DNA chain termination activity and inhibition of human immunodeficiency virus reverse transcriptase by carbocyclic 2',3'-didehydro-2',3'-dideoxyguanosine triphosphate

Enantioselective syntheses of carbocyclic nuleosides 5'-homocarbovir, epi-4'-homocarbovir and their cyclopropylamine analogs using facially selective Pd-mediated allylations

Carbocyclic nucleosides (-)-5'-homocarbovir and (+)-epi-4'-homocarbovir were prepared from an acylnitroso-derived hetero Diels-Alder cycloadduct. A kinetic enzymatic resolution generated an enantiopure aminocyclopentenol and Pd(0)-mediated decarboxylative allylations of allyl 2,2,2-trifluoroethyl malonates were used to install the 4'-hydroxyethyl groups. Late stage derivatization gave access to the cyclopropylamine congenors, (-)-5'-homoabacavir and (+)-epi-4'-homoabacavir. All carbonucleoside target molecules were evaluated for antiviral activity.

Carbocyclic 5'-nor "reverse" fleximers. Design, synthesis, and preliminary biological activity

A series of 5'-nor carbocyclic "reverse" flexible nucleosides or "fleximers" have been designed wherein the nucleobase scaffold resembles a "split" purine as well as a substituted pyrimidine. This modification was employed to explore recognition by both purine and pyrimidine metabolizing enzymes. The synthesis of the carbocyclic fleximers and the results of their preliminary biological screening are described herein.

Abacavir pharmacokinetics during chronic therapy in HIV-1-infected adolescents and young adults

The pharmacokinetics of abacavir and its metabolites were investigated in 30 human immunodeficiency virus (HIV)-infected adolescents and young adults 13-25 years of age, equally divided into two groups: <18 years of age and >or=18 years of age. All the subjects received the recommended adult dose of 300 mg twice daily. The area under the plasma concentration-time curve (AUC) and half-life of abacavir did not differ significantly between the age groups or by gender or race, and there were only modest associations of age with apparent abacavir clearance and with volume of distribution. There were no significant correlations of carboxylate or glucuronide metabolite levels with age or gender, although glucuronide AUC was higher in Hispanic subjects than in African-American subjects. Zidovudine and lamivudine concentration profiles were also similar in the two age groups. A novel aspect of the study included an assessment of intracellular carbovir, zidovudine, and lamivudine triphosphate levels, and these were found to be similar in the two age-based groups. Overall, these findings suggest that current recommendations relating to adult dosages are appropriate for adolescents and young adults.

Enantiomeric synthesis of carbocyclic analogs ofD- andL-6-azapyrimidine ribonucleosides

An effective and practical synthesis of carbocyclic D- and L-6-azapyrimidine nucleosides (3–8) was described. Starting from D-ribose, a new efficient methodology for the synthesis of L-2,3-O-cyclohexylidene-4-cyclopentenone (23) was developed via a ring-closing metathesis, which was applied for the synthesis of L-cyclopentyl-6-azapyrimidine nucleosides (6–8). The regiospecific introduction of 6-azauracil on the carbocyclic moiety (9 and 25) was also achieved by masking its N3position with a 4-methylthio group.Key words: carbocyclic nucleosides, 6-azapyrimidine nucleosides, enantiomeric synthesis.

Synthesis of dinucleoside polyphosphates catalyzed by firefly luciferase and several ligases

The findings presented here originally arose from the suggestion that the synthesis of dinucleoside polyphosphates (Np(n)N) may be a general process involving enzyme ligases catalyzing the transfer of a nucleotidyl moiety via nucleotidyl-containing intermediates, with release of pyrophosphate. Within this context, the characteristics of the following enzymes are presented. Firefly luciferase (EC 1.12. 13.7), an oxidoreductase with characteristics of a ligase, synthesizes a variety of (di)nucleoside polyphosphates with four or more inner phosphates. The discrepancy between the kinetics of light production and that of Np(n)N synthesis led to the finding that E*L-AMP (L = dehydroluciferin), formed from the E*LH(2)-AMP complex (LH(2) = luciferin) shortly after the onset of the reaction, was the main intermediate in the synthesis of (di)nucleoside polyphosphates. Acetyl-CoA synthetase (EC 6.2.1.1) and acyl-CoA synthetase (EC 6.2.1. 8) are ligases that synthesize p(4)A from ATP and P(3) and, to a lesser extent, Np(n)N. T4 DNA ligase (EC 6.5.1.1) and T4 RNA ligase (EC 6.5.1.3) catalyze the synthesis of Np(n)N through the formation of an E-AMP complex with liberation of pyrophosphate. DNA is an inhibitor of the synthesis of Np(n)N and conversely, P(3) or nucleoside triphosphates inhibit the ligation of a single-strand break in duplex DNA catalyzed by T4 DNA ligase, which could have therapeutic implications. The synthesis of Np(n)N catalyzed by T4 RNA ligase is inhibited by nucleoside 3'(2'),5'-bisphosphates. Reverse transcriptase (EC 2.7.7.49), although not a ligase, catalyzes, as reported by others, the synthesis of Np(n)ddN in the process of removing a chain termination residue at the 3'-OH end of a growing DNA chain.

