Diversity Oriented Synthesis of Novel Xanthones Reveal Potent Doxorubicin-Inspired Analogs

Inspired by potent antiproliferative xanthone natural products and so far limited examples of derived bioactive agents, a structure activity study of architecturally novel types of xanthones is reported. Their preparation was enabled in a short and divergent manner by a modular chlorination in combination with optimized protocols for a polar condensation and a hetero-cyclization. Application of these procedures allowed for the synthesis of various polyhalogenated representatives (including mixed bromo/chloro xanthones) that were obtained in up to fourfold improved yields as compared to previous procedures. Subsequent Suzuki coupling of either halide enabled access to phenyl- and chloro-bearing xanthones, which may be functionalized at four out of five non-hydroxylated positions. Antiproliferative assays against breast cancer cell lines revealed potent activities of some of these simplified analogs that are in the range of pharmaceutically used anticancer drug doxorubicin.

Quaternary Carbon Synthesis by Titanocene Catalyzed Radical Allyl Transfer on Epoxides

A versatile titanocene-catalyzed radical allyl transfer reaction on epoxides is reported. Epoxide opening occurs regioselectively at the more hindered side, and variously substituted allyl sulfone may be coupled to this position in an efficient manner, enabling a rapid access to quaternary carbon centers with useful functionalities for further elaboration. Furthermore, the procedure can be expanded to stereoselective variants. This new radical allyl transfer expands the scope of allylation in organic synthesis.

Strategies and tactics for the synthesis of lipid I and II and shortened analogues: functional building blocks of bacterial cell wall biosynthesis

Covering: the literature up to 2022This study discusses various synthetic strategies for the synthesis of lipid II, the pivotal bacterial cell wall precursor. In detail, it examines different solution phase approaches, reviews various solid phase sequences, and evaluates enzymatic ventures. The underlying rationale, scope, limitations, and perspectives of these strategies are discussed. The focus is on the tactics and strategies towards the authentic peptidoglycan compound, as well as analogues thereof with shortened side chains, which are increasingly recognized as more beneficial surrogates with more favorable physicochemical properties.

Mucosal-associated invariant T cells contribute to suppression of inflammatory myeloid cells in immune-mediated kidney disease

Mucosal-associated invariant T (MAIT) cells have been implicated in various inflammatory diseases of barrier organs, but so far, their role in kidney disease is unclear. Here we report that MAIT cells that recognize their prototypical ligand, the vitamin B2 intermediate 5-OP-RU presented by MR1, reside in human and mouse kidneys. Single cell RNAseq analysis reveals several intrarenal MAIT subsets, and one, carrying the genetic fingerprint of tissue-resident MAIT17 cells, is activated and expanded in a murine model of crescentic glomerulonephritis (cGN). An equivalent subset is also present in kidney biopsies of patients with anti-neutrophil cytoplasmatic antibody (ANCA)-associated cGN. MAIT cell-deficient MR1 mice show aggravated disease, whereas B6-MAITCAST mice, harboring higher MAIT cell numbers, are protected from cGN. The expanded MAIT17 cells express anti-inflammatory mediators known to suppress cGN, such as CTLA-4, PD-1, and TGF-β. Interactome analysis predicts CXCR6 - CXCL16-mediated cross-talk with renal mononuclear phagocytes, known to drive cGN progression. In line, we find that cGN is aggravated upon CXCL16 blockade. Finally, we present an optimized 5-OP-RU synthesis method which we apply to attenuating cGN in mice. In summary, we propose that CXCR6+ MAIT cells might play a protective role in cGN, implicating them as a potential target for anti-inflammatory therapies.

Synthesis and biological evaluation of simplified ajudazol derivatives reveal potent 5-lipoxygenase inhibition and considerable apoptotic activity in neuroblastoma cells

Simplified analogues of the myxobacterial polyketide ajudazol were obtained by synthesis and evaluated for their biological activities. Potent simplified 5-lipoxygenase inhibitors were identified. Moreover, strong antiproliferative and apoptotic activities were observed in brain cancer cell lines at low nano- to micromolar concentrations.

