Cholesteryl-terminal alkyne-functionalized helical polyisocyanide polymer orientation medium, its preparation method and application

Abstract

The present invention discloses a cholesteryl terminal alkyne-functionalized helical polyisocyanide polymer as a liquid crystal alignment medium, and its preparation method and application, belonging to the technical field of organic analysis. The structure of the helical polymer poly-2 is shown as follows: It is obtained by adding a chiral isocyanide monomer to initiate a reaction in a polymerization flask using cholesteryl terminal alkyne palladium(II) as a catalyst. The polymer is rapidly self-assembled in deuterated dichloromethane to construct a novel lyotropic liquid crystal alignment medium. This polymer chiral alignment medium can effectively align natural product organic small molecules to achieve accurate determination of nuclear magnetic resonance residual dipolar coupling for chiral recognition and analysis of organic molecules. Its preparation method is simple and the alignment strength is appropriate, making the spectral signals in the determination of nuclear magnetic resonance residual dipolar coupling clear and avoiding interference from background signals to the spectral analysis; moreover, as a chiral alignment medium, it has excellent chiral recognition performance, laying a foundation for the determination of the absolute configuration of organic molecules or natural products.

Description

Technical Field

[0001] The present invention belongs to the technical field of organic analysis, and particularly relates to a cholesteryl-terminal-alkyne-functionalized helical polyisocyanide polymer liquid crystal alignment medium, a preparation method thereof, and an application thereof. Background Art

[0002] Undoubtedly, the structural analysis of natural products or synthetic organic small molecules is one of the most important links in chemical research, and the correct structure is an important basis for ensuring the normal progress of subsequent research. In recent years, the rapid development of anisotropic NMR (Nat. Protoc., 2019, 14, 217) has continuously enriched the "toolbox" of organic chemists, making this novel nuclear magnetic resonance spectroscopy technology more widely used.

[0003] Residual dipolar couplings (RDCs) is an important nuclear magnetic resonance anisotropic parameter developed in recent years. It can reflect the structural information between two directly connected or non-bonded nuclei. Its magnitude is related to the distance between the two nuclei and the angle of the internuclear bond vector relative to the applied magnetic field. This value is usually denoted by D is and is represented. RDCs can be combined with classical NOE and 3The short-range information of J coupling constants is complementary. By measuring and analyzing RDCs, the stereostructure of unknown molecules that are difficult to determine in natural products or organic reactions can be obtained; RDCs are related to the spatial arrangement of atoms and are used to construct the global stereostructure of molecules, and can push the molecular structure analysis more precisely into three-dimensional space, especially reflecting the precise conformational information that is difficult to obtain even by single-crystal diffraction and electron microscopy. Although RDCs show powerful capabilities in precisely analyzing the molecular stereostructure, the prerequisite for measuring RDCs is to limit the molecular motion of the sample to be measured or constrain it to be anisotropic through certain methods, so that the dipolar coupling effect cannot be completely canceled, thereby generating a weak "residual dipolar coupling"; in addition, the dipolar coupling effect cannot be too strong, so that the test spectrum has high resolution and narrow linewidth to facilitate the precise extraction of appropriate RDC values. At present, the slow development of organic solvent-compatible alignment media has made the application of RDCs in organic structure analysis (Eur. J. Org. Chem., 2008, 5673; Magn. Reson. Chem., 2017, 55, 54; Nat. Prod. Bioprospect., 2018, 8, 279; Macromol. Rapid Commun., 2022, 43, 2100898) far less extensive than that in biomacromolecules (Chem. Rev., 2022, 122, 9307), and constructing lyotropic liquid crystals through self-assembly strategies to make the sample to be measured have an oriented arrangement has become a research hotspot in this field: for example, the liquid crystal of graphene oxide GO (Lei, X. X. et al. J. Am. Chem. Soc. 2014, 126, 11280; Angew. Chem. Int. Ed., 2016, 55, 3690); amphiphilic oligopeptide self-assembled liquid crystal OPA, etc. (Lei, X. X. et al. Angew. Chem. Int. Ed., 2017, 56, 12857; Angew. Chem. Int. Ed., 2020, 59, 17097; Chem. Sci., 2022, 13, 5838), the PBLG polymer liquid crystal system in the organic chloroform system (Thiele, C. M. et al. Org. Lett. 2003, 5, 705; Chem. Eur. J. 2017, 23, 9114; Chem. Eur. J., 2018, 24, 14373; Chem. Eur. J., 2018, 24, 15631; Macromolecules, 2019, 52, 6025; Chem. Eur. J., 2020, 26, 7831. Macromolecules, 2021, 54, 1648; Angew. Chem. Int. Ed. 2021, 60, 21040). At present, there is still a lack of excellent chiral liquid crystal alignment media systems to break the bottleneck for the wide application of RDCs technology. Summary of the Invention

