Synthesis and antimicrobial evaluation of carbohydrate and polyhydroxylated non-carbohydrate fatty acid ester and ether derivatives

A series of fatty acid ester and ether derivatives have been chemically synthesised based on carbohydrate and non-carbohydrate polyhydroxylated scaffolds. The synthesised compounds, along with their corresponding fatty acid monoglyceride antimicrobials, were evaluated for antimicrobial activity against Staphylococcus aureus and Escherichia coli. Of the derivatives synthesised, several of the carbohydrate-based compounds have antimicrobial efficacy comparable with commercially available antimicrobials. The results suggest that the nature of the carbohydrate core plays a role in the efficacy of carbohydrate fatty acid derivatives as antimicrobials.     

Iridoid glucosides from Strychnos nux-vomica

From seeds of Strychnos nux-vomica three iridoids, 6'-O-acetylloganic acid, 4'-O-acetylloganic acid and 3'-O-acetylloganic acid were isolated together with two known iridoid glucosides, loganic acid and 7-O-acetylloganic acid. The structures of the compounds were established by ESI-MS and by 1D and 2D NMR spectroscopic methods.     

Inhibition of estrogen signaling through depletion of estrogen receptor alpha by ursolic acid and betulinic acid from Prunella vulgaris var. lilacina

Extracts of Prunella vulgaris have been shown to exert antiestrogenic effects. To identify the compounds responsible for these actions, we isolated the constituents of P. vulgaris and tested their individual antiestrogenic effects. Rosmarinic acid, caffeic acid, ursolic acid (UA), oleanolic acid, hyperoside, rutin and betulinic acid (BA) were isolated from the flower stalks of P. vulgaris var. lilacina Nakai (Labiatae). Among these constituents, UA and BA showed significant antiestrogenic effects, measured as a decrease in the mRNA level of GREB1, an estrogen-responsive protein; the effects of BA were stronger than those of UA. UA and BA were capable of suppressing estrogen response element (ERE)-dependent luciferase activity and expression of estrogen-responsive genes in response to exposure to estradiol, further supporting the suppressive role of these compounds in estrogen-induced signaling. However, neither UA nor BA was capable of suppressing estrogen signaling in cells ectopically overexpressing estrogen receptor α (ERα). Furthermore, both mRNA and protein levels of ERα were reduced by treatment with UA or BA, suggesting that UA and BA inhibit estrogen signaling by suppressing the expression of ERα. Interestingly, both compounds enhanced prostate-specific antigen promoter activity. Collectively, these findings demonstrate that UA and BA are responsible for the antiestrogenic effects of P. vulgaris and suggest their potential use as therapeutic agents against estrogen-dependent tumors.     

The chemotaxonomic and medicinal significance of phenolic acids in Arctopus and Alepidea (Apiaceae subfamily Saniculoideae)

The occurrence of (R)-3′-O-β-d-glucopyranosylrosmarinic acid, rosmarinic acid and caffeic acid in two important South African medicinal plants is reported for the first time. (R)-3′-O-β-d-Glucopyranosylrosmarinic acid and rosmarinic acid were isolated and identified in several samples from three species of the genus Arctopus L. (sieketroos) and three species of the genus Alepidea F. Delaroche (ikhathazo), both recently shown to be members of the subfamily Saniculoideae of the family Apiaceae. The compounds occur in high concentrations (up to 15.3 mg of (R)-3′-O-β-d-glucopyranosylrosmarinic acid per g dry wt) in roots of Arctopus. Our results provide a rationale for the traditional uses of these plants, as the identified compounds are all known for their antioxidant activity, with rosmarinic acid further contributing to a wide range of biological activities. Furthermore, we confirm the idea that (R)-3′-O-β-d-glucopyranosylrosmarinic acid is a useful chemotaxonomic marker for the subfamily Saniculoideae.     

