Synthesis and antitumor activity of s-tetrazine derivatives

Article abstract of DOI:10.1016/j.bmcl.2003.12.056

Fifty-five compounds of s-tetrazine derivative including hexahydro-, 1,6-dihydro, 1,4-dihydro-, 1,2-dihydro- and aromatic s-tetrazine were prepared. Their antitumor activities were evaluated in vitro by MTT method for P-388 cell and SRB method for A-549 cell. The results show that there are 9 compounds which in 10^-6 μM have more than 50% inhibition rate to A-549 cancer cell growth, and 7 compounds in 10^-6 μM have more than 50% inhibition rate to P-388 cancer cell growth. The IC₅₀ of compound 3q for P-388, Bel-7402, MCF-7 and A-549 are 0.6 μM, 0.6 μM, 0.5 μM and 0. 7 μM, respectively. So s-tetrazine derivative is a kind of compound which possesses potential antitumor activities and is worth to research further.

Full text of DOI:10.1016/j.bmcl.2003.12.056

Bioorganic & Medicinal Chemistry Letters 14 (2004) 1177–1181
Synthesis and antitumor activity of s-tetrazine derivatives
Wei-Xiao Hu,* Guo-Wu Rao and Ya-Quan Sun
College of Pharmaceutical Science, Zhejiang University of Technology, Hangzhou, 310014, People’s Republic of China
Received 25 October 2003; revised 15 December 2003; accepted 16 December 2003
Abstract—Fifty-five compounds of s-tetrazine derivative including hexahydro-, 1,6-dihydro, 1,4-dihydro-, 1,2-dihydro- and aro-
matic s-tetrazine were prepared. Their antitumor activities were evaluated in vitro by MTT method for P-388 cell and SRB method
for A-549 cell. The results show that there are 9 compounds which in 10ꢀ6 mM have more than 50% inhibition rate to A-549 cancer
cell growth, and 7 compounds in 10ꢀ6 mM have more than 50% inhibition rate to P-388 cancer cell growth. The IC50 of compound
3q for P-388, Bel-7402, MCF-7 and A-549 are 0.6 mM, 0.6 mM, 0.5 mM and 0.7 mM, respectively. So s-tetrazine derivative is a kind
of compound which possesses potential antitumor activities and is worth to research further.
# 2003 Elsevier Ltd. All rights reserved.
There are several reviews1 indicating that the use of
compounds containing the 1,2,4,5-tetrazine skeleton
had been claimed for use as pharmaceuticals. For exam-
ple, 3-amino-6-aryl-1,2,4,5-tetrazines showed modest
antimalarial activity,2 some hexahydro-s-tetrazines
proved to have useful analgesic and antiflammatory
activity.3 For a series of tetrahydro-s-tetrazines the
antibacterial and antifungal activities have been eval-
uated,4 a special 1,4-dihydro-s-tetrazine derivative was
pronounced antiviral activity.1b
reaction of 2a–b with substituted phenyl isocyanate
under 4-dimethylaminopyridine (DMAP) as catalyst.8
The stereostructure of 3d was determined by X-ray
analysis as shown in Figure 2, 9 which clearly shows the
N,N0-substituents are at the 1,4-positions as we expec-
ted. Therefore, it proved that 3 are 1,4-dihydro-s-tetra-
zine derivatives and that a rearrangement occurs in the
reaction. And the structure of 4c was determined by
X-ray analysis as shown in Figure 3,10 which clearly
shows N,N0-substituents are at the 1,2-positions, thus
proving that 4 are 1,2-dihydro-s-tetrazine derivatives.
Among them, the hexahydro-s-tetrazine (Fig. 1) was
recommended as an antitumor agent.5 Although there
was not any data about antitumor activities to be
reported, it is the first time to announce that this kind of
compound may possess potential antitumor activity. We
are interested in whether changing the structure is pos-
sible to improve the antitumor activity or not.
The antitumor activities in vitro for these compounds
were evaluated by method MTT for P-388 cell and SRB
for A-549. The results were summarized in Table 2.
