Terpenoids from Myrrh and Their Cytotoxic Activity against HeLa Cells.

The oleo-gum resin of Commiphora myrrha (Nees) Engl. has a long history of medicinal use, although many of its constituents are still unknown. In the present investigation, 34 secondary metabolites were isolated from myrrh resin using different chromatographic techniques (silica flash chromatography, CPC, and preparative HPLC) and their structures were elucidated with NMR spectroscopy, HRESIMS, CD spectroscopy, and ECD calculations. Among the isolated substances are seven sesquiterpenes (1-7), one disesquiterpene (8), and two triterpenes (23, 24), which were hitherto unknown, and numerous substances are described here for the first time for C. myrrha or the genus Commiphora. Furthermore, the effects of selected terpenes on cervix cancer cells (HeLa) were studied in an MTT-based in vitro assay. Three triterpenes were observed to be the most toxic with moderate IC50 values of 60.3 (29), 74.5 (33), and 78.9 µM (26). Due to the different activity of the structurally similar triterpenoids, the impact of different structural elements on the cytotoxic effect could be discussed and linked to the presence of a 1,2,3-trihydroxy substructure in the A ring. The influence on TNF-α dependent expression of the intercellular adhesion molecule 1 (ICAM-1) in human microvascular endothelial cells (HMEC-1) was also tested for 4-6, 9-11, 17, 18, 20, and 27 in vitro, but revealed less than 20% ICAM-1 reduction and, therefore, no significant anti-inflammatory activity.

Homoadamantane and Adamantane Acylphloroglucinols from Hypericum hirsutum.

1H NMR-guided fractionation of the petroleum ether extract of the aerial parts from Hypericum hirsutum yielded to the isolation of 19 polyprenylated polycyclic acylphloroglucinols. Structure elucidation based on 1D and 2D NMR spectroscopy together with high-resolution electrospray ionization mass spectroscopy revealed 14 acylphloroglucinols with a homoadamantane scaffold (1: -14: ), while 5 further compounds showed an adamantane skeleton (15: -19: ). Except for hookerione C (15: ), all isolated metabolites are hitherto unknown. While structurally-related metabolites have been isolated from other Hypericum species, it is the first report of admantan and homoadamantan type acylphloroglucinols in section Taeniocarpium Jaub. & Spach (Hypericaceae). The isolated compounds have been tested in a crystal violet-based in vitro assay on their properties to reduce the proliferation of human microvascular endothelial cells compared to hyperforin as the positive control. They showed a moderate reduction of proliferation with IC50 values in the range ~ 3 - 22 µM, with the homoadamantane-based compounds 2: and 4: being the most active. In addition, inhibition of the TNF-α-induced ICAM-1 expression was determined for 1:  - 5, 7,: and 10:  - 12: . Substances 3: and 12: reduced the ICAM-1 expression significantly (to 46.7% of control for 3: , 62.3% for 12,: at 50 µM).

Prenylated Acylphloroglucinols from Hypericum jovis with Anti-inflammatory Potential.

Thirteen prenylated acylphloroglucinols (1: -13: ), including 2 previously undescribed compounds (1: ) and (2: ), were isolated from Hypericum jovis. Their structures were elucidated by high-field NMR spectroscopy. The isolated prenylated acylphloroglucinols were evaluated for their anti-inflammatory effects in vitro through the reduction of the intercellular adhesion molecule 1 expression induced by TNF-α in the human microvascular endothelial cells 1 cell line. Compounds 3, 5, 6, 8,: and 12: significantly reduced intercellular adhesion molecule 1 expression in a concentration-dependent manner with IC50 values of 16.9, 34.4, 4.0, 3.2, and 7.7 µM, respectively. In addition, compound 12: showed notable inhibitory activity on the formation of cyclooxygenase-1- and 12-lipoxygenase-derived inflammatory mediators in an ex vivo cyclooxygenase-lipoxygenase assay. Eleven further constituents were isolated (14: -24: ), including the rare quercetin 3-O-(2-O-acetyl)-arabinofuranoside (18: ).

In Vitro Metabolism of Six C-Glycosidic Flavonoids from Passiflora incarnata L.

