KR100525835B1 - Proline derivatives and preparing method thereof - Google Patents

Abstract

The present invention relates to a proline derivative and a method for preparing the same, and more particularly, L-proline-d-tocopherol having a structure represented by the following formula (1) which is a proline derivative, a method for preparing the same, and containing the same as an active ingredient The present invention relates to a cosmetic composition and a pharmaceutical composition, and the proline derivative according to the present invention is effective in treating skin diseases such as sensitive skin improvement, atopy and dryness.

<Formula 1>

R ₁ to R ₅ are as defined in the specification.

Description

Proline derivatives and preparation method thereof

The present invention relates to proline derivatives and methods of making the same. More specifically, the present invention relates to L-proline-d-tocopherol having a structure of Formula 1, a preparation method thereof, a cosmetic composition comprising the same, and a pharmaceutical composition.

(In the above, R ₁ , R ₂ , R ₃ are all hydrogen, or when any one of them is a hydroxyl group, the rest is hydrogen,

R ₄ and R ₅ are hydrogen or a methyl group.)

In general, a person's skin is exposed to UV rays, smoking, dieting, hot bathing, mental stress or aging inevitably leads to wrinkles, loss of elasticity, loosening of the skin, elasticity and moisture. The loss of reserves usually leads to a process called aging.

The reason why skin cannot avoid these symptoms is complicated. An important factor among the various causes of this aging is due to structural changes deep within the skin that cause dermal degradation, ie loss of activity, within the skin.

As the tissue breaks down more and more, the outer skin loses its original elasticity and gradually becomes loose. This series of processes is caused by changes in the amount of collagen.

Collagen is a protein through which the fibers form three-dimensional bonds through the dermis, and fibroblasts are cells that produce collagen. They are the central cells that connect and cross-link collagen fibers in their structure to make them stronger and more stable. It plays a role in regulating contractile action.

The binding is a type of binding that has a special interaction between the matrix to strengthen the binding between the cells to firmly stabilize the skin and automatically increase the resistance.

Over time, the part of the cell spliced to the matrix becomes weaker and the density of its structure decreases with the total number of interacting cells, and the three-dimensional structure of the tissue gradually degrades, causing collagen fibers to contract. As the capacity of fibroblasts decreases, the skin becomes less elastic.

In addition, the destruction of cellular tissues by free radicals is a major factor in aging and wrinkle formation. In general, oxygen radicals have been studied as one of the major harmful factors as a cause of damage to DNA or other cellular components.

The living body gives electrons (e) generated during metabolism to oxygen molecules (O ₂ ), which are electron acceptors, to generate water, and uses energy generated at this time. However, if oxygen is only water to produce such a complete reduction, there is nothing wrong with it, but oxygen molecules are converted into highly reactive oxygen products by the relocation of electrons in their electron angles, which are commonly referred to as reactive oxygen, active oxygen, harmful oxygen or oxygen ( Free radicals are called.

They are highly reactive, destroying lipids, proteins, polysaccharides, and nucleic acids, which are the major constituents of cells, leading to cell deterioration.

Oxygen radicals are constantly generated during normal energy metabolic processes as well as other mechanisms, and are simultaneously removed by various enzymes and non-enzymatic antioxidants, thus balancing their production and elimination in normal living organisms.

However, under certain special circumstances, if the production increases rapidly or the defense ability to remove oxygen radicals decreases, the living body is damaged by oxygen radicals. If this phenomenon occurs suddenly, the disease is caused. If you receive this stress constantly, even if not severe damage in the short-term, if you accumulate in the long-term throughout life, eventually cell function is deteriorated, which is to see it as aging.

Therefore, in order to prevent the aging phenomenon of the skin, studies have been actively conducted to give substances that have excellent collagen production ability or have strong antioxidant power. For example, among the various proteins, the characteristic constituent amino acid of collagen, which is the closest protein to aging, Much research is being done on proline.

Proline is an important biosynthetic starting material among the constituent amino acids of collagen and is a characteristic amino acid found only in collagen.

Collagen is usually a structure of glycine × X × Y and has a repeating sequence consisting of hydroxyproline at the X position and proline at the Y position.

Such proline is an essential element for the growth of animal cells and its derivatives, and many studies have been conducted for medicinal use such as hypertension inhibitors, triglyceride breakers, and angiotensin II antagonists.

