Synthesis and anti-HIV activity of alkylated quinoline 2,4-diols

Naturally occurring quinolone alkaloids, buchapine (1) and compound 2 were synthesized as reported in literature and evaluated for anti-HIV potential in human CD4+ T cell line CEM-GFP, infected with HIV-1_NL4.3 virus by p24 antigen capture ELISA assay. The compounds 1 and 2 showed potent inhibitory activity with IC₅₀ value of 2.99 and 3.80 μM, respectively. Further, 45 alkylated derivatives of quinoline 2,4-diol were synthesized and tested for anti-HIV potential in human CD4+ T cell line CEM-GFP. Among these, 13 derivatives have shown more than 60% inhibition. We have identified three most potent inhibitors 6, 9 and 23; compound 6 was found to be more potent than lead molecule 1 with IC₅₀ value of 2.35 μM and had better therapeutic index (26.64) as compared to AZT (23.07). Five derivatives 7, 19a, 19d, 21 and 24 have displayed good noticeable anti-HIV activity. All active compounds showed higher CC₅₀ values which indicate that they have better therapeutic indices.     

Conjugates of betulin derivatives with AZT as potent anti-HIV agents

Fourteen novel conjugates of 3,28-di-O-acylbetulins with AZT were prepared as anti-HIV agents, based on our previously reported potent anti-HIV triterpene leads, including 3-O-acyl and 3,28-di-O-acylbetulins. Nine of the conjugates (49–53, 55, 56, 59, and 60) exhibited potent anti-HIV activity at the submicromolar level, with EC₅₀ values ranging from 0.040 to 0.098 μM in HIV-1_NL4-3 infected MT-4 cells. These compounds were equipotent or more potent than 3-O-(3′,3′-dimethylsuccinyl)betulinic acid (2), which is currently in Phase IIb anti-AIDS clinical trial.     

Altertoxins with potent anti-HIV activity from Alternaria tenuissima QUE1Se,a fungal endophyte of Quercus emoryi

Screening of a small library of natural product extracts derived from endophytic fungi of the Sonoran desert plants in a cell-based anti-HIV assay involving T-cells infected with the HIV-1 virus identified the EtOAc extract of a fermentation broth of Alternaria tenuissima QUE1Se inhabiting the stem tissue of Quercus emoryi as a promising candidate for further investigation. Bioactivity-guided fractionation of this extract led to the isolation and identification of two new metabolites, altertoxins V (1) and VI (2) together with the known compounds, altertoxins I (3), II (4), and III (5). The structures of 1 and 2 were determined by detailed spectroscopic analysis and those of 3–5 were established by comparison with reported data. When tested in our cell-based assay at concentrations insignificantly toxic to T-cells, altertoxins V (1), I (3), II (4), and III (5) completely inhibited replication of the HIV-1 virus at concentrations of 0.50, 2.20, 0.30, and 1.50 μM, respectively. Our findings suggest that the epoxyperylene structural scaffold in altertoxins may be manipulated to produce potent anti-HIV therapeutics.     

Concise synthesis of 5,6-dihydrovaltrate leading to enhanced Rev-export inhibitory congener

The concise synthesis of 5,6-dihydrovaltrate (2), the bioisostere of valtrate (1) showing anti-HIV activity by inhibition for nuclear export of Rev, has been achieved from the commercially available iridoid genipin (3). Analysis of steric influence of the substituents linked to the three hydroxyl groups was conducted by the synthesized three analogs (2a–2c). Consequently, attenuation of steric hindrance around the epoxy portion was revealed to enhance inhibitory potency for Rev-export. In addition to this finding, 1-acetoxy analog 2b was disclosed as the promising Rev-export inhibitor superior to 1.     

Structural modifications of 5,6-dihydroxypyrimidines with anti-HIV activity

A series of 5,6-dihydroxypyrimidine analogs were synthesized and evaluated for their anti-HIV activity in vitro. Among all of the analogs, several compounds exhibited significant anti-HIV activity, especially 1b and 1e, which showed the most potent anti-HIV activity with EC₅₀ values of 0.14 and 0.15 μM, and TI (therapeutic index) values of >300 and >900, respectively. Further docking studies revealed that the representative compounds 1e and 3a could meet the HIV-1 integrase inhibition minimal requirements of a chelating domain (two metal ions) and an aromatic domain (π–π stacking interactions).     

