Purin-6-One Derivatives as Phosphodiesterase-2 Inhibitors

Article abstract of DOI:10.1155/2016/6878353

A series of purin-6-one derivatives were synthesized, and their in vitro inhibitory activity against phosphodiesterase-2 (PDE2) was evaluated by using a fluorescence polarization assay. Three compounds, that are, 2j, 2p, and 2q, showed significant inhibitory activity against PDE2 with IC₅₀ values of 1.73, 0.18, and 3.43 M, respectively. Structure-activity relationship (SAR) analysis was performed to explore the relationship between the chemical structures of these compounds and their inhibitory activity. Compounds 2j, 2p, and 2q were further selected for molecular docking study. The docking results suggested that these ligands bind with hydrophobic pockets of the catalytic active site of PDE2, where a Tyr655 residue was found to be important in binding with compound 2p, the most potent inhibitor identified in this study. Our present study provides useful information for the future design of novel PDE2 inhibitors.

Full text of DOI:10.1155/2016/6878353

Hindawi Publishing Corporation
Journal of Chemistry
Volume 2016, Article ID 6878353, 10 pages
http://dx.doi.org/10.1155/2016/6878353
Research Article
Purin-6-One Derivatives as Phosphodiesterase-2 Inhibitors
Wei Yuan,1 Xin-Yun Zhao,1 Xi Chen,1 and Chang-Guo Zhan2
1College of Chemistry and Materials Science, South-Central University for Nationalities, Wuhan 430074, China
2Department of Pharmaceutical Sciences, College of Pharmacy, University of Kentucky, 789 S. Limestone, Lexington, KY 40536, USA
Correspondence should be addressed to Xin-Yun Zhao; 45551525@qq.com and Xi Chen; ccnuchen@yahoo.com
Received 12 December 2015; Revised 14 January 2016; Accepted 17 January 2016
Academic Editor: Jose´ L. A. Mediano
Copyright © 2016 Wei Yuan et al. is is an open access article distributed under the Creative Commons Attribution License, which
permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
A series of purin-6-one derivatives were synthesized, and their in vitro inhibitory activity against phosphodiesterase-2 (PDE2) was
evaluated by using a fluorescence polarization assay. ree compounds, that are, 2j, 2p, and 2q, showed significant inhibitory activity
against PDE2 with IC values of 1.73, 0.18, and 3.43 ꢀM, respectively. Structure-activity relationship (SAR) analysis was performed
50
to explore the relationship between the chemical structures of these compounds and their inhibitory activity. Compounds 2j, 2p,
and 2q were further selected for molecular docking study. e docking results suggested that these ligands bind with hydrophobic
pockets of the catalytic active site of PDE2, where a Tyr655 residue was found to be important in binding with compound 2p, the
most potent inhibitor identified in this study. Our present study provides useful information for the future design of novel PDE2
inhibitors.
1. Introduction
and PDP (Figure 1) exhibited excellent inhibitory activities
against PDE2A with IC values of 4.7 and 0.6 nM, respec-
50
Mammalian cyclic nucleotide phosphodiesterases (PDEs)
could catalyze the hydrolysis of ubiquitous intracellular sec-
ond messengers cyclic adenosine monophosphate (cAMP)
and/or cyclic guanosine monophosphate (cGMP) into inac-
tive 5ꢀ-AMP and/or 5ꢀ-GMP to modulate a number of
physiological processes. Numerous studies have proved that
PDEs were excellent drug targets for the development of
therapeutic agents against various diseases [1, 2]. e human
genome encodes 11 PDE families (PDE1 to PDE11) to produce
a series of PDE isoenzymes [3–5]. ere is only one gene
coding for PDE2, namely, PDE2A. PDE2A has been described
to degrade both substrates cAMP and cGMP. Its enzymatic
activity can be allosterically activated by cGMP. Additionally,
PDE2A is preferentially expressed in the mammalian heart
[6] and brain tissues [7]. Animal behavioral models have
indicated that PDE2 inhibition plays a key role in the control
of memory and anxiety [8–10]. It could also be considered as
a promising therapeutic target for cognition enhancement in
Alzheimer’s disease [11].
Among the as-reported PDE2 selective inhibitors, there
are four inhibitors particularly interesting to many scien-
tists. As shown in Figure 1, EHNA was the first reported
PDE2 inhibitor with IC value of 1 ꢀM [12]. BAY 60-7550
tively [8, 13]. ND7001 was under development by Neuro
3D and advanced into clinical phase I in 2005, showing
potent inhibitory activity against PDE2 [14] with IC value
50
of 57 nM. However, according to the reports of omson
Reuters Pharma, developments of BAY 60-7550 and ND7001
were ceased due to their poor pharmacokinetics perfor-
mances [15].
Despite various X-ray crystal structures for PDE2 having
been reported [16, 17], the shape of the binding pocket of
PDE2 remained uncertain until 2013, when Huang et al. have
reported the X-ray crystal structure of PDE2A complexed
with BAY 60-7550 [18]. e crystal structure revealed that
this compound binds to the PDE2 active site using not only
the conserved glutamine-switch mechanism for substrate
binding but also a binding induced hydrophobic pocket,
which is lined by Leu770, His773, r805, Leu809, Ile866,
and Ile870 (Figure 2). It has never been reported before. e
binding mode of BAY 60-7550 with the active site of PDE2
in crystal state is depicted in Figure 2. As shown in this
figure, the –NH-CO– moiety of BAY 60-7550 forms bidentate
hydrogen bonding to the invariant glutamine (Gln859) and
the imidazotriazin-4-one core stack against the side chain of
Phe862 and Phe830. In addition, the phenyl ring is filled into
50

2
Journal of Chemistry
O
N
performed to investigate the binding modes of these purin-6-
one derivatives with the PDE2 catalytic domain. Our present
studies provide useful information for the design of novel
PDE2 inhibitors.
HN
NH2
N
N
N
N
N
N
2. Results and Discussion
OH
OCH3
OCH3
OH
2.1. Chemistry. All compounds synthesized in this study
have been summarized in Table 1. e general synthetic
routes of these target compounds are depicted in Scheme 1.
e key intermediates 5-amino-1-substituted-imidazole-4-
carboxamides 1(1a, 1c, 1d, 1i, 1n, and 1p) were firstly synthe-
sized (Scheme 1) using amines, 2-amino-2-cyanoacetamide,
and triethyl orthoformate as raw materials. eir synthetic
route was modified from the work of Banerjee et al. [19] by
adding pyridine as catalyst under the refluxing conditions.
e yield of 1a (R = CH CH OH) was higher (73.2%) than
H3C
HN
EHNA
BAY 60-7550
O
N
O
N
N
H3CO
Ph
N
N
O
2
2
OCH3
OCH3
that reported (42%) in the work of Banerjee et al. e melting
CONH2
point and 1H NMR of 1c (R = CH C H ) were found to be
PDP
ND7001
2
6
5
consistent with those reported by Shaw and Alhede [20, 21].
Compounds 1n and 1p were synthesized by using 3-amino-
4-phenyl-butan-2-ol and 3-amino-6-phenyl-hexan-2-ol as
starting materials. Target compounds were synthesized by
refluxing intermediates 1 and the corresponding esters in
the presence of sodium methoxide. Purin-6-one derivative
2c was then reacted with allyl bromide to give N1-alkylated
(2c-1) and O6-alkylated (2c-2) products in the presence of
NaH. Compounds 2n and 2o were further oxidized to 2r
and 2s under DMSO using SO /pyridine complex [22]. eir
Figure 1: Structures of EHNA, BAY 60-7550, PDP, and ND7001.
