Antifouling activity of synthesized peptide analogs of the sponge metabolite barettin

Barettin (cyclo [(6-bromo-8-en-tryptophan) arginine]), a diketopiperazine isolated from the marine sponge Geodia barretti, is a potent inhibitor of barnacle larvae settlement with an EC50-value of 0.9 microM. In the present study, 14 analogs of barettin and its structural congener dipodazine were synthezised and tested for their ability to inhibit larval settlement. Two of the analogs have an intact barettin skeleton. The remaining analogs have a dipodazine skeleton (a diketopiperazine where arginine is replaced with glycine). Six of the tested synthetic analogs displayed significant settlement inhibition with the most potent inhibitor being benzo[g]dipodazine, which displayed even stronger activity than barettin (EC50-value 0.034 microM). The effect of benzo[g]dipodazine was also shown to be readily reversible, when cyprids were transferred to filtered seawater (FSW).     

Efficacy of methylenecyclopropane analogs of nucleosides against herpesvirus replication in vitro

We have reported previously that purine methylenecyclopropane analogs are potent agents against cytomegaloviruses. In an attempt to extend the activity of these compounds, the 2-amino-6-cyclopropylaminopurine analog, QYL-1064, was selected for further study by modifying the purine 6 substituent. A total of 22 analogs were tested against herpes simplex virus types 1 and 2 (HSV-1, HSV-2), varicella zoster virus (VZV), human cytomegalovirus (HCMV), murine cytomegalovirus (MCMV), Epstein-Barr virus (EBV), human herpesvirus type 6 (HHV-6) and human herpesvirus type 8 (HHV-8). Ten of the analogs had activity against at least one of the viruses tested. One compound had moderate activity against HSV-1 and six had activity against VZV. All but one compound was active against HCMV with a mean EC50 of 2.1 +/- 0.6 microM, compared with a mean EC50 of 3.9 +/- 0.8 microM for ganciclovir. Of special interest was the fact that eight of the ten compounds were active against both HHV-6A and HHV-6B with mean EC50 values of 6.0 +/- 5.2 mciroM and <2.4 +/- 1.5 microM, respectively. Only two compounds had activity against EBV, whereas all but one compound was active against HHV-8 with a mean EC50 of 3.1 +/- 1.7 microM. These results indicate that members of this series of methylenecyclopropane analogs are highly active against HCMV, HHV-6, and HHV-8 but are less active against HSV, VZV, and EBV.     

Structure-affinity relationships of 5'-aromatic ethers and 5'-aromatic sulfides as partial A1 adenosine agonists, potential supraventricular anti-arrhythmic agents

Atrial fibrillation (AF) is the most commonly encountered sustained clinical arrhythmia with an estimated 2.3 million cases in the US (2001). A(1) adenosine receptor agonists can slow the electrical impulse propagation through the atrioventricular (AV) node (i.e., negative dromotropic effect) resulting in prolongation of the stimulus-to-His bundle (S-H) interval to potentially reduce ventricular rate. Compounds that are full agonists of the A(1) adenosine receptor can cause high grade AV block. Therefore, it is envisioned that a compound that is a partial agonist of the A(1) adenosine receptor could avoid this deleterious effect. 5(') Phenyl sulfides (e.g., 17, EC(50)=1.26 microM) and phenyl ethers (e.g., 28, EC(50)=0.2 microM) are partial agonists with respect to their AV nodal effects in guinea pig isolated hearts. Additional affinity, GTPgammaS binding data suggesting partial activity of the A(1) adenosine receptor, and PK results for 5(') modified adenosine derivatives are shown.     

Flavone and isoflavone derivatives of terrestrial plants as larval settlement inhibitors of the barnacle Balanus amphitrite

To determine whether they could serve as non-toxic or less damaging alternative antifouling (AF) agents, 17 flavone and isoflavone derivatives were isolated from terrestrial plant extracts, purified and examined for their ability to inhibit the settlement of barnacle (Balanus amphitrite) cyprids. In larval bioassays, eight compounds showed strong anti-larval settlement activities, with EC(50) values <10 microg ml(-1). Through an analysis of the structure-activity relationship of these compounds, it was found that (1) the structural difference between flavones and isoflavones did not affect their AF activities; (2) the 5-hydroxyl group on the skeletons played a key role in AF activities; and (3) the presence of hydroxyl group or bulky group on C3 significantly reduced AF activities. A hydrolysis experiment using genistein, a typical active compound in this study, indicated that it was decomposed in the marine environment by hydrolysis reaction and that the degradation speed was significantly affected by pH. In a field AF test, genistein inhibited the attachment of B. amphitrite on panels coated with genistein-paint mixtures.     

