5-phosphonato-3,4-dihydropyrimidin-2(1H)-ones: Zinc triflate-catalyzed one-pot multi-component synthesis, X-ray crystal structure and anti-inflammatory activity

Article abstract of DOI:10.1016/j.molstruc.2017.04.054

Herein we report a simple and efficient one-pot three-component synthesis of 5-phosphonato-3,4-dihydropyrimidin-2(1H)-ones, through the zinc triflate-catalyzed Biginelli-type reaction of β-ketophosphonates, aldehydes and urea. The compounds obtained were characterized by various spectroscopic tools including IR, NMR (¹H, ³¹P, ¹³C) spectroscopy, mass spectrometry and single crystal X-ray diffraction. All the synthesized compounds were screened, for the first time, for anti-inflammatory activity by carrageenan-induced hind paw edema method, using female Wister rats and they showed significant anti-inflammatory activity in some cases higher than the standard indomethacin.

Full text of DOI:10.1016/j.molstruc.2017.04.054

Accepted Manuscript
5-phosphonato-3,4-dihydropyrimidin-2(1H)-ones: Zinc triflate-catalyzed one-pot multi-
component synthesis, X-ray crystal structure and anti-inflammatory activity
Idris Essid, Karima Lahbib, Werner Kaminsky, Cherif Ben Nasr, Soufiane Touil
PII:
S0022-2860(17)30496-9
10.1016/j.molstruc.2017.04.054
MOLSTR 23677
DOI:
Reference:
To appear in: Journal of Molecular Structure
Received Date: 31 January 2017
Revised Date: 13 April 2017
Accepted Date: 13 April 2017
Please cite this article as: I. Essid, K. Lahbib, W. Kaminsky, C. Ben Nasr, S. Touil, 5-phosphonato-3,4-
dihydropyrimidin-2(1H)-ones: Zinc triflate-catalyzed one-pot multi-component synthesis, X-ray
crystal structure and anti-inflammatory activity, Journal of Molecular Structure (2017), doi: 10.1016/
j.molstruc.2017.04.054.
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ACCEPTED MANUSCRIPT
R2
O
O
Me
(R1O)2P
P(OR1)2
NH
O
N
O
H
Zn(OTf)2
up to 86% yield
toluene, reflux, 3h
R2
H
H2N
NH2
O
O
Good anti-inflammatory
activity

ACCEPTED MANUSCRIPT
5-Phosphonato-3,4-dihydropyrimidin-2(1H)-ones: Zinc triflate-catalyzed one-
pot multi-component synthesis, X-ray crystal structure and anti-inflammatory
activity
Idris Essid*a, Karima Lahbiba, Werner Kaminskyb, Cherif Ben Nasrc, Soufiane Touila
a Laboratory of Heteroatom Organic Chemistry, University of Carthage, Faculty of Sciences of Bizerte, 7021 - Jarzouna, Tunisia.
b Department of Chemistry, BOX 351700 University of Washington Seattle, WA 98195, USA.
c Laboratoire de Chimie des Matériaux, Université de Carthage, Faculté des Sciences de Bizerte, 7021 - Jarzouna, Tunisie.
HIGHLIGHTS
• One-pot three-component synthesis of 5-phosphonato-3,4-dihydropyrimidin-2(1H)-ones.
• Synthesized compound were characterized by single crystal X-ray diffraction.
• The synthesized compounds were screened for their anti-inflammatory activity.
ARTICLE INFO
Article history:
Received
Accepted
Available online
ABSTRACT
Herein we report a simple and efficient one-pot three-
component synthesis of 5-phosphonato-3,4-dihydropyrimidin-
2(1H)-ones, through the zinc triflate-catalyzed Biginelli-type
reaction of β-ketophosphonates, aldehydes and urea. The
compounds obtained were characterized by various
spectroscopic tools including IR, NMR (1H, 31P, 13C)
spectroscopy, mass spectrometry and single crystal X-ray
diffraction. All the synthesized compounds were screened, for
the first time, for anti-inflammatory activity by carrageenan-
induced hind paw edema method, using female Wister rats and
they showed significant anti-inflammatory activity in some
cases higher than the standard indomethacin.
Keywords:
Multi-component reactions
Dihydropyrimidinones
Biginelli reaction
β-Ketophosphonates
X-ray crystal structure
Anti-inflammatory activity
1. Introduction
3,4-Dihydropyrimidin-2(1H)-ones and their derivatives are an important class of
compounds in medicinal chemistry with a wide range of biological properties, including
antitumoral [1], antimalarial [2], anti-inflammatory [3] and anti-HIV [4] activities; some are also
medicinally important as calcium channel modulators and α1a-adrenergic receptor antagonists [5].
The introduction of a phosphonate functionality on 3,4-dihydropyrimidinones, may be very
interesting for the enhancement of the biological properties of these molecules, in a similar way to
that reported for other pharmaceuticals [6,7]. It is also known that phosphonate and phosphonic
acid moieties regulate important biological functions by mimicking carboxylic acid groups [8].
* Corresponding author. E-mail address: idris_essid@hotmail.fr

