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Riburonic and Lyxuronic Purine Nucleoside Derivatives - Synthesis, Separation, and Structural Elucidation of the Various Linkage Isomers
Schmidt, Richard R.,Loesch, Gabriele R.,Fischer, Peter
, p. 2891 - 2915 (2007/10/02)
By direct, molten state condensation of riburonic (1) and lyxuronic acid derivatives (14) with silylated purine (2a), chloro- and amino-purines (2b-g), respectively, N-7 and N-9 purinyl nucleosides with both α- and β-configuration were obtained in mixtures of varying composition, depending, inter alia, on the structure of the carboxyl function; the linkage isomers were separated quantitatively by medium pressure chromatography on silica gel columns of high separation potential.To test the known criteria for structural assignment on the wide range of glycosidic isomers thus available, UV, 1H-NMR and 13C-NMR spectra were recorded under standardized conditions for all derivatives.Assignment of purine regiochemistry from UV data proved not reliable; it can be established, though, unequivocally from the 13C-NMR data of the aglycone.The configuration at the anomeric center of the sugar mioety, on the other hand, is readily determined from the furanoside 13C-shifts of the 2',3'-O-isopropylidenated nucleosides.
