Synthesis of 2,8-disubstituted imidazo[1,5-a]pyrimidines with potent antitumor activity

Article abstract of DOI:10.1021/jm980731y

Seventeen 1,2,3,4-tetrahydroimidazo[1,5-a]pyrimidine derivatives bearing electron-withdrawing substituents were designed and synthesized by novel ring closure as potential antitumor agents. They were screened for their activities against mouse leukemia L1210 and human oral epidermoid carcinoma KB cell lines, and relationships of structure and antitumor activity in vitro are discussed. It was found that 8-thiocarbamoyl-1,2,3,4- tetrahydroimidazo[1,5-α]pyrimidin-2(1H)-thione (8c) exhibited activity comparable to that of 5-fluorouracil against both L1210 and KB cells. The existence of both 2-thioxo and 8-substituent with a thioxo group in the molecule is crucial for the cytotoxicity against L1210 and KB cells. A novel procedure for introduction of a double bond between C-3 and C-4 in 8c was developed. Introduction of the 3,4-double bond increased the activity against L1210, but against KB cells the activity decreased by 4-fold. Cytotoxicity of compounds 8c and 8-thiocarbamoyl-1,2-dihydroimidazo[1,5-α]pyrimidin-2(1H)- thione (11c) against human solid tumor and leukemia cell lines was further evaluated. The saturation of the 3,4-double bond led to a significant increase in cytotoxicity against tumor cell lines tested.

Full text of DOI:10.1021/jm980731y

J . Med. Chem. 1999, 42, 1661-1666
1661
Syn th esis of 2,8-Disu bstitu ted Im id a zo[1,5-a ]p yr im id in es w ith P oten t An titu m or
Activity
,
†
§
†
‡
†
Hiroatsu Matsumoto,* Kazuyoshi Ikeda, Nobuyuki Nagata, Hiroaki Takayanagi, Yoshihisa Mizuno,
∇
,∇
Motohiro Tanaka, and Takuma Sasaki*
Research Laboratory, Minophagen Pharmaceutical Company, 2-2-3 Komatsubara, Zama 228-0002, J apan,
Center for Instrumental Analysis, Hokkaido University, Sapporo 060-0812, J apan, School of Pharmaceutical Sciences,
Kitasato University, Minato-ku, Tokyo 108, J apan, and Cancer Research Institute, Kanazawa University,
Kanazawa 920-0934, J apan
Received December 28, 1998
Seventeen 1,2,3,4-tetrahydroimidazo[1,5-a]pyrimidine derivatives bearing electron-withdrawing
substituents were designed and synthesized by novel ring closure as potential antitumor agents.
They were screened for their activities against mouse leukemia L1210 and human oral
epidermoid carcinoma KB cell lines, and relationships of structure and antitumor activity in
vitro are discussed. It was found that 8-thiocarbamoyl-1,2,3,4-tetrahydroimidazo[1,5-a]pyri-
midin-2(1H)-thione (8c) exhibited activity comparable to that of 5-fluorouracil against both
L1210 and KB cells. The existence of both 2-thioxo and 8-substituent with a thioxo group in
the molecule is crucial for the cytotoxicity against L1210 and KB cells. A novel procedure for
introduction of a double bond between C-3 and C-4 in 8c was developed. Introduction of the
3
,4-double bond increased the activity against L1210, but against KB cells the activity decreased
by 4-fold. Cytotoxicity of compounds 8c and 8-thiocarbamoyl-1,2-dihydroimidazo[1,5-a]pyri-
midin-2(1H)-thione (11c) against human solid tumor and leukemia cell lines was further
evaluated. The saturation of the 3,4-double bond led to a significant increase in cytotoxicity
against tumor cell lines tested.
In tr od u ction
Ch a r t 1
Previously, we described the synthesis of a variety of
5
-substituted imidazo[1,5-a]thiazin-7(3H)-ones, e.g., the
base moiety of 6-thiaoxanosine (1), as potential antiviral
and anticancer agents.1 During our attempts to syn-
thesize the base moiety of 5-vinyl-7-thione analogue of
,2
1
, namely, 5-ethenylimidazo[4,5-d][1,3]thiazin-7(3H)-
thione (3), via 2 by the known cyclization procedure
Chart 1), we unexpectedly discovered an interesting
(
ring-closure reaction which led to the synthesis of
imidazo[1,5-a]pyrimidin-2(1H)-ones. Thus, when ethyl
5
-aminoimidazole-4-carboxylate (4) was acylated with
acryloyl chloride, we obtained 8-ethoxycarbonyl-1,2,3,4-
tetrahydroimidazo[1,5-a]pyrimidin-2(1H)-one (7a; Scheme
1
7
) instead of 5-acryloylamino derivative 2. Thiation of
a with Lawesson’s reagent afforded monothiated de-
spectively) with aliphatic or aromatic acyl chloride in
the presence of base usually gives rise to the corre-
sponding 4-substituted 5-acylaminoimidazoles. How-
ever, when 4 was treated with acryloyl chloride in
acetonitrile at 80 °C for 3 h in the presence of triethyl-
amine, we obtained a crystalline product which was
analyzed correctly for the desired 5-acryloylaminoimi-
rivative 7b and dithiated derivative 7c, respectively,
and 7c was found to be more active against L1210 and
KB cells than 7a and 7b . We, therefore, synthesized
derivatives of imidazo[1,5-a]pyrimidines by exploitation
of our new ring-closure reaction in search of more potent
derivatives and for structure-activity relationship stud-
ies. We also describe a novel synthetic procedure for the
1
dazole (2) in 56% yield. The H NMR spectrum of this
product, however, showed the lack of vinyl protons but
the presence of two-proton triplets at δ 2.75 and 4.23.
