Synthesis and BZR affinity of pyrazolo[1,5-a]pyrimidine derivatives. Part 1: Study of the structural features for BZR recognition

Article abstract of DOI:10.1016/S0968-0896(99)00232-1

Examination of the pharmacophoric points of the pyrazolo[1,5-a]pyrimidine derivatives, ligands for BZR, previously published led us to the design of a novel class of 3,6-diaryl-4,7-dihydro-pyrazolo[1,5-a]pyrimidin-7-ones and to determine the groups involved in the BZR recognition. Copyright (C) 1999 Elsevier Science Ltd.

Full text of DOI:10.1016/S0968-0896(99)00232-1

Bioorganic & Medicinal Chemistry 7 (1999) 2705±2711
Synthesis and BZR Anity of Pyrazolo[1,5-a]pyrimidine
Derivatives. Part 1: Study of the Structural
Features for BZR Recognition
Silvia Selleri, a Fabrizio Bruni, a,* Camilla Costagli, a Annarella Costanzo, a
Gabriella Guerrini, a Giovanna Ciciani, a Barbara Costa b and Claudia Martini b
aDepartment of Pharmaceutical Sciences, University of Firenze, Via G. Capponi 9, 50121 Florence, Italy
bDepartment of Psychiatry, Neurobiology, Pharmacology and Biotechnologies, Via Bonanno 6, 56126 Pisa, Italy
Received 26 March 1999; accepted 21 June 1999
AbstractÐExamination of the pharmacophoric points of the pyrazolo[1,5-a]pyrimidine derivatives, ligands for BZR, previously
published led us to the design of a novel class of 3,6-diaryl-4,7-dihydro-pyrazolo[1,5-a]pyrimidin-7-ones and to determine the
groups involved in the BZR recognition. # 1999 Elsevier Science Ltd. All rights reserved.
Introduction
We have previously reported the syntheses and BZR
anities of many 3-aryl-4,7-dihydro-6-pyrazol-30(50)-yl-
pyrazolo[1,5-a]pyrimidin-7-ones9 (5.14Ki(nM)41880)
and we have proposed the alignment of this class
according to the model reported by Zhang and co-
workers.10 In this model the anchoring of the ligand
(lead compound of 3-aryl-6-pyrazolyl derivatives) to the
BZR (Fig. 1) involves C7ˆO, N1 and N4±H with
hydrogen bonding sites H1 (donor site) and H2/A3
(donor/acceptor site) on the receptor protein, respec-
tively. The 3-aromatic substituent is proposed to occupy
the lipophilic regions L1/L2 and/or L3. Moreover the 6-
pyrazol-30(50)-yl moiety was located in the area of
hydrogen bonding acceptor site A2, whose role in BZR
interaction has roused much controversy.11±13 Receptor
descriptors S are regions of negative steric/electrostatic
repulsion.
A rational design of new benzodiazepine receptor
(BZR) ligands based on reliable pharmacophore models
has been proposed on the basis of binding data dis-
played at multiple BZR subtypes by various structural
families of BZR ligands. Such models could be useful
starting points for identi®cation of the molecular deter-
minants of recognition and activation of the BZRs. An
examination of the structure±activity relationships of
anity (SAFIR) and ecacy of many classes of com-
pounds at the BZR has assisted in the development of
several pharmacophoric models for ligand±receptor
interaction at the BZR. All these models are character-
ized by a number of points of lipophilic and hydrogen-
bonding ligand±receptor interaction1±5 and in some
cases areas of steric hindrance have also been de®ned.6±8
In order to obtain a better level of molecular under-
standing, much emphasis over the past few years has
been paid to the synthesis of small molecules as BZR
ligands. With a similar goal, we are developing a SAR
study to identify new ¯exible 3,6-substituted pyr-
azolo[1,5-a]pyrimidine derivatives with high binding
potency and low intrinsic activity.
