Fluorocyclopropane Analogs of the Duocarmycins
J. Am. Chem. Soc., Vol. 118, No. 37, 1996 8869
plug, washed with ice H2O (7 mL), saturated aqueous NaCl (10 mL),
dried (MgSO4), and concentrated under reduced pressure to afford the
crude amine 15 which was used directly in the following reaction. For
15: 1H NMR (CDCl3, 400 MHz) δ 7.95 (dd, 1H, J ) 2.1, 6.2 Hz),
7.85 (m, 1H), 7.56 (m, 2H), 7.00 (s, 1H), 4.40-4.56 (m, 4H), 4.35 (q,
2H, J ) 7.1 Hz), 1.88 (s, 3H), 1.40 (t, 3H, J ) 7.1 Hz); 19F NMR
(CDCl3, 376 MHz) δ -86.1 (d, J ) 40.0 Hz), -88.2 (dd, J ) 24.0,
layer was removed. The aqueous layer was extracted with EtOAc (3
× 3 mL), and the combined organic solutions were washed with
saturated aqueous NaCl (10 mL), dried (MgSO4), filtered, and
concentrated under reduced pressure. PTLC (SiO2, 10 × 10 cm, 25%
EtOAc-hexane) provided 19 (2.5 mg, 5.7 mg theoretical, 44%) as a
beige wax: 1H NMR (CDCl3, 400 MHz) δ 8.21 (d, 1H, J ) 7.2 Hz,
C5-H), 7.49 (m, 2H, C6 and C7-H), 7.00 (m, 1H, C8-H), 6.85 (br s,
1H, C3-H), 4.29 (m, 1H, C1-H), 4.20 (m, 1H, C1-H), 3.09 (dd, 1H, J
) 10.3, 10.4 Hz, C9a-H), 1.56 (s, 9H, C(CH3)3); 19F NMR (CDCl3,
376 MHz) δ -113.4 (d, J ) 160.0 Hz), -123.5 (dd, J ) 11.0, 160.0
Hz); IR (film) νmax 2918, 1727, 1634 cm-1; FABHRMS (NBA-CsI)
m/z 460.0219 (M + Cs+, C18H17F2NO3 requires 460.0231).
40.0 Hz); IR (film) νmax 3456, 3358, 3241, 1747, 1654, 1242 cm-1
;
FABHRMS (NBA-NaI) m/z 364.1252 (M+, C18H18F2N2O4 requires
364.1235).
The crude 15 (flask wrapped in foil) was cooled to -30 °C under
Ar, and i-C5H11ONO (500 µL as solvent) was added followed by 4 M
HCl-CH3OH (10 µL), CH2Cl2 (500 µL), and CH3OH (500 µL). The
reaction mixture was stirred at -30 °C for 16 h and diluted with
saturated aqueous NaHCO3 (5 mL) and CH2Cl2 (7 mL). Throughout
the following workup and purification, the mixture was protected from
light. The organic solution was removed, and the aqueous solution
was extracted with CH2Cl2 (2 × 5 mL). The organic solutions were
combined, dried (Na2CO3), and concentrated under reduced pressure.
Chromatography (SiO2, 30% EtOAc-hexane) yielded 16 (12.0 mg,
15.0 mg theoretical, 80% overall from 14) as a tan oil: 1H NMR
(CDCl3, 400 MHz) δ 8.42 (d, 1H, J ) 7.9 Hz), 7.72 (dd, 1H, J ) 7.4,
7.4 Hz), 7.50 (dd, 1H, J ) 7.3, 7.6 Hz), 7.34 (d, 1H, J ) 7.9 Hz), 6.33
(s, 1H), 4.45 (m, 2H), 4.17 (m, 1H), 2.08 (s, 3H); 13C NMR (CDCl3,
100 MHz) δ 180.9, 169.3, 161.0, 158.0, 144.4, 132.6, 130.2, 128.2,
128.0, 127.1, 123.2, 120.8, 74.2 (dd, J ) 89.0, 89.0 Hz), 42.0, 21.8;
19F NMR (CDCl3, 376 MHz) δ -84.7 (d, J ) 36.0 Hz), -87.3 (dd, J
F2CBI-TMI (24). A suspension of NaH (60% dispersion in oil,
0.6 mg, 0.015 mmol) in DMF (100 µL) under Ar at 25 °C was treated
with a solution of 18 (3.3 mg, 0.014 mmol) in DMF (250 µL). The
reaction mixture was protected from the light and was stirred at 25 °C
for 2 min. A solution of 23 (130 µL of a 0.052 M solution, 0.006
mmol) was added, and the reaction mixture was stirred for 1 h before
it was partitioned between H2O (3 mL) and EtOAc (3 mL). The organic
solution was removed, and the aqueous solution was extracted with
