Synthesis of 5-phenyl-10-methyl-7H-pyrimido[4,5-f][1,2,4]triazolo[4,3-a][1,4]diazepine and its evaluation as an anticonvulsant agent

Article abstract of DOI:10.1139/v98-221

The homolytic benzoylation (benzoyl radical) of 5-tert-butylcarbonylaminopyrimidine (6, 1 equiv.) in the presence of benzaldehyde (3 equiv.), water, sulfuric acid, and acetic acid, upon treatment with FeSO₄·7H₂O (3 equiv.) and 70% t-

Full text of DOI:10.1139/v98-221

216
Synthesis of 5-phenyl-10-methyl-7H-
pyrimido[4,5-f][1,2,4]triazolo[4,3-a][1,4]diazepine
and its evaluation as an anticonvulsant agent
Oludotun A. Phillips, K.S. Keshava Murthy, Charles Y. Fiakpui,
and Edward E. Knaus
Abstract: The homolytic benzoylation (benzoyl radical) of 5-tert-butylcarbonylaminopyrimidine (6, 1 equiv.) in the
presence of benzaldehyde (3 equiv.), water, sulfuric acid, and acetic acid, upon treatment with FeSO4·7H2O (3 equiv.)
and 70% t-BuOOH (3 equiv.) at 5–10°C for 10 min afforded a mixture of 4-benzoyl-5-tert-butylcarbonylaminopyrimidine (7,
23%), 4,6-dibenzoyl-5-tert-butylcarbonylaminopyrimidine (8, 44%), and 4-benzoyl-5-tert-butylcarbonylamino-6-
methylpyrimidine (9, 10%). When a similar reaction was performed using 1 equiv. each of PhCHO, FeSO4·7H2O, and
t-BuOOH, to prevent formation of the 4,6-dibenzoyl product 8, the monobenzoyl (7, 38%) and 4-benzoyl-6-methyl (9,
6%) products were obtained. A similar homolytic benzoylation of 5-bromopyrimidine (10) using 1.5 equiv. of reagents
to generate the benzoyl radical afforded 4-benzoyl-5-bromopyrimidine (11, 61%) as the predominant product.
Elaboration of 11 via a six-step reaction sequence afforded 2-hydrazino-5-phenyl-3H-pyrimido[5,4-e][1,4]diazepine (17)
in 5.2% overall yield. The acid-catalyzed reaction of 17 with triethyl orthoacetate gave the title compound 5-phenyl-
10-methyl-7H-pyrimido[4,5-f][1,2,4]triazolo[4,3-a][1,4]diazepine (18, 62%). The triazolo compound 18 was more potent
than valproic acid (Depakene®) in both the subcutaneous metrazol (scMet) and maximal electroshock (MES)
anticonvulsant screens, and more potent than clonazepam in the MES anticonvulsant screen but less potent than
clonazepam in the scMet anticonvulsant screen.
Key words: homolytic benzoylation, pyrimidines, pyrimidodiazepines, anticonvulsants.
Résumé : La benzoylation homolytique (radical benzoyle) de la 5-tert-butylcarbonylaminopyrimidine (6, 1 équiv.), en
présence de benzaldéhyde (3 équiv.), d’eau, d’acide sulfurique et d’acide acétique, par réaction avec du FeSO4·7H2O
(3 équiv.) et du t-BuOOH à 70% (3 équiv.) à 5–10°C pendant 10 min conduit à un mélange de 4-benzoyl-5-tert-butyl-
aminopyrimidine (7, 23%), de 4,6-dibenzoyl-5-tert-butylaminopyrimidine (8, 44%) et de 4-benzoyl-5-tert-butylamino-6-
méthylpyrimidine (9, 10%). Quand on effectue la même réaction en utilisant un équivalent chacun de PhCHO,
FeSO4·7H2O et t-BuOOH pour empêcher la formation du produit 4,6-dibenzoylé 8, on obtient les produits monoben-
zoyle (7, 38%) et 4-benzoyl-6-méthyle (9, 6%). Une benzoylation homolytique semblable de la 5-bromopyrimidine (10)
en utilisant 1,5 équiv. des réactifs pour générer le radical benzoyle conduit à la formation de la 4-benzoyl-5-
bromopyrimidine (11, 61%) comme produit principal. Une séquence de synthèse en six étapes à partir du produit 11
permet d’obtenir la 2-hydrazino-5-phényl-3H-pyrimido[5,4-e][1,4]diazépine (17) avec un rendement global de 5,2%. La
réaction acidocatalysée de 17 avec l’orthoacétate de triéthyle fournit le composé mentionné dans le titre, la 5-phényl-
10-méthyl-7H-pyrimido[4,5-f][1,2,4]triazolo[4,3-a][1,4]diazépine (18, 62%). Le composé triazolo 18 est plus actif que
l’acide valproïque (Depakenc®) dans les épreuves sous-cutanées métrazel (« scMet ») que dans celles anticonvulsantes
avec électrochocs maximaux (« MES »); comparé au clonazépame, il est plus actif dans les épreuves anticonvulsantes
MES, mais moins actif dans l’épreuve anticonvulsante scMet.
Mots clés : benzoylation homolytique, pyrimidines, pyrimidodiazépines, anticonvulsants.
[Traduit par la Rédaction] Phillips et al. 222
X-substituent at C-7 is an essential requirement for anti-
convulsant, sedative, hypnotic, and muscle relaxant activi-
ties (1–3). In earlier studies, we showed that the 1,3-
Structure–activity studies for the benzo[1,4]diazepin-2-one
class of compounds (1) indicated that an electronegative
dihydro-5-phenyl-2H-pyrido[3,4-e][1,4]diazepin-2-one (2)
Received July 20, 1998.
