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Myrtucommulones belong to a class of pharmacologically active natural compounds which offer various alternatives to the treatment of pain, inflammation and cancer. Their stereoselective synthesis remains therefore a key-challenge towards its use in the pharmaceutical industry. In the present work myrtucommulone A and B were synthesised through metal catalysis with 81 and 72% ee respectively. Thanks to the use of cinchonidine as an organocatalyst, 82 and 84% de were reached for myrtucommulone A and myrtucommulone F respectively. Simultaneously, a new synthetic method emerged and gave access to new range of possibilities for the preparation of myrtucommulone derivatives under mild conditions or through a one-pot reaction.

The antimicrobial peptide LL-37 is the sole member of the human cathelicidin family with immune system-modulating properties and roles in autoimmune disease development. Small molecules able to interact with LL-37 and to modulate its functions have not been described yet. Boswellic acids (BAs) are pentacyclic triterpene acids that are bioactive principles of frankincense extracts used as anti-inflammatory remedies. Although various anti-inflammatory modes of action have been proposed for BAs, the pharmacological profile of these compounds is still incompletely understood. Here, we describe the identification of human LL-37 as functional target of BAs. In unbiased target fishing experiments using immobilized BAs as bait and human neutrophils as target source, LL-37 was identified as binding partner assisted by MALDI-TOF mass spectrometry. Thermal stability experiments using circular dichroism spectroscopy confirm direct interaction between BAs and LL-37. Of interest, this binding of BAs resulted in an inhibition of the functionality of LL-37. Thus, the LPS-neutralizing properties of isolated LL-37 were inhibited by 3-O-acetyl-β-BA (Aβ-BA) and 3-O-acetyl-11-keto-β-BA (AKβ-BA) in a cell-free limulus amoebocyte lysate assay with EC50=0.2 and 0.8 μM, respectively. Also, LL-37 activity was inhibited by these BAs in LL-37-enriched supernatants of stimulated neutrophils or human plasma derived from stimulated human whole blood. Together, we reveal BAs as inhibitors of LL-37, which might be a relevant mechanism underlying the anti-inflammatory properties of BAs and suggests BAs as suitable chemical tools or potential agents for intervention with LL-37 and related disorders.

Age-related diseases, such as osteoarthritis, Alzheimer’s disease, diabetes, and cardiovascular disease, are often associated with chronic unresolved inflammation. Neutrophils play central roles in this process by releasing tissue-degenerative proteases, such as cathepsin G, as well as pro-inflammatory leukotrienes produced by the 5-lipoxygenase (5-LO) pathway. Boswellic acids (BAs) are pentacyclic triterpene acids contained in the gum resin of the anti-inflammatory remedy frankincense that target cathepsin G and 5-LO in neutrophils, and might thus represent suitable leads for intervention with age-associated diseases that have a chronic inflammatory component. Here, we investigated whether, in addition to BAs, other triterpene acids from frankincense interfere with 5-LO and cathepsin G. We provide a comprehensive analysis of 17 natural tetra- or pentacyclic triterpene acids for suppression of 5-LO product synthesis in human neutrophils. These triterpene acids were also investigated for their direct interference with 5-LO and cathepsin G in cell-free assays. Furthermore, our studies were expanded to 10 semi-synthetic BA derivatives. Our data reveal that besides BAs, several tetra- and pentacyclic triterpene acids are effective or even superior inhibitors of 5-LO product formation in human neutrophils, and in parallel, inhibit cathepsin G. Their beneficial target profile may qualify triterpene acids as anti-inflammatory natural products and pharmacological leads for intervention with diseases related to aging.

Myrtucommulone A (MC A) (1), isolated from Myrtus communis (myrtle), shows the same pharmacological activity for inhibition of inflammation and induction of apoptosis as synthetic MC A, which consists of three stereoisomers, i.e., two enantiomers and one meso form. This led to the question of whether the natural MC A is a pure stereoisomer or a mixture of stereoisomers. The specific rotation and electronic circular dichroism (ECD) data of natural MC A (1) as well as of a pentacyclic derivative 4 revealed that naturally occurring MC A (1) consists of the racemate and the meso form in a 1:1 ratio. A probable precursor of MC A (1), nor-semimyrtucommulone (5), was also isolated from myrtle as a racemate. The absolute configurations of the enantiomers of 1 and 5 were determined using a combination of experimental and quantum-chemical calculated ECD spectra.

The acylphloroglucinols hyperforin (Hypf) and myrtucommulone A (MC A) induce death of cancer cells by triggering the intrinsic/mitochondrial pathway of apoptosis, accompanied by a loss of the mitochondrial membrane potential and release of cytochrome c. However, the upstream targets and mechanisms leading to these mitochondrial events in cancer cells remain elusive. Here we show that Hypf and MC A directly act on mitochondria derived from human leukemic HL-60 cells and thus, disrupt mitochondrial functions. In isolated mitochondria, Hypf and MC A efficiently impaired mitochondrial viability (EC50 = 0.2 and 0.9 µM, respectively), caused loss of the mitochondrial membrane potential (at 0.03 and 0.1 µM, respectively), and suppressed mitochondrial ATP synthesis (IC50 = 0.2 and 0.5 µM, respectively). Consequently, the compounds activated the adenosine monophosphate-activated protein kinase (AMPK) in HL-60 cells, a cellular energy sensor involved in apoptosis of cancer cells. Side by side comparison with the protonophore CCCP and the ATP synthase inhibitor oligomycin suggest that Hypf and MC A act as protonophores that primarily dissipate the mitochondrial membrane potential by direct interaction with the mitochondrial membrane. Together, Hypf and MC A abolish the mitochondrial proton motive force that on one hand impairs mitochondrial viability and on the other cause activation of AMPK due to lowered ATP levels which may further facilitate the intrinsic mitochondrial pathway of apoptosis.