ACCEPTED MANUSCRIPT
With this in mind, and in the continuation of our interest to develop efficient protocols for
the synthesis of heterocyclic phosphonates with possible biological properties [9-11], we report
herein a simple and efficient one-pot multi-component synthesis of 5-phosphonato-3,4-
dihydropyrimidin-2-ones, through the zinc triflate-catalyzed Biginelli-type reaction [12-17] of β-
ketophosphonates, aldehydes and urea.
To the best of our knowledge, there are only two reports on the use of β-ketophosphonates
as substrates in the Biginelli reaction, which employed ytterbium triflate [18] or p-toluenesulfonic
acid [19] as catalyst. However, in spite of their potential utility, these procedures suffer from one
or the other drawbacks such as the unsatisfactory yields, tedious work-up or long reaction time.
By comparison with these existing strategies, our method offers significant advantages
such as efficiency, short reaction time, easy work-up and high yields. In addition, the zinc triflate
catalyst used is known for its low toxicity, low cost, and environmentally benignity. This is very
beneficial for safely obtaining phosphonodihydropyrimidinone derivatives of pharmacological
interest.
All the synthesized compounds were screened for anti-inflammatory activity by
carrageenan-induced hind paw edema method [20], using female Wister rats and they showed
significant anti-inflammatory activity in some cases higher than the standard indomethacin.
2. Experimental
2.1. Methods and Materials
1H, 31P and 13C NMR spectra were recorded with CDCl3 or DMSO-d6 as the solvent, on a
Bruker AC-300 spectrometer operating at 300.1 MHz for 1H, 121.5 MHz for 31P and 75.5 MHz for
1
13
13C. The chemical shifts are reported in ppm relative to TMS (internal reference) for H and C
31
NMR and relative to 85% H3PO4 (external reference) for P NMR. The coupling constants are
1
reported in Hz. For the H NMR, the multiplicities of signals are indicated by the following
abbreviations: s: singlet; d: doublet; t: triplet; q: quartet; m: multiplet and br s: broad singlet. Mass
spectra were determined on an Agilent 5975B spectrometer, under electronic impact (EI)
conditions. FT-IR spectra were recorded on a Nicolet IR200 spectrometer, the number of scans
was 32, the scanning range was 4000–400 cm-1 and the resolution 4 cm-1. The progress of the
reactions was monitored by TLC. Purification of products was performed by column
chromatography using silica gel (Fluka). The starting β-ketophosphonates 1 were synthesized by
literature procedures [21].
2.2. General procedure for the synthesis of 5-phosphonato-3,4-dihydropyrimidin-2(1H)-ones (3)

