What Are the Benefits of Rhodiola Rosea Root?

1 Introduction of Rose Rhodiola

Rhodiola rosea is a perennial herbaceous plant of the genus Rhodiola in the family of Rhodiolaceae, and the height of the plant usually ranges from 10 to 30 cm. The growing environment of Rhodiola rosea is relatively poor, mainly growing in East Asia, Central Asia, Siberia, and North America in high altitude areas of rock crevices or scrub, Rhodiola rosea is mainly distributed in our country in Tibet, Qinghai, and Sichuan and other places [1].

There are more than 90 varieties of Rhodiola rosea, and different varieties of Rhodiola rosea have different uses and values due to the different types and contents of active ingredients. The species that have been reported for medicinal or health care applications are Rhodiola rosea, Rhodiola alpina, Rhodiola rosea, Rhodiola stenopetalum, Rhodiola santa and Rhodiola longifolia, while other species of Rhodiola are not applicable due to the small number of types of active ingredients or the low content of the active ingredient. Among the currently used species, Rhodiola rosea has received widespread attention for the presence of the specific active ingredient “total loserine”, which is not present in other species or is present in very low levels, and has the highest medicinal and economic value[2] .

Rhodiola rosea has a long history of medicinal use, as recorded in many ancient medical books[2] . Throughout the history of China, people often used Rhodiola rosea as a tonic to strengthen the body, eliminate the fatigue caused by physical labor and resist the adverse effects of the alpine zone, as well as for the treatment of related diseases[3]. Rhodiola rosea not only has a profound medicinal history in China, but also has a long history of research and application in Europe. As early as 1755, Rhodiola rosea was included in the Swedish Pharmacopoeia, and it was often used by Vikings to strengthen their resistance.

In the 1960s, scientists in the Soviet Union discovered that rhodiola rosea was a metabolic regulator that could enhance the immune system, improve the ability of organisms to adapt to environmental damage, and restore the organism from disorders to normal. It is found that these medicinal functions are closely related to the fact that Rhodiola rosea contains total colchicine, and it is proposed that total colchicine is a unique active ingredient of Rhodiola rosea, which is why it is used as a health care product for astronauts and athletes to combat fatigue and enhance their ability to adapt to the environment. China's research on Rhodiola rosea started in the 1980s. In recent years, domestic and foreign research on Rhodiola rosea has been gradually deepened, and there are competitions in the development of Rhodiola rosea-related medicines, health care products and cosmetics, and teas, medicinal wines, medicinal porridges, and dishes made from Rhodiola rosea have been regarded as the best products for health care and keeping in good health[3] .

2 Medicinal active ingredients of Rhodiola rosea extract

Studies have shown that the medicinal active ingredients of Rhodiola rosea mainly come from its roots and stems, and the ingredients and contents of the extracts from different origins are different. The main chemical components of Rhodiola rosea extracts include glycosides, flavonoids, polysaccharides, phenylpropanoids, coumarins, volatile oils and organic acids[4] (Figure 1). Glycosides include Rhodiola rosea glycosides, glycoside tyrosol, etc. Flavonoids include quercetin and kaempferol, etc. Polysaccharides include L-arabinose, L-rhamnose, D-glucose, etc. Coumarins include coumarin, 7-hydroxycoumarin, scopoletin, etc. Volatile oils include geraniol, n-octanol, etc. Organic acids include gallic acid, myristic acid, etc. Ursolic acid, etc. The volatile oils of the plant are also included in the list, Organic acids include gallic acid, myristic acid, ursolic acid and so on. Besides, the extract also contains starch, protein, fat, pectin and essential amino acids, inorganic elements and vitamins[5] . The most important active ingredients in Rhodiola rosea extracts are rhodiola rosea glycosides and glycosides and phenylpropanoid compounds, among which the phenylpropanoid compounds, Rosavin, Rosarin and Rosin (collectively referred to as total Rosavin, Rosavins) are active substances unique to Rhodiola rosea (Fig. 1), which are not present or are present in very low amounts in other species of Rhodiola rosea. Other species of Rhodiola contain no or very low levels. It was found that Rosavin is an important active substance in Rhodiola rosea, and the content of Rosavin is currently used as an indicator substance for evaluating the quality of Rhodiola rosea extracts.

