Medical Applications of Chromatography

The isolation and purification of compounds is of critical importance to medicinal chemists discovering and developing drugs. In these activities it is extremely important to be able to produce mg quantities of the target compounds, from a synthetic reaction mixture. Then later on use the same separation technologies to provide gram and Kilo quantities. Similarly, the technique can isolate, purify and concentrate suitable quantities of low level impurities and metabolites to support compound identification and further characterisation.

One of the key advantages of high performance counter current chromatography is that it scales easily and simply. This allows the medicinal chemist to focus on the value-added part of the development process i.e. the chemistry, and alleviates the need to waste time developing scaled-up chromatography techniques, as demand for the quantity of compound increases.

A further important issue is sample solubility since this can affect the throughput to produce a specified quantity of the compound of interest. Typically, this can become an issue when the purification is performed in reverse phase (RP) which generates aqueous fractions. These aqueous fractions are laborious to concentrate by evaporation and this process can lead to degradation of the product.

As scale of production increases the volumes of solvents used and those of product containing fractions also increase. This is particularly an issue where RP-HPLC produces large volumes of aqueous fractions. High performance counter current chromatography can be used in normal phase for the same separation which means that fractions can be collected in essentially non-aqueous solvents which makes their processing simpler, faster and less energy consuming. However, as production scale increases a major advantage of HPCCC becomes apparent as it uses only ten to twenty percent of the solvent per unit mass compared with RP-HPLC and since it is normally operated in isocratic mode the opportunities for solvent recycling are much greater. Even if HPCCC is operated in RP mode (where fractions are eluted in aqueous or largely aqueous solvents there is significant benefit if only ten to twenty percent of the volume produced by RP_HPLC has to be processed. Significantly, when set against NP flash, HPCCC produces no solid waste for disposal. Overall when using high performance counter current chromatography, up front solvent costs are less but added to this is that the process produces less waste solvent which these days is a significant factor.

HPCCC offers the medicinal chemist an alternative tool and approach. The liquid/liquid nature of the technique allows the sample to be injected in either phase, without affecting the separation. This in turn expands the options on solubility without the problem of premature (breakthrough) elution. Further, the HPCCC process can be operated in either normal phase (NP) with the obvious benefits to the subsequent evaporative concentration stage or in reverse phase.

HPCCC has found many applications in medicinal chemistry, to which the Spectrum or Midi bench top products are normally found to be the most suitable for the quantities of compound required.