Synthesis of 5-aryl and 5-amidocamptothecins

Article abstract of DOI:10.1002/jhet.590

A variety of 5-aryl-(20S)-camptothecin derivatives were synthesized by the reaction of 5-hydroxy-(20S)-camptothecin with aromatic hydrocarbons under Friedel-Craft reaction conditions in moderate to good yield as diastereomeric pairs. The methodology was t

Full text of DOI:10.1002/jhet.590

540
Synthesis of 5-Aryl and 5-Amidocamptothecins
Suresh Babu Meruva,a A. Raghunadh,a N. Anil Kumar,a U. K. Syam Kumar,a*
Vol 48
R. Vasu Dev,b and P. K. Dubeyc
aTechnology Development Centre, Custom Pharmaceutical Services, Dr. Reddys Laboratories Ltd.,
Miyapur, Hyderabad - 500 049, India
bDiscovery Research, Dr. Reddys Laboratories Ltd., Miyapur, Hyderabad - 500 049, India
cDepartment of Chemistry, College of Engineering, JNTU, Kukatpally, Hyderabad, India
*E-mail: syam_kmr@yahoo.com
Received March 3, 2010
DOI 10.1002/jhet.590
Published online 17 February 2011 in Wiley Online Library (wileyonlinelibrary.com).
A variety of 5-aryl-(20S)-camptothecin derivatives were synthesized by the reaction of 5-hydroxy-
(20S)-camptothecin with aromatic hydrocarbons under Friedel-Craft reaction conditions in moderate to
good yield as diastereomeric pairs. The methodology was then extended for the synthesis of 5-amido-
(20S)-camptothecin derivatives by reacting 5-hydroxy-(20S)-camptothecin with alkyl and aryl nitriles
under Ritter type reaction conditions. The reaction is presumed to proceed through an iminium ion in-
termediate under Friedel Craft and Ritter type reaction condition, which is further trapped by nucleo-
phile present in the reaction medium.
J. Heterocyclic Chem., 48, 540 (2011).
INTRODUCTION
masked aldehyde functionality 5 (Scheme 1) embedded
in 5-hydroxy-(20S)-camptothecin 2 under basic reaction
conditions [7]. However, literature reports on the reac-
tivity of 5-hydroxy-(20S)-camptothecin 2 under Lewis
or protic acid conditions are very rare [8]. 5-Hydroxy-
(20S)-camptothecin 2 can form an iminium ion 6 under
Lewis or protic acid conditions, which on further reac-
tion with nucleophiles will yield 5-substituted (20S)-
camptothecin analogues. To the best of our knowledge,
5-aryl or 5-amido-(20S)-camptothecin analogues are not
reported in the literature. In the course of a synthetic
project, we need a general method to prepare 5-aryl and
5-amido-(20S)-camptothecin analogues and found that 5-
hydroxy-(20S)-camptothcin is one of the potential syn-
thon for synthesis of these target molecules. Herein, we
report a full account of our studies toward the successful
synthesis of these novel camptothecin analogues.
(20S)-Camptothecin 1 is an alkaloid with novel penta-
cyclic structural frame work, isolated from leaves and
barks of Camptotheca accuminata (Nyssacease) and
Nothapodytes foetida [1]. Camptothecin displayed signif-
icant activity in mice leukemia L1210 and Walker 256
sarcoma in rats (Fig. 1) [2]. Camptothecin exerts its bio-
logical effects by stabilizing the covalent binary com-
plex formed between DNA and topoisomerase 1 inhibi-
tor during DNA relaxation time and lead to cell death
[3]. Antitumor drugs such as irinotecan 3 (formerly
called as CPT-11 and now called campstar) [4], and top-
otecan 4 (now called hycamtin) [5] were developed
from camptothecin and currently used for the treatment
of ovarian and small lung cancer, and for colorectal can-
cer. At present, a number of camptothecin-based drugs
are in different stages of clinical development [6].
The 5-hydroxy-(20S)-camptothecin required for our
study was prepared according to the reported literature
procedure [9]. 5-Aryl and 5-amido-(20S)-camptothecin
analogues described herein were synthesized by a one
pot reaction of 5-hydroxy-(20S)-camptothecin 2 with
various aromatic hydrocarbons, aryl, and alkyl nitriles in
RESULTS AND DISCUSSIONS
Several reports are known in the literature for the syn-
thesis of (20S)-camptothecin analogues by utilizing the
C
V
2011 HeteroCorporation

May 2011
Synthesis of 5-Aryl and 5-Amidocamptothecins
541
the ratio 22.13%, 45.38%, 7.81%, and 23.09%, respec-
tively along with two unidentified impurities of around
1.3%. Products were then separated by preparative TLC
as diastereomeric pairs. Structure of the products was
then confirmed by NMR, Mass spectrum analysis, and by
other analytical methods as 5-(4-methylphenyl)-(20S)-
camptothecin (8) as major and 5-(2-methylphenyl)-(20S)-
camptothecin (9) as minor isomer [10].
To prove the assigned structure, NOESY, HMBC, and
COSY NMR experiments were conducted. These studies
further confirmed 5-para isomer
8 as the major
regioisomer formed in the reaction. Our attempt to gen-
erate a single crystal of the major diastereomer from
product mixture with various solvents were not success-
ful, however a single crystal in the form of twin crystal
was able to generate from chloroform and XRD of the
twin crystal was studied further. ORTEP diagram of the
twin crystal confirms (5R), (20S) configuration at asym-
metric centers of the products 8 and 9 [11]. Thus, dia-
stereoselectivity of the reaction is partly influenced by
remote chiral C-(20S) carbon atom in which bulky ethyl
group is trans to the incoming nucleophile (Fig. 2).
