Design and synthesis of novel 5,6-bisindolylpyrimidin-4-ones structurally related to ruboxistaurin (LY333531)

Article abstract of DOI:10.1016/j.tet.2010.10.020

2, 3-Bis(1-methyl-1H-indol-3-yl) methyl-3-oxopropionate is a key intermediate in the synthesis of a new family of LY333531 analogues. Base-mediated cyclocondensation with thiourea afforded novel 5, 6-bis(1-methyl-1H-indol-3-yl)-2-thioxo-2, 3-dihydropyrimidin-4(1H)-one, which was efficiently converted to the pyrimidin-2, 4(1H,3H)-dione congener. Synthesis of a six-membered K-252c analogue, 5, 6-bis(1-methyl-1H-indol-3-yl)pyrimidin- 4(3H)-one, is also described.

Full text of DOI:10.1016/j.tet.2010.10.020

Tetrahedron 66 (2010) 9754e9761
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Design and synthesis of novel 5,6-bisindolylpyrimidin-4-ones structurally related
to ruboxistaurin (LY333531)
*
Larry T. Pierce, Michael M. Cahill, Florence O. McCarthy
Department of Chemistry, Analytical and Biological Chemistry Research Facility, Western Road, University College Cork, Cork, Ireland
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 26 May 2010
Received in revised form 21 September 2010
Accepted 11 October 2010
Available online 15 October 2010
2,3-Bis(1-methyl-1H-indol-3-yl) methyl-3-oxopropionate is a key intermediate in the synthesis of a new
family of LY333531 analogues. Base-mediated cyclocondensation with thiourea afforded novel 5,6-bis(1-
methyl-1H-indol-3-yl)-2-thioxo-2,3-dihydropyrimidin-4(1H)-one, which was efficiently converted to the
pyrimidin-2,4(1H,3H)-dione congener. Synthesis of a six-membered K-252c analogue, 5,6-bis(1-methyl-
1H-indol-3-yl)pyrimidin-4(3H)-one, is also described.
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Bisindolylmaleimides
Bisindolylpyrimidines
Uracil formation
Oxidative desulfurisation
Kinase inhibition
1. Introduction
inhibition reported to suppress the growth of cultured cancer cell
lines while displaying a narrow therapeutic window.7
Protein kinases modulate cell signal transduction by phos-
phorylating tyrosine, threonine and serine residues inproteins
implicated in a multitude of disease states, including cancer, di-
abetes and inflammation.1 Misregulation of protein kinase C (PKC)
activity and expression has been reported in several malignancies,
and consequently, PKC has been established as a valid clinical target
for the chemotherapeutic treatment of cancer.2 Kinase inhibition
has become a central target, along with DNA, at the forefront of
anti-cancer drug development, due to an urgent need for research
into more potent and selective, next generation anti-tumour ther-
apies to overcome resistant cancers.3
Recent progress in the development of PKC isoform-selective
inhibitors has been highlighted by the new drug application sub-
mitted to the FDA by Eli Lilly, in February 2006, following successful
H
H
N
N
O
O
O
N
N
O
N
N
H
H
1
2
Initial interest in indolocarbazole alkaloids as clinical anti-tu-
mour agents began as a result of the extraction in 1977, of an anti-
fungal natural product glycoside, staurosporine 1, from cultures of
Streptomyces staurosporeus (Fig. 1).4 The broad spectrum of bi-
ological activity displayed by 1 was rationalized in 1986 to be due to
its behaviour as a non-specific ATP-competitive kinase inhibitor,
exhibiting strong cytotoxic activity against cancer cell lines due to
its nanomolar PKC activity, as well as CDK inhibition, in vitro.5,6 The
closely related bisindolylmaleimide (3,4-di-1H-indol-3-yl-1H-pyr-
role-2,5-dione) scaffold based on Arcyriarubin A 2, isolated as the
pigment from myxomycetes, such as Arcyria denudata and Arcyria
O
O
H
N
NH
O
O
H
N
O
N
N
N
N
N
4
3
nutans, represents
a potential template for selective kinase
N
O
N
* Corresponding author. E-mail address: f.mccarthy@ucc.ie (F.O. McCarthy).
Fig. 1. Examples of clinically relevant indolocarbazoles and bisindolylmaleimides.
0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.10.020

L.T. Pierce et al. / Tetrahedron 66 (2010) 9754e9761
9755
clinical phase III trials, for the macrocyclic bisindolylmaleimide,
ruboxistaurin mesylate (ArxxantÒ) 3.8 Interestingly, compound 3
was reported to confer quite discrete enzyme selectivity; IC50
developed. This structural optimisation could be envisaged to be
due to its critical incorporation of a modified imide structural unit.
In particular, the pyrimidin-2,4-dione (uracil) sub-unit at the 3-
position of both indole moieties (X¼OH; 8), would be of interest
since the uracil nucleus is an important constituent of nucleosides,
which play a crucial role in biological systems (Fig. 3). Synthesis of
a novel kinase inhibitory template possessing unique utility by
displaying lactam H-bonding functionality, similar to staurosporine
1, rather than the imide motif conserved in 3,4-disubstituted mal-
eimide alkaloids, would also provide an interesting investigational
compound, exploiting its close structural similarity to K-252c 9da
cytotoxic anti-PKC indolocarbazole derived from the actinomycete
strain, Nocardiopsis sp. K-290.18
values for PKC-b1 and b2 (4.7 and 5.9 nM, respectively), are more
than 40-fold greater than for other PKC isoforms, and vastly more
potent than against other ATP-dependent kinases, e.g., Src tyrosine
kinase.9,10 This clinical candidate possesses attractive efficacy in
reducing vision loss in patients with diabetic peripheral retinopa-
thy, and is currently defined as the first chemotherapeutic treat-
ment for this serious complication of diabetes.
The orally-administered enzastaurin 4 has also been evaluated
favourably in clinical trials for the treatment of glioblastoma and
colo-rectal cancer, and is described to operate via induction of
apoptosis, in addition to inhibition of VEGF-mediated angiogene-
sis.11 Pre-clinical data published to date also supports the potential
of 4 for the treatment of large B-cell lymphoma and Akt-mediated
X
8
X = OH = ; R = CH3
3
H
HN
2
N
4
O
1
diseases, due to its highly attractive PKCb
and AKT/PI3 activity.12 It
O
N
5
6
has also been proposed that the bisindolylmaleimide framework
constitutes an ABCG2 inhibitory pharmacophore, which may in-
crease the oral bioavailability of co-administered ABCG2 substrate
drugs, in order to potentiate an effective therapeutic response and
significantly improve subsequent clinical outcome.13
N
N
N
N
H
H
R
R
General structure of 5,6-
bisindolylpyrimidin-4(3H)-ones
K-252c 9
SAR analysis suggests that application of precise structural fea-
tures to probe interactions between the maleimide head group and
essential residues within the conservedenzyme ATP-binding pocket
is still challenging, requiring further elucidation of exact mecha-
nisms of inhibition.14 Accomplishing distinct kinase selectivity with
sufficient potency (in the presence of intracellular ATP concentra-
tions) represents the ultimate goal of vast research within this area;
however, little work to date has assessed the protein backbone-
interacting pyrrole-2,5-dione molecular domain as a viable target
for inhibitory optimisation in order to achieve this overall aim.