Met845
Leu770
Met847
Ile866
His773
3
structures were confirmed by H NMR, 13C NMR, IR, and
mass spectroscopy. e single-crystal structure of compound
2a was also determined by our X-ray crystallography [23].
1
Leu858
Phe830
Tyr827
BAY 60-7550
r805
2.9
2.7
2.2. Inhibitory Activity of Purin-6-One Derivatives against
PDE2 and SAR Studies. e in vitro inhibitory activity
against the recombinant human PDE2 was evaluated for final
compounds by using fluorescence polarization assay. e
inhibition ratios of target compounds against PDE2 in the
presence of 10 ꢀM of inhibitor were summarized in Table 1.
Results from Table 1 indicated that varying substituent at the
2- and 9-position will lead to remarkably different inhibitory
activities. Keeping R = −CH CH OH, replacing R1 (3-
Ile870
Leu809
Gln859
Tyr655
Figure 2: e interaction of BAY 60-7550 with the catalytic
domain of PDE2 (PDB ID: 4HTX). e BAY compound is rendered
with green color scheme. Residues that form key interactions
with BAY compound are rendered with orange color scheme. e
environmental protein surrounding is rendered in orange. For the
convenience of display, some residues are not shown.
2
2
methoxybenzyl) in compound 2a with 3,4-dimethoxybenzyl
(compound 2b) will increase inhibitory ratio from 48%
(2a) to 78% (2b). When R and R1 were, respectively, to
be –CH C H and 2-methylbenzyl (compound 2c), the
2
6
5
inhibitory ratio value decreased to 35%. It was postulated that
large nonpolar groups at R substituent will be unfavorable for
PDE2A inhibition. is assumption is further confirmed by
the inhibitory values (18–42%) of compounds 2d and 2f–2h,
R groups of which were nonpolar group −(CH ) C H . e
the binding induced hydrophobic pocket, which significantly
contributes to the binding of BAY 60-7550 with PDE2.
Inspired by the information mentioned in Figure 2, a
series of purin-6-one derivatives were designed and synthe-
sized by keeping the core scaffolds purin-6-one and changing
the substituents at 2- and 9-positions on the purin-6-one.
Fluorescence polarization assay was performed to test the
inhibitory effect in vitro using recombinant human PDE2 in
the presence of 10 ꢀM of inhibitors. For those compounds
2 3
6
5
only exception is compound 2e; the inhibitory ratio is 78%,
which is the same as the inhibitory value of 2b. Increasing
the chain length of R in compound 2e to –(CH ) C H leads
2 4
6
5
to compound 2i, which has an inhibitory activity essentially
identical to that of 2e. Further adding a methoxyl group to
3-position of phenyl ring of R1 in 2i results in compound
2j, which has a significant stronger inhibitory activity with
a value of 95%. In contrast, adding a methyl group to
with higher inhibitory activity, IC values against PDE2
50
were also determined. Ligand-protein docking studies were

Journal of Chemistry
Table 1: Molecular structures and PDE2 inhibitory activity of purin-6-one derivatives (see Scheme 1, compounds 2a–2q).
3
Compound
R
R1
3-Methoxybenzyl
3,4-Dimethoxybenzyl
2-Methylbenzyl
3,4-Dimethoxyphenyl
Benzyl
2-Methylbenzyl
4-Chlorophenyl
2,4-Dichlorophenoxyethyl
Benzyl
3-Methoxybenzyl
2-Methylbenzyl
2,4-Dichlorophenoxyethyl
4-Chlorophenyl
Benzyl
% Inhibition (at 10 ꢀM inhibitor)
2a
2b
2c
2d
2e
–CH CH OH
–CH CH OH
–CH C H
48
78
35
44
2
2
2
2
2
6
5
–(CH ) C H
2
3
6
5
5
5
5
5
5
5
5
5
5
–(CH ) C H
78
35
18
42
2
3
6
2f
–(CH ) C H
2
3
6
2g
2h
2i
2j
2k
2l
2m
2n
2o
2p
2q
2r
–(CH ) C H
2
3
6
–(CH ) C H
2
3
6
–(CH ) C H
78
2
4
6
–(CH ) C H
95 (1731a)
2
4
6
–(CH ) C H
24
34
30
73
2
4
6
–(CH ) C H
2
4
6
–(CH ) C H
2
4
6
–(CH CHOH)CHCH C H
3
2
6
5
–(CH CHOH)CHCH C H
2-Methylbenzyl
Benzyl
4-Chlorophenyl
Benzyl
70
3
2
6
5
–(CH CHOH)CH(CH ) C H
100 (184a)
3
2
3
6
5
5
–(CH CHOH)CH(CH ) C H
99 (3427a)
3
2
3
6
5
–(CH CO)CHCH C H
–(CH CO)CHCH C H
1-Allyl-9-benzyl-2-(2-methyl-benzyl)-1,9-dihydro-purin-6-one
6-Allyloxy-9-benzyl-2-(2-methyl-benzyl)-9H-purine
75
78
56
9
3
2
6
5
2s
2-Methylbenzyl
3
2
6
2c-1
2c-2
aIC (nM).
50
O
O
EtO
OEt
H2N
N
N
Pyridine
H2N
+
+
RNH2
NH2
OEt
acetonitrile
H2N
CN
R
1
O
O
N
H2N
N
6
5
HN
1
2
CH3ONa
7
9
R1COOCH3
8
N
+
4
reflux
3
N
R1
H2N
N
R
R
2a–q
2c-1
SO3/pyridine
Alkylated
2n/2o
2r/2s
2c
DMSO
2c-2
Scheme 1: Synthesis of purin-6-one derivatives.
the 2-position of phenyl ring of R1 in 2i (compound 2k) leads
to a much less potent inhibitory with a value of only 24%. e
difference of R1 groups and inhibitory values between 2j and
2k clearly demonstrates that adding a moderately nonpolar
group at the 3- or 5-position of benzyl at R1-position is
favorable.
Based on the discussion above, we further compare the
structure of 2b and 2d. It could be found that the presence
of a hydroxyl (e.g., –CH CH OH) in R group is more
2
2
favorable than a nonpolar R substituent (e.g., –(CH ) C H )
2 3
6
5
without a hydroxyl. In addition, comparing the inhibition
ratio of 2d (44%) to that of 2j (95%), one can find that

4
Journal of Chemistry
Table 2: Calculated binding free energies in comparison with
the bulkiness of R group should also be important to the
PDE2A inhibition. Combining these two points, we tried
available experimental data((aa) ll in kcal/mol).
to introduce a bulky –(CH )CH(OH) group to the existing
3
(b)
cal
exp
Compound
2j
ΔGbind
IC (ꢀM)
ΔGbind
50
R group of 2i. e resulting compound, that is, 2p, shows
excellent inhibitory activities with inhibition ratio of 100%.
However, when the –(CH CHOH)CH(CH ) C H group
−9.11
1.731
0.184
3.427
−7. 8
2p
2q
−9.80
−8.85
−9.2
−7. 4
3
2 3
6
5
of compound 2p was replaced with a less bulky group,
that is, –(CH CHOH)CHCH C H (compound 2n), the
corresponding inhibition ratio drops to 73%. Hence, the
presence of hydroxyl and bulky size of R group are both
important for inhibition activity.
(a)
Binding free energies predicted by AUTODOCK.
3
2
6
5
(b)
Binding free energies derived from the experimental IC values.