ACCEPTED MANUSCRIPT
A mixture containing the β-ketophosphonate (2 mmol), aldehyde (2 mmol), urea (3
mmol) and Zn(OTf)2 (15 mol%) in toluene (8 mL), was refluxed for 3 h. After completion of the
reaction, as indicated by TLC, the solvent was removed under reduced pressure, then CHCl3 (30
mL) was added. The organic phase was washed with H2O (2 × 10 mL), dried over Na2SO4 and
concentrated under vacuum. The crude obtained was purified by chromatography on a silica gel
column, using EtOAc as eluent.
5-Diethoxyphosphoryl-6-methyl-4-phenyl-3,4-dihydropyrimidin-2(1H)-one (3a).
White Solid; mp 169-170 °C. IR (neat): νP=O = 1235 cm-1; νC=O = 1703 cm-1; νNH = 3116-3224 cm-
1. 31P NMR (121.5 MHz, CDCl3): δ = 18.8. 1H NMR (300 MHz, CDCl3): δ = 0.97 (t, 3H, 3JHH
=
6.0 Hz, CH3-CH2-O); 1.11 (t, 3H, 3JHH = 6.0 Hz, CH3-CH2-O); 2.12 (d, 3H, 4JPH = 3.0 Hz, CH3);
3.49 – 3.83 (m, 4H, 2 CH3-CH2-O); 5.05 (dd, 1H, 3JPH = 9.0 Hz, 3JHH = 3.0 Hz, CH-NH); 6.14 (br
s, 1H, N-H) 7.18-7.30 (m, 5H, arom-H); 8.73 (d, 1H, 3JHH = 3.0 Hz, N-H). 13C NMR (75.5 MHz,
CDCl3): δ 16.0 (d, 3JCP = 7.5 Hz, CH3-CH2-O); 16.3 (d, 3JCP = 6.0 Hz, CH3-CH2-O); 18.2 (d, 3JCP
2
2
= 3.7 Hz CH3); 56.6 (d, JCP = 15.7 Hz, CH-NH); 61.3 (d, JCP = 5.1 Hz, CH3-CH2-O); 61.4 (d,
2JCP = 5.1 Hz, CH3-CH2-O); 96.0 (d, 1JCP = 206.8 Hz, P-C=C); 147.0 (d, 2JCP = 20.6 Hz, P-C=C);
154.23 (s, C=O); phenyl carbons: δ 126.9, 128.2, 128.7, 143.8; EI-HRMS: calculated for
C15H21N2O4P: 324.1239 (M+); Found: 324.1238.
5-Dimethoxyphosphoryl-6-methyl-4-phenyl-3,4-dihydropyrimidin-2(1H)-one (3b).
White Solid; mp 198-200 °C. IR (neat): νP=O 1236 cm-1; νC=O 1700 cm-1; νNH = 3119-3258 cm-1.
1
31P NMR (121.5 MHz, DMSO-d6): δ = 22.9. H NMR (300 MHz, DMSO-d6): δ = 2.15 (d, 3H,
4JHP = 2.7 Hz, CH3); 3.34 (d, 3H, 3JPH = 11.3 Hz, CH3-O); 3.46 (d, 3JPH = 11.5 Hz, CH3-O); 4.89
(dd, 1H, 3JPH = 8.6 Hz, 3JHH = 3.2 Hz, CH-NH); 7.32-7.40 (m, 5H, arom-H); 7.77 (br s, 1H, N-H);
3
13
3
9.28 (d, 1H, JHH = 3.1 Hz, N-H). C NMR (75.5 MHz, DMSO-d6): δ = 17.3 (d, JCP = 3.5 Hz,
2
2
2
CH3); 51.3 (d, JCP = 4.9 Hz, CH3-O); 51.4 (d, JCP = 5.2 Hz, CH3-O); 54.9 (d, JCP = 15.2 Hz,
CH-NH); 92.5 (d, 1 JCP = 205.8 Hz, P-C=C); 148.8 (d, 2 JCP = 20.7 Hz, P-C=C); 152.5 (s, C=O);
phenyl carbons: 126.5, 127.4, 128.4, 144.5; EI-HRMS: calculated for C13H17N2O4P: 296.0926
(M+); Found: 296.0922.
5-Diethoxyphosphoryl-6-methyl-4-(4-nitrophenyl)-3,4-dihydropyrimidin-2(1H)-one (3c).
Yellow Solid; mp 219-220 °C. IR (neat): νP=O = 1225 cm-1; νC=O = 1700 cm-1; νNH = 3120-3232
cm-1. 31P NMR (121.5 MHz, DMSO-d6): δ = 19.2. 1H NMR (300 MHz, DMSO-d6): δ = 1.00 (t,
3H, 3JHH = 7.0 Hz, CH3-CH2-O); 1.13 (t, 3H, 3JHH = 7.0 Hz, CH3-CH2-O); 2.12 (d, 3H, 4JPH = 2.2
3
3
Hz, CH3); 3.59-3.84 (m, 4H, 2 CH3-CH2-O); 5.01 (dd, 1H, JPH = 8.5 Hz, JHH = 3.4 Hz, CH-
4
NH); 7.53-8.25 (m, 4H, , arom-H); 7.81 (d, 1H, JPH = 1.7 N-H); 9.31 (d, 1H, 3JHH = 3.0 Hz, N-
13
3
3
H). C NMR (75.5 MHz, DMSO-d6): δ = 15.7 (d, JCP = 6.6 Hz, CH3-CH2-O); 16.0 (d, JCP
=