As a result of partial studies, acylation of L-alanine derivatives and proline derivatives has been reported to be useful as an antihypertensive agent (Korean Patent Application Publication No. 10-1994-0014327). Condensation reaction of t-butyloxy carboxyyl tyrosine has been reported to study the effect of inhibiting the increase in body weight and triglycerides as a novel proline derivative (Korean Patent Application Publication No. 10-2000-0073891).

As an anti-aging patent, cosmetic compositions of derivatives of amino acid mixtures which are hydrolysis products of proline, hydroxyproline and / or collagen (French Patent No. 87121832) have been reported as anti-aging cosmetics, but the patent also discloses hydrolysis products of collagen. It is merely expecting a synergy effect as collagen constituent amino acids, such as glycine and hydroxy proline, as various amino acids.

In another patent, research has been conducted to improve the penetration of the skin by esterifying palmitic acid to hydroxyproline and imparting its lipophilic properties, and then inducing a natural decomposition there. Have been reported (European Patent No. 2 683 038).

However, the above patent has a problem that it is difficult to expect a high yield when esterification of palmitic acid to hydroxyproline.

Accordingly, the inventors of the present invention have been trying to esterify tocopherol as a vitamin while examining the introduction of a new substance to proline in consideration of excellent collagen biosynthesis and antioxidant power, stability and safety of proline itself.

In general, many studies have been conducted on tocopherols and derivatives thereof having strong antioxidant power as vitamins.

However, despite the fact that the strong antioxidant power and collagen biosynthesis of tocopherol itself is excellent, it is known that there is a lot of restrictions on the practical use due to the unstable phase stability to heat and light.

In order to solve this problem, microencapsulation and storage stability enhancement method (Korean Patent Application Publication No. 10-2002-0006926) has been provided by gelatinizing a mixed solution of agar and starch, but the phase stability period of tocopherol itself is provided. Can be increased for a period of time, but there is a limit to the practical application.

In order to improve the stability of tocopherol as another method, many derivatives have been developed. For example, there are compounds (US Pat. No. 4,564,686) which improve the stability by phosphoric esterification of tocopherol and ascorbic acid. There is no sufficient phase stability necessary for the application.

As another patent, polyoxypropylene polyoxyethylene is added to tocopherol to secure phase stability and add hydrophilicity to present a compound having skin improvement and emulsifying power (Korean Patent Application Publication No. 2002-0063650), but improving hydrophilicity. The addition of harmful ethylene oxide, on the other hand, causes toxicity to cause irritation to the skin, and in particular, its phase stability was still a problem.

In order to solve the above problems, the present inventors have found a novel proline derivative stabilized by ester-linking proline to tocopherol during research to maintain the physiological activity while maintaining the physiological activity while increasing the phase stability of tocopherol. It came.

That is, the present invention is not only stable, less toxic and relatively superior in physiological activity, and has no chemical phase stability and skin toxicity compared to conventional tocopherols, and actively improves skin aging with excellent collagen biosynthesis performance and excellent antioxidant power. Of course, it is an object of the present invention to provide a proline derivative of the formula (1) and a method for preparing the same, which have excellent effects on the treatment of skin diseases such as sensitive skin improvement, atopy, and dry skin.

In another aspect, the present invention provides a cosmetic composition and a pharmaceutical composition containing a proline derivative of the formula (1) as an active ingredient.

The above and other objects of the present invention can be achieved by the present invention described below.

The present invention to achieve the above object,

It provides a compound defined by the formula (1) and a pharmaceutically acceptable salt thereof.

<Formula 1>

(In the above, R ₁ , R ₂ , R ₃ are all hydrogen, or when any one of them is a hydroxyl group, the rest is hydrogen,

R ₄ and R ₅ are hydrogen or a methyl group.)

In another aspect, the present invention provides a cosmetic composition, characterized in that the compound of Formula 1 is included as an active ingredient. Compound of Formula 1 may be included in an amount of 0.01 to 20% by weight based on the total weight.

In another aspect, the present invention provides a pharmaceutical composition for treating skin diseases, characterized in that the compound of Formula 1 is included as an active ingredient.

