Structure and stereochemistry of psorospermin and related cytotoxic dihydrofuranoxanthones from Psorospermum febrifugum

Design, synthesis and anticancer activity of novel dihydrobenzofuro[4,5-b][1,8]naphthyridin-6-one derivatives

On the basis of the chemical structures of psorospermin with a xanthone template and acronycine derivatives with an acridone template, rac-1 and rac-2 constructed on an 1,2-dihydrobenzofuro[4,5-b][1,8]naphthyridin-6(11H)-one scaffold were designed and synthesized as potential anticancer agents. Their anticancer activities were evaluated against five human cancer cell lines. Rac-2 showed similar anticancer activity to doxorubicin and rac-1 exhibited even higher anticancer activity against LNCaP (IC(50)=0.14 μM), DU145 (IC(50)=0.15 μM), PC3 (IC(50)=0.30 μM) and MCF-7 (IC(50)=0.26 μM) cancer lines than doxorubicin and rac-2. Also, rac-1 revealed very potent anticancer activity (IC(50)=0.15 μM) against MCF-7/ADR cell (doxorubicin-resistant breast cancer cell) lines and induced G2/M phase arrest of the cell cycle in MCF-7/ADR cells.

Ionic liquid promoted and mediated green preparation of arylbispyranylmethane and pyran derivatives and their hybrid with a pyrimidine nucleoside

The utilisation of an ionic liquid-[bmim][BF4] as both reaction medium and promoter for the reaction between aldehyde and 4-hydroxy-6-methylpyran-2-one is described. Without any added catalyst, this reaction was realised efficiently to give arylbispyranylmethane derivatives in high yields. Alternatively, when this reaction was carried out in the presence of acetic anhydride, fused pyran derivatives were obtained. These two novel procedures have advantages such as an environmentally benign nature, high efficiency, simple operation process and mild reaction conditions. As an application, these procedures were used in the preparation of novel 5-substituted pyrimidine nucleoside derivatives with potential antiviral activities.

Antitumor psoropermum xanthones and sarcomelicope acridones: privileged structures implied in DNA alkylation

Fused isopropylfuran and dimethylpyran units are privileged structures present in numerous bioactive natural products exemplified, in the field of anticancer drugs, by the furanoxanthone psorospermin and the pyranoacridone acronycine. Psorospermin binds to the N-7 position of the guanine units in the presence of topoisomerase II. In contrast, acronycine derivatives such as cis-1,2-diacetoxy-1,2-dihydrobenzo[b]acronycine alkylate the 2-amino group of DNA guanine residues in the minor groove. Hybrid compounds associating the acridone or benzo[b]acridone chromophore of acronycine derivatives and the epoxyfuran alkylating unit present in psorospermin also display very potent antiproliferative activities, alkylating DNA guanine units at position N-7 in the major groove, as natural xanthones belonging to the psorospermin series.

Cytotoxic xanthones from Psorospermum molluscum from the Madagascar rain forest

Two new cytotoxic xanthones were isolated from extracts of the Madagascar rain forest plant Psorospermum cf. molluscum using bioassay-guided fractionation with the Escherichia coli SOS chromotest. The structures of the new dihydrofuranoxanthones, designated 3',4'-deoxy-4'-chloropsoroxanthin-(3',5'-diol) ( 1) and psoroxanthin ( 4), were determined on the basis of 2D-NMR, MS, and UV spectroscopic data and are structurally related to the psorospermins, a known class of plant antitumor agents. A new hydroxyprenylated xanthone ( 5) is also described. Xanthones 1 and 4 showed selective in vitro cytotoxicity against ABAE cells (bovine endothelial cell line).

Stereoselective Syntheses of the 2-Isopropenyl-2,3-dihydrobenzofuran Nucleus: Potential Chiral Building Blocks for the Syntheses of Tremetone, Hydroxytremetone, and Rotenone

The first enantioselective synthesis of the 2-isopropenyl-2,3-dihydrobenzofuran skeleton of tremetone and hydroxytremetone from (E)-4-(2-hydroxyphenyl)-2-methyl-2-butenyl methyl carbonate and (E)-4-(2,6-dihydroxyphenyl)-2-methyl-2-butenyl methyl carbonate, respectively, is described. The key step is a catalytic palladium-mediated reaction in the presence of the chiral Trost ligand.

