A novel synthesis of N1-(substituted)-pyrimido[5,4-e]-1,2,4-triazine-5,7(1H,6H)-diones

Article abstract of DOI:10.1016/j.tetlet.2009.02.084

A new synthesis of N₁-(substituted)-pyrimido[5,4-e]-1,2,4-triazine-5,7(1H,6H)-diones, which are analogues of the natural product toxoflavin, is reported. Condensation of preformed alkyl or aryl hydrazones with 6-chloro-3-methyl-5-nitrouracil ef

Full text of DOI:10.1016/j.tetlet.2009.02.084

Tetrahedron Letters 50 (2009) 1996–1997
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Tetrahedron Letters
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A novel synthesis of N1-(substituted)-pyrimido[5,4-e]-1,2,
4-triazine-5,7(1H,6H)-diones
*
Anjanette J. Turbiak, H. D. Hollis Showalter
Department of Medicinal Chemistry, University of Michigan, 428 Church St., Ann Arbor, MI 48109-1065, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
A new synthesis of N1-(substituted)-pyrimido[5,4-e]-1,2,4-triazine-5,7(1H,6H)-diones, which are ana-
logues of the natural product toxoflavin, is reported. Condensation of preformed alkyl or aryl hydrazones
with 6-chloro-3-methyl-5-nitrouracil efficiently provides pyrimidotriazinediones in a three-step process
that broadens the scope of R1 substituents.
Received 30 January 2009
Revised 10 February 2009
Accepted 11 February 2009
Available online 15 February 2009
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Pyrimido[5,4-e]-1,2,4-triazine-5,7(1H,6H)-
diones
Toxoflavin
Hydrazones
Cyclizations
Zinc
Toxoflavin (1; Fig. 1), which was originally isolated from Pseu-
domonas cocovenenans, was first synthesized in 1961.1 Since then,
a number of analogues have been prepared in order to explore
the potent antibiotic and pharmacological properties of the pyrim-
ido[5,4-e]-1,2,4-triazine-5,7(1H,6H)-dione class represented by
this natural product.2 Many of these analogues have the same
methyl substituent found at the N1 position of toxoflavin, partially
due to the ease with which a methyl group can be incorporated via
the use of methylhydrazine early in the synthesis.3 Other ana-
logues have either a proton at N1 or a variety of alkyl and benzyl
groups. Conspicuously absent, however, are pyrimido[5,4-e]-
1,2,4-triazine-5,7(1H,6H)-diones with an aryl substituent at the
N1 position. This can be attributed to the classical route that has
been utilized, which requires that nucleophilic attack of 6-
chloro-3-methyluracil proceed via the secondary nitrogen of the
mono-substituted hydrazine. However, for mono-aryl hydrazines,
such attack typically proceeds via the primary nitrogen. Herein,
we report a novel and efficient route to pyrimido[5,4-e]-1,2,4-tri-
azine-5,7(1H,6H)-diones that allows for incorporation of aryl and
alkyl substituents at N1 of this ring system, thus broadening the
scope of accessible analogues.
zone (4a) was then treated with 6-chloro-3-methyl-5-nitrouracil (5),
derived from nitration of commercially-available 6-chloro- 3-meth-
yluracil by the published method.4 The resultant 6-(2-(4-methoxy-
benzylidene)-1-phenyl)hydrazinyl-3-methyl-5-nitrouracil (6a) was
cyclized to 3-(4-methoxyphenyl)-6-methyl-1-phenylpyrimido[5,4-
e][1,2,4]triazine-5,7(1H,6H)-dione (7a) upon treatment with zinc
(4 equiv) and ammonium chloride (2 equiv) while exposed to air
and with vigorous stirring in refluxing 50% aq ethanol. The N1-phen-
ylpyrimidotriazinedione was isolated cleanly by treating the suspen-
sion with 1 N aq HCl to dissolve residual zinc and then washing the
precipitate with 1 N aq HCl while filtering.5 The zinc-mediated cycli-
zation was also tried in pure water or ethanol as the solvent, but the
yields wereconsiderably diminished. While hydrogenationoverPd/C
has been shown to yield pyrimidotriazinediones previously from
intermediates analogous to 6a, the reported yields are deplorable,
usually only 2–5%.6 In stark contrast, the cyclization conditions re-
ported here yield the desired pyrimidotriazinediones in 51–81%
yield.
O
Our strategy is shown in Scheme 1 and is exemplified with phen-
ylhydrazine. First, phenylhydrazine (2) was treated with p-anisalde-
hyde (3a) under reflux conditions to form hydrazone 4a, which
readily precipitated out of ethanol upon cooling. The resulting hydra-
N
CH3
O
3
N
6
1
N
N
N
CH3
1
* Corresponding author. Tel.: +1 734 764 5504; fax: +1 734 647 8430.
E-mail address: showalh@umich.edu (H.D.H. Showalter).
Figure 1. Structure and numbering of 1,6-dimethylpyrimido[5,4-e][1,2,4]triazine-
5,7(1H,6H)-dione (toxoflavin).
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.02.084

