Q. Li et al. / Bioorg. Med. Chem. Lett. 16 (2006) 2000–2007
2007
hydrophobic pocket defined by amino acid residues of
Val57, Ala70, Val104, Met120, Leu173, and Thr183.
C-1 of the isoquinoline is buried deep inside the binding
of the Industrial Macromolecular Crystallography
Association.
˚
cavity with a distance of merely 3.2 A between C-1 and
the carbonyl group of Glu121, leaving little space for
any group larger than hydrogen atom. Interestingly, if
the C-1 hydrogen of the isoquinoline were capable of
hydrogen bonding, it might be a perfect fit. The nitrogen
of the central pyridine hydrogen bonds to the amino
group of Lys72 (distance between the nitrogens is
References and notes
1. (a) Druker, B. J. Adv. Cancer Res. 2004, 91, 1; (b) Krause,
D. S.; Van Etten, R. A. N. Engl. J. Med 2005, 353, 172; (c)
Ross, J. S.; Schenkein, D. P.; Pietrusko, R.; Rolfe, M.;
Linette, G. P.; Stec, J.; Stagliano, N. E.; Ginsburg, G. S.;
Symmans, W. F.; Pusztai, L.; Hortobagyi, G. N. Am. J.
Clin. Pathol. 2004, 122, 598.
2. For recent reviews on Akt see: (a) Barnett, F. S.;
Bilodeau, M. T.; Lindsley, C. W. Curr. Top. Med. Chem.
2005, 5, 109; (b) Bellacosa, A.; Kumar, C. C.; Di
Cristofano, A.; Testa, J. R. Adv. Cancer. Res. 2005, 94,
29; (c) Mitsiades, C. S.; Mitsiades, N.; Koutsilieris, M.
Curr. Cancer Drug Targets 2004, 4, 235; (d) Gills, J. J.;
Dennis, P. A. Expert Opin. Investig. Drugs 2004, 13, 787;
(e) Vivanco, I.; Sawyers, C. L. Nat. Rev. Cancer 2002, 2,
489; (f) Li, Q.; Zhu, G.-D. Curr. Top. Med. Chem. 2002,
2, 939.
˚
2.8 A). The charged primary amine of the side chain sits
tightly in the Mg-binding loop, binding to Asn171 and
Asp184 via H-bonds and ionic interactions. The indole
ring packs underneath the glycine-rich loop with an aver-
˚
age distance of 3.5 A to the loop. Note that the entrance to
the ATP-binding pocket near the hinge region is partially
blocked by residues 315–327 of the C-terminal domain.
The nearest distance from the isoquinoline to Phe327 is
˚
approximately 3.5 A, enabling the isoquinoline of 13a to
fit tightly in the hinge region.
Overlay of structures of 12 and 13a (Fig. 2b) in complex
with PKA revealed that 12 binds similarly to 13a, except
that the side chain of 12 is forced into an unfavorable
position due to the clash between H-5 of the isoquino-
line and H-a of the side chain (Fig. 1). This change leads
to weakened hydrogen bonding interactions of the pri-
mary amino group with Asn171 and Asp184. The dis-
tances of the hydrogen bonds are in sub-optimal
3. Hanks, S.; Hunter, T. FASEB 1995, 9, 576.
4. (a) Liu, X.; Shi, Y.; Han, E. K.; Chen, Z.; Rosenberg, S.
H.; Giranda, V.; Luo, Y.; Ng, S. C. Neoplasia 2001, 3, 278;
(b) Cheng, J. Q.; Ruggeri, B.; Klein, W. M.; Sonoda, G.;
Altomare, D. A.; Watson, D. K.; Testa, J. R. Proc. Natl.
Acad. Sci. U.S.A. 1996, 93, 3636.
5. (a) Zhao, Z.; Leister, W. H.; Robinson, R. G.; Barnett,
S. F.; Defeo-Jones, D.; Jones, R. E.; Hartman, G. D.;
Huff, J. R.; Huber, H. E.; Duggan, M. E.; Lindsley, C.
W. Bioorg. Med. Chem. Lett. 2005, 15, 905; (b)
Lindsley, C. W.; Zhao, Z.; Leister, W. H.; Robinson,
R. G.; Barnett, S. F.; Defeo-Jones, D.; Jones, R. E.;
Hartman, G. D.; Huff, H. E.; Duggan, M. E. Bioorg.
