Synthesis and biological evaluation of novel 7-acyl homocamptothecins as Topoisomerase I inhibitors

Article abstract of DOI:10.1016/j.ejmech.2011.03.024

A series of novel 7-acyl derivatives of homocamptothecin (hCPT) were designed and synthesized with the purpose to improve antitumor activity of hCPT, via Minisci free-radical reaction from 10-methoxyhomocamptothecin. All the compounds were evaluated for i

Full text of DOI:10.1016/j.ejmech.2011.03.024

European Journal of Medicinal Chemistry 46 (2011) 2408e2414
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Synthesis and biological evaluation of novel 7-acyl homocamptothecins
as Topoisomerase I inhibitors
1
1
*
Wenfeng Liu , Lingjian Zhu , Wei Guo, Chunlin Zhuang, Yongqiang Zhang, Chunquan Sheng ,
*
Pengfei Cheng, Jianzhong Yao, Wenya Wang, Guoqiang Dong, Shengzheng Wang, Zhenyuan Miao ,
**
Wannian Zhang
School of Pharmacy, Second Military Medical University, 325 Guohe Road, Shanghai 200433, People’s Republic of China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of novel 7-acyl derivatives of homocamptothecin (hCPT) were designed and synthesized with
the purpose to improve antitumor activity of hCPT, via Minisci freeeradical reaction from 10-methox-
yhomocamptothecin. All the compounds were evaluated for in vitro cytotoxicity against three cancer cell
lines (A549, MDA-MB-435 and HCT116). For MDA-MB-435 cell line, compounds, 6a, 6b, 6k and all of 7-
alkylcabonyl homocamptothecin derivatives showed higher in vitro inhibitory activities than topotecan
(TPT). Furthermore, compounds 6d, 6e, and 6k showed highly potent inhibitory activities with the IC50
values from less than 1 nM to 2.2 nM. In Topoisomerase I (Topo I)-induced DNA cleavage assay,
compounds 6a, 6d, and 6k, as compared to CPT, revealed higher Topo I inhibitory activity.
Ó 2011 Elsevier Masson SAS. All rights reserved.
Received 11 January 2011
Received in revised form
7 March 2011
Accepted 13 March 2011
Available online 23 March 2011
Keywords:
Homocamptothecin
Camptothecin
Antitumor activity
Topoisomerase I inhibitor
1. Introduction
undergoes rapid hydrolysis to the biologically inactive carboxylate
form under physiological conditions [6]. Considering that it is the
20(S)-Camptothecin (CPT) [1], a naturally occurring quinoline
alkaloid, was first isolated from the leaves of the Camptotheca
acuminata tree by Wall and Wani in 1966. The molecular target of
CPT is DNA-Topo I, a nuclear enzyme which is required for topo-
logical manipulation of DNA during cellular events such as repli-
cation, transcription and repair. CPT has remarkable antitumoral
and antileukemic activity, and thus became one of the prominent
lead compounds in anticancer drug development. Two of its water-
soluble derivatives, topotecan (Hycamtin) [2] and irinotecan
(Camptosar) [3,4] have been approved by the Food and Drug
Administration (FDA) to treat ovarian cancers and small-cell lung
cancers (SCLC), respectively, and several other analogs are currently
under clinical development at various stages [5]. Although CPT
analogs remain a promising class of antitumor agents, the intrinsic
OH group adjacent to the cyclic carboxylic ester function which
weakens the intrinsic stability of the lactone ring, a novel family of
CPT analogs in which a methylene spacer was inserted between the
carboxylic and alcoholic functions of the E-ring was designed and
synthesized by Lavergne et al in 1997 [7]. This new family of very
active seven-member hydroxylactone derivatives represents a new
promising class of Topo I inhibitors. Among these hCPT derivatives,
9,10-difluoro analog (diflomotecan) is one of the most potent Topo I
inhibitors and was the first hCPT to be selected for clinical trials
(Fig. 1) [8].
Most structural modification of CPT have focused on quinoline
(A/B) ring [9] and achieved many potent antitumor agents of 7-
substituted, 9-substituted and 10-substituted CPT derivatives. From
the structureeactivity relationship (SAR) of CPT [10], it appears that
substituent on position 7 is very important to the activity of the CPT
analogs. The previous studies have also demonstrated that there is
a wide space for substitutions on position 7 of CPT without steric
clash [11]. A number of analogs with substituents on position 7
show enhanced biological profiles [12].
instability of the highly electrophilic a-hydroxylactone of the E-ring
* Corresponding author. Tel./fax: þ86 21 81871233.
** Corresponding author. Tel./fax: þ86 21 81871243.
In our laboratory, a series of analogs with substituent on position
7 of hCPT derivatives have been synthesized and many compounds
showed superior activity comparable to the marketed CPTs [13,14].
E-mail addresses: shengcq@hotmail.com (C. Sheng), miaozhenyuan@hotmail.
com (Z. Miao), zhangwnk@hotmail.com (W. Zhang).
1
These two authors contributed equally to this work.
0223-5234/$ e see front matter Ó 2011 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2011.03.024

W. Liu et al. / European Journal of Medicinal Chemistry 46 (2011) 2408e2414
2409
Fig. 1. Camptothecin, homocamptothecin and representative analogs.
Furthermore, there are many CPTor hCPT derivatives with electron-
donating groups on position 7 such as silatecan and BN80927
(Fig. 2), which have remarkable antitumor activity [15,16]. These
results indicate that CPT or hCPT with a proper electron-donating
substituent on position 7 may have therapeutic advantages [17].
However, Li and co-workers reported that 7-cyclopropylcabonyl-
camptothecin exhibited higher antitumor activities than TPT [18],
which reveals that a proper electron-withdrawing substituent on
position 7 might also achieve high activities. Based on the ternary
complex of DNA-Topo I-CPT [19], we presented a presumed binding
mode of this class compounds with DNA-Topo I complex. In this
model, we found a large space around the C-7 position of hCPT that
allowed the introduction of substituted acyl groups, and two key
hydrogen bonds were reserved (Fig. 3). Therefore, we recently
synthesized a series of racemic 7-acyl homocamptothecin analogs,
hoping that these derivatives might have remarkable antitumor
activity.
Fig. 3. Hypothetical model for the binding of 7-C¼O linked homocamptothecin (6k)
with DNA-Topo I complex. The figure was prepared from PDB entry: 1T8I, Using PyMol
(http://pymol.souceforge,net/).
