Process for preparing polyprenols

Abstract: Provided according to the present invention is a process for the preparation of a polyprenol represented by the following formula (1): wherein Y and Z individually represent a hydrogen atom or are coupled together to form a carbon-carbon bond; R represents a hydrogen atom or a protective group of a hydroxyl group; and n stands for 0 or an integer not smaller than 1, which comprises bringing an organic complex of an alkaline metal into contact with a compound represented by the following formula (2): wherein concerning V, W and X, V represents a halogen atom, while W and X are coupled together to form a carbon-carbon bond or X represents a halogen atom, while V and W are coupled together to form a carbon-carbon bond; A represents a protective group of a hydroxyl group; and Y,Z and n have the same meanings as defined above.

Description: This invention relates to a process for the preparation of polyprenols. The polyprenols prepared by the present invention are useful as pharmaceuticals or synthesis intermediates therefor. Among the polyprenols prepared by the present invention, for example, 3,7,11,15,19,23,27-heptamethyl-6,10,14,18,22,26-octacosahexaen-1-ol is useful as a preventive or remedy for diseases caused by immunodeficiency of human beings or animals (Refer to US-A-4839389). As a general reduction method of an allylic terminal, known are: (1) a method to cause NaBH 4 act on by using dimethylsulfoxide as a solvent [refer to J. Am. Chem. Soc., 92 , 4463(1970)], (2) a method to cause LiAlH 4 act on [refer to J. Am. Chem. Soc., 95 , 553(1973)], (3) a method to use sodium formate as a hydrogen source in the presence of a palladium catalyst [refer to Chem. Lett., 1463(1986)], and (4) a method to use diisobutyl aluminum hydride (DIBAL) as a hydrogen source in the presence of a palladium catalyst [refer to J. Org. Chem., 56 , 2918(1991)]. In the case of the synthesis of a polyprenol from a terminal allyl halide, it is necessary not only to conduct dehalogenation but also to constitute a carbon-carbon double bond at a selected position. Upon dehalogenation of a terminal allyl halide, the adoption of the above-described method (1), however, causes hydroboration owing to BH 3 formed after dehalogenation. The more carbon-carbon double bonds are contained in the molecule, the more eminent such a tendency becomes, which brings about a reduction in the yield of a polyprenol. In the above-described method (2), on the other hand, it is difficult from the industrial viewpoint to handle LiAlH 4 because it is in the powdery form and has ignition properties. The above-described method (3) involves a problem in selectivity because many position isomers of a carbon-carbon double bond are formed. The above-described method (4) has high positional selectivity of a carbon-carbon double bond, but is accompanied with the problems that a temperature as low as -78°C is necessary for the reaction and in addition, the palladium catalyst to be used is expensive. Accordingly, any one of the above methods are not satisfactory for the preparation of a polyprenol selectively and industrially advantageously. An object of the present invention is to provide a process for preparing a polyprenol selectively and industrially advantageously by dehalogenating a terminal allyl halide, thereby constituting a carbon-carbon double bond at a selected position. This object has been achieved by the surprising finding of a process for preparing a polyprenol ["which will hereinafter be abbreviated as Polyprenol (1)"] represented by the following formula (1) : wherein Y and Z individually represent a hydrogen atom or are coupled together to form a carbon-carbon bond; R represents a hydrogen atom or a protective group of a hydroxyl group; and n stands for 0 or an integer not smaller than 1, which comprises bringing an organic complex of an alkaline metal and