Synthesis and vasorelaxant potency of monagra. A chiral 5-(2-methyl-2,3-dihydro-7-benzofuryl)-pyrazolopyrimidone analog of viagra

Article abstract of DOI:10.3987/com-01-9218

Synthesis and properties of a chiral 5-(2-methyl-2,3-dihydro-7-benzofuryl)pyrazolo[4,3-d]pyrimidin-7-one (3), an analog of Viagra (1) and Biagra (2), are described. The key material, (±)-3-methyl-2,3-dihydrobenzofuran-7-carboxylic acid (8a) was resolved into the (S)-8b (95% ee) and (R)-8c (99% ee) enantiomers using, respectively, (-)-cinchonidine and (+)-cinchonine. The absolute configuration of 8c was determined as R by X-Ray measurements. Preliminary in vitro experiments on rat isolated thoracic aorta show that the vasorelaxant potency of 3b,c is truly higher than that of 1 and 2.

Full text of DOI:10.3987/com-01-9218

HETEROCYCLES, Vol. 55, No. 9, pp. 1789 – 1804, Received, 6th April, 2001
SYNTHESIS AND VASORELAXANT POTENCY OF MONAGRA .
A CHIRAL 5-( 2-METHYL–2,3 –DIHYDRO-7-BENZOFURYL)-
®
PYRAZOLOPYRIMIDONE ANALOG OF VIAGRA
a
a
b
c
Nader R. Al-bojuk , Mustafa M. El-Abadelah* , Salim S. Sabri , Alain Michel ,
d
e
f
Wolfgang Voelter , Cäcilia M.-Mössmer , and Yousef Al-Abed
a
Chemistry Department, Faculty of Science, Jordan University, Amman, Jordan
b
Faculty of Arts and Sciences, University of Sharjah, P.O . Box 27272, UAE
Laboratoire de Pharmacologie, Faculte´ de Pharmacie, 15, Avenue Charles
c
Flahaut, 34060-Montpellier, Cedex 2, France
d
Abteilung für Physikalische Biochemie, Physiologisch-chemisches Institut der
Universität Tübingen, Hoppe-Seyler-Straβe 4, D-72076 Tübingen, Germany
e
Institut für Anorganische Chemie auf der Morgenstelle 18, Universität Tübingen,
D-72076 Tübingen, Germany
f
The Picower Institute for Medical Research, 350 Community Drive, Manhasset
NY 11030, USA
Abstract- Synthesis and properties of a chiral 5-(2-methyl-2,3-dihydro-7-
®
benzofuryl)pyrazolo[4,3-d]pyrimidin-7-one (3), an analog of Viagra (1) and
Biagra (2), are described. The key material, (±)-3-methyl-2,3-dihydrobenzofuran-
7
-carboxylic acid (8a) was resolved into the (S)-8b (95% ee) and (R)-8c (99% ee)
enantiomers using, respectively, (-)-cinchonidine and (+)-cinchonine.The absolute
configuration of 8c was determined as R by X-Ray measurements. Preliminary in
vitro experiments on rat isolated thoracic aorta show that the vasorelaxant potency
of 3b,c is truly higher than that of 1 and 2.
Introduction
®
1,2
The advent of introducing Viagra (1) as a medicament for treatment of impotence has attracted
widespread attention. This therapeutic agent potently inhibits cyclic guanosine monophosphate (cGMP)
1
specific phosphodiesterase (PDE 5) isozyme. Sexual arousal causes increased release of nitric oxide

(
NO) from non-cholinergic non-adrenergic parasympathetic nerve endings in the walls of the arteries and
3
sinusoids of the penile corpora cavernosa (PCC). Some NO is also released by endothelial cells lining
the blood vessels and sinusoids of PCC. Acting as a diffusion signalling molecule, NO stimulates a
cytoplasmic guanylyl cyclase to increase cGMP production from guanosine triphosphate (GTP). As a
second messenger in the erectile cycle, cGMP triggers the relaxation of smooth muscle cells-such as in
4
the arterial walls of the sinusoids, as well as the sinusoids themselves. This vasodilating event reduces
the resistance to the blood flow into the penis, thereby increasing the amount of blood flow into the
sinusoids with consequent attainment of penile erection. Thereafter, cGMP is rapidly hydrolyzed into
®
inactive GMP in a substrate-specific manner. Viagra depends on this NO/cGMP pathway for its
1
,5
®
erectogenic effect by working as a potent selective PDE-5 inhibitor. In this way, Viagra would block
cGMP breakdown and therefore act synergistically with NO to elevate cGMP concentration and cause
penile smooth muscle relaxation-erection interplay.
6
Quite recently, we have reported on the synthesis and properties of biagra (2), a 5-(2,3-dihydro-7-
benzofuryl)pyrazolo[4,3-d]pyrimidone derivative which showed in vitro vasorelaxant activity on rat
®
7
isolated thoracic aorta comparable to viagra (1). This result motivated us to design structural
modifications on 2 for improvement of the observed potency. We anticipate that introduction of a methyl
group at C-2´ of the dihydrofuryl moiety (ring D of biagra 2) would result in compound (3) which, from
®
molecular modeling, closely resembles viagra (1). The modified structure (±)-3a (we call it monagra)
also has a stereogenic center and is obtainable in its optically pure (S)- and (R)-enantiomers (3b and 3c,
respectively) that are expected to show enantioselective activity as PDE-V inhibitors and as smooth
muscle vasorelaxants. This follows from the fact that enantiomers can elicit vastly different biological
responses in living organisms and the biological activity of enantiomers often differ widely. Besides, the
O
CH3
N
O
CH3
N
O
CH3
1
CH3
7
N
N
6
7
a
N
O
C
HN
HN
O
HN
O
2'
B
N
A
B
N
A
*D
B
A
N
D
5
2
3
'
7'a
3
a
3
N
4
3
'a
7
'
C
C
4
'
6'
5
'
O
S
O
O
S
O
O
S
O
N
N
N
6
"
"
2"
3"
5
N
N
N
CH3
CH3
(2)
CH3
(3a-c)
(1)

