Transformation of Santonin to a Naproxen Analogue with Anti-Inflammatory Activity

Santonin, a natural product, was aromatized with molecular iodine as the catalyst. The new compound was characterized as ( S)-methyl-2-(7-hydroxy-5,8-dimethylnaphthalen-2-yl) propanoate (2) based on 2D NMR spectroscopic data. Structurally, compound 2 was highly similar to the anti-inflammatory drug naproxen. The new naproxen analogue had significant potency against cyclooxygenase 1 and 2 (IC₅₀ = 31.0 and 66.1 μM, respectively).

A Molecular Electron Density Theory Study of the Chemoselectivity, Regioselectivity, and Diastereofacial Selectivity in the Synthesis of an Anticancer Spiroisoxazoline derived from α-Santonin

The [3 + 2] cycloaddition (32CA) reaction of an α-santonin derivative, which has an exocyclic C–C double bond, with p-bromophenyl nitrile oxide yielding only one spiroisoxazoline, has been studied within the molecular electron density theory (MEDT) at the MPWB1K/6-311G(d,p) computational level. Analysis of the conceptual density functional theory (CDFT) reactivity indices and the global electron density transfer (GEDT) account for the non-polar character of this zwitterionic-type 32CA reaction, which presents an activation enthalpy of 13.3 kcal·mol⁻¹. This 32CA reaction takes place with total ortho regioselectivity and syn diastereofacial selectivity involving the exocyclic C–C double bond, which is in complete agreement with the experimental outcomes. While the C–C bond formation involving the β-conjugated carbon of α-santonin derivative is more favorable than the C–O one, which is responsible for the ortho regioselectivity, the favorable electronic interactions taking place between the oxygen of the nitrile oxide and two axial hydrogen atoms of the α-santonin derivative are responsible for the syn diastereofacial selectivity.

Measurement of residual chemical shift anisotropies in compressed polymethylmethacrylate gels. Automatic compensation of gel isotropic shift contribution

Mechanical compression of polymer gels provides a simple way for the measurement of residual chemical shift anisotropies, which then can be employed, on its own, or in combination with residual dipolar couplings, for structural elucidation purposes. Residual chemical shift anisotropies measured using compression devices needed a posteriori correction to account for the increase of the polymer to solvent ratio inside the swollen gel. This correction has been cast before in terms of a single-free parameter which, as shown here, can be simultaneously optimized along with the components of the alignment tensor while still retaining discriminating power of the different relative configurations as illustrated in the stereochemical analysis of α-santonin and 10-epi-8-deoxycumambrin B.

Synthesis of α-santonin derivatives for diminutive effect on T and B-cell proliferation and their structure activity relationships

A new library of 20 compounds from α-santonin was synthesized and tested against Con-A induced T-cell proliferation and LPS-induced B-cell proliferation via MTT assay. The study resulted in the identification of potent immunosuppressant molecules, which were further screened along with α-santonin for Tumor Necrosis Factor Alpha (TNF-α) inhibitory activity. One of the molecules (7) at 10 μM showed equipotency to that of dexamethasone (1 μM conc.) used as a standard. Structure activity relationships of the synthesized compounds along with our earlier reported α-santonin derivatives have been studied. Inferences from the modifications carried out at all the three sites of α-santonin have been elaborated. Computational study of the active compounds shows TNF-α protein as its preferable target rather than Inosine Monophosphate Dehydrogenase (IMPDH).

Novel platensimycin derivatives with herbicidal activity

BACKGROUND

Faced with the need to develop herbicides with different modes of action on account of weed resistance to existing herbicides, the sesquiterpene lactones can be the starting point in the search for new bioactive compounds. Lumisantonin and five novel amides have been evaluated against two monocotyledons and three dicotyledons.