O.A. Phillips and C.Y. Fiakpui. SynPhar Laboratories Inc., 4290–92A Street, Edmonton, AB T6E 5V2, Canada.
K.S.K. Murthy. Brantford Chemicals Inc., 34 Spalding Drive, Brantford, ON N3T 6B8, Canada.
E.E. Knaus.1 Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, AB T6G 2N8, Canada.
1Author to whom correspondence may be addressed. Telephone: (780) 492–5993. Fax: (780) 492–1217.
e-mail: eknaus@pharmacy.ualberta.ca
Can. J. Chem. 77: 216–222 (1999)
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Phillips et al.
217
Fig. 1. A comparison of the inductive and resonance effects exhibited by the chlorophenyl substituent in chlorobenzene (1) and the
ring nitrogens in pyrimidine (15).
and 1,3-dihydro-5-phenyl-2H-pyrido[3,2-e][1,4]diazepin-2-one
(3) classes of compounds, which are electronically analo-
gous to 7-chloro(nitro)-benzo[1,4]diazepin-2-one (1), exhib-
ited anticonvulsant activity (4, 5). It was therefore of interest
to extend these structure–activity relationships to include the
1,3-dihydro-5-phenyl-2H-pyrimido[5,4-e][1,4]diazepin-2-one (15)
class of compounds, which also are electronically analogous
to the chlorophenyl analog (1, X = Cl), since they possess
similar electron-density profiles at equivalent positions.
When the inductive and resonance effects of a chloro sub-
stituent (1, X = Cl) and the pyrimido ring nitrogen atoms of
the pyrimido compound (15) are compared, the resulting
electron densities are qualitatively similar for the chloro-
phenyl and pyrimido ring systems at equivalent positions as
illustrated in Fig. 1. This study was therefore initiated to de-
termine whether the chlorophenyl and pyrimido ring systems
are bioisosteric with respect to anticonvulsant activities,
since these ring systems are similar in size and shape
(phenyl and pyrimido), and they possess similar electron-
density profiles at equivalent positions. Furthermore, the
pyrimido nitrogen atom free-electron pairs have the potential
to act as H-bond acceptors, which may provide a receptor
binding interaction that is not possible with a chlorophenyl
ring. Accordingly, it is plausible that the chlorophenyl (1)
and pyrimido (15) classes of compounds could interact with
the same receptor site(s) to elicit anticonvulsant activities.
midine (4), which was elaborated to 5-tert-butylcarbonyl-
aminopyrimidine (6) upon reaction with trimethylacetyl
chloride and Et3N, were unsuccessful. Although ortho-
lithiation occurs at the C-4 position of 6, this lithio, or radi-
cal anion, species attacks either the highly electron-deficient
C-4, or C-2, position of 6 to exclusively afford bis(5-tert-
butylcarbonylaminopyrimidine) products prior to addition of
an electrophilic reagent such as benzaldehyde. Similar self-
condensation coupling reactions of pyrimidine and pyridine
derivatives in the presence of lithium diisopropylamide have
been reported (8–10).
To overcome the formation of bis(5-tert-butylcarbonyl-
aminopyrimidine) self-condensation products during the
ortho-directed lithiation of 5-tert-butylcarbonylaminopyrim-
idine (6), the nucleophilic character of an acyl radical gener-
ated in a one-step reaction (11) from an aldehyde in water
containing sulfuric acid, tert-butylhydroperoxide, ferrous
sulfate, and acetic acid reported for the acylation of quino-
line (11, 12), 4-cyanopyridine (13), 2-substituted-pyrazines
(14, 15), and quinoxaline (16) was investigated. Accord-
ingly, this selective homolytic acylation of protonated heter-
aromatic bases was used for the benzoylation of 5-tert-
butylcarbonylaminopyrimidine (6). Thus, the homolytic
benzoylation of 6 (1 equiv.) in the presence of benzaldehyde
(3 equiv.), water, sulfuric acid, and acetic acid, upon treat-
ment with FeSO4·7H2O (3 equiv.) and 70% t-BuOOH (3
equiv.) at 5–10°C for 10 min afforded a mixture of 4-
benzoyl-5-tert-butylcarbonylaminopyrimidine (7, 23%),
4,6-dibenzoyl-5-tert-butylcarbonylaminopyrimidine (8, 44%),
and 4-benzoyl-5-tert-butylcarbonylamino-6-methylpyrimidine
(9, 10%) (see Scheme 1). Introduction of the 6-methyl sub-
stituent into 9 likely arises from decomposition of t-BuOOH
to acetone and a methyl radical which adds to the C-6 posi-
tion of 4-benzoyl-5-tert-butylcarbonylaminopyrimidine (7).
