Transfer reactions catalyzed by β-D-xylosidase from Penicillium wortmanni

The β-D-xylosidase from Penicillium wortmanni catalyses (i) the hydrolysis of β-D-xylopyranosides and α-L-arabinopyranosides, (ii) the transfer of the corresponding glycosyl residue to alcohols, and (iii) the dismutation of aryl β-D-xylopyranoside substrates. These reactions all occur with retention of configuration and can be rationalized by a symmetrical reaction scheme. The key intermediate is an enzyme–glycosyl complex with a lifetime that is sufficient for the diffusion away of the leaving (aglycon) group and the binding of an acceptor group before water reacts with the intermediate. The exact nature of this complex is unknown, but it must contain an aglycon site which binds preferentially alcohols and sugar molecules having the D-xylose structure

Synthesis and conformational features of a series of benzyl 4-O-(aldopentopyranosyl)-2,3-anhydro-β-D-ribopyranosides

A series of benzyl 4-0-(aldopentopyranosyl)-2,3-anhydro-β-D-ribopyranosides has been synthesized. The 1H-nmr parameters of these compounds have been obtained at 300 MHz in pyridine-d5 solution. Chemical shift increments of pyranoid systems in pyridine solution are advanced. The conformation of the 2,3-anhydro-β-D-ribopyranoside moiety is discussed. It occurs in a nearly equi-energetic equilibrium of the 0H5 and 5H0 forms