3 Pharmacological benefits of the medicinal active ingredients of rose rhodiola rosea extract

3.1 Anti-fatigue activity

Fatigue is considered to be an important indicator of the decline of health and human body functions. After a long period of continuous work with high intensity or long hours, the human body will experience a state of fatigue such as weakness, sluggishness of thinking and irritability, which will cause a series of damages to the body if it is not effectively relieved for a long time. The mechanism of fatigue there are three main theories: (1) “energy failure theory” [6] that the human liver and muscle tissue in the important energy substance glycogen in the human prolonged exercise continues to depletion, resulting in a decrease in the concentration of plasma glucose, which in turn promotes protein degradation, generating more blood urea nitrogen, plasma free fatty acid levels rise, leading to exercise and fatigue.

The increase in plasma free fatty acid level leads to insufficient supply of energy to the exercising muscles, resulting in a decrease in work capacity; (2) “Metabolite accumulation theory” [7] believes that the accumulation of energy metabolite phosphoric acid compounds in the body and the lowering of pH in the body caused by lactic acid produced by anaerobic cellular respiration during strenuous exercise lead to metabolic disorders in the human body and cause fatigue; (3) “Central fatigue” [8] believes that the decrease in the concentration of plasma glucose leads to the decrease in the concentration of plasma glucose, which promotes the decomposition of protein, producing more blood ureaurea nitrogen and plasma free fatty acid. (3) “central fatigue theory” that the brain serotonin, dopamine, acetylcholine concentration imbalance during prolonged exercise, affecting the central nervous system's ability to process information, reducing muscle coordination, leading to a decline in the body's ability to exercise, resulting in a sense of fatigue [8].

Ma Li [9] and Wang Hongxin [10] demonstrated that rhodiola rosea rosea glycosides and loserine could significantly prolong the exhaustion swimming time of mice, which proved that these two active ingredients could alleviate the fatigue symptoms of mice. Among them, rhodiola rosea glycosides can affect the metabolism of sugar, fat and amino acid in mice after prolonged exercise. Losevi can improve the symptoms of hypoglycemia by maintaining the content of glycogen, increase the amount of hemoglobin, and enhance the exercise load capacity of mice by inhibiting the increase of blood urea nitrogen and the production of blood lactic acid, and its effect of relieving physical fatigue is more obvious than that of rhodiola rosea. In addition to rhodiola rosea and loserine, Guo Changjiang's research team [11] demonstrated that quercetin can reduce fatigue by improving energy metabolism through the protection of muscle mitochondrial function in mice.

3.2 Antihypoxic activity

Hypoxia is a state caused by the inability of the tissues to receive sufficient oxygen supply or sufficient oxygen supply, which results in a decrease in the body's ability to utilize oxygen. Hypoxia induces apoptosis, pulmonary hypertension, and in severe cases, brain cell energy metabolism disorders, nerve cell damage and other symptoms [12]. Hypoxia increases the NO content in the body and reacts with oxygen radicals to form more toxic groups, resulting in a cascade reaction leading to brain tissue pathology and brain dysfunction. The contractile function of the heart decreases during hypoxia and reperfusion myocardial injury occurs as a consequence.

Jin Xuelian research team [13] demonstrated that rhodiola rosea glycosides can significantly prolong the survival time of mice under hyperbaric and normobaric hypoxia, and the survival time of mice with atopic myocardial hypoxia and nitrite poisoning. Wang Jun's research team [14] found that Rhodiola rosea glycosides can increase the content of intracellular ATP by increasing the expression of P13K, HK and GLUT-1 genes, thus counteracting the decline in metabolic capacity of the body caused by hypoxia. Luo Dingqiang's research team [15] found that flavonoids have the efficacy of scavenging free radicals, thus reducing myocardial oxygen consumption, accelerating lactate and aerobic metabolism, and improving the symptoms of fatigue and hypoxia in mice.

3.3 Antioxidant and aging activity

Free radicals with high reactivity are formed during metabolism[16] , which can react with other organic compounds produced in the body to cause nucleic acid damage and changes, lipid peroxidation and biofilm damage, skin wrinkles caused by collagen cross-linking, apoptosis and oxidative damage to mitochondria, resulting in aging and various organ or tissue lesions, etc. In addition, the human superoxide dismutase (SD) activity in the body can reduce cardiac oxygen consumption, accelerate lactate and oxygen metabolism, and improve fatigue hypoxia in mice. Superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) are capable of scavenging free radicals in a timely manner[17] , while malondialdehyde (MDA), a lipid peroxidation product, can affect normal cellular metabolism and accelerate human aging. Therefore, SOD, GSH-Px and MDA are currently used as indicators of human aging.