3. Results and discussion
3.1. In vitro antitumor activities
The antitumor activities of these synthetic compounds 6ae6t
were tested on human lung cancer (A549), breast cancer (MDA-MB-
435) and colon cancer (HCT116) cell lines. To obtain more mean-
ingful comparisons of relative potencies, TPT was tested as a positive
control. From the data reported in Table 1, it appears that the alkyl
and alkylcarbonyl groups onposition 7 could promote the antitumor
activity of hCPTs, however, the aroyl groups on position 7 did not get
the same results, which indicates that it is not favorable to introduce
the aroyl groups on position 7. It may be due to that aromatic groups
conjugating with carbonyl group disturb the electronic factor in ring
B more obviously than alkyl groups. The results also revealed that
2. Chemistry
Detailed synthetic strategy to 7-substituted homocamptothecin
derivatives 6ae6t is illustrated in Scheme 1. According to published
procedures [20], 2-amino-5-methoxybenzaldehyde 3 was prepared
from 5-hydroxy-2-nitro-benzaldehyde 1 by methylation and hydro-
genation. The key intermediate CDE ring 4 was synthesized according
tothe previously reportedmethod [13], and thesynthetic process was
optimized in our present studies [21]. Reaction of 2-amino-5-
methoxybenzaldehyde 3 with intermediate 4 in the presence of
p-methylbenzenesulfonic acid (P-TSA) yielded the 10-methox-
yhomocamptothecin 5. Treatment of compound 5 and commercially
available aldehyde via Minisci freeeradical reaction led to the desired
7-substituted homocamptothecin 6ae6t with the yield of 22%e36%.
In Minisci freeeradical reaction, there is a little different between
7-cycloalkyl and 7-acyl derivatives, which use hydrogenperoxide and
tert-butyl hydroperoxide as oxidant, respectively.
l
Scheme 1. Reagents and conditions: (a) CH3I, CH3CN, reflux, 92%; (b) H2, PdeC, ethyl
acetate, 30 ꢀC, 6 h, 70%; (c) P-TSA, toluene, reflux, 6 h, 51%; (d) aldehyde derivatives,
H2O2, AcOHeH2O, H2SO4, FeSO4$7H2O, 0e5 ꢀC, 3 h, 22e30%; and (e) aldehyde deriv-
atives, t-BuOOH, AcOH-H2O, H2SO4, FeSO4$7H2O, 0e5 ꢀC, 3 h, 22e36%.
Fig. 2. Structures of silatecan and BN80927.

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W. Liu et al. / European Journal of Medicinal Chemistry 46 (2011) 2408e2414
Table 1
In vitro antitumor activity of 7-substituted-10-methoxyhomocamptothecin.
a
Compounds
IC50
(
m
M)
A549
MDA-MB-435
HCT116
6a
6b
6c
6d
6e
6f
6g
6h
6i
6j
6k
6l
6m
6n
6o
6p
6q
6r
0.730
0.657
2.48
0.430
0.669
8.96
0.0415
0.0761
0.0482
<0.001
<0.001
0.0633
0.198
0.198
0.133
0.0216
0.00218
1.61
2.21
2.09
15.9
7.17
1.48
16.3
0.0714
0.118
0.00593
0.00217
0.446
0.0560
0.268
0.277
0.317
0.404
0.294
2.19
2.94
3.02
13.1
8.17
1.91
2.07
Fig. 4. Effect of the selected compounds on Topoisomerase I mediated DNA relaxation
in single concentration. Topo I was Topoisomerase I and DNA without drugs. The
samples were reacted with 10
m
M drugs at 37 ꢀC for 15 min. Reactions were then
stopped by adding 0.5% SDS. Gels were photographed under UV transilluminator.
14.1
7.03
0.478
2.27
<0.001
0.607
1.77
0.665
7.79
3.39
accompanied by a dose-dependent increase in the level of cleavable
complexes. Importantly, 6d and 6k showed lower intensity of the
migrating band (corresponding to nicked DNA) than CPT regardless
of low concentration (1 mM) or high concentration (50 mM). The
relative potency between the three compounds, as indicated by the
remaining amount of intact DNA, is CPT, 6d, and 6k in increasing
order (Fig. 5).
0.625
9.25
6s
6t
48.0
>100
3.16
>100
>100
0.448
26.3
22.8
1.10
4. Conclusion
Topotecan
A series of novel 7-acyl and 7-cycloalkyl derivatives of hCPT
have been obtained based on our synthetic route. Based on the
results (discussed above), all compounds indicated potent growth
inhibitory effect and most compounds showed more effective
antitumor activity than TPT. Several compounds, such as 6a, 6d, 6i,
6k, 6l and 6q, were also very potent as Topo I poisons, and
compound 6k was found to exhibit more reasonably strong Topo I-
dependent cytotoxic activity than CPT. In conclusion, this study
provides evidence that a proper electron-withdrawing substituent
on position 7 of hCPT skeleton might also improve antitumor
activity of hCPT. A better understanding of this feature could
provide meaningful insights for the development of more effective
Topoisomerase I inhibitors.
a
Values were measured with MTT method.
these compounds were more sensitive against MDA-MB-435 cell
line than against A549 and HCT116 cell lines. For MDA-MB-435 cell
line, 6a, 6b, 6k and all of 7-alkylcabonyl homocamptothecin deriv-
atives showed higher in vitro inhibitory activities than TPT. Espe-
cially, compounds 6d, 6e, and 6k showed very high inhibitory
activities with the IC50 values from less than 1 nM to 2.2 nM.
According to HCT116 cell line, eleven compounds showed higher
inhibitory activities than TPT. Among them, the antitumor activities
of compounds 6c and 6d reached nM level. The IC50 values were 5.93
and 2.17 nM respectively. With regard to A549 cell line, thirteen
compounds showed good inhibitory activities comparable to or
higher thanTPT. The IC50 of 6kwas lower than1 nM. Inparticular, the
activity of the most promising compounds, 6d and 6k, showedbroad
in vitro antitumor spectrum and are more potent than TPT. Further
pharmacological and toxicological evaluation of these promising
compounds is in progress. The further SAR analysis of the synthe-
sized compounds revealed that the length of alkyl chain was
important to in vitro cytotoxic activity. For example, with regard to
HCT116 cancer cell, the antitumor activity of compound, 6f, 6g, 6h,
and 6i, showed a decreasing tendency with the increase of the alkyl
chain length. For the compounds with aromatic groups from 6m to
6r, the SAR analysis showed that compounds with electron-with-
drawing groups at position 4 of phenyl ring exhibited a distinct
tendency to increase in vitro antitumor activity, while compound 6o
with fluorine substitution revealed relatively low cytotoxic activity.
To our surprise, compounds 6s and 6t showed weak antiproliferative
activity, which may be accounted for by the changed molecule-
binding model to the targeted enzyme due to their relatively bigger
substituents.