Epilepsy and nodding syndrome in association with an Onchocerca volvulus infection drive distinct immune profile patterns

Previous studies have described the association of onchocerciasis (caused by Onchocerca volvulus) with epilepsy, including nodding syndrome, although a clear etiological link is still missing. Cases are found in different African countries (Tanzania, South Sudan, Uganda, Democratic Republic of the Congo, Central African Republic and Cameroon). In our study we investigated immunological parameters (cytokine, chemokine, immunoglobulin levels) in individuals from the Mahenge area, Tanzania, presenting with either epilepsy or nodding syndrome with or without O. volvulus infection and compared them to O. volvulus negative individuals from the same endemic area lacking neurological disorders. Additionally, cell differentiation was performed using blood smears and systemic levels of neurodegeneration markers, leiomodin-1 and N-acetyltyramine-O, β-glucuronide (NATOG) were determined. Our findings revealed that cytokines, most chemokines and neurodegeneration markers were comparable between both groups presenting with epilepsy or nodding syndrome. However, we observed elevated eosinophil percentages within the O. volvulus positive epilepsy/nodding syndrome patients accompanied with increased eosinophilic cationic protein (ECP) and antigen-specific IgG levels in comparison to those without an O. volvulus infection. Furthermore, highest levels of NATOG were found in O. volvulus positive nodding syndrome patients. These findings highlight that the detection of distinct biomarkers might be useful for a differential diagnosis of epilepsy and nodding syndrome in O. volvulus endemic areas. Trial-registration: NCT03653975.

Total Synthesis of Pentamycin by a Conformationally Biased Double Stille Ring Closure with a Trienyl-bis-stannane

The total synthesis of the potent polyene macrolide antibiotic pentamycin was accomplished by an expedient strategy involving a highly stereoselective assembly of the polyol segment in combination with an adventurous double Stille cross-coupling with a trienyl-bis-stannane closing the macrolactone and installing the sensitive pentaene fragment. Presumably, this remarkable linchpin insertion is enhanced by the linear hydrogen bonding skeleton of the polyol substrate. Further key features include a tailored Rychnovsky alkylation of cyanohydrin acetonides and elaborate Krische couplings to set the characteristic hydroxyl and hydroxymethyl bearing centers with excellent selectivity and yield. The total synthesis unequivocally confirms the full relative and absolute stereochemistry of this polyketide, including a previously uncertain hydroxyl bearing center.

Sequential Methods for Di- and Tetrahydro-Pyranone Synthesis Enable Concise Access to Tuscolid δ-Lactone

Two novel tandem sequences for stereoselective synthesis of elaborate hydropyranones are reported. The first one relies on an aldol-lactonization procedure of a chiral enolate with an unprotected aldehyde, while the second one is based on a challenging dienolate ketone addition with concomitant cyclization and substrate controlled reduction. Both approaches proceed with high efficiency and stereoselectivity and enable very short accesses to the authentic pyranone subunit of the complex polyketide tuscolid and will be important to develop a first total synthesis of this structurally unique macrolide and to evaluate the tuscolid-tuscoron rearrangement.

Chemical modulation of microtubule structure through the laulimalide/peloruside site

Taxanes are microtubule-stabilizing agents used in the treatment of many solid tumors, but they often involve side effects affecting the peripheral nervous system. It has been proposed that this could be related to structural modifications on the filament upon drug binding. Alternatively, laulimalide and peloruside bind to a different site also inducing stabilization, but they have not been exploited in clinics. Here, we use a combination of the parental natural compounds and derived analogs to unravel the stabilization mechanism through this site. These drugs settle lateral interactions without engaging the M loop, which is part of the key and lock involved in the inter-protofilament contacts. Importantly, these drugs can modulate the angle between protofilaments, producing microtubules of different diameters. Among the compounds studied, we have found some showing low cytotoxicity and able to induce stabilization without compromising microtubule native structure. This opens the window of new applications for microtubule-stabilizing agents beyond cancer treatment.

