N/N Bridge Type and Substituent Effects on Chemical and Crystallographic Properties of Schiff-Base (Salen/Salphen) Niii Complexes

In total, 13 ligands R-salen (N,N’-bis(5-R-salicylidene)ethylenediamine (where R = MeO, Me, OH, H, Cl, Br, NO2) and R-salphen (N,N’-bis(5-R-salicylidene)-1,2-phenylenediamine (where R = MeO, Me, OH, H, Cl, Br) and their 13 nickel complexes NiRsalen and NiRsalphen were synthesized and characterized using IR (infrared) spectroscopy, mass spectrometry, elemental analysis, magnetic susceptibility, NMR (nuclear magnetic resonance), UV-vis (ultraviolet-visible) spectroscopy, cyclic voltammetry, and X-ray crystal diffraction. Previous studies have shown that all complexes have presented a square planar geometry in a solid state and as a solution (DMSO). In electrochemical studies, it was observed that in N/N aliphatic bridge complexes, the NiII underwent two redox reactions, which were quasi-reversible process, and the half-wave potential followed a trend depending on the ligand substituent in the 5,5’-R position. The electron-donor substituent—as -OH, and -CH3 decreased the E1/2 potential—favored the reductor ability of nickel. The crystals of the complexes NiMesalen, NiMeOsalen, NiMeOsalphen, and Nisalphen were obtained. It was shown that the crystal packaging corresponded to monoclinic systems in the first three cases, as well as the triclinic for Nisalphen. The Hirshfeld surface analysis showed that the packaging was favored by H∙∙∙H and C∙∙∙H/H∙∙∙C interactions, and C-H∙∙∙O hydrogen bridges when the substituent was -MeO and π-stacking was added to an aromatic bridge. Replacing the N/N bridge with an aromatic ring decreased distortion in square-planar geometry where the angles O-Ni-N formed a perfect square-planar.

Two-stage threecomponent synthesis of 6,11-diaza-1,5(2,5)-dioxazole- 3(1,2)-benzenecycloundecapha ne-14,54- dicarbonitrile

The possibilities of 2-amino-3,3-dichloroacrylonitrile (ADAN) used for the construction of macrocyclic structures such as cyclophanes with two oxazole fragments are investigated. For this purpose, bifunctional reagents were used in the classic ADAN transformation into 5-amino-4-cyanooxazoles (sequential treatment of ADAN with acyl chloride and a primary or secondary amine). As a result of the reaction of 2,2'‎-(1,2-phenylene)-diacetyl chloride with 2 eq of ADAN, a compound with two acrylonitrile fragments, 2,2' ‎- (1,2-phenylene)bis(N- (2,2-dichloro-1-cyanovinyl)acetamide), was obtained. In this substance, both ADAN residues can interact with amines and form oxazole cycles: for example, the treatment with an excess of dimethylamine produces 2,2'‎ - (1,2-phenylenebis(methylene))bis(5-(dimethylamino)oxazole-4-carbonitrile). The target macrocyclic structure was obtained by the interaction of 2,2'‎ - (1,2-phenylene)bis(N-(2,2-dichloro-1-cyanovinyl)acetamide) with butane-1,4-diamine, as a result the simultaneous forming of both oxazole rings and an aliphatic bridge connected with them was happened. At this stage, it was used a procedure, that is typical of the creation of macrocyclic structures based on polyfunctional reagents, — strong dilution (about 0.04 M). The molecule of the synthesized 6,11-diaza-1,5(2,5)-dioxazole-3(1,2)-benzenecycloundecaphan-14,54-dicarbonitrile has high spatial symmetry, which is confirmed by the presence of only one series of peaks in the 1H and 13C NMR spectra (for example, the butane-1,4-diamine fragment in the aliphatic part of the spectrum looks likes two triplets). The formation of a macrocyclic structure is evidenced by HPLC-MS data, as well as homo- and heteronuclear correlations in the NMR spectra. The proposed procedure for the synthesis of 6,11-diaza-1,5(2,5)-dioxazole-3(1,2)-benzenecycloundecaphan- 14,54-dicarbonitrile is based on the use of simple and inexpensive reagents, and the total yield of the target substance in two stages starting with the 2,2'‎ - (1,2-phenylene)diacetyl chloride, is 51 %.

