Process for the preparation of lysine
United States Patent [191 Pisanchyn et al.  
 [ 51 Apr. s, 1975 4] PROCESS FOR THE PREPARATION OF LYSINE [75 Inventors: John Pisanchyn, Morristown; Robert Fuhrmann, Morris Plains; Stylianos Sifniades, Parsippany; Allen Abraham Tunick, Denville, all of 211 Appl. No.: 203,914  
 Related U.S. Application Data [62] Division of Scr. No. 852,947, Aug. 25, 1969, Pat. No.  
 [52] U.S. Cl 260/482 R; 260/534 L; 260/566 A;  
  260/586 R [5i] Int. Cl. C07c 101/54 [58] Field of Search 260/482 R, 534 L McGraw-Hill.  
 Buehler, C. A; et 211., Survey of Organic Synthesis, Wiley, lnterscience 1970.  
 Primary Exqjrziiter-Lorraine A. Weinberger Assistant E.\&#39;g &#39;i ziiterPaul J. Killos Attorney, Agent, or FirmArthur .l. Plantamura 571 ABSTRACT Lysine is produced by a process comprising the steps of 1. Nitrating cyclohexanone to form 2-nitrocyclohexanone;  
 2. Nitrosating the 2-nitrocyclohexanone to form 2-nitro-6-oximinocyclohexanone;  
 3. Ring opening the 2-nitro--oximinocyclohexanone in alcoholic base to form an ester of 2-oximino-6-nitrocaproic acid;  
 4. Hydrogenating the 2-oximino6-nitro caproic acid alkyl ester to form an alkyl ester of lysine; and  
 5. Saponifying the lysine alkyl ester to afford lysine or a salt thereof.  
 13 Claims, No Drawings BACKGROUND OF THE INVENTION This is a division, of application Ser. No. 852,947 filed Aug. 25, 1969, now U.S. Pat. No. 3,681,460.  
 Lysine is well known as one of the essential amino acids. Its use in dietary supplements is unfortunately restricted due to its high price. This high price is necessitated by the fact that currently known synthetic methods for producing lysine involve expensive starting materials and reagents and/or complex processing steps.  
 SUMMARY OF THE INVENTION It is an object of this invention to provide an inexpensive, facile route to lysine.  
  It has now been found in accordance with this invention that lysine can be readily produced from cyclohexanone by the following synthetic method:  
  1. Nitration of cyclohexanone to form 2- nitrocyclohexanone;  
  2. Nitrosation of said 2-nitrocyclohexanone to form 2-nitro-6-oximinocyclohexanone;  
  3. Ring opening said 2-nitro-6- oximinocyclohexanone in alcoholic base to form an alkyl ester of 2-oximino-6-nitrocaproic acid;  
  4. Hydrogenating said 2-oximino-6-nitrocaproic acid alkyl ester to form an alkyl ester of lysine; and  
  5. Saponifying said lysine alkyl ester to afford lysine or lysine hydrochloride.  
  This synthesis can be schematically represented as follows:  
 aqueous H01 NHg EH action of the cyclohexanone with a carboxylic acid an- ;hydride or with ketene. The enol acylate is reacted with a nitrating agent such as acetyl nitrate to form the 2- nitrocyclohexanone. The preparation of 2- nitrocyclohexanone, also known as a-nitrocyclohexanone, is described, for example, in J. Org. Chem., 31, 357(1966).  
  The second step in our synthetic sequence and the product thereof, i.e., 2-nitro-6-oximinocyclohexanone, are both unknown.  
  The nitrosation of Z-nitrocyclohexanone to form 2- nitro-6-oximinocyclohexanone is most suitably carried out in an inert solvent for the nitrocyclohexanone so as to provide good Contact between the nitrocyclohexanone and the nitrosating agent and to facilitate temperature control. Although the nitrosation can be carried out at virtually any temperature between the freezing and boiling points of the selected solvent, we have found that the preferred reaction temperature is between 30C-, and +10C. Below 30C, the reaction rate is very low. Above about +10C, side reactions tend to occur which reduce the yield of 2-nitro-6- oximinocyclo&#39;liexanone and cause the formation of difficult to remove contaminants. The preferred reaction temperature range is about C to +5C.  
