Efficient Chemoenzymatic Synthesis, Cytotoxic Evaluation, and SAR of Epoxysterols

Anti-Inflammatory Steroids from the South China Sea Soft Coral Lobophytum sarcophytoides

Three new steroids, along with two known related analogs, were isolated from the Xisha Island soft coral Lobophytum sarcophytoides. The structures and absolute configurations of the new compounds were elucidated by extensive spectroscopic data analyses, time dependent density functional theory electronic circular dichroism calculation, and comparison with the spectral data previously reported in the literature. In in vitro bioassay, four compounds showed interesting suppressive effects on lipopolysaccharide (LPS) induced inflammation in BV-2 microglial cells at 10 μM level.

Epoxidation of olefins using diaryltellurium dicarboxylates

This paper reports an efficient method for the epoxidation of a variety of functionalized olefins using diaryltellurium dicarboxylates as hypervalent tellurium compounds. This method is able to efficiently convert olefins into epoxides using catalytic amounts of tellurium and urea hydrogen peroxide. Furthermore, we propose that this reaction proceeds via the formation of peroxides of phenol, carboxylic acid, and tellurium peroxide when diaryltellurium dicarboxylates and hydrogen peroxide react. This is the first example of an epoxidation reaction using hypervalent tellurium compounds.

Structure-Activity Relationships of Withanolides as Antiproliferative Agents for Multiple Myeloma: Comparison of Activity in 2D Models and a 3D Coculture Model

Multiple myeloma (MM) is a hematological cancer in which relapse and resistance are highly frequent. Therefore, alternatives to conventional treatments are necessary. Withaferin A, a withanolide isolated from Withania somnifera, has previously shown promising activity against various MM models. In the present study, structure-activity relationships (SARs) were evaluated using 56 withanolides. The antiproliferative activity was assessed in three MM cell lines and in a 3D MM coculture model to understand the in vitro activity of compounds in models of various complexity. While the results obtained in 2D allowed a quick and simple evaluation of cytotoxicity used for a first selection, the use of the 3D MM coculture model allowed filtering compounds that perform better in a more complex setup. This study shows the importance of the last model as a bridge between 2D and in vivo studies to select the most active compounds and ultimately lead to a reduction of animal use for more sustained in vivo studies. NF-κB inhibition was determined to evaluate if this could be one of the targeted pathways. The most active compounds, withanolide D (2) and 38, should be further evaluated in vivo.

Designed whole-cell-catalysis-assisted synthesis of 9,11-secosterols

A method for the synthesis of 9,11-secosteroids starting from the natural corticosteroid cortisol is described. There are two key steps in this approach, combining chemistry and synthetic biology. Stereo- and regioselective hydroxylation at C9 (steroid numbering) is carried out using whole-cell biocatalysis, followed by the chemical cleavage of the C-C bond of the vicinal diol. The two-step method features mild reaction conditions and completely excludes the use of toxic oxidants.

Regio- and Stereoselective Addition of HO/OOH to Allylic Alcohols

A range of allylic alcohols are shown to readily react with ethereal H₂O₂ in the presence of catalytic amounts of Na₂MoO₄-gly or MoO₂(acac)₂, affording the C═C trans hydroxylation-hydroperoxylation products in good yields with high regio- and stereoselectivity. Use of enantiomers of cyclic substrates resulted in corresponding enantiopure diol-tert-hydroperoxides. The possibility of further conversion of the diol-tert-hydroperoxides into triols or linear building blocks with an isolated tert-peroxy group containing a quaternary center is also exemplified.

