Synthesis of 5-hydroxyisatin thiosemicarbazones, spectroscopic investigation, protein-ligand docking, and in vitro anticancer activity.

A series of novel modifications were performed at the N(4) position of 5-hydroxyisatin thiosemicarbazone (TSC). The structure-activity approach is applied to design and synthesize derivatives by condensing thiosemicarbazides with 5-hydroxy isatin. The TSCs were characterized by various spectroscopic techniques viz. FTIR, 1H NMR, 13C NMR, UV-Vis, HRMS data, CHN elemental analysis, and single crystal X-ray diffraction. Biological evaluation of the synthesized compounds revealed the anticancer potency of the TSC analogues against breast cancer (MD-AMD-231, MCF-7), lung cancer (A549, NCI-H460), prostate cancer (PC3), and skin cancer (A431). The molecules, L2, L3, and L6 showed activity in the micromolar range (IC50; 0.19-2.19 µM). L6 exhibited the highest potency against skin cancer A431 cell line, with an IC50 of 0.19 µM compared to 1.8 µM with triapine and showed low toxicity against PNT-2 cells with an SI index of >100 µM. The mechanistic study revealed that L6 inhibited cancer cell proliferation, colony formation, and 3-dimensional spheroid formation by targeting the Ras/MAPK axis. It induced DNA damage and impaired DNA damage repair machinery, which led to the accumulation of DSB. Also, it lowered the ERK1/2 expression, which affected the caspase 3 activity and showed higher binding affinity compared to the FDA-approved drug Lenalidomide in molecular docking studies. Our findings demonstrated the possible future anticancer drug potency of L6 in the skin cancer A431 cells.

Bis-benzimidazolyl diamide based fluorescent probe for copper(II): synthesis, structural and fluorescence studies.

A new fluorescent probe based on a bis-benzimidazole diamide N (2),N (2')-bis[(1-ethyl-benzimidazol-2-yl)methyl]biphenyl-2,2'-dicarboxamide ligand L 1 with a biphenyl spacer group and a Copper(II) trinuclear metallacycle has been synthesized and characterized by X-ray single crystallography, elemental and spectral (FT-IR, (1)H & (13)C NMR, UV-Visible) analysis. The fluorescence spectra of L 1 in MeOH show an emission band centered at 300 nm. This band arises due to benzimidazolyl moiety in the ligating system. The diamide L 1 in the presence of Cu(2+) show the simultaneous 'quenching' of (300 nm) and 'enhancement' of (375 nm) emission band. Similar fluorescence behavior was found in water-methanol mixture (9:1). The new emission band at 375 nm is attributed to intra ligand π-π* transition of the biphenyl moiety. L 1 exhibited high selectivity and sensitivity towards Cu(2+) in both the medium over other common metal ions like Ni(2+), Co(2+), Mn(2+), Mg(2+), Zn(2+), Pb(2+) and Hg(2+). The binding constant with Cu(2+) was calculated by the Benesi-Hildebrand equation. Selective "off-on-off" behavior of L 1 in methanol has also been studied. The fluorescent intensity of 375 nm bands in L 1 enhances (turns-on) upon addition of Cu(2+) and quenches (turn-off) upon addition of Na2-EDTA.

5-Methoxyisatin N(4)-Pyrrolidinyl Thiosemicarbazone (MeOIstPyrd) Restores Mutant p53 and Inhibits the Growth of Skin Cancer Cells, In Vitro.

A series of novel thiosemicarbazone derivatives containing 5-methoxy isatin were designed and synthesized with modification on N(4) position. Derivatives considering structure-activity relationship have been designed and synthesized by condensing thiosemicarbazide with 5-methoxy isatin. The synthesized compounds were characterized by elemental analysis, FT-IR spectroscopy, UV-visible spectroscopy, NMR (1H, 13C) spectroscopy, mass spectrometry, and a single-crystal study. Biological evaluation of the synthesized compounds revealed that MeOIstPyrd is the most promising compound against skin cancer cell line, A431, with an IC50 value of 0.9 µM. In addition, MeOIstPyrd also exhibited low toxicity against the normal human fibroblast and the human embryonic kidney 293 cell line, HLF-1, and HEK293, respectively. Furthermore, the mechanistic study revealed that MeOIstPyrd efficiently inhibited cell proliferation, migration, and spheroid formation by activating the mitochondrial intrinsic apoptotic pathway. MeOIstPyrd also induces DNA damage and activates p53 irrespective of the p53 status. It increases the half-life of p53 and stabilizes p53 by phosphorylating it at ser15. Moreover, MeOIstPyrd was found to bind to MDM2 in the p53 sub-pocket and, therefore, block p53-MDM2 interaction. Our result exhibited potential anticancer activity of MeOIstPyrd in the A431 cell line and its ability in restoring mutant p53, which is an interesting and promising strategy for cancer therapeutics.

Antimalarial evaluation of copper(II) nanohybrid solids: inhibition of plasmepsin II, a hemoglobin-degrading malarial aspartic protease from Plasmodium falciparum.

