The present invention provides a one-pot process for preparation of nelfinavir or salts thereof. The present invention further provides novel crystalline form of Nelfinavir mesylate and process for its preparation. The novel crystalline form of Nelfinavir mesylate has been designated as Form I of Nelfinavir mesylate.
Nelfinavir is chemically [3S-[2(2S*,3S*),3a,4ap,8ap]]-N-(1,1-dimethylethyl)decahydro-2-[2-hydroxy-3-[(3-hydroxy-2-methylbenzoyl)amino]-4-(phenylthio)butyl]-3-isoquinoline carboxamide. It is commercially available in the form of its mono-methanesulfonate of Formula I.
(Formula Removed)
Nelfinavir formerly known as AG1343 belongs to the class of HIV-protease inhibitor indicated for the treatment of HIV infection when antiretroviral combination therapy is warranted. It was originally used in combination with antiretroviral nucleoside analogues for the treatment of HIV-1 in adults, adolescents and children. Nelfinavir is a member of the group of drugs referred to as protease inhibitors (Pis). This class of drug combats viral replication of HIV by blocking HIV's protease protein. This protein or enzyme is used by HIV to break up large viral proteins into smaller particles from which new HIV particles can be formed. Protease inhibitors ensure that these new particles are immature and incapable of infecting new cells, thus inhibiting the HIV replication process.
Several processes are known in the literature for preparation of nelfinavir or salt thereof, viz., PCT Application No. 95/09843; European Patent No. 983,999; PCT Application No. 98/09951; PCT Application No. 98/09952 and PCT Application No. 01/29013. All the processes provide amorphous nelfinavir mesylate.
However, these known processes isolate each and every intermediate formed in the reaction sequence and therefore are time consuming and less yielding.
The present inventors have surprisingly found that Nelfinavir or salts thereof can be prepared by a one-pot process involving reaction of (2S,3R)-1,2-epoxy-3-N-(protected)-amino-4-phenylthiobutane of Formula II or salt thereof, wherein R1 and R2 are independently hydrogen or amino protecting group with proviso that both R1 and R2 are not hydrogen or R1 and R2 do not combine together to form a divalent amino protecting group,
(Formula Removed)
with 3-t-butylcarboxamide perhydroisoquinoline of Formula III.
(Formula Removed)
The product of Formula IV so obtained wherein R1 and R2 are as defined earlier,
(Formula Removed)
is deprotected to get compound of Formula V.
(Formula Removed)
which is then condensed with 3-acetoxy-2-methyl benzoyl chloride of Formula VI wherein R3 represents hydroxy protecting group,
(Formula Removed)
Removal of the hydroxy protecting group provides nelfinavir, which can be then converted to its salt. The entire reaction sequence is characterized by the fact that no intermediate is isolated. It is observed that the yield of the so obtained nelfinavir is
increased significantly. Also the time required for preparation of nelfinavir or salt thereof is appreciably reduced thus making the process more viable on commercial scale. In-situ processes have inherent drawback of purity as the isolation and purification of intermediates is not possible. However, it is observed that the resultant nelfinavir obtained is of superior quality and the impurity content is comparable with that obtained earlier. Suitable amino and hydroxy protecting groups are known to a person skilled in the art.
The present inventors have also surprisingly found that nelfinavir mesylate exists in novel crystalline form designated herein after as Form I of Nelfinavir mesylate. Amorphous forms have problems associated with stability and their formulation poses several problems. Crystalline Form I of nelfinavir mesylate is advantageous as it can be prepared by simple methods and is present in pure form stable at normal and accelerated stability conditions.
A first aspect of the present invention provides crystalline Form I of Nelfinavir mesylate having X-Ray Diffraction pattern (XRD) as depicted in Figure I of the accompanied drawings. The XRD of form I shows characteristic 29 values at 7.74, 9.54, 10.84, 11.16, 12.00, 12.40, 12.90, 13.42, 13.56, 15.40, 16.54, 17.26, 17.66, 18.14, 18.60, 19.20, 19.60, 20.08, 20.86, 21.82, 22.16, 22.96, 23.46, 23.84, 24.42, 25.04, 25.24, 25.70, 26.08, 26.24, 26.70, 27.08, 27.42, 27.98, 28.20, 28.58, 29.28, 29.40, 30.08, 30.22, 30.78, 31.82, 32.34, 32.76, 32.92, 33.44, 33.62, 34.32, 34.62, 34.72, 36.12. The Crystalline Form I of Nelfinavir mesylate has characteristic Differential Scanning Calorimetric (DSC) thermogram as depicted in Figure II of the accompanied drawings wherein the characteristic endothermic absorption is observed between 118°C and 128°C. The Fourier Transform Infrared (FTIR) spectrum of crystalline Form I of Nelfinavir mesylate has been depicted in Figure III of the accompanied drawings.
