An efficient one-pot synthesis of benzothiazolo-4β-anilino- podophyllotoxin congeners: DNA topoisomerase-II inhibition and anticancer activity

Article abstract of DOI:10.1016/j.bmcl.2010.11.002

An efficient one-pot iodination methodology for the synthesis of benzothiazolo-4β-anilino-podophyllotoxin (5a-h) and benzothiazolo-4β- anilino-4-O-demethylepipodophyllotoxin (6a-h) congeners has been successfully developed by using zirconium tetrachloride

Full text of DOI:10.1016/j.bmcl.2010.11.002

Bioorganic & Medicinal Chemistry Letters 21 (2011) 350–353
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
An efficient one-pot synthesis of benzothiazolo-4b-anilino-podophyllotoxin
congeners: DNA topoisomerase-II inhibition and anticancer activity
Ahmed Kamal a, , B. Ashwini Kumar a, Paidakula Suresh a, Nagula Shankaraiah b, M. Shiva Kumar a
⇑
a Division of Organic Chemistry, Indian Institute of Chemical Technology, Hyderabad 500 607, India
b National Institute of Pharmaceutical Education and Research (NIPER), Hyderabad 500 037, India
a r t i c l e i n f o
a b s t r a c t
Article history:
An efficient one-pot iodination methodology for the synthesis of benzothiazolo-4b-anilino-podophyllotoxin
(5a–h) and benzothiazolo-4b-anilino-4-O-demethylepipodophyllotoxin (6a–h) congeners has been success-
fully developed by using zirconium tetrachloride/sodium iodide. Interestingly, this protocol demonstrates
enhancement of stereoselectivity apart from the improvement in the yields in comparison to previous
methods reported for such related podophyllotoxin derivatives. These compounds have been designed and
synthesized using association strategy by coupling of 4b-podophyllotoxin and 4b-demethylepipodophyllo-
toxin with a variety of substituted aminoaryl benzothiazoles. Some of the representative compounds have
been evaluated for their cytotoxicity against selected human cancer cell lines and DNA topoisomerase-II
inhibition activity.
Received 5 August 2010
Revised 29 October 2010
Accepted 1 November 2010
Available online 11 November 2010
Keywords:
Podophyllotoxin
Benzothiazoles
Iodination
Zirconium tetrachloride
DNA topoisomerase-II inhibition
Anticancer activity
Ó 2010 Elsevier Ltd. All rights reserved.
A variety of reagent systems have been reported in the literature
for the iodination of alcohols.1–6 However, most of the reaction pro-
cedures suffer from several drawbacks such as long reaction times,
harsh reaction conditions, non-commercially available materials
and tedious work-up procedures. In this article, we wish to report
the synthesis of 4b-arylaminopodophyllotoxin derivatives employ-
ing zirconium tetrachloride in combination with sodium iodide
(ZrCl4/NaI) as an efficient and selective reagent. This reagent system
has not been explored much in the literature except for the iodin-
ation of simple benzyl as well as allyl alcohols.7 Moreover, zirconium
salts have been biologically screened that exhibit lower toxicities
and, for example,8 the LD50 of ZrCl4 given orally to rats is
1688 mg kgꢀ1. In this context we decided to explore this protocol
for the one-pot conversion of structurally diverse and sterically hin-
dered 4b-podophyllotoxin to their iodides. These iodo intermediates
have been utilised for the preparation of a new class of substituted
benzothiazolo-4b-anilino-podophyllotoxins.
Podophyllotoxin and its derivatives are important members of
the lignane class of natural products derived from plants of the
genus Podophyllum (1, Fig. 1).9,10 This antimitotic cyclolignan, was
extensively investigated as an antitumour agent, but failed in clini-
cal studies due to severe gastrointestinal side effects.11 However,
some of the semisynthetic derivatives led to the development of
new anticancer drugs like etoposide (2) and teniposide (3),12–15 that
are currently being used in clinic for the treatment of a variety of
malignancies (lung and testicular cancers, lymphoma, nonlympho-
cytic leukaemia, and glioblastoma multiforme).16 Etoposide is
known to block the catalytic activity of DNA topoisomerase II by sta-
bilizing a cleavage enzyme-DNA complex in which the DNA is
cleaved and covalently linked to the enzyme.17 Inspite of its widely
usage in clinic there are several limitations for these semisynthetic
podophyllotoxin derivatives, which has inspired to further search
for new effective anticancer agents based on this scaffold.18
Similarly, the structurally simple and synthetically accessible,
2-(4-aminophenyl)benzothiazole class of compounds have shown
potent and selective antitumour properties. The original member of
this series, 2-(4-aminophenyl)benzothiazole 4a (CJM 126) is found
to exhibit potent and selective in vitro activity against certain cancer
cell lines.19 This compound subsequently superseded as a lead com-
pound with the discovery that certain 30-substituents (CH3, Cl, Br, I)
conferred low nanomolar growth inhibitory activity in an extended
set of human tumour cell lines, from which 2-(4-amino-3-methyl-
phenyl)benzothiazole 4b (DF 203) has been selected as a potent and
selective antitumour agent (Fig. 1).20 In a research programme, we
have been involved in the design and synthesis of new podophyllo-
toxin derivatives as potential DNA topoisomerase-II inhibiting anti-
cancer agents.21–30 In continuation of these efforts, we have
undertaken the synthesis of some new analogues of podophyllotoxin
bylinkingittoabenzothiazolemoietythroughanarylaminospacerat
C-4 position of the podophyllotoxin scaffold with a view to combine
the pharmacological characteristics of both these chromophores.