Natural indole alkaloids fused to a pyrimidine nucleus have recently
been revealed to constitute an important pharmacological class,
based on their ability to modulate important biological functions.
Meridianin D 5 isolated from the marine tunicate Aplidium mer-
idianum, displayed cytotoxicity towards LMM3(murinemammarian
Fig. 3. Development of a novel kinase inhibitory template.
The primary method for converting simple alkyl b-ketoesters to
the corresponding pyrimidin-4-one moiety involves exposure of
the substrate to either urea or thiourea, in the presence of sodium
alkoxide in alcohol, and heating of this mixture for an extended
period.19 In 2002, it was first reported that simple
b-ketoester
precursors could be converted directly to corresponding 5,6-alkyl
substituted uracils by conventional microwave irradiation in the
presence of urea, under solvent-free conditions.20
This report includes work carried out on the first reported
conversion of a 2,3-bis(heteroaryl) methyl-3-oxopropionate to
heterocyclic 5,6-disubstituted pyrimidin-4-ones. This heterocycle-
forming process was optimised for an array of nucleophiles,
affording derivatives of acute biological importance. Some strategic
difficulties associated with conventional heterogeneous trans-
formations performed in aqueous media also necessitated careful
selection of novel reagent types, solvent nature and reaction times.
Targeted synthesis of these title bisindolylpyrimidinones, display-
ing improved solubility profiles, can now be reported under mild
and versatile conditions for oxidative and reductive desulfurisation.
adenocarcinoma cell line), with an IC50 value of 33.9 mM, as well as
being an inhibitor of several protein kinases, while a bisindolyl py-
rimidine analog 6, reported by Jiang et al., exhibited excellent in-
hibition against leukaemia CCRF-CEM cell line (GI50¼1.13
m
M).15,16
Extrapolating from this evidence, the design of inhibitors such as
ꢀ
indolyluracil 7 was postulated by Casar et al. to be a putative scaffold
capable of conferring significant cytotoxicity (Fig. 2).17
N
H3CO
2. Results and discussion
NH2
N
N
N
Recent advances in our laboratory have enabled a complete pro-
tocol for the synthesis of a series of novel 5,6-bisindolyl pyrimidin-
4-one congeners, to be established, starting from cheap, readily
available precursors. Initial investigations revealed that modification
of pre-existing, classical chemical routes to this novel heterocyclic
class was impractical. Extensive investigation was then carried out
into the specific preparation of these derivatives by a convergent
synthesisdit can now be reported that 2,3-bis(1-methyl-1H-indol-
3-yl) methyl-3-oxopropionate 10 afforded access to the pyri-
midinone nucleus via a cyclocondensation route (Scheme 1).
N
N
N
Br
H
H
H
5
6
O
HN
O
NH
Starting from the commercially available indole-3-acetic acid 11,
the one-pot preparation of the N-methyl protected methyl indole-
3-acetate ester 12, was achieved in a yield of 82%, via reaction with
dimethyl carbonate and potassium carbonate as base, at 130 ꢀC, for
20 h.21 N-Methyl indol-3-yl carbonyl chloride 13, was obtained in
quantitative yield from the corresponding acid 14, in the presence
of oxalyl chloride, suspended in dry DCM, and stirred at room
temperature, for 75 min.22 This method was highly advantageous
N
H
Br
7
Fig. 2. Indole alkaloids with kinase inhibitory activity.
At the outset of this work, a similar awareness of the intrinsic
ability of related pyrimidin-4-one H-bonding networks to mimic
and enhance specific spatial contacts between other potent kinase
inhibitors, such as 3, and essential kinase active site residues was

9756
L.T. Pierce et al. / Tetrahedron 66 (2010) 9754e9761
OH
O
O
O
(i)
O
O
O
N
H
N
(iii)
11
12
N
N
+
O
O
Cl
OH
10
(ii)
(iv)
N
N
NH2
N
13
14
HN
O
N
N
16
Scheme 1. Reaction conditions: (i) 1 equiv K2CO3, 3 equiv (CH3)2CO3, DMF, 130 ꢀC, 12 h, 12¼82%; (ii) 1.1 equiv (COCl)2, DCM, rt, 75 min, 13¼100%, (iii) (a) 2.2 equiv LDA, 1.3 equiv
N-methyl indole-3-carbonyl chloride (13), THF, ꢁ78 ꢀCdrt, 16 h; (b) NH4Cl/H2O, 10¼80%; (iv) (i) (a) 20 equiv NaOMe, 5 equiv [NH2(C]NH2)NH2]2CO3, MeOH, reflux, 24 h, (b) 10%
HCl/H2O, 16¼45%.
compared with the reported synthesis involving stirring of 14 with
thionyl chloride, at room temperature for 20 h, which was limited
by formation of an appreciable amount of the 2-chlorinated acid
urea analogues under base-mediated conditions was studied and
the results of this reactant study are described in Table 1.
chloride side-product.23 The novel
b-dicarbonyl intermediate 10
2.1. Reaction with bi-dentate N-nucleophilesdurea
derivatives
was prepared by modified Claisen reaction of 12, in the presence of
LDA in THF, with acid chloride 13, at ꢁ78 ꢀC.
Synthesis of the corresponding
b-enaminoester, a common
As an obvious methodology for accessing 5,6-bis(1-methyl-1H-
indol-3-yl) pyrimidine-2,4(1H,3H)-dione 8, reaction of urea with
10, in methanol, heated to reflux temperature, in the presence of
sodium methoxide did not yield any anticipated product upon acid
work-up, even after 72 h. Preliminary microwave reactions carried
out have also been unpromising to date. Similarly, reaction with
5 equiv of O-methyl isourea yielded only starting material 10 fol-
lowing heating for 36 h. Utilising aqueous inorganic base-mediated
conditions, as reported by Botta et al.,24 we also attempted con-
version to 2-methoxy-4(3H)-pyrimidinone 15 following reaction of
10 with 2.2 equiv of Ca(OH)2 and O-methyl isourea, stirred in water
at 70 ꢀC for 48 h, prior to acidification and heating for a further 20 h.
