. Saponins are widely distributed in terrestrial plants, with a small amount in marine organisms such as sponges, starfish and corals [1]. Saponins can be divided into triterpenoids and steroidal saponins according to their aglycone carbon skeleton structure. Triterpenoid saponins are widely distributed in Leguminosae (liquorice, astragalus, etc.), Araliaceae (ginseng, Panax notoginseng, etc.), platycodonaceae (Platycodon, etc.), Polygalaceae (Polygala, etc.), Umbelliferae (bupleurum, etc.) and Caryophyllaceae; Steroidal saponins are mostly distributed in Liliaceae (Anemarrhena asphodeloides, Paris polyphylla, etc.), dioscoreaceae (Dioscorea, etc.) and Scrophulariaceae. Saponins widely exist in traditional Chinese medicine and have biological activities such as antitumor, antiviral, anti-inflammatory, antibacterial, antipyretic and sedative [2].
Unlike other natural products such as alkaloids and flavonoids, the bioavailability of saponin prototype components is relatively low after oral administration, but secondary saponins and aglycones with relatively high bioavailability can be obtained through biotransformation, and their biological activities are enhanced. Studies have found that the pharmacodynamic activity of ginsenosides is related to the number of glycosyls of ginsenosides. For example, rare ginsenosides have higher pharmacological activity and better pharmacokinetic properties than prototypical ginsenosides [3-4]. Rare ginsenosides and ginsenosides have the same mother nucleus structure, but the number of glycosyls is different, indicating that modifying the glycosyl part of saponin molecules is of great significance to improve its pharmacological activity and bioavailability.
Natural saponins can be hydrolyzed to obtain secondary saponins and their derivatives, aglycones. Common methods include physical (heating), chemical (acid, alkali hydrolysis) and biotransformation. Biotransformation includes intestinal flora transformation, microbial transformation and in vitro enzyme catalysis. Acid hydrolysis reaction conditions are violent, which easily causes structural changes such as dehydration, double bond shift and cyclization of aglycones [5-6], and cannot control the selective hydrolysis of glycosyl. In addition, there are many side reaction products in the method of hydrolyzing saponins with acid and alkali, and the hydrolysates still need further treatment.
Therefore, in recent years, the research on the transformation of saponins into secondary saponins and aglycones mainly focuses on the field of biotransformation. Due to its mild reaction conditions and stronger positional selectivity and stereoselectivity, it is widely used in research and production. The main reaction types of biotransformation include glycosyl hydrolysis reaction, redox reaction, hydroxylation and break rearrangement reaction [7-8], among which glycosyl hydrolysis reaction is the most widely used. In this paper, combined with the research results at home and abroad in recent years, the literature on the hydrolysis of glycosyl by biotransformation of different types of saponin compounds was sorted out, providing ideas and references for the subsequent research on the research and development and utilization of saponin oriented modified glycosyl.
Biopurify technology can help customers customize the biotransformation services of specified saponins, including but not limited toSaponin components are transformed into secondary saponins and aglycones, or some structural modifications are made.
1 biotransformation of triterpenoid saponins
1.1 tetracyclic triterpenoids
1.1.1 ginsenosides
Ginsenosides can be divided into dammarane, octreol and oleanane types according to their aglycone skeleton. Most of the ginsenosides belong to dammarane type in their parent nuclear structure [9] and are the main active ingredients of ginseng. According to the different positions of aglycone hydroxyl groups, dammarane ginsenosides are further divided into protopanaxadiol (PPD) and protopanaxatriol (ppt) types. The glycosyl of PPD ginsenosides is located at the C-3 and C-20 positions of dammarane, and the glycosyl of PPT ginsenosides is located at the C-6 and C-20 positions [10].