  A suitable solvent should not only be liquid in the preferred reaction temperature range, but it must also be inert to the nitrosating agent being used. This limits the readily available usable solvents to halogenated C -C alkanes and to alkane monoand diethers of 4-8 carbons. The term halogenated alkane connotes nor isoalkanes that have at least one-third of the hydrogens thereof replaced by fluorine, chlorine or bromine, preferably fluorine orchlorine. Suitable examples of such halogenated alkanes include CCl tetrachloroethane, dichloroethane, CH CI CHCI tetrachloroethylene, bromoform, perfluorobutane, and the various fluorochlorohydrocarbons sold commercially under the trademark Genetron or Freon. Suitable alkane ethers include diethyl ether, glyme, diglyme, diethyl- The&#34;? LIA ROH CH2 2 )s-CH-CUR -CH-COH NHg -HCl NHz The first step in our novel synthesis of lysine is the nitration of cyclohexanone to form 2- nitrocyclohexanone. This is a known reaction and compound. The preferred method of nitration is to form the enol acylate of the carbonyl group, for example, by recarbitol, and the like. The solvent is preferably substantially or completely water free.  
  Suitable nitrosating agents include the C -C alkyl nitrites, nitrosyl formate, nitrosyl chloride, nitrosyl bromide, and N 0 The preferred nitrosating agent is methyl nitrite, or nitrosyl chloride. The nitrosation is ordinarily carried out by dissolving the 2- nitrocyclohexanone in solvent, cooling the solution to about l5C, and then adding 1.0-1.5 mols of the nitrosating agent per mol of nitrocyclohexanone. The nitrosation reaction is ordinarily complete within from l-l2 hours after at least a molar equivalent of nitrosating agent has been added. Completion of the nitrosation reaction is most conveniently ascertained by the vapor phase chromatographic analysis of an aliquot of the reaction mixture. Although the reaction is not strongly endothermic or exothermic, it is desirable to maintain the reaction mixture within the desired temperature range through the course of the nitrosation reaction. The reaction is not pressure sensitive and can be carried out at ambient or superatmospheric pressure.  
  We have found that the nitrosation reaction proceeds much more readily in the presence of a strong acid catalyst. Any nonoxidizing acid having a pKa of less than 1 is suitable such as hydrochloric, hydrobormic, sulfuric, phosphoric, p-toluene sulfonic, or methane sulfonic acid. The amount of acid present in the reaction mixture is not critical but it should preferably be sufficient to make the solution 0.5-20 molar in acid. Because of its high volatility, hydrochloric acid is readily removed from the reaction mixture after completion of the reaction and for this reason it is preferred. In the case of HCl, the preferred concentration is 5 to 20 molar. The acid can be added prior to or simultaneously with the nitrosating agent, preferably prior to the nitrosating agent. Work-up of the nitrosation mixture, after completion of the reaction, is most advantageously carried out by stripping off the reaction solvent, any excess nitrosating agent, and the HCl catalyst under reduced pressure, preferably at a temperature below about 0C. If a nonvolatile acid catalyst is used, it must be removed from the reaction mixture or neutralized prior to removal of the solvent by stripping.  
  The residue remaining after removal of solvent, excess nitrosating agent, and acid catalyst consists essentially of 2-nitro-6-oximinocyclohexanone which can be utilized without further purification in the next step which entails opening, i.e., cleaving, of the cyclohexanone ring to form an alkyl ester of 2-oximino-6- nitrocaproic acid. Alternatively, and preferably, the residue is purified by being triturated at low temperature with methanol or ethanol prior to ring opening.  
