Furanes heterocyclic cores

The treatment of iodoalkynol derivatives of xylose 123 with PhI(OH)OTs and iodine under similar conditions furnishes p,[3-diiodoenol ethers 124 with a furo[3,4-fe]furan heterocyclic core (Scheme 3.49) [135],... 

It is assumed that the heterocyclic core structure is responsible for the appropriate orientation of the aromatic rings in space and finally for binding to the enzyme. A wide variety of heterocycles can serve as templates, i.e. pyrrole, thiazole, oxazole furane, furanone, imidazole, isoxazole, pyrimidine and thiophene, but at the moment pyrazole and cylopentenone seem to be the most appropriate for achieving COX-2 specificity. For optimal activity, one aromatic ring must be substituted with a methylsulfonyl or a sulfonamide substituent in the para position. Substitution at position 4 of one of the aromatic systems with a sulfonamide or a methylsulfonyl group is essential for COX inhibition. Replacement of the methylsulfonyl group by a sulfonamide group reduces COX-2 selectivity but improves oral bioavailability. 

Furan derivatives are one of the most important heterocyclic compounds as fimctionalized furans exhibit a wide range of biological activities [60]. In many naturally occurring compounds furan is foxmd to form the core unit [61]. The synthesis of furan derivatives by supported heterogeneous metal catalyst is foxmd to be more acceptable in industries because of its several advantages over homogeneous counterpart [62]. 

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