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Abstract
The work in the thesis entitled “Design, Synthesis and Biological Evaluation of New
Pyrrolo[2,1-c][1,4]benzodiazepines as Antimitotic and Anticancer Agents” has been
undertaken with an aim to synthesize new pyrrolo[2,1-c][1,4] benzodiazepine analogues
and their dimers, to explore their DNA binding activity and anticancer activity. In
recent years combination chemotherapy with different mechanisms of action is one of
the methods that is being adopted to treat cancer. Therefore, a single molecule
containing more than one pharmacophore, each with different modes of action could be
beneficial for the treatment of cancer. The work carried out has been described in four
chapters.
CHAPTER-I: This chapter contains general introduction on cancer and chemotherapy,
covalent
interactions
of
drug
with
DNA,
particularly
by
pyrrolo[2,1-
c][1,4]benzodiazepine (PBD) antitumour antibiotics. It also gives an introduction to the
objectives of present work.
CHAPTER-II: This chapter deals with general introduction to chemotherapeutic
anticancer agents and classification based on their mode of action (mechanism),
particularly inhibition of tubulin polymerization and effect on cell cycle process. Recent
developments in the area of PBD analogues with different mechanisms have been
demonstrated, followed by the description of design, synthesis and biological
evaluation of a new class of cinnamido linked pyrolobenzodiazepine hybrids and their
dimers. Their antimitotic activity, inhibition of tubulin polymerization and effect on cell
cycle process has been investigated and these results are discussed.
CHAPTER-III: This chapter illustrates the introduction on dendrimers and its
biological importance in the field of medicinal chemistry. Dendrimers have the ability
to improve solubility, enhance anticancer activity and most importantly act as drug
carriers. This study describes the synthesis, DNA-binding ability and anticancer of C8
linked G1 dendrimer-pyrrolobenzodiazepine conjugates.
CHAPTER-IV: This chapter describes the design, synthesis, DNA binding affinities and
anticancer activity of some new hybrids of 1,4-diarylimidazolinones and pyrrolo[2,1c][1,4] benzodiazepines.
CHAPTER-I
General introduction on cancer
Cancer is a group of more than 100 different diseases sharing the common
characteristic of abnormal cellular division that is not subject to normal growth controls.
Cancer occurs when cells become abnormal and keep dividing and forming more cells
without control or order. All organs of the body are made up of cells. Normally, cells
divide to produce more cells only when the body needs them. If cells divide when new
ones are not needed, they form a mass of excess tissue, called a tumor. Tumors can be
benign or malignant. Often, benign tumors can be removed by surgery, and they are not
likely to return. However malignant tumors are cancerous. They have a tendency to
spread, invade and destroy nearby tissues and organs. Cancer cells can also break away
from a malignant tumor and travel through the bloodstream (leukemia) or the
lymphatic system (lymphoma) to form new tumors in other parts of the body. The
spread of cancer is called metastasis. Prognosis of cancer has improved greatly in
modern times owing to treatment advances and early detection programs. However,
although survival rates have improved, cancer still remains the 2nd top cause of death,
second only to heart disease in the United States and is a major public health problem in
the other developed countries. The rate of its induction throughout the world is
increasing every year, making it a challenging area for major focus for both physicians
as well as scientists.
Types of treatment for cancer
Treatment of cancer primarily consists of surgery, radiation, and chemotherapy. The
most common rationale for the use of chemotherapy is to control the cell population by
cell-kill mechanism. Current chemotherapy consists of cytotoxic (cell-killing) agents and
anti-hormonal drugs, which reduce the proliferative drive of the tumour. Many
compounds with good cell-killing activity have been discovered, but few have found
clinical utility. The lack of discrimination between a malignant (tumour) and normal
tissue is one of the major hurdles. The cell-cycle dependency of many cytotoxic drugs
and their frequent susceptibility to induce drug resistance and significant side-effects
are the difficulties often encountered during chemotherapy. The cell division in
malignant cells occur at a much faster rate in comparison to the normal cells and thus
provides a potential target area for the development of chemotherapeutic agents. The
role of chemotherapy is now apparent, in the effective treatment of a majority of solid
tumours, as an adjuvant to initial therapy by surgical or radiotherapeutic procedures.
