A barbituric acid derivative with aggregation-induced emission effect and preparation method thereof

Abstract

This invention relates to the field of fluorescence detection technology, specifically to a barbituric acid derivative with aggregation-induced emission (AIE) and its preparation method. In this invention, five structurally similar barbituric acid derivatives were designed and synthesized to explore their fluorescence mechanisms. Molecular spectroscopy analysis revealed that BNCA-1 exhibits a strong AIE effect in aprotic mixed solvents. To clearly understand the specific binding sites of intermolecular hydrogen bonds, two other structurally similar compounds (BNCA-0 and DM-BNCA-1) were designed and synthesized for comparative studies. Comparison of molecular fluorescence phenomena demonstrated the enhancing effect of intermolecular hydrogen bonds on the molecular AIE effect. Based on this, two molecules, BNCA-2 and BNCA-3, were synthesized to understand the influence of intermolecular distance on the molecular AIE effect. It is believed that this invention will enhance our understanding of barbituric acid AIE compounds and contribute to the study of the important role of hydrogen bonds in the fluorescence of AIE compounds.

Description

Technical Field

[0001] This invention relates to the field of fluorescence detection technology, specifically to a barbituric acid derivative with aggregation-induced emission effect and its preparation method. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Barbiturate, as an organic compound, has a wide range of applications, such as as an analytical reagent, a raw material for organic synthesis, an intermediate in plastics and dyes, and a catalyst for polymerization reactions. In particular, barbituric acid is used in drug synthesis and is a key ingredient in some sedative and hypnotic drugs. Furthermore, due to its excellent ability to form coordinate bonds and non-covalent interactions, barbituric acid has also attracted considerable attention in the fields of coordination and supramolecular chemistry.

[0004] In recent years, various D-π-A (donor-π-acceptor) molecules synthesized from barbituric acid have emerged, with barbituric acid acting as a strong electron acceptor. Most of these barbituric acid derivatives exhibit excellent aggregation-induced emission (AIE) effects. AIE materials display unusual fluorescence properties: they do not emit light after dissolving in good solvents, but aggregate and emit fluorescence in poor solvents. Due to their unique fluorescence characteristics, AIE materials show great application potential in optoelectronic devices, chemical and biological sensors, and smart materials. While a large number of AIE molecules have been created, efforts are being made to discover and refine their fluorescence mechanisms. Well-known fluorescence mechanisms include: restricted intramolecular motion (RIM), intramolecular coplanarity, suppression of photochemical or photophysical processes, non-compact packing, and the formation of J-aggregates, among others. However, current research on the fluorescence mechanisms of barbituric acid derivatives exhibiting aggregation-induced emission effects is limited. Summary of the Invention

[0005] To overcome the above problems, the present invention provides a barbituric acid derivative with aggregation-induced emission effect and a method for preparing the same.

[0006] In a first aspect, the invention provides a barbituric acid derivative of formula I or formula II that has an aggregation-induced emission effect.

[0007]

[0008]

[0009] A second aspect of the present invention provides a method for preparing a barbituric acid derivative having aggregation-induced emission effect as shown in Formula I or Formula II above, comprising the following steps:

[0010] (1) The preparation method of the barbituric acid derivative with aggregation-induced emission effect shown in Formula I includes:

[0011] Compound B1 was obtained by replacing the active hydrogen on the amino group of N-ethylaniline with ethyl bromoacetate. B1 was then subjected to a Vilsmeier-Haack reaction to obtain compound B2. Compound B2 underwent a deprotection reaction to generate compound B3. Compound B3 was then condensed with barbiturate in ethanol solution to generate BNCA-1.

[0012]

[0013] (2) The preparation method of the barbituric acid derivative with aggregation-induced emission effect shown in Formula II includes:

[0014] Compound C1 was obtained by replacing the active hydrogen on the amino group of N-ethylaniline with ethyl 3-bromopropionate. C1 was then subjected to a Vilsmeier-Haack reaction to obtain compound C2. Compound C2 underwent a deprotection reaction to generate compound C3. Compound C3 was then condensed with barbiturate in ethanol solution to generate BNCA-2.

[0015]

[0016] In one or more embodiments, the method of replacing the active hydrogen on the amino group of N-ethylaniline with ethyl bromopropionate (ethyl 3-bromopropionate) includes:

[0017] N-ethylaniline, ethyl bromopropionate (ethyl 3-bromopropionate), and triethylamine were added to toluene in sequence and stirred to react. After the reaction was completed, the mixture was cooled to room temperature, deionized water was added, and the mixture was extracted with ethyl acetate. The organic phase was collected, dried with anhydrous MgSO4, and the solvent was removed to obtain compound B1 (C1).

[0018] Preferably, the molar ratio of N-ethylaniline to ethyl bromoacetate (ethyl 3-bromopropionate) is 1:0.8 to 1.2.

[0019] Preferably, the temperature of the stirring reaction is 75–85°C, and the stirring reaction time is 20–30 h.

[0020] In one or more embodiments, a method for obtaining compound B2 (C2) via the Vilsmeier-Haack reaction includes:

[0021] POCl3 was added dropwise to a mixture of B1 (C1) and N,N-dimethylformamide (DMF) under ice bath conditions, with vigorous stirring during the addition. After the addition was complete, the reaction was stirred under ice bath conditions. Then the ice bath was removed and the mixture was slowly raised to room temperature. After standing, the mixture was heated and then cooled to room temperature. Ice water was then added to adjust the pH to 6-8, and the solvent was removed to obtain compound B2 (C2).

[0022] Preferably, after the addition is completed, the reaction is stirred in an ice bath for 30 to 50 minutes.

[0023] Preferably, the ice bath is removed and the temperature is slowly raised to room temperature, with a settling time of 15–30 minutes.

[0024] Preferably, the heating temperature is 85–100°C, and the stirring time is 2–4 hours.

[0025] In one or more embodiments, the method for the deprotection reaction of compound B2 (C2) to generate compound B3 (C3) includes:

[0026] Compound B2 (C2) was dispersed in an aqueous solution of sodium hydroxide and ethanol, and the mixture was stirred at room temperature. After the reaction was completed, the pH was adjusted to 8-9, the solvents ethanol and water were removed, the residual solid was dissolved in ethyl acetate, the undissolved solid was filtered out, and the ethyl acetate was removed to obtain compound B3 (C3).

[0027] Preferably, in the ethanol-water solution, the volume ratio of ethanol to water is 1.5 to 2.5:1, more preferably 2:1.

