Ambident anion derived from phosphorothioselenoates was glycosylated with 1
,2,3,4-tetra-O-acetyl-beta-D-xylopyranose in the presence of boron trifluor
ide etherate to yield Se-xylosyl and S-xylosyl phosphorothioselenoates. Str
uctures of the products were established on the basis of selective oxidatio
n, P-31 NMR, H-1 NOE studies and unambiguously by X-ray diffraction.