FORM2
THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)
1. Title of the invention. - AN IMPROVED PROCESS FOR THE PREPARATION
OF ERYTHROMYCIN A

2. Applicant(s)
(a) NAME :
(b) NATIONALITY:
(c) ADDRESS :

ALEMBIC LIMITED
An Indian Company.
Alembic Campus, Alembic Road, Vadodara - 390 003, Gujarat, India.

3. PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed:

Field of the Invention
The present invention relates to an improved process for the preparation of Erythromycin A (I).

Background of the invention
Erythromycin A (I) was first discovered in 1950s. Erythromycin A and its salts are widely used in the treatment of various infections, caused by both Gram-positive and Gram-negative organisms. The product was launched commercially in 1952 under the brand name llosone (after the Philippine region of lloilo where it was originally collected from). Erythromycin was formerly also called as llotycin.
In 1981, Nobel laureate (1965 in chemistry) and Professor of Chemistry at Harvard University (Cambridge, MA) Robert B. Woodward and a large team of researchers reported the first stereo controlled asymmetric chemical synthesis of Erythromycin A. Erythromycin A (I) belongs to Macrolide class of compound and is well known for its antibiotic activity.
Generally, Erythromycin A is prepared by fermentation process. The fungus Saccharopolyspora erythaeas is the source of a number of structurally related


macrolide antibiotics known collectively as erythromycins. Among these, Erythromycin A (I) has proven to be of great importance, occupying a prominent position in medicine by virtue of its useful antibacterial activity and low toxicity (Ref: Current Pharmaceutical Design, 2000, 6, 181-223) than Erythromycin B. Erythromycin A is a key intermediate for the preparation of other semi synthetic Macrolides such as Clarithromycin, Azithromycin and Roxithromycin.
Various patent/ applications describes/claims process for the preparation of Erythromycin and Erythromycin A particularly US2823203, US2833696, US2864817, US2894943, US2812287, US 2809151, US2808363, US2806024, GB762976, GB762702, GB754030, GB754029 and GB754028. But these processes remains silent about the yield and purity of final product as most of these processes utilizes fermentation broth as starting material. We have also observe that most of the prior art process as mentioned herein above does not results a highly pure Erythromycin A with good consistent yield and impurity level.
Therefore, there is a need to develop a process for the preparation Erythromycin A which is cost effective and which gives consistent result with respect to good yield and purity.
Present inventors develop an improved process for the preparation of Erythromycin A which is not only cost effective but also gives consistent result with respect to high purity and yield of final product. This process involves the production of Erythromycin A by the conversion of erythromycin thiocyanate by utilizing a base in halogenated solvent, the improvement which comprises forming said erythromycin A and concentrating a mother liquor of the same to obtain erythromycin technical; combining said erythromycin technical back to the reaction vessel for erythromycin A production while decreasing the mol ratio of erythromycin thiocyanate.


Objects of the invention
The primary object of this invention is to provide an improved process for the preparation of Erythromycin A (I).
Other object of this invention is to provide an improved process for the preparation of amorphous Erythromycin A (I).
Another object of the invention is to provide an improved process for the preparation of highly pure Erythromycin A (I).
Another object of the invention is to provide an improved process for the preparation of Erythromycin A (I) which gives consistent result with regards to high yield and purity.
A further object of the invention is to provide an improved process for the preparation of Erythromycin A (I) which involves conversion of erythromycin thiocyanate to Erythromycin A by utilizing a base in halogenated solvent, the improvement which comprises forming said erythromycin A and concentrating a mother liquor of the same to obtain erythromycin technical; combining said erythromycin technical back to the reaction vessel for erythromycin A production while decreasing the mole ratio of erythromycin thiocyanate.
Brief description of the accompanying figures
Fig. 1 depicts the powder X-ray diffraction (XRD) pattern of Erythromycin A (I) as prepared in accordance with the present invention.
Detailed description of the invention
The present invention provides an improved process for the preparation of Erythromycin A (I) which involves conversion of Erythromycin thiocyanate to Erythromycin A by utilizing a base in halogenated solvent, the improvement which comprises forming said Erythromycin A and concentrating a mother liquor of the same to obtain Erythromycin technical; combining said Erythromycin technical back