[0028] Preferably, the concentration (mass fraction of solute) of sodium hydroxide in ethanol-water is 5% to 7%.

[0029] Preferably, the stirring reaction time at room temperature is 6–8 hours.

[0030] In one or more embodiments, the method for condensing compound B3 (C3) with barbiturate in an ethanol solution to generate BNCA-1 (BNCA-2) includes:

[0031] Compound B3 (C3) was dispersed in ethanol, barbituric acid was added, and the mixture was heated and stirred to react. After the reaction was completed, the mixture was cooled for a short time and then filtered under reduced pressure to produce BNCA-1 (BNCA-2).

[0032] In one or more embodiments, the temperature for heating and stirring the reaction is 75–90°C, and the stirring time is 3–6 hours.

[0033] The beneficial effects of this invention are as follows:

[0034] In this invention, five structurally similar barbituric acid derivatives were designed and synthesized. The influence of molecular structure factors on the AIE effect of these barbituric acid derivatives was studied, and the mechanism of the AIE effect of barbituric acid derivatives was explored. The results showed that in the mixed solvent dichloromethane-petroleum ether (DCM-PE), BNCA-1 molecules aggregated through intermolecular hydrogen bonds, leading to a sharp increase in fluorescence intensity and a more pronounced AIE phenomenon. Furthermore, the interaction effects (AIE) of BNCA-1 molecules were compared with those of BNCA-0 (which, compared to BNCA-1, does not contain a carboxyl group) and DM-BNCA-1 (where the NH group in the barbiturate group is replaced by N-CH3). The results showed that the AIE effect of BNCA-1 molecules with COOH was more pronounced than that of BNCA-0; and the AIE effect of BNCA-1 molecules with NH was more pronounced than that of DM-BNCA-1. This demonstrates that both COOH and NH can promote molecular aggregation because both COOH and NH can form hydrogen bonds, increasing the formation of intermolecular hydrogen bonds and thus enhancing the AIE effect. Molecular spectral comparisons confirmed the mechanism of the AIE phenomenon in BNCA-1 molecules and determined the specific binding mode. In a DCM-PE mixed solvent, BNCA-1 molecules gradually aggregated with increasing PE%, reaching a high concentration at 60% PE through intermolecular hydrogen bonds. They linked end-to-end to form aggregates. The carbonyl group (C=O) on the barbiturate ester forms a hydrogen bond with the active hydrogen (OH) of the carboxyl group in another molecule, while the active hydrogen on the amino group (NH) forms an intermolecular hydrogen bond with the hydroxyl hydrogen (-OH) on the carboxyl group. The formation of numerous intermolecular hydrogen bonds makes the intermolecular bonding tighter and effectively prevents internal vibrations and rotations, giving the BNCA-1 molecule a strong AIE effect. Finally, comparing the molecular spectra of BNCA-2 and BNCA-3 with those of BNCA-1 demonstrates that the length of the carbon chain containing the carboxyl group affects the intermolecular distance in the aggregate and thus influences the AIE effect. This research contributes to the study of the important role of hydrogen bonds in the fluorescence of AIE compounds and is of great significance for the development of subsequent AIE compounds. Attached Figure Description

[0035] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0036] Figure 1 The preparation methods of compounds BNCA-1, BNCA-2, BNCA-0, DM-BNCA-1, and BNCA-3 in Examples 1-2 and Comparative Examples 1-3 of the present invention are described.

[0037] Figure 2 Synthetic characterization of the BNCA-1 molecule includes: 1 H NMR(a), 13 C NMR (b) and HRMS spectra (c);

[0038] Figure 3 Synthetic characterization of the BNCA-0 molecule includes: 1 H NMR(a), 13 C NMR (b) and HRMS spectra (c);

[0039] Figure 4 Synthetic characterization of the DM-BNCA-1 molecule includes: 1 H NMR(a), 13 C NMR (b) and HRMS spectra (c);

[0040] Figure 5 Synthetic characterization of the BNCA-2 molecule includes: 1 H NMR(a), 13 C NMR (b) and HRMS spectra (c);

[0041] Figure 6 Synthetic characterization of the BNCA-6 molecule includes: 1 H NMR(a), 13 C NMR (b) and HRMS spectra (c);

[0042] Figure 7 The calculation results for the molecular structure and optical properties of BNCA-1 are shown below: (a) LUMO and HOMO energy levels, band gap, and electron cloud distribution of BNCA-1 in the ground state and (b) excited state (contour plot at 0.02 au); (c) molecular structure of BNCA-1 in the ground and excited states; (d) UV-Vis absorption spectrum of the molecule obtained from calculation and experiments; and (e) fluorescence emission spectrum (λ). ex =450nm, C BNCA-1 =10μM);

[0043] Figure 8 (a) Fluorescence spectrum of BNCA-1 in DCM-PE and (b) Position and intensity variation of the maximum fluorescence peak (λ) ex =450nm); (c) UV-Vis spectrum of BNCA-1 in DCM-PE and (d) absorption peak intensity variation; (e) BNCA-1 (C BNCA-1 Front view of a transparent electrostatic potential map (10 μM);

[0044] Figure 9The absorption and fluorescence spectra of BNCA-0 and DM-BNCA-1 molecules are shown; specifically: (a) the UV-Vis absorption spectra of BNCA-0 and (b) DM-BNCA-1 and (c) the changes in absorption peak intensity in DCM-PE; (d) the fluorescence spectra of BNCA-0 and (e) DM-BNCA-1 and (f) the changes in fluorescence peak intensity in DCM-PE (λ). ex =430nm, C BNCA-0 =CDM-BNCA-1=10μM); Front view of the transparent electrostatic potential diagrams of (g)BNCA-0 and (h)DM-BNCA-1;

[0045] Figure 10 (a) BNCA-0, (b) BNCA-1, (c) DM-BNCA-1 photographs under UV light in DCM-PE (λ) ex =365nm, C BNCA-1 =10μM);

[0046] Figure 11 This describes the way BNCA-1 molecules form aggregates in a DCM-PE mixed solution.