When the reaction was performed using 1 equiv. each of
PhCHO, FeSO4·7H20 and t-BuOOH, to prevent the forma-
tion of the 4,6-dibenzoyl product 8, the monobenzoyl prod-
In earlier studies, we developed synthetic methodologies,
involving ortho-directed lithiation of 3-tert-butylcarbonyl-
aminopyridine, that were applicable to the preparation of 3-
tert-butylcarbonylamino-4-benzoylpyridines (6, 7). In con-
trast, all attempts to prepare 4-benzoyl-5-tert-butylcarbonyl-
aminopyrimidine (7) using a similar ortho-directed lithiation
of 5-tert-butylcarbonylaminopyrimidine (6), prepared by the
Pd/C catalyzed dechlorination of 5-amino-4,6-dichloropyri-
© 1999 NRC Canada

218
Can. J. Chem. Vol. 77, 1999
Scheme 1. Reagents: i, 10% Pd/C, 20% w/v aqueous NaOH, H2 gas at 30 psi, Et2O, 25°C; ii, Me3COCl, Et3N, CH2Cl2, 0°C for
30 min and then 25°C for 3 h; iii, H2O, concentrated H2SO4, PhCHO (3 equiv.), HOAc, 0°C and then FeSO4·7H2O (3 equiv.), 70%
w/v t-BuOOH (3 equiv.), 5–10°C, 10 min.
uct 7, the 4-benzoyl-6-methyl product 9, and unreacted 6
were obtained in 38, 6, and 23% (recovery) chemical yields,
respectively. It has been reported that the yield of
monoacylation product can be increased by replacement of
HOAc with CH2Cl2 in homolytic acylation reactions (15).
When HOAc is used, the reaction mixture is homogenous.
Alternatively, in the absence of HOAc a heterogeneous me-
dium is obtained, which has be proposed to result in the
monoacylation product being extracted into the organic layer
(CH2Cl2) where it is more soluble thereby protecting the
monoacylation product from further acylation. However, in
this study, replacement of HOAc by CH2Cl2 was not suc-
cessful, since no reaction occurred and the starting material
6 was recovered.
afforded 1,3-dihydro-5-phenyl-2H-pyrimido[5,4-e][1,4]diaze-
pin-2-one (15, 67%), which was elaborated to the corre-
sponding 2-thione derivative (16, 70%). Reaction of 16 with
H2NNH2·H2O in MeOH gave the 2-hydrazino-5-phenyl-3H-
pyrimido[5,4-e][1,4]diazepine (17, 80%), which was imme-
diately converted to 5-phenyl-10-methyl-7H-pyrimido[4,5-
f][1,2,4]triazolo[4,3-a][1,4]diazepine (18, 62%) upon reac-
tion with triethyl orthoacetate in the presence of concen-
trated H2SO4.
A similar homolytic benzoylation (benzoyl radical) of
5-bromopyrimidine (10) was investigated with the objective
of increasing the yield of the monoacylation product and
preventing the formation of the dibenzoylation (8) and
methyl radical (9) products previously observed upon reac-
tion with 5-tert-butylcarbonylaminopyrimidine (6). This
rationale is based on the premise that (i) a bromo substituent
should direct predominately ortho-substitution and (ii) the
The anticonvulsant activities of 5-phenyl-10-methyl-7H-
pyrimido[4,5-f][1,2,4]triazolo[4,3-a][1,4]diazepine (18) were
determined by the Antiepileptic Drug Development (ADD)
Program that is administered by the Section on Epilepsy,
United States National Institutes of Health, Bethesda, Md.
Anticonvulsant activities against subcutaneous metrazol
(scMet) and maximal electroshock (MES) induced seizures,
which are models for absence (petit mal) and generalized
tonic clonic (grand mal) seizures, respectively, were mea-
sured in mice and (or) rats at various time intervals after
intraparietoneal (ip), or oral (po), administration of the test
compound 18 using procedures previously reported (7). In
the Phase II quantitative screen in mice, 18 was moderately
active (ED50 = 79.5 mg/kg ip at 1 h post drug administra-
bromo substituent can be displaced by
a nitrogen
nucleophile (14). Accordingly, homolytic benzoylation of
5-bromopyrimidine (10) with a benzoyl radical, as described
previously (see Scheme 1) afforded 4-benzoyl-5-bromo-
pyrimidine (11) as the predominant, or exclusive, product
which was readily purified by silica-gel column chromatog-
raphy (61% yield) (see Scheme 2). Amination of 11 using
aqueous NH4OH in the presence of CuSO4·5H2O yielded
5-amino-4-benzoylpyrimidine (12, 22%). The subsequent
reduction of 12 with NaBH4 in MeOH gave 5-amino-4-(α-
hydroxybenzyl)pyrimidine (13, 75%), which was converted to
4-benzoyl-5-benzyloxycarbonylaminomethylcarbonylamino-
pyrimidine (14, 84%) by coupling to the carboxyl group of
PhCH2OCONHCH2CO2H in the presence of dicyclohexyl-
carbodiimide (DCC) and then oxidation of the alcohol using
MnO2. Cyclization of 14 with 33% w/v HBr in HOAc
tion) against MES-induced seizures, very active (ED50
6.2 mg/kg ip at 15 min post drug administration) against
scMet-induced seizures, and it was nontoxic (TD50
=
>
150 mg/kg ip at 15 min post drug administration in mice).
The ED50 values for the standard reference drugs in these
anticonvulsant screens were clonazepam (scMet, ED50
=
0.02 mg/kg; MES, ED50 = 86.6 mg/kg) and valproic acid
(scMet, ED50 = 148.6 mg/kg; MES, ED50 = 271.7 mg/kg). In
© 1999 NRC Canada

Phillips et al.
