Fig. 2: Characterizations of the CAST conjugation.
From: Copper assisted sequence-specific chemical protein conjugation at a single backbone amide
a CAST peptide reaction with 1. The chromatograms shown are at 214 nm absorption from LC‒MS analysis. Source data are provided as a Source Data file. b CAST peptide and molecule 1 reaction kinetics study. c LC‒MS/MS analysis of the CAST peptide conjugation product. The spectrum indicates that the modification is at residue D9 colored in red. The observed b ions and y ions are shown in green and red colors. d Partial NOESY spectrum of the CAST peptide conjugation product. e The CAST peptide maintains reactivity with functional handle-modified styrylboronic acid (1 A, 1B or 1 C). Peaks marked at black star, black diamond are non-peptide byproducts from 1 A, 1B, or 1 C. Red star indicates the corresponding modification of the boronic acid. f The CAST peptide maintains reactivity when inserted at the C-terminus, N-terminus, or in the middle of polypeptides. g The CAST conjugation reaction is compatible with the disulfide bond. Note. SM starting material. Mod modified product. Reactions conditions: CAST peptide (-FFKKDDHAA-, 50 μM), CuCl2·2H2O (150 μM), trans-beta-styrylboronic acid 1, 1 A, 1B or 1 C (500 μM), NMM (50 mM, pH = 7.4), 37 °C, 10 min (a), 15 min (e–g).
