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1 2002

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Synteza polihydroksyindolizydyn z L,B-nienasyconych [delta]-laktonów

Rabiczko J., Socha D., Jurczak M., Chmielewski M.

Wiadomości Chemiczne

2002

[Z] 56, 7-8

561-583

The isolation, synthesis and biological properties of polyhydroxylated alkaloids (iminosugars) constitute a well-visible trend in organic chemistry nowadays. Due to their structural resemblance to sugars, iminosugars are recognized by glycosidases, the enzymes that catalyse the hydrolysis of glycosidic bonds in carbohydrates and glycoconjugates. Since glycosidases play a very important role in many biological systems, the iminosugars which inhibit them display interesting biological activities. Indolizidines represented by castanospermine, swainsonine and lentiginosine are particularly interesting as they exhibit a variety of important biomedical properties. The present paper is not a survey of the literature, but only deals with syntheses towards lentiginosine, with the aim of illustrating representative approaches in the syntheses of polyhydroxyindolizidines. The high stereoselectivity of both the conjugate addition of hydrazine and the (1,3)-dipolar cycloaddition of nitrones to the a,b-unsaturated sugar d-lactones, prompted us to use the adducts of both reactions as substrates for the syntheses of polihydroxyindolizidines. The conjugate addition offers a stereocontrolled entry to derivaties of both D- and L-2-pyrrolidineacetic acids which can be easily transformed into desired indolizidines. As an example, the syntheses of lentiginosine are demonstrated. The (1,3)-dipolar cycloaddition of Brandi's nitrone to the title lactones proceeded with high stereoselectivity in the case of D- and L-glycero lactones, whereas there was a high kinetic resolution in the case of racemic D,L-glycero lactone. It was shown that adducts can be easily transformed into lentiginosine, 7-hydroxylentiginosine and 7,8-dihydroxylentiginosine.