United States Patent (19) (11) 4,391,977 Shin 45) Jul. 5, 1983

54 ADENINE PRODUCTION 4,216,317 8/1980 Shuman et al...... 544/277 (75) Inventor: Kju H. Shin, Baton Rouge, La. FOREIGN PATENT DOCUMENTS 73 Assignee: Ethyl Corporation, Richmond, Va. 1949091 4/1970 Fed. Rep. of Germany. 1394.322 2/1965 France. (21) Appl. No.: 331,036 42-7915 3/1967 Japan. (22 Filed: Dec. 16, 1981 51-26897 3/1976 Japan. 51) Int. Cl...... C07D 473/34 Primary Examiner-Nicholas S. Rizzo 52 U.S. C...... 544/277 Attorney, Agent, or Firm-Donald L. Johnson; John F. 58) Field of Search ...... 544/277; 424/253 Sieberth; Patricia J. Hogan (56) References Cited 57 ABSTRACT U.S. PATENT DOCUMENTS Adenine is produced by reacting cyanide 3,287,452 11/1966 Wakamatsu et al...... 260/252 with formamide in the presence of an salt 3,398,149 8/1968 Morita et al...... 260/252 and a catalytic amount of methyldisulfide at elevated 3,427,315 2/1969 Nomura et al...... 260/252 3,671,649 6/1972 Yamada et al...... 260/252 temperature and pressure. 4,059,582 11/1977 Yonemitsu et al...... 260/252 4,092,314 5/1978 Vander Zwan et al...... 544/277 10 Claims, No Drawings 4,391,977 1. 2 diaminomaleonitrile, or diaminofumaronitrile, with ADENINE PRODUCTION formaldehyde in the presence of , BACKGROUND SUMMARY 5 In accordance with the present invention, there is Adenine is widely present in the tissues of animals provided a novel process for producing adenine in a and plants as a main constituent of nucleic and single step and in good yields which comprises reacting coenzymes. Adenine and its derivatives also are known with formamide in the presence of an as having pharmacological effects and are very useful in ammonium salt and a catalytic amount of methyldisul the medical and biochemical fields. 10 fide at elevated temperature and pressure. There are several known methods for producing Optionally, a catalytic amount of methyldisulfide in adenine. For example, U.S. Pat. No. 3,287,452 discloses combination with phosphorous pentoxide may be used a method of producing adenine and 4,5- in the practice of the present process...... dicyanoimidazole which comprises reacting a source of ; : The hydrogen cyanide component of the reaction hydrogen cyanide with ammonia in the liquid state in 15 mixture may be anhydrous hydrogen cyanide in liquid the absence of an amount of water greater than ten mole or gaseous form. - percent of the combined amounts of the hydrogen cya The formic derivative component of the instant nide and said ammonia at a temperature of 60' C. to 150 process is both a reactant and a reaction solvent. Thus, C., wherein the mole ratio of ammonia to hydrogen an excess of formamide is employed in the process, i.e., cyanide is at least two to one. ... . 20 up to 20 moles of formamide per mole of hydrogen U.S. Pat. No. 3,398,149 discloses a process for prepar cyanide. Optimally, about 5 moles of formamide per ing adenine by heating formamide with a memberse mole of hydrogen cyanide are employed in the process. lected from the group consisting of phosphorous tri The ammonium salts used in the practice of the pres chloride, phosphorous oxychloride, phosphorous pen ent invention may include the ammonium salts of any toxide, polyphosphoric acid, pyrophosphoric acid, tet 25 inorganic or organic acid. For example, they may in rachloropyrophosphoric acid, thionyl chloride, sulfuryl clude ammonium acetate, sulfate, iodide, chloride, am chloride, chlorosulfonic acid and tosylchloride within monium carbonate, ammonium propionate, ammonium the range from about 70° C. to about 200° C. in a sealed benzoate, and the like. Ammonium vessel. • acetate is the preferred ammonium salt for use in the U.S. Pat. No. 3,427,315 discloses a