The convergent synthesis of novel cytotoxic certonardosterol D2 from diosgenin

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.

Concise synthesis of E/F ring spiroethers from tigogenin. Carbaanalogs of steroidal sapogenins and their biological activity

A four-step synthesis of five- and six-membered E/F ring spiroethers from tigogenin has been developed. An efficient strategy that features bis-Grignard reaction of dinorcholanic lactone with appropriate bis(bromomagnesio)alkanes followed by acid-mediated spirocyclization was employed to construct a new class of steroid compounds having E and F ring junction as an oxa-carbacyclic system. The synthesized carbaanalogs interact with liposomes and albumin, and also exhibit antibacterial and antifungal activity, demonstrating their pharmacological potential.

Clionamines stimulate autophagy, inhibit Mycobacterium tuberculosis survival in macrophages, and target Pik1

The pathogen Mycobacterium tuberculosis (Mtb) evades the innate immune system by interfering with autophagy and phagosomal maturation in macrophages, and, as a result, small molecule stimulation of autophagy represents a host-directed therapeutics (HDTs) approach for treatment of tuberculosis (TB). Here we show the marine natural product clionamines activate autophagy and inhibit Mtb survival in macrophages. A yeast chemical-genetics approach identified Pik1 as target protein of the clionamines. Biotinylated clionamine B pulled down Pik1 from yeast cell lysates and a clionamine analog inhibited phosphatidyl 4-phosphate (PI4P) production in yeast Golgi membranes. Chemical-genetic profiles of clionamines and cationic amphiphilic drugs (CADs) are closely related, linking the clionamine mode of action to co-localization with PI4P in a vesicular compartment. Small interfering RNA (siRNA) knockdown of PI4KB, a human homolog of Pik1, inhibited the survival of Mtb in macrophages, identifying PI4KB as an unexploited molecular target for efforts to develop HDT drugs for treatment of TB.

Synthesis and biological in vitro evaluation of the effect of hydroxyimino steroidal derivatives on breast cancer cells

Breast cancer is the most common cause of cancer death in women, according to Global Cancer Observatory. This fact forces scientists to continue in the search for effective treatments against this aggressive type of cancer. Breast cancer frequently metastasizes to other organs, most often the bones, lungs, and liver. Breast cancer is normally associated with estrogen and progestogen levels and can be hormone or non-hormone dependent. In current experiments herein reported, some hydroxyimino spirostan derivatives showed great potential against MCF-7 breast cancer, a Luminal-A cancer. On the other hand, a set of synthesized 6-hydroxyimino-22-oxocholestane compounds had excellent activity against the MDA-MB-231 breast cancer cell line. The synthesis of hydroxyamino derivatives from spirostan and 22-oxocholestane compounds was improved. The hydroxyimino compounds enhanced the bioactivity when compared with their parent carbonyl skeletons.

Biotransformation of Phytosterols to Androst-1,4-Diene-3,17-Dione by Mycobacterium sp. ZFZ Expressing 3-Ketosteroid-Δ1-Dehydrogenase

As an important hormone drug intermediate, androst-1,4-diene-3,17-dione can be bio-converted from phytosterols. However, separation and purification in the downstream process are very difficult due to the similarity in structure and physiological characteristics between ADD and androstenedione (AD). This phenomenon was correlated to the insufficient enzyme activity of 3-ketosteroid-Δ1-dehydrogenase (KSDD), which specifically catalyzes the C1,2 dehydrogenation of AD. In order to obtain a highly purified ADD from phytosterols, the dehydrogenation effect of different kinds of KSDDs and the transcription effect of four promoter sequences on ksdd were analyzed in Mycobacterium sp. ZFZ (ZFZ), the cell host that transform phytosterols to AD in the oil-aqueous system. A tandem KSDD expression cassette containing strain ZFZ-2111 yielded 2.06 ± 0.09 g L−1 ADD, with a molar ratio of ADD/AD at 41.47:1.00 in 120 h. In waste cooking oil-aqueous media, the proportion of ADD in the fermentation by ZFZ-2111 was 92%. The present study provides a reliable theoretical basis for the step-by-step transformation of phytosterols to ADD.

Synthesis and application of steroidal 22,16β-carbolactones: A review

In the plant kingdom, steroidal lactones occur as glycosides, compounds consisting of a sugar moiety linked to a steroid aglycone. Steroidal lactones consist of five fused rings, with a total of 22 carbon atoms. Numerous methods for the preparation of steroidal lactones take advantage of the fact that steroid spirostanes may be degraded from six- to a five-rings structure. One of the most striking features common to reactions of steroid sapogenins is the C₂₂-lactone formation. In the review, different methods for the preparation of steroidal lactones are presented with consideration of the structure of starting material. In addition, examples of lactones used in the synthesis of biologically active compounds and their analogues are described.

