Strukturelle Abwandlungen anN-Acetylneuraminsäure, 3

From methyl-5-acetylamino-7,8-anhydro-4,9-O-bis-(t-butyldimethylsilyl)-3,5-dideoxy--D-glycero-D-galacto-2-nonulopyranosidonic acid methylester (1) the derivatives1 a and1 b were obtained by removing the 9-O-(t-butyldimethylsilyl)group withBu ₄NF, followed by acetylation. Treatment of1 b with 80% acetic acid and acetanhydride/pyridine yields the 8-epi-N-acetylneuraminic acid derivative2 a and the 7-epi-N-acetylneuraminic acid derivative3 a in a ratio of 3:1 (Scheme 1). The structure elucidation of2 b was achieved by converting2 b via the 4,9-bis-O-(tBDMSi)-8-O-tosyl-derivative2 d into the epoxide1 (Scheme 2). Using the same sequence the epoxides4 and5 were transformed into theN-acetylneuraminic acid derivative6 a and the 7,8-bis-epi-N-acetylneuraminic acid derivative7 a (Scheme 3). After treatment with sodium hydroxide and 0.025m HCl and Dowex 50 H⁺ the 8-epi-, 7-epi- and 7,8-bis-epi-N-acetylneuraminic acids2,3, and7 were obtained. These three compounds were tested withCMP-N-acetylneuraminic acid synthetase.

Herrn KollegenK. Schlögl mit den besten Wünschen zum 60. Geburtstag.     

Zur Bildung von Xylol-tricarbonylchrom (Dimethylbenchrotrenen) aus Di-n-butylether und Hexacarbonylchrom

The reaction of fluorenone ethyleneketal (9), diphenic anhydride as well as of biphenyls such as4 with Cr(CO)₆ in refluxing di-n-butylether (BE) gives dimethylbenchrotrenes [xylene-Cr(CO)₃,7] which are also formed by refluxing pureBE with Cr(CO)₆—although with much lower yields. Similarily, from di-n-pentylether and Cr(CO)₆ isobutyl- and 1-methyl-3-propyl-benchrotrene (13 and14) were obtained, whilst from di-n-propyl- and-hexylether, resp., and Cr(CO)₆ no benchrotrenes could be isolated.Tentative assumptions on the catalytic action of certain functional groups were confirmed by the reaction ofBE and Cr(CO)₆ in the presence of carbonamides, such as acetamide, urea and pyrrolidone, where 1,4-dimethylbenchrotrene (7 c) was formed with appreciable yields.Studies using dideuteratedBE showed that—at least for the reaction of9 with Cr(CO)₆ (giving a much lower yield of7 than with undeuteratedBE)—a simple bimolecular mechanism can be excluded.

     

Gas chromatography of halogenated adamantanes

The main thermodynamic characteristics of the adsorption of haloadamantanes on graphitized thermal carbon black were determined by experimental measurements and by calculations in terms of molecular-statistic theory of adsorption. Using experimental data, the Kovac retention indices were calculated and the optimum conditions for gas-chromatographic separation of haloadamantanes on stationary phases with different polarity were elucidated. The influence of the cage effect in the adamantane unit on the chromatographic properties of haloadamantanes was established.     

3β-Methoxyolean-18-ene (miliacin) from the marine fungus Chaetomium olivaceum

A pentacyclic tritepenoid, 3-methoxyolean-18-ene (miliacin), was isolated for the first time from the marine fungus Chaetomium olivaceum. Its structure was determined on the basis of 2D NMR spectroscopy and X-ray diffraction data.     

Naphthalene Complexation by β-Cyclodextrin: Influence of Added Short Chain Branched and Linear Alcohols

Naphthalene forms 1 : 1 complexes with -cyclodextrin (-CD)in water. The binding constant is 377 ± 35 M^-1. Addition of linear or branched alcohols causes a reduction in the apparent strength of naphthalene binding (K_app) compared to the value in the absence of additives. For example, 1% 1-pentanol reduces K_app to 184 ± 31 M^-1. Branching does not alter K_app much for a given number of carbon atoms, e.g., it is 113 ± 9 M^-1for 2-pentanol and 116 ± 8 M^-1for 3-pentanol. The exception to this is tert-butanol for which K_app is 577 ± 40 M^-1. The variation in K_app as a function of [1-pentanol] yields values for the individual equilibrium constants contributing to K_app. This reveals that a ternary complex forms involving naphthalene, the CD and 1-pentanol. The constant for formation of the ternary complex is 99 ± 29 M^-2. NaI quenching of naphthalene fluorescence indicates that the CD cavity partially protects the naphthalene excited state fromthis water phase quencher. Interestingly, the Stern–Volmer constant is lower in the presence of 1-pentanol than in its absence, although there should be more unbound (and therefore more NaI accessible) naphthalene in the former system than in the latter. These apparently contradictory results are discussed in terms of ternary complex formation.     

