Synthesis and in vitro evaluation of the anticancer activity of novel fluorinated thiazolo[4,5-d]pyrimidines

Article abstract of DOI:10.1002/ardp.200300734

The synthesis of several thiazolo[4,5-d]pyrimidines containing a fluorophenyl moiety substituted at different positions and through different bridges is described. Twenty new compounds were prepared and evaluated for their anticancer activity using the US

Full text of DOI:10.1002/ardp.200300734

216 Fahmy et al.
Arch. Pharm. Pharm. Med. Chem. 2003, 336, 216–225
Hesham T. Y. Fahmya,b
Sherif A. F. Rostoma,
Manal N. Saudia,
Jordan K. Zjawionyb,
David J. Robinsc
,
Synthesis and in vitro evaluation of the anticancer
activity of novel fluorinated
thiazolo[4,5-d]pyrimidines
The synthesis of several thiazolo[4,5-d]pyrimidines containing a fluorophenyl moie-
ty substituted at different positions and through different bridges is described.Twen-
ty new compounds were prepared and evaluated for their anticancer activity using
the USA-NCI in-vitro screening program.Three compounds were found active and
their anticancer activity against 60 human tumor cell lines are described in detail.
a
Department of
Pharmaceutical Chemistry,
Faculty of Pharmacy,
University of Alexandria,
Alexandria, Egypt
Department of
Keywords: Thaizole; Fluorinated; Thiazolo[4,5-d]pyrimidines; Anticancer activity
b
c
Pharmacognosy,
Received: October 15, 2002; Accepted: February 20, 2003 [FP734]
DOI 10.1002/ardp.200300734
School of Pharmacy,
University of Mississippi,
USA
Department of Chemistry,
University of Glasgow,
Scotland, UK
the lipid solubility of a drug thereby enhancing its rate of
in vivo absorption.The high electro negativity of fluorine
Introduction
Thiazolo[4,5-d]pyrimidines can be considered as thia-
analogues of the naturally occurring purine bases, ade-
nine and guanine, due to the insertion of a sulphur atom
in the place of the nitrogen atom at position 7 of the pu-
rine ring.These compounds have acquired a growing im-
portance as anticancer immunotherapeutic agents [1],
antiviral agents used in the treatment of human cyto-
megalovirus (HCMV) [2–6], antitumour [7] and antibac-
terial agents [8]. Recently they have been found to
strongly antagonise the activity of the corticotropin re-
leasing factor (CRF) and thus have the potential to be
CNS active agents [9, 10]. Thiazolo[4,5-d]pyrimidines
have also been reported to have antidepressive activity
[11]. Many of these compounds are therefore of interest
to major pharmaceutical companies [3–6, 9–11].
frequently alters electronic effects, and thereby, chemi-
cal reactivity and physical properties of compounds.Flu-
orine imparts increased oxidative and thermal stability
because the C-F bond is stronger than the C-H bond.
The therapeutic benefits of different pharmacological
classes of drugs, such as anticancer agents, have re-
cently been enriched through the use of fluorinated
drugs. Fluoropyrimidines and purine nucleotides such
as 5-fluorouracil and Fludarabine are examples of such
compounds. Other fluorinated anticancer compounds
include Gemcitabine and the antitumor agents ME 2303,
Flutamide, and Casodex [13].
Previously, we described methods developed to synthe-
size and modify the structure of the thiazolo[4,5-d] pyr-
imidine ring system to obtain biologically active com-
pounds [14–18]. Here we describe structural modifica-
tions of the thiazolo[4,5-d] pyrimidine ring system to in-
troduce a fluorophenyl moiety into different positions of
the molecule using various bridges. The prepared com-
pounds were then evaluated for their anticancer activity.
Three compounds were found to possess anticancer ac-
tivity using the NCI screening program.The full antican-
cer activity spectrum of the active compounds is de-
scribed in detail.
In recent decades, advances in organic fluorine chemis-
try have been successfully utilized in the field of medici-
nal chemistry for the development of new drugs [12, 13].
