How to extract the active ingredients from plants?

The compound system contained in plants is extremely complex, and the number of its types often exceeds the conventional cognitive scope. Not only does the content of different compounds differ significantly, but the overall difference between various plant compound groups is also very obvious.

From the perspective of overall classification, plant compounds can usually be divided into two categories: one is primary metabolites, such as proteins, amino acids, etc., which belong to this category. They are the core substances for plants to maintain basic life activities; The second is secondary metabolites, such as alkaloids, flavonoids, terpenoids, etc., which are transformed from some primary metabolites through complex metabolic processes in plants. At present, their specific roles in plant physiological activities have not been fully explored.

Extraction: The scheme of this link is mainly determined by the physical and chemical properties of the target compound (covering key indicators such as acidity, thermal stability and solubility), and the core purpose is to maximize and stabilize the extraction of the target compound.Common extraction methods include water decoction, organic solvent thermal reflux, ultrasonic extraction, etc.; for thermally unstable compounds, low temperature extraction methods, such as cold immersion, ultra-low temperature critical extraction, etc., should be selected.The selection of extraction solvents needs to combine the polarity and acidity and alkalinity of the compound. Taking alkaloids as an example, because they are alkaline, in most cases acid extraction is used, which first allows the alkaloids to form salts that are easily soluble in water. Complete the extraction, and then restore the original structure through alkalization treatment; you can also use an alkaline solution to free the alkaloids first, and then select a suitable polar solvent for extraction.Then look at polysaccharides, most of these ingredients are easily soluble in water, difficult to dissolve in alcohols, usually by water extraction and alcohol precipitation to complete the preliminary extraction and purification.In view of the wide variety of plant compounds, they are not listed here.

Purification: Its core idea is similar to that of extraction, but it requires higher separation accuracy.Generally, extraction operation will be carried out according to the polarity difference of compounds, and the extracts will be preliminarily divided into different polar components, and then silica gel column chromatography, gel column chromatography, macroporous resin adsorption, high-speed countercurrent extraction and other methods will be used for fine separation. The separation principles of these technologies correspond to the polarity difference, molecular weight size, affinity difference with resin, distribution coefficient difference in different solvents, etc. of compounds.For some compounds with low purity requirements or special properties, sometimes the purification target can be achieved only by recrystallization operation.Overall, the purification process takes a long time and requires sufficient care and patience from the operator.

Identification: At the stage of compound structure identification, core techniques such as nuclear magnetic resonance hydrogen spectroscopy, carbon spectroscopy and X-ray crystal diffraction are usually used to clarify the precise configuration of the compound; at the same time, ultraviolet spectroscopy and infrared spectroscopy are supplemented to provide supplementary evidence for the structural identification of the compound.