Synthesis and biological evaluation of benzothiazole derivatives as potent antitumor agents

Article abstract of DOI:10.1016/j.bmcl.2005.05.077

Based on 2-methyl-4-nitro-2H-pyrazole-3-carboxylic acid[2- (cyclohexanecarbonylamino)benzothiazol-6-yl]amide (1), which shows selective cytotoxicity against tumorigenic cell lines, 2,6-dichloro-N-[2- (cyclopropanecarbonylamino)benzothiazol-6-yl]benzamide (13b) was designed and synthesized as a biologically stable derivative containing no nitro group. The highly potent derivative 13b exhibited excellent in vivo inhibitory effect on tumor growth.

Full text of DOI:10.1016/j.bmcl.2005.05.077

Bioorganic & Medicinal Chemistry Letters 15 (2005) 3328–3332
Synthesis and biological evaluation of benzothiazole derivatives
as potent antitumor agents
Masao Yoshida,a Ichiro Hayakawa,b Noriyuki Hayashi,b Toshinori Agatsuma,c
Youko Oda,c Fumie Tanzawa,d Shiho Iwasaki,d Kumiko Koyama,e
Hidehiko Furukawa,c Shinichi Kurakatad and Yuichi Suganob,*
aMedicinal Chemistry Research Laboratories, Sankyo Co. Ltd., Shinagawa-ku, Tokyo 140-8710, Japan
bLead Discovery Research Laboratories, Sankyo Co. Ltd., Shinagawa-ku, Tokyo 140-8710, Japan
cBiomedical Research Laboratories, Sankyo Co. Ltd., Shinagawa-ku, Tokyo 140-8710, Japan
dBiological Research Laboratories, Sankyo Co. Ltd., Shinagawa-ku, Tokyo 140-8710, Japan
eDrug Metabolism and Pharmacokinetics Research Laboratories, Sankyo Co. Ltd., Shinagawa-ku, Tokyo 140-8710, Japan
Received 12 April 2005; revised 10 May 2005; accepted 12 May 2005
Abstract—Based on 2-methyl-4-nitro-2H-pyrazole-3-carboxylic acid[2-(cyclohexanecarbonylamino)benzothiazol-6-yl]amide (1),
which shows selective cytotoxicity against tumorigenic cell lines, 2,6-dichloro-N-[2-(cyclopropanecarbonylamino)benzothiazol-6-
yl]benzamide (13b) was designed and synthesized as a biologically stable derivative containing no nitro group. The highly potent
derivative 13b exhibited excellent in vivo inhibitory effect on tumor growth.
Ó 2005 Elsevier Ltd. All rights reserved.
Cancer is a disease of striking significance in the world
today. It is the second leading cause of death in the
United States after cardiovascular disease and it is pro-
jected to becoming the primary cause of death there
within the coming years.1 In our project to develop
new anticancer drugs as small molecules,2 2-methyl-4-
nitro-2H-pyrazole-3-carboxylic acid[2-(cyclohexanecar-
bonylamino)benzothiazol-6-yl]amide (1) was selected
as one of the most promising screening hit compounds.
Compound 1 with a benzothiazole core3 exhibited
potent and selective cytotoxicity against a tumorigenic
tests. This article describes our procedure to discover
derivatives that possess remarkable in vivo inhibitory ef-
fect on tumor growth by stabilizing metabolic degrada-
tion, along with improving in vitro activity, employing a
structure–activity relationship (SAR) study.
Figure 1 illustrates the two regions of interest for SAR
evaluation of screening hit 1. In general, the nitro group
in the structure of 1 is not preferred for drug design in
medicinal chemistry on account of its metabolic instabil-
ity.4 To evaluate the structural requirements of the
left-hand acyl group region, Region 1, solid-phase chem-
istry, which is a powerful tool for large-size library
construction, was employed for examining the diverse
cell line, WI-38 VA-13 subline 2RA (VA-13) (EC50
=
26 ng/mL), despite the fact that no cytotoxicity was
observed against the normal parental cell line, WI-38
(EC50 > 4000 ng/mL).2 Screening hit 1 showed remark-
able biological activity in the cell-based screening.