⇑
Corresponding author. Tel.: +91 40 27193157; fax: +91 40 27193189.
E-mail address: ahmedkamal@iict.res.in (A. Kamal).
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.11.002

A. Kamal et al. / Bioorg. Med. Chem. Lett. 21 (2011) 350–353
351
H
stannous chloride affords the benzothiazoles (11d,e) as shown in
Scheme 1. Later, 2-(4-aminophenyl)-4-chlorobenzothiazole (11f)
and 2-(4-aminophenyl)-4,6-dichlorobenzothiazole (11g) were pre-
pared from substituted 2-aminobenzothiazoles (7f,g). These benzo-
thiazoles converted to their appropriate 2-aminothiophenols by
using 50% aqueous KOH and ethylene glycol (10f,g). The thiophenol
was heated with 4-aminobenzoic acid (7a) in polyphosphoric acid
to afford the appropriate benzothiazoles (11f,g) as shown in Scheme
1. Finally, the 2-(4-amino-3-bromophenyl)benzothiazole (11h) was
synthesized from 2-(40-aminophenyl)benzothiazole (11a) in the
presence of bromine.
O
R
O
OH
C
O
O
HO
O
OH
O
O
R
A
O
D
B
O
O
N
S
H2N
O
O
E
H3CO
OCH3
R = H; 4a
R = CH3;
H3CO
OCH3
4b
OCH3
OH
1
R = methyl; 2
R = thiophenyl; 3
2-(40-Aminophenyl)benzothiazole
linked
podophyllotoxin
R1
R1
N
N
S
R2
R2
congeners (5a–h and 6a–h) were synthesized by employing
ZrCl4/NaI reagent system. The reaction proceeds via the formation
of 4b-iodoepipodophyllotoxin (12) or 4b-iodo-4-O-demethylpodo-
phyllotoxin (13) as intermediates. Moreover, as the iodo interme-
diates are highly reactive and susceptible to nucleophilic attack
in the presence of slightest moisture, these have been subjected
in the crude form for the next step of the reaction to yield the final
products. The synthetic strategy developed for the preparation of
these 2-(4-aminophenyl)benzothiazole substituted popodophyllo-
toxin congeners is shown in Scheme 2. It is interesting to observe
that by employing CH3CN as the solvent produced 2-(4-aminophe-
nyl)benzothiazole substituted epipodophyllotoxin analogues (5a–
h)33 without 4-O-demethylation in 70–85% yield, whereas as the
use of CH2Cl2 as the solvent produces 2-(40-aminophenyl)benzothi-
azole substituted 40-O-demethylepipodophyllotoxin (6a–h)33 in
60–75% yield. The substitution via SN1 mechanism occurs on the
C-4 benzylic carbonium ion, wherein the bulky pendent aromatic
ring-E and ZrCl4/NaI directs the substitution stereoselectively
resulting in high yield of C-4b isomer as the main product. The
present method employing ZrCl4/NaI provides the desired products
in good yields with the required stereoselectivity. The ratio for the
S
HN
HN
O
O
O
O
O
O
O
O
H3CO
OCH3
H3CO
OCH3
OCH3
OH
6a
R
R
1 = H, 2'-Cl, 3'-CH3, 3'-Br
2 = 6-OCH3, 6-F, 4-Cl, 4,6-dichloro
5a
−
h
h
−
Figure 1. Naturally occurring podophyllotoxin (1), clinically using etoposide (2),
teniposide (3), CJM-126 (4a), DF-203 (4b) and the new substituted benzothiazolo-4b-
anilino-podophyllotoxin (5a–h) and 4b-N-demethylepipodophyllotoxin congeners
(6a–h).
A new class of substituted benzothiazolo-4b-anilino-podophyllo-
toxin (5a–h) and 4b-N-demethylepipodophyllotoxin congeners
(6a–h) were synthesized by the coupling of various substituted and
unsubstituted2-(4-aminophenyl)benzothiazoles(11a–h) withpodo-
phyllotoxin (1). Initially, we synthesized a number of aryl substi-
tuted-benzothiazoles with an amino functionality. All the
substituted-benzothiazoles were prepared by employing the litera-
ture methods. Compounds 11a–c were accomplished in a single step
by the mixing of substituted aminobenzoic acid (7a–c) and 2-amino-
thiophenol(8) inpolyphosphoricacid(PPA)athigher temperatures.31
Then, the 2-(4-aminophenyl)-6-methoxybenzothiazole (11d) and 2-
(4-aminophenyl)-6-fluorobenzothiazole (11e) were obtained from
different approaches.32 Reaction of substituted anilines (7d,e) with
p-nitrobenzoylchloride yields the appropriate benzanilides (9d,e).
