CZ64296A3 - Process for preparing 9-(2-hydroxy)ethoxymethyl guanine - Google Patents

Abstract

The present invention relates to a process for the preparation of 9- (2-hydroxy) ethoxymethyl-guanine, of acyclovir of formula I, wherein β 2 -formylguanine is present Formula 3 is alkylated with 2-oxa-1,4-diacyloxybutane a the resulting N 2 -formyl-9- (2-acyloxy) ethoxymethylguanine of formula 4 wherein R is hydrogen, alkyl of 1 to 4 atoms carbon or phenyl is hydrolyzed, the resulting acyclovir is isolated and optionally purifies.

Description

Technical field

The invention relates to an improved process for the preparation of 9- (2-hydroxy) ethoxymethylguanine, also referred to as acyclovir.

ΐ

BACKGROUND OF THE INVENTION

Acyclovir is widely used as an antiviral agent for therapeutic effects. The process for its preparation has been described, for example, in Belgian patent specification 833,006. The process of this patent is based on guanine which is first subjected to trimethylsilylation at three positions, namely at the amino group at position 2 and at positions 6 and 9. The resulting silylated intermediate is then treated with 2-benzoyloxyethoxymethyl chloride to give 9- (2-benzoyloxy) ethoxymethylguanine after deprotection of the nitrogen atoms at the 2- and 6-positions, then acyclovir is isolated. A large excess of silylating agent has to be used in the process, so that the process is expensive and, moreover, waste problems arise, the product is usually contaminated with the 7-substituted isomer in an amount that is unacceptable for pharmaceutical use.

In the British-Pa-Te-Tumble State. Another method in which the amino group at the 2-position is protected by acylation is described. They are mentioned as acylating groups in the claims; however, only N, 9-ciacetylguanine was reacted with 2-oxa-1,4-diacetoxybutane to form N-acetyl-9- (acetyl, propionyl, butyryl and benzoyl). 2-acetoxy) ethoxymethylguaninu which is hydrolyzed to produce the final acyclovir, the yield could be satisfactory if it could not produce large quantities of 7-isomer, which reduces the purity of the resulting produktu.vzhledem ^that: is produced only in %, so that the product needs to be further purified in a costly manner.

U.S. Pat. No. 4,146,671 proposes a process for preparing guanine derivatives, including acyclovir, by reacting a diacylated guanine with a 2-oxy- or 2-thiabutane diol diester followed by hydrolysis of the reaction product.

V * E? No. 532,878 describes a process for preparing acyclovir starting from guanosine, 2-oxa-cutanediol diester and acetic anhydride followed by hydrolysis. The desired product is obtained together with the 7-isomer, which must then be converted to the desired 9-isomer.

SUMMARY OF THE INVENTION

It has now been unexpectedly found that the acyclovir formula

can be obtained in high yield in the absence of the undesired 7-isomer by alkylation directly in the 9-position of the purine ring by treatment of N-formylguanine with 2-oxa-1,4-diacetoxybutane and the resulting N-formyl -9- (2-acyloxy) ethoxymethylguanine is hydrolyzed.

The starting N-formylguanine is described in the literature, for example in Shapiro, Biochemistry, 8, 231-245,

1969. According to this publication, the substance can be prepared by treating a glyoxal-guanine addition product with sodium periodate and / or periodic acid. * The process proceeds with a high yield, although -uvedenou látku- can also be obtained in another manner, for example '' · ^'r' oxidation of the adduct. the product of glyoxal and guanine with peracetic acid, hydrogen peroxide or lead acetate by direct formylation of guanine with formic acid, optionally in the presence of a solvent such as dimethylformamide or dimethylsulfoxide and optionally in the presence of decyclohexylcarbodiimide.

by direct formylation of guanine with formylacetic anhydride, optionally in a solvent such as dimethylformamide, dimethylsulfoxide, hexamethylphosphoric triamide or formic acid.

