486
K. L. Milkiewicz et al. / Bioorg. Med. Chem. Lett. 10 (2000) 483±486
Scheme 3.
chain with the indole scaold. The most active naph-
thalene inhibitor 3 from the previous report was used as
a template upon which the analogous indole inhibitor 2e
and the homologated indole inhibitor 2k were super-
imposed. The three most important side-chain func-
tionalities in naphthalene inhibitor 3 are considered to
be the 6-hydroxy group (H-bond donor and acceptor),
the hydrogen from the 3-hydroxy group (H-bond
donor), and the side-chain hydroxy group (H-bond
acceptor) based upon the rational design and SAR for
both series of inhibitors. This three point pharmaco-
phore model is identi®ed in both series by asterisks in
Scheme 3.
of the potency (2s, 57% versus 2k, 74% and 2r, 21%
versus 2e, 30%). Consequently, the ¯uoro analogue 2s
has only one hydroxy group left for potential Phase II
metabolism (e.g. glucuronide formation), and this remain-
ing hydroxy group is a current target for replacement.8
Using the same method as in the preceding paper,5 the
most potent inhibitor from the current indole series (2k)
was analyzed for ATP competition by monitoring the %
inhibition at increasing [ATP] while holding the inhi-
bitor concentration constant. Since the [ATP] had little
eect on the % inhibition,9 2k is non-competitive with
respect to ATP under these assay conditions.
The `multi®t', energy minimization and `®t atoms' facil-
ities within SYBYLTM (6.4, Tripos, St Louis) were used
in sequence to superimpose 2e and 2k onto 3. This
overall ®tting process was carried out with spring con-
stants (multi®t) and weights (®t atoms) chosen such that
the highest emphasis was on optimally superimposing
the scaold pharmacophore Os and Hs (100), followed
by the side chain Os (10) and then the intervening amide
bond (1). The `multi®t' process adjusted the conforma-
tions for maximum pharmacophore ®t, the subsequent
minimization produced the nearest local minimum
energy conformations and ®nally the `®t atoms' process
produced the best pharmacophore superimposition of
these minimized conformations. As expected, the
scaold pharmacophore Os and Hs of both 2e and 2k
superimposed closely and similarly upon the
corresponding atoms in 3 (all within ca. 0.50 A).
However, the side chain pharmacophore Os of 2e and
2k diered signi®cantly in their superimposition on the
corresponding O of 3, with displacements of 1.8 A
versus only 0.08 A, respectively. This close ®t of the
three key pharmacophore sites between 2k and 3
provides a rationalization for their potency diering by
only a factor of 2.4 (IC50s 38 mM versus 16 mM, respec-
tively).
In summary, an indole scaold has been designed, and
an initial SAR carried out, for the development of non-
ATP competitive pp60c-src inhibitors. The potency of the
best indole-based inhibitor from the current series was
found to be close to that of the best naphthalene-based
inhibitor from the preceding paper.
Acknowledgements
We gratefully acknowledge the Kapoor Foundation for
providing ®nancial support (to D.G.H.) for this work.
T.H.M. and K.L.M. gratefully acknowledge the
American Foundation for Pharmaceutical Education
for support as AFPE Fellows.
References and Notes
1. Parsons, J. T.; Parsons, S. J. Curr. Opin. Cell Biol. 1997, 9,
187.
2. Mao, W. G.; Irby, R.; Coppola, D.; Fu, L.; Wioch, M.;
Turner, J.; Yu, H.; Garcia, R.; Jove, R.; Yeatman, T. J.
Oncogene 1997, 15, 3083.
3. Ellis, L. M.; Staley, C. A.; Liu, W.; Fleming, R. Y.; Parikh,
N. U.; Bucana, C. D.; Gallick, G. E. J. Biol. Chem. 1998, 273,
1052.
4. Karni, R.; Jove, R.; Levitzki, A. Oncogene 1999, 18, 4654.
5. Marsilje, T. H.; Milkiewicz, K. L.; Hangauer, D. G. Bioorg.
Med. Chem. Lett. 2000, 10, 477.
6. Staley, C. A.; Parikh, N. U.; Gallick, G. E. Cell Growth
Di. 1997, 8, 269.
7. PyBOP=(benzotriazol-l-yloxy)tripyrrolidino-phosphonium-
hexa¯uorophosphate.
8. Lai, J. H.; Marsilje, T. H.; Choi, S.; Nair, S. A.; Hangauer,
D. G. J. Peptide Res. 1998, 51, 271.
9. The % inhibition was 46% and 41% with 2k at 45 mM and
[ATP] at 200 or 1000 mM, respectively.
Extending the amide side chain by another carbon atom
reduced the activity (2m, 21% versus 2l, 54%). Adding a
methyl group to the benzylic carbon of 2k, in either
stereochemistry, greatly reduced the activity (2y, 15%
and 2z, 13% versus 2k, 74%). Replacing the side-chain
hydroxy group (in the para position) with a carboxylate
anion (2n, 0% versus 2l, 54% and 2p, 7% versus 2f, 45%)
reduced the activity whereas the corresponding methyl
esters (2o, 11% and 2q, 32%, respectively) showed a
smaller loss of potency. Importantly, replacing the side
chain hydroxy group with a ¯uorine maintained much