Discovery and Structure Enabled Synthesis of 2,6-Diaminopyrimidin-4-one IRAK4 Inhibitors

Article abstract of DOI:10.1021/acsmedchemlett.5b00279

We report the identification and synthesis of a series of aminopyrimidin-4-one IRAK4 inhibitors. Through high throughput screening, an aminopyrimidine hit was identified and modified via structure enabled design to generate a new, potent, and kinase selective pyrimidin-4-one chemotype. This chemotype is exemplified by compound 16, which has potent IRAK4 inhibition activity (IC₅₀ = 27 nM) and excellent kinase selectivity (>100-fold against 99% of 111 tested kinases), and compound 31, which displays potent IRAK4 activity (IC₅₀ = 93 nM) and good rat bioavailability (F = 42%).

Full text of DOI:10.1021/acsmedchemlett.5b00279

Letter
pubs.acs.org/acsmedchemlett
Discovery and Structure Enabled Synthesis of
2,6-Diaminopyrimidin-4-one IRAK4 Inhibitors
W. Michael Seganish,*,† Thierry O. Fischmann,‡ Brad Sherborne,§ Julius Matasi,† Brian Lavey,†
William T. McElroy,† Deen Tulshian,† James Tata,† Christopher Sondey,∥ Charles G. Garlisi,∥
Kristine Devito,∥ James Fossetta,⊥ Daniel Lundell,⊥ and Xiaoda Niu∥
†Discovery Chemistry, ‡Structural Sciences, §Computational Chemistry, ∥In Vitro Pharmacology, and ⊥Respiratory and Immunology,
Merck Research Laboratories, 2015 Galloping Hill Road, Kenilworth, New Jersey 07033, United States
S
* Supporting Information
ABSTRACT: We report the identification and synthesis of a series of aminopyrimidin-4-one IRAK4 inhibitors. Through high
throughput screening, an aminopyrimidine hit was identified and modified via structure enabled design to generate a new, potent,
and kinase selective pyrimidin-4-one chemotype. This chemotype is exemplified by compound 16, which has potent IRAK4
inhibition activity (IC50 = 27 nM) and excellent kinase selectivity (>100-fold against 99% of 111 tested kinases), and compound
31, which displays potent IRAK4 activity (IC50 = 93 nM) and good rat bioavailability (F = 42%).
KEYWORDS: IRAK4, kinase inhibitor, inflammation, structure-based drug design
nterluekin-1 receptor associated kinase-4 (IRAK4) is a
Imember of the IRAK4 family of serine-threonine kinases
and is known to have biologically relevant kinase activity.1 In
addition, all members of the family (including IRAK1, IRAK2,
and IRAKM) are thought to have key protein scaffolding and
regulatory functions in various signaling pathways.2 IRAK4 is a key
mediator in the interluekin-1 receptor (IL-1R) and Toll-like
receptor (TLR) signaling cascades.3 These signaling pathways
play crucial roles in the innate immune response.4 IRAK4 functions
as an upstream signal transducer that effects the activation of
transcription factors kappa light chain enhancer of activated B cells
(NF-κB) and activator protein-1 (AP-1) resulting in the generation
of secondary inflammatory mediators.5 The importance of IRAK4
has been demonstrated with studies of IRAK4 kinase dead, knock-in
mice. Mice possessing this genotype are resistant to joint inflamma-
tion in several rodent arthritis models.6 Additionally, a small IRAK4
deficient human population has been identified. Cells from these
patients have impaired responses to ILR/TLR receptor stimula-
tion.7 The data in rodents and humans implies that an IRAK4
inhibitor could modulate the production of key inflammatory
cytokines and cytokine induced pathologies.
and ligand binding efficiency (LBE)12 resulting in compounds such
as pyrimidine 2 with subnanomolar IRAK4 inhibition and good
LBE, but with modest kinase selectivity. Subsequent SAR work
identified compounds with improved kinase selectivity (90−96%,
cf., inhibitor 2 at 85%) and cellular potencies.13 These improve-
ments in potency and selectivity were realized by altering the
substituents around the periphery of the pyrimidine core, specifically
at the C-2 and C-5 positions. An additional route that was inves-
tigated to improve the kinase selectivity of the series was to make
changes to the pyrimidine core itself, specifically, changing the
pyrimidine ring to a pyridine.13 While several pyridine analogues
were examined, it was found that these compounds had similar
kinase selectivity profiles to the parent pyrimidines.