Several medical plants, such as Passiflora incarnata L., contain C-glycosylated flavonoids, which may contribute to their efficacy. Information regarding the bioavailability and metabolism of these compounds is essential, but not sufficiently available. Therefore, the metabolism of the C-glycosylated flavones orientin, isoorientin, schaftoside, isoschaftoside, vitexin, and isovitexin was investigated using the Caco-2 cell line as an in vitro intestinal and epithelial metabolism model. Isovitexin, orientin, and isoorientin showed broad ranges of phase I and II metabolites containing hydroxylated, methoxylated, and sulfated compounds, whereas schaftoside, isoschaftoside, and vitexin underwent poor metabolism. All metabolites were identified via UHPLC-MS or UHPLC-MS/MS using compound libraries containing all conceivable metabolites. Some structures were confirmed via UHPLC-MS experiments with reference compounds after a cleavage reaction using glucuronidase and sulfatase. Of particular interest is the observed cleavage of the C-C bonds between sugar and aglycone residues in isovitexin, orientin, and isoorientin, resulting in unexpected glucuronidated or sulfated luteolin and apigenin derivatives. These findings indicate that C-glycosidic flavones can be highly metabolized in the intestine. In particular, flavonoids with ortho-dihydroxy groups showed sulfated metabolites. The identified glucuronidated or sulfated aglycones demonstrate that enzymes expressed by Caco-2 cells are able to potentially cleave C-C bonds in vitro.

In Vitro Liver Metabolism of Six Flavonoid C-Glycosides.

Several medical plants belonging to the genera Passiflora, Viola, and Crataegus accumulate flavonoid C-glycosides, which likely contribute to their efficacy. Information regarding their phase I and II metabolism in the liver are lacking. Thus, in vitro liver metabolism of orientin, isoorientin, schaftoside, isoschaftoside, vitexin, and isovitexin, all of which accumulated in Passiflora incarnata L., was investigated by incubation in subcellular systems with human liver microsomes and human liver S9 fraction. All metabolite profiles were comprehensively characterized using HPLC-DAD and UHPLC-MS/MS analysis. Mono-glycosylic flavones of the luteolin-type orientin and isoorientin showed a broad range of mono-glucuronidated and mono-sulfated metabolites, whereas for mono-glycosylic flavones of the apigenin-type vitexin and isovitexin, only mono-glucuronidates could be detected. For di-glycosylic flavones of the apigenin-type schaftosid and isoschaftosid, no phase I or II metabolites were identified. The main metabolite of isoorientin was isolated using solid-phase extraction and prep. HPLC-DAD and identified as isoorientin-3'-O-α-glucuronide by NMR analysis. A second isolated glucuronide was assigned as isoorientin 4'-O-α-glucuronide. These findings indicate that vitexin and isovitexin are metabolized preferentially by uridine 5'-diphospho glucuronosyltransferases (UGTs) in the liver. As only orientin and isoorientin showed mono-sulfated and mono-glucuronidated metabolites, the dihydroxy group in 3',4'-position may be essential for additional sulfation by sulfotransferases (SULTs) in the liver. The diglycosylic flavones schaftoside and isoschaftoside are likely not accepted as substrates of the used liver enzymes under the chosen conditions.

New antifungal ent-labdane diterpenes against Candida glabrata produced by microbial transformation of ent-polyalthic acid.

Candida glabrata, the most common non-albicans Candida species and one of the primary causes of candidemia, exhibits decreased susceptibility to azoles and more recently to echinocandins. Polyalthic acid 1, a furan diterpene, has been shown promising biological potential and in this study ent-polyalthic acid derivatives with antifungal activity against Candida glabrata were produced by microbial transformation. Incubation of 1 with Aspergillus brasiliensis afforded two known (compounds 5 and 10) and eight new derivatives (compounds 2-4, 6-9 and 11). The most common reaction was hydroxylation, but isomerization of the double bond and acetylation were also detected. None of the tested compounds showed cytotoxicity against HeLa, MCF-7 and MCF-10A cell lines showing IC50 values ranging from 62.6 µM to > 500 µM. Compounds 1, 5, 6, 8 and 11 showed fungistatic effects (ranging from 34.1 µM to 39.5 µM) on C. glabrata at lower concentrations than fluconazole (163.2 µM). Compounds 1, 6 and 8 were more potent fungicides (ranging from 79.0 to 143.6 µM) than fluconazole, which showed fungicidal effect at concentrations higher than 163.2 µM. These results suggest that ent-polyalthic acid and some of its derivatives could be used as lead compounds to develop new antifungal agents.

Sesquiterpenes from Myrrh and Their ICAM-1 Inhibitory Activity In Vitro.