a polycyclic aromatic compound into contact with a compound ("which will hereinafter be abbreviated as Compound (2)") represented by the following formula (2): wherein concerning V, W and X, V represents a halogen atom, while W and X are coupled together to form a carbon-carbon bond or X represents a halogen atom, while V and W are coupled together to form a carbon-carbon bond; A represents a protective group of a hydroxyl group; and Y, Z and n have the same meanings as defined above. In the above formula, no particular limitation is imposed on the protective group of a hydroxyl group represented by A or R insofar as it is used for the purpose of protecting an alcohol. Examples of the protective group include acyl groups such as acetyl, butyryl, benzoyl and p-methoxybenzoyl; 1-alkoxyalkyl groups such as methoxymethyl, 1-ethoxyethyl and tetrahydropyranyl; aralkyl groups such as benzyl and p-methoxybenzyl; and tri-substituted silyl groups such as trimethylsilyl. Examples of the halogen atom represented by V or X include chlorine, bromine and iodine. Examples of the alkaline metal forming the organic complex of an alkaline metal which complex is used in the preparation process of the present invention include lithium and sodium. As a compound which forms the organic complex with the above-exemplified alkaline metal, polycyclic aromatic compounds such as naphthalene, methyl naphthalene, anthracene and biphenyl are used. From the viewpoint of economy and handling ease, it is preferred to use, among them, sodium as an alkaline metal and naphthalene as a compound forming an organic complex with the alkaline metal. The alkaline metal is preferably used in an amount falling within a range of from 2 to 20 mole equivalents based on Compound (2), with a range of from 2 to 10 mole equivalents being more preferred. The compound which forms an organic complex with the alkaline metal is preferably used in an amount falling within a range of 2 to 20 mole equivalents based on Compound (2), with a range of 5 to 10 mole equivalents being more preferred. The alkaline metal and the compound forming an organic complex therewith may be added to the reaction system separately. Alternatively, it is possible to form an organic metal complex in advance from them and then add the resulting organic metal complex to the reaction system. For example, when sodium and naphthalene are used, a solidified sodium-naphthalene complex can be prepared by dispersing metal sodium in molten naphthalene. The reaction in the present invention can be conducted in the presence or absence of a solvent, but reaction in the presence of a solvent is preferred. Preferred examples of the solvent include ether solvents such as diethyl ether, tetrahydrofuran, dimethoxyethane and diglyme. Among them, tetrahydrofuran is preferred. The solvent is preferably used in an amount falling within a range of 2 to 50 times the weight of Compound (2), with a range of 2 to 10 times the weight being more preferred. In the reaction of the present invention, a lower alkylamine can be added to the reaction system in order to improve the reaction selectivity to Polyprenol (1) which is a target product. Examples of such a lower alkylamine include monoalkylamines such as butylamine and dialkylamines such as diethylamine and diisopropylamine. Among them, diethylamine is preferred. The lower alkylamine is preferably used in an amount falling within a range of 1 to 10 mole equivalents based on Compound (2), with a range of 2 to 4 mole equivalents being more preferred. It is generally proper to effect the reaction at a temperature ranging from -50 to 50°C, preferably -30 to 0°C. After the completion of the reaction, Polyprenol (1) can be isolated from the reaction mixture in a manner known per se in the art. For example, Polyprenol (1) is isolated by pouring the reaction mixture in water, extracting with a solvent, for example, a hydrocarbon