Agric. Biol. Chem., 52 (2), 589-591, 1988 589 Note carried out at iuu~zuirc under an increased pressure/' Here, we present a novel single-step synthesis of 5-(/?- methylthioethyl)hydantoin (2), in which we employed Single-step Synthesis of 5-(j6- single-step reactions of acrolein cyanohydrin (AC, 4), Methylthioethyl)hydantoin methyl mercaptan and ammoniumcarbonate in polar solvents (the AC method), and of acrolein (AL, 1), from Acrolein Cyanohydrin hydrogen cyanide, methyl mercaptan and ammonium and Acrolein carbonate (the ALmethod), accompanied with the for- mation of a-ureido-y-methylthiobutyramide (UMA, 5). Chisei Shibuya and Shunji Ouchi* By an alkaline hydrolysis of these products, dl- methionine (MT, 3) was obtained in an 85%yield on the Food Products & Pharmaceuticals Plant, bases of acrolein cyanohydrin and of acrolein. Asahi Chemical Industry Co., Ltd., Whenthe single-step hydantoination was carried out 6-2700 Asahimachi, Nobeoka, from ACor AL, a mixture of 2 and 5 was obtained. Miyazaki 882, Japan Approximately 12mol% of 5 was formed in each case of *Analytical Research Center, using AL and AC. Asahi Chemical Industry Co., Ltd., These new reactions are summarized in the following 1-3-1 Yako, Kawasaki-ku, Kawasaki-shi, equations: Kanagawa 210, Japan According to this procedure, acrolein and acrolein Received July 27, 1987 cyanohydrin, which are unstable to alkali, were not polymerized by the presence of excess ammoniumcar- bonate,-and the desired reaction proceeded in high yields. Single-step hydantoination of ACusing methanol as the A number of methods for DL-methionine synthesis solvent was carried out, and the effect of quantities of through the hydantoin intermediate have been reported methyl mercaptan, hydrogen cyanide and ammonium since Pierson1* obtained methionine in a 50%yield starting carbonate on the yield of MTwas investigated. 120 mol% from acrolein. These methods basically involved three-step of methyl mercaptan was sufficient, while 200 ~ 300 mol% reactions. In the first step, /?-methylthiopropionaldehyde of methyl mercaptan was required in the conventional was synthesized from acrolein (1) and methyl mercaptan in methods. Using 200 mol% of methyl mercaptan, the yield the presence of such catalysts as peroxides,2) metallic of MTwas not decreased, but the reaction mixture was a salts3>4) and bases.5'6) The second step was hydantoina- little colored. The yield of methionine was 83%without tion7) to form 5-(j3-methylthioethyl)hydantoin (MH, 2) hydrogen cyanide, and when 20mol% of hydrogen cya- by the reaction of /?-methylthiopropionaldehyde with hy- nide was added, the yield was almost the same (84%). drogen cyanide (or sodium cyanide) and ammoniumcar- When 100 mol%of hydrogen cyanide was added, however, bonate. The solubility-promoting agent8} for hydantoina- the reaction yield was reduced (81%), and the reaction tion was favorable because the aldehyde was sparingly mixture was markedly colored. Thusthere was no need to soluble in water and the reaction required a long time. To add hydrogen cyanide with the ACmethod. The lower complete the reaction in a short time, hydantoination was limit for the quantity of ammoniumcarbonate required AC Method (Acrolein Cyanohydrin Method) 590 C. Shibuya and S. Ouchi for hydantoination by the AC method was found to be 57°C; mobile phase, 1.6~0.9% gradient citrate buffer; 1.5mol per mol of AC. In addition to ammoniumcar- flow rate, 0.3 ml/min; detection, absorbance at 570 nm. bonate, ammoniumbicarbonate, ammoniumcarbamate, and ammoniaand carbon dioxide were also effective as Isolation of5-(P-methylthioethyl)hydantoin and a-ureido- hydantoination agents. y-methylthiobutyramide from the single-step hydan toination In the case of the ALmethod, it was found that the reaction mixture use of 120mol% of methyl mercaptan resulted in the ACmethod. To a mixture of commercially available same high yield of methionine (84%) as with the AC ammoniumcarbonate (9.6g), methyl mercaptan (2.3 g) method. When the amount of methyl mercaptan was as and methanol (40ml) in a 100ml stainless steel autoclave high as the 300mol% that is usually used in the con- was added acrolein cyanohydrin10'11* (3.3g) at -30°C. ventional method, coloration of reaction mixture increas- After closing the autoclave, the reaction was carried out ed and the yield of MTdecreased. An amount of 120 with stirring at 80°C for 1.5hr. After completing the mol%of hydrogen cyanide wassufficient to obtain the reaction, the vessel was cooled to room temperature, the maximumyield of MT. residual gases were released and the reaction mixture was In both the AC and ALmethods, the optimum reaction concentrated to dryness under