Highly regioselective synthesis of N-3 organophosphorous derivatives of 3,4-dihydropyrimidin-2(1H)-ones and their calcium channel binding studies

Article abstract of DOI:10.1016/j.ejmech.2012.05.017

A series of novel N-3 substituted 3,4-dihydropyrimidin-2(1H)-ones derivatives bearing diaminophosphinyl, phosphonate and phosphorous containing heterocycles were obtained from 3,4-dihydropyrimidinones (DHPMs) in a regioselective manner through an efficient reaction protocol, tolerant to substitutional variation at the key diversity positions around the DHPM core. None of the representative compounds screened for calcium channel blocking activity was found to have significant activity compared to nifedipine.

Full text of DOI:10.1016/j.ejmech.2012.05.017

European Journal of Medicinal Chemistry 54 (2012) 397e402
Contents lists available at SciVerse ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Highly regioselective synthesis of N-3 organophosphorous derivatives
of 3,4-dihydropyrimidin-2(1H)-ones and their calcium channel binding studies
,
a
b
b
Kamaljit Singh a , Kawaljit Singh , Danielle M. Trappanese , Robert S. Moreland
*
a Organic Synthesis Laboratory, Department of Applied Chemical Sciences and Technology, UGC SAP (DRS-1) Department, Guru Nanak Dev University, Amritsar 143005, India
b Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, PA 19102, USA
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
< Novel 3,4-dihydropyrimidinones are
obtained in highly regioselective
manner.
< Organophosphorous compounds are
valuable owing to therapeutic
potential.
< N3-substituted
dihydropyr-
imidinones are prized for different
biological effects.
< Calcium channel binding study has
been
compounds.
< X-Ray shows structure similar to
receptor bound conformation
similar to nifedipine.
conducted
on
new
a r t i c l e i n f o
a b s t r a c t
Article history:
A
series of novel N-3 substituted 3,4-dihydropyrimidin-2(1H)-ones derivatives bearing diamino-
Received 21 February 2012
Received in revised form
11 May 2012
Accepted 11 May 2012
Available online 26 May 2012
phosphinyl, phosphonate and phosphorous containing heterocycles were obtained from 3,4-
dihydropyrimidinones (DHPMs) in a regioselective manner through an efficient reaction protocol,
tolerant to substitutional variation at the key diversity positions around the DHPM core. None of the
representative compounds screened for calcium channel blocking activity was found to have significant
activity compared to nifedipine.
Ó 2012 Elsevier Masson SAS. All rights reserved.
Keywords:
DHPM
Biginelli compounds
Organophosphorous
Regioselective
Calcium channel blockers
Vascular smooth muscle
1. Introduction
treatment of cardiovascular diseases such as hypertension, cardiac
arrhythmias and angina pectoris [1,2]. Recently, structurally related
1,4-dihydropyridine (DHP) derivative nifedipine 1 is a well-
known calcium channel blocker (CCB) used for the clinical
3,4-dihydropyrimidin-2(1H)-ones (DHPMs), also known as Bigi-
nelli compounds [3] have been identified as efficient calcium
channel blockers [4,5] as well as a1a-adrenergic receptor antago-
nists, mitotic kinesin inhibitors, and hepatitis B virus replication
suppressors. Several marine natural products containing the DHPM
core [6,7] are potent HIV gp-120CD inhibitors.
* Corresponding author. Tel.: þ91 183 2258853; fax: þ91 183 2258819, þ91 183
2258820.
E-mail address: kamaljit19in@yahoo.co.in (K. Singh).
0223-5234/$ e see front matter Ó 2012 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2012.05.017

398
K. Singh et al. / European Journal of Medicinal Chemistry 54 (2012) 397e402
NO2
CF3
S
NO2
O
O
O
i-PrOOC
Me
MeOOC
Me
COOMe
N
i-PrO
Me
N
NH2
N
N
H
N
H
Me
N
H
3
2
1
F
F
F
CH3
NH
O
O
O
N
O
O
O
RO2C
Me
P
N
MeO
N
H
3
N
O
N
H
5
Me
H
OMe
4
Fig. 1. Biologically important 3,4-dihydropyrimidin-2(1H)-ones derivatives.
Over a century old acid catalyzed three-component Biginelli
regioselective reaction giving access to DHPMs bearing a dia-
minophosphinyl, phosphonate as well as phosphorous heterocyclic
unit at the N-3 position as well as report their calcium channel
binding activity.
condensation [3] as well as a plethora of its variants furnish DHPMs
in moderate to excellent yields, although rationally designed tailor-
made diversification of six (N1, C2, N3, C4, C5 and C6) positions
around the DHPM core [8e12] gave access to those DHPMs which
could not be procured through the three-component route owing
to either inaccessibility of the latter route or non-availability of one
of these components. Most of the potent DHPM based calcium
2. Chemistry
Reaction of DHPM lacking an N3 substituent with phosphorous
oxychloride yielding a DHPM bearing a reactive phosphorous
oxychloride group at the more basic N3 presented itself as
a method of choice owing to ease in availability of reagents as well
as operational ease of this as well as its further reactions with
various nucleophiles. Thus, when DHPM 6 was treated with POCl3
at 105 ꢀC (Scheme 1), N3-elaborated 7 was obtained in 90e95%
yield. Lower stability of 7 at ambient temperature meant that it
could only be used in subsequent reaction without purification.
