Regioselective synthesis of 1,3,5-¹³ C₃ and 2,4-¹³ C₂-labeled 2-deoxyribonolactones

The synthesis of 1,3,5-¹³ C_3- and 2,4-¹³ C₂-labeled 5-0-bromobenzyl2-deoxyribonolactones 2, precursors to ¹³C-enriched nucleoside phosphoramidites for solid-phase synthesis of DNA oligonucletides, is described. An equimolar combination of these two multiply labeled lactones affords a "population-labeled" mixture of isotopomers which exhibits an approximately 50-fold increase in the sensitivity of ¹³C-NMR compared to natural abundance measurements. The ¹³C^-13 C 2-bond and 4-bond coupling constants are reported for the lactones; all are < 2Hz, confirming that this labeling scheme should be especially useful for NMR-relaxation measurements.