Method for preparing an acetal-protected sugar involving the step of reacting a diol group of a sugar selected from the group consisting of an aldopentose and an aldohexose with one or two compounds of formula (Ia) and/or (Ib) in the presence of a homogenous or heterogenous catalyst to form an acetal-protected sugar selected from the group consisting of a compound of formula (II), (III) and (IV) wherein R1 and/or R2 are independent from each other -Z-X, and wherein Z is a linear, branched or cyclic hydrocarbon moiety with 1 to 10 carbon atoms, optionally substituted with 1 to 4 C1- C4-alkyl groups or 1 to 4 halogen atoms, or -B-D, wherein B is a linear hydrocarbon moiety with 1 to 3 carbon atoms and may be present or absent, D is an aromatic moiety having 6 carbon atoms, optionally substituted with 1 to 4 C1-C4-alkyl groups, 1 to 2 -OH groups, 1 to 2 -OCH3 groups or 1 to 4 halogen atoms and combinations thereof, and wherein Z may be present or absent, and X is -COOH, -CH(COOH)2, -COOR3, CHO, -C2H3, -C2H, -CHOR4OR5, - N3, -NHR6, -NR7R8, -F, -Cl, -Br, -I, or if Z is present, -OH, NH2, or -SH; R3, R4 and R5 are independently selected from the group consisting of a linear, branched or cyclic hydrocarbon moiety having 1 to 20 carbon atoms, optionally substituted with 1 to 4 C1 to C4 alkyl groups and/or 1 to 4 halogen atoms selected from the group consisting of fluoro, chloro, bromo and iodo; R6 is a C1-C4-alkyl group; R7, R8 and R9 are independently from each other a C1-C4-alkyl group; R30 and R31 are independently selected from the group consisting of hydrogen and a linear or branched hydrocarbon moiety having 1 to 4 carbon atoms, with the proviso that R30 and R31 cannot both be hydrogen; R10 is selected from the group consisting of -H, -OH, - CH2OH, -OR13 or -CH2OR14; R11 and R12 are independently selected from the group consisting of -OH or -OR13; R13 and R14 are independently selected from a hydrocarbon moiety with 1 to 10 carbon atoms; and n and p are independently from each other either 0 or 1.