A facile synthesis of [N1,NH2-15N2]-, [N3,NH2-15N2]-, and [N1,N3,NH2-15N3]-labeled adenine

Full text of DOI:10.1021/jo010253q

6
472
J . Org. Chem. 2001, 66, 6472-6475
Notes
1
5
A F a cile Syn th esis of [N1,NH
2
- N
2
]-,
phism, in which interproton nuclear Overhauser effects
(NOEs) are often severely underdetermined.
1
5
[
N3,NH
2
- N
2
]-, a n d
The synthesis of nucleosides with 15N at relevant sites
can be achieved either by chemical transformations of
an intact nucleoside or by total synthesis, i.e., labeling
of the base followed by its glycosylation with an ap-
propriately functionalized sugar derivative. By the use
of the first approach, N1 labeling of adenosine was
carried out by reacting activated hypoxanthine, i.e., N1-
1
5
[
N1,N3,NH
2
- N
3
]-La beled Ad en in e
Moti L. J ain, Ya-Ping Tsao, Nan-Lu Ho, and
J ya-Wei Cheng*
Division of Structural Biology and Biomedical Science,
Department of Life Science, National Tsing Hua University,
Hsinchu 300, Taiwan, ROC
aryl20 or -nitro derivatives, with NH and also by N1-
21
15
3
2
2
23
benzyl-mediated or N1-methoxy-mediated Dimroth
rearrangement of [6- NH ]adenosine derivatives. How-
2
1
5
jwcheng@life.nthu.edu.tw
Received March 8, 2001
ever, the second approach is more appropriate to achieve
N3 labeling of the purines. The earlier method reported
by several groups2
4-26
to prepare N3-labeled adenine
The 15N labeling of oligonucleotides at specific sites has
proven to be very useful as a probe in NMR studies to
15
involves nitration of 4-bromoimidazole with H NO ,
whereas another strategy used by Rhee and J ones
3
2
7
1
-4
elucidate nucleic acid structures
and nucleic acid
involves bromination of ethyl imidazole-4,5-dicarboxylate
interactions with protein, ligands, or drugs5 as well as
to provide direct evidence for H bonding in Watson-
Crick, Hoogsteen, or non-Watson-Crick base pairs.1
The recent direct detection of H bonds by spin-spin
scalar coupling between nuclei of H-donor and -acceptor
-9
15
followed by its azo coupling to introduce N label at the
C-5 position in its key steps. However, both methods
require either protection of the imidazole nitrogen (earlier
method) or blocking of the C-2 position to force the azo
coupling at the required site (the later case). The J ones
group further explored their methodology to prepare
doubly labeled 5-amino-4-imidazolecarboxamide (AICA),
0-14
moieties in RNA as well as DNA provides a new approach
These new parameters are
particularly valuable for studying nucleic acid polymor-
for probing H bonds.1
5-19
1
5
2 3
4c, and to convert it to [N1,N3,NH - N ]adenosine and
1
5
28
[
1,2,3- N
3
]guanosine. Chiriac et al. have recently re-
1
3
15
15
*
To whom correspondence should be addressed. Tel: 886-3-
742763. Fax: 886-3-5721746.
1) Marriappan, S. V. S.; Silks, L. A.; Bradbury, E. M.; Gupta, G. J .
Mol. Biol. 1998, 283, 111-120.
2) Lynch, S. R.; Tinoco, I., J r. Nucleic Acids Res. 1998, 26, 980-
87.
ported synthesis of [8- C-1,3,7- N
urea and its conversion to [8- C-1,3,7-NH - N ]adenine.
2 4
3
]xanthine from
N
5
13
15
29
(
However, their method involved many steps, and the
overall yield is not satisfactory. Because the N3 site of
purine is not involved in Watson-Crick H bonding or
Hoogsteen pairing, it is available as a minor groove DNA-
binding site for several small molecules acting as anti-
(
9
(
(
3) Kainosho, M. Nat. Struct. Biol. 1997, 4, 858-861.
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(
5) Masse, J . E.; Allain, F. H.-T.; Yen, Y.-M.; J ohnson, R. C.; Feigon,
30
viral, antibiotic, and antineoplastic agents, including
J . J . Am. Chem. Soc. 1999, 121, 3547-3548.
Netropsin3
1,32
and Distamycin.
33-35
Therefore, a practical
(
6) Kim, I.; Muto, Y.; Inoue, M.; Watanabe, S.; Kitamura, A.;
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(
7) Ramesh, V.; Xu, Y.-Z.; Roberts, G. C. K. FEBS Lett. 1995, 363,
6
1-64.