Recent reports have highlighted several novel and diverse
series of IRAK4 inhibitors.8−10 We previously identified a unique
series of aminopyrimidine compounds (1) from a high throughput
screen.11 These hits were optimized to improve the IRAK4 potency
Received: July 9, 2015
Accepted: July 12, 2015
© XXXX American Chemical Society
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Figure 1. X-ray cocrystal structure of pyrimidine 1 bound to the IRAK4
hinge.
Upon examination of the X-ray cocrystal structure of
pyrimidine 1 (Figure 1), it was observed that there appeared to
be a small pocket adjacent to the C-6 position of the pyrimidine
ring of the inhibitor and in the vicinity of the Val263 backbone
carbonyl. It had been previously shown that this space could be
filled with a Cl, methyl, or amino group.11 Another substituent
that was considered was a hydroxyl/carbonyl group. The
presence of a hydroxyl group could potentially form an additional
hydrogen bond interaction with the Val263 backbone carbonyl.
However, studies of aminoisocytosine derivatives have shown
that the oxo tautomeric form predominates in both solution and
solid state.14 While it was believed that the pocket could spatially
accommodate the carbonyl moiety, it was hypothesized that
predominance of the oxo tautomer would lead to electrostatic
repulsion from the Val263 carbonyl, which would force the
inhibitor away from the hinge with a concomitant loss in potency.
It was feasible that this altered binding mode could lead to
improved kinase selectivity. If there was a loss in potency, it was
assumed that it could be improved by modifications elsewhere
in the molecule, and the perceived risk of loss of IRAK4 potency
was acceptable in order to provide a greater overall kinase
selectivity profile.
Pyrimidine 3 was chosen as the parent compound as it had
reasonable IRAK4 potency and a smaller group (cyclopropyl) on
the C-2 amino position, which would be more accommodating to
shifts in binding mode, compared to the more potent pyrimidine
compounds that had large substituted aryl rings at this posi-
tion (cf., 2). When the corresponding pyrimidin-4-one 4 was
synthesized, it was found to have a significant improvement in
potency over the parent pyrimidine 3. Upon obtaining and
solving the X-ray cocrystal structure, it was observed that the
compound bound in a new binding mode as the pyrimidin-
4-one tautomer (Figure 2A). The key change from the
pyrimidine core was that the inhibitor had shifted down in
the ATP binding site. This became readily apparent when the
structures of pyrimidine 1 and pyrmidin-4-one 4 were overlaid
(Figure 2B). While the pyrimidin-4-one was still forming two
hydrogen bond interactions with the hinge motif (like the
pyrimidine), these were now being made with a different
donor−acceptor pair. Where the pyrimidine ring nitrogen was
functioning as a hydrogen bond acceptor, now the pyrimidin-
4-one carbonyl was forming this key bond (Figure 2C). Like-
wise, where the C-2 amino of the pyrimidine ring had functioned
Figure 2. (A) X-ray cocrystal structure of pyrimidin-4-one 4. (B)
Overlay of the X-ray structures of pyrimidine 1 (cyan) and pyrimidin-
4-one 4 (orange). (C) Alignment of the hinge binding motifs between 1
(cyan) and 4 (orange).
as the hydrogen bond donor, the pyrimidin-4-one ring NH was
now filling this role.
Several key interactions were retained between the two
chemotypes. It appeared that the π−π stacking interaction
between the benzothiazole of the inhibitor and the tyrosine
gatekeeper had been preserved. Additionally, an intramolecular
hydrogen bond between the nitrogen of the benzothiazole ring
and the C-4 amino group had also been maintained. Like for
the case of the pyrimidine core,11 it is thought that this intra-
molecular hydrogen bond plays an important role in helping
to preorganize the inhibitor into a coplanar orientation that
facilitates binding.
