One pot synthesis of α-bromo and α-iodo ketones from epoxides

α-bromo and α-iodo ketones are obtained in good yieid and in one. pot by reaction of terminal and disubstituted epoxides with trimethylsilyl halides and further oxidation (CrO₃/H₂SO₄     

Nouvolle synthcse de la dihydro-5,6 methoxy-6 2H-pyrannone-5

The α,β-ethylenic ketone 5 was obtained in 35% yield in four steps from 1. The intermediate product was a brominated ketal obtained in the form of a mixture of two isomers 6 and 7 . The stereochemistry and conformation was established by a study of the 250 MHz nmr spectra. During the dehydrobromination of 6 and 7 , a relatively easy isomerization of the α,β-ethylenic ketal occured by displacement of the double bond giving theβ,γ-ethylenic ketal 10 .     

Determination of total fat in milk- and soy-based infant formula powder by supercritical fluid extraction

Commercially available simple benchtop systems using CO2 supercritical fluid extraction (SFE) eliminate expensive organic solvent disposal problems and offer potential to meet a demand for rapid, accurate high-volume gravimetric determinations of total fat content of infant formula powders. A Data Quality Objectives (DQOs) approach was used to evaluate the performance characteristics of instrumental SFE extraction for determination of total gravimetric fat in infant formula. The established DQOs included the following: ACCURACY: Correct values were obtained for a suitable reference material, SRM 1846 Infant Formula [National Institute of Standards and Technology (NIST), Gaithersburg, MD]. RUGGEDNESS: Variables were defined as (1) extraction time (35 min optimum); (2) ratio of sample size to diatomaceous earth support material (1 g sample/2 g support); (3) ratio of distilled water to alcohol (50% isopropanol optimum for both milk- and soy-based infant formula samples); (4) extraction flow rate was 3-3.5 mL/min optimum. PRECISION: Relative standard deviations of multiple determinations fell within the Horwitz limits of acceptability of < or = 2.8% at the level of analyte determined (0.34-2.5% obtained). SCOPE OF APPLICABILITY: Includes milk- and soy-based infant formula powders. Research data were obtained by use of a commercially available fat analyzer. Samples of the SRM, 2 commercial milk-based and 3 commercial soy-based infant formula products were distributed to 2 additional collaborating laboratories. Very good agreement was obtained among the submitting and collaborating laboratories for these samples. The use of clearly defined DQOs to establish method performance characteristics, along with the commercially available reference material, provided the mechanism for verification and validation of analytical methodology.     

First 2-hydroxy-3-methylbut-3-enyl substituted xanthones isolated from plants: structure elucidation,synthesis and antifungal activity

Two new 2-hydroxy-3-methylbut-3-enyl substituted xanthones, (+/-)-caledol 1 and (+/-)-dicaledol 2 were isolated from a dichloromethane extract of the leaves of Calophyllum caledonicum (Clusiaceae). Compounds 1 and 2 are the first 2-hydroxy-3-methylbut-3-enyl substituted xanthones isolated from natural source. Their structures were elucidated by means of combined analytical methods including HRFABMS, 1D and 2D NMR spectroscopies and also confirmed by total synthesis using biomimetic ortho-prenylphenols photooxygenation (1O2) as a key step. The antifungal activity against Aspergillus fumigatus is reported.     

Elimination of the concentration dependence in mass isotopomer abundance mass spectrometry of methyl palmitate using metastable atom bombardment

