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Erickson for modeling support. We would also like to
thank R. Brier, D. K. Laigle, J. Huang, T. Yin, and D.
Czilli for performing bioassays, as well as Drs. N.
McClure, W.-K. Yeh for providing critical reagents.
Acknowledgments should also be made to Drs. M.
Wiley, T. Burkholder, Y.-C. Xu, J. Munroe, and J.
Audia for helpful discussions and encouragement.
References and notes
1. (a) Alloul, K.; Sauriol, L.; Kennedy, W.; Laurier, C.;
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Gerontol. Geriatr. 1998, 27, 189. (b) Wolfe, M. S. J. Med.
Chem. 2001, 44, 2039.
Figure 2. Crystal structure of the (S)-18 binding with BACE-1.
2. Enz, A.; Amstutz, R.; Boddeke, H.; Gmelin, G.; Mala-
nowski, J. Prog. Brain Res. 1993, 98, 431.
3. Roggo, S. Curr. Top. Med. Chem. 2002, 2, 359.
4. Ghosh, A. K.; Hong, L.; Tang, J. Curr. Med. Chem. 2002,
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IC50 values, indicating that the whole cell activities
obtained with these inhibitors are reliable.
5. (a) Talaga, P. Mini Rev. Med. Chem. 2001, 1, 175. (b)
Hetenyi, C.; Szabo, Z.; Klement, E.; Datki, Z.; Kortve-
lyesi, T.; Zarandi, M.; Penke, B. Biochem. Biophys. Res.
Commun. 2002, 292, 931.
4. Enzyme–inhibitor interaction
6. (a) Schenk, D. B.; Rydel, R. E.; May, P.; Little, S.;
Panetta, J.; Lieberburg, I.; Sinha, S. J. Med. Chem. 1995,
21, 4141. (b) Selko, D. J. Nature 1999, 399A, 23.
7. (a) BACE enzyme: Vassar, R. J.; Bennett, B. D.; Citron,
M. Science 1999, 286, 735. (b) Hussain, et al. Mol. Cell.
Neurosci. 1999, 14, 419. (c) Sinha, et al. Nature 1999, 402,
537. (d) Tang, J.; Lin, X.; Koelsch, G. PNAS 2000, 97,
1456. (e) Bienkowski, M. J.; Gurney, M. E.; Heinrikson,
R. L.; Parodi, L. A.; Yan, R. Nature 1999, 402, 533. (f)
For BACE subsite specificity, see: Turner, R. T., III;
Koelsch, G.; Hong, L.; Castanheira, P.; Ghosh, A.; Tang,
J. Biochemistry 2001, 40, 10001.
8. For gamma secretase inhibitors with in vivo activities, see:
Dovey, H. F.; John, V.; Anderson, J. P.; Chen, L. Z.;
Andrieu, de Saint; Fang, L. Y.; Freedman, S. B.; Folmer,
B.; Goldbach, E.; Holsztynska, E. J.; Hu, K. L.; Johnson-
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J. E.; Latimer, L. H.; Lee, M.; Liao, Z.; Lieberburg, I. M.;
Motter, R. N.; Mutter, L. C.; Nietz, J.; Quinn, K. P.;
Sacchi, K. L.; Seubert, P. A.; Shopp, G. M.; Thorsett,
E. D.; Tung, J. S.; Wu, J.; Yang, S.; Yin, C. T.; Schenk,
D. B.; May, P. C.; Alstiel, L. D.; Bender, M. H.; Boggs,
L. N.; Britton, T. C.; Clemens, J. C.; Czilli, D. L.; Dieck-
man-McGinty, D. K.; Droste, J. J.; Fuson, K. S.; Gitter,
B. D.; Hyslop, P. A.; Johnstone, E. M.; Li, W.-Y.; Little,
S. P.; Mabry, T. E.; Miller, F. D.; Ni, B.; Nissen, J. S.;
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The co-crystal structure of the P3 (S)-isomer of inhi-
bitor 18 with hu-BACE enzyme was obtained using
standard protocol.22,23 As can be seen from Figure 2,
the inhibitor side chains were positioned at the expected
binding pockets, with the P3-tetrafluoroNva occupying
the S3 pocket. The types of interactions made by the N-
termini Boc as well as the C-termini pyridyl moieties
suggest that these functional groups may be modified
without compromising enzyme inhibitory activity. It is
also interesting to point out that the more potent (S)-
isomer [relative to its (R)-isomer at P3] was pre-
ferentially co-crystallized with the enzyme target.
Beginning with the C-termini Val-Pyridine bearing
inhibitor 5 (Ab IC50=1.7 uM),13 we have designed and
synthesized, on the basis of BACE substrate specificity,
a novel series of C-termini pyridyl bearing Phe*-Ala
based inhibitors endowed with good water solubility. As
a result of systematic P2 and P3 modifications, we
found that replacement of the Val-Met (P3–P2)
sequence as seen in 5 with Ile-Ala (P3–P2) led to inhi-
bitor 12 (Ab IC50=0.41 mM) displaying improved
enzyme (2ꢀ) and whole cell activity (4ꢀ) as well as
reduced molecular weight in comparison to inhibitor 5.
Furthermore, our data also shows that fluorination at
the P3 residue such as diFAbu seen in 17 (Ab
IC50=0.40 mM) resulted in 6ꢀ enhancement of the
whole cell activity relative to its P3 non-fluorinated
counterpart 10. In summary, in contrast to the poor
cellular activity found with the pentapeptidyl BACE
inhibitors reported by Tang’s group,12 we have dis-
covered a novel Val-Pyridine C-termini bearing inhibi-
tors endowed with impressive enzyme as well as whole
cell activity (<0.5 mM).
9. (a) Olson, R. E.; Thompson, L. A. Annu. Rep. Med.
Chem. 2000, 36, 31. (b) Varghese, J.; Tung, J. S.; Ashley,
G.; Davis, D.; Hom, R.; Thorsett, E. D.; Anderson, J.;
Sinha, S. 224th ACS National Meeting, Boston, MA,
Aug. 18- 22, 2002. MEDI-004.
10. Ghosh, A. K.; Shin, D.; Downs, D.; Koelsch, G.; Lin, X.;
Ermolieff, J.; Tang, J. J. Am. Chem. Soc. 2000, 122, 3522.
11. Boyd, J. G.; Singleton, D. H. Pfizer Patent EP 1233021
A2, Aug. 21, 2002.
12. Ghosh, A. K.; Bilcer, G.; Harwood, C.; Kawahama, R.;
Shin, D.; Hussain, K. A.; Hong, L.; Loy, J. A.; Nguyen,
C.; Koelsch, G.; Ermolieff, J.; Tang, J. J. Med. Chem.
2001, 44, 2865.
Acknowledgements
We are indebted to L. Patterson, E. E. Bunel for pro-
viding valuable fluorinated amino acid and Dr. J.
13. For C-termini SAR, see: D. Brooks and J. Hu et al.
Bioorg. Med. Chem. Lett., manuscript in preparation.