It is hoped that the incorporation of fluorine will result in
drugs with increased therapeutic efficacy and improved
pharmacological properties. As the second smallest
substitute, fluorine most closely mimics hydrogen with
respect to steric requirements at enzyme receptor sites.
Furthermore, the presence of fluorine often increases
Correspondence: Hesham T. Y. Fahmy, Department of
Pharmacognosy, School of Pharmacy, P. O. Box 3479,
University of Mississippi, MS 38677, USA. Phone:
+1 662 915-7290, Fax: +1 662 915-7026, e-mail:
heshamfahmy@hotmail.com
Chemistry
The synthetic pathways utilized to prepare the target
compounds are illustrated in Schemes 1–4.
© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
0365-6233/04–05/0216 $ 17.50+.50/0

Arch. Pharm. Pharm. Med. Chem. 2003, 336, 216–225 Anticancer activity of novel fluorinated thiazolo[4,5-d]pyrimidines 217
The starting 4-amino-5-carboxamido-2,3-dihydrothi-
azole-2-thione 1 was prepared form cyanoacetamide,
sulphur and 4-fluorophenyl isothiocyanate according to
the procedure reported by Gewald [19].This compound
was cyclized to the thiazolo[4,5-d]pyrimidine 2 using a
triethylorthoformate/acetic anhydride mixture as de-
scribed [19]. 7-mercaptothiazolo[4,5-d]pyrimidine 3 was
obtained through reaction of 2 with phosphorus pen-
tasulphide, following which S-alkylation was carried out
to obtain the 7-fluorobenzylthio derivatives 4 a, b. N-
Scheme 1

218 Fahmy et al.
Arch. Pharm. Pharm. Med. Chem. 2003, 336, 216–225
Scheme 2
Scheme 3

Arch. Pharm. Pharm. Med. Chem. 2003, 336, 216–225 Anticancer activity of novel fluorinated thiazolo[4,5-d]pyrimidines 219
alkylation of 2 gave the 6-fluorobenzyl derivatives 5 a, b.
Reaction of 2 with dimethylsulphate followed by reaction
of the produced 2-methylthiothiazolium salt 6 with fluoro-
benzyl amines as described [20] gave the 2-fluorobenzyl
derivatives 7 a, b.
anhydride using our reported procedure [15]. Chlorin-
ation of 8 with phosphorus oxalyl cholride gave the 7
chlorothiazolo[4,5-d] pyrimdine 9 which upon treatment
with fluorobenzyl amines gave the 7-fluorobenzylamines
10 a, b. Treatment of compound 9 with 4-fluoroaniline
gave the 7-(4-fluorophenyl)amino derivative 11, but the
reaction required the presence of a basic catalyst such
The second parent thiazolo[4,5-d]pyrimidine 8 was pre-
pared by cyclization of the starting thiazole 1 with acetic
Scheme 4

220 Fahmy et al.
Arch. Pharm. Pharm. Med. Chem. 2003, 336, 216–225
as triethylamine to proceed. It is worth mentioning that
the 2,4-difluorophenylamine failed to react even in the
presence of strong bases. This may be attributed to its
poor nucleophilicity due to the electron withdrawing ef-
fects of the 2 fluorine atoms.
with hydrazine hydrate to give the 2-hydrazono com-
pound 17 which then under went condensation with 2,4-
difluorobenzaldehyde to yield compound 18.The 6-(2,4-
difluorobenzylidineaminothiazolo[4,5-d] pyrimidine 21
was prepared by first generating the 4-amino-5-[2,4-di-
fluorobenzylidenehydrazinecarbonyl-2,3-dihydrothi-
azole-2-thione 20 which was then cyclized with triethyl
orthoformate.
Another starting thiazole derivative, the 4-amino-5-fluor-
ophenylaminocarbonyl-2,3-dihydrothiazole-2-thione 13
was prepared from fluorophenylamino cyanoacet-
amides 12 a, b following the same reaction procedure as
described for 1. When 12 a, b were cyclized with ortho-
formate, they yielded the 3,6-fluoro phenylthiazolo[4,5-
d]pyrimidines 14 a, b.
Results and discussion
The prepared compounds were evaluated for their anti-
cancer activities using the NCI in-vitro anticancer
screening assay [21–25].