5. Experimental protocols
5.1. General
All reagents and solvents were reagent grade or were purified by
standard methods before use. The melting points were determined
using an electrothermal apparatus and are uncorrected. 1H and 13
C
NMR spectra were recorded at 500 MHz with a Bruker instrument,
and reported with TMS as internal standard and DMSO-d6 as
solvent. Chemical shifts (d values) and coupling constants (J values)
are given in ppm and Hz, respectively. Elemental analyses were
performed with a MOD-1106 instrument and were consistent with
theoretical values within ꢁ0.4%. TLC analysis was carried out on
silica gel plates GF254 (Qindao Haiyang Chemical, China). Flash
column chromatography was carried out on silica gel 300e400
mesh. Anhydrous solvent and reagents were all analytical pure and
dried through routine protocols.
3.2. Topoisomerase I mediated DNA cleavage
The ability of selected hCPT derivatives 6a, 6d, 6i, 6k, 6l and 6q
to inhibit Topo I was investigated in the cleavable complex assay.
The results presented in Fig. 4 indicated that all compounds as
cytotoxic agents were also very potent as Topo I poisons, and
compounds 6a, 6d, and 6k were more potent as Topo I poisons than
CPT, which was consistent with in vitro antitumor activity.
Furthermore, the increasing concentrations of CPT, 6d, or 6k are
Fig. 5. Effect of compounds CPT, 6d, and 6k on Topoisomerase
relaxation in concentration gradient. Topo I was Topoisomerase I and DNA without
drugs; the samples were reacted with 1, 10, and 50
M drugs at 37 ꢀC for 15 min.
Reactions were then stopped by adding 0.5% SDS. Gels were photographed under UV
transilluminator.
I mediated DNA
m

W. Liu et al. / European Journal of Medicinal Chemistry 46 (2011) 2408e2414
2411
5.2. 10-Methoxyhomocamptothecin (5)
5.4.1. 7-Cyclopropylcabonyl-10-methoxyhomocamptothecin (6c)
The general synthetic method described above afforded 6c as
A solution of the tricyclic ketone 4 (6.1 g, 21.9 mmol) and 2-
Amino-5-methoxybenzaldehyde 3 (5.3 g, 35.1 mmol) in toluene
was refluxed using a DeaneStark trap for 30 min. P-TSA (1.3 g,
6.6 mmol) was then added and refluxing was continued for an
additional 3 h. The solvent was removed and the crude product was
washed by acetone (100 mL) and methanol (100 mL) to give 5 as
yellow solid (4.38 g, 51%), mp >250 ꢀC (dec). 1H NMR (500 MHz,
yellow solid (30%), mp > 260 ꢀC (dec). 1H NMR (500 MHz, DMSO-
d6)
d: 0.87 (t, 3H, 18-CH3, J ¼ 7.3 Hz), 1.33e1.46 (m, 4H), 1.86 (q, 2H,
19-CH2, J ¼ 7.3 Hz), 2.75 (t,1H, eCH(CH2)2, J ¼ 4.2 Hz), 3.05e3.49 (q,
2H, 21-CH2, J ¼ 13.9 Hz), 3.94 (s, 3H, eOCH3), 5.33 (s, 2H, 5-CH2),
5.38e5.54 (q, 2H, 17-CH2, J ¼ 15.3 Hz), 6.03 (s, 1H, 20-OH), 7.38 (s,
1H, 14H), 7.48 (d, 1H, 9H, J ¼ 2.7 Hz), 7.61 (dd, 1H, 11H, Jo ¼ 2.6 Hz,
Jm ¼ 9.3 Hz), 8.17 (d, 1H, 12H, J ¼ 9.3 Hz). ESI-MS: m/z, 459.35
[M ꢂ H]ꢂ. Anal. calcd. for C26H24N2O6: C, 67.82; H, 5.25; N, 6.08.
Found: C, 67.89; H, 5.24; N, 6.09.
DMSO-d6)
d
: 0.87 (t, 3H, 18-CH3, J ¼ 7.4 Hz), 1.86 (q, 2H, 19-CH2,
J ¼ 7.5 Hz), 3.04e3.48 (q, 2H, 21-CH2, J ¼ 13.8 Hz), 3.95 (s, 3H,
eOCH3), 5.25 (s, 2H, 5-CH2) 5.37e5.54 (q, 2H, 17-CH2, J ¼ 15.1 Hz),
6.00 (s, 1H, 20-OH), 7.35 (s, 1H, 14H), 7.50 (d, 1H, 9H, J ¼ 2.8 Hz), 7.51
(d,1H,11H, J ¼ 8.6 Hz), 8.05 (d,1H,12H, J ¼ 10.7 Hz), 8.54 (s, 1H, 7H).
ESI-MS: m/z, 391.40 [M ꢂ H]ꢂ. Anal. calcd. for C22H20N2O5: C, 67.34;
H, 5.14; N, 7.14. Found: C, 67.22; H, 5.15; N, 7.14.
5.4.2. 7-Cyclopentylcabonyl-10-methoxyhomocamptothecin (6d)
The general synthetic method described above afforded 6d as
yellow solid (35%), mp > 260 ꢀC (dec). 1H NMR (500 MHz, DMSO-
d6)
d
: 0.86 (t, 3H, 18-CH3, J ¼ 7.4 Hz), 1.63e1.93 (m, 10H), 3.04e3.49
(q, 2H, 21-CH2, J ¼ 13.9 Hz), 3.74 (t, 1H, eCH(CH2)4, J ¼ 3.9 Hz), 3.92
(s, 3H, eOCH3), 5.28 (s, 2H, 5-CH2), 5.37e5.53 (q, 2H, 17-CH2,
J ¼ 15.1 Hz), 6.03 (s, 1H, 20-OH), 7.15 (d, 1H, 9H, J ¼ 2.7 Hz), 7.37 (s,
1H, 14H), 7.60 (dd, 1H, 11H, Jo ¼ 2.7 Hz, Jm ¼ 9.3 Hz), 8.15 (d, 1H, 12H,
5.3. General procedure for the synthesis of 7-cycloalkyl
homocamptothecin derivatives (6ae6b)
To a suspension of 10-methoxyhomocamptothecin (100 mg,
0.25 mmol) and FeSO4$7H2O (142 mg, 0.5 mmol) in 50% aqueous
acetic acid (9 mL) was added dropwise 0.9 mL of concentrated
H2SO4 and different aldehyde (1.3 mmol). After cooling at 0 ꢀC, 30%
H2O2 (108 mg, 3.2 mmol) were added, and the mixture was stirred
overnight at room temperature. Dilution with water, filtration of
the precipitate, extraction with dichloromethane, and chromatog-
raphy of the extract (CH2Cl2/MeOH 98/2) gave the product.
J ¼ 9.3 Hz); 13C NMR (125 MHz, DMSO-d6)
d: 8.67, 26.07, 29.14,
36.77, 42.83, 50.57, 51.73, 56.18, 61,66, 73.59, 99.53, 103.71, 122.72,
123.48, 125.23, 126.80, 131.74, 140.21, 144.17, 144.60, 145.06, 150.88,
156.23, 159.34, 172.26, 207.60. ESI-MS: m/z, 487.44 [M ꢂ H]ꢂ. Anal.
calcd. for C28H28N2O6: C, 68.84; H, 5.78; N, 5.73. Found: C, 68.96; H,
5.77; N, 5.71.
