Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D409/00—Heterocyclic compounds containing two or more hetero rings, at least one ring having sulfur atoms as the only ring hetero atoms
  • C07D409/02—Heterocyclic compounds containing two or more hetero rings, at least one ring having sulfur atoms as the only ring hetero atoms containing two hetero rings
  • C07D409/06—Heterocyclic compounds containing two or more hetero rings, at least one ring having sulfur atoms as the only ring hetero atoms containing two hetero rings linked by a carbon chain containing only aliphatic carbon atoms
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K31/00—Medicinal preparations containing organic active ingredients
  • A61K31/33—Heterocyclic compounds
  • A61K31/395—Heterocyclic compounds having nitrogen as a ring hetero atom, e.g. guanethidine or rifamycins
  • A61K31/435—Heterocyclic compounds having nitrogen as a ring hetero atom, e.g. guanethidine or rifamycins having six-membered rings with one nitrogen as the only ring hetero atom
  • A61K31/44—Non condensed pyridines; Hydrogenated derivatives thereof
  • A61K31/4427—Non condensed pyridines; Hydrogenated derivatives thereof containing further heterocyclic ring systems
  • A61K31/4436—Non condensed pyridines; Hydrogenated derivatives thereof containing further heterocyclic ring systems containing a heterocyclic ring having sulfur as a ring hetero atom
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D335/00—Heterocyclic compounds containing six-membered rings having one sulfur atom as the only ring hetero atom
  • C07D335/02—Heterocyclic compounds containing six-membered rings having one sulfur atom as the only ring hetero atom not condensed with other rings

Definitions

• the present invention relates to a method of treating acne or psoriasis by topically administering Tazarotene, a compound of formula (I), substantially free of dimer impurity 4,4-dimethyl-6-[4-(4,4-dimethylthiochroman-6-yl)-buta- 1 ,3-diynyl]- thiochroman, a compound of formula (II)
• Tazarotene (Formula I) is the international common accepted name for ethyl 6-[(4,4- dimethylthiochroman-6-yl)ethynyl]nicotinate, and has an empirical formula of C 2
• US Patent No. 5,089,509 (the '509 patent) disclosed a process for preparation of tazarotene which includes following steps:
• US Patent application No. 2006/0106233 discloses Sonogashira coupling of 4,4- dimethyl-6-ethynylthiochroman (formula VIII) with ethyl 6-chloronicotinate (formula IX) using triethnolamine, palladium catalyst and cuprous iodide to give tazarotene which is converted to its hydrochloride salt by treatment with ethyl acetate HC1 solution.
• PCX application No. 2006/040644 discloses use of sulfuric acid or p-toluenesulfonic acid for cyclization of phenyl 3-methylbut-2-enyl sulfide (formula V) to give 4,4- dimethylthiochroman (formula VI). It also discloses conversion of 4,4-dimethyl-6- acetylthiochroman (formula VII) to 4,4-dimethyl-6-ethynylthiochroman (formula VIII) by sequential reaction with hydrazine and iodine.
• US Patent No. 5,602,130 discloses alternative method for preparation of 4,4-dimethyl-6-ethynylthiochroman (formula VIII) by using 4-bromothiophenol (formula X) instead of thiophenol.
• 4-Bromothiophenol is reacted with l-bromo-3-methyl-2-butene (formula III) and subsequently cyclized to give 6-bromo-4,4-dimethylthiochroman (formula XII).
• 6-Bromo-4,4-dimethylthiochroman is coupled with trimethylsilylacetylene using palladium catalyst to give 6-(trimethylsilylethynyl)-4,4-dimethylthiochroman ' (formula XIII) which on desilylation with a base gives 4,4-dimethyl-6- ethynylthiochroman (formula VIII).
• the reaction sequence is represented as per scheme- II:
• US Patent No. 7,273,937 discloses the process for preparation of tazarotene, wherein 4,4- dimethyl-6-bromothiochroman (formula XII) is oxidized to the corresponding 6-bromo- 4,4-dimethylthiochroman-l -oxide (formula XIV), which is reacted with 2-methyl-3- butyn-2-ol to give 4-(4,4-dimethyl-l-oxothiochroman-6-yl)-2-methylbut-3-yn-2-ol (formula XV).
• Tazarotene is available as cream, gel and aerosol foam in the markets. Journal article titled "The safety and efficacy of tazarotene gel, a topical acetylenic retinoid, in the treatment of psoriasis" published in Archives of dermatology, Volume: 134, Issue: 1, Pages: 57-60 states that most common adverse effect associated with tazarotene were mild to moderate burning, pruritus, stinging and erythema. In most cases erythema was manifestation of mild to moderate irritation. Adverse events associated with tazarotene resulted in cessation of treatment in about 5 % of patient population.
