S-Fluorenylmethyl protection of the cysteine side chain upon N^α-Fmoc deprotection

• Johannes W. Wehner and
• Thisbe K. Lindhorst

Beilstein J. Org. Chem. 2012, 8, 2149–2155, doi:10.3762/bjoc.8.242

• transprotection reaction was studied. Keywords: Fmoc protecting group; glycoamino acids; N-Fmoc→S-Fm transprotection; protecting groups; Introduction In the course of our work on the synthesis of glycoamino acids, we have recently used L-cysteine as a scaffold for the synthesis of various glycoclusters [1][2][3

• and H-βb protons on the other hand. N-Fmoc→S-Fm transprotection was reported earlier by Katritzky et al. for cysteine peptides [15]. In this case, DBU was employed as the base and the reaction was conducted in dry THF at 0 °C for 15 min to give the rearrangement products in 69–87% yield. The

• mechanistic rational proposed by the Katrizky group is based on a report by Rich et al., where the influence of the employed base on N-Fmoc→S-Fm transprotection was studied [16]. According to the proposal provided by Rich et al., formation of the cysteine derivative 7 can be explained by an elimination