50
Beltman et al. have reported a series of cGMP analogues
and evaluated the inhibitory activities of these compounds
against PDE2. e N1-methylated cGMP analogues generally
exhibited weak inhibitory activity, as compared to those
cGMP analogues with a hydrogen on N1. SAR study sug-
gested that N1-methylation of cGMP analogues will result
in the loss of a hydrogen bond or increase the steric hin-
drance with the binding pocket of PDE2, which will lead
to reduced inhibitory activities [24]. is study concerns
the importance of maintaining bidentate hydrogen bonds
formed between the ꢁ-amide of Gln859 and the carbonyl
O6, NH moiety of the inhibitors. To testify this idea, we also
synthesized N1-allylated derivative of compound 2c, namely,
2c-1. Interestingly, we observed a remarkably improved
inhibitory activity of compound 2c-1 (N1-allylation), which
is contrary to Beltman’s reports. As can be seen from Table 1,
the inhibitory ratio of 2c-1 is higher (57%) than that (35%)
of 2c. Although 2c-1 loses a hydrogen donor at its N1-
position because of the allylation at this place, the loss of
the hydrogen bonding interaction can be compensated by
the hydrophobic interaction formed between the allyl group
and the surrounding hydrophobic pocket of PDE2. Hence,
for purine-6-one derivatives it is not necessary to form a
bidentate hydrogen bond between the N1-H and ꢁ-amide
of Gln859 to maintain optimal PDE2 inhibitory activity. On
the other hand, when the O6-position of 2c is attached with
an allyl group, the resulting compound 2c-2 shows a much
weaker inhibitory activity (9%), as compared to that (35%)
for 2c. Our present study shows that the carbonyl oxygen
at 6-position of purin-6-one scaffold (the scaffold consists
of atoms 1 to 9. See Table 1 for numbering of these atoms)
probably plays a key role in binding with PDE2.
the complex-ligand and water molecules were removed from
the complex structure, except for four water molecules and
a hydroxide ion that bound with the metal ions Zn2+ and
Mg2+ at the catalytic pocket. en hydrogen atoms were
added by using the Leap tools implemented in AMBER
sofware. e molecular structures of 2j, 2p, and 2q were con-
structed by GaussView followed by geometrical optimization
at PM3 level. For the receptor and each ligand, the nonpolar
hydrogen atoms were merged and Gasteiger charges were
added. en AUTODOCK4.2 program was used to search
for the most favorable binding mode of the ligands and
PDE2 catalytic domain. During the docking process, atoms
in the receptor were kept constant. 100 docking runs were
performed for each ligand and the conformations with the
lowest binding free energies were selected for analysis.
Molecular docking revealed that all of these inhibitors
bind with PDE2 in a similar binding mode (Figure 3). From
this figure, it could be found that each of the PDE2 inhibitors
was fitted in a cavity formed by Phe830, Phe862, Ile826,
Gln859, Met845, Met847, Leu770, His773, Leu809, Ile866,
and Ile870 residues. In the PDE2-ligand binding complexes
(Figure 3), the common purin-6-one scaffold of the inhibitors
is lodged in the hydrophobic pocket surrounded by the side
chains of Ile826, Ile866, Phe830, and Phe862 residues, causing
a high degree of surface complementarities. Hydrogen bonds
were formed between the purin-6-one and the ꢁ-amide of
Gln859. In addition, R groups of ligands were clapped by
the hydrophobic H pocket formed by His773, Leu809, Ile866,
and Ile870 residues, which was also observed in the crystal
structure of PDE2 in complex with BAY 60-7550. R1 group
of the inhibitors formed additional hydrophobic interaction
with the peripheral residues Met847, Leu858, and Ile866.
In addition to the common features mentioned above,
the hydroxyl group of R1 substituent of inhibitor 2p forms
an extra hydrogen bonding interaction with the side chain
of Tyr655 (see Figure 3(b)), which will enhance the binding
of 2p with PDE2. Compared to the binding mode of 2p,
2j (Figure 2(a)) and 2q (Figure 2(c)) do not interact with
Tyr655, implying that their binding affinities with PDE2 will
be weaker than that of 2p. As can be seen from Table 2, the
binding free energies (ΔGbindcal) predicted by AUTODOCK
are consistent with the corresponding experimental binding
free energies (ΔGbindexp), suggesting that the present binding
modes of these compounds are reliable.
e values in Table 1 show that compounds 2j, 2p, and
2q have potent inhibitory activities. ese three compounds
were then selected for further inhibitory activity tests at
various concentrations in order to calculate IC value, which
50
showed a submicromolar inhibitory activity.
2.3. Molecular Modeling. e results from the preliminary
activities prompted us to pay attention to three of the more
potent compounds (2j, 2p, and 2q) with higher inhibitory
activity against PDE2. In an effort to gain an understanding
of the structural basis for the empirical structure-activity
relationships observed, we further studied the binding mode
of the compounds (2j, 2p, and 2q) through molecular
docking. For this purpose, the crystal structure of PDE2 in
complex with BAY 60-7550 (PDB ID: 4HTX) was selected
as the receptor for molecular docking. Before docking,
It is worth noting that the interaction with Tyr655 has
never been reported before. Hence, this residue can be
considered as a new site for the development of novel PDE2

Journal of Chemistry
5
Met845
Met847
Met845
Met847
Leu770
Ile866
Leu770
Ile866
His773
His773
Leu858
Tyr827
Leu858
Tyr827
Phe830
Phe830
Compound 2j
Compound 2p
r805
r805
2.7
3.0
Leu809
Leu809
Ile870
Ile870
2.9
2.6
Gln859
Gln859
3.0
Tyr655
Tyr655
(a)
(b)
Met845
Met847
Leu770
Ile866
His773
Leu858
Tyr827
Phe830
3.1
2.9
Compound 2q
Leu809
r805
Ile870
Gln859
Tyr655
(c)
Figure 3: Binding mode of compounds 2j (a), 2p (b), and 2q (c) in the active site pocket of PDE2. Each ligand is rendered as balls and sticks
and the surrounding residues are rendered as sticks. For the convenience of display, some residues and atoms are not shown. See Figure 2 for
the color codes of the atom types.
inhibitors. Compound 2p can be regarded as a good starting
structure for the design of new PDE2 inhibitors.
is promising to be a leading structure for the design of novel
PDE2 inhibitors.
4. Experimental Section
3. Conclusions
4.1. Chemistry. 1H NMR spectra were recorded on a Varian
NMR 600 MHz instrument or Mercury plus 400 MHz, and
the chemical shifs, ꢂ, are in ppm and tetramethylsilane
as internal standard. Graphical 1H NMR spectra of the
compounds 2b–2s in this work are collected in the Supple-
mentary Material available online at http://dx.doi.org/10.1155/
2016/6878353. Mass spectra were determined using Trace MS
2000 organic mass spectrometry, and signals are given in
m/z. Melting points were recorded on Bu¨chi B-545 melting
point apparatus. Elemental analysis (EA) was carried out
with a Vario EL III CHNSO elemental analyzer. Conventional
heating was carried out on Corning stirrer/hotplates with oil
A series of purin-6-one derivatives were designed and synthe-
sized as potential PDE2 inhibitors. SAR studies suggested that
the carbonyl oxygen at 6-position of purin-6-one derivatives
played a key role in maintaining the inhibitory activity against
PDE2 enzyme. ree more potential compounds 2j, 2p,
and 2q were identified to have submicromolar IC values.
