Fragment condensation stepwise

Note that proteins are now synthesized routinely by stepwise assembly or fragment condensation (see Vol. E22a, Section 4.1 ) 67 68 and chances of product contamination with shorter fragments that may have similar retention times under RP-HPLC should be considered 69 Additionally, size-exclusion HPLC was found to be particularly useful in distinguishing linear from cyclic peptides. 

Elongation of the peptide bearing a reduced bond can be performed stepwise or by fragment condensation. In the latter case, the carbonyl of the amino acid involved in the reduced peptide bond can be activated (Scheme 1) as no racemization by the oxazol-5(4//)-one mechanism can occur. 

Coiled-coil polypeptides can also be prepared by stepwise fragment condensations on a solid support. A unique feature of the heptad sequence used in de novo designed coiled coils is that a Gly residue can be incorporated as the C-terminal residue of the heptad sequence without the ability of the polypeptide to form stable two-stranded a-helical coiled coils being affected. Although the fragment condensation methodology can be performed with minimal... 

Synthesis of the peptide Ac-A-Bn-C-OH was performed by a stepwise solid-phase fragment condensation approach, as shown in Scheme 3, using the general procedures of the automated solid-phase method. The synthesis began with Boc-C-resin support and continued with the stepwise addition of protected peptide fragments until the completed peptide was assembled on the resin. The supported peptide Ac-A-Bn-C-resin was obtained after deprotection of Boc-A-Bn-C-resin and acetylation of the free amino groups. 

Stepwise Solid-Phase Fragment Condensation General Procedure 21 ... 

Conventional method stepwise synthesis or fragment condensation using an optimized choice of protecting group combination and the most favorable coupling methods 1 8 ... 

Two general routes are available for the synthesis of calixarenes the base-and acid-promoted one-step synthesis and the convergent stepwise synthesis (fragment condensation).2,3... 

All the methods of peptide bond formation described in Section 3 are useful for the synthesis of peptides on solid support [solid-phase peptide synthesis (SPPS)]. The ideal method would rapidly allow quantitative coupling reactions under mild conditions, avoiding side reactions, racemization, and generating side-products which could be easily removed by single washings from the peptide-resin. Various techniques have been explored by peptide chemists, but the focus of this section will be on the small number which have been widely used. These techniques have been applied to stepwise synthesis , the addition of one residue at a time, and to fragment condensation , which is the condensation of long sequences of amino acids. 

Fig. 13. Scheme of the N-terminal peptide elongation in polymer phase by stepwise fragment condensation... 

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