PROBLEM TO BE SOLVED: To provide a compound which modulates the activity of mammalian GPI-PLC (glycosylphosphatidylinositol-specific phospholipase C). SOLUTION: There are provided the compounds of formula (I) (wherein R1 R2 R3and R4are each independently H OH or F; and R5is 1-20C alkyl or 1-20C alkenyl) in all their stereoisomeric forms and mixtures thereof in all ratios and their physiologically acceptable salts. COPYRIGHT: (C)2011JPO&INPIT