A novel triterpene extract from mistletoe induces rapid apoptosis in murine B16.F10 melanoma cells

The European mistletoe Viscum album L. is a plant used for remedies in cancer treatment. The benefit of commonly used aqueous extracts is controversial but the plant contains water insoluble triterpene acids providing interesting anticancer properties. Triterpene extracts (TE) from plants and single triterpenoids such as oleanolic acid (OA) or betulinic acid (BA) are known for their cytotoxic effects on cancer cell lines in vitro. We report here cytotoxic effects of a novel OA-rich triterpene extract from mistletoe (V. album L., Santalaceae) solubilized by 2-hydroxypropyl-β-cyclodextrin (2-HP-β-CD) on B16.F10 mouse melanoma cells. The 2-HP-β-CD solubilized triterpene extract (STE) was highly cytotoxic by causing DNA fragmentation, followed by loss of membrane integrity and intracellular adenosine-5'-triphosphate (ATP). Blocking the caspase machinery by inhibitors aborted DNA fragmentation and delayed the cytotoxic effects but did not prevent cell death. The solubilization by 2-HP-β-CD allows a solvent-free application of triterpene extracts in the in vitro setting. These findings suggest the use of STE from mistletoe as a solvent-free anticancer drug for preclinical animal experiments and clinical trials.

Diversity Oriented Synthesis: Concise Entry to Novel Derivatives of Yohimbine and Corynanthe Alkaloids

A novel MCAP-cycloaddition sequence has been applied to the facile synthesis of β-carboline intermediates to gain rapid access to novel derivatives of yohimbine-like and corynanthe-like compounds that may be easily diversified by cross-coupling reactions and N-derivatizations to generate small compound libraries.

Libraries of 2,3,4,6,7,11b-hexahydro-1H-pyrido[2,1-a]isoquinolin-2-amine derivatives via a multicomponent assembly process/1,3-dipolar cycloaddition strategy

A Mannich-type multicomponent assembly process/1,3-dipolar cycloaddition strategy has been developed for the rapid and efficient construction of a parent tetrahydroisoquinoline fused isoxazolidine scaffold, which was subsequently functionalized using well-established protocols to access a diverse 70-membered library of novel 2,3,4,6,7,11b-hexahydro-1H-pyrido[2,1-a]isoquinoline-2-amine derivatives.

Tandem Electrocyclic Ring Opening/Radical Cyclization: Application to the Total Synthesis of Cribrostatin 6

A concise total synthesis ofcribrostatin 6 (1), an antimicrobial and antineoplastic agent,was accomplished using a tandem electrocyclic ring opening/radical cyclization sequence. Specifically, intermediate4 underwent a 4π-electrocyclic ring opening, radical cyclization, and homolytic aromatic substitution sequence followed by an oxidation to afford the natural product1in one pot. Owing to the rapid buildup of complexity in the key step, 1 could be synthesized from commercially available starting materials in only four linear steps. Application of this chemistry to the concise syntheses of analogs of cribrostatin 6 (1) is also reported.

Facile Syntheses of Substituted, Conformationally-Constrained Benzoxazocines and Benzazocines via Sequential Multicomponent Assembly and Cyclization

A multicomponent assembly process (MCAP) was utilized to prepare versatile intermediates that are suitably functionalized for subsequent cyclizations via Ullmann and Heck reactions to efficiently construct substituted 2,6-methanobenzo[b][1,5]oxazocines and 1,6-methanobenzo[c]azocines, respectively. The intramolecular Ullmann cyclization was conducted in tandem with an intermolecular arylation that enabled the rapid syntheses of a number of O-functionalized methanobenzoxazocines.

Protein-ligand interactions: thermodynamic effects associated with increasing nonpolar surface area

Thermodynamic parameters were determined for complex formation between the Grb2 SH2 domain and Ac-pTyr-Xaa-Asn derived tripeptides in which the Xaa residue is an α,α-cycloaliphatic amino acid that varies in ring size from three- to seven-membered. Although the six- and seven-membered ring analogs are approximately equipotent, binding affinities of those having three- to six-membered rings increase incrementally with ring size because increasingly more favorable binding enthalpies dominate increasingly less favorable binding entropies, a finding consistent with an enthalpy-driven hydrophobic effect. Crystallographic analysis reveals that the only significant differences in structures of the complexes are in the number of van der Waals contacts between the domain and the methylene groups in the Xaa residues. There is a positive correlation between buried nonpolar surface area and binding free energy and enthalpy, but not with ΔC(p). Displacing a water molecule from a protein-ligand interface is not necessarily reflected in a favorable change in binding entropy. These findings highlight some of the fallibilities associated with commonly held views of relationships of structure and energetics in protein-ligand interactions and have significant implications for ligand design.

