Syringolin A and Derivatives as Eukaryotic 20S Proteasome Inhibitors
17.64, 15.41 ppm. HRMS (ESI): calcd. for C25H41O6N5H+ [M +
H]+ 508.3130; found 508.3134.
(dd, J = 15.4, 5.3 Hz, 1 H), 6.42 (d, J = 8.7 Hz, 1 H), 6.26 (d, J =
9.1 Hz, 1 H), 6.10 (d, J = 15.5 Hz, 1 H), 5.55–5.64 (m, 1 H), 5.34–
5.42 (m, 1 H), 4.87–4.93 (m, 1 H), 4.12 (dd, J = 9.1, 5.6 Hz, 1 H),
4.05–4.11 (m, 1 H), 4.03 (dd, J = 8.7, 5.3 Hz, 1 H), 3.61 (s, 3 H),
3.09–3.24 (m, 2 H), 2.23–2.31 (m, 1 H), 1.84–2.01 (m, 3 H), 1.69–
1.77 (m, 1 H), 0.95 (d, J = 6.6 Hz, 3 H), 0.91 (d, J = 6.6 Hz, 3 H),
0.86 (d, J = 6.8 Hz, 3 H), 0.84 (d, J = 6.9 Hz, 3 H), 0.80 (d, J =
6.7 Hz, 3 H), 0.77 (d, J = 6.8 Hz, 3 H) ppm. 13C NMR (125 MHz,
[D6]DMSO): δ = 172.98, 171.24, 169.03, 166.25, 157.41, 143.20,
133.11, 126.03, 121.46, 57.82, 57.27, 55.44, 53.52, 51.37, 42.52,
34.98, 31.36, 30.18, 19.66, 19.19, 19.08, 19.02, 17.79, 17.44 ppm.
HRMS (ESI): calcd. for C25H41O6N5H+ [M + H]+ 508.3130; found
508.3127.
SylA-L-D Methyl Ester (36b): Compound 32 (7 mg, 25 µmol,
1.1 equiv.), 35 (5.8 mg, 23 µmol, 1 equiv.), PyBop (15 mg, 28 µmol,
1.2 equiv.), and HOAt (4 mg, 28 µmol, 1.2 equiv.) were dissolved in
N,N-dimethylformamide (1.0 mL) in a 10-mL flask. The solution
was cooled to 0 °C and N,N-diisopropylethylamine (8 µL, 46 µmol,
2 equiv.) was added. The reaction was stirred for 40 min at room
temperature. After concentration to dryness, the crude product was
purified by flash column chromatography (10% methanol in
dichloromethane) to yield 36b (10.1 mg, 20 µmol, 87%) as a color-
less solid. TLC (8% methanol in dichloromethane): Rf = 0.30.
HPLC (gradient 2): tR = 6.93 min. 1H NMR (500 MHz, [D6]-
DMSO): δ = 8.10 (d, J = 7.0 Hz, 1 H), 8.01 (d, J = 8.2 Hz, 1 H),
7.43 (t, J = 6.9 Hz, 1 H), 6.68 (dd, J = 15.5, 5.4 Hz, 1 H), 6.51 (d,
J = 8.9 Hz, 1 H), 6.27 (d, J = 9.2 Hz, 1 H), 6.10 (d, J = 15.5 Hz,
1 H), 5.55–5.64 (m, 1 H), 5.42 (dd, J = 16.0, 7.7 Hz, 1 H), 4.86–
4.92 (m, 1 H), 4.05–4.12 (m, 3 H), 3.62 (s, 3 H), 3.09–3.24 (m, 2
H), 2.24–2.32 (m, 1 H), 1.85–2.02 (m, 3 H), 1.70–1.78 (m, 1 H),
0.95 (d, J = 6.6 Hz, 3 H), 0.91 (d, J = 6.6 Hz, 3 H), 0.85 (d, J =
6.9 Hz, 3 H), 0.83 (d, J = 6.5 Hz, 3 H), 0.82 (d, J = 6.5 Hz, 3 H),
0.77 (d, J = 6.8 Hz, 3 H) ppm. 13C NMR (125 MHz, [D6]DMSO):
δ = 173.04, 171.33, 168.88, 166.20, 157.24, 143.12, 133.08, 125.81,
121.45, 57.45, 57.10, 55.42, 53.55, 51.43, 42.51, 34.98, 31.41, 31.36,
30.58, 19.70, 19.14, 19.09, 18.87, 17.64, 17.47 ppm. HRMS (ESI):
calcd. for C25H41O6N5H+ [M + H]+ 508.3130; found 508.3126.