However, it was observed that no reaction had occurred under
these conditions (Table 1).
precursor to pyrimidin-4-ones, was attempted via numerous ap-
proaches including imine formation from the -ketoester 10,
modified Blaise reaction (using 1-methyl-3-cyanoindole and zinc
b
chloride), etc., with none yielding
intermediate.
a viable route to this
However, it has been widely established that reaction of
a dicarbonyl intermediate with an appropriate nitrogen nucleo-
phile represents a viable route to heterocyclic systems bearing
a pyrimidine moiety. The application of this reaction with related
Table 1
Reaction of 10 with panel of analogous urea nucleophilesa
R3
N
R1
N
O
O
O
2.2. Reaction with bi-dentate N-nucleophilesdguanidine
R3
O
R2
derivatives
R1
R2
N
N
H
H
Following an initial lack of success with urea, it was determined
that cyclisation with an alternative nucleophile to form 2-amino-
5,6-bis(1-methyl-1H-indol-3-yl)pyrimidin-4(3H)-one 16 consti-
tuted a highly interesting target with potential biological activity.
Compound 8 mayalso be accessed via chemical derivatisation of this
N
N
N
N
10
R1
R2
R3
Conditionsb
Time
Result
H
H
H
H
H
H
CH3
H
H
H
d
d
d
O (8)
A
A
A
A
72 h
24 h
24 h
48 h
24 h
20 h
24 h
d
precursor 16. As shown in Scheme 1, reaction of b-ketoester 10 with
S (17)
NH (16)
H (22)
SeCH3 (18)
OeCH3 (15)
S (19)
24%
45%
d
guanidine (pre-formed in situ from the initial reaction of guanidine
carbonate with excess sodium methoxide) afforded crude 16, from
which any remaining impurity was eliminated by chromatography,
in order to derive pure compound 16 in a yield of 45% (Scheme 1).
It was initially postulated that a diazotisation route could in-
troduce the hydroxyl group in order to convert isocytosine de-
rivative 16 to the corresponding pyrimidine-2,4-dione 8.25
However, attempted reaction of the amino group of 16 with so-
dium nitrite/HCl, tert-butyl nitrite/acetic acid or tert-butyl nitrite/
aqueous 2-propanol, to form a diazonium salt, which could be
A, C or D
A or B
A
d
d
CH3
d
a
In each case, reaction was performed with 2,3-bis(1-methyl-1H-indol-3-yl)
methyl-3-oxopropionate (10) under nitrogen atmosphere.
b
Methods: A 20 equiv NaOMe/MeOH, 5 equiv R1NH(CR3)NHR2 reagent, reflux,
24e72 h; B Ca(OH)2, 5 equiv R1NH(CR3)NHR2 reagent H2O, H2SO4 80 ꢀC, 36 h; C 10%
KOH/H2O, 5 equiv R1NH(CR3)NHR2 reagent, rt, 24 h; D 20 equiv. KOH, 5 equiv R1NH
(CR3)NHR2 reagent, THF, 65 ꢀC, 24 h.

L.T. Pierce et al. / Tetrahedron 66 (2010) 9754e9761
9757
S
O
hydrolysed to uracil 8, yielded only unreacted 16, in each case.
HN
HN
Similarly, attempted hydrolytic reaction with aqueous 10% HCl at
85 ꢀC resulted in detection of only starting material 16 upon in-
vestigation of the final reaction mixture after 7 days (Table 2).
O
N
O
NH
(ii),( iii) or (iv)
(i)
17
Table 2
N
N
N
N
Conditions for attempted conversion of 16 to 8a
18
8
(v)
Reagent
Equiv.
Conditions
Time
Result
NaNO2
NaNO2
t-BuONO
t-BuONO
10% HCl
5.0
5.0
5.0
5.0
AcOH, 0 ꢀCdrt
10% HCl, 0 ꢀCd70 ꢀC
AcOH, 0 ꢀCdrt
IPA/H2O, 0 ꢀCdrt
H2O, 85 ꢀC
20 h
24 h
20 h
24 h
7d
d
d
d
d
d
S
N
O
N
>100
a
In each case, reaction was performed in presence of 16, on 150 mg scale and
assessed by qualitative 13C NMR and ESI-MS analysis.
N
N
21
2.3. Reaction with bi-dentate N-nucleophilesdthiourea
Scheme 2. Reaction conditions: (i) 2 equiv CH3I, 1.1 equiv K2CO3, MeOH, 30 ꢀC, 20 h,
18¼35%; (ii) 2 equiv OxoneÒ, 1,4-dioxane/H2O, 70 ꢀC, 3d; (iii) 30% aq NaOH, 1,4-
dioxane, 70 ꢀC, 24 h; (iv) 10% aq HCl, 1,4-dioxane, 70 ꢀC, 24 h; (v) 3 equiv Br(CH2)2Br,
2 equiv K2CO3, cat. TBAB, 1,4-dioxane, rt, 16 h, 21¼66%.
derivatives
Formation of a thiouracil analogue 17 was also deemed to be an
important derivative for comparison with target compound 8. The
use of thiourea was attractive due to its superior reactivity and the
nature of the thiocarbonyl bond also permitted access to further
secondary derivatives, including a possible route to 8.
dibromoethane in the presence of potassium carbonate, along with
TBAB as catalyst, in 1,4-dioxane, for 16 h at room temperature,
provided the S,N-dialkylated derivative, which was crystallised from
95% ethanol, to afford 2H-thiazolo[3,2-a]pyrimidin-5-one 21 as an
yellow powder in a yield of 66% (Scheme 2).
b-Ketoester 10 was converted to the corresponding 5,6-bis-
(1-methyl-1H-indol-3-yl)-2-thioxo-2,3-dihydropyrimidin-4(1H)-
one 17, in the presence of sodium methoxide and excess thiourea
following reflux in methanol for 24 h (method A; Table 1). The yield
for this reaction was found to be 20e24%, independent of whether
the reaction time was extended to 48 h or if further excess of base
was employed. The crude residue was purified by trituration with
boiling absolute ethanol, and filtration of this mixture yielded the
novel 17, as a pale yellow powder. Condensation of 10 was also
attempted with a number of thiourea analogues (Table 1).
2.4. Oxidative desulfurisation: pyrimidine-2,4-dione
synthesis
Synthesis of simple 5,6-dialkyl uracils from thiouracil precursors
is known to be performed in the presence of 10% w/v chloroacetic
acid, necessitatingextended reaction times and high temperature, in
moderate to good yields.29 Following elimination of other alterna-
tive routes to 8, work was undertaken in order to directly convert 17
to the attractive uracil ring system, 8 (Table 3). It appears that this is
the first investigation of the oxidation conditions required for suc-
cessful transformation of a 5,6-bis(heteroaryl)-2-thioxo-2,3-dihy-
dropyrimidin-4(1H)-one to its corresponding pyrimidine-2,4(1H,
3H)-dione analogue.