Scheme 4 describes different approaches to prepare
thiazolo[4,5-d]pyrimidines derivatives substituted with a
2,4-difluorobenzylideneamino moiety at positions 2, 6 or
7. To prepare 7-(2,4-difluorobenzylidenehydrazino-
thiazol[4,5-d]pyrimidine 16, the chloro compound 9 was
reacted with hydrazine hydrate to give the 7-hydrazino
derivative 15 which was then condensated with 2,4-di-
fluorobenzaldehyde to yield the target compound. The
2-(2,4-difluorobenzylidenehydrazonothiazolo[4,5-d] py-
rimidine 18 was prepared from the thiazlo[4,5-d]pyrimi-
dine 2 through its reaction with dimethylsulphate and
then reacting the produced 2-methylthio thiazolium salt
a) Primary anticancer assay (3-cell line/one dose as-
say):
In this assay, a panel of 3 cell lines consisting of MCF-7
(Breast), NCI-H460 (Lung), and SF-268 (CNS) was
used. Each cell line was seeded and pre-incubated on
micro titer plates.Test agents were then added at a sin-
gle concentration and the culture incubated for an addi-
tional 48 hours. End point determinations were made
with alamar blue.The results for each test agent were re-
Table 1. Anticancer activity of compounds in the 3 cell line/one dose assay.
Compound
Number
Concentration
Growth percentage
Breast
Activity
Lung
CNS
NCI-H460
MCF7
SF-268
2
3
100 µM
100 µM
100 µM
100 µM
100 µM
100 µM
100 µM
100 µM
100 µM
100 µM
100 µM
100 µM
100 µM
100 µM
100 µM
100 µM
100 µM
100 µM
100 µM
100 µM
77
71
81
79
73
40
90
77
96
71
82
82
0
67
66
81
69
93
69
6
98
89
93
94
73
78
91
59
91
1
91
91
0
72
76
91
80
92
85
2
94
97
105
96
74
71
75
80
96
2
67
67
0
90
92
103
68
112
93
14
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
Active
Inactive
Inactive
Active
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
Active
4 a
4 b
5 a
5 b
7 a
7 b
8
9
10 a
10 b
11
14 a
14 b
15
16
17
18
21

Arch. Pharm. Pharm. Med. Chem. 2003, 336, 216–225 Anticancer activity of novel fluorinated thiazolo[4,5-d]pyrimidines 221
ported as the percent of growth of treated cells com-
pared to untreated control cells. Compounds which re-
duced the growth any of the cell lines to 32 % or less
(negative numbers indicate cell kill) were then evaluated
for their anticancer activity (over a 5-log dose range) us-
ing an extended panel of 60 cell lines.
screening program [21–25].Initially, they were evaluated
using the 3-cell line/one dose assay, the results of which
are presented in Table 1. Three compounds (9, 11, and
20) were considered active in the initial screen.
The anticancer activity of these compounds was then
evaluated using an extensive panel of 60 human cell
lines.The compounds showed variable antitumor activi-
ties against most of the tested sub-panel tumor cell lines
as evaluated by the calculated GI50 values. The median
growth inhibitory concentration (the average sensitivity
of each sub-panel towards each of the test compounds)
and the full panel mean graph mid point (MG-MID) (the
average of all cell lines towards each of the test com-
pounds) for the sub-panel tumor cell lines are reported in
Table 2. Compound 9 displayed good antitumor activity
against all of the cell lines used in the screen which
GI50 values of 0.004 µM/mL (ovarian cancer) and
0.003 µM/mL (prostate cancer). Compounds 11 and 21
were less active with GI50 values of 0.054–0.144 µM/mL
and 0.021–0.038 µM/mL, respectively.
b) Full anticancer assay:
The NCI’s in vitro antitumor screen consists of 60 human
cell lines derived from nine types of cancer.The antican-
cer activity of the novel fluorinated thiazolo[4,5-d]pyrimi-
dines were tested at a minimum of five concentrations
using 10-fold dilutions (0.01–100 µM) on these cell lines.
