Regioselective chemoenzymatic syntheses of ferulate conjugates as chromogenic substrates for feruloyl esterases

摘要

Generally, carbohydrate-active enzymes are studied using chromogenic substrates that provide quick and easy color-based detection of enzyme-mediated hydrolysis.For feruloyl esterases, commercially available chromogenic ferulate derivatives are both costly and limited in terms of their experimental application.In this study, we describe solutions for these two issues, using a chemoenzymatic approach to synthesize different ferulate compounds.The overall synthetic routes towards commercially available 5-bromo4-chloro-3-indolyl and 4-nitrophenyl 5-O-feruloyl-α-?-arabinofuranosides were significantly shortened (from 7 or 8 to 4–6 steps), and the transesterification yields were enhanced (from 46 to 73% and from 47 to 86%, respectively).This was achieved using enzymatic (immobilized Lipozyme? TL IM from Thermomyces lanuginosus) transesterification of unprotected vinyl ferulate to the primary hydroxy group of α‐?‐arabinofuranosides.Moreover, a novel feruloylated 4-nitrocatechol-1-yl-substituted butanetriol analog, containing a cleavable hydroxylated linker, was also synthesized in 32% overall yield in 3 steps (convergent synthesis).The latter route combined the regioselective functionalization of 4-nitrocatechol and enzymatic transferuloylation.The use of this strategy to characterize type A feruloyl esterase from Aspergillus niger reveals the advantages of this substrate for the characterizations of feruloyl esterases.