Selective C-7 Functionalization of Phenanthridines by Microwave-Assisted Claisen Rearrangements of 8-Allyloxyphenanthridines.

Carbon-carbon bond formation in the phenanthridine 7-position was achieved by microwave-assisted Claisen rearrangement of 8-allyloxyphenanthridines. The reactions took place with excellent regioselectivity and high chemical yields. If the 7-position was substituted, rearrangement to C-9 took place, but the reaction occurred less readily. Rearrangements of 8-allyloxy-5,6-dihydrophenanthridines (phenanthridines with a saturated B-ring) gave a mixture of 7- and 9-substituted products. The experimental results were supported by DFT (density functional theory) calculations.

A Semivolatile Floral Scent Marks the Shift to a Novel Pollination System in Bromeliads.

Perfume flowers (sensu Vogel1) produce intense scents that function both as attractants and as the sole rewards for pollinators. The scent is collected exclusively by male euglossine bees and used during pre-mating behavior.2-5 Perfume flowers have evolved independently in 15 angiosperm families, with over 1,000 reported species across the Neotropical region.6 Members of Cryptanthus (Bromeliaceae) represent a puzzling exception among perfume flowers, as flowers produce nectar and do not emit a noticeable scent yet still attract euglossine males.7 Here, we studied the pollination ecology of Cryptanthus burle-marxii and decode the chemical communication between its flowers and euglossine males. Field observations revealed euglossine males and hummingbirds as potential pollinators. The bees always contacted anthers/stigma of C. burle-marxii while scraping the petals to obtain chemicals, whereas nectar-seeking hummingbirds normally only contacted the anthers. Based on gas chromatography-mass spectrometry/nuclear magnetic resonance analyses of flower scent samples and bioassays, we identified the diterpene copalol as the only floral scent compound triggering scent-gathering behavior in euglossine males. Unlike euglossine-bee-mediated pollination, hummingbird pollination is ancestral in the Cryptanthus clade, suggesting a case of an ongoing pollinator shift8-10 mediated by the evolution of perfume as a reward. Copalol was previously unknown as a floral scent constituent and represents the heaviest and least-volatile compound known to attract euglossine males. Our study provides the first experimental evidence that semivolatile floral compounds can mediate euglossine bee interactions. Male euglossine pollination in other plant species lacking noticeable floral scents11-13 suggests that semivolatile-mediated pollinator attraction is more widespread than currently appreciated.

Bioactive Metabolites of Marine Origin Have Unusual Effects on Model Membrane Systems.

Marine sponges and soft corals have yielded novel compounds with antineoplastic and antimicrobial activities. Their mechanisms of action are poorly understood, and in most cases, little relevant experimental evidence is available on this topic. In the present study, we investigated whether agelasine D (compound 1) and three agelasine analogs (compound 2-4) as well as malonganenone J (compound 5), affect the physical properties of a simple lipid model system, consisting of dioleoylphospahtidylcholine and dioleoylphosphatidylethanolamine. The data indicated that all the tested compounds increased stored curvature elastic stress, and therefore, tend to deform the bilayer which occurs without a reduction in the packing stress of the hexagonal phase. Furthermore, lower concentrations (1%) appear to have a more pronounced effect than higher ones (5-10%). For compounds 4 and 5, this effect is also reflected in phospholipid headgroup mobility assessed using 31P chemical shift anisotropy (CSA) values of the lamellar phases. Among the compounds tested, compound 4 stands out with respect to its effects on the membrane model systems, which matches its efficacy against a broad spectrum of pathogens. Future work that aims to increase the pharmacological usefulness of these compounds could benefit from taking into account the compound effects on the fluid lamellar phase at low concentrations.

Synthesis and antimicrobial activities of N6-hydroxyagelasine analogs and revision of the structure of ageloximes.

(+)-N6-Hydroxyagelasine D, the enantiomer of the proposed structure of (-)-ageloxime D, as well as N6-hydroxyagelasine analogs were synthesized by selective N-7 alkylation of N6-[tert-butyl(dimethyl)silyloxy]-9-methyl-9H-purin-6-amine in order to install the terpenoid side chain, followed by fluoride mediated removal of the TBDMS-protecting group. N6-Hydroxyagelasine D and the analog carrying a geranylgeranyl side chain displayed profound antimicrobial activities against several pathogenic bacteria and protozoa and inhibited bacterial biofilm formation. However these compounds were also toxic towards mammalian fibroblast cells (MRC-5). The spectral data of N6-hydroxyagelasine D did not match those reported for ageloxime D before. Hence, a revised structure of ageloxime D was proposed. Basic hydrolysis of agelasine D gave (+)-N-[4-amino-6-(methylamino)pyrimidin-5-yl]-N-copalylformamide, a compound with spectral data in full agreement with those reported for (-)-ageloxime D.

