DESC:Field of Invention:
The present invention is in field of process for synthesis of tildipirosin. More particularly, the present invention provides a process for the preparation of amorphous Tildipirosin.

Background of Invention:
Tildipirosin is an antimicrobial drug. It is a macrolide compound having chemical name as 20-Deoxo-23-deoxy-5-O-[3,6-dideoxy-3-(dimethylamino)-ß-D-glucopyranosyl]-20,23-di-1-piperidinyltylonolide as represented by Formula I.

Formula I
In view of its importance, synthesis of Tildipirosin is gaining momentum. Making a quality product with due care safety, cost, consistency and yield is a challenge in API pharmaceutical industries.

Few processes for synthesis of tildipirosin have been disclosed in CN104497082, CN103554203, CN106046086 and CN109721633.

The process as disclosed in CN104497082 uses 23-hydroxy-20-piperidinyl-5-O-mycaminoseyl-tylolactones as starting material.

CN103554203 discloses an amorphous crystalline form of tildipirosin, which has good stability and bioavailability. The preparation is simple, does not require special equipment, and does not have recognizable diffraction peaks in its XRPD spectrum. The crystalline substance of tildipirosin of the present invention, is useful in preparing drug formulations, and its formulation can be a pre-mixture, tablet, pill, powder, granule, capsule or injection. Compared with other crystal forms of Tildipirosin, the formulation has better solubility and higher bioavailability.

CN106046086 relates to a method for preparing amorphous Tildipirosin. The preparation method comprises dissolving Tildipirosin in isopropyl ether, adding water to crystallize solid, filtering to obtain wet sample, and drying to obtain amorphous product. Compared with other crystal forms, the obtained amorphous product has better solubility and higher bioavailability. The amorphous product has good stability and can be preserved for a long period without degradation. The amorphous tildipirosin of CN ‘086 is used for preparing a pharmaceutical preparation, and the dosage form of the pharmaceutical preparation can be a premix, tablets, pills, powder, granules, capsules or injections. Tildipirosin as prepared by the process as disclosed in CN ‘086 has no recognizable diffraction peak in an XPRD spectrum. The process of CN ‘086 uses compound desolvation phase inversion method for forming the amorphous tildipirosin.

CN109721633 discloses a preparation method which includes dissolving tildipirosin raw material (polymorphic tildipirosin, solvated crystal-form tildipirosin or amorphous tildipirosin) in an organic solvent (methanol, ethanol, etc.), stirring at 0-35°C to obtain tildipirosin solution, dripping into purified water to precipitate for 30 - 200 min, crystallizing for 1-5 h, filtering, and vacuum drying at 40-90°C for 10-12 h. Tildipirosin obtained by process of CN ‘633 has high purity, low impurity content, and good stability, and has application in treating animal respiratory tract infection.

In keeping with the above efforts of various inventors, the present inventors provide a novel process for synthesis of tildipirosin which is cheap and provides a more stable form of tildipirosin.

Objects of Invention:
In view of above, it is an object of invention to provide an economical process for synthesis of tildipirosin.

In another object, the invention intends to provide a novel amorphous form of tildipirosin.

Summary of the invention:
The principal aspect of the present invention is to provide a process for the preparation of Tildipirosin of formula I, which comprises:

I
a) hydrolyzing compound of Formula VII with acid-base treatment in an organic solvent to obtain Desmycarosyl Tylosin of formula VI.

Formula VII

Formula VI
b) i) Reacting Piperidine with Desmycarosyl Tylosin of Formula VI in organic solvent followed by reaction with an organic acid to obtain compound of Formula V.

Formula V
ii) reacting Desmycarosyl piperidinyl tylosin (Formula V) with a dilute inorganic acid in a first organic solvent followed by basification with an aqueous base in a second organic solvent to obtain compound of formula IV.

Formula IV

c) i) dissolving compound of formula IV in an organic solvent to obtain RM-II and further mixing with RM-I solution to obtain compound of formula III.

RM – I

Formula III

ii) 23-Iodo-20-piperidinyl-5-O-mycaminoseyl-tylosin (Formula III) is reacted with piperidine in presence of carbonate base in an organic solvent to obtain crude compound of formula I.

