Synthesis and Application of Alkynyl Substitutes of Di(2-Ethylhexyl) Phthalate
By synthesizing alkynyl substitutes and applying them to trace analysis, the problem of studying the metabolic status and toxicological mechanism of DEHP is solved, and efficient tracking and analysis of DEHP and its metabolites is achieved.
Patent Information
- Application Number
- CN202310095167.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-01-19
- Publication Date
- 2025-05-23
- Estimated Expiration
- 2043-01-19
AI Technical Summary
It is difficult to effectively study and analyze the metabolic status and toxicological mechanism of di(2-ethylhexyl) phthalate in biological organisms.
By synthesizing and applying alkynyl substitutes, traceability analysis is performed using azide-alkynyl cycloaddition reaction (CuAAC), to achieve efficient tracking and research of di(2-ethylhexyl) phthalate and its metabolites.
A detailed analysis of the spatial distribution and metabolic status of DEHP and its metabolites in organisms was achieved, and an in-depth understanding of its toxicological mechanism and metabolic pathways were achieved.
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Figure CN116173243B_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the technical field of di(2-ethylhexyl)phthalate analysis, and in particular to the synthesis and application of alkynyl substitutes of di(2-ethylhexyl)phthalate. Background Art
[0002] Di(2-ethylhexyl) phthalate (DEHP) is the most widely used plasticizer in the world. Its addition amount in plastic products is only lower than that of polymers. A large number of experimental studies have shown that DEHP can easily enter the human and animal bodies through breathing and contact, thereby causing reproductive toxicity, developmental toxicity, immunotoxicity, embryotoxicity, liver toxicity, neurotoxicity and carcinogenicity, etc. It has been listed as a priority environmental pollutant by many countries. However, the metabolism and toxicological mechanism of DEHP in organisms are still not very clear, so it is very important to conduct in-depth research on the metabolic state of DEHP in vivo.
[0003] Tracing technology is an important means to study the metabolism of compounds in vivo, and the design of tracers is the key to influencing the in vivo tracing performance. The copper-catalyzed azide-alkynyl cycloaddition reaction (CuAAC) is a classic click chemistry reaction. This reaction connects molecules through modular reactions of azide groups and terminal alkynes. Since terminal alkyne groups are small in size and almost non-existent in organisms, they are ideal labels for in vivo metabolic tracers. Therefore, introducing terminal alkyne groups into the structure of target molecules is the key to synthesizing click chemistry-based tracers. Summary of the invention
[0004] In view of this, the present application provides the synthesis and application of alkynyl substitutes of di(2-ethylhexyl)phthalate, which can potentially realize the tracer analysis of di(2-ethylhexyl)phthalate and its metabolites.
[0005] In a first aspect, the present application provides an alkynyl substitute for use in tracer analysis of di(2-ethylhexyl) phthalate and its metabolites, wherein the alkynyl substitute has the following molecular structure:
[0006]
[0007] In a second aspect, the present application provides a tracing method for di(2-ethylhexyl) phthalate and its metabolites, comprising the following steps:
[0008] Performing alkynyl modification on di(2-ethylhexyl)phthalate and its metabolites to be traced to obtain an alkynyl substitute, wherein the alkynyl substitute has a molecular structure corresponding to the use as claimed in claim 1;
[0009] The alkynyl surrogate was used to replace the di(2-ethylhexyl)phthalate and its metabolites for tracer analysis.
[0010] Suitable but not limiting, the tracer analysis specifically comprises the following steps:
[0011] A. Using an azido-labeled probe to label tissues or organs with alkynyl substitutes to form a target marker;
[0012] B. imaging or specifically displaying the target marker;
[0013] C. By analyzing the imaging, the distribution and metabolic status of the alkynyl substitute in the tissue or organ are obtained, that is, the metabolic status of di(2-ethylhexyl) phthalate and its metabolites in the tissue or organ.
[0014] Suitably but not limitingly, the labeled probe is a fluorescent probe or a mass spectrometry probe.
[0015] Suitably, but not limitingly, the means for imaging the target marker is fluorescence imaging or liquid chromatography-mass spectrometry.