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(
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(
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NMR 1999, 15, 207-211.
(
1
(
(
(
(
(29) Chiriac, M.; Axente, D.; Palibroda, N.; Craescu, C. T. J . Labelled
Compd. Radiopharm. 1999, 42, 377-385 and references therein.
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Acad. Sci. U.S.A. 1987, 84, 8385-8389.
8
(
1
(
(
1
(
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25, 3296-3303.
1
0.1021/jo010253q CCC: $20.00 © 2001 American Chemical Society
Published on Web 08/23/2001

Notes
J . Org. Chem., Vol. 66, No. 19, 2001 6473
Sch em e 1
and more convenient route for N3 labeling of purine is
highly desired. Besides this, our major goal was to
develop a common pathway for both adenine and guanine
in such a way that labeling can be done at the desired
position and in the desired combination. AICA is an ideal
intermediate because it can be converted easily to both
can be used to prepare its labeled derivative. Thus,
1
5
heating 1 with NH NO or NH NO in sulfuric acid for
4
3
4
3
12 h at 100 °C resulted in smooth nitration of 1 at the
required C-5 site to afford 2a or its labeled analogue 2b
in 76% and 73% yield, respectively. The introduction of
15
13
2
NO functionality in 2b was indicated from its C NMR
3
6
adenine and guanine and can also afford the corre-
spectrum, which showed a doublet for C-5 (J C-N ) 26.4
sponding desired labeled nucleosides.2
8,37
15
Hz), and also from its N NMR spectrum exhibiting a
We envisioned that nitration of commercially available
signal at δ 364.2.
4
-imidazolecarboxylic acid (1) can provide a simple route
Conversion of acid 2b to its carboxamide 3b via dimeric
1
5
to introduce an N label at the required C-5 position and
can shorten the overall synthesis of this labeled key
intermediate 4. Herein, we report a facile synthesis of
4
1,42
lactum using SOCl
2
followed by its reaction with
ammonia gas afforded only 40% of the desired product.
However, excellent yield (95%) was obtained by in situ
activation of the acid 2b using 1,1′-carbonyldiimidazole
4
a -c from 1 in excellent overall yields and their conver-
15 15
sion to [N1,NH
2
- N
2
]adenine (7a ), [N
3
,NH
2 2
- N ]adenine
(
CDI)43 in DMF and subsequent bubbling of excess
1
5
(
(
7b), and [N1,N3,NH
Scheme 1).
The literature method to prepare 5-nitro-4-imidazole-
2 3
- N ]adenine (7c), respectively
ammonia into it. To introduce a label at the amide
1
5
position, the reaction was carried out using NH
3
(gener-
ated in situ with 15NH
Cl/K CO ) in CH CN giving 3a or
4
2
3
3
carboxylic acid (2a ) involves conversion of 4-methyl-5-
doubly labeled amide 3c in 90% and 92% yields, respec-
nitroimidazole to its styryl derivative followed by oxida-
1
tion,38 resulting in poor overall yields. Surprisingly, a
tively. The amide protons in the H NMR of these
carboxamides appeared as two singlets for 3b and two
doublets (J N-H ≈ 90 Hz) for 3a and 3c because of the
proximity of the adjacent nitro group at the C-5 position.
The 13C NMR spectrum of 3c showed two doublets at δ
survey of the literature showed scanty information
regarding nitration of the acid 1. Our initial approach
for nitration of 1 under different conditions using tri-
3
9
fluoroacetic anhydride/ammonium nitrate and potas-
sium nitrate together with sulfuric acid40 resulted in
either failure or poor yield of the desired product.
However, reaction conditions were optimized to use a
143.8 (J C-N
) 26.8 Hz) and δ 159.3 (J
C-N
) 18.6 Hz) as
expected, and also its 15N NMR spectrum displaying
signals at δ 113.0 and 362.9 for amino and nitro func-
tionalities, respectively, further supported its structure.
solid nitrating agent (NH
the corresponding cheaper and easy to handle NH
4 3 3
NO ) instead of HNO so that
1
5
4
NO
3
Catalytic reduction of 3a -c using 10% Pd/C in MeOH/
AcOH (9:1) at 45 psi for 6 h afforded singly (4a ,b) or
doubly labeled (4c) key intermediate AICAs, which were
isolated as their HCl salts in 85-88% yields. The overall
yields of 4a -c from 1 were 57-61%. Ring closure of 4a -c
(
35) Pelton, J . G.; Wemmer, D. E. Biochemistry 1988, 27, 8088-
096.