Crude Formula I

d) purifying crude Tildipirosin of Formula I with acid-base treatment to obtain Tildipirosin of Formula I, without use of any solvent.

Detailed Description of the Invention:
The invention will now be described in detail in connection with certain preferred and optional embodiments, so that various aspects thereof may be more fully understood and appreciated. However, any skilled person will appreciate the extent to which such embodiments could be extrapolated in practice.

Unless specified otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art, to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are described.

Unless stated to the contrary, any of the words “contains”, “containing”, "including," "includes," "comprising," and "comprises" mean "including without limitation" and shall not be construed to limit any general statement that it follows to the specific or similar items or matters immediately following it. Embodiments of the invention are not mutually exclusive, but may be implemented in various combinations. The described embodiments of the invention and the disclosed examples are given for the purpose of illustration rather than limitation of the invention.
Further, words like “a”, “an”, “at least” and “the” should be construed to not only cover singular quantities but also plural quantities of the elements immediately following them.
Described herein is a process for synthesis of Tildipirosin Amorphous form as per Scheme I, infra, wherein the process comprises of following steps:
Scheme I:

Accordingly, in an embodiment, tildipirosin of Formula I is synthesised starting from compound of Formula VII. The compound of formula VII is hydrolysed with a dilute inorganic acid in presence of an inorganic base in a solvent, preferably in water/Methylene dichloride mixture to obtain compound of Formula VI. Preferably, the inorganic acid is H2SO4 and the inorganic base is NaOH.

The compound of Formula VI is then reacted with piperidine in presence of organic acid and a solvent to obtain compound of formula V. Followed by conversion of compound of Formula V to compound of Formula IV in presence of an acid and base in organic solvent preferably, the acid is H2SO4 in toluene and the base is Aq. Ammonia in methylene dichloride and methyl tert-butyl ether to give compound of formula IV, that is, 23-hydroxyl-20-pierdinyl-5-O-mycaminoseyl-tylolactones.

Compound of Formula III is obtained by iodinating compound of formula IV with Iodotriphenylphosphorane in a solvent, preferably methylene dichloride, or the like. In subsequent embodiment, the Iodotriphenylphosphorane is obtained by reacting Iodine and triphenyl phosphine in pyridine.

The compound of Formula III is then reacted with piperidine in presence of an inorganic carbonate, organic solvent and acid/base to give crude Tildipirosin compound of Formula II. The compound of Formula II is finally purified by using dilute acid in presence of base in water media to obtained compound of formula I.

In accordance to the above embodiment, inorganic acid may be selected from, but not limited to, Hydrochloric acid, Phosphoric acid, Sulphuric acid, Hydrobromic acid, Perchloric acid and others.

In accordance to above embodiment organic acid may be selected from, but not limited to, Citric acid, Acetic acid, Formic acid, Oxalic acid, Tartaric acid, Propionic acid, Benzoic acid and others.

The process of the present invention is advantageous over prior art, some of them are stated below:
1. The novelty of invention lies in use of dilute sulfuric acid, instead of hydrobromic acid for hydrolysis of sugar moiety.
2. The final amorphous form is obtained without using any solvent, only with acid base treatment, whereas reported process involve dissolving crude tildipirosin in an organic solvent and adding water to precipitate the product.

The following abbreviations and terms are used herein.
List of abbreviations
MDC Methylene dichloride TPP Triphenyl phosphine
MTBE Methyl tert butyl ether ACN Acetonitrile
HCl Hydrochloric acid RM Reaction mass
IPA Isopropyl alcohol

EXAMPLES
The following examples, which fully illustrate the practice of the preferred embodiments of the present invention. The examples are intended to be for illustrative purpose only and should not be considered in any way to limit the scope of the present invention.
Example 1: Preparation of Desmycarosyl Tylosin (Compound of formula VI)

