.51, 59.12, 57.24, 56.24, 54.28, 33.07, 29.21, 28.07.
MALDI-HRMS (matrix: HCCA) calculated for C17H26N2O5, [M +
H]+ m/z 339.1914, found 339.1914.
Synthesis of 2,2′-(7-(2-((3-(4-aminophenyl)propyl)
(carboxymethyl)amino)ethyl)-1,4,7-triazonane-1,4-diyl)-
diacetic acid (8). Compound 7 (65 mg, 0.2 mmol) in 0.5 mL of
DCM in an ice bath was treated with 1 mL TFA/DCM (1:1). The
reaction mixture was warmed to room temperature and stirred
overnight. The solvent was evaporated in vacuo. The residue was taken
up in deionized (DI) water and passed through a 0.45 μm nylon
syringe filter. The aqueous solution was concentrated in vacuo to
Synthesis of tert-Butyl 2-((2-bromoethyl) (3-(4-nitrophenyl)-
propyl)amino)acetate (4). To a solution of 3 (3.42 g, 12.9 mmol) in
50 mL MeCN at 0 °C was added PPh3 (3.72 g, 14.2 mmol). NBS
(2.53 g, 14.2 mmol) was then added, in portions, over 1 h. The
reaction mixture was stirred at 0 °C for 30 min, after which the
reaction mixture was allowed to warm to room temperature and stirred
for 3 h. The resulting mixture was evaporated into a yellowish solid.
The residue was passed through a short silica column eluted with 5%
1
provide 8 (50 mg, 83.3%) as a yellow solid. H NMR (400 MHz,
D2O) δ 7.35−7.17 (m, 4H, Ar−H), 3.96 (s, 2H, N−CH2CO−), 3.88
(s, 4H, N−CH2CO−), 3.48−3.35 (m, 2H, N−CH2−), 3.27 (s, 4H,
N−CH2−), 3.23−3.05 (m, 8H, N−CH2−), 2.96−2.88 (m, 4H, N−
CH2−), 2.65 (t, J = 7.3 Hz, 2H, Ar−CH2−), 2.07−1.85 (m, 2H,
−CH2CH2CH2−). 13C NMR (101 MHz, D2O) δ 171.33, 168.68,
141.49, 130.07, 128.02, 123.20, 56.24, 54.48, 51.12, 50.02, 49.80,
48.59, 31.04, 24.25. MALDI-HRMS (matrix: HCCA) calculated for
C23H37N5O6, [M + H]+ m/z 480.2817, found 480.2822.
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EA in PE to obtain 4 (3.75 g, 72.7%) as a yellow oil. H NMR (400
MHz, CDCl3) δ 8.12 (d, J = 8.7 Hz, 2H, NO2−Ar−H), 7.34 (d, J = 8.6
Hz, 2H, Ar−H), 3.41−3.34 (m, 2H, Br−CH2−), 3.32 (s, 2H,
COCH2N), 3.05 (t, J = 7.1 Hz, 2H, −CH2CH2Br), 2.81−2.74 (m, 2H,
NH−CH2CH2−), 2.70 (t, J = 7.0 Hz, 2H, Ar−CH2−), 1.87−1.73 (m,
2H, −CH2−), 1.51−1.38 (m, 9H, CH3).13C NMR (101 MHz, CDCl3)
δ 170.48, 150.12, 146.33, 129.24, 123.63, 81.30, 56.13, 55.68, 53.38,
33.07, 30.55, 29.34, 28.16.
