G. Makris and D. Papagiannopoulou
5.03 (s, 1H, NH), 4.57–4.51 (m, 1H, H-8′), 4.39–4.32 (m, 1H, H-7′),
3.25–3.17 (m, 1H, H-6′), 2.96 (dd, J = 12.8, 5.0 Hz, 1H, H-9′), 2.76 (d,
J = 13.2 Hz, 1H, H-9′), 2.73 (t, J = 7.4 Hz, 2H, H-2′), 1.93–1.72 (m, 4H,
H-3′,5′), 1.65–1.52 (m, 2H, H-4′). 13C NMR (75 MHz, CDCl3) δ 169.4 (C-1′),
163.8 (C-10′), 146.0 (d, J = 244 Hz, C-TFP), 140.6 (d, J = 239 Hz, C-TFP),
103.1 (t, C-TFP), 62.4 (C-7′), 60.6 (C-8′), 55.4 (C-6′), 40.4 (C-9′), 33.1 (C-2′),
28.2 (C-4′/C-5′), 24.6 (C-3′). Anal. calc. for C16H16F4N2O3S: C, 48.98; H,
4.11; N, 7.14. Found: C, 48.45; H, 3.94; N, 7.08%.
Synthesis of L3
2-Amino-3-(1-carboxy-2-(1H-imidazol-4-yl)ethylthio)propanoic acid
(3). Compound 3 was prepared similarly as compound 2: cysteine
hydrochloride monohydrate (528 mg, 3 mmol) was used in the place of
cysteamine hydrochloride followed by dropwise addition of aqueous
NaOH (6 mL, 2 M). After stirring for 3 days, the reaction mixture was
adjusted to pH 4 by addition of aqueous HCl 5 M and was concentrated
to 2 mL under vacuum. The concentrate was loaded on a conditioned
Sep-Pak® C18 cartridge, and the product was eluted with water to afford
a white crystalline solid. Yield: 486 mg (50%). 1H NMR (300 MHz, D2O) δ
8.21 (s, 1H, H-1), 7.08 (s, 1H, H-2), 3.88–3.76 (m, 1H, H-8), 3.53 (t, 1H,
H-5), 3.14–2.89 (m, 4H, H-4,7). 13C NMR (75 MHz, D2O) δ 177.7 (COOH),
172.6 (COOH), 133.6 (C-1), 131.3 (C-3), 116.6 (C-2), 53.8 (C-8), 49.7 (C-5),
31.3 (C-7), 27.8 (C-4). Anal. calc. for C9H13N3O4S·2HCl·0.5H2O: C, 31.68; H,
4.73; N, 12.31. Found: C, 31.78; H, 4.80; N, 12.12%.
Ethyl 2-((5-biotinamidopentyl)(pyridin-2-ylmethyl)amino)acetate (L1Et).
Biotin-TFP ester (158 mg, 0.4 mmol), ethyl 2-((5-aminopentyl)(pyridin-2-
ylmethyl)amino)acetate (1′) (327 mg, 0.84 mmol) and triethylamine (418 μL,
3 mmol) were added in methanol–acetonitrile (1:1 v/v, 10 mL), and the
solution was stirred at room temperature for 4 h. The solvents were
evaporated to dryness under vacuum, and the product was purified by silica
gel column chromatography (SiO2, 230–400 mesh, 15 g) using
dichloromethane–methanol 9:1 v/v as eluent to afford a greenish solid.
Yield: 170 mg (83%). 1H NMR (300 MHz, CDCl3) δ 8.43 (d, J = 4.2 Hz, 1H,
H-5), 7.59 (td, J = 7.7, 1.6 Hz, 1H, H-3), 7.42 (d, J = 7.8 Hz, 1H, H-2), 7.08 (dd,
J = 6.4, 5.3 Hz, 1H, H-4), 6.77 (s, 1H, NH), 6.55 (s, 1H, NH), 6.13 (s, 1H, NH),
4.46–4.36 (m, 1H, H-8′), 4.25–4.16 (m, 1H, H-7′), 4.06 (q, 2H, J = 7.1 Hz CH2CH3),
3.83 (s, 2H, H-6), 3.30 (s, 2H, H-7), 3.15–2.97 (m, 3H, Η-6′,13), 2.80 (dd, J = 12.7,
4.5 Hz, 1H, H-9′), 2.64 (d, J = 12.7 Hz, 1H, H-9′), 2.57 (t, J = 7.1 Hz, 2H, Η-9), 2.10
(t, J = 7.3 Hz, 2H, Η-2′), 1.70–1.51 (m, 4H, Η-5′,3′), 1.47–1.26 (m, 8H, H-
10,11,12,4′), 1.17 (t, J = 7.1 Hz, 3H, CH2CH3). 13C NMR (75 MHz, CDCl3) δ
173.3 (C-1′), 171.4 (C-8), 164.3 (C-10′), 159.4 (C-1), 148.9 (C-5), 136.6 (C-3),
123.1 (C-4), 122.1 (C-2), 61.7 (C-7′), 60.3 (CH2CH3), 60.2 (C-8′), 60.1 (C-6), 55.8
(C-6′), 55.0 (C-9), 54.1 (C-7), 40.5 (C-13), 39.3 (C-9′), 36.0 (C-2′), 29.3 (C-12),
28.3 (C-4′), 28.1 (C-5′), 27.1 (C-10), 25.8 (C-3′), 24.4 (C-11), 14.2 (CH2CH3). Anal.