Whichever method is used for the preparation of N-formylguanine, the subsequent reaction of this with 2-oxa-1,4-ciacetoxybutane yields above 9C% and, importantly, formation of only traces of the 7-isomer to give N -formyl-9- (2-acetoxy) ethoxymethylguanine, which is then deacylated in a single step with an aqueous alkali metal hydroxide solution or is first deformylated in an acidic medium and then subjected to deacylation by hydrolysis with an alkali metal hydroxide. The process of the invention is summarized in the following reaction scheme.

° s X u — υ

In the above reaction scheme R is hydrogen, alkyl of 1 to 4 carbon atoms therefrom phenyl «Dici vóuixc no. It is possible to isolate in high yield, ^so: that the guanine of Formula 1 is suspended in water, an aqueous solution of glyoxal and a mixture The mixture was heated at 80 ° C for 4 hours. This procedure has been described in R. Shapiro and J, Kachmann, Biochemistry, 5, 2799, 1966. The diol of formula 2 can then be oxidized to the naphthyl derivative of formula 3 in very good yield using a stoichiometric amount. sodium periodate in water while maintaining a pH in the range of 1.3 to 2.2.

The N-formguanine of formula 3, which can also be obtained by direct formylation of guanine, as mentioned above, can then be subjected to an alkylation reaction to give a compound of formula 4 alkylated at the 9-position nitrogen in high yield without formation of the alkylated product. in position 7 in larger quantities. From the compound of formula 4, acyclovir of formula I can be obtained by hydrolysis of an aqueous sodium hydroxide solution in a very high yield.

Accordingly, the present invention provides a process by which the desired product of formula (I) can be prepared in a very satisfactory yield, higher than in the prior art, and most importantly, without producing a larger amount of 7-alkylated by-product.

The acyclovir thus obtained can be further purified in the final purification step of the process of the invention to obtain substantially guanine-free acyclovir. The resulting product is then obtained in highly pure form.

It has been shown that by eluting an aqueous basic solution of acyclovir from a strongly anion exchange resin, the desired end product can be obtained in a substantially guanine-free form.

Thus, the purification step of the process according to the invention consists in:

a) Acyclovir is dissolved in an aqueous basic solution and diluted with water.

(b) the dilute solution obtained in step (a) is applied to a strong aniorite ion exchange resin column using a resin to acyclovir weight ratio of 2 to 1.5;

c) eluting the column with the solution at a flow rate of 200 to 300 ml / h of the eluent,

d) eluting the acyclovir with an eluting agent consisting of a mixture of lower alcohol and an aqueous base solution in a volume ratio of 0.8 to 1.2, the ratio of the eluent volume to the amount of acyclovir being in the range of 15: 1 to 20: 1 (1 / kg) at the flow rate indicated in step c) to give the eluate,

e). from the eluate obtained in step d), the acyclovite is isolated.

Anionic exchange resins include basic type resins consisting of polymers of varying degrees of crosslinking and bearing quaternary ammonium groups. The resins used in the process of the invention are strongly basic resins.

The strongly basic type resins include dextrans, agarose, cellulose, divinylbenzene, all of which may carry quaternary ammonium groups.

Resins of this type are commonly sold under the names

R R R R

Amberlite, Dowex, Sephacel Sephadex and the like.

R R

Preferred materials are Amberlite IRA-400, Relite 3A and IMA.C HP-441. *

Chromatography is carried out on the resin using the basic form of the resin.

The elution of the resulting product was carried out at room temperature.

The basic aqueous solution in step a) is an alkali metal hydroxide such as lithium, sodium or potassium hydroxide. The concentration of the base is in the range of 5 to 15%, preferably 10% sodium hydroxide solution.

The preferred resin to acyclovir weight ratio is 1.75. The preferred flow rate of the eluent is 250 ml / h.

The lower alcohol in step (d) may be methyl alcohol, ethyl alcohol or propyl alcohol. The solution of the base in water in step d) consists of an alkali metal hydroxide in a molar concentration of 0.3 to 1.2 M. It is preferred to use methanol and 1 M sodium hydroxide solution in a volume ratio of 1: 1.

The ratio by volume of eluent to the amount by weight of acyclovir is preferably 17.5 (1 / kg).

