Transformação de carbociclo em carboidrato : rotas sinteticas para analogos de açucares superiores

AUTOR(ES)

Giselle Cerchiaro

DATA DE PUBLICAÇÃO

2001

RESUMO

In this work are described methodologies for a synthetic pathway that aim the transformation of a carbocycle in a high carbohydrate (more than 6 atoms of C in its chain). The carbohydrate in study is interesting for the preparation of sialic acid analogous (carbohydrates with 9C), being the N-acetilneuraminic acid the most known among them. The purpose of this transformation is the obtention of a hight carbohydrate, a heptose, that could originate compounds with potential ability for sialidase enzyme inhibition. Sialidase is one of the glycoproteic enzymes that recover the influenza virus, and it is responsible for the infection cycle inside human organisms. The (3R,5R)-(-)-quinic acid, an optically active polyhydroxilated carbocycle, was chosen as starting material mainly due to the suitable inter relashionship between the stereochemistry of its asymmetric centers and those in the target structure, besides the possibility of preparation of versatile intermediates. In the first step, during the protection of the C3 and C4 hydroxy groups of (-)-quinic acid as an acetal, a lactonization reaction also occurred between the carboxylic acid at C1 and the C5 hydroxy group. Following the sequence, the lactone was treated with an alcoxide or amine to furnish the corresponding hydroxy ester or hydroxy amide. Oxidation reaction of the C5 hydroxy group led to a corresponding carbonyl compound, and subsequent regioselective elimination of the hydroxy group at C1 furnished an enone, with the necessary insaturation for the oxidative cleavage last step. In the prior step envisaging the desired carbohydrate, a chemo and stereoselective reduction of the carbonyl group of C5 was made. Then, an ozonolysis reaction performed under mild conditions led promptly to the carbohydrate (seven carbons) in high yield. In the second step of this synthesis, the opening of the lactone ring, we were able to verify the efficiency of microwave induced reactions, working without solvents. These reactions have shown to be clean, quick and less aggressive to the environment.

ASSUNTO(S)

sintese organica acidos

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