Carbodiimide based activation represents a powerful method for coupling amino acids at elevated temperature [1]. An adjusted carbodiimide process is presented that both enhanced coupling rates and demonstrated a reduction in epimerization [2]. This method was applied to the coupling of standard Fmoc amino acids at temperatures > 90°C with minimal epimerization.
Significant efficiency improvements were achieved by combining this new more rapid coupling method with a one pot coupling and deprotection process that together reduced an entire cycle time to ~ 2 minutes. For example, using this process a difficult 10 mer peptide (0.1mmol scale) can be made in ~ 20 minutes with < 100mL total waste.
The applicability of this technology was expanded through the use of the hyper-acid sensitive Cl-TCP linker with increased stability at elevated temperature [3] and the development of a larger scale microwave peptide synthesizer with reactor volumes up to 17L.