APPLICATIONS OF MULTICOMPONENT ASSEMBLY PROCESSES TO THE FACILE SYNTHESES OF DIVERSELY FUNCTIONALIZED NITROGEN HETEROCYCLES

Several multicomponent assembly processes have been developed for the synthesis of intermediates that may be elaborated by a variety of cyclizations to generate a diverse array of highly functionalized heterocycles from readily-available starting materials. The overall approach enables the efficient preparation of libraries of small molecules derived from fused, privileged scaffolds.

General and expedient synthesis of 1,4-dioxygenated xanthones

A facile entry to 1,4-dioxygenated xanthones having a variety of substitution patterns and substituents was developed that features a novel application of the Moore cyclization using substrates that were readily assembled in a highly convergent fashion by an acetylide stitching process. The practical utility of the methodology was demonstrated by an efficient synthesis of a naturally occurring xanthone and correction of the structure of dulcisxanthone C.

Novel approach to the lundurine alkaloids: synthesis of the tetracyclic core

The tetracyclic core of the lundurine family of alkaloids has been synthesized by a novel approach that features a double ring-closing olefin metathesis to form the five-and eight-membered rings.

Studies Toward the Syntheses of Pluramycin Natural Products. The First Total Synthesis of Isokidamycin

We report the first total synthesis of the complex C-aryl glycoside isokidamycin, the epimer of the naturally-occurring pluramycin antibiotic kidamycin. The synthesis features a highly efficientDiels-Alder reaction between a substituted naphthyne and a glycosylatedfuran to form the anthracene core bearing a pendant angolosamine C-glycoside. The regiochemical outcome of the Diels-Alder reaction was controlled by employing a disposable silicon-tether to link the reactive napthyne and the glycosyl furan, rendering the cycloaddition intramolecular. The benzopyranone moietyof the aromatic nucleus was appended by cyclization of a functionalized vinylogous amide onto an advanced anthrol intermediate. The vancosamine amino glycoside was introduced by an O→C-glycoside rearrangement that produced the β-anomer. Subsequent refunctionalizations then led to isokidamycin.

Mechanisms of chemical-induced innate immunity in allergic contact dermatitis

Allergic contact dermatitis (ACD) is one of the most prevalent occupational skin diseases and causes severe and long-lasting health problems in the case of chronification. It is initiated by an innate inflammatory immune response to skin contact with low molecular weight chemicals that results in the priming of chemical-specific, skin-homing CD8(+) Tc1/Tc17 and CD4(+) Th1/Th17 cells. Following this sensitization step, T lymphocytes infiltrate the inflamed skin upon challenge with the same chemical. The T cells then exert cytotoxic function and secrete inflammatory mediators to produce an eczematous skin reaction. The recent characterization of the mechanisms underlying the innate inflammatory response has revealed that contact allergens activate innate effector mechanisms and signalling pathways that are also involved in anti-infectious immunity. This emerging analogy implies infection as a potential trigger or amplifier of the sensitization to contact allergens. Moreover, new mechanistic insights into the induction of ACD identify potential targets for preventive and therapeutic intervention. We summarize here the latest findings in this area of research.

Multicomponent assembly strategies for the synthesis of diverse tetrahydroisoquinoline scaffolds

Several novel multicomponent assembly processes have been developed for the rapid and efficient assembly of various heterocyclic scaffolds bearing a tetrahydroisoquinoline core, each of which allows for facile derivatization to access a diverse array of compounds. This work led to the serendipitous discovery of a new method for the synthesis of a fused quinazolone ring system, which was applied to a one-step total synthesis of the quinazolinocarboline alkaloid rutaecarpine.

