Regioselective synthesis of pyrimido[1,2-a][1,3,5]triazin-6-ones via reaction of 1-(6-oxo-1,6-dihydropyrimidin-2-yl)guanidines with triethylorthoacetate: Observation of an unexpected rearrangement

Article abstract of DOI:10.1039/c2ob25195g

A novel thermal rearrangement, involving pyrimidine ring opening and subsequent ring closure leading to recyclization of the system, was identified in the reaction of (6-oxo-1,6-dihydropyrimidin-2-yl)guanidines 3 (where NR ¹R² = NH₂, NH alkyl, NH aralkyl, NHCH ₂Ph(R)) with triethyl orthoacetate, affording 4-substituted-2-methyl- 6H-pyrimido[1,2-a][1,3,5]triazin-6-ones 6 and their ring opened products. However, no such rearrangement was observed with (6-oxo-1,6-dihydropyrimidin-2- yl)guanidines 3 bearing a tertiary amino or anilino substituent (i.e. where NR¹R² = N(CH₃)₂, indoline, morpholino, NHAr). As expected, 2-substituted-4-methyl-6H-pyrimido[1,2-a][1,3,5] triazin-6-ones 4 were obtained as the final products. Experimental structural determination and theoretical studies were carried out to get an understanding of the observed thermal rearrangement. In addition, an attempt to obtain similar pyrimido[1,2-a][1,3,5]triazin-6-ones using N,N-dimethylacetamide dimethyl acetal (DMA-DMA) as one carbon inserting synthon had furnished triazine ring annulated product 14 bearing N,N-dimethyl enamino substituent at position 4 as a result of further reaction with a second molecule of DMA-DMA.

Full text of DOI:10.1039/c2ob25195g

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PAPER
Regioselective synthesis of pyrimido[1,2-a][1,3,5]triazin-6-ones via reaction of
1-(6-oxo-1,6-dihydropyrimidin-2-yl)guanidines with triethylorthoacetate:
observation of an unexpected rearrangement†
Nikhil Sachdeva,a Anton V. Dolzhenkob and Wai Keung Chui*a
Received 26th January 2012, Accepted 3rd April 2012
DOI: 10.1039/c2ob25195g
A novel thermal rearrangement, involving pyrimidine ring opening and subsequent ring closure leading to
recyclization of the system, was identified in the reaction of (6-oxo-1,6-dihydropyrimidin-2-yl)guanidines
3 (where NR1R2 = NH2, NH alkyl, NH aralkyl, NHCH2Ph(R)) with triethyl orthoacetate, affording 4-
substituted-2-methyl-6H-pyrimido[1,2-a][1,3,5]triazin-6-ones 6 and their ring opened products. However,
no such rearrangement was observed with (6-oxo-1,6-dihydropyrimidin-2-yl)guanidines 3 bearing a
tertiary amino or anilino substituent (i.e. where NR1R2 = N(CH3)2, indoline, morpholino, NHAr). As
expected, 2-substituted-4-methyl-6H-pyrimido[1,2-a][1,3,5]triazin-6-ones 4 were obtained as the final
products. Experimental structural determination and theoretical studies were carried out to get an
understanding of the observed thermal rearrangement. In addition, an attempt to obtain similar pyrimido-
[1,2-a][1,3,5]triazin-6-ones using N,N-dimethylacetamide dimethyl acetal (DMA–DMA) as one carbon
inserting synthon had furnished triazine ring annulated product 14 bearing N,N-dimethyl enamino
substituent at position 4 as a result of further reaction with a second molecule of DMA–DMA.
[1,3,5]triazine moiety have been reported to exhibit antimicro-
Introduction
bial,9 potent fungicidal and average serotoninergic (5-HT1A and
5-HT1B receptor) activities10 as well as GSK-3β inhibitory
1,3,5-Triazine nucleus is a prominent structural core present in
numerous biologically active compounds. Hexamethylmelamine,
irsogladine and 5-aza-2′-deoxycytidine, which are structurally
based on the 1,3,5-triazine scaffold, have been found to exhibit
anti-cancer and antiangiogenic properties.1 Various 1,3,5-triazine
derivatives fused to quinazoline,2 benzimidazole,3 pyrazole4,5
and 1,2,4-triazine6 have been reported to show anti-cancer prop-
erties. Moreover, numerous derivatives of pyrimidine fused
systems such as pyrido[2,3-d]pyrimidine (PD-0332991)7 and
pyrimido[1,2-a]pyrimidine (4)8 have also demonstrated promis-
ing anticancer properties as well. Due to the close structural
similarity with the above pyrimido fused bicyclic scaffolds and
reports on antiproliferative activity from 1,3,5-triazino fused het-
erocycles, the derivatives of pyrimido[1,2-a][1,3,5]triazine scaf-
fold were anticipated to possess anticancer property (Fig. 1). To
date, heterocyclic compounds possessing a pyrimido[1,2-a]-
activity with potential for the treatment of neurodegenerative
diseases.11
In the literature, synthetic access to pyrimido[1,2-a][1,3,5]tria-
zine analogues (in which one of the four nitrogen atoms is
located at the junction of the two cycles) is rather limited and
most of the synthetic approaches described cannot provide the
flexibility of different substitution at various positions around the
fused rings. The synthesis of pyrimido[1,2-a][1,3,5]triazine
system12 can be categorized into two approaches: (1) annulation
of pyrimidine onto a 1,3,5-triazine scaffold;13 (2) annulation of
the 1,3,5-triazine ring onto a pyrimidine scaffold.14 The latter
approach has been largely adopted for the preparation of pyri-
mido[1,2-a][1,3,5]triazines and most authors largely focussed on
the formation of dioxo/dithio/oxothiooxo derivatives of the scaf-
fold.14g–p Therefore, there is a need to find more practical
approaches for the synthesis of these pyrimido[1,2-a][1,3,5]-
triazines.
Since orthoesters are versatile one-carbon building blocks in
ring annulation reactions, it was expected that unsymmetrically
substituted pyrimidin-2-yl guanidine 3 (acting as a penta atomic
synthon) would react with this one-carbon building block to
yield, theoretically, either one of the regioisomeric pyrimido[1,2-
a][1,3,5]triazin-6-ones 4 or 5 or both as product/s. However, the
possibility of structure 5 was excluded, as no cross-peaks were
found between the R3 group protons of pyrimidine ring and
aDepartment of Pharmacy, Faculty of Science, National University of
Singapore, 18 Science Drive 4, Singapore 117543, Singapore. E-mail:
phacwk@nus.edu.sg, nicks.sachdeva81@gmail.com; Fax: +65 6779
1554; Tel: +65 6516 2933
bSchool of Pharmacy, Curtin Health Innovation Research Institute,
Curtin University of Technology, GPO Box 1987, Perth, Western
Australia 6845, Australia
†Electronic supplementary information (ESI) available. CCDC 791289,
788427 and 838638. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c2ob25195g
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Fig. 1 Structurally similar nitrogen containing heterocyclic scaffolds.