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Table 1. Modification of the C-2 Position
It was hypothesized that the change in the binding mode
would have SAR ramifications for the series, perhaps leading to a
divergent set of active compounds. This became readily apparent
when the most potent C-2 amino substituent, 2,6-dimethylpyr-
idine, was appended to the pyrmidin-4-one core to generate
compound 5. This substituent on the pyrimidine core provided
compounds with single digit nanomolar or subnanomolar
potency (cf., pyrimidine 2 above). In the case of pyrimidin-
4-one 5, not only was there a loss of potency but there was also an
associated drop in the ligand efficiency of the compound,
particularly when compared to the cyclopropyl analogue 4. This
result clearly indicated that the structure−activity relationships
(SARs) between the pyrimidines and the pyrimidinones were
divergent.
In another point of differentiation, the crystal structure of
pyrimidin-4-one 4 indicated that the C-2 amino group was no
longer participating in a hydrogen bond interaction with the
IRAK4 hinge. This hinted at the possibility that it would be
feasible to remove the C-2 amino group altogether. This
modification would provide a step forward in improving the
drug-like qualities of the compound by removing a hydrogen
bond donor, and also provide additional SAR flexibility at this
position. A survey of different substituents at the C-2 position
was undertaken (Table 1). Methyl (compound 6) and ethyl
(compound 7) substituents were tolerated, but with a loss in
potency. Neither a hydroxyl/oxo group (compound 8) nor a
cyclobutyl ether (compound 9) were able to generate potent
inhibitors. For comparison, when these substituents were
explored in the pyrimidine core they yielded compounds that
were completely inactive (IRAK4 IC50 > 50 μM). In the case of
the pyrimidin-4-one, although these modifications produced
compounds that had a weaker potency than the parent
(pyrimidin-4-one 4), it is in a range that warranted additional
SAR optimization efforts. Switching to a thiomethyl ether
(compound 10) or a dimethyl amine (compound 11) provided
compounds of comparable potency to the alkyl substituents
(6 and 7). This indicated that, while it was possible to remove the
C-2 amino group, more electron rich groups appeared to be
preferred at this position. In view of that, when electron rich
cyclic amines (compounds 12−14) were examined, potencies
below 100 nm could be achieved. When the more electron
deficient difluoropiperidine 15 was tested, several fold loss of
potency was observed compared to the parent piperidine
(compound 14). However, increasing the size of the substituent
to tetrahydroisoquinoline 16 maintained the potency.
a
See Supporting Information for assay protocol.
changes were encouraging as they revealed that this position was
amenable to changes that could improve the physiochemical
properties or potentially the kinase selectivity of the compounds,
but not have a drastic impact on the IRAK4 potency.
Having established promising SAR trends at the C-2 position,
attention was focused on the carboribose ring. It was clear that in
order to improve the drug-like properties of the series, it would
be necessary to reduce the number of hydroxyl groups present
on the carboribose ring. Metabolite identification studies
indicated that oxidative as well as conjugative metabolism of
the carboribose ring were major concerns. It was observed from
the overlays of the pyrimidine and pyrimidin-4-one X-ray
structures (Figure 2B) that, in addition to the core itself, the
carboribose ring had shifted down in the binding site. This shift
brought the carboribose ring in closer proximity to a region of
an acidic residue, Asp272. In the structure of pyrimidin-4-one 4,
The addition of a basic nitrogen in the form of an N-methyl
piperizine ring (compound 17) was tolerated, as was an un-
substituted morpholine ring (compound 18). These last three
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a hydrogen bond interaction between a carboribose hydroxyl and
the Asp272 was formed (Figure 2A).
Table 2. Modification of the C-6 Position
This observation prompted the idea that perhaps it would be
possible to remove all the hydroxyl groups and add a basic
nitrogen into the ring (i.e., a pyrrolidine or a piperidine ring) that
could still make the key hydrogen bond interaction with Asp272
(Figure 3). This would have the net benefit of reducing the
Figure 3. Charge surface map indicating potential interactions of the
inhibitor with ASP272.
a
See Supporting Information for assay protocol.
