Synthesis and biological activity of furostanic analogues of brassinosteroids bearing the 5alpha-hydroxy-6-oxo moiety

Methyl Esters of 23,24-Dinor-5α-cholan-22-oic Acids as Brassinosteroid Analogues. Synthesis, Evaluation of Plant Growth Promoting Activity and Molecular Docking

Five new brassinosteroid analogues were synthetized from 3β-acetoxy-23,24-dinorchol-4-en-22-oic acid. All the obtained compound showed significant activity in the Rice Lamina Inclination Test. Interestingly the effects of the methyl ester of 3β-hydroxy-6-oxo-23,24-dinorcholan-22-oic acid (14) at concentrations of 1 x 10^-7 and 1 x 10^-6 M proved to be higher than those produced by brassinolide. In silico Molecular Docking and Induced fit docking (IFD) simulations for the compounds with the highest biological activity data were carried out to investigate the binding mode interactions into the brassinolide-binding groove which revealed that the compound 14 had high binding energy values and a good affinity.

Steroidal Saponins with Plant Growth Stimulation Effects; Yucca schidigera as a Commercial Source

Plant growth-stimulation bioactivity of triterpenoid saponins is well known, especially for oleanane-type compounds. Nevertheless, a few phytotoxicity bioassays performed on some steroidal saponins have shown hormesis profiles and growth stimulation on Lactuca sativa roots. The focus of the work described here was on the use of the wheat coleoptile bioassay to evaluate plant growth stimulation, and on the search for a commercially available source of active saponins by bio-guided fractionation strategy. Selected saponins were tested and a cluster analysis showed that those saponins with a sugar chain of more than five units had a hormesis profile, while saponins with growth enhancement had fewer sugar residues. Two saponins showed similar activity to the positive control, namely the phytohormone indole-3-butyric acid (IBA). As a potential source of these metabolites, a commercial extract of Yucca schidigera used as a fertilizer was selected. Bio-guided fractionation led to the identification of two fractions of defined composition and these showed stimulation values similar to the positive control. It was observed that the presence of a carbonyl group at C-12 on the aglycone skeleton led to improved activity. A saponin-rich fraction from Y. schidigera could be proposed to enhance crop quality and production.

An unexpected acid-catalyzed rearrangement of diacetoxy benzylidenespirostanes to spirochromene acetals and spiroindenes with radical scavenger activity

23E-diacetoxybenzylidenespirostanes underwent rearrangement when treated with HCl in CH₂Cl₂/CH₃OH. The course of the rearrangement depends on the substitution pattern in the phenyl ring. While compounds bearing an acetoxy group at the ortho position produced spirochromenes, the partners with no substituent at the ortho position led to spiroindenes. All the rearranged compounds exhibited moderate antioxidant activity.

Synthesis of New Steroidal Carbamates with Plant-Growth-Promoting Activity: Theoretical and Experimental Evidence

A priority of modern agriculture is to use novel and environmentally friendly plant-growth promoter compounds to increase crop yields and avoid the indiscriminate use of synthetic fertilizers. Brassinosteroids are directly involved in the growth and development of plants and are considered attractive candidates to solve this problem. Obtaining these metabolites from their natural sources is expensive and cumbersome since they occur in extremely low concentrations in plants. For this reason, much effort has been dedicated in the last decades to synthesize brassinosteroids analogs. In this manuscript, we present the synthesis and characterization of seven steroidal carbamates starting from stigmasterol, β-sitosterol, diosgenin and several oxygenated derivatives of it. The synthesis route for functionalization of diosgenin included epoxidation and epoxy opening reactions, reduction of carbonyl groups, selective oxidation of hydroxyl groups, among others. All the obtained compounds were characterized by ¹H and ¹³C NMR, HRMS, and their melting points are also reported. Rice lamina inclination test performed at different concentrations established that all reported steroidal carbamates show plant-growth-promoting activity. A molecular docking study evaluated the affinity of the synthesized compounds towards the BRI1-BAK1 receptor from Arabidopsis thaliana and three of the docked compounds displayed a binding energy lower than brassinolide.