Scheme 1 Reagents and Conditions: (i) ethyl 3-oxobutanoate/ethyl 4,4,4-trifluoro-3-oxobutanoate, aq. NaOH, r.t., 12 h (77%); (ii) procedure 1
HNR1R2. HCl, MW, 160 °C, 15 min or procedure 2 NR1R2, TMSCl, CH3CN, 12 min., 160 °C followed by iPrOH, 125 °C, 30 sec. (62%–79%); (iii)
HNR1R2·HCl, C4H9OH, reflux, 6 h (40%); (iv) CH3C(OEt)3, AcOH, reflux, 3–9 h.
methyl group protons of triazine ring in 2D NOESY experiment
(Scheme 1). Moreover, according to DFT calculations in gas
phase, the structure 5 was found to be highly unfavourable ener-
getically (vide infra). In addition, a regioisomeric product similar
to 4 was observed exclusively when other one-carbon inserting
synthon like aldehyde was used with similar substrate.15
However, to our surprise, products 4 (Table 1) were found
readily rearranged in situ to thermodynamically more favourable
products of type 6 and the corresponding ring-opened products
6′ (Scheme 3), depending upon the NR1R2 group present in the
starting material guanidine (Table 2). Herein, the details of this
unexpected thermal rearrangement are presented.
(Scheme 1). In method A, 3 was synthesized via microwave
(MW) assisted nucleophilic addition of amines onto (4-methyl-
6-oxo-1,6-dihydropyrimidin-2-yl)cyanamide 1 using either con-
centrated hydrochloric acid or trimethyl silyl chloride (TMSCl)
catalyzed conditions; whereas in method B, cyclocondensation
of β-keto ester with substituted biguanides 2 yielded 3 as
reported by Curd et al.16 (Scheme 1). Method A was found to be
more versatile and robust for molecular library generation. In the
presence of protic acid (method A procedure 1) or TMSCl
(method A procedure 2) catalyzed conditions, the reaction times
were shorter, workup was easy obviating the need of column
chromatography and appreciable yields of
3 (56–93%)
were obtained with a variety of primary and secondary amines
with alkyl, aryl and aralkyl substituents. In the latter case (i.e.
method A procedure 2), TMSCl not only acted as a source of
anhydrous HCl, but it also activated cyanamide 1 as shown in
Scheme 2.
Results and discussion
The starting material N-(4-substituted-6-oxo-1,6-dihydropyrimi-
din-2-yl)guanidines, 3, were prepared either by method A or B
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Table 1 Structures and yields of intermediates and isolated pyrimido[1,2-a][1,3,5]triazin-6-one products
3
Isolated product
Isolated yield (%)
70
58
60
52
73
33
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Table 1 (Contd.)
3
Isolated product
Isolated yield (%)
38
53
59
78
69
71
The structures of the products were deduced from their mass
spectra, NMR data and elemental analyses. The reactions were
carefully monitored using TLC and the reactions were stopped
immediately when no trace of the starting material was observed.
The reaction proceeded only on heating at 100 °C. The reaction
between these guanidines (3) and triethyl orthoacetate (in
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Scheme 2 Synthesis of 1,6 dihydropyrimidinyl guanidines 3 under TMSCl catalyzed conditions.
Table 2 Relative energies according to ab-initio calculations
Relative energies, kcal mol−1
4
5
6
a R1 = R2 = H
4.14
0.00
21.81
17.65
0.00
8.72
i R1 = R2 = CH3
presence of glacial acetic acid) yielded product 4 predominantly
when the guanidine 3 contained a tertiary amino group (3i–k)
(NR1R2 = N(CH3)2, –N(CH2CH2)2O, indolino). Similarly when
an aryl secondary amino group was included as in 3d, 3e, 3f and
3l (NR1R2 = NHPh, NHPh(3-Br), NHPh(3-Cl), NHPh(4-OMe)),
the predominant compound was 4. Product 4 was characterized
by the diagnostic methyl peak of the triazine ring at δ 2.85–2.91
in 1H NMR and 26.2–27.8 in 13C NMR as well as X-ray crystal-
lography of 4i (Fig. 2; please refer to ESI† for structural details).
However, upfield shift to δ 2.18–2.29 in 1H NMR and 25.2–25.6
in 13C NMR were observed, surprisingly, in isolated products
when unsubstituted (3a), alkylsubstituted (3b) or aralkyl guani-
dines (3g, 3h) were used as a substrate under similar conditions.
Therefore, the respective product obtained from reactants 3a, 3b,
3c, 3g and 3h was expected to have a structure different from 4
even though the mass spectra showed expected values corre-
sponding to structure 4. Hence, to confirm this aspect, X-ray
crystallographic study of the product obtained from 3a was
performed.
Fig. 2 X-ray crystal structure of 2-(dimethylamino)-4,8-dimethyl-6H-
pyrimido[1,2-a][1,3,5]triazin-6-one 4i (displacement ellipsoids are
drawn at 50% probability level) CCDC 791289.
The fact that there were clearly differentiated chemical shifts
at δ 10.18 and 9.26 for the product obtained by the reaction of
triethyl orthoacetate with 3a in the 1H NMR spectrum supported
the existence of hydrogen bonding between the peri-carbonyl
and the proximate exocyclic N–H which is not possible in struc-
ture 4. Moreover, similar lowfield shifts of NH proton in 1H
NMR from 10.18–13.20 ppm were observed in 6b–c and 6g–h.
X-ray crystallographic study17 of this product (Fig. 3) revealed
that the product 4a (not isolated) underwent a smooth rearrange-
ment to an isomeric product 6a in situ as suspected from NMR
studies. So, structure 6 was assigned to the rearranged product
with upfield shift, in the cases of 3a, 3b, 3c, 3g and 3h. More-
over, NMR studies were found to be consistent with the X-ray
crystallographic data of 6a (Fig. 3) where hydrogens attached to
N5 have unequal bond lengths and the amino group was found
to be locked in the plane of pyrimido[1,2-a][1,3,5]triazine
nucleus due to the π-electron delocalization with the heterocycle.
The proposed mechanism for the formation of rearranged
product 6 is depicted in Scheme 3. The reaction starts with the
exchange of alkoxy groups of the orthoester (in excess) under
acid catalysis, which then reacted with the guanidine 3 (nucleo-
phile) to give iminium ion intermediate 7. Subsequent loss of
EtOH gave 4. Thermal rearrangement is then assumed to
Fig. 3 X-ray crystal structure of 4-amino-2,8-dimethyl-6H-pyrimido-
[1,2-a][1,3,5]triazin-6-one 6a CCDC 788427.