Usually, when the concentration of the compound
solution is 10ꢀ6 mol/L, the inhibition ratio of the solu-
tion to cancer cell growth is more than 50%, the com-
pound is considered as a strong effective. According this
standard, it can be found from Table 2 that hexahydro-
s-tetrazine (1a–g), 1,6-dihydro-s-tetrazine (2a–m), 1,2-
dihydro-s-tetrazine (4a–g) and aromatic s-tetrazine (5a–
j) have almost no activities except 4f which has strong
Fifty-five compoundsy including hexahydro- (1), 1,6-dihy-
dro- (2), 1,4-dihydro- (3), 1,2-dihydro- (4) and aromatic
(5) s-tetrazines were prepared according literature
methods.6 The routes of synthesis are shown in Scheme
1 and Scheme 2. The results were summarized in Table
1. When preparing 2a–b from 1a–c, the Skorianetz meth-
od6c was modified with using of cheaper Pd/C catalyst
instead of PtO2.7 The 3a–z were prepared by the new
Keywords: Synthesis; Antitumor activity; s-tetrazine; X-ray analysis.
* Corresponding author. Tel.: +86-571-88320557; fax: +86-571-
85133199; e-mail: huyang@mail.hz.zj.cn
y
All new compounds were characterized by IR, 1H NMR, MS and
elemental analysis.
Figure 1.
0960-894X/$ - see front matter # 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2003.12.056

1178
W.-X. Hu et al. / Bioorg. Med. Chem. Lett. 14 (2004) 1177–1181
Scheme 1.
Fig.2. X-ray structure of 3d.
Scheme 2.
effective to P-388. Among 1,4-dihydro-s-tetrazine (3a–
z), there are 9 compounds which have strong effective to
A-549 cell and 6 compounds having strong effective to
P-388 cell. Especially, compounds 3i, 3q, 3t, 3w, 3z have
strong effective to both P-388 and A-549 cell. In addi-
tion, the substitutes on phenyl have much more effect on
the activity. Electrondonor substitutes are of benefit to
the inhibition ratio, and the compounds with meta
electrondonor substitute have more strong effective than
that compounds with the same substitute but at ortho
or para position.
For more accurately to examine antitumor activity, the
3q was selected to test the IC50. The IC50 of 3q for P-
388, Bel-7402, MCF-7 and A-549 are 0.6 mM, 0.6 mM,
0.5 mM and 0.7 mM, respectively. The results were sum-
marized in Table 3. So the s-tetrazine especially 1,4-
dihydro-s-tetrazine is a kind of compound which may
have potential antitumor activities. It is a good lead
compound that warrants further investigation.
Fig.3. X-ray structure of 4c.

W.-X. Hu et al. / Bioorg. Med. Chem. Lett. 14 (2004) 1177–1181
Table 1. Physical data and elemental analysis
