MED
column chromatography (silica gel;
hexane/EtOAc, 10:1) to give the
title compound as a white solid
(1.47 g, 4.8 mmol, 96%): 1H NMR
(400 MHz, CDCl3): d=7.57 (2H, d,
J=8.8 Hz), 6.69 (2H, d, J=9.2 Hz),
4.59 (2H, s), 4.27 (2H, q, J=7.2 Hz),
1.29 ppm (3H, t, J=7.2 Hz);
13C NMR (100 MHz, CDCl3): d=
168.3, 157.6, 138.2, 116.9, 83.9,
65.2, 61.3, 14.1 ppm; MS (ESI+):
m/z 328.9 [M+Na]+.
Table 1. The effect of carboranes 5, 6, 8, 11–14 and adamantine 15 on caspase-like (b1), trypsin-like (b2), and
chymotrypsin-like (b5) activities of the 20S proteasome[a] and growth inhibition of HeLa cells.[b]
Compound[c]
b1 [%]
b2 [%]
b5 [%]
GI50 [mm]
o-carborane
138Æ6.4
102Æ5.6
94.0Æ1.8 103Æ7.8
>100
R=H
R=Ac
R=COPh
5
76.0Æ0.8 124Æ1.9
95.2Æ0.1 106Æ4.4
17.1Æ3.7
>100
21.9Æ1.4
6a 116 Æ18.6
6b 176Æ1.8
160Æ2.5
358Æ57.9
Ethyl 2-(4-(2-(trimethylsilyl)ethy-
nyl)phenoxy)acetate (7): Trimeth-
ylacetylene (3.4 mL, 2.4 mmol) was
added to a solution of 2-(4-iodo-
phenoxy)acetate (8 mmol), PdCl2-
(PPh3)2 (110 mg, 0.16 mmol), CuI
(76 mg, 0.4 mmol), and Et3N
(8.1 mL, 78 mmol) in DMF under Ar.
The mixture was heated by micro-
wave irradiation to 1208C for
25 min. The solvent was removed
in vacuo, and the residue was dis-
solved in EtOAc. The mixture was
washed with aq HCl (2n), neutral-
ized with saturated aq NaHCO3,
washed with brine, dried over
anhyd MgSO4, filtered and concen-
trated in vacuo. Purification by
column chromatography (silica gel;
R=OEt
R=OCH2Ph
R=OH
R=OPh
R=NHPh
R=
8
12
106Æ12.7
73.7Æ1.2
91.5Æ0.8
56.2Æ1.9
23.4Æ0.1
67.1Æ20.9 81.1Æ0.5 133Æ41.4
13 111 Æ7.3
14
97.1Æ17.3 70.0Æ3.8 145Æ8.5
11 a 350Æ28.4 205Æ26.5 87.6Æ3.5 >100
102Æ7.0
124Æ7.2
>100
85.7Æ12.1
11 b 181Æ7.7
373Æ49.8
4.5Æ1.0
20.3Æ0.8
15 149Æ15.5 114Æ11.8 192Æ15.8 >100
PA28
Betulinic acid
526Æ4.3
206Æ2.7
128Æ6.0
N.D.
15.9Æ0.4
609.5Æ24.0 522.8Æ24.9 545.2Æ39.6
[a] Human 20S proteasome activities were measured using specific fluorophore-tagged peptides (Z-LLE-AMC
for b1; Boc-LRR-AMC for b2;, Suc-LLVY-AMC for b5). [b] HeLa cells were incubated for 72 h with various concen-
trations (100 nm–100 mm) of compounds, and viable cells were determined by MTT assay. The drug concentra-
tion required to inhibit cell growth by 50% (GI50) was determined from semi-logarithmic dose–response plots,
and results represent the mean ÆSD of triplicate samples. [c] Proteasome activities were measured with com-
pounds (10 mm), PA28 (500 ng), or betulinic acid (10 mm).