Scheme 3 Proposed mechanism for the formation of compound 6.
proceed at around 100 °C for substrates 3a, 3b, 3c, 3f and 3g
(i.e. when either R1 or R2 = H) according to Scheme 3. The
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Scheme 5
Scheme 4 Alternate plausible mechanism for the rearrangement in
pyrimido[1,2-a][1,3,5]triazin-6-ones via pyrimidine ring opening
leading to regioisomeric product 12 instead of proposed 10.
mechanism may have involved: (a) acid catalyzed ethanolytic
ring opening of pyrimidine at amide linkage with the formation
of ring open triazine carbenone 6′ (acrylic acids were isolated);
(b) intramolecular nucleophilic attack by N-1 nitrogen of 1,3,5-
triazine on the carbonyl group and subsequent ring closure that
gave final product 6. It is worth mentioning that the thermally
assisted rearrangement of 4-amino-8-methylpyrimido[1,2-a]-
[1,3,5]triazin-6-one
8
to 4-amino-6-methylpyrimido[1,2-a]-
[1,3,5]triazin-6-one 10 was reported14b to have resulted from
1,3,5-triazine ring opening via carbodiimide intermediate 9
(Scheme 4). However, the rearrangement involving pyrimidine
ring opening similar to the one proposed in Scheme 3 (depicted
using hashed arrows in Scheme 4) leading to product 12 via
ketene intermediate 11 could not be avoided. Moreover, careful
analysis of the provided 1H NMR spectral data seems to corrobo-
rate structure 12 (2-amino-8-methylpyrimido[1,2-a][1,3,5]-
triazin-6-one) as ∼1.2 ppm downfield shift of the methine proton
(in blue) signal on the triazine ring after the rearrangement can
only be accounted to the deshielding effect of the neighboring
carbonyl group in 12.
Intramolecular hydrogen bonding between the 4-amino hydro-
gen and carbonyl oxygen (Fig. 3) as well as involvement of
amino group (directly attached to the ring) in π-electron delocali-
zation with the pyrimido[1,2-a][1,3,5]triazin-6-one nucleus pro-
vides additional stability to the rearranged product 6 which
might provide the driving force for such a rearrangement. There-
fore, an attempt was made to assess the relative stability of the
two possible cyclocondensation products-4 and 6 in gas phase
for substitutions a (R1 = R2 = H) and i (R1 = R2 = Me) using
Gaussian 03 software package.18 Regioisomer 5 was also
included in the study as the similar cyclization of benzimidazol-
2-yl guanidines (unsymmetrically substituted in the phenylene
fragment) with one carbon inserting reagents did not proceed
regioselectively in one of our previous works.3 The results of
these calculations are presented in Table 2. Rearranged product
6a was found to be energetically more favourable than 4a
whereas 4i was found to be more favourable over 6i (Table 2).
This was found to be in agreement with the experimental obser-
vation. Theoretical calculations at B3LYP/6-311G 2d,2p//
B3LYP/6-311G d,p explained the formation of exclusively one
regioisomeric product as both 5a and 5i were highly energeti-
cally unfavourable (might be due to steric factors).
Fig. 4 X-ray crystal structure of (E)-2-(dimethylamino)-4-(2-(dimethyl-
amino)prop-1-enyl)-8-methyl-6H-pyrimido[1,2-a][1,3,5]triazin-6-one 14
(displacement ellipsoids are drawn at 50% probability level), CCDC
838638.
synthon-DMA-DMA 13 (N,N-dimethylacetamide dimethyl
acetal) yielded a product having m/z 288.3 (Scheme 5). The
product formation started after 1 hour and completed in
2.5–3 hours. The 1H NMR and 13C spectra of the compound had
two sets of NMe2 signals at 3.10 and 3.15 as well as 37.1 and
37.3 ppm respectively. Based on the above observations, results
of DEPT experiment, as well as the 2D NOESY crosspeaks, it
was suggested that a second molecule of DMA–DMA could
have contributed to the vC(CH3)–NMe2 fragment, although the
stereochemistry around the double bond in the enamine substitu-
ent at position 4 could be E or Z. The structure 14, a new hetero-
cyclic pyrimido[1,2-a][1,3,5]triazin-6-one, was assigned based
on the crystal structure (Fig. 4). Analogous product was obtained
with 3j also.
A reaction mechanism for the formation of the product is pro-
posed in Scheme 6. The mechanism of formation of 1,3,5-tria-
zine 14 can be rationalized through the reaction with an iminium
+
ion, MeC(OMe) = NMe2, derived from 13 to form the required
enamine 15; this is followed by cyclisation and tautomerization
with the loss of HNMe2 to give 4i (not isolated in this case) and
subsequent reaction with the electrophile from the second mol-
ecule of DMA–DMA leading to the isolated product 14.
The comparison of bond lengths obtained from X-ray crystal
structures of three pyrimido[1,2-a][1,3,5]triazin-6-ones 6a, 4i
and 14 revealed interesting findings (Table III, ESI†). The
C4
N3 bond length (C5
N4 according to crystallographic
numbering) in triazine ring of 4i was found to be unusually short
(1.289 Å) suggesting higher order of double bond character
In an attempt to obtain similar pyrimido[1,2-a][1,3,5]triazin-
6-ones, the reaction of 3i with another one carbon electrophilic
whereas C4
N5 bond length (C6
N1 according to
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Experimental
General
Melting points (uncorrected) were determined on a Gallenkamp
melting point apparatus. NMR spectra were recorded on a
Bruker DPX-300 spectrometer using Me2SO-d6 as a solvent and
TMS as an internal reference. IR spectra were performed on a
Perkin Elmer Spectrum 100 FT-IR spectrophotometer in potass-
ium bromide pellets. Mass spectra were obtained on a Shimadzu
LCMS-IT-TOF system using electron spray ionization (ESI)
mode. The course of the reactions was monitored by TLC on
Silica gel 60 F254 plates (Merck, Germany). HPLC analysis was
performed on an Agilent Eclipse XDB-C18 (4.6 × 250 mm,
5 μm) column at 30 °C, with a flow rate of 1 mL min−1 5–90%
Gradients of MeOH/MeCN (solvent A) and H2O (solvent B)
were used as mobile phases. Microwave reactions were con-
ducted using a commercially available monomode microwave
unit (CEM Discover). Elemental analyses were performed on the
Perkin Elmer 2400 Elemental Analyzer Series II.
Scheme 6 Mechanistic rationale for the formation of 14.
crystallographic numbering) of 14 was unusually large
suggesting more sp3 character of bridge head nitrogen. The pyri-
midine and 1,3,5-triazine rings were found to be coplanar for
both 6a and 4i in the crystal structures as well as in their opti-
mized geometries obtained from DFT calculations (vide infra).
However, CvO of pyrimidine ring bent downwards while the
position of 4 enamine side chain of triazine ring is twisted
upwards (torsional angle C1–N1–C6–N3 = 20.6°) increasing
O⋯C10 bond distance in 14 to 2.762 Å compared to O⋯C8
bond distance which is 2.64 Å. Stereochemistry of the enamine
fragment at position 4 was found to be E.
Crystal structure determinations. The single-crystal X-ray
diffraction study was carried out on a Bruker APEX diffracto-
meter attached to a CCD detector and graphite-monochromated
MoKα radiation (λ, 0.71073 Å) using a sealed tube. Absorption
corrections were made with the program SADABS20 and the
crystallographic package SHELXTL21 was used for all
calculations.
Next, the antiproliferative activity of the synthesized
compounds was assessed using MTT assay.19 In particular,
lung A549 and MDA-MB-231 breast cancer cell lines
were used. No appreciable antiproliferative activity was
obtained for all the synthesized compounds except for 2-(3-
chlorophenylamino)-4,8-dimethyl-6H-pyrimido[1,2-a][1,3,5]-
triazin-6-one (4e) which demonstrated IC50 value of 37.5
2.8 μM and 51.2 3.5 μM for A549 and MDA-MB231 cell line
respectively.
