DESC:FIELD OF THE INVENTION
The present invention relates to an improved process for the preparation of Trilaciclib or its salts and its key intermediate 2'-Chloro-7',8'-dihydrospiro[cyclohexane-1,9'(6'H)-pyrazino[1',2':1,5]pyrrolo[2,3-d]pyrimidin]-6'-one.

BACKGROUND OF THE INVENTION:
Trilaciclib dihydrochloride is chemically known as 2'-{[5-(4-Methylpiperazin-1-yl)pyridin-2-yl]amino}-7',8'¬-dihydro-6'H-spiro[cyclohexane-1,9'-pyrazino[1',2':1,5]pyrrolo[2,3-d] pyrimidin]-6'-one and has the structural Formula(I):

Trilaciclib or its pharmaceutically acceptable salts were developed by G1 Therapeutics Inc. it is a CDK4 and CDK6 inhibitor, indicated to reduce the incidence of chemotherapy induced myelosuppression in patients before topotecan-containing or platinum and etoposide-containing chemotherapy for extensive stage small cell lung cancer and has been approved by USFDA and marketed by G1 Therapeutics under the brand name Cosela® in the form of injection having dosage strength of 300 mg vial.

Trilaciclib was first disclosed in US patent No. 8,598,186 B2 (herein after referred as US ‘186). This patent discloses the process for preparation of Trilaciclib, which is shown as below:

US patent No. 10,865,210 B2 (herein after referred as US‘210) discloses alternate processes for preparation of Trilaciclib, which is shown as below:

The prior-art process are not suitable for commercial scale as the process involves more number of steps and involves the use of costly reagents like Pd Catalysts and ligands and also product obtained in low yields as well as required use of column chromatography techniques for the isolation and purification of Trilaciclib.

The prior-art process for preparing Trilaciclib compound of Formula I produces below mentioned compound of Formulae VI, VII, VIII, IX, X and XI as impurities.

The key intermediate 2'-Chloro-7',8'-dihydrospiro[cyclohexane-1,9'(6'H)-pyrazino[1',2':1,5]pyrrolo[2,3-d]pyrimidin]-6'-one used in the preparation of Trilaciclib involves column purification and use of palladium catalyst, which are not suitable for commercial preparation.

Accordingly there is provided an improved process of preparing Trilaciclib compound of Formula I which is free of impurities of Formulae VI, VII, VIII, IX, X and XI.

OBJECTIVES OF THE INVENTION
The objective of the present invention is to provide safer, cost- effective and industrially viable process for preparation of Trilaciclib.

Another objective of the present invention is to provide a process for preparation of Trilaciclib, with high yields.

SUMMARY OF THE INVENTION
The present invention relates to a process for the preparation of Trilaciclib compound of Formula I,

Formula I
which comprising the following steps:
i) converting Sulfone compound of formula II to hydroxy compound of
formula III in presence of a base and solvent;
ii) chlorinating hydroxy compound of formula III to yield chloro compound of formula IV in presence of a chlorination reagent;
iii) condensing chloro compound of formula IV with amine compound of formula V in presence of strong base to yield Trilaciclib compound of formula I; and
iv) isolating Trilaciclib compound of formula I and optionally converting into Trilaciclib pharmaceutically salt thereof.
The present invention also relates to process for preparation of Trilaciclib compound of Formula I The present invention relates to a process for the preparation of Trilaciclib compound of Formula I,

Formula I
which comprising the following steps:
i) condensing chloro compound of formula IV with amine compound of formula V in presence of strong base to yield Trilaciclib compound of formula I; and
iv) isolating Trilaciclib compound of formula I and optionally converting into Trilaciclib pharmaceutically salt thereof.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to process for the preparation of Trilaciclib compound of Formula I, comprising converting sulfone compound of Formula II 2’-(Methylsulfonyl)-7’,8’-dihydro-6’H-spiro-[cyclohexane-1,9’-pyrazino[1’2’:1,5]pyrrolo-[2,3-d]pyrimidin]-6’-one to compound of Formula III 2’-Hydroxy-7’-8’-dihydro-6’H-spiro[cyclohexane-1,9’-pyrazino[1’,2’:1,5]-pyrrolo[2,3-d]pyrimidin]-6’-one in presence of base and solvent, wherein base is selected from the group consisting of sodium hydroxide, potassium hydroxide, lithium hydroxide. Chlorinating hydroxy compound of formula III in presence of chlorination reagent to yield compound of formula IV Chloro-7’,8’-dihydro-6’H-spiro[cyclohexane-1,9’-pyrazino[1’,2’:1,5]pyrrolo[2,3-d]pyrimidin]-6’-one, where in chlorinating reagent selected from the group consisting of thionyl chloride, phosphorus oxychloride, and oxalyl chloride. Condensing chloro compound of formula IV with with 5-(4-Methylpiperazine-1-yl)pyridine-2-amine in presence of strong base to yield Trilaciclib compound of Formula I. wherein strong base is selected from the group consisting of lithium bis(trimethylsilyl)amide, sodium bis(trimethylsilyl)amide, potassium bis(trimethylsilyl)amide, sodium hydride, potassium hydride, lithium hydride, lithium diisopropylamide, sodium methoxide, potassium methoxide, potassium tert-butoxide.

