Synthesis and reactivity of 3-amino-1H-pyrazolo[4,3-c]pyridin-4(5H)-ones: development of a novel kinase-focussed library

Article abstract of DOI:10.1016/j.tet.2010.02.047

3-Amino-1H-pyrazolo[4,3-c]pyridin-4(5H)-ones represent a potentially attractive heteroaromatic scaffold for drug-discovery chemistry. In particular, the arrangement of hydrogen bond donor and acceptor groups in the bicyclic core can fulfil the requirement

Full text of DOI:10.1016/j.tet.2010.02.047

Tetrahedron 66 (2010) 2843–2854
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis and reactivity of 3-amino-1H-pyrazolo[4,3-c]pyridin-4(5H)-ones:
development of a novel kinase-focussed library
,
Lynette A. Smyth a, Thomas P. Matthews a, Peter N. Horton b, Michael B. Hursthouse b, Ian Collins a
*
a Cancer Research UK Centre for Cancer Therapeutics, The Institute of Cancer Research, 15 Cotswold Road, Belmont, Surrey SM2 5NG, UK
b EPSRC UK National Crystallography Service, School of Chemistry, University of Southampton, Highfield, Southampton SO17 1BJ, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
3-Amino-1H-pyrazolo[4,3-c]pyridin-4(5H)-ones represent a potentially attractive heteroaromatic scaf-
fold for drug-discovery chemistry. In particular, the arrangement of hydrogen bond donor and acceptor
groups in the bicyclic core can fulfil the requirements for ATP competitive binding to kinase enzymes.
Efficient and regioselective routes from simple starting materials to novel functionalised 3-amino-1H-
pyrazolo[4,3-c]pyridin-4(5H)-ones and related 3-amino-2H-pyrazolo[4,3-c]pyridines were explored and
adapted for parallel synthesis, resulting in a library of compounds suitable for screening against kinases
and other cancer drug targets. Methods for substituent variation at five distinct positions around the
bicyclic core were devised to generate sets of compounds containing two- or three-point diversity.
Ó 2010 Elsevier Ltd. All rights reserved.
Received 19 November 2009
Received in revised form 21 January 2010
Accepted 8 February 2010
Available online 13 February 2010
Keywords:
Pyridone
Pyrazole
Synthesis
Kinase
1. Introduction
ways. In particular, the presence of several hydrogen bond donor–
acceptor pairs in different spatial relationships renders the scaffold
Medicinal chemistry often relies on the synthesis of core
chemical scaffolds, which can be further derivatised to improve
their biological activity or pharmacokinetic properties. These
scaffolds are often mono- or bicyclic aromatic heterocycles, which
are relatively easy to make and functionalise.1,2 Similarities be-
tween scaffolds are evident when looking at inhibitors of particular
classes of enzymes, which have very distinctive binding pockets.
For example, ATP competitive kinase inhibitors tend to be struc-
turally quite similar as the binding pocket is conserved across the
entire class of enzymes.3,4 This leads to a number of problems, in-
cluding similar scaffolds being identified multiple times in
screening campaigns and therefore limiting access to new chemical
space.5,6 There is therefore a need for new heterocyclic compounds
to be synthesised for screening against new targets.2 This would
give novel start points for drug-discovery projects.
attractive as a potential ligand for the well-characterised ATP bind-
ing site in protein kinase enzymes.5,7 The scaffold also has a number
of possible points at which it can be derivatised. Thus if a member of
the library is found to be active against a particular protein target,
the structure can be rapidly modified to find favourable interactions
to improve the inhibitor’s potency. This is extremely important in
early drug discovery,8 and if the chemistry to functionalise the
scaffold has already been developed, the process can be accelerated.
At the outset of this project, limited prior reports on the syntheses of
3-amino-1H-pyrazolo[4,3-c]pyridin-4(5H)-ones encouraged us that
convenient routes to novel compounds in the library could be
established.9–15 Although 3-amino-1H-pyrazolo[4,3-c]pyridin-
4(5H)-ones have not been previously investigated in the context of
drug discovery, the simpler 3-amino-pyrazolo[4,3-c]pyridines have
some precedent as inhibitors of kinase enzymes.16–18
One problem with starting from a new scaffold can be a lack of
knowledge of its reactivity, so more effort may be required in the
synthesis of analogues. With this in mind, we describe here
the development of a kinase-focussed library where exploration of
the reactivity of scaffold was carried out in parallel with the library
synthesis. The 3-amino-1H-pyrazolo[4,3-c]pyridin-4(5H)-one scaf-
fold (Fig. 1) was chosen because it contains multiple hydrogen bond
donors and acceptors and could bind to protein targets in numerous
Figure 1. General structure of proposed 3-amino-1H-pyrazolo[4,3-c]pyridine-4(5H)-
one kinase inhibitors.
Chemistry was developed to allow parallel syntheses of a library
of scaffolds with two variable substituents starting from simple
building blocks, and a further three positions for derivatisation
* Corresponding author. Tel.: þ44 208 722 4317; fax: þ44 208 722 4205.
E-mail address: ian.collins@icr.ac.uk (I. Collins).
0040-4020/$ – see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.02.047

2844
L.A. Smyth et al. / Tetrahedron 66 (2010) 2843–2854
i
were explored. Importantly, the chemistry was developed to enable
rapid preparation of analogues,19 with the incorporation of parallel
synthesis procedures where possible.
using hydrazine in PrOH and heating at reflux (Scheme 2).12 We
found that a faster reaction was obtained when the mixture was
heated in the microwave in a sealed tube at higher temperatures.
Although this reaction has not been reported for substituted hy-
drazines, similar conditions yielded the N-methylpyrazole com-
pounds 8–11 (Scheme 3).
2. Results and discussion
2.1. Scaffold synthesisdpyridone
There are sporadic reports of the syntheses of 3-amino-1H-
pyrazolo[4,3-c]pyridin-4(5H)-ones.9–15 Our first attempt at pre-
paring the core revealed an unexpected misassignment of the
structure yielded by one literature method.10,11 A more thorough
investigation of the products of the reaction and possible mecha-
nisms for their formations ensued.20 Subsequently, an alternative
route was adopted and successfully led to the desired scaffold.12–15
This synthesis involved the formation of a functionalized pyridone
followed by condensation with hydrazine to install the fused
pyrazole.
Two methods were used to make the pyridone ring. 6-Methyl-
pyridone 1 was conveniently made by direct condensation of ace-
tone and 2-(bis(methylthio)-methylene)malononitrile (Scheme
1A). For the production of 6-phenylpyridone 4, acetophenone was
converted to the bis(methylthio)but-3-en-2-one 3 and condensed
with cyanoacetamide (Scheme 1B). This latter route could also be
used to prepare 1. This was of benefit as the same conditions could
be employed to make both 6-alkyl- and 6-arylpyridones, and were
altered to enable parallel synthesis (Scheme 1C). The disodium salt
2 was no longer isolated before methylation of the sulfurs, as in
some cases the salt was hygroscopic. Rather, methanol and iodo-
methane were added directly to the reaction mixture. In addition
the solvent was changed from toluene to the more volatile THF. This
enabled the rapid parallel synthesis of a set of 12 pyridones bearing
varied alkyl and aryl substituents at C-6.
i
i
Scheme 2. (a) H2N–NH2, PrOH, reflux, 2 h; (b) H2N–NH2, PrOH, m
W, 120 ꢀC, 40 min.
n
Scheme 3. (a) H(Me)N–NH2, Et3N, BuOH, 150 ꢀC,
mW, 20 min.
The regiochemical outcome of the pyrazole forming reaction
was predicted to depend on the nature of the hydrazine used, as
had been shown for the reaction of substituted hydrazines with
other scaffolds.21–24 In the case of methylhydrazine, both N1 and N2
substituted pyrazoles were often observed. Although electronic
effects presumably favoured initial attack of the alkyl substituted,
and thus more nucleophilic, nitrogen at C-4 of the pyridone to give
the N1-substituted product, competing steric factors favoured N2
substitution. Fortunately, the N1 methylpyrazoles 8 and 10 pre-
cipitated from solution (Scheme 3). Substitution at N1 was always
the major regioisomer from the reactions with methylhydrazine,
but in cases where the N2 methyl isomer was also formed, it could
be isolated by preparative TLC from the mother liquors. This syn-
thesis was extended to multiple 4-methylthio-3-cyano-2-pyridone
starting materials.
Although the reactions of methylhydrazine and hydrazine pro-
ceeded under simple microwave conditions, the reaction of phe-
nylhydrazine was not as trivial due to its poor nucleophilicity. To
promote reaction, the thiomethyl substituent was converted into
a better leaving group.25 The sulfur was oxidized with m-CPBA,
making it more electron withdrawing and allowing the SNAr to
proceed, although a further acid catalysed cyclisation step was re-
quired to complete formation of the pyrazole ring (Scheme 4). The
oxidation could be carefully controlled to produce either the sulf-
oxide or sulfone, by varying the stoichiometry of the oxidising
agent. However, since both sulfoxide and sulfone reacted to give the
desired products, it was generally more convenient to prepare
mixtures during the oxidation and use these directly in the dis-
placements. Applying these methods, a 36-membered library of
compounds was synthesised in parallel with two points of varia-
tion; on the pyridone from 12 different methyl ketones and on the
pyrazole from 3 hydrazines.
Scheme 1. (a) (i) KOH, wet DMSO, rt, 8 h (ii) HCl (aq); (b) NaOtBu, CS2, PhCH3, 0 ꢀC, 5 h;
(c) MeI, MeOH, reflux, 15 min; (d) NaOiPr, cyanoacetamide, iPrOH, reflux, 50 min; (e) (i)
CS2, NaOtBu, THF, 0 ꢀC, 4 h, Ar; (ii) MeI, MeOH, reflux, 15 min.
2.2. Scaffold synthesisdpyrazolopyridone
Fused, N-unsubstituted pyrazole rings, such as in 6, had been
introduced previously into 4-methylthio-3-cyano-2-pyridones

L.A. Smyth et al. / Tetrahedron 66 (2010) 2843–2854
2845
amide formation, the excess acid anhydride was removed by re-
action with trisamine resin to capture the remaining anhydride and
the resulting acid by-product was removed by filtration through
a basic ion exchange resin. The scope of urea forming reactions was
somewhat limited, presumably resulting from low nucleophilicity
of the aminopyrazole. Although reactions with aryl isocyanates
generally went well, no reaction was seen with the less electro-
philic alkyl isocyanates. However, reactions with highly activated
isocyanates also failed to give the desired product. For example, 4-
cyanophenylisocyanate decomposed to form the bis-cyanophenyl
urea rather than reacting on the amine.
Scheme 4. (a) m-CPBA, EtOH, rt, 24 h; (b) H2N–N(Ph)H, iPrOH, reflux, 2 h; (c) HCl,
dioxane, reflux, 3 h.
2.3. Scaffold synthesisdregiochemistry
The regiochemistry of substitution for the major and minor N-
methyl isomers 10 and 11 was determined by 1H NMR (NOESY) and
confirmed by X-ray crystallography of 10 (Fig. 2). Likewise, NOESY
and X-ray crystallography confirmed the regiochemistry of 17.
Scheme 5. (a) PhCH2COCl, Et3N, DCM, 0 ꢀC to rt; (b) ArS(O)2Cl, Py, rt, 24 h; (c) ArNCO,
Py, rt; (d) (ArCO)2O, Py, 100 ꢀC, 24 h; (e) benzaldehyde, NaBH3CN, AcOH, NaOAc, EtOH/
H2O (1:1), rt.
Similar functionalisation of the N-phenyl and N-unsubstituted
pyrazolopyridone scaffolds 17 and 6 was attempted but did not
proceed successfully. In the case of 17 no reaction with sulfonyl
chlorides was observed, ascribed to increased steric hindrance from
the aryl substituent and a further reduction in amine nucleophi-
licity. For the N-unsubstituted scaffold 6, mixtures of multiple
products were observed on reaction with sulfonyl chlorides or acid
anhydrides, presumed to result from the multiple reactive nitrogen
atoms present.
Figure 2. Structures of 10, 11 and 17 (arrows show through space interactions between
hydrogens as indicated by NOESY) and ORTEP representation of X-ray crystallographic
structures for 10 and 17.26
2.4. Amine derivatisation
2.5. C7 derivatisationdincorporation into scaffold
A number of different electrophiles could be reacted with the
aminopyrazole motif of the N-methyl pyrazolopyridines such as 8
and 10, although some reactions were more amenable to parallel
synthesis than others (Scheme 5). Sulfonylation and reaction with
isocyanates were high yielding and the resulting products were
isolated by filtration requiring no further purification. Reductive
amination and reactions with benzyl bromide and phenyl acetyl
chloride did require purification due to the presence of by-products
or double addition of the electrophiles. Reactions with acid anhy-
drides and acid chlorides needed excess reagent for complete re-
action, which had to be removed during work-up. Parallel synthesis
protocols for sulfonylation, urea formation and amidations using
acid anhydrides were established for the dimethyl scaffold 8. For
There are a number of possible approaches to adding func-
tionality at the C7 position of the pyrazolopyridone scaffold. One is
to introduce it during the first step of the synthesis. In the example
shown (Scheme 6), 1-phenylpropan-2-one was used to place
a phenyl group at the C7 position and allowed the synthesis of 26–
28. However this method was unsuccessful with substrates bearing
alkyl groups at the same position, as the reaction of the bis-
methylthio compound with cyanoacetamide yielded no pyridine
product, possibly due to the lack of an electron withdrawing aryl
group to raise the acidity of the
a-protons, which have to be re-
moved for the reaction to proceed. Syntheses of 5-alkylpyridones
have been reported in the literature using the alternative route
(Scheme 1A) described for compound 1.15