Extracellular hemin is a reverse use-dependent gating modifier of cardiac voltage-gated Na+ channels

Heme (Fe²⁺-protoporphyrin IX) is a well-known protein prosthetic group; however, heme and hemin (Fe³⁺-protoporphyrin IX) are also increasingly viewed as signaling molecules. Among the signaling targets are numerous ion channels, with intracellular-facing heme-binding sites modulated by heme and hemin in the sub-µM range. Much less is known about extracellular hemin, which is expected to be more abundant, in particular after hemolytic insults. Here we show that the human cardiac voltage-gated sodium channel hNa_V1.5 is potently inhibited by extracellular hemin (IC ₅₀ ≈ 80 nM), while heme, dimethylhemin, and protoporphyrin IX are ineffective. Hemin is selective for hNa_V1.5 channels: hNa_V1.2, hNa_V1.4, hNa_V1.7, and hNa_V1.8 are insensitive to 1 µM hemin. Using domain chimeras of hNa_V1.5 and rat rNa_V1.2, domain II was identified as the critical determinant. Mutation N803G in the domain II S3/S4 linker largely diminished the impact of hemin on the cardiac channel. This profile is reminiscent of the interaction of some peptide voltage-sensor toxins with Na_V channels. In line with a mechanism of select gating modifiers, the impact of hemin on Na_V1.5 channels is reversely use dependent, compatible with an interaction of hemin and the voltage sensor of domain II. Extracellular hemin thus has potential to modulate the cardiac function.

Modular Synthesis of Halogenated Xanthones by a Divergent Coupling Strategy

A versatile strategy to halogenated xanthones was developed that relies on a modular coupling of vanillin derivatives with a dibromoquinone. Depending on the reaction conditions, either the 6- or the 7-bromo heterocycles may be obtained in a divergent manner. These heterocycles may be readily further elaborated by sequential Sonogashira couplings, and the sequence may be successfully applied to substructures of the antibiotic lysolipin.

Versatile synthesis of pathogen specific bacterial cell wall building blocks

Full details on the design, strategies and tactics for development of a novel synthetic sequence to farnesyl lipid I and II analogs is reported. The modular route was based on a three coupling strategy involving an efficient solid phase synthesis of the elaborate peptide fragment, which proceeded with excellent yield and stereoselectivity and was efficiently applied for the convergent synthesis of 3-lipid I and II. Furthermore, the generality of this route was demonstrated by synthesis of 3-lipid I congeners that are characteristic for S. aureus and E. faecalis. All 3-lipid I and II building blocks were obtained in high purity revealing high spectroscopic resolution.

A modular three coupling strategy involving a versatile solid phase peptide synthesis enables access to pathogen specific lipid analogs in high yield, revealing high spectroscopic resolution of these key bacterial cell wall building blocks.

Dihydroxylation Studies of Isoquinolinones: Synthesis of the EF-Ring of Lysolipin I

Inspired by the potent polycyclic xanthone antibiotic lysolipin I, a general study on asymmetric dihydroxylation reactions of variously substituted isoquinolinones was performed. Different isoquinolinones were efficiently prepared, either by a Pomeranz–Fritsch type condensation or a Curtius rearrangement. Under a broad variety of conventional oxygenation procedures, they proved very unreactive. However, either by suitable substitution of the appending aromatic ring or more forcing conditions a dihydroxylation could finally be performed, which allowed the synthesis of the EF-ring of lysolipin I.

Modular Total Synthesis of iso-Archazolids and Archazologs

Full details on the design, development, and successful implementation of suitable synthetic strategies directed toward the total synthesis of iso-archazolids and archazologs are reported. Both a biomimetic and a multistep total synthesis of iso-archazolid B, the most potent and least abundant archazolid, are described. The bioinspired conversion from archazolid B was realized by a high-yielding 1,8-Diazabicyclo[5.4.0]undec-7-ene catalyzed one-step double-bond shift. A highly stereoselective total synthesis was accomplished in 25 steps, involving a sequence of highly stereoselective aldol reactions, an efficient aldol condensation to forge two elaborate fragments, and a challenging ring-closing metathesis macrocyclization with an unusual Stewart-Grubbs catalyst. These strategies proved to be generally useful and could be successfully implemented for the preparation of three novel iso-archazolids as well as five novel archazologs, lacking the thiazole side chain. A wide variety of further archazolids and archazologs may now be targeted for exploration of the promising anticancer potential of these polyketide macrolides.

