General Papers ARKIVOC 2005 (xiv) 20-28
Efficient and selective cleavage of the tert-butoxycarbonyl (Boc) group under basic condition
Debendra K. Mohapatra* and Kulbhushan A. Durugkar
Division of Organic Chemistry: Technology, National Chemical Laboratory Pune-411008, India E-mail:
[email protected]
Abstract
A simple, efficient and mild method for the selective cleavage of tert-butoxycarbonyl (Boc) from dicarbamates and a carbonyl or aromatic ring in conjugation with the nitrogen atom bearing the Boc-group is described under basic condition.
Keywords: a-Amino acids, di-t-butylimidodicarbonate, selective deprotection, celogenitins, racemization
Introduction
The natural and unnatural a-amino acids play a central role in chemistry and biology.1 In addition, to their key biological roles as components of peptides, proteins, and other natural products, a-amino acids are utilized in the pharmaceutical, agrochemical, and related industries. The use of a-amino acids and their derivatives solely depend on the protecting group attached to the amine and acid functionality.2 Among the various protecting groups for amine functionality, the t-butoxycarbonyl (Boc) group is one of the most frequently used in organic synthesis due to its chemical stability to basic and mildly acidic conditions and its ease of removal under specific conditions.3 However, selective cleavage of the di-t-butylimidodicarbonate, oftenly found as valuable intermediates in Mitsunobu4 and Gabriel type5 processes towards the synthesis of several bio-active molecules, protected a-amino acids to mono-Boc compounds still lacks efficient and milder methods. Numerous methods are available for the removal of the Bocgroup, 7 including trifluoroacetic acid,8 trimethylsilyl iodide,9 hydrochloric acid in ethyl acetate,10 ceric ammonium nitrate,11 tin tetrachloride,12 tetrabutylammonium fluoride,13 zinc bromide,14 boron trifluoride,15 thermolytic removal16 etc. However, there are very few methods for the selective cleavage17a-f of the di-Boc protected a-amino acids to mono-Boc compounds. Still organic community seeks simple, efficient and milder methods for selective deprotection of the well known protecting groups by preserving the other functionalities.
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