PROCESS FOR REMOVING AN AMINO PROTECTING GROUP

Abstract: In a process for the production of an amino compound the improvement wherein a protected amino compound containing an amino group protected with a 2-­ alkenyloxycarbonyl group is deprotected in contact with a compound of a platinum group metal as a catalyst in the presence of a formic acid compound selected from formic acid and salts thereof.

Description: Process for production of amino compounds This invention relates to a process wherein an amino group protected with a 2-alkenyloxycarbonyl group is deprotected in good efficiency. In a variety of organic synthesis reactions including synthesis of peptides or glycoproteins, the amino group in the starting compound has been often protected in an inert form to the reaction. As a method that enables deprotection under relatively moderate conditions, a method has been lately developed wherein an allyloxycarbonyl group is introduced into an amino group and the resulting amino group is then deprotected with a palladium catalyst in the presence of nucleophilic reagent such as 5,5-dimethyl-1,3-cyclohexanedione (hereinafter called "Dimedone") or 2-ethylhexanoic acid (Angew. Chem. Int. Ed. Engl. 23, 436, 1984; U.S. Patent 4,314,942). The above method however can hardly separate final products because Dimedone or 2-ethylhexanoic acid is allylated to form high-boiling by-products, and uses costly reagents, posing an economical problem. The present inventors have therefore made extensive studies to eliminate such defects of the prior art and consequently found that the use of formic acid or salts thereof is effective. This finding has led to completion of the present invention. This invention is to provide a process for the production of an amino compound, characterized in that a protected amino compound containing an amino group protected with a 2-alkenyloxycarbonyl group is deprotected in contact with a compound of a platinum group metal as a catalyst in the presence of a formic acid compound selected from formic acid and salts thereof. The protected amino compound used in this invention is a compound wherein a primary or secondary amino group in a molecule is protected with a 2alkenyloxycarbonyl group. Any 2-alkenyloxycarbonyl group will do if it is commonly used as a protective group. Usually, said group is a group represented by formula EMI2.1 wherein R1, R2, R3, R4 and R5 each denote a hydrogen atom or a hydrocarbon residue that may have a substituent. Concrete examples of the 2-alkenyl group include an allyl group, a methallyl group, a crotyl group, a prenyl group, a 2-pentenyl group, a 2-ethyl-2-butenyl group, a cinnamyl group, a p-chlorocinnamyl group, a geranyl group, a neryl group and lower alkoxy derivatives of these groups. The number of carbon atoms of the 2-alkenyl group may properly be selected taking account of the separation of alkenes formed after the reaction and the ease of obtaining the starting material. Usually, a 2-alkenyl group having not more than 10 carbon atoms is adopted. In case of a 2-alkenyl group having not more than 5 carbon atoms, by-product alkenes can be removed outside the system in gaseous state. One protective group in a molecule is commonly used, but the number of the protective group is not limited thereto. Two or more protective groups may be also introduced. Meanwhile, examples of the amine compound to be protected (i.e. a compound wherein a protective group is replaced with a hydrogen atom) may be any amine compounds if they have a primary or secondary amino group, including aliphatic amine compounds, alicyclic amine compounds, aromatic amine compounds and heterocyclic amine compounds. One or more reactive sites such as a carbon-carbon double bond, a carboncarbon triple bond, a carboxyl group, a hydroxyl group, a thiol group, a carbonyl group, an epoxy group, a nitrile group, a sulfonyl group, a sulfone group, an ester linkage, an ether linkage, thioether linkage, an acetal linkage and a chlorine atom may be contained in the molecule. The molecular weight of such amine compound is, though not exerting a big influence on the reaction, usually 5,000 or less, and the number of carbon atoms of the amine compound is usually 100 or less, more preferably 5 or less. Among the amine compounds, primary amines are preferable. Secondary amines wherein a nitrogen atom of an amino group does not form a ring are desirable. In this invention, the