6,6'-Di-O-(tert-butyldiphenylsilyl)-3,2',3',4'-tetra-O-acetyl-2-thio-1-O-2-S-(1,2,3,6-tetrahydro-1,3-dimethyl-2,6-dioxo-4,5-pyrimidinediyl)-.alpha.-D-lactopyranose AIDS-113400 AIDS113400