For instance, 6'-N-t-butoxycarbonylkanamycin may be prepared in a high yield by reacting kanamycin in solution in a mixture of pyridine, water and triethylamine with a 1 to 3 molar proportion of t-butoxycarbonyl azide added dropwise thereto under agitation, stirring the admixture at ambient temperature overnight, concentrating the reaction mixture to dryness in vacuo and then purifying the solid residue in a column chromatography with a cation-exchange resin such as Amberlite CG 50 (NH4 form), while recovering the unreacted kanamycin. Moreover, 2',6'-di-N-t-butoxycarbonylkanamycin B or 3',4'-dideoxykanamycin B may be prepared in a high yield, for example, by reacting kanamycin B or 3',4'-dideoxykanamycin B in solution in a mixture of pyridine, water and triethylamine with a 2-3 molar proportion of t-butoxycarbonyl azide added dropwise thereto under agitation, stirring the admixture at ambient temperature overnight, concentrating the reaction mixture to dryness in vacuo, and then purifying the solid residue in column chromatography with a cation-exchange resin such as Amberlite CG 50 (NH4 form). When this preparation procedure is repeated with 2 molar proportions or less of t-butoxycarbonyl azide, there may be obtained 6'-N-t-butoxycarbonyl-kanamycin B or 3',4'-dideoxykanamycin B in a high yield. 6'-N-t-butoxycarbonyl-kanamycin B or 3',4'-dideoxykanamycin B once isolated may also be converted into the 2',6'-di-N-t-butoxycarbonyl derivative by further reacting with 1 to 2 molar proportions of t-butoxycarbonyl azide in a similar manner. The compounds of the formula (IV) prepared in the above procedures may be employed as a starting compound in the process of this invention without purification.