In another aspect of the present invention relates to process for preparation of Trilaciclib or its pharmaceutical acceptable salts. Trillaciclib free base is converted to Trilacilib dihydrochloride. Trilaciclib free base was dissolved in solvent and adding hydrochloric acid or mixture of solvent with hydrochloric acid to yield Trilaciclib dihydrochloride.

In another aspect of the present invention is advantageous over prior art as follows:
• Palladium free condensation of chloro-intermediate with amine
• avoiding impurities of Formulae VI, VII, VIII, IX, X and XI
• Cost effective route

The use of strong base in condensation of 2’-Chloro-7’,8’-dihydro-6’H-spiro[cyclohexane-1,9’-pyrazino[1’,2’:1,5]pyrrolo[2,3-d]pyrimidin]-6’-one with 5-(4-Methylpiperazine-1-yl)pyridine-2-amine is cost-effective and suitable for large scale preparation, which avoid use of costly reagents and ligands. Further the advantages of the present invention w.r.t. prior art process is as follows:

Prior-Art Present Invention
Catalyst Pd2(dba)3 Strong base

7.96% 0.14

1.21 -

4.13 -

0.62 -

1.46 -

0.28 -

In another embodiment of the present invention, the solvents used throughout the invention are selected from water, non-polar solvents, polar protic solvents, polar aprotic solvents wherein non-polar solvents are hydrocarbons, halogenated hydrocarbons; wherein polar protic solvents are selected from alcohols; wherein polar aprotic solvents are selected from group comprising of ketones, nitriles, esters, amides, ethers.

In another embodiment of the present invention, hydrocarbons selected from the group comprising aliphatic hydrocarbons comprising alkanes from C1-7 alkanes, aromatic hydrocarbons selected from toluene, xylene or mixtures thereof and cycloalkanes selected from cyclohexane, cylcopentane or mixtures thereof, C1-7 alkanes are selected from hexane, heptane or mixtures thereof; halogenated hydrocarbons are selected from methylene dichloride, ethylene dichloride, chloroform, carbon tetrachloride or mixtures thereof; polar protic solvents used throughout the invention are selected from the group comprising alcohols selected from aliphatic alcohols selected from the group comprising of methanol, ethanol, n-propanol, isopropanol, n-butanol, pentanol, isobutanol, tertiary butanol, cyclopropanol, cyclobutanol, cyclopentanol, cyclohexanol or mixtures thereof, aromatic alcohols used throughout the invention are selected from the group comprising of phenols, benzylalcohol or mixtures thereof; polar aprotic solvents used throughout the invention are ketones selected from the group comprising aliphatic ketones selected from the group comprising acetone, diethyl ketone, methyl ethyl ketone, methyl isobutyl ketone and methyl propyl ketone, cyclobutanone, cyclopentanone, cyclohexanone or mixtures thereof, nitriles used throughout the invention are selected from the group comprising of aliphatic nitriles such as C2-C8 nitrile; esters used throughout the invention are aliphatic esters or aromatic esters wherein aliphatic esters are selected from ethyl acetate, methyl acetate, isopropyl acetate, tert-butyl methyl acetate, ethyl formate or mixtures thereof; amides used throughout the invention are selected from dimethylacetamide, dimethylformamide or mixtures thereof; ethers used throughout the invention are selected from the group comprising of symmetrical or asymmetrical ethers or cyclic ethers selected from diethyl ether, methyl tert-butyl ether, diisopropyl ether, tetrahydrofuran or mixtures thereof.

In another embodiment of the present invention, the reactions are carried out at heating or cooling or at room temperatures depending on the reaction conditions.

In another embodiment of the present invention, heating is carried out at a temperature in the range of 200 C to 2000 C.

In another embodiment of the present invention, cooling is carried out at a temperature in the range of 200 C to -200 C.

In another embodiment of the present invention, isolation is carried out by conventional methods.

In the following section embodiments are described by way of examples to illustrate the process of invention. However, these do not limit the scope of the present invention. Variants of these examples would be evident to persons ordinarily skilled in the art.

Example 1: process for preparation of 2’-Hydroxy-7’-8’-dihydro-6’H-spiro[cyclohexane-1,9’-pyrazino[1’,2’:1,5]-pyrrolo[2,3-d]pyrimidin]-6’-one.

