Concise total synthesis of (+/-)-aloperine and 6-epi-aloperine

[reaction: see text] Total synthesis of aloperine and 6-epi-aloperine is reported. The crucial steps of the synthetic strategy are an aza-annulation reaction and an intermolecular Diels-Alder reaction. The synthetic plan proceeds from commercially available piperidine-2-ethanol.     

Local flat duality of abelian varieties

 Let K be a field complete for a discrete valuation and with algebraically closed residue field of positive characteristic p. We prove the existence of a non-degenerate pairing between the first (flat) cohomology group of an abelian variety A _K over K and the fundamental group of the Néron model of the dual abelian variety. This pairing extends to the p-primary components a pairing introduced by Shafarevich in [16]. We relate this pairing with Grothendieck's pairing. Received: 7 January 2002 / Revised version: 6 December 2002 Published online: 24 April 2003 Mathematics Subject Classification (2000): 14k05, 14F20, 14G22     

Photocatalytic oxidation of methyl-orange in aqueous suspension: comparison of the performance of different polycrystalline titanium dioxide

The photocatalytic oxidation of methyl-orange (C14H14N3SO3Na) dye was carried out in aqueous suspensions of polycrystalline TiO2 irradiated with artificial light until its complete mineralization was achieved. The performances of two widely used semiconductor powders were studied for comparison purposes. The dependence of dye photo-oxidation rate on various experimental parameters, including substrate concentration, semiconductor amount, and pH was investigated by using both catalysts. The observed dye degradation rates followed pseudo-first order kinetics with respect to the substrate concentration under the experimental conditions used. The two investigated TiO2 powders (Degussa P25 and Merck) showed different photoactivities. TOC analyses confirmed the complete mineralization achievable using both photocatalysts. Three main transient products still maintaining the chromophoric azo group were identified prior to their transformation into other degradation products which are non-absorbing in the visible region.     

Stabilizzabilita' di equazioni paraboliche

L'argomento di questo seminario è il problema della stabilizzabilità di equazioni paraboliche lineari del secondo ordine, con coefficienti costanti o periodici rispetto al tempo. Viene considerato sia il caso di controlli a parametri distribuiti che il caso di controlli sulla frontiera. The subject of this talk is the problem of stabilization of linear second order parabolic equations, with constant or periodic coefficients with respect to time. Both distributed parameter controls and boundary controls are considered.

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(Conferenza tenuta il 20 gennaio 1989)     

A novel hydrogen peroxide-dependent oxidation pathway of dopamine via 6-hydroxydopamine

In the presence of excess H₂O₂, oxidation of dopamine was diverted from the usual pigment-forming pathway to afford 6-hydroxydopamine and then a colorless reaction mixture comprising a polar non-extractable product. The latter was obtained in 20% yield by oxidation of 6-hydroxydopamine and was tentatively formulated as the novel 5-(2-aminoethyl)-2-hydroxy-5-(3-hydroxy-2-oxotetrahydro-1aH-oxireno[2,3]cyclopenta[1,2-b]pyrrol-3a(4H)-yl)cyclohex-2-ene-1,4-dione by extensive spectral analysis and conversion to a tetraacetyl derivative. Mechanistic experiments suggested that formation of the product proceeds via 6-hydroxydopamine by H₂O₂-dependent epoxidation and cyclization steps followed by dimerization and ring contraction with decarboxylation.     

A reinvestigation of the structure of melanochrome

Reduction and subsequent acetylation of melanochrome, the last UV detectable intermediate in the biosynthesis of eunelanins, leads to the isolation of a crystalline derivative, leucomelanochrome A acetate, identified as 5,6,5′,6′-tetraacetoxy-2,2′-biindolyl ($\text{5}$).