Antitumor agents. 174. 2',3',4',5,6,7-Substituted 2-phenyl-1,8- naphthyridin-4-ones: Their synthesis, cytotoxicity, and inhibition of tubulin polymerization

Article abstract of DOI:10.1021/jm960858s

Two series of 2',3',4',5,6,7-substituted 2-phenyl-l,8-naphthyridin-4- ones and 2-phenylpyrido[1,2-a]pyrimidin-4-ones have been synthesized and evaluated as cytotoxic compounds and as inhibitors of tubulin polymerization. Most 2-phenyl-1,8-naphthyridin-4-ones showed potent cytotoxic and antitubulin activities, whereas 2-phenylpyrido[1,2-a]pyrimidin-4-ones showed no activity in either assay. In general, a good correlation was found between cytotoxicity and inhibition of tubulin polymerization in the 2-phenyl-1,8- naphthyridin-4-one series. The 2-phenyl-1,8-naphthyridin-4-ones (44-49) with a methoxy group at the 3'-position showed potent cytotoxicity against most tumor cell lines with GI₅₀ values in the low micromolar to nanomolar concentration range in the National Cancer Institute's 60 human tumor cell line in vitro screen. Introduction of substituents (e.g. F, Cl, CH₃, and OCH₃) at the 4'-position led to compounds with reduced or little activity and substitution at the 2'-position resulted in inactive compounds. The effects of various A-ring substitutions on activity depend on the substitution in ring C. Compounds 44-50 were potent inhibitors of tubulin polymerization, with activity nearly comparable to that of the potent antimitotic natural products colchicine, podophyllotoxin, and combretastatin A-4. Compounds 44-49 also inhibited the binding of radiolabeled colchicine to tubulin, but the inhibition was less potent than that obtained with the natural products. Further investigation is underway to determine if substitution at the 3'-position and multisubstitutions in ring C will result in compounds with increased activity.

Full text of DOI:10.1021/jm960858s

2266
J . Med. Chem. 1997, 40, 2266-2275
An titu m or Agen ts. 174. 2′,3′,4′,5,6,7-Su bstitu ted
2-P h en 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
Ke Chen,† Sheng-Chu Kuo,‡ Ming-Chieh Hsieh,‡ Anthony Mauger,§ Chii M. Lin,| Ernest Hamel,| and
Kuo-Hsiung Lee*,†
Natural Products Laboratory, Division of Medicinal Chemistry and Natural Products, School of Pharmacy, University of North
Carolina at Chapel Hill, North Carolina 27599, Graduate Institute of Pharmaceutical Chemistry, China Medical College,
Taichung 400, Taiwan, Republic of China, Drug Synthesis and Chemistry Branch, Developmental Therapeutics Program,
Division of Cancer Treatment, Diagnosis and Centers, and Laboratory of Molecular Pharmacology, Division of Basic Sciences,
National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892
Received December 19, 1996X
Two series of 2′,3′,4′,5,6,7-substituted 2-phenyl-1,8-naphthyridin-4-ones and 2-phenylpyrido-
[1,2-a]pyrimidin-4-ones have been synthesized and evaluated as cytotoxic compounds and as
inhibitors of tubulin polymerization. Most 2-phenyl-1,8-naphthyridin-4-ones showed potent
cytotoxic and antitubulin activities, whereas 2-phenylpyrido[1,2-a]pyrimidin-4-ones showed no
activity in either assay. In general, a good correlation was found between cytotoxicity and
inhibition of tubulin polymerization in the 2-phenyl-1,8-naphthyridin-4-one series. The
2-phenyl-1,8-naphthyridin-4-ones (44-49) with a methoxy group at the 3′-position showed
potent cytotoxicity against most tumor cell lines with GI50 values in the low micromolar to
nanomolar concentration range in the National Cancer Institute’s 60 human tumor cell line in
vitro screen. Introduction of substituents (e.g. F, Cl, CH3, and OCH3) at the 4′-position led to
compounds with reduced or little activity and substitution at the 2′-position resulted in inactive
compounds. The effects of various A-ring substitutions on activity depend on the substitution
in ring C. Compounds 44-50 were potent inhibitors of tubulin polymerization, with activity
nearly comparable to that of the potent antimitotic natural products colchicine, podophyllotoxin,
and combretastatin A-4. Compounds 44-49 also inhibited the binding of radiolabeled colchicine
to tubulin, but the inhibition was less potent than that obtained with the natural products.
Further investigation is underway to determine if substitution at the 3′-position and
multisubstitutions in ring C will result in compounds with increased activity.
In tr od u ction
common feature has been described as a “biaryl” system
connected by a hydrocarbon bridge of variable length.11,12
The simplicity of these molecules provides promise for
the discovery or rational design of mitotic inhibitors as
antitumor agents.
The microtubule system of eukaryotic cells is an
attractive target for the development of compounds
useful in anticancer chemotherapeutics. Microtubules
show highly dynamic instability and play an important
role in mitosis.2 Chemicals that attack microtubules
through their major structural component, tubulin,
disrupt or suppress both microtubule structure and
normal functions by inhibition or promotion of micro-
tubule assembly, resulting in cell arrest in mitosis.
Examples of clinically used antimitotic agents are the
vinca alkaloids,3 which inhibit microtubule polymeri-
zation, and the taxoids,4 which promote microtubule
assembly. Colchicine (Figure 1) is another important
antimitotic agent. Although it has limited medicinal
application due to its high toxicity, colchicine has played
a fundamental role in elucidation of the properties and
functions of tubulin and microtubules.5 Many natural
products, such as cornigerine,6 podophyllotoxin,7 stega-
nacin,8 and combretastatin,9,10 bind to the colchicine
site. Structurally, the compounds binding to this site
are much simpler than those binding to vinca alkaloid
or taxol domains. These compounds generally share
“homology” with the A and C rings of colchicine; this
In the course of our search for novel plant-derived
potent cytotoxic agents that are active against slow-
growing solid tumors,13 we have isolated several fla-
vonols as antitumor principles from a phytochemically
and biologically uninvestigated plant, Polanisia dode-
candra.14 Among these flavonols, 5,3′-dihydroxy-
3,6,7,8,4′-pentamethoxyflavone showed remarkable cy-
totoxicity in vitro against panels of central nervous
system, lung, ovarian, colon, and renal cancers and
against melanoma and leukemia cell lines with GI50
values in the low micromolar to nanomolar concentra-
tion range. Flavonoids belong to the biaryl structural
pattern and would be predicted to have antimitotic
activity. Actually, this compound was found to be a
strong inhibitor of tubulin polymerization with an IC50
value of 0.83 ( 0.2 µM and to be a potent inhibitor of
radiolabeled colchicine binding to tubulin, showing 59%
inhibition when present in an equimolar concentration
with colchicine, and, accordingly, can be classified as a
colchicine site drug.
In parallel with our studies of plant antitumor agents,
we synthesized a large series of 2-arylquinolones, the
amino analogs of cytotoxic antimitotic flavonoids, and
found that many of these compounds were cytotoxic and
inhibitors of tubulin polymerization and colchicine bind-
* To whom correspondence should be addressed.
† University of North Carolina.
‡ China Medical College.
§ Drug Synthesis and Chemistry Branch, NCI.
| Laboratory of Molecular Pharmacology, NCI.
X Abstract published in Advance ACS Abstracts, J une 15, 1997.
S0022-2623(96)00858-8 CCC: $14.00 © 1997 American Chemical Society

2′,3′,4′,5,6,7-Substituted 2-Phenyl-1,8-naphthyridin-4-ones
J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 14 2267
F igu r e 1.
ing to tubulin.15-17 Structure-activity relationship
studies of this class of antimitotic and antitumor agents
led to the discovery of a particularly potent compound,
NSC 664171, which showed inhibitory activity against
tubulin polymerization and radiolabeled colchicine bind-
ing to tubulin comparable to that of the potent antimi-
totic natural products colchicine, podophyllotoxin, and
combretastatin A-4. NSC 664171 also showed strong
cytotoxic effects with GI50 values in the nanomolar or
subnanomolar concentration range in most human
tumor cell lines tested by the National Cancer Institute
(NCI).
and substituted benzaldehydes (3). Cyclization of 4 with
chloroacetyl chloride and triethylamine gave the corre-
sponding pyridopyrimidinones, which were converted to
the target compounds on heating.18,19 The starting
substituted ethyl benzoylacetates (2) were prepared
according to a literature method.20 Condensation of
substituted acetophenones (5) with diethyl carbonate (6)
in the presence of sodium hydride formed the required
ethyl benzoylacetates. The structures and chemical
features of the synthesized compounds are summarized
in Table 1.
Resu lts a n d Discu ssion
Encouraged by these promising results, we have
extended our investigation of the 2-phenyl-4-quinolones
to a novel, structurally related azo series, in which a
nitrogen atom was introduced into the 4a-, 5-, 6-, 7-, or
8-position. A preliminary study showed that incorpora-
tion of the nitrogen atom at the 4a-, 5-, 6-, or 7-position
failed to yield significantly cytotoxic compounds, while
introduction of the nitrogen atom at the 8-position gave
active agents, which equal or exceed the potency of the
corresponding 2-phenyl-4-quinolones. In a direct com-
parison of the naphthyridinone and quinolone series,
2-(3′-methoxyphenyl)-1,8-naphthyridin-4-one (44) showed
about 100-fold greater activity than the corresponding
2-(3′-methoxyphenyl)-4-quinolone (71) (Table 1), and 44
also showed potent cytotoxic effects against prostate and
breast cancer cell lines (Table 2). Moreover, the most
active members of the 2-phenyl-l,8-naphthyridin-4-one
series are potent inhibitors of tubulin assembly (Table
1). On the basis of the initial results, a systematic
investigation of substituted 2-phenyl-1,8-naphthyridin-
4-ones as antitubulin and cytotoxic agents was initiated,
as reported here.
a . Eva lu a tion of th e Cytotoxicity of 2-P h en yl-
n a p h th yr id in -4-on es. The 2-phenylpyrido[1,2-a]py-
rimidin-4-ones were assayed at the School of Medicine,
University of North Carolina at Chapel Hill, for their
cytotoxicity in vitro against six tumor cell lines, includ-
ing human epidermoid carcinoma of the nasopharynx
(KB), lung carcinoma (A-549), ileocecal carcinoma (HCT-
8), melanoma (PRMI-7951), and medulloblastoma (TE-
671), as well as one murine leukemia cell line (P-388).
The results (data not shown) demonstrated that es-
sentially all 2-phenylpyrido[1,2-a]pyrimidin-4-ones were
inactive (EC50 > 4 µg/mL); only a few compounds
showed marginal activity.
The 2-phenyl-1,8-naphthyridin-4-ones were tested in
the NCI’s in vitro disease-oriented antitumor screen.21,22
This assay involves determinations of a test agent’s
effect on growth parameters against a panel of ap-
proximately 60 human tumor cell lines, which consist
largely of solid tumors and a few leukemia cell lines.
The cytotoxic effects of each compound are obtained as
GI50 or TGI values, which represent the molar drug
concentrations required to cause half growth inhibition
and total growth inhibition, respectively. The results
are expressed in Table 2 as log GI50 values for selected
cell lines and in Table 1 as average log GI50 values for
the entire panel of cell lines. Among the compounds
tested, 44-49 showed the strongest inhibitory effects
against a variety of tumor cell lines, including leukemia,
colon, CNS, melanoma, ovarian, renal, prostate, breast,
and small cell lung cancer cell lines, with values in the
low micromolar to nanomolar concentration range. It
is notable that compounds 44, 46, 47, and 49 show
highly selective effects on several cell lines from the
Ch em istr y
2-Phenyl-1,8-naphthyridin-4-ones were synthesized
according to the two general methods shown in Scheme
1. Condensation of substituted 2-aminopyridines (1)
with substituted ethyl benzoylacetates (2) in the pres-
ence of polyphosphoric acid (PPA) formed the corre-
sponding pyridopyrimidinones (7-38). These kineti-
cally favored products were then thermally converted
at 350 °C in mineral oil to the target compounds (39-
70). The second method involved the formation of a
Schiff base (4) between substituted 2-aminopyridines (1)

2268 J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 14
Chen et al.
