title: pH-regulated formation of side products in the reductive amination approach for differential labeling of peptides in relative quantitative experiments.
abstract: Among the most common stable-isotope labeling strategies, the reaction of formaldehyde with peptides in the presence of NaCNBH₃ features many attractive aspects that are conducive to its employment in quantitation experiments in proteomics. Reductive amination, with formaldehyde and d(2)-formaldehyde, is reported to be a fast, easy, and specific reaction, undoubtedly inexpensive if compared with commercially available kits for differential isotope coding. Acetaldehyde and d(4)-acetaldehyde could be employed as well without a substantial increase in terms of cost, and should provide a wider spacing between the differentially tagged peptides in the mass spectrum. Nevertheless, only a single paper reports about a diethylation approach for quantitation. We undertook a systematic analytical investigation on the reductive amination of some standard peptides pointing out the occasional occurrence of side reactions in dependence of pH or reagents order of addition, particularly observing the formation of cyclic adducts ascribable to rearrangements involving the generated Schiff-base and all the nucleophilic sites of its chemical environment. We also tried to evaluate how much this side-products amount may impair isotope coded relative quantitation.
authors.forename: Stefano
authors.initials: S
authors.lastname: Levi Mortera
authors.forename: Ilaria
authors.initials: I
authors.lastname: Dioni
authors.forename: Viviana
authors.initials: V
authors.lastname: Greco
authors.forename: Cristina
authors.initials: C
authors.lastname: Neri
authors.forename: Paolo
authors.initials: P
authors.lastname: Rovero
authors.forename: Andrea
authors.initials: A
authors.lastname: Urbani
mesh_terms: D000586:Amination; D002851:Chromatography, High Pressure Liquid; D005557:Formaldehyde / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007553:Isotope Labeling; D008745:Methylation; D009842:Oligopeptides / Q000032:analysis* / Q000737:chemistry*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D009842:Oligopeptides; D005557:Formaldehyde