The natural acylphloroglucinol myrtucommulone A (1) inhibits microsomal prostaglandin E2 synthase (mPGES)-1 and 5-lipoxygenase (5-LO), and induces apoptosis of cancer cells. Starting from 1 as lead, 28 analogues were synthesized following a straightforward modular strategy with high yielding convergent steps. Major structural variations concerned (I) replacement of the syncarpic acid moieties by dimedone or indandione, (II) cyclization of the syncarpic acid with the acylphloroglucinol core, and (III) substitution of the methine bridges and the acyl residue with isopropyl, isobutyl, n-pentyl or phenyl groups, each. The potency for mPGES-1 inhibition was improved by 12.5-fold for 43 (2-(1-(3-hexanoyl-2,4,6-trihydroxy-5-(1-(3-hydroxy-1-oxo-1H-inden-2-yl)-2-methylpropyl)phenyl)-2-methylpropyl)-3-hydroxy-1H-inden-1-one) with IC50 = 0.08 μM, and 5-LO inhibition was improved 33-fold by 47 (2-((3-hexanoyl-2,4,6-trihydroxy-5-((3-hydroxy-1-oxo-1H-inden-2-yl) (phenyl)methyl)phenyl) (phenyl)methyl)-3-hydroxy-1H-inden-1-one) with IC50 = 0.46 μM. SAR studies revealed divergent structural determinants for induction of cell death and mPGES-1/5-LO inhibition, revealing 43 and 47 as non-cytotoxic mPGES-1 and 5-LO inhibitors that warrant further preclinical assessment as anti-inflammatory drugs.

Myrtucommulone-A is the active compound derived from Myrtus communis. The molecular targets of myrtucommulone-A is widely unknown, which impedes its potential therapeutic use. In this study, we demonstrated the cytotoxicity of MC-A and its potential to induce apoptosis in cancer cells. Myrtucommulone-A was also found to be antiproliferative and strongly inhibited cancer cell migration. Eighty four apoptotic pathway genes were used to assess the effect of myrtucommulone-A on cancer cells. Myrtucommulone-A mediated an increase in apoptotic genes including Fas, FasL, Gadd45a, Tnf, Tnfsf12, Trp53, and caspase 4. The increase in myrtucommulone-A dose (25 μM versus 6.25 μM) also upregulated the expression of genes, which are involved mainly in apoptosis, regulation of apoptosis, role of mitochondria in apoptotic signaling, cytokine activity, and tumor necrosis factor signaling. Our data indicate that myrtucommulone-A could be utilized as a potential therapeutic compound with its molecular targets in apoptotic pathways.

An approach to a model compound for polycyclic polyprenylated acylphloroglucinols is developed using a ring-closing metathesis approach to give a substituted cyclooctene. This undergoes cyclization via an intramolecular acylation leading to a substituted bicyclo[3.3.1]nonan-9-one related to hyperforin, nemorosone, clusianone, garsubellin A and other members of the polyprenylated acylphloroglucinol.

Besides all their conformational degrees of freedom, drug-like molecules and natural products often also undergo tautomeric interconversions. Compared to the huge efforts made in experimental investigation of tautomerism, open and free algorithmic solutions for prototropic tautomer generation are surprisingly rare. The few freely available software packages limit their output to a subset of the possible configurational space by sometimes unwanted prior assumptions and complete neglection of ring-chain tautomerism. Here, we describe an adjustable fully automatic tautomer enumeration approach, which is freely available and also incorporates the detection of ring-chain variants. The algorithm is implemented in the MolTPC framework and accessible on SourceForge. © 2013 Wiley Periodicals, Inc.

In the genome of Bacillus megaterium DSM319, a strain who has recently been sequenced to fully exploit its potential for biotechnological purposes, we identified a gene encoding the cytochrome P450 CYP106A1 as well as genes encoding potential redox partners of CYP106A1. We cloned, expressed, and purified CYP106A1 and five potential autologous redox partners, one flavodoxin and four ferredoxins. The flavodoxin and three ferredoxins were able to support the activity of CYP106A1 displaying the first cloned natural redox partners of a cytochrome P450 from B. megaterium. The CYP106A1 system was able to convert the pentacyclic triterpene 11-keto-β-boswellic acid (KBA) belonging to the main bioactive constituents of Boswellia serrata gum resin extracts, which are used to treat inflammatory disorders and arthritic diseases. In order to provide sufficient amounts of the KBA products to characterize them structurally by NMR spectroscopy, recombinant whole-cell biocatalysts were constructed based on B. megaterium MS941. The main product has been identified as 7β-hydroxy-KBA, while the side product (∼20 %) was shown to be a mixture of 7β,15α-dihydroxy-KBA and 15α-hydroxy-KBA. Without further optimization 560.7 mg l−1 day−1 of the main product, 7β-hydroxy-KBA, could be obtained thus providing a suitable starting point for the efficient production of modified KBA by chemical tailoring to produce novel KBA derivatives with increased bioavailability and this way more efficient drugs.

A total synthesis of the mniopetals A, B, C and D is described. Key steps are a Sharpless asymmetric dihydroxylation and a selective esterification of an equatorial hydroxy group vicinal to an axial hydroxy function.