Ta ble 1. Physical Properties, Cytotoxicity, and Antimicrotubule Effects of Substituted 2-Phenyl-1,8-naphthyridin-4-ones
ITPa
IC50 (µM)
( SD
ICBb
(% inhibn) GI50
avc log
yield,
%
e
compd
R5
R6
R7
R2′
R3′
R4′
formulad
mp, °C
f
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
H
CH3
H
H
CH3
H
CH3
H
H
CH3
H
H
H
CH3
H
H
CH3
H
CH3
H
H
CH3
H
H
H
H
CH3
H
H
H
H
CH3
H
H
Cl
Br
H
H
CH3
H
H
H
H
CH3
H
H
Cl
H
H
CH3
H
H
H
CH3
H
H
H
H
H
OCH3
OCH3
OCH3
H
H
H
H
H
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
> 40
-4.39 C15H12N2O2
196-197 27
199-200 23
202-203 38
198-199 48
203-204 38
H
H
H
H
H
H
H
H
H
H
H
20 ( 1
18 ( 1
-5.55 C16H14N2O2
-4.50 C16H14N2O2
-4.10 C16H14N2O2
-4.24 C17H16N2O2‚0.25H2O
-6.87 C15H12N2O2
-7.23 C16H14N2O2
-7.02 C16H14N2O2
-7.24 C16H14N2O2
-6.19 C17H16N2O2
-7.01 C15H12ClN2O2‚H2O
CH3 OCH3
CH3 OCH3
H
H
H
CH3
CH3
H
H
H
H
H
CH3
CH3
H
H
H
CH3
CH3
H
H
H
H
CH3
CH3
H
H
CH3
CH3
>40
>40
0.96 ( 0.1
f
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
27 ( 1
28 ( 3
31 ( 4
29 ( 4
22 ( 2
35 ( 6
183-184 42
0.62 ( 0.1
0.80 ( 0.2
0.75 ( 0.2
0.88 ( 0.08
0.73 ( 0.2
1.5 ( 0.07
208-209 40
215-216 39
213-214 63
206-207 60
264-265 30
f
NTg
C15H12BrN2O2‚0.5H2O
245-247
0.8 (B)
OCH3 >40
OCH3
OCH3
OCH3 >40
OCH3 >40
-4.42 C15H12N2O2
-4.89 C16H14N2O2
-5.21 C16H14N2O2
-4.04 C16H14N2O2
-4.48 C17H16N2O2‚0.5H2O
217-218 33
f
8.8 ( 3
7.7 ( 0.7
196-197 35
f
261-262 36
f
255-256 59
213-214 56
200-202 33
F
F
F
F
F
F
Cl
Cl
Cl
Cl
Cl
CH3
CH3
CH3
CH3
>40
18 ( 2
20 ( 0.2
>40
>40
16 ( 3
22 ( 0.1
-4.34
C14H9FN2O‚0.25H2O
f
-4.42 C15H11FN2O
-4.58 C15H11FN2O
-4.49 C15H11FN2O
-4.39 C16H13FN2O‚H2O
245-247 48
286-288 29
250-251 77
f
228-230 21
-4.66
-4.41
C
C
14H8ClFN2O
14H9ClN2O
>300
>300
31
32
f
CH3
H
H
CH3
CH3
H
4.8 ( 1.4
2.0 ( 0.01
11 ( 0.7
-5.29 C15H11ClN2O
-5.43 C15H11ClN2O
-5.31 C15H11ClN2O
-4.71 C16H13ClN2O
261-262 44
f
290-292 64
f
263-265 72
f
32 ( 8
262-263 35
2.9 ( 0.7
2.4 ( 0.8
4.9 ( 0.2
9.8 ( 2
NTg
C16H14N2O
C16H14N2O
C16H14N2O
C17H16N2O
218-220 35
254-265 31
255-257 61
236-237 63
236-237 63
NTg
H
CH3
NTg
NTg
1.4 ( 0.4
0.80 ( 0.07h
0.46 ( 0.02h
0.53 ( 0.05h
-5.21
-7.24
-7.54
-8.18
C17H16N2O
colchicine
podophyllotoxin
combretastatin A-4
76 ( 5
91 ( 2
a
b
ITB ) inhibition of tubulin polymerization. ICB ) inhibition of colchicine binding and evaluated only when polymerization IC50
e
1 µM. c Data obtained from NCI’s 60 human tumor cell line in vitro screen and calculated from all cell lines tested. All compounds were
d
analyzed for C, H, and N, and results agreed to (0.4% of the theoretical values. e All yields were calculated from aminopyridines and
obtained by method A unless indicated; see the Experimental Section. f Decomposed. Not tested. Previously obtained data, see ref 17.
g
h
leukemia, breast, and non-small lung cancer panels at
the TGI level. The log TGI values for these four
compounds are -7.19 to -7.40 in the HL-60 cell line,
-6.16 to -7.12 in the NCI-H226 cell line, and -7.40 to
-7.67 in MDA-MB-435 and MDA-N cell lines. Growth
of cells from more sensitive cell lines was arrested at a
concentration approximately log 2.5-3.7 concentration
lower than less sensitive cell lines.
present at different position(s) in ring A without sub-
stantially affecting cytotoxicity. For 2′- and 4′-substi-
tuted compounds, substitution at the 5- or 6-position
generated slightly greater activity than no substitution
or substitution at the 7-position or the 5- and 7-positions
in ring A. It is notable that all less active compounds
nevertheless showed moderate cytotoxicity on two breast
cancer cell lines, MDA-MB-435 and MDA-N.
In terms of average cytotoxicity, compounds substi-
tuted at the 4′-position were substantially less active
than those substituted at the 3′-position, while com-
pounds with a methoxy group at the 2′-position were
the least active. Among the tested compounds with a
4′-substituent, only minor differences in cytotoxicity
were obtained, suggestive of a potency order of chloro
> methoxy > fluoro. The effects of substitutions at the
5-, 6-, and/or 7-positions in ring A depend on the
substitution in ring C. All 3′-substituted compounds
with different substituents in ring A showed potent
cytotoxicity, indicating that the substitution(s) can be
b. In ter a ction s of 2-P h en yl-1,8-n a p h th yr id in -4-
on es w ith Tu bu lin . Previously, 2-phenyl-4-quinolones
were found to be antimitotic agents that interact with
tubulin at the colchicine site.15-17 Structurally, 2-phen-
yl-1,8-naphthyridin-4-ones can be considered isosteres
of 2-phenyl-4-quinolones. Since incorporation of an
additional nitrogen atom into the quinolone at the
8-position does not change the basic 2-phenyl-4-qui-
nolone skeleton, 2-phenyl-1,8-naphthyridin-4-ones could
be predicted to have similar biological activity to
2-phenyl-4-quinolones. Thus, the series of substituted
2-phenyl-1,8-naphthyridin-4-ones were evaluated for

2′,3′,4′,5,6,7-Substituted 2-Phenyl-1,8-naphthyridin-4-ones
J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 14 2269
Ta ble 2. Inhibition of in Vitro Tumor Cell Growth by Substituted 2-Phenyl-1,8-naphthyridin-4-onesa
cytotoxicity log GI50 (M)b
HL-60
compd
(TB)c
NCI-H460 HCT-116 SF-295
U-251
SK-MEL-5 OVCAR-3
786-0
PC-3
MDA-MB-435 MDA-N
71
39
40
41
42
43
44
45
46
47
48
49
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
-5.68
-4.41
-4.68
-5.02
-4.13
-4.52
-7.79
-7.89
-7.72
-7.74
-6.76
-7.57
-4.89
-5.36
-5.64
-5.40
-4.41
-4.62
-4.49
-4.01
-4.15
-7.04
-7.32
-7.36
-7.36
-6.35
-7.20
-4.58
-5.21
-5.39
-5.24
-4.56
-5.12
-4.37
-4.42
-4.13
-7.44
-7.35
-7.65
-7.33
-6.39
-6.92
-4.75
-5.19
-5.38
-5.64
-4.63
-4.63
-4.51
-5.02
-4.17
-4.45
-4.56
>-4
n td
-5.26
-4.32
-4.89
-4.71
-5.29
-4.44
-4.22
-4.38
>-4
n t
n t
n t
-4.50
-4.65
-4.69
-4.29
-4.47
-7.27
-7.65
-7.59
-7.47
-6.54
-6.90
-4.46
-5.41
-5.43
-4.32
-4.75
-4.52
-4.79
-4.66
-4.50
-4.58
-5.18
-4.54
-5.46
-5.66
-5.36
-4.85
-4.53
-4.68
-4.57
-4.40
-5.19
-5.52
-4.66
-4.49
<-8.00
<-8.00
<-8.00
<-8.00
<-8.00
-7.49
-4.70
-5.62
-5.74
-4.37
-4.54
-4.92
-5.54
-5.58
-5.23
-4.73
-5.59
-5.23
-6.12
-6.22
-6.04
-5.39
-4.70
-5.08
-5.35
-4.70
-4.48
<-8.00
<-8.00
<-8.00
-7.96
<-8.00
-7.50
-4.68
-5.68
-5.77
-4.26
-4.48
-4.85
-5.45
-5.52
-4.93
-4.60
-5.53
-5.08
-5.88
-6.25
-6.00
-5.44
>-4
>-4
>-4
-4.27 >-4
-4.19
-7.26
-7.59
-7.38
-7.65
-6.60
-6.31
-4.52
-4.86
-5.53
>-4
-4.32
-7.03
-7.58
-7.37
-7.48
-6.51
-6.86
-4.50
-4.74
-5.27
-7.28
-7.54
-7.43
-7.52
-6.38
-7.22
-4.19
-4.71
-5.28
-7.26
-7.21
-7.29
-7.43
-7.27
-6.36
-6.37
-4.25
-4.60
-5.29
>-4
-4.23
-4.35
-4.47
-4.49
-4.38
-4.10
-4.49
-4.47
-5.40
-5.20
-5.20
-4.67
-7.23
-7.35
-7.27
-6.77
-6.70
-4.27
-5.20
-5.38
>-4
>-4
>-4
-4.05 >-4
>-4
>-4
-4.809
-4.89
-5.32
-5.62
-4.83
-4.81
-5.41
-4.78
-5.75
-5.65
-5.53
-4.60
-4.39
-4.46
-4.49
-4.47
-4.47
-4.29
-4.52
-4.42
-5.43
-5.41
-5.35
-4.65
-4.44
-4.37
-4.79
-4.62
-4.47
-4.30
-4.77
-4.49
-5.43
-5.55
-5.48
-4.83
-4.37
-4.30
-4.10
-4.53
-4.43
-4.30
-4.67
-4.39
-5.27
-5.62
-5.34
-4.79
-4.04
-4.49
-4.34
-4.25
-4.65
-4.49
-4.36
-4.76
-4.63
-5.50
-5.65
-5.59
-4.74
-4.62
-4.34
-4.29
-4.59
-4.68
-4.52
-4.66
-4.32
-5.54
-5.94
-5.78
-5.20
-4.32
-4.44
-4.60
-4.43
-4.02
-4.53
-4.40
-5.34
-5.52
-5.32
-4.52
a
b
Data obtained from NCI’s in vitro disease-oriented human tumor cells screen (see refs 21 and 22 for details). Log concentrations
which reduced cell growth to 50% of level at start of experiment. c HL-60 (TB), leukemia cell line; NCI-H460, non-small-cell lung cancer
cell line; HCT-116, colon cancer cell line; SF-295, U251, CNS cancer cell lines; SK-MEL-5, melanoma cell line; OVCAR-3, ovarian cancer
d
cell line; 786-0, renal cancer cell line; PC-3, prostate cancer cell line; MDA-MB-435, MDA-N, breast cancer cell lines. Not tested.
Sch em e 1. General Synthetic Routes to 2-Phenyl-1,8-naphthyridin-4-ones
their relative potency as inhibitors of tubulin assembly
to elucidate the pharmacophore requirements for bind-
ing to the protein and for comparison with the cytotox-
icity data summarized above. The results are summa-
rized in Table 1, with a comparison to previously
obtained data17 with the potent antimitotic natural
products colchicine, podophyllotoxin, and combretasta-
tin A-4 (the same tubulin preparation and reaction
conditions were used in the study of ref 17 as in the
current experiments).
lent correlation between cytotoxicity and inhibition of
tubulin polymerization. These six strongly cytotoxic
agents were the most potent inhibitors of assembly in
the series. All had IC50 values below 1.0 µM, as did the
three natural products. These six agents were also
examined for inhibitory effects on the binding of [3H]-
colchicine to tubulin (1.0 µM tubulin), with inhibitor and
drug at equimolar concentrations (5.0 µM). Significant
and similar inhibition was observed with all six com-
pounds, although they were substantially less potent
than podophyllotoxin or combretastatin A-4 (Table 1).