Nevertheless, the results of an in vivo antitumor test
of compound 1 were disappointing. It was predicted that
metabolic instability of compound 1 could make a
difference in the results between the in vitro and in vivo
Keywords: Anticancer.
*
Figure 1. Selected regions of interest for SAR evaluation of screening
hit compound 1.
Corresponding author. Tel.: +81 3 3492 3131; fax: +81 3 5436 8578;
e-mail: ysugan@sankyo.co.jp
0960-894X/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2005.05.077

M. Yoshida et al. / Bioorg. Med. Chem. Lett. 15 (2005) 3328–3332
3329
Table 1. Cytotoxicity of amide, urethane, urea, thiourea and sulfon-
amide derivatives (Region 1)
Compound R1
Cytotoxicity
EC50 (ng/mL)a
1
2-Methyl-4-nitro-2H-pyrazol-3-yl
2-Methylphenyl
26
85
5a
5bb
5cb
5db
5e
2-Fluorophenyl
2-Chlorophenyl
140
25
2-Trifluoromethylphenyl
2-Phenoxyphenyl
3-Fluorophenyl
24
100
Scheme 1. Solid-phase synthesis of amide, urethane, urea, thiourea,
and sulfonamide derivatives. Reagents and conditions: (a) cyclohex-
anecarbonyl chloride, 4-pyrrolidinopyridine, DMA, 25 °C, 15 h; (b)
H2/Pd-C, THF, 25 °C, 5 h (93%, two steps); (c) FMPB AM resin (10,
0.94 mmol/g), MgSO4, DMA–AcOH (9:1), 80 °C, 1 h, then NaBH-
(OAc)3, 80 °C, 4 h; (d) 5: R1CO2H, PPh3, N-chlorosuccinimide,
pyridine, DCM, 25 °C, 2 h, 6: R1OC(O)Cl, NaHCO3, THF, 80 °C,
4 h; 7: R1NCO, DCM, 25 °C, 20 h; 8: R1NCS, DCM, 25 °C, 20 h; 9:
R1SO2Cl, pyridine, 60 °C, 16 h; (e) 5–9: 20% TFA in DCM, 25 °C,
20 h.
5f
640
520
5g
5h
5i
3-Cyanophenyl
3-Phenoxyphenyl
4-Methoxyphenyl
4-Methylphenyl
>4000
4900
5100
3300
>4000
>4000
15
5j
5k
5l
4-Cyanophenyl
4-Bromophenyl
5m
5nb
5ob
5p
5q
5r
2,4-Dichlorophenyl
2,6-Dichlorophenyl
2-Fluoro-6-trifluoromethylphenyl
Methyl
32
2700
140
2-Pentyl
2-Methylbut-2-yl
substructures for potent anticancer agents. The structural
optimization of the right-hand region, Region 2, was
carried out by parallel solution-phase chemistry.5
1000
1300
75
5s
2-Tetrahydrofuranyl
2-Chloropyridin-3-yl
2-Methyl-2H-pyrazol-3-yl
2,5-Dimethyl-2H-pyrazol-3-yl
1,3,5-Trimethyl-1H-pyrazol-4-yl
2,4-Dimethylthiazol-5-yl
2,4-Dimethylfuran-3-yl
1,2,5-Trimethyl-1H-pyrrol-3-yl
Allyl
5tb
5uc
5vc
5wc
5x
5yc
5zc
6a
6b
7a
7b
8a
8b
9a
9b
580
120
Scheme 1 summarizes our synthesis of Region 1 deriva-
tives of hit compound 1. Acylation of commercially
available 2-amino-6-nitrobenzothiazole (2) with cyclo-
hexanecarbonyl chloride was executed, and the product
was reduced to furnish key intermediate 3. Compound 3
was then loaded onto a polystyrene solid support with a
BAL-type linker,6 4-(4-formyl-3-methoxyphenoxy)buty-
rylamide resin (FMPB AM resin, 10), purchased from
Novabiochem Corp. by reductive amination. The result-
ing secondary amine 4 was acylated with one of the
various reagents to give amide,7 urethane, urea, thio-
urea, or sulfonamide resins, and the ensuing cleavage