RESULTS

An efficient and versatile synthesis of lumisantonin and the five novel amides has been accomplished from readily available α-santonin. These compounds were subjected to evaluation for their biological activity against Sorghum bicolor (sorghum), Allium cepa (onion), Cucumis sativus (cucumber), Solanum lycopersicum (tomato) and Bidens pilosa (beggartick). Lumisantonin has inhibited the development of the aerial parts of sorghum and onion by 76 and 67% at 1000 µM respectively. One of the novel amides has prevented the growth of shoots and radicles of sorghum by 80 and 71% at 1000 µM respectively.

CONCLUSION

All of the tested compounds have been found to exhibit promising seed germination inhibition. We can conclude that lumisantonin was on average the most lethal against all plant species evaluated; however, two of the novel amides have exhibited inhibition selectivity against monocotyledons when compared with dicotyledons. © 2015 Society of Chemical Industry.

The Colorimetric Determination of Santonin in Artemisia

A new colorimetric method for the estimation of santonin in artemisia using hydroxylamine and ferric chloride has been evolved and compared with a gravimetric and a volumetric method. Improvements in the method of extraction of santonin have also been proposed.

Pursuing structure in microcrystalline solids with independent molecules in the unit cell using 1H-13C correlation data

The (1)H-(13)C solid-state NMR heteronuclear correlation (HETCOR) experiment is demonstrated to provide shift assignments in certain powders that have two or more structurally independent molecules in the unit cell (i.e. multiple molecules per asymmetric unit). Although this class of solids is often difficult to characterize using other methods, HETCOR provides both the conventional assignment of shifts to molecular positions and associates many resonances with specific molecules in the asymmetric unit. Such assignments facilitate conformational characterization of the individual molecules of the asymmetric unit and the first such characterization solely from solid-state NMR data is described. HETCOR offers advantages in sensitivity over prior methods that assign resonances in the asymmetric unit by (13)C-(13)C correlations and therefore allows shorter average analysis times in natural abundance materials. The (1)H-(13)C analysis is demonstrated first on materials with known shift assignments from INADEQUATE data (santonin and Ca(OAc)(2) phase I) to verify the technique and subsequently is extended to a pair of unknown solids: (+)-catechin and Ca(OAc)(2) phase II. Sufficient sensitivity and resolution is achieved in the spectra to provide assignments to one of the specific molecules of the asymmetric unit at over 54% of the sites.

Natural Products in Parallel Chemistry––Novel 5-Lipoxygenase Inhibitors from BIOS-Based Libraries Starting from α-Santonin

Recently, we developed a concept known as biology-oriented synthesis (BIOS), which targets the design and synthesis of small- to medium-sized compound libraries on the basis of genuine natural product templates to provide screening compounds with high biological relevance. We herein describe the parallel solution phase synthesis of two BIOS-based libraries starting from alpha-santonin (1). Modification of the sesquiterpene lactone 1 by introduction of a thiazole moiety followed by a Lewis-acid-mediated lactone opening yielded a first library of natural product analogues. An acid-mediated dienone-phenol rearrangement of 1 and a subsequent etherification/amidation sequence led to a second natural product-based library. After application of a fingerprint-based virtual screening on these compounds, the biological screening of 23 selected library members against 5-lipoxygenase resulted in the discovery of four potent novel inhibitors of this enzyme.

Biotransformation of alpha- and 6beta-santonin by fungus and plant cell cultures

One fungus, Abisidia coerulea IFO 4011, and suspended cell cultures of one plant, Asparagus officinalis, were employed to bioconvert alpha- and 6beta-santonin. Incubation of alpha-santonin with the cell cultures of the fungus afforded two products, 11beta-hydroxy-alpha-santonin (1, in 76.5% yield) and 8alpha-hydroxy-alpha-santonin (2, in 2.0% yield). And from 6beta-santonin, four major products (3, 4, 5 and 6) and four minor products (7, 8, 9 and 10) were obtained, including 8alpha-hydroxylated products in trace yields. Very interestingly, a skeletal rearrangement occurred and a guaiane product (13) formed in a very low yield when alpha-santonin incubating with A.officinalis cell cultures, while not in the case of 6beta-santonin as substrate. Among the obtained 15 products, 2, 7, 8, 9, 10 and 12 are new compounds. The fact of 8alpha hydroxylation of santonin enables the formation of 8,12-eudesmanolide instead of 6,12-eudesmanolide and some useful modification at C-8 position. In addition, these reactions would provide evidence for the biogenesis between different types of eudesmane and/or guaiane compounds in the plants in nature.