Compounds 50, 52, 53, 63, 64, and 67-70 showed
With the most active compounds (44-49; no cytotox-
icity data available for compound 50), there was excel-

2270 J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 14
Chen et al.
Ta ble 3. COMPARE Correlations at GI50 and TGI Levels for Compounds 44-49a
colchicine
maytansine
vincristine
vinblastine
rhizoxin
paclitaxel
seed
GI50
TGI
GI50
TGI
GI50
TGI
GI50
TGI
GI50
TGI
GI50
TGI
44
45
46
47
48
49
0.66
0.69
0.73
0.79
0.71
0.70
0.55
0.47
0.53
0.47
0.55
0.58
0.65
0.73
0.69
0.74
0.71
0.63
0.64
0.37
0.62
0.45
0.51
0.69
0.58
0.61
0.58
0.71
0.62
0.62
0.45
0.41
0.44
0.43
0.48
0.55
0.47
0.60
0.56
0.64
0.65
0.51
0.67
0.53
0.62
0.56
0.64
0.77
0.60
0.58
0.54
0.61
0.65
0.55
0.60
0.40
0.58
0.45
0.51
0.62
0.36
0.30
0.40
0.41
0.46
0.31
0.63
0.47
0.53
0.55
0.61
0.65
a
See refs 23 and 24 for details.
reduced inhibitory effects on tubulin polymerization,
with IC50 values ranging from 1.5 to 9.8 µM. Slight
inhibition was observed with compounds 40, 41, 57, 58,
61, 62, 65, and 66 (IC50 values ranging from 11 to 32
µM), while the remaining compounds (39, 42, 43, 51,
54-56, 59, and 60) were inactive, with IC50 values
greater than 40 µM. Although it is not dramatic among
these less active compounds, those with greater anti-
tubulin activity (IC50 values < 10 µM) tend to be more
cytotoxic than those with little or no antitubulin activity.
From the tubulin data, the 3′-substitution of a meth-
oxy group was well-tolerated, while the 4′- and 2′-
methoxy substituents resulted in large, progressive
losses of activity or total loss of activity. On the other
hand, the series of 4′-substituents indicate that the
methyl and chloride groups are better tolerated than
the methoxy group and that the fluoride group is
equivalent to the methoxy substituent at position 4′.
This suggests that a strong electron-withdrawing or a
large electron-donating group at the 4′-position is
unfavorable for the drug-tubulin interaction.
The tubulin assay also yielded data of interest re-
garding A-ring substituents. No clear pattern was
observed in the potent 3′-methoxy-substituted subseries
(compounds 44-50), for a variety of substituents at
different position(s) of ring A were well-tolerated. These
substituents include both an electron-donating group
(CH3) and electron-withdrawing groups (Cl and Br). The
size of the substituents (as small as hydrogen, compound
44, and as large as two methyl groups, compound 48)
and their positions (no substitution or different positions
of both mono- and disubstitution) did not greatly affect
relative compound activities.
N in the former series, and a C in the latter series. Both
series have two aryl rings connected by a pyridinone
ring. Thus, the 2-phenyl-1,8-naphthyridin-4-ones and
2-phenyl-4-quinolones together with other natural prod-
ucts, such as podophyllotoxin and combretastatin, fall
into a group of colchicine site compounds that have two
aryl ring systems connected by a hydrocarbon bridge of
variable length.11,12,14,15 In both classes of compounds,
derivatives with a methoxy at the 3′-position were the
most active compounds within their series and were
much more active than isomers with the same substitu-
ent at the 2′- or 4′-position. However, unlike the
2-phenyl-4-quinolones, in which a 4′-methoxy group
reduced activity more than a 2′-methoxy substituent,
in the 2-phenyl-1,8-naphthyridin-4-ones, a 2′-methoxy
group reduced activity more than did a 4′-methoxy
substituent. Moreover, in the 2-phenyl-4-quinolone
series, A-ring substituents were optimal at positions 6
and 7, whereas in the 2-phenyl-1,8-naphthyridin-4-one
series, it appears that A-ring substituents are optimal
at positions 5 and 6. These findings indicate that the
binding site(s) for these two series might not completely
overlap.
c. COMP ARE Cor r ela tion . The COMPARE com-
puter program uses the patterns of cellular responsive-
ness in the NCI 60 cell line screen to calculate Pearson
correlation coefficients between data for seed compounds
and those for past agents in the database.23 The
significance of these computations is that the observed
correlation coefficients are greatest in pairs of com-
pounds sharing common intracellular targets.24 COM-
PARE computations for the six most potent compounds
(44-49) against several known tubulin/microtubule
binding agents are shown in Table 3 at both the GI50
and TGI levels. Correlation coefficients >0.6 at either
level can be considered significant. These compounds
display higher correlations with colchicine and may-
tansine than with the vinca alkaloids or rhizoxin, while
correlations with paclitaxel (Taxol) are comparatively
weak.
However, a consistent pattern for A-ring substitution
emerged in the other five subseries (2′-methoxy, 4′-
methoxy, 4′-fluoride, 4′-chloride, and 4′-methyl). In all
cases, C-5 and C-6 substituents (generally methyl
groups) enhanced activity relative to the unsubstituted
derivative and to those bearing a C-7 substituent or two
substituent groups.
The most active 2-phenyl-1,8-naphthyridin-4-ones
approach colchicine in their potency as inhibitors of
tubulin polymerization. While these compounds appear
to interact at the colchicine binding site of tubulin, they
only weakly inhibit the binding of radiolabeled colchi-
cine to tubulin. This apparent discrepancy probably
arises from a relatively slow binding and/or rapid
dissociation reaction of these agents with tubulin rela-
tive to the binding and dissociation reactions of colchi-
cine with the protein. These properties are similar to
those of a structurally related class of antimitotic
agents, the 2-phenyl-4-quinolones, which were devel-
oped in our laboratory. The only structural difference
between the 2-phenyl-1,8-naphthyridin-4-ones and
2-phenyl-4-quinolones is the atom at the 8-position: a
d . Su m m a r y We have synthesized a series of novel
2′,3′,4′,5,6,7-substituted 2-phenyl-1,8-naphthyridin-4-
ones. Compounds 44-49 showed potent inhibitory
effects in vitro on tubulin polymerization and appear
to interact at the colchicine binding site of tubulin.
Compounds 44-49 also showed potent inhibitory effects
in vitro on the growth of a variety of human tumor cell
lines with high selectivity for several cell lines from the
leukemia, breast, and non-small-cell lung cancer panels.
In general, there was good correlation between cytotox-
icity and inhibition of in vitro tubulin polymerization.
Compounds with a 3′-methoxy group had the highest
potency in the two assays. Introduction of substituents
(e.g. F, Cl, CH3, and OCH3) at the 4′-position led to
compounds with reduced or little activity, while a

2′,3′,4′,5,6,7-Substituted 2-Phenyl-1,8-naphthyridin-4-ones
J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 14 2271
7.04 (br d, J ) 8.5 Hz, 1 H, H-3′), 3.92 (s, 3 H, OCH3-2′); MS
m/ z 252 (M+). Anal. C, H, N.
methoxy attached at the 2′-position resulted in inactive
compounds. The effects of various substitutions in ring
A on activity depend on the substitution in ring C. The
2-phenyl-1,8-naphthyridin-4-one series is more potent
than the 2-phenyl-4-quinolone series. The discovery of
a potent antimitotic and antitumor agent NSC 664171
in the 2-phenyl-4-quinolone series and promising results
in the preliminary structure-activity relationship (SAR)
studies of the 2-phenyl-1,8-naphthyridin-4-one series
indicate that these compounds warrant further inves-
tigation.
2-(2′-Meth oxyp h en yl)-8-m eth ylp yr id o[1,2-a ]p yr im id in -
4-on e (8): obtained from ethyl (2′-methoxybenzoyl)acetate and
2-amino-4-picoline; prisms; mp 154-155 °C; 1H NMR (CDCl3)
δ 8.96 (d, J ) 7.0 Hz, 1 H, H-6), 7.95 (dd, J ) 7.5, 1.5 Hz, 1 H,
H-6′), 7.57 (br s, 1 H, H-9), 7.44 (td, J ) 7.5, 1.5 Hz, 1 H, H-4′),
7.09 (t, J ) 7.5 Hz, 1 H, H-5′), 7.05 (s, 1 H, H-3), 7.02 (br d, J
) 8.0 Hz, 1 H, H-7), 6.97 (dd, J ) 7.5, 1.5 Hz, 1 H, H-3′), 3.90
(s, 3 H, OCH3-2′), 2.49 (s, 3 H, CH3-8); MS m/ z 266 (M+). Anal.
C, H, N.
2-(2′-Meth oxyp h en yl)-7-m eth ylp yr id o[1,2-a ]p yr im id in -
4-on e (9): obtained from ethyl (2′-methoxybenzoyl)acetate and
2-amino-5-picoline; prisms; mp 148-149 °C; 1H NMR (CDCl3)
δ 8.89 (s, 1 H, H-6), 7.96 (dd, J ) 7.9, 1.9 Hz, 1 H, H-6′), 7.74
(d, J ) 9.0 Hz, 1 H, H-9), 7.60 (dd, J ) 9.0, 2.0 Hz, 1 H, H-8),
7.44 (td, J ) 7.9, 1.9 Hz, 1 H, H-4′), 7.12 (s, 1 H, H-3), 7.10
(dt, J ) 7.9 1.9 Hz, 1 H, H-5′), 7.03 (d, J ) 7.9, Hz, 1 H, H-3′),
3.91 (s, 3 H, OCH3-2′), 2.45 (s, 3 H, CH3-7); MS m/ z 266 (M+).
Anal. C, H, N.
2-(2′-Meth oxyp h en yl)-6-m eth ylp yr id o[1,2-a ]p yr im id in -
4-on e (10): obtained from ethyl (2′-methoxybenzoyl)acetate
and 2-amino-6-picoline; prisms; mp 153-154 °C; 1H NMR
(CDCl3) δ 7.99 (dd, J ) 7.5, 1.7 Hz, 1 H, H-6′), 7.52 (d, J ) 9.0
Hz, 1 H, H-9), 7.42 (t, J ) 9.0, Hz, 1 H, H-8), 7.42 (td, J ) 7.5,
1.7 Hz, 1 H, H-4′), 7.09 (t, J ) 7.5 Hz, 1 H, H-5′), 7.01 (d, J )
7.5, Hz, 1 H, H-3′), 6.97 (s, 1 H, H-3), 6.64 (d, J ) 9.0 Hz, 1 H,
H-7), 3.91 (s, 3 H, OCH3-2′), 3.09 (s, 3 H, CH3-6); MS m/ z 266
(M+). Anal. C, H, N.
2-(2′-Met h oxyp h en yl)-6,8-d im et h ylp yr id o[1,2-a ]p yr i-
m id in -4-on e (11): obtained from ethyl (2′-methoxybenzoyl)-
acetate and 2-amino-4,6-dimethylpyridine; prisms, mp 170-
171 °C; 1H NMR (CDCl3) δ 7.96 (dd, J ) 7.5, 1.7 Hz, 1 H, H-6′),
7.41 (td, J ) 7.5, 1.7 Hz, 1 H, H-4′), 7.33 (br s, 1 H, H-9), 7.08
(t, J ) 7.5 Hz, 1 H, H-5′), 7.01 (d, J ) 7.5, Hz, 1 H, H-3′), 6.88
(s, 1 H, H-3), 6.49 (br s, 1 H, H-7), 3.90 (s, 3 H, OCH3-2′), 3.06
(s, 3 H, CH3-6), 2.34 (s, 3 H, CH3-8); MS m/ z 280 (M+). Anal.
C, H, N.
2-(3′-Me t h oxyp h e n yl)p yr id o[1,2-a ]p yr im id in -4-on e
(12): obtained from ethyl (3′-methoxybenzoyl)acetate and
2-aminopyridine; prisms; mp 156-157 °C; 1H NMR (CDCl3) δ
9.08 (d, J ) 7.0 Hz, 1 H, H-6), 7.76 (d, J ) 7.0 Hz, 1 H, H-9),
7.75 (t, J ) 7.0 Hz, 1 H, H-8), 7.67 (s, 1 H, H-2′), 7.66 (d, J )
7.5, Hz, 1 H, H-6′), 7.42 (t, J ) 7.5 Hz, 1 H, H-5′), 7.15 (ddd,
J ) 7.0, 7.0, 2.0 Hz, 1 H, H-7), 7.05 (td, J ) 7.5 Hz, 1 H, H-4′),
6.92 (s, 1 H, H-3), 3.92 (s, 3 H, OCH3-3′); MS m/ z 252 (M+).