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L.A. Smyth et al. / Tetrahedron 66 (2010) 2843–2854
Subsequently it was found that the presence of any protic sol-
vents in the reaction mixture led to significant debromination. Al-
though different palladium sources and ligands made little
difference to the yield, the use of a stronger base (NaOtBu) and
higher temperature led to the formation of 27 as the main product
(Scheme 8).
Scheme 8. (a) PhB(OH)2, Pd(PPh3)4, NaOtBu, tol, 150 ꢀC,
mW, 1 h.
This method was used for other Suzuki couplings, for example,
to form 30. Methylpyrazole 8 was also a successful substrate for
carbonylation reactions27 and Heck coupling28 to form 31–35
(Scheme 9). A simple hydrogenation could be used to remove the
double bonds next to the ester groups of 32 and 34. Although these
reactions were not sufficiently high-yielding for parallel synthesis,
a number of compounds with C7 substitution were made.
Scheme 6. (a) (i) CS2, NaOtBu, THF, 0 ꢀC, 5 h; (ii) MeI, MeOH, reflux, 30 min; (b)
i
NCCH2CONH2, NaOiPr, iPrOH, 2 h; (c) H2N–NH2, PrOH, 120 ꢀC,
m
W, 40 min; (d) H2N–
i
N(Me)H, PrOH, 150 ꢀC,
m
W, 1 h; (e) m-CPBA, EtOH, rt, 18 h; (f) H2N–N(Ph)H, iPrOH,
reflux, 2 h; (g) HCl, dioxane, reflux, 30 min.
2.6. C7 derivatisationdlate stage addition to scaffold
A drawback of the approach shown in Scheme 6 was the need to
carry out the entire synthesis for each different analogue. We
therefore sought to add C7 functionality to the preformed scaffold
and investigated bromination of the C7 position followed by pal-
ladium mediated coupling reactions. Bromination of 8 proceeded
smoothly to form 29 in good yield (Scheme 7).
Scheme 9. Compounds made using palladium coupling reactions. Yields given from 29.
2.7. C7 derivatisationdan alternative approach
Scheme 7. (a) NBS, MeOH, reflux, 1 h.
Although both 6 and 16 could also be brominated under the same
conditions as 8, the palladium coupling reactions failed to proceed.
However, going back one step to the pyrazole 1 (Scheme 10), this
could be brominated to give 36 and the couplings carried out before
formation of the fused pyrazoles. Although the yields were generally
low, some compounds inaccessible by the direct coupling route were
made by this method.
However, under standard Suzuki coupling conditions
(Na2CO3(aq), Pd(PPh3)4, DME–EtOH) using 29 and phenylboronic
acid, the main product formed was 8, the debromination product
(Table 1).
Table 1
Conditions for Suzuki coupling reactions to 29
Catalyst
Temperature
(ꢀC)
Solvent
Base
Time
(h)
29/8/27a
Pd(PPh3)4
Pd(PPh3)4
105 (Thermal)
Dioxane
DME/EtOH
(50:50)
DME
Tol
Tol
Tol
Tol
Tol
Tol/MeCN
(95:5)
Na2CO3
Na2CO3(aq)
24
1
100:0:0
0:85:15
100 (
m
W)
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
100 (
100 (
100 (
100 (
130 (
150 (
150 (
m
m
m
m
m
m
m
W)
W)
W)
W)
W)
W)
W)
Cs2CO3
Cs2CO3
K3PO4
1
1
1
1
1
1
1
75:14:11
70:15:15
56:22:22
42:42:16
13:13:74
0:13:87
NaOtBu
NaOtBu
NaOtBu
NaOtBu
0:13:87
Scheme 10. (a) NBS, MeOH, reflux, 1 h; (b) PhB(OH)2, Pd(PPh3)4, NaOtBu, tol/MeCN
(95:5), 150 ꢀC,
mW, 1 h.
a
Conversion as measured by HPLC of crude reaction mixtures.

L.A. Smyth et al. / Tetrahedron 66 (2010) 2843–2854
2847
2.8. C4 derivatisationdchlorination and trial reactions
formation of the pyrazole (Scheme 14). A further step, sulfur oxi-
dation, was required to overcome the pyridine’s reduced electro-
philicity resulting from replacement of the pyridine carbonyl by the
electron donating amino group. Several examples using this se-
quence were demonstrated. Again, both the sulfoxide and sulfone
reacted to form the desired product, so in most cases a mixture was
taken through the synthesis.
To derivatise at the C4 position, POCl3 was used to form chlor-
opyridines 37 and 38 from the pyridones (Scheme 11). This con-
version was also successful for the phenylpyrazoles 16 and 17 using
the same conditions.
Scheme 11. (a) (i) POCl3, 80 ꢀC, 24 h; (ii) water, NaHCO3.
A number of SNAr reactions were attempted from 37 to give 39–
43 (Scheme 12). Reactions with amine nucleophiles were carried
out by microwave heating in nBuOH. Sulfur and oxygen nucleo-
philes in the presence of base also worked, although oxygen nu-
cleophiles required the presence of an excess of the reagent and
otherwise gave poor yields. Other trial reactions using amine nu-
cleophiles were successful and a general work-up was developed
using an acidic ion exchange resin column catch and release
method to remove excess amine. This allowed parallel synthesis of
24 compounds.
Scheme 14. (a) (i) POCl3, 80 ꢀC, 24 h; (ii) NaHCO3, water; (b) piperidine, nBuOH, 160 ꢀC,
i
mW, 30 min; (c) m-CPBA, EtOH, 6 h, rt; (d) H2N–NH2, PrOH, reflux, 6 h.
3. Conclusions
In summary, the syntheses of four distinct polysubstituted
pyrazolopyridone scaffolds were developed (Fig. 3). Of the four
synthetic sequences, three were amenable to medium-throughput
parallel synthesis, although in some cases this was limited to spe-
cific starting materials. This chemistry enabled the synthesis of sets
of compounds with two or three points of variation around the core
scaffold. In total a library of approximately 200 novel compounds
was prepared according to these methods, the biological charac-
terisation of which will be reported separately. We have demon-
strated how the pyrazolopyridone scaffold can be efficiently
derivatised at several positions around the molecule. The ability to
rapidly prepare analogues of the initial library is likely to be of
benefit for the further investigation of pyrazolopyridone com-
pounds arising as hits in targeted drug-discovery screens, enabling
exploration of possible binding modes and improvements to the
compound activity.
Scheme 12. (a) Piperidine, nBuOH, 160 ꢀC, W, 30 min; (b) aniline, nBuOH, 160 ꢀC,
m mW,
30 min; (c) PhSH, K2CO3, MeCN, reflux, 3 h; (d) NaOiPr, iPrOH, reflux, 18 h; (e) PhOH,
Cs2CO3, DMSO, 130 ꢀC, 18 h.
Bi-functional reagents could be reacted with 37 to form a third
fused ring as shown (Scheme 13). Thus glycine methyl ester was used
as the nucleophile and also functioned as an electrophile reacting
with the aminopyrazole to form the novel tricyclic scaffold 44.
Figure 3. Summary of the substitution patterns accessible using parallel synthetic
chemistry to prepare a library of approximately 200 compounds.
n
Scheme 13. (a) H2NCH2COOMe$HCl, Et3N, BuOH, 160 ꢀC,
m
W, 30 min.
4. Experimental
2.9. C4 derivatisationdalternative route
4.1. General experimental
For the unsubstituted pyrazole 6, although the POCl3 chlorina-
tion seemed to yield some product by LCMS and 1H NMR analysis, it
quickly decomposed, so an alternative approach was sought. Re-
action of the intermediate pyridone 1 with POCl3 gave chloropyr-
idine 45, which then underwent SNAr reactions before the
All reagents and anhydrous solvents were obtained from com-
mercial suppliers and used without further purification. Infrared
spectra were recorded on a Perkin–Elmer Spectrum RX-1 FT-IR
spectrometer. 1H and 13C nuclear magnetic resonance spectra were
recorded at 500 MHz and 126 MHz, respectively, on Bruker

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L.A. Smyth et al. / Tetrahedron 66 (2010) 2843–2854
i
AMX500 spectrometers using an internal deuterium lock. Micro-
analysis was carried out by Warwick Analytical Service, and X-ray
crystallography was carried out by the EPSRC UK National Crystal-
lography Service at the University of Southampton. HPLC-MS
analyses were performed on a Micromass LCT/Waters Alliance
2795 HPLC system with Phenomenex Gemini (PG) or Merck Chro-
molith SpeedROD (MC) columns at 22 ꢀC, eluting with a MeOH/
water gradient. UV detection was at 254 nm and ionisation was by
positive or negative ion electrospray. Molecular weight scan range
was 50-1000. HRMS values were determined on an Agilent 6210 ToF
phenylhydrazine (10 equiv) were stirred in PrOH at reflux for 2 h.
The 6-methyl-2-oxo-4-(2-phenylhydrazinyl)-1,2-dihydropyridine-
3-carbonitriles formed were collected by filtration. Where the
compounds did not precipitate from PrOH, ether or ethyl acetate
i
was used to aid precipitation of the product.
The 2-oxo-4-(2-phenylhydrazinyl)-1,2-dihydropyridine-3-car-
bonitriles (0.05 M) were isolated and cyclised by heating at reflux in
1 M HCl in dioxane for 2 h, whereupon the product precipitated out
of solution as the HCl salt.
MS with a Phenomenex Gemini 3
Suitable crystals were selected and data collected on a Bruker
Nonius KappaCCD Area Detector at the window of a Bruker Nonius
m
C18 (3 cmꢁ4.6 mm i.d.) column.
4.1.7. General method G: Suzuki couplings to 5-bromopyridin-2-ones
and 7-bromo-1H-pyrazolo[4,3-c]pyridin-4(5H)-ones. The appropri-
ate heteroaromatic bromide (0.06 M) and boronic acid (2.2 equiv)
were stirred in toluene/MeCN (95:5) in a microwave vial for 5 min
while bubbling Ar through the suspension. NaOtBu (3 equiv) and
Pd(PPh3)4 (0.05 equiv) were added and the mixture was stirred for
a further 10 min while purging with Ar. The vial was sealed and
heated in the microwave for 1 h at 150 ꢀC. The solvent was removed
in vacuo and the residue purified.
FR591 rotating anode (Mo K
a
¼0.71073 Å) driven by COLLECT29 and
DENZO30 software at 120 K. The structures were determined in
SHELXS-97331 and refined using SHELXL-974.32 Crystallographic
data (excluding structure factors) for the structures in this paper
have been deposited with the Cambridge Crystallographic Data
Centre as supplementary publication numbers 751882 and 751883.
Copies of the data can be obtained, free of charge, on application to
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (Fax: þ44(0)-1223-
336033 or e-mail: deposit@ccdc.cam.ac.uk).
4.1.8. General method H: bromination of pyridin-2-ones and pyr-
azolo[4,3-c]pyridin-4(5H)-ones. The appropriate heteroaromatic
compound (0.1 M) and N-bromosuccinimide (1.2 equiv) were stir-
red in refluxing MeOH for 1 h. The solvent was removed in vacuo
and the residue was washed with water. The product was collected
by filtration.
4.1.1. General method A: bis(methylthio)but-3-en-2-ones. NaOtBu
(2 equiv) in dry toluene was stirred at 0 ꢀC under Ar for 10 min. The
appropriate ketone (0.3 M) was added followed by CS2 (1 equiv).
The solution was stirred for a further 4 h at 0 ꢀC whereupon the
disodium salt was collected by filtration, washed using hexane and
dried in a vacuum dessicator over silica. Dry MeOH (1 M) and MeI
(2 equiv) were added to the salt. This solution was heated at reflux
for 15 min. Water was added and the desired bis(methylthio)but-3-
en-2-ones precipitated from the solution and were isolated by fil-
tration unless otherwise stated.
4.1.9. General method I: chlorination of pyridin-2-ones and pyr-
azolo[4,3-c]pyridin-4(5H)-ones. The appropriate heteroaromatic
compound (0.12 M) was stirred in POCl3 for 20 h at 80 ꢀC. The
yellow suspension was added to iced water (10ꢁPOCl3 volume).
After leaving for 30 min to quench, NaHCO3 was slowly added to
neutralise the solution. The aqueous solution was extracted with
CH2Cl2 (5ꢁ30 mL), the combined organic extracts were dried
(Na2SO4) and the solvent was removed in vacuo to leave a pale
yellow solid. Purification was carried out by flash column chro-
matography, eluting with EtOAc/Pet unless otherwise stated.
4.1.2. General method B: pyridone formation from the bis(methylth-
io)but-3-en-2-ones. NaOiPr was made by the dissolution of sodium
i
(1.1 equiv) in PrOH. To this was added cyanoacetamide (1 equiv)
and the appropriate 1-substituted-4,4-bis(methylthio)but-3-en-2-
ones (0.29 M). The mixture was stirred at reflux for 2 h and the
solid formed was dissolved by the addition of water. The 4-
4.1.10. General method J: SNAr displacements of 2-chloropyridines
and 4-chloro-1H-pyrazolo[4,3-c]pyridines. The appropriate hetero-
aromatic chloride (0.45 M) and amine (3.1 equiv) in nBuOH were
heated in the microwave at 160 ꢀC for 30 min. The resulting mix-
ture was dissolved in MeOH/CH2Cl2 (50:50), absorbed on a pre-
pared isolute SCX-2 ion exchange column and washed through
with two column volumes of the solvent mixture. The product was
released using 0.1 M NH3 in MeOH and the solvent was removed in
vacuo to give the products.
(methylthio)-2-oxo-1,2-dihydropyridine-3-carbonitriles
pre-
cipitated on neutralisation with 10% HCl solution and were isolated
by filtration.
4.1.3. General method C: N-unsubstituted pyrazolopyridones. The
appropriate 4-(methylthio)-2-oxo-1,2-dihydropyridine-3-carbon-
itriles were placed in a microwave reaction vessel with iPrOH
(0.25 M) and hydrazine hydrate (20 equiv). This mixture was
heated at 120 ꢀC for 40 min. The products precipitated on cooling
and were collected by filtration unless otherwise stated.
4.1.11. 6-Methyl-4-(methylthio)-2-oxo-1,2-dihydropyridine-3-car-
bonitrile (1)15,34. Method (i):
A mixture of 2-(bis(methylth-
io)methylene)malononitrile (2.00 g, 11.8 mmol), wet DMSO
(35 mL), acetone (8.62 mL, 118 mmol) and ground KOH pellets
(2.64 g, 47.1 mmol) was stirred at rt for 8 h. The brown suspension
was poured into iced water (120 mL) then acidified with 10% HCl
solution. The red-brown precipitate, which formed was collected
by filtration and washed with hot MeOH to give 1 as a pale orange
solid (1.46 g, 8.13 mmol, 69%).
4.1.4. General method D: N-methylpyrazolopyridones. The appro-
priate 4-(methylthio)-2-oxo-1,2-dihydropyridine-3-carbonitriles
i
were placed in a microwave reaction vessel with PrOH (0.25 M)
and methylhydrazine (5 equiv). The mixture was heated at 150 ꢀC
for 20 min. Over this time the products precipitated and were
collected by filtration and the solid washed with cold nBuOH.
Method (ii): General method A, using acetone (0.24 mL,
3.23 mmol). The disodium salt was not isolated. Instead, MeOH and
MeI were added to the reaction mixture in toluene and this mixture
was heated at reflux for 15 min. The solvent was removed in vacuo.
The residue was partitioned between water (20 mL) and ethyl ac-
etate (3ꢁ20 mL). The combined organic extracts were dried using
brine followed by Na2SO4. Upon removal of the solvent, the brown
oil was purified by recrystallisation from hexane to give pale brown
4.1.5. General method E: oxidation of 4-(methylthio)pyridones. The
appropriate 4-(methylthio)-2-oxo-1,2-dihydropyridine-3-carbon-
itrile (0.07 M) was stirred at rt in EtOH with m-CPBA (ꢂ77% by wt,
5 equiv) for 24 h. The product was isolated by filtration and taken
on to the next step.
4.1.6. General method F: N-phenylpyrazolopyridones. The 4-(meth-
ylsulfinyl)-2-oxo-1,2-dihydropyridine-3-carbonitriles (0.25 M) and
needles of 4,4-bis(methylthio)but-3-en-2-one
5
(217 mg,