A second aspect of the present invention provides a one pot process for preparation of Nelfinavir or salts thereof, wherein the said process comprises of, a) reacting compound of Formula II or salt thereof,
(Formula Removed)
wherein R1 and R2 are independently hydrogen or amino protecting group with proviso that both R1 and R2 are not hydrogen or R1 and R2 do not combine together to form a divalent amino protecting group with 3-t-butylcarboxamide perhydroisoquinoline of Formula III,
(Formula Removed)
to get compound of Formula IV,
(Formula Removed)
wherein R1 and R2 are as described herein before
b) deprotecting the compound of Formula IV to get compound of Formula V,

(Formula Removed)
c) condensing the compound of Formula V with compound of Formula VI,
(Formula Removed)
wherein R3 represents hydroxy protecting group, to get protected nelfinavir,
d) deprotecting the hydroxy protecting group of protected nelfinavir,
e) isolating Nelfinavir or salt thereof from the reaction mixture thereof.
wherein the entire process is characterized by the fact that it is carried out in-situ without isolation of any intermediate.
A solution of (2S,3R)-1,2-epoxy-3-N-(protected)-amino-4-phenylthiobutane of Formula II and 3-t-butylcarboxamide perhydroisoquinoline of Formula III in a suitable organic solvent comprising of C1-4 alkanols; C3-10 ketones; polar aprotic solvents; chlorinated hydrocarbons; non-polar aprotic solvents; C2-10 esters; C4-8 ethers was stirred for 15 hours at about 30 to 50°C and the reaction monitored for formation of compound of Formula IV. After completion of the reaction an aqueous solution of a suitable deprotecting agent selected from inorganic or organic bases was added to deprotect
the protected-amino group in the compound of formula IV to get compound of formula V and the resulting suspension heated to reflux for about 15-30 hours. The reaction mixture was charged with water and organic solvent comprising of chlorinated hydrocarbons; non-polar aprotic solvents; C2-10 esters; C4-8 ethers. The organic layer was separated and treated with a base selected from inorganic or organic bases. To the reaction mixture was added a solution of 3-O-protected-2-methyl benzoyl chloride (compound of formula VI) in organic solvent comprising of chlorinated hydrocarbons; non-polar aprotic solvents; C2-10 esters; C4-8 ethers at about 5-30°C with stirring for 0.5-1 hour. The reaction mixture was charged with water, the organic layer was separated and evaporated under vacuum at about 25-40°C to obtain O-protected nelfinavir. The resulting paste was charged with an organic solvent comprising of C1-4 alkanols; C3-10 ketones; polar aprotic solvents; chlorinated hydrocarbons; non-polar aprotic solvents; C2-10 esters; C4-8 ethers and treated with a suitable deprotecting agent selected from inorganic or organic bases to deprotect the O-protected nelfinavir. pH of the reaction mixture was adjusted to about 7-8. Water was charged and the resulting mass was heated to about 50-70°C, filtered, washed and dried to obtain Nelfinavir free base. Nelfinavir free base thus obtained can be converted to its salts.
The inorganic or organic bases can be selected from the group comprising of alkali and alkaline earth metal hydroxide or alkoxide or carbonate or bicarbonate, ammonia, triethylamine, dicyclohexylamine amine or diisopropylamine and the like.
A third aspect of the present invention provides process for preparation of crystalline Form I of Nelfinavir mesylate, wherein the said process comprises of,
a) treating nelfinavir free base with methanesulphonic acid in presence of C3-10
ketone, C1-4 alkanol or mixture thereof
b) crystallizing Form I of nelfinavir mesylate from the reaction mixture thereof.
Nelfinavir free base can be prepared by methods known in the art or according to the process of the present invention. Nelfinavir free base was suspended in a suitable solvent comprising of C3-10 ketone, C1-4 alkanol and the suspension heated to about
40-60°C. To this solution methanesulphonic acid was added and the reaction mixture stirred for about 10-20 minutes. The reaction mixture was charged with active carbon, stirred, filtered. The filtrate was stirred for about 2 hours at room temperature and then refluxed for 1 hour. The solution was allowed to cool to about 50°C to ambient temperature for crystallization to occur after which crystalline Form I of Nelfinavir mesylate was isolated and purified by suitable means. Adding seed crystals of Form I of nelfinavir mesylate can also effect the crystallization.
Figure 1 depicts the X-Ray Diffraction Pattern of crystalline Form I of Nelfinavir
mesylate.
Figure 2 depicts Differential Scanning Calorimetric (DSC) thermogram of crystalline
Form I of Nelfinavir mesylate.
Figure 3 depicts Fourier Transform Infrared (FTIR) spectrum of crystalline Form I of
Nelfinavir mesylate.
