posted 03-04-2008 12:25 AM            

TOAC (2,2,6,6-tetramethylpiperidine-1oxyl-4-amino-4-carboxylic acid) is a nitroxide spin-label used in electron spin resonance, ESR (also known as electron paramagnetic resonance, EPR) studies.1,2 This Ca-tetrasubstituted cyclic structure unnatural amino acid is an excellent and relatively rigid ESR probe, making it a useful tool in the study of peptide backbone conformational properties.2 TOAC has been shown to be an effective ß-turn and 310/a-helix promoter in peptides as well as a fluorescence quencher. Publications have reported the use of Fmoc-TOAC-OH in the synthesis of internally containing spin probe peptide sequence,3,4 which was previously not possible with BOC protected TOAC. The incorporation of this amino acid has also been reported in the synthesis of a biologically active hormone.2

Fmoc-Lys(Nvoc)-OH

4, 5-dimethoxy-2-nitrobenzyloxycarbonyl (Nvoc) is a photocleavable protecting group used for side-chain amine protection or for a-amine blocking. Compared with another photocleavable protecting group Z(2-NO2), Nvoc deprotection gave a higher yield under similar condition. Fmoc-Lys(Nvoc)-OH has been used in the solid phase peptide synthesis of selectively functionalized HIV and caged peptides.5,6 The removal of the Nvoc group, from the protected peptide, is compatible with the presence of a reactive maleimide linker which is useful for conjugation of peptides to proteins containing thiol groups.5
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