L.A. Smyth et al. / Tetrahedron 66 (2010) 2843–2854
2849
1.34 mmol, 41%); mp 66–69 ꢀC (hexane) (lit. 67 ꢀC; petrol ether)14
;
(10:90, MeOH/CH2Cl2); IR (Nujol mull, cmꢃ1) 3413 (NH2), 1653
(C]O); 1H NMR (500 MHz, (CD3)2SO) dH 5.21 (2H, br s, NH2), 6.40
(1H, br s, C7-H), 7.43–7.48 (3H, m, ArH), 7.69–7.71 (2H, m, ArH),
10.81 (1H, br s, NH), 11.89 (1H, br s, NH); 13C NMR (126 MHz,
(CD3)2SO) dC 90.5, 98.3, 126.8, 128.7, 129.2, 134.2, 143.2, 145.4,
152.1, 160.6; MS (ESI) m/z 227 (MþH)þ; HRMS (MþH)þ calcd for
C12H11N4O¼227.0933, found¼227.0929; HPLC (PG) tR¼3.17 min;
purity ꢄ95%. Anal. Calcd for C12H10N4O$0.1(H2O): C, 63.21; H,
4.51; N, 24.57%. Found C, 63.25; H, 4.22; N, 24.60%.
Rf¼0.67 (10:90, MeOH/CH2Cl2); IR (Nujol mull, cmꢃ1) 1639 (C]O);
1H NMR (500 MHz, CDCl3) dH 2.20 (3H, s, C-CH3), 2.45 (3H, s, S-CH3),
2.48 (3H, s, S-CH3), 6.05 (1H, s, C5-H); 13C NMR (126 MHz,
(CD3)2CO) dC 14.6 (CH3), 17.5, (CH3), 30.2 (CH3), 114.2 (CH), 162.2,
192.2; MS (ESI) m/z 163 (MþH)þ; HRMS (MþH)þ calcd for
C6H11OS2¼163.0246, found¼163.0243; HPLC (PG) tR¼3.31 min;
purity ꢄ95%.
4,4-Bis(methylthio)but-3-en-2-one (5) (200 mg, 1.23 mmol)
was subjected to the conditions described in general method B to
give 1 as a pale yellow solid (131 mg, 0.72 mmol, 59%). A sample
was recrystallised from MeOH; mp 327–328 ꢀC (MeOH) (lit. 325 ꢀC;
4.1.16. 3-Amino-1,6-dimethyl-1H-pyrazolo[4,3-c]pyridin-4(5H)-one
(8) and 3-amino-2,6-dimethyl-2H-pyrazolo[4,3-c]pyridin-4(5H)-one
(9). General method D. Compound 8: small colourless crystals
(244 mg, 1.37 mmol, 62%); mp 290–291 ꢀC; Rf¼0.57 (20:80, MeOH/
CH2Cl2); IR (Nujol mull, cmꢃ1) 1635 (C]O); 1H NMR (500 MHz,
(CD3)2SO) dH 2.14 (3H, s, C-CH3), 3.57 (3H, s, N-CH3), 5.15 (2H, s,
NH2), 6.11 (1H, s, C7-H), 10.59 (1H, s, NH); 13C NMR (126 MHz,
(CD3)2SO) dC 18.9, 34.6, 90.1, 98.1, 141.9, 144.7, 152.1, 159.9. MS (ESI)
m/z 179 (MþH)þ; HRMS (MþH)þ calcd for C8H11N4O¼179.0933,
found¼179.0931; HPLC (PG) tR¼2.04 min; purity ꢄ95%. Anal. Calcd
for C8H10N4O: C, 53.92; H, 5.66; N, 31.44%. Found C, 53.74; H, 5.63;
N, 31.11%.
A second isomer was also isolated from the mother liquor by
prep. TLC eluting with MeOH/CH2Cl2 (10:90) 9: Pale brown powder
(6.4 mg, 0.04 mmol, 2%); mp 229–233 ꢀC (phase change 186 ꢀC);
Rf¼0.50 (20:80, MeOH/CH2Cl2); IR (Nujol mull, cmꢃ1) 1628 (C]O);
1H NMR (500 MHz, (CD3)2SO) dH 2.04 (3H, s, C-CH3), 3.56 (3H, s, N-
CH3), 5.79 (1H, s, C7-H), 6.09 (2H, s, NH2), 9.99 (1H, s, NH); 13C NMR
(126 MHz, (CD3)2SO) dC 19.0, 34.0, 94.7, 95.1, 139.4, 146.3, 149.2,
161.1; MS (ESI) m/z 179 (MþH)þ; HRMS (MþH)þ calcd for
C8H11N4O¼179.0933, found¼179.0931; HPLC (PG) tR¼1.78 min;
purity ꢄ95%.
MeOH)34; Rf¼0.74 (10:90, MeOH/CH2Cl2); IR (Nujol mull, cmꢃ1
)
2210 (CN), 1565 (C]O); 1H NMR (500 MHz, (CD3)2SO) dH 2.26 (3H,
s, C-CH3), 2.57 (3H, s, S-CH3), 6.28 (1H, s, CH), 12.21 (1H, br s, NH);
13C NMR (126 MHz, (CD3)2SO) dC 14.3, 19.1, 93.3, 101.4, 115.4, 151.2,
159.9, 164.0; MS (ESI) m/z 181 (MþH)þ; HRMS (MþH)þ calcd for
C8H9N2OS¼181.0436, found¼181.0434; HPLC (PG) tR¼2.50 min;
purity ꢄ95%. Anal. Calcd for C8H8N2OS: C, 53.31; H, 4.47; N, 15.54%.
Found C, 53.09; H, 4.34; N, 15.62%.
4.1.12. 3, 3-Bis(methylthio)-1-phenylprop-2-en-1-one
(3)14,35. General method A, using acetophenone (0.97 mL,
8.33 mmol) to give pale yellow precipitate (1.12 g, 5.02 mmol, 66%).
Purified by recrystallisation from EtOH to give bright yellow nee-
dles of 3 (1.06 g, 4.72 mmol, 57%); mp 89–93 ꢀC (EtOH) (lit. 92.5–
94 ꢀC)35; Rf¼0.74 (50:50, EtOAc/hexane); IR (Nujol mull, cmꢃ1
)
1667 (C]O); 1H NMR (500 MHz, CDCl3) dH 2.56 (3H, s, CH3), 2.57
(3H, s, CH3), 6.79 (1H, s, CH), 7.44–7.47 (2H, m, ArH), 7.50–7.53 (1H,
m, ArH), 7.92–7.94 (2H, m, ArH); 13C NMR (126 MHz, CDCl3) dC 15.2,
17.5, 110.3, 128.8, 129.7, 133.1, 140.6, 170.2, 187.6; MS (ESI) m/z 225
(MþH)þ; HRMS (MþH)þ calcd for C11H13OS2¼225.0408,
found¼225.0406; HPLC (PG) tR¼4.41 min; purity ꢄ95%. Anal. Calcd
for C11H12OS2: C, 58.89; H, 5.39%. Found C, 58.70; H, 5.37%.
4.1.17. 3-Amino-1-methyl-6-phenyl-1H-pyrazolo[4,3-c]pyridin-
4(5H)-one (10) and 3-amino-2-methyl-6-phenyl-2H-pyrazolo[4,3-c]
pyridin-4(5H)-one (11). General method D. Compound 10: cream
coloured solid (482 mg, 2.01 mmol, 67%). A sample was recrystal-
lised from AcOH; mp 255–259 ꢀC (AcOH); Rf¼0.71 (20:80, MeOH/
CH2Cl2); IR (Nujol mull, cmꢃ1) 1641 (C]O); 1H NMR (500 MHz,
(CD3)2SO) dH 3.69 (3H, s, CH3), 5.27 (2H, s, NH2), 6.70 (1H, s, C7-H),
7.45–7.49 (3H, m, ArH), 7.74–7.78 (2H, m, ArH), 10.83 (1H, br s, NH);
13C NMR (126 MHz, (CD3)2SO) dC 34.8 (CH3), 90.6 (CH), 98.6, 126.8
(CH), 128.6 (CH), 129.3 (CH), 134.1, 143.2, 144.6, 152.2, 160.2; MS
4.1.13. 4-(Methylthio)-2-oxo-6-phenyl-1,2-dihydropyridine-3-car-
bonitrile (4)13,34. General method B, using 3 (5.06 g, 22.5 mmol).
The pale yellow solid formed was collected by filtration and washed
with EtOAc to give 4 (4.82 g, 19.9 mmol, 88%). A sample was
recrystallised from acetone/water (1:1); mp 292–293 ꢀC (279–
284 ꢀC phase change) (acetone/water) (lit. 282 ꢀC; MeOH)34
;
Rf¼0.50 (80:20, EtOAc/hexane); IR (Nujol mull, cmꢃ1) 2214 (CN),
1648 (C]O); 1H NMR (500 MHz, (CD3)2SO) dH 2.70 (3H, s, CH3), 6.58
(1H, br s, C5-H), 7.52–7.60 (3H, m, ArH), 7.84 (2H, d, J¼7.0 Hz, ArH),
12.46 (1H, br s, NH); 13C NMR (126 MHz, (CD3)2SO) dC 13.9, 94.6,
100.1,115.3,127.8,128.8, 131.2,132.2,150.3,160.3,163.9; MS (ESI) m/
z 243 (MþH)þ; HRMS (MþH)þ calcd for C13H11N2OS¼243.0592,
found¼243.0583; HPLC (PG) tR¼4.41 min; purity ꢄ95%.
(ESI)
m/z
241
(MþH)þ;
HRMS
(MþH)þ
calcd
for
C13H13N4O¼241.1089, found¼241.1078; HPLC (PG) tR¼3.55 min;
purity ꢄ95%. Anal. Calcd for C13H12N4O$0.1(H2O): C, 64.50; H, 5.08;
N, 23.14%. Found C, 64.68; H, 5.01; N, 22.85%.
A second isomer was isolated from the mother liquor by prep.
TLC eluting with MeOH/CH2Cl2 (6:94) 11: White solid (13 mg,
0.05 mmol, 7%); mp 253–256 ꢀC; Rf¼0.74 (20:80, MeOH/CH2Cl2); IR
(Nujol mull, cmꢃ1) 1646 (C]O); 1H NMR (500 MHz, (CD3)2SO) dH
3.62 (3H, s, CH3), 6.22 (2H, s, NH2), 6.35 (1H, br d, J¼1.5 Hz, C7-H),
7.38–7.45 (3H, m, ArH), 7.66–7.68 (2H, m, ArH), 10.24 (1H, br s, NH);
13C NMR (126 MHz, (CD3)2SO) dC 34.3, 95.4, 95.6, 126.4, 128.6, 128.7,
134.8, 141.5, 146.5, 148.9, 161.3; MS (ESI) m/z 241 (MþH)þ; HRMS
(MþH)þ calcd for C13H13N4O¼241.1089, found¼241.1085; HPLC
(PG) tR¼3.62 min; purity ꢄ95%.
4.1.14. 3-Amino-6-methyl-2H-pyrazolo[4,3-c]pyridin-4(5H)-one ac-
etate (6)12. General method C. Pale brown solid (67 mg, 0.41 mmol,
51%). A sample was recrystallised from AcOH; mp 314–317 ꢀC
(AcOH); (lit. 368 ꢀC; AcOH)12; Rf¼0.40 (20:80, MeOH/CH2Cl2); IR
(Nujol mull, cmꢃ1) 3415 (NH2). 3283 (NH), 1663 (C]O); 1H NMR
(500 MHz, (CD3)2SO) dH 1.91 (3H, s, CH3COOH), 2.16 (3H, s, CH3),
5.16 (2H, s, NH2), 5.94 (1H, s, C7-H), 10.56 (1H, s, NH), 11.80 (1H, br s,
NH); 13C NMR (126 MHz, (CD3)2SO) dC 18.8 (AcOH), 21.0, 91.1, 97.9,
141.6, 145.6, 152.2, 160.3, 172.0 (AcOH); MS (ESI) m/z 165 (MþH)þ;
HRMS (MþH)þ calcd for C7H9N4O¼165.0776, found¼165.0779;
HPLC (PG) tR¼1.30 min; purity ꢄ95%. Anal. Calcd for C7H8N4O-
$AcOH$0.1(H2O): C, 47.83; H, 5.44; N, 24.79%. Found C, 47.56; H,
5.64; N, 24.41%.
4.1.18. 4-(Methylsulfinyl)-2-oxo-6-phenyl-1,2-dihydropyridine-3-
carbonitrile (13). General method E. Bright yellow solid (87 mg,
0.33 mmol, 82%); mp 300–302 ꢀC; IR (Nujol mull, cmꢃ1) 2216 (CN),
1668 (C]O), 1027 (S]O); 1H NMR (500 MHz, (CD3)2SO) dH 2.96
(3H, s, CH3), 7.05 (1H, br s, C5-H), 7.55–7.64 (3H, m, ArH), 7.89 (2H, d,
J¼7.0 Hz, ArH), 13.19 (1H, br s, NH); HMQC (500 MHz, (CD3)2SO,
water) dC 41.2 (CH3), (C7-H not observed), 127.8 (ArCH), 128.9
(ArCH), 131.8 (ArCH); MS (ESI) m/z 259 (MþH)þ; HRMS (MþNa)þ
4.1.15. 3-Amino-6-phenyl-1H-pyrazolo[4,3-c]pyridin-4(5H)-one
(7)12. General method C. White crystalline solid (38 mg,
0.17 mmol, 67%); mp 321–323 ꢀC (lit. 320 ꢀC; AcOH)12; Rf¼0.42

