Hagen et al.
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1H), 3.13-3.20 (m, 2H), 3.51 (s, 4H), 4.20 (s, 2H), 5.26 (s, 2H),
6.20 (s, 1H), 6.44 (d, J=7.5, 1H), 6.58 (s, 1H), 6.63 (d, J=7.8,
1H), 7.57 (t, J=5.4, 1H), 7.85 (s, 1H), 8.63 (bs, 1H), 8.71 (bs,
1H), 12.67 (bs, 2H); 13C NMR (75.5 MHz, DMSO-d6) δ=34.8,
42.4, 47.9, 53.5 (2C), 60.8, 106.1, 108.3, 110.2 (2C), 115.5, 115.9,
119.2, 127.1, 129.9, 143.6, 145.1, 151.5, 151.7, 155.2, 157.4,
159.3, 172.2 (2C); HRMS (ESI) C24H23BrN2O11, m/z [M þ
H]þ calcd 595.0558, found 595.0547.
4.26 (d, J=5.8, 2H), 5.26-5.41 (m, 2H), 5.55 (s, 2H), 6.26 (s,
1H), 6.84 (d, J=8.1, 1H), 7.04 (s, 1H), 7.20 (d, J=8.1, 1H), 7.90
(s, 1H), 8.31 (t, J=5.8, 1H), 12.69 (bs, 2H); 13C NMR (75.5
MHz, DMSO-d6) δ=22.5 (2C), 24.8, 28.7, 30.3, 31.7, 35.2, 41.7,
47.9, 53.5 (2C), 55.7, 65.2, 106.2, 108.7, 109.8, 110.3, 111.8,
119.1, 121.8, 126.6, 127.2, 137.3, 138.1, 139.5, 149.3, 150.3,
151.7, 152.2, 157.7, 159.2, 172.1, 172.2 (2C); HRMS
(ESI): C34H39BrN2O12, m/z [M - H]- calcd 745.1614, found
745.1684.
N-[(6-Bromo-7-hydroxycoumarin-4-yl)methoxycarbonyl]-
dopamine (2b). Compound 8 (1.19 g, 4.40 mmol), 4-nitrophenyl
chloroformate (1.06 g, 5.28 mmol), and DIPEA (919 μL, 5.28
mmol) in THF (15 mL) were stirred for 1 h at room temperature,
and then the solvent was evaporated. The formed (6-bromo-7-
hydroxycoumarin-4-yl)methyl 4-nitrophenyl carbonate, dopa-
mine (11, 1.0 g, 5.28 mmol), and DMAP (1.29 g, 10.55 mmol)
were dissolved in DMF (20 mL), and the mixture was stirred for
8 h at room temperature. The solvent was evaporated and the
residue purified by flash chromatography. Elution using
CH2Cl2/MeOH (50:1 to 10:1, v/v) yielded 2b (897 mg, 45%) as
a colorless solid: mp 183-184 °C; TLC Rf = 0.13 (n-hexane/
AcOEt, 1:1, v/v); tR=8.89 min (analytical HPLC, 20-95% B in
A in 20 min, eluent A, H2O/0.1% TFA; eluent B, CH3CN); 1H
NMR (300 MHz, DMSO-d6) δ=2.55 (t, J=7.2, 2H), 3.16 (dt,
J=7.0 and 6.4, 2H), 5.25 (s, 2H), 6.19 (s, 1H), 6.43 (d, J=7.8,
1H), 6.58 (s, 1H), 6.63 (d, J=8.0, 1H), 6.92 (s, 1H), 7.57 (t, J=
5.4, 1H), 7.87 (s, 1H), 8.62 (s, 1H), 8.71 (s, 1H), 11.48 (bs, 1H);
13C NMR (75.5 MHz, DMSO-d6) δ=34.8, 42.4, 60.8, 103.2,
106.2, 108.4, 110.5, 115.5, 115.9, 119.2, 128.4, 129.9, 143.6,
145.1, 151.2, 153.8, 155.2, 157.5, 159.7; HRMS (ESI)
C19H16BrNO7, m/z [M þ H]þ calcd 450.0183, found 450.0181.