These were converted to their thiobenzanilides by using Lawesson’s
reagent. The thiobenzanilides were then converted to their 2-(4-
nitrophenyl)-6-benzothiazoles by the Jacobson’s cyclization21
employing K3[Fe(CN)6]. Reduction of these nitro compounds with
formation of C-4b and C-4a isomers is about 9:1.
A series of newly synthesized compounds (5a–h and 6a–h) have
been screened for their cytotoxicity on selected human cancer cell
lines (Zr-75-1, MCF7, KB, Gurav, DWD, A2780, Colon, A549, PC3, oral,
lung, and SiHa). However, few compounds 5a,b,d and 6a,b,f are
showing significant in vitro cytotoxic activity against the selected
cancer cell lines that comprise of colon (Colo 205), lung (Hop-62),
and oral (HT1080, DWD). The screening procedure is based on the
routine method adopted by the Developmental Therapeutic
Programme of National Cancer Institute (NCI)34 and the results are
described in Table 1. All the new compounds were compared with
the standard drug tested, that is, adriamycin (ADR) and podopyllo-
NH2
NH2
SH
R
+
R = H, 2-Cl, 3-CH3
NO2
CO2H
7a
8
c
−
i
NH2
R
NH2
SH
N
S
N
ii, iii
iv, v
NH
i, 7a
vi
S
NH2
NH2
S
R
R
R
11a−g
R
10f,g
7f,g
7d e
,
R = 4-Cl, 4,6-dichloro
vii
R = OCH3, F
R
9d,e
Br
N
NH2
S
11h
Scheme 1. Reagents and conditions: (i) PPA, 220 °C, 3 h, 50ꢀ60%; (ii) p-nitrobenzoylchloride, pyridine, reflux, 2 h, 90%; (iii) Lawesson’s reagent, chlorobenzene, reflux, 3 h,
73%; (iv) K3[Fe(CN)6], 30% aq NaOH, reflux, 30 min, 25%; (v) SnCl2ꢁ2H2O, ethanol, ref lux, 4 h, 90%; (vi) 50% KOH, ethylene glycol, reflux, 48 h, 60%; (vii) 11a, Br2, CH2Cl2, ꢀ5 °C,
2 min, 75%.

352
A. Kamal et al. / Bioorg. Med. Chem. Lett. 21 (2011) 350–353
I
I
OH
O
O
O
O
O
O
O
O
O
iii
i
ii
iii
5a
h
−
6a−h
O
O
O
H3CO
OCH3
OCH3
12
H3CO
OCH3
H3CO
OCH3
OH
OCH3
1
13
Scheme 2. Reagents and conditions: (i) ZrCl4/NaI, CH3CN rt, 15 min; (ii) ZrCl4/NaI, CH2Cl2, rt, 5 h; (iii) 11a–h, THF, BaCO3, rt, 8 h, 70–85%.
Table 1
In vitro (IC50
nificantly in comparison to the activity of the individual
pharmacophores.
lM) cytotoxicity data for some representative compounds
DNA topoisomerase-II inhibition is the pharmacological target
of clinical relevance for most of the podophyllotoxin semisynthetic
derivatives. Therefore, some of the representative compounds (5a
and 6a,d,h) have been evaluated for its inhibition by employing
previous procedure.35 The compounds 6a and 6h from this series
exhibited interesting DNA topoisomerase-II inhibition activity,
suggesting that these new molecules also exhibit biological activity
based on this mechanism similar to the etoposide prototypes. All
these compounds exhibited comparable in vitro inhibition of
topo-II catalytic activity to m-AMSA and the results are illustrated
in Figure 2. Moreover, these results agree with the hypothesis that
the bulky substitution at C-4 position can enhance the activity pro-
file for such compounds.
In conclusion, we have designed and synthesized a series of
benzothiazolo-4b-anilino-podophyllotoxin derivatives by employ-
ing zirconium tetrachloride and sodium iodide reagent system, al-
most in a stereoselective manner with enhanced yields. These
compounds have also shown potent in vitro cytotoxic activity with
better topoisomerase-II inhibition. Moreover, efforts are in pro-
gress to improve the bioavailability of such compounds.
Compounds
Colo 205 (colon)
Hop-62 (lung)
Oral
HT1080
DWD
5a
6a
5d
6b
5f
6f
8.1
2.7
7.0
8.3
7.1
8.3
5.1
5.0
>80
30.1
15.2
8.6
60.3
10.1
5.4
8.2
9.7
9.5
>80
9.1
>80
22
2.3
5.2
6.5
7.3
9.1
2.8
6.1
ADR
Podophyllotoxin
4.7
8.1
13.1
ADR = Adriamycin, podophyllotoxin are the control drug.
toxin, with the concentration of the compound produces to 50% inhi-
bition of cell growth (IC50).