Toward a total synthesis of the stemofoline alkaloids: Advancement of a 1,3-dipolar cycloaddition strategy

Novel, intramolecular 1,3-dipolar cycloadditions of azomethine ylides have been applied to the synthesis of functionalized core structures of the stemofoline alkaloids. In an effort to maximize the efficiency of this key transformation in the context of an eventual total synthesis of these complex natural products, a number of strategic modifications to the cycloaddition substrate were investigated. These collective efforts have provided useful insights into the operative, regiochemical control elements for 1,3-dipolar cycloadditions leading to stemofoline alkaloids. A potential intermediate in the synthesis of these alkaloids was prepared.

Multicomponent assembly and diversification of novel heterocyclic scaffolds derived from 2-arylpiperidines

A collection of structurally diverse, polyheterocyclic scaffolds comprising a 2-arylpiperidine subunit were synthesized using a Mannich-type multicomponent assembly process, followed by appropriately sequenced ring-forming reactions. An improved procedure for removal of N-4-pentenoyl groups was developed; one-pot sequences for tandem urea/thiourea formation and cyclization and tandem enolate arylation/alkylation were discovered. A novel entry to bridged tetrahydroquinoline scaffolds exploiting A(1,3) strain was also invented. Derivatization of several scaffolds was achieved by cross-coupling and N-functionalization.

Facile Access to Sterically Hindered Aryl Ketones via Carbonylative Cross-Coupling: Application to the Total Synthesis of Luteolin

A general and mild protocol for achieving the carbonylative cross-coupling of sterically-hindered, ortho-disubstituted aryl ketones is reported. The commercially available PEPPSI-IPr catalyst is shown to efficiently promote the carbonylative cross-coupling of hindered ortho-disubstituted aryl iodides to give diaryl ketones; traditional phosphine catalysts are less effective. Carbonylative Suzuki-Miyaura cross-couplings provide a diverse array of biaryl ketones in good to excellent yields. The same catalyst is also shown to catalyze a carbonylative Negishi cross-coupling reaction, utilizing a variety of alkynyl zinc reagents to give the corresponding alkynyl aryl ketones. Application of this new methodology to the synthesis of the natural product luteolin is reported.

Facile and unified approach to skeletally diverse, privileged scaffolds

A novel strategy has been developed to generate a diverse array of privileged scaffolds from readily available tetrahydropyridine precursors that may be prepared by a multicomponent assembly process followed by a ring-closing metathesis. The functionality embedded in these key intermediates enables their facile elaboration into more complex structures of biological relevance by a variety of ring-forming processes and refunctionalizations.

Synthesis and diversification of 1,2,3-triazole-fused 1,4-benzodiazepine scaffolds

A substituted heterocyclic scaffold comprising a 1,4-benzodiazepine fused with a 1,2,3-triazole ring has been synthesized and diversified via a variety of refunctionalizations. The strategy features the rapid assembly of the scaffold by combining 3-4 reactants in an efficient multicomponent assembly process, followed by an intramolecular Huisgen cycloaddition.

Enantioselective synthesis of 2,2,5-tri- and 2,2,5,5-tetrasubstituted tetrahydrofurans via [4 + 2] cycloaddition and ring-opening cross-metathesis

A chiral vinyl sulfoxide has been developed that undergoes highly diastereoselective Diels-Alder cycloadditions with various substituted furans in excellent yield. The cycloadducts can be stereoselectively transformed into 2,2,5-tri- and 2,2,5,5-tetrasubstituted tetrahydrofurans, which are structural subunits of many natural products, via regioselective ring-opening metathesis/cross-metathesis or oxidative cleavage/refunctionalization.

The purinergic receptor P2Y2 receptor mediates chemotaxis of dendritic cells and eosinophils in allergic lung inflammation

BACKGROUND

Extracellular ATP contributes to the pathogenesis of asthma via signalling at purinergic receptors. However, the precise purinergic receptors subtypes mediating the pro-asthmatic effects of ATP have not been identified, yet.

METHODS

In vivo studies were performed using the OVA-alum model. Functional expression of the P2Y(2) purinergic receptor subtype on human monocyte-derived dendritic cells and eosinophils was investigated using real-time PCR, migration assays, and production of reactive oxygen species.