Thus, treating 7 in situ with ammonia gas dissolved in dry THF for
45 min at room temperature, led to the smooth formation of N3-
diaminophosphinyl DHPM 8 in excellent yields, after recrystalli-
zation from methanol (Table 1). This fairly simple and efficacious
channel blockers for example SQ 32926 2 and SQ 32547 3 or a1a
-
adrenergic receptor like SNAP 6201 4 [5] are substituted at N3
position (Fig. 1). A series of 1,4-dihydropyridine-5-cyclic phospho-
nate derivatives 5 (Fig. 1) were found to have activities superior or
comparable to that of nifedipine 1 [13]. Recently phosphorous
heterocycles have received widespread attention due to their
ubiquity in biological systems [14,15] and their potential to serve as
novel pharmaceuticals [16e19]. In continuation of our interest in N-
3 substitution of DHPMs [11,12], we wondered, if an organophos-
phorus group or heterocyclic moiety at N3 could yield a beneficial
cardiovascular effect as well as furnish hitherto unknown DHPM
derivatives. In this paper we report
a useful and highly
O
R1
O
P
NH2
NH2
R2O
N
s
Me
N
O
a
g
H3
T
N
8
R3
T
R
/
F
H
R1
O
R1
O
P
O
Cl
Cl
O
R1
O
P
XR4
XR4
R2O
N
R2O
NH
POCl3
105 0
Amine/dioxane
or EtOH/80 o
R2O
N
C
C
Me
N
R3
7
O
Me
N
O
Me
O
N
O
R3
R3
9
6
R1
(90-95%)
O
P
R2O
N
N
H
XH
X
n
Me
N
O
R3
10
Scheme 1. Synthesis of N3-substituted 3,4-dihydropyrimidin-2(1H)-ones.

K. Singh et al. / European Journal of Medicinal Chemistry 54 (2012) 397e402
399
Table 1
Synthesis of N3-substituted 3,4-dihydropyrimidin-2(1H)-ones.
Entry
Product
R1
R2
R3
R4/X
Yield (%)
1.
2.
3.
4.
5.
6.
7.
8.
8a
8b
8c
8d
8e
8f
8g
9a
9b
C6H5
C2H5
C2H5
(CH3)2CH
CH3
C2H5
C2H5
CH3
C2H5
C2H5
C2H5
C2H5
C2H5
C2H5
C2H5
H
H
H
H
H
H
H
H
H
H
H
H
H
CH3
e
95
95
95
93
85
92
83
66
60
70
72
65
64
65
4-OMeC6H4
3-NO2C6H4
C6H5
H
CH3
CH3
C6H5
C6H5
C6H5
C6H5
CH3
C6H5
C6H5
e
e
e
e
e
e
C4H9/NH
C6H5/NH
C2H5/O
-/NH
-/NH
-/O
9.
10.
11.
12.
13.
14.
9c
10a
10b
10c
10d
-/O
reaction served as a general protocol for obtaining a range of
regioselectively N-3 substituted DHPMs tolerant to substitutional
variation around DHPM core as shown in Table 1. In addition to 31P
NMR and spectral data the characteristic feature of the 1H NMR
spectrum of C-4 aryl derivatives (8ae8d) is the presence of doublet
corresponding to C4eH, due to PeH coupling.
In analogy with the reactions of 7 with ammonia, reactions of
various amines with 7 led to the formation of N3-dialkylamino-
phosphinyl substituted DHPMs 9. Thus, when a solution of appro-
priate N3-dichlorophosphinyl appended DHPM in dry dioxane was
treated with amines such as n-butylamine and benzylamine or
ethanol (80 ꢀC) (Scheme 1) corresponding N-3 substituted DHPMs
9ae9c were obtained in good yield after purification with column
chromatography (entries 8e10, Table 1). Similar reactions with
diamines and amino alcohols in dry dioxane at room temperature
furnished DHPMs derivatives 10ae10d The scope and limitations
of this reaction protocol has been explored by varying substituents
at C-4 position as well as ring size of phosphorous containing
heterocyclic ring substituted at N-3 position (Table 1). All these
novel compounds have been well characterized using spectroscopic
techniques and presence of phosphorous in these compounds has
been ascertained by recording their 31P NMR spectrum.
Fig. 2. X-ray crystal structure of 8b showing the stereoview of the molecule and the
numbering scheme used in the structure analysis. (N2, C8, C13 positions may be read
as N3, C4 and C6, respectively, following IUPAC nomenclature scheme).
depolarization induced contraction of vascular smooth muscle. For
this purpose, swine carotid arteries were obtained from a slaugh-
terhouse and transported to the laboratory in an ice-cold physio-
logical salt solution (PSS) buffered (pH 7.4) with 3-[N-morpholino]
propane sulfonic acid (MOPS). The PSS contained, in mM: 140 NaCl,
4.7 KCl, 1.2 MgSO4, 1.6 CaCl2, 1.2 Na2HPO4, MOPS, 5
D-glucose, and
0.02 Na2-ethylenediaminetetraacetic acid (EDTA). Arteries were
cleaned of connective tissue, and then dissected free of both intima
and adventitia leaving a thin medial layer for experimentation.
