1-Aryl-4,6-diamino-1,2-dihydrotriazine as antimalarial agent: A new synthetic route

Article abstract of DOI:10.1016/j.bmcl.2004.12.049

Some novel derivatives of 1-aryl-4,6-diamino-1,2-dihydrotriazines have been synthesized using neat technology under microwaves. These were tested in vitro against both sensitive and resistant Plasmodium falciparum strains for antimalarial activity.

Full text of DOI:10.1016/j.bmcl.2004.12.049

Bioorganic & Medicinal Chemistry Letters 15 (2005) 915–917
1-Aryl-4,6-diamino-1,2-dihydrotriazine as antimalarial
agent: a new synthetic route
M. Kidwai,a,* P. Mothsra,a R. Mohana and S. Biswasb
aDepartment of Chemistry, University of Delhi, Delhi 110007, India
bMalaria Research Centre (ICMR), 22 Sham Nath Marg, Delhi 110054, India
Received 2 November 2004; revised 17 December 2004; accepted 20 December 2004
Available online 13 January 2005
Abstract—Some novel derivatives of 1-aryl-4,6-diamino-1,2-dihydrotriazines have been synthesized using neat technology
under microwaves. These were tested in vitro against both sensitive and resistant Plasmodium falciparum strains for antimalarial
activity.
ꢀ 2004 Elsevier Ltd. All rights reserved.
1. Introduction
ciency, eco-friendly nature, cost effectiveness, and ease
of manipulation. Though neat reaction technology is
one step ahead in the direction of solvent less synthesis
wherein no solvent is required at any stage of reaction.
In continuation of our earlier work,15 neat reaction tech-
nology showed better energy usage with improved yields
and limits the use of hazardous solvents. All these fall in
the domain of Green Chemistry.16 This prompted us to
perform one pot neat synthesis of 1-aryl-4,6-diamino-
1,2-dihydrotriazines (4) using microwaves. The one pot
synthesis minimizes the yield and energy loss. This con-
densation reaction is best effected under anhydrous con-
ditions. The formation of water during reaction resulted
in incomplete condensation or no reaction at all. This
incomplete condensation leads to the formation of aryl
biguanide as a side product which prevent the formation
of titled compound. Triethyl orthoacetate17 or triethyl
orthoformate18 were used in the synthesis of 1-aryl-
4,6-diamino-1,2-dihydrotriazine (4) as dehydrating
agents in normal course of reaction but in neat reaction
using microwave no dehydrating agent is required. It is
possible to take advantage of microwave exposure to in-
duce equilibrium shifting by evaporation of light polar
molecules such as water.
Most of the tropical and subtropical countries including
Africa are prone to malarial diseases. In spite of contin-
uous efforts to control malaria, it remains a major threat
owing to drug resistant parasite.1 This has highlighted
the urgent need for the discovery and development of
novel antimalarial agents aimed at combating the
emerging resistant parasite. 1-Aryl-4,6-diamino-1,2
dihydrotriazines (4) are potent inhibitors of Plasmodium
falciparum dihydrofolate reductase,2 one of a few de-
fined drug targets for antimalarial therapy. In the course
of continuing efforts to develop new antimalarial drugs,
a variety of novel-1-aryl-4,6-diamino-1,2-dihydrotri-
azine derivatives were synthesized as antimalarial agent.
In addition to antimalarial activity, 1-aryl-4,6-diamino-
1,2-dihydrotriazines (4) also exhibit antivitamin,3–5
antitumor,6,7 anticoccidial,8,9 anthelminthic,8,10 and
antibacterial3 activities.
2. Chemistry20
Conventionally, 1-aryl-4,6-diamino-1,2-dihydrotriazine
(4) had been synthesized by two major routes viz.
three11,12 and two component synthesis.13,14 In recent
years, the use of solvent free conditions coupled with
microwave have got momentum because of high effi-
Literature reveals that only aromatic aldehydes can be
used successfully for 1-aryl-4,6-diamino-1,2-dihydrotri-
azine (4) in three component synthesis barring aliphatic
aldehydes.11 While in two step reaction aliphatic alde-
hydes reacts rapidly, though standard protocol using
formaldehyde does not give the desired product.
Dimethoxymethane is used as the formaldehyde19
*
Corresponding author. Tel./fax: +91 11 27666235; e-mail:
kidwai_chemistry@yahoo.co.uk
0960-894X/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2004.12.049

916
M. Kidwai et al. / Bioorg. Med. Chem. Lett. 15 (2005) 915–917
equivalent. However when formaldehyde is used under
microwave, the desired product formed in excellent
yields even in three component synthesis. Keeping in
view it was thought worth while to synthesize 1-aryl-
4,6-diamino-1,2-dihydrotriazines22 (4) using one pot
neat reaction technology under microwave.
pounds 4g and 4j also exhibited some activity in both
parasites, but 4e found to be best among five, yet the
activity of parent compound, Pyr* was at about 200-
fold less concentration in case of sensitive and about
80-fold less concentration in resistant parasites. These
compounds found equally active against both sensitive
and resistant strains.
