Method for producing pyridine compound

Abstract: The present invention provides a method for producing, at a high yield and a high purity in a safe manner, sulfoxides useful as medicaments such as inhibitors of gastric acid secretion, anti-ulcer agents, etc., or as intermediates for producing medicaments. The method for producing a sulfoxide (II) according to the present invention comprises the step of oxidizing the thioether (I) in the presence of a base with an N-halosuccinimide, a 1,3-dihalo-5,5-dimethylhydantoin or a dichloroisocyanurate: wherein R 1 is a hydrogen atom, a methoxy group or a difluoromethoxy group; R 2 is a methyl group or a methoxy group; R 3 is a 3-methoxypropoxy group, a methoxy group or a 2,2,2-trifluoroethoxy group; and R 4 represents a hydrogen atom or a methyl group.

Description: Field of the Invention The present invention relates to a method for producing a sulfoxide which is useful as a medicament such as an inhibitor of gastric acid secretion or an anti-ulcer agent or an intermediate for producing medicaments, as described in JP-A 1-6270 (Example 32), JP-A 61-50978 (Example 2), JP-A 54-141783 (Example 21) or JP-A 61-22079, in a good yield at a high purity with safety. Prior Art Conventionally, sulfoxide has been produced by oxidizing thioether with oxidants such as hydrogen peroxide, m-chloroperbenzoic acid, sodium hypochlorite, and sodium bromite, as described in JP-A 1-6270 (EP-268956, US-5045552), JP-A 61-50978 (EP-174726, US-4628098), JP-A 54-141783 (EP-5129, US-4255431) or JP-A 61-22079 (EP-166287, US-4758579). (See the following formula, wherein R 1 to R 4 have the same meanings as described below). Among the above oxidants, from viewpoints of readiness in weighing, storage stability and reaction activity and the like, m-chloroperbenzoic acid is frequently used. In Example 32 of JP-A 1-6270, for example, thioether is oxidized by using 0.96 equivalent (on a purity basis) of m-chloroperbenzoic acid, to produce sulfoxide at a yield of 80%, which is not an industrially satisfactory yield. Depending on the reaction conditions, disadvantageously, the reaction does not ceased at the stage of sulfoxide production but further proceeds to a side reaction where a part of the produced sulfoxide is furthermore oxidized to sulfone as shown in the following reaction scheme. When sulfone is formed, there is a problem not only that the yield of the objective sulfoxide is reduced, but also that it is difficult to separate and purify them, since there is a close resemblance in physicochemical property between the two. (In the formula, R 1 to R 4 have the same meanings as described below.) In JP-A 1-6270 and the like, additionally, the oxidation is conducted in dichloromethane (methylene chloride), but from a viewpoint of environmental strategies, there is a problem that halogenated hydrocarbon solvents can never be used industrially. Additionally, since m-chloroperbenzoic acid is expensive, it is extremely disadvantageous from a viewpoint of the production cost. Still additionally, m-chloroperbenzoic acid is listed as a dangerous material and therefore requires deep attention for the use and storage thereof, inconveniently for large-scale handling. EP-A-0 197 013 and US 4,045,563 relate to substituted benzimidazoles. The synthesis of these compounds may involve the oxidation of a sulphur linkage group to the corresponding sulfinyl group using oxidants. In these references, a large number of suitable oxidants, including N-halosuccinimide, is given. However, in the synthetic examples, m-chloroperbenzoic acid is used in all cases. US 5,374,730 relates to omeprazole and lansoprazole, in particular, two novel synthetic methods for their preparation. According to this document, amide analogues of the underlying thioether compounds are oxidized to the corresponding sulfinyl compounds. Apart from hydrogen peroxide, a large number of oxidants is exemplified, among those, N-bromo(-chloro)succinimide and 1,3-dibromo-5,5-dimethylhydantoin. The scientific article by B. Staskun in J . Org. Chem ., 1988, Vol. 53, pages 5287-5291, relates to "Azepino[1,2- a ]indole Synthesis from a 1,2,3,4-Tetrahydro-9(10 H )-acridinone and Sodium Dichloroisocyanurate or Singlet Oxygen". In the synthesis, substituted quinolinones are oxidized with dichloroisocyanurate as an oxidant. EP-A-0 216 696 is concerned with a process for preparing cotarnine. The process for this compound involves the oxidation of the amino group of a specific tetrahydroisoquinoline compound. N-bromosuccinimide and N-chlorosuccinimide are exemplified as oxidizing agents. A base is said to promote the reaction when used in combination with the oxidizing agent. As has been described above, no industrially excellent method for producing sulfoxide (II) has been established yet. Accordingly, a novel excellent method for producing sulfoxide (II) has been required. Disclosure of the Invention The present inventors have made intensive investigations so as to solve the above-mentioned problems. As a result, they have found that the objective sulfoxide (II) can be produced in a good yield with no formation of a byproduct sulfone, safty, with no use of any halogenated hydrocarbon solvent. Thus, they have accomplished the present invention. The present invention is a method for producing sulfoxide (II) represented by the following formula (II) : (wherein R 1 to R 4 have the same meanings as described below), which comprises the step of oxidizing thioether (I) represented by the following formula (I): (wherein R 1 represents hydrogen atom, methoxy group or difluoromethoxy group; R 2 represents methyl group or methoxy group; R 3 represents 3-methoxypropoxy group, methoxy group