[0047] Figure 12 The effect of intermolecular distance on the fluorescence of molecular aggregates: (a) fluorescence spectrum of BNCA-2 and (b) changes in the position and intensity of fluorescence peaks in DCM-PE (λ). ex (c) UV-Vis absorption spectrum of BNCA-2; (d) Changes in absorption peak intensity in DCM-PE; (e) Front view of electrostatic potential diagram of BNCA-2 (CBNCA-2 = 10 μM);

[0048] Figure 13 (a) Fluorescence spectrum of BNCA-3 and (b) Fluorescence intensity variation in DCM-PE (λ) ex (c) UV-Vis absorption spectrum of BNCA-3; (d) Changes in absorption peak intensity in DCM-PE; (e) Front view of electrostatic potential diagram of BNCA-3 (CBNCA-3 = 10 μM);

[0049] Figure 14 The diagram illustrates the way BNCA-2 and BNCA-3 molecules form aggregates in a DCM-PE mixed solution, where a represents BNCA-2 and b represents BNCA-3. Detailed Implementation

[0050] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0051] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0052] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0053] Figure 1 This describes the preparation methods of compounds BNCA-1, BNCA-2, BNCA-0, DM-BNCA-1, and BNCA-3 in Examples 1-2 and Comparative Examples 1-3 of the present invention.

[0054] Example 1

[0055] refer to Figure 1 The compound BNCA-1 was synthesized.

[0056] N-ethylaniline (7 mL) was mixed with ethyl bromoacetate (7 mL), triethylamine (10 mL), and toluene (30 mL), and stirred at 80 °C for 24 h. After cooling to room temperature, the mixture was washed with H₂O (20 mL). The mixture was extracted with ethyl acetate, and the organic phase was washed twice with water. The yellow solution was dried overnight on anhydrous MgSO₄, and then the solvent was removed to give a brown oily substance B1.

[0057] POCl3 (4g) was added at 0°C to a mixture of N-ethyl-N-phenylglycine ethyl ester (B1, 5g) and DMF (5mL), and stirred vigorously for another 40 min at 0°C. The mixture was then slowly raised to room temperature, allowed to stand for 20 min, and stirred at 90°C for 3 h to obtain a dark green solution. The mixture was then cooled to room temperature in air, and ice water (20mL) was added. After adjusting the pH to 6–8 with 30% Na2CO3 solution, the solvent was removed to obtain a yellow oily substance, B2.

[0058] N-ethyl-N-(4-tolyl)glycine ethyl ester (B2, 2 g) was dispersed in an aqueous solution of sodium hydroxide in ethanol (ethanol (20 mL), NaOH (1.5 g), water (10 mL)) and stirred at 25 °C for 7 h. The pH was then adjusted to 8–9 with diluted HCl solution. Ethanol and water were removed, and the remaining solid was dissolved in ethyl acetate (50 mL). Since sodium chloride produced during the post-treatment process is insoluble in ethyl acetate, it was removed by filtration. The filtered ethyl acetate was rotary evaporated to obtain a yellow viscous solution, which was collected and dried under vacuum to obtain B3.

[0059] N-ethyl-N-(4-tolyl)glycine (B3, 1 g) was added to ethanol (20 mL), followed by barbituric acid (1 g) in a 100 mL flask. The mixture was stirred at 80 °C for 4 hours. After the reaction was complete, the mixture was cooled briefly and then filtered under reduced pressure to obtain a red solid powder product (compound BNCA-1). 1 H NMR (400MHz, DMSO-d6) δ12.88(s,1H),11.09(s,1H),10.96(s,1H),8.40(d,J=7.2Hz,2H),8.15 (s,1H),6.73(d,J=7.2Hz,2H),4.27(s,2H),3.55(q,J=8.0,7.6Hz,2H),1.15(t,J=6.0Hz,3H). 13 C NMR (400MHz, DMSO-d6) δ171.65,165.21,163.25,155.95,153.28,150.86,139.56,120.90,111.69,110.66,56.56,51.96,46.49,19.10,12.73.

[0060] Example 2

[0061] refer to Figure 1 The compound BNCA-2 was synthesized.

[0062] N-ethylaniline (7 mL) was mixed with ethyl 3-bromopropionate (6.8 mL), triethylamine (10 mL), and toluene (30 mL), and stirred at 80 °C for 24 h. After cooling to room temperature, the mixture was washed with H₂O (20 mL). The solution was extracted with ethyl acetate, and the organic phase was washed twice with water. The yellow solution was dried overnight with anhydrous MgSO₄ to remove the solvent, yielding a dark green oily substance, Cl.

[0063] POCl3 (4 g) was added dropwise to a mixture of ethyl 3-(phenyl)aminoethyl)propionate (C1, 5 g) and DMF (5 mL), and the mixture was stirred vigorously at 0 °C for 40 min. The mixture was then slowly heated to room temperature, allowed to stand for 20 min, and stirred at 90 °C for 3 h to obtain a dark green solution. The mixture was then cooled to room temperature in air, and then ice water (20 mL) was added. After adjusting the pH to 6–8 with 30% Na2CO3 solution, the yellow oily substance C2 was obtained by removing the solvent.

[0064] Ethyl 3-ethyl(4-tolyl)aminopropionate (C2, 2 g) was dispersed in an aqueous solution of sodium hydroxide in ethanol (ethanol (20 mL), NaOH (1.5 g), water (10 mL)) and stirred at 25 °C for 7 h. The pH was then adjusted to 8–9 with diluted HCl solution. Ethanol and water were removed, and the remaining solid was dissolved in ethyl acetate (50 mL). Since sodium chloride produced during the post-treatment process is insoluble in ethyl acetate, it was removed by filtration. The filtered ethyl acetate was rotary evaporated to obtain a yellow viscous solution, which was collected and dried under vacuum to obtain C3.

[0065] 3-(ethyl(4-tolyl)amino)propionic acid (C3, 1 g) was added to ethanol (20 mL), followed by the addition of barbituric acid (1 g) to a 100 mL three-necked flask. The mixture was stirred at 80 °C for 4 hours. After the reaction was complete, the mixture was cooled briefly and filtered under reduced pressure to obtain a red solid powder product (BNCA-2). 1 H NMR (400MHz, DMSO-d6) δ12.39(s,1H),11.03(s,1H),10.91(s,1H),8.38(d,J=9.0Hz,2H),8.10(s,1H),6.77 (d,J=9.1Hz,2H),3.65(t,J=7.2Hz,2H),3.50(q,J=7.0Hz,2H),2.53(t,J=7.2Hz,2H),1.09(t,J=7.0Hz,3H). 13 C NMR(400MHz,DMSO-d6)δ173.37,165.27,163.29,155.86,152.64,150.87,1 39.90,120.55,111.63,110.13,56.56,46.18,45.21,32.62,19.10,12.72.

[0066] Comparative Example 1

[0067] refer to Figure 1 The compound BNCA-0 was synthesized.

