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Method for Racemization of Optically Active Amines

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Method for Racemization of Optically Active Amines Europaisches Patentamt European Patent Office Office europeen des brevets (11) EP 0 900 780 A1 (12) EUROPEAN PATENT APPLICATION published in accordance with Art. 158(3) EPC (43) Date of publication: (51) |nt. CI.6: C07C 21 1/03, C07C 211/15, 10.03.1999 Bulletin 1999/10 C07C 21 1/2g C07C 209/68, (21) Application number: 97908531.3 C07B 55/00 (22) Date of filing: 27.03.1997 (86) International application number: PCT/JP97/01058 (87) International publication number: WO 97/35833 (02.10.1997 Gazette 1997/42) (84) Designated Contracting States: (72) Inventors: AT BE CH DE DK ES Fl FR GB GR IE IT LI LU MC • INOUE, Toru; NL PT SE Research Development Center of Nishi-ku, Kobe-shi; Hyogo 651-22 (JP) (30) Priority: 28.03.1996 J P 73758/96 . HIRAYAMA, Yoshihiko; Research Development Center (71) Applicant: Nishi-ku, Kobe-shi; Hyogo 651-22 (JP) NAGASE & COMPANY, LTD. Osaka-shi, Osaka 550-91 (JP) (74) Representative: VOSSIUS & PARTNER Siebertstrasse 4 81675 Munchen (DE) (54) METHOD FOR RACEMIZATION OF OPTICALLY ACTIVE AMINES (57) The present invention provides a process for effectively racemizing an amine compound in which an asymmetric carbon is located at the p-position of the amino group or more distant therefrom, which com- prises reacting the amine compound with a complex of an alkali metal and a polycyclic aromatic hydrocarbon. < O CO r»- o o o Q_ LU Printed by Xerox (UK) Business Services 2.16.7/3.6 EP 0 900 780 A1 Description TECHNICAL FIELD 5 [0001 ] The present invention relates to a process for racemizing optically active amines of the formula (1) below which comprises reacting said optically active amine with a complex of an alkali metal and a polycyclic aromatic hydrocarbon. BACKGROUND ART 10 [0002] Useful as optical resolution agents, as asymmetric auxiliary agents, as ligands for metals in an asymmetric reaction, Or as intermediates for pharmaceuticals are optically active amines of the following formula (1): 15 20 wherein R1 is an unsubstituted aryl group; an aryl group substitute with one to five substituents selected from the group consisting of C1-C4 alkyl groups, C1-C4 alkoxy groups and halogen atoms; or an unsubstituted or substituted heterocy- clic group; 25 R2 is a C-|-C8 alkyl group; a C-|-C8 alkyl group substituted with one to three aryl groups; a C-|-C8 alkoxy group; a Ci -C8 alkoxy group substituted with one to three aryl groups; an unsubstituted aryloxy group; an aryloxy group sub- stituted with one to five substituents selected from the group consisting of halogen atoms, C1-C4 alkyl groups optionally substituted with one to three halogen atoms and C1-C4 alkoxy groups optionally substituted with one to three halogen atoms; or 30 an unsubstituted aryl group; an aryl group substituted with one to five substituents selected from the group consist- ing of C-|-C4 alkyl groups, C-|-C4 alkoxy groups and halogen atoms; or an unsubstituted or substituted heterocyclic group; provided that these unsubstituted and substituted aryl and heterocyclic groups are not identical to R1 ; R3 and R4, which may be identical or different, are chosen from hydrogen atoms, C-| -C4 alkyl groups, C-| -C4 alkyl groups substituted with one to three aryl groups, or C-|-C4 alkyl-CO-groups; 35 A is a C1-C10 alkylene group; and * indicates the position of the asymmetric carbon atom. [0003] In particular, the optically active amine of the formula (1) wherein R1 is phenyl, R2 is isopropyl, R3 and R4 are both hydrogen atoms, and A is methylene, i.e., optically active 3-methyl-2-phenylbutylamine (PBA) is a useful com- 40 pound as an optical resolution agent. The compound is used as an optical resolution agent for obtaining only one opti- cally active isomer from racemic ibuprofen [2-(4-isobutylphenyl)propionic acid], ketoprofen [2-(3- benzoylphenyl)propionic acid] or the like, the isomer being useful as an anti-inflammatory, analgesic, antipyretic or antirheumatic agent [Japanese Patent Publication (Kokai) Nos. 229986/1993 and 151344/1996]. [0004] At present, optically active PBA can be obtained by resolving racemic PBA with an optically active acid such 45 as mandelic acid [Japanese Patent Publication (Kokai) No. 1 72853/1 986] or by selectively hydrolyzing an amide of PBA with an enzyme [Japanese Patent Application No. 215722/1995]. A method utilizing a reaction in which a nitrile under- goes optically selective hydration catalyzed by an enzyme has also been developed [Japanese Patent Publication (Kokai) No. 303496/1995]. [0005] If an optically active compound having either one of the steric configurations is desired and if one intends to so obtain the optically active compound by optical resolution of its racemate, in general, the desired optically active com- pound is obtained only in 50% yield even at maximum, and not less than 50% of undesired optically active compound is discarded. Accordingly, if one intends to obtain an optically active compound by an optical resolution process, it is important to develop a process for racemization and/or inversion of the steric configuration of the undesired optically active compound so as to increase the yield of the desired optically active compound. 