A method for synthesizing alkyl galactosides using immobilized cells with monosaccharides as glycosyl donors

Abstract

The present application relates to a kind of methods for synthesizing alkyl galactoside using immobilized cells with monosaccharide as glycosyl donor.The method comprises the following steps: (1) culturing beta-galactosidase-producing yeast; (2) treating the yeast cells with ethanol; (3) adding genipin to the ethanol-treated yeast cells to construct a cross-linking system; reacting the cross-linking system for 0.5-4 h, centrifuging to obtain immobilized cells; (4) mixing galactose and alkyl alcohol uniformly, adding the immobilized cells, reacting for 2-16 h, centrifuging to separate the solid and liquid, taking the supernatant to obtain alkyl galactoside. The present application provides a green and efficient method for synthesizing alkyl galactoside, which is the first time to use immobilized yeast cells to synthesize glycoside with monosaccharide as glycosyl donor. The reaction system only contains alkyl glycoside and residual substrate after completion, the product types are few, easy to purify, suitable for large-scale synthesis of alkyl glycoside, and has broad application prospects.

Description

Technical Field

[0001] The invention relates to a method for synthesizing alkyl galactoside by utilizing immobilized cells and monosaccharide as a glycosyl donor, and belongs to the technical field of sugar engineering. Background Art

[0002] Alkyl glycosides (AGSs) are a new, green, nonionic surfactant composed of a hydrophilic sugar group and a hydrophobic fatty alkyl chain. Traditionally used in detergents and industrial emulsifiers, AGSs exhibit excellent wettability and surface tension reduction, electrolyte and hard water tolerance, stability over a wide pH range, and synergistic properties with other surfactants. With the expansion of functional research, AGSs have found widespread application in food processing, cosmetics, the pharmaceutical industry, and scientific research. As a safe and non-toxic food additive, AGSs can help evenly mix food ingredients, provide foaming and thickening effects, improve food taste, and extend its shelf life. Furthermore, AGSs are mild and non-irritating, making them suitable for cosmetic formulations and can be added as stabilizers to medicinal skin products. As highly effective stabilizers, AGSs can also stabilize lipid nanoparticles for drug delivery. In recent years, alkyl glycosides have been gradually applied to clinical research. For example, they can serve as transmucosal delivery enhancers for intranasal administration; prevent aggregation of peptide and protein drugs, reduce immunogenicity, and retain activity; enhance insulin permeability across epithelial mucosa; effectively improve the bioavailability of calcitonin administered intranasally and ocularly; and alkyl glycosides with specific structures have renal targeting. Alkyl glycosides are also used as pharmaceutical intermediates in the synthesis of some drugs. For example, α-amylase inhibitors based on alkyl glycoside structures can suppress postprandial hyperglycemia and excessive insulin secretion in patients with type 2 diabetes. In basic research, alkyl glycosides, as excellent surfactants, have been widely used in the preparation and research of membrane proteins.

[0003] Currently, the synthesis of alkyl glycosides is primarily chemical, including the Koneigs-Knorr method and Fischer glycosylation. These methods require multiple steps, including protection, deprotection, and activation, resulting in high energy consumption and environmental pollution. To simplify the reaction steps and reduce environmental pollution, there is an urgent need to develop green and environmentally friendly synthesis methods. Enzymatic synthesis of alkyl glycosides allows for a one-step, green, and pollution-free synthesis. Currently, enzymatic synthesis of alkyl glycosides primarily involves alkyl glucosides, typically using β-glucosidase, with some employing a combination of amylase and pullulanase, or aldolase. Enzymatic synthesis of alkyl galactosides is rare, primarily using β-galactosidase to catalyze the transglycosylation reaction using the disaccharide substrate lactose as the glycosyl donor. This results in a high number of byproducts, hindering the isolation and purification of the alkyl glycoside product. Currently, there are no reports on the one-step enzymatic synthesis of alkyl galactosyl glycosides using immobilized cells as the enzyme source and a monosaccharide as the glycosyl donor. Summary of the Invention

[0004] In view of the deficiencies of the prior art, the present application provides a method for synthesizing alkyl galactoside by immobilized cells using monosaccharide as a glycosyl donor.