Chemical Modification of Santonin into a Diacetoxy Acetal Form Confers the Ability to Induce Differentiation of Human Promyelocytic Leukemia Cells via the Down-regulation of NF-κB DNA Binding Activity

Many sesquiterpene lactone compounds either induce or enhance the cell differentiation of human leukemia cells. However, we reported in a previous study that santonin, a eudesmanolide sesquiterpene lactone, exerts no effects on the differentiation of leukemia cells. In this report, to evaluate the possibility of chemically modifying santonin into its derivatives with differentiation inducing activity, we synthesized a series of santonin derivatives, and determined their effects on cellular differentiation in the human promyelocytic leukemia HL-60 cell system. A diacetoxy acetal derivative of santonin (DAAS) was found to induce significant HL-60 cell differentiation in a dose-dependent manner, whereas santonin in its original form did not. The HL-60 cells were differentiated into a granulocytic lineage when exposed to DAAS. In addition, the observed induction in cell differentiation closely correlated with the levels of NF-kappaB DNA binding activity inhibited by DAAS. Both Western blot analyses and kinase inhibitor studies determined that protein kinase C, ERK, and phosphatidylinositol 3-kinase were upstream components of the DAAS-mediated inhibition of NF-kappaB binding activity in HL-60 leukemia cells. The results of this study indicate that santonin can, indeed, be chemically modified into a derivative with differentiation inducing abilities, and suggest that DAAS might prove useful in the treatment of neoplastic diseases.

Biotransformation of 6beta-santonin by Phytolacca acinosa cell suspension cultures

AIM

To obtain more valuable derivatives for the further structural modification of 6beta-santonin (1) via biotransformation by using cell suspension cultures of Phytolacca acinosa.

METHODS

The substrate 1 was incubated with cell suspension cultures of P. acinosa, the products were obtained by chromatography, and identified on the basis of their physical and spectral data (HRMS, 1D NMR, 2D NMR, NOE and IR).

RESULTS

After incubation with cell suspension cultures of P. acinosa, 1 was converted into five products. Among them, 3 is a new compound.

CONCLUSION

6beta-santonin could be selectively reduced and hydroxylated by the cell suspension cultures of P. acinosa, which would provide valuable intermediates for its further structural modification.

Biotransformation of α-Santonin by Cell Suspension Cultures of Five Plants

Cell suspension cultures of five plants (Catharanthus roseus, Ginkgo biloba, Platycodon grandiflorum, Taxus cuspidata, Phytolacca asinosa) were employed to bioconvert the eudesmanolide compound, alpha-santonin. Reactions occurring were hydroxylation (C-1, C-11 and C-15), reduction of the double bond [1(2) or 3(4)], rearrangment of the eudesmanolide skeleton to a guaianolide skeleton and lactone-ring hydrolysis. Four new compounds were identified.

Synthesis of Spirovetivane Sesquiterpenes from Santonin. Synthesis of (+)-Anhydro-β-rotunol and All Diastereomers of 6,11-Spirovetivadiene

