JP2002316960A - Abietic acid derivative and clathrate compound using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new host compound having a structure different from those of conventionally well-known ones. SOLUTION: This new clathrate compound (salt) is shown by the formula (1) (wherein, R<1> and R<2> are each a substituent; m and n are each an integer of 0-5; and when m and n are each an integer of >=2, a plurality of R<1> and R<2> may be the same as or different from each other).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an optically active abietic acid derivative, an inclusion compound using the abietic acid derivative, and use thereof. The abietic acid derivative of the present invention is useful for separation of optically active isomers, selective separation and purification of useful compounds, chemical stabilization, non-volatilization, powdering, and the like. It has high utility value in the fields of chemicals, insecticides, fragrances and the like.

[0002]

2. Description of the Related Art An optical resolution method using an inclusion compound is a method utilizing an optically active host compound forming an inclusion compound only with one optically active substance in a racemic guest. After forming the clathrate compound, the compound is separated by a method such as a distillation method, a recrystallization method after re-dissolution, or the like, thereby recovering the optically active guest compound. Optical resolution by the inclusion complexation method using such an optically active host compound,
This is a simple and inexpensive method for producing an optically active substance. As the optically active host compound, several types of compounds including an optically active propargyl alcohol-based molecule and a tartaric acid derivative have been known.

[0003] However, since the host compound recognizes a slight difference in the structure of the guest compound to form an inclusion compound, it is difficult to predict an optimal combination of the host compound and the guest compound. Therefore, it is also preferable from the viewpoint of efficiency to prepare a large number of host compounds in advance and establish a method for selectively using the host compounds according to the type of the guest compound to be isolated.

[0004]

An object of the present invention is to provide a novel host compound having a structure different from that of a conventionally known host compound. That is, the present invention provides a novel host compound which is useful for isolating a target compound from a mixture containing impurities with high purity, and is useful for, for example, separating stereoisomers and optical isomers. Issues to be solved.

[0005]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have succeeded in synthesizing a novel optically active abietic acid derivative, and this compound has been used for various guest compounds and clathrates. The inventors have found that the present invention is formed, and have completed the present invention.

That is, according to the present invention, there is provided a compound represented by the following formula (1) or a salt thereof.

Embedded image (Wherein, R ¹ and R ² each independently represent a substituent, m and n each independently represent an integer of 0 to 5, and when m or n represents an integer of 2 or more, a plurality of R ¹ And R ² may be the same or different.)

Preferably, R ¹ and R ² in the formula (1)
Are the same. Preferably, m and n in the formula (1)
Is each independently 0 or 1. Preferably, in Formula (1), m and n are 0 or 1, and when m and n are 1, R ¹ and R ² are in the para position. Preferably, in the formula (1), R ¹ and R ² each independently represent a lower alkyl group, an aryl group, a lower alkoxy group, an aryloxy group, a hydroxyl group, a halogen atom, an amino group, an alkylamino group, a mercapto group, or an alkylthio group. , Amidino group, guanidino group, ureido group, carboxyl group, nitro group and alkoxycarbonyl group.

According to the present invention, preferably, the following formula (1)
a) a compound having a structure of any one of (a) to (1d), a salt thereof, or a mixture thereof;

Embedded image (Wherein, R ¹ and R ² each independently represent a substituent, m and n each independently represent an integer of 0 to 5, and when m or n represents an integer of 2 or more, a plurality of R ¹ And R ² may be the same or different.)

According to another aspect of the present invention, the above formula (1)
An inclusion compound comprising a compound of the formula (I) or a salt thereof as a host compound is provided.

According to a further aspect of the present invention, there is provided a method for separating a guest compound from a mixture, comprising forming an inclusion compound using the compound of the above formula (1) or a salt thereof. You. Preferably, preferably, (1) the compound of the formula (1) or a salt thereof is brought into contact with a mixture containing a guest compound to form an inclusion compound containing the compound of the formula (1) or a salt thereof as a host compound (2) a step of collecting the formed inclusion compound; and (3) a step of separating the guest compound from the collected clathrate compound.