General method for the preparation of 3a–j
Method A procedure 1. Into a 5 mL microwave vessel was
added N-(4-substituted-6-oxo-1,6-dihydropyrimidin-2-yl)cyana-
mide (2 mmol) followed by amine hydrochloride (2.12 mmol)
and isopropanol/ACN (1.0 ml). The vial was sealed and the
mixture was irradiated at 160–170 °C for 15 min and allowed to
cool. The white solid obtained was filtered, washed with solution
of sodium hydrogen carbonate and cold water and dried.
Procedure 2. Into a 5 mL microwave vessel was added N-(4-
substituted-6-oxo-1,6-dihydropyrimidin-2-yl)cyanamide (2 mmol),
amine (2.1 mmol) followed by the slow addition of a 2 N sol-
ution of TMSCl (1.04 mL, 2.1 mmol, 1.1 equiv) in CH3CN
under cold conditions. After the vial was capped, reaction
mixture was irradiated for 12 min at 160 °C. After the mixture
was cooled to approximately 60 °C, iPrOH (0.55mL, 6 mmol,
3.0 equiv) was added. The mixture was stirred for 10 s and then
irradiated a second time at 125 °C for 30 s. Upon cooling, the
hydrochloride salts of guanidines 3 precipitated, and it was col-
lected, washed with cold CH3CN and then with solution of
sodium hydrogen carbonate and cold water and finally dried to
obtain slightly better yields of pyrimidinyl guanidines.
Conclusion
In summary, the reactions of N-(4-methyl-6-oxo-1,6-dihydropyr-
imidin-2-yl)guanidines with triethyl orthoacetate were investi-
gated. 2-amino-4-methylpyrimido[1,2-a][1,3,5]triazin-6-ones 4
and the products of unexpected rearrangement, namely 4-amino-
2-methylpyrimido[1,2-a][1,3,5]triazin-6-ones 6, were obtained
depending upon the starting guanidine 3. The rearrangement
involved opening of the pyrimidine ring as was shown by
isolation of acrylic acid intermediates. The requirements for
the rearrangement were discussed on the basis of results
obtained from experimental and theoretical studies. This
approach opened the opportunities to insert different
substituents at position 2 and position 4 of triazine ring, depend-
ing upon the starting guanidine. The attempt to obtain similar
pyrimido[1,2-a][1,3,5]triazin-6-ones using DMA–DMA was
unsuccessful, as unexpected cyclocondensation product 14
formed as a result of overreaction. Further work is in progress to
explore the propensity of the reagent to form C–C bond
formation.
Method B. Biguanides were synthesized according to
Uohama and Sakai22 and subsequent pyrimidine ring annulation
was done using method described by Curd et al.16
Experimental data for some representative compounds:
N-(4-Methyl-6-oxo-1,6-dihydropyrimidin-2-yl)guanidine (3a).
1
Yield: 93%; Method B; mp >300 °C; lit23 mp 304–305 °C; H
NMR (300 MHz, Me2SO-d6): δ 2.08 (3H, s, Me), 5.58 (1H, s,
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H-5), 8.03 (4H, br. s, guanidino NHs), 11.52 (1H, br. s, NH);
13C NMR (75 MHz, Me2SO-d6): δ 23.2 (Me), 103.0 (CH),
158.5, 159.8, 163.0 (br. s), 166.9 (br. s).
NH–C(vNH)N), 10.58 (1H, br. s, NH); 13C NMR (75 MHz,
Me2SO-d6): δ 23.6 (CH3), 36.4 (N(CH3)2), 102.2 (C-5), 157.9
(C-2), 158.3 (C-4), 162.9 (CvNH), 163.7 (CvO).
1-(6-Oxo-4-phenyl-1,6-dihydropyrimidin-2-yl)guanidine (3b).
Yield: 37%; Method B (using NaOMe instead of aq NaOH in
second step); mp 273 °C (decomposed); lit24 mp 273 °C;
LC-MS (APCI) m/z = 229.1 (MH+); 1H NMR (300 MHz,
Me2SO-d6): d 6.24 (1H, s, CH), 7.87 (2H, d, J = 7.9 Hz, H-2′
and H-6′), 7.38–7.49 (3H, m, H-3′, H-4′ and H-5′), 8.27 (4H, br.
s, NHC(vNH)NH2), 11.53 (1H, s, NH).
N-(4-Methyl-6-oxo-1,6-dihydropyrimidin-2-yl)morpholine-4-
̲
carboxamidine (3j). Yield 36%; Method A (procedure 1/2) or
1
Method B; mp 271–272 °C (EtOH); lit28 mp 272–273 °C; H
NMR (300 MHz, Me2SO-d6): δ 2.03 (3H, s, Me), 2.75 (3H, d,
3J = 4.5 Hz, N Me), 5.49 (1H, s, H-5), 7.96–9.20 (3H, br. s,
NH–C(vNH)NH), 10.86 (1H, br. s, NH).
N-(4-Methyl-6-oxo-1,6-dihydropyrimidin-2-yl)indoline-1-car-
boxamidine (3k). Yield 61%; Method A (procedure 1/2); mp
N-Methyl-N′-(4-methyl-6-oxo-1,6-dihydropyrimidin-2-yl)gua-
nidine (3c). Yield 62%; Method A (procedure 1/2); mp
272–273 °C; TLC (silica gel, MeOH/CH2Cl2, 1 : 6): Rf 0.38. H
NMR (300 MHz, Me2SO-d6): δ 2.03 (3H, s, CH3), 2.75 (3H, d,
3J = 4.5 Hz, NCH3), 5.49 (1H, s, H-5), 7.96–9.20 (3H, br. s,
NH–C(vNH) NH), 10.86 (1H, br. s, NH).
1
268–269 °C; H NMR (300 MHz, Me2SO-d6): δ 2.10 (3H, s,
1
3
3
CH3), 3.15 (2H, t, J = 8.5 Hz, CH2), 3.97 (2H, t, J = 8.5 Hz,
3
3
CH2), 6.93 (1H, t, J = 7.2 Hz), 7.09 (1H, t, J = 7.7 Hz), 7.17
3
3
(1H, d, J = 7.2 Hz), 8.64 (1H, d, J = 8.3 Hz), 11.24 (1H, s,
NH). 13C NMR (75 MHz, Me2SO-d6): δ 23.5 (CH3), 26.4 (3′-
CH2), 47.3 (2′-CH2), 103.5 (C-5), 118.1, 122.1, 124.1, 126.9,
131.6, 142.4, 157.9 (C-2), 155.3 (C-4), 162.7 (CvNH), 163.7
(CvO).
1-(4-Methyl-6-oxo-1,6-dihydropyrimidin-2-yl)-3-phenylguani-
dine (3d). Yield 90%; Method A (procedure 1/2) or Method B;
mp 248–249 °C; lit25 mp 244–246 °C; 1H NMR (300 MHz,
Me2SO-d6): δ 2.09 (3H, s, Me), 5.60 (1H, s, CH), 7.00 (1H, t, J
= 7.2 Hz, H-4′), 7.26 (2H, t, J = 7.5 Hz, H-3′ and H-5′), 7.66
(2H, d, J = 7.5 Hz, H-2′ and H-6′), 8.12 (2H, br. s, NH–C
(vNH)N), 9.04 (1H, s, NH), 11.18 (1H, s, NH); 13C NMR
(75 MHz, Me2SO-d6): 23.5 (Me), 103.7 (C-6), 120.3, 122.3,
128.6, 138.9, 155.9, 158.3, 163.0, 163.7.
