Figure 1.

The 12-plex DiLeu general structure. (A) The DiLeu isobaric labeling reagent consists of a reporter group, balance group, and amine-reactive triazine ester group. Stars indicate positions of isotopic substitution. (B) Stable isotopes (¹³C, ²H, and ¹⁵N) incorporated into the reporter group are mass-balanced by stable isotopes (¹³C, ¹⁸O) in the carbonyl balance group. Unique combinations of isotopes incorporated into the reporter group yield two 115 variants, three 116 variants, three 117 variants, and four 118 variants whose isotopologues differ in mass by approximately 6 mDa.