The o-diphenol hydroxyl group in the molecular structure of quercetin has strong antioxidant activity because it can form intramolecular hydrogen bonds with free radicals generated in the body and form a more stable benzoquinone due to resonance[18] . Wu Jiu-hong's research team[19] demonstrated that eight compounds including rutinoside, isoquercitrin, rhodiola rosea glycoside and loserine contained in Rhodiola rosea have obvious antioxidant activities, and the structure and number of hydroxyl groups in the molecular structure determine the strength of their antioxidant properties. Ye Gang's research team[20] found that SOD and GSH-Px activities increased and MDA content decreased in aged mice after administration of Rhodiola rosea extracts. Fan Guiqiang's research team[21] found that the antioxidant property of Rhodiola rosea extract was much stronger than that of Rhodiola rosea glucoside, indicating that Rhodiola rosea extract also contains other leading antioxidant active ingredients.

3.4 Prevention of cardiovascular diseases

In recent years, due to unhealthy diet and irregular work and rest and other reasons, so that China's cardiovascular morbidity is increasing year by year, rose rhodiola rosea extract can effectively promote the metabolism of cholesterol and other lipids in the human body, and by impeding the aggregation of platelets to prevent thrombosis, at the same time rose rhodiola rosea can also reduce the viscosity of the blood to improve blood circulation, so as to reduce myocardial ischemia and hypoxia caused by the degree of damage to treat acute myocardial infarction, inhibit atherosclerosis, and improve blood circulation.  It can reduce the damage caused by myocardial ischemia and hypoxia, treat acute myocardial infarction, inhibit atherosclerosis, and improve the symptoms of hypertension[22] .

Cao Xuebin's research group[23] found that the area of cardiac ischemia and hypoxia in rats injected with rhodiola rosea glycosides was smaller after exhaustive exercise, and that rhodiola rosea glycosides decreased the apoptosis rate of cardiomyocytes by decreasing pro-apoptotic proteins, such as aspartic acid protein hydrolase, and by increasing the expression of anti-apoptotic proteins, such as B-lymphotropic cytosolic cell-2. Yugang Gao and Lianxue Zhang[24] found that the serum levels of total cholesterol, triglycerides, low-density lipoprotein (LDL), which are representative of hyperlipidemia, were reduced, and the levels of beneficial high-density lipoprotein (HDL) were significantly increased in hyperlipidemic mice under the effect of Rhodiola rosea extract.  

3.5 Nervous System Regulation

Rhodiola rosea can play an active role in protecting human nerve cells, promoting nerve cell growth, regulating central neurotransmitters, improving agitation and depression, improving sleep quality, concentration and memory[25] , and treating neurological diseases such as Parkinson's disease and Alzheimer's disease. Glutamine is a transmitter involved in the transmission of messages in the nervous system, but in excess, it can cause damage to neurons. Ding Fei research team[26] found that Rhodiola rosea extract can significantly improve glutamate-induced intracellular Ca2+ overload, reduce the activity of apoptosis-expressed protein caspase-3, and enhance the activity of hippocampal neurons after glutamate injury. Hong Gui Zhu research group[27] found that rhodiola rosea glycosides can promote the expression of NRF-2, HO-1 and other related proteins, of which NRF-2 protein is a regulator of cellular defense-related active enzyme gene expression, the active enzyme on the HO-1 protein catalyzes the body's hemoglobin production of free radical scavengers, thus rhodiola rosea glycosides can reduce the damage of nerve function.

3. 6 Anti-tumor effect

Tumor is one of the diseases that endanger human health, rhodiola rosea can enhance the anti-tumor ability of human body by enhancing the value-added transformation of immune cells and the phagocytosis of leukocytes[28] . Zhang Min's research team[29] found that after injection of Rhodiola rosea ethanol extract into Lewis lung cancer mice, the number of CD4+ type helper T cells and CD8+ cytotoxic T lymphocytes with antitumor effect increased, the killing activity was enhanced, the content of interleukin-2 and γ-interferon in the serum, which are used to regulate the cellular immunity, increased, and the growth rate of tumors also increased due to the effects of T-2, which is used to promote tumor growth, on the body under the effect of Rhodiola rosea. The rate of tumor growth was also reduced due to the decrease in the number of T-lymphocytes that promote tumor growth under the effect of Rhodiola rosea. Rhodiola rosea extract can also achieve anti-tumor effects by acting on the growth cycle of tumor cells and inducing their apoptosis. Li Huixin's research team[30] concluded that rhodiola rosea glycosides can significantly reduce the expression of c y clinB1, Cdc2, CDK2 and c y clinA, which are proteins related to human cervical squamous carcinoma cell cycle, and cause the proliferation of tumor cells to be blocked in the G2/M and S phases, respectively.

