Pharma Disclosure For IPDC 2023

INVENTION DISCLOSURE FORM
Malaria is re-emerging as the biggest infectious killer with an estimated 3.3 billion people
at risk in 2010 and is currently the first priority tropical disease of the World Health Organization
(WHO). The four identified species of the parasite responsible for inflicting human malaria are
Plasmodium falciparum, Plasmodium vivax, Plasmodium ovale, and Plasmodium malariae. Of
these, the former two account for more than 95 % of malaria cases in the world. Although, the
disease can be treated in just 48 h, it can cause fatal complications, if the diagnosis and treatment
are delayed. The parasite is observed to develop resistance to conventional anti-malarial drugs
due to mutations in the active site of their DHFR. As a result, discovery of novel anti-malarial
agents effective against resistant strains of the parasite is one of the greatest challenges facing the
control of malaria today. Discovering new drugs that attack key targets which are involved in the
metabolism of the malarial pathogen is the need of the hour.
It has been observed from the literature that several heterocyclic scaffolds such as
pyrazoline, imidazole, indole, triazine, quinoline, pyrimidines, traizole, pyarazole, isooxazole
etc. have already disclosed as anti-malarial agents. Out of them, aminopyrimidines is one of the
potential heterocyclic ring which may be used for designing and synthesizing anti-malarial
compounds. Falco et al. [J. Med. Chem., 2010, 45, 658-668] reported novel heterocyclic
compounds having potential antiplasmodial activity. Out of them, the pyrimidine compound (7)
showed IC50 value of 15µg/mL.
(7)
Further, Karle et al. [Bioorg. Med Chem., 2014, 22, 56-65] also reported one pyrimidine
containing diaryl compound (14b) showed IC50 value of 30µg/mL.
(14b)
In view of the above, we have also designed and synthesized a novel series of 4,6-diaryl-
2-aminopyrimidines (8a–o) and evaluated for in vitro antiplasmodial activity against
Plasmodium falciparum. Out of the 15 compounds, 6 compounds have shown IC 50 values in the
range of 1.61–9.53 µg/mL. These compounds are several times more potent than chloroquine
and quinine, the two standard drugs used for the purpose of comparison.
EXPERIMENTAL PROCEDURE
General method for the preparation of 4,6-diaryl-2-aminopyrimidine derivatives (8a–o)
A mixture of an appropriate flavone (7a–o) (0.5 g, 0.002 mol), guanidine hydrochloride (0.7 g,
0.07 mol) and potassium hydroxide (1.5 g) was refluxed in methanol (30 ml) for 6–8 h. After the
completion of the reaction, the mixture was poured into crushed ice-acetic acid mixture (50 g, 30
%). The yellow solid so obtained was filtered, washed with water, and recrystallized from
methanol (Scheme 1).
Scheme 1: Synthesis of 4,6-diaryl-2-aminopyrimidines

4-(2’-Hydroxy-4’-methoxyphenyl)-6-(4’’-chlorophenyl)-2-aminopyrimidine (8a): Yield 33
%; Yellow crystals from MeOH; mp 215–217 °C; IR (KBr) vmax: 3494, 3365, 2923, 1618 cm -1;
1
H NMR (400 MHz, CDCl3): d 3.89 (s, 3H, OCH3), 5.19 (s, 2H, NH2), 6.59 (s, 1H, ArH), 7.29–
7.30 (m, 2H, ArH), 7.32–7.34 (d, J = 7.6, 2H, ArH), 7.40 (1H, Pyri), 7.42–7.44 (d, J = 7.4, 2H,
ArH); MS m/z; 328.76 (M+1); Anal. Calcd for C 17H14ClN3O2: C, 62.30; H, 4.31; N, 12.82.
Found: C, 62.35; H, 4.22; N, 13.02.
4-(2’-Hydroxy-4’-methoxyphenyl)-6-(4’’-methoxyphenyl)-2-aminopyrimidine (8b): Yield 35

%; Yellow crystals from MeOH; mp 223–225 °C; IR (KBr) vmax: 3410, 3300 (NH 2), 3173.9
(OH), 1635 cm-1; 1H NMR (400 MHz, CDCl3): d 3.88 (s, 3H, OCH3), 3.91 (s, 3H, OCH3), 5.15
(s, 2H, NH2), 6.54–6.57 (m, 2H, ArH), 6.60 (s, 1H, ArH), 7.35 (s, 1H, pyri), 7.36–7.37 (d, J =
7.8, 2H, ArH), 7.42–7.43 (d, J = 7.84, 2H, ArH); MS m/z; 324.13 (M+1); Anal. Calcd for
C18H17N3O3: C, 66.86; H, 5.30; N, 13.00. Found: C, 66.78; H, 5.21, N, 13.00.
4-(2’-Hydroxy-4’-methoxyphenyl)-6-(4’’-fluorophenyl)-2-aminopyrimidine (8c): Yield 25