1-(3-Bromophenyl)-3-(6-oxo-4-(trifluoromethyl)-1,6-dihydro-
pyrimidin-2-yl)guanidine (3l). Yield 70%; mp 161–162 °C
1
(EtOH); H NMR (300 MHz, Me2SO-d6): δ 6.18 (1H, s, H-7),
7.12–7.28 (2H, m, HAr), 7.74–7.89 (2H, m, HAr), 8.32 (1H, br.
s, NH), 10.19 (1H, br. s, NH), 12.05 (1H, br. s, NH); 13C NMR
3
(75 MHz, Me2SO-d6): δ 103.4 (q, JC–F = 3.1 Hz, C-7), 119.1,
120.9 (q,1JC–F = 274.4 Hz, CF3), 121.4, 121.9, 122.8, 125.0,
1-(3-Chlorophenyl)-3-(4-methyl-6-oxo-1,6-dihydropyrimidin-
2-yl)guanidine (3e). Yield 90%; Method A (procedure 1/2) or
Method B; mp 235–236 °C; lit26 mp 239 °C; 1H NMR
(300 MHz, Me2SO-d6): δ 2.10 (s, 3H, CH3), 5.62 (s, 1H, CH),
7.02 (dd, 1H, J = 7.9 Hz, 1.2 Hz, H-4′), 7.26 (t, 1H, J = 8.1 Hz,
H-5′), 7.63 (d, 1H, J = 7.9 Hz, H-6′), 7.75 (s, 1H, H-2′), 8.24
(br. s, 2H,), 9.10 (s, 1H, NH), 11.43 (s, 1H, NH); 13C NMR
(75 MHz, Me2SO-d6): 26.7 (CH3), 107.4 (C-5), 121.8, 122.5,
125.2, 133.4, 136.3, 144.0 (C-1′), 158.9, 161.5, 166.2, 167.0.
2
130.4, 140.8, 150.9 (q, JC–F = 33.3 Hz, C-8), 156.2, 159.5,
163.4.
N-(4-Methyl-6-oxo-1,6-dihydropyrimidin-2-yl)cyanamide
(1). Yield 61%; mp >300 °C; lit29 mp >300 °C; TLC (silica gel,
MeOH/CH2Cl2, 1 : 6): Rf 0.43. 1H NMR (300 MHz, Me2SO-d6):
δ 1.93 (3H, s, Me), 5.20 (1H, s, C-5), 10.22 (1H, s, NH); 13C
NMR (75 MHz, Me2SO-d6): δ 23.8 (Me), 98.7 (C-5), 120.9
(CN), 161.6 (C-2), 164.4 (C-4), 165.6 (CvO).
1-(4-Methoxyphenyl)-3-(4-methyl-6-oxo-1,6-dihydropyrimi-
din-2-yl)guanidine (3f). Yield 76%; Method A (procedure 1/2)
1
or Method B; mp 256–258 °C lit27 mp 259–260 °C; H NMR
General method for the preparation of 8(2)-substituted 4
(8)-methylpyrimido[1,2-a][1,3,5]triazin-6(4)-ones 4 or 6:
(300 MHz, Me2SO-d6): δ 2.01 (3H, s, Me), 3.72 (3H, s, OMe),
4.35 (2H, d, J = 4.9 Hz, CH2), 5.46 (1H, s, CH), 6.89 (2H, d, J
= 8.3 Hz, H-3′ and H-5′), 7.28 (2H, d, J = 8.7 Hz, H-2′ and
H-6′), 7.82 (2H, br. s, NH–C(vNH)N), 10.67 (1H, s, NH).
Guanidines (3a–j), 0.25 ml acetic acid and excess triethyl
orthoacetate were refluxed under nitrogen atmosphere for
0.3–9 h. Solvent was evaporated to dryness on rotary evaporator,
purified using column chromatography and finally recrystallised
using suitable solvent.
1-(4-Chlorobenzyl)-3-(4-methyl-6-oxo-1,6-dihydropyrimidin-
2-yl)guanidine (3g). Yield 68%; Method B; mp 227–228 °C; 1H
NMR (300 MHz, Me2SO-d6): δ 2.04 (3H, s, Me), 5.22 (2H, s,
CH2), 5.60 (1H, s, H-5), 7.14 (2H, br. s, NH–C(vNH)N), 7.33
(2H, d, J = 8.7 Hz, H-3′ and H-5′), 7.47 (2H, d, J = 8.7 Hz, H-2′
and H-6′), 10.71 (1H, br. s, NH); 13C NMR (75 MHz, Me2SO-
d6): δ 23.4 (Me), 42.7 (CH2), 101.3 (C-5), 127.8 (C3′ and C-5′),
130.0 (C-2′ and C-4′), 131.1 (C-1′), 137.7 (C-4′), 157.5 (C-2),
159.7 (C-4), 161.0, 162.6.
4,8-Dimethyl-2-(phenylamino)-6H-pyrimido[1,2-a][1,3,5]-
triazin-6-one (4d). mp 220–221 °C (EtOAc); TLC (silica gel,
9 : 1 EtOAc/hexane): Rf 0.53; LC–MS (ESI) analysis (m/z) calcd
267.1120; found 268.1141(MH+). Anal. Calcd for C14H13N5O
(267.1120): found 62.61, 4.95, 26.03; requires C, 62.91; H,
1
4.90; N, 26.20. H NMR (300 MHz, Me2SO-d6): δ 2.18 (3H, s,
3
8-Me), 2.90 (3H, s, 4-Me), 5.92 (1H, s, H-7), 7.13 (1H, t, J =
3
N,N-Dimethyl-N′-(4-methyl-6-oxo-1,6-dihydropyrimidin-2-yl)-
guanidine (3i). Yield 59%; Method A (procedure 1/2) or
Method B; mp 227–228 °C; TLC (silica gel, MeOH/CH2Cl2,
7.4 Hz, H-5′), 7.38 (2H, t, J = 7.7 Hz, H-3′ and H-5′), 7.86
3
(2H, d, J = 7.5 Hz, H-2′ and H-6′), 10.63 (1H, s, NH); 13C
NMR (75 MHz, Me2SO-d6): δ 23.7 (2-Me), 26.2 (8-Me), 103.6
(C-5), 120.4 (C-2′ and C-6′), 123.9 (C-4′), 128.6 (C-3′ and
C-5′), 138.0 (C-1′), 152.9, 156.8 (C-2), 160.0, 163.8, 166.7; IR
1
1 : 6): Rf 0.57. H NMR (300 MHz, Me2SO-d6): δ 2.03 (3H, s,
CH3), 2.97 (6H, s, N(CH3)2), 5.45 (1H, s, H-5), 8.46 (2H, br. s,
This journal is © The Royal Society of Chemistry 2012
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2-(Indolin-1-yl)-4,8-dimethyl-6H-pyrimido[1,2-a][1,3,5]-
triazin-6-one (4k). mp 212–213 °C (EtOAc); TLC (silica gel,
9 : 1 EtOAc/hexane): Rf 0.32; Anal. Calcd for C16H15N5O
(293.1277): found C, 65.27; H, 5.14; N, 23.74; requires: C,
(KBr); v 3109 br NH, 1685 CvO, 1627, 1535, 1244, 1036,
821, 752.
