Antitumor agents. 196. Substituted 2-thienyl-1,8-naphthyridin-4-ones: Their synthesis, cytotoxicity, and inhibition of tubulin polymerization

Article abstract of DOI:10.1021/jm990208z

As part of our continuing search for potential anticancer drug candidates in the 2-aryl-1,8-naphthyridin-4-one series, we have synthesized a series of substituted 2-thienyl-1,8-naphthyridin-4-ones. Most compounds showed significant cytotoxic effects (log GI₅₀ < -4.0; log molar drug concentration required to cause 50% growth inhibition) against a variety of human tumor cell lines in the National Cancer Institute's in vitro screen, including cells derived from solid tumors such as non-small-cell lung, colon, central nervous system, melanoma, ovarian, prostate, and breast cancers. The most active compounds (31-33, 40) demonstrated strong cytotoxic effects with ED₅₀ values in the micromolar or submicromolar range in most of the tumor cell lines. The most cytotoxic compounds inhibited tubulin polymerization at concentrations substoichiometric to the tubulin concentration. The most potent inhibitors of polymerization (40, 42, 43) had effects comparable to those of the potent antimitotic natural products podophyllotoxin and combretastatin A-4 and to that of NSC 664171, a particularly potent, structurally related analogue. Only compound 40 was a potent inhibitor of the binding of radiolabeled colchicine to tubulin, and it was both the most cytotoxic agent and the most effective inhibitor of polymerization among the newly synthesized compounds.

Full text of DOI:10.1021/jm990208z

J . Med. Chem. 1999, 42, 4081-4087
4081
An titu m or Agen ts. 196.† Su bstitu ted 2-Th ien yl-1,8-n a p h th yr id in -4-on es: Th eir
Syn th esis, Cytotoxicity, a n d In h ibition of Tu bu lin P olym er iza tion 1
Shun-Xiang Zhang,§ Kenneth F. Bastow,§ Yoko Tachibana,§ Sheng-Chu Kuo,∇ Ernest Hamel,‡ Anthony Mauger,
Ven L. Narayanan, and Kuo-Hsiung Lee*,§
Natural Products Laboratory, Division of Medicinal Chemistry and Natural Products, School of Pharmacy, University of North
Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, Graduate Institute of Pharmaceutical Chemistry, China Medical
College, Taichung 400, Taiwan, Republic of China, Laboratory of Drug Discovery Research and Development, Developmental
Therapeutics Program, Division of Cancer Treatment and Diagnosis, National Cancer Institute, Frederick Cancer Research
Center, Frederick, Maryland 21702, and Drug Synthesis and Chemistry Branch, Developmental Therapeutics Program,
Division of Cancer Treatment and Diagnosis, National Cancer Institute, National Institutes of Health,
Bethesda, Maryland 20892
Received April 26, 1999
As part of our continuing search for potential anticancer drug candidates in the 2-aryl-1,8-
naphthyridin-4-one series, we have synthesized a series of substituted 2-thienyl-1,8-naphthy-
ridin-4-ones. Most compounds showed significant cytotoxic effects (log GI50 < -4.0; log molar
drug concentration required to cause 50% growth inhibition) against a variety of human tumor
cell lines in the National Cancer Institute’s in vitro screen, including cells derived from solid
tumors such as non-small-cell lung, colon, central nervous system, melanoma, ovarian, prostate,
and breast cancers. The most active compounds (31-33, 40) demonstrated strong cytotoxic
effects with ED50 values in the micromolar or submicromolar range in most of the tumor cell
lines. The most cytotoxic compounds inhibited tubulin polymerization at concentrations
substoichiometric to the tubulin concentration. The most potent inhibitors of polymerization
(40, 42, 43) had effects comparable to those of the potent antimitotic natural products
podophyllotoxin and combretastatin A-4 and to that of NSC 664171, a particularly potent,
structurally related analogue. Only compound 40 was a potent inhibitor of the binding of
radiolabeled colchicine to tubulin, and it was both the most cytotoxic agent and the most effective
inhibitor of polymerization among the newly synthesized compounds.
In tr od u ction
of tubulin. In general, compounds binding to the colchi-
cine domain are structurally much simpler than those
binding to vinca or taxoid domains and include many
natural products, such as cornigerine,7 podophyllotoxin,8
steganacin,9 combretastatin A-4,10,11 and some fla-
vonones12 (Figure 1). These compounds share “homol-
ogy” with the A and C rings of colchicine, and this
common feature has been described as a “biaryl” system
connected by a hydrocarbon bridge of variable length.13,14
The simplicity of these molecules provides for the
discovery or rational design of mitotic inhibitors as
antitumor agents.
Microtubules are cylindrical organelles found in al-
most all cell types in eukaryotes. They are involved in
many cellular processes, including mitosis, cell signal-
ing, and motility,2 and consequently are an important
target for development of compounds potentially useful
as anticancer chemotherapeutics. Microtubule dynamics
play an important role in cell proliferation, and inhibi-
tion of microtubule dynamics now appears to be the
mechanistic basis underlying the antitumor effects of
most antimitotic compounds. Numerous chemically
diverse antimitotic agents, many of which are derived
from natural products, have been found to interact
specifically with tubulin rather than with other com-
ponents of microtubules or other proteins involved in
mitosis.3 Examples of clinically used antimitotic agents
are the vinca alkaloids,4 which inhibit microtubule
polymerization, and the taxoids,5 which promote micro-
tubule assembly. Colchicine is another important anti-
mitotic agent, and it plays a limited role in the therapy
of selected inflammatory diseases. Colchicine has also
been of major importance in studying the functions of
microtubules.6 Taxoids, vinca alkaloids, and colchicino-
ids appear to bind to three different binding domains
In our continuing search for potent and selective
cytotoxic antitumor agents, we synthesized two series
of substituted heterocyclic ketones, 2-phenyl-4-quino-
lones15-17 and 2-phenyl-1,8-naphthyridin-4-ones,18,19 and
discovered potent antimitotic agents in each series.
Structure-activity relationship (SAR) studies of the
phenylquinolone and arylnaphthyridinone classes led
to the discovery of the particularly potent compounds
NSC 664171 and NSC 679036, respectively. These
agents inhibited the growth of the NCI tumor cell lines
at nanomolar concentrations (log GI50 < -8.0). Both
compounds acted as inhibitors of tubulin polymerization
and colchicine binding to tubulin, and their potencies
were comparable to those of natural products, such as
combretastatin A-4 and 5,3′-dihydroxy-3,6,7,8,4′-pen-
tamethoxyflavone. We have now extended this study to
the synthesis and cytotoxic evaluation of a related series
† For Part 195, see ref 1.
