1) By methylation of gentamicin C1a (I) with methyl p-toluenesulfonate (A) in acetonitrile. 2) By methylation of gentamicin C1a (I) with methyl bromide (B) in methanol. 3) The reaction of gentamicin C1a (I) with CS2 in ethanol gives the 6'-N-dithiocarbamylgentamicin (II), C1a which is reduced with LiAlH4 in refluxing THF.
4) The reaction of gentamicin C1a (I) with formaldehyde in ethanol gives 6'-N-methylenegentamicin C1a (III), which is then reduced with NaBH4, or with hot formic acid. 5) The reaction of gentamicin C1a (I) with ethyl chloroformate (C) by means of NaOH in dioxane yields ethyl 6'-carbamategentamicin C1a (IV), which is then reduced with LiAlH4 in THF.