KR101331912B1

KR101331912B1 - O-benzoyl chitosan derivative and method for preparing the same

Info

Publication number: KR101331912B1
Application number: KR1020120036340A
Authority: KR
Inventors: 채규윤; 이덕희; 정진아; 송미선; 박기석
Original assignee: 원광대학교산학협력단
Priority date: 2012-04-06
Filing date: 2012-04-06
Publication date: 2013-11-21
Also published as: KR20130113825A

Abstract

The present invention relates to O-benzoyl chitosan derivatives and methods for their preparation. In the method for preparing an O-benzoyl chitosan derivative according to the present invention, a low-cost phosphoric acid is added together with a benzoic acid derivative and a trifluoroacetic anhydride to obtain a mixed phosphoric acid-benzoic acid anhydride, followed by reaction with chitosan, thereby shortening the reaction step. The composition of the conditions can be easily induced to selectively induce O-benzoylation even at low temperatures, and can be mass-produced on a large scale. The expensive trifluoroacetic anhydride used as a catalyst can be easily recovered by distillation after the reaction is completed. It is economical because it can be done. Therefore, the O-benzoyl chitosan derivative prepared by the production method of the present invention can be dissolved in an organic solvent such as DMF, DMSO, acetone, etc. and can be used in various industrial fields.

Description

O-benzoyl chitosan derivative and method for preparing the same

The present invention relates to O-benzoyl chitosan derivatives and methods for their preparation.

Chitin is chemically a kind of mucopolysaccharide, and it is a substance that forms the cell wall of exoskeleton or fungus of crustaceans such as crabs, lobsters, shrimps and insects. Chitosan can be obtained by deacetylation of chitin by treatment with a strong alkali such as sodium hydroxide. The chemical structure of chitin and chitosan is similar to cellulose and the structural formula of chitin and chitosan is as follows.

[Chitin]

[Chitosan]

In particular, chitosan can be applied in various fields such as medicine, cosmetics, agriculture, food, and materials science, and has recently received a lot of attention. Chitosan has excellent biodegradability and can produce films and fibers as polymer materials. It is a material that is expected to be useful in various fields because it is rich in nature. However, despite this superiority, chitosan has very limited solvent dissolving except acid solvents such as acetic acid due to the hard crystal structure due to the formation of hydrogen bonds between amino and hydroxy groups and low solubility in general solvents. Because of poor workability, the use and commercialization of everyday life and industrial fields is limited. Therefore, there is an urgent need for research on the synthesis of chitosan derivatives to improve physical properties such as biological activity of chitosan or solubility in organic solvents, and the following studies have been reported.

In the case of chitin, which is similar in structure to chitosan, acid anhydride, mixed anhydride, acyl chloride, benzoyl chloride and methane sulfonic acid, p-toluene Several methods of acylating chitin using p-toluene sulfonyl chloride, lithium chloride and carboxylic acid have been reported. Among them, the mixed anhydride method using trifluoroacetic anhydride, phosphoric acid, and carboxylic acid was most remarkable in terms of reaction yield, reaction conditions, low cost, and recyclability of the reagent. Have been used to prepare aliphatic and aromatic ester derivatives of chitin.

However, in the case of chitosan, unlike chitin, since it has a hydroxyl group of 3 and 6 carbon atoms and an amino group of 2 carbon atoms, which are assumed to be essential for biological activities such as antimicrobial or antiviral properties, The reaction environment is rather complicated. The acylation reaction of chitosan is not known. Okamoto et al. Produced tribenzoyl chitosan using 4-dimethylaminopyridine group as a catalyst along with benzoyl chloride. Okamoto et al. Synthesized N- (2-carboxy) benzoyl chitosan and N-phthaloyl chitosan derivatives using chitosan and phthalic anhydride. Reported that they could. Alternatively, the acyl chloride (benzoyl) method is used by Feng etc., Vasnev etc., Zhu etc., Jiangtao etc. It has been reported that the method is characterized by the use of acyl chloride alone or as acyl chloride as a protecting group to protect free amino groups while simultaneously using acyl chloride as a catalyst with strong acids such as methanesulfonic acid.