* To whom correspondence should be addressed.
§ University of North Carolina at Chapel Hill.
∇ China Medical College.
‡ Laboratory of Drug Discovery Research and Development, NCI.
Drug Synthesis and Chemistry Branch, NCI.
10.1021/jm990208z CCC: $18.00 © 1999 American Chemical Society
Published on Web 09/14/1999

4082 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 20
Zhang et al.
F igu r e 1. Structures of vinblastine, taxol, colchicine, cornigerine, podophyllotoxin, steganacin, combrestatin A-4, flavonol,
quinolones, and naphthyridinone derivatives.
containing a thienyl ring: substituted 2-thienyl-1,8-
naphthyridin-4-ones.
Resu lts a n d Discu ssion
a . Eva lu a tion of Cytotoxicity of 2-Th ien yln a p h -
th yr id in -4-on es. In preliminary testing of 7-methyl-
2-heterocyclic-1,8-naphthyridin-4-ones against seven
human tumor cell lines (Table 1), several compounds
were active at micromolar concentrations, in particular
compounds with a thienyl substituent. Therefore, a
series of substituted thienyl compounds were synthe-
sized and submitted to the NCI for in vitro testing
against human tumor cell lines derived from multiple
tumor types. All submitted compounds were active
against these cell lines (Table 2) with average log GI50
(M) values ranging from -4.3 (38) to -7.8 (40) (GI50 is
the molar concentration causing 50% cell growth inhibi-
tion). Table 2 also presents log GI50 values for selected
cell lines. Among compounds tested, 40 showed the
strongest inhibitory effects against a variety of tumor
cell lines, with values in the low micromolar to nano-
molar concentration range. Notably, 40 showed highly
selective effects on several cell lines from the leukemia,
colon, and breast cancer panels.
Ch em istr y
The syntheses of substituted 2-heterocyclic-1,8-naph-
thyridin-4-ones are outlined in Scheme 1. Substituted
2-aminopyridines 1 were condensed with substituted
ethyl thiophenecarbonylacetates 2 in the presence of
polyphosphoric acid (PPA) to form the corresponding
pyridopyrimidinones (8-19 and 21-25). These kineti-
cally favored products were then thermally converted
at 350 °C in mineral oil to the target compounds 26-
43.20-22 The starting substituted ethyl thiophenecarbo-
nylacetates 2 were prepared according to a literature
method: condensation of substituted acetylthiophene 4
with diethyl carbonate (3) in the presence of sodium
hydride.23 Compound 38 could be synthesized by the
same method, but dimethyl R-benzo[b]thiophene-2-
carbonylmalonate (7) was substituted for the ethyl
thiophenecarbonylacetates. Compound 7 was prepared
by condensation of R-benzo[b]thiophene-2-carbonyl chlo-
ride (6) with dimethyl malonate in the presence of
sodium hydride.24

Substituted 2-Thienyl-1,8-naphthyridin-4-ones
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 20 4083
Ta ble 1. In Vitro Cytotoxic Activities of Substituted 2-Thienyl-1,8-naphthyridin-4-ones
a
ED50 (µM)
compd
KBb
3
>10
A-549
4.6
>10
>6.3
>6.3
1.3
2.5
>3.1
0.20
HCT-8
CAKI-1
MCF-7
SKMEL-2
KB-Vinr
26
27
28
29
30
31
36
41
42
43
2.1
>10
NDc
>3.1
0.9
5.0
>10
1.2
>20
>1.6
>3.1
1.1
>10
>10
NDc
NDc
>2.5
NDc
>10
NDc
0.135
NDc
2.5
NDc
9.5
6.3
6.3
1.1
1.3
NDc
NDc
1.25
>5
NDc
1.1
1.0
1.1
1.9
0.8
>0.8
NDc
0.057
NDc
NDc
>0.25
0.134
>0.5
>0.8
0.25
0.125
0.50
0.5
0.04
0.027
0.12
NDc
NDc
NDc
0.056
0.30
a
Cytotoxicity as ED50 for each cell line, the concentration of compound that caused a 50% reduction in adsorbance at 562 nm relative
b
to untreated cells using SRB assay. KB, human epidermoid carcinoma of the nasopharynx; A-549, human lung carcinoma; HCT-8, human
ileocecal carcinoma; CAKI-1, human renal cancer; MCF-7, human breast cancer; SKMEL-2, human melanoma cancer. c ND, not determined.
Ta ble 2. Inhibition of in Vitro Tumor Cell Growth by Substituted 2-Thienyl-1,8-naphthyridin-4-onesa
cytotoxicity (log GI50) (M)b
compd
HL-60(TB)c
NCI-H23
SW-620
U251
SK-MEL-5
OVCAR-3
RXF-393
PC-3
MDA-MB-435
MDA-N
28
29
31
32
33
34
35
37
38
39
40
-5.57
-5.66
ntd
-5.36
-5.73
nt
-5.53
-6.00
-5.38
-7.32
-6.84
-5.85
nt
-5.00
>-4.00
-4.70
<-8.00
-4.77
-5.41
-5.04
-6.49
-6.33
-5.46
-5.92
nt
-5.22
-5.59
-5.69
-6.69
-6.75
-6.18
-6.42
-5.47
>-4.00
-4.83
<-8.00
-4.51
-5.29
-5.42
-6.59
-6.18
-5.55
-5.69
-4.67
>-4.00
-4.71
<-8.00
-4.95
-5.49
-5.35
-6.71
-6.20
-5.72
-5.69
-4.44
-4.29
-4.77
<-8.00
-5.03
-5.51
-5.27
-6.69
-6.61
-5.65
-5.80
nt
-5.70
-6.31
-6.49
-7.63
-6.97
-6.43
-6.42
-5.45
>-4.00
-5.32
<-8.00
-5.73
-6.44
-6.17
-7.64
-7.11
-6.20
-6.73
-5.41
>4.00
-4.77
<-8.00
-7.11
-6.76
-5.81
-6.69
-5.26
>-4.00
-4.73
<-8.00
-6.86
-6.84
-5.91
-6.00
-5.22
>-4.00
-4.71
-7.66
>-4.00
-4.41
nt
>-4.00
-4.48
nt
a
b
Data obtained from NCI’s in vitro disease-oriented human tumor cells screen (see refs 29 and 30 for details). Log concentrations
which reduced cell growth to 50% of level obtained in untested controls. c HL-60(TB), leukemia cell line; NCI-H23, non-small-cell lung
cancer cell line; SW-620, colon cancer cell line; U251, CNS cancer cell line; SK-MEL-5, melanoma cell line; OVCAR-3, ovarian cancer cell
d
line; RXF-393, renal cancer cell line; PC-3, prostate cancer cell line; MDA-MB-435, MDA-N, breast cancer cell lines. nt, Not tested.