Figure 1. Structure of camptothecin and camptothecin based anti-
cancer drugs.
presence of protic acids at moderate temperature in good
to average yields. Synthesis of 5-aryl and 5-amido-(20S)-
camptothecin derived from 5-hydroxy-(20S)-camptothecin
is outlined in Scheme 2. To a suspension of 5-hydroxy-
(20S)-camptothecin 2 in toluene (7), sulphuric acid was
added at room temperature and the reaction mixture was
refluxed in toluene at 110–115ꢀC for 4–5 h. After com-
plete disappearance of the starting material 2 (by TLC),
reaction mixture was cooled to room temperature, diluted
with ethyl acetate and washed with 5% aq. sodium bicar-
bonate solution and water. Organic layer was then sepa-
rated, concentrated under reduced pressure, and the prod-
uct was isolated by chromatographic purification in 66%
of yield (Scheme 2) as light yellow solid. HPLC analysis
of the product indicated the presence of four isomers in
A typical mechanism of the reaction involves protona-
tion of C5-hydroxyl group by protic acid and subsequent
elimination of water molecule leads to the formation of
iminium ion 11. Iminium ion 11 is then trapped by the
nucleophile present (in this case toluene) in the reaction
medium resulted in the formation of 12, which on further
proton loss leads to products 8 and 9. Depending on the
nature of substitution pattern on aromatic hydrocarbon,
reaction will result regioisomeric mixture of 5-aryl-
(20S)-camptothecins as diastereomeric pairs (Scheme 3).
Encouraged by these findings, reactivity of 5-
hydroxy-(20S)-camptothecin toward other aromatic
hydrocarbons were then studied in detail under protic
acid conditions. 5-Hydroxy-(20S)-camptothecin (2) thus
Scheme 1
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S. B. Meruva, A. Raghunadh, N. Anil Kumar, U. K. Syam Kumar, R. Vasu Dev, and P. K. Dubey Vol 48
Scheme 2
was reacted with aromatic hydrocarbons such as benzene
(13), fluorobenzene (14), anisole (15), biphenyl (16), and
naphthalene (21), respectively in presence of various
protic acids, and the products 5-aryl-(20S)-camptothecins
(17–20b) were isolated in moderate to good yields. The
reaction of 5-hydroxy-(20S)-camptothecin (2) with ben-
zene, fluorobenzene, anisole, and biphenyl were per-
formed under neat reaction conditions in presence of sul-
phuric acid. As expected, the reaction of fluorobenzene,
anisole and biphenyl with 2 resulted in regioisomeric
mixture of ortho and para products as a diastereomeric
pairs, where as benzene resulted (5R,S)-phenyl-(20S)-
camptothecin 17 in 1.2:1 diastereomeric ratio in 86% of
yield. In the case of reaction of 2 with fluorobenzene
(14), anisole (15), and biphenyl (16), major product iso-
lated were the para regioisomer. The formation of para
regioisomer as major product in these reactions can be
attributed solely to the less steric crowding during nucle-
ophilic attack on the so-formed iminium ion by the sub-
stituted aromatic hydrocarbons. Thus the reaction of 2
with fluorobenzene (14) resulted 5-(4-fluorophenyl)-
(20S)-camptothecin (18a) and 5-(2-fluorophenyl)-(20S)-
camptothecin (18b) in overall 37.9% of yield, where as
anisole (15) and biphenyl (16) resulted the products, 19a,
b and 20a, b in overall 43.3% and 45.7% yields, respec-
tively (Scheme 4). Structure of the products was then
confirmed by NMR, mass spectral data, and by other ana-
lytical and spectroscopic methods.
ticipate in Ritter type reaction [12]. Thus we have
attempted the reaction of 2 with acetonitrile in a view to
synthesis hither to unreported 5-amido substituted camp-
tothecins under Ritter reaction conditions (Scheme 6).
Thus to a suspension of 5-hydroxy-(20S)-camptothecin 2
in acetonitrile (23), trifluoroacetic acid was added, and
the reaction mixture was refluxed for 6–8 h. After usual
aqueous work up and column chromatographic purifica-
tion, product 5-acetamido-(20S)-camptothecin (24) was
isolated in low yield (25%) as yellow crystalline solid
without any diastereoselectivity. The LCMS analysis of
the crude reaction mixture also indicated the formation
of 5-diacetamido-(20S)-camptothecin (25) in 5–7%.
However our attempt to isolate the product 25 in pure
form was not successful.
Reaction of 5-hydroxy-(20S) camptothecin 2 with
naphthalene 21 was then studied in detail. The reaction
was conducted in 1, 2-dichloroethane in presence of
trifluoroacetic acid at 60–70ꢀC (Scheme 5). Marked
improvement in diastereoselectivity was observed in this
reaction, as naphthalene resulted product, (5R,S)-naph-
thyl-(20S)-camptothecin (22) in 5:1 ratio, however prod-
uct was isolated in low yield (40%). The low yield of
product formation 22 is solely due to increased steric
repulsion between the planar bulky molecules, naphtha-
lene, and camptothecin.