Anal. C, H, N.
2-(3′-Meth oxyp h en yl)-8-m eth ylp yr id o[1,2-a ]p yr im id in -
4-on e (13): obtained from ethyl (3′-methoxybenzoyl)acetate
and 2-amino-4-picoline; plates; mp 136-137 °C; 1H NMR
(CDCl3) δ 8.97 (d, J ) 7.0 Hz, 1 H, H-6), 7.66 (br s, 1 H, H-2′),
7.64 (d, J ) 7.5, 1 H, H-6′), 7.54 (s, 1 H, H-9), 7.41 (t, J ) 7.5
Hz, 1 H, H-5′), 7.04 (dd, J ) 7.5, 2.0 Hz, 1 H, H-4′), 6.98 (d, J
) 7.0 Hz, 1 H, H-7), 6.85 (s, 1H, H-3), 3.91 (s, 3 H, OCH3-3′),
2.51 (s, 3 H, CH3-8); MS m/ z 266 (M+). Anal. C, H, N.
2-(3′-Meth oxyp h en yl)-7-m eth ylp yr id o[1,2-a ]p yr im id in -
4-on e (14): obtained from ethyl (3′-methoxybenzoyl)acetate
and 2-amino-5-picoline; prisms; mp 163-164 °C; 1H NMR
(CDCl3) δ 8.90 (s, 1 H, H-6), 7.70 (d, J ) 9.0 Hz, 1 H, H-9),
7.66 (d, J ) 2.0 Hz, 1 H, H-2′), 7.65 (d, J ) 7.8 Hz, 1 H, H-6′),
7.62 (dd, J ) 9.0, 1.8 Hz, 1 H, H-8), 7.42 (t, J ) 7.8, Hz, 1 H,
H-5′), 7.04 (td, J ) 7.8, 2.0 Hz, 1 H, H-4′), 6.90 (s, 1 H, H-3),
3.91 (s, 3 H, OCH3-3′), 2.46 (s, 3 H, CH3-7); MS m/ z 266 (M+).
Anal. C, H, N.
Exp er im en ta l Section
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. The solvents for crystallization are MeOH
for 2-phenyl-1,8-naphthyridin-4-ones and Me2CO for 2-phe-
nylpyrido[1,2-a]pyrimidin-4-ones. Elemental analyses were
performed on a Carlo Erba EA 1108 elemental analyzer. 1H
NMR spectra were measured on a Bruker AC-300 spectrom-
eter 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.
P r ep a r a tion of Su bstitu ted Eth yl Ben zoyla ceta tes.
The substituted ethyl benzoylacetates (2) were prepared
according to procedures described by Krapcho et al.20 To a
vigorously stirred suspension of NaH and CO(OEt)2 in toluene
was added dropwise a solution of substituted acetophenone
(5) in toluene under reflux. The mixture was allowed to reflux
and was stirred for 20 min after the addition was complete.
When cooled to room temperature, the mixture was acidified
with glacial AcOH. After ice-cold water was added, the
mixture was extracted with toluene. Workup and distillation
gave the corresponding substituted ethyl benzoylacetates.
P r oced u r es for Meth od A.18 A mixture of substituted
2-aminopyridine (1), substituted ethyl benzoylacetate (2), and
PPA was heated at 125 °C with stirring. The reaction was
monitored by TLC. After the reaction was complete, the
mixture was cooled to room temperature and neutralized with
4 M NaOH. After extraction with CH2Cl2, the extract was
passed through a silica gel column to give 2-phenylpyrido[1,2-
a]pyrimidin-4-one (7-38). The 2-phenylpyrido[1,2-a]pyrimi-
din-4-one was then added to liquid paraffin at 350 °C with
stirring. The oil was maintained at 350 °C for 2 h after the
addition was complete. The cooled mixture was subjected to
silica gel column chromatography. Elution with CH2Cl2-
EtOAc gave the corresponding 2-phenyl-1,8-naphthyridin-4-
one (39-70).
P r oced u r es for Meth od B.19 The substituted 2-aminopy-
ridine (1) and substituted aldehyde (3) in equimolar concentra-
tion were heated in refluxing m-xylene until 90-95% of the
theoretical amount of H2O was collected in a Dean-Stark trap.
After the m-xylene was evaporated at atmospheric pressure,
the residue was distilled in vacuo to afford 2-(arylideneamino)-
pyridine 4. The 2-(arylideneamino)pyridine 4 and Et3N were
dissolved in anhydrous Et2O; a solution of chloroacetyl chloride
in anhydrous Et2O was then added dropwise with stirring at
-15 to -10 °C. After the addition was complete, the mixture
was stirred for 1 h. The precipitated triethylamine chloride
was filtered, and the filtrate was concentrated in vacuo. The
residue was chromatographed on silica gel with CH2Cl2-
EtOAc as eluant to give 2-phenylpyrido[1,2-a]pyrimidin-4-one,
which was converted to the corresponding 2-phenyl-1,8-naph-
thyridin-4-one according to the procedures described above.
2-(2′-Me t h oxyp h e n yl)p yr id o[1,2-a ]p yr im id in -4-on e
(7): obtained from ethyl 2′-(methoxybenzoyl)acetate and
2-(3′-Meth oxyp h en yl)-6-m eth ylp yr id o[1,2-a ]p yr im id in -
4-on e (15): obtained from ethyl (3′-methoxybenzoyl)acetate
and 2-amino-6-picoline; prisms; mp 115-116 °C; 1H NMR
(CDCl3) δ 7.63 (s, 1 H, H-2′), 7.61 (d, J ) 7.5 Hz, 1 H, H-6′),
7.49 (d, J ) 8.5, Hz, 1 H, H-9), 7.45 (dd, J ) 8.5, 6.3 Hz, 1 H,
H-8), 7.39 (t, J ) 7.5 Hz, 1 H, H-5′), 7.02 (td, J ) 7.5, 2.0 Hz,
1 H, H-4′), 6.72 (s, 1 H, H-3), 6.64 (d, J ) 6.3 Hz, 1 H, H-7),
3.90 (s, 3 H, OCH3-3′), 3.08 (s, 3 H, CH3-6); MS m/ z 266 (M+).
Anal. C, H, N.
1
2-aminopyridine; needles; mp 148-149 °C; H NMR (CDCl3)
δ 9.08 (d, J ) 7.0 Hz, 1 H, H-6), 7.98 (dd, J ) 7.5, 1.5 Hz, 1 H,
H-6′), 7.78 (d, J ) 7.0 Hz, 1 H, H-9), 7.74 (t, J ) 7.0 Hz, 1 H,
H-8), 7.44 (td, J ) 7.5, 1.5 Hz, 1 H, H-4′), 7.15 (s, 1 H, H-3),
7.14 (t, J ) 7.5 Hz, 1 H, H-5′), 7.12 (t, J ) 7.0 Hz, 1 H, H-7),
2-(3′-Met h oxyp h en yl)-6,8-d im et h ylp yr id o[1,2-a ]p yr i-
m id in -4-on e (16): obtained from ethyl (3′-methoxybenzoyl)-
acetate and 2-amino-4,6-dimethylpyridine; prisms, mp 139-

2272 J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 14
Chen et al.
1
140 °C; H NMR (CDCl3) δ 7.61 (br s, 1 H, H-2′), 7.60 (d, J )
H, H2-3′,5′), 6.99 (dd, J ) 7.3, 2.0 Hz, 1 H, H-7), 6.80 (s, 1 H,
H-3), 2.52 (s, 3 H, CH3-8); MS m/ z 254 (M+). Anal. C, H, N.
2-(4′-F lu or op h en yl)-7-m eth ylp yr id o[1,2-a ]p yr im id in -4-
on e (26): obtained from ethyl (4′-fluorobenzoyl)acetate and
2-amino-5-picoline; amorphous; mp 174-175 °C; 1H NMR
(CDCl3) δ 8.89 (s, 1 H, H-6), 8.10 (dd, J ) 8.8, 5.7 Hz, 2 H,
H2-2′,6′), 7.67 (d, J ) 9.0 Hz, 1 H, H-9), 7.63 (dd, J ) 9.0, 2.0
Hz, 1 H, H-8), 7.19 (t, J ) 8.8 Hz, 2 H, H2-3′,5′), 6.85 (s, 1 H,
H-3), 2.46 (s, 3 H, CH3-7); MS m/ z 254 (M+). Anal. C, H, N.
2-(4′-F lu or op h en yl)-6-m eth ylp yr id o[1,2-a ]p yr im id in -4-
on e (27): obtained from ethyl (4′-fluorobenzoyl)acetate and
2-amino-6-picoline; prisms; mp 179-181 °C; 1H NMR (CDCl3)
δ 8.07 (dd, J ) 8.8, 5.2 Hz, 2 H, H2-2′,6′), 7.48 (dd, J ) 8.5, 2.0
Hz, 1 H, H-9), 7.44 (dd, J ) 8.5, 6.5 Hz, 1 H, H-8), 7.17 (t, J )
8.8 Hz, 2 H, H2-3′,5′), 6.67 (s, 1 H, H-3), 6.64 (dd, J ) 6.5, 2.0
Hz, 1 H, H-7), 3.09 (s, 3 H, CH3-6); MS m/ z 254 (M+). Anal.
C, H, N.
2-(4′-F lu or op h en yl)-6,8-d im eth ylp yr id o[1,2-a ]p yr im i-
d in -4-on e (28): obtained from ethyl (3′-fluorobenzoyl)acetate
and 2-amino-4,6-dimethylpyridine; prisms; mp 199-201 °C;
1H NMR (CDCl3) δ 8.05 (dd, J ) 8.7, 5.3 Hz, 2 H, H2-2′, 6′),
7.27 (br s, 1 H, H-9), 7.16 (t, J ) 8.7 Hz, 2 H, H2-3′,5′), 6.61 (s,
1 H, H-3), 6.51 (br s, 1 H, H-7), 3.06 (s, 3 H, CH3-6), 2.36 (s, 3
H, CH3-8); MS m/ z 268 (M+). Anal. C, H, N.
7.5, Hz, 1 H, H-6′), 7.38 (t, J ) 7.5 Hz, 1 H, H-5′), 7.28 (br s,
1 H, H-9), 7.01 (dd, J ) 7.5, 2.0 Hz, 1 H, H-4′), 6.64 (s, 1 H,
H-3), 6.49 (br s, 1 H, H-7), 3.89 (s, 3 H, OCH3-3′), 3.05 (s, 3 H,
CH3-6), 2.34 (s, 3 H, CH3-8); MS m/ z 280 (M+). Anal. C, H,
N.
2-(3′-Meth oxyp h en yl)-7-ch lor op yr id o[1,2-a ]p yr im id in -
4-on e (17): obtained from ethyl (3′-methoxybenzoyl)acetate
and 2-amino-5-chloropyridine; needles; mp 172-173 °C; 1H
NMR (CDCl3) δ 9.08 (d, J ) 1.5 Hz, 1 H, H-6), 7.67 (br d, 1 H,
H-2′), 7.66 (d, J ) 10.0 Hz, 1 H, H-8), 7.65 (d, J ) 10.0 Hz, 1
H, H-9), 7.63 (d, J ) 7.7 Hz, 1 H, H-4′), 7.41 (t, J ) 7.7, Hz, 1
H, H-5′), 7.05 (dd, J ) 7.7, 2.0 Hz, 1 H, H-6′), 6.92 (s, 1 H,
H-3), 3.91 (s, 3 H, OCH3-3′); MS m/ z 286 (M+). Anal. C, H,
N.
2-(3′-Meth oxyp h en yl)-7-br om op yr id o[1,2-a ]p yr im id in -
4-on e (18): obtained from ethyl (3′-methoxybenzoyl)acetate
and 2-amino-5-bromopyridine; needles; mp 197-198 °C; 1H
NMR (CDCl3) δ 8.19 (d, J ) 2.0 Hz, 1 H, H-6), 7.77 (dd, J )
9.5, 2.0 Hz, 1 H, H-8), 7.64 (br s, 1 H, H-2′), 7.63 (d, J ) 7.7
Hz, 1 H, H-4′), 7.62 (dd, J ) 9.0, 2.0 Hz, 1 H, H-9), 7.42 (t, J
) 7.7, Hz, 1 H, H-5′), 7.05 (dd, J ) 7.7, 2.0 Hz, 1 H, H-6′), 6.93
(s, 1 H, H-3), 3.91 (s, 3 H, OCH3-3′); MS m/ z 330 (M+, 97),
332 (M+ + 2, 92). Anal. C, H, N.