2850
L.A. Smyth et al. / Tetrahedron 66 (2010) 2843–2854
calcd for C13H10N2O2SNa¼281.0355, found¼281.0353; HPLC (PG)
tR¼3.09 min; purity ꢄ95%.
sulfonyl chloride (45.3 mg, 0.22 mmol) and 8 (35.6 mg, 0.2 mmol)
were stirred at rt in dry pyridine (1.2 mL) for 18 h. Water was added
and 19 was collected by filtration as a white solid (63 mg,
0.18 mmol, 91%); IR (Nujol mull, cmꢃ1) 3584, 3113 (NH), 1652
(C]O), 1338, 1163 (S]O); 1H NMR (500 MHz, (CD3)2SO) dH 2.17
(3H, s, C-CH3), 3.69 (3H, s, N-CH3), 3.81 (3H, s, O-CH3), 6.26 (1H, s,
C7-H), 7.16 (1H, ddd, J¼8.0, 2.5, 1.0 Hz, ArH), 7.43 (1H, dd, J¼8.0,
8.0 Hz, Ar ArH), 7.51 (1H, ddd, J¼8.0, 1.5, 1.0 Hz, ArH), 7.56 (1H, dd,
J¼2.5, 1.5 Hz, ArH), 10.00 (1H, br s, NH), 10.93 (1H, br s, NH); 13C
NMR (126 MHz, (CD3)2SO) dC 18.8, 35.4, 55.5, 89.9, 102.6, 112.1,
118.7, 119.3,129.8, 141.3, 142.2, 142.7, 145.3, 158.3, 159.0; MS (ESI) m/
z 349 (MþH)þ; HRMS (MþH)þ calcd for C15H17N4O4S¼349.0965,
found¼349.0971; HPLC (PG) tR¼3.44; purity ꢄ95%. Anal. Calcd for
C15H16N4O4S$0.75(H2O): C, 49.78; H, 4.87; N, 15.48%. Found C,
49.49; H, 4.78; N, 15.31%.
4.1.19. 3-Amino-6-methyl-2-phenyl-2H-pyrazolo[4,3-c]pyridin-
4(5H)-one (16). General methods E and F. The product was isolated
as the HCl salt by filtration as a white solid. This was dissolved in
water (100 mL) and the solution was neutralised using saturated
NaHCO3 solution. The aqueous solution was extracted with CH2Cl2
(3ꢁ30 mL), the combined organic extracts dried (Na2SO4) and the
solvent was removed in vacuo to leave 16 as a white solid (1.03 g,
4.27 mmol, 39%); mp 300–304 ꢀC; Rf¼0.56 (10:90, MeOH/CH2Cl2);
IR (Nujol, cmꢃ1) 3404 (NH2), 3263, 3156 (NH), 1653 (C]O); 1H NMR
(500 MHz, (CD3)2SO) dH 2.11 (3H, s, C-CH3), 5.92 (1H, s, C7-H), 6.25
(2H, s, NH2), 7.35–7.46 (1H, m, ArH), 7.54 (2H, dd, J¼7.5, 7.5 Hz, ArH),
7.62 (2H, d, J¼7.5 Hz, ArH), 10.22 (1H, s, NH); 13C NMR (126 MHz,
(CD3)2SO) dC 19.1, 94.6, 96.0, 123.3, 127.1, 129.3, 138.2, 140.9, 146.3,
150.4, 162.6; MS (ESI) m/z 241 (MþH)þ; HRMS (MþH)þ calcd for
C13H13N4O¼241.1084, found¼241.1089; HPLC (PG) tR¼3.28 min;
purity ꢄ95%. Anal. Calcd for C13H12N4O: C, 64.99; H, 5.03; N, 23.32%.
Found C, 64.78; H, 4.96; N, 23.32%.
4.1.23. 1-(1,6-Dimethyl-4-oxo-4,5-dihydro-1H-pyrazolo[4,3-c]pyr-
idin-3-yl)-3-(3-methoxyphenyl)urea (20). 3-Methoxyphenyl iso-
cyanate (32.8 mg, 0.22 mmol) and 8 (35.6 mg, 0.2 mmol) were
stirred at rt in dry pyridine (1.2 mL) for 18 h. Water was added and
20 was collected by filtration as a white solid (31 mg, 0.095 mmol,
47%); IR (Nujol mull, cmꢃ1) 3390, 3268 (NH), 1703, 1661, 1633
(C]O); 1H NMR (500 MHz, (CD3)2SO) dH 2.21 (3H, s, C-CH3), 3.28
(3H, s, O-CH3), 3.74 (3H, s, N-CH3), 6.33 (1H, s, C7-H), 6.60 (1H, dd,
J¼8.0, 2.0 Hz, ArH), 6.99 (1H, dd, J¼8.0, 2.0 Hz, ArH), 7.20 (1H, dd,
J¼8.0, 8.0 Hz, ArH), 7.24 (1H, br dd, J¼2.0, 2.0 Hz, ArH), 8.21 (1H, s,
NH), 9.78 (1H, s, NH), 11.06 (1H, br s, NH); 13C NMR (126 MHz,
(CD3)2SO) dC 19.0, 35.3, 55.0, 90.3, 99.6, 104.4, 107.9, 110.9, 129.6,
140.4, 143.1, 144.1, 144.6, 150.5, 159.3, 159.7; MS (ESI) m/z 328
(MþH)þ; HRMS (MþH)þ calcd for C16H18N5O3¼328.1404,
found¼328.1404; HPLC (PG) tR¼4.36; purity ꢄ95%. Anal. Calcd for
C16H17N5O3: C, 58.71; H, 5.23; N, 21.39%. Found C, 58.34; H, 5.13; N,
21.77%.
4.1.20. 3-Amino-2,6-diphenyl-2H-pyrazolo[4,3-c]pyridin-4(5H)-one
(17). General method F: 2-Oxo-6-phenyl-4-(2-phenylhydrazinyl)-
1,2-dihydropyridine-3-carbonitrile (15) was isolated as a pale yellow
solid (480 mg, 1.59 mmol, 85%); 1H NMR (500 MHz, (CD3)2SO) dH
6.21 (1H, br s, C5-H), 6.73 (2H, d, J¼8.0 Hz, ArH), 6.77 (1H, t, J¼7.5 Hz,
ArH), 7.19 (2H, dd, J¼8.0, 7.5 Hz, ArH), 7.45–7.50 (3H, m, ArH), 7.61
(2H, d, J¼6.5 Hz, ArH), 8.13 (1H, s, NH), 9.41 (1H, s, NH),11.50 (1H, br s,
NH); MS (ESI) m/z 303 (MþH)þ; HPLC (PG) tR¼4.40 min purity ꢄ95%.
After acid treatment of 15, the resulting crude 17 was dissolved in the
minimum amount of CH2Cl2:MeOH (50:50), passed through a pre-
pared isolute SCX-2 ion exchange column and washed through with
two column volumes of the solvent mixture. The product was eluted
in a 0.1 M solution of NH3 in MeOH to give 17 a white solid on re-
moval of the solvent (442 mg, 1.46 mmol, 90%); mp 250–253 ꢀC;
Rf¼0.20 (10:90, MeOH/CH2Cl2); IR (Nujol mull, cmꢃ1) 3430, 3344
(NH2), 3097 (NH),1659 (C]O); 1H NMR (500 MHz, (CD3)2SO) dH 6.34
(2H, s, NH2), 6.46 (1H, s, C7-H), 7.41–7.48 (4H, m, ArH), 7.55 (2H, dd,
J¼8.0, 8.0 Hz, ArH), 7.65 (2H, dd, J¼8.5, 1.0 Hz, ArH), 7.72 (2H, dd,
J¼8.0, 1.5 Hz, ArH), 10.44 (1H, s, NH); 13C NMR (126 MHz, CDCl3) dC
96.6, 97.4, 124.0, 126.1, 128.4, 129.2, 129.5, 129.9, 135.2, 137.7, 142.5,
145.8, 151.0, 162.2; MS (ESI) m/z 303 (MþH)þ; HRMS (MþH)þ calcd
for C18H15N4O¼303.1240, found¼303.1247; HPLC (PG) tR¼4.41 min;
purity ꢄ95%. Anal. Calcd for C18H14N4O: C, 71.51; H, 4.67; N, 18.53%.
Found C, 71.46; H, 4.57; N, 18.55%.
4.1.24. 4-Methoxy-N-(1-methyl-4-oxo-6-phenyl-4,5-dihydro-1H-
pyrazolo[4,3-c]pyridin-3-yl)benzamide (21). 4-Methoxybenzoic an-
hydride (215 mg, 0.75 mmol) and 10 (36 mg, 0.15 mmol) were
stirred at 100 ꢀC in dry pyridine (0.8 mL) for 24 h. The majority of
the pyridine was removed by evaporation. Toluene was added and
then evaporated in vacuo to remove the remaining pyridine as an
azeotrope. The residue was dissolved in CH2Cl2 (2 mL) and stirred
with PS-trisamine for 18 h. MeCN (2 mL) was added and the solu-
tion was passed through an isolute NH2 ion exchange column. Two
fractions were collected separately, the first by eluting with MeCN/
CH2Cl2 (50:50) and a second using MeOH. The solvent was removed
to give 21 (35 mg, 0.09 mmol, 62%); IR (Nujol mull, cmꢃ1) 3398,
3170 (NH), 1654 (C]O); 1H NMR (500 MHz, (CD3)2SO) dH 3.85 (3H,
s, O-CH3), 3.94 (3H, s, N-CH3), 6.91 (1H, s, C7-H), 7.08 (2H, d,
J¼9.0 Hz, ArH), 7.47–7.53 (3H, m, ArH), 7.78 (2H, dd, J¼8.0, 1.5 Hz,
ArH), 7.97 (2H, d, J¼9.0 Hz, ArH), 10.04 (1H, s, NH), 11.10 (1H, s, NH);
13C NMR (126 MHz, (CD3)2SO) dC 35.6, 55.4, 90.4, 105.1, 113.7, 125.1,
127.1, 128.7, 129.6, 129.6, 133.9, 142.8, 143.7, 145.2, 158.7, 162.1,
164.6; MS (ESI) m/z 375 (MþH)þ; HRMS (MþH)þ calcd for
C21H19N4O3¼375.1452, found¼375.1456; HPLC (PG) tR¼4.42; purity
ꢄ95%. Anal. Calcd for C20H18N4O$0.4(H2O): C, 62.23; H, 4.13; N,
14.51%. Found C, 61.91; H, 3.94; N, 14.25%.
4.1.21. N-(1-Methyl-4-oxo-6-phenyl-4,5-dihydro-1H-pyrazolo[4,3-
c]pyridin-3-yl)-2-phenylacetamide (18). To
a suspension of 10
(50 mg, 0.21 mmol) in CH2Cl2 (4.9 mL) at 0 ꢀC was added phenyl-
acetylchloride (0.061 mL, 0.54 mmol) and Et3N (0.093 mL,
0.56 mmol). The mixture was stirred for 5 min at 0 ꢀC, warmed to rt
and stirred for 24 h. Water was added and the precipitated product
was collected by filtration. Preparative TLC eluting with MeOH/
CH2Cl2 (10:90) gave 18 as a white solid (9 mg, 0.025 mmol, 12%);
mp 267–268 ꢀC; 1H NMR (500 MHz, (CD3)2SO) dH 3.73 (2H, s, CH2),
3.90 (3H, s, N-CH3), 6.90 (1H, s, C7-H), 7.25 (1H, t, J¼8.0 Hz, ArH),
7.33 (2H, dd, J¼8.0, 8.0 Hz, ArH), 7.38–7.41 (2H, br, ArH), 7.49–7.53
(3H, m, ArH), 7.79 (2H, dd, J¼7.5, 1.5 Hz, ArH), 9.83 (1H, br s, NH),
11.16 (1H, br s, NH); HMQC (500 MHz, (CD3)2SO) dC 36.0 (N-CH3),
42.5 (CH2), 90.8 (CH),126.7 (ArCH),127.2 (ArCH),127.3 (ArCH),128.5
(ArCH), 129.3 (ArCH), 129.8 (ArCH); MS (ESI) m/z 359 (MþH)þ;
HRMS (MþH)þ calcd for C21H19N4O2¼359.1503, found¼359.1503;
HPLC (PG) tR¼4.28 min; purity ꢄ95%.
4.1.25. 3-(Benzylamino)-1-methyl-6-phenyl-1H-pyrazolo[4,3-c]pyr-
idin-4(5H)-one (22). To 10 (50 mg, 0.21 mmol) and benzaldehyde
(0.17 mL, 1.7 mmol) in MeOH (6.0 mL), was added NaCNBH3
(78.5 mg, 1.25 mmol). The white suspension was stirred at rt for
48 h. 1 M HCl (1.0 mL) was added and the mixture was stirred for
a further 1 h, after which it was neutralised with 1 M NaOH, and the
product extracted into EtOAc. The organics were washed with
water (2ꢁ10 mL) and brine (10 mL) and dried over Na2SO4. The
4.1.22. N-(1,6-Dimethyl-4-oxo-4,5-dihydro-1H-pyrazolo[4,3-c]pyr-
idin-3-yl)-3-methoxybenzenesulfonamide (19). 3-Methoxybenzene
solvent was removed in vacuo to leave a pale yellow oil.