. In contrast, secondary ginsenosides F2, CK, Rg3, and Rh2 account for less than 0.1% of total ginsenosides [13]. According to the comprehensive literature analysis, the glycosyl hydrolysis reaction of ginsenosides mainly occurs at C-3, C-6 and C-20 positions, hydrolyzing and removing glucosyl, rhamnosyl, furan arabinose and pyran arabinose. The main metabolic pathway of ginsenosides in vivo is step-by-step deglycosylation. PPD ginsenosides Rd, F2, Rg3, CK, Rh2 were incubated with human intestinal flora in vitro. It was found that the main transformation products of ginsenoside RD were ginsenoside F2, Rg3, Rh2, CK and PPD; Ginsenoside F2 was mainly transformed into ginsenoside compound K and PPD; The main transformation products of Ginsenoside Rg3 are ginsenoside Rh2 and PPD; And ginsenoside Rh2 and ginsenoside compound K can generate ppd[14-15].
The hydrolysis of ginsenoside Rb1 by isolated rat intestinal flora is also a step-by-step deglycosylation process [16]. The metabolism of total ginsenosides in the intestinal flora in vivo is consistent with that in vitro. Guo et al. [17] verified the process of conversion of Panax notoginseng saponins by intestinal flora. The results showed that ginsenosides F1, Rh2, CK and PPT were detected in the plasma of conventionally fed rats, but not in the plasma of sterile rats. Therefore, it is inferred that the basic rule of ginsenoside metabolism in vivo is tetrasaccharide saponin → trisaccharide saponin → disaccharide saponin → monosaccharide saponin → sapogenin [18].
Chi et al [19] found that multiple microorganisms can synergistically transform ginsenoside Rb1 into ginsenoside compound K and Rh2 through the pathway of ginsenoside Rd → ginsenoside F1 → ginsenoside compound K; Ginsenoside Re was transformed into ginsenoside Rh1 through the pathway of ginsenoside Re → ginsenoside Rg2, Rg2 → ginsenoside Rh1. Various strains extracted from Korean staple kimchi, such asLeuconostoc citreum LH1， PPD Type Ginsenosides can be well converted into ginsenoside compound k[20].
Kim et al [21] screened 12 strains, of whichM. trithecenlyticumGinsenoside Rb1 can be converted to ginsenoside Rh2. Zhou et al. [22-23] showed that,A.niger 3.3883 andA. oryzae 3. The mixed spore solution of strain 591 can convert ginsenoside Rb1 into ginsenoside RD and Rg3 in 7% sodium alginate mediumLactobacillus paracasei subsp. tolerans， It can hydrolyze the glucose group at the C-3 position of Ginsenoside Rg3 to obtain ginsenoside rh2[24].
Hu et al [25] used data fromBifidobacterium adolescentis β - glucosidase of atcc15703 studies the biotransformation of ginsenosides. With ginsenoside Rb1 and RD as substrates, the C-3 glucosyl portion of ginsenoside Rb1 is hydrolyzed to generate Gypenoside XVII (gyp- ⅩⅤii), ginsenoside Rd removes the C-3 lateral glucosyl to generate ginsenoside F2; ginsenoside Rb1 removes the C-3 and C-20 lateral glucosyl to hydrolyze to generate gyp XVII and ginsenoside Rd.
The structure of ginsenosides includes 1-4 glycosidic bonds, and the common glycosyls are β - glucosylL-Arabinosyl andL-. Therefore, by using specific glycosidases such as α-L-Furan arabinosidase α-L-Glucopyranosylase, β - glucosidase or pectinase) selectively hydrolyze sugar groups at different positions, and it is feasible to hydrolyze ginsenosides to prepare secondary ginsenosides [26]. Zhang et al. [27] cloned and optimized the furan type arabinosidase gene from Bacillus subtilis, which can specifically hydrolyze the arabinose glycosyl of ginsenoside RC and convert it to ginsenoside Rd. Kim et al. [28] reported a recombinant enzyme α-L-Glucopyranosylase can efficiently catalyze the conversion of ginsenoside Rb2 to ginsenoside rd by selectively hydrolyzing the glucopyranosyl group at position C-20.