such as n-hexane or toluene, or an ether such as diisopropyl ether, and then distilling off the solvent from the resulting extract. When Polyprenol (1) having as R a protective group of a hydroxyl group is prepared by the reaction of the present invention, another Polyprenol (1) having as R a hydrogen atom can be obtained by deprotection. When Polyprenol (1) having as R a hydrogen atom is prepared, on the other hand, another Polyprenol (1) having as R a protective group of a hydroxyl group can be obtained by protecting the hydroxyl group. Protection or deprotection of the hydroxyl group is conducted in a manner known per se in the art. Polyprenol (1) obtained above is able to have an increased purity by distillation, chromatography on a silica gel or the like means. Incidentally, Compound (2) can be prepared by halogenating an allyl alcohol represented by the following formula (3): wherein Y, Z, A and n have the same meanings as defined above with thionyl chloride, phosphorus trichloride or phosphorus tribromide in the presence of an ether solvent such as diisopropyl ether (refer to US 5714645). Examples The present invention will hereinafter be described in detail by examples but it should however be borne in mind that the present invention is not limited to or by the following examples. Referential Example 1 Synthesis of 1-benzyloxy-28-chloro-3,7,11,15,19,23,27-heptamethyl-6,10,14,18,22,26-octacosahexaene [Compound (2); V = Cl, W and X = carbon-carbon bond, Y = H atom, Z = H atom, A = benzyl group, n = 5] and 1-benzyloxy-26-chloro-3,7,11,15,19,23,27-heptamethyl-6,10,14,18,22,27-octacosahexaene [Compound (2); X = Cl, V and W = carbon-carbon bond, Y = H atom, Z = H atom, A = benzyl group, n = 5] In a 100-ml reaction vessel purged with argon, 8.77 g (14.5 mmol) of 1-benzyloxy-3,7,11,15,19,23,27-heptamethyl-6,10,14,18,22,27-octacosahexaen-26-ol [a compound represented by the formula (3); Y = H atom, Z = H atom, A = benzyl group, n = 5] and 0.0106 g (0.145 mmol) of dimethylformamide were charged, followed by the addition of 40 ml of diisopropyl ether to dissolve the former two compounds in the latter. The resulting solution was cooled to -5 to 0°C. To the reaction mixture, 2.76 g (23.2 mmol) of thionyl chloride dissolved in 8 ml of diisopropyl ether were added dropwise at a temperature range of from -5 to 0°C. The reaction was effected at the same temperature for one hour, followed by heating the reaction temperature to room temperature. The reaction was effected at 25°C for 3 hours. The reaction mixture was added in portions to 132 g of a 10% aqueous solution of sodium bicarbonate carefully so as not to cause foaming, followed by extraction with diisopropyl ether. The extract was washed with saturated saline and the solvent was distilled off. As a result of analysis of 16.06 g of the residue by liquid chromatography, it contained a mixture of 1-benzyloxy-28-chloro-3,7,11,15,19,23,27-heptamethyl-6,10,14,18,22,26-octacosahexaene and 1-benzyloxy-26-chloro-3,7,11,15,19,23,27-heptamethyl-6,10,14,18,22,27-octacosahexaene (mixing ratio: primary chloride : secondary chloride = 91 : 9, content of a chloride compound: 56.4 wt.%). Example 1 Synthesis of 3,7,11,15,19,23,27-heptamethyl-6,10,14,18,22,26-octacosahexaen-1-ol [Polyprenol (1); Y = H atom, Z = H atom, R = H atom, n = 5] In a 200-ml reaction vessel purged with argon, 8.03 g (content of a chloride compound: 56.4 wt.