Design and Synthesis of Simplified Polyketide Analogs: New Modalities beyond the Rule of 5

Natural products provide important lead structures for development of pharmaceutical agents or present attractive tools for medicinal chemistry. However, structurally complex and thus less accessible metabolites defying conventional drug-like properties, as expressed by Pfizer's rule of five, have received less attention as medicinal leads. Traditionally, research focus has been on realizing total syntheses rather than developing more readily available analogs to resolve the critical supply issue. However, very recent studies with complex myxobacterial polyketides have demonstrated that considerable structural simplification may be realized with retention of biological potencies. The context, underlying rationale and importance of tailored synthetic strategies of three such case studies are presented, which may inspire further related activities and may eventually help exploiting the largely untapped biological potential of complex metabolites in general.

Modular Fragment Synthesis and Bioinformatic Analysis Propose a Revised Vancoresmycin Stereoconfiguration

Elaborate fragments of the proposed stereostructure of the complex polyketide antibiotic vancoresmycin have been synthesized in a stereoselective fashion based on a modular and convergent approach. Significant nuclear magnetic resonance differences in one of these subunits compared with the natural product question the proposed stereoconfiguration. Consequently, an extensive bioinformatics analysis of the biosynthetic gene cluster was carried out, leading to a revised stereoconfigurational proposal for this highly potent antibiotic.

SAR Studies of the Leupyrrins: Design and Total Synthesis of Highly Potent Simplified Leupylogs

Leupyrrins are highly potent antifungal agents. A structure-activity-relationship study of natural and synthetic derivatives is reported which reveals important insights into the biological relevance of several structural subunits leading to the discovery of highly potent but drastically simplified leupylogs that incorporate a stable and readily available aromatic side chain. For their synthesis a concise strategy is described that enables a short and versatile access.

SAR Studies of the Leupyrrins: Design and Total Synthesis of Highly Potent Simplified Leupylogs

Invited for the cover of this issue is the group of Dirk Menche at the University of Bonn. The image depicts the natural product leupyrrin A₁ and a synthetic leupylog in balance on an IC50 weighing scale. Read the full text of the article at 10.1002/chem.202002622.

Modular Total Synthesis of Farnesyl Analogues of Cell Wall Precursors Lipid I and II Containing the Staphylococcus aureus Pentaglycine Bridge Modification

A scalable and modular total synthesis of 3-lipid I and 3-lipid II was accomplished by a novel route involving an efficient solid phase synthesis of the peptide fragment and an effective chemoenzymatic attachment of the second sugar moiety. The generality of this route was further documented by the synthesis of an analogue bearing the pentaglycine interpeptidic bridge modification characteristic for the human pathogen Staphylococcus aureus.

Synthesis of Tetramic Acid Fragments Derived from Vancoresmycin Showing Inhibitory Effects towards S. aureus

An efficient route to various vancoresmycin‐type tetramic acids has been developed. The modular route is based on an effective Fries‐type rearrangement to introduce various appending acetyl residues. The minimum inhibitory concentration (MIC) values of the new tetramic acids against Staphylococcus aureus and Escherichia coli were determined, revealing that three of the new compounds exhibit antimicrobial activity against S. aureus. These bioactive compounds were structurally most closely related to the authentic vancoresmycin building block. Additionally, the compounds induced a lial‐lux bioreporter, which responds to cell wall stress induced by antibiotics that interfere with the lipid II biosynthesis cycle. These data suggest the tetramic acid moiety to be a part of the vancoresmycin pharmacophore.

Design, Synthesis and Biological Evaluation of Highly Potent Simplified Archazolids

The archazolids are potent antiproliferative compounds that have recently emerged as a novel class of promising anticancer agents. Their complex macrolide structures and scarce natural supply make the development of more readily available analogues highly important. Herein, we report the design, synthesis and biological evaluation of four simplified and partially saturated archazolid derivatives. We also reveal important structure‐activity relationship data as well as insights into the pharmacophore of these complex polyketides.