• Formula II also referred as the dimer impurity in present specification may be formed due to homocoupling of 4,4-dimethyl-6-ethynylthiochroman used as an intermediate during the synthesis of tazarotene. Isolation and characterization of the dimer impurity is disclosed in Journal of Pharmaceutical and Biomedical Analysis, Volume: 46 (2008), Issue 3, Pages: 574-576, titled "Impurities of tazarotene: Isolation and structural characterization". However, the article is silent on the toxic properties of the impurity. In fact none of the literature available till date talks about the toxicity of this impurity. We have surprisingly found that this dimer impurity is
• the present invention provides a method of treating acne or psoriasis by topically administering tazarotene, a compound of formula (I), substantially free of dimer impurity 4,4-dimethyl-6-[4-(4,4-dimethylthiochroman-6-yl)-buta-l ,3-diynyl]- thiochroman, a compound of formula (II).
• the present invention provides a method of treating acne or psoriasis by topically administering tazarotene substantially free of dimer impurity of Formula II
• the present invention provides a process for purification .of a compound of Formula I (tazarotene) to obtain tazarotene having dimer impurity content of less than 100 ppm wherein the process comprises:
• step b adding the tazarotene acid addition salt obtained in step b to an organic solvent and adding an aqueous solution of a base to obtain a biphasic mixture
• the present invention provides Tazarotene, a compound of formula (I), substantially free of dimer impurity 4,4-dimethyl-6-[4-(4,4-dimethylthiochroman-6-yl)-buta-l ,3-diynyl]- thiochroman, a compound of formula (II).
• the term substantially free is intended to mean that the dimer impurity in tazarotene does not exceed 100 ppm when analyzed as per the analytical method exemplified in this specification.
• the dimer impurity may be generated during Sonogashira coupling between 4,4- dimethyl-6-ethynylthiochroman and ethyl 6-chloronicotinoate, homocoupling of 4,4- dimethyl-6-ethynylthiochroman as shown in Scheme V.
• Table 1 shows the variable concentration of dimer impurity samples. Each sample (100 ⁇ ) was applied topically once daily on the left and right ear of the animals (Sprague Dawley Rats) of the respective groups from day 0 to day 9. Animals were checked for recovery from day 10 to day 14. Ear thickness measurement was repeated on day 3, 7, 10, 12 and 14. The results are provided in Table 2 and in Figure 1.
• the present invention provides a method of treating acne or psoriasis by topically administering tazarotene substantially free of dimer impurity of Formula II.
• the content of dimer impurity in tazarotene is less than 100 ppm.
• the content of the dimer impurity is less than 30 ppm. More preferably, the content of the dimer impurity is less than 10 ppm. Most preferably, the content of the dimer impurity is less than 5 ppm.
• the method of the present invention requires application of a topical composition of tazarotene wherein, the content of a compound of Formula II in tazarotene is less than 50 ppm.
• the content of the dimer impurity is less than 30 ppm. More preferably, the content of the dimer impurity is less than 10 ppm. Most preferably, the content of the dimer impurity is less than 5 ppm.
• topically administrable composition or “topical composition,” or a “topical formulation,” as used herein, means any formulation or composition which is pharmaceutically acceptable for topical delivery of the specified compound according to embodiments of the invention.
• exemplary forms of composition that can be used for topical administration in embodiments, of the present invention include, but are not limited to, sprays, mists, aerosols, solutions, lotions, gels, creams, ointments, pastes, unguents, emulsions and suspensions.
• the present invention provides a process for preparation of Tazarotene substantially free of dimer impurity of Formula II comprising:
• step b adding the tazarotene acid addition salt obtained in step b to an organic solvent and adding an aqueous solution of a base to obtain a biphasic mixture
• Tazarotene used in step 'a' with high dimer impurity content of 400 ppm or more can be obtained by the processes known in the art for example the '509 patent.
• Tazarotene containing dimer impurity is dissolved in an organic solvent selected from the group comprising of ester like ethyl acetate, ethyl butyrate, isopropyl acetate, methyl acetate, methyl propionate, propyl acetate etc., ether like dioxane, tetrahydrofuran (THF), 2- methyl tetrahydrofuran, diethyl ether, methyl tert-butyl ether, diisopropyl ether etc., saturated hydrocarbon like hexane, heptane etc., aromatic hydrocarbon like toluene, benzene etc., halogenated solvent like carbon tetrachloride, chlorobenzene, chloroform, 1,1-dichlor
• step 'b' Tazarotene with dimer impurity content of more than 400 ppm is converted into its acid addition salt via reaction with suitable acid in a manner well known to those skilled in the art.