ACCEPTED MANUSCRIPT
2
6.2 Hz, CH3-CH2-O); 17.4 (d, 3JCP = 3.4, CH3); 54.6 (d, JCP =15.1 Hz, CH-NH); 60.6 (d, 2JCP
=
2
1
5.1 Hz, CH3- CH2-O); 60.7 (d, JCP = 5.2 Hz, CH3-CH2-O); 92.7 (d, JCP = 206.4 Hz, P-C=C);
2
149.1 (d, JCP = 20.6 Hz, P-C=C); 152.2 (s, C=O); phenyl carbons: 123.7, 127.8, 146.7, 151.6;
EI-HRMS: calculated for C15H20N3O6P: 369.1090 (M+); found: 369.1092.
5-Dimethoxyphosphoryl-6-méthyl-4-(4-nitrophenyl)-3,4-dihydropyrimidin-2(1H)-one (3d).
Yellow Solid; mp 235-237 °C. IR (neat): νP=O = 1228 cm-1; νC=O = 1701 cm-1 ; νNH = 3142-3232
31
1
cm-1. P NMR (121.5 MHz, DMSO-d6): δ = 22.3. H NMR (300 MHz, DMSO-d6): δ 2.16 (d,
3H, 4 JPH = 2.2 Hz, CH3); 3.41 (d, 3H, 3JPH = 11.2 Hz, CH3-O); 3.50 (d, 3H, 3JPH = 11.4 Hz, CH3-
3
3
O); 5.05 (dd, 1H, JPH = 8.5 Hz, JHH = 3.4 Hz, CH-NH); 7.59-8.30 (m, 4H, arom-H); 7.90 (d,
1H, 4JPH = 1.7 Hz, N-H); 9.42 (d, 1H, 3JHH = 3.0 Hz, N-H). 13C NMR (75.5 MHz, DMSO-d6): δ =
17.3 (d, 3JCP = 3.5 Hz, CH3); 51.5 (d, 2JCP = 5.1 Hz, CH3-O); 51.6 (d, 2JCP = 5.3 Hz, CH3-O); 54.5
(d, 2JCP = 15.3 Hz, CH-NH); 91.5 (d, 1JCP = 206.9 Hz, P-C=C);149.7 (d, 2JCP = 20.5 Hz, P-C=C);
152.1 (s, C=O); phenyl carbons: 123.8, 127.8, 146.7, 151.5; EI-HRMS: calculated for
C13H16N3O6P: 341.0777 (M+); found: 341.0776.
5-Diethoxyphosphoryl-6-méthyl-4-(4-chlorophenyl)-3,4-dihydropyrimidin-2(1H)-one (3e).
White Solid; mp 120-122 °C. IR (neat): νP=O = 1227 cm-1; νC=O = 1700 cm-1; νNH = 3127-3243 cm-
1. 31P NMR (121.5 MHz, DMSO-d6): δ = 19.1. 1H NMR (300 MHz, DMSO-d6): δ = 1.03 (t, 3H,
3JHH = 7.0 Hz, CH3-CH2-O); 1.13 (t, 3H, 3JHH = 7.0 Hz, CH3-CH2-O); 2.12 (d, 3H, 4 JPH = 2.1 Hz,
3
3
CH3); 3.57-3.86 (m, 4H, 2 CH3-CH2-O); 5.02 (dd, 1H, JPH = 8.1 Hz, JHH = 2.8 Hz, CH-NH);
7.07 (br s, 1H, N-H), 7.17-7.27 (m, 4H, arom-H); 9.00 (br s, 1H, N-H). 13C NMR (75.5 MHz,
3
DMSO-d6): δ = 15.0 (d, 3JCP = 7.0 Hz, CH3-CH2-O); 15.2 (d, JCP = 6.7 Hz, CH3-CH2-O); 16.9
(d, 3JCP = 3.6 Hz, CH3); 54.5 (d, 2JCP = 15.6 Hz, CH-NH); 60.2 (d, 2JCP = 5.2 Hz, 2 CH3-CH2-O);
1
2
93.7 (d, JCP = 207.4 Hz, P-C=C); 146.9 (d, JCP = 20.6 Hz, P-C=C); 152.8 (s, C=O); phenyl
carbons: 127.4, 127.5, 132.2, 141.8. EI-HRMS calculated for C15H20ClN2O4P: 358.0849 (M+);
found: 358.0811.
5-Dimethoxyphosphoryl-6-méthyl-4-(4-chlorophenyl)-3,4-dihydropyrimidin-2(1H)-one (3f).
White Solid; mp 226-227 °C. IR (neat): νP=O = 1227 cm-1; νC=O = 1702 cm-1; νNH = 3128-3251 cm-
1
1. 31P NMR (121.5 MHz, DMSO-d6): δ = 22.7. H NMR (300 MHz, DMSO-d6): δ = 2.14 (d, 3H,
4JPH = 2.0 Hz, CH3); 3.39 (d, 3H, 3JPH = 11.3 Hz, CH3-O); 3.48 (d, 3H, 3JPH = 11.4 Hz, CH3-O);
4.91 (dd, 1H, 3JPH = 8.6 Hz, 3JHH = 3.4 Hz, CH-NH); 7.33-7.48 (m, arom-H); 7.80 (d, 1H, 4JPH
=
3
13
1.6 Hz N-H) ; 9.33 (d, 1H, JHH = 3.1 Hz, N-H). C NMR (75.5 MHz, DMSO-d6): δ = 17.3 (d,
2
3JCP = 3.5 Hz, CH3); 51.4 (d, 2JCP = 5.0 Hz, CH3-O); 51.5 (d, 2JCP = 5.3 Hz, CH3-O); 54.3 (d, JCP
1
2
= 15.3 Hz, CH-NH); 92.1(d, JCP = 206.3 Hz, P-C=C); 149.1 (d, JCP = 20.7 Hz, P-C=C); 152.3
(s, C=O); phenyl carbons: 128.4, 131.9, 143.4.
5-Diethoxyphosphoryl-6-methyl-4-(4-methoxyphenyl)-3,4-dihydropyrimidin-2(1H)-one
(3g).

