Solution-phase parallel synthesis of new 2H-pyrimido-[4,5-e][1,2,4]triazin- 3-ylidenecyanamides

Article abstract of DOI:10.1016/j.tetlet.2004.10.127

A practical synthesis of 2H-pyrimido[4,5-e][1,2,4]triazin-3- ylidenecyanamides has been developed. The key step is the coupling reaction of an aryldiazonium salt with 1-cyano-3-(2,6-dioxo-1,2,3,6-tetrahydropyrimidin-4- ylamino)-2-methylisothiourea followed by intramolecular cyclization. A library of 2H-pyrimido[4,5-e][1,2,4]triazin-3-ylidenecyanamides was prepared in two steps from 6-aminouracils using this method.

Full text of DOI:10.1016/j.tetlet.2004.10.127

Tetrahedron
Letters
Tetrahedron Letters 45 (2004) 9319–9322
Solution-phase parallel synthesis of new
2H-pyrimido-[4,5-e][1,2,4]triazin-3-ylidenecyanamides
Ill Young Lee,a,* Sang Yo Kim,b Jin Young Lee,c Chan-Mo Yu,b
Duck Hyung Leec and Young-Dae Gonga
aMedicinal Science Division, Korea Research Institute of Chemical Technology, PO Box 107, Yusong, Taejon 305-600, Korea
bDepartment of Chemistry, Sungkyunkwan University, Suwon 440-746, Korea
cDepartment of Chemistry, Sogang University, Seoul 121-742, Korea
Received 14 September 2004; revised 18 October 2004; accepted 25 October 2004
Available online 6 November 2004
Abstract—A practical synthesis of 2H-pyrimido[4,5-e][1,2,4]triazin-3-ylidenecyanamides has been developed. The key step is the
coupling reaction of an aryldiazonium salt with 1-cyano-3-(2,6-dioxo-1,2,3,6-tetrahydropyrimidin-4-ylamino)-2-methylisothiourea
followed by intramolecular cyclization. A library of 2H-pyrimido[4,5-e][1,2,4]triazin-3-ylidenecyanamides was prepared in two steps
from 6-aminouracils using this method.
Ó 2004 Elsevier Ltd. All rights reserved.
The solution-phase parallel synthesis of heterocyclic
libraries is an attractive method for discovering biologi-
cally active compounds.1 However, the construction of
heterocyclic small-molecule libraries requires the devel-
opment of new solution-phase synthetic methodologies.
Since pyrimidotriazines exhibit various types of pharma-
cological activity, such as antibacterial, antiviral, and
anticancer activities,2 this skeleton is an attractive target
for generating combinatorial libraries. There has been
considerable interest in the 7-azapteridines (2H-pyrimido-
[5,4-e][1,2,4]triazine ring system) because of their bio-
logical activity. Of particular interest has been the
naturally occurring antibiotic 2-methylfervenulone
(MSD-92, Fig. 1), which was isolated from fermentation
broth of Actinomycetes and shown to have broad bio-
logical activities.3 The synthesis and structural modifica-
tion of MSD-92 has received growing attention over the
past few decades.4 Recently, derivatives of MSD-92
have been reported with inhibitory activity toward
several protein tyrosine phosphatases5 (PTPases). The
6-azapteridines (2H-pyrimido[4,5-e][1,2,4]triazine ring sys-
tem) have also received attention because of antiviral
activity and their structural similarity with pteridines
O
O
N
O
N
R2
O
N
N
R3
N
N
O
N
N
R
O
N
N
N
N
N
N
N
R1
CN
O
N
O
1
2
MSD-92
Figure 1.
or purines.6 However, only a few synthetic routes to
6-azapteridines from the appropriate pyrimidine precur-
sors have been reported.6a,d Synthesis of one of the
6-azapteridines, 2H-pyrimido[4,5-e][1,2,4]triazine 1 was
achieved using either photo-induced or thermally
induced (210°C) cyclization.6f The replacement of a
urea or thiourea by a cyanoguanidine group is a recog-
nized method of increasing the biological activity of
drug-like compounds.7,8 We focused our efforts on the
synthesis of a new 2H-pyrimido[4,5-e][1,2,4]triazin-3-
ylidenecyanamide system 2 that would incorporate N-
cyanoimino group as an isosteric replacement of the
urea in 1.
Here, we report a new method for synthesizing the 2H-
pyrimido[4,5-e][1,2,4]triazine skeleton 5 by coupling an
aryldiazonium salt with 1-cyano-3-(2,6-dioxo-1,2,3,6-
tetrahydropyrimidin-4-ylamino)-2-methylisothioureas
4, followed by intramolecular cyclization4b,9 with the
elimination of methanethiol at room temperature. We
Keywords: 2H-Pyrimido[4,5-e][1,2,4]triazin-3-ylidenecyanamides; Pyr-
imidotriazine; Solution-phase parallel synthesis.
*
Corresponding author. Tel.: +82 42 860 7693; fax: +82 42 861
1291; e-mail: iylee@krict.re.kr
0040-4039/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2004.10.127

