Niggula Praveen Kumar

Microwave-assisted direct oxidative synthesis of α-ketoamides from aryl methyl ketones and amines by a water soluble Cu(I)-complex

A stable and isolable bis[(tetrabutylammonium) di-μ-iodo-diiododicuprate(I)] complex has been identified for the direct oxidative synthesis of α-ketoamides from substituted aryl methyl ketones and secondary amines in the presence of molecular oxygen. Gratifyingly, this Cu(I) complex acts as an effective catalytic system with enhanced solubility in both water and organic solvents. These reactions were effectively accelerated by microwave irradiation in water and were applied for the synthesis of a variety of substituted α-ketoamides with good yields. It was interesting to note that, in these optimized microwave reaction times, α-ketoamides were the exclusive products and amide byproducts observed in previous reports were not formed.

TBAI/TBHP-catalyzed [3 + 2]cycloaddition/oxidation/aromatization cascade and online ESI-MS mechanistic studies: synthesis of pyrrolo[2,1-a]isoquinolines and indolizino[8,7-b]indoles

A facile [3 + 2]cycloaddition/oxidation/aromatization cascade reaction for the synthesis of pyrrolo[2,1-a]isoquinolines and indolizino[8,7-b]indoles has been developed. This tandem approach was accomplished by employing tert-butyl hydroperoxide (TBHP) as the environmentally benign stoichiometric oxidant, with the catalysis of non-toxic tetrabutylammonium iodide (TBAI) and isopropanol as the green solvent. Gratifyingly, this protocol is highly versatile, as the construction of polycyclics could be tailored by readily available dipolarophiles. Only a catalytic amount of TBAI was required, as the hypervalent electrophilic iodine species (IOH) can be recovered in situ by oxidation with TBHP. Furthermore, for the first time, the mechanistic aspects and the putative intermediates associated with this cascade have been intercepted and characterized by online monitoring of the reaction by using ESI-MS/MS.

One-pot synthesis of podophyllotoxin–thiourea congeners by employing NH2SO3H/NaI: Anticancer activity, DNA topoisomerase-II inhibition, and apoptosis inducing agents

A facile one-pot method for the synthesis of novel podophyllotoxin-thiourea congeners has been developed by using NH2SO3H/NaI system. Interestingly, 4β-azido podophyllotoxin reduction with concomitant aryl isothiocyanates coupling under mild reaction conditions has been achieved. These compounds have been investigated for their in vitro cytotoxicity against A549, MDA MB-231, DU-145, LNCaP, and HGC-27 cancer cell lines. Some of the representative compounds have selectively exhibited cytotoxicity on DU-145 (human prostate cancer) cells and the most potent compound was 4a (IC50 of 0.50 ± 0.03 μM) with optimal safety therapeutic window (81.7 fold) on normal human prostate cell line (RWPE-1, IC50 of 40.85 ± 0.78). The flow-cytometric analysis of the compound 4a in prostate cancer cells indicated a strong G2/M-phase arrest and significant topoisomerase II inhibition activity. Furthermore, these compounds induce apoptosis as observed by Acridine Orange and Ethidium Bromide (AO/EB) staining and Annexin V binding assay. Molecular docking results of the title compounds with topoisomerase-IIα were presented as theoretical support for the experimental data.

Silver(I)-catalysed domino alkyne-annulation/Diels–Alder reaction: a mild synthetic approach to tetrahydrospiro[carbazole-4,3′-indoline] scaffolds

A mild and efficient AgOTf catalyzed alkyne-annulation/Diels–Alder cascade for the construction of tetrahydrospiro[carbazole-4,3′-indoline] derivatives has been established from N-tosyl-2-(but-3-en-1-yn-1-yl) aniline in the presence of methyleneindolinones. This strategy provides access to the one-pot synthesis of a new class of various novel and structurally complex spirooxindole molecules with high diastereoselectivity.

Synthesis of different heterocycles-linked chalcone conjugates as cytotoxic agents and tubulin polymerization inhibitors

A series of new heterocycles-linked chalcone conjugates has been designed and synthesized by varying different alkane spacers. These conjugates were tested for their in vitro cytotoxic potential against a panel of selected human cancer cell lines namely, lung (A549 and NCI-H460), prostate (DU-145 and PC-3), colon (HCT-15 and HCT-116), and brain (U-87 glioblastoma) by MTT assay. Notably, among all the tested compounds, 4a exhibited potent cytotoxicity on NCI-H460 (lung cancer) cells with IC50 of 1.48±0.19µM. The compound 4a showed significant inhibition of tubulin polymerization and disruption of the formation of microtubules (IC50 of 9.66±0.06μM). Moreover, phase contrast microscopy and DAPI staining studies indicated that compound 4a can induce apoptosis in NCI-H460 cells. Further, the flow-cytometry analysis revealed that compound 4a arrests NCI-H460 cells in the G2/M phase of the cell cycle. In addition, molecular docking studies of the most active compounds 4a and 4b into the colchicine site of the tubulin, revealed the possible mode of interaction by these new conjugates.