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White Solid; mp 138-140 °C. IR (neat): νP=O = 1229 cm-1; νC=O = 1703 cm-1; νNH = 3116-3242 cm-
1. 31P NMR (121.5 MHz, DMSO-d6): δ = 19.9. 1H NMR (300 MHz, DMSO-d6): δ = 1.04 (t, 3H,
3JHH = 7.0 Hz, CH3-CH2-O); 1.19 (t, 3H, 3JHH = 7.0 Hz, CH3-CH2-O); 2.16 (d, 3H, 4JPH = 2.2 Hz,
3
3
CH3); 3.42-3.87 (m, 4H, CH3-CH2-O); 3.78 (s, 3H, OCH3); 4.85 (dd, 1H, JPH = 8.7 Hz, JHH
=
3.2 Hz, CH-NH); 6.93-7.26 (m, 4H, arom-H); 7.64 (d, 1H, 4JPH = 1.6 Hz, N-H); 9.16 (d, 1H, 3JHH
= 3.1 Hz, N-H). 13C NMR (75.5 MHz, DMSO-d6): δ = 15.8 (d, 3JCP = 6.8 Hz, CH3-CH2-O); 16.0
3
3
2
(d, JCP = 6.3 Hz, CH3-CH2-O); 17.3 (d, JCP = 3.5 Hz, CH3); 54.4 (d, JCP = 15.0 Hz, CH-NH);
55.1 (s, CH3-O); 60.4 (d, 2JCP = 5.5 Hz, CH3-CH2-O); 60.5 (d, JCP = 5.6 Hz, CH3-CH2-O); 94.0
2
(d, 1JCP = 205.1 Hz, P-C=C); 147.9 (d, 2JCP = 20.9 Hz, P-C=C); 152.5 (s, C=O); phenyl carbons:
113.6, 127.7, 136.7, 158.5; EI-HRMS: calculated for C16H23N3O5P: 354.1344 (M+); found:
354.1343.
5-Diethoxyphosphoryl-6-methyl-4-(4-methylphenyl)-3,4-dihydropyrimidin-2(1H)-one (3h).
Yellow Solid; mp 158-159 °C. IR (neat): νP=O = 1230 cm-1; νC=O (amide) = 1701 cm-1; νNH = 3120-
1
3252 cm-1. 31P NMR (121.5 MHz, DMSO-d6): δ = 19.8. H NMR (300 MHz, DMSO-d6): δ =
3
3
0.98 (t, 3H, JHH = 7.0 Hz, CH3-CH2-O); 1.13 (t, 3H, JHH = 7.1 Hz, CH3-CH2-O); 2.11 (d, 3H,
4JPH = 2.3 Hz, CH3); 2.27 (s, CH3); 3.38-3.80 (m, 4H, 2 CH3-CH2-O); 4.82 (dd, 1H, JPH = 8.8
3
3
4
Hz, JHH = 3.3 Hz, CH-NH); 7.11-7.19 (m, 4H, arom-H); 7.61 (d, 1H, JPH = 1.7 Hz, N-H); 9.12
(d, 1H, JHH = 3.0 Hz, N-H). 13C NMR (75.5 MHz, DMSO-d6): δ = 15.7 (d, 3JCP = 6.7 Hz, CH3-
3
CH2-O); 16.0 (d, 3JCP = 6.3 Hz, CH3-CH2-O); 17.3 (d, 3JCP = 3.5 Hz, CH3); 30.6 (s, CH3); 54.7 (d,
2JCP = 15.1 Hz, CH-NH); 60.4 (d, 2JCP = 5.0 Hz, CH3-CH2-O); 60.5 (d, 2JCP = 5.2 Hz, CH3-CH2-
O); 93.9 (d, 1JCP = 205.4 Hz, P-C=C); 148.1 (d, 2JCP = 20.9 Hz, P-C=C); 152.6 (s, C=O); phenyl
carbons: 126.4, 128.7, 136.5, 141.5.
2.3 X-ray diffraction data of compound 3a
A single crystal was carefully selected under a polarizing microscope in order to perform
its structural analysis by X-ray diffraction. The data were integrated and scaled using hkl-
SCALEPACK [22]. Solution by direct methods (SHELXS, SIR97 [23]) produced a complete
heavy atom phasing model consistent with the proposed structure. The structure was completed
by difference Fourier synthesis with SHELXL97 [24-27]. Scattering factors are from Waasmair
and Kirfel [28]. Hydrogen atoms were placed in geometrically idealized positions and
constrained to ride on their parent atoms with C---H distances in the range 0.95-1.00 Angstrom.
Isotropic thermal parameters Ueq were fixed such that they were 1.2Ueq of their parent atom Ueq
for CH's and 1.5Ueq of their parent atom Ueq in case of methyl groups. All non-hydrogen atoms
were refined anisotropically by full-matrix least-squares. The drawings were made with Diamond

ACCEPTED MANUSCRIPT
[29] and Mercury [30]. Crystal data and experimental parameters used for the intensity data
collection are summarized in Table 1.
Table 1. Crystal data and structure refinement of C15H21N2O4P, 0.065(H2O).
Empirical formula
Formula weight
Temperature
Crystal size
3
3
C15 H21.13 N2 O4.06 P
325.43
0.30 x 0.27 x 0.21 mm
2.06 to 28.30°.
Theta range for data
collection
Crystal size
130(2) K
0.30 x 0.27 x 0.21 mm
2.06 to 28.30°.
Theta range for data
collection
Wavelength
0.71073 Å
Index ranges
-20<=h<=20, -14<=k<=15, -
25<=l<=25
Crystal system
Monoclinic
Space group
Reflections collected
68023
P 21/n
Unit cell dimensions
Independent reflections
8056 [R(int) = 0.0594]
99.8 %
a = 15.3175(5) Å
Completeness to theta =
25.00°
b = 11.7656(5) Å
Max. and min. transmission 0.9616 and 0.9458
Refinement method
c = 19.4907(6) Å
2
β= 111.483(3)°
Full-matrix least-squares on F
Data / restraints / parameters 8056 / 6 / 426
3
Volume
3268.6(2) Å
2
1.038
Z
8
Goodness-of-fit on F
3
Final R indices [I>2sigma(I)] R1 = 0.0526, wR2 = 0.1298
Density (calculated)
1.323 Mg/m
Absorption
coefficient
R indices (all data)
R1 = 0.1001, wR2 = 0.1457
-1
0.188 mm
F(000)
Largest diff. peak and hole
-3
1381
0.397 and -0.441 e.Å
2.4. Anti-inflammatory activity
Anti-inflammatory activity of the synthesized compounds 3a-h and indomethacin used as
standard, was determined by carrageenan-induced hind paw edema method [20], using female
Wister rats. Test compounds, dissolved in ethanol 10%, were given to rats intraperitoneally at a
dose of 10 mg/kg of body weight of rats and at a volume of 100 µL/100 g of body weight of rats.
The same volume of ethanol 10% was given to the control group. One hour after treatment, the