from the polymer support under acidic conditions
yielded the desired derivatives 5–9. In this process, a
ca. 200-member library was constructed employing a
solid-phase strategy. Individual library members were
identified via radiofrequency encoding using IRORITM
tags and MiniKanTM technologies.8,9
12
390
2700
>6200
580
Isobutyl
2,6-Dimethylphenyl
Phenethyl
720
560
700
1,4-Benzodioxan-6-yl
2-Trifluoromethoxyphenyl
4-Butoxyphenyl
1600
2300
750
5-Fluoro-2-methylphenyl
700
a Selective cytotoxicity against a tumorigenic cell line, WI-38 VA-13
subline 2RA (VA-13), and no cytotoxicity was observed against the
normal parental cell line, WI-38.
b Synthesized from 3 with acyl chloride under standard conditions
(NEt3, DCM, 25 °C).
c Synthesized from 3 with carboxylic acid under standard conditions [1-
(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, 1-hy-
droxy-benzotriazole hydrate, DMF, 25 °C].
The cytotoxicity of the synthesized derivatives is given in
Table 1. Most of the compounds that had a substitute at
the ortho-position (5a–e) of the benzene ring showed
almost the same or a slightly weaker cytotoxicity
than hit compound 1. While derivatives with a meta sub-
stituent (5f–h) weakened the biological activity, those
that had a substituent at the para-position (5i–m) com-
pletely lost their biological activity. The ortho-di-substi-
tuted compounds (5n and o) displayed a stronger
biological activity, and 2,6-dichlorophenyl amide 5n
(EC50 = 15 ng/ml) was, in particular, more potent than
hit compound 1. The characteristic heterocycle substruc-
ture of hit compound 1 was revealed to be replaceable
with readily available simple phenyl groups. In addition,
derivatives possessing aliphatic substituents (5p–s),
instead of the benzene ring, showed a relatively weak
cytotoxicity. Among the derivatives with heterocycles
as the amide substituent (5t–z), compound 5w (EC50 =
12 ng/ml) was revealed to possess remarkable potency.

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M. Yoshida et al. / Bioorg. Med. Chem. Lett. 15 (2005) 3328–3332
Although various types of urethane, urea, thiourea, and
sulfonamide were synthesized, derivatives with different
bonding structures were less potent than amide com-
pounds. The biological activities of a few representative
examples (6a–9b) out of the synthesized compounds are
also indicated in the table.
This study of Region 1 derivatization resulted in the dis-
covery of biologically potent derivatives (5n for exam-
ple) possessing a benzene ring instead of a singular
hetero-ring with a nitro substituent.
Scheme 3. Synthesis of amine derivatives. Reagents and conditions: (a)
HNO3, H2SO4, 0–25 °C, 3 h (quant.); (b) Zn, AcOH, THF–MeOH
(1:1), 60 °C, 2 h (56%); (c) 2,6-dichlorobenzoyl chloride, DMA, 25 °C,
17 h (77%); (d) R3NH2, EtOH, a sealed tube, 120–130 °C, 24 h.
