Adenine preparation

Adenine is prepared by reacting a dinitrile of diaminomaleic acid with N-methyldichloroformidinium chloride and ammonia at elevated temperature in the presence of formamide and an ammonium salt of a lower alkanoic acid.

BACKGROUND 
Adenine is widely present in the tissues of animals and plants as a main 
constituent of nucleic acids and coenzymes. Adenine and its derivatives 
also are known as having pharmacological effects and are very useful in 
the medical and biochemical fields. 
There are serval known methods for producing adenine. For example, U.S. 
Pat. No. 3,287,452 discloses a method of producing adenine and 
4,5-dicyanoimidazole which comprises reacting a source of hydrogen cyanide 
with ammonia in the liquid state in the absence of an amount of water 
greater than ten mole percent of the combined amounts of the hydrogen 
cyanide and the ammonia at a temperature of 60.degree. C. to 150.degree. 
C., wherein the mole ratio of ammonia to hydrogen cyanide is at least two 
to one. 
U.S. Pat. No. 3,398,149 discloses a process for preparing adenine by 
heating formamide with a member selected from the group consisting of 
phosphorous trichloride, phosphorous oxychloride, phosphorous pentoxide, 
polyphosphoric acid, pyrophosphoric acid, tetrachloropyrophosphoric acid, 
thionyl chloride, sulfuryl chloride, chlorosulfonic acid and tosyl 
chloride within the range of from about at 70.degree. C. to about 
200.degree. C. in a sealed vessel. 
U.S. Pat. No. 3,427,315 discloses a process for preparing adenine or 
hypoxanthine wherein free formamidine is reacted in a non-aqueous solvent 
in the presence of ammonia with an .alpha.-amino-.alpha.-cyanoacetic acid 
derivative of the formula 
##STR1## 
wherein R.sub.2 is hydrogen, formyl, acetyl or propionyl, and R.sub.3 is 
lower alkoxycarbonyl or carbamoyl. 
U.S. Pat. No. 3,671,649 discloses a method of producing adenine and/or 
4,5-dicyanoimidazole and derivatives thereof by reacting 
diaminomaleonitrile or diaminofumaronitrile with an amidine salt in an 
organic medium. 
U.S. Pat. No. 4,059,582 discloses a process for preparing adenine by 
reacting at least one member selected from the class of 
diaminomaleonitrile and diaminofumaronitrile, a formic acid derivative and 
at least one member selected from the class of ammonia and ammonium salts 
in the presence or absence of a solvent. 
U.S. Pat. No. 4,092,314 discloses a process for preparing 
4,6-diamino-5-arylazopyromidine from an arylazomalonitrile in the presence 
of ammonium chloride and formamide. The 4,6-diamino-5-arylazopyrimidine 
may then be hydrogenated to form 4,5,6-triaminopyrimidine which, when the 
hydrogenation is carried out in the presence of formic acid or its 
derivative, gives adenine. 
Japanese Patent Publication No. 42-7915 discloses a method of preparing 
adenine by reacting hydrogen cyanide with ammonia, or an alkali cyanide 
with ammonium salt and ammonia in the presence of formamide with heating. 
Japanese Patent Publication No. 51-26897 discloses a method of preparing 
adenine by reacting diaminomaleonitrile or diaminofumaronitrile with 
formaldehyde in the presence of ammonia. 
Of particular interest with respect to the present invention is 
aforementioned U.S. Pat. No. 3,671,649 which teaches a process for 
producing adenine (and 4,5-dicyanoimidazole) by reacting 
diaminomaleonitrile (DAMN) or diaminofumaronitrile (DAFN) with an amidine 
salt having the formula: 
EQU [H.sub.2 N.dbd.C(R)NH.sub.2 ].sup.+ x.sup.- 
wherein R is hydrogen or a methyl group and X is an organic or inorganic 
acid with heating in an organic medium selected from the group consisting 
of an aliphatic lower alkyl alcohol having one to four carbon atoms, 
formamide, dimethylformamide, dimethylacetamide, dimethylaniline, anisole, 
dioxane and pyridine, and optionally in the presence of an ammonium salt 
of a lower alkanoic acid. The use of an amidine salt in this process is 
undesirable because of its relatively high cost. Thus, it would be highly 
desirable to employ a less expensive substitute for the amidine salt in 
the practice of the process and still obtain good yields of adenine. In 
accordance with the present invention, it has been found that 
N-dichloromethylformamidinium chloride and ammonia can be used in place of 
an amidine salt in the practice of the prior art process to give good 
yields of adenine while at the same time affording a cost savings over the 
use of an amidine salt. 
SUMMARY 
Thus, the present invention provides a process for the preparation of 
adenine by reacting a dinitrile of diaminomaleic acid with 
N-dichloromethylformamidinium chloride and ammonia at elevated temperature 
in the presence of formamide and an ammonium salt of a lower alkanoic 
acid. 
The starting compound DAMN can be easily obtained in nearly quantitative 
yield by the polymerization of hydrogen cyanide in the presence of alumina 
(U.S. Pat. No. 2,499,441). 
N-dichloromethylformamidinium chloride is a known compound and is easily 
synthesized in high yields by reacting 2 moles of liquid hydrogen cyanide 
with an excess of hydrogen chloride in ether at -10.degree. C. to 
-15.degree. C. It is expected that the salt gives 2 moles of formamidinium 
chloride when reacted with ammonia. N-dichloromethylformamidinium chloride 
is employed in an amount of from about 1 to 6 moles of 
N-dichloromethylformamidinium chloride per mole of DAMN. 
The reaction proceeds when a mixture of DAMN, N-dichloromethylformamidinium 
chloride, ammonia and formamide is heated to 80.degree. C. to 130.degree. 
C., preferably about 100.degree. C. 
Formamide is employed in an amount of from about 30 ml to 200 ml, 
preferably 100 ml to 150 ml per mole of DAMN. 
In general, from about 2 to 6 moles of ammonia per mole of DAMN are used in 
the practice of the present process. Conveniently, both the ammonia and 
the formamide can be added to the reaction mixture by forming an 
ammoniacal formamide solution containing the desired amounts of formamide 
and ammonia. Alternatively, liquid ammonia by itself can simply be added 
to the formamide-containing reaction mixture in the proper amounts. 
As disclosed in U.S. Pat. No. 3,671,649, the yields of adenine are 
increased by the addition of an ammonium salt of a lower aliphatic 
carboxylic acid, such as ammonium formate, ammonium acetate and ammonium 
propionate. The usual addition amount of the ammonium salt is 0.5-20 
(wt./vol.)% to the reaction mixture consisting of DAMN, 
N-dichloromethylformamidinium chloride, ammonia and formamide. 
Adenine in the reaction mixture is quantitatively determined by HPLC with 
external standard. Qualitative analysis of the products is carried out 
with HPLC (Waters Associates, Inc., Model 244) using .mu.-Bondapak C18. 
The products are eluted with water/methanol (9/1) and detected by 
UV-detector. The work-up of the reaction mixture involves the following 
steps: centrifugation of the solids; evaporation of the volatiles and 
formamide solvent; solubilizing the residue with aqueous ammonium 
hydroxide; charcoal treatment; filtration; neutralization of the filtrate 
with hydrochloric acid; crystallization from the concentrated aqueous 
solution, and recrystallization from water. 
The following examples are given solely for the purpose of illustration and 
are not to be construed as limitations of this invention.

