Automation and Control of Solid-phase Peptide Synthesis: Methods and Technology

Solid-phase techniques have been introduced in the early sixties by Bruce Merrifield (Nobel Prize in 1984) and, up to now, a wide number of commercial applications have been applied to biopolymers synthesis, supported organic chemistry, and heterogeneous catalysis. In the specific case of peptide, polypeptide and protein synthesis, the possibility offered by solid-phase method to automate the operations required by the chemical procedures, is still hampered by the lack of adequate devices for monitoring and controlling the key steps of the synthetic cycle, namely deprotection and coupling. Deprotection allows removing masking group from the amino terminal of the last residue of the growing chain, while coupling enables to condense a new amino acid derivative. These steps are subsequently repeated until the complete sequence is assembled on the solid matrix. Afterwards, the crude product is cleaved from the support, purified and characterized. Direct, in-real-time, evaluation of the yield of both deprotection and coupling represents a crucial step in order to achieve a satisfactory level of process automation. Accordingly, many efforts have been made to define different procedures and some have been also commercially applied. However, an integrated system able to perform the overall control of the synthetic cycle is still to come. This paper reviews the efforts that have led us to develop an original method for the on-line prediction of the coupling yield. Our results are compared to the main contributions in the field of solid-phase peptide synthesis automation.