Tethered Indoxyl-Glucuronides for Enzymatically Triggered Cross-Linking

Indoxyl-glucuronides, upon treatment with beta-glucuronidase under physiological conditions, are well known to afford the corresponding indigoid dye via oxidative dimerization. Here, seven indoxyl-glucuronide target compounds have been prepared along with 22 intermediates. Of the target compounds, four contain a conjugatable handle (azido-PEG, hydroxy-PEG, or BCN) attached to the indoxyl moiety, while three are isomers that include a PEG-ethynyl group at the 5-, 6-, or 7-position. All seven target compounds have been examined in indigoid-forming reactions upon treatment with beta-glucuronidase from two different sources and rat liver tritosomes. Taken together, the results suggest the utility of tethered indoxyl-glucuronides for use in bioconjugation chemistry with a chromogenic readout under physiological conditions.

Automated summary

In this study, seven target compounds and 22 intermediates were synthesized, and their corresponding indigo dyes were obtained through treatment with β-glucuronidase under physiological conditions. The results indicate that these tethered indoxyl-glucuronides can be used for bioconjugation chemistry with a visible chromogenic readout under physiological conditions.