 &#39; o HON=C /\CH-NO2 N ra)...  
 wherein n is 2 to 9. These are novel compounds and can be ring-opened even as the six-membered ring compound to provide precursors for the biodynamic C to C a,w-diamino acids.  
  This ring opening is most suitably effected by heating the 2-nitro-6-oximinocyclohexanone at a temperature of about 50 to 90C with an alcoholic solution of strong base.  
  Suitable alcohols are many of the C -C normal alkanols, i.e., methanol, ethanol, n-propanol, and nbutanol, preferably methanol. Suitable bases include 25 the alkali metal hydroxides or the alkali metal alkoxide of the alcohol used as solvent. The concentration of base is not critical, and we have found that in the range of 0025-1 .0 mols of base per mol of 2-nitro-6- oximino-cyclohexane no significant effect is noted. Preferably 0.05-0.10 mols of base per mol of 2-nitro-6oximinocyclohexanone is utilized.  
  The ring opening is rapid, and heating for about 1 hour is ordinarily sufficient to effect complete ring opening. Longer heating does no harm, however. The  
 concentration of 2-nitro-6-oximinocyclohexanone in the alcoholic base solution is not critical-the only requirement is that at least one mol of alcohol be present per mol of 2-nitro-6-oximinocyclohexanone. For convenience of handling, the concentration of 2-nitro-6- oximino-cyclohexanone in the alcoholic solution is preferably from about 1 to about 25 percent by weight.  
  The heating with alcoholic base results in ring opening with essentially simultaneous formation of the ester of 2-oximino- 6-nitrocaproic acid corresponding to the alcohol used as the solvent.  
  While we do not wish to be bound by any mechanistic interpretation, it is believed the ring opening reaction proceeds as follows:  
 o t q OR o l T HOll v.02 nor. L H OR H &#34;Th 0&#39;? N02 9 N02 1201:  
 ROH  
  0 9 &#39;OR OR H H N02 liO2(CH2)/ HCOn H OH (2-o :irnino.E-nitrocaproic acid ester) This 2-oximino-6-nitrocaproic acid ester is then recovered by various conventional methods including, for example, neutralilzation of any excess base with acid, evaporation of the alcohol solvent, and extraction of the nonvolatile residue with water to remove the alkali metal salt of the neutralizing acid thereby leaving the desired ester as a residue. Alternatively, the nonvolatile residue can be extracted with an organic solvent such as ether which affords an ethereal solution of ester, the ether then being evaporated off to afford the ester. Purification of this ester prior to the next step, i.e., reduction, is not necessary.  
  Reduction of the nitro and oximino groups of the ester to afford the ester of lysine is best effected by catalytic hydrogenation. For ease of handling, about a /2 to weight percent solution of the 2-oximino-6- nitrocaproic acid ester is dissolved in a suitable inert solvent such as a C -C alcohol, or a C -C monoor diether such as glyme, diglyme, diethyl carbitol, diethyl ether, and the like, from 1 to 20 weight percent based on the weight of the ester of hydrogenation catalyst added and the ester/solvent/catalyst mixture then heated, preferably with agitation, in a suitable pressure vessel at 20 200C under a hydrogen atmosphere. A hydrogen pressure of from about 10 up to as much as 5000 psig is suitable. Ordinarily, a pressure of 50-500 psig is preferred. Hydrogenation is rapid and is ordinarily complete after from about 1 to 24 hours depending upon the hydrogen pressure, catalyst, degree of agitation, and temperature of hydrogenation.  
  Suitable catalysts include palladium on a support such as carbon, alumina, calcium carbonate, or barium sulfate. The concentration of paladium on the support is suitable from about 1 to 10 weight percent.  