8
benzofuran entity is known to occur in several biologically interesting natural (and synthetic) products.
Accordingly, the present work aims at evaluating the in vitro vasorelaxant activity of 3a-c as compared to
and 2. Herein we describe the synthesis and properties of 3 starting with 2-methyl-2,3-
1
dihydrobenzofuran-7-carboxylic acid (8) (Schemes I and II).
Results and Discussion
Synthesis
9
,10
The requisite racemic acid (8a) was prepared according to published procedures
utilizing methyl O-
1
0
9
allylsalicylate (4) which, upon heating, delivers 5 in a [3,3] sigmatropic Claisen rearrangement.
Subsequent cyclization of 5 using mercuric acetate, followed by demercuration with sodium borohydride
9
in alkali, furnished 8a (method A, Scheme I). An alternative route toward 8a involves selective lithiation
at C-7 of 3-methyl-2,3-dihydrobenzofurn (7) (prepared by cyclization of 2-allylphenol (6) with zinc
1
1
o
chloride and hydrochloric acid), and quenching with dry ice at -78 C (method B, Scheme I).
Scheme I
CO Me
CO Me
2
2
O
OH
(
i )
(
ii ) ~ ( v )
method A
CO H
2
O
CH3
4
5
*
OH
[ a : (±)]
8
(
vi )
CH3
(
vii ) ( ix )
~
O
*
method B
6
7
o
(
i) 210-215 C under N
ii) Hg(OAc) , THF, ∆
iii) NaBH , 12% NaOH
iv) 25 % NaHCO3
2
(vi) conc. HCl, ZnCl /AcOH, ∆
2
(
(
(
(
2
(vii) n-BuLi in hexane/TMEDA
o
4
(viii) CO
2
(s), -78 C
(ix) conc. HCl
o
v) 15 % KOH, ∆; then 15 % HCl (0 C)
6
,9
The methodology adopted here is essentially similar to that reported for related systems. The racemic
acid (8a) was resolved into its enantiomers (-)-8b and (+)-8c by fractional crystallization of their (-)-

cinchonidine and (+)-cinchonine diastereomeric salts, respectively, following reported procedures for
1
2
13
resolving the 5-chloro and 5-sulfamoyl analogs of 8a.
Scheme II
O
OH
O
Cl
9
O
CH3
O
CH3
(
i )
*
*
8
O
O
CH3
N 1
CH3
CH3
1´
O
H N
N
2
H N
( ii )
2´
´
5
( iii )
( iv )
2
*
O
N 2
3
N
(9)
+
3
4
N
H
H N
2
3´a
7´
4´
6´
5´
10
11
O
N
O
N
CH3
CH3
CH3
CH3
*
N
N
O
HN
O
HN
( vi )
(
v )
*
N
N
3
SO Cl
2
12
13
(
(
(
(
(
(
i) SOCl
ii) ΝΕt
2
/ benzene, ∆
Compounds (3,8,9 and 11-13)
a
b
c
3
/ benzene, ∆
−
+
iii) tert−ΒuΟ Κ / tert −ΒuΟΗ , ∆
(S)
(R)
(
±)
iv) 3N aq. HCl
0
v) ClSO H / 65-70 C, 2 h
3
vi) 1-methylpiperazine, THF / rt