NH2
Acknowledgements
NH
O
Ar
N
N
C
mν
conc. HCl
R
NH2
NH–CN + R
R' + Ar–NH2
.HCl
NH2
One of the author P. Mothsra is thankful to the Council
of Scientific and Industrial Research, New Delhi for the
financial assistance.
R'
N
4(a-l)
(1)
(2)
(3)
4a R0 = H
4b R0 = H
R = H
R = H
Ar = C6H5
References and notes
Ar =
N
4c R0 = H
4d R0 = H
R = H
R = H
Ar = C6H4–CH3(p)
Ar = C6H4–Cl(p)
1. Sirawaraporn, W.; Sathitkul, T.; Sirawaraporn, R.;
Yuthavong, Y.; Somti, D. V. Proc. Natl. Acad. Sci.
U.S.A. 1997, 94, 1124.
2. Blaney, J. H.; Hansch, C.; Silipo, C.; Vittoria, A. Chem.
Rev. 1984, 84, 333.
F
4e R0 = H
R = H
Ar =
3. Modest, E. J.; Foley, G. E.; Pechet, M. M.; Farber, S. J.
Am. Chem. Soc. 1952, 74, 855.
4. Foley, G. E.; Modest, E. J. Proc. 52nd General Meeting,
Society of American Bacterists, Boston, Mass, May 1,
1952, 63.
5. (a) Foley, G. E. Proc. Soc. Biol. Med. 1953, 83, 733; (b)
Foley, G. E. Proc. Soc. Biol. Med. 1953, 740.
6. Farber, S.; Diamond, I.; Foley, G.; Modest, E. J. Am. J.
Pathol. 1952, 28, 559.
7. Farber, S.; Foley, G.; Down, V.; Appleton, R.; King, J.
Proc. Am. Assoc. Cancer Res. 1953, 1, 15.
Cl
4f
R0 = H
R = C6H5
R = C6H5
Ar = C6H5
4g R0 = H
Ar =
N
4h R0 = H
R = C6H5
R = C6H5
Ar = C6H4–CH3(p)
Ar = C6H4–Cl(p)
4i
4j
R0 = H
R0 = H
F
R = C6H5
Ar =
Cl
4k R0 = CH3 R = C2H5
4l
R0 = H
Ar = C6H4–Cl(p)
R = C6H4– Ar = C6H5
OCH3(p)
8. Schalit, S.; Cutur, R. A. J. Org. Chem. 1959, 24, 573.
9. Lux, R. E. Antibiot. Chemother. 1954, 4, 971.
10. Roth, B.; Burrows, R. B.; Hitchings, G. H. J. Med. Chem.
1963, 6, 370.
11. Modest, E. J. J. Org. Chem. 1956, 21, 1.
12. Carrington, H. C.; Crowther, A. F.; Stacey, G. J. J. Chem.
Soc. 1954, 1017.
13. Modest, E. J.; Levine, P. J. Org. Chem. 1956, 21, 14.
14. Newman, H.; Moon, E. L. J. Org. Chem. 1964, 29, 2061.
15. Kidwai, M.; Saxena, S.; Mohan, R.; Venkataramanan, R.
J. Chem. Soc., Perkin Trans. 1 2002, 16, 1845.
16. Kidwai, M.; Venkataramanan, R.; Dave, B. Green Chem.
2001, 3, 278.
3. Biological evaluation: antimalarial activity in vitro21
The antimalarial activity of compounds 4b,c,e,g, and 4j
were tested against drug sensitive and resistant parasite
lines. The effect of pyrimethamine and its analogues
against both sensitive and resistant P. falciparum strain
is shown in Table 1. Of the five new compounds, 4e
showed good in vitro antiplasmodial activity. Com-
17. Saesaengseerung, N.; Vilaivan, T.; Thebtaranonth, Y.
Synth. Commun. 2002, 32, 2089.
18. Baker, B. R.; Johnson, M. A. J. Heterocycl. Chem. 1967,
4, 447.
19. Yuthavong, Y.; Vilaivan, T.; Chareonsethakul, N.; Kam-
chonwongpaisan, S.; Sirawaraporn, W.; Quarrell, R.;
Lowe, G. J. Med. Chem. 2000, 43, 2738.
