The three types of glycosyl donors (Table 1, donors 1-6) used in these investigations are easily accessible by reac-tion of phosphorothio-, dithio-and selenoates with gly-cosyl halides, 18'19 by reaction of 1-O-acetyl sugars with phosphorothioic, selenoic20 and dithioic acids21 in the presence of boron trifluoride—diethy1 ether complex, and by addition of phosphorodithioic acids to tetra-O-acetyl-1, 5-anhydro-D-arabin0-hex-1-enitol, ...