process for prepar 30 present process. The ammonium salts are generally used ing adenine or hypoxanthine wherein free formamidine in amounts of from about 0.5 mole to about 3 moles of is reacted in a non-aqueous solvent in the presence of ammonium salt per mole of hydrogen cyanide. The ammonia with an a-amino-a-cyanoacetic acid deriva optimum mole ratio of ammonium salt to hydrogen tive of the formula cyanide is about 0.66:1. ; : 35 While ammonium acetate per se can be used in the NHR2 practice of the present invention, ammonium acetate can be generated in situ from gaseous ammonia and NeC-CH-R . acetic acid (1:1 mole ratio) in the practice of the present process. . wherein R2 is hydrogen, formyl, acetyl or propionyl, The reaction of the present invention is carried out at and R3 is lower alkoxycarbonyl or carbamoyl. temperatures of from about 60° C. to about 180 C., U.S. Pat. No. 3,671,649 discloses a method of produc preferably from about 120° C. to about 140 C. in a ing adenine and/or 4,5-dicyanoimidazole and deriva sealed vessel. tives thereof by reacting diaminomaleonitrile or The reaction time may vary from approximately 1 to diaminofumaronitrile with an amidine salt in an organic 45 20 hours. Adenine yield was found not to increase after medium. a reaction period of 20 hours at 130° C. Typically, the U.S. Pat. No. 4,059,582 discloses a process for prepar reation is complete at the end of 4 hours or less. ing adenine by reacting at least one member selected The pressure should be high enough to maintain the from the class of diaminomaleonitrile and reactants at least partially in the liquid state. In general, diaminofumaronitrile, a formic acid derivative and at 50 the reaction pressure is normally below approximately least one member selected from the class of ammonia 100 psi. and ammonium salts in the presence or absence of a In carrying out the reaction, methyldisulfide or a solvent. combination of methyldisulfide and phosphorous pen U.S. Pat. No. 4,092,314 discloses a process for prepar toxide is employed as catalysts. These are the only two ing 4,6-diamino-5-arylazopyrimidine from an 55 catalysts found thus far to be effective in the present arylazomalononitrile in the presence of ammonium process. Catalysts which were found not to be effective chloride and formamide. The 4,6-diamino-5- were methylsulfide, ethylsulfide, t-butyldisulfide, ben arylazopyrimidine may then be hydrogenated to form Zyldisulfide, ethanethiol, methyltrisulfide, ammonium 4,5,6-triaminopyrimidine which, when the hydrogena thiocyanate, thiourea, thioformamide, elemental sulfur, tion is carried out in the presence of formic acid or its 60 formic acid and polyphosphoric acid. However the derivatives, gives adenine. combination of anhydrous with me Japanese Patent Publication No. 42-7915 discloses a thyldisulfide gave good yields of adenine but not as high method of preparing adenine by reacting hydrogen as the combination of phosphorous pentoxide with me cyanide with ammonia, or an alkali cyanide with ammo thyldisulfide. nium salt and ammonia in the presence of formamide 65 As indicated in the table below, conducting the reac with heating. tion in the absence of a catalyst (methyldisulfide) pro Japanese Patent Publication No. 51-26897 discloses a duced less adenine and gave more of a black polymer method of preparing adenine by reacting by-product. In the presence of the catalyst, however, 4,391,977 3 4. polymer production decreased and adenine yield in work-up of the reaction mixture involved the following creased. Usually, but not always, the amount of poly steps: centrifugation of the solids; evaporation of the mer increased when a catalyst was not used. volitiles and formamide