Phosphoramidates Build Cells N e w route leads to nucleoside diphosphates a t much lower costs
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derstanding of ribonucleic acid's Carbohydrate b i o l o g i c a l role comes to an end. Now, a new chemical route makes all four naturally occurring nucleoside diphosphates in volume amounts. Before, these vital substrates, used to synthesize RNA-like compounds enzymatically (C&EN Jan. 28, 1957, page 24) could be made only in minute quantities. The new synthesis revolves around a new group of chemical intermediates —nucleoside 5' - phosphoramidates. These high energy compounds react rapidly with phosphoric acid to form nucleoside diphosphates in good yield, Robert Warner Chambers, New York University College of Medicine, told the Division of Carbohydrate Chemistry. Before, these diphosphates sold commercially for astronomical p r i c e s some, such as cytidine diphosphate, for $2000 a gram. The new route makes these products in gram quantities, and should slash present prices to half and in some cases to one tenth of today's. Moreover, should demand warrant it, the process can be scaled up to give kilogram yields which will drop the prices even more, Chambers claims. Biggest advantage to the new route to the phosphoramidate intermediates, says Chambers, is its lack of side reactions. A simple, one-step synthesis takes advantage of the novel reaction between the appropriate 5'-nucleotide, ammonia, and dicyclohexyl carbodiimide to give high yields (80 to 9 0 % ) of the nucleoside 5'-phosphoramidates. Ortho phosphoric acid treatment of the amidate converts it to the corresponding nucleoside 5'-diphosphate. Previously, the most popular method to synthesize nucleoside diphosphates was the carbodiimide reaction. While successfully used to make certain nucleotide coenzymes, this route often isn't the best because it lacks specificity in causing condensation between
two dissimilar phosphate esters. This results in highly complex mixtures which are hard to separate, leading to extremely low yields. Chambers has already made all four nucleoside diphosphates that naturally occur in RNA (adenosine, guanosine, cytidine, and uridine diphosphates), and H. G. Khorana and J. G. Moffatt of British Columbia Research Council, have extended the new method to other unsymmetrical nucleotide coenzymes, UDPG (uridine diphosphate glucose) and FAD ( flavinadenine dinucleotide). The new process is not confined to
reactions with phosphoric acid alone. Alcohols react with phosphoramidates to form esters. Right now, tests are under way at Sloan Kettering Institute to look for pharmacological activity in one of the methyl esters, as well as in the amidates. Phosphoramidates also react with carboxylic acids to form mixed anhydrides. A compound of this type formed between acetic acid and adenosine monophosphate has been identified as an intermediate in the biosynthesis of acetyl coenzyme A—the focal point of metabolism of fats and carbohydrates. •
New Route to Nuclèoside Diphosphotes means Lower Costs for RNÂ-Liké Compounds
Start with à Nucleotide;
React:
To Get Nucleoside Phosphoramidates:
React:
To Get Nucleoside Diphosphate:
To Give Four Nucleoside Diphosphates Occurring in RNA Where R is:
GUANINE
ADÉNÎNÉ
URACIL; APRIL
21,
CYTOSINE
1958
C&EN
45