High-affinity binding and catalytic activity of His/Tyr-based sequences: Extending heme-regulatory motifs beyond CP

BACKGROUND & MOTIVATION

Peptides and proteins can interact with heme through His, Tyr, or Cys in heme-regulatory motifs (HRMs). The Cys-Pro dipeptide is a well investigated HRM, but for His and Tyr such a distinct motif is currently unknown. In addition, many heme-peptide complexes, such as heme-amyloid β, can display a peroxidase-like activity, albeit there is little understanding of how the local primary and secondary coordination environment influences catalytic activity. We thus systematically evaluated a series of His- and Tyr-based peptides to identify sequence features for high-affinity heme binding and their impact on the catalytic activity of heme.

METHODS

We employed solid-phase peptide synthesis to produce 58 nonapeptides, which were investigated by UV/vis, resonance Raman, and 2D NMR spectroscopy. A chromogenic assay was used to determine the catalytic activity of the heme-peptide complexes.

RESULTS

Heme-binding affinity and binding mode were found to be dependent on the coordinating amino acid and spacer length between multiple potential coordination sites in a motif. In particular, HXH and HXXXH motifs showed strong heme binding. Analysis of the peroxidase-like activity revealed that some of these peptides and also HXXXY motifs enhance the catalytic activity of heme significantly.

CONCLUSIONS

We identify HXH, HXXXH, and HXXXY as potential new HRMs with functional properties. Several peptides displayed a strikingly high peroxidase-like activity.

GENERAL SIGNIFICANCE

The identification of HRMs allows to discover yet unknown heme-regulated proteins, and consequently, enhances our current understanding of pathologies involving labile heme.

Differential role of vacuolar (H+)-ATPase in the expression and activity of cyclooxygenase-2 in human monocytes

Monocytes are professional immune cells that produce abundant levels of pro-inflammatory eicosanoids including prostaglandins and leukotrienes during inflammation. Vacuolar (H⁺)-ATPase (V-ATPase) is critically involved in a variety of inflammatory processes including cytokine trafficking and lipid mediator biosynthesis. However, its role in eicosanoid biosynthetic pathways in monocytes remains elusive. Here, we present a differential role of V-ATPase in the expression and in the activity of cyclooxygenase (COX)-2 in human monocytes. Pharmacological targeting of V-ATPase increased the expression of COX-2 protein in lipopolysaccharide-stimulated primary monocytes, which was paralleled by enhanced phosphorylation of p38 MAPK and ERK-1/2, without impacting the NF-κB and SAPK/JNK pathways. Targeting of both p38 MAPK and ERK-1/2 pathways showed that the kinase pathways are crucial for COX-2 expression in human monocytes. Despite increased COX-2 protein levels, however, suppression of V-ATPase activity impaired the biosynthesis of COX- and also of 5-lipoxygenase (LOX)-derived lipid mediators in monocytes without affecting 12-/15-LOX products, assessed by a metabololipidomics approach using UPLC-MS-MS analysis. Our results indicate that changes in the intracellular pH may contribute to suppression of COX-2 and 5-LOX activities. We suggest that V-ATPase on one hand limits COX-2 protein levels via restricting p38 MAPK and ERK-1/2 activation, while on the other hand it governs the cellular activity of COX-2 through appropriate adjustment of the intracellular pH.

Stereochemical Determination of Tuscolid/Tuscorons and Total Synthesis of Tuscoron D and E: Insights into the Tuscolid/Tuscoron Rearrangement

The stereochemistry of the structurally unique myxobacterial polyketides tuscolid/tuscorons was determined by a combination of high-field NMR studies, molecular modeling, and chemical derivatization and confirmed by a modular total synthesis of tuscorons D and E. Together with the discovery of three novel tuscorons, this study provides detailed insight into the chemically unprecedented tuscolid/tuscoron rearrangement cascade.