[0005] The technical solution of the present application is as follows:

[0006] A method for synthesizing alkyl galactoside by immobilized cells using monosaccharide as a glycosyl donor, comprising the following steps:

[0007] (1) Culturing a yeast producing β-galactosidase, and collecting the yeast cells;

[0008] (2) Suspending the yeast cells using an ethanol solution, stirring at 20-30°C for 1-10 min, and centrifuging to obtain ethanol-treated yeast cells;

[0009] (3) Adding genipin to the ethanol-treated yeast cells to construct a cross-linking system; reacting the cross-linking system at 20-30°C and 100-150 rpm for 0.5-4 h, and centrifuging to obtain immobilized cells;

[0010] (4) Mixing galactose and alkyl alcohol uniformly, adding the immobilized cells, and reacting at 30-50°C for 2-16 h; after solid-liquid separation by centrifugation, taking the supernatant, removing organic solvents, and performing silica gel column chromatography separation and freeze-drying to obtain alkyl galactoside.

[0011] According to the present application, preferably in step (1), the yeast producing β-galactosidase is Kluyveromyces lactis, and the preservation number is CGMCC 2.1494.

[0012] According to the present application, preferably in step (2), the concentration of the ethanol solution is 40-50%.

[0013] According to the present application, preferably in step (3), the concentration of genipin in the cross-linking system is 0.05%, and the concentration of ethanol-treated yeast cells is 0.05-0.2 mg / μL.

[0014] According to the present application, preferably in step (4), the concentration of galactose is 0.4-0.8 M.

[0015] According to the present application, preferably in step (4), the concentration of alkyl alcohol is 10-40%.

[0016] According to the present application, preferably in step (4), the alkyl alcohol is methanol, ethanol, n-propanol, isopropanol, n-butanol, n-pentanol, or n-hexanol.

[0017] According to the present application, preferably in step (4), the amount of immobilized cells added is 80-200% of the mass of galactose.

[0018] Preferably, according to the present invention, in step (4), the silica gel column chromatography conditions are: methanol:ethyl acetate = 3:7 as the mobile phase, the sample loading amount is 1-2 mL, and the elution flow rate is 0.5-0.8 mL / min.

[0019] The alkyl galactoside described in the present invention is methyl-β-D-galactoside, ethyl-β-D-galactoside, n-propyl-β-D-galactoside, isopropyl-β-D-galactoside, n-butyl-β-D-galactoside, n-pentyl-β-D-galactoside or n-hexyl-β-D-galactoside, corresponding to the alkyl alcohol substrate.

[0020] The yeast producing β-galactosidase in the present invention is a yeast that uses galactose as a substrate for synthesis reaction, and other steps not specified are carried out according to the existing technology.

[0021] Beneficial effects

[0022] 1. The present invention provides a green and efficient method for synthesizing alkyl galactosides. For the first time, immobilized yeast cells are used to synthesize glycosides in a single step using monosaccharides as glycosyl donors. In the synthesis process of the present invention, the reaction system contains only the alkyl glycoside and the remaining substrate after completion, resulting in a small number of products and easy purification. Compared to chemical synthesis of alkyl glycosides, the present invention has simple steps, does not require the group protection and deprotection processes required in chemical synthesis, is environmentally friendly, has mild reaction conditions, is easy to operate, is suitable for large-scale synthesis of alkyl glycosides, and has broad application prospects.

[0023] 2. The present invention uses immobilized yeast cells to synthesize alkyl glycosides, which does not require enzyme purification. In addition, the immobilized cells are prepared by cross-linking with genipin, which does not require the use of an additional carrier, thereby reducing the cost of the immobilized enzyme. The enzyme can be recycled for the synthesis of alkyl glycosides, greatly reducing costs and having broad application prospects.