1
H NMR (400 MHz, CDCl3): d 3.8 (s, 3H, OCH3), 5.1 (2H, NH2), 7.39 (s, 1H, Pyri), 6.9–7.6 (7H,
13
ArH), 13.19 (br, 1H, OH); C NMR (400 MHz, CDCl3): d 55.44, 100.91, 101.90, 107.47,
110.56, 115.78, 116.00, 128.35, 129.20, 129.28, 133.25, 160.22, 163.08, 163.28, 163.80, 164.47,
165.87; MS m/z; 312.1 (M+1); Anal. Calcd for C17H14FN3O2: C, 65.59; H, 4.53; N, 13.50. Found:
C, 65.50; H, 4.62; N, 13.39.
4-(2’-Hydroxy-4’-methoxyphenyl)-6-(4’’-methylphenyl)-2-aminopyrimidine (8d): Yield 16

1
H NMR (400 MHz, CDCl3): d 2.44 (s, 3H, CH3), 3.8 (s, 3H, OCH3), 5.1 (2H, NH2), 6.4–8.0 (m,
7H, ArH), 7.34 (s, 1H, Pyri), 13.96 (br, 1H, OH); MS m/z; 308.2 (M+1); Anal. Calcd for
C18H17N3O2: C, 70.34; H, 5.58; N, 13.67. Found: C, 70.30; H, 5.62; N, 13.60.
4-(2’-Hydroxy-5’-methoxyphenyl)-6-(3’’-methoxyphenyl)-2-aminopyrimidine (8e): Yield 54

1
H NMR (400 MHz, CDCl3): d 3.8 (s, 3H, OCH3), 4.1 (s, 3H, OCH3) 5.1 (2H, NH2), 7.36 (s, 1H,
Pyri), 6.9–7.8 (7H, ArH), 13.19 (br, 1H, OH); MS m/z; 324.2 (M+1); Anal. Calcd for
4-(2’-Hydroxy-5’-methoxyphenyl)-6-(2’’-chlorophenyl)-2-aminopyrimidine (8f): Yield 52
1
ArH), 13.09 (br, 1H, OH); MS m/z; 328.2 (M+1); Anal. Calcd for C 17H14ClN3O2: C, 62.30; H,
4.31; N, 12.82. Found: C, 62.34; H, 4.27; N, 12.79.
4-(2’-Hydroxy-5’-methoxyphenyl)-6-(3’’-chlorophenyl)-2-aminopyrimidine (8g): Yield 70

1
13
ArH), 13.84 (br, 1H, OH); C NMR (400 MHz, CDCl3): d 56.13, 102.10, 111.48, 117.36,
119.37, 119.84, 125.27, 127.38, 130.08, 130.78, 135.01, 139.14, 152.24, 154.94, 160.79, 165.16,
166.00; MS m/z; 328.2 (M+1); Anal. Calcd for C 17H14ClN3O2: C, 62.30; H, 4.31; N, 12.82.
Found: C, 62.36; H, 4.30; N, 12.85.
4-(2’-Hydroxy-5’-methoxyphenyl)-6-(4’’-fluorophenyl)-2-aminopyrimidine (8h): Yield 56

1
ArH), 13.16 (br, 1H, OH); MS m/z; 312.2 (M+1); Anal. Calcd for C 17H14FN3O2: C, 65.59; H,
4.53; N, 13.50. Found: C, 65.51; H, 4.57; N, 13.54.
4-(4’-Benzyloxyphenyl-2’-hydroxy)-6-(4’’-methoxyphenyl)-2-aminopyrimidine (8i): Yield

55 %; Yellow crystals from MeOH; mp 226–227 °C; IR (KBr) vmax: 3495, 3347, 3223, 1652
cm-1; 1H NMR (400 MHz, CDCl3): d 3.4 (s, 3H, OCH3), 5.12 (s, 2H, OCH2Ar), 6.5 (2H, NH2),
6.6–8.1 (m, 12H, ArH), 7.35 (s, 1H, Pyri), 10.07 (br, 1H, OH); MS m/z; 400.2 (M+1); Anal.
Calcd for C24H21N3O3: C, 72.16; H, 5.30; N, 10.52. Found: C, 72.21; H, 5.28; N, 10.52.
4-(4’-Benzyloxyphenyl-2’-hydroxy)-6-(3’’-methoxyphenyl)-2-aminopyrimidine (8j): Yield

