Novel bis(1H-indol-2-yl)methanones as potent inhibitors of FLT3 and platelet-derived growth factor receptor tyrosine kinase

Article abstract of DOI:10.1021/jm058033i

FLT3 receptor tyrosine kinase is aberrantly active in many cases of acute myeloid leukemia (AML). Recently, bis(1H-indol-2-yl)methanones were found to inhibit FLT3 and PDGFR kinases. To optimize FLT3 activity and selectivity, 35 novel derivatives were synthesized and tested for inhibition of FLT3 and PDGFR autophosphorylation. The most potent FLT3 inhibitors 98 and 102 show IC ₅₀ values of 0.06 and 0.04 μM, respectively, and 1 order of magnitude lower PDGFR inhibiting activity. The derivatives 76 and 82 are 20- to 40-fold PDGFR selective. Docking at the recent FLT3 structure suggests a bidentate binding mode with the backbone of Cys-694. Activity and selectivity can be related to interactions of one indole moiety with a Hydrophobic pocket including Phe-691, the only different binding site residue (PDGFR Thr-681). Compound 102 inhibited the proliferation of 32D cells expressing wildtype FLT3 or FLT3-ITD similarly as FLT3 autophosphorylation, and induced apoptosis in primary AML patient blasts.

Full text of DOI:10.1021/jm058033i

J. Med. Chem. 2006, 49, 3101-3115
3101
Novel Bis(1H-indol-2-yl)methanones as Potent Inhibitors of FLT3 and Platelet-Derived Growth
Factor Receptor Tyrosine Kinase
Siavosh Mahboobi,†,§,* Andrea Uecker,‡,§ Andreas Sellmer,† Christophe Ce´nac,† Heymo Ho¨cher,† Herwig Pongratz,†
Emerich Eichhorn,† Harald Hufsky,†,X Antje Tru¨mpler,‡ Marit Sicker,‡ Florian Heidel,| Thomas Fischer,| Carol Stocking,
Sigurd Elz,† Frank-D. Bo¨hmer,‡,§,* and Stefan Dove†,§
Institute of Pharmacy, Faculty of Chemistry and Pharmacy, UniVersity of Regensburg, D-93040 Regensburg, Germany;
Institute of Molecular Cell Biology, Jena UniVersity Hospital, D-07747 Jena, Germany; Department of Medicine III,
Hematology-Oncology, UniVersity of Mainz, D-55101 Mainz, Germany; and Research Group Molecular Pathology,
Heinrich-Pette-Institute, D-20251, Hamburg, Germany
ReceiVed June 14, 2005
FLT3 receptor tyrosine kinase is aberrantly active in many cases of acute myeloid leukemia (AML). Recently,
bis(1H-indol-2-yl)methanones were found to inhibit FLT3 and PDGFR kinases. To optimize FLT3 activity
and selectivity, 35 novel derivatives were synthesized and tested for inhibition of FLT3 and PDGFR
autophosphorylation. The most potent FLT3 inhibitors 98 and 102 show IC50 values of 0.06 and 0.04 µM,
respectively, and 1 order of magnitude lower PDGFR inhibiting activity. The derivatives 76 and 82 are 20-
to 40-fold PDGFR selective. Docking at the recent FLT3 structure suggests a bidentate binding mode with
the backbone of Cys-694. Activity and selectivity can be related to interactions of one indole moiety with
a hydrophobic pocket including Phe-691, the only different binding site residue (PDGFR Thr-681). Compound
102 inhibited the proliferation of 32D cells expressing wildtype FLT3 or FLT3-ITD similarly as FLT3
autophosphorylation, and induced apoptosis in primary AML patient blasts.
Introduction
kinase. Activating point mutations in the kinase activation loop
are found in another subset of patients. Finally, elevated
expression of wildtype FLT3 and autocrine activation by its
cognate ligand FL (FLT3 ligand) is found in many other cases
of AML and may potentially also contribute to the disease.8
Compounds of several structural families, including quinoxalines
such as 1a (AG1295) and 1b (AGL2043), the indolinones 1c
(SU5416) and 1d (SU11248), the indolocarbazoles 1e (PKC412,
Midostaurin) and 1f (CEP701), and the piperazonylquinazoline
1g (CT53518) are potent inhibitors of FLT3 kinase (lit.7 and
references therein), as well as the quinoline-urea Ki23819 (exact
structure and chemical name not published yet9). Some of them
have been promising in first clinical trials. FLT3 is, however,
refractory for inhibition by 2 (STI571, Imatinib, Glivec,
Gleevec),10 the potent inhibitor of Abl/Bcr-Abl, c-Kit, and
PDGFR. Phe691 in the ATP binding site of FLT3 prevents
binding of 2.11
One of the hallmarks in cancer development is the acquisition
of growth factor independence.1 Aberrant activation of tyrosine
kinases often represents the underlying mechanism.2 Both,
activated cytoplasmic or receptor tyrosine kinases can drive
growth factor-independent proliferation and, therefore, represent
suitable targets for cancer therapy. Since molecular defects in
tyrosine kinases usually represent only one of multiple molecular
lesions in a given cancer cell, the beneficial effects of tyrosine
kinase inhibition may be very variable. Definition of patient
populations which will maximally benefit from tyrosine kinase
inhibition, use of selective inhibitors of mutated kinase versions
or of drugs which inhibit a panel of targets in a “multitargeted”
fashion, and combination with other types of therapy, are issues
which are currently intensely pursued.3-5 Survival and subse-
quent propagation of resistant molecular versions of tyrosine
kinases under chronic medication is another recently observed
phenomenon, often resulting in relapse of the tumor.6 Obviously,
there is a need for compounds with novel therapeutic profiles
based on specific binding modes, well-defined kinase selectivity
and activity toward clinically relevant kinase mutants.
We have previously reported the inhibition of the class III
receptor tyrosine kinase PDGFR by the bis(1H-indol-2-yl)-
methanone 3 and more particularly by its monosubstituted
derivatives, as for example those depicted in Figure 1 (see also
Table 1 and lit.12). Members of this compound family, like 4a
(known as D-64406), are also reasonably potent inhibitors of
FLT3 (cf. Table 1 and lit.13). However, the 5-monosubstituted
derivatives investigated so far were rather PDGFR-selective or
at the most equiactive at both kinases. The question arose
whether FLT3 selectivity may be obtained by variation of other
positions or even more by substitution of both indole moieties.
This strategy appeared reasonable since the previous data and
models indicated that the unsubstituted indole fits to the internal
walls of the binding pockets containing the only significant
differences of FLT3 and PDGFR. Here, we present synthesis
and structure-activity relationships (SAR) for novel, more
potent FLT3 inhibitors of the bisindolylmethanone family.
Despite the close similarity of the inhibitor binding pockets,
some compounds exhibit selectivity for FLT3 versus PDGFR
Fms-like (McDonough feline sarcoma viral oncogene homo-
logue-like) tyrosine kinase 3 (FLT3) is aberrantly active in many
cases of acute myeloid leukemia (AML).7 Mutations conferring
constitutive kinase activity are found in up to 30% of cases.
Most prevalent are mutations denoted “internal tandem duplica-
tions” (ITD) which occur in the juxtamembrane domain of the
* General correspondence and correspondence on chemical aspects to
Siavosh Mahboobi [e-mail: siavosh.mahboobi@chemie.uni-regensburg.de,
fax: +49 (0)941 943 1737, phone: +49 (0)941 943 4824]. Correspondence
on biological aspects to Frank-D. Bo¨hmer [e-mail: i5frbo@rz.uni-jena.de].
† University of Regensburg.
‡ Jena University Hospital.
| University of Mainz.
Heinrich-Pette-Institute.
X Present address: Novartis Pharma AG, CH-4057 Basel, Switzerland.
§ Authors contributed equally to this work.
10.1021/jm058033i CCC: $33.50 © 2006 American Chemical Society
Published on Web 05/09/2006

3102 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 11
Mahboobi et al.
Figure 1. Bisindolylmethanone (3) and selected monosubstituted derivatives (4a and 4b) as leads for the development of novel FLT3 inhibitors,
along with structures of known FLT3 and PDGFR inhibitors.
Scheme 1a
a A: (1) n-Buli or LDA, THF, -78 °C; (2) CO2 (s). B: SOCl2, reflux. C: THF, -78 °C. D: (1) n-Buli or LDA, THF, -78 °C; (2) DMF. E: PDC/PTFA,
DCM, 25 °C.
and vice versa. The structure-activity and -selectivity relation-
ships are explained with the help of molecular models of
inhibitor-kinase complexes based on the novel PDB crystal
structure 1rjb of FLT3.14
especially halogens, methyl, and hydroxy/alkoxy groups were
introduced in different positions.
The N-phenylsulfonated bisindolylmethanones 45-68 were
synthesized according to Scheme 1 by coupling of an indolyl
carboxylic acid chloride (35-38, 40) with its respective lithiated
indolyl. The acyl chlorides 35-41 themselves were obtained
from their corresponding N-protected indoles (6, 11, 14, 16,
19, 21, and 23) following Procedures A and B (see legend of
Scheme 1). Furthermore the desired bis(1-phenylsulfonyl-1H-
indol-2-yl)methanones (44) can be prepared by coupling of the
respective aldehydes (42) and 2-lithiated indoles, followed by
oxidation of the resulting carbinols (43).
Deprotection of the N-phenylsulfonated ketones 44-68 by
tetra-n-butylammonium fluoride or sodium hydroxide led to the
respective bis(1H-indol-2-yl)methanone derivatives 72-96
(Scheme 2). The (5-benzyloxy-1H-indol-2-yl)(7-ethyl-1H-indol-
2-yl)methanone 97 was obtained by modification of the usual
Chemistry
Since the 1,3-di(sec-amino)propan-2-one substructure (em-
phasized in Figure 1) seemed to be essential for kinase
inhibition,12 the bis(1H-indol-2-yl)methanone scaffold was
retained unchanged throughout the series, aside from two
compounds synthesized in order to verify the suggested binding
mode at FLT3. According to the previous SAR of PDGFR
inhibition,12 one indole moiety was substituted in 5-position
mostly by hydroxy or methoxy groups. Assuming that the
interior of the binding site is spatially restricted, substituents
of the second indole should be rather small, but cover a certain
range of hydrophobic and electronic properties. Therefore

Inhibitors of FLT3 and PGDFR Tyrosine Kinase
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 11 3103
Table 1. Inhibition of FLT3 and PDGFR Tyrosine Kinases by Bis(1H-indol-2-yl)methanones and Related Compounds in Cell Assays
a Assayed with endogenous FLT3 in EOL-1 cells. b Assayed with endogenous PDGFR in Swiss 3T3 fibroblasts. Consistent results were obtained for
inhibition of FLT3 and PDGFR-â, overexpressed in HEK293 cells (not shown). c Previously published syntheses and results on PDGFR inhibition.12 d Previously
published synthesis.12 # Selectivity significant with p < 0.05.