According to still another aspect of the present invention, there is provided an optical resolution method comprising forming a clathrate compound using the compound of the above formula (1) or a salt thereof. Preferably, (1) a step of contacting the compound of the formula (1) or a salt thereof with a mixture of optical isomers to form an inclusion compound containing the compound of the formula (1) or a salt thereof as a host compound; An optical resolution method is provided, comprising: (2) a step of recovering the formed inclusion compound; and (3) a step of separating an optical isomer from the recovered inclusion compound.

According to still another aspect of the present invention, there is provided the use of the compound of the above formula (1) or a salt thereof as a host compound.

[0013]

Embodiments of the present invention will be described below in detail. (1) Abietic acid derivative of the present invention The abietic acid derivative of the present invention has a structure represented by the following formula (1).

[0014]

Embedded image

(Wherein R ¹ and R ² each independently represent a substituent, m and n each independently represent an integer of 0 to 5,
Alternatively, when n represents an integer of 2 or more, a plurality of R ¹ and R ² may be the same or different. In the formula (1), R ¹ and R ² may be the same or different from each other, but preferably, R ¹ and R ² are the same.
The substituents represented by R ¹ and R ² are monovalent substituents, and the type thereof is not particularly limited as long as the function of the abietic acid derivative represented by the formula (1) as a host compound is not significantly impaired. Those skilled in the art of organic synthesis can appropriately select any substituent. Specific examples of the substituent include a lower alkyl group (for example, a methyl group, an ethyl group,
-Propyl group, i-propyl group, n-butyl group, i-butyl group, t-butyl group, pentyl group, alkyl group having 1 to 6 carbon atoms such as hexyl group), aryl group (for example,
An aryl group having 6 to 12 carbon atoms such as a phenyl group), a lower alkoxy group (for example, a methoxy group, an ethoxy group,
-A propoxy group, an i-propoxy group, an n-butoxy group,
an alkoxy group having 1 to 6 carbon atoms such as an s-butoxy group, a t-butoxy group, a pentoxy group, and a hexyloxy group; an aryloxy group (for example, a carbon atom having 6 carbon atoms such as a phenoxy group);
To 12 aryloxy groups), hydroxyl group, halogen atom (fluorine atom, chlorine atom, bromine atom or iodine atom), amino group, alkylamino group (for example, methylamino group, ethylamino group, dimethylamino group, diethylamino group An amino group substituted with one or two alkyl groups having 1 to 6 carbon atoms such as an ethylmethylamino group),
Mercapto group, alkylthio group (for example, alkylthio group having 1 to 6 carbon atoms such as methylthio group and ethylthio group), amidino group, guanidino group, ureido group, carboxyl group, nitro group, alkoxycarbonyl group (for example, methoxycarbonyl group and the like) And the like, but are not limited thereto.

Preferred examples of R ¹ and R ² include a methyl group, an ethyl group, an n-propyl group, an i-propyl group,
lower alkyl groups such as n-butyl group, i-butyl group, t-butyl group and the like, methoxy group, ethoxy group, n-propoxy group, i-propoxy group, n-butoxy group, s-butoxy group, t-butoxy group Examples thereof include lower alkoxy groups such as a group, and halogen atoms such as a fluorine atom, a chlorine atom, and a bromine atom.

[0017] formula (1), m and n are each independently an integer of 0 to 5, when m or n represents an integer of 2 or more, R ¹ and R ² existing in plural numbers are identical or different from each other You may. In the formula (1), m and n are preferably each independently 0 or 1, and when m and n are 1, R ¹ and R ² are present in any of the ortho, meta and para positions. Preferably, R ¹ and R ² are in the para position.

The structure of a particularly preferred compound of the present invention is shown below.

[0019]

Embedded image

In the formula, R ¹ and R ² are as defined above, and the preferred range is also as defined above.

The compound of the formula (1) can be present in the form of a salt depending on the types of the substituents represented by R ¹ and R ^2. The compounds of 1) are also within the scope of the present invention. The kind of the salt is not particularly limited, and examples thereof include an acid addition salt, a metal salt, an ammonium salt, and an organic amine addition salt. Examples of the acid addition salts include inorganic acid salts such as hydrochloride, sulfate, nitrate, and phosphate, and organic acid salts such as acetate, maleate, fumarate, and citrate. Examples of the metal salt include an alkali metal salt such as a sodium salt and a potassium salt; an alkaline earth metal salt such as a magnesium salt and a calcium salt; an aluminum salt or a zinc salt; and the ammonium salt includes ammonium or tetramethylammonium. And organic amine addition salts such as morpholine and piperidine. When it is desired to obtain a salt of the compound of the formula (1), when the compound of the formula (1) is obtained in the form of a salt, it may be purified as it is,
When it is obtained in a free form, it may be dissolved or suspended in an appropriate solvent, and a salt may be formed by adding an acid or a base to isolate and purify.