Phomonaphthalenone A: A novel dihydronaphthalenone with anti-HIV activity from Phomopsis sp. HCCB04730

A novel dihydronaphthalenone, phomonaphthalenone A (1) was isolated from solid cultures of the endophytic fungus Phomopsis sp. HCCB04730, together with six known naphthoquinones (2–7). The structure of 1 was elucidated through spectroscopic and X-ray crystallographic analysis. Cytotoxic and anti-HIV activities of compounds 1–7 were also investigated. All compounds exhibited cytotoxic and anti-HIV activities. Compounds 1 and 7 showed moderate anti-HIV activities with IC₅₀ values of 11.6 and 9.4 μg/mL, and relatively low cytotoxicity. Compounds 2, 4, and 5 showed significant cytotoxicity with IC₅₀ values less than 4.7 μg/mL against A549, MDA-MB-231 and PANC-1 cell lines.     

Anti-AIDS agents 84. Synthesis and anti-human immunodeficiency virus (HIV) activity of 2′-monomethyl-4-methyl- and 1′-thia-4-methyl-(3′R,4′R)-3′,4′-di-O-(S)-camphanoyl-(+)-cis-khellactone (DCK) analogs

In a continuing investigation into the pharmacophores and structure–activity relationship (SAR) of (3′R,4′R)-3′,4′-di-O-(S)-camphanoyl-(+)-cis-khellactone (DCK) as a potent anti-HIV agent, 2′-monomethyl substituted 1′-oxa, 1′-thia, 1′-sulfoxide, and 1′-sulfone analogs were synthesized and evaluated for inhibition of HIV-1 replication in H9 lymphocytes. Among them, 2′S-monomethyl-4-methyl DCK (5a)³ and 2′S-monomethyl-1′-thia-4-methyl DCK (7a) exhibited potent anti-HIV activity with EC₅₀ values of 40.2 and 39.1 nM and remarkable therapeutic indexes of 705 and 1000, respectively, which were better than those of the lead compound DCK in the same assay. In contrast, the corresponding isomeric 2′R-monomethyl-4-methyl DCK (6) and 2′R-monomethyl-1′-thia-4-methyl DCK (8) showed much weaker inhibitory activity against HIV-1 replication. Therefore, the bioassay results suggest that the spatial orientation of the 2′-methyl group in DCK analogs can have important effects on anti-HIV activity of this compound class.     

Solution- and solid-phase synthesis and anti-HIV activity of maslinic acid derivatives containing amino acids and peptides

Maslinic acid (1) has been coupled at C-28 with several α- and ω-amino acids by using solution- and solid-phase synthetic procedures. Twelve derivatives (2–13) with a single amino acid residue were prepared in solution phase, whereas a dipeptide (14), a tripeptide (15), and a series of conjugate dipeptides (16–24) were synthesized in solid phase. The anti-HIV activity of these compounds was assessed on MT-2 cells infected with viral clones carrying the luciferase gene as a reporter. While in maslinic acid (1) were present both cytotoxic and antiviral activities, only the derivatives 13 and 24 showed anti-HIV-1 activity and therefore represent a novel class of anti-HIV-1 compounds.     

Synthesis and biological evaluation of novel dihydro-aryl/alkylsulfanyl-cyclohexylmethyl-oxopyrimidines (S-DACOs) as high active anti-HIV agents

A novel dihydro-aryl/alkylsulfanyl-cyclohexylmethyl-oxopyrimidines (S-DACOs) combinatory library was synthesized and evaluated with C8166 cells infected by the HIV-1_IIIB in vitro, using Nevirapine (NVP) and Zidovudine (AZT) as positive control. The anti-HIV screening results revealed that C-6-cyclohexylmethyl substituted pyrimidinones possessed higher selective index than its 6-arylmethyl counterparts. Compounds 1g, 1c, 1e and 1b showed potent anti-HIV activities with EC₅₀ values of 0.012, 0.025, 0.088 and 0.162 nM, respectively.     