[0004] To solve the above technical problems, the object of the present invention is to provide a cholesteric terminal alkyne-functionalized helical polyisocyanide polymer liquid crystal alignment medium, and at the same time provide a chiral polymer liquid crystal self-assembly system with low concentration and adjustable alignment angle, and apply it to the accurate determination of nuclear magnetic resonance RDCs for chiral recognition and analysis of organic molecules, laying a foundation for the determination of the absolute configuration of organic molecules or natural products, and having potential application prospects.

[0005] To achieve the object of the present invention, chiral cholesteric terminal alkyne palladium(II) is used as a catalyst, chiral isocyanide monomer is added to a polymerization flask to initiate the reaction, and finally methanol is added to terminate the polymerization reaction. The obtained product is washed, centrifuged, and dried under vacuum to obtain a cholesteric terminal alkyne-functionalized helical polyisocyanide chiral polymer, and its polymer structural formula is shown as follows:

[0006]

[0007] Where the degree of polymerization n = 20 - 200, and n is an integer.

[0008] The cholesteric terminal alkyne-functionalized helical polyisocyanide polymer rapidly self-assembles in deuterated dichloromethane (CD2Cl2) to realize the construction of a novel chiral liquid crystal alignment medium.

[0009] Preferably, based on the above scheme, the mass concentration of the chiral liquid crystal alignment medium in the deuterated dichloromethane solution is 7.2%wt - 12.8%wt, and the resonance of deuterium in the solution shows a residual quadrupolar splitting coupling value (RQCs) of 16.8 Hz - 68.0 Hz.

[0010] The advantages of the present invention are as follows: 1. The chiral liquid crystal alignment medium can effectively align natural product organic small molecules, realize the accurate determination of nuclear magnetic resonance residual dipole coupling, and be used for chiral recognition and analysis of organic molecules. The alignment strength is appropriate, the signals in the measured nuclear magnetic resonance residual dipole coupling spectrum are clear, and the interference of background signals on the spectrum analysis is avoided. 2. Its preparation method is simple, and it has excellent chiral recognition performance as a chiral alignment medium. The chiral liquid crystal alignment medium is used to measure the RDCs of enantiomeric organic molecules isopinocampheol ((+)-IPC and (-)-IPC), obtain its alignment structure information, realize excellent chiral recognition and analysis of its performance, and lay a foundation for determining the absolute configuration of natural product molecules in the future. Brief Description of the Drawings

[0011] Figure 1 is the 1H nuclear magnetic resonance spectrum of the cholesteric terminal alkyne-functionalized polyisocyanide chiral polymer poly-2 synthesized by the present invention, 1a is poly-2-L, and 1b is poly-2-D;

[0012] Figure 2 Gel permeation chromatography diagram of cholesteryl terminal alkyne-functionalized polyisocyanide chiral polymer poly-2 synthesized in the present invention;

[0013] Figure 3 Self-assembly photo of cholesteryl terminal alkyne-functionalized polyisocyanide polymer prepared in Example 3 of the present invention in a nuclear magnetic tube and its nuclear magnetic resonance deuterium spectrum ([[]] 2 H NMR) diagram of the oriented medium formed at different concentrations;

[0014] Figure 4 Nuclear magnetic resonance deuterium spectrum ([[]] 2 H NMR) diagram of poly-2-L prepared in Example 4 of the present invention as an oriented medium for measuring RDCs of (-)-IPC molecules;