Myrtucommulone A (1), which was isolated from myrtle and other species of the myrtaceae family, was synthesized through an enantioselective Michael addition of isobutyryl phloroglucinol (5) to isobutylidene syncarpic acid (4) that was induced by a chiral Al–Li–BINOL (1,1′-bi-2-naphthol) complex [(S,S)-ALB]. Because there is significant steric crowding in Michael acceptor 4, myrtucommulone A (1) was obtained with an ee value of 70 % along with meso-1 in 77 % chemical yield.

Isoprenoids derive from two universal precursors: isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP).[1] In mammals, these key intermediates are crucial for cell survival, e.g. in cholesterol biosynthesis, and are generated via the mevalonate pathway, while in most bacteria as well as in malaria parasites such as Plasmodium falciparum, the 1-deoxy-D-xylulose 5-phosphate (DXP) pathway is used.[2] The DXP pathway is absent in humans and is, therefore, considered to be an important drug target against many infectious diseases.[3] Scheme 1 shows the last step of the DXP pathway, the conversion of (E)-4-hydroxy-3-methylbut-2-enyl diphosphate (HMBPP, 1) to a mixture of IPP (2) and DMAPP (3). This reaction is catalyzed by HMBPP reductase (IspH), a monomeric enzyme that consists of three domains binding to a redox-active [Fe4S4] cluster in its central cavity (Figure 1a).[4] The cluster is linked to the protein by the side-chains of three cysteine residues, and one of the iron atoms possesses an unoccupied coordination site that has not been found to bind to any amino acid residue. Mechanistic studies with wild type Escherichia coli IspH as well as IspH mutants have revealed two different conformations of 1 inside the active site that are adopted in the catalytic cycle (Figure 1b and c): one in which O1 binds to the 4th iron atom, and a second in which it undergoes numerous hydrogen bond interactions with its diphosphate group and protein residues.[5] Figure 1 Crystal structure of IspH in complex with 1. a) Top and side view of the overall structure of E. coli IspH. Active site of b) wild type IspH forming an alkoxide complex with 1 and c) the IspH E126Q mutant bound to 1 in the cyclic conformation revealing ... Scheme 1 Reductive dehydration catalyzed by IspH. The proposed mechanism for the IspH reaction is shown in Scheme 2 and involves four intermediate states that have been identified by crystallography, Mosbauer and electron paramagnetic resonance (EPR) spectroscopy.[5–6] The detailed structure of IspH in the absence of exogenous ligands is not known (state 0) but binding of 1 to oxidized IspH leads to formation of an alkoxide complex with weak pi interactions (state I; spin S=0). One-electron reduction of the cluster results in [Fe4S4]+ with spin S=1/2, and correlates with a rotation of the ligand's hydroxymethyl group away from the cluster to form a cyclic conformation (state II) which has essential impact on the stereochemical course of the IspH reaction.[7] The transfer of two electrons from the cofactor to the substrate produces a HiPIP-type [Fe4S4]3+ cluster and leads to C-O bond cleavage and water release. The allyl anion (state III) then abstracts a proton from the diphosphate group, either at the ligand's C2 or C4 atom, to form IPP and DMAPP, respectively. Scheme 2 Proposed mechanism of IspH catalysis. Besides the intensive investigation of the IspH reaction mechanism, a remarkable effort was put into the design and characterization of inhibitors.[8] Recently, synthesis and spectroscopic studies of three substrate analogs with the hydroxyl group in HMBPP replaced by fluoro (4)[9], amino (5)[10], or thiol (6) groups have been reported. Compound 4 is slowly converted by IspH, whereas 5 and 6 inhibit the enzyme. In order to analyze the structure-function relationship of these derivatives we synthesized 4[11], 5[12], and 6 (see SI), performed co-crystallization with E. coli IspH and determined the crystal structure of the complexes. The X-ray structure of IspH in complex with the fluoro analog 4 was determined to 1.8 A resolution [Rfree = 23.2%, Figure 2a, Protein Data Bank (PDB)[13] ID 4H4C] and reveals that 4 binds to the active site of IspH in a similar way as the substrate 1.[14] However, the C-F bond is rotated by 106° compared to the C-O bond in the IspH:1 complex (Figure 2b), the fluorine atom is thus located inside a hydrophobic pocket stabilized by van der Waals interactions with His74Cδ (3.6 A), Ala73C (3.9 A), and Ala73Cβ (3.9 A). This unique conformation allows water molecules to occupy positions W1 and W2.[14] Although it displays an unusual orientation, 4 is converted to 2 or 3 by IspH, but with a decreased rate (kcat = 28 min−1) compared to 1 (kcat = 604 min−1). The differences in these reaction rates are likely due, at least in part, to the increased bond energies of C-F versus C-O.