Lothar W. Bieber

Larvicidal activity of lectins from Myracrodruon urundeuva on Aedes aegypti

Aedes aegypti transmits etiologic agents of yellow fever and dengue. Vaccine for dengue virus is not available and vector control is essential to minimize dengue incidence. This report deals with the larvicidal activity of lectins isolated from Myracrodruon urundeuva bark (MuBL) and heartwood (MuHL). The lectins were isolated by ammonium sulphate treatment of crude extracts followed by chromatography on chitin. MuBL and MuHL were evaluated by electrophoresis under native (PAGE) and denaturing conditions (SDS-PAGE). Carbohydrate specificity of lectins was evaluated by hemagglutinating activity (HA) inhibition assay using N-acetyl-d-glucosamine and by affinity chromatography on N-acetyl-D-glucosamine immobilized in agarose gel. Larvicidal activity against A. aegypti was investigated with the extracts, salt fractions and isolated lectins. MuBL and MuHL were characterized by PAGE as basic proteins of molecular masses of 14.0 and 14.4 kDa, respectively. The interaction of lectins with N-acetylglucosamine was detected by inhibition of HA by monosaccharide and lectin adsorptions on N-acetyl-D-glucosamine matrix. All M. urundeuva preparations promoted larvae mortality. LC16, LC50 and LC84 values of 0.077, 0.125, 0.173 for MuBL and 0.03, 0.04 and 0.05 mg/mL for MuHL were obtained. To our knowledge this is the first report of larvicidal activity of lectins against A. aegypti.

Antibacterial and antifungal activities of Myracrodruon urundeuva heartwood

The aim of this work was to isolate a lectin from Myracrodruon urundeuva heartwood and to evaluate its antimicrobial activity against bacteria and fungi that attack plants, including woods. The lectin was isolated from heartwood through affinity chromatography on a chitin column monitored by hemagglutination assay. The lectin inhibited Gram-negative and Gram-positive bacteria and was more effective than antifungal Cercobin in growth inhibition of phytopathogenic fungi. The detected antimicrobial activity reveals the possible role of the lectin in the resistance of M. urundeuva heartwood against deteriorative biological agents. The M. urundeuva lectin is the first bioactive peptide found in heartwood, probably stored as a chemical protection against biodegradation.

General synthesis of alkyl phenyl selenides from organic halides mediated by zinc in aqueous medium

Abstract Organic halides of different structural types react with diphenyl diselenide and zinc dust in aqueous medium to give alkyl phenyl selenides. Benzylic and allylic bromides, α-bromoesters, acids and ketones and some primary alkyl iodides produce high yields even under acidic conditions. Less reactive halides need basic medium. The reaction proceeds equally well in the presence of various unprotected functional groups. Control experiments support a S H 2 mechanism via alkyl radicals.

Short and Efficient Synthesis of Optically Active N-Tosyl Aziridines from 2-Amino Alcohols

Two alternative and complementary one-pot procedures for the direct transformation of 2-amino alcohols to N-tosyl aziridines are presented. The unsubstituted parent compound and its less hindered homologues can be obtained in high yields by tosylation and in situ cyclisation effected by potassium hydroxide in water/dichloromethane. Higher substituted amino alcohols give better yields using potassium carbonate in acetonitrile. Both procedures use simple inorganic bases and produce only inorganic salts as byproducts.

Barbier-type allylation of iminium ions generated in situ in aqueous medium

Iminium ions, generated in aqueous solution from secondary amines and formaldehyde, undergo a Barbier-type allylation mediated by tin, aluminum and zinc. The reaction is catalyzed by copper and produces tertiary homoallylamines in up to 85% yield.

Regioselective alkylation of substituted quinones by trialkylboranes

Abstract 2-Methoxy-1,4-benzoquinone can be alkylated selectively with trialkylboranes in position 5, givinghigh yields of 5-alkyl-2-methoxy-1,4-benzoquinones after oxidative work up. In the case of 2-hydroxy-1,4-naphthoquinone, the same procedure leads to 3-alkylated products. A radical chain mechanism is proposed to explain the observed selectivity.

ZINC BARBIER REACTION OF PROPARGYL HALIDES IN WATER

Abstract The reaction of propargyl halides and carbonyl compounds with zinc powder proceeds in concentrated aqueous salt solutions affording with high selectivity homopropargylic alcohols. Preparatively useful yields are obtained with aromatic and aliphatic aldehydes. Ketones and 2-hydroxybenzaldehydes react partially. A surface process of two SET is discussed.

Silver catalyzed zinc Barbier reaction of benzylic halides in water

Abstract Benzylic chlorides react in aqueous dibasic potassium phosphate under silver catalysis with aromatic aldehydes in the presence of zinc dust to give 1,2-diaryl alcohols in moderate to good yields. Dimerization to bibenzyls and reduction of the halide are important side reactions. A wide range of substituted aromatic and heteroaromatic aldehydes and of substituted benzylic chlorides can be used. Aliphatic aldehydes and ketones are unreactive. A mechanism of two SET on the metal surface is discussed.

Reductive coupling reaction of benzyl, allyl and alkyl halides in aqueous medium promoted by zinc

Organic halides undergo reductive dimerization (Wurtz-type coupling) promoted by zinc at room temperature in aqueous medium. The reaction yields are strongly enhanced by copper catalysis. This coupling procedure provides an efficient and simple method for the homocoupling of benzylic and allylic bromides and primary alkyl iodides.

Meroterpenoid naphthoquinones from Cordia corymbosa.

Cordiaquinones A and B, the first examples of a new type of merosesquiterpenoid quinones, have been isolated from the roots of Cordia corymbosa. The structures of these 6-alkylsubstituted 1,4-naphthoquinones were elucidated by high field 1H NMR spectroscopy, mass spectrometry and chemical derivatization.