Hydrolysis of the amide bond in histidine- and methionine-containing dipeptides promoted by pyrazine and pyridazine palladium(II)-aqua dimers: Comparative study with platinum(II) analogues

Chelating Picolinaldehyde Hydrazone Amides as Protecting Groups for Carboxylic Acids: Orthogonal Reactivities of Hydrazone Amides and Esters in Hydrolysis

We report a chelating hydrazone amide as a protecting group for carboxylic acids. Unlike most esters, 2-picolinaldehyde hydrazone amides are stable under acidic or basic hydrolytic conditions. However, hydrazone amides can be easily converted to the corresponding carboxylic acids via Ni-mediated hydrolysis. Orthogonal reactivities of the hydrazone amides and representative protecting groups were verified by control experiments and peptide synthesis, demonstrating that chelating hydrazone amides are highly useful protecting groups.

Bis(triazinyl)pyridine complexes of Pt(II) and Pd(II): studies of the nucleophilic substitution reactions, DNA/HSA interactions, molecular docking and biological activity

Four new complexes of Pt(II) and Pd(II), [Pd(L1)Cl]Cl 1, [Pd(L2)Cl]Cl 2, [Pt(L1)Cl]Cl 3 and [Pt(L2)Cl]Cl 4 (where L1 = 2,6-bis(5,6-diphenyl-1,2,4-triazin-3-yl)pyridine and L2 = 2,6-bis(5,6-dipropyl-1,2,4-triazin-3-yl)pyridine), were synthesized. Characterization of the complexes was performed using elemental analysis, IR, ¹H NMR spectroscopy and MALDI-TOF mass spectrometry. The substitution reactions of 1-4 complexes with L-methionine (L-met), L-cysteine (L-cys) and guanosine-5'-monophosphate (5'-GMP), were studied spectrophotometrically at physiological conditions. Complexes with ligand L1 (1 or 3) were more reactive than those with ligand L2 (2 or 4) by a factor ranging up to 1.57 and 3.71, respectively. The order of reactivity of the nucleophiles was: L-met > L-cys > 5'-GMP. The interactions of complexes with calf thymus-DNA (CT-DNA) and human serum albumin (HSA) were studied by Uv-Vis absorption and fluorescence emission spectroscopy. Competitive binding studies with intercalative agent ethidium bromide (EB) and minor groove binder Hoechst 33258 were performed as well. All studied complexes can interact with DNA through the intercalation and minor groove binding, where the latter was preferred. The binding constants (10³ and 10⁴ M^-1) for the interaction of complexes with HSA indicate the moderate binding affinity of complexes 1-4 to protein. The trends in the experimental results of binding studies between complexes 3 and 4 with DNA and HSA were compared to those obtained from the molecular docking study. Biological evaluation of cytotoxicity of 1 and 2 on HCT-116 and MDA-MB-231 cell lines showed significant cytotoxic and prooxidative character, while 2 also exerted extraordinary selectivity towards colon cancer in comparison to breast cancer cells. The nucleophilic substitution reactions, DNA/HSA interactions, molecular docking and biological activity of bis(triazinyl)pyridine complexes of Pt(II) and Pd(II) were studied.

New dinuclear palladium(II) complexes with benzodiazines as bridging ligands: interactions with CT-DNA and BSA, and cytotoxic activity

Three new dinuclear Pd(II) complexes with general formula [{Pd(en)Cl}₂(μ-L)](NO₃)₂ [L is bridging ligand quinoxaline (Pd1), quinazoline (Pd2) and phthalazine (Pd3)] were synthesized and characterized by elemental microanalyses, UV-Vis, IR and NMR (¹H and ¹³C) spectroscopy. The interaction of dinuclear Pd1-Pd3 complexes with calf thymus DNA (CT-DNA) has been monitored by viscosity measurements, UV-Vis and fluorescence emission spectroscopy in aqueous phosphate buffer solution (PBS) at pH 7.40 and 37 °C. In addition, these experimental conditions have been applied to investigate the binding affinities of Pd1-Pd3 complexes to the bovine serum albumin (BSA) by fluorescence emission spectroscopy. In vitro antiproliferative and apoptotic activities of the dinuclear Pd(II) complexes have been tested on colorectal and lung cancer cell lines. All tested Pd(II) complexes had lower cytotoxic effect than cisplatin against colorectal cancer cells, but also had similar or even higher cytotoxicity than cisplatin against lung cancer cells. All complexes induced apoptosis of colorectal and lung cancer cells, while the highest antiproliferative effect exerted Pd2 complex.

Amide Bond Activation of Biological Molecules

Amide bonds are the most prevalent structures found in organic molecules and various biomolecules such as peptides, proteins, DNA, and RNA. The unique feature of amide bonds is their ability to form resonating structures, thus, they are highly stable and adopt particular three-dimensional structures, which, in turn, are responsible for their functions. The main focus of this review article is to report the methodologies for the activation of the unactivated amide bonds present in biomolecules, which includes the enzymatic approach, metal complexes, and non-metal based methods. This article also discusses some of the applications of amide bond activation approaches in the sequencing of proteins and the synthesis of peptide acids, esters, amides, and thioesters.

Hydrolysis of Methionine- and Histidine-Containing Peptides Promoted by Dinuclear Platinum(II) Complexes with Benzodiazines as Bridging Ligands: Influence of Ligand Structure on the Catalytic Ability of Platinum(II) Complexes

Dinuclear platinum(II) complexes, [{Pt(en)Cl}₂(μ-qx)]Cl₂·2H₂O (1), [{Pt(en)Cl}₂(μ-qz)](ClO₄)₂ (2), and [{Pt(en)Cl}₂(μ-phtz)]Cl₂·4H₂O (3), were synthesized and characterized by different spectroscopic techniques. The crystal structure of 1 was determined by single-crystal X-ray diffraction analysis, while the DFT M06-2X method was applied in order to optimize the structures of 1-3. The chlorido Pt(II) complexes 1-3 were converted into the corresponding aqua species 1a-3a, and their reactions with an equimolar amount of Ac-L-Met-Gly and Ac-L-His-Gly dipeptides were studied by ¹H NMR spectroscopy in the pH range 2.0 < pH < 2.5 at 37°C. It was found that, in all investigated reactions with the Ac-L-Met-Gly dipeptide, the cleavage of the Met-Gly amide bond had occurred, but complexes 2a and 3a showed lower catalytic activity than 1a. However, in the reactions with Ac-L-His-Gly dipeptide, the hydrolysis of the amide bond involving the carboxylic group of histidine was observed only with complex 1a. The observed disparity in the catalytic activity of these complexes is thought to be due to different relative positioning of nitrogen atoms in the bridging qx, qz, and phtz ligands and consequent variation in the intramolecular separation of the two platinum(II) metal centers.