B. Johnson
1970
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Journal
Annual Reports in Medicinal Chemistry
Abstract
Publisher Summary This chapter describes recent advances in the methods used in peptide synthesis. The N -protecting group was introduced by the use of 2-( p -biphenylyl) isopropylphenyl carbonate, a reagent that is stable at 0°. The advantage of this group is its ready removal by dilute acetic acid even in the presence of the t-butyloxycarbonyl (BOC) group. The useful derivatives, BOC-γ-benzyl-glutamic acid and BOC-β-benzyl-aspartic acid, have been prepared by an improved method and various S-substituted derivatives of cysteine have been converted to their corresponding BOC compounds using the Schnabel method. An ion exchange method for selectively removing the BOC group, even in the presence of the tert-butyl ester, has been reported. A new amino acid carboxyl protecting group, the 4-(methylthio) phenyl ester, has been developed. These esters are easily prepared by the N,N'-dicyclohexyl-carbodiimide method, and the BOC and carbobenzoxy protecting groups can be easily removed in their presence The preparation and properties of some 4-picolyl esters of amino acids have been reported. These esters are cleaved by cold alkali, by catalytic hydrogenation, by sodium in liquid ammonia, and by electrolytic reduction. A new procedure for the facilitation of peptide synthesis is also reported in which the carboxyl-terminal residue is incorporated as its 4-picolyl ester, and after each coupling reaction, the product is separated by extraction into an acidic phase.