5.4.3. 7-Cyclohexylcabonyl-10-methoxyhomocamptothecin (6e)
The general synthetic method described above afforded 6e as
yellow solid (36%), mp > 260 ꢀC (dec). 1H NMR (500 MHz, DMSO-d6)
5.3.1. 7-Cyclopentyl-10-methoxyhomocamptothecin (6a)
The general synthetic method described above afforded 6a as
d
: 0.86 (t, 3H, 18-CH3, J ¼ 7.5 Hz), 1.24e1.95 (m, 12H), 3.04e3.49 (q,
yellow solid (28%), mp > 260 ꢀC (dec). 1H NMR (500 MHz, DMSO-d6)
d
2H, 21-CH2, J ¼ 13.9 Hz), 3.20 (t, 1H, eCH(CH2)5, J ¼ 3.9 Hz), 3.92 (s,
3H, eOCH3), 5.26 (s, 2H, 5-CH2), 5.37e5.53 (q, 2H, 17-CH2,
J ¼ 15.1 Hz), 6.02 (s,1H, 20-OH), 7.10 (d,1H, 9H, J ¼ 2.7 Hz), 7.37 (s,1H,
14H), 7.59 (dd, 1H, 11H, Jo ¼ 2.7 Hz, Jm ¼ 9.3 Hz), 8.15 (d, 1H, 12H,
J ¼ 9.3Hz). ESI-MS:m/z, 501.39 [Mꢂ H]ꢂ. Anal. calcd. for C29H30N2O6:
C, 69.31; H, 6.02; N, 5.57. Found: C, 69.22; H, 6.01; N, 5.58.
: 0.85 (t, 3H, 18-CH3, J ¼ 7.4 Hz), 1.83e2.24 (m, 10H), 3.03e3.49 (q,
2H, 21-CH2, J ¼ 13.8 Hz), 3.92(t,1H, eCH(CH2)4, J ¼ 9.1 Hz), 3.97 (s, 3H,
eOCH3), 5.36 (s, 2H, 5-CH2), 5.37e5.54 (q, 2H, 17-CH2, J ¼ 15.1 Hz),
6.01 (s, 1H, 20-OH), 7.33 (s, 1H, 14H), 7.51 (dd, 1H, 11H, Jo ¼ 2.6 Hz,
Jm ¼ 9.2 Hz), 7.55 (d,1H, 9H, J ¼ 2.4 Hz), 8.07 (d,1H,12H, J ¼ 9.2 Hz).13
C
NMR (125 MHz, DMSO-d6) d: 8.66, 26.70, 31.77, 36.79, 40.89, 42.84,
50.90, 56.10, 61,72, 73.59, 99.00,103.69,122.08,122.37,128.01,128.48,
131.96, 144.93, 145.35, 145.92, 150.40, 156.23, 158.26, 159.37, 172.31.
ESI-MS: m/z, 459.66 [M ꢂ H]ꢂ. Anal. calcd. for C27H28N2O5: C, 70.42;
H, 6.13; N, 6.08. Found: C, 70.30; H, 6.14; N, 6.09.
5.4.4. 7-Propionyl-10-methoxyhomocamptothecin (6f)
The general synthetic method described above afforded 6f as
yellow solid (36%), mp > 200 ꢀC (dec). 1H NMR (500 MHz, DMSO-
d6)
d
: 0.86 (t, 3H, 18-CH3, J ¼ 7.3 Hz), 1.23 (t, 3H, eCH2CH3,
J ¼ 7.0 Hz),1.86 (q, 2H,19-CH2, J ¼ 7.7 Hz), 3.04e3.49 (q, 2H, 21-CH2,
J ¼ 13.7 Hz), 3.16 (q, 2H, eCH2CH3, J ¼ 7.1 Hz), 3.94 (s, 3H, eOCH3),
5.32 (s, 2H, 5-CH2), 5.38e5.54 (q, 2H, 17-CH2, J ¼ 15.3 Hz), 6.02 (s,
1H, 20-OH), 7.30 (d, 1H, 9H, J ¼ 2.6 Hz), 7.37 (s, 1H, 14H), 7.60 (dd,
5.3.2. 7-Cyclohexyl-10-methoxyhomocamptothecin (6b)
The general synthetic method described above afforded 6b as
yellow solid (30%), mp > 260 ꢀC (dec). 1H NMR (500 MHz, DMSO-
d6)
d
: 0.85 (t, 3H, 18-CH3, J ¼ 7.3 Hz), 1.61e1.94 (m, 12H), 3.03e3.49
1H, 11H, Jo ¼ 2.4 Hz, Jm ¼ 9.2 Hz), 8.15 (d, 1H, 12H, J ¼ 9.1 Hz). 13
C
(q, 2H, 21-CH2, J ¼ 13.7 Hz), 3.99 (s, 3H, eOCH3), 5.38e5.54 (q, 2H,
17-CH2, J ¼ 15.1 Hz), 5.41 (s, 2H, 5-CH2), 6.01 (s, 1H, 20-OH), 7.33 (s,
1H, 14H), 7.54 (dd, 1H, 11H, Jo ¼ 2.6 Hz, Jm ¼ 9.2 Hz), 7.58 (d, 1H, 9H,
J ¼ 1.2 Hz), 8.07 (d, 1H, 12H, J ¼ 9.2 Hz). ESI-MS: m/z, 473.37
[M ꢂ H]ꢂ. Anal. calcd. for C28H30N2O5: C, 70.87; H, 6.37; N, 5.90.
Found: C, 70.99; H, 6.36; N, 5.88.
NMR (125 MHz, DMSO-d6) d: 8.21, 8.65, 36.74, 37.06, 42.81, 50.70,
56.22, 61.67, 73.58, 99.50, 103.94, 122.69, 123.46, 125.03, 127.01,
131.63, 139.68, 144.55, 145.13, 150.74, 156.24, 159.32, 159.37, 172.26,
205.53. ESI-MS: m/z, 447.38 [M ꢂ H]ꢂ. Anal. calcd. for C25H24N2O6:
C, 66.95; H, 5.39; N, 6.25. Found: C, 66.83; H, 5.40; N, 6.27.