or 2,2,2-trifluoroethoxy group; and R 4 represents hydrogen atom or methyl group) with an N-halosuccinimide, 1,3-dihalo-5,5-dimethylhydantoin or dichloroisocyanurate in the presence of a base. More specifically, thioether (I) is a compound which is identical to 2-{[4-(3-methoxypropoxy)-3-methylpyridin-2-yl]methylthio}-1H-benzimidazole described in JP-A 1-6270 (Example 31), the compound described in JP-A 61-50978 (Example 1) (R 1 =H, R 2 =CH 3, R 3 =H, R 4 =CH 2 CF 3 and n=0; chemical name: 2-{[4-(2,2,2-trifluoroethoxy)-3-methylpyridin-2-yl]methylthio}-1H-benzimidazole), 5-methoxy-2-[(4-methoxy-3,5-dimethyl-2-pyridyl)methylthio]-1H-benzimidazole as a precursor of the compound described in JP-A 54-141783 (Example 21) or 5-difluoromethoxy-2-[(4,5-dimethoxy-2-pyridyl)methylthio]-1H-benzimidazole as a precursor of the compound described in JP-A 61-22079, and is a starting material of the present invention. All the compounds can be produced by the methods described in each publication. More specifically, sulfoxide (II) is identical to 2-{[4-(3-methoxypropoxy)-3-methylpyridin-2-yl]methylsulfinyl}-1H-benzimidazole (general name: Rabeprazole free base) described in JP-A 1-6270 (Example 32), the compound described in JP-A 61-50978 (Example 2) (R 1 =H, R 2 =CH 3 , R 3 =H, R 4 =CH 2 CF 3 and n = 1; general name: Lansoprazole; chemical name: 2-{[4-(2,2,2-trifluoroethoxy)-3-methylpyridin-2-yl]methylsulfinyl}-1H-benzimidazole), 5-methoxy-2-[(4-methoxy-3,5-dimethyl-2-pyridyl)methylsulfinyl]-1H-benzimidazole (general name: Omeprazole) described in JP-A 54-141783 (Example 21) or 5-difluoromethoxy-2-[(4,5-dimethoxy-2-pyridyl)methylsulfinyl]-1H-benzimidazole (general name: Pantoprazole) described in JP-A 61-22079, and is the objective compound of the present invention. More specifically, sulfoxide (II) includes for example the following compounds: The method of production of the present invention is now described in detail. The type of N-halosuccinimide which is used as an oxidant is not limited, but generally, N-chlorosuccinimide (CAS Registration No. 128-09-6) or N-bromosuccinimide (CAS Registration No. 128-08-5) ispreferable. Additionally, N-halosuccinimide is also commercially available as a reagent and an industrial raw material and the like. The amount of N-halosuccinimide to be used is not also limited, but generally it is used in the range of from 0.8 to 1.7 equivalents, more preferably from 0.85 to 1.6 equivalents and further preferably from 0.9 to 1.5 equivalents to thioether (I). Next, the type of 1,3-dihalo-5,5-dimethylhydantoin is not also limited, but generally, 1,3-dichloro-5,5-dimethylhydantoin (CAS Registration No. 118-52-5) or 1,3-dibromo-5,5-dimethylhydantoin (CAS Registration No. 77-48-5) is preferable. Additionally, 1,3-dihalo-5,5-dimethylhydantoin is also commercially available as a reagent and an industrial raw material and the like. The amount of 1,3-dihalo-5,5-dimethylhydantoin is not also limited, but generally it is used in the range of from 0.3 to 1.0 equivalent, more preferably from 0.35 to 0.9 equivalent, further preferably from 0.4 to 0.8 equivalent to thioether (I). The type of dichloroisocyanurate used is not also limited, but generally, sodium dichloroisocyanurate (CAS Registration No. 2893-78-9) or potassium dichloroisocyanurate (CAS Registration No. 2244-21-5) is preferable. Furthermore, the dichloroisocyanurate is also commercially available as reagents and industrial raw materials and the like. The amount of dichloroisocyanurate to be used is not limited, but generally it is used in the range of from 0.3 to 1.0 equivalent, more preferably from 0.35 to 0.9 equivalent, further preferably from 0.4 to 0.8 equivalent to thioether (I). The base used is not limited so long as it is inert to thioether (I), sulfoxide (II) or oxidants, but generally, inorganic bases are preferable. More specifically, the base includes for example sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium carbonate, potassium carbonate, sodium hydrogencarbonate, potassium hydrogencarbonate, sodium phosphate, potassium phosphate, sodium hydrogenphosphate, sodium formate, potassium formate, sodium acetate, potassium acetate and the like, and additionally includes mixtures of two or more thereof. The amount of base to be used is not limited, but generally, it ranges from 0.8 to 4.0 equivalents, more preferably 0.85 to 3.5 equivalents and further preferably 0.9 to 3.0 equivalents to N-halosuccinimide. Additionally, the base is generally used in an amount of 0.4 to 2.0 equivalents, more preferably 0.4 to 1.75 equivalents and further preferably 0.4 to 1.5 equivalents to 1,3-dihalo-5,5-dimethylhydrantoin or dichloroisocyanurate. For the reaction, any solvent inactive to thioether I, sulfoxide II, further the oxidant or base may be used singly or in combination, with no limitation. Preferable results are brought about by using one or more of N,N-dimethylformamide, acetonitrile, toluene, tetrahydrofuran, lower fatty acid esters and water. The solvent may be a mixture. As the solvent, a combination of one or more solvents selected from N,N-dimethylformamide, acetonitrile, toluene, tetrahydrofuran and lower fatty acid esters in the presence of water is further preferable, and it brings about more excellent results. The amount of water to be used is not limited, but generally, it ranges in amount from 0.1 to 50 ml, more preferably 0.25 to 20 ml and further preferably 0.5 to 10 ml per 1 g of thioether (I). The lower fatty acid esters are not limited so long as they are formed by dehydrating together a lower fatty acid having 6 or less carbon atoms and a lower alcohol having 6 or less carbon atoms. The concrete examples thereof include methyl