WO2015153216A1

WO2015153216A1 - Pentynyl cellulose ethers

Info

Publication number: WO2015153216A1
Application number: PCT/US2015/022414
Authority: WO
Inventors: Roland Adden; Christian BORK; Petra MISCHNICK; Marian RINKEN
Original assignee: Dow Global Technologies Llc
Priority date: 2014-04-02
Filing date: 2015-03-25
Publication date: 2015-10-08

Abstract

A compound which is a cellulose ether having an average of 1.0 to 2.5 C₁-C₆ alkyl ether groups per glucopyranosyl unit and an average of 0.02 to 1 pentynyl ether groups per glucopyranosyl unit.

Description

PENTYNYL CELLULOSE ETHERS

This invention relates to new pentynyl cellulose ethers and methods for preparing and using them.

Pentynyl ethers of some carbohydrate polymers are known. For example, M.N. Tahir et al., Macromolecular Chemistry and Physics, vol. 211 (2010), pages 1648-1662 discloses pentynyl ethers of dextrans. However, this reference does not disclose the compounds claimed herein.

STATEMENT OF INVENTION

The present invention provides a compound which is a cellulose ether having an average of 1.0 to 2.5 Ci-C₆ alkyl ether groups per glucopyranosyl unit and an average of 0.02 to 1 pentynyl ether groups per glucopyranosyl unit.

The present invention is further directed to a process for preparing a cellulose ether comprising 1,2,3-triazole rings; said process comprising contacting a cellulose ether having an average of 1.0 to 2.5 Ci-C₆ alkyl ether groups per glucopyranosyl unit and an average of 0.02 to 1 pentynyl ether groups per glucopyranosyl unit with a compound having an azido group.

DETAILED DESCRIPTION

Percentages are weight percentages (wt ) and temperatures are in °C, unless specified otherwise. Operations were performed at room temperature (20-25 °C), unless specified otherwise. An "alkyl" group is a saturated, substituted or unsubstituted hydrocarbyl group having from one to twenty-two carbon atoms in a linear or branched arrangement. Substitution on alkyl groups of one or more hydroxy, carboxylic acid or salts thereof (attached to alkyl via carbon, e.g., carboxymethyl cellulose), halo or alkoxy groups is permitted. Preferably, alkyl groups are substituted by hydroxyl or unsubstituted. An "alkenyl" group is an alkyl group having at least one carbon-carbon double bond, preferably one carbon-carbon double bond. An "aryl" group is a substituent derived from an aromatic hydrocarbon compound. An aryl group has a total of from six to twenty ring atoms, unless otherwise specified, and has one or more rings which are separate or fused. Substitution on aryl groups of one or more alkyl or alkoxy groups is permitted. An "aralkyl" group is an "alkyl" group substituted by an "aryl" group.

In the compound of this invention, preferably the alkyl ether groups are C1-C4 alkyl; preferably C1-C3 alkyl; preferably methyl, ethyl, 2-hydroxyethyl or 2-hydroxypropyl; preferably Ci or C3 alkyl; preferably methyl or 2-hydroxypropyl. More than one type of alkyl group may be present on a cellulose ether. Especially preferred cellulose ethers include, e.g., methylcellulose (MC), ethylcellulose (EC), ethyl methyl cellulose, hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC), hydroxyethyl methyl cellulose (HEMC), hydroxypropyl methyl cellulose (HPMC) and carboxymethyl cellulose (CMC). HPMC and MC are preferred cellulose-based polymers. Specific examples of preferred cellulose based polymers include METHOCEL polymers commercially available from Dow Chemical Company. Preferably, the cellulose ether has no more than 2.3 alkyl ether groups per glucopyranosyl unit, preferably no more than 2.1. The number of alkyl ether groups per glucopyranosyl unit is determined by analysis of the weight % of the substituents. For example, for METHOCEL polymers the determination of the % methoxyl and %

hydroxypropoxyl in hydroxypropyl methylcellulose is carried out according to the United States Pharmacopeia (USP 32). The values obtained are % methoxyl and %

hydroxypropoxyl. These are subsequently converted into degree of substitution (DS) for methyl substituents and molar substitution (MS) for hydroxypropyl substituents. Residual amounts of salt have been taken into account in the conversion.

Preferably, the pentynyl ether is a 4-pentynyl ether, i.e., a substituent HC≡C(CH₂)3- is attached to a hydroxyl oxygen. Preferably, the cellulose ether has at least 0.03 pentynyl ether groups per glucopyranosyl unit, preferably at least 0.05, preferably at least 0.08, preferably at least 0.1, preferably at least 0.15; preferably no more than 0.8, preferably no more than 0.6, preferably no more than 0.5, preferably no more than 0.45, preferably no more than 0.4. The average number of pentynyl ether groups per glucopyranosyl unit, also known as the degree of substitution (DS) is measured by DS-GC.