calc. for C25H39N5O4S: C, 59.38; H, 7.77; N, 13.85. Found: C, 58.80; H, 7.76; N,
13.37%.
2-Biotinamido-3-(1-carboxy-2-(1H-imidazol-4-yl)ethylthio)propanoic
acid (L3). Biotin-TFP ester (140 mg, 0.35 mmol), compound 3 (220 mg,
0.65 mmol), and NaHCO3 (140 mg, 1.67 mmol) were dissolved in water–
acetone (1:3 v/v, 9 mL), and the mixture was stirred at room temperature
for 24 h. The product was purified by chromatography under the same
conditions used for L2, and a white solid was afforded. Yield: 82 mg
(47%). 1H NMR (300 MHz, MeOD) δ 8.65 (s, 1H, Η-1), 7.35 (s, 1H, Η-3),
4.60–4.48 (m, 2H, H-8,8′), 4.42–4.33 (m, 1H, H-7′), 3.68 (t, J = 7.4 Hz, 1H,
Η-5), 3.30–3.17 (m, 3H, Η-7,6′), 3.26 (dd, J = 15.0, 8.0 Hz, 1H, Η-4), 3.11
(dd, J = 15.1, 6.9 Hz, 1H, Η-4), 2.97 (dd, J = 12.8, 4.9 Hz, 1H, Η-9′) 2.74
(d, J = 13.0 Hz, 1H, Η-9′), 2.31 (t, J = 7.2 Hz, 2H, Η-2′), 1.93–1.57 (m, 4H,
Η-3′,5′), 1.57–1.37 (m, 2H, Η-4′). 13C NMR (75 MHz, MeOD) δ 176.5, 176.4
(C-6/C-91), 175.5 (C-1′), 166.1 (C-10′), 134.1 (C-3), 131.9 (C-1), 118.0 (C-2),
63.1 (C-7′), 61.4 (C-8′), 56.6 (C-6′), 54.2 (C-8), 48.5 (C-5), 40.9 (C-9′), 36.5
(C-2′), 34.3 (C-7), 29.2 (C-4′), 29.0 (C-5′), 28.0 (C-4), 26.4 (C-3′). Anal. calc.
for C19H27N5O6S2·H2O: C, 45.32; H, 5.80; N, 13.91. Found: C, 45.48; H,
5.72; N, 13.81%.
Synthesis of L2
2-(2-Aminoethylthio)-3-(1H-imidazol-4-yl)propanoic acid (2). 2-Chloro-
3-(1H-imidazol-4-yl)propanoic acid (500 mg, 2.86 mmol) and cysteamine
hydrochloride (340 mg, 3 mmol) were dissolved in a degassed mixture
of water–ethanol (1:1 v/v, 10 mL), followed by dropwise addition of
aqueous NaOH (4.5 mL, 2 M), under N2. The mixture was stirred for 3 days.
The pH was then adjusted to 6 by addition of aqueous HCl 5 M, and the
solvents were evaporated to dryness. The residue was extracted in
methanol (5 mL), and the filtrate was dried. The residue was recrystallized
twice from water–ethanol, and a white crystalline solid was afforded.
Yield: 285 mg (39%). MP: 182–185 °C. 1H NMR (300 ΜHz, d6-dmso) δ 7.78
(s, 1H, H-1), 6.92 (s, 1H, H-2), 3.63 (t, 1H, H-5), 2.91–3.11 (m, 3Η, H-8,4β),
2.76–2.90 (m, 3Η, H-7,4α). 13C NMR (75 ΜHz, d6-dmso) δ 173.4 (C-6),
134.4 (C-1), 133.4 (C-3), 116.7 (C-2), 48.9 (C-5), 39.8 (C-8), 29.0 (C-4), 28.1
(C-7). Anal. calc. for C8H13N3O2S·HCl·0.5 H2O: C, 36.85; H, 5.80; N, 16.12.
Found: C, 37.21; H, 5.59; N, 16.14%.
