Cyclic lactam compound and liquid phase synthesis method thereof

Abstract

The invention relates to a cyclic lactam compound and a liquid-phase synthesis method thereof, and belongs to the technical field of organic synthesis. The cyclic lactam compound has a structural formula as shown in a general formula I: # imgabs0 #, in the general formula I, n is a positive integer from 1 to 49, R1 is a substituent group on a proline alpha carbon atom, and R2 is a substituent group on a natural amino acid alpha carbon atom. The liquid-phase synthesis method of the cyclic lactam compound comprises the following steps: S1, providing a straight-chain compound with two tail ends respectively containing amino and carboxyl; and S2, in the presence of disaccharide, carrying out cyclization reaction on the straight-chain compound to obtain the cyclic lactam compound. The cyclic lactam compounds described herein exhibit good antibacterial activity against Escherichia coli and Staphylococcus aureus. The liquid-phase synthesis method of the cyclic lactam compound is low in raw material and equipment cost, the yield is as high as 80-85%, and the liquid-phase synthesis method is suitable for large-scale production.

Description

Technical Field

[0001] The present application relates to the field of organic synthesis and biomedicine technology, and in particular to a cyclic lactam compound and a liquid phase synthesis method thereof. Background Art

[0002] Cyclic lactam compounds, also known as cyclopeptides, are compounds with broad application prospects, and their synthesis and application research have received widespread attention. This type of compound has a special molecular structure, which contains a cyclic skeleton and a peptide chain. Due to its special molecular structure, cyclopeptide compounds not only have good stability, but also have multiple biological activities, such as antibacterial, anti-tumor, anti-inflammatory, etc., so they have broad application prospects in the fields of medicine, agriculture, environmental protection, etc.

[0003] Cyclic peptides are the most widely used in the pharmaceutical field and are excellent candidate molecules for drug development. Compared with linear peptides, cyclic peptides have a more rigid structure and therefore have higher stability and affinity, and are not easily degraded; compared with small molecules, cyclic peptides have a larger surface area and can potentially form multiple hydrogen bonds to improve the specificity and selectivity of the target; compared with protein drugs, cyclic peptides are more convenient for various chemical modifications, and the assembly components are usually natural amino acids, which are safer and more economical. In addition, cyclic peptides can also improve the pharmacokinetic properties of absorption. Special cyclic peptides such as bicyclic peptides have stronger cell penetration properties.

[0004] These physicochemical properties and physiological activities make cyclic peptides widely used as therapeutic drug molecules, drug auxiliary molecules, protein-protein interaction research and drug screening. They have broad prospects for drug development in the fields of anti-cancer, anti-viral, anti-fungal and enzyme inhibition. With the help of high-throughput screening technologies such as phage display, the development efficiency of cyclic peptides has been further improved, and their medicinal value has been greatly improved. At present, among the more than 60 peptide drugs approved by the FDA and EMA, cyclic peptide drugs account for as much as 2 / 3. On average, about one new cyclic peptide drug enters the therapeutic market every year, making it a well-deserved "new star" among peptide drugs. In addition, the application research of cyclic peptide compounds in the field of environmental protection has also received widespread attention. Some cyclic peptide compounds have the effect of inhibiting bacteria and fungi, so they have been used in fields such as water treatment and waste gas treatment.

[0005] The liquid phase synthesis methods of cyclic oligopeptide compounds mainly include solid phase synthesis and liquid phase synthesis. The solid phase synthesis method requires the purchase of equipment such as solid phase synthesizers for synthesis. These equipment are usually expensive, resulting in relatively high costs. The solid phase synthesis method requires the use of a carrier, and the reaction is carried out in the pores of the carrier. If the post-reaction washing is not thorough, the wrong amino acid sequence may be introduced into the polypeptide chain. In addition, the solid phase synthesis method usually adopts a full protection strategy to connect the terminal amino or carboxyl group to the solid phase carrier, which is also not conducive to the synthesis of end-to-end cyclic peptides.

[0006] In the existing liquid phase synthesis method of cyclic oligopeptide compounds, the efficiency of the head-to-tail cyclization of cyclic oligopeptide compounds is not high, and the yield of cyclic lactam is also not high, generally less than 10%.

[0007] Therefore, there is a continuous need in the art to develop cyclic lactam compounds with novel structures and liquid phase synthesis methods of cyclic lactam compounds with high yields. Summary of the invention

[0008] The purpose of the present application is to provide a cyclic lactam compound with a novel structure, wherein the structural unit includes a residue derived from the condensation of proline and a residue derived from other amino acids that form a ring with proline. The cyclic lactam compound described herein exhibits good antibacterial activity against Escherichia coli and Staphylococcus aureus.

[0009] The present application also aims to provide a pharmaceutically acceptable salt of a cyclic lactam compound.

[0010] The purpose of the present application is also to provide a liquid phase synthesis method for a cyclic lactam compound. The liquid phase synthesis method comprises providing a straight-chain compound having a terminal amino group at one end and a terminal carboxyl group at the other end, and then creatively using a disaccharide as a cyclization catalyst to cyclize the straight-chain compound to obtain a cyclic lactam compound. Disaccharides can significantly improve the efficiency of the head-to-tail connection of the straight-chain compound, thereby improving the yield of the cyclized compound.

[0011] The present application also aims to provide a new use of a disaccharide as a catalyst in the process of synthesizing a cyclic lactam compound or a pharmaceutically acceptable salt thereof.

[0012] In order to solve the above technical problems, this application provides the following technical solutions.

[0013] In a first aspect, the present application provides a cyclic lactam compound or a pharmaceutically acceptable salt thereof, wherein the cyclic lactam compound has a structural formula as shown in general formula I:

[0014]

[0015] Wherein, n is a positive integer from 1 to 49;

[0016] Wherein, R1 is a substituent group on the α-carbon atom of proline;

[0017] Wherein, R2 is a substituent group on the α-carbon atom of a natural amino acid;

[0018] The natural amino acids are selected from one or more of the following: glycine, alanine, valine, leucine, isoleucine, methionine, proline, tryptophan, serine, tyrosine, cysteine, phenylalanine, asparagine, glutamine, threonine, aspartic acid, glutamic acid, lysine, arginine, histidine, selenocysteine ​​and pyrrolysine.

[0019] In a second aspect, the present application provides a liquid phase synthesis method of the cyclic lactam compound as described above, the method comprising the following steps:

[0020] S1: providing a linear compound containing one or more amino acid structural units, wherein one end of the linear compound contains an amino group, and the other end of the linear compound contains a carboxyl group;

[0021] S2: In the presence of a disaccharide, the linear compound is subjected to a cyclization reaction to condense the amino group and the carboxyl group to obtain the cyclic lactam compound.

[0022] In a third aspect, the present application provides the use of a disaccharide as a catalyst in the process of preparing a cyclic lactam compound or a pharmaceutically acceptable salt thereof as described above. In this embodiment, the disaccharide may include one or more of the following: sucrose, maltose, trehalose, cellobiose and chitobiose.

[0023] Compared with the prior art, the positive effect of the present invention is that the cyclic lactam compound with a novel structure disclosed herein has excellent antibacterial activity. Secondly, the liquid phase synthesis method of the cyclic lactam compound described herein has low raw material and equipment costs, high yield, and is suitable for large-scale production. DETAILED DESCRIPTION

[0024] Unless otherwise indicated, implied from the context, or customary in the prior art, all parts and percentages in this application are based on weight, and the test and characterization methods used are all current as of the filing date of this application. Where applicable, the contents of any patent, patent application or publication referred to in this application are fully incorporated herein by reference, and their equivalent patent families are also incorporated by reference, especially the definitions of synthesis techniques, product and processing designs, polymers, comonomers, initiators or catalysts disclosed in these documents in the art. If the definition of a specific term disclosed in the prior art is inconsistent with any definition provided in this application, the definition of the term provided in this application shall prevail.

[0025] Numerical ranges in this application are approximate values, so unless otherwise specified, they may include numerical values ​​outside the range. Numerical ranges include all numerical values ​​from the lower limit to the upper limit increased by 1 unit, provided that there is an interval of at least 2 units between any lower value and any higher value. For example, if the recorded component, physical or other properties (such as molecular weight, melt index, etc.) are 100 to 1000, it means that all single values ​​are clearly listed, such as 100, 101, 102, etc., and all sub-ranges, such as 100 to 166, 155 to 170, 198 to 200, etc. For a range containing a numerical value less than 1 or containing a fraction greater than 1 (such as 1.1, 1.5, etc.), 1 unit is appropriately regarded as 0.0001, 0.001, 0.01 or 0.1. For a range containing a single digit less than 10 (such as 1 to 5), 1 unit is usually regarded as 0.1. These are only specific examples of what is intended to be expressed, and all possible combinations of values ​​between the lowest and highest values ​​listed are considered to be clearly recorded in this application. It should also be noted that the terms "first", "second", etc. in this article do not limit the order of precedence, but are only used to distinguish substances with different structures.

[0026] When used with respect to chemical compounds, unless expressly specified otherwise, the singular includes all isomeric forms and vice versa (e.g., "hexane" includes all isomers of hexane, individually or collectively). In addition, nouns using "a," "an," or "the" also include their plural forms unless expressly specified otherwise.