With the aim of supporting this hypothesis in the BZR
recognition, it seemed worthwhile to investigate the role
of the tautomeric group N4H-C7O and of the pyrazole
substituent at the 6-position with respect to the receptor
protein. In view of the uncertain function of A2 in the
hydrogen bonding ligand±receptor interaction, we syn-
thesized new molecules devoid of the hydrogen bonding
donor site. Therefore 3,6-diphenyl-4,7-dihydro-pyr-
azolo[1,5-a]pyrimidin-7-one
1 was synthesized and
investigated by a binding assay using [3H]RO15-1788 as
radioligand and bovine brain membranes from brain
tissues as receptor source.14 We have tried to predict the
in vitro ecacy of the most active compounds by
Key words: Benzodiazepine receptor (BZR) binding studies; pyr-
azolo[1,5-a]pyrimidine derivatives; structure±anity relationship
(SAFIR); partial agonists..
* Corresponding author. Tel.:+39-055-2757291/296; fax+39-055-
240776; e-mail: sell@farm®.scifarm.uni®.it
0968-0896/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved.
PII: S0968-0896(99)00232-1

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S. Selleri et al. / Bioorg. Med. Chem. 7 (1999) 2705±2711
determining the GABA ratio (IC50 without GABA/IC50
with GABA). The resulting anity and ecacy were
quite comparable with the reference compound of the 6-
pyrazol-30(50)-yl series,9 thus identifying a potential new
lead molecule 1 (Fig. 2).
Chemistry
The syntheses of 4,7-dihydro-3,6-substituted pyr-
azolo[1,5-a]pyrimidin-7-ones (1, 10±17) were performed
by a one-step reaction between 3(5)-amino-4-aryl pyr-
azoles (4-phenyl A, 4-thien-30-yl B, 4,30-methoxyphenyl
C) and ethyl 2-aryl-3-hydroxypropenoates (2-phenyl- D,
2-thien-30-yl-E, 2-thien-20-yl F, ethyl 2,30-methoxy-
phenyl- G) at re¯ux in diglyme or ethylene glycol (see
Experimental).
Since it is well known that structural requirements for
interaction and activation of the BZR involve the phar-
macophoric points model mentioned above, we synthe-
sized several new derivatives bearing substantial
modi®cations either on C7=O group or concerning the
N1 and N4H. As a consequence, the enol form of com-
pound 1 was blocked as 7-methoxy derivative (2), the
oxygen was replaced either by a sulfur atom (3) or with
an amino group (4); the carbonyl group by a methine
(5) or a methylene group (6). As regards N1 and N4,
alkylderivatives 7±9 were prepared (Fig. 3).
7-Chloro-3,6-diphenyl-pyrazolo[1,5-a]pyrimidine, ob-
tained from compound 1 by reaction with POCl3,
proved to be a useful intermediate for the synthesis of
compounds 2 and 3. In fact, by means of this reagent,
compound 2 was obtained using sodium methoxide.
Compound 3 was obtained, via the same 7-chloro deri-
vative by treatment with thiourea and subsequent acidic
hydrolysis, since compound 1 was una€ected either by
Lawesson reagent or by phosphorus pentasul®de (P2S5)
(see Experimental).
As an extension of this study, the phenyl groups at 3-
and 6-positions were in turn replaced either by 30-meth-
oxyphenyl or by a thienyl ring to verify the maintenance
of BZR recognition and possibly to identify a potential
bioisosteric series (10±17) (Scheme 1). The choice of
these substituents at the 3-position is justi®ed by high
anity values observed in the 6-pyrazol-30(50)-yl series
as appeared in our previous paper.9
Figure 3. Molecular formulas of compounds 2±9.
Figure 1. Schematic representation of the interaction between 4,7-dihy-
dro-3-phenyl-6-pyrazol-30-yl-pyrazolo-[1,5-a]pyrimidin-7-one (lead com-
pound) and BZR.
Figure 2. Molecular formulas and biological data of lead molecules.
Scheme 1. One-step reaction for the synthesis of compounds 1 and 10±17.