50
Molecular docking of compounds 2j, 2p, and 2q into the
catalytic domain of the PDE2 revealed a similar binding
profile with PDE2 to that of BAY 60-7550. Residue Tyr655,
which has been never reported before, was found to be
potential binding target for PDE2 inhibitors. e binding
mode analysis indicates that optimization of 2p compound

6
Journal of Chemistry
baths. in layer chromatography (TLC) inspections were
ꢃ = = Hz), 4.18–4.22 (m, 1H, CH), 3.90–3.93 (m, 1H, CH),
3.12–3.26 (m, 2H, CH ), 1.05 (d, 3H, CH , ꢃ = = Hz). EI-MS:
carried out on a silica gel GF plates. Triethyl orthoformate,
254
2
3
2-cyano-2-amino-acetamide, and other chemical reagents
otherwise noted were commercially available. Solvents were
dried in a routine way and redistilled. Esters were prepared
using acid as raw materials in the presence of acetyl chloride
and alcohol.
m/z (relative intensity) 274.2 (M+, 5), 166 (2), 126 (17), 109
(15), 91.2 (100), 77.0 (17), 65.0 (27), 51.2 (12), 45.3 (60).
(6) 5-Amino-1-[1-(1-hydroxyethyl)-4-phenylbutyl]-1H-imida-
1
zole-4-carboxamide (1p). H NMR (600 MHz, DMSO-d ):
6
ꢂ, 7.12–7.26 (m, 6H, ArH+1H), 6.75, 6.60 (pair of s, 2H,
CONH ), 5.74 (s, 2H, NH ), 5.13 (d, 1H, OH, ꢃ = =.8 Hz),
2
2
4.1.1. General Procedures for Synthesis of the Intermedi-
ate 5-Amino-4-carboxamide-1-substituted-1H-imidazole (1).
20 mmol of 2-amino-2-cyanoacetamide was suspended in
30 mL absolute acetonitrile, and 23 mmol of triethyl ortho-
formate and 0.03 g pyridine as a catalyst were added to
the suspension with stirring. e suspension was heated
to reflux temperature using an oil bath preheated to 100∘C
and the suspension was held at boiling temperature for 1 h
and then 20 mmol of substituted amine was then added
over a 3 to 5 min period and boiling was continued for an
additional 15 min. e reaction was quickly cooled to room
temperature and then solvent was evaporated, and the residue
was recrystallized from DMF-ethanol to give the product.
3.82–3.83 (m, 2H, CH+CH), 2.53–2.61 (m, 2H, CH ), 1.80–
2
1.91 (m, 2H, CH ), 1.32–1.41 (m, 2H, CH ), 0.95 (d, 3H, CH ,
2
2
3
ꢃ = = Hz). EI-MS: m/z (relative intensity) 303.6 (M+1, 13),
302.2 (M+, 73), 268.1 (25), 240.4 (8), 256.9 (168), 152.9 (208),
126 (100), 108.9 (71), 91.1 (83), 77.0 (13), 65.1 (14), 55.2 (14),
43.1 (25).
4.1.2. General Procedure for the Preparation of Purin-6-One
Derivatives (2a–2q). 1.4 mmol of 5-amino-1-substituted-4-
carboxamide-1H-imidazole (1) was dissolved in 10 mL of
absolute methanol. en 5.6 mmol of the appropriate ester is
added into this solution. is mixture was added in 10 mL of
methoxide-methanol solution prepared from sodium (0.15 g,
6.3 mmol) and 10 mL of absolute methanol. e mixture
was refluxed for 15–20 h. Afer cooling, the solvent was
evaporated off and the residue was taken into ethyl acetate.
e organic phase was dried over Na SO and evaporated.
(1) 5-Amino-1-(2-hydroxyethyl)-1H-imidazole-4-carboxamide
(1a). M.p.: 142.6∘C, Yield: 73.2%. 1H NMR (400 MHz,
DMSO-d ): ꢂ, 7.06 (s, 1H, CH), 6.72, 6.58 (pair of s, br, 2H,
6
CONH ), 5.68 (s, 2H, ArNH ), 5.03 (s, 1H, OH), 3.83 (t, 2H,
2
2
2
4
ꢃ = 5.2 Hz, CH O), 3.61 (t, 2H, ꢃ = = Hz, CH N). EI-MS: m/z
And the residue was purified via silica gel chromatography
(eluent: the mixture of ethyl acetate and methanol) to obtain
the pure product (2a–2q).
2
2
(relative intensity) 170.9 (M+1, 55), 169.8 (97), 125.8 (91), 109.8
(74), 108.7 (100), 44.8 (67).
(2) 5-Amino-1-benzyl-1H-imidazole-4-carboxamide (1c). M.p.:
(1) 9-(2-Hydroxy-ethyl)-2-(3-methoxy-benzyl)-1,9-dihydro-
purin-6-one (2a). e data of 1H NMR, IR, EI-MS, elemental
analysis, and X-ray crystal was reported in our previous
study [23].
250.8∘C, Yield: 76%. 1H NMR (600 MHz, DMSO-d ): ꢂ, 7.19–
6
7.37 (m, 6H, ArH+CH), 6.64, 6.79 (pair of s, 2H, CONH ),
2
5.84 (s, 2H, ArNH ), 5.07 (s, 2H, ArCH ). EI-MS: m/z
2
2
(relative intensity) 216.2 (M+, 23), 91.2 (100), 65.1 (26), 44.3
(7).
(2) 2-(3,4-Dimethoxy-benzyl)-9-(2-hydroxy-ethyl)-1,9-dihy-
1
dro-purin-6-one (2b). M.p.: 223.6∘C, Yield: 76%. H NMR
(3) 5-Amino-1-(3-phenylpropyl)-1H-imidazole-4-carboxamide
(400 MHz, DMSO-d ): ꢂ, 12.27 (s, NH, 1H), 7.95 (s, CH,
6
(1d). M.p.: 198.1∘C, Yield: 76%. 1H NMR (600 MHz, DMSO-
1H), 7.02 (s, ArH, 1H), 6.86–6.93 (m, ArH, 2H), 4.97 (t,
d ): ꢂ, 7.17–7.30 (m, 5H, ArH), 7.11 (s, 1H, CH), 6.61, 6.76
OH, 1H, ꢃ = 2.8 Hz), 4.15 (t, CH , 2H, ꢃ = 5.2 Hz), 3.86 (s,
6
2
(pair of s, 2H, CONH ), 5.80 (s, 2H, NH ), 3.82 (t, CH ,
CH , 2H), 3.74–3.71 (8H, OCH +CH ). 13C NMR (100 MHz,
2
2
2
2
3
2
ꢃ = 7.2 Hz), 2.50–2.58 (m, 2H, CH ), 1.91–1.99 (m, 2H, CH ).
DMSO-d ): ꢂ, 157.8, 157.3, 149.4, 149.1, 148.3, 141.1, 129.4, 122.4,
2
2
6
EI-MS: m/z (relative intensity): 244.2 (M, 44), 210.3 (26), 140.1
(61), 123.1 (82), 117.1 (42), 109 (33), 91.1 (100), 77.0 (18), 65.0
(25), 44.2 (14).
