SYNOPSIS
The
thesis
entitled
“Design
and
Synthesis
of
New
Pyrrolo[2,1-
c][1,4]benzodiazepine Hybrids as DNA Interactive Antitumour Agents“ has been
divided into four chapters. Chapter I gives the general introduction about cancer
chemotherapy, covalent, non-covalent interactions of drug-DNA, particularly of
pyrrolo[2,1-c][1,4]benzodiazepine antitumour antibiotics and objectives of the
present work. Chapter II comprises of two sections; section A consists of the
design, synthesis and DNA binding ability of novel anthraquinone-pyrrolo[2,1c][1,4]benzodiazepine hybrids and their activity. While section B describes the
design and synthesis of a first example of bifunctional PBDs with an intercalater
and their biological activity. Chapter III is also divided into two sections; section
A describes the synthesis, DNA binding affinity and in vitro anticancer activity of
a series of pyrrolobenzodiazepine hybrids in which DC-81 has been linked to
naphthalimide through piperazine moiety comprising of different alkyl chain
lengths. Section B of chapter III describes the design, synthesis and biological
activity of novel fluorenone-, and flavone-PBD hybrids. Chapter IV describes the
development of a new methodology for the protection of carbonyls as
thioacetals, its application in the synthesis of novel podophyllotoxin-PBD
hybrids and their in vitro cytotoxicity.
Chapter I: General introduction
Cancer is a disease where cells grow and divide in an uncontrolled
manner. The four types of treatment for cancer are surgery, radiation,
chemotherapy and biological therapy. A major advantage of chemotherapy is its
ability to treat cancer cells that have metastasized (spread) to other parts of the
body, whereas surgery and radiation therapy are used to treat localized cancers.
The major categories of chemotherapeutic agents are antitumour antibiotics,
I
DNA topoisomerase I and II inhibitors, DNA interactive agents and other
miscellaneous agents. Pyrrolo[2,1-c][1,4]benzodiazepines (PBDs) are a well
known class of antibiotics. PBDs have potential as regulators of gene expression
with possible therapeutic application in the treatment of genetic disorders
including cancer and as probes and tools for use in molecular biology.
The
pyrrolo[2,1-c][1,4]benzodiazepine
(PBD)
class
of
antitumour
antibiotics are derived from various Streptomyces species. Lemgruber et al
described the first PBD antitumour antibiotic anthramycin in 1968 and since then
a number of compounds have been developed based on PBD ring system. These
compounds exert their biological activity by covalent binding to the N2 of
guanine in the minor groove of DNA through the imine or imine equivalent
functionality at N10-C11 of PBD. These molecules have a right-handed twist,
which provides the appropriate three dimensional shape for the isohelicity with
the minor groove of B-form DNA leading to a snug fit at the binding site.
H3C
OR H
N
OCH3
HO
H
N
8
11
7
N
CONH2
O
N
H3CO
O
DC-81
Anthramycin
N
H
O
N
N
O
OCH3
N
H3CO
O
O
SJG-136
Cl
O
N
( )5
O
N
O
CBI - PBD Conjugate
II
H
N
H3CO
OH
H
H
O
HN
H2N
HO
O
N
N
N
DNA
N
HO
H
N
HN N
H
N
DNA
N
MeO
N
MeO
H
N
HN
O
O
C(11) (R/S) aminal
C (11)-N(10) imine
Formation of PBD-DNA covalent adduct
Chapter II-Section A: Design, synthesis and biological evaluation of
novel anthraquinone-pyrrolo[2,1-c][1,4]benzodiazepine hybrids
Recently, there has been growing interest in modifying and extending the
recognition patterns of DNA binding ligands. Pyrrolo[2,1-c][1,4]benzodiazepine
antitumour antibiotics bind covalently to the N2 of guanine in the minor groove
of DNA. In the past few years, several PBD analogues have been designed and
synthesized with the aim of finding related compounds showing better
antitumour activity. The PBDs have been used as a scaffold to attach EDTA,
epoxide, (+)-Cyclopropapyrroloindole and Cyclopropapylbenzindole moieties
leading to novel unsymmetrical hybrids of PBD, which have exhibited novel
sequence selective DNA cleaving and cross-linking properties.
