PREPARATION OF TETRAHYDROLIPSTATIN BY HYDROGENATION OF LIPSTATIN, SOLVENT EXTRACTION AND PURIFICATION
FIELD OF THE INVENTION The present invention discloses a method of obtaining substantially pure 2-Formylamino-4-methyl-pentanoic acid l-(3-hexyl- 4-oxo-oxetan-2-ylmethyl)-dodecyl ester; wherein the crude (2S/3S 5S/7Z 10Z)-5-[(S)-2-formamido-4-methyl-valeryloxy]-2-hexyl- 3-hydroxy-7,10-hexadecadienoic 1,3 acid lactone is hydrogenated and purified to afford substantially pure 2-Formylamino-4-methyl- pentanoic acid l-(3-hexyl-4-oxo-oxetan-2-ylmethyl)-dodecyl ester. BACKGROUND The compound (2S,3S,5S,7Z,10Z)-5-[(S)-2-formamido-4-methyl- valeryloxy]-2-hexyl-3-hydroxy-7,10-hexadecadienoic 1,3 acid lactone, also called lipstatin, a pancreatic lipase inhibitor is produced by fermentation of Streptomyces toxytricini. 2-Formylamino-4-methyl- pentanoic acid l-(3-hexyl-4-oxo-oxetan-2-ylmethyl)-dodecyl ester, also called tetrahydrolipstatin, the active substance of the anti-obesity drug, is chemically reduced derivative of (2S,3S,5S,7Z,10Z)-5-[(S)-2- formamido-4-methyl-valeryloxy]-2-hexyl-3-hydroxy-7,10- hexadecadienoic 1,3 acid lactone and is obtained by hydrogenation of (2S,3S,5S,7Z,10Z)-5-[(S)-2-formamido-4-methyl-valeryloxy]-2-hexyl- 3-hydroxy-7,10-hexadecadienoic 1,3 acid lactone. KR 9709294 discloses novel active substance (2S,3S,5S,7Z,10Z)- 5-[(S)-2-formamido-4-methyl-valeryloxy]-2-hexyl-3-hydroxy-7,10- hexadecadienoic 1,3 acid lactone, which is produced by a Streptomyces sp. (KCTC-9303) isolated from soil. EP 0 803 576, this patent discloses a process for the
fermentative production of (2S,3S,5S,7Z,10Z)-5-[(S)-2-formamido-4- methyl-valeryloxy]-2-hexyl-3-hydroxy-7,10-hexadecadienoic 1,3 acid lactone, which comprises (a) aerobically cultivating a micro-organism of the order of actinomycetes which produces (2S,3S,5S,7Z,10Z)-5- [(S)-2-formamido-4-methyl-valeryloxy]-2-hexyl-3-hydroxy-7,10- hexadecadienoic 1,3 acid lactone, in an aqueous culture medium, substantially free of fats and oils, containing a suitable carbon and nitrogen sources and inorganic salts, (b) adding to the broth linoleic acid, optionally together with caprylic acid, their ester(s) or salt(s), stabilized by an antioxidant. (2S,3S,5S,7Z,10Z)-5-[(S)-2-formamido- 4-methyl-valeryloxy]-2-hexyl:3-hydroxy-7,10-hexadecadienoic 1,3 acid lactone can be isolated from the broth and hydrogenated to 2- Formylamino-4-methyl-pentanoic acid l-(3-hexyl-4-oxo-oxetan-2- ylmethyl)-dodecyl ester. EP 0 129 748, discloses a process for the production of t (2S,3S,5S,7Z,10Z)-5-[(S)-2-formamido-4-methyl-valeryloxy]-2-hexyl- 3-hydroxy-7,10-hexadecadienoic 1,3 acid lactone by fermentation of Streptomyces toxytricini, in a liquid nutrient media comprising potato starch, glucose, soybean meal, (NH4)2S04, ribose, glycerol, and peptone 0.2% and incubated at 28°C for 124 h with stirring and aeration, followed by extraction of the product. EP 1 028 115 describes a process for purifying (2S,3S,5S/7Z,10Z)-5-[(S)-2-f6rmamido-4-methyl-valeryloxy]-2-hexyl- 3-hydroxy-7,10-hexadecadienoic 1,3 acid lactone comprising; a) oxidation of methionine-analogofus (2S,3S,5S,7Z,10Z)-5-[(S)-2- formamido-4-methyl-valeryloxy]-2-hexyl-3-hydroxy-7,10- hexadecadienoic 1,3 acid lactone, b) double-current extraction of