3104 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 11
Mahboobi et al.
Scheme 2a
Scheme 4a
a i: Procedure G. ii: (1) NaH, THF; (2) TBDMSCl, 40 °C.
ment of halogen by hydrogen, we modified the synthetic route
shown in Scheme 1 by use of the 2-lithiated species of the
5-(tert-butyldimethylsilyloxy)-1-phenylsulfonyl-1H-indole 26 for
coupling with the 4-halo-1-phenylsulfonyl-1H-indole-2-car-
boxylic acid chlorides 39 and 41. This leads to the N-
phenylsulfonylated silyl ethers 69 and 70, allowing access to
compounds 110 and 111 by one-step alkaline complete depro-
tection (Scheme 2).
The ethers 112-115 bearing a polar alkoxy chain were
synthesized from the corresponding 5-hydroxy derivatives 98,
104, and 107 by alkylation with N,N-dimethyl-2-chloroethy-
lamine or 1-(2-chloroethyl)-piperidine.
The bisindolylmethanes 11612 and 117 were obtained by
reduction of the carbonyl bridge of the corresponding bisin-
dolylmethanones 4b12 and 78 using the Huang-Minlon modi-
fication16 of the Wolff-Kishner reaction.
Results and Discussion
The structures of the bisindolylmethanones and their IC50
values for inhibition of FLT3 and PDGFR are shown in Table
1. The most potent FLT3 inhibitors 98 and 102 show a FLT3
IC50 value of 0.06 and 0.04 µM, respectively. They are approxi-
mately 2 orders of magnitude more potent than the quinoxaline
1a,17,18 which was tested as a reference compound. Interestingly,
their inhibitory potency for PDGFR is about 1 order of magnitude
lower (IC50 ) 0.96 and 0.30 µM, respectively). Another group of
compounds is characterized by moderate but selective inhibition
of PDGFR, notabably compond 82. Similar potency and selec-
tivity data as in the cellular assays were obtained for the selected
compounds 82, 98, 102, and 113 when tested with recombinant
kinases and an exogenous peptide substrate in cell-free assays.
Also, the rank order of potency for the individual kinases could
be reproduced in the in vitro assays. The data establish that dif-
ferences in the cellular uptake and metabolism were not impor-
tant for the observed selectivities of these compounds (Table 2).
A more detailed discussion of the SAR must be based on the
probable binding mode and on the symmetry of the bis(1H-
indol-2-yl)methanone scaffold. As suggested from a homology
model of the PDGFR and from SAR of the previous, mainly
monosubstituted bis(1H-indol-2-yl)methanone series,12 the com-
pounds may bind to the ATP site in a mode resembling the
interaction of 118 (PD173074, 1-tert-butyl-3-[2-(4-diethylami-
nobutylamino)-6-(3,5-dimethoxyphenyl)-pyrido[2,3-d]pyrimidin-
7-yl]-urea) in a crystallized complex with the FGFR-1.19 This
mode is generally confirmed by the recent crystal structure (PDB
1rjb) of FLT3.14 The key interactions (see Figure 2) are two
hydrogen bonds of an indole NH and the methanone oxygen
with the CO and the NH moiety, respectively, of the backbone
of FLT3 Cys-694 (PDGFR Cys-684). In contrast to the
bisindolylmethanones 4b and 78, the bisindolylmethane homo-
logues 116 and 117, respectively, are inactive. Their methylene
bridge between the indole moieties is incompatible with the
putative binding mode. The bidentate hydrogen bond donor-
acceptor system lets one indole ring point inward and the other
outward and enables, by this, the definition of an inner and an
outer binding pocket (see Figure 2B). The outer indole is open
for substitution in positions 5 and 6 even with larger polar, e.g.,
piperidinoethoxy or quinolylcarboxy groups.12 Whereas ether
a F: TBAF, THF, 60 °C or NaOH (10%), EtOH, 1:2, reflux. G:
HCO2NH4, Pd/C, MeOH or THF/MeOH 1:1, 40-60 °C. H: NaH, DMF,
25 °C. I: NaOH, H2O, 60 °C. J: KOH, (NH2)2, (CH2OH)2, microwave
200 W.
Scheme 3a
a i: DIBOC DMAP, MeCN. C: t-BuLi, THF, -78 °C. ii: (1) TBAF,
THF, reflux; (2) TFA, DCM.
synthetic route shown in Scheme 1; protection of 7-ethyl-1H-
indole was performed by the tert-butoxycarbonyl group15 instead
of the phenylsulfonyl increment (Scheme 3). In case of R1 )
OBn or R1 ) R2 ) OBn hydrogenolytic cleavage of the
benzyloxy group was then performed to obtain the phenolic
compounds 98-109.
After observation that Pd/C catalyzed benzyloxy deprotection
of chloro-substituted bisindolylmethanones also leads to replace-

Inhibitors of FLT3 and PGDFR Tyrosine Kinase
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 11 3105
Table 2. Inhibition of FLT3 and PDGFR Tyrosine Kinases by Selected Bis(1H-indol-2-yl)methanones in Cell-Free Assaysa
a Assayed in vitro with recombinant kinase domains expressed as GST-fusion proteins in Sf9 cells, [32Pγ]ATP, and an exogenous peptide substrate. The
results are mean values ( standard error of the mean (SEM) of four independent titration experiments. Sig.: probability of error from two-tail Student’s
t-test of the pIC50 difference between hFLT3 and hPDGFR-â.
Figure 2. Suggested binding mode of 98 at FLT3 and 82 at PDGFR, demonstrated by minimized complexes with the FLT3 crystal structure 1rjb.14
(A) Overview of the model with 98 and with representation of some important amino acids. Specific regions are highlighted on the ribbon/tube
backbone: light cyan, inhibitor binding site consisting of parts of â5 and the hinge region; yellow, nucleotide binding loop; red orange, catalytic
loop; green, activation loop. (B) Detailed view of the binding site of 98 with all amino acids lying within a sphere of 3 Å around the ligand.
Backbone atoms are dark, side chains light. C atoms orange, hydrophobic pocket (Phe-691, Val-675); C atoms green, activation loop residues.
Yellow lines, hydrogen bonds of Cys-694 with the ligand. The gray line separates the inner (right) from the outer (left) binding pocket. (C) MOLCAD
van der Waals surface of FLT3 with 98 in ball-and-stick representation. (D) Putative PDGFR binding site of 82 with all amino acids lying within
a sphere of 3 Å around the ligand. The model was derived from the FLT3 crystal structure by mutation of the only different binding site residue,
Phe-691, into PDGFR Thr-681 (side chain conformation like Thr-315 in the Abl kinase crystal structure 1iep21). Numbers of amino acids corresponding
to hPDGFR-â. The side chain C and H atoms of Thr-681 are magenta, coloring of all other atoms such as in panel B.
substituents were not superior to 5-OH, PDGFR inhibition could
be increased by ester moieties. The 5-substituents are surrounded
by short chains of the â1 strand and of the hinge region and
protrude into the solvent.
These general considerations will help to understand most
of the SAR of the derivatives in Table 1 by suggesting which
substituents probably belong to the inner and outer indole,
respectively. Substituents in 4′-position should be inside the

3106 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 11
Mahboobi et al.
pocket because of probable steric hindrance when present at
the outer ring (see Figure 2). The FLT3 kinase seems to provide
a specific interaction site especially for methyl in 4′-position.
Compound 98 is significantly FLT3 selective in both cellular
(IC50 ) 0.06 µM compared to 0.96 µM at PDGFR) and in vitro
assays (IC50 ) 0.07 µM vs. 0.46 µM, see Table 2). The
5-piperidinoethoxy-4′-methyl derivative 113, FLT3 selective in
both assays, too, confirms the inner position of the methyl since
the large polar group must point outward. The 4′-halogen-
substituted compounds 106, 110, and 111 are at least 10-fold
less active at FLT3 than the methyl derivative 98 and unselec-
tive. The order of activity of the 4′-halogen groups is F > Cl >
Br (FLT3) and Cl g F > Br (PDGFR), respectively. A
4′-methoxy group on its own has no effect on activity and
selectivity (compare 3 and 72). The hydroxy group in the 5-OH-
4′-OMe derivative 103 increases inhibition of both kinases.
indicate that a 6′-methoxy group may interact with the inner
pocket without marked loss of potency. Interestingly, the 6′-
substituted 5-OMe compounds are all significantly PDGFR
selective. In the case of hydrophobic 6′-substituents such as
methyl and chloro (76 and 82), the selectivity is even 20- to
40-fold because of the surprisingly high PDGFR and very weak
FLT3 inhibition. For 82, PDGFR selectivity was confirmed in
vitro (see Table 2).
Together with a 5-OH group at the other ring, the 7′-
substituted compounds 101, 105, and 109 are generally weakly
active. Compound 83 (5-OMe-7′-Cl) is inactive at both kinases.
Modeling of the Putative Binding Mode. The PDB crystal
structure 1rjb of FLT314 offers the possibility to suggest
interactions of bisindolylmethanones by docking into the ATP
binding site. Figure 2 represents the final model with the highly
active 5-OH-4′-Me derivative 98 as ligand. An overview of the
binding site location is shown in panel A. The ligand fits to a
bank of four residues, Phe-691 to Cys-694, belonging to â5
and the hinge region. Within 3 Å around compound 98, Phe-
691 is the only mutated amino acid compared to the PDGFR
(Thr-681) and, therefore, the primary candidate for explaining
selectivity. Lys-644 (â3) and Glu-661 (RC), forming a salt
bridge as in other tyrosine kinases, are close to the 5-position
of the inner indole ring. From the C-terminal domain, parts of
â7, â8, and the DFG motif with Phe-830 make the bottom of
the binding site. The course of the activation loop allows the
fit of much larger ligands such as 2 (see Figure 1) which inhibits
a FLT3 Phe-691-Thr mutant (IC50 ) 0.1-0.3 µM20). With
respect to the whole Imatinib binding site, a FLT3 model mainly
based on homology with the Abl kinase20 was closely similar
to the FLT3 crystal structure (rms distance of CR atoms 0.85
Å). Prerequisite of Imatinib activity is the inactive conformation
of the activation loop, characterized by an autoinhibitory position
of the unphosphorylated Tyr-842. The bis(1H-indol-2-yl)-
methanones are not assumed to extend into the binding pocket
like 2 because of the interaction with the backbone of Cys-
694, which in the case of 2 forms a hydrogen bond with the
terminal pyridine nitrogen. In the docking mode of 98, neither
the nucleotide binding nor the catalytic loop participate in
binding.
An important new insight is that a 5-OH group at the inner
ring is favorable and may lead to FLT3 selectivity. The 5,5′-
dihydroxy derivative 102 is the most active FLT3 inhibitor
within the series (cellular IC50 ) 0.04 µM, in vitro IC50 ) 0.033
µM). The contributions of the hydroxy groups to FLT3
inhibition are similar and additive (ca. 1 order of magnitude,
compare 3, 4a, and 102). The data of the lead 3 indicate that
the PDGFR incorporates an unsubstituted indole moiety into
the inner pocket somewhat better than FLT3. Introduction of
one 5-OH substituent (4a) increases PDGFR as well as FLT3
inhibition (5- and 8-fold, respectively). An additional hydroxy
group in 5′-position does not further improve PDGFR activity
(102). In conclusion, this different behavior of both kinases
might be due to a favorable effect of a polar 5-substituent at
the outer ring and to a specific FLT3 binding site for an inner
5′-hydroxy group.
Single 5-F substitution (73) reduces activity at both kinases
by a factor of ca. 4 compared to 5-OH (4a). Fluorine may
interact with the inner pocket as indicated by the data of the
5-methoxy, 5-benzoxy, and 5-piperidinoethoxy derivatives 78,
94, and 115, respectively. It should be noted that an about 10-
fold reduction of PDGFR inhibition from 5-piperidinoethoxy
to 5-benzyloxy compounds corresponds to the trend observed
in similar monosubstituted analogues,14 i.e., larger substituents
with polar termini are always superior to more hydrophobic
groups. Taken together, the data of the compounds with small
substituents such as F, OH, and Me in 5-position raise the
question whether in some cases the measured IC50 values are
based on a mixture of both binding orientations and/or even
different modes at both kinases. For example, 5′-Me and 5′-F
in the 5-OH compounds 99 and 107, respectively, are generally
able to fit in the inner and the outer pocket. It may be suggested
that the more lipophilic moiety is preferentially transferred into
the interior via hydrophobic patches.
The detailed interactions of compound 98 are shown in Figure
2B. In contrast to previous suggestions,12 the conformation of
the outer indole is synperiplanar (sp, cis) and of the inner indole
antiperiplanar (ap, trans) based on the respective NC-CO
torsion angle. Provided that the bidentate hydrogen bond exists,
the FLT3 crystal structure has no specific counterpart for the
inner indole NH function in both possible energy minima, sp/
ap and sp/sp, but the 3-position is in hydrophobic contact with
Val-675 in the sp/ap minimum conformation (see Figure 2).
An additional H bond of the inner indole NH with the backbone
oxygen of Glu-692 as suggested for PDGFR binding in sp/sp
orientation12 is impossible since then the 4′- and 7′-positions
bump into the side chains of Phe-830 and Phe-691, respectively.
AMPAC 6.55 calculations of 98 with the COSMO water
solvation model result in the lowest energy for a sp/sp propeller-
like conformation with NC-CO torsion angles of about 30/30
or -30/-30 degrees. However, the sp/ap minimum is only about
0.6 kcal/mol higher in energy, and the polar surface accessible
to water is slightly larger. A reaction coordinate calculation of
the rotation of the inner indole results in a barrier of only 2.2
kcal/mol. Therefore, each conformation is energetically possible
in the bound state. However, a hydrophobic patch mainly
consisting of Val-675, Phe-691, and Leu-818 appears to fit the
A single 5-OMe group reduces FLT3 activity compared to
5-OH and leads to significant PDGFR selectivity (cf. 4a and
4b). An inner methoxy substituent in 5-position is unfavorable,
since the 5,5′-di-OMe derivative has an IC50 of only about 10-
30 µM at PDGFR.12 All 5-OMe compounds with R2 substituents
at the other moiety are either unselective or PDGFR selective.
In the 5′-halogen series, activity at both kinases decreases in
the order of F > Cl g Br.
The 6-OMe derivative 5 is by a factor 3 to 5 more active
than the unsubstituted lead 3. The introduction of an additional
5-OH group at the other moiety does not significantly change
activities (104). The 6′-substituted 5-OH derivatives 100, 104,
and 108 are unselective and do not significantly differ in
potency. Compounds 112 and 114 with large polar 5-substituents