Intact medial strips of swine carotid artery (7 ꢁ 0.7 mm) were
suspended between a Grass FT.03 force transducer and a stationary
clip in water jacketed organ baths. The strips were equilibrated in
PSS at 37 ꢀC, pH 7.4 and bubbled with 100% O2 for 90e120 min. A
passive force of w2 g was applied to all tissues. The passive force
sets the muscles at a length that approximates Lo, the length at
which maximal active force is generated. During the equilibration
period, tissues were maximally contracted with 110 mM KCl
(equimolar substitution for NaCl) several times until similar levels
of force were attained.
3. Result and discussion
3.1. Structural correlation with receptor bound conformation
In order to unambiguously establish the incorporation of the
diaminophosphinyl group at N-3 positions of 6 and to establish
correlation with proposed receptor bound confirmation with
nifedipine as well as DHPM type calcium channel blockers, struc-
ture of 8b was additionally confirmed by single crystal X-ray
analysis (Fig. 2) [20].
The solid state structure of 8b (Fig. 2) shows a half-boat type
conformation of the dihydropyrimidinone ring. The C-4 aryl ring is
perpendicular to the molecular plane and bisects the half-boat
conformation of the DHPM ring. The C-5 ester is in cis orientation
with respect to the C5, C6 double bond of the ring and coplanar
with the DHPM ring, so is the N3–P¼O link, the P]O oxygen
pointing in the direction of C4-H of the DHPM unit. Such confor-
mations drawn close analogy with the proposed receptor bound
conformation of DHPMs resulting in the observed calcium channel
blocking activity (calcium antagonists) [21].
The equilibrated vascular strips were contracted with 110 mM
KCl containing PSS, allowed to achieve a stable level of force and
then subjected to the cumulative addition of calcium channel
blockers (0.001
mMe10 mM), nifedipine (0.001 mMe10 mM) or
DMSO as a vehicle control. Data are presented (Fig. 3) as
a percent of the initial maximal response to 110 mM KCl at
each dose of compound. The calcium channel blockers were
compared against nifedipine
1 for their ability to relax a
membrane depolarization induced contraction which is almost
exclusively dependent on the influx of extra-cellular calcium
[22]. The novel compounds and nifedipine were tested across a
concentration range of 0.001
relaxed the KCl-induced contractions with an IC50 of approxi-
mately 0.01 M against 110 mM KCl. In contrast the compounds
mMe10 mM. Nifedipine completely
3.2. Calcium channel binding studies
m
8aeg, 9aec and 10aec maximally relaxed the KCl-induced
contractions by only 0e25% with the relaxation only significant
Representative compounds 8e10 were screened for calcium
blocking activity based on their ability to relax a membrane
at 10 mM.

400
K. Singh et al. / European Journal of Medicinal Chemistry 54 (2012) 397e402
Nifedipine
pressure and last traces of POCl3 were removed through azeotropic
120
100
80
60
40
20
0
8a
distillation with dry benzene to furnish the N3-dichlorophosphinyl
DHPM derivatives 7 in 90e95% yield, and were used for subsequent
reactions without further purification.
8b
8c
8d
8e
5.3. General procedure for the synthesis of N3-substituted DHPM
derivatives 8
8f
8g
9a
N3-dichlorophosphinyl DHPM derivative 7 (0.5 g) was treated
with ammonia gas (evolved by warming 30% aqueous ammonia
solution using standard assembly and dried through KOH trap)
dissolved in THF at room temperature for 45 min. White precipi-
tates formed in the reaction mixture were filtered and recrystal-
lized from methanol to obtain pure compound. The characteristic
data of the compounds is given below.
9b
9c
10a
10b
10c
[Compound]/M
Fig. 3. Medial strips from the swine carotid artery were contracted with 110 mM
KClePSS and then subjected to the cumulative addition of calcium channel blocker to
determine their potential for relaxation. Nifedipine and 13 novel calcium channel
blockers (8aeg, 9aec and 10aec) were tested.
5.3.1. 5-Ethoxycarbonyl-6-methyl-3-(diaminophosphinyl)-4-
phenyl-3,4-dihydropyrimidin-2(1H)-one (8a)
White crystalline solid. Rf: 0.4 (methanol:ethyl acetate/10:90).
Yield: 95%. M.p. 258e260 ꢀC (methanol). IR (KBr): nmax 1090, 1220,
4. Conclusion
1615, 1680, 3320 cmꢂ1. 1H NMR (300 MHz, DMSO-d6, 25 ꢀC):
d 1.17
(t, J ¼ 7.2 Hz, 3H, ester-CH3), 2.23 (s, 3H, C6-CH3), 4.02 (br, 2H, D2O
exchangeable, NH2), 4.04e4.15 (m, 2H, ester-CH2), 4.33 (br, 2H, D2O
exchangeable, NH2), 6.09 (d, J ¼ 7.2 Hz, 1H, C4-H), 7.17e7.32 (m, 5H,
ArH), 9.62 (br, 1H, D2O exchangeable, N1-H). 13C NMR (75 MHz,
Thus an efficient protocol using neutral reaction conditions for
the regioselective synthesis of N3-substituted DHPM derivatives
has been developed. DHPM derivatives bearing
a
dia-
minophosphinyl, phosphonate as well as phosphorous containing
heterocycles at N-3 position has been synthesized. Among the
novel compounds tested the calcium channel blocking activity was
less compared to nifedipine in a screen using relaxation of
a membrane depolarized vascular tissue as the end-point.