Isolation of the resulting product from the eluate of step e) is carried out in a conventional manner. Preferably, acyclovir is precipitated by acidifying the eluate with the appropriate acid.

The resulting product thus obtained contains guanine in an amount of less than 0.1%.

When purifying the resulting product by the method of the invention, the acyclovir obtained is 3 to 4 times cleaner than the purest commercially available products.

The above-mentioned very pure form of acyclovir also forms part of the invention.

The final purification process mentioned in the last step of the process according to the invention can be included in any known process for the production of acyclovir. For example, the aforementioned processes of BE 833 006 and GB 1 567 671 result in a final product containing 1 to 3% guanine, which is an unacceptable amount since the US Pharmacopoeia permits an upper limit of 0.7%.

Thus, a method for purifying acyclovir by the novel process is. also part of the invention.

’Ί

The following examples illustrate the invention.

DETAILED DESCRIPTION OF THE INVENTION

Example 1. ,. '

(a) Glyoxalguanine (2)

100 g, 0.662 mol of guanine, 800 ml of water and 150 ml of an aqueous solution of glyoxal containing 50% by weight. 1.32 moles of this material were mixed at room temperature in a round-bottomed flask with a volume of 0.25 ml. with a reflux condenser, a thermometer and a magnetic stirrer, the mixture is heated at 80 ° C for 4 hours, then gradually cooled to 5 ° C, filtered and the solid washed with water. After drying under vacuum to constant weight, 136 g of product are obtained in 98% yield, the purity of which is greater than 98% by HPLC analysis.

¹ 2

(b) N-formylguanine (3)

A suspension of 100 g (0.478 mol) of glyoxalguanine in 800 ml of water is brought to pH 1.8-2.2 by adding 6 ml of phosphoric acid and then mixed with 107.4 g (0.502 mol) of periodate. with mechanical stirring and maintaining the temperature at 30 ° C using a water bath, while continuously monitoring the pH to be maintained in the range of 1.8 to 2.2. The reaction is constantly slightly exothermic until complete, which lasts approximately 2 hours after the addition of the oxidizing agent. After this time, the reaction mixture was cooled to 5 ° C, filtered, washed with water and dried. Yield: 82 g of formylguanine (96%), HPLC purity > 98%.

c) N-formyl-9- (acetoxy) ethoxymethylguanine (4, R = CH 2)

100 g, 0.559 mol of formylguanine of formula 3, 300 g, 1.705 mol of 2-oxa-1,4-diacetoxybutane and 2 g, 0.0105 mol of p-toluenesulfonic acid are placed in a round-bottomed flask with - 500 ml capacity in an oil bath, equipped with a thermometer and a distillation apparatus. The mixture is heated under a vacuum of 4 to 5.3 kPa until an internal temperature of 113 to 122 ° C is reached within one hour. the acetic acid formed is removed by distillation. The mixture was then cooled to 50-60 ° C and diluted with 150 ml of acetone, n-butyl alcohol or ethyl acetate, cooled to 0-5 ° C, filtered and the solid dried under vacuum at 60-70 ° C to give a solid. in 90% yield, 148.3 g of the product of formula 4 in which R is methyl. Elemental analysis and spectroscopic values confirm the assumed structure of the product.

d) Acyclovir (I) g, 0.220 mol of the product of formula 4 in which R is methyl is dispersed in 650 ml of a 5% NaOH solution and checked for complete dissolution of the solid. After stirring for 12 hours, the mixture was neutralized to pH 5-6 by addition of aqueous hydrochloric acid. The mixture is cooled to 20-25 ° C, the solid is filtered off and washed with 400 ml of deionized water. After drying under vacuum at 60-70 ° C, 46.1 g of the resulting acyclovir of formula I are obtained in 93% yield.

Example 2

(a) 9- (2-acetoxy) ethoxymethylguanine (6);

300 ml, 95% ethanol, 29.5 g, 0.1 mol of intermediate 4 and 40.4 g, 0.4 mol of triethylamine are placed in a 500 ml round bottom flask equipped with a thermometer, stirrer and reflux condenser. . The mixture was refluxed for 5 hours, then adjusted to pH 5-6 by addition of aqueous hydrochloric acid, cooled to 15-20 ° C, filtered and washed with 200 ml deionized water. 22.8 g of the product of formula 6 are obtained in a yield of 85%.

