C. Ji, M. J. Miller / Bioorg. Med. Chem. 20 (2012) 3828–3836
3835
4.1.13. O-Bn-O0-TBS ciprofloxacin conjugate (20)
173.9, 173.3, 172.4, 171.2, 171.2, 170.3, 165.8, 154.3, 152.7,
148.5, 147.1, 146.3, 144.4, 138.2, 136.6, 135.7, 135.5, 135.4,
134.6, 131.8, 129.4, 129.4, 129.4, 129.2, 129.1, 129.0, 128.9,
128.9, 128.9, 128.7, 128.3, 128.2, 128.1, 123.5, 120.0, 110.4,
105.2, 76.9, 76.5, 76.5, 70.3, 70.2, 66.6, 49.6, 45.7, 45.5, 45.1,
41.2, 40.1, 39.6, 35.0, 34.7, 32.2, 32.1, 31.1, 30.8, 30.8, 29.9, 29.9,
29.8, 29.8, 29.7, 29.6, 29.5, 29.4, 29.4, 29.2, 29.0, 28.8, 28.6, 28.3,
28.2, 28.0, 27.5, 27.2, 26.7, 26.6, 26.1, 24.1, 24.0, 23.9, 23.8, 22.9,
To a solution of acid 19 (143 mg, 0.23 mmol) in 5 mL of anhy-
drous CH2Cl2 cooled to 0 °C were added EDC (88 mg, 0.46 mmol)
and HOBt (62 mg, 0.46 mmol). The mixture was stirred at that tem-
perature for 5 min before O-benzyl ciprofloxacin (106 mg,
0.25 mmol), Et3N (130 lL, 0.92 mmol), DMAP (2 mg) were added.
The reaction mixture was warmed to room temperature and stirred
for 18 h. The mixture was diluted with 30 mL of CH2Cl2 and the or-
ganic layer was washed sequentially with water, sat. NaHCO3, brine,
dried over Na2SO4 and filtered. The solvent was removed in vacuo
and the crude product was purified by chromatography on a silica
gel column (5% methanol in CH2Cl2) to yield 20 (138 mg, 59%) as a
light yellow oil: 1H NMR (500 MHz, CDCl3) d 8.54 (s, 1H), 8.08 (d,
J = 13.2 Hz, 1H), 7.52–7.54 (m, 2H), 7.37–7.40 (m, 2H), 7.26–7.33
(m, 11H), 7.15 (d, J = 7.0 Hz, 1H), 6.98 (s, 1H), 5.40 (s, 2H), 5.04–
5.13 (m, 4H), 3.68–3.70 (m, 2H), 3.43–3.45 (m, 2H), 3.31–3.36 (m,
1H), 3.05–3.07 (m, 2H), 2.94–2.96 (m, 2H), 2.95 (s, 2H), 2.38 (s,
3H), 2.06 (s, 3H), 1.63 (s, 6H), 1.25–1.29 (m, 2H), 1.06–1.09 (m,
2H), 1.02 (s, 9H), 0.15 (s, 6H); 13C NMR (125 MHz, CDCl3) d 170.5,
165.9, 150.1, 148.6, 144.0, 136.7, 135.7, 130.4, 129.0, 128.9, 128.8,
128.3, 128.2, 128.1, 127.2, 119.8, 113.8, 113.6, 110.5, 105.2, 70.1,
66.7, 45.8, 45.5, 41.2, 40.1, 34.7, 32.3, 26.3, 19.0, 18.9, 17.8, 8.4, -
2.9; HRMS (ESI) calcd for C57H67FN3NaO9PSi (M+Na)+: 1038.4260,
found 1038.4257.
20.7, 16.9, 16.5, 14.3, 8.3; HRMS (ESI) calcd for C101H121FN9NaO19
P
(M+Na)+: 1836.8393, found 1836.8407.