Inhibitors of FLT3 and PGDFR Tyrosine Kinase
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 11 3107
lipophilic edge of the inner indole (3- and 4-positions) and,
therefore, to prefer the sp/ap conformation of the compounds.
The docking mode in Figure 2B explains the FLT3 selectivity
of 4′-Me substituted derivatives by an about 3 Å distance of
the methyl group to the phenyl plane of Phe-691, and also the
hydrophobic interaction with Val-675 is optimal in case of 4′-
Me. The lower FLT3 inhibition of the 4′-halogen substituted
compounds 77, 80, 106, 110 and 111 may be due to electrostatic
repulsion with the π system of Phe-691. The 5′-position is
directed toward the phenyl plane, too. In compound 102, the
5′-OH group is 2.9 Å distant from the Phe-691 phenyl center,
indicating that electrostatic interaction of the positively charged
hydrogen with the π system contributes to the high FLT3
activity and selectivity. Generally, the 5′-OH substituent may
also directly or via water interact with Lys-644 and Glu-661
(NH3+...O and CO2-...H distances of ca. 4 Å). A 5′-Me
substituent fits well to Phe-691, but not to Val-675. Insofar,
the reduced activity of compound 99 corresponds to the given
docking mode.
A polar group in 6-position may generally point into the
solvent like a 5-substituent (see Figure 2A and C). Three of
the compounds with a probable inner location of the 6′-substi-
tuent (76, 79 and 82) are PDGFR selective. Comparing the data
of the 5-OMe derivatives for both kinases, the 5′- and 6′-posi-
tions of all substituents except F seem to be nearly equivalent
with respect to FLT3 activity, whereas the PDGFR prefers hy-
drophobic 6′-substituents such as methyl and chloro. The simp-
lest hypothetic explanation for this rather unexpected finding
may be given if the sp/ap binding mode is suggested for the
PDGFR, too. Replacing FLT3 Phe-691 into the corresponding
PDGFR Thr-681 with a conformation of the side chain like Thr-
315 in the Abl kinase crystal structure 1iep21 indicates interaction
of the 6′-substituents with the methyl branch of Thr-681 (dis-
tance ca. 2.9 Å), whereas the OH hydrogen points to the indole
ring (see Figure 2D). Contrariwise, larger groups in 5′-position
like in compounds 75 and 84 clash with the threonine side chain.
Figure 3. Inhibition of FLT3-dependent cell proliferation by the bis-
(1H-indol-2-yl)methanone 102. 32Dcl3 cells expressing wildtype FLT3
or FLT3-ITD (as indicated) were grown with different concentrations
of the inhibitor in the absence or presence of FL or IL-3, as indicated,
for 2 days. Cell amounts were subsequently determined with the MTT
assay. Values are means ( SD (n ) 6). Note that very low
concentrations of inhibitor sometimes led to stimulation of proliferation
under these conditions.
Also the 7′-substituents rather belong to the inner indole ring.
The FLT3 model indicates that bulky groups in this position
should be sterically hindered especially by Val-624 and Ala-
642. Compared to FLT3, the higher PDGFR activity of
compounds 101, 105, and 109 cannot be explained without a
more precise PDGFR model.
ships of the bis(1H-indol-2-yl)methanone derivatives on a
qualitative level, ascribing activity differences between FLT3
and PDGFR mainly to the Phe-Thr exchange. The symmetry
of the scaffold and the similar energy of the minimum
conformations actually suggest different binding orientations and
conformations and even multiple modes of individual com-
pounds and/or different modes at both kinases. It is, therefore,
somewhat surprising that much of the data fit to a unique model.
However, the lacking equivalence of the “inner” indole positions
(4 and 7, 5 and 6), corresponds to a single binding mode.
Further Biological Tests. The most potent compound 102
was further explored for inhibition of FLT3-ITD in a cellular
model of FLT3-driven proliferation. As depicted in Figure 3,
proliferation of 32D cells in dependence on wild-type FLT3 or
FLT3-ITD was inhibited with an activity (IC50 approximately
0.1 µM) close to that for FLT3 kinase inhibition in EOL-1 cells.
IL-3 fully abolished inhibition, indicating that 102 is selective
as it is not affecting kinases in the IL-3 signaling cascade.
Equally potent inhibition of wild-type FLT3 and FLT3-ITD
distinguishes compound 102 from other FLT3 inhibitors such
as the indolocarbazole 1e, which preferentially inhibit FLT3-
ITD.22 Furthermore, compounds 98 and 102 potently induced
apoptosis in primary blast cells obtained from AML patients
(Figure 4, upper panels). All tested patient blasts contained wild-
type FLT3 (data not shown), consistent with the capacity of
102 to block this version of FLT3. Thus, 102 and related bis-
The binding site of the inner indole ring is completed by the
side chains of Ala-642 (â3) from the top and of Val-624 (â2),
Leu-818 (â7), Cys-828 (â8, also in contact with the 4′-Me
group), and Phe-830 (DFG-motif) from the bottom. Additionally
to the hydrogen bond with the Cys-694 backbone, the outer
indole interacts with the N-terminal domain residues Leu-616
(â1) and Tyr-693 (hinge) as well as with Phe-830. Figure 2C
shows a volume representation of the binding site region,
indicating how the outer indole moiety protrudes into the
solvent. Obviously, the 5- and 6-positions are free and remain
solvated in the bound state, whereas substituents in 4- and
7-positions should be sterically hindered. With this model, it
becomes plausible that generally increased polarity (water
solubility) and lower hydrophobicity of 5- and 6-substituents
lead to higher activity at both kinases (compare 5-hydroxy with
5-methoxy, 5-benzyloxy with 5-piperidinoethoxy). Correspond-
ing to previous results on PDGFR,12 ether moieties in 5-position
do not improve inhibition as compared to 5-hydroxy, and groups
with polar termini like in compounds 112-115 are superior to
derivatives with nonpolar ones.
In conclusion, the model in Figure 2 reasonably explains a
lot of the structure-activity and structure-selectivity relation-

3108 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 11
Mahboobi et al.
Figure 4. Activity of bisindolylmethanones in other biological assays. Apoptosis induction in primary human AML blasts by treatment with the
bis(1H-indol-2-yl)methanones 98 (upper left panel) or 102 (upper right panel) for 72 h. The fraction of apoptotic cells was measured as Sub-G1
population by FACS analysis. Inhibition of c-Kit-dependent DNA synthesis in a FDC-P1 background by compound 98 (lower left panel) or 102
(lower right panel). Parental FDC-P1 cells or cell lines expressing different variants of KIT were treated for 42 h with the compounds in absence
or presence of IL-3 or stem cell factor (SCF) as indicated. Subsequently, incorporation of [3H]thymidine was determined.
(1H-indol-2-yl)methanones deserve further exploration as an-
titumor agents in AML.
inhibition by compound 102 than FLT3. Comparison of Abl
crystal structures21 in complex with 2 and 119 (PD173955,
6-(2,6-dichlorophenyl)-8-methyl-2-(3-methylsulfanylphenylamino)-
8H-pyrido[2,3-d]pyrimidin-7-one),24 respectively, with FLT3
indicates that the conformations of the nucleotide binding loops
are very different. In Abl, this loop is inwardly folded,
approaching Tyr-253 (corresponding to FLT3 Phe-621) to the
putative bisindolylmethanone binding site and constricting the
available “inner” pocket. Thus, the Abl binding mode of the
compounds may differ from that at FLT3. Anyway, the weaker
activity at the Abl kinase is not uniquely due to the FLT3 Phe-
691 Abl Thr-315 exchange, since also the PDGFR with the
corresponding Thr-681 is more strongly inhibited than Abl by
all tested derivatives (Table 1 and data not shown).
Activating mutations in the KIT/stem cell factor (SCF)
receptor have also been found in AML blasts,23 and the KIT
kinase domain is homologous to that of FLT3 and PDGFR.
Therefore, the inhibition of KIT signaling activity by the most
potent compounds 98 and 102 was tested, employing the IL-
3-dependent FDC-P1 cells expressing either KIT wildtype or
activated KIT mutants. As shown in Figure 4 (lower panels),
KIT was generally less susceptible to inhibition than FLT3, with
IC50 values ranging from approximately 0.5 µM with the KIT
V558D mutant to 0.5-2 µM for wildtype KIT. The KIT D814V
mutant was completely resistant to both compounds. A lower
susceptibility of KIT for other members of this compound family
has been observed by us earlier.13
Prompted by the high structural similarity of the ATP binding
sites of FLT3 and the Abl-kinase, we also explored the inhibitory
potency of selected bisindolylmethanones toward Abl. Potency
for Abl inhibition of the bis(1H-indol-2-yl)methanones was,
however, generally lower than for FLT3, exemplified by an IC50
for compound 102 of 1.3 µM for inhibition of recombinant Abl
in vitro and 4.2 µM for inhibition of oncogenic Bcr-Abl kinase
in K562 cells. Thus, Abl was 30- to 100-fold less sensitive to
Conclusions
Bis(1H-indol-2-yl)methanones are a new family of potent
FLT3 and PDGFR inhibitors. Despite the relatively small and
simple scaffold, some compounds clearly exhibit selectivity
among both kinases, depending on the substitution pattern. The
most potent FLT3 inhibitors, compounds 98 and 102, result in
IC50 values of ca. 0.05 µM. Their potency for PDGFR is about
1 order of magnitude lower. In the case of 5-OMe and