Chemotherapy becomes critical for effective treatment for the reason that, only systemic
therapy can cure micrometastases. The chemotherapeutic agents can be categorized
based on their mode of action, like alkylating agents, antimetabolites, antibiotics and
antimitotics.
Pyrrolo[2,1-c][1,4]benzodiazepines as anticancer agents
The pyrrolo[2,1-c][1,4]benzodiazepines (PBDs) belonging to the class of DNAinteractive antitumour antibiotics have the potential as regulators of gene expression
with possible therapeutic application in the treatment of genetic disorders including
cancer. The first PBD antitumour antibiotic anthramycin has been described by
Leimgruber et. al. in 1963, and since then a number of compounds have been developed
based on PBD ring system leading to DNA binding ligands.
H3C 8
OH H
OCH3
9 N 11
H
10
11a
7
6
5
2
N
4
N
HO
H
1
N
CONH2 H3CO
3
O
Anthramycin
N
HO
N
H3CO
O
Tomaymycin
N
H
O
N
O
DC-81
N
O
H
N
OCH3 H3CO
O
H
O
SJG-136
Representative pyrrolobenzodiazepine molecules
Figure 1
Pyrrolo[2,1-c][1,4]benzodiazepines (PBDs) are a family of potent naturally occurring
low molecular weight antitumour antibiotics originally isolated from various
Streptomyces species. A number of naturally occurring and synthetic compounds based
on PBD ring system, such as anthramycin, tomaymycin, DC-81 (Figure 1) and its dimers
(presently SJG-136 is under clinical evaluation), have shown varying degrees of DNA
binding affinity and anti-cancer activity. Their interaction with DNA has been
extensively investigated and it is considered unique since they bind within the minor
groove of DNA forming a covalent aminal bond between the C11-position of the central
B-ring and the N2 amino group of guanine base (Fig. 2)
O
O
N
HN
H2N
N
H
N
HN
H
N
HH N
N
H
N
DNA
N
N
O
O
11R/S aminal
N10-C11 Imine
PBD-DNA interaction
Figure 2
CHAPTER - II
N
N
DNA
A New Class of Cinnamido linked Pyrrolo[2,1-c][1,4]benzodiazepine
Conjugates and their Dimers as Anti-mitotic Agents
Most chemotherapeutic anti-cancer drugs used in the clinic today include agents
that target the cell cycle in order to inhibit the hyperproliferation state of tumor cells
and subsequently to induce apoptosis, which is the desired outcome of chemotherapy.
Based on their mode of action these chemotherapeutic drugs can be subdivided into
distinct groups:

Drugs that interfere with DNA synthesis

Drugs that introduce DNA damage

Drugs that inhibit the function of the mitotic spindle
The latter have been proven to be exceptionally successful in the clinic and are
classically represented by microtubule binding drugs frequently referred to as spindle
poisons. These drugs, which include taxanes and various Vinca alkaloids, bind to and
inhibit the function of microtubules of the mitotic spindle apparatus, which leads to a
stop of the cell cycle in mitosis and subsequently to the induction of tumor cell death.
Therefore, novel drug targets that spare microtubules, but inhibit the progression of
mitosis are highly desired and already exploited for the development of novel antimitotic drugs. Thus, current drug development programs focus not only on improved
novel anti-microtubule drugs, but also on novel mitotic drug targets that include
mitotic kinesins and mitotic kinases. In addition, the use of drugs that abrogate the cell
cycle arrest imposed by DNA damaging agents leading to an unscheduled entry into
mitosis in the presence of DNA damage is a promising strategy to induce mitosisassociated cell death in tumor cells.
Recently, Jeh-Jeng Wang and co-workers have shown that a PBD hybrid (IN6CPBD)
agent can activate the apoptotic pathway mediated by mitochondria and reported that
induction of apoptosis by DC-81-indole conjugate agent through NF-KB and JNK/AP-1
pathway.
Based on the previous findings and new mechanisms, this research has been prompted
for the synthesize of a series of C-8 linked cinnamido-pyrrolo[2,1-c][1,4]benzodiazepine
monomers and their dimers. This is moreover in context towards the interest in the
structural modifications and development of new synthetic strategies.
