Pawel Sowinski

Revised structure of the repeating unit of the O-specific polysaccharide from Azospirillum lipoferum strain SpBr17

A neutral O-polysaccharide liberated by mild acid hydrolysis of a lipopolysaccharide isolated from Azospirillum lipoferum SpBr17 was investigated using 1D and 2D (1)H and (13)C NMR spectroscopy, including HSQC, HMBC, and NOESY as well as SDS-PAGE electrophoresis along with sugar and methylation analyses. The structure of the O-specific polysaccharide repeating unit was established as follows: [Formula: see text]. The presented structure is a revised version of the formula that was published earlier in the Abstracts of the 9th International Congress on Nitrogen Fixation in Cancun (Mexico, 1992).

The stereostructure of candicidin D

The candicidin D stereostructure was established based on NMR studies including DQF-COSY, ROESY, HSQC and HMBC experiments. The relative configurations of the candicidin D stereogenic centers were assigned as the following: 9R*, 11S*, 13S*, 15R*, 17S*, 18R*, 19S*, 21R*, 36S*, 37R*, 38S*, 40S* and 41S*. The geometry of the heptaene chromophore was defined as 22E, 24E, 26Z, 28Z, 30E, 32E and 34E.

The products of electro- and photochemical oxidation of 2-hydroxyacridinone, the reference compound of antitumor imidazoacridinone derivatives

Abstract Electrochemical oxidation of 2-hydroxyacridinone, the reference compound of antitumor imidazoacridinone derivatives, was studied by cyclic voltammetry (CV), spectroelectrochemical methods and controlled potential electrolysis. The photochemical oxidation was also investigated. The studies aimed to elucidate the pathway of the oxidative metabolic activation of antitumor hydroxyacridinones under biological conditions. The cyclic voltammogram at a glassy-carbon electrode in water, pH 7.4 showed the electrochemical oxidation to be an irreversible process. The main peak potential (Ep) is pH-dependent in the range of 3–10 pH units. The spectroelectrochemical experiments performed at pH 7.4 revealed that four products of electrochemical and chemical reactions were formed during the forward potential scan and they were reduced during the reverse scan. One product of this reduction represents the reversible process. Two products of the oxidative transformation of 2-hydroxyacridinone were identified by means of MS and NMR spectroscopy. The first one, p1, turned out to be a dimer: 1,1-bi(2-hydroxyacridinone), whereas the second one, p2, was an extremely unstable orthoquinone derivative. Cyclic voltammograms of p1 and p2 allowed us to identify the current peaks observed in the voltammograms of the substrate. Two pathways of 2-hydroxyacridinone electrooxidation were proposed. The contribution of each pathway to the formation of products p1 and p2 depended on the electrochemical potential (Ecp) and pH conditions. The proposed pathways were discussed with respect to the metabolic activation of hydroxyacridinones in the organism. It was suggested that the electrooxidation might be a suitable method for the synthesis of adducts between antitumor hydroxyacridinones and DNA.