[0027] The terms "comprising", "including", "having" and their derivatives do not exclude the presence of any other components, steps or processes, and are irrelevant to whether these other components, steps or processes are disclosed in this application. To eliminate any doubt, unless explicitly stated, all compositions using the terms "comprising", "including", or "having" in this application may include any additional additives, adjuvants or compounds. On the contrary, except for those necessary for operating performance, the term "essentially consisting of..." excludes any other components, steps or processes from the scope of any description of the term below. The term "consisting of..." does not include any components, steps or processes that are not specifically described or listed. Unless explicitly stated, the term "or" refers to the listed individual members or any combination thereof.

[0028] Cyclic lactam compounds are widely used in biomedicine and environmental protection fields. However, the existing solid phase synthesis method of cyclic lactam compounds has the disadvantages of low yield, high cost and difficulty in scale-up, which limits the large-scale application of cyclic lactam compounds. The existing liquid phase synthesis method for synthesizing cyclic lactam compounds usually has a yield of less than 10%. Although mass production can be achieved, it will cause a large amount of raw material waste, which indirectly increases the cost of obtaining cyclic lactam compounds.

[0029] In order to overcome the shortcomings of the existing synthesis methods of cyclic lactam compounds, the inventors of the present application conducted a large number of experiments and surprisingly found that when disaccharides are used as cyclization catalysts for the cyclization reaction of linear peptides in the liquid phase synthesis method, the efficiency of the head-to-tail cyclization of the terminal amino group and the terminal carboxyl group of the linear peptide can be significantly improved, and the yield of cyclic lactam compounds can be increased to 80-85%.

[0030] Cyclic lactam compounds

[0031] In one embodiment, the present application provides a cyclic lactam compound, wherein the cyclic lactam compound has a structural formula as shown in Formula I:

[0032]

[0033] In general formula I, n is a positive integer of 1-49, R1 is a substituent group on the alpha carbon atom of proline, and R2 is a substituent group on the alpha carbon atom of a natural amino acid. In this embodiment, the natural amino acid is selected from one or more of the following: glycine, alanine, valine, leucine, isoleucine, methionine, proline, tryptophan, serine, tyrosine, cysteine, phenylalanine, asparagine, glutamine, threonine, aspartic acid, glutamic acid, lysine, arginine, histidine, selenocysteine ​​and pyrrolysine. In a specific embodiment, the structural formula of each amino acid is as follows:

[0034]

[0035] In other words, the cyclic lactam compound described herein is a homopolymeric peptide, all structural units are derived from amino acids, and different structural units are connected by peptide bonds. The cyclic lactam compound described herein includes at least one residue derived from proline, because the proline residue has a certain inhibitory effect on racemization, so the original cis-trans configuration is maintained, so that the peptide chain with proline is easier to cyclize (J Meienhofer et.al.Syntheses ofactinomycin and analogs.III.Total synthesis of actinomycin D(C1)via peptidecyclization between proline and sarcosine.J.Am.Chem.Soc.92(12),3771-3777).

[0036] In a specific embodiment, the cyclic lactam compound described herein may include 2-50 amino acid structural units. In a preferred embodiment, the cyclic lactam compound described herein may include 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50 or a range or sub-range of amino acid structural units between any two of them. In a specific embodiment, n may be 4-11.

[0037] In one embodiment, the cyclic lactam compound can be selected from the following group:

[0038]

[0039]

[0040]

[0041]

[0042] Pharmaceutically acceptable salts of cyclic lactam compounds

[0043] In one embodiment, the present application provides a pharmaceutically acceptable salt of a cyclic lactam compound. Examples of pharmaceutically acceptable salts of cyclic lactam compounds may include acid addition salts and base addition salts. Examples of acid addition salts include inorganic acid salts, organic acid salts, and the like. Examples of inorganic acid salts include hydrochlorides, hydrobromides, sulfates, hydroiodides, nitrates, phosphates, and the like. Examples of organic acid salts include citrates, oxalates, acetates, formates, propionates, benzoates, trifluoroacetates, maleates, tartrates, methanesulfonates, benzenesulfonates, p-toluenesulfonates, and the like. Examples of base addition salts include inorganic base salts and organic base salts, and the like. Examples of inorganic base salts include sodium salts, potassium salts, calcium salts, magnesium salts, ammonium salts, and the like. Examples of organic base salts include triethylammonium salts, triethanolammonium salts, pyridinium salts, diisopropylammonium salts, and the like.

[0044] Liquid phase synthesis method of cyclic lactam compounds

[0045] In another embodiment, the present application provides a liquid phase synthesis method of the cyclic lactam compound as described above, and the method may include the following steps: S1: providing a straight-chain compound containing one or more amino acid structural units, one end of the straight-chain compound contains an amino group, and the other end of the straight-chain compound contains a carboxyl group; S2: in the presence of a disaccharide, subjecting the straight-chain compound to a cyclization reaction, so that the amino group and the carboxyl group are condensed to obtain the cyclic lactam compound.

[0046] In one specific embodiment, in step S1, the linear compound is selected from the following group:

[0047]

[0048]

[0049] In a specific implementation, the step S1 may include:

[0050] S11: reacting a first amino acid whose terminal amino group is protected by a tert-butyloxycarbonyl group with a second amino acid-third amino acid dipeptide ethyl ester to obtain a linear tripeptide whose terminal amino group is protected by a tert-butyloxycarbonyl group and whose terminal carboxyl group is protected by an ethyl group;

[0051] S12: performing a deprotection reaction on a linear tripeptide whose terminal amino group is protected by a tert-butyloxycarbonyl group and whose terminal carboxyl group is protected by an ethyl group, removing the tert-butyloxycarbonyl group to obtain a linear tripeptide whose terminal carboxyl group is protected by an ethyl group;

[0052] S13: subjecting the linear tripeptide whose terminal carboxyl group is protected by an ethyl group to a deethylation reaction in a THF / H2O mixed solvent to obtain a linear tripeptide whose terminal amino group is protected by a tert-butyloxycarbonyl group;

[0053] S14: condensing the linear tripeptide whose terminal amino group is protected by a tert-butyloxycarbonyl group and the linear tripeptide whose terminal carboxyl group is protected by an ethyl group to obtain a linear hexapeptide whose terminal amino group is protected by a tert-butyloxycarbonyl group and whose terminal carboxyl group is protected by an ethyl group;

[0054] S15: performing a deprotection reaction on the linear hexapeptide in which the terminal amino group is protected by a tert-butyloxycarbonyl group and the terminal carboxyl group is protected by an ethyl group to obtain the linear compound.

[0055] In a specific embodiment, in step S2, the disaccharide comprises one or more of the following: sucrose, maltose, trehalose, cellobiose and chitobiose.

[0056] In one embodiment, the structural formulas of various disaccharides are as follows:

[0057]

[0058] In a specific embodiment, in step S2, the molar ratio of the linear compound to the disaccharide is 10: 1 to 10: 0.1. For example, the molar ratio of the linear compound to the disaccharide may be 10: 0.1, 10: 0.2, 10: 0.3, 10: 0.4, 10: 0.5, 10: 0.6, 10: 0.7, 10: 0.8, 10: 0.9, 10: 1, or a range or sub-range between any two of these values.

[0059] In a specific embodiment, the liquid phase synthesis method described herein comprises the following steps: coupling Boc-Gly-OH with NH2-Pro-OMe to obtain two dipeptide fragments (which can be purchased through commercial channels), then saponifying Boc-Gly-Pro-OMe and coupling it with NH2-Gln-OMe to obtain a Boc-Gly-Pro-Gln-OMe tripeptide fragment, which is then saponified and coupled with NH2-Gly-Pro-Gln-OMe to obtain a hexapeptide fully protected The fragment is deprotected and purified to obtain Boc-Gly-Pro-Gln-Gly-Pro-Gln-OMe, and the hexapeptide is cyclized to obtain the target cyclic peptides Cyclo(Gly-Pro-Gln-Gly-Pro-Gln), Cyclo(Ala-Pro-Gln-Ala-Pro-Gln), and Cyclo(Gly-Pro-Gln-Gly-Pro-Gln-Gly-Pro-Gln-Gly-Pro-Gln). The target cyclic peptide can be further prepared into pharmaceutically acceptable salts.

[0060] Example

[0061] The following will be combined with the embodiments of the present application to clearly and completely describe the technical solution of the present application. Unless otherwise specified, the reagents and raw materials used can be purchased through commercial channels. The experimental methods in the following examples that do not specify specific conditions are selected according to conventional methods and conditions, or according to the product specifications.

[0062] In the following examples, the test method of nuclear magnetic resonance spectrum is as follows. The prepared compound was characterized by a 500 MHz nuclear magnetic resonance spectrometer (Bruker BioSpin, Germany, AVANCE III HD) to determine the correctness of the product structure. Considering the solubility, the deuterated reagent was deuterated dimethyl sulfoxide (DMSO-d6: δH = 2.50 ppm, δC = 39.52 ppm), and tetramethylsilane (TMS) was used as an internal standard, and its chemical shift was 0 ppm.

