No Byproduct Strategy for Prodrugs of Taxoids
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 7 2663
3
CH2), 4.97 (dd, 3J(H,H) ) 1.9, 9.6 Hz, 1H, CH), 4.81 (d, 3J(H,H)
) 8.8 Hz, 1 H, CH), 4.30 (dd, 3J(H,H) ) 6.6, 11.0 Hz, 1 H,
CH), 4.17, 4.14 (2d, 2J(H,H) ) 9.0 Hz, 2 H, CH2), 3.72 (d,
3J(H,H) ) 7.3 Hz, 1 H, CH), 2.50-2.42 (m, 1 H, CH2), 2.27 (s,
3 H, CH3), 2.17 (s, 3 H, CH3), 1.91 (dd, 3J(H,H) ) 9.3 Hz,
2J(H,H) ) 15.4 Hz, 1 H, CH2), 1.81 (d, 4J(H,H) ) 1.3 Hz, 3 H,
CH3), 1.82-1.76 (m, 1 H, CH2), 1.63 (s, 3 H, CH3), 1.49 (dd,
3J(H,H) ) 9.0 Hz, 2J(H,H) ) 15.4 Hz, 1 H, CH2), 1.13 (s, 3 H,
CH3), 1.10 (s, 3 H, CH3). HRMS (FAB+): calcd for C48H54NO15
[M+ + H] 884.3493, found 884.3486. Anal. (C48H55ClNO15‚
1.5H2O) C, H, N.
2J(H,H) ) 8.8 Hz, 2 H, CH2), 3.79 (d, J(H,H) ) 7.0 Hz, 1 H,
3
CH), 3.58 (d, J(H,H) ) 5.3 Hz, 1 H, OH) 2.59-2.51 (m, 1 H,
CH2), 2.46 (bs, 1 H, OH), 2.37 (s, 3 H, CH3), 2.33-2.27 (m, 1
H, CH2), 2.25 (s, 3 H, CH3), 2.13-2.08 (m, 2H, CH2), 1.91-
1.84 (m, 1 H, CH2), 1.81 (d, 4J(H,H) ) 1.1 Hz, 3 H, CH3), 1.68
(s, 3 H, CH3), 1.64-1.59 (m, 1 H, CH2, partially overlapping
with signal from H2O), 1.44-1.35 (m, 2H, CH2), 1.26 (s, 3 H,
CH3), 1.15 (s, 3 H, CH3), 0.87 (t, 3J(H,H) ) 7.3 Hz, 3 H, CH3).
HRMS (FAB+): calcd for C46H56NO14 [M+ + H] 846.3701,
found 846.3707.
3′-N-(Hexanoyl)-3′-N-debenzoylpaclitaxel (17). The above
procedure with hexanoic acid afforded 17 (56%). 1H NMR
(CDCl3, 400 MHz): δ ) 8.12-8.10 (m, 2 H, CH), 7.64-7.60
(m, 1 H, CH), 7.53-7.32 (m, 7 H, CH), 6.28 (s, 1 H, CH), 6.23-
3′-N-Debenzoylpaclitaxel (14). Zinc dust was added in
three portions (a total of 0.71 g, 10.9 mmol) to the stirring
solution (9 mL) of 7 (400 mg, 0.363 mmol) in AcOEt:AcOH (8:
1) within 5 h and the reaction mixture was stirred for an
additional 3 h at room temperature. The zinc dust was filtered,
and the resulting mixture was diluted with AcOEt and washed
with saturated NaHCO3 three times. The organic layer was
dried over MgSO4 and the solvent was removed under reduced
pressure. The resulting oil was purified by silica gel column
chromatography (MeOH:CHCl3 10:1) to yield a white powder
3
6.20 (m, 2 H, CH, NH), 5.68 (d, J(H,H) ) 7.1 Hz, 1 H, CH),
3
3
5.58 (dd, J(H,H) ) 2.3, 8.9 Hz, 1H, CH), 4.94 (dd, J(H,H) )
3
1.8, 9.5 Hz, 1 H, CH), 4.68 (bs, 1 H, CH), 4.40 (dd, J(H,H) )
2
6.4, 11.0 Hz, 1 H, CH), 4.30, 4.19 (2d, J(H,H) ) 8.3 Hz, 2 H,
3
CH2), 3.79 (d, J(H,H) ) 7.0 Hz, 1 H, CH), 3.47 (bs, 1 H, OH)
2.58-2.50 (m, 1 H, CH2), 2.47 (bs, 1 H, OH), 2.34 (s, 3 H, CH3),
2.32-2.25 (m, 1 H, CH2), 2.25 (s, 3 H, CH3), 2.19 (t, 3J(H,H) )
7.6 Hz, 2H, CH2), 1.93-1.84 (m, 1 H, CH2), 1.82 (d, 4J(H,H) )
1.13 Hz, 3 H, CH3), 1.68 (s, 3 H, CH3), 1.65-1.53 (m, 3 H, CH,
CH2), 1.28-1.22 (m, 4H, CH2), 1.27 (s, 3 H, CH3), 1.15 (s, 3 H,
CH3), 0.83 (t, 3J(H,H) ) 7.0 Hz, 3 H, CH3). HRMS (FAB+):
calcd for C46H58NO14 [M+ + H] 848.3857, found 848.3864.