Table 1. Antimalarial activities, IC50, and IC90 of new dihydrotriazine
compounds against cycloguanil sensitive (FJB-D9) and resistant (FJB-
D4) P. falciparum strain
20. Experimental: general procedure: A mixture of equimolar
neat reactants in an Erlenmeyer flask, that is, (0.01 mol)
aldehyde, (0.01 mol) cyanoguanidine, and (0.01 mol)
aromatic amine with concd HCl was subjected to
microwave irradiation for 2–3 min. Microwave irradia-
tion was carried out in Kenstar Microwave Oven
(2450 MHz, 800 W). More than 1 equiv of HCl was
added as excess acid functions as a catalyst. Reaction was
monitored at an interval of 30 s by TLC. Temperature of
the reaction raise up to 80 ꢁC in 30 s interval. The
temperature of the reaction mixture was measured
through a noncontact thermometer (AZ, Mini Gun type,
model 8868). Final sticky solid obtained was triturated
Compound
Inhibitory activity (lM)
FJB-D9 FJB-D4
IC90
IC50
IC50
IC90
4b
4c
618.1
584.5
17.28
81
>1000
>1000
629.1
501.04
14.7
>1000
>1000
4e
4g
47.6
388.4
331.9
49.5
363.6
282.5
52.9
81.9
4j
Pyr*
87.6
0.0016
0.006
0.005
0.028
*Pyr: pyrimethamine.

M. Kidwai et al. / Bioorg. Med. Chem. Lett. 15 (2005) 915–917
917
with minimum amount of a suitable solvent to afford
product in high yield. The structure of all the products
were established on the basis of 1H NMR, mass, and
elemental analysis.
Compound 4c: mp 242–248 ꢁC; yield: 93%; 1H NMR
60 MHz (CD3OD): d 2.45 (s, Me-40), 4.71 (s, CH2), 7.3 (m,
Ar–C–H), 7.8 (br s, NH). Anal. Calcd for C10H14ClN5: C,
50.10; H, 5.84; N, 29.22. Found: C, 50.40; H, 5.84; N,
29.10; m/z 204 (MꢀCl)+.
21. (a) Biological activity in vitro: Assay was conducted in
pyrimethamine (Pyr) sensitive and resistant parasite lines.
P. falciparum isolates, FJB-D9 (drug sensitive) and FJB-
D4 (drug resistant) were cultured by the established
method. FJB-D4 and FJB-D9 (Jabalpur, Central India)
isolates were collected from patients in 1990. The growth
medium used for culturing and drug sensitivity testing was
RPMI 1640 with no added p-amino benzoic acid or folic
acid (GIBCO, UK), supplemented with 25 mM HEPES
buffer and sodium bicarbonate and enriched with 10%
human AB+ serum (obtained from blood donor belonging
to malaria nonendemic area). Flat bottomed 96-well tissue
culture plates were closed separately with various concen-
tration of Pyr and five new compounds (0.0005–100 lg).
An aliquot of 100 rmuL culture was added in control and
drug dosed wells. The plates were incubated in candle jar
at 37 ꢁC for 30 h. After incubation, supernatant was
aspirated from each well, pellet was mixed and thick/thin
smears were prepared for microscopic examination.
Growth of the parasites from duplicate wells of each and
every concentrations of drug was monitored microscopi-
cally by counting number of Schizonts per 200 asexual
parasites and total numbers of parasites per 500 RBCÕs.
Schizonts having eight or more nuclei were counted. The
assays were considered successful of 10% or more of the
parasites in the control wells developed into schizonts with
eight or more nuclei. Percent schizont maturation inhibi-
tion was calculated by the formula: (1 ꢀ Nt/Nc) · 100,
where Nt and Nc represent the number of schizont in the
test and control wells respectively. Inhibitory concentra-
tions 50 and 90 were calculated in both isolates by noting
the drug concentrations at which 50% and 90% Schizont
maturation were effected at 30 h; (b) Sundar, N.; Jacob, V.
T.; Bhat, V. S.; Valecha, N.; Biswas, S. Bioorg. Med.
Chem. Lett. 2001, 11, 2269.
Compound 4d: mp 276–280 ꢁC; yield: 95.6%; 1H NMR
60 MHz (CD3OD): d 4.6 (s, CH2), 7.3–7.7 (m, Ar–C–H).
Anal. Calcd for C9H11Cl2N5: C, 41.54; H, 4.23; N, 26.92.
Found: C, 41.38; H, 4.23; N, 26.80; m/z 224 (MꢀCl)+.