• a solution of inorganic mineral acid is added to above solution to get precipitate of tazarotene acid addition salt.
• Solution of inorganic mineral acid can be made in a compatible solvent like water or an alcohol.
• Alcohol used in the step can selected from the group of C1 -C4 alkanols.
• the alcohol is ethanol.
• Inorganic mineral acid used in the step can be selected from the group of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid.
• the inorganic mineral acid is hydrochloric acid.
• the precipitate is filtered, washed with the organic solvent and dried to give tazarotene acid addition salt.
• the organic solvent used for washing can be same as that used for salt preparation.
• the tazarotene acid addition salt is suspended in a water immiscible organic solvent selected from the group of ether like dioxane, tetrahydrofuran (THF), 2-methyl tetrahydrofuran, diethyl ether, methyl tert- butyl ether, diisopropyl ether etc., C 6 to C 7 substituted or unsubstituted acyclic or cyclic aliphatic hydrocarbon like hexane, heptane, cyclohexane etc., aromatic hydrocarbons like toluene, benzene etc., and treated with an aqueous solution of inorganic base.
• a water immiscible organic solvent selected from the group of ether like dioxane, tetrahydro
• the inorganic base is selected from the group of sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, lithium carbonate, lithium bicarbonate, cesium carbonate, cesium bicarbonate.
• Organic layer is separated, dried and concentrated to get tazarotene free base.
• tazarotene obtained in step 'c' is suspended in non-polar organic solvent and stirred for 30 minutes to 3 hours. The mixture can be heated to temperature from 40 °C to reflux temperature of the solvent.
• the non-polar solvent is selected from the group of n-heptane, hexane, cyclohexane, benzene, toluene, cyclopentane, pentane, 1 ,4-dioxane, diethyl ether.
• the suspension is filtered and dried to obtain tazarotene with content of dimer impurity of less than 100 ppm.
• step a to step d may be repeated 1 to 3 times to obtain the desired purity of tazarotene.
• tazarotene obtained by the process can be formulated into topical compositions like cream, gel or aerosol foam.
• topical compositions like cream, gel or aerosol foam.
• Tazarotene (9 g, obtained in example 1) was suspended in ethyl acetate (135 ml) at 25-30 °C. To the above suspension ethanolic HC1 (15 ml) was added and stirred for 2 hours. The resulted solid was filtered and washed with ethyl acetate (75 ml) and dried to yield 10 g of tazarotene hydrochloride. (HPLC purity of tazarotene hydrochloride - 99.28 %, Content of dimer impurity - 0.01%)
• Example 3 Preparation of pure Tazarotene
• Tazarotene hydrochloride (10 g as obtained in example 2) was suspended in ethyl acetate (100 ml) at 25-30 °C. To the above suspension saturated aqueous sodium bicarbonate solution was added to get biphasic mixture. The product enriched organic layer was separated, washed with brine solution, dried over anhydrous sodium sulfate (5 g) and solvent was distilled off completely to get residual mass. To the residual mass n-heptane (50 ml) was added and stirred at 25-30 °C for 1 hour. The resulting solid was filtered off, washed with n-heptane and dried to obtain 9 g of pure tazarotene. (HPLC purity of tazarotene - 99.8%, Content of dimer impurity - Nil)
• Example 4 Determination dimer impurity of Tazarotene Buffer preparation :
• Potassium dihydrogen orthophosphate (3.4 g) was dissolved in 1000 ml water and pH of the solution was adjusted to 7.00 ⁇ 0.05 with triethylamine.
• Mobile phase prepared by mixing 100 volumes of buffer solution, 900 volumes of methanol.
• RS dimer impurity Reference Standard
• Ultra-Performance Liquid Chromatograph (UPLC) with the following conditions.
• Retention time of dimer impurity is about 2.6 min. Percentage RSD of area counts for dimer Impurity peak was calculated from standard preparation.
• the system is valid only if the % RSD of area counts for dimer Impurity peak is not more than 10.0 %.
• WS Weight of dimer impurity RS in standard preparation (in mg.)
• WT Weight of sample in mg.
• Example 5 Composition for Tazarotene Gel (0.1% w/w)

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• 2014
  • 2014-12-15 US US15/103,444 patent/US9688667B2/en not_active Expired - Fee Related
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