Paper
Improved selectivity in the removal of the tert.-butyloxycarbonyl group
Published Jan 12, 2009 · M. Bodanszky, A. Bodanszky
International Journal of Peptide and Protein Research
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Abstract
Removal of the tert.-butyloxycarbonyl group by trifluoroacetic acid in the presence of benzyloxycarbonyl groups, benzyl esters and benzyl ethers is rendered more selective by dilution with acetic acid. Trifluoroacetic acid-acetic acid mixtures, however, cause acetylation of hydroxyl groups and also some formation of tert.-butyl esters at free carboxyls. Hence, such mixtures are useful only for the deprotection of intermediates in which the hydroxyl and carboxyl groups are fully blocked. A search for a diluent without such inherent limitation led to the application of a mixture of phenol and p-cresol. Dilution of trifluoroacetic acid with phenols both improved the selectivity in the removal of the tert.-butyloxycarbonyl group and suppressed the alkylation of amino acid side chains as well. A 4:3:3 mixture of trifluoroacetic acid, phenol and p-cresol was found useful in the practical execution of partial deprotection.
Dilution of trifluoroacetic acid with phenols improves selectivity in removing tert.-butyloxycarbonyl groups and suppresses alkylation of amino acid side chains in partial deprotection.
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