Tylosin tartrate and process water were added into a flask under stirring at 25° to 35°C. Dilute sulfuric acid solution was added to the flask containing above mixture. Stir the reaction mass at 15° to 25°C for 4 – 5hrs. Upon completion of reaction, toluene was added and stirred for 30 minutes at 15° to 25°C and aqueous layer was separated. Methylene dichloride (MDC) is added to the aqueous layer, and the pH is adjusted to 9.0 – 10.0, by using 30? sodium hydroxide solution, at 0 – 10 ?C. The reaction mixture was allowed to settle for 15 – 20 minutes at 15 – 25?C. Both the layers were separated, MDC layer contained the product. Isopropyl alcohol was added to the MDC layer and distilled out, under vacuum, at below 50?C. The reaction mixture was cooled to 25 – 35?C and stirred for 2-3 hours. The reaction mixture was further cooled to 0 – 10?C and maintained for 2-3 hours. Solids were filtered and washed with chilled IPA and sucked dry and the material unloaded. The material was dried at 45 – 55?C under vacuum for 6-8 hours. After completion of reaction, a solid is obtained.
Yield: 0.65 Kg.

Example 2: Preparation of 23-Hydroxyl-20-Pierdinyl-5-O-Mycaminoseyl-Tylonilide (Compound of formula IV)
Step 1: Preparation of Desmycarosyl piperdinyl tylosin (Compound of formula V)

Toluene was added to Tildipirosin stage-I and Piperidine at 25 – 35?C. Formic acid was added, and the mixture was stirred for 15 – 20 minutes. the reaction mass was heated to 50°C ± 5?C. Maintain the reaction mixture for 2.0-3.0 hours at 50±5?C. After completion of reaction, the reaction mixture was cooled to 25 – 35?C. Water was added.

Step 2: Preparation of 23-Hydroxyl-20-Pierdinyl-5-O-Mycaminosyl-Tylonilide (Compound of formula IV)

Water was added to step-I reaction mass. Aq. sulfuric acid solution was added and the reaction mass was heated to 100?C for 3 – 4 hours. After completion of the reaction, the reaction mass was cooled to 25?C to 35?C. Toluene was added and stirred for 15 – 20 minutes. Dichloromethane was added and the pH was adjusted to 9.0 – 10.0, by using aq. ammonia solution at 0 – 10?C and stirred for 15 – 20 minutes. MTBE was added and distilled out, MDC was added to reaction mass and stirred under vacuum for one hour at 25 – 35?C, and the reaction mixture was further cooled to 0?C and maintained for one hour. the solids obtained were filtered and washed with chilled MTBE, suck dried and the material was unloaded. the material was dried at 40-45?C under vacuum for 6-8 hours.
Yield: 0.5 – 0.65 w/w.

Example-3: Preparation of Tildipirosin crude (Compound of formula II)
Step 1: Preparation of 23-Iodo-20-Piperdinyl-5-O-Mycaminosyel-Tylonilide (Compound of formula III)

RM-I: Methylene dichloride was added under nitrogen atmosphere at 25?C to 35?C. Triphenyl phosphine was added at 25?C to 35?C. Pyridine was added and reaction mixture was cooled to 5?C±5?C and Iodine was added at 5?C±5?C and stirred for 20-30 minutes at 5?C±5?C.

RM-2: Methylene dichloride was added to Tildipirosin stage-II under nitrogen atmosphere at 25?C to 35?C and stir for 10-15 minutes and the reaction mixture is cooled to 5?C±5?C.

RM-2 was added to RM-I at 5?C±5?C and maintained for 5.0 hours at 5?C±5?C. After completion of the reaction, aq. Sodium sulfite solution was added and stirred for 20-30 minutes and the layers were separated below 10?C. Methylene dichloride was added to RB flask which is later distilled out, to form a thick stirrable volume, under vacuum. Acetonitrile was added to the solution and reaction mass was cooled to 25?C to 35?C.

Step-2: Preparation of Tildipirosin crude (Compound of formula II)
Potassium carbonate was added at 25?C to 35?C and stirred for 10-15 minutes. Piperidine was added at 25?C to 35?C and reaction mixture was maintained for 12.0 hours at 25?C to 35?C.

