Abstract
Propargyl esters are employed as effective protecting groups for the carboxyl group during solution-phase peptide synthesis. The propargyl ester groups can be introduced onto free amino acids by treating them with propargyl alcohol saturated with HCl. The reaction between propargyl groups and tetrathiomolybdate is exploited to deblock the propargyl esters. The removal of the propargyl group with the neutral reagent tetrathiomolybdate ensures that most of the other protecting groups used in peptide synthesis are untouched. Both acid labile and base labile protecting groups can be removed in the presence of a propargyl ester. Amino acids protected as propargyl esters are employed to synthesize di- to tetrapeptides in solution-phase demonstrating the possible synthetic utilities of the methodology. The methodology described here could be a valuable addition to currently available strategies for peptide synthesis.
Highlights
Several methods are available for the protection of the carboxyl group of amino acids during peptide synthesis [1]
The reaction did not produce any other diastereomer of Boc-Ile-OH (2d) suggesting that the deprotection of propargyl esters with 1 does not result in the racemization of amino acids, as evident from the 1H NMR spectrum of the compound. These results suggest that the propargyl esters of amino acids can be used for the protection of the carboxyl group
The results suggest that propargyl esters of amino acids are suitable for solutionphase peptide synthesis, especially when the α-amino group is protected as a Boc derivative
Summary
Several methods are available for the protection of the carboxyl group of amino acids during peptide synthesis [1]. With the advent of combinatorial chemistry and with medicinal chemistry developing into a separate branch of science, the use of amino acids having multiple functionalities and which are different from the natural amino acids has become very common. This has brought up the requirement of additional protecting groups, which are orthogonal to those being used. We report a systematic study demonstrating the utility of propargyl esters as a protecting group for carboxyl groups in solution-phase peptide synthesis
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