Bioactive aporphine alkaloids from the stems of Dasymaschalon rostratum

Three undescribed aporphine alkaloids dasymaroine A (1), 3-methoxyoxoputerine N-oxide (2), and dasymaroine B (3), along with nine known analogues (4–12) were isolated from the stems of Dasymaschalon rostratum Merr. The structures were elucidated using spectroscopic methods and by comparison with published NMR spectroscopic data. Compound 1 is a rarely reported nitro aporphine alkaloid and its absolute configuration was defined based on negative specific rotation and single-crystal X-ray diffraction. Compound 2 represents the first example of oxoaporphine alkaloid N-oxide. All compounds were evaluated for their activities of six pathogenic bacteria, 1 exhibited significant inhibition against Escherichia coli and Saphylococcus aureus with MIC values of 1.2 and 2.5 μM, respectively. As well as compounds 1–5, 7, 10, 12 were evaluated for their anti-HIV activities with EC₅₀ ranged from 1.93 to 9.70 μM.     

Spirodiketopiperazine-based CCR5 antagonist: discovery of an antiretroviral drug candidate

Following the discovery that hydroxylated derivative 3 (Fig. 1) was one of the oxidative metabolites of the original lead 1, it was found that hydroxylated compound 4 possesses higher in vitro anti-HIV potency than the corresponding non-hydroxylated compound 2. Structural hybridation of 4 with the orally available analog 5 resulted in another orally-available spirodiketopiperazine CCR5 antagonist 6a that possesses more favorable pharmaceutical profile for use as a drug candidate.     

Synthesis,biophysical characterization and anti-HIV activity of d(TG3AG) Quadruplexes bearing hydrophobic tails at the 5′-end

Novel conjugated G-quadruplex-forming d(TG₃AG) oligonucleotides, linked to hydrophobic groups through phosphodiester bonds at 5′-end, have been synthesized as potential anti-HIV aptamers, via a fully automated, online phosphoramidite-based solid-phase strategy. Conjugated quadruplexes showed pronounced anti-HIV activity with some preference for HIV-1, with inhibitory activity invariably in the low micromolar range. The CD and DSC monitored thermal denaturation studies on the resulting quadruplexes, indicated the insertion of lipophilic residue at the 5′-end, conferring always improved stability to the quadruplex complex (20 < ΔTm < 40 °C). The data suggest no direct functional relationship between the thermal stability and anti-HIV activity of the folded conjugated G-quartets. It would appear that the nature of the residue at 5′ end of the d(TG₃AG) quadruplexes plays an important role in the thermodynamic stabilization but a minor influence on the anti-HIV activity. Moreover, a detailed CD and DSC analyses indicate a monophasic behaviour for sequences I and V, while for ODNs (II–IV) clearly show that these quadruplex structures deviate from simple two-state melting, supporting the hypothesis that intermediate states along the dissociation pathway may exist.     

Design,synthesis and biological evaluation of low molecular weight CXCR4 ligands

The chemokine receptor CXCR4/stromal cell-derived factor-1 (SDF-1: CXCL12) signaling axis represents a crucial drug target due to its relevance to several diseases such as HIV-1 infection, cancer, leukemia, and rheumatoid arthritis. With the aim of enhancing the binding affinity and anti-HIV activity of a potent CXCR4 ligand as a lead, 23 low molecular weight compounds containing dipicolylamine (Dpa) and cyclam cationic moieties with varying spacers and spatial positioning were designed, synthesized and biologically evaluated. All of the synthesized compounds screened at 1.0 μM in the NanoBRET assay system exhibited >70% inhibition of the binding of a competitive probe TAMRA-Ac-TZ14011 (10 nM) to CXCR4 in the presence of zinc (II) ion. Furthermore, selected compounds 3, 8, 9, 19 and 21 with spatial distances between the next carbon to Dpa and the next carbon to cyclam within the range of 6.5–7.5 Å showed potent binding affinity selective for CXCR4 with IC₅₀ values of 1.6, 7.9, 5.7, 3.5 and 4.5 nM, respectively, with corresponding high anti-HIV activity with EC₅₀s of 28, 13, 21, 28 and 61 nM, respectively, in the presence of zinc (II) ion. Some compounds with remarkably more potent CXCR4-binding affinity than that of an initial lead were obtained. These compounds interact with different but overlapping amino acid residues of CXCR4. The present studies have developed new low molecular weight CXCR4 ligands with high CXCR4-binding and anti-HIV activities, which open avenue into the development of more potent CXCR4 ligands.     