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I. Y. Lee et al. / Tetrahedron Letters 45 (2004) 9319–9322
used this route to construct a library of 2H-pyrim-
ido[4,5-e][1,2,4]triazine compounds.
1.5equiv of phenyldiazonium salt with 4a in acetonitrile
(entry 1), significant amounts of starting material was
recovered. To generate the phenyldiazonium salt, the
procedure using NaNO2 in water, HCl, and aniline in
EtOH was the most practical one, followed by the reac-
tion in DMF to provide 5aA in 53% isolated yield (entry
4). Similarly, using DMSO instead of DMF increased
the yield of 5aA by 10% due to the increased solubility
of 4a in DMSO. Further optimization used a 3-fold
molar excess of phenyldiazonium chloride, generated
in situ from the reaction of aniline with NaNO2 and
HCl in water and EtOH, coupled with 4a in DMSO to
give 5aA in 77% yield (entry 6). When we changed the
generation method of the phenyldiazonium salt to
isobutyl nitrite, the yield of 5aA was acceptable at 73%
(entry 7).
In our synthetic approach for preparing pyrimidotri-
azines 5, the key intermediate, 1-cyano-3-(2,6-dioxo-
1,2,3,6-tetrahydropyrimidin-4-ylamino)-2-methylisothio-
urea 4a, was obtained from 6-aminouracil 3a. 6-Amino-
1,3-dimethyluracil 3a and dimethyl N-cyanodithioimido-
carbonate was heated in DMF at 130°C for 5h in
the presence of K2CO3.10 After concentrating this reac-
tion mixture, it was purified by recrystallization from
water and EtOH to provide the previously unknown
compound 4a as a white solid in 77% isolated yield.
5-Phenylazouracils are intermediates in the synthesis of
various heterocycles containing the uracil moiety.11 We
applied the phenyldiazonium salt coupling to our inter-
mediate 4a to synthesize a diverse library of pyrimidotri-
azines 5 via cyclization of 5-phenylazouracil in a one-pot
process.
To prepare a combinatorial library of pyrimidotriazines
5, new compounds 4b–f were readily obtained from the
corresponding 6-aminouracils 3b–f and dimethyl N-
cyanodithioimidocarbonate by heating in DMF at
130°C for 3–5h, in 72–92% yields, as shown in Scheme
1. Of the 6-aminouracils 3a–f, 3a, and 3f were commer-
cially available and 3b–e were prepared from the
corresponding urea using a known method.12 The 6-
aminouracil 3d has not been previously reported.
The phenyldiazonium salt was coupled with 4a under
the conditions shown in Table 1. The yield of 5aA was
influenced by the solubility of 4a. Generally, the starting
material 4a was dissolved in relatively polar aprotic sol-
vents. When we initially tried the coupling reaction of
Table 1. Optimization studies for the synthesis of 5aA
O
O
Me
Me
O
N
N
Ph
N
N
SCH3
N
+
N
N
PhN2
0 oC-rt, 1 h
O
N
Me
N
H
CN
N
Me
CN
5aA
4a
Entry
Phenyldiazonium salt (solvent ratio)
Equiv
Solvent
Yield (%)
1
2
3
4
5
6
7
i-BuONO, HCl/EtOH–acetone (1:1)
i-BuONO, HCl/EtOH–acetone (1:1)
i-BuONO, TFA/CH2Cl2–CH3CN (2:1)
NaNO2, HCl/EtOH–H2O (2:1)
1.5
1.5
1.5
1.5
1.5
3.0
3.0
CH3CN
DMF
DMF
15 [54]a
45
47
DMF
53
63
NaNO2, HCl/EtOH–H2O (2:1)
NaNO2, HCl/EtOH–H2O (2:1)
i-BuONO, TFA/CH2Cl2–CH3CN (2:1)
DMSO
DMSO
DMSO
77
73
a Recovered starting material.
O
O
O
Ar
R2
O
R2
O
N
N
R2
O
N
N
N
SCH3
i
SCH3
ii
N
R1
NH2
N
R1
N
H
N
R1
N
H
N CN
N
CN
3
4
Yield (%)
77
- CH3SH
R
1 = Me, R2 = Me
4a
R1 = Bn, R2 = Bn
R1 = Ph, R2 = Me
4b
4c
4d
4e
4f
86
72
73
83
92
O
R2
O
N
N
Ar
R
1 = Ph, R2 = 4-MeOBn
R1 = Bn, R2 = Me
1 = Me, R2 = H
N
N
N
R1
N CN
R
5
Scheme 1. Reagents and conditions: (i) dimethyl N-cyanodithioimidocarbonate, K2CO3, DMF, 1 30°C, 5h; (ii) ArN2+, DMSO, 0°C to rt, 1h.