In principle, any functionality capable of producing a
carbonium ion under acidic conditions will able to par-
Figure 2. The ORTEP presentation of 5-para toluyl (8) and 5-ortho
toluylcamptothecins (9).
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Synthesis of 5-Aryl and 5-Amidocamptothecins
543
Scheme 3
The Ritter type reaction was then extended to alkyl
nitriles like propionitrile (26), and phenylacetonitrile
(27), also with benzonitrile (28) under identical reaction
conditions (Scheme 7). The product 5-propionamido-
(20S)-camptothecin (29), phenylacetamidocamptothecin
(30), and benzamidocamptothecin (31), were isolated in
40%, 31%, and 37% of yields, respectively, as yellow
crystalline solid. In the case of reaction of propionitrile
with 2, diamido compound 32 was isolated in 9% of
yield and was fully characterized. Formation of diamide
Scheme 4
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S. B. Meruva, A. Raghunadh, N. Anil Kumar, U. K. Syam Kumar, R. Vasu Dev, and P. K. Dubey Vol 48
Scheme 5
Scheme 6
25 as well as 32 under Ritter reaction conditions prob-
ably due to less bulky nature of acetonitrile and propio-
nitrile, and further the reaction of these nitrile with so-
formed monoamides 24 and 25 [13]. All the amido-
camptothecin were isolated as diastereomeric pairs with-
out any diastereoselectivity.
these analogues could serve as potential scaffolds for
the development of novel anticancer agents.
CONCLUSION
We have evaluated compounds 8, 9, 17, 18a, b, and
19a, b for in vitro anticancer activity in three human
cancer cell lines HT-29 (colon), NCI-H460 (lung), and
LoVo (colon) following the NCI standard protocol for
screening anticancer molecules [14]. The compounds
were tested at 100, 10, 1.0, 0.1, and 0.01 lM concentra-
tions (Table 1). The average concentration that causes
50% growth inhibition (GI50 value) of cells with these
compounds was found to be 32, 45, 52, and 13 lM,
respectively. Compound 19a, b exhibited significant
anticancer properties. This study thus indicates that
In conclusion, we have demonstrated that 5-hydroxy-
(20S)-camptothecin 2 can utilize as a potential source
for the generation of iminium ion at C-5 position of
camptothecin. The iminium ion thus formed can be
trapped with different nucleophiles present in the reac-
tion medium. The diastereoselectivity of these nucleo-
philic substitution reactions are partly controlled by the
remote C-(20S) carbon atom bearing the ethyl group.
No diastereoselectivity was observed during the reaction
of aromatic and alkyl nitriles with 2 under Ritter type
reaction conditions. As a result of these studies, a new
Scheme 7
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Synthesis of 5-Aryl and 5-Amidocamptothecins
545
Table 1
Results of anticancer activity stadies of several compounds.
Cell line
% Growth
Growth inhibition in lM
Compound no: 8, 9
100 lM
34
3
13
10 lM
85
62
1 lM
78
81
0.1 lM
90
91
0.01 lM
97
101
G150
49
16
TG1
HT29
H460
100
100
100
100
LoVo
Average
Compound no: 17
89
90
100
113
33
32
100 lM
49
20
10 lM
94
54
1 lM
104
91
0.1 lM
103
97
0.01 mM
103
98
G150
94
13
28
45
TG1
100
100
100
100
HT29
H460
LoVo
Average
Compound no: 18a, b
11
81
99
100
101
100 lM
51
23
10 lM
98
73
1 lM
101
89
0.1 lM
101
97
0.01 lM
G150
100
29
TG1
100
100
100
100
HT29
H460
92
94
92
LoVo
Average
14
76
90
89
26
52
Compound no: 19a, b
100 lM
10 lM
73
34
1 lM
97
77
0.1 lM
102
91
0.01 lM
104
94
G150
28
4
5
13
TG1
100
100
100
100
HT29
H460
LoVo
Average
22
11
4
40
79
97
99
GI50 is the concentration of test drug where 100 ꢁ (T ꢂ T0)/(C ꢂ T0) ¼ 50, where the optical density of the test cell after a 48-h period of expo-
sure to test drug is T, the optical density at time zero is T0, and the control optical density is C. The TGI is the concentration of test drug where
100 ꢁ (T ꢂ T0)/(C ꢂ T0) ¼ 0. Thus, the TGI signifies a cytostatic effect.
ture, diluted with 5% aq. sodium bicarbonate solution (100
mL) and extracted with ethyl acetate (3 ꢁ 75 mL). The or-
ganic layer was then separated and washed with water (2 ꢁ
100 mL) and dried over sodium sulphate. The solvent was
then removed under vacuum to obtain the crude product which
was further purified by column chromatography to yield 1.6 g
of product in 66% of yield, as pale yellow solid; mp 238–
240ꢀC; HPLC purity: 21.13, 42.38, 7.81, and 23.09%; IR
(KBr) cmꢂ1: 3422, 1750, 1659, 1617, 1405, 1156, 1041, 824;
1H-NMR (400 MHz, CDCl3) d 8.36 (s, 1H), 8.19 (d, J ¼ 8.4
Hz, 1H), 8.06 (d, J ¼ 8Hz, 1H), 7.86 (t, J ¼ 7.6 Hz, 1H), 7.67
(t, J ¼ 7.6 Hz, 1H), 7.4 (dd, J ¼ 4, 3.2 Hz, 1H), 7.3 (d, J ¼
7.2 Hz, 0.5 H), 7.12 (t, J ¼ 6.8 Hz, 1.5H), 6.98 (dd, J ¼ 9.6,
5.6 Hz, 1H), 6.74 (s, 1H), 6.51 (dd, J ¼ 4.0, 4.4 Hz, 1H), 5.35
(tddd, 2H), 2.8 (s, 1H), 2.23 (s, 3H), 1.85 (m, 2H), 0.90 (t,
3H); 13C-NMR (100 MHz, DMSO): d 172.4, 156.4, 151.4,
150.1, 148.2, 145.3, 137.3, 136.5, 135.7, 134.7, 134.5, 131.6,
130.6, 129.3, 128.9, 128.1, 127.6, 126.7, 124.6, 120.4, 96.7,
72.3, 65.2, 61.3, 30.3, 20.6, 7.8; Mþ (m/e): 439 (97%), 395
(12%), 243 (8%), 215 (5%), 137(10%); Anal calcd for
C27H22N2O4: C, 73.94; H, 5.06; N, 6.39; Found: C, 73.94; H,
4.83; N, 6.38, O, 14.59.