to the reaction vessel for Erythromycin A production while decreasing the mole ratio of Erythromycin thiocyanate.
The "halogenated solvent" used herein that includes but not limited to methylene dichloride, ethylene dichloride, chloroform, carbon tetrachloride and the like or mixture thereof. The preferred solvent is methylene dichloride.
The "base" as used herein that includes but not limited to organic bases or inorganic bases such as imidazole, triethyl amine, diethyl amine, methylamine, t-butylamine, pyrrolidine, pyridine, morpholine, di-N-propylamine, n-butylamine, isopropylamine, piperidine, picoline, ammonia, alkali or alkaline earth metal hydroxide, alkali or alkaline earth metal carbonate or bicarbonate, alkali or alkaline earth metal hydrides and the like or mixture thereof. The preferred base is ammonia in the form of aq. ammonia or ammonia gas. The preferred one is aq. Ammonia.
According to present invention, Erythromycin thiocyanate is dissolved in halogenated solvent and further treated with ammonia to obtain clear solution. After pH adjustment, Erythromycin A (I) is isolated from the solution by extraction
Accordingly, Erythromycin thiocyanate is dissolved in halogenated solvent and further treated with ammonia by maintaining pH to obtain clear layers. The layers were separated. The organic layer is washed with water and separates out. The aqueous layer is washed with organic solvent particularly methylene dichloride. The all organic layers were combined and again washed with water, sodium bicarbonate and brine. Finally, the organic layer is cooled to 0°C to 10 °C and stirred for 2 to 4 hrs to obtain solid of Erythromycin A which is filtered and washed with organic solvent, particularly methylene dichloride. The filtrate i.e. mother liquor which is concentrated under vacuum to obtain Erythromycin technical. This Erythromycin technical is combined back to the reaction vessel for Erythromycin A production with decreasing the mole ratio of Erythromycin thiocyanate and the process is continued.


Erythromycin A (I) prepared in accordance with the present invention is substantially free of other forms and other impurities and avoids further purification.
Erythromycin A (I) as prepared in accordance with the present invention is crystalline in nature and characterized by powder X-ray diffraction peaks at about 5.6, 7.3, 9.3, 10.8, 12.0, 12.6 and 12.8 ±0.2 degree two-theta as shown in Fig.1.
Erythromycin technical as mentioned hereinabove may contain impure forms of Erythromycin base, Erythromycin thiocyanate or other impurities.
The mother liquor used for preparation of Erythromycin technical as mentioned hereinabove may be concentrated completely or partially.
Following is the comparable data characterized by HPLC which shows consistency of the process of present invention with regards to yield and purity of final product i.e. Erythromycin A.

Abbreviations
Ery. Thio. : - Erythromycin Thiocyanate Ery. Tech.:- Erythromycin Technical
UK:- Unknown Impurity
Ery. C: - Erythromycin C
Ery. E: - Erythromycin E
Ery. A: - Erythromycin A
Ery. B: - Erythromycin B
ND:- Not detected
Following are the advantages of the present invention:-
1) Input of starting material particularly erythromycin thiocyanate get minimized up to 8 to 10%.
2) Erythromycin A (I) as prepared by using mixture of Erythromycin thiocyanate and Erythromycin Technical in accordance with the present invention has same purity and yield compare with the Erythromycin A as prepared by using Erythromycin thiocyanate .
3) Erythromycin A (I) as prepared in accordance with the present invention is substantially free of other forms and other impurities.
4) The final product i.e. Erythromycin A (I) as prepared in accordance with the present invention does not required further purification.
5) The process of the present invention is cost effective due to utilization of only one organic solvent in reaction and work up which results easy recovery.


While the present invention has been described in terms of its specific embodiments, certain modifications and equivalents will be apparent to those skilled in the art and are intended to be included within the scope of the present invention.
The process of the present invention is described by the following examples, which are illustrative only and should not be construed so as to limit the scope of the invention in any manner.
Example 1:- Preparation of Erythromycin Base form Erythromycin thiocyanate
Erythromycin Thiocyanate (100gm) was charged with methylene dichloride (400ml)
at room temperature. Then the solution was heated up to 30-35°C. The solution was stirred for 5-10min. at 30-35°C followed by slowly addition of 25 % ammonia solution (100 ml) by maintaining pH 9 to 12 at same temperature. The reaction mixture was stirred for 5-10 min. at 30-35°C followed by the layer separation at 30-35°C to get organic layer 1 and aqueous layer. The aqueous layer was extracted with methylene dichloride (100ml) at 30-35°C. The layer was settled at 30-35°C and the organic layer 2 was separated at 30-35°C. Organic layer 1 and 2 were combined and washed with DM Water, 5% Sodium bicarbonate and DM water at 30-35°C. Then the organic layer was cooled to 0-5°C and stirred at 0-5°C for 2 hr. to get solid product of erythromycin A which was filtered under suction followed by washing with chilled methylene dichloride. The filtrate is used as mother liquor for the preparation of Erythromycin Technical which is used back to the reaction vessel for erythromycin A production. The solid was dried at 55-60°C in air dry till moisture content comes to below 2.0%. Yield: -68- 71 gm HPLC Purity: -95 to 98 %
Example 1a:- Preparation of Erythromycin Technical
Mother Liquor of methylene dichloride (450 - 550ml) from Example-1 was charged at room temperature. This mother liquor was concentrated with atmospherically recovery of methylene dichloride (recovery approx. 315 - 385 ml about 70%) at 40-