(E)-[8-[Bis(tert-butoxycarbonylmethyl)aminomethyl]-6-bromo-
4-[-8-[Bis(methoxycarbonylmethyl)aminomethyl]-6-bromo-7-
hydroxycoumarin-4-yl]-2-phenyl-1,3-dioxolane (15). Parafor-
maldehyde (120 mg, 4.0 mmol CH2O) and KOH (235 mg, 4.0
mmol) were dissolved in EtOH (10 mL) and cooled to 0 °C, and
then dimethyl iminodiacetate hydrochloride (790 mg, 4.0 mmol)
was added. The reaction mixture was stirred for 1 h at room
temperature and then added dropwise to a solution of 4b (200
mg, 0.66 mmol) in EtOH (10 mL). The reaction mixture was
heated to reflux for 7 h, the solvent was evaporated, and the
resulting crude product was purified by preparative RP-HPLC
by using a linear gradient of 30-95% B in A in 60 min (eluent A,
H2O/0.1% TFA; eluent B, CH3CN). The main fraction with tR=
58.45-62.00 min was collected, evaporated, redissolved in
CH3CN/H2O, and lyophilized to give the desired product
(colorless solid, 100 mg, 27%) as diastereomer mixture: mp
>120 °C dec; TLC Rf =0.37 (n-hexane/AcOEt 2:1 v/v); tR =
18.32 and 18.54 min (analytical HPLC: 5-95% B in A in 20 min,
1
eluent A, H2O/0.1% TFA; eluent B, CH3CN); H NMR (300
MHz, DMSO-d6) δ = 3.63 (s, 4H), 3.66 (s, 6H), 3.73-3.78/
4.02-4.08a (m, 1H), 4.18/4.19a (s, 2H), 4.56/4.79a (t, J = 8.0,
1H), 5.64-5.73 (m, 1H), 5.96/6.12a (s, 1H), 6.22/6.45a (s, 1H),
7.44-7.49 (m, 3H), 7.55-7.60(m, 2H), 7.90 (s, 1H), 11.77 (s, 1H);
13C NMR (75.5 MHz, DMSO-d6) δ=47.9, 51.8 (2C), 53.6 (2C),
70.0/70.2a, 72.9/73.0a, 103.8/103.9a, 106.3, 107.0, 107.9, 110.4,
110.5, 126.8 (2C), 127.3, 128.3, 128.6, 129.5/129.7a, 136.3/137.4a,
152.0, 154.2/154.3a, 157.1/157.2a, 159.4/159.5a, 171.2 (2C);
HRMS (ESI) C25H24BrNO9 m/z [M þ H]þ calcd 562.0713, found
562.0704. aDiastereomers gave varying single signals.
4-[8-[Bis(carboxymethyl)aminomethyl]-6-bromo-7-hydroxy-
coumarin-4-yl]-2-phenyl-1,3-dioxolane (BBHC-ED-Caged Ben-
zaldehyde, 4a). Compound 15 (100 mg, 0.18 mmol) was dissolved
in THF/H2O (5 mL, 1:1 v/v). LiOH ꢀ H2O (15.1 mg, 0.36 mmol)
was added, and the solution was stirred for 24 h at room tempera-
ture. The solvent was evaporated, and the resulting crude product
was purified by preparative RP-HPLC using a linear gradient of
5-95% B in A in 60 min (eluent A, H2O/0.1% TFA; eluent B,
CH3CN). The main fraction with tR = 35.37-41.72 min was
collected, evaporated, redissolved in CH3CN/H2O, and lyophilized
to give the desired diastereomer mixture (46 mg, 48%) as a colorless
solid: mp >200 °C dec;tR=14.45 and 14.67 min (analytical HPLC:
5-95% B in A in 20 min, eluent A, H2O/0.1% TFA; eluent B,
CH3CN); 1H NMR (300 MHz, DMSO-d6) δ = 3.52 (s, 4H)
3.74-3.79/4.02-4.06a (m, 1H), 4.21/4.22a (s, 2H), 4.56/4.79a (t,
J=8.0, 1H), 5.64-5.72 (m, 1H), 5.96/6.12a (s, 1H), 6.22/6.44a (s,
1H), 7.44-7.48 (m, 3H), 7.55-7.57 (m, 2H), 7.89 (s, 1H), 12.67 (bs,
2H); 13C NMR (75.5 MHz, DMSO-d6) δ=48.0, 53.5 (2C), 70.0/
70.2a, 72.9/73.0a, 103.8/103.9a, 106.3, 106.9, 107.7, 110.2, 110.3,
126.7 (2C), 127.1, 128.3, 128.5, 129.4/129.7a, 136.3/137.4a, 152.0,
154.1/154.2a, 157.4/157.5a, 159.4/159.5a, 172.1 (2C); HRMS (ESI)
C23H20BrNO9 m/z [M - 3H þ 2Na]- calcd 575.9888, found 575.