Cells were exposed to the compounds for 48 hours. Cell
viability and growth was then estimated using the sul-
forhodamine B (SRB) protein assay.
The five concentrations of each compound tested were
used to create log concentration-% growth inhibition
curves. Three response parameters (GI50, TGI, and
LC50) were calculated for each cell line. The GI50 value
corresponds to the concentration of compound which
decreases net cell growth by 50 %.The TGI value is the
concentration of compound which results in total growth
inhibition and the LC50 value is the concentration of com-
pound which causes a net 50 % loss of initial cells at the
end of the incubation period (48 h). Sub-panel and full
panel mean-graph midpoint values (MG-MID) for certain
agents are the average of individual real and default GI50,
TGI, or LC50 values of all cell lines in the sub-panel or the
full panel, respectively [21].
The ratio obtained by dividing a compound’s full panel
MG-MID (µM) by its individual sub-panel MG-MID (µM)
is considered a measure of its selectivity. Ratios be-
tween 3 and 6 indicate a compound is moderately se-
lective whereas ratios greater than 6 indicate high se-
lectivity towards the corresponding cell line. Com-
pounds with ratios below 3 are considered non-selec-
tive [24].With the exception of compound 11, which was
highly selective against Colon cancer (selectivity ratio of
6), the active compounds in the present study proved to
be non-selective against the nine tumor sub-panels
tested.
In the present study, the prepared compounds were
evaluated for their antitumor activity using the NCI
Table 2. Median growth inhibitory concentration (GI50) and full panel mean graph mid points (MG-MID) for sub-panel
tumor cell lines.
Sub-panel
Compound number
Tumor cell line
9
11
21
Leukemia
0.014
0.031
0.014
0.014
0.018
0.004
0.014
0.034
0.034
0.013
0.042
0.034
0.023
0.036
0.031
0.041
0.037
0.043
0.031
0.145
0.133
0.067
0.181
0.050
0.078
0.060
0.050
0.060
0.110
0.073
Lung cancer
Colon Cancer
CNS cancer
Melanoma
Ovarian cancer
Renal cancer
Prostate cancer
Breast cancer
MG-MID

222 Fahmy et al.
Arch. Pharm. Pharm. Med. Chem. 2003, 336, 216–225
NMR (δ-ppm) spectra were recorded on a Bruker (400 MHz)
spectrometer using tetramethylsilane as the internal standard
and CDCl3 as the solvent. The elemental analyses were per-
formed using a Perkin-Elmer RE 2400 C H N S Analyzer.All val-
ues for C, H, N and S are within 0.4 % of the calculated data.
Acknowledgments
The authors are grateful to the staff of the Department of
Health and Human Services, National Cancer Institute,
Bethesda, Maryland, USA for the anticancer evaluation.
4-Amino-5-carbamoyl-3-(4-fluorophenyl)thiazole-2(3H)thione
(1)
4-Fluorophenyl isothiocyanate (7.65 g, 50 mmol) was added to
a solution of 2-cyanoacetamide (4.2 g, 50 mmol), sulphur
(1.6 g, 50 mmol) and triethylamine (6 mL) in ethanol (50 mL).
The reaction mixture was heated under reflux for 1 h during
which the product partially crystallized. After cooling, the prod-
uct was filtered, washed with cold ethanol, dried and recrystal-
Experimental
Melting points were determined in open-glass capillaries using
a Gallenkamp melting point apparatus and are uncorrected.
The infrared (IR) spectra were determined with a Perkin-Elmer
1430 spectrophotometer using the KBr disc technique.The 1H-
Table 3. Yields, melting points, molecular formulae and molecular weights of newly prepared thiazoles intermediates.
Compound No
Yield (%)
M.P. (C)
Mol. formula
Mol. Weight
1
85
78
72
83
270–272
250–252
260–262
280–282
C10H8N3FOS2
C16H11N3F2OS2
C16H10N3F3OS2
C17H11N4F3OS2
269.32
363.41
381.40
408.43
13 a
13 b
20
Results for C, H, N, S are within 0.4 % of the theoretical values for the formulae given.