By using various chromatographic steps (silica flash, CPC, preparative HPLC), 16 sesquiterpenes could be isolated from an ethanolic extract of myrrh resin. Their chemical structures were elucidated by 1D and 2D NMR spectroscopy and HRESIMS. Among them, six previously unknown compounds (1-6) and another four metabolites previously not described for the genus Commiphora (7, 10, 12, 13) could be identified. Sesquiterpenes 1 and 2 are novel 9,10-seco-eudesmanes and exhibited an unprecedented sesquiterpene carbon skeleton, which is described here for the first time. New compound 3 is an 9,10 seco-guaian and the only peroxide isolated from myrrh so far. Compounds 1, 2, 4, 7-9, 11, 13-16 were tested in an ICAM-1 in vitro assay. Compound 7, as well as the reference compound furanoeudesma-1,3-diene, acted as moderate inhibitors of this adhesion molecule ICAM-1 (IC50: 44.8 and 46.3 µM, respectively). These results give new hints on the activity of sesquiterpenes with regard to ICAM-1 inhibition and possible modes of action of myrrh in anti-inflammatory processes.

Cytotoxic properties of the alkaloid rutaecarpine and its oligocyclic derivatives and chemical modifications to enhance water-solubility.

The alkaloid rutaecarpine and its derivatives have been described as cytotoxic and hold potential as antitumor agents. Nevertheless, their synthesis is demanding and compounds display poor water solubility. Herein, we describe the synthesis of two sets of rutaecarpine derivatives with amine functions to improve solubility. Using a classic shake-flask experiment and a potentiometric titration platform, the water solubility of the compounds was determined. Solubility improved significantly with the amine functions connected over the indole-N atom. Reduction of metabolic activity and cell viability on HeLa cells was in the same range or better for these derivatives compared to the chemically unaltered parent compounds prepared in a new synthetic procedure established in our group.

Diarylheptanoid Glycosides of Morella salicifolia Bark.

A methanolic extract of Morella salicifolia bark was fractionated by various chromatographic techniques yielding six previously unknown cyclic diarylheptanoids, namely, 7-hydroxymyricanol 5-O-ß-d-glucopyranoside (1), juglanin B 3-O-ß-d-glucopyranoside (2), 16-hydroxyjuglanin B 17-O-ß-d-glucopyranoside (3), myricanone 5-O-ß-d-gluco-pranosyl-(1→6)-ß-d-glucopyranoside (4), neomyricanone 5-O-ß-d-glucopranosyl-(1→6)-ß-d-glucopyranoside (5), and myricanone 17-O-α-l-arabino-furanosyl-(1→6)-ß-d-glucopyranoside (6), respectively, together with 10 known cyclic diarylheptanoids. The structural diversity of the diarylheptanoid pattern in M. salicifolia resulted from varying glycosidation at C-3, C-5, and C-17 as well as from substitution at C-11 with hydroxy, carbonyl or sulfate groups, respectively. Structure elucidation of the isolated compounds was achieved on the basis of one- and two-dimensional nuclear magnetic resonance (NMR) as well as high-resolution electrospray ionisation mass spectrometry (HR-ESI-MS) analyses. The absolute configuration of the glycosides was confirmed after hydrolysis and synthesis of O-(S)-methyl butyrated (SMB) sugar derivatives by comparison of their ¹H-NMR data with those of reference sugars. Additionally, absolute configuration of diarylheptanoid aglycones at C-11 was determined by electronic circular dichroism (ECD) spectra simulation and comparison with experimental CD spectra after hydrolysis.

1-Acetyl-3-[(3R)-hydroxyfatty acyl]glycerols: Lipid Compounds from Euphrasia rostkoviana Hayne and E. tetraquetra (Bréb.) Arrond.

Five homologous acetylated acylglycerols of 3-hydroxyfatty acids (chain lengths C(14) - C(18)), named euphrasianins A - E, were characterized for the first time in Euphrasia rostkoviana Hayne (Orobanchaceae) by gas chromatography/mass spectrometry (GC/MS) and high-performance liquid chromatography/atmospheric pressure chemical ionization-mass spectrometry (HPLC/APCI-MS(n) ). In addition to mass spectrometric data, structures of euphrasianins were verified via a three-step total synthesis of one representative homologue (euphrasianin A). The structure of the latter was confirmed by 1D- and 2D-NMR experiments as well as high-resolution electrospray ionization-mass spectrometry (HR-ESI-MS). The absolute configuration of the 3-hydroxyfatty acid moiety at C(3) was found to be R in the natural euphrasianins, which was determined by alkaline hydrolysis and methylation of a purified fraction, followed by chiral GC analysis. Furthermore, in extracts of Euphrasia tetraquetra (Bréb.) Arrond. euphrasianins C and E were detected exclusively, indicating that this subclass of lipid constituents is possibly valuable for fingerprinting methods.