2-(4′-Me t h oxyp h e n yl)p yr id o[1,2-a ]p yr im id in -4-on e
(19): obtained from ethyl (4′-methoxybenzoyl)acetate and
2-aminopyridine; needles; mp 153-154 °C; H NMR (CDCl3)
2-(4′-F lu or op h en yl)-7-ch lor op yr id o[1,2-a ]p yr im id in -4-
on e (29): obtained from ethyl (4′-fluorobenzoyl)acetate and
1
1
2-amino-5-chloropyridine; prisms; mp 187-189 °C; H NMR
δ 9.07 (d, J ) 7.2 Hz, 1 H, H-6), 8.09 (d, J ) 9.0 Hz, 2 H,
H2-2′, 6′), 7.76 (d, J ) 4.0 Hz, 2 H, H2-8, 9), 7.12 (dd, J ) 7.2,
4.0 Hz, 1 H, H-7), 7.04 (d, J ) 9.0 Hz, 2 H, H2-3′, 5′), 6.88 (s,
1 H, H-3), 3.90 (s, 3 H, OCH3-4′); MS m/ z 252 (M+). Anal. C,
H, N.
2-(4′-Meth oxyp h en yl)-8-m eth ylp yr id o[1,2-a ]p yr im id in -
4-on e (20): obtained from ethyl (4′-methoxybenzoyl)acetate
and 2-amino-4-picoline; needles; mp 167-168 °C; 1H NMR
(CDCl3) δ 8.96 (d, J ) 7.2 Hz, 1 H, H-6), 8.08 (d, J ) 8.8 Hz,
2 H, H2-2′,6′), 7.55 (br s, 1 H, H-9), 7.02 (d, J ) 8.8 Hz, 2 H,
H2-3′,5′), 6.96 (dd, J ) 7.2, 1.7 Hz, 1 H, H-7), 6.79 (s, 1 H,
H-3), 3.89 (s, 3 H, OCH3-4′), 2.51 (s, 3 H, CH3-8); MS m/ z 266
(M+). Anal. C, H, N.
(CDCl3) δ 9.09 (s, 1 H, H-6), 8.10 (dd, J ) 8.7, 5.6 Hz, 2 H,
H2-2′,6′), 7.70 (dd, J ) 9.0, 2.0 Hz, 1 H, H-8), 7.67 (d, J ) 9.0
Hz, 1 H, H-9), 7.20 (t, J ) 8.7 Hz, 2 H, H2-3′,5′), 6.89 (s, 1 H,
H-3); MS m/ z 274 (M+). Anal. C, H, N.
2-(4′-C h lo r o p h e n y l)p y r id o [1,2-a ]p y r im id in -4-o n e
(30): obtained from ethyl (4′-chlorobenzoyl)acetate and 2-ami-
1
nopyridine; amorphous; mp 202-203 °C; H NMR (CDCl3) δ
9.10 (d, J ) 7.0 Hz, 1 H, H-6), 8.07 (d, J ) 8.5 Hz, 2 H, H2-
2′,6′), 7.90 (d, J ) 9.0 Hz, 1 H, H-9), 7.83 (dd, J ) 9.0, 6.5 Hz,
1 H, H-8), 7.50 (d, J ) 8.5 Hz, 2 H, H2-3′,5′), 7.21 (dd, J ) 7.0,
6.5 Hz, 1 H, H-7), 6.88 (s, 1 H, H-3); MS m/ z 256 (M+). Anal.
C, H, N.
2-(4′-Ch lor op h en yl)-8-m et h ylp yr id o[1,2-a ]p yr im id in -
4-on e (31): obtained from ethyl (4′-chlorobenzoyl)acetate and
2-amino-4-picoline; needles; mp 211-213 °C; 1H NMR (CDCl3)
δ 8.98 (d, J ) 7.3 Hz, 1 H, H-6), 8.04 (d, J ) 8.5 Hz, 2 H,
H2-2′,6′), 7.56 (br s, 1 H, H-9), 7.48 (d, J ) 8.5 Hz, 2 H, H2-
3′,5′), 7.00 (dd, J ) 7.3, 1.0 Hz, 1 H, H-7), 6.81 (s, 1 H, H-3),
2.53 (s, 3 H, CH3-8); MS m/ z 270 (M+). Anal. C, H, N.
2-(4′-Ch lor op h en yl)-7-m et h ylp yr id o[1,2-a ]p yr im id in -
4-on e (32): obtained from ethyl (4′-chlorobenzoyl)acetate and
2-amino-5-picoline; needles; mp 195-196 °C; 1H NMR (CDCl3)
δ 8.90 (s, 1 H, H-6), 8.05 (d, J ) 8.6 Hz, 2 H, H2-2′,6′), 7.77 (d,
J ) 8.9 Hz, 1 H, H-9), 7.67 (dd, J ) 8.9, 1.5 Hz, 1 H, H-8),
7.48 (d, J ) 8.6 Hz, 2 H, H2-3′,5′), 6.86 (s, 1 H, H-3), 2.47 (s, 3
H, CH3-7); MS m/ z 270 (M+). Anal. C, H, N.
2-(4′-Ch lor op h en yl)-6-m et h ylp yr id o[1,2-a ]p yr im id in -
4-on e (33): obtained from ethyl (4′-chlorobenzoyl)acetate and
2-amino-6-picoline; needles; mp 154-156 °C; 1H NMR (CDCl3)
δ 8.02 (d, J ) 8.5 Hz, 2 H, H2-2′,6′), 7.51 (d, J ) 8.5 Hz, 1 H,
H-9), 7.47 (d, J ) 8.5 Hz, 2 H, H2-3′,5′), 7.46 (dd, J ) 8.5, 6.3
Hz, 1 H, H-8), 6.69 (s, 1 H, H-3), 6.67 (d, J ) 6.3 Hz, 1 H,
H-7), 3.09 (s, 3 H, CH3-6); MS m/ z 266 (M+). Anal. C, H, N.
2-(4′-Ch lor op h en yl)-6,8-d im eth ylp yr id o[1,2-a ]p yr im i-
d in -4-on e (34): obtained from ethyl (3′-chlorobenzoyl)acetate
and 2-amino-4,6-dimethylpyridine; needles; mp 210-212 °C
dec; 1H NMR (CDCl3) δ 8.01 (d, J ) 8.5 Hz, 2 H, H2-2′,6′), 7.46
(d, J ) 8.5 Hz, 2 H, H2-3′,5′), 7.27 (s, 1 H, H-9), 6.61 (s, 1 H,
H-3), 6.57 (s, 1 H, H-7), 3.07 (s, 3 H, CH3-6), 2.39 (s, 3 H, CH3-
8); MS m/ z 284 (M+). Anal. C, H, N.
2-(4′-Meth oxyp h en yl)-7-m eth ylp yr id o[1,2-a ]p yr im id in -
4-on e (21): obtained from ethyl (4′-methoxybenzoyl)acetate
and 2-amino-5-picoline; prisms; mp 197-198 °C; 1H NMR
(CDCl3) δ 8.87 (s, 1 H, H-6), 8.07 (d, J ) 8.8 Hz, 2 H, H2-2′,6′),
7.67 (d, J ) 9.0 Hz, 1 H, H-9), 7.60 (dd, J ) 9.0, 2.0 Hz, 1 H,
H-8), 7.02 (d, J ) 8.8 Hz, 2 H, H2-3′,5′), 6.85 (s, 1 H, H-3), 3.89
(s, 3 H, OCH3-4′), 2.44 (s, 3 H, CH3-7); MS m/ z 266 (M+). Anal.
C, H, N.
2-(4′-Meth oxyp h en yl)-6-m eth ylp yr id o[1,2-a ]p yr im id in -
4-on e (22): obtained from ethyl (4′-methoxybenzoyl)acetate
and 2-amino-6-picoline; prisms; mp 143-144 °C; 1H NMR
(CDCl3) δ 8.05 (d, J ) 9.0 Hz, 2 H, H2-2′,6′), 7.48 (dd, J ) 8.7,
1.4 Hz, 1 H, H-9), 7.42 (dd, J ) 6.8, 8.7 Hz, 1 H, H-8), 7.00 (d,
J ) 9.0 Hz, 2 H, H2-3′,5′), 6.67 (s, 1 H, H-3), 6.62 (d, J ) 6.8
Hz, 1 H, H-7), 3.88 (s, 3 H, OCH3-4′), 3.08 (s, 3 H, CH3-6); MS
m/ z 266 (M+). Anal. C, H, N.
2-(4′-Met h oxyp h en yl)-6,8-d im et h ylp yr id o[1,2-a ]p yr i-
m id in -4-on e (23): obtained from ethyl (3′-methoxybenzoyl)-
acetate and 2-amino-4,6-dimethylpyridine; amorphous; mp
1
187-188 °C; H NMR (CDCl3) δ 8.03 (d, J ) 9.0 Hz, 2 H, H2-
2′, 6′), 7.28 (br s, 1 H, H-9), 7.00 (d, J ) 9.0 Hz, 2 H, H2-3′,5′),
6.60 (s, 1 H, H-3), 6.48 (br s, 1 H, H-7), 3.88 (s, 3 H, OCH3-4′),
3.06 (s, 3 H, CH3-6), 2.35 (s, 3 H, CH3-8); MS m/ z 280 (M+).
Anal. C, H, N.
2-(4′-F lu o r o p h e n y l)p y r id o [1,2-a ]p y r im id in -4-o n e
(24): obtained from ethyl (4′-fluorobenzoyl)acetate and 2-ami-
nopyridine; needles; mp 193-195 °C; 1H NMR (CDCl3) δ 9.08
(d, J ) 7.2 Hz, 1 H, H-6), 8.12 (dd, J ) 8.8, 5.2 Hz, 2 H, H2-
2′,6′), 7.79 (dd, J ) 9.0, 1.5 Hz, 1 H, H-9), 7.75 (dd, J ) 9.0,
6.5 Hz, 1 H, H-8), 7.20 (t, J ) 8.8 Hz, 2 H, H2-3′,5′), 6.88 (s, 1
H, H-3); MS m/ z 240 (M+). Anal. C, H, N.
2-(4′-F lu or op h en yl)-8-m eth ylp yr id o[1,2-a ]p yr im id in -4-
on e (25): obtained from ethyl (4′-fluorobenzoyl)acetate and
2-amino-4-picoline; amorphous; mp 191-193 °C; 1H NMR
(CDCl3) δ 8.97 (d, J ) 7.3 Hz, 1 H, H-6), 8.10 (dd, J ) 8.8, 5.7
Hz, 2 H, H2-2′,6′), 7.53 (br s, 1 H, H-9), 7.19 (t, J ) 8.8 Hz, 2
2-(4′-Meth ylp h en yl)-8-m eth ylp yr id o[1,2-a ]p yr im id in -
4-on e (35): obtained from ethyl (4′-methylbenzoyl)acetate and
2-amino-4-picoline; prisms; mp 176-177 °C; 1H NMR (CDCl3)
δ 8.96 (d, J ) 7.3 Hz, 1 H, H-6), 7.99 (d, J ) 8.2 Hz, 2 H,
H2-2′,6′), 7.54 (br s, 1 H, H-9), 7.31 (d, J ) 8.2 Hz, 2 H, H2-
3′,5′), 6.96 (dd, J ) 7.3, 1.5 Hz, 1 H, H-7), 6.83 (s, 1 H, H-3),
2.50 (s, 3 H, CH3-8), 2.43 (s, 3 H, CH3-4′); MS m/ z 250 (M+).
Anal. C, H, N.

2′,3′,4′,5,6,7-Substituted 2-Phenyl-1,8-naphthyridin-4-ones
J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 14 2273
2-(4′-Meth ylp h en yl)-7-m eth ylp yr id o[1,2-a ]p yr im id in -
4-on e (36): obtained from ethyl (4′-methylbenzoyl)acetate and
2-amino-5-picoline; prisms; mp 171-172 °C; 1H NMR (CDCl3)
δ 8.88 (s, 1 H, H-6), 7.99 (d, J ) 8.2 Hz, 2 H, H2-2′,6′), 7.68 (d,
J ) 9.0 Hz, 1 H, H-9), 7.60 (dd, J ) 9.0, 2.0 Hz, 1 H, H-8),
7.31 (d, J ) 8.2 Hz, 2 H, H2-3′,5′), 6.88 (s, 1 H, H-3), 2.44 (s, 3
H, CH3-7), 2.43 (s, 3 H, CH3-4′); MS m/ z 250 (M+). Anal. C,
H, N.
