Z-Gly-Phe-OH

The success of solid-phase peptide synthesis is often dependent upon solvation of the resin and the growing resin-bound peptide chain. We investigated the relationship between solvent properties and solvation of the resin and peptide-resin in order to obtain satisfactory coupling yields for the rapid solid-phase peptide synthesis, using butyloxycarbonyl-(Boc)-amino acid derivatives, of human-alpha-calcitonin gene-related peptide(8-37) (CGRP(8-37)). Solvation of (p-methylbenzhydrylamine)copoly(styrene-1% divinylbenzene (DVB) (resin) and resin covalently bound to the fully protected amino acid sequence of CGRP(8-37) (peptide-resin) was correlated to solvent Hildebrand solubility (delta) and hydrogen-bonding (delta(h)) parameters. Contour solvation plots of delta(h) vs. delta revealed maximum solvation regions of resin and peptide-resin. Maximum resin solvation occurred with N-methylpyrrolidinone (NMP), NMP : dimethylsulfoxide (DMSO) (8 : 2) and DMSO. Inefficient solvation of the peptide-resin occurred with these solvents and resulted in poor syntheses with average coupling yields of 78.1, 88.9 and 91.8%, respectively. Superior peptide-resin solvation was obtained using dimethylacetamide (DMA) and dimethylformamide (DMF), resulting in significantly higher average coupling yields of 98.0 and 99.5%, respectively. Thus, the region of maximum peptide-resin solvation shifts to solvents with higher delta(h) values. DMF provided the most effective peptide-resin solvation and was the only solvent from which CGRP(8-37) was obtained as a single major product in the crude cleaved material.

It has been proved that the principal component of senile plaques is aggregates of beta-amyloid peptide (Abeta) in cases of one of the most common forms of age-related neurodegenerative disorders, Alzheimer's disease (AD). Although the synthetic methods for the synthesis of Abeta peptides have been developed since their first syntheses, Abeta[1-42] is still problematic to prepare. The highly hydrophobic composition of Abeta[1-42] results in aggregation between resin-bound peptide chains or intrachain aggregation which leads to a decrease in the rates of deprotection and repetitive incomplete coupling reactions during 9-flurenylmethoxycarbonyl (Fmoc) synthesis. In order to avoid aggregation and/or disrupt internal aggregation during stepwise Fmoc solid phase synthesis and to improve the quality of crude products, several attempts have been made. Since highly pure Abeta peptides in large quantities are used in biological experiments, we wanted to develop a method for a rational synthesis of human Abeta[1-42] with high purity and adequate yield. This paper reports a convenient methodology with a novel solvent system for the synthesis of Abeta[1-42], its N-terminally truncated derivatives Abeta[4-42] and Abeta[5-42], and Abeta[1-42] labeled with 7-amino-4-methyl-3-coumarinylacetic acid (AMCA) at the N-terminus using Fmoc strategy. The use of 10% anisole in Dimethylformamide/Dichloromethane (DMF/DCM) can substantially improve the purity and yield of crude Abeta[1-42] and has been shown to be an optimal coupling condition for the synthesis of Abeta[1-42]. Anisole is a cheap and simple aid in the synthesis of 'difficult sequences' where other solvents are less successful in the prevention of aggregation during the synthesis.

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 degrees 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 beta-sheet structures. Only the combination of CLEAR-amide resin, 60 degrees 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 beta-sheet structures.