Yu. A. Zhdanov

The problem of acoplanarity of aromatic azomethines

Abstract The interaction of electronic and steric factors in aromatic azomethine molecules has been investigated. The theoretical calculations predict and the experimental data confirm that the azomethine molecule exists as a stable non-planar conformation in which the dihedrical angle between the amino nucleus and the rest of the molecule plane is 40–60° and that substituents in the aryl nucleus have little effect. Acoplanarity of the azomethine molecule suggests the possibility of finding atropoisomers and account for some specific features of their physical and chemical properties. The benzalaniline electronic spectra have been calculated by ASMO CI method. In addition the nature of electronic transitions and their connection with molecular conformation of benzalaniline have been investigated.

The Wittig Reaction in Carbohydrate Chemistry

Publisher Summary The Wittig reaction is considered one of the fundamental synthetic methods of modern organic chemistry. It is the most convenient route to unsaturated compounds. The remarkable features of this reaction include mild reaction conditions, high quantitative yields, and the absence of migration of the bond formed. A number of natural compounds such as carotenoids and methylenic steroids are synthesized by using this reaction. This chapter summarizes the advances in the application of the Wittig reaction in the carbohydrate field. The Wittig reaction involves the interaction of an oxo compound with phosphonium ylides, through an intermediate betaine to yield the appropriate alkene and triphenylphosphine oxide. The Wittig reaction generally results in the preponderant formation of the trans-isomer. The yield of the cis-isomer is increased with decrease in stability of the phosphorane. It is noted that the application of the Wittig reaction in the carbohydrate field is accompanied by certain difficulties. A correct choice of the initial sugar components is the main problem, owing to the basicity of phosphoranes.

Quantum chemistry of carbohydrates : Part I. The electronic structure of some pentoses

Abstract The simple LCAO-MO method of inductive parameters, in the form derived by Del Re, has been applied to the calculation of the electronic structure of some pentoses. The calculated data have been used for the interpretation of some chemical properties of pentoses.

Allantoin as a vitamin.

Inactivation of the gene ( Uox ) in primates, which is responsible for the synthesis of theenzyme urikase, has determined new ways of social and intellectual evolution of mammals [1, 2]. Almost simultaneously with this process, a mutation occurred, as a result of which primates lacked the capability of endogenous synthesis of ascorbate. These mutations sharply changed the systems of antioxidant defense by eliminating vitamin C and allantoin from the overall profile of intracellular nonenzymatic inactivation of reactive oxygen species. Water-soluble vitamins—active quenchers of intracellular free-radical processes—are characterized by a considerable similarity of biological effects, although the role of allantoin is more specific. This is also confirmed by the results of comparative analysis of thermodynamics of oxidation of ascorbic acid ( c 2 A ) and allantoin (Hall) by hydroxyl radicals, which was performed using quantum-chemical reagents [3, 4]. Earlier, it was shown experimentally and theoretically that allantoin is an effective antioxidant that is readily attacked by reactive oxygen species [3, 5]. It is also known that the reducing properties of ascorbic acid are the key factor that determines its function as a vitamin [4]. In aqueous medium, ascorbic acid dissociates according to the known scheme: When comparing hydroxylation of allantoin and dianion ascorbate, it is seen that the mechanisms of interaction of ascorbate and allantoin with the H radicals are different: allantoin 1 forms a fairly stable planar radical 2 [1], whereas ascorbate 3 is converted into stable dihydroascorbic acid 4 , inactivating two hydroxyl radicals [2]:

Allantoin as a Free-Radical Scavenger

In vertebrates, free purine bases are deaminated mainly to hypoxantine (Ia) or xantine (Ib), which are further oxidized to uric acid (Ic) in the presence of oxygen. Its further conversion (Ic to If) is shown in the following scheme:

Dipolar spirocyclic σ-complexes based on of 4,6-dinitrobenzofuroxan

The first dipolar spiro-σ-complexes with a superelectrophilic dinintrobenzofuroxan fragment and tropolone systems with diastereotopic substituents were synthesized. The kinetics of their enantiotopomerization, which occursvia cleavage-formation of the Cspiro-heteroatom bond, was studied by dynamic1H NMR. The stereorigidity of dinitrobenzofuroxan spiro-complexes in this degenerated process increases in the series: tropolone<aminotropone<aminothiotropone≈aminotroponimine. The two last posses the highest kinetic stability compared to all known zwitterionic spiro-complexes.

Reactions of 4-oxo-1,3-benzoxazinium perchlorates with guanidines

Condensation of 2-methyl-4-oxo-1,3-benzoxazinium perchlorate with various aromatic and heterocyclic aldehydes provided previously unknown arylvinyl-and hetarylvinyl-substituted salts whose recyclization under treatment with guanidine resulted in formerly undescribed 1,3,5-triazines. The reaction of perchlorates obtained with guanidinebenzoxazole led to the formation of bishetarylamines, with guanidinebenzimidazole formed triazinebenzimidazoles, the cyanoguanidine reacted with 4-oxo-1,3-benzoxazinium perchlorates to give cyanamides.

On the nature of the anomeric effect

Abstract Calculations of the interaction energies of heteroatoms X and Y unshared electron pairs in structures (I) and (II) have been performed for molecules of 2-methoxytetrahydropyran and fluoromethanol, by semi-empirical EHMO and CNDO/2 methods, as well as by classical dipole-dipole approximation. This type of interaction was shown not to be a factor responsible for the stability of the gauche structure (II). The current interpretation that the anomeric effect is an electrostatic interaction of heteroatom unshared electron pairs (the “rabbit ears” effect) is, therefore, groundless.

Synthesis of 1-C-substituted, unsaturated ketoses

Abstract Using the Wittig reaction, higher α,β-unsaturated ketose derivatives, having substituents at C-1, were synthesised from the acetylated aldehydo forms of D -galactose, D -glucose, and D -mannose, using (acetyl- and aroyl-methylene) triphenylphosphoranes. The structures of the ketose derivatives were examined by i.r. and u.v. spectroscopy. In the deacetylated products, the presence of acyclic ketose structures was indicated by periodate oxidation studies. Certain properties of the ketose derivatives are influenced by the nature of the substituent at C-1. The Wittig reaction enables olefinic bonds to be introduced into monosaccharides which may then be converted into 2,3-dideoxy derivatives.

Acylotropic Tautomerism: XXXV. RL-Inversion of Configuration of Dipolar Spyrocyclic and Open-Chain 2-Arylaminotropone Isomers

RL-Inversion of chiral spirocyclic and open-chain 2-arylaminotropone derivatives with varied heteroatom (O, S, N) has been studied. Kinetic relations holding in the RL-permutation are discussed. Its mechanism includes formation and dissociation of spiro bonds and torsion stereodynamics.