Discovery of novel low-molecular-weight HIV-1 inhibitors interacting with cyclophilin A using in silico screening and biological evaluations

Cyclophilin A has attracted attention recently as a new target of anti-human immunodeficiency virus type 1 (HIV-1) drugs. However, so far no drug against HIV-1 infection exhibiting this mechanism of action has been approved. To identify new potent candidates for inhibitors, we performed in silico screening of a commercial database of more than 1,300 drug-like compounds by using receptor-based docking studies. The candidates selected from docking studies were subsequently tested using biological assays to assess anti-HIV activities. As a result, two compounds were identified as the most active. Specifically, both exhibited anti-HIV activity against viral replication at a low concentration and relatively low cytotoxicity at the effective concentration inhibiting viral growth by 50 %. Further modification of these molecules may lead to the elucidation of potent inhibitors of HIV-1.

Synthesis,anti-HIV and anti-oxidant activities of caffeoyl 5,6-anhydroquinic acid derivatives

In our continued research on chlorogenic acid analogues and derivatives with improved bioactivity, we have synthesized some caffeoyl 5,6-anhydroquinic acid derivatives. The 1,7 acetonides of chlorogenic acid (15), and of the mono-caffeoyl 5,6-anhydroquinic acids (7–8) showed appreciable anti-HIV activity. The 3,4-dicaffeoyl 5,6-anhydroquinic acid (12) exhibited an anti-HIV activity twice as that of 3,5-dicaffeoylquinic acid (22). The caffeoyl 5,6-anhydroquinic acid derivatives displayed potent anti-oxidant activities. The mono-caffeoyl 5,6-anhydroquinic acids (10–11) were more than twice stronger than chlorogenic acid (21) on SOD-like activity.     

Biomimetic synthesis and anti-HIV activity of dimeric phloroglucinols

Plants are an important source of a variety of bioactive compounds with different modes of action. Anti-HIV agents from plant sources can be useful in developing novel therapies for inhibiting HIV infection. Based on the reported anti-HIV activity of plant derived phloroglucinols, several new dimeric phloroglucinols were synthesized in the present study by varying substitution on aromatic ring and at methylene bridge. Some of the synthesized compounds have shown good HIV inhibitory activity in a human CD4+ T cell line (CEM-GFP) infected with HIV-1 NL_4.3 virus isolate. Structure–activity studies indicate that phenyl, 4-benzyloxy-1-phenyl and cyclohexyl substitution at methylene bridge gave compounds with better anti-HIV activity. Compounds 22 and 24 showed highest anti-HIV activity with an IC₅₀ of 0.28 μM and 2.71 μM, respectively, former was more active than the positive standard AZT in cell based assay.     

Synthesis of 5-thiodidehydropyranylcytosine derivatives as potential anti-HIV agents

As a part of our ongoing efforts to identify new anti-HIV agents, a 5′-thiopyrano-nucleoside derivative 4, designed based on 4′-thioD4C 1 and cyclohexenylnucleoside 3, was synthesized. The dihydrothiopyran skeleton of 4 was constructed by the ring closing metathesis of 21 which was synthesized from but-2-yne-1,4-diol. After converting the protecting group from MOM to TBS followed by oxidation, a Pummerer-type thioglycosylation reaction of 24 with persilylated uracil gave the desired 5-thiodihydrothiopyranyluracils 25 and 26 as a mixture of anomers. The conversion of 25 to a cytosine derivative and subsequent deprotection gave a 5-thiodidehydropyranosylcytosine derivative 4 in good yield. The anti-HIV activity of 4 was also evaluated.     

5′-O-Aliphatic and amino acid ester prodrugs of (−)-β-d-(2R,4R)-dioxolane-thymine (DOT): Synthesis,anti-HIV activity,cytotoxicity and stability studies

A series of (?)-β-d-(2R,4R)-dioxolane-thymine-5′-O-aliphatic acid esters as well as amino acid esters were synthesized as prodrugs of (?)-β-d-(2R,4R)-dioxolane-thymine (DOT). The compounds were evaluated for anti-HIV activity against HIV-1_LAI in human peripheral blood mononuclear (PBM) cells as well as for their cytotoxicity in PBM, CEM and Vero cells. Improved anti-HIV potency in vitro was observed for the compound 2–4 (5′-O-aliphatic acid esters) without increase in cytotoxicity in comparison to the parent drug. Chemical and enzymatic hydrolysis of the prodrugs was also studied, in which the prodrugs exhibited good chemical stability with the half-lives from 3 h to 54 h at pH 2.0 and 7.4 phosphate buffer. However, the prodrugs were relatively labile to porcine esterase with the half-lives from 12.3 to 48.0 min.