1179
Compd
R
R0
mp (ꢁC)
Yield (%)
Formula
Elem. Anal. (%) Cal./ Found
H
C
N
1a
1b
1c
1d
1e
1f
1g
2a
2b
2c
2d
2e
2f
2g
2h
2i
2j
2k
2l
2m
3a
3b
3c
3d
3e
3f
3g
3h
3i
Me
Et
n-Pr
Me
Et
58–606c
127–1316c
129–1306c
200–2166b
184–193
196–206
188–190
107–1086a
71–726c
Liq.6a
Liq.
Liq.
Liq.
Liq.
Liq.
Liq.
Liq.
Liq.
Liq.
Liq.
128–130
91–93
120–121
131–133
90–91
184–186
154–156
223–224
183–184
204–206
74.2
53.2
56.9
45.0
65.8
46.9
63.4
35.0
43.6
92.9
86.9
95.3
86.2
89.4
83.2
83.2
81.7
85.0
92.9
73.0
47.7
34.5
27.3
52.9
24.9
5.8
Me
Me
Me
Me
C10H20N4O2
C12H24N4O2
C14H28N4O2
52.86/52.61
56.22/56.26
59.16/59.12
8.99/8.83
9.44/9.52
9.87/9.92
24.48/24.54
21.86/21.83
19.79/19.70
n-Pr
n-Bu
Me
n-Pr
Me
Me
Me
Me
Me
Me
n-Pr
n-Pr
n-Pr
n-Pr
n-Pr
n-Pr
n-Pr
n-Pr
Et
Me
n-Pr
Ph
CH2Ph
n-C5H11
i-C5H11
Me
C8H14N4O2
C11H12N4O2
C12H14N4O2
C10H18N4O2
C10H18N4O2
C10H18N4O2
C11H20N4O2
C15H26N4O2
C14H26N4O2
C14H26N4O2
C22H26N6O2
C24H30N6O2
C22H24Cl2N6O2
C20H22N6O2
C22H26N6O2
C18H30N6O2
C20H22N6O2
C26H22N6O2
C18H18N6O2
C20H16F6N6O2
48.47/48.52
56.89/56.49
58.53/58.60
53.08/52.95
53.08/53.21
53.08/53.15
54.98/54.90
61.20/61.24
59.55/59.58
59.55/59.57
65.01/65.03
66.34/66.17
55.59/55.47
63.48/63.40
65.01/65.02
59.65/59.98
63.48/63.40
69.32/69.24
61.70/61.76
49.39/49.73
7.12/7.08
5.21/5.08
5.73/5.77
8.02/8.00
8.02/8.14
8.02/8.26
8.39/8.36
8.90/9.06
9.28/9.37
9.28/9.36
6.45/6.66
6.96/7.04
5.09/5.08
5.86/5.88
6.45/6.46
8.34/8.44
5.86/6.12
4.92/4.95
5.18/5.08
3.32/3.39
28.27/28.28
24.13/24.17
22.75/22.75
24.76/24.69
24.76/24.84
24.76/24.82
23.32/23.41
19.03/19.06
19.84/19.90
19.84/20.04
20.67/20.75
19.34/19.44
17.68/17.63
22.21/22.38
20.67/20.55
23.19/22.84
22.21/21.86
18.65/18.48
23.99/23.97
17.28/17.59
Et
Cyclohexyl
n-C5H11
i-C5H11
Ph
m-CH3Ph
m-ClPh
Ph
m-CH3Ph
Cyclohexyl
PhCH2
a-Naphthyl
Ph
Et
Me
Me
Me
Me
Me
20.7
4.8
58.0
32.4
3j
m-CF3Ph
3k
Me
216–217
77.8
C24H26N6O6
58.29/58.22
5.30/5.23
16.99/17.18
3l
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
m-NO2Ph
o-ClPh
m-ClPh
254–255
199–201
210–211
231–232
185–187
138–139
201–202
198–199
136–137
180–182
19.7
47.2
64.7
29.8
24.7
37.5
19.4
7.8
C18H16N8O6
C18H16Cl2N6O2
C18H16Cl2N6O2
C18H16Cl2N6O2
C20H22N6O2
C20H22N6O2
C20H22N6O2
C20H22N6O4
C20H22N6O4
C20H22N6O4
49.09/48.85
51.56/51.60
51.56/51.75
51.56/51.57
63.48/63.71
63.48/63.72
63.48/63.62
58.53/58.24
58.53/58.55
58.53/58.75
3.66/3.75
3.85/3.85
3.85/4.08
3.85/3.99
5.86/5.93
5.86/6.09
5.86/5.63
5.40/5.04
5.40/5.34
5.40/5.57
25.44/25.18
20.04/20.25
20.04/20.09