1
14 after lyophilization (164 mg, 0.219 mmol, 60%). H NMR
(CDCl3, 400 MHz): δ ) 8.07-8.05 (m, 2 H, CH), 7.67-7.63
(m, 1 H, CH), 7.54-7.50 (m, 2H, CH), 7.38-7.36 (m, 4 H, CH),
7.28-7.21 (m, 1 H, CH), 6.27 (s, 1 H, CH), 6.14 (dt, 4J(H,H) )
1.3 Hz, 3J(H,H) ) 8.9 Hz, 1 H, CH), 5.63 (d, 3J(H,H) ) 7.1 Hz,
3
1 H, CH), 4.93 (dd, J(H,H) ) 2.0, 9.5 Hz, 1H, CH), 4.40 (dd,
3′-N-Debenzoyl-3′-N-isopropyloxycarbonylpaclitaxel
(18). 3′-N-Debenzoylpaclitaxel 14 (10.0 mg, 13.3 µmol) was
dissolved in CH2Cl2 (0.5 mL) and a saturated solution of
NaHCO3 (0.5 mL) was added. Then isopropyloxycarbonyl
chloride (1.7 µL, 17 µmol) was added with vigorous stirring.
After 1 h, the next portion of isopropyloxycarbonyl chloride
(1.7 µL, 17 µmol) was added, and after an hour, the reaction
mixture was diluted with EtOAc and washed with water. The
organic layer was dried over MgSO4 and the solvent was
removed under reduced pressure. The crude product was
applied to preparative HPLC, which was eluted with a linear
gradient of 30%-70% CH3CN in 12 mM aqueous HCl over 80
min at a flow rate of 5 mL/min. The desired fraction was
collected and lyophilized to give a white powder of 18 (9.7 mg,
11.6 µmol, 87%). 1H NMR (CD3OD, 400 MHz): δ ) 8.10 (d,
3J(H,H) ) 7.3 Hz, 2 H, CH), 7.68-7.64 (m, 1 H, CH), 7.58-
7.54 (m, 2 H, CH), 7.39 (d, 3J(H,H) ) 4.6 Hz, 4 H, CH), 7.28-
3J(H,H) ) 6.7, 10.9 Hz, 1 H, CH), 4.31-4.26 (m, 3H, CH2, CH),
4.14(d, 3J(H,H) ) 8.2 Hz, 1H, CH), 3.75 (d, 3J(H,H) ) 7.0 Hz,
1 H, CH), 2.57-2.49 (m, 1 H, CH2), 2.24 (s, 3 H, CH3), 2.13 (s,
3 H, CH3), 2.19-1.82 (m, 3 H, CH2), 1.87 (d, 4J(H,H) ) 1.3
Hz, 3 H, CH3), 1.65 (s, 3 H, CH3), 1.24 (s, 3 H, CH3), 1.13 (s, 3
H, CH3). HRMS (FAB+): calcd for C40H48NO13 [M+ + H]
750.3126, found 750.3120. Anal. (C40H47NO13‚H2O) C, H, N.
