title: Formation of Fmoc-beta-alanine during Fmoc-protections with Fmoc-OSu.
abstract: During the Fmoc-protection of H-alpha-Me-Val-OH, an unknown side product was found and isolated. The characterization using various analytical methods led unambiguously to the result that Fmoc-beta-Ala-OH was formed during the reaction. The reagent Fmoc-OSu was proven to be the source of Fmoc-beta-Ala-OH, following a mechanism that involved many deprotonation and elimination steps and a Lossen-type rearrangement as key sequence. The impurity Fmoc-beta-Ala-OH was found in a variety of reactions in which Fmoc-OSu was applied, either in the reaction mixture or as a contamination of the crude product. Purification of the Fmoc-amino acid derivatives from this impurity incurred high costs and significant reductions in yield.
authors.affiliation: Bachem AG, Bubendorf, Switzerland.
authors.forename: Markus
authors.initials: M
authors.lastname: Obkircher
authors.forename: Christian
authors.initials: C
authors.lastname: Stähelin
authors.forename: Fritz
authors.initials: F
authors.lastname: Dick
mesh_terms: D000409:Alanine / Q000138:chemical synthesis* / Q000737:chemistry; D005452:Fluoresceins / Q000138:chemical synthesis* / Q000737:chemistry; D013058:Mass Spectrometry
chemical_list: D005452:Fluoresceins; D000409:Alanine