Preferably, the cellulose ether having an average of 1.0 to 2.5 Ci-C₆ alkyl ether groups per glucopyranosyl unit has a viscosity, measured from a 2 wt solution in water at 20 °C, of 2.4 to 100,000 mPa-s, preferably 5 to 60,000, preferably 15 to 10,000, preferably 50 to 8,000, preferably 100 to 6,000. Viscosities were measured for cellulose ethers having a viscosity of less than 600 mPa- s by preparing 2% by weight cellulose ether solutions in water according to United States Pharmacopeia (USP 35, "Hypromellose", pages 3467-3469) followed by an Ubbelohde viscosity measurement according to DIN 51562-1:1999-01

(January 1999). Viscosities were measured for cellulose ethers having a viscosity higher than 600 mPa- s by preparing 2% by weight cellulose ether solutions in water according to United States Pharmacopeia (USP 35, "Hypromellose", pages 3467-3469) followed by viscosity measurement with a rotational rheometer (e.g. Haake RS600) with cone & plate geometry at 20 °C at a steady shear rate = 10 s^"1. Viscosities of cellulose ethers have been correlated with molecular weights, and accordingly, one skilled in the art would understand the meaning of either measurement. See CM. Keary, Carbohydrate Polymers, vol. 45 (2001), pages 293- 303. Cellulose polymers contain repeat units having a l,4'- -glucopyranosyl structure, also known as anhydroglucose.

Preferably, the cellulose ether is of formula (I)

wherein R¹, R² and R³ are independently selected from: hydrogen and alkyl; wherein alkyl groups may comprise from one to six carbon atoms which may be unsubstituted or substituted with hydroxyl, carboxylic acid or salts thereof (attached to alkyl via carbon, e.g., carboxymethyl cellulose), halo or C C₄ alkoxy; and n is from 25 to 7,500. Preferably, alkyl groups are unsubstituted or substituted only with hydroxyl. Preferably, n is from 50 to 5,000, preferably 100 to 2,500. Preferably, alkyl groups have from one to four carbon atoms, preferably from one to three.

The compounds disclosed herein may be prepared by applying alkylation methods known in the art, e.g., alkylation of a carbohydrate hydroxyl group with an alkynyl halide in the presence of base. For example, a compound of this invention may be prepared according to the following example reaction scheme,

Base

wherein R² and R³ are as defined previously, R¹ is hydrogen and the halo group is chloro. The symbol attached to the 1,4 oxygen atoms indicates the presence of neighboring glucopyranosyl units. Solvents which may be useful include, e.g., polar aprotic solvents, especially DMSO. Suitable bases include, e.g., metal (especially alkali metal) alkoxides and organolithium compounds. Preferably, the reaction is carried out at a temperature from 0°C to 50°C, preferably from 10°C to 30°C. A similar reaction would be expected on glucopyranosyl units in which R² or R³ were hydrogen instead of R¹ being hydrogen, and multiple alkylations are possible as well, but would be expected to occur less frequently given the low degree of substitution of alkynyl groups claimed herein. There also may be some glucopyranosyl units having three alkyl ether groups which would be unreactive to the pentynyl halide.

Compounds of this invention may also be prepared by reaction of cellulose with a base (e.g., alkali metal hydroxide), pentynyl halide and an alkylating agent (e.g., ethylene oxide (EO), propylene oxide (PO), methyl chloride, ethyl chloride. This results in direct formation of pentynyl alkylcellulose from cellulose. Preferably this reaction is carried out at higher than atmospheric pressure (500 to 3,500 kPa) and at a temperature from 40 to 120 °C.

The compounds of this invention are useful as reactants for forming a family of triazole compounds. The conversion of a pentynyl alkylcellulose polymer to a triazole may be achieved by the Huisgen 1,3-dipolar cycloaddition of azides and alkynes to 1,2,3-triazole products. This reaction is regioselective with respect to the azide orientation in the [2+3] cycloaddition and is reported to give high yields under mild conditions, to have high tolerance of other functionalities and to require minimal work-up and purification. This reaction has been described in many publications, e.g., W.H.Binder et al., Macromol. Rapid Commun. , 2007, 28, 15-54; H.C. Kolb et al., Drug Discovery Today, 2003, 8, 1128-1137. The reaction scheme is shown below with Cu(I) as the catalyst. The pentynyl alkylcelluloses serve as the alkyne starting material. The Cu(I) catalysis may be provided by reduction of CuS0₄ hydrate, e.g., with sodium ascorbate in situ or by Cu(I) salts prepared by other means, e.g., Cu(I) complexes with triarylphosphines, Cu(I) bromide or iodide, or by reduction of Cu(II) acetate. Other useful catalysts for this reaction include, e.g., Ru, Pd(II), Pt(II) and Ni(II).