219
Scheme 2. Reagents: i, PhCHO (1.5 equiv.), HOAc, 4N H2SO4 and then FeSO4·7H2O (1.5 equiv.), H2O, 70% t-BuOOH (1.5 equiv.),
0–5°C for 0.5 h and then 25°C for 2 h; ii, 37% w/v aqueous NH4OH, CuSO4.5H2O, 0.5 h at 25°C and then 90°C for 20 h;
iii, NaBH4, MeOH, 0–5°C and then 25° for 1.5 h; iv, dicyclohexylcarbodiimide, THF–CH2Cl2 (1:1, v/v), PhCH2OCONHCH2CO2H,
20 min at 25°C and then 2.5 h at reflux; MnO2, CHCl3, 25°C, 20 h; v, 33% w/v HBr in HOAc, 25°C, 2.5 h and then Et2O, 10% w/v
aqueous MeOH, NH4OH, 25°C, 6 h; vi, Lawesson’s reagent (2,4-bis(4-methoxyphenyl)-1,3-dithia-2,4-diphosphetane-2,4-disulfide),
benzene, reflux under argon, 1 h; vii, H2NNH2·H2O, MeOH, 25°C, 2h; viii, triethyl orthoacetate, EtOH, concentrated H2SO4,
0°C → 25°C, 4 h.
addition, 18 also exhibited good anticonvulsant activity in
the Phase VIa rat oral screen where a 50 mg/kg oral dose
protected 2/4, 2/4, and 1/4 rats against seizures at 15 min,
1 h, and 4 h post drug administration, respectively, in the
MES screen, and 4/4, 4/4, and 2/4 rats were protected at
15 min, 1 h and 4 h post drug administration, respectively,
in the scMet screen.
(5-(2-chlorophenyl)-7-nitrobenzo[1,4]diazepin-2-one, IC50 =
0.003 µM).
The results of this study indicate 18 is more potent than
valproic acid (Depakene®) in both the scMet and MES
screens, more potent than clonazepam in the MES screen,
but less potent than clonazepam in the scMet screen.
The ability of 18 to prevent convulsions induced by other
convulsion-inducing agents was also investigated in mice at
15 min following an ip dose of 18 (sc bicuculline test: ED50
> 10 mg/kg; sc picrotoxin test: ED50 = 7.72 mg/kg; and sc
strychnine test: ED50 > 10 mg/kg). Bicuculline blocks γ-
aminobutyric acid (GABA) receptors and this interferes with
GABA inhibitory function thereby inducing both clonic and
tonic extensor convulsions. Picrotoxin interferes with chlo-
ride channels that are regulated by GABA receptors thereby
inducing minimal threshold seizures.
The ability of 18 to displace 50% of 10 nM [3H]flu-
nitrazepam from mouse whole brain P2 pellets (IC50 = 72 µM)
indicates it has a weaker affinity for the benzodiazepine re-
ceptor site(s) as compared to the reference drug clonazepam
Melting points were determined using a Buchi capilliary
apparatus and are uncorrected. Nuclear magnetic resonance
spectra (1H NMR, 13C NMR) were determined on a Bruker
AM-300 spectrometer. The assignment of exchangeable pro-
tons (OH, NH) was confirmed by the addition of D2O. 13C
NMR spectra were acquired using the J modulated spin-echo
technique where methyl and methine carbon resonances ap-
pear as positive peaks, and methylene and quaternary carbon
resonances appear as negative peaks. Infrared (IR) spectra
were acquired using a Nicolet 550 Series II Magna FT-IR
spectrometer. Silica-gel column chromatography was carried
out using Merck 7734 silica gel (60–200 mesh). Preparative
© 1999 NRC Canada

220
Can. J. Chem. Vol. 77, 1999
thin-layer chromatography (TLC) was performed using
Keiselgel silica-gel (Camag) plates, 1.0 mm in thickness. All
reagents were purchased from the Aldrich Chemical Co.
which was separated by preparative TLC using benzene–
EtOAc (1:1, v/v) as development solvent. Extraction of the
band having Rf 0.69 yielded 7 (73 mg, 23%); mp 84–85°C
(EtOAc–hexane); IR (CCl4): 3320 (NH), 2967 (CH), 1742
1
(CϭO), 1703 (CONH) cm–1; H NMR (CDCl3) δ: 7.54 (t,
5-Aminopyrimidine (5)
J = 9.0 Hz, 2H, phenyl H-3, H-5), 7.64–7.68 (m, 1H, phenyl
H-4), 8.04 (dd, J = 2.0, 9.0 Hz, 2H, phenyl H-2, H-6), 9.06
(s, 1H, H-2), 10.24 (s, 1H, H-6), 10.85 (br s, 1H, NH). Anal.
calcd. for C16H17N3O2: C 67.82, H 6.05, N 14.83; found: C
68.10, H 6.07, N 14.80. Extraction of the band having Rf
0.86 afforded 8 (190 mg, 44%); mp 166–167°C (EtOAc–
hexane); IR (CCl4): 3361 (NH), 2969 (CH), 1691 (br, CϭO
A solution of 5-amino-4,6-dichloropyrimidine (2.0 g,
12.2 mmol) in ether (240 mL) and then 10% palladium-on-
charcoal (160 mg) was added to a solution of 20% w/v
NaOH (8 g) in water (32 mL) in a low-pressure hydrogena-
tion bottle, and the mixture was agitated at 25°C under hy-
drogen gas at 30 psi (1 psi = 6.895 kPa) until the uptake of
hydrogen gas had ceased. The reaction mixture was filtered
through a celite pad which was then washed with warm wa-
ter (2 × 16 mL). The pH of the combined filtrates was made
strongly alkaline by addition of NaOH at less than 5°C.
