Oro: Experimental Organic Cosmochemistry 475 



Synthesis of Pyrimidines 



With regard to the formation of pyrimidines it was proposed recently^- that 

 derivatives from the C3 molecular species found in comets could be the source 

 of these heterocyclic compounds. One of these C3 derivatives is malonamide 

 semialdimine or its isomer /3-aminoacrylamide which by condensation with urea 

 could be expected to yield uracil. 



Because (S-aminoacrylamide was not available to us, we tested some of the 

 C3 compounds which are formed in the experiments with electric discharges 

 and which are considered to be intermediates in the formation of i3-alanine. 

 These intermediates are acrylonitrile, /3-aminopropionitrile, and /3-aminopro- 

 pionanide. When each of these compounds was allowed to react with urea in 

 aqueous ammonia systems at 130° C, the formation of small amounts of uracil 

 was observed in each case.''*'^ Uracil was characterized by paper and ion 

 exchange column chromatography and by ultraviolet spectrophotometry. The 

 yields obtained from /3-aminopropionanide were approximately 2 and 5 times 

 higher than those obtained from /(i-aminopropionitrile and acrylonitrile, respec- 

 tively. This is what would be expected if acrylonitrile has to undergo first 

 amination into /3-aminopropionitrile and this, in turn, has to undergo hydrolysis 

 into /3-aminopropionanide. Because this amide is, in fact, the dihydroderiva- 

 tive of /3-aminoacrylamide it is obvious that the mechanism of the reaction 

 must involve a dehydrogenation step either before or after the cyclization. 



The mechanism of uracil formation involving |S-aminoacrylamide or its 

 isomer, malonamide semialdimire, is in line with the well known chemical 

 synthesis of uracil from malic acid and urea in the presence of a strong mineral 

 acid.^''^''^'^ A strong mineral acid transforms malic acid into malonic semialde- 

 hyde which then condenses with urea to form uracil. '^^ Also, in line with the 

 above mechanism, it is known from the work of Bredereck et al.,^'^^ that the 

 pyrimidine ring can be formed in good yield from either aminoacrolein or 

 malonodialdehyde. In theory the 3 pyrimidines found in nucleic acids could 

 conceivably be formed in aqueous systems under possible primitive earth 

 conditions by the mechanism described above. In addition to /3-aminoacryl- 

 amide yielding uracil, /3-aminoacrylamidine could be expected to condense with 

 urea into cytosine, and a-methyl-;3-aminoacrylamide into thymine. 



A possible pathway for the conversion of the symmetrical C3 species of comets 

 into ;8-aminoacrylamide or malonamide semialdimine is through the formation 

 of carbon suboxide (C3O2), which has been suggested to exist in several cosmic 

 bodies.''^*' By the addition of hydrogen and ammonia to carbon suboxide, 

 malonamide semialdehyde or malonamide semialdimine might be obtained. In 

 fact, malonic acid derivatives have been obtained recently in the laboratory 

 from carbon suboxide.^^^ In addition to purines and pyrimidines, preliminary 

 data have been obtained on the synthesis of other heterocyclic compounds and 

 fluorescent pigments. ^•^- 



Synlhesis of Polypeptides 

 The early literature on the direct polymerization of unsubstituted amino 

 acids has been previously reviewed in some detail. '•^^"^'•^ Current studies on 

 the synthesis of peptides and of polymers containing amino acids, under condi- 

 tions presumed to have existed on the primitive Earth were initiated by Fox and 



