Alkylation of the isosteviol terpenoid and its oxime with dibromoalkanes in the KOH-DMSO system

The reaction of 16-hydroximinoisosteviol with dihaloalkanes in the KOH-DMSO results in coupling of two isosteviol carcasses by the carboxy groups. The same products were previously synthesized by hydroximination of isosteviol diesters.     

Least Squares Method: Application to Analysis of the Flavor Dependence of the QCD Relation Between Pole and Scheme Running Heavy Quark Masses

Theoretical and Mathematical Physics - We consider the ordinary least squares method, which allows solving overdetermined systems of algebraic equations and estimating the error of the obtained...     

New perturbation theory representation of the conformal symmetry breaking effects in gauge quantum field theory models

We propose a hypothesis on the detailed structure for the representation of the conformal symmetry breaking term in the basic Crewther relation generalized in the perturbation theory framework in QCD renormalized in the [`(MS)]\overline {MS} scheme. We establish the validity of this representation in the O(α _s ⁴ ) approximation. Using the variant of the generalized Crewther relation formulated here allows finding relations between specific contributions to the QCD perturbation series coefficients for the flavor nonsinglet part of the Adler function D _A ^ns for the electron-positron annihilation in hadrons and to the perturbation series coefficients for the Bjorken sum rule S _Bjp for the polarized deep-inelastic lepton-nucleon scattering. We find new relations between the α _s ⁴ coefficients of D _A ^ns and S _Bjp . Satisfaction of one of them serves as an additional theoretical verification of the recent computer analytic calculations of the terms of order α _s ⁴ in the expressions for these two quantities.     

Interplay of Magnetic Exchange Interactions and Ni?S?Ni Bond Angles in Polynuclear Nickel(II) Complexes

The ability of bridging thiophenolate groups (RS^?) to transmit magnetic exchange interactions between paramagnetic Ni^II ions is examined. Specific attention is paid to complexes with large Ni? SR? Ni angles. For this purpose, dinuclear [Ni₂L¹(μ‐OAc)?I₂][I₅] ( 2 ) and trinuclear [Ni₃L²(OAc)₂][BPh₄]₂ ( 3 ), where H₂L¹ and H₂L² represent 24‐membered macrocyclic amino‐thiophenol ligands, are prepared and fully characterized by IR‐ and UV/Vis spectroscopy, X‐ray crystallography, static magnetization M measurements and high‐field electron spin resonance (HF‐ESR). The dinuclear complex 2 has a central N₃Ni₂(μ‐S)₂(μ‐OAc)Ni₂N₃ core with a mean Ni? S? Ni angle of 92°. The macrocycle L² supports a trinuclear complex 3 , with distorted octahedral N₂O₂S₂ and N₂O₃S coordination environments for one central and two terminal Ni^II ions, respectively. The Ni? S? Ni angles are at 132.8° and 133.5°. We find that the variation of the bond angles has a very strong impact on the magnetic properties of the Ni complexes. In the case of the Ni₂‐complex, temperature T and magnetic field B dependencies of M reveal a ferromagnetic coupling J=?29 cm^?1 between two Ni^II ions (H=JS₁S₂). HF‐ESR measurements yield a negative axial magnetic anisotropy (D<0) which implies a bistable (easy axis) magnetic ground state. In contrast, for the Ni₃‐complex we find an appreciable antiferromagnetic coupling J′=97 cm^?1 between the Ni^II ions and a positive axial magnetic anisotropy (D>0) which implies an easy plane situation.     

Synthetic glycosides of <Emphasis Type="Italic">ent</Emphasis>-caurene series containing substituents with benzyl,phenoxyl, and uracyl fragments

New 19-O esters of steviolobioside containing benzyl, phenoxyl, and 6-methyluracyl fragments were synthesized. Molecular structure of two glycosides was established by the X-ray diffraction analysis.     

Wagner-Meerwein rearrangement of steviol 16α,17- and 15α,16-epoxides

16α,17- and 15α,16-Epoxy derivatives of diterpenoid steviol having ent-kaurane structure were found for the first time to undergo Wagner-Meerwein rearrangement in alkaline medium or by the action of boron trifluoride-diethyl ether complex to give products with ent-beyerane structure. The geometric parameters of steviol 16α,17- and 15α,16-epoxides were determined by X-ray analysis.     

Polarographic Behavior of Methyl 4-Aryl-2,4-dioxobutanoates

Polarographic reduction of methyl 4-aryl-2,4-dioxobutanoates in aqueous 2-propanol involves two cathodic waves and yields methyl 4-aryl-2,4-dihydroxybutanoates.     

Chemistry and Structure of Diterpene Compounds of the Kaurane Series: VII. Chiral Complexes of Isosteviol with Aromatic Compounds

(4,8,13)-13-Methyl-16-oxo-17-norkaurane-18-carboxylic acid (isosteviol) forms with aniline, dimethylaniline, and toluene individual 2:1 molecular complexes whose crystals are isostructural. According to X-ray diffraction data, the supramolecular crystal structure of these complexes is formed by chiral double helices with a 4₃ screw axis, consisting of isosteviol molecules. The strands of the helices are linked together by intermolecular hydrogen bonds involving the carboxy and carbonyl groups of two isosteviol molecules of neighboring helices. In their turn, the two hydrogen-bonded isosteviol molecules form head-to-tail pseudocage dimers. The aromatic guests occupy fairly large cavities between the strands of isosteviol helices.