Peptides partially protected

K Barlos, D Gatos, S Kutsogianni, G Papaphotiou, C Poulus, T Tsegenidis. Solid phase synthesis of partially protected and free peptides containing disulphide bonds by simultaneous cysteine oxidation-release from 2-chlorotrityl resin. Int J Pept Prot Res 38, 562, 1991. 

FIGURE 8.18 Methylation of the amino group of a support-bound peptide.92 The amino group is partially protected, methylated by a reagent that does not methylate peptide bonds and then deprotected.91 DMF = dimethylformamide. 

The advantage of normal phase over the reversed-phase mode of liquid chromatography is that the column load can be 10-fold higher in the former. The main limitation of normal phase is that only those peptides that are soluble in organic solvents, such as chloroform and methanol or ethanol mixtures, will yield some separation. As a result, RP-HPLC is preferred for the separation of unprotected peptides as well as of protected or partially protected derivatives. 

In the presence of PPi, known to bind strongly to the enzyme active site (Section III,E), there was a weak protective effect. The experimental points fell in the shaded area of Fig. 6, and the data were analyzed with equations developed by Scrutton and Utter (45). The results of this treatment led to the conclusion that TNBS can react with both free enzyme and enzyme-PPi complex to cause catalytic inactivation the differences are only quantitative (45). Either TNBS can displace PP, from an active site lysine or TNBS modifies a different lysine, apart from the active site, and the presence of PPi on the enzyme partially protects against TNBS inactivation by some indirect mechanism. Unfortunately, as discussed above, this issue cannot be settled with these kinetic analyses. Furthermore, because all of the enzyme lysines are to some extent reactive with TNBS (Fig. 5), the single super-reactive lysine whose modification leads to inactivation cannot be isolated and identified, as, for example, in a particular peptide fragment. A variety of interpretations are possible, as discussed elsewhere (45). 

Partially protected peptide thioesters that are prepared from SPPS and purified by RP-HPLC can condense with other peptide segments to form highly homologous peptides which can comprise as many as 100 amino acid residues. 9 Syntheses of peptide thioesters using Boc-SPPS have been quite successful.161214 However, the preparation of thioesters by Fmoc chemistry is difficult because the piperidine used to remove the Fmoc group attacks the carbonyl moiety of the resin-bound thioester to release the peptide from solid support. However, peptide thioesters have been prepared by SPPS using Fmoc chemistry. 9 ... 

A 28 kDa protein was identified as the target of a mAb that conferred partial protection (41-49%) on mice (Harn etal., 1992). Peptide sequencing of the protein revealed it as the 5. mansoni homologue of mammalian triose phosphate isomerase (TPI), present in all stages of the parasite and transiently on the surface... 

To distinguish peptides and partially protected peptidic by-products carrying an aromatic protecting group (e.g., Fmoc, benzyl), it is advantageous to record the... 

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