Asteriscunolides A,B, C and D,the first humulanolides; Two pairs of conformationally stable stereoisomers

Following a preliminary comunication on Asteriscunolide A (the first reported natural humulanolide), three more configurationally and/or conformationally isomeric Asteriscunolides ( B, C and D ) from the same plant ($\text{Asteriscus aquaticus}$ L.) are described. The absolute configurations and the stable conformations of all four Asteriscunolides are established by an array of spectroscopic methods (CD, ¹H and ¹³C NMR) without resorting to X ray analysis.     

Synthesis of (+)-8-deoxyvernolepin and its 11,13-dihydroderivative. A novel reaction initiated by sulfene elimination leads to the 2-Oxa-cis-decalin skeleton

The title compounds are interesting candidates for antifungal screening. This paper describes the enantiospecific synthesis of these compounds starting from (+)-costunolide isolated from a commercially available extract. We used two novel reactions as key synthetic steps in this work: the acid-induced cyclization of an delta,epsilon-epoxy ester, which stereoselectively gave a hydroxymethyl-substituted delta-lactone, with the hydroxyalkyl group in the desired beta-equatorial disposition, and a reaction cascade, initiated by a base-promoted sulfene elimination, which led to a 10-oxiranyl-2-oxa-cis-decalin from the mesylate of a trans-fused delta-lactone. We also found that the reaction between selenium dioxide and the 1,5-diene system of elemanolides gave selenadecalins analogous to natural eudesmanolides. Our results prove that the synthetic strategy employed, on the basis of biomimetic concepts, is a useful procedure for the enantiospecific preparation of (+)-vernolepin-related compounds from accessible germacrolides.     

Unified synthesis of eudesmanolides,combining biomimetic strategies with homogeneous catalysis and free-radical chemistry

[reaction: see text] A general procedure for the synthesis of both 12,6- and 12,8-eudesmanolides has been developed. The key step is the titanocene-catalyzed radical cyclization of accessible epoxygermacrolides. The novel reagent 2,4,6-trimethyl-1-trimethylsilylpyridinium chloride, both compatible with oxiranes and capable of regenerating Cp(2)TiCl(2) from Cp(2)Ti(Cl)H and Cp(2)Ti(Cl)OAc, played an important role in the catalytic cycle leading to exocyclic alkenes.     

Micellar medium for the analysis of complex mixtures of molybdenum and tungsten by derivative synchronous spectrofluorimetry in steels

The cationic surfactant hexadecyltrimethylammonium bromide enhances the fluorescence intensity of both molybdenum and tungsten complexes obtained with Alizarin Red S. This characteristic has been used for a sensitive simultaneous spectrofluorimetric determination of both ions over the range 32-4000 ng/ml and 49-2500 ng/ml for Mo and W, respectively. Good selectivity is achieved applying the well known synchronous derivative technique with a minucious pH selection. The proposed method has been applied to a certified steel sample with recoveries between 96 and 102%.     

Determination of albumin in biological fluids by flow injection analysis using the peroxyoxalate chemiluminescent system in micellar medium

A novel chemiluminescence (CL) method for the determination of papaverine (PAP) has been developed by combining the flow injection technique and its sensitizing effect on the weak CL reaction between sulfite and acidic permanganate. A mechanism for the CL reaction has been proposed on the basis of fluorescent and chemiluminescence spectra. The CL response is proportional to the concentration of PAP over the range 0.2-10 micro mol L(-1). The detection limit of PAP is 0.10 micro mol L(-1) (3 s) with a relative standard deviation (RSD) of 2.0% for 10 repetitive determinations of 1.0 micro mol L(-1) PAP. Interferences from other alkaloids in the opium, such as morphine and codeine, are negligible except that of narcotine. The method has been satisfactorily used for the determination of PAP in injections and compound liquorice tablets.     

A biosensor for ferric ion

A new biosensor for monitoring iron has been developed. The active solid phase is pyoverdin, a natural fluorescent pigment biosynthesized by Pseudomonas fluorescens immobilized on controlled pore glass (CPG) and packed in a quartz flow-through cell. The biosensor is very selective for iron(III) and can be easily regenerated in about 2 min by passing 1M HCl through the cell. The optimum conditions and analytical characteristics (detection limit, precision and linear range) for the new sensor in solution (DL = 10 ng/ml) and in immobilized form (DL = 3 ng/ml) are reported. The biosensor has good stability and can be used continuously over a period for at least 3 months (over 1000 determinations). The sensor was successfully applied to determine iron in different water samples. There were no significant differences between the new method and the Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) reference method at the 95% confidence level.     

Reductive coupling of terpenic allylic halides catalyzed by Cp2TiCl: a short and efficient asymmetric synthesis of onocerane triterpenes

[reaction: see text] Titanocene chloride catalyzes the regioselective alpha,alpha'-homocoupling of terpenic allylic halides. This process has been employed in the short and effective synthesis of terpenoids such as beta-onoceradiene (1), beta-onocerin (2), and squalene (3). Evidence is presented for eta1-allyltitanium species being involved in the coupling.     

Antibacterial diterpenoids from Cedrus atlantica

Four diterpene alcohols were isolated from the neutral hexane extract of the cones of Cedrus atlantica, and their structures were confirmed after comparing their spectral data with literature values. These products exhibited significant antibacterial activity against gram (+/-) bacteria.