It is interesting to note that one of the most active compounds
being the 40-O-demethyl-4b-[4-(1,3-benzothiazole-2-yl)anilino]-
4-desoxypodophyllotoxin derivative 6a with an IC50 2.7
205) and 2.3 M (DWD) as more potent than the standard adriamy-
cin and podophyllotoxin (5.1 and 5.0 M). These new podophyllo-
lM (colon
l
l
toxin analogues exhibit significant anticancer activity against Colo
205, HT1080, and DWD cell lines, and moderate activity against
Hop-62 cell lines as illustrated in Table 1. It is observed from the data
that by linking benzothiazole moiety thorough an arylamino spacer
at C-4 position of the podophyllotoxin scaffold has shown moderate
improvement in the activity for certain cell lines. However, by
combining these two chromophores the activity has not altered sig-
Acknowledgments
The authors B.A.K and P.S. are thankful to CSIR, New Delhi for
the award of research fellowships.
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5a
Supercoiled DNA
1
1
2
2
3
4
5
6
7
8
9
Supercoiled DNA
Supercoiled DNA
Supercoiled DNA
6a
6d
6h
3
4
5
6
7
8
7
9
8
10
1
2
3
4
5
6
9
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New York, 1991; pp 199–214.
1
2
3
4
5
6
7
8
9
10
Figure 2. Lane number 1 contain supercoiled PBR322 DNA in the absence of
topisomerase II, where the upper band is nicked open circular (OC) DNA and the
lower brighter band is supercoiled covalently closed circular (CCC) DNA. Lane 2
shows CCC DNA related by topoisomerase II. There are various topoisomers and the
upper thick band of relaxed CCC DNA co-migrates with nicked DNA, which is also
relaxed. Lane 3 shows the inhibitory effect of m-AMSA. Lane 4–10 shows the
inhibitory effects of 5a, 6a, 6d and 6h in increasing concentrations, that is, 10, 50,
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2H), 6.5 (s, 1H), 6.61 (d, 2H, J = 8.3 Hz), 6.79 (s, 1H), 7.48 (s, 1H), 7.71 (s, 1H),
3390, 2908, 1773, 1605, 1508, 1481 cmꢀ1
.
9
8.95 (d, 2H, J = 8.3 Hz). IR (KBr):
t
MS (FAB): m/z 691 [M++H]. 4b-[4-(1,3-Benzothiazole-2-yl)-2-bromoanilino]-4-
desoxypodophyllotoxin (5h). Yield (452 mg, 81%), Mp: 125–128 °C, ½a D25
= ꢀ90.0
ꢂ
(c = 1.0 in CHCl3), 1H NMR (300 MHz, CDCl3): d 2.89–3.10 (m, 1H), 3.18 (dd, 1H,
J = 14.6, 4.5 Hz), 3.78 (s, 6H), 3.82 (s, 3H), 4.42 (t, 1H, J = 7.5 Hz), 4.68 (d, 1H,
J = 3.8 Hz), 4.88–5.46 (m, 2H), 6.01 (s, 2H), 6.35 (s, 2H), 6.58 (s, 1H), 6.63 (d, 1H,
J = 8.0 Hz), 6.79 (s, 1H), 7.32–7.55 (m, 2H), 7.85–8.1 (m, 3H), 8.29 (d, 1H,
J = 2.1 Hz). 13C NMR (75 MHz, CDCl3): d 38.4, 41.7, 43.5, 52.3, 56.2, 60.7, 68.3,
101.6, 107.6, 108.3, 109.0, 110.0, 121.4, 122.6, 124.8, 126.3, 128.2, 129.2, 131.8,
132.0, 134.5, 134.3, 137.7, 145.9, 147.8, 148.5, 152.6, 154.0, 166.2, 174.0. IR (KBr):
ꢀ1
+
3394, 2924, 2854, 1776, 1594, 1510, 1484 cm . MS (FAB): m/z 740 [M +K]. 40-
9
t
O-Demethyl-4b-[4-(1,3-benzothiazole-2-yl)anilino]-4-desoxypodophyllotoxin
(6a).