Scheme 2 illustrates the synthesis of Region 2 derivatives
of compound 5n. The tert-butoxycarbonyl (Boc) protec-
tion of the amino group of 2 was followed by reduction
of the nitro group to afford 11. Acylation of 11 with
commercially available 2,6-dichlorobenzoyl chloride
was undertaken in N,N-dimethylacetamide (DMA),
and the resulting product was treated with hydrochloric
acid to remove the N-Boc group, giving 12. The amino
group of 12 was acylated with one of the various acyl
groups to yield the desired derivatives 13–15. Unfortun-
ately, the final step to furnish urethane derivatives was
problematic, giving a mixture of 14 and excess
acylated 16. The only fruitful method to afford pure
14 was to treat the resulting mixture with trifluoroacetic
acid (TFA) in situ after acylation of 12 was completed
with an excess of chloroformate. The derivatives
prepared by the optimized procedure employing a
solution-phase strategy maintained sufficient purity for
evaluation without chromatographic purification.
by acylation of the resulting amino group with 2,6-di-
chlorobenzoyl chloride to furnish 18. Amination of chlo-
ride 18 under thermal conditions [ethanol, sealed tube,
120–130 °C, 24 h] afforded the desired derivatives 19.
The results of the cytotoxicity test of the synthesized
derivatives are shown in Table 2. Most of the com-
pounds possessing aliphatic substituents (13a–f) had
almost the same potency as compound 5n, except when
a smaller substituent, such as the methyl group (13c), or
a longer substituent, such as the heptyl group (13f), was
placed at the aliphatic parts. A few derivatives that had
an amino group (13g) or a carboxylic acid (13h) at the
terminus of their aliphatic chains had completely lost
their biological activity. Interestingly, new-type deriva-
tives (14a–f) designed by replacing the original amide
part with the corresponding urethane were more potent
(EC50 = 2.5–11 ng/ml). While tert-butoxycarbonyl com-
pound 14g with a bulky substituent showed a slightly
lower activity, benzyl (14h) or phenyl (14i) derivatives
possessing an aromatic ring faced considerable loss of
cytotoxicity. Additionally, the derivatives of urea link-
age types (15a–e) also had the same potency as the
amide or urethane compounds. Lastly, as shown in
Table 3, the amine derivatives (19a–e) that were lacking
an original carbonyl group (C@O) showed a relatively
weak cytotoxicity.
In addition, our synthetic method of amine derivatives
of 5n is given in Scheme 3. The initial 2-chlorobenzo-
thiazole (17) was converted to a 6-nitrated compound,10
and the product was treated with zinc powder, followed
This study of Region 2 SAR indicated that urethane
derivatives (14b for instance) were ca. 10 times as
biologically potent as the original amide derivatives as
a hit compound 1.
As the most promising substructures were determined
by derivatization around Regions 1 and 2, the next
challenge was modification of the benzothiazole core
structure. We first attempted to synthesize benzothiazole
derivatives possessing an amide substituent at the fifth
position (Scheme 4). A key intermediate, 2-amino-5-
nitrobenzothiazole (22), was readily prepared from
commercially available 20 by a previously reported
procedure.11 Acylation of 22 with ethyl chloroformate,
followed by hydrogenation of the nitro group, furnished
compound 23. An amino group of compound 23 was
acylated with 2,6-dichlorobenzoyl chloride to afford
the desired compound 24, which possesses an amide
substituent at the fifth position. To our surprise, the
Scheme 2. Solution-phase synthesis of amide, urethane, and urea
derivatives. Reagents and conditions: (a) Boc2O, DMAP (cat.), DCM,
25 °C, 18 h (92%); (b) H2/Pd-C, THF, 25 °C, 13 h (91%); (c) 2,6-
dichlorobenzoyl chloride, DMA, 25 °C, 20 h (93%); (d) 4 N HCl–l,4-
dioxane, 1,4-dioxane–EtOH (5:1), 25 °C, 17 h (92%); (e) 13: R2C(O)Cl,
DMA, 25 °C, 24 h; or R2CO2H, 1-(3-dimethylaminopropyl)-3-ethyl-
carbodiimide hydrochloride, 1-hydroxy-7-azabenzotriazole, NEt3,
DMF, 60 °C, 20 h; 14: R2OC(O)Cl, DMA, 25 °C, 17 h, then TFA,
40 °C, 5 h; 15: R2NCO, pyridine, 60 °C, 16 h.