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 NELFINAVIR FREE BASE
A solution of (2S,3R)-1,2-epoxy-3N-(benzyloxycarbonyl)-amino-4-phenylthiobutane (50 g) and 3-t-butylcarboxamide perhydroisoquinoline (39.9 g) in ethanol (100 ml) was stirred at 40°C for 15 hours and monitored (Thin Layer Chromatography/High Performance Liquid Chromatography). After the completion of reaction a solution of NaOH (12.1 g) in water (12.1 ml) was added. The resulting suspension was heated to reflux for 20 hours. After the completion of reaction water (250 ml) and dichloromethane (250 ml) were charged. The mixture was stirred for 10 minutes and allowed to settle. The lower dichloromethane layer was collected. To the
dichloromethane layer triethylamine (42 ml) was charged under stirring. This mixture was added dropwise to a solution of 3-acetoxy-2-methyl benzoyl chloride (32.3 g) in dichloromethane (100 ml) at 5-25°C in 30 minutes. The reaction mixture was stirred for 30 minutes and monitored (Thin Layer Chromatography/High Performance Liquid Chromatography). Water (250 ml) was charged followed by stirring again for 10 minutes. This mixture was allowed to settle for 5 minutes and the dichloromethane layer collected and evaporated under vacuum at 35°C. To the resulting paste ethanol (100 ml) and a solution of NaOH (12.1 g) in water (12.1 ml) were added and the mixture stirred for 2 hours and the reaction monitored (Thin Layer Chromatography/High Performance Liquid Chromatography). The pH of the mixture was adjusted to 7.5 by adding a mixture of acetic acid (15 ml) in water (15 ml). Water (750 ml) was charged and the resulting white mass was heated to 60°C and stirred for 1 hour. The white solid was filtered and slurry washed with water. The solid so obtained was dried in air at 80°C to afford Nelfinavir free base. Purity = 80% by HPLC
EXAMPLE 2
PREPARATION OF CRYSTALLINE FORM I OF NELFINAVIR MESYLATE
Nelfinavir obtained in Example 1 was suspended in acetone (600 ml) and the suspension heated to 55°C. To this solution methane sulphonic acid (14.2 g) was added and the reaction mixture stirred for 15 minutes at 55°C. Active carbon was charged at 55°C with stirring for 15 minutes followed by filtration through hyflow. The resulting clear filtrate was stirred for 2.0 hours at room temperature and heated to reflux for 1 hour after which heating was stopped. The reaction mixture was allowed to attain a temperature of 40°C, filtered and slurry washed with acetone (50 ml x 2). The solid so obtained was dried under vacuum at 80°C for 24 hours to afford crystalline Form I of Nelfinavir mesylate. Yield = 65 g Purity = 99.5% by HPLC

WE CLAIM:
1. Crystalline Form I of Nelfinavir mesylate.
2. Crystalline Form I of Nelfinavir mesylate having a XRPD pattern wherein
characteristic 20 values are obtained at 7.74, 9.54, 10.84, 11.16, 12.00, 12.40, 12.90,
13.42, 13.56, 15.40, 16.54, 17.26, 17.66, 18.14, 18.60, 19.20, 19.60, 20.08, 20.86,
21.82, 22.16, 22.96, 23.46, 23.84, 24.42, 25.04, 25.24, 25.70, 26.08, 26.24, 26.70,
27.08, 27.42, 27.98, 28.20, 28.58, 29.28, 29.40, 30.08, 30.22, 30.78, 31.82, 32.34,
32.76, 32.92, 33.44, 33.62, 34.32, 34.62, 34.72, 36.12.
3. Crystalline Form I of Nelfinavir mesylate having characteristic endothermic melting
point between 118-128°C.
4. A one pot process for preparation of Nelfinavir or salts thereof, wherein the said
process comprises of,
a) reacting compound of Formula II or salt thereof,
(Formula Removed)
wherein R1 and R2 are independently hydrogen or amino protecting group with the provisos that both R1 and R2 are not hydrogen or R1 and R2 do not combine together to form a divalent amino protecting group, with 3-t-butylcarboxamide perhydroisoquinoline of Formula III,
(Formula Removed)
to get compound of Formula IV,
(Formula Removed)
wherein R1 and R2 are as described herein before
b) deprotecting the compound of Formula IV to get compound of Formula V,
(Formula Removed)
c) condensing the compound of Formula V with compound of Formula VI,
(Formula Removed)
wherein R3 represents hydroxy protecting group to get protected nelfinavir,
d) deprotecting the hydroxy protecting group of protected nelfinavir,
e) isolating Nelfinavir or salt thereof from the reaction mixture thereof.
wherein the entire process is characterized by the fact that it is carried out in-situ without isolation of any intermediate.
5. The process according to claim 4, wherein step a) is carried out in an organic
solvent selected from the group comprising of C1-4 alkanols; C3-10 ketones; polar
aprotic solvents; chlorinated hydrocarbons; non-polar aprotic solvents; C2-10 esters;
C4-8 ethers.
6. The process according to claim 4, wherein in steps b) and d) the deprotecting agent
is an organic or inorganic base.
7. The process according to claim 4, wherein in step c) the condensation reaction is
carried out in the presence of an organic or inorganic base.
8. The process according to claims 5 and 6 wherein the base is selected from the
group comprising of alkali and alkaline earth metal hydroxide or alkoxide or
carbonate or bicarbonate, ammonia, triethylamine, dicyclohexylamine amine or
diisopropylamine and the like.
9. A process for preparation of crystalline Form I of Nelfinavir mesylate, wherein the
said process comprises of,
a) treating nelfinavir free base with methanesulphonic acid in presence of C3-10
ketone, C1-4 alkanol or mixture thereof,
b) crystallizing Form I of nelfinavir mesylate from the reaction mixture thereof.
10. The process according to claim 9 wherein the reaction is carried out between 25-
80°C.