[0016] In a third aspect, the present application provides a method for synthesizing an alkynyl substitute, as follows:
[0017] Ⅰ. When the structure of the alkynyl substitute is as shown in the formula,
[0018]
[0019] The synthesis method comprises the following steps:
[0020] Step 1. Dissolve the reactant 3-hydroxyheptyne (30 mmol, 3.4 g) in dichloromethane (30 mL), add carbon tetrabromide (30 mmol, 10 g) and triphenylphosphine (45 mmol, 11 g), and react at room temperature for 1 hour. After the reaction is completed, dilute with ethyl acetate, filter, and rotary evaporate the filtrate to obtain a compound shown in the structural formula A.
[0021] Step 2. The obtained compound A (16mmol, 2.73g) was dissolved in tetrahydrofuran / water (30mL, 1 / 1), and formaldehyde solution (4mL), iodine (16.2mmol, 5g), lithium iodide (16.2mmol, 2.7g), indium powder (4.8mmol, 4.6g) were added in sequence, and the reaction was carried out for 3 hours at room temperature. After the reaction was completed, ethyl acetate was added to dilute and filter, and the filtrate was extracted with ethyl acetate three times. The combined organic layer was washed once with saturated salt water, dried and filtered with anhydrous sodium sulfate, and the filtrate was rotary evaporated to obtain a compound shown in structural formula B.
[0022] Step 3. The obtained compound B (7.9mmol, 1g) was dissolved in dichloromethane, triethylamine (24mmol, 3.3mL) and 4-dimethylaminopyridine (0.8mmol, 97mg) were added, and phthaloyl chloride (4mmol, 804mg) was added dropwise under ice bath conditions, and the mixture was reacted for 1 hour under ice bath conditions. After the reaction was completed, the mixture was poured into ice water and extracted three times with dichloromethane. The combined organic layer was washed once with saturated brine, dried over anhydrous sodium sulfate and filtered, and the filtrate was rotary evaporated to obtain a compound shown in the structural formula C.
[0023] Step 4. The obtained compound C (0.5mmol, 200mg) was dissolved in dimethyl sulfoxide / water (5mL, 20 / 1), and 0.5M KOH (1.8mL) was added under ice bath conditions, and the reaction was carried out for 3 hours under this condition. After the reaction was completed, it was diluted with water, and the pH was adjusted to 5 with 1M HCl, and then extracted with ethyl acetate three times. The combined organic layer was washed with saturated brine, then dried over anhydrous sodium sulfate, and the filtrate was rotary evaporated to obtain a compound shown in the structural formula D.
[0024]
[0025] Ⅱ 、 When the structure of the alkynyl substitute is as shown below,
[0026]
[0027] The corresponding synthesis method comprises the following steps:
[0028] Step 1. At room temperature, the reactant 1,4-pentanediol (96mmol, 10g) or 1,3-pentanediol (96mmol) or 5-hydroxypentanoic acid (96mmol) or 3,5-dihydroxypentanoic acid (96mmol) or 4-hydroxybutyric acid (96mmol) or 3-hydroxypropionic acid (96mmol) is dissolved in dimethyl sulfoxide (100mL), 2-iodoacylbenzoic acid (0.24mol, 60g) is added, and the reaction is carried out at room temperature for 12 hours under nitrogen protection. After the reaction is completed, saturated sodium sulfite aqueous solution (50mL) is added to quench, and then saturated sodium carbonate aqueous solution is added to adjust the pH to 9, and extracted three times with dichloromethane. The combined organic layer is washed once with saturated brine, dried over anhydrous sodium sulfate and filtered, and the filtrate is rotary evaporated to obtain the compound shown in the structural formula E.
[0029] Step 2. The obtained compound E (12mmol, 1.2g) was dissolved in anhydrous tetrahydrofuran (30mL), protected by nitrogen, cooled to -5°C in an ice-salt bath, and alkynylmagnesium bromide (0.5M, 12mL) was added dropwise, and reacted at -5°C for 0.5 hours. After the reaction was completed, the reaction solution was poured into an ice-saturated aqueous ammonium chloride solution and extracted three times with ethyl acetate. The combined organic layer was washed once with saturated brine, dried with anhydrous sodium sulfate and filtered, and the filtrate was rotary evaporated to obtain the compound shown in the structural formula F.