5.4.5. 7-Butyryl-10-methoxyhomocamptothecin (6g)
5.4. General procedure for the synthesis of 7-acyl
homocamptothecin derivatives (6ce6t)
The general synthetic method described above afforded 6g as
yellow solid (26%), mp > 200 ꢀC (dec). 1H NMR (500 MHz, DMSO-
d6)
d: 0.86 (t, 3H, 18-CH3, J ¼ 7.4 Hz), 1.01 (t, 3H, eCH3, J ¼ 7.4 Hz),
To a suspension of 10-methoxyhomocamptothecin (100 mg,
0.25 mmol) and FeSO4$7H2O(142 mg, 0.5 mmol) in 50% aqueous
acetic acid (9 mL) was added dropwise 0.9 mL of concentrated H2SO4
and different aldehyde (1.3 mmol). After cooling at 0 ꢀC, 80% t-
BuOOH (57 mg, 0.5 mmol) were added, and the mixture was stirred
overnight at room temperature. Dilution with water, filtration of the
precipitate, extraction with dichloromethane, and chromatography
of the extract (CH2Cl2/MeOH 98/2) gave the product.
1.79 (q, 2H, eCH2CH3, J ¼ 7.3 Hz), 1.86 (q, 2H, 19-CH2, J ¼ 7.5 Hz),
3.04e3.49 (q, 2H, 21-CH2, J ¼ 13.8 Hz), 3.14 (t, 2H, eCH2CH2CH3,
J ¼ 7.1 Hz), 3.93 (s, 3H, eOCH3), 5.31 (s, 2H, 5-CH2), 5.38e5.54 (q,
2H, 17-CH2, J ¼ 15.1 Hz), 6.03 (s, 1H, 20-OH), 7.27 (d, 1H, 9H,
J ¼ 2.7 Hz), 7.37 (s, 1H, 14H), 7.59 (dd, 1H, 11H, Jo ¼ 2.7 Hz,
Jm ¼ 9.3 Hz), 8.15 (d, 1H, 12H, J ¼ 9.3 Hz). ESI-MS: m/z, 461.48
[M ꢂ H]ꢂ. Anal. calcd. for C26H26N2O6: C, 67.52; H, 5.67; N, 6.06.
Found: C, 67.63; H, 5.68; N, 6.03.

2412
W. Liu et al. / European Journal of Medicinal Chemistry 46 (2011) 2408e2414
5.4.6. 7-Pentanoyl-10-methoxyhomocamptothecin (6h)
d
: 0.87 (t, 3H, 18-CH3, J ¼ 7.4 Hz), 1.86 (q, 2H, 19-CH2, J ¼ 7.3 Hz),
The general synthetic method described above afforded 6h as
3.04e3.49 (q, 2H, 21-CH2, J ¼ 13.8 Hz), 3.82 (s, 3H, eOCH3), 5.04 (d,
2H, 5-CH2, J ¼ 5.2 Hz), 5.34e5.50 (q, 2H,17-CH2, J ¼ 15.1 Hz), 6.03 (s,
1H, 20-OH), 7.11 (d, 1H, 9H, J ¼ 2.8 Hz), 7.27 (t, 1H, 40-H, J ¼ 4.4 Hz),
7.41 (s,1H,14H), 7.61 (dd,1H,11H, Jo ¼ 2.8 Hz, Jm ¼ 9.3 Hz), 7.73 (d,1H,
30-H, J ¼ 3.7 Hz), 8.20 (d, 1H, 12H, J ¼ 9.3 Hz), 8.35 (d, 1H, 50-H,
yellow solid (30%), mp > 200 ꢀC (dec). 1H NMR (500 MHz, DMSO-d6)
d: 0.86 (t, 3H,18-CH3, J ¼ 7.3 Hz), 0.93 (t, 3H, eCH3, J ¼ 7.3 Hz),1.42 (q,
2H, eCH2CH3, J ¼ 7.5 Hz),1.74 (t, 2H, eCH2CH2CH3, J ¼ 7.4 Hz),1.84 (q,
2H, 19-CH2, J ¼ 7.4 Hz), 3.04e3.49 (q, 2H, 21-CH2, J ¼ 13.8 Hz), 3.15
(t, 2H, eCH2CH2CH2CH3, J ¼ 7.2 Hz), 3.93 (s, 3H, eOCH3), 5.31 (s, 2H,
5-CH2), 5.37e5.53 (q, 2H, 17-CH2, J ¼ 15.1 Hz), 6.03 (s, 1H, 20-OH),
7.28 (d, 1H, 9H, J ¼ 2.6 Hz), 7.37 (s, 1H, 14H), 7.60 (dd, 1H, 11H,
Jo ¼ 2.6 Hz, Jm ¼ 9.2 Hz), 8.15 (d, 1H, 12H, J ¼ 9.3 Hz). 13C NMR
J ¼ 4.9 H). 13C NMR (125 MHz, DMSO-d6)
d: 8.67, 36.76, 42.81, 50.47,
56.11, 61.64, 73.59, 99.64, 103.71, 122.69, 123.57, 125.93, 127.63,
129.72, 130.04, 131.66, 137.80, 138.66, 139.29, 142.54, 144.68, 145.02,
150.90, 156.32, 159.27, 172.26, 186.33. ESI-MS: m/z, 501.54 [M ꢂ H]ꢂ.
Anal. calcd. for C27H22N2O6S: C, 64.53; H, 4.41; N, 5.57. Found: C,
64.42; H, 4.42; N, 5.58.
(125 MHz, DMSO-d6) d: 8.64, 14.29, 22.22, 25.84, 36.74, 42.81, 43.34,
50.61, 56.19, 61.66, 73.57, 99.51,103.78,122.69,123.45,124.95,126.91,
131.67, 139.75, 144.21, 144.54, 145.13, 150.78, 156.23, 159.31, 172.25,
205.17. ESI-MS: m/z, 475.50 [M ꢂ H]ꢂ. Anal. calcd. for C27H28N2O6: C,
68.05; H, 5.92; N, 5.88. Found: C, 68.17; H, 5.92; N, 5.90.
5.4.11. 7-Benzoyl-10-methoxyhomocamptothecin (6m)
The general synthetic method described above afforded 6m as
yellow solid (36%), mp > 260 ꢀC (dec). 1H NMR (500 MHz, DMSO-
5.4.7. 7-Heptanoyl-10-methoxyhomocamptothecin (6i)
d6)
d
: 0.87 (t, 3H, 18-CH3, J ¼ 7.4 Hz), 1.86 (q, 2H, 19-CH2, J ¼ 7.4 Hz),
The general synthetic method described above afforded 6i as
3.03e3.48 (q, 2H, 21-CH2, J ¼ 13.9 Hz), 3.75 (s, 3H, eOCH3), 4.93 (d,
2H, 5-CH2, J ¼ 8.2 Hz), 5.33e5.48 (q, 2H,17-CH2, J ¼ 15.1 Hz), 6.03 (s,
1H, 20-OH), 7.03 (d, 1H, 9H, J ¼ 2.7 Hz), 7.41 (s, 1H, 14H), 7.59e7.64
(m, 3H, 11, 30-H, 50-H), 7.80 (t, 1H, 40-H, J ¼ 7.4 Hz), 7.91 (d, 2H, 20-H,
60-H, J ¼ 8.3 Hz), 8.20 (d, 1H, 12H, J ¼ 9.3 Hz). ESI-MS: m/z, 495.33
[M ꢂ H]ꢂ. Anal. calcd. For C29H24N2O6: C, 70.15; H, 4.87; N, 5.64.