Figure 4. X-ray cocrystal structure of pyrimidine 19.
piperidine 19 were improved: the number of hydrogen bond
acceptors was reduced (9 to 7), the number of hydrogen bond
donors reduced (5 to 3), and the polar surface area was reduced
as well (140 to 91). The X-ray cocrystal structure of com-
pound 19 was solved confirming the hypothesis that a properly
positioned basic group maintained a key interaction with the
Asp272 residue (Figure 4).
overall number of hydrogen bond donors and acceptors, and also
removing a metabolically labile primary hydroxyl group that did
not appear to be involved in any interactions with the IRAK4
protein. In practice, when the carboribose ring of morpholine
analogue 18 was replaced with a 3-piperidine ring to provide
compound 19, it was found that the IRAK4 potency could be
maintained with this modification and a slight increase in the
binding efficiency was realized. Moreover, the properties of
Capitalizing on the success with the piperidine ring, several
additional carboribose replacement motifs were surveyed, and
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Table 3. PK, Cell Activity, and Kinase Selectivity of Selected Compounds
a
b
c
d
e
f
Cpd
IRAK4 IC50 (nM)
Cell IC50 (nM)
Kinase Selectivity
Papp (×10−6 cm/s)
Solubility (μM)
Rat Cl (mL/min/kg)
Rat %F
12
13
16
18
19
26
31
18
67
27
11
19
85
93
78
96
96
99
94
90
96
97
12
18
5
26
23
12
63
21
8
−
−
4
292
141
375
187
333
580
75
88
98
45
43
51
0
7
0
29
9
13
2
15
13
42
a
b
See Supporting Information for assay protocol. Percent kinases with >100-fold selectivity (n = 111) versus IRAK, IC50, see Supporting Information
c
d
e
for additional details. Measured in LLC-PK1 cells. Measured kinetic solubility at pH 7. IV dosed at 1 mg/kg as a solution of 1 mg/mL in 20%
HPBCD. PO dosed at 10 mg/kg as a suspension of 2 mg/mL in 0.4% methylcellulose. See Supporting Information for full PK parameters for
f
compounds 19 and 31.
the results are presented in Table 2. In addition to piperidine,
pyrrolidine (compounds 20 and 21) was tolerated although there
was a clear stereochemical bias favoring the R configuration.
This carried over into the piperidine modification as well as
with the enantiomer of piperidine 19 having >13-fold loss in
potency (data not shown). Methylation of the piperidine to give
compound 22 resulted in a loss of potency compared to the
parent piperidine 19. It was possible to move the basic nitrogen
out of the ring, as in amino cyclohexane 23. The size of the ring
could also be increased from 6 to 7 exemplified by azepane 24,
having only a slight loss in potency. However, if the basicity of the
nitrogen was reduced, a significant loss of potency was observed
with lactam 25 having a potency over 2 μM. If the piperidine ring
was substituted with a hydroxyl group (compound 26) a slight
loss in potency was observed. Like the seven-membered ring
example, when the basicity of the piperidine ring was reduced,
in this case a piperidone ring (compound 27), a significant loss
in potency was observed. Moving from a 3-piperidine to a
4-piperidine ring (compound 28) saw a slight drop in potency.
A hydroxyl group could be reinstalled at the 3-position in place of
the basic nitrogen (compound 29), but with a loss in potency.
Finally, methyl substituents were tolerated vicinal to the
piperidine nitrogen (compounds 30 and 31). Like the R vs S
configuration bias for the parent piperidine, a preference for a
single methyl isomer was observed (R, compound 31).
Several potent pyrimidin-4-ones were selected for additional
follow up (Table 3). These compounds were assessed for their
potency in a cellular pathway engagement assay by measuring
the effect of the IRAK4 inhibitors on NF-κB activation. A reporter
cell line, THP1-XBlue, stably expressing NF-κB-inducible secreted
embryonic alkaline phosphatase (SEAP), was stimulated with
lipopolysaccharide (LPS) and the resulting SEAP activity
assessed quantitatively.15 All of the selected compounds were
active in this assay, although several compounds displayed a
significant activity shift compared to the biochemical enzyme
inhibition assay. In particular, pyrimidin-4-ones 12 and 19
displayed potency shifts of approximately 60-fold. This did not
appear to be attributable to poor solubility (26 and 21 μM) or
permeability (Papp = 12 and 29 × 10−6 cm/s) for these com-
pounds. Pyrimidinone 19 was also active in human peripheral
blood mononuclear cells (hPBMCs) stimulated with IL1β
(IC50 = 1.9 μM) or the TLR 7/8 agonist R848 (IC50 = 4.2 μM),
although the potency was right shifted analogous to the THP-1
data. Kinase selectivity was generally good across the class with
most compounds displaying >100-fold selectivity against 95%
of the kinases screened (n = 111). In particular compound 16
only had one off target kinase hit (FLT3). This kinase proved
particularly problematic as all of the compounds had less than
100-fold selectivity against it. However, none of the compounds
had any significant selectivity problems with inflammation-
related kinases,16 a fact that makes them amenable to develop-
ment for further in vivo studies. To this end, the pharmacoki-
netics of the selected compounds was also evaluated.
