The smoothed number of Pareto-optimal solutions in bicriteria integer optimization

Mathematical Programming - A well-established heuristic approach for solving bicriteria optimization problems is to enumerate the set of Pareto-optimal solutions. The heuristics following this...     

Derivatives of 3′-Azidothymidine with 6-Cyanopyridone as Base or as Phosphoramidate Ester and their Antiretroviral Activity

Strongly pairing ethynylpyridone C-nucleosides are attractive surrogates for thymidine in oligonucleotides. Exploratory work on the antiviral activity of 3′-azidothymidine (AZT) derivatives with ethynylpyridone as base had identified strong lipophilicity as a limiting factor. Two strategies are being pursued to overcome this issue. In order to make the base more polar, the ethynyl group has been replaced with a cyano group, leading to a cyanopyridone C-nucleoside, whose eleven-step synthesis is reported here, together with the synthesis of a 3′-azido-2′,3′-dideoxynucleoside derivative. The base pairing with adenine in a DNA duplex was studied by UV melting analysis of a self-complementary hexamer containing the 6-cyano-2′-deoxynucleoside instead of thymidine. A melting point increase of 2 °C compared to the unmodified control was found. The other strategy employs a phosphoramidate prodrug design with less lipophilic amino acid esters. Here, anti-HIV test of the alaninyl and prolinyl methyl esters of AZT gave promising results in cell culture experiments, increasing the selectivity index up to 5.8-fold for the III_B strain and up to 5-fold for the ROD strain of the virus, as compared to the parent nucleoside. These findings help to design the next generation of pyridone C-nucleosides with potential applications as antivirals.     

Stiba-, Arsa- and Phosphastannenes: Syntheses and Reactivities

A facile synthesis for unprecedented stibastannene ( 10 ) featuring a Sn=Sb-double bond together with the homologous arsa- ( 9 ) and phosphastannenes ( 8 ) is presented. Chloride abstraction from respective stannyl pnictinidenes [E=P ( 5 ), As ( 6 ), Sb ( 7 )], which were made accessible by reduction of ECl₃ addition products at an intramolecular phosphine-stabilized stannylene, gave the pnictastannenes in moderate yields. The pnictastannenes coordinate Pd(PPh₃)₂ fragments ( 12 – 14 ) and the phosphastannene forms also a nickel coordination compound with the Ni(PPh₃)₂-fragment ( 11 ). 2,3-Dimethylbutadiene shows a [2+4]-cycloaddition ( 15 – 17 ) in reaction with the pnictastannenes ( 8 – 10 ). Products of a [2+2]-addition ( 18 , 19 ) were isolated as the phosphaalkyne reaction products for 8 and 9 . Addition of an O−H bond at the Sn=P-bond was found in reaction of water with phosphastannene 8 . Reaction with ammonia afforded the NH₃-adducts ( 21 – 23 ) at the tin atom for pnictastannenes 8 – 10 . Only in the case of the arsastannene an azide reaction product featuring a three membered Sn−As−N-ring was obtained.