4.1.16. Desferrioxamine B-ciprofloxacin conjugate (23)
Compound 22 (17.5 mg, 9.6 lMol) was dissolved in 4 mL of
THF/H2O = 10:1 solution under argon. To this solution was added
10% Pd/C (5 mg) and the flask was flushed with H2 gas and left to
stir under a hydrogen atmosphere (balloon) at room temperature
for 6 h. After removal of the catalyst by filtration, the solvent was
evaporated under reduced pressure. The resulting yellow oil was
dissolved in 0.5 mL of CH3CN/H2O = 1:1 solution and further puri-
fied by chromatography on a reverse-phase silica gel column (C18
,
100% H2O to CH3CN/H2O = 1:1) to afford 23 (4.3 mg, 35%) as a yel-
low foam: 1H NMR (600 MHz, CD3OD) d 8.82 (s, 1H), 7.92 (d,
J = 13.2 Hz, 2H), 7.52 (d, J = 7.34 Hz, 1H), 7.40 (s, 1H), 3.72–3.79
(m, 2H), 3.57–3.62 (m, 6H), 3.52–3.54 (m, 2H), 3.13–3.22 (m,
8H), 3.06–3.13 (m, 4H), 2.87 (m, 2H), 2.71–2.80 (m, 4H), 2.52 (m,
2H), 2.41–2.50 (m, 4H), 2.23 (s, 3H), 2.09 (s, 3H), 2.02 (s, 3H),
1.74 (s, 6H), 1.20–1.64 (m, 22H); 13C NMR (150 MHz, CD3OD) d
177.1, 173.5, 173.0, 173.0, 172.4, 172.2, 172.1, 171.1, 168.3,
154.5, 152.9, 150.1, 147.9, 145.6, 145.6, 144.0, 139.4, 134.0,
133.9, 130.2, 128.2, 119.3, 119.2, 119.2, 111.0, 110.8, 106.6,
106.3, 105.0, 49.2, 49.0, 47.2, 45.8, 43.6, 41.2, 40.5, 38.9, 38.8,
35.6, 30.1, 30.0, 29.8, 28.6, 28.5, 28.5, 27.5, 27.5, 25.9, 23.5, 23.5,
18.8, 15.6, 15.3, 7.2; HRMS (ESI) calcd for C59H86FN9O19P (M+H)+:
1274.5756, found 1274.5799.
4.1.14. O-Bn ciprofloxacin conjugate (21)
Compound 20 (101 mg, 97 lMol) was dissolved in a DMF/
H2O = 5:1 solution (2 mL). Argon was bubbled through the solution
for 5 min before KF (12 mg, 0.21 mmol) was added and the mixture
was vigorously stirred for 30 min. The reaction was quenched by
adding 10 mL of sat. NH4Cl and extracted with chloroform
(5 mL ꢁ 3). The organic layers were combined and washed sequen-
tially with brine, dried over Na2SO4 and filtered. After removal of
the solvent under vacuum, the residue was applied to a preparative
silica gel TLC plate, eluted with 5% MeOH in CHCl3 to afford 21
(65 mg, 74%) as a clear oil: 1H NMR (600 MHz, CD3OD) d 8.60 (s,
1H), 7.82 (d, J = 13.2 Hz, 1H), 7.47–7.48 (m, 2H), 7.36–7.38 (m,
2H), 7.28–7.33 (m, 12H), 6.84 (s, 1H), 5.31 (s, 2H), 5.06–5.18 (m,
4H), 3.61–3.62 (m, 2H), 3.50–3.54 (m, 1H), 3.46–3.47 (m, 2H),
3.11–3.12 (m, 2H), 2.98–2.99 (m, 2H), 2.98 (s, 2H), 2.41 (s, 3H),
2.06 (s, 3H), 1.60 (s, 6H), 1.23–1.28 (m, 2H), 1.06–1.09 (m, 2H);
13C NMR (150 MHz, CD3OD) d 172.4, 155.5, 153.9, 152.4, 152.3,
150.1, 145.8, 145.8, 143.9, 143.9, 139.7, 137.9, 136.9, 136.8,
136.2, 136.1, 129.9, 129.7, 129.7, 129.6, 129.6, 129.4, 129.3,
129.2, 129.2, 128.5, 128.4, 127.8, 127.7, 124.5, 120.6, 120.6,
113.2, 113.0, 107.2, 71.4, 71.4, 71.2, 71.2, 67.2, 51.0, 50.5, 47.0,
46.8, 42.3, 40.7, 36.3, 32.5, 31.9, 17.3, 17.2, 16.6, 16.5, 8.5; HRMS
(ESI) calcd for C51H54FN3O9P (M+H)+: 902.3576, found 902.3599.