Reaction with 5 equiv of N,N0-dimethyl thiourea yielded only
starting material following heating for 36 h. S-Methyl-
isothiouronium hemisulfate was synthesised by reaction of thiourea
with 2.5 equiv of dimethyl sulfate, in a yield of 87%. Reaction of
5 equiv of this salt under standard methoxide conditions did not
result in formationofanyproduct 18, evenfollowingextended reflux
for 72 h. Similarly, when reaction of 5 equiv of the salt was carried
out, along with 10, in 10% aqueous KOH, the absence of either 19 or 2-
amino oxazin-4(5H)-one was observed (method C; Table 1).19 Due to
concerns over these heterogeneous reaction conditions, a modified
reaction was attempted involving mixing of 20 equiv of pulverised
KOH along with 5 equiv of this salt along with 10, in THF, heated for
16 h (method D; Table 1), but without any success.
As an alternative route to target compound 8, methylation of 17
was undertaken by treatment with iodomethane in methanol at
30 ꢀC, in the presence of potassium carbonate to provide
2-methylthiopyrimidin-4(3H)-one 18 in a moderate yield of 35%
(Scheme 2). Chromatography employing ethyl acetate and a few
drops of methanol enabled elution of a small proportion of
unreacted 17, and following addition of a drop of triethylamine to
the eluent, 18 could be rapidly isolated as a straw-coloured
powder.
Subsequent hydrolytic conversion of 2-methylthiopyrimidin-4-
one 18 to 8 was unsuccessful under conditions for an analogous
transformation reported by Gibson et al., involving heating of 18
with OxoneÒ in aqueous 1,4-dioxane, for 3 days at 70 ꢀC.26 Similarly,
treatment of sulfide 18 with either a solution of aqueous 30% NaOH
or 10% HCl, in 1,4-dioxane, under similar conditions to Lu et al.,
yielded only starting material in each case, following investigation of
the reaction mixture after heating for 24 h.27 However, it was found
that cycloalkylated analogues of thiouracil 17 could be synthesised
under mild phase-transfer conditions.28 Reaction with 1,2-
Table 3
Oxidative desulfurisation of 2-thiopyrimidin-4(3H)-one 17 to pyrimidine-2,4
(1H,3H)-dione 8
Reagent
Stoichiometry Solvent
Reflux Product formation
(time)
X¼SH (17) X¼OH (8)
ClCH2CO2H
ClCH2CO2H
ClCH2CO2H
ClCH2CO2H
BrCH2CO2Et 1.5 equiv
BrCH2CO2Et 1.1 equiv
BrCH2CO2Et 2.5 equiv
10% w/v
10% w/v
10% w/v
5 equiv
H2O
AcOH
DMF
MeOH
DMF
MeOH
72 h
72 h
72 h
72 h
24 h
24 h
O
O
O
O
O
d
d
O
O
O
d
d
18%
45%
MeOH/H2O 48 h
Treatment with aqueous chloroacetic acid for 72 h, afforded only
an inseparable mixture of starting 2-thiopyrimidin-4-one 17, along
with a variable proportion of desired compound 8, following 13C
NMR analysis of the crude reaction residue, under a range of con-
ditions. It was postulated that reaction heterogeneity prevented full
reactant conversion; however, when solvent conditions were al-
tered in order to increase thiouracil solubility (e.g., DMF or meth-
anol), these non-aqueous conditions then seemed to inhibit the
oxidative desulfurisation process.Following the partial success of
these initial efforts, further trials uncovered that a stoichiometric
quantity of ethyl bromoacetate,30 in dry methanol, heated at reflux
for 16 h, allowed synthesis of the final product 8, as an off-white

9758
L.T. Pierce et al. / Tetrahedron 66 (2010) 9754e9761
powder, in a moderate yield of 18%, following recrystallisation from
DMF/H2O (5:1). This yield could be improved once 2.5 equiv of ethyl
bromoacetate were heated in the presence of 17, in methanol, for
48 h, to provide 8 exclusively, in an enhanced yield of 45%, fol-
lowing crystallisation (Scheme 3).
simplified ruboxistaurin derivatives has been produced and cur-
rently, the route to full macrocyclic ruboxistaurin derivatives is
underway. In parallel, work is in progress to establish a full meth-
odology for the synthesis of corresponding indolo[2,3-a]pyr-
imidino[5,6-c]carbazoles, via oxidative cyclisation, to form the
central carbocyclic ring system from these acyclic precursors.
O
S
4. Experimental
HN
HN
NH
O
NH
O
4.1. General experimental procedures
(i
)
(ii)
10
Melting points were determined with a Thomas Hoover Capillary
Melting Point apparatus and are uncorrected. IR spectra were
recorded on a PerkineElmer Paragon 1000 spectrophotometer. 1H
(300 MHz) and 13C NMR (75 MHz) spectrawere recorded on a Bruker
Avance 300 NMR spectrometer. All spectra were recorded in deu-
terated chloroform (CDCl3) or DMSO (DMSO-d6), with tetrame-
thylsilane (TMS) as internal standard. Mass spectra were recorded
on a Waters Quattro Micro (QAA1202) in electrospray ionization
(ESI) positive or negative modes. High resolution mass spectra
(HRMS) were recorded on a Waters Micromass LCT Premier mass
spectrometer (Instrument number KD 160) in ESI positive mode.
Thin layer chromatography (TLC) was carried out on pre-coated
silica gel 60 (Merck PF254) plates and compounds were visualised by
UV (254 nm) light detection. Column chromatography was carried
out using Merck PF254 silica gel 60A. DCM was distilled from P2O5,
ethyl acetate was distilled from K2CO3, hexane was distilled prior to
use, ethanol and methanol were distilled from magnesium/iodine
and THF was distilled from benzophenone ketal. All commercial
reagents, anhydrous DMF and 1,4-dioxane were purchased from
Aldrich and were used without further purification.
N
N
N
N
8
17
Scheme 3. Reaction conditions: (i)(a) 10 equiv NaOMe, 5 equiv NH2CSNH2, MeOH,
reflux, 24 h, (b) 10% HCl/H2O, 17¼24%; (ii)(a) 2.5 equiv BrCH2CO2Et, MeOH, reflux, 48 h;
(b) H2O, 8¼45%.
