The present invention provides a process for the preparation of amorphous Doripenem.
(4R,5S,6S)-3-[[(3S,5S)-5-[[(aminosulfonyl)amino]methyl]-3-pyrrolidinyl]thio]-6-[(1R)-1-
hydroxyethyl]-4-methyl-7-oxo-1-azabicyclo[3.2.0]hept-2-ene-2-carboxylic acid,
commonly known as doripenem of Formula I is a synthetic, broad-spectrum, carbapenem antibiotic.
(Formula Removed)

FORMULA I
Doripenem exhibits potent, broad and well-balanced antibacterial activity against a wide range of both Gram-positive and Gram-negative bacteria including Pseudomonas aeruginosa.
US Patent No 5,317,016 provides a process for the isolation of doripenem by lyophilization. Similar processes for preparing lyophilized doipenem have also been described in Yasuyoshi Iso et al, J. Antibiot. 1996, 49, 199-209 and Yasuyoshi Iso et al, J. Antibiot. 1996, 49, 478-484.
US Patent No 6,111,098 and US Patent No 5,703,243 provide processes for preparing crystalline and amorphous forms of lyophilized doripenem. US Patent Publication No 2003/0153191 provides processes for preparing Type III and Type IV crystals of doripenem. Yutaka Nishino et al, Org. Process Res. Dev. 2003, 7, 846-850 provide a process for the preparation of sterile crystalline doripenem by crystallization from 2-propanol. The process employs use of inorganic salts for isolation of doripenem which are difficult to remove and contaminate the product.
The present inventors have developed a novel process for the preparation of amorphous doripenem by solvent precipitation. Using the process of the present invention it is possible to isolate amorphous doripenem directly from the reaction mixture by solvent precipitation without the use of lyophilization, column chromatography or reverse osmosis. This helps in improving the time cycle and process economics.
The present process avoids the use of inorganic salts during isolation of doripenem and thus the contamination of these salts in the final product is avoided.
The term "protecting group" in the present invention refers to those used in the art and serve the function of blocking the carboxyl, amino or hydroxyl groups while the reactions are carried out at other sites of the molecule. Examples of a carboxyl protecting group include, but not limited to, optionally substituted C1-C8 alkyl, optionally substituted C3-C8 alkenyl, optionally substituted C7-C19 aralkyl, optionally substituted C6-C12 aryl, optionally substituted C1-C12 amino, optionally substituted C3-C12 hydrocarbonated silyl, optionally substituted C3-C12 hydrocarbonated stannyl, and a pharmaceuticaly active ester forming group. Examples of hydroxyl and amino protecting groups include, but not limited to, lower alkylsilyl groups, lower alkoxymethyl groups, aralkyl groups, acyl groups, lower alkoxycarbonyl groups, alkenyloxycarbonyl groups and aralkyloxycarbonyl groups.
A first aspect of the present invention provides a process for preparation of amorphous doripenem which comprises,
a) treating an aqueous solution of doripenem with a water miscible organic solvent,
b) isolating amorphous doripenem from the reaction mass thereof.
An aqueous solution of doripenem can be reaction mixture resulting from any process known to the skilled person for the preparation of doripenem. The water miscible solvent is selected from the group comprising of methanol, ethanol, 1-propanol, 2-propanol, acetone and acetonitrile.
After treating the aqueous solution of doripenem with a water miscible organic solvent, the resultant mixture is stirred for sufficient time to effect complete precipitation. The stirring is carried out preferably at a temperature less than about 25°C. The precipitate so obtained is further washed with the same organic solvent, or a different solvent, or a mixture thereof to get amorphous doripenem.
A second aspect of the present invention provides a process for preparation of amorphous doripenem which comprises a) reacting enol-phosphate of Formula II
(Formula Removed)

FORMULA II
wherein P-\ represents a carboxyl protecting group, P2 represents hydrogen or a hydroxyl protecting group and X represents OP(0)(OR)2 or OSO2R, wherein R represents substituted or unsubstituted C1-6 alkyl, aralkyl or aryl with a thiopyrrolidine of Formula III
(Formula Removed)

