PL178037B1 - Method of obtaining pure polyethylene glycol monoethers - Google Patents

Abstract

The method of obtaining pure poly (ethylene glycol) monoethers, characterized by that contaminated MPEG preparations are subjected to liquid chromatography on silica gel, using chloroform as eluent with a small, gradually increasing amount methanol, preferably up to 2.5%.

Description

The present invention relates to a process for the preparation of pure polyethylene glycol (MPEG) monomethyl ethers from MPEG contaminated with polyethylene glycol (PEG).

MPEG has multiple uses for biomedical purposes. They are used, inter alia, in the synthesis of peptides, modification of pharmaceuticals and proteins (enzymes). Their conjugates with biologically active agents show greater solubility, lower toxicity and immunogenicity, extended residence time in the body.

The commercial MPEG preparations used so far contain up to 20% of impurities in the form of PEG. There is a need to obtain pure MPEG as this avoids the side reactions of formation of branched or cross-linked insoluble conjugates.

Monomethyl (MPEG) ethers of poly (ethylene glycol) and poly (ethylene glycols) (PEG) as chain polymers, under ordinary conditions, in polar solvents appear in the form of a random coil. At the same time, both polymers have the same molecular weights and are characterized by an almost identical chemical structure. The end groups, the two OH (polar) groups for PEG and the OH (polar) and OCH ₃ (non-polar) groups for MPEG, are inside the coil. Therefore, both polymers do not separate under these conditions on a chromatography column packed with silica gel.

Surprisingly, it has been found that it is possible to isolate pure monofunctional products from commercial MPEG-contaminated pure monofunctional products by using the method of the invention, ie by using a suitable solvent such that both MPEG and PEG are in a "compact" bundle. In this embodiment, these polymers contain almost no solvent particles in the coil, and the end groups are pushed out of the coil.

The method of obtaining pure polyethylene glycol monoethers according to the invention is that impure MPEG preparations are subjected to liquid chromatography on silica gel using chloroform with a small, gradually increasing amount of methanol as eluent, preferably up to 2.5%.

The process of the invention produces poly (ethylene glycol) monoethers with a purity of 99%.

The purity of the separated MPEG was confirmed by thin layer chromatography (TLC) and by analysis of the1H NMR spectra of the MPEG reaction product with trifluoroacetic acid anhydride.

The following are non-limiting examples of the invention.

Example 1 A solution of 10.2 g of commercial MPEG 2000, 80% pure, in 40 ml of dry chloroform was prepared. Separation was carried out on a silica gel column (h = 20 cm). 100 ml fractions were collected. Analysis of the eluate was performed by TLC on silica gel. The developing agent was a mixture of chloroform-methanol (10: 1.5). Chromatograms were developed with iodine or Dragendorf's reagent.

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Chloroform-methanol was used as eluent. In the range of fractions 1-13, the methanol content in the mixture was gradually increased to 2.5%, and then it was kept at a constant level - 2.5% methanol (fractions 14 - 46). A 10% methanol solution was used during the elution of fractions 47-57.

Pure MPEG 2000 (1 TLC spot) was present in fractions 6-46. Fractions 48-51 contained a mixture of 2 products (MPEG 2000 + PeG) - 2 TLC spots, while fractions 52 57 contained mainly PEG (2 TLC spots). The isolated products were purified by precipitation with diethyl ether from the chloroform solution.

Received:

3.5 g pure MPEG 2000 (34.3% yield; 99% purity),

5.2 g of MPEG + PEG mixture (51.0% yield; about 60% purity),

0.9 g of product consisting mainly of pEg (8.8% yield; approx. 20% MPEG).

Example II. A solution of 10.2 g of commercial MPEG 5000 (90% pure) in 40 ml of dry chloroform was prepared. The procedure of Example 1 was continued. A mixture of chloroform - methanol (5: 1) was used to develop the TLC chromatograms.

Chloroform-methanol was also used as an eluent. In the range of fractions 1-20, the methanol content in the mixture was gradually increased to 2%, and then it was kept at a constant level (2% methanol) - fractions 21-51. In the following fractions 52-89, the methanol concentration was gradually increased to 10%.

Pure MPEG 5000 (1 TLC spot) was present in fractions 23-61 and the other product collected (2 TLC spots) was present in fractions 86-89. The isolated products were purified as in example 1.

Received:

9.0 g MPEG 5000 (88.2% yield; 99% purity),

0.4 g of a mixture of 2 products (3.9% yield).

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Publishing Department of the UP RP. Circulation of 70 copies. Price PLN 2.00.

Claims (1)

Patent claim A method for the preparation of pure poly (ethylene glycol) monoethers, characterized in that impure MPEG preparations are subjected to liquid chromatography on silica gel, using chloroform as the eluent with a small, gradually increasing amount of methanol, preferably up to 2.5%.