ACCEPTED MANUSCRIPT
right hind paw volume of all rats was measured with a plethysmometer, then, carrageenan 0.1 mL
(1%, w/v) solution in ultrapure water was subcutaneously injected into the planter surface of the
right hind paw of all rats. Carrageenan-induced paw edema was measured at 1 h, 2 h, 3 h, 4 h and
6 h following Carrageenan-treatment. All experiments were done in triplicate.
Anti-inflammatory activities of compounds 3a-h and indomethacin were determined by
comparing their results with the ones obtained in the control group. The anti-inflammatory effect
of the test compounds was calculated by the following equation:
Anti-inflammatory activity (I %) = (1 − D/C) × 100, where D represents the percentage
difference in paw volume after the test compound administration to the rats, and C represents the
percentage difference of volume in the control group.
3. Results and discussion
3.1 Chemistry
In order to establish the optimum reaction conditions for the formation of the target
compounds, we used β-ketophosphonate 1a, benzaldehyde and urea as model substrates. The
reaction was studied with various mole ratios of zinc triflate in different conditions. As shown in
Table 1, the best results were obtained with 15 mol% of the catalyst, in refluxing toluene, for 3 h
(Table 2, entry 8).
Table 2. Optimization of the reaction conditions
Entry
Zn(OTf)2 ratio (mol%)
Solvent
toluene
toluene
MeCN
dioxane
THF
Time (h)
Yield (%)a
1
2
3
4
5
6
7
8
0
5
24
3
0
70
66
26
0
5
3
5
3
5
3
5
DCE
3
41
76
82
10
15
toluene
toluene
3
3

ACCEPTED MANUSCRIPT
9
20
toluene
3
82
a Isolated yield.
With these optimized reaction conditions in hand, we next studied the scope of this
methodology. A variety of structurally diverse aldehydes and β-ketophosphonates were
investigated and a series of 5-phosphonato-3,4-dihydropyrimidin-2(1H)-ones of type 3 were
afforded in good yields (Table 3). It is noteworthy to mention that the present method was found
to be tolerant toward various aromatic aldehydes bearing either electron-withdrawing or electron-
donating substituents. In general, aromatic aldehydes with electron-withdrawing groups, which
are more reactive, afforded higher yields than those with electron-donating ones.
Table 3. Substrate scope studies
R2
R2
O
(R1O)2P
O
P(OR1)2
NH
Me
Zn(OTf)2 (15 mol%)
toluene, reflux, 3 h
H
H2N
NH2
Me
N
H
O
O
O
O
1
2
3
a Isolated yield.

ACCEPTED MANUSCRIPT
Based on our experimental results and the known literature precedents [12-16, 31,32], a
mechanistic rationalization for this reaction is provided in Scheme 1. This proposed mechanism
involves the nucleophilic addition of urea to the aldehyde, catalysed by the Lewis acid Zn(OTf)2,
giving rise to an imine intermediate. The interception of this last one by the β-ketophosphonate
through its enol tautomer leads, after intramolecular cyclization and dehydration, to the
dihydropyrimidinone 3.
Scheme 1. Proposed mechanism for the formation of compounds 3
3.2. Molecular structure
The structures of compounds 3 were established using various spectroscopic techniques
including IR, NMR (1H, 31P, 13C) spectroscopy, mass spectrometry as well as single crystal X-ray
diffraction. The IR spectra revealed the presence of absorption bands towards 1230, 1700 and
3300 cm-1 corresponding, respectively to the P=O, C=O and N-H vibrators. The 1H NMR spectra
of compounds 3 showed, in particular, a doublet of doublets around 5 ppm relative to the CH
proton at the β position with respect to the phosphorus atom. Such a multiplicity is characteristic
of the coupling with phosphorus (3JPH
NH proton resonates then as a doublet (3JHH
̴
9 Hz) and the vicinal NH proton (3JHH
3 Hz) at 8-9 ppm, while the other NH proton gives
̴ 3 Hz). This last
̴