S. Selleri et al. / Bioorg. Med. Chem. 7 (1999) 2705±2711
2707
Following described procedures compounds 415 and 516
were prepared. Both of them lack the carbonyl oxygen
and N4H groups, even if the former could exist as N4H-
7-imino form in tautomeric equilibrium of compound 4.
they do not possess the structural features required for
binding to the BZR. In particular compounds 2±6, which
are devoid of the carbonyl function, do not possess any
BZR recognition, whereas N-alkylderivatives (compounds
7 and 8) maintain the recognition, although to a lesser
extent of anity. On the other hand a remarkable decre-
ment of BZR anity was shown by compound 9, bearing a
methyl group at the nitrogen 1. This result agrees with our
previous hypothesis, according to which the essential
anchoring of the ligand to the hydrogen bond donor site
H1 on the receptor protein is e€ected by the carbonyl
group and the unsubstituted N1 in a three-centred interac-
tion. The above ®ndings could be clari®ed by the observa-
tion of the negative anity trend ranging from Ki value
369 nM for compound 1, through 863 nM for compound
7, to 3090nM for compound 9. In fact, whereas compound
7 is still able to interact with a three-centred hydrogen
bond with H1 losing its ability to bind with H2/A3, for
compound 9 a complete reverse situation is observed.
The replacement of the 7-carbonyl group with methyl-
ene group was accomplished by reaction of 5 with
NaBH4, which reduced the pyrimidine moiety17 to give
the 4,7-dihydro derivative 6.
Alkylation of compound 1 with iodomethane in anhydrous
dimethylformamide (DMF) in the presence of potassium
carbonate (K2CO3) unexpectedly a€orded compound 9
instead of compound 7, unlike our previous experiences18
according to which the above alkylation method selectively
gave N4-alkyl derivatives.
In order to verify unequivocally the structure of the
former, 3-amino-1-methyl-4-phenylpyrazole19 was reac-
ted with ethyl 3-hydroxy-2-phenylpropenoate giving a
compound chromatographically and spectroscopically
identical to compound 9.
The 3-substitution by a 3-thienyl ring or a 3-methoxy-
phenyl group which resulted in successfully improving
the BZR anity in the 6-pyrazol-30(50)-yl series9 a€or-
ded again as many new ligands with an enhanced
(compounds 10±13, 16±17) or similar potency (com-
pounds 14,15) compared with the lead molecule 1.
So far as the role of N4H group in the BZR recognition is
concerned, the N-alkyl derivatives (compounds 7 and 8)
were prepared by reaction of ethyl 3-hydroxy-2-phenyl-
propenoate with 3-aminomethyl or 3-aminoethyl-4-phe-
nylpyrazole, respectively. Those intermediates were, in
turn, obtained starting from 3-formamido-4-phenylpyr-
azole or 3-acetamido-4-phenylpyrazole, which were
reduced with borane methylsul®de (BH3(CH3)2S).
As regards the intrinsic activity, the compounds of this
new class, with the exception of full agonists 1, 7 and 11,
display in vitro properties consistent with a partial agonist
ecacy. More importantly, compounds 13 and 16 which
exhibit the best anity values, possess the lowest values of
intrinsic activity. This feature appeared intriguing since
the clinical interest in partial agonists, due to their ability
to act as modulators of BZR, is well known.20
Results and Discussion
The low overall BZR anities (Table 1) of compounds 2±9
reported here and their lack of consistent SAR suggest that
Conclusion
Table 1. Biological data of compounds 1±17
The removal of the 6-pyrazolyl moiety in the previous
parent compounds9 and its substitution with a phenyl or
a thienyl ring, proved the marginal role of the interac-
tion with the acceptor site A2. Taking into account this
observation, four possible orientations, by which the
interaction of the new ligands with the receptor protein
might occur, can be drawn, as depicted in Figure 4.