formate, ethyl formate, propyl formate, butyl formate, amyl formate, methyl acetate, ethyl acetate, n-propyl acetate, i-propyl acetate, n-butyl acetate, i-butyl acetate, t-butyl acetate, n-amyl acetate, i-amyl acetate, sec-amyl acetate, t-amyl acetate, n-butyl propionate, ethyl butyrate, i-propyl butyrate, methyl isobutyrate, ethyl isobutyrate, methyl valerate, ethyl isovalerate, ethyl pivalate and the like. Ethyl acetate is more preferable. When the solvent is a mixture, the ratio of the mixed solvents is not limited, but the reaction may be conducted at an optionally ratio of the mixed solvents. The amount of the solvent is not also limited, but generally, it ranges from 1 to 100 ml, more preferably from 5 to 50 ml, further preferably from 10 to 30 ml per 1 g of thioether (I). The reaction temperature is not also limited, but generally, the reaction is conducted at -50 °C to room temperature, more preferably at -30 °C to 20 °C, further preferably at -20 °C to 10 °C. The sequence of adding the each reagent (raw material) for the reaction is not also limited, but the following sequence, for example, can bring about more preferable results. 1. A base is added to a solution or suspension of thioether (I), to which is then added N-halosuccinimide at low temperature, followed by stirring. 2. A solution of thioether (I) and a base is added to a solution of N-halosuccinimide at low temperature, followed by stirring. 3. A base solution is added dropwise into a solution of thioether (I) and N-halosuccinimide. 4. A base is added to a solution of thioether (I), followed by the addition of 1,3-dihalo-5,5-dimethylhydantoin at low temperature and stirring. 5. A solution of thioether (I) and a base is added to a solution of 1,3-dihalo-5,5-dimethylhydantoin at low temperature, followed by stirring. 6. A base solution is added dropwise into a solution of thioether (I) and 1,3-dihalo-5,5-dimethylhydantoin, followed by stirring. 7. A base is added to a solution of thioether (I), followed by the addition of a dichloroisocyanurate and subsequent stirring. 8. A solution of thioether (I) and a base is added to a solution of a dichloroisocyanurate at low temperature, followed by stirring. 9. A base solution is added dropwise into a solution of thioether (I) and a dichloroisocyanurate, followed by stirring. In the practice of the procedures (1) to (9) described above, more preferable results can be observed by confirming that the pH of the reaction solution is always at basicity, more preferably at pH 12 or higher, under monitoring. The reaction time varies, depending on the amount of the solvent used, the reaction temperature, and the type and amount of an oxidant, but generally, the reaction is completed in about 30 min to 6 hr. The treatment after the completion of the reaction is not also limited, and for example, sodium hydrosulfite and additionally adding reducing agents such as sodium hyposulfite and sodium thiosulfate to decompose excess reagents and, if necessary, adjusting the pH of the aqueous layer and the aqueous layer is extracted with the solvent. Furthermore, the mixture is evaporated, or the resulting crystals are collected by filtration. The resulting sulfoxide (II) can be purified by conventional methods such as crystallization, recrystallization, column chromatography and the like. If necessary, the sulfoxide (II) may be converted into a salt according to known methods. Furthermore, Tetrahedron Letters, 29 (24), 2967-2968, 1988 discloses a reaction comprising oxidation of olefin with sodium perborate · tetrahydrate in the presence of an acetic anhydride in methylene chloride, to give epoxide or α,β-diol · monoacetate, however the reaction is totally different from the reaction of the present invention comprising oxidation of thioether to give sulfoxide. JP-A 54-141783 (EP-5129, US-4255431) describes that the following oxidants can be used for the oxidation of thioether into sulfoxide; nitric acid, hydrogen peroxide, peracid, perester, ozone, dinitrogen tetraoxide, iodobenzene, 1-chlorobenzotriazole, tert-butyl hypochlorite, a complex of diazo-bicyclo [2,2,2] octane with bromine, sodium metaperiodate, selenium dioxide, manganese dioxide, chromic acid, ceric ammonium nitrate, bromine, chlorine and sulfuryl chloride, as well as N-halosuccinimide. However, m-chloroperbenzoic acid which is a peracid is the only one specifically disclosed in the Examples of the above-mentioned JP-A 54-141783. Any description that only N-halosuccinimide is specifically excellent among the above various oxidants is never found in the entirety of the specification or any description suggesting the excellency is absolutely never found therein. Further, any description that the presence of a base is essential or preferable is absolutely never found therein. Accordingly, the description about oxidants in JP-A 54-141783 is regarded as a mere example of general oxidants, with no influence on the novelty of the present invention. In J.O.C., 33 (10), 3976-7, 1968, the reaction which relates to the oxidation of sulfide (thioether) with N-halosuccinimide is described. However, the sulfide specifically disclosed in the reference includes only six compounds, namely dimethyl sulfide, diethyl sulfide, di-n-propyl sulfide, dibenzyl sulfide, benzyl phenyl sulfide and diphenyl sulfide, and is entirely different from the thioether (I) of the present invention in structure. Consequently, to describe the present invention more in detail, Examples and Referential Examples will be given below. However, it is needless to say that the present invention is not limited thereto. Examples 1 to 9 : Oxidation with N-halosuccinimide Examples 10 to 13 : Oxidation with 1,3-dihalo-5,5-dimethylhydantoin Example 14 : Oxidation with dichloroisocyanurate Conditions for HPLC analysis Solid phase NUCLEOSIL 5 C 18 (4.6 mm I.D. × 150 mm, 5µm) Mobile phase MeOH/0.05M phosphate buffer (pH 7) = 3 : 2 Flow rate 1.0 ml/min Temperature 25 °C Detector UV detector at 290 nm Example 1 : Synthesis of 2-{[4-(3-methoxypropoxy)-3-methylpyridin-2-yl]methylsulfinyl}-1H-benzimidazole (Rabeprazole free base) 2-{[4-(3-Methoxypropoxy)-3-methylpyridin-2-yl]methylthio}-1H-benzimidazole (5. 