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. Author manuscript; available in PMC: 2016 Apr 8.

Published in final edited form as: ACS Chem Biol. 2015 Jan 20;10(4):998–1009. doi: 10.1021/cb5007745

Table 3.

Inhibition of the 20S proteasome trypsin-, chymotrypsin-, and caspase-like activities by thiostrepton analogs

Compound	IC₅₀ (μM)
Compound	Trypsin	Chymotrypsin	Caspase
Thiostrepton A	0.95 ± 0.15	1.02 ± 0.12	0.59 ± 0.06
Ala4Asn	0.38 ± 0.06	0.89 ± 0.17	0.86 ± 0.14
Ala4Cys F1	1.75 ± 0.23	1.54 ± 0.18	0.32 ± 0.03
Ala4Cys F2	0.83 ± 0.05	1.38 ± 0.23	0.70 ± 0.06
Ala4Dha	2.46 ± 0.43	2.73 ± 0.20	2.43 ± 0.30
Ala4Dhb	0.29 ± 0.03	0.25 ± 0.02	0.28 ± 0.02
Ala4Gln	> 10.7^a	4.19 ± 0.48	0.31 ± 0.02
Ala4Gly	0.41 ± 0.05	0.77 ± 0.04	0.48 ± 0.04
Ala4His	0.51 ± 0.09	0.76 ± 0.15	0.53 ± 0.03
Ala4Ile	0.24 ± 0.05	0.27 ± 0.03	0.20 ± 0.04
Ala4Leu	0.34 ± 0.04	0.53 ± 0.02	0.31 ± 0.03
Ala4Met	> 0.59^a	> 0.59^a	0.46 ± 0.05
Ala4Phe	0.24 ± 0.03	0.37 ± 0.09	0.27 ± 0.05
Ala4Ser	0.39 ± 0.03	1.11 ± 0.06	0.40 ± 0.06
Ala4Trp	> 0.19^a	> 0.19^a	> 0.19^a
Ala4Tyr	0.25 ± 0.02	0.63 ± 0.09	0.36 ± 0.03
Ala4Val	0.59 ± 0.04	0.49 ± 0.03	0.18 ± 0.03
Thr7Ala	0.71 ± 0.07	0.57 ± 0.05	0.28 ± 0.04
SL105-1	0.77 ± 0.12	0.77 ± 0.12	0.56 ± 0.09
Thr7Val	1.33 ± 0.27	5.38 ± 0.97	1.68 ± 0.19
SL106-1	> 11^a	6.30 ± 0.95	6.72 ± 0.40
Bortezomib	1.62 ± 0.20	0.005 ± 0.001	0.049 ± 0.003

^a

IC₅₀ not determined due to solubility limitations.