Inhibitors of FLT3 and PGDFR Tyrosine Kinase
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 11 3109
7-Fluoro-1-phenylsulfonyl-1H-indole (18). Preparation from
7-fluoro-1H-indole (Lancaster) as described above, Yield: 8.81 g
(65%) beige crystals. Mp: 86-87 °C. Anal. (C14H10FNO2S): C,
H, N.
hydrophobic 6′-substituents as in compounds 76 and 82, 20- to
40-fold PDGFR selectivity is obtained. The putative binding
mode at both kinases is based on a bidentate hydrogen bond of
the outer indole NH and the methanone oxygen with the
backbone of a cysteine residue in the hinge region. FLT3 activity
and selectivity seem to depend on interactions of the inner indole
moiety with a hydrophobic pocket including Val-675 and Phe-
691, the only amino acid of the binding site which is different
in the PDGFR kinase (Thr-681). Compound 102 potently
inhibited wild-type FLT3 as well as FLT3-ITD-dependent
proliferation of cells. Further structural optimization and further
biological tests will help to investigate the role of bis(1H-indol-
2-yl)methanones as potential drugs against tumors associated
with constitutive FLT3 or PDGFR activation.
4-Chloro-1-phenylsulfonyl-1H-indole (19). Preparation from
4-chloro-1H-indole (Acros) as described above, Yield: 10.62 g
(92%). Mp: 134-134.2 °C. Anal. (C14H10ClNO2S): C, H, N.
5-Chloro-1-phenylsulfonyl-1H-indole34 (20). Preparation from
5-chloro-1H-indole (Lancaster) as described above, Yield: 14.41
g (96%).
6-Chloro-1-phenylsulfonyl-1H-indole35 (21). Preparation from
6-chloro-1H-indole (Lancaster) as described above, Yield: 7.1 g
(70%).
7-Chloro-1-phenylsulfonyl-1H-indole (22). Preparation from
7-chloro-1H-indole (Lancaster) using DMF instead of THF as
described above, Yield: 3.99 g (72%). Mp: 80-81 °C. Anal.
(C14H10ClNO2S): calcd. C 57.64, H 3.45, N 4.80; found C 58.31,
H 3.86, N 4.81.
Experimental Section
Chemical Procedures. General. NMR spectra were recorded
with a Bruker Avance 300 MHz spectrometer at 300 K, using TMS
as an internal standard. IR spectra (KBr or pure solid) were
measured with a Bruker Tensor 27 spectrometer. Melting points
were determined with a Bu¨chi B-545. MS spectra were measured
with a Finnigan MAT 95 (EI, 70 eV). All reactions were carried
out under nitrogen atmosphere. Elemental analyses were performed
by the Analytical Lab. of the University of Regensburg.
Synthesis of 1-Phenylsulfonyl-1H-indoles. During 20 min, 60%
NaH in paraffin (1.29 g, 43.0 mmol) was added to a stirred solution
of the respective indole (42.0 mmol) in 60 mL of anhydrous THF
at 0 °C. After stirring at room temperature for 1 h, benzenesulfonyl
chloride (4.9 mL, 43.0 mmol) was added slowly. The reaction
mixture was stirred for an additional 1 h and then poured into 500
mL of 5% aq. NaHCO3 and extracted with ether (3 × 250 mL).
The combined organic layers were dried (Na2SO4), and the solvent
was removed under reduced pressure to give a beige solid.
Recrystallization from ethanol afforded the title compound as
colorless crystals.
4-Bromo-1-phenylsulfonyl-1H-indole32 (23). Preparation from
4-bromo-1H-indole (Biosynth) as described above, Yield: 7,47 g
(87%).
5-Bromo-1-phenylsulfonyl-1H-indole36 (24). Preparation from
5-bromo-1H-indole (Lancaster) as described above, Yield: 12.29
g (87%).
Further N-Protected Indoles. 5-Hydroxy-1-phenylsulfonyl-
1H-indole31 (25) was prepared from 5-benzyloxy-1-phenylsulfonyl-
1H-indole 14 according to Procedure G (see below) in methanolic
solution. Crystallization from dichloromethane/hexane yielded the
product. Yield: 7.80 g (86%). Mp: 152.6-152.7 °C.
5-(tert-Butyldimethylsilanyloxyl)-1-phenylsulfonyl-1H-in-
dole (26). During 20 min, 60% NaH in paraffin (2.20 g, 55.0 mmol)
was added to a stirred solution of 25 (13.7 g, 50.0 mmol) in 750
mL of anhydrous THF at 25 °C. After stirring at room temperature
for 1 h, tert-butyldimethylchorosilane (8.29 g, 55.0 mmol) was
added. The reaction mixture was stirred at 40 °C for an additional
1 h, the solvent removed in vacuo, the residue extracted with hot
anhydrous hexane (2 × 100 mL), the hot suspension filtered over
a pad of Na2SO4, and the product crystallized at -18 °C overnight.
Yield: 19.18 g (99%). Mp: 77.8-78.8 °C. Anal. (C20H25NO3-
SSi): C, H, N.
1-Phenylsulfonyl-1H-indole25 (6). Preparation from 1H-indole
(Merck) as described above, Yield: 8.20 g (76%).
4-Methyl-1-phenylsulfonyl-1H-indole26 (7). Preparation from
4-methyl-1H-indole (Acros) as described above, Yield: 51.44 g
(89%).
7-Ethylindole-1-carboxylic Acid tert-Butyl Ester15 (27). Prepa-
ration from 7-ethyl-1H-indole (Acros) as follows: DMAP (0.52 g,
4.27 mmol) and di-tert-butyl dicarbonate (11.2 g, 51.24 mmol) were
added to a 80 mL acetonitrile solution of the indole derivative (6.20
g, 42.7 mmol). The reaction mixture was then stirred till completion
at room temperature (approximately 3 h, TLC control) before
addition of 1.6 mL (15 mmol) of diethylamine. After 10 min of
additional stirring, 80 mL of diethyl ether were poured into the
mixture which was successively washed with a sat. potassium
hydrogen sulfate aq. solution, water, and a sat. sodium hydrogen
carbonate aq. solution. The organic phase was dried and evaporated.
The crude product was subjected to column chromatography (SiO2,
petroleum ether/diethyl ether 3:1) to afford a light yellowish oil.
Yield: 8.62 g (82%).
5-Methyl-1-phenylsulfonyl-1H-indole27 (8). Preparation from
5-methyl-1H-indole (Acros) as described above, Yield: 8.2 g (80%)
colorless oil.
6-Methyl-1-phenylsulfonyl-1H-indole28 (9). Preparation from
6-methyl-1H-indole (Acros) as described above, Yield: 6.9 g (71%).
4-Methoxy-1-phenylsulfonyl-1H-indole29 (10). Preparation from
4-methoxy-1H-indole (Lancaster) as described above, Yield: 9.52
g (79%).
5-Methoxy-1-phenylsulfonyl-1H-indole30 (11). Preparation from
5-methoxy-1H-indole (Acros) as described above, Yield: 7.12 g
(89%).
6-Methoxy-1-phenylsulfonyl-1H-indole30 (12). Preparation from
6-methoxy-1H-indole (Biosynth) as described above, Yield: 8.70
g (69%).
Procedure A: Preparation of (1-Phenylsulfonyl-1H-indol-2-
yl)carbonic Acids. Metalation with n-Butyllithium. Method I:
n-Butyllithium (1.6 M in hexane; 10.0 mL, 16.0 mmol) was added
dropwise to a solution of the respective 1-phenylsulfonyl-1H-indole
(15.0 mmol) in dry THF (50 mL) at -78 °C, to yield the respective
(1H-indol-2-yl)lithium after stirring for 1 h. An excess of solid
carbon dioxide was added, the mixture was warmed to room
temperature, and the solvent was removed under reduced pressure.
The white solid obtained was dissolved in water (100 mL) and the
aqueous solution extracted with ethyl acetate (2 × 50 mL). The
aqueous solution was separated, filtered, vigorously stirred, and
acidified with concentrated HCl, yielding the respective carbonic
acid. Crystallization from ethanol/water afforded an analytical pure
sample. According to Method I the following carbonic acids were
synthesized: 28-33.
7-Methoxy-1-phenylsulfonyl-1H-indole31 (13). Preparation from
7-methoxy-1H-indole (Aldrich) as described above, Yield: 8.45 g
(67%).
5-Benzyloxy-1-phenylsulfonyl-1H-indole12 (14). Preparation
from 5-benzyloxy-1H-indole (Lancaster) as described above,
Yield: 19.72 g (87%).
4-Fluoro-1-phenylsulfonyl-1H-indole32 (15). Preparation from
4-fluoro-1H-indole (Aldrich) as described above, Yield: 7.74 g
(67%).
5-Fluoro-1-phenylsulfonyl-1H-indole33 (16). Preparation from
5-fluoro-1H-indole (Acros) as described above, Yield: 12.84 g
(90%).
6-Fluoro-1-phenylsulfonyl-1H-indole (17). Preparation from
6-fluoro-1H-indole (Acros) as described above, Yield: 3.40 g
(56%). Mp: 101.3-101.4 °C. Anal. (C14H10FNO2S): C, H, N.
Metalation with Lithiumdiisopropylamide (LDA). Method II:
To a solution of the appropriate 1-phenylsulfonyl-1H-indole (15.0

3110 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 11
Mahboobi et al.
mmol) in dry THF (100 mL) was added commercially available
LDA (2 M solution in THF/n-heptane) at -78 °C. After stirring
for 1 h, an excess of solid carbon dioxide was added. The mixture
was warmed to room temperature and the solvent removed under
reduced pressure. To the white solid obtained, dichloromethane
(about 3.0 mL per mmol) and hydrochloric acid (2 N, 1.0 mL/
mmol) were added, and the mixture was refluxed for 1 h. The
organic layer was washed with hydrochloric acid (2 N, 1.0 mL/
mmol) and dried (Na2SO4). Removing the solvent under reduced
pressure left an oily residue which was crystallized from diethyl
ether. According to Method II the carboxylic acid 34 was
synthesized.
respective the aldehyde 42 (5.5 mmol) (cf. Procedure D) in THF.
The mixture was allowed to warm to room-temperature overnight,
hydrolyzed with 300 mL 2% aq. NaHCO3, and extracted with CH2-
Cl2 (3 × 50 mL), and the combined organic layers were dried (Na2-
SO4). Column chromatography (SiO2, CH2Cl2) and crystallization
from diethyl ether/light petrol (4:1) afforded the product as colorless
to faintly yellowish crystals.
(4-Methoxy-1-phenylsulfonyl-1H-indol-2-yl)-(1-phenylsulfo-
nyl-1H-indol-2-yl)methanole (43). Metalation of 10 was performed
according to procedure A, Method II. Yield: 5.83 g (73%). Mp:
86-89 °C. Anal. (C30H24N2O6S2): C, H, N.
(5-Fluoro-1-phenylsulfonyl-1H-indol-2-yl)-(1-phenylsulfonyl-
1H-indol-2-yl)methanone (45). Metalation of 16 was performed
according to Procedure A, Method II. Yield: 0.78 g (26%). Mp:
220.0-221.3 °C. Anal. (C29H19FN2O5S2): C, H, N.
1-Phenylsulfonyl-1H-indole-2-carboxylic Acid12,25 (28). Prepa-
ration according to Procedure A, Modification I. Yield: 7.3 g (79%)
colorless crystals.
5-Methoxy-1-phenylsulfonyl-1H-indole-2-carboxylic Acid (29).
Preparation according to Procedure A, Modification I. Yield: 32.5
g (91%) colorless crystals. Mp: 173.4-173.5 °C. Anal. (C16H13-
NO5S): calcd. C 58.00, H 3.95 N 4.23; found C 57.93, H 3.95, N
3.14.
(5-Methoxy-1-phenylsulfonyl-1H-indol-2-yl)-(4-methyl-1-phe-
nylsulfonyl-1H-indol-2-yl)methanone (46). Metalation of 7 was
performed according to Procedure A, Method II. Yield: 1.02 g
(47%). Mp: 214.7-214.9 °C. Anal. (C31H24N2O6S2): C, H, N.
(5-Methoxy-1-phenylsulfonyl-1H-indol-2-yl)-(5-methyl-1-phe-
nylsulfonyl-1H-indol-2-yl)methanone (47). Metalation of 8 was
performed according to Procedure A, Method I. Yield: 1.30 g
(38%). Mp: 208-209 °C. Anal. (C31H24N2O6S2): calcd. C 63.68,
H 4.14, N 4.79; found C 63.11, H 4.22, N 4.85.
5-Benzyloxy-1-phenylsulfonyl-1H-indole-2-carboxylic Acid12
(30). Preparation according to Procedure A, Method I. Yield: 35.20
g (61%) colorless crystals.
5-Fluoro-1-phenylsulfonyl-1H-indole-2-carboxylic Acid (31).
Preparation according to Procedure A, Modification I. Yield: 3.49
g (57%) colorless crystals. Mp: 190-192 °C. Anal. (C15H10-
FNO4S): C, H, N.
4-Chloro-1-phenylsulfonyl-1H-indole-2-carboxylic Acid (32).
Preparation according to Procedure A, Modification I. Yield: 5.93
g (84%) colorless crystals. Mp: 164-164.2 °C. Anal. (C15H10-
ClNO4S): C, H, N.
6-Chloro-1-phenylsulfonyl-1H-indole-2-carboxylic Acid (33).
Preparation according to Procedure A, Modification I. Yield: 5.03
g (63%) colorless crystals. Mp: 139-140 °C. Anal. (C15H10-
ClNO4S): C, H, N.
4-Bromo-1-phenylsulfonyl-1H-indole-2-carboxylic Acid (34).
Preparation according to Procedure A, Modification II. Yield: 4.49
g (63%) colorless crystals. Mp: 173.5-174 °C. Anal. (C15H10-
BrNO4S): C, H, N.
Procedure B: Preparation of 1-Phenylsulfonyl-1H-indole-2-
carbonyl Chlorides. The appropriate 1-phenylsulfonyl-1H-indole-
2-carboxylic acid (5.0 mmol) was dissolved in thionyl chloride (10.0
mL) and refluxed for 1 h. Excess of thionyl chloride was removed
under reduced pressure, and the acid chloride was dried in vacuo.
35-41 were used for further synthesis without purification. Analyti-
cal samples could be obtained by column chromatography (SiO2,
DCM) and crystallization from DCM/hexane.
(5-Methoxy-1-phenylsulfonyl-1H-indol-2-yl)-(6-methyl-1-phe-
nylsulfonyl-1H-indol-2-yl)methanone (48). Metalation of 12 was
performed according to Procedure A, Method I. Yield: 0.89 g
(29%). Mp: 194-195 °C. Anal. (C31H24N2O6S2): C, H, N.
(4-Fluoro-1-phenylsulfonyl-1H-indol-2-yl)-(5-methoxy-phe-
nylsulfonyl-1H-indol-2-yl)methanone (49). Metalation of 15 was
performed according to Procedure A, Method I. Yield: 1.52 g
(36%). Mp: 223-224 °C. Anal. (C30H21FN2O6S2): C, H, N.
(5-Fluoro-1-phenylsulfonyl-1H-indol-2-yl)-(5-methoxy-1-phe-
nylsulfonyl-(1H-indol-2-yl)methanone (50). Metalation of 16 was
performed according to Procedure A, Method II. Yield: 1.20 g
(38%). Mp: 179.4-182.9 °C. Anal. (C30H21FN2O6S2): C, H, N.
(6-Fluoro-1-phenylsulfonyl-1H-indol-2-yl)-(5-methoxy-1-phe-
nylsulfonyl-1H-indol-2-yl)methanone (51). Metalation of 17 was
performed according to Procedure A, Method II. Yield: 0.85 g
(40%). Mp: 224.3-226.5 °C. Anal. (C30H21FN2O6S2): C, H, N.
(4-Chloro-1-phenylsulfonyl-1H-indol-2-yl)-(5-methoxy-phe-
nylsulfonyl-1H-indol-2-yl)methanone (52). Metalation of 19 was
performed according to Procedure A, Method I. Yield: 2.59 g
(63%). Mp: 239-240 °C. Anal. (C30H21ClN2O6S2): C, H, N.
(5-Chloro-1-phenylsulfonyl-1H-indol-2-yl)-(5-methoxy-1-phe-
nylsulfonyl-1H-indol-2-yl)methanone (53). Metalation of 20 was
performed according to Procedure A, Method II. Yield: 1.46 g
(47%). Mp: 186.9-188.7 °C. Anal. (C30H21ClN2O6S2): C, H, N.
(6-Chloro-1-phenylsulfonyl-1H-indol-2-yl)-(5-methoxy-1-phe-
nylsulfonyl-1H-indol-2-yl)methanone (54). Metalation of 11 was
performed according to Procedure A, Method I. Yield: 1.44 g
(40%). Mp: dec 186-187 °C. Anal. (C30H21ClN2O6S2): C, H, N.
(7-Chloro-1-phenylsulfonyl-1H-indol-2-yl)-(5-methoxy-1-phe-
nylsulfonyl-1H-indol-2-yl)methanone (55). Metalation of 22 was
performed according to Procedure A, Method I. Yield: 0.89 g
(28%). Mp: 199.0-199.3 °C. Anal. (C30H21ClN2O6S2): C, H, N.
(5-Bromo-1-phenylsulfonyl-1H-indol-2-yl)-(5-methoxy-1-phe-
nylsulfonyl-1H-indol-2-yl)methanone (56). Metalation of 24 was
performed according to Procedure A, Method II. Yield: 0.64 g
(80%). Mp: 259.9-251.0 °C. Anal. (C30H12BrN2O6S2): C, H, N.
(5-Fluoro-1-phenylsulfonyl-1H-indol-2-yl)-(4-methyl-1-phe-
nylsulfonyl-1H-indol-2-yl)methanone (57). Metalation of 7 was
performed according to Procedure A, Method II. Yield: 1.08 g
(51%). Mp: 214.9-217.1 °C. Anal. (C30H21FN2O5S2): C, H, N.
(5-Benzyloxy-1-phenylsulfonyl-1H-indol-2-yl)-(4-methyl-1-
phenylsulfonyl-1H-indol-2-yl)methanone (58). Metalation of 7
was performed according to Procedure A, Method II. Yield: 2.12
g (36%). Mp: 207-208 °C. Anal. (C37H28N2O6S2): C, H, N.
(5-Benzyloxy-1-phenylsulfonyl-1H-indol-2-yl)-(5-methyl-1-
phenylsulfonyl-1H-indol-2-yl)methanone (59). Metalation of 8
1-Phenylsulfonyl-1H-indole-2-carbonyl Chloride12 (35).
Yield: 3.24 g (99%) colorless crystals.
5-Methoxy-1-phenylsulfonyl-1H-indole-2-carbonyl Chloride
(36). Yield: 14.82 g (99%). Mp: 146.3-146.4 °C. Anal. (C16H12-
ClNO4S): C, H, N.
5-Benzyloxyl-1-phenylsulfonyl-1H-indole-2-carbonyl Chlo-
ride12 (37). Yield: 7.83 g (99%) beige crystals.
5-Fluoro-1-phenylsulfonyl-1H-indole-2-carbonyl Chloride (38).
Yield: 3.46 g (99%). Mp: 125-130 °C. Anal. (C15H9ClFNO3S):
C, H, N.
4-Chloro-1-phenylsulfonyl-1H-indole-2-carbonyl Chloride (39).
Yield: 3.31 g (99%). Mp: 151-156 °C. Anal. (C15H9Cl2NO3S):
C, H, N.
6-Chloro-1-phenylsulfonyl-1H-indole-2-carbonyl Chloride (40).
Yield: 3.92 g (99%). Mp: 204.2-204.3 °C. Anal. (C15H9Cl2-
NO3S): C, H, N.
4-Bromo-1-phenylsulfonyl-1H-indole-2-carbonyl Chloride (41).
Yield: 3.87 g (99%). Mp: 161-162 °C. Anal. (C15H9BrClNO3S):
C, H, N.
Procedure C: Preparation of N-protected Bis(1H-indol-2-
yl)methanones (45-70) and -methanole (43). At -78 °C to a
solution of the appropriate N-protected (1H-indol-2-yl)lithium (5.0
mmol) (cf. Procedure A) was added the respective (1-phenylsul-
fonyl-1H-indol-2-yl)carbonic acid chloride 35-41 (cf. Procedure B)