Yield (310 mg, 62%), Mp: 143–147 °C, ½a D25
ꢂ
= ꢀ116.0 (c = 1.0 in CHCl3), 1H
NMR (200 MHz, DMSO-d6+CDCl3): d 2.69–3.04 (m, 1H), 3.28 (dd, 1H, J = 14.3,
4.4 Hz), 3.76 (s, 6H), 3.88–4.16 (m, 2H), 4.34 (t, 1H, J = 8.9 Hz), 4.53 (d, 1H,
J = 4.5 Hz), 4.85 (br s, 1H), 5.95 (d, 2H, J = 4.6 Hz), 6.28 (s, 2H), 6.50 (s, 1H), 6.72
(d, 2H, J = 8.9 Hz), 6.8 (s, 1H), 7.28 (t, 1H, J = 7.1 Hz), 7.4 (t, 1H, J = 7.1 Hz), 7.84
9
33. 4b-[4-(1,3-Benzothiazole-2-yl)anilino]-4-desoxypodophyllotoxin (5a). To
a
(m, 4H). IR (KBr): t
3392, 2914, 1773, 1610, 1510, 1483 cmꢀ1. MS (FAB): m/z
solution of podophyllotoxin (1) (414 mg, 1 mmol) in dry CH3CN (10 mL),
sodium iodide (298 mg, 2 mmol) was added and stirred for 5 min. To this
stirred suspension ZrCl4 (458 mg, 2 mmol) was added drop wise at room
temperature and the stirring was continued for another 15 min at same
temperature. This solution was then evaporated in vacuo and used for the next
reaction without further purification. To the crude product, anhydrous BaCO3
(395 mg, 2 mmol) and 2-(40-aminophenyl)benzothiazole (11a) (271 mg,
1.2 mmol) in 10 mL of dry THF under nitrogen was added and stirred for 8 h
at room temperature. The reaction mixture was filtered, diluted with EtOAc
and washed with water, 10% aqueous sodium thiosulphate solution, dried over
anhydrous Na2SO4 and purified via column chromatography using ethyl
acetate/hexane (1:1) as eluent to afford 5a in 80% yield. Mp: 172–175 °C,
626 [M++NH4]. 4-O-Demethyl-4b-[4-(1,3-benzothiazole-2-yl)-3-chloroanilino]-4-
desoxypodophyllotoxin (6b). Yield (340 mg, 65%), Mp: 157–160 °C,
½
a 2D5
ꢂ
= ꢀ124.0 (c = 1.0 in CHCl3), 1H NMR (300 MHz, CDCl3): d 2.79–3.02 (m,
2H), 3.8 (s, 6H), 4.25–4.40 (m, 2H), 4.55–4.65 (m, 1H), 4.75–4.99 (m, 1H,), 5.40
(br s, 1H), 5.93 and 5.98 (ABq, 2H, J = 1.5 Hz), 6.29 (s, 2H), 6.51 (s, 1H), 6.6 (dd,
1H, J = 9.0, 2.2 Hz), 6.69 (d, 1H, J = 2.2 Hz), 6.77 (s, 1H), 7.37 (t, 1H, J = 8.3 Hz),
7.48 (t, 1H, J = 8.3 Hz), 7.9 (d, 1H, J = 7.5 Hz), 8.03 (d, 1H, J = 7.5 Hz), 8.22 (d, 1H,
J = 9.0 Hz). 13C NMR (75 MHz, CDCl3): d 38.3, 41.8, 43.3, 52.0, 56.4, 68.4, 101.5,
107.2, 107.8, 109.1, 109.8, 111.1, 112.9, 121.1, 122.7, 124.8, 126.2, 127.4, 129.3,
130.3, 132.0, 133.0, 134.1, 135.5, 136.6, 146.4, 147.0, 147.5, 148.3, 149.3, 174.3.
9
IR (KBr):
[M++2].
t
3395, 2920, 1772, 1607, 1520, 1482 cmꢀ1. MS (FAB): m/z 646
4-O-Demethyl-4b-[4-(1,3-benzothiazole-2-yl)-2-methylanilino]-4-
½
a 2D5
ꢂ
= ꢀ120.0 (c = 1.0 in CHCl3), 1H NMR (300 MHz, CDCl3): d 2.69–3.04 (m,
desoxypodophyllotoxin (6c). Yield (381 mg, 75%), Mp: 133–135 °C,
2H), 3.77 (s, 6H), 3.8 (s, 3H), 3.97 (t, 1H, J = 9.6 Hz), 4.29–4.40 (m, 2H), 4.55 (d,
