When it comes to polar organic compound purification, many chemists turn to normal-phase flash chromatography often utilizing dichloromethane and methanol as the eluting solvents. While this can work, it often can be challenging to optimize due to methanol’s high polarity and protic chemistry.
Improvements in solid phase peptide synthesis strategies and development of resin linkages susceptible to low acid cleavage conditions has enabled synthesis of long peptides while keeping the protecting groups intact. This strategy is now used for the preparation of chemically synthesized proteins, wherein shorter peptide fragments are ligated together. They are also found in the synthesis of peptide macrocycles that utilize head-to-tail cyclization strategies. Although linear synthesis of protected peptides is generally straightforward, purification of these compounds using traditional reversed phase methods is quite challenging. Herein we describe the use of normal phase chromatography for purification of fully protected peptides.
Flash purification is a separation technique developed in 1978 by Professor W.C. Still that uses a stationary phase (a column or cartridge filled with an insoluble solid support) and a mobile phase (elution solvent mixture) to separate and purify a mixture of organic compounds.
As reversed-phase flash chromatography gains traction in medicinal chemistry labs the need to monitor its cost and safety are becoming more important. Commonly used reversed-phase solvents typically include water with an organic solvent such as methanol or acetonitrile – each have advantages and disadvantages.
Reversed-phase chromatography is typically used when you need to separate several milligrams of relatively polar compounds that either are not soluble in normal-phase solvents or are not compatible with bare silica because they react, stick, or both. If you are currently using reversed-phase at preparative scale, such as flash chromatography, you know the mobile phase limitations – water with either methanol, acetonitrile, or THF. As with normal-phase flash chromatography, when it comes time to purify you want your crude sample fully solubilized in the weakest possible solvent at the highest possible concentration. ACS 2016
Although capable of very high resolution, RP-HPLC is often limited by low column loading capacity, therefore demanding a significant time investment for peptide purification. As an alternative strategy, reversed-phase flash chromatography can also be used to purify synthetic peptides. The larger particle size used in flash column chromatography enables much larger loading capacity, thereby significantly reducing the time required for peptide purification.
Natural product chemistry deals with discovering the previously unknown in nature. Compounds found in nature are typically found in low quantity and thus extractions are needed to isolate certain compounds classes or at least compounds with similar solubility.
Flash purification involves a simple liquid chromatography technique » Method development uses TLC as a way of deciding the parameters for the separation » Isocratic separations are easiest to develop, but gradient separations are more powerful » Software in the Isolera helps with conversion of an isocratic separation to a gradient » It is possible with the Spektra software to run step gradients » Loading options are dependent on the column type » SNAP offers the most flexibility » Care must be taken to choose the best loading option to get good purifications
For those chemists performing organic synthesis, reaction mixture purification by flash column chromatography is an integral and necessary part of the synthesis process. However, flash chromatography consumes large volumes of solvent which either needs to be recycled or disposed. ACS 2016.
Normal-phase flash chromatography1 has been widely adopted as the method of choice for separation of product mixtures and reaction by-products. One of the most significant developments in this area concerns the practical separation of polar molecules. Reversed-phase purification is a modification of normalphase chromatography that provides an efficient mechanism for the separation of polar compounds.
For most organic and natural product chemists flash chromatography is a necessary part of their research. As such, many chemists need quick isolation of at least one desired component from a crude mixture in relatively high yield and purity. This need for speed, purity, and yield pits these desires against each other as you can typically optimize on only two of the three goals. In this poster, we will describe some techniques that help chemists optimize flash purification and maximize speed, yield, and purity.
Traditional approaches to compound purification involving chromatography utilize large volumes of relatively toxic and expensive solvents, and significantly contribute to the environmental footprint of organizations involved in molecular research. Current directives for greener chemistry have put pressure on organizations to reduce the environmental impact of their work.
To save money on consumables, many chemists choose to reuse silica flash cartridges. This is true but risks purification results because chromatographic separation performance will change from run to run which reduces purification quality, especially in normal phase systems. Regardless of the cartridge brand used, repeated use of silica flash cartridges results in loss of compound resolution and therefore fraction purity.