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Fig. 2. Molecular model of compound 9a, which binds with cathepsin K. Compound
9a is shown as a stick model and colored according to its atom color. Cathepsin K is
shown as a cartoon model and colored according to its secondary structure. The S2
and S3 subsites of cathepsin K are labeled accordingly. This figure was generated
with an automated molecular docking and database screening program DOCK 4.0
[26].
required for activity. Molecular modeling showed a large, flat
cavity occupied by the ethyl group, indicating further improve-
ments in this part of the structure can be achieved.
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necarb oxylate (EST), a new inhibitor of cysteine proteinases, Chem. Pharm. Bull.
35 (1987) 1098–1104.
The R2 groups in 9d (IC90 = 0.005
< 0.005 mol/L), and 9k (IC50 = 0.005 mol/L) all fit well in the
S3 pocket. The activity of 9b (invalid), 9f (IC50 = 0.1 mol/L), and 9c
mmol/L), 9e (IC90
m
m
m
[20] R. Yoshioka, O. Ohtsuki, T. Date, et al., Optical resolution, characterization, and X-
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catalyzed epoxidation of a,b-unsaturated acids, J. Org. Chem. 24 (1959) 54–55.
(invalid) is much weaker owing to the lack of hydrophobic groups.
Heterocycles are not tolerated for the R2 group such as the cases in
9m and 9n, which may be attributed to the loss of hydrophobic
interaction between the R2 group and the S3 pocket.
20
[22] Analytic data for compounds. 3: ½aꢂD + 107.1 (c 1.00, EtOH). 9a: Mp: 126–127 8C;
½aꢂ2D0+ 51.7 (c 1.00, EtOH); 1H NMR (400 MHz, CDCl3): d 6.80 (d, 1H, J = 8.0 Hz),
6.16 (s, 1H), 4.35 (m, 1H), 4.27 (s, 2H), 3.69 (s, 1H), 3.48 (s, 1H), 3.11–3.41 (m, 2H),
1.47-1.76 (m, 4H), 1.41 (q, 2H, J = 7.0 Hz), 1.32 (t, 3H, J = 7.0 Hz), 0.85–1.04 (m,
12H); 13C NMR (100 MHz, CDCl3): d 170.9, 166.5, 166.2, 62.3, 53.8, 52.9, 50.4, 41.3,
41.2, 24.6, 23.2, 22.8, 22.7, 22.2, 13.9, 12.3, 11.3; MS (FAB) m/z 343.2 (M+). Anal.
Calcd. for C17H30N2O5: C 59.63, H 8.83, N 8.18; Found: C 59.78, H 8.60, N 7.95. IR
(KBr, cmꢁ1): 3290, 2960, 1755, 1642, 1555, 900. 9b: Mp: 138–139 8C; 1H NMR
(400 MHz, CDCl3): d 8.57 (d, 1H, J = 8.4 Hz), 6.04 (s, 1H), 4.10–4.40 (m, 3H), 3.71 (s,
1H), 3.58 (s, 1H), 2.90–3.10 (m, 2H), 0.80–1.70 (m, 17H); 13C NMR (100 MHz,
CDCl3): d 170.9, 166.5, 166.0, 62.4, 53.8, 52.9, 51.4, 41.3, 41.2, 24.8, 22.8, 22.7,
22.2, 14.0, 11.3; MS (FAB) m/z 315.2 (M+). 9c: Mp: 154–156 8C; 1H NMR (400 MHz,
CDCl3): d 6.90 (d, 1H, J = 8.6 Hz), 7.95 (d, 1H, J = 7.6 Hz), 4.25–4.41 (m, 3H), 4.03–
4.04 (m, 1H), 3.70 (s, 1H), 3.49 (s, 1H), 0.91–1.57 (m, 18H); 13C NMR (100 MHz,
CDCl3): d 170.1, 166.6, 165.9, 62.3, 53.8, 52.7, 51.4, 41.6, 41.5, 24.8, 22.8, 22.5,
22.4, 22.2, 13.99; MS (FAB) m/z 315.2 (M+). 9d: Mp: 139–141 8C; 1H NMR