1H, J = 4.4 Hz), 4.63–4.76 (m, 1H), 5.96 (d, 2H, J = 4.7 Hz), 6.27 (s, 2H), 6.52 (s,
1H), 6.63 (d, 2H, J = 8.1 Hz), 6.8 (s, 1H), 7.32 (t, 1H, J = 7.4 Hz), 7.44 (t, 1H,
J = 7.4 Hz), 7.84 (d, 1H, J = 8.1 Hz), 7.96 (m, 3H). 13C NMR (75 MHz, CDCl3): d
38.6, 41.7, 43.5, 52.1, 56.3, 60.6, 68.6, 101.5, 108.6, 109.2, 109.8, 112.1, 121.4,
123.7, 124.5, 126.1, 129.4, 129.8, 131.8, 134.5, 135.0, 147.5, 148.2, 149.8, 152.7,
9
½
a 2D5
ꢂ
= ꢀ130.0 (c = 1.0 in CHCl3), 1H NMR (300 MHz, CDCl3): d 2.21 (s, 3H),
2.89–3.10 (m, 1H), 3.18 (dd, 1H, J = 14.5, 4.5 Hz), 3.8 (s, 6H), 3.90 (t, 1H,
J = 9.7 Hz), 4.41 (t, 1H, J = 7.6 Hz), 4.64 (d, 1H, J = 4.2 Hz), 4.88–5.67 (m, 1H),
6.01 (d, 2H, J = 4.1 Hz), 6.35 (s, 2H), 6.58 (s, 1H), 6.69 (s, 1H), 7.14–7.50 (m, 4H),
3397, 2907, 1773, 1607, 1508, 1484 cmꢀ1. MS
9
t
7.82–8.05 (m, 3H). IR (KBr):
(FAB): m/z 623 [M++H]. 4-O-Demethyl-4b-[4-(6-methoxy-1,3-benzothiazole-2-
yl)anilino]-4-desoxypodophyllotoxin (6d). Yield (329 mg, 63%), Mp: 142–146 °C,
154.2, 168.0, 174.3. IR (KBr):
t
3362, 2925, 1772, 1604, 1505, 1483 cmꢀ1. MS
(FAB): m/z 623 [M++H]. 4b-[4-(1,3-Benzothiazole-2-yl)-3-chloroanilino]-4-
desoxypodophyllotoxin (5b). Yield (443 mg, 85%), Mp: 156–160 °C,
½
a 2D5
ꢂ
= ꢀ109.0 (c = 1.0 in CHCl3), 1H NMR (300 MHz, CDCl3): d 2.89–3.06 (m,
2H), 3.80 (s, 6H), 3.89 (s, 3H), 4.35–4.56 (m, 2H), 4.60 (d, 1H, J = 4.0 Hz), 4.77–
4.90 (m, 1H), 5.40 (br s, 1H), 5.95 (s, 1H), 5.98 (s, 1H), 6.30 (s, 2H), 6.52 (s, 1H),
6.61 (d, 2H, J = 8.8 Hz), 6.79 (s, 1H), 7.02 (dd, 1H, J = 9.2, 2.4 Hz), 7.31 (d, 1H,
J = 2.4 Hz), 7.82–7.91 (m, 3H). 13C NMR (75 MHz, CDCl3): d 38.4, 41.7, 43.3,
52.0, 55.7, 56.4, 68.6, 101.5, 104.2, 107.8, 109.1, 109.8, 112.0, 115.1, 122.8,
123.7, 128.9, 129.7, 130.4, 131.9, 134.0, 146.4, 147.4, 148.2, 148.6, 149.2,
9
½
a 2D5
ꢂ
= ꢀ122 (c = 1.0 in CHCl3), 1H NMR (300 MHz, CDCl3): d 2.93–3.07 (m,
2H), 3.73 (s, 6H), 3.76 (s, 3H), 3.94 (t, 1H, J = 9.0 Hz), 4.38 (t, 2H, J = 7.5 Hz),
4.45–4.60 (m, 1H), 4.72–4.89 (m, 1H), 5.93 (s, 2H), 6.23 (s, 2H), 6.46 (s, 1H), 6.6
(d, 1H, J = 8.3 Hz), 6.70 (s, 1H), 6.75 (s, 1H), 7.34 (t, 1H, J = 8.3 Hz), 7.45 (t, 1H,
J = 8.3 Hz), 7.87 (d, 1H, J = 7.5 Hz), 7.98 (d, 1H, J = 8.3 Hz), 8.21 (d, 1H,
J = 8.3 Hz). 13C NMR (75 MHz, CDCl3): d 38.3, 41.6, 43.4, 51.9, 56.1, 56.2, 68.5,
101.6, 108.1, 109.2, 109.7, 110.9, 113.0, 121.1, 121.5, 122.5, 124.7, 126.0, 129.1,
131.7, 132.9, 134.1, 134.8, 135.4, 137.1, 147.4, 148.3, 149.5, 152.3, 152.6, 164.3,
9
157.2, 174.5. IR (KBr):
t
3367, 2922, 1771, 1605, 1509, 1484 cmꢀ1. MS (FAB):
m/z 677 [M++K]. 4-O-Demethyl-4b-[4-(6-fluoro-1,3-benzothiazole-2-yl)anilino]-
4-desoxypodophyllotoxin (6e). Yield (378 mg, 74%), Mp: 200–205 °C,
