Observations relevant to the mechanism of the reductive aminations of ketones with sodium cyanoborohydride and ammonium acetate

Abstract Fortimicin B ( 2 ) has been converted to 6'- epi -fortimicin B 5 and 6'- epi -fortimicin A 4 both of which have the same diaminosugar moiety as that present in gentamicin C 2 3 . The syntheses of the 6'- epi -fortimicins and their antibacterial activities are reported. Although reductive amination of 1,2'-di-N-benzyloxycarbonyl-6'-oxo-fortimicin B-4,5-carbamate 17 with sodium cyanoborohydride and ammonium acetate in methanol gave a mixture of 1,2'-di-N-benzyloxycarbonyl-6'- epi -fortimicin B-4,5-carbamate 18 and 1,2'-di-N-benzyloxycarbonylfortimicin B-4,5-carbamate 14 , attempted reduction of 1,2'-di-N-benzyloxycarbonyl-6'-iminofortimicin B-4,5-carbamate 16 , under identical conditions gave only recovered imine. The significance of these results relative to the mechanism of the reductive amination of carbonyl compounds with sodium cyanoborohydride and amine salts is discussed.