M.J.G. Fernandes et al. / Tetrahedron 67 (2011) 2422e2426
2425
performed at the ‘C.A.C.T.I.dUnidad de Espectrometria de Masas’,
at University of Vigo, Spain.
reactionwas completed, cold diethyl ether was added (1 mL), and the
precipitate filtered off and washed with the same solvent to give 2a as
a yellow solid (0.035 g, 98%). Mp¼189.0e190.8 ꢂC. 1H NMR (DMSO-
4.2. Synthesis procedure for conjugates 1b and 1c
d6):
d
¼2.60e2.70 (m, 2H, CH2), 3.01 (t, J 7.2 Hz, 2H, CH2), 3.94 (s, 3H,
OCH3), 5.13 (d, J 0.8 Hz, 2H, CH2 Bba), 6.72 (s, 1H, H-2), 7.27 (dd, J 8.8
and 2.4 Hz,1H, H-8), 7.38 (d, J 8.8 Hz,1H, H-5), 7.74 (d, J 2.4 Hz,1H, H-
10), 7.98 (d, J 9.2 Hz, 1H, H-7), 8.10 (d, J 8.8 Hz, 1H, H-6). 13C NMR
4.2.1. Synthesis of N-(tert-butyloxycarbonyl)-L-tyrosine (9-methoxy-
(5,6)-benzocoumarin-1-yl) methyl ester, Boc-Tyr-OBba 1b. 1-Choro-
methyl-9-methoxy-(5,6)-benzocoumarin,
Bba-Cl
(0.083
g,
(DMSO-d6):
d
¼31.70 (CH2), 34.87 (CH2), 51.71 (OCH3), 62.54 (CH2
0.302 mmol) was dissolved in dry DMF (3 mL), potassium fluoride
(0.053 g, 0.907 mmol) and Boc-Tyr-OH (0.085 g, 0.302 mmol) were
added. The reaction mixture was stirred at room temperature for 3
days. The solvent was removed by rotary evaporation under re-
duced pressure and the crude residue was purified by column
chromatography in silica gel using dichloromethane/methanol
100:1 as eluent, to give compound 1b as a yellow solid (0.118 g,
Bba),106.49 (C-10),111.77 (C-2),112.25 (C-4b),114.84 (C-5),116.69 (C-
8), 125.95 (C-6a), 130.52 (C-6b), 130.98 (C-7), 133.51 (C-6), 154.78 (C-
4a), 158.19 (C-1), 159.04 (C-9), 159.81 (C-3), 170.85 (CO2CH2). IR (KBr
1%, cmꢀ1):
n
¼3378, 3288, 3218, 3089, 2965, 2260, 1717, 1683, 1427,
1554, 1519, 1427, 1375, 1365, 1337, 1279, 1203, 1131, 1068, 1050, 1025,
987, 857, 722. HRMS (ESI): calcd for C18H18NO5 [MþþH]: 328.11795;
found: 328.11723.
96%). Mp¼96.6e98.2 ꢂC. 1H NMR (DMSO-d6):
d
¼1.32 (s, 9H, C
(CH3)3), 2.81e2.89 (m, 2H,
b-CH2), 3.94 (s, 3H, OCH3), 4.22e4.25 (m,
4.3.2. Synthesis of L-tyrosine (9-methoxy-(5,6)-benzocoumarin-1-yl)
1H,
a
-CH), 5.79 (d, J 6.0 Hz, 2H, CH2 Bba), 6.62 (d, J 8.4 Hz, 2H, H-3
methyl ester, H-Tyr-OBba 2b. To a solution of Boc-Tyr-OBba 1b
(0.062 g, 0.119 mmol) in dichloromethane (2 mL), trifluoroacetic
acid (1 mL) was added and the reaction mixture was stirred at
room temperature for 24 h. The process was followed by TLC
(dichloromethane/methanol 50:1). After evaporation, aqueous