Ether (20 mL) was added, the mixture was extracted by stir-
ring overnight at 25°C, the ether layer was separated, and
the aqueous fraction was further extracted with ether (3 ×
80 mL). The combined ether extracts were dried (MgSO4),
and the solvent was removed in vacuo to give 5 as colorless
crystals after recrystallization from benzene containing a
few drops of methanol (1.1 g, 95%); mp 170–171°C (lit. mp
1
and CONH) cm–1; H NMR (CDCl3) δ: 1.24 (s, 9H, CMe3),
7.55 (t, J = 8.7 Hz, 4H, phenyl H-3, H-5), 7.68 (t, J =
8.7 Hz, 2H, phenyl H-4), 8.08 (d, J = 8.7 Hz, 4H, phenyl
H-2, H-6), 9.18 (s, 1H, H-2), 10.30 (br s, 1H, NH). Anal.
calcd. for C23H21N3O3: C 71.30, H 5.46, N 10.85; found: C
70.93, H 5.34, N 10.67. Extraction of the band having Rf
0.38 yielded 9 (33 mg, 10%); mp 144–145°C (hexane–
EtOAc); IR (CCl4): 3407 (NH), 2968 (CH), 1742 (CϭO),
1699 (CONH) cm–1; 1H NMR (CDCl3) δ: 1.28 (s, 9H,
CMe3), 2.56 (s, 3H, C-6 Me), 7.52 (t, J = 7.0 Hz, 2H, H-3,
H-5), 7.66 (t, J = 7.0 Hz, 1H, phenyl H-4), 8.01 (d, J =
7.0 Hz, 2H, phenyl H-2, H-6), 8.70 (br s, 1H, NH), 9.06
(s, 1H, H-2). Anal. calcd. for C17H19N3O2: C 68.67, H 6.44,
N 14.13; found: C 68.62, H 6.38, N 13.95.
1
171–172°C (17)); H NMR (CDCl3) δ: 3.80 (br s, 2H, NH2),
8.25 (s, 2H, H-4, H-6), 8.70 (s, 1H, H-2).
5-tert-Butylcarbonylaminopyrimidine (6)
A solution of trimethylacetyl chloride (1.67 g, 13.9 mmol)
in dry CH2Cl2 (1.5 mL) was added dropwise to an ice-
cooled solution of 5 (1.2 g, 12.6 mmol) and Et3N (1.6 g,
15.8 mmol) in dry CH2Cl2 (25 mL) at 0°C with stirring dur-
ing 30 min. The reaction was allowed to proceed with stir-
ring at 25°C for 3 h, and the reaction mixture was poured
onto water (40 mL). Extraction with CH2Cl2 (2 × 100 mL),
washing the combined CH2Cl2 extracts with 10% w/v
NaHCO3, and then brine (25 mL), drying the CH2Cl2 frac-
tion (Na2SO4) and removal of the solvent in vacuo gave a
yellow–brown viscous oil that was purified by preparative
TLC using MeOH–EtOAc (1:20, v/v) as development sol-
vent. Extraction of the band (Rf = 0.56) gave a yellow oil
which was recrystallized from EtOAc–hexane (1:3, v/v) to
afford 6 as needle-like crystals (1.14 g, 50%); mp 120–121°C;
IR (CHCl3): 3442 (NH), 1693 (CϭO) cm–1; 1H NMR
(CDCl3) δ: 1.36 (s, 9H, CMe3), 7.40 (br s, 1H, NH), 8.98
(s, 1H, H-2), 9.00 (s, 2H, H-4, H-6). Anal. calcd. for
C9H13N3O: C 60.31, H 7.31, N 23.45; found: C 60.46,
H 7.39, N, 23.24.
4-Benzoyl-5-bromopyrimidine (11)
Solutions of FeSO4·7H2O (110 g, 396 mmol) in water
(280 mL) and t-BuOOH (54 mL of 70% w/v, 394 mmol)
were added simultaneously to an ice-cooled solution of 10
(42 g, 264 mmol) and benzaldehyde (40 mL, 394 mmol) in
HOAc (280 mL) and sulfuric acid (182 mL of 4.5 N) with
stirring during 20 min. After 30 min, the cooling bath was
removed, and the reaction was allowed to proceed for 2 h at
25°C. Extraction with EtOAc (4 × 200 mL), and removal of
the solvents including acetic acid in vacuo at 40°C gave a
residue which was neutralized by treatment with saturated
aqueous NaHCO3 solution prior to extraction with EtOAc
(4 × 100 mL). The combined EtOAc extracts were washed
with water (100 mL), brine (60 mL), and the EtOAc fraction
was dried (Na2SO4). Removal of the solvent in vacuo gave a
residue which was purified by silica-gel column chromato-
graphy (4 × 30 cm column) using EtOAc–hexane (1:9, v/v)
as eluant to yield 11 (42.2 g, 61%) as an apparently homoge-
neous oil (silica-gel TLC, EtOAc–hexane (4:1, v/v) as de-
velopment solvent, Rf = 0.38). This oil, upon standing in
hexane at 25°C crystallized as colorless crystals after several
4-Benzoyl-5-tert-butylcarbonylaminopyrimidine (7),
5-tert-butylcarbonylamino-4,6-dibenzoylpyrimidine (8)
and 4-benzoyl-5-tert-butylcarbonylamino-6-
hours; mp 41–42°C; IR (KBr): 1680 (CϭO) cm–1; H NMR
1
(CDCl3) δ: 7.42–7.60 (m, 2H, phenyl H-3, H-5), 7.65 (dt,
J = 7.5, 1.5 Hz, 1H, phenyl H-4), 7.78–7.80 (m, 2H, phenyl
H-2, H-6), 9.00 (s, 1H, H-6), 9.21 (s, 1H, H-2); 13C NMR
(CDCl3) δ: 117.02, 128.82 (2C), 130.11 (2C), 133.64,
134.63, 156.26, 159.97, 162.54, 190.73 (CϭO). Anal. calcd.
