Novel diphenylmethyl-derived amide protecting group for efficient liquid-phase peptide synthesis: AJIPHASE

An efficient method for the synthesis of peptides bearing an amide at the C-terminal is described. This method involves the attachment of a C-terminal protecting group bearing long aliphatic chains, followed by the repetition of simple reaction and precipitation steps with the combined advantages of liquid-phase peptide synthesis (LPPS) and solid-phase peptide synthesis (SPPS). Using this method, a hydrophobic peptide was successfully synthesized in good yield and high purity, which cannot be obtained satisfactorily by SPPS.

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.