36) Ewing, D. F.; Mackenzie, G. In Rodd’s Chemistry of Carbon
8
(
Compounds, 2nd suppl.; Sainsbury, M., Ed.; Elsevier: Amsterdam,
Netherlands, 1999; Vol. IV, pp 127-177.
(37) Orji, C. C.; Silks, L. A. J . Labelled Compd. Radiopharm. 1995,
3
8, 624-630.
(41) Lunt, E.; Newton, C. G.; Smith, C.; Stevens, G. P.; Stevens, M.
F. G.; Straw, C. G.; Walsh, R. J . A.; Warren, P. J .; Fizames, C.; Lavelle,
F.; Langdon, S. P.; Vickers, L. M. J . Med. Chem. 1987, 30, 357-366.
(42) Varoli, L.; Burnelli, S.; Garuti, L.; Guarnieri, A.; Rossi, M.
Pharmazie 1997, 52, 578-581.
(
38) Allsebrook, W. E.; Gulland, J . M.; Story, L. F. J . Chem. Soc.
1
942, 232-236.
(
(
39) Crivello, J . V. J . Org. Chem. 1981, 46, 3056-3060.
40) Stambaugh, J . E.; Manthei, R. W. J . Chromatogr. 1967, 31,
1
28-136.
(43) Staab, H. A. Angew. Chem., Int. Ed. Engl. 1962, 1, 351-367.

6
474 J . Org. Chem., Vol. 66, No. 19, 2001
Notes
with triethyl orthoformate44 in DMF at 140 °C to hypox-
4. The solid obtained was filtered, washed with water, and
recrystallized from ethanol to afford pure desired product.
anthines 5a -c, followed by their chlorination using
1
5
and dimethylaniline,28 gave the corresponding N-
15
[CONH
2
- N]-5-Nitr o-4-im id a zoleca r boxa m id e (3a ). Pre-
POCl
3
pared from 2a by following the general procedure in 90% yield;
4
5
labeled 6-chloropurines 6a -c. Finally, ammonolysis of
OH in MeOH afforded the corresponding
1
mp >300 °C; H NMR (DMSO-d
6
) δ 7.86 (s, 1H), 8.12 (d, J N-H
)
C
6
a -c with 15NH
4
13
8
9.5 Hz, 1H), 8.16 (d, J N-H ) 89.0 Hz, 1H), 13.83 (br s, 1H);
desired doubly labeled (7a and 7b) or triply labeled
NMR (DMSO-d ) δ 126.1 (d, J ) 9.9 Hz), 135.6, 144.3, 159.8 (d,
6
J ) 18.8 Hz); 15N NMR (DMSO-d
) δ 112.9; HRMS m/z 157.0262
(calcd for C H O N3 N, 157.0254).
adenine (7c). All of the adenines showed a doublet (J N-H
6
1
4
15
≈
90 Hz) in their H NMR spectrum, and also, their 15N
1
4
4
3
1
5
[
NO
2
- N]-5-Nit r o-4-im id a zoleca r b oxa m id e (3b ). Pre-
NMR spectrum exhibited a signal at δ 79.5 confirming
pared from 2b by following the general procedure in 95% yield;
the presence of the 15NH
functionality, besides signals
2
1
mp >300 °C; H NMR (DMSO-d
6
) δ 7.84 (s, 1H), 8.11 (s, 1H),
.16 (s, 1H), 13.83 (br s, 1H); C NMR (DMSO-d ) δ 126.1, 135.5,
144.4 (d, J ) 25.0 Hz), 159.8; N NMR (DMSO-d ) δ 362.9;
at δ 237.8, 234.9, or both in the case of 7a , 7b, or 7c,
respectively. The overall yields of 7a -c from 1 were 43-
13
8
6
1
5
6
1
4
15
4
8%.
HRMS m/z 157.0249 (calcd for C
4
H
4
O
3
N
3
N, 157.0254).
]-5-Nitr o-4-im id a zoleca r boxa m id e (3c).