DMSO-d6, 25 ꢀC)
d
14.2, 17.5, 54.5, 59.6, 102.6, 126.1, 127.0, 128.2,
142.7, 148.1, 153.3 and 165.4. 31P NMR (121 MHz, DMSO-d6, 25 ꢀC):
d
11.95. Anal. Calcd. for C14H19N4O4P: C, 49.70; H, 5.62; N, 16.57;
Found: C, 49.77; H, 5.93; N, 16.20. MS: m/z 339 (Mþþ1).
5.3.2. 5-Ethoxycarbonyl-6-methyl-3-(diaminophosphinyl)-4-(4-
methoxyphenyl)-3,4-dihydropyrimidin-2(1H)-one (8b)
5. Experimental section
Wite crystalline solid. Rf: 0.2 (methanol:ethyl acetate/10:90).
5.1. General
Yield: 95%. M.p. 260e262 ꢀC (methanol). IR (KBr): nmax 1091, 1235,
1631, 1690, 3399 cmꢂ1 1H NMR (300 MHz, DMSO-d6, 25 ꢀC):
d 1.16
All liquid reagents were dried/purified following recommended
(t, J ¼ 7.2 Hz, 3H, ester-CH3), 2.23 (s, 3H, C6-CH3), 3.36 (s, 3H, OCH3),
3.95 (br, 2H, D2O exchangeable, NH2), 4.02e4.10 (m, 2H, ester-CH2),
4.30 (br, 2H, D2O exchangeable, NH2), 6.00 (d, J ¼ 6.9 Hz, 1H, C4-H),
6.80e6.83 (m, 2H, ArH), 7.22 (d, J ¼ 8.7 Hz, 2H, ArH), 9.59 (br, 1H,
D2O exchangeable, N1-H). 13C NMR (75 MHz, DMSO-d6, 25 ꢀC):
drying agents and/or distilled over 4 Å molecular sieves. 1H NMR
(400 MHz and 300 MHz), 13C NMR (100 MHz and 75 MHz) and 31
P
(162 MHz and 121 MHz) spectra were recorded in DMSO-d6 and
CDCl3 on a multinuclear Bruker-400 MHz and Jeol FT-AL-300
instruments with chemical shifts being reported in parts per
d
14.3, 17.4, 54.2, 55.0, 59.5, 102.7, 113.5, 127.5, 134.7, 147.8, 153.2,
million (
d
) relative to internal tetramethylsilane (TMS,
d
0.0, 1H
158.3 and 165.3. 31P NMR (121 MHz, DMSO-d6, 25 ꢀC):
d
12.04. Anal.
NMR or CDCl3,
d
77.0, 13C NMR). Mass spectra were recorded from
Calcd. for C15H21N4O5P: C, 48.91; H, 5.71; N, 15.22; Found: C, 49.19;
H, 6.01; N, 15.25. MS: m/z 369 (Mþþ1).
Indian Institute of Integrative Medicine (CSIR), Jammu, under
electron impact at 70 eV on a Bruker Daltonics Esquire 3000
spectrometer. Elemental analysis was performed on FLASH EA 112
(Thermoelectron Corporation) analyzer at Department of Chem-
istry, Guru Nanak Dev University, Amritsar and the results are
quoted in %. IR recorded on FTIR Shimadzu 8400 Fourier-transform
spectrophotometer in the range 400e4000 cmꢂ1 using KBr.
Melting points were determined in open capillaries and are
uncorrected. For monitoring the progress of a reaction and for
comparison purpose, thin layer chromatography (TLC) was per-
formed on pre-coated aluminium sheets Merck (60F254, 0.2 mm)
using an appropriate solvent system. The chromatograms were
visualized under UV light. For column chromatography silica gel
(60e120 mesh) was employed and eluents were ethyl acetate/
hexane mixtures.
5.3.3. 5-Isopropoxycarbonyl-6-methyl-3-(diaminophosphinyl)-4-
(3-nitrophenyl)-3,4-dihydropyrimidin-2(1H)-one (8c)
White crystalline solid. Rf: 0.5 (methanol:ethyl acetate/10:90).
Yield: 95%. M.p. 268e270 ꢀC (methanol). IR (KBr): nmax 1090, 1225,
1525, 1635, 1680, 3320 cmꢂ1 1H NMR (300 MHz, DMSO-d6, 25 ꢀC):
d
1.12 (d, J ¼ 6.3 Hz, 3H, ester-CH3),1.21 (d, J ¼ 6.3 Hz, 3H, ester-CH3),
2.24 (s, 3H, C6-CH3), 4.08 (br, 2H, D2O exchangeable, NH2), 4.41 (br,
2H, D2O exchangeable, NH2), 4.87e4.95 (m, 1H, ester-CH), 6.12 (d,
J ¼ 6.6 Hz, 1H, C4-H), 7.59 (t, J ¼ 7.8 Hz, 1H, ArH), 7.74 (d, J ¼ 7.8 Hz,
1H, ArH), 8.08e8.14 (m, 2H, ArH), 9.86 (br, 1H, D2O exchangeable,
N1-H). 13C NMR (75 MHz, DMSO-d6, 25 ꢀC):
d
17.5, 21.6, 54.8, 67.1,
101.8, 121.1, 122.2, 130.0, 132.9, 145.2, 147.7, 148.6, 152.7 and 164.5.