for C11H7BrN2O: C 50.22, H 2.68, N 10.65; found: C 49.94,
H 2.61, N 10.62.
methylpyrimidine (9)
A saturated solution of FeSO4·7H2O (0.93 g, 3.26 mmol)
in water (12 mL) and 70% w/v t-BuOOH (303 mg,
3.36 mmol) were added simultaneously to a mixture contain-
ing 6 (0.20 g, 1.12 mmol), water (2 mL), concentrated
H2SO4 (80 µL), benzaldehyde (357 mg, 3.36 mmol), and
HOAc (3 mL) at 5–10°C with stirring. The reaction was al-
lowed to proceed at 5–10°C for 10 min with stirring prior to
neutralization with saturated aqueous NaHCO3 at 0°C. Ex-
traction with EtOAc (3 × 100 mL), drying the EtOAc extract
(Na2SO4), and removal of the solvent in vacuo yielded an oil
5-Amino-4-benzoylpyrimidine (12)
A mixture of 11 (12.0 g, 46 mmol), aqueous NH4OH
(100 mL of a 37% w/v solution), and CuSO4·5H2O (1.1 g,
44 mmol) were placed in a glass pressure flask, and the
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Phillips et al.
221
reaction was allowed to proceed with stirring at 25°C for
30 min, and then at 90°C for 20 h. After cooling to 10°C,
the reaction mixture was transferred to a separatory funnel,
the pressure flask was rinsed with chloroform (2 × 40 mL),
and the chloroform solution was transferred to the separa-
tory funnel. The organic fraction was separated, and the
aqueous fraction was extracted with chloroform (4 × 50 mL).
The combined organic extracts were dried (Na2SO4), and the
solvent was removed in vacuo to give a gummy yellow solid
which was purified by silica-gel column chromatography
(4.5 × 30 cm column) using EtOAc–hexane (3:2, v/v) as
eluant to afford 12 (2.0 g, 22%) as bright yellow needles;
mp 109–110°C (ether–hexane); Rf = 0.56 (EtOAc–hexane,
4:1, v/v as development solvent); IR (KBr): 3451, 3328 (NH2),
EtOAc–hexane (9:1, v/v) afforded the hydroxy intermediate
as an oil which was dissolved in chloroform (250 mL). Acti-
vated MnO2 (16.0 g, 200 mmol) was added, and the oxida-
tion reaction was allowed to proceed at 25°C for 20 h with
stirring. The reaction mixture was filtered through a small
celite pad, the celite pad was washed with chloroform (2 ×
20 mL), and the chloroform filtrate was filtered. Removal of
the solvent in vacuo gave an oily residue which was purified
by silica-gel column chromatography (4.5 × 26 cm column)
using EtOAc–hexane (7:3, v/v) as eluant to afford 14
(11.5 g, 84%); mp 86–87°C; IR (KBr): 3312, 3058, 1712,
1
1655, 1565 cm–1; H NMR (CDCl3) δ: 4.05 (d, J = 6.0 Hz,
2H, CH2NH), 5.14 (s, 2H, OCH2), 5.73 (t, J = 6.0 Hz, 1H,
CH2NH), 7.10–7.42 (m, 5H, CH2Ph), 7.47 (t, J = 7.5 Hz,
2H, benzoyl H-3, H-5), 7.62 (t, J = 7.5 Hz, 1H, benzoyl
H-4), 7.95 (d, J = 8.0 Hz, 2H, benzoyl H-2, H-6), 8.05
(s, 1H, H-6), 9.09 (s, 1H, H-2), 10.86 (br s, 1H,
NHCOCH2); 13C NMR (CDCl3) δ: 45.51, 67.56, 128.21
(2C), 129.48, 131.22 (2C), 133.73, 133.85, 135.68, 135.91,
143.77, 151.95, 152.07, 156.60, 168.72, 195.74. Anal. calcd.
for C21H18N4O4: C 64.61, H 4.65, N 14.35; found: C 64.58,
H 4.74, N 14.66.
1
1630 (CϭO) cm–1; H NMR (CDCl3) δ: 6.03 (br s, 2H,
NH2), 7.40–7.60 (m, 3H, phenyl H-3, H-4, H-5), 8.00–8.10
(m, 2H, phenyl H-2, H-6), 8.44 (s, 1H, H-6), 8.64 (s, 1H,
H-2); 13C NMR (CDCl3) δ: 127.95 (2C), 130.69 (2C),
132.53, 137.21, 137.26, 142.63, 146.28, 148.92, 196.21
(CϭO). Anal. calcd. for C11H9N3O: C 66.32, H 4.55, N
21.09; found: C 66.12, H 4.60, N 21.07.
5-Amino-4-(α-hydroxybenzyl)pyrimidine (13)
Sodium borohydride (1.5 g, 40 mmol) was added to an
ice-cooled solution of 12 (3.0 g, 15 mmol) in methanol
(80 mL), and the reaction was allowed to proceed for 1.5 h
with stirring. Saturated aqueous NH4Cl (30 mL) was added,
the mixture was stirred for 3 h at 25°C, most of the MeOH
was removed in vacuo, and the aqueous residue was ex-
tracted with chloroform (6 × 50 mL). The combined chloro-
form extracts were washed with water (50 mL), brine
(50 mL), and the chloroform fraction was dried (Na2SO4).