crude (2S,3S,5S,7Z,10Z)-5-t(S)-2-formamido-4-methyl-valeryloxy]-2- hexyl-3-hydroxy-7,10-hexadecadienoic 1,3 acid lactone in about 95 % acetic acid/heptane; c) diluting the (2S,3S,5S,7Z,10Z)-5~[(S 2- formamido-4-methyl-valeryloxy]-2-hexyl-3-hydroxy-7,10- hexadecadienoic 1,3 acid lactone solution with water to about 80 % acetic acid; and d) counter-current extraction of the solution with heptane. This process may be followed by hydrogenation of (2S,3S,5S,7Z,10Z)-5-[(S)-2-formamido-4-methyl-valery)oxy]-2-hexyl- 3-hydroxy-7,10-hexadecadϊenoic 1,3 acid lactone to 2-Formylamino-4- methyl-pentanoic acid l-(3-hexyl-4-oxo-oxetan-2-ylmethyl)~dodecyl ester, optionally followed by crystallization of 2-Formylamino-4- methyl-pentanoic acid l-(3-hexyl-4-oxo-oxetan-2-ylmethyl)-dodecyl ester. Existing prior art does not demonstrate ease of purification, handling large-scale preparation and scalability in the production of said pancreatic lipase inhibitor 2-Formylamino-4-methyl-pentanoic acid l~(3-hexyl-4-oxo-oxetan-2-ylmethyl)-dodecy( ester. EP 1 028 115 teaches method of purifying (2S,3S,5$,7Z,10Z)-5-[(S)-2-formarnido-4- methyl-valeryloxy]-2-hexyl-3-hydroxγ-7,10-hexadecadJenoic 1,3 acid lactone by liquid-liquid extraction that involves counter-current extraction of the solution with heptane where the commercial viability of the process is compromised. Accordingly the objective of the instant invention is to provide a novel commercially viable process for the purification of 2- Formylamino-4-methyl-pentanoic acid l-(3~hexy(-4~oxo-oxetan-2~ ylmethyl)-dodecyl ester with ability of large-scale preparation and scalability.
SUMMARY OF THE INVENTION The instant invention discloses a novel process for obtaining pure
2-Formylamino-4-methyl-pentanoic acid l-(3-hexyl-4-oxo-oxetan-2- ylmethyl)-dodecyl ester comprising of: a) extraction of a water miscible layer containing (2S,3S,5S,7Z,10Z)- 5-[(S)-2-formamido-4-methyl-valeryloxy]-2-hexyl-3-hydroxy-7,10- hexadecadienoic 1,3 acid lactone with a water immiscible solvent, b) concentration of the water immiscible layer, c) extraction of the concentrate with a water miscible solvent, and optional treatment with water immiscible solvent, d) addition of palladium on carbon to the water miscible layer and hydrogenation under pressure to afford 2-Formylamino-4-methyl- pentanoic acid l-(3-hexyl-4-oxo-oxetan-2-ylmethyl)-dodecyl ester, e) filtration of the hydrogenated reaction mixture of (d), f) addition of water or water miscible solvent, g) extraction with water immiscible solvent and concentration, h) affording 2-Formylamino-4-methyl-pentanoic acid l-(3-hexy!-4- oxo-oxetan-2-ylmethyl)-dodecyl ester, i) treating with water miscible solvent j) optionally, treating with neutral alumina and filtration k) affording 2-Formylamino-4-methyl-pentanoic acid l-(3-hexyl-4- oxo-oxetan-2-ylmethyl)-dodecyl ester of acceptable pharmaceutical purity. The instant process has the following major advantages: 1. Easy scalability. 2. It is economic and efficient
