N-glycosides. 9. Reaction of 3,5-O-isopropylidenexylofuranosylamine with β-isothiocyanatoaldehydes. Synthesis of new cyclonucleosides with a hexahydropyrimidine aglycone

The reaction of 3,5-O-isopropylidenexylofuranosylamine p-toluenesulfonate with -isothiocyanatoaldehydes in the presence of triethylamine gives 4,2-anhydro-4-hydroxy-3-(3,5-O-isopropylidene--D-xylofuranosyl)hexahydropyrimidine-2-thiones. The structure of these compounds and their deblocking products was studied by IR, UV, PMR, and ORD spectroscopy and mass spectrometry.For Communication 8, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1252–1258, September, 1993.     

Reaction of a chlorovinylcarbene with ketenealkyl silyl acetals. Synthesis of new α- and β-allenic carboxylates.

The reaction of ketenealkylsilylacetals with 1,1-dimethyl-2,2,3-trichlorocyclopropane in the presence of methyllithium leads to cyclopropane compounds, which, when treated with tetrabutylammonium fluoride give α- or β-allenic carboxylates.     

β-Fragmentation of alkoxy radicals. An approach to the synthesis of ring a of vernolepin

A model of ring A of vernolepin is synthesized by 1,4-fragmentation of γ-thiyl and γ-stannyl alkoxy-radicals, generated by photolysis of the corresponding δ-lactols (4) and (5) in the presence of iodosobenzene diacetate and iodine. It should be pointed out that the δ-lactone ring and the angular vinyl group are introduced in one step.     

The Effect of Temperature on Nucleation of Condensed Water Phase on the Surface of a β-AgI Crystal. 1. Structure

The Monte Carlo method has been employed to study the effect of temperature on the structure and the mechanism of retaining condensed water phase nuclei on the surface of the basal face of a silver iodide crystal. Comparative calculations of spatial correlation functions and computer images of vapors being condensed at 260 and 320 K have indicated an increased stability of monomolecular water-film spots with respect to thermal fluctuations. The disturbances of the regular “honeycomb” structure have a collective character and occur according to the “domino principle”; i.e., the rupture of a hydrogen bond between neighboring molecules releases enhanced libration motions of the latter, which, in turn, provoke the rupture of bonds with other neighbors. In accordance with this scenario, the distortion of the hexagonal structure of the film under the action of thermal fluctuations develops with the formation of growing spots of destruction. The thermal fluctuations significantly affect the orientational molecular order and the degree of clustering on the surface. The positions of molecules relative to the ions of the surface crystallographic layer of a substrate weakly depend on temperature.     

The Effect of Temperature on Nucleation of Condensed Water Phase on the Surface of a β-AgI Crystal. 2. Formation Work

In the condensation mechanism of heterogeneous ice formation, water crystallization occurs after a necessary amount of the liquid phase has accumulated on a substrate surface. In this way, the ice-forming activity of the surface is governed by its adsorption ability with respect to water vapor. The Monte Carlo canonical statistical ensemble method has been used to calculate the free energy, entropy, and work of nucleation of a disordered condensed water phase on the surface of crystalline silver iodide and to determine the surface tension. Comparative calculations have been performed at 260 and 320 K for the defect-free surface of a basal face of a crystal. The surface of a β-AgI crystal is completely covered with a monomolecular film even in unsaturated water vapors. The surface tension at the growing nucleus–substrate interface substantially increases due to the formation of the underlying film, and the growth of the nucleus becomes possible only in a supersaturated vapor. As the vapor density increases, the thickness of the condensed water layer grows, and, at negative Celsius temperatures, conditions are created for its crystallization. The underlying film with pronounced hydrophobic properties hinders nucleation, thereby decreasing the ice-forming activity of the surface in the condensation process. Under these conditions, the observed abnormally high ice-forming activity of silver-iodide aerosol particles may be explained by the presence of numerous crystal defects on the particle surface, with these defects representing channels that provide overcoming the hindering action of the film.     

Photosolvolysis of a carboncarbon bond. The photolysis of n,n-dimethyl- 2,2-diphenylethylamine in methanol.1

The title compound is photolyzed in methanol to give good yields (ca. 50%) of diphenylmethane indicating that the CC bond undergoes a formal heterolytic cleavage from the excited state as predicted from the measured redox potentials of the two ions.     

Inclusion of Nonopiate Analgesic Drugs in Cyclodextrins. I. X-Ray Structure of a 1 : 1 β-Cyclodextrin-p-bromoacetanilide Complex

The preparation and X-ray crystal structure of a 1 : 1 complex between -cyclodextrin (-CD) and the analgesic p-bromoacetanilide are reported. Thermogravimetric and UV spectrophotometric analyses of single crystals grown from an aqueous solution containing host and guest in 1 : 1 molar ratio yielded the composition -CD p-bromoacetanilide $ 13.5H2O. Crystals of the complex are triclinic, space group P1, with a = 15.197(3), b = 15.613(2), c = 15.743(4) Å, = 87.16(2), = 98.29(2), = 103.39(1)° and Z = 2 crystallographically independent complex units per unit cell. The -CD molecules form head-to-head dimers which pack in the channel-mode. Each dimer contains two guest molecules whose acetylamino substituents are located at the dimer interface while the bromine atoms protrude from the -CD primary faces. The acetyl residues of both guest molecules were found to be disordered but the X-ray data permitted     

The heterometric micro-analysis of cobalt with α-nitroso - β-naphthol. a general study.