Synthesis of New Brassinosteroid 24-Norcholane Type Analogs Conjugated in C-3 with Benzoate Groups

The metabolism of brassinosteroid leads to structural modifications in the ring skeleton or the side alkyl chain. The esterification and glycosylation at C-3 are the most common metabolic pathways, and it has been suggested that conjugate brassinosteroids are less active or inactive. In this way, plants regulate the content of active brassinosteroids. In this work, the synthesis of brassinosteroid 24-norcholane type analogs conjugated at C-3 with benzoate groups, carrying electron donor and electron attractant substituents on the aromatic ring, is described. Additionally, their growth-promoting activities were evaluated using the Rice Lamina Inclination Test (RLIT) and compared with that exhibited by brassinolide (used as positive control) and non-conjugated analogs. The results indicate that at the lowest tested concentrations (10-8-10-7 M), all analogs conjugated at C-3 exhibit similar or higher activities than brassinolide, and the diasteroisomers with S configuration at C-22 are the more active ones. Increasing concentration (10-6 M) reduces the biological activities of analogs as compared to brassinolide.

Studies on the reactivity of 23E-benzylidene spirostanes

A study of the reactivity of 25R and 25S 23E-benzylidene spirostanes that includes epoxidation, catalytic hydrogenation as well as Lewis or Brønsted acid-catalyzed rearrangements is described. Exhaustive NMR characterization of the obtained compounds is presented. Additionally the structures of some of the obtained compounds were confirmed by single crystal X-Ray Diffraction studies.

Synthesis of 2-Deoxybrassinosteroids Analogs with 24-nor, 22(S)-23-Dihydroxy-Type Side Chains from Hyodeoxycholic Acid

Natural brassinosteroids are widespread in the plant kingdom and it is known that they play an important role in regulating plant growth. In this study, two new brassinosteroid analogs with shorter side chains but keeping the diol function were synthesized. Thus, the synthesis of 2-deoxybrassinosteroids analogs of the 3α-hydroxy-24-nor, 22,23-dihydroxy-5α-cholestane side chain type is described. The starting material is a derivative from hyodeoxycholic acid (4), which was obtained with an overall yield of 59% following a previously reported five step route. The side chain of this intermediate was modified by oxidative decarboxylation to get a terminal olefin at the C22-C23 position (compound 20) and subsequent dihydroxylation of the olefin. The resulting epimeric mixture of 21a, 21b was separated and the absolute configuration at the C22 carbon for the main product 21a was elucidated by single crystal X-ray diffraction analysis of the benzoylated derivative 22. Finally, lactonization of 21a through a Baeyer-Villiger oxidation of triacetylated derivative 23, using CF₃CO₃H/CHCl₃ as oxidant system, leads to lactones 24 and 25 in 35% and 14% yields, respectively. Deacetylation of these compounds leads to 2-deoxybrassinosteroids 18 and 19 in 86% and 81% yields. Full structural characterization of all synthesized compounds was achieved using their 1D, 2D NMR, and HRMS data.

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.

Baeyer-Villiger reaction of steroid sapogenins by CF3COOH-H2O2. A short cut to pregnan-3β,16β,20-triol 3-monoacetates

Treatment of steroid sapogenins with H₂O₂ in CF₃COOH for 15min followed by reflux in CH₃OH/H₂O afforded good yields of pregnan-3β,16β,20-triol 3-monoacetates. When the hydrolysis step was carried out with KOH in refluxing methanol excellent yields pregnantriols were obtained. The resulting compounds were characterized by their melting points and NMR spectral data. An X-ray diffraction analysis of compound 3a confirmed the proposed structure and provided detailed information about the bond lengths, bond angles and conformation.

