Synthesis of Deoxytetrahydrouridine

Abstract

The α-hydroxyamido functionality of 2′-deoxytetrahydrouridine (dTHU) makes this seemingly simple and generally useful compound difficult to obtain. Reported synthetic strategies produce extremely poor yields and multiple products, and full characterization data is not available. Described herein is a two-step approach for synthesizing dTHU in increased yields and purity; stability concerns are also addressed. Catalytic reduction (5% Rh/alumina) of 2′-deoxyuridine, followed by reduction with sodium borohydride as a limiting reagent produces dTHU and limits formation of side products. Evidence was obtained for formation of a methoxy-substituted analog during purification. By this strategy, dTHU of >95% purity can be obtained in 40% yield on a 150mg scale.Reduced nucleoside analogs are of great interest as tools for understanding the chemistry and biology of nucleic acids, for probing proteins to which they bind, and for their medicinal properties. [1][2][3][4][5] Tetrahydrouridines (THUs) and dihydrouridines (DHUs) (Figure 1) have been used in various studies, including as transition-state analogs of cytidine deaminase inhibitors (CDA). 6,7 Our own interest in the deoxynucleoside of THU relates to ongoing studies of the human APOBEC3G cytidine deaminase domain, which plays a defensive role in HIV infection. 8,9 In studies of CDA substrate analog inhibitors, a tetrahedral transition state is proposed, such as that involving in situ generation of zebularine hydrate 2 from zebularine 1 (Scheme 1). 10 Reduced pyrimidine analogs enabled the study of the hydrate as a discreet chemical entity. 11 Thus,3,4,5, and the deoxy-analog dTHU have been subjects of research for over forty years. 1, 12 However, we were surprised to find that reported methods to prepare the compound are notably inefficient, and no diagnostic spectroscopic data are available in the literature. This report addresses a long-standing need for a reliable method to synthesize dTHU and provides its full chemical characterization. Photoreduction, catalytic hydrogenation, and borohydride reduction have been used to transform pyrimidine nucleosides to their hydropyrimidinone analogues. 1,13 Typically referenced for the synthesis of dTHU is a 1967 study by Hanze and co-workers detailing the synthesis of THU. 1 The procedure involves Rh/alumina-catalyzed hydrogenation of cytidine, to yield 3,4,5,6-tetrahydrocytidine. Acetic acid-mediated hydrolysis of this intermediate is reported to provide THU after multiple purification steps. While this general procedure can be used to synthesize the deoxy-analog dTHU from deoxycytidine (Scheme 2), in our experience, yields are poor (<1%) for a >95% purity sample of dTHU. The major drawback in application of Hanze's route is the difficult separation of dTHU from multiple impurities generated during the synthesis. Our experiences with dTHU preparation are consistent with Hanze's observations for the synthesis of THU. On the basis of MS and 1 H NMR analysis of the resulting mixture, major contaminants result from inco...

Acyclic and Cyclic Ureas (Update 2013)

“…Thus, they can be prepared by reduction of the corresponding aromatic counterparts. Several methods can be used for this transformation (photoreduction, borohydride reduction, hydrogenation), but hydrogenation in the presence of rhodium [276] or ruthenium [277] catalysts is particularly useful. This approach has been used for the syntheses of dihydropyrimidine-2,4(1H,3H)-diones 54 spiro-fused at the 5-position to pyrrolidines, [278] or the 1,3,6-trisubstituted dihydropyrimidine-2,4(1H,3H)-diones 55 [279] or 56 (Scheme 106).…”

Design, Synthesis, and Pharmacological Evaluation of Fluorinated Tetrahydrouridine Derivatives as Inhibitors of Cytidine Deaminase

“…For the preparation of fluorinated analogues of 5, we used a procedure similar to the one described previously by the Sturla group for the synthesis of 2′-deoxytetrahydrouridine. 17 As illustrated in Scheme 1, compound 2 served as a starting material for the synthesis of 2′-deoxy-2′,2′-difluorotetrahydrouridine. Rhodium-catalyzed hydrogenation of 2 gave 2′deoxy-2′,2′-difluorodihydrouridine 6.…”