A. J. Turbiak, H. D. H. Showalter / Tetrahedron Letters 50 (2009) 1996–1997
1997
O
O
O2N
Cl
CH3
O
H
N
H
N
Δ
N
NH2
+
H
N
+
EtOH
N
H
R
3a-c
R
2
4a-c
5
O
N
O
O2N
CH3
O
N
N
CH3
O
Zn, NH4Cl
AlCl3
N
R
N
N
N
Δ, THF
H2O/EtOH
N
H
N
R
Δ
6a-c
7a-c
Scheme 1. Synthesis of N1-phenylpyrimido[5,4-e]-1,2,4-triazine-5,7(1H,6H)-diones.
R1 substituents reported herein as well the R3 and R6 positions of
the pyrimido[5,4-e]-1,2,4-triazine-5,7(1H, 6H)-dione core toward
uncovering agents with novel pharmacological properties.
Table 1
Substrates and reaction yields for hydrazone (4) addition to 6-chloro-3-methyl-5-
nitrouracil (5) and zinc-mediated ring closure to pyrimidotriazinediones (7)
Aldehyde (3)
Hydrazine (2)
Reaction yield
for addition of
hydrazone to
uracil (%)
Reaction
yield for
ring
Acknowledgments
closure (%)
A.J.T. gratefully acknowledges financial support of the NIGMS
(grant number GM007767), the American Chemical Society Divi-
sion of Medicinal Chemistry, Sheila B. Cresswell, and Fred and
Dee Lyons Graduate Fellowships.
O
H
65
53
73
78 (7a)
72 (7b)
81 (7c)
62 (7d)
51 (7e)
H3CO
Cl
NHNH2
O
H
References and notes
NHNH2
1. Daves, G. D.; Robins, R. K.; Cheng, C. C. J. Am. Chem. Soc. 1961, 83, 3904–3905.
2. Levenberg, B.; Linton, S. N. J. Biol. Chem. 1966, 241, 846–852.
3. Nagamatsu, T.; Yamasaki, H.; Hirota, T.; Yamato, M.; Kido, Y.; Shibata, M.;
Yoneda, F. Chem. Pharm. Bull. 1993, 41, 362–368.
O
H3C
F
NHNH2
H
4. Black, H. T. J. Heterocyclic Chem. 1987, 24, 1373–1375.
5. Typical experimental procedures. 1-(4-Methoxybenzylidene)-2-phenylhydrazine
(4a): A mixture of phenylhydrazine (2.0 mL, 20.3 mmol) and p-anisaldehyde
(2.7 mL, 22.3 mmol) was dissolved in 30 mL abs EtOH. The solution was heated at
reflux for 90 min and then cooled to 25 °C. The precipitated solid was collected by
filtration and rinsed thoroughly with EtOH to afford 3.91 g (85%) of pale peach
product; mp 226–228 °C: 1H NMR (DMSO-d6, 500 MHz) d 3.78 (s, 3H), 6.72 (t,
J = 7.2 Hz, 1H), 6.96 (d, J = 8.7 Hz, 2H), 7.06 (d, J = 7.75 Hz, 2H), 7.21 (t, J = 7.8 Hz,
2H), 7.59 (d, J = 8.7 Hz, 2H), 7.84 (s, 1H). 6-(2-(4-Methoxybenzylidene)-1-
phenylhydrazinyl)-3-methyl-5-nitropyrimidine-2,4(1H,3H)-dione (6a): Hydrazone
4a (200 mg, 0.88 mmol) was suspended in anhydrous THF under nitrogen. AlCl3
(118 mg, 0.88 mmol) and 6-chloro-3-methyl-5-nitrouracil (5)4 (164 mg,
0.80 mmol) were added, and the mixture was heated at reflux for 4 h, during
which time it became homogeneous and dark green. The mixture was cooled to
25 °C and then on ice, and the precipitated solid was collected by filtration and
washed with THF and EtOH to leave 490 mg (65%) of product as a pale lime green