0 g, 14.6 mmol; referred to as Compound I hereinafter) was dissolved in 20 ml of N,N-dimethylformamide, followed by the addition of a 2N aqueous solution of sodium hydroxide (18 ml). A solution (10 ml) of N-chlorosuccinimide (2.71 g, 20.3 mmol) in N,N-dimethylformamide was added dropwise to the solution at -20 °C to -10 °C. The reaction mixture was reacted at -15 °C to -7°C for 1.5 hr. To the reaction mixture was added a 10% aqueous solution of sodium thiosulfate (5 ml), stirred for 2 min and then, a solution (60 ml) of ammonium acetate (23.1 g) in water was added thereto. 60 ml of ethyl acetate and 10 g of sodium chloride were added thereto to extract the reaction mixture, and the aqueous layer was further extracted with ethyl acetate (40 ml). The organic layers were combined, washed with a 15% aqueous solution of sodium chloride (80 ml) for three times and then, the solvent was evaporated. To the resulting oil was added 12 ml of ethyl acetate, 28 ml of hexane and 10 ml of toluene, followed by stirring at room temperature for 1 hr. The resulting crystals were collected by filtration, washed with a solvent mixture (10 ml) of 30% ethyl acetate and hexane for two times and then, dried under reduced pressure, to give the title compound (4.7 g, yield; 90.6%) as grayish white crystals. 1 H-NMR (400MHz, DMSO-d 6 ); δ (ppm) 1.10(t,J=7.2Hz,3H), 2.13(s,3H), 3.50(q,J=7.2Hz,2H), 3.71(m,2H), 4.16(m,2H), 4.70(d,J=13.6Hz,1H), 4.78(d,J=13.6Hz,1H), 6.96(d,J=5.6Hz,1H), 7.28(m,2H), 7.62(m,2H), 8.20(d,J=5.6Hz,1H). Example 2 : Synthesis of 2-{[4-(3-methoxypropoxy)-3-methylpyridin-2-yl]methylsulfinyl}-1H-benzimidazole (Rabeprazole free base) The Compound I (5.0 g, 14.6 mmol) was suspended in 20 ml of acetonitrile, followed by the addition of a 2N aqueous solution of sodium hydroxide (14.5 ml). To the resulting solution was added dropwise a solution (8 ml) of N-chlorosuccinimide (2.13 g, 16.0 mmol) inN,N-dimethylformamide at -18 °C to -8 °C. The reaction mixture was reacted at -15 °C to -0 °C for 1.5 hr. To the reaction mixture was added a 10% aqueous solution of sodium thiosulfate (5 ml), and stirred for 2 min, followed by the addition of a solution (60 ml) of ammonium acetate (10 g) in water. Ethyl acetate (60 ml) and sodium chloride (10 g) were added thereto to extract, and further the aqueous layer was extracted with ethyl acetate (40 ml). The organic layers were combined, washed with a 15% aqueous solution of sodium chloride (80 ml) for three times, and then the solvent was evaporated. Ethyl acetate (12 ml), hexane (28 ml) and toluene (12 ml) were added to the resulting oil, and the resulting mixture was stirred at room temperature for 1 hr. The resulting crystals were collected by filtration, washed with a solvent mixture (10 ml) of 30 % ethyl acetate and hexane for two times, and then dried under reduced pressure, to give the title compound (4.68 g, yield; 90.0%) as white crystals. Example 3 : Synthesis of 2-{[4-(3-methoxypropoxy)-3-methylpyridin-2-yl]methylsulfinyl}-1H-benzimidazole (Rabeprazole free base) The Compound I (5.0 g, 14.6 mmol) was suspended in a solvent mixture of toluene (20 ml) and acetonitrile (10 ml), followed by the addition of a 2N aqueous solution of sodium hydroxide (14.5 ml). To the resulting solution was added dropwise a solution (8 ml) of N-chlorosuccinimide (2.13 g, 16.0 mmol) in N,N-dimethylformamide at 0 °C to 9 °C. The reaction mixture was reacted at 0 °C to 15 °C for 1.5 hr. To the reaction mixture was added a 10% aqueous solution of sodium thiosulfate (5 ml) and stirred for 2 min, followed by the addition of a 2N aqueous solution of sodium hydroxide (14.5 ml). After adding toluene (10 ml) thereto to separate the organic layer, acetic acid (2.2 ml) was added to the aqueous layer to adjust it to pH 8.5. Ethyl acetate (60 ml) and sodium chloride (5 g) were added thereto to extract and further the aqueous layer was extracted with ethyl acetate (40 ml). The organic layers were combined, washed with a 15% aqueous solution of sodium chloride (80 ml) for three times and then the solvent was evaporated. Ethyl acetate (10 ml), toluene (10 ml) and t-butyl methyl ether (20 ml) were added to the resulting oil and the mixture was stirred at room temperature for 1 hr. The resulting crystals were collected by filtration, washed with t-butyl methyl ether (10 ml) for two times, and then dried under reduced pressure, to give the title compound (3.9 g, yield; 74. 8%) as grayish white crystals. Example 4 : Synthesis of 2-{[4-(3-methoxypropoxy)-3-methylpyridin-2-yl]methylsulfinyl}-1H-benzimidazole (Rabeprazole free base) The Compound I (5.0 g, 14.6 mmol) was suspended in 20 ml of tetrahydrofuran, followed by the addition of a 2N aqueous solution of sodium hydroxide (14.5 ml). To the resulting solution was added dropwise a solution (8 ml) of N-chlorosuccinimide (2.13 g, 16.0 mmol) in N,N-dimethylformamide at 0 °C to 9 °C. The reaction mixture was reacted at 5 °C to 0 °C for 1 hr. To the reaction mixture was added 5 ml of a 10% aqueous solution (5 ml) of sodium thiosulfate was added to the reaciton mixture and stirred for 2 min, followed by the addition of a 2N aqueous solution (14.5 ml) of sodium hydroxide. 