Synthesis and Cytotoxic Activity of Benzo[a]pyrano[3,2-h] and [2,3-i]xanthone Analogues of Psorospermine, Acronycine, and Benzo[a]acronycine

Condensation of 2-hydroxy-1-naphthalenecarboxylic acid with phloroglucinol afforded 9,11-dihydroxy-12H-benzo[a]xanthen-12-one (6). Construction of an additional dimethylpyran ring onto this skeleton, by alkylation with 3-chloro-3-methyl-1-butyne followed by Claisen rearrangement, gave access to 6-hydroxy-3,3-dimethyl-3H,7H-benzo[a]pyrano[3,2-h]xanthen-7-one (12) and 5-hydroxy-2,2-dimethyl-2H,6H-benzo[a]pyrano[2,3-i]xanthen-6-one (13), which were methylated into 6-methoxy-3,3-dimethyl-3H,7H-benzo[a]pyrano[3,2-h]xanthen-7-one (14) and 5-methoxy-2,2-dimethyl-2H,6H-benzo[a]pyrano[2,3-i]xanthen-6-one (15), respectively. Osmium tetroxide oxidation of 14 and 15 gave the corresponding (+/-)-cis-diols 16 and 17, which afforded the corresponding esters 18-21 upon acylation. Similarly, condensation of 2-hydroxy-1-naphthalenecarboxylic acid with 3,5-dimethoxyaniline gave 11-amino-9-methoxy-12H-benzo[a]xanthen-12-one (23) which was converted into 11-amino-9-hydroxy-12H-benzo[a]xanthen-12-one (24) upon treatment with hydrogen bromide in acetic acid. Alkylation with 3-chloro-3-methyl-1-butyne followed by Claisen rearrangement afforded 6-amino-3,3-dimethyl-3H,7H-benzo[a]pyrano[3,2-h]xanthen-7-one (25) and 5-amino-2,2-dimethyl-2H,6H-benzo[a]pyrano[2,3-i]xanthen-6-one (26). The new benzopyranoxanthone derivatives only displayed marginal antiproliferative activity when tested against L1210 and KB-3-1 cell lines. The only compounds found significantly active against L1210 cell line, 16 and 20, belong to the benzo[a]pyrano[3,2-h]xanthen-7-one series, which possess a pyran ring fused angularly onto the xanthone basic core.

Algicidal and antifungal compounds from the roots of Ruta graveolens and synthesis of their analogs

Bioassay-guided fractionation of the ethyl acetate extract of Ruta graveolens roots yielded rutacridone epoxide with potent selective algicidal activity towards the 2-methyl-isoborneol (MIB)-producing blue-green alga Oscillatoria perornata, with relatively little effect on the green alga Selenastrum capricornutum. The diol-analog of rutacridone epoxide, gravacridondiol, which was also present in the same extract, had significantly less activity towards O. perornata. Rutacridone epoxide also showed significantly higher activity than commercial fungicides captan and benomyl in our micro-bioassay against the agriculturally important pathogenic fungi Colletotrichum fragariae, C. gloeosporioides, C. acutatum, and Botrytis cineara and Fusarium oxysporium. Rutacridone epoxide is reported as a direct-acting mutagen, precluding its use as an agrochemical. In order to understand the structure-activity relationships and to develop new potential biocides without toxicity and mutagenicity, some analogs containing the (2-methyloxiranyl)-dihydrobenzofuran moiety with an epoxide were synthesized and tested. None of the synthetic analogs showed comparable activities to rutacridone epoxide. The absolute stereochemistry of rutacridone was determined to be 2'(R) and that of rutacridone epoxide to be 2'(R), 3'(R) by CD and NMR analysis.