Novel Selective Butyrylcholinesterase Inhibitors Incorporating Antioxidant Functionalities as Potential Bimodal Therapeutics for Alzheimer's Disease.

Isosorbide-2-carbamates-5-aryl esters are highly potent and very selective butyrylcholinesterase inhibitors. The objective of the present work was to address the hypothesis that the isosorbide-aryl-5-ester group could be replaced with an antioxidant functionality while maintaining inhibitor effects and selectivity. We successfully incorporated ferulic acid or lipoic acid groups producing potent selective inhibitors of butyrylcholinesterase (BuChE). The hybrid compounds were non-toxic to the murine hippocampal cell line HT-22 and lipoate esters were neuroprotective at 10 and 25 µM when the cells were challenged with glutamate (5 mM) in a similar manner to the positive control quercetin. The benzyl carbamate 7a was a potent inhibitor of BuChE (IC50 150 nM) and it was effective in reducing glutamate toxicity to neuronal cells at >5 µM. Representative compounds exhibited an antioxidant effect in the oxygen radical absorbance capacity assay as the lipoate 7d was not active, whereas the ferulate 8a showed a weak, but significant, activity with 0.635 ± 0.020 Trolox Equivalent.

Unconventional application of the Mitsunobu reaction: Selective flavonolignan dehydration yielding hydnocarpins.

Various Mitsunobu conditions were investigated for a series of flavonolignans (silybin A, silybin B, isosilybin A, and silychristin A) to achieve either selective esterification in position C-23 or dehydration in a one-pot reaction yielding the biologically important enantiomers of hydnocarpin D, hydnocarpin and isohydnocarpin, respectively. This represents the only one-pot semi-synthetic method to access these flavonolignans in high yields.

Structure-Dependent Deconjugation of Flavonoid Glucuronides by Human ß-Glucuronidase - In Vitro and In Silico Analyses.

Flavonoid glycosides are extensively metabolized to glucuronidated compounds after oral intake. Recently, a cleavage of quercetin glucuronides by ß-glucuronidase has been found. To characterize the deglucuronidation reaction and its structural prerequisites among the flavonoid subtypes more precisely, four flavonol glucuronides with varying glucuronidation positions, five flavone 7-O-glucuronides with varying A- and B-ring substitution as well as one flavanone- and one isoflavone-7-O-glucuronide were analyzed in a human monocytic cell line. Investigation of the deglucuronidation rates by HPLC revealed a significant influence of the glucuronidation position on enzyme activity for flavonols. Across the flavonoid subtypes, the C-ring saturation also showed a significant influence on deglucuronidation, whereas A- and B-ring variations within the flavone-7-O-glucuronides did not affect the enzymes' activity. Results were compared to computational binding studies on human ß-glucuronidase. Additionally, molecular modeling and dynamic studies were performed to obtain detailed insight into the binding and cleavage mode of the substrate at the active site of the human ß-glucuronidase.

Natural phenolic metabolites with anti-angiogenic properties - a review from the chemical point of view.

Considering the many secondary natural metabolites available from plants, phenolic compounds play a particularly important role in human health as they occur in significant amounts in many fruits, vegetables and medicinal plants. In this review natural phenolic compounds of plant origin with significant anti-angiogenic properties are discussed. Thirteen representatives from eight different natural or natural-like phenolic subclasses are presented with an emphasis on their synthesis and methods to modify the parent compounds. When available, the consequence of structural variation on the pharmacological activity of the molecules is described.

Design, synthesis and in vitro evaluation of novel uni- and bivalent ligands for the cannabinoid receptor type 1 with variation of spacer length and structure.

Using rimonabant, a potent inverse agonist for cannabinoid receptor type 1 (CB1R), as parent ligand, a series of novel univalent and bivalent ligands were designed by variation of spacer length and its chemical structure. The ligands synthesized were evaluated for affinity and selectivity by radioligand displacement and a functional steady-state GTPase assay. The results showed the nature of the spacer influences the biological readout. Albeit all compounds show significantly lower affinities than rimonabant, this fact could be used to demonstrate that affinities and selectivity are influenced by the chemical structure and length of the spacer and might be helpful for designing bivalent probes for other GPCR receptors.

Cyclic acyl guanidines bearing carbamate moieties allow potent and dirigible cholinesterase inhibition of either acetyl- or butyrylcholinesterase.