3′-N-(1-Cyclohexenylcarbonyl)-3′-N-debenzoylpacli-
taxel (15). A solution of 14 (10.4 mg, 0.014 mmol), 1-cyclo-
hexenecarboxylic acid (2.1 mg, 0.017 mmol), HOBt (2.5 mg,
0.017 mmol), and EDC‚HCl (3.2 mg, 0.017 mmol) in DMF (1
mL) was stirred at room temperature for 3 h. Then DMF was
removed under reduced pressure and the reaction mixture was
dissolved with AcOEt. After washing with 10% citric acid three
times and water and saturated NaHCO3 twice, the organic
layer was dried over MgSO4 and the solvent was removed
under reduced pressure. The crude product was applied to
preparative HPLC, which was eluted with a linear gradient
of 40%-80% CH3CN in 12 mM aqueous HCl over 80 min at a
flow rate of 5 mL/min. The desired fraction was collected and
lyophilized to give a white powder of 15 (9.2 mg, 10.7 µmol,
77%). 1H NMR (CDCl3, 400 MHz): δ ) 8.13-8.10 (m, 2 H,
CH), 7.64-7.60 (m, 1 H, CH), 7.53-7.49 (m, 2H, CH), 7.41-
7.38 (m, 4 H, CH), 7.37-7.31 (m, 1 H, CH), 6.65-6.63 (m, 1H,
3
7.24 (m, 1 H), 6.46 (s, 1 H, CH), 6.15 (t, J(H,H) ) 10.0 Hz, 1
H, CH), 5.64 (d, 3J(H,H) ) 7.3 Hz, 1 H, CH), 5.15 (bs, 1H, CH),
5.00-4.97 (m, 1 H, CH), 4.81-4.75 (m, 1 H, CH), 4.52 (d,
3J(H,H) ) 4.4 Hz, 1 H, CH), 4.32 (dd, 3J(H,H) ) 6.6, 11.0 Hz,
1 H, CH), 4.18 (bs, 2 H, CH2), 3.82 (d, 3J(H,H) ) 7.1 Hz, 1 H,
CH), 2.50-2.42 (m, 1 H, CH2), 2.33 (s, 3 H, CH3), 2.28-2.19
(m, 1 H, CH2), 2.17 (s, 3 H, CH3), 2.00-1.95 (m, 1 H, CH2),
1.92 (s, 3 H, CH3), 1.84-1.77 (m, 1 H, CH2), 1.66 (s, 3 H, CH3),
3
3
1.19 (d, J(H,H) ) 6.4 Hz, 6 H, CH3), 1.17 (s, 3 H, CH3), 1.16
CH), 6.47 (d, J(H,H) ) 8.8 Hz, 1 H, NH) 6.27 (s, 1 H, CH),
(s, 3 H, CH3). HRMS (FAB+): calcd for C44H54NO15 [M+ + H]
3
3
6.20 (bt, J(H,H) ) 8.2 Hz, 1 H, CH), 5.67 (d, J(H,H) ) 7.0
Hz, 1 H, CH), 5.61 (dd, 3J(H,H) ) 2.8, 8.8 Hz, 1H, CH), 4.95-
836.3493, found 836.3502.
3
4.93 (m, 1H, CH), 4.71 (dd, J(H,H) ) 2.8, 5.4 Hz, 1 H, CH),
3′-N-n-Butyloxycarbonyl-3′-N-debenzoylpaclitaxel (19).
