Asymmetric Assembly of Steroidal Tetracyclic Skeletons

Time and Pot Economy in Total Synthesis

We would all like to make or obtain the materials or products we want as soon as possible. This is human nature. This is true also for chemists in the synthesis of organic molecules. All chemists would like to make their target molecules as soon as possible, particularly when their interest is in the physical or biological properties of those molecules.As demonstrated by today's COVID-19 (SARS-CoV-2) pandemic, rapid synthesis is also crucial to enable chemists to deliver effective therapeutic agents to the community. Several concepts are currently well-accepted as important for achieving this: atom economy, step economy, and redox