3. It avoids tedious purification steps of intermediates.
5 4. Eliminates use expensive solvents like heptane. DETAILED DESCRIPTION The instant invention discloses a novel process for obtaining pure 2-Formylamino-4-methyl-pentanoic acid l-(3-hexyl-4-oxo-oxetan-2- ylmethyl)-dodecyl ester comprising of: ιo a) extraction of a water miscible layer containing (2S,3S,5S,7Z,10Z)- 5-[(S)-2-formamido-4-methyl-valeryloxy]-2-hexyl-3-hydroxy-7,10- hexadecadienoic 1,3 acid lactone with a water immiscible solvent, b) concentration of the water immiscible layer, c) extraction of the concentrate with a water miscible solvent, and i5 optional treatment with water immiscible solvent, d) addition of palladium on carbon to the water miscible layer and hydrogenation under pressure to afford 2-Formylamino-4-methyl- pentanoic acid l-(3-hexyl-4-oxo-oxetan-2-ylmethyl)-dodecyl ester, e) filtration of the hydrogenated reaction mixture of (d),0 f) addition of water or water miscible solvent, g) extraction with water immiscible solvent and concentration, h) affording 2-Formylamino-4-methyl-pentanoic acid l-(3-hexyl-4- oxo-oxetan-2-ylmethyl)-dodecyl ester, i) treating with water miscible solvent,5 j) optionally, treating with neutral alumina and filtration k) affording to get 2-Formylamino-4-methyl-pentanoic acid l-(3- hexy!-4-oxo-oxetan-2-ylmethyl)-dodecyl ester of acceptable pharmaceutical purity. The water immiscible solvent can be selected from esters oro hydrocarbons, heterocyclic solvents or any suitable water immiscible
solvent. Preferably, the water immiscible solvent is selected from ethyl acetate, isopropyl acetate or butyl acetate. The water miscible solvent can be selected from water, carboxylic acids, alcohols, dipolar aprptic solvents or any suitable water miscible solvent. Preferably, the water miscible solvent is an alcohol. Preferably the alcohol is methanol. The filtration steps can be carried out with a filter aid, preferably cellite. The hydrogenation reaction in step (d) can be carried out for 2 - 12 hour. The hydrogenation reaction is carried out under pressure, preferably at 1 to 10 kg. 2-Formylamino-4-methyl-pentanoic acid l-(3-hexyl-4-oxo- oxetan-2-ylmethyl)-dodecyl ester can be afforded by change of the physical state of the solvent selected or the product. Preferably the changed physical state of the solvent is gaseous state. Preferably the changed physical state of the product is solid state. The change in the physical state can be carried out either by heating or by cooling, optionally under reduced pressure. The change in the physical state can be carried out by concentration. The cooling can be carried out at a temperature below the freezing point of the solvent employed. The drying can be carried out at higher temperature to evaporate the solvent, optionally under reduced pressure, or at low temperature under reduced pressure to vaporize the solvent employed.
The instant invention discloses a novel process for obtaining pure 2-Formylamino-4-methyl-pentanoic acid l-(3-hexyl-4-oxo- oxetan-2-ylmethyl)-dodecyl ester comprising of: a. extraction of an aqueous layer containing (2S,3S,5S,7Z,10Z)-5- [(S)-2-formamido-4-methyl-valeryloxy]-2-hexyl-3-hydroxy-7,10- hexadecadienoic 1,3 acid lactone with ethyl acetate, b. concentration of the ethyl acetate layer, c. extraction of the concentrate with methanol, and optionally treating with petroleum ether, d. addition of palladium on carbon to the methanol layer and hydrogenation under pressure to afford 2-Formylamino-4-methyl- pentanoic acid l-(3-hexyl-4-oxo-oxetan-2-ylmethyl)-dodecyl ester, e. filtration of the hydrogenated reaction mixture of (d), f. addition of water to the reaction mixture, g. extraction with petroleum ether and concentration, h. affording 2-Formylamino-4-methyl-pentanoic acid l-(3-hexyl-4-oxo- oxetan-2-ylmethyl)-dodecyl ester, i. treating with acetonitrile, j. optionally, treating with neutral alumina and filtration k. affording 2-Formylamino-4-methyl-pentanoic acid l-(3-hexyl-4-oxo- oxeta n-2-y I methyl )-dodecyl ester of acceptable pharmaceutical purity.