A series of cyclic acyl guanidine with carbamate moieties have been synthesized and evaluated in vitro for their AChE and BChE inhibitory activities. Structure-activity relationships identified compound 23 as a nanomolar and selective BChE inhibitor, while compound 32 exhibited nanomolar and selective AChE inhibition, selectivity depending on both the structure of the carbamate substituent as well as the position of guanidines-N substitution. The velocity of enzyme carbamoylation was analyzed and showed similar behavior to physostigmine. Phenolic compounds formed after carbamate transfer to the active site of cholinesterases showed additional neuroprotective properties on a hippocampal neuronal cell line (HT-22) after glutamate-induced intracellular reactive oxygen species generation.

Synthesis and biological evaluation of bivalent cannabinoid receptor ligands based on hCB2R selective benzimidazoles reveal unexpected intrinsic properties.

The design of bivalent ligands targeting G protein-coupled receptors (GPCRs) often leads to the development of new, highly selective and potent compounds. To date, no bivalent ligands for the human cannabinoid receptor type 2 (hCB2R) of the endocannabinoid system (ECS) are described. Therefore, two sets of homobivalent ligands containing as parent structure the hCB2R selective agonist 13a and coupled at different attachment positions were synthesized. Changes of the parent structure at these positions have a crucial effect on the potency and efficacy of the ligands. However, we discovered that bivalency has an influence on the effect at both cannabinoid receptors. Moreover, we found out that the spacer length and the attachment position altered the efficacy of the bivalent ligands at the receptors by turning agonists into antagonists and inverse agonists.

Synthesis of natural and non-natural curcuminoids and their neuroprotective activity against glutamate-induced oxidative stress in HT-22 cells.

A strategy for the synthesis of natural and non-natural 5-deoxy-6,7-dihydrocurcuminoids (diarylheptanoids) was developed for the preparation of 14 compounds with varying aromatic substituent patterns and a different functionality in the aliphatic seven-carbon chain. The in vitro protective activity against glutamate-induced neuronal cell death was examined in the murine hippocampal cell line HT-22 to find structural motifs responsible for neuroprotective effects in vitro. Among the tested compounds the ferulic acid-like unit, present in the structures of (E)-1,7-bis(4-hydroxy-3-methoxyphenyl)hept-1-en-3-one (5) and (E)-1-(4-hydroxy-3-methoxyphenyl)-7-(4-hydroxyphenyl)hept-1-en-3-one (7), appeared to be an important feature for protection against glutamate-induced neurotoxicity. Both compounds demonstrated significant neuroprotective activity in a concentration range between 1 and 25 µM without showing toxic effects in a cytotoxicity assay with HT-22 cells. Furthermore, (E)-1,7-bis(3,4-dihydroxyphenyl)hept-1-en-3-one (9), exhibiting a caffeic acid-like structural motif, displayed a neuroprotective activity at a nontoxic concentration of 25 µM. In contrast, (1E,6E)-1,7-bis(3,4-dihydroxyphenyl)hepta-1,6-diene-3,5-dione (4, di-O-demethylcurcumin) showed mainly cytotoxic effects. A corresponding single-ring analogue that contains the ferulic acid-like unit as an enone was not active.

Flavonoids, flavonoid metabolites, and phenolic acids inhibit oxidative stress in the neuronal cell line HT-22 monitored by ECIS and MTT assay: a comparative study.

A real-time and label-free in vitro assay based on electric cell-substrate impedance sensing (ECIS) was established, validated, and compared to an end-point MTT assay within an experimental trial addressing the cytoprotective effects of 19 different flavonoids, flavonoid metabolites, and phenolic acids and their methyl esters on the HT-22 neuronal cell line, after induction of oxidative stress with tert-butyl hydroperoxide. Among the flavonoids under study, only those with a catechol unit and an additional 4-keto group provided cytoprotection. The presence of a 2,3-double bond was not a structural prerequisite for a neuroprotective effect. In the case of the phenolics, catechol substitution was the only structural requirement for activity. The flavonoids and other phenolics with a ferulic acid substitution or a single hydroxy group showed no activity. Electrochemical characterization of all compounds via square-wave voltammetry provided a rather specific correlation between cytoprotective activity and redox potential for the active flavonoids, but not for the active phenolics with a low molecular weight. Moreover this study was used to compare label-free ECIS recordings with results of the established MTT assay. Whereas the former provides time-resolved and thus entirely unbiased information on changes of cell morphology that are unequivocally associated with cell death, the latter requires predefined exposure times and a strict causality between metabolic activity and cell death. However, MTT assays are based on standard lab equipment and provide a more economic way to higher throughput.