R⁵ represents the remainder of a pentynyl alkylcellulose.

The R⁴ substituent can be any organic substituent, i.e., one in which carbon, hydrogen, oxygen, sulfur and nitrogen atoms comprise at least 85% of its weight, preferably at least 90% preferably at least 95%. Preferably, the organic substituent has a molecular weight no greater than 50,000, preferably no greater than 35,000, preferably no greater than 25,000, preferably no greater than 15,000. When the organic substituent is a polymer having a molecular weight distribution, the molecular weight is measured as the number- average molecular weight (Mn). Preferably addition polymers are formed in solution. In one preferred embodiment, the organic substituent has from one to thirty carbon atoms;

preferably no more than twenty-two carbon atoms, preferably no more than fifteen carbon atoms, preferably no more than ten carbon atoms. When the organic substituent contains additional azide groups, these may react with molecules of pentynyl alkylcellulose to form a polymer or network structure. In a preferred embodiment of the invention R⁴ is a biomolecule, e.g., protein, carbohydrate (e.g., cyclodextrin, saccharide), lipid (e.g., steroid, glycolipid, phospholipid, prostaglandin, leukotriene), nucleoside, nucleotide.

EXAMPLES

Process to create Pentynylmethylcellulose. The procedure listed below is a lab based procedure. This product could also be obtained via a pressurized synthesis where the methyl cellulose (or cellulose) is alkalized with NaOH and then etherified with pentynyl halide (bromide, chloride or iodide) (or as well methyl chloride / EO / PO) at elevated temperature and pressure.

As starting material a methylcellulose with a degree of substitution (DS) of 1.8 methyl groups per glucopyranosyl units and a methylcellulose with a DS of 1.19 methyl groups per glucopyranosyl units were used.

General procedure

Methylcellulose was filled in a nitrogen flushed flask and dried at high vacuum. As solvent 50 mL DMSO (dry) was added under nitrogen and stirred overnight. The base "Li-dimsyl" was freshly prepared as followed. A flask filled with DMSO (dry) was briefly evacuated in high vacuum and the equal volume of methyl lithium (1.6 molar in diethyl ether) was added drop-wise under nitrogen. The mixture was flushed for 1 h (with needles in a septum) under stirring to remove ether and methane. After the volume corresponds again to the DMSO employed, the calculated amount of "Li- dimsyl" was transferred into the flask with MC in DMSO under nitrogen and stirred at room temperature for 30 min. Under cooling, the calculated amount of pentynyl chloride was added drop-wise. The reaction mixture was stirred for 2 days while its color turns from pale yellow to dark orange. For purification the reaction mixture was dialyzed against tap and finally distilled water (MWCO 14000 g/mol). Afterwards the charge of the dialysis tube was freeze dried. In Table 0-1 amounts of reagents, starting material and raw products are summarized.

Table 0-1: Preparation parameters of pentynyl methylcelluloses (PyMC) from MC

Sample PyMC29A PyMC29B PyMC65A PyMC65B

1 2 3 4

DS (methyl) starting

1.8 1.8 1.19 1.19 material

methylcellulose (mg) 493 506 500^* 495^* eq. Li-dimsyl/OH 1.10 1.60 1.10 1.60

Li-dimsyl (mL) 2.18 3.25 3.50 5.04 eq. 5-chloro-l-pentyne/OH 1.60 2.10 1.60 2.10

5-chloro-l-pentyne (mL) 0.54 0.72 0.86 1.12

Raw product PyMC (mg) 480 520 525 515 after drying at high vacuum

Table 0-2: Properties of pentynyl methylcelluloses (PyMC)

Sample 1 2 3 4

DS-GCpentynyl 0.22 0.24 0.32 0.32

Yield % 20.0 15.0 29.1 20.0

Note: Yield is calculated based on the ratio of DS-GC pentynyl and eq. Li-dimsyl/OH

There are multiple ways to analyze the Pentynyl-DS. No method is generally accepted. For the purposes of this invention, the DS-GC values are used to determine the degree of substitution (DS).

The analysis of the substitution patterns of methyl- and pentynyl-groups was performed by GLC and GLC-MS. Each sample was analyzed in duplicate.