[0030] Step 3. The obtained compound F (1.7 mmol, 217 mg) was dissolved in dichloromethane, and carbon tetrabromide (2.0 mmol, 685 mg) and triphenylphosphine (3.4 mmol, 902 mg) were added, and the mixture was reacted at room temperature for 2 hours. After the reaction was completed, ethyl acetate was added for dilution, and the mixture was filtered and the filtrate was rotary evaporated to obtain the compound shown in the structural formula G.
[0031] Step 4. The obtained compound G (1.4mmol, 268mg) was dissolved in tetrahydrofuran / water (3mL, 1 / 1), and formaldehyde aqueous solution (37%, 0.6mL), iodine (1.5mmol, 396mg), lithium iodide (1.5mmol, 209mg), indium powder (4.2mmol, 488mg) were added in sequence, and the reaction was carried out at room temperature for 6 hours. After the reaction was completed, the mixture was filtered, and the filtrate was extracted three times with ethyl acetate. The combined organic layer was washed once with saturated brine, dried with anhydrous sodium sulfate and filtered, and the filtrate was rotary evaporated to obtain the compound shown in the structural formula H.
[0032] Step 5. The obtained compound H (0.37mmol, 52mg) was dissolved in dichloromethane (1mL), and triethylamine (0.74mmol, 75mg), 4-dimethylaminopyridine (0.04mmol, 9mg), and phthalic anhydride (0.4mmol, 61mg) were added in sequence, and the reaction was carried out at room temperature for 3 hours. After the reaction was completed, water was added to quench the reaction, and dichloromethane was used for extraction three times. The combined organic layer was washed twice with 1M HCl, washed once with saturated brine, and then dried with anhydrous sodium sulfate and filtered. Finally, the filtrate was rotary evaporated to obtain the compound shown in the structural formula I,
[0033] BRIEF DESCRIPTION OF THE DRAWINGS
[0034] The technical solution and other beneficial effects of the present application will be made apparent by describing in detail the specific implementation methods of the present application in conjunction with the accompanying drawings.
[0035] Figure 1a -b is the NMR diagram of Alkyne-DEHP provided in Example 1 of the present application.
[0036] Figure 2a -b provides the NMR chart of Alkyne-MEHP in Example 2 of the present application.
[0037] Figure 3a -b is the NMR chart of Alkyne-5-Oxo-MEHP provided in Example 3 of the present application. DETAILED DESCRIPTION
[0038] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.
[0039] In the description of the present application, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present application, "plurality" means two or more, unless otherwise clearly and specifically defined.
[0040] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or mutual communication; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.
[0041] The disclosure below provides many different embodiments or examples to realize the different structures of the present application. In order to simplify the disclosure of the present application, the parts and settings of specific examples are described below. Of course, they are only examples, and the purpose is not to limit the present application. In addition, the present application can repeat reference numbers and / or reference letters in different examples, and this repetition is for the purpose of simplification and clarity, which itself does not indicate the relationship between the various embodiments and / or settings discussed. In addition, the various specific processes and material examples provided by the present application, but those of ordinary skill in the art can appreciate the application of other processes and / or the use of other materials.
