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Syntheses and Reactions of 1', 2'-Unsaturated 2', 3'-Seconucleoside 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, 2 and 18, respectively, 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 HC(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. ZnBr2 in dry CH2Cl2 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-azido-3-deoxy-5-O-2, 3-secouridine (22) that reacted with KO(t-Bu) under opening of the oxazole ring and double-bond formation at C(1).

nucleoside analogs; synthesis; reactions

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