In the first step, glucosidic linkages were cleaved by methanolysis to gain the monomer units as methyl glucoside derivatives. Methanolic hydrochloric acid (MeOH/HCl) was prepared from dry methanol and acetyl chloride under ice cooling. Around 1-2 mg of PyMC was weighted in a V-Vial, covered with 1.5 M MeOH/HCl, mixed well, and treated for 2 h at 90 °C. After cooling to room temperature (r.t.) solvent was removed in a stream of nitrogen. Subsequently, the residue was co- distilled repeatedly with some drops of methanol.

The second step, trimethylsilylation (TMS) of remaining free OH groups was performed by adding 10 μL· pyridine, 50 μL· dichloromethane and 50 μL· N,0- Bis(trimethylsilyl)trifluoroacetamide (BSTFA) to the methanolysed and dried sample, and heating for 1 h at 100 °C. After cooling to r.t. 1 mL dichloromethane was added and an appropriate dilution of this sample solution was used for GLC analysis. GLC- MS was recorded for one of the samples. For the GLC, we used the following temperature program:

Rate Temperature Hold time

60 °C 1 min

20 °C/min 130 °C 0 min

4 °C/min 290 °C 10 min

20 °C/min 310 °C 10 min

The column used was Phenomenex Zebron ZB-5MS, film thickness 0.25 μιη, length 25.0 m, inner diameter 0.25 mm ID. Injection was splitless, temperature 250 °C, carrier gas H2, pressure 56.1 kPa, linear velocity mode 45 cm/sec.

Peaks of the methyl 0-alkynyl-0-methyl-0-TMS-a, -glucosides (i.e. two peaks/pattern) were assigned by interpretation of their mass spectra. With three different substituents in positions 2, 3, and 6, -H, -CH₃, -(CH₂)₃C≡CH, 33 = 27 combinations are possible, and thus up to 54 peaks are expected (27 pairs of α,β- glucosides). For example, a 3-O-pentynyl glucose can be combined with 2-0-, 6-0-, and 2,6-di-O-methyl or no further substitution, resulting in up to 8 compounds. We could assign 18 α,β-glucoside pairs, beside the 8 pairs of pure MC additional 10 pairs containing pentynyl at any position, and detect even more, but not assign and quantify all tiny and overlapping peaks. Therefore the pentynyl-DS is probably slightly underestimated.

Quantitative monomer composition data are obtained from the peak areas measured by GLC with FID detection. Molar responses of the monomers are calculated in line with the effective carbon number (ECN) concept but modified as described in the table below. The effective carbon number (ECN) concept has been described by Ackman (R.G. Ackman, J. Gas Chromatogr., 2 (1964) 173-179 and R.F. Addison, R.G. Ackman, J. Gas Chromatogr., 6 (1968) 135-138) and applied to the quantitative analysis of partially alkylated alditol acetates by Sweet et. al (D.P. Sweet, R.H. Shapiro, P. Albersheim, Carbohyd. Res., 40 (1975) 217- 225).

ECN increments used for ECN calculations:

In order to correct for the different molar responses of the monomers, the peak areas are multiplied by molar response factors MRFmonomer which are defined as the response relative to the 2,3,6-TMS monomer, which represents the unsubstituted monomer in the pentynyl derivative prior to the sample preparation for the GC DS determination.

MRFmonomer = ECN2,3,6-TMS / ECNmonomer

Conversion of Pentynylmethylcellulose into a Triazole Product.

Three different azides have been used for the reaction:

The first reaction was carried out with aminoethylazide and PyMC29A. Secondly, thiolpropylazide was reacted with PyMC29B, and finally carboxypropylazide was submitted to the cycloaddition with PyMC65A.

Reaction of pentynyl methylcellulose with aminoethylazide (-» PyMC29A-amino)

For the reaction with pentynyl methylcellulose PyMC29A, 101 mg (0.14 mmol alkynyl, Mw (AGU) = 209.8 g/mol, DSMe = 2.0, DSPy = 0.3 assumed) of the polymer was filled in a flask and 50 μL· (43 mg, 0.5 mmol, 3.45 eq. per alkynyl) of 2-aminoethylazide was added. Then 8 mL of DMSO and 2 mL of water were added, and the yellowish solution was stirred overnight. As catalyst 180 μL· (0.18 mmol) of a sodium ascorbate solution (1 M stock solution: 990.5 mg sodium 1-ascorbate in 5 mL dist. water) and subsequently 12 mg (0.045 mmol) of CuS0₄ · 5 H₂0 dissolved in 0.17 mL water were added. The reaction was stirred for 4 days at room temperature. The product was isolated by dialysis against dist. water (dialysis tube MWCO 14000). After freeze drying 116 mg raw product PyMC29A-amino was obtained. GLC monomer analysis after methanolysis and trimethylsilylation was accomplished as described above.