SylA-L-L (37a): Compound 36a (20.0 mg, 39.4 µmol, 1 equiv.) and
aluminum bromide (84 mg, 316 µmol, 8 equiv.) were dissolved in
tetrahydrothiophene (2 mL) under an atmosphere of argon in a 10-
mL flame-dried flask. The resulting mixture was stirred for 1 h at
room temperature. After concentration to dryness, the remaining
residue was purified by preparative HPLC (using H2O with 0.1%
TFA (solvent A) and acetonitrile with 0.1% TFA (solvent B) at a
flow rate of 25 mLmin–1. Gradient: from 0 to 10 min: 90% sol-
vent A/10% solvent B; from 10 to 30 min: from 90% solvent A/
10% solvent B to 70% solvent A/30% solvent B; from 30 to 50 min:
from 70% solvent A/30% solvent B to 40% solvent A/60% sol-
vent B; from 50 to 60 min: from 40% solvent A/60% solvent B to
0% solvent A/100% solvent B; from 60 to 80 min: 0% solvent A/
100% solvent B) to yield 37a (SylA--; 16.3 mg, 33.1 µmol, 84%)
as a colorless solid. TLC (2% acetic acid + 15% methanol in
dichloromethane): Rf = 0.32. HPLC (gradient 2): tR = 6.13 min. 1H
NMR (400 MHz, [D6]DMSO): δ = 12.35 (br. s, 1 H), 8.03 (d, J =
8.4 Hz, 1 H), 7.99 (d, J = 6.7 Hz, 1 H), 7.40–7.48 (m, 1 H), 6.68
(dd, J = 15.2, 4.3 Hz, 1 H), 6.32 (d, J = 8.9 Hz, 1 H), 6.25 (d, J =
9.0 Hz, 1 H), 6.10 (d, J = 15.4 Hz, 1 H), 5.59 (dt, J = 15.5, 7.1 Hz,
1 H), 5.40 (dd, J = 15.5, 7.5 Hz, 1 H), 4.82–4.88 (m, 1 H), 4.01–
4.10 (m, 2 H), 3.97 (dd, J = 8.7, 4.7 Hz, 1 H), 3.07–3.25 (m, 2 H),
2.23–2.32 (m, 1 H), 1.86–2.03 (m, 3 H), 1.69–1.78 (m, 1 H), 0.94
(d, J = 6.2 Hz, 3 H), 0.90 (d, J = 6.3 Hz, 3 H), 0.80–0.88 (m, 9 H),
0.77 (d, J = 6.5 Hz, 3 H) ppm. 13C NMR (100 MHz, [D6]DMSO):
δ = 173.95, 171.37, 168.83, 166.18, 157.60, 143.19, 132.97, 125.90,
121.51, 57.50, 57.35, 55.42, 53.53, 42.50, 34.96, 31.36, 31.02, 30.12,
19.71, 19.21, 19.17, 19.13, 17.58, 17.53 ppm. HRMS (ESI): calcd.
for C24H39O6N5H+ [M + H]+ 494.2973; found 494.2978.
SylA-D-L Methyl Ester (36c): Compound 29 (7 mg, 25 µmol,
1.1 equiv.), 35 (5.8 mg, 23 µmol, 1 equiv.), PyBop (15 mg, 28 µmol,
1.2 equiv.), and HOAt (4 mg, 28 µmol, 1.2 equiv.) were dissolved in
N,N-dimethylformamide (1.0 mL) in a 10-mL flask. The solution
was cooled to 0 °C and N,N-diisopropylethylamine (8 µL, 46 µmol,
2 equiv.) was added. The reaction was stirred for 40 min at room
temperature. After concentration to dryness, the crude product was
purified by flash column chromatography (10% methanol in
dichloromethane) to yield 36c (9.6 mg, 19 µmol, 76%) as a colorless
solid. TLC (8% methanol in dichloromethane): Rf = 0.30. HPLC
1
(gradient 2): tR = 6.95 min. H NMR (500 MHz, [D6]DMSO): δ =
8.16 (d, J = 7.5 Hz, 1 H), 8.00–8.06 (m, 1 H), 7.43 (t, J = 6.4 Hz,
1 H), 6.68 (dd, J = 15.5, 3.2 Hz, 1 H), 6.53 (d, J = 8.9 Hz, 1 H),
6.31 (d, J = 9.1 Hz, 1 H), 6.10 (d, J = 15.4 Hz, 1 H), 5.55–5.66 (m,
1 H), 5.34–5.42 (m, 1 H), 4.87–4.94 (m, 1 H), 4.16 (dd, J = 8.9,
5.6 Hz, 1 H), 4.05–4.12 (m, 2 H), 3.62 (s, 3 H), 3.09–3.22 (m, 2 H),
2.23–2.32 (m, 1 H), 1.84–2.02 (m, 3 H), 1.69–1.77 (m, 1 H), 0.89–
0.97 (m, 6 H), 0.85 (d, J = 6.8 Hz, 3 H), 0.82 (d, J = 6.8 Hz, 3 H),
0.80 (d, J = 6.7 Hz, 3 H), 0.76 (d, J = 6.7 Hz, 3 H) ppm. 13C NMR
(125 MHz, [D6]DMSO): δ = 173.02, 171.26, 169.02, 166.23, 157.26,
143.18, 132.97, 126.03, 121.49, 57.48, 57.06, 55.43, 53.64, 51.44,
42.61, 34.99, 31.58, 31.34, 30.58, 19.65, 19.19, 19.06, 18.89, 17.63,
17.42 ppm. HRMS (ESI): calcd. for C25H41O6N5H+ [M + H]+
508.3130; found 508.3127.
