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Zusammenfassung:
An extension of methods already used for the preparation of adenosine phosphorothioates was used to prepare guanosine phosphorothioates in quantities sufficient for extensive 31P-NMR studies. Guanosine phosphorothioates were used to exemplify the influence of Cd2+ and Mg2+ complexation on 31P-NMR parameters as pK-values, chemical shifts, and P[sbnd]O[sbnd]P coupling constants. pKa values decrease in general in the order pK(α-S) a > pK(β-S) a > pK(γ-S) a; the magnitude of the pKa decrease on metal complexation is also in this order. The chemical shifts for the P[sbnd]S resonances are changed downfield on Mg2+ complexation and upfield on Cd2+ complexation. P[sbnd]O[sbnd]P coupling constants are increased by about 7 Hz on sulfur substitution at one of the contributing phosphorus atoms; this difference is at least partially ineffective in the Cd2+ complexes.