There is one deuterium-exchangeable (NH, δ 9.83) and
one aromatic (δ 7.46) proton in the molecule. Moreover,
this compound exhibited the correlation among meth-
ylene protons at δ 4.23 and three carbons at δ 132.48
1
,2-dihydroimidazo[1,5-a]pyrimidine ring system.
Ch em istr y
Acylation of 5-amino-4-ethoxycarbonyl-, 5-amino-4-
carbamoyl-, and 5-amino-4-cyanoimidazoles (4-6, re-
1
13
(
C-6), 136.30 (C-8a), and δ 162.23 (C-2) in H- C
heteronuclear multiple bond connectivity. These data
are fully consistent only with the 8-ethoxycarbonyl-
1,2,3,4-tetrahydroimidazo[1,5-a]pyrimidin-2(1H)-onestruc-
ture (7a ; Scheme 1). A plausible mechanism for the
†
Minophagen Pharmaceutical Co.
Hokkaido University.
Kitasato University.
Kanazawa University.
§
‡
∇
1
0.1021/jm980731y CCC: $18.00 © 1999 American Chemical Society
Published on Web 04/17/1999

1
662 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 9
Matsumoto et al.
Sch em e 1a
formation of 7a from 4 would be intramolecular Michael
addition which occurred between the initially formed
enone and the imidazole nitrogen. A similar treatment
of 5 and 6 afforded 8a and 9a , respectively.
Thiation of 7a with Lawesson’s reagent in xylene at
1
30 °C for 16 h produced mono- and dithiated products
7
b and 7c in 24% and 66% yields, respectively. The
structural determination of the dithio compound as
-ethoxythiocarbonyl-1,2,3,4-tetrahydroimidazo[1,5-a]-
8
1
pyrimidin-2(1H)-thione (7c) rests upon spectral data ( H
NMR, 13C NMR, and MS) as well as elemental analyses.
Selective thiation at C-2 was accomplished by reducing
the reaction time to 30 min (yield of 7b was 74%).
Reaction of 8a with the same reagent in dioxane at 100
°
C for 1 h afforded dithio derivative 8c in 77% yield.
When the reaction was carried out at lower temperature
70 °C), the sole thiated product was 2-thioxo derivative
F igu r e 1. ORTEP drawing of 9b and 12a and the crystal-
(
lographic numbering scheme.
8
8
b which was isolated in 28% yield. The isomeric 2-oxo-
-thioamide 8d was obtained in 87% yield from 9a by
The structures of these thiated products 7b, 8b-d ,
and 9b were established by spectral ( H NMR,
1
13
treatment with H2S. These experiments clearly showed
that a cyclic amide carbonyl is more readily thiated than
an exocyclic amide carbonyl group. In a similar treat-
ment of 9a in dioxane at 100 °C for 1 h, 2-thio derivative
9
8
conversion of 9a into 8c. Formation of the thioamide
from the cyano group occurred more rapidly in dioxane
than in xylene probably due to the abundance of
moisture in the former. Thus, we developed a method
for a one-step synthesis of the active compound 8c from
C
NMR, and MS) as well as elemental analyses. Surpris-
ingly, no geminal couplings, anticipated for the meth-
ylene protons in 7b-9b, were observed. The X-ray
crystallographic analysis of 9b firmly confirmed the
1,2,3,4-tetrahydroimidazo[1,5-a]pyrimidine structure (Fig-
ure 1).
For the synthesis of 1,2-dihydro compounds 10a , 11a ,
and 12a , acylation of 4-6 with propiolic acid with
various coupling reagents including DMC and DCC
failed to obtain the desired products in satisfactory
yields. However, we found that these products can be
b (55%) was obtained along with the dithio product
c (29%). Prolonged heating (3 h) caused complete
9
a .