[0015] Figure 5 Two-dimensional nuclear magnetic resonance CLIP-HSQC superimposed spectrum of poly-2-L prepared in Example 4 of the present invention as an oriented medium for measuring (-)-IPC molecules under isotropic conditions and in an anisotropic environment;

[0016] Figure 6 Linear fitting relationship diagram of experimental RDCs and theoretical RDCs of (-)-IPC molecules measured with poly-2-L prepared in Example 4 of the present invention as an oriented medium;

[0017] Figure 7 Comparison diagram of experimental RDCs values of four test samples of enantiomeric IPC molecules measured with poly-2-L and poly-2-D prepared in Example 5 of the present invention as oriented media;

[0018] Figure 8 Result diagram of chiral recognition and analysis of enantiomeric IPC molecules measured with poly-2-L and poly-2-D prepared in Example 5 of the present invention as oriented media. Detailed implementation mode

[0019] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it. The following embodiments are used to illustrate the present invention, but are not used to limit the scope of the present invention.

[0020] Example 1: Synthesis of chiral cholesteryl terminal alkyne palladium catalyst 1

[0021] At room temperature of 25 °C, bis(triethylphosphine)palladium(II) chloride (40 mg, 0.0978 mmol), copper(I) chloride (9.7 mg, 0.0978 mmol) and a magnetic stir bar were placed in a branched reaction tube and sealed. The tube was evacuated and filled with nitrogen about three times to ensure an anhydrous and anaerobic reaction environment. Distilled triethylamine (0.5 mL) and cholesterylamide ethynyl dissolved in anhydrous dichloromethane (0.5 mL) (52 mg, 0.0978 mmol) were successively added to the branched reaction tube via a microsyringe under a nitrogen atmosphere. Then the reaction flask was placed on a magnetic stirrer. After reacting for four hours, the reaction was monitored by thin-layer chromatography until completion. The insoluble substances were removed by vacuum filtration under reduced pressure, and the filter cake was washed with petroleum ether. The solution was then rotary evaporated and n-hexane was added to form a clear supersaturated solution for recrystallization. After recrystallization, white crystalline catalyst 1 was filtered out again using petroleum ether as the washing solvent, with a yield of 70%. The reaction equation is as follows:

[0022]

[0023] M.p. = 175.4 - 176.3 °C. (c 0.1, in CHCl3). 1 1H NMR (400 MHz, CDCl3) δ 7.30–7.14 (m, 4H, aromatic), 6.50 (s, 1H), 5.44–5.36 (m, 1H), 4.63–4.53 (m, 1H), 2.47–2.39 (m, 1H) 2.36–2.27 (m, 1H), 2.01–1.93 (m, 16H), 1.71–1.40 (m, 10H), 1.24–1.13 (m, 27H), 1.06–1.03 (m, 6H), 0.92–0.85 (m, 10H), 0.68 (s, 3H). 13 13C NMR (101 MHz, CDCl3) δ 152.91, 139.58, 135.70, 131.35, 122.81, 118.34, 106.03, 74.97, 56.68, 56.12, 50.00, 42.32, 39.73, 39.53, 38.46, 36.97, 36.58, 36.19, 35.82, 31.92, 31.87, 28.26, 28.10, 28.04, 24.31, 23.84, 22.86, 22.59, 21.06, 19.36, 18.73, 15.51, 15.37, 15.24, 11.88, 8.36. 31 31P NMR (162 MHz, CDCl3) δ 17.88. HRMS m / z (ESI) anal. calcd for C 48 H 80ClNO2P2Pd 905.4388, found [M+Na] + 928.4288.

