Extracting and Purifying Natural Products

Extracting and Purifying Natural Products

A leading Australian contract development and manufacturing organisation, Luina Bio offers a range of capabilities in natural products extraction, purification and characterisation

 A “natural product” is a chemical compound or substance produced by a living organism. Natural products provide an unparalleled source of chemical diversity for the discovery of valuable biologically active molecules for use in medicines, cosmetics and many other products.

Natural products are produced by the chemical extraction of plant or animal tissues, followed by isolation and purification of the final product. A molecule may also be harvested from an organism and then used as a precursor molecule further modification outside the organism to produce the desired product—a process called “semi synthesis”.

Alternately, “total synthesis” is the complete chemical synthesis of complex organic molecules from simpler precursors without the use of biological processes. However, not all natural products can be fully synthesized this way, and many have very complex structures that are either too difficult or expensive (or both) to synthesize on an industrial.

Natural products that can be isolated or produced from plants are called “phytochemicals.” In particular, the natural products industry is interested in secondary metabolic compounds found in plants. These “secondary metabolites” are organic compounds not directly involved in the normal development, growth or reproduction of an organism. In agriculture, for instance, many secondary metabolites are known to protect against insect attacks and plant diseases. Secondary metabolites produced by plants are used in medicines, as flavorings, or in consumer products.

Extracting the active compound

If the lead compound (or active principle) of interest is present in a mixture of other compounds from a natural source, it has to be extracted and purified. Secondary metabolites can be extracted from a variety of natural sources, including plants, microbes, marine animals, insects and amphibians.

In laboratory-scale processes, the initial and bulk extraction of active the compounds from plant and microbial sources involves several steps before extraction can occur, including plant selection, collection, identification, drying and grinding. After the source material has been prepared, there are several extraction methods available, such as maceration, ultrasound-assisted solvent extraction, percolation, pressurized solvent extraction, Soxhlet extraction, extraction under reflux, steam distillation and acid/based extraction.

In general, the extraction process must be streamlined to reduce solvent consumption, since solvent removal can present a significant process bottleneck. Another consideration is to choose an extraction method that supports the first step in the fractionation process.

Fractionation processes

For initial fractionation of any crude extract, it is preferable to avoid generating too many fractions as this can dilute the target compound to such low concentrations that it cannot be detected. A more effective approach is to collect only a few, relatively large fractions and then to home in on those containing the target compound.

Preparation chromatography is often used to separate the fractions. In this method, the components to be separated are distributed between two phases, one of which is stationary (the stationary phase) while the other (the mobile phase) moves in a specific direction. One example of preparation chromatography is liquid chromatography. The active fractions from liquid chromatography then undergo a finer fractionation using semi-preparative or high-performance liquid chromatography, often guided by an on-line detection method, such as ultraviolet light or mass spectrometry.

Purification

Once detected, the chemical structure of the compound will need to be determined. For this step, nuclear magnetic resonance spectroscopy (NMR) is often used. In NMR, information about the arrangement of the individual hydrogen and carbon atoms in the compound is provided, allowing for a detailed reconstruction of its molecular structure to be made.

In the final step, it is essential to determine if a compound purified using the above techniques has biological activity. The presence (or absence) of biological activity is determined using bioassays to detect properties necessary for the intended purpose of the molecule (e.g., antibacterial, antifungal, anticancer, anti-HIV, anti-diabetic, etc.). Such bioassays can involve the use of in vivo systems (e.g., whole animal experiments), ex vivo systems (isolated tissues and organs), or in vitro systems (e.g., cultured cells).

 

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