Removal of the solvent in vacuo gave a residue which was
purified by either recrystallization from chloroform–hexane,
or by silica-gel column chromatography using EtOAc as
eluant, to afford 13 as a colorless crystalline solid (2.27 g,
75%); mp 148–149°C; IR (KBr): 3425, 3312, 3181, 2853,
1,3-Dihydro-5-phenyl-2H-pyrimido[5,4-e][1,4]diazepin-2-
one (15)
A solution of 32% w/v HBr in HOAc (120 mL) was
added to 14 (10.0 g, 25.6 mmol), and the reaction was al-
lowed to proceed at 25°C for 2.5 h with stirring. Ether
(100 mL) and 10% aqueous NaOH (200 mL) were added,
and the mixture was cooled in an ice-bath prior to neutral-
ization with aqueous NH4OH. The resulting mixture was al-
lowed to stand for 6 h at 25°C, extracted with chloroform (6
× 60 mL), the combined chloroform extracts were dried
(Na2SO4), and the solvent was removed in vacuo to afford a
viscous oil. Purification by silica-gel column chromatogra-
phy (4.5 × 30 cm column) using EtOAc as eluant gave 15
(4.5 g, 67%); mp 184–185°C (CH2Cl2–hexane); IR (KBr):
1
1
1630, 1573 cm–1; H NMR (DMSO-d6) δ: 5.46 (br s, 2H,
3156, 1696, 1622 cm–1; H NMR (CDCl3) δ: 4.42 (s, 2H,
NH2), 5.79 (d, J = 5.0 Hz, 1H, CH-OH), 6.37 (d, J = 5.0 Hz,
1H, CH-OH), 7.15–7.37 (m, 3H, phenyl H-3, H-4, H-5),
7.37–7.50 (m, 2H, phenyl H-2, H-6), 8.10 (s, 1H, H-6), 8.36
(s, 1H, H-2); 13C NMR (DMSO-d6) δ: 74.40, 126.06 (2C),
127.03, 127.90 (2C), 139.78, 141.72, 143.34, 146.16,
152.64. Anal. calcd. for C11H11N3O: C 65.66, H 5.51, N
20.88; found: C 65.29, H 5.51, N 20.93.
CH2), 7.30–7.50 (m, 3H, phenyl H-3, H-4, H-5), 7.50–7.60
(m, 2H, phenyl H-2, H-6), 8.75 (s, 1H, H-9), 9.08 (s, 1H, H-
7), 10.21 (br s, 1H, NH); 13C NMR (CDCl3) δ: 56.51,
128.22 (2C), 129.43 (2C), 130.92, 133.50, 136.70, 149.58,
150.94, 153.23, 169.10, 171.71. Anal. calcd. for C13H10N4O:
C 65.54, H 4.23, N 23.52; found: C 65.29, H 4.00, N 23.44.
1,3-Dihydro-5-phenyl-2H-pyrimido[5,4-e][1,4]diazepin-2-
thione (16)
4-Benzoyl-5-benzyloxycarbonyl-
aminomethylcarbonylaminopyrimidine (14)
A mixture of 15 (5.65 g, 23.7 mmol) and Lawesson’s re-
agent (2,4-bis(4-methoxyphenyl)-1,3-dithia-2,4-diphosphe-
tane-2,4-disulfide) (5.0 g, 12.3 mmol) in benzene (150 mL)
was refluxed for 1 h under argon, the resulting dark-colored
solution was cooled to 25°C, and EtOAc (150 mL) was
added. This mixture was washed with 10% w/v aqueous
NaOH (150 mL), water (50 mL), and the aqueous fractions
were combined. The combined aqueous fractions were neu-
tralized with 1N HCl, and this mixture was extracted with
EtOAc (3 × 50 mL). The combined EtOAc extracts were
washed with brine (50 mL) and the EtOAc extract was dried
(Na2SO4). Removal of the solvent in vacuo at 25°C gave a
semi-solid residue which was purified by silica-gel column
chromatography (4.5 × 30 cm column) using EtOAc–hexane
N-Benzyloxycarbonylglycine (10.5 g, 50 mmol) was
added in small aliquots to a solution of dicyclohexylcarbo-
diimide (10.3 g, 50 mmol) in dry THF–CH2Cl2 (1:1, v/v,
200 mL) at which time a white solid separated in a few min-
utes after mixing the two reagents. The resulting suspension
was stirred for 20 min at 25°C, 13 (7.0 g, 34.8 mmol) was
added as a single aliquot, and the reaction mixture was
heated at reflux for 2.5 h. The reaction mixture was cooled
to 25°C, the solid was removed by filtration, and the solvent
was removed in vacuo to give an oily residue that was puri-
fied by silica-gel column chromatography (4.5 × 30 cm col-
umn). Elution with EtOAc–hexane (1:1, v/v) eluted
impurities which were discarded. Further elution with
© 1999 NRC Canada

222
Can. J. Chem. Vol. 77, 1999
(2:3, v/v) as eluant to yield 16 (4.2 g, 70%) as a yellow
solid; mp 198–205°C (dec.) (MeOH–hexane); 1H NMR
(MeCOMe-d6) δ: 4.86 (s, 2H, CH2), 7.32–7.50 (m, 3H,
phenyl H-3, H-4, H-5), 7.60–7.70 (s, 2H, phenyl H-2, H-6),
8.97 (s, 1H, H-9), 9.04 (s, 1H, H-7), 11.50 (br s, 1H, NH);
13C NMR (MeCOMe-d6) δ: 64.75, 128.74 (2C), 128.40,
130.38 (2C), 131.25, 135.00, 138.19, 151.59, 151.88,
152.80, 169.14. Product 16 was used immediately in the
subsequent reaction for the preparation of 17.
