Ligand for Radiation Cancer Therapy
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 1 123
(s), 155.9 (s). Anal. Calcd for C14H20N2O5: C, 56.75; H, 6.80.
Found: C, 56.77; H, 7.03.
(CDCl3) δ 28.01 (q), 47.0 (t), 47.3 (t), 47.7 (t), 47.9 (t), 49.1 (t),
49.4 (t), 50.0 (t), 51.3 (t), 52.0 (t), 52.1 (t), 52.6 (t), 79.1 (s), 79.2
(s), 155.3 (s), 155.5 (s).
Toluene-4-sulfonic Acid 2-tert-Butoxycarbonylamino-3-(4-
nitrophenyl)propyl Ester (7). To a solution of 6 (7.15 g, 24.1
mmol) and Et3N (8.79 g, 86.9 mmol) in THF (50 mL) were added
DMAP (50 mg) and TsCl (5.51 g, 28.9 mmol). The resulting
mixture was stirred for 48 h at room temperature. Saturated
NaHCO3 solution (50 mL) was added, and the reaction mixture
was extracted with ether (3 × 200 mL). The combined ether layers
were washed with saturated citric acid (100 mL), H2O (100 mL),
5% NaHCO3 (100 mL), and H2O (100 mL). The ether layer was
dried, filtered, concentrated to ∼150 mL, and left in the freezer,
and the precipitate was filtered while washing with EtOH to provide
7 (10.4 g, 96%). For preparation of analytical sample, the residue
could be purified via column chromatography on silica gel eluting
with 30% EtOAc in hexanes. Pure 7 was thereby obtained as a
white solid. 1H NMR (CDCl3) δ 1.38 (s, 9 H), 2.48 (s, 3 H),
2.85–3.04 (m, 2 H), 3.88 (d, J ) 6.9 MHz, 1 H), 4.05 (d, J ) 8.4
MHz, 2 H), 4.81 (d, J ) 8.3 MHz, 1 H), 7.27 (d, J ) 7.9 MHz, 2
H), 7.36 (d, J ) 8.1 MHz, 2 H), 7.77 (d, J ) 7.9 MHz, 2 H), 8.09
(d, J ) 8.1 MHz, 2 H); 13C NMR (CDCl3) δ 21.6 (q), 28.1 (q),
37.1 (t), 50.5 (d), 70.1 (t), 80.0 (s), 123.6 (d), 127.9 (d), 130.0 (d,
2C), 132.1 (s), 144.8 (s), 145.4 (s), 146.7 (s), 154.9 (s). Anal. Calcd
for C21H26N2O7S: C, 55.99; H, 5.82. Found: C, 55.81; H, 5.87.
4-(4-Nitrobenzyl)oxazolidin-2-one (8). To a mixture of N-BOC-
protected TACN 10 (278 mg, 0.84 mmol) and K2CO3 (116 mg,
4.2 mmol) in CH3CN (30 mL) was added 7 (378 mg, 0.84 mmol).
The resulting mixture was heated to reflux and stirred for 5 days.
The reaction mixture was cooled to room temperature and
evaporated to dryness. The residue was purified via column
chromatography on neutral alumina eluting with 2% MeOH in
Di-tert-butyl 7-[2-tert-Butoxycarbonylamino-3-(4-nitrophenyl)-
propyl][1,4,7]triazanonane-1,4-dicarboxylate (11). To a solution of
10 (5.7 g, 17.3 mmol) in CH3CN (20 mL) were added 9 (4.58 g,
16.48 mmol) and diisopropylethylamine (2.34 g, 18.13 mmol). The
resulting mixture was refluxed for 5 days, at which time the reaction
mixture was cooled to room temperature and evaporated. The
residue was purified via column chromatography on silica gel
eluting with 25% EtOAc/hexane. Pure 11 (7.2 g, 72%) was thereby
1
obtained as a light yellow solid. H NMR (CDCl3) 1.31–1.48 (m,
27 H), 2.51–2.64 (m, 6 H), 2.91–3.92 (m, 12 H), 7.34–7.37 (m, 2
H), 8.09–8.13 (m, 2 H); 13C NMR (CDCl3) δ 28.4 (q), 28.5 (2C,
q), 39.2 (t), 39.5 (t), 40.2 (t), 47.8 (t), 48.8 (t), 49.6 (t), 50.2 (t),
50.5 (t), 50.6 (t), 51.3 (t), 53.0 (t), 53.3 (t), 53.4 (t), 54.0 (t), 54.1
(t), 55.3 (t), 60.2 (d), 60.5 (d), 79.3 (s), 79.4 (s), 79.7 (s), 79.8 (s),
79.9 (s), 123.35 (d), 123.41 (d), 123.5 (d), 130.1 (d), 146,1 (s),
146.5 (s), 146.8 (s), 147.0 (s), 155.4 (s), 155.5 (s), 155.8 (s), 156.0
(s). HRMS (positive ion FAB) Calcd for C30H49N5O8 [M + H]+
m/z 740.2635. Found: [M + H]+ m/z 740.2636. Anal. Calcd for
C30H49N5O8: C, 59.29; H, 8.13. Found: C, 58.56; H, 8.31.