Mimicking natural phytohormones. 26-Hydroxycholestan-22-one derivatives as plant growth promoters

26-Hydroxycholestan-22-one derivatives with oxygenated functions in the rings A and/or B were successfully synthesized from diosgenin. After the modifications of rings A and B, the spiroketal side chain was selectively opened through a Lewis acid mediated acetolysis to afford the cholestane derivatives. These compounds incorporate pharmacophores, which mimic the activity of natural phytohormones and show high growth promoting activity in Mexican rice cultivars using the rice lamina inclination test.

Synthesis of Five Known Brassinosteroid Analogs from Hyodeoxycholic Acid and Their Activities as Plant-Growth Regulators

Brassinosteroids (BRs) are plant hormones that promote growth in different plant organs and tissues. The structural requirements that these compounds should possess to exhibit this biological activity have been studied. In this work, a series of known BR analogs 5–15, were synthesized starting from hyodeoxycholic acid 4, and maintaining the alkyl side chain as cholic acid or its methyl ester. The growth-promoting effects of brassinolide (1) and synthesized analogs were evaluated by using the rice lamina inclination assay at concentrations ranging from 1 × 10⁻⁸–1 × 10⁻⁶ M. Our results indicate that in this concentration range the induced bending angle of rice seedlings increases with increasing concentration of BRs. Analysis of the activities, determined at the lowest tested concentration, in terms of BR structures shows that the 2α,3α-dihydroxy-7-oxa-6-ketone moiety existing in brassinolide is required for the plant growing activity of these compounds, as it has been proposed by some structure-activity relationship studies. The effect of compound 8 on cell elongation was assessed by microscopy analysis, and the results indicate that the growth-promoting effect of analog 8 is mainly due to cell elongation of the adaxial sides, instead of an increase on cell number.

Quantitative and stereospecific dihydroxylations of δ(5)-steroids: a green synthesis of plant growth hormone intermediates

Dihydroxylated Δ(5)-steroids are key intermediates in preparing steroids bearing a 5α-hydroxy-6-oxo moiety, which are plant growth hormones. Quantitative and stereospecific dihydroxylations of Δ(5)-steroids have been realized, using H2O2 catalyzed by KI and H2SO4 at 80 °C in aqueous dioxane. The workup consisted only of concentrating the solvents and filtering the products; no chromatography was needed. The reaction conditions tolerate various functional groups on the Δ(5)-steroids. A mechanism for this reaction is proposed and the reason that the reaction is quantitative and stereospecific is explained.

Acceleration of cutaneous wound healing by brassinosteroids

Brassinosteroids are plant growth hormones involved in cell growth, division, and differentiation. Their effects in animals are largely unknown, although recent studies showed that the anabolic properties of brassinosteroids are possibly mediated through the phosphoinositide 3-kinase/protein kinase B signaling pathway. Here, we examined biological activity of homobrassinolide (HB) and its synthetic analogues in in vitro proliferation and migration assays in murine fibroblast and primary keratinocyte cell culture. HB stimulated fibroblast proliferation and migration and weakly induced keratinocyte proliferation in vitro. The effects of topical HB administration on progression of wound closure were further tested in the mouse model of cutaneous wound healing. C57BL/6J mice were given a full-thickness dermal wound, and the rate of wound closure was assessed daily for 10 days, with adenosine receptor agonist CGS-21680 as a positive control. Topical application of brassinosteroid significantly reduced wound size and accelerated wound healing in treated animals. mRNA levels of transforming growth factor beta and intercellular adhesion molecule 1 were significantly lower, while tumor necrosis factor alpha was nearly suppressed in the wounds from treated mice. Our data suggest that topical application of brassinosteroids accelerates wound healing by positively modulating inflammatory and reepithelialization phases of the wound repair process, in part by enhancing Akt signaling in the skin at the edges of the wound and enhancing migration of fibroblasts in the wounded area. Targeting this signaling pathway with brassinosteroids may represent a promising approach to the therapy of delayed wound healing.

