Cyclophellitol 44 proved to behighly active and very selective in labeling the human lysosomal retainingβ-glucosidase, glucosylceramide (glucocerebroside, GBA1).44 Genetic deficiency in GBA1 is at the basis ofthe lysosomal storage disorder, Gaucher disease, and a variety ofmutations in the gene encoding for GBA1 can lead to various diseasestates ranging from mild to severe. Here, GBA1 is linked to Gaucher disease.