L.A. Smyth et al. / Tetrahedron 66 (2010) 2843–2854
2851
Crystallisation from MeOH yielded 22 as a white solid (33 mg,
0.10 mmol, 48%); mp 228–231 ꢀC; Rf¼0.64 (10:90, MeOH/EtOAc); IR
(Nujol mull, cmꢃ1), 1696 (C]O), 1641 (C]N); 1H NMR (500 MHz,
CDCl3) dH 3.80 (3H, s, N-CH3), 4.57 (2H, d, J¼5.0 Hz, CH2), 5.39 (2H, t,
J¼5.0 Hz, C3-NH), 6.34 (1H, s, C7-H), 7.30–7.47 (8H, m, ArH), 7.64–
7.67 (2H, m, ArH), 9.92 (1H, br s, NH); 13C NMR (126 MHz, CDCl3) dC
35.2, 47.5, 90.5, 99.0, 126.5, 127.2, 128.0, 128.5, 129.0, 129.9, 134.4,
139.4, 144.0, 145.3, 153.7, 160.9; MS (ESI) m/z 331 (MþH)þ; HRMS
(MþH)þ calcd for C20H19N4O¼331.1559, found¼331.1559; HPLC
(PG) tR¼4.68 min; purity¼90%.
0.04 mmol, 34%); mp >350 ꢀC; Rf¼0.63 (10:90, MeOH/CH2Cl2); IR
(Nujol mull, cmꢃ1) 3385, 3314 (NH2), 3134 (NH), 1645 (C]O); 1H
NMR (500 MHz, (CD3)2SO) dH 1.88 (3H, s, C-CH3), 2.92 (3H, s, N-
CH3), 5.21 (2H, s, NH2), 7.30–7.33 (2H, m, ArH), 7.41–7.50 (3H, m,
ArH), 10.85 (1H, br s, NH); 13C NMR (126 MHz, (CD3)2SO) dC 16.6,
36.7, 98.9, 105.4, 128.0, 128.7, 131.1, 134.4, 139.1, 143.1, 151.8, 159.6;
MS (ESI) m/z 255 (MþH)þ; HRMS (MþH)þ calcd for
C14H15N4O¼255.1240, found¼255.1242; HPLC (PG) tR¼3.84 min;
purity ꢄ95%.
4.1.30. 3-Amino-6-methyl-2,7-diphenyl-2H-pyrazolo[4,3-c]pyridin-
4(5H)-one (28). General methods E and F from 24 (76.8 mg,
0.30 mmol). White solid (62 mg, 0.18 mmol, 59%); mp 315–320 ꢀC
(dec); Rf¼0.40 (10:90, MeOH/CH2Cl2); IR (Nujol mull, cmꢃ1) 3409,
3325 (NH2), 3140 (NH), 1651 (C]O); 1H NMR (500 MHz, (CD3)2SO)
dH 2.05 (3H, s, CH3), 6.26 (2H, br s, NH2), 7.27–7.56 (10H, m, ArH),
10.34 (1H, br s, NH); 13C NMR (126 MHz, (CD3)2SO) dC 17.0, 96.1,
108.4,123.7,126.6,127.3,127.9,129.3,130.5,135.1,136.9,138.1,146.6,
150.5, 160.9; MS (ESI) m/z 317 (MþH)þ; HRMS (MþH)þ calcd for
C19H17N4O¼317.1397, found¼317.1400; HPLC (PG) tR¼4.47 min;
purity ꢄ95%.
4.1.26. 4,4-Bis(methylthio)-3-phenylbut-3-en-2-one (23)14. General
method A from 1-phenylpropan-2-one using THF instead of tolu-
ene. The solvent was removed in vacuo to leave a yellow oil, which
was dissolved in EtOAc, washed with water (2ꢁ30 mL), brine
(1ꢁ30 mL) and dried (Na2SO4). Flash column chromatography
eluting with EtOAc/hexane (90:10) gave 23 as a yellow oil (1.04 g,
4.37 mmol, 58%); Rf¼0.79 (10:90, MeOH/CH2Cl2); IR (thin film,
cmꢃ1) 1696 (C]O); 1H NMR (500 MHz, (CD3)2CO) dH 2.18 (3H, s, S-
CH3), 2.24 (3H, s, S-CH3), 2.41 (3H, s, C-CH3), 7.27–7.40 (5H, m, ArH);
13C NMR (126 MHz, (CD3)2CO) dC 17.6, 18.1, 30.3, 128.2, 128.5, 129.1,
136.9, 141.1, 146.2, 200.5; MS (ESI) m/z 239 (MþH)þ; HRMS (MþH)þ
calcd for C12H15OS2¼239.0559, found¼239.0562; HPLC (PG)
tR¼4.78 min; purity ꢄ95%.
4.1.31. 3-Amino-7-bromo-1,6-dimethyl-1H-pyrazolo[4,3-c]pyridin-
4(5H)-one (29). General method H from 8 (1.00 g, 5.61 mmol).
Orange solid (1.23 g, 4.80 mmol, 86%); mp 243–245 ꢀC (dec);
Rf¼0.55 (10:90, MeOH/CH2Cl2); IR (Nujol, cmꢃ1) 3416 (NH2), 3267,
3187, 3127 (NH), 1651 (C]O); 1H NMR (500 MHz, (CD3)2SO) dH 2.27
(3H, s, C-CH3), 3.93 (3H, s, N-CH3), 5.31 (2H, s, NH2), 11.11 (1H, br s,
NH); 13C NMR (126 MHz, (CD3)2SO) dC 19.0, 37.3, 83.4, 99.9, 140.7,
140.9, 151.6, 158.9; MS (ESI) m/z 257 (79Br), 259 (81Br) (MþH)þ;
4.1.27. 6-Methyl-4-(methylthio)-2-oxo-5-phenyl-1,2-dihydropyr-
idine-3-carbonitrile (24). Method (i): General method B from 23.
Residual starting material was removed with a hexane wash to give
24 as a white solid (434 mg, 1.70 mmol, 39%).
Method (ii): General method G from 36 (78 mg, 0.30 mmol) and
phenylboronic acid. Purification was carried out by flash column
chromatography eluting with MeOH/CH2Cl2 (6:94) to yield 24 as
a pale brown solid (36 mg, 0.87 mmol, 47%); mp 323–325 ꢀC
(MeOH); Rf¼0.48 (10:90, MeOH/CH2Cl2); IR (Nujol, cmꢃ1) 3282
(NH), 2216 (CN) 1644 (C]O); 1H NMR (500 MHz, (CD3)2SO) dH 1.94
(3H, s, C-CH3), 2.41 (3H, s, S-CH3), 7.23–7.24 (2H, m, ArH), 7.38–7.46
(3H, m, ArH), 12.53 (1H, br s, NH); 13C NMR (126 MHz, (CD3)2SO) dC
17.6, 18.3, 99.2, 116.0, 119.5, 128.2, 128.6, 130.8, 134.7, 147.8, 160.2,
161.6; MS (ESI) m/z 257 (MþH)þ. HRMS (MþH)þ calcd for
C14H13N2OS¼257.0743, found¼257.0743; HPLC (MC) tR¼2.26 min;
purity ꢄ95%.
HRMS (MþH)þ calcd for C8H10BrN4O
(
79Br)¼257.0033,
found¼257.0034; HPLC (PG) tR¼3.22 min; purity ꢄ95%.
4.1.32. 3-Amino-7-(4-methoxyphenyl)-1,6-dimethyl-1H-pyr-
azolo[4,3-c]pyridin-4(5H)-one (30). General method
J from 29
(30 mg, 0.12 mmol) and 4-methoxyphenylboronic acid. Purification
was carried out using semi-prep. HPLC (gradient) to give 30 as
a pale brown solid (17 mg, 0.06 mmol, 51%); mp 290–291 ꢀC;
Rf¼0.56 (10:90, MeOH/CH2Cl2); IR (Nujol, cmꢃ1) 3397, 3311 (NH2),
1652 (C]O); 1H NMR (500 MHz, (CD3)2SO) dH 1.89 (3H, s, C-CH3),
2.97 (3H, s, N-CH3), 3.80 (3H, s, O-CH3), 5.21 (2H, s, NH2), 7.02 (2H, d,
J¼8.5 Hz, ArH), 7.21 (2H, d, J¼8.5 Hz, ArH), 10.75 (1H, s, NH); 13C
NMR (126 MHz, (CD3)2SO) dC 16.6, 36.7, 55.1, 98.9, 105.0, 114.1,
126.2, 132.2, 139.4, 143.4, 151.8, 158.9, 159.5; MS (ESI) m/z 285
(MþH)þ; HRMS (MþH)þ calcd for C15H16N4O2¼285.1346,
found¼285.1349; HPLC (PG) tR¼3.85 min; purity ꢄ95%.
4.1.28. 3-Amino-6-methyl-7-phenyl-1H-pyrazolo[4,3-c]pyridin-
4(5H)-one (26)12. General method
C
from 24 (15.1 mg,
0.059 mmol). Pale brown solid (14 mg, 0.059 mmol, quant.); mp
315–318 ꢀC (dec) (lit. 312–314 ꢀC (dec); AcOH)12; Rf¼0.20 (10:90,
MeOH/CH2Cl2); IR (Nujol mull, cmꢃ1) 3442, 3326 (NH2), 3138 (NH),
1636 (C]O); 1H NMR (500 MHz, (CD3)2SO) dH 2.03 (3H, s, C-CH3),
5.20 (2H, br s, NH2), 7.31–7.38 (3H, m, ArH), 7.44 (2H, dd, J¼7.5,
7.5 Hz, ArH), 10.67 (1H, br s, NH), 11.44 (1H, br s, NH); HMQC
(500 MHz, (CD3)2SO) dC 17.0 (C-CH3), 127.6 (ArCH), 129.0 (ArCH),
130.6 (ArCH); MS (ESI) m/z 241 (MþH)þ; HRMS (MþH)þ calcd for
C13H13N4O¼241.1084, found¼241.1089; HPLC (PG) tR¼3.22 min;
purity ꢄ95%. Anal. Calcd for C13H12N4O.0.2(H2O): C, 64.03; H, 5.13;
N, 22.97%. Found C, 64.33; H, 4.95; N, 22.57%.
4.1.33. Methyl
3-amino-1,6-dimethyl-4-oxo-4,5-dihydro-1H-pyr-
azolo[4,3-c]pyridine-7-carboxylate (31). Compound 29 (117 mg,
0.45 mmol), PPh3 (47 mg, 0.18 mmol), Pd(OAc)2 (20 mg, 0.09 mmol,
0.20 equiv) and K2CO3 (62 mg, 0.45 mmol) were stirred in DMSO
and MeOH (9:1, 9.0 mL) whilst CO was bubbled through the sus-
pension for 20 min. The mixture was then heated to 110 ꢀC under
1 atm of CO overnight. After cooling, solids were removed by fil-
tration and the filtrate purified by semi-prep. HPLC (gradient) to
give 34 as a pale yellow solid (20 mg, 0.09 mmol, 19%); mp 252–
254 ꢀC. Rf¼0.31 (10:90, MeOH/CH2Cl2); IR (Nujol, cmꢃ1) 3415 (NH2),
3281, 3199 (NH), 1712, 1682 (C]O); 1H NMR (500 MHz, (CD3)2SO)
dH 2.28 (3H, s, C-CH3), 3.52 (3H, s, N-CH3), 3.84 (3H, s, O-CH3), 5.30
(2H, s, NH2), 11.12 (1H, br s, NH); 13C NMR (126 MHz, (CD3)2SO) dC
17.4, 37.7, 52.0, 98.2, 99.1, 140.8, 145.6, 152.0, 159.1, 165.4; MS (ESI)
m/z 237 (MþH)þ; HRMS (MþH)þ calcd for C10H13N4O3¼237.0982,
found¼237.0890; HPLC (MC) tR¼1.49 min; purity ꢄ95%.
4.1.29. 3-Amino-1,6-dimethyl-7-phenyl-1H-pyrazolo[4,3-c]pyridin-
4(5H)-one (27). Method (i): General method D from 24 (102.5 mg,
0.40 mmol). On washing with a mixture of MeOH/CH2Cl2/DMSO
the white solid remaining was found to be the desired product (27)
(22 mg, 0.09 mmol, 22%).
Method (ii): General method G from 3-amino-7-bromo-1,6-di-
methyl-1H-pyrazolo[4,3-c]pyridin-4(5H)-one
(29)
(30 mg,
0.12 mmol) and phenylboronic acid. Purification was carried out
using semi-prep HPLC (20:80 MeCN/water, isocratic) and the sol-
vent was removed in vacuo to leave 27 as a pale brown solid (10 mg,
4.1.34. (E)-Methyl 3-(3-amino-1,6-dimethyl-4-oxo-4,5-dihydro-1H-
pyrazolo[4,3-c]pyridin-7-yl)acrylate (32). Compound 29 (300 mg,

