Stereochemistry of seven-membered heterocycles: XLV. Highly diastereoselective addition of dimethyl 1,2,4,5-tetrazine-3,6-dicarboxylate to 2-substituted 1,3-dithiacyclohept-5-enes

Conformationally heterogeneous 2-substituted 1,3-dithiacyclohept-5-enes (R = Ph, Me, t-Bu), which exist in solution as chair and boat conformers, react with dimethyl 1,2,4,5-tetrazine-3,6-dicarboxylate with high exo-diastereoselectivity: only the chair conformer is involved. The steric structure of 4-methyl-3,5-dithia-9,10-diazabicyclo[5.4.0]undeca-7,10-diene was determined by X-ray analysis. Its crystal packing and supramolecular structure were also analyzed.     

Stereochemistry of Seven-membered Heterocycles: XLIV. Spatial Structure of 4-R-3,5-Dioxabicyclo[5.1.0]octanes

4-R-3,5-Dioxabicyclo[5.1.0]octanes were prepared in good yields by reduction of the corresponding 8,8-dichloro derivatives in a system Li-t-BuOH. According to the data of dynamic ¹H and ¹³CNMR spectroscopy involving experiments in the NOESY mode the formal (R = H) at −93°C in (CD₃)₂CO exists in nearly equally occupied chair forms with endo- and exo-oriented three-membered ring. The like structure were found in the diastereomeric 4-Me(t-Bu)-analogs. The characteristic feature of ¹³C NMR spectra consists in considerable difference in the chemical shifts of the C⁸ atoms (Δδ∼16–17 ppm). The data on epimerization of diastereomers and calculations along AM1 procedure suggest for formal a three-component equilibrium including a twist-form.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 2, 2005, pp. 301–305.Original Russian Text Copyright © 2005 by Fedorenko, Baryshnikov, Khairutdinov, Vafina, Shtyrlin, Klochkov, Klimovitskii.     

Structure, Stability, and Lability of Copper(II) Complexes with Triglycine

Equilibrium constants of complex formation, rate constants of chemical exchange reactions, and characteristics of electronic absorption spectra for species detected in aqueous solution of copper(II) with triglycine were determined, and conclusions on the structure of the complexes were made. A possibility of H-bond formation between the ammonium group of the zwitter-ionic form of the ligand and the second peptide oxygen in the anionic form of an adjacent ligand was shown. Kinetics and mechanisms of ligand and proton exchanges in solutions of copper(II) bistripeptide complexes with the ligand containing a deprotonated peptide nitrogen atom were studied. A new mechanism was proposed for hydroxide-catalyzed substitution reactions in copper(II) complexes with tripeptides.     

Exchange kinetics of amino acid anions in solutions of ternary copper(II) complexes with diethylenetriamine

Rate constants for the chemical exchange of some amino acid anions in solutions of copper(II) ternary complexes with diethylenetriamine have been determined by the NMR method. The coordination of amino acid anions in ternary and binary species is different and ligand substitution in the Cu(II) complexes follows an associative mechanism.

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- (II) . - (II).

     

Stereochemistry of Seven-Membered Heterocycles: XLIII. Steric Structure of Diastereoisomeric 8,8-Dichloro(dibromo)-4-R-3,5-dioxabicyclo[5.1.0]octanes

Dichloro- and dibromocyclopropanation of 2-substituted 1,3-dioxacyclohept-5-enes according to Makosza resulted in formation of the corresponding 4-substituted 8,8-dichloro(dibromo)-3,5-dioxabicyclo[5.1.0]octanes in good yields. Ultrasonic activation of the process considerably shortened the reaction time. According to the ^{1 3}C NMR spectra, the chair-twist equilibrium is essentially displaced toward the chair conformer for the exo isomers and toward the twist conformer for the endo structures. Similar results were obtained by AM1 semiempirical calculations which indicated that the CCl···O interaction largely determines the conformational equilibrium. The state of the diastereoisomer epimerization equilibrium depends on the size of the substituent at the acetal carbon atom.     

Chemistry of pyridoxine in drug design

Russian Chemical Bulletin - Pyridoxine and its derivatives, pyridoxamine and pyridoxal, are the three main forms of vitamin B6, which play exceptionally important biological roles in living...     

Novel approach to 6-alkenyl-substituted pyridoxine derivatives based on the Heck reaction

A new synthetic approach to 6-alkenyl-substituted pyridoxine derivatives was developed based on the Heck reaction. The reaction, which was catalyzed using a mixture of Pd(OAc)₂, (o-Tol)₃P and Bu₃N as a base, led to seven new 6-alkenyl pyridoxine derivatives. When acrylic acid was used the products of decarboxylation and dimerization were formed.     

Synthesis and antiadrenergic properties of β-substituted alcohols based on 6-hydroxymethylpyridoxine

An approach to the synthesis of epoxides based on 6-hydroxymethylpyridoxine acetals was developed. The epoxides obtained were involved in the ring opening reactions by nitrogen-, oxygen-, and sulfur-containing nucleophiles. Cytotoxicity and antiadrenergic properties of some synthesized compounds were studied on the models in situ and in vivo.     

Structure and Dynamical Behaviour of Bis(N-Diisopropoxy-Phosphorylthiobenzamido) Copper(II)

Abstract

Among the new compounds of N-(thio)phosphorylthiómides. the copper(II) complex with N-diisopropoxyphosphorylthiohenzamide (Cul. 2) exhibits series of unusual properties which have been extcnsively investigated in the present work. The X-ray structure of CuL₂ has been determined Crystals of CuL₂ are monoclinic. P2₁/c, a = 15.610, b = 11.880, and c = 18.320 Å, β = 106.74°. Z = 4. The CuL₂ complex has the cis-structure with Cu-S distances ranging from 2.238 to 2.253 Å and Cu-O distances being from 1.919 to 1.937 Å (Figure).     

Stereochemical transformations of some seven-membered pyridoxine dimethyl ketals

According to the data of single crystal X-ray diffraction analysis and computational methods, the seven-membered rings of acylated pyridoxine acetonides have C ₂ symmetry. Two stereochemical transformations in solutions, enantiotopomerization of P-, M-conformations with spiral chirality of twist-boat forms and diastereotopomerization of structures that differ in the configuration of the phenolic oxygen substituents, were revealed by dynamic ¹H NMR spectroscopy.