Electro-Oxidation of Hispanolone and Anti-Inflammatory Properties of the Obtained Derivatives

Application of Pauson-Khand reaction in the total synthesis of terpenes

The Pauson-Khand reaction (PKR) is a formal [2 + 2 + 1] cycloaddition involving an alkyne, an alkene and carbon monoxide mediated by a hexacarbonyldicobaltalkyne complex to yield cyclopentenones in a single step. This versatile reaction has become a method of choice for the synthesis of cyclopentenone and its derivatives since its discovery in the early seventies. The aim of this review is to point out the applications of PKR in the total synthesis of terpenes.

Isolation, reactivity, pharmacological activities and total synthesis of hispanolone and structurally related diterpenes from Labiatae plants

Hispanolone is a furolabdane diterpene isolated from Ballota hispanica, whose natural product chemistry has been summarized and updated here, including several aspects associated with the isolation, structure determination, hemisynthesis, total synthesis, and pharmacology, and related hispanolone diterpenoids that have attracted the interest of different laboratories from diverse perspective and expertise in the last forty-two years.

Total Syntheses of Marrubiin and Related Labdane Diterpene Lactones

Total syntheses of the labdane diterpene lactones marrubiin, marrulibacetal, desertine, marrulibacetal A, marrubasch F, cyllenine C, marrulanic acid, and marrulactone are described. The trans-decalin moiety of these molecules was constructed in a stereoselective manner by a Pauson-Khand reaction, and the resultant cyclopentenone was oxidatively cleaved for formation of the lactone ring. Elongation of the side chain at C9 was achieved by an epoxide-opening reaction with a variety of nucleophiles, and the functional group manipulations completed the syntheses of these natural products. Stereochemistries of desertine could be established by the transformations.

Electrochemical strategies for C-H functionalization and C-N bond formation

Conventional methods for carrying out carbon-hydrogen functionalization and carbon-nitrogen bond formation are typically conducted at elevated temperatures, and rely on expensive catalysts as well as the use of stoichiometric, and perhaps toxic, oxidants. In this regard, electrochemical synthesis has recently been recognized as a sustainable and scalable strategy for the construction of challenging carbon-carbon and carbon-heteroatom bonds. Here, electrosynthesis has proven to be an environmentally benign, highly effective and versatile platform for achieving a wide range of nonclassical bond disconnections via generation of radical intermediates under mild reaction conditions. This review provides an overview on the use of anodic electrochemical methods for expediting the development of carbon-hydrogen functionalization and carbon-nitrogen bond formation strategies. Emphasis is placed on methodology development and mechanistic insight and aims to provide inspiration for future synthetic applications in the field of electrosynthesis.

Synthetic Organic Electrochemical Methods Since 2000: On the Verge of a Renaissance

Electrochemistry represents one of the most intimate ways of interacting with molecules. This review discusses advances in synthetic organic electrochemistry since 2000. Enabling methods and synthetic applications are analyzed alongside innate advantages as well as future challenges of electroorganic chemistry.

Total Syntheses of (+)-Marrubiin and (-)-Marrulibacetal

A stereoselective total synthesis of (+)-marrubiin has been accomplished starting from a chiral building block via the CyNH2-promoted Pauson-Khand reaction (PKR) followed by oxidative cleavage of the resultant cyclopentenone ring. Two successive oxidations and internal transacetalization culminated in the total synthesis of the antispasmodic labdane diterpenoid (-)-marrulibacetal.

8,9-Dehydrohispanolone-15,16-lactol diterpene prevents LPS-triggered inflammatory responses by inhibiting endothelial activation