Anti-AIDS agents. Part 62: anti-HIV activity of 2'-substituted 4-methyl-3',4'-di-O-(-)-camphanoyl-(+)-cis-khellactone (4-methyl DCK) analogs

Four 4-methyl-3',4'-di-O-(-)-camphanoyl-(+)-cis-khellactone (4-methyl DCK) analogs (7a-d) with different alkyl substituents at the 2'-position were synthesized and evaluated for inhibition of HIV-1 replication in H9 lymphocytes. 2'-Methyl-2'-ethyl-4-methyl DCK (7b) was more potent (EC(50)=0.22 microM, TI>175) than the other three compounds (7a, 7c, and 7d), but significantly less potent than 4-methyl DCK (2, EC(50)=0.0059 microM, TI>6600). The bioassay results indicated that the 2'-substituents had a strong effect on the anti-HIV activity, and gem-dimethyl substitution at the 2'-position was greatly preferable to larger alkyl substituents or hydrogen atoms.     

Mini-review: Marine natural products and their synthetic analogs as antifouling compounds: 2009–2014

This review covers 214 marine natural compounds and 23 of their synthetic analogs, which were discovered and/or synthesized from mid-2009 to August 2014. The antifouling (AF) compounds reported have medium to high bioactivity (with a threshold of EC₅₀ < 15.0 mg ml^?1). Among these compounds, 82 natural compounds were identified as new structures. All the compounds are marine-derived, demonstrating that marine organisms are prolific and promising sources of natural products that may be developed as environmentally friendly antifoulants. However, this mini-review excludes more than 200 compounds that were also reported as AF compounds but with rather weak bioactivity during the same period. Also excluded are terrestrial-derived AF compounds reported during the last five years. A brief discussion on current challenges in AF compound research is also provided to reflect the authors’ own views in terms of future research directions.     

Glutamate receptor ligands: synthesis, stereochemistry, and enantiopharmacology of methylated 2-aminoadipic acid analogs

Homologation and substitution on the carbon backbone of (S)-glutamic acid [(S)-Glu, 1], as well as absolute stereochemistry, are structural parameters of key importance for the pharmacological profile of (S)-Glu receptor ligands. We describe a series of methyl-substituted 2-aminoadipic acid (AA) analogs, and the synthesis, stereochemistry, and enantiopharmacology of 3-methyl-AA (4a-d), 4-methyl-AA (5a-d), 5-methyl-AA (6a-d), and (E)-Delta(4)-5-methyl-AA (7a and 7b) are reported. The compounds were resolved using chiral HPLC and the configurational assignments of the enantiomers were based on X-ray crystallographic analyses, chemical correlation, and CD spectral analyses. The effects of the individual stereoisomers at ionotropic and metabotropic (S)-Glu receptors (iGluRs and mGluRs) were characterized. Compounds with S-configuration at the alpha-carbon generally showed mGluR2 agonist activity of similar or slightly lower potencies than (S)-AA [e.g., EC(50) = 76 microM for (2S,4S)-4-methyl-AA (5a) as compared to EC(50) = 35 microM for (S)-AA]. The position of the methyl substituent had a profound effect on the observed pharmacology, whereas the absolute stereochemistry at the methylated carbon atom had a very limited effect on pharmacology. Structure-activity relationships at iGluRs in the rat cortical wedge preparation showed a complex pattern, some compounds being NMDA receptor agonists [e.g., EC(50) =110 microM for (2S,5RS)-5-methyl-AA (6a,b)] and some compounds showing NMDA receptor antagonist effects [e.g., IC(50) = 300 microM for (2R,4S)-4-methyl-AA (5d)]. The two unsaturated analogs (S)- (7a) and (R)-(E)-Delta(4)-5-methyl-AA (7b) turned out to be a weak AMPA receptor agonist and a weak mixed NMDA/AMPA receptor antagonist, respectively.     

