S-Fluorenylmethyl protection of the cysteine side chain upon N(α)-Fmoc deprotection.
Deprotection of an N(α)-Fmoc-protected glycocysteine derivative 7 with an excess of morpholine unexpectedly led to the fluorenylmethyl-protected thioether 8 in high yield. The suggested mechanism for this reaction comprises the addition of the cysteine thiolate on the exocyclic double bond of dibenzofulvene, which is formed during Fmoc deprotection. The influence of base concentration on this transprotection reaction was studied.
Otto Diels Institute of Organic Chemistry, Christiana Albertina University of Kiel, Otto-Hahn-Platz 3/4, 24098 Kiel, Germany.
Johannes W
JW
Wehner
Thisbe K
TK
Lindhorst
Fmoc protecting group; N-Fmoc→S-Fm transprotection; glycoamino acids; protecting groups