Synthesis and properties of hypervalent electron-rich pentacoordinate nitrogen compounds

Organohypervalent heterocycles

This review summarizes the structural and synthetic aspects of heterocyclic molecules incorporating an atom of a hypervalent main-group element. The term "hypervalent" has been suggested for derivatives of main-group elements with more than eight valence electrons, and the concept of hypervalency is commonly used despite some criticism from theoretical chemists. The significantly higher thermal stability of hypervalent heterocycles compared to their acyclic analogs adds special features to their chemistry, particularly for bromine and iodine. Heterocyclic compounds of elements with double bonds are not categorized as hypervalent molecules owing to the zwitterionic nature of these bonds, resulting in the conventional 8-electron species. This review is focused on hypervalent heterocyclic derivatives of nonmetal main-group elements, such as boron, silicon, nitrogen, carbon, phosphorus, sulfur, selenium, bromine, chlorine, iodine(III) and iodine(V).

Novel Antineoplastic Inducers of Mitochondrial Apoptosis in Human Cancer Cells

I propose a new strategy to suppress human cancer completely with two entirely new drug compounds exploiting cancer's Warburg effect characterized by a defective mitochondrial aerobic respiration, substituted by cytosolic aerobic fermentation/glycolysis of D-(+)-glucose into L-(+)-lactic acid. The two essentially new drugs, compound 1 [P(op)T(est)162] and compound 3 (PT167), represent new highly symmetric, four-bladed propeller-shaped polyammonium cations. The in vitro antineoplastic highly efficacious drug compound 3 represents a covalent combination of compound 1 and compound 2 (PT166). The intermediate drug compound 2 is an entirely new colchic(in)oid derivative synthesized from colchicine. Compound 2's structure was determined using X-ray crystallography. Compound 1 and compound 3 were active in vitro versus 60 human cancer cell lines of the National Cancer Institute (NCI) Developmental Therapeutics Program (DTP) 60-cancer cell testing. Compound 1 and compound 3 not only stop the growth of cancer cells to ±0% (cancerostatic effect) but completely kill nearly all 60 cancer cells to a level of almost -100% (tumoricidal effect). Compound 1 and compound 3 induce mitochondrial apoptosis (under cytochrome c release) in all cancer cells tested by (re)activating (in most cancers impaired) p53 function, which results in a decrease in cancer's dysregulated cyclin D1 and an induction of the cell cycle-halting cyclin-dependent kinase inhibitor p21Waf1/p21Cip1.

Structure-property-function relationships of stabilized and persistent C- and N-based triaryl radicals

Structurally similar C- and N-based triaryl radicals are among the most commonly used structural motifs in stable, open-shell, organic molecules. The application of such species is associated with their stability, properties and structural design. This study summarizes the basic stabilization and persistence principles of C- and N-based triaryl radicals and highlights recent advances in design strategies of radicals tailored for specific applications.

Synthesis and Characterization of Hypervalent Pentacoordinate Carbon Compounds Bearing a 7-6-7-Ring Skeleton

To stabilize S_N 2 transition state-like penta-coordinate carbon species, triaryl-substituted cationic carbon compounds bearing a moderately flexible 7-6-7-ring skeleton with sulfur donors were synthesized and characterized. Electronic effects of para substituents (R=Cl, F, H, CH₃ , SMe, OMe) of the two equatorial aryl groups bound to the cationic central carbon were investigated systematically along with a planar bidentate thioxanthene derivative. X-ray analysis on their solid-state structures showed that the parent (R=H), chloro-, fluoro- and methyl-derivatives were tetracoordinate carbon (sulfonium) structures, while the p-MeO and thioxanthenyl system were pentacoordinate carbocation structures. The Hammett substituent constants for the para substituents (σ_p ⁺ ) correlates well with the bonding in these compounds. The methylthio-derivative with intermediate Hammett substituent constants (p-MeS; σ_p ⁺ =-0.60) showed a tetracooridnate solid-state structure, though solution UV-Vis properties suggested the presence of a penta-coordinate structure. These findings amount to the first unambiguous solution evidence of the hypervalent apical 3c-4e interactions in pentacoordinate carbon compounds.