Synthetic Routes to N-9 Alkylated 8-Oxoguanines; Weak Inhibitors of the Human DNA Glycosylase OGG1.

The human 8-oxoguanine DNA glycosylase OGG1 is involved in base excision repair (BER), one of several DNA repair mechanisms that may counteract the effects of chemo- and radiation therapy for the treatment of cancer. We envisage that potent inhibitors of OGG1 may be found among the 9-alkyl-8-oxoguanines. Thus we explored synthetic routes to 8-oxoguanines and examined these as OGG1 inhibitors. The best reaction sequence started from 6-chloroguanine and involved N-9 alkylation, C-8 bromination, and finally simultaneous hydrolysis of both halides. Bromination before N-alkylation should only be considered when the N-substituent is not compatible with bromination conditions. The 8-oxoguanines were found to be weak inhibitors of OGG1. 6-Chloro-8-oxopurines, byproducts in the hydrolysis of 2,6-halopurines, turned out to be slightly better inhibitors than the corresponding 8-oxoguanines.

Mechanistic insights on the stereoselective nucleophilic 1,2-addition to sulfinyl imines.

The asymmetric nucleophilic 1,2-addition of (S)-N-benzylidene-2-methylpropane-2-sulfinamide with methylmagnesium bromide and methyllithium has been investigated using DFT(B3LYP) computations. The calculated ratio of the two diastereomers agrees with experimental observations, and the factors that determine the diastereomeric ratio are discussed. The preference for the E isomer and the rapid equilibrium between the E and Z isomers of N-tert-butanesulfinyl imine are two key features for understanding the mechanism of this reaction. Methylmagnesium bromide and methyllithium have bifunctional roles, acting as both Lewis acid and nucleophile, and the Lewis acid character plays a determining role in the stereoselectivity of the reaction.

(E)-9-(But-2-en-1-yl)-6-chloro-9H-purine.

The asymmetric unit of the title compound, C9H9ClN4, contains two mol-ecules. In the crystal, the mol-ecules are ordered in a chain-like fashion along the a axis, and form layers offset relative to the C plane by approximately 30°. This ordering does not, however, appear to be directed by classical hydrogen bonding.The allylic side chains of both independent mol-ecules are disordered, with occupancies of 0.870 (4) and 0.934 (3) for the major components. The disorder components represent two possible spatial orientations of the atoms around the C=C double bond.

Synthesis of phenanthridine derivatives by microwave-mediated cyclization of o-furyl(allylamino)arenes.

A novel and efficient synthesis of phenanthridines and aza analogues is reported. The key step is a microwave-mediated intramolecular Diels-Alder cyclization of o-furyl(allylamino)arenes. In the presence of a catalytic amount of acid, the DA-adduct reacts further to give the dihydrophenanthridines, which easily can be oxidized to fully aromatic compounds by air in the presence of UV light or by DDQ.

When inhibitors do not inhibit: critical evaluation of rational drug design targeting chorismate mutase from Mycobacterium tuberculosis.

Tuberculosis (TB) is a devastating disease that claims millions of lives every year. Hindered access or non-compliance to medication, especially in developing countries, led to drug resistance, further aggravating the situation. With current standard therapies in use for over 50 years and only few new candidates in clinical trials, there is an urgent call for new TB drugs. A powerful tool for the development of new medication is structure-guided design, combined with virtual screening or docking studies. Here, we report the results of a drug-design project, which we based on a publication that claimed the structure-guided discovery of several promising and highly active inhibitors targeting the secreted chorismate mutase (*MtCM) from Mycobacterium tuberculosis. We set out to further improve on these compounds and synthesized a series of new derivatives. Thorough evaluation of these molecules in enzymatic assays revealed, to our dismay, that neither the claimed lead compounds, nor any of the synthesized derivatives, show any inhibitory effects against *MtCM.

Synthesis and antimycobacterial activities of non-purine analogs of 6-aryl-9-benzylpurines: Imidazopyridines, pyrrolopyridines, benzimidazoles, and indoles.