Bioavailability was generally low or zero for the carboribose
containing compounds (12, 13, 16, 18), but began to improve as
the carboribose was replaced with a piperidine ring (19, 26, 31).
Compound 19 possessed a reasonable 13% bioavailability, which
could be improved to 42% in compound 31 after the addition
of a methyl group adjacent to the piperidine nitrogen. Although
further improvement of the in vivo clearance is warranted,
replacement of the carboribose (13, 16, 18) with piperidine (19,
26, 31) and the concomitant improvement in clearance indicates
this is a tractable issue with a potential path forward. This trend
toward improving clearance could also be observed in hepatocyte
stability studies (data not shown) providing a useful in vitro/
in vivo correlation for further SAR efforts.
In summary, a structure enabled design strategy facilitated
the development of a series of kinase selective IRAK4
aminopyrimidin-4-ones from an original aminopyrimidine lead
series. Owing to a novel binding mode, these pyrimidin-4-ones
displayed SAR that was divergent from the pyrimidines. This
allowed for the incorporation of novel groups at the C-2 position,
as well as replacement of the carboribose moiety. These modi-
fications expedited the improvement of the physiochemical
characteristics of the series, while maintaining excellent kinase
selectivity, eventually leading to several compounds with
moderate to good oral bioavailability in rat. These attributes
make this series attractive for follow up optimization toward the
development of a highly selective IRAK4 in vivo tool compound.
ASSOCIATED CONTENT
* Supporting Information
■
S
Synthetic schemes, procedures, analytical data (including kinase
selectivity) for compounds 4 and 19, conditions for the biological
assays, kinase selectivity screen, and full PK data for 19 and 31.
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acsmedchem-
lett.5b00279.
Accession Codes
X-ray coordinates for compounds 1, 4, and 19 have been
uploaded to the Protein Data Bank with the codes 4ZTL, 4ZTM,
and 4ZTN, respectively.
AUTHOR INFORMATION
Corresponding Author
*Tel: 908-740-6129. E-mail: william.seganish@merck.com.
■
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(16) Gaestel, M.; Kotlyarov, A.; Kracht, M. Targeting innate immunity
protein kinase signaling in inflammation. Nat. Rev. Drug Discovery 2009,
8, 480−499.
Notes
The authors declare no competing financial interest.
REFERENCES
■
(1) Staschke, K. A.; Dong, S.; Saba, J.; Zhao, J.; Brooks, N. A.; Hepburn,
D. L.; Xia, J.; Gulen, M. F.; Kang, Z.; Altuntas, C. Z.; Tuohy, V. K.;
Gilmour, R.; Li, X.; Na, S. IRAK4 Kinase Activity Is Required for Th17
Differentiation and Th17-Mediated Disease. J. Immunol. 2009, 183,
568−577.
(2) Song, K. W.; Talamas, F. X.; Suttmann, R. T.; Olson, P. S.; Barnett,
J. W.; Lee, S. W.; Thompson, K. D.; Jin, S.; Hekmat-Nejad, M.; Cai, T.
Z.; Manning, A. M.; Hill, R. J.; Wong, B. R. The kinase activities of
interleukin-1 receptor associated kinase (IRAK)-1 and 4 are redundant
in the control of inflammatory cytokine expression in human cells. Mol.
Immunol. 2009, 46, 1458−1466.
(3) Brzezinska, A. A.; Johnson, J. L.; Munafo, D. B.; Ellis, B. A.; Catz, S.
D. Signaling mechanisms for Toll-like receptor-activated neutrophil
exocytosis: key roles for interleukin-1-receptor-associated kinase-4 and
phosphatidylinositol 3-kinase but not Toll/IL-1 receptor (TIR)
domain-containing adaptor inducing IFN-beta (TRIF). Immunology
2009, 127, 386−397.
(4) Akira, S.; Takeda, K. Toll-like receptor signaling. Nat. Rev.
