Stereochemistry of base-catalyzed ring opening of 1,3,2-oxathiaphospholanes. Absolute configuration of 2-{N-[(Rc)-1-(.alpha.-naphthyl)ethyl]amino}-2-thiono-1,3,2-oxathiaphospholanes and O,S-dimethyl N-[(Rc)-1-(.alpha.-naphthyl)ethyl]phosphoramidothioates

Mononucleoside phosphorodithiolates as mononucleotide prodrugs

The synthesis and in vitro anti-HIV activity of a novel series of pronucleotides are reported. These prodrugs were characterized by a phosphorodithiolate structure, incorporating two O-pivaloyl-2-oxyethyl substituents as biolabile phosphate protections. The compounds were obtained following an original one-pot three-step procedure, involving the formation of a phosphorodithioite intermediate which is in situ oxidized. In vitro, comparative anti-HIV evaluations demonstrate that such original prodrugs are able to allow the efficient intracellular release of the corresponding 5'-mononucleotide. The pronucleotide of 2',3'-dideoxyadenosine (ddA) 3 exhibited a very potent antiretroviral effect with 50% effective concentration (EC₅₀) values in nanomolar concentration range in various cell lines. In primary monocytes/macrophages, this derivative was 500 times more potent in inhibiting HIV replication (EC₅₀ 0.23 pM) than ddA and the selectivity index of the prodrug is fifty times higher than the one of the parent nucleoside.

P-stereocontrolled synthesis of oligo(nucleoside N3'→O5' phosphoramidothioate)s - opportunities and limitations

3'-N-(2-Thio-1,3,2-oxathiaphospholane) derivatives of 5'-O-DMT-3'-amino-2',3'-dideoxy-ribonucleosides (NOTP-N), that bear a 4,4-unsubstituted, 4,4-dimethyl, or 4,4-pentamethylene substituted oxathiaphospholane ring, were synthesized. Within these three series, NOTP-N differed by canonical nucleobases (i.e., AdeBz, CytBz, GuaiBu, or Thy). The monomers were chromatographically separated into P-diastereomers, which were further used to prepare NNPSN' dinucleotides (3), as well as short P-stereodefined oligo(deoxyribonucleoside N3'→O5' phosphoramidothioate)s (NPS-) and chimeric NPS/PO- and NPS/PS-oligomers. The condensation reaction for NOTP-N monomers was found to be 5-6 times slower than the analogous OTP derivatives. When the 5'-end nucleoside of a growing oligomer adopts a C3'-endo conformation, a conformational 'clash' with the incoming NOTP-N monomer takes place, which is a main factor decreasing the repetitive yield of chain elongation. Although both isomers of NNPSN' were digested by the HINT1 phosphoramidase enzyme, the isomers hydrolyzed at a faster rate were tentatively assigned the R P absolute configuration. This assignment is supported by X-ray analysis of the protected dinucleotide DMTdGiBu NPSMeTOAc, which is P-stereoequivalent to the hydrolyzed faster P-diastereomer of dGNPST.

Applications and stereoselective syntheses of P-chirogenic phosphorus compounds

This review reports the best stereoselective or asymmetric syntheses, the most efficient P*-building blocks and functionalisation of P-chirogenic compounds, in the light of chiral phosphorus compound applications.

New androst-4-en-17-spiro-1,3,2-oxathiaphospholanes. Synthesis, assignment of absolute configuration and in vitro cytotoxic and antimicrobial activities

The reactions of 17α-hydroxyprogesterone with Lawesson's reagent (LR) in toluene, CH(2)Cl(2) and/or CCl(4) gave, depending on the duration of the reaction, two diastereoisomeric androst-4-en-17-spiro-1,3,2-oxathiaphospholane-2-sulfide pairs 2a,b and 3a,b in approximately 7:3 ratio, differing in configuration at the phosphorus atom. A parallel analysis of heteronuclear 2D (1)H-(13)C spectra (HSQC and HMBC) and homonuclear 2D spectra (NOESY) enabled complete (1)H and (13)C assignments of each isomer. Also, analysis of NOESY correlations provided evidence for the preferred conformation. X-ray analysis of 3a confirmed the structure and absolute configuration on phosphorus. A pathway for the formation of 1,3,2-oxathiaphospholane ring was proposed. Cytotoxic activity in vitro was tested against three tumor cell lines (human cervix carcinoma HeLa cells and two human breast carcinoma MDA-MB-361 and MDA-MB-453 cells). Compound 3a and mixture 3a,b showed a moderate activity against HeLa and MDA-MB-453 cell lines while against MDA-MB-361 cell line all tested compounds exerted very weak cytotoxic effect. Antimicrobial activity against Gram-positive, Gram-negative bacteria and fungal cells, toxicity to brine shrimp Artemia salina, were evaluated. All tested compounds showed strong antifungal activity.