ACCEPTED MANUSCRIPT
4
a broad singlet (in some cases a doublet with a small JPH coupling constant of about 2 Hz)
towards 6-7 ppm. The alkoxy groups on the phosphorus atom showed a signal doubling
indicating that they are not magnetically equivalent, probably due to the neighbouring chiral
carbon. The 31P NMR shift recorded for compounds 3 was δ = 18-22 ppm which is consistent
with the dialkyl phosphonate chemical shift values. The 13C NMR spectra display the
characteristic signals of all carbons and particularly those corresponding to the
dihydropyrimidinone ring. The sp2 carbons at the α and β positions to the phosphorus atom
resonate each one as a doublet towards 92 ppm (1JCP
̴ ̴ 20 Hz)
205 Hz) and 148 ppm (2JCP
respectively. The CH-N carbon gives also a doublet around 55 ppm. Such a doublet is
2
characteristic of the coupling with phosphorus with a JCP coupling constant of about 15 Hz. As
for the C=O carbon, it resonates as a singlet at near 152 ppm. Structures of compounds 3 were
supported additionally by the mass spectra which showed the correct molecular ion peaks.
Unambiguous structure elucidation of phosphonodihydropyrimidinones 3 was achieved
by X-ray crystallography. Single crystals of C15H21N2O4P,0.065(H2O) were obtained by slow
evaporation at room temperature of n-hexane into a chloroform (3a) solution. The molecular
structure of (3a) as the result of a single crystal X-ray study is shown in Figure 1. It contains two
crystallographically independent molecules with one of the ethyl groups of the second molecule
is disordered over two orientations in a 0.729(2):0.271(8) ratio. In the atomic arrangement, these
molecules are interconnected via N—H···O hydrogen bonds to form layers parallel to (b, c) plan
2
(Figure 2, Table 4). Within the layers, R2 (8) graph-set motif connecting two adjacent molecules
are observed. These layers, located around x = 1/4 and x = 3/4, connect each other via C—H···O
to form a three dimensional network (Figure 3, Table 5). A small amount of water (about 12.5%)
can be incorporated into the structure, causing disorder in the ethyl moiety C29 and C30. The
water contributes to connect the aforementioned layers by O—H···O hydrogen bond interactions.
Within the dihydropyrimidin-2(1H)-one rings, an examination of the bond length data
(Table 5) shows that N1-C3 [1.348(3) Å], N2-C3 [1.367(3) Å], N2-C4 [1.385(3) Å], N3-C18
[1.342(3) Å], N4-C18 [1.370(3) Å] and N4-C19 [1.384(3) Å] can be attributed as having clear
double bond character, which is due to the n-σ-π conjugation. The C1-C4 [1.353(3) Å] and C16-
C19 [1.341(3) Å] in agreement with the presence of the C-C double bonds. The N1-C2 [1.466(3)
Å], N3-C17 [1.463(3) Å], C1-C2 [1.531(3) Å] and C16-C17 [1.530(3) Å], clearly indicate the
presence of C-C single bonds.

ACCEPTED MANUSCRIPT
These molecules exhibit a regular spatial configuration with normal C-C distances and C-
C-C, angles. The average value of the C-C bond lengths of the two phenyl rings is 1.388(3) and
1.387(3) Å which are between a single and double bond and agree with those in the literature [29,
30].
Concerning the P-O, the P1-O2 [1.469(1) Å] and P2-O6 [1.472(1) Å] are consistent with
P-O double bonds, while P1-O3 [1.582(2) Å], P1-O4 [1.575(2) Å], P2-O7 [1.575(2) Å] and P2-
O8 [1.583(2) Å] correspond to P-O single bonds.
Figure 1. Asymmetric unit of C15H21N2O4P, 0.065(H2O). Displacement ellipsoids are drawn at the 50% probability level.

ACCEPTED MANUSCRIPT
Figure 2. View of a layer parallel to the (a, b) plane in C15H21N2O4P, 0.065(H2O). Dotted lines indicate hydrogen bonds.
Disorder of ethyl groups are omitted for clarity.
Figure 3. Crystal packing of C15H21N2O4P, 0.065(H2O). Hydrogen bonds are denoted by dotted. Disorder of ethyl groups are
omitted for clarity.
Table 4. Hydrogen-bond geometry (Å, º) in C15H21N2O4P, 0.065(H2O).

ACCEPTED MANUSCRIPT
D—H···A
D—H
H···A
D···A
D—H···A
C30—H30C···O9
C29B—H29D···O9
C5—H5A···O3
C20—H20A···O7
C24—H24···O2i
N1—H1···O2ii
0.98
0.99
0.98
0.98
0.95
0.88
0.88
0.88
0.88
0.80
0.80
1.52
2.47
2.54
2.36
2.59
2.07
2.01
2.04
1.98
2.23
2.01
2.449
157
148
130
132
159
143
155
151
160
171
154
3.349
3.249 (3)
3.103 (3)
3.492 (4)
2.823 (2)
2.830 (2)
2.842 (2)
2.822 (2)
3.020
N2—H2···O5iii
N3—H3···O6iv
N4—H4···O1v
O9—H9P···O6vi
O9—H9O···O5iii
2.750
Symmetry codes : (i) x−1/2, −y+3/2, z+1/2; (ii) −x+5/2, y−1/2, −z+3/2; (iii) x, y−1, z; (iv) −x+5/2, y+1/2, −z+5/2;
(v) x, y+1, z; (vi) −x+5/2, y−1/2, −z+5/2.