31P NMR (121 MHz, DMSO-d6, 25 ꢀC):
11.90. Anal. Calcd. for
d
C15H20N5O6P: C, 45.34; H, 5.04; N, 17.63; Found: C, 45.19; H, 5.22; N,
5.2. General procedure for the synthesis of N3-dichlorophosphinyl
DHPM derivatives 7
17.43. MS: m/z 398 (Mþþ1).
5.3.4. 5-Methoxycarbonyl-6-methyl-3-(diaminophosphinyl)-4-
phenyl-3,4-dihydropyrimidin-2(1H)-one (8d)
Appropriate DHPM 6 (0.01 mol) was suspended in phosphorous
oxychloride (10 ml) and heated at 105 ꢀC for 30 min. Excess
phosphorous oxychloride (POCl3) was removed under reduced
White crystalline solid. Rf: 0.7 (methanol:ethyl acetate/20:80).
Yield: 93%. M.p. 253e255 ꢀC (methanol). IR (KBr): nmax 1024, 1237,

K. Singh et al. / European Journal of Medicinal Chemistry 54 (2012) 397e402
401
1551, 1631, 1698, 3317 cmꢂ1 1H NMR (300 MHz, DMSO-d6, 25 ꢀC):
2.23 (s, 3H, C6-CH3), 3.62 (s, 3H, OCH3), 4.06 (br, 2H, D2O
5.4.1. 5-Ethoxycarbonyl-6-methyl-3-[bis(butylamino)phosphinyl]-
3,4-dihydropyrimidin-2(1H)-one (9a)
d
exchangeable, NH2), 4.36 (br, 2H, D2O exchangeable, NH2), 6.09 (d,
White crystalline solid. Rf: 0.7 (methanol:ethyl acetate/10:90).
Yield: 66%. M.p. 115e117 ꢀC (dichloromethane/hexane). IR (KBr):
nmax 1023, 1235, 1407, 1634, 1697, 3356 cmꢂ1 1H NMR (400 MHz,
J ¼ 7.2 Hz, 1H, C4-H), 7.20e7.29 (m, 5H, ArH), 9.67 (br, 1H, D2O
exchangeable, NH). 13C NMR (75 MHz, DMSO-d6, 25 ꢀC):
d 17.6, 51.3,
54.7,102.5,126.3,127.3,128.2,142.5,148.7,152.4 and 166.0. 31P NMR
(121 MHz, DMSO-d6, 25 ꢀC):
11.93. Anal. Calcd. for C13H17N4O4P: C,
CDCl3, 25 ꢀC):
d
0.76 (t, J ¼ 7.2 Hz, 3H, CH3), 0.88 (t, J ¼ 7.2 Hz, 3H,
d
CH3), 1.03e1.16 (m, 4H, 2 ꢁ CH2), 1.19 (t, J ¼ 7.0 Hz, 3H, ester-CH3),
1.29e1.36 (m, 2H, CH2), 1.41e1.46 (m, 2H, CH2), 2.38 (s, 3H, C6-CH3),
2.48e2.58 (m, 2H, CH2), 2.75 (br, 1H, D2O exchangeable, NH),
2.90e2.98 (m, 2H, CH2), 3.06 (br, 1H, D2O exchangeable, NH),
4.05e4.14 (m, 2H, ester-CH2), 6.12 (d, J ¼ 6.0 Hz, 1H, C4-H),
7.23e7.32 (m, 3H, ArH), 7.46e7.48 (m, 2H, ArH), 8.44 (br, 1H, D2O
48.15; H, 5.25; N, 17.28; Found: C, 48.42; H, 5.46; N, 16.96. MS: m/z
325 (Mþþ1).
5.3.5. 5-Ethoxycarbonyl-6-methyl-3-(diaminophosphinyl)-3,4-
dihydropyrimidin-2(1H)-one (8e)
White crystalline solid. Rf: 0.3 (methanol:ethyl acetate/15:85).
Yield: 85%. M.p. 260e262 ꢀC (methanol). IR (KBr): nmax 1096, 1291,
1658, 1710, 1741, 3398 cmꢂ1 1H NMR (300 MHz, DMSO-d6, 25 ꢀC):
exchangeable, NH). 13C NMR (100 MHz, CDCl3, 25 ꢀC):
d 13.6, 13.7,
14.1, 17.9, 19.6, 19.8, 33.7, 33.8, 40.0, 40.6, 56.9, 60.2, 104.2, 127.5,
127.9,128.4,142.5,145.6,154.2 and 165.2. 31P NMR (162 MHz, CDCl3,
d
1.19 (t, J ¼ 7.2 Hz, 3H, ester-CH3), 2.16 (s, 3H, C6-CH3), 4.07 (q,
25 ꢀC):
d 12.21; Anal. Calcd. for C22H35N4O4P: C, 58.67; H, 7.78; N,
J ¼ 6.9 Hz, 2H, ester-CH2), 4.19 (br, 4H, D2O exchangeable, 2 ꢁ NH2),
12.44; Found: C, 58.30; H, 7.50; N, 12.22. MS: m/z 473 (Mþþ23).
