Application of a unique automated synthesis system for solution-phase peptide synthesis

Delay of coupling caused by excess additives

Use of excess quantity of additives such as 1-hydroxybenzotriazole, 1-hydroxy-7-azabenzotriazole, or 3,4-dihydro-3-hydroxy-4-oxo-1,2,3-benzotriazine could retard carbodiimide-mediated peptide coupling or aminolysis of the active esters in organic solvents generally employed in peptide chemistry. Solubility test and infrared spectroscopic data suggested that the amine components interacted with the additives to form some aggregates, which were less reactive toward acylation. The use of 0.1 equimolar additives against carboxyl components or carbodiimides was advantageous for rapid and efficient coupling reaction, especially when the carboxyl components were amino acids carrying urethane type N-protecting groups.

A novel method for repetitive peptide synthesis in solution without isolation of intermediates

A novel method was developed for the large-scale manufacture of peptides in solution, called DioRaSSP-Diosynth Rapid Solution Synthesis of Peptides. This method combines the advantages of the homogeneous character of classical solution-phase synthesis with the universal character and the amenability to automation inherent to the solid-phase approach. The process consists of repetitive cycles of coupling and deprotection in a permanent organic phase and is further characterized by the fact that intermediates are not isolated. Couplings are mediated by water-soluble carbodiimide. Several types of function may be applied for temporary amino protection depending on the sequence of the actual peptide, including Z, Fmoc, Msc and Nsc. Formate is the preferred hydrogen donor during hydrogenolysis of the Z function, while 1,8-diazabicyclo[5.4.0]undec-7-ene is used to deprotect Fmoc, Msc and Nsc. Morpholine is added during the deprotection of Msc and Nsc to scavenge the arising alkenes. Processes according to this highly efficient synthesis method are easy to scale up and yield products of reproducible high purity, which is guaranteed by a new quenching method for residual activated compounds, applying an anion-forming amine such as a beta-alanine ester. This ester should display a lability similar to that of the temporary amino-protecting function, allowing simultaneous deprotection of the growing peptide and the quenched compound. The DioRaSSP approach assures the completely quantitative removal of deprotected quenched compounds before the coupling step of the next cycle of the synthesis by basic aqueous (that is active) extraction, while the growing peptide remains anchored in the organic phase due to the presence of hydrophobic protecting functions.

Solution-phase automated synthesis of tripeptide derivatives

An improved general method for automated synthesis of tripeptides was developed, in which methanesulfonic acid (MSA) was used in place of trifluoroacetic acid (TFA), thus making it possible to avoid, 1) corrosion of the apparatus by strong acid vapor, 2) formation of emulsions, and 3) use of the restricted solvent, dichloromethane. As an application of the automated synthesis apparatus, 216 fragment tripeptide derivatives were synthesized systematically using the MSA method, in excellent yield and with increased efficiency.