Anthracenediones
represent
an
important
class
of
intercalating
antitumour compounds. Mitoxantrone, which is the lead compound in this series
is routinely used in clinic for the treatment of certain hematological
malignancies, as well as ovarian and breast cancers.
The objective of the present work is to combine the features of both
intercalating and DNA binding properties in the same molecule. Therefore, it has
been considered of interest to couple anthraquinone to the C8-position of the
III
PBD through its amino functionality. In the present chapter the synthesis, DNA
binding affinity and in vitro cytotoxicity of the novel anthraquinone-PBD hybrids
have been described.
Synthesis of these novel anthraquinone-PBD hybrids has been carried out
by employing N-(9,10-dihydro-9,10-dioxo-1-anthracenyl)-1-bromo-alkanamide
(1a-b) as one of the precursors, which has been obtained by the reaction of an
appropriate acid chloride with 1-aminoanthraquinone (Scheme-1).
The other precursor (2S)-N-(4-hydroxy-5-methoxy-2-nitrobenzoyl)pyrrolidine-2-carboxaldehyde diethyl thioacetal 9 has been prepared by employing
commercially available vanillin. Oxidation of vanillin followed by esterification
employing literature method provides vanillin methyl ester 2. This on
benzylation gives 3, which upon nitration followed by ester hydrolysis affords 5.
L-Proline methyl ester has been coupled with 5 to give the nitro ester 6. This
nitro ester upon treatment with DIBAL-H followed by protection of aldehyde
with ethanethiol gives diethyl thioacetal 8. This upon debenzylation provides the
compound 9. This nitrothioacetal has been coupled with N-(9,10-dihydro-9,10dioxo-1-anthracenyl)-1-bromo-alkanamide
(1a-b)
to
give
10a-b.
This
nitrothioacetal has been reduced to give 11a-b. The deprotection of the thioacetal
group afforded the desired compounds 12a-b (Scheme 2).
O
Scheme 1
O
NH2
O
NH
( )n Br
i
O
O
n = 3-4
1 a-b
Reagents and conditions : (i) bromo alkionyl chloride, pyridine, toluene, 60 oC, 4h.
IV
Scheme 2
HO
BnO
i
OMe
H3CO
OMe
H3CO
NO2
H3CO
O
3
2
NO2
4
NO2
BnO
iv
OH
H3CO
iii
OMe
O
O
BnO
BnO
ii
6
7
8
v
COOMe
vi
N
H3CO
NO2
BnO
N
H3CO
O
O
5
CH(SEt)2
O
6
8
O
HO
NO2
vii
N
H3CO
CH(SEt)2
O
( )n O
NH
NO2
viii
CH(SEt)2
N
H3CO
O
O
O
9
10 a-b
ix
O
O
( )n O
NH
NH2
CH(SEt)2
N
H3CO
O
O
11 a-b
x
O
O
NH
( )n O
N
H
N
H3CO
O
O
12 a-b
12a : n = 3,
12b : n = 4.
Reagents and conditions : (i) BnBr, K2CO3, acetone, reflux , 12h; (ii) SnCl4/HNO3, CH2Cl2, -25 oC , 5 min;
(iii) 2N LiOH, THF, MeOH, H2O (3:1:1), rt, 12h; (iv) SOCl2, benzene, L-proline methylester hydrochloride,
Et3N, H2O, 3h; (v) DIBAL-H, CH2Cl2, -78 oC, 1h; (vi) EtSH, TMSCl, CH2Cl2, rt, 8h; (vii) EtSH-BF3.OEt2,
CH2Cl2, rt, 12h; (viii) compound 1a-b, K2CO3, acetone, reflux, 15h; (ix) SnCl2.2H2O, MeOH, 4h, reflux; (x)
HgCl2, CaCO3, CH3CN/H2O, rt, 12h.