The following non-limiting examples illustrate the inventors' preferred method for preparing the compound of the invention. EXAMPLES EXAMPLE 1 The fermentation broth (3 KL) is extracted with ethyl acetate (3 x 1500 L) and concentrated. The syrup containing crude
(2S,3S,5S,7Z,10Z)-5-[(S)-2-formamido-4-methyl-valeryloxy]-2-hexyl- 3-hydroxy-7,10-hexadecadienoic 1,3 acid lactone (weighing ~30 Kg) was extracted with methanol (4 x 30L). Water (6 L) was added to the combined methanol extract and washed with petroleum ether (2 x 30 L). The methanol layer was treated with activated charcoal (5 Kg) and stirred for 30 minutes. It was filtered over celite bed. To the clear filtrate, Palladium on Carbon (1.5 Kg, 10%, wet by water 1:1) was added and hydrogenated under pressure (5 Kg) for 8 hours. After completion of the reaction (by TLC), reaction mixture was filtered over celite bed. The clear filtrate was diluted with water (50 L) and extracted with petroleum ether (3 x 50 L). Combined extract was concentrated and chilled to -5 to 0° C and crystals of crude 2- Formylamino-4-methyl-pentanoic acid l-(3-hexyl-4-oxo-oxetan-2- ylmethyl)-dodecyl ester filtered. The crude product was dissolved in acetonitrile (50 L) and neutral alumina (1.0 Kg) was added. After stirring for 1 hour, the mixture was filtered over celite bed and evaporated to get title compound of acceptable pharmaceutical purity. Yield: 6.0 Kg EXAMPLE 2 The fermentation broth (300 L) is extracted with isobutyl acetate (3 x 150 L) and concentrated. The syrup containing crude
(2S,3S,5S,7Z,10Z)-5-[(S)-2-formamido-4-methyl-valeryloxy]-2-hexyl- 3-hydroxy-7,10-hexadecadienoic 1,3 acid lactone (weighing ~3 Kg) was and extracted with ethanol (4 x 3 L). Water (1 L) was added to the combined ethanol extract and washed with petroleum ether (2 x 3 L). The ethanol layer was treated with activated charcoal (0.5 Kg) and stirred for 30 minutes. It was filtered over celite bed. To the clear filtrate, Palladium on Carbon (0.15 Kg, 10%, wet by water 1:1) was added and hydrogenated under pressure (3 Kg) for 5 hours. After completion of the reaction (by TLC), reaction mixture was filtered over celite bed. The clear filtrate was diluted with water (5 L) and extracted with petroleum ether (3 x 5 L). Combined extract was concentrated and chilled to -5 to 0° C and crystals of crude 2- Formylamino-4-methyl-pentanoic acid l-(3-hexyl-4-oxo-oxetan-2- ylmethyl)-dodecyl ester filtered. The crude product was dissolved in acetonitrile (5 L) and neutral alumina (0.1 Kg) was added. After stirring for 1 hour, the mixture was filtered over celite bed and evaporated to get title compound of acceptable pharmaceutical purity. Yield: 500 G EXAMPLE 3 The fermentation broth (300 L) is extracted with butyl acetate (3 x 150 L) and concentrated. The syrup containing crude
(2S,3S,5S,7Z,10Z)-5-[(S)-2-formamido-4-methyl-valeryloxy]-2-hexyl- 3-hydroxy-7,10-hexadecadienoic 1,3 acid lactone (weighing ~3 Kg) was and extracted with isopropanol (4 x 3 L). Water (1 L) was added to the combined isopropanol extract and washed with petroleum ether (2 x 3 L). The isopropanol layer was treated with activated charcoal (0.5 Kg) and stirred for 30 minutes. It was filtered over celite bed. To
the clear filtrate, Palladium on Carbon (0.15 Kg, 10%, wet by water 1:1) was added and hydrogenated under pressure (4 Kg) for 6 hours. After completion of the reaction (by TLC), reaction mixture was filtered over celite bed. The clear filtrate was diluted with water (5 L) and extracted with petroleum ether (3 x 5 L). Combined extract was concentrated and chilled to -5 to 0° C and crystals of crude 2- Formylamino-4-methyl-pentanoic acid l-(3-hexyl-4-oxo-oxetan-2- ylmethyl)-dodecyl ester filtered. The crude product was dissolved in acetonitrile (5 L) and neutral alumina (0.1 Kg) was added. After stirring for 1 hour, the mixture was filtered over celite bed and evaporated to get title compound of acceptable pharmaceutical purity. Yield: 550 G