(R)-4-[1-Hydroxy-3-((2R,3R,4R,5R,6R)-3,4,5-tris-benzyloxy-6-benzyloxymethyl-tetrahydro-pyran-2-yl)-prop-2-ynyl]-2,2-dimethyl-oxazolidine-3-carboxylic acid tert-butyl ester