[0063] Synthesis Example

[0064] Example 1: In an ice-water bath, N-Boc-glutamine (10 mmol) and proline-glycine dipeptide ethyl ester (10 mmol) were dissolved in dichloromethane, and then nitrogen methylmorpholine (NMM, 10 mmol) was added. After stirring for 5-10 minutes, hydroxybenzotriazole (HOBT, 11 mmol) was added, followed by a dichloromethane solution of DCC (10 mmol). The reaction was allowed to react at 0°C for 5 hours, and then stirred at 4°C overnight. Dicyclohexylurea (DCU) was then filtered off, and the filtrate was evaporated to dryness by rotary evaporation. The product was then dissolved in ethyl acetate, washed with water, saturated sodium bicarbonate (20 ml×3), and then dried over anhydrous sodium sulfate. The washed product was separated and purified by silica gel column chromatography to obtain product A. Yield: 81%. 1 H NMR(500MHz,DMSO-d6)δ8.23(s,1H),7.95(s,1H),6.60(s,2H),4.59–4.42(m,3H),4.01 (d,J=12.2Hz,1H),3.82(d,J=12.5Hz,1H),3.69–3.52(m,2H),3.25(dt,J=9.5,7.1Hz,1H ),2.53–2.44(m,1H),2.34(dq,J=13.8,7.0Hz,1H),2.19–2.05(m,2H),2.07–1.95(m,2H ),1.98–1.80(m,2H),1.66(dt,J=13.2,7.0Hz,1H),1.39(s,10H),1.21(t,J=8.0Hz,3H). 13CNMR(125MHz,Common NMR Solvents) δ175.47,172.43,171.99,168.85,156.77,79.66,61.36,60.21,52.88,49.19,43.50,32.26,29.18,28.30,27.88,27.19,14.10.

[0065] The structural formula of compound A is shown below:

[0066]

[0067] Example 2: Tripeptide A (1 mmol) protected by tert-butyloxycarbonyl (Boc) and ethyl (CH2CH3) was dissolved in saturated HCl-ethyl acetate solution (20 ml) and reacted at room temperature for 2 hours. The solution was then concentrated by rotary evaporation and petroleum ether (100 ml) was added to precipitate the product. The supernatant was then poured out and petroleum ether (100 ml) was added again, and the product continued to precipitate. Finally, the petroleum ether was poured out and the crude product B of the Boc removal product remained in the bottle. Yield: 98%. 1 H NMR(500MHz,DMSO-d6)δ8.23(s,1H),6.56(s,2H),5.07(s,2H),4.55–4.40(m,3H) ,4.13(dt,J=9.4,6.7Hz,1H),3.74(d,J=12.5Hz,1H),3.40(dq,J=12.5,8.0Hz,1H) ,3.24(dt,J=9.5,6.9Hz,1H),3.15(d,J=12.5Hz,1H),2.25(td,J=12.5,2.3Hz,1H ),2.18–1.97(m,4H),1.98–1.89(m,1H),1.93–1.79(m,2H),1.21(t,J=8.0Hz,3H). 13 C NMR (125MHz, Common NMR Solvents) δ175.47,172.43,171.99,165.84,61.36,60.21,52.88,48.68,45.59,32.26,29.18,27.88,27.19,14.10.

[0068] The structural formula of compound B is shown below:

[0069]

[0070] Example 3: Boc, ethyl protected tripeptide B (1 mmol) was dissolved in a THF / H2O (10 ml-10 ml) mixed solvent, and solid LiOH (1.1 mmol) was added at room temperature. After stirring for 30 minutes, water (30 ml) and citric acid solution (1 ml) were added to quench. The aqueous phase solution was extracted with ethyl acetate (3×25 ml), and then the layers were separated, dried over anhydrous sodium sulfate, filtered, and evaporated to obtain a crude deethylated product C. Yield: 92%. 1 H NMR(500MHz,DMSO-d6)δ8.23(s,1H),7.95(s,1H),7.42(s,2H),4.38–4.27(m ,3H),3.88(d,J=12.5Hz,1H),3.54(dt,J=9.4,7.0Hz,1H),3.23(dt,J=9.4,7. 0Hz,1H),2.43(ddt,J=12.4,5.5,1.5Hz,1H),2.27–2.18(m,1H),2.21–2.14( m,1H),2.18–2.10(m,1H),2.02–1.77(m,3H),1.69–1.57(m,1H),1.39(s,9H). 13 C NMR (125MHz, Common NMR Solvents) δ175.47,175.17,171.99,168.85,156.77,79.66,60.21,52.40,49.19,43.50,32.26,29.18,28.30,27.81,27.19.

[0071] The structural formula of compound C is shown below:

[0072]

[0073] Example 4: The tripeptide C (1 mmol) was dissolved in dichloromethane. In an ice-water bath, N-methylmorpholine (NMM, 1 mmol) was added. After 5-10 minutes, the selectively de-tert-butyloxycarbonylated tripeptide B (1 mmol) and HOBT were added, followed by DCC (2 mmol). The mixture was reacted at 0°C for 5 hours, and then left to react overnight at 0°C. The reaction solution was then filtered. The filter cake was washed with an ethanol solution, and the ethanol solution was then evaporated to obtain a crude product of the tert-butyloxycarbonyl and ethyl-protected hexapeptide. The crude product was then purified by silica gel column chromatography to obtain a pure hexapeptide product D. Yield: 86%. 1H NMR(500MHz,DMSO-d6)δ8.49(d,J=16.5Hz,2H),8.30(s,2H),7.30(s,2H),5.32–5.20(m,2H),4.64( dt,J=28.0,7.0Hz,2H),4.48–4.37(m,2H),3.96–3.84(m,2H),3.63(d,J=12.5Hz,1H),3.50(dt,J=9. 5,7.1Hz,1H),3.37–3.27(m,2H),3.30–3.17(m,2H),2.57–2.45(m,2H),2.48–2.32(m,2H),2.19–2. 06(m,2H),2.02–1.71(m,6H),1.74–1.53(m,2H),1.39(s,9H),1.39–1.29(m,1H),1.15–1.05(m,4H). 13 C NMR (125MHz, Common NMR Solvents)δ175.21,174.76,173.32,172.79,171.99,168.85,156.77,80.27,79.66,63.34,59.90, 59.75,52.50,49.19,43.50,42.13,32.43,32.00,30.06,29.18,28.96,28.30,27.45,27.19,15.06.

[0074] The structural formula of compound B is shown below:

[0075]

[0076] Example 5: D (1.16 g, 1.7 mmol) was dissolved in 20 ml of trifluoroacetic acid and stirred at room temperature for 1 hour. The solution was then evaporated to dryness and washed with ether, and the suspension was filtered to obtain the de-tert-butyloxycarbonyl product. Under ice-water bath conditions, the de-tert-butyloxycarbonyl product in the previous step was dissolved in a mixed solvent of THF / H2O, and then LiOH·H2O (14.3 mg, 3.4 mmol, 2 eq) was added, stirred for 10 hours, and finally neutralized with 1N hydrochloric acid to neutrality. The solution was extracted with ethyl acetate, the organic phase was dried over anhydrous sodium sulfate, filtered and then evaporated to dryness to obtain the deprotected product E. Yield: 91%. 1H NMR(500MHz,DMSO-d6)δ8.43(s,1H),8.23(s,1H),7.40(s,2H),6.64(s,2H),4.96–4.89(m,2H),4. 79(s,1H),4.42(dt,J=24.8,6.8Hz,2H),3.97(s,3H),3.74(d,J=12.5Hz,1H),3.69–3.48(m,4H),3. 32–3.13(m,3H),2.94(d,J=12.5Hz,1H),2.69–2.60(m,1H),2.55–2.47(m,1H),2.47–2.35(m,1H), 2.27–2.15(m,4H),2.13–2.02(m,2H),1.98–1.68(m,6H),1.51–1.41(m,1H),1.04(t,J=8.0Hz,3H). 13 C NMR (125MHz, Common NMR Solvents)δ175.2,174.8,173.3,172.8,172.0,169.0,168.2,80.3,63.3,60.2,59.8 ,52.5,52.5,49.2,48.7,42.1,36.3,32.4,32.0,30.1,29.2,29.0,27.4,27.2,15.1.

[0077] The structural formula of compound E is shown below:

[0078]

[0079] Embodiment 6:

[0080] The deprotected product E (1 mmol) was dissolved in THF (40 ml), and HOBT (2 mmol) was added, followed by a THF solution of DCC (2 mmol) and a sucrose catalyst (0.05 mmol). The reaction was carried out at 0°C for 5 hours, and then at 4°C overnight. The filtrate was filtered out, and the filter cake was washed with ethanol. The ethanol solution was evaporated to obtain a crude product of cyclopeptide F, which was purified by silica gel column chromatography to obtain cyclopeptide F. Yield: 85%. 1H NMR(500MHz,Deuterium Oxide)δ5.46(dd,J=10.4,1.8Hz,1H),4.74–4.62(m,2H),4.51–4.43(m,2H),4.37(t,J=6.6Hz,1H),3.94(dt,J=9.6,7.0Hz,1H) ,3.77–3.67(m,2H),3.54–3.35(m,4H),2.73–2.52(m,4H),2.33(dt,J=12.4,3.3Hz,1H),2.23–2.12(m,2H),2.13–1.81(m,8H). 13 C NMR (125MHz, Deuterium Oxide)δ175.2,174.8,173.5,173.3,172.0,169.0,165.8,74.6,60.2,59. 8,52.5,49.2,48.7,45.6,42.1,33.4,32.0,31.9,29.2,29.0,27.4,27.2.

[0081] Example 6-1:

[0082] The deprotected product E (1 mmol) was dissolved in THF (40 ml), HOBT (2 mmol) was added, and then a THF solution of DCC (2 mmol) and a maltose catalyst (0.05 mmol) were added. The reaction was carried out at 0°C for 5 hours, and then at 4°C overnight. The filtrate was filtered out, and then the filter cake was washed with ethanol. The ethanol solution was evaporated to obtain a crude product of cyclopeptide F, which was purified by silica gel column chromatography to obtain cyclopeptide F. Yield: 82%.