EtOAc (3 × 4 mL). The combined organic solutions were washed
with saturated aqueous NaCl (6 mL), dried (MgSO4), filtered, and
concentrated under reduced pressure. Chromatography (SiO2, 40%
EtOAc-hexane) provided 24 (1.4 mg, 3.1 mg theoretical, 45%) as a
yellow wax in addition to recovered 18 (1.0 mg, 30% recovery). For
24: 1H NMR (acetone-d6, 400 MHz) δ 10.60 (br s, 1H, NH), 8.12 (dd,
1H, J ) 1.0, 7.6 Hz, C5-H), 7.65 (dt, 1H, J ) 1.5, 7.5 Hz, C6-H), 7.56
(dt, 1H, J ) 1.2, 7.5 Hz, C7-H), 7.37 (dd, 1H, J ) 7.8, 8.2 Hz, C8-H),
7.26 (s, 1H, C3′-H), 7.23 (s, 1H, C4′-H), 6.95 (s, 1H, C3-H), 5.05 (m,
1H, C1-H), 4.92 (br s, 1H, C1-H), 4.00 (br s, 3H, OCH3), 3.86 (s, 3H,
OCH3), 3.85 (s, 3H, OCH3), 3.27 (m, 1H, C9a-H); 19F NMR (acetone-
d6, 376 MHz) δ -117.0 (d, J ) 160.0 Hz), -127.2 (dd, J ) 11.0,
) 28.0, 36.0 Hz); IR (film) νmax 2926, 2077, 1746, 1594 cm-1
;
FABHRMS (NBA-NaI) m/z 304.0855 (M + H+, C15H11F2N2O2 requires
304.0898).
3-Acetyl-9,9-difluoro-1,2,9,9a-tetrahydrocyclopropa[c]benzo[e]-
indol-4-one (17). A suspension of 16 (16.0 mg, 0.05 mmol) and Rh2-
(OAc)4 (2.5 mg, 5.3 µmol) in toluene (5 mL) under Ar was warmed at
110 °C for 0.5 h. The reaction mixture was concentrated under reduced
pressure, and the residue was purified by chromatography (SiO2, 35%
EtOAc-hexane) to provide 17 (10.7 mg, 14.5 mg theoretical, 74%) as
a tan powder: 1H NMR (CDCl3, 400 MHz) δ 8.21 (dd, 1H, J ) 1.7,
7.5 Hz, C5-H), 7.55 (ddd, 1H, J ) 1.5, 6.2, 6.2 Hz, C7-H), 7.50 (ddd,
1H, J ) 1.5, 7.2, 7.4 Hz, C6-H), 7.03 (m, 2H, C4-H and C8-H), 4.45
(m, 1H, C1-H), 4.28 (m, 1H, C1-H), 3.14 (m, 1H, C9a-H), 2.35 (s,
160.0 Hz); IR (film) νmax 3261, 2933, 1645, 1634, 1393, 1267 cm-1
MS (electrospray+) m/z 489 (M + Na+), 467 (M+), 429, 385.
;
Solvolysis Reactivity. pH 3: N-BOC-F2CBI (19, 50 µg) was
dissolved in CH3OH (1.5 mL) and mixed with pH 3 aqueous buffer
(1.5 mL). The buffer contained 4:1:20 (v:v:v) 0.1 M citric acid, 0.2
M Na2HPO4, and H2O, respectively. The solvolysis solution was sealed
and kept at 25 °C protected from the light. The UV spectrum was
measured at regular intervals, every 3 min for 1.5 h, every 15 min for
the next 4.5 h, and finally every 1 h for 5 h. The decrease in the long-
wavelength absorption at 318 nm and the increase in the short-
wavelength absorption at 265 nm were monitored, Figure 3. The
solvolysis rate constant (k ) 7.05 × 10-4 s-1) and half-life (t1/2 ) 0.26
h) were calculated from data recorded at the long-wavelength from
the least-squares treatment (r ) 1.0) of the slope of the plot of time
versus ln[(Af - Ai)/(Af - A)].
Similarly, F2CBI (18, 30 µg) was dissolved in CH3OH (1.5 mL)
and mixed with pH 3 aqueous buffer (1.5 mL). The solvolysis solution
was sealed and kept at 25 °C protected from light. The UV spectrum
was recorded every 2 min for 10 min, every 15 min for 7 h, and every
8 h for 48 h. The decrease in the long-wavelength absorption at 338
nm and the increase in the short-wavelength absorption at 247 nm were
monitored, Figure 3. The solvolysis rate constant (k ) 4.54 × 10-5
s-1) and half-life (t1/2 ) 4.2 h) were determined as detailed above (r )
1.0).
