FIELD OF THE INVENTION

The present invention relates to a robust, economically feasible and environmentally friendly manufacturing process of Clarithromycin, Formula (I) with controlled levels of side products. A total of eight impurities are characterized in Clarithromycin finished product based on HPLC analysis. The Clarithromycin manufactured by following the present invention is having a total impurities, (known & unknown) to the level of less than 3.0 % by HPLC. Another aspect of the present invention relates to producing Clarithromycin Polymorph-II as revealed by XRD, the said polymorphic Form II is obtained by a mixture of halogenated and protic solvent.

Formula (I)

Clarithromycin

BACKGROUND OF THE INVENTION

Erythromycin A is known to be a useful macrolide antibiotic having a strong activity against Gram-positive bacteria, this compound has an undesirable property that it loses rapidly the antibacterial activity by the acid in stomach when administered orally, where-

upon its blood concentration remains at a low level. 6-0-Alkyl derivatives of Erythromycin- A are well known as an useful antibacterial agents. 6-O-Methyl-Erythromycin-A (Clarithromycin) and a pharmaceutically acceptable salt is a potent macrolide antibiotic as reported in US Patent No. 4,331 ,803. Clarithromycin is stable in acidic medium and also remarkable in vivo activity and has a strong antibacterial property against Gram-positive bacteria compared to Erythromycin- A. This compound shows excellent effect for the treatment of infections by oral administration.

A number of synthetic processes have been reported for preparing 6-O-alkyl erythromycin. US Patent No. 4,331 ,803 discloses a method for the preparation of Clarithromycin by methylating 6-OH group of 2'-O-3'-N-benzyloxycarbonyl erythromycin

Formula (III)

2 ¹ ,3'-O-Protected Erythromycin

Methylation of 6-OH group of the 2',3'-benzyloxycarbonyl erythromycin was carried out using methyl iodide in the presence of a suitable base in a solvent. Clarithromycin was obtained from the compound after removing benzyloxycarbonyl group by hydrogenolysis and then subjecting to the reductive methylation in the presence of excess amount of farmaldehyde.

Clarithromycin can also be synthesized by the methylation of 6-OH position of Erythromycin-A-9-Oxime

Formula (II)

Erythromycin-9-Oxime

Synthesis of Clarithromycin using 9-oxime or its derivatives are well reported in US Patent Nos. 5,274,085; 4,680,386; 4,668,776; 4,670,549 and 4,672,109. In case of Erythromycin-9-Oxime derivatives, the oxime is protected before methylation step with 2- alkenyl group (US Patent Nos. 4,670,549; 4,668,776) or benzyl group (US Patent Nos. 4,680,386 and 4,670,549). However, it has been reported (Ref. Journal of Antibiotics 46, No. 6, Page No. 647, year 1993) that when the Erythromycin-A-9-Oxime is protected by trimethylsilyl group, which is very unstable under basic condition pose potential impurities formation during methylation. There are some methods reported in US Patent Nos., e.g. , 4,680,386; 4,670,549 and US Patent No. 4,311,803 for the synthesis of Clarithromycin by using chlorobenzyloxycarbonyl group for protection at 2' and 3' function of of Erythromycin-A-9-Oxime derivatives.

For the protection of 2'-OH group (US Patent No. 4,311 ,803) requires large amounts of benzyl chloroformate which poses problems in handling because of its severe irritating and toxic properties. This protection step also leads to the formation of 3' -N- demethylation, which requires an additional re-methylation step. The de-protection of chlorobenzyloxy carbonyl group leads to the formation of undesired side products.

In earlier reported processes, e.g. , US Patent No. 4,990,602; EP 0,272,110 Al where the methylation has been done on Erythromycin-A-9-Oxime derivatives by the protection of 2' and 4" hydroxyl groups using DMSO and THF as a solvent at 0° to 5 ⁰ C or at room temperature, smooth methylation takes place with less side product formation. However, by using the above methylation processes the formation of 6, 11-O-dimethyl erythromycin- A (Compound- A) is always more than 1.0 % in Clarithromycin. Hence, there is a need for an efficient methylation process for the production of Clarithromycin with lesser amount of 6,11-O-dimethyl erythromycin-A than reported previously.

