18O-Labeled Adenosine and 9-(β-D-Arabinofuranosyl)Adenine (ARA-A): Synthesis, Mass Spectrometry, and Studies of18O-Induced13C NMR Chemical Shifts

[2′-18O]- and [3′-18O]-Adenosine and [2′-18O]- and [3′-18O]-9-(β-D-arabinofuranosyl) adenine were synthesized from−appropriate nucleoside precursors. The sites of 18O-incorporation were determined by mass spectrometry. 18O-Induced 13C NMR shifts were measured for 2′-and 3′-labeled adenosines as 1.2 and 1.6 Hz, respectively.