47 %; Yellow crystals from MeOH; mp 154–155 °C; IR (KBr) vmax: 3400, 3338, 3223, 1652
cm-1; 1H NMR (400 MHz, CDCl3): d 3.9 (s, 3H, OCH3), 5.12 (s, 2H, OCH2Ar), 5.3 (2H, NH2),
Calcd for C24H21N3O3: C, 72.16; H, 5.30; N, 10.52. Found: C, 72.18; H, 5.29; N, 10.52.
4-(4’-Benzyloxyphenyl-2’-hydroxy)-6-(3’’,4’’-dimethoxyphenyl)-2-aminopyrimidine (8k):
Yield 32 %; Yellow crystals from MeOH; mp 198–200 °C; IR (KBr) vmax: 3420, 3322, 3210,
1647 cm-1; 1H NMR (400 MHz, CDCl3): d 3.9 (s, 3H, OCH3), 4.0 (s, 3H, OCH3), 5.12 (s, 2H,
OCH2Ar), 5.3 (2H, NH2), 6.9–7.9 (m, 12H, ArH), 7.36 (s, 1H, Pyri), 11.03 (br, 1H, OH); MS
m/z; 430.2 (M+1); Anal. Calcd for C25H23N3O4: C, 69.92; H, 5.40; N, 9.78. Found: C, 69.95; H,
5.37; N, 9.77.
4-(4’-Benzyloxyphenyl-2’-hydroxy)-6-(4’’-fluorophenyl)-2-aminopyrimidine (8l): Yield 45

1
H NMR (400 MHz, CDCl3): d 5.12 (s, 2H, OCH2Ar), 6.5 (2H, NH2), 6.6–8.1 (m, 12H, ArH),
7.35 (s, 1H, Pyri), 12.01 (br, 1H, OH); MS m/z; 388.2 (M+1); Anal. Calcd for C 23H18FN3O2: C,
71.31; H, 4.68; N, 10.85. Found: C, 71.27; H, 4.70; N, 10.86.
4-(4’-Benzyloxyphenyl-2’-hydroxy)-6-(2’’-chlorophenyl)-2-aminopyrimidine (8m): Yield 35

1
H NMR (400 MHz, CDCl3): d 5.10 (s, 2H, OCH2Ar), 5.15 (2H, NH2), 7.34–7.39 (m, 5H, ArH),
Calcd for C23H18ClN3O2: C, 68.40; H, 4.49; N, 10.40. Found: C, 68.40; H, 4.51; N, 10.40.
4-(4’-Benzyloxyphenyl-2’-hydroxy)-6-(4’’-methylphenyl)-2-aminopyrimidine (8n): Yield 56

1
H NMR (400 MHz, CDCl3): d 2.4 (s, 3H, CH3), 5.10 (s, 2H, OCH2Ar), 6.44 (2H, NH2), 7.2–7.4
(m, 5H, ArH), 7.4–7.8 (m, 7H, ArH), 7.35 (s, 1H, Pyri); MS m/z; 384.1 (M+1); Anal. Calcd for
4-(4’-Benzyloxyphenyl-2’-hydroxy)-6-(3’’-methylphenyl)-2-aminopyrimidine (8o): Yield 29