Table 4. Yields, melting points, molecular formulae and molecular weights of newly prepared thiazolo[4,5-d]pyrim-
idines.
Compound No
Yield (%)
M.P. (C)
Mol. formula
Mol. Weight
2
3
85
80
87
82
77
74
72
70
88
78
72
70
73
74
72
70
80
72
83
85
338–340
325–327
237–239
239–241
220–222
223–225
312–314
320–322
385–387
260–262
305–307
288–290
285–287
236–238
212–214
344–346
275–277
>400
C11H6N3FOS2
C11H6N3FS3
279.32
263.32
403.50
421.49
387.43
405.42
370.38
388.37
293.34
311.79
400.48
418.46
386.45
373.41
391.40
307.37
431.46
277.28
401.37
418.42
4 a
4 b
5 a
5 b
7 a
7 b
8
C18H11N3F2S3
C18H10N3F3S3
C18H11N3F2OS2
C18H10N3F3OS2
C18H12N4F2OS
C18H11N4F3OS
C12H8N3FOS2
C12H7N3ClFS2
C19H14N4F2S2
C19H13N4F3S2
C18H12N4F2S2
C17H9N3F2OS2
C17H8N3F3OS2
C12H10N5FS2
C19H12N5F3S2
C11H8N5FOS
C18H10N5F3OS
C18H9N4F3OS2
9
10 a
10 b
11
14 a
14 b
15
16
17
18
21
365–367
245–247
Results for C, H, N, S are within 0.4 % of the theoretical values for the formulae given.

Arch. Pharm. Pharm. Med. Chem. 2003, 336, 216–225 Anticancer activity of novel fluorinated thiazolo[4,5-d]pyrimidines 223
lized from glacial acetic acid (Table 3). IR 3350, 3250 (N-H),
1660 (C=O), 1590, 1510 (C=C), 1570 (δNH), 1533, 1240 ,
1085, 940 (N-C=S), 1215, 1020 (C-S-C) cm–1.
(N-C=S), 1234 (C-S-C) cm–1.1H-NMR (CDCl3):7 a:4.51 (s, 2 H,
Benzyl-CH2), 7.03–7.55 (m, 8 H, Ar-H), 8.25 (s, 1 H, C5-H). 7 b:
4.56 (s, 2 H, Benzyl-CH2), 7.02–7.49 (m, 7 H Ar-H), 8.00 (s, 1 H,
C5-H).
3-(4-Fluorophenyl)-thiazolo[4,5-d]pyrimidin-7(6H)-one-2(3H)-
thione (2)
3-(4-Fluorophenyl)-5-methyl-thiazolo[4,5-d]pyrimidin-7(6H)-
one-2(3H)-thione (8)
A solution of compound 1 (2.96 g, 10 mmol) in a mixture of tri-
ethyl orthoformate and acetic anhydride (20 mL, 1:1) was heat-
ed under reflux for 1 h.After cooling, the crystalline product was
filtered, washed with cold ethanol, dried and recrystallized from
glacial acetic acid (Table 4). IR 3162 (N-H), 1681 (C=O), 1630
(CN), 1579, 1510 (C=C), 1533, 1240, 1085 (N-C=S), 1215 (C-
S-C) cm–1. 1H-NMR (CDCl3): 7.19–7.27 (m, 4 H, Ar-H), 7.92 (s,
1H, C5-H).
A solution of 1 (2.69 g, 10 mmol) in acetic anhydride (20 mL)
was heated under reflux for 3 h during which the product par-
tially crystallized. After cooling, the product was filtered,
washed with ethanol, dried and recrystallized from aqueous
DMF (1:9) (Table 4). IR 3100–3000 (N-H), 1676 (C=O), 1640
(CN), 1584, 1510 (C=C), 1554 (δ N-H), 1254, 1090 (N-C=S),
1230, 1048 (C-S-C) cm–1. 1H-NMR (CDCl3): 2.4 (s, 3 H, CH3),
7.18–7.27 (m, 4 H, Ar-H).
