472 Annals New York Academy of Sciences 



With regard to the formation of sulfur containing amino acids, simple 

 nonenzymatic pathways can also be visualized. Cysteine could be formed in a 

 similar manner as serine by condensation of thioformaldehyde"'* with a methyl- 

 ene-activated glycine derivative, such as glycine nitrile, glycinamide, poly- 

 glycine or a metal chelate of glycine. Methionine could be formed by the addi- 

 tion of methyl mercaptan to acrolein, followed by the condensation of the 

 resulting methional"'^ with hydrogen cyanide and subsequent hydrolysis of the 

 nitrile. One of the possible pathways for the synthesis of aromatic amino acids 

 could be through monosaccharides or similar compounds obtained from form- 

 aldehyde.**^ 



Synthesis of Monosaccharides 



Since the early studies of Butlerow,"'"' Loew,"^ and Fischer"* it has been 

 known that formaldehyde in aqueous solutions condenses into sugars by the 

 action of basic catalysts. As a result of the work of Fischer"* and others,"^-'-" 

 fructose, sorbose, xylulose, and glycolaldehyde were identilied among other 

 compounds in the formaldehyde reaction product. 



Relatively recently, Mariani and Torraca'^^ analyzed by two-dimensional 

 paper chromatography the product of the base catalyzed condensation of 

 formaldehyde and confirmed and extended the previous results. They detected 

 the presence of the hexoses galactose, glucose, mannose, fructose and sorbose, 

 and the pentoses arabinose, ribose, ribulose, xylose, xylulose, and lyxose in 

 addition to 10 more unidentified monosaccharides. More recent studies by 

 Mayer and Jaschke^- and by Pfeil and Ruckert^-^ have shown the formation of 

 glycolaldehyde, glyceraldehyde, dihydroxyacetone and tetroses in addition to 

 pentoses and hexoses. Dendroketose was also obtained as the product of the 

 condensation of two moles of dihydrox3^acetone. 



The reaction is supposed to be initiated by the condensation of two moles of 

 formaldehyde into glycolaldehyde which occurs at a very slow rate (induction 

 phase) .1-* This is followed by aldol condensations which lead to the formation 

 of trioses, tetroses, pentoses, and hexoses and use up all the formaldehyde in a 

 very short time (autocatalytic phase) .^-^ The overall reaction is catalyzed by 

 calcium carbonate, calcium oxide, and other bases. 



Because no attempts had been reported on the synthesis of 2-deoxypentoses. 

 in particular 2-deoxyribose, we undertook the synthesis of this compound,^" 

 which is known to be one of the essential building blocks of deoxyribonucleic 

 acid. This deoxypentose and its isomer, 2-deoxyxylose, were obtained in 

 yields of about 5 per cent by the condensation of acetaldehyde with glyceral- 

 dehyde in aqueous systems. The reaction occurs very rapidly at room tem- 

 perature when catalyzed by calcium, magnesium and other divalent metallic 

 oxides. Results from our laboratory have shown that the reaction is also 

 catalyzed by ammonia and other simple nitrogen bases which may have been 

 the predominant bases in the primitive Earth's environment. In contrast to 

 the fast reaction which divalent metallic oxides catalyze, the reaction occurs 

 in a slow and controllable manner when ammonium hydroxide is used as cata- 

 lyst. In fact, the continuous synthesis of this compound was observed for an 

 uninterrupted period of more than 2 months. 2-Deoxyribose was also obtained 