A new class of copper(II) nanohybrid solids, LCu(CH(3)COO)(2) and LCuCl(2), have been synthesized and characterized by transmission electron microscopy, dynamic light scattering, and IR spectroscopy, and have been found to be capped by a bis(benzimidazole) diamide ligand (L). The particle sizes of these nanohybrid solids were found to be in the ranges 5-10 and 60-70 nm, respectively. These nanohybrid solids were evaluated for their in vitro antimalarial activity against a chloroquine-sensitive isolate of Plasmodium falciparum (MRC 2). The interactions between these nanohybrid solids and plasmepsin II (an aspartic protease and a plausible novel target for antimalarial drug development), which is believed to be essential for hemoglobin degradation by the parasite, have been assayed by UV-vis spectroscopy and inhibition kinetics using Lineweaver-Burk plots. Our results suggest that these two compounds have antimalarial activities, and the IC(50) values (0.025-0.032 microg/ml) are similar to the IC(50) value of the standard drug chloroquine used in the bioassay. Lineweaver-Burk plots for inhibition of plasmepsin II by LCu(CH(3)COO)(2) and LCuCl(2) show that the inhibition is competitive with respect to the substrate. The inhibition constants of LCu(CH(3)COO)(2) and LCuCl(2) were found to be 10 and 13 microM, respectively. The IC(50) values for inhibition of plasmepsin II by LCu(CH(3)COO)(2) and LCuCl(2) were found to be 14 and 17 microM, respectively. Copper(II) metal capped by a benzimidazole group, which resembles the histidine group of copper proteins (galactose oxidase, beta-hydroxylase), could provide a suitable anchoring site on the nanosurface and thus could be useful for inhibition of target enzymes via binding to the S1/S3 pocket of the enzyme hydrophobically. Both copper(II) nanohybrid solids were found to be nontoxic against human hepatocellular carcinoma cells and were highly selective for plasmepsin II versus human cathepsin D. The pivotal mechanism of antimalarial activity of these compounds via plasmepsin II inhibition in the P. falciparum malaria parasite is demonstrated.

Oxidation of substituted phenols using copper(II) metallatriangles formed through ligand sharing.

Reaction of N(2),N(2')-bis-[(1-butyl-benzimidazol-2yl)methyl]biphenyl-2,2'-dicarboxamide (L) with CuX2⋅nH2O in methanol leads to the assembly of four trinuclear Cu(II) complexes with the general formula [Cu3(L)3X3]⋅3X⋅nH2O⋅mMeCN, where X=Cl(-), Br(-), NO3(-) and C6H5COO(-) and n=0-5, m=0-8 (compounds 1-4, respectively). The structure of one of the complex contains three Cu(II) metal ions at the corners of an equilateral triangle. Each of the copper(II) are coordinated through two benzimidazolyl imine N-atoms and two amide carbonyl O-atoms and the apical position is occupied by an anionic nitrate ion, leading to a distorted square pyramidal environment. The magnetic susceptibility data were analyzed through Hamiltonian H=-J (S1S2+S2S3+S1S3) obtaining -J=0.16, 0.12, 0.15 and 0.14cm(-1) for 1-4, respectively. X-Band EPR spectra typically show a broad single line at 120K with g∼2.11. Oxidation of phenols was studied homogeneously using copper(II) metallatriangles (1-3) as catalyst in acetonitrile. The oxidation of 2,4,6-tri-tert-butyl phenol yields the corresponding quinone after oxidative dealkylation. The oxidation of 2-amino-5-methyl phenol yields the corresponding phenoxazinone while the oxidation of 2-amino-4-tert-butyl phenol yields the phenoxazine instead of phenoxazinone. The products so obtained were analyzed by NMR and X-ray single crystallography.

Synthesis of a new N-substituted bis-benzimidazolyl diamide ligand and its trinuclear copper(II) complex: structural and fluorescence studies.

The synthesis of a new N-substituted fluorescent probe based on a bis-benzimidazole diamide N(2),N(2')-bis[(1-(4-methylbenzyl)-benzimidazol-2-yl)methyl]biphenyl-2,2'-dicarboxamide (L1) with a biphenyl spacer group and its trinuclear copper(II) complex [Cu3(L1)3Cl3]·3Cl·3H2O] has been described. X-ray studies shows that the trinuclear complex crystallizes as [{Cu3(L1)3Cl3}2·6Cl·13CH3CN·2H2O] in triclinic space group P-1 with two independent molecules in the asymmetric unit. Each copper(II) adopts a distorted penta-coordinated geometry in each unit. The fluorescence spectra of L1 in methanol show an emission band centered at 300 nm. This band arises due to benzimidazolyl moiety in the ligating system. The diamide L1 in the presence of Fe(3+) show the simultaneous 'quenching' of (300nm) and 'enhancement' of (375 nm) emission band. The new emission band at 375 nm is attributed to intra ligand π-π(*) transition of the biphenyl moiety. While Cu(2+) and Ag(+) show only the quenching of the 300 nm band. No such behavior was observed with other metal ions like Ni(2+), Co(2+), Mn(2+), Mg(2+), Zn(2+) and Pb(2+). The quenching constant with Fe(3+), Ag(+) and Cu(2+) are calculated by the Stern-Volmer plots.

Dimeric copper(II) complex of a new Schiff base ligand: effect of morphology on the catalytic oxidation of aromatic alcohol.

An antiferromagnetically coupled, dimeric µ-naphthanoxo bridged copper(II) complex is used heterogeneously to catalyze oxidation of p-chlorobenzylalcohol to aldehyde selectively. PL and PXRD studies reveal that during recycling the catalyst remains essentially intact. However loss of catalytic efficiency upon reuse is in consonance with a loss in morphology as indicated by SEM.