Carboxylic anhydride methods are often used for the N-acylation of chitosan. The mixed anhydride method using trifluoroacetic anhydride and carboxylic acid has been applied to the production of chitin acylated derivatives by Yang et al., Et al., And also successfully applied to the production of aliphatic chitosan acylated derivatives by the researchers. There is a bar. However, in the reaction of acylating chitosan using the above-mentioned methods and the carboxylic anhydride method, N-acylation always occurs due to the preferential reaction of amino groups. Therefore, in order to induce only O-acylation, the amino group must be protected and reacted first, and then deprotected. This reaction has to be carried out at a high temperature for a long time. have. Therefore, there is an urgent need for a technology development regarding a method for preparing an O-acylated chitosan derivative in which the reaction is simple and economical, and the N-acylation is essentially blocked.

The present inventors prepared a mixed phosphoric acid-benzoic acid anhydride by reacting a benzoic acid compound with trifluoroacetic anhydride and phosphoric acid, and reacting it with chitosan, and thus, O-benzoyl which selectively benzoylated the hydroxy group of chitosan rapidly even at a low temperature. It was confirmed that derivatives of chitosan were produced, and it was confirmed that O-benzoyl chitosan prepared by this method was excellent in solubility in organic solvents (DMF, DMSO, acetone) and completed the present invention.

The present invention provides O-benzoyl chitosan derivatives and methods for their preparation.

In the method for preparing an O-benzoyl chitosan derivative according to the present invention, a low-cost phosphoric acid is added together with a benzoic acid derivative and a trifluoroacetic anhydride to obtain a mixed phosphoric acid-benzoic acid anhydride, followed by reaction with chitosan, thereby shortening the reaction step. The composition of the conditions can be easily induced to selectively induce O-benzoylation even at low temperatures, and can be mass-produced on a large scale. The expensive trifluoroacetic anhydride used as a catalyst can be easily recovered by distillation after the reaction is completed. It is economical because it can be done. Therefore, the O-benzoyl chitosan derivative prepared by the production method of the present invention can be dissolved in an organic solvent such as DMF, DMSO, acetone, etc. and can be used in various industrial fields.

1 is a diagram showing ^-1 H-NMR spectrum of the O-benzoyl chitosan derivative of the present invention [(a) CTS: chitosan, (b) CTS-b: chitosan benzoate, (c) CTS-m: chitosan p -Methoxybenzoate].
Figure 2 is a diagram showing the FT-IR spectrum of the O-benzoyl chitosan derivative of the present invention ((a) CTS: chitosan, (b) CTS-b: chitosan benzoate, (c) CTS-m: chitosan p-meth Oxybenzoate].
Figure 3 is a view of the surface of the O- benzoyl chitosan derivative of the present invention by SEM (Scanning electronic microscope) microscope (upper: 25,000 times magnification, lower: 5000 times magnification, chitosan, chitosan benzoate, chitosan p- from the left) Methoxybenzoate).

Hereinafter, the present invention will be described in detail.

The present invention provides an O-benzoyl chitosan derivative represented by the following Chemical Formula 1.

In Formula 1, R is a phenyl group or p-methoxyphenyl group, n is an integer of 2 to 1 million.

O-benzoyl chitosan derivative of Formula 1 is characterized in that the hydroxy group 3 and 6 of the chitosan benzoylated.

In addition, the present invention (a) mixing the benzoic acid derivatives with trifluoroacetic anhydride at 30 ~ 50 ℃; (b) cooling the mixture of step (a) to 15-25 ° C., and then adding 70-95% phosphoric acid and mixing to prepare phosphoric acid-carboxylic anhydride; And (c) adding chitosan to the phosphoric acid-carboxylic anhydride of step (b) and mixing at 15-25 ° C., followed by reacting at 30-65 ° C. for 15-25 hours; It provides an O-benzoyl chitosan derivative comprising a.

The method for preparing an O-benzoyl chitosan derivative according to the present invention is characterized by benzoylation of 3, 6 hydroxyl groups of the chitosan (benzoylation), and is represented by Scheme 1 below.

In Scheme 1, R is a phenyl group or p-methoxyphenyl group, n is an integer of 2 to 1 million.

In the step (a), the benzoic acid derivative may be stirred with trifluoroacetic anhydride at 35 to 45 ° C. for 50 to 90 minutes, then heated to 50 ° C., and then further stirred for 50 to 90 minutes, preferably 40 After 60 minutes of stirring at 50 ° C., the mixture was heated to 50 ° C. and further stirred for 60 minutes.