Compound
Inhibition(%)a
Ki (nM)b
GABA ratioc
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
91‹4.2
60‹1.2
24‹6.4
2.7‹0.3
14‹3.5
6‹1.9
71‹3.6
80‹2.7
89.6‹3.6
95‹5.6
93‹3.8
94‹6.2
92‹0.8
88‹4.3
84‹4.2
100‹6.7
96‹2.5
100‹5.2
100‹4.2
99‹1.1
369‹2.4
Ð
Ð
2.12
Ð
Ð
Ð
Ð
Ð
1.97
Ð
Ð
Ð
Ð
867‹8.2
1860‹9.7
3090‹240
72.2‹3.2
192‹2.5
111‹4.2
42.2‹1.7
363‹5.3
597‹0.8
16.3‹1.3
87.7‹0.9
2.17‹0.2
0.44‹0.08
1.01‹0.3
Since interaction with the receptor site H1 is more critical
than binding to site H2,6 we believe that the present work
demonstrates the essential function of C7-carbonyl group
and N1 in the anchoring to the H1 receptor protein
through a three-centred hydrogen bond (as highlighted by
the loss of BZR recognition exhibited by compounds 2±6
and 9 in comparison with compounds 7 and 8). In fact, as
regards the role of N4H, it appears to a€ect the binding
anity potency involving the H2/A3 (donor/acceptor
hydrogen bond) receptor site, which is well known as
being less critical to anity binding than the H1.6
Ð
1.67
3.08
1.71
1.25
1.46
1.62
1.30
1.56
1.57
0.80
0.98
17
Flunitrazepam
bCC-E
RO 15±87
a
Percent of inhibition of speci®c [3H]RO15-1788 binding at 10 mM con-
centration are means ‹ SEM of ®ve determinations (the tests were carried
out using DMSO as solvent).
Therefore, the two orientations of the ligands 4b, 4b0 are
to be ruled out on the basis of the above considerations,
while in our opinion, the guide criterion for choosing
between 4a, 4a0 orientations could be the de®nition of
b
Ki values are means ‹ SEM of ®ve determinations.
GABA ratio=IC50 compound/IC50 compound+10 mM GABA. Fluni-
c
trazepam (agonist), bCC-E (inverse agonist), RO 15±87 (antagonist) are
used as reference compounds.

2708
S. Selleri et al. / Bioorg. Med. Chem. 7 (1999) 2705±2711
Figure 4. Schematic representation of four possible orientations (4a, 4a0; 4b, 4b0) of compound 1 respect to BZR.
the receptor lipophilic regions (as L1/L2 and L3) by
means of suitable 3- and 6-substitutions.
were removed under reduced pressure. Microanalyses
were performed by Laboratories of Dipartimento Farm-
aco Chimico Tecnologico of University of Siena, Italy
with a Perkin±Elmer Model 240 C Elemental Analyzer
and values are within ‹0.4% of the theoretical values.
Further work concerning 3- and 6-substitution is plan-
ned in order to carry out structure activity studies on the
BZR. In fact these substitutions, combined together,
open up the way to a large variety of possible modi®ca-
tions for obtaining new ligands with high anity and low
intrinsic activity; in vivo investigations on the ecacy of
these new partial agonists is currently in progress.
General procedure for obtaining compounds 1 and 10±17.
A suspension of 3-amino-4-arylpyrazole (A±C) (10 mmol)
and ethyl-2-formyl-2-aryl acetate (10 mmol) (D±G) in the
appropriate solvent (20 mL) was re¯uxed under magnetic
stirring for 8 h (Table 2). The precipitate was collected by
®ltration from the reaction mixture and used without fur-
ther puri®cation as judged pure by TLC.
Experimental
Melting points were determined on a Gallenkamp melt-
1
ing point apparatus and are uncorrected. The H NMR
4,7-Dihydro-3,6-diphenyl-pyrazolo[1,5-a]pyrimidin-7-one
(1). White crystals. 1H NMR (DMSO-d6) d 7.34±7.52 (m,
6H, ArH), 7.63±7.72 (m, 4H, ArH), 7.99 (s, 1H, H-2), 8.30
(s, 1H, H-5), 12.56 (bs, 1H, NH). Anal. calcd for C18H13
N3O: C, 75.25; H, 4.56; N, 14.62. Found: C, 75.03; H,
4.77; N, 14.26.
spectra were recorded with a Varian Gemini 200 instru-
ment; chemical shifts are reported in d (ppm) high fre-
quency from tetramethylsilane as secondary reference
standard and coupling constants in Hz. Silica gel plates
(Merk F254) were used for analytical TLC. Solvents

S. Selleri et al. / Bioorg. Med. Chem. 7 (1999) 2705±2711
2709
Table 2. Reaction conditions, physical and chemical data of com-
pounds 1 and 10±17a
yield by ®ltration and recrystallized from ethanol; mp
197±198ꢀC; H NMR (DMSO-d6) d 7.25±7.33 (m, 1H,
1
ArH), 7.42±7.63 (m, 5H, ArH), 7.87 (pseudo d, 2H,
ArH), 8.20 (pseudo d, 2H, ArH), 8.83 (s, 1H, H-2), 9.09
(d, J=2.2 Hz, 1H, H-5), 9.54 (d, J=2.2 Hz, 1H, H-7).
