D. X. Sun et al. / Bioorg. Med. Chem. Lett. 14 (2004) 4333–4338
4337
P10 moiety produced a slightly less potent enzyme
inhibitor 11, introduction of (S)-MeBn moiety as the P10
binder indeed gave rise to 6-fold more potent inhibitors
12 (Ki ¼ 31 nM) and 13 (Ki ¼ 27 nM) relative to 10; (3)
replacing the C-termini phenyl with basic pyridine
moiety led to 14 endowed with 4-fold weaker potency;
and (4) incorporation of carboxylic acid C-termini re-
sulted in more potent inhibitors 15 (2 ·) and 16 (8 ·) in
comparison to the neutral C-termini bearing inhibitor
10. As far as enzyme selectivity is concerned, it is evident
that the C-termini acid bearing ones, 15 and 16, exhib-
ited much greater HNE selectivity (as high as >1000-
fold detected for 16) relative to 10 (7-fold only). When
evaluated in the cell based luciferase replicon assay (at
50 lM), compounds 10 through 13 were found to be
inactive, presumably due to having polar tetrazole as
their P4 caps. In contrast, the P4 pyrazine capped
inhibitor 9 (included as the positive control) demon-
strated whole cell activity with IC50 value of 11.6 lM.
When tested for their cytotoxicity in the Huh-7 liver
cells, four compounds tested (10–13) were considered to
be noncytotoxic at the highest concentration tested
(50 lM).
J. Colacino, C. Lopez, and G. Cassell at Eli Lilly and
Company for helpful discussions and encouragement.
References and notes
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Tan, S.-L.; Pause, A.; Shi, Y.; Sonenberg, N. Nat. Rev.
2002, 1, 867; (c) Perni, R. B.; Kwong, A. D. In Progress in
Medicinal Chemistry; King, F. D., Oxford, A. W., Eds.;
Elsevier Science, 2002; pp 215–255 (d) Walker, M. P.;
Appleby, T. C.; Zhong, W.; Lau, J. Y. N.; Hong, Z.
Antiviral Chem. Chemother. p 1.
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R.; Goudreau, N.; Kukolj, G.; LaPlante, S. R.; Llinas-
Brunet, M.; Nar, H.; Lamarre, D. Angew. Chem., Int. Ed.
2003, 42, 1356; (b) Boehringer Ingelheim (Canada) Ltd
PCT patent: WO 2003/064455 A2 (Aug. 7, 2003).
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Three P3 and P4 modified HCV protease inhibitors 17–
19 were synthesized and evaluated in the bioassays.
Consistent with our previous finding regarding P4 SAR,
the P4 Chg bearing inhibitor 19 was found to be the
most potent one within this set (Ki ¼ 30 nM). Inhibitors
18 and 19 failed to show activity in the luciferase repli-
con assay and were also found to be noncytotoxic at the
highest dose tested.
6. (a) Han, W.; Hu, Z.; Jiang, X.; Decicco, C. P. Bioorg.
Med. Chem. Lett. 2000, 10, 711; (b) Vertex Pharmaceu-
tical, Inc. U.S. patent: US-265380 (Jul. 24, 2001).
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Q. M.; Barket, D.; Glass, J. I.; Jin, L.; Liu, L.; Venable,
D.; Wakulchik, M.; Xie, C.; Heinz, B.; Villarreal, E.;
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Vol. 4, pp 123–146.
8. (a) Vertex patent regarding a-ketoamide based NS3ꢁ4A
inhibitors: U.S. 6,265,380, 2001; (b) Perni, R. B.; Pitlik, J.;
Britt, S. D.; Court, J. J.; Courtney, L. F.; Deininger, D.
D.; Farmer, L. J.; Gates, C. A.; Harbeson, S. L.; Levin, R.
B.; Lin, C.; Lin, K.; Moon, Y.-C.; Luong, Y.-P.; O’Mal-
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1441; (c) Perni, R. B.; Farmer, L. J.; Cottrell, K. M.;
Court, J. J.; Courtney, L. F.; Deininger, D. D.; Gates, C.
A.; Harbeson, S. L.; Kim, J. L.; Lin, C.; Lin, K.; Luong,
Y.-P.; Maxwell, J. P.; Murcko, M. A.; Pitlik, J.; Rao, B.
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4. Conclusions
Prompted by the preliminary finding by our collabora-
tors from Vertex, we designed and synthesized a number
of novel P4 cap modified tetrapeptidyl a-ketoamides as
HCV NS3 protease inhibitors. We found that com-
pound 6 bearing tetrazole moiety as P4 cap demon-
strated excellent enzyme inhibitory activity (Ki ¼
6.1 nM), which was 10-fold more potent than its corre-
sponding P4 adipic acid capped inhibitor 3. Subse-
quently, we synthesized and evaluated a series of P2
bicycloproline containing inhibitors 10–19. Of those
inhibitors bearing P4 tetrazole caps, compounds 12, 13,
16, and 19 were found to be highly potent enzyme
inhibitors with Ki values ranging from 22 to 31 nM.
Furthermore, inhibitors 8, 15, and 16, all bearing car-
boxylic acid as their C-termini, showed excellent selec-
tivity (131–1185 ·) against human neutrophil elastase
(HNE). Perhaps as a result of having polar tetrazole or
adipic acid as P4 cap, none of the newly synthesized
inhibitors (e.g. 3, 6, 10–13) showed cell based activity.
On the other hand, all inhibitors tested were found to be
noncytotoxic (up to 50 lM).18
9. (a) Perni, R. B.; Britt, S.; Court, J. C.; Courtney, L. F.;
Deininger, D. D.; Farmer, L. J.; Gates, C. A.; Harbeson,
S. L.; Kim, J. L.; Landro, J. A.; Levin, R. B.; Luong,
Y.-P.; O’Mally, E. T.; Pitlik, J.; Rao, G.; Schairer, W. C.;
Thomson, J. A.; Tung, R. D.; Van Drie, J. H.; Wei, Y.
Bioorg. Med. Chem. Lett. 2003, 13, 4059; (b) Ingallinella,
P.; Altamura, S.; Bianchi, E.; Taliani, M.; Ingenito, R.;
Acknowledgements
We shall thank R. Perni, A. D. Kwong and their col-
laborators at Vertex and R. Miller, J. Munroe, J. Audia,