Sch em e 1. General Synthetic Routes to 2-Thienyl-
observed between the 2-(â-benzo[b]thienyl) (40) and the
2-(R-benzo[b]thienyl) (38, 39) substituted compounds.
For 40, low nanomolar GI50 values (log < -8.00) were
observed in many cell lines. In contrast, marginal or no
activity was obtained with 38 and 39. Nevertheless,
several less active compounds showed moderate cyto-
toxicity against two breast cancer cell lines, MDA-MB-
435 and MDA-N.
1,8-naphthyridinesa
b. In ter a ction s of 2-Th ien yl-1,8-n a p h th yr id in -4-
on es w ith Tu bu lin . In our previous studies, we
demonstrated that potent cytotoxic 2-phenyl-1,8-naph-
thyridin-4-ones strongly interacted with tubulin at the
colchicine site.18,19 They inhibited the polymerization of
12 µM tubulin by 50% at concentrations below 1.0 µM,
as did colchicine, combretastatin A-4, podophyllotoxin,
and NSC 664171. In addition, they had moderate
activity as inhibitors of the binding of [3H]colchicine to
tubulin, in contrast to the more potent inhibitory effects
of combretastatin A-4, podophyllotoxin, and NSC 664171
on colchicine binding. Structurally, 2-thienyl-1,8-naph-
thyridin-4-ones can be considered isosteres of 2-phenyl-
1,8-naphthyridin-4-ones, and thus, 2-thienyl-1,8-naph-
thyridin-4-ones could be predicted to have similar
biological activity to 2-phenyl-1,8-naphthyridin-4-ones.
COMPARE computations25 were performed on the NCI
screening data for the most active compound 40 and
showed that this compound is an antimitotic agent, with
Pearson correlation coefficients above 0.6 at all three
levels against antimitotic agents in the NCI “Standard
Agent” database. This postulate was confirmed when
the series of substituted 2-thienyl-1,8-naphthyridin-4-
ones were evaluated for their relative potencies as
a
For a specific R group, see Table 3.
In terms of average cytotoxicity, compounds without
a methyl group in the C ring were substantially less
active than those with a methyl group. Compounds with
a methyl at the 5′-position (30, 32) were more active
than those substituted at the 3′-position (31, 33) or at
both the 2′- and 5′-positions (34). 5′-Chloro substitution
(35) did not increase activity compared to 5′-methyl
substitution. Compound 37 has a 5′-phenyl in place of
the methyl group in 34 but was less active. Among the
tested compounds with a 2-(R-thienyl) or 2-(â-thienyl)
substituent, only minor differences in cytotoxicity were
obtained. However, a fairly dramatic difference was

4084 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 20
Ta ble 3. Antitubulin Effects of Compounds 26-43
Zhang et al.
average
log GI50
ITPb
IC50 (µM) ( SD
ICBc
(% inhibit)
compd
R2
R5
R6
R7
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
3′-pyridyl
2′-furyl
2′-thienyl
3′-thienyl
2′-(5′-methylthienyl)
2′-(3′-methylthienyl)
2′-(5′-methylthienyl)
2′-(3′-methylthienyl)
3′-(2′,5′-dimethylthienyl)
2′-(5′-chlorothienyl)
2′-(5′-bromothienyl)
2′-(3′-methyl-5′-phenylthienyl)
2′-benzo[b]thienyl
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
CH3
H
H
H
H
H
CH3
CH3
H
H
H
H
H
H
H
H
H
H
CH3
H
CH3
CH3
CH3
CH3
H
not testede
not testede
-4.83
7.7 ( 2
14 ( 2
6.0 ( 1
-5.40
7.0 ( 2
not testede
-5.13
2.7 ( 0.4
3.8 ( 0.7
1.7 ( 0.01
2.8 ( 0.2
4.8 ( 0.7
1.7 ( 0.2
1.5 ( 0.2
14 ( 3
H
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
H
-6.39
-6.26
-5.43
-5.81
not testede
-4.79
19 ( 2
-4.25
>40
13 ( 2
2′-(3′-methylbenzo[b]thienyl)
3′-benzo[b]thienyl
3′-benzo[b]thienyl
3′-benzo[b]thienyl
3′-benzo[b]thienyl
-4.7
-7.78
0.37 ( 0.04
1.2 ( 0.2
0.91 ( 0.04
0.78 ( 0.1
0.59 ( 0.04
0.66 ( 0.1
0.49 ( 0.07
0.72 ( 0.08
65 ( 1
22 ( 5
not testede
not testede
not testede
H
CH3
26 ( 0.9
26 ( 4
CH3
podophyllotoxin
combretastatin A-4
NSC 664171
84 ( 0.6
98 ( 1
94 ( 0.5
33 ( 2
NSC 679036d
a
b
Data obtained from NCI’s 49-human tumor cell line in vitro screen and calculated from all cell lines tested. ITP, inhibition of tubulin
polymerization. c ICB, inhibition of colchicine binding; evaluated only when polymerization IC50 e 1.0 µM; the concentration of both
[3H]colchicine and inhibitors was 5 µM. Data from ref 19. e Cytotoxic data, see Table 1.
d
inhibitors of tubulin assembly. The results obtained are
summarized in Table 3, together with those for the
potent antimitotic natural products podophyllotoxin and
combretastatin A-4 and the highly potent NSC 664171.
Excellent correlation was found between cytotoxicity
and inhibition of tubulin polymerization. The least
cytotoxic compounds (37-39) had minimal inhibitory
effects on tubulin polymerization. Conversely, all cyto-
toxic compounds were substoichiometric inhibitors of
tubulin polymerization, and the highly cytotoxic com-
pounds (40-43) were also the most potent inhibitors of
tubulin polymerization, with IC50 values of 0.37-1.2 µM.
F igu r e 2. Stereoview of compounds 38 (orange) and 40 (cyan).
Compound 40 was as good an inhibitor of assembly as
podophyllotoxin, combretastatin A-4, and NSC 664171,
but it was somewhat less effective as an inhibitor of the
binding of [3H]colchicine to tubulin. Further, although
previously examined 2-phenyl-1,8-naphthyridin-4-ones18,19
were not reexamined in the current studies, compound
40 appears to interact more strongly with tubulin than
did these earlier compounds.