121.2, 113.1, 112.3, 59.85, 56.03, 55.95, 55.9, 46.5. EI-MS: m/z
(relative intensity) 330.0 (M+, 100), 299.1 (39), 285.1 (15),
271.0 (33), 239.0 (17), 151.1 (24), 135.1 (23), 109.1 (19), 91.1 (12),
77.1 (16), 65.2 (18), 51.2 (7), 45.2 (13). IR (cm−1): 3327 (N-H),
3079, 2939, 1711 (C=O), 1583, 1516, 1439, 1408, 1262, 1237, 1162,
1067, 1058, 1020, 647. Anal. calcd for C H N O : C, 58.17;
(4) 5-Amino-1-(4-phenylbutyl)-1H-imidazole-4-carboxamide
(1i). M.p.: 222∘C, Yield: 72%. 1H NMR (600 MHz, DMSO-d ):
6
16 18
4
4
ꢂ, 7.14–7.27 (m, 5H, ArH), 7.07 (s, 1H, CH), 6.57, 6.70 (pair of
H, 5.49; N, 16.96. Found: C, 58.15; H, 5.82; N, 16.63.
s, 2H, CONH ), 5.76 (s, 2H, NH ), 3.80 (t, CH , ꢃ = = Hz),
2
2
2
(3)
9-Benzyl-2-(2-methyl-benzyl)-1,9-dihydro-purin-6-one
2.58 (t, CH , ꢃ = 7.8 Hz), 1.62–1.66 (m, 2H, CH ), 1.49–1.54
2
2
(m, 2H, CH ). EI-MS: m/z (relative intensity) 258.5 (M+, 51),
(2c). e data of 1H NMR, 13C NMR, IR, EI-MS, and
2
224.2 (22), 213.8 (9), 154.1 (13), 149.9 (22), 137.2 (12), 126.1 (17),
108.9 (28), 91.1 (100), 76.9 (14), 65.0 (26).
elemental analysis was reported in our previous study [25].
(4) 2-(3,4-Dimethoxy-phenyl)-9-(3-phenyl-propyl)-1,9-dihy-
1
dro-purin-6-one (2d). M.p.: 235.3∘C, Yield: 45%. H NMR
(5) 5-Amino-1-[1-(1-hydroxyethyl)-2-phenylethyl]-1H-imida-
zole-4-carboxamide (1n). M.p.: 231.4∘C, Yield: 67%. 1H NMR
(600 MHz, DMSO-d ): ꢂ, 12.33 (br, s, 1H, NH), 8.11 (s, 1H,
6
(600 MHz, DMSO-d ): ꢂ, 7.12–7.23 (m, 6H, ArH), 6.56, 6.69
CH), 7.75 (s, 1H, ArH), 7.80 (d, 1H, ArH, ꢃ = 4.2 Hz), 7.18–7.29
6
(pair of s, 2H, CONH ), 5.60 (s, 2H, NH ), 5.31 (d, 1H, OH,
(m, 5H, ArH), 7.11 (d, 1H, ArH, ꢃ = 4.5 Hz), 4.21 (t, 2H, CH ,
2
2
2

Journal of Chemistry
7
ꢃ = 7.2 Hz), 3.86 (s, 3H, OCH ), 3.85 (s, 3H, OCH ), 2.63
2.03–2.05 (m, 2H, CH ). EI-MS: m/z (relative intensity) 430.4
3
3
2
(t, 2H, CH , ꢃ = 7.8 Hz), 2.17–2.22 (m, 2H, CH ). 13C NMR
(M+1, 7), 429.5 (M+, 7), 428.0 (18), 393.1 (10), 344.5 (6), 277.3
(18), 268.5 (33), 266.9 (70), 240.2 (17), 198.6 (8), 182.9 (8), 164.2
(72), 161.8 (100), 125.9 (12), 98.0 (15), 91.1 (28), 62.6 (21). IR
(cm−1): 3441 (N-H), 3098, 3027, 2939, 2811, 1718 (C=O), 1600,
1532, 1482, 1456, 1412, 1301, 818, 753, 699, 504. Anal. calcd for
C H Cl N O : C, 58.75; H, 4.23; N, 13.05. Found: C, 58.39;
2
2
(100 MHz, DMSO-d ): ꢂ, 158.0, 153.0, 151.92, 159.86, 149.4,
6
149.0, 148.9, 141.3, 141.0, 128.8, 126.4, 124.9, 121.6, 112.0, 111.3,
56.2, 56.1, 43.3, 32.6, 31.5. EI-MS: m/z (relative intensity)
390.2 (M+, 75), 363.5 (19), 285.0 (100), 269.1 (10), 198.9 (17),
164.2 (12), 148 (8), 117.2 (13), 104.2 (10), 91.1 (67), 77.2 (13),
65.0 (21), 51.3 (7). IR (cm−1): 3431 (N-H), 3093, 3012, 2933,
1685 (C=O), 1559, 1539, 1514, 1304, 1269, 1223, 1178, 1024, 876,
754, 702. Anal. calcd for C H N O : C, 67.68; H, 5.68; N,
21 18
2
4
2
H, 4.11; N, 13.12.
(9) 2-Benzyl-9-(4-phenyl-butyl)-1,9-dihydro-purin-6-one (2i).
22 22
4
3
M.p.: 197.3∘C, Yield: 73%. 1H NMR (600 MHz, DMSO-d ): ꢂ,
14.35. Found: C, 68.05; H, 5.38; N, 14.18.
6
12.38 (s, 1H, NH), 8.04 (s, 1H, CH), 7.13–7.33 (m, 10H, ArH),
(5)
2-Benzyl-9-(3-phenyl-propyl)-1,9-dihydro-purin-6-one
4.12 (t, 2H, CH , ꢃ = 6.6 Hz), 3.94 (s, 2H, CH ), 2.56 (t, 2H,
2
2
(2e). M.p.: 225.1∘C, Yield: 62%. 1H NMR (600 MHz, DMSO-
CH , ꢃ = 7.8 Hz), 1.76–1.81 (m, 2H, CH ), 1.46–1.51 (m, 2H,
2
2
d ): ꢂ, 12.38 (s, 1H, NH), 8.04 (s, 1H, CH), 7.15–7.36 (m, 10H,
CH ). EI-MS: m/z (relative intensity) 358.1 (M+, 55.51), 330.1
6
2
ArH), 4.12 (t, 2H, CH , ꢃ = 7.2), 3.96 (s, 2H, CH ), 2.54 (t,
(28.66), 267.2 (8.26), 253.1 (20.71), 239.1 (26.38), 225.3 (45.65),
213 (9.66), 109.0 (15.93), 91.1 (100.00), 77.0 (10.93), 65.0 (17.75),
55.2 (7.37), 45.2 (14.01). IR (cm−1): 3427 (N-H), 3103, 3061,
2936, 2860, 1723 (C=O), 1578, 1454, 1412, 1373, 1357, 1127, 944,
748, 698, 658. Anal. calcd for C H N O: C, 73.72; H, 6.19;
2
2
2H, CH , ꢃ = 7.8 Hz), 2.08–2.13 (m, 2H, CH ). 13C NMR
2
2
(100 MHz, DMSO-d ): ꢂ, 157.8, 157.0, 149.3, 141.3, 140.6, 137.2,
6
129.2, 128.9, 128.8, 128.7, 127.3, 126.4, 122.6, 43.4, 39.4, 32.5,
31.4. EI-MS: m/z (relative intensity) 344.3 (M+, 2), 239.2 (22),
183.1 (6), 117.2 (10), 91.1 (100), 77.2 (22), 65.2 (24), 51.2 (15),
44.2 (29). IR (cm−1): 3442 (N-H), 3097, 2940, 2864, 1724
(C=O), 1581, 1494, 1453, 1410, 1361, 1128, 718, 698, 654. Anal.
calcd for C H N O: C, 73.23; H, 5.85; N, 16.27. Found: C,
22 22
4
N, 15.63. Found: C, 73.79; H, 6.14; N, 15.93.