In step (b), the phosphate-benzoic acid derivative anhydride may be prepared by stirring the 70-95% phosphoric acid at 15-25 ° C. with a mixture of the benzoic acid derivative and trifluoroacetic anhydride of step (a) for 5-15 minutes. Preferably, 85% phosphoric acid is stirred at 20 ° C. for 10 minutes to prepare a phosphoric acid-benzoic acid derivative anhydride.

In the step (c), the chitosan may be stirred and mixed at 15 to 25 ° C. for 20 to 40 minutes, and then reacted at 45 to 50 ° C. for 18 to 22 hours to prepare an O-benzoyl chitosan derivative. Chitosan was stirred and mixed at 20 ° C. for 30 minutes, and then reacted at 45˜50 ° C. for 20 hours to prepare an O-benzoyl chitosan derivative.

The mechanism of the O-benzoyl chitosan derivative of step (a) to (c) is shown in Scheme 2 below.

In Scheme 2, R is a phenyl group or p-methoxyphenyl group, n is an integer of 2 to 1 million.

Benzoylation of chitosan according to the invention was carried out using mixed anhydrides derived from trifluoroacetic anhydride, benzoic acid derivatives (benzoic acid and p-methoxybenzoic acid), and phosphoric acid. Using this synthesis method, it is estimated that the molar ratio of benzoic acid derivatives and trifluoroacetic acid to chitosan is lower than that of benzoylation of chitosan using a mixed anhydride derived from trifluoroacetic anhydride (TFAA) and benzoic acid derivatives. This is because it seems to be an efficient response.

That is, as shown in Scheme 2, the benzoylation of the chitosan of the present invention was made only in the hydroxyl group, and the trifluoroacetic anhydride, benzoic acid derivative, 85% phosphoric acid of steps (a) and (b) As input, a phosphate-benzoic acid derivative anhydride is produced, resulting in 8 moles of trifluoroacetic acid. 6 moles of 8 moles of trifluoroacetic anhydride are produced as a by-product of the reaction, and 2 moles are produced as a result of hydrolysis with water contained in 85% phosphoric acid. Trifluoroacetic acid is strongly acidic, which blocks protonation by protonation of amino groups at the 2nd carbon site of chitosan, and prevents acylation reactions. Chitosan is a benzoic acid derivative that forms a phosphate-benzoic acid anhydride intermediate. Since it is added in step (c) only after the production, acylation cannot occur in the amino group at the 2nd carbon site of chitosan, and benzoylation occurs only at the hydroxyl group at the 3rd and 6th carbon sites.

Hereinafter, preferred embodiments of the present invention will be described in order to facilitate understanding of the present invention. However, the following examples are provided only for the purpose of easier understanding of the present invention, and the present invention is not limited by the examples.

Example 1. O- of the present invention Benzoyl Chitosan derivatives (chitosan Benzoate Manufacturing

1. Preparation of sample

Chitosan (molecular weight: 1000 or less, deacetylation: about 90%, water content: 6.8%) was purchased from KITTO LIFE of Korea, and trifluoroacetic anhydride (TFAA) was purchased from Acros Oraganics. Benzoic acid and p-methoxybenzoic acid, 85% phosphoric acid were purchased from Sigma Aldrich, and DMSO-d ₆ (dimethyl sulfoxide-d ₆ ) was purchased from Cambridge Isotope Laboratories, Inc. (Andover, MA, USA). Other chemicals were used in the reagent grade, and the used samples were used without further purification.

2. O- of chitosan Acylation

1.44 g of benzoic acid was added to a flask containing 6.56 g of trifluoroacetic anhydride (TFAA) and stirred at 40 ° C. for 1 hour. The reaction mixture was heated to 50 ° C. and stirred for another 1 hour until the reaction mixture became a clear pale yellow solution. After the reaction temperature had dropped to 20 ° C., 0.343 g of 85% phosphoric acid was added to the solution and stirred for 10 minutes. After adding 1.0 g of chitosan (equivalent to 12.10 mmol of hydroxyl groups) to the solution, the reaction mixture was stirred at 20 ° C. for 30 minutes and then heated to 45-50 ° C. Then, the reaction solution was vigorously stirred for 20 hours until the brown syrup was maintained at the same temperature. About 5 g of anhydrous ethanol was added to the syrup and stirred for 10 minutes. After completely removing the volatiles under reduced pressure using a rotary evaporator, the solution was mixed well with 30 ml of anhydrous ethanol and filtered through gauze. The filtrate was concentrated back to syrup under reduced pressure. The syrup was dissolved in 10-15 ml of a mixed solvent of ethanol and acetone mixed at a volume ratio of 1: 1 (v / v), and then dissolved in 300 ml of diethyl ether to precipitate the product, followed by a refrigerator (0-0). At 5 ° C.) for 2 to 3 hours. The product was filtered off and washed several times with diethyl ether to give a solid powder. The resulting solid powder was repeated 20 times or more in dissolution and washing until it became colorless. The resulting powder was dried at 50 ° C. for 5 hours under vacuum conditions. The yields of O-benzoyl chitosan derivatives in powder form are shown in Table 1.