Prepared from 2c by following the general procedure in 92%
1
5
[
2 2 2
NO ,CONH - N
In summary, the labeling at N1 and N3 (using 1.5
equiv of cheap and solid regents, 15NH
15
4
4 3
Cl and NH NO ,
1
yield; mp >300 °C; H NMR (DMSO-d
6
) δ 7.86 (s, 1H), 8.12 (d,
as labeling source) and also at the amino group in any
required combination for adenine was achieved from
J
1
N-H ) 89.5 Hz, 1H), 8.16 (d, J N-H ) 88.6 Hz, 1H), 13.84 (br s,
13
6
H); C NMR (DMSO-d ) δ 126.1, 135.5, 144.3 (d, J ) 26.8 Hz),
15
4
-imidazolecarboxylic acid via a facile and straightfor-
6
159.8 (d, J ) 18.6 Hz); N NMR (DMSO-d ) δ 113.0, 362.9;
15
1
4
4 4 3 2 2
HRMS m/z 158.0218 (calcd for C H O N N , 158.0224).
ward synthesis of AICA in high yields.
Gen er a l P r oced u r e for P r ep a r a tion of 5-Am in o-4-im i-
d a zoleca r boxa m id e (AICA). A suspension of 3 (4.0 mmol) in
MeOH (18.0 mL) containing AcOH (2.0 mL) was purged with
nitrogen before the catalyst (0.312 g of 10% activated Pd/C) was
added and hydrogenated in a Parr hydrogenator with shaking
at 45 psi for 6 h. The color of the solution changed from yellow
to red during the reaction. The mixture was filtered through
Celite, and dry HCl(g) was bubbled into the filtrate for 15 min
at 0 °C. After the solvent was evaporated, the residue was
triturated with ethanol, filtered, and dried to afford the desired
product as its hydrochloride salt.
Exp er im en ta l Section
The melting points were recorded on a Gallenkamp melting
1
point apparatus and are uncorrected. H NMR spectra were
1
3
acquired at 500 or 600 MHz, and C NMR spectra were acquired
1
5
at 125.7 or 150.9 MHz. N NMR spectra were acquired at 50.6
or 60.8 MHz, and chemical shifts are reported relative to NH
3
1
5
using external 1 M [ N]urea in DMSO (77.0 ppm) as a reference.
The δ and δ values are expressed relative to the internal
DMSO-d (δ 2.5 ppm; δ 39.5 ppm), unless otherwise noted.
Solvents were dried and distilled before use.
H
C
6
H
C
-15N]-5-Am in o-4-im ida zoleca r boxa m ide (4a ). Pre-
[
CONH
2
pared from 3a by following the general procedure in 85% yield;
1
5
15
15
The NH
4
Cl, NH
4
NO
3
, and NH
4
OH were purchased from
1
mp 268-270 °C (dec); H NMR (DMSO-d
6
) δ 6.40 (br s, 2H),
Cambridge Isotope Laboratories Inc. General reagents and
chemicals were purchased from commercial sources and used
without further purification.
Gen er a l P r oced u r e for P r ep a r a tion of 5-Nitr o-4-im id a -
zoleca r boxylic Acid . To a solution of 4-imidazolecarboxylic acid
13
7
1
.56 (d, J ) 85.8 Hz, 2H), 8.54 (s, 1H); C NMR (DMSO-d ) δ
6
15
02.4 (d, J ) 8.2 Hz), 128.2, 143.2, 161.2 (d, J ) 16.5 Hz);
) δ 104.0; HRMS m/z 127.0512 (calcd for
N, 127.0512).
- N]-5-Am in o-4-im id a zoleca r boxa m id e (4b). Pre-
pared from 3b by following the general procedure in 86% yield;
N
NMR (DMSO-d
6
14
15
4 6 3
C H O N
15
[
NH
2
(
1, 10 mmol) in concentrated H
2
SO
4 4
(8.0 mL) at 100 °C, NH -
1
5
NO
3
or NH
4
NO
3
(15 mmol) was added slowly with stirring,
1
mp 268-270 °C (dec); H NMR (DMSO-d
6
) δ 6.36 (br s, 2H),
.52 (br s, 2H), 8.48 (s, 1H); C NMR (DMSO-d ) δ 102.4, 128.2,
) δ 52.6; HRMS
N, 127.0512).
and the mixture was further heated at 100 °C for 12 h. The
reaction mixture was cooled and poured into crushed ice. After
13
15
7
1
6
43.1 (d, J ) 17.8 Hz), 161.8; N NMR (DMSO-d
6
its pH was adjusted to 2 using NH
4
OH, the mixture was
14
15
m/z 127.0511 (calcd for C
4
H
6
O
N
3
extracted continuously with ethyl acetate (1.5 L) for 24 h. The
organic layer was separated, washed with water, and dried over
15
[
NH
2
,CONH
2
- N
2
]-5-Am in o-4-im idazolecar boxam ide (4c).