2
,8-Disubstituted Imidazol[1,5-a]pyrimidines
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 9 1663
Ta ble 1. Physical Properties of Imidazo[1,5-a]pyrimidine
Derivatives
saturation of the 3,4-double bond in the imidazo[1,5-a]-
pyrimidine ring system led to a significant increase in
cytotoxicity against human solid tumor cell lines. This
effect was found most dramatically in the case of KATO
III cell line. Whereas the unsaturated derivative 11c
exhibited no cytotoxicity even at 100 µM concentration
against this cell line, the 3,4-saturated compound 8c
became very active (IC50, 4.7 µM). The increase in
activity was more than 20-fold. The influence of the 3,4-
double bond on the activity against leukemic cells was
not so apparent as both thioamide derivatives 8c and
a
a
1
1c showed similar activity against most of the five
leukemic cell lines tested (Table 3).
The role of sulfur on cytotoxic effect is remarkable
a
(
Table 2). Compounds without sulfur (7a -12a ) did not
exhibit cytotoxicity. Monothio substitution at C-2 (7b-
2b and 8d ) made these compounds active against
a
a
1
L1210 cells; 9b, 11b, and 12b became cytotoxic even
against KB cells. A dramatic increase in cytotoxicity by
introduction of an additional sulfur (7c, 8c, and 11c)
implies that the existence of both the 2- and 8-thioxo
groups in these heterocyclic compounds is decisively
important for potent cytotoxicity against these cell lines.
It is also to be noted that the function of the 3,4-double
bond is significant for cytotoxicity. As is apparent from
the X-ray structure (Figure 1), the double bond makes
the six-membered ring flattened and restricts confor-
mational flexibility compared to the 3,4-saturated struc-
ture. It is most likely that the conformational flexibility
of the six-membered ring moiety is a significant factor
to be active against solid tumor cells.
a
a
a
a
Decomposed. b Analyses of all new compounds for C, H, N, and
S agree with calculated values in the range of (0.4%.
synthesized in 46-71% yields by the reaction of 4-6
with N-succinimidyl 3-succinimidoxypropenoate (13;
Scheme 1). Reagent 13 was prepared in 73% yield by
treatment of propiolic acid with N,N′-disuccinimidyl
carbonate in acetonitrile in the presence of pyridine. The
structure of 12a and the geometry around the double
bond, in particular, were further confirmed by X-ray
crystallography (Figure 1).
Con clu sion
In this paper we described novel ring closure reactions
which led to the synthesis of derivatives containing the
rarely studied imidazo[1,5-a]pyrimidine ring system:
there are only four publications available dealing with
Thiation of 10a , 11a , and 12a gave the corresponding
mono- and dithiated products 10b, 11b, 12b, 10c, and
1c, respectively in 34-73% yields depending upon the
4
-7
the chemistry of this ring system.
7 compounds that we prepared, two of them, 8-thio-
carbamoyl-1,2,3,4-tetrahydroimidazo[1,5-a]pyrimidin-
(1H)-thione (8c) and 8-thiocarbamoyl-1,2-dihydroimi-
Among a total of
1
1
reaction conditions.
2
dazo[1,5-a]pyrimidin-2(1H)-thione (11c), showed potent
cytotoxicity. Thus, cytotoxicity of 8c against both mouse
leukemia L1210 (IC50, 0.61 µM) and human solid tumor
KB (IC50, 3.2 µM) cells was found to be as potent as that
of 5-FU (IC50, 0.61 and 2.3 µM, respectively). Compound
Cytotoxicity a n d Discu ssion
All newly synthesized compounds were screened for
their cytotoxicity against mouse leukemia L1210 cells
and human oral epidermoid carcinoma KB cells by the
3
method of Carmichael et al., and the results are
1
1c, on the other hand, exhibited exceptional potency
summarized in Table 2. These results clearly showed
that the sulfur-free compounds 7a -12a are totally
inactive against both cell lines. Introduction of one
sulfur atom to the molecules 7a -12a exerted a slight
cytotoxicity only against L1210 cells. Addition of the
second sulfur atom to the molecules dramatically in-
creased the cytotoxicity of the compounds against both
cell lines. Thus, compounds 8c and 11c exhibited potent
activity against these cell lines. Against L1210, 11c was
found to show the most potent activity (IC50, 0.31 µM)
among the new compounds tested. The 3,4-saturated
analogue 8c exhibited activity as potent as 5FU against
both L1210 cells (IC50, 0.61 µM) and KB cells (IC50, 3.2
µM).
against L1210 (IC50, 0.31 µM), while its activity against
KB cells was somewhat low (IC50, 12.8 µM). The
presence of two sulfur atoms in the molecule is essential
for potent cytotoxicity, and in general, 3,4-saturated
derivatives are more potent against solid tumors than
the unsaturated counterparts, while both are active
against leukemic cell lines. Compounds 8c and 11c may
serve as useful lead compounds for the search of more
powerful antineoplastic agents.