series of hither to unreported novel classes of 5-aryl and
5-amido substituted (20S)-camptothecin analogues were
synthesized. The biological properties of few of these
compounds were tested against HT-29 (colon), NCI-
H460 (lung), and LoVo (colon) cell line panels and
found that some of these compounds can be potential
scaffold for the development of novel anticancer agents.
EXPERIMENTAL
Experimental section. Solvents and reagents are obtained
from commercial sources and are not purified unless specified.
1H-NMR data was recorded on Varian Gemini 400 MHz FT
NMR spectrometer and 13C was recorded on Varian Gemini
100 MHz FT NMR spectrometer. Infrared spectra (IR) were
recorded on Perkin-Elmer 1650 FT-IR spectrometer. Mass
spectra were recorded on HP-5989A quadrapole mass spec-
trometer. Melting points were taken in open capillaries and are
uncorrected. The HPLC analysis was performed on Water
HPLC system with Millennium software.
Synthesis of 5-(4-methylphenyl)-(20S)-camptothecin (8)
and 5-(2-methylphenyl)-(20S)-camptothecin (9). To a well
stirred suspension of 5-hydroxy-(20S)-camptothecin (2) (2.0 g,
5.49 mmol) in toluene (20 mL, 10 volume) was added, conc.
sulfuric acid (1.6 g, 16.44 mmol) at room temperature. The
reaction mixture was slowly refluxed for 3–4 h (monitored by
TLC). The reaction mixture was then cooled to room tempera-
Synthesis of 5-phenyl-(20S)-camptothecin (17). The syn-
thesis of 17 was achieved by adopting the same procedure of
8, instead of toluene (7); benzene (13) was used as the solvent.
The reaction was done with 1 g (2.74 mmol) of 5-hydroxy-
(20S)-camptothecin 2. The reaction yielded the product 17 (1.0
g, 86%) as a mixture of diastereomers in 54.65:44.51 ratiosꢂi1n
HPLC. pale yellow solid, mp 255–256ꢀC. IR (KBr) cm
:
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1
3462, 1749, 1657, 1609, 1155, 824, 616; H-NMR (400 MHz,
DMSO) d 8.4 (s, 1H), 8.2 (d, J¼ 8.4 Hz, 1H), 8.08 (d, J ¼ 8.0
Hz, 1H), 7.86 (t, J ¼ 7.6 Hz, 1H), 7.67 (t, J ¼ 7.6 Hz, 1H),
7.42 (d, J ¼ 3.6Hz, 1H), 7.38–7.22 (m, 5H), 6.83 (d, J ¼ 11.6
Hz, 1H), 6.53 (d, J ¼ 10.8 Hz, 1H), 5.34 (dtd, J ¼ 6.4, 6.6,
4.8 Hz, 2H), 1.85 (m, 2H), 0.87 (t, 3H); 13C-NMR (100 MHz,
DMSO) d 172.3, 157.1, 156.4, 151.1, 150.2, 148.2, 145.1,
137.5, 134.5, 131.6, 130.5, 128.9, 128.7, 128.5, 128.1, 127.8,
127.6, 126.6, 120.4, 96.8, 79.5, 78.8, 72.3, 65.1, 30.3, 7.8; Mþ
(m/e): 425 (97%), 381 (43%), 95 (2%); Anal calcd for
C26H20N2O4: C, 73.56; H, 4.75; N, 6.60; Found: C, 73.56; H,
4.75; N, 6.60; O, 15.07.