Fatty acids as natural specific inhibitors of the proto-oncogenic protein Shp2

Src homology-2 domain-containing protein tyrosine phosphatase (Shp2), a novel proto-oncogenic protein, is an important target in cancer therapy research. Approximately 2000 plant extracts were screened to find its natural specific inhibitors, with the ethyl acetate (EtOAc) active extract of the root of Angelica dahurica showing considerable inhibitory effects (IC(50)=21.6 mg/L). Bioguided isolation of EtOAc extract led to 13 compounds, including 10 fatty acids and derivatives. All these compounds were isolated from the plant for the first time. The inhibitory effects of these compounds on the enzyme activities of Shp2, VH1-related human protein (VHR), and hematopoietic protein tyrosine phosphatase (HePTP) were investigated. 8Z,11Z-Feptadecadienoic acid (4), 14Z,17Z-tricosadienoic acid (5), caffeic acid (9), and 2-hydroxy-3-[(1-oxododecyl) oxy]propyl-β-d-glucopyranoside (11) showed considerable selective inhibition of Shp2 activity. After treatment of HepG2 cells with the compounds, only compound 5, a polyunsaturated fatty acid, strongly induced poly (ADP-ribose) polymerase (PARP) cleavage in a dose- and time-dependent manner and increased the activities of caspase-3, caspase-8, and caspase-9 at 100 μM. Compound 5 also inhibited colony formation of HepG2 cells in a dose-dependent manner. Thus, this study reported fatty acids as specific Shp2 inhibitors and provided the molecular basis of one active compound as novel potential anticancer drug.     

Mulberry anthracnose antagonists (iturins) produced by Bacillus amyloliquefaciens RC-2

Bacillus amyloliquefaciens strain RC-2 produced seven antifungal compounds (1-7) secreted into the culture filtrate. These compounds inhibited the development of mulberry anthracnose caused by the fungus, Colletotrichum dematium. Chemical structural analyses by NMR and FAB-MS revealed that all these compounds were iturins (cyclic peptides with the following sequence: L-Asn --> D-Tyr --> D-Asn --> L-Gln --> L-Pro --> D-Asn --> L-Ser --> D-beta-amino acid -->) and compounds 1-6 are identical to iturins A-2-A-7, respectively. Compound 7 (iturin A-8) is a new iturin, which has a -(CH(2))(10)CH(CH(3))CH(2)CH(3) group as a side chain in the beta-amino acid in the molecule.     

Response of scab-susceptible (McIntosh) and scab-resistant (Liberty) apple tissues to treatment with yeast extract and Venturia inaequalis

Yeast extract and Venturia inaequalis treated intact scab-susceptible (McIntosh) and scab-resistant (Liberty) apple plants and their organs were analyzed for phenolic metabolites. The major phenolic compounds found in both non-treated and treated leaves were phloridzin and phloretin which accumulated in mM concentrations. Untreated and treated stems and roots contained only phloridzin as the major detectable metabolite during the course of the investigation. The accumulation of phloridzin and phloretin was not developmentally regulated, since they were present in both young and old leaves, and also in the intercellular washings of both scab-susceptible and scab-resistant plants. The major metabolites of both McIntosh and Liberty fruits were cinnamyl glucose and p-coumarylquinic acid, which increased 20-fold in Liberty fruit upon yeast extract treatment. The same compounds increased only 2-fold in McIntosh fruits. Minor compounds in the fruits of both cultivars were p-coumaric acid, phloridzin and phloretin, the latter compound being present at the threshold of detection. Biphenyl and dibenzofuran compounds, the major metabolites of elicitor treated Liberty cell suspension cultures, could not be detected in the intact plants. These results indicate differential response of plant organs and cell suspension cultures to elicitor treatment or pathogen invasion.     