3-(4-Fluorophenyl)-7-mercaptothiazolo[4,5-d]pyrimidine-2(3H)-
thione (3)
7-Chloro-3-(4-fluorophenyl)-5-methylthiazolo[4,5-d]pyrimidine-
2(3H)-thione (9)
A mixture of 2 (2.97 g, 10 mmol) and phosphorous pentasul-
phide (4.44 g, 10 mmol) in dry xylene (20 mL) was heated un-
der reflux for 5 h and then cooled. The product obtained after
addition of petroleum ether was filtered, washed with ethanol,
dried and recrystallized from DMF (Table 4). IR 3119 (N-H),
1635 (CN), 1584, 1507 (C=C), 1552 (δ N-H), 1427, 1263, 1165
(N-C=S), 1234 (C-S-C) cm–1. H1-NMR (CDCl3): 7.28–7.39 (m,
4H, Ar-H), 8.88 (s, 1H, C5-H).
A solution of 8 (2.93 g, 10 mmol) in phosphorus oxalyl chloride
(20 mL) was heated under reflux for 1 h.After cooling, the reac-
tion mixture was poured into ice-water (100 mL).The obtained
product was filtered, washed with aqueous ethanol , dried and
recrystallized from ethanol (Table 4). IR 1650 (CN), 1590, 1510
(C=C), 1552, 1245, 1090, 920 (N-C=S), 1230, 1032, 1036 (C-
S-C) cm–1. 1H-NMR (CDCl3): 2.5 (s, 3 H, CH3), 7.18–7.28 (m,
4 H, Ar-H).
3-(4-Fluorphenyl)-7-(4-fluorobenzyl or 2,4-difluorobenzyl)-
mercaptothiazolo[4,5-d] pyrimidine-2(3H)- thiones (4 a, b)
3-(4-Fluorophenyl)-7-(4-fluorobenzyl or 2,4-difluorobenzyl)-5-
Fluorobenzyl bromide (10 mmol) was added to a mixture of 3
(2.63 g, 10 mmol) and anhydrous potassium carbonate
(1.38 g, 10 mmol) in dry acetone (20 mL).The reaction mixture
was heated under reflux for 3 h and then cooled.The crystalline
product was filtered, washed with cold ethanol, dried and re-
crystallized from aqueous DMF (1:9) (Table 4). IR 1650 (C=N),
1604, 1511 (C=C), 1557, 1264, 1090, 841 (N-C=S), 1232, 1038
(C-S-C) cm–1. 1H-NMR (CDCl3): 4 a: 4.63 (s, 2 H, Benzyl-CH2),
7.00–7.44 (m, 8 H, Ar-H), 8.70 (s, 1 H, C5-H). 4 b: 4.56 (s, 2 H,
Benzyl-CH2), 6.73–7.44 (m, 7 H, Ar-H), 8.65 (s, 1 H, C5-H).
methylthiazolo[4,5-d]pyrimidines (10 a, b)
The selected fluorobenzyl amine (20 mmol) was added to a so-
lution of 9 (3.11 g, 10 mmol) in ethanol (20 mL). The reaction
mixture was heated under reflux for 3 h during which the prod-
uct partially crystallized. After cooling, the product was filtered,
washed with ethanol, dried and recrystallized from aqueous
DMF (1:9) (Table 4). IR) 1645 (CN), 1602, 1510 (C=C), 1535,
1260, 1100 (N-C=S), 1224, 1041 (C-S-C) cm–1. 1H-NMR
(CDCl3): 10 a: 2.40 (s, 3 H, CH3), 3.60 (t, 3 H, NH), 4.72 (d, 2 H,
Benzyl-CH2), 6.76–7.26 (m, 8 H, Ar-H). 10 b: 2.41 (s, 3 H, CH3),
3.55 (t, 1 H, NH), 4.67 (d, 2 H, Benzyl-CH2), 6.98–7.30 (m, 7 H,
Ar-H).