Exp er im en ta l Section
Melting points were determined on a Yanagimoto mi-
1
13
cromelting point apparatus and are uncorrected. H and
NMR were recorded on J EOL J NL-GX270 (270 M Hz) and
EX400 (400 MHz) spectrometers with Me Si as the internal
standard. Spectra were taken in DMSO-d , and the chemical
C
4
The activity of three compounds (7c, 8c, and 11c) that
were found to be quite cytotoxic to both L1210 and KB
cell lines was further evaluated against human solid
tumor and leukemic cell lines (Table 3). In general,
6
shifts are reported in parts per million (δ). Resonance patterns
are reported with the following notations: b (broad), s (singlet),
d (doublet), t (triplet), and q (quartet). Mass spectra were run

1
664 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 9
Matsumoto et al.
Ta ble 2. Growth Inhibitory Effect of Imidazo[1,5-a]pyrimidine Derivatives on Murine Leukemia L1210 and Human Oral Epidermoid
a
Carcinoma KB Cells
a
3
The tetrazolium-based semiautomated colorimetric assay (MTT assay), developed by Carmichael, was modified and used for the in
3
vitro assay. Each tumor cell (2 × 10 /well) was incubated in the presence or absence of compound for 72 h. Then, 3-(4,5-dimethylthiazol-
2
-yl)-2,5-diphenyltetrazolium bromide was added. After incubation for 4 h more, the resulting MTT-formazan was dissolved in DMSO
and the OD (540 nm) was measured. Percent inhibition was calculated as follows: % inhibition ) [1 - OD of sample well/OD of control
b
c
d
well] × 100. IC50 (µM) was given as the concentration at 50% inhibition of cell growth. 5-Fluorouracil. ND, not determined.
on a J EOL J MS-DX303 spectrometer. Flash chromatography
was performed on Merck Kieselgel 60 (70-230 mesh) and a
Yamazen Ultra Pack ODS-A-40B column.
38.84, 66.24, 121.69, 133.13, 136.02, 197.31, 201.09; EIMS m/z
241 (M ). Anal. (C H N OS ) C, H, N, S.
9 11 3 2
+
8-Ca r ba m oyl-1,2,3,4-tetr a h yd r oim id a zo[1,5-a ]p yr im i-
d in -2(1H)-on e (8a ). To a solution of 5 (406 mg, 2.5 mmol) and
imidazole (590 mg, 8.7 mmol) in dry DMF (15 mL) was added
dropwise a solution of acryloyl chloride (0.5 mL, 6.3 mmol) in
dry DMF (3 mL) at room temperature. The mixture was heated
at 80 °C for 3 h and then concentrated in vacuo. The residue
8
-Eth oxyca r bon yl-1,2,3,4-tetr a h yd r oim id a zo[1,5-a ]p y-
r im id in -2(1H)-on e (7a ). To a solution of 4 (780 mg, 5 mmol)
and Et N (1.1 mL) in dry MeCN (25 mL) was added dropwise
a solution of acryloyl chloride (0.61 mL, 7.5 mmol) in dry MeCN
2 mL) at room temperature. The mixture was kept at 50 °C
for 16 h and then concentrated in vacuo, and the residue was
, 5:98.5 v/v) to give pure 7a
580 mg, 56%): H NMR (DMSO-d ) δ 1.26 (t, 3H, CH CH ),
CH ), 4.23 (t, 2H, H-4), 7.46
) δ 14.43,
0.10, 38.81, 59.10, 112.52, 136.30, 162.10, 166.47; EIMS m/z
3
(
was chromatographed (MeOH-CHCl
3
, 8:92 v/v) to give pure
8a (213 mg, 47%): H NMR (DMSO-d ) δ 2.76 (t, 2H, H-3),
4.24 (t, 2H, H-4), 6.99 (bs, 2H, NH ), 7.40 (s, 1H, H-6), 9.12
(bs, 1H, 1-NH); 13C NMR (DMSO-d
) δ 38.66, 45.21, 114.79,
130.61, 135.59, 164.94, 165.41; EIMS m/z 180 (M ). Anal.
1
chromatographed (MeOH-CHCl
3
6
1
(
6
3
2
2
2
.75 (t, 2H, H-3), 4.22 (q, 2H, CH
3
2
6
1
3
+
(s, 1H, H-6), 9.83 (bs, 1H, 1-NH); C NMR (DMSO-d
6
1
3
2
(C
9
H
8
N
4
O
2
‚ /
2 2
H O) C, H, N.
+
09 (M ). Anal. (C
-Eth oxyca r bon yl-1,2,3,4-tetr a h yd r o[1,5-a ]p yr im id in e-
(1H)-th ion (7b) and 8-Eth oxyth ioca r bon yl-1,2,3,4-tet-
9 11 3 3
H N O ) C, H, N.