Med. Chem. Lett. 2005, 15, 761; (c) Breitenlechner, C.
B.; Wegge, T.; Berillon, L.; Graul, K.; Marzenell, K.;
Friebe, W.-G.; Thomas, U.; Schumacher, R.; Huber, R.;
Engh, R. A.; Masjost, B. J. Med. Chem. 2004, 47, 1375;
(d) Reuveni, H.; Livnah, N.; Geiger, T.; Klein, S.; Ohne,
O.; Cohen, I.; Benhar, M.; Gelllerman, G.; Levitzki, A.
Biochemistry 2002, 41, 10304.
6. Li, Q., Li, T.; Zhu, G-D.; Gong, J.; Claiborne, A.; Dalton,
C.; Luo, Y.; Liu, X.; Klinghofer, V.; Bauch, J. L.; March,
K. C.; Bouska, J. J.; Airies, S.; De Jong, R.; Oltersdorf, T.;
Stoll, V. S.; Jakob, C. G.; Rosenberg, S. H.; Giranda, V.
˚
lengths of 3.4 and 4.1 A, respectively. In comparison,
˚
the primary amino group of 13a is positioned 2.9 A
equally from the above residues.
In summary, structure-based design and synthesis of the
3,40-bispyridinylethylene series of Akt/PKB inhibitors
led to the discovery of 3-isoquinolinylpyridine 13a,
which exhibits an IC50 of 1.3 nM against Akt1. Com-
pound 13a shows excellent selectivity against distinct
families of kinases such as TK and CAMK, and displays
poor to marginal selectivity against closely related ki-
nases in the AGC and CMGC families. Moreover, 13a
demonstrates potent cellular activity comparable to
staurosporine. Inhibition of the phosphorylation of the
Akt downstream target GSK3 by 13a was also observed
in FL5.12-Akt1 cells. With the available X-ray struc-
tures of the Akt inhibitors in complex with PKA, further
structural refinements of this series via structure-based
design to optimize the physiochemical and biological
properties of molecules is ongoing, the results of which
will be published in due course.10
7. Wolfe, J. P.; Ahman, J.; Sadighi, J. P.; Singer, R. A.;
Buckwald, S. L. Tetrahedron Lett. 1997, 38, 6367.
8. Cragoe, E., Jr.; Robb, C. A.; Bealor, M. D. J. Org. Chem.
1953, 18, 552.
9. PKA and Akt inhibitors (12 and 13a) were co-crystallized in
a solution containing PKA (20 mg/mL) and PKI peptide.6
The structures were determined and refined to resolutions of
˚
˚
3.0 A for 12 (Rwork = 22.97% and RFree = 31.61%) and 2.0 A
for 13a (Rwork = 28.26% and RFree = 32.28%). Crystallo-
graphic data described in this paper have been deposited
with PDB (ID 2F7Z for 12 and 2F7E for 13a).
Acknowledgments
The authors are grateful to Mr. Rick Clark, Dr. Moshe
Weitzberg, Dr. Matt Hensen, Dr. Robert Keyes, Dr. Curt
Cooper, and Dr. Chris Krueger for proofreading and
valuable suggestions. X-ray crystallographic data were
collected at beamline 17-ID in the facilities of the Indus-
trial Macromolecular Crystallography Association Col-
laborative Access Team (IMCA-CAT) at the Advanced
Photon Source, which are supported by the companies
10. Luo, Y.; Shoemaker, A.; Liu, X.; Woods, K.; Thomas, S.;
de Jong, R.; Han, E.; Li, T.; Stoll, S. S.; Powelas, J. A.;
Oleksijew, A.; Mitten, M. J.; Shi, Y.; Guan, R.; McGon-
igal, T. P.; Klinghofer, V.; Johnson, E. F.; Leverson, J. D.;
Bouska, J. J.; Mamo, M.; Smith, R. A.; Gramling-Evans,
E. E.; Zinker, B. A.; Mika, A. K.; Nguyen, P. T.;
Oltersdorf, T.; Rosenberg, S. H.; Li, Q.; Giranda, V. Mol.
Cancer Ther. 2005, 4, 977.