Simultaneous determination of optical and chemical purities of a drug with two chiral centers by liquid chromatography-circular dichroism detection on a non-chiral stationary phase

The need for a rapid and cheap chromatographic technique for the simultaneous determination of diastereoisomeric and chemical purities of a drug has led to develop a non-enantioselective HPLC method on a porous graphitic carbon (PGC) sorbent and by using circular dichroism (CD) detection. Among a lot of non-chiral chromatographic supports tested, PGC was the only one allowing the separation of all benzoxathiepin diastereoisomers. After optimization of the chromatographic conditions, a mobile phase composed of chloroform, acetonitrile and methanol was suitable to elute the diastereoisomers with their related chemical impurities in less than 20 min by gradient mode. CD detection was found to be compatible with elution gradient and both the UV, CD and g anisotropy factor signals were recorded without disturbance. The determination of chemical purity was achieved with UV detection (254 nm) whereas the diastereoisomeric purity was determined using CD detection (258 nm) by plotting the anisotropy factors (R,S-S,R and R,R-S,S) versus the enantiomeric excess of each couple of enantiomers. A mathematic model was developed in order to express the diastereoisomeric excess versus the enantiomeric excess of each couple of enantiomers. Hence, the HPLC-UV/CD method was convenient to give access simultaneously to the optical and chemical purities of a chiral drug.     

Synthese totale d'un analogue azote d'endoperoxyde de prostaglandine

The total synthesis of a prostaglandin endoperoxyde analogue in which the upper side chain is attached to a nitrogen atom, is presented.     

Obtention d'un oxiranne far actiom de l'ozone sur un vinylsulfure

Ozone reacts with one vinyl sulphide and gives an oxirane, this fact confirms that oxirane is probably an intermediate in course of reactions of ozone with vinyl derivatives which give products containing unmodified hydrocarbon chains.     

Tight bounds for periodicity theorems on the unbounded Knapsack problem

Three new bounds for periodicity theorems on the unbounded Knapsack problem are developed. Periodicity theorems specify when it is optimal to pack one unit of the best item (the one with the highest profit-to-weight ratio). The successive applications of periodicity theorems can drastically reduce the size of the Knapsack problem under analysis, theoretical or empirical. We prove that each new bound is tight in the sense that no smaller bound exists under the given condition.     

Surface diffusion of lead on tungsten

Field electron microscopy is used to study the surface diffusion of lead on tungsten. A simple method to measure rough values of the diffusion coefficient and its dependence on sub-monolayer coverage is described and tested. In the region around (001) the displacement energy found is about 1.30 eV/atom up to 10¹⁵ atoms/cm² where it decreases to 0.78 eV/atom. In the residual region except (110) this energy at 1.5×10¹⁴ atoms/cm² is 1.22 eV/atom, it decreases at 4 × 10¹⁴ atoms/cm² to 0.61 eV/atom and increases at 10¹⁵ atoms/cm² to 0.78 eV/atom. Corresponding values of the diffusion coefficient D and of the preexponential D₀ are given. The dependence of D on submonolayer coverage is discussed.