Considering structure-activity aspects based solely
on inhibition of tubulin polymerization, the 5′-chloro,
5′-bromo, and 5′-methyl substituents (30, 32, 33, 35, 36)
appeared to be essentially equivalent (IC50 values, 1.5-
2.8 µM), and derivatives with methyl groups at different
positions in the A ring had nearly comparable activity
(cf. 30 with 32; 31 with 33; 40-43). Adding a phenyl
group (37) greatly reduced activity (cf. 37 with 33).
Although the 2-(R-thienyl) and 2-(â-thienyl) derivatives
(28, 29) had comparable activity, the 2-(â-benzo[b]-
thienyl) (40) and 2-(R-benzo[b]thienyl) (38) compounds
had totally different behavior. The former was the most
active compound in the new series (IC50 ) 0.37 µM),
while the latter was nearly inert (IC50 > 40 µM). The
conformations of both compounds were studied care-
fully, and our findings may explain the different effects
of these compounds on tubulin polymerization. The
lowest-energy conformation of compound 40 is similar
to (aR,7S)-colchicine31 (the active enantiomer), but that
of compound 38 more closely resembles (aS,7R)-colchi-
cine31 (the inactive enantiomer) (Figure 2). With colchi-
cinoids and allocolchicinoids, the conformation of the
biaryl system is important in the drug-tubulin interac-
tion.6,26,27 Thus, in the 2-thienyl-1,8-naphthyridin-4-one
class, the relationship between conformations in the
biaryl system and tubulin binding warrants further
investigation.
Exp er im en ta l Section
A. Ch em istr y. a . Gen er a l Exp er im en ta l P r oced u r es.
Melting points were determined on a Fisher-J ohns melting
point apparatus and are uncorrected. Elemental analyses were
performed by Atlantic Microlabs, Atlanta, GA. 1H NMR spectra
were measured on a Bruker AC-300 spectrometer with TMS
as internal standard. Chemical shifts are reported in δ (ppm).
Mass spectra (MS) were obtained on a TRIO 1000 mass
spectrometer. Flash column chromatography was performed
on silica gel (mesh 25-150 µm) using a mixture of CH2Cl2 and
EtOAc as eluant. Precoated silica gel plates (Kieselgel 60 F254
0.25 mm; Merck) were used for TLC analysis.

Substituted 2-Thienyl-1,8-naphthyridin-4-ones
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 20 4085
b. P r epar ation of Su bstitu ted Eth yl Th ioph en ecar bon -
yla ceta tes. The substituted ethyl thiophenecarbonylacetates
2 were prepared according to procedures described by Krapcho
et al.23 To a vigorously stirred suspension of NaH and CO-
(OEt)2 (3) in toluene was added dropwise a solution of
substituted acetylthiophene 4 in toluene under reflux. The
mixture was allowed to reflux and stirred for 20 min after the
addition was completed. When cooled to room temperature,
the mixture was acidified with glacial HOAc. After ice-cold
water was added, the mixture was extracted with toluene.
Workup and distillation gave the corresponding substituted
ethyl thiophenecarbonylacetates.
c. P r oced u r es for Meth od A.20-22 A mixture of substituted
2-aminopyridine 1, substituted ethyl thiophenecarbonylacetate
2, and PPA was heated at 100-125 °C with stirring. The
reaction was monitored by TLC. After the reaction was
completed, the mixture was cooled to room temperature and
neutralized with 4 M NaOH. After extraction with CH2Cl2, the
2-(5′-Met h yl-2′-t h ien yl)-6-m et h ylp yr id o[1,2-a ]p yr im i-
d in -4-on e (14): obtained from ethyl 5-methylthiophene-2-
carbonylacetate and 2-amino-6-picoline with yield 41%; prisms,
1
mp 181-182 °C; H NMR (CDCl3) δ 7.51 (d, J ) 3.5 Hz, 1 H,
H-3′), 7.40 (m, 2 H, H-7,9), 6.81 (d, J ) 3.5 Hz, 1 H, H-4′),
6.61 (m, 1 H, H-8), 6.53 (s, 1 H, H-3), 3.06 (s, 3 H, CH3-5′),
2.55 (s, 3 H, CH3-6); MS m/z 256 (M+).
2-(3′-Met h yl-2′-t h ien yl)-6-m et h ylp yr id o[1,2-a ]p yr im i-
d in -4-on e (15): obtained from ethyl 3-methylthiophene-2-
carbonylacetate and 2-amino-6-picoline with yield 46%; needles,
1
mp 113-114 °C; H NMR (CDCl3) δ 7.40 (m, 3 H, H-5′,7,9),
6.95 (d, J ) 3.5 Hz, 1 H, H-4′), 6.62 (t, J ) 4.0 Hz, 1 H, H-8),
6.55 (s, 1 H, H-3), 3.06 (s, 3 H, CH3-3′), 2.57 (s, 3 H, CH3-6);
MS m/z 256 (M+).
2-(2′,5′-Dim eth yl-3′-th ien yl)-6-m eth ylp yr id o[1,2-a ]p y-
r im id in -4-on e (16): obtained from ethyl 2,5-dimethyl-
thiophene-3-carbonylacetate and 2-amino-6-picoline with yield
1
26%; cubic, mp 106-107 °C; H NMR (CDCl3) δ 7.42 (d, J )
4.5 Hz, 2 H, H-7,9), 7.04 (s, 1 H, H-4′), 6.63 (t, J ) 4.5 Hz, 1
H, H-8), 6.41 (s, 1 H, H-3), 3.07 (s, 3 H, H-2′), 2.68 (s, 3 H,
CH3-5′), 2.44 (s, 3 H, CH3-6); MS m/z 270 (M+).