The optical purity of (+)-8c was measured as 99% ee, and the configuration at C-2 of (+)-8c was
determined as R by X-Ray crystallogrpahy (vide infra). The general synthetic route to prepare the target
compounds(3a-c) commenced with the formation of the bis-amides (11a-c) via coupling of the particular
acid chloride (9a-c) with 4-amino-1-methyl-3-propylpyrazole-5-carboxamide (10) (Scheme II). The latter
1
,14
is obtained from ethyl 2,4-dioxoheptanoate according to established methodology.
Cyclization of
1
1a-c with potassium tert-butoxide in refluxing tert-butanol yielded the corresponding pyrazolo[4,3-
d]pyrimidin-7-one derivatives (12a-c). Selective chlorosulfonylation at C-7 of 12a-c gave the
corresponding intermediates (13a-c) which, upon treatment with 1-methylpiperazine, furnished the
desired products (3a-c).
Spectral Data
The IR, MS and NMR spectral data and microanalyses of the new compounds (3,11-13) conform with the
suggested structures, and are included in the experimental part. Thus, their MS spectra display the correct
+
M for which the measured high resolution data are in good agreement with the calculated values based
1
on the respective molecular formulas. H-Signal assignments to the different protons are straightforward.
1
3
C-Assignments follow from DEPT, HMBC and HMQC experiments.
Crystal Structure Determination of (+)-8c
Colorless block crystals were grown by allowing a solution of 8c in isopropyl ether / dichloromethane
solvent system (10:3 v/v) to stand at ambient temperature for 48 h (open flask); crystal dimensions: 0.25
×
0.2 × 0.15 mm. Crystal data for C10
H
10
O
3
: FW = 178.18, monoclinic, space group P2
1
with a = 7.4840
3
(
5), b = 9.3550 (7), c = 12.7760 (7) Å , α = 90°, β = 105.502 (5)°, γ = 90°, V = 861.94 (10) Å , Z = 2,
3
dcalc = 1.373 g/cm . Data collection was made at 213 (2) Κ , using an ENRAF - NONIUS CAD4
diffractometer operating in the omega scan mode . 3851 Independent reflections were measured within
the range θ = 5.94 - 64.92° using Cu-K
α
radiation ( λ = 1.54184 Å ). The unit cell parameters and
orientation matrices for the data collection were obtained using the setting angles of 25 reflections (θ =
1
5
1
7.12 - 29.4°). The structure was solved by direct method using the program SHELXS 86. All non -
2
hydrogen atoms were refined anisotropically by full - matrix least - squares procedure based on F using
1
6
all unique data with SHELXL 97. The hydrogen atoms have been found in the difference Fourier map
and were refined isotropically. This resulted in R-values R /wR = 0.0558 / 0.1396 for all data and 0.0491
0.1338 for the 2903 observed reflections and 316 variable parameters ; GOF = 1.066, largest peak and
1
2
/
3
hole in final Fourier difference map were 0.202 and - 0.184 e / Å , respectively .

Selected bond lengths and angles are given in Table 1 for (R )-8c, and for which the molecular structure is
displayed in Figure 1 . The asymmetric unit comprises two half-molecules, thus forming a unit cell with
slightly different molecules of the same configuration .
Table 1 . Selected bond lengths (Å ) and angles ( ° ) for (R) –8c
O (1)-C(8)
O (1)-C(2)
C (2)-C(3)
C (3)-C(9)
C (8)-C(9)
1.357(3)
1.475(3)
1.533(3)
1.502(3)
1.392(3)
C (8)-O(1)-C(2)
O (1)-C(2)-C(20)
O (1)-C(2)-C(3)
C (20)-C(2)-C(3)
C (9)-C(3)-C(2)
C (9)-C(8)-C(7)
C (8)-C(9)-C(3)
O (3)-O(70)-O(2)
108.0 (2)
107.9 (2)
105.7 (2)
115.3 (3)
103.0 (2)
121.6 (3)
108.0 (3)
122.1 (3)
C (2)-C(20) 1.496(3)
O (2)-C(70) 1.304(3)
O (3)-C(70) 1.237(3)
Figure 1. ORTEP plot of the molecular structure of (R)-8c
1
6
Calculations based on SHELXL 97 using Fiedel pairs led to a Flack parameter of 0.1233. This value
indicates R-configuration for (+)-8c. Further information of the crystal structure data can be ordered from
the Cambridge Crystallographic Data Center under the depository number CCDC 161090 .

Preliminary Pharmacological Results
®
Viagra (1) and Biagra (2) were previously noted to induce relaxation of the artery with almost the same
7
potency. In the present work, the in vitro vasorelaxant activity of the enantiomers (3b) and (3c) has been
evaluated on rat isolated thoracic aorta precontracted with 40 mM KCl ( that induced stable contraction
for 90 min) in the presence of endothelium. It can be seen from the preliminary results, as presented in
Figure 2, that the vasorelaxant potencies of (R)-3b and (S)-3c are very close, but clearly higher than that
®
of Biagra (2) and, by inference, Viagra (1).
1
00
2
3
3
b
c
80
60
40
20
0
-7
-6
-5
-4
-3
log [Compounds]
Figure 2 . Vasorelaxant activity of 2 and 3b,c
We envisage that 2 and 3 operate as vasodilating agents by two different, albeit complementary,
mechanisms: (i) Direct inhibition of cellular smooth muscle PDE-V, in a relatively rapid mode of action.
(
ii) Stimulation of NO Synthase with ultimate increase in NO levels, perhaps via a comparatively slower
and indirect process. The latter hypothesis is currently the subject of experimental investigation, and
additional bio-studies with this series of molecules will be reported in due course.
EXPERIMENTAL
2
-Allylphenol, N, N, N,′N ′-tetramethylethylenediamine (TMEDA ), n-butyllithium solution (2.5M, in n-
hexane), (+)-cinchonine and (-)-cinchonidine were purchased from ACROS Organics . Melting points
1
13
(
uncorrected) were determined on an electrothermal Mel-Temp. Apparatus. H- and C-NMR spectra

