engleski

Investigations on Unsaturated Seconucleosides Analogues

The 1’, 2‘-unsaturated 2’, 3‘-secoadenosine and 2’, 3’-secouridine analogues were synthesized by the regioselective elimination of the corresponding 2’, 3’-ditosylates, under basic conditions. The observed regioselectivity may be explained by the higher acidity and, hence, preferential elimination of the anomeric H-C(1’) in comparison to H-C(4). The retained (tol-4-yl)sulfonyloxy group at C(3’) of 3 allowed the preparation of the 3’-azido, 3’-chloro, and 3‘-hydroxy derivatives 5-7 by nucleophilic substitution. ZnBr, in dry CH2C12 was found to be successful in the removal (85%) of the trityl group without any cleavage of the acid-sensitive, ketene-derived N, O-ketal function. In the uridine series, base-promoted regioselective elimination (+ 19), nucleophilic displacement of the tosyl group by azide (+20), and debenzylation of the protected N(3)-imide function gave 1’, 2’-unsaturated 5’-O-trityl-3’-azido-secouridine derivative 21. The same compound was also obtained by the elimination performed on 2, 2’-anhydro-3’-azido-3‘-deoxy-5‘-~-~rityl-2‘, 3’-secouridi(n2e2 ) that reacted with KO(f-Bu) under opening of the oxazole ring and double-bond formation at C(1’).

nucleoside derivatives; protective groups; synthesis

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