2’-(Methylsulfonyl)-7’,8’-dihydro-6’H-spiro-[cyclohexane-1,9’-pyrazino[1’2’:1,5]pyrrolo-[2,3-d]pyrimidin]-6’-one was dissolved in 1,4-dioxane and potassium hydroxide was added dropwise to above solution and reaction mass was heated up to 80o-85oC and stirred to 4-5 hours and cooled to 0 to 5oC. Adjust to pH 2 to 3 with aq. Hydrochloric acid at 0o to 5oC and stirred to 30-45 minutes at 30o to 35o C. filter the solid and washed with water and heptane and dried for 30 minutes.
Purity: 98.2% by HPLC

Example 2: Process for preparation of 2’-Chloro-7’,8’-dihydro-6’H-spiro[cyclohexane-1,9’-pyrazino[1’,2’:1,5]pyrrolo[2,3-d]pyrimidin]-6’-one.

Charged 2’-Hydroxy-7’-8’-dihydro-6’H-spiro[cyclohexane-1,9’-pyrazino[1’,2’:1,5]-pyrrolo[2,3-d]pyrimidin]-6’-one in reaction flask and cooled to 0° to 5°, POCl3 was added to dropwise drop wise at same temperature and stirred to 30-45 minutes. The temperature of reaction mass was raised up to 90-95oC and stirred 7-8 hours. Cooled to 28° to 30°C and slowly added to cold water at 0° to 5°C and stirred to 30 – 45 minutes. The temperature of the reaction mass slowly raised to 28° to 30°C and stirred for 1 hour to 1 hour 30 minutes and extract the aqueous layer with 15% methanol, dichloromethane solvent, combined organic layer and concentrated the organic layer at reduced pressure to get crude solid. The crude solid was dissolved in water and cooled to 0° to 5°C and adjusted the pH of rection mass 7-8 with Na2CO3 and stirred 30-45 minutes. Filtered the solid and washed with water and heptane and suck dried to 30 minutes. The obtained solid was charged in dichloromethane and stirred for 1 hour and filter the solid and washed with dichloromethane and dried for 10 hours.
Purity: 97.7% by HPLC

Example 3: Process for preparation of Trilaciclib.

5-(4-Methylpiperazine-1-yl)pyridine-2-amine was dissolved in Tetrahydrofuran at 25-30° and stirred. The reaction mass was cooled to 3 to 2°C and LiHMDS was added to dropwise to above reaction mass at same temperature and stirred for 30 to 40 minutes. 2’-Chloro-7’,8’-dihydro-6’H-spiro[cyclohexane-1,9’-pyrazino[1’,2’:1,5]pyrrolo[2,3-d]pyrimidin]-6’-one was added to above reaction mass and stirred for 60 minutes. The temperature of the reaction mass slowly raised to 28° to 30°C and stirred for 5, cold water was added at 3° to 2°C and stirred for 45 – 60 minutes at 28° to 30°C. filter the solid and suck dried the wet material for 1 hour. The wet material was charged with water and stirred for 1 hour and filtered the solid and suck dried the wet material for 1 hour. The dried material was charged with 20% methanol and dichloromethane at 25-30o C and stirred for 1 hour at 28° to 30°C. filter the solid and washed with dichloromethane and dried.
Purity: 98.2% by HPLC

Example 4: Process for preparation of Trilaciclib dihydrochloride.

Trilaciclib free base was dissolved in methanol and dichloromethane at 25-30°C and Isopropanol-HCl solution was added dropwise to above reaction mass and stirred for 1 hour. Filter the reaction mas and washed with dichloromethane suck the filtered solid 20 minutes and dried.
Purity: 99.3% by HPLC ,CLAIMS:We claim:
1. A process for the preparation of Trilaciclib compound of Formula I,

Formula I
which comprising the following steps:
i) converting Sulfone compound of formula II

to hydroxy compound of formula III

in presence of a base and solvent;
ii) chlorinating hydroxy compound of formula III

to yield chloro compound of formula IV

in presence of a chlorination reagent;
iii) condensing chloro compound of formula IV

with amine compound of formula V

in presence of strong base to yield Trilaciclib compound of formula I; and
iv) isolating Trilaciclib compound of formula I and optionally converting into Trilaciclib pharmaceutically salt thereof.
2. The process according to claim 1, wherein base in step(i) is selected from the group consisting of sodium hydroxide, potassium hydroxide and lithium hydroxide

3. The process according to claim 1, wherein chlorination reagent is selected from the group consisting of thionyl chloride, phosphorus oxychloride, and oxalyl chloride

4. The process according to claim 1, wherein base in step(iii) is selected from the group consisting of
lithium bis(trimethylsilyl)amide, sodium bis(trimethylsilyl)amide, potassium bis(trimethylsilyl)amide, sodium hydride, potassium hydride, lithium hydride, lithium diisopropylamide, sodium methoxide, potassium methoxide, potassium tert-butoxide.

Dated 29th day of November 2024

Dr. RATHNAKAR REDDY KURA
DIRECTOR
HETERO LABS LIMITED