Prepared from 3c by following the general procedure in 88%
anhydrous MgSO
4
. Concentration of the organic layer afforded
1
yield; mp 268-271 °C (dec); H NMR (DMSO-d
6
) δ 6.40 (br s,
) δ 53.0, 103.9.
Its other spectroscopic characteristics were identical to those
the desired product, which was recrystallized from CH
afford the pure nitro compound.
3
CN to
15
2
H), 7.57 (d, J ) 87.6 Hz); N NMR (DMSO-d
6
5
-Nitr o-4-im id a zoleca r boxylic Acid (2a ). Prepared from
by following the general procedure using NH NO in 73% yield;
mp >300 °C (lit. mp 302-303 °C); H NMR (DMSO-d ) δ 7.91
) δ 119.3, 135.8,
28
reported for its formate salt.
1
4
3
15
[
N1, N]Hyp oxa n th in e (5a ). Prepared from 4a by following
3
8
1
44
1
6
the literature procedure in 84% yield; mp >300 °C; H NMR
DMSO-d ) δ 7.95 (d, J ) 7.0 Hz, 1H), 8.10 (s, 1H), 12.9 (d, J )
0.0 Hz, 1H); C NMR (DMSO-d
7.5 Hz), 153.2, 155.3 (d, J ) 10.5 Hz); N NMR (DMSO-d ) δ
172.6; HRMS m/z 137.0358 (calcd for C H O N3 N, 137.0355).
[N3, N]Hyp oxa n th in e (5b). Prepared from 4b by following
1
3
(
1
s, 1H), 14.03 (br s, 1H); C NMR (DMSO-d
47.2, 159.1.
NO
15N]-5-Nit r o-4-im id a zoleca r b oxylic Acid
Prepared from 1 by following the general procedure using
6
(
9
6
13
6
) δ 119.2, 140.1, 144.8 (d, J )
15
[
2
-
(2b ).
6
1
4
15
5
4
1
5
1
15
NH
(
4
NO
3
in 76% yield; mp >300 °C; H NMR (DMSO-d
6
) δ 7.92
) δ 119.3, 135.8 (d,
J ) 3.9 Hz), 147.21 (d, J ) 26.4), 159.1; N NMR (DMSO-d ) δ
N, 158.0094).
Gen er a l P r oced u r e for P r ep a r a tion of 5-Nitr o-4-im id a -
zoleca r boxa m id e. To a mixture of 2a or 2b (4.0 mmol) and
,1′-carbonyldiimidazole (4.0 mmol), anhydrous DMF (6.0 mL)
was added under N . After 4 h, the reaction mixture was diluted
with 10 mL of aqueous THF (5% H
and K CO (8.0 mmol) were subsequently added to it (in the case
1
3
44
1
s, 1H), 14.02 (br s, 1H); C NMR (DMSO-d
6
the literature procedure in 88% yield; mp >300 °C; H NMR
1
5
6
(DMSO-d ) δ 7.95 (d, J ) 13.0 Hz, 1H), 8.09 (s, 1H), 12.3 (br s,
6
1
4
15
13
3
64.1; HRMS m/z 158.0094 (calcd for C
4
H
3
O
4
N
2
1H); C NMR (DMSO-d ) δ 118.9, 140.1, 144.9 (d, J ) 7.3 Hz),
6
1
5
153.2, 155.8; N NMR (DMSO-d
6
) δ 225.9; HRMS m/z 137.0357
1
4
15
(calcd for C
5
H
N
4
O
N
3
N, 137.0355).
]Hyp oxa n th in e (5c). Prepared from 4c by fol-
lowing the literature procedure in 87% yield. Its physical
properties and spectroscopic characteristics were identical to
[N1,N3,15
1
2
4
4
2
1
5
2
4
O), and NH Cl (6.0 mmol)
2
8
2
3
those reported.