Chemical synthesis of marine saponins

Covering: 1989-2017 Saponins are characteristic metabolites of starfish and sea cucumbers, and occasionally are also found in sponges, soft coral, and small fish. These steroid or triterpenoid glycosides often show remarkable biological and pharmacological activities, such as antifungal, antifouling, shark repellent, antitumor and anti-inflammatory activities. Over one thousand marine saponins have been characterized; the majority of them can be categorized into three major structural types, i.e., asterosaponins, polyhydroxysteroid glycosides, and holostane glycosides. Thus far, only 12 marine saponins have been synthesized; those representing the major types were successfully synthesized recently. The syntheses involve preparation of the aglycones from the terrestrial steroid or triterpene materials, installation of the carbohydrate units, and manipulation of the protecting groups. Herein, we provide a comprehensive review on these syntheses.

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.

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.

Synthesis and in vitro anticancer activity of 23(23')E-benzylidenespirostanols derived from steroid sapogenins

Benzylidenespirostanols were prepared by two-step synthesis including BF₃·Et₂O-catalyzed aldol condensation of several acetylated steroid sapogenins with benzaldehyde followed by saponification. The obtained compounds showed moderate cytotoxicity against three cancer cell lines (T-lymphoblastic leukemia cell line CEM, breast carcinoma cell line MCF7 and cervical carcinoma cell line HeLa) and normal human fibroblasts (BJ). The most active of the five tested substances was 3c (lowest IC₅₀ for MCF7 cells 19.9±0.1µM) without any selectivity towards human cancer and normal cells, respectively.

Total Synthesis of Linckosides A and B, the Representative Starfish Polyhydroxysteroid Glycosides with Neuritogenic Activities

Linckosides A and B, two starfish metabolites with promising neuritogenic activities, are synthesized in a longest linear sequence of 32 steps and 0.5% overall yield; this represents the first synthesis of members of the polyhydroxysteroid glycoside family, which occur widely in starfishes.

Highly efficient and scalable synthesis of clionamine D

Herein we describe an efficient and scalable synthesis of clionamine D (4), a special member with autophagy bioactivity and an unprecedented spirobislactone side chain in the novel aminosteroid clionamines. This synthesis features a quick access to α-methylene-γ-lactone 8 and a Mn(OAc)3-mediated radical [3 + 2] reaction to assemble the unique spirobislactone unit. Clionamine D (4) can also serve as a key synthetic precursor to other clionamine members.

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.

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.

Studies on the BF3·Et2O catalyzed Baeyer-Villiger reaction of spiroketalic steroidal ketones

During reactions of 23-oxosapogenins and the corresponding isomeric 22-oxo-23-spiroketals with MCPBA in the presence of BF(3)·Et(2)O, equilibration occurs between the ketones. The Baeyer-Villiger type oxidation is followed by fragmentation to the dinorcholanic lactones and 3-methylbutyrolactone. The mechanistic aspects of these reactions in the 25R and 25S series are discussed.

On reactions of steroidal 23-oxo and 23,24-epoxysapogenins with Lewis acids

The reaction of 23-oxotigogenin acetate with TMSOTf in THF afforded the corresponding bisnorcholanic lactone in 60% yield. The analogous reactions carried out in dichloromethane or benzene gave the rearranged products--the isomeric spirostanic ketone (10-15%) and bisfuran (40-42%). Similar products were also obtained upon treatment of 23,24-epoxysapogenins with BF(3). The epoxides treated with TiCl(4) afforded mostly chlorohydrins and no rearranged products were detected.

Beckmann reactions of steroidal spirocyclic oximes derived from the 16beta,23:23,26-diepoxy-22-oxo moiety

The Beckmann rearrangement of the syn and anti isomers of the spirocyclic oxime derived from a 16beta,23:23,26-diepoxy-5beta-cholestan-22-one was studied. Whereas the anti isomer always follows the Beckmann fragmentation course, the syn isomer, depending on the reaction conditions, follows the normal Beckmann rearrangement course and/or the isomerization to the anti isomer followed by the fragmentation course.

Synthesis of "glycospirostanes"--steroid sapogenins with a sugar-like ring F

The synthesis of two "glycospirostanes" from 23-oxotigogenin acetate is described. (23S,24S,25R)-5alpha-Spirostane-3beta,23,24,25-tetraol was obtained by dehydrogenation followed by stereoselective reduction of the 23-oxo group and OsO(4) dihydroxylation of the C24-C25 double bond. Allylic hydroxylation with SeO(2) of 3beta-acetoxy-5alpha-spirost-23-ene obtained from 23-oxotigogenin acetate followed by OsO(4) dihydroxylation of the C23-C24 double bond afforded (23R,24S,25R)-5alpha-spirostane-3beta,23,24,25-tetraol.