Synthesis of Nucleoside Boranophosphoramidate Prodrugs Conjugated with Amino Acids

[structure: see text] Nucleoside boranophosphates and nucleoside amino acid phosphoramidates have been shown to be potent antiviral and anticancer agents with the potential to act as nucleoside prodrugs. A combination of these two types of compounds results in a boranophosphoramidate linkage between the nucleoside and amino acid. This new class of potential prodrugs is expected to possess advantages conferred by both types of parent compounds. Two approaches, specifically the H-phosphonate and oxathiaphospholane approaches, are described here to synthesize nucleoside boranophosphoramidate prodrugs conjugated with amino acids. The H-phosphonate approach involves a key intermediate, silylated nucleoside amino acid phosphoramidite 6, prepared from a series of reactions starting from nucleoside H-phosphonate in the presence of condensing reagent DPCP. Due to the lengthy procedure and the difficulties in removing DPCP from the final products, we switched to the oxathiaphospholane approach in which the DBU-assisted oxathiaphospholane ring-opening process constituted a key step for the generation of nucleoside amino acid boranophosphoramidates 24. We demonstrate that this key step did not cause any measurable C-racemization of boranophosphorylated amino acids 22. Diastereomers of compounds 24a-f were separated by RP-HPLC. An "adjacent"-type mechanism is proposed to explain the diastereomer ratio in the final products obtained via the oxathiaphospholane approach. A tentative assignment of configuration for the diastereomers was carried out based on the mechanism, molecular modeling, and (1)H NMR. Conclusively, the oxathiaphospholane methodology proved to be more facile and efficient than H-phosphonate chemistry in the preparation of the nucleoside amino acid boranophosphoramidate analogues that are promising as a new type of antiviral prodrugs.

Enhanced stereoselectivity in internucleotidic bond formation by the use of the chiral ribose moiety of thymidine

This paper deals with the synthesis of new cyclic thymidine 3'-phosphoramidite building blocks having a covalent linker between the trityl type 5'-hydroxyl protecting group and the phosphorus atom attached to the 3'-hydroxyl group of thymidine. The ring structures were designed to reduce the conformational freedom around the phosphorus center so that the stereoselectivity in the internucleotide linkage formation would be improved. The linkers were also designed to be removed readily by treatment with aqueous ammonia. These building blocks were synthesized in good yield by one-pot cyclization of the diol precursors with dichloro(N,N-diisopropylamino)phosphine, despite their large-membered ring. Various activators having 1H-tetrazole, imidazole, and triazole structures were investigated to find the best selectivity in the synthesis of thymidylyl(5'-3')thymidine phosphorothioate. It turned out that our cyclic phosphoramidites gave preferentially the R(p) diastereoisomer in high coupling yield applicable to the solid-phase synthesis of oligodeoxynucleotides. It should be noted that high stereoselectivity was achieved without any chiral sources other than the 2'-deoxyribose moiety itself. The mechanistic studies revealed the importance of the steric bulk and the acidity of the activators. It was also found that the steric bulk of the alcoholic nucleophile was an important factor that determined the stereoselectivity in our systems.

Structural modifications of antisense oligonucleotides

Antisense oligonucleotides are efficient tools for the inhibition of gene expression in a sequence specific way. Natural oligonucleotides are decomposed rapidly in biological systems, which strongly restrict their application. In contrast, artificial oligonucleotides are designed to be more stable against degradation than the target mRNA, which results in a catalytic effect of the drug. Modification of the phosphate linkage has been the first successful strategy for antisense drug developments and Fomivirsene the first antisense drug in therapy. The launch of Fomivirsene has resulted in a revolutionary spin off to antisense research leading to a second generation of antisense oligonucleotides, which are stable against oligonucleotide cleaving enzymes. Among these, oligonucleotides bearing an alkoxy substituent in position 2' were the most successful ones. The third generation of antisense oligonucleotides contains structure elements, which enhance the antisense action. Zwitterionic oligonucleotides show remarkable results, first, because the stability against ribozymes is largely increased, and secondly, because the electrostatic repulsion between the anionic sense and the zwitterionic antisense cords is minimized. Promising new target molecules in antisense research are oligonucleotide chimäres, which enhance the antisense action (chimäres with intercalators, chelators or polyamines) or enable an application as sequence specific detectors (chimäres with biotin, fluorescein or radioligands).

Stereochemical study of phosphonothioate cleavage by a metallomicelle

[reaction: see text] The copper metallomicellar hydrolysis of O-methyl O-4-nitrophenyl phenylphosphonothioate to O-methyl phenylphosphonothioic acid takes place with effectively complete inversion at phosphorus.