Anal. calcd for C18H13N3: C, 79.68; H, 4.83; N, 15.49.
Found: C, 79.55; H,4.80; N, 15.33.
Compound
Reagents
Reaction solvent
Yield %
mp (ꢀC)
4
4
1
A+D
B+D
C+D
A+E
C+E
C+F
A+G
B+E
B+F
Dyglime
Dyglime
Dyglime
25
30
28
45
28
15
15
46
50
>300
>300
290±291
>300
>300
289±290
>300
>300
10
11
12
13
14
15
16
17
Dyglime
Ethylene glycol
Ethylene glycol
Dyglime
Ethylene glycol
Dyglime
4,7-Dihydro-3,6-diphenyl-pyrazolo[1,5-a]pyrimidine (6).
To a suspension of compound 5 (1 mmol) in methanol
(40 mL) NaBH4 (50 mmol) was added and kept under
magnetic stirring at room temperature for 2 h. After eva-
poration of the solvent, compound 6 was collected by ®l-
tration and accurately washed with water to remove any
inorganic materials. Paleꢀyellow solid in 51% yield from
isopropanol; mp 242±243 C; 1H NMR (DMSO-d6) d 5.08
>300
A=3-amino-4-phenylpyrazole, B=3-amino-4-thien-30-yl pyrazole,
C=3-amino-4-(30-methoxyphenyl)pyrazole, D=ethyl-2-phenyl-3-hyd-
roxypropenoate, E=ethyl-2-thien-30-yl-3-hyeroxypropenoate, F= ethyl -
a
2-thien-20-yl-3-hydroxypropenoate,
hydroxypropenoate.
F=ethyl-2-(30-methoxyphenyl)-3-
3
(bs, 2H, CH2), 7.00 (d, J=5.0Hz, 1H, H-5), 7.20±7.51
(m, 10H, ArH), 7.74 (s, 1H, H-2), 9.20 (d, 3J=5.0 Hz 1H,
NH, exchangeable). Anal.calcd for C20H19N3: C, 79.70;
H, 6.35; N, 13.94. Found: C, 79.52; H, 6.15; N, 13.71.
3,6-Diphenyl-7-methoxy-pyrazolo[1,5-a]pyrimidine (2).
To 100 mL of methanol in a two-necked ¯ask, clean
metallic sodium (0.6 mmol) was slowly added under
magnetic stirring. After dissolution of sodium 3,6-
diphenyl-7-chloro-pyrazolo[1,5-a]pyrimidine 0.18 g (0.6
mmol), synthesized according to a procedure described
for a similar compound21 (yellow crystals, mp 157±
158ꢀC, 65% yield. 1H NMR (DMSO-d6) d 7.46±7.70 (m,
8H, ArH), 8.18±8.22 (pseudo d, 2H, ArH), 8.72 (s, 1H,
H-2), 8.95 (s, 1H, H-5)), was added and re¯uxed for 5 h.
The solvent was reduced under vacuum and crude pro-
duct was ®ltered o€; compound 2 was obtained by col-
umn chromatography (cyclohexane:ethyl acetate 1:1).
General procedure for obtaining compounds 7 and 8.
Compounds 7 and 8 were obtained via boranemethyl-
sul®de reduction from 3-formamido-4-phenylpyrazole
and 3-acetamido-4-phenylpyrazole according to a general
method.22
4,7-Dihydro-3,6-diphenyl-4-methyl-pyrazolo[1,5-a]pyrimi-
din-7-one (7). White crystals in 69% yield from ethanol;
mp >229ꢀC; 1H NMR (DMSO-d6) d 3.54 (s, 3H, N±CH3)
7.25±7.52 (m, 8H, ArH), 7.60±7.75 (m, 2H, ArH), 7.99 (s,
1H, H-2), 8.22 (s, 1H, H-5). Anal.calcd for C19H15N3O: C,
75.73; H, 5.02; N, 13.94. Found: C, 75.70; H, 5.15; N,
14.06.
