FORM 2
THE PATENT ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
Title of the invention
"AN IMPROVED PROCESS FOR THE PREPARATION OF LYMECYCLINE"
Enaltec Labs Pvt Ltd. an Indian Company, having its Registered Office at 17th Floor. Kesar Solitaire, Plot No.5 Sector-19, Sanpada, Navi Mumbai Maharashtra, India. Pin Code: 400705
1. The following specification particularly describes the invention and the manner in which it is to be performed.

AN IMPROVED PROCESS FOR THE PREPARATION OF LYMECYCLINE

FIELD OF THE INVENTION

The present invention relates to an improved process for the preparation of lymecycline compound of formula I comprising treating L-lysine with tetracycline compound of formula II and formaldehyde. The present invention also relates to a substantially pure lymecycline compound of formula I obtained by treating lymecycline hydrochloride with ammonia or an organic base.

BACKGROUND OF THE INVENTION

Lymecycline is chemically (2S)-2-Amino-6-[[[[[(4S,4aS,5aS,6S,12aS)-4-(dimethylamino)-3,6,10,12,12a-pentahydroxy-6-methyl-1,11-dioxo-1,4,4a,5,5a,6,11,12a-octahydrotetracen-2-yl]carbonyl]amino]methyl]amino]hexanoic acid and is known from U.S. Patent No. 3,042,716 and is represented by compound of structural formula I.

U.S. Patent No. 3,042,716 describes a process for the preparation of lymecycline compound of structural formula I wherein tetracycline compound of structural formula II is reacted with an aqueous solution of L-lysine hydrochloride compound of structural formula III and 37% aqueous solution of formaldehyde in tetrahydrofuran solvent to get an oily residue. The lymecycline is isolated in the form of hydrochloride salt by treating oily residue with isopropanol and acetone respectively. This process yields impure lymecycline compound of structural formula I due to the degradation of tetracycline compound of structural formula II by hydrochloric acid.

The prior art process for the preparation of lymecycline compound of structural formula I is suffered from the disadvantages of low yield and impure product and therefore there is a need in the art to develop an improved process for the preparation of lymecycline compound of structural formula I.

SUMMARY OF THE INVENTION

A first aspect of the present invention is to provide an improved process for the preparation of lymecycline compound of structural formula I. which obviates the disadvantages of prior art process for the preparation of lymecycline.

A second aspect of the present invention is to provide a substantially pure lymecycline compound of structural formula I.

A third aspect of the present invention is to provide an improved process for the preparation of lymecycline compound of structural formula I comprising the steps of:
a. reacting tetracycline compound of structural formula II with L-lysine compound of structural formula IV and formaldehyde to get lymecycline compound of structural formula I and
b. isolating substantially pure lymecycline compound of structural formula I.

A fourth aspect of the present invention is to provide a substantially pure lymecycline compound of structural formula I obtained by treating crude lymecycline hydrochloride with ammonia or an organic base.

A fifth aspect of the present invention is to provide substantially pure lymecycline compound of structural formula I comprising the steps of
a) reacting L-lysine hydrochloride compound of structural formula III with tetracycline compound of structural formula II and formaldehyde to get crude lymecycline hydrochloride,
b) treating crude lymecycline hydrochloride with ammonia or an organic base and
c) isolating substantially pure lymecycline compound of structural formula I.

DETAIL DESCRIPTION OF THE INVENTION:

Tetracycline compound of structural formula II may be formed by methods known in the art such as those described in U. S. patent no. 2,731,497 and 2,734,018 and J.A.C.S. 75: 4621-4622, September 1953.

The reaction of tetracycline compound of structural formula II with L-lysine compound of structural formula IV and formaldehyde may be carried out in an ether solvent.

The examples of ether solvents may include tetrahydrofuran, dioxane, diisopropyl ether, dibutyl ether, diethyl ether, 2-methyl tetrahydrofuran, di-n-propyl ether, methyl tertiary butyl ether or mixture(s) thereof.
The reaction of tetracycline compound of structural formula II with L-lysine compound of structural formula IV and formaldehyde may be carried out at a temperature in the range of 10C to 30C for 15 minutes to 4 hours.

The substantially pure lymecycline compound of structural formula I refer to the lymecycline compound having more than 99% purity as determined by HPLC method.

The substantially pure lymecycline compound of structural formula I refer to the lymecycline compound having less than 0.15% weight / weight of following compound of structural formula V, VI and VII.

The limit of detection (LOD) and limit of quantitation (LOQ) of compound of structural formula V is 0.015 % weight / weight and 0.01% weight / weight.

The limit of detection (LOD) and limit of quantitation (LOQ) of compound of structural formula VI is 0.001 % weight / weight and 0.05% weight / weight.

The limit of detection (LOD) and limit of quantitation (LOQ) of compound of structural formula VII is 0.025 % weight / weight and 0.1% weight / weight.

The isolation of substantially pure lymecycline compound of structural formula I may be carried out by first quenching the reaction mixture with an alcohol solvent and then slurrying the resulting solids in a mixture of an alcohol and water in the presence of a base.

The examples of alcohol solvent may be selected from the group comprising of methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, pentanol or mixture(s) thereof.

The examples of organic base may include ammonia, triethylamine, dibutyl amine, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, di-n-propyl amine or diethyl amine.

The reaction of L-lysine hydrochloride compound of structural formula III with tetracycline compound of structural formula II and formaldehyde may be carried out in above mentioned ether solvent to get crude lymecycline hydrochloride.