The synthesis and biological activities of PBDs that are linked to the cinnamido moiety
through different alkyl chain spacers at C-8 position is described. Interestingly, these
cinnamido-PBD conjugates and their dimers have shown significant in vitro cytotoxicity
(nM concentration in some selected cell lines) and some compounds among them
exhibit inhibition of tubulin polymerization leading to a stop of the cell cycle in mitosis
and subsequently to the induction of tumor cell death.
Synthesis of
Conjugates
Cinnamido
linked
Pyrrolo[2,1-c][1,4]benzodiazepine
The synthetic pathway (Scheme 1) starts from commercially available 3,4,5trimethoxy benzoic acid, which was treated with sulphonyl chloride and then coupled
to N-bocpiperazine in the presence of a base to give the corresponding coupled
compound 2. Further deprotection of boc by employing TFA in CH2Cl2 gave compound
3 and then coupled with E 4-hydroxy-3-methoxycinnamic acid chloride to give the
required intermediate 4.
Morpholine in dry THF in the presence of triethylamine was added E 4-hydroxy3-methoxy cinnamic acid chloride to give compound 5. Further the piperazine in dry
THF in the presence of a base was added to the E 4-hydroxy-3-methoxy cinnamic acid
chloride to give the dimer intermediate compound 6 as shown in Scheme 2.
O
H3CO
O
O
Cl
i
H3CO
H3CO
ii
N
NBoc
H3CO
OCH3
OCH3
1
H3CO
N
NH
H3CO
OCH3
2
3
O
iii
H3CO
N
N
H3CO
O
OCH3
4
OCH3
OH
Scheme 1. Reagents and conditions: (i)TEA, N-Boc Piperazine, dry THF, 0oC to rt, 85-87%;
(ii) CF3COOH, CHCl3, 8h, rt, 86-88% (iii) Trans-3-methoxy-4-hydroxy cinnamoyl chloride, TEA
dry THF, 0o C to rt, 80-83%.
O
i
H3CO
HO
N
O
5
O
H3CO
O
Cl
H3CO
HO
N
ii
N
HO
O
6
OCH3
OH
Scheme 2. Reagents and conditions : (i) dry THF, morpholine, triethylamine, 0o C to rt, 85%
(ii) dry THF, piperazine, triethylamine, 0oC to rt, 81%
Synthesis of cinnamido-pyrrolo[2,1-c][1,4]benzodiazepine (PBD) conjugates 12ad and 13a-d and their dimers (16a-d) has been carried out by employing, (2S)-N-(4benzyloxy-5-methoxy-2-nitrobenzoyl)pyrrolidine-2-carboxaldehyde diethyl thio- acetal
17 as one of the starting material. This has been prepared by the method reported in the
literature.
This
upon
debenzylation
gives
(2S)-N-(4-hydroxy)-5-methoxy-2-
nitrobenzoyl)pyrrolidine-2-carboxaldehyde diethylthioacetal 18. After etherification of
hydroxyl group of the above compound with dibromoalkanes gives (2S)-N-[(nbromoalkyloxy)-3-methoxy-2-nitrobenzoyl)]pyrrolidine-2-carboxaldehy-
dediethyl
thioacetal 7a-d. Further coupling of them with compounds 4, 5 and 6 in the presence of
K2CO3 in acetonitrile gives the desired intermediate nitro compounds (2S)-{[methyl4-[3[4-(methoxycarbonyl)benzyl]oxy-5-(piperazinometh
-
yl)phenoxy]methylbenzoate]butyloxy-5-methoxy-2-nitrobenzoyl}pyrrolidine-2carboxaldehyde diethyl thioacetals 8a-d, 9a-d and 14a-d respectively which upon
reduction with SnCl2.2H2O gives 10a-d, 11a-d and 15a-d. The deprotection of these
thioacetals by employing HgCl2/CaCO3 affords the target imine compounds 12a-d, 13ad and 16a-d (Schemes 3 and 4).