SUMMARY OF THE INVENTION

The present invention discloses the robust manufacturing process for the production of Clarithromycin having less than 1.0 % of 6, 11-O-dimethyl erythromycin-A, a potential side product in Clarithromycin (Compound A). The manufacturing process of Clarithromycin effects from Erythromycin A. Erythromycin-A is reacted with hydroxylamine hydrochloride in presence of caustic solution and acetic acid to get Erythromycin-A-9-Oxime in 85 to 90 % yield. The Erythromycin-A-9-Oxime is treated with 2-methoxy propene and hexamethyl disilazane (HMDS) in dichloromethane to obtain 2',4"-disilyated-erythromycin-A-9-methoxypropyl oxime (CAM-III). A total of eight impurities have been characterized in the finished product with help of HPLC impurity profile.

In one embodiment CAM-III is treated with methyl iodide in presence of potassium hydroxide powder using DMSO-diethyl ether (1 : 1) solvent mixture at room temperature for 90 minutes to produce 2 ^> ,4"-disilylated-clarithromycin-9-methoxypropyl oxime (CAM- IV). Further CAM-IV, i.e. , methylated product is treated with 98 % formic acid in Isopropyl alcohol-Water mixture (1: 1) followed by treatment with sodium metabisulphite in Isopropyl alcohol-Water mixture (1 : 1) to get Clarithromycin. The process reported in the present invention provides oxime free Clarithromycin with total impurities less than 3.0 % having less than 1.0 % compound A.

In the next embodiment a total of 8 impurities are also identified which are associated with the purified Clarithromycin.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a HPLC profile of the Clarithromycin and 6,11-Di-O-methyleryhtromycin A using 1 % standard preparation.

Figure 2 is a HPLC profile of impurities detected from the isolated Clarithromycin

DETAILED DESCRIPTION OF THE INVENTION

6-O-Methyl-erythromycin (Clarithromycin) being a potent inhibitor of gram positive bacteria, a systematic study for its large scale production with high purity is under taken. This resulted in controlled methylation of 6-OH group of 2', 4"-OH protected erythromycin. The present invention relates to the production of a better purity level of Clarithromycin (Formula I)

Formula (I)

In the first embodiment Clarithromycin obtained by this method is having less than 1.0 % of 6,11-O-dimethyl erythromycin-A, a potential side product. The present invention is directed towards the industrial process of Clarithromycin associated with controlled level

of side products. A total of eight impurities have been characterized in the finished product by HPLC analysis.

According to one embodiment the present invention, Clarithromycin Form II is prepared according to the following synthetic reaction scheme:

(a) Reaction of Erythromycin-A with hydroxylamine hydrochloride (Erythtromycin-A-9- Oxime)

Hydroxylamine hydrochloride is treated with caustic flakes in aqueous isopropyl alcohol at 10° to 2O ⁰ C to generate the hydroxylamine base in solution followed by addition of Erythromycin A.

NhLOH HCI isopropyl Alcohol

Erythromycin - A Erythromycin - A - 9 - Oxime

The pH of the reaction mixture is adjusted between 6.5 to 7.0 by careful slow addition of glacial acetic acid. To the stirred reaction mixture Erythromycin -A is added and stirred for further 28 hours at 55 ⁰ C. After completion of reaction, the mixture is neutralized by adding aqueous ammonia and water and stirring is continued for 1 hour. Additional volume of water is added to the mixture to get the precipitate of Erythromycin- A-9-Oxime in 85 to 90 % yield.