I. Y. Lee et al. / Tetrahedron Letters 45 (2004) 9319–9322
9321
F
Et
NO2
Me
O2N
H2N
F
H2N
H2N
H2N
H2N
H2N
E
J
A
F
D
Me
B
G
C
H
SMe
Cl
F
F
H2N
Me
H2N
H2N
H2N
I
Cl
Cl
Cl
O2N
H2N
OCF3
Br
Me
H2N
H2N
H2N
H2N
O
M
N
L
K
Figure 2. Anilines used for preparing the pyrimidotriazines 5.
Table 2. 2H-Pyrimido[4,5-e][1,2,4]triazin-3-ylidenecyanamide 5a array (isolation yields and puritiesb)
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
4a 5aA
5aB
5aC
5aD
5aE
5aF
5aG
5aH
5aI
5aJ
5aK
5aL
5aM
5aN
5aO
77(94) 72(85) 65(91) 42(92) 54(91) 52(87) 58(96) 78(96) 42(87) 45(82) 42(83) 68(92) 55(87) 62(82) 55(90)
4b 5bA 5bB 5bC 5bD 5bE 5bF 5bG 5bH 5bI 5bJ 5bK 5bL 5bM 5bN 5bO
70(92) 68(95) 85(83) 50(83) 72(87) 62(88) 42(95) 52(93) 63(93) 52(94) 52(84) 72(96) 67(82) 62(92) 53(85)
4c 5cA 5cB 5cC 5cD 5cE 5cF 5cG 5cH 5cI 5cJ 5cK 5cL 5cM 5cN 5cO
65(87) 65(94) 52(94) 65(92) 65(93) 43(91) 36(94) 42(91) 52(91) 47(85) 45(91) 47(84) 45(85) 65(84) 62(84)
4d 5dA 5dB 5dC 5dD 5dE 5dF 5dG 5dH 5dI 5dJ 5dK 5dL 5dM 5dN 5dO
45(92) 52(97) 48(87) 65(94) 62(91) 62(90) 45(85) 67(88) 76(94) 72(93) 54(96) 58(92) 52(90) 47(94) 47(94)
4e 5eA 5eB 5eC 5eD 5eE 5eF 5eG 5eH 5eI 5eJ 5eK 5eL 5eM 5eN 5eO
69(95) 61(91) 52(95) 42(95) 44(89) 42(92) 62(87) 51(95) 42(93) 32(86) 54(91) 45(91) 56(88) 55(88) 51(94)
4f 5fA 5fB 5fC 5fD 5fE 5fF 5fG 5fH 5fI 5fJ 5fK 5fL 5fM 5fN 5fO
61(93) 47(92) 46(94) 43(87) 42(92) 35(87) 51(96) 51(92) 42(85) 43(88) 32(81) 45(92) 54(90) 42(92) 47(95)
a Reaction conditions: 5aA–5aO, 5bA–5bO, 5cA–5cO, 5dA–5dO, and 5eA–5eO were obtained by condition of entry 6 in Table 1 (NaNO2, HCl,
DMSO, EtOH, H2O). 5fA–5fO were obtained by condition of entry 7 in Table 1 (i-BuONO, DMSO, CH2Cl2, CH3CN).
b % Purity based on NMR and LCMS analysis.
We prepared various pyrimidotriazines 5 by parallel
synthesis from 4a–f and anilines A–O (15 compounds,
Fig. 2) as shown in Table 2. Due to the good yield,
the reaction condition of entry 6 in Table 1 was initially
chosen as the standard procedure. The coupling reaction
of 4a and the aryldiazonium chloride salts from the 15
anilines in Figure 2 using the Bohdan Miniblock system
afforded the expected 2H-pyrimido[4,5-e][1,2,4]triazin-3-
ylidenecyanamides 5aA–5aO in acceptable yields
without any apparent steric or electronic effect of
substituents on the aromatic ring.13 Similarly, when we
investigated the influence of the structure of N-1,3-
disubstituted uracils 4b–e with the same procedure, the
desired products of 5bA–5eO were isolated in moderate
yields and high purities. This method is applicable to the
N-3 unsubstituted uracil 4f, where the hydrogen at the
N-3 position mimics that of uracil derivatives and their
nucleosides, this being essential for hydrogen bonding
with purine bases in biology.14 For the reaction of 4f
with phenyldiazonium chloride salts using the procedure
described above, only 5fA was isolated, and in only 36%
yield. To improve the solubility of 4f in the solvent sys-
tem, we tried to generate the phenyldiazonium salt using
isobutyl nitrite in the aprotic solvent CH3CN and
CH2Cl2 (entry 7 in Table 1). Under this condition, 4f
in DMSO gave 5fA in 61% yield. With this procedure,
the parallel synthesis of compounds 5fA–5fO was
achieved by coupling 4f with aryldiazonium salts (A–
O) as shown in Table 2.
In summary, we have developed a highly efficient and
mild synthetic method for the preparation of the pyrim-
idotriazine system starting from 6-aminouracils in two
steps. The coupling reaction of 4, obtained from the
reaction of 6-aminouracil 3 with dimethyl N-cyano-
dithioimidocarbonate in DMF on heating at 130°C,
with several aryldiazonium salts proceeded via intramo-
lecular cyclization to produce the corresponding pyrim-
idotriazine adducts 5 at room temperature. A library
of new 2H-pyrimido[4,5-e][1,2,4]triazin-3-ylidenecyan-
amides 5 (90 compounds) was constructed using solu-
tion-phase synthesis. Currently, efforts to expand the

