Total synthesis of kendomycin: a macro-C-glycosidation approach

Kendomycin, also known as (-)-TAN 2162, is a novel polyketide-derived ansamycin isolated from Streptomyces sp., which exhibits potent antagonist and agonist activities at the endothelin and calcitonin receptors, respectively. This bacterial metabolite also possesses a strong antibiotic activity against a range of gram-positive and -negative bacteria and cytostatic effects on the growth of human cancer cell lines. When a novel macroglycosidation reaction is employed as the key step, the first enantioselective total synthesis of kendomycin has been accomplished. A Friedel-Crafts-type ring closure of the acyclic precursor containing tetrahydropyran and benzofuran moieties produces the macrocycle as a single stereoisomer in good yield, thus establishing the aryl C-glycosidic linkage of the ansa core. This reaction requires a phenolic glycosyl acceptor and appears to proceed through a rapid O-glycosidation followed by a slow rearrangement to an aryl C-glycoside. The requisite secomacrocycle is prepared by the Pd(0)-catalyzed B-alkyl Suzuki-Miyaura cross-coupling of two subunits, which in turn can be expeditiously assembled from readily available building blocks in a modular fashion.     

Oxidation of 2,4-Dinitrotoluene with an Ozone-Oxygen Mixture

Oxidation of 2,4-dinitrotoluene to 2,4-dinitrobenzoic acid with an ozone-oxygen mixture in glacial acetic acid was studied.     

Calorimetric determination of solubility of water in pectin and physical state diagram of a pectin-water system

For the mixtures of pectin of different esterification degrees and water, heat capacities in the range of 80–320 K have been measured, and DTA measurements have been carried out in the range 80–450 K. The effect of water on the physical transitions of pectin has been studied, and the solubility of water in pectins of different esterification degrees at the temperature of melting of a liquid component has been determined. On the basis on the experimental data, the physical state diagram of the pectin-water system has been constructed and analyzed for the whole range of component concentrations within a wide temperature interval.     

A new diterpenoid related to eunicellin and cladiellin from a Muricellasp.

The isolation and structure elucidation of a new diterpenoid from a horny-coral (Gorgonaceae) are reported. The ¹H and ¹³C-NMR spectra are discussed.     

Ethynyl carbonium ions. 1. Reaction of 2.6-diaryl-4-phenylethynylpyrulium perchlorates with oxygen-containing nucleophiles

When 2,6-diaryl-4-phenylethynylpyrylium perchlorates are refluxed in water, methanol, or ethanol, they are converted to monomethinecyanines, the formation of which is explained by hydration of the phenylethynyl group and subsequent [2+2]-cycloaddition of the resulting 2,6-diaryl-4-benzoylmethylenepyrans to the starting pyrylium salt. The corresponding pyridine derivatives were obtained by the action of ammonia and aniline on the monomethinecyanines. The IR and PMR spectra of the compounds and the results of x-ray diffraction analysis of 2,6-diphenyl-4-[1-(2,6-diphenyl-4-pyranylidene)-2-phenyl-3-benzoylallyl]pyridine are presented.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 885–890, July, 1988.     

Synthesis and properties of (4-hydroxy-5-methoxycarbonylthieno)-tetrathiafulvalenes

6-Hydroxy-5-methoxycarbonylthieno[2,3-d]-1,3-dithiol-2-thione, -2-one, and 2-selenone were prepared by intramolecular cyclocondensation of 4-methoxycarbonylmethylthio-1,3-dithiol-2-thione-, 2-one-, and 2-selenone-5-carboxylic acid methyl ester. 2,6(7)-Di(methoxycarbonylmethylthio)-3,7(6)-di(methoxycarbonyl)tetra-thiafulvalene, 2-methoxycarbonylmethylthio-3-methoxycarbonyl-6,7-ethylenedithiotetrathiafulvalene, and the corresponding thieno-condensed tetrafulvalene derivatives were synthesized from them. The electrochemical oxidation potentials of the new tetrafulvalene derivatives were determined.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 761–768, June, 1993.     

Hetero analogs of alloxazines. 2. Structure and tautomerism of 6,8-dimethyl-7,9-dioxo-5h-6,7,8,9-tetrahydropyrimido[4,5-b][4′,5′-e][1,4]thiazines

It is demonstrated by ¹³C NMR spectroscopy that the dipyrimidothiazines that are formed in the reaction of 1,3-dimethyl-5-nitro-6-chlorouracil with 4-R-5-amino-6-mercaptopyrimidines are dipyrimido[4,5-b][4,5-e] [1,4]thiazines. The tautomeric transformations of these compounds were studied.For communication 1, see [1]Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1426–1432, October, 1992.     

Sorption of Ion Associates on Polyurethane Foams and Its Application to Sorption–Spectroscopic and Test Methods of Analysis

The results of studying the sorption of various ion associates on polyurethane foams were generalized. The main sorption-affecting factors were found to be the nature, hydrophobicity, and charge of the associate ion; the nature and concentration of the counter ion; the composition of the polymer unit of the polyurethane foam; and the pH and salt composition of the aqueous phase. Correlation equations were proposed to relate the partition coefficients with the hydration energy of counter ions in the ion associates of cationic dyes and metal complexes of 1,10-phenanthroline and with the number of carbon atoms in the alkyl fragment of cationic alkyltrimethylammonium surfactants. A sorption scheme was proposed and substantiated. Examples were given of the practical use of sorption for determining anionic and cationic surfactants, phenols, 1-naphthol, Fe(III), and Ru(IV).     

Quantum-chemical Analysis of Reactions between Alkenes and Sulfenyl Chlorides. Position of Episulfuran and Tight Ion Pair on the Reaction Coordinate

In the first stage the reaction between 3,3-dimethyl-1-butene and 1-phenyl-5-tetrazolylsulfenyl chloride gives rise to intermediate of tight ion pair type that, in the course of system movement along the reaction coordinate, transforms into an intermediate species of sulfuran type or directly into an adduct. The intermediate of sulfuran type also transforms into an adduct going over the energy barrier of 40 kcal mol^-1. The formation of an episulfuran type intermediate directly from the reagents requires overcoming an energy barrier that is by 10 kcal mol^-1 higher than in going through a tight ion pair.     

Reactions of hydrazine derivatives

Conditions were worked out for the synthesis of a number of 1-arylpyrazolidines with alkyl groups in the 4 and 5 positions of the five-membered ring by reduction of the corresponding 3- or 5-pyrazolidones with lithium aluminum hydride.See [1, 2] for communications XLVI And XLVII.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 118–121, January, 1971.