Immunol. 2004, 4, 499−511.
(5) Suzuki, N.; Saito, T. IRAK-4 - a shared NF-kappa B activator in
innate and acquired immunity. Trends Immunol. 2006, 27, 566−572.
(6) Koziczak-Holbro, M.; Littlewood-Evans, A.; Poellinger, B.;
Kovarik, J.; Dawson, J.; Zenke, G.; Burkhart, C.; Mueller, M.; Gram,
H. The Critical Role of Kinase Activity of Interleukin-1 Receptor-
Associated Kinase 4 in Animal Models of Joint Inflammation. Arthritis
Rheum. 2009, 60, 1661−1671.
(7) Picard, C.; Puel, A.; Bonnet, M.; Ku, C. L.; Bustamante, J.; Yang, K.;
Soudais, C.; Dupuis, S.; Feinberg, J.; Fieschi, C.; Elbim, C.; Hitchcock,
R.; Lammas, D.; Davies, G.; Al-Ghonaium, A.; Al-Rayes, H.; Al-Jumaah,
S.; Al-Hajjar, S.; Al-Mohsen, I. Z.; Frayha, H. H.; Rucker, R.; Hawn, T.
R.; Aderem, A.; Tufenkeji, H.; Haraguchi, S.; Day, N. K.; Good, R. A.;
Gougerot-Pocidalo, M. A.; Ozinsky, A.; Casanova, J. L. Pyogenic
bacterial infections in humans with IRAK-4 deficiency. Science 2003,
299, 2076−2079.
(8) Chaudhary, D.; Robinson, S.; Romero, D. L. Recent Advances in
the Discovery of Small Molecule Inhibitors of Interleukin-1 Receptor-
Associated Kinase 4 (IRAK4) as a Therapeutic Target for Inflammation
and Oncology Disorders. J. Med. Chem. 2015, 58, 96−110.
(9) Hynes, J.; Nair, S. K. Advances in the Discovery of Small-Molecule
IRAK4 Inhibitors. Annu. Rep. Med. Chem. 2014, 49, 117−133.
(10) Tumey, L. N.; Boschelli, D. H.; Bhagirath, N.; Shim, J.; Murphy, E.
A.; Goodwin, D.; Bennett, E. M.; Wang, M.; Lin, L.-L.; Press, B.; Shen,
M.; Frisbie, R. K.; Morgan, P.; Mohan, S.; Shin, J.; Rao, V. R.
Identification and optimization of indolo[2,3-c]quinoline inhibitors of
IRAK4. Bioorg. Med. Chem. Lett. 2014, 24, 2066−2072.
(11) McElroy, W. T.; Seganish, W. M.; Herr, R. J.; Harding, J.; Yang, J.;
Yet, L.; Komanduri, V.; Prakash, K. C.; Lavey, B.; Tulshian, D.; Greenlee,
W. J.; Sondey, C.; Fischmann, T.; Niu, X. Discovery and hit to lead
optimization of 2,6-diaminopyrimidine inhibitors of interleukin
receptor-associated kinase 4. Bioorg. Med. Chem. Lett. 2015, 25, 1836−
1841.
(12) Hopkins, A. L.; Groom, C. R.; Alex, A. Ligand efficiency: a useful
metric for lead selection. Drug Discovery Today 2004, 9, 430−431.
(13) Seganish, W. M.; McElroy, W. T.; Herr, R. J.; Brumfield, S.;
Greenlee, W. J.; Harding, J.; Komanduri, V.; Matasi, J.; Prakash, K. C.;
Tulshian, D.; Yang, J.; Yet, L.; Devito, K.; Fossetta, J.; Garlisi, C. G.;
Lundell, D.; Niu, X.; Sondey, C. Initial optimization and series evolution
of 2,6-diaminopyrimidine inhibitors of interleukin-1 receptor associated
kinase 4. Bioorg. Med. Chem. Lett. 2015, 25, 3203−3207.
(14) Craciun, L.; Custelcean, R.; Mager, S. Molecular structure of an
isocytosine analog: Combined X-ray structural and computational study
of 2-Diethylalmino-6-methyl-5-n-propyl-4(3H)-pyrimidinone. Struct.
Chem. 1999, 10, 303−310.
(15) See Supporting Information for experimental protocol.
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