Sterculic Acid and Its Analogues Are Potent Inhibitors of Toxoplasma gondii

Toxoplasmosis is a serious disease caused by Toxoplasma gondii, one of the most widespread parasites in the world. Lipid metabolism is important in the intracellular stage of T. gondii. Stearoyl-CoA desaturase (SCD), a key enzyme for the synthesis of unsaturated fatty acid is predicted to exist in T. gondii. Sterculic acid has been shown to specifically inhibit SCD activity. Here, we examined whether sterculic acid and its methyl ester analogues exhibit anti-T. gondii effects in vitro. T. gondii-infected Vero cells were disintegrated at 36 hr because of the propagation and egress of intracellular tachyzoites. All test compounds inhibited tachyzoite propagation and egress, reducing the number of ruptured Vero cells by the parasites. Sterculic acid and the methyl esters also inhibited replication of intracellular tachyzoites in HFF cells. Among the test compounds, sterculic acid showed the most potent activity against T. gondii, with an EC₅₀ value of 36.2 μM, compared with EC₅₀ values of 248-428 μM for the methyl esters. Our study demonstrated that sterculic acid and its analogues are effective in inhibition of T. gondii growth in vitro, suggesting that these compounds or analogues targeting SCD could be effective agents for the treatment of toxoplasmosis.     

Biotransformation of betulinic and betulonic acids by fungi

Betulinic acid (1), a triterpenoid found in many plant species, has attracted attention due to its important pharmacological properties, such as anti-cancer and anti-HIV activities. The closely related, betulonic acid (2) also has similar properties. In order to obtain derivatives potentially useful for detailed pharmacological studies, both compounds were submitted to incubations with selected microorganisms. In this work, both were individually metabolized by the fungi Arthrobotrys, Chaetophoma and Dematium, isolated from the bark of Platanus orientalis as well as with Colletotrichum, obtained from corn leaves; such fungal transformations are quite rare in the scientific literature. Biotransformations with Arthrobotrys converted betulonic acid (2) into 3-oxo-7beta-hydroxylup-20(29)-en-28-oic acid (3), 3-oxo-7beta,15alpha-dihydroxylup-20(29)-en-28-oic acid (4) and 3-oxo-7beta,30-dihydroxylup-20(29)-en-28-oic acid (5); Colletotrichum converted betulinic acid (1) into 3-oxo-15alpha-hydroxylup-20(29)-en-28-oic (6) acid whereas betulonic acid (2) was converted into the same product and 3-oxo-7beta,15alpha-dihydroxylup-20(29)-en-28-oic acid (4); Chaetophoma converted betulonic acid (2) into 3-oxo-25-hydroxylup-20(29)-en-28-oic acid (7) and both Chaetophoma and Dematium converted betulinic acid (1) into betulonic acid (2). Those fungi, therefore, are useful for mild, selective oxidations of lupane substrates at positions C-3, C-7, C-15, C-25 and C-30.     

Synthesis and cytotoxic activity of the N-acetylglucosamine-bearing triterpenoid saponins

Fourteen ursolic acid and oleanolic acid saponins with N-acetyl-β-d-glucosamine, and (1→4)-linked and (1→6)-linked N-acetyl-β-d-glucosamine oligosaccharide residues were synthesized in a convergent manner. The structures of all compounds were confirmed by ¹H NMR and ¹³C NMR spectroscopy and by mass spectrometry, and their cytotoxic activities were assayed in three cancer cell lines. Only oleanolic acid-3-yl β-d-GluNAc showed significant cytotoxicity against HL-60 and BGC-823.     

Non-natural cinnamic acid derivatives as substrates of cinnamate 4-hydroxylase

Cinnamate 4-hydroxylase (C4H), a monooxygenase in the plant phenylpropanoid pathway, was assayed for its ability to hydroxylate 29 substrate analogues. Nine of the tested analogues with various aromatic side chains, including 3-coumaric acid, were metabolized by C4H. Seven products from these reactive analogues were characterized using LC/MS, 1H NMR and 13C NMR spectroscopic analysis. For example, caffeic acid was the product of 3-coumaric acid. The products 4-hydroxy-2-chlorocinnamic acid and 4-hydroxy-2-ethoxycinnamic acid are novel compounds that have not been previously reported. The kinetic parameters of C4H towards these analogues were determined.     