powder; mp 225–229 °C: 1H NMR (DMSO-d6, 500 MHz) d 3.16 (s, 3H), 3.80 (s, 3H),
6.97 (d, J = 8.7 Hz, 2H), 7.39 (d, J = 6.05 Hz, 2H), 7.43 (s, 1H), 7.60 (m, 5H), 11.50 (br
s, 1H); 13C NMR (DMSO-d6, 125 MHz) d 27.69, 55.80, 114.65, 122.21, 125.98,
128.78, 129.37, 130.57, 130.84, 134.62, 145.07, 147.27, 149.19, 157.44, 161.74. 3-
(4-Methoxyphenyl)-6-methyl-1-phenylpyrimido[5,4-e][1,2,4]triazine-5,7(1H,6H)-
dione (7a): To a suspension of 6a (1.25 mmol) in 6 mL of 50% aq EtOH were added
zinc dust (327 mg, 5.0 mmol) and ammonium chloride (134 mg, 2.5 mmol). The
suspension was stirred vigorously and heated at reflux overnight with exposure to
the air. The mixture was cooled to 25 °C, diluted with 5 mL of 1 N aq HCl, and
stirred further for 1 h at 25 °C. The precipitated solid was collected by filtration,
washed with 1 N aq HCl and then EtOH, and dried to leave 84 mg (78%) of product
as a red powder; mp 315–317 °C (dec): 1H NMR (DMSO-d6, 500 MHz) d 3.34 (s,
3H), 3.88 (s, 3H), 7.14 (d, J = 8.4 Hz, 2H), 7.67 (m, 3H), 7.76 (m, 2H), 8.15 (d,
J = 8.3 Hz, 2H); 13C NMR (TFA-d, 125 MHz) d 24.68, 50.69, 117.96, 119.92, 126.77,
127.18, 130.03, 132.30, 137.09, 139.86, 143.29, 153.81, 160.79; MS m/z 362.2
(M+H).
O
H
O
H
NH2NHCH2CH2CH(CH3)2 52
H3CO
H3CO
NH2NHCH2CH2OH
67
Moreover, as shown in Table 1, the method is applicable to
substituted phenylhydrazines and alkyl hydrazines, although the
yields in the ring closure are slightly lower with alkyl substituents
at N1. Unlike aryl hydrazones derived from aryl hydrazines, those
derived from alkyl hydrazines do not require the use of AlCl3 in
the condensation with 6-chloro-3-methyl-5-nitrouracil, and the
reaction occurs much faster, usually within minutes. Attempts
were also made to condense the hydrazones with the less activated
6-chloro-3-methyluracil. These efforts were unsuccessful, how-
ever, as the presence of the nitro group at the 5-position of the ura-
cil was found to be critical for making the uracil sufficiently
electrophilic for Michael-type addition of the hydrazone, even in
the presence of AlCl3.
In conclusion, we describe a novel and efficient route to pyrim-
ido[5,4-e]-1,2,4-triazine-5,7(1H,6H)-diones. The methodology al-
lows for the incorporation of both aryl and alkyl groups at the R1
position of this ring system, which broadens the scope of accessible
substituents. Future reports will describe expanding the scope of
6. Lacrampe, J. F. A; Connors, R. W.; Ho, C. Y.; Richardson, A.; Freyne, E. J. E.;
Buijnsters, P. J. J.; Bakker, A. C. ‘3-Phenyl Analogs of Toxoflavine as Kinase
Inhibitors’ (Janssen Pharmaceutica N.V.), WO 2004007498 A3, 70 pp, 22 January
2004.