%, 7.3 mmol) of a mixture (mixing ratio: primary chloride : secondary chloride = 91 : 1 9) obtained in Referential Example 1, said mixture being composed of 1-benzyloxy-28-chloro-3,7,11,15,19,23,27-heptamethyl-6,10,14,18,22,26-octacosahexaene and 1-benzyloxy-26-chloro-3,7,11,15,19,23,27-heptamethyl-6,10,14,18,22,27-octacosahexaene and 5.32 g (41.5 mmol) of naphthalene were charged, followed by the addition of 70 ml of tetrahydrofuran to dissolve the former two compounds in the latter. The resulting solution was cooled to -40 to -30°C and 2.43 g (33.2 mmol) of diethylamine were added thereto. To the reaction mixture, 0.95 g (41.3 mmol) of metal sodium was added at the same temperature and they were reacted at the same temperature for 3 hours. Then, the reaction was effected further for 3 hours at -20 to -10°C. The reaction mixture was poured into 100 ml of a saturated aqueous solution of ammonium chloride, followed by extraction with diisopropyl ether. The extract was washed with saturated saline and the organic layer so obtained was analyzed by the internal standard method, whereby 2.69 g of 3,7,11,15,19,23,27-heptamethyl-6,10,14-18,22,26-octacosahexaen-1-ol were obtained (yield from 1-benzyloxy-3,7,11,15,19,23,27-heptamethyl-6,10,14,18,22,27-octacosahexaen-26-ol: 74%). Example 2 Synthesis of 3,7-dimethyl-6-octen-1-ol [Polyprenol (1); Y = H atom, Z = H atom, R = H atom, n = 0] In a 50-ml reaction vessel purged with argon, 0.324 g (content of a chloride compound: 86.6 wt.%, 1.0 mmol) of a mixture (mixing ratio: primary chloride : secondary chloride = 70 : 30) of 1-benzyloxy-8-chloro-3,7-dimethyl-6-octene [Compound (2); V = Cl, W and X = carbon-carbon bond, Y = H atom, Z = H atom, A = benzyl group, n =0] and 1-benzyloxy-6-chloro-3,7-dimethyl-7-octene [Compound (2); X = Cl, V and W = carbon-carbon bond, Y = H atom, Z = H atom, A = benzyl group, n = 0] and 0.4 g (3.1 mmol) of naphthalene were charged, followed by the addition of 10 ml of tetrahydrofuran to dissolve the former two compounds in the latter. The resulting solution was cooled to -40 to -30°C and 0.076 g (1.0 mmol) of diethylamine was added thereto. To the reaction mixture, 0.096 g (4.2 mmol) of metal sodium was added at the same temperature and they were reacted at the same temperature for 3 hours. Then the reaction mixture was reacted further for 3 hours at -20 to -10°C. The reaction mixture was poured into 10 ml of a saturated aqueous solution of ammonium chloride, followed by extraction with diisopropyl ether. The extract was washed with saturated saline and the organic layer so obtained was analyzed by the internal standard method, whereby 0.109 g of 3,7-dimethyl-6-octen-1-ol was obtained (yield: 70%). Example 3 Synthesis of 3,7-dimethyl-6-octen-1-ol In a 50-ml reaction vessel purged with argon, 0.68 g (content of a chloride compound: 82.5 wt.%, 2.0 mmol) of 1-benzyloxy-6-chloro-3,7-dimethyl-7-octene and 0.769 g (6.0 mmol) of naphthalene were charged, followed by the addition of 10 ml of tetrahydrofuran to dissolve the former two compounds in the latter. The resulting solution was cooled to -40 to -30°C and 0.146 g (2.0 mmol) of diethylamine was added thereto. To the reaction mixture, 0.184 g (8.0 mmol) of metal sodium was added at the same temperature and they were reacted at the same temperature for 3 hours. Then the reaction was effected further for 3 hours at -20 to -10°C. The reaction mixture was poured into 10 ml of a saturated aqueous solution of ammonium chloride, followed by extraction with diisopropyl ether. The extract was washed with saturated saline and the organic layer so obtained was analyzed by the internal standard method, whereby 0.231 g of 3,7-dimethyl-6-octen-1-ol was obtained (yield: 74%). Example 4 Synthesis of 3,7,11,15,19,23,27-heptamethyl-6,10,14,18,22,26-octacosahexaen-1-ol [Polyprenol (1); Y = H atom, Z = H atom, R = H atom, n = 5] In a 100-ml reaction vessel purged with argon, 2.30 g (content of a chloride compound: 64.8 wt.