20.04/20.39
22.21/22.49
22.21/22.57
22.21/22.46
20.48/20.67
20.48/20.67
20.48/20.65
3m
3n
3o
3p
3q
3r
3s
3t
p-ClPh
o-CH3Ph
m-CH3Ph
p-CH3Ph
o-CH3OPh
m-CH3OPh
p-CH3OPh
37.4
28.7
3u
3v
3w
3x
3y
3z
Me
Me
Me
Me
Me
172–174
170–172
235–237
236–237
230–231
37.4
20.0
44.2
30.8
52.5
C24H26N6O6
C22H28N8O2
C18H14Cl4N6O2
C22H26N6O2
C22H26N6O6
58.29/58.45
60.53/60.44
44.29/44.31
65.01/65.29
56.16/55.92
5.30/5.45
6.46/6.50
2.89/2.92
6.45/6.53
5.57/5.64
16.99/17.13
25.67/25.83
17.22/17.29
20.67/20.54
17.86/17.75
4a
4b
4c
4d
4e
4f
4g
5a
5b
5c
Ph
Ph
Ph
Ph
Ph
Ph
Ph
H
Me
Et
n-Pr
Me
i-Pr
194–1966e
173–174
121–122
111–112
164–165
195–196
210–211
200(d)
85
67
34
64
85
46
31
39
83
38
C18H16N4O4
C20H20N4O4
C22H24N4O4
C16H14N4O
C18H18N4O
C22H19N5O2
C10H6N8
61.36/61.34
63.15/63.17
64.69/64.65
69.05/69.14
70.57/70.76
68.56/68.66
50.41/50.64
4.58/4.56
5.30/5.29
5.92/6.04
5.07/5.03
5.92/6.00
4.97/4.86
2.54/2.15
15.90/15.94
14.73/14.93
13.72/13.81
20.13/20.22
18.29/18.10
18.17/18.02
47.04/47.21
o-CH3OPh
Pyrazinyl
Ph
p-CH3Ph
194–1966f
220–2316f
5d
179–180
47
C14H12N6
63.61/63.79
58.02/58.34
4.59/4.82
3.65/3.61
31.40/31.80
16.91/16.73
5e
5f
5g
5h
5i
m-ClPh
p-ClPh
o-ClPh
PhCH2
p-ClPhCH2
p-CF3Ph
208–2106f
180–1906f
178–1806f
63–656f
131–132
6f
250(d)
44
87
52
50
57
89
C16H12Cl2N4
5j

1180
W.-X. Hu et al. / Bioorg. Med. Chem. Lett. 14 (2004) 1177–1181
Table 2. Inhibition of in vitro tumor cell growth by tetrazine derivatives
Compd
Rate of inhibition of P388,
C (tetrazine)/(mol.Lꢀ1
Rate of inhibition of A549,
C (tetrazine)/(mol.Lꢀ1
)
)
10ꢀ4
10ꢀ5
10ꢀ6
10ꢀ7
10ꢀ8
10ꢀ4
10ꢀ5
10ꢀ6
10ꢀ7
10ꢀ8
1d
1e
1f
1g
2a
2b
2c
2d
2e
2f
2g
2h
2i
2j
2k
2l
2m
3a
3b
3c
3e
3f
3g
3h
3i
14.5
38.9
38.5
37.9
100
0.1
0.0
5.5
0.0
19.7
0.0
7.8
13.5
27.9
3.0
19.8
17.8
17.3
15.0
33.6
7.7
14.3
61.5
63.9
58.7
63.5
0.0
4.3
0.0
3.2
0.0
9.2
0.0
0.0
9.0
13.6
2.0
7.3
13.6
4.5
2.2
38.3
5.6
6.9
22.8
0.0
0.0
0.0
0.0
50.3
0.0
90.6
9.5
1.6
0.0
0.0
3.1
0.0
15.9
0.0
11.3
8.7
1.2
2.3
0.0
0.8
1.7
5.0
44.8
0.0
7.3
4.4
4.8
0.0
0.0
0.0
22.0
0.0
87.5
0.0
0.0
20.6
0.0
0.0
7.4
0.0
0.0
0.0
0.0
0.0
0.0
5.7
5.2
0.0
1.0
0.0
0.0
3.3
3.6
4.5
0.0
9.9
4.1
0.0
0.0
0.0
0.0
19.6
0.0
81.3
0.0
0.0
22.2
0.0
0.0
0.0
0.0
96.8
0.0
0.0
92.2
0.0
0.0
90.7
0.0
0.0
73.1
0.0
3.3
2.8
2.5
9.2
46.9
0.0
0.0
0.0
4.5
0.0
4.3
16.1
12.6
0.0
0.0
9.7
68.5
47.5
59.8
47.6
67.7
61.7
75.9
16.7
32.1
0.0
22.8
0.0
59.6
12.5
25.8
0.0
89.4
56.6
93.3
91.3
90.4
58.9
64.4
56.6
76.5
39.3
27.3
0.9
28.8
21.2
53.4
80.0
84.8
24.6
80.0
87.7
24.2
67.0
93.2
42.0
86.4
87.5
87.6
35.5