Work up: after completion of the reaction, the inorganics were filtered and washed with acetonitrile. The acetonitrile was distilled out, under vacuum, to form a thick stir able volume.

Methylene dichloride was added and distilled to form a thick stirrable volume under vacuum and the reaction mass was cooled to 25?C±5?C. Water was added and the reaction mass was stirred for 10 – 15 minutes at 25?C±5?C and allowed to settle for 10-15 minutes and the layers were separated at 25?C±5?C. Methylene dichloride and water were added to RBF to cool the reaction mass to 5?C±5?C. Dilute sulfuric acid solution was added slowly at 5?C±5?C and allowed to settle for 10-15 minutes and the layers were separated at below 5?C±5?C. The aq. layer was washed with MDC at 5?C±5?C. The aq. layer containing the product was treated with MDC. the pH was adjusted to 9.0 to 10.0 using sodium hydroxide solution at 5?C±5?C. The MDC layer was washed with water and brine solution at 25?C to 35?C and stirred for 10-15 minutes and the organic layer was separated below 10?C. The MDC layer was added to RBF and distilled to a thick stirrable volume under vacuum. Acetonitrile was added and heated to 45-50?C to form clear solution. Said solution was than maintained for 10-15 minutes followed by slowly cooling the RM to 25?C±5?C and stirred for 2.0 hours. Further the reaction mass was cooled to 0?C±5?C and maintained for 2.0 hours. Solids obtained were filtered at 0?C±5?C and washed with chilled acetonitrile and again filtered. The material was dried under vacuum at 40 to 50?C for 6-8 hours.
Yield: 0.55 – 0.6 w/w
Example 4: Preparation of Tildipirosin API (Compound of formula I)
Purified water and Tildipirosin crude were added at 25-35?C to RBF the reaction mass was stirred for 15 minutes at 25 – 35?C and was cooled to 10?C±5?C. dilute sulfuric acid solution was added to form clear solution and reaction mass was filtered at 10?C±5?C. The filtrate was charged into RBF and the pH was adjusted using dilute sodium hydroxide solution at 10-20?C. The reaction mass was raised to 20-30?C and stirred for 4.0-5.0 hours at 20 – 30?C and the solids obtained were filtered, washed with purified water in RBF at 20 – 30?C. The reaction mass was stirred for 2.0-3.0 hours and the solids obtained were filtered at 20-30?C and washed with purified water and chilled acetonitrile+purified water mixture at 10?C. The material was dried at 50 to 55?C under vacuum for 6-8 hours.
Yield: 0.9 w/w.
,CLAIMS:1. A process for preparation of amorphous Tildipirosin which comprises;
a. hydrolyzing compound of Formula VII with acid-base treatment in an organic solvent to obtain Desmycarosyl Tylosin of formula VI,

b. reacting piperidine with desmecarosyl tylosin (Formula VI) in presence of organic acid to give desmecarosyl piperidinyl tylosin (Formula V);

c. reacting Desmecarosyl piperidinyl tylosin with inorganic acid to give compound of formula IV;

d. reacting RM-I with compound of formula IV to give compound of formula III;

e. reacting compound of formula III with piperidine to give tildipirosin; and,

f. purifying tildipirosin with acid base without any solvent to give the amorphous form of tildipirosin,

and wherein, hydrolysis of sugar moiety using dilute sulfuric acid, instead of hydrobromic acid.

2. The process as claimed in claim 1, wherein the inorganic acid is selected from Hydrochloric acid, Phosphoric acid, Sulphuric acid, Hydrobromic acid, Perchloric acid and others.
3. The process as claimed in claim 2, wherein the inorganic acid is sulphuric acid.
4. The process as claimed in claim 1, wherein the organic acid is selected from Citric acid, Acetic acid, Formic acid, Oxalic acid, Tartaric acid, Propionic acid, Benzoic acid and others.
5. The process as claimed in claim 1, wherein the organic acid is formic acid.

6. The process as claimed in to claim 1, wherein the amorphous tildipirosin is free from organic solvent.

7. The process as claimed in to claim 1, wherein the amorphous tildipirosin s obtained by acid base reaction.