[0024] 3. This invention, for the first time, utilizes genipin to directly crosslink yeast cells, resulting in carrier-free immobilized yeast cells. This method eliminates the need for additional carrier materials and offers the advantages of low cost, ease of operation, and high stability. Furthermore, genipin, a naturally derived crosslinker, exhibits negligible toxicity compared to existing crosslinkers, making the carrier-free immobilization process of this invention non-toxic and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 These are the hydrogen and carbon spectra of methyl-β-D-galactoside.

[0026] Figure 2 Figure 2. Batch synthesis of methylgalactosidase by carrier-free immobilized yeast cells.

[0027] Figure 3These are the hydrogen and carbon spectra of ethyl-β-D-galactoside.

[0028] Figure 4 These are the hydrogen and carbon spectra of n-propyl-β-D-galactoside.

[0029] Figure 5 These are the hydrogen and carbon spectra of isopropyl-β-D-galactoside.

[0030] Figure 6 These are the hydrogen and carbon spectra of n-butyl-β-D-galactoside.

[0031] Figure 7 These are the hydrogen and carbon spectra of n-pentyl-β-D-galactoside.

[0032] Figure 8 These are the hydrogen and carbon spectra of n-hexyl-β-D-galactoside. DETAILED DESCRIPTION

[0033] The present invention will be further described below with reference to the embodiments, but the protection scope of the present invention is not limited thereto.

[0034] The Kluyveromyces lactis with the deposit number CGMCC 2.1494 of the present invention is available at the China General Microbial Culture Collection Center.

[0035] Example 1 Preparation of immobilized yeast cells

[0036] 1. Kluyveromyces lactis CGMCC 2.1494 was inoculated onto a slant culture medium containing 1% glucose, 1% peptone, 0.5% yeast extract, and 1.5% agar, grown at 30°C for 24 hours, and then transferred to a liquid seed culture medium. After culturing at 200 rpm and 30°C for 24 hours, the culture medium was transferred to a fermentation medium containing 1% glucose, 1% peptone, 0.5% yeast extract, and 1% lactose at a volume ratio of 3%, cultured at 30°C for 32 hours, and collected after centrifugation to obtain Kluyveromyces lactis cells. The cells were suspended in 50% ethanol and mixed for 1 minute, and washed twice with buffer to obtain ethanol-treated Kluyveromyces lactis cells.

[0037] 2. Prepare a 50 mM genipin solution in potassium phosphate buffer (pH 7.5) and mix thoroughly with the ethanol-treated Kluyveromyces lactis cells to create a crosslinking system. The genipin concentration in the crosslinking system was 0.05%, and the yeast cell concentration was 0.1 mg / mL. The mixture was then reacted at 25°C and 125 rpm for 4 hours. The immobilized yeast cells were then centrifuged at 11,000 rpm for 2 minutes.

[0038] Example 2: Synthesis of methylgalactoside catalyzed by immobilized yeast cells

[0039] 1. Synthesis of methyl galactoside

[0040] A method for synthesizing alkyl galactosides using immobilized cells and monosaccharides as glycosyl donors comprises the following steps:

[0041] A 1M D-galactose solution was prepared using a pH 7.5, 50mM potassium phosphate buffer. Immobilized yeast cells were then added to 3.5mL of methanol and 6mL of 1M D-galactose, with the amount added being 140% of the mass of the D-galactose. Buffer was then added to bring the reaction volume to 10mL. After reacting at 37°C for 8 hours, the mixture was centrifuged at 11,000rpm for 2 minutes, and the supernatant was retained to obtain the alkyl galactoside.