1
3H, CH3CO); H NMR (acetone-d6, 400 MHz) δ 8.08 (dd, 1H, J )
1.2, 7.8 Hz, C5-H), 7.62 (dt, 1H, J ) 1.5, 7.5 Hz, C6- or C7-H), 7.53
(dt, 1H, J ) 1.2, 7.5 Hz, C7 or C6-H), 7.29 (m, 1H, C8-H), 7.16 (br
s, 1H, C3-H), 4.61 (m, 2H, C1-H2), 3.79 (m, 1H, C9a-H), 2.32 (s, 3H,
CH3CO); 13C NMR (CDCl3, 100 MHz) δ 160.0, 152.0, 142.3, 131.7,
128.2, 127.2, 124.3, 111.7, 109.6, 50.0, 27.6 (t, J ) 9.9 Hz), 24.9; 19
F
NMR (CDCl3, 376 MHz) δ -113.8 (d, J ) 160.0 Hz), -125.2 (dd, J
) 11.0, 160.0 Hz); IR (solid film) νmax 1702, 1691 cm-1; FABHRMS
(NBA) m/z 276.0836 (M + H+, C15H11F2NO2 requires 276.0836). A
single-crystal X-ray structure determination conducted on plates grown
from EtOAc-hexane established the structure of 17.46
9,9-Difluoro-1,2,9,9a-tetrahydrocyclopropa[c]benzo[e]indol-4-
one (18). A solution of 17 (5.6 mg, 0.020 mmol) in CH3OH (800 µL)
cooled to -10 °C under Ar was treated with 1 N aqueous LiOH (20
µL, 0.020 mmol). The reaction mixture was stirred for 10 min before
being concentrated under a stream of N2. Chromatography (SiO2, 40%
EtOAc-hexane) afforded 18 (4.3 mg, 4.7 mg theoretical, 92%) as a
beige wax: 1H NMR (CDCl3, 400 MHz) δ 8.20 (m, 1H, C5-H), 7.45
(m, 2H, C6 and C7-H), 6.99 (m, 1H, C8-H), 5.72 (s, 1H, C3-H), 5.28
(br s, 1H, NH), 4.02 (m, 2H, C1-H2), 3.18 (dd, 1H, J ) 10.8, 11.1 Hz,
C9a-H); 19F NMR (CDCl3, 376 MHz) δ -112.0 (d, J ) 160.0 Hz),
-122.5 (dd, J ) 11.0, 160.0 Hz); IR (film) νmax 3178, 2926, 1611,
1230 cm-1; FABHRMS (NBA-NaI) m/z 256.0558 (M + Na+, C13H9F2-
NO requires 256.0550).
pH 7: Samples of 18 and 19 (50 µg) were dissolved in CH3OH (1.5
mL) and H2O (1.5 mL). The solutions were sealed at 25 °C and
protected from the light. UV spectra were recorded at regular intervals
until constant values were obtained for the long and short-wavelength
absorbances (260 and 338 nm for 18, 252 and 308 nm for 19). The
solvolysis rate constants were determined from the slope of the lines
obtained from linear least-squares treatments of plots of ln[(Af - Ai)/
(Af - A)] versus time using the long-wavelength measurements (Figure
8). The first order rate constants determined under these conditions
were 8.27 × 10-5 s-1 (t1/2 ) 2.3 h, r ) 0.98) for N-BOC-F2CBI (19)
and 4.66 × 10-7 s-1 (t1/2 ) 422 h, r ) 0.99) for F2CBI (18).
3-tert-Butyloxycarbonyl-9,9-difluoro-1,2,9,9a-tetrahydrocyclopro-
pa[c]benzo[e]indol-4-one (19). A suspension of NaH (0.8 mg, 0.020
mmol) in DMF (300 µL) under Ar was treated with a solution of 18
(4.0 mg, 0.017 mmol) in DMF (750 µL). The reaction mixture was
protected from the light and was stirred for 5 min. BOC2O (5 µL,
0.022 mmol) was added, and the reaction mixture was stirred at 25 °C
for 3.5 h. EtOAc (5 mL) and H2O (5 mL) were added, and the organic
Acid-Catalyzed Addition of CH3OH to N-Acetyl-F2CBI (17):
3-Acetamido-1-(1,1-difluoro-1-methoxymethyl)-5-hydroxy-1,2-dihy-
dro-3H-benzo[e]indole (25). A solution of 17 (1.9 mg, 6.91 µmol)
in CH3OH (750 µL) was treated with 0.010 M CF3SO3H-CH3OH (83