2,4,9‐Triazaadamantanes with “Clickable” Groups: Synthesis, Structure and Applications as Tripodal Platforms

1,4,6,10-Tetraazaadamantanes (TAADs) with N-amino groups: synthesis and formation of boron chelates and host–guest complexes

A synthetic route to 1,4,6,10-tetraazaadamantanes (TAADs) bearing free and protected amino groups at the bridge N-atoms has been developed via intramolecular cyclotrimerization of C=N units in the corresponding tris(hydrazonoalkyl)amines. In a similar fashion, unsymmetrically substituted TAADs having both amino and hydroxy groups at the bridge N-atoms were prepared via a hitherto unknown co-trimerization of oxime and hydrazone groups. The use of N-TAAD derivatives as potential ligands and receptors was showcased through forming boron chelates and host–guest complexes with water and simple alcohols.

Facile construction of the all-bridge-position-functionalized 2,4,6,8-tetraazaadamantane skeleton and conversion of its N-functionalities

An unusual protocol of a “one-pot” three-step strategy to build the 2,4,6,8-tetraazaadamantane skeleton was developed. 17 products were obtained in 19–46% yields, and the N-benzyl groups were transferred to nitroso, acetyl, benzoyl and nitro groups.

Azaadamantanes, a New Promising Scaffold for Medical Chemistry

Azaadamantanes are nitrogen-containing analogs of adamantane, which contain one or more nitrogen atoms instead of carbon atoms. This substitution leads to several specific chemical and physical properties. The azaadamantane derivatives have less lipophilicity compared to their adamantane analogs, which affects both their interaction with biological targets and bioavailability. The significant increase in the number of publications during the last decade (2009-2020) concerning the study of reactivity and biological activity of azaadamantanes and their derivatives indicates a great theoretical and practical interest in these compounds. Compounds with pronounced biological activity have been already discovered among azaadamantane derivatives. The review is devoted to the biological activity of azaadamantanes and their derivatives. It presents the main methods for the synthesis of di- and triazaadamantanes and summarizes the accumulated data on studying the biological activity of these compounds. The prospects for the use of azaadamantanes in medical chemistry and pharmacology are discussed.

Revealing the Structure of Transition Metal Complexes of Formaldoxime

Aerobic reactions of iron(III), nickel(II), and manganese(II) chlorides with formaldoxime cyclotrimer (tfoH₃) and 1,4,7-triazacyclononane (tacn) produce indefinitely stable complexes of general formula [M(tacn)(tfo)]Cl. Although the formation of formaldoxime complexes has been known since the end of 19th century and applied in spectrophotometric determination of d-metals (formaldoxime method), the structure of these coordination compounds remained elusive until now. According to the X-ray analysis, [M(tacn)(tfo)]⁺ cation has a distorted adamantane-like structure with the metal ion being coordinated by three oxygen atoms of deprotonated tfoH₃ ligand. The metal has a formal +4 oxidation state, which is atypical for organic complexes of iron and nickel. Electronic structure of [M(tacn)(tfo)]⁺ cations was studied by XPS, NMR, cyclic (CV) and differential pulse (DPV) voltammetries, Mössbauer spectroscopy, and DFT calculations. Unusual stabilization of high-valent metal ion by tfo^3- ligand was explained by the donation of electron density from the nitrogen atom to the antibonding orbital of the metal-oxygen bond via hyperconjugation as confirmed by the NBO analysis. All complexes [M(tacn)(tfo)]Cl exhibited high catalytic activity in the aerobic dehydrogenative dimerization of p-thiocresol under ambient conditions.

Merging Boron with Nitrogen-Oxygen Bonds: A Review on BON Heterocycles

Cyclic boronate esters play important roles in organic synthesis, pharmacology, supramolecular chemistry and materials science owing to their stability in air and versatile reactivity. Most of these compounds contain a B-O-C linkage with an alkoxy- or carboxylate group bound to the boron atom (e.g. boronate-diol esters, MIDA boronates). Boron chelates comprising a B-O-N motif (BON heterocycles) are much less explored, although first representatives of this class were prepared in the early 1960s. In recent years, there has been a growing interest in BON heterocycles as new chemotypes for drug design. The exocyclic B-O-N linkage, which is readily formed under mild conditions, shows surprising hydrolytic and thermal resistance. This allows the formation of BON heterocycles to be used as click-type reactions for the preparation of bioconjugates and functionally modified polymers. We believe that BON heterocycles are promising yet underrated organoboron derivatives. This review summarizes the scattered information about known types of BON heterocycles, including their synthesis, reactivity and structural data. Available applications of BON heterocycles in materials science and medicinal chemistry, along with their prospects, are also discussed. The bibliography contains 289 references.