3.7 Anti-radiation effects

Radiation can lead to molecular denaturation by breaking the chemical bonds of biomolecules in the human body, resulting in the generation of a large number of oxygen radicals, causing DNA damage in the body, leading to the destruction of proteins, resulting in mutations in tissues and cells, cancer and inactivation of biologically active enzymes[31] , which in turn cause damage to tissues and organs of the human body, inducing disorders of metabolism and other systemic functions, and causing great harm to the human body's health. This can cause great harm to human health.

Wu Jiuhong Research Group[32] found that isoquercitrin, tyrosol, lorcaserin, arbutin and loserine in Rhodiola rosea extracts significantly increased the proliferative activity of human lymphoblastoid cell lines injured by primary exposure to 10Gy60 Co gamma radiation, and the strongest antiradiation effect was found in loserine at a concentration of 25 μg/mL. Liu Jexiu's research team[33] found that rhodiola rosea glycosides could reduce the activity of endothelial progenitor cells under 4Gy60 Coγ radiation by enhancing the expression of p-Akt protein in endothelial progenitor cells, increase the adhesion and migration ability of radiation-damaged endothelial progenitor cells, and reduce the number of cellular apoptosis under irradiation. Shi Fei Research Group[34] demonstrated that the disintegration and degranulation of fibroblasts cultured in Rhodiola rosea at concentrations above 200 μg/mL were reduced by UV radiation, and that the survival rate of the cells was positively correlated with the concentration of Rhodiola rosea added to the culture medium.

4 Rose Rhodiola rosea active ingredient extraction method

4.1 Alcohol extraction

Alcohol extraction[35] is a traditional method of extracting active ingredients from plants, and its principle is to extract the active ingredients from plant tissues by leaching with the solvent ethanol. The ethanol extraction method can be subdivided into percolation, maceration, dissolution and dilution, with percolation being the most popular method. The ethanol extraction of Rhodiola rosea has the advantages of safety, non-toxicity and low cost, but the extraction rate is low, more impurities are leached out, and there are also the disadvantages of complicated and time-consuming operation.

4.2 Enzymatic method

Enzymatic digestion[36] is a method that uses specific enzymes to break down and destroy plant cellular tissues and reduce the resistance of the active ingredients to be released outside the cell wall, thus shortening the extraction time, increasing the utilization of raw materials and reducing the leaching of impurities without changing the chemical structure and biological activity of the natural products, but the enzymes have to be used in an environment with controlled temperature and pH in order to maximize the activity of the enzymes, and it may be relatively time-consuming. Yanli Dong's research team[37] showed that the factors affecting the yield of the enzymatic method were, in descending order, enzymatic temperature, pH of the extraction solution, extraction time, and the proportion of the enzyme added to the fibrillinase. Guo Jianpeng Research Group[38] proved that the cellulase ratio of 1.75% and 65 ℃ were the best conditions for enzymatic extraction, and the yield of rhodiola rosea glycosides was 1.66 times higher than that of the aqueous extraction method.

4.3 Microwave-assisted extraction

Microwave-assisted extraction method[39] is the use of different molecules due to the different rotation frequency and absorption of different frequencies of microwaves, and changes in the direction of the external electric field occurs when the direction of the molecular spin reversal, the friction and collision between the molecules generated by the heat selective heating of the extraction of certain substances to promote the extraction of substances and the separation of the principle of the system.

This method is widely used in the industrial production of rhodiola rosea glycosides because of its advantages of environmental protection, high product purity, short extraction time and high solvent selectivity. Xiang Feijun research team[40] used the results of single factor as a reference, and then combined with the results of orthogonal experiments, from the perspective of industrial production efficiency to 10 times the amount of water as a solvent to extract Rhodiola rosea glycosides, set the microwave extraction power of 463 W, select the raw material particle size of 50 mesh sieve and the volume ratio of the material to liquid ratio of 1:10, soak herbs in advance for 1.5h, and extracted in three times for 90s each time, the extraction of Rhodiola rosea glycosides efficiency reached the highest. At this time, the efficiency of extracting Rhodiola rosea glucoside was maximized. Xue Changhui research team[41] found that with the increase of extraction time, ethanol concentration and microwave power, the extraction efficiency increased and then decreased, the extraction efficiency reached the peak under the conditions of heating time of 4 min, 70% ethanol as the extracting solution and 600 W microwave power, the extraction efficiency increased slowly after 80 ℃ and thus set the optimal extraction temperature at 80 ℃, and finally determined the optimal material-liquid volume ratio of 1:40 by comparison, and the extraction efficiency reached the highest at the time of extraction. Finally, the optimal volume ratio was determined to be 1:40, and the extraction rate of flavonoids reached 2.68% under the above conditions.