(400 MHz, CDCl3): d 8.56 (d, 1H, J = 8.6 Hz), 8.03 (d, 1H, J = 7.4 Hz), 4.29-4.31
(m, 1H), 4.17–4.19 (m, 2H), 3.71 (s, 1H), 3.57 (s, 1H), 2.90–3.10 (m, 2H), 1.10–1.60
(m, 12H), 0.85–1.04 (m, 9H); 13C NMR (100 MHz, CDCl3): d 170.9, 166.5, 166.0,
62.4, 53.8, 52.9, 51.4, 41.3, 41.2, 24.8, 23.2, 22.8, 22.7, 22.2, 14.0, 11.3; MS (FAB) m/
z 329.2 (M+). 9e: Mp: 133–135 8C; 1H NMR (400 MHz, CDCl3): d 6.54 (d, 1H,
J = 8.4 Hz), 5.91 (s, 1H), 4.25–4.29 (m, 3H), 3.68 (s, 1H), 3.46 (s, 1H), 3.22–3.26 (m,
2H), 1.30-1.54 (m, 12H), 0.90–0.93 (m, 9H); 13C NMR (100 MHz, CDCl3): d 170.7,
166.5, 166.0, 62.4, 53.8, 53.0, 51.3, 41.2, 39.7, 29.1, 28.9, 24.8, 22.8, 22.3, 22.1,
14.0; MS (FAB) m/z 343.2 (M+). 9f: Mp: 175–177 8C; 1H NMR (400 MHz, CDCl3): d
6.89 (d, 1H, J = 8.6 Hz), 6.14 (t, 1H, J = 3.2 Hz), 4.22-4.27 (m, 3H), 3.71 (d, 1H,
J = 1.6 Hz), 3.54 (d, 1H, J = 1.6 Hz), 3.15–3.28 (m, 2H), 0.92–1.85 (m, 17H);
13C NMR (100 MHz, CDCl3): d 170.2, 166.6, 165.9, 62.3, 57.6, 53.8, 52.9, 52.7,
41.3, 37.3, 25.0, 22.7, 15.2, 14.0, 11.3, 11.1; MS (FAB) m/z 315.2 (M+). 9g: Mp: 211–
212 8C; 1H NMR (400 MHz, CDCl3): d 6.87 (d, 1H, J = 8.0 Hz), 5.84 (s, 1H), 4.15–
4.29 (m, 4H), 3.70 (s, 1H), 3.55 (s, 1H), 0.90–1.81 (m, 18H); 13C NMR (100 MHz,
CDCl3): d 169.1, 166.6, 165.9, 62.3, 57.3, 53.8, 52.9, 52.7, 41.7, 37.5, 25.0, 22.8,
22.7, 22.5, 15.2, 14.0, 11.2; MS (FAB) m/z 315.2 (M+). 9h: Mp: 187–188 8C; 1H NMR
(400 MHz, CDCl3): d 6.88 (d, 1H, J = 12.0 Hz), 6.10 (s, 1H), 4.21–4.29 (m, 3H), 3.70
(s, 1H), 3.49 (s, 1H), 3.21–3.33 (m, 2H), 0.90-1.85 (m, 19H); 13C NMR (100 MHz,
CDCl3): d 170.0, 166.6, 166.0, 62.3, 57.4, 53.9, 53.8, 52.9, 39.3, 37.3, 31.4, 25.0,
20.0, 15.3, 14.0, 13.7, 11.1; MS (FAB) m/z 329.2 (M+). 9i: Mp: 189-190 8C; 1H NMR
(400 MHz, CDCl3): d 7.12 (m, 1H), 6.43 (s, 1H), 4.25–4.29 (m, 1H), 3.73–3.81
(m, 3H), 3.18-3.53 (m, 3H), 0.90-1.84 (m, 20H); 13C NMR (100 MHz, CDCl3):
d 170.2, 167.2, 165.9, 57.5, 53.8, 52.6, 38.2, 37.9, 37.4, 25.8, 25.0, 22.4, 22.3, 15.3,
11.1; MS (FAB) m/z 343.2 (M+). 9j: Mp: 158–159 8C; 1H NMR (400 MHz, CDCl3):
d 6.75 (d, 1H, J = 8.2 Hz), 5.86 (s, 1H), 4.16–4.29 (m, 3H), 3.69 (s, 1H), 3.47 (s, 1H),
3.21–3.32 (m, 2H), 0.89-1.85 (m, 21H); 13C NMR (100 MHz, CDCl3): d 169.9, 166.5,
4. Conclusion
In summary, we synthesized a series of epoxysuccinic acid
derivatives and evaluated their inhibitory activity against cathep-
sin K in vitro. Several analogs such as 9e, 9d, 9j, 9k and 9p showed
similar or improved potency compared to the lead compound 9a.
Less hydrophobic compounds showed weaker potency, which can
be explained by the hydrophobic nature of the cathepsin K binding
pockets.
Acknowledgment
This project was supported by the National High-Tech Research
and Development Program of China (No. 2012AA020301).
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