[0042]
[0043] Embodiment 1
[0044] Synthesis of Di(2-ethynylhexyl) Phthalate (Alkyne-DEHP)
[0045]
[0046] The reactant 3-hydroxyheptyne 1a (30mmol, 3.4g) was dissolved in dichloromethane (30mL), carbon tetrabromide (30mmol, 10g) and triphenylphosphine (45mmol, 11g) were added, and the reaction was carried out at room temperature for 1 hour. After the reaction was completed, it was diluted with ethyl acetate, filtered, and the filtrate was spin-dried using a rotary evaporator to obtain a crude product, and compound 2a (16mmol, 2.73g) was obtained by purification by silica gel column chromatography (eluent was petroleum ether). The obtained compound 2a was dissolved in tetrahydrofuran / water (30mL, 1 / 1), and formaldehyde solution (37%, 4mL), iodine (16.2mmol, 5g), lithium iodide (16.2mmol, 2.7g), indium powder (4.8mmol, 4.6g) were added thereto in sequence, and the reaction was carried out at room temperature for 3 hours. After the reaction is completed, the mixture is filtered, and the filtrate is extracted three times with ethyl acetate. The combined organic phase is washed once with saturated saline, dried with anhydrous sodium sulfate and filtered. Finally, the filtrate is rotary evaporated to obtain a crude product, which is purified by silica gel column chromatography (petroleum ether / ethyl acetate=5 / 1) to obtain compound 3a (7.9mmol, 1g). The obtained compound 3a is dissolved in dichloromethane (10mL), and triethylamine (24mmol, 3.3mL) and 4-dimethylaminopyridine (0.8mmol, 97mg) are added in sequence, and then phthaloyl chloride 4a (4mmol, 804mg) is added dropwise under ice bath conditions, and the reaction is carried out under ice bath conditions for 1 hour. After the reaction, the reaction solution was poured into ice water, extracted three times with dichloromethane, the combined organic layer was washed once with saturated brine, dried over anhydrous sodium sulfate and filtered, the filtrate was rotary evaporated to obtain a crude product, and purified by silica gel column chromatography (petroleum ether / ethyl acetate=10 / 1) to obtain a yellow oily product Alkyne-DEHP (1.24 g), with a yield of 40.9%; 1 H NMR (400MHz, DMSO-d6) δ7.84–7.63(m,4H),4.23(d,J=6.2Hz,4H),2.99(d,J=2.4Hz,2H),2.80-2.76(m,2H),1.59–1.26(m,12H),0.88(t,J=7.2Hz,6H). 13C NMR (101MHz, DMSO-d6)δ167.0,132.3,131.8,129.3,84.5,73.8,67.4,31.0,30.8,29.0,22.3,14.3. (NMR spectrum as shown Figure 1a -b).
[0047] Embodiment 2 Synthesis of Mono-(2-ethynylhexyl) Phthalate (Alkyne-MEHP)
[0048]
[0049] Alkyne-DEHP (0.5 mmol, 200 mg) was dissolved in DMSO / H 2 O (5mL, 20 / 1), add KOH (0.5M, 1.8mL) under ice bath conditions, and react under ice bath conditions for 3h. After the reaction is completed, add water (10mL) to dilute, use 1M HCl to adjust the pH to 5, then extract with ethyl acetate three times, wash the combined organic layer once with saturated brine, add anhydrous sodium sulfate to dry and filter, and use a rotary evaporator to spin dry the filtrate to obtain a crude product, which is purified by thin layer silica gel chromatography (petroleum ether / ethyl acetate = 1 / 1) to obtain a yellow oily product Alkyne-MEHP (25mg), with a yield of 34.9%; 1 H NMR(400MHz,DMSO-d6)δ13.25(s,1H),7.82–7.73(m,1H),7.68–7.60(m,3H),4.28-4.10(m ,2H),2.98(d,J=2.4Hz,1H),2.82-2.76(m,1H),1.59–1.23(m,6H),0.88(t,J=7.2Hz,3H). 13 C NMR (101MHz, DMSO-d6)δ168.39,167.83,132.64,132.60,131.85,131.66,129.39,128.64,84.56,73.72,67.21,31.02,30.79,29.00,22.30,14.32. (NMR spectrum as shown Figure 2a -b).
