NEW METHODOLOGIES FOR PRODUCTS OF BIOLOGICAL INTEREST BY SUITABLY SUBSTITUTED FURANS

Furans represent an interesting class of heterocycles. New synthetic methods for their preparation and elaboration have been described that provide a significant tool for glycosides and lignan-like compounds with important implications in pharmacological applications. In particular, a novel methodology based on a one-pot process starting from glycosyl furans has been developed for the synthesis of spiro compounds and, in particular, of new chiral [6,6]-, [5,6]- and [5,5]-spiroketals of sugars. The spiroketal moiety represents a privileged substructure since it can be found in many simple as well as complex natural products characterized by important and assorted biological properties, from antibiotic to anticancer. It is to be noted that despite numerous methodologies for spiro compounds few synthetic strategies for derivatives oxidized at the 2-position are reported. Novel pyridazine C-nucleosides have also been synthetized by a one-pot procedure. The pyridazine nucleus and its 3-oxo derivatives have been recognized as versatile pharmacophores and great attention in last years has been devoted to the synthesis of these compounds. Interesting results have been obtained in the field of polysustituted furans. Indeed, starting from aryl trisubstituted derivatives a novel synthetic method for diarylfurans with a lignan backbone has been developed using a variant of the Friedel-Crafts reaction. Preliminary biological tests have evidenced antibiotic activities of some derivatives. The presence of furan system in these compounds highlights manifold elaborations of the heterocyclic ring to a variety of product types. In this context, in the field of dye-sensitized photooxygenation, starting from some trisubstituted furans bearing b,bࢠelectron withdrawing groups, previously not investigated, useful C-4 synthons have been obtained in excellent yields in one-pot manner. All the reaction conditions, based on the combination of photooxygenation with reduction or basic treatment, are particularly mild respect to classical oxidation procedures, often not compatible with functional groups which are frequently present in synthetic intermediates. Hence these procedure represents useful alternatives to classical methods. Many of compounds prepared have various lignan-like structures that confirm the role of furans in the synthesis of interesting products.