Antifouling activity of sponge-derived polybrominated diphenyl ethers and synthetic analogues

The antifouling (AF) activity of 2-hydroxy-4-(3-hydroxy-5-methylphenoxy)- 6-methylbenozoic acid methyl ester (1), 3,5-dibromo-2-(2',4'-dibromophenoxy)phenol (2); 3,4,5-tribromo-2-(2',4'-dibromophenoxy)phenol (3), 3,4,5-tribromo-2-(2'-bromophenoxy)phenol (4), 3,5-dibromo-2(2',4'-dibromophenoxy)phenol (5), 3,4,5,6-tetrabromo-2-(2'-bromophenoxy)phenol (6); 4-phenoxyphenol (7), 4-phenoxyaniline (9), 1-chloro-4-phenoxybenzene (10); 1-bromo-4-phenoxybenzene (13) was investigated against marine bacteria, a diatom, barnacle larvae and mussel juveniles. The naturally occurring compound 2 showed the strongest AF activity in all bioassays but lacked toxicity. It inhibited the growth of all tested bacterial strains (MIC = 0.02 - 1.52 microM) and its 50% effective concentrations (EC(50)) were 0.24 microM (diatom test), 0.66 microM (mussel test) and 1.26 microM (barnacle test). Among the commercially available derivates, compound 7 was the most active in bacterial and diatom bioassays but its activity was lower than that of compound 2. Overall, the naturally occurring compounds showed stronger activity than the commercially available analogues and could be possible future non-toxic AF candidates.     

Synthetic FP-prostaglandin-induced contraction of rat uterus smooth muscle in vitro

Numerous synthetic FP-class prostaglandin (PG) analogs stimulated the contraction of isolated non-pregnant female rat uterus in a concentration-dependent manner with the following agonist potencies: bimatoprost acid (17-phenyl-trinor PGF(2alpha); EC(50)=0.68+/-0.06 nM)=cloprostenol (EC(50)=0.73+/-0.01 nM)>travoprost acid (EC(50)=1.3+/-0.07 nM)>latanoprost acid (EC(50)=2.7+/-0.08 nM)>PGF(2alpha) (EC(50)=52+/-11 nM)>unoprostone (UF-021; EC(50)=310+/-101 nM)>S-1033 (EC(50)=610+/-4 nM)>bimatoprost (EC(50)=1130+/-173 nM). The FP-receptor antagonist, AL-8810, antagonized the contractile effects of PGF(2alpha) (K(i)=2.9+/-0.2 microM), travoprost acid (K(i)=0.6+/-0.1 microM) and bimatoprost (K(i)=0.2+/-0.02 microM). Agonist and antagonist potencies for rat uterus contraction by these PGs compared well with their potencies for inducing/blocking functional responses in other systems (r=0.83-0.94) except with bovine iris sphincter (r=0.2; p<0.7). In conclusion, the rat uterus contains functionally active FP-receptors whose activation by a variety of free acid and an amide forms of synthetic PGs leads to the contraction of this tissue and which can be pharmacologically blocked by an FP-receptor antagonist, AL-8810.     

Nontoxic piperamides and their synthetic analogues as novel antifouling reagents

Bioassay-guided isolation of an acetone extract from a terrestrial plant Piper betle produced four known piperamides with potent antifouling (AF) activities, as evidenced by inhibition of settlement of barnacle cypris larvae. The AF activities of the four piperamides and 15 synthesized analogues were compared and their structure–activity relationships were probed. Among the compounds, piperoleine B and 1-[1-oxo-7-(3′,4′-methylenedioxyphenyl)-6E-heptenyl]-piperidine (MPHP) showed strong activity against settlement of cyprids of the barnacle Balanus amphitrite, having EC₅₀ values of 1.1?±?0.3 and 0.5?±?0.2?μg?ml^?1, respectively. No toxicity against zebra fish was observed following incubation with these two compounds. Besides being non-toxic, 91% of piperoleine B-treated cyprids and 84% of MPHP-treated cyprids at a concentration of 100?μM completed normal metamorphosis in recovery bioassays, indicating that the anti-settlement effect of these two compounds was reversible. Hydrolysis and photolysis experiments indicated that MPHP could be decomposed in the marine environment. It is concluded that piperamides are promising compounds for use in marine AF coatings.     