EXAMPLE 1 
DAMN (0.727 g; 0.1 mole), N-dichloromethylformamidinium chloride (0.12 g; 
0.01 mole) and ammonium acetate (0.51 g; 0.01 mole) were charged to a 3 
oz. Aerosol Compatibility Tube (Fischer and Porter Co.) at room 
temperature. An ammoniacal formamide solution consisting of 15 ml of 
formamide and 0.343 g ammonia was then added to the tube. The reaction was 
run for 2 hours at 100.degree. C. with magnetic stirring. The mixture was 
cooled to 40.degree. C. and a black solid by-product which formed during 
the reaction was filtered. HPLC indicated an adenine yield of 41.5%. 
EXAMPLE 2 
DAMN (0.86 g; 0.1 mole), N-methyldichloroformidinium chloride (1.33 g; 0.1 
mole), and ammonium acetate (0.61 g; 0.1 mole) were charged to a 3 oz. 
Aerosol Compatibility Tube (Fischer and Porter Co.) at room temperature. 
An ammoniacal formamide solution consisting of 17.8 ml formamide of 0.377 
g of ammonia was then added to the tube. The reaction was run for 2 hours 
at 100.degree. C. with magnetic stirring. The mixture was cooled to 
40.degree. C. and black solid by-product which formed during the reaction 
was filtered. HPLC indicated an adenine yield of 23.1%. 
EXAMPLE 3 
This example demonstrates that ammonia must be present in the process of 
the present invention in order to obtain adenine. 
DAMN (0.23 g; 0.1 mole), N-methyldichloroformidinium chloride (0.8 g; 0.1 
mole), ammonium acetate (0.37 g; 0.1 mole) and formamide (20 ml) were 
charged to a 3 oz. Aerosol Compatibility Tube (Fischer and Porter Co.) at 
room temperature. The reaction was run for 2 hours at 100.degree. C. with 
magnetic stirring. The mixture was cooled to 40.degree. C. HPLC indicated 
no adenine was formed by the reaction. 
Having disclosed the process of the present invention, one skilled in the 
art can readily envision variations, modifications and changes within the 
scope and spirit of this invention. Therefore, it is desired that the 
present invention be limited only by the lawful scope of the following 
claims.