Vacuolar (H+)-ATPase Critically Regulates Specialized Proresolving Mediator Pathways in Human M2-like Monocyte-Derived Macrophages and Has a Crucial Role in Resolution of Inflammation

Alternative (M2)-polarized macrophages possess high capacities to produce specialized proresolving mediators (SPM; i.e., resolvins, protectins, and maresins) that play key roles in resolution of inflammation and tissue regeneration. Vacuolar (H⁺)-ATPase (V-ATPase) is fundamental in inflammatory cytokine trafficking and secretion and was implicated in macrophage polarization toward the M2 phenotype, but its role in SPM production and lipid mediator biosynthesis in general is elusive. In this study, we show that V-ATPase activity is required for the induction of SPM-biosynthetic pathways in human M2-like monocyte-derived macrophages (MDM) and consequently for resolution of inflammation. Blockade of V-ATPase by archazolid during IL-4-induced human M2 polarization abrogated 15-lipoxygenase-1 expression and prevented the related biosynthesis of SPM in response to pathogenic Escherichia coli, assessed by targeted liquid chromatography-tandem mass spectrometry-based metabololipidomics. In classically activated proinflammatory M1-like MDM, however, the biosynthetic machinery for lipid mediator formation was independent of V-ATPase activity. Targeting V-ATPase in M2 influenced neither IL-4-triggered JAK/STAT6 nor the mTOR complex 1 signaling but strongly suppressed the ERK-1/2 pathway. Accordingly, the ERK-1/2 pathway contributes to 15-lipoxygenase-1 expression and SPM formation in M2-like MDM. Targeting V-ATPase in vivo delayed resolution of zymosan-induced murine peritonitis accompanied by decreased SPM levels without affecting proinflammatory leukotrienes or PGs. Together, our data propose that V-ATPase regulates 15-lipoxygenase-1 expression and consequent SPM biosynthesis involving ERK-1/2 during M2 polarization, implying a crucial role for V-ATPase in the resolution of inflammation.

V-ATPase inhibition increases cancer cell stiffness and blocks membrane related Ras signaling - a new option for HCC therapy

Hepatocellular carcinoma (HCC) is the fifth most frequent cancer worldwide and the third leading cause of cancer-related death. However, therapy options are limited leaving an urgent need to develop new strategies. Currently, targeting cancer cell lipid and cholesterol metabolism is gaining interest especially regarding HCC. High cholesterol levels support proliferation, membrane-related mitogenic signaling and increase cell softness, leading to tumor progression, malignancy and invasive potential. However, effective ways to target cholesterol metabolism for cancer therapy are still missing. The V-ATPase inhibitor archazolid was recently shown to interfere with cholesterol metabolism. In our study, we report a novel therapeutic potential of V-ATPase inhibition in HCC by altering the mechanical phenotype of cancer cells leading to reduced proliferative signaling. Archazolid causes cellular depletion of free cholesterol leading to an increase in cell stiffness and membrane polarity of cancer cells, while hepatocytes remain unaffected. The altered membrane composition decreases membrane fluidity and leads to an inhibition of membrane-related Ras signaling resulting decreased proliferation in vitro and in vivo. V-ATPase inhibition represents a novel link between cell biophysical properties and proliferative signaling selectively in malignant HCC cells, providing the basis for an attractive and innovative strategy against HCC.

Total syntheses of the archazolids: an emerging class of novel anticancer drugs

V-ATPase has recently emerged as a promising novel anticancer target based on extensive in vitro and in vivo studies with the archazolids, complex polyketide macrolides which present the most potent V-ATPase inhibitors known to date, rendering these macrolides important lead structures for the development of novel anticancer agents. The limited natural supply of these metabolites from their myxobacterial source renders total synthesis of vital importance for the further preclinical development. This review describes in detail the various tactics and strategies employed so far in archazolid syntheses that culminated in three total syntheses and discusses the future synthetic challenges that have to be addressed.