Compounds 12a-b have been evaluated for their in vitro cytotoxicity in
selected human cancer cell lines of colon (HT-29, HCT-15), lung (A-549, HOP-62)
V
and cervix (SiHa) origin. Compounds 12a and 12b exhibit significant cytotoxicity
against some of the cancer cell lines. Compound 12a suppresses HT-29 and HCT15 cell growth by 68% and 59% respectively. It is inhibiting HOP-62 cell growth
by 74%. Compound 12b suppressing HT-29 and HCT-15 cell growth by 73% and
61%. It is also inhibiting A-549 and HOP-62 cell growth by 56% and 73%.
The DNA binding affinity of these novel PBD hybrids has been evaluated
through thermal denaturation studies with duplex-form of calf thymus DNA
(CT-DNA). Melting studies show that these compounds stabilize the thermal
helix to coil transition of the CT-DNA efficiently. In this assay, compound 12a
has melting temperature of 9.1 C after incubation for 18 h at 37 C. Compound
12b elevates the melting temperature of CT-DNA by 5.2 C after incubation for
18 h. On the other hand, the naturally occurring DC-81 exhibits a ∆Tm of 0.7 C.
Thus demonstrating that these PBD hybrids have significant DNA binding
ability.
Chapter II-Section B: Design, synthesis and biological activity of novel
bifunctional PBDs with intercalating anthraquinone
The cytotoxicity and antitumour activity of PBDs are attributed to their
ability to form covalent adducts. PBD monomers span three base pairs with a
preference for Pu-G-Pu motifs (where Pu = purine, G = guanine). In an attempt
to extend the number of base pairs spanned by these molecules, PBD dimers
have been synthesized, with the hope that enhanced sequence selectivity might
increase selectivity for tumour cells.
Since, Suggs and coworkers have reported the first PBD dimer comprising
of two PBD units joined through their A-C7/A-C7’ positions, a number of PBD
dimers have been designed and synthesized that exhibited varying degree of
cytotoxicity and DNA cross-linking activity. These PBD dimers have been joined
VI
through different positions A-C8/A-C8’, C-C2/C-C2’, A-C8/C-C2’. Among
these, A-C8/A-C8’ linked PBD dimers have shown promising cytotoxicity and
efficient cross-linking properties. Thurston and coworkers synthesized A-C8/AC8’ alkane diyldioxy bridged PBD dimers (DSB-120) and C2/C2’ exounsaturated PBD dimer (SJG-136) which span six base pairs of DNA and exhibit
high DNA binding affinity and antitumour activity.
The main objective of this work is to synthesize the bifunctional PBDs
with an intercalater to enhance sequence selectivity and anticancer activity.
Therefore, the synthesis of new PBD dimers in which two PBD units have been
joined to the 1 and 4 positions of anthraquinone through their A-C8 positions via
alkane diyldioxy bridge with linkers of varying lengths has been carried out.
Synthesis of these novel PBD hybrids has been carried out by employing
1,4-bis-(n-bromoalkyloxy)anthracene-9,10-diones (13a-c) as one of the precursors,
which have been obtained by etherification of 1,4-dihydroxy anthraquinone with
dibromoalkanes.
The
other
precursor
(2S)-N-[4-hydroxy-5-methoxy-2-
nitrobenzoyl]pyrrolidine-2-carboxaldehyde diethyl thioacetal (9) has been
prepared as described in section-A. Compounds 13a-c have been coupled with 9
to
give
1,4-bis-{n-[(2S)-N-(4-oxy-5-methoxy-2-nitrobenzoyl)-pyrrolidine-2-
carboxaldehyde diethyl thioacetal]alkyloxy}anthracene-9,10-diones (14a-c). These
anthraquinone coupled nitro thioacetal intermediates 14a-c have been efficiently
reduced to afford the corresponding amino thioacetals 15a-c. Deprotection of the
thioacetal group afforded the desired bifunctional PBDs with an intercalating
anthraquinone moiety in compounds 16a-c (Scheme 3).