Design, synthesis, and evaluation of psorospermin/quinobenzoxazine hybrids as structurally novel antitumor agents

Topoisomerase II, an enzyme that catalyzes changes in the topology of DNA, plays several key roles in DNA metabolism and chromosome structure, and it is the primary cytotoxic target for a number of clinically important DNA intercalating agents such as doxorubicin. It seems likely that if these intercalating topoisomerase II poisons are structurally modified to also be DNA alkylating agents, they will have increased dwell time on the topoisomerase II-DNA complex and increased potency and selectivity for cancer cells. On the basis of insights into the mechanisms of action of psorospermin and the quinobenzoxazine A-62176 and molecular modeling studies of these compounds with duplex DNA, we have designed and synthesized a series of novel hybrid DNA-interactive compounds that alkylate DNA most efficiently at sequences directed by topoisomerase II. The epoxydihydrofuran ring of psorospermin was used as a DNA alkylating moiety, and this was fused to the pyridobenzophenoxazine ring of A-62176. The chlorohydrin ring opened form of the epoxide was also prepared and tested. These hybrid compounds showed enhanced DNA alkylating activity in the presence of topoisomerase II, exhibited significant activity against all the cancer cells tested at submicromolar concentrations, and were more potent than both parent compounds. However, the biochemical assays indicated that they lost some of the topoisomerase II and Mg(2+) dependency for reaction with DNA that is associated with psorospermin and A-62176, respectively.

Benzophenone synthase and chalcone synthase from Hypericum androsaemum cell cultures: cDNA cloning, functional expression, and site-directed mutagenesis of two polyketide synthases

Benzophenone derivatives, such as polyprenylated benzoylphloroglucinols and xanthones, are biologically active secondary metabolites. The formation of their C13 skeleton is catalyzed by benzophenone synthase (BPS; EC 2.3.1.151) that has been cloned from cell cultures of Hypericum androsaemum. BPS is a novel member of the superfamily of plant polyketide synthases (PKSs), also termed type III PKSs, with 53-63% amino acid sequence identity. Heterologously expressed BPS was a homodimer with a subunit molecular mass of 42.8 kDa. Its preferred starter substrate was benzoyl-CoA that was stepwise condensed with three malonyl-CoAs to give 2,4,6-trihydroxybenzophenone. BPS did not accept activated cinnamic acids as starter molecules. In contrast, recombinant chalcone synthase (CHS; EC 2.3.1.74) from the same cell cultures preferentially used 4-coumaroyl-CoA and also converted CoA esters of benzoic acids. The enzyme shared 60.1% amino acid sequence identity with BPS. In a phylogenetic tree, the two PKSs occurred in different clusters. One cluster was formed by CHSs including the one from H. androsaemum. BPS grouped together with the PKSs that functionally differ from CHS. Site-directed mutagenesis of amino acids shaping the initiation/elongation cavity of CHS yielded a triple mutant (L263M/F265Y/S338G) that preferred benzoyl-CoA over 4-coumaroyl-CoA.

Synthesis, cytotoxic activity, NMR study and stereochemical effects of some new pyrano[3,2-b]thioxanthen-6-ones and pyrano[2,3-c]thioxanthen-7-ones

Some new substituted pyrano[3,2-b]thioxanthen-6-ones and pyrano[2,3-c]thioxanthen-7-ones were prepared and their cytotoxic activity was evaluated using acronycine as the reference compound. The conformation of the molecules was also investigated in an effort to correlate this parameter with the biological activity.

Synthesis and cytotoxic activity of benzopyranoxanthone analogues of benz

Condensation of 3-hydroxy-2-naphthalenecarboxylic acid with phloroglucinol afforded 1,3-dihydroxy-12H-benzo[b]xanthen-12-one. Construction of an additional dimethylpyran ring onto this skeleton, by alkylation with 3-chloro-3-methyl-1-butyne followed by Claisen rearrangement, gave access to a series of benzo[b]pyrano[2,3-i]xanthen-6-ones and benzo[b]pyrano[3,2-h]xanthen-7-ones related to psorospermine and benzo[b]acronycine. In contrast with what is observed in the pyridoacridone and benzopyridoacridone series, the linear benzo[b]-pyrano[2,3-i]xanthen-6-one derivatives were more potent than their angular benzo[b]pyrano[3,2-h]xanthen-7-one isomers. cis-3,4-Diacetoxy-5-methoxy-2,2-dimethyl-3,4-dihydro-2H,6H-benzo[b]pyrano[2,3-i]xanthen-6-one, the most active among the new compounds, was more potent than acronycine in inhibiting the proliferation of L1210 murine leukemia cells.