Stimulation of adenylate cyclase in the heart of Aplysia californica by biogenic amines

The effects of serotonin (5-HT), dopamine (DA), several peptides including FMRFamide and arginine vasotocin, the diterpene forskolin and Ca2+ were examined on adenylate cyclase in a particulate fraction from hearts of Aplysia californica. Enzyme activity was stimulated 6-7-fold by 5-HT (EC50, 1 microM) in the presence of GTP. Several 5-HT analogs particularly 5-methoxytryptamine and 5-methoxy-N-N-dimethyltryptamine were also active. The stimulatory action of 5-HT was antagonized by the 5-HT receptor blockers methergoline and metitepine and by the DA receptor blocker chlorpromazine. Dopamine had weak stimulatory action (EC50, 10 microM) and an efficacy relative to that of 5-HT of 0.3. The action of DA was antagonized by chloropromazine and metitepine. Several peptides including FMRFamide and arginine vasotocin had no effect on adenylate cyclase when tested over the concentration range 0.1-100 microM. The enzyme was stimulated 6-fold by the diterpene forskolin (EC50, 2 microM). 5-HT-stimulated activity was strongly inhibited by Ca2+. Calmodulin had no action on the enzyme in the presence of Ca2+.     

μ-Opioid Receptors Mediate the Inhibitory Effect of Opioids on Dopamine-Sensitive Adenylate Cyclase in Primary Cultures of Rat Neostriatal Neurons

The receptors mediating the inhibition of D1 dopamine receptor-stimulated adenylate cyclase by opioids were examined in primary cultures of rat neostriatal neurons. Adenylate cyclase activity was dose-dependently increased by the selective D1 dopamine receptor agonist SKF 38393 (EC50 = 0.05 microM). This stimulation was fully antagonized by the selective D1 dopamine receptor antagonist SCH 23390 (1 microM). SKF 38393 (1 microM)-stimulated adenylate cyclase activity was strongly reduced (by almost 60%) by the highly selective mu-agonist [D-Ala2, MePhe4, Gly-ol5]-enkephalin (DAGO; EC50 = 0.006 microM) and high concentrations of the selective delta-agonist [D-Ser2(O-tert-butyl), Leu5]-enkephalyl-Thr6 (DSTBU-LET; EC50 = 0.13 microM) but not by the selective delta-agonist [D-penicillamine2, D-penicillamine5]enkephalin (DPDPE). D1 dopamine receptor-stimulated adenylate cyclase activity was also slightly reduced (by approximately 20%) by high concentrations of the kappa-agonist U50,488 (EC50 = 0.63 microM). The inhibitory effects of submaximally effective concentrations of DAGO, DSTBULET, and U50,488 were equally well antagonized by the mu-opioid receptor-selective antagonist naloxone (EC50 of approximately 0.1 microM). Neither the irreversible delta-ligand fentanyl isothiocyanate (1 microM) nor the reversible delta-antagonist ICI 174864 (1 microM) reversed the inhibitory effects of DSTBULET. The inhibitory effects of DAGO and U50,488 were equally well reversed by high concentrations (greater than 0.1 microM) of the kappa-opioid receptor-selective antagonist norbinaltorphimine. The effect of DAGO (1 microM) was already detectable after 1 day in culture, whereas DPDPE (1 microM) had no effect even after 28 days in culture. These data indicate that an homogeneous population of mu-opioid receptors coupled as inhibitors to D1 dopamine receptor-stimulated adenylate cyclase is expressed in rat neostriatal neurons in primary culture.     

Synthesis and biological activity of diaryl ether inhibitors of malarial enoyl acyl carrier protein reductase. Part 2: 2'-substituted triclosan derivatives

2'-Substituted analogs of triclosan have been synthesized to target inhibition of the key malarial enzyme Plasmodium falciparum enoyl acyl carrier protein reductase (PfENR). Many of these compounds exhibit good potency (EC50<500 nM) against in vitro cultures of drug-resistant and drug-sensitive strains of the P. falciparum parasite and modest (IC50=1-20 microM) potency against purified PfENR enzyme. Compared to triclosan, this survey of 2'-substituted derivatives has afforded gains in excess of 20- and 30-fold versus the 3D7 and Dd2 strains of parasite, respectively.     

Covalent incorporation of 3'-O-(4-benzoyl)benzoyl-ATP into a P2 purinoceptor in transformed mouse fibroblasts.