compound of the platinum group metal is used as a catalyst in the reaction. The compound of the platinum group metal here referred to as the catalyst is the compound of the platinum group metal per se or a compound comprising the compound of the platinum group metal and a ligand. The compound of the platinum group metal used is a salt or a complex of palladium, ruthenium, platinum or rhodium. Concrete examples thereof include tris(dibenzylideneacetone) dipalladium (0), tris(tribenzylideneacetylacetone) tripalladium (0), tetrakis(triphenylphosphine) palladium (0), palladium acetate, palladium propionate, palladium butyrate, palladium benzoate, palladium acetylacetonate, palladium nitrate, palladium sulfate, palladium chloride, ruthenium dihydrotetrakis (triphenylphosphine), ruthenium acetylacetonate, platinous acetate and platinum acetylacetonate. Of platinum group metals, palladium is desirable from the aspect of reactivity. Above all, a zerovalent complex or a divalent organic compound of palladium is preferable. The ligand used is a monodentate or multidentate electron donor compound having an element of Group V of the periodic table as a ligand atom. Concrete examples of the ligand include nitrogen compounds such as pyridine, quinoline, trimethylamine, triethylamine, tributylamine, a ,a '-dipyridyl, l,10-phenanthroline and N,N,N',N'-tetramethylethylenediamine; phosphorus compounds such as triethylphosphine, tri-n-butylphosphine, tri-n-dodecylphosphine, triphenylphosphine, tri-o-tolylphosphine, tri-p-biphenylphosphine, tri-o-methoxyphenylphosphine, phenyldiphenoxyphosphine, triethyl phosphite, tri-n-butyl phosphite, tri-n-hexyl phosphite, triphenyl phosphite, ti-o-tolyl phosphite, triphenylthio phosphite, ,-ethylene-di-(diphenyl)phosphine, a,ss-ethylene- di-(dibutyl)phosphine and a,y-propylene-di-(diphenyl)phosphine; arsenic compounds such as triethylarsenic, tributylarsenic and triphenylarsenic; and antimony compounds such as tripropylantimony and triphenylantimony. Of these, the phosphorus compounds are preferable in the aspects of activity selectivity and economics. Such ligand is not altogether needed as a catalyst component, but the use of the ligand in a suitable amount can greatly improve the stability of the catalyst. The amount of the ligand used is not necessarily fixed depending on the type, but is usually not more than 50 mols, preferably 2 to 20 mols per mol of the platinum group metal compound. The amount of the catalyst in this invention is properly selected. Said amount is usually such that the amount of the platinum metal compound is 0.01 to 10 mols, preferably 0.1 to 5 mols per 100 mols of the protected amino compound. This amount is found when the number of the protective group is 1. In case of the protected amino compound having two or more protective groups, the amount is increased depending on the number of the protective groups. The platinum group metal compound and the ligand may previously be reacted. Usually, the catalyst is prepared by contacting the respective catalyst components in the reaction system. The reaction in this invention is performed by contacting the protected amino compound with the catalyst in the presence of the formic acid compound selected from formic acid and salts thereof. By this reaction the protected amino group is deprotected, and an olefin corresponding to the 2-alkenyl group and carbon dioxide gas are concurrently formed as by-products. Concrete examples of the formic acld compound used include formic acid a ammonium formate, monomethylamine formate, dimethylamine formate, trimethylamine formate, triethylamine formate, triethanolamine formatea morpholine formate, pyridine formate, sodium formatea potassium formate and calcium formate. Of these, formic acid, ammonium formate and formic acid lower amine salts are preferable in view of the ease of removal after the reaction and economics. The amount of the formic acid compound is properly selected. It is usually one or more molecules, preferably 2 to 5 molecules per protected amino group of the starting material. A method of adding such formic acid compound is not limited in particular. For example, the formic acid compound is added at the stage of preparing the catalyst, at the time the reaction starts, or during the reaction. It is also possible that the formic acid compound is added in two or more divided portions as occassion demands. When a metal salt of