1-(4-Nitrobenzyl)-2-[1,4,7]triazanonan-1-ylethylamine (12). 11
(6.3 g, 10.4 mmol) in an ice bath was treated with 4 M HCl/dioxane
(60 mL), gradually allowed to warm to ambient temperature, and
stirred for 18 h, after which time ethyl ether (300 mL) was added
into the reaction mixture with vigorous stirring. The resulting slurry
was placed in the freezer for 2 h. The precipitate was collected
and washed with ethyl ether, immediately dissolved in water, and
lyophilized to provide pure 12 as a yellow solid (4.37 g, 93%). 1H
NMR (D2O, pD 1) δ 2.36–2.79 (m, 10 H), 3.11–3.28 (m, 5 H),
3.40–3.61 (m, 5 H), 3.65–3.80 (m, 1 H), 7.16 (d, J ) 8.6 Hz, 2 H),
7.82 (d, J ) 8.6 Hz, 2 H); 13C NMR (D2O, pD 1) δ 36.4 (t), 41.3
(t), 43.3 (d), 48.2 (t), 49.3 (t), 58.0 (t), 123.7 (d), 130.1 (d), 142.6
(s), 146.3 (s). HRMS (positive ion FAB) Calcd for
C15H25N5O2 ·4HCl [M + H]+ m/z 308.2087. Found: [M + H]+
m/z 308.2095. Anal. Calcd for C15H25N5O2(HCl)4(H2O)2: C, 39.79;
H, 7.12. Found: C, 40.31; H, 7.09. Analytical HPLC (tR ) 9.79
min, method 1).
1
EtOAc to provide product 8 as a white solid (141 mg, 76%). H
NMR (CDCl3) δ 2.96 (d, J ) 6.4 MHz, 2 H), 4.08–4.18 (m, 2 H),
4.41–4.50 (m, 1 H), 7.36 (d, J ) 9 MHz, 2 H), 8.18 (d, J ) 9
MHz, 2 H); 13C NMR (CDCl3) δ 40.8 (t), 53.0 (d), 69.1 (t), 123.8
(d), 129.96 (d), 143.55 (s), 146.96 (s), 159.73 (s). HRMS (positive
ion FAB) Calcd for C10H11N4O2 [M + H]+ m/z 223.0719. Found:
[M + H]+ m/z 223.0713. Anal. Calcd for C10H10N2O4: C, 53.95;
H, 4.56. Found: C, 54.05; H, 4.54.
tert-Butyl 2-(4-Nitrobenzyl)aziridine-1-carboxylate (9). To a
slurry of NaH (0.9 g, 44.6 mmol) in THF (150 mL) at 0 °C was
added a solution of 7 (9.5 g, 44.6 mmol) in THF (150 mL) over
1 h. The resulting mixture was stirred for 2 h at 0 °C and
continuously stirred for 6 h at room temperature while the progress
of the reaction was monitored by TLC analysis. The reaction
mixture was poured into cold saturated NH4Cl solution and
extracted with EtOAc (2 × 100 mL). The combined EtOAc layer
was washed with brine (100 mL), dried, filtered, and concentrated
under vacuum. The residue solid was recrystallized to provide 9
(11.8 g, 95%). For preparation of analytical sample, the residue
could be purified via column chromatography on silica gel eluting
with 15% EtOAc in hexanes. Pure 9 was thereby obtained as a
tert-Butyl {4-[2-(Bis-(tert-butoxycarbonylmethyl)amino)-3-(4-
nitrophenyl)propyl]-7-tert-butoxycarbonylmethyl[1,4,7]triaza-
nonan-1-yl}acetate (13). To a slurry of 12·HCl (454 mg, 1 mmol)
in DMF (10 mL) at 0 °C were added diisopropylethylamine (1.72 g,
13.3 mmol) and KI (266 mg, 1.6 mmol). tert-Butyl bromoacetate (2.34
g, 4.4 mmol) was added dropwise over 20 min. The resulting mixture
was stirred for 2 h at 0 °C and for 2 h at room temperature. The reaction
mixture was heated to 90 °C and stirred for 19 h, after which time the
reaction mixture was cooled to room temperature and then to 0 °C.