2.5. Reaction with bi-dentate N-nucleophilesdamidine
derivatives
Direct reaction of formamidine acetate with 10 under normal
sodium methoxide conditions (Table 1; method A), for 24 h, failed
to yield any of the desired reduced 2-(1H)-pyrimidine-4-one,
22dpostulated to be an attractive acyclic K-252c 9 analogue. The
synthesis of this congener was subsequently effected by stirring of
compound 17 overnight, with 5 equiv of nickel bromide in distilled
methanol, in the presence of 15 equiv of sodium borohydride, to
afford 5,6-bis(1-methyl-1H-indol-3-yl)pyrimidin-4(3H)-one 22, in
52% yield, following filtration of the black reaction mixture and
chromatographic purification (Scheme 4).31
4.1.1. Methyl (1-methyl-1H-indol-3-yl) acetate (12)21. Dimethyl
carbonate (8.6 mL,101.6 mmol) was added to a mixture of indole-3-
acetic acid 11 (6.002 g, 29.6 mmol), anhydrous potassium carbonate
(6.007 g, 43.2 mmol) and DMF (70 mL), which was then stirred at
130 ꢀC for 16 h. Following solvent removal, the product residue was
extracted with ethyl acetate (150 mL), which was washed with
water (2ꢂ150 mL) and brine (1ꢂ100 mL). The combined organic
layers were dried using magnesium sulfate, filtered and evaporated
in vacuo. The pure ester 12 was obtained, as a straw-coloured oil,
following column chromatography, using an 80:20 mixture of
hexane and ethyl acetate (5.722 g, 82%); dH (300 MHz) CDCl3 3.70
[3H, s, OeCH3], 3.76 [3H, s, NeCH3], 3.77 [2H, s, CH2], 7.02 [1H, s,
aromatic CeH2], 7.09e7.15 [1H, t, J¼7.86 Hz, aromatic CeH5],
7.20e7.25 [1H, t, J¼7.98 Hz, aromatic CeH6], 7.27e7.30 [1H, d,
J¼8.07 Hz, aromatic CeH7], 7.58e7.61 [1H, d, J¼7.86 Hz, aromatic
CeH4]; dC (75 MHz) CDCl3 31.0 [CH2], 32.7 [NeCH3], 52.0 [OeCH3],
106.7 [aromatic quat. C], 109.3 [aromatic CeH], 118.9 [aromatic
CeH], 119.2 [aromatic CeH], 121.8 [aromatic CeH], 126.6 [aromatic
quat. C], 127.7 [aromatic CeH], 136.9 [aromatic quat. C], 172.6
[eCO2CH3]; nmax/cmꢁ1 (KBr) 2951, 1732, 1616, 1556; m/z (ESI) 204.1
[(MþH)þ, 100%].
S
HN
HN
O
N
O
NH
N
(i)
N
N
N
22
17
Scheme 4. Reaction conditions: (i) 5 equiv NiBr2, 15 equiv NaBH4, MeOH, rt, 16 h,
22¼52%.
3. Conclusion
We now report that reaction of 10 with thiourea and guanidine
carbonate affords the corresponding bisindolyl heterocyclic ana-
logues and overall represents a validated route to a versatile range
of analogues within this novel compound class. Key structural traits
existing within the enzyme-interacting imide H-bonding domain of
biologically significant bisindolylmaleimide analogues (2e4) were
modified and augmented by incorporation of an analogueous pyr-
imidin-4-one pharmacophore (Fig. 3), in order to retain chemical
efficacy, as well as to afford derivatives displaying improved bio-
physical parameters, e.g., enhanced aqueous solubility. Biological
testing of these compounds will identify further structural re-
finements through modelling of their non-covalent interactions
with key active site residues in silico, in comparison to the highly
active, five-membered 3,4-bis(indol-3-yl)-1H-pyrrole-2,5-dione
core 2.
4.1.2. 1-Methyl-1H-indol-3-yl carbonyl chloride (13). N-Methyl in-
dole-3-carboxylic acid 14 (0.502 g, 2.85 mmol) was suspended in
dry DCM (15 mL), followed by the careful addition of oxalyl chloride
(0.25 mL, 2.86 mmol) over several minutes. Following stirring at
ambient temperature for 75 min, gas evolution had ceased, and the
solvent was evaporated under reduced pressuredyielding a light
red solid, (0.540 g, 98%), which was used without any further pu-
rification, following IR analysis; nmax/cmꢁ1 (KBr) 1748 (C]O).
An initial study on overcoming challenges associated with the
synthesis of novel uracil 8, along with derivatisation of the 5,6-bis
(1-methyl-1H-indol-3-yl)pyrimidin-4(3H)-one system has been
completed and a successful route has been identified. A series of
4.1.3. Methyl 2,3-bis(1-methyl-1H-indol-3-yl)-3-oxopropanoate (10).
A solution of LDA (36.2 mL, 65.1 mmol, 2.2 equiv) was added over
10 min to a flask containing dry THF (50 mL), followed by cooling

L.T. Pierce et al. / Tetrahedron 66 (2010) 9754e9761
9759
to ꢁ78 ꢀC. A mixture of N-methyl ester 12 (6.005 g, 29.6 mmol) in
THF (3 mL) was then added slowly to the flask, while stirring, under
inert atmosphere. The acid chloride 13 (38.5 mmol, 1.3 equiv, based
on corresponding acid 14) was dissolved in THF (15 mL), and then
added dropwise to the reaction vessel. The reaction was allowed to
warm up to room temperature, while stirring was maintained
overnight. Following solvent removal, the product was extracted
with ethyl acetate (3ꢂ150 mL), followed by washing with saturated
ammonium chloride (250 mL), water (4ꢂ250 mL) and brine
(2ꢂ150 mL). The combined organic layers were dried using mag-
nesium sulfate, filtered and evaporated in vacuo. The optimised yield
metal (1.595 g, 69 mmol, 10 equiv) in dry methanol (120 mL), under
inert atmosphere, was added thiourea (2.627 g, 35 mmol, 5 equiv)
followed by vigorous stirring for 15 min. Methyl 2,3-bis(1-methyl-
1H-indol-3-yl)-3-oxopropanoate 10 (2.508 g, 6.9 mmol) was then
charged to the reaction mixture and heated at reflux for 24 h.