[0024] Example 2: Synthesis of Cholesteryl-Terminated Alkyne-Functionalized Polyisocyanide Chiral Polymer poly-2

[0025] Chiral cholesteryl-terminated alkyne palladium catalyst 1 (2.8 mg, 0.00335 mmol), chiral phenyl isocyanide monomer 2 with amino acid side chain (120 mg, 0.335 mmol), and a magnetic stir bar were placed in a 10 mL polymerization flask, and the apparatus was sealed. To ensure an anhydrous and anaerobic reaction environment, the flask was evacuated and filled with nitrogen about three times. Under a nitrogen atmosphere, anhydrous CHCl3 solution (1 mL) was added to the polymerization flask using a microsyringe. Then the polymerization flask was placed in an oil bath and reacted at 55 - 60 °C for 10 - 15 h. After the reaction product was cooled to room temperature, it was transferred to a centrifuge tube, and a little dichloromethane was added to wash the polymerization flask several times. A large amount of yellow precipitate immediately precipitated when a large amount of methanol was added to the centrifuge tube. The centrifuge tube was placed in a centrifuge to separate the solid precipitate. The upper turbid liquid was carefully poured out, and methanol was added again and centrifuged three times repeatedly to remove the reaction monomers and oligomers. The yellow solid product polymer poly-2 was obtained by vacuum pumping. The reaction formula is as follows:

[0026]

[0027] poly-L-2: SEC: M n = 104.3 kDa, M w / M n = 1.28. (c 0.10, in CHCl3). poly-D-2: SEC: M n = 101.1 kDa, M w / M n = 1.32. (c 0.10, in CHCl3). 1H NMR spectrum of cholesteryl-terminated alkyne-functionalized polyisocyanide chiral polymer poly-2-L is as Figure 1a shown, and 1H NMR spectrum of the enantiomeric form cholesteryl-terminated alkyne-functionalized polyisocyanide chiral polymer poly-2-D is as Figure 1b shown; their relative molecular weights were measured by gel permeation chromatography (SEC), as Figure 2 shown.

[0028] Example 3: Preparation of Chiral Liquid Crystal Alignment Medium poly-2-L or poly-2-D

[0029] Weigh 50 mg of cholesteryl-alkyne-functionalized helical polyisocyanide polymer poly-2-L or poly-2-D and place it in a nuclear magnetic resonance tube with a diameter of 5 mm. Add 300 μL of CD2Cl2 to dissolve it. Seal the sample in the nuclear magnetic resonance tube and shake it back and forth to mix evenly. After about half an hour, the polymer completes self-assembly in the solution. Subsequently, through nuclear magnetic resonance deuterium spectrum experiment ( 2 1H NMR) test, the deuterium quadrupole splitting coupling value in the solvent reaches the range of 16.8 Hz to 68.0 Hz, confirming the generation of an anisotropic liquid crystal phase, which is an orientation medium for nuclear magnetic resonance residual dipole coupling measurement that can be used for organic analysis. As Figure 3 shown, the mass concentration in the deuterated dichloromethane solution is 7.2% wt to 12.8% wt. As the concentration is diluted, the RQCs gradually decrease, indicating that the orientation intensity can be adjusted by concentration.

[0030] To confirm that the chiral liquid crystal orientation medium of cholesteryl-alkyne-functionalized helical polyisocyanide polymer can be used to measure the RDCs of organic molecules and achieve excellent chiral recognition and analysis of its performance, the following uses a pair of enantiomeric molecules isopinocampheol ((+)-IPC and (-)-IPC) as an example to illustrate:

[0031] Example 4: Application of chiral liquid crystal orientation medium poly-2-L in measuring the RDCs of dextrorotatory isopinocampheol (-)-IPC

[0032] Weigh 9 mg of (-)-IPC molecules and add them to the chiral liquid crystal phase formed by the assembly of poly-2-L polymer, allowing dextrorotatory isopinocampheol to diffuse evenly into the orientation medium. Subsequently, on a 400 MHz Bruker instrument, through nuclear magnetic resonance deuterium spectrum experiment monitoring, the quadrupole splitting value of solvent deuterium RQCs = 24.9 Hz, indicating its appropriate orientation intensity (as Figure 4 shown, the nuclear magnetic resonance deuterium spectrum of (-)-IPC molecules measured under the chiral liquid crystal orientation medium formed by the assembly of poly-2-L). The RDCs value of dextrorotatory isopinocampheol is obtained through the acquisition, assignment, and calculation of the nuclear magnetic resonance two-dimensional CLIP-HSQC spectrum, and the signal of the measured nuclear magnetic resonance residual dipole coupling spectrum is clear (as Figure 5 shown, the nuclear magnetic resonance two-dimensional CLIP-HSQC superimposed spectrum of (-)-IPC molecules collected under isotropic conditions and in an anisotropic environment).