formic acid is employed, it is advisable for increasing reactivity that said metal salt of formic acid is fed in the form of an aqueous solution or water is present in the reaction system. A diluent can be present in the reaction. Concrete examples of the diluent include nitriles such as acetonitrile, propionitrile, butyronitrile and benzonitrile; amines such as dimethylformamide, diethylformamide, dimethylacetamide, dimethylpropioamide and nmethylpyrrolidone; ethers such as tetrahydrofuran, dioxane, dibutyl ether and ethylene glycol dimethyl ether; ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone cyclohexanone; esters such as methyl acetate, ethyl acetate, propyl acetate and ethyl propionate; alcohols such as ethanol, propanol, tert.butanol, ethylene glycol and diethylene glycol monoethyl ether; sulfoxides such as dimethyl sulfoxide and diethyl sulfoxide; and hydrocarbons such as n-hexane, cyclohexane, benzene, toluene and xylene. Of these, the nitriles, the amides, the ethers, the ketones, the esters and the alcohols are preferable. Water may properly be present. The diluent is commonly used at such ratio that the concentration of the protected amino group reaches 1 to 50% by weight. The diluent can improve reactivity, selectivity and stability of the catalyst. The other reaction conditions can properly be chosen. The reaction temperature is usually OOG or above, preferably 10 to 1500G, and the reaction time is usually 5 minutes to 20 hours. After the reaction terminates, the deprotected amino compound is separated from the reaction liquid; the high-purity amino compound thus results. The formic acid compound remaining in the system can easily be removed by vacuum distillation, weak alkali treatment or water-washing. The subsequent treatment may be performed by a usual method such as a method wherein the compound is extracted with a solvent and the extract is then dried, a method wherein the compound is separated by distillation or a method wherein the compound is recrystallized. The thus obtained amino compounds are, for example, aliphatic amines, alicyclic amines,d aromatic amines, amino acids, peptides, glycoproteins, aminoglycosides, alkaloids, nucleosides, nucleotides and various heterocyclic compounds. These compounds are available as medicines, agricultural chemicals, industrial chemicals and intermediates thereof. According to this invention, the intended amino compounds can be yielded in good efficiency by a simple operation without forming by-products hard to separate. The process of this invention moreover has the advantage that since the reaction conditions are moderate, racemization does not occur even if using optically active amino acids. The following Examples illustrate this invention in more detail. Example 1: A reaction vessel was charged with 1 millimol of N-allyloxycarbonylcyclohexylamine, 6.2 millimols of tetrahydrofuran, 0.05 millimol of dipalladium tris(di benzylideneacetone).chloroform complex, 0.2 millimol of triphenylphosphine and 4 millimols of formic acid, and the mixture was stirred at 300C for 3 hours under nitrogen atmosphere. After stirring, the solvent and the remaining formic acid were distilled off under reduced pressure. The content was dissolved in ether and washed with an aqueous solution containing a small amount of sodium hydroxide to recover the resulting cyclohexylamine. The yield was, when measured by gas chromatography, found to be 98 mol%. Example 2: The procedure in Example 1 was repeated except that N-allyloxycarbonyldiisopropylamine was used as a protected amino compound and the reaction time was changed to 1 hour. As a result, diisopropylamine was obtained in a yield of 97 mol%. Example 3: The procedure in Example 1 was repeated except that amino acid having an amino group protected with an allyloxycarbonyl group was used as a protected amino compound and the reaction time was changed as shown in Table 1. After the reaction, the remaining formic acid and the solvent were distilled off under reduced pressure to obtain a solid product. Subsequently, the solid product was washed with tetrahydrofuran and then with ether to obtain a nearly pure amino acid. The resulting amino acid was measured for specific rotation under given conditions shown in Table 1 (C indicates a concentration, H20 an aqueous solution and HCl a hydrochloric acid aqueous solution, respectively). When the measured value was compared with a