lution (100 mL) and extracted with dichloromethane (3 ꢁ 75
mL). The organic layer was separated and washed with water
(2 ꢁ 100 mL), solvent removed under reduced pressure to
obtain the crude product. It was then purified by column chro-
matography furnished 20a (0.56 g, 40.7%); Major isomer:
Melting range 189–190ꢀC; IR (KBr) cmꢂ1: 3395, 3057, 2969,
1747, 1662, 1617, 1559, 1404, 1221, 1155, 1045, 824, 757,
1
704; H-NMR (400 MHz, DMSO) d 8.2 (s, 1H), 8.16 (d, J ¼
8.4 Hz, 1H), 8.08 (d, J ¼ 7.6 Hz, 1H), 7.9 (dd, J ¼ 7.2, 6.4
Hz, 1H), 7.85 (t, J ¼ 8.0 Hz, 1H), 7.66 (t, J ¼ 8.0 Hz, 1H),
7.58 (t, J ¼ 7.2 Hz, 1H), 7.47 (t, J ¼ 8.0 Hz, 1H), 7.36 (t, J
¼ 8.0 Hz, 3H), 7.16 (t, J ¼ 8.0 Hz, 1H), 6.85 (s, 1H), 6.75 (s,
1H), 6.56 (t, J ¼ 4.0 Hz, 1H), 6.53 (s, 1H), 5.31 (d, J ¼ 7.6
Hz, 1H), 1.86 (m, 2H), 1.24 (s, 1H), 0.87 (t, J ¼ 7.2 Hz, 3H);
13C-NMR (100 MHz, DMSO): d 172.2, 156.3, 151.1, 150.0,
148.0, 145.3, 141.7, 135.2, 134.8, 130.9, 130.5, 130.2, 129.8,
128.8, 128.4, 128.2, 128.0, 127.7, 127.6, 127.4, 124.7, 120.3,
96.7, 72.2, 65.2, 32.1, 30.3, 7.7. Mþ (m/e): 501.2. Anal calcd
for C32H24N2O4: C, 76.78; H, 4.83; N, 5.60; O, 12.79. Found:
C, 76.77; H, 4.84; N, 5.59; O, 12.78.
Synthesis of 5-(fluorophenyl)-(20S)-camptothecin (18a,
b). The product 18a and 18b were synthesized as per the pro-
cedure adopted for compound (8), using fluorobenzene (14) as
the solvent instead of toluene (7). The reaction was done with
1.0 g (2.74 mmol) of 5-hydroxy-(20S)-camptothecin 2 and
yielded 18a, b (0.45 g, 37.9%) as pale yellow solid, mp 245–
248ꢀC; HPLC Purity: 38.35, 17.3, and 41.5%; IR (KBr) cmꢂ1
:
3235, 2927, 1749, 1656, 1608, 1590, 1406, 1229, 1196, 1157,
1039, 824, 767; 1H-NMR (400 MHz, CDCl3) d 8.4 (s, 1H),
8.17 (t, J ¼ 8.8 Hz, 1H), 8.08 (t, J ¼ 7.2 Hz, 1H), 7.87 (t,
1H), 7.68 (t, J ¼ 7.6 Hz ,1H), 7.4 (d, J ¼ 3.2 Hz, 1H), 7.38
(t, J ¼ 4, 0.5H), 7.31 (dd, J ¼ 3.6, 3.2, 2.0 Hz, 1H), 7.21 (s,
0.5H), 7.15 (ddd, J ¼ 3.6, 3.6, 3.6 Hz, 1H), 6.97 (dd, J ¼ 7.68
Hz, 1H), 6.84 (S, 1H), 6.53 (td, J ¼ 4, 3.2 Hz, 1H), 5.35 (q,
2H), 1.87 (m, 2H), 0.90 (t, 3H); 13C-NMR (100 MHz, DMSO)
d 172.2, 159.2, 156.4, 151.2, 150.1, 148.2, 145.1, 143.4, 134.5,
133.5, 132.7, 131.8, 131.3, 130.7, 129.0, 128.6, 128.1, 127.7,
124.8, 120.5, 115.8, 74.3, 72.3, 65.1, 30.2, 7.7; Mþ (m/e): 443
(97%), 399 (60%), 154 (18%); Anal calcd for C26H19N2O4F:
C, 70.72, H, 4.11, N, 6.16; Found: C, 70.41; H, 4.16, N, 6.17,
F, 4.28.
Synthesis of 5-(4-methoxy phenyl)-(20S)-camptothecin
and 5-(2-methoxy phenyl)-(20S)-camptothecin (19a, b). The
product 19a and 19b was synthesized as per the procedure
adopted for compound 8, using anisole (15) as the solvent
instead of toluene (7). The reaction was done with 1.0 g (2.74
mmol) of 5-hydroxy-(20S)-camptothecin 2 and yielded 19a
and 19b (0.46 g, 43.37%) as pale yellow solid; mp 166–
168ꢀC; HPLC Purity: 22.35, 48.07, 24.76, and 1.25%; IR
(KBr) cmꢂ1: 3392, 2935, 1751, 1660, 1608, 1511, 1461, 1406,
Minor isomer (20b): Yield 5%; Melting range 192–194ꢀC;
IR (KBr) cmꢂ1: 3418, 3056, 2969, 1746, 1662, 1618, 1559,
1404, 1222, 1155, 1046, 824, 758, 702; 1H-NMR (400 MHz,
DMSO) d 8.45 (s, 0.5H), 8.14 (d, J ¼ 8.4 Hz, 1H), 8.08 (t,
J ¼ 7.6, 7.2 Hz, 1H), 7.93 (t, J ¼ 6.8, 6.4 Hz, 1H), 7.87 (q,
J ¼ 8.8 Hz, 1H), 7.68 (t, J ¼ 7.2 Hz, 1H), 7.6 (q, J ¼ 8.0
Hz, 2H), 7.44 (m, 2H), 7.36 (m, 3H), 7.16 (d, J ¼ 6.8 Hz,
1H), 6.8 (s, 0.5H), 6.75 (s, 1H), 6.55 (d, J ¼ 8.8 Hz, 1H),
5.34 (m, 2H), 1.89 (m, 2H), 1.24 (s, 1H), 0.93 (t, J ¼ 7.2
Hz, 3H); 13C-NMR (100 MHz, DMSO): d 172.2, 156.4,
151.2, 150.1, 148.2, 145.1, 139.8, 139.5, 135.0, 134.5, 131.7,
130.6, 129.8, 128.8, 128.5, 127.3, 126.5, 120.4, 96.7, 72.2,
65.1, 30.3, 7.9. Mþ (m/e): 501.2. Anal calcd for
C32H24N2O4: C, 76.78; H, 4.83; N, 5.60; O, 12.79. Found:
C, 76.71; H, 4.80; N, 5.56; O, 12.74.