HCl (6 M, 0.7 mL) and heptane (20 mL) were sequentially added to
the solution. The resulting solution was vigorously stirred for 5 min,
and the heptane layer was separated. The aqueous layer was extracted
with heptane (2 × 20 mL) and treated with 10% Na2CO3 (10 mL).
Additional heptane was added into the aqueous solution, the resulting
mixture was stirred for 30 min, and the heptane layer was separated.
The combined heptane layers were washed with water (20 mL), dried,
filtered, and concentrated under vacuum. The residue was purified via
column chromatography on silica gel (220–400 mesh) eluted with 3%
CH3OH/CH2Cl2 starting from CH2Cl2 (gradual increase of 0.5%
polarity) to provide pure 13 (412 mg, 54%). 1H NMR (CDCl3) δ 1.52
(s, 9 H), 1.55 (s, 18 H), 1.59 (s, 9 H), 2.01–2.05 (m, 1 H), 2.30–2.41
(m, 4 H), 2.60–3.15 (m, 12 H), 3.29 (s, 2 H), 3.37 (s, 2 H), 3.43 (s, 4
H), 7.34 (d, J ) 7.72 Hz, 2 H), 8.14 (d, J ) 7.72 Hz, 2 H); 13C NMR
(CDCl3) δ 28.1 (q), 34.9 (t). 50.6 (t), 51.6 (t), 52.1 (t), 53.0 (t), 56.1
(t), 56.2 (t), 56.8 (t), 57.2 (t), 59.3 (d), 80.7 (s), 80.8 (s), 81.2 (s),
123.6 (d), 130.1 (d), 146.5 (s), 147.5 (d), 169.8 (s), 170.7 (s), 170.8
(s). HRMS (positive ion FAB) Calcd for C39H65N5O10 [M + H]+ m/z
764.9805. Found: [M + H]+ m/z 764.4810. Analytical HPLC (tR )
31.24 min, method 1). Isolation of 13 from the reaction mixture using
semipreparative HPLC (method 3) was also successfully performed.
The reaction mixture was dissolved in 1 mL of CH3OH, and the
fraction at ∼35 min was collected, evaporated, dissolved in CH2Cl2,
1
white solid. H NMR (CDCl3) δ 1.73 (s, 9 H), 2.02 (d, J ) 3.37
MHz, 1 H), 2.35 (d, J ) 5.1 MHz, 1 H), 2.58–2.66 (m, 1 H), 2.82
(dd, J ) 4.0 MHz, 1 H), 2.97 (dd, J ) 4.0 MHz, 1 H), 7.51 (d, J
) 8.9 MHz, 2 H), 8.15 (d, J ) 8.9 MHz, 2 H); 13C NMR (CDCl3)
δ 27.7 (q), 31.1 (t), 37.2 (t), 38.1 (d), 81.3 (s), 123.5 (d), 129.6 (d),
145.8 (s), 146.7 (s), 162.0 (s). Anal. Calcd for C14H18N2O4: C,
60.42; H, 6.52. Found: C, 60.36; H, 6.70.
Di-tert-butyl [1,4,7]Triazanonane-1,4-dicarboxylate (10). Com-
pound 10 was prepared according to a modification of a synthetic
procedure reported previously.23 To a solution of TACN (1 g, 7.7
mmol) in CHCl3 (25 mL) was added in portions BOC-ON (3.77 g,
15.3 mmol). The resulting mixture was stirred for 72 h and the
solvent evaporated under vacuum. The residue was partitioned
between 10% NaOH solution (10 mL) and diethyl ether (30 mL).
The ether layer was separated and washed with 10% NaOH solution
(10 mL) and water (10 mL) several times. The ether layer was
dried (MgSO4), filtered, and concentrated under vacuum to provide
pure 10 (2.33 g, 95%), which was directly used for the next step.
1H NMR (CDCl3) δ 1.48 (s, 18 H), 3.01–3.52 (m, 13 H); 13C NMR