40 ml of toluene was added to separate the organic layer, 2.2 ml of acetic acid was added to the aqueous layer to adjust it to pH 8.5. Ethyl acetate (60 ml) and sodium chloride (4 g) were added thereto to extract and further the aqueous layer was extract with ethyl acetate (40 ml). The organic layers were combined, washed with a 15% aqueous solution of sodium chloride (80 ml) for three times, and then the solvent was evaporated. Ethyl acetate (10 ml), toluene (10 ml) and t-butyl methyl ether (20 ml) were added to the resulting oil, and stirred at room temperature for 1 hr. The resulting crystals were collected by filtration, washed with t-butyl methyl ether (10 ml) for two times, and then dried under reduced pressure, to give the title compound (3.9 g, yield; 74.8%) as grayish white crystals. Example 5 : Synthesis of 2-{[4 - (3-methoxypropoxy)-3-methylpyridin-2-yl]methylsulfinyl}-1H-benzimidazole (Rabeprazole free base) The compound I (5.0 g, 14.6 mmol) was suspended in 20 ml of acetonitrile, followed by the addition of a 2N aqueous solution of sodium hydroxide (14.5 ml). To the resulting solution was added dropwise a solution (8.5 ml) of N-chlorosuccinimide (2.32 g, 17.4 mmol) in N,N-dimethylformamide at -5 °C to 5 °C. During the dropwise addition, the pH of the reaction mixture was monitored, and a 2N aqueous solution of sodium hydroxide (10 ml) was simultaneously added dropwise thereto so as not to lower the pH value of the reaction solution below pH 12. After the completion of the dropwise addition, the mixture was reacted for further 45 min at -3 °C to 0 °C. After adding a 10% aqueous solution of sodium thiosulfate (10 ml) to the reaction mixture and strring the mixture for 2 min, water (60 ml) was added thereto. The resulting mixture was adjusted to pH 9.2, by adding about 2.5 ml of acetic acid thereto, followed by the addition of ethyl acetate (60 ml) and sodium chloride (12 g) to extract. Further, the aqueous layer was extracted with ethyl acetate (40 ml). The organic layers were combined, washed with a 15% aqueous solution of sodium chloride (80 ml) for three times, and then the solvent was evaporated. Ethyl acetate (12 ml), hexane (28 ml) and toluene (10 ml) were added to the resulting oil, and the mixture was stirred at room temperature for 1 hr. The resulting crystals were collected by filtration, washed with a solvent mixture (10 ml) of 30% ethyl acetate and hexane for two times, and the dried under reduced pressure, to give the title compound (4.76 g, yield; 91.3%) as grayish white crystals. Example 6 : Synthesis of 2-{[4-(3-methoxypropoxy)-3-methylpyridin-2-yl]methylsulfinyl}-1H-benzimidazole (Rabeprazole free base) The Compound I (5.0 g, 14.6 mmol) was suspended in 20 ml of acetonitrile, followed by the addition of a 2N aqueous solution of sodium hydroxide (14.5 ml). To the resulting solution was added dropwise 8.5 ml of a solution of N-chlorosuccinimide (2.32 g, 17.4 mmol) in N, N-dimethylformamide at -5 °C to 5 °C. During the dropwise addition, the pH of the reaction solution was monitored, and 10 ml of a 2N aqueous solution of sodium hydroxide (10 ml) solution was simultaneously dropwise added to the reaction solution so as not to lower the pH value of the reaction solution below pH 12. After the termination of the dropwise addition, the reaction solution was reacted at -3 °C to 0 °C for further 45 min. To the reaction mixture was added a 10% aqueous solution of sodium thiosulfate (10 ml), stirred for 2 min and then, the acetonitrile was evaporated. The resulting solution was adjusted to pH 9.1, by adding 85 ml of water and about 1.2 ml of acetic acid to the solution, followed by stirring at 4 °C for 12 hr. The resulting crystals were collected by filtration, washed with water (20 ml) for three times and dried under reduced pressure, to give the title compound (3.97 g, yield; 76.2%) as grayish white crystals. Example 7 : Synthesis of 2-{[4-(3-methoxypropoxy)-3-methylpyridin-2-yl]methylsulfinyl}-1H-benzimidazole (Rabeprazole free base) The Compound I (5.0 g, 14.6 mmol) was suspended in 20 ml of acetonitrile, followed by the addition of a 2N aqueous solution of sodium hydroxide (14.5 ml). To the resulting solution was added dropwise 8.5 ml of a solution of N-chlorosuccinimide (2.32 g, 17.4 mmol) in N,N-dimethylformamide at -5 ° C to 5 °C. During the dropwise addition, the pH of the reaction solution was monitored, and a 2N aqueous solution of sodium hydroxide (10 ml) was simultaneously dropwise added to the reaction solution so as not to lower the pH value of the reaction solution below pH 12. After the completion of the dropwise addition, the reaction solution was reacted at -3 °C to 0 °C for further 45 min. To the reaction mixture was added a 10% aqueous solution of sodium thiosulfate (10 ml), stirred for 2 min and then, 60 ml of water was added thereto. The resulting solution was adjusted to pH 9.2, by adding about 1.3 ml of acetic acid to the solution, followed by the addition of 50 ml of isopropyl acetate and 50 ml of hexane. Then, the resulting mixture was stirred at 4 °C for 12 hr. The resulting crystals were collected by filtration, washed with 10 ml of a solvent mixture of 30 % isopropyl acetate and hexane, and dried under reduced pressure, to give the title compound (3.47 g, yield; 66.6%) as grayish white crystals. Example 8 : Synthesis of 2-{[4-(3-methoxypropoxy)-3-methylpyridin-2-yl]methylsulfinyl}-1H-benzimidazole (Rabeprazole free base) The Compound I (15.0 g, 43.7 mmol) was suspended in 75 ml of acetonitrile, followed by the addition of 75 ml of a 2N aqueous solution of sodium hydroxide. To the resulting solution was added dropwise N-chlorosuccinimide (6.42 g, 48 mmol) little by little at -5 °C. The reaction mixture was reacted at -5 °C