8-Ca r ba m oyl-1,2,3,4-tetr a h yd r o[1,5-a ]p yr im id in -2(1H)-
8
th ion e (8b). A mixture of 8a (90 mg, 0.5 mmol) and Lawes-
son’s reagent (212 mg, 0.3 mmol) in dry dioxane (8 mL) was
heated at 70 °C for 1 h. After concentration of the mixture in
2
r ah ydr oim idazo[1,5-a ]pyr im idin -2(1H)-th ion e (7c). A mix-
ture of 7a (92 mg, 0.44 mmol) and Lawesson’s reagent (355
mg, 0.88 mmol) in dry xylene (15 mL) was heated at 130 °C
for 16 h. After concentration of the mixture in vacuo, the
vacuo, the residue was chromatographed (MeOH-CHCl
3
, 4:96
) δ 3.22 (t,
1
v/v) to give 8b (27 mg, 28%): H NMR (DMSO-d
6
2H, H-3), 4.17 (t, 2H, H-4), 7.29 (bs, 1H, NH), 7.38 (bs, 1H,
NH), 7.54 (s, 1H, H-6), 10.09 (bs, 1H, 1-NH); 13C NMR (DMSO-
residue was chromatographed (MeOH-CHCl
3
, 1.4:98.6 v/v) to
separate 7b (24 mg, 24%) and 7c (70 mg, 66%).
d ) δ 38.78, 39.70, 115.76, 132.07, 164.83, 195.19; EIMS m/z
6
1
+
7
b: H NMR (DMSO-d
6
) δ 1.28 (t, 3H, CH
CH
H-6), 11.46 (bs, 1H, 1-NH); C NMR (DMSO-d ) δ 14.52, 38.89,
9.30, 59.84, 116.64, 133.87, 162.12. 197.01; EIMS m/z 225
3
CH
2
), 3.21 (t,
7 8 4
196 (M ). Anal. (C H N OS).
2
H, H-3), 4.16 (t, 2H, H-4), 4.25 (q, 2H, CH
3
2
), 7.60 (s, 1H,
8-Th ioca r ba m oyl-1,2,3,4-tetr a h yd r oim id a zo[1,5-a ]p y-
r im id in -2(1H)-th ion e (8c). A mixture of 8a (246 mg, 1.52
mmol) and Lawesson’s reagent (140 mg, 1.14 mmol) in dioxane
(20 mL) was heated at 100 °C for 1 h. After concentration of
1
3
6
3
+
(
M ). Anal. (C
9
H
11
N
3
O
2
S) C, H, N, S.
c: H NMR (DMSO-d ) δ 1.40 (t, 3H, CH
H, H-3), 4.21 (t, 2H, H-4), 4.64 (q, 2H, CH CH
) δ 13.70, 38.42,
1
7
6
3
CH
2
), 3.28 (t,
the mixture in vacuo, the residue was chromatographed
1
2
3
2
), 7.62 (s, 1H,
(MeOH-CHCl
3
, 1:19 v/v) to give 8c (248 mg, 77%): H NMR
1
3
H-6), 11.71 (bs, 1H, 1-NH); C NMR (DMSO-d
6
(DMSO-d
6
) δ 3.25 (t, 2H, H-3), 4.21 (t, 2H, H-4), 7.63 (s, 1H,

2
,8-Disubstituted Imidazol[1,5-a]pyrimidines
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 9 1665
Ta ble 3. Effects of 7c, 8c, 11c, and 6MP on the Growth of Various Human Tumors in Vitroa
H-6), 9.10 (bs, 1H, NH), 9.43 (bs, 1H, NH), 12.23 (bs, 1H,
3
mg, 2.8 mmol, vide infra), and Et N (2 mL) in dry MeCN (25
1
3
1
1
-NH); C NMR (DMSO-d
86.96, 195.84; EIMS m/z 212 (M ). Anal. (C
6
) δ 38.17, 38.90, 131.91, 133.88,
mL) was heated at 50 °C for 16 h. After concentration in vacuo,
the residue was treated with MeOH (20 mL) and the mixture
was stirred at 60 °C for 30 min. The insoluble materials were
filtered, and the filtrate was concentrated and chromato-
+
7
8 4 2
H N S ) C, H,
N, S.
-Th ioca r ba m oyl-1,2,3,4-tetr a h yd r oim id a zo[1,5-a ]p y-
8
r im id in -2(1H)-on e (8d ). A solution of 9a (640 mg, 4.0 mmol)
and KOH (2.4 g) in MeOH (100 mL) was chilled to 0 °C, and
graphed (MeOH-CHCl
3
, 4:96 v/v) to give 10a (238 mg, 46%):
) δ 1.28 (t, 3H, CH CH ), 4.28 (q, 2H,
), 6.11 (d, 1H, H-3, J ) 7.81 Hz), 7.91 (s, 1H, H-6),
1
H NMR (DMSO-d
CH CH
8.39 (d, 1H, H-4, J ) 7.81 Hz), 11.18 (bs, 1H, 1-NH); C NMR
(DMSO-d
6
3
2
H
2
S was bubbled in for 1 h. The mixture was heated in a steel
3
2
1
3
bomb at 100 °C for 1 h and then poured onto crushed ice. The
solution was neutralized with dilute AcOH to pH 4, and the
pale-yellow precipitates were filtered to afford 417 mg of 8d .