  The lysine ester is recovered from the hydrogenation mixture by filtering off the catalyst and evaporating off the solvent leaving behind the lysine-ester as a residue. If the ester is the ethyl ester, it may be resolved to obtain the nutrionally active L-enantiomer or it may be used directly as a dietary supplement with or without further purification, e.g., by recrystallization. A suitable recrystallization solvent is a C -C alkanol. If an ester other thanthe ethyl ester is present, hydrolysis to lysine by refluxing the ester in aqueous hydrochloric acid followed by neutralization with one equivalent of base and cooling results in precipitation of the lysine monohydrochloride, which may then be recovered by filtration. The hydrochloride is now ready for use as a food supplement or for resolution by known methods into the nutritionally active L-isomer.  
  lf basic saponification to afford the basic lysine salt followed by neutralization is carried out, neutral lysine is obtained. This material is not generally used in food supplements because of its unpleasant odorthe odorless monohydrochloride being preferred. Suitable bases for saponification or neutralization are the alkali metal hydroxides or carbonates, and the alkaline earth metal oxides or hydroxides.  
 The invention can be more fully understood by reference to the following examples. All parts are parts by weight unless otherwise expressly noted.  
 EXAMPLE 1 A solution of 31.2 grams (0.218 mol) 2- nitrocyclohexanone in 600 ml. anhydrous ether was saturated with anhydrous HCl at 0C. To this solution, 23 g. (0.223 mol) n-butylnitrite was added dropwise during 10 minutes under a nitrogen atmosphere while keeping the temperature at 0 to 5C. After standing for an additional 10 minutes at 05C, the reaction mixture was stripped under reduced pressure in a rotary evaporator. The light yellow crystals of 2-nitro-6- oximinocyclohexanone (NOC) which formed in the concentrated solution were recovered by filtration and then washed with ether: weight after drying 13.0 g. (35% yield).  
 EXAMPLE 2 Nitrosation of Nitrocyclohexanone With Methyl Nitrite in Ether Ten grams (0.070 mol) of 2-nitrocyclohexanone was dissolved in about 300 ml. of diethyl ether which had been saturated at 0C atmospheric pressure with dry HCl gas. The solution was then treated with 6.0 ml. (6.0 grams, 0.098 mol) of methyl nitrite, added in one portion at -20C. The solution was allowed to warm to 10C and was kept at that temperature for 1.5 hours. The solution was then evaporated to dryness on the rotary evaporator keeping the temperature below 10C. The residual yellow oil was scratched to induce crystallization, and the resulting yellow crystals of NOC were triturated with cold ether ml.) and collected by filtration. Yield: 3.8 grams (32%); melting point, C  
 nitrocyclohexanone was dissolved in 350 ml. of ION HCl in dry 1,2-dimethoxyethane (glyme) and the resulting solution then treated with 6.0 ml. (6.0 gram, 0.098 mol) of methyl nitrite at 20C. After 3.5 hours at l3C, a 50-ml. aliquot was removed for work-up and analysis. Nearly quantitative conversion of the nitrocyclohexanone to the desired l-nitro-6- oximinocyclohexanone was indicated by gas chromatographic analysis of the aliquot.  
  The remaining solution was worked up after an additional standing of one-half hour as follows: the volatile components were stripped on a rotary evaporator at l0C and the residue triturated with cold methanol. The resulting yellow crystals of NOC were collected by filtration and washed with a few milliliters of cold methanol. The 50-ml. aliquot was worked up in a similar fashion. Yield from both portions: 7.74 grams (64.5%).  
 EXAMPLE 4 Nitrosation of tit-Nitrocyclohexanone with-Nitrosyl Chloride in Glyme A l0.0-gram (0.070 mol) sample of lX-I&#39;lltIOCYClOhCX- anone was dissolved in 350 ml. of ION HCl in glyme, and the solution then treated with 3.1 ml. (about 4.5 g, 0.07 mol) of nitrosyl chloride at -20C. The temperature of the mixture was kept at 20C for 2.5 hours and then at l5C for 3 hours. At this point, the conversion of nitrocyclohexanone was 80 percent and the reaction mixture was evaporated to dryness on the rotary evaporator at about 10C. The evaporation residue was triturated with about 20 ml. cold methanol, filtered, and washed with a few additional milliliters of cold methanol. The resulting light-yellow crystalline powder weighed 5.21 grams. The mother liquor contained an additional 0.93 grams for a total yield of 6.14 grams; yield 64 percent based on reacted nitrocyclohexanone.  