[15] Furthermore, the lack of a direct interaction with the apical iron atom leads to the high Km value of 4 (Km = 104 μM) compared to 1 (Km = 20 μM). Figure 2 Complex structure of IspH bound to the fluorinated derivative 4. a) Active site of IspH showing the bound ligand and two water molecules. A 2FO-FC omit electron density map (blue mesh, contoured at 1.0 σ) is shown for the [Fe4S4] cluster, the ... Recent inhibition studies have shown that the amino and thiol substrate analogs 5 and 6 exhibit potent inhibition of IspH with IC50 values of 0.15 μM and 0.21 μM, respectively.[10] Additionally, Mosbauer spectroscopy has suggested that both ligands interact with the [Fe4S4] cluster. However, it is not immediately obvious that 5 binds to the 4th iron atom via its amino group, or whether it forms an alternative complex that allows a water molecule to coordinate to the 4th iron atom as previously observed with an acetylene inhibitor.[8c] The structure of 5 in complex with IspH was determined to 1.35 A resolution (Rfree = 21.0% Figure 3a, PDB[13] ID 4H4D) and clearly shows two ligand conformations within the same crystal[16]: (i) a ligand-cluster complex in which the amino group coordinates to the apical iron atom and (ii) a conformation in which the amino group is rotated by approximately 74° in the opposite direction to that observed with 4. The amino-iron complex is similar to that seen with the alkoxide-iron complex formed by 1 (Figure 3b), indicating that the affinity of the free amino group with the [Fe4S2]2+ cluster is comparable to that of the hydroxyl group. The second conformation observed in the crystal structure is stabilized by hydrogen bonding of the amino (or ammonium) group to one of the diphosphate oxygen atoms (2.8 A), Glu126Oe (2.9 A) and Thr167Oγ (3.1 A), and a water molecule in the W1 position (3.1 A). Figure 3 X-ray structure of IspH in complex with the amino derivative 5. a) Active site with the ligand in two orientations. The electron density map is displayed according to Figure 2a. b) Superposition of the IspH:5 complex structures with the alkoxide complex ... The amino-iron complex is in good agreement with the Mosbauer spectroscopic data indicating a tetrahedral (3S/N) coordination sphere at the apical iron atom.[10] Thus, it seems likely that the alternative conformation may have arisen due to cluster reduction in the X-ray beam – a result that would be of particular interest in the context of inhibition of the IspH reaction which is, of course, carried out under reducing conditions.[17] However, unlike with 1, no turnover was observed with 5. One possible explanation for this is the formation of a stable ammonium-carboxylate ion pair that prevents the release of ammonia (Scheme 4). Scheme 4 Mechanism of IspH catalysis with 1 and inhibition by 5. a) Dehydroxylation of 1, facilitated by an acidic proton donor (Glu126OH or the diphosphate) represented by X-OH. b) Corresponding hypothetical reaction with 5. c) Formation of a stable ammonium-carboxylate ... Next, we determined the crystal structure of IspH bound to 6 to 1.7 A resolution (Rfree = 21.3%, Figure 4a, PDB[13] ID 4H4E), which displays complex formation between the unique iron atom of the cluster and the thiol group of 6. No solvent molecule is located in the active site, since the increased size of the bridging group leads to movement of the hydrocarbon chain of 6 towards the diphosphate moiety. Furthermore, the hydrogen bond network is modified, preventing the stabilization of the water molecules in the position as found in the IspH:1 complex (Figure 4b). The coordination by the ligand's thiol group generates a [Fe4S4] cluster that is coordinated by four sulfur ligands, similar to that found in most proteins catalyzing electron transfer reactions.[18] Figure 4 IspH bound to the thiol derivative 6. a) Active site with thiol-iron complex. The electron density map is displayed according to Figure 2a. b) Structural superposition of IspH:6 with the alkoxide complex in the IspH:1 structure and the cyclic ligand orientation ... In conclusion, the results presented here provide new insights into the mechanism of the IspH reaction with the artificial substrate 4, which involves a previously unknown intermediate that is not bound to the [Fe4S4] cluster. With the amino (5) and thiol (6) species, we find in both cases that the ligands bind to the 4th iron atom. However, it still remains to be determined whether IspH inhibition is due to bonding of these ligands to the oxidized protein, the reduced protein, or both. With 5, we see evidence for a second conformation in which the side-chain is not interacting with the cluster and propose formation of a non-reactive ion-pair complex with Glu126Oe and the diphosphate group (possibly in both oxidized and reduced IspH). As expected, the IspH:6 complex reveals that the ligand's sulfur atom binds to the 4th iron atom, and there is no alternative conformation, most likely due to the fact that the SH group is a poor base/hydrogen bond acceptor. The structures of these substrate analogs thus provide new mechanistic insights, as well as suggest novel strategies for the development of antibiotic and antimalarial drugs.