95.3
23.4
85.1
83.8
90.9
60.6
60.4
90.3
0.0
6.0
9.7
8.6
13.1
4.8
0.5
19.6
11.0
0.0
0.0
4.6
0.0
0.0
0.0
5.2
3.6
10.1
4.0
6.4
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
23.5
2.3
7.4
2.9
1.2
4.8
5.5
0.0
0.0
0.0
0.0
0.0
1.1
0.0
0.0
0.0
18.1
0.0
0.0
6.1
4.0
10.8
16.7
0.0
32.0
10.0
60.3
10.7
0.0
0.0
0.0
0.0
7.4
0.0
81.8
7.7
0.0
89.2
0.0
5.7
73.9
0.0
0.0
75.0
0.0
0.0
0.0
0.0
0.0
29.6
0.0
0.0
27.1
0.0
0.0
0.0
0.0
0.0
0.0
1.1
0.0
3.2
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
7.6
0.0
0.0
0.0
1.0
2.5
0.0
2.5
0.0
0.0
1.6
0.0
14.1
4.4
50.0
16.1
0.0
0.0
0.0
0.0
0.0
0.0
80.3
12.3
0.0
86.2
0.0
1.1
69.3
0.0
0.0
26.1
0.0
0.0
0.0
0.0
0.0
29.5
0.0
0.0
29.7
0.0
0.0
0.0
0.0
0.0
0.0
8.7
0.0
42.2
60.5
34.8
85.3
24.1
42.6
28.8
90.4
35.4
44.0
32.8
83.5
85.4
81.6
84.4
91.6
72.6
92.8
60.5
89.1
73.0
63.5
69.8
90.5
85.9
50.0
82.8
96.8
73.4
59.4
95.3
73.0
46.3
95.4
30.6
90.7
94.4
55.8
50.5
93.9
80.9
62.7
82.5
64.5
69.9
15.5
56.4
2.6
0.7
0.0
0.0
78.3
84.2
88.4
84.1
3.5
82.3
16.9
77.9
10.7
28.8
0.0
0.0
7.6
14.8
0.0
83.3
9.2
0.0
86.2
0.9
12.5
83.0
0.0
73.9
79.3
69.0
0.0
10.8
29.8
0.0
46.6
72.6
3.9
9.5
17.0
0.0
48.3
74.1
59.6
81.1
0.0
81.8
9.1
79.4
8.9
0.0
0.0
0.0
0.0
1.9
0.0
80.3
6.2
0.0
84.6
0.0
6.8
80.7
0.0
37.5
77.3
0.0
0.0
0.0
0.5
0.0
38.7
4.7
57.5
6.3
90.6
28.6
25.4
58.7
41.3
29.7
14.8
18.8
96.8
4.7
17.2
93.8
36.5
0.0
84.3
5.9
91.7
88.8
67.2
14.6
35.6
54.8
10.9
61.1
25.2
0.0
3j
3k
3l
38.1
1.6
6.3
1.9
1.6
98.4
3.1
3m
3n
3o
3p
3q
3r
3s
3t
3u
3v
3w
3x
3y
3z
4a
4b
4c
4d
4e
4f
4g
5a
5b
5c
5d
5e
5f
5g
5h
5i
0.0
96.8
3.1
0.0
95.2
6.3
0.0
88.9
0.0
1.6
93.8
14.3
0.0
89.8
1.9
31.5
88.9
5.4
11.6
7.0
4.5
6.6
52.0
7.4
0.0
0.0
4.4
0.0
0.0
90.7
10.2
5.2
4.9
4.3
5.5
24.9
0.8
0.0
0.0
2.4
0.0
13.5
19.4
14.6
4.6
8.9
19.5
0.0
20.3
0.0
0.0
0.0
0.0
0.0
4.3
13.1
0.0
0.0
8.3
3.6
26.5
35.1
2.8
15.6
29.1
44.4
40.3
52.3
8.2
51.0
58.4
51.5
33.2
29.0
5.6
18.5
9.3
0.0
0.0
0.0
66.8
65.8
40.2
0.0
0.0
0.0
61.7
57.1
2.5
5j
33.0
Table 3. Determine the IC50 of compound 3q
Cancer cell
Rate of inhibition (%)
IC50 (mM)
Concentration (mM)
0
5.0
3.125
2.5
1.563
1.25
1.0
0.781 0.625
0.5
0.399
0.313 0.25
0.195
0.125
0.0625
P-388
—
—
—
—
—
87.8
—
97.3
—
—
—
—
89.0
—
91.1
—
—
—
—
77.8
—
—
—
71.2
93.6
83.1
—
—
—
—
54.2
—
—
—
64.3
36.6
55.4
—
—
—
—
27.4
—
—
—
35.7
0
2.3
—
—
—
—
—
1.1
0
—
—
0
0.6
0.6
0.5
0.7
Bel-7402
MCF-7
A-549
—
—
—
—
—
0

W.-X. Hu et al. / Bioorg. Med. Chem. Lett. 14 (2004) 1177–1181
1181
Acknowledgements
7. Sun, Y.-Q.; Hu, W.-X.; Yuan, Q. Synth. Commun. 2003,
33, 2769.
