Furanoside-Pyranoside Isomerization of Tubercidin and its 2'-Deoxy Derivatives: Influence of Nucleobase and Sugar Structure on the Proton-catalysed Reaction
2'-Deoxy-2-methoxytubercidin (6a) which was prepared from the nucleobase (1a) with the halogenose (2) via phase-transfer glycosylation isomerizes rapidly under acidic conditions.Two pyranosides and the anomeric furanoside (5a) are formed.The isomerization process was followed kinetically, demonstrating that furanoside formation is kinetically controlled whereas the β-pyranoside (7a) is the thermodynamically most stable product.From 2'-deoxytubercidin (6b) similar results were obtained but isomerization was slow, compared with (6a).The ribonucleoside tubercidin (6c) did isomerize only under vigorous acid treatment leading to the α-furanoside (5c) and the nucleobase (1c) by cleavage of the N-glycosylic bond.
Seela, Frank,Menkhoff, Sabine,Behrendt, Silvia
p. 525 - 530
(2007/10/02)
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