2-(5′-Ch lor o-2′-th ien yl)-6-m eth ylpyr ido[1,2-a ]pyr im idin -
4-on e (17): obtained from ethyl 5-chlorothiophene-2-carbo-
nylacetate and 2-amino-6-picoline with yield 24%; prisms, mp
169-170 °C; 1H NMR (CDCl3) δ 7.70 (d, J ) 3.5 Hz, 1 H, H-5′),
7.52 (d, J ) 5.0 Hz, 1 H, H-9), 7.44 (m, 2 H, H-3′,7), 7.15 (m,
1 H, H-4′), 6.64 (m, 1 H, H-8), 6.62 (s, 1 H, H-3), 3.07 (s, 3 H,
CH3-6); MS m/z 276 (M+).
extract was passed through
a silica gel column to give
2-thienylpyrido[1,2-a]pyrimidin-4-one (8-19, 21-25). This
compound was then added to mineral oil at 300-350 °C with
stirring. The oil was maintained at 350 °C for 2 h after the
addition was completed. The cooled mixture was subjected to
silica gel column chromatography. Elution with CH2Cl2-EtOAc
gave the corresponding 2-thienyl-1,8-naphthyridin-4-one (26-
43).
d . P r oced u r es for Meth od B. This procedure is the same
as method A but replaces ethyl thiophenecarbonylacetate with
dimethyl benzo[b]thiophene-2-carbonylmalonate (7), which
was prepared by condensation of benzo[b]thiophene-2-carbonyl
chloride (6) with dimethyl malonate in the presence of sodium
hydride to form the corresponding dimethyl benzo[b]thiophene-
2-carbonylmalonate (7).24
2-(3′-P yr id in yl)-6-m e t h ylp yr id o[1,2-a ]p yr im id in -4-
on e (8): obtained from ethyl 3′-pyridinylacetate and 2-amino-
6-picoline with yield 25%; needles, mp 159-160 °C; H NMR
(CDCl3) δ 9.26 (s, 1 H, H-2′), 8.70 (d, J ) 4.0 Hz, 1 H, H-9),
8.34 (d, J ) 8.0 Hz, 1 H, H-6′), 7.45 (m, 3 H, H-7,8,5′), 6.69
(m, 2 H, H-3,4′), 3.09 (s, 3 H, CH3-6); MS m/z 237 (M+).
2-(2′-F u r yl)-6-m eth ylp yr id o[1,2-a ]p yr im id in -4-on e (9):
obtained from ethyl 2′-furylacetate and 2-amino-6-picoline with
2-(5′-Br om o-2′-th ien yl)-6-m eth ylpyr ido[1,2-a ]pyr im idin -
4-on e (18): obtained from ethyl 5-bromothiophene-2-carbo-
nylacetate and 2-amino-6-picoline with yield 27%; prisms, mp
1
163-164 °C; H NMR (CDCl3) δ 7.44 (m, 3 H, H-4′,8,9), 7.11
(d, J ) 4.0 Hz, 1 H, H-3′), 6.65 (d, J ) 6.0 Hz, H-7), 6.52 (s, 1
H, H-3), 3.07 (s, 3 H, CH3-6); MS m/z 321 (M+).
2-(2′-Meth yl-5′-p h en yl-3′-th ien yl)-6-m eth ylp yr id o[1,2-
a ]p yr im id in -4-on e (19): obtained from ethyl 2-methyl-5-
phenylthiophene-3-carbonylacetate and 2-amino-6-picoline with
1
1
yield 28%; prisms, mp 119-120 °C; H NMR (CDCl3) δ 7.61
(m, 3 H, H-2′′,6′′,9), 7.46 (m, 2 H, H-3′′,5′′), 7.40 (m, 2 H,
H-4′′,7), 7.29 (s, 1 H, H-4′), 6.67 (m, 1 H, H-8), 6.50 (s, 1 H,
H-3), 3.10 (s, 3 H, CH3-2′), 2.78 (s, 3 H, CH3-6); MS m/z 332
(M+).
1
yield 31%; needles, mp 179-180 °C; H NMR (CDCl3) δ 7.60
2-(r-Ben zo[b]th ien yl)-6-m eth ylp yr id o[1,2-a ]p yr im id in -
4-on e (20): obtained from dimethyl benzo[b]thiophene-2-
carbonylmalonate and 2-amino-6-picoline with yield 31%;
prisms, mp 168-170 °C; 1H NMR (CDCl3) δ 7.99 (s, 1 H, H-3′),
7.90 (m, 2 H, H-9,7′), 7.48 (m, 2 H, H-4′,7′), 7.40 (m, 2 H,
H-5′,6′), 6.74 (s, 1 H, H-3), 6.67 (m, 1 H, H-8), 3.09 (s, 3 H,
CH3-6); MS m/z 292 (M+).
(s, 1 H, H-5′), 7.42 (d, J ) 4.0 Hz, 2 H, H-9,7), 7.17 (d, J ) 3.5
Hz, 1 H, H-3′), 7.15 (m, 1 H, H-4′), 6.62 (m, 1 H, H-8), 6.56 (s,
1 H, H-3), 3.06 (s, 3 H, CH3-6); MS m/z 226 (M+).
2-(2′-Th ien yl)-6-m et h ylp yr id o[1,2-a ]p yr im id in -4-on e
(10): obtained from ethyl thiophene-2-carbonylacetate and
2-amino-6-picoline with yield 25%; needles, mp 148-149 °C;
1H NMR (CDCl3) δ 7.70 (d, J ) 3.5 Hz, 1 H, H-5′), 7.52 (d, J
) 5.0 Hz, 1 H, H-9), 7.44 (m, 2 H, H-3′,7), 7.15 (m, 1 H, H-4′),
6.64 (m, 1 H, H-8), 6.62 (s, 1 H, H-3), 3.07 (s, 3 H, CH3-6); MS
m/z 242 (M+).
2-(3′-Meth yl-2′-Ben zo[b]th ien yl)-6-m eth ylp yr id o[1,2-a ]-
p yr im id in -4-on e (21): obtained from dimethyl 3-methylben-
zo[b]thiophene-2-carbonylmalonate and 2-amino-6-picoline with
1
yield 26%; prisms, mp 176-177 °C; H NMR (CDCl3) δ 7.85
2-(3′-Th ien yl)-6-m et h ylp yr id o[1,2-a ]p yr im id in -4-on e
(11): obtained from ethyl thiophene-2-carbonylacetate and
2-amino-6-picoline with yield 32%; needles, mp 133-134 °C;
1H NMR (CDCl3) δ 8.10 (dd, J ) 1.5, 3.0 Hz, 1 H, H-9), 7.62
(dd, J ) 1.5, 4.5 Hz, 1 H, H-5′), 7.45 (s, 1 H, H-2′), 7.41 (m, 2
H, H-4′,7), 6.64 (t, J ) 4.5 Hz 1 H, H-8), 6.60 (s, 1 H, H-3),
3.08 (s, 3 H, CH3-6); MS m/z 242 (M+).