Inhibitors of FLT3 and PGDFR Tyrosine Kinase
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 11 3111
was performed according to Procedure A, Method I. Yield: 4.38 g
(33%). Mp: 141-143 °C. Anal. (C37H28N2O6S2): C, H, N.
(5-Benzyloxy-1-phenylsulfonyl-1H-indol-2-yl)-(6-methyl-1-
phenylsulfonyl-1H-indol-2-yl)methanone (60). Metalation of 9
was performed according to Procedure A, Method I. Yield: 8.34 g
(75%). Mp: 203 °C. Anal. (C37H28N2O6S2): C, H, N.
Bis-(5-benzyloxy-1-phenylsulfonyl-1H-indol-2-yl)meth-
anone (61). Metalation of 14 was performed according to Procedure
A, Method I. Yield: 3.37 g (41%). Mp: 179.5-180 °C. Anal.
(C43H32N2O7S2): C, H, N.
PDC (pyridinium dichromate) (11.66 g, 31.0 mmol) and PTFA
(pyridinium trifluoroacetate) (2.48 g, 155 mmol) were added to a
solution of bis(1-phenylsulfonyl-1H-indol-2-yl)methanole (6.2 mmol)
in 40 mL of dry CH2Cl2. When the oxidation was completed (2 to
12 h, TLC control), solid chromium waste was removed by filtration
through SiO2. Evaporation of the solvent left a foamy material
which was purified by column chromatography on silica gel with
DCM as eluent leading to light yellow crystals.
(1-Phenylsulfonyl-1H-indol-2-yl)-(4-methoxy-1-phenylsulfo-
nyl-1H-indol-2-yl)methanone (44). Preparation from the N-
phenylsulfonated methanol derivative 43 as described above,
Yield: 2.05 g (58%). Mp: 176-177 °C. Anal. (C30H22N2O6S2):
C, H, N.
Procedure F: Removal of the Phenylsulfonyl Protection
Group. Formation of Bis(1H-indol-2-yl)methanones. Cleavage
with TBAF. Method I: A mixture of a N-protected methanone
derivative (1.8 mmol) and TBAF (tetrabutylammonium fluoride
trihydrate) (1.14 g, 3.6 mmol) in THF (30 mL) was gently refluxed.
When TLC indicated that the reaction was completed (30 min to
12 h), the mixture was poured into water (250 mL) and extracted
with ethyl acetate (3 × 50 mL), the organic layer dried (Na2SO4),
and a part of the solvent removed to allow precipitation of the
yellow product. According this method compounds 73-96 were
prepared.
Cleavage with NaOH Solution. Method II: The N-protected
methanone derivative (1.8 mmol) was heated in ethanol (40 mL)
and 10% aq. NaOH (20 mL) under reflux for 12 h. After cooling,
the solution was poured into brine (100 mL) and extracted with
ethyl acetate (3× 50 mL). The combined organic layers were dried
(Na2SO4) and evaporated under reduced pressure to leave the crude
product, which was subjected to column chromatography (SiO2,
CH2Cl2). Method II was used for preparation of compound 72.
(1H-Indol-2-yl)-(4-methoxy-1H-indol-2-yl)methanone (72).
Yield: 0.30 g (85%). Mp: 200 °C. Anal. (C18H14N2O2): C, H, N.
(5-Fluoro-1H-indol-2-yl)-(1H-indol-2-yl)methanone (73).
Yield: 0.32 g (55%). Mp: 252.8-253.3 °C. Anal. (C17H11FN2O):
C, H, N.
(5-Benzyloxy-1-phenylsulfonyl-1H-indol-2-yl)-(4-methoxy-1-
phenylsulfonyl-1H-indol-2-yl)methanone (62). Metalation of 10
was performed according to Procedure A, Method I. Yield: 5.90 g
(58%). Mp: 190-192 °C. Anal. (C37H28N2O7S2): C, H, N.
(5-Benzyloxy-1-phenylsulfonyl-1H-indol-2-yl)-(6-methoxy-1-
phenylsulfonyl-1H-indol-2-yl)methanone (63). Metalation of 12
was performed according to Procedure A, Method II. Yield: 9.49
g (49%). Mp: 208.1-209.5 °C. Anal. (C37H28N2O7S2): C, H, N.
(5-Benzyloxy-1-phenylsulfonyl-1H-indol-2-yl)-(7-methoxy-1-
phenylsulfonyl-1H-indol-2-yl)methanone (64). Metalation of 13
was performed according to Procedure A, Method I. Yield: 10.62
g (61%). Mp: 146.1-146.3 °C. Anal. (C37H28N2O7S2): C, H, N.
(5-Benzyloxy-1-phenylsulfonyl-1H-indol-2-yl)-(4-fluoro-1-phe-
nylsulfonyl-1H-indol-2-yl)methanone (65). Metalation of 15 was
performed according to Procedure A, Method II. Yield: 1.98 g
(32%). Mp: dec 135 °C. Anal. (C36H25FN2O6S2): C, H, N.
(5-Benzyloxy-1-phenylsulfonyl-1H-indol-2-yl)-(5-fluoro-1-phe-
nylsulfonyl-1H-indol-2-yl)methanone (66). Metalation of 16 was
performed according to Procedure A, Method II. Yield: 7.01 g
(55%). Mp: 237.1-237.6 °C. Anal. (C36H25FN2O6S2): calcd. C
65.05, H 3.79, N 4.21; found C 64.42, H 4.20, N 3.80.
(5-Benzyloxy-1-phenylsulfonyl-1H-indol-2-yl)-(6-fluoro-1-phe-
nylsulfonyl-1H-indol-2-yl)methanone (67). Metalation of 17 was
performed according to Procedure A, Method II. Yield: 1.48 g
(25%). Mp: 196.2-196.7 °C. Anal. (C36H25FN2O6S2): C, H, N.
(5-Benzyloxy-1-phenylsulfonyl-1H-indol-2-yl)-(7-fluoro-1-phe-
nylsulfonyl-1H-indol-2-yl)methanone (68). Metalation of 18 was
performed according to Procedure A, Method I. Yield: 2.18 g
(20%). Mp: 146.1-146.3 °C. Anal. (C36H25FN2O6S2): C, H, N.
(5-(tert-Butyldimethylsilanyloxy)-1-phenylsulfonyl-1H-indol-
2-yl)-(4-chloro-1-phenylsulfonyl-1H-indol-2-yl)methanone (69).
Metalation of 26 was performed according to Procedure A, Method
I. Yield: 4.70 g (64%). Mp: 183-184 °C. Anal. (C35H33ClN2O6S2-
Si): C, H, N.
(5-Methoxy-1H-indol-2-yl)-(4-methyl-1H-indol-2-yl)meth-
anone (74). Yield: 0.22 g (48%). Mp: 209.0-213.7 °C. Anal.
(C19H16N2O2): C, H, N.
(5-Methoxy-1H-indol-2-yl)-(5-methyl-1H-indol-2-yl)meth-
anone (75). Yield: 0.46
g (88%). Mp: 296 °C. Anal.
(C19H16N2O2): C, H, N.
(5-Methoxy-1H-indol-2-yl)-(6-methyl-1H-indol-2-yl)meth-
anone (76). Yield: 0.14 g (50%). Mp: 228,5-229 °C. Anal.
(C19H16N2O2): C, H, N.
(4-Fluoro-1H-indol-2-yl)-(5-Methoxy-1H-indol-2-yl)meth-
anone (77). Yield: 0.09 g (19%). Mp: 194-195 °C. Anal. (C18H13-
FN2O2): C, H, N.
(5-Fluoro-1H-indol-2-yl)-(5-methoxy-1H-indol-2-yl)meth-
anone (78). Yield: 0.17 g (34%). Mp: 187.8-187.9 °C. Anal.
(C18H13FN2O2): C, H, N.
(6-Fluoro-1H-indol-2-yl)-(5-methoxy-1H-indol-2-yl)meth-
anone (79). Yield: 0.10 g (28%). Mp: 207.8-209.2 °C. Anal.
(C18H13FN2O2‚1/6 CH2Cl2): C, H, N.
(4-Chloro-1H-indol-2-yl)-(5-methoxy-1H-indol-2-yl)meth-
anone (80). Yield: 0.7 g (39%). Mp: 236.5-237 °C. Anal. (C18H13-
ClN2O2): C, H, N.
(5-Chloro-1H-indol-2-yl)-(5-methoxy-1H-indol-2-yl)meth-
anone (81). Yield: 0.15 g (48%). Mp: 221.8-221.9 °C. Anal.
(C18H13ClN2O2): C, H, N.
(6-Chloro-1H-indol-2-yl)-(5-methoxy-1H-indol-2-yl)meth-
anone (82). Yield: 0.25 g (42%). Mp: 228.5-229 °C. Anal.
(C18H13ClN2O2): C, H, N.
(7-Chloro-1H-indol-2-yl)-(5-methoxy-1H-indol-2-yl)meth-
anone (83). Yield: 0.16 g (47%). Mp: 228.6-229.2 °C. Anal.
(C18H13ClN2O2): C, H, N.
(4-Bromo-1-phenylsulfonyl-1H-indol-2-yl)-(5-(tert-butyldim-
ethylsilanyloxy)-1-phenylsulfonyl-1H-indol-2-yl)methanone (70).
Metalation of 26 was performed according to Procedure A, Method
I. Yield: 2.85 g (43%). Mp: 167.6-167.7 °C. Anal. (C35H33-
BrN2O6S2Si): C, H, N.
2-(1-Phenylsulfonyl-5-benzyloxy-1H-indole-2-carbonyl)-7-eth-
yl-indole-1-carboxylic Acid tert-butyl ester (71). Metalation of
27 was performed with 1.02 eq of tert-Butyllithium (1.5 M in
Pentane). Yield: 2.25
(C37H34N2O6S): C, H, N.
g (64%). Mp: 78-82 °C. Anal.
Procedure D: Preparation of 2-formyl-1-phenylsulfonyl-1H-
indoles. To a solution of the respective 1-phenylsulfonyl-1H-indole
(15.0 mmol) in dry THF (100 mL) was added commercially
available LDA (2M solution in THF/n-heptane) at -78 °C. After
stirring for 1 h at room temperature, the solution was cooled again
to -78 °C and DMF (30.0 mmol) added dropwise. Once more the
solution was stirred at room temperature for 1 h and then poured
on 40 mL of a saturated aqueous ammonium chloride solution. After
extraction with ethyl acetate, the combined organic layers were dried
over magnesium sulfate and evaporated under reduced pressure.
The oily residue thus obtained was crystallized by addition of diethyl
ether, removed by filtration, and washed with petroleum ether.
1-Phenylsulfonyl-1H-indol-2yl carbaldehyde (42). Preparation
from 1-phenylsulfonyl-1H-indole 6 as described above, Yield: 13
g (76%). Mp: 143.0-143.5 °C (lit.37 Mp 111-111.5°C).
(5-Bromo-1H-indol-2-yl)-(5-methoxy-1H-indol-2-yl)meth-
anone (84). Yield: 0.16 g (70%). Mp: 227.9-228.3 °C. Anal.
(C18H13BrN2O2): calcd. C, H, N.
Procedure E: Preparation of Bis(1-phenylsulfonyl-1H-in-
dolyl)methanones by Oxidation of Their Respective Carbinols.