2-(3-Chlorophenylamino)-4,8-dimethyl-6H-pyrimido[1,2-a]-
[1,3,5]triazin-6-one (4e). mp 239–240 °C (EtOAc); TLC (silica
gel, 9 : 1 EtOAc/hexane): Rf 0.60; LC–MS (ESI) analysis (m/z)
calcd 301.0730; found 302.0708 (MH+); Anal. Calcd for
C14H12ClN5O (301.0730): found: C, 55.49; H, 4.05; Cl 11.50;
1
65.52; H, 5.15; N, 23.88. H NMR (300 MHz, Me2SO-d6): δ
2.18 (3H, s, 8-Me) and 2.21 (3H, s, 8-Me), 2.94 (3H, s, 4-Me)
3
and 3.00 (3H, s, 4-Me), 3.20 (2H, t, J = 8.5 Hz, 3′CH2), 4.19
3
3
(1H, t, J = 8.3 Hz, CH2) and 4.32 (1H, t, J = 8.9 Hz, CH2),
5.92 (2H, s, CH), 6.98–7.16 (2H, m, H-4′), 7.21–7.40 (4H, m,
H-5′ and H-6′), 8.29 (1H, d, 3J = 8.2 Hz, H-7′), 8.49 (1H, d, 3J =
8.1 Hz, H-7′); 13C NMR (75 MHz, Me2SO-d6): δ 23.5 (Me),
26.4 (3′-CH2), 47.3 (2′-CH2), 103.5 (C-5), 118.1, 122.1, 124.1,
126.9, 131.6, 142.4, 157.9 (C-2), 155.3 (C-4), 162.7 (CvNH),
163.7 (CvO). IR (KBr); v 3446 br NH, 2935 (CH), 2918, 2854,
1707 CvO, 1624, 1576, 1481, 1456, 1249, 1195, 785.1.
1
N, 22.98; requires C, 55.73; H, 4.01; Cl, 11.75; N, 23.21. H
NMR (300 MHz, Me2SO-d6): δ 2.19 (1H, s, 8-Me), 2.91 (1H, s,
3
4-Me), 5.96 (1H, s, H-7), 7.18 (1H, d, J = 8.3 Hz, H-4′), 7.40
3
3
(1H, t, J = 8.1 Hz, H-5′), 7.76 (1H, d, J = 7.9 Hz, H-6′), 8.06
(1H, s, H-2′), 10.79 (1H, s, NH); 13C NMR (75 MHz, Me2SO-
d6): 23.8 (8-Me), 26.2 (4-Me), 104.0 (C-7), 118.7, 119.5, 123.5,
130.3, 133.0, 139.7 (C-1′), 152.7, 156.9, 160.0, 164.3, 166.7; IR
(KBr); v 3273 br NH, 3103 (CH), 3082, 1678 CvO, 1636,
1095, 866, 788, 717.
2-(3-Bromophenylamino)-4-methyl-8-(trifluoromethyl)-6H-
pyrimido[1,2-a][1,3,5]triazin-6-one (4l). Yield: 70%; mp
216–217 °C (EtOH); TLC (silica gel, 9 : 1 EtOAc/hexane): Rf
2-(4-Methoxyphenylamino)-4,8-dimethyl-6H-pyrimido[1,2-a]-
[1,3,5]triazin-6-one (4f). mp 177–178 °C (EtOAc); TLC (silica
gel, 9 : 1 hexane/EtOAc): Rf 0.25; LC–MS (ESI) analysis (m/z)
calcd 297.1226; found 298.1296 (MH+); Anal. Calcd for
C15H15N5O2 (297.1226): found: C, 60.47; H, 5.10; N, 23.29;
requires: C, 60.60; H, 5.09; N, 23.56. 1H NMR (300 MHz,
Me2SO-d6): δ 2.16 (3H, s, 8-Me), 2.88 (3H, s, 4-Me), 3.75 (3H,
1
0.90. H NMR (300 MHz, Me2SO-d6): δ 2.91 (1H, s, Me), 6.54
3
(1H, s, H-7), 7.32–7.42 (2H, m, H-4′ and H-5′), 7.86 (1H, d, J
= 6.8 Hz, H-6′), 8.10 (1H, s, H-2′), 11.08 (1H, s, NH); 13C
NMR (75 MHz, Me2SO-d6): δ 26.07 (CH3), (C-4), 103.3 (q,
3JC–F = 2.6 Hz, C-7), 119.5, 120.6 (q,1JC–F = 275.4 Hz, CF3),
2
121.5, 122.8, 127.1, 130.8, 139.2, 152.6 (q, JC–F = 34.0 Hz,
3
C-8), 155.1, 157.2, 160.2, 164.4; IR (KBr); v 3282 NH, 3081,
2945, 1699 CvO, 1631, 1608, 1587, 1552, 1465, 1375, 1340,
1278, 1192, 1155, 1101, 1083, 925, 875, 788, 707; % purity
>95% tR = 7.1 min.
s, OMe), 5.89 (1H, s, H-7), 6.96 (2H, d, J = 8.8 Hz, H-3′ and
3
H-5′), 7.74 (2H, d, J = 8.8 Hz, H-2′ and H-6′), 10.52 (1H, s,
NH); 13C NMR (75 MHz, Me2SO-d6): 23.7 (4-Me), 26.2 (8-
Me), 55.2 (OMe), 103.2 (C-7), 113.8 (C-2′ and C-6′), 122.1
(C-3′ and C-5′), 130.9 (C-1′), 153.1 (C-4′), 155.8, 156.5, 160.1,
163.5, 166.7; IR (KBr); v 3109, 2920 (CH), 2850, 1670 CvO,
1627, 1541, 1419, 1236, 1174, 1028, 831, 788.
4-Amino-2,8-dimethyl-6H-pyrimido[1,2-a][1,3,5]triazin-6-one
(6a). mp 264–265 °C; TLC (silica gel, CH2Cl2): Rf 0.55; LC–
MS (ESI) analysis (m/z) calcd 191.0807; found 192.0841
(MH+); Anal. Calcd for C8H9N5O (191.0807): found C, 50.35,
H, 4.95, N, 36.03; requires: C, 50.26; H, 4.74; N, 36.63. 1H
NMR (300 MHz, Me2SO-d6): δ 2.18 (1H, s, 2-Me), 2.24 (1H, s,
8-Me), 6.04 (1H, s, H-7), 9.26 (1H, s, NH), 10.18 (1H, s, NH);
13C NMR (75 MHz, Me2SO-d6): 23.8 (8-Me), 25.2 (2-Me),
104.6 (C-7), 152.9, 156.8, 162.7, 167.6, 172.7; IR (KBr); v
3294 NH, 3116 br, 1695 CvO, 1647, 1575, 1400, 1197, 1170,
1060, 821, 792, 748, 702.