55 [0006] A number of processes for racemizing an amine compound in which a carbon atom at the a-position of the amino group is an asymmetric one have been developed, including, amongst others, a process of heating the amine compound under an atmosphere of pressurized hydrogen with a catalyst for catalytic reduction such as Raney nickel, Raney cobalt or the like [Japanese Patent Publication (Kokai) No. 185943/1988], a process utilizing an imine formed by 2 EP 0 900 780 A1 a reaction of the amine compound with a carbonyl compound [Japanese Patent Publication (Kokai) Nos. 23824/1988 and 188120/1995], a process utilizing sodium hydride or sodium amide [DE-OS 2,348,801], and a process utilizing sodium activated by a polycyclic aromatic compound or by a carrier such as alumina [Japanese Patent Publication (Kokai) Nos. 50328/1975, 50344/1975 and 49235/1975]. 5 [0007] However, up to now, no process has been known for effectively racemizing an amine compound in which an asymmetric carbon is located at the p-position of the amino group or more distant therefrom, as illustrated by PBA. [0008] In view of these facts, the present inventors intended to develop an industrially applicable process for effec- tively racemizing an amine compound in which an asymmetric carbon is located at the p-position of the amino group or more distant therefrom, as illustrated by PBA 10 DISCLOSURE OF THE INVENTION [0009] Surprisingly, it was found that an amine compound in which an asymmetric carbon is located at the p-position of the amino group or more distant therefrom can be effectively racemized by reacting it with a complex of an alkali 15 metal and a polycyclic aromatic hydrocarbon. [001 0] Thus, the present invention provides a process for racemizing optically active amines of the following formula (1): 20 wherein R1 is an unsubstituted aryl group; an aryl group substituted with one to five substituents selected from the group consisting of C1-C4 alkyl groups, C1-C4 alkoxy groups and halogen atoms; or an unsubstituted or substituted het- erocyclic group; 30 R2 is a C-|-C8 alkyl group; a C-|-C8 alkyl group substituted with one to three aryl groups; a C-|-C8 alkoxy group; a Ci -C8 alkoxy group substituted with one to three aryl groups; an unsubstituted aryloxy group; an aryloxy group sub- stituted with one to five substituents selected from the group consisting of halogen atoms, C1-C4 alkyl groups optionally substituted with one to three halogen atoms and C1-C4 alkoxy groups optionally substituted with one to three halogen atoms; or 35 an unsubstituted aryl group; an aryl group substituted with one to five substituents selected from the group consist- ing of C-|-C4 alkyl groups, C-|-C4 alkoxy groups and halogen atoms; or an unsubstituted or substituted heterocyclic group; provided that these unsubstituted and substituted aryl and heterocyclic groups are not identical to R1 ; R3 and R4, which may be identical or different, are chosen from hydrogen atoms, C-| -C4 alkyl groups, C-| -C4 alkyl groups Substituted with one to three aryl groups, or C1-C4 alkyl-CO-groups; 40 A is a C1-C10 alkylene group; and * indicates the position of the asymmetric carbon atom; which comprises reacting said amines with a complex of an alkali metal and a polycyclic aromatic hydrocarbon. [0011] Base-induced racemization usually requires hydrogen atom abstraction reaction at the asymmetric carbon. 45 Accordingly, such racemization becomes more prone to take place as the acidity of the hydrogen atom increases which is bound to the asymmetric carbon. However, the acidity of the hydrogen atom at the p-position of the amino group or more distant therefrom tends to become lower than the one at the a-position due to the attenuation in the inductive effect caused by the amino group. Therefore, it could not be assumed that a process which can effectively racemize an amine compound having an asymmetric carbon atom at the a-position of the amino group would be applicable to an 50 amine compound in which an asymmetric carbon atom is located at the p-position of the amino group or more distant therefrom, as well. [001 2] As stated above, several processes for racemizing an amine compound in which an asymmetric carbon atom is located at the a-position of the amino group are known. These processes include a one which utilizes a complex of an alkali metal (sodium) and a polycyclic aromatic hydrocarbon (naphthalene or anthracene) [Japanese Patent Publi- 55 cation (Kokai) No.
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