M. Yoshida et al. / Bioorg. Med. Chem. Lett. 15 (2005) 3328–3332
3331
Table 2. Cytotoxicity of amide, urethane, and urea derivatives
(Region 2)
Table 3. Cytotoxicity of amine derivatives (Region 2)
Compound R3
Yield (%)a Cytotoxicity EC50
R2
Yield (%)a
Cytotoxicity
EC50 (ng/mL)b
(ng/mL)b
Compound
19a
19b
19c
19d
19e
Cyclohexylmethyl 66
Pentyl 15
4300
270
5n
Cyclohexyl
Cyclobutyl
Cyclopropyl
Methyl
—
86
15
13
13a
13b
13c
13d
13e
13f
13g
13h
14a
14b
14c
14d
14e
14f
14gf
14h
14i
4-Methoxyphenyl 46
3-Methoxyphenyl 22
2-Methoxyphenyl 75
870
>7200
>7200
35
52
13
600
10
Propyl
Isobutyl
Heptyl
62
92
a Yields were not optimized.
12
b Selective cytotoxicity against a tumorigenic cell line, WI-38 VA-13
subline 2RA (VA-13), and no cytotoxicity was observed against the
normal parental cell line, WI-38.
56
180
5300
>6600
9.5
2.6
2.5
2.6
3.5
11
Aminoethyl
HOC(O)CH2CH2
Methyl
34c
39d
20e
93
Ethyl
Propyl
5.8e
11e
17e
91
Isopropyl
Isobutyl
Methoxyethyl
tert-butyl
Benzyl
—
27
8.6e
10e
50
180
1100
32
Phenyl
Ethyl
15a
15b
15c
15d
15e
Isopropyl
Butyl
Hexyl
41
60
30
28
45
9.3
290
150
Benzyl
a Yields were not optimized.
b Selective cytotoxicity against a tumorigenic cell line, WI-38 VA-13
subline 2RA (VA-13), and no cytotoxicity was observed against the
normal parental cell line, WI-38.
Scheme 4. Synthesis of benzothiazole derivatives possessing an amide
substituent at the fifth position. Reagents and conditions: (a)
MeC(O)NCS, acetone, 25 °C, 3 days (quant.); (b) NaOH, THF–
MeOH (2:1), 70 °C, 10 h (76%); (c) ethyl chloroformate, DMA, 50 °C,
18 h (88%); (d) H2/Pd-C, THF–MeOH–AcOH (8:4:1), 25 °C, 4 h
(quant.); (e) 2,6-dichlorobenzoyl chloride, DMA, 25 °C, 15 h (42%).
c Yield was calculated after the removal of Boc-protecting group for
the amino group.
d Synthesized from 12 with succinic anhydride under standard condi-
tions (pyridine, DMAP, 60 °C).
e Yields without TFA treatment.
f The derivative 14g is the intermediate in Scheme 2.
Table 4. Antitumor activity of benzothiazole derivatives against an
LLC xenograft modela
biological activity of compound 24 (EC50 = 2500 ng/ml)
was a thousand times weaker than that of the corre-
sponding compound 14b. This unexpected result sug-
gested that the nitrogen and sulfur atoms of the
benzothiazole ring are not interchangeable and that they
might play an important role, since the difference be-
tween 14b and 24 lies simply in the positions of these
atoms.
Exp.
Compound
Dose
(mg/kg/shot)b
Schedule
(day)
TGI (%)c
at day 11
1
2
3
4
1
5n
40
40
5
1, 4, 7
1, 4, 7
1, 4, 7
1
15
35
13b
13b
63*
68*
20
a Mouse Lewis lung carcinoma (LLC) was inoculated subcutaneously
into BDF1 female mice (n = 6) on Day 0. Each compound was
administered iv in a vehicle of 10% DMA/10% HCO60 (poly-oxy-
ethylene hydrogenated castor oil 60)/80% saline.
b The applied dose was the maximum tolerated dose.
c Percent of inhibition of tumor growth (by volume).