were measured on a Bruker WM-400 and a Bruker DPX-300 instruments with TMS as internal reference.
EIMS spectra were obtained using a Finnigan MAT TSQ-70 spectrometer at 70 eV; ion source
temperature = 200 °C. IR spectra were recorded as KBr discs on a Burker IFS 48. Microanalysis was
preformed at the Microanalytical Laboratory-Inorganic Chemistry Department, Morgenstelle 18
(
Tübingen Universität , Germany ).
Enantioselective Gas -Chromatographic Analysis
Enantioselective analysis was performed on a gas chromatograph (Carlo Erba instrumentation, Milan,
Italy) equipped with a flame ionization detector (FID). The chiral stationary phase , Chirasil β. Dex with
1
1 spacer Permethylated-β-cyclodextrin, 40%(w/w) was dissolved in PDMS+SI-H(Gelest,ABCR GmbH
Co, Karlsruhe, Germany) and coated on 20 m × 0.25 mm fused silica capillary column (0.25 µm film
&
thickness). The analysis conditions were: Injector temperature = 250 °C, FID temperature = 300 °C, oven
temperature = 145 °C during the simultaneous separation of enantiomers of the racemic acid (8a).
Hydrogen was used as the carrier gas (60 Kpa column head pressure). The retention time of the (S)-8b
and (R)-8c acids were 57.1 and 59.6 min., respectively. The acid was identified by using GC/MSD-
system HP 6890/5973 (Hewlett Packared, Waldbronn,Germany) equipped with an HP 7683 autosampler.
The enantiomeric excess ( % ee ) was found to be 99 % for the (R )-compound (8c), and 95 % for the
(
S )-enantiomer (8b).
(
±)-2-Methyl-2,3-dihydrobenzofuran-7-carboxylic acid (8a)
1
0
Method A : the title compopund was prepared from methyl O-allylsalicylate (4) according to a
9
o
9
o
published procedure. Overall yield of 8a 46% ; mp 128-129 C (lit., mp 127-128 C).
Method B : Compound (8a) was also prepared according to the following procedure as reported for
9
11
related analogs : To a solution of (±)-2-methyl-2,3-dihydrobenzofuran (7) ( 9.0 g ; 67 mmol) and
TMEDA (17.4 g ; 150 mmol) in anhydrous n-hexane (250 mL) was added at rt n-butyllitium solution
o
(
2.5 M, in n-hexane ; 60 mL). The reaction mixture was further stirred at rt for 1 h , cooled to –78 C and
transferred, via a double-ended needle, onto excess dry ice (100 g). The whole operation was conducted
under dry argon atmosphere. The resulting mixture was allowed to warm-up to rt, treated with 4 N
aqueous NaOH solution (250 mL) and ether (250 mL), and shaken well in a separatory funnel. The
aqueous phase was separated, made acidic with 6 N hydrochloric acid and extracted with
2 4
dichloromethane (2 x 150 mL). The combined organic extracts were dried (Na SO ), dichloromethane
was evaporated and the residual solid product was recrystallized from isopropyl ether-methanol solvent
o
pair (95:5 v/v). Yield of pure 8a 8.0 g (67 %) ; mp 129-130 C, undepressed upon admixture with an
authentic sample of 8a prepared via method A above.

Optical resolution of the acid ((±)-8a)
Optical resolution of the racemic acid (8a) was achieved according to the following procedure which was
1
2
13
reported for the (±) 5-chloro and 5-sulfamoyl analogs of 8.
(
S)-2-Methyl- 2,3- dihydrobenzofuran -7-carboxylic acid (8b)
A mixture of (-)-cinchonidine (10.3 g ; 35 mmol) and isopropanol (40 mL) was added to a mixture of
racemic 2-methyl-2,3-dihydrobenzofuran-7-carboxylic acid (8a) (6.2 g; 35 mmol) and isoprpanol (40
mL). The resulting mixture was dissolved by warming and was allowed to stand overnight at rt. The
precipitated diastereomeric salts were collected by filtration, recrystallized from EtOH / MeOH (20 mL
/
10 mL), and then recrystallized once more from EtOH / MeOH (15 mL /8 mL) to give 1.4 g of the (-)-
cinchonidine salt of (S)-8b. This salt was suspended in water (15 mL) and acidified by addition of 6 N
HCl with stirring. The precipitate was collected by suction filtration and recrystallized from aqueous
2
0
o
EtOH to affored pure (S)-8b. Yield 0.56 g (9%); mp 130-131 °C. [α] = - 6.2 (c~0.2,
D
3 10 3
CHCl ). Anal. Calcd for C10H O : C, 67.41; H, 5.66. Found : C, 67.12; H, 5.48 .
(
R)-2-Methyl-2,3-dihydrobenzofuran-7- carboxylic acid ( 8c )
A mixture of (+)-cinchonine (10.3 g; 35 mmol) and EtOH (50 mL) was added to a mixture of racemic 8a
6.2 g; 35 mmol) and EtOH (50 mL). The mixture was dissolved by warming and was allowed to stand
(
overnight at rt. The precipitated diasteriomeric salts were collected by filtration, recrystallized from
EtOH (60 mL), and then recrystallized once more from isopropanol (50 mL) to give 1.3 g of the
cinchonine salt of (R)-(8c) which was suspended in water (15 mL) and acidified by addition of 6 N HCl
with stirring. The white precipitate was collected by suction filtration and recrystallized from aqueous
2
0
o
EtOH to affored 0.5 g (8 %) of (R)-8c; mp 130°-131 °C. [α] = + 6.5 (c~0.2, CHCl
). Anal. Calcd
3
D
for C H O : C, 67.41; H, 5.66. Found: C, 67.31; H, 5.43. The (S)-and (R)-acids (8b, 8c), thus
1
0
10
3
1
13
obtained, display identical spectral properties (IR, H- / C - NMR, MS-EI) to those described for the
racemic acid (8a).
(
±) 4-(2-Methyl-2,3-dihydro-7-benzofuroyl)amino-1-methyl-3-propyl-5-pyrazolecarboxamide (11a )
A mixture of the (±)-acid (8a) (3.0 g ; 17 mmol) and SOCl (12 mL; 165 mmol) in dry benzene (30 mL)
was refluxed (oil bath, 85 °C) for 3 h. Excess SOCl and benzene were then removed in vaccuo, and the
2
2
1
4
residual acid chloride was treated with a solution of the 4-aminopyrazole derivative (10) (3.1 g ; 17
mmol) in anhydrous benzene (25 mL), followed by addition of triethylamine (5 mL; 36 mmol). The
resulting mixture was refluxed for 3 h, benzene was then evaporated, the solid residue was soaked in cold
water (80 mL), the remaining solid product was collected by suction filtration, washed with water and

