One-pot two-step enzymatic coupling of pyrimidine bases to 2-deoxy-D-ribose-5-phosphate. A new strategy in the synthesis of stable isotope labeled deoxynucleosides

The enzymatic synthesis of thymidine from 2-deoxy-D-ribose-5-phosphate is achieved, in a one-pot two-step reaction using phosphoribomutase (PRM) and commercially available thymidine phosphorylase (TP). In the first step the sugar-5-phosphate is enzymatically rearranged to alpha-2-deoxy-D-ribose-1-phosphate. Highly active PRM is easily obtained from genetically modified overproducing E. coli cells (12,000 units/84 mg protein) and is used without further purification. In the second step thymine is coupled to the sugar-1-phosphate. The thermodynamically unfavorable equilibrium is shifted to the product by addition of MnCl(2) to precipitate inorganic phosphate. In this way the overall yield of the beta-anomeric pure nucleoside increases from 14 to 60%. In contrast to uracil, cytosine is not accepted by TP as a substrate. Therefore, 2'-deoxy-cytidine is obtained by functional group transformations of the enzymatically prepared 2'-deoxy-uridine. The method has been demonstrated by the synthesis of 2',5'-(13)C(2)]- and 1',2',5'-(13)C(3)]thymidine as well as 1',2',5'-(13)C(3)]2'-deoxyuridine and 3',4'-(13)C(2)]2'-deoxycytidine. In addition the nucleoside bases thymine and uracil are tetralabeled at the (1,3-(15)N(2),2,4-(13)C(2))-atomic positions. All compounds are prepared without any scrambling or dilution of the labeled material and are thus obtained with a very high isotope enrichment (96-99%). In combination with the methods that have been developed earlier it is concluded that each of the (13)C- and (15)N-positions and combination of positions of the pyrimidine deoxynucleosides can be efficiently labeled starting from commercially available and highly (13)C- or (15)N-enriched formaldehyde, acetaldehyde, acetic acid, potassium cyanide, methylamine hydrochloride, and ammonia.