3-(4-Fluorophenyl)-6-(4-Fluorobenzyl or 2,4-difluorobenzyl)-
thiazolo[4,5-d] pyrimidine-2(3H)thiones (5 a, b)
Fluorobenzyl bromide (10 mmol) was added to a solution of 2
(2.79 g, 10 mmol) and an equimolar amount of potassium hy-
droxide (0.6 g) in ethanol (20 mL). The reaction mixture was
heated under reflux for 5 h and then cooled.Water (10 mL) was
added and the product obtained was filtered, washed with cold
ethanol, dried and recrystallized from acetone (Table 4). IR
1697–1692 (C=O), 1640 (CN), 1604, 1512-1509 (C=C),
3-(4-Fluorphenyl)-7-(4-fluorophenylamino)-5-methylthi-
azolo[4,5-d]pyrimidine-2(3H)-thione (11)
4-Fluoroaniline (1.11 g, 10 mmol) and triethylamine (0.5 mL)
were added to a solution of 9 (3.11 g, 10 mmol) in ethanol
(20 mL). The reaction mixture was heated under reflux for 3 h
during which the product partially crystallized.After cooling, the
product was filtered, washed with ethanol, dried and recrystal-
lized from aqueous DMF (1:9) (Table 4). IR 3178 (N-H), 1645
(CN), 1580, 1510 (C=C), 1563 (δ N-H), 1539, 1244, 1157, 920
(N-C=S), 1220, 1049 (C-S-C) cm–1. 1H-NMR (CDCl3): 2.55 (s,
3 H, CH3), 7.17–7.43 (m, 8 H, Ar-H).
1
1252–1248, 1101, 852 (N-C=S) cm–1. H-NMR (CDCl3): 5 a:
5.07 (s, 2 H, Benzyl-CH2), 6.92–7.30 (m, 8 H, Ar-H), 7.94 (s,
1 H, C5-H). 5 b: 5.17 (s, 2 H, Benzyl-CH2), 6.84–7.64 (m, 7 H,
Ar-H), 8.20 (s, 1 H, C5-H).
3-(4-Fluorophenyl)-2-(4-fluorobenzylidine or 2,4-difluoroben-
zylidene)thiazolo [4,5-d]pyrimidine-2(3H)-thiones (7 a, b)
4-Amino-3-(4-fluorophenyl)65-(4-fluorophenyl, or 2,4-fluoro-
phenylaminocarbonyl thiazol-2(3H)-thiones (13 a, b)
Dimethyl sulfate (1.89 g, 1.42 mL, 15 mmol) was added to a so-
lution of 2 (2.79 g, 10 mmol) in acetonitrile (20 mL).The reaction
mixture was heated under reflux for 1 h and then cooled. The
selected fluorobenzyl amine (10 mmol) was then added. The
reaction mixture was heated under reflux for 1 h and cooled.
The separated white crystalline product was filtered, washed
with cold ethanol, dried and recrystallized from aqueous DMF
(1:9) (Table 4). IR 3500 (N-H), 1694–1680 (C=O), 1656–1648
(C=N), 1610–1604, 1514–1512 (C=C), 1535, 1256, 1159, 825
Compounds 13 a and b were prepared from N(fluorophenyl)cy-
anoacetamides 12 a, b (10 mmol), finely divided sulphur
(0.32 g, 10 mmol), 4-fluorophenyl isothiocyanate (1.53 g,
10 mmole) as described for compound 1.The product obtained
was filtered, washed with cold ethanol, dried and recrystallized
from ethanol (Table 3).IR:3350, 3250 (N-H), 1670 (C=O), 1635
(C=N), 1602, 1509 (C=C), 1560 (δNH), 1550, 1295, 1080, 890
(N-C=S), 1234, 1025 (C-S-C).

224 Fahmy et al.
Arch. Pharm. Pharm. Med. Chem. 2003, 336, 216–225
3,6-Di(4-fluorophenyl)-thiazolo[4,5-d]pyrimidin-7(6H)-one-
2(3H)-thione (14 a) and 3-(4-fluorophenyl)-6-(2,4-difluoro-
phenyl)-thiazolo[4,5-d]pyrimidin-7(6H)-one-2(3H)-thione (14 b)
(0.32 g, 10 mmol) and 4-fluorophenyl isothiocyanate (1.53,
10 mmol) as described for compound 1 and was recrystallized
from glacial acetic acid (Table 3). IR: 3350, 3250 (N-H), 1660
(C=O), 1630 (C=N), 1600, 1510 (C=C), 1570 (δNH), 1550,
1290, 1075, 870 (N-C=S), 1230, 1020 (C-S-C). 1H-NMR
(CDCl3): 7.20–7.80 (m, 4H, Ar-H), 7.9 (s, 1 H, H-C=N).
