Synthesis and NMR Structural Analysis of 2′‐OMe‐Uridin‐3′‐yl (3′,5′)‐5′‐O‐(N‐Isobutyryl‐2′‐OMe‐Cytidine) Methylthiophosphonates

Detailed analysis of the molecular structures of both the Fast ‐eluted and the Slow ‐eluted (the notation Slow and Fast corresponds to the relative mobility properties of compounds in silica gel column chromatography under normal phase conditions, see Exp. Sect. for details) diastereomers of 5 ′ ‐OH‐2 ′ ‐OMe‐uridin‐3 ′ ‐yl (3 ′ ,5 ′ )‐5 ′ ‐ O ‐( N ‐isobutyryl‐2 ′ ‐OMe‐cytidine) methylthiophosphonate ( 1 ) was performed with the aid of 1 H, 13 C, 1D and 2D homo‐ and heteronuclear PFG (Pulse Field Gradient) NMR studies. The absolute configurations [( R P ) and ( S P )] of the diastereomers of 1 were unambiguously assigned by 1 H ROESY experiments. The pseudorotation parameters of the ribose ring were calculated with the aid of the PSEUDOROT program, and compared with data obtained from X‐ray structure analysis. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)