 EXAMPLE To a solution of 10.0 grams (0.058 mol) of NOC in 400 ml. absolutemethanol was added at 50C a solution of 2.40 grams (0.058 mol) of sodium hydroxide in 400 ml. absolute methanol. A voluminous yellow precipitate appeared, which dissolved after several minutes. After standing at 50C for 5% hours, the reaction mixture was cooled to room temperature and then treated with a solution containing 5 ml. 12M HCl and 7 grams urea in 500 ml. water. The resulting solution was concentrated to 450 ml. by stripping under reduced pressure, and it was exhaustively extracted with ether.  
  After drying of the ether extracts and evaporation of the ether, 11.6 grams of crude methyl-2-oximino-6- nitrohexanoate was obtained. The material was of sufficient purity for hydrogenation without additional purification.  
 EXAMPLE 6 EXAMPLE 7 The procedure of Example 6 was repeated with varying amounts of NaOH and NOC in methanol at reflux temperature. It was found that ring opening of NOC took place satisfactority even with ratios NaOH/NOC as low as 0.025. A low NaOH/NOC ratio has the advantage of reducing salt by-product formation in the subsequent neutralization step prior to hydrogenation. The conversion of NOC after 140 minutes of refluxing is shown in the table below. In all cases; the only detectable product was methyl-2-oximino-6-nitrohexanoate.  
 NOC Reaction in Refluxing Methanol (Reaction time 140 min.)  
 NOC NaOH NaOH/- Volume NOC Conversion NOC (mmol) (mmol) (ml.) (Mol 7r) EXAMPLE 8 To a solution of 0.258 g. (1.5 millimol) NOC in 21 ml. ethanol, 3.0 ml. of 0.1 molar ethanolic NaOH was added at reflux. After refluxing for 6 hours, ultraviolet analysis of the reaction mixture revealed that 87 percent of the NOC had been consumed. The reaction mixture was stripped to dryness and the residue was dissolved in 3 ml. chloroform and refined by passing through a column of grams silica gel. Chloroform was used as the eluent. A cut composed ofa chromatographically pure oily material was obtained. It weighed 0.166 grams. The infrared spectrum of this material was consistent with that of ethyl-2-oximino-6- nitrnhexannate EXAMPLE 9 To a solution of 0.258 grams (1.5 millimols) NOC in 5.0 ml. n-butanol, 3.0 ml. of 0.1N NaOH in n-butanol was added at 85C. After standing for 6 hours at 85C about 99 percent of the NOC was consumed. The reaction mixture was then flashed to dryness and refined by passing through a column of 15 grams silica gel using chloroform as the eluent. 0.185 Gram of a chromatographically pure oil was obtained. The infrared spectrum of this material was consistent with that of nbutyl-2-oximino-6-nitrohexanoate.  
 EXAMPLE l0 Hydrogenation of Methyl-6-Nitro-2-Oximinohexanoate A SIS-mg. (2.5mmol) sample of methyl-6-nitro-2- oximonohexanoate was dissolved in 20 ml. of methanol containing 1 ml. concentrated HC] and 500 mg. 5 percent palladium on carbon. The mixture was hydroge nat&#39;ed at 60C and 50-70 psig hydrogen pressure in a Parr bomb. The uptake of hydrogen was 97 percent of theoretical in 69 hours. The mixture was filtered, evaporated to dryness on a rotary evaporator, and the residue refluxed with 50 ml. 6N HCl for 3 hours. The resulting solution was concentrated on a rotary evaporator to a thick syrup, which wasdissolved in 10 ml. percent EtOH at reflux. The solution was treated with 0.5 ml. pyridine in 1 ml. 95 percent ethanol, cooled slowly, and left standing for 25 hr. at room temperature followed by 16 hours in the refrigerator. The lysine hydrochloride which precipitated was collected by suction filtration, washed with ethanol, and dried in air at C.  