Following solvent evaporation, water (100 mL) was added to the
complex residue, prior to acidification with 10% HCl to pH 3. Fil-
tration of the resultant dark brown solid, followed by trituration of
the crude pyrimidinone 17 with boiling absolute ethanol (40 mL),
produced a slurry, which, following filtration and successive
washing of the yellow powder with water and diethyl ether, was
identified as the pure thiouracil product 17 (0.640 g, 24%); mp
317e320 ꢀC; dH (300 MHz) DMSO-d6 3.63 [3H, s, NeCH3], 3.70 [3H,
of the
b-ketoester 10da dark yellow crystalline solid, following
gradient column chromatography employing ethyl acetate/hexane,
was 8.815 g (82%); mp 142e144 ꢀC; dH (300 MHz) CDCl3 3.74 [3H, s,
NeCH3], 3.74 [3H, s, NeCH3], 3.76 [3H, s, OeCH3 (ester)], 5.70 [1H, s,
eCeHa], 7.12e7.17 [1H, td, J¼6.90,1.35 Hz, aromatic CeH5], 7.19e7.25
0
s, NeCH3], 6.74e6.80 [2H, m, aromatic CeH5,5 ], 6.96e7.01 [2H, m,
0
0
aromatic CeH7,7 ], 7.02e7.07 [2H, t, J¼7.85 Hz, aromatic CeH6,6 ],
7.21 [1H, s, aromatic CeH2], 7.24e7.27 [1H, d, J¼8.19 Hz, aromatic
0
0
[1H, td, J¼8.16, 1.26 Hz, aromatic CeH5 ], 7.28e7.30 [4H, m, aromatic
CeH4], 7.30e7.33 [1H, d, J¼8.19 Hz, aromatic CeH4 ], 7.65 [1H, s,
0
0
0
CeH6,6 ,7,7 ], 7.32 [1H, s, aromatic CeH2], 7.66e7.68 [1H, d, J¼7.65 Hz,
aromatic CeH2 ]; 12.15 [1H, br s, thioamide NeH]; 12.51 [1H, br s,
0
aromatic CeH4], 7.78 [1H, s, aromatic CeH2 ], 8.42e8.45 [1H, m, ar-
imide NeH]; dC (75 MHz) DMSO-d6 32.4 [NeCH3], 32.7 [NeCH3],
105.7 [aromatic quat. C], 106.3 [aromatic quat. C], 109.1 [aromatic
quat. C], 109.4 [aromatic CeH], 110.0 [aromatic CeH], 118.5 [aro-
matic CeH], 119.5 [aromatic CeH], 119.6 [aromatic CeH], 119.7
[aromatic CeH], 120.6 [aromatic CeH], 121.4 [aromatic CeH], 125.1
[aromatic quat. C], 127.0 [aromatic quat. C], 130.7 [aromatic CeH],
132.4 [aromatic CeH], 135.9 [aromatic quat. C], 136.0 [aromatic
quat. C], 144.9 [aromatic quat. C], 161.3 [eC]O], 174.3 [eC]S];
nmax/cmꢁ1 (KBr) 2922, 1651, 1541, 1452; m/z (ESI) 387.2 [(MþH)þ,
20%], 115.0 (75), 73.9 (100); HRMSd(ESIþ) requires: 387.1280,
found: 387.1272 (C22H19N4OS).
0
omatic CeH4 ]; dC (75 MHz) CDCl3 32.9 [NeCH3], 33.6 [NeCH3], 52.7
[OeCH3], 53.2 [eCeHa] 107.5 [aromatic quat. C], 109.6 [aromatic
CeH],109.7 [aromatic CeH], 115.0 [aromatic quat. C], 118.3 [aromatic
CeH], 119.5 [aromatic CeH], 121.8 [aromatic CeH], 122.8 [aromatic
CeH], 122.9 [aromatic CeH], 123.7 [aromatic CeH], 126.8 [aromatic
quat. C], 127.2 [aromatic quat. C], 129.0 [aromatic CeH], 136.2 [aro-
matic CeH], 136.7 [aromatic quat. C], 137.4 [aromatic quat. C], 170.3
[eC]O(eOCH3)], 188.0 [CeC]O(eC)]; nmax/cmꢁ1 (KBr) 2927, 1732,
1644, 1529; m/z (ESI) 361.3 [(MþH)þ, 100%], 259.3 (80); HRMSd
(ESIþ) requires: 361.1548, found: 361.1552 (C22H21N2O3).
4.1.4. 2-Amino-5,6-bis(1-methyl-1H-indol-3-yl)pyrimidin-4(3H)-one
(16). Sodium metal (1.742 g, 76 mmol, 20 equiv)was dissolvedin dry
methanol (60 mL) under an inert atmosphere followed by stirring at
room temperature for 20 min. Guanidinium carbonate (3.421 g,
19 mmol, 5 equiv) was then added to the flask in a single portion, and
the heterogeneous mixture was stirred vigorously for 25 min at
ambient temperature. Methyl 2,3-bis(1-methyl-1H-indol-3-yl)-3-
oxopropanoate 10 (1.366 g, 3.8 mmol) was carefully added to this
suspension and the dark orange reaction was then heated to reflux
for 24 h. Following solvent removal under reduced pressure, the
residue was dissolved in a minimum volume of water (30 mL), and
subsequentlyacidified with 10% HCl to pH 3. The crude 2-amino-5,6-
bis(1-methyl-1H-indol-3-yl)pyrimidin-4(3H)-one 16 was then fil-
tered, washed successively with water and diethyl ether and dried.
Gradient chromatography afforded a fraction, eluting with 0.5%
methanol/DCM, which was evaporated to provide the isocytosine
derivative 16 as a light brown amorphous powder (0.627 g, 45%); mp
195e197 ꢀC; dH (300 MHz) DMSO-d6 3.40 [3H, s, NeCH3], 3.80 [3H, s,
NeCH3], 6.41 [2H, br s, NH2], 6.65 [1H, s, aromatic CeH2], 6.78e6.83
[1H, t, J¼7.47 Hz, aromatic CeH5], 6.98e7.13 [4H, m, aromatic
4.1.6. 5,6-Bis(1-methyl-1H-indol-3-yl)-2-(methylthio)pyrimidin-4
(3H)-one (18). Distilled methanol (15 mL) was added to a flask
containing anhydrous potassium carbonate (0.203 g, 1.42 mmol,
1.1 equiv), along with 17 (0.507 g, 1.29 mmol). Iodomethane
(0.16 mL, 2.58 mmol, 2 equiv) was then added and the mixture was
stirred vigorously at 30 ꢀC for a further 20 h. Following solvent
removal, the residue was taken up in ethyl acetate (15 mL) and
filtered, to remove any unreacted base. This ethyl acetate solution
was evaporated to yield a light beige solid, which was subjected to