recrystallized from aqueous ethanol. Yield 4.6 g (79 %) ; mp 140 – 141 °C. Anal. Calcd for
C
18
H
22
N
4
O
3
: C, 63.14; H, 6.48; N, 16.36. Found: C, 63.09; H, 6.42; N, 16.25 ; MS-EI m/z (% rel.
+
int.): 342 (M , 4); HRMS-Calcd: 342.16919. Found: 342.17270), 325(5), 324 (4), 310 (1), 161(100), 133
-1
(
8), 105 (4); IR ( KBr ) : ν /cm = 3536(m), 3339 (s), 3270 (m), 2962 (m), 2929 (w), 2870 (w), 1685 ( s,
1
amide), 1647 (m), 1609 (w), 1533 (m), 1450 (m), 1290 (s), 1191 (m), 1028 (s); H NMR (300 MHz,
CDCl
3
): δ 0.94 (t, J = 7.4 Hz, 3H, CH
2
CH
2
CH
3
3 c
), 1.56 (d, J = 6.3 Hz, 3H, C2′-CH ), 1.65 (m , 2H ,
CH CH CH ), 2.55 (t , J = 7.6 Hz, 2H, CH CH CH ), 2.95 ( dd, J = 15.6 Hz, JAX = 7.5 Hz , 1H, C3′-
2
2
3
2
2
3
AB
H
A
, part of ABX system), 3.45 (dd, JBA = 15.6 Hz , JBX = 8.8 Hz , 1H , C3′-H
X-portion of the ABX system), 4.06 (s, 3H , N-CH ), 5.89, 7.96 (two br s, 1H each of CONH
J = 7.9 Hz, J = 8.5 Hz, 1H , C5′-H), 7.39 (dd, J = 8.5 Hz, J = 1.1 Hz,1H, C4′-H), 7.94 (dd, J = 7.9 Hz,
B
), 5.20 (m
c
, 1H , C2′-H ,
3
2
), 7.00 (dd,
1
3
J = 1.1 Hz,1H, C6′-H), 9.04 (s, 1H, NHCO); C NMR (75 MHz , CDCl
3
): δ 13.9 (CH
), 36.3 (C-3′) , 39.3 (N-CH ), 82.2 (C-2′), 114.4
C-7′), 115.7 (C-4), 121.3 (C-5′), 128.2 (C-3′a), 129.5 (C-6′), 129.6 (C-4′), 133.1(C-5), 146.9 (C-3 ),
57.5 (C-7′a), 161.7 (CONH ), 166.0 (NHCO).
2 2 3
CH CH ), 21.8
(
C2′- CH
3
), 22.4 (CH
2
CH
2
CH
3
), 27.7 (CH
2
CH
2
CH
3
3
(
1
2
(
S)-(4-(2-Methyl-2,3-dihydro-7-benzofuroyl)amino-1-methyl-3-propyl-5-pyrazolecarboxamide (11b)
This compound was prepared from (S)-(8b) (0.50 g; 2.8 mmol) and 10 (0.51 g; 2.8 mmol) by following
the same procedure described above for obtaining (±)-11b. Yield 0.78 g (81 %); mp 141-142 °C.
2
0
o
[
α] = -17.9 (c~0.2 , CHCl
3 22 4 3
). Anal. Calcd for C18H N O : C, 63.14; H, 6.48; N, 16.36. Found: C,
D
6
2.88; H, 6.39; N, 16.37.
(
R)-4-(2-Methyl-2,3-dihydro-7-benzofuroyl)amino-1-methyl-3-propyl-5-pyrazolecarboxamide (11c)
This compound was prepared from (R)-8c (0.50 g ; 2.8 mmol) and 10 (0.51 g ; 2.8 mmol) by following
the same procedure described above for obtaining (±)-8a. Yield 0.75 g (78 %); mp 141-142 °C.
2
0
o
[
α] = +18.8 (c~0.2, CHCl ). Anal. Calcd for C H N O : C, 63.14; H, 6.48; N, 16.36. Found: C,
D
3
18 22
4
3
6
2.94; H, 6.42; N, 16.34. The (S)- and (R)-bisamides (11b, 11c), thus obtained, display identical spectral
properties to those listed above for the racemate (11a).
(
±)-5-(2-Methyl-2,3-dihydro-7-benzofuryl)-1-methyl-3-propyl-1,6-dihydro-7H-pyrazolo[4,3-
d]pyrimidin-7- one (12a )
Potassium t-butoxide (3.5 g ; 30 mmol) was added to a stirred suspension of the bis-amide ((±)-11a) (3.4
g ; 10 mmol) in t-butanol (80 mL), and the resulting mixture was heated under reflux for 10 h (oil bath,