5.73 (s, 2H, C4-CH2), 9.89 (br, 1H, D2O exchangeable, N1-H). 13C
NMR (75 MHz, DMSO-d6, 25 ꢀC):
d
14.2, 16.9, 42.1, 59.3, 97.0, 148.1,
5.4.2. 5-Ethoxycarbonyl-6-methyl-3-[bis(benzylamino)
phosphinyl]-3,4-dihydropyrimidin-2(1H)-one (9b)
153.4 and 165.0. 31P NMR (121 MHz, DMSO-d6, 25 ꢀC):
d
12.87. Anal.
Calcd. for C8H15N4O4P: C, 36.64; H, 5.72; N, 21.37; Found: C, 36.68;
White crystalline solid. Rf: 0.7 (methanol:ethyl acetate/10:90).
Yield: 60%. M.p. 183e185 ꢀC (dichloromethane/hexane). IR (KBr):
nmax 1086, 1233, 1634, 1700, 3374 cmꢂ1 1H NMR (300 MHz,
H, 6.00; N, 20.89. MS: m/z 263 (Mþþ1).
5.3.6. 5-Ethoxycarbonyl-4,6-dimethyl-3-(diaminophosphinyl)-3,4-
dihydropyrimidin-2(1H)-one (8f)
White crystalline solid. Rf: 0.3 (methanol:ethyl acetate/20:80).
Yield: 92%. M.p. 265e267 ꢀC (methanol). IR (KBr): nmax 1029,
1245, 1411, 1635, 1696, 3401 cmꢂ1 1H NMR (400 MHz, DMSO-d6,
CDCl3, 25 ꢀC):
d
1.22 (t, J ¼ 6.9 Hz, 3H, ester-CH3), 2.29 (s, 3H,
C6-CH3), 3.11 (br, 1H, D2O exchangeable, NH), 3.56 (t, J ¼ 7.2 Hz,
1H, D2O exchangeable, NH), 3.68e3.85 (m, 2H, CH2), 4.08e4.19
(m, 4H, ester-CH2 and CH2), 6.13 (d, J ¼ 6.0 Hz, 1H, C4-H),
6.71 (br, 1H, D2O exchangeable, NH), 7.01e7.04 (m, 2H, ArH),
7.16e7.31 (m, 11H, ArH), 7.43e7.46 (m, 2H, ArH). 13C NMR
25 ꢀC):
d
0.91 (d, J ¼ 6.4 Hz, 3H, C4-CH3), 0.98 (t, J ¼ 7.0 Hz, 3H,
ester-CH3), 1.96 (s, 3H, C6-CH3), 3.82e3.92 (m, 2H, ester-CH2),
3.95 (br, 2H, exchanged with D2O, NH2), 3.99 (br, 2H, exchanged
with D2O, NH2), 4.71 (t, J ¼ 6.2 Hz, 1H, C4-H), 9.28 (br, 1H,
exchanged with D2O, NH). 13C NMR (100 MHz, DMSO-d6, 25 ꢀC):
(75 MHz, CDCl3, 25 ꢀC)
128.0, 128.8, 143.7, 146.2, 153.3 and 165.7. 31P NMR (162 MHz,
CDCl3, 25 ꢀC):
11.85. Anal. Calcd. for C28H31N4O4P: C, 64.86; H,
d 14.2, 18.8, 29.7, 55.8, 60.1, 101.5, 126.7,
d
5.98; N, 10.81; Found: C, 64.66; H, 6.32; N, 10.52. MS: m/z 517
d
14.3, 17.3, 21.1, 48.6, 59.3, 103.2, 147.2, 153.0 and 165.0. 31P NMR
(Mꢂ-1).
(162 MHz, DMSO-d6, 25 ꢀC):
d 12.02. Anal. Calcd. for C9H17N4O4P:
C, 39.13; H, 6.16; N, 20.29; Found: C, 38.92; H, 6.44; N, 19.94. MS:
5.4.3. 5-Ethoxycarbonyl-6-methyl-3-(diethylphosphonate)-4-
phenyl-3,4-dihydropyrimidin-2(1H)-one (9c)
m/z 277 (Mþþ1).
Compound 7 (R1 ¼ Ph, R2 ¼ Et, R3 ¼ H)was treated with
ethanol at 80 ꢀC for 3 h and after completion of reaction (TLC)
solvent was removed under reduced pressure. Purification of the
residue by column chromatography using hexane and ethyl-
acetate as eluents resulted in the isolation of compound 9c as
a white crystalline solid. Rf: 0.8 (methanol:ethyl acetate/20:80).
Yield: 70%. M.p. 112e114 ꢀC (dichloromethane/hexane). IR (KBr):
nmax 1024, 1243, 1390, 1636, 1704, 3236 cmꢂ1 1H NMR (300 MHz,
5.3.7. 5-Methoxycarbonyl-4,6-dimethyl-3-(diaminophosphinyl)-
3,4-dihydropyrimidin-2(1H)-one (8g)
White crystalline solid. Rf: 0.2 (methanol:ethyl acetate/20:80).