6,9-Disubstituted purines and 7-deazapurines are known to be powerful inhibitors of Mycobacterium tuberculosis (Mtb) in vitro. Analogs modified in the six-membered ring (imidazopyridines, pyrrolopyridines, benzimidazoles, and indoles) were synthesized and evaluated as Mtb inhibitors. The targets were prepared by functionalization on the bicyclic heterocycle or from simple pyridines. The results reported herein, indicate that the purine N-1, but not N-3, is important for binding to the unknown target. The 3-deazapurines appears to be slightly more active compared to the parent purines and slightly less active than their 7-deazapurine isomers. Removal of both the purine N-3 and N-7 did not result in further enhanced antimycobacterial activity but the toxicity towards mammalian cells was increased. Both 3-deaza and 3,7-dideazapurines exhibited a modest activity against of the Mtb isolate in the state of non-replicating persistence.

Antimicrobial and antineoplastic activities of agelasine analogs modified in the purine 2-position.

Agelasines are 7,9-dialkylpurinium salts found in marine sponges (Agelas sp.), which display a variety of antimicrobial and cytotoxic effects. We have synthesized simplified agelasine analogs modified in the purine 2-position and examined their antimicrobial and anticancer activities. The compounds were screened against Staphylococcus aureus, Escherichia coli, Mycobacterium tuberculosis, Candida krusei, and Candida albicans, protozoa causing tropical diseases (Plasmodium falciparum, Leishmania infantum, Trypanosoma cruzi, and Trypanosoma brucei), a panel of human cancer cell lines (U-937 GTB, RPMI 8226/s, CEM/s, and ACHN) as well as VERO and/or MRC-5 cells. The results indicate that the introduction of a methyl group in the purine 2-position is beneficial for antimycobacterial and antiprotozoal activity, and that amino groups may enhance activity against several cancer cell lines.

Synthesis of non-purine analogs of 6-aryl-9-benzylpurines, and their antimycobacterial activities. Compounds modified in the imidazole ring.

Purine analogs modified in the five-membered ring have been synthesized and examined for antibacterial activity against Mycobacterium tuberculosis H(37)Rv in vitro employing the microplate alamar blue assay (MABA). The 9-deaza analogs were only found to be weak inhibitors, but the 8-aza-, 7-deaza- and 8-aza-7-deazapurine analogs studied displayed excellent antimycobacterial activities, some even substantially better than the parent purine. In the 7-deazapurine series, MIC values between 0.08 and 0.35 µM, values comparable or better than the reference drugs used in the study (MIC rifampicin 0.09 µM, MIC isoniazid 0.28 µM and MIC PA-824 0.44 µM). The five most active compounds were also examined against a panel of drug-resistant Mtb strain, and they all retained their activity. The compounds examined were significantly less active against M. tuberculosis in a state of non-replicating persistence (NRP). MIC in the low-oxygen-recovery assay (LORA) ≥ 60 µM. The 7-deazapurines were somewhat more toxic towards mammalian cells, but still the selectivity indexes were excellent. The non-purine analogs exhibit a selective antimycobacterial activity. They were essentially inactive against Staphylococcus aureus and Escherichia coli.

Synthesis and biological evaluation of pyrimidine analogs of antimycobacterial purines.

Pyrimidine analogs of antimycobacterial 6-aryl-9-benzylpurines have been synthesized and screened for antibacterial activity against Mycobacterium tuberculosis H(37)Rv in vitro. Several active compounds were identified and the best results were observed for 5-formamidopyrimidines. These compounds generally displayed IC(90) values < or =1microg/mL, and they exhibited low toxicity towards mammalian cells. Imidazolylpyrimidines, which may be regarded as fleximer analogs of the parent purines, were also synthesized and one of them was found to be quite a potent inhibitor of M. tuberculosis (IC(90) 14microg/mL).

Synthesis of imidazole derivatives with antimycobacterial activity.

4-Substituted 1-(p-methoxybenzyl)imidazoles were designed and synthesized in order to mimic parts of the structure of highly potent antimycobacterial 6-aryl-9-(p-methoxybenzyl)purines. 4-Haloimidazoles were subjected to Pd-catalyzed cross-coupling in order to introduce a (hetero)aryl group, or they were converted to Grignard reagents and reacted with (hetero)arylaldehydes. Further transformations of the adducts gave a variety of potential antimycobacterials with different "spacers" between the imidazole and (hetero)aryl group. The adduct from furfural was rearranged to a cyclopentenone derivative when treated with methanol under acidic conditions. Several target compounds exhibited antimycobacterial activity in vitro (IC(90 )13 microg/mL for the best inhibitors), but they were not as active as the most potent purines and pyrimidines synthesized before.

