N-[[(9- β-D-RibofuranSyl-9H-purin-6-yl)amino]carbonyl]-L-threonine-1,2,3,4-13C4-15N; N-(6-Nebularinylcarbamoyl)threonine-13C4,15N; N-(6-Purinylcarbamoyl)-L-threonine RibSide-13C4,15N; N-[(9- β-D-RibofuranSyl-9H-purin-6-yl)carbamoyl]-L-threonine-13C4,15N; N-[(9- β-D-RibofuranSyl-9H-purin-6-yl)carbamoyl]threonine-13C4,15N; N-[(9- β-D-RibofuranSylpurin-6-yl)carbamoyl]threonine-13C4,15N; N-[N-(9- β-D-RibofuranSylpurin-6-yl)carbamoyl]threonine-13C4,15N; N-[[(9- β-D-RibofuranS