Synthesis of 5-(1-naphthyl)-(20S)-camptothecin (22). To a
suspension of 5-hydroxy-(20S)-camptothecin 2 (2.5 g, 6.86
mmol) in 1, 2-dichloroethane (25 mL) at room temperature
was added naphthalene (21) (8.79 g, 68.6 mmol) and stirred
for 10 min. To this suspension, trifluoroacetic acid (8.65 g)
was added. The reaction mixture was heated to 65–75ꢀC and
maintained for 12–16 h (monitored by TLC). It was then
cooled to room temperature, diluted with 5% aq. sodium bicar-
bonate solution (100 mL), and extracted with dichloromethane
(3 ꢁ 75 mL). The organic layer was separated and washed
with water (2 ꢁ 100 mL), and the solvent removed under
reduced pressure to obtain crude product. Purification by col-
umn chromatography furnished 22 (1.3 g, 40%) as a yellow
solid. mp 197–198ꢀC; HPLC Purity: 58.18 and 34.81%; IR
(KBr) cmꢂ1: 3433, 1794, 1759, 1673, 1623, 1143, 825, 789,
1
1247, 1157, 1046, 757; H-NMR (400 MHz, CDCl3) d 8.36 (s,
1H), 8.17 (t, J ¼ 7.2 Hz, 1H), 8.07 (d, J ¼ 8.4, 1H), 7.86 (q,
J ¼ 8.0Hz, 1H), 7.65 (q, J ¼ 6.8 Hz, 1H), 7.4 (d, J ¼ 3.6 Hz,
1H), 7.28 (m, 0.5 H), 7.14 (dd, J ¼ 2.4, 2.0, 2.8 Hz, 1H), 6.91
(m, 0.5 H), 6.87 (dd, J ¼ 2.4, 2.0, 2.4 Hz, 1H), 6.77 (s, 1H),
6.5 (dd, J ¼ 4.0, 3.2 Hz, 1H), 5.36 (q, 2H), 3.74 (s, 3H), 1.88
(m, 3H), 0.89 (t, 3H); 13C-NMR (100 MHz, DMSO): d 172.5,
158.9, 156.4, 151.2, 150.1, 148.2, 145.6, 145.0, 134.9, 131.6,
130.5, 129.4, 128.9, 128.3, 128.2, 128.1, 127.6, 125.0, 120.7,
114.1, 112.1, 96.6, 72.3, 65.2, 55.7, 30.3, 7.7; Mþ (m/e): 455
(97%), 411 (8%); Anal calcd for C27H22N2O5: C, 71.34; H,
4.88; N, 6.11; Found: C, 71.34; H, 4.88; N, 6.16; O, 17.60.
Synthesis of 5-(4-biphenyl)-(20S)-camptothecin and 5-(2-
biphenyl)-(20S)-camptothecin (20a, b). 5-Hydroxy-(20S)-
camptothecin 2 (1.0 g, 2.74 mmol), biphenyl (16) (0.466 g,
3.02 mmol) and trifluoroacetic acid (1.23 g, 8.22 mmol) were
taken in round bottomed flask under nitrogen atmosphere at
room temperature. Reaction mixture was heated to 65–75ꢀC
and maintained for 10–14 h. Reaction mixture was cooled to
room temperature, diluted with 5% aq. sodium bicarbonate so-
1
and 772; H-NMR (400 MHz, DMSO) d 8.82 (s, 1H), 8.26 (d,
J ¼ 7.2 Hz, 1H), 8.2 (d, J ¼ 8.4 Hz, 1H), 8.07 (d, J ¼ 8.4
Hz, 1H), 8.01 (d, J ¼ 8.0 Hz, 1H), 7.92 (m, 2H), 7.82 (q, 2H),
7.71 (t, J ¼ 7.4 Hz, 1H), 7.63 (t, J ¼ 7.6 Hz, 1H), 7.51 (dd, J
¼ 3.2, 3.6 Hz, 2H), 7.32 (m, 1H), 6.76 (dd, J ¼ 7.2 Hz, 1H),
5.45 (m, 2H), 2.36 (m, 2H), 1.02 (t, 3H); 13C-NMR (100
MHz, DMSO): d 165.3, 155.8, 150.7, 148.1, 146.7, 143.5,
135.1, 133.7, 133.2, 132.9, 130.7, 128.8, 128.6, 128.2, 128.2,
127.7, 126.9, 126.2, 125.6, 123.5, 121.7, 120.5, 120.5, 94.3,
80.5, 72.3, 66.4, 61.0, 29.8, 7.8; Mþ (m/e): 474.5 (25%), 473.4
(50%) 443 (12%), 346.9 (8%); Anal calcd for C30H22N2O4: C,
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

May 2011
Synthesis of 5-Aryl and 5-Amidocamptothecins
547
75.94; H, 4.67; N, 5.90; O, 13.49, Found: C, 75.92; H, 4.60;
N, 5.86; O, 13.41.