4.1.17. Succinyl O-Bn desferrioxamine B-ciprofloxacin
conjugate (25)
To a solution of O-benzyl desferrioxamine succinic acid 24
(84 mg, 0.09 mmol) in 3 mL of anhydrous CH2Cl2 cooled to 0 °C
were added EDC (35 mg, 0.18 mmol) and HOBt (24 mg,
0.18 mmol). The mixture was stirred at that temperature for
5 min before O-benzyl ciprofloxacin (50 mg, 0.12 mmol), Et3N
(50 lL, 0.36 mmol) and DMAP (2 mg) were added. The reaction
mixture was warmed to room temperature and stirred for 18 h.
The mixture was diluted with 20 mL of CH2Cl2 and the organic
layer was washed sequentially with water, sat. NaHCO3, brine,
dried over Na2SO4 and filtered. The solvent was removed in vacuo
and the crude oil was purified by chromatography on a silica gel
column (5% methanol in CH2Cl2) to give 25 (90 mg, 75%) as a light
yellow oil: 1H NMR (600 MHz, CDCl3) d 8.55 (s, 1H), 8.10 (d,
J = 12.91 Hz, 1H), 7.29–7.53 (m, 20H), 7.26 (d, J = 7.5 Hz, 1H),
6.51–6.62 (m, 2H), 6.37 (br. s., 1H), 5.40 (s, 2H), 4.85 (s, 4H), 4.81
(s, 2H), 3.82 (m, 2H), 3.73 (m, 2H), 3.64 (br. s., 6H), 3.41 (m, 1H),
3.27 (m, 2H), 3.20 (m, 8H), 2.82 (m, 4H), 2.73 (t, J = 6.90 Hz, 2H),
2.58 (t, J = 7.04 Hz, 2H), 2.49 (m, 4H), 2.09 (s, 3H), 1.60–1.66 (m,
6H), 1.49–1.53 (m, 6H), 1.26–1.31 (m, 8H), 1.08–1.15 (m, 2H);
13C NMR (150 MHz, CDCl3) d 173.2, 172.3, 170.9, 165.8, 154.4,
152.7, 148.6, 144.3, 144.2, 138.2, 136.6, 129.4, 129.4, 129.2,
128.9, 128.7, 128.2, 128.1, 123.9, 113.9, 113.8, 110.5, 105.3, 76.6,
76.5, 66.6, 50.4, 50.0, 45.5, 41.7, 39.6, 34.7, 31.4, 30.8, 30.7, 29.3,
28.7, 26.8, 26.6, 24.2, 23.9, 23.8, 8.4; HRMS (ESI) calcd for
4.1.15. O-Bn desferrioxamine B-ciprofloxacin conjugate (22)
To a solution of 21 (33 mg, 37
amine succinic acid (70 mg, 75
was added EDC (30 mg, 156
lMol) and O-benzyl desferriox-
l
Mol) in 1 mL anhydrous DMF,
l
Mol) in one portion. After stirring
at room temperature for 24 h, the reaction was diluted with
30 mL of CHCl3. The solution was washed sequentially with sat.
NaHCO3, brine, dried over Na2SO4 and filtered. After removal of
the solvent under vacuum, the residue was applied to a preparative
silica gel TLC plate and eluted with 10% MeOH in CHCl3 to afford 22
(30 mg, 45%) as a white foam: 1H NMR (600 MHz, CDCl3) d 8.53 (s,
1H), 8.08 (d, J = 13.2 Hz, 1H), 7.24–7.52 (m, 30H), 7.16 (d, J = 7.0 Hz,
1 H), 7.06 (s, 1H), 6.40 (br. s., 3H), 5.40 (s, 2H), 5.07 (m, 4H), 4.77–
4.89 (m, 6H), 3.56 - 3.71 (m, 8H), 3.40 (m, 2H), 3.35 (m, 1H), 3.12–
3.24 (m, 6H), 3.05 (m, 2H), 2.94 (m, 4H), 2.80 (m, 4H), 2.57–2.67
(m, 4H), 2.42–2.53 (m, 4H), 2.30 (s, 3H), 2.06–2.12 (m, 3H), 1.98
(s, 3H), 1.55–1.68 (m, 12H), 1.42–1.54 (m, 6H), 1.21–1.37 (m,
8H), 1.05–1.08 (m, 2H); 13C NMR (150 MHz, CDCl3) d 174.3,
C
74H93FN9O13 (M+H)+: 1334.6871, found 1334.6874.
4.1.18. Succinyl desferrioxamine B-ciprofloxacin conjugate (26)
Compound 25 (40 mg, 0.03 mmol) was dissolved in 5 mL of
MeOH under argon. 10% Pd/C (4 mg) was added and the flask