An additional crop of 8d was obtained from the filtrate upon
concentration to give the total yield of 734 mg (87%): 1H NMR
6
) δ 14.41, 59.21, 108.78, 110.18, 128.45, 134.76,
+
9 9 3 3
135.81, 158.99, 161.59; EIMS m/z 207 (M ). Anal. (C H N O )
C, H, N.
8-Eth oxycar bon yl-1,2-dih ydr oim idazo[1,5-a ]pyr im idin -
2(1H)-th ion e (10b). A mixture of 10a (181 mg, 0.87 mmol)
and Lawesson’s reagent (211 mg, 0.52 mmol) in dry xylene
(10 mL) was heated at 130 °C for 1 h. After concentration of
(
DMSO-d
6
) δ 2.81 (t, 2H, H-3), 4.27 (t, 2H, H-4), 7.51 (s, 1H,
H-6), 8.88 (bs, 1H, NH), 9.18 (bs, 1H, NH), 10.40 (bs, 1H,
1
1
1
3
-NH); C NMR (DMSO-d
36.63, 165.71, 187.18; EIMS m/z 196 (M ). Anal. (C
O) C, H, N, S.
-Cya n o-1,2,3,4-t et r a h yd r oim id a zo[1,5-a ]p yr im id in -
(1H)-on e (9a ). To a solution of 6 (540 mg, 5.0 mmol) and
6
) δ 29.46, 38.88, 118.45, 130.76,
+
7
H
8
N
4
-
the mixture in vacuo, the residue was chromatographed
1
OS‚1/4H
2
(MeOH-CHCl
(DMSO-d ) δ 1.31 (t, 3H, CH
(d, 1H, H-3, J ) 7.69 Hz), 8.05 (s, 1H, H-6), 8.27 (d, 1H, H-4,
J ) 7.15 Hz); 13C NMR (DMSO-d
) δ 14.28, 59.75, 110.48,
118.47, 127.98, 128.97, 133.99, 161.52, 182.86; EIMS m/z 223
3
, 1:99 v/v) to give 10b (92 mg, 44%): H NMR
8
6
3 2 3 2
CH ), 4.32 (q, 2H, CH CH ), 6.74
2
imidazole (612 mg, 9.0 mmol) in dry MeCN (15 mL) was added
dropwise a solution of acryloyl chloride (0.61 mL, 7.5 mmol)
in dry MeCN (3 mL) at 80 °C. The mixture was stirred at 80
6
+
9 9 3 2
(M ). Anal. (C H N O S) C, H, N, S.
°
C for 3 h and then concentrated in vacuo. The residue was
chromatographed (MeOH-CHCl , 6:94 v/v) to give 9a (320 mg,
) δ 2.72 (t, 2H, H-3), 4.22 (t, 2H,
8-Eth oxyth ioca r bon yl-1,2-d ih yd r oim id a zo[1,5-a ]p yr i-
m id in -2(1H)-th ion e (10c). A mixture of 10a (120 mg, 0.87
mmol) and Lawesson’s reagent (469 mg, 1.16 mmol) in dry
xylene (16 mL) was heated at 130 °C for 16 h. After concentra-
3
1
4
0%): H NMR (DMSO-d
H-4), 7.55 (s, 1H, H-6), 11.50 (bs, 1H, 1-NH); C NMR (DMSO-
) δ 29.92, 39.08, 92.79, 114.88, 133.72, 138.79, 166.73; EIMS
6
1
3
d
6
tion of the mixture in vacuo, the residue was chromatographed
+
1
m/z 162 (M ). Anal. (C
-Cya n o-1,2,3,4-t et r a h yd r oim id a zo[1,5-a ]p yr im id in -
(1H)-th ion e (9b). A mixture of 9a (246 mg, 1.52 mmol) and
7
H
6
N
4
O) C, H, N.
using CHCl
(DMSO-d ) δ 1.42 (t, 3H, CH
(d, 1H, H-3, J ) 7.15 Hz), 8.03 (s, 1H, H-6), 8.35 (d, 1H, H-4,
J ) 7.81 Hz), 12.45 (bs, 1H, 1-NH); 13C NMR (DMSO-d
) δ
13.62, 66.32, 118.98, 128.65, 128.87, 135.50, 182.73, 200.23;
3
as an eluent to give 10c (68 mg, 49%): H NMR
8
6
3 2 3 2
CH ), 4.69 (q, 2H, CH CH ), 6.87
2
Lawesson’s reagent (460 mg, 1.14 mmol) in dioxane (20 mL)
was heated at 100 °C for 1 h. After concentration of the
mixture in vacuo, the residue was triturated with CHCl
6
+
3
to
) δ 3.17 (t,
H, H-3), 4.15 (t, 2H, H-4), 7.67 (s, 1H, H-6), 13.49 (bs, 1H,
EIMS m/z 239 (M ). Anal. (C
9
H
9
N
3
OS
2
2
‚1/9H O) C, H, N, S.