(10) 2-(3-Methoxy-benzyl)-9-(4-phenyl-butyl)-1,9-dihydro-
purin-6-one (2j). M.p.: 177.3∘C, Yield: 41%. 1H NMR
21 20
4
(600 MHz, DMSO-d ): ꢂ, 12.34 (s, 1H, NH), 8.03 (s, 1H, CH),
73.59; H, 6.10; N, 16.62.
6
7.12–7.26 (m, 6H, ArH), 6.95 (s, 1H, ArH), 6.88 (d, 1H, ArH,
(6) 2-(2-Methyl-benzyl)-9-(3-phenyl-propyl)-1,9-dihydro-pur-
ꢃ = 3.6 Hz), 6.81 (d, 1H, ArH, ꢃ = 3.9 Hz), 4.13 (t, 2H, CH ,
2
in-6-one (2f ). M.p.: 214.2∘C, Yield: 57%. 1H NMR (600 MHz,
ꢃ = 6.6 Hz), 3.91 (s, 2H, CH ), 3.71 (s, 3H, OCH ), 2.56 (t,
2
3
DMSO-d ): ꢂ, 12.33 (s, 1H, NH), 8.03 (s, 1H, CH), 7.11–7.26
2H, CH , ꢃ = 7.2 Hz), 1.78–1.80 (m, 2H, CH ), 1.48–1.51 (m,
6
2
2
(m, 9H, ArH), 4.06 (t, 2H, CH , ꢃ = 7.2 Hz), 3.97 (s, 2H,
2H, CH ). 13C NMR (100 MHz, DMSO-d ) ꢂ 159.7, 157.8,
2
2
6
CH ), 2.50 (t, 2H, CH , ꢃ = 10.8 Hz), 2.34 (s, 3H, CH ),
156.9, 149.3, 142.2, 140.6, 138.5, 130.0, 128.7, 128.7, 126.2, 122.5,
121.3, 115.1, 112.6, 55.4, 43.3, 40.7, 34.8, 29.5, 28.3. EI-MS:
m/z (relative intensity) 388.2 (M+, 59), 342.9 (22), 283.9
(32), 269.0 (35), 255.2 (74), 239.5 (23), 225.8 (60), 212.4 (23),
182.8 (33), 160.8 (28), 147.3 (29), 131.2 (37), 109.0 (38), 102.8
(39), 90.6 (100), 76.6 (28), 44.3 (27). IR (cm−1): 3433 (N-H),
3085, 2938, 1673 (C=O), 1582, 1453, 1379, 1257, 1146, 1049, 747,
700. Anal. calcd for C H N O : C, 71.11; H, 6.23; N, 14.42.
2
2
3
2.04–2.07 (m, 2H, CH ). 13C NMR (100 MHz, DMSO-d ): ꢂ,
2
6
157.8, 156.9, 149.3, 141.2, 140.59, 140.57, 137.0, 135.7, 130.5, 129.5,
128.8, 128.6, 127.3, 126.4, 122.6, 43.5, 38.2, 32.5, 31.3, 19.9. EI-
MS: m/z (relative intensity) 358.3 (M+, 35), 343.2 (20), 253.3
(100), 254.4 (40), 240.3 (16), 228.3 (16), 105.3 (15), 91.2 (52). IR
(cm−1): 3433 (N-H), 3069, 3026, 2948, 2867, 1718 (C=O), 1582,
1493, 1454, 1410, 1364, 1157, 1125, 756, 695, 651. Anal. calcd for
C H N O: C, 73.72; H, 6.19; N, 15.63. Found: C, 74.09; H,
23 24
4
2
Found: C, 71.39; H, 6.20; N, 14.78.
22 22
4
6.25; N, 15.98.
(11) 2-(2-Methyl-benzyl)-9-(4-phenyl-butyl)-1,9-dihydro-pur-
in-6-one (2k). M.p.: 219.4∘C, Yield: 62%. 1H NMR (600 MHz,
(7) 2-(4-Chloro-phenyl)-9-(3-phenyl-propyl)-1,9-dihydro-pur-
in-6-one (2g). M.p.: 248.4 C, Yield: 42%. 1H NMR (600 MHz,
DMSO-d ): ꢂ, 12.31 (s, 1H, NH), 8.02 (s, 1H, CH), 7.10–
4.22 (t, 2H, CH , ꢃ = 7.2∘Hz), 2.62 (t, 2H, CH , ꢃ = 7.2 Hz),
1.42–1.45 (m, 2H, CH ). EI-MS: m/z (relative intensity) 372.3
6
DMSO-d ): ꢂ, 12.53 (s, 1H, NH), 8.16 (s, 1H, CH), 8.13 (d, 2H,
7.25 (m, 9H, ArH), 4.06 (t, 2H, CH , ꢃ = 6.6 Hz), 3.96
6
2
ꢃ = 4.2 Hz), 7.62 (d, 2H, ꢃ = 3.9 Hz), 7.18–7.29 (m, 5H, ArH),
(s, 2H, CH ), 2.32 (s, 3H, CH ), 1.73–1.75 (m, 2H, CH ),
2
3
2
2
2
2
2.17–2.20 (m, 2H, CH ). EI-MS: m/z (relative intensity) 364
(M+, 12.41), 344.3 (19.98), 253.3 (14.56), 240.3 (100.00), 224.3
(14.22), 91.2 (29.45), 76.4 (7.32). IR (cm−1): 3440 (N-H), 3102,
3026, 2942, 2860, 1723 (C=O), 1582, 1559, 1493, 1452, 1410,
1364, 1159, 1123, 759, 696, 652. Anal. calcd for C H N O:
2
(M+, 23), 343.5 (15), 277.5 (17), 259.0 (100), 240.5 (16), 225.5
(20), 199.4 (12), 118.6 (26), 103.5 (18), 91.0 (43), 77.1 (12), 65.1
(13), 44.3 (21). IR (cm−1): 3433 (N-H), 3097, 2940, 2860, 1705
(C=O), 1549, 1493, 1452, 1411, 1364, 1128, 1090, 1008, 846, 787,
755, 698, 682. Anal. calcd for C H ClN O: C, 65.84; H, 4.70;
23 24
4
C, 74.17; H, 6.49; N, 15.04. Found: C, 74.21; H, 6.45; N,
15.34.
20 17
4
N, 15.36. Found: C, 66.17; H, 5.04; N, 15.03.
(12) 2-(2,4-Dichloro-phenoxymethyl)-9-(4-phenyl-butyl)-1,9-
dihydro-purin-6-one (2l). M.p.: 208.6∘C, Yield: 72%. 1H
(8) 2-(2,4-Dichloro-phenoxymethyl)-9-(3-phenyl-propyl)-1,9-
dihydro-purin-6-one (2h). M.p.: 188.2∘C, Yield: 66%. 1H NMR
NMR (600 MHz, DMSO-d ): ꢂ, 12.51 (s, 1H, NH), 8.09 (s,
6
(600 MHz, DMSO-d ): ꢂ, 12.51 (s, 1H, NH), 8.11 (s, 1H, CH),
1H, CH), 7.60 (s, 1H, ArH), 7.36 (d, 1H, ArH, ꢃ = 4.5 Hz),
6
7.58 (s, 1H, ArH), 7.13–7.34 (m, 7H, ArH), 5.14 (s, 2H, CH ),
7.12–7.25 (m, 6H, ArH), 5.14 (s, 2H, CH ), 4.10 (t, 2H, CH ,
2
2
2
4.11 (t, 2H, CH , ꢃ = 6.6 Hz), 2.50 (t, 2H, CH , ꢃ = 12.6 Hz),
ꢃ = 6 Hz), 2.50–2.53 (2H, CH ), 1.69–1.72 (m, 2H, CH ),
2
2
2
2

8
Journal of Chemistry
1.40–1.44 (m, 2H, CH ). EI-MS: m/z (relative intensity) 443.6
(17) 2-(4-Chloro-phenyl)-9-[1-(1-hydroxy-ethyl)-4-phenyl-bu-
tyl]-1,9-dihydro-purin-6-one (2q): e Mixture of Isomers
(1 : 1). M.p.: 263.4∘C, Yield: 39%. 1H NMR (600 MHz, DMSO-
2
(M+, 71), 442.3 (51), 372.4 (29), 369.2 (40), 356.4 (99), 328.8
(54), 296.2 (28), 256.1 (100), 239.0 (44), 211.8 (70), 160.8 (39),
103.2 (72), 91.2 (37), 77.3 (59), 76.2 (74), 51.3 (24), 43.2 (36).