(b) Protection of Oxime, T and 4"-OH functions of Erythromycin-A-9-Oxime

Erythromycin-A-9-Oxime obtained by the above process is treated with 2-methoxy propene and pyridine hydrochloride in dichlorome thane. The reaction mixture is stirred for 6 hours at 8° to 12 ⁰ C followed by the addition of hexamethyldisilazane (HMDS)

Stirring is continued for about 15 hours at an ambient temperature. After complete protection of oxime and 2' & 4" -OH functions of Erythromycin - A-9-oxime, the fully protected stuff is isolated by usual work up and filtration method. After vacuum drying CAM-III is obtained in more than 90 % yield. Melting Point = 125° - 127 ⁰ C.

(c) Methylation of 6-OH group and subsequent deprotection of oxime, 2' & 4'-OH functions of CAM-III

2',4"-O-Bis(trimethylsilyl)-erythromycin-A-9-[O-(l-methox ymethyl ethyl)oxime] is treated with methyl iodide in presence of potassium hydroxide powder in a mixture of suitable solvent system to generate 2',4"-disilylated-Clarithromycin-9-methoxypropyl oxime (CAM-IV). CAM-IV on subsequent hydrolysis produces Clarithromycin-9-Oxime as shown below:

(CAM-IN) Clarithromycin-9-Oxime

Suitable solvent system for this reaction include, but are not limited to a mixture of DMSO and diethyl ether. The volume ratio of diethyl ether in DMSO is between about 40 to about 60 % and preferably about 50 % . This reaction is carried out typically at temperatures between about 10° to 6O ⁰ C, preferably between about 15° to about 25 ⁰ C, with reaction times being between about 40 minutes to 2 hours, preferably between about 80 to 100 minutes.

The ratio of methyl iodide and potassium hydroxide powder is very critical, as otherwise it leads to many unwanted side products. After exhaustive experimentation it is observed that 1.75 mole of methyl iodide and 1.20 moles of potassium hydroxide affords final product with controlled impurities after giving one or two re-crystallizations. The advantage of the methylation process of the present invention using DMSO-Diethyl ether is that the ether layer gets separated after quenching the reaction mixture with 40% dimethylamine solution. The ether layer contains exclusively the methylated product and the DMSO layer contains impurities, which is taken for recovery of DMSO (solvent). Further CAM-IV, i.e., methylated product is treated with 98 % formic acid in 1 : 1 volume ratio of Isopropyl alcohol and water for 30 minutes at 25° to 35 ⁰ C to get Clarithromycin-9- Oxime.

(d) Conversion of Clarithromycin-9-Oxime to Clarithromycin

Clarithromycin-9-Oxime is further treated with sodium metabisulphite in Isopropyl alcohol- Water (1 : 1 , v/v) for 6 to 8 hours at 80 ⁰ C to produce Clarithromycin.

Formula (I)

Clarithromycιn-9-Oxιme Clarithromycin

The deoximation of Clarithromycin-9-Oxime as reported in US Patent No. 6,617,436 to get essentially Oxime free Clarithromycin involves the deoximating step using two fold use of deoximating agent, i.e. , sodium metabisulphite which is large excess (i.e. 7.0 moles with respect to Clarithromycin-9-Oxime). The process reported in the present invention involves the use of sodium metabisulphite 1 to 3 moles preferably 2.50 moles with respect to Clarithromycin-9-Oxime to obtain Clarithromycin which is Oxime free (detected by HPLC).

The Clarithromycin obtained using the above process after purification using Isopropyl alcohol-Chloroform as solvent mixture has the following levels of the known (characterized) impurities with total impurities less than 3.0 % by HPLC analysis and Compound-A less than 1.0 % (quantitative amount in Clarithromycin Figure 1).

The content of 6,11-di-O-methyleryhtromycin A in isolated Clarithromycin is calculated using the formula,

x x Response factor x 100

As concentration of test solution

where AUM is peak area of 6,11-di-O-methylerythromycin-A (Compound A) in test solution, As is peak area of Clarithromycin in 1 % Standard preparation and Cs is concentration of Clarithromycin in 1 % Standard preparation.