[N1,15N]-6-Ch lor op u r in e (6a ). Prepared from 5a by follow-
of 3a and 3c), or ammonia gas was bubbled through it for 30
min (in the case of 3b). After being stirred further for 48 h at
room temperature, the reaction mixture was concentrated to
dryness, diluted with water, and acidified with 1 N HCl to pH
2
8
1
ing the literature procedure in 93% yield; mp >300 °C; H NMR
(DMSO-d ) δ 8.67 (s, 1H), 8.73 (d, J ) 15.0 Hz, 1H), 13.91 (br s,
1H); 1 C NMR (DMSO-d
) δ 130.5, 145.8, 147.7, 151.5 (d, J )
.2 Hz), 152.8 (br s); 15N NMR (DMSO-d
) δ 255.2; HRMS m/z
NCl, 155.0017).
N3,15N]-6-Ch lor op u r in e (6b). Prepared from 5b by follow-
6
3
6
3
1
6
1
4
15
5 3 3
55.0012 (calcd for C H N
(
44) Birkett, P. R.; Chapleo, C. B.; Mackenzie, G. Synthesis 1991,
[
1
4
57-159.
2
8
1
(
45) Leonard, N. J .; Henderson, T. R. J . Am. Chem. Soc. 1975, 97,
ing the literature procedure in 91% yield; mp >300 °C; H NMR
(DMSO-d ) δ 8.66 (s, 1H), 8.73 (d, J ) 15.0 Hz), 13.89 (br s, 1H);
990-4999.
6

Notes
J . Org. Chem., Vol. 66, No. 19, 2001 6475
1
3
15
C NMR (DMSO-d
6
) δ 130.6, 145.8, 147.7 (br s), 151.5 (d, J )
2 3
[N1,N3,NH - N ]Ad en in e (7c). Prepared from 5c by fol-
1
5
45
1
3
1
.2 Hz), 152.8; N NMR (DMSO-d
55.0013 (calcd for C
6
) δ 273.5; HRMS m/z
NCl, 155.0017).
]-6-Ch lor op u r in e (6c). Prepared from 5c by
lowing the literature procedure in 92% yield; mp >300 °C; H
NMR (DMSO-d ) δ 7.09 (d, J ) 89.7 Hz, 2H), 8.09 (s, 1H), 8.11
(t, J ) 15.4 Hz, 1H), 12.85 (br s, 1H); C NMR (DMSO-d
1
4
15
5
H
3
N
3
6
1
5
13
[
N1,N3,
N
2
6
) δ
118.3, 139.2, 150.4, 152.4 (br s), 155.5 (br s); N NMR (DMSO-
) δ 79.5, 227.8, 234.9; HRMS m/z 138.0461 (calcd for
2
8
15
following the literature procedure in 88% yield. Its physical
properties and spectroscopic characteristics were identical to
those reported.
N1,NH
literature procedure using 6a in 98% yield; mp >300 °C; H
NMR (DMSO-d
d
6
2
8
14
15
5 5 2 3
C H N N , 138.0456).
1
5
[
2 2
- N ]Ad en in e (7a ). Prepared by following the
4
5
1
Ack n ow led gm en t . Nan-Lu Ho is supported by
6
) δ 7.08 (d, J ) 89.6 Hz, 2H), 8.07 (s, 1H), 8.10
the Regional Instrument Center at Hsinchu and Na-
tional Science Council (NSC) of Taiwan, Republic of
China (ROC). We thank NSC of the ROC for research
grants.
1
3
(d, J ) 15.5 Hz), 12.37 (br s, 1H); C NMR (DMSO-d
6
) δ 118.3,
1
5
1
7
1
39.2, 150.2, 152.4 (br s), 155.5 (br s); N NMR (DMSO-d ) δ
9.5, 234.8; HRMS m/z 137.0489 (calcd for
37.0486).
6
1
4
15
5 5 3 2
C H N N ,
1
5
[
N3, NH
the literature procedure in 94% yield; mp >300 °C; H NMR
DMSO-d ) δ 7.10 (d, J ) 89.7 Hz, 2H), 8.08 (s, 1H), 8.10 (d, J
14.8 Hz), 12.85 (br s, 1H); C NMR (DMSO-d
50.2, 152.4 (br s), 155.5 (br s); 15N NMR (DMSO-d
2
- N
2
]Ad en in e (7b). Prepared from 6b by following
Su p p or tin g In for m a tion Ava ila ble: 1H and 15N NMR
spectra for compounds 2b, 3c, and 7c. This material is
available free of charge via the Internet at http://pubs.acs.org.
4
5
1
(
6
1
3
)
1
2
6
) δ 118.3, 139.3,
) δ 79.5,
, 137.0486).
6
1
4
15
27.9; HRMS m/z 137.0482 (calcd for C
5
H
5
N
3
N
2
J O010253Q