Alkaloids are a kind of nitrogen-containing alkaline organic compounds existing in nature (mainly plants, but some also exist in animals). They have alkali like properties, so they were called pseudobases in the past.Most of them have complex ring structure, and nitrogen is mostly contained in the ring, with significantbiological activity, is one of the important effective ingredients in Chinese herbal medicine.haveOptical activity。Some nitrogen containing organic compounds that do not contain alkali but come from plants have obvious biological activity, so they are still included in the scope of alkaloids.Some are derived from natural nitrogen-containing organic compounds, such asvitamin、amino acidPeptides are not used to belong to "alkaloids".
There are many kinds of alkaloids known, about 10000 kinds, and some structural formulas have not been completely determined.Their structures are complex and can be divided into 59 types.With the discovery of new alkaloids, the classification will be updated accordingly.As there are many kinds of alkaloids with different structural formulas, their properties will be different.But the alkaloids are nitrogenousOrganic compound, there are always some similar properties, because in its biosynthetic pathwayamino acidIt is the starting material, mainly includingOrnithine、Lysine、Phenylalanine、histidine、TryptophanAnd mainly experienced two reaction types: cyclization reaction and carbon nitrogen bondsplitting, so there are always some similar properties.
Alkaloids have a ring structure and are insoluble in water. They can form salts with acidsoptical rotationAnd absorption spectrum, mostly bitter.It is colorless crystal, and a few are liquid.There are thousands of alkaloids, which are synthesized from different amino acids or their direct derivatives. As one of the secondary metabolites, alkaloids have toxic or strong physiological effects on biological organisms.
Physical and chemical properties
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form
Most alkaloids are crystalline solids;Some are amorphous powders;A few are liquid at room temperature, such asnicotine（Nicotine）、Hemeroine(Coniine), etc.
colour
Generally colorless.Only a few are colored, such asberberine（Berberine）、Magnolia alkaloid（Magnoflorine）、Serpentine(Serpentine), etc. are yellow.
Taste
No matter the alkaloids themselves or their salts, they have a bitter taste, some of which are extremely bitter and spicy, and some of which stimulate the burning sensation of the lips and tongue.
acid-base
Most of them areAlkaline reaction。But there are also neutral reactions, such asColchicine；There are also acidic reactions, such astheophyllineAnd theobromine;There are also sexual reactions, such asmorphine(Morphine) andArecoline（Arecaadine）。
solubility
Most alkaloids are almost insoluble or insoluble in water.Soluble inchloroform、Ether、alcohol、acetone、benzeneAnd other organic solvents.It can also be dissolved in dilute acid aqueous solution to form salts.The salts of alkaloids are mostly soluble in water.However, there are many exceptions, such as Ephedrine, which is soluble in water and organic solvents.Another examplenicotine、Ergometrine(Ergonovine) and others also have greater solubility in water.
optical rotation
Most alkaloids contain asymmetric carbon atoms and are optically active. Most alkaloids are optically left-handed.Only a few alkaloids have asymmetric carbon atoms in their molecules. For example, Narceine has no optical activity.A few alkaloids, such as nicotine and hydrazine, are left handed in neutral solution and right handed in acid solution.
volatility
Most alkaloids are nonvolatile at normal pressure.Direct heating first melts, then decomposes;It may also melt and decompose at the same time.Only under high vacuum can sublimation occur due to heating.However, there are some exceptions, such as ephedrine, which is volatile under normal pressure;caffeineWhen heated to above 180 ℃ under normal pressure, it will sublimate without decomposition.Alkaloids are mostly used for medical treatment and research.A few varieties are used for analysis [such as Bruce's determination of nitrate] or as comparison samples.Alkaloids are generally stable in nature and do not need special storage except for protection from light.
type
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According to the basic structure of alkaloids, they can be divided into about 60 categories.There are mainly the following types:
12. Others, such asGalanthamineTripterygium wilfordii.
Existing form
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1. Free alkali: It is extremely weak and exists in the form of free.
2. Salts: organic acids that form salts with them include citric acid, tartaric acid, etc;Special acids: aconitic acid, chlorogenic acid, etc;Inorganic acid: sulfuric acid, hydrochloric acid, etc.
3. Glycosides: They exist in plants in the form of glycosides.
4. Amides: such as colchicine, camptothecin, etc.
5. N-oxide: There are more than 100 kinds of nitrogen oxides in plants.
In addition, there are aza aldehydes, enamines, imines, etc.
(2) Few alkaloids are distributed inLower plantMedium.
(3) Plants of the same family and genus may contain alkaloids of the same structural type.
(4) Several or dozens of alkaloids coexist in a plant, and their chemical structures are similar.
Chromogenic reaction
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Some alkaloids can react with some reagents to form special colors, called color reaction, which is often used to identify certain alkaloids.However, the color reaction is greatly affected by the purity of alkaloids. The purer the alkaloids are, the more obvious the color is.Common color developing agents include:
1. Ammonium aluminate concentrated sulfuric acid solution (Mandelin reagent) is 1% ammonium aluminate concentrated sulfuric acid solution.If atropine appears red, codeine appears blue, and strychnine appears purple to red.
2. Ammonium molybdate concentrated sulfuric acid solution (Frohde reagent) is 1% sodium molybdate or ammonium molybdate concentrated sulfuric acid solution. If encountering aconitine, it will appear yellow brown, berberine will appear brown green, and atropine will not appear.
3. Formaldehyde concentrated sulfuric acid reagent (Marquis reagent) is a mixed solution of 0.2mL 30% formaldehyde solution and 10mL concentrated sulfuric acid.In case of morphine, it appears orange to purple, and codeine appears red to yellowish brown.
4. If concentrated sulfuric acid encounters aconitine, it will appear purple, berberine will appear green, and atropine will not appear.
5. If concentrated nitric acid meets berberine, it will be brownish red, colchicine will be blue, and caffeine will not be colored.