α - rhamnosidase can hydrolyze rhamnose at the C-6 position of PPT type ginsenoside to produce ginsenosides Rg1 and rh1[29]. In addition, Chang et al. [30] showed that the enzyme fromAspergillus niger The β - glucosidase of kccm 11239 was optimized. The enzyme hydrolyzed the glucose group at the C-20 position of ginsenoside Rb1 to generate ginsenoside RD and Rg3, and hydrolyzed the glucose group at the C-3 position to generate ginsenoside F2. β - glucosidase mt619 converted ginsenoside Rb1 into secondary ginsenoside compound K and PPD by two transformation pathways[31]: ginsenoside RB1 → gyp XVII → gyp lxxv → ginsenoside compound K → PPD; Ginsenoside Rb1 → gyp XVII → ginsenoside F2 → ginsenoside compound K → PPD, pectinase can convert ginsenoside Rb1 to ginsenoside rd[32]. See Figure 1 for the transformation pathway and biotransformation of ginsenosides.
1.1.2
At present,Gypenoside（The biotransformation research of gyp) coincides with ginsenosides, such as gyp XVII and lxxv transformation pathways. See Figure 2 for gyp biotransformation pathways. Chen et al [33] found that after giving gyp LVI to rats, its main transformation and metabolism processes in rats were deglycosylation and dehydration, and the five metabolites wereGypenosideXLVI、GypenosideL、GypenosideLI、 Damulin B and a. the main transformants of Lactobacillus bulgaricus to gyp XLVI were consistent with the rat gastrointestinal tract transformation products, respectivelyGypenosideL、GypenosideLI、 Damulin A and b[34].
Using high-performance liquid chromatography for comparative analysis, it was found thatGypenosideBy microorganismsAspergullus glaucusAfter transformation, low polarity secondary saponins were produced. Chenlianghua et al. [35] used rhamnosidase obtained from microbial strain ffcdl-90 to convert gyp-5 to ginsenoside Rd. using polysaccharide based prototype gyp as substrate, strains with high gyp glycosidase production were screened outAbsida sp.GYP4r， Gyp glycosidase was isolated and purified by ion exchange chromatography, which can specifically hydrolyze gyppNP-α-D-Glc、pNP-β-D-Glc、pNP-α-D-Gal has hydrolysis ability [36-38].
through the use ofFervidobaterium pennivorans The recombinase produced by dsm9078 willGypenoside,GypenosideXLVI is converted to gyp-tn-1 by naringinase[40]. Liu Yue [41] used nlz-r and nlz-x to specifically hydrolyze the rhamnose glycosyl and xylose glycosyl of gyp-nplc0394 to generate compounds a-c; Snail enzyme can hydrolyze the glucose group of gyp LVI and gyp XLVI to produce 2-hydroxy-3-O-β-D-Glucopyranosyl - (20S)-protopanaxadiol- 20-O-[β-D-Xylopyranosyl - (1 → 6)]-β-D-Glucopyranoside (I), 2-hydroxy - (20S)-protopanaxadiol-20-O-[β-D-Xylopyranosyl - (1 → 6)]-β-D-Glucopyranoside (II), 2-hydroxy-3-O-β-D-Glucopyranose - (20S)-protopanaxadiol-20-O-β-D-Glucopyranoside (III), 2-hydroxy - (20S)-protopanaxadiol-20-O-β-D-Glucopyranoside (IV).
1.1.3 astragaloside
. At present, there are few studies on the biotransformation of astragaloside, but the rules of its saponin structure modification, such as deacetylation and deglycosylation, are fully summarized. The main transformation pathways of astragaloside in intestinal flora include deglycosylation, deacetylation, dehydrogenation, etc., and the CO transformation product is cycloastragalol (CA). Mengxintong et al [42] showed that astragaloside IV (as-iv) can be deglycosylated by human intestinal flora and converted into CA that is easily absorbed into the blood. Rat intestinal bacteria can also remove xylose and glucose groups at C-3 and C-6 positions of ASI to produce cycloastragalol-6-O-β-. As-iv was incubated with rat intestinal flora for 4 h in vitro, and the C-3 and C-6 glycosyls were removed and hydrolyzed to formCycloastragalol glucoside(brachyoside B, bra b), cyclogaleginoside B (CYC b), Ca and oxidized ca[44].