9
5 °C), then allowed to cool to rt . Water (70 mL) was added, the solution was neutralized with 5 % HCl
to pH ∼ 7, and cooled to about 5-10 °C. The precipitated solid product was collected by suction filtration,
washed with cold water and dried. Yield 2 g ( 86 %) ; mp 176-178 °C. Anal. Calcd for C18
H
20
N
4
O
2
: C,
+
6
5
1
6.65; H, 6.21; N, 17.27. Found: C, 66.32; H, 6.03; N, 17.10 ; MS-EI m/z (% rel. int.): 324 (M ,
3); HRMS-calcd: 324.15863. Found: 324.16106), 309(27), 296(100), 281(5), 182(14), 153(10), 136(49),
-1
32(10); IR (KBr) : ν /cm = 3314 (s), 2962 (m), 2923 (w), 2864 (w), 1693 (s , pyrimidone), 1569 (s),
1
1
3
440 (m), 1384 (m), 1313 (w), 1206 (m), 1039 (w); H NMR (300 MHz , CDCl
3
) : δ 1.05 (t , J = 7.4 Hz,
H, CH
2
CH
2
CH
3
), 1.60 (d , J = 6.3 Hz , 3H , C2′-CH
3
) , 1.87 ( m
c
, 2H , CH
2
CH CH ), 2.92 (t , J = 7.5
2
3
Hz, 2H, CH
2
CH
2
CH ), 2.90 (dd, JAB = 15.6 Hz , JAX = 7.4 Hz , 1H, C3′-H
3
A
, part of ABX system ), 3.39
(
dd , JBA = 15.6 Hz , JBX = 8.7 Hz , 1H , C3′-H ), 5.20 (m , 1H, C2′-H, X-portion of the ABX system),
B
c
4
.25 (s, 3H, N-CH
3
), 7.00 (dd, J = 7.3 Hz, J = 7.8 Hz, 1H ,C5′-H), 7.26 (dd , J = 7.3 Hz, J = 1.0 Hz, 1H,
1
3
C4′-H), 8.23 (dd, J = 7.8 Hz, J = 1.0 Hz, 1H, C6′-H), 10.80 (br s, 1H, N6-H); CNMR (75 MHz,
CDCl ): δ 14.1 (CH CH CH ), 21.9 (C2′-CH ), 22.3 (CH CH CH ), 27.8 (CH CH CH ), 36.2 (C-3′),
8.2 (N-CH ), 82.0 (C-2′), 114.4 ( C-7′), 121.5 (C-5′), 124.4 (C-7a), 127.4 (C-4′), 127.7 (C-6′), 128.4
3
2
2
3
3
2
2
3
2
2
3
3
3
(
C-3′a) , 146.5 (C-3), 147.3 (C-5), 154.1 (C-7), 156.4 (C-7′a) .
(
S)-5-(2-Methyl-2,3-dihydro-7-benzofuryl)-1-methyl-3-propyl-1,6-dihydro-7H-pyrazolo[4,3-
d]pyrimidin-7- one (12b)
This compound was prepared from (S)-11b (0.68 g ; 2.0 mmol) by following the same procedure
2
0
o
[
α]D
described above for obtaining (±)-12a . Yield 0.52 g (80 %) ; mp 178 - 179° C.
c~0.3, CHCl ). Anal. Calcd for C18 : C, 66.65; H, 6.21; N, 17.27. Found: C, 66.30; H, 6.15; N,
7.08.
= +38.2
(
3
20 4 2
H N O
1
(
R)-5-(2-Methyl-2,3-dihydro-7-benzofuryl)-1-methyl-3-propyl-1,6-dihydro-7H-pyrazolo[4,3-
d]pyrimidin-7- one (12c)
This compound was prepared from (R)-11c ( 0.68 g ; 2.0 mmol ) by following the same procedure
2
0
o
described above for obtaining (±)-12a . Yield 0.54 g (83 %) ; mp 178-179 °C , [α] = -40.2
D
(
c~0.3, CHCl
7.15. Each of the (S)- and (R)-enantiomers (12b,12c), thus obtained, displays identical spectral
properties to those noted above for the racemate (12a).
3 20 4 2
). Anal. Calcd for C18H N O : C, 66.65; H, 6.21; N, 17.27. Found: C, 66.42; H, 6.10; N,
1

