Hydrangenone, a new isoprenoid with an unprecedented skeleton from Salvia hydrangea

Hydrangenone, a new heptacyclic isoprenoid with a 6/7/6/5/5 membered carbon ring skeleton, was isolated from the aerial parts of Salvia hydrangea. The structure was established by extensive NMR spectroscopic methods. The relative and absolute configuration of 1 was assigned by NOESY and X-ray crystallographic analysis and by comparison of experimental and calculated electronic circular dichroism (ECD) spectra. Compound 1 showed in vitro antiplasmodial activity, with an IC(50) value of 1.4 μM against P. falciparum. A plausible biosynthetic pathway of 1 was also proposed.     

Development of a novel approach for the production of dried genomic DNA for use as standards for qualitative PCR testing of food-borne pathogens

As part of a multi-centre European project, FOOD-PCR, the feasibility of a novel approach for production of dried bacterial DNA that could be used as certified reference materials (CRM) was assessed. Selected strains of Salmonella typhimurium, Listeria monocytogenes, Escherichia coli O157, Campylobacter jejuni and Yersinia enterocolitica were used to produce genomic DNA (gDNA). These preparations gave support to method development for qualitative polymerase chain reaction (PCR) detection methods for food-borne pathogens. Purified gDNA was transformed into stable and dry gDNA by using polypropylene vials as carrier and applying a vacuum-drying technique. The gDNA preparations were shown to be sufficiently stable under ambient transport conditions without cooling and proved to have long-term stability at 5°C of at least 22 months. The dried DNA was easily reconstituted by addition of distilled water then gentle shaking. These studies have shown that production of stable and dry bacterial gDNA material is feasible and could help satisfy the increasing need for certified reference DNA positive control samples in the field of PCR testing for detection and verification of food-borne microbial pathogens.

     

Studying the structure and electrical conductivity of thin granulated bimetallic films

The surface resistance of bimetallic granular films prepared by means of laser-induced deposition is studied. The possibility of modeling their conductivity is demonstrated, depending on their morphological properties.     

Excited-State Properties of Thymidine and Their Relevance to Its Heterogeneous Emission in Double-Stranded DNA

Published results on synthetic polynucleotides point to T as the major emitting fluorophore in DNA. We have reported also that the bases of the nonalternating polynucleotide poly(dA).poly(dT), in which T was selectively excited, undergo large-amplitude motions on the picosecond-nanosecond time scales (S. Georghiou et al., Biophys. J. 70, 1909-1922, 1996). In that study, the fluorescence decay profile of the T bases of this polynucleotide was found to contain a number of components; these may be considered to be the result of the motions of the bases that give rise to a distribution of stacked geometries of varying rigidity as well as dispersion and polar interactions. Here, we report the results of a study that we have undertaken in order to test this hypothesis. To this effect, we have studied the photophysical properties of thymidine (1) in aqueous buffer and in a number of organic solvents and (2) in aqueous sucrose solutions of viscosity extending to 149 cP. The results suggest that the fluorescence quantum yield decreases with an increase in the polarizability of the solvent, whereas it increases with an increase in the solvent polarity (on the basis of the empirical parameter of solvent polarity ETN) or viscosity. These findings suggest the following for the photophysical properties of the T bases in DNA: (1) Base stacking results in two antagonistic effects, namely it causes a reduction in fluorescence as a result of dispersion interactions and an enhancement as a result of a reduction in the motions of the bases and (2) exposure of the bases to the aqueous environment results in fluorescence enhancement.     

Cyclization of Propargylic Amides: Mild Access to Oxazole Derivatives

The substrate scope, the mechanistic aspects of the gold‐catalyzed oxazole synthesis, and substrates with different aliphatic, aromatic, and functional groups in the side chain were investigated. Even molecules with several propargyl amide groups could easily be converted, delivering di‐ and trioxazoles with interesting optical properties. Furthermore, the scope of the gold(I)‐catalyzed alkylidene synthesis was investigated. Further functionalizations of these isolable intermediates of the oxazole synthesis were developed and chelate ligands can be obtained. The use of Barluenga’s reagent offers a new and mild access to the synthetically valuable iodoalkylideneoxazoles from propargylic amides, this reagent being superior to other sources of halogens.