Synthesis and anti-human immunodeficiency virus type 1 integrase activity of hydroxybenzoic and hydroxycinnamic acid flavon-3-yl esters

Nanonization of a chemically synthesized flavone HMDF (3-hydroxy-3',4'-methylenedioxyflavone) by entrapping within calcium phosphate nanoparticles and exploring its antioxidant role on neural cellsin vitroand zebrafishin vivo

The chemical synthesis of 3-hydroxy-3',4'-methylenedioxyflavone (HMDF) was reported to generate a modified flavone of potent antioxidant activity with significant neuropharmacological properties. In this study, HMDF was nanonized by entrapping within calcium phosphate nanoparticles (CPNPs). HMDF-CPNPs were of (i) size 25 nm, (ii) zeta potential (-) [22 ± 3] mV and (iii) entrapment efficiency 67%. HMDF-CPNPs, but not HMDF alone, inhibited thein vitroactivity of acetylcholinesterase enzymes to break down the major neurotransmitter compound acetylcholine. Moreover, nanonized HMDF had more antioxidant activity than bulk HMDF, as observed from its ability to protect mouse neural (N2A) cells from oxidative damage caused by H₂O₂exposure at the levels of cell viability, intracellular reactive oxygen species, mitochondrial membrane potential, cell cycle stages, nuclear integrity and neural connectivity. Anin vivostudy on zebrafish larvae (Denio rerio) also demonstrated that H₂O₂-mediated larval death was checked by HMDF-CPNP treatment. These results, therefore, suggest that HMDF-CPNPs may be developed as a potential antioxidant, particularly as a neuroprotectant.

Ribonuclease H, an unexploited target for antiviral intervention against HIV and hepatitis B virus

Ribonucleases H (RNases H) are endonucleolytic enzymes, evolutionarily related to retroviral integrases, DNA transposases, resolvases and numerous nucleases. RNases H cleave RNA in RNA/DNA hybrids and their activity plays an important role in the replication of prokaryotic and eukaryotic genomes, as well as in the replication of reverse-transcribing viruses. During reverse transcription, the RNase H activity of human immunodeficiency virus (HIV) and hepatitis B virus (HBV) degrades the viral genomic RNA to facilitate the synthesis of viral double-stranded DNA. HIV and HBV reverse transcriptases contain DNA polymerase and RNase H domains that act in a coordinated manner to produce double-stranded viral DNA. Although RNase H inhibitors have not been developed into licensed drugs, recent progress has led to the identification of a number of small molecules with inhibitory activity at low micromolar or even nanomolar concentrations. These compounds can be classified into metal-chelating active site inhibitors and allosteric inhibitors. Among them, α-hydroxytropolones, N-hydroxyisoquinolinediones and N-hydroxypyridinediones represent chemotypes active against both HIV and HBV RNases H. In this review we summarize recent developments in the field including the identification of novel RNase H inhibitors, compounds with dual inhibitory activity, broad specificity and efforts to decrease their toxicity.

Design, synthesis, and biologic evaluation of novel galloyl derivatives as HIV-1 RNase H inhibitors

Human immunodeficiency virus (HIV) reverse transcriptase (RT)-associated ribonuclease H (RNase H) remains as the only enzyme encoded within the viral genome not targeted by current antiviral drugs. In this work, we report the design, synthesis, and biologic evaluation of a novel series of galloyl derivatives with HIV-1 RNase H inhibitory activity. Most of them showed IC₅₀ s at sub- to low-micromolar concentrations in enzymatic assays. The most potent compound was II-25 that showed an IC₅₀ of 0.72 ± 0.07 μM in RNase H inhibition assays carried out with the HIV-1_{BH 10} RT. II-25 was 2.8 times more potent than β-thujaplicinol in these assays. Interestingly, II-25 and other galloyl derivatives were also found to inhibit the HIV IN strand transfer activity in vitro. Structure-activity relationships (SAR) studies and molecular modeling analysis predict key interactions with RT residues His539 and Arg557, while providing helpful insight for further optimization of selected compounds.