[0050] Embodiment 3
[0051] Synthesis of Mono-(2-Ethylene-5-Carboxyhexyl) Phthalate (Alkyne-5-Oxo-MEHP)
[0052]
[0053] At room temperature, the reactant 1,4-pentanediol 5a (96mmol, 10g) was dissolved in dimethyl sulfoxide (100mL), 2-iodobenzoic acid (0.24mol, 60g) was added, and the reaction was carried out at room temperature for 12 hours under nitrogen protection. After the reaction was completed, saturated sodium sulfite aqueous solution (50mL) was added to quench, and then saturated sodium carbonate aqueous solution was added to adjust the pH to 9, and dichloromethane was used for extraction three times. The combined organic layer was washed once with saturated salt water, anhydrous sodium sulfate was added to dry and filtered, and the filtrate was dried using a rotary evaporator to obtain a crude product, which was purified by silica gel column chromatography (pentane / ether=5 / 1) to obtain compound 6a (3.5g). Compound 6a (12mmol, 1.2g) was dissolved in anhydrous THF (30mL), nitrogen protection, ice salt bath cooled to -5°C, alkynyl magnesium bromide 7a (0.5M in THF, 12mL) was added dropwise, and the reaction was carried out at -5°C for 0.5 hours. After the reaction is complete, the reaction solution is poured into an ice-saturated aqueous ammonium chloride solution, extracted with ethyl acetate three times, and the combined organic layer is washed once with saturated common salt water, anhydrous sodium sulfate drying is added and filtered, and the filtrate is spin-dried to obtain a crude product using a rotary evaporator, and silica gel column chromatography (petroleum ether / ethyl acetate=2 / 1) is utilized to purify to obtain compound 8a (1.7mmol, 217mg). Compound 8a (1.7mmol, 217mg) is dissolved in dichloromethane, carbon tetrabromide (2.0mmol, 685mg), triphenylphosphine (3.4mmol, 902mg) are added, and reacted at room temperature for 2 hours. After the reaction is complete, ethyl acetate is added to dilute, and filtered, and the filtrate is spin-dried to obtain a crude product using a rotary evaporator, and silica gel column chromatography (petroleum ether / ethyl acetate, 15 / 1) is utilized to purify to obtain compound 9a (1.4mmol, 268mg). Compound 9a was dissolved in tetrahydrofuran / water (3mL, 1 / 1), and formaldehyde solution (37%, 0.6mL), iodine (1.5mmol, 396mg), lithium iodide (1.5mmol, 209mg), and indium powder (4.2mmol, 488mg) were added in sequence, and the mixture was reacted at room temperature for 6 hours. After the reaction was completed, the mixture was filtered, and the filtrate was extracted three times with ethyl acetate. The combined organic layer was washed once with saturated brine, dried with anhydrous sodium sulfate, and filtered. The filtrate was dried by rotary evaporation to obtain a crude product, which was purified by silica gel column chromatography (petroleum ether / ethyl acetate = 5 / 1) to obtain compound 10a (0.37mmol, 52mg). Compound 10a was dissolved in dichloromethane (1mL), and triethylamine (0.74mmol, 75mg), 4-dimethylaminopyridine (0.04mmol, 9mg), and phthalic anhydride 11a (0.4mmol, 61mg) were added in sequence, and the mixture was reacted at room temperature for 3 hours.After the reaction, water was added to quench the reaction, and the mixture was extracted three times with dichloromethane. The combined organic layer was washed twice with 1M HCl and then once with saturated brine, dried over anhydrous sodium sulfate and filtered. The filtrate was dried by rotary evaporation to obtain a crude product, which was purified by thin layer silica gel chromatography (dichloromethane / methanol=10 / 1) to obtain a yellow oily product, Alkyne-5-Oxo-MEHP (43 mg), with a yield of 36.2%. 1 H NMR(400MHz,Chloroform-d)δ7.87–7.80(m,1H),7.73–7.68(m,1H),7.58–7.52(m,2H),4.45(dd,J=10.8,5.6Hz,1H),4.22(dd,J= 10.8,7.8Hz,1H),2.95–2.85(m,1H),2.75–2.66(m,2H),2.18(s,3H),2.16(d,J=2.8Hz,1H),2.08–1.97(m,1H),1.74–1.64(m,1H). 13 C NMR (101MHz, Chloroform-d)δ209.25,167.82,132.25,131.80,131.31,131.03,129.34,128.80,82.67,71.68,66.87,40.50,30.45,30.17,25.08. (NMR spectrum as shown Figure 3a -b).