3112 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 11
Mahboobi et al.
(5-Fluoro-1H-indol-2-yl)-(4-methyl-1H-indol-2-yl)meth-
anone (85). Yield: 0.18 g (45%). Mp: 240.9-241.4 °C. Anal. (C18H13-
FN2O): C, H, N.
(5-Hydroxy-1H-indol-2-yl)-(4-methyl-1H-indol-2-yl)meth-
anone (98). Yield: 0.90 g (79%). Mp: dec >82 °C. Anal.
(C18H14N2O2): C, H, N.
(5-Benzyloxy-1H-indol-2-yl)-(4-methyl-1H-indol-2-yl)meth-
anone (86). Yield: 0.53 g (92%). Mp: 236-237 °C. Anal.
(C25H20N2O2): calcd. C 78.93, H 5.30, N 7.36; found C 78.08, H
5.24, N 7.20.
(5-Benzyloxy-1H-indol-2-yl)-(5-methyl-1H-indol-2-yl)meth-
anone (87). Yield: 1.5 g (74%). Mp: 196-197 °C. Anal.
(C25H20N2O2): C, H, N.
(5-Hydroxy-1H-indol-2-yl)-(5-methyl-1H-indol-2-yl)meth-
anone (99). Yield: 0.21 g (24%). Mp: 225-226 °C. Anal.
(C18H14N2O2‚1/4 MeCO2Et): C, H, N.
(5-Hydroxy-1H-indol-2-yl)-(6-methyl-1H-indol-2-yl)meth-
anone (100). Yield: 0.21 g (63%). Mp: 273.3-273.5 °C. Anal.
(C18H14N2O2):
C, H, N.
(7-Ethyl-1H-indol-2-yl)-(5-hydroxy-1H-indol-2-yl)meth-
anone (101). Yield: 0.25 g (54%). Mp: 197-199 °C. Anal.
(C19H16N2O2‚1/3 MeCO2Et): C, H, N.
Bis-(5-hydroxy-1H-indol-2-yl)methanone (102). Yield: 0.11
g (21%). Mp: dec 215 °C. Anal. (C17H12N2O3‚1/6 MeCO2Et): C,
H, N.
(5-Hydroxy-1H-indol-2-yl)-(4-methoxy-1H-indol-2-yl)meth-
anone (103). Yield: 0.62 g (48%). Mp: 251-252 °C. Anal.
(C18H14N2O3): C, H, N.
(5-Hydoxy-1H-indol-2-yl)-(6-methoxy-1H-indol-2-yl)meth-
anone (104). Yield: 1.95 g (92%). Mp: 165.1-169.4 °C. Anal.
(C18H14N2O3): C, H, N.
(5-Hydroxy-1H-indol-2-yl)-(7-methoxy-1H-indol-2-yl)meth-
anone (105). Yield: 0.54 g (29%). Mp: 252.2-253.5 °C. Anal.
(C18H14N2O3): C, H, N.
(4-Fluoro-1H-indol-2-yl)-(5-hydroxy-1H-indol-2-yl)meth-
anone (106). Yield: 0.08 g (52%). Mp: dec >270 °C. Anal.
(C17H11FN2O2): C, H, N.
(5-Benzyloxy-1H-indol-2-yl)-(6-methyl-1H-indol-2-yl)meth-
anone (88). Yield: 0.60
g (84%). Mp: 94 °C. Anal.
(C25H20N2O2): calcd. C 78.93, H 5.30, N 7.36; found C 78.42, H
5.36, N 7.22.
Bis-(5-benzyloxy-1H-indol-2-yl)methanone (89). Yield: 1.12
g (62%). Mp: 192.5-193 °C. Anal. (C31H24N2O3): C, H, N.
(5-Benzyloxy-1H-indol-2-yl)-(4-methoxy-1H-indol-2-yl)meth-
anone (90). Yield: 2.16 g (81%). Mp: 239-240 °C. Anal.
(C25H20N2O3): C, H, N.
(5-Benzyloxy-1H-indol-2-yl)-(6-methoxy-1H-indol-2-yl)meth-
anone (91). Yield 3.25 g (63%). Mp: 198.9-199.0 °C. Anal.
(C25H20N2O3): C, H, N.
(5-Benzyloxy-1H-indol-2-yl)-(7-methoxy-1H-indol-2-yl)meth-
anone (92). Yield: 2.37 g (48%). Mp: 201.0-201.8 °C. Anal.
(C25H20N2O3): C, H, N.
(5-Benzyloxy-1H-indol-2-yl)-(4-fluoro-1H-indol-2-yl)meth-
anone (93). Yield: 0.24 g (67%). Mp: 224 °C. Anal. (C24H17-
FN2O2): C, H, N.
(5-Benzyloxy-1H-indol-2-yl)-(5-fluoro-1H-indol-2-yl)meth-
anone (94). Yield: 2.63 g (69%). Mp: 245.3-246.3 °C. Anal.
(C24H17FN2O2): C, H, N.
(5-Benzyloxy-1H-indol-2-yl)-(6-fluoro-1H-indol-2-yl)meth-
anone (95). Yield: 0.62 g (57%). Mp: 216.5-216.6 °C. Anal.
(C24H17FN2O2): C, H, N.
(5-Benzyloxy-1H-indol-2-yl)-(7-fluoro-1H-indol-2-yl)meth-
anone (96). Yield: 0.20 g (22%). Mp: dec 249 °C. Anal. (C24H17-
FN2O2): calcd. C 74.99, H 4.46, N 7.29; found C 74.22, H 4.48,
N 7.08.
Consecutive Phenylsulfonyl and tert-Butoxycarbonyl Protec-
tion Groups Cleavage Leading to the Bisindolylmethanone
Derivative (97). A THF solution (50 mL) of 71 (2.0 g, 3.15 mmol)
and TBAF (4 g) was heated to reflux for 3 h. The solution was
then poured into 500 mL of water, followed by extraction with
dichloromethane. The combined organic layers were dried over
sodium sulfate and filtered before addition of trifluoroacetic acid
(20 mL). Additional stirring for 18 h of the reaction mixture was
followed by hydrolysis with a saturated sodium hydrogen carbonate
solution. Separation of the organic layer and evaporation of the
solvent led to the crude product which was purified by column
chromatography (SiO2, dichloromethane/ethyl acetate 10:1).
(5-Benzyloxy-1H-indol-2-yl)-(7-ethyl-1H-indol-2-yl)meth-
anone (97). Yield: 0.72 g of a foam (58%). Mp: 162-165 °C.
Anal. (C26H22N2O2): calcd. C 79.16, H 5.62, N 7.10; found C 78.88,
H 6.06, N 6.71.
Procedure G: Hydrogenolytic Preparation of Hydroxymeth-
anones. A mixture of the respective benzyloxy compound 86-97
(10.92 mmol), ammonium formate (12.00 g, 188.80 mmol), and
5-10% Pd/C (2.0 g) in 1:1 (v/v) methanol/THF (200 mL) was
stirred at 40 to 60 °C for 4 h. After removing the catalyst, the solvent
was evaporated to leave an oily material. Ethyl acetate (200 mL)
and water (100 mL) were added. The organic layer was washed
with water and dried (Na2SO4), and the solvent was evaporated.
Treatment of the residue with a little diethyl ether results in
crystallization of the respective compounds, which were washed
with additional ether. According to this procedure compounds 98-
109 were prepared.
(5-Fluoro-1H-indol-2-yl)-(5-hydoxy-1H-indol-2-yl)meth-
anone (107). Yield: 1.68 g (94%). Mp: 204.7-224.7 °C. Anal.
(C17H11FN2O2):
C, H, N.
(6-Fluoro-1H-indol-2-yl)-(5-hydoxy-1H-indol-2-yl)meth-
anone (108). Yield: 0.19 g (55%). Mp: 261.4-262.2 °C. Anal.
(C17H11FN2O2‚1/2 EtOH):
C, H, N.
(7-Fluoro-1H-indol-2-yl)-(5-hydroxy-1H-indol-2-yl)meth-
anone (109). Yield: 0.67 g (73%). Mp: 262 °C. Anal. (C17H11-
FN2O2): C, H, N.
Procedure H for the Preparation of Alkyl Derivatives:
Alkylation of (5-Hydroxy-1H-indol-2-yl)-(1H-indol-2-yl)meth-
anones. The respective alkyl halide, respective of its hydrohalide
(1.50 mmol), was added together with KOH (3.00 mmol in the
case of alkyl halide, in case of hydrohalides as alkylating agents
4.50 mmol) to a solution of 98, 104, or 107 (1.00 mmol) in acetone
(40 mL). The mixture was stirred at room temperature for 15 min
till 3 h (TLC control). The mixture was poured into ice-water (250
mL) and extracted with ethyl acetate. The organic layer was dried
(Na2SO4) and the solvent removed in vacuo. The crude product
was purified by column chromatography (SiO2, ethyl acetate/
methanol 1:1) and crystallized from ethyl acetate/diethyl ether to
yield the compounds as yellow crystals. According to this procedure,
compounds 112-115 were prepared.
[5-(2-Dimethylaminoethoxy)-1H-indol-2-yl]-(6-methoxy-1H-
indol-2-yl)methanone (112). Yield: 0.09 g (24%). Mp: 189.4-
192.5 °C. Anal. (C22H23N3O3‚1/4 H2O): C, H, N.
(4-Methyl-1H-indol-2-yl)-[5-(2-piperidin-1-yl-ethoxy)-1H-in-
dol-2-yl]methanone (113). Yield: 0.08 g (23%). Mp: 172 °C.
Anal. (C25H27N3O2): C, H, N.
(6-Methoxy-1H-indol-2-yl)-[5-(2-piperidin-1-yl-ethoxy)-1H-in-
dol-2-yl]methanone (114). Yield: 0.08 g (19%). Mp: 161.5-163.2
°C. Anal. (C25H27N3O3‚1/2 H2O): C, H, N.
(5-Fluoro-1H-indol-2-yl)-[5-(2-piperidin-1-yl-ethoxy)-1H-in-
dol-2-yl]methanone (115). Yield: 0.11 g (27%). Mp: 147.9-148.9
°C. Anal. (C24H24FN3O2): C, H, N.
Procedure I: Simultaneous Phenylsulfonyl and tert-Bu-
tyldimethylsilyl Deprotection of 69 and 70 with NaOH. The
N-protected halo derivative (1.56 mmol) and 50 mL of a 10% aq.
NaOH solution were stirred at 60 °C for 8 to 12 h under nitrogen
atmosphere. After completion of the reaction (TLC control), the
mixture was neutralized with aq. HCl, filtered, and dried. The crude
product was purified by column chromatography (SiO2, DCM).
Remark: Debenzylation of protected bis(1H-indol-2yl)metha-
nones bearing also a chloro substituent resulted in addition in
cleavage of the C-Cl bond yielding the respective unhalogenated
5-hydroxy compounds.

