- Overcoming Chemical Challenges in the Solid-Phase Synthesis of High-Purity GnRH Antagonist Degarelix. Part 2
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The hydrolysis and rearrangement of the dihydroorotic (Hor) residue in the presence of bases, leading to the formation of the hydantoin (Hyd) impurity, represent one of the major problems in manufacturing of the gonadotropin-releasing hormone antagonist Degarelix. In an attempt to find efficient strategies to overcome this problem, we carried out a screening of organic bases in order to select those which afforded both the rapid Fmoc deprotection during the solid-phase synthesis and the absence of this peculiar rearrangement. Among the bases tested, only tert-butylamine did not affect the peptide molecule and was able to perform fast Fmoc removal. The use of tert-butylamine for the synthesis of Degarelix led to a product with excellent purity and yield without a detectable amount of the hydantoin impurity. Thus, we showed that tert-butylamine can be a suitable alternative to piperidine for industrial-scale production of Degarelix or other Hor-containing peptide pharmaceuticals.
- Biondi, Barbara,Cabri, Walter,Formaggio, Fernando,Guryanov, Ivan,Orlandin, Andrea,Ricci, Antonio,Viola, Angelo
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- Self-assembled nanostructures of long-acting GnRH analogs modified at position 7
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It is well known that GnRH analogs can self-assemble into amyloid fibrils and that the duration of action of GnRH analogs depends on the ability of the amyloid to slowly release active peptides. The aim of this study was to investigate the influence of the amino acid residues at position 7 of GnRH analogues on peptide self-assembly. It was found that the dominant shape of the nanostructure can be changed when the structures of the residues at position 7 differ significantly from that of leucine in Degarelix. When the backbone length was extended (peptide 9), or the side chain of the residue at position 7 was replaced by an aromatic ring (peptide 6), or the rotation of the amide bond was restricted (peptide 8), the nanostructure changed from fibrils to vesicles. The results also indicate that the increasing hydrophilicity had little influence on the nanostructure morphology. In addition, a suitable release rate was found to play a more important role for the duration of the peptide action by maintaining the equilibrium between the drug concentration and the persistent release time, while the nanostructure shape was found to exert little influence on the duration of the peptide action.
- Zhou, Ning,Gao, Xing,Lv, Yujian,Cheng, Junping,Zhou, Wenxia,Liu, Keliang
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- Overcoming Chemical Challenges in the Solid-Phase Synthesis of High-Purity GnRH Antagonist Degarelix. Part 1.
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The highly potent, long-acting, gonadotropin-releasing hormone antagonist Degarelix is known to be very efficient for prostate cancer treatment. The synthesis of decapeptide Degarelix is complicated because of the presence in its sequence of several unnatural α-amino acids, which are prone to rearrangements and side reactions. In particular, the rearrangement of the dihydroorotic (Hor) moiety with following hydantoin formation in the presence of bases represents one of the major problems. In this study, we describe a novel chemical strategy to overcome this obstacle by the use of the corresponding p-nitrophenylalanine derivative, which is reduced on the solid support to p-aminophenylalanine and acylated with dihydroorotic acid at the end of the solid-phase synthesis. Thus, the contact of Hor with the bases required for Fmoc deprotection is completely avoided. This approach provides a superior purity of Degarelix when the synthesis is carried out in the industrial scale as well.
- Guryanov, Ivan,Orlandin, Andrea,Viola, Angelo,Biondi, Barbara,Badocco, Denis,Formaggio, Fernando,Ricci, Antonio,Cabri, Walter
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- AJIPHASE: A Highly Efficient Synthetic Method for One-Pot Peptide Elongation in the Solution Phase by an Fmoc Strategy
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We previously reported an efficient peptide synthesis method, AJIPHASE, that comprises repeated reactions and isolations by precipitation. This method utilizes an anchor molecule with long-chain alkyl groups as a protecting group for the C-terminus. To further improve this method, we developed a one-pot synthesis of a peptide sequence wherein the synthetic intermediates were isolated by solvent extraction instead of precipitation. A branched-chain anchor molecule was used in the new process, significantly enhancing the solubility of long peptides and the operational efficiency compared with the previous method, which employed precipitation for isolation and a straight-chain aliphatic group. Another prerequisite for this solvent-extraction-based strategy was the use of thiomalic acid and DBU for Fmoc deprotection, which facilitates the removal of byproducts, such as the fulvene adduct.
- Takahashi, Daisuke,Inomata, Tatsuji,Fukui, Tatsuya
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p. 7803 - 7807
(2017/06/27)
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