buffer solution (pH 8) was added (5 mL) to the resulting residue
followed by extraction with ethyl acetate. Compound 2b was
obtained as a yellow solid (0.046 g, 76%). Mp¼146.8e147.9 ꢂC. 1H
and H-5 Tyr), 6.63 (s, 1H, H-2), 7.01 (d, J 8.4 Hz, 2H, H-2 and H-6
Tyr), 7.29 (dd, J 9.2 and 2.4 Hz, 1H, H-8),7.40 (d, J 8.8 Hz, 1H, H-5),
7.46 (d, J 7.6 Hz, 1H,
(d, J 8.8 Hz, 1H, H-7), 8.14 (d, J 8.8 Hz, 1H, H-6). 13C NMR (DMSO-d6):
-CH2), 55.30 (OCH3), 55.82 ( -C), 64.41
a-NH), 7.50 (d, J 1.6 Hz, 1H, H-10), 8.00
d¼28.05 (C(CH3)3), 35.45 (
b
a
(CH2 Bba), 78.45 (C(CH3)3), 105.96 (C-10), 111.53 (C-4b), 112.24 (C-
2),114.79 (C-5),114.95 (C-3 and C-5 Tyr),116.83 (C-8),125.97 (C-6a),
127.30 (C-1 Tyr), 129.98 (C-2 and C-6 Tyr), 130.16 (C-6b), 131.21 (C-
7), 133.94 (C-6), 151.51 (C-1), 154.89 (C-4a), 155.49 (CONH), 155.96
(C-4 Tyr), 159.15 (C-9 and C-3), 171.73 (CO2CH2). IR (KBr 1%, cmꢀ1):
NMR (DMSO-d6):
d¼2.74e2.90 (m, 2H,
b-CH2), 3.80e3.90 (m, 1H,
a-CH), 3.94 (s, 3H, OCH3), 5.70e5.85 (m, 2H, CH2 Bba), 6.53 (br s,
2H, NH2), 6.60 (s, 1H, H-2), 6.61 (d, J 8.8 Hz, 2H, H-3 and H-5 Tyr),
6.96 (d, J 8.8 Hz, 2H, H-2 and H-6 Tyr), 7.30 (dd, J 9.0 and 2.4 Hz, 1H,
H-8), 7.41 (d, J 9.2 Hz, 1H, H-5), 7.52 (d, J 2.0 Hz, 1H, H-10), 8.02 (d, J
9.2 Hz, 1H, H-7), 8.15 (d, J 8.8 Hz, 1H, H-6), 9.21 (s, 1H, OH). 13C NMR
n
¼3383, 2977, 2934, 1714, 1625, 1517, 1446, 1366, 1272, 1233, 1186,
1105, 1062, 1023, 989, 944, 838, 729. HRMS (ESI): calcd for
C29H30NO8 [MþþH]: 520.19720; found: 520.19745.
(DMSO-d6):
d
¼38.62 (
b-CH2), 55.32 (OCH3), 55.40 (a-C), 64.35 (CH2
4.2.2. Synthesis of N-(tert-butyloxycarbonyl)-3,4-dihydroxy-L-phe-
nylalanine (9-methoxy-(5,6)-benzocoumarin-1-yl) methyl ester, Boc-
DOPA-OBba 1c. Starting from Bba-Cl (0.112 g, 0.41 mmol), DMF
(3 mL), potassium fluoride (0.071 g, 1.22 mmol) and Boc-BOPA-OH
(0.121 g, 0.41 mmol), following the same procedure as described for
1b, compound 1c was obtained as a yellow solid (0.166 g, 76%).
Bba), 106.05 (C-10), 111.80 (C-4b), 112.52 (C-2), 114.86 (C-5), 115.06
(C-3 and C-5 Tyr), 116.81 (C-8), 126.01 (C-6a), 126.63 (C-1 Tyr),
130.06 (C-6b), 130.15 (C-2 and C-6 Tyr), 131.29 (C-7), 134.02 (C-6),
151.38 (C-1), 154.94 (C-4a), 156.11 (C-4 Tyr), 159.16 (C-9), 159.22 (C-
3), 172.90 (CO2CH2). IR (KBr 1%, cmꢀ1):
n
¼3365, 3225, 1712, 1625,
1552, 1517, 1445, 1364, 1233, 1200, 1178, 1140, 1062, 1023, 949, 839,
722. HRMS (ESI): calcd for C24H22NO6 [MþþH]: 420.14416; found:
420.14481.
