The invention relates to compounds of formula I, and pharmaceutically usable derivatives, solvates, salts, prodrugs, tautomers, enantiomers, racemates and stereoisomers thereof, including mixtures thereof in all ratios and compounds of formula I, wherein one or more H atoms may be replaced by D (deuterium) which are useful as glycosidase inhibitors, useful in the treatment of tauopathies and Alzheimer’s disease. Compounds of formula I wherein, R is (un)branched alkyl; L is CH₂, NH₂ and derivatives, N(CH₂)_0-2, etc.; Q¹ is CH₂, CO; Q² is CH₂ and CO; n = 0 – 2; A is benzothiazolyl, benzofuranyl, imidazolpyridyl, etc.; Z is H, halo, CN, OH, etc.; are claimed. The example compound II was prepared by condensation of 3-methyl-1,3,8-triazaspiro[4.5]decane-2,4-dione with 5-(1-chloroethyl)benzo[d]thiazole. Compounds I were evaluated for their glycosidase inhibtory activity (some data given).