Chemo-enzymatic synthesis of 4-methylumbelliferyl β-(1→4)-d-xylooligosides: new substrates for β-d-xylanase assays

Abstract

Transglycosylation catalyzed by a β-D-xylosidase from Aspergillus sp. was used to synthesize a set of 4-methylumbelliferyl (MU) β-1→4-D-xylooligosides having the common structure [β-D-Xyl-(1→4)]_2–5-β-D-Xyl-MU. MU xylobioside synthesized chemically by the condensation of protected MU β-D-xylopyranoside with ethyl 2,3,4-tri-O-acetyl-1-thio-β-D-xylopyranoside was used as a substrate for transglycosylation with the β-D-xylosidase from Aspergillus sp. to produce higher MU xylooligosides. The structures of oligosaccharides obtained were established by ¹H and ¹³C NMR spectroscopy and electrospray tandem mass spectrometry. MU β-D-xylooligosides synthesized were tested as fluorogenic substrates for the GH-10 family β-D-xylanase from Aspergillus orizae and the GH-11 family β-D-xylanase I from Trichoderma reesei. Both xylanases released the aglycone from MU xylobioside and the corresponding trioside. With substrates having d.p. 4 and 5, the enzymes manifested endolytic activities, splitting off MU, MUX, and MUX₂ primarily.