column chromatography, employing a gradient from 100% ethyl
acetate, to 90% ethyl acetate/10% methanol, and finally with the
addition of a few drops of Et3N, to isolate polar 18. The product
fractions were combined and evaporated to a light yellow powder,
under reduced pressure (0.180 g, 35%); mp 273e276 ꢀC; dH
(300 MHz) DMSO-d6 2.66 [3H, s, SeCH3], 3.46 [3H, s, NeCH3], 3.82
[3H, s, NeCH3], 6.76e6.81 [1H, t, J¼7.65 Hz, aromatic CeH5], 6.87
[1H, s, aromatic CeH2], 6.93e6.95 [1H, d, J¼7.86 Hz, aromatic
0
CeH7], 7.00e7.05 [1H, t, J¼7.35 Hz, aromatic CeH5 ], 7.05e7.10 [1H,
t, J¼7.26 Hz, aromatic CeH6], 7.10e7.15 [1H, t, J¼7.02 Hz, aromatic
0
0
CeH6 ], 7.32e7.35 [1H, d, J¼8.10 Hz, aromatic CeH7 ], 7.37 [1H, s,
0
0
0
0
CeH5 ,6,6 ,7], 7.17 [1H, s, aromatic CeH2 ], 7.27e7.29 [1H, d, J¼8.04 Hz,
aromatic CeH2 ], 7.41e7.44 [1H, d, J¼8.16 Hz, aromatic CeH4];
0
0
aromatic CeH7 ], 7.39e7.42 [1H, d, J¼8.19 Hz, aromatic CeH4],
8.06e8.09 [1H, d, J¼7.95 Hz, aromatic CeH4 ], 12.50 [1H, br s, NeH];
0
8.32e8.35 [1H, d, J¼7.98 Hz, aromatic CeH4 ],10.83 [1H, br s, NH]; dC
dC (75 MHz) DMSO-d6 12.92 [SeCH3], 32.5 [NeCH3], 32.6 [NeCH3],
107.5 [aromatic quat. C], 109.6 [aromatic CeH], 109.8 [aromatic
CeH], 112.7 [aromatic quat. C], 118.6 [aromatic CeH], 119.7 [aro-
matic CeH], 119.7 [aromatic quat. C], 119.9 [aromatic CeH], 120.7
[aromatic quat. C], 120.8 [aromatic CeH], 121.5 [aromatic CeH],
122.1 [aromatic CeH], 126.3 [aromatic quat. C], 126.7 [aromatic
quat. C], 130.3 [aromatic CeH], 132.7 [aromatic CeH], 136.3 [aro-
matic quat. C], 136.5 [aromatic quat. C], 156.6 [N]C(SCH3)], 161.9
[C]O]; nmax/cmꢁ1 (KBr) 3434, 2923, 1628, 1521, 1461; m/z (ESI)
401.1 [(MþH)þ, 30%]; HRMSd(ESIþ) requires: 401.1436, found:
401.1430 (C23H21N4OS).
(75 MHz) DMSO-d6 32.4 [NeCH3], 32.7 [NeCH3], 105.5 [aromatic
quat. C], 106.6 [aromatic quat. C], 109.0 [2ꢂaromatic quat. C], 109.5
[aromatic CeH], 110.0 [aromatic CeH], 118.5 [aromatic CeH], 119.6
[aromatic CeH], 119.9 [aromatic CeH], 120.7 [aromatic CeH], 121.2
[aromatic CeH],121.8 [aromatic CeH],125.6 [aromatic quat. C],127.1
[aromatic quat. C], 130.5 [aromatic CeH], 132.2 [aromatic CeH],
136.2 [aromatic quat. C], 136.3 [aromatic quat. C], 152.7 [eC]N
(NH2)], 161.8 [eC]O(NH)]; nmax/cmꢁ1 (KBr) 3384, 2925, 1686, 1627,
1517, 1462; m/z (ESI) 370.1 [(MþH)þ, 100%], 371.1 (25); HRMSd
(ESIþ) requires: 370.1677, found: 370.1668 (C22H20N5O).
4.1.5. 5,6-Bis(1-methyl-1H-indol-3-yl)-2-thioxo-2,3-dihydropyr-
4.1.7. 6,7-Bis(1-methyl-1H-indol-3-yl)-2H-thiazolo[3,2-a]pyrimidin-
imidin-4(1H)-one (17). To a sodium methoxide solution sodium
5(3H)-one (21). To a solution of compound 17 (0.101 g, 0.26 mmol)

9760
L.T. Pierce et al. / Tetrahedron 66 (2010) 9754e9761
in 1,4-dioxane (10 mL)were added anhydrous potassium carbonate
(0.072 g, 0.52 mmol, 2 equiv) and TBAB (0.025 g, 0.078 mmol,
0.33 equiv). 1,2-Dibromoethane (0.07 mL, 0.78 mmol, 3 equiv) was
then syringed into the reaction flask, with vigorous stirring of the
mixture allowed to proceed overnight. The dioxane solution was
filtered, prior to washing with DCM (10 mL). The clarified filtrate
was evaporated in vacuo, and the residue was then washed with
a small volume of hexane, to remove any excess starting reagent.
The resultant beige solid was dissolved in hot absolute ethanol
(8 mL), followed by cooling to room temperature and subsequently
to 0 ꢀC. The heterocyclic product 21 was then filtered and dried to
provide a light yellow powder (0.071 g, 66%); mp>300 ꢀC; dH
(300 MHz) DMSO-d6 3.52 [3H, s, NeCH3], 3.64e3.69 [2H, t,
J¼7.56 Hz, SeCH2eCH2eN], 3.87 [3H, s, NeCH3], 4.46e4.51 [2H, t,
J¼7.56 Hz, SeCH2eCH2eN], 6.84e6.89 [1H, t, J¼7.59 Hz, aromatic
CeH5], 6.89 [1H, s, aromatic CeH2], 7.02e7.04 [1H, d, J¼7.89 Hz,
15 equiv) was added cautiously to the reaction mixture portion-
wise, and the reaction was allowed to stir for 2 h at room
temperature. TLC analysis indicated full consumption of starting
material had occurred at this point. Following stirring at room
temperature for a further 14 h, the reaction mixture was then fil-
tered through a pad of CeliteÒ and washed with additional meth-
anol (2ꢂ20 mL), followed by ethyl acetate (3ꢂ15 mL). Following
evaporation of these combined extracts, the light orange residue
was dissolved in ethyl acetate (70 mL). This material was then
washed with water (75 mL), and the aqueous layer further
extracted with ethyl acetate (2ꢂ25 mL). The ethyl acetate layers
were combined and washed with water (3ꢂ100 mL) and brine
(100 mL). The organic layer was dried over magnesium sulfate,
filtered and evaporated in vacuo. The pyrimidin-4(3H)-one de-
rivative 22 was then purified by flash chromatography (1% meth-