FORMULA III
wherein P3 represents hydrogen or an amino protecting group, to get a compound of Formula IV,
(Formula Removed)
FORMULA IV
wherein P1 P2 and P3 are as defined above,
b) deprotecting the compound of Formula IV in a biphasic system comprising aqueous
and water-immiscible solvents,
c) treating the aqueous layer of the reaction mixture with a water miscible organic solvent,
d) isolating amorphous doripenem from the reaction mass thereof.
Enol-phosphate of Formula II and thiopyrrolidine of Formula III can be prepared by processes disclosed in the prior-art as mentioned earlier. Enolphosphate is added to a mixture containing thiopyrrolidine in an organic solvent at about 0°C. To this reaction mass is added a secondary or tertiary amine optionally in a drop-wise manner so as to control the temperature between -5°C and 25°. After stirring the reaction mass for sufficient time to effect the coupling reaction, it is poured into a mixture of a water immiscible organic solvent and water.
Following the separation of layers, an aqueous buffer is added to the organic layer containing the condensed product and the resultant biphasic mass is hydrogenated using a noble metal catalyst. For this purpose hydrogen gas or a compound capable of generating hydrogen gas can be used as a source of hydrogen.
After completion of the reaction, the aqueous layer comprising the product is added to a water miscible organic solvent at ambient temperature. The reaction mixture so obtained is stirred for sufficient time to effect complete precipitation, filtered and washed to yield amorphous doripenem.
The water miscible solvent is selected from the group comprising of methanol, ethanol, 1-propanol, 2-propanol, acetone and acetonitrile.
Figure I depict powder X-ray diffraction patterns of amorphous doripenem prepared by the present invention.
Powder XRD of the samples were determined by using X-Ray Difractometer, Rigaku Corporation, RU-H3R, Goniometer CN2155A3, X-Ray tube with Cu target anode, Divergence slits 1 0, Receiving slit 0.15mm, Scatter slit 1°, Power: 40 KV, 100 mA, Scanning speed: 2 deg/min step: 0.02 deg, Wave length: 1.5406 A
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.
EXAMPLE 1
PREPARATION OF AMORPHOUS DORIPENEM
A mixture of 4-nitrobenzyl(2S,4S)-4-(acetylthio)-2-{[(aminosulfonyl)(tert- butoxy carbonyl)amino]methyl}pyrrolidine-1-carboxylate (53.5 g) and concentrated sulfuric acid (25 g) in methanol (250 ml) were refluxed for 3 hours, followed by cooling to ambient temperature. To the reaction mixture was poured into a mixture of methylene chloride (500 ml) and water (500 ml). The organic layer was separated and washed with water (2 X 500 ml) and concentrated under reduced pressure to give a concentrate containing 4-nitrobenzyl (2S,4S)-2-{[(aminosulfonyl)amino]methyl}-4-mercaptopyrrolidine-1-carboxylate. The concentrate so obtained was dissolved in N,N-dimethylformamide (50 ml) and added to enolphosphate (50 g) dissolved in N,N-dimethylformamide (200 ml) at 0° to 5°C, followed by drop wise addition of diisopropylethylamine (15.1 g) at the same temperature. After stirring for 18 hours at 0° to 5°C, the reaction mixture was poured into a mixture of ethylacetate (500 ml) and water (300 ml). The pH was adjusted to 2.5 to 3.0 and the organic layer was separated. The organic layer so obtained was added to a mixture of 5% palladium on
carbon (50 g) in aqueous buffer (300 ml) containing N-methylmorpholine and acetic acid (pH 6.0 to 7.0). The biphasic reaction mass was then hydrogenated for 3 to 4 hours under pressure at 10° to 20°C. After the completion of the reaction, the reaction mixture was filtered and the aqueous layer (350 ml) was separated. The aqueous layer was then added to absolute ethanol (3.5 L) at 20° to 25°C in 15 to 20 minutes. After stirring at 0° to 5°C for 60 minutes, the reaction mixture was filtered and washed with absolute ethanol followed by acetone to yield the title compound.
Yield: 20 g
EXAMPLE 2
PREPARATION OF AMORPHOUS DORIPENEM