Misassigned Polyoxygenated Sterols and Reassignments of Their Structures

This review will summarize the authors’ studies on the reassignments of structures of 9 natural polyoxygenated sterols (24 S)-24-ethylcholest-8-ene-3β,5α,6β,7α-tetrol (1), (24 S)-24-ethylcholest-8(14)-ene-3β,5α,6β,7α-tetrol (2), (22 E)-24-methylcholesta-8(14),22-diene-3β,5α,6β,7α-tetrol (3), 5β,6β-epoxy-(22 E)-ergosta-8,22-diene-3β,7β-diol (4), (22 E)-ergosta-7,22-diene-3β,5α,6β,9α,14α-pentol (5), 3β,5α,6β,8β,14α-pentahydroxy-(22 E)-ergost-22-en-7-one (6), 5β,6β-epoxy-24-methylenecholesta-8,24(28)-diene-3β,7α,11α-triol (7), 6β-acetoxy-(22 E)-10α-ergosta-7,22-diene-3β,5α-diol (8), and 8α,9α-epoxy-(22 E)-ergosta-6,22-diene-3β,5α,14α-triol (9). The structures of 1 to 9 have been reassigned as (24 S)-5α,6α-epoxy-24-ethylcholest-8-ene-3β,7α-diol (16), (24 S)-5α,6α-epoxy-24-ethylcholest-8(14)-ene-3β,7α-diol (17), 5α,6α-epoxy-(22 E)-ergosta-8(14),22-diene-3β,7α-diol (13), 5α,6α-epoxy-(22 E)-ergosta-8,22-diene-3β,7α-diol (12), (22 E)-ergosta-7,22-diene-3β,5α,6β,9α,14β-pentol (25), 5α,6α;8α,14α-diepoxy-3β-hydroxy-(22 E)-ergost-22-en-7-one (18), 5α,6α-epoxyergosta-8,24(28)-diene-3β,7α,11α-triol (21), 6β-acetoxy-(22 E)-ergosta-7,22-diene-3β,5α-diol (26), and 8α,14α-epoxy-(22 E)-ergosta-6,22-diene-3β,5α,9α-triol (28), respectively, from the results of careful reexamination of the published1H and13C NMR spectral data.

Biotin attenuation of oxidative stress, mitochondrial dysfunction, lipid metabolism alteration and 7β-hydroxycholesterol-induced cell death in 158N murine oligodendrocytes

Mitochondrial dysfunction and oxidative stress are involved in neurodegenerative diseases associated with an enhancement of lipid peroxidation products such as 7β-hydroxycholesterol (7β-OHC). It is, therefore, important to study the ability of 7β-OHC to trigger mitochondrial defects, oxidative stress, metabolic dysfunctions and cell death, which are hallmarks of neurodegeneration, and to identify cytoprotective molecules. The effects of biotin were evaluated on 158N murine oligodendrocytes, which are myelin synthesizing cells, exposed to 7β-OHC (50 µM) with or without biotin (10 and 100 nM) or α-tocopherol (positive control of cytoprotection). The effects of biotin on 7β-OHC activities were determined using different criteria: cell adhesion; plasma membrane integrity; redox status. The impact on mitochondria was characterized by the measurement of transmembrane mitochondrial potential (ΔΨm), reactive oxygen species (ROS) overproduction, mitochondrial mass, quantification of cardiolipins and organic acids. Sterols and fatty acids were also quantified. Cell death (apoptosis, autophagy) was characterized by the enumeration of apoptotic cells, caspase-3 activation, identification of autophagic vesicles, and activation of LC3-I into LC3-II. Biotin attenuates 7β-OHC-induced cytotoxicity: loss of cell adhesion was reduced; antioxidant activities were normalized. ROS overproduction, protein and lipid oxidation products were decreased. Biotin partially restores mitochondrial functions: attenuation of the loss of ΔΨm; reduced levels of mitochondrial O₂^•- overproduction; normalization of cardiolipins and organic acid levels. Biotin also normalizes cholesterol and fatty acid synthesis, and prevents apoptosis and autophagy (oxiapoptophagy). Our data support that biotin, which prevents oligodendrocytes damages, could be useful in the treatment of neurodegeneration and demyelination.