O
N
O
()
n
Br
OCH3
+
X
NO2 CH(SEt)2
N
H3CO
OH
O
X = N-R
(7a-d)
i
R= 3,4,5-trimethoxy benzoyl (4)
X = O (5)
O
OCH3
N
X
()
n
O
X = N-R
O
NO2 CH(SEt)2
N
H3CO
R= 3,4,5-trimethoxy benzoyl (8a-d)
O
ii
X= O (9a-d)
O
OCH3
N
X
O
X = N-R
()
n
O
NH2 CH(SEt)2
N
H3CO
R= 3,4,5-trimethoxy benzoyl (10a-d)
O
iii
X= O (11a-d)
O
N
X
X = N-R
R= 3,4,5-trimethoxy benzoyl (12a-d)
OCH3
O
()
n
O
N
H
N
H3CO
O
X= O (13a-d)
Scheme 3. Reagents and conditions: (i) K2CO3, acetone,18 h, refllux, 65-73%; (ii) SnCl2.2H2O,
MeOH, 3 h, reflux, 86-88%; (iii) HgCl2-CaCO3, CH3CN-H2O (4:1), 12 h, rt, 70-72%.
O
H3CO
O
N
OCH3
N
Br
+
HO
6
O
N
O
()
n
OCH3
N
O
7a-d
i
(EtS)2HC O2N
NO2 CH(SEt)2
H3CO
OH
H3CO
O
()
n
O
N
OCH3
N
O
O
14a-d
()
n
O
O
ii
O
H3CO
N
O
()
n
OCH3
N
H3CO
O
(EtS)2HC H2N
NO2 CH(SEt)2
O
N
O
OCH3
N
O
15a-d
()
n
O
NH2 CH(SEt)2
N
H3CO
O
O
iii
O
H3CO
N
H
N
N
OCH3
O
()
n
OCH3
N
O
O
O
16a-d
O
O
()
n
H3CO
N
H
N
O
Scheme 4 Reagents and conditions: (i) K2CO3, acetone, 18 h, refllux, 88-91%; (ii) SnCl2.2H2O, MeOH,
2 h, reflux, 85-87%; (iii) HgCl2-CaCO3, CH3CN-H2O (4:1), 12 h, rt, 67-69%.
A new series of cinnamido-pyrrolo[2,1-c][1,4]benzodiazepine conjugates 12a-d, 13a-d
and dimers (16a-d) with different linker architectures have been designed, synthesized
and evaluated for their biological activities such as DNA-binding affinity and
cytotoxicity. The anti-proliferative profile of compound 4a has been evaluated for its
anticancer activity against 60 human cancer cell lines.
This compound has shown significant potent with GI50 values ranging from 68-732 nM
towards 53 out of 60 human cancer cell lines tested; particularly it is active at <90 nM in
CCRF-CEM (leukemia), NCI-H522 (Non-small cell Lung Cancer), MCF7 & MDA-MB-455
(Breast Cancer). In PBD monomers 13a, 13c & 13d and in PBD dimers 16a, 16c & 16d
have shown remarkable cytotoxic activity with GI50 values were <10-7 M concentrations
in a number cell lines. DNA thermal denaturation studies suggested that these
analogues have been promising DNA binding interactions compared to unsubstituted
DC-81. These results demonstrated that the conjugation of cinnamido component to the
PBD has been remarkably enhanced cytotoxic activity and DNA binding affinity.
CHAPTER-III
Synthesis, DNA-binding ability and Biological Activity of C8 Linked G1
Dendrimer-Pyrrolobenzodiazepine Conjugates as Anticancer Agents
Dendrimers have been of great interest in the application to drug delivery systems;
however their use in this area has remained largely unexplored. In recent years, several
attempts have been made to design dendrimers as drug carriers. It has been shown that
dendrimers can be combined to drug molecules via a covalent bond. For example, Zhuo
and coworkers have synthesized the polyamidoamine (PAMAM) dendrimers with a
cyclic core and linked them to an anticancer drug like 5-fluorouracil. Similarly polyether
dendritic compounds bearing folate residues on their surface have been prepared as
model drug carriers with potential tumor cell specificity. Further methotrexate (MTX)
has been conjugated to the chain ends of hydrazide terminated poly(aryl
ether)dendrimers.