Compound 4e: mp 184–188 ꢁC; yield: 96%; 1H NMR
300 MHz (DMSO): d 4.79 (s, CH2), 7.0 (br s, ex NH), 7.51
(m, Ar–C–H), 7.63 (s, NH2), 7.75 (br s, ex NH), 8.78 (s,
NH+). Anal. Calcd for C9H10Cl2FN5: C, 38.84; H, 3.59;
N, 25.18. Found: C, 38.52; H, 3.70; N, 25.42; m/z 242
(MꢀCl)+.
Compound 4f: mp 215–220 ꢁC; yield: 92.3%; 1H NMR
60 MHz (DMSO): d 6.0 (s, H-2), 7.4–7.6 (m, Ar–C–H).
Anal. Calcd for C15H16ClN5: C, 59.70; H, 5.31; N, 23.22.
Found: C, 59.99; H, 5.53; N, 23.52; m/z 266 (MꢀCl)+.
Compound 4g: mp 215–220 ꢁC; yield: 84.3%; 1H NMR
60 MHz (DMSO): d 5.99 (s, H-2), 6.6–7.3 (m, Ar–C–H),
8.3 (m, Ar–C–H). Anal. Calcd for C14H15ClN6: C, 55.54;
H, 4.96; N, 27.77. Found: C, 55.29; H, 5.30; N, 27.52; m/z
267 (MꢀCl)+.
Compound 4h: mp 225–230 ꢁC; yield: 89.7%; 1H NMR
60 MHz (CD3OD): d 2.4 (s, Me-40), 6.02 (s, H-2), 7.4 (m,
Ar–C–H and NH2), 7.87 (br s, ex NH), 8.23 (s, NH+).
Anal. Calcd for C16H18ClN5: C, 60.85; H, 5.70; N, 22.19.
Found: C, 60.23; H, 5.72; N, 22.26; m/z 280 (MꢀCl)+.
Compound 4i: mp 218–220 ꢁC; yield: 89%; 1H NMR
60 MHz (CD3OD): d 6.06 (s, H-2), 7.47 (m, Ar–C–H).
Anal. Calcd for C15H15Cl2N5: C, 53.57; H, 4.46; N, 20.83.
Found: C, 53.32; H, 4.47; N, 21.02; m/z 300 (MꢀCl)+.
Compound 4j: mp 252 ꢁC (decomposition pt.); yield: 78%;
1H NMR 300 MHz (DMSO): d 5.94 (s, H-2), 6.78 (br s, ex
NH), 7.1 (m, Ar–C–H), 7.55 (m, Ar–C–H), 7.9 (br s, ex
NH), 9.2 (s, NH+). Anal. Calcd for C15H14Cl2FN5: C,
50.85; H, 3.95; N, 19.77. Found: C, 50.60; H, 3.58; N,
19.91; m/z 318 (MꢀCl)+.
22. Compound 4a: mp 230 ꢁC (decomposition pt.); yield: 76%;
1H NMR 60 MHz (DMSO): d 4.6 (s, CH2), 6.9 (br s, ex
NH), 7.1–7.6 (m, Ar–C–H and NH2), 7.80 (br s, ex NH),
8.58 (s, NH+). Anal. Calcd for C9H12ClN5: C, 47.89; H,
5.32; N, 31.04. Found: C, 47.84; H, 5.26; N, 30.86; m/z 190
(MꢀCl)+.
Compound 4k: mp 200–205 ꢁC; yield: 68%; 1H NMR
300 MHz (CD3OD): d 0.9 (t, CH3), 1.28 (s, CH3), 1.8 (q,
CH2), 7.28–7.35 (m, Ar–C–H). Anal. Calcd for
C12H17Cl2N5: C, 47.68; H, 5.63; N, 23.18. Found: C,
47.72; H, 5.47; N, 23.28; m/z 266 (MꢀCl)+.
Compound 4l: mp 176–180 ꢁC; yield: 79%; 1H NMR
300 MHz (DMSO): d 3.83 (s, 40-OCH3), 5.87 (s, H-2), 6.8
(br s, ex NH), 7.27–7.49 (m, Ar–C–H and NH2), 7.6–7.8
(m, Ar–C–H and NH), 8.9 (s, NH+). Anal. Calcd for
C16H18ClN5O: C, 57.92; H, 5.43; N, 21.12. Found: C,
57.68; H, 5.71; N, 21.10; m/z 296 (MꢀCl)+.
Compound 4b: mp 222 ꢁC (decomposition pt.); yield:
1
83.4%; H NMR 60 MHz (DMSO): d 4.67 (s, CH2), 7.0–
7.2 (m, Ar–C–H), 8.45 (m, Ar–CH). Anal. Calcd for
C8H11ClN6: C, 42.38; H, 4.85; N, 37.08. Found: C, 42.39;
H, 4.70; N, 37.23; m/z 191 (MꢀCl)+.