Crystal structure of a fluorescent C-shaped molecule containing closely stacked bithiophene-substituted quinoxaline rings

Molecules with well-defined structures that feature closely stacked aromatic rings are important for understanding π–π interactions. A previously reported C-shaped molecule with bithiophene-substituted quinoxaline rings suspended from an aliphatic bridge that holds the aromatic rings in close proximity exists as a pair of syn and anti diastereomers. The anti isomer, namely (1α,2β,4β,5α,16α,17β,19β,20α)-1,5,16,20-tetrachloro-31,31,32,32-tetramethoxy-11,26-bis[5-(thiophen-2-yl)thiophen-2-yl]-7,14,22,29-tetraazanonacyclo[18.10.1.15,16.02,19.04,17.06,15.08,13.021,30.023,28]dotriaconta-6(15),7,9,11,13,21(30),22,24,26,28-decaene chloroform monosolvate, C48H36Cl4N4O4S4·CHCl3, whose X-ray structure is described herein, has cofacial quinoxaline rings with bithiophene rings attached on opposite sides. The molecular structure is approximately C-shaped and consists of an aliphatic spacer with a boat-shaped cyclohexane ring in the middle. The centroid-to-centroid distance between the quinoxaline rings is 3.950 (1) Å, with ring-offset distances of 0.354 (3) and 0.816 (2) Å. The pendant bithiophene rings are oriented parallel to one another, which results from the thiophene rings connected to the quinoxaline rings being oriented such that their S atoms are rotated inward toward one another, but are not overlapped. Intermolecular packing is largely governed by van der Waals forces and a few weak C—H...X (X = N or O) interactions.

Toxicity in tumor cells, DNA binding mode, and resistance to decomposition by sulfur nucleophiles of new dinuclear bifunctional trans-PtII complexes containing long alkane linkers

In an effort to design dinuclear PtII compounds that maintain the target (DNA) binding profile of the trans-oriented dinuclear bifunctional PtII complexes containing aliphatic linker chains but are less susceptible to metabolic decomposition, the new, long-chain dinuclear PtII complexes—[{trans-PtCl(dien)}2-μ-(CH2)n]2+ (n = 7,10,12, dien = diethylenetriamine)—were synthesized. The toxicity of these metallodrugs was examined in ovarian tumor cell lines. The results showed that the activity of these complexes increased with growing length of the linker; the activity of complex containing the longest linker (n = 12) was comparable with that of cis-diamminedichloridoplatinum(II) (cisplatin). This observation correlated with the results of DNA binding studies performed in cell-free media. The results of these studies demonstrated that the growing length of the aliphatic bridge promoted more distorting conformational alterations induced in DNA. Attention was also paid to the reactivity of {[Pt(dien)Cl]2-alkane} compounds with glutathione (GSH). The results of these experiments support the thesis that the dinuclear structure of {[Pt(dien)Cl]2-alkane} complexes remains stable in the presence of S-containing compounds without undergoing chemical degradation as previously observed for some di/trinuclear bifunctional PtII complexes. This enhanced stability represents a favorable property which may contribute to reduce side effects and increase therapeutic efficacy of the dinuclear {[Pt(dien)Cl]2-alkane} compounds.

Rifamide (rifocin-M)

The rifamycins are antibiotics derived from Streptomyces mediterranei.1 Their chemical structure is novel, with a long aliphatic bridge spanning an aromatic system. They act by inhibiting bacterial RNA polymerase, as do the actinomycins. Of the five compounds originally isolated, only rifamycin B was obtained in stable crystalline form, and three substances derived from this have come into clinical use: rifamycin SV, 2 rifampicin,3 and rifamycin B-diethylamide or rifamide (Rifocin-M - Lepetit).4