  Generally, carbohydrate-active enzymes are studied using chromogenic
substrates that provide quick and easy color-based detection of enzyme-mediated
hydrolysis. In the case of 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-bromo-4-chloro-3-indolyl and 4-nitrophenyl
O-5-feruloyl-$\alpha$-l-arabinofuranosides 1a and 1b were significantly
shortened (7-8 steps reduced to 4-6) and transesterification yields enhanced
(from 46 to 73% for 1a and 47 to 86 % for 1b). This was achieved using
enzymatic (immobilized Lipolase 100T from Thermomyces lanuginosus)
transesterification of unprotected vinyl ferulate to the primary hydroxyl group
of $\alpha$-l-arabinofuranosides. Moreover, a novel feruloylated-butanetriol
4-nitrocatechol-1-yl analog 12, containing a cleavable hydroxylated linker was
also synthesized in 29% overall yield in 3 steps (convergent synthesis). The
latter route combined regioselective functionalization of 4-nitrocatechol and
enzymatic transferuloylation. The use of 12 as a substrate to characterize type
A feruloyl esterase from Aspergillus niger reveals the advantages of this
substrate for the characterizations of feruloyl esterases.