Superoxes,high temperature universal phases in (GC)2

Most of the common classes of organic compounds chromatograph normally on Superoxes. There is no tailing or adverse effect from excessively different activity different activity coefficients. Superoxes are therefore universal phases for gas chromatography. This is also expressed by a wide useful temperature range from ～50° to ～300°. High MW Superox-4 has a MAOT about 20° higher than the lower MW Superox-0.1. Several applications illustrating the versatility of Superox phases in (GC)² are presented.     

A new general-purpose isothermal microcalorimeter for use at temperatures up to 200 °C

The design and some properties of a new general-purpose isothermal microcalorimeter are reported. The instrument is a twin thermopile heat conduction calorimeter, which is designed for use up to 200 °C. The calorimetric units and surrounding heat sink are suspended inside a hollow aluminium construction, which is thermostated. Above that unit a second thermostated block is positioned and the whole assembly is suspended inside a Dewar vessel. When the instrument is used at room temperature and below, the thermostated units are cooled by use of an insertion Peltier effect cooler. The instrument can be used with a wide range of different reaction vessels (diameter 14 mm). Baseline experiments have been conducted in the temperature range 15-200 °C. Typical values obtained during 10 h periods at 200 °C are ±3 and ±10 nW for the baseline drift and baseline fluctuations, respectively. The heat detection limit, determined by release of electrical energy, is about 2 μJ. Preliminary stability measurements have been conducted at 100 °C on samples of stabilised and non-stabilised polyamide film.     

The inclusion of rhodium(II)α-methyl-cinnamate in β-cyclodextrin

The preparation and characterization of the 1:1 inclusion compound of rhodium(II) -methyl cinnamate in -cyclodextrin is reported. Evidence of inclusion was obtained from X-ray powder diffraction results, Raman, IR and UV-Vis spectroscopic studies and thermal analysis. Given the potential antitumor activity of the rhodium(II) carboxylate and its virtual insolubility in water, its inclusion in -cyclodextrin opens the possibility for its transference to the aqueous phase.     

Synthesis of phosphorus (silicon,tin)-containing derivatives of mercaptoketenes and some of their properties

Some newS-phosphorylated,S-silylated, andS-stannylated derivatives of -mercaptoketones were obtained. The reactions of some of these compounds induced by the temperature and by molecular oxygen as well as the phosphorylation of the Si- and Sn-containing derivatives were studied.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 353–357, February, 1995.     

Enantiomer differentiation in intramolecular carbon—hydrogen insertion reactions of racemic secondary alkyl diazoacetates catalyzed by chiral dirhodium(ii) carboxamidates

Highly efficient kinetic resolution of racemic secondary alkyl diazoacetates in intramolecular carbon-hydrogen insertion reactions has been achieved using chiral dirhodium(ii) carboxamidates. Products formed from catalytic diazo decomposition of racemic 2-octyl diazoacetate and, separately, its (2R)- and (2S)-enantiomeric forms, as well as bothcis- andtrans-2-methylcyclohexyl diazoacetates, have been systematically evaluated. Enantioselectivities up to 99 %ee have been obtained for -lactone formation. -Lactone production has been observed and, although minor with cyclohexyl diazoacetates, is the major insertion pathway for diazo decomposition of 2-octyl diazoacetate.Dedicated to Academician of the RAS N. S. Zefirov (on his 60th birthday).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1798–1803, September, 1995.Financial support for this research from the National Institutes of Health (GM 46503) and the National Science Foundation of the United States is gratefully acknowledged. We thank D. A. Pierson for her preparation of 2-methylcyclohexyl diazoacetates and preliminary studies of their diazo decomposition and A. Melekhov from the Higher College of Chemistry for his preparation and catalytic studies of rac-2-octyl diazoacetate.