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.