In another aspect, the present invention is the first step of reacting the compound of formula 2 by adding benzylchloro formate (Formula 3) in a solvent to obtain a reactant; A second step of adding the tocopherol (Formula 5) to the reactant obtained in the first step again in the presence of a catalyst in a solvent to obtain a reactant; A third step of subjecting the reactant obtained in the second step to a bubble reaction under hydrogen gas at room temperature to separate benzyl chloroformate; And a fourth step of filtrating and concentrating the reactant obtained in the third step to obtain a compound of Chemical Formula 1. It provides a method for producing a proline derivative, characterized in that consisting of.

(Wherein R ₁ , R ₂ , R ₃ are the same as defined in Formula 1).

(Wherein R ₁ , R ₂ , R ₃ are the same as defined in Formula 1).

(In the above, R ₄ , R ₅ is hydrogen or methyl group.)

(In the above, R ₁ , R ₂ , R ₃ are all hydrogen, or when any one of them is a hydroxyl group, the rest is hydrogen,

R ₄ and R ₅ are hydrogen or a methyl group.)

Hereinafter, the present invention will be described in detail with an example in which all of R ₁ , R ₂ , and R ₃ in the following Chemical Formulas 1 to 6 are hydrogen.

In the first step for adding benzylchloroformate (Formula 3) to L-proline (Formula 2), the pH is adjusted with sodium hydroxide solution to protect the reaction of the amine group of L-proline and then under ethanol or methanol After stirring, the pH was adjusted with hydrochloric acid to make the compound of Chemical Formula 4.

N, N-dimethylaminopyridine (DMAP) and 1,3-dicyclohexylcarbodimide were mixed with the catalyst for promoting the condensation reaction on the dried product, and then tocopherol, a compound of Formula 5, was chlorohydrolyzed. After addition to carbon (CH ₂ Cl ₂ ) and reacted at room temperature, the obtained product is filtered and concentrated to obtain the compound of formula (6).

The obtained product was added with Pd / C as a catalyst, subjected to a bubbling reaction under hydrogen gas at room temperature, and then the inorganics were removed and concentrated to obtain the final compound of formula 1 (L-proline-d-tocopherol).

The compound of formula 1 prepared by the above-described method can be purified using conventional separation and purification methods such as recrystallization or column chromatography.

In addition, the base, the condensing agent, the catalyst, and the solvent that can be used in the present invention are not limited to those listed above, and any conventionally known in the art may be used within a range that does not adversely affect the reaction.

In addition, the present invention is not limited to L-proline as a starting material, and L-hydroxyproline may also be prepared by the same preparation method as above to prepare L-hydroxyproline-d-tocopherol.

In addition, the compound of Formula 1 of the present invention has the strong antioxidant power of tocopherol as well as the characteristics of L-proline, which is a representative amino acid of collagen, and is superior to the strong antioxidant power, collagen biosynthesis effect and fibroblast proliferation effect in improving skin aging. Characteristics.

In addition, L-proline-d-tocopherol of the present invention has a very low cytotoxicity is very excellent in skin safety, especially the phase stability in accordance with the characteristics of medicines, cosmetics, etc., whose titer should be preserved during long-term distribution. I am doing it.

According to the above properties, L-proline-d-tocopherol can be conveniently used as a cosmetic medical additive to prevent skin aging, sensitive skin improvement and atopic skin improvement, improvement of dry skin and the like for therapeutic medical additives.

Experiments to confirm the physiological activity of the compound of Formula 1 was carried out as follows.

First of all, cytotoxicity test was performed at the concentration of 10 ^-6 to 10 ^-3 % (W / V) with normal human fibroblasts (NV). Patch experiments were performed on the skin.

In addition, the efficacy effect of L-proline-d-tocopherol of the present invention measured the effect of cell regeneration to enhance collagen biosynthesis on human fibroblasts, and also the antioxidant power of free radicals, which can be a skin harmful substance, is anti-DPPH radical It could be confirmed through the oxidation test.

In addition, the evaluation of the long-term phase stability of the L-proline-d-tocopherol of the present invention confirmed the stability through quantitative analysis at time at 40 ℃.

As a result of the test, L-proline-d-tocopherol according to the present invention has been used in pharmaceutics such as cosmetics for anti-aging, improvement of skin diseases (atopic, dry, sensitive), which have been used commercially, tocopherol, tocopheryl acetate, di Cytotoxicity is lower in cytotoxicity than palmitoylhydroxyproline, retinol, etc., and collagen synthesis enhancement effect is better than that of existing dipalmitoylhydroxyproline, and is almost equivalent to retinol or tocopherol, especially for phase stability. Experiments showed superior phase stability effect compared to conventional tocopherols and retinol.