An important problem in mass isotopomer abundance mass spectrometry (MIAMS) is the dependence of measured mass isotopomer abundances on sample concentration. We have evaluated the role of ionization energy on mass isotopomer abundance ratios of methyl palmitate as a function of sample concentration. Ionization energy was varied using electron impact ionization (EI) and metastable atom bombardment (MAB). The latter generates a beam of metastable species capable of ionizing analyte molecules by Penning ionization. We observed that ionization of methyl palmitate by EI (70 eV) showed the greatest molecular ion fragmentation and also showed the greatest dependence of relative isotopomer abundance ratios on sample concentration. Ionization using the 3P2 and 3P0 states of metastable krypton (9.92 and 10.56 eV, respectively) resulted in almost no molecular ion fragmentation, and the isotopomer abundances quantified were essentially independent of sample concentration. Ionization using the 3P2 and 3P0 states of metastable argon (11.55 and 11.72 eV, respectively) showed molecular ion fragmentation intermediate between that of EI and MAB(Kr) and showed an isotopomer concentration dependence which was less severe than that observed with EI but more severe than that observed with MAB(Kr). The observed decrease in the dependence of isotopomer abundance on sample concentration with a decrease in molecular ion fragmentation is consistent with the hypothesis that proton transfer from a fragment cation to a neutral molecule is the gas phase reaction mechanism responsible for the concentration dependence. Alternative explanations, e.g., hydrogen abstraction from a neutral molecule to a molecular cation, is not supported by these results. Moreover, the MAB ionization technique shows potential for eliminating one source of error in MIAMS measurements of methyl palmitate, in particular, and of fatty acids methyl esters, in general.     

Some effects of protonation on the electronic structure of pyridine and cytosine

The effects of protonation on the charge distributions of pyridine and cytosine are investigated with the help of the Iterative Extended Hückel technique. The polarization of the -electrons is then included explicitly in a Pariser-Parr-Pople computation of the - ^* transition energies of the pyridinium and cytosinium ions.

---

Zusammenfassung Mit Hilfe der IEH-Methode wird die Auswirkung der Protonierung auf die Ladungsverteilung bei Pyridin und Cytosin untersucht. Die Polarisierung der -Elektronen wird dann in eine PPP-Rechnung der - ^*-übergangsenergie beim Pyridinium- und Cytosiniumion übernommen.

---

Résumé On étudie, à l'aide de la méthode de Hückel étendue iterative, les effets de la protonation sur la répartition des électrons dans les molécules de pyridine et de cytosine. On introduit ensuite explicitement la polarisation des électrons dans le calcul des énergies de transition - ^* des ions pyridinium et cytosinium par la méthode de Pariser, Parr et Pople.

---

---

This work was supported by grant n GM-12229 of the U.S. Public Health Service (National Institute of General Medical Sciences).     

Long-range self-assembly of a polyunsaturated linear organosilane at the n-tetradecane/Au(111) interface studied by STM

We report on the formation of self-assembled monolayers of 13-(trimethylsilyl)-1-tridecene-6,12-diyne [C13H17-Si(CH3)3], an organosilane derivative with a linear polyunsaturated chain, on Au(111) substrates. Molecular resolution STM images recorded at the liquid-solid interface between gold and tetradecane reveal a long-range and densely packed hexagonal lattice with a ( radical3 x radical3)R30 degrees -like structure commensurate against gold adlattice.     

A practical synthesis of LFA-1 inhibitors utilizing CuCl-promoted intramolecular cyclization of thiohydantoins

An efficient and chromatography-free approach for synthesis of a new class of LFA-1 inhibitors was developed. A copper(I) chloride-promoted intramolecular cyclization of thiohydantoins 7a-b serves as a key step to highly functionalized bicyclic guanidines 5a-b, that were subsequently converted to 1H-imidazo[1,2-a]imidazol-2-one LFA-1 inhibitors. This process has been successfully implemented in the pilot plant to produce multikilogram quantities of LFA-1 inhibitors such as 1a-b.     

FT-Raman and high-pressure infrared spectroscopic studies of dicalcium phosphate dihydrate (CaHPO4·2H2O) and anhydrous dicalcium phosphate (CaHPO4)

The FT-Raman spectra and the pressure dependence of the infrared spectra of the hydrated and anhydrous forms of dicalcium phosphate, CaHPO₄ · 2H₂O and CaHPO₄, have been studied. The hydrated salt exhibits a phase transition at 21 kbar (1.0 kbar=0.1 Gpa) but no high pressure transition was observed for anhydrous dicalcium phosphate. The O–H stretching frequencies of the water molecules in CaHPO₄·2H₂O all showed negative pressure dependences and correlate with the OO distances. The PO–H stretch increased with increasing pressure, indicating a strong hydrogen bond. The frequencies associated with the phosphate ion showed a normal pressure dependence.