The acylphloroglucinol myrtucommulone A (MC) causes mitochondrial dysfunctions by direct interference leading to apoptosis in cancer cells, but the molecular targets involved are unknown. Here, we reveal the chaperonin heat-shock protein 60 (HSP60) as a molecular target of MC that seemingly modulates HSP60-mediated mitochondrial functions. Exploiting an unbiased, discriminative protein fishing approach using MC as bait and mitochondrial lysates from leukemic HL-60 cells as target source identified HSP60 as an MC-binding protein. MC prevented HSP60-mediated reactivation of denatured malate dehydrogenase in a protein refolding assay. Interference of MC with HSP60 was accompanied by aggregation of two proteins in isolated mitochondria under heat shock that were identified as Lon protease-like protein (LONP) and leucine-rich PPR motif-containing protein (LRP130). Together, our results reveal HSP60 as a direct target of MC, proposing MC as a valuable tool for studying HSP60 biology and for evaluating its value as a target in related diseases, such as cancer.

Mounting evidence suggests that signalling cross-talk plays a significant role in the regulation of epithelial-mesenchymal transition (EMT) in cancer cells. However, the complex network regulating the EMT in different cancer types has not been fully described yet which affects the development of novel therapeutic strategies. In the present study, we investigated the signalling pathways involved in EMT of bladder cancer cells and demonstrated the effects of two novel agents in the regulation of EMT. Myrtucommulone-A (MC-A) and thymoquinone (TQ) have been shown to possess anti-cancer properties. However, their targets in the regulation of cancer cell behavior are not well defined. Here, we defined the effects of two putative anti-cancer agents on bladder cancer cell migration and their possible intracellular targets in the regulation of EMT. Our results suggest that MC-A or TQ treatment affected N-cadherin, Snail, Slug, and beta-catenin expressions and effectively attenuated mTOR activity. The downstream components in mTOR signalling were also affected. MC-A treatment resulted in the concomitant inhibition of extracellular matrix-regulated protein kinases 1 and 2 (ERK 1/2), p38 mitogen-activated protein kinase (MAPK) and Src activity. On the other hand, TQ treatment increased Src activity while exerting no effect on ERK 1/2 or p38 MAPK activity. Given the stronger inhibition of EMT-related markers in MC-A-treated samples, we concluded that this effect might be due to collective inhibition of multiple signalling pathways which result in a decrease in their cross-talk in bladder cancer cells. Overall, the data in this study proposes novel action mechanisms for MC-A or TQ in bladder cancer cells and highlights the potential use of these active compounds in the regulation of EMT.

Eicosanoids are potent lipid mediators derived from phospholipase (PL)-released arachidonic acid (AA) coupled to subsequent metabolism by cyclooxygenase (COX)-1/2 or lipoxygenases (LO) which are involved in a variety of homeostatic biological functions and inflammation. We have investigated three lupeolic acids (LA) from the gum resin of Boswellia carterii for their ability to interfere with eicosanoid biosynthesis in human blood cells. A novel, yet unknown C(28)-hydroxylated LA, that is, 3α-acetoxy-28-hydroxylup-20(29)-en-4β-oic acid (Ac-OH-LA) was found to inhibit the biosynthesis of COX-, 5-LO- and 12-LO-derived eicosanoids from endogenous AA in activated platelets, neutrophils, and monocytes from human blood with consistent IC(50) values of 2.3-6.9 μM. In contrast, two other LAs lacking the C(28)-OH moiety were essentially inactive in this respect. Inhibition of eicosanoids by Ac-OH-LA correlated with reduced release of AA in intact cells. When AA was exogenously provided as substrate for cellular eicosanoid biosynthesis the inhibitory effects of Ac-OH-LA were essentially reversed, even though some inhibition of 5-LO and COX-1 product formation still remained. Finally, by means of a cell-free phospholipid hydrolysis assay using human recombinant cytosolic PLA(2)α, we show that Ac-OH-LA may directly interfere with cPLA(2)α activity (IC(50) = 3.6 μM). Together, we identified a novel, naturally occuring C(28)-hydroxylated LA which acts as efficient inhibitor of cPLA(2)α and consequently suppresses eicosanoid biosynthesis in intact cells.

The [4Fe-4S] protein IspH in the methylerythritol phosphate isoprenoid biosynthesis pathway is an important anti-infective drug target, but its mechanism of action is still the subject of debate. Here, by using electron paramagnetic resonance (EPR) spectroscopy and (2)H, (17)O, and (57)Fe isotopic labeling, we have characterized and assigned two key reaction intermediates in IspH catalysis. The results are consistent with the bioorganometallic mechanism proposed earlier, and the mechanism is proposed to have similarities to that of ferredoxin, thioredoxin reductase, in that one electron is transferred to the [4Fe-4S](2+) cluster, which then performs a formal two-electron reduction of its substrate, generating an oxidized high potential iron-sulfur protein (HiPIP)-like intermediate. The two paramagnetic reaction intermediates observed correspond to the two intermediates proposed in the bioorganometallic mechanism: the early π-complex in which the substrate's 3-CH(2)OH group has rotated away from the reduced iron-sulfur cluster, and the next, η(3)-allyl complex formed after dehydroxylation. No free radical intermediates are observed, and the two paramagnetic intermediates observed do not fit in a Birch reduction-like or ferraoxetane mechanism. Additionally, we show by using EPR spectroscopy and X-ray crystallography that two substrate analogues (4 and 5) follow the same reaction mechanism.

Introduction Resins of the genus Boswellia are currently an interesting topic for pharmaceutical research since several pharmacological activities (e.g. anti-inflammatory, anti-microbial, anti-tumour) are reported for extracts and compounds isolated from them. Unambiguous identification of these resins, by simple and convenient analytical methods, has so far not clearly been verified. Objective For differentiation and identification of three important Boswellia species (Boswellia serrata Roxb., Boswellia papyrifera Hochst. and Boswellia carterii Birdw., respectively Boswellia sacra Flueck.), possible even for minimally equipped laboratories, a thin-layer chromatography (TLC) method was developed, allowing unambiguous identification of the three species. Methodology Crude resin samples (commercial samples and a voucher specimen) were extracted with methanol or diethyl ether and subjected to TLC analysis (normal phase). A pentane and diethyl ether (2:1) with 1% acetic acid eluent was used. Chromatograms were analysed by UV detection (254 nm) and dyeing with anisaldehyde dyeing reagent. Significant spots were isolated and structures were assigned (mass spectrometry; nuclear magnetic resonance spectroscopy). Results Incensole and incensole acetate are specific biomarkers for Boswellia papyrifera. Boswellia carterii/Boswellia sacra reveal s-caryophyllene oxide as a significant marker compound. Boswellia serrata shows neither incensole acetate nor s-caryophyllene oxide spots, but can be identified by a strong serratol and a sharp 3-oxo-8,24-dien-tirucallic acid spot. Conclusion The TLC method developed allows unambiguous identification of three different olibanum samples (Boswellia papyrifera, Boswellia serrata, Boswellia carterii/Boswellia sacra). Evidence on the specific biosynthesis routes of these Boswellia species is reported. Copyright © 2011 John Wiley & Sons, Ltd.

