**5. Conclusion**

*Peptide Synthesis*

under physiological condition (**Figure 4B**).

**38**

**Figure 5.**

*condensation using O-isopeptide method.*

*Segment condensation of peptides. (A) Conventional segment condensation between peptides. (B) Segment* 

generate bioactive molecules in situ *via* a 'click' appear to be useful tools for chemical biology research. Synthesis of photo-click peptide was shown in **Figure 4A**. Photo-click Aβ1-42 could prepare on a resin in a similar manner showed in **Figure 3A**, using photo-cleavable protected amino acid instead of Boc-Ser-OH. Photo-cleavable protected amino acid, 6-nitroveratryloxycalbonyl (Nvoc)-Ser-OH, was coupled to protected Aβ27-42 on the resin after Fmoc-deprotection, and then Fmoc-Gly-OH was coupled on the hydroxyl group of Ser26 using DIPCDI in the presence of catalytic amount of DMAP. The remaining peptide bonds formation using the Fmoc-based SPPS formed the protected *O*-isoacyl-Aβ1-42. Deprotection and cleavage from resin released *O*-isoacyl-Aβ1-42. Photo-click Aβ1-42 could rapidly release the native Aβ1-42 peptide by photo-irradiation and subsequent *O*-*N* intramolecular acyl migration

**4. Segment condensation of peptides using** *O***-isoacylpeptides**

Although NCL by Kent et al. allowed to preparing the long chain peptides, in general, conventional segment condensation other than NCL often involves the

> Recently, some important synthesis methods such as NCL and pseudoproline method for preparation of long chain and difficult sequence-containing peptides had been reported. Although these approaches allow to preparing some long chain peptides without a genetic engineered approach. However, these methodologies are not a panacea for a long chain and difficult sequence-containing peptides. We supply alternative solution for the long chain and difficult sequence-containing peptide preparation. Namely, we have developed the *O*-isoacylpeptide method for peptide preparation. *O*-isoacylpeptides that have a/some ester bonds can be converted into the parent peptides under physiological condition *via* the *O*-*N* intramolecular acyl migration. Moreover, we developed segment condensation with no racemization using the *O*-isoacylpeptide method. The segment condensation based on *O*-isoacylpeptides may be alternative choice to NCL method. We desire to apply to these methodologies of various peptide preparations for drug, diagnosis, and molecular research.