for 1.5 hr. To the reaction mixture was added 5 ml of a 1 M aqueous solution of sodium thiosulfate solution, followed by stirring for 2 min and washing with toluene (10 ml) for two times. Subsequently, 4.2 g of formic acid was added to the aqueous layer at 5 °C, to adjust the aqueous layer to pH 9.0. The resulting mixture was stirred as it was at the same temperature for about 15 hr, and then the resulting slurry was filtered. The resulting solid was dried, to give the title compound (14.00 g, yield; 89.2%, purity; 99.8%) as white crystals. Example 9 : Synthesis of 2-{[3-methyl-4-(2,2,2-trifluoroethoxy)pyridin-2-yl]methylsulfinyl}-1H-benzimidazole (Lansoprazole) 2-{[3-Methyl-4-(2,2,2-trifluoroethoxy)pyridin-2-yl]methylthio}-1H-benzimidazole (1.0 g, 2.83 mmol) was suspended in 8 ml of acetonitrile, followed by the addition of 3.5 ml of a 2N aqueous solution of sodium hydroxide. A solution (2 ml) of N-chlorosuccinimide (453 mg, 3.40 mmol) in N,N-dimethylformamide was added dropwise to the solution at -4 °C to 3 °C. The reaction mixture was subsequently reacted at -3 °C to 0 °C for 1.5 hr. To the reaction mixture was added a 10% aqueous solution of sodium thiosulfate (2 ml) was added to the reaction mixture and the resulting mixture was stirred for 2 min, followed by the addition of water (20 ml) and acetic acid (0.4 ml) to adjust the solution to about pH 8.5. Ethyl acetate (20 ml) and sodium chloride (3 g) were added thereto to extract and the aqueous layer was further extracted with ethyl acetate (10 ml). The organic layers were combined, washed with a 15 % aqueous solution of sodium chloride (10 ml) for three times, and the solvent was evaporated. Ethyl acetate (3 ml), hexane (7 ml) and toluene (2.5 ml) were added to the resulting oil, and then stirred at room temperature for 1 hr. The resulting crystals were collected by filtration, washed with a solvent mixture (3 ml) of 30 % ethyl acetate and hexane for two times, and then dried under reduced pressure, to give the title compound (0.88 g, yield; 84.1%) as grayish white crystals. 1 H-NMR (400MHz, DMSO-d 6 ); δ (ppm) 2.16(s, 3H), 4.74(d,J=13.7Hz,1H), 4.87(d,J=13.7Hz,1H), 4.88(d,J=8.8Hz,1H), 4.91(d,J=8.8Hz,1H), 7.08(d,J=5.9Hz,1H), 7.29(m,2H), 7.56(m,1H), 7.70(m,1H), 8.27(d,J=5.9Hz,1H), 13.55(s,1H). Example 10 : Synthesis of 2-{[4-(3-methoxypropoxy)-3-methylpyridin-2-yl]methylsulfinyl}-1H-benzimidazole (Rabeprazole free base) The Compound I (10.0 g, 29.1 mmol) was dissolved in 80 ml of dimethylformamide, followed by the addition of a solution of potassium hydrogen carbonate (2.91 g, 29.1 mmol) in water (20 ml). The resulting mixture solution was stirred under ice-cooling. At the same temperature, a solution of 1,3-dichloro-5,5-dimethylhydantoin (4.01 g, 20.37 mmol) in dimethylformamide (15 ml) was added dropwise thereinto over 3 min, and stirred as it was at the same temperature for 70 min. Additionally, 1,3-dichloro-5,5-dimethylhydantoin (0.34 g; 8.73 mmol) was added to the resulting mixture, and then it was stirred for 40 min. An aqueous solution (10 ml) of sodium hyposulfite (5.13 g, 40.74 mmol) was added to the resulting mixture, stirred for 5 min, and then a 2M aqueous solution of sodium hydroxide (6 ml) was added thereto to adjust the solution to pH 8. Water (80 ml) was added thereto, and the resulting aqueous layer was extracted with ethyl acetate (200 ml) for two times and with 100 ml thereof once, and the extracted aqueous layers were combined together. The organic layer was washed with a 10% aqueous solution of brine for two times. The organic layer was evaporated, and to the resulting residue were added ethyl acetate (30 ml), toluene (30 ml) and n-hexane (30 ml), and the resulting mixture was stirred at -15 °C for 11 hr. The resulting crystals were filtered under reduced pressure, washed with t-butyl ethyl ether (25 ml) for two times and then dried to give the title compound (7.33 g, yield; 70.0%, an HPLC purity; 98.9%) as a white solid. Example 11 : Synthesis of 2-{[4-(3-methoxypropoxy)-3-methylpyridin-2-yl]methylsulfinyl}-1H-benzimidazole (Rabeprazole free base) The Compound I (10.0 g, 29.1 mmol) was dissolved in 80 ml of dimethylformamide, followed by the addition of a solution (20 ml) of sodium hydrogencarbonate (2.46 g, 29.2 mmol) in water. The resulting mixture was stirred under ice-cooling. At the same temperature, a solution (20 ml) of 1,3-dichloro-5,5-dimethylhydantoin (4.01 g, 20.37 mmol) in dimethylformamide was added dropwise thereinto over 10 min and stirred at the same temperature for 80 min. Further, 1,3-dichloro-5,5-dimethylhydantoin (115 mg, 0.58 mmol) was added thereto and stirred for 20 min. A 1.0 M aqueous solution of sodium thiosulfate (30 ml) was added thereto and stirred for 5 min. Then, 30 ml of brine was added thereto and the extracted with ethyl acetate (100 ml × 2). The organic phase was rinsed in 100 ml of an aqueous 15 % sodium chloride solution and in 15 ml thereof and concentrated under reduced pressure. Toluene (15 ml), ethyl acetate (15 ml) and t-butyl methyl ether (15 ml) were added to the resulting residue, and the mixture was stirred at -10 °C for 13 hr. The resulting crystals were filtered under reduced pressure, washed with t-butyl methyl ether (50 ml) for two times, and then dried, to give the title compound (7.05 g, yield; 67.0%) as a white solid. Example 12 : Synthesis of 2-{[4-(3-methoxypropoxy)-3-methylpyridin-2-yl]methylsulfinyl}-1H-benzimidazole (Rabeprazole free base) The Compound I (5.0 g, 14.5 mmol) was dissolved in 25 ml of ethyl acetate, followed by the addition of a solution of sodium hydrogencarbonate (3.21 g, 32.1 mmol) in water (25 ml). The resulting mixture solution was stirred under ice-cooling. At the same