[0042] 2. Purification and structural identification of methylgalactoside

[0043] The supernatant reaction solution of step 1 was taken, the organic solvent was removed by rotary evaporation, and then freeze-dried. The resulting powder was dissolved with 1 mL of mobile phase (methanol: ethyl acetate = 3:7), wet-loaded and added to a silica gel column filled with 200-300 mesh silica gel and a specification of 25 mm × 340 mm. The elution flow rate was 0.5 mL / min, and the eluted samples were collected and detected by thin layer chromatography. The eluted samples with purer products were combined, and then the organic solvent was removed by rotary evaporation. After freeze-drying, the pure glycoside product was obtained.

[0044] 15 mg of the glycoside product prepared above was dissolved in 450 μL of deuterated water and subjected to nuclear magnetic resonance analysis, including hydrogen spectrum ( 1 HNMR), carbon spectrum ( 13 C NMR), hydrogen-hydrogen correlation spectroscopy (COSY), high-speed quantitative carbonyl correlation spectroscopy (HSQC), and high-hydrogen long-range carbonyl correlation spectroscopy (HMBC) were used to determine the chemical shift of the glycoside product, confirming that the glycoside product was methyl-β-D-galactoside.

[0045] like Figure 1 As shown, the chemical shift of methyl-β-D-galactoside is: 1 H NMR(400MHz,D2O): δ4.28(d,1H,H-1,J 1,2 =8.0Hz),3.89(dd,1H,H-4),3.75(m,2H,H-6,H-5),3.67(dd,1H,H-6),3.61(dd,1H,H-3),3.54(s,3H,H-7),3.47(dd,1H,H-2); 13 C NMR (100MHz, D2O): δ103.79(C-1), 75.11(C-5), 72.74(C-3), 70.71(C-2), 68.64(C-4), 60.95(C-6), 57.13(C-7).

[0046] The above-mentioned methyl-β-D-galactoside has the molecular formula C7H 14 O6, chemical structure is shown in formula (1):

[0047]

[0048] The instrument used for the above-mentioned nuclear magnetic resonance analysis was a Bruker Daltonics 400 MHz nuclear magnetic resonance spectrometer (USA).

[0049] The immobilized cells obtained by centrifugation in step 1 of the present invention were subjected to a new batch synthesis reaction according to the above conditions. Figure 2 As shown, after 10 batches of reaction, the immobilized enzyme can still retain a relative yield of more than 70% compared with the first batch, and the relative enzyme activity of the immobilized cells is still retained at more than 60%.

[0050] Example 3 Synthesis of Ethylgalactoside Catalyzed by Immobilized Yeast Cells

[0051] A method for synthesizing alkyl galactosides using immobilized cells and monosaccharides as glycosyl donors, the steps and conditions are the same as those in Example 2, except that the glycosyl acceptor is ethanol.

[0052] 15 mg of the alkyl galactoside product prepared in this example was dissolved in 450 μL of deuterated water and subjected to nuclear magnetic resonance analysis, including hydrogen spectrum ( 1 H NMR), carbon spectrum ( 13 C NMR), hydrogen-hydrogen correlation spectroscopy (COSY), high-speed quantitative carbonyl correlation spectroscopy (HSQC), and high-hydrogen long-range carbonyl correlation spectroscopy (HMBC) were used to determine the chemical shift of the glycoside product, confirming that the glycoside product was ethyl-β-D-galactoside.

[0053] like Figure 3 As shown, the chemical shift of ethyl-β-D-galactoside is: 1 H NMR(400MHz,D2O):δ4.4(d,1H,H-1,J 1,2 =8.0Hz),3.98(dq,1H,H-7),3.92(d,1H,H-4),3.76(m,2H,H-6),3.70(m,2H,H-7,H-5),3.64(dd,1H,H-3),3.49(dd,1H,H-2),1.23(t,3H,H-8); 13 C NMR (100MHz, D2O): δ102.46(C-1), 75.11(C-5), 72.86(C-3), 70.76(C-2), 68.67(C-4), 66.12(C-7), 60.95(C-6), 14.30(C-8).