solvent; solubilizing the residue Phosphorous pentoxide itself is not as effective a with aqueous ammonium hydroxide; charcoal treat catalyst as methyldisulfide. However, a mixture of me- 5 ment; filtration; neutralization of the filtrate with hydro thyldisulfide and a small amount of phorphorous pen- chloric acid; crystallization from the concentrated toxide gave the highest yield of adenine obtained by the aqueous solution, and recrystallization from water. instant process (approximately 38%). It is not understood at this time why only methyldi- EXAMPLE 1 sulfide or a combination of methyldisulfide and phor- 10 This example demonstrates the preparation of ade phorous pentoxide is an effective catalyst in the present nine according to the process of the present invention. process. A reasonable interpretation might be that the Ammonium acetate (23.2g, 0.301 mole) methyldisul catalyst stabilizes hydrogen cyanide in such a way that fide (approximately 15.5 ml; 16.64 g; 0.177 mole), form the catalyst hinders the polymerization of hydrogen amide (approximately 91 ml, 102.49 g) and phosphorous cyanide and drives the reaction toward adenine forma- 15 pentoxide (3.5 g; 0.0247 mole) were charged to a 300 ml tion. Hastelloy B autoclave. The clave was cooled in an The amount of catalyst employed in the process is a ice-salt bath. Liquid hydrogen cyanide (approximately catalytic amount. When methyldisulfide alone is used as 17 ml; 12.27 g) was weighed in a cooled syringe and the catalyst, a mole ratio of catalyst to hydrogen cya- injected into the clave through the injection port. The nide of from about 0.5 to 4 moles of catalyst per mole of 20 reaction was run for 4 hours at 130° C. with stirring. hydrogen cyanide can be used. The optimum mole ratio The pressure in the clave was about 50 psi at 130 C. of hydrogen cyanide to methyldisulfide at 130° C. is After the reaction, the clave was cooled to 40 C. and approximately 2.5:1. When phosphorous pentoxide is to the gas vented through a caustic scrubber. The mixture be used in conbination with methyldisulfide, the mole was discharged and the clave was rinsed with form ratio of methyldisulfide to phorphorous pentoxide will 25 amide. The combined mixture was centrifuged and the be from about 4 to 10 moles of methyldisulfide per mole black solid was rinsed again with formamide and aque of phosphorous pentoxide, with an optimum mole ratio ous acetic acid, followed by centrifugation. The com of 7:1. bined formamide solution (502.94 g) aqueous solution Hydrogen cyanide is completely consumed in the (192.73 g) were submitted for analysis. reaction. Typically, about 55% of the methyldisulfide is 30 HPLC analysis showed that adenine yield was ap recovered after reaction. The fate of the rest of the proximately 38.0%. The mixture also contained 1.3% catalyst is not known, however, a small percentage of diaminomaleonitrile and 0.5% 4,5-dicyanoimidazole. the catalyst is converted to methylsulfide and methane- The dried black solid (overnight at 120° C.) weighed thiol. 1.82 g (14.8% based on hydrogen cyanide). Hydrogen Adenine in the reaction mixture was quantitatively 35 cyanide was completely converted. determined by HPLC with external standard. Qualita- In a similar manner, several other experiments were tive analysis of the products was carried out with carried out varying the kinds and amounts of reactants HPLC (Waters Associates, Inc., Model 244) using 82- and reaction conditions with the results being given in Bondapak C18. The products were eluted with water/- the following table. methanol (9/1) and detected by UV-detector. The TABLE I Adenine Synthesis (CH3)2S2 or Yield HCN NH4OAc other HCONH2 Time Temp. NH3 Adenine DAMN DCI Exp. No. (mole) (mole) sulfides (mole) (hr) (C.) (mole) % % % Polymer 2 0.429 0.301 Et-S-Et 2.25 20 130 17.9 5.5 0.6 29.0 0.178 3 0.420. 