ATP, 3'-O-(4-benzoyl)benzoyl-ATP (BzATP), a photoaffinity analog of ATP, and several other ATP analogs induced an increase in plasma membrane permeability to monovalent ions and normally impermeant metabolites, including nucleotides, in transformed 3T6 mouse fibroblasts. The rank order of agonist potency for induction of nucleotide channels was BzATP (EC50 = 15 microM) greater than ATP (EC50 = 50 microM) approximately adenosine 5'-O-(1-thiotriphosphate) (ATP alpha S) greater than 2-methylthio-ATP (EC50 = 75 microM) approximately 3'-amino-3'-deoxy-ATP greater than adenosine 5'-O-(3-thiotriphosphate) (ATP gamma S) (EC50 = 175 microM). Long wavelength UV illumination of 3T6 cells in the presence of greater than or equal to 20 microM BzATP at 4 degrees C, a nonpermeabilizing temperature, followed by removal of unbound BzATP, resulted in the efflux of 86Rb+ and the release of a prelabeled pool of cytoplasmic nucleotides when the temperature was shifted to 37 degrees C. Photoincorporation of BzATP was inhibited by ATP, ATP alpha S, ATP gamma S, and other ATP analogs that induced an increase in plasma membrane permeability to nucleotides in 3T6 cells under nonphotoactivating conditions. GTP, ITP, UTP, adenosine, and ATP analogs that did not alter plasma membrane permeability to nucleotides under nonphotoactivating conditions also had no effect on BzATP photoincorporation. Photoincorporation of BzATP occurred optimally between pH 6.6 and pH 8.2 but was inhibited at pH 6.0. Photoincorporation of BzATP was also modulated by the osmolarity and the divalent cation concentration of the assay medium. The increase in plasma membrane permeability to nucleotides induced by photoincorporated BzATP occurred at the same rate and had the same temperature, pH, ionic strength, and divalent cation requirements as the increase in plasma membrane permeability to nucleotides induced by ATP and BzATP under nonphotoactivating conditions. These findings support the hypothesis that BzATP can be covalently incorporated into a P2 purinoceptor in 3T6 cells that is coupled to plasma membrane channels for ions and other metabolites.     

Antifouling properties of 10beta-formamidokalihinol-A and kalihinol A isolated from the marine sponge Acanthella cavernosa

Many soft-bodied sessile marine invertebrates such as sponges and soft corals defend themselves against fouling directly through the production of antifouling compounds, or indirectly through regulating the epibiotic microbes that affect larval settlement. In this study, 10beta-formamidokalihinol-A and kalihinol A were isolated and purified from the marine sponge Acanthella cavernosa (Dendy). The results indicated that both compounds inhibited the growth of bacteria isolated from the natural environment whereas kalihinol A suppressed larval settlement of a major fouling polychaete, Hydroides elegans with an EC50 of 0.5 microg ml(-1). Kalihinol A was incorporated in Phytagel that was exposed to the bacterial consortia in natural seawater for biofilm formation. Biofilms that developed on the Phytagel surfaces were analysed for bacterial abundance and bacterial species composition using a DNA fingerprinting technique, terminal restriction fragment length polymorphism (T-RFLP). The results showed that kalihinol A only slightly reduced bacterial abundance (t-test, p = 0.0497), but modified the bacterial species composition of the biofilms. Inhibition of H. elegans larval settlement was observed when biofilms developed under the influence of kalihinol A were exposed to larvae, suggesting that compounds like kalihinol A from the sponge A. cavernosa may change bacterial community composition on the sponge surface, which in turn, modulates larval settlement of fouling organisms.     

Discovery and SAR of indole-2-carboxylic acid benzylidene-hydrazides as a new series of potent apoptosis inducers using a cell-based HTS assay

A series of indole-2-carboxylic acid benzylidene-hydrazides has been identified as a new class of potent apoptosis inducers through a novel cell-based caspase HTS assay. The screening hit, 5-chloro-3-methyl-indole-2-carboxylic acid (4-nitrobenzylidene)-hydrazide (3a), was found to arrest T47D cells in G(2)/M and to induce apoptosis as measured by the flow cytometric analysis assay. A SAR study was carried out by modification of the substitutions on the indole and benzene rings. Substitution at the 3-position of the indole ring was found to be important for apoptotic activity. A 20-fold increase of apoptotic activity was achieved from screening hit 3a to 5-methyl-3-phenyl-indole-2-carboxylic acid (4-methylbenzylidene)-hydrazide (9a) and 5-chloro-3-phenyl-indole-2-carboxylic acid (4-nitrobenzylidene)-hydrazide (9b), with EC(50) value of 0.1microM in the caspase activation assay in T47D breast cancer cells. Compound 9b also was found to be highly active in a standard growth inhibition assay with a GI(50) value of 0.9microM in T47D cells. Compound 3a and its analogs were found to inhibit tubulin polymerization, which is the most probable primary mechanism of action of these compounds.     