During the last decade, many piperazine derivatives have been synthesized as
useful chemotherapeutic agents. Michejda and co-workers reported symmetrical
bifunctional agents that possess a piperazine moiety in its linker spacer as promising
class of antitumour compounds with remarkable selectivity against colon cancer.
Studies in this laboratory on the PBD dimers incorporating a piperazine moiety in their
alkane spacer linker exhibited enhanced DNA binding ability as well as promising
anticancer activity. It has been observed that the inclusion of a piperazine moiety in
these compounds has enhanced the DNA binding ability to a significant extent
probably due to their non-covalent interactions that could take place by this moiety in
the minor groove of DNA. In continuation of these efforts and interest in this laboratory
on the development of new structurally modified PBD molecules as well as new
synthetic stratagies for their preparation. Synthesis of PBD linked to a G1 poly (aryl
ether) dendrimerhas been investigated. The linkage between these conjugates has been
carried out by various alkane spacers at C-8 position of the PBD ring to the dendrimer
through a piperazine moiety with a view to enhance their lipophilicity as well as
biological activity.
Based on previous studies on dendrimers and their interesting biological
applications like as drug carrier property, targeting on DNA, gene delivery, cancer
diagnosis, and solubilization property prompted to synthesize a series of new
pyrrolo[2,1-c][1,4]benzodiazepine-G1 poly (aryl ether) dendrimer hybrids. It has been
observed that the incorporation of piperazine moiety between dendrimer and PBD has
shown significant enhancement in the DNA binding ability
Synthesis of C8 Linked G1 Dendrimer-Pyrrolobenzodiazepine Conjugates
The dendritic benzyl bromide 4 has been prepared as shown in Scheme 1 by
employing the reported procedure. Further, this upon coupling with boc-protected
piperazine followed by deprotection provides the required key intermediate methyl 4[3-[4-(methoxycarbonyl)benzyl]oxy-5-(piperazinomethyl)phenoxy]methylbenzo- ate 6
(Scheme 1).
OH
Br
OH
O
i
+
HO
O
OH
COOCH3
6
5
COOCH3
7
COOCH3
ii
NH
N
N
Boc
Br
N
iv
O
O
COOCH3
iii
O
COOCH3
COOCH3
10
O
O
O
COOCH3
COOCH3
9
COOCH3
8
Reagents and conditions: (i) K2CO3, 18-crown-6, acetone, reflux, 24h, 87%; (ii) dry DCM,
PBr3 , 1h, 83%; (iii) N-BOCPiperazine, K2CO3, acetonitrile, 48h, 83%; (iv) TFA, dry DCM, 8h.
Synthesis of G1 dendrimer-pyrrolo[2,1-c][1,4]benzodiazepine (PBD) conjugates
12a-d has been carried out by following methods, (2S)-N-(4-benzyloxy-5-methoxy-2nitro benzoyl) pyrrolidine-2-carboxaldehydediethylthioacetal 6 as one of the starting
material. This has been prepared by the method reported in the literature. This upon
debenzylation
gives
(2S)-N-(4-hydroxy)-5-methoxy-2-nitro-
benzoyl)pyrrolidine-2-
carboxaldehyde diethyl thioacetal. After etherification of hydroxyl group of the above
compound with different dibromo alkanes give (2S)-N-[(n-bromoalkyloxy)-3-methoxy2-nitrobenzoyl)]pyrrolidine-2-carboxaldehyde
diethyl
thioacetals
12a-d.
Further
coupling of them with compound 6 in the presence of K2CO3 in acetonitrile gives the
desired
intermediate
nitro
compound
(2S)-{[methyl4-[3-[4-
(methoxycarbonyl)benzyl]oxy-5-(piperazinomethyl)phenoxy]
ate]butyloxy-5-methoxy-2-nitrobenzoyl}pyrrolidine-2-carboxaldehyde
methylbenzodiethyl
thioacetals 10a-d, which upon reduction with SnCl2.2H2O gives 11a-d. The deprotection
of these thioacetals by employing HgCl2/CaCO3 affords the target imine compounds
12a-d (Scheme 2)
NH
N
N
N
Br
O
O
+
O
()
n
NO2
H3CO
N
O
()
n
CH(SEt)2
N
H3CO
O
CH(SEt)2
i
NO2
O
O
O
COOCH3
COOCH3
COOCH3
COOCH3
13a-d
12a-d
11
ii
N
N
O
()
n
N
5a-d
N
COOCH3
O
()
n
NH2
CH(SEt)2
N
H3CO
O
iii
O
O
COOCH3
N
N
H3CO
O
O
H
O
COOCH3
COOCH3
14a-d
Scheme 2. Reagents and conditions:(i) K2CO3, dry-acetonitrile, reflux, 24 h, 80-85% ;
(ii) SnCl2. 2H2O, CH3OH, reflux, 2 h; (iii) HgCl2, CaCO3, CH3CN-H2O, (4:1), 55-60%.