The compounds of formula (1) have optical isomers, and all possible isomers, as well as mixtures containing two or more such isomers in any ratio, are also within the scope of the present invention. Things. As the optical isomer of the compound of the formula (1),
The compound having any one of the formulas (1a) to (1d) described above in the present specification is exemplified.

The compound of the formula (1) and a salt thereof may exist in the form of an adduct (hydrate or solvate) with water or various solvents, and these adducts are also used in the present invention. Are within the range. Also, any crystal forms of the compound of formula (1) and its salts are within the scope of the present invention.

Next, a method for obtaining and producing the compound of the formula (1) of the present invention will be described. The abietic acid derivative represented by the formula (1) of the present invention can be synthesized, for example, by reacting a lower alkyl ester of abietic acid with phenyl (or substituted phenyl) magnesium halide. The lower alkyl ester of abietic acid can be prepared by reacting abietic acid with a lower alcohol (eg, ethanol) in an inert solvent such as toluene in the presence of sulfuric acid (esterification reaction). Phenyl (or substituted phenyl)
Magnesium halide (Grignard reagent) is THF
For example, by reacting magnesium and phenyl halide (or phenyl halide having a desired substituent) in an inert solvent such as

A lower alkyl ester of abietic acid,
The reaction with phenyl (or substituted phenyl) magnesium halide is a usual Grignard reaction, and those skilled in the art can appropriately select suitable reaction conditions (reaction temperature, reaction time, etc.). The reaction temperature is generally 0 to 200 ° C,
Preferably, it is 10 to 100 ° C., and the reaction time is generally 0.01 to 100 hours, preferably 1 to 50 hours.
Time. As an example, the synthesis can be carried out by refluxing a mixture of a lower alkyl ester of abietic acid and a phenyl (or substituted phenyl) magnesium halide in an inert solvent for several hours or more. The ratio of the amount of the lower alkyl ester of abietic acid to the amount of the phenyl (or substituted phenyl) magnesium halide can be appropriately set, and preferably, the lower alkyl ester of abietic acid: phenyl (or substituted phenyl) magnesium halide = 1 : 2 to 1: 2
0 (equivalent ratio).

After the reaction, the compound of the present invention can be isolated by post-treating the reaction mixture by a conventional method.
Specifically, for example, the reaction is terminated by adding water or dilute hydrochloric acid to the reaction mixture. Thereafter, the reaction mixture is extracted by adding a water-insoluble organic solvent such as toluene.
The compound of the present invention can be isolated by drying the obtained extract with anhydrous sodium sulfate or the like and concentrating it. Further, if necessary, the compound of the present invention can be isolated and purified by recrystallizing the obtained solid with isopropanol or the like.

(2) Use of the compound of the present invention or a salt thereof as a host compound By using the compound of the formula (1) of the present invention as a host compound, a package comprising the host compound of the present invention and a wide range of guest compounds can be obtained. An indirect compound can be formed. Such inclusion compounds are also within the scope of the present invention. The kind of the guest compound that can be used in the present invention is not particularly limited as long as it forms an inclusion compound with the host compound of the present invention. Specific examples of the guest compound include ketones such as acetone, cyclopentanone, cyclopentenone, and 2-methylcyclopentanone; monocyclic nitrogen-containing heterocyclic compounds such as pyridine and picoline; and sulfoxides such as dimethyl sulfoxide. And amides such as dimethylformamide.