[0033] Table 1 shows the C-H one-bond coupling values, experimental RDCs values, and theoretical RDCs values of (-)-IPC molecules under isotropic conditions (deuterated dichloromethane solution) and in an anisotropic environment (chiral liquid crystal solution formed by the assembly of poly-2-L). The linear graph of the experimental detection value of RDCs of (-)-IPC molecules and the calculated value of its crystal DFT optimized structure is shown in Figure 6 .

[0034] Table 1

[0035]

[0036] Example 5: Chiral recognition application of chiral liquid crystal alignment medium poly-2-L or poly-2-D for determining enantiomeric isopinetol RDCs

[0037] As shown in Example 4, two portions of 9 mg of (+)-IPC and (-)-IPC were accurately weighed respectively and added into two chiral liquid crystal phases formed by self-assembly of poly-2-L and poly-2-D polymers to prepare four test samples. On a 400 MHz Bruker instrument, through nuclear magnetic resonance deuterium spectrum experiment monitoring, the RQCs of the four samples were made about 24 Hz by diluting the sample concentration to keep the alignment intensity as consistent as possible. The RDCs value of the organic molecule isopinetol was obtained by collecting, assigning and calculating the nuclear magnetic resonance two-dimensional CLIP-HSQC spectrum (as Figure 7 shown, the comparison diagram of experimentally determined RDCs values of enantiomeric IPC molecules in four test samples). The calculated fitting alignment tensor of RDCs was obtained by MSpin V2.3.4, and the chiral recognition and analysis were calculated by the GCB tensor formula to obtain the recognition angle. As Figure 8 shown, this chiral alignment medium achieved excellent chiral recognition and analysis performance, laying a foundation for determining the absolute configuration of natural product molecules in the future.

Claims

1. A helical polyisocyanide, characterized in that, Its molecular structural formula is as follows: Where the degree of polymerization n = 20 - 200, and n is an integer.

2. A method for synthesizing a helical polyisocyanide as claimed in claim 1, characterized in that, It is achieved through the following steps: (1) Synthesis of chiral cholesteryl terminal alkyne palladium catalyst 1 At room temperature, bis(triethylphosphine)palladium chloride, copper chloride, and a magnetic stir bar are placed in a reaction tube. Under anhydrous and anaerobic conditions, triethylamine and cholesteryl amide phenylacetylene compound 1' dissolved in anhydrous dichloromethane are added to the reaction tube, and the mixture is stirred for reaction. After the reaction is completed, it is filtered, washed, and recrystallized to obtain chiral cholesteryl terminal alkyne palladium catalyst 1; (2) Synthesis of helical polyisocyanide Chiral cholesteryl terminal alkyne palladium catalyst 1, phenyl isocyanide monomer 2 with a chiral amino acid side chain, and a magnetic stir bar are placed in a sealed polymerization flask. Under anhydrous and anaerobic conditions, anhydrous chloroform is added to the polymerization flask, and the mixture is heated for reaction. After the reaction is completed, the reaction product is cooled to room temperature and then transferred to a centrifuge tube, and the polymer is collected by centrifugal separation to obtain the target product; 3. The alignment medium prepared from the helical polyisocyanide according to claim 1, characterized in that, The helical polyisocyanide is dissolved in deuterated dichloromethane solution to obtain a helical polyisocyanide alignment medium.

4. The orientation medium prepared from the helical polyisocyanide according to claim 3, characterized in that, Its mass concentration in the deuterated dichloromethane solution is 7.2%wt - 12.8%wt.

5. Use of the directional medium according to claim 3 or 4, characterized in that, It is used for the accurate determination of NMR RDCs to perform chiral recognition and analysis of organic molecules.

6. The application of the directional medium according to claim 5, characterized in that, It is used for the determination of RDCs of enantiomeric isopinol.

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