Chemotaxonomic evaluation of Turkish species of Salvia: Fatty acid compositions of seed oils

Fatty acid composition of nine species of Salvia, naturally growing in Turkey was determined: Salvia syriaca, Salvia potentillifolia, Salvia candidissima ssp. occidentalis, Salvia macrochlamys, Salvia poculata, Salvia tomentosa, Salvia recognita, Salvia virgata and Salvia ceratophylla. The main compounds were found to be linoleic acid (18:2; 24.3–69.2%), linolenic acid (18:3; 0.6–40.8%), oleic acid (18:1; 8.3–31.0%), palmitic acid (16:0; 3.8–21.0%) and stearic acid (18:0; 1.8–5.2%). Fatty acid composition of Salvia seed oils could be used as a chemotaxonomical marker.     

Ellagic acid derivatives and cytotoxic cucurbitacins from Elaeocarpus mastersii

Bioassay-guided investigation of the bark of Elaeocarpus mastersii using KB (human oral epidermoid carcinoma) cells as a monitor led to the isolation of two cucurbitacins, cucurbitacin D and cucurbitacin F as cytotoxic principles, together with two ellagic acid derivatives, 4'-O-methylellagic acid 3-(2",3"-di-O-acetyl)-alpha-L-rhamnoside (1) and 4,4'-O-dimethylellagic acid 3-(2",3"-di-O-acetyl)-alpha-L-rhamnoside (2). These compounds were evaluated against a panel of human tumor cell lines.     

Racemic and optically active 2-methoxy-4-oxatetradecanoic acids: novel synthetic fatty acids with selective antifungal properties

The unprecedented (+/-)-2-methoxy-4-oxatetradecanoic acid and the optically pure (S)-2-methoxy-4-oxatetradecanoic acid were synthesized in six steps and in 11-14% overall yields starting with either 1,2-O-isopropylidene-rac-glycerol or 1,2-O-isopropylidene-(S)-glycerol. The key step in the synthesis was the selective monosilylation of a dibutylstannylene intermediate. The title compounds displayed selective fungitoxicity in the range of 0.08-0.22 mM against Cryptococcus neoformans ATCC 66031 and Aspergillus niger ATCC 16404, but no significant activity against C. albicans ATCC 14053 and ATCC 60193 (>2.6 mM). Albeit being good substrates for N-myristoyltransferases (NMTs), the racemic and the S-enantiomer of the oxygenated 2-methoxylated compounds showed no significant difference in antifungal activity. This finding suggests an alternative mechanism of fungitoxicity other than NMT inhibition.     

Anti-babesial ellagic acid rhamnosides from the bark of Elaeocarpus parvifolius

Bioassay-guided investigation of the bark of Elaeocarpus parvifolius led to the isolation of three new ellagic acid derivatives, 4-O-methylellagic acid 3'-alpha-rhamnoside (2), 4-O-methylellagic acid 3'-(3'-O-acetyl)-alpha-rhamnoside (3), and 4-O-methylellagic acid 3'-(4'-O-acetyl)-alpha-rhamnoside (4) in addition to the known ellagic acid derivative, 4-O-methylellagic acid 3'-(2',3'-di-O-acetyl)-alpha-rhamnoside (1). Their structures were elucidated on the basis of analysis of 1H NMR, 13C NMR, HMQC, HMBC and MS spectroscopic data. Compounds 1-4 were evaluated for their growth-inhibitory effect on Babesia gibsoni in vitro. Compounds 2 and 4 showed very weak activity, while compounds 1 and 3 showed moderate activity, with IC50 values of 28.5 and 52.1 microg/ml, respectively.     

Aliphatic acid amides of the fruits of Zanthoxylum piperitum

Six aliphatic acid amides (1-6) were isolated from the pericarp of Zanthoxylum piperitum fruits. MS and NMR spectroscopic investigation revealed that these compounds have a ketone and/or hydroxyl group(s) in the unsaturated aliphatic acid moiety of the structure of the amides. Combinations 3-4 and 5-6 are stereoisomers in terms of the relative configurations of their two asymmetric carbons.     

