Acanthoscurrin fragment 101–132: Total synthesis at 60°C of a novel difficult sequence

Abstract Glycine‐rich proteins (GRPs) serve a variety of biological functions. Acanthoscurrin is an antimicrobial GRP isolated from hemocytes of the Brazilian spider Acanthoscurria gomesiana . Aiming to contribute to the knowledge of the secondary structure and stepwise solid‐phase synthesis of GRPs' glycine‐rich domains, we attempted to prepare G 101 GGLGGGRGGGYG 113 GGGGYGGGYG 123 GGY 126 GGGKYK 132 ‐NH 2 , acanthoscurrin C‐terminal amidated fragment. Although a theoretical prediction did not indicate high aggregation potential for this peptide, repetitive incomplete aminoacylations were observed after incorporating Tyr 126 to the growing peptide‐MBHA resin (Boc chemistry) at 60°C. The problem was not solved by varying the coupling reagents or solvents, adding chaotropic salts to the reaction media or changing the resin/chemistry (Rink amide resin/Fmoc chemistry). Some improvement was made when CLEAR amide resin (Fmoc chemistry) was used, as it allowed for obtaining fragment G 113 –K 132 . NIR‐FT‐Raman spectra collected for samples of the growing peptide‐MBHA, ‐Rink amide resin and ‐CLEAR amide resin revealed the presence of β‐sheet structures. Only the combination of CLEAR‐amide resin, 60°C, Fmoc‐(Fmoc‐Hmb)Gly‐OH and LiCl (the last two used alternately) was able to inhibit the phenomenon, as proven by NIR‐FT‐Raman analysis of the growing peptide‐resin, allowing the total synthesis of desired fragment Gly 101 –K 132 . In summary, this work describes a new difficult sequence, contributes to understanding stepwise solid‐phase synthesis of this type of peptide and shows that, at least while protected and linked to a resin, this GRP's glycine‐rich motif presents an early tendency to assume β‐sheet structures. © 2008 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 92: 65–75, 2009. This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com