Reactant Chitosan (g) Trifluoroacetic anhydride (g) Benzoic acid Phosphoric Acid Product / output * Molar ratio One 8 2 2 input 1 g 6.56 1.44 0.343 CTS-b / 1.8g

* Based on Glucosamine Unit, Chitosan Benzoate ( CTS -b)

Example 2. O- Benzoyl Chitosan derivatives (chitosan p- Methoxybenzoate Manufacturing

Except for using p-methoxybenzoic acid instead of benzoic acid in Example 1 was prepared in the same manner as in Example 1 O-benzoyl chitosan derivatives (chitosan p-methoxybenzoate) in powder form. The yields of O-benzoyl chitosan derivatives in powder form are shown in Table 2.

Reactant Chitosan (g) Trifluoroacetic anhydride (g) Benzoic acid (g) Phosphoric Acid (g) Product / output * Molar ratio One 8 2 2 input 1 g 6.56 ** 1.80 0.343 CTS-m / 1.5g

* Based on glucosamine units, ** p- Methoxybenzoic acid , Chitosan p- Methoxybenzoate ( CTS -m)

Experimental Example O- Benzoyl Spectroscopic Characteristics of Chitosan Derivatives ( Spectral characterization )

(One) Hydrogen Nuclear Magnetic Resonance ( Nuclear Magnetic Resonance , ^One H- NMR ) analysis

The nuclear magnetic resonance spectra of the O-benzoyl chitosan derivatives prepared in Examples 1 and 2 were measured using a 5 mm diameter tube with a JEOL JNM-ECP 500 spectrometer (500 MHz) at room temperature (20 ° C.). Samples were diluted to a concentration of 15 mg / ml using DMSO-d6 solvent mixed with a small amount of deuterated water to perform ¹ H-NMR analysis.

¹ H-NMR analysis of the O-benzoyl chitosan derivative of the present invention is shown in FIG.

As shown in FIG. 1, characteristic signals indicating protons attached to aromatic carbon atoms and anomer carbons were observed between δ7.5 and δ7.9, and at δ4.5, respectively. Substitution ratios were approximately 0.89 for benzoic acid and 1.0 for p-methoxybenzoic acid, respectively.

Chitosan p-methoxybenzoate (DMSO-d6, 1 drop of D ₂ O): δ7.9 (doublet, aromatic Hs: ortho), δ4.5 (aromatic Hs: meta), δ4.5 (anomeric CH, 1.12 H ), δ3.2 ~ 3. (C-Hs of carbohydrate backbone), Degree of substitution: 0.89

(2) Fourier transform infrared spectrum ( Fourier transform infrared , FT - IR ) analysis

Fourier transform infrared spectra of the O-benzoyl chitosan derivatives prepared in Examples 1 and 2 were measured with a Shimadzu Prestige-21 FT-IR spectrometer. Samples were prepared in KBr pellets and scanned in the wavelength range of 4000-400 cm ^-1 as compared to blank KBr pellets.

FT-IR results of the O-benzoyl chitosan derivative of the present invention are shown in FIG. 2.

2, the benzoyl chitosan, the other strong peaks in the strong and broad peak with 1,210cm ^-1 vicinity of 1,735cm ^-1 newly generated near said been observed, which each ester carbonyl stretching absorption (stretching absoption) and esters It corresponds to the stretch absorption of CO single bonds. These peaks did not appear in the FT-IR graph of chitosan. In addition, an NH stretching peak near 3450 cm ⁻¹ was observed in the IR spectrum, while an amide peak near 1670 cm ⁻¹ was not observed. This means that the amino group of chitosan was not acylated.

The absorption peak characteristics according to the functional group of the FT-IR are as follows.