  A total of 275 mg. was obtained. Analysis of the mother liquors indicated the presence of an additional 35 mg. of lysine hydrochloride, for a total yield of 310 mg. (68%). A small amount (30 mg.) of pipecolinic acid was also present in the mother liquor.  
 We claim:  
 1. A process comprising the steps of a. nitrosating 2-nitrocyclohexanone to form 2-nitro- 6-oximinocyclohexanone;  
 b. ring opening said 2-nitro-6-oximinocyclohexanone in a substantially absolute alcoholic base to form an alkyl ester of 2-oximino-6-nitrocaproic acid;  
 c. hydrogenating said 2-oximino-6-nitrocaproic acid alkyl ester to form an alkyl ester of lysine.  
  2. A process in accordance with claim 1 further comprising the steps of saponifying said alkyl ester of lysine in hydrochloric acid solution to afford lysine dihydrochloride and neutralizing said lysine dihydrochloride to form lysine hydrochloride.  
  3. A process in accordance with claim 1 further comprising the steps of saponifying said alkyl ester of lysine with base to afford the salt of lysine followed by neutralization of said salt.  
  4. A process in accordance with claim 1 wherein said nitration is effected by forming the enol acetate of cyclohexanone by reacting cyclohexanone with acetic anhydride or ketene and nitrating said cyclohexanone enol acetat with acetyl nitrate.  
  5. A process in accordance with claim 1 wherein said nitrosation is carried out in a solvent selected from the group consisting of halogenated C -C alkanes and alkane monoand diethers of 4 to 8 carbons at a temperature between 30C and +10C.  
  6. A process in accordance with claim 5 wherein said temperature is -20C to +5C.  
  10 said ring opening is effected by heating said 2-nitro-6- oximinocyclohexanone at a temperature of 50 to 90c in a substantially absolute C to C alkanol solution of an alkali metal hydroxide or alkoxide.  
  12. A process in accordance with claim 11 wherein said alkanol is substantially absolute methanol or ethano].  
  13. A process in accordance with claim 1 wherein said hydrogenation is effected in the presence of a catalyst consisting of palladium on a carbon, alumina, calcium carbonate, or barium sulfate support.  
  UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,876,685  
 DATED April 8, 1975 INVENTOR( I John Pisanchyn, Robert Fuhrmarm, Stylianos Sifniades and a l A. Tuni k Y It IS certmeflhafi rror appearsfi n the ab0ve:dent|f|ed patent and that said Letters Patent are hereby corrected as shown below:  
 Col. 3, line 21, &#34;hydrobormic&#34; should be hydrobromic Col. 4, line 22, &#34;many&#34; should be any line 31, &#34;2nitro-6oximinocyclohexanone&#34; should be 2-nitro6oximinocyclohexanone Col. 5, line 33, &#34;paladium&#34; should be palladium line 39, &#34;nutrionally&#34; should be nutritionally Col. 6, Example 4, line 59, 20C&#34; should be 20C Col. 7, Example 6, line 27, &#34;NaoH&#34; should be NaOH Example 7, line 38, &#34;satisfactority&#34; should be satisfactorily Col. 8, Claim 4, line 63, &#34;acetat&#34; should be acetate Col. 10, Claim 11, line 2, &#34;90C&#34; should be 90C Signed and Scaled this fourteenth Day Of October 1975 [SEAL] Attest:  
 RUTH C. MASON Arresting Officer