2-(5′-Met h yl-2′-t h ien yl)-7-m et h ylp yr id o[1,2-a ]p yr im i-
d in -4-on e (12): obtained from ethyl 5-methylthiophene-2-
carbonylacetate and 2-amino-5-picoline with yield 28%; prisms,
mp 187-188 °C; 1H NMR (CDCl3) δ 8.85 (s, 1 H, H-6), 7.59 (d,
J ) 1.5 Hz, 2 H, H-8,9), 7.55 (d, J ) 3.5 Hz, 1 H, H-4′), 6.84
(d, J ) 3.5 Hz, 1 H, H-3′), 6.72 (s, 1 H, H-3), 2.56 (s, 3 H, CH3-
7), 2.43 (s, 3 H, CH3-5′); MS m/z 256 (M+).
(m, 2 H, H-9,7′), 7.43 (m, 4 H, H-7,4′,5′,6′), 6.68 (m, 2 H, H-3.8),
3.10 (s, 3 H, CH3-3′), 2.76 (s, 3 H, CH3-6); MS m/z 306 (M+).
2-(â-Ben zo[b]th ien yl)-5-m eth ylp yr id o[1,2-a ]p yr im id in -
4-on e (22): obtained from methyl benzo[b]thiophene-3-car-
bonylacetate and 2-amino-6-picoline with yield 48%; prisms,
1
mp 152-153 °C; H NMR (CDCl3) δ 8.55 (d, J ) 8.0 Hz, 1 H,
H-9), 8.06 (s, 1 H, H-2′), 7.92 (d, J ) 8.0 Hz, 1 H, H-7), 7.46
(m, 4 H, H-4′,5′,6′,7′), 6.71 (m, 2 H, H-3,8), 3.13 (s, 3 H, CH3-
5); MS m/z 292 (M+).
2-(â-Ben zo[b]th ien yl)-7-m eth ylp yr id o[1,2-a ]p yr im id in -
4-on e (23): obtained from methyl benzo[b]thiophene-3-car-
bonylacetate and 2-amino-4-picoline with yield 27%; prisms,
1
mp 178-180 °C; H NMR (CDCl3) δ 9.02 (d, J ) 7.0 Hz, 1 H,
H-5), 8.59 (d, J ) 7.0 Hz, 1 H, H-6), 8.06 (s, 1 H, H-2′), 7.93 (d,
J ) 7.5 Hz, 1 H, H-7′), 7.58 (s, 1 H, H-8), 7.49-7.43 (m, 2 H,
H-4′,5′), 7.02 (d, J ) 6.0 Hz, 1 H, H-6′), 6.83 (s, 1 H, H-3), 2.53
(s, 3 H, CH3-7); MS m/z 292 (M+).
2-(3′-Met h yl-2′-t h ien yl)-7-m et h ylp yr id o[1,2-a ]p yr im i-
d in -4-on e (13): obtained from ethyl 3-methylthiophene-2-
carbonylacetate and 2-amino-5-picoline with yield 25%; prisms,
1
mp 145-146 °C; H NMR (CDCl3) δ 8.86 (s, 1 H, H-6), 7.61
2-(â-Ben zo[b]th ien yl)-6-m eth ylp yr id o[1,2-a ]p yr im id in -
4-on e (24): obtained from methyl benzo[b]thiophene-3-car-
bonylacetate and 2-amino-5-picoline with yield 71%; prisms,
mp 155-157 °C; 1H NMR (CDCl3) δ 8.95 (s, 1 H, H-5), 8.59 (d,
(br s, 2 H, H-8,9), 7.41 (d, J ) 5.0 Hz, 1 H, H-5′), 6.97 (d, J )
5.0 Hz, 1 H, H-4′), 6.75 (s, 1 H, H-3), 2.60 (s, 3 H, CH3-7), 2.44
(s, 3 H, CH3-3′); MS m/z 256 (M+).

4086 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 20
Zhang et al.
J ) 7.5 Hz, 1 H, H-8), 8.07 (s, 1 H, H-2′), 7.93 (d, J ) 8.0 Hz,
1 H, H-7), 7.75-7.65 (m, 2 H, H-4′,7′), 7.52-7.41 (m, 2 H, H-5′,
6′), 6.89 (s, 1 H, H-3), 2.48 (s, 3 H, CH3-6); MS m/z 292 (M+).
2-(â-Ben zo[b]t h ien yl)-6,8-d im et h ylp yr id o[1,2-a ]p yr i-
m id in -4-on e (25): obtained from methyl benzo[b]thiophene-
3-carbonylacetate and 2-amino-4,6-dimethylpyridine with yield
30%; prisms, mp 170-172 °C; 1H NMR (CDCl3) δ 8.55 (d, J )
1.5 Hz, 1 H, H-5), 8.02 (s, 1 H, H-2′), 7.91 (d, J ) 1.5 Hz, 1 H,
H-7), 7.47-7.32 (m, 3 H, H-5′,6′,7′), 6.63 (s, 1 H, H-4′), 6.54 (s,
1 H, H-3), 3.08 (s, 3 H, H-8), 2.37 (s, 3 H, CH3-6); MS m/z 306
(M+).
7-Meth yl-2-(3′-th ien yl)-1,8-n a p h th yr id in -4-on e (26): ob-
tained from compound 8 with yield 54%; prisms, mp 263-264
°C; 1H NMR (CDCl3 + MeOD-d4) δ 8.96 (s, 1 H, H-2′), 8.73 (d,
J ) 4.5 Hz, 1 H, H-6′), 8.54 (7.90, d, J ) 8.0 Hz, 1 H, H-5),
8.06 (d, J ) 8.0 Hz, 1 H, H-6), 7.51 (m, 1 H, H-5′), 7.23 (d, J
) 8.0 Hz, 1 H, H-4′), 6.56 (s, 1 H, H-3), 2.65 (s, 3 H, CH3-7);
MS m/z 237 (M+). Anal. C, H, N.
8.0 Hz, 1 H, H-6), 7.03 (d, J ) 4.0 Hz, 1 H, H-3′), 6.49 (s, 1 H,
H-3), 2.64 (s, 3 H, CH3-7); MS m/z 276 (M+). Anal. C, H, N.
7-Met h yl-2-(5′-b r om o-2′-t h ien yl)-1,8-n a p h t h yr id in -4-
on e (36): obtained from compound 18 with yield 61%; prisms,
1
mp 274-275 °C; H NMR (CDCl3 + MeOD-d4) δ 8.46 (d, J )
8.0 Hz, 1 H, H-5), 7.40 (d, J ) 4.0 Hz, 1 H, H-4′), 7.18 (d, J )
8.0 Hz, 1 H, H-6), 7.13 (d, J ) 4.0 Hz, 1 H, H-3′), 6.47 (s, 1 H,
H-3), 2.63 (s, 3 H, CH3-7); MS m/z 321 (M+). Anal. C, H, N.