[0068] POCl3 (4g) was added dropwise to a mixture of N,N-diethylaniline (5g) and DMF (5mL) at 0℃, and the mixture was stirred vigorously and then stirred at 0℃ for 40 min. The mixture was slowly heated to room temperature, allowed to stand for 20 min, and then stirred at 90℃ for 3 h to obtain a dark green solution. The mixture was cooled in air and then ice water (20mL) was added. The pH was adjusted to 6–8 using 30% Na2CO3 solution. The green precipitate A was collected by desolvation and vacuum drying.

[0069] 4-(diethylamine)benzaldehyde (A, 1 g) was added to ethanol (20 mL), followed by the addition of barbituric acid (1 g) to a 100 mL three-necked flask. The mixture was stirred at 80 °C for 4 hours. After the reaction was complete, the mixture was cooled briefly and filtered under reduced pressure to obtain a red solid powder product (BNCA-0). 1 H NMR (400MHz, DMSO-d6) δ11.04(s,J=2.1Hz,1H),10.91(s,J=2.0Hz,1H),8.42(d,J=9.1H z,2H),8.12(s,1H),6.78(d,J=9.2Hz,2H),3.51(q,J=7.0Hz,4H),1.15(t,J=7.0Hz,6H). 13 C NMR (400MHz, DMSO-d6) δ165.34,163.32,155.80,152.75,150.88,140.10,120.19,111.44,109.46,44.78,29.85,19.10,13.02.

[0070] Comparative Example 2

[0071] refer to Figure 1 The compound DM-BNCA-1 was synthesized.

[0072] N-ethylaniline (7 mL) was mixed with ethyl bromoacetate (7 mL), triethylamine (10 mL), and toluene (30 mL), and stirred at 80 °C for 24 h. After cooling to room temperature, the mixture was washed with H₂O (20 mL). The mixture was extracted with ethyl acetate, and the organic phase was washed twice with water. The yellow solution was dried overnight on anhydrous MgSO₄, and then the solvent was removed to give a brown oily substance B1.

[0073] POCl3 (4g) was added at 0°C to a mixture of N-ethyl-N-phenylglycine ethyl ester (B1, 5g) and DMF (5mL), and stirred vigorously for another 40 min at 0°C. The mixture was then slowly raised to room temperature, allowed to stand for 20 min, and stirred at 90°C for 3 h to obtain a dark green solution. The mixture was then cooled to room temperature in air, and ice water (20mL) was added. After adjusting the pH to 6–8 with 30% Na2CO3 solution, the solvent was removed to obtain a yellow oily substance, B2.

[0074] N-ethyl-N-(4-tolyl)glycine ethyl ester (B2, 2 g) was dispersed in an aqueous solution of sodium hydroxide in ethanol (ethanol (20 mL), NaOH (1.5 g), water (10 mL)) and stirred at 25 °C for 7 h. The pH was then adjusted to 8–9 with diluted HCl solution. Ethanol and water were removed, and the remaining solid was dissolved in ethyl acetate (50 mL). Since sodium chloride produced during the post-treatment process is insoluble in ethyl acetate, it was removed by filtration. The filtered ethyl acetate was rotary evaporated to obtain a yellow viscous solution, which was collected and dried under vacuum to obtain B3.

[0075] N-ethyl-N-(4-tolyl)glycine (B3, 1 g) was added to ethanol (20 mL), followed by 1,3-dimethylbarbituric acid (1 g) in a 100 mL three-necked flask. The mixture was stirred at 80 °C for 4 hours. After the reaction was complete, the mixture was cooled briefly and filtered under reduced pressure to obtain a red solid powder product (DM-BNCA-1). 1 H NMR(400MHz,DMSO-d6)δ12.86(s,1H),8.35(d,J=9.1Hz,2H),8.18(s,1H),6.70(d,J =9.1Hz,2H),4.24(s,2H),3.52(q,J=7.1Hz,2H),3.17(s,6H),1.12(t,J=7.0Hz,3H). 13 C NMR (400MHz, DMSO-d6) δ171.98,163.73,161.70,156.79,155.27,153.37,151. 76,139.58,120.93,111.69,110.45,51.96,46.51,37.44,29.07,28.44,12.73.

[0076] Comparative Example 3

[0077] refer to Figure 1 The compound BNCA-3 was synthesized.

[0078] N-ethylaniline (7 mL) was mixed with ethyl 4-bromobutyrate (6.5 mL), triethylamine (10 mL), and toluene (30 mL), and stirred at 80 °C for 24 h. After cooling to room temperature, the mixture was washed with H₂O (20 mL). The solution was then extracted with ethyl acetate, and the organic phase was washed twice with water. The yellow solution was dried overnight with anhydrous MgSO₄ to remove the solvent, yielding a black oily substance (D1).

[0079] POCl3 (4 g) was added dropwise to a mixture of ethyl 4-(phenyl)aminoethyl)butyrate (D1, 5 g) and DMF (5 mL), and the mixture was stirred vigorously at 0 °C for 40 min. The mixture was then slowly heated to room temperature, allowed to stand for 20 min, and stirred at 90 °C for 3 h to obtain a dark green solution. The mixture was then cooled to room temperature in air, and then ice water (20 mL) was added. After adjusting the pH to 6–8 with 30% Na2CO3 solution, the solvent was removed to obtain a yellow oily substance (D2).

[0080] Ethyl 4-ethyl(4-tolyl)aminobutyrate (D2, 2 g) was dispersed in an aqueous solution of sodium hydroxide in ethanol (ethanol (20 mL), NaOH (1.5 g), water (10 mL)) and stirred at 25 °C for 7 h. The pH was then adjusted to 8–9 with diluted HCl solution. After removing the ethanol and water, the precipitated yellow solid was dissolved in ethyl acetate (50 mL). Since sodium chloride produced during the post-treatment process is insoluble in ethyl acetate, it was removed by filtration. The filtered ethyl acetate was then rotary evaporated to obtain a yellow viscous solution, which was collected and dried under vacuum to obtain D3.