2-(4′-Meth ylp h en yl)-6-m eth ylp yr id o[1,2-a ]p yr im id in -
4-on e (37): obtained from ethyl (4′-methylbenzoyl)acetate and
2-amino-6-picoline; prisms; mp 140-141 °C; 1H NMR (CDCl3)
δ 7.97 (d, J ) 8.2 Hz, 2 H, H2-2′,6′), 7.50 (d, J ) 8.3 Hz, 1 H,
H-9), 7.42 (dd, J ) 8.3, 6.5 Hz, 1 H, H-8), 7.30 (d, J ) 8.2 Hz,
2 H, H2-3′,5′), 6.71 (s, 1 H, H-3), 6.64 (d, J ) 6.5 Hz, 1 H, H-7),
3.08 (s, 3 H, CH3-6), 2.42 (s, 3 H, CH3-4′); MS m/ z 250 (M+).
Anal. C, H, N.
2-(4′-Meth ylp h en yl)-6,8-d im eth ylp yr id o[1,2-a ]p yr im i-
d in -4-on e (38): obtained from ethyl (3′-methylbenzoyl)acetate
and 2-amino-4,6-dimethylpyridine; amorphous; mp 196-198
°C; 1H NMR (CDCl3) δ 7.95 (d, J ) 8.2 Hz, 2 H, H2-2′,6′), 7.30
(s, 1 H, H-9), 7.29 (d, J ) 9.0 Hz, 2 H, H2-3′,5′), 6.64 (s, 1 H,
H-3), 6.49 (s, 1 H, H-7), 3.06 (s, 3 H, CH3-6), 2.42 (s, 3 H, CH3-
4′), 2.35 (s, 3 H, CH3-8); MS m/ z 264 (M+). Anal. C, H, N.
2-(2′-Meth oxyp h en yl)-1,8-n a p h th yr id in -4-on e (39): ob-
tained from compound 7; plates; 1H NMR (CDCl3) δ 8.65 (d, J
) 8.0 Hz, 1 H, H-5), 8.62 (d, J ) 4.5 Hz, 1 H, H-7), 7.64 (dd,
J ) 8.0, 1.7 Hz, 1 H, H-6′), 7.49 (td, J ) 8.0, 1.7 Hz, 1 H, H-4′),
7.34 (dd, J ) 8.0, 4.5 Hz, 1 H, H-6), 7.10 (t, J ) 8.0 Hz, 1 H,
H-5′), 7.06 (d, J ) 8.0 Hz, 1 H, H-3′), 6.62 (s, 1 H, H-3), 3.94
(s, 3 H, OCH3-2′); MS m/ z 252 (M+). Anal. C, H, N.
2-(2′-Me t h oxyp h e n yl)-5-m e t h yl-1,8-n a p h t h yr id in -4-
on e (40): obtained from compound 8; needles; 1H NMR
(CDCl3) δ 10.45 (br s, 1 H, NH-1), 8.19 (d, J ) 5.0 Hz, 1 H,
H-7), 7.65 (dd, J ) 7.5, 1.0 Hz, 1 H, H-6′), 7.50 (td, J ) 7.5,
1.0 Hz, 1 H, H-4′), 7.13 (t, J ) 7.5 Hz, 1 H, H-5′), 7.04 (d, J )
7.5 Hz, 1 H, H-3′), 6.98 (d, J ) 5.0 Hz, 1 H, H-6), 6.56 (s, 1 H,
H-3), 3.89 (s, 3 H, OCH3-2′), 2.99 (s, 3 H, CH3-5); MS m/ z 266
(M+). Anal. C, H, N.
2-(2′-Me t h oxyp h e n yl)-6-m e t h yl-1,8-n a p h t h yr id in -4-
on e (41): obtained from compound 9; needles; 1H NMR
(CDCl3) δ 11.19 (br s, 1 H, NH-1), 8.48 (d, J ) 1.8 Hz, 1 H,
H-5), 8.01 (d, J ) 1.8 Hz, 1 H, H-7), 7.62 (dd, J ) 8.0, 1.7 Hz,
1 H, H-6′), 7.52 (td, J ) 8.0, 1.7 Hz, 1 H, H-4′), 7.13 (t, J ) 8.0
Hz, 1 H, H-5′), 7.01 (d, J ) 8.0 Hz, 1 H, H-3′), 6.59 (s, 1 H,
H-3), 3.78 (s, 3 H, OCH3-2′), 2.40 (s, 3 H, CH3-6); MS m/ z 266
(M+). Anal. C, H, N.
2-(2′-Me t h oxyp h e n yl)-7-m e t h yl-1,8-n a p h t h yr id in -4-
on e (42): obtained from compound 10; needles; 1H NMR
(CDCl3) δ 10.66 (br s, 1 H, NH-1), 8.57 (d, J ) 8.0 Hz, 1 H,
H-5), 7.63 (dd, J ) 7.5, 1.5 Hz, 1 H, H-6′), 7.49 (td, J ) 7.5,
1.5 Hz, 1 H, H-4′), 7.15 (d, J ) 8.0 Hz, 1 H, H-6), 7.12 (t, J )
7.5 Hz, 1 H, H-5′), 6.95 (d, J ) 7.5 Hz, 1 H, H-3′), 6.59 (s, 1 H,
H-3), 3.73 (s, 3 H, OCH3-2′), 2.42 (s, 3 H, CH3-7); MS m/ z 266
(M+). Anal. C, H, N.
2-(2′-Meth oxyp h en yl)-5,7-d im eth yl-1,8-n a p h th yr id in -
4-on e (43): obtained from compound 11; prisms; 1H NMR
(CDCl3) δ 7.62 (dd, J ) 7.5, 1.5 Hz, 1 H, H-6′), 7.47 (td, J )
7.5, 1.5 Hz, 1 H, H-4′), 7.10 (t, J ) 7.5 Hz, 1 H, H-5′), 6.95 (d,
J ) 7.5 Hz, 1 H, H-3′), 6.84 (s, 1 H, H-6), 6.50 (s, 1 H, H-3),
3.77 (s, 3 H, OCH3-2′), 2.95 (s, 3 H, CH3-5), 2.35 (s, 3 H, CH3-
7); MS m/ z 280 (M+). Anal. C, H, N.
2-(3′-Meth oxyp h en yl)-1,8-n a p h th yr id in -4-on e (44): ob-
tained from compound 12; amorphous; 1H NMR (CDCl3) δ
11.10 (br s, 1 H, NH-1), 8.70 (dd, J ) 8.0, 1.5 Hz, 1 H, H-5),
8.10 (dd, J ) 4.5, 1.5 Hz, 1 H, H-7), 7.45 (t, J ) 8.0 Hz, 1 H,
H-5′), 7.31 (d, J ) 8.0, Hz, 1 H, H-6′), 7.26 (br s, 1 H, H-2′),
7.24 (dd, J ) 8.0, 4.5 Hz, 1 H, H-6), 7.10 (dd, J ) 8.0, 2.0 Hz,
1 H, H-4′), 6.60 (s, 1 H, H-3), 3.85 (s, 3 H, OCH3-3′); MS m/ z
252 (M+). Anal. C, H, N.
3.85 (s, 3 H, OCH3-3′), 2.97 (s, 3 H, CH3-5); MS m/ z 266 (M+).
Anal. C, H, N.
2-(3′-Me t h oxyp h e n yl)-6-m e t h yl-1,8-n a p h t h yr id in -4-
1
on e (46): obtained from compound 14; amorphous; H NMR
(CDCl3) δ 10.75 (s, 1 H, NH-1), 8.49 (d, J ) 2.0 Hz, 1 H, H-5),
8.00 (d, J ) 2.0 Hz, 1 H, H-7), 7.46 (t, J ) 8.0 Hz, 1 H, H-5′),
7.29 (d, J ) 8.0 Hz, 1 H, H-6′), 7.23 (t, J ) 1.8 Hz, 1 H, H-2′),
7.11 (dd, J ) 8.0, 1.8 Hz, 1 H, H-4′), 6.58 (s, 1 H, H-3), 3.85 (s,
3 H, OCH3-3′), 2.39 (s, 3 H, CH3-6); MS m/ z 266 (M+). Anal.
C, H, N.
2-(3′-Me t h oxyp h e n yl)-7-m e t h yl-1,8-n a p h t h yr id in -4-
1
on e (47): obtained from compound 15; amorphous; H NMR
(CDCl3) δ 9.13 (br s, 1 H, NH-1), 8.57 (d, J ) 8.0 Hz, 1 H,
H-5), 7.45 (t, J ) 8.0 Hz, 1 H, H-5′), 7.26 (d, J ) 8.0 Hz, 1 H,
H-6′), 7.21 (d, J ) 8.0 Hz, 1 H, H-6), 7.20 (s, 1 H, H-2′), 7.08
(d, J ) 8.0 Hz, 1 H, H-4′), 6.60 (s, 1 H, H-3), 3.88 (s, 3 H, OCH3-
3′), 2.60 (s, 3 H, CH3-7); MS m/ z 266 (M+). Anal. C, H, N.
2-(3′-Meth oxyp h en yl)-5,7-d im eth yl-1,8-n a p h th yr id in -
4-on e (48): obtained from compound 16; prisms; 1H NMR
(CDCl3) δ 9.42 (br s, 1 H, NH-1), 7.40 (t, J ) 8.0 Hz, 1 H, H-5′),
7.22 (d, J ) 8.0 Hz, 1 H, H-6′), 7.15 (t, J ) 2.0 Hz, 1 H, H-2′),
7.05 (dd, J ) 8.0, 2.0 Hz, 1 H, H-4′), 6.88 (s, 1 H, H-6), 6.50 (s,
1 H, H-3), 3.83 (s, 3 H, OCH3-3′), 2.94 (s, 3 H, CH3-5), 2.40 (s,
3 H, CH3-7); MS m/ z 280 (M+). Anal. C, H, N.
2-(3′-Me t h oxyp h e n yl)-6-ch lor o-1,8-n a p h t h yr id in -4-
on e (49): obtained from compound 17; needles; 1H NMR
(DMSO-d6) δ 12.57 (s, 1 H, NH-1), 8.85 (d, J ) 2.7 Hz, 1 H,
H-5), 8.44 (d, J ) 2.0 Hz, 1 H, H-7), 7.47 (t, J ) 8.0 Hz, 1 H,
H-5′), 7.41 (d, J ) 8.0 Hz, 1 H, H-6′), 7.41 (br s, 1 H, H-2′),
7.13 (br d, J ) 8.0, Hz, 1 H, H-4′), 6.49 (s, 1 H, H-3), 3.87 (s,
3 H, OCH3-3′); MS m/ z 286 (M+). Anal. C, H, N.
2-(3′-Me t h oxyp h e n yl)-6-b r om o-1,8-n a p h t h yr id in -4-
1
on e (50): obtained from compound 18; amorphous; H NMR
(DMSO-d6) δ 12.54 (s, 1 H, NH-1), 8.90 (d, J ) 2.3 Hz, 1 H,
H-5), 8.55 (d, J ) 2.3 Hz, 1 H, H-7), 7.46 (t, J ) 7.8 Hz, 1 H,
H-5′), 7.42 (d, J ) 7.8 Hz, 1 H, H-6′), 7.41 (s, 1 H, H-2′), 7.12
(br d, J ) 7.8 Hz, 1 H, H-4′), 6.49 (s, 1 H, H-3), 3.87 (s, 3 H,
OCH3-3′); MS m/ z 330 (M+, 100), 332 (M+ + 2, 94). Anal. C,
H, N.
2-(4′-Meth oxyp h en yl)-1,8-n a p h th yr id in -4-on e (51): ob-
tained from compound 19; plates; 1H NMR (CDCl3) δ 8.69 (dd,
J ) 8.0, 2.0 Hz, 1 H, H-5), 8.35 (dd, J ) 5.2, 2.0 Hz, 1 H, H-7),
7.70 (d, J ) 8.8 Hz, 2 H, H2-2′,6′), 7.30 (dd, J ) 8.0, 5.2 Hz, 1
H, H-6), 7.06 (d, J ) 8.8 Hz, 2 H, H2-3′,5′), 6.61 (s, 1 H, H-3),
3.91 (s, 3 H, OCH3-4′); MS m/ z 252 (M+). Anal. C, H, N.