Synthesis of 5-phenylacetamido-(20S)-camptothecin (30). 5-
Hydroxy-(20S)-camptothecin 2 (2.0 g, 5.49 mmol) was sus-
pended in phenyl acetonitrile (27) (0.75 g, 6.0 mmol) and
stirred for 10 min. Trifluoroacetic acid (2.5 g) was added into
the reaction mass at room temperature. Reaction mixture was
heated to 65–75ꢀC and maintained for 8–12 h. Reaction mix-
ture was cooled to room temperature, diluted with 5% aq. so-
dium bicarbonate solution (100 mL) and extracted with
dichloromethane (3 ꢁ 75 mL). The organic layer was washed
with water (2 ꢁ 100 mL), separated and solvent was removed
under reduced pressure to obtain the crude product which was
further purified by column chromatography and resulted 30 in
31% (0.82 g) of yield, mp: 155–156ꢀC; IR (KBr) cmꢂ1: 3302,
3060, 2973, 1747, 1662, 1614, 1567, 1403, 1227, 1157, 1046,
Synthesis of 5-acetamido-(20S)-camptothecin (24). 5-
Hydroxy-(20S)-camptothecin 2 (2.5 g, 6.86 mmol) was sus-
pended in acetonitrile (23) (25.0 g) and stirred for 10 min.
To the reaction mixture was added, trifluoroacetic acid (8.65
g, 41.2 mmol) at room temperature. Reaction mixture was
heated to 65–75ꢀC and maintained for 12–16 h. Reaction
mixture was cooled to room temperature, diluted with 5% aq.
sodium bicarbonate solution (100 mL) and extracted with
dichloromethane (2 ꢁ 75 mL). The organic layer was sepa-
rated and washed with water (2 ꢁ 100 mL), solvent was
removed under reduced pressure to obtain the crude product.
It was then purified by column chromatography resulted 24
as yellow solid in 25% (0.69 g) of yield, mp: 269–270ꢀC;
HPLC Purity: 54.8 and 43.1%; IR (KBr) cmꢂ1: 3376, 1744,
1667, 1618, 1158, 760; 1H-NMR (400 MHz, DMSO) d 9.1
(dd, J ¼ 8.0, 8.0 Hz, 1H), 8.54 (d, J ¼ 5.6 Hz, 1H), 8.15 (t,
J ¼ 8.2 Hz, 2H), 7.87 (t, J ¼ 7.8 Hz, 1H), 7.70 (t, J ¼ 7.2
Hz, 1H), 7.27 (d, J ¼ 7.6 Hz, 1H), 7.14 (dd, J ¼ 8.4, 6.8
Hz, 1H), 6.51 (d, J ¼ 4.4 Hz, 1H), 5.4 (m, 2H), 1.84 (m,
5H), 0.89 (m, 3H); 13C-NMR (100 MHz, DMSO): d 172.2,
169.1, 156.6, 151.7, 150.1, 148.3, 144.6, 131.9, 131.1, 130.6,
128.9, 128.7, 128.2, 127.6, 120.9, 96.4, 72.2, 66.3, 65.2,
30.2, 22.5, 7.7; Mþ (m/e): 406.3 (97%), 347.3 (30%), 303
(10%); Anal calcd for C22H19N3O5: C, 65.18; H, 4.72; N,
10.37; O, 19.73. Found: C, 65.10; H, 4.79; N, 10.35; O,
19.69.
1
758; H-NMR (400 MHz, DMSO) d 9.43 (d, J ¼ 7.2 Hz, 1H),
8.68 (d, J ¼ 2.8 Hz, 1H), 8.47 (s, 1H), 8.17 (d, J ¼ 8.4 Hz,
1H), 8.12 (d, J ¼ 8 Hz, 1H), 7.9 (q, J ¼ 8 Hz, 1H), 7.7 (dd, J
¼ 8.4, 8.6 Hz, 1H), 7.33–7.18 (m, 3H), 7.13 (d, J ¼ 7.2 Hz,
1H), 6.97 (dd, J ¼ 8.0, 8.4 Hz, 1H), 6.33 (s, 1H), 5.4 (d, J ¼
8.0 Hz, 2H), 3.46 (m, 2H), 1.86 (m, 2H), 0.88 (m, 3H); 13C-
NMR (100 MHz, DMSO): d 172.3, 170.1, 167.1, 157.1, 156.1,
151.8, 151.2, 150.4, 150.0, 150.1, 148.7, 144.7, 143.5, 136.5,
135.5, 132.8, 132.3, 131.8, 130.9, 129.3, 129.1, 129.0, 128.8,
128.1, 127.7, 126.4, 121.4, 120.9, 96.4, 82.7, 72.2, 66.6, 65.3,
40.2, 30.2, 7.8; Mþ (m/e): 481.5 (100%); Anal calcd for
C27H21N3O5: C, 69.37; H, 4.53; N, 8.99; O, 17.11. Found: C,
69.40, H, 4.51; N, 8.90; O, 17.09.