[0081] 4-(ethyl(4-tolyl)amino)butyric acid (D3, 1 g) was added to ethanol (20 mL), followed by the addition of barbituric acid (1 g) to a 100 mL three-necked flask. The mixture was stirred at 80 °C for 4 hours. After the reaction was complete, the mixture was cooled briefly and filtered under reduced pressure to obtain a red solid powder product (BNCA-3). 1 H NMR (400MHz, DMSO-d6) δ12.14(s,1H),11.07-10.99(m,1H),10.90(s,1H),8.42(d,J=9.3Hz,2H),8.13(s,1H),6. 83(d,J=9.4Hz,2H),3.60-3.39(m,5H),2.33(t,J=7.1Hz,2H),1.79(p,J=7.2Hz,2H),1.14(q,J=6.3,5.7Hz,4H). 13CNMR(400MHz,DMSO-d6)δ165.28,163.29,155.80,153.01,150.83,139.95,111.56,109.75,49.49,45.18,31.10,22.88,12.82.

[0082] Example 3 Synthesis and Characterization

[0083] To determine whether the BNCA-1 molecule was successfully synthesized, its... 1 H NMR, 13 The spectra of BNCA-1 were analyzed using C1NMR and HRMS. First, the spectra of BNCA-1 were measured in DMSO-d6. 1 The 1H NMR spectrum, the results are shown in Figure 2a. Figure 2 In α, proton peaks representing hydrogen on the carboxyl group (Ha) and hydrogen on the double bond (Hc) were found at 12.88 ppm and 8.15 ppm, respectively, while the characteristic chemical shifts for hydrogen on the phenyl group (Hb) occurred at 8.40 ppm and 6.73 ppm. Another characteristic peak for NH (Hd) appeared at 11.09 ppm and 10.96 ppm. Other proton peaks (He, Hf, and Hg) were respectively associated with... Figure 1 The peaks e, f, and g in the sequence match. Then, in Figure 2 In b, BNCA-1 13 The C10 NMR spectrum showed peaks equal to the number of carbon atoms in the molecule. High-resolution mass spectrometry (HRMS) was used to measure BNCA-1 in methanol. Figure 2 (c) The relative molecular mass is the same as that of the BNCA-1 molecule (m / z = 346). These results indicate the successful synthesis of the BNCA-1 molecule.

[0084] The structures of the other four molecules (BNCA-0, DM-BNCA-1, BNCA-2, and BNCA-3) were also obtained by 1H NMR spectroscopy. Figure 3 (middle a, 4middle a, 5middle a and 6middle a), 13C NMR spectrum ( Figure 3 (middle b, 4 middle b, 5 middle b and 6 middle b) and HRMS spectrum ( Figure 3 The results of (c in 4, c in 5, and c in 6) have been confirmed.

[0085] Example 4: Calculation Study of the Molecular Structure and Optical Properties of BNCA-1

[0086] First, calculate the BNCA-1 molecule in its ground state ( Figure 7 a) and excited state ( Figure 7(b) Frontier Molecular Orbitals (FMOs). At the highest occupied molecular orbital (HOMO), the electron density is mainly distributed in dialkylamines and the benzene ring, while at the lowest unoccupied molecular orbital (LUMO), the electron density is mainly distributed in the benzene ring and barbiturates. From HOMO to LUMO, the electron density of dialkylamines decreases, while the electron density of barbiturates increases significantly. Clearly, during excited-state transitions, there is a significant intramolecular charge transfer from electron donors to acceptors, indicating that the BNCA-1 molecule exhibits an intramolecular charge transfer (ICT) effect. Furthermore, the energy level gaps were calculated separately. It can be found that the ICT effect of the BNCA-1 molecule is stronger in the excited state. Compared to the ground state, the energy level gaps of the excited-state molecule are smaller, which may be related to changes in molecular structure.

[0087] Therefore, we investigated the molecular structure of BNCA-1 in the ground and excited states. Figure 7 c). By comparing the structures of ground-state and excited-state molecules, it can be found that the ground-state molecular structure exhibits good planarity, while the excited-state molecular structure is twisted by about 90°. The twisting of the molecular structure may be caused by the TICT effect of a single molecule under excited-state conditions.

[0088] The absorption spectrum of the BNCA-1 molecule was calculated experimentally, such as... Figure 7 As shown in d, the absorption spectrum of the BNCA-1 molecule measured in DMF solvent has a strong absorption peak at 400 nm. Figure 7 The solid black line in d) is due to the ICT effect of the electron donor of the dialkylamine to the electron acceptor of barbiturate. However, the calculated absorption spectrum ( Figure 7 (d, solid purple line) Compared to the experimental spectrum, the light spectrum shows a 57 nm blue shift, which may be due to neglecting intermolecular interactions in the spectrum calculation. Furthermore, the emission spectrum of the BNCA-1 molecule was experimentally calculated, as shown below. Figure 7 As shown in Figure e, the emission spectrum of BNCA-1 was measured in DMF solvent at an excitation wavelength of 450 nm. Figure 7 (The black solid line in e) shows that the calculated fluorescence emission spectrum has a strong absorption at 390 nm. Figure 7 (The red dashed line in e) may be caused by the twisting of the molecular structure in the excited state.

[0089] It can be seen that the measured absorption and fluorescence spectra are similar in shape to the calculated spectra, but both show a significant redshift. This is because the calculation of the molecular absorption and emission spectra only considered individual molecules and did not take into account the interactions between BNCA-1 molecules. Therefore, the intramolecular torsion is relatively strong, and the degree of molecular conjugation is greatly reduced. The actual measured spectra are obtained in flux, where there are interactions between molecules, which restrict the molecular torsion and maintain a relatively good total amount of excited states, resulting in a larger redshift in the calculated spectra.

[0090] Example 5: Absorption and fluorescence spectra of BNCA-1 under different environments

[0091] BNCA-1 was found to exhibit good AIE performance in a dichloromethane-petroleum ether (DCM-PE) mixed solvent (DCM being a good solvent and PE a poor solvent), such as... Figure 8 As shown in a. The reason why an aqueous mixed solvent was not chosen to study its AIE effect is that BNCA-1 undergoes structural changes in water, thus affecting the molecule's AIE effect.

[0092] Fluorescence spectra of BNCA-1 molecules were measured in DCM-PE mixtures with different proportions using 450 nm as the excitation wavelength. Figure 8 a) It can be observed that when the PE content (PE%) in the mixed solution is 0-50%, the fluorescence intensity of the solution does not change significantly. However, when PE% = 60%, the fluorescence intensity suddenly increases. When PE% = 80%, the fluorescence intensity reaches its maximum value, which is 18.2 times that when PE% = 0. But when PE% is greater than 80%, the fluorescence intensity of the solution begins to decrease.