The method for forming the clathrate compound is not particularly limited. For example, the clathrate compound can be formed by the following method. (A) The host compound and the guest compound may be heated, if necessary, under heating with an appropriate solvent (for example, a solvent such as hexane, diethyl ether, benzene, toluene, methanol, or ethanol; or the guest compound itself may be used as the solvent. When possible, the host compound and the guest compound are mixed and the host compound may be dissolved), and then cooled or a solvent having low solubility is added to obtain a clathrate compound crystal (also known as a recrystallization method). (B) a method of suspending a host compound and a guest compound in a solvent in which the compound is insoluble or only partially soluble (for example, water or hexane) (also referred to as a suspension method); and (c) A) a method of directly mixing a host compound and a guest compound in the absence of a solvent (also referred to as a mixing method):

The reaction temperature and reaction time for forming the clathrate compound vary greatly depending on the combination of the host compound and the guest compound. In some cases, an interaction occurs only by mixing the host compound and the guest compound at room temperature to form an inclusion compound, and in other cases, heating is performed as necessary. When heating, the heating is performed within a range lower than the lowest temperature among the boiling points or the thermal decomposition temperatures of the host compound, the guest compound and the solvent. After the clathrate is formed, the clathrate may be precipitated at the same time, or the temperature may be lowered as necessary. The ratio of the amounts of the host compound and the guest compound used is not particularly limited, but depends on the theoretical equivalent ratio of the host compound and the guest compound forming the clathrate, the clathrate formation conditions, the clathrate precipitation conditions, and the like. Choose the optimal ratio. The guest compound itself may be used as a solvent, and in that case, the guest compound may be used in a stoichiometric equivalent or more to dissolve the host compound. For example, when the host compound is R of the formula (1a)
^{When 1} and R ² are the same as each other, are a hydrogen atom, a methoxy group, and a chlorine atom, and the guest compound is methylcyclopentanone or the like, preferably, the host compound: guest compound = 1: 5 to 5: 1 Yes, more preferably host compound: guest compound = 1: 2 to 2: 1 (equivalent ratio). It is confirmed that the solid obtained by the above method shows physical properties (melting point, crystal form, etc.) different from the starting material, and if it contains a host compound and a guest compound, it forms an inclusion compound can do. Alternatively, the formation of the clathrate can be confirmed by IR spectra.

The method of recovering the clathrate compound formed by the above method depends on the method of forming the clathrate compound (specific examples include the above-mentioned recrystallization method, suspension method and mixing method). And can be selected appropriately. For example, when the inclusion compound is formed by a recrystallization method or a suspension method, the inclusion compound can be separated by filtration into a powder by filtration. In this case, the non-inclusion compound other than the target compound is present in the filtrate. In the mixed method, the clathrated guest compound is distilled off at a higher temperature than the non-clathrated guest compound due to the interaction with the host compound (hydrogen bond, van der Waals force, etc.). The inclusion compound can be isolated by heating a mixture of the compound and the non-inclusion guest compound (distillation method).

The present invention further relates to a method for separating a guest compound from a mixture, which comprises forming an inclusion compound using the compound of the present invention or a salt thereof. A specific method for separating the guest compound from the mixture includes, for example, a method including the following steps. (1) contacting the compound of the present invention or a salt thereof with a mixture containing a guest compound to form an clathrate; (2) collecting the formed clathrate; and (3) collecting the clathrate. Separating the guest compound from the clathrate compound;

Further, the present invention also relates to an optical resolution method characterized by forming an inclusion compound using the compound of the present invention or a salt thereof. As a specific method of the optical division method, for example, a method including the following steps can be mentioned. (1) a step of contacting the compound of the present invention or a salt thereof with a mixture of optical isomers to form an inclusion compound; (2) a step of collecting the formed inclusion compound; and (3) a collected packet. Separating the optical isomer from the contact compound;

Steps (1) and (2) in the method for separating the guest compound from the mixture and the method for optical resolution can be performed by the methods described above in this specification, respectively. Step (3) is a step of separating a guest compound (for example, an optical isomer or the like) from the collected clathrate compound. This step (3) is a step of separating the clathrate compound into a host compound and a guest compound (for example, an optical isomer or the like) to obtain a target compound. This step is
Any method may be used, for example, a method of heating to a predetermined temperature or higher at normal pressure or reduced pressure (distillation method), a method of extracting with a solvent, a chromatography method, a guest exchange method, and the like. The guest exchange method referred to here is to contact a clathrate compound consisting of a host compound and a guest compound with a different guest compound to form a new clathrate compound of the host compound and a different guest compound, Is a method of separating the guest compound of the above. As the different guest compound, a compound which is relatively easy to form an inclusion compound with the host compound than the intended guest compound is selected.

