Bovine serum albumin uptake and polypeptide disaggregation studies of hypoglycemic ruthenium(II) uracil Schiff-base complexes

Our prior studies have illustrated that the uracil ruthenium(II) diimino complex, [Ru(H3ucp)Cl(PPh3)] (1) (H4ucp = 2,6-bis-((6-amino-1,3-dimethyluracilimino)methylene)pyridine) displayed high hypoglycemic effects in diet-induced diabetic rats. To rationalize the anti-diabetic effects of 1, three new derivatives have been prepared, cis-[Ru(bpy)2(urdp)]Cl2 (2) (urdp = 2,6-bis-((uracilimino)methylene)pyridine), trans-[RuCl2(PPh3)(urdp)] (3), and cis-[Ru(bpy)2(H4ucp)](PF6)2 (4). Various physicochemical techniques were utilized to characterize the structures of the novel ruthenium compounds. Prior to biomolecular interactions or in vitro studies, the stabilities of 1-4 were monitored in anhydrous DMSO, aqueous phosphate buffer containing 2% DMSO, and dichloromethane (DCM) via UV-Vis spectrophotometry. Time-dependent stability studies showed ligand exchange between DMSO nucleophiles and chloride co-ligands of 1 and 3, which was suppressed in the presence of an excess amount of chloride ions. In addition, the metal complexes 1 and 3 are stable in both DCM and an aqueous phosphate buffer containing 2% DMSO. In the case of compounds 2 and 4 with no chloride co-ligands within their coordination spheres, high stability in aqueous phosphate buffer containing 2% DMSO was observed. Fluorescence emission titrations of the individual ruthenium compounds with bovine serum albumin (BSA) showed that the metal compounds interact non-discriminately within the protein's hydrophobic cavities as moderate to strong binders. The metal complexes were capable of disintegrating mature amylin amyloid fibrils. In vivo glucose metabolism studies in liver (Chang) cell lines confirmed enhanced glucose metabolism as evidenced by the increased glucose utilization and glycogen synthesis in liver cell lines in the presence of complexes 2-4.

N-[(E)-Thio-phen-2-yl-methyl-idene]-1,3-benzothia-zol-2-amine

In the title thio­phene-derived Schiff base compound, C₁₂H₈N₂S₂, the thio­phene ring is slighty rotated from the benzothia­zole group mean plane, giving a dihedral angle of 12.87 (6)°. The largest displacement of an atom in the mol­ecule from the nine-atom mean plane defined by the non-H atoms of the benzothia­zole ring system is 0.572 (1) Å, exhibited by the C atom at the 3-position of the thio­phene ring. In the crystal, weak C—H⋯S hydrogen bonds involving the thio­phene group S atom and the 4-position thio­phene C—H group of a symmetry-related mol­ecule lead to an infinite one-dimensional chain colinear with the c axis. The structure is further stabilized by π–π inter­actions; the distance between the thia­zole ring centroid and the centroid of an adjacent benzene ring is 3.686 (1) Å. The crystal studied was an inversion twin with the ratio of components 0.73 (3):0.27 (3).

6-Amino-1,3-dimethyl-5-[(E)-2-(methylsulfanyl)benzylideneamino]pyrimidine-2,4(1H,3H)-dione–1,3,7,9-tetramethylpyrimido[5,4-g]pteridine-2,4,6,8-tetrone (1/1)

In the title co-crystal, C₁₂H₁₂N₆O₄·C₁₄H₁₆N₄O₂S, both mol­ecules are essentially planar [maximum deviations = 0.129 (1) and 0.097 (1) Å, respectively]. The tricyclic and Schiff base mol­ecules are alternately stacked along the a axis and are linked by π–π inter­actions with centroid–centroid distances of 3.5170 (16) and 3.6576 (17) Å. An intra­molecular C—H⋯O hydrogen bond and a C—H⋯S contact occur in the Schiff base molecule. In the crystal, N—H⋯O, N—H⋯N and C—H⋯O hydrogen bonds lead to the formation of a three-dimensional network.