Chemistry, biochemistry, metabolic fate and mechanism of action of 6-oxo-cholestan-3β,5α-diol (OCDO), a tumor promoter and cholesterol metabolite

Oxygenation products of cholesterol, named oxysterols, were suspected since the 20th century to be involved in carcinogenesis. Among the family of oxysterol molecules, cholesterol-5,6-epoxides (5,6-EC) retained the attention of scientists because they contain a putative alkylating epoxide group. However, studies failed into demonstrating that 5,6-EC were direct carcinogens and revealed a surprising chemical stability and unreactivity towards nucleophiles in standard conditions. Analyses of 5,6-EC metabolism in normal cells showed that they were extensively transformed into cholestane-3β,5α,6β-triol (CT) by the cholesterol-5,6-epoxide hydrolase (ChEH). Studies performed in cancer cells showed that CT was additionally metabolized into an oxysterol identified as the 6-oxo-cholestan-3β,5α-diol (OCDO), by the 11β-hydroxysteroid dehydrogenase of type 2 (HSD2), the enzyme which inactivates cortisol into cortisone. Importantly, OCDO was shown to display tumor promoter properties in breast cancers, by binding to the glucocorticoid receptor, and independently of their estrogen receptor status, revealing the existence of a new tumorigenic pathway centered on 5,6-EC. In breast tumors from patients, OCDO production as well as the expression of the enzymes involved in the pathway producing OCDO, namely ChEH subunits and HSD2, were higher compared to normal tissues, and overexpression of these enzymes correlate with a higher risk of patient death, indicating that this onco-metabolism is of major importance to breast cancer pathology. Herein, we will review the actual knowledge and the future trends in OCDO chemistry, biochemistry, metabolism and mechanism of action and will discuss the impact of OCDO discovery on new anticancer therapeutic strategies.

Structure Revision of (22E)-24-Methylcholesta-8(14),22-diene-3β,5α,6β,7α-tetraol from the Marine-Derived Fungus Penicillium sp

Careful reexamination of the published 1H- and 13C-NMR spectral data of (22 E)-24-methylcholesta-8(14),22-diene-3β,5α,6β,7α-tetraol (1), isolated from the marine-derived fungus Penicillium sp., indicates that, in reality, the compound is 5α,6α-epoxy-(22 E,24 R)-24-methylcholesta-8(14),22-diene-3β,7α-diol (5).

Induction of oxiapoptophagy on 158N murine oligodendrocytes treated by 7-ketocholesterol-, 7β-hydroxycholesterol-, or 24(S)-hydroxycholesterol: Protective effects of α-tocopherol and docosahexaenoic acid (DHA; C22:6 n-3)

In demyelinating or non-demyelinating neurodegenerative diseases, increased levels of 7-ketocholesterol (7KC), 7β-hydroxycholesterol (7β-OHC) and 24(S)-hydroxycholesterol (24S-OHC) can be observed in brain lesions. In 158N murine oligodendrocytes, 7KC triggers a complex mode of cell death defined as oxiapoptophagy, involving simultaneous oxidative stress, apoptosis and autophagy. In these cells, 7KC as well as 7β-OHC and 24S-OHC induce a decrease of cell proliferation evaluated by phase contrast microscopy, an alteration of mitochondrial activity quantified with the MTT test, an overproduction of reactive oxygen species revealed by staining with dihydroethidium and dihydrorhodamine 123, caspase-3 activation, PARP degradation, reduced expression of Bcl-2, and condensation and/or fragmentation of the nuclei which are typical criteria of oxidative stress and apoptosis. Moreover, 7KC, 7β-OHC and 24S-OHC promote conversion of microtubule-associated protein light chain 3 (LC3-I) to LC3-II which is a characteristic of autophagy. Consequently, 7β-OHC and 24S-OHC, similarly to 7KC, can be considered as potent inducers of oxiapoptophagy. Furthermore, the different cytotoxic effects associated with 7KC, 7β-OHC and 24S-OHC-induced oxiapoptophagy are attenuated by vitamin E (VitE, α-tocopherol) and DHA which enhances VitE protective effects. In 158N murine oligodendrocytes, our data support the concept that oxiapoptophagy, which can be inhibited by VitE and DHA, could be a particular mode of cell death elicited by cytotoxic oxysterols.