The distillation method is particularly advantageous for industrial applications because the above steps (1) to (3) can be performed continuously in one vessel. Furthermore, the clathrate compound of the present invention can also perform a chemical reaction (for example, photoreaction) in the clathrate state to induce the guest molecule to another molecule.

By using the above method characterized in that an inclusion compound is formed using the compound of the present invention, it is possible to separate the isomers or to obtain the target compound with high purity from a mixture containing impurities. it can. In addition, by using an optically active abietic acid derivative among the compounds represented by the formula (1) of the present invention, the objective optical isomer can be isolated and purified from a mixture of optical isomers to increase the optical purity. Can be.

Further, the compounds of the present invention can be applied in the fields of medicine, agricultural chemicals and the like. For example, in the field of agrochemicals, stabilization can be achieved by inclusion complexation of agrochemicals and antibacterials that are significantly chemically degraded. Pesticides and antimicrobial agents, which are guest compounds, are gradually dissociated from the clathrate compound, and the effectiveness can be maintained for a long time. In addition, inclusion complexing can avoid direct contact of the skin with pesticides and antibacterial agents, and is therefore useful for reducing skin irritation. The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the examples and the like.

[0037]

EXAMPLES Example 1 Synthesis of Host Compound 1 14.6 g of magnesium in anhydrous THF (500 ml)
(0.60 mol) and 94.2 g of bromobenzene (0.
60 mol), and 25.0 g (0.075 mol) of abietic acid ethyl ester was slowly added to a phenylmagnesium boromide / THF solution prepared by the reaction with the mixture, and the mixture was refluxed for 15 hours. After treatment with dilute hydrochloric acid, the mixture was extracted with toluene. After drying over anhydrous sodium sulfate, the mixture was concentrated. The obtained solid was recrystallized from isopropanol to obtain 26.0 g of the following compound 1 (yield: 79).
%). FIG. 1 shows an infrared spectrum chart of Compound 1 thus obtained. The absorption wavelength of the hydroxyl group was 3573 cm ^-1 .

Melting point: 167 to 169 ° C., [α] D: + 66.0 ° (c0.1, toluene) (provided that [α] D = 100α / lc; where α is optical rotation,
l indicates the optical path length (10 cm), and c indicates the concentration of the active substance. The same applies hereinafter in the present specification)

[0039]

Embedded image

Example 2 Synthesis of Host Compound 2 The following compound 2 was synthesized in the same manner as in Example 1 except that 4-bromoanisole was used instead of bromobenzene in Example 1. The yield was 53%. Melting point is 1
83 to 186 ° C, [α] D is + 97.3 ° (c0.1,
Toluene).

[0041]

Embedded image

Example 3 Synthesis of Host Compound 3 The following compound 3 was synthesized in the same manner as in Example 1 except that p-chlorobromobenzene was used instead of bromobenzene. The yield was 48%. Melting point: 161-163 ° C., [α] D: + 91.5 ° (c
0.1, toluene).

[0043]

Embedded image

Example 4: Separation of stereoisomers 1: 1 mixture of 2-methylcyclopentanone and 3-methylcyclopentanone (0.45 g, 4.54 mmol)
The compound 1 synthesized in Example 1 (1.5 g, 3.40 m
mol) was heated and dissolved, and allowed to stand at room temperature for 12 hours, to obtain 1.5 g of a 1: 1 inclusion complex crystal of compound 1 and racemic 2-methylcyclopentanone (C ₃₈ H ₅₀ O).
₂ Calculated; C, 84.71; H, 9.35 : Found; C, 84.85; H,
9.11). The crystals were heated under reduced pressure to separate Compound 1 and 2-methylcyclopentanone, which gave 100% pure 2
0.075 g of -methylcyclopentanone was obtained. Purity was determined by gas chromatography using GL Science's column TC-5.