Found: C, 70.29; H, 4.86; N, 5.63.
yellow solid (30%), mp > 200 ꢀC (dec). 1H NMR (500 MHz, DMSO-
d6)
d: 0.86 (m, 6H, 18-CH3, eCH3), 1.25 (q, 2H, eCH2CH3, J ¼ 5.6 Hz),
1.30 (t, 2H, eCH2CH2CH3, J ¼ 6.0 Hz), 1.39 (t, 2H, eCH2CH2CH2CH3,
J ¼ 6.5 Hz), 1.76 (t, 2H, eCH2CH2CH2CH2CH3, J ¼ 7.4 Hz), 1.85 (q, 2H,
19-CH2, J ¼ 7.3 Hz), 3.04e3.49 (q, 2H, 21-CH2, J ¼ 13.7 Hz), 3.14 (t,
2H, eCH2CH2CH2CH2CH2CH3, J ¼ 7.2 Hz), 3.93 (s, 3H, eOCH3), 5.31
(s, 2H, 5-CH2), 5.37e5.53 (q, 2H,17-CH2, J ¼ 15.0 Hz), 6.03 (s, 1H, 20-
OH), 7.28 (d, 1H, 9H, J ¼ 2.6 Hz), 7.37 (s, 1H, 14H), 7.60 (dd, 1H, 11H,
Jo ¼ 2.6 Hz, Jm ¼ 9.4 Hz), 8.15 (d, 1H, 12H, J ¼ 9.3 Hz); 13C NMR
5.4.12. 7-(4-Chlorbenzoyl)-10-methoxyhomocamptothecin (6n)
The general synthetic method described above afforded 6n as
yellow solid (36%), mp > 300 ꢀC (dec). 1H NMR (500 MHz, DMSO-
(125 MHz, DMSO-d6) d: 8.65, 14.33, 22.43, 23.68, 28.71, 31.56, 36.75,
42.81, 43.60, 50.62, 56.18, 61.66, 73.58, 99.51, 103.78, 122.70, 123.48,
124.96, 126.92, 131.68, 139.77, 144.22, 144.55, 145.15, 150.80, 156.23,
159.32, 172.25, 205.20. ESI-MS: m/z, 503.55 [M ꢂ H]ꢂ. Anal. calcd.
for C29H32N2O6: C, 69.03; H, 6.39; N, 5.55. Found: C, 68.95; H, 6.38;
N, 5.58.
d6)
d
: 0.87 (t, 3H, 18-CH3, J ¼ 7.3 Hz), 1.86 (q, 2H, 19-CH2, J ¼ 7.1 Hz),
3.03e3.49 (q, 2H, 21-CH2, J ¼ 13.9 Hz), 3.76 (s, 3H, eOCH3), 4.95 (d,
2H, 5-CH2, J ¼ 8.2 Hz), 5.33e5.49 (q, 2H,17-CH2, J ¼ 15.1 Hz), 6.03 (s,
1H, 20-OH), 7.03 (s, 1H, 9H), 7.41 (s, 1H, 14H), 7.60 (dd, 1H, 11H,
Jo ¼ 2.1 Hz, Jm ¼ 9.0 Hz), 7.67 (d, 2H, 30-H, 50-H, J ¼ 8.4 Hz), 7.92 (d,
2H, 20-H, 60-H, J ¼ 8.5 Hz), 8.20 (d, 1H, 12H, J ¼ 9.3 Hz). ESI-MS: m/z,
529.40 [M ꢂ H]ꢂ. Anal. calcd. for C29H23ClN2O6: C, 65.60; H, 4.37; N,
5.28. Found: C, 65.78; H, 4.36; N, 5.27.
5.4.8. 7-Isobutyryl-10-methoxyhomocamptothecin (6j)
The general synthetic method described above afforded 6j as
yellow solid (22%), mp > 200 ꢀC (dec). 1H NMR (500 MHz, DMSO-
d6)
d
: 0.87 (t, 3H, 18-CH3, J ¼ 7.3 Hz), 1.21 (d, 6H, eCH(CH3)2,
5.4.13. 7-(4-Fluorobenzoyl)-10-methoxyhomocamptothecin (6o)
The general synthetic method described above afforded 6o as
yellow solid (35%), mp > 300 ꢀC (dec). 1H NMR (500 MHz, DMSO-
J ¼ 6.9 Hz),1.85 (q, 2H,19-CH2, J ¼ 7.4 Hz), 3.05e3.49 (q, 2H, 21-CH2,
J ¼ 13.8 Hz), 3.46e3.48 (m, 1H, eCH(CH3)2), 3.93 (s, 3H, eOCH3),
5.26 (s, 2H, 5-CH2), 5.37e5.53 (q, 2H, 17-CH2, J ¼ 15.1 Hz), 6.04 (s,
1H, 20-OH), 7.10 (d,1H, 9H, J ¼ 2.7 Hz), 7.37 (s,1H,14H), 7.59 (dd,1H,
11H, Jo ¼ 2.7 Hz, Jm ¼ 9.2 Hz), 8.14 (d,1H,12H, J ¼ 9.3 Hz). ESI-MS: m/
z, 461.54 [M ꢂ H]ꢂ. Anal. calcd. for C26H26N2O6: C, 67.52; H, 5.67; N,
6.06. Found: C, 67.63; H, 5.66; N, 6.04.
d6)
d: 0.87 (t, 3H, 18-CH3, J ¼ 7.3 Hz), 1.86 (q, 2H, 19-CH2, J ¼ 7.2 Hz),
3.03e3.49 (q, 2H, 21-CH2, J ¼ 13.9 Hz), 3.76 (s, 3H, eOCH3), 4.95 (d,
2H, 5-CH2, J ¼ 8.3 Hz), 5.33e5.49 (q, 2H,17-CH2, J ¼ 15.0 Hz), 6.03 (s,
1H, 20-OH), 7.01 (d, 1H, 9H, J ¼ 2.5 Hz), 7.41 (s, 1H, 14H), 7.42 (d, 2H,
30-H, 50-H, J ¼ 8.8 Hz), 7.60 (dd, 1H, 11H, Jo ¼ 2.5 Hz, Jm ¼ 9.1 Hz),
8.00 (dd, 2H, 20-H, 60-H, Jo ¼ 5.5 Hz, Jm ¼ 8.6 Hz), 8.20 (d, 1H, 12H,
J ¼ 9.3 Hz). ESI-MS: m/z, 513.32 [M ꢂ H]ꢂ. Anal. calcd. for
C29H23FN2O6: C, 67.70; H, 4.51; N, 5.44. Found: C, 67.58; H, 4.51; N,
5.46.