reduced pressure, before temperature was found to be approximately 80°C, since 100ml of acetone was added to dissolve the soluble the yield decreased at 60°C or at 100°C. The optimal materials by stirring at room temperature. The remaining reaction time was between 60 and 90 min. white precipitate was filtered, washed with acetone and In the single-step hydantoination from AC, it was found dried to give 0.9g (12% yield based on AC) ofa-ureido-y- that the effect of the solvent on the yield varied signi- methylthiobutyramide (UMA). The precipitate was re- ficantly. Using a polar organic solvent such as methanol, crystallized from water to give pure UMA. mp ethanol, isopropanol, acetonitrile, dimethylformamide, 173~174°C; IR vmax (KBr)cm-1: 1690, 1650, 1590, 1550; dimethylsulfoxide or pyridine in this reaction, the yield of !H-NMR S (DMSO): 1.83 (2H), 2.02 (s, 3H), 2.44 (2H), methionine could be more than 80%. The yield was 4.24(q, 1H), 5.61 (s, 1H), 6.21 (d, 1H),7.18(d,2H). Anal. Found: C, 37.0; H, 7.01; N, 21.8; S, 16.2%. Calcd. for reduced to 60%whenonly water was used as the solvent. C6H13N3O2S: C, 37.7; H, 6.84; N, 22.0; S, 16.8%. The This seems to have been due to the instability of ACin the water-AC-ammoniumcarbonate system. acetone solution was concentrated to give 5.9g of 5-(/?- Single-step hydantoination using a mixed solvent system methylthioethyl)hydantoin as a solid (85% yield based on containing H2O and a polar organic solvent could be AC). The solid was recrystallized from water to give a carried out without reducing the yield. In order to main- white crystalline powder, mp 106~107°C; IR vmax tain the yield at more than 80%, the H2Oamount had to (KBr)cm"1: 1775, 1740; !H-NMR (D2O): 2.ll (3H, 2H), be limited, and it seemed to depend on the molar ratio of 2.63 (2H), 4.40 (t, 1H). Anal. Found: C, 41.1; H, 5.95; N, H2Oto ACor AL, and on the total amount of the sol- 15.8; S, 18.6%. Calcd. for C6H10N2O2S: C, 41.4; H, 5.81; vent. In the case of the ACand ALmethods shown N, 16.1; S, 18.4%. in the experimental section using aqueous methanol in- stead of methanol as a solvent, a suitable molar quantity Preparation of methionine by employing single-step hy- ofH2O was 5~20mol per mol of AC and AL. The yield dantoination of ACand AL of MT was reduced by 5~10% when ammonium carba- ACmethod. To a mixture of ammoniumcarbonate mate was used as the hydantoination reagent, and this (9.6g), methyl mercaptan (2.3 g) and methanol (40ml) in a seems to have been caused by the absence of H2Oin the 100ml stainless steel autoclave was added AC(3.3g) at reaction system. -30°C. After sealing the autoclave, the reaction was carried out with stirring at 80°C for 1.5 hr. After complet- EXPERIMENTAL ing the reaction, the vessel was cooled to roomtempera- ture, the residual gases were released, and the reaction Authentic 5-(/?-methylthioethyl)hydantoin (MH) was mixture was concentrated to dryness under reduced pres- prepared from /?-methylthiopropionaldehyde according to sure. The residual solid was dissolved into a homo- Bucherer-Berg's method.7) Authentic a-ureido-y-methyl- geneous solution by adding 100ml of water and 20ml of thiobutyramide was isolated from the mother liquors 4n NaOH,and hydrolysis was carried out in a 300ml of the MHpreparation.7) sealed autoclave at 160°C for 1.5 hr with stirring. Melting points (mp) are uncorrected. IR spectra were The reaction mixture was decolorized with active car- measured on a JASCOIRA-1 spectrometer, and NMR bon and treated with a cation exchange resin column spectra wererecorded at 60MHzwith TMSas an internal (Amberlite IR-200). MT adsorbed on the resin column standard on a JEOL JNM-PMX60 spectrometer. The was eluted with 5%aqueous ammonia, and the eluate was purity of methionine was determined with a Yanagimoto concentrated to give 5.4g of crude methionine crystals. LC-8Aamino acid analyzer under these conditions: col- The purity of the MTwas assayed by the amino acid umn, Yanako AC-101 1, 4 x 125mm;column temperature, analyzer, using authentic MT, and was determined to be Single-step Synthesis of 5-(/?-Methylthioethyl)hydantoin 591 93%. The crude MTwas recrystallized from water to give REFERENCES the purified MT as scaly crystals (4.8g, 80%). mp 270~272°C (decomp; lit., 271 ~273°C (decomp.)). Anal. Found: C, 40.6; H, 7.50; N, 9.45; S, 21.3%. Calcd. for 1) E. H. Pierson, M. Giella and M. Tishler, /. Am. C5HnNO2S: C, 40.8; H, 7.43; N, 9.39; S, 21.5%. The Chem. Soc, 70, 1450 (1948). product gave a single spot on TLCthat was detectable 2) J. C. Vander Weele, U. S. Patent, 2521677 (1950). 3) E. H. Pierson and M. Tishler, U. S. Patent, 2523633 with ninhydrin coloration, the Rf value of which was (1950).