NO2
BnO
NO2 CO2Me
BnO
i
OH
MeO
N
MeO
HO
ii
N
N
H
N
O
N
iii
H
N
H3CO
O
O
H
O
18
17
() O
n
O
MeO
O
O
16
H
N
Br
O
iv
() O
n
H
N
O
H
N
H3CO
O
n=2
n=3
COOCH3 n = 4
n=5
COOCH3
5e
5f
5g
5h
19a-d
5e-h
Scheme 3 Reagents and conditions: (i) Dibromoalkanes, K2CO3, DMF, rt, 24 h, 70%; (ii) 10% Pd/C, H2 40 PSI,
ethanol, rt, 6 h 62%; (iii) dibromoalkanes, K2CO3, DMF, rt, 24 h, 70%; (iv) 10, K2CO3, acetonitrile, 48 h, reflux,
80-82%.
The DNA binding affinity of these G1 dendrimer-PBD conjugates 12a-d and 13ad has been investigated by the thermal denaturation studies using calf thymus (CT)
DNA duplex at pH 7.0. Interestingly, these compounds 12a-d and 13a-d elevate the
helix melting temperature of CT-DNA in the range 3.2-19.0 oC after 18 h incubation at
37 oC. The Tm value for one of the PBD-dendrimer conjugate (12b) is highly significant
and shows that this compound provides a favourable interaction with DNA which has
a four carbon spacer between C-8 position of PBD and the piperazine moiety.
Compounds 12a-c have been evaluated for their in vitro cytotoxicity in selected
human cancer cell lines like Hop62 (lung), SiHa (cervix), MCF7 and ZR75-1 (breast),
Colon205 (colon), PC3 (prostate) and A2780 (ovarian) by employing the sulforhodamine
B (SRB) assay. The GI50 value is a response parameter and represents the concentration
of the compound that induces 50% cell line growth inhibition. When the concentration
of the compound is less than or equal to 10-5 mol/L, and the growth inhibition 50% or
more, then the compound is considered as an effective agent. According to this
standard, it has been observed from Table 2 that compounds 12a-c exhibit significant
cytotoxic activity against some of the cell lines and the activity was comparable with
adriamycin (ADR). Therefore, it appears that incorporation of G1 poly (aryl ether)
dendrimer to a PBD ring system through a piperazine moiety enhances the cytotoxic
potency. For example the GI50 values for compound 12c exhibits strong effect in some of
these cell lines 0.20 (A-549), 0.16 (DWD), 0.17 (A2780) and 0.16 (colo 205) μM. Moreover,
the in vitro cytotoxicity (GI50) for naturally occurring DC-81 is 0.38, and 0.33 μM in
L1210 and PC-3 cell lines.
CHAPTER-IV
In current research, combination chemotherapy with different mechanisms of
action is one of the methods that are being adopted to treat cancer. Therefore, a single
molecule containing more than one pharmacophore, each with different mode of action
could be beneficial for the treatment of cancer. The imine or carbinolamine-containing
pyrrlo[2,1-c][1,4]benzodiazepines are a family of low molecular weight antitumour
antibiotics originally isolated from various Streptomyces species. These antibiotics bind
selectively in the minor groove of DNA through a covalent aminal bond between the
electrophilic C11 position of the PBD moiety and the nucleophilic N2-amino group of a
guanine base, resulting in the possible biological activity. It has been observed that the
contribution by such non-covalent component plays an important role in the overall
DNA binding affinity in such mixed-type of PBD dimers. During the course of efforts
directed towards the development of new anticancer agents in this laboratory, it is
observed that some new molecules based on PBD linked conjugates like PBD-chalcones
exhibited potential anticancer activity. Chalcones have received significant attention for
their antitumour properties over the last few years, particularly in view of their similar
mode of action to the structurally related combretastatin. The anticancer activity of
certain chalcones, known to result in binding to tubulin and prevent it from
polymerizing microtubules, are the targets for a number of clinical useful anticancer
compounds including natural products like paclitaxel, vincristine, and colchicine.