5.4.9. 7-(2-Furoyl)-10-methoxyhomocamptothecin (6k)
The general synthetic method described above afforded 6k as
yellow solid (31%), mp > 260 ꢀC (dec). 1H NMR (500 MHz, DMSO-
d6)
d
: 0.87 (t, 3H, 18-CH3, J ¼ 7.3 Hz), 1.86 (q, 2H, 19-CH2, J ¼ 7.6 Hz),
3.04e3.49 (q, 2H, 21-CH2, J ¼ 13.9 Hz), 3.83 (s, 3H, eOCH3), 5.09 (d,
2H, 5-CH2, J ¼ 4.1 Hz), 5.35e5.49 (q, 2H,17-CH2, J ¼ 15.0 Hz), 6.03 (s,
1H, 20-OH), 6.85 (d, 1H, 40-H, J ¼ 2.0 Hz), 7.12 (d, 1H, 9H, J ¼ 2.6 Hz),
7.40 (s, 1H, 14H), 7.55 (d, 1H, 30-H, J ¼ 3.6 Hz), 7.60 (dd, 1H, 11H,
Jo ¼ 2.4 Hz, Jm ¼ 9.0 Hz), 8.19 (d, 1H, 12H, J ¼ 9.3 Hz), 8.26 (s, 1H, 50-
5.4.14. 7-(4-Toluyl)-10-methoxyhomocamptothecin (6p)
The general synthetic method described above afforded 6p as
yellow solid (36%), mp > 260 ꢀC (dec). 1H NMR (500 MHz, DMSO-
d6)
d
: 0.87 (t, 3H, 18-CH3, J ¼ 7.3 Hz), 1.86 (q, 2H, 19-CH2, J ¼ 7.1 Hz),
2.43 (s, 3H, eCH3), 3.03e3.48 (q, 2H, 21-CH2, J ¼ 13.9 Hz), 3.76 (s,
3H, eOCH3), 4.90 (d, 2H, 5-CH2, J ¼ 6.9 Hz), 5.33e5.48 (q, 2H, 17-
CH2, J ¼ 15.1 Hz), 6.02 (s,1H, 20-OH), 7.02 (d,1H, 9H, J ¼ 2.7 Hz), 7.40
(s, 1H, 14H), 7.41 (d, 2H, 30-H, 50-H, J ¼ 7.7 Hz), 7.59 (dd, 1H, 11H,
Jo ¼ 2.7 Hz, Jm ¼ 9.3 Hz), 7.82 (d, 2H, 20-H, 60-H, J ¼ 8.2 Hz), 8.19 (d,
H); 13C NMR (125 MHz, DMSO-d6)
d: 8.68, 36.78, 42.80, 50.46, 56.15,
61.62, 73.60, 99.60, 103.62, 114.16, 122.72, 123.70, 124.84, 126.12,
128.07, 131.66, 137.13, 144.65, 145.05, 150.57, 150.90, 151.24, 151.36,
156.29, 159.29, 172.26, 180.40. ESI-MS: m/z, 485.41 [M ꢂ H]ꢂ. Anal.
calcd. for C27H22N2O7: C, 66.66; H, 4.56; N, 5.76. Found: C, 66.57; H,
4.57; N, 5.77.
1H, 12H, J ¼ 9.3 Hz). 13C NMR (125 MHz, DMSO-d6)
d: 8.64, 21.85,
36.73, 42.79, 50.37, 56.03, 61.61, 73.56, 99.63,103.92,122.64,123.48,
126.23, 127.82, 130.45, 130.51, 131.67, 133.46, 138.19, 144.65, 145.04,
146.46, 150.78, 156.28, 159.17, 159.24, 172.23, 194.25. ESI-MS: m/z,
509.38 [M ꢂ H]ꢂ. Anal. calcd. for C30H26N2O6: C, 70.58; H, 5.13; N,
5.49. Found: C, 70.61; H, 5.13; N, 5.47.
5.4.10. 7-(2-Thenoyl)-10-methoxyhomocamptothecin (6l)
The general synthetic method described above afforded 6l as
yellow solid (30%), mp > 260 ꢀC (dec). 1H NMR (500 MHz, DMSO-d6)

W. Liu et al. / European Journal of Medicinal Chemistry 46 (2011) 2408e2414
2413
5.4.15. 7-(4-Triflouromethylbenzoyl)-10-
methoxyhomocamptothecin (6q)
solution (5 mg/mL) was added to each well, and after shaking for
1 min the plate was incubated further for 4 h. Formazan crystals
The general synthetic method described above afforded 6q as
were dissolved with 100 mL DMSO. The absorbance (OD) was
yellow solid (35%), mp > 300 ꢀC (dec). 1H NMR (500 MHz, DMSO-
d6)
quantitated with microplate spectrophotometer at 570 nm. Wells
containing no drugs were used as blanks for the spectrophotom-
eter. The survival of the cells was expressed as percentage of
untreated control wells.
d
: 0.87 (t, 3H, 18-CH3, J ¼ 7.3 Hz), 1.86 (q, 2H, 19-CH2, J ¼ 7.2 Hz),
3.03e3.49 (q, 2H, 21-CH2, J ¼ 13.8 Hz), 3.74 (s, 3H, eOCH3), 4.97 (d,
2H, 5-CH2, J ¼ 10.3Hz), 5.33e5.48 (q, 2H, 17-CH2, J ¼ 15.3 Hz), 6.03
(s, 1H, 20-OH), 7.04 (d, 1H, 9H, J ¼ 2.6 Hz), 7.41 (s, 1H, 14H), 7.61 (dd,
1H, 11H, Jo ¼ 2.8 Hz, Jm ¼ 9.2 Hz), 7.96 (d, 2H, 30-H, 50-H, J ¼ 8.3 Hz),
8.09 (d, 2H, 20-H, 60-H, J ¼ 8.4 Hz), 8.21 (d, 1H, 12H, J ¼ 9.3 Hz); 13C
5.6. DNA Topoisomerase I activity assays
NMR (125 MHz, DMSO-d6) d: 8.67, 36.77, 42.81, 50.50, 56.06, 61.60,
Camptothecin was obtained from the company of Tianzunzez-
hong in China. Topo I (calf thymus), buffer, BSA, loading buffer and
supercoiled DNA pBR322 were all from TaKaRa Biotechnology CO.,
Ltd.