2852
L.A. Smyth et al. / Tetrahedron 66 (2010) 2843–2854
1.17 mmol), PPh3 (42.8 mg, 0.16 mmol), Pd(OAc)2 (18.3 mg,
0.08 mmol, 0.07 equiv), methyl acrylate (0.21 mL, 2.33 mmol) and
Et3N (0.49 mL, 3.50 mmol) were stirred in DMF (1.8 mL) in a mi-
crowave vial for 10 min while bubbling Ar through the suspension.
The vial was sealed and heated in the microwave for 30 min at
150 ꢀC. Water was added to the dark green mixture and a green-
brown solid was obtained by filtration. Purification was carried
out using flash column chromatography eluting with MeOH/CH2Cl2
(10:90) to give 32 as a yellow solid (62 mg, 0.24 mmol, 20%); mp
278–280 ꢀC; Rf¼0.31 (10:90, MeOH/CH2Cl2); IR (Nujol, cmꢃ1) 3460
(NH2), 3294, 3202, 3151 (NH), 1716, 1686 (C]O); 1H NMR
(500 MHz, (CD3)2SO) dH 2.27 (3H, s, C-CH3), 3.70 (3H, s, N-CH3), 3.74
(3H, s, O-CH3), 5.29 (2H, s, NH2), 6.10 (1H, d, J¼16.0 Hz, CH), 7.77
(1H, d, J¼16.0 Hz, CH), 11.02 (1H, s, NH); 13C NMR (126 MHz,
(CD3)2SO) dC 17.5, 38.2, 51.5, 99.2, 100.5, 122.5, 137.8, 142.3, 142.4,
151.9, 159.1, 166.2; MS (ESI) m/z 263 (MþH)þ; HRMS (MþH)þ calcd
(50 mg, 0.16 mmol) was dissolved in AcOH (20 mL) and the double
bond was reduced using Pd/C and free flowing H2 by running
through an H-cube flow reactor at 0.9 mL/min two times at 25 ꢀC.
The AcOH was removed in vacuo, the residue was dissolved in
water (50 mL) and neutralised with saturated NaHCO3 solution. The
aqueous solution was extracted with CH2Cl2 (3ꢁ20 mL), the organic
layer was dried (Na2SO4) and the solvent was removed in vacuo to
leave 35 as a white solid (33 mg, 0.10 mmol, 66%); mp 216–219 ꢀC;
Rf¼0.25 (10:90, MeOH/CH2Cl2); IR (Nujol, cmꢃ1) 3436 (NH2), 3287,
3196, 3150 (NH), 1726, 1674 (C]O); 1H NMR (500 MHz, CDCl3) dH
1.22 (3H, t, J¼7.0 Hz, CH2CH3), 2.32 (3H, s, C-CH3), 2.47–2.63 (2H, m,
C-CH2CH2C(O)), 2.97–3.10 (2H, m, C-CH2CH2C(O)), 3.54 (2H, q,
J¼7.0 Hz, CH2CH3), 3.64 (2H, t, J¼5.0 Hz, C(O)OCH2CH2O), 3.94 (3H,
s, N-CH3), 4.21 (2H, t, J¼5.0 Hz, C(O)OCH2CH2O), 4.66 (2H, s, NH2),
10.18 (1H, br s, NH); 13C NMR (126 MHz, CDCl3) dC 15.1, 16.8, 21.5,
34.8, 38.0, 64.0, 66.7, 68.2, 100.9, 102.7, 138.7, 144.6, 151.9, 160.6,
172.1; MS (ESI) m/z 323 (MþH)þ; HRMS (MþH)þ calcd for
C15H23N4O4¼323.1714, found¼323.1718; HPLC (MC) tR¼1.68 min;
purity ꢄ95%. Anal. Calcd for C15H22N4O4: C, 55.89; H, 6.88; N,
17.38%. Found C, 55.85; H, 6.87; N, 17.27%.
for
C12H15N4O3¼263.1139,
found¼263.1142;
HPLC
(PG)
tR¼3.02 min; purity ꢄ95%.
4.1.35. Methyl 3-(3-amino-1,6-dimethyl-4-oxo-4,5-dihydro-1H-pyr-
azolo[4,3-c]pyridin-7-yl)propanoate (33). Compound 32 (40 mg,
0.15 mmol) was dissolved in AcOH (20 mL) and the double bond
was reduced using Pd/C and free flowing H2 by running through an
H-cube flow reactor at 0.9 mL/min two times at 25 ꢀC. The AcOH
was removed in vacuo, the residue was dissolved in water (50 mL)
and neutralised with saturated NaHCO3 solution. The aqueous so-
lution was extracted with CH2Cl2 (3ꢁ20 mL), the organic layer was
dried (Na2SO4) and the solvent was removed in vacuo to leave 33 as
a white solid (23 mg, 0.09 mmol, 57%); mp 275–279 ꢀC; Rf¼0.28
(10:90, MeOH/CH2Cl2); IR (Nujol, cmꢃ1) 3313 (NH2), 1735 (C]O),
1644 (C]O); 1H NMR (500 MHz, CDCl3) dH 2.31 (3H, s, C-CH3),
2.49–2.59 (2H, m, C(O)CH2CH2), 2.98–3.10 (2H, m, C(O)CH2), 3.73
(3H, s, N-CH3), 3.94 (3H, s, O-CH3), 4.66 (2H, s, NH2), 9.63 (1H, s,
NH); 13C NMR (126 MHz, CDCl3) dC 16.7, 21.6, 34.7, 38.0, 51.9, 100.9,
102.7, 138.7, 144.6, 151.9, 160.6, 172.5; MS (ESI) m/z 265 (MþH)þ;
HRMS (MþH)þ calcd for C12H17N4O3¼265.1295, found¼265.1300;
HPLC (MC) tR¼1.50 min; purity ꢄ95%. Anal. Calcd for
C12H16N4O3.0.2(H2O): C, 53.80; H, 6.17; N, 20.91%. Found C, 54.03;
H, 6.00; N, 20.64%.
4.1.38. 5-Bromo-6-methyl-4-(methylthio)-2-oxo-1,2-dihydropyr-
idine-3-carbonitrile (36). General method
H from 1 (200 mg,
1.12 mmol). Cream solid (226 mg, 0.87 mmol, 79%); mp 271 ꢀC
(dec); Rf¼0.66 (10:90, MeOH/CH2Cl2); IR (Nujol, cmꢃ1) 3289 (NH),
1645 (C]O); 1H NMR (500 MHz, (CD3)2SO) dH 2.38 (3H, s, C-CH3),
2.79 (3H, s, S-CH3), 12.76 (1H, br s, NH); 13C NMR (126 MHz,
(CD3)2SO) dC 18.4, 21.2, 99.9, 100.7, 115.4, 149.6, 159.7, 161.3; MS
(ESI) m/z 259 (79Br), 261 (81Br) (MþH)þ; HRMS (MþH)þ calcd for
C8H8BrN2OS
tR¼1.84 min; purity ꢄ95%.
(
79Br)¼258.9535, found¼258.9543; HPLC (MC)
4.1.39. 4-Chloro-1,6-dimethyl-1H-pyrazolo[4,3-c]pyridin-3-amine
(37). General method I from 8 (700 mg, 3.93 mmol). Purification
was carried out by flash column chromatography, eluting with
EtOAc/Pet (60:40), to yield 37 as a white solid (303 mg, 1.54 mmol,
39%); mp 172–174 ꢀC; Rf¼0.27 (60:40, EtOAc/Pet); IR (Nujol, cmꢃ1
)
3450, 3294, 3197 (NH2), 1611 (C]N); 1H NMR (500 MHz, CDCl3) dH
2.57 (3H, s, C-CH3), 3.78 (3H, s, N-CH3), 4.59 (2H, s, NH2), 6.81 (1H, s,
C7-H); 13C NMR (126 MHz, CDCl3) dC 24.3, 34.9, 101.6, 107.7, 143.4,
146.2, 147.5, 153.8; MS (ESI) m/z 197 (35Cl), 199 (37Cl) (MþH)þ;
4.1.36. (E)-2-Ethoxyethyl 3-(3-amino-1,6-dimethyl-4-oxo-4,5-dihy-
dro-1H-pyrazolo[4,3-c]pyridin-7-yl)acrylate (34). Compound 29
(300 mg, 1.17 mmol), PPh3 (42.8 mg, 0.16 mmol), Pd(OAc)2
(18.3 mg, 0.08 mmol, 0.07 equiv), ethylethoxyacrylate (0.34 mL,
2.33 mmol) and Et3N (0.49 mL, 3.50 mmol) were stirred in DMF
(1.8 mL) in a microwave vial for 10 min while bubbling Ar through
the suspension. The vial was sealed and heated in the microwave
for 30 min at 150 ꢀC. Water was added to the dark green mixture
and a green-brown solid was obtained by filtration. Purification was
carried out using flash column chromatography eluting with
MeOH/CH2Cl2 (10:90). The solvent was removed in vacuo to yield
34 as a pale yellow solid (104 mg, 0.33 mmol, 28%); mp 242–
243 ꢀC; Rf¼0.31 (10:90, MeOH/CH2Cl2); IR (Nujol, cmꢃ1) 3445
(NH2), 3281, 3200, 3153 (NH), 1716, 1674 (C]O); 1H NMR
(500 MHz, (CD3)2SO) dH 1.11 (3H, t, J¼7.0 Hz, OCH2CH3), 2.27 (3H, s,
C-CH3), 3.47 (2H, q, J¼7.0 Hz, OCH2CH3), 3.62 (2H, t, J¼5.0 Hz,
C(O)OCH2CH2O), 3.70 (3H, s, N-CH3), 4.26 (2H, t, J¼5.0 Hz,
C(O)OCH2CH2O), 5.27 (2H, s, NH2), 6.10 (1H, d, J¼16 Hz,
C(O)CH]CH), 7.78 (1H, d, J¼16 Hz, C(O)CH]CH), 11.01 (1H, s, NH);
13C NMR (126 MHz, (CD3)2SO) dC 15.0, 17.6, 38.2, 63.5, 65.6, 67.7,
99.2, 100.5, 122.3, 138.0, 142.4, 142.4, 151.9, 159.1, 165.8; MS (ESI) m/
z 321 (MþH)þ; HRMS (MþH)þ calcd for C15H21N4O4¼321.1557,
found¼321.1560; HPLC (MC) tR¼1.83 min; purity ꢄ95%.
HRMS
(MþH)þ
calcd
for
C8H10ClN4
(
35Cl)¼197.0589,
found¼197.0590; HPLC (MC) tR¼1.58 min; purity ꢄ95%.
4.1.40. 4-Chloro-1-methyl-6-phenyl-1H-pyrazolo[4,3-c]pyridin-3-
amine (38). General method I from 10 (380 mg, 1.58 mmol). Puri-
fication was carried out by flash column chromatography, eluting
with EtOAc/petrol (70:30), to yield 38 as a cream solid (162 mg,
0.63 mmol, 40%); mp 238–242 ꢀC; Rf¼0.33 (70:30, EtOAc/petrol); IR
(Nujol, cmꢃ1) 3454, 3306, 3197 (NH2); 1H NMR (500 MHz, CDCl3) dH
3.89 (3H, s, N-CH3), 7.37 (1H, s, C7-H), 7.41–7.47 (1H, m, ArH), 7.47–
7.52 (2H, m, ArH), 7.98–8.09 (2H, m, ArH); 13C NMR (126 MHz,
CDCl3) dC 35.1, 99.1, 108.1, 127.2, 128.8, 129.3, 138.2, 144.3, 146.3,
147.5, 153.8; MS (ESI) m/z 259 (35Cl), 261 (37Cl) (MþH)þ; HRMS
(MþH)þ calcd for C13H12ClN4
(
35Cl)¼259.0745, found¼259.0747;
HPLC (MC) tR¼2.41 min; purity ꢄ95%.
4.1.41. 1,6-Dimethyl-4-(piperidin-1-yl)-1H-pyrazolo[4,3-c]pyridin-3-
amine (39). General method J from 37 (20 mg, 0.10 mmol) and pi-
peridine. White solid (24 mg, 0.10 mmol, 96%); mp 161–164 ꢀC;
Rf¼0.48 (10:90, MeOH/CH2Cl2); IR (Nujol, cmꢃ1) 3368, 3303, 3212
(NH2); 1H NMR (500 MHz, (CD3)2SO) dH 1.54–1.59 (2H, m,
N(CH2CH2)2CH2), 1.65–1.70 (4H, m, 2ꢁN-CH2–CH2), 2.33 (3H, s, C-
CH3), 3.27–3.15 (4H, m, 2ꢁN-CH2–CH2), 3.63 (3H, s, N-CH3), 4.93
(2H, s, NH2), 6.67 (1H, s, C7-H); 13C NMR (126 MHz, (CD3)2SO) dC
24.2, 24.4, 25.4, 34.3, 50.9, 96.8, 100.6, 146.8, 147.7, 150.8, 157.6; MS
4.1.37. 2-Ethoxyethyl 3-(3-amino-1,6-dimethyl-4-oxo-4,5-dihydro-
1H-pyrazolo[4,3-c]pyridin-7-yl)propanoate (35). Compound 34