[0083] Example 6-2:

[0084] The deprotected product E (1 mmol) was dissolved in THF (40 ml), HOBT (2 mmol) was added, and then a THF solution of DCC (2 mmol) and a trehalose catalyst (0.05 mmol) were added. The reaction was carried out at 0°C for 5 hours, and then at 4°C overnight. The filtrate was filtered out, and then the filter cake was washed with ethanol. The ethanol solution was evaporated to obtain a crude product of cyclopeptide F, which was purified by silica gel column chromatography to obtain cyclopeptide F. Yield: 86%.

[0085] Example 6-3:

[0086] The deprotected product E (1 mmol) was dissolved in THF (40 ml), HOBT (2 mmol) was added, and then a THF solution of DCC (2 mmol) and a cellobiose catalyst (0.05 mmol) were added. The reaction was carried out at 0°C for 5 hours, and then at 4°C overnight. The filtrate was filtered out, and then the filter cake was washed with ethanol. The ethanol solution was evaporated to obtain a crude product of cyclopeptide F, which was purified by silica gel column chromatography to obtain cyclopeptide F. Yield: 83%.

[0087] Example 6-4:

[0088] The deprotected product E (1 mmol) was dissolved in THF (40 ml), HOBT (2 mmol) was added, and then a THF solution of DCC (2 mmol) and a chitobiose catalyst (0.05 mmol) were added. The reaction was carried out at 0°C for 5 hours, and then at 4°C overnight. The filtrate was filtered out, and then the filter cake was washed with ethanol. The ethanol solution was evaporated to obtain a crude product of cyclopeptide F, which was purified by silica gel column chromatography to obtain cyclopeptide F. Yield: 81%.

[0089] The structural formula of compound F is shown below:

[0090]

[0091] Embodiment 7:

[0092] Using N-Boc-glutamine and proline-alanine dipeptide ethyl ester as raw materials, the synthesis methods of Examples 1 to 5 were used to prepare the pure hexapeptide product G. The total yield was 60%. 1 H NMR (500MHz, DMSO-d6): δ9.75(s,1H),8.23(s,2H),8.05(s,2H),6.88(s,2H),4.74–4.66( m,2H),4.51–4.38(m,4H),3.78(q,J=6.8Hz,1H),3.58(dt,J=9.4,6.9Hz,1H),3.21(ddt,J= 27.3,9.4,7.0Hz,2H),2.98(ddd,J=12.7,10.4,2.4Hz,1H),2.55–2.28(m,5H),2.25–2.12( m,2H),2.06–1.94(m,1H),1.92–1.66(m,7H),1.34(d,J=6.8Hz,3H),1.27(d,J=6.8Hz,3H).

[0093] The structural formula of compound G is shown below:

[0094]

[0095] Embodiment 8:

[0096] Polypeptide G (1 mmol) was dissolved in THF (40 mL), HOBT (2 mmol) was added, and then a THF solution of DCC (2 mmol) and a catalyst of p-tert-butylphenol (0.1 mmol) were added. The reaction was carried out at 0°C for 5 hours, and then at 4°C overnight. The filtrate was filtered out, and then the filter cake was washed with ethanol. The ethanol solution was evaporated to obtain a crude product of cyclopeptide F, which was purified by silica gel column chromatography to obtain cyclopeptide H. Yield: 82%. 1 H NMR (500MHz, DMSO-d6) δ9.90 (s, 1H), 8.27 (d, J = 9.2 Hz, 4H), 4.92 (dq, J = 39.2, 6. 8Hz,2H),4.48–4.28(m,4H),3.68(dt,J=9.4,6.9Hz,1H),3.51(dt,J=9.3,6.9Hz, 1H),3.46–3.37(m,2H),2.73–2.59(m,2H),2.58–2.44(m,2H),2.48–2.31(m,2H) ,2.22–2.11(m,1H),2.04–1.69(m,7H),1.60–1.47(m,2H),1.34(d,J=6.8Hz,6H).

[0097] The structural formula of compound H is shown below:

[0098]

[0099] Example 8-1:

[0100] Polypeptide G (1 mmol) was dissolved in THF (40 mL), HOBT (2 mmol) was added, and then a THF solution of DCC (2 mmol) and a sucrose catalyst (0.05 mmol) were added. The reaction was carried out at 0°C for 5 hours, and then at 4°C overnight. The filtrate was filtered out, and then the filter cake was washed with ethanol. The ethanol solution was evaporated to obtain a crude product of cyclopeptide F, which was purified by silica gel column chromatography to obtain cyclopeptide H. Yield: 86%.

[0101] Example 8-2:

[0102] Polypeptide G (1 mmol) was dissolved in THF (40 mL), HOBT (2 mmol) was added, and then a THF solution of DCC (2 mmol) and a maltose catalyst (0.05 mmol) were added. The reaction was carried out at 0°C for 5 hours, and then at 4°C overnight. The filtrate was filtered out, and then the filter cake was washed with ethanol. The ethanol solution was evaporated to obtain a crude product of cyclopeptide F, which was purified by silica gel column chromatography to obtain cyclopeptide H. Yield: 84%.

[0103] Example 8-3:

[0104] Polypeptide G (1 mmol) was dissolved in THF (40 mL), HOBT (2 mmol) was added, and then a THF solution of DCC (2 mmol) and a trehalose catalyst (0.05 mmol) were added. The reaction was carried out at 0°C for 5 hours, and then at 4°C overnight. The filtrate was filtered out, and then the filter cake was washed with ethanol. The ethanol solution was evaporated to obtain a crude product of cyclopeptide F, which was purified by silica gel column chromatography to obtain cyclopeptide H. Yield: 81%.

[0105] Example 8-4:

[0106] Polypeptide G (1 mmol) was dissolved in THF (40 mL), HOBT (2 mmol) was added, and then a THF solution of DCC (2 mmol) and a cellobiose catalyst (0.05 mmol) were added. The reaction was carried out at 0°C for 5 hours, and then at 4°C overnight. The filtrate was filtered out, and then the filter cake was washed with ethanol. The ethanol solution was evaporated to obtain a crude product of cyclopeptide F, which was purified by silica gel column chromatography to obtain cyclopeptide H. Yield: 85%.

[0107] Example 8-5:

[0108] Polypeptide G (1 mmol) was dissolved in THF (40 mL), HOBT (2 mmol) was added, and then a THF solution of DCC (2 mmol) and a chitobiose catalyst (0.05 mmol) were added. The reaction was carried out at 0°C for 5 hours, and then at 4°C overnight. The filtrate was filtered out, and then the filter cake was washed with ethanol. The ethanol solution was evaporated to obtain a crude product of cyclopeptide F, which was purified by silica gel column chromatography to obtain cyclopeptide H. Yield: 80%.

[0109] Embodiment 9:

[0110] Using N-Boc-glutamine and proline-leucine dipeptide ethyl ester as raw materials, the synthesis methods of Examples 1 to 5 were used to prepare the hexapeptide pure product I. The total yield was 62%. 1H NMR (500MHz, DMSO-d6) δ8.22(d,J=15.0Hz,5H),7.93(s,2H),6.71(s,2H),4.58(t,J=7.0Hz,1H),4.28(t ,J=7.0Hz,1H),4.11(t,J=6.9Hz,1H),3.71(dt,J=9.5,7.0Hz,1H),3.51(dt,J=9.5,7.1Hz,1H),3.42–3. 20(m,3H),2.61(dq,J=14.0,7.0Hz,1H),2.56–2.47(m,2H),2.38–2.27(m,2H),2.14–1.97(m,2H),1.98– 1.64(m,12H), 1.44(dt,J=13.0,7.0Hz,1H), 1.34(t,J=6.8Hz,2H), 0.90(ddd,J=25.0,6.8,5.0Hz,12H).

[0111] The structural formula of compound I is shown below:

[0112]

[0113] Embodiment 10:

[0114] Peptide I (1 mmol) was dissolved in THF (40 mL), HOBT (2 mmol) was added, and then a THF solution of DCC (2 mmol) and a catalyst of p-tert-butylphenol (0.01 mmol) were added. The reaction was carried out at 0°C for 5 hours, and then at 4°C overnight. The filtrate was filtered out, and then the filter cake was washed with ethanol. The ethanol solution was evaporated to obtain a crude product of cyclopeptide F, which was purified by silica gel column chromatography to obtain cyclopeptide J. Yield: 86%. 1 H NMR(500MHz,DMSO-d6)δ8.35(s,2H),6.57(s,2H),4.77(t,J=5.9Hz,1H),4.70(t,J=7.0Hz,1H) ,4.62(t,J=5.0Hz,1H),4.47(t,J=6.9Hz,2H),4.24(t,J=6.8Hz,1H),3.66(dt,J=9.4,6.9Hz,1H ),3.48–3.29(m,3H),2.66–2.54(m,3H),2.46(ddd,J=12.5,10.2,5.0Hz,1H),2.31–2.10(m,3H) ,2.01–1.65(m,12H),1.56(ddtd,J=26.4,13.8,6.9,5.9Hz,3H),0.90(dd,J=25.0,6.8Hz,12H).