Sun Ping et al [42] used Rhodiola rosea as raw material for the extraction of Rhodiola rosea polysaccharides, the use of microwave reactor at 400 W power conditions, the use of petroleum ether, ethyl ether and 80% of ethanol for reflux pre-treatment, and then in 560 W power water reflux extraction, and finally the extracted liquid is concentrated, decolorized, and added to 95% ethanol starching, static filtration, to get the Rhodiola rosea polysaccharide extract, measured polysaccharide content in the extract was 2.68%, and the extraction rate of flavonoids reached 2.68%. After static filtration, Rhodiola rosea polysaccharide extract was obtained, and the polysaccharide content in the extract was measured as 3.9%.

4.4 Supercritical fluid extraction method

Supercritical fluid extraction[43] is a separation technique that uses supercritical fluids to dissolve and separate extracts in a supercritical state, and then analyzes the extracts by adjusting the pressure or temperature. It is suitable for extracting substances with poor thermal stability, and has the advantages of high extraction efficiency, high safety, green and harmless, and low cost. Wang Dan's research team[44] found that the increase in extraction pressure has been positively promoting the extraction rate of rhodiola rosea glycosides, and the optimal extraction pressure was selected as 40 MPa in consideration of the conditional efficacy, and the extraction rate first increased and then decreased with the increase in extraction temperature. The extraction temperature was set at 55 ℃, and the higher the mass fraction of ethanol, the higher the extraction rate. Therefore, anhydrous ethanol was used as the entraining agent, and the extraction rate of rhodiola rosea was maximized after 5 h of extraction. Dey research team[45] found that the use of pure water as a cosolvent can increase the yield, because water can interact with the polar groups in the lignin and cellulose in the herb by hydrogen bonding, at the same time, water can increase the bulk density of the fluid mixture so that the lignin and cellulose in the herb can be softened and expanded, which is conducive to the penetration of CO2, at a temperature of 80 ℃ extraction for 5h can be obtained with a recovery rate of 4.5% of the lignin and cellulose in the herb.

4. 5 Ultra-high-pressure extraction technology

Ultra-high pressure extraction technology[46] is a solvent in ultra-high pressure under the action of rapid penetration into the plant cells to fully dissolve the active ingredients, after the pressure is removed, in the plant cells inside and outside of the role of the pressure difference, the active ingredients with the solution quickly diffuse to the plant periphery technology. This technique has the advantages of low solvent consumption, short extraction time, low extraction temperature and good stability of the extract, and is suitable for the extraction of small molecules. The maximum extraction rate of 9.29 mg/g of tyrosol was obtained by using 73.3% ethanol and a liquid-solid ratio of 29.5 mL/g for 2 min at 255.5 MPa using the star-point design-area of effect (AoE) method by Xinxin Yin's research group[47] . Liu Changjiao's research team[48] found that the total flavonoids extracted by this technique were higher than those extracted by ultrasonic extraction, refluxing and immersion, and the extraction time was shorter than that by 57, 117, and 77 min, respectively, which further confirmed the advantages of the UHP extraction method.

4.6 Ultrasonic wall-breaking extraction method

Ultrasonic wall-breaking extraction method[49] is the use of ultrasound cavitation effect, mechanical vibration, thermal effects, etc. to make plant cells rupture and increase the frequency and speed of molecular movement, thereby accelerating the target components into the solvent method. The extraction rate of target analytes can be improved by using ionic liquids instead of traditional organic solvents to extract the active substances of natural products. Wang Hongxin's research team[49] found that imidazolium ionic liquids containing bromine ions have a strong ability to dissolve fibrillin and destroy cell walls, and that the glycosyl and tyrosol molecules of Rhodiola rosea contain negative charges at both ends, which can act as nucleophilic sites to interact electrostatically with imidazolium rings. Compared with the traditional ethanol extraction method, the yields of Rhodiola rosea and Tyrosol extracted by brominated 1-octyl-3-methyl imidazole as solvent were increased by 31.8% and 4.06% respectively.