value described in a literature, it was ascertained that racemization did not occur. Table 1 EMI8.1 <tb> Run <SEP> Protected <SEP> amino <SEP> Re- <SEP> Product <SEP> Specific <SEP> Yield <tb> compound <SEP> action <SEP> rotation <SEP> (mol%) <tb> <SEP> time <tb> <SEP> (hr) <SEP> <tb> <SEP> 1 <SEP> N-allyloxyearbonyl- <SEP> 1 <SEP> Glycine <SEP> - <SEP> <tb> <SEP> glycine <tb> <SEP> 2 <SEP> N-allyloxycarbonyl <SEP> - <SEP> 2 <SEP> L-phenyl- <SEP> [&alpha;]D23 <SEP> = <SEP> -33.9 <SEP> 76 <tb> <SEP> phenylalanine <SEP> alanine <SEP> (C=1, <SEP> H2O) <tb> <SEP> 3 <SEP> N-allyloxycarbonyl- <SEP> 3 <SEP> L-leucine <SEP> <SEP> [&alpha; ;]D23 <SEP> = <SEP> +14.9 <SEP> <SEP> 86 <SEP> <tb> <SEP> leucine <SEP> <tb> <SEP> (C=2, <SEP> 6N <SEP> HCl) <SEP> <tb> <SEP> 4 <SEP> N-allyloxycarbonyl- <SEP> 3 <SEP> L-methionine <SEP> 2[&alpha;]D25 <SEP> <SEP> = <SEP> +25.3 <SEP> 74 <SEP> <tb> <SEP> methionine <SEP> D <SEP> <tb> <SEP> (C=3, <SEP> IN <SEP> HCI) <SEP> <tb> Example 4: The procedure in Example 1 was followed except that ammonium formate was used instead of formic acid. Cyclohexylamine was obtained in a yield of 95 mol%. Example 5: The procedure in Example 1 was followed except that triethylamine formate was used instead of formic acid. Cyclohexylamine was obtained in a yield of 97 mol%. Example 6: The procedure in Example 1 was followed except that tributylphosphine was used as a ligard instead of triphenylphosphine. Approximately the same results as in Example 1 were obtained. Example 7: A reaction vessel was charged with 5 millimols of N-allyloxycarbonylhexylamine, 40 millimols of tetrahydrofuran, P.3 millimol of palladium acetate, 0.6 millimol of triphenylphosphine and 20 millimols of formic acid, and the reaction was performed as in Example 1. There resulted hexylamine in a yield of 95 to1%.

Claims: What we claim is: 1. In a process for the production of an amino compound, the improvement wherein a protected amino compound containing an amino group protected with a 2alkenyloxycarbonyl group is deprotected in contact with a compound of a platinum group metal as a catalyst in the presence of a formic acid compound selected from formic acid and salts thereof. 2. The process of claim 1 wherein the formic acid compound is formic acid. 3. The process of claim 1 wherein the formic acid compound is a formic acid salt. 4* The process of claim 3 wherein the formic acid salt is ammonium formate or a formic acid lower amine salt. 5. The process of claim 1 wherein the formic acid compound is used in an amount of at least one molecule per protected amino group. 6. The process of claim 1 wherein the compound of the platinum group metal is used in an amount of 0.01 to 10 mols per 100 mols of the protected amino compound. 7. The process of claim 1 using a catalyst composed of a compound of a platinum group metal and a ligand. 8. The process of claim 7 wherein the ligand is an electron donor compound containing an element of Group V of the periodic table as a ligand atom. 9. The process of claim 8 wherein the electron donor compound is a phosphorus compound. 10. The process of claim 1 wherein the compound of the platinum group metal is a salt or a complex of palladium, ruthenium, platinum or rhodium. 11. The process of claim 1 wherein the compound of the platinum group metal is a zero-valent complex of palladium 12. The process of claim 1 wherein the compound of the platinum group metal is a divalent organic compound of palladium. 13. The process of claim 1 wherein the 2-alkenyl group of the 2-alkenyloxycarbonyl group has not more than 10 carbon atoms. 14. The process of claim 1 wherein the amine compound to be protected is a compound containing a primary or secondary amino group and having a molecular weight of not more than 5,000. 15. The process of claim 14 wherein the amine compound has not more than 100 carbon atoms. 16. The process of claim 14 wherein the amine compound is an aliphatic amine compound, an alicyclic amine compound, an aromatic amine compound or a heterocyclic amine compound. 17. The process of claim 1 wherein the reaction is carried out in the presence of a diluent. 18. The process of claim 1 wherein the reaction is carried out at a temperature of OOC or above for 5 minutes to 20 hours.

Inventors: TSUJI, JIRO
Applicants: NIPPON ZEON CO., LTD.
Application year: 1986
Main classification: C07B43
IPC codes: C07C67, C07C209, C07B43, C07B31, C07C227, C07B51, C07B61, B01J31