The use of cytochromes P450 for the regio- and stereoselective hydroxylation of non-activated carbon atoms in biotechnological applications reflects an efficient and cost-effective alternative in comparison to classical organic chemistry. The prokaryotic cytochrome P450 CYP106A2 from Bacillus megaterium ATCC 13368 hydroxylates a variety of 3-oxo-Δ⁴ steroids and recently it was identified to carry out a one-step regioselective allylic hydroxylation of the diterpene abietic acid. The anti-inflammatory pentacyclic triterpene 11-keto-β-boswellic acid (KBA) was found to be a further substrate of CYP106A2, being the first report of a pentacyclic triterpene conversion by a prokaryotic P450. The reaction products were analyzed by HPLC and the corresponding kinetic parameters were investigated. Structure determination of the main product by NMR revealed a 15α-hydroxylation of this substrate. In order to overcome the inability of a recombinant P450 whole-cell system in E. coli for the uptake of acids with terpene structure, we developed for the first time an expression system for cytochromes P450 in B. megaterium (strains MS941 and ATCC 13368). Interestingly, CYP106A2 was only successfully expressed in the plasmid-less B. megaterium strain MS941 but not in ATCC13368. This recombinant system, with the co-expressed heterologous redox chain of the P450, bovine adrenodoxin reductase (AdR), and bovine adrenodoxin (Adx), was applied for the whole-cell conversion of KBA. The formation of 15α-hydroxy-KBA was increased 15-fold in comparison with the naturally CYP106A2-expressing B. megaterium strain ATCC 13368.

A semi-automatic two dimensional high-performance liquid chromatography (HPLC) gradient method with photo diode array detection was developed, capable of separating and quantifying up to 17 different triterpenic acids in the gum resin of the frankincense species Boswellia papyrifera. The here reported quantitation of 14 of the possible 17 compounds contains boswellic, tirucallic and lupeolic acids. All compounds were isolated from B. papyrifera and used as external standards. Quantitation of these compounds was performed after minimizing the matrix by liquid–liquid separation, using alkaline, acidic and organic media to separate the acids from interfering matrix compounds. Therefore, two different extraction procedures were tested, giving two different extraction profiles. Within the first run (1st dimension) 13 compounds could be quantified. Quantitation of β-boswellic acid, which was proved to elute as inhomogeneous peak, was achieved by introduction of a second dimension, leading to a fully validated semi-automatic homomodal 2D chromatography. The method is applicable for determination of compounds occurring in different types of frankincense and their pharmaceutical products. It also can be applied to distinguish between different kinds of frankincense. Moreover, it is the first published method feasible of separating and quantifying five different types of tirucallic acids.

BACKGROUND AND PURPOSE Frankincense, the gum resin derived from Boswellia species, showed anti-inflammatory efficacy in animal models and in pilot clinical studies. Boswellic acids (BAs) are assumed to be responsible for these effects but their anti-inflammatory efficacy in vivo and their molecular modes of action are incompletely understood.

Frankincense preparations, used in folk medicine to cure inflammatory diseases, showed anti-inflammatory effectiveness in animal models and clinical trials. Boswellic acids (BAs) constitute major pharmacological principles of frankincense, but their targets and the underlying molecular modes of action are still unclear. Using a BA-affinity Sepharose matrix, a 26-kDa protein was selectively precipitated from human neutrophils and identified as the lysosomal protease cathepsin G (catG) by mass spectrometry (MALDI-TOF) and by immunological analysis. In rigid automated molecular docking experiments BAs tightly bound to the active center of catG, occupying the same part of the binding site as the synthetic catG inhibitor JNJ-10311795 (2-[3-{methyl[1-(2-naphthoyl)piperidin-4-yl]amino}carbonyl)-2-naphthyl]-1-(1-naphthyl)-2-oxoethylphosphonic acid). BAs potently suppressed the proteolytic activity of catG (IC50 of ∼600 nM) in a competitive and reversible manner. Related serine proteases were significantly less sensitive against BAs (leukocyte elastase, chymotrypsin, proteinase-3) or not affected (tryptase, chymase). BAs inhibited chemoinvasion but not chemotaxis of challenged neutrophils, and they suppressed Ca2+ mobilization in human platelets induced by isolated catG or by catG released from activated neutrophils. Finally, oral administration of defined frankincense extracts significantly reduced catG activities in human blood ex vivo vs placebo. In conclusion, we show that catG is a functional and pharmacologically relevant target of BAs, and interference with catG could explain some of the anti-inflammatory properties of frankincense.