Hereinafter, the present invention will be described in more detail with reference to the following examples, but the scope of the present invention is not limited to the examples.

Example 1

Preparation of L-Proline-d-Tocopherol of Formula 1

A) 2.00g (17.36mmol) of L-proline was added to a 100 ml reaction vessel, and 2N sodium hydroxide (10 ml) was added to a cooling bath.

Separately, 2.96 ml (20.84 mmol) of benzyl chloroformate was dissolved in 20 ml of ethanol and added to the reaction. The reaction was further stirred for 1 hour on an ice bath. The reaction was transferred to a separatory filter, an aqueous layer (pH = 9) was separated, acidified with 2N hydrochloric acid (pH = 2), and extracted with ethanol (20 ml × 3 times).

The extract was washed with water (50ml) and brine (50ml), dried over sodium sulfate, filtered and concentrated.

The product obtained was 3.87 g (yield = 89%) as a colorless transparent oil liquid.

(See Qualitative NMR data in FIG. 1)

B) 1.00g (4.01mmol) of product N-CBZ-L-proline, 1.51g (7.29mmol) of dicyclohexylcarbodimide, and 0.45g (3.65mmol) of DMAP were mixed after drying. CH ₂ Cl ₂ was added and dissolved.

After stirring for 30 minutes at room temperature, 1.57 g (3.65 mmol) of DL-α-tocopherol was dissolved in CH ₂ Cl ₂ (10 ml) and added slowly. The reaction mixture was stirred at rt for 4 h.

The reaction was stopped by adding water (100ml), extracted with ethanol (20ml × 2 times), washed with brine (50ml), dried over sodium sulfate, filtered and concentrated. The residue obtained was purified by column chromatography (SiO ₂ , 40-63 μm) to separate the desired product.

The product obtained is 1.38 g (88% yield) and is a light yellow oil liquid.

(See Qualitative NMR data in FIG. 2)

C) N-CBZ-L-proline-O-tocopherol 1.13 g (1.71 mmol) obtained in the reaction vessel was added thereto, and 10 ml of ethanol and 10 ml of methanol were added thereto and stirred.

10% Pd / C (0.11 g) was added to the reaction, and the reaction was bubbled at room temperature under hydrogen gas for 1 hour. The reaction mixture was passed through a Celite column to remove inorganics and concentrated to give a residue.

The residue was separated by column chromatography (SiO ₂ , 40-63 μm, 50 g).

The product obtained 0.87 g (97% yield) and was a colorless transparent oil liquid.

(See qualitative NMR data in FIG. 3)

[Test Example 1]

Cell survival rate according to cytotoxicity (%)

In order to verify the primary safety as a raw material used in medicine and cosmetics, the MTT test method (normal: Mossman T. (1983), Rapid colorimetric assay) using a normal human fibroblast (newborn) for the compound of Formula 1 For cellural growth & amp: survival: application to proliferation & Cytotoxity assays Journal of Immunological Methods 65, 55 ~ 63) to investigate the cytotoxicity and the results are shown in Table 1 below.

The number shown in the table shows the number of living cells, ie, survival rate (%), by the concentration of the sample treated when the number of living cells of cells grown only in the medium without any treatment as 100.

division Tocopherol Tocopheryl Acetate L-proline-d-tocopherol Retinyl palmitate density(%) 0.0000 100.0 100.0 100.0 100.0 0.0012 99.3 100.3 97.4 98.2 0.0025 95.6 92.1 94.2 97.0 0.0050 96.1 94.3 97.2 80.0 0.0100 94.5 96.0 95.3 25.0

In this test, retinyl palmitate, which is effective in removing wrinkles, was compared as a comparative example to compare cytotoxicity. As can be seen from the above results, the L-proline-d-tocopherol of the present invention was similar to tocopherol and tocopheryl acetate. Results were obtained, but superior to retinyl palmitate. Therefore, the L-proline-d-tocopherol of the present invention was found to have a low intracellular toxicity.

[Test Example 2]

Skin irritation test (adhesive patch test: 24 hours, 20 people)

In order to confirm the skin irritation of the L-proline-d-tocopherol of the present invention, a patch test was performed using the skin of a normal person.