2,2-Dimethyl-2H-anthra[2,3-b]pyran-6,11-diones: a new class of cytotoxic compounds

The synthesis and cytotoxic activity of some new 2,2-dimethyl-2H-anthra[2,3-b]pyran-6,11-diones is described. Certain compounds possess interesting activity against murine leukemia L-1210 cells. Relationships between the biological activity and the pyrano-ring conformations are discussed.

Tetraoxygenated naturally occurring xanthones

This review, with 350 references, gives information on the chemical study of 234 naturally occurring tetraoxygenated xanthones in 12 families, 53 genus and 182 species of higher plants, and two which are described as fungal and lichen metabolites. The value of these groups of substances in connection with pharmacological activity and therapeutic use of some species is described. The structural formulas of 135 isolated compounds, and their distribution, are also given.

Hedamycin intercalates the DNA helix and, through carbohydrate-mediated recognition in the minor groove, directs N7-alkylation of guanine in the major groove in a sequence-specific manner

BACKGROUND

The pluramycins are a class of antitumor antibiotics that exert their biological activity through interaction with DNA. Recent studies with the analog altromycin B have determined that these agents intercalate into the DNA molecule, position carbohydrate substituents into both major and minor grooves, and alkylate the DNA molecule by epoxide-mediated electrophilic attack on N7 of guanine located to the 3' side of the drug molecule. Alkylation is sequence dependent and appears to be modulated by glycoside substituents attached at the corners of a planar chromophore. The altromycin B-like analogs preferentially alkylate 5'AG sequences; hedamycin-like analogs prefer 5'TG and 5'CG sequences. Although the mechanism of guanine modification by altromycin B has been extensively studied, the mechanism of action of hedamycin has not been previously determined.

RESULTS

Using high-field NMR, we have shown that hedamycin stacks to the 5' side of the guanine nucleotide at the site of intercalation in a DNA decamer, positioning both aminosaccharides into the minor groove to direct alkylation by the epoxide moiety on N7 of guanine. The C10 linked N,N-dimethylvancosamine sugar moiety interacts to the 5' side of the intercalation site, while the C8 linked anglosamine moiety interacts to the 3' side. The binding interactions of the two aminosugars steer the C2 double epoxide located in the major groove into the proximity of N7 of guanine. Unexpectedly, it is not the first epoxide that undergoes electrophilic addition to N7 of guanine, which would correspond to altromycin B, but the second, terminal epoxide.

CONCLUSIONS

We have used two-dimensional NMR to elucidate the sequence-selective recognition of DNA by hedamycin and the mechanism of covalent modification of guanine by this antibiotic. Characterization of the intermolecular interactions between both hedamycin and altromycin B and their targeted DNA sequences has yielded a better understanding of the reasons for variations in sequence selectivity and alkylation reactivity among the pluramycin compounds.

Gamma-pyrone compounds as potential anti-cancer drugs

The gamma-pyrones, artomunoxanthotrione epoxide, cyclocommunol, cyclomulberrin, and cyclocommunin exhibited potent inhibition of human PLC/PRF/5 and KB cells in-vitro. Dihydroisocycloartomunin showed significant and potent inhibition of human PLC/PRF/5 and KB cells in-vitro, respectively. Cyclomorusin, dihydrocycloartomunin and artomunoxanthone showed significant inhibition of KB cells in-vitro. Based on the above finding and the reported antileukaemic activity of xanthone psorospermin, a series of natural gamma-pyrones was prepared and the inhibition of human PLC/PRF/5 and KB cells in-vitro was measured. Structure-activity analysis indicated the epoxide group substituted at 3-hydroxyl and 2,6-; 3,6-; and 3,5-dihydroxyl xanthone enhanced the anti-tumour activity. The epoxide group substituted at the 6-hydroxyl group of 1,6-dihydroxyxanthone did not show anti-tumour activity.