4.19 (d, Jgem = 12 Hz, 1H, H-7′), 5.59 (d, Jgem = 12 Hz,
1H, H-7 ), 7.30–7.50 (m, 3H, phenyl H-3, H-4, H-5), 7.55–
7.62 (m, 2H, phenyl H-2, H-6), 9.02 (s, 1H, H-1), 9.35 (s,
1H, H-3); 13C NMR (CDCl3) δ: 12.09, 46.08, 128.25 (2C),
129.17 (2C), 129.39, 131.10, 136.74, 149.94, 151.94,
152.63, 155.02, 156.76, 166.89. Anal. calcd. for C15H12N6:
C 65.21, H 4.38, N 30.42; found: C 64.83, H 4.26, N 30.46.
′′
We are grateful to the Medical Research Council of Can-
ada (grant no. MT-4888) for financial support of this re-
search, to the Alberta Heritage Foundation for Medical
Research for a Fellowship to one of us (C.Y.F.), and to the
Anticonvulsant Drug Development Program, Epilepsy
Branch, NINCDS, Bethesda, for anticonvulsant testing.
2-Hydrazino-5-phenyl-3H-pyrimido[5,4-e][1,4]diazepine
(17)
Hydrazine monohydrate (7.4 mL, 151 mmol) was added
dropwise using a syringe to a solution of 16 (4.0 g,
15.7 mmol) in MeOH (100 mL) at 25°C with stirring, and
the reaction was allowed to proceed at 25°C with stirring for
2 h prior to pouring onto ice-water (100 mL). Methanol was
removed from the mixture in vacuo at 25°C, and the aque-
ous residue was extracted with chloroform (4 × 60 mL). The
combined chloroform extracts were washed with water
(40 mL), brine (40 mL), and the chloroform fraction was
dried (Na2SO4). Removal of the solvent in vacuo yielded 17
1. L.O. Randall, W. Schallek, L.H. Sternbach, and R.Y. Ning. In
Psychopharmacological agents. Edited by M. Gordon. Aca-
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2. L.H. Sternbach. J. Med. Chem. 22, 1 (1979).
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therein.
4. C.Y. Fiakpui, O.A. Phillips, K.S.K. Murthy, and E.E. Knaus.
Drug Des. Discovery, 10, 45 (1993).
5. C.Y. Fiakpui and E.E. Knaus. Drug Des. Discovery, 10, 173
(1993).
6. C.Y. Fiakpui and E.E. Knaus. Can. J. Chem. 65, 1158 (1987).
7. C.Y. Fiakpui, M.N. Namchuk, and E.E. Knaus. Drug Des. De-
livery, 6, 111 (1990).
8. T.J. Kress. J. Org. Chem. 44, 2081 (1979).
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12. T. Caronna, G. Fronza, F. Minisci, and O. Porta. J. Chem. Soc.
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13. G. Heinisch and G. Lotsch. Angew. Chem. Intl. Ed. Engl. 24,
692 (1985).
1
(3.17 g, 80%) as a yellow solid; H NMR (CDCl3) δ: 3.60–
4.70 (br m, 5H, NHNH2, H-3), 7.26–7.70 (m, 5H, phenyl
hydrogens), 8.74 (s, 1H, H-9), 8.90 (s, 1H, H-7). Since 17
was quite pure (1H NMR) and since it decomposes slowly
on standing in air, or in chloroform solution at 25°C, it was
used immediately in the subsequent reaction for the prepara-
tion of 18.
5-Phenyl-10-methyl-7H-pyrimido[4,5-f][1,2,4]tri-
azolo[4,3-a][1,4]diazepine (18)
Concentrated H2SO4 (1.2 mL) was added dropwise with
stirring to an ice-bath cooled solution of 17 (3.0 g, 11.9 mmol)
and triethyl orthoacetate (11.0 mL, 60 mmol) in 98% EtOH
(120 mL), and the reaction was allowed to proceed at 25°C
for 4 h. The reaction mixture was neutralized with a satu-
rated solution of aqueous NaHCO3 and the mixture was con-
centrated in vacuo at 25°C. The residue was extracted with
chloroform (3 × 50 mL), the combined chloroform extracts
were washed with water (50 mL), brine (50 mL), and the
chloroform fraction was dried (Na2SO4). Removal of the
solvent in vacuo, and purification of the product by silica-
gel column chromatography using EtOAc–methanol (4:1,
v/v) as eluant afforded 18 (2.0 g, 62%); mp 223–224°C
14. Y. Houminer, E.W. Southwick, and D.L. Williams. J. Org.
Chem. 54, 640 (1989).
15. Y. Houminer, E.W. Southwick, and D.L. Williams. J.
Heterocyl. Chem. 23, 497 (1986).
16. G.P. Gardini and F. Minisci. J. Chem. Soc. C, 929 (1970).
17. N. Whittaker. J. Chem. Soc. 1565 (1951).
1
(CH2Cl2–hexane); H NMR (CDCl3) δ: 2.68 (s, 3H, CH3),
© 1999 NRC Canada