45°C till residual volume remains approx. 150ml. Then this solution was cooled to 35
- 40°C and again concentrated under vacuum at 35- 40°C till residual volume
remains approx. 35ml - 45ml (recovery approx. 85-90ml, 15 %). This concentrated
mass was cooled to 0-5°C and stirred for 2.0 hrs at same temperature to get solid
which was filtered under suction and washed with methylene dichloride. The solid
was dried at 55-60°C in air dry till LOD is NMT 5.0 % to get erythromycin technical
which is used back to the reaction vessel ( in example 2) for Erythromycin A
production.
Yield: -8.0-11.0 gm
Recovery of methylene dichloride: ~ 80 - 90%
Example 2:- Preparation of Erythromycin Base form a mixture of Erythromycin thiocyanate and Erythromycin technical
Erythromycin Thiocyanate (92gm) and Erythromycin Technical obtained from example 1a (8gm) were charged with methylene dichloride (400ml) at room temperature. Then the solution was heated up to 30-35°C. The solution was stirred for 5-10min. at 30-35°C followed by slowly addition of 25 % ammonia solution (100 ml) by maintaining pH 9 to 12 at same temperature. The reaction mixture was stirred for 5-10 min. at 30-35°C followed by the layer separation at 30-35°C to get organic layer 1 and aqueous layer. The aqueous layer was extracted with methylene dichloride (100ml) at 30-35°C. The layer was settled at 30-35°C and the organic layer 2 was separated at 30-35°C. Organic layer 1 and 2 were combined and washed with DM Water, 5% Sodium bicarbonate and DM water at 30-35°C. Then the organic layer was cooled to 0-5°C and stirred at 0-5°C for 2 hr. to get solid product of Erythromycin A which was filtered under suction followed by washing with chilled methylene dichloride. The filtrate is used as mother liquor for the preparation of Erythromycin Technical which is used back to the reaction vessel for Erythromycin A production. The solid was dried at 55-60°C in air dry till moisture content comes to below 2.0%. Yield:-68-71 gm HPLC Purity: ~ 95 to 98 %


We claim,
1. An improved process for the preparation of Erythromycin A which involves conversion of Erythromycin thiocyanate to Erythromycin A by utilizing base in halogenated solvent, the improvement which comprises forming said Erythromycin A and concentrating a mother liquor of the same to obtain Erythromycin technical; combining said Erythromycin technical back to the reaction vessel for Erythromycin A production while decreasing the mole ratio of Erythromycin thiocyanate.
2. The process according to claim 1, wherein halogenated solvent used is selected from methylene dichloride, ethylene dichloride, chloroform, carbon tetrachloride or mixture thereof.
3. The process according to claim 2, wherein halogenated solvent used is methylene dichloride.
4. The process according to claim 1, wherein base used is selected from organic bases or inorganic bases such as imidazole, triethyl amine, diethyl amine, methylamine, t-butylamine, pyrrolidine, pyridine, morpholine, di-N-propylamine, n-butylamine, isopropylamine, piperidine, picoline, ammonia, alkali or alkaline earth metal hydroxide, alkali or alkaline earth metal carbonate or bicarbonate, alkali or alkaline earth metal hydrides or mixture thereof.
5. The process according to claim 4, wherein base used is ammonia.
6. Crystalline form of Erythromycin A , characterized by powder X-ray diffraction peaks at about 5.6, 7.3, 9.3, 10.8, 12.0, 12.6 and 12.8 ±0.2 degree two-theta



ABSTRACT
The present invention relates to an improved process for the preparation of Erythromycin A which involves conversion of Erythromycin thiocyanate to Erythromycin A by utilizing base in halogenated solvent, the improvement which comprises forming said Erythromycin A and concentrating a mother liquor of the same to obtain erythromycin technical; combining said erythromycin technical back to the reaction vessel for erythromycin A production while decreasing the mole ratio of erythromycin thiocyanate.