As a carrier medium, the experiment was performed with squalane, and the results are shown in Table 2 below.

sample Stimulation index Stimulus Squalane + L-proline-d-tocopherol (1.00%) 2.5 Mild stimulation Squalane + Tocopherol (1.00%) 2.0 Mild stimulation Squalane + Tocopheryl Acetate (1.00%) 1.3 Mild stimulation Squalane + Retinyl Palmitate (1.00%) 7.5 Severe irritation Squalane 2.0 Mild stimulation

As a result of the experiment of Table 2, L-proline-d-tocopherol of the present invention shows a stimulation index similar to squalane as a carrier medium, such as tocopherol and tocopheryl acetate, and a very mild stimulation index compared to retinyl palmitate as a comparative group.

[Test Example 3]

Collagen Synthesis Effect Experiment

In order to confirm the usefulness of the L-proline-d-tocopherol of the present invention as a skin aging inhibitor, the results of comparative experiments with the collagen synthesis effect with tocopherol, tocopheryl acetate, retinol, dipalmitoylhydroxyproline as a control material are as follows. It is shown in Table 3.

Collagen Synthesis Effect division L-proline-d-tocopherol Tocopherol Tocopheryl Acetate Retinol Retinyl palmitate Dipalmitoylhydroxyproline 0.01% 52 73 22 71 43 52

As can be seen from the above experimental results, the L-proline-d-tocopherol of the present invention had a lower collagen synthesis effect than tocopherol and retinol, which had unstable phase stability, but obtained better results than tocopheryl acetate and dipalmitoyl hydroxyproline.

In particular, the collagen synthesis effect was superior to retinyl palmitate having an unstable phase stability.

[Test Example 4]

Antioxidant power test

In order to confirm the efficacy of the free radicals of the L-proline-d-tocopherol of the present invention, by eliminating the relatively stable blue-blue DPPH (1,1-diphenyl-2-picryl-hydrazyl) radical produced while dissolved in methanol, The degree of change and the decrease in absorbance at the wavelength of 516 nm were measured. Tocopherol, tocopheryl acetate and retinol were compared as a comparison group. The results are as shown in Table 4 below.

Free radical scavenging activity L-proline-d-tocopherol Tocopherol Retinol Tocopheryl Acetate Concentration (µg / ml) 50 96.08 88.23 no effect no effect 500 100.00 or more 100.00 or more 76.8 no effect 5000 100.00 or more 100.00 or more 100.00 or more 55.12

(The numbers shown in the table above represent radical inhibition rates to eliminate free radicals.)

Antioxidant test results showed that the L-proline-d-tocopherol of the present invention had a similar result to that of tocopherol and superior to retinol, due to the cytotoxicity of retinol itself, and tocopheryl acetate has excellent phase stability. Instead, the antioxidant power was found to be very low.

[Test Example 5]

Stability experiment

In order to test the stability of L-proline-d-tocopherol of the present invention, HPLC quantitative analysis was performed by comparing phase stability for 2 months in a constant temperature and humidity chamber at room temperature and 40 ° C. Squalane was used as a continuous phase for the experiment, and the content of L-proline-d-tocopherol was performed at 1%, and tocopherol, tocopheryl acetate, retinyl palmitate, etc. were compared at 1%. The results are shown in Table 5 below.

Phase stability test results division L-proline-d-tocopherol Tocopherol Tocopheryl acetate Retinyl palmitate Room temperature 40 ℃ Room temperature 40 ℃ Room temperature 40 ℃ Room temperature 40 ℃ Initial value 100 100 100 100 100 100 100 100 1 week later 98.2 99.2 98.3 95.3 99.3 99.6 74.2 56.0 1 month later 99.7 99.3 90.5 87.4 98.4 99.4 54.3 42.3 2 months later 99.2 98.2 87.3 85.2 98.5 99.1 53.2 34.5

As shown in Table 5, the thermal phase stability of the L-proline-d-tocopherol of the present invention is superior to tocopherol and is almost similar to tocopheryl acetate. In particular, retinol derivatives are relatively more stable than retinyl palmitate.

[Examples 2 to 5]

Application experiment as cosmetic

The L-proline-d-tocopherol of the present invention can be applied to an emulsion-type cosmetic (cream, lotion, micro emulsion) formulation in the form of O / W or W / O emulsion as a cosmetic composition.