9921. aDiastereomers gave varying single signals.
7-hydroxycoumarin-4-yl]methyl
2-Methoxy-4-[(8-methylnon-
6-enamido)methyl]phenyl Carbonate. The activated carbonate
10 was prepared from 9 (264.2 mg, 0.5 mmol), 4-nitrophenyl
chloroformate (121 mg, 0.6 mmol), and DIPEA (171.2 μL, 1.0
mmol) in THF (10 mL) by stirring for 4.5 h and workup as
described for the bis-tert-butyl ester of 2a. Dissolution of 10 in
CH2Cl2 (10 mL), addition of DMAP (73.3 mg, 0.6 mmol) and
capsaicin (12, 183.3 mg, 0.6 mmol), stirring overnight at room
temperature, evaporation, and purification by flash chromatog-
raphy (n-hexane/AcOEt 4:1 to 2:3, v/v) gave the desired product
(300 mg, 69.8%) as a colorless solid: mp 67-70 °C; TLC Rf=
0.54 (n-hexane/THF, 1:1, v/v); tR=18.66 min (analytical HPLC,
50-95% B in A in 20 min, eluent A, H2O/0.1% TFA; eluent B,
CH3CN); 1H NMR (300 MHz, DMSO-d6) δ=0.92 (d, J=6.7,
6H), 1.33 (quintet, J=7.4, 2H), 1.43 (s, 18H), 1.52 (quintet, J=
7.4, 2H), 1.94 (q, J=7.0, 2H), 2.07-2.25 (m, 3H), 3.47 (s, 4H),
3.78 (s, 3H), 4.18 (s, 2H), 4.26 (d, J=5.8, 2H), 5.26-5.41 (m,
2H), 5.55 (s, 2H), 6.27 (s, 1H), 6.84 (dd, J=8.1 and 2.2, 1H), 7.04
(s, 1H), 7.20 (d, J=8.2, 1H), 7.91 (s, 1H), 8.31 (t, J=5.9, 1H); 13
C
NMR (75.5 MHz, DMSO-d6) δ = 22.5 (2C), 24.8, 27.7 (6C),
28.7, 30.3, 31.6, 35.2, 41.7, 47.9, 54.6 (2C), 55.7, 65.2, 81.5 (2C),
106.2, 108.8, 110.0, 110.2, 111.8, 119.1, 121.8, 126.6, 127.4,
137.3, 138.1, 139.5, 149.3, 150.3, 151.7, 152.2, 157.4, 159.0,
169.8 (2C), 172.1; HRMS (ESI) C42H55BrN2O12 m/z [M þ
H]þ calcd 859.3011, found 859.3013.
(E)-[8-[Bis(carboxymethyl)aminomethyl]-6-bromo-7-hydroxy-
coumarin-4-yl]methyl 2-Methoxy-4-[(8-methylnon-6-enamido)-
methyl]phenyl Carbonate (BBHCMOC-Caged Capsaicin, 3).
Compound 3 was prepared by deprotection of the bis-tert-butyl
ester of 3 (100 mg, 0.116 mmol) with a mixture (15 mL) of TFA/
CH2Cl2/H2O (75:24:1) by stirring for 2 h at room temperature.
Workup as described for 1a gave 3 (82 mg, 95%) as a colorless
solid: mp 175-177 °C; tR=14.6 min (analytical HPLC, 20-95%
B in A in 20 min, eluent A, H2O/0.1% TFA; eluent B, CH3CN);
1H NMR (300 MHz, DMSO-d6) δ=0.92 (d, J=6.76, 6H), 1.33
(quintet, J=7.4, 2H), 1.52 (quintet, J=7.4, 2H), 1.94 (q, J=7.0,
2H), 2.12-2.25 (m, 3H), 3.52 (s, 4H), 3,79 (s, 3H), 4.21 (s, 2H),
Solubility. Saturated solutions of compounds 1-4 in
CH3CN/HEPES buffer (10 mM HEPES, 120 mM KCl adjusted
to pH 7.2 with 2 N KOH) (5:95 v/v) were analyzed by analytical
RP-HPLC at room temperature.
Hydrolytic Stability. Freshly prepared solutions of 1-4 in
CH3CN/HEPES buffer (5:95 v/v), pH 7.2, were left in the dark
at room temperature and monitored over a period of 24 h by
using analytical RP-HPLC.
2796 J. Org. Chem. Vol. 75, No. 9, 2010