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I. Y. Lee et al. / Tetrahedron Letters 45 (2004) 9319–9322
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scope of the method in combination with its application
to the synthesis of pharmaceutical molecules are ongo-
ing in our laboratory.
Acknowledgements
The authors acknowledge the financial support by the
Korea Research Institute of Chemical Technology and
the Ministry of Commerce, Industry and Energy of
Korea.
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13. General procedure for the parallel synthesis of 5aA–5aO:
On the Mettler-Toledo Miniblock synthesizer, a stirred
solution of anilines (A–O, 0.72mmol, 15 compounds) in
EtOH (0.4mL) was cooled to 0°C. After addition of HCl
(0.14mL, 0.72mmol) to the reaction mixtures, then a
solution of sodium nitrite (0.2mL, 0.36M in H2O) was
slowly added. After 30min, to this solution was added 1-
cyano-3-(1,3-dimethyl-2,6-dioxo-1,2,3,6-tetrahydro-pyr-
imidin-4-yl)-2-methylisothiourea 4a (0.8mL, 0.3M in
DMSO) at 0°C. The blocks were shaken for 1h at 25 °C.
The reaction mixture was concentrated under reduced
pressure in a Genevac HT-4X. The residue was purified on
a Biotage Quad 3+ using a flash 12M using ethyl acetate
and hexane solvent. 5aA: (58mg, 77%). Mp = 290–292°C
1
(decomposition). H NMR (200MHz, CDCl3) d: 7.53 (s,
5H), 3.68 (s, 3H), 3.49 (s, 3H). 13C NMR (75MHz,
CDCl3) d: 158.9, 155.4, 150.9, 149.3, 140.1, 130.3, 129.3,
125.6, 124.2, 114.0, 29.9, 29.2. IR (cmÀ1): 2192, 1697,
1654, 1571. LCMS (m/z): 309.
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