A mixture of 4-nitrobenzyl(2S,4S)-4-(acetylthio)-2-{[(aminosulfonyl)(tert- butoxy carbonyl)amino]methyl}pyrrolidine-1-carboxylate (53.5 g) and concentrated sulfuric acid (25 g) in methanol (250 ml) were refluxed for 3 hours, followed by cooling to ambient temperature. To the reaction mixture was poured into a mixture of methylene chloride (500 ml) and water (500 ml). The organic layer was separated and washed with water (2 X 500 ml) and concentrated under reduced pressure to give a concentrate containing 4-nitrobenzyl (2S,4S)-2-{[(aminosulfonyl)amino]methyl}-4-mercaptopyrrolidine-1-carboxylate. The concentrate so obtained was dissolved in N,N-dimethylformamide (50 ml) and added to enolphosphate (50 g) dissolved in N,N-dimethylformamide (200 ml) at 0° to 5°C, followed by drop wise addition of diisopropylethylamine (15.1 g) at the same temperature. After stirring for 18 hours at 0° to 5°C, the reaction mixture was poured into a mixture of ethylacetate (500 ml) and water (300 ml). The pH was adjusted to 2.5 to 3.0 and the organic layer was separated. The organic layer so obtained was added to a mixture of 5% palladium on carbon (50 g) in aqueous buffer (300 ml) containing N-methylmorpholine and acetic acid (pH 6.0 to 7.0). The biphasic reaction mass was then hydrogenated for 3 to 4 hours under pressure at 10° to 20°C. After the completion of the reaction, the reaction mixture was filtered and the aqueous layer (350 ml) was separated. The aqueous layer was then added to isopropyl alcohol (3.5 L) at 20° to 25°C in 15 to 20 minutes.
After stirring at 0° to 5°C for 60 minutes, the reaction mixture was filtered and washed with isopropyl alcohol followed by acetone to yield the title compound.
Yield: 20 g
EXAMPLE 3
PREPARATION OF AMORPHOUS DORIPENEM
A mixture of 4-nitrobenzyl(2S,4S)-4-(acetylthio)-2-{[(aminosulfonyl)(tert- butoxy carbonyl)amino]methyl}pyrrolidine-1-carboxylate (53.5 g) and concentrated sulfuric acid (25 g) in methanol (250 ml) were refluxed for 3 hours, followed by cooling to ambient temperature. To the reaction mixture was poured into a mixture of methylene chloride (500 ml) and water (500 ml). The organic layer was separated and washed with water (2 X 500 ml) and concentrated under reduced pressure to give a concentrate containing 4-nitrobenzyl (2S,4S)-2-{[(aminosulfonyl)amino]methyl}-4-mercaptopyrrolidine-1-carboxylate. The concentrate so obtained was dissolved in N,N-dimethylformamide (50 ml) and added to enolphosphate (50 g) dissolved in N,N-dimethylformamide (200 ml) at 0° to 5°C, followed by drop wise addition of diisopropylethylamine (15.1 g) at the same temperature. After stirring for 18 hours at 0° to 5°C, the reaction mixture was poured into a mixture of ethylacetate (500 ml) and water (300 ml). The pH was adjusted to 2.5 to 3.0 and the organic layer was separated. The organic layer so obtained was added to a mixture of 5% palladium on carbon (50 g) in aqueous buffer (300 ml) containing N-methylmorpholine and acetic acid (pH 6.0 to 7.0). The biphasic reaction mass was then hydrogenated for 3 to 4 hours under pressure at 10° to 20°C. After the completion of the reaction, the reaction mixture was filtered and the aqueous layer (350 ml) was separated. The aqueous layer was then added to methanol (3.5 L) at 20° to 25°C in 15 to 20 minutes. After stirring at 0° to 5°C for 60 minutes, the reaction mixture was filtered and washed with methanol followed by acetone to yield the title compound.
Yield: 10 g

WE CLAIM:
1. A process for preparation of amorphous doripenem which comprises,
a) treating an aqueous solution of doripenem with a water miscible organic solvent,
b) isolating amorphous doripenem from the reaction mass thereof.

2. A process as claimed in claim 1 wherein the aqueous solution comprises of reaction mixture containing doripenem.
3. A process for preparation of amorphous doripenem of Formula I
(Formula Removed) which comprises
a) reacting enol-phosphate of Formula II
FORMULA II
wherein P1 represents a carboxyl protecting group, P2 represents hydrogen or a hydroxyl protecting group and X represents OP(0)(OR)2 or OS02R,
wherein R represents substituted or unsubstituted C1-6 alkyl, aralkyl or aryl with a thiopyrrolidine of Formula III
(Formula Removed)
6. A process as claimed in claim 5 wherein deprotection is carried out in presence of a buffering agent.
7. A process as claimed in claim 8 wherein the buffering agent comprises N-methylmorpholine and acetic acid.