[0093] First, the good AIE activity of BNCA-1 molecules was demonstrated, with the increase in fluorescence intensity indicating molecular aggregation. Within the aggregates, rotation and vibration inhibit the formation of nonradiative transition channels within the BNCA-1 molecules, leading to enhanced fluorescence. Due to the precipitation of some molecules from the solvent, the fluorescence at PE% decreased by more than 80%. Furthermore, a significant red shift in the fluorescence emission peak was observed with increasing PE% in the mixed solution. Figure 8 As shown in b, this further demonstrates that intermolecular aggregation occurs, leading to increased molecular coupling and a redshift of the emission peak.

[0094] In addition, ultraviolet-visible absorption spectra were detected under the same conditions, such as Figure 8 As shown in c, the absorbance remains essentially constant with increasing PE%, until PE = 50%, at which point the absorption peak intensity suddenly decreases. Figure 8d) The absorption peak broadens. When PE% = 60%–80%, the broadening of the absorption peak is more pronounced, further demonstrating that as PE increases to a certain level, the solubility of BNCA-1 molecules decreases, and the molecules rapidly aggregate. This aggregation mode may be caused by the formation of hydrogen bonds between the molecular hydrogen bond donors (OH and NH) and hydrogen bond acceptors (C=O).

[0095] Calculate the electrostatic potential of the BNCA-1 molecule, such as... Figure 8 As shown in e. The blue positions indicate the positive charge of the functional groups, such as the hydroxyl group on the carboxyl group and the amino group on the barbiturate ring (e). Figure 8 The dark blue positions (e) represent potential hydrogen bond donors with positive charge from active hydrogen. The red positions indicate the electronegativity of functional groups, such as the carbonyl group on the carboxyl group and the barbiturate ring (e). Figure 8 (e., red position). These functional groups with lone pair electronegativity are potential hydrogen bond acceptors. Electrostatic analysis of the BNCA-1 molecule demonstrated the potential for intermolecular hydrogen bonds to form between the hydrogen bond donors (hydroxyl and amino groups) and the hydrogen bond acceptors (carbonyl groups).

[0096] Example 6: Absorption and fluorescence spectra of BNCA-0 and DM-BNCA-1 molecules

[0097] To further explore the specific mechanisms of molecular aggregation, we modified the functional groups of the molecule to verify this hypothesis. First, we removed the carboxyl group from the molecule to synthesize BNCA-0. We then used DCM and PE as good and poor solvents, respectively, to detect the UV-Vis absorption spectrum of the molecule. Figure 9 a) and fluorescence spectrum ( Figure 9 d). Furthermore, we substituted the NH group on the barbiturate group with N-CH3 to obtain compound DM-BNCA-1, which reduced the number of hydrogen bond donors on the barbiturate. Then, we measured the absorption spectrum of molecule DM-BNCA-1 in DCM-PE. Figure 9 b) and fluorescence spectrum ( Figure 9 e).

[0098] First, the absorption spectra of BNCA-0 and DM-BNCA-1 molecules were compared, and it was found that the absorption peak intensities of both molecules did not change significantly with increasing PE% in the mixed solution. Figure 9Furthermore, it was observed that the absorption peak intensities of the two molecules remained relatively stable, indicating that no significant intermolecular aggregation occurred. The fluorescence spectra of these two molecules were measured at an excitation wavelength of 430 nm. For the BNCA-0 molecule, with increasing PE%, the solubility decreased, the molecules gradually aggregated, and the fluorescence intensity gradually increased. At PE% = 90%, the maximum fluorescence intensity of the BNCA-0 molecule was 2.3 times that at PE% = 0. The fluorescence intensity of the DM-BNCA-1 molecule did not increase significantly, nor did it decrease significantly. The maximum fluorescence intensity at PE% = 90% was 1.14 times that at PE% = 0. However, the emission peaks of the fluorescence spectra of these two molecules did not show a large-scale redshift or a sharp increase in intensity. Compared with BNCA-1, neither compound showed a strong AIE effect.

[0099] In addition, the electrostatic potentials of BNCA-0 and DM-BNCA-1 molecules were calculated. The electrostatic potentials of BNCA-0 and DM-BNCA-1 molecules are the same as those of BNCA-1 molecules. The blue part represents the functional group with a positive charge, and the red part represents the functional group with a negative charge. Figure 9 In this context, g represents the electrostatic potential of the BNCA-0 molecule. Compared to BNCA-1 ( Figure 8 e) After removing the carboxyl group, there are fewer negatively charged functional groups on the alkyl chain (the red part is reduced), and the hydrogen atom on the methyl group is less reactive than the hydrogen atom on the carboxyl group (the dark blue color turns blue). This indicates that the reduction in hydrogen bond donors (-OH) and hydrogen bond acceptors (C=O) may lead to a decrease in the degree of intermolecular aggregation and also a weakening of the molecular AIE effect.

[0100] For DM-BNCA-1 molecules with carboxyl groups ( Figure 9 h) reveals that the hydroxyl group on the carboxyl group carries a strong positive charge (dark blue portion), while the carbonyl group on the carboxyl group carries a negative charge (light red portion). However, compared to BNCA-1 ( Figure 8 e) The loss of active hydrogen in the barbiturate ring reduces the positive charge of the amino group (the dark blue color changes to light blue), and also reduces the number of molecular hydrogen bond donors (NH), thereby reducing the degree of intermolecular aggregation and weakening the AIE effect of the molecule.

[0101] In summary, the analysis of the electrostatic changes of the two molecules shows that both carboxyl and amino groups are important components of intermolecular hydrogen bonds and also important functional groups that promote molecular aggregation.

[0102] Example 7: Fluorescence of BNCA-0, BNCA-1, and DM-BNCA-1 under ultraviolet light

[0103] We conducted a comparative study on the fluorescence changes of the three molecules under ultraviolet light to observe the fluorescence phenomena in the solution. Figure 10a, 10b, and 10c are images of molecules BNCA-0, BNCA-1, and DM-BNCA-1 under ultraviolet light, respectively.

[0104] It can be observed that as the percentage of PE in the mixed solvent increases, Figure 10 The color of solution a did not change significantly. The solution with DCM:PE = 1:9 showed different fluorescence phenomena, which is due to the low solubility of the molecules, causing some fluorescent molecules to precipitate. Figure 10 c shows essentially the same phenomenon. This indicates that there is no strong intermolecular aggregation between BNCA-0 and DM-BNCA-1 molecules, which can also be observed in their fluorescence spectra. Figure 9 d and Figure 9 The position of the maximum fluorescence peak of the molecule in e remains basically unchanged.