The synthesis of the spirovetivane sesquiterpenes (+)-anhydro-beta-rotunol and all the diastereomers of 6,11-spirovetivadiene in enantiomerically pure form has been achieved starting from santonin. The key step is the silicon-guided acid-promoted rearrangement of a 1-trimethylsilyl-4,5-epoxyeudesmane prepared from santonin in several steps involving lactone reductive opening, conjugate addition of TMSLi-CuCN, deoxygenation of a carbonyl group, and epoxidation. Rearrangement of the epoxide gave a spiro[4,5]decanediol which was used as a synthetic intermediate. From this compound, (+)-anhydro-beta-rotunol was prepared after elimination of the primary hydroxyl group in the side chain, followed by allylic oxidation at C8 and elimination of the tertiary hydroxyl group in the cyclohexane ring. On the other hand, elimination of the hydroxyl group in the side chain and reduction of the hydroxyl in the cyclohexane ring gave (-)-premnaspirodiene and (-)-hinesene. The synthesis of the rest of the diastereomers for these compounds required formal inversion of the C5 spiro carbon. The synthesis of these compounds showed that the structure of (-)-agarospirene isolated from Scapania sp. was erroneously assigned, and it has been corrected to be identical to that of (-)-hinesene.

Synthesis of phytuberin. 4-endo-tet acid-catalyzed cyclization of alpha-hydroxy epoxides

The total synthesis of phytuberin, a phytoalexin of the Solanum genus, from (-)-alpha-santonin is reported. The key steps include (a) reductive cleavage of the C-O bond of the gamma-lactone with concomitant protection of the C1 double bond, (b) Sharpless stereocontrolled hydroxy-assisted epoxidation of allylic alcohol 6 and simultaneous deprotection of the C1 double bond, (c) a rare 4-endo-tet acid-catalyzed cyclization of an alpha-hydroxy epoxide, and (d) an unprecedented 4-exo selenocyclization of a homoallylic alcohol.

Stereoselective synthesis of (+)-11betaH,13-dihydroestafiatin, (+)-11betaH,13-dihydroludartin, (-)-compressanolide, and (-)-11betaH,13-dihydromicheliolide from santonin

Starting from 2 and 3, obtained from santonin (1), we have synthesized natural guaianolides 4-7. Chemoselective epoxidation of 2 gave (+)-11betaH,13-dihydroestafiatin (4), and epoxidation of 3 followed by regioselective elimination of the hydroxyl group afforded (+)-11betaH,13-dihydroludartin (5). Sharpless' mild regioselective ring-opening of 4 and 5 followed by hydrogenolysis yielded (-)-compressanolide (6) and (-)-11betaH,13-dihydromicheliolide (7), respectively.

Synthesis of plagiochiline N from santonin

This article reports the transformation of O-acetylisophotosantonin, obtained by photochemical rearrangement of santonin, into plagiochiline N, an ent-2,3-secoaromadendrane isolated from Plagiochila ovalifolia. The synthesis was carried out in a sequence involving as the key steps (a) the substitution of the lactone moiety by a gem-dimethylcyclopropane ring through a synthetic intermediate having a C(6)-C(7) double bond and (b) the ozonolysis of the C(2)-C(3) bond followed by cyclization to the dihydropyran ring characteristic of plagiochiline N. Spectroscopic data of the synthetic product fully coincided with the reported data for the natural product.

Stereoselective synthesis of 7,11-guaien-8,12-olides from santonin. Synthesis of podoandin and (+)-zedolactone A

Photochemical rearrangement of hydroxy ester 2, easily obtained from santonin (1), afforded butenolide 4, a good starting material for the synthesis of 7,11-guaien-8,12-olides. Compound 4 has been transformed into compound 10, which has been used for the synthesis of podoandin (5) and (+)-zedolactone A (ent-6). Regioselective elimination of the acetyl group on C10 afforded directly podoandin (5). For the synthesis of ent-6, a hydroxyl group has been regio- and stereoselectively introduced at the 4alpha-position through the 3alpha,4alpha-epoxide 15. The basic hydrolysis of the 10-acetyl group in compound 18 took place with concomitant intramolecular conjugated addition of the alkoxide to the butenolide moiety to give ether 19. Cleavage of the 7,10-oxido bridge via the lactone enolate afforded (+)-zedolactone A (ent-6). This synthesis has allowed for the establishment of the absolute stereochemistry of natural zedolactone A as the enantiomer of our synthetic product.