2-(Dimethylamino)-4,8-dimethyl-6H-pyrimido[1,2-a][1,3,5]-
triazin-6-one (4i). mp 190–191 °C (EtOAc); TLC (silica gel,
CH2Cl2): Rf 0.30; LC–MS (ESI) analysis (m/z) calcd 219.112;
found 220.1198 (MH+); Anal. Calcd for C10H13N5O (219.112):
found: C, 54.42; H, 5.87; N, 31.69; requires: C, 54.78; H, 5.98;
1
N, 31.94. H NMR (300 MHz, Me2SO-d6): δ 2.12 (3H, s, 8-
Me), 2.85 (3H, s, 4-Me), 3.14 (3H, s, N(Me)2), 3.25 (3H, s, N
(Me)2), 5.78 (1H, s, H-7); 13C NMR (75 MHz, Me2SO-d6): δ
23.8 (8-Me), 26.6 (4-Me), 36.3 (N(Me)2, 36.4 (N(Me)2, 101.8
(C-7), 153.1, 158.0, 160.1, 163.5, 167.2 (CvO); IR (KBr); v
3420 br NH, 3034 (CH), 2978, 1714, 1670 CvO, 1620, 1516,
1317, 1238, 1192, 1078, 1033, 966, 825, 794, 717.
4-Amino-2-methyl-8-phenyl-6H-pyrimido[1,2-a][1,3,5]triazin-
6-one (6b). Yield: 58%; mp 258–259 °C (80 : 20 EtOAc/
hexane); TLC (silica gel, 9 : 1 EtOAc/hexane): Rf 0.45; % purity
>95%; tR 8.9 min. 1H NMR (300 MHz, Me2SO-d6): δ 2.29 (1H,
s, 2-CH3), 6.77 (1H, s, H-7), 7.44–7.61 (3H, m, H-3′, H-4′,
3
4,8-Dimethyl-2-morpholino-6H-pyrimido[1,2-a][1,3,5]triazin-
6-one (4j). mp 191–192 °C; TLC (silica gel, 9 : 1 CH2Cl2/
hexane): Rf 0.40; LC–MS (ESI) analysis (m/z) calcd 261.1;
found 262.0 (MH+); Anal. Calcd for C12H15N5O2 (261.1): found
C, 55.22; H, 5.77; N, 26.86; requires: C, 55.16; H, 5.79; N,
H-5′), 8.12 (2H, d, J = 8.1 Hz, H-2′ and H-6′), 9.32 (1H, s,
NH), 10.22 (1H, s, NH); 13C NMR (75 MHz, Me2SO-d6): 25.2
(2-CH3), 101.2 (C-7), 127.1, 128.6, 131.1, 135.6 (C-1′), 153.4,
156.8, 162.3, 163.6, 172.9; IR (KBr); v 3344 NH, 3213, 1674
CvO, 1624, 1570, 1544, 1448, 1382, 1220, 1174, 908, 778.
1
26.80. H NMR (300 MHz, Me2SO-d6): δ 2.13 (3H, s, 8-Me),
2.86 (3H, s, 4-Me), 3.67 (4H, t, J = 4.5 Hz, (CH2)2O), 3.78 (2H,
t, J = 4.3 Hz, N(CH2), 3.89 (2H, t, J = 4.3 Hz, N(CH2), 5.81
(1H, s, H-7); 13C NMR (75 MHz, Me2SO-d6): δ 25.0 (8-Me),
27.8 (4-Me), 44.8 (CH2), 45.3 (CH2), 66.7 (CH2), 67.1 (CH2),
103.3 (C-7), 154.4, 158.3, 161.2, 165.5, 168.3 (CvO); IR
(KBr); v 3388 br NH, 3076 (CH), 2950, 1627 CvO, 1543,
1508, 1406, 1352, 1246, 1181, 1028, 966, 834.
2,8-Dimethyl-4-(methylamino)-6H-pyrimido[1,2-a][1,3,5]-
triazin-6-one (6c). mp 166–167 °C (EtOAc); TLC (silica gel,
9 : 1 EtOAc/hexane): Rf 0.16; LC–MS (ESI) analysis (m/z) calcd
205.0964; found 206.0946 (MH+); Anal. Calcd for C9H11N5O
(205.0964): found: C, 52.49, H, 5.69, N, 32.83; requires: C,
1
52.67; H, 5.40; N, 34.13. H NMR (300 MHz, Me2SO-d6): δ
2.18 (3H, s, 2-Me), 2.28 (3H, s, 8-Me), 2.98 (3H, d, J = 4.9 Hz,
4594 | Org. Biomol. Chem., 2012, 10, 4586–4596
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NMe), 6.07 (1H, s, H-7), 10.90 (1H, d, J = 4.5 Hz, NH); 13C
NMR (75 MHz, Me2SO-d6): 23.7 (8-Me), 25.6 (2-Me), 28.4
(NMe), 104.8 (C-7), 152.6, 155.5, 163.0, 167.5, 172.3; IR
(KBr); v 3324 NH, 3201, 1690 CvO, 1642, 1574, 1440, 1187,
1165, 1065, 793, 774.
Me2SO-d6): δ 2.12 (3H, s, 4-Me), 2.17 (3H, s, Me), 3.74 (3H, s,
OMe), 4.57 (2H, d, J = 5.7 Hz, CH2), 5.66 (1H, s, H-3), 7.37
(2H, d, J = 8.7 Hz, H-3′ and H-5′), 7.48 (1H, d, J = 8.3 Hz,
H-2′ and H-6′), 9.30 (1H, t, J = 5.7 Hz, NH), 11.63 (1H, br s,
NH), 13.72 (1H, s, COOH).
3
3
4-(4-Chlorobenzylamino)-2,8-dimethyl-6H-pyrimido[1,2-a]-
[1,3,5]triazin-6-one (6g). mp 133–134 °C; TLC (silica gel, 9 : 1
EtOAc/hexane): Rf 0.8; LC–MS (ESI) analysis (m/z) calcd
315.0887; found 316.0817 (MH+); Anal. Calcd for
C15H14ClN5O (315.0887): found C, 56.99; H, 4.51; Cl 11.44; N,
Western blot analysis
Equal amounts of protein (50 μg) in each lysate sample were sep-
arated by 10% sodium dodecyl sulfate (SDS)–polyacrylamide
gel. Proteins were then electroblotted on nitrocellulose mem-
branes and the blot was probed with a primary antibody followed
by a secondary antibody (rabbit anti-PARP, goat anti-β-actin)
conjugated to horseradish peroxidase.
1
22.05; requires C, 57.06; H, 4.47; Cl, 11.23; N, 22.18. H NMR
(300 MHz, Me2SO-d6): δ 2.19 (3H, s, 8-Me), 2.25 (3H, s, 2-
3
Me), 4.69 (2H, s, CH2), 6.08 (1H, s, H-7), 7.39 (2H, d, J = 8.7
3
Hz, H-3′ and H-5′), 7.43 (2H, d, J = 8.7 Hz, H-2′ and H-6′),
11.43 (1H, br. s, NH); 13C NMR (75 MHz, Me2SO-d6): 23.8 (2-
Me), 25.6 (8-Me), 43.9 (CH2), 105.0 (C-7), 128.3 (C-3′and
C-5′), 129.5 (C-2′ and C-6′), 131.8 (C-4′), 136.4 (C-1′), 152.7,
155.2, 163.2, 167.6, 172.3; IR (KBr); v 3170 br NH, 1689
CvO, 1618, 1411, 1377, 1344, 827, 794, 711.