Synthesis of 2,2′-(7-(2-((carboxymethyl)(3-(4-
isothiocyanatophenyl)propyl)amino)ethyl)-1,4,7-triazonane-
1,4-diyl)diacetic acid (9, p-SCN-PhPr-NE3TA). To a solution of 8
(4.8 mg, 0.01 mmol) in DI water was added a 1 M solution of
thiophosgene in CHCl3. The resulting mixture was stirred for 4 h at
room temperature. The aqueous layer was separated and washed with
CHCl3. The aqueous layer was evaporated to dryness to provide 9 (5
Synthesis of Di-tert-butyl-2,2′-(7-(2-((2-(tert-butoxy)-2-
26
oxoethyl)(3-(4-nitrophenyl)propyl)amino) ethyl)-1,4,7-triazo-
nane-1,4-diyl)diacetate (5). To a solution of NO2AtBu (1 g, 2.8
1
mg, 95.7%) as a yellowish solid. H NMR (400 MHz, D2O) δ 7.26−
mmol) in 10 mL of MeCN was added ethyldiisopropylamine (DIEA)
(0.72 g, 5.6 mmol) and 4 (1.12 g, 2.8 mmol). The reaction mixture
was left at room temperature overnight. The resulting solution was
filtered and concentrated. The residue was purified using silica column
eluted with 10% MeOH in DCM to obtain 5 (1 g, 52.9%) as a waxy
solid. 1H NMR (400 MHz, CDCl3) δ 8.09 (d, J = 8.6 Hz, 2H, NO2−
Ar−H), 7.31 (d, J = 8.6 Hz, 2H, Ar−H), 3.27 (s, 4H, COCH2N), 3.22
(s, 2H, COCH2N), 3.01−2.63 (m, 18H, N−CH2), 2.63−2.56 (m, 2H,
Ar−CH2−), 1.81−1.70 (m, 2H, −CH2−), 1.40 (s, 18H, CH3), 1.40 (s,
9H, CH3).13C NMR (101 MHz, CDCl3) δ 171.40, 170.79, 150.33,
146.29, 129.22, 123.56, 80.84, 80.71, 59.78, 56.14, 55.48, 54.04, 33.32,
29.06, 28.19, 28.16. MALDI-HRMS (matrix: HCCA) calculated for
C35H59N5O8, [M + H]+ m/z 678.4436, found 678.4435.
7.14 (m, 4H, Ar−H), 3.85 (s, 2H, −NCH2CO−), 3.72−3.57 (m, 4H,
N−CH2−), 3.40−3.29 (m, 2H, N−CH2−), 3.12 (s, 4H,
−NCH2CO−), 3.09−2.58 (m, 14H, N−CH2−, Ar−CH2−), 2.08−
1.92 (m, 2H, −CH2CH2CH2−). MALDI-HRMS (matrix: HCCA)
calculated for C24H35N5O6S, [M + H]+ m/z 522.2381, found
522.2387.
Synthesis of NE3TA-PEG4-LLP2A. To a solution of LLP2A-PEG4
and DIEA (3 equiv) in DMF was added p-SCN-PhPr-NE3TA (1.2
equiv). The mixture was reacted at room temperature for 4 h. The
solvent was lyophilized, and the residue was purified using HPLC with
a stepwise gradient method at a flow rate of 1.5 mL/min. The elution
method started with 18% B for 3 min, followed by 18% to 35% B over
30 min (retention time of ∼22 min). The purity was determined to be
>95%, while the isolation yield was 65%. ESI-MS: observed, m/z (M +
2H)2+ = 846.544, calculated, (M + 2H)2+ = 847.437.
Synthesis of NOTA-PEG4-LLP2A. To a solution of LLP2A-PEG4
and DIEA (3 equiv) in DMF was added SCN-Bn-NOTA (1.2 equiv).
The mixture was reacted at room temperature for 4 h. The solvent was
lyophilized, and the residue was purified using HPLC with a stepwise
gradient method at a flow rate of 1.5 mL/min. The elution method
started with 18% B for 3 min, followed by 18% to 35% B over 30 min
(retention time of ∼26 min). The purity was determined to be >95%,
while the isolation yield was 63%. MALDI-TOF: observed, m/z (M +
H)+ = 1642.67, calculated, (M + H)+ = 1622.78.
Cu(II) Selectivity Evaluation (LC-MS). Stock solution A, which
contained 5 mM CuCl2 and 5 mM FeCl3, stock solution B, which
contained 5 mM CuCl2 and 50 mM FeCl3, and chelator 6 (20 mM)
were prepared using 0.1 M NH4OAc buffer (pH 4). All reagents used
were trace metal grade. Fifteen microliters (15 μL) of chelator 6 (300
nmol) was mixed with 5 μL stock solution A (25 nmol Cu(II), 25
nmol Fe(III)) and 192 μL buffer. The mixture was incubated at 70 °C
for 30 min to make all ions chelated. After cooling to room
temperature, an ESI-MS analysis was applied to check the mass
intensity of Fe(III)-6 complex and Cu(II)-6 complex. To further check
the Cu(II) selectivity of chelator 6 over Fe(III), 2 μL of chelator 6 (40
nmol) stock solution was mixed with 8 μL stock solution B (40 nmol
Cu(II), 400 nmol Fe(III)) and 190 μL buffer, and the resulting
mixture was incubated at 37 °C for 30 min. ESI-MS was used to check
the mass intensity of Fe(III)-6 complex and Cu(II)-6 complex. For
comparison purposes, the same procedures were also performed using
chelator p-NH2−Bn-NOTA instead of chelator 6.