[0054] Application Examples
[0055] When the molecular structure of the alkynyl substitute is Alkyne-DEHP as shown below,
[0056]
[0057] By gavaging rats with Alkyne-DEHP (dissolved in corn oil), various organs and tissues were collected, and the organs and tissues of the gavaged rats were marked using azido fluorescent probe reagents or azido mass spectrometry probe reagents. The spatial distribution of DEHP in various organs of rats was explored using fluorescence imaging technology, or the metabolites of DEHP in vivo were studied using liquid chromatography-mass spectrometry technology, thereby promoting the understanding of the metabolic mechanism and toxicological mechanism of DEHP in vivo.
[0058] The above is only a preferred specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed in the present application should be covered within the protection scope of the present application.
Claims
1. Use of an alkynyl substitute in the preparation of a tracer for tracer analysis of di(2-ethylhexyl)phthalate, It is characterized in that The alkynyl substitute has the following molecular formula, ； The tracer analysis comprises the following steps: Performing alkynyl modification on di(2-ethylhexyl)phthalate to be traced to obtain the alkynyl substitute; Substituting the alkynyl surrogate for the di(2-ethylhexyl)phthalate for tracer analysis; The specific steps include: A. Using an azido-labeled probe to label tissues or organs with alkynyl substitutes to form a target marker; B. imaging or specifically displaying the target marker; C. By analyzing the imaging, the distribution and metabolic status of the alkynyl substitute in the tissue or organ are obtained, that is, the metabolic status of di(2-ethylhexyl) phthalate in the tissue or organ; The labeling probe is a fluorescent probe or a mass spectrometry probe; The method for imaging or specifically displaying the target marker is fluorescence imaging or liquid chromatography-mass spectrometry analysis.
2. A method for synthesizing an alkynyl substitute, It is characterized in that The alkynyl surrogate has the structural formula shown below, ； The synthesis method comprises the following steps: Step 1. Dissolve the reactant 3-hydroxyheptyne in dichloromethane, add carbon tetrabromide and triphenylphosphine, and react at room temperature to obtain a compound as shown in the structural formula A; Step 2. dissolving the obtained compound A in tetrahydrofuran / water, and sequentially adding formaldehyde aqueous solution, elemental iodine, lithium iodide, and indium powder, and reacting at room temperature to obtain a compound with the structural formula shown in B; Step 3. Dissolve the obtained compound B in dichloromethane, add triethylamine and 4-dimethylaminopyridine, add phthaloyl chloride dropwise under ice bath conditions, and react under ice bath conditions to obtain a compound with structural formula C; Step 4. Dissolve the obtained compound C in a mixture of dimethyl sulfoxide and water, add KOH under ice bath conditions, and react under these conditions to obtain a compound with the structural formula D; 。 3. A method for synthesizing an alkynyl substitute, It is characterized in that The alkynyl surrogate has the structural formula shown below, ； The synthesis method comprises the following steps: Step 1. At room temperature, dissolve the reactant 1,4-pentanediol in 100 mL of dimethyl sulfoxide, add 2-iodoacylbenzoic acid, and react at room temperature under nitrogen protection to obtain a compound shown in the structural formula E; Step 2. Dissolve the obtained compound E in anhydrous tetrahydrofuran, protect with nitrogen, cool to -5°C in an ice-salt bath, add alkynylmagnesium bromide dropwise, and react at -5°C to obtain a compound with the structural formula F; Step 3. Dissolve the obtained compound F in dichloromethane, add carbon tetrabromide and triphenylphosphine, and react at room temperature to obtain a compound with the structural formula G; Step 4. The obtained compound G is dissolved in a mixture of tetrahydrofuran and water, and formaldehyde aqueous solution, iodine, lithium iodide, and indium powder are added in sequence, and reacted at room temperature to obtain a compound with the structural formula H; Step 5. The obtained compound H is dissolved in dichloromethane, and triethylamine, 4-dimethylaminopyridine and phthalic anhydride are added in sequence, and the reaction is carried out at room temperature to obtain a compound shown in the structural formula I. in: .