L.A. Smyth et al. / Tetrahedron 66 (2010) 2843–2854
2853
(ESI)
m/z
246
(MþH)þ;
HRMS
(MþH)þ
calcd
for
(24 mg, 0.094 mmol, 46%); mp 132–133 ꢀC; Rf¼0.50 (10:90, MeOH/
CH2Cl2); IR (Nujol, cmꢃ1) 3461, 3295, 3173 (NH2); 1H NMR
(500 MHz, CDCl3) dH 2.40 (3H, s, C-CH3), 3.79 (3H, s, N-CH3), 4.49
(2H, s, NH2), 6.61 (1H, br s, C7-H), 7.23 (1H, tt, J¼7.5, 1.0 Hz, ArH),
7.26–7.30 (2H, m, ArH, overlaps with solvent peak), 7.42 (2H, dd,
J¼7.5, 7.5 Hz, ArH); 13C NMR (126 MHz, CDCl3) dC 24.5, 34.9, 98.2,
98.8,121.4,124.6,129.3,147.8,148.1,152.8,153.4, 156.9; MS (ESI) m/z
255 (MþH)þ; HRMS (MþH)þ calcd for C14H15N4O¼255.1240,
found¼255.1242; HPLC (MC) tR¼2.13 min; purity ꢄ95%. Anal. Calcd
for C14H14N4O: C, 66.13; H, 5.55; N, 22.03%. Found C, 66.01; H, 5.48;
N, 21.97%.
C13H20N5¼246.1713, found¼246.1709; HPLC (MC) tR¼1.25 min;
purity ꢄ95%. Anal. Calcd for C13H19N5.0.2(H2O): C, 62.73; H, 7.86; N,
28.13%. Found C, 62.55; H, 7.69; N, 27.90%.
4.1.42. 1,6-Dimethyl-N4-phenyl-1H-pyrazolo[4,3-c]pyridine-3,4-di-
amine (40). General method J from 37 (20 mg, 0.10 mmol) and
aniline. Further purification by flash column chromatography,
eluting with EtOAc/hexane (80:20), gave 40 as a yellow solid
(17 mg, 0.067 mmol, 66%); mp 125–126 ꢀC; Rf¼0.21 (80:20, EtOAc/
hexane); IR (Nujol, cmꢃ1) 3413, 3340 (NH2), 3269, 3191 (NH); 1H
NMR (500 MHz, CDCl3) dH 2.52 (3H, s, C-CH3), 3.73 (2H, br s, NH2),
3.78 (3H, s, N-CH3), 6.48 (1H, s, C7-H), 7.03 (1H, t, J¼8.0 Hz, ArH),
7.34 (2H, dd, J¼8.0, 8.0 Hz, ArH), 7.46 (1H, s, NH), 7.71 (2H, d,
J¼8.0 Hz, ArH); 13C NMR (126 MHz, CDCl3) dC 24.8, 34.8, 95.4, 100.4,
119.0, 122.1, 129.0, 140.7, 145.8, 147.1, 149.9, 153.5; MS (ESI) m/z 254
(MþH)þ; HRMS (MþH)þ calcd for C14H16N5¼254.1400,
found¼254.1401; HPLC (MC) tR¼1.25 min; purity ꢄ95%.
4.1.46. 2-Methyl-4-phenyl-2,6,7,9-tetrahydro-1,2,5,6,9-pentaaza-
benzo[cd]azulen-8-one (44). Compound 38 (130 mg, 0.50 mmol),
methyl 2-aminoacetate hydrochloride (189 mg, 1.5 mmol) and Et3N
(0.14 mL, 1.0 mmol) in nBuOH (1.1 mL) were heated in the micro-
wave at 160 ꢀC for 30 min. Water (30 mL) and CH2Cl2 (30 mL) were
added to the resulting mixture. The two phases were separated and
the aqueous fraction was washed with CH2Cl2 (2ꢁ30 mL). The or-
ganic fractions were combined, dried (Na2SO4) and the solvent was
removed in vacuo. Flash column chromatography, eluting with
MeOH/CH2Cl2 (5:95), gave 44 as a pale yellow solid. Recrystallised
from MeOH (41 mg, 0.15 mmol, 29%); mp 270–275 ꢀC (MeOH);
Rf¼0.45 (10:90, MeOH/CH2Cl2); IR (Nujol, cmꢃ1) 3666, 3352 (NH),
1683 (C]O); 1H NMR (500 MHz, (CD3)2SO) dH 3.89 (3H, s, N-CH3),
3.95 (2H, d, J¼3.5 Hz, NH-CH2), 7.27 (1H, t, J¼3.5 Hz, NH-CH2), 7.37–
7.41 (1H, m, ArH), 7.42 (1H, s, C3-H), 7.43–7.49 (2H, m, ArH), 8.02–
8.14 (2H, m, ArH), 11.02 (1H, s, NH); 13C NMR (126 MHz, (CD3)2SO)
dC 35.1, 51.4, 92.6, 99.7, 126.7, 128.4, 128.4, 139.5, 141.3, 146.5, 151.9,
155.9, 168.5; MS (ESI) m/z 280 (MþH)þ; HRMS (MþH)þ calcd for
C15H14N5O¼280.1193, found¼280.1194; HPLC (MC) tR¼1.31 min;
purity ꢄ95%. Anal. Calcd for C15H13N5O.0.5(H2O): C, 62.49; H, 4.89;
N, 24.29%. Found C, 62.36; H, 4.58; N, 24.17%.
4.1.43. 1,6-Dimethyl-4-(phenylthio)-1H-pyrazolo[4,3-c]pyridin-3-
amine (41). Compound 37 (40 mg, 0.20 mmol), benzenethiol
(50 mL, 0.49 mmol) and K2CO3 (34 mg, 0.24 mmol) in MeCN
(0.88 mL) were heated at reflux for 3 h. The resulting mixture was
dissolved in MeOH/CH2Cl2 (50:50, 2 mL), absorbed on a prepared
isolute SCX-2 ion exchange column and washed through with three
column volumes of the solvent mixture. The product was released
using 0.1 M NH3 in MeOH and the solvent was removed in vacuo to
give 41 as a pale yellow solid (48 mg, 0.18 mmol, 87%); mp 174–
175 ꢀC; Rf¼0.52 (10:90, MeOH/CH2Cl2); IR (Nujol, cmꢃ1) 3448,
3302, 3200 (NH2); 1H NMR (500 MHz, (CD3)2SO) dH 2.33 (3H, s, C-
CH3), 3.70 (3H, s, N-CH3), 5.39 (2H, s, NH2), 7.04 (1H, s, C7-H), 7.32–
7.44 (3H, m, ArH), 7.50 (2H, d, J¼7.0 Hz, ArH); 13C NMR (126 MHz,
(CD3)2SO) dC 24.5, 35.0, 101.3, 109.5, 128.6, 129.6, 131.5, 133.1, 145.2,
148.6, 150.2, 153.0; MS (ESI) m/z 271 (MþH)þ; HRMS (MþH)þ calcd
for C14H15N4S¼271.1012, found¼271.1014; HPLC (MC) tR¼1.52 min;
purity ꢄ95%. Anal. Calcd for C14H14N4S.0.2(H2O): C, 61.38; H, 5.30;
N, 20.45%. Found C, 61.59; H, 5.12; N, 20.07%.
4.1.47. 2-Chloro-6-methyl-4-(methylthio)nicotinonitrile
(45). General method I from 1 (700 mg, 3.88 mmol). On quenching
45 was isolated by filtration as a pale brown solid (672 mg,
3.38 mmol, 87%); mp 166–167 ꢀC; Rf¼0.76 (10:90, MeOH/CH2Cl2);
IR (Nujol, cmꢃ1) 2231 (CN); 1H NMR (500 MHz, CDCl3) dH 2.59 (3H,
s, CH3), 2.60 (3H, s, CH3), 6.92 (1H, s, C5-H); 13C NMR (126 MHz,
CDCl3) dC 14.5, 24.9, 104.5, 113.3, 116.2, 152.7, 158.7, 161.9; MS (ESI)
m/z 199 (35Cl), 201 (37Cl) (MþH)þ; HRMS (MþH)þ calcd for
C8H8ClN2S¼199.0091, found¼199.0094; HPLC (MC) tR¼1.99 min;
purity ꢄ95%.
4.1.44. 4-Isopropoxy-1,6-dimethyl-1H-pyrazolo[4,3-c]pyridin-3-
amine (42). Sodium metal (30 mg) was dissolved in PrOH (2 mL)
i
and 37 (20 mg, 0.10 mmol) was added and the resulting solution
was heated at reflux overnight. To this solution was added water
(10 mL) and the mixture was neutralised with NaHCO3. The aque-
ous solution was extracted with CH2Cl2 (3ꢁ20 mL) and dried
(Na2SO4). The solvent was removed in vacuo to leave 42 as a pale
yellow solid (22 mg, 0.10 mmol, 98%); mp 99–101 ꢀC; Rf¼0.40
(80:20, EtOAc/Pet); IR (Nujol, cmꢃ1) 3485, 3294, 3197 (NH2); 1H
NMR (500 MHz, CDCl3) dH 1.40 (6H, d, J¼6.0 Hz, OCH(CH3)2), 2.44
(3H, s, C-CH3), 3.71 (3H, s, N-CH3), 4.41 (2H, s, NH2), 5.55 (1H, hept,
J¼6.0 Hz, OCH(CH3)2), 6.45 (1H, s, C7-H); 13C NMR (126 MHz, CDCl3)
dC 22.2, 24.7, 34.8, 68.0, 96.3, 98.2, 147.6, 148.2, 152.7, 157.8; MS (ESI)
4.1.48. 6-Methyl-4-(methylthio)-2-(piperidin-1-yl)nicotinonitrile
(46). General method J from 45 (120 mg, 0.60 mmol) and piperi-
dine. Pale brown solid (143 mg, 0.58 mmol, 96%); mp 92–94 ꢀC;
Rf¼0.78 (10:90, MeOH/CH2Cl2); IR (thin film, cmꢃ1) 2207 (CN); 1H
NMR (500 MHz, (CD3)2SO) dH 1.60 (6H, br s, N(CH2CH2)2CH2), 2.36
(3H, s, C-CH3), 2.55 (3H, s, S-CH3), 3.47–3.58 (4H, m, 2ꢁN-CH2CH2),
6.69 (1H, s, C5-H); 13C NMR (126 MHz, (CD3)2SO) dC 14.4, 24.6, 25.2,
26.0, 49.7, 89.0, 108.3, 116.8, 157.5, 160.2, 161.8; MS (ESI) m/z 248
(MþH)þ; HRMS (MþH)þ calcd for C13H18N3S¼248.1216,
found¼248.1218; HPLC (MC) tR¼2.70 min; purity ꢄ95%.
m/z
179
((M-OiPr)þH)þ;
HRMS
(MþH)þ
calcd
for
C11H17N4O¼221.1397, found¼221.1400; HPLC (MC) tR¼1.75 min;
purity ꢄ95%. Anal. Calcd for C11H16N4O: C, 59.98; H, 7.32; N, 25.44%.
Found C, 59.70; H, 7.28; N, 25.13%.
4.1.45. 1,6-Dimethyl-4-phenoxy-1H-pyrazolo[4,3-c]pyridin-3-amine
(43). Compound 37 (40 mg, 0.20 mmol), phenol (21 mg,
0.22 mmol) and Cs2CO3 (73 mg, 0.22 mmol) in DMSO (0.23 mL)
were heated in a sealed tube overnight at 130 ꢀC. The resulting dark
mixture was dissolved in MeOH/CH2Cl2 (50:50, 2 mL), absorbed on
a prepared isolute SCX-2 ion exchange column and washed through
with three column volumes of the solvent mixture. The product
was released using 0.1 M NH3 in MeOH and the solvent was re-
moved. The product was purified by flash column chromatography,
eluting with EtOAc/Pet (60:40), to give 43 as a pale brown solid
4.1.49. 6-Methyl-4-(piperidin-1-yl)-1H-pyrazolo[4,3-c]pyridin-3-
amine (48). Compound 46 (140 mg, 0.57 mmol) and m-CPBA
(ꢂ77% by wt, 381 mg, 1.70 mmol) in EtOH (5.4 mL) were stirred at
rt for 6 h. To the resulting yellow solution was added water
(10 mL) and saturated NaHCO3 (10 mL). 6-Methyl-4-(methyl-
sulfinyl)-2-(piperidin-1-yl)nicotinonitrile 47 precipitated from
solution and was collected by filtration as a pale yellow solid
(103 mg, 65%); MS (ESI) m/z 280 (MþH)þ, HPLC (MC) tR¼2.39 min.
A mixture of 47 (88 mg, 0.31 mmol) and hydrazine hydrate
i
(0.30 mL, 6.68 mmol) in PrOH (1.7 mL) was stirred at reflux for