%, 2.4 mmol) of a mixture (mixing ratio: primary chloride : secondary chloride = 91 : 9) of 1-benzyloxy-28-chloro-3,7,11,15,19,23,27-heptamethyl-6,10,14,18,22,26-octacosahexaene and 1-benzyloxy-26-chloro-3,7,11,15,19,23,27-heptamethyl-6,10,14,18,22,27-octacosahexaene and 1.79 g (14.0 mmol) of naphthalene were charged, followed by the addition of 30 ml of tetrahydrofuran to dissolve the former two compounds in the latter. The resulting solution was cooled to -40 to -30°C and 0.77 g (11.0 mmol) of diethylamine were added thereto. To the reaction mixture, 0.10 g (14.0 mmol) of metal lithium was added at the same temperature and they were reacted at the same temperature for 3 hours. Then, the reaction was effected further for 3 hours at -20 to -10°C. The reaction mixture was poured into 10 ml of a saturated aqueous solution of ammonium chloride, followed by extraction with diisopropyl-ether. The extract was washed with saturated saline and the organic layer so obtained was analyzed by the internal standard method, whereby 1.00 g of 3,7,11,15,19,23,27-heptamethyl-6,10,14-18,22,26-octacosahexaen-1-ol were obtained (yield from 1-benzyloxy-3,7,11,15,19,23,27-heptamethyl-6,10,14,18,22,27-octacosahexaen-26-ol: 84%). Example 5 Synthesis of 3,7,11,15,19,23,27-heptamethyl-6,10,14,18,22,26-octacosahexaen-1-ol [Polyprenol (1); Y = H atom, Z = H atom, R = H atom, n = 5] In a 100-ml reaction vessel purged with argon, 2.30 g (content of a chloride compound: 64.8 wt.%, 2.4 mmol) of a mixture (mixing ratio: primary chloride : secondary chloride = 91 : 9) of 1-benzyloxy-28-chloro-3,7,11,15,19,23,27-heptamethyl-6,10,14,18,22,26-octacosahexaene and 1-benzyloxy-26-chloro-3,7,11,15,19,23,27-heptamethyl-6,10,14,18,22,27-octacosahexaene and 4.32 g (28.0 mmol) of biphenyl were charged, followed by the addition of 50 ml of tetrahydrofuran to dissolve the former two compounds in the latter. The resulting solution was cooled to -40 to -30°C and 0.77 g (10.5 mmol) of diethylamine were added thereto. To the reaction mixture, 0.65 g (28.3 mmol) of metal sodium was added at the same temperature and they were reacted at the same temperature for 3 hours. Then, the reaction was effected further for 3 hours at -20 to -10°C. The reaction mixture was poured into 100 ml of a saturated aqueous solution of ammonium chloride, followed by extraction with diisopropyl ether. The extract was washed with saturated saline and the organic layer so obtained was analyzed by the internal standard method, whereby 0.92 g of 3,7,11,15,19,23,27-heptamethyl-6,10,14-18,22,26-octacosahexaen-1-ol were obtained (yield from 1-benzyloxy-3,7,11,15,19,23,27-heptamethyl-6,10,14,18,22,27-octacosahexaen-26-ol: 77%).

Claims: A process for the preparation of a polyprenol represented by the following formula (1): wherein Y and Z individually represent a hydrogen atom or are coupled together to form a carbon-carbon bond, R represents a hydrogen atom or a protective group of a hydroxyl group, and n stands for 0 or an integer not smaller than 1, which comprises bringing an organic complex of an alkaline metal and a polycyclic aromatic compound into contact with a compound represented by the following formula (2): wherein concerning V, W and X, V represents a halogen atom, while W and X are coupled together to form a carbon-carbon bond or X represents a halogen atom, while V and W are coupled together to form a carbon-carbon bond; A represents a protective group of a hydroxyl group; and Y, Z and n have the same meanings as defined above. A process according to claim 1, wherein the organic complex of an alkaline metal and a polycyclic aromatic compound is a complex formed of an alkaline metal such as sodium or lithium and a polycyclic aromatic compound selected from naphthalene, methyl naphthalene, anthracene and biphenyl. A process according to claim 1 or 2 wherein the reaction is conducted in the presence of an ether solvent. A process according to any one of claims 1 to 3, wherein the reaction is effected in the presence of a lower alkylamine in the reaction system.

Inventors: KANEHIRA KOICHI, TAMAI YOSHIN C O KURARAY CO LT, UJITA KATUJI, KANEHIRA, KOICHI, TAMAI, YOSHIN, UJITA, KATUJI, Tamai, Yoshin, c/o Kuraray Co. Ltd., Ujita, Katuji, c/o Kuraray Co.Ltd
Applicants: KURARAY CO, KURARAY CO., LTD.
Application year: 1998
Main classification: C07C29
IPC codes: C07C29