8. Synthesis of 3d: A mixture of 3,6-diethyl-1,6-dihydro-s-
tetrazine (1.40 g, 10 mmol), 4-dimethylaminopyridine
(0.50 g, 4 mmol), phenyl isocyanate (2.66 g, 20 mmol) and
chloroform (50 cm3) was heated at reflux for 72 h. After
removing the solvent, n-hexane was added to the residue
of the mixture, and then cooled. The resulting precipitate
was filtered, and recrystallized from alcohol to give 3d
(2.00 g, 52.9%) as colorless crystal (Found: C, 63.40; H,
5.88; N, 22.38. Calc. for C20H22N6O2: C, 63.48; H, 5.86;
N, 22.21%); Mp 131ꢂ133 ꢁC; nmax/cmꢀ1 3340 (NH),
3040 (Ph), 2963, 2928 (CH3), 1698, 1593, 1505 (Ph), 1443,
1317 (C=N), 1222, 973, 756 and 735; dH (400 MHz;
CDCl3; Me4Si) 9.25 (2H, s, NH), 7.10–7.60 (10H, m, Ph),
2.89 (4H, q, CH2) and 1.15 (6H, t, CH3); m/z 378 (M+,
13%), 141(9), 140(100), 119(12), 91(12), 77(17), 65(9),
56(49). Compounds of 3a–z were prepared as described
above for 3d.
The authors thank the National Natural Science Foun-
dation of China (20272053) for financial support and
National Center for Drug Screening, Shanghai, China
for evaluation of antitumor activities.
References and notes
1. (a) Neunhoeffer, H. Comprehensive Heterocyclic Chemistry,
I; Katritzky, A. R., Ed.; Pergamon: Frankfurt, 1984; Vol. 3,
p 531. (b) Sauer, J. Comprehensive Heterocyclic Chemistry,
I; Boulton, A. J., Ed.; Elsevier: Oxford, 1996; Vol. 6, p 901.
2. Werbel, L. M.; Mcnamara, D. J. J. Heterocycl. Chem.
1979, 16, 881.
3. Kigasawa, K.; Hiiragi, M.; Wagatsuma, N.; Kohagizawa,
T.; Inoue, H. JP Patent 54,163,579, 1979.
4. Mohan, J. Org. Prep. Proced. Int. 1992, 24, 523.
5. (a) Eremeev, A. V.; Tikhomirov, D. A.; Tyusheva, V. A.;
Liepins, F. Khim. Geterotsikl. Soedin 1978, 753. (b) Ere-
meev, A. V.; Tikhomirov, D. A.; Zidermane, A. U.S.S.R.
686,336, 1980.
6. (a) Jennison, C. P. R.; Mackay, D.; Watson, K. N.; Tay-
lor, N. J. J. Org. Chem. 1986, 51, 3034. (b) Jensen, K. A.;
Hammerum, S. Acta Chemical Scan. 1972, 26, 1258. (c)
Skorianetz, W.; Kovatz, E. Sz. Helv. Chim. Acta 1971, 54,
1922. Skorianetz, W.; Kovatz, E. Sz. Helv. Chim. Acta
1970, 53, 251. (d) Kauffmann, Th.; Ruckelshauss, G.;
Schulz, J. Angew. Chem. 1963, 75, 1204. (e) Abdel-Rahman,
M. O.; Kira, M. A.; Tolba, M. N. Tetrahedron Lett. 1968, 9,
3871. (f) Neunhoeffer, H.; Wiley, P. F. Chem. Heterocycl.
Compd. 1978, 33, 1033. (g) Neugebauer, F. A.; Krieger,
C.; Fischer, H.; Siegel, R. Chem. Ber. 1983, 116, 2261.
9. Crystal data of 3d. C20H22N6O2, M=378.44, Orthor-
˚
hombic, a=16.287(2), b=11.347(4), c=20.975(4) A,
3
˚
U=3876.4(16) A , T=293(2) K, space group Pbca (no.
,
61), Z=8, Dc=1.297 g cmꢀ3, m (Mo-Ka)=0.088 mmꢀ1
3856 reflections measured, 3486 unique (Rint=0.0284)
which were used in all calculations. Fine R1=0.034,
wR(F2)=0.1035 (all data). CCDC reference number
220758.
10. Crystal data of 4c. C20H20N4O4, M=380.40, triclinic,
˚
a=8.915(2), b=10.444(2), c=11.509(3) A, a=103.268(3),
3
˚
˚
b=102.844(3), g=100.765(3) A, U=984.4(4) A ,
T=293(2) K, space group P-1 (no. 2), Z=2, Dc=1.283 g
cmꢀ3, m(Mo-Ka)=0.092 mmꢀ1, 4947 reflections mea-
sured, 4179 unique (Rint=0.0188) which were used in all
calculations. Fine R1=0.059, wR(F2)=0.1969. CCDC
reference number 220757.