Endothelial activation contributes to lung inflammatory disorders by inducing leucocyte recruitment to pulmonary parenchyma. Consequently, vascular-targeted therapies constitute promising strategies for the treatment of inflammatory pathologies. In the present study, we evaluated the effect of 8,9-dehydrohispanolone-15,16-lactol diterpene (DT) on lung endothelium during inflammation. Lung endothelial cells pre-treated with DT and activated with lipopolysaccharide (LPS) or tumour necrosis factor-α (TNF-α) exhibited reduced expression of the pro-inflammatory cytokines Cxcl10, Ccl5 and Cxcl1, whereas the anti-inflammatory molecules IL1r2 and IL-10 were induced. Consistent with this result, DT pre-treatment inhibited nuclear factor κB (NF-κB) nuclear translocation, by interfering with IκBα phosphorylation, and consequently NF-κB transcriptional activity in endothelium activated by LPS or TNF-α. Furthermore, DT, probably through p38 signalling, induced transcriptional activation of genes containing activator protein 1 (AP-1)-binding elements. Inhibition of p38 prevented IL1r2 mRNA expression in endothelium incubated with DT alone or in combination with LPS or TNF-α. Accordingly, conditioned medium (CM) from these cells failed to stimulate leucocytes as measured by a reduction in adhesive ability of the leucocyte cell line J774 to fibronectin (FN). Additionally, DT reduced the expression of the endothelial adhesion molecules E-selectin, vascular cell adhesion molecule 1 (VCAM-1) and intercellular adhesion molecule 1 (ICAM-1) after activation. Similarly, expression of VCAM-1 and ICAM-1 molecules on the lung endothelial layer of C57/BL6 mice pre-treated with DT and challenged with LPS were unchanged. Finally, inhibition of vascular adhesion molecule expression by DT decreased the interaction of J774 cells with lung endothelial cells in an inflammatory environment. Our findings establish DT as a novel endothelial inhibitor for the treatment of inflammatory-related diseases triggered by Gram-negative bacteria or by the associated cytokine TNF-α.

Structure–activity relationship of terpenes with anti-inflammatory profile – a systematic review

Inflammation is a complex biological response that in spite of having available treatments, their side effects limit their usefulness. Because of this, natural products have been the subject of incessant studies, among which the class of terpenes stands out. They have been the source of study for the development of anti-inflammatory drugs, once their chemical diversity is well suited to provide skeleton for future anti-inflammatory drugs. This systematic review reports the studies present in the literature that evaluate the anti-inflammatory activity of terpenes suffering any change in their structures, assessing whether these changes also brought changes in their effects. The search terms anti-inflammatory agents, terpenes, and structure–activity relationship were used to retrieve English language articles in SCOPUS, PUBMED and EMBASE published between January 2002 and August 2013. Twenty-seven papers were found concerning the structural modification of terpenes with the evaluation of antiinflammatory activity. The data reviewed here suggest that modified terpenes are an interesting tool for the development of new anti-inflammatory drugs.

Antispasmodic effects and structure-activity relationships of labdane diterpenoids from Marrubium globosum ssp. libanoticum

Marrubium globosum ssp. libanoticum is a medicinal plant used in Lebanon to reduce pain and smooth muscle spasms. A chloroform extract obtained from M. globosum aerial parts reduced acetylcholine-induced contractions in the isolated mouse ileum. The purification of this extract identified, among 12 isolated labdane diterpenoids, four new compounds, named 13-epicyllenin A (4), 13,15-diepicyllenin A (5), marrulibacetal (9), and marrulactone (11). Their structures were determined by spectroscopic methods. Compound 9, which exerted antispasmodic activity, is likely the active ingredient of the extract. Preliminary structure-activity relationships for this class of compounds are suggested.

Suppression of inflammatory responses by labdane-type diterpenoids

A series of 11 labdane-type diterpenoids (1-11) with various patterns of substitution were tested for potential anti-inflammatory activity. Of these compounds, 4 and 11 were selected to evaluate their influence on targets relevant to the regulation of the inflammatory response. These diterpenoids reduced the production of nitric oxide (NO), prostaglandin E2, and tumor necrosis factor-alpha in LPS-activated RAW 264.7 macrophages, with IC50 in the range 1-10 microM. Inhibition of these inflammatory mediators was related to inhibition of the expression of nitric oxide synthase-2 (NOS-2) and cyclooxygenase-2 (COX-2) at the transcriptional level, as determined by western-blot and RT-PCR. Examination of the effects of these diterpenoids on nuclear factor kappaB signaling showed that both compounds inhibit the phosphorylation of IkappaBalpha and IkappaBbeta, preventing their degradation and the nuclear translocation of the NF-kappaB p65 subunit. Inhibition of IKK activity was also observed. These derivatives displayed significant anti-inflammatory activity in vivo, suppressing mouse ear edema induced by 12-O-tetradecanoylphorbol-13-acetate (TPA) and inhibiting myeloperoxidase activity, an index of neutrophil infiltration. The anti-inflammatory effects of these labdane diterpenoids, together with their low cell toxicity, suggest potential therapeutic applications in the regulation of the inflammatory response.

Diterpenoids

This review covers the isolation and structures of diterpenoids, including labdanes, clerodanes,pimaranes, abietanes, kauranes, cembranolides, taxanes and marine diterpenoids. The literature from January to December 2005 is reviewed, and 195 references are cited.