The synthesis of pyrimidine unsaturated keto and exomethylene arabinopyranonucleoside analogs as potential antitumor and antiviral agents is described. Commercially available 1,2,3,4-tetra-O-acetyl-D-arabinopyranose (1) was condensed with silylated thymine, uracil, 5-fluorouracil, N(4)-benzoyl cytosine and 5-(trifluoromethyl)uracil, respectively, deacetylated and acetylated to afford 1-(3,4-O-isopropylidene-α-D-arabinopyranosyl)pyrimidine analogs 4. Two different synthetic routes were investigated for the conversion of compounds 4 into the new 1-(2,3,4-trideoxy-2-methylene-α-pent-3-enopyranosyl)nucleoside derivatives of thymine (10a), uracil (10b), 5-fluorouracil (10c) and N(4)-benzoyl cytosine (10d). Only the first approach could afford derivative 10d. Debenzoylation of 10d afforded 1-(2,3,4-trideoxy-2-methylene-α-pent-3-enopyranosyl)cytosine (10f). The first approach resulted also to the 2-keto-3,4-unsaturated analogs 9. The new analogs did not show inhibition of DNA and RNA virus replication in cell culture. The 2'-ketonucleoside derivatives 9 were found to be more cytostatic than the corresponding 2'-exomethylene nucleosides 10. The 5-fluorouracil unsaturated keto derivative 9c and the exomethylene derivatives 10c and 13c showed antiproliferative activity in the lower micromolar range. Experimental evidence revealed that 9c, 10c and 13c may act as novel types of 5-fluorouracil releasing prodrugs, and points to thymidylate synthase as target for their cytostatic action.
This report describes the synthesis of unsaturated exomethylene lyxopyranonucleoside analogues as potential biologically active agents. Commercially available 1,2,3,4-tetra-O-acetyl-alpha-D-lyxopyranose 1 was condensed with silylated thymine and uracil, respectively, deacetylated and acetalated to afford 1-(2,3-O-isopropylidene-alpha-D-lyxopyranosyl)thymine 4a and 1-(2,3-O-isopropylidene-alpha-D-lyxopyranosyl)uracil 4b. The new derivatives 1-(2,3,4-trideoxy-4-methylene-alpha-pent-2-enopyranosyl)thymine 8a and 1-(2,3,4-trideoxy-4-methylene-alpha-pent-2-enopyranosyl)uracil 8b were prepared via two different key intermediates, 7a, b and 13a, b in order to elucidate the influence of 2',3'-unsaturation and to clarify the difference between the keto and exomethylene group on the biological activity of the target molecules. Compounds 7a, b, 8a, b, and 13a, b were evaluated for their antiviral and cytostatic activity using several virus strains and cell lines. Whereas no marked antiviral activity was noticed, 13a and 13b showed a cytostatic activity that ranged between 7 and 23 muM for 13a and 26 and 38 muM for 13b against murine leukemia L1210, human lymphocyte Molt4/C8 and CEM cells, and human breast carcinoma MCF7 cells.
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