1-Aryl-tetrahydroisoquinoline analogs as active anti-HIV agents in vitro

A series of 1-aryl-6,7-dihydroxyl(methoxy)-1,2,3,4-tetrahydroisoquinolines (compounds 1-36) were synthesized via Pictet-Spengler cyclization. All the synthesized compounds were assayed for activities against HIV-1(IIIB) in C8166 cell cultures by MTT method for the first time. The results of the anti-HIV screening revealed that 6,7-dihydroxytetrahydroisoquinolines possessed higher selective index than 6,7-dimethoxyl analogs due to the significantly decreased cytotoxicities. Compounds 6, 24, and 36 showed potent anti-HIV activities with EC(50) values of 8.2, 4.6, and 5.3microM respectively, and the cytotoxicities (CC(50)) of these three compounds were 784.3, 727.3, and 687.3microM, which resulted in SI values larger than 95, 159, and 130 respectively.     

Vialinin A, a novel 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenger from an edible mushroom in China

While screening for bioactive compounds from edible mushrooms, a new potent antioxidant, vialinin A (1), together with a known compound, ganbajunin B (2), and a mixture of ganbajunins D (3) and E (4), were isolated from the dry fruiting bodies of Thelephora vialis. The structure of 1, 5',6'-bis(phenylacetoxy)-1,1':4',1'-terphenyl-2',3',4,4'-tetraol, was elucidated by spectroscopic and chemical methods. This compound had strong 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical-scavenging activity with an EC(50) value of 14.0 microM, nearly equal to that of butylated hydroxytoluene (BHT; EC(50) = 10.0 microM). A radical scavenging experiment using 1 and DPPH radicals indicated that 1 donated two hydrogen atoms to two molecules of the DPPH radical under hydrophobic conditions.     

Chemical transformation and biological studies of marine sesquiterpene (S)-(+)-curcuphenol and its analogs

Chemical transformation studies of the marine sesquiterpene phenol (S)-(+)-curcuphenol (1), isolated from the Jamaican sponges Myrmekioderma styx, were accomplished. In order to optimize the activity and better understand the SAR of (S)-(+)-curcuphenol, nineteen semisynthetic analogs were prepared and evaluated for activity against infectious diseases. A number of analogs showed significant activity against Mtb and Leishmania donovani, while showed good to moderate activities in antibacterial and antifungal assays as well as against Plasmodium falciparium (D6 clone) and (W2 clone). The analogs a, c, h, and r exhibited Mtb activity with MICs of 24.6, 41.2, 6.90, and 50.5 microM, respectively. Analog f showed enhanced activity against L. donovani with an IC50 of 0.6 microM and IC90 of 40 microM respectively.     

Synthesis and biological evaluation of novel 5(H)-phenanthridin-6-ones, 5(H)-phenanthridin-6-one diketo acid, and polycyclic aromatic diketo acid analogs as new HIV-1 integrase inhibitors

A new series of phenanthridinone derivatives, and diketo acid analogs, as well as related phenanthrene and anthracene diketo acids have been synthesized and evaluated as HIV integrase (IN) inhibitors. Several new beta-diketo acid analogs with the phenanthridinone scaffold replaced by phenanthrene, anthracene or pyrene exhibited the highest IN inhibitory potency. There is a general selectivity against the integrase strand transfer step. The most potent IN was 2,4-dioxo-4-phenanthren-9-yl-butyric acid (27f) with an IC(50) of 0.38microM against integrase strand transfer. The phenanthrene diketo acids 27d-f were more potent (IC(50)=2.7-0.38microM) than the corresponding phenanthridinone diketo acid 16 (IC(50)=65microM), suggesting that the polar amide bridge in the phenanthridinone system decreases inhibitory activity relative to the more lipophilic phenanthrene system. This might have to do with the possible binding of the aryl group of the compounds binding to a lipophilic pocket at the integrase active site as suggested by the docking simulations. Molecular modeling also suggested that effectiveness of chelation of the active site Mg(2+) contributes to IN inhibitory potency. Finally, some of the potent compounds inhibited HIV-1 replication in human peripheral blood mononuclear cells (PBMC) with EC(50) down to 8microM for phenanthrene-3-(2,4-dioxo)butyric acid (27d), with a selectivity index of 10 against PBMCs.