2-(4′-Me t h oxyp h e n yl)-5-m e t h yl-1,8-n a p h t h yr id in -4-
on e (52): obtained from compound 20; plates; 1H NMR
(CDCl3) δ 8.09 (d, J ) 4.8 Hz, 1 H, H-7), 7.67 (d, J ) 8.8 Hz,
2 H, H2-2′,6′), 7.05 (d, J ) 8.8 Hz, 2 H, H2-3′,5′), 6.98 (d, J )
4.8 Hz, 1 H, H-6), 6.51 (s, 1 H, H-3), 3.90 (s, 3 H, OCH3-4′),
2.98 (s, 3 H, CH3-5); MS m/ z 266 (M+). Anal. C, H, N.
2-(4′-Me t h oxyp h e n yl)-6-m e t h yl-1,8-n a p h t h yr id in -4-
1
on e (53): obtained from compound 21; amorphous; H NMR
(CDCl3) δ 8.50 (s, 1 H, H-5), 8.30 (s, 1 H, H-7), 7.69 (d, J ) 8.7
Hz, 2 H, H2-2′, 6′), 7.07 (d, J ) 8.7 Hz, 2 H, H2-3′, 5′), 6.63 (s,
1 H, H-3), 3.90 (s, 3 H, OCH3-4′), 2.45 (s, 3 H, CH3-6); MS m/ z
266 (M+). Anal. C, H, N.
2-(4′-Me t h oxyp h e n yl)-7-m e t h yl-1,8-n a p h t h yr id in -4-
1
on e (54): obtained from compound 22; amorphous; H NMR
(CDCl3) δ 8.60 (d, J ) 8.0 Hz, 1 H, H-5), 7.68 (d, J ) 8.8 Hz,
2 H, H2-2′,6′), 7.23 (d, J ) 8.0 Hz, 1 H, H-6), 7.07 (d, J ) 8.8
Hz, 2 H, H2-3′,5′), 6.61 (s, 1 H, H-3), 3.90 (s, 3 H, OCH3-4′),
2.67 (s, 3 H, CH3-7); MS m/ z 266 (M+). Anal. C, H, N.
2-(4′-Meth oxyp h en yl)-5,7-d im eth yl-1,8-n a p h th yr id in -
4-on e (55): obtained from compound 23; amorphous; 1H NMR
(CDCl3) δ 7.62 (d, J ) 8.8 Hz, 2 H, H2-2′,6′), 7.02 (d, J ) 8.8
Hz, 2 H, H2-3′,5′), 6.89 (s, 1 H, H-6), 6.48 (s, 1 H, H-3), 3.88 (s,
3 H, OCH3-4′), 2.94 (s, 3 H, CH3-5), 2.47 (s, 3 H, CH3-7); MS
m/ z 280 (M+). Anal. C, H, N.
2-(3′-Me t h oxyp h e n yl)-5-m e t h yl-1,8-n a p h t h yr id in -4-
on e (45): obtained from compound 13; plates; 1H NMR
(CDCl3) δ 10.74 (br s, 1 H, NH-1), 7.84 (d, J ) 5.0 Hz, 1 H,
H-7), 7.43 (t, J ) 8.0 Hz, 1 H, H-5′), 7.29 (d, J ) 8.0 Hz, 1 H,
H-6′), 7.22 (t, J ) 2.5 Hz, 1 H, H-2′), 7.09 (dd, J ) 8.0, 2.5 Hz,
1 H, H-4′), 6.93 (d, J ) 5.0 Hz, 1 H, H-6), 6.52 (s, 1 H, H-3),
2-(4′-F lu or op h en yl)-1,8-n a p h th yr id in -4-on e (56): ob-
tained from compound 24; prisms; 1H NMR (CDCl3) δ 8.66 (dd,
J ) 7.9, 1.5 Hz, 1 H, H-5), 8.62 (dd, J ) 4.5, 1.5 Hz, 1 H, H-7),
7.74 (dd, J ) 8.5, 5.0 Hz, 2 H, H2-2′,6′), 7.36 (dd, J ) 8.0, 4.5
Hz, 1 H, H-6), 7.23 (d, J ) 8.5 Hz, 2 H, H2-3′,5′), 6.56 (s, 1 H,
H-3); MS m/ z 240 (M+). Anal. C, H, N.

2274 J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 14
2-(4′-F lu or op h en yl)-5-m et h yl-1,8-n a p h t h yr id in -4-on e
Chen et al.
Hz, 1 H, H-6), 6.59 (s, 1 H, H-3), 2.57 (s, 3 H, CH3-7), 2.44 (s,
1
(57): obtained from compound 25; needles; H NMR (CDCl3)
3 H, CH3-4′); MS m/ z 250 (M+). Anal. C, H, N.
δ 8.35 (d, J ) 4.7 Hz, 1 H, H-7), 7.71 (dd, J ) 8.5, 5.0 Hz, 2 H,
H2-2′,6′), 7.21 (t, J ) 8.5 Hz, 2 H, H2-3′,5′), 7.04 (d, J ) 4.7
Hz, 1 H, H-6), 6.47 (s, 1 H, H-3), 2.93 (s, 3 H, CH3-5); MS m/ z
254 (M+). Anal. C, H, N.
2-(4′-Meth ylp h en yl)-5,7-d im eth yl-1,8-n a p h th yr id in -4-
on e (70): obtained from compound 38; prisms; 1H NMR
(CDCl3) δ 7.57 (d, J ) 8.1 Hz, 2 H, H2-2′,6′), 7.31 (d, J ) 8.1
Hz, 2 H, H2-3′,5′), 6.89 (s, 1 H, H-6), 6.50 (s, 1 H, H-3), 2.93 (s,
3 H, CH3-5), 2.48 (s, 3 H, CH3-7), 2.44 (s, 3 H, CH3-4′); MS
m/ z 264 (M+). Anal. C, H, N.
2-(4′-F lu or op h en yl)-6-m et h yl-1,8-n a p h t h yr id in -4-on e
1
(58): obtained from compound 26; needles; H NMR (CDCl3)
δ 8.47 (d, J ) 2.0 Hz, 1 H, H-5), 8.45 (br s, 1 H, H-7), 7.73 (dd,
J ) 8.8, 5.2 Hz, 2 H, H2-2′,6′), 7.22 (t, J ) 8.8 Hz, 2 H, H2-
3′,5′), 6.55 (s, 1 H, H-3), 2.46 (s, 3 H, CH3-6); MS m/ z 254 (M+).
Anal. C, H, N.
Cytotoxicity Assa ys. Compounds 7-38 were assayed for
in vitro cytotoxicity with a panel of human and murine tumor
cell lines at the School of Medicine, University of North
Carolina at Chapel Hill, according to procedures described
previously.25 The cell lines include human epidermoid carci-
noma of the nasopharynx (KB), lung carcinoma (A-549),
ileocecal carcinoma (HCT-8), melanoma (PRMI-7951), and
medulloblastoma (TE-671), as well as one murine leukemia
cell line (P-388). Compounds 39-49 and 51-66 were submit-
ted 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 60 human
tumor cell lines.21,22 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 represent the molar drug concentrations required to
cause 50% inhibition or total growth inhibition, respectively.
2-(4′-F lu or op h en yl)-7-m et h yl-1,8-n a p h t h yr id in -4-on e
1
(59): obtained from compound 27; prisms; H NMR (CDCl3)
δ 9.04 (br s, 1 H, NH-1), 8.58 (d, J ) 8.0 Hz, 1 H, H-5), 7.71
(dd, J ) 8.5, 5.0 Hz, 2 H, H2-2′,6′), 7.26 (t, J ) 8.5 Hz, 2 H,
H2-3′,5′), 7.23 (d, J ) 8.0 Hz, 1 H, H-6), 6.55 (s, 1 H, H-3), 2.64
(s, 3 H, CH3-7); MS m/ z 254 (M+). Anal. C, H, N.
2-(4′-F lu or op h en yl)-5,7-d im et h yl-1,8-n a p h t h yr id in -4-
on e (60): obtained from compound 28; prisms; 1H NMR
(CDCl3) δ 8.88 (br s, 1 H, NH-1), 7.68 (dd, J ) 8.7, 5.1 Hz, 2
H, H2-2′,6′), 7.24 (t, J ) 8.7 Hz, 2 H, H2-3′,5′), 6.92 (s, 1 H,
H-6), 6.45 (s, 1 H, H-3), 2.94 (s, 3 H, CH3-5), 2.53 (s, 3 H, CH3-
7); MS m/ z 268 (M+). Anal. C, H, N.
2-(4′-F lu or op h en yl)-6-ch lor o-1,8-n a p h t h yr id in -4-on e
1
(61): obtained from compound 29; prisms; H NMR (DMSO-
d6) δ 12.58 (br s, 1 H, NH-1), 8.85 (d, J ) 2.4 Hz, 1 H, H-5),
8.44 (d, J ) 2.4 Hz, 1 H, H-7), 7.92 (dd, J ) 8.5, 5.5 Hz, 2 H,
H2-2′,6′), 7.40 (t, J ) 8.5 Hz, 2 H, H2-3′,5′), 6.45 (s, 1 H, H-3);
MS m/ z 274 (M+). Anal. C, H, N.
2-(4′-Ch lor op h en yl)-1,8-n a p h th yr id in -4-on e (62): ob-
tained from compound 30; plates; 1H NMR (CDCl3) δ 8.67 (dd,
J ) 4.5, 1.5 Hz, 1 H, H-7), 8.63 (dd, J ) 8.0, 1.5 Hz, 1 H, H-5),
7.68 (d, J ) 8.7 Hz, 2 H, H2-2′,6′), 7.49 (d, J ) 8.8 Hz, 2 H,
H2-3′,5′), 7.37 (dd, J ) 8.0, 4.5 Hz, 1 H, H-6), 6.64 (s, 1 H,
H-3); MS m/ z 256 (M+). Anal. C, H, N.
2-(4′-Ch lor op h en yl)-5-m et h yl-1,8-n a p h t h yr id in -4-on e
(63): obtained from compound 31; amorphous; 1H NMR
(CDCl3) δ 8.36 (d, J ) 5.0 Hz, 1 H, H-7), 7.68 (d, J ) 8.5 Hz,
2 H, H2-2′,6′), 7.49 (d, J ) 8.5 Hz, 2 H, H2-3′,5′), 7.06 (d, J )
5.0 Hz, 1 H, H-6), 6.57 (s, 1 H, H-3), 2.95 (s, 3 H, CH3-5); MS
m/ z 270 (M+). Anal. C, H, N.
Ma ter ia ls for Tu bu lin Bioa ssa ys. Electrophoretically
homogeneous bovine brain tubulin was purified as described
previously.26 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,
podophyllotoxin from Aldrich, and monosodium glutamate
from USB.
Tu bu lin P olym er iza tion Assa y. The tubulin polymeri-
zation assay was performed as described previously.15-17 In
brief, tubulin at 1.2 mg/mL (12 µM) was preincubated for 15
min at 26 °C in a 0.24-mL volume of 0.8 M monosodium
glutamate (pH 6.6 with NaOH in a 2 M stock solution) with
varying drug concentrations. The drug stock solutions were
in DMSO, and the final solvent concentration was 4% (v/v).
All concentrations are in terms of the final reaction volume
(0.25 mL). The reaction mixtures were chilled on ice, and 10
µL of 10 mM GTP was added to each reaction mixture.
Samples were transferred to cuvettes held at 0 °C by an
electronic temperature controller in Gilford spectrophotom-
eters. Baselines were established at 350 nm, and polymeri-
zation was initiated by a temperature jump to 26 °C. The jump
took about 50 s to complete. After 20 min, turbidity readings
were recorded, and the temperature controller was set to 0
°C. When depolymerization was complete, turbidity readings
were again recorded. Generally, turbidity readings were about
90% cold-reversible, and the cold-reversible turbidity was
taken to represent the extent of assembly for each reaction
mixture. IC50 values were obtained graphically from inhibition
of polymerization by different drug concentrations. Four
spectrophotometers were used for each experimental sequence,
with two control reactions (no drug) in each set. Generally,
the control reactions were within 5% of their average, and IC50
values obtained with this polymerization assay are usually
highly reproducible. Generally, standard deviations were
within 20% of the mean values, but in some cases, the standard
deviations were 30-35% of the mean. Therefore, we can
conservatively estimate that a 50% difference in IC50 values
represents a difference in the relative activity of two agents.
2-(4′-Ch lor op h en yl)-6-m et h yl-1,8-n a p h t h yr id in -4-on e
1
(64): obtained from compound 32; needles; H NMR (CDCl3)
δ 8.49 (s, 1 H, H-5), 8.41 (s, 1 H, H-7), 7.66 (d, J ) 8.5 Hz, 2
H, H2-2′,6′), 7.47 (d, J ) 8.5 Hz, 2 H, H2-3′,5′), 6.60 (s, 1 H,
H-3), 2.44 (s, 3 H, CH3-6); MS m/ z 270 (M+). Anal. C, H, N.