LiuXiaoHui [45] screened strains that can transform total saponins of Astragalus membranaceus into as-iv from molds from different sources——Absidia corymbifera AS2。 The microbial transformation technology was used to increase the content of as-iv by fermentation transformation with total saponins of Astragalus membranaceus as substrate. Four compounds that can be transformed into as-iv were identified in total saponins of Astragalus membranaceus, which were identified as astragaloside I (ASI), isoasi (isoasi), ASII and isoasii by structure identification. Further Study on the biotransformation mechanism of this strain revealed that the acetylesterase expressed by it could effectively hydrolyze the acetyl group of xylopyranosyl residue at position C-3 in ASII, and the transformation pathways were ASII → ASI, isoasii → ASII → as-iv, ASI → (ASII, isoasii) → as- IV, respectively.Iv, isoasi → ASII → as-iv[46-47].
utilizePenicillium canescensIt can also transform total saponins of Astragalus membranaceus into as-iv, which significantly increases the content of as-iv, which is 5.51 times higher than that before transformation [48]. Eight different strains were used for the biotransformation of as-iv, and it was found thatA. niger M85 has the strongest biotransformation activity, and the content of as-iv after transformation is 11.7 times that before transformation [49]. Ruan Ming [50] used different medicinal (edible) fungi to ferment Astragalus membranaceus and found that ASI could be transformed into isoas-iv. it is presumed that the transformation mechanism is that xylosidase produced during the growth of the strain hydrolyzes the xylosyl group at position C-3 of as-iv and converts it into isoas-iv. Wang et al. [51] usedBacillussp. Lg-502 successfully transformed ASI into ca. according to nuclear magnetic resonance and mass spectrometry analysis, it is presumed that the transformation pathway of as-iv is similar to that of intestinal bacteria, and the transformation mechanism isBacillus sp.Glucosidase and xylosidase secreted by lg-502, as-iv preferentially removes the glucose group at position C-6 under the action of glucosidase with higher activity, and then removes the xylose group at position C-3 to generate ca. see Figure 3 for the biotransformation pathway of Astragalosides.
Cheng et al [52] used data fromTrichoderma reeseiTwo enzymes (β - xylosidase and β - glucosidase) of as-iv convert as-iv into caDictyoglomus thermophilumβ - glucosidase and β - xylosidase can also transform as-iv into ca[53-54]. Commercial β - glucosidase can remove the xylosyl group at the C-3 position of astragaloside IV to generate bra b[55]. fromAbsida The high-yielding strain of astragalosidase was screened out from six strains of sp. A3R, a84r, a9r, a8r, a38r, arr, which can transform polysaccharide based astragaloside into low sugar based secondary saponins [56-57]. The study also found that the high-yield strain of astragalosidase from the low sugar group astragaloside was obtained from the low sugar group astragaloside glycosides of sp.a3r, a84r, aAbsidia sp. .
1.1.4 Momordica grosvenorii saponins
Zhou et al. [59] found deglycosyl metabolites of momordoside V in plasma, urine, bile and fecal samples after ig of momordoside V in rats. Its transformation is to remove glucose in different amounts and positions in turn. Li dianpeng et al. [60] reached the same conclusion in the in vitro metabolism study of rats. After incubation with human intestinal flora, Momordica grosvenorii saponin III successively removes the glucose group at the C-3 position and hydrolyzes the gentiobiosyl group at the C-24 position to produce the secondary saponin Momordica grosvenorii saponin iia1 and the saponin Gen Momordica grosvenoril [61].
