Selective blocking of some amino groups in a polyamino organic compound having at least one pair of available neighboring hydroxyl and amino groups is effected by first preparing in situ transition metal salt complexes of available neighboring amino and hydroxyl group pairs in said polyamino organic compound, followed by introduction of blocking groups on the non-complexed amino groups and, finally, removing the transition metal cations from the selectively N-blocked polyamino organic compound complex to obtain a polyamino organic compound having selectively blocked amino groups.This process is particularly valuable when carrying out aminocyclitol-aminoglycoside transformations utilizing transition metal salt complexes of cupric acetate, nickel (II) acetate, cobalt (II) acetate or mixtures thereof.