Cytotoxic naphthoquinones and plumbagic acid glucosides from Plumbago zeylanica

Two plumbagic acid glucosides, 3'-O-beta-glucopyranosyl plumbagic acid and 3'-O-beta-glucopyranosyl plumbagic acid methylester along with five naphthoquinones (plumbagin, chitranone, maritinone, elliptinone and isoshinanolone), and five coumarins (seselin, 5-methoxyseselin, suberosin, xanthyletin and xanthoxyletin) were isolated from the roots of Plumbago zeylanica. All coumarins were not previously found in this plant. Cytotoxicity of these compounds to various tumor cells lines was evaluated, and plumbagin significantly suppressed growth of Raji, Calu-1, HeLa, and Wish tumor cell lines.     

Constituents of Chrysothamnus viscidiflorus

A phytochemical investigation of the aerial parts of Chrysothamnus viscidiflorus var. viscidiflorus afforded three new [chrysothol (1), 2 and 4] and seven known compounds, including five sesquiterpenes, two cinnamic acid derivatives, two ketoalcohol derivatives and one coumarin glucoside. The structures of two previously reported compounds, 1b and 1c, were revised on the basis of chemical reaction. Structures of the compounds were determined by extensive NMR studies, including DEPT, COSY, NOE, HMQC, HMBC and X-ray analysis. The unpublished X-ray data of the known compounds 6 and 7 are reported. Compounds chrysothol (1), and 8-10 showed anti-cancer activity against human breast cancer cells.     

alpha-Glucosidase inhibitory constituents from stem bark of Terminalia superba (Combretaceae)

The CH(2)Cl(2)/CH(3)OH (1/1) extract of the dried stem bark of Terminalia superba afforded two compounds, (7S,8R,7'R,8'S)-4'-hydroxy-4-methoxy-7,7'-epoxylignan and meso-(rel 7S,8R,7'R,8'S)-4,4'-dimethoxy-7,7'-epoxylignan along with 11 known compounds. The structures of the compounds were established by analysing the spectroscopic data and also comparing it with the data of previously known analogues. All the isolated compounds were evaluated for their glycosidase inhibition activities. Gallic acid and methyl gallate showed significant alpha-glucosidase inhibition activity.     

Microbial oligosaccharides differentially induce volatiles and signalling components in Medicago truncatula

Plants perceive biotic stimuli by recognising a multitude of different signalling compounds originating from the interacting organisms. Some of these substances represent pathogen-associated molecular patterns, which act as general elicitors of defence reactions. But also beneficial microorganisms like rhizobia take advantage of compounds structurally related to certain elicitors, i.e. Nod-factors, to communicate their presence to the host plant. In a bioassay-based study we aimed to determine to what extent distinct oligosaccharidic signals are able to elicit overlapping responses, including the emission of volatile organic compounds which is mainly considered a typical mode of inducible indirect defence against herbivores. The model legume Medicago truncatula Gaertn. was challenged with pathogen elicitors (beta-(1,3)-beta-(1,6)-glucans and N,N',N',N'-tetraacetylchitotetraose) and two Nod-factors, with one of them being able to induce a nodulation response in M. truncatula. Single oligosaccharidic elicitors caused the emission of volatile organic compounds, mainly sesquiterpenoids. The volatile blends detected were quite characteristic for the applied compounds, which could be pinpointed by multivariate statistical methods. As potential mediators of this response, the levels of jasmonic acid and salicylic acid were determined. Strikingly, neither of these phytohormones exhibited changing levels correlating with enhanced volatile emission. All stimuli tested caused an overproduction of reactive oxygen species, whereas nitric oxide accumulation was only effected by elicitors that were equally able to induce volatile emission. Thus, all signalling compounds tested elicited distinct reaction patterns. However, similarities between defence reactions induced by herbivory and pathogen-derived elicitors could be ascertained; but also Nod-factors were able to trigger defence-related reactions.