[0054] The above-mentioned ethyl-β-D-galactoside has the molecular formula C8H 16 O6, chemical structure is shown in the following formula (2):

[0055]

[0056] Example 4 Synthesis of n-propyl galactoside catalyzed by immobilized yeast cells

[0057] A method for synthesizing alkyl galactosides using immobilized cells and monosaccharides as glycosyl donors, the steps and conditions are the same as those in Example 2, except that the glycosyl acceptor is n-propanol.

[0058] 15 mg of the alkyl galactoside product prepared in this example was dissolved in 450 μL of deuterated water and subjected to nuclear magnetic resonance analysis, including hydrogen spectrum ( 1 H NMR), carbon spectrum ( 13 C NMR), hydrogen-hydrogen correlation spectroscopy (COSY), high-speed quantitative carbonyl chromatography (HSQC), and high-hydrogen long-range carbonyl chromatography (HMBC) spectroscopy confirmed that the glycoside product was n-propyl-β-D-galactoside.

[0059] like Figure 4 As shown, the chemical shift of n-propyl-β-D-galactoside is: 1 H NMR(400MHz,D2O): δ4.39(d,1H,H-1,J 1,2 =8.0Hz),3.92(d,1H,H-4),3.86(m,1H,H-7),3.75(m,2H,H-6),3.68(m,1H,H-5 ),3.63(m,2H,H-7,H-3),3.50(dd,1H,H-2),1.63(m,2H,H-8),0.91(t,3H,H-9); 13 C NMR (100MHz, D2O): δ102.71(C-1),75.08(C-5),72.85(C-3),72.20(C-7),70.80(C-2),68.67(C-4),60.95(C-6),22.19(C-8),9.64(C-9).

[0060] The above-mentioned n-propyl-β-D-galactoside has the molecular formula C9H 18 O6, chemical structure is shown in formula (3):

[0061]

[0062] Example 5 Synthesis of Isopropylgalactoside Catalyzed by Immobilized Yeast Cells

[0063] A method for synthesizing alkyl galactoside using immobilized cells with monosaccharide as glycosyl donor, the steps and conditions are the same as in Example 2, except that the glycosyl acceptor is isopropyl alcohol.

[0064] Take 15 mg of the alkyl galactoside product prepared in this example and dissolve it in 450 μL of deuterated water for nuclear magnetic analysis, including hydrogen spectrum 1 (H NMR), carbon spectrum 13 (C NMR), hydrogen-hydrogen correlation spectrum (COSY), carbon-hydrogen direct correlation spectrum (HSQC), and carbon-hydrogen remote correlation spectrum (HMBC), to confirm that the glycoside product is isopropyl-β-D-galactoside.

[0065] As shown in Figure 5 , the chemical shifts of isopropyl-β-D-galactoside are: 1 H NMR (400 MHz, D2O): δ 4.47 (d, 1H, H-1, J 1,2 = 8.0 Hz), 4.11 (m, 1H, H-7), 3.92 (d, 1H, H-4), 3.76 (m, 2H, H-6), 3.69 (m, 1H, H-5), 3.64 (m, 1H, H-3), 3.46 (dd, 1H, H-2), 1.22 (m, 6H, H-8, H-9); 13 C NMR (100 MHz, D2O): δ 100.98 (C-1), 75.06 (C-5), 73.00 (C-7), 72.90 (C-3), 70.83 (C-2), 68.64 (C-4), 60.90 (C-6), 22.39 (C-8), 20.99 (C-9).

[0066] The above isopropyl-β-D-galactoside has a molecular formula of C9H 18 O6, and a chemical structural formula as shown in formula (4):

[0067]

[0068] Example 6 Synthesis of n-butyl galactoside catalyzed by immobilized yeast cells

[0069] A method for synthesizing alkyl galactoside using immobilized cells with monosaccharide as glycosyl donor, the steps and conditions are the same as in Example 2, except that the glycosyl acceptor is n-butanol, and the instrument used for nuclear magnetic analysis is a Bruker Dalton 600 MHz nuclear magnetic resonance spectrometer (USA).

