Selective separation of gentamicins from the biosynthetic mixture by reactive extraction

The experiments on reactive extraction of gentamicins C1, C1a, C2 and C2a with D2EHPA dissolved in dichloromethane indicated the possibility to selectively separate the gentamicin C1 from the mixture obtained by biosynthesis. The selectivity of its extraction is positively influenced by increasing the pH-value of aqueous solution and by using a D2EHPA concentration in organic phase near the value needed for an equimolecular ratio between the extractant and this gentamicin. The maximum value of the selectivity factor has been reached at pH 8 and 10 g l−1 D2EHPA. Therefore, the raffinate will be enriched in gentamicins C1a, C2 and C2a, their overall ratio increasing from 68% in the biosynthetic product to 84.6%.The second step of the experiments consists on the recovery of gentamicins C1, C1a, C2 and C2a from the extracts previously obtained by re-extraction with sulfuric acid solutions. Thus, it is possible to re-extract mainly the most active gentamicins, namely C1a, C2 and C2a. The selectivity of their separation is positively influenced by using the sulfuric acid concentrations near to the values stoichiometric needed for reacting only with gentamicins C1a, C2 and C2a. The mixture resulted by re-extraction contains 92.6% gentamicins C1a, C2 and C2a.By bringing together the aqueous solutions obtained by reactive extraction and re-extraction, the ratio of the active gentamicins becomes 89%, their loss reaching 0.3% related to the initial biosynthetic product.