Success of cycloadditions was obvious from the disappearance or strong reduction of alkynyl-related absorption bands in the IR spectra. ATR FTIR spectra of the product have been generated. All IR spectra are normalized with respect to the most intense absorption band at 1053 cm^"1. The C≡C-H valence vibration at 3280 cm^"1 of the pentynyl derivatives has disappeared after the cycloaddition reaction.

Reaction of pentynyl methylcellulose with thiolpropylazide (-> PyMC29B-thiol)

Reaction of pentynyl methylcellulose PyMC29B with 3 -thiolpropylazide was carried out in the same manner. 70 mg (0.1 mmol alkynyl, Mw (AGU) = 209.8 g/mol, DSMe = 2.0, DSPy = 0.3 assumed) polymer, 40 mg (0.345 mmol, 3.45 eq. per alkynyl) azide, 8 mL DMSO, 2 mL water, 123 μL· (0.123 mmol) sodium ascorbate stock solution (1 M) and 7.9 mg (0.03 mmol) CuS0₄ · 5 H₂0 in 0.12 mL water were applied. After dialysis and lyophilisation 133 mg raw product of PyMC29B -thiol was obtained. GLC monomer analysis was performed as described above, but by a slightly modified procedure. Since the PyMC-thiol did not fully dissolve, methanolysis was extended for 120 min. at 120 °C additionally. A second entry with successful dissolving was carried out with 3 M MeOH/HCl for 120 min. at 90 °C and additionally for 60 min. at 120 °C.

Success of cycloadditions was obvious from the disappearance or strong reduction of alkynyl-related absorption bands in the IR spectra. ATR FTIR spectra of the product have been generated. All IR spectra are normalized with respect to the most intense absorption band at 1053 cm^"1. The C=C-H valence vibration at 3280 cm^"1 of the pentynyl derivatives has disappeared after the cycloaddition reaction.

Reaction of pentynyl methylcellulose with carboxypropylazide PyMC65A-carboxy)

60 mg (0.116 mmol alkynyl, Mw (AGU) = 206.6 g/mol, DSMe = 1.3, DSPy = 0.4 assumed) polymer PyMC65A, 40 μL· (38 mg, 0.29 mmol, 2.5 eq. per alkynyl) carboxypropylazide, 8 mL DMSO, 2 mL water, 106 (0.106 mmol) sodium ascorbate stock solution (1 M) and 6.7 mg (0.027 mmol) CuS04 · 5 Η20 in 0.1 mL water solution were applied. Ca. 56 mg of PyMC65A-carboxy raw product was obtained after dialysis and lyophilisation. GLC monomer analysis was accomplished after methanolysis and trimethylsilylation. Methanolysis was carried out as follows: (1) two samples of 1-2 mg polymer PyMC65A-carboxy in 1 mL 1.5 M MeOH/HCl were heated for 120 min. at 90 °C. Since they were not completely dissolved, they were additionally heated for 120 min. at 120 °C. (2) Full dissolution was achieved when heating with 3.0 M MeOH/HCl for 120 min. at 90 °C. Further treatment was performed as described above.

Claims

1. A compound which is a cellulose ether having an average of 1.0 to 2.5 Ci-C₆ alkyl ether groups per glucopyranosyl unit and an average of 0.02 to 1 pentynyl ether groups per glucopyranosyl unit.

2. The compound of claim 1 having a viscosity, measured from a 2 wt solution in water at 20 °C, of 50 mPa- s to 60,000 mPa- s.

3. The compound of claim 2 in which the alkyl ether groups have from one to three carbon atoms.

4. The compound of claim 3 having an average of 0.1 to 0.5 pentynyl ether groups per glucopyranosyl unit.

5. The compound of claim 4 in which the alkyl ether groups are unsubstituted or substituted only by a single hydroxyl group.

6. The compound of claim 1 in which the compound has an average of 50 to 5000 glucopyranosyl units.

7. The compound of claim 6 in which the alkyl ether groups have from one to three carbon atoms.

8. The compound of claim 7 in which the alkyl ether groups are unsubstituted or substituted only by a single hydroxyl group.

9. The compound of claim 8 having an average of 0.1 to 0.5 pentynyl ether groups per glucopyranosyl unit.

10. A process for preparing a cellulose ether comprising 1,2,3-triazole rings; said process comprising contacting a cellulose ether having an average of 1.0 to 2.5 Ci-C₆ alkyl ether groups per glucopyranosyl unit and an average of 0.02 to 1 pentynyl ether groups per glucopyranosyl unit with a compound having an azido group.