temperature, 1,3-dichloro-5,5-dimethylhydantoin (2.87 g, 14.6 mmol) was added thereto, and then stirred for 2 hr. Additionally, the resulting mixture was stirred at -10 °C for 30 min. The resulting crystals were filtered under reduced pressure, washed with water (10 ml × 2) and t-butyl methyl ether (10 ml × 2), and then dried, to give the title compound (2.79 g, yield; 53.3%, an HPLC purity; 98.8%) as white crystals. Example 13 : Synthesis of 2-{[4-(3-methoxypropoxy)-3-methylpyridin-2-yl]methylsulfinyl}-1H-benzimidazole (Rabeprazole free base) The Compound I (10.0 g, 29.1 mmol) was dissolved in 40 ml of ethyl acetate, followed by the addition of a solution of sodium hydrogencarbonate (13.9 g, 140 mmol) in water (55 ml). The resulting mixture was stirred at -5 °C. At the same temperature, a solution of 1,3-dichloro-5,5-dimethylhydantoin (6.88 g, 34.92 mmol) in ethyl acetate (60 ml) added thereto. After stirring for 2 hr, a 10% aqueous solution of sodium hydrosulfite (50 ml) was added, and then stirred for 10 min. A mixture solution (110 ml) of n-hexane/toluene (1:1) was added thereto and the resulting mixture was stirred at -20 °C for 1.5 hr. The resulting crystals were collected by filtration, washed with water (50 ml × 4) and t-butyl methyl ether (25 ml × 2), and then dried, to give the title compound (7.09 g, yield; 68%, an HPLC purity; 98.2%) as white crystals. Example 14 : Synthesis of 2-{[4-(3-methoxypropoxy)-3-methylpyridin-2-yly]methylsulfinyl}-1H-benzimidazole (Rabeprazole free base) The Compound I (5.0 g, 14.5 mmol) was dissolved in 20 ml of acetonitrile, followed by the addition of a 2M aqueous solution of sodium hydroxide (29.1 ml). The resulting mixture solution was stirred at -15 °C. At the same temperature, a solution of sodium dichloroisocyanurate (2.24 g, 10.2 mmol) in water (15 ml) was added dropwise thereinto over 10 min. During the addition, the temperature of the reaction mixture was raised from -15 °C to -5.6 °C. After stirring for 15 min at the same temperature, a solution (5 ml) of sodium hydrosulfite (0.50 g) in water was added thereto, stirred for 30 min, and the insoluble matters were filtered off. The filtrate was adjusted to pH 7, by adding about 3 ml of formic acid thereto. The aqueous layer was extracted with ethyl acetate (25 ml) once and with 10 ml thereof once. The organic layer was washed with brine (10 ml) and evaporated. Ethyl acetate (20 ml), toluene (12 ml) and n-hexane (20 ml) were added to the resulting residue, followed by stirring at -15 °C for 11 hr. The resulting crystals were filtered under reduced pressure, washed with t-butyl methyl ether (20 ml) for two times, and then dried, to give the title compound (3.71 g, yield; 70.8%, an HPLC purity; 97.3%) as pale yellowish white crystals. Next, to show the excellent effect of the present invention, Reference Examples in which the oxidants (nitric acid, sodium metaperiodate) disclosed in JP-A 54-141783 are used as comparative controlls, and sodium borate and sodium chlorate are used as other oxidants, to produce the sulfoxide (II) of the present invention. The oxidants excerpt the above oxidants disclosed in JP-A 54-141783 are disadvantageously unstable, dangerous (explosive), unavailable at large volume and expensive, and cause pollution. Thus, these oxidants are not applicable as industrial raw materials. Referential Examples Referential Example 1 : Synthesis of 2-{[4-(3-methoxypropoxy)-3-methylpyridin-2-yl]methylsulfinyl}-1H-benzimidazole (Rabeprazole free base) (oxidant: nitric acid) The Compound I (2 g, 5.82 mmol) was dissolved in 20 ml of methanol, followed by the dropwise addition of 61% nitric acid (0.6 g, 5.82 mmol) at room temperature. After the dropwise addition, reacting the resulting mixture at room temperature for 2 hr. Subsequently, the change of the reaction mixture was confirmed by TLC (methanol/ethyl acetate=1/6; refer to the same hereinafter). Consequently, no formation of the title compound was observed. Referential Example 2 : Synthesis of 2-{[4-(3-methoxypropoxy)-3-methylpyridin-2-yl]methylsulfinyl}-1H-benzimidazole (Rabeprazole free base) (oxidant: sodium metaperiodate) The Compound I (2 g; 5.82 mmol) was dissolved in 50 ml of methanol and the solution was cooled to 0 °C. After cooling, sodium metaperiodate (1.26 g, 5.82 mmol) dissolved in water (25 ml) was added dropwise thereto. After the dropwise addition, reacting the mixture at room temperature for 22 hr. Subsequently, the change of the reaction mixture was confirmed by TLC. Consequently, no formation of the title compound was confirmed. Referential Example 3 : Synthesis of 2-{[4-(3-methoxypropoxy)-3-methylpyridin-2-yl]methylsulfinyl}-1H-benzimidazole (Rabeprazole free base) (oxidant: sodium bromate) The Compound I (2 g, 5.82 mmol) was dissolved in 30 ml of dioxane, followed by the dropwise addition of sodium bromate (1.69 g, 8.14 mmol) dissolved in water (5 ml). After the dropwise addition, reacting the mixture at room temperature for 1.5 hr. Subsequently, the change of the reaction mixture was confirmed by TLC. Consequently, no formation of the title compound was observed. Reference Example 4 : Synthesis of 2-{[4-(3-methoxypropoxy)-3-methylpyridin-2-yl]methylsulfinyl}-1H-benzimidazole (Rabeprazole free base) (oxidant: sodium bromate) The Compound I (2 g, 5.82 mmol) was dissolved in 40 ml of methanol, followed by the dropwise addition of sodium bromate (1.69 g, 8.14 mmol) dissolved in water (20 ml). After the dropwise addition, reacting the mixture at room temperature for 16 hr. Subsequently, the change of the reaction mixture was confirmed by TLC. Consequently, no formation of the title compound was observed. Referential Example 5 : Synthesis of 