IR (cm−1): 3437 (N-H), 3098, 3028, 2932, 2862, 1718 (C=O),
1602, 1481, 1456, 1411, 1234, 820, 720, 699, 651, 506. Anal.
calcd for C H Cl N O : C, 59.60; H, 4.55; N, 12.64. Found:
d ): ꢂ, 12.54 (s, 1H, NH), 8.16 (s, 1H, CH), 8.11–8.13 (m, 3H,
6
ArH), 8.07 (s, 1H, ArH), 7.61 (d, 4H, ArH), 5.15 (dd, 1H, OH,
ꢃ = 6 Hz), 4.35–4.45 (m, 1H, CH), 4.04–4.10 (m, 1H, CH),
2.51–2.63 (m, 2H, CH ), 1.87–2.11 (m, 2H, CH ), 1.29–1.41 (m,
22 20
2
4
2
2
2
C, 59.31; H, 4.23; N, 12.31.
2H, CH ), 0.95 (d, 3H, CH , ꢃ = 6 Hz). EI-MS: m/z (relative
2
3
intensity) 423.0 (M+, 4), 246.9 (3), 138.1 (7), 104.2 (7), 91.1
(100), 77.2 (10), 65.0 (17), 51.2 (6), 45.1 (37). IR (cm−1): 3436
(N-H), 3084, 2930, 1687 (C=O), 1599, 1548, 1492, 1367, 1089,
(13) 2-(4-Chloro-phenyl)-9-(4-phenyl-butyl)-1,9-dihydro-pur-
in-6-one (2m). M.p.: 228.1∘C, Yield: 30%. 1H NMR (600 MHz,
DMSO-d ): ꢂ, 12.52 (s, 1H, NH), 8.14 (s, 1H, CH), 8.11 (d, 2H,
6
840, 699, 549. Anal. calcd for: C H ClN O : C, 65.32; H,
23 23
4
2
ꢃ = 4.2 Hz), 7.61 (d, 2H, ꢃ = 4.2 Hz), 7.14–7.24 (m, 5H, ArH),
4.23 (t, 2H, CH , ꢃ = 6.6 Hz), 2.62 (t, 2H, CH , ꢃ = 7.2 Hz),
5.48; N, 13.25. Found: C, 65.66; H, 6.59; N, 13.58.
2
2
1.85–1.87 (m, 2H, CH ), 1.54–1.57 (m, 2H, CH ). EI-MS: m/z
2
2
4.1.3. General Procedures of Synthesis of 2r and 2s
(relative intensity) 379.3 (M+1, 24), 378.1 (M+, 49), 337.9 (30),
274.9 (14), 259.3 (38), 224.3 (3), 164.3 (13),109.3 (17), 91.1 (100).
IR (cm−1): 3435 (N-H) 3103, 3026, 2937, 2859, 1688 (C=O),
1600, 1549, 1494, 1454, 1411, 1367, 1090, 1011, 842, 787, 732, 699,
498, 472. Anal. calcd for C H ClN O: C, 66.58; H, 5.05; N,
(1) 2-Benzyl-9-(1-benzyl-2-oxo-propyl)-1,9-dihydro-purin-6-
one (2r). 15 mL of absolute dichloromethane and triethyl-
amine (5.22 g, 6.39 mmol) was added to 2n (0.58 g,
1.55 mmol) and the mixture was cooled to 0∘C using an
ice-bath. 1.5 mL of DMSO and 3.26 g of pyridine/sulphur
trioxide complex were added, and the mixture was then
under an atmosphere of nitrogen, stirred in ice bath for 1 h,
and heated at 60∘C for further 6 h. 20 mL of water was added
to the solution, and the mixture was extracted three times
with in each case 25 mL of dichloromethane. e organic
phases were washed with water and then dried over sodium
sulfate and concentrated using a rotary evaporator. e crude
product was purified by chromatography to give 0.43 g of
21 19
4
14.79. Found: C, 66.28; H, 4.88; N, 14.46.
(14) 2-Benzyl-9-(1-benzyl-2-hydroxy-propyl)-1,9-dihydro-pur-
in-6-one (2n). M.p.: 225.2∘C, Yield: 66%. 1H NMR (600 MHz,
CDCl ): ꢂ, 12.49 (s, 1H, NH), 6.83–7.42 (m, 11H, ArH), 4.38–
3
4.40 (m, 2H, CH ), 4.13 (s, 2H, CH ), 3.21–3.31 (m, 2H, CH ),
2
2
2
1.39 (d, 3H, CH , ꢃ = 3 Hz). EI-MS: m/z (relative intensity):
3
374.4 (M+, 22), 330.4 (27), 329.2 (24), 283.3 (7), 226.3 (83),
225.0 (57), 102.8 (21), 91.1 (100), 77.0 (17), 65.0 (22), 45.3 (18).
IR (cm−1): 3214, 1677 (C=O), 1591, 1455, 1374, 716, 691. Anal.
calcd for C H N O : C, 70.57; H, 5.92; N, 14.96. Found: C,
title compound.
1
22 22
4
2
M.p.: 60∘C, Yield: 74.7%. H NMR (600 MHz, CDCl ):
3
70.39; H, 5.84; N, 14.77.
ꢂ, 12.84 (br, 1H, NH), 7.75 (s, 1H, CH), 6.96–7.38 (m, 10H,
ArH), 5.40 (dd, 1H, CH, ꢃ = 5.4 Hz, ꢃ = 10.2 Hz), 4.07 (s,
(15) 9-(1-Benzyl-2-hydroxy-propyl)-2-(2-methyl-benzyl)-1,9-
2H, CH ), 3.57 (dd, 1H, CH, ꢃ = 5.4 Hz, ꢃ = 14.4 Hz), 3.29
2
dihydro-purin-6-one (2o). M.p.: 86.6∘C, Yield: 88%. 1H
(dd, 1H, CH, ꢃ = 10.2 Hz, ꢃ = 13.8 Hz), 2.18 (s, 3H, CH ).