(
±)-5-(5-Chlorosulfonyl -2-methyl-2,3-dihydro-7-benzofuryl)-1-methyl-3-propyl-1,6-dihydro-7H-
pyrazolo[4,3-d]pyrimidin-7-one (13a)
Compound ((±)-12a) (3.24g ;10 mmol) was added protionwise to chlorosulfonic acid (10 mL; 150 mmol)
at 0 °C (ice-salt bath) with stirring. The resulting yellow solution was then allowed to warm to rt, and was
then heated slowly to 65-70 °C (oil bath) for 2 h. The reaction mixture was cautiously poured into
crushed ice (100g), the white solid (chlorosulfonyl derivative), that has precipitated , was filtered
immediately, dried, and used as such in the next step. Yield 3.6 g (85 %); mp 170-172 °C. Anal. Calcd
for C18
H
19
N
4
O
4
ClS: C, 51.12; H, 4.53; N, 13.25; Cl, 8.38; S, 7.58. Found: C, 50.81; H, 4.74; N,
+
1
4
3
3.31; Cl, 8.20; S, 7.36; MS-EI m/z (% rel. int.): 422(M , 54); HRMS-calcd: 422.08156. Found:
-1
22.08396), 407(19), 394(100), 323(22), 294(17), 279(4), 147(11), 136(51), 103(8); IR (KBr): ν /cm =
323 (s, NH) , 2963 (m), 2916 (w), 2848 (w), 1703 (s, pyrimidone), 1636 (w), 1603 (m), 1443 (m), 1374
1
(
s), 1217 (s , 1073 (w); H NMR (400 MHz , CDCl
3
): δ 1.05 (t , J = 7.4 Hz , 3H, CH
2
CH
2
3
CH ), 1.70 (d ,
J = 6.3 Hz , 3H , C2′-CH
3
), 1.87 (m
c
, 2H, CH
2
CH
2
CH ), 2.95 (t, J = 7.6 Hz, 2H, CH CH
3
2
2
CH ), 3.06 (dd ,
3
JAB = 16.2 Hz , JAX = 7.3 Hz , 1H, C3′-H , part of ABX system), 3.60 (dd , J = 16.2 Hz , J = 8.9 Hz,
A
BA
BX
1
H, C3′- H
B
), 5.44 (m
c
, 1H, C2′-H, X-portion of the ABX system), 4.27 (s, 3H , N-CH
3
), 7.90 (d, J =
1
3
1
.8 Hz ,1H , C4′-H ), 8.96 (d, J = 1.8 Hz,1H, C6′-H), 10.55 (br s, 1H , N6-H); C NMR (100 MHz ,
): δ 14.0 (CH CH CH ), 21.9 (C2′-CH ), 22.4 (CH CH CH ), 27.6 (CH CH CH ), 35.6 (C-3′),
8.3 ( N-CH ), 84.4 (C-2′), 115.2 ( C-7′), 124.5 (C-7a), 125.6 (C-4′), 128.9 (C-6′), 131.3 (C-3′a),
37.7 (C-5′), 138.0 (C-3a), 144.7 (C-5), 147.1 (C-3), 153.6 (C-7), 161.1 (C-7′a).
CDCl
3
2
2
3
3
2
2
3
2
2
3
3
1
3
(
S)-5-(5-Chlorosulfonyl -2-methyl-2,3-dihydro-7-benzofuryl)-1-methyl-3-propyl-1,6-dihydro-7H-
pyrazolo[4,3-d]pyrimidin-7-one (13b)
This compound was prepared from (S)-12b (0.39 g ; 1.2 mmol) by following the same procedure
2
0
o
described above for obtaining (±)-13a. Yield 0.42 g (83 %) ; mp 170-171 °C. [α] = +14.9
D
(
c~0.2, CHCl
3
+ MeOH (1:1 v/v)). Anal. Calcd for C18
19 4 4
H N O ClS: C, 51.12; H, 4.53; N, 13.25; Cl,
8
.38; S, 7.58. Found: C, 51.21; H, 4.33; N, 13.18; Cl, 8.31; S, 7.65.
(
R)-5-(5-Chlorosulfonyl -2-methyl-2,3-dihydro-7-benzofuryl)-1-methyl-3-propyl-1,6-dihydro-7H-
pyrazolo[4,3-d]pyrimidin-7-one (13c)
This compound was prepared from (R)-12c (0.39 g ; 1.2 mmol) by following the same procedure
2
0
o
described above for obtaining (±)-13a. Yield = 0.41 g (81 %) ; mp 170-171 °C.
α]D = - 15.7
[
(
3 19 4 4
c~0.2, CHCl +MeOH (1:1 v/v)). Anal. Calcd for C18H N O ClS: C, 51.12; H, 4.53; N, 13.25; Cl,