Anti-leukemic effects of the V-ATPase inhibitor Archazolid A

Prognosis for patients suffering from T-ALL is still very poor and new strategies for T-ALL treatment are urgently needed. Our study shows potent anti-leukemic effects of the myxobacterial V-ATPase inhibitor Archazolid A. Archazolid A reduced growth and potently induced death of leukemic cell lines and human leukemic samples. By inhibiting lysosomal acidification, Archazolid A blocked activation of the Notch pathway, however, this was not the mechanism of V-ATPase inhibition relevant for cell death induction. In fact, V-ATPase inhibition by Archazolid A decreased the anti-apoptotic protein survivin. As underlying mode of action, this work is in line with recent studies from our group demonstrating that Archazolid A induced S-phase cell cycle arrest by interfering with the iron metabolism in leukemic cells. Our study provides evidence for V-ATPase inhibition as a potential new therapeutic option for T-ALL.

Design, Synthesis, EPR-Studies and Conformational Bias of Novel Spin-Labeled DCC-Analogues for the Highly Regioselective Labeling of Aliphatic and Aromatic Carboxylic Acids

Novel types of spin-labeled N,N'-dicyclohexylcarbodiimides (DCC) are reported that bear a 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO) residue on one side and different aromatic and aliphatic cyclohexyl analogues on the other side of the diimide core. These readily available novel reagents add efficiently to aliphatic and aromatic carboxylic acids, forming two possible spin-labeled amide derivatives with different radical distances of the resulting amide. The addition of aromatic DCC analogues proceeds with excellent selectivity, giving amides where the carboxylic acid is exclusively connected to the aromatic residue, while little or no selectivity was observed for the aliphatic congeners. The usefulness of these adducts in structural studies was demonstrated by EPR (electron paramagnetic resonance) measurements of biradical adducts of biphenyl-4,4'-dicarboxylic acids. These analyses also reveal high degrees of conformational bias for aromatic DCC derivatives, which further underlines the powerfulness of these novel reagents. This observation was further corroborated by quantum chemical calculations, giving a detailed understanding of the structural dynamics, while detailed information on the solid state structure of all novel reagents was obtained by X-ray structure analyses.

Modular synthesis of the pyrimidine core of the manzacidins by divergent Tsuji-Trost coupling

The design, development and application of an efficient procedure for the concise synthesis of the 1,3-syn- and anti-tetrahydropyrimidine cores of manzacidins are reported. The intramolecular allylic substitution reaction of a readily available joint urea-type substrate enables the facile preparation of both diastereomers in high yields. The practical application of this approach is demonstrated in the efficient and modular preparation of the authentic heterocyclic cores of manzacidins, structurally unique bromopyrrole alkaloids of marine origin. Additional features of this route include the stereoselective generation of the central amine core with an appending quaternary center by an asymmetric addition of a Grignard reagent to a chiral tert-butanesulfinyl ketimine following an optimized Ellman protocol and a cross-metathesis of a challenging homoallylic urea substrate, which proceeds in good yields in the presence of an organic phosphoric acid.

MDM2 antagonist nutlin-3a sensitizes tumors to V-ATPase inhibition

Treating cancer is one of the big challenges of this century and it has become evident that single chemotherapeutic treatment is rarely effective. As tumors often carry multiple mutations using combination therapy which addresses different targets seems therefore more beneficial. One of the most frequently mutated genes in tumors is the tumor suppressor p53. Significant work has been put in the development of p53 activators, which are now in clinical studies against diverse cancers. Recently, we could show that inhibition of V-ATPase, a multisubunit proton pump, by archazolid induces p53 protein levels in cancer cells. In this study, we provide evidence that the combination of archazolid with the p53 activator nutlin-3a is synergistically inducing cell death in different p53 wild type tumor cell lines. Mechanistically, this effect could presumably be attributed to reduction of glycolysis as TIGAR mRNA levels were increased and glucose uptake and Glut1 protein levels were reduced. In addition, combination treatment highly activated pro-apoptotic pathways including IGFBP3 and Bax inducing caspase-9 and PARP cleavage. Remarkably, combination of archazolid and nutlin-3a was more efficient in reducing tumor growth compared to single dose treatment in a U87MG mouse model in vivo. Hence, our findings suggest the combination of archazolid and nutlin-3a as a highly promising strategy for the treatment of p53 wild type tumors.