5) '' '' Acyclic's ......- ......____________________

Intermediate 6 (26.7 g, 0.1 mol) was treated with 5% sodium hydroxide as described in Example 1 (d). In this way, the resulting acyclovir is obtained in substantially quantitative yield.

Example 3

The procedure of Example 1 was repeated except that a corresponding amount of 2-oxo-1 was used in place of the 2-oxa-1,4-dimethoxybutanate of the alkyl and N-formguanine. 4-diformyloxybutane or 2-oxa-1,4-dibenzoyloxybutane. The corresponding intermediates of formula 4 in which R represents a hydrogen atom or a phenyl are obtained in substantially the same yield as the intermediate in Example 1c, V and the intermediates. Yippee. then the resulting acyclovir can be easily obtained by the method of Example 1d).

.Example 4

37.5 g, 125 ml (d = 0.7) of the strongly basic Amberlite IRA-400 resin are suspended in deionized water and loaded onto a 4 cm diameter and 40 cm high chromatography column. After the usual column loading and conventional recovery procedure consisting of sequential elution or 2''-NaOH, '2'M HCl; The solution obtained by dissolving 50 g of acyclovir in 100 ml of a 10% NaOH solution and diluted with water to 200 ml is applied to the column with 2 M HaOH and distilled water until neutral. The resulting product is eluted at a flow rate of 250 ml / h (4.2 ml / min). After passing this solution, the column is washed at the same rate using 900 ml of a 1: 1 v / v mixture of methanol and 1 M NaOH. The eluate obtained is adjusted to pH 5-6 with aqueous HCl, the precipitated solid is filtered off, washed with water and dried. 45 g of guanine-free acyclovir are obtained in a yield of 90%.

Represented by:

Claims (5)

PATENT 'CLAIMS A process for the preparation of 9- (2-hydroxy) ethoxymethylguanine, acyclovir of formula I Characterized in that N-formylguanine of formula 3 is subjected to alkylation with 2-oxa-1,4-diacyloxybutane and the resulting N-formyl-9- (2-acyloxy) ethoxymethylguanine of formula 4 in which R represents a hydrogen atom , alkyl of 1 to 4 carbon atoms or phenyl is hydrolyzed according to the scheme: 0 = ^ s 2. A process according to claim 1 wherein the intermediate of formula 4 is simultaneously deformylated and O-deacylated by treatment with a dilute aqueous sodium hydroxide solution. 3. The process of claim 1 wherein the intermediate of formula 4 is first deformylated by treatment with triethylamines in ethanol and the resulting 9- (2-acyloxy) ethoxymethylguanine is then hydrolyzed to acyclovil with dilute aqueous sodium hydroxide solution. A process according to claim 1, characterized in that N-formylguanine is alkylated prepared by direct formylation of guanine with formic acid or fummylacetic anhydride. 5. The process of claim 1 wherein the resulting acyclovir is purified a) by dissolving acyclovir in an aqueous basic solution and diluting the resulting solution with water, (b) the dilute solution of step (a) is applied to a strong anion exchange column at a resin to acyclovir weight ratio of 2 to 1.5; (c) the column is eluted at a flow rate of .200 to 300 ml / h; (d) the acyclovir is eluted with a mixture of a lower alcohol and a base in water solution in a volume ratio of 0.8 to 1.2, the volume ratio of eluent to the amount of acyclovir being in the range of 15: 1 to 20: 1 1 / kg at the same flow rate as in step c) to give an eluate, e) acyclovir is isolated from the eluate of step d). 5. A process according to claim 5, characterized in that 9- (2-hydroxy) ethoxymethyl-guaniri, although lovir, is substantially free of guanine. 7_. Method according to claim 5, "you _r considerable u_ r a c s. characterized in that 9- (2-hydroxy) ethoxymethylguanine, acyclovir is obtained, containing less than or equal to 9% by weight. 0, 1 'guanine. .............. 'Represents;