Manda Sathish

Design and Synthesis of C3-Pyrazole/Chalcone-Linked Beta-Carboline Hybrids: Antitopoisomerase I, DNA-Interactive, and Apoptosis-Inducing Anticancer Agents

A series of β‐carboline hybrids bearing a substituted phenyl and a chalcone/(N‐acetyl)‐pyrazole moiety at the C1 and C3 positions, respectively, was designed, synthesized, and evaluated for anticancer activity. These new hybrid molecules showed significant cytotoxic activity, with IC50 values ranging from <2.0 μM to 80 μM, and the structure–activity relationships (SAR) associated with substitutions at positions 1 and 3 of these hybrids was clearly addressed. Further, induction of apoptosis was confirmed by Annexin V‐FITC, Hoechst staining, and DNA fragmentation analysis. In addition, DNA photocleavage studies proved that two of the hybrids, (E)‐1‐(furan‐2‐yl)‐3‐(1‐(4‐(trifluoromethyl)phenyl)‐9H‐pyrido[3,4‐b]indol‐3‐yl)prop‐2‐en‐1‐one (7 d) and 1‐(3‐(furan‐2‐yl)‐5‐(1‐(4‐(trifluoromethyl)phenyl)‐9H‐pyrido[3,4‐b]indol‐3‐yl)‐4,5‐dihydro‐1H‐pyrazol‐1‐yl)ethanone (8 d) could effectively cleave pBR322 plasmid DNA upon irradiation with UV light. Active hybrid 8 d inhibited DNA topoisomerase I activity efficiently and preserved DNA in the supercoiled form. To further corroborate the biological activities, as well as to understand the nature of the interaction of these hybrids with DNA, spectroscopic studies were also performed. Unlike simple β‐carboline alkaloids, the binding mode of these new hybrid molecules with DNA was not similar, and both biophysical as well as molecular docking studies speculated a combilexin‐type of interaction with DNA. Further, an in silico study of these β‐carboline hybrids revealed their drug‐like properties.

DNA-binding affinity and anticancer activity of β-carboline–chalcone conjugates as potential DNA intercalators: Molecular modelling and synthesis

A new series of DNA-interactive β-carboline-chalcone conjugates have been synthesized and evaluated for their in vitro cytotoxicity and DNA-binding affinity. It has been observed that most of these new hybrids have shown potent cytotoxic activities on A-549 (lung adenocarcinoma) cell lines with IC50 values lower than 10 μM. The hybrid 7b is more effective against some of the selected cancer cell lines with IC50 values less than 50 μM. In addition, compounds 7e, 7k, 7p-u has displayed significant elevation in ΔTm of DNA in comparison to Adriamycin, suggesting significant interaction and remarkable DNA stabilization. The DNA intercalation of these new hybrids has been investigated by fluorescence titration, DNA viscosity measurements, molecular docking as well as molecular dynamics and the results are in agreement with the thermal denaturation studies.

Design and synthesis of dithiocarbamate linked β-carboline derivatives: DNA topoisomerase II inhibition with DNA binding and apoptosis inducing ability.

A series of new β-carboline-dithiocarbamate derivatives bearing phenyl, dithiocarbamate and H/methyl substitutions at position-1, 3 and 9, respectively, were designed and synthesized. These derivatives 8a-l and 13a-l and their starting precursors (7 a-d and 12 a-d) have been evaluated for their in vitro cytotoxic activity on selected human cancer cell lines. Among the derivatives tested, 7 c, 12 c, 8 a, 8 d, 8 i, 8 j, 8 k, 8l and 13 d-l exhibited considerable cytotoxicity against most of the tested cancer cell lines (IC50<10μM). Interestingly, most of the derivatives (8 a-l and 13a-l) exhibited enhanced activity than their precursors (7 a-d and 12 a-d), which indicates that the combination of dithiocarbamate with β-carboline enhances the cytotoxicity of 8 a-l and 13 a-l. Moreover, the derivatives 8 j and 13 g exhibited significant cytotoxic activity with IC50 values of 1.34 μM and 0.79 μM on DU-145 cancer cells, respectively. Further, the induction of apoptosis by these derivatives was confirmed by Annexin V-FITC and Hoechst staining assays. However, both biophysical as well as molecular docking studies suggested a combilexin-type of interaction between these derivatives and DNA, unlike simple β-carbolines. With a view to understand their mechanism of action, DNA topoisomerase II (topo II) inhibition assay was also performed. Overall, the present study emphasizes the importance of linking a dithiocarbamate moiety to the β-carboline scaffold for exhibiting profound activity.

A one-pot ‘click’ reaction from spiro-epoxides catalyzed by Cu(I)-pyrrolidinyl-oxazole-carboxamide

An efficient Cu(I)-pyrrolidinyl-oxazolo-carboxamide catalyst has been employed for the ‘one-pot’ synthesis of novel 3-substituted-1,2,3-triazolo-3-hydroxy-indolin-2-ones. This reaction involves an in situ azide generation from spiro-epoxide by a concomitant ‘click’ reaction in aqueous media. This protocol has the advantage of avoiding the interim purification of toxic organic azide intermediates resulting in significant enhancement of the overall yield with reduced reaction time. The regiospecificity of epoxide ring-opening has been unequivocally established on the basis of single X-ray crystallographic analysis and quantum chemical calculations. Moreover, this approach offers a broad scope to access diversely substituted indolino-O/N-linked 1,2,3-triazoles as novel privileged scaffolds.