174.2. IR (KBr):
t
3398, 2924, 1771, 1615, 1508, 1481 cmꢀ1. MS (FAB): m/z 659
½
a 2D5
ꢂ
= ꢀ128.0 (c = 1.0 in CHCl3), 1H NMR (300 MHz, DMSO-d6+CDCl3):
d
[M++2]. 4b-[4-(1,3-Benzothiazole-2-yl)-2-methylanilino]-4-desoxypodophyllotoxin
2.89–3.00 (m, 1H), 3.24 (dd, 1H, J = 14.1, 5.2 Hz), 3.7 (s, 6H), 3.80 (t, 1H,
J = 10.4 Hz), 4.29 (t, 1H, J = 7.4 Hz), 4.48 (d, 1H, J = 5.2 Hz), 4.82–5.13 (m, 1H),
5.90 (s, 2H), 6.23 (s, 2H), 6.45 (s, 1H), 6.67 (d, 2H, J = 8.9 Hz), 6.75 (s, 1H), 7.10–
7.39 (m, 1H), 7.52 (dd, 1H, J = 8.1, 2.9 Hz), 7.76–7.89 (m, 3H). 13C NMR
(75 MHz, CDCl3): d 38.5, 41.8, 43.3, 52.1, 56.4, 68.6, 101.5, 107.5, 107.8, 109.1,
109.9, 112.1, 114.4, 114.7, 123.1, 123.3, 123.5, 129.2, 129.6, 130.3, 132.0, 143.1,
9
146.4, 147.6, 148.3, 149.5, 150.7, 158.5, 161.7, 167.7, 174.5. IR (KBr): t 3356,
(5c). Yield (426 mg, 84%), Mp: 152–155 °C, ½a D25
ꢂ
= ꢀ139.0 (c = 1.0 in CHCl3), 1H
NMR (200 MHz, CDCl3): d 2.16 (s, 3H), 2.79–3.08 (m, 1H), 3.15–3.39 (dd, 1H,
J = 14.6, 4.4 Hz), 3.78 (s, 6H), 3.82 (s, 3H), 3.90 (t, 1H, J = 9.2 Hz), 4.42 (t, 1H,
J = 7.7 Hz), 4.63 (d, 1H, J = 4.2 Hz), 4.85–5.09 (m, 2H), 5.98 (s, 2H), 6.32 (s, 2H),
9
t 3411,
6.56 (s, 1H), 6.8 (s, 1H), 7.10–7.58 (m, 4H), 7.82–8.04 (m, 3H). IR (KBr):
2923, 1773, 1607, 1515, 1483 cmꢀ1. MS (FAB): m/z 637 [M++H]. 4b-[4-(6-
Methoxy-1,3-benzothiazole-2-yl)anilino]-4-desoxypodophyllotoxin (5d). Yield
2903, 2834, 1773, 1605, 1509, 1483 cmꢀ1. MS (FAB): m/z 627 [M++H]. 4-O-
Demethyl-4b-[4-(4-chloro-1,3-benzothiazole-2-yl)anilino]-4-desoxypodophyllotoxin
(415 mg, 80%), Mp: 102–105 °C,
½
a 2D5
ꢂ
= ꢀ85.0 (c = 1.0 in CHCl3), 1H NMR
(300 MHz, CDCl3): d 2.69–3.01 (m, 2H), 3.75 (s, 6H), 3.78 (s, 3H), 3.87 (s, 3H),
4.39–4.45 (m, 2H), 4.51 (d, 1H, J = 3.7 Hz), 4.73–5.03 (m, 1H), 5.92 and 5.95
(ABq, 2H, J = 1.5 Hz), 6.25 (s, 2H), 6.48 (s, 1H), 6.60 (d, 2H, J = 8.3 Hz), 6.77 (s,
1H), 7.0 (dd, 1H, J = 9.0, 2.2 Hz), 7.28 (d, 1H, J = 2.2 Hz), 7.80–7.88 (m, 3H). 13C
NMR (75 MHz, CDCl3): d 38.5, 41.7, 43.5, 52.0, 55.7, 56.2, 60.7, 68.6, 101.5,
104.2, 108.1, 109.1, 109.8, 112.1, 115.1, 122.8, 123.8, 129.0, 129.7, 131.7, 131.9,
134.9, 135.6, 137.1, 147.5, 148.2, 148.4, 149.2, 152.5, 157.3, 165.7, 174.4. IR
9
(6f). Yield (346 mg, 66%), Mp: 155–158 °C, ½a D25
ꢂ
= ꢀ124.0 (c = 1.0 in CHCl3), 1
H
NMR (200 MHz, CDCl3): d 2.80–3.08 (m, 2H), 3.8 (s, 6H), 4.35–4.55 (m, 2H),
4.60 (d, 1H, J = 3.5 Hz), 4.80–5.18 (m, 1H), 5.42 (br s, 1H), 5.94 and 5.97 (ABq,
2H, J = 1.4 Hz), 6.32 (s, 2H), 6.53 (s, 1H), 6.62 (d, 2H, J = 8.5 Hz), 6.79 (s, 1H),
7.24–7.39 (m, 1H), 7.47 (dd, 1H, J = 8.2, 1.4 Hz), 7.74 (dd, 1H, J = 8.2, 1.4 Hz),
9
7.78 (d, 2H, J = 8.5 Hz). IR (KBr):
t .