2854
L.A. Smyth et al. / Tetrahedron 66 (2010) 2843–2854
6 h. The resulting yellow solution was concentrated in vacuo and
dissolved in MeOH/CH2Cl2 (50:50, 5 mL), absorbed on a prepared
isolute SCX-2 ion exchange column and washed through with
three column volumes of the solvent mixture. The product was
released using 0.1 M NH3 in MeOH and the solvent was removed
in vacuo to leave a yellow oil. Flash column chromatography,
eluting with MeOH/CH2Cl2 (10:90), gave 48 as a pale brown glass
(30 mg, 0.13 mmol, 41%); mp 179–180 ꢀC; Rf¼0.27 (10:90, MeOH/
CH2Cl2); IR (Nujol, cmꢃ1) 3442, 3356 (NH2), 3142 (NH); 1H NMR
(500 MHz, CDCl3) dH 1.65 (2H, quin, J¼5.5 Hz, N(CH2CH2)2CH2),
1.76 (4H, tt, J¼5.5, 5.5 Hz, 2ꢁN-CH2CH2), 2.46 (3H, s, C-CH3), 3.33
(4H, t, J¼5.5 Hz, 2ꢁN-CH2CH2), 4.41 (2H, s, NH2), 6.58 (1H, s, C7-H),
9.34 (1H, br s, NH); 13C NMR (126 MHz, CDCl3) dC 24.1, 25.6, 27.3,
52.8, 99.6, 102.6, 149.4, 150.5, 153.5, 160.4; MS (ESI) m/z 232
(MþH)þ; HRMS (MþH)þ calcd for C12H18N5¼232.1557,
found¼232.1558; HPLC (MC) tR¼1.23 min; purity ꢄ95%. Anal.
Calcd for C12H17N5.0.33(H2O): C, 60.75; H, 7.50; N, 29.52%. Found
C, 61.05; H, 7.24; N, 29.33%.
Acknowledgements
We are grateful to The Institute of Cancer Research for funding
(studentship to L.A.S.). This work was supported by Cancer Re-
search UK [CUK] grant numbers C309/A2187, C309/A8274 and
C309/A8365. We acknowledge NHS funding to the NIHR Bio-
medical Research Centre. We thank Warwick Analytical Services
Ltd. and Jill Maxwell at the University of London for microanal-
ysis data. We thank Dr. Amin Mirza, Dr. Maggie Liu and Mr.
Meirion Richards for their expert assistance in the collection of
NMR and MS data. We thank Professor Keith Jones, Dr. Ted
McDonald and Professor Julian Blagg for their interest in this
work and for helpful discussions. We acknowledge the use of the
EPSRC Chemical Database Service.33
References and notes
1. Hert, J.; Irwin, J. J.; Laggner, C.; Keiser, M. J.; Shoichet, B. K. Nat. Chem. Biol. 2009,
5, 479.
2. Pitt, W. R.; Parry, D. M.; Perry, B. G.; Groom, C. R. J. Med. Chem. 2009, 52, 2952.
3. Chang, Y.-T.; Gray, N. S.; Rosania, G. R.; Sutherlin, D. P.; Kwon, S.; Norman, T. C.;
Sarohia, R.; Leost, M.; Meijer, L.; Schultz, P. G. Chem. Biol. 1999, 6, 361.
4. Aronov, A. M.; Murcko, M. A. J. Med. Chem. 2004, 47, 5616.
5. Scapin, G. Curr. Drug Targets 2006, 7, 1443.
4.2. Statistical data for the X-ray crystal structure
determinations of 10 and 17
6. Li, B.; Liu, Y.; Uno, T.; Gray, N. Comb. Chem. High Throughput Screening 2004, 7, 453.
7. Noble, M. E. M.; Endicott, J. A.; Johnson, L. N. Science 2004, 303, 1800.
8. Workman, P.; Collins, I. In Cancer Drug Design and Discovery; Neidle, S., Ed.;
Academic: Oxford, 2008; pp 3–38.
9. Attaby, F. A.; Eldin, S. M. Arch. Pharm. Res. 1990, 13, 274.
10. Taylor, E. C.; Hartke, K. S. J. Am. Chem. Soc. 1959, 81, 2456.
11. Taylor, E. C., Jr.; Hartke, K. S. J. Am. Chem. Soc. 1959, 81, 2452.
12. Kumar, A.; Ila, H.; Junjappa, H. J. Chem. Soc., Perkin Trans. 1 1978, 857.
13. Rastogi, R. R.; Kumar, A.; Ila, H.; Junjappa, H. J. Chem. Soc., Perkin Trans. 1
1978, 549.
10
17
Empirical formula
Formula weight
Temperature
Wavelength
Crystal system
Space group
Unit cell
C13H12N4O
240.27
120(2) K
0.71073 Å
Monoclinic
C2/c
C18H14N4O
302.33
120(2) K
0.71073 Å
Orthorhombic
Pbca
a¼13.4275(7) Å,
b¼7.1815(4) Å,
c¼23.9546(10) Å
a¼14.7295(4) Å,
b¼14.7023(4) Å,
c¼26.7711(8) Å
dimensions
14. Thuillier, A.; Vialle, J. Bull. Soc. Chim. Fr. 1959, 1398.
a
g
¼90ꢀ,
¼90ꢀ
b
¼102.587(2)ꢀ,
a
¼90ꢀ,
b
¼90ꢀ,
g
¼90ꢀ
15. Tominaga, Y.; Kawabe, M.; Hosomi, A. J. Heterocycl. Chem. 1987, 24, 1325.
16. Witherington, J. Intl. Patent Appl. WO 80609, 2003; Chem. Abstr. 2003,139, 292248.
17. Ronan, B.; Tabart, M.; Halley, F.; Bacque, E.; Souaille, C.; Ugolini, A.; Viviani, F.
Intl. Patent Appl. WO 77319, 2006; Chem. Abstr. 2006, 145, 167240.
18. Dai, Y.; Hartandi, K.; Soni, N. B.; Pease, L. J.; Reuter, D. R.; Olson, A. M.; Osterling,
D. J.; Doktor, S. Z.; Albert, D. H.; Bouska, J. J.; Glaser, K. B.; Marcotte, P. A.; Stewart,
K. D.; Davidsen, S. K.; Michaelides, M. R. Bioorg. Med. Chem. Lett. 2008, 18, 386.
19. Collins, I. J. Chem. Soc., Perkin Trans. 1 2002, 1921.
20. Smyth, L. A.; Matthews, T. P.; Horton, P. N.; Hursthouse, M. B.; Collins, I. Tet-
rahedron 2007, 63, 9627.
21. Rudorf, W. D.; Augustin, M. J. Prakt. Chem. 1981, 323, 55.
22. Pratap, R.; Ram, V. J. Tetrahedron Lett. 2007, 48, 8547.
23. Khan, M. A.; Rolim, A. M. C.; Guarconi, A. E. J. Heterocycl. Chem. 1983, 20, 475.
24. Augustin, M.; Jahreis, G. J. Prakt. Chem. 1979, 321, 699.
25. Teague, S. J. J. Org. Chem. 2008, 73, 9765.
26. Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.
27. Orito, K.; Miyazawa, M.; Kanbayashi, R.; Tokuda, M.; Suginome, H. J. Org. Chem.
1999, 64, 6583.
28. Shiraiwa, M.; Sakamoto, T.; Yamanaka, H. Chem. Pharm. Bull. 1983, 31, 2275.
29. Hooft, R. Collect: Data Collection Software; Nonius BV: Delft: Netherlands, 1998.
30. Otwinowski, Z.; Minor, W. In Methods in Enzymology, Macromolecular Crystal-
lography; Carter, C. W., Jr., Sweet, R. M., Eds.; Academic: Oxford, 1997; Vol. 276;
Part A, pp 307–326.
31. Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467.
32. Sheldrick, G. M. SHELXL 97: Program for the refinement of crystal structures;
University of Go¨ttingen: Germany, 1997.
Volume
Z
Density (calculated)
Absorption
coefficient
F(000)
2254.4(2) Å3
8
5797.5(3) Å3
16
1.416 mg/m3
0.095 mmꢃ1
1.386 mg/m3
0.090 mmꢃ1
1008
2528
Crystal
Crystal size
Cut shard; colourless
0.45ꢁ0.28ꢁ0.16 mm3
3.49ꢃ27.48ꢀ
Slab; colourless
0.34ꢁ0.12ꢁ0.05 mm3
q
range for data
collection
3.01ꢃ27.48ꢀ
Reflections
collected
Independent
reflections
Completeness
11,796
26,155
2582 [Rint¼0.0476]
99.7%
6537 [Rint¼0.0498]
98.5%
to
q
¼27.47ꢀ
Data/restraints
/parameters
2582/0/177
6537/4/428
Goodness-of-fit on F2
Final R indices
1.019
1.107
R1¼0.0424, wR2¼0.1001
R1¼0.0654, wR2¼0.1202
[F2>2 (F2)]
s
R indices (all data)
Largest diff.
peak and hole
R1¼0.0770, wR2¼0.1170
0.230 and ꢃ0.212 e Åꢃ3
R1¼0.0912, wR2¼0.1346
0.320 and ꢃ0.263 e Åꢃ3
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