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Example 7
LC-ESI-HRMS Method for the Determination of Varenicline Nitroso-Drug Substance Related Impurity, U.S. FDA, Aug. 6, 2021, www.fda.gov/media/151470/download (accessed Feb. 27, 2022) can be used to test for impurities.
Other analytical methods for the entire process can be used to test for impurities. The methods are validated as per ICH guideline.
For example, HPLC RS methods are used for quantifying the impurities. The nitrosamines, monomethyl and dimethyl tartaric acid esters are quantified by LCMS methods.
Example 18
A solution of Varenicline free base (25.0 g) in methylene dichloride (125 mL) was stirred with the aqueous solution of succinic acid (16.77 g, 1.2 eq in 125 mL of water). The aqueous layer containing Varenicline succinate was stirred with methylene dichloride to remove the nitrosamine impurity by solvent extraction. Thereafter, follow the general procedure for the isolation of Varenicline base from the aqueous layer. Yield 15.6 g
Example 21
A solution of Varenicline free base (5.0 g) in methanol (50 mL) was stirred under hydrogen (6.0 kg/cm2) pressure in the presence of 10% Palladium on carbon (0.5 g, 50% wet) at 25-35° C. After 6 hours and the reaction mass was filtered through celite pad and rinsed with methanol (50 ml). The filtrate was distilled completely under reduced pressure and co-distilled with methyl tert-butyl ether to remove traces of methanol & water. methyl tert-butyl ether (50.0 mL, 10.0 volume) was added to the concentrated mass and stirred at 5-10° C. for 3 hours. The product was isolated by filtration and washed with chilled methyl tert-butyl ether by twice. The wet material was dried at 40° C. under vacuum. Yield: 4.2 g
Example 19
A solution of Varenicline free base (20.0 g) in methylene dichloride (100 ml) was stirred with the aqueous solution of Oxalic acid (14.35 g, 1.2 eq in 100 ml of water). The aqueous layer containing Varenicline oxalate was stirred with methylene dichloride to remove the nitrosamine impurity by solvent extraction. Thereafter, follow the general procedure for the isolation of Varenicline base from the aqueous layer. Yield: 14.6 g.
Example 22
Varenicline free base (7 g) was dissolved in methanol (140 ml) at 25-30° C. In a separate flask, tartaric acid (4.92 g) was dissolved in 70 ml water at 25-30° C. Varenicline solution was mixed with tartaric acid solution at 25-35° C. The resulting clear solution was stirred for 30 min at 25-35° C. to form the Varenicline tartrate salt solution. Maltodextrin (119.84 g) was dissolved in water (420.53 ml) at 25-35° C. separately and added this Maltodextrin solution into Varenicline tartrate solution prepared earlier. The resulting clear solution was stirred for 30 minutes, filtered through a micron filter and washed with water (2×70 ml). The clear filtrate was subjected to spray drying using a spray dryer to obtain the amorphous Varenicline Tartrate Maltodextrin Premix (1:10) API. Yield: 130.0 g. Purity by HPLC: 99.99%.