A useful application of mutagenesis has been the development
of a new method of oligosaccharide synthesis.
This involved using a mutant of a b-glucosidase from
Agrobacterium sp., wherein the nucleophilic carboxyl had
been modified to alanine, in conjunction with activated
glycosyl fluorides of the opposite anomeric configuration
to that of the normal substrate [49••]. The mutated glycosidase
(glycosynthase) catalyzes the synthesis of
glycosidic bonds, but is incapable of their hydrolysis, thus
allowing yields of over 90% to be achieved (Figure 5). A
recent development is a new glycosynthase containing
serine in place of the nucleophile that results in 24-fold
faster synthesis and thus improved product yields and
reduced reaction times [50]. A likely role for the serine
hydroxyl group is in hydrogen bonding with the departing
anomeric fluoride. Endoglycosidases have also been
developed as glycosynthases, allowing oligosaccharyl
fluorides to act as glycosyl donors