The previously unknown stereostructure of glucolipsin A (1), a complex glycolipid endowed with glucokinase-activating properties, was unambiguously elucidated as (2 R, 2'R, 3 S, 3'S) by comparison of its spectroscopic and analytical data with those of all conceivable C 2- symmetric stereoisomers. This set of macrodiolides was prepared by a sequence comprising auxiliary guided aldol reactions, glycosidation of the resulting β-hydroxy acid derivatives ...