Inhibitors of FLT3 and PGDFR Tyrosine Kinase
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 11 3113
(4-Chloro-1H-indol-2-yl)-(5-hydroxy-1H-indol-2-yl)meth-
anone (110). Yield: 0.17 g (26%). Mp: 262 °C. Anal. (C17H11-
ClN2O2): C, H, N.
(4-Bromo-1H-indol-2-yl)-(5-hydroxy-1H-indol-2-yl)meth-
anone (111). Yield: 0.04 g (22%). Mp: 207-210 °C. Anal.
(C17H11BrN2O2): C, H, N.
Procedure J: Preparation of Bisindolylmethanes. A suspen-
sion of the appropriate bisindolylmethanone derivative (5.0 mmol),
KOH (25.0 mmol) and hydrazine hydrate (0.5 mL) in ethylene
glycol was heated to 195 °C (200 W) within 1 h in a focused
microwave apparatus (CEM Discover). A 50 mL amount of sat.
ammonium chloride aq. solution was added to the mixture, which
was then extracted with DCM. The combined organic extracts were
dried over Na2SO4, the solvent was removed under vacuo, and the
crude product was subjected to chromatography (SiO2, DCM).
(1H-Indol-2-yl)-(5-methoxy-1H-indol-2-yl)methane12 (116).
Preparation from (1H-indol-2-yl)-(5-methoxy-1H-indol-2-yl)-
methanone 4b. Yield: 0.28 g (84%). Mp: 112 °C.
(5-Fluoro-1H-indol-2-yl)-(5-methoxy-1H-indol-2-yl)-
methane (117). Preparation from (5-fluoro-1H-indol-2-yl)-(5-
methoxy-1H-indol-2-yl-methanone 78, Yield: 0.15 g (60%). Mp:
130.2-130.3 °C. Anal. (C18H15FN2O): C, H, N.
Biochemical and Cellular Assays. Most cell lines, antibodies,
and cDNAs used in this study were described earlier.11-13 A GST-
Abl construct38 was kindly provided by Dr. B. Druker (Oregon
University). K562 cells were obtained from the German Collection
of Cells and Microorganisms (Braunschweig). Anti-Abl antibodies
(cat. # 2862) and anti-active Abl antibodies (cat. # 2861) were from
Cell Signaling (Frankfurt, Germany).
Assays for FLT3 and PDGFR-â autophosphorylation in tran-
siently transfected HEK293 cells and for PDGFR autophosphory-
lation in Swiss3T3 cells have also been previously described.11,12
For measuring autophosphorylation of endogenous FLT3 in EOL-1
cells, 5 × 106 cells per well were seeded into 12-well plates with
RPMI1640 medium without serum. Inhibitors were added from 100-
fold concentrated stocks directly into the medium (final DMSO
concentration 1%), and plates were incubated at 37 °C, 5% CO2
for 1 h. Stimulation was carried out with FL (50 ng/mL or solvent
for control) at room temperature for 10 min. Cells were transferred
to ice and lysed in 1 mL of TX100-containing lysis buffer.11 Cell
extracts were subjected to incubation with 15 µL (1:1 slurry) of
wheat germ agglutinin-agarose (Amersham) with end-over-end
rotation at 4 °C for 1 h. The beads were washed twice with lysis
buffer and extracted with SDS-PAGE sample buffer at 50 °C for
20 min. Immunoblotting and determination of IC50 values were
performed as described.12
To measure FLT3-dependent cell proliferation, 32Dcl3 cells
stably transfected with hFLT3-ITD, or wild-type FLT3, kindly
provided by C. Choudhary and H. Serve (University of Mu¨nster)39
were employed. Proliferation assays were performed as described
earlier.13 In brief, 105 cells per well were seeded in 96-well plates
in RPMI1640 medium, supplemented with 10% FCS. IL-3 (3 ng/
mL R&D Systems) was added as indicated in the corresponding
figure legend. Inhibitors or solvent DMSO were added (final DMSO
concentration 0.1%), and cells were cultivated for 2 or 3 days. At
this time-point, cell amounts were determined using 3-(4,5-
dimethylthiazol-2-yl)-2,5-diphenyl-3H-tetrazol-2-ium bromide (MTT)
with a kit of Roche (Mannheim) according to the instructions of
the manufacturer. The effect of compounds on KIT-dependent cell
proliferation was assayed exactly as described before.23
mixture was incubated at 30 °C for 20 min. A 20 µL aliquot was
taken before the start and at the end of the incubation. Aliquots
were mixed with 20 µL of 500 mM EDTA, pH 8.0, 2 mg/mL bovine
serum albumin. Protein was precipitated by addition of 20 µL of
20% (w/w) ice-cold trichloroacetic acid, incubation on ice for 30
min, and centrifugation in a microfuge for 5 min. Two 20 µL
aliquots of the supernatant were spotted onto phosphocellulose
(Whatman P81). After drying, the membrane was washed with 75
mM phosphoric acid four times for at least 5 min, dried again, and
exposed to an imaging screen of a BioRad GS250 molecular imager.
Relative incorporation of radioactivity, corrected by subtraction of
the values at the starting point, was used for calculation of IC50
values. GST-FLT3 and GST-PDGFR-â had similar activity with
this substrate peptide, and the reaction was nearly linear over at
least 30 min.
Measurement of GST-Abl kinase activity in vitro was performed
similar to that described by Corbin et al..38 In brief, 0.5 µg of a
GST-fusion protein of the c-Abl catalytic domain was incubated
in kinase buffer containing 50 mM Tris-HCl, pH 7.5, 10 mM
MgCl2, 10 µM sodium orthovanadate, 1 mM dithiothreitol, and
inhibitor or solvent control (added from a 100-fold stock solution
in DMSO) on ice for 10 min. Then, ATP was added (1 µCi [32Pγ]-
ATP, final ATP concentration 111 nM, final volume 30 µL), and
samples were incubated at 30 °C for 30 min with agitation (500
rpm). The reaction was quenched by addition of 10 µL of 6-fold
concentrated SDS-PAGE sample buffer. Samples were subjected
to electrophoresis, and gels were stained with Coomassie and dried.
Radioactivity incorporated into the GST-Abl protein was quantified
using a BioRad GS250 molecular imager and normalized to fusion
protein amount in the sample revealed by Coomassie-staining and
densitometric scanning. Inhibition of autophosphorylation of Bcr-
Abl in K562 cells was analyzed by incubating 2 × 106 cells in 1
mL of serum-free RPMI1640 medium with inhibitor or solvent
control (1% DMSO) at 37 °C in a CO2 incubator for 2 h. Cells
were transferred into 1.5 mL tubes, spun down at 200g for 5 min,
and lysed in 100 µL of lysis buffer. Lysates were analyzed by SDS-
PAGE in 7.5% gels, wet transferred to PVDF membranes, and
immunodetected with anti-pAbl and anti-Abl antibodies.
All IC50 values are derived from duplicate or triplicate determi-
nations and were determined from a concentration curve comprising
six concentrations using the program SigmaPlot (Systat Software
Inc.) as described earlier.12 The standard errors of the mean (SEM)
are always in the range of (50%.
Primary AML-cells were obtained from blood of patients with
newly diagnosed acute myeloid leukaemia. Mononuclear cells
(MNC) were isolated by means of Ficoll-Hypaque (Seromed, Berlin,
Germany) density gradient centrifugation. The cells were incubated
in medium supplemented with fetal calf serum for 24 h at 37 °C.
Then, 200 000 cells were plated in 2 mL of medium with or without
the kinase inhibitors. The incubation period was 96 h. Thereafter,
cell cycle analysis was performed as previously described,40 and
the sub-G1 population was quantified. The spontaneous apoptosis
rate in the individual patients ranged from 4.7 to 54.4%.
Molecular Modeling. An initial computer model of the FLT3
kinase was generated from the PDB crystal structure 1rjb14 using
the molecular modeling package SYBYL 6.9 (Tripos Inc., St. Louis,
MO) on a Silicon Graphics Octane workstation. After adding
hydrogens, compound 98 was docked in different poses derived
from previous results (ref 12 and references therein). The two
possible binding conformations of 98, sp/ap and sp/sp, their energies
and rotational barriers were calculated by the semiempirical
quantum chemical program AMPAC 6.55 (Semichem Inc., 7128
Summit, Shawnee, KS 66216) with the AM1 Hamiltonian, the
TRUSTE minimization algorithm, and the COSMO water solvation
model41 as implied in SYBYL 6.9. After docking, the FLT3-ligand
complexes were energy minimized using the AMBER 4.1 force
field42 with AMBER 95 charges for the protein (distance-dependent
dielectricity constant 4, first 50 cycles with constrained backbone
and the steepest descent method). For that purpose, compound 98
and other derivatives were provided with AMBER 4.1 atom types
by analogy with corresponding amino acid atoms, as well as with
For in vitro kinase assays, GST-fusion proteins containing the
cytoplasmic domains of wild-type FLT3, or human PDGFR-â, were
obtained as described earlier.12,13 As exogenous substrate, a synthetic
peptide corresponding to the PDGFR-â autophosphorylation site
tyrosine 751 with the sequence KKKSKDESVDYVPMLDMKG
was employed. Approximately 100 ng of recombinant kinase were
incubated with inhibitors (6 concentrations) or DMSO (solvent, final
concentration 1%) on ice in a reaction mixture containing 50 mM
Hepes, pH 7.5, 5 mM MnCl2, 0.1 mM sodium orthovanadate, and
2 mM substrate peptide in a total volume of 95 µL for 15 min.
Then, [32Pγ]ATP was added (5 µL, 2-5 µCi), and the reaction