These findings provided further impetus to explore the combination of certain
non-covalent interacting groups with a PBD moiety that led to the design and synthesis
of a variety of PBD hybrids. The research in this direction in this laboratory afforded a
number of such PBD hybrids with enhanced DNA binding ability and significant
anticancer potential. In continuation of these efforts and above said aspects it has been
considered of interest to design and synthesis molecules based on PBD linked to 1,4diarylimidazolinones.
Synthesis of 1,4-diarylimidazolinone linked pyrrolobenzodiazepine hybrids
The synthesis of intermediates 6a-r has been carried out as shown in Scheme 1. The
coupling of 3,4,5-trimethoxy aniline (1) with different substituted phenacyl bromides
(2a-g) afford the corresponding compounds (3a-g), which upon cyclization in the
presence of potassium isocyanato gives the 1,4-diarylimidazole-2-ones (4a-g). Then
these imidazolones on Pd/C under hydrogen pressure gives the imidazolidinones (5ag). These compounds have been further reaction with dibromoalkanes in the presence
of anhydrous K2CO3 resulted the intermediate compounds (6a-r)
Compound 7 has been coupled to compounds 6a-r to produce corresponding 8ar. These coupled nitrothioacetal intermediates 8a-r upon reduction with SnCl2.2H2O in
methanol gives the aminothioacetal precursors 9a-r and these on deprotection by
HgCl2/CaCO3 affords the desired PBD hybrids 10a-r (Scheme 2).
O
H3CO
H3CO
Br
R
i
NH2 +
H3CO
H3CO
R1
H3CO
2a-g
1
H3CO
R2
O
H
N
R
R1
3a-g
R2
R = H, OCH3
R1 = H, OCH3, Cl, F, CF3
ii
R2 = H, OCH3
O
H3CO
O
NH
R
R1
H3CO
H3CO
H3CO
iii
N
R
R1
H3CO
R2
5a-g
NH
N
H3CO
R2
4a-g
iv
O
H3CO
N
Br
()
n
R1
H3CO
H3CO
R
N
6a-r
R2
Scheme 1.Reagents and conditions: i) NaHCO3, EtOH, rt, 16h; ii) KCNO, AcOH, 60-65 oC, 2h; iii) H2, Pd/C,
EtOH, 6h. iv) DMF, anhydrous K2CO3, dibromo alkanes, rt, 12h.
OCH3
H3CO
O
H3CO
N
N
()
n Br
HO
+
NO2
N
H3CO
6a-r
n = 2, 3, 4
O
R
R2
CH(SEt)2
7
R1
i
OCH3
H3CO
H3CO
O
N
() O
n
N
NO2
N
H3CO
8a-r
R2
CH(SEt)2
O
R
R1
ii
OCH3
H3CO
H3CO
O
N
() O
n
N
NH2
N
H3CO
9a-r
R2
CH(SEt)2
O
R
R1
iii
OCH3
H3CO
H3CO
O
N
() O
n
N
N
N
H3CO
R2
R
10a-r
H
O
R = H, OCH3
R1 = H, OCH3, Cl, F, CF3
R2 = H, OCH3
n = 2, 3, 4
R1
Scheme 2. Reagents and conditions: i) DMF, anhydrous K2CO3, rt, 12h; ii) SnCl2 2H2O, MeOH, reflux, 6h; iii) HgCl2,
CaCO3, CH3CN:H2O(3:1)
In conclusion the thesis describes the development of pyrrolo[2,1-c][1,4]benzodiazepine conjugates and their dimers as potential DNA interactive, anticancer agents
with antimitotic and inhibition of tubulin polymerization properties.