5 Synthesis method of effective components of Rhodiola rosea

The research on the synthesis method of Rhodiola rosea active ingredients mainly focuses on the efficient synthesis of Rhodiola rosea glycosides and total loserine, and the synthesis method is mainly chemical synthesis, while there are also a small number of reports on biosynthesis methods. At present, the chemical synthesis of rhodiola rosea glycosides is relatively mature, and the scale of synthesis can be above the kilogram level, but the chemical synthesis and biosynthesis of total loserivi (Rosavin, Rosarin and Rosin) are less studied. The chemical synthesis of Rosavin has the disadvantages of long process route, complicated operation, low overall yield and difficult purification. The biosynthesis has the disadvantages of small amount of synthesis and no mass production, therefore, the research on the synthesis method of total loserine needs to be further deepened.

5. 1 Rhodiola rosea glycoside chemical synthesis method

In the 1980s, the research team of Ming Haiquan and Ji Shufang[50] used p-amino-phenethyl alcohol 1 as the starting material, and obtained diazonium salt intermediate 2 by diazotization reaction, and then hydrolyzed to produce p-hydroxyphenethyl alcohol3 . Then, p-hydroxyphenethyl alcohol 3 was hydrolyzed to obtain p-hydroxyphenethyl alcohol 3. Then, in anhydrous ether solution, silver carbonate was used as a promoter, and tetraacylglucopyranose bromide 4 was reacted to obtain glycosidized intermediate 5, and finally rhodiola rosea glycoside was obtained by removing the acetyl protecting group under the action of sodium methanol (Scheme 1). This route is not suitable for industrial production because the phenolic hydroxyl group of hydroxyphenylethanol 3 is not protected during the reaction, resulting in a low reaction yield, and because of the danger of preparing diazonium salts.

In 1996, Li Guoqing's research team[51] used p-hydroxyphenylacetic acid ethyl ester 6 as the starting material, and firstly protected its phenolic hydroxyl group to produce p-benzyloxyphenylacetic acid ethyl ester 7, and then reduced with lithium aluminium hydride to obtain p-benzyloxyphenylethanol 8, and then reacted with bromotetracosanol glucose 4 to obtain the glucosidylated product 9 by the reaction of compound 8 with silver carbonate, and then the product was deacylated under the action of sodium methanol to obtain the precursor compound of Rhodiola rosea. Then the product was deacetylated under the action of sodium methanol to obtain Rhodiola rosea glycoside precursor compound 10, and the Rhodiola rosea glycoside was further obtained by debenzylation reaction catalyzed by palladium carbonate, and the total yield of the reaction was 56% (Scheme 2).

Zhang Sanqi research group[52] used p-bromophenol as the starting material, firstly, the phenolic hydroxyl group of p-bromophenol 11 was protected by aryl ether to obtain compound 12, and then Grignard reaction with ethylene oxide to obtain intermediate 13, and then reacted with bromotetraacylglucose 4 to obtain glycosidized product 14, and then stripped off the acetyl and aryl groups to obtain rhododendron glycoside in turn. This synthetic route is due to the fact that the synthesizing steps are not easy to accomplish. This synthetic route is not suitable for industrial production due to the many synthetic steps and inconvenient operation, and the cost of preparation is also higher due to the use of a precious metal palladium catalyst in the reaction (Scheme 3).

Sun Xiaomei's research team[53] used p-hydroxyphenylacetic acid 16 as the starting material, and firstly acetylated the phenolic hydroxyl group to protect the compound 17, and then reduced the carboxyl group to the alcoholic hydroxyl group by sodium borohydride to obtain p-acetoxyphenylethanol 18, and then the synthesis method was consistent with that of Zhang Sanqi's research team, and finally deacetylated to obtain rhodiola rosea. This method has a short reaction step and a certain potential for industrialization, but in the reduction of carboxyl group to hydroxyl group, iodine monomer was used in the reduction reaction of sodium borohydride, which is hazardous due to the large amount of borane produced in the process and the large amount of waste liquid after the reaction (Scheme 4).

In 2013, Wang Yang's research team[54] used full acetyl glucose 20 as the starting material, which was catalyzed by anhydrous SnCl4 to directly react with hydroxyphenethyl alcohol 21 to produce glycosidized product 22 under the condition of molecular sieve, and then removed the acetyl group to obtain rhodiola rosea glycoside. Compared with the previous synthesis method, this method is more concise, and avoids the use of expensive silver carbonate and the complicated reduction reaction, which makes the reaction safer and cheaper, but the use of stannous tetrachloride as the catalyst in the reaction will cause greater environmental pollution and the problem of heavy metal ions in the product, so there is still room for further improvement of this synthesis method.  Therefore, there is still room for further improvement of this synthesis method (Scheme 5).