Boswellic acids inhibit the transformation of arachidonic acid to leukotrienes via 5-lipoxygenase but can also enhance the liberation of arachidonic acid in human leukocytes and platelets. Using human platelets, we explored the molecular mechanisms underlying the boswellic acid-induced release of arachidonic acid and the subsequent metabolism by platelet-type 12-li-poxygenase (p12-LO). Both beta-boswellic acid and 3-O-acetyl-11-keto-boswellic acid (AKBA) markedly enhanced the release of arachidonic acid via cytosolic phospholipase A2 (cPLA2), whereas for generation of 12-hydro(pero)xyeicosatetraenoic acid [12-H(P)ETE], AKBA was less potent than beta-boswellic acid and was without effect at higher concentrations (> or =30 microM). In contrast to thrombin, beta-boswellic acid-induced release of ara-chidonic acid and formation of 12-H(P)ETE was more rapid and occurred in the absence of Ca2+. The Ca2+-independent release of arachidonic acid and 12-H(P)ETE production elicited by beta-boswellic acid was not affected by pharmacological inhibitors of signaling molecules relevant for agonist-induced arachidonic acid liberation and metabolism. It is noteworthy that in cell-free assays, beta-boswellic acid increased p12-LO catalysis approximately 2-fold in the absence but not in the presence of Ca2+, whereas AKBA inhibited p12-LO activity. No direct modulatory effects of boswellic acids on cPLA2 activity in cell-free assays were evident. Therefore, immobilized KBA (linked to Sepharose beads) selectively precipitated p12-LO from platelet lysates but failed to bind cPLA2. Taken together, we show that boswellic acids induce the release of arachidonic acid and the synthesis of 12-H(P)ETE in human platelets by unique Ca2+-independent routes, and we identified p12-LO as a selective molecular target of boswellic acids.

Previously, we showed that 11-keto-boswellic acid and 3-O-acetyl-11-keto-BA (AKBA) stimulate Ca(2+) mobilization and activate mitogen-activated protein kinases (MAPKs) in human polymorphonuclear leukocytes (PMNLs). Here, we addressed the effects of boswellic acids on the intracellular Ca(2+) concentration ([Ca(2+)](i)) and on the activation of p38(MAPK) and extracellular signal-regulated kinase (ERK) in the human monocytic cell line Mono Mac (MM) 6. In contrast to PMNLs, AKBA concentration dependently (1-30 microM) decreased the basal [Ca(2+)](i) in resting MM6 cells but also in cells where [Ca(2+)](i) had been elevated by stimulation with platelet-activating factor (PAF). AKBA also strongly suppressed the subsequent elevation of [Ca(2+)](i) induced by N-formyl-methionyl-leucyl-phenylalanine (fMLP), PAF, or by the direct phospholipase C activator 2,4, 6-trimethyl-N-(meta-3-trifluoromethyl-phenyl)-benzenesulfonamide, but AKBA failed to prevent Ca(2+) signals induced by thapsigargin or ionomycin. Suppression of Ca(2+) homeostasis by AKBA was also observed in primary monocytes, isolated from human blood. Moreover, AKBA inhibited the activation of p38(MAPK) and ERKs in fMLP-stimulated MM6 cells. Although the effects of AKBA could be mimicked by the putative phospholipase C (PLC) inhibitor U-73122 (1-[6-[[17beta-methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-1H-pyrrole-2,5-dione), AKBA appears to operate independent of PLC activity since the release of intracellular inositol-1,4,5-trisphosphate evoked by 2,4,6-trimethyl-N-(meta-3-trifluoromethyl-phenyl)-benzenesulfonamide was hardly diminished by AKBA. Inhibitor studies indicate that AKBA may decrease [Ca(2+)](i) by blocking store-operated Ca(2+) and/or nonselective cation channels. Together, AKBA interferes with pivotal signaling events in monocytic cells that are usually required for monocyte activation by proinflammatory stimuli. Interruption of these events may represent a possible mechanism underlying the reported anti-inflammatory properties of AKBA.

3-O-Acetyl-11-oxo-β-boswellic acid (AKBA), found in incense, is a potent inhibitor of 5-lipoxygenase, p38 and p42 MAP kinase and topoisomerases. Starting from crude extracts from incense, procedures are presented for the efficient large-scale synthesis of AKBA and other boswellic acids (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

A synthesis of anhydromarasmone is presented using, as key step, an iridium-catalyzed double-bond isomerization from a homoallyl ether to an allyl ether. Other transition metal complexes employed for double-bond transposition resulted in the vinyl ether as the final product. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

(E)-1-Hydroxy-2-methylbut-2-enyl 4-diphosphate (6) has been recently detected as an intermediate of isoprenoid biosynthesis via 1-deoxy-D-xylulose 5-phosphate. The compound was synthesized in two steps from 2-methyl-2-vinyloxirane with an overall yield of 72%. We also report a method affording [1-H-3]-6 and [1-H-2(1)]-6 from the same starting material in four steps where the hydrogen isotope is introduced in the last reaction step from deuterated or tritiated sodium borohydride. The radiochemical yield of [1-H-3]-6 was 15%. (C) 2002 Elsevier Science Ltd. All rights reserved.

The microsomal prostaglandin E2 synthase (mPGES)-1 is the terminal enzyme in the biosynthesis of prostaglandin (PG)E2 from cyclooxygenase (COX)-derived PGH2. We previously found that mPGES-1 is inhibited by boswellic acids (IC50 = 3–30 μM), which are bioactive triterpene acids present in the anti-inflammatory remedy frankincense. Here we show that besides boswellic acids, additional known triterpene acids (i.e., tircuallic, lupeolic, and roburic acids) isolated from frankincense suppress mPGES-1 with increased potencies. In particular, 3α-acetoxy-8,24-dienetirucallic acid (6) and 3α-acetoxy-7,24-dienetirucallic acid (10) inhibited mPGES-1 activity in a cell-free assay with IC50 = 0.4 μM, each. Structure–activity relationship studies and docking simulations revealed concrete structure-related interactions with mPGES-1 and its cosubstrate glutathione. COX-1 and -2 were hardly affected by the triterpene acids (IC50 > 10 μM). Given the crucial role of mPGES-1 in inflammation and the abundance of highly active triterpene acids in frankincence extracts, our findings provide further evidence of the anti-inflammatory potential of frankincense preparations and reveal novel, potent bioactivities of tirucallic acids, roburic acids, and lupeolic acids.