Concentrations: Cone, of Clarithromycin = 20.16 ppm, cone, of Clarithromycin sample = 2008 ppm, Assay of Clarithromycin = 100 %, Response factor of 6,11-di-O- methylerythromycin A = 0.68. The 6,11-di-O-methyleryhtromycin A using the above formula is found 0.510 % in Clarithromycin (Figure 1).

These impurities has been identified by comparing each and every impurity by authentic samples using HPLC analysis. Similar retention times of these impurities with their corresponding standard samples confirmed their presence in the Clarithromycin.

An HPLC method is developed for determination of impurities associated with the isolated Clarithromycin. The said impurities comprises (Figure 2), e.g. , Clarithromycin impurity I (3-O-decladinosyl-6-O-methylerythromycin-A, RT = 8.117), Erythromycin-A (E-base, RT = 11.542). Clarithromycin impurity J (Erythromycin A-9 (E)-Oxime, RT = 12.658), Z-Oxime-(6-O-Methylerythromycin A-9 (Z)-Oxime, RT = 15.592), 3'-N- DMMEO (S'-N-dimethyl-ό-O-methylerythromycin A-9 (E)-Oxime, RT = 17.600), Clarithromycin impurity C (6-O-Methylerythromycin A-9 (E)-Oxime, RT = 19.117), Clarithromycin impurity E (6, 11-di-O-methylerythromycin, RT = 29.500), 6-0-MEMMO {6-O-methylerythromycin A-9-N-[O-(l-methoxy-l-methyl-l-methyletyl)Oxime-RT = 42.775]} and for unknown impurities in Clarithromycin and is further validated for precision, accuracy, ruggedness, linearity and range.

Following is the list of impurities characterized with their levels analyzed in Clarithromycin by HPLC profile,

1. 6-O-Methyl erythromycin A-9-(Z)-Oxime (Result = Not Detected)

2. 6, 11-di-O-methyl erythromycin-A (Result = Not more than 1.0 %)

3. 6-O-Methylerythromycin-A-9 (E)-Oxime (Result = Not more than 0.5 %)

4. 3-O-decladinosyl-6-O-methyl erythromycin-A (Result = Not Detected)

5. Erythromycin-A-9 (E)-Oxime (Result = Not Detected)

6. Erythromycin A (E-base) (Result = Not more than 0.5 %)

7. 3'-N-demethyl-6-O-methyl erythromycin A-9- (E)-Oxime (Result = Not Detected)

8. 6-O-Methyl erythromycin-A-9-N [O-(l-methoxy-l-methylethyl) Oxime] (Result = Not more than 0.5 %)

9. Total impurities (Known + Unknown) (Result = Not more than 3.0%)

The isolated Clarithromycin having the above associated impurities are identified by their respective retention time using same solvents and gradient keeping other parameter constant. The Clarithromycin reported in the present invention after crystallizing in

Isopropyl alcohol-Chloroform mixture has the characteristic XRD which is similar to XRD pattern polymorphic Form II, identical to reported in WO 98/04574.

Examples

The following examples illustrate the invention, but is not limiting thereof,

EXAMPLE 1

Erythromycin-A-9-Oxime

To a solution of 201 Ltr water in 561 Kg isopropyl alcohol is added 282 Kg (4057 mol) of hydroxyl amine hydrochloride under stirring and the reaction mixture is brought to 10 to 20 ⁰ C. Caustic flakes (162 Kg, 4050 mol) is added slowly to the reaction mixture by keeping temperature between 10° to 20 ⁰ C. After 15 minutes of completion of addition, pH of reaction mixture is adjusted to 6.5 to 7.0 by the slow addition of glacial acetic acid (96 Ltr, 100.8 Kg, 1678.6 mole). To the stirred reaction mass is added 300 Kg (408.8 mole) of Erythromycin-A base and reaction mixture is stirred at 55° C for 28 hours. After completion of the reaction, mixture is brought to ambient temperature and to it a mixture of ammonia solution (270 Kg) and water (600 Ltr) is added within 1 hour followed by 3000 Ltr of fresh water in next two hours and stirred the reaction mass for further 1 hour. White solid product obtained is centrifuged, wet cake is washed with water and dried at 6O ⁰ C for 12 hours to give 270 Kg of erythromycin-A Oxime. Melting point = 156° to 158°C.