Mp¼113.1e114.7 ꢂC. 1H NMR (DMSO-d6):
¼1.32 (s, 9H, C(CH3)3),
d
2.48e2.50 (m, 2H, b-CH2), 3.95 (s, 3H, OCH3), 4.18e4.23 (m, 1H, a-
CH), 5.80 (d, J 3.6 Hz, 2H, CH2 Bba), 6.46 (dd, J 8.0 and 2.0 Hz,1H, H-6
DOPA), 6.60 (d, J 8.8 Hz, 1H, H-5 DOPA), 6.61 (d, J 1.6 Hz, 1H, H-2
DOPA), 6.65 (s, 1H, H-2), 7.30 (dd, J 9.2 and 2.4 Hz, 1H, H-8), 7.41 (d, J
4.3.3. Synthesis of 3,4-dihydroxy-L-phenylalanine (9-methoxy-(5,6)-
benzocoumarin-1-yl) methyl ester, H-DOPA-OBba 2c. Starting from
Boc-DOPA-OBba 1c (0.166 g, 0.31 mmol), dichloromethane (1 mL)
and trifluoroacetic acid (0.5 mL), following the same procedure as
described for compound 2b, compound 2c was obtained as a yellow
solid (0.041 g, 31%). Mp¼277.2e278.5 ꢂC. 1H NMR (DMSO-d6):
8.8 Hz, 1H, H-5), 7.42 (d, J 8.0 Hz, 1H,
10), 8.01 (d, J 8.8 Hz, 1H, H-7), 8.15 (d, J 8.8 Hz, 1H, H-6), 8.68 (s, 1H,
OH), 8.71 (s, 1H, OH). 13C NMR (DMSO-d6):
¼28.06 (C(CH3)3), 35.66
-CH2), 55.31 (OCH3), 55.88 ( -C), 64.41 (CH2 Bba), 78.47 (C(CH3)3),
a-NH), 7.50 (d, J 1.2 Hz, 1H, H-
d
(b
a
105.95 (C-10), 111.54 (C-4b), 112.16 (C-2), 114.80 (C-5), 115.29 (C-5
DOPA), 116.38 (C-2 DOPA), 116.85 (C-8), 119.74 (C-6 DOPA), 125.97
(C-6a), 128.02 (C-1 DOPA), 130.17 (C-6b), 131.22 (C-7), 133.95 (C-6),
143.89 (C-4 DOPA), 144.91 (C-3 DOPA), 151.58 (C-1), 154.90 (C-4a),
155.50 (CONH), 159.16 (C-3 and C-9), 171.76 (CO2CH2). IR (KBr 1%,
d
¼2.83e2.86 (m, 2H,
b-CH2), 3.92 (s, 3H, OCH3), 3.98e4.02 (m, 1H,
a-CH), 5.11 (s, 2H, CH2 Bba), 6.41 (dd, J 8.0 and 2.0 Hz, 1H, H-6
DOPA), 6.54 (d, J 2.0 Hz, 1H, H-2 DOPA), 6.64 (d, J 8.0 Hz, 1H, H-5
DOPA), 6.70 (s, 1H, H-2), 7.25 (d, J 8.8 and 2.4 Hz, 1H, H-8), 7.37 (d, J
8.8 Hz, 1H, H-5), 7.72 (d, J 2.4 Hz, 1H, H-10), 7.92 (d, J 8.8 Hz, 1H, H-
7), 8.08 (d, J 8.8 Hz, 1H, H-6), 8.93 (br s, 2H, 2ꢁOH). 13C NMR
cmꢀ1):
n
¼3378, 2977, 2935, 1712, 1625, 1552, 1519, 1445, 1367, 1282,
1233, 1162, 1115, 1062, 1022, 950, 840, 821, 804, 730. HRMS (ESI):
(DMSO-d6):
d
¼36.53 (
b-CH2), 54.14 (a-C), 55.51 (OCH3), 62.79 (CH2
calcd for C29H30NO9 [MþþH]: 536.19210; found: 536.19221.
Bba), 106.71 (C-10), 112.00 (C-2), 112.49 (C-4b), 115.08 (C-5), 115.89
(C-5 DOPA), 116.79 (C-2 DOPA), 116.94 (C-8), 120.40 (C-6 DOPA),
125.68 (C-1 DOPA), 126.19 (C-6a), 130.74 (C-6b), 131.28 (C-7), 133.84
(C-6), 144.71 (C-4 DOPA), 145.44 (C-3 DOPA), 155.01 (C-4a), 158.45
(C-1),159.30 (C-9),160.25 (C-3),170.85 (CO2CH2). IR (KBr 1%, cmꢀ1):
4.3. Synthesis procedures for conjugates 2aee
4.3.1. Synthesis of b-alanine (9-methoxy-(5,6)-benzocoumarin-1-yl)
methyl ester hydrobromide, HBr$H-
hydrobromic acid in acetic acid (36
b
-Ala-OBba 2a. A 45% solution of
L), and acetic acid (0.5 mL) were
-alanine-(9-methoxy-(5,6)-ben-
-Ala-OBba 1a7 (0.040 g,
n
¼3220, 2260, 1752, 1709, 1625, 1552, 1492, 1446, 1232, 1197, 1140,
m
1062, 1025, 956, 839, 801, 723. HRMS (ESI): calcd for C24H22NO7
added to N-(benzyloxycarbonyl)-
b
[MþþH]: 436.13908; found: 436.13901.
zocoumarin-1-yl)methyl ester, Z-
b
0.087 mmol) with stirring, at room temperature. The reaction mix-
turewasmaintained inthese conditions forfourdays, and theprocess
was followed by TLC (dichloromethane/methanol 50:1). When the
4.3.4. Synthesis of 2-amino-5-methyl-1-(9-methoxy-(5,6)-benzocou-
marin-1-yl)methyl pentanedioate hydrobromide, HBr$H-Glu(OMe)-
OBba 2d. Starting from 2-(N-benzyloxycarbonyl)amino-5-methyl-