(E)-2-(Dimethylamino)-4-(2-(dimethylamino)prop-1-enyl)-8-
methyl-6H-pyrimido[1,2-a][1,3,5]triazin-6-one (14). Appropriate
guanidine and excess equivalent of DMA–DMA (with/without
toluene) were refluxed under nitrogen atmosphere. The reaction
was monitored using TLC. The solvent was evaporated to
dryness on rotary evaporator, purified using column chromato-
graphy and finally recrystallized using suitable solvent.
Yield: 73%; physical appearance: orange; mp 212–213 °C
(MeOH/EtOAc); LC–MS (ESI) analysis (m/z) calcd 288.17;
found: 289.1 (MH+); Anal. calc. for C14H20N6O (288.17): C,
4-(4-Methoxybenzylamino)-2,8-dimethyl-6H-pyrimido[1,2-a]-
[1,3,5]triazin-6-one (6h). mp 138–139 °C; TLC (silica gel, 9 : 1
EtOAc/hexane): Rf 0.26; LC–MS (ESI) analysis (m/z) calcd
311.1382; found 312.1409 (MH+); Anal. Calcd for C16H17N5O2
(311.1382): found: C, 61.78; H, 5.42; N, 22.52; requires: C,
1
1
58.31; H, 6.99; N, 29.15; found: 58.54; H, 7.17; N, 28.89. H
61.72; H, 5.50; N, 22.49. H NMR (300 MHz, Me2SO-d6): δ
NMR (300 MHz, Me2SO-d6): δ 2.06 (3H, s, 9-Me), 2.64 (3H, s,
4-Me), 3.05 (6H, s, (N(Me)2), 3.05 (6H, s, (N(Me)2), 3.10 (6H,
s, (NMe)2), 5.63 (1H, s, 8-CH), 6.13 (1H, s, = CH-N); 13C NMR
(75 MHz, Me2SO-d6): 18.2 (4-Me), 23.6 (9-Me), 36.2 (N(Me)2),
36.4 (N(Me)2), 90.9 (vCH–N), 101.1 (C-8), 154.7, 157.5,
158.4 (C-5), 157.5, 158.4, 161.3, 164.9, 166.1.
2.19 (3H, s, 2-Me), 2.28 (3H, s, 8-Me), 3.74 (3H, s, OMe), 4.62
(2H, d, J = 5.7 Hz, CH2), 6.07 (1H, s, H-3), 6.91 (1H, d, J =
3
8.7 Hz, H-3′ and H-5′), 7.34 (1H, d, 3J = 8.3 Hz, H-2′ and H-6′),
11.36 (1H, t, J = 5.7 Hz, NH); 13C NMR (75 MHz, Me2SO-d6):
23.8 (8-Me), 25.6 (2-Me), 44.1 (CH2), 55.0 (OMe), 104.9 (C-7),
113.8 (C-2′ and C-6′), 128.9 (C-1′), 129.2 (C-3′ and C-5′), 152.6
(C-4′), 155.1, 158.6, 163.3, 167.7, 172.4; IR (KBr); v 3109 br
NH, 2950 (CH), 1683 CvO, 1629, 1516, 1458, 1379, 1342,
1172, 1114, 1026, 821, 792.
(E)-4-(2-(Dimethylamino)prop-1-enyl)-8-methyl-2-morpho-
lino-6H-pyrimido[1,2-a][1,3,5]triazin-6-one (14j). Yield: 69%;
physical appearance: yellow; mp 217–218 °C (MeOH/EtOAc);
LC–MS (ESI) analysis (m/z) calcd 330.1; found: 331.0 (MH+);
1H NMR (300 MHz, Me2SO-d6): δ 2.06 (3H, s, 9-Me), 2.61
(3H, s, 4-Me), 3.11 (6H, s, (N(Me)2), 3.65 (4H, m, (CH2)2, 3.72
(4H, m, (CH2)2), 5.67 (1H, s, 8-CH), 6.17 (1H, s,vCH–N); 13C
NMR (75 MHz, Me2SO-d6): 18.5 (4-Me), 23.5 (9-Me), 43.8 (O
(CH2)2), 65.8 (N(CH2)2), 91.2 (vCH–N), 101.5 (C-8), 154.8,
157.6, 158.0 (C-5), 161.2, 165.4, 165.9; IR (KBr); v 3352 br.,
1681 CvO, 1616, 1565, 1171, 979.
3-(6-Methyl-4-(phenylamino)-1,3,5-triazin-2(1H)-ylidene-
amino)but-2-enoic acid (6′d). LC–MS (ESI) analysis (m/z) calcd
285.1226; found 285.1293 (MH+); TLC (silica gel, 9 : 1 EtOAc/
hexane): Rf 0.16; Anal. Calcd for C14H15N5O2 (285.1226):
found C, 56.18, H 4.89, N 23.58; requires C, 58.94; H, 5.30; N,
1
24.55. H NMR (300 MHz, Me2SO-d6): δ 2.17 (3H, s, 8-Me),
2.25 (3H, s, 4-Me), 5.77 (1H, s, CH), 7.13 (1H, t, J = 7.3 Hz,
H-4′), 7.33 (2H, t, 3J = 7.7 Hz, H-3′ and H-5′), 7.84 (2H, d, 3J =
7.9 Hz, H-2′ and H-6′), 10.94 (1H, s, NHPh), 12.06 (1H, br s,
NH), 13.75 (1H, br s, COOH).
Acknowledgements
3-(4-(4-Methoxyphenylamino)-6-methyl-1,3,5-triazin-2(1H)-
ylideneamino)but-2-enoic acid (6′f). LC–MS (ESI) analysis
(m/z) calcd 315.1331; found 316.1255 (MH+); TLC (silica gel,
9 : 1 hexane/EtOAc): Rf 0.11; Anal. Calcd for C15H17N5O3
(315.1331): found C, 57.44; H, 5.21; N, 22.45; requires C,
This work is supported by the National Medical Research
Council, Singapore (NMRC/NIG/0020/2008) and the National
University of Singapore (R-148–050-091-101/133 and R-148-
000-069-112). The authors thank Koh Lip Lin, Tan Geok Kheng
and Woo Su Fen for the X-ray crystallography study and Ms Tan
Beejen for assisting in western blot analysis of compound 4e.
1
57.13; H, 5.43; N, 22.21. H NMR (300 MHz, Me2SO-d6): δ
2.17 (3H, s, 8-Me), 2.24 (3H, s, 4-Me), 3.75 (3H, s, OMe), 5.74
3
(1H, s, CH), 6.87 (2H, d, J = 8.3 Hz, H-2′and H-6′), 7.74 (2H,
3
Notes and references
d, J = 9.0 Hz, H-3′and H-5′), 10.82 (1H, s, NHPh), 11.97 (1H,
s, NH), 13.72 (1H, s, COOH).
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