Next, we investigated the configurational stability of the per-O-acylated 1-thiosugars under the reaction conditions. Treating 1-thiosugar 6a with 1 mol% Cu[ClO4]2•6H2O in MeCN did not lead to anomeric epimerization on the reaction time scale, also not after addition of acetic acid to mimic the acidic conditions in presence of Fdx (pKa 6.8 17 ) (Suppl. Fig. ). Thus, introducing the b-anomer of 1-thiosugars allows to control the configuration of the glycosidic linkage, that proved challenging to access for glycosylation of the aglycone. Therefore, we next aimed to synthesize a per-O-protected 1-thio-b-D-noviose derivative.