The total saponins of Momordica grosvenorii were biotransformed by Penicillium j-9, which produces highly active β - glucosidase, and the chemical structure of the secondary saponin product was obtained: Momordica grosvenoril-24-O-β-D-Glucopyranosyl - (1 → 2) - β-D-Glucopyranoside (a) and B are siraitoside IIIE (b), 11-one-siraitol-3-O-β-D-Glucopyranosyl - 24-O-β-D-Glucopyranosyl - (1 → 2) - β-D-. The total saponins of Momordica grosvenorii were hydrolyzed by β - glucosidase once, and the main products were trisaccharide saponins and tetrasaccharide saponins; The product hydrolyzed twice was identified to be mainly monosaccharide saponin and a small amount of disaccharide saponin connected with a β - glucosyl group at position C-3 or C-24 [64]. Siraitoside V was hydrolyzed and transformed by β - glucanase to generate secondary saponins such as siraitoside IIIE, III, ive and saimenside I connected with different numbers of glycosyl groups [65]. The biotransformation pathway is shown in Figure 4.
1.1.5 jujube seed saponins
Duchenghui et al [66] found that the main transformation pathway of jujube saponins in normal human intestinal flora was deglycosylation reaction by using uplc-q-orbitrap-ms analysis, and different transformation products would be generated by deglycosylation sequence. The transformation pathway of Zizyphus Jujuboside in rat intestinal flora is similar to that of human origin, and both secondary saponins and Zizyphus Jujuboside will be produced. Jujuboside A (Ju a) is hydrolyzed by glucosidase in Poria cocos fungus to remove the glucose group at the C-3 position and generate Ju b[67]. Ju a can also be transformed into Jujuboside b[68-69] in human intestinal flora in vitro. See Figure 5 for the transformation pathway of Jujuboside in intestinal flora and microorganisms. Matsuda et al. [70] removed the glucose groups at positions a, B and B1 c-23 of Jujuboside by enzymatic hydrolysis and transformed it into known Jujuboside.
1.2 pentacyclic triterpenoids
1.2.1 glycyrrhizic acid
Most liquorice saponins have pentacyclic triterpene structure, and glycyrrhizic acid is the most abundant component, which is also a representative compound of liquorice saponins. GL is an oleanane type triterpenoid saponin with 2 molecules of glucuronic acid group at the C-3 position [71].
Akao team [72-74] clarified that there are mainly two ways of intestinal flora transformation of glycyrrhizin, see Figure 6. (1) Glycyrrhizic acid is hydrolyzed once to remove two glucuronic acids and directly generate glycyrrhetinic acid; (2) First hydrolyze one glucuronic acid group at the end of the C-3 position to generate the intermediate glycyrrhetinic acid monoglucuronide (gamg), and then hydrolyze and remove one glucuronic acid to generate glycyrrhetinic acid.
Some studies found that sterile rats could not absorb glycyrrhizic acid into the blood and did not undergo the conversion reaction of deglycosylation, indicating that the conversion of intestinal bacteria is a necessary link for the absorption of glycyrrhizin components into the blood. Subsequently, the research team isolated and screened strains involved in the conversion of glycyrrhizic acid from human feces, such asEubacterium sp. GLH、Ruminococcus sp. Po1-3 andStreptococcus sp. Lj-22 et al., of whichStreptococcus sp. Lj-22 was confirmed to specifically hydrolyze one glucuronic acid group at the C-3 end of Glycyrrhizin to generate gamg[75]. -The transformation mode of intestinal flora of triterpenoid saponins such as acetoxyglycyrrhizic acid is the same as that of glycyrrhizic acid, both of which produce secondary saponins and aglycones after deglycosylation.
In recent years, researchers have done more research on the microbial transformation of glycyrrhizic acid [77-79], and found many strains that can successfully transform glycyrrhizic acid, but the transformation pathway of glycyrrhizic acid is simple and consistent with that of intestinal flora. Strains used for microbial transformation produce β-D-Glucuronidase, enzymes from different sources have stereoselectivity for the position of deglycosylation, fromStreptococcus LJ-22[80]、Penicillium purpurogenum Li-3[81] andTalaromyces pinophilus The isolated and purified glucuronidase from li-93[82] only hydrolyzes the glucuronic acid group at the C-3 position of Glycyrrhizin to generate gamg, and hydrolyzes to generate glycyrrhetinic acid. FromAspergillus niger[83] andEubacterium The glucuronidase of l-8[84] can completely hydrolyze glycyrrhizic acid to produce glycyrrhetinic acid.