VII
Scheme 3
O
O
OH
O
(CH2)n
Br
i
O
O
OH
O (CH2)n Br
13a-c
ii
(EtS)2HC O2N
N
O ( )n O
O
OCH3 O
O
()
n O
NO2 CH(SEt)
2
N
H3CO
O
O
14a-c
iii
(EtS)2HC H2N
N
O
()
n O
O
O
O
OCH3
()
n O
NH2 CH(SEt)
2
N
H3CO
O
O
15a-c
iv
N
H
N
()
n O
O
OCH3 O
O
O
O
()
n O
N
H
N
H3CO
O
16a n = 3
16b n = 4
16a-c
16c n = 5
Reagents and conditions : (i) Dibromoalkane, K2CO3, acetone, reflux , 24h; (ii) compound 9,
K2CO3, acetonitrile, reflux, 24h; (iii) SnCl2.2H2O, MeOH, reflux, 4h; (iv) HgCl2, CaCO3,
CH3CN/H2O, rt, 12h.
Compounds have been evaluated for their in vitro cytotoxicity in selected
human cancer cell lines of colon (Colo205), lung (HOP-62), prostate (PC3) and
cervix (SiHa) origin. Compound 16a has promising cytotoxicity in Colo205 and
VIII
SiHa cell lines. Compound 16b has not shown significant cytotoxicity.
Compound 16c has potent cytotoxicity in Colo205, HOP-62, PC3 and SiHa cell
lines.
Chapter III-Section A: Synthesis, DNA binding affinity and in vitro
anticancer activity of naphthalimide-pyrrolo[2,1-c][1,4]benzodiazepine
hybrids
Cancer chemotherapy continues to be an important research avenue.
Complex structures built out of groove binders linked to other moieties which
interact with the DNA via intercalation or groove interactions or molecules
which cleave DNA, are of interest in terms of inter alia. These compounds are
capable of recognizing heterogeneous DNA sequences.
Many drugs that possess chemotherapeutic activity intercalate with DNA.
The orientation in the geometry of the limited drug-DNA complexes has been
studied using X-ray diffraction, NMR spectroscopy and traditional solution
methods. It has also been shown that a wide variety of planar ring systems can
intercalate with DNA to exert their antitumour activity.
In the present work, the design and synthesis of new PBD hybrids in
which naphthalimides have been linked to PBD through alkyl piperazine moiety
side armed by identical or mixed alkane chain spacers has been carried out. This
study is with an objective to improve the lipophilicity, antitumour activity and
DNA sequence specificity.
The synthesis of these new PBD hybrids has been carried out by
employing piperazine linked naphthalimides 20a-c as one of the precursors.
These have been obtained by alkylation of naphthalimide with dibromo
compounds followed by coupling with N-boc piperazine and deprotection of boc
with trifluoroacetic acid (Scheme 4).
IX
Scheme 4
O
17
i
ii
17
18
19
O
NH
N
O
O
O
(CH2)n N
1
Nboc
iii
N
(CH2)n N
NH
1
O
19a-c
20a-c
n1 = 2, 3, 4
Reagents and conditions: (i) Dibromo alkanes, K2CO3, acetonitrile, reflux, 12 h; (ii) N-Boc piperazine,
K2CO3, acetonitrile, reflux, 8 h; (iii) CF3COOH, CHCl3, r.t., 8 h.
Synthesis of the other precursor (2S)-N-[4-(n-bromoalkyloxy)-5-methoxy2-nitrobenzoyl]pyrrolidine-2-carboxaldehyde diethyl thioacetal 25a-c has been
carried out by employing the commercially available vanillin. Oxidation of
vanillin followed by esterification employing literature methods provides the
vanillin methyl ester (21). The mono alkylation of 21 has been achieved by using
three molar equivalents of the dibromo alkanes. Nitration of 22a-c followed by
ester hydrolysis and coupling of (2S)-pyrrolidine-2-carboxaldehyde diethyl
thioaetal affords 25a-c. This nitro thioacetal has been coupled with 2-[n’(piperazine-1-yl)alkyl]benz[de]isoquinoline-1,3-dione (20a-c) to give C8-linked
naphthalimide nitro thioacetal 26a-e. This compound has been efficiently
reduced by employing SnCl2.2H2O to afford the corresponding amino thioacetal.
