Tert-Butoxycarbonyl, protecting group peptide synthesis

As mentioned in Section 10.6.2, synthesis of 1-hydroxyethylene peptides can be initiated by adding a ferf-butoxycarbonyl N-protected a-amino aldehyde to an optically active Grignard reagent (Scheme 7)J11-13 This reaction affords a diastereomeric mixture of the C4 epimers of the hydroxy ether in good yields. In most cases the mixture is enriched in the 45-epimer and the epimers are readily separable. The yields and the ratios of the resulting 45- and 4R-epimers obtained from several examples of this reaction are summarized in Table 1. When this reaction was attempted with the aldehyde prepared from Aa,Ae-bis-tert-butoxycarbonyl-protected Lys, the desired product was not obtained. The anion of the Lys Ne-tert-butoxy-carbonylamino group probably reacts with the aldehyde to form a cyclic aminol that does not... 

Solvent-free deprotection of the N-tert-butoxycarbonyl (Boc) groups, a very commonly used protection group in organic synthesis, has been accomplished in the presence of neutral alumina that is doped with aluminum chloride (Scheme 2.2-26) [87]. This approach may find application in a typical peptide-bond-forming re-... 

The tert-butoxycarbonyl (i-BOC) group is often used for protection of the amino, hydroxy, and sulfhydryl groups. This kind of defense is usual in the protection of amino acids in peptide synthesis. 

Peptide synthesis is made possible by the use of selective protecting groups. An N-protected amino acid with a free carboxyl group is coupled to an 0-protected amino acid with a free amino group in the presence of dicyclo-hexylcarbodiimide (DCC). Amide formation occurs, the protecting groups are removed, and the sequence is repeated. Amines are usually protected as their tert-butoxycarbonyl (BOO derivatives, and acids are protected as esters. This synthetic sequence is often carried out by the Merrifield solid-phase technique, in which the peptide is esterified to an insoluble polymeric support. 

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