73.60, 99.67, 104.15, 122.76, 123.67, 126.05, 126.76, 128.58, 130.54,
131.21, 131.77, 134.14, 134.39, 136.95, 139.22, 144.57, 145.14, 150.95,
156.28, 159.25, 172.23, 194.32. ESI-MS: m/z, 563.30 [M ꢂ H]ꢂ. Anal.
calcd. for C30H23F3N2O6: C, 63.83; H, 4.11; N, 4.96. Found: C, 63.92;
H, 4.10; N, 4.98.
All reactions were carried out in 20
distilled water, 2 L DNA-Topo I buffer, 2
0.25
m
L volumes (16
mL double
m
m
L 0.1% BSA) including
m
g supercoiled DNA, 0.5 U Topo I with or without drug. The
reactions were incubated at 37 ꢀC for 15 min and then stopped
5.4.16. 7-(4-Methoxylbenzoyl)-10-methoxyhomocamptothecin (6r)
The general synthetic method described above afforded 6r as
yellow solid (36%), mp > 300 ꢀC (dec). 1H NMR (500 MHz, DMSO-
by adding SDS (0.5% final concentration). To the reaction
mixtures, 3.5
m
L, 6 ꢃ loading buffer (0.1 mM EDTA, 7% Glycerol,
d6)
d
: 0.87 (t, 3H, 18-CH3, J ¼ 7.4 Hz), 1.86 (q, 2H, 19-CH2, J ¼ 7.4 Hz),
0.01% Xylene Cyanol FF, Bromopenol Blue 0.01%) was added.
The mixtures were electrophoresed in 0.8% agarose gel in TAE
buffer for 40 min at 120 V. The gel was stained with ethidium
bromide at room temperature and photographed with UV
transilluminator.
3.03e3.48 (q, 2H, 21-CH2, J ¼ 13.9 Hz), 3.77 (s, 3H,10-OCH3), 3.88 (s,
3H, eOCH3), 4.92 (d, 2H, 5-CH2, J ¼ 6.5 Hz), 5.33e5.48 (q, 2H, 17-
CH2, J ¼ 15.0 Hz), 6.03 (s,1H, 20-OH), 7.02 (d,1H, 9H, J ¼ 2.7 Hz), 7.10
(d, 2H, 30-H, 50-H, J ¼ 9.0 Hz), 7.40 (s, 1H, 14H), 7.59 (dd, 1H, 11H,
Jo ¼ 2.8 Hz, Jm ¼ 9.3 Hz), 7.89 (d, 2H, 20-H, 60-H, J ¼ 8.9 Hz), 8.19 (d,
1H, 12H, J ¼ 9.3 Hz). 13C NMR (125 MHz, DMSO-d6)
d: 8.66, 36.75,
5.7. Computational protocols
42.80, 50.35, 56.05, 56.27, 61.61, 73.58, 99.63, 103.94, 115.21, 122.64,
123.48, 126.30, 126.69, 128.71, 131.68, 132.99, 138.55, 144.73,145.03,
150.81, 156.28, 159.14, 159.28, 165.13, 172.23, 192.85. ESI-MS: m/z,
525.32 [M ꢂ H]ꢂ. Anal. calcd. for C30H26N2O7: C, 68.43; H, 4.98; N,
5.32. Found: C, 68.32; H, 4.97; N, 5.34.
The crystallographic coordinates of the ternary complex of
CPT-DNA-Topo I (3.0 Å resolution, Rcryst ¼ 0.244) were obtained
from the Brookhaven Protein Databank entry 1T8I. All crystallo-
graphic water molecules were removed from the coordinate set.
The binding region was defined as all the atoms that are 15 Å
around the centroid of CPT in the crystal structure. The ligands
were extracted from the X-ray complexes, which were subse-
quently docked into their corresponding proteins by means of
Gold 3.0.1.
5.4.17. 7-(3,5-Dimethylbenzoyl)-10-methoxyhomocamptothecin
(6s)
The general synthetic method described above afforded 6s as
yellow solid (36%), mp > 260 ꢀC (dec). 1H NMR (500 MHz, DMSO-
d6)
d
: 0.88 (t, 3H, 18-CH3, J ¼ 7.3 Hz), 1.86 (q, 2H, 19-CH2, J ¼ 7.4 Hz),
2.33 (s, 6H, -CH3), 3.04e3.47 (q, 2H, 21-CH2, J ¼ 13.9 Hz), 3.78 (s, 3H,
eOCH3), 4.87 (d, 2H, 5-CH2, J ¼ 5.9 Hz), 5.33e5.48 (q, 2H, 17-CH2,
J ¼ 15.1 Hz), 6.01 (s, 1H, 20-OH), 7.03 (d, 1H, 9H, J ¼ 2.7 Hz), 7.40 (s,
1H, 14H), 7.44 (s, 1H, 40-H), 7.55 (s, 2H, 20-H, 60-H), 7.59 (dd, 1H, 11H,
Jo ¼ 2.8 Hz, Jm ¼ 9.3 Hz), 8.18 (d, 1H, 12H, J ¼ 9.3 Hz). ESI-MS: m/z,
523.33 [M ꢂ H]ꢂ. Anal. calcd. for C31H28N2O6: C, 70.98; H, 5.38; N,
5.34. Found: C, 71.10; H, 5.37; N, 5.32.
Acknowledgments
This research was supported in part by the Key Project of Science
and Technology of Shanghai (No. 09431901700), Major Special
Project for the Creation of New Drugs (Grant Nos. 2009ZX09301-
011) and Shanghai Leading Academic Discipline Project (Project
Nos. B906).
5.4.18. 7-(2-Naphthoyl)-10-methoxyhomocamptothecin (6t)
The general synthetic method described above afforded 6t as
yellow solid (32%), mp > 260 ꢀC (dec). 1H NMR (500 MHz, DMSO-
References
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Chem. Soc. 88 (1966) 3888e3890.
d6)
d
: 0.88 (t, 3H, 18-CH3, J ¼ 7.3 Hz), 1.87 (q, 2H, 19-CH2, J ¼ 7.4 Hz),
3.03e3.48 (q, 2H, 21-CH2, J ¼ 13.9 Hz), 3.74 (s, 3H, eOCH3), 4.94 (d,
2H, 5-CH2, J ¼ 8.1 Hz), 5.31e5.45 (q, 2H, 17-CH2, J ¼ 15.1 Hz), 6.03 (s,
1H, 20-OH), 7.10 (d, 1H, 9H, J ¼ 2.6 Hz), 7.44 (s, 1H, 14H), 7.60e7.74
(m, 3H, 11H, 60-H, 70-H), 8.02e8.18 (m, 4H, 30-H, 40-H, 50-H, 80-H),
8.23 (d, 1H, 12H, J ¼ 9.3 Hz), 8.46 (s, 1H, 10-H). ESI-MS: m/z, 545.38
[M ꢂ H]ꢂ. Anal. calcd. for C33H26N2O6: C, 72.52; H, 4.79; N, 5.13.
Found: C, 72.62; H, 4.78; N, 5.12.
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