3114 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 11
Mahboobi et al.
(13) Teller, S.; Kra¨mer, D.; Bo¨hmer, S.-A.; F.Tse, K.; Small, D.;
Mahboobi, S.; Wallrapp, C.; Beckers, T.; Kratz-Albers, K.; Schwa¨ble,
J.; Serve, H.; Bo¨hmer, F. D. Bis(1H-2-indolyl)-1-methanones as
inhibitors of the hematopoietic tyrosine kinase Flt3. Leukemia 2002,
16, 1528-1534.
(14) Griffith, J.; Black, J.; Faerman, C.; Swenson, L.; Wynn, M.; Lu, F.;
Lippke, J.; Saxena, K. The structural basis for autoinhibiton of FLT3
by the juxtmembrane domain. Mol. Cell. 2004, 13, 169-178.
(15) Bentley, J. M.; Hebeisen, P.; Muller, M.; Richter, H.; Roever, S.;
Mattei, P.; Taylor, S. Piperazine derivatives. WO 02/10169 A1 2002.
(16) Huang-Minlon A simple modification of the Wolff-Kishner Reduc-
tion. J. Am. Chem. Soc. 1946, 68, 2487-2488.
(17) Kovalenko, M.; Gazit, A.; Bo¨hmer, A.; Rorsman, C.; Ronnstrand,
L.; Heldin, C. H.; Waltenberger, J.; Bo¨hmer, F. D.; Levitzki, A.
Selective platelet-derived growth factor receptor kinase blockers
reverse sis-transformation. Cancer Res. 1994, 54, 6106-6114.
(18) Tse, K. F.; Novelli, E.; Civin, C. I.; Bohmer, F. D.; Small, D.
Inhibition of FLT3-mediated transformation by use of a tyrosine
kinase inhibitor. Leukemia 2001, 15, 1001-1010.
(19) Mohammadi, M.; Froum, S.; Hamby, J. M.; Schroeder, M. C.; Panek,
R. L.; Lu, G. H.; Eliseenkova, A. V.; Green, D.; Schlessinger, J.;
Hubbard, S. R. Crystal structure of an angiogenesis inhibitor bound
to the FGF receptor tyrosine kinase domain. EMBO J. 1998, 17,
5896-5904.
Gasteiger-Hueckel charges. New parameters describing the central
NHC(CH)COC(CH)NH moiety had to be added to the AMBER
4.1 force field (derived from the Tripos force field and from
comparison with similar AMBER parameters). The final minimiza-
tion up to a RMS gradient of 0.05 kcal/(mol‚Å) was performed
with the Powell conjugate gradient method. Considerations on the
PDGFR kinase were based on the FLT3 crystal structure with
simple mutation of the only different binding site residue, FLT3
Phe-691, into PDGFR Thr-681. Handling of compound 82 and its
docking into the PDGFR model were performed like that in the
case of the FLT3-compound 98 complex.
Acknowledgment. This work was supported by a grant from
the Deutsche Krebshilfe (10-2100-Do2, to F.D.B., S.D., and
S.M.) and the Deutsche Krebshilfe grant Oncogene Networks
in the Pathogenesis of AML (to F.D.B., T.F., and C.S.). We
gratefully acknowledge provision of reagents from H. Serve
(University of Mu¨nster) and B. Druker (University of Oregon),
and thank Ulla Bergholz for excellent technical assistance.
(20) Bo¨hmer, F. D.; Karagyozov, L.; Uecker, A.; Serve, H.; Botzki, A.;
Mahboobi, S.; Dove, S. A Single Amino Acid Exchange Inverts
Susceptibility of Related Receptor Tyrosine Kinase for the ATP Site
Inhibitor STI-571. J. Biol. Chem. 2003, 278, 5148-5155.
(21) Nagar, B.; Bornmann, W. G.; Pellicana, P.; Schindler, T.; Veach, D.
R.; Miller, W. T.; Clarkson, B.; Kuriyan, J. Crytal structure of the
kinase domain of c-Abl in complex with the small molecule inhibitors
PD173955 and imatinib (STI-571). Cancer Res. 2002, 62, 4236-
4243.
(22) Weisberg, E.; Boulton, C.; Kelly, L. M.; Manley, P.; Fabbro, D.;
Meyer, T.; Gilliland, D. G.; Griffin, J. D. Inhibition of mutant FLT3
receptors in leukemia cells by the small molecule tyrosine kinase
inhibitor PKC412. Cancer Cell 2002, 1, 433-443.
(23) Cammenga, J.; Horn, S.; Bergholz, U.; Sommer, G.; Besmer, P.;
Fiedler, W.; Stocking, C. Extracellular KIT receptor mutants,
commonly found in core binding factor AML, are constitutively active
and respond to imatinib mesylate. Blood 2005, 106, 3958-3961.
(24) Moasser, M. M.; Srethapakdi, M.; Sachar, K. S.; Kraker, A. J.; Rosen,
N. Inhibition of Src kinases by a selective tyrosine kinase inhibitor
causes mitotic arrest. Cancer Res. 1999, 59, 6145-6152.
(25) Sundberg, R. J.; Russel, F. Syntheses with N-Protected 2-Lithioin-
doles. J. Org. Chem. 1973, 38, 3324-3330.
(26) Ishibashi, H.; Akamatsu, S.; Iriyama, H.; Ikeda, M. Convenient
synthesis of 4-alkyl, alkenyl, and alkynyl substituted N-(phenyl-
sulfonyl)indoles. Chem. Pharm. Bull. 1994, 42, 2150-2153.
(27) Mahboobi, S.; Pongratz, H.; Hufsky, H.; Hockemeyer, J.; Frieser,
M.; Lyssenko, A.; Paper, D. H.; Bu¨rgermeister, J.; Bo¨hmer, F.-D.;
Fiebig, H.-H.; Burger, A. M.; Baasner, S.; Beckers, T. Synthetic
2-Aroylindole Derivatives as a New Class of Potent Tubulin-
Inhibitory, Antimitotic Agents. J. Med. Chem. 2001, 44, 4535-4553.
(28) Wenkert, E.; Moeller, P. D. R.; Piettre, S. R. Five-Membered
Aromatic Heterocycles as Dienophile in Diels-Alder Reactions.
Furan, Pyrrole and Indole. J. Am. Chem. Soc. 1988, 110, 7188-
7194.
(29) Ishibashi, H.; Akamatsu, S.; Iriyama, H.; Hanaoka, K.; Tabata, T.;
Ikeda, M. New, concise route to indoles bearing oxygen or sulfur
substituent at the 4-position. Synthesis of (()- and (S)-(-)-pindolol
and (()-chuangxinmycin. Chem. Pharm. Bull. 1994, 42, 271-276.
(30) Sundberg, R. J.; Parton, R. L. Lithiation of Methoxyindoles. J. Org.
Chem. 1976, 41, 163-165.
(31) Fuji, M.; Muratake, H.; Natsume, M. Preparation of alkyl-substituted
indoles in the benzene portion. Part 6. Synthetic procedure for 4-,
5-, 6- or 7-alkoxy- and hydroxyindole derivatives. Chem. Pharm.
Bull. 1992, 40, 2344-2352.
(32) Matsumoto, M.; Ishida, Y.; Hatanaka, N.A facile one-step synthesis
of 4-aminoindoles from 5-halo-4-oxo-4,5,6,7-tetrahydroindoles. Het-
erocycles 1986, 24, 1667-1674.
(33) Ketcha, D. M.; Gribble, G. W. A convenient synthesis of 3-acylin-
doles via Friedel Crafts acylation of 1-(phenylsulfonyl)indole. A new
route to pyridocarbazole-5, 11-quinones and ellipticine. J. Org. Chem.
1985, 50, 5451-5457.
(34) Kano, S.; Sugino, E.; Shibuya, S.; Hibino, S. Synthesis of Carbazole
Alkaloids Hyellazole and 6-Chlorohyellazole. J. Org. Chem. 1981,
46, 3856-3859.
(35) Silvestri, R.; Martino, G. D.; Regina, G. L.; Artico, M.; Massa, S.;
Vargiu, L.; Mura, M.; Loi, A. G.; Marceddu, T.; Colla, P. L. Novel
Indolyl Aryl Sulfones Active against HIV-1 Carrying NNRTI
Resistance Mutations: Synthesis and SAR Studies. J. Med. Chem.
2003, 46, 248-2493.
Supporting Information Available: Spectroscopic data (IR,
NMR, MS) and detailed combustion analyses. This material is
available free of charge via the Internet at http://pubs.acs.org.
References
(1) Hanahan, D.; Weinberg, R. A. The hallmarks of cancer. Cell 2000,
100, 57-70.
(2) Blume-Jensen, P.; Hunter, T. Oncogenic kinase signalling. Nature
2001, 411, 355-365.
(3) Pietras, K.; Sjoblom, T.; Rubin, K.; Heldin, C. H.; Ostman, A. PDGF
receptors as cancer drug targets. Cancer Cell 2003, 3, 439-443.
(4) George, P.; Bali, P.; Cohen, P.; Tao, J.; Guo, F.; Sigua, C.;
Vishvanath, A.; Fiskus, W.; Scuto, A.; Annavarapu, S.; Moscinski,
L.; Bhalla, K. Cotreatment with 17-allylamino-demethoxygeldana-
mycin and FLT-3 kinase inhibitor PKC412 is highly effective against
human acute myelogenous leukemia cells with mutant FLT-3. Cancer
Res. 2004, 64, 3645-3652.
(5) Wilhelm, S. M.; Carter, C.; Tang, L.; Wilkie, D.; McNabola, A.;
Rong, H.; Chen, C.; Zhang, X.; Vincent, P.; McHugh, M.; Cao, Y.;
Shujath, J.; Gawlak, S.; Eveleigh, D.; Rowley, B.; Liu, L.; Adnane,
L.; Lynch, M.; Auclair, D.; Taylor, I.; Gedrich, R.; Voznesensky,
A.; Riedl, B.; Post, L. E.; Bollag, G.; Trail, P. A. BAY 43-9006
exhibits broad spectrum oral antitumor activity and targets the RAF/
MEK/ERK pathway and receptor tyrosine kinases involved in tumor
progression and angiogenesis. Cancer Res. 2004, 64, 7099-7109.
(6) Daub, H.; Specht, K.; Ullrich, A. Strategies to overcome resistance
to targeted protein kinase inhibitors. Nat. ReV. Drug. DiscoVery 2004,
3, 1001-1010.
(7) Schmidt-Arras, D.; Schwable, J.; Bohmer, F. D.; Serve, H. Flt3
receptor tyrosine kinase as a drug target in leukemia. Curr. Pharm.
Des. 2004, 10, 1867-1883.
(8) Ozeki, K.; Kiyoi, H.; Hirose, Y.; Iwai, M.; Ninomiya, M.; Kodera,
Y.; Miyawaki, S.; Kuriyama, K.; Shimazaki, C.; Akiyama, H.;
Nishimura, M.; Motoji, T.; Shinagawa, K.; Takeshita, A.; Ueda, R.;
Ohno, R.; Emi, N.; Naoe, T. Biologic and clinical significance of
the FLT3 transcript level in acute myeloid leukemia. Blood 2004,
103, 1901-1908.
(9) Komeno, Y.; Kurokawa, M.; Imai, Y.; Takeshita, M.; Matsumura,
T.; Kubo, K.; Yoshino, T.; Nishiyama, U.; Kuwaki, T.; Kubo, K.;
Osawa, T.; Ogawa, S.; Chiba, S.; Miwa, A.; Hirai, H. Identification
of Ki23819, a highly potent inhibitor of kinase activity of mutant
FLT3 receptor tyrosine kinase. Leukemia 2005, 19, 930-935.
(10) Sattler, M.; Verma, S.; Byrne, C. H.; Shrikhande, G.; Winkler, T.;
Algate, P. A.; Rohrschneider, L. R.; Griffin, J. D. BCR/ABL directly
inhibits expression of SHIP, an SH2-containing polyinositol-5-
phosphatase involved in the regulation of hematopoiesis. Mol. Cell.
Biol. 1999, 19, 7473-7480.
(11) Bo¨hmer, F. D.; Karagyozov, L.; Uecker, A.; Serve, H.; Botzki, A.;
Mahboobi, S.; Dove, S. A single amino acid exchange inverts
susceptibility of related receptor tyrosine kinases for the ATP site
inhibitor STI-571. J. Biol. Chem. 2003, 278, 5148-5155.
(12) Mahboobi, S.; Teller, S.; Pongratz, H.; Hufsky, H.; Sellmer, A.;
Botzki, A.; Uecker, A.; Beckers, T.; Baasner, S.; Schachtele, C.;
Uberall, F.; Kassack, M. U.; Dove, S.; Bo¨hmer, F.-D. Bis(1H-2-
indolyl)methanones as a Novel Class of Inhibitors of the Platelet-
Derived Growth Factor Receptor Kinase. J. Med. Chem. 2002, 45,
1002-1018.

Inhibitors of FLT3 and PGDFR Tyrosine Kinase
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 11 3115
(36) Ketcha, D. M. The manganese(III) acetate oxidation of N-protected
indolines. Tetrahedron Lett. 1988, 29, 2151-2154.
(37) Saulnier, M. G.; Gribble, G. W. Generation and Reactions of 3-Lithio-
1-(phenylsulfonyl)indole. J. Org. Chem. 1982, 47, 757-761.
(38) Corbin, A. S.; Buchdunger, E.; Pascal, F.; Druker, B. J. Analysis of
the structural basis of specificity of inhibition of the Abl kinase by
STI571. J. Biol. Chem. 2002, 277, 32214-32219.
(39) Mizuki, M.; Schwable, J.; Steur, C.; Choudhary, C.; Agrawal, S.;
Sargin, B.; Steffen, B.; Matsumura, I.; Kanakura, Y.; Bohmer, F.
D.; Muller-Tidow, C.; Berdel, W. E.; Serve, H. Suppression of
myeloid transcription factors and induction of STAT response genes
by AML-specific Flt3 mutations. Blood 2003, 101, 3164-3173.
(40) Kindler, T.; Breitenbuecher, F.; Kasper, S.; Stevens, T.; Carius, B.;
Gschaidmeier, H.; Huber, C.; Fischer, T. In BCR-ABL-positive cells,
STAT-5 tyrosine-phophorylation integrates signals induced by ima-
tinib mesylate and Ara-C. Leukemia 2003, 17, 999-1009.
(41) Klamt, A. Conductor-like Screening Model for Real Solvents: A
New Approach to the Quantitative Calculation of Solvation Phe-
nomena. J. Phys. Chem. 1995, 99, 2224-2235.
(42) Cornell, W. D.; Cieplak, P.; Bayly, C. I.; Gould, I. R.; Merz, K. M.
J.; Ferguson, D. M.; Spellmeyer, D. C.; Fox, T.; Caldwell, J. W.;
Kollman, P. A. A second generation force field for the simulation of
proteins and nucleic acids. J. Am. Chem. Soc. 1995, 117, 5179-5197.
JM058033I