Synthesis and plant growth promoting activity of dinorcholanic lactones bearing the 5α-hydroxy-6-oxo moiety

The naturally occurring dinorcholanic lactone vespertilin and two other non-natural derivatives bearing the 5α-hydroxy-6-oxo moiety were synthesized starting from the readily available steroid sapogenin diosgenin. The obtained compounds showed plant growth promoting activity in the bean's second internode elongation assay.

BF₃·Et₂O-induced stereoselective aldol reaction with benzaldehyde, and steroid sapogenins and its application to a convenient synthesis of dinorcholanic lactones

Treatment of steroid sapogenins with benzaldehyde and BF(3)·Et(2)O cleanly produces E-23(23')-benzylidenspirostanes in good yields in a reaction pathway which consists on an aldol reaction followed by a dehydration step. The obtained E-23(23')-benzylidenspirostanes can be easily converted to dinorcholanic lactones by treatment with CrO(3) in acetic acid. The synthetic sequence to dinorcholanic lactones is compatible with the presence of double bonds and carbonyl groups in the steroid framework.

Synthesis and plant growth promoting activity of polyhydroxylated ketones bearing the 5α-hydroxy-6-oxo moiety and cholestane side chain

Three polyhydroxylated ketones bearing the 5α-hydroxy-6-oxo moiety were obtained from cholesterol. Two of them show plant growth promoting activity in the bean's second internode bioassay. The obtained results indicate that the presence of the 5α-hydroxy-6-oxo moiety may be capable to induce plant growth promotion even the absence oxygenated functions in the side chain.

On the reactivity of 23-methoxycarbonyl furospirostanes

Brønsted and Lewis acid-catalysed reactions of the 23-methoxycarbonyl furospirostanic side chain are described. While bromination, deuteration and BF(3)·Et(2)O/AcOH treatment involve regioselective F-ring opening with exclusive participation of Δ(22)-furostenic intermediates, BF(3)·Et(2)O/Ac(2)O treatment leads to irreversible E- or F-ring cleavage.

Akt-dependent anabolic activity of natural and synthetic brassinosteroids in rat skeletal muscle cells

Brassinosteroids are plant-derived polyhydroxylated derivatives of 5α-cholestane, structurally similar to cholesterol-derived animal steroid hormones and insect ecdysteroids. In this study, we synthesized a set of brassinosteroid analogues of a natural brassinosteroid (22S,23S)-homobrassinolide (HB, 1), including (22S,23S)-homocastasterone (2), (22S,23S)-3α-fluoro-homobrasinolide (3), (22S,23S)-3α-fluoro-homocastasterone (4), (22S,23S)-7-aza-homobrassinolide (5), and (22S,23S)-6-aza-homobrassinolide (6) and studied their anabolic efficacy in the L6 rat skeletal muscle cells in comparison to other synthetic and naturally occurring brassinosteroids (22R,23R)-homobrassinolide (7), (22S,23S)-epibrassinolide (8), and (22R,23R)-epibrassinolide (9). Presence of the 6-keto group in the B ring and stereochemistry of 22α,23α-vicinal hydroxyl groups in the side chain were critical for the anabolic activity, possibly due to higher cytotoxicity of the 22β,23β-hydroxylated brassinosteroids. All anabolic brassinosteroids tested in this study selectively activated PI3K/Akt signaling pathway as evident by increased Akt phosphorylation in vitro. Plant brassinosteroids and their synthetic derivatives may offer a novel therapeutic strategy for promoting growth, repair, and maintenance of skeletal muscles.

1H and 13C NMR characteristics of synthetic derivatives of steroid sapogenins. Part III. 16Beta,23:23,26-diepoxy side chains

The full assignments of the (1)H and (13)C NMR signals of steroids bearing the 16beta,23:23,26-diepoxy side chain are provided. Differentiation of the diasterotopic H-26 pair was achieved with the aid of NOESY experiments. The main substituent and steric effects associated with this moiety and their influence on the chemical shifts of the neighboring atoms are discussed.