RESUMO
[reaction: see text]. While exploring the application of radical cyclizations to the construction of bridged polycyclic systems, we have discovered a novel tandem process consisting of an endo-cyclization of a vinyl radical onto a terminal alkene followed by a one-carbon ring expansion promoted by the resulting secondary radical.
Assuntos
Hidrocarbonetos Aromáticos com Pontes/síntese química , Química Orgânica/métodos , Ciclização , Radicais Livres/química , Espectroscopia de Ressonância Magnética , Modelos Químicos , Modelos Moleculares , Polivinil/química , EstereoisomerismoRESUMO
One-pot coupling of an intramolecular thermal [5C + 2C] pyrone-alkene cycloaddition to a [4C + 2C] Diels-Alder reaction provides immediate access to 6,7,5-tricarbocyclic systems bearing a 1,4-oxa-bridge in the seven-membered carbocycle. The transformation entails the net formation of four carbon-carbon bonds and creates three new cycles and a minimum of five new stereocenters. Preliminary attempts to open the oxa-bridge by reaction of the adducts with samarium diiodide and trimethylsilyl triflate led to relatively unexpected deoxygenated and aromatized products.
RESUMO
With the aim of generating a virus-cell system to introduce alterations in proteins of interest--which may be of use in studies of their biological functions--we established a persistent infection on a B-lymphoma cell line (A20.2J) with vaccinia virus (VV) recombinants. As a model, we used a vaccinia virus recombinant expressing the human immunodeficiency virus HIV-1 env gene. In this unique virus-cell system, we found that it is possible to introduce several structural and functional alterations in the env protein with passage numbers. From passage 10-20, two new env products emerged: an uncleaved gp160 and a glycoprotein fragment of 110 kDa. The uncleaved gp160 exhibit interesting properties as an immunogen. This protein forms stable oligomers, is not released from the cells, cannot fuse CD4+ presenting HeLa cells and activates a stronger cellular immune response than the parental cleaved env. In contrast, the 110 kDa product is a poor immunogen, since it lacks the gp41 domain, cannot form oligomers, accumulates intracellularly and cannot fuse CD4+ cells. In the persistently infected cells we have also found alterations in another heterologous protein-beta-galactosidase-a gene inserted in the same locus of VV as the env gene. This alteration resulted in a truncation of the (beta-galactosidase protein from 125 kDa to about 70 kDa. A similar size truncation of env and of beta-galactosidase was observed in many of the isolated VV recombinants.