7-Met h yl-2-(2′-m et h yl-5′-p h en yl-3′-t h ien yl)-1,8-n a p h -
th yr id in -4-on e (37): obtained from compound 19 with yield
1
48%; prisms, mp 275-276 °C; H NMR (MeOD-d4) δ 8.47 (d,
J ) 8.0 Hz, 1 H, H-5), 7.40 (d, J ) 7.5 Hz, 2 H, H-2′′,6′′), 7.50
(s, 1 H, H-4′), 7.35 (m, 4 H, H-6,3′′,4′′,5′′), 6.39 (s, 1 H, H-3),
2.62 (s, 3 H, CH3-7), 2.66 (s, 3 H, CH3-2′); MS m/z 332 (M+).
Anal. C, H, N.
7-Met h yl-2-(2′-b en zo[b]t h ien yl)-1,8-n a p h t h yr id in -4-
on e (38): obtained from compound 20 with yield 61%; prisms,
1
mp >300 °C dec; H NMR (CDCl3) δ 8.98 (s, 1 H, H-1), 8.55
7-Meth yl-2-(2′-th ien yl)-1,8-n a p h th yr id in -4-on e (27): ob-
tained from compound 9 with yield 80%; prisms, mp 283-284
(d, J ) 8.0 Hz, 1 H, H-5), 7.90 (m, 2 H, H-4′,7′), 7.80 (s, 1 H,
H-3′), 7.47 (m, 2 H, H-5′,6′), 7.22 (d, J ) 8.0 Hz, 1 H, H-6),
6.72 (s, 1 H, H-3), 2.67 (s, 3 H, CH3-7); MS m/z 292 (M+). Anal.
C, H, N.
1
°C; H NMR (CDCl3 + MeOD-d4) δ 8.49 (d, 1 H, J ) 8.0 Hz,
H-5), 7.65 (1 H, s, H-5′), 7.19 (d, J ) 8.0 Hz, 1 H, H-6), 7.10 (d,
J ) 3.5 Hz, 1 H, H-3′), 6.62 (m, 2 H, H-3, 4′), 2.63 (s, 3 H,
CH3-7); MS m/z 226 (M+). Anal. C, H, N.
7-Meth yl-2-(3′-m eth yl-2′-ben zo[b]th ien yl)-1,8-n a p h th y-
r id in -4-on e (39): obtained from compound 21 with yield 40%;
prisms, mp 233 °C; 1H NMR (CDCl3) δ 8.90 (s, 1 H, H-1), 8.57
(d, J ) 8.0 Hz, 1 H, H-5), 7.85 (m, 2 H, H-4′,7′), 7.51 (m, 2 H,
H-5′,6′), 7.23 (d, J ) 8.0 Hz, 1 H, H-6), 6.55 (s, 1 H, H-3), 2.64
(s, 6 H, CH3-7,3′); MS m/z 306 (M+). Anal. C, H, N.
7-Met h yl-2-(3′-b en zo[b]t h ien yl)-1,8-n a p h t h yr id in -4-
on e (40): obtained from compound 22 with yield 43%; prisms,
mp 264 °C; 1H NMR (CDCl3) δ 9.18 (s, 1 H, H-1), 8.59 (d, J )
8.0 Hz, 1 H, H-5), 8.08 (m, 1 H, H-4′), 7.98 (m, 1 H, H-7′), 7.85
(s, 1 H, H-2′), 7.49 (m, 2 H, H-5′,6′), 7.22 (d, J ) 8.0 Hz, 1 H,
H-6), 6.64 (s, 1 H, H-3), 2.62 (s, 3 H, CH3-7); MS m/z 292 (M+).
Anal. C, H, N.
7-Meth yl-2-(2′-th ien yl)-1,8-n a p h th yr id in -4-on e (28): ob-
tained from compound 10 with yield 51%; prisms, mp 274-
275 °C; 1H NMR (CDCl3) δ 8.98 (s, 1 H, H-1), 8.53 (d, J ) 8.0
Hz, 1 H, H-5), 7.56 (m, 2 H, H-3′,5′), 7.21 (m, 2 H, H-6,4′),
6.63 (s, 1 H, H-3), 2.64 (s, 3 H, CH3-7); MS m/z 242 (M+). Anal.
C, H, N.
7-Meth yl-2-(3′-th ien yl)-1,8-n a p h th yr id in -4-on e (29): ob-
tained from compound 11 with yield 58%; prisms, mp 283-
1
284 °C; H NMR (CDCl3 + MeOD-d4) δ 8.51 (d, J ) 8.0 Hz, 1
H, H-5), 7.90 (s, 1 H, H-2′), 7.49 (m, 2 H, H-4′,5′), 7.19 (d, J )
8.0 Hz, 1 H, H-6), 6.61 (s, 1 H, H-3), 2.63 (s, 3 H, CH3-7); MS
m/z 242 (M+). Anal. C, H, N.
5-Met h yl-2-(3′-b en zo[b]t h ien yl)-1,8-n a p h t h yr id in -4-
on e (41): obtained from compound 23 with yield 54%; prisms,
mp 270 °C dec; 1H NMR (CDCl3) δ 9.52 (m, 1 H, H-1), 8.20 (d,
J ) 4.5 Hz, 1 H, H-7), 8.08 (m, 1 H, H-7′), 7.98 (m, 1 H, H-4′),
7.85 (s, 1 H, H-2′), 7.49 (m, 2 H, H-5′,6′), 7.02 (d, 1 H, J ) 4.5
Hz, H-6), 6.58 (s, 1 H, H-3), 3.00 (s, 3 H, CH3-5); MS m/z 292
(M+). Anal. C, H, N.
6-Met h yl-2-(5′-m et h yl-2′-t h ien yl)-1,8-n a p h t h yr id in -4-
on e (30): obtained from compound 12 with yield 56%; prisms,
mp 263-264 °C; 1H NMR (CDCl3) δ 9.13 (s, 1 H, H-1), 8.45 (s,
2 H, H-5,7), 7.38 (d, J ) 3.5 Hz, 1 H, H-4′), 6.87 (d, J ) 3.5
Hz, 1 H, H-3′), 6.56 (s, 1 H, H-3), 2.58 (s, 3 H, CH3-6), 2.46 (s,
3 H, CH3-5′); MS m/z 256 (M+). Anal. C, H, N.
6-Met h yl-2-(3′-m et h yl-2′-t h ien yl)-1,8-n a p h t h yr id in -4-
on e (31): obtained from compound 13 with yield 54%; prisms,
mp 222-223 °C; 1H NMR (CDCl3) δ 9.87 (s, 1 H, H-1), 8.48 (d,
1 H, J ) 2.0 Hz, H-5), 8.13 (d, J ) 2.0 Hz, 1 H, H-7), 7.46 (d,
J ) 5.0 Hz, 1 H, H-5′), 7.04 (d, J ) 5.0 Hz, 1 H, H-4′), 2.45 (s,
3 H, CH3-6), 2.44 (s, 3 H, CH3-3′); MS m/z 256 (M+). Anal. C,
H, N.