Synthesis of 5-benzamido-(20S)-camptothecin (31). 5-
Hydroxy-(20S)-camptothecin 2 (2.0 g, 5.49 mmol) was sus-
pended in benzonitrile (28) (1.7 g, 16.4 mmol) and stirred for
10 min. Trifluoroacetic acid (2.5 g) was added into the reac-
tion mixture at room temperature. The contents were heated to
65–75ꢀC and maintained for 8–12 h. Reaction mixture was
cooled to room temperature, diluted with 5% aq. sodium bicar-
bonate solution (100 mL) and extracted with dichloromethane
(3 ꢁ 75 mL). The organic layer was washed with water (2 ꢁ
100 mL) separated and solvent was removed under reduced
pressure to obtain the crude product which was further purified
by column chromatography and resulted 31 in 37% (0.95 g) of
yield, mp: 204–205ꢀC; IR (KBr) cmꢂ1: 3366, 3302, 3058,
2972, 1751, 1658, 1614, 1578, 1529, 1520, 1403, 1367, 1226,
1155, 1055, 790, 743, 683; 1H-NMR (400 MHz, DMSO) d
9.68 (d, J ¼ 8.0 Hz 1H), 8.77 (d, J ¼ 6.8 Hz, 1H), 8.62 (d, J
¼ 8.0 Hz, 1H), 8.2 (d, J ¼ 8.8 Hz, 1H), 8.15 (d, J ¼ 8.4 Hz,
1H), 7.9 (s, 1H), 7.88 (dd, J ¼ 8.4, 8.6 Hz, 2H), 7.69 (m, 1H),
7.6–7.4 (m, 4H), 7.38 (s, 1H), 7.34 (d, J ¼ 9.4 Hz, 1H), 5.37
(t, J ¼ 9.2 Hz, 2H), 1.88 (m, 2H), 0.88 (m, 3H); 13C-NMR
(100 MHz, DMSO): d 172.1, 167.7, 165.5, 156.6, 150.0,
144.8, 134.1, 133.0, 131.8, 131.0, 130.6, 128.9, 128.6, 128.2,
128.0, 127.3, 120.8, 96.3, 72.2, 66.6, 30.2, 7.8; Mþ (m/e): 419
(100%); Anal calcd for C28H21N3O5: C, 69.84; H, 4.81; N,
8.73; O, 16.61, Found: C, 69.80; H, 4.80; N, 8.71; O, 16.60.
Synthesis of 5-propionamido-(20S)-camptothecin (29). 5-
Hydroxy-(20S)-camptothecin 2 (2.0 g, 5.49 mmol) was sus-
pended in propionitrile (26) (7.45 g, 68.6 mmol) and stirred
for 10 min. To the reaction mixture was added trifluoroacetic
acid (2.5 g) in at room temperature. Reaction mixture was
heated to 65–75ꢀC and maintained for 8–12 h. Reaction mix-
ture was cooled to room temperature, diluted with 5% aq.
sodium bicarbonate solution (100 mL) and extracted with
dichloromethane (3 ꢁ 75 mL). The combined organic layer
was washed with water (2 ꢁ 100 mL) and separated. Organic
layer was concentrated under reduced pressure to obtain the
crude product which was further purified by column chroma-
tography and obtained 29 in 40% (0.92 g) of yield, mp: 208–
209ꢀC; IR (KBr) cmꢂ1: 3314, 3061, 2975, 1746, 1663, 1614,
1
1562, 1406, 1227, 1155, 1044, 791, 769; H-NMR (400 MHz,
DMSO) d 9.04 (dd, J ¼ 8.0, 8.4 Hz, 1H), 8.64 (dd, J ¼ 3.2,
6.8 Hz, 1H), 8.17 (dd, J ¼ 8.4, 8.2 Hz, 2H), 7.88 (t, J ¼ 6.8
Hz, 1H), 7.77 (t, J ¼ 5.6 Hz, 1H), 7.26 (dd, J ¼ 4.0, 4.4 Hz,
1H), 7.18 (dd, J ¼ 8,7.6 Hz, 1H), 6.54 (dd, J ¼ 4.0, 2.0 Hz,
1H), 5.4 (m, 2H), 2.13 (m, 2H), 1.88 (m, 2H), 0.99 (m, 3H),
0.89 (m, 3H); 13C-NMR (100 MHz, DMSO): d 172.7, 172.3,
156.8, 151.5, 150.1, 148.5, 144.6, 143.7, 133.1, 132.3, 131.9,
131.8, 131.1, 130.9, 130.6, 128.9, 128.7, 128.2, 127.5, 120.8,
120.5, 96.3, 73.0, 72.3, 69.7, 66.3, 65.2, 30.2, 28.2, 9.3, 7.7;
Mþ (m/e): 419 (100%); Anal calcd for C23H21N3O5: C, 65.86;
H, 5.05; N, 10.02; O, 19.07, Found: C, 65.80; H, 5.01; N,
10.08; O, 19.01.
Acknowledgments. We thank Dr. Vilas Dahanukar of Dr.
Reddys Laboratories for his support and constant encouragement.
1
5-(N,N-Dipropionamide-(20S)-camptothecin (32). H-NMR
(400 MHz, DMSO): d 8.97 (d, 1H, J ¼8.4,8.0), 8.53 (s, 2H),
8.15 (m, 2H), 7.86 (t. 2H, J ¼8,7.2), 7.7 (t, 1H, J ¼6.8,8.4),
7.2 (m, 1H), 6.96 (s, 1H), 5.4 (d, 2H, J ¼13.6), 2.51 (s, 4H),
2.12 (m, 2H), 1.09 (m, 6H), 0.94 (t, 3H, J ¼3.2,4.4); Mþ (m/
e): 476.2 (100%), 403 (10%).
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Journal of Heterocyclic Chemistry
DOI 10.1002/jhet