In 2015, Guo Jianfeng's research team[55] used glucose 23 as the starting material and reacted it with isobutyryl chloride to obtain fully isobutyryl-protected glucose 24, and then reacted it with trifluoroacetic anhydride under the action of a boron trifluoride catalyst to obtain the sugar donor 25, which reacted with benzyl-protected p-hydroxyphenylethanol under the catalyst of boron trifluoride to produce glycosidic acid 27, and then reacted with sodium methanol to form the glycosidic acid 27, and then reacted with sodium methanol to form a glycosidic acid 27, and then reacted with sodium methanol to form a glycosidic acid 27. Glycosidization of compound 25 with benzyl-protected p-hydroxyphenethyl alcohol 26 catalyzed by boron trifluoride resulted in the glycosidized product 27, and the isobutyryl-protecting group was finally removed to produce rhodioloside under the action of sodium methanol, with an overall yield of 55% (Scheme 6). This strategy avoids the use of metal catalysts and provides a simple synthesis route with high overall yields. The solvent and the by-product, isobutyric acid, can be recycled and has the potential for industrial scale-up.

5.2 Enzymatic synthesis of rhodiola rosea glycosides

The biosynthesis of rhodiola rosea glucoside consists of two steps, namely the biosynthesis of tyrosol and the synthesis of rhodiola rosea glucoside from glucose uridine diphosphate and tyrosol catalyzed by glycosidases[56] . Biological enzyme synthesis is much simpler than chemical synthesis in the overall synthesis route, there is no protection and deprotection of functional groups, and there is no problem of environmental pollution, but the biggest difficulty in the enzymatic synthesis of rhodiola rosea is the industrial scale-up, the preparation of small quantities, the reaction cycle is long, and the cost of enzyme production is high, and there is the problem of inactivation of enzyme, which are factors that limit the popularization and use of the rhodiola rosea glucoside biosynthetic enzyme technology [57]. These factors have limited the promotion and use of rhodioloside bioenzymatic synthesis technology.

The research team of Yanfang Li and Younian Wang[57] demonstrated that tyrosine decarboxylase could regulate the synthesis of tyrosol and rhodiol glycosides, and tyrosine was the best substrate for the recombinant encoded tyrosine decarboxylase, and its overexpression significantly increased the content of tyrosol and rhodiol glycosides. Wei Shenghua's research team[58] produced β-glucose nanogel by aqueous in situ polymerization, and rhodiola rosea glucoside was obtained after 96h of enzymatic reaction in tert-butanol system with 5% water content, and the yield could reach 23.7%, and the maximal concentration of the product was 71.13 mmol/L. Wang Mengliang's research team[59] also synthesized tyrosine, which was the best substrate for recombinant encoded tyrosine decarboxylase, and its overexpression significantly increased the content of tyrosol and rhodiola glucoside. Wang Mengliang's research team[59-60] found that β-glucosidase can effectively help the enzyme and the substrate to fully fit under the polarity of ionic liquid, and better play the catalytic function of the enzyme, and the enzyme can be reused in ionic liquid solvent, which can effectively reduce the cost of the biosynthesis of rhodiola rosea.

5.3 Chemical synthesis of Rosavin and Rosin

In 2006, Kuchin et al.[61] reported a method for the synthesis of Rosavin (Scheme 7), in which the researchers used 1-bromo fully acetylated arabinopyranose 28 as the sugar donor, and prepared the disaccharide intermediate 30 by Koenigs-Knorr reaction with hydroxyl-protected glucose 29, and then prepared the thioether 31 from its C-1 position, and then reacted it with cinnamyl alcohol under the action of iodine monomers. The C-1 position was then prepared as a thioether 31 and reacted with cinnamyl alcohol in the presence of iodine monomers to obtain the Rosavin precursor, which was finally stripped of its acetyl protecting group. This strategy uses silver perchlorate as a catalyst for the preparation of disaccharide 30, which is relatively expensive and needs to be used in quantity. In addition, the preparation of sugar-sulphide requires the use of methyl mercaptan, which is a toxic and unpleasant reagent, and more importantly, the yield of iodine monomer-catalyzed preparation of Rosavin is extremely low, so the method is not of practical production significance.

In 2007, Akita systematically described the biosynthesis of a series of naturally occurring β-glucosidated products catalyzed by β-glucosidase using D-glucose 23 as a substrate[62] , which was inefficient, taking 4-7 days to complete the reaction and yielding only 8% of Rosin. The authors used this method to synthesize the sugar C-1 allylated β-glucosidated product 33 in 68% yield, and used compound 33 as the starting material to obtain Rosavin (Scheme 8) by constructing the glycosidic bond through the Koenigs-Knorr method and the Mizoroki-Heck reaction using the Linear Synthesis strategy. Rosavin was synthesized by Koenigs-Knorr method and Mizoroki-Heck reaction to construct glycosidic bonds (Scheme 8).