Antioxidant flavone analog functionalized fluorescent silica nanoparticles: Synthesis and exploration of their possible use as biomolecule sensor

For the first time, a synthetic fluorescent antioxidant flavone analog was successfully anchored onto the surface of the APTES-modified mesoporous silica nanoparticles (NPs) through sulfonamide linkage. The surface chemistry and morphology of the flavone modified fluorescent silica (FMFS) NPs were studied in detail. The flavone moiety when attached onto the FMFS NP surface, imparted its characteristic fluorescence and antioxidant activities to these NPs. Moreover, the NPs are highly biocompatible as evidenced from their cytotoxicity assay on normal lung cell (L132). The fluorescence activity of these biocompatible NPs was further utilized to study their interaction with a biomolecule, BSA (Bovine Serum Albumin). It was interesting to note that the fluorescence behavior of FMFS NPs completely changed on their binding with BSA. On the other hand, the intrinsic fluorescence activity of BSA was also significantly modified due to its interaction with FMFS NPs. Thus, the sensing and detection of biomolecules like BSA in presence of FMFS NPs can be accomplished by monitoring changes in the fluorescence behavior of either FMFS NPs or BSA. Furthermore, these FMFS NPs retained their intrinsic fluorescence behavior in the cellular medium which opens up their possible use as biocompatible cell imaging agents in future.

An Approach towards the Quantitative Structure-Activity Relationships of Caffeic Acid and its Derivatives

Caffeic acid and its derivatives are already known to possess a wide range of biological activities. We have developed quantitative structure-activity relationships (QSARs) for different series of caffeic acid derivatives (including caffeic acid) in order to understand the chemical-biological interactions governing antitumor activity against six different tumor cell lines, nitric oxide production, anti-HIV and enzymatic activities, and binding affinity to the lck domain. QSAR results have shown that the different activities of caffeic acid and its derivatives are largely dependent on their hydrophobicity or molar refractivity, with a bilinear correlation being the most important.

Novel compounds in preclinical/early clinical development for the treatment of HIV infections

Virtually all the compounds that are currently used, or under advanced clinical trial, for the treatment of HIV infections, belong to one of the following classes: (i) nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs), (ii) non-nucleoside reverse transcriptase inhibitors (NNRTIs) and (iii) protease inhibitors (PIs). In addition to the reverse transcriptase and protease step, various other events in the HIV replicative cycle are potential targets for chemotherapeutic intervention: (i) viral adsorption, through binding to the viral envelope glycoprotein gp120 (polysulphates, polysulphonates, polyoxometalates, zintevir, negatively charged albumins); (ii) viral entry, through blockade of the viral coreceptors CXCR4 and CCR5 [bicyclams (AMD3100), polyphemusins (T22), TAK-779]; (iii) virus-cell fusion, through binding to the viral glycoprotein gp41 [T-20 (DP-178), siamycins, betulinic acid derivatives]; (iv) viral assembly and disassembly, through NCp7 zinc finger-targeted agents [2,2'-dithiobisbenzamides (DIBAs), azadicarbonamide (ADA)]; (v) proviral DNA integration, through integrase inhibitors such as L-chicoric acid; (vi) viral mRNA transcription, through inhibitors of the transcription (transactivation) process (peptoid CGP64222, fluoroquinolone K-12, Streptomyces product EM2487). Also, in recent years new NRTIs, NNRTIs and PIs have been developed that possess, respectively, improved metabolic characteristics (i.e. phosphoramidate and cyclosaligenyl pronucleotides of d4T), or increased activity against NNRTI-resistant HIV strains, or, in the case of PIs, a different, non-peptidic scaffold. Given the multitude of molecular targets with which anti-HIV agents can interact, one should be cautious in extrapolating from cell-free enzymatic assays to the mode of action of these agents in intact cells. A number of compounds (i.e. zintevir and L-chicoric acid, on the one hand; and CGP64222 on the other hand) have recently been found to interact with virus-cell binding and viral entry in contrast to their proposed modes of action targeted at the integrase and transactivation process, respectively.

Anti-picornavirus activity of synthetic flavon-3-yl esters

The in vitro antiviral activity against picornaviruses (rhinovirus serotype 1B and 14, and poliovirus type 2) of new synthetic 3-hydroxyflavones, 3-acetoxyflavones, and substituted cinnamic and benzoic acid flavon-3-yl esters was evaluated. The maximum non-toxic concentration of compounds was determined in a human cell line (HeLa) suitable for the replication of the three viruses. Their antiviral potency was measured by a plaque reduction assay. Generally, rhinoviruses exhibited a higher sensitivity to the new flavonoids than poliovirus. Flavones, with sterically small substituents in position 3, showed good activity against both rhinoviruses tested. However, the introduction of bulky substituents in the same position resulted in analogues with a higher toxicity and often with a lower efficacy.