Structure Revision of Two Polyoxygenated Sterols from the Marine Sponge Neofibularia nolitangere

Careful reexamination of the published 1H- and 13C-NMR spectral data of (24 S)-24-ethylcholest-8-ene-3β,5α,6β,7α-tetraol (1) and (24 S)-24-ethylcholest-8(14)-ene-3β,5α,6β,7α-tetraol (2), isolated from the marine sponge Neofibularia nolitangere, indicates that, in reality, compounds 1 and 2 are (24 S)-5α,6α-epoxy-24-ethylcholest-8-ene-3β,7α-diol (9) and (24 S)-5α,6α-epoxy-24-ethylcholest-8(14)-ene-3β,7α-diol (10), respectively.

Recent advances in cholesterol chemistry

This review article presents advances in cholesterol chemistry since 2000. Various transformations (chemical, enzymatic, electrochemical, etc.) of cholesterol are presented. A special emphasis is given to cholesterol oxidation reactions, but also substitution of the 3β-hydroxyl group, addition to the C5-C6 double bond, C-H functionalization, and C-C bond forming reactions are discussed.

Anticancer steroids: linking natural and semi-synthetic compounds

Steroids, a widespread class of natural organic compounds occurring in animals, plants and fungi, have shown great therapeutic value for a broad array of pathologies. The present overview is focused on the anticancer activity of steroids, which is very representative of a rich structural molecular diversity and ability to interact with various biological targets and pathways. This review encompasses the most relevant discoveries on steroid anticancer drugs and leads through the last decade and comprises 668 references.

5α,6α-Ep-oxy-7-norcholestan-3β-yl acetate

The title cholestan, C(28)H(46)O(3), was prepared by epoxidation of 7-norcholest-5-en-3β-yl acetate and crystallized by slow evaporation from an ethano-lic solution. All rings are trans fused. The 3β-acetate and the 17β-cholestane side chain are in equatorial positions. The mol-ecule is highly twisted due to its B-nor characteristic. A quantum chemical ab-initio Roothaan Hartree-Fock calculation of the equilibrium geometry of the isolated mol-ecule gives values for bond lengths and valency angles in close agreement with the experimental ones.

Smardaesidins A-G, isopimarane and 20-nor-isopimarane diterpenoids from Smardaea sp., a fungal endophyte of the moss Ceratodon purpureus

Five new isopimarane diterpenes, smardaesidins A-E (1- 5) and two new 20-nor-isopimarane diterpenes, smardaesidins F (6) and G (7), together with sphaeropsidins A (8) and C-F (10-13) were isolated from an endophytic fungal strain, Smardaea sp. AZ0432, occurring in living photosynthetic tissue of the moss Ceratodon purpureus . Of these, smardaesidins B (2) and C (3) were obtained as an inseparable mixture of isomers. Chemical reduction of sphaeropsidin A (8) afforded sphaeropsidin B (9), whereas catalytic hydrogenation of 8 yielded 7-O-15,16-tetrahydrosphaeropsidin A (14) and its new derivative, 7-hydroxy-6-oxoisopimara-7-en-20-oic acid (15). The acetylation and diazomethane reaction of sphaeropsidin A (8) afforded two of its known derivatives, 6-O-acetylsphaeropsidin A (16) and 8,14-methylenesphaeropsidin A methyl ester (17), respectively. Methylation of 10 yielded sphaeropsidin C methyl ester (18). The planar structures and relative configurations of the new compounds 1-7 and 15 were elucidated using MS and 1D and 2D NMR experiments, while the absolute configurations of the stereocenters of 4 and 6-8 were assigned using a modified Mosher's ester method, CD spectra, and comparison of specific rotation data with literature values. Compounds 1-18 were evaluated for their potential anticancer activity using several cancer cell lines and cells derived from normal human primary fibroblasts. Of these, compounds 8, 11, and 16 showed significant cytotoxic activity. More importantly, sphaeropsidin A (8) showed cell-type selectivity in the cytotoxicity assay and inhibited migration of metastatic breast adenocarcinoma (MDA-MB-231) cells at subcytotoxic concentrations.