* p < 0.05 (t test).
The in vivo antitumor activity of synthesized derivatives
is shown in Table 4.12 Although in vivo tests of hit com-
pound 1 (Exp. 1) and derivative 5n13 (Exp. 2) did not
show any significant therapeutic effect at 40 mg/kg iv
administration, compound 13b14 (Exp. 3) presented a
strong inhibiting effect on tumor growth, even at a much
lower dose (5 mg/kg). Figure 2 illustrates the plasma
concentration of 1, 5n, and 13b after iv administration
to mice. As expected, compound 5n (t1/2 = 1.10 h), which
was designed by replacing the nitro pyrazole ring of 1
with a 2,6-dichlorobenzene ring, exhibited improved sta-
bility in plasma, rather than screening hit compound 1
(t1/2 = 0.53 h). Furthermore, as cyclohexylamide of 5n

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M. Yoshida et al. / Bioorg. Med. Chem. Lett. 15 (2005) 3328–3332
3. Benzothiazole derivatives in common with the structure of
1 were quite recently reported as p56lck inhibitors by Das,
J.; Lin, J.; Moquin, R. V.; Shen, Z.; Spergel, S. H.;
Wityak, J.; Doweyko, A. M.; DeFex, H. F.; Fang, Q.;
Pang, S.; Pitt, S.; Shen, D. R.; Schieven, G. L.; Barrish, J.
C. Bioorg. Med. Chem. Lett. 2003, 13, 2145.
4. Uetrechet, J. In Drug Metabolizing Enzymes; Lee, J. S.,
Obach, R. S., Fisher, M. B., Eds.; FontisMedia and
Marcel Dekker: New York, 2003, pp 87–145.
5. Dolle, R. E. J. Comb. Chem. 2004, 6, 623.
6. (a) Alsina, J.; Jensen, K. J.; Albericio, F.; Barany, G.
Chem. Eur. J. 1999, 5, 2787; (b) Jensen, K. J.; Alsina, J.;
´
Songster, M. F.; Vagner, J.; Albericio, F.; Barany, G. J.
Am. Chem. Soc. 1998, 120, 5441; (c) Boojamra, C. G.;
Burrow, K. M.; Thompson, L. A.; Ellman, J. A. J. Org.
Chem. 1997, 62, 1240.
Figure 2. Plasma concentration of screening hit compound 1, deriv-
atives 5n and 13b after iv administration to BDF1 female mice at a
dose of 10 mg/kg (n = 2, mean). The concentration of remained
compounds was determined by HPLC.
7. Nishida, A.; Fuwa, M.; Naruto, S.; Sugano, Y.; Saito, H.;
Nakagawa, M. Tetrahedron Lett. 2000, 41, 4791.
8. IRORI, a Discovery Partners International Company:
http://www.discoverypartners.com/index.html.
9. (a) Nicolaou, K. C.; Pfefferkorn, J. A.; Mitchell, H. J.;
Roecker, A. J.; Barluenga, S.; Cao, G.-O.; Affleck, R. L.;
Lillig, J. E. J. Am. Chem. Soc. 2000, 122, 9954; (b)
Nicolaou, K. C.; Evans, R. M.; Roecker, A. J.; Hughes,
R.; Downes, M.; Pfefferkorn, J. A. Org. Biomol. Chem.
2003, 1, 908.
was converted to the cyclopropylamide of 13b, deriva-
tive 13b showed an excellent plasma concentration
(t1/2 = 3.29 h). This result suggested that metabolic
hydrolysis of the amide bond of Region 2 was controlled
by placing the cyclopropylamide instead of cyclohexyl-
amide. The excellent concentration of 13b in plasma also
brought about a strong inhibitory effect on tumor
growth with a single dosing of 20 mg/kg (Exp. 4).