Synthesis, structure, and antimycobacterial activity of 6-[1(3H)-isobenzofuranylidenemethyl]purines and analogs.

6-Benzofuryl-, styryl, benzyl, and furfurylpurines as well as 6-[1(3H)-isobenzofuranylidenemethyl]purines have been synthesized and their activities against Mycobacterium tuberculosis (Mtb) determined. Several compounds displayed profound antimycobacterial activity in combination with low toxicity towards mammalian cells. NMR and X-ray crystallography were employed to determine the detailed structures and the results were supported by quantum chemical calculations.

Synthesis and antimycobacterial activity of 5-formylaminopyrimidines; analogs of antibacterial purines.

Pyrimidine analogs of antimycobacterial purines have been synthesized and their biological activities evaluated. Several 5-formamidopyrimidines exhibited profound activity against Mycobacterium tuberculosis in vitro (IC(90)< or =1.5 microg/mL), and they were essentially inactive against other bacteria.

Screening of agelasine D and analogs for inhibitory activity against pathogenic protozoa; identification of hits for visceral leishmaniasis and Chagas disease.

There is an urgent need for novel and improved drugs against several tropical diseases caused by protozoa. The marine sponge (Agelas sp.) metabolite agelasine D, as well as other agelasine analogs and related structures were screened for inhibitory activity against Plasmodium falciparum, Leishmania infantum, Trypanosoma brucei and T. cruzi, as well as for toxicity against MRC-5 fibroblast cells. Many compounds displayed high general toxicity towards both the protozoa and MRC-5 cells. However, two compounds exhibited more selective inhibitory activity against L. infantum (IC(50) <0.5 microg/mL) while two others displayed IC(50) <1 microg/mL against T. cruzi in combination with relatively low toxicity against MRC-5 cells. According to criteria set up by the WHO Special Programme for Research & Training in Tropical Diseases (TDR), these compounds could be classified as hits for leishmaniasis and for Chagas disease, respectively. Identification of the hits as well as other SAR data from this initial screening will be valuable for design of more potent and selective potential drugs against these neglected tropical diseases.

Antifouling activity of the sponge metabolite agelasine D and synthesised analogs on Balanus improvisus.

This study reports a screening study for antifouling (AF) activity of the natural compound agelasine D isolated from marine sponges of the genus Agelas and 20 synthesised analogs of agelasines and agelasimines. Agelasine D, together with two of the analogs, ie AV1003A and AKB695, displayed a strong inhibitory effect on settlement of Balanus improvisus cypris larvae. Agelasine D had an EC50 value of 0.11 microM while the two analogs AV1033A and AKB695 had EC50 values of 0.23 and 0.3 microM, respectively. None of these three compounds affected larval mortality as was the case with several of the analogs tested. Moreover, the effect of AV1033A and AKB695 was reversible. When cyprids after 24 h exposure to the compounds were transferred to fresh seawater, the settlement frequency compared with the controls was completely recovered. The properties of the agelasine D analogs AV1003A and AKB695 make them highly attractive candidates as AF agents in future marine coatings.

Synthesis, antimicrobial and antineoplastic activities for agelasine and agelasimine analogs with a beta-cyclocitral derived substituent.

Agelasines and agelasimines are antimicrobial and cytotoxic purine derivatives isolated from marine sponges (Agelas sp.). We have synthesized structurally simplified analogs of these natural products starting from beta-cyclocitral. The novel compounds were found to be strong inhibitors of a wide variety of pathogenic microorganisms (incl. Mycobacterium tuberculosis) as well as cancer cell lines. The biological activities were generally in the same range as those previously found for the structurally more complex agelasines and agelasimines isolated in small amounts from natural sources. We also report for the first time that agelasine and agelasimine analogs inhibit growth of protozoa (Acanthamoeba castellanii and Acanthamoeba polyphaga). Acanthamoeba keratitis is an increasingly common and severe corneal infection, closely associated with contact lens wear.

Screening of terpenes and derivatives for antimycobacterial activity; identification of geranylgeraniol and geranylgeranyl acetate as potent inhibitors of Mycobacterium tuberculosis in vitro.

Several terpenes as well as synthetic analogues were screened for activity against Mycobacterium tuberculosis in vitro using the microplate alamar blue assay . Geranylgeraniol (MIC 1.56 microg/mL) and geranylgeranyl acetate (MIC 3.13 microg/mL) were identified as potent and selective inhibitors of M. tuberculosis.