(1) In the case of chitosan benzoate (KBr pellet): 3450cm ^-1 vicinity (NH bond), 3050 cm ^-1 vicinity (aromatic CH bond), 2960 cm ^-1 vicinity (aliphatic CH bond), 1710 cm ^-1 (aromatic Ester carbonyl), 1270 cm ^-1 (aromatic CH bond)

(2) Chitosan p- methoxy benzoate For (KBr pellet): 3450cm ^-1 vicinity (NH bond), 3050 cm ^-1 vicinity (aromatic CH bond), 2960 cm ^-1 vicinity (aliphatic CH bond), 1710 cm ^-1 (aromatic ester carbonyl group), 1270 cm ^-1 (aromatic CH bond)

Experimental Example 2. Scanning electron microscope Scanning electron microscope , SEM )

The surface structure of the O-benzoyl chitosan derivative of the present invention was observed using a scanning electron microscopy (SEM) (S-4800, Hitachi, Japan). The sample was electron accelerated to 5 kV and analyzed at a magnification of 5000 to 25,000 times.

The surface structure of chitosan and benzoyl chitosan is shown in FIG. 3.

As shown in Figure 3, the surface structure of chitosan and benzoyl chitosan showed a clear difference. Many pores were irregularly arranged in chitosan, and the pore diameter was about 0.5-2.0 μm. The shape of the pores was also relatively constant. However, in the case of benzoyl chitosan, it was observed that the shape of the pores varied and the diameter of the pores was 5-20 μm, which is much larger than that of chitosan. As a result of increasing magnification, chitosan appeared to overlap the net, but the surface of the benzoyl chitosan had a slightly molten coral-like dendritic structure. This difference means that due to the breakdown of hydrogen bonds and the hydrophobic interaction of the newly introduced phenyl group, a large structural change occurred in the back bone of the chitosan benzoate polymer.

Experimental Example 3. Solubility

The solubility of the O-benzoyl chitosan derivatives prepared in Examples 1 and 2 was measured by dissolution until the metered sample was no longer dissolved in each solvent at room temperature (20 ° C.).

The solubility of the O-benzoyl chitosan derivative according to the solvent is shown in Table 3 below.

<O- depending on solvent Benzoyl Solubility of Chitosan Derivatives>

As shown in Table 3, the solubility of the O-benzoyl chitosan derivative of the present invention in the organic solvent was determined using DMSO (dimethylsulfoxide), DMF (dimethylformamide), acetone (acetone), ethanol, and THF (tetrahydrofuran). Was measured. Benzoyl chitosan and p-methoxybenzoyl chitosan were both dissolved in DMSO, DMF and acetone, but not in THF and ethanol.

Claims

O-benzoyl chitosan derivatives represented by Formula 1 below:
[Formula 1]

The method of claim 1,
O-benzoyl chitosan derivative of Formula 1 is characterized in that the hydroxyyl group 3, 6 of the chitosan benzoylated, O-benzoyl chitosan derivatives.

(a) mixing a benzoic acid derivative with trifluoroacetic anhydride at 30 to 50 ° C;
(b) cooling the mixture of step (a) to 15-25 ° C., then adding 70-95% phosphoric acid and mixing to prepare a phosphoric acid-carboxylic anhydride; And
(c) adding chitosan to the phosphoric acid-carboxylic anhydride of step (b) and mixing at 15 to 25 ° C., followed by reacting at 30 to 65 ° C. for 15 to 25 hours; To include, and the preparation method of O-benzoyl chitosan derivative represented by Scheme 1 below:
<Reaction Scheme 1>

The method of claim 3,
In the step (a), the benzoic acid derivatives are stirred with the trifluoroacetic anhydride at 35-45 ° C. for 50-90 minutes, and then heated to 50 ° C., further stirring for 50-90 minutes, Method for preparing O-benzoyl chitosan derivative.

The method of claim 3,
In the step (b), 70 to 95% phosphoric acid is stirred at 15 to 25 ℃ with the mixture of the step (a) for 5 to 15 minutes to prepare a phosphoric acid-benzoic acid anhydride, O-benzoyl chitosan derivative Manufacturing method.

The method of claim 3,
In the step (c), the chitosan is stirred by mixing for 20 to 40 minutes at 15 ~ 25 ℃, and then reacted for 18 to 22 hours at 45 ~ 50 ℃, the production method of O-benzoyl chitosan derivatives.

The method of claim 3,
The molar ratio of the reactant is 1 mole of chitosan, 2 moles of benzoic acid derivative, 8 moles of trifluoroacetic acid, and 2 moles of phosphoric acid.