Yield: 83%. M.p. 272e274 ꢀC (methanol). IR (KBr): nmax 1080, 1212,
1487, 1642, 1703, 3431 cmꢂ1 1H NMR (300 MHz, DMSO-d6, 25 ꢀC):
d
1.11 (d, J ¼ 6.6 Hz, 3H, C4-CH3), 2.16 (s, 3H, C6-CH3), 3.61 (s, 3H,
OCH3), 4.16 (br, 4H, D2O exchangeable, 2 ꢁ NH2), 4.93 (t, J ¼ 6.3 Hz,
1H, C4-H), 9.48 (br, 1H, D2O exchangeable, NH). 13C NMR (75 MHz,
CDCl3, 25 ꢀC):
d
1.07 (t, J ¼ 6.9 Hz, 3H, ester-CH3), 1.22 (t,
DMSO-d6, 25 ꢀC):
d
17.3, 21.1, 48.6, 51.0, 103.1, 147.5, 153.1 and 165.5.
J ¼ 7.2 Hz, 3H, CH3), 1.32 (t, J ¼ 7.2 Hz, 3H, CH3), 2.38 (s, 3H, C6-
CH3), 3.52e3.67 (m, 1H, CHH), 3.72e3.82 (m, 1H, CHH), 4.07e4.26
(m, 4H, 2 ꢁ CH2), 6.08 (d, J ¼ 6.9 Hz, 1H, C4-H), 7.26e7.31 (m, 3H,
ArH), 7.40e7.46 (m, 2H, ArH), 7.69 (br, 1H, D2O exchangeable, NH).
31P NMR (121 MHz, DMSO-d6, 25 ꢀC):
d
11.93. Anal. Calcd. for
C8H15N4O4P: C, 36.64; H, 5.72; N, 21.37; Found: C, 36.52; H, 5.92; N,
21.13. MS: m/z 263 (Mþþ1).
13C NMR (75 MHz, CDCl3, 25 ꢀC):
d
14.1, 15.9, 17.9, 58.2, 60.3, 63.7,
64.4, 104.1, 127.2, 128.1, 128.5, 141.9, 145.8, 153.0 and 165.0. 31P
NMR (162 MHz, CDCl3, 25 ꢀC):
5.4. General procedure for the synthesis of N3-substituted DHPM
derivatives 9
d
ꢂ0.53. Anal. Calcd. for
C18H25N2O6P: C, 54.54; H, 6.31; N, 7.07.; Found: C, 54.20; H, 6.52;
N, 6.80. MS: m/z 419 (Mþþ23).
To a stirred solution of appropriate 7 (1 equiv.) in dry dioxane
(10 ml) appropriate amine (1.5 equiv.) was added and resulting
solution was stirred at room temperature for 2e4 h. After
completion of reaction (TLC), dioxane was removed under reduced
pressure and residue was dissolved in ethylacetate (20e30 ml)
and washed with water (2 ꢁ 30 ml). Organic phase was dried
over anhydrous sodium sulphate and compounds 9a-b were
obtained through column chromatography using hexane and
ethylacetate as eluents. The characteristic data of the compounds
is given below.
5.5. General procedure for the synthesis of N3-substituted DHPM
derivatives bearing phosphorous containing heterocycles 10
To a stirred solution of appropriate 7 (1 equiv.) in dry dioxane
(10 ml) an appropriate diamine or amino alcohols (1.5 equiv.)
was added and the resulting solution was stirred at room
temperature for 2e3 h. After completion of reaction (TLC)
dioxane was removed under reduced pressure and residue was
dissolved in ethylacetate (20e30 ml) and washed with water

402
K. Singh et al. / European Journal of Medicinal Chemistry 54 (2012) 397e402
(2 ꢁ 30 ml). Organic phase was dried over anhydrous sodium
sulphate and compound 10 was obtained through crystallization
with methanol. The characteristic data of the compounds is given
below.
(100 MHz, DMSO-d6, 25 ꢀC):
d 14.1, 15.7, 25.3, 30.5, 41.1, 54.4, 59.9,
69.4, 106.2, 125.8, 127.3, 128.3, 141.2, 150.2, 153.8 and 165.2. Anal.
Calcd. for C18H24N3O5P: C, 54.96; H, 6.10; N, 10.68; Found: C, 54.66;
H, 6.21; N, 10.40. MS: m/z 416 (Mþþ23).
5.5.1. 2-[5-ethoxycarbonyl-6-methyl-4-phenyl-3,4-
dihydropyrimidin-2(1H)-one]-3-yl-1,3,4,5,6,7-hexahydro [1e3]
diazaphosphepine-2-oxide (10a)
Acknowledgements
We thank CSIR [01/(2364)/10/EMR-II], UGC [F. No. 37-188/
2009(SR)] and SAP (DRS-1) UGC, New Delhi for providing financial
assistance.
White crystalline solid. Rf: 0.3 (methanol:ethyl acetate/10:90).