1
crystallize 9b (150 mg, 55%): H NMR (DMSO-d
6
8-Ca r b a m oyl-1,2-d ih yd r oxyim id a zo[1,5-a ]p yr im id in -
2(1H)-on e (11a ). A solution of 5 (163 mg, 1.0 mmol), 13 (316
2
1
1
1
3
-NH); C NMR (DMSO-d
6
) δ 38.86, 39.28, 93.98, 114.54,
mg, 1.1 mmol), and Et
heated at 50 °C for 16 h. After cooling, the crystalline product
11b was filtered, washed with H O, and dried (238 mg, 46%):
) δ 6.05 (d, 1H, H-3, J ) 8.25 Hz), 7.16 (bs,
), 8.36 (s, 1H, H-6), 8.38 (d, 1H, H-4, J ) 7.69 Hz),
3
N (0.8 mL) in dry MeCN (25 mL) was
+
34.80, 135.99, 197.58; EIMS m/z 178 (M ). Anal. (C
7
6 4
H N S)
C, H, N, S.
-Eth oxycar bon yl-1,2-dih ydr oim idazo[1,5-a ]pyr im idin -
(1H)-on e (10a ). A solution of 4 (388 mg, 2.5 mmol), 13 (790
2
1
8
H NMR (DMSO-d
2H, NH
6
2
2

1
666 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 9
0.36 (bs, 1H, 1-NH); 13C NMR (DMSO-d
) δ 108.50, 112.84,
Matsumoto et al.
1
1
6
carbonate (5.38 g, 21 mmol), and pyridine (1.6 mL) in dry
MeCN (100 mL) was stirred at room temperature for 16 h.
The colorless crystals precipitated were collected by filtration
+
26.83, 133.46, 134.71, 158.26, 164.57; EIMS m/z 160 (M ).
‚3/5H O) C, H, N.
-Ca r b a m oyl-1,2-d ih yd r oim id a zo[1,5-a ]p yr im id in -2-
1H)-th ion e (11b). A mixture of 11a (45 mg, 0.25 mmol) and
Anal. (C
7
H
6
N
4
O
2
2
1
8
and washed with H O to give 13 (4.3 g, 73%): H NMR
2
(
(DMSO-d ) δ 2.73 (s, 4H, CH2), 2.83 (s, 4H, CH2), 6.29 (d, 1H,
-CHd, J ) 12.2 Hz), 8.28 (d, 1H, -CHd, J ) 12.2 Hz); EIMS
6
Lawesson’s reagent (46 mg, 0.11 mmol) in dry dioxane (8 mL)
was heated under reflux for 45 min. After concentration of the
mixture in vacuo, 11b (17 mg, 35%) was separated by medium-
+
m/z 282 (M ).
pressure liquid chromatography (MeCN-2% aqueous AcOH,
Ack n ow led gm en t. The authors thank Professor
Kyoichi A. Watanabe, Cornell University Graduate
School of Medical Sciences, for helpful discussions
during the preparation of this manuscript.
1
3
5:65 v/v): H NMR (DMSO-d
6
) δ 6.70 (d, 1H, H-3, J ) 7.32
Hz), 7.44 (bs, 1H, NH), 7.58 (bs, 1H, NH), 8.03 (s, 1H, H-6),
.28 (d, 1H, H-4, J ) 7.81 Hz), 11.39 (bs, 1H, 1-NH); 13C NMR
DMSO-d ) δ 113.05, 117.74, 127.39, 128.76, 132.20, 164.61,
8
(
1
6
+
1
81.69; EIMS m/z 194 (M ). Anal. (C
7
H
6
N
4
4 2
OS‚ / H O) C,H, N,
S.
Su p p or tin g In for m a tion Ava ila ble: ORTEP drawings
of 9b and 12a , crystal data and refinement parameters,
coordinates, anisotropic temperature factors, distances, and
angles. This information is available free of charge via the
Internet at http://pubs.acs.org.
8
-Th ioca r ba m oyl-1,2-d ih yd r oim id a zo[1,5-a ]p yr im id in -
2
(1H)-th ion e (11c). A mixture of 11a (89 mg, 0.5 mmol) and
Lawesson’s reagent (303 mg, 0.75 mmol) in dioxane (8 mL)
was refluxed for 2 h. After cooling, the crystals deposited were
filtered and washed with EtOH to give 11c (77 mg, 73%): 1
H
NMR (DMSO-d
6
) δ 6.79 (d, 1H, H-3), 8.09 (s, 1H, H-6), 8.32
Refer en ces
(
1
1
d, 1H, H-4), 9.22 (bs, 1H, NH), 9.51 (bs, 1H, NH), 12.93 (bs,
H, 1-NH); C NMR (DMSO-d
34.18, 181.76, 186.35; EIMS m/z 210 (M ). Anal. (C
1
3
6
) δ 116.07, 118.23, 128.76,
(1) Kaneko, T.; Hara, S.; Matsumoto, H.; Takeuchi, T.; Mori, T.;
Ikeda, K.; Mizuno, Y. A series of novel acyclic nucleosides. IV.