3364, 2925, 1773, 1610, 1508, 1485 cmꢀ1
MS (FAB): m/z 645 [M++2]. 4-O-Demethyl-4b-[4-(4,6-dichloro-1,3-benzothiazole-
2-yl)anilino]-4-desoxypodophyllotoxin (6g). Yield (330 mg, 60%), Mp: 155–
(KBr):
t
3366, 2924, 2853, 1772, 1606, 1506, 1481 cmꢀ1. MS (FAB): m/z 675
[M++Na]. 4b-[4-(6-Fluoro-1,3-benzothiazole-2-yl)anilino]-4-desoxypodophyllotoxin
158 °C, ½a 2D5
ꢂ
= ꢀ124.0 (c = 0.5 in CHCl3), 1H NMR (300 MHz, CDCl3): d 3.01–
(5e). Yield (410 mg, 81%), Mp: 168–172 °C, ½a D25
ꢂ
= ꢀ130.0 (c = 1.0 in CHCl3), 1H
3.77 (m, 2H), 3.79 (s, 6H), 3.88–4.23 (m, 1H), 4.34–4.47 (m, 1H), 4.54–4.69 (m,
1H), 4.86–5.14 (m, 1H), 5.38 (br s, 1H), 5.98 (s, 2H), 6.32 (s, 2H), 6.53 (s, 1H),
6.73 (d, 2H, J = 8.5 Hz), 6.83 (s, 1H), 7.46 (s, 1H), 7.78 (s, 1H), 7.89 (d, 2H,
9
NMR (300 MHz, CDCl3): d 2.79–3.01 (m, 2H), 3.75 (s, 6H), 3.78 (s, 3H), 3.83–
3.99 (m, 1H), 4.34–4.54 (m, 3H), 4.75–5.18 (m, 1H), 5.93 (s, 1H), 5.96 (s, 1H),
6.25 (s, 2H), 6.49 (s, 1H), 6.61 (d, 2H, J = 8.6 Hz), 6.77 (s, 1H), 7.15 (m, 1H), 7.5
9
J = 8.5 Hz). IR (KBr):
t
3362, 2925, 1774, 1597, 1507, 1482 cmꢀ1. MS (FAB): m/z
(dd, 1H, J = 8.6, 2.6 Hz), 7.84–7.91 (m, 3H). IR (KBr):
t
3334, 2912, 2839, 1774,
695 [M++NH4]. 4-O-Demethyl-4b-[4-(1,3-benzothiazole-2-yl)-2-bromoanilino]-4-
1604, 1506, 1481 cmꢀ1
.
MS (FAB): m/z 641 [M++H]. 4b-[4-(4-Chloro-1,3-
desoxypodophyllotoxin (6h). Yield (339 mg, 60%), Mp: 177–180 °C, ½a D25
= ꢀ91.0
ꢂ
benzothiazole-2-yl)anilino]-4-desoxypodophyllotoxin (5f). Yield (420 mg, 83%),
(c = 1.0 in CHCl3), 1H NMR (300 MHz, CDCl3): d 2.69–3.13 (m, 2H), 3.81 (s, 6H),
4.4 (t, 1H, J = 7.5 Hz), 4.68 (d, 1H, J = 3.8 Hz), 4.85–5.17 (m, 2H), 5.45 (s, 1H),
6.01 (s, 2H), 6.35 (s, 2H), 6.59 (s, 1H), 6.64 (d, 1H, J = 8.0 Hz), 6.79 (s, 1H), 7.32–
9
Mp: 136–140 °C, ½a D25
ꢂ
= ꢀ117.0 (c = 1.0 in CHCl3), 1H NMR (200 MHz, CDCl3): d
2.79–3.01 (m, 2H), 3.76 (s, 6H), 3.80 (s, 3H), 4.37–4.49 (m, 2H), 4.53–4.67 (m,
1H), 4.75–5.45 (m, 1H), 5.93 and 5.97 (ABq, 2H, J = 1.5 Hz), 6.26 (s, 2H), 6.5 (s,
1H), 6.59 (d, 2H, J = 9.0 Hz), 6.80 (s, 1H), 7.21–7.39 (m, 1H), 7.44 (d, 1H,
9
7.56 (m, 2H), 7.85–8.06 (m, 3H), 8.29 (d, 1H, J = 2.2 Hz). IR (KBr):
2852, 1774, 1598, 1520, 1487 cmꢀ1. MS (FAB): m/z 689 [M++2].
t 3393, 2923,
J = 8.3 Hz), 7.72 (d, 1H, J = 8.3 Hz), 7.96 (d, 2H, J = 8.3 Hz). IR (KBr):
t
3392,
34. Skehn, P.; Storeng, R.; Scudiero, A.; Monks, J.; McMohan, D.; Vistica, D.;
Jonathan, T. W.; Bokesch, H.; Kenney, S.; Boyd, M. R. J. Natl. Cancer Inst. 1990,
82, 1107.
35. Kondapi, A. K.; Mulpuri, N.; Mandraju, R. K.; Sasikaran, B.; Rao, K. S. Int. J. Dev.
Neurosci. 2004, 22, 19.
2923, 1773, 1610, 1506, 1481 cmꢀ1. MS (FAB): m/z 658 [M++H]. 4b-[4-(4,6-
Dichloro-1,3-benzothiazole-2-yl)anilino]-4-desoxy podophyllotoxin (5g). Yield
(460 mg, 84%), Mp: 160–163 °C, ½a D25
ꢂ
= ꢀ102.0 (c = 0.5 in CHCl3), 1H NMR
(300 MHz, CDCl3): d 2.69–3.02 (m, 2H), 3.76 (s, 6H), 3.8 (s, 3H), 4.38–4.49 (m,
2H), 4.55–4.64 (m, 1H), 4.75–4.99 (m, 1H), 5.95 (s, 1H), 5.98 (s, 2H), 6.28 (s,