Continuous flow brings SPPS to a new level
Vapourtec ’ s chief scientific officer Manuel Nuño talks about the journey of peptide synthesis in flow
Over the last decade , the focus of the pharmaceutical industry has been steadily shifting from small molecules to treatments based on peptides . In 2014 , sales of peptide-based therapeutics exceeded $ 1 trillion worldwide . 1 Between 2015 and 2019 , 15 out of the 208 drugs approved by the FDA were peptides . 2 For peptide-based drug development , it is crucial to be able both to synthesise peptide libraries and to optimise the synthesis rapidly before scaling to gram quantities for pre-clinical trials . In early 2017 , New Path Molecular Research challenged Vapourtec to adapt its platform for library synthesis to facilitate automated continuous solid-phase peptide synthesis ( SPPS ) flow . This kick-started Vapourtec ’ s journey into addressing the key issues associated with peptide synthesis in flow . SPPS is the most convenient chemical route to synthesise a peptide quickly . It is based on a repetitive sequence of deprotection and coupling steps quickly . As Figure 1 shows , a Fmoc protecting group is removed before a new Fmocprotected amino acid is coupled to it . 3 The first continuous flow peptide synthesisers ( CF-SPPS ) were developed in the 1980 , but batch synthesisers remained the preferred choice and dominated the market into the early 2000s . 4 Over the last decade , interest in CF-SPPS has grown again after excellent work published by many researcher group , including the work in fast peptide synthesis by the Pentelute lab at MIT . 5-8
Figure 1 – Chemical reactions in SPPS
Currently , flow platforms offer an extraordinary level of automation and in-line data , which is inherently difficult to obtain with a batch system . In flow , solid reagents are typically handled by using a fixed bed reactor . This simple set-up works well with solid catalysts , for example , as there is no volume change .
SPPS on the R-Series
To tackle CF-SPPS we built on our knowledge of how to do automated library synthesis . Our R-Series can perform automated library synthesis of compounds . Reagents are automatically loaded in the flow network via sample loops . For CF-SPPS , we would just need to prepare in vials as many different Fmoc-protected amino acids as the sequence contains . For CF-SPPS to succeed , one of the key unsolved issues was how to handle the solid support . As the peptide is grown attached to the resin , there are significant volume changes that a fixed bed reactor simply cannot accommodate . For example , synthesising a 30-mer peptide will double the initial resin volume . If the volume is not adjusted , the resin will compress so much that it loses structure and causes blockages . If this volume increment is not accounted for from the beginning , solvent voids will cause dilution and lack of packing density will allow reagents to channel through the reactor , reducing the overall efficiency of the process . With a standard packed bed reactor , CF-SPPS was possible in our R-Series , but it required manual intervention from the users . As the peptide grew , to prevent issues , they needed to adjust the packed bed reactor every couple of cycles .
48 SPECIALITY CHEMICALS MAGAZINE ESTABLISHED 1981