23.2 0.430 2.26 20 130 28.6 2. 0.7 9.7 4. --0.370 0.30 0.257 Othe 10 130 18.3 13.6 3.0 8.3 5 0,430 0.301 0.169 One 10 130 16.1 1.5 1.2 26.1 6 0.879 0.599 Ote Ione 10 130 11.0 2.5 0.2 39.0 7 0.45 0.30 CH3SCH3 2.27 20 130 18.8 7.4 7.2 31.6 0.298 8 0.458 0.301 CH3S-CH3 2.27 20 130 - 19.9 - 11.3 - 1.7 -35.3 0.299 9 0.455 0.301 2.26 2 130 0.190 O 30 36.8 5.3 0.8 8.1 10 0,460 0.301 0,171 2.28 2 30 10 30 33.2 2.6 0.6 .2 11 0.444 0.301 One 2.27 20 130 9. 4.9 0.4 39.6 12 0.448 0.301 0.177 2.27 20 130 33.7 2.7 0.8 3.7 13 0.451 0.301 S 2.25 10 130 8.0 8.6 0.9 0.6 0.19 14 0.301 2.27 2 45 0.45 0.78 10 130 31.0 3. 1.0 8.0 5 0.48 0.301 0.085 2.276 20 130 25.5 2.6 . 16 0.428 0.301 C2H5SH 2.255 20 130 1.5 5.9 3.5 9.4 0.172 17 0.301 2.257 4. 30 0.439 0.175 10 130 33.2 3.7 1.2 18 0.425 0.301 CH3S3CH3 2.258 19.0 3.2 1. 7.4 0.091 19 0.30 2.270 l 30 4,391,977 5 6 TABLE I-continued -a-a-a-ammurrum-r-r-H . Adenine Synthesis s (CH3)2S2 or Yield HCN NH4OAc other HCONH2 Time Temp. NH3 Adenine , DAMN DCE Exp. No. (mole) (mole) sulfides . (mole) (hr) (C) (mole) % % % Polymer 0.433 0.176 10 130 32.1 2.0 1.1 7.3 20 0.416 0.301 dBCH2SSCH2d 2.265 15.2 2.1 0.7 0.085 2 0.438 0.301 0.188 2.272 4 130 13.1 0.6 0.5 46.8 22 0.443 0.301 0.192 2.272 34.3 1.7 0.3 23 0.436 0.301 0.87 2.252 4 130 32.3 0.08 0.6 24 0.436 0.443 0.177 2.259 4. 130 29.8 2. 1.2 10.9 25 0.436 0.301 HCSNH2 2.252 4. 30 5.9 4.8 2. 14.2 0.082 26 0.301 NH4 SCN 2.261 3 130 16.7 5.0 0.4 27.8 0.187 . 27 0.482 0.301 0.168 2.246 0.5 130 3 30 NH3 26.2 2.1 0.4 16.7 0.294 28 0.427 0.301 thiourea 2.246 4 130 13.9 4.6 0.7 35.8 0.18 29 0.49 0.150 0.74 2.267 1.5 60 25.5 2.1 0 3 130 28.9 30 0,439 0.301 0.171 2.266 15 60 3 130 29.4 0.81 0.3 21.7 31 0.506 0.101 0.18 2.252 4 130 HCOOH 29.8 0.8 0.3 11.8 -- 0.019 32 0.449 0.30 0.174. 2.251 4 130 H3PO4 34.7 1.2 0.2 12.1 0.031 33 0,453 0.30 - 2,280 4. 130 H3PO4 19.1 1.0 1.1 46.8 0.031 34 0.454 0.301 0.177 2.276 4. 130 P2O5 38.0 1.3 0.5 14.8 0.025 35 0.441 0.301 - 2,270 4. 130 P2O5 18.1 7.1 0.9 61.6 0.025 36 0.444 0.301 0.76 0,714 4 30 P2O5 27.2 2.1 0.6 25.0 0.025 37 0.445 0.301 0.173 2.245 4. 130 Poly H3PO4 31.7 3.2 0.8 13.6 4.99g 38 0.435 0.30 0,173 1,042 4. 130 POs 30.1 2.6 0.9 18.1 0.025 39 0,446 0.30 0.176 2.249 4. 130 P2Os 33.6 8.4 2.2 24.5 0.074 40 0.439 0.301 0,169 2.264 4. 130 0.049 32.6 5.2 .9 19.0 4. 0.449 0.301 0.171 1492 4. 130 POs 28.2 4.5 0.6 25.1 0.025 It appears that the optimum mole ratio of formamide Reference to the table (Exp. No. 11) shows that con to hydrogen cyanide is about 5:1 (Exp. No. 34). De ducting the reaction in the absence of a catalyst (me creasing the amounts of formamide to approximately thyldisulfide) gave adenine in a yield of 19% and a large one-half and one-third of that amount resulted in a de amount (40%) of the black polymer was the main prod 45 creased yield of adenine to approximately 30% and uct. In the presence of the catalyst, the polymer yield 27%, respectively at the conditions given (Exp. Nos. 38 increased to 14% and the adenine yield increased to and 36). 34% (Exp. No. 12). Usually, but not always, the amount Reference to Exp. No. 2 shows that ethylsulfide is not of the polymer increased when a catalyst was not effec an effective catalyst in the present process, nor is meth tive. 50 ylsulfide as indicated in Exp. Nos. 7 and 9. Exp. Nos. 16 Phosphorous pentoxide by itself was not as effective and 18 indicate that ethylmercaptan also is ineffective as as a catalyst as methyldisulfide as demonstrated by Exp. is benzyldisulfide (Exp. No. 20). Thioformamide (Exp. No. 35 in the table in which an adenine yield of only No. 