1
H NMR (400 MHz, CDCl3): d 2.1 (s, 3H, CH3), 5.11 (s, 2H, OCH2Ar), 6.2 (2H, NH2), 7.2–7.4
(m, 5H, ArH), 6.9–7.8 (m, 7H, ArH), 7.35 (s, 1H, Pyri); MS m/z; 384.1 (M+1); Anal. Calcd for
RESULTS AND DISCUSSION
The diarylpyrimidine derivatives were prepared according to Scheme 1. The key intermediate
1,3-diketones (6a–o) required for the work were obtained from the esters (5a–o), by base-
catalyzed Baker-Venkataraman transformation. Condensation of 2-hydroxyacetophenones with
various substituted benzoic acids in dry pyridine and POCl 3 furnished the esters (5a–o). IR
spectra of 1,3-diketones showed absorption bands for C=O in the range of 1,615–1,625 cm -1.
Treatment of the diketones with conc. H 2SO4 led to formation of flavones (7a–o). Formation of
the flavones 7a–o was confirmed by the appearance of C=O absorption bands at 1,640–1,660 cm -
1
in their IR spectra. Reaction of the flavones (7a–o) with a slight excess of guanidine
hydrochloride in alkaline medium afforded 4,6-diaryl-2-amino-pyrimidines (8a–o). All the
synthesized compounds were characterized by spectral and elemental analysis.
Compounds (8a–o) showed a characteristic peak at around 3,200 cm -1 for O–H stretching and
asymmetric and symmetric N–H stretching bands at 3,500 and 3,350 cm -1, respectively in their
IR spectra. In the 1H NMR spectra, NH2 protons appeared at d 5.1–6.0 and the pyrimidinyl
proton (C5–H) appeared as a sharp singlet at d 7.3–7.5. A downfield value of d 13–14 for the –
OH protons is indicative of the existence of a partial six-membered ring as shown in the
13
structure. In the C NMR spectra, the d values of the carbons are in confirmity with the
structures of the synthesized compounds.
Antiplasmodial activity: All the synthesized compounds were screened for antiplasmodial
activity on chloroquine sensitive P. falciparum MRC 20 strains. Strain of P. falciparum was
cultured continuously according to the candle jar method, in vitro in human red blood cells
(blood type B+) with 5 % hematocrit in LIQUID RPMI 1640 medium (HIMEDIA) supplemented
with 25 mM HEPES (Sigma), 0.2 % sodium bicarbonate (Sigma) and 10 % human B + serum.
Slides of culture were observed after 3, 6, and 24 h for regular development of parasite stages.
The inhibition of parasite growth in the drug-treated groups was calculated. Dose–response
curves were obtained by plotting percentage inhibition against log concentration. The values of
the compounds provided a mid-point value where parasite growth would be 50 %. Linear
regression analysis was applied to the linear portion of the sigmoidal curve and IC 50 values were
derived for each test compound. The IC 50 value of chloroquine and quinine was determined to be
10 and 29 µg/mL, respectively. The IC50 values of test compounds are given in Table 1.
The in vitro biological activity of the synthesized pyrimidine derivatives has shown
encouraging results against the chloroquine sensitive strain. Out of the 15 novel compounds, two
compounds 8b and 8k have been found to be more potent than the standard drug chloroquine
with IC50 values of 1.78 and 1.61 µg/mL, respectively. Compound 8b bears 4-methoxy
substitution on both the phenyl rings of the pyrimidine ring system. Replacement of 4’’-methoxy
group of phenyl ring of compound 8b by methyl group caused a decrease in potency (8d). The
weak activity of halo-substituted compounds might be due to decrease in electron density in the
phenyl ring. Compound 8k with 3’’,4’’-dimethoxy group on phenyl ring and highly hydrophobic
benzyloxy substitution on hydroxyphenyl ring showed the highest potency. Compounds with
benzyloxy group and methoxy or methyl groups showed comparable activities. Compounds 8d,
8g, 8i, and 8j showed IC50 values <10 µg/mL. These compounds may serve to be ideal leads for
further optimization of their structures to provide newer and safer anti-malarial/anti-plasmodial
drugs.

Pharma Disclosure For IPDC 2023

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INVENTION DISCLOSURE FORM

General method for the preparation of 4,6-diaryl-2-aminopyrimidine derivatives (8a–o)

Scheme 1: Synthesis of 4,6-diaryl-2-aminopyrimidines

4-(2’-Hydroxy-4’-methoxyphenyl)-6-(4’’-methoxyphenyl)-2-aminopyrimidine (8b): Yield 35

4-(2’-Hydroxy-4’-methoxyphenyl)-6-(4’’-fluorophenyl)-2-aminopyrimidine (8c): Yield 25

4-(2’-Hydroxy-4’-methoxyphenyl)-6-(4’’-methylphenyl)-2-aminopyrimidine (8d): Yield 16

4-(2’-Hydroxy-5’-methoxyphenyl)-6-(3’’-methoxyphenyl)-2-aminopyrimidine (8e): Yield 54

4-(2’-Hydroxy-5’-methoxyphenyl)-6-(3’’-chlorophenyl)-2-aminopyrimidine (8g): Yield 70

4-(2’-Hydroxy-5’-methoxyphenyl)-6-(4’’-fluorophenyl)-2-aminopyrimidine (8h): Yield 56

4-(4’-Benzyloxyphenyl-2’-hydroxy)-6-(4’’-methoxyphenyl)-2-aminopyrimidine (8i): Yield

4-(4’-Benzyloxyphenyl-2’-hydroxy)-6-(3’’-methoxyphenyl)-2-aminopyrimidine (8j): Yield

4-(4’-Benzyloxyphenyl-2’-hydroxy)-6-(4’’-fluorophenyl)-2-aminopyrimidine (8l): Yield 45

4-(4’-Benzyloxyphenyl-2’-hydroxy)-6-(2’’-chlorophenyl)-2-aminopyrimidine (8m): Yield 35

4-(4’-Benzyloxyphenyl-2’-hydroxy)-6-(4’’-methylphenyl)-2-aminopyrimidine (8n): Yield 56

4-(4’-Benzyloxyphenyl-2’-hydroxy)-6-(3’’-methylphenyl)-2-aminopyrimidine (8o): Yield 29

RESULTS AND DISCUSSION

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