1.2.2 saikosaponins
Shimizu et al. [85] showed that saikosaponins a, B1, B2, D, G, etc. were mainly deglycosylated in the rat intestine. First, the glucose group at the C-3 position was removed to generate the secondary glycoside protosaikosaponins F, a, h, G, D, and then the fucose at the C-3 position was removed to generate saponins F, a, h, G, D. Kida et al. [86] obtained the same conclusion after CO culturing saikosaponins with human feces, and screened out the human intestinal strainsEubacterium sp. A-44， The mechanism of this strain participating in biotransformation was studied. Research findings fromE. The enzymes (β - glucosidase and β - fucosidase) isolated from sp. a-44 can gradually remove fucose and glucose at the C-3 position of saikosaponin, and finally produce saikosaponin. Yu et al [87] found that the transformation pathway of saikosaponin C in human intestinal flora was similar to that of saikosaponin a, B1, B2, D, G, which were all gradually deglycosylated in vivo. Domestic scholars found that saikosaponin a was transformed into saikosaponin F and saikosapogenin f by rat intestinal flora [88], further proving the transformation pathway of saikosaponin in intestinal bacteria.
Xujinli and fuyaoyao found spc42、Microbacterium Sp.gs514-saiko andRhodanobacter The enzymes produced by sp.gs3054 can convert saikosaponin into secondary saponins with low sugar base [89-90]. .
1.2.3 Pulsatilla saponins
. Pulsatilla saponins D, B7 and BD also undergo similar deglycosylation reactions in intestinal flora in vitro to obtain secondary saponins and ivy saponins [94-95].
At present, there have been a lot of studies on the biotransformation of Pulsatilla Saponin glycosidases, and a variety of glycosidases that can transform Pulsatilla saponins have been isolated from them [96-97]Absidia The enzyme of sp.p00r converts the hexasaccharide Pulsatilla Saponin into the secondary saponin Ivy saponin-3 containing two sugar groups-O-L-Rhamnopyranosyl - (1 → 2)-L-Arabinopyranoside [98]. Utilizing strainsAbsidia sp．The hydrolase generated by p39r hydrolyzes the rhamnosyl group at the c-28 position of Pulsatilla Saponin h to obtain Pulsatilla Saponin PS-I; The glucosyl groups at positions C-3 and c-28 were removed to obtain Pulsatilla Saponin ps-ii; .
1.2.4 saponins from placenta equina
Zoysia is a plant of zijinniuke family, and ardipusilloside-i (ads-i) and Zoysia saponin Ag3 are two representative saponins in this medicinal material. The biotransformation of ads-i was studied by simulating human intestinal flora in vitro, and the structures of four metabolites from M1 to M4 were preliminarily deduced [99]. The metabolites M1, M2, M4 are the same as the transformation products of ads-i in rat intestine [100], which are all aglycons (M4) generated after the removal of glucose (M1), glucose and rhamnosyl (M2) at C-3 position and the removal of all glycosyl groups at C-3 position of ads-i respectively..the results showed that the metabolites M1, M2, M4 were the same as those of ads-i in rat intestine [100].The aglycones were produced after the removal of glucose (M1. M3 with three glycosyl removed is a unique transformation product of human intestinal bacteria, and M5 with rhamnosyl removed from the C-3 terminus is a unique transformation product of rat intestinal bacteria, suggesting that the composition of human and animal microbiota is different, and the biotransformation products of ads-i will also change.
