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Oxime Carbonates: Novel Reagents for the Introduction of Fmoc and Alloc Protecting Groups, Free of Side Reactions
Author(s) -
Khattab Sherine N.,
SubirósFunosas Ramon,
ElFaham Ayman,
Albericio Fernando
Publication year - 2010
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201000028
Subject(s) - chemistry , oxime , dipeptide , reagent , protecting group , tripeptide , combinatorial chemistry , peptide synthesis , organic chemistry , peptide , alkyl , biochemistry
Fmoc and Alloc protecting groups represent a consistent alternative to classical Boc protection in peptide chemistry. The former was established in the last decades as the α‐amino protecting group of choice, whereas the latter allows a fully orthogonal protection strategy with Fmoc and Boc. Usually, the introduction of the Fmoc and Alloc moieties takes place through their halogenoformates, azides, or activated carbonates. This rather simple reaction is accompanied by several side reactions, specially the formation of Fmoc/Alloc dipeptides and even tripeptides. The present work describes new promising Fmoc/Alloc‐oxime reagents, which are easy to prepare, stable, and highly reactive crystalline materials that afford almost contaminant‐free Fmoc/Alloc‐amino acids in high yields by following a conventional procedure. Amongst the Fmoc‐oxime derivatives, the N ‐hydroxypicolinimidoyl cyanide derivative ( N ‐{[(9H‐fluoren‐9‐yl)methoxy]carbonyloxy}picolinimidoyl cyanide) gave the best results for the preparation of Fmoc‐Gly‐OH, which is the most predisposed to give side reactions. The same Alloc‐oxime analogue afforded the preparation of Alloc‐Gly‐OH in good yield, purity, and extremely low dipeptide formation, as analyzed by reverse‐phase HPLC and NMR spectroscopy.