anol/DCM), to yield a dark brown powder (0.049 g, 52%); mp
218e221 ꢀC; dH (300 MHz) DMSO-d6 3.38 [3H, s, NeCH3], 3.74 [3H,
0
aromatic CeH7], 7.02e7.07 [1H, t, J¼7.62 Hz, aromatic CeH5 ],
0
0
7.11e7.17 [1H, t, J¼9.03 Hz, aromatic CeH6], 7.14e7.19 [1H, t,
s, NeCH3], 6.68e6.73 (1H, t, J¼7.05 Hz, CeH5 ), 6.80 (1H, s, CeH2 ),
0
0
J¼7.20 Hz, aromatic CeH6 ], 7.36e7.39 [1H, d, J¼8.16 Hz, aromatic
6.84e6.86 (1H, d, J¼7.89 Hz, CeH7 ), 6.88e6.93 (1H, t, J¼7.83Hz,
0
0
CeH7], 7.39 [1H, s, aromatic CeH2 ], 7.47e7.50 [1H, d, J¼8.22 Hz,
CeH5), 6.96e7.01 (1H, t, J¼7.56 Hz, CeH6 ), 7.01e7.06 (1H, t,
0
aromatic CeH4], 7.97e8.00 [1H, d, J¼7.98 Hz, aromatic CeH4 ]; dC
J¼6.99 Hz, CeH6), 7.23e7.25 (1H,d, J¼8.01 Hz, CeH7), 7.33e7.35
(1H, d, J¼5.85 Hz, CeH4), 7.35 (1H, s, CeH2), 7.95e7.98 (1H, d,
(75 MHz) DMSO-d6 26.3 [NeCH2CH2eS], 32.5 [NeCH3], 32.7
[NeCH3], 49.0 [NeCH2CH2-S], 107.4 [aromatic quat. C], 109.0 [aro-
matic quat. C], 109.6 [aromatic CeH], 109.8 [aromatic CeH], 112.2
[aromatic quat. C], 118.6 [aromatic CeH], 119.7 [aromatic CeH],
119.9 [aromatic CeH], 120.8 [aromatic CeH], 121.5 [aromatic CeH],
122.1 [aromatic CeH], 126.4 [aromatic quat. C], 126.5 [aromatic
quat. C], 130.3 [aromatic CeH], 132.7 [aromatic CeH], 136.2 [aro-
matic quat. C], 136.6 [aromatic quat. C], 155.5 [aromatic quat. C],
160.8 [NeC]N], 161.1 [eC]O]; nmax/cmꢁ1 (KBr) 2923, 1644, 1562,
1520, 1479, 1460; m/z (ESI) 413.0 [(MþH)þ, 100%]; HRMSd(ESIþ)
requires: 413.1436, found: 413.1432 (C24H21N4OS).
0
J¼7.86 Hz, CeH4 ), 8.13 (1H, s, N]CeH), 12.23 (1H, br s, NeH); dC
(75 MHz) DMSO-d6 32.5 [NeCH3], 32.6 [NeCH3], 107.5 [aromatic
quat. C], 109.6 [aromatic CeH], 109.7 [aromatic CeH], 112.7 [aro-
matic quat. C], 114.7 [aromatic quat. C], 118.6 [aromatic CeH], 119.8
[2ꢂaromatic CeH], 120.8 [aromatic CeH], 121.4 [aromatic CeH],
122.3 [aromatic CeH], 126.1 [aromatic quat. C], 126.6 [aromatic
quat. C], 130.5 [aromatic CeH], 132.5 [aromatic CeH], 136.3 [aro-
matic quat. C]; 136.5 [aromatic quat. C], 146.3 [aromatic quat. C],
155.7 [eN]CeH(NH)], 161.7 [eC]O(NH)]; nmax/cmꢁ1 (KBr) 3426,
2926, 1633, 1528, 1465, 1372; m/z (ESI) 355.1 [(MþH)þ, 100%];
HRMSd(ESIþ) requires: 355.1559, found: 355.1569 (C22H19N4O).
4.1.8. 5,6-Bis(1-methyl-1H-indol-3-yl)pyrimidine-2,4(1H,3H)-dione
(8). The bisindolyl-2-thiopyrimidin-4-one derivative 17 (0.100 g,
0.26 mmol) was stirred in the presence of methanol (15 mL) and ethyl
bromoacetate (0.108 g, 0.07 mL, 0.65 mmol, 2.5 equiv) at reflux, for
24 h, prior to the addition of a few drops of water and heating for
a further 24 h. Following evaporation of the solvent under reduced
pressure, a hot DMF/H2O solution (5:1) (15 mL) was added to the
resultant beige residue. The milky slurry was allowed to cool to room
temperature and then filtered under reduced pressure. The resulting
off-white powder was washed with water and diethyl ether succes-
sively, prior to drying under high vacuum overnight, to afford the
Acknowledgements
We are grateful to the Irish Research Council for Science Engi-
neering and Technology (IRCSET) for their financial support
throughout this work.
Supplementary data
Supplementary data associated with this article can be found in
the online version at doi:10.1016/j.tet.2010.10.020.
pure 5,6-bisindolyl uracil
8
(0.044 g, 45%); mp>320 ꢀC; dH
(300 MHz) DMSO-d6 3.63 [3H, s, NeCH3], 3.67 [3H, s, NeCH3],
0
6.75e6.81 [2H, m, aromatic CeH5,5 ], 6.96e7.08 [4H, m, aromatic
References and notes
0
0
0
CeH6,6 ,7,7 ], 7.11 [1H, s, aromatic CeH2 ], 7.24e7.27 [1H, d, J¼8.19 Hz,
0
aromatic CeH4], 7.30e7.33 [1H, d, J¼8.25 Hz, aromatic CeH4 ], 7.50
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[1H, s, aromatic CeH2], 10.69 [1H, br s, amide NeH], 11.12 [1H, br s,
imide NeH]; dC (75 MHz) DMSO-d6 32.3 [NeCH3], 32.7 [NeCH3],
103.8 [aromatic quat. C], 106.6 [aromatic quat. C], 107.4 [aromatic
quat. C], 109.2 [aromatic CeH], 109.9 [aromatic CeH], 118.3 [aro-
matic CeH], 119.5 [aromatic CeH], 119.6 [aromatic CeH], 119.8 [aro-
matic CeH], 120.5 [aromatic CeH], 121.5 [aromatic CeH], 125.1
[aromatic quat. C], 127.6 [aromatic quat. C], 130.5 [aromatic CeH],
131.6 [aromatic CeH], 136.0 [2ꢂaromatic quat. C], 145.2 [aromatic
quat. C], 151.1 [NHeC]O(eNH)], 164.2 [NHeC]O(eC]C)]; nmax
/
cmꢁ1 (KBr) 3425, 2925, 1703, 1639, 1555, 1453; m/z (ESI) 371.1
[(MþH)þ, 80%], 369.1 (40%); HRMSd(ESIþ) requires:371.1508, found:
371.1506 (C22H19N4O2).
4.1.9. 5,6-Bis(1-methyl-1H-indol-3-yl)pyrimidin-4(3H)-one
(22). Thiouracil 17 (0.105 g, 0.26 mmol) was added to a flame-dried
flask along with nickel bromide (0.290 g, 1.3 mmol, 5 equiv) and dry
methanol (10 mL). Sodium borohydride (0.152 g, 3.89 mmol,
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