Pale yellow crystals, mp 99±100ꢀC, 35% yield. 1H NMR
(CDCl3) d 4.19 (s, 3H, OCH3), 7.29±7.32 (m, 2H, ArH),
7.44±7.56 (m, 6H, ArH), 8.04±8.09 (m, 2H, ArH), 8.48 (s,
1H, H-2), 8.58 (s, 1H, H-5). Anal. calcd for C19H15N3O:
C, 75.73; H, 5.02; N, 13.94. Found: C, 75.53; H,4.99; N,
13.81.
4,7-Dihydro-3,6-diphenyl-4-ethyl-pyrazolo[1,5-a]pyrimi-
din-7-one (8). White crystals in 38% yield from ethanol;
mp 188±189ꢀC; H NMR (DMSO-d6) 0.97 (t, 3H, NH±
1
CH2CH3,), 3.99 (q, 2H, NH±CH2CH3), 7.30±7.55 (m, 8H,
ArH), 7.65±7.75 (m, 2H, ArH), 7.98 (s, 1H, H-2), 8.27 (s,
1H, H-5). Anal. calcd for C20H17N3O: C, 76.17; H, 5.43;
N, 13.32. Found: C, 76.02; H, 5.27; N, 13.50.
4,7-Dihydro-3,6-diphenyl-pyrazolo[1,5-a]pyrimidin-7-
thione (3). 3,6-Diphenyl-7-chloro-pyrazolo[1,5-a]pyrimi-
dine 0.15g (0.5 mmol), was suspended in ethanol and
re¯uxed for 3 h in presence of thiourea 0.76g (1 mmol). A
solution of KOH (5%) 5 mL was added and re¯uxed for
10min. The suspended solid was ®ltered o€ and the solu-
tion was acidi®ed with AcOH. The yellow precipitate was
collected and used without further puri®cation as judged
suciently pure (TLC analysis). mp>300ꢀC, 53% yield.
1H NMR (DMSO-d6) d 7.22±7.46 (m, 6H, ArH), 7.63±
7.67 (m, 2H, ArH), 7.93±8.02 (m, 3H: 2H, ArH; 1H, H-2),
8.50 (s, 1H, H-5). Anal. calcd for C18H13N3S: C, 71.26; H,
4.32; N, 13.85. Found: C, 71.68; H,4.70; N, 13.45.
1,7-Dihydro-3,6-diphenyl-1-methyl-pyrazolo[1,5-a]pyrimi-
din-7-one (9). Method A Iodomethane (2 mmol) was
added to a stirred solution of 1 (2 mmol) in dimethylfor-
mamide (20 mL) containing potassium carbonate (2 mmol)
and the reaction mixture was maintained at 80ꢀC for 3 h.
After cooling, the insoluble materials were ®ltered o€ and a
minimum amount of water was added to the solution. A
white solid, consisting of a mixture of compound 9 with
compound 7 in trace precipitated. Compound 9 was pur-
i®ed via chromatography by eluting with CH2Cl2:MeOH,
100:1. The expected compound was obtained as a pale pink
solid in 50% yield; mp 211±212ꢀC; H NMR (CDCl3) d
15
1
3,6-Diphenyl-7-amino-pyrazolo[1,5-a]pyrimidine (4).