ACCEPTED MANUSCRIPT
Table 5. Selected and important bond length and bond angle values (Å, °) in C15H21N2O4P, 0.065(H2O).
Atoms
Bond Length (Å)
Atoms
Bond Angle
(°)
C1-C4
C1-C2
1.353(3)
1.531(3)
1.466(3)
1.237(3)
1.348(3)
1.367(3)
1.385(3)
1.341(3)
1.530(3)
1.463(3)
1.246(3)
1.342(3)
1.370(3)
1.384(3)
1.503(3)
1.455(6)
1.390(3)
1.391(3)
1.390(3)
1.382(3)
1.386(4)
1.390(3)
1.387(2)
1.397(3)
1.391(3)
1.389(4)
1.372(4)
1.394(3)
1.582(2)
1.469(2)
1.582(2)
1575(2)
1.472(2)
1.574(2)
C11-C6-C2
119.7(2)
C8-C7-C6
120.2(2)
C2-N1
C9-C8-C7
120.3(2)
C3-O1
C8-C9-C10
120.0(2)
C3-N1
C9-C10-C11
119.7(2)
C3-N2
C10-C11-C6
120.6(2)
C4-N2
C22-C21-C26
119.2(2)
C16-C19
C16-C17
C17-N3
C18-O5
C18-N3
C18-N4
C19-N4
C19-C20
C29-O8
C6-C7
C21-C22-C32
120.3(2)
C24-C23-C22
120.3(3)
C25-C24-C23
119.6(2)
C24-C25-C26
120.7(2)
C25-C26-C21
119.9(2)
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
C6-C11
C7-C8
C9-C9
C9-C10
C10-C11
C21-C22
C21-C26
C22-C23
C23-C24
C24-C25
C25-C26
O8-P2
O2-P1
O3-P1
O4-P1
O6-P2
O7-P2

ACCEPTED MANUSCRIPT
3.3. Anti-inflammatory activity
Given that 3,4-dihydropyrimidinones are well-known for their promising anti-
inflammatory properties [3,33-37], we focused our efforts, in the second part of this work, to
evaluate the in vivo anti-inflammatory activity of the synthesized 5-phosphonato-3,4-
dihydropyrimidin-2(1H)-ones 3a-h. We shall note here that the search for novel anti-
inflammatory agents to treat an inflammatory reaction and consequent diseases such as rheumatic
manifestations, fractures and stomatitis, is a contemporary field.
Anti-inflammatory activity of the synthesized compounds 3a-h and indomethacin used as
standard, was determined by carrageenan-induced hind paw edema method [20], using female
Wister rats. The results of these experiments are summarized in Figures 4 and 5. They showed
that the synthesized compounds 3a-h exhibited significant anti-inflammatory activity in some
cases higher than the standard drug indomethacin. It was found that compound 3g has the highest
anti-inflammatory activity at 58.42 % when compared with other compounds. The remaining
compounds exhibited an anti-inflammatory activity in the following order: 3c (52.45 %), 3b
(48.29 %), 3d (33.37 %), 3h (29.95 %), 3e (23.76 %), 3f (17.11 %), 3a (13.06 %), and compared
with indomethacin (37.77 %). Thus, the most promising compounds in the present series are 3g,
3c and 3b which showed excellent anti-inflammatory activity, higher than the standard drug
indomethacin.
Figure 4: Anti-inflammatory activity (3a-h: tested compounds,
Ind: indomethacin, Cont: control)

ACCEPTED MANUSCRIPT
Figure 5: Anti-inflammatory activity after 60 min of treatment
4. Conclusion
We have developed a novel one-pot three-component protocol for the synthesis of 5-
phosphonato-3,4-dihydropyrimidin-2(1H)-ones, through the zinc triflate-catalyzed Biginelli-type
reaction of β-ketophosphonates, aldehydes and urea. This method offers significant advantages
over prior reports, such as efficiency, good yields, shorter reaction time and easy work-up.
Furthermore, the zinc triflate catalyst used is known for its low toxicity, low cost, and
environmentally
benignity,
which
is
very
beneficial
for
safely
obtaining
phosphonodihydropyrimidinone derivatives for biological screening. The compounds obtained
were characterized by various spectroscopic tools including IR, NMR (1H, 31P, 13C) spectroscopy,
mass spectrometry and single crystal X-ray diffraction. All the synthesized compounds were
evaluated for the first time for the anti-inflammatory activity and were found to be promising
anti-inflammatory agents for further drug discoveries.
Acknowledgement
The authors are grateful to the Tunisian Ministry of Higher Education and Scientific Research for
financial support.
Supplementary material
Supporting Information [Copy of NMR (1H, 31P, 13C) and IR spectra for 5-phosphonato-3,4-
dihydropyrimidin-2(1H)-ones 3] is available on the publishers Web site along with the published
article.
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