Fig. 4
From: Accelerated microfluidic native chemical ligation at difficult amino acids toward cyclic peptides
Optimized microfluidic setup. a Details of the optimized microfluidic system. The pH of the MPAA feed solution was set at 7.80, leading to an optimum internal pH of 7.3 within microfluidic element µF2, and the residence time t2 to 4 min. ϕ1 = ϕ2 = 3.3 µL min−1, ϕ3 = 35 µL min−1. The back pressure regulator (BPR) was set at 2.5 bars. The peptide concentration in the Feed solution 1 was 7 mM. For 7c, the reactor effluent was quenched in 10% aqueous acetic acid. MPAA was then extracted with diethylether (5×) before HPLC analysis and purification (workup 1). For 7d-k, the cyclic peptide co-eluted by HPLC with the starting SEAon peptide 4. Therefore, the reactor effluent was treated first with AcA-MPA 8/TCEP dissolved in pH 7.4 phosphate buffer (workup 2) and then according to workup 1. 1 Isolated yields after HPLC purification. R′ and R′′ are for side-chain amino acids (see Fig. 1). b Representative HPLC chromatogram for cyclized peptide 7d after workup 1 (top) or workup 2 and 1 (bottom)