4.43 (s, 3H, NCH3), 7.28±7.48 (m, 6H, ArH), 7.70±7.78 (m,
3H: 2H ArH, 1H H-2), 7.93±8.05 (m, 2H, ArH), 8.36 (s,
1H, H-5). Anal. calcd for C19H15N3O: C, 75.73; H, 5.02; N,
13.94. Found: C, 76.11; H, 5.40; N, 14.30.
3,6-Diphenyl-pyrazolo[1,5-a]pyrimidine (5). Phenylma-
londialdehyde (5 mmol),16 was added in one batch to a
stirred solution of 3-amino-4-phenylpyrazole (5 mmol)
in glacial acetic acid (15 mL) and the reaction mixture
was re¯uxed for 1 h. The disappearance of starting
materials was monitored by TLC analysis. After cool-
ing, compound 5 was obtained as a yellow solid in 90%
Method B: A suspension of 3-amino-1-methyl-4-phe-
nylpyrazole19 (1 mmol) and ethyl-2-formyl-2-phenyl
acetate (1 mmol) in diglyme (5 mL) was re¯uxed under

2710
S. Selleri et al. / Bioorg. Med. Chem. 7 (1999) 2705±2711
magnetic stirring for 10 h. The solvent was reduced
under vacuum and the crude product was puri®ed by
column chromatography (cyclohexane:ethyl acetate 1:1).
The expected compound 9 was obtained in 50% yield.
4,7-Dihydro-3-thien-30-yl-6-thien-20-yl-pyrazolo[1,5-a]pyr-
imidin-7-one (17). Light green crystals; H NMR (DM
1
SO-d6) d ppm: 7.09±7.18 (m, 1H, thienyl), 7.37±7.59 (m,
2H, thienyl), 7.63±7.68 (m, 1H, thienyl), 7.69±7.76 (m, 1H,
thienyl), 7.78±7.81 (m, 1H, thienyl), 8.36 (s, appears as
pseudo d, 2H: 1H, H-2, 1H, H-5), 12.55±12.85 (bs,1H,
NH, exch.). Anal. calcd for C14H9N3OS2: C, 56.17; H,
3.03; N, 14.04. Found: C, 55.95; H, 2.99; N, 14.11.
4,7-Dihydro-3-thien-30-yl-6-phenyl-pyrazolo[1,5-a]pyrimi-
din-7-one (10). Pale pink crystals. 1H NMR (DMSO-d6) d
ppm: 7.34±7.80 (m, 8H: 5H, ArH, 3H, thienyl), 8.00 (s, 1H,
H2), 8.32 (s, 1H, H-5). Anal. calcd for C16H11N3OS: C,
65.51; H, 3.78; N, 14.32. Found: C, 65.58; H, 3.75; N,
14.11.
Molecular modelling
The low energy conformations of the ligands were cal-
culated by AM1 routine in MOPAC, and the graphic
presentations were obtained using Insight II software by
Molecular Simulation Inc.
4,7-Dihydro-3-(30methoxyphenyl)-6-phenyl-pyrazolo[1,5-
a]pyrimidin-7-one (11). White crystals; H NMR (DM
1
SO-d6) d ppm: 3.86 (s, 3H, OCH3) 6.85±6.95 (m, 1H, ArH)
7.20±7.25 (m, 2H, ArH) 7.30±7.50 (m, 4H, ArH), 7.70±
7.82 (m, 2H, ArH) 7.97 (s, 1H, H-2) 8.31 (s, 1H, H-5)
12.51 (bs, 1H, NH exch.). Anal. calcd for C19H15N3O2: C,
71.91; H, 4.76; N, 13.24. Found: C, 71.82; H, 4.55; N,
13.33.
Acknowledgements
This work was supported, in part, by MURST (`Co®-
nanziamento Nazionale'). The authors are grateful to
Dr. Paola Gratteri (Department of Pharmaceutical Sci-
ences, University of Firenze) for her help in generating
some of the ®gures.
4,7-Dihydro-3-phenyl-6-thien-30-yl-pyrazolo[1,5-a]pyrimi-
1
din-7-one (12). White crystals; H NMR (DMSO-d6) d
ppm: 7.30±7.40 (m, 1H, thienyl) 7.45±7.56 (m, 2H, ArH)
7.60±7.74 (m,4H: 3H ArH,1H thienyl) 8.08±8.15 (m, 1H,
thienyl) 8.24 (s, 1H, H-2) 8.30 (s, 1H, H-5) 12.85 (bs, 1H,
NH exch.). Anal. calcd for C16H11N3OS: C, 65.51; H,
3.78; N, 14.32. Found: C, 65.53; H, 3.89; N, 14.25.
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1
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a]pyrimidin-7-one (15). Ivory crystals; H NMR (DM
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ArH) 7.21±7.40 (m, 4H, ArH) 7.42±7.56 (m, 2H, ArH)
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