EXAMPLE 2

2',4"-O-Bis(trimethylsilyl)-erythro?nycin-A-9[O-(l-methox y-l-methyl ethyl)oxime

To a solution of 80 Kg (106.8 mole) of Erythromycin-A-9-Oxime in 400 Ltr of dichloromethane is added 38.50 Kg (534 mole) of 2-methoxy propene at 10 ⁰ C temperature 19.25 Kg (166.6 mole) of pyridine hydrochloride is added under stirring and the reaction mixture is stirred at 8 to 12° C for 6 hours then to it is added 19.30 Kg (119.5 mole) of HMDS and stirring is continued for 12 to 15 hours at 15° to 18°C temperature. After completion of reaction, 400 Ltr of saturated aqueous sodium carbonate solution is added and the mixture is stirred thoroughly at room temperature. Aqueous layer is further extracted with fresh DCM (100 Ltr). Both DCM extracts are mixed together and washed

with water (200 Ltr) followed by brine solution (200 Ltr). The solvent is evaporated under reduced pressure. To the obtained crude solid mass is charged isopropyl alcohol (240 Ltr) and distilled out 80 Ltr of isopropyl alcohol. To the reaction mixture 160 Ltr of water is charged and stirring continued at room temperature for 1 hour. Solid crystalline product obtained is centrifuged and dried at 60° to 65 ⁰ C for 8 hours under vacuum to give 85 Kg of title compound. Melting point = 125° to 126°C. HPLC Purity = More than 90 % .

EXAMPLE 3

Clarithromycin-9- Oxime

To a solution of 80 Kg (82.98 mole) of 2',4"-O-bis(trimethylsilyl)-erythromycin-A- 9-[O-(l-methoxy methyl ethyl)Oxime] in 1200 Ltr of a mixture of dimethyl sulfoxide and diethylether (1 : 1) are added methyl iodide (20.62 Kg, 145.2 mole) and 6.48 Kg (98.35 mole) of 85 % potassium hydroxide powder and the reaction mixture is stirred for 90 minutes at room temperature. To the reaction mass is added 53 Kg of 40 % dimethylamine solution and stirring is continued for 1 hour diethylether layer is separated and DMSO layer is further extracted with fresh diethylether (200 Ltr). Combined ether layer is washed with water and concentrated in vacuum. To the obtained semi solid mass 330 Ltr of isopropyl alcohol is charged and then distilled out 165 Ltr of isopropyl alcohol. To the obtained slurry 165 Ltr of water and 21.71 Kg formic acid (99%) are added and the mixture is stirred at room temperature for 30 minutes. 622 Ltr of water is added to the reaction mixture and pH is adjusted between 10.5 and 11.5 with 25 % aqueous sodium hydroxide solution. Solid compound obtained is centrifuged and wet cake is kept as such for further reaction on the basis of moisture content. Wet weight = 95 Kg, Moisture Content = 33 %, Dried weight = 62 Kg

EXAMPLE 4

6-O-Methyl erythromycin- A (Clarithromycin)

62 Kg of 6-O-Methyl erythromycin-9-Oxime is charged into a mixture of 434 Ltr of isopropyl alcohol and water (1: 1) and to it is added 38.80 Kg of sodium metabisulphite (203 mole) and then the mixture is heated to reflux for 6 to 8 hours. To the reaction mixture is charged water (620 Ltr) at ambient temperature and then the mixture is adjusted to pH

about 10.5 to 11.5 by adding 25% aqueous sodium hydroxide solution and stirred for further 1 hour. White solid crude product is centrifuged, washed with water (300 Ltr), dried at 65° to 75 ⁰ C for 8 hours to give 40 Kg of crude Clarithromycin which on re- crystallization with chloroform isopropyl alcohol mixture provided 20 Kg of Clarithromycin (Form II).