Example 5: Separation of optical isomer Compound 1 synthesized in Example 1 (2 g, 4.54 mmol)
l) and 2-methylcyclopentanone (3 g, 30 mmol)
l) was heated and dissolved, and allowed to stand at room temperature for 12 hours to obtain 1.52 g of a 1: 1 inclusion complex crystal of compound 1 and 2-methylcyclopentanone (calculated value of C ₃₈ H ₅₀ O ₂ ; C , 84.7
1; H, 9.35: found; C, 84.85; H, 9.11). FIG. 2 shows an infrared spectrum chart of the obtained clathrate complex. The absorption wavelengths of the hydroxyl group and the carbonyl group are each 3500
And 1735 cm ^-1 . The crystals were heated under reduced pressure to separate Compound 1 from 2-methylcyclopentanone. As a result, 2-methylcyclopentanone having a specific rotation [α] D of -10.1 ° (c 0.85, methanol) was obtained. 0.1
8 g were obtained. This specific rotation corresponded to an optical purity of 9% ee. From the above results, it was demonstrated that by forming an inclusion compound using the host compound 1 of the present invention, optically active 2-methylcyclopentanone can be isolated.

[0046]

According to the present invention, a novel host compound is provided. The compound of the present invention is useful for isolating a target compound with high purity from a mixture containing impurities, for example, useful for separating stereoisomers and optical isomers.

[Brief description of the drawings]

FIG. 1 shows an infrared spectrum chart of Compound 1 obtained in Example 1.

FIG. 2 shows Compounds 1 and 2 obtained in Example 5.
1 shows an infrared spectrum chart of a 1: 1 inclusion complex of methylcyclopentanone.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) // C07B 57/00 340 C07B 57/00 340 63/02 63/02 B C07M 7:00 C07M 7:00

Claims (12)

[Claims] 1. A compound represented by the following formula (1) or a salt thereof. Embedded image (Wherein, R ¹ and R ² each independently represent a substituent, m and n each independently represent an integer of 0 to 5, and when m or n represents an integer of 2 or more, a plurality of R ¹ And R ² may be the same or different.) 2. The compound according to claim 1, wherein R ¹ and R ² in formula (1) are the same, or a salt thereof. 3. The compound according to claim 1, wherein m and n in formula (1) are each independently 0 or 1, or a salt thereof. 4. The method according to claim 1, wherein in formula (1), when m and n are 0 or 1, and m and n are 1, R ¹ and R ² are in the para position. Or a salt thereof. 5. In the formula (1), R ¹ and R ² are each independently a lower alkyl group, an aryl group, a lower alkoxy group,
Aryloxy group, hydroxyl group, halogen atom, amino group,
The substituent according to any one of claims 1 to 4, which is a substituent selected from the group consisting of an alkylamino group, a mercapto group, an alkylthio group, an amidino group, a guanidino group, a ureido group, a carboxyl group, a nitro group, and an alkoxycarbonyl group. Or a salt thereof. 6. The compound according to claim 1, having a structure represented by any of the following formulas (1a) to (1d), a salt thereof, or a mixture thereof. Embedded image (Wherein, R ¹ and R ² each independently represent a substituent, m and n each independently represent an integer of 0 to 5, and when m or n represents an integer of 2 or more, a plurality of R ¹ And R ² may be the same or different.) 7. An inclusion compound comprising the compound according to claim 1 or a salt thereof as a host compound. 8. A method for separating a guest compound from a mixture, comprising forming an inclusion compound using the compound according to claim 1 or a salt thereof. 9. (1) The compound according to any one of claims 1 to 6, or a salt thereof, is brought into contact with a mixture containing a guest compound, and the compound according to any one of claims 1 to 6 or a mixture thereof. 9. A step of forming an inclusion compound containing a salt as a host compound; (2) a step of collecting the formed inclusion compound; and (3) a step of separating a guest compound from the collected inclusion compound. 14. A method for separating a guest compound from a mixture according to the above. 10. An optical resolution method comprising forming a clathrate compound using the compound according to any one of claims 1 to 6 or a salt thereof. (1) The compound or a salt thereof according to any one of claims 1 to 6 by contacting the compound or a salt thereof according to any one of claims 1 to 6 with a mixture of optical isomers. 11. A step of forming an inclusion compound containing as a host compound; (2) a step of recovering the formed inclusion compound; and (3) a step of separating an optical isomer from the collected inclusion compound. Optical splitting method according to 1. 12. Use of the compound according to claim 1 or a salt thereof as a host compound.