More specifically, as shown in Table 6 below, after completely dissolving the oil phase part and the water phase part, the head phase is sufficiently stirred, emulsified, cooled, and then the L-proline-d-tocopherol of the present invention is usually 0.01% at 40 ° C. To 20.00% and sufficiently stirred and dissolved. Specific manufacturing steps are as follows.

1) Stir and warm the oil phase to 75 ° C to dissolve completely.

2) The aqueous phase is stirred to 75 ° C, warmed and completely dissolved.

3) After complete dissolution, the oil phase is gradually added to the water phase and stirred and emulsified.

4) Add neutralizing agent, stir well, and slowly cool to 40 ℃.

5) Add L-proline-d-tocopherol, stir well and add fragrance.

Emulsifying Cosmetic Preparation Example 2 Example 3 Example 4 Example 5 Paid Cetostearyl alcohol 1.0 1.0 1.0 1.0 Glycol monostearate 0.7 0.7 0.7 0.7 Floating paraffin 10.0 10.0 10.0 10.0 Stearic acid 1.4 1.4 1.4 1.4 Twin 60 1.5 1.5 1.5 1.5 Profile paraben 0.1 0.1 0.1 0.1 Awards Purified water to 100 to 100 to 100 to 100 glycerin 6.0 6.0 6.0 6.0 Carbomer 0.14 0.14 0.14 0.14 EDTA-2Na 0.05 0.05 0.05 0.05 Methylparaben 0.20 0.20 0.20 0.20 corrector Triethanolamine 0.20 0.20 0.20 0.20 additive L-proline-d-tocopherol 0.01 1.00 10.00 20.00 Spices Spices 0.10 0.10 0.10 0.10

As described above, the proline derivative of Formula 1 according to the present invention is not only non-irritating, but also has enhanced collagen synthesis efficiency, excellent antioxidant properties, and stability to light (UV light) or heat (40 ° C. high temperature). By exhibiting this enhanced property, it can be usefully used as a functional cosmetic for preventing aging, and as a raw material for the treatment of skin diseases such as sensitive skin improvement, atopic skin, and dry skin.

While the invention has been described in detail above with reference to the described embodiments, it will be apparent to those skilled in the art that various modifications and variations are possible within the scope and spirit of the invention, and such modifications and variations fall within the scope of the appended claims. It is also natural.

1 is a graph showing qualitative NMR data of a compound represented by Chemical Formula 4 below.

2 is a graph showing qualitative NMR data of the compound represented by Chemical Formula 6.

3 is a graph showing qualitative NMR data of the proline derivative of the present invention.

Claims (4)

A compound defined by the following Chemical Formula 1 and a pharmaceutically acceptable salt thereof. <Formula 1> In the above, R ₁ , R ₂ , R ₃ are all hydrogen, or when any one of them is a hydroxyl group, the rest is hydrogen, R ₄ and R ₅ are hydrogen or a methyl group. Cosmetic composition characterized in that the compound of Formula 1 comprises as an active ingredient. The method of claim 2, Cosmetic composition, characterized in that the compound of Formula 1 comprises 0.01 to 20% by weight relative to the total weight. A first step of reacting a compound of Formula 2 with addition of benzylchloro formate (Formula 3) in a solvent to obtain a reactant; The reactant obtained in the first step was again tocopherol (Formula 5) in the presence of at least one catalyst selected from the group comprising N, N-dimethylaminopyridine (DMAP) and 1,3-dicyclohexylcarbodimide in a solvent Adding a second step to obtain a reactant; A third step of separating the benzyl chloroformate by subjecting the reactant obtained in the second step (Formula 6) to a bubble reaction under hydrogen gas at room temperature; And And a fourth step of filtrating and concentrating the reactant obtained in the third step to obtain a compound of Chemical Formula 1. <Formula 2> (Wherein R ₁ , R ₂ , R ₃ are the same as defined in Formula 1). <Formula 3> <Formula 5> (In the above, R ₄ , R ₅ is hydrogen or methyl group.) <Formula 6> (In the above, R ₁ , R ₂ , R ₃ are all hydrogen, or when any one of them is a hydroxyl group, the rest is hydrogen, R ₄ and R ₅ are hydrogen or a methyl group.)