Deprotection of the thioacetal group with HgCl2 and CaCO3 afforded the desired
naphthalimide-PBD hybrids 28a-e (Scheme 5).
X
Scheme 5
HO
i
Br(CH2)n O
OMe
H3CO
2
OMe
H3CO
OMe
H3CO
NO2
Br(CH2)n O
ii
2
O
O
O
21
23a-c
22a-c
iii
NO2 CH(SEt)
2
Br(CH2)n O
2
N
H3CO
NO2
Br(CH2)n O
iv
2
OH
H3CO
O
O
25a-c
24a-c
v
O
N () N
n1
N () O
n
2
O
NO2 CH(SEt)
2
N
H3CO
O
26a-e
vi
O
N () N
n
1
O
N () O
n
2
H3CO
27a-e
NH2 CH(SEt)
2
N
O
vii
O
N () N
n1
N () O
n2
O
N
N
H3CO
28a-e
H
O
28a : n1 = 2,
28b : n1 = 2,
28c : n1 = 2,
28d : n1 = 3,
28e : n1 = 4,
n2 = 2
n2 = 3
n2 = 4
n2 = 3
n2 = 4
Reagents and conditions: (i) Dibromo alkanes, K2CO3, acetone, reflux , 48 h; (ii) SnCl4/HNO3, CH2Cl2, -25
o
C , 5 min; (iii) 2N LiOH, THF, MeOH, H2O (3:1:1), rt, 12 h; (iv) SOCl2, DMF, THF, H2O, (2S)-pyrrolidine
carboxaldehyde diethyl thioacetal, Et3N; (v) compound 20a-c, K2CO3, acetonitrile, reflux, 12 h; (vi) SnCl2.
2H2O, methanol, reflux, 3.5 h; (vii) HgCl2, CaCO3, acetonitrile/H2O, r.t., 15 h.
Compounds have been evaluated for their in vitro cytotoxicity in selected
human cancer cell lines of colon (HT-29, HCT-15), lung (A-549, HOP-62) and
XI
cervix (SiHa) origin. These compounds exhibit potent cytotoxicity. These
compounds exhibit more than 75% inhibition even at 10-6 mol/L concentration
in some of the cell lines. Compound 28b suppresses HT-29 and HOP-62 cell
growth by 91% and 72% while compound 28c suppressing HT-29 and HOP-62
cell growth by 80% and 86% at 10-6 mol/L concentration. Compound 28d is
inhibiting HT-29 cell growth by 63% and compound 28e inhibiting HT-29 and
HOP-62 cell growth by 67% and 80% at the same concentration.
The DNA binding affinity of these novel PBD hybrids has been evaluated
through thermal denaturation studies with duplex-form of calf thymus DNA
(CT-DNA). The results show that these compounds stabilize the thermal helix to
coil transition of CT-DNA duplex more efficiently. There is an increase in the
melting temperature when incubation time is increased from 0 to 18 h at 37 C.
Compounds 28a and 28c elevate the helix melting temperature of CT-DNA by
22.7 C and 23.9 C respectively after incubation for 18 h at 37 C. Compounds
28d and 28e have shown a Tm of 12.9 C and 20.8 C. In this series, compound
28b has shown highest Tm value and it is increasing the helix-melting
temperature by 26.5 C. In the same experiment, the naturally occurring DC-81
exhibits a ΔTm of 0.7 C and its dimer (DSB-120) gives a ΔTm of 15.4 C. This
demonstrates that these new PBD hybrids have remarkable DNA binding
affinity.