[0115] The structural formula of compound B is shown below:

[0116]

[0117] Embodiment 11:

[0118] Using N-Boc-glutamine and proline-valine dipeptide ethyl ester as raw materials, the synthesis methods of Examples 1 to 5 were used to prepare the pure hexapeptide product K. The total yield was 60%. 1 H NMR (500MHz, DMSO-d6) δ8.25–8.14(m,7H),6.56(s,2H),4.63(d,J=7.2Hz,1H),4.54(t,J=6.7Hz,1H),4.43(t,J =6.8Hz,1H),4.29(q,J=6.8Hz,2H),3.74(dt,J=9.2,6.9Hz,1H),3.52(dt,J=9.4,6.8Hz,1H),3.44(d,J=6.9Hz,1 H),3.33(dt,J=9.3,6.9Hz,1H),3.19(dt,J=9.1,6.8Hz,1H),2.72(dp,J=13.6,6.9Hz,1H),2.32–2.15(m,3H),2 .18–1.99(m,3H),2.00–1.60(m,10H),1.05(d,J=6.8Hz,3H),0.87(dd,J=8.7,6.8Hz,6H),0.71(d,J=6.8Hz,3H).

[0119] The structural formula of compound K is shown below:

[0120]

[0121] Embodiment 12:

[0122] Peptide K (1 mmol) was dissolved in THF (40 mL), HOBT (2 mmol) was added, and then a THF solution of DCC (2 mmol) and a catalyst of p-tert-butylphenol (0.07 mmol) were added. The reaction was carried out at 0°C for 5 hours, and then at 4°C overnight. The filtrate was filtered out, and then the filter cake was washed with ethanol. The ethanol solution was evaporated to obtain a crude product of cyclopeptide F, which was purified by silica gel column chromatography to obtain cyclopeptide L. Yield: 81%. 1H NMR (500MHz, DMSO-d6) δ8.35(s,2H),6.66(s,2H),4.84(d,J=7.0Hz,1H),4.76(d,J=7.1Hz,1H),4.47(t ,J=7.0Hz,1H),4.24(dt,J=13.9,6.7Hz,2H),3.63(dt,J=9.4,6.9Hz,1H),3.44–3.23(m,3H),2.73(dq, J=13.7,6.9Hz,2H),2.62–2.48(m,2H),2.42–2.28(m,2H),2.28–1.90(m,5H),1.91–1.70(m,6H),1.60– 1.51 (m, 1H), 0.88 (d, J = 6.8Hz, 3H), 0.82 (d, J = 6.9Hz, 3H), 0.75 (d, J = 6.8Hz, 3H), 0.62 (d, J = 6.8Hz, 3H).

[0123] The structural formula of compound L is shown below:

[0124]

[0125] Embodiment 13:

[0126] Using N-Boc-glutamine and proline-glycine dipeptide ethyl ester as raw materials, the synthesis methods of Examples 1 to 5 were used to prepare a pure pentapeptide product M. The total yield was 59%. 1 H NMR(500MHz,DMSO-d6)δ8.23(s,2H),8.12(s,2H),7.37(s,2H),5.07(s,2H),4.71–4.61(m,2H),4.33( t,J=6.9Hz,1H),4.24(d,J=12.5Hz,1H),3.76(d,J=12.5Hz,1H),3.58(ddt,J=42.1,9.5,7.1Hz,2H),3. 40(dt,J=9.5,7.0Hz,1H),3.26(dt,J=9.5,7.1Hz,1H),2.80–2.66(m,J=6.8Hz,1H),2.58(dq,J=13.4, 6.8Hz,1H),2.24(dq,J=13.9,7.0Hz,1H),2.05–1.94(m,2H),1.95–1.62(m,7H),0.93(d,J=6.8Hz,6H).

[0127] The structural formula of compound M is shown below:

[0128]

[0129] Embodiment 14:

[0130] Peptide M (1 mmol) was dissolved in THF (40 mL), HOBT (2 mmol) was added, and then a THF solution of DCC (2 mmol) and a catalyst of p-tert-butylphenol (0.03 mmol) were added. The reaction was carried out at 0°C for 5 hours, and then at 4°C overnight. The filtrate was filtered out, and then the filter cake was washed with ethanol. The ethanol solution was evaporated to obtain a crude product of cyclic peptide F, which was purified by silica gel column chromatography to obtain cyclic peptide Cyclo (Gly-Pro-Gln-Gly-Pro) N. Yield: 84%. 1 H NMR (500MHz, DMSO-d6) δ6.58 (s, 2H), 4.61–4.53 (m, 2H), 4.46 (t, J = 6.8Hz, 1H), 4. 30(t,J=6.8Hz,1H),4.05(d,J=13.5Hz,1H),3.98–3.89(m,2H),3.83(dt,J=9.5,6 .9Hz,1H),3.64(d,J=13.2Hz,1H),3.29(ddt,J=32.6,9.5,7.0Hz,2H),2.59–2.42 (m,2H),2.42–2.23(m,3H),2.07(tdd,J=12.7,7.0,2.2Hz,1H),1.96–1.68(m,6H).

[0131] The structural formula of compound N is shown below:

[0132]

[0133] Embodiment 15:

[0134] Using N-Boc-glutamine and proline-glycine dipeptide ethyl ester as raw materials, the synthesis methods of Examples 1 to 5 were used to prepare pure dodecapeptide product O. The total yield was 61%. 1 H NMR(500MHz,DMSO-d6)δ8.86(s,1H),8.52–8.44(m,5H),8.38(s,1H),8.23(s, 4H),7.11(s,2H),6.67(s,2H),5.23(d,J=12.4Hz,1H),5.07(s,2H),4.96(d,J= 12.4Hz,1H),4.56–4.40(m,5H),4.01(d,J=12.4Hz,1H),3.95–3.86(m,2H),3.7 3(d,J=12.4Hz,1H),3.68–3.48(m,6H),3.50–3.19(m,6H),2.41–1.54(m,30H).

[0135] The structural formula of compound O is shown below:

[0136]

[0137] Embodiment 16:

[0138] Peptide O (1 mmol) was dissolved in THF (40 mL), HOBT (2 mmol) was added, and then a THF solution of DCC (2 mmol) and a p-tert-butylphenol catalyst (0.02 mmol) were added. The reaction was carried out at 0°C for 5 hours, and then at 4°C overnight. The filtrate was filtered out, and then the filter cake was washed with ethanol. The ethanol solution was evaporated to obtain a crude product of cyclic peptide P, which was purified by silica gel column chromatography to obtain a pure product of cyclic peptide Cyclo (Gly-Pro-Gln-Gly-Pro-Gln-Gly-Pro-Gln-Gly-Pro-Gln) P. Yield: 80%. 1 H NMR(500MHz,Deuterium Oxide)δ4.89–4.77(m,4H),4.78–4.60(m,6H),4.12–3.99(m,2H),3.99–3.91(m,2H),3.81–3.62(m,4H),3.33(ddt,J=17.7, 9.6,7.0Hz,2H),3.12(ddt,J=36.3,9.5,7.1Hz,2H),3.00(td,J=12.8,2.2Hz,1H),2.77–2.37(m,12H),2.32–1.69(m,19H).

[0139] The structural formula of compound P is shown below:

[0140]

[0141] Embodiment 17:

[0142] Cyclohexapeptide Q1 was prepared using N-Boc-asparagine and proline-glycine dipeptide ethyl ester as raw materials using the synthetic methods of Examples 1 to 5. The total yield was 53%. 1H NMR(500MHz,DMSO-d6)δ9.40(s,1H),7.26(s,2H),6.79(s,2H),4.93(t,J=7.0Hz,1H),4.60(t, J=7.1Hz,1H),4.55–4.45(m,3H),3.95(d,J=18.7Hz,1H),3.76–3.62(m,3H),3.48–3.23(m,3H) ,2.96(ddd,J=12.5,9.9,7.0Hz,2H),2.51(dd,J=12.4,7.1Hz,1H),2.32(ddd,J=12.5,6.9,5.2 Hz,2H),2.13(dt,J=12.7,7.0Hz,2H),2.00–1.84(m,2H),1.88–1.80(m,2H),1.84–1.74(m,2H).

[0143] The structural formula of compound Q1 is shown below:

[0144]

[0145] Embodiment 18:

[0146] Cyclohexapeptide Q2 was prepared using N-Boc-phenylalanine and proline-glycine dipeptide ethyl ester as raw materials using the synthetic methods of Examples 1 to 5 and 8. The total yield was 54%. 1 H NMR(500MHz, DMSO-d6)δ7.19(s,10H),5.01(t,J=6.9Hz,1H),4.84(t,J=6.9Hz,1H),4.40–4. 25(m,3H),4.20(d,J=18.8Hz,1H),3.92(t,J=18.7Hz,2H),3.54(ddt,J=22.0,9.5,7.0Hz,2H ),3.37(ddt,J=10.5,9.5,7.0Hz,2H),3.21(td,J=12.0,7.0Hz,2H),3.06(dd,J=12.4,7.0Hz ,1H),2.78(dd,J=12.4,7.0Hz,1H),2.52–2.39(m,1H),2.25–2.03(m,3H),1.95–1.73(m,4H).

