A new route for the preparation of the 22,23-dioxocholestane side chain from diosgenin and its application to the stereocontrolled construction of the 22R,23S-diol function

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.

Steroidal glycosides from Ornithogalum dubium Houtt

The phytochemical study of Ornithogalum dubium Houtt. (Asparagaceae) led to the isolation of five undescribed steroidal glycosides together with two known ones. Their structures were established by using NMR analysis and mass spectrometry as (25R)-3β-hydroxyspirost-5-en-1β-yl O-α-L-arabinopyranosyl-(1 → 2)-α-L-rhamnopyranoside, (25S)-3β-hydroxyspirost-5-en-1β-yl O-β-D-glucopyranosyl-(1 → 6)-β-D-glucopyranoside, (22S)-16β-[(α-L-rhamnopyranosyl)oxy]-22-hydroxycholest-5-en-3β-yl O-β-D-glucopyranosyl-(1 → 4)-β-D-glucopyranoside, (22S,23S)-1β,3β,11α,16β,23-pentahydroxy-5α-cholest-24-en-22β-yl β-D-glucopyranoside, (22S,23S)-3β-[(β-D-glucopyranosyl)oxy]-22,23-dihydroxy-5α-cholest-24-en-16β-yl O-α-L-rhamnopyranosyl)-(1 → 4)-β-D-glucopyranoside. Their cytotoxic activities against two human cells, a lung carcinoma A-549 and a promyelocytic leukemia HL-60 cell lines, were evaluated by using the XTT method. The results showed no significant cytotoxicity on the tested cells. The influence of the potentiation of cisplatin cytotoxicity in A-549 cells was also investigated and a slight effect was observed only for the (25R) spirostane-type derivative.

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.

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.

Synthetic pathway to 22,23-dioxocholestanic chain derivatives and their usefulness for obtaining brassinosteroid analogues

Recognizing the functionality of the pentacyclic steroidal derivative 7a as important synthon to obtain new brassinosteroid analogs, we have accomplished the derivatization of hecogenin, a sapogenin from the 25R serie containing a carbonyl group at C-12, to a 22,23-dioxocholestanic chain derivative. Starting from hecogenin acetate (5a) or hecogenin tosylate (5b), we obtained two pentacyclic derivatives (7a and 7b) which were subjected to an oxidation reaction on the double bond at C-12(23) to obtain a 22,23-dioxocholestanic chain, with the regeneration of the carbonyl group at C-12. Reduction of the carbonyl groups lead to the 20-epi-12,23-dihydroxy-22-oxo system 11a-b. The absolute configuration of compound 11a was established by X-ray diffraction analysis.

Diosgenone synthesis, anti-malarial activity and QSAR of analogues of this natural product

Solanum nudum Dunal steroids have been reported as being antimalarial compounds; however, their concentration in plants is low, meaning that the species could be threatened by over-harvesting for this purpose. Swern oxidation was used for hemisynthesis of diosgenone (one of the most active steroidal sapogenin diosgenin compounds). Eighteen structural analogues were prepared; three of them were found to be more active than diosgenone (IC₅₀ 27.9 μM vs. 10.1 μM, 2.9 μM and 11.3 μM). The presence of a 4-en-3-one grouping in the A-ring of the compounds seems to be indispensable for antiplasmodial activity; progesterone (having the same functional group in the steroid A-ring) has also displayed antiplasmodial activity. Quantitative correlations between molecular structure and bioactivity were thus explored in diosgenone and several derivatives using well-established 3D-QSAR techniques. The models showed that combining electrostatic (70%) and steric (30%) fields can explain most variance regarding compound activity. Malarial parasitemia in mice became reduced by oral administration of two diosgenone derivatives.

Ulososides and urabosides--triterpenoid saponins from the Caribbean marine sponge Ectyoplasia ferox

Three new triterpene glycosides, named ulososide F (1), urabosides A (2) and B (3), together with the previously reported ulososide A (4), were isolated from the Caribbean marine sponge Ectyoplasia ferox. Their structures were elucidated using extensive interpretation of 1D and 2D-NMR data, as well as HRESIMS. The aglycon of all compounds is a rare 30-norlonastane and the sugar residues were identified after acid hydrolysis and GC analyses. Cytotoxicities of the isolated compounds were evaluated against Jurkat and CHO cell lines by a MTT in vitro assay as well as a hemolysis assay. Unexpectedly, all these saponin derivatives showed very low activity in our bioassays.

(25R)-16β-Acet-oxy-3β-bromo-23',26-ep-oxy-23',25-dimethyl-5α-cholest-23,23'-en-6-one dichloro-methane monosolvate

The crystal structure of the title compound, C31H45BrO5·CH2Cl2, prepared in six steps from diosgenin, confirmed that the configurations of the stereogenic centers, positions 20S and 25R, remain unchanged during the reaction. The six-membered A, B and C rings have chair conformations. The five-membered ring D has an envelope conformation (with the methyl-substituted C atom fused to ring C as the flap) and the six-membered dihydro-pyran ring E adopts a twist-boat conformation. In the crystal, mol-ecules are linked via C-H⋯O and C-H⋯Cl hydrogen bonds, the latter involving the dichloro-methane solvent mol-ecule, forming a three-dimensional supra-molecular network.

A diversity-oriented synthesis approach to macrocycles via oxidative ring expansion

Macrocycles are key structural elements in numerous bioactive small molecules and are attractive targets in the diversity-oriented synthesis of natural product-based libraries. However, efficient and systematic access to diverse collections of macrocycles has proven difficult using classical macrocyclization reactions. To address this problem, we have developed a concise, modular approach to the diversity-oriented synthesis of macrolactones and macrolactams involving oxidative cleavage of a bridging double bond in polycyclic enol ethers and enamines. These substrates are assembled in only 4–5 synthetic steps and undergo ring expansion to afford highly functionalized macrocycles bearing handles for further diversification. In contrast to macrocyclization reactions of corresponding seco-acids, the ring expansion reactions are efficient and insensitive to ring size and stereochemistry, overcoming key limitations of conventional approaches to systematic macrocycle synthesis. Cheminformatic analysis indicates that these macrocycles access regions of chemical space that overlap with natural products, distinct from currently-targeted synthetic drugs.

Stereospecific synthesis of new steroidal isoxazoles in dry media

An easy and fast procedure was developed for one-pot synthesis of steroidal isoxazoles starting from 23-acetylsapogenins derivatives in presence of P2O5/SiO2 in dry media under microwaves irradiation is described. Substrates of the 25S and 25R series were used as raw materials, establishing that this new methodology is applicable to both series.

Novel steroidal penta- and hexacyclic compounds derived from 12-oxospirostan sapogenins

The E ring regioselective acid-catalyzed opening of spirostanic sapogenins possessing a carbonyl group at C-12, such as botogenin and hecogenin, provided the new 12,23-cyclo-22,26-epoxycholesta-11,22-diene skeleton, in addition to new compounds of the already known 12,23-cyclocholest-12(23)-en-22-one frameworks. This transformation proceeds in a single step, under slightly acidic conditions. Both, penta- and hexacyclic steroids were obtained with retention of configuration of all asymmetric centers.