Dithiocarbamate/piperazine bridged pyrrolobenzodiazepines as DNA-minor groove binders: Synthesis, DNA-binding affinity and cytotoxic activity

A new series of C8-linked dithiocarbamate/piperazine bridged pyrrolo[2,1-c][1,4]benzodiazepine conjugates (5a-c, 6a,b) have been synthesized and evaluated for their cytotoxic potential and DNA-binding ability. The representative conjugates 5a and 5b have been screened for their cytotoxicity against a panel of 60 human cancer cell lines. Compound 5a has shown promising cytotoxic activity on selected cancer cell lines that display melanoma, leukemia, CNS, ovarian, breast and renal cancer phenotypes. The consequence of further replacement of the 3-cyano-3,3-diphenylpropyl 1-piperazinecarbodithioate in 5b and 5c with 4-methylpiperazine-1-carbodithioate yielded new conjugates 6a and 6b respectively. In addition, the compounds 5c and 6a,b have been evaluated for their in vitro cytotoxicity on some of the selected human cancer cell lines and these conjugates have exhibited significant cytotoxic activity. Further, the DNA-binding ability of these new conjugates has been evaluated by using thermal denaturation (ΔTm) studies. The correlation between structure and DNA-binding ability has been investigated by molecular modeling studies which predicted that 6b exhibits superior DNA-binding ability and these are in agreement with the experimental DNA-binding studies.

Synthesis of podophyllotoxin linked β-carboline congeners as potential anticancer agents and DNA topoisomerase II inhibitors

A series of new podophyllotoxin linked β-carboline congeners have been synthesized by coupling various substituted β-carboline acids with 4β-aminopodophyllotoxin. Evaluation of their anticancer activity against a panel of human cancer cell lines such as lung cancer (A549), prostate cancer (DU-145), MDA MB-231 (breast cancer), HT-29 (colon cancer) and HeLa (cervical cancer) suggested that 7i and 7j are the most cytotoxic compounds with IC50 values of 1.07 ± 0.07 μM and 1.14 ± 0.16 respectively against DU-145 cell line. Further, detailed biological studies such as cell cycle analysis, topoisomerase II inhibition, Comet assay, DNA binding studies and docking studies have revealed that these congeners are DNA interacting topoisomerase II inhibitors.

Iron-Mediated One-Pot Synthesis of 3,5-Diarylpyridines from β-Nitrostyrenes

An operationally simple and mild one-pot protocol for the synthesis of a variety of 3,5-diarylpyridines from β-nitrostyrenes was achieved by using elemental iron. This reaction proceeds via reduction of the nitro group, resulting in in situ imine formation followed by trimolecular condensation with concomitant debenzylative aromatization. By employing this method, a series of symmetrical and unsymmetrical 3,5-diarylpyridines were synthesized with good to excellent yields. In addition, this method was also utilized for the synthesis of Sch-21418, an anti-inflammatory agent on gram scale.

Synthesis and biological evaluation of benzimidazole–oxindole conjugates as microtubule-targeting agents

A series of benzimidazole-oxindole conjugates were synthesized and evaluated for their cytotoxic activity. The cytotoxicity assay results suggest that conjugates 5c and 5p exhibit promising cytotoxicity against human breast cancer cell line (MCF-7). The Cell cycle analysis revealed that these conjugates induced cell cycle arrest at G2/M phase in MCF-7 cells. The tubulin polymerization assay results suggested that these conjugates inhibit tubulin polymerization with IC50 values 1.12 and 1.59μM respectively. Immunofluorescence analysis also suggested that these conjugates effectively inhibited the microtubule assembly in MCF-7 cells. Further, molecular docking studies indicated that these conjugates 5c and 5p interact and binds efficiently with the tubulin protein. By and large, the results demonstrated that these benzimidazole-oxindole conjugates possess cytotoxic property by inhibiting the tubulin polymerization.

An efficient one-pot decarboxylative aromatization of tetrahydro-β-carbolines by using N-chlorosuccinimide: total synthesis of norharmane, harmane and eudistomins

A facile method for the synthesis of a variety of β-carbolines and their natural products such as norharmane (2a), harmane (2b), eudistomins I, N, T, and U (6, 7, 9 and 10, respectively) has been successfully developed via a decorboxylative aromatization tool by employing N-chlorosuccinimide (NCS) as a mild and efficient reagent. Gratifyingly, this reagent system proceeds in a one-pot manner and converted all the tetrahydro-β-carboline acids into their corresponding decorboxylative aromatic products with good to excellent yields. Additionally, this system works well in the case of tetrahydro-β-carboline esters to produce their aromatic partners in high yields.

Synthesis of DNA interactive C3-trans-cinnamide linked β-carboline conjugates as potential cytotoxic and DNA topoisomerase I inhibitors

A series of new C3-trans-cinnamide linked β-carboline conjugates has been synthesized by coupling between various β-carboline amines and substituted cinnamic acids. Evaluation of their anti-proliferative activity against a panel of selected human cancer cell lines such as A549 (lung cancer), MCF-7 (breast cancer), B16 (melanoma), HeLa (cervical cancer) and a normal cell line NIH3T3 (mouse embryonic fibroblast cell line), suggested that the newly designed conjugates are considerably active against all the tested cancer cell lines with IC50 values 13-45 nM. Moreover, the conjugates 8v and 8x were the most active against MCF-7 cells (14.05 nM and 13.84 nM respectively) and also even potent on other cell lines tested. Further, detailed investigations such as cell cycle analysis, apoptosis induction study, topoisomerase I inhibition assay, DNA binding affinity and docking studies revealed that these new conjugates are DNA interactive topoisomerase I inhibitors.