The present invention relates to a method for preparing an at least partially acetal-protected sugar involving the step of reacting a sugar or a sugar derivative selected from the group consisting of an aldopentose, an aldohexose, an aldopentoside and an aldohexoside with an aldehyde or an aldehyde source in the presence of heterogeneous acidic catalyst to form the at least partially acetal-protected sugar selected from the group consisting of a compound of formula (I), (II), (III), (IV), (V), (VI), (VII), (VIII), (IX), (X,) (XI) and (XII) wherein R1, R1', R2, R2', R3, R3', R4, R5, R6, R7, R8, R9, R10, R11, R12, and R12' are Y or Z-E, and wherein R1 and R1', R2 and R2', R3 and R3', and R12 and R12' are the same or different from each other and Y is hydrogen or a linear, branched or cyclic hydrocarbon moiety having 1 to 20 carbon 69 atoms, Z is a linear, branched or cyclic hydrocarbon moiety with 0 to 12 carbon atoms, optionally substituted with 1 to 4 C1 to C4 alkyl groups, 1 to 4 halogen atoms, or benzyl groups and E is -COOH, - CH(COOH)2, -COOR19, -CH(COOR20)(COOR21), -CHO, -CH(CHO)2, -C2H3, CH(C2H3)2, -CHCHR22, -CHCR23R24, -C2H, -C2R25, -N3, -NH2, -CH(NH2)2, - NHR26, -CH(NHR27)(NHR28), -NR29R30, -CH(NR31R32)(NR33R34), -OH, -OR35, - CH(R36OH)(R37OH), and R19, R20, R21, R22, R23, R24, R25, R26, R27, R28, R29, R30, R31, R32, R33, R34, and R35, are independent from each other C1 to C20 alkyl, and R20 and R21, R23 and R24, R27 and R28, R29 and R30, R31 and R32, as well as R33 and R34 are the same or different from each other, and R36 and R37 are independent from each other absent or a linear or branched C1 to C12 hydrocarbon chain and R13, R14, R15, R16, R17 and R18 are independent from each other hydrogen or a linear, branched or cyclic hydrocarbon moiety having 1 to 20 carbon atoms.