Yield: 72%. M.p. 218e220 ꢀC (methanol). IR (KBr): nmax 1029, 1228,
1390,1641,1690, 3369 cmꢂ1 1H NMR (300 MHz, CDCl3, 25 ꢀC):
d 1.23
(t, J ¼ 7.2 Hz, 3H, ester-CH3), 1.60e1.62 (m, 4H, 2 ꢁ CH2), 2.39 (s, 3H,
C6-CH3), 3.03e3.12 (m, 3H, CH2 and D2O exchangeable, NH),
3.24e3.32 (m, 2H, CH2), 3.71e3.73 (m, 1H, D2O exchangeable, NH),
4.09e4.19 (m, 2H, ester-CH2), 6.25 (d, J ¼ 7.5 Hz, 1H, C4-H),
7.22e7.31 (m, 3H, ArH), 7.40e7.43 (m, 2H, ArH), 7.87 (br, 1H, D2O
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d
14.2, 16.0,
30.1, 34.6, 39.0, 111.0, 126.1, 126.9, 128.0, 144.0, 148.3, 158.0 and
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5.5.2. 5-Ethoxycarbonyl-4,6-dimethyl-3-(1,3,2-
diazaphosphorinane-2-oxide)-3,4-dihydropyrimidin-2(1H)-one
(10b)
White crystalline solid. Rf: 0.5 (methanol:ethyl acetate/20:80).
Yield: 65%. M.p. 233e235 ꢀC (methanol). IR (KBr): nmax 1010, 1242,
1313, 1635, 1699, 3353 cmꢂ1 1H NMR (400 MHz, DMSO-d6, 25 ꢀC):
d
0.87 (d, J ¼ 6.5 Hz, 3H, C4-CH3), 0.94 (t, J ¼ 7.0 Hz, 3H, ester-CH3),
1.65e1.72 (m, 2H, CH2), 1.94 (s, 3H, C6-CH3), 2.64 (t, J ¼ 7.5 Hz, 4H,
2 ꢁ CH2), 3.81e3.88 (m, 2H, ester-CH2), 4.28 (br, 1H, D2O
exchangeable, NH), 4.56 (br, 1H, D2O exchangeable, NH), 4.61 (q,
J ¼ 6.3 Hz, 1H, C4-H), 9.24 (br, 1H, D2O exchangeable, N1-H). 13C
NMR (100 MHz, DMSO-d6, 25 ꢀC):
d 14.3, 17.2, 21.0, 25.0, 41.6, 49.0,
59.3, 103.2, 147.2, 153.5 and 165.0. 31P NMR (162 MHz, DMSO-d6,
25 ꢀC):
d 4.81. Anal. Calcd. for C12H21N4O4P: C, 45.57; H, 6.64; N,
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a
site selective functionalization of Biginelli
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4-phenyl-3,4-dihydropyrimidin-2(1H)-one (10c)
White crystalline solid. Rf: 0.2 (methanol:ethyl acetate/10:90).
Yield: 65%. M.p. 208e210 ꢀC (methanol). IR (KBr): nmax 1019, 1247,
1365, 1635, 1705, 3333 cmꢂ1 1H NMR (400 MHz, DMSO-d6, 25 ꢀC):
d
1.16 (t, J ¼ 7.0 Hz, 3H, ester-CH3), 1.72e1.84 (m, 2H, CH2), 2.28 (s,
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3H, C6-CH3), 3.04e3.15 (m, 1H, CHH), 3.29e3.34 (m, 1H, CHH),
4.05e4.14 (m, 2H, ester-CH2), 4.16e4.28 (m, 1H, CHH), 4.54e4.56
(m, 1H, CHH), 5.45e5.48 (m, 1H, D2O exchangeable, NH), 6.07 (d,
J ¼ 7.5 Hz, 1H, C4-H), 7.20e7.32 (m, 5H, ArH). 13C NMR (100 MHz,
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DMSO-d6, 25 ꢀC):
d 14.2, 17.4, 25.4, 41.2, 55.9, 59.8, 69.4, 102.7, 126.1,
127.3, 128.4, 142.1, 148.1, 153.3 and 165.2. 31P NMR (162 MHz,
DMSO-d6, 25 ꢀC):
d
ꢂ0.94. Anal. Calcd. for C17H22N3O5P: C, 53.83; H,
5.80; N, 11.08. Found: C, 53.52; H, 5.63; N, 10.82. MS: m/z 402
(Mþþ23).
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5.5.4. 5-Ethoxycarbonyl-1,6-dimethyl-3-(1,3,2-oxazaphosphino-2-
yl)-4-phenyl-3,4-dihydropyrimidin-2(1H)-one (10d)
White crystalline solid. Rf: 0.4 (methanol:ethyl acetate/20:80).
Yield: 65%. M.p. 213e215 ꢀC (methanol). IR (KBr): nmax 1015, 1225,
1345, 1665, 1710, 3343 cmꢂ1 1H NMR (400 MHz, DMSO-d6, 25 ꢀC):
d
1.18 (t, J ¼ 7.0 Hz, 3H, ester-CH3), 1.74e1.87 (m, 2H, CH2), 2.50 (s,
3H, C6-CH3), 3.07e3.13 (m, 4H, N1-CH3 and CHH), 3.28e3.34 (m,
1H, CHH), 4.13e4.18 (m, 2H, ester-CH2), 4.21e4.29 (m, 1H, CHH),
4.58e4.64 (m, 1H, CHH), 5.45e5.48 (m, 1H, D2O exchangeable, NH),
6.13 (d, J ¼ 8.0 Hz, 1H, C4-H), 7.22e7.33 (m, 5H, ArH). 13C NMR
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