Synthesis of conformationally North-locked pyrimidine nucleosides built on an oxabicyclo[3.1.0]hexane scaffold.

Beginning with a known 3-oxabicyclo[3.1.0]hexane scaffold (I), the relocation of the fused cyclopropane ring bond and the shifting of the oxygen atom to an alternative location engendered a new 2-oxabicyclo[3.1.0]hexane template (II) that mimics more closely the tetrahydrofuran ring of conventional nucleosides. The synthesis of this new class of locked nucleosides involved a novel approach that required the isocyanate II (B = NCO) with a hydroxyl-protected scaffold as a pivotal intermediate that was obtained in 11 steps from a known dihydrofuran precursor. The completion of the nucleobases was successfully achieved by quenching the isocyanate with the lithium salts of the corresponding acrylic amides that led to the uracil and thymidine precursors in a single step. Ring closure of these intermediates led to the target, locked nucleosides. The anti-HIV activity of 29 (uridine analogue), 31 (thymidine analogue), and 34 (cytidine analogue) was explored in human osteosarcoma (HOS) cells or modified HOS cells (HOS-313) expressing the herpes simplex virus 1 thymidine kinase (HSV-1 TK). Only the cytidine analogue showed moderate activity in HOS-313 cells, which means that the compounds are not good substrates for the cellular kinases.

3'-Carbon-substituted pyrimidine nucleosides having a 2',3'-dideoxy and 2',3'-didehydro-2',3'-dideoxy structure: synthesis and antiviral evaluation.

The bis(tributylstannyl) derivative of 2',3'-didehydro-2',3'-dideoxyuridine (d4U) underwent an anionic 5'-O-->3'-C stannyl migration to yield the 3'-tributylstannyl-d4U. This compound, with its vinylstannane structure, allowed ready access to the preparation of 3'-carbon-substituted analogues through the Stille reaction. A conventional transformation of the uracil moiety of these d4U analogues led to the corresponding 2',3'-didehydro-2',3'-dideoxycytidine (d4C) counterparts. Some 2',3'-dideoxycytidine (ddC) analogues were also synthesized. Antiviral evaluation revealed that none of these analogues showed activity against HIV, hepatitis B virus, herpes simplex virus-1 (HSV-1) and HSV-2.

Synthesis and evaluation of [18F] labeled pyrimidine nucleosides for positron emission tomography imaging of herpes simplex virus 1 thymidine kinase gene expression.

Synthesis of three novel 2'-deoxy-2'-[18F]fluoro-1-beta-D-arabinofuranosyluracil derivatives [18F]FPAU, [18F]FBrVAU, and [18F]FTMAU is reported. The compounds were synthesized by coupling of 1-bromo-2-deoxy-2-fluoro sugars with corresponding silylated uracil derivatives. In vitro cell uptake indicated that all three compounds are taken up selectively in RG2TK+ cells with negligible uptake in RG2 cells. The results indicate that [18F]FBrVAU and [18F]FTMAU have better uptake profiles in comparison to [18F]FPAU and have potential as PET probes for imaging HSV1-tk gene expression.

Synthesis and antiviral screening of some thieno[2,3-d]pyrimidine nucleosides.

Some cyclic and acyclic nucleosides of thieno[2,3-d]-pyrimidine derivatives were synthesized via the reaction of compounds 1 and 2 or 3 and 4 with 2-chloroethyl methyl ether or 2,3,4, 6-tetra-O-acetyl-alpha-D-glucopyranosyl bromide. Nucleosides 9, 10, 15, and 16 were tested as antiviral agents against herpes simplex virus type-1 (HSV-1) and hepatitis-A virus (HAV). Compound 15 showed the highest effect on HSV-1 than the other three compounds, while the four tested compounds did not show any activity against HAV.

Generation of predictive pharmacophore model for SARS-coronavirus main proteinase.

Pharmacophore-based virtual screening is an effective, inexpensive and fast approach to discovering useful starting points for drug discovery. In this study, we developed a pharmacophore model for the main proteinase of severe acute respiratory syndrome coronavirus (SARS-CoV). Then we used this pharmacophore model to search NCI 3D database including 250, 251 compounds and identified 30 existing drugs containing the pharmacophore query. Among them are six compounds that already exhibited anti-SARS-CoV activity experimentally. This means that our pharmacophore model can lead to the discovery of potent anti-SARS-CoV inhibitors or promising lead compounds for further SARS-CoV main proteinase inhibitor development.

Synthesis and biological evaluation of clitocine analogues as adenosine kinase inhibitors.

Adenosine kinase (AK) is the primary enzyme responsible for adenosine metabolism. Inhibition of AK effectively increases extracellular adenosine concentrations and represents an alternative approach to enhance the beneficial actions of adenosine as compared to direct-acting receptor agonists. Clitocine (3), isolated from the mushroom Clitocybe inversa, has been found to be a weak inhibitor of AK. We have prepared a number of analogues of clitocine in order to improve its potency and demonstrated that 5'-deoxy-5'-amino-clitocine (7) improved AK inhibitory potency by 50-fold.

An efficient method for the preparation of 1'alpha-branched-chain sugar pyrimidine ribonucleosides from uridine: the first conversion of a natural nucleoside into 1'-substituted ribonucleosides.

The 1'alpha-phenylselenouridine derivative 13 was successfully synthesized by enolization of the 3',5'-O-TIPDS-2'-ketouridine 8, and was subjected to a radical reaction with a vinylsilyl tether--an efficient procedure for preparing 1'alpha-branched-chain sugar pyrimidine nucleosides. Successive treatment of 8 with LiHMDS and PhSeCl in THF at < -70 degrees C gave the desired 1'-phenylseleno products in 85% yield as an anomeric mixture of the 1'alpha-product 11 and the 1'beta-product 12 (11/12= 2.5:1). Highly stereoselective reduction at the 2'-carbonyl of the 1'alpha-product 11 occurred from the beta-face by using NaBH4/CeCl3 in MeOH, and subsequent introduction of a dimethylvinylsilyl tether at the 2'-hydroxyl gave the radical reaction substrate 14. The photochemical radical atom-transfer reaction of 14 by using a high-pressure mercury lamp proceeded effectively in benzene to give the exo-cyclized PhSe-transferred product 18, in which (PhSe)2 proved to be essential as an additive for radical atom-transfer cyclization reactions. Subsequent phenylseleno-group elimination of 18 gave the sugar-protected 1'alpha-vinyluridine. With this procedure, 1'alpha-vinyluridine (22) and -cytidine (25), designed to be potential antitumor agents, were successfully synthesized. This study is the first example of functionalization at the anomeric 1'-position of a nucleoside by starting from a natural nucleoside to produce a ribo-type 1'-modified nucleoside.