The authors first protected the hydroxyl group of glucoside compound 33 by a two-step reaction to obtain compound 34, then hydrolyzed the hydroxyl group at C-6 position by hydrolysis with hydrochloric acid to obtain compound 35, which was glycosidized with 1-bromophenylbenzyl-protected arabinopyranose 36 to obtain the disaccharide compound 37, and then reacted with phenylboronic acid 38 by a palladium catalyst to obtain Rosa-virgina (Scheme 8). The Mizoroki-Heck reaction with phenylboronic acid 38 in the presence of a palladium catalyst gave the Rosa-vin precursor compound 39, and the final product Rosavin was obtained by removing the hydroxyl protecting group under alkaline conditions. This reaction strategy uses expensive silver trifluoromethanesulfonate for glycosidic bonding and palladium acetate for catalyzing the Mizoroki-Heck reaction, in which the silver trifluoromethanesulfonate needs to be used in equivalent amounts, so the reaction is very costly and prone to heavy-metal residues in the product.

In 2009, Hui-Yong-Jung et al.[63-64] published a method for the synthesis of Rosa-vin, which still used a linear convergent synthesis strategy. In this strategy, arabinose 40 was used as the starting material, and the hydroxyl group was first acetylated to obtain the sugar donor 41, then glycosidized with the hydroxyl-protected glucose donor 43 to obtain disaccharide 44, which was modified to the trichloroacetimidate disaccharide donor 45, and then reacted with cinnamyl alcohol 46 to obtain the precursor 47, and the hydroxyl-protecting group was removed to obtain the precursor 47, which was used to synthesize the rosavin (Scheme 9), which was then modified with a linear convergent strategy. Rosavin (Scheme 9).

In this method, the reaction yield is greatly reduced when the disaccharide 44 is formed and then prepared into the sugar donor 45, and it is difficult to prepare the desired disaccharide donor 45 using this strategy for the preparation of Ro-savin. In addition, the linear synthesis strategy inherently suffers from a gradual decrease in yield, especially when one of the reaction steps becomes the yield-limiting step, the overall yield decreases significantly, thus making this synthesis strategy less promising for the preparation of large quantities of Rosavin.

5.4 Rosin biosynthesis

In 2017, Liu et al[65] reported a method to produce Rosin in E. coli via a biosynthetic route (Scheme 10). The researchers first constructed a biosynthetic pathway in recombinant E. coli for the synthesis of the glycosyl ligand cinnamyl alcohol from phenylalanine, and then introduced the UGT gene derived from Rhodiola rosea (UGT73B6) into recombinant E. coli, where UDP-glucose and cinnamyl alcohol were used to produce Rosin under the action of glucuronidotransferase. In this report, only the biosynthesis of Rosin was realized, but it was not possible to mass produce it, and it has no production value.

6 Conclusion

Rhodiola rosea contains a large number of medicinal active ingredients, which is a precious natural medicinal resource. Its active ingredients have the effects of eliminating fatigue, relieving hypoxia, antioxidant, anti-aging, etc. They can also help to improve cardiovascular function, protect the nervous system, and have the effects of anti-tumor and anti-radiation, which has a wide range of medical and health care applications. The unique component of Rhodiola rosea, Total Loxevir, is recognized as an ideal anti-fatigue healthcare drug due to its obvious fatigue-relieving and antidepressant effects and no toxic side effects.

At present, the market demand for Rhodiola rosea is increasing day by day, but because of the harsh growing environment of Rhodiola rosea, the plant has a long growth cycle and the production is very limited, making Rhodiola rosea a scarce natural plant resource. In the future, the research of Rhodiola rosea will be centered on the following aspects: (1) further in-depth research on the application of Rhodiola rosea in the field of medicine and health care products, so as to expand the application fields of Rhodiola rosea; (2) strengthen the research on chemical synthesis and biosynthesis methods of the active ingredients of Rhodiola rosea to ensure the effective supply of Rhodiola rosea resources; (3) in-depth research on the pharmacological activity of the active ingredients of Rhodiola rosea, in order to provide a comprehensive utilization of the Rhodiola rosea. (3) In-depth study on the pharmacological activity of active ingredients of Rhodiola rosea to provide theoretical basis for the comprehensive utilization of Rhodiola rosea. The comprehensive utilization of Rhodiola rosea will certainly usher in greater development with the in-depth research in the future.

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