7-Met h yl-2-(5′-m et h yl-2′-t h ien yl)-1,8-n a p h t h yr id in -4-
on e (32): obtained from compound 14 with yield 45%; prisms,
mp 252-253 °C; 1H NMR (CDCl3) δ 8.83 (s, 1 H, H-1), 8.51 (d,
J ) 8.0 Hz, 1 H, H-5), 7.36 (d, J ) 3.5 Hz, 1 H, H-3′), 7.18 (d,
J ) 8.0 Hz, 1 H, H-6), 6.86 (d, J ) 3.5 Hz, 1 H, H-4′), 6.54 (s,
1 H, H-3), 2.63 (s, 3 H, CH3-5′), 2.57 (s, 3 H, CH3-7); MS m/z
256 (M+). Anal. C, H, N.
7-Met h yl-2-(3′-m et h yl-2′-t h ien yl)-1,8-n a p h t h yr id in -4-
on e (33): obtained from compound 15 with yield 41%; prisms,
mp 214-215 °C; 1H NMR (CDCl3) δ 9.03 (s, 1 H, H-1), 8.55 (d,
J ) 8.0 Hz, 1 H, H-5), 7.42 (d, J ) 5.0 Hz, 1 H, H-3′), 7.19 (d,
J ) 8.0 Hz, 1 H, H-6), 6.99 (d, J ) 5.0 Hz, 1 H, H-4′), 6.45 (s,
1 H, H-3), 2.58 (s, 3 H, CH3-3′), 2.45 (s, 3 H, CH3-7); MS m/z
256 (M+). Anal. C, H, N.
6-Met h yl-2-(3′-b en zo[b]t h ien yl)-1,8-n a p h t h yr id in -4-
on e (42): obtained from compound 24 with yield 38%; prisms,
1
mp 275 °C; H NMR (CDCl3 + MeOD-d4) δ 8.51 (d, J ) 1.0
Hz, 1 H, H-5), 8.44 (d, J ) 1.0 Hz, 1 H, H-7), 8.06 (m, 1 H,
H-4′), 7.95 (m, 1 H, H-7′), 7.90 (s, 1 H, H-2′), 7.48 (m, 2 H,
H-5′,6′), 6.64 (s, 1 H, H-3), 2.48 (s, 3 H, CH3-7); MS m/z 292
(M+). Anal. C, H, N.
5,7-Met h yl-2-(3′-b en zo[b]t h ien yl)-1,8-n a p h t h yr id in -4-
on e (43): obtained from compound 25 with yield 50%; prisms,
1
mp 273-275 °C; H NMR (CDCl3) δ 9.17 (m, 1 H, H-1), 8.07
(m, 1 H, H-6), 7.97 (m, 1 H, H-7′), 7.82 (s, 1 H, H-4′), 7.47 (m,
2 H, H-5′,6′), 6.91 (s, 1 H, H-2′), 6.55 (s, 1 H, H-3), 2.96 (s, 3
H, CH3-5), 2.48 (s, 3 H, CH3-7); MS m/z 306 (M+). Anal. C, H,
N.
B. Biologica l Assa ys. a . Cytotoxicity Assa ys. Com-
pounds 26-31, 36, and 41-43 were assayed for in vitro
cytotoxicity in a panel of human and murine tumor cell lines
at the School of Pharmacy, University of North Carolina at
Chapel Hill, according to procedures described previously.28
The cell lines include human epidermoid carcinoma of the
nasopharynx (KB), lung carcinoma (A-549), ileocecal carcinoma
(HCT-8), human renal cancer (CAKI-1), human breast cancer
(MCF-7), and human melanoma cancer (SKMEL-2). Com-
pounds 28, 29, 31-35, and 37-40 were submitted to NCI and
assayed in the NCI’s in vitro disease-oriented antitumor
screen, which involves determination of a test compound’s
effects on the growth of approximately 49 human tumor cell
lines.29,30 These lines include leukemia, non-small-cell lung,
colon, central nervous system (CNS), melanoma, ovarian,
renal, prostate, and breast cancers. The cytotoxic effects of each
compound were obtained as GI50 or TGI values, which repre-
7-Meth yl-2-(2′,5′-d im eth yl-3′-th ien yl)-1,8-n a p h th yr idin -
4-on e (34): obtained from compound 16 with yield 51%;
prisms, mp 253-254 °C; 1H NMR (CDCl3) δ 8.82 (s, 1 H, H-1),
8.55 (d, J ) 8.0 Hz, 1 H, H-5), 7.19 (d, J ) 8.0 Hz, 1 H, H-6),
6.79 (s, 1 H, H-4′), 6.33 (s, 1 H, H-3), 2.59 (s, 3 H, CH3-2′),
2.56 (s, 3 H, CH3-7), 2.45 (s, 3 H, CH3-5′); MS m/z 270 (M+).
Anal. C, H, N.
7-Met h yl-2-(5′-ch lor o-2′-t h ien yl)-1,8-n a p h t h yr id in -4-
on e (35): obtained from compound 17 with yield 56%; prisms,
1
mp 279-280 °C; H NMR (CDCl3 + MeOD-d4) δ 8.51 (d, J )
8.0 Hz, 1 H, H-5), 7.42 (d, J ) 4.0 Hz, 1 H, H-4′), 7.20 (d, J )

Substituted 2-Thienyl-1,8-naphthyridin-4-ones
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sent the molar drug concentrations required to cause 50%
inhibition or total growth inhibition, respectively.
b. Tu bu lin Assa ys. Electrophoretically homogeneous bo-
vine brain tubulin was purified as described in ref 10.
Combretastatin A-4 was a generous gift of Dr. G. R. Pettit,
Arizona State University. [3H]Colchicine was obtained from
DuPont, nonradiolabeled colchicine from Sigma, and podo-
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was 12 µM. In the colchicine binding assays, the tubulin
concentration was 1 µM, and the concentration of both [3H]-
colchicine and inhibitors was 5 µM.
Ack n ow led gm en t . This investigation was sup-
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(CA-17625) awarded to K. H. Lee. We would like to
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