Design and synthesis of 1,2,3-triazolo-phenanthrene hybrids as cytotoxic agents

A series of new 1,2,3-triazolo-phenanthrene hybrids has been synthesized by employing Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. These compounds were evaluated for their in vitro cytotoxic potential against various human cancer cell lines viz. lung (A549), prostate (PC-3 and DU145), gastric (HGC-27), cervical (HeLa), triple negative breast (MDA-MB-231, MDA-MB-453) and breast (BT-549, 4T1) cells. Among the tested compounds, 7d displayed highest cytotoxicity against DU145 cells with IC50 value of 1.5±0.09µM. Further, the cell cycle analysis shown that it blocks G0/G1 phase of the cell cycle in a dose dependent manner. In order to determine the effect of compound on cell viability, phase contrast microscopy, AO/EB, DAPI, DCFDA and JC-1 staining studies were performed. These studies clearly indicated that the compound 7d inhibited the cell proliferation of DU145 cells. Relative viscosity measurements and molecular docking studies indicated that these compounds bind to DNA by intercalation.

Synthesis of 1,2,4-triazole-linked urea/thiourea conjugates as cytotoxic and apoptosis inducing agents

A new series of 1,2,4-triazole-linked urea and thiourea conjugates have been synthesized and evaluated for their in vitro cytotoxicity against selected human cancer cell lines namely, breast (MCF-7, MDA-MB-231), lung (A549) prostate (DU145) and one mouse melanoma (B16-F10) cell line and compared with reference drug. The compound 5t showed significant cytotoxicity on MCF-7 breast cancer cell line with a IC50 value of 7.22 ± 0.47 µM among all the tested compounds. Notably, induction of apoptosis by compound 5t on MCF-7 cells was evaluated using different staining techniques such as acridine orange/ethidium bromide (AO/EB), annexin V-FITC/PI, and DAPI. Further, clonogenic assay indicates the inhibition of colony formation on MCF-7 cells by compound 5t. Moreover, the flow-cytometric analysis also revealed that compound 5t caused the arrest of cells at G0/G1 phase of cell cycle. In addition, the compounds when tested on normal human cells (L-132) were found to be safer with low cytotoxicity profile.

Sulfamic acid promoted one-pot synthesis of phenanthrene fused-dihydrodibenzo-quinolinones: Anticancer activity, tubulin polymerization inhibition and apoptosis inducing studies

A facile one-pot method for the synthesis of new phenanthrene fused-dihydrodibenzo-quinolinone derivatives has been successfully accomplished by employing sulfamic acid as catalyst. These new compounds were evaluated for their in vitro cytotoxic potential against human lung (A549), prostate (PC-3 and DU145), breast (MCF-7) and colon (HT-29 and HCT-116) cancer cell lines. Among all the tested compounds, one of the derivatives 8p showed good anti-proliferative activity against A549 lung cancer cell line with an IC50 of 3.17 ± 0.52 µM. Flow cytometric analyses revealed that compound 8p arrested both Sub G1 and G2/M phases of cell cycle in a dose dependent manner. The compound 8p also displayed significant inhibition of tubulin polymerization and disruption of microtubule network (IC50 of 5.15 ± 0.15 µM). Molecular docking studies revealed that compound 8p efficiently interacted with critical amino acid Cys241 of the α/β-tubulin by a hydrogen bond (SH…O = 2.4 Å). Further, the effect of 8p on cell viability was also studied by AO/EB, DCFDA and DAPI staining. The apoptotic characteristic features revealed that 8p inhibited cell proliferation effectively through apoptosis by inducing the ROS generation. Analysis of mitochondrial membrane potential through JC-1 staining and annexin V binding assay indicated the extent of apoptosis in A549 cancer cells.

Effect of Sulfamic Acid on 1,3-Dipolar Cycloaddition Reaction: Mechanistic Studies and Synthesis of 4-Aryl-NH-1,2,3-triazoles from Nitroolefins

A facile and new metal-free 1,3-dipolar cycloaddition reaction for the synthesis of 4-aryl-NH-1,2,3-triazoles from nitroolefins and NaN3 employing NH2SO3H has been developed. Sulfamic acid proved to be an efficient additive in this transformation by inhibiting the formation of triaryl benzene. Mechanistic aspects and key intermediates associated with this transformation have also been characterized by online monitoring of the reaction using electrospray ionization tandem mass spectrometry method (ESI-MS/MS). The protocol emphasizes broad substrate scope for many functionalities, simple reaction conditions such as stability to open air, less reaction time, easy work-up, eco-friendly and with good to excellent yields.

Synthesis of New 1,2,3-Triazolo-naphthalimide/phthalimide Conjugates via ‘Click’ Reaction: DNA Intercalation and Cytotoxic Studies

Cancer is a complex disease which involves abnormalities of multiple cellular pathways. Current chemotherapeutic drugs are mainly designed to target the DNA and cell division. Therefore, in the present study, we have synthesized a new series of 1,2,3-triazolo-naphthalimide/phthalimide conjugates and evaluated their in vitro cytotoxicity against selected human cancer cells. Among the tested compounds, one of them displayed notable cytotoxic activity against A549 lung cancer cells with an IC50 (half maximal inhibitory concentration) value of 7.6 ± 0.78 μM. To determine the effect of this compound on cell viability, acridine orange/ethidium bromide (AO/EB) and 4’,6-diamidino-2-phenylindole (DAPI) staining studies were performed. These apoptotic features were clearly indicating that the compound inhibited cell proliferation by apoptosis. Further, relative viscosity measurements and molecular docking studies with the most three active compounds indicated that these new compounds bind to DNA by intercalation.