The reaction of L-lysine hydrochloride compound of structural formula III with tetracycline compound of structural formula II and formaldehyde may be carried out at a temperature in the range of 10C to 30C for 15 minutes to 3 hours.

The crude lymecycline hydrochloride may be treated with ammonia or an organic base at a temperature in the range of 25C to 30C to get a substantially pure lymecycline compound of structural formula I.

The examples of an organic base may include but not limited to triethyl amine, dibutyl amine, diisopropyl amine, diethyl amine or di-n-propyl amine,

The substantially pure lymecycline compound of structural formula I may be isolated by the steps of filtration, centrifugation, washing, drying and the combinations thereof.

The substantially pure lymecycline compound of structural formula I may be dried at a temperature in the range of 45C to 60C under reduced pressure.

The following examples are given for the purpose of illustrating the present invention and should not be considered as limitations on the scope or spirit of the invention.

EXAMPLE 1: PREPARATION OF SUBSTANTIALLY PURE LYMECYCLINE

A solution of tetracycline (100gm) in tetrahydrofuran (1000ml) was added into the reaction mixture containing a solution of L-lysine (35gm) in water (150ml) and formaldehyde (37%, 20ml) at 10C and then resulting reaction mixture was stirred for 2 hours at 10-15C. The reaction mixture was quenched with isopropanol (1000ml) and resulting solids were filtered, and then it was first slurred into a mixture of methanol (1500ml), water (500ml) and ammonia (25ml) at 25-30C and then in a methanol solvent (1000ml) to get a substantially pure lymecycline compound of structural formula I.
Yield: 120gm
Purity: 99.95% (By HPLC)
Compound of structural formula V: 0.01% (By HPLC)
Compound of structural formula VI: Not detectable
Compound of structural formula VII: Not detectable

EXAMPLE 2: PREPARATION OF SUBSTANTIALLY PURE LYMECYCLINE

A solution of tetracycline (100gm) in tetrahydrofuran (1500ml) was added into the reaction mixture containing a solution of L-lysine hydrochloride (40gm) in water (200ml) and formaldehyde (37%, 25ml) at 10C and then resulting reaction mixture was stirred for 3 hours at 10-15C. The reaction mixture was quenched with isopropanol (1500ml) and resulting solids were filtered, and then it was first slurred into a mixture of methanol (2000ml),water (1000ml) and ammonia (30ml) at 25-30C and then in a methanol solvent (1250ml) to get a substantially pure lymecycline compound of structural formula I.
Yield: 125gm
Purity: 99.98% (By HPLC)
Compound of structural formula V: Not detectable
Compound of structural formula VI: Not detectable
Compound of structural formula VII: Not detectable

WE CLAIM:

1. A process for the preparation of lymecycline compound of structural formula I comprising the steps of:
a. reacting tetracycline compound of structural formula II with L-lysine compound of structural formula IV and formaldehyde to get lymecycline compound of structural formula I and

b. isolating substantially pure lymecycline compound of structural formula I.

2. The process according to claim no. 1 wherein reaction of tetracycline compound of structural formula II with L-lysine compound of structural formula IV and formaldehyde is carried out in an ether solvent such as tetrahydrofuran, dioxane, diisopropyl ether, dibutyl ether, diethyl ether, 2-methyl tetrahydrofuran, di-n-propyl ether, methyl tertiary butyl ether or mixture(s) thereof at a temperature in the range of 10C to 30C for 15 minutes to 4 hours.

3. The process according to claim no.1 wherein isolation of substantially pure lymecycline compound of structural formula I is carried out by first quenching the reaction mixture with an alcohol solvent and then slurrying the resulting solids in a mixture of an alcohol and water in the presence of a base.

4. The process according to claim no. 3 wherein alcohol solvent is selected from the group comprising of methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, pentanol or mixture(s) thereof and base is selected from the group comprising of ammonia, triethylamine, dibutyl amine, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, di-n-propyl amine or diethyl amine.

5. A process for preparing substantially pure lymecycline compound of structural formula I comprising the steps of
a) reacting L-lysine hydrochloride compound of structural formula III with tetracycline compound of structural formula II and formaldehyde to get crude lymecycline hydrochloride,
b) treating crude lymecycline hydrochloride with ammonia or an organic base and
c) isolating substantially pure lymecycline compound of structural formula I.

6. The process according to claim no. 5, wherein reaction of L-lysine hydrochloride compound of structural formula III with tetracycline compound of structural formula II and formaldehyde is carried out in ether solvent at a temperature in the range of 10C to 30C for 15 minutes to 3 hours to get crude lymecycline hydrochloride.

7. The process according to claim nos. 5 and 6, wherein crude lymecycline hydrochloride is treated with ammonia or an organic base at a temperature in the range of 25C to 30C to get a substantially pure lymecycline compound of structural formula I.

8. The process according to claim no. 7, wherein organic base is selected from the group comprising of triethyl amine, dibutyl amine, diisopropyl amine, diethyl amine or di-n-propyl amine.

9. The process according to claim nos. 1 and 5, wherein substantially pure lymecycline compound of structural formula I may be isolated by the steps of filtration, centrifugation, washing, drying and the combinations thereof.

10. The process according to claim nos. 1 and 5, wherein substantially pure lymecycline compound of structural formula I refer to the lymecycline compound having less than 0.15% weight / weight of following compound of structural formula V, VI and VII.