2-(4′-Ch lor op h en yl)-7-m et h yl-1,8-n a p h t h yr id in -4-on e
1
(65): obtained from compound 33; needles; H NMR (CDCl3)
δ 8.52 (d, J ) 8.0 Hz, 1 H, H-5), 7.67 (d, J ) 8.5 Hz, 2 H,
H2-2′,6′), 7.49 (d, J ) 8.5 Hz, 2 H, H2-3′,5′), 7.22 (d, J ) 8.0
Hz, 1 H, H-6), 6.60 (s, 1 H, H-3), 2.64 (s, 3 H, CH3-7); MS m/ z
266 (M+). Anal. C, H, N.
2-(4′-Ch lor op h en yl)-5,7-d im et h yl-1,8-n a p h t h yr id in -4-
on e (66): obtained from compound 34; prisms; 1H NMR
(CDCl3) δ 7.66 (d, J ) 8.5 Hz, 2 H, H2-2′,6′), 7.52 (d, J ) 8.5
Hz, 2 H, H2-3′,5′), 6.95 (s, 1 H, H-6), 6.51 (s, 1 H, H-3), 2.96 (s,
3 H, CH3-5), 2.56 (s, 3 H, CH3-7); MS m/ z 284 (M+). Anal. C,
H, N.
2-(4′-Meth ylp h en yl)-5-m eth yl-1,8-n a p h th yr id in -4-on e
1
(67): obtained from compound 35; needles; H NMR (CDCl3)
δ 7.97 (d, J ) 4.9 Hz, 1 H, H-7), 7.61 (d, J ) 8.2 Hz, 2 H,
H2-2′,6′), 7.34 (d, J ) 8.2 Hz, 2 H, H2-3′,5′), 6.95 (d, J ) 4.9
Hz, 1 H, H-6), 6.52 (s, 1 H, H-3), 2.98 (s, 3 H, CH3-5), 2.46 (s,
3 H, CH3-4′); MS m/ z 250 (M+). Anal. C, H, N.
2-(4′-Meth ylp h en yl)-6-m eth yl-1,8-n a p h th yr id in -4-on e
(68): obtained from compound 36; needles; H NMR (CDCl3)
Colch icin e Bin d in g Assa y. The binding of radiolabeled
colchicine to tubulin was measured by the DEAE-cellulose
filter technique, as described previously.15 In brief, each 0.1-
mL reaction mixture contained 0.1 mg (1.0 µM) of tubulin, 1.0
M commercial monosodium glutamate (pH 6.6 with HCl), 1
mM MgCl2, 0.1 mM GTP, 5.0 µM [3H]colchicine, 5% (v/v)
DMSO, and 5.0 µM inhibitor. Incubation was for 20 min at
37 °C. Each reaction mixture was filtered under reduced
vacuum through a stack of two DEAE-cellulose paper filters,
washed with water, and radioactivity quantitated in a liquid
scintillation counter.
1
δ 10.61 (br s, 1H, NH-1), 8.49 (d, J ) 1.5 Hz, 1 H, H-5), 8.00
(d, J ) 1.5 Hz, 1 H, H-7), 7.62 (d, J ) 8.1 Hz, 2 H, H2-2′,6′),
7.36 (d, J ) 8.1 Hz, 2 H, H2-3′,5′), 6.59 (s, 1 H, H-3), 2.47 (s, 3
H, CH3-6), 2.39 (s, 3 H, CH3-4′); MS m/ z 250 (M+). Anal. C,
H, N.
2-(4′-Meth ylp h en yl)-7-m eth yl-1,8-n a p h th yr id in -4-on e
1
(69): obtained from compound 37; needles; H NMR (CDCl3)
δ 8.57 (d, J ) 8.0 Hz, 1 H, H-5), 7.59 (d, J ) 8.2 Hz, 2 H,
H2-2′,6′), 7.33 (d, J ) 8.8 Hz, 2 H, H2-3′,5′), 7.19 (d, J ) 8.0

2′,3′,4′,5,6,7-Substituted 2-Phenyl-1,8-naphthyridin-4-ones
J ournal of Medicinal Chemistry, 1997, Vol. 40, No. 14 2275
(15) Kuo, S. C.; Lee, H. Z.; J uang, J . P.; Lin, Y. T.; Wu, T. S.; Chang,
J . J .; Lednicer, D.; Paull, K. D.; Lin, C. M.; Hamel, E.; Lee, K.
H. Synthesis and cytotoxicity of 1,6,7,8-substituted 2-(4′-
substituted-phenyl)-4-quinolones and related compounds: Iden-
tification as antimitotic agents interacting with tubulin. J . Med.
Chem. 1993, 36, 1146-1156.
Ack n ow led gm en t . This investigation was sup-
ported by a grant from the National Cancer Institute
No. CA-17625 awarded to K. H. Lee.
Refer en ces
(16) Li, L.; Wang, H. K.; Kuo, S. C.; Wu, T. S.; Lednicer, D.; Lin, C.
M.; Hamel, E.; Lee, K. H. Antitumor agents. 150. 2′,3′,4′,5′,5,6,7-
Substituted 2-phenyl-4-quinolones and related compounds: Their
synthesis, cytotoxicity, and inhibition of tubulin polymerization.
J . Med. Chem. 1994, 37, 1126-1135.
(17) Li, L.; Wang, H. K.; Kuo, S. C.; Wu, T. S.; Mauger, A.; Lin, C.
M.; Hamel, E.; Lee, K. H. Antitumor agents. 155. Synthesis and
biological evaluation of 3′, 6,7-substituted 2-phenyl-4-quinolones
as antimicrotubule agents. J . Med. Chem. 1994, 37, 3400-3407.
(18) Chandler, C. J .; Deady, L. W.; Reiss, J . A.; Tzimos, V. The
synthesis of macrocyclic polyether-diesters incorporating 1,10-
phenanthrolino and 1,8-naphthyridino subunits. J . Heterocycl.
Chem. 1982, 19, 1017-1019.
(19) Katagiri, N.; Kato, T. Studies on ketene and its derivatives. Part
119. Reactions of haloketenes with 2-arylideneaminopyridines.
J . Heterocycl. Chem. 1984, 21, 407.
(20) Krapcho, A. P.; Diamanti, J .; Cayen, C.; Bingham, R. 2-Carbe-
thoxycyclooctanone. Org. Synth. 1973, 5, 198-201.
(21) Boyd, M. R. Status of the NCI preclinical antitumor drug
discovery screen. In Cancer: Principles and Practice of Oncology
Updates; De Vita, V. T., Hellman, S., Rosenberg, S. A., Eds.; J .
B. Lippincoft: Philadelphia, 1989; pp 1-12.
(22) Monks, A.; Scudiero, D.; Skehan, P.; Shoemaker, R.; Paull, K.;
Vistica, D.; Hose, C.; Langley, J .; Cronise, P.; Vaigro-Woiff, A.;
Gray-Goodrich, M.; Campbell, H; Mayo, J .; Boyd, M. Feasibility
of a high-flux anticancer drug screen utilizing a derived panel
of human tumor cell lines in culture. J . Natl. Cancer Inst. 1991,
83, 757-766.
(23) Paull, K. D.; Shoemaker, R. H.; Hodes, L.; Monks, A. P.; Scudiero,
D. A.; Rubinstein, L. V.; Plowman, J .; Boyd, M. R. Display and
analysis of patterns of differential activity of drugs against
human tumor cell lines: Development of mean graph and
COMPARE algorithm. J . Natl. Cancer Inst. 1989, 81, 1088-
1092.
(24) Weinstein, J . N.; Kohn, K. W.; Grever, M. R.; Viswanadhan, V.
N.; Rubinstein, L. V.; Monks, A. P.; Scudiero, D. A.; Welch, L.;
Koutsoukos, A. D.; Chiausa, A. J .; Paull K. D. Neural computing
in cancer drug development: Predicting mechanism of action.
Science 1992, 258, 447-451.
(25) Lee, K. H.; Lin, Y. M.; Wu, T. S.; Zhang, D. C.; Yamagish, T.;
Hayashi, T.; Hall, I. H.; Chang, J . J .; Wu, R. Y.; Yang, T. H.
The cytotoxic principles of Prunella vulgaris, Psychotria serpens,
and Hyptis captitata: Ursolic acid and related derivatives.
Planta Medica 1988, 54, 308-312.
(26) Hamel, E.; Lin, C. M. Separation of active tubulin and micro-
tubule-associated proteins by ultracentrifugation and isolation
of a component causing the formation of microtubule bundles.
Biochemistry 1984, 23, 4173-4184.
(1) For another part in this series, see: Bastow, K. F.; Wang, H.
K.; Cheng, Y. C.; Lee, K. H. Antitumor agents. 173. Synthesis
and evaluation of camptothecin-4â-amino-4′-O-demethyl epi-
podophyllotoxin conjugates as inhibitors of mammalian DNA
topoisomerases and as cytotoxic agents. Bioorg. Med. Chem., in
press.
(2) For a review, see: Wordenmam, L.; Mitchison, T. J . Dynamics
of microtubule assembly in vivo. In Microtubules; Hyams, J . S.,
Lloyd, C. W., Eds.; Wiley-Liss, Inc.: New York, 1994; pp 287-
301.
(3) Rowinsky, E. K.; Donehower, R. C. The clinical pharmacology
and use of antimicrotubule agents in cancer chemotherapeutics.
Pharmacol. Ther. 1992, 52, 35-84.
(4) Verwij, J .; Clavel, M.; Chevalier, B. Paclitaxel (Taxol) and
docetaxel (Taxotere): Not simply two of a kind. Ann. Oncol.
1994, 5, 495-505.
(5) Hastie, S. B. Interaction of colchicine with tubulin. Pharmacol.
Ther. 1991, 51, 377-401.
(6) Hamel, E.; Ho, H. H.; Kang, G. J .; Lin, C. M. Cornigerine, a
potent antimitotic Colchicum alkaloid of unusual structure:
Interactions with tubulin. Biochem. Pharmacol. 1988, 37, 2445-
2449.
(7) Kelly, M.; Hartwell, J . The biological effects and the chemical
composition of podophyllin. A Review. J . Natl. Cancer Inst. 1954,
14, 967-1010.
(8) Wang, R. W. J .; Rebhun, L. I.; Kupchan, S. M. Antimitotic and
antitubulin activity of the tumor inhibitor steganacin. Cancer
Res. 1977, 37, 3071-3079.
(9) Lin, C. M.; Ho, H. H.; Pettit, G. R.; Hamel, E. Antimitotic natural
products combretastatin A-4 and combretastatin A-2; studies on
the mechanism of their inhibition of binding of colchicine to
tubulin. Biochemistry 1989, 28, 6984-6991.
(10) Pettit, G. R.; Singh, S. B.; Boyd, M. R.; Hamel E.; Pettit, R. K.;
Schmidt, J . M.; Hogan, F. Antineoplastic agents. 291. Isolation
and synthesis of combretastatins A-4, A-5, and A-6 (1a). J . Med.
Chem. 1995, 38, 1666-1672.
(11) Lin, C. M.; Singh, S. B.; Chu, P. S.; Dempcy, R. O.; Schmidt, J .
M.; Pettit, G. R.; Hamel, E. Interaction of tubulin with potent
natural and synthetic analogs of the antimitotic agents com-
bretastatin, a structure-activity study. Mol. Pharmacol. 1988,
34, 200-208.
(12) Hamel, E. Interactions of tubulin with small ligands. In Micro-
tubule Proteins; Avila, J ., Ed.; CRC Press: Boca Raton, FL, 1990;
pp 89-191.
(13) Lee, K. H. Antineoplastic agents from Chinese Traditional
Medicine and their analogs. In Human Medicinal Agents from
plants; Kingdom, A. D., Balandrin, M., Eds.; American Chemical
Society Symposium Series 534; American Chemical Society:
Washington, DC, 1993; Chapter 12, pp l70-l90.
(14) Shi, Q.; Chen, K.; Li, L.; Chang, J . J .; Autry, C.; Kozuka, M.;
Konoshima, T.; Estes, J . R.; Lin, C. M.; Hamel, E.; McPhail, A.
T.; McPhail, D. R.; Lee, K. H. Antitumor agents, 154. Cytotoxic
and antimitotic flavonols from Polanisia dodecandra. J . Nat.
Prod. 1995, 58, 475-482.
J M960858S