[0105] The difference is that when the PE% in the BNCA-1 solution increases to 50%, the fluorescence of the solution changes from weak blue to purple. This color change indicates that BNCA-1 molecules form aggregates in the mixed solution, which also corresponds to the fluorescence spectrum. Figure 8 (A shows a strong red shift in the maximum fluorescence peak when PE% = 50-90%). Color changes of the three molecules were observed in the mixed solvent, further confirming the formation of BNCA-1 molecular aggregates from a macroscopic perspective.

[0106] Example 8 Molecular aggregation mechanism

[0107] Through the above discussion, we have obtained the specific mechanisms by which BNCA-1 molecules form aggregates, such as... Figure 11 As shown, in the DCM-PE mixed solvent, BNCA-1 molecules gradually aggregate with increasing PE%. When PE% = 60%, a large number of molecules aggregate through intermolecular hydrogen bonds. They connect end-to-end to form aggregates. The carbonyl group (C=O) on the barbiturate group forms a hydrogen bond with the active hydrogen (OH) of the carboxyl group of another molecule, and the active hydrogen on the amino group (NH) forms an intermolecular hydrogen bond with the hydroxyl hydrogen (-OH) on the carboxyl group. The formation of a large number of intermolecular hydrogen bonds makes the bonding between molecules tighter and also effectively prevents internal vibration and rotation of molecules, giving BNCA-1 molecules a strong AIE effect.

[0108] Example 9: Effect of intermolecular distance on fluorescence of molecular aggregates

[0109] The above studies not only confirmed the formation of BNCA-1 molecular aggregates in mixed solutions, but also revealed the specific mode of intermolecular aggregation through comparison of intermolecular spectra. However, to further investigate the relationship between the internal structure of molecular aggregates and molecular fluorescence, we designed and synthesized BNCA-2 and BNCA-3 molecules by increasing the length of the alkyl chains containing carboxyl groups.

[0110] Figure 12 a shows the fluorescence spectrum of BNCA-2 molecules in a DCM-PE mixed solution. It can be observed that when PE% = 70%, a significant red shift occurs in the fluorescence peak, and the intensity of the fluorescence peak continuously increases with increasing PE%. Figure 12 This can be observed more clearly in b. Under the same conditions, when PE% = 60%, the maximum fluorescence peak of the BNCA-1 molecule showed a significant red shift ( Figure 8 a) However, this phenomenon occurs later in the BNCA-2 molecule due to the increased alkyl chain. Furthermore, it was found that at PE% = 90%, the fluorescence intensity of the BNCA-2 molecule was approximately 5.8 times stronger than at PE% = 0%, significantly lower than the 18.2 times stronger intensity of the BNCA-1 molecule. This is because the increased alkyl chain leads to a lack of tight intermolecular aggregation. Therefore, to obtain molecules with good AIE performance, it is necessary to consider not only the influence of intermolecular forces but also the influence of molecular structure.

[0111] Figure 12 c represents the UV-Vis absorption spectrum of BNCA-2 molecules in a DCM-PE mixed solution. When PE% = 60%, the absorption peak intensity decreases slightly. When PE% = 70%, the absorption peak intensity decreases significantly, and a distinct peak apex appears on the right side of the peak, similar to the absorption spectrum of BNCA-1 under the same conditions. Figure 8 c) further proves the generation of molecular aggregates. Figure 12 The decrease in the intensity of the absorption peak of the BNCA-2 molecule can be observed more clearly with d.

[0112] The electrostatic potential of molecule BNCA-2 in the ground state was calculated. Figure 12 e), it can be found that its electrostatic potential is similar to that of molecule BNCA-1 ( Figure 8 e). The hydroxyl group (-OH) on the carboxyl group and the amino group (NH) on the barbituric acid ring are positively charged. Figure 12 (the dark blue position in e), the carbonyl group on the carboxyl group and the barbituric acid ring are negatively charged ( Figure 12 (e, the red position).

[0113] By analyzing the fluorescence spectrum of BNCA-2 molecules ( Figure 12 a) It can be observed that increasing the alkyl chain length reduces the AIE effect of the molecule. To further confirm this phenomenon, we performed spectroscopic detection and electrostatic potential analysis on BNCA-3 molecules with longer alkyl chains in a DCM-PE mixture. In BNCA-1 ( Figure 8 a) and BNCA-2( Figure 12 In the fluorescence spectrum of a), a large-scale redshift and enhancement of the maximum fluorescence peak were observed. However, in the fluorescence spectrum of BNCA-3 ( Figure 13 a) With increasing unfavorable solvent concentration, the fluorescence peak intensity first increased and then decreased, with no significant red shift or enhancement of the maximum fluorescence peak. Furthermore, the fluorescence of BNCA-3 molecule reached its maximum at PE% = 50%, which is 1.39 times that at PE% = 0%. This is significantly lower than the 18.2 times of molecule BNCA-1 and the 5.8 times of molecule BNCA-2. This indicates that BNCA-3 molecule does not exhibit good AIE performance, possibly due to the further increase in alkyl chain length, resulting in excessively large internal space after aggregation, which cannot effectively restrict internal rotation and vibration. At PE% = 80%, a weak fluorescence peak was observed at 610 nm for BNCA-3, which may indicate weak aggregation of BNCA-3 molecules in the mixed solvent.

[0114] Figure 13 c represents the UV-Vis absorption spectrum of BNCA-3 molecules in a DCM-PE mixed solution. It can be observed that the intensity of the absorption peak first increases and then decreases with increasing PE percentage in the mixed solution, such as... Figure 13 As shown in d, no obvious peak broadening or shoulder peaks were observed, which also indicates that the molecules did not aggregate in large quantities in the mixed solvent.

[0115] Finally, the electrostatic potential of the BNCA-3 molecule in the ground state was calculated. Figure 13 e) It can be observed that the increase in the alkyl chain does not affect the charge strength of the carboxyl group, nor does it significantly affect the charge strength of the functional groups on the barbiturate ring. The hydroxyl (-OH) and amino (NH) groups on the carboxyl group of the barbiturate ring still carry a strong positive charge. Figure 13 (in dark blue in e), the carbonyl and carboxyl groups on the barbiturate ring still carry a strong negative charge. Figure 13 (The red position in e). This also shows that the electronegativity and electronegativity of the intramolecular groups have not been weakened, and BNCA-3 molecules still aggregate through the formation of intermolecular hydrogen bonds. In other words, the reason why the molecule has a weak AIE effect is that the growth of carbon chains increases the internal space of the aggregate.