A solution of 13 a, b (10 mmol) in a mixture of triethylorthofor-
tate (10 mL) and acetic anhydride (10 mL) was heated under
reflux for 3 h and then cooled. The product obtained was fil-
tered, washed with cold ethanol, dried and recrystallized from
ethanol (Table 4). IR 1692-1681 (C=O), 1650 (C=N), 1613–
1604, 1510 (C=C), 1256, 844 (N-C=S), 1222, 1048 (C-S-C)
cm–1. 1H-NMR (CDCl3): 14 a: 7.25–7.54 (m, 8 H, Ar-H), 8.1 (s,
1 H, C5-H), 14 b: 7.08–7.45 (m, 7 H, Ar-H), 7.95 (s, 1 H, C5-H).
6-(2,4-Difluorobenzylideneamino)-3-(4-fluorophenyl)-thi-
azolo[4,5-d]pyrimidin-7(6H)-one-2(3H)-thione (21)
Compound 21 was prepared from 20 (4.08 g, 10 mmol) and tri-
ethyl orthoformate/acetic anhydride mixture as described for
compound 2. The product was recrystallized from aqueous
DMF (1:9) (Table 4). IR 1695 (C=O), 1646 (C=N), 1613, 1516
(C=C), 1554, 1288, 1092, 856 (N-C=S), 12737, 1047 (C-S-C)
cm–1. 1H-NMR (CDCl3): 6.92–8.1 (m, 7 H, Ar-H), 8.40 (s, 1 H,
C5-H), 9.70 (s, 1 H, H-C=N).
3-(4-Fluorophenyl)-7-hydrazino-5-methylthiazolo[4,5-d]pyrim-
idine-2(3H)-thione (15)
Hydrazine hydrate (1.0 g, 20 mmol) was added to a solution of 9
(3.11 g, 10 mmol) in ethanol (20 mL),.The reaction mixture was
heated under reflux for 1 h during which the product crystal-
lized. After cooling, the product was filtered, washed with etha-
nol, dried and recrystallized from aqueous DMF (1:9) (Table 4).
IR 3300, 3250 (N-H), 1640(CN), 1603, 1513 (C=C), 1570 (δ
N-H), 1534, 1304, 1091, 940 (N-C=S), 1047 (C-S-C) cm–1. 1H-
NMR (CDCl3):2.39 (s, 3 H, CH3), 4.31 (bs, 2 H, NH2), 7.19–7.26
(m, 4 H, Ar-H), 10.4 (bs, 1 H, NH).
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Tobacco,coffee,
Manfred Hesse
and other poisons
Alkaloids
Nature´s Curse or Blessing?
Contents:
2002. 414 pages, 185 images, 110 in color. Hardcover.
e 129.–* / sFr 190.– / £ 75.–
PART A: CHEMICAL ASPECTS
Introduction / Classification of Alkaloids / Structural
Analysis / Artefacts / Chiroptical Properties / Synthesis
ISBN 3-906390-24-1
*The e-Price is valid only for Germany.
PART B: BIOLOGICAL ASPECTS
Chemotaxonomy / Aspects of Biogenesis / Importance of
Alkaloids for their Producers and Owners
Alkaloids, nitrogen-containing natural substances produced by plants, animals, and micro-
organisms, have been captivating and fascinating mankind from ancient times because of
their varied and often strong physiological effects.Typical and well-known alkaloids include,
for example, cocaine, heroin, strychnine, curarine, and caffeine.
PART C: HISTORICAL ASPECTS
With its focus on structures and syntheses this book also covers the biological, biosynthetic, and
pharmacological aspects of alkaloids. A chapter detailing the cultural and historical significance
of the most important agents completes this unique compendium.
Chemistry of Alkaloids / Cultural History and Active
Principles of Selected Alkaloids
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