Synthesis and photolytic activation of 6″-O-2-nitrobenzyl uridine-5′-diphosphogalactose: a ‘caged’ UDP-Gal derivative

Placing an 2-nitrobenzyl group on O-6 of the galactosyl residue in uridine-5′-diphosphogalactose (UDP-Gal) gives 6″-O-2-nitrobenzyl-UDP-Gal that is shown to be inactive as a donor substrate for β-(1→4)-galactosyltransferase (GalT). On irradiation at 365 nm, the nitrobenzyl group is completely removed yielding native UDP-Gal that then transfers normally to produce the expected βGal-(1→4)-βGlcNAc disaccharidic linkage. 6″-O-2-Nitrobenzyl-UDP-Gal thus fulfils the minimum requirements of a ‘caged’ UDP-Gal for application in time-resolved crystallographic studies of β-(1→4)-GalT.

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