SylA-L-D (37b): Compound 36b (10.0 mg, 19.7 µmol, 1 equiv.) and
aluminum bromide (42 mg, 158 µmol, 8 equiv.) were dissolved in
tetrahydrothiophene (1 mL) under an atmosphere of argon in a 10-
mL flame-dried flask. The resulting mixture was stirred for 1 h at
room temperature. After concentration to dryness, the remaining
residue was purified by preparative HPLC (using H2O with 0.1%
TFA (solvent A) and acetonitrile with 0.1% TFA (solvent B) at a
flow of 25 mL/min. Gradient: from 0 to 10 min: 90% solvent A/
10% solvent B; from 10 to 30 min: from 90% solvent A/10% sol-
vent B to 70% solvent A/30% solvent B; from 30 to 50 min: from
70% solvent A/30% solvent B to 40% solvent A/60% solvent B;
from 50 to 60 min: from 40% solvent A/60% solvent B to 0% sol-
vent A/100% solvent B; from 60 to 80 min: 0% solvent A/100%
solvent B) to yield 37b (SylA--; 9.0 mg, 18.3 µmol, 93%) as a
colorless solid. TLC (2% acetic acid + 15% methanol in dichloro-
SylA-D-D Methyl Ester (36d): Compound 34 (7 mg, 25 µmol,
1.1 equiv.), 35 (5.8 mg, 23 µmol, 1 equiv.), PyBop (15 mg, 28 µmol,
1.2 equiv.), and HOAt (4 mg, 28 µmol, 1.2 equiv.) were dissolved in
N,N-dimethylformamide (1.0 mL) in a 10-mL flask. The solution
was cooled to 0 °C and N,N-diisopropylethylamine (8 µL, 46 µmol,
2 equiv.) was added. The reaction was stirred for 40 min at room
temperature. After concentration to dryness, the crude product was
purified by flash column chromatography (10% methanol in
dichloromethane) to yield 36d (12.0 mg, 24 µmol, 95%) as a color-
less solid. TLC (8% methanol in dichloromethane): Rf = 0.21.
HPLC (gradient 2): tR = 6.75 min. 1H NMR (500 MHz, [D6]-
1
methane): Rf = 0.40. HPLC (gradient 2): tR = 6.51 min. H NMR
(500 MHz, [D6]DMSO): δ = 12.43 (br. s, 1 H), 8.07 (d, J = 6.6 Hz,
1 H), 8.00 (d, J = 8.5 Hz, 1 H), 7.43 (t, J = 6.7 Hz, 1 H), 6.68 (dd,
J = 15.4, 4.9 Hz, 1 H), 6.40 (d, J = 9.1 Hz, 1 H), 6.28 (d, J =
8.9 Hz, 1 H), 6.10 (d, J = 15.6 Hz, 1 H), 5.60 (dt, J = 15.8, 7.2 Hz,
DMSO): δ = 8.00–8.12 (m, 2 H), 7.43 (t, J = 6.9 Hz, 1 H), 6.69 1 H), 5.42 (dd, J = 15.8, 8.1 Hz, 1 H), 4.88 (t, J = 6.6 Hz, 1 H),
Eur. J. Org. Chem. 2010, 3991–4003
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
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