8
.38; S, 7.58. Found: C, 51.05; H, 4.66; N, 13.12; Cl, 8.20 ; S, 7.44. Each of the (S)-13b and (R)-13c,
thus obtained, shows identical spectral properties to those noted above for the racemate (13a ).
(
±)5-[2-Methyl-5-(4-methylpiperazin-1-ylsulfonyl)-2,3-dihydro-7-benzofuryl]-1-methyl-3-propyl-1,6-
dihydro-7H-pyrazolo[4,3-d]pyrimidin-7- one (3a)
The sulfonyl chloride derivative ((±)-13a) (3.5 g ; 8.3 mmol) was dissolved in dry THF (35 mL) and
treated with a solution of 1-methylpiprazine (2 mL ; 18 mmol) in THF (10 mL). The resulting mixture
was stirred at rt for 2.5 h, THF was then removed and the residue was treated with cold water (80 mL).
The resulting pale yellow precipitate was filtered under suction, washed with cold water, and
30 6 4
recrystallized from aqueous EtOH. Yield 3.4 g (84 %); mp 184 –186 °C. Anal. Calcd for C23H N O S:
C,56.77; H, 6.21; N, 17.27; S, 6.59. Found: C, 56.39; H, 5.98; N, 17.07; S, 6.48 ; MS-EI m/z (%
+
rel. int.): 486 (M , 1); HRMS-calcd: 486.20493. Found: 486.20448), 416 (18), 323 (3), 136(3), 99 (100).
-1
IR ( KBr ) : ν /cm = 3326 (s, NH), 2939 (w), 2847 (w), 2798 (m), 1693 (s, pyrimidone), 1605 (m),
1
1
571 (s), 1489 (w), 1447 (m), 1390 (w), 1356 (m), 1287 (m), 1170 (s), 1077 (w); H NMR (400 MHz,
CDCl
3
): δ 1.05 (t , J = 7.4 Hz , 3H, CH
2
CH
2
CH
3
3 c
), 1.65 (d , J = 6.3 Hz , 3H , C2′-CH ), 1.85 (m , 2H,
CH
2
CH CH ), 2.28 (s, 3H, N4″-CH ), 2.51 (t, J = 4.8 Hz, 4H, C-3″-H/C-5″-H), 2.85 (t, J = 7.6 Hz, 2H,
2
3
3
CH CH CH ) , 3.10 (br t, J = 4.8Hz, 4H, C-2″-H/C-6″-H), 3.06 (dd, J = 16.0 Hz, JAX = 7.3 Hz, 1H,
2
2
3
AB
C3′-H
A
, part of ABX system), 3.50 (dd, JBA = 16.0 Hz, JBX = 8.9 Hz, 1H , C3′-H
B
c
), 5.35 (m , 1H, C-2′H,
X-portion of the ABX system), 4.27 (s, 3H , N
1
-CH ), 7.65 (d, J = 1.3 Hz ,1H , C4′-H), 8.65 (d, J = 1.3
3
1
3
Hz, 1H, C6′-H), 10.60 (br s, 1H , N6-H); C NMR (100 MHz, CDCl ): δ 14.0 (CH CH CH ), 21.9 (C2′
3
2
2
3
-
(
CH
3
), 22.2 (CH
2
CH
2
CH
3
), 27.6 (CH
2
CH
2
CH
3
), 35.8 (C-3′), 38.3 (N
1
-CH
3
), 45.7 (N4″-CH
3
), 46.0
C-2″/C-6″), 54.0 (C-3″/C-5″), 83.8 (C-2′), 115.0 (C-7′) , 124.5 (C-7a), 126.5 (C-4′), 128.0 (C-6′),
29.0 (C-3′a), 130.1 (C-5′), 138.2 (C-3a), 145.5 (C-5), 147.0 (C-3), 153.7 (C-7), 159.5 (C-7′a).
1
(
S)-5-[2-Methyl-5-(4-methylpiperazin-1-ylsulfonyl)-2,3-dihydro-7-benzofuryl]-1-methyl-3-propyl-1,6-
dihydro-7H-pyrazolo[4,3-d]pyrimidin-7- one (3b)
This compound was prepared from (S)-13b (0.42 g; 1.0 mmol) by following the same procedure
2
0
o
described above for obtaining (±)-(3a). Yield 0.38 g (78 %) ; mp 186-187 °C. [α] = + 15.2 (c ~
D
0
.2, CHCl ). Anal. Calcd for C H N O S: C,56.77; H, 6.21; N, 17.27; S, 6.59. Found: C, 56.48; H,
3
23 30
6
4
5
.10; N, 17.05; S, 6.36.

(
R)-5-[2-Methyl-5-(4-methylpiperazin-1-ylsulfonyl)-2,3-dihydro-7-benzofuryl]-1-methyl-3-propyl-1,6-
dihydro-7H-pyrazolo[4,3-d]pyrimidin-7- one (3c)
This compound was prepared from (R)-13c (0.42 g; 1.0 mmol) by following the same procedure
2
0
o
described above for obtaining ((±)-3a). Yield 0.39 g (80 %); mp 186-187 °C .
= -16.0 (c~0.2,
[
α]D
3 30 6 4
CHCl ). Anal. Calcd for C23H N O S: C,56.77; H, 6.21; N, 17.27; S, 6.59. Found: C, 56.42; H, 6.07;
N, 17.11; S, 6.42. The (S)- and (R)- compounds (3b and 3c) display identical spectral properties to those
described for the racemic modification (3a).
ACKNOWLEDGEMENTS
We wish to thank BMBF, Bonn-Germany, the University of Jordan and the University of Sharjah-UAE
for financial support. Our thanks are also due to Professor V. Schurig and Mr. A. Ghanem ( Tübingen
Universität ) for the chiral HPLC measurements .
REFERENCES
(
* ) Corresponding author, e-mail: mustelab@ju.edu.jo
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1