Synthesis of N1-sulfur analogues of acyclovir, directed toward
improved antiviral activities. Chem. Pharm. Bull. 1991, 39, 871-
+
7
6 4 2
H N S )
C, H, N, S.
-Cya n o-1,2-d ih yd r oim id a zo[1,5-a ]p yr im id in -2(1H )-
on e (12a ). A solution of 6 (700 mg, 6.5 mmol), 13 (2.2 g, 7.8
mmol), and Et N (4 mL) in dry MeCN (50 mL) was heated at
0 °C for 16 h. After concentration in vacuo, the residue was
8
8
75.
(
2) Hara, S.; Kaneko, T.; Matsumoto, H.; Nishino, T.; Takeuchi, T.;
Mori, T.; Ikeda, K.; Mizuno, Y. Synthesis of 6-sulfur analogues
of oxanosine and closely related derivatives thereof. Nucleosides
Nucleotides 1992, 11, 571-582.
3) The cytotoxicity of these compounds was determined by a
published method: Carmichael, J .; DeGraff, W. G.; Grazdar, A.
F.; Minna, J . D.; Mitchell, J . B. Assessment of chemosensitivity
testing. Cancer Res. 1987, 47, 936-942.
3
5
1
2
crystallized from H O to give 12a (735 mg, 71%): H NMR
(
(
8
(
1
DMSO-d
6
) δ 6.11 (d, 1H, H-3, J ) 6.05 Hz), 7.98 (s, 1H, H-6),
.40 (d, 1H, H-4, J ) 7.15 Hz), 12 88 (bs, 1H, 1-NH); 1 C NMR
3
DMSO-d
6
) δ 90.65, 109.01, 114.48, 129.26, 134.65, 138.55,
+
59.31; EIMS m/z 160 (M ). Anal. (C
7
H
4
N
4
O) C, H, N.
(
(
(
4) Ochiai, E.; Shibata, S. Polarization of aromatic heterocycles (IV).
Polarization of imidazole ring systems. J . Pharm. Soc. J pn. 1939,
59, 185-195.
8
-Cya n o-1,2-d ih yd r oim id a zo[1,5-a ]p yr im id in -2(1H )-
th ion e (12b). A mixture of 12a (160 mg, 1.0 mmol) and
Lawesson’s reagent (202 mg, 0.5 mmol) in dry dioxane (10 mL)
was heated under reflux for 1 h. After concentration of the
mixture in vacuo, 12b (71 mg, 40%) was separated by medium-
5) Novison, T.; O’Brien, D. E.; Robins, R. K. The synthesis of certain
8
-cyano-2,4-disubstituted imidazo[1,5-a]pyrimidines. J . Hetero-
cycl. Chem. 1974, 11, 873-878.
6) Chern, J .-W.; Lee, C.-C.; Liaw, Y.-C.; Wang, A. H.-J . Heterocyclic
compounds I. Reaction of o-amino-carboxyamide with â-dike-
tones: Synthesis of imidazo[1,5-a]pyrimidine and pyrazolo[1,5-
a]pyrimidine derivatives. Heterocycles 1992, 34, 1133-1145.
pressure liquid chromatography (MeCN-2% aqueous AcOH,
1
3
5:65 v/v): mp 243-248 °C dec; H NMR (DMSO-d
6
) δ 7.41
(
d, 1H, H-3, J ) 7.32 Hz), 8.45 (s, 1H, H-6), 8.89 (d, 1H, H-4,
13
(7) Al-Shaar, A. M. H.; Chambers, R. K.; Gilmour, D. W.; Lythgoe,
D. J .; McClenaghan, I.; Ramsdem, C. A. The synthesis of
heterocycles via addition-elimination reactions of 4- and 5-ami-
noimidazoles. J . Chem. Soc., Perkin Trans. I 1992, 2789-2811.
J ) 7.82 Hz); C NMR (DMSO-d ) δ 90.98, 114.10, 119.22,
1
6
+
27.69, 129.95, 136.24, 183.45; EIMS m/z 176 (M ). Anal.
1
(C
7
H
4
N
4
S‚ /10
H
2
O) C, H, N, S.
N-Su ccin im id yl 3-Su ccin im id oxyp r op en oa te (13). A
mixture of propiolic acid (1.47 g, 21 mmol), N,N′-disuccinimidyl
J M980731Y