Application of centrifugal counter-current chromatography to the separation of macrolide antibiotic analogues. I. Selection of solvent systems based on solubility and partition coefficient investigations

Adsorption of ofloxacin on carbon nanotubes: solubility, pH and cosolvent effects

The adsorption of ofloxacin (OFL) on carbon nanotubes (CNTs) has been investigated using the solubility, pH and cocolvent effects. In this work, solubilities of OFL and sorption of OFL on three multi-walled CNTs at different pHs and different methanol volume fractions (f(c)) of methanol/water mixture solutions were systematically measured. The solubilities of different OFL species were obtained based on the analysis of pH-dependent solubility. Cationic and anionic OFL showed much higher solubilities than zwitterionic OFL. The highest sorption was not observed at the pH with lowest OFL solubility, indicating hydrophobic interaction was not the dominant sorption mechanism. The sorption decreasing in pH range of 5-8 was consistent with cationic OFL species distribution, suggesting cation exchange may play an important role. With the increased methanol fraction, both OFL solubility and sorption decreased, which was different from hydrophobic organic contaminants (HOCs). Analysis of methanol-fraction-dependent OFL sorption suggested that cosolvent-sorbent (methanol-CNTs) interactions were much stronger than solute-cosolvent (OFL-methanol) interactions. This statement was also confirmed in sorption isotherm study as evidenced by decreased sorption and increased linearity of the isotherms in methanol than those in water.

Apolar chromatography on Sephadex LH-20 combined with high-speed counter-current chromatography

A novel high yield isolation procedure for lipophilic cyclic peptide derivatives is presented. Destruxin (dtx) A, B, D, E, and E-diol retrieval from Metarhizium anisopliae culture broth was achieved with a three-step purification protocol. After liquid-liquid extraction column chromatography over Sephadex LH-20 served as enrichment step. High-speed counter-current chromatography (HSCCC) was used for the final purification. Within the first chromatographic step dtx D and dtx E-diol were separated in purities exceeding 90%. The separation of dtx A, B, and E was achieved from an enriched Sephadex LH-20 fraction by a HSCCC protocol using light petroleum-ethyl acetate-methanol-water = 2:5:2:5 (v/v) as eluent system. These derivatives were obtained in purities above 98% and total yields exceeding 40%.

Antibiotic purification from fermentation broths by counter-current chromatography: analysis of product purity and yield trade-offs

Counter-current chromatography (CCC) is a low pressure, liquid-liquid chromatographic technique which has proven to be a powerful purification tool for the high-resolution fractionation of a variety of active pharmaceutical compounds. The successful integration of CCC into either existing or new manufacturing processes requires the predictable purification of target compounds from crude, fermentation-derived, feed streams. This work examines the feasibility of CCC for the purification of fermentation-derived erythromycin A (EA) from its structurally and chemically similar analogues. At the laboratory scale, the effect of feed pre-treatment using either clarified, forward extracted (butyl acetate) or back extracted broth on EA separation was investigated. This defined the degree of impurity removal required, i.e. back extracted broth, to ensure a reproducible elution profile of EA during CCC. Optimisation and scale-up of the separation studied the effects of mobile phase flow (2-40 ml.min(-1)) and solute loading (0.1-10 g) on the attainable EA purity and yield. The results in all cases demonstrated a high attainable EA purity (>97% w/w) with throughputs up to 0.33 kg.day(-1). Secondly, a predictive scale-up model was applied demonstrating, that from knowledge of the solute distribution ratio of EA (K(EA)) at the laboratory scale, the EA elution time at the pilot scale could be predicted to within 3-10%, depending upon the solute injection volume. In addition, this study has evaluated a "fractionation diagram" approach to visually determine the effects of key operational variables on separation performance. This resulted in accurate fraction cut-point determination for a required degree of product purity and yield. Overall, the results show CCC to be a predictable and scaleable separation technique capable of handling real feed streams.

Application of coil centrifugal counter-current chromatography to the separation of macrolide antibiotic analogues III. Effects of flow-rate, mass load and rotation speed on the peak resolution

As the third part of our methodology studies on the application of centrifugal counter-current chromatography to the preparative separation of macrolide antibiotic analogues, we have investigated the effects of various parameters on the retention of stationary phase and peak resolution. Our results show that the retention percentage of the stationary phase has linear relationships with both flow-rate at 1 to 3 ml/min and rotation speed at 100 to 700 rpm, but their correlation coefficients are negative (-1.000) and positive (0.9821), respectively. The peak resolution (Rs) is inversely proportional to the flow-rate (Fr) and mass load (Ml), but directly proportional to the rotation speed (Rrev). Their correlation coefficients in linear regression for the preparative separation in laboratory scale are -0.981 to -1.000 for Rs=a+bFr at flow-rates of 1 to 3 ml/min, -0.929 to -0.993 for Rs=a+bMl at mass loads of 12.5 to 100 mg, and 0.975 to 0.998 for Rs=a+bRrev at rotation speeds of 300 to 700 rpm, respectively. Preparative separation of six very closely related macrolide antibiotics, which belong to ascomycin and rapamycin analogues, has also been successfully achieved under optimized conditions.