Synthesis of 2,2′-(7-(2-((carboxymethyl)(3-(4-nitrophenyl)-
propyl)amino)ethyl)-1,4,7-triazonane-1,4-diyl)diacetic acid (6).
Compound 5 (500 mg, 0.74 mmol) in 2 mL of DCM on an ice bath
was treated with 10 mL TFA/DCM (1:1). The resulting mixture was
gradually warmed to ambient temperature and stirred overnight. The
solvents were evaporated and further coevaporated with 20 mL of
CHCl3 three times to obtain 6 (400 mg, 100%) as a yellow oil as its
1
TFA salts. H NMR (400 MHz, D2O) δ 7.98 (d, J = 8.8 Hz, 2H,
NO2−Ar−H), 7.33 (d, J = 8.7 Hz, 2H, Ar−H), 3.99 (s, 2H,
COCH2N), 3.86 (s, 4H, COCH2N), 3.47−3.37 (m, 2H, N−CH2),
3.24 (m, 4H, N−CH2), 3.21−3.04 (m, 8H, N−CH2), 2.92 (m, 4H,
N−CH2), 2.71 (t, J = 7.3 Hz, 2H, Ar−CH2−), 2.11−1.91 (m, 2H,
−CH2−).13C NMR (101 MHz, D2O) δ 171.19, 168.53, 148.59,
146.21, 129.48, 123.85, 56.17, 54.42, 54.33, 51.10, 50.92, 49.86, 49.81,
48.55, 31.43, 23.94. MALDI-HRMS (matrix: HCCA) calculated for
C23H35N5O8, [M + H]+ m/z 510.2558, found 510.2588.
Synthesis of Di-tert-butyl-2,2′-(7-(2-((3-(4-aminophenyl)-
propyl)(2-(tert-butoxy)-2-oxoethyl)amino) ethyl)-1,4,7-triazo-
nane-1,4-diyl)diacetate (7). To a solution of 6 (136 mg, 0.2
mmol) in 5 mL MeOH was added 10% Pd/C. The resulting mixture
was bubbled with H2 at room temperature for 3 h. The reaction
mixture was filtered and the filtrate was concentrated in vacuo to
provide pure 7 (100 mg, 77.1%). 1H NMR (400 MHz, CDCl3) δ 6.88
(d, J = 8.3 Hz, 2H, NO2−Ar−H), 6.56 (d, J = 8.3 Hz, 2H, NO2−Ar−
H), 3.61 (brs, 2H, −NH2−), 3.33 (s, 4H, COCH2N), 3.20 (s, 2H,
COCH2N), 3.29−2.47 (m, 18H, −NCH2−), 2.42 (t, J = 7.5 Hz, 2H,
Ar−CH2−), 1.69−1.59 (m, 2H, −CH2−), 1.39 (s, 18H, −CH3), 1.37
(s, 9H, −CH3). 13C NMR (101 MHz, CDCl3) δ 170.66, 170.56,
144.50, 131.35, 129.07, 115.28, 81.52, 81.39, 58.05, 55.58, 53.90,
53.45, 53.23, 52.66, 49.93, 49.87, 32.35, 28.68, 28.14, 28.11. MALDI-
HRMS (matrix: HCCA) calculated for C35H61N5O6, [M + H]+ m/z
648.4695, found 648.4701.
Cu(II) Selectivity Evaluation (UV-vis). All stock solutions were
prepared using 0.1 M NH4OAc buffer (pH 4). All reagents used were
trace metal grade. Chelator 6 (10 mM) was mixed with 10 mM Cu(II)
or 10 mM Fe(III) at a volume ratio of 1:1, and the mixtures were
H
Inorg. Chem. XXXX, XXX, XXX−XXX