Metabolism of O6-propyl and N6-propyl-carbovir in CEM cells

The metabolism of O6-propyl-carbovir and N6-propyl-carbovir, two selective inhibitors of HIV replication, has been evaluated in CEM cells. Both compounds were phosphorylated in intact cells to carbovir-5'-triphosphate. The metabolism of these two agents was inhibited by deoxycoformycin and mycophenolic acid, but not erythro-9-(2-hydroxy-3-nonyl)adenine. No evidence of the 5'-triphosphate of either compound was detected in CEM cells.

Development and optimization of anti-HIV nucleoside analogs and prodrugs: A review of their cellular pharmacology, structure-activity relationships and pharmacokinetics

Significant improvements in antiviral therapy have been realized over the past 10 years. Numerous nucleoside analogs, as well as prodrugs of active compounds, have been synthesized and tested for anti-HIV activity. In addition to the five nucleoside analogs currently used clinically for the treatment of HIV infection, a broad spectrum of anti-HIV nucleoside analogs (including 2',3'-dideoxynucleoside analogs, oxathiolanyl 2',3'-dideoxynucleoside analogs, dioxolanyl 2',3'-dideoxynucleoside analogs, carbocyclic 2',3'-dideoxynucleoside analogs and acyclic nucleoside analogs) and their prodrugs (including ester prodrugs, phospholipid prodrugs, dihydropyridine prodrugs, pronucleotides and dinucleotide analogs), targeted at HIV reverse transcriptase, are reviewed with focus on structure-activity relationships, cellular pharmacology and pharmacokinetics. Several of these anti-viral agents show promise in the treatment of AIDS.

The intracellular phosphorylation of (-)-2'-deoxy-3'-thiacytidine (3TC) and the incorporation of 3TC 5'-monophosphate into DNA by HIV-1 reverse transcriptase and human DNA polymerase gamma

(-)-2'-deoxy-3'-thiacytidine (3TC) has been shown to be a potent, selective inhibitor of HIV replication in vitro, which requires phosphorylation to its 5'-triphosphate for antiviral activity. The intracellular concentration of 3TC 5'-triphosphate in phytohaemagglutinin (PHA)-stimulated peripheral blood lymphocytes (PBL) shows a linear dependence on the extracellular concentration of 3TC up to an extracellular 3TC concentration of 10 microM. At this extracellular concentration of 3TC, the resulting intracellular concentration of 3TC 5'-triphosphate is 5 microM. This value is similar to the inhibition constant (Ki) values for the competitive inhibition of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase and human DNA polymerases (10-16 microM) by 3TC 5'-triphosphate. Since the concentration of 3TC producing 90% inhibition (IC90) of HIV replication in PBLs has been reported to be 76 nM, the antiviral activity of 3TC requires intracellular concentrations of 3TC 5'-triphosphate, which would result in very little inhibition of reverse transcriptase if its sole mode of action was competitive inhibition. This apparent discrepency may be explained by the ability of 3TC 5'-triphosphate to act as a substrate for reverse transcriptase. Primer extension assays have shown that 3TC 5'-triphosphate is a substrate for HIV-1 reverse transcriptase and DNA polymerase gamma, resulting in the incorporation of 3TC 5'-monophosphate into DNA. In the case of DNA polymerase gamma, the product of this reaction (i.e. double-stranded DNA with 3TC 5'-monophosphate incorporated at the 3'-terminus of the primer strand) is also a substrate for the 3'-5' exonuclease activity of this enzyme. This may explain the low levels of mitochondrial toxicity observed with 3TC.