Zhang Jing [101] screened endophytic bacteria and soil bacteria and obtained three strains with the ability to transform Pegasus saponin Ag3, which wereSphingomonas yabuuchiae GTC868T（AB071955）、Bacillus licheniformis Atcc14580t (ae017333) andBacillus asahii MA001T（AB109209）。 The team also found that pectinase could also transform Pegasus saponin Ag3 to produce secondary saponins A-1, A-2, A-3 and aglycones. The biotransformation pathways of ads-i and zoysin Ag3 are shown in Figure 9.
1.2.5 other pentacyclic triterpenoid saponins
The transformation pathway of platycodin intestinal bacteria is mainly to remove the C-3 glycosyl [102]. After transformation by Aspergillus niger and Rhizopus Niger, the chromatographic peak of total saponins of Platycodon grandiflorum obviously shifted back, indicating that the glycosylation of saponins was removed to generate secondary saponins or aglycones [103]. Shin et al [104-105] found that the acid tolerant pectinase cytolase PCL5 can hydrolyze the glucose group at C-3 position and xylosyl and apiosyl groups at c-28 position of platycodin e with substrate specificity. Cytolase PCL5 is a mixed enzyme, so it may be specific for a variety of glycosyls. Similarly, pluszyme 2000p from Aspergillus niger only hydrolyzes the glucose group at position C-3 of platycodin [106]. Using snail enzyme to hydrolyze total platycodin [107], platycodin E and D3 with similar structure can be converted into platycodin D; fromTrichoderma reesei、Aspergillus oryzae[108]、Aspergillus usamii KFRI 1004[109]、P. grandiflorus[110] andAspergillus aculeatus[111] purified cellulase, β - galactosidase β-Both glucosidase and pectinase can convert platycodin E and D3 into platycodin D.
. ESA is deglycosylated by biotransformation to generate ESB, which has reduced hemolysis and enhanced anti-inflammatory activity [113-114]. ESA by microorganismsStreptomyces griseus ATCC 13273 removes xylosyl and glucosyl groups at the C-3 position to generate ESB and aglycone phytolac methyl ester [115].
Both recombinant glycosidase and snail enzyme react with ESA to hydrolyze the C-3 terminal glucose group to generate esb[91], and snail enzyme has the highest yield at 48.28 ℃ and pH 6.4 [116]. Laidaowan [117] used Aspergillus niger β - glucosidase, bitter almond enzyme, snail enzyme and other enzymes to hydrolyze the glucose group in ESA and generate ESB. Among them, only snail enzyme can completely hydrolyze the C-3 glycosyl side chain of ESA to obtain its saponin.
Watanabe et al [118-119] fromAspergillus oryzae PF1224、N. vasinfecta var. vasinfecta P f1225 andEupenicillium brefeldianum A. terreus II can transform the total saponins of soybean into soybean sterol B with maximum efficiency. Tian Jing et al. [121] used eight mold strains to explore the hydrolysis ability of soybean saponin glycosyl, and obtained Aspergillus oryzaeA. oryzae 39s、A. oryzae Slows and Aspergillus nigerA. niger 848s, three strains with high activity, hydrolyzed the partial glycosyl of soybean saponins to produce low glycosyl saponins and aglycones.
The results showed that the main transformation pathway of Achyranthes bidentata saponin in the intestine was deglycosylation, and the transformation products of prototypic saponins such as Panax japonicus saponins V, IV, IVA were ginger like Notoginsenoside R1, 28 deglucose based Panax japonicus saponin IVA and oleanolic acid. According to the characteristic fragments of the product, the deglycosylation reaction mainly occurred at the glycosidic bonds at positions C-3 and c-28 [122].
In the biotransformation of triterpenoid saponins such as ginsenosides, Astragalosides and liquorice saponins, the reaction mechanism is mainly the hydrolysis reaction of deglycosylation, which usually occurs at positions C-3, C-6, C-20, C-21, c-23, C-24 and c-28. The transformed secondary saponins and aglycones can not only improve bioavailability, but also enhance anti-inflammatory, antiviral and anticancer effects [79123].