Syntheses of the rhenium complexes
fac-[Re(CO)3(L1)] (ReL1)
To a solution of ligand L1Et (80 mg, 0.16 mmol) in water (4 mL), aqueous
NaOH (240 μL, 0.48 mmol) was added, and the reaction mixture was
stirred for 20 min. The completion of hydrolysis was confirmed by HPLC,
and then the pH was adjusted to 6 with aqueous HCl 1 M. (NEt4)2[Re(CO)
3Br3] (122 mg, 0.16 mmol) and methanol (5 mL) were added to the
aforementioned solution, and the mixture was refluxed for 2 h. The
volume of the reaction mixture was reduced under vacuum to 1.5 mL,
and the solution was kept at 4 °C for 2 days. The precipitate formed
was recrystallized by slow evaporation from water–methanol, and a
greenish crystalline solid was afforded. Yield: 70 mg (59%). tR (min)
= 16.8. IR (KBr, cmÀ1) 2023, 1896, 1637. NMR data are in Table 1. MS
(ESI) (m/z): Calc. for C26H34N5O7ReS, M = 747.2. (+) Found: [M + H]+,
748.1 (100%); [M + Na]+, 770.1 (69%). (À) Found: [M À H]À, 746.10
(67%); [M + CH2O2-H]À, 792.1 (100%).
2-(2-Biotinamidoethylthio)-3-(1H-imidazol-4-yl)propanoic acid (L2).
Biotin-TFP ester (100 mg, 0.25 mmol), compound 2 (100 mg, 0.39 mmol),
and triethylamine (143 μL, 1 mmol) were added in methanol–acetonitrile
(1:1 v/v, 10 mL), and the solution was stirred at room temperature for
24 h. The solvents were evaporated to dryness, and the residue was
dissolved in water (2 mL) and loaded on a conditioned Sep-Pak® C18
fac-[Re(CO)3(L2/L3)] (ReL2 and ReL3)
To a solution of [Re(CO)3(H2O)3]Br (0.06 mmol) in water (4 mL), L2 (28 mg,
cartridge. The product was eluted with water–methanol (4:1 v/v), and 0.06 mmol) or L3 (29 mg, 0.06 mmol) was added, and the mixture was
after removal of the solvents, a white powder was afforded. Yield: refluxed for 1.5 h. The complex precipitated from water and was
95 mg (82%). 1H NMR (300 MHz, CDCl3) δ 8.61 (s, 1H, H-1), 7.36 (s, 1H, collected as a light yellow solid for ReL2 or an off-white solid for ReL3.
H-2), 4.69 (dd, J = 7.6, 4.9 Hz, 1H, H-8′), 4.51 (dd, J = 7.8, 4.5 Hz, 1H,
ReL2: Yield: 31 mg (73%). tR (min) = 14.8. IR (KBr, cmÀ1) 2025, 1902, 1629.
H-7′), 3.68 (t, J = 7.4 Hz, 1H, C-5), 3.56–3.37 (m, 3H, H-8,6′), 3.30 (dd,
NMR data are in Table 1. MS (ESI) (m/z): Calc. for C21H26N5O7ReS2,
M = 711.1. (+) Found: [M + H]+, 712.1 (100%); [M + Na]+, 734.1 (31%). (À)
Found: [M À H]À, 710.1 (100%).
J = 15.0, 8.2 Hz, 1H, H-4), 3.16 (dd, J = 15.6, 6.9 Hz, 1H, H-4), 3.08 (dd,
J = 13.0, 4.9 Hz, 1H, H-9′), 2.92–2.80 (m, 3Η, H-7,9′), 2.35 (t, J = 7.0 Hz,
2H, Η-2′), 1.86–1.56 (m, 4H, Η-3′,5′), 1.56–1.44 (m, 2H, Η-4′). 13C NMR
(75 MHz, D2O) δ 178.1 (C-6), 176.7 (C-1′), 165.3 (C-10′), 133.2 (C-1),
131.0 (C-3), 116.7 (C-2), 62.2 (C-7′), 60.4 (C-8′), 55.5 (C-6′), 49.6 (C-5),
39.9 (C-9′), 38.7 (C-2′), 35.6 (C-8), 30.7 (C-4), 28.0 (C-7), 27.9 (C-4′),
27.8 (C-5′), 25.2 (C-3′). Anal. calc. for C18H27N5O4S2·H2O: C, 47.04; H,
6.36; N, 15.24. Found: C, 46.72; H, 6.52; N, 14.92%.
1 C-9 corresponds to the carboxylate of the cysteine linker, marked as R in
Figure 1.
J. Label Compd. Radiopharm 2016, 59 95–102
Copyright © 2016 John Wiley & Sons, Ltd.