3
13C NMR (100 MHz, CDCl ): ꢂ, 202.47, 159.49, 149.46, 157.5,
NMR (600 MHz, DMSO-d ): ꢂ, 12.24 (s, 1H, NH), 7.99 (s,
6
3
1H, CH), 6.88–7.21 (m, 10H, ArH), 4.42–4.45 (m, 1H, CH),
149.62, 139.1, 135.5, 135.3, 129.3, 128.9, 128.7, 127.4, 127.3, 122.1,
64.3, 41.3, 36.9, 28.0. EI-MS: m/z (relative intensity) 372.0
(M+, 16), 329.2 (100), 224.9 (38), 212.7 (8), 102.8 (33), 91.1 (79),
76.9 (19), 65.0 (21), 51.2 (7), 43.2 (43). IR (cm−1): 3440 (N-H),
3087, 3029, 2922, 1684 (C=O), 1580, 1455, 1410, 717, 699. Anal.
calcd for: C H N O : C, 70.95; H, 5.41; N, 15.04. Found: C,
3.93–4.04 (m, 1H, CH), 3.91 (s, 2H, CH ), 3.21–3.23 (m,
2
1H, CH), 2.32 (s, 3H, CH ), 0.91 (d, 3H, CH , ꢃ = 3 Hz).
3
3
13C NMR (100 MHz, DMSO-d ): ꢂ, 157.7, 156.5, 149.3, 140.1,
6
138.4, 136.99, 135.7, 130.5, 129.4, 128.9, 128.5, 127.3, 126.5, 126.3,
122.3, 68.4, 63.1, 38.1, 35.6, 20.7, 19.9. EI-MS: m/z (relative
intensity) 388.3 (M+, 99), 342.6 (25), 240.3 (100), 223.4 (26),
212.3 (21), 131.3 (35), 91.1 (17), 76.8 (16), 42.9 (17). IR (cm−1):
3389 (N-H), 3087, 2970, 1680 (C=O), 1586, 1495, 1456, 1408,
1372, 1154, 1124, 746, 701, 650. Anal. calcd for C H N O :
22 20
4
2
70.76; H, 5.73; N, 14.56.
(2) 9-(1-Benzyl-2-oxo-propyl)-2-(2-methyl-benzyl)-1,9-dihy-
dro-purin-6-one (2s). 2s was prepared by oxidating 2o using
similar method to that of compound 2r.
23 24
4
2
C, 71.11; H, 6.23; N, 14.42. Found: C, 71.09; H, 6.50; N,
14.07.
M.p.: 209.0∘C, Yield: 72%. 1H NMR (600 MHz, CDCl ):
3
ꢂ, 12.12 (s, 1H, NH), 7.72 (s, 1H, CH), 6.94–7.28 (m, 9H, ArH),
5.30 (dd, 1H, CH , ꢃ = 5.4 Hz, ꢃ = 9 Hz), 3.52 (dd, 1H, CH ,
(16) 2-Benzyl-9-[1-(1-hydroxy-ethyl)-4-phenyl-butyl]-1,9-dihy-
2
2
dro-purin-6-one (2p). M.p.: 180.4∘C, Yield: 78%. H NMR
1
ꢃ = 5.4 Hz, ꢃ = 14.4 Hz), 3.24 (dd, 1H, CH , ꢃ = 13.8 Hz,
2
(600 MHz, DMSO-d ): ꢂ, 12.38 (s, 1H, NH), 8.05 (s, 1H, CH),
ꢃ = 10.2 Hz), 2.31 (s, 3H, CH ), 2.10 (s, 3H, CH CO). EI-MS:
6
3
3
m/z (relative intensity) 386.4 (M+, 8), 342.8 (17), 298.5 (13),
225.3 (30), 199.5 (9), 171.3 (12), 143.2 (19), 103.3 (35), 91.0 (100),
77.2 (10), 65.2 (12), 43.6 (8). 13C NMR (101 MHz, DMSO-
7.02–7.33 (m, 10H, ArH), 5.14 (d, 1H, OH, ꢃ = 5.4 Hz), 4.22–
4.26 (m, 1H, CH), 3.94 (3H, CH +CH), 2.41–2.45 (m, 2H,
2
CH ), 2.00–2.06 (m, 2H, CH ), 1.21–1.29 (m, 2H, CH ), 0.87
2
2
2
(d, 3H, CH , ꢃ = 6 Hz). IR (cm−1): 3397 (N-H), 3085, 3026,
d ) ꢂ 203.6, 157.6, 157.1, 149.2, 140.5, 137.0, 135.6, 130.5, 129.4,
3
6
2934, 1666 (C=O), 1581, 1402, 1372, 749, 699. Anal. calcd for:
C H N O : C, 71.62; H, 6.51; N, 13.92. Found: C, 71.39; H,
129.0, 128.7, 127.3, 127.0, 126.3, 122.3, 64.9, 38.1, 35.1, 27.5, 19.9.
IR (cm−1): 3440 (N-H), 3081, 3025, 2905, 1731 (C=O), 1660,
1587, 1458, 1408, 1354, 1234, 1174, 748, 732, 655. Anal. calcd for:
24 26
4
2
6.58; N, 14.04.

Journal of Chemistry
9
C H N O : C, 71.48; H, 5.74; N, 14.50. Found: C, 71.31; H,
e value of fluorescence polarization (FP ) from the reac-
23 22
4
2
ꢁ
6.09; N, 14.48.
tions without the compound was defined as 100% activity.
In the absence of PDE2 and the compound, the value of
fluorescent polarization (FP ) was defined as 0% activity.
4.1.4. e Procedure for Synthesis of 2c-1 and 2c-2 [26]. A
mixture of 2c (0.22 g) and NaH (70%, 0.04 g) in 6 mL of dry
DMF was stirred at room temperature for 0.5 h; then ally
bromide (0.15 g) was added to this solution and stirred for
4.5 h at the same temperature. And ice-water (100 mL) was
added to the solution with stirring; the solid deposited was
filtered and washed with water. e two regioisomers cropped
were separated by column chromatography on silica gel using
the mixture of petroleum ether and EtOAc as eluting solvent
to afford the corresponding 2c-1 (0.08 g) and 2c-2 (0.13 g) as
the first and second fractions, respectively.
ꢂ
e percent activity in the presence of the compound was
calculated according to the following equation: activity% =
(FP − FP )/(FP − FP ) × 100%. In the equation, FP is the
ꢂ
ꢁ
ꢂ
fluorescence polarization in the presence of the compound.
Conflict of Interests
e authors declare that there is no conflict of interests
regarding the publication of this paper.
Acknowledgments
(1) 1-Allyl-9-benzyl-2-(2-methyl-benzyl)-1,9-dihydro-purin-6-
one 2c-1. M.p.: 82∘C, Yield: 33%. 1H NMR (600 MHz, DMSO-
e research was supported in part by National Institutes
of Health (Grant RC1MH088480), National Natural Science
Foundation of China (Grant 21273089), and the Special Fund
for Basic Scientific Research of Central Colleges, South-
Central University for Nationalities (CZY14004).
d ): ꢂ, 8.21 (s, 1H, CH), 7.02–7.30 (m, 9H, ArH), 5.99–6.00 (m,
6
1H, CH ), 5.09 (dd, 2H, CH , ꢃ = 52.2 Hz, ꢃ = 62.4 Hz), 5.08
2
2
(s, 2H, CH ), 4.75–4.98 (m, 2H, CH ), 4.20 (s, 3H, CH ), 2.14
2
2
3
(s, 3H, CH ). EI-MS: m/z (relative intensity) 370.1 (M+, 16),
3
355.0 (10), 278.9 (6), 265.3 (8), 238.2 (6), 171.1 (19), 105.0 (21),
91.3 (100), 76.8 (8), 65.0 (22), 44.2 (6). IR (cm−1): 3442, 3085,
2945, 1689 (C=O), 1553, 1515, 1354, 1186, 750, 718. Anal. calcd
for: C H N O: C, 74.57; H, 5.99; N, 15.12. Found: C, 73.91;
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23 22
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