2 biotransformation of steroidal saponins
2.1 dioscin
Dioscin is hydrolyzed one by one in the human intestinal flora to form the corresponding secondary saponins and Diosgenin [8124]. Tang et al [125] characterized the metabolic profile of total dioscin, dioscin and diosgenin in rats after administration, and the results showed that the stepwise deglycosylation of dioscin was the most important transformation process.
Chen et al. [126] usedLactobacillus caseiDeglycosylation of C-3 position of dioscin to produce diosgenin, Liu et al. [127] from Aspergillus oryzaeAspergillus oryzaeThe hydrolase isolated and purified from Curvularia lunata can hydrolyze the C-3 terminal α - 1,4-rhamnosyl and C-26 glucosyl of protodioscin to produce dioscin A. from Curvularia lunataCurvularia lunataα isolated and purified from-L-Rhamnosidase can hydrolyze the C-3 terminal α - 1,2-rhamnosyl group to generate progenin v[128]. Rhamnosidase isolated from fresh bovine liver can hydrolyze two rhamnosyl groups to produce secondary dioscin with one glucose group at the C-3 position [129]. Jin et al. [130] fromAbsidia Diosgenin hydrolase was isolated and purified from sp. D38, which can remove all the side chain glycosyl of diosgenin and hydrolyze to produce diosgenin.
2.2 anemarrhenin b-ii/iii
In the intestinal flora of rats, the transformation reactions of Anemarrhena saponins b-II and b-iii mainly include deglycosylation, dehydration, hydroxylation, E-ring cleavage and oxidation reactions [7131-133]. Deglycosylation is the pathway we focus on. The transformation pathway is that the C-3 position of Anemarrhena saponin b-II successively removes the glucosyl and galactosyl groups to obtain secondary Anemarrhena saponins b-ii-a and b-ii-b; At position C-26, the glucose group was removed to produce anemarrhenin A-III; The glucosyl and galactosyl groups were removed from the C-3 position of Anemarrhena saponin b-iii to obtain secondary Anemarrhena saponins b-iii-a and b-iii-b. Utilizing microorganismsAspergillus niger As 3.0739[134] andColletotrichum gloeosporioideis[135] transformed Anemarrhena saponin b-II, which would hydrolyze and remove the glycosyls at positions C-3 and C-26 to obtain secondary saponins.
In the biotransformation of steroidal saponins, mostly the mutual transformation between saponins and sapogenins, and the deglycosylation hydrolysis reaction mainly occurs at the C-3 and C-26 positions. Compared with triterpenoid saponins, the biotransformation mechanism of steroidal saponins is simpler and involves fewer reaction types.
3 conclusion and Prospect
Taking several representative triterpenoid saponins and steroidal saponins as examples, the research progress on the biotransformation of saponins in traditional Chinese medicine was reviewed. . In addition, intestinal bacteria can also hydroxylate, oxidize and demethylate saponins, which is a secondary transformation pathway of intestinal bacteria. Due to the differences in species composition and diversity between human intestinal flora and model animals, there are also species differences in the intestinal transformation of saponins. For example, the transformation products of ads-i in human and rat intestinal flora are partially consistent [99-100]. Screening suitable strains or enzymes from microorganisms for biotransformation is an effective way to prepare secondary saponins.
Most of the strains selected for biotransformation research mainly include four sources: (1) select excellent strains that can transform saponins from human or rat intestinal flora; (2) ; (3) Excellent strains with transformation advantages were selected from the growing soil of medicinal plants; (4) Excellent strains were screened from plant endophytes. With the development of enzyme engineering and genetic engineering research, some research groups have stored specific purified enzymes or recombinant enzymes for bioconversion. If the highly specific glycosidases can be converted into products and the industrial production of hydrolases can be realized, it has far-reaching significance for the bioconversion research and economic benefits of saponins, so as to meet the needs of subsequent drug likeness research and new drug development.
Source: Li Yihong, Liang yuliu, Xie Jiaqi, Wang can, Huang Jianmei. Research progress on biotransformation of saponins in traditional Chinese medicine [j]. Chinese herbal medicine, 2024, 55 (3): 989-1003
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