Synthesis, structural characterization and biological studies of copper complexes with 2-aminobenzothiazole derivatives

Synthesis of a chiral dinuclear Cu(II)-benzothiazolamine complex: evidence of cuprophilic interaction in its structure and exploration of its electrochemical properties and catalytic performance

The synthesis of a chiral dinuclear [Cu(OAc)2(L1)]2 complex (A) and its analogues Cu(OAc)2(L1)2 (B), Cu(OAc)2(L1)PPh3 (C), CuBr(L1)PPh3 (D), and Cu(OAc)2(L2) (E) is described. The X-ray structure of A reveals a cuprophilic interaction (2.65 Å) and shows that L1 behaves as a monodentate ligand. The stereogenic centre in L1 aligns the NH group to form non-covalent interactions with the paddle-wheel acetate groups at variable distances (2.4-2.5 Å and 2.2-2.7 Å). Thermogravimetric analysis confirmed our hypothesis that two equivalents of L1 (B) or a combination of L1 and PPh3 (C) would disrupt the cuprophilic interaction. All complexes, except D, showed irreversible redox waves by cyclic voltammetry. Complexes C and E have lower oxidative peaks (at 10 V s-1) than complex A between +0.40 and +0.60 V. This highlights the influence of ligand(s) on the redox behaviour of Cu(II) complexes. The significance of this electrochemical behaviour was evident in the Chan-Lam (CL) coupling reaction, where 2.5 mol% of A successfully facilitated the formation of a C-N bond. This study showcased the structure, thermal stability, electrochemical properties and catalytic performance of a chiral dinuclear copper(II)-benzothiazolamine complex.

Synthesis, characterization, in vitro, in silico and in vivo investigations and biological assessment of Knoevenagel condensate β-diketone Schiff base transition metal complexes

A novel Schiff base ligand was synthesized by the Knoevenagel condensation of β-diketone (obtained from substituted Curcumin and Cuminaldehyde) and 4-amino antipyrine. Metal complexes were made from this Schiff base by reacting with metal salts such as Cu(II), Ni(II), Ru(III), VO(IV), and Ce(IV). Physicochemical approaches such as UV-Vis, FT-IR, NMR, EPR, and Mass spectroscopy were used to determine the geometry of the complexes. The thermodynamic stability and biological accessibility of the complexes were investigated using density functional theory (DFT) calculations at the B3LYP/6-31G(d) level. A molecular docking analysis was also performed on 1BNA receptor. Both the Schiff base ligand and metal complexes interacted well to this protein receptor. All metal complexes have a significant potential to bind to CT DNA via the intercalation mechanism. All the in vivo and in vitro screening studies showed that the complexes exhibit higher activities than the free Schiff base.Communicated by Ramaswamy H. Sarma.

Synthesis and Structural Characterization of Palladium(II) Mixed-Ligand Complexes of N-(Benzothiazol-2-yl)benzamide and 1,2-Bis(diphenylphosphino)ethane

Three novel palladium(II) mixed-ligand complexes of N-(benzothiazol-2-yl)benzamide (HL) and 1,2-bis(diphenylphosphino)ethane (dppe), [Pd(HL)(dppe)]Cl₂ (1), [Pd(L)(dppe)]Cl (2), and [Pd(L)₂(dppe)] (3), were synthesized and fully characterized using Fourier transform infrared, ¹H, ¹³C, and ³¹P NMR, and molar conductivity measurements. Complex 3 was characterized by single-crystal X-ray diffraction. The ligand HL showed three different coordination modes: a neutral bidentate chelate bound through the endocyclic nitrogen and exocyclic oxygen atoms in 1, a negatively charged L bound as a bidentate chelate through the endocyclic nitrogen and negatively charged exocyclic oxygen atoms in 2, and a monodentate bound through the negatively charged endocyclic nitrogen atom in 3.

Isothioureas, Ureas, and Their N-Methyl Amides from 2-Aminobenzothiazole and Chiral Amino Acids

In this investigation, the reaction of 2-dithiomethylcarboimidatebenzothiazole with a series of six chiral amino-acids was studied. The reaction proceeds through the isolable sodium salt of SMe-isothiourea carboxylates as intermediates, whose reaction with methyl iodide in stirring DMF as solvent affords SMe-isothiourea methyl esters. The presence of water in the reaction leads to the corresponding urea carboxylates as isolable intermediates, whose methyl esters were obtained. Finally, the urea N-methyl amide derivatives were isolated when SMe-isothiourea or urea methyl esters were reacted with methylamine in the presence of water. The structures of synthesized compounds were established by ¹H and ¹³C nuclear magnetic resonance and the structures of SMe-isothiourea methyl esters derived from (l)-glycine, (l)-alanine, (l)-phenylglycine, and (l)-leucine, by X-ray diffraction analysis. This methodology allows to functionalize 2-aminobenzothiazole with SMe-isothiourea, urea, and methylamide groups derived from chiral amino acids to get benzothiazole derivatives containing coordination sites and hydrogen bonding groups. Further research on the biological activities of some of these derivatives is ongoing.

Pharmacophore hybrid approach of new modulated bis-diimine Cu(II)/Zn(II) complexes based on 5-chloro Isatin Schiff base derivatives: Synthesis, spectral studies and comparative biological assessment

Novel bioactive 5-chloro isatin based Schiff base ligands, (N,N'E,N,N'Z)-N,N'-(5-chloroindoline-2,3-diylidene)bis(5-nitrobenzo [d]thiazol-2-amine), L(1) and (N,N'E,N,N'Z)-N,N'-(5-chloroindoline-2,3-diylidene)bis(5-nitrothiazol-2-amine), L(2) derived from 2-amino 5-nitrobenzothiazole and 2-amino 5-nitrothiazole and their metal complexes, [Cu(L(1))2]Cl2;1, [Zn(L(1))2(H2O)2]Cl2;2, [Cu(L(2))2]Cl2;3 and [Zn(L(2))2(H2O)2]Cl2;4 have been synthesized. The composition, stoichiometry and geometry of the proposed ligands and their complexes have been envisaged by the results of elemental analyses and spectroscopic data (FT-IR, (1)H NMR and (13)C NMR, Mass and EPR). The molar conductivity values of the metal complexes revealed their ionic nature. The thermal stability of metal complexes was demonstrated by TGA/DTA studies while the crystalline nature of the complexes has been ascertained by XRD. Furthermore, a comparative account of in vitro antibacterial study against different bacterial strains with respect to standard antibiotic and scavenging activity against standard control at different concenterations unfolded pronounced antibacterial and radical scavenging potencies of the metal complexes as compared to free ligands. In addition, in vitro cytotoxicity of ligands and its metal complexes was also screened on MCF7 (Human breast adenocarcinoma), HeLa (Human cervical carcinoma) and HepG2 (Human Hepatocellular carcinoma), cell lines and normal cells (PBMC). The antiproliferative outcomes revealed that metal complexes exhibit superior activity in general as compared to free ligands (L(1) and L(2)) where metal complexes (1 and 2) of 5-chloro isatin linked benzothiazole motif (L(1)) are found to have better prospect of acting as chemotherapeutic agents which can be explained in terms of greater biopotency, planarity and conjugation against all the tested cancer cell lines with IC50<2.80 μM.