100% hexane) gave
7.32 mmol, 91%):
7
(2.02 g,
1H NMR
(400 MHz, CDCl3): d=7.40 (2H, d,
J=9.2 Hz), 6.82 (2H, d, J=8.8 Hz),
4.61 (2H, s), 4.27 (2H, q, J=7.2 Hz),
1.29 (3H, t, J=7.2 Hz), 0.23 ppm
gesting that a carborane framework is more suitable for induc-
(9H, s); 13C NMR (72 MHz, CDCl3): d=168.5, 157.8, 133.5, 116.4,
114.5, 104.7, 92.9, 65.3, 61.4, 14.1 ppm; MS (ESI+): m/z 299.0
[M+Na]+, 315.0 [M+K]+.
tion of the 20S proteasome activities.
In conclusion, carborane derivatives 6b, 11 a, and 11 b were
found to be potent inducers of b5, b1, and b2 activities of the
20S proteasome, respectively. The carborane framework is es-
sential for induction of the 20S proteasome activities. Since
small-molecule proteasome activators have not been devel-
oped, the current compounds represent potential chemical
probes for the investigation of proteasome-dependent degra-
dation pathways.
2-(4-Ethynylphenoxy) acetic acid (9): A solution of 7 (1.98 g,
7.2 mmol) in THF/H2O (1:1; 40 mL) was treated with LiOH·H2O
(1.21 g, 28.8 mmol) at RT overnight. After neutralization of the reac-
tion with aq HCl (1n), the mixture was extracted with EtOAc,
washed with brine, dried over anhyd MgSO4, filtered and concen-
trated in vacuo. Purification by column chromatography (silica gel;
1
100% EtOAc) gave 9 (379 mg, 1.8 mol, quant): H NMR (400 MHz,
CDCl3): d=7.45 (2H, d, J=8.8 Hz), 6.87 (2H, d, J=8.8 Hz), 4.69 (2H,
s), 3.01 ppm (1H, s); 13C NMR (72 MHz, CD3OD): d=172.3, 159.7,
134.4, 116.6, 115.7, 84.1, 77.3, 65.7 ppm; MS (ESIÀ): m/z 175.9
[MÀNa]À.
Experimental Section
Synthesis
2-(4-Ethynylphenoxy)-N-phenylacetamide (10a): A DMF solution
of 9 (100 mg, 0.57 mmol), aniline (0.08 mL, 0.85 mmol), EDCI
(164 mg, 0.85 mmol), HOBt (131 mg, 0.86 mmol), and DIPEA
(0.146 mL, 8.56 mmol) was stirred at RT overnight. The reaction
was quenched with H2O, extracted with EtOAc, washed with brine,
dried over anhyd MgSO4, filtered and concentrated in vacuo. Purifi-
cation by column chromatography (silica gel; hexane/EtOAc, 3:1)
The experimental procedure for the synthesis of compound 11 a
from 4-iodophenol (1) is reported below. Spectral data of all tested
compounds 5, 6a–b, 8, 12–14, and 15 are described in the Sup-
porting Information.
Ethyl 2-(4-iodophenoxy)acetate: Ethyl chloroacetate (0.54 mL,
5.1 mmol) was added to a mixture of 1 (1.1 g, 5 mmol) and K2CO3
(2.1 g, 15 mmol) in DMF. The mixture was stirred at RT overnight,
and the reaction was quenched with H2O. The mixture was extract-
ed with EtOAc, washed with brine, dried over anhyd MgSO4, fil-
tered and concentrated in vacuo. The residue was purified by
1
gave 10a (143 mg, 0.57 mmol, quant) as a colored solid: H NMR
(400 MHz, CDCl3): d=8.21 (1H, br s), 7.57 (2H, d, J=7.6 Hz), 7.48
(2H, d, J=8.8 Hz), 7.35 (2H, t, J=7.6, 8.4), 7.16 (1H, t, J=7.6, 7.6),
6.94 (2H, d, J=6.8), 4.60 (2H, s), 3.04 ppm (1H, s); 13C NMR
1238
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ChemMedChem 2010, 5, 1236 – 1241