The first total synthesis of Mniopetal F in fourteen steps is reported. Key steps are a new and highly diastereoselective lithium phenylselenide-induced Baylis−Hillman reaction with Feringa′s butenolide, an endo-selective intramolecular Diels−Alder reaction (IMDA), inversion of a highly hindered secondary alcohol and a new variant of the Parikh−Doering oxidation.

A thermal intramolecular endo -selective Diels–Alder reaction with a substituted Feringa-butenolide is described. The structure of the main product is determined by single crystal X-ray analysis. By double activation of the dienophile substructure a dramatic increase in reactivity is reported, which leads to a decrease in reaction temperature by more than 100°C.

An improved synthesis of enantiomerically pure(S, E)-(+)-5-methylhept-2-en-4-one from(S)-(+)-2-methyl-1-butanol in four steps is reported. An improved chiral-pool synthesis of enantiomerically pure(S)-(+)-filbertone, starting from(S)-(+)-2-methyl-1-butanol in four steps is reported. Download : Download full-size image

The synthesis of new chiral calix[n]arenes, related to Corey's phenyl-menthol, is described. Starting from enantiomerically pure (R)-(+)-pulegone, calix[n]arenes with different ring sizes could be obtained in reasonable yield.

The first epc-synthesis of a chiral calix[8]arene starting from (−)-menthone is described. In a three step sequence a new enantiomerically pure calix[8]arene derivative is obtained in good yield.

Syntheses of kuehneromycin B and panudial are presented starting from kuehneromycin A using a thermal decarboxylation under pH control.

Incensole and incensole acetate, found in incense, are encouraging potent bioactive diterpenic cembrenoids, inhibiting Nuclear Factor-κB activation. Furthermore, incensole acetate elicits psycho-activity in mice by activating the TRPV3 channels in the brain. Starting from crude extracts of the incense species Boswellia papyrifera Hochst., a convenient procedure for the efficient large-scale synthesis of incensole and its acetate is presented. Additionally, a reversed-phase, diode-array-detection, high-performance liquid chromatography (RP-DAD-HPLC) method for the quantification of incensole and incensole acetate is reported, indicating that these two compounds are typical biomarkers for B. papyrifera.

A modified and improved procedure for the Rubottom oxidation of bicyclic silyl enol ethers is described. The stereochemical outcome of this reaction is studied.

Lipophilic extracts of gum resins of Boswellia species (BSE) are used in folk medicine to treat various inflammatory disorders and infections. The molecular background of the beneficial pharmacological effects of such extracts is still unclear. Various boswellic acids (BAs) have been identified as abundant bioactive ingredients of BSE. Here we report the identification of defined BAs as direct inhibitors of lipopolysaccharide (LPS) functionality and LPS-induced cellular responses. In pull-down experiments, LPS could be precipitated using an immobilized BA, implying direct molecular interactions. Binding of BAs to LPS leads to an inhibition of LPS activity which was observed in vitro using a modified limulus amoebocyte lysate assay. Analysis of different BAs revealed clear structure-activity relationships with the classical β-BA as most potent derivative (IC 50 = 1.8 μM). In RAW264.7 cells, LPS-induced expression of inducible nitric oxide synthase (iNOS, EC 1.14.13.39) was selectively inhibited by those BAs that interfered with LPS activity. In contrast, interferon-γ-induced iNOS induction was not affected by BAs. We conclude that structurally defined BAs are LPS inhibiting agents and we suggest that β-BA may contribute to the observed anti-inflammatory effects of BSE during infections by suppressing LPS activity.

Resins of the genus Boswellia are currently an interesting topic for pharmaceutical research since several pharmacological activities (e.g. anti-inflammatory, anti-microbial, anti-tumour) are reported for extracts and compounds isolated from them. Unambiguous identification of these resins, by simple and convenient analytical methods, has so far not clearly been verified.For differentiation and identification of three important Boswellia species (Boswellia serrata Roxb., Boswellia papyrifera Hochst. and Boswellia carterii Birdw., respectively Boswellia sacra Flueck.), possible even for minimally equipped laboratories, a thin-layer chromatography (TLC) method was developed, allowing unambiguous identification of the three species.Crude resin samples (commercial samples and a voucher specimen) were extracted with methanol or diethyl ether and subjected to TLC analysis (normal phase). A pentane and diethyl ether (2:1) with 1% acetic acid eluent was used. Chromatograms were analysed by UV detection (254 nm) and dyeing with anisaldehyde dyeing reagent. Significant spots were isolated and structures were assigned (mass spectrometry; nuclear magnetic resonance spectroscopy).Incensole and incensole acetate are specific biomarkers for Boswellia papyrifera. Boswellia carterii/Boswellia sacra reveal ß-caryophyllene oxide as a significant marker compound. Boswellia serrata shows neither incensole acetate nor ß-caryophyllene oxide spots, but can be identified by a strong serratol and a sharp 3-oxo-8,24-dien-tirucallic acid spot.The TLC method developed allows unambiguous identification of three different olibanum samples (Boswellia papyrifera, Boswellia serrata, Boswellia carterii/Boswellia sacra). Evidence on the specific biosynthesis routes of these Boswellia species is reported.