[0147] The structural formula of compound Q2 is shown below:

[0148]

[0149] Embodiment 19:

[0150] Cyclohexapeptide Q3 was prepared using N-Boc-methionine and proline-glycine dipeptide ethyl ester as raw materials using the synthetic methods of Examples 1 to 5 and 8. The total yield was 47%. 1 H NMR(500MHz,DMSO-d6)δ9.36(s,1H),9.08(s,1H),4.50(td,J=6.8,4.6Hz,2H),4.41(d,J=17.4Hz,1H),4. 35–4.30(m,1H),4.30–4.21(m,2H),3.79(dd,J=24.2,17.8Hz,2H),3.63–3.45(m,3H),3.32(dtd,J=9.5,7. 0,5.0Hz,2H),2.95(tt,J=12.5,3.1Hz,1H),2.85(dt,J=12.6,7.0Hz,1H),2.43–2.31(m,2H),2.22–2.07(m ,3H),2.07(s,7H),2.08–2.01(m,1H),1.95–1.83(m,2H),1.87–1.75(m,3H),1.30(tt,J=12.5,2.7Hz,1H).

[0151] The structural formula of compound Q3 is shown below:

[0152]

[0153] Embodiment 20:

[0154] Cyclohexapeptide Q4 was prepared using N-Boc-methionine and proline-glutamine dipeptide ethyl ester as raw materials using the synthetic methods of Examples 1 to 5 and 8. The total yield was 46%. 1H NMR(500MHz,DMSO-d6)δ9.06(s,1H),8.50(s,1H),6.61(d,J=2.9Hz,4H),5.32(t,J=7.0Hz,1H),5.13(t,J=7.0 Hz,1H),4.51(dt,J=27.2,6.7Hz,2H),4.31–4.22(m,2H),4.01(ddt,J=29.0,9.4,6.9Hz,2H),3.29–3.10(m,3H) ,3.02(dd,J=12.4,7.0Hz,1H),2.85(ddd,J=12.5,9.7,6.3Hz,1H),2.72(dd,J=12.5,7.0Hz,1H),2.64–2.46(m ,3H),2.38(ddd,J=12.5,9.2,5.9Hz,1H),2.07(s,7H),2.26–1.70(m,10H),1.22(tdd,J=12.5,3.3,2.0Hz,1H).

[0155] The structural formula of compound Q4 is shown below:

[0156]

[0157] Embodiment 21:

[0158] Cyclohexapeptide Q5 was prepared using N-Boc-glutamine and proline-asparagine dipeptide ethyl ester as raw materials using the synthetic methods of Examples 1 to 5 and 8. Total yield: 57%. 1 H NMR(500MHz,DMSO-d6)δ9.03(s,1H),8.10(s,2H),7.90(s,2H),7.74(s,2H),6.69(s,2H),4.80(t,J=7.1H z,1H),4.69(t,J=7.0Hz,1H),4.44(td,J=6.9,0.8Hz,1H),4.35–4.23(m,3H),4.03(dt,J=9.5,7.0Hz,1H) ,3.71(dt,J=9.5,6.9Hz,1H),3.18(ddt,J=18.9,9.5,6.9Hz,2H),2.98(dd,J=12.5,7.0Hz,1H),2.65–2.5 0(m,3H),2.47–2.34(m,3H),2.34–2.02(m,5H),1.94–1.84(m,2H),1.87–1.79(m,2H),1.81–1.62(m,4H).

[0159] The structural formula of compound Q5 is shown below:

[0160]

[0161] Embodiment 22:

[0162] Cyclohexapeptide Q6 was prepared using N-Boc-phenylalanine and proline-asparagine dipeptide ethyl ester as raw materials using the synthetic methods of Examples 1 to 5 and 8. Total yield: 55%. 1 H NMR(500MHz,DMSO-d6)δ9.62(s,1H),8.42(s,2H),8.34(s,1H),7.19(s,9H),6.60(s,2H),5.16–5.03(m, 3H),4.54(t,J=7.0Hz,1H),4.36(dt,J=28.0,6.9Hz,2H),3.73(dt,J=9.2,6.9Hz,1H),3.44(ddt,J=33.0 ,9.6,7.1Hz,2H),3.23–3.10(m,3H),2.91(dd,J=12.4,7.0Hz,1H),2.76(dd,J=12.4,7.0Hz,1H),2.58(d dd,J=32.0,12.4,7.0Hz,2H),2.41(ddd,J=12.3,7.0,2.3Hz,2H),2.23–2.06(m,2H),2.04–1.56(m,6H).

[0163] The structural formula of compound Q6 is shown below:

[0164]

[0165] Embodiment 24:

[0166] Using N-Boc-glutamine and proline-glycine dipeptide ethyl ester as raw materials, the linear hexapeptide E was prepared by the synthesis methods of Examples 1 to 5. Then E (1 mmol) was dissolved in water, tert-butyloxycarbonyl anhydride (Boc2O, 1.5 mmol) and triethylamine (Et3N, 1.5 mmol) were added, and after stirring at room temperature for 8 hours, the supernatant was removed by centrifugation and dried to obtain a crude Boc anhydride protected hexapeptide, which was then dissolved in ethyl acetate (40 ml), phenylalanine ethyl ester (1.5 mmol) and 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDCI, 1.5 mmol) were added, stirred at room temperature overnight, saturated ammonium chloride (40 ml) was added for washing, the organic layer was evaporated to dryness, dissolved in 20 ml trifluoroacetic acid, and stirred at room temperature for 1 hour. The solution was then evaporated to dryness and then washed with ether, and the suspension was filtered to obtain the de-tert-butyloxycarbonyl product. Under ice-water bath conditions, the product of the previous step of de-tert-butyloxycarbonylation was dissolved in a mixed solvent of THF / H2O, followed by the addition of LiOH·H2O (14.3 mg, 3.4 mmol, 2 eq), stirred for 10 hours, and finally neutralized with 1N hydrochloric acid to neutrality. The solution was extracted with ethyl acetate, the organic phase was dried over anhydrous sodium sulfate, filtered and then evaporated to dryness to obtain the deprotected product R4. Total yield: 46%. 1 H NMR(500MHz,DMSO-d6)δ9.98(s,1H),8.30(s,2H),8.23(s,2H),7.91(d,J=2.9Hz,4H),7.19(p,J=3.8Hz,5H), 4.44(dt,J=23.6,6.8Hz,2H),4.09(d,J=12.4Hz,1H),4.01–3.93(m,2H),3.83(t,J=6.9Hz,1H),3.73–3.63(m, 3H),3.41–3.25(m,2H),3.17–3.00(m,3H),2.69–2.48(m,3H),2.36(td,J=12.7,1.8Hz,1H),2.23–1.98(m,5H) ,2.01–1.84(m,2H),1.84(ddd,J=8.9,4.3,2.0Hz,2H),1.84–1.71(m,2H),1.60(tdd,J=12.7,7.1,2.4Hz,1H).

[0167] The structural formula of compound R4 is shown below:

[0168]

[0169] Embodiment 25:

[0170] The linear peptide R4 was used as the raw material to prepare the cyclic heptapeptide R1 using the synthesis method of Example 4. The total yield was 79%.1 H NMR (500MHz, DMSO-d6) δ8.68(d,J=20.0Hz,2H),7.86(s,2H),7.19(s,5H),6.74(s,1H),6.60(s,2H),5.10(t,J=7.0Hz,1H),4. 61(t,J=7.0Hz,1H),4.49–4.38(m,3H),4.30(t,J=7.0Hz,1H),4.05(d,J=18.1Hz,1H),3.82(d,J=18.3Hz,1H),3.67(dt,J=9.4, 6.8Hz,1H),3.58(dt,J=9.5,7.1Hz,1H),3.40–3.29(m,2H),3.25(dt,J=9.6,6.9Hz,1H),3.04–2.89(m,2H),2.64(td,J=12.6, 2.2Hz,1H),2.35–2.22(m,2H),2.19–2.02(m,2H),2.06–1.95(m,2H),1.98–1.85(m,4H),1.89–1.76(m,2H),1.79–1.64(m,3H).

[0171] The structural formula of compound R1 is shown below:

[0172]

[0173] Embodiment 26:

[0174] Cycloheptapeptide R2 was prepared using N-Boc-methionine, proline-glycine dipeptide ethyl ester and phenylalanine ethyl ester as raw materials using the synthetic methods of Example 24 and Example 25. Total yield: 38%. 1H NMR (500MHz, DMSO-d6) δ9.88(s,1H),9.65(s,1H),9.39(d,J=3.7Hz,2H),7.19(s,5H),4.75(t,J=7.1Hz,1H),4.66(p,J=1.6Hz, 1H),4.53(t,J=6.9Hz,1H),4.48–4.38(m,2H),4.14(d,J=18.7Hz,1H),3.95–3.79(m,3H),3.63(ddt,J=22.4,9.5,6.9Hz,2H),3 .28(dt,J=9.5,7.0Hz,2H),2.95–2.85(m,2H),2.79(dd,J=12.4,7.0Hz,1H),2.53–2.42(m,1H),2.32(td,J=12.4,3.5Hz,1H),2 .19–2.06(m,2H),2.07(s,7H),2.10–1.99(m,4H),2.03–1.89(m,2H),1.93–1.81(m,2H),1.84–1.71(m,2H),1.48–1.36(m,1H).