2-{[4-(3-methoxypropoxy)-3-methylpyridin-2-yl]methylsulfinyl}-1H-benzimidazole (Rabeprazole free base) (oxidant : sodium chlorate) The Compound I (5 g, 14.6 mmol) was dissolved in a solvent mixture of ethyl acetate (75 ml), methanol (25 ml) and water (30 ml), followed by the dropwise addition of a 5% aqueous solution of sodium chlorate (22 g, 14.6 mmol) at 5 °C. 1 hr after the dropwise addition, the change of the reaction mixture was confirmed. Consequently, the formation of a slight amount of the title compound at a slight amount was confirmed, but great quantities of byproducts were also observed, although no raw materials remained. Referential Example 6 : Synthesis of 2-{[4-(3-methoxypropoxy)-3-methylpyridin-2-yl]methylsulfinyl}-1H-benzimidazole (Rabeprazole free base) (oxidant: manganese dioxide) The Compound I (1 g, 2.9 mmol) was dissolved in dichloromethane (10 ml), followed by the addition of active manganese oxide (5 g) at room temperature. After reacting at room temperature for 21 hr, the change of the reaction solution was confirmed by HPLC. Consequently, no formation of the title compound was confirmed. Referential Example 7 : Synthesis of 2-{[4-(3-methoxypropoxy)-3-methylpyridin-2-yl]methylsulfinyl}-1H-benzimidazole (Rabeprazole free base) (oxidant: pyridinium dichromate) The Compound I (1 g, 2.9 mmol) was dissolved in dichloromethane (10 ml) , followed by the addition of pyridinium dichromate (1.1 g, 2.9 mmol) at room temperature. After reacting at room temperature for 21 hr, the change of the reaction mixture was confirmed by HPLC. Consequently, the formation of 3.2% (yield) of the title compound was confirmed but 96 % of the Compound I still remained unreactive. Referential Example 8 : Synthesis of 2-{[4-(3-methoxypropoxy)-3-methylpyridin-2-yl]methylsulfinyl}-1H-benzimidazole (Rabeprazole free base) (oxidant: cerium diammonium nitrate) The Compound I (1 g, 2.9 mmol) was suspended in a solvent mixture of acetonitrile (20 ml) and water (10 ml), and then, cerium diammonium nitrate (1.59 g, 2.9 mmol) was added dropwise thereinto. After reacting at room temperature for 20 hr, the change of the reaction mixture was confirmed by HPLC. Consequently, the formation of 0.5% of the title compound was observed, but 98 % of the Compound I still remained unreactive. The above results apparently indicate that the objective sulfoxide (II) can be obtained in a good yield and safety by the present invention. Further, N-halosuccinimide, 1,3-dihalo-5,5-dimethylhydantoin and dichloroisocyanurate are not dangerous materials and are also handled easily at a greater amount. Thus, the present invention is proved to be an industrially excellent method for producing sulfoxide (II).

Claims: A method for producing a sulfoxide (II) represented by the following formula (II): (wherein R 1 , R 2 , R 3 and R 4 have the same meanings as defined below), which comprises the step of oxidizing a thioether (I) represented by the following formula (I): (wherein R 1 represents a hydrogen atom, methoxy group or difluoromethoxy group; R 2 represents a methyl group or methoxy group; R 3 represents a 3-methoxypropoxy group, methoxy group or 2,2,2-trifluoroethoxy group; and R 4 represents a hydrogen atom or methyl group) with an N-halosuccinimide, a 1,3-dihalo-5,5-dimethylhydantoin or a dichloroisocyanurate in the presence of a base. The method as claimed in Claim 1, wherein the N-halosuccinimide is N-chlorosuccinimide or N-bromosuccinimide. The method as claimed in Claims 1 or 2, wherein the N-halosuccinimide is used in an amount of 0.9 to 1.5 equivalents to the thioether (I). The method as claimed in Claim 1, wherein the 1,3-dihalo-5,5-dimethylhydantoin is 1,3-dichloro-5,5-dimethylhydantoin or 1,3-dibromo-5,5-dimethylhydantoin. The method as claimed in Claims 1 or 4, wherein the 1,3-dihalo-5,5-dimethylhydantoin is used in an amount of 0.4 to 0.8 equivalents to the thioether (I). The method as claimed in Claim 1, wherein the dichloroisocyanurate is sodium dichloroisocyanurate or potassium dichloroisocyanurate. The method as claimed in Claims 1 or 6, wherein the dichloroisocyanurate is used in an amount of 0.4 to 0.8 equivalents to the thioether (I). The method as claimed in any one of the preceding Claims, wherein the base is an inorganic base. The method as claimed in any one of the preceding Claims, wherein the base is at least one selected from the group consisting of sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium carbonate, potassium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, sodium phosphate, potassium phosphate, sodium hydrogen phosphate, sodium formate, potassium formate, sodium acetate and potassium acetate. The method as claimed in any one of the preceding Claims, wherein the base is used in an amount of 0.9 to 3.0 equivalents to the N-halosuccinimide, and of 0.4 to 1.5 equivalents to the 1,3-dihalo-5,5-dimethylhydantoin or dichloroisocyanurate salt. The method as claimed in any one of the preceding Claims, wherein the oxidation is conducted in a solvent which is at least one selected from the group consisting of N, N-dimethylformamide, acetonitrile, toluene, tetrahydrofuran, lower fatty acid esters and water. The method as claimed in any one of the preceding Claims, wherein the oxidation is conducted in a solvent which is at least one selected from the group consisting of N, N-dimethylformamide, acetonitrile, toluene, tetrahydrofuran and lower fatty acid esters, in the presence-of water.

Inventors: KAYANO AKIO, KURODA HIROFUMI, NIIKAWA NOBUO, TAGAMI KATSUYA, KAYANO, AKIO, KURODA, HIROFUMI, NIIKAWA, NOBUO, TAGAMI, KATSUYA
Applicants: EISAI CO LTD, EISAI CO., LTD.
Application year: 1998
Main classification: C07D401
IPC codes: C07D401