Chapter III-Section B: Synthesis and biological activity of novel
fluorenone- and flavone-pyrrolo[2,1-c][1,4]benzodiazepine hybrids
The biological activity of certain low molecular weight compounds
appears to be related with their mode and specificity of interaction with
particular DNA sequences. In the search of antitumour compounds with
improved biological activity, an approach of hybrid ligands combining two
modes of binding to DNA has been developed. Coupling of a polyaromatic
XII
heterocyclic to an addressing molecule does not only provide extra strength of
binding but can also influence the sequence selectivity of the conjugate. With
such hybrid molecules, it has been demonstrated that DNA is able to accept two
types of binding in close proximity, despite their unique distortions.
Furthermore, the length and flexibility of the spacer arms in conjugates seems to
be critical for optimal positioning of both parts of the molecule. In view of the
importance of the conjugates, synthesis of fluorenone- and flavone-PBD
conjugates has been carried out to improve DNA binding ability and anticancer
activity.
Synthesis of these novel hybrids has been carried out by employing (2S)N-[4-(n-bromoalkyloxy)-5-methoxy-2-nitrobenzoyl]-pyrrolidine-2-carboxaldehyde diethyl thioacetal (25b-d) as a precursor. This nitro thioacetal 25b-d has been
coupled with 2-hydroxy fluorenone or 6-hydroxy flavone to give 29a-f. This
intermediate has been reduced with SnCl2.2H2O to give amino thioacetal 30a-f.
The deprotection of the thioacetal group afforded the desired compounds 31a-f
(Scheme 6).
XIII
Scheme 6
Br(CH2)n O
NO2 CH(SEt)
2
N
H3CO
R O
O
( )n
NO2 CH(SEt)2
i
H3CO
O
O
29a-f
25b-d
n = 3, 4, 5
ii
R O
O
( )n
NH2 CH(SEt)2
H3CO
O
30a-f
iii
R O
O
( )n
N
H
N
H3CO
31a-c R =
O
31a-f
O
O
n = 3, 4, 5
31d-f R =
O
Reagents and conditions: (i) 2-hydroxy fluorenone or 6-hydroxy flavone, K2CO3, acetonitrile, reflux, 24 h;
(ii) SnCl2. 2H2O, methanol, reflux, 5 h; (iii) HgCl2, CaCO3, acetonitrile/H2O, r.t., 12 h.
The DNA binding affinity of these novel PBD hybrids has been evaluated
through thermal denaturation studies with duplex-form of calf thymus DNA
(CT-DNA). In fluorenone series, compound 31a has shown a ΔTm of 6.1 C while
compounds 31b and 31c elevate the helix melting temperature by 3.8 C and 3.9
C after incubation for 18 h. In flavone series, compound 31d has shown melting
temperature of 3.8 C at 0 h and the melting temperature increases to 6.2 C after
incubation for 18 h at 37 C. Compounds 31e and 31f elevate the helix melting
temperature of the CT-DNA by 1.8 C and 2.6 C after incubation for 18 h.
XIV
Compounds have been evaluated for their in vitro cytotoxicity in selected
human cancer cell lines of colon (HT-29, HCT-15), lung (A-549, HOP-62) and
cervix (SiHa) origin. Compound 31d has a strong effect to HT-29, HCT-15 and
HOP-62 cell lines. Compound 31e has not shown any significant cytotoxicity.
Compound 31f is suppressing HCT-15 and A-549 cell growth by 69% and 63%.
Chapter
IV:
Synthesis
and
in
vitro
cytotoxicity
of
novel
podophyllotoxin-pyrrolo[2,1-c][1,4]benzodiazepine hybrids
The protection of carbonyl groups as acetals and thioacetals is most
commonly used as an important synthetic technique in the course of preparation
of many organic compounds including multifunctional complex molecules.
Thioacetals are comparably more stable than the corresponding acetals under
acidic conditions and are useful in organic synthesis as acyl carbanion
equivalents in carbon-carbon bond forming reactions. Many of the reported
methods suffer from some disadvantages.