[0175] The structural formula of compound R2 is shown below:

[0176]

[0177] Embodiment 27:

[0178] Cycloheptapeptide R3 was prepared using N-Boc-asparagine, proline-glycine dipeptide ethyl ester and phenylalanine ethyl ester as raw materials using the synthetic methods of Example 24 and Example 25. Total yield: 39%. 1H NMR (500MHz, DMSO-d6) δ8.84(s,1H),6.65(s,2H),5.22(t,J=7.0Hz,1H),4.75(td,J=3.4,1.9Hz,1H),4.53–4.44 (m,2H),4.42–4.33(m,1H),4.12(d,J=13.6Hz,1H),4.05(d,J=18.7Hz,1H),3.83(d,J=13.6Hz,1H),3.58–3.45(m, 2H),3.38(dt,J=9.5,6.9Hz,1H),3.28–3.17(m,2H),2.82–2.69(m,2H),2.56(dd,J=12.4,7.1Hz,1H),2.41–2.30( m,2H),2.07(s,7H),2.11–1.77(m,9H),1.79–1.66(m,1H),1.32–1.22(m,1H),0.92(tdd,J=12.5,3.4,2.2Hz,1H).

[0179] The structural formula of compound R3 is shown below:

[0180]

[0181] Embodiment 29:

[0182] Cyclooctapeptide S1 was prepared using proline-glycine dipeptide ethyl ester and Boc proline-glycine dipeptide as raw materials using the synthetic methods of Examples 1 to 5. The total yield was 57%. 1 H NMR(500MHz,DMSO-d6)δ8.62(s,1H),4.57–4.36(m,5H),4.33(d,J=18.5Hz,1H),4.24(d,J=17.9Hz,1H) ,4.10(d,J=13.2Hz,1H),3.78–3.54(m,6H),3.50–3.24(m,6H),2.54–2.28(m,3H),2.15–1.71(m,12H).

[0183] The structural formula of compound S1 is shown below:

[0184]

[0185] Embodiment 29:

[0186] Cyclooctapeptide S2 was prepared using proline-glutamine dipeptide ethyl ester and Boc proline-glutamine dipeptide as raw materials using the synthetic methods of Examples 1 to 5. The total yield was 48%. 1H NMR(500MHz,DMSO-d6)δ8.29(s,2H),7.95(d,J=10.4Hz,3H),7.10(s,2H),6.59(s,2H),4.5 4–4.34(m,5H),4.31–4.19(m,2H),3.65–3.54(m,2H),3.57–3.51(m,2H),3.34–3.25(m,2H) ,3.17(ddt,J=21.3,9.2,6.8Hz,2H),2.56(tt,J=12.7,5.6Hz,2H),2.44–2.30(m,2H),2.22 –2.04(m,5H),2.07–1.69(m,11H),1.68–1.47(m,5H),1.42(ddd,J=12.3,10.6,6.8Hz,1H).

[0187] The structural formula of compound S2 is shown below:

[0188]

[0189] Embodiment 29:

[0190] Cyclooctapeptide S3 was prepared using proline-valine dipeptide ethyl ester and Boc proline-valine dipeptide as raw materials using the synthetic methods of Examples 1 to 5. The total yield was 55%. 1 H NMR (500MHz, DMSO-d6) δ9.34(s,1H),9.10(s,1H),4.77–4.69(m,2H),4.67(d,J=6.9Hz,1H),4.58(d,J=6.9Hz,1H ),4.47(dt,J=13.9,6.9Hz,2H),4.35(t,J=7.0Hz,2H),3.52–3.37(m,4H),3.25(dddt,J=55.3,31.0,9.5,6.9Hz, 4H),2.80–2.66(m,J=6.8Hz,4H),2.62–2.44(m,2H),2.15(dq,J=14.0,7.1Hz,1H),2.05–1.90(m,2H),1.82(ddtd ,J=18.9,12.9,6.9,2.0Hz,7H),1.75–1.60(m,2H),1.63–1.49(m,1H),0.94(t,J=7.1Hz,6H),0.90–0.74(m,18H).

[0191] The structural formula of compound S3 is shown below:

[0192]

[0193] Embodiment 31:

[0194] Using N-Boc-glutamine and proline-glycine dipeptide ethyl ester as raw materials, the linear hexapeptide E was prepared by the synthesis methods of Examples 1 to 5. E (1 mmol) was then dissolved in water, tert-butyloxycarbonyl anhydride (Boc2O, 1.5 mmol) and triethylamine (Et3N, 1.5 mmol) were added, and after stirring at room temperature for 8 hours, the supernatant was removed by centrifugation and dried to obtain a crude Boc anhydride-protected hexapeptide. Subsequently, using proline-glycine dipeptide ethyl ester as raw material, the synthesis methods of Examples 1 and 5 were used to obtain a nonapeptide. Then, the method of Example 8 was used to synthesize the cyclic nonapeptide T1. 1 H NMR(500MHz,DMSO-d6)δ8.89(s,1H),7.57(s,2H),7.51(s,1H),6.60(s,2H),6.54(s,2H),4.66(dt ,J=12.3,6.8Hz,3H),4.45(dt,J=11.4,6.8Hz,2H),4.25–4.17(m,2H),4.11(d,J=15.7Hz,1H),3.7 6–3.45(m,6H),3.37(dt,J=9.5,6.8Hz,1H),3.19(ddt,J=20.1,9.6,6.9Hz,2H),2.57–2.42(m,4H) ,2.42–2.31(m,2H),2.32–2.21(m,2H),2.17–2.07(m,1H),2.07–1.59(m,14H),1.46–1.35(m,1H).

[0195] The structural formula of compound T1 is shown below:

[0196]

[0197] Embodiment 32:

[0198] Cyclic nonapeptide T2 was prepared using N-Boc-methionine and proline-glycine dipeptide ethyl ester as raw materials using the synthetic method of Example 31d. 1H NMR(500MHz,DMSO-d6)δ9.09(s,1H),8.94(d,J=9.2Hz,2H),4.78–4.62(m,3H),4.51(t,J=7.0Hz,1H),4.47–4 .40(m,2H),4.19–4.06(m,3H),3.81–3.69(m,3H),3.61–3.48(m,3H),3.34(ddt,J=12.1,9.4,7.1Hz,2H),3.23 (dt,J=9.5,7.1Hz,1H),2.74(td,J=12.5,2.8Hz,1H),2.68–2.44(m,3H),2.35–2.23(m,2H),2.25–2.11(m,2H ),2.14–2.06(m,2H),2.07(s,9H),2.08–1.75(m,8H),1.78–1.38(m,6H),0.95(tdd,J=12.5,11.4,3.5Hz,1H).

[0199] The structural formula of compound T2 is shown below:

[0200]

[0201] Embodiment 33:

[0202] Cyclic nonapeptide T3 was prepared using N-Boc-phenylalanine and proline-glutamine dipeptide ethyl ester as raw materials using the synthesis method of Example 31. 1H NMR(500MHz,DMSO-d6)δ9.85(s,1H),9.18(s,1H),8.07(s,2H),7.71(s,2H),7.19(s,15H),6.60(s,2H),5.56(t,J=7.0Hz,1H),5. 14(dt,J=19.6,7.0Hz,2H),4.97(t,J=6.9Hz,1H),4.70(td,J=6.8,1.3Hz,1H),4.46–4.33(m,3H),4.29(t,J=6.8Hz,1H),3.59(dt, J=9.3,6.8Hz,1H),3.43(ddt,J=23.2,9.5,6.9Hz,2H),3.23(ddd,J=12.4,4.8,2.0Hz,1H),3.10–2.98(m,4H),2.94(ddd,J=12.4, 7.0,3.1Hz,2H),2.90–2.80(m,2H),2.49(ddd,J=12.4,6.6,1.0Hz,1H),2.34–2.16(m,2H),2.11–1.59(m,17H),1.44–1.33(m,1H).

[0203] The structural formula of compound T3 is shown below:

[0204]

[0205] Embodiment 34:

[0206] Using N-Boc-glutamine and proline-glycine dipeptide ethyl ester as raw materials, a tripeptide was prepared using the synthesis methods of Examples 1 to 4. Then, using the prepared tripeptide and phenylalanine-glycine dipeptide ethyl ester as raw materials, a pentapeptide was prepared using the method of Example 1. Finally, using the prepared pentapeptide as raw materials, a cyclodecapeptide U1 was prepared using the synthesis methods of Examples 5 and 8. 1H NMR(500MHz,DMSO-d6)δ9.49(s,1H),8.83(s,1H),8.47(s,1H),8.27(s,1H),7.86(s ,1H),7.19(s,10H),6.95(s,1H),6.55(d,J=9.0Hz,4H),5.21(t,J=7.0Hz,1H),4.80 (dt,J=12.1,6.9Hz,2H),4.72–4.65(m,2H),4.58(dd,J=13.5,11.3Hz,2H),4.50(d, J=13.7Hz,1H),4.20(t,J=6.8Hz,1H),4.10(d,J=13.9Hz,1H),3.94(dt,J=9.5,7.0H z,1H),3.81–3.67(m,3H),3.64(d,J=13.3Hz,1H),3.36(ddt,J=19.6,9.4,7.0Hz,2H ),3.22(dd,J=12.4,7.0Hz,1H),3.03(ddd,J=25.9,12.4,7.0Hz,2H),2.81(dd,J=12 .4,7.0Hz,1H),2.52–2.33(m,3H),2.27–2.13(m,2H),2.11–1.98(m,2H),2.02–1.94 (m,2H),1.98–1.88(m,2H),1.91–1.86(m,2H),1.88–1.80(m,2H),1.72–1.59(m,1H).