RESULTS

Compared to wild-type animals P2Y(2) -/- mice showed reduced allergic airway inflammation which can be explained by defective migration of blood myeloid DCs towards ATP in vitro and in vivo, whereas the influence of ATP on maturation and cytokine production was not changed. Additionally, ATP failed to induce migration of bone marrow-derived eosinophils from P2Y(2) R-deficient animals. The relevance of our findings for humans was confirmed in functional studies with human monocyte-derived DCs and eosinophils. Interestingly, stimulation of human DCs derived from allergic individuals with house dust mite allergen induced functional up-regulation of the P2Y(2) R subtype. Furthermore, eosinophils isolated from asthmatic individuals expressed higher levels of P2Y(2) R compared to healthy controls. This was of functional relevance as these eosinophils were more sensitive to ATP-induced migration and production of reactive oxygen metabolites.

CONCLUSIONS

In summary, P2Y(2) R appears to be involved in asthmatic airway inflammation by mediating ATP-triggered migration of mDCs and eosinophils, as well as reactive oxygen species production. Together our data suggest that targeting P2Y(2) R might be a therapeutic option for the treatment of asthma.

Constraining binding hot spots: NMR and molecular dynamics simulations provide a structural explanation for enthalpy-entropy compensation in SH2-ligand binding

NMR spectroscopy and molecular dynamics (MD) simulations were used to probe the structure and dynamics of complexes of three phosphotyrosine-derived peptides with the Src SH2 domain in an effort to uncover a structural explanation for enthalpy-entropy compensation observed in the binding thermodynamics. The series of phosphotyrosine peptide derivatives comprises the natural pYEEI Src SH2 ligand, a constrained mimic, in which the phosphotyrosine (pY) residue is preorganized in the bound conformation for the purpose of gaining an entropic advantage to binding, and a flexible analogue of the constrained mimic. The expected gain in binding entropy of the constrained mimic was realized; however, a balancing loss in binding enthalpy was also observed that could not be rationalized from the crystallographic structures. We examined protein dynamics to evaluate whether the observed enthalpic penalty might be the result of effects arising from altered motions in the complex. (15)N-relaxation studies and positional fluctuations from molecular dynamics indicate that the main-chain dynamics of the protein show little variation among the three complexes. Root mean squared (rms) coordinate deviations vary by less than 1.5 A for all non-hydrogen atoms for the crystal structures and in the ensemble average structures calculated from the simulations. In contrast to this striking similarity in the structures and dynamics, there are a number of large chemical shift differences from residues across the binding interface, but particularly from key Src SH2 residues that interact with pY, the "hot spot" residue, which contributes about one-half of the binding free energy. Rank-order correlations between chemical shifts and ligand binding enthalpy for several pY-binding residues, coupled with available mutagenesis and calorimetric data, suggest that subtle structural perturbations (<1 A) from the conformational constraint of the pY residue sufficiently alter the geometry of enthalpically critical interactions in the binding pocket to cause the loss of binding enthalpy, leading to the observed enthalpy-entropy compensation. We find no evidence to support the premise that enthalpy-entropy compensation is an inherent property and conclude that preorganization of Src SH2 ligand residues involved in binding hot spots may eventuate in suboptimal interactions with the domain. We propose that introducing constraints elsewhere in the ligand could minimize enthalpy-entropy compensation effects. The results illustrate the utility of the NMR chemical shift to highlight small, but energetically significant, perturbations in structure that might otherwise go unnoticed in an apparently rigid protein.

Approach toward the total synthesis of 5-hydroxyaloin A

The synthesis of a thiomethyl analogue of 5-hydroxyaloin A has been achieved using benzyne and naphthyne [4 + 2] cycloadditions with substituted furans. A regiocontrolled cycloaddition was achieved using a silicon tether, and a regioselective ring opening was accomplished using a sulfide as a directing group.

Concise total synthesis of (+/-)-pseudotabersonine via double ring-closing metathesis strategy

A concise synthesis of (+/-)-pseudotabersonine from commercially available 1-(phenylsulfonyl)-3-indolecarboxaldehyde has been accomplished. This synthesis features the convergent assembly of a key intermediate via a stepwise variant of a Mannich-type multicomponent coupling process, a double ring-closing metathesis, and a one-pot deprotection/cyclization reaction.