1. The reaction between cobaltous or cobaltic and α-nitroso-β-naphthol was extensively studied heterometrically both in water and in alcoholic solutions. The influence of complexing agents and of the acidity on the precipitation of cobalt-α-nitroso-β-naphthol was investigated. In all cases the molar ratios : [Co] [αβ] at the end of the precipitation were established and the possible compounds which were obtained were discussed. 2. Micro-analytical heterometric methods are given for the determination of cobalt or α-nitroso-β-naphthol. The determination can be carried out with precision even in concentrations as low as 0.0001M Co. Conversely, very dilute alcoholic solutions of α-nitroso-β-naphthol may be titrated with precision with a dilute solution of cobalt nitrate. 0.2–0.5 mg cobalt in 20 ml solution are required for the analysis. The error lies between zero and 3%.     

Hydrocarbon dispersion of nanospherical silica by a sol–gel process. 1. Tetraethoxysilane homopolymerization

This study focused on the preparation of a hydrocarbon dispersion of nanospherical silica using tetraethoxysilane homopolymerization by a sol–gel process catalyzed by NH₄OH in ethanol. The silica surface was rendered hydrophobic by the introduction of trimethylchlorosilane or trimethylethoxysilane as a terminator. Organophilic particles with diameters in the range 10–130 nm were obtained under controlled conditions. Nevertheless, the organophilic fraction dispersed in hexane was not greater than 62%. The homopolymerization reaction time was directly related to the particle size and, in some cases, its insolubility. High terminator concentration and low termination temperature favored the increase in the number of organophilic particles. The chlorine-containing terminator was more efficient in promoting the production of hydrocarbon hydrophobic nanospheres. Received: 21 February 2000/Accepted: 21 June 2000     

Isolation and Characterization of a Bioactive Polysaccharide from Panax Quinquefolium L.

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A stereocontrolled synthesis of a novel prostacyclin analog “allene-carbacyclin”. Application of molecular mechanics calculations to organic synthesis.

The synthesis of a novel Prostacyclin/Carbacyclin analog 1a has been achieved in a stereocontrolled manner starting from the readily available bicyclic ketone 3. A key strategic feature of the synthesis is a nucleophilic acetylide anion addition to 3, the stereochemistry of which is predicted by MM2 calculations.     

Tandem β-fragmentation-intramolecular functionalization of alkoxyradicals. An approach to the synthesis of a and a'rings of limonin

A tandem β-fragmentation-intramolecular functionalization reaction is observed by photolysis of steroidal lactols in the presence of several oxidation agents under oxygen. An application of this reaction to the synthesis of A and A'rings of limonin (1) is described.     

Sebiferone,a New Triterpenoid from Stem Bark of Sapium sebiferum （L.）Roxb.

From the stem bark of Sapium sebiferum a new triterpenoid,anmed sebiferone (1),was isolated.The structure of the new compound was clucidated as 3β-acetoxy-D-friedoolen-14-en-1-one-28-oic acid on the basis of spectral and chemical methods.     

Total Synthesis of Angucyclines. XVII. First Synthesis of Antibiotic 100‐1, a Deoxydisaccharide Angucycline Antibiotic of the Urdamycinone B‐Type

Two routes to the deoxydisaccharide angucycline antibiotic 100‐1 (3) are described. Key steps comprise the regioselective oxidation/bromination of the 1,5‐diacetoxyolivose C‐saccharide 7 to the bromoquinone 8. Diels–Alder reaction of the bromoquinone with the diene 9 followed by HBr elimination afforded the urdamycinone B precursor 11 as a diastereomeric mixture. Selective protection as the TBDMS ether 13, acetylation and deprotection of the silyl ether afforded the alcohol 15 which was selectively glycosylated to the α‐rhamnal glycoside 17 in 72% yield (at 70% conversion) using benzoyl rhamnal (16) as the glycoside donor and scandium triflate as the promotor. The silyl group at C‐3 of the aglycone was then transformed into a hydroxyl group. Zemplén deacylation and photooxidation of the benzylic position at C‐1 then converted the two diastereoisomers into the natural product 3 and the C‐3 diastereoisomer 20. At this stage the diastereomers 3 and 20 were separated. Alternatively and more easily, the diastereomers were separated at the stage of the urdamycinone B analogues 21a and 21b, followed by a similar reaction sequence to the natural disaccharide 3.