25), ammonium thiocyanate (Exp. No. 26), thiourea 18.1% was obtained along with a 61.6% yield of black (Exp. No. 28) and elemented sulfur (Exp. No. 13) also polymer. This was also the case when phosphoric acid 55 were not effective in catalyzing the instant reaction. was used as a catalyst (Exp. No. 33). However, when Having disclosed the process of the present inven methyldisulfide was present, the yield of adenine in tion, one skilled in the art can readily envision varia creased to 38% in the case of phosphorous pentoxide tions, modifications and changes within the scope and (Exp. No. 34) and 34.7% in the case of phosphoric acid spirit of this invention. Therefore, it is desired that the (Exp. No. 32). present invention be limited only by the lawful scope of Reference to Exp. No. 6 shows that the reaction the following claims. proceeds without formamide and methyldisulfide, how What is claimed is: ever a yield of only 11% of adenine was obtained. 1. A process for producing adenine which comprises In the presence of the catalyst, and absence of form reacting hydrogen cyanide with formamide in the pres amide, the adenine yield improved to 16-18%. (Exp. 65 ence of an ammonium salt and a catalytic amount of Nos. 4 and 5). The yield increased to approximately methyldisulfide at elevated temperature and pressure. 34% when both the catalyst and formamide were pres 2. A process according to claim 1, wherein said reac ent (Exp. No. 12). tion is carried out at a temperature in the range of from 4,391,977 7. 8 about 60° C. to about 180 and at a pressure of 100 psi or to about 4 moles of methyldisulfide per mole of hydro less. - - "gen cyanide. . . . . 3. A process according to claim 1, wherein th 8. A process according to claim 1, wherein phospho amount of formamide present is from about 2 to 20 rous pentoxide is additionally present in the reaction. moles of formamide per mole of hydrogen cyanide. 9. A process according to claim 8, wherein the 4. A process according to claim 1, wherein said am amount of phosphorous pentoxide present is from about monium salt is selected from ammonium acetate, ammo 4 to 10 moles of methyldisulfide per mole of phospho nium sulfate, , , rous pentoxide. , ammonium propionate, ammo 10. The process of claim 1 wherein one molar propor nium benzoate and ammonium nitrate. 10 5. A process according to claim 1, wherein the tion of hydrogen cyanide is reacted with about 2-20 amount of ammonium salt present is from about 0.5 to molar proportions of formamide in the presence of about 3 moles of ammonium salt per mole of hydrogen about 0.5-3 molar proportions of an ammonium salt and cyanide. about 0.5-4 molar proportions of methyldisulfide at a 6. A process according to claim 1, wherein said am 15 temperature in the range of about 60°-180° C. and a monium salt is generated in situ from gaseous ammonia pressure sufficient to maintain the reactants at least and the corresponding inorganic or organic acid. partially in the liquid state but not greater than about 7. A process according to claim 1, wherein said me 100 psi. thyldisulfide is present in an amount of from about 0.5 is it is 20

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65 UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. : 4,391, 977 DATED : July 5, 1983 INVENTOR(S) : Kju Hi Shin it is certified that error appears in the above-identified patent and that said Letters Patent is hereby Corrected as shown below: Column 3, line 38, '82-' should read -- u- - -. Column 5, line 47, 'increased' (first instance) should read -- decreased --. signed and sealed this Twenty-ninth D 2 y of November 1983 SEAL Attest:

GERALD J. MOSSINGHOFF Attesting Officer Commissioner of Patents and Trademarks