[0207] The structural formula of compound U1 is shown below:

[0208]

[0209] Embodiment 35:

[0210] Cyclic decapeptide U2 was prepared using the synthesis method of Example 34 using N-Boc-methionine, proline-glycine dipeptide ethyl ester and phenylalanine-glycine dipeptide as raw materials. 1H NMR(500MHz,DMSO-d6)δ9.68(s,1H),8.69(s,1H),8.06(s,1H),7.64(s,1H),7. 19(s,10H),6.63(s,2H),6.58(s,2H),5.29(t,J=6.9Hz,1H),5.11(t,J=7.0Hz,1 H),4.98(t,J=7.0Hz,1H),4.74(dd,J=11.5,1.3Hz,1H),4.56–4.47(m,2H),4.45 –4.36(m,2H),4.26(dd,J=13.6,5.0Hz,2H),4.12–4.04(m,2H),3.57(ddt,J=39. 2,9.5,7.0Hz,2H),3.35(dt,J=9.4,7.0Hz,1H),3.22(dd,J=12.4,7.0Hz,1H),3. 18–3.08(m,2H),3.01(dd,J=12.4,7.0Hz,1H),2.72(dd,J=12.4,7.0Hz,1H),2.6 7–2.31(m,5H),2.28–2.20(m,1H),2.07(s,7H),2.14–1.96(m,4H),1.97(ddd,J= 10.6,4.6,2.1Hz,2H),1.96–1.68(m,7H),1.68–1.45(m,3H),1.27–1.15(m,1H).

[0211] The structural formula of compound U2 is shown below:

[0212]

[0213] Embodiment 36:

[0214] Cyclic decapeptide U3 was prepared using the synthesis method of Example 34 using N-Boc-methionine, proline-glycine dipeptide ethyl ester and phenylalanine-valine dipeptide as raw materials. 1H NMR(500MHz,DMSO-d6)δ9.45(s,1H),9.27(s,1H),9.20(s,1H),9.05(s,1H ),8.49(s,2H),6.55(s,2H),4.62–4.51(m,4H),4.48–4.40(m,2H),4.33(t ,J=7.0Hz,1H),4.27–4.20(m,2H),4.14(d,J=18.8Hz,1H),3.92(d,J=13.6 Hz,1H),3.84(d,J=19.0Hz,1H),3.64–3.41(m,4H),3.24(dt,J=9.5,7.1Hz ,1H),2.86(ddt,J=12.5,5.2,1.5Hz,1H),2.73(dq,J=13.7,6.9Hz,2H),2. 37(tdd,J=12.7,7.0,2.9Hz,1H),2.24–2.00(m,9H),2.07(s,7H),1.97–1. 59(m,9H),1.58–1.49(m,1H),1.45(dddd,J=12.5,5.2,2.7,1.2Hz,1H),1. 36(tdd,J=12.3,5.8,1.8Hz,1H),1.12(d,J=6.8Hz,3H),0.93–0.83(m,9H).

[0215] The structural formula of compound U3 is shown below:

[0216]

[0217] Performance Characterization Example

[0218] In order to determine the antibacterial activity of the synthesized cyclic lactam compounds, the inventors chose the minimum inhibitory concentration (MIC) as an indicator to represent the antibacterial activity of the synthesized substances. The inventors referred to the method in the literature (ZENG J, HU Y, JIA T, et al. Chemoenzymatic synthesis of sialylated lactuloses and their inhibitory effects on Staphylococcus aureus [J]. PLoS One, 2018, 13 (6): e0199334.) and adopted a 96-well plate bioassay method to perform high-throughput screening of the antibacterial activity of the substances. First, 100mM stock solutions of 18 compounds were prepared, and then the 100mM stock solutions were gradiently diluted to 1mM, 500μM, 250μM, 125μM, 62.5μM, and 31.25μM test solutions using LB medium under a sterile environment. Then, the gradient diluted test solution was added to each vertical row of wells in order according to the dilution concentration from high to low, and 100 μL of the diluted compound was added to each well, and three parallels were set for each concentration. Subsequently, the overnight bacterial culture was diluted to 0.8 McFarland (McFarland turbidimetric standard) using LB medium under a sterile environment, and 100 μL of the diluted bacterial suspension was added to each well. In this way, the total volume of liquid in each microwell was 200 μL, and the final concentrations of the test compounds were 500 μM, 250 μM, 125 μM, 62.5 μM, 31.25 μM and 15.625 μM, respectively. After the addition of the drug, the 96-well plate was placed in a 37°C constant temperature incubator for 24 hours. In order to reduce evaporation and allow free air exchange, the gaps of the plate were covered with plastic film before culturing. After 24 hours of culturing, the lowest concentration corresponding to the microwell without bacterial growth was the minimum inhibitory concentration (MIC) of the test compound for bacteria.

[0219] Test results:

[0220] The cyclic peptide derivatives showed significant antibacterial activity with MIC values ​​ranging from 62.5 to 500 μM. The minimum inhibitory concentration (MIC) of each compound against Escherichia coli and Staphylococcus aureus is listed in Table 1.

[0221] Table 1 Minimum inhibitory concentration (MIC) of compounds against Escherichia coli and Staphylococcus aureus

[0222]

[0223] As shown in Table 1, cyclic peptides have stronger antibacterial activity than linear peptides. Cyclic peptides are a type of peptide with a special structure. Compared with linear peptides, the molecular structure of cyclic peptides is closed and has stronger chemical stability. Secondly, the cyclic structure can improve the resistance of the molecule to enzymatic hydrolysis. Its amide bond is inside the ring, making it difficult for the enzyme active center to approach the peptide bond. At the same time, cyclic peptides have good permeability and can penetrate the bacterial cell membrane faster to exert an antibacterial effect.

[0224] The above description of the embodiments is to facilitate those of ordinary skill in the art to understand and apply the present application. It is obvious that those familiar with the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without having to pay creative labor. Therefore, the present application is not limited to the embodiments herein, and improvements and modifications made by those skilled in the art based on the contents disclosed in the present application without departing from the scope and spirit of the present application are within the scope of the present application.

Claims

1. A cyclic lactam compound, characterized in that The cyclic lactam compound has a structural formula as shown in general formula I: Wherein, n is a positive integer from 1 to 49; Wherein, R1 is a substituent group on the α-carbon atom of proline; Wherein, R2 is a substituent group on the α-carbon atom of a natural amino acid; The natural amino acids are selected from one or more of the following: glycine, alanine, valine, leucine, isoleucine, methionine, proline, tryptophan, serine, tyrosine, cysteine, phenylalanine, asparagine, glutamine, threonine, aspartic acid, glutamic acid, lysine, arginine, histidine, selenocysteine ​​and pyrrolysine.

2. The cyclic lactam compound according to claim 1, characterized in that The n is 4-11.

3. The cyclic lactam compound according to claim 1, characterized in that The cyclic lactam compound is selected from the group consisting of:

4. A pharmaceutically acceptable salt of the cyclic lactam compound according to any one of claims 1 to 3.

5. A liquid phase synthesis method for a cyclic lactam compound as claimed in any one of claims 1 to 3, characterized in that: The method comprises the following steps: S1: providing a linear compound containing one or more amino acid structural units, wherein one end of the linear compound contains an amino group, and the other end of the linear compound contains a carboxyl group; S2: In the presence of a disaccharide, the linear compound is subjected to a cyclization reaction to condense the amino group and the carboxyl group to obtain the cyclic lactam compound.

6. The liquid phase synthesis method according to claim 5, characterized in that In step S1, the linear compound is selected from the group consisting of:

7. The liquid phase synthesis method according to claim 5, characterized in that: The step S1 comprises: S11: reacting a first amino acid whose terminal amino group is protected by a tert-butyloxycarbonyl group with a second amino acid-third amino acid dipeptide ethyl ester to obtain a linear tripeptide whose terminal amino group is protected by a tert-butyloxycarbonyl group and whose terminal carboxyl group is protected by an ethyl group; S12: performing a deprotection reaction on a linear tripeptide whose terminal amino group is protected by a tert-butyloxycarbonyl group and whose terminal carboxyl group is protected by an ethyl group, removing the tert-butyloxycarbonyl group to obtain a linear tripeptide whose terminal carboxyl group is protected by an ethyl group; S13: subjecting the linear tripeptide whose terminal carboxyl group is protected by an ethyl group to a deethylation reaction in a THF / H2O mixed solvent to obtain a linear tripeptide whose terminal amino group is protected by a tert-butyloxycarbonyl group; S14: condensing the linear tripeptide whose terminal amino group is protected by a tert-butyloxycarbonyl group and the linear tripeptide whose terminal carboxyl group is protected by an ethyl group to obtain a linear hexapeptide whose terminal amino group is protected by a tert-butyloxycarbonyl group and whose terminal carboxyl group is protected by an ethyl group; S15: performing a deprotection reaction on the linear hexapeptide in which the terminal amino group is protected by a tert-butyloxycarbonyl group and the terminal carboxyl group is protected by an ethyl group to obtain the linear compound.

8. The liquid phase synthesis method according to claim 5, characterized in that: In step S2, the disaccharide comprises one or more of the following: sucrose, maltose, trehalose, cellobiose and chitobiose.

9. The liquid phase synthesis method according to claim 1 or 2, characterized in that: In step S2, the molar ratio of the linear compound to the disaccharide is 10:1 to 10:0.

1.

10. Use of a disaccharide as a catalyst in the process of preparing a cyclic lactam compound as claimed in any one of claims 1 to 3 or a pharmaceutically acceptable salt of a cyclic lactam compound as claimed in claim 4, wherein the disaccharide preferably comprises one or more of the following: sucrose, maltose, trehalose, cellobiose and chitobiose.

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