The above procedure with n-butyloxycarbonyl chloride afforded
4.43-4.37 (m, 1 H, CH), 4.30, 4.19 (2d, 2J(H,H) ) 8.3 Hz, 2 H,
3
3
1
3
CH2), 3.78 (d, J(H,H) ) 7.0 Hz, 1 H, CH), 3.57 (d, J(H,H) )
19 (93%). H NMR (CD3OD, 400 MHz): δ ) 8.10 (d, J(H,H)
) 7.5 Hz, 2 H, CH) 7.68-7.64 (m, 1 H, CH), 7.58-7.54 (m, 2
5.5 Hz, 1 H, OH) 2.59-2.51 (m, 1 H, CH2), 2.47 (d, 3J(H,H) )
3
3
4.0 Hz, 1 H, OH), 2.35 (s, 3 H, CH3), 2.29 (dd, J(H,H) ) 5.2
H, CH), 7.39 (d, J(H,H) ) 4.6 Hz, 4 H, CH), 7.28-7.24 (m, 1
Hz, 2J(H,H) ) 8.9 Hz, 1 H, CH2), 2.25 (s, 3 H, CH3), 2.22-
2.11 (m, 4H, CH2), 1.91-1.85 (m, 1 H, CH2), 1.85 (s, 1H, OH),
1.79 (d, 4J(H,H) ) 1.1 Hz, 3 H, CH3), 1.68 (s, 3 H, CH3), 1.66-
1.63 (m, 5 H, CH2, partially overlapping with signal from H2O),
1.26 (s, 3 H, CH3), 1.15 (s, 3 H, CH3). HRMS (FAB+): calcd
for C47H56NO14 [M+ + H] 858.3701, found 858.3696.
3
H), 6.46 (s, 1 H, CH), 6.16 (bt, J(H,H) ) 8.5 Hz, 1 H, CH),
5.64 (d, 3J(H,H) ) 7.3 Hz, 1 H, CH), 5.17 (d, 3J(H,H) ) 4.6
3
Hz, 1 H, CH), 4.99 (dd, J(H,H) ) 1.8, 9.5 Hz, 1H, CH), 4.54
3
3
(d, J(H,H) ) 4.0 Hz, 1H, CH), 4.33 (dd, J(H,H) ) 6.6, 11.0
Hz, 1 H, CH), 4.19, 4.17 (2d, 2J(H,H) ) 8.8 Hz, 2 H, CH2),
3
4.05-3.94 (m, 2 H, CH, CH2), 3.82 (d, J(H,H) ) 7.3 Hz, 1 H,
CH), 2.50-2.42 (m, 1 H, CH2), 2.34 (s, 3 H, CH3), 2.29-2.18
(m, 1 H, CH2), 2.17 (s, 3 H, CH3), 2.03-1.97 (m, 1H, CH2),
1.92 (s, 3 H, CH3), 1.84-1.77 (m, 1 H, CH2), 1.66 (s, 3 H, CH3),
1.61-1.55 (m, 2 H, CH2), 1.38-1.29 (m, 2H, CH2), 1.18 (s, 3
H, CH3), 1.16 (s, 3 H, CH3), 0.90 (t, 3J(H,H) ) 7.2 Hz, 3 H,
CH3). HRMS (FAB+): calcd for C45H55NO15 [M+ + H] 872.3469,
found 884.3477.
3′-N-(trans-2-Hexenoyl)-3′-N-debenzoylpaclitaxel (16).
The above procedure with trans-2-hexenoic acid afforded 16
1
(56%). H NMR (CDCl3, 400 MHz): δ ) 8.14-8.12 (m, 2 H,
CH), 7.64-7.60 (m, 1 H, CH), 7.55-7.31 (m, 7 H, CH), 6.79
(dt, 3J(H,H) ) 7.0, 15.4 Hz, 1H, CH), 6.27 (s, 1 H, CH), 6.25-
6.17 (m, 2 H, CH, NH), 5.79 (bd, 3J(H,H) ) 15.6 Hz, 1 H, CH),
3
3
5.67 (d, J(H,H) ) 7.0 Hz, 1H, CH), 5.62 (dd, J(H,H) ) 2.6,
3
8.6 Hz, 1H, CH), 4.94 (dd, J(H,H) ) 2.0, 7.3 Hz, 1 H, CH),
4.71 (bs, 1 H, CH), 4.43-4.38 (m, 1H, CH), 4.30, 4.19 (2d,
3′-N-Benzyloxycarbonyl-3′-N-debenzoylpaclitaxel (20).
The above procedure with benzyloxycarbonyl chloride afforded