[0116] Based on the spectral analysis of BNCA-2 and BNCA-3 molecules, the following aggregation fluorescence mechanism is proposed ( Figure 14Comparing the possible aggregation modes of BNCA-2 and BNCA-3 molecules, it was found that, during aggregate formation, the distance between BNCA-3 molecules with longer alkyl chains is significantly greater than that between BNCA-2 molecules. Furthermore, due to the flexibility of alkyl chains, the increase in the number of alkyl chains also increases the probability of intramolecular motion. These structural changes lead to a decrease in the fluorescence intensity and AIE effect of the molecules. Therefore, the intermolecular distance of the aggregates is also an important factor affecting the molecular AIE effect. The closer the molecular distance, the stronger the AIE effect. We believe that the results of this study will provide some assistance in exploring the relationship between molecular aggregation structure and molecular AIE effect.

[0117] in conclusion:

[0118] Five structurally similar barbiturate compounds were designed and synthesized. In the mixed solvent DCM-PE, BNCA-1 molecules aggregated through intermolecular hydrogen bonds, leading to a sharp increase in fluorescence intensity and a more pronounced AIE (Alternating Intense Emission) effect. Furthermore, the AIE interactions of BNCA-1 with BNCA-0 and DM-BNCA-1 molecules were compared. The BNCA-1 molecule with the carboxyl group exhibited a stronger AIE interaction. This demonstrates that introducing a carboxyl group into the molecule increases the formation of intermolecular hydrogen bonds, resulting in a stronger AIE effect. In addition, the mechanism of the AIE phenomenon in BNCA-1 was demonstrated through molecular spectral comparison, and the specific binding mode was identified. Finally, the molecular spectra of BNCA-2 and BNCA-3 were compared with those of BNCA-1, proving that the carbon chain length containing the carboxyl group affects the intermolecular distance in the aggregate and thus influences the AIE effect. We believe that this study will not only enhance our understanding of barbiturate AIE compounds but also contribute to the investigation of the important role of hydrogen bonds in the AIE effect of barbiturate AIE compounds.

[0119] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a barbituric acid derivative with aggregation-induced emission effect as shown in Formula I or Formula II, characterized in that, Includes the following steps: 、 Formula I and Formula II; (1) The preparation method of the barbituric acid derivative with aggregation-induced emission effect shown in Formula I includes: Compound B1 was obtained by replacing the active hydrogen on the amino group of N-ethylaniline with ethyl bromoacetate. B1 was then subjected to a Vilsmeier-Haack reaction to obtain compound B2. Compound B2 underwent a deprotection reaction to generate compound B3. Compound B3 was then condensed with barbiturate in ethanol solution to generate BNCA-1. (2) The preparation method of the barbituric acid derivative with aggregation-induced emission effect shown in Formula II includes: Compound C1 was obtained by replacing the active hydrogen on the amino group of N-ethylaniline with ethyl 3-bromopropionate. C1 was then subjected to a Vilsmeier-Haack reaction to obtain compound C2. Compound C2 underwent a deprotection reaction to generate compound C3. Compound C3 was then condensed with barbiturate in ethanol solution to generate BNCA-2. 。 2. The preparation method according to claim 1, characterized in that, Methods that utilize ethyl bromoacetate or ethyl 3-bromopropionate to replace the active hydrogen on the amino group of N-ethylaniline include: N-ethylaniline, ethyl bromoacetate or ethyl 3-bromopropionate and triethylamine were added to toluene in sequence and stirred to react. After the reaction was completed, the mixture was cooled to room temperature, deionized water was added, and then extracted with ethyl acetate. The organic phase was collected, dried with anhydrous MgSO4, and the solvent was removed to obtain compound B1 or C1.

3. The preparation method according to claim 2, characterized in that, The molar ratio of N-ethylaniline to ethyl bromoacetate or ethyl 3-bromopropionate is 1:0.8~1.2; Alternatively, the temperature of the stirring reaction is 75~85 ℃, and the stirring reaction time is 20~30 h.

4. The preparation method according to claim 1, characterized in that, Methods for obtaining compounds B2 or C2 via the Vilsmeier-Haack reaction include: POCl3 was added dropwise to a mixture of B1 or C1 and N,N-dimethylformamide under ice bath conditions, with vigorous stirring during the addition. After the addition was complete, the reaction was stirred under ice bath conditions. Then the ice bath was removed and the mixture was slowly raised to room temperature. After standing, the reaction was heated and then cooled to room temperature. Ice water was then added to adjust the pH to 6-8, and the solvent was removed to obtain compound B2 or C2.

5. The preparation method according to claim 4, characterized in that, After the addition is complete, continue stirring the reaction in an ice bath for 30-50 minutes. Alternatively, remove the ice bath and slowly raise the temperature to room temperature, allowing it to stand for 15-30 minutes. Alternatively, the temperature of the heating reaction is 85~100 ℃, and the stirring time is 2~4 h.

6. The preparation method according to claim 1, characterized in that, Methods for the deprotection reaction of compound B2 or C2 to generate compound B3 or C3 include: Compound B2 or C2 was dispersed in an aqueous solution of sodium hydroxide and ethanol, and the mixture was stirred at room temperature. After the reaction was completed, the pH was adjusted to 8-9, the solvents ethanol and water were removed, the residual solid was dissolved in ethyl acetate, the undissolved solid was filtered out, and the ethyl acetate was removed to obtain compound B3 or C3.

7. The preparation method according to claim 6, characterized in that, In an aqueous ethanol solution, the volume ratio of ethanol to water is 1.5~2.5:

1. Alternatively, the mass fraction concentration of sodium hydroxide in ethanol-water is 5% to 7%; Alternatively, the reaction time at room temperature is 6-8 hours.

8. The preparation method according to claim 7, characterized in that, In an aqueous ethanol solution, the volume ratio of ethanol to water is 2:

1.

9. The preparation method according to claim 1, characterized in that, Methods for the condensation of compounds B3 or C3 with barbiturates in ethanol solution to form BNCA-1 or BNCA-2 include: Compound B3 or C3 was dispersed in ethanol, barbituric acid was added, and the mixture was heated and stirred to react. After the reaction was completed, the mixture was cooled for a short time and then filtered under reduced pressure to produce BNCA-1 or BNCA-2.

10. The preparation method according to claim 9, characterized in that, The temperature for heating and stirring the reaction is 75~90 ℃, and the stirring time is 3~6 h.

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