The present chapter describes a
simple and convenient method for the protection of aldehydes as thioacetals
using Cu(BF4)2.xH2O under solvent-free conditions. The present chapter also
describes the application of this methodology in the synthesis of novel
podophyllotoxin-PBD hybrids and their in vitro anticancer activity.
Various aldehydes have been subjected to thioacetal formation by the
treatment of carbonyl compound with ethanethiol under the catalytic influence
of 5 mol% Cu(BF4)2.xH2O.
Scheme 7
O
R
Cu(BF4)2.xH2O
H
EtSH, r.t., neat
XV
RCH(SEt)2
Synthesis of these novel podophyllotoxin-PBD hybrids has been carried
out by employing (2S)-N-[4-benzyloxy-5-methoxy-2-nitrobenzoyl]pyrrolidine-2carbox-aldehyde as one of the precursors, which has been obtained as described
in chapter II. Protection of this aldehyde with ethanethiol in presence of
Cu(BF4)2.xH2O afforded diethyl thioacetal 32. This upon debenzylation provides
the
compound
(2S)-N-[4-hydroxy-5-methoxy-2-nitrobenzoyl]pyrrolidine-2-
carboxaldehyde diethyl thioacetal (33). Etherification of compound 33 by methyl
bromoalkanoate provides 34a-b. Basic hydrolysis of these esters gives the desired
precursor acids 35a-b. The other precursor 4’-O-demethyl-4-amino-4-deoxy
podophyllotoxin has been prepared by literature method. Amidation of this with
acid
35a-b
in
presence
of
EDCI/HOBt
affords
the
corresponding
podophyllotoxin coupled nitro thioacetal intermediates 36a-b. This upon
reduction affords 37a-b. The deprotection of the thioacetal group using
HgCl2/CaCO3 resulted in the formation of the desired podophyllotoxin linked
PBD hybrids 38a-b (Scheme 8).
Compounds 38a-b have been evaluated for their in vitro cytotoxicity in a
panel of six human cancer cell lines. Compound 38a exhibit GI50 values in the
range of 9.5-38.7 mM and GI50 values of compound 38b is 13.7-36.6 mM.
In conclusion, the thesis describes the design, synthesis and biological
activity of novel pyrrolo[2,1-c][1,4]benzodiazepine analogues with the potential
to develop as anticancer agents.
XVI
Scheme 8
CHO
NO2
BnO
NO2
BnO
CH(SEt)2
i
N
H3CO
CH(SEt)2
NO2
HO
ii
N
H3CO
O
N
H3CO
O
O
32
33
iii
(CH2)n O
HO
O
NO2
H3CO
CH(SEt)2
iv
N
NO2
(CH2)n O
H3CO
O
N
H3CO
O
CH(SEt)2
O
34a-b
35a-b
v
O
NH
O
(CH2)n O
O
NO2
H3CO
O
O
N
NH
CH(SEt)2
(CH2)n O
O
vi
CH(SEt)2
N
O
O
H3CO
H3CO
O
O
O
NH2
O
OCH3
H3CO
OH
OCH3
OH
37a-b
36a-b
vii
O
NH
(CH2)n O
O
O
N
H3CO
O
H
N
O
O
n = 3, 4
H3CO
OCH3
OH
38a-b
Reagents and conditions : (i) EtSH, Cu(BF4)2.xH2O, CH2Cl2, rt, 10min; (ii) EtSH-BF3.OEt2, CH2Cl2, rt, 12h; (iii)
methyl bromoalkanoate, K2CO3, acetone, reflux, 15h; (iv) 2N LiOH, THF, MeOH, H2O (3:1:1), rt, 12h; (v) 4'-Odemethyl-4 -amino-4-deoxy podophyllotoxin, EDCI, HOBt, CH2Cl2, rt, 12h; (vi) SnCl2.2H2O, MeOH, 4h, reflux; (vii)
HgCl2, CaCO3, CH3CN/H2O, rt, 12h.
XVII