Although the urethane derivatives (14b15 for example)
showed strong in vitro activity, they were not applied
in an in vivo test on account of their low solubility.
10. Katz, L. J. Am. Chem. Soc. 1951, 73, 4007.
11. Sedalk, M.; Hanuek, J.; Holcapek, M.; Sterba, V. J. Phys.
Org. Chem. 2001, 14, 187.
12. Tsuruo, T. Jpn. J. Cancer Chemother. 1987, 14, 2809, and
other references cited therein.
1
13. Compound 5n: yellow powder, mp 157–160 °C; H NMR
(270 MHz, DMSO-d6, d): 12.2 (s, 1H), 10.9 (s, 1H), 8.40
(d, 1H, J = 1.6 Hz), 7.71 (d, 1H, J = 8.9 Hz), 7.57–7.62 (m,
3H), 7.51 (dd, 1H, J = 9.5, 6.2 Hz), 2.41–2.60 (m, 1H),
1.60–1.93 (m, 5H), 1.10–1.52 (m, 5H); MS (APCI, m/z)
448, 450 [M+1]+; HRMS (ESI) Calcd for
C21H19Cl2N3O2S: [M+1]+, 448.06533. Found: 448.06831.
14. Compound 13b: off-white solid, mp 290–292 °C; 1H NMR
(270 MHz, DMSO-d6, d): 12.6 (s, 1H), 10.9 (s, 1H), 8.39
(d, 1H, J = 1.6 Hz), 7.72 (d, 1H, J = 8.6 Hz), 7.58–7.62 (m,
3H), 7.51 (dd, 1H, J = 9.5, 6.5 Hz), 1.91–2.09 (m, 1H),
0.82–1.01 (m, 4H); MS (APCI, m/z) 406, 408 [M+1]+;
HRMS (EI) Calcd for C18H13Cl2N3O2S [M+2]+, 407.0079.
Found: 407.0076.
In conclusion, derivative 13b, which had both biological
potency and excellent plasma concentration, was de-
signed as a derivative of a screening hit compound 1.
Synthesized compound 13b exhibited strong in vivo
inhibitory effect on tumor growth.
References and notes
1. Gibbs, J. B. Science 2000, 287, 1969.
2. (a) Hayakawa, I.; Shioya, R.; Agatsuma, T.; Furukawa, H.;
Naruto, S.; Sugano, Y. Bioorg. Med. Chem. Lett. 2004, 14,
455; (b) Hayakawa, I.; Shioya, R.; Agatsuma, T.; Furuk-
awa, H.; Sugano, Y. Bioorg. Med. Chem. Lett. 2004, 14,
3411; (c) Hayakawa, I.; Shioya, R.; Agatsuma, T.; Furuk-
awa, H.; Naruto, S.; Sugano, Y. Bioorg. Med. Chem. Lett.
2004, 14, 4383; (d) Hayakawa, I.; Shioya, R.; Agatsuma, T.;
Sugano, Y. Chem. Pharm. Bull. 2005, 53, 638.
1
15. Compound 14b: off-white solid, mp 335–338 °C (dec.); H
NMR (270 MHz, DMSO-d6, d): 12.0 (br s, 1H), 10.9 (s,
1H), 8.39 (d, 1H, J = 1.9 Hz), 7.66 (d, 1H, J = 8.6 Hz),
7.54–7.61 (m, 3H), 7.50 (dd, 1H, J = 9.5, 6.5 Hz), 4.25 (q,
2H, J = 7.0 Hz), 1.29 (t, 3H, J = 7.0 Hz); MS (APCI, m/z)
410, 412 [M+1]+; HRMS (EI) Calcd for C17H13Cl2N3O3S
[M]+, 409.0055. Found: 409.0056.