Microreactors peptide synthesis

Watts P, Wiles C, Haswell SJ, Pombo-ViUar E, Styring P (2001) The Synthesis of Peptides Using Microreactors. Chem Comm 11 990-991 Watts P, Wiles C, Haswell S, Pombo-Villar E (2002a) Investigation of Racemi-sation in Peptide Synthesis within a Microreactor. Lab Chip 2 141-144 Watts P, Wiles C, Haswell S, Pombo-Villar E (2002b) Solution Phase Synthesis of Beta-Peptides Using Microreactors. Tetrahedron 58 5427-5439... 

Microreaction technology has also been applied to peptide synthesis. Haswell and coworkers demonstrated that, using a borosilicate glass microreactor, the desired... 

The Nervous System Research branch of Novartis Pharma Ltd in Basel, Switzerland, and the University of Hull investigated peptide synthesis in chip-based microreactors... 

To develop an EOF based system. Watts et al. have conducted an extensive study on peptide synthesis, where they prepared a library of peptide derivatives within a computer-controlled microreactor system operating under EOF [25-28]. The authors demonstrated that dipeptides could be prepared from pre-activated carboxylic acids. They optimized the reaction using the pentafluorophenyl (PFP) ester of Fmoc- 3-alanine 4 with amine 5 to give dipeptide 6 quantitatively in 20 min (Scheme 14.2). This represented a significant increase in yield compared with the traditional batch synthesis, where only a 50% yield was obtained in 24 h. 

Flogel et al. [97] described a silicon microreactor (the same as in Figure 1.11) for peptide synthesis, which also allows a quick screening of reaction conditions. Using peptide couplings with Boc- and Fmoc-protected amino acids, significant amounts of peptides could be made in 1-5 min at temperatures as high as 120 °C. Synthesis efficiency was further enhanced by the use of a fiuorous benzyl tag for the assembly of P peptides this method is particularly useful for the purification of poorly soluble products. 

The Nervous System Research branch of Novartis Pharma Ltd in Basel, Switzerland, and the University of Hull investigated peptide synthesis in chip-based microreactors [5]. P-Amino adds were chosen for demonstrating feasibility of microreactor processing, as there are no chiral centers that may complicate the analysis of the products [6]. 

Microreaction technology has also been applied to peptide synthesis. Haswell and coworkers demonstrated that, using a borosihcate glass microreactor, the desired dipeptide was obtained by the reaction of N-Fmoc-(3-alanine with P-alanine Dmab ester in the presence of DCC (1,3-dicydohexykarbodiimide) (Scheme 5.30) [41,42]. It also was demonstrated that the Fmoc group could be removed by DBU... 

Flogel O, Codee JDC, Seebach D, Seeberger PH (2006) Microreactor Synthesis of Beta-Peptides. Angew Chem Int Ed 45 7000-7003 Geyer K, Codee JDC, Seeberger PH (2006) Microreactors as Tools for Synthetic Chemists - The Chemists Round-Bottomed Flask of the 21st Century Chem Eur J 12 8434-8442... 

Challenging applications, such as the synthesis of P-peptides [30] or examples of flash chemistry (like the reaction of electrochemically generated reactive cation pools [31]) have been successfully realized using microreactors. 

Seeberger and coworkers prepared synthetically useful amounts of P-peptides (0.2-0.6mmol) by using a microreactor (reactor volume = 78.3 pi). The reaction of add fluoride and the TFA salt of amino acid benzyl ester in the presence of N-methylmorpholine (NMM) at 90 °C (3 min residence time) gave the dipeptide in 92% yield (Scheme 4.19). A fluorous tag method was used for an effident synthesis of tetrapeptides. Amino acid esters having fluorous tags were used to facilitate purification by fluorous solid-phase extraction (FSPE) (Scheme 4.20). 

In this chapter, we will focus on those bioorganic reactions in which biocatalysts, in particular, play a crucial role. We will not discuss peptide or natural product synthesis, as conventional organic chemistry will be covered by other chapters in this book. Also the discussion of the development of DN A chips, certainly one of the most exciting developments in the field of pTAS, is beyond the scope of this chapter, and the interested reader is referred to some excellent reviews [330,331], First, the application of bioorganic chemistry in diagnostics will be discussed. This will be followed by a discussion on biocatalysis in microreactors. Finally, the recent development of cells on a chip is highlighted. 

Fig. 14.6 Microreactor manifold for synthesis and electrophoretic purification of peptides.

The highly ordered mass and heat transfer processes within microreactors often produce very selective reactions. As will be seen later this has implications for nanomaterial synthesis, but even within well-known reactions this selectivity can be important. Burns and Ramshaw [31] showed that nitration processes within microfluidic systems produce cleaner products than bulk scale systems. Similarly high yields and low by-product formation has been reported in on-chip peptide formation [32]. This is almost certainly attributable to the thermal flatness found within microfluidic channels and the ordered and predictable mixing within the system. It appears that reactions within the microfluidic regime are cleaner and often quicker, than their bulk equivalents. 

Synthesis of another p-peptide was also performed. Seeberger et al. performed the synthesis of oUgo p-amino acid using amino acid fluoride in a siUcmi microreactor [2]. They... 

FIdgel O, Codee JDC, Seebach D, Seeberger PH (2006) Microreactor synthesis of fl-peptides. Angew Chem Int Ed 45 7000-7003... 

Watts et al. demonstrated multi-step solution-phase synthesis of peptides in a glass microreactor with quantitative yield in 20 min [94]. This should be compared with batch reactions where only moderate yields (40-50%) were obtained in 24 h. Common protecting groups were used, viz. Fmoc was selected for N-protection and Dmab ester for protection of the carboxylic add. The reaction was carried out in the microreactor under electroosmotic flow. Deprotection, which is required to extend the peptide chains beyond dipeptides, was also demonstrated with quantitative yield in the microreactor. In this first microreactor demonstration, only alanine-based peptides were synthesized in later work other amino acids were also used ]95, 96]. 

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