[0070] Take 15 mg of the alkyl galactoside product prepared in this example and dissolve it in 450 μL of deuterated water for nuclear magnetic analysis, including hydrogen spectrum 1 (H NMR), carbon spectrum 13C NMR), hydrogen-hydrogen correlation spectroscopy (COSY), high-speed hydrocarbon correlation spectroscopy (HSQC), and high-hydrogen long-range hydrocarbon correlation spectroscopy (HMBC) confirmed that the glycoside product was n-butyl-β-D-galactoside.

[0071] like Figure 6 As shown, the chemical shift of n-butyl-β-D-galactoside is: 1 H NMR(600MHz,D2O):δ4.40(d,1H,H-1,J 1,2 =6.0Hz),3.93(m,2H,H7,H-4),3.77(qd,2H,H-6),3.69(td,2H,H-7,H-5),3.65(dd, 1H,H-3),3.5(dd,1H,H-2),1.61(dt,2H,H-8),1.38(dq,2H,H-9),0.91(t,3H,H-10); 13 CNMR(150MHz,D2O): δ102.73(C-1),75.07(C-5),72.82(C-3),70.77(C-2),70 .35(C-7),68.65(C-4),60.91(C-6),30.88(C-8),18.46(C-9),13.08(C-10).

[0072] The above-mentioned n-butylpropyl-β-D-galactoside has the molecular formula C9H 18 O6, chemical structure is shown in formula (5):

[0073]

[0074] Example 7 Synthesis of n-pentylgalactoside catalyzed by immobilized yeast cells

[0075] A method for synthesizing alkyl galactosides using immobilized cells and monosaccharides as glycosyl donors, the steps and conditions are the same as those in Example 2, except that the glycosyl acceptor is n-pentanol.

[0076] 15 mg of the alkyl galactoside product prepared in this example was dissolved in 450 μL of deuterated water and subjected to nuclear magnetic resonance analysis, including hydrogen spectrum ( 1 H NMR), carbon spectrum ( 13 C NMR), hydrogen-hydrogen correlation spectroscopy (COSY), high-speed quantitative carbonyl chromatography (HSQC), and high-hydrogen long-range carbonyl correlation spectroscopy (HMBC) confirmed that the glycoside product was n-pentyl-β-D-galactoside.

[0077] like Figure 7 As shown, the chemical shift of n-pentyl-β-D-galactoside is: 1 H NMR(400MHz,D2O): δ4.39(d,1H,H-1,J1,2 =8.0Hz),3.92(m,2H,H7,H-4),3.76(m,2H,H-6),3.65(m,3H,H-7,H-5,H-3),3 .49(dd,1H,H-2),1.63(p,2H,H-8),1.33(m,4H,H-9,H-10),0.89(m,3H,H-11); 13 C NMR(100MHz,D2O): δ102.73(C-1),75.07(C-5),72.83(C-3),70.77(C-2),70.64(C- 7),68.64(C-4),60.90(C-6),28.44(C-8),27.31(C-9),21.77(C-10),13.26(C-11).

[0078] The above-mentioned n-pentyl-β-D-galactoside has the molecular formula C 10 H 20 O6, chemical structure is shown in formula (6):

[0079]

[0080] Example 8 Synthesis of n-hexylgalactoside catalyzed by immobilized yeast cells

[0081] A method for synthesizing alkyl galactosides using immobilized cells and monosaccharides as glycosyl donors, the steps and conditions are the same as those in Example 2, except that the glycosyl acceptor is n-hexanol.

[0082] 15 mg of the alkyl galactoside product prepared in this example was dissolved in 450 μL of deuterated water and subjected to nuclear magnetic resonance analysis, including hydrogen spectrum ( 1 H NMR), carbon spectrum ( 13 C NMR), hydrogen-hydrogen correlation spectroscopy (COSY), high-speed quantitative carbonyl chromatography (HSQC), and high-hydrogen long-range carbonyl chromatography (HMBC) spectroscopy confirmed that the glycoside product was n-hexyl-β-D-galactoside.

[0083] like Figure 8 As shown, the chemical shift of n-hexyl-β-D-galactoside is: 1 H NMR(400MHz,D2O): δ4.43(d,1H,H-1,J 1,2 =8.0Hz),3.95(m,2H,H7,H-4),3.81(m,2H,H-6),3.71(m,2H,H-7,H-5),3.67(d,2H,H-3 ),3.52(dd,1H,H-2),1.65(p,2H,H-8),1.33(m,4H,H-9,H-10,H-11),0.91(m,3H,H-12);13 CNMR(100MHz,D2O): δ102.75(C-1),75.08(C-5),72.84(C-3),70.77(C-2),70.81(C-7),70. 70(C-4),60.95(C-6),30.85(C-10),28.74(C-8),24.76(C-9),21.95(C-11),13.36(C-12).

[0084] The above n-hexyl-β-D-galactoside has the molecular formula C 11 H 22 O6, chemical structure is shown in formula (7):

[0085]

[0086] In summary, the present invention is the first to use immobilized yeast cells to synthesize methyl-β-D-galactoside, ethyl-β-D-galactoside, n-propyl-β-D-galactoside, isopropyl-β-D-galactoside, n-butyl-β-D-galactoside, n-pentyl-β-D-galactoside or n-hexyl-β-D-galactoside in one step using a monosaccharide as a glycosyl donor. The process is simple, and there is no group protection and deprotection process required in chemical synthesis. The process is environmentally friendly, has mild reaction conditions, is easy to operate, is suitable for large-scale synthesis of alkyl glycosides, and has broad application prospects.

Claims

1. A method for synthesizing alkyl galactosides using immobilized cells and monosaccharides as glycosyl donors, characterized in that: The following steps are involved: (1) Cultivating β-galactosidase-producing yeast and collecting yeast cells; (2) Suspend the yeast cells in an ethanol solution, stir at 20-30°C for 1-10 min, and centrifuge to obtain ethanol-treated yeast cells; (3) Genipin was added to the yeast cells after ethanol treatment to construct a cross-linking system; The cross-linking system was reacted at 20-30°C and 100-150 rpm for 0.5-4 h, and then centrifuged to obtain immobilized cells. Wherein, the concentration of genipin in the cross-linking system is 0.05%, and the concentration of ethanol-treated yeast cells is 0.05-0.2 mg / μL; (4) Galactose and alkyl alcohol are mixed evenly, added to immobilized cells, reacted at 30-50°C for 2-16 hours, centrifuged to separate the solid and liquid, and the supernatant is collected. The organic solvent is removed, silica gel column chromatography is performed, and freeze-dried to obtain alkyl galactoside; Wherein, the concentration of the galactose is 0.4-0.8 M; the concentration of the alkyl alcohol is 10-40%.

2. The synthesis method according to claim 1, wherein In step (1), the β-galactosidase-producing yeast is Kluyveromyces lactis, with a preservation number of CGMCC 2.1494.

3. The synthesis method according to claim 1, wherein In step (2), the concentration of the ethanol solution is 40-50%.

4. The synthesis method according to claim 1, wherein In step (4), the alkyl alcohol is methanol, ethanol, n-propanol, isopropanol, n-butanol, n-pentanol or n-hexanol.

5. The synthesis method according to claim 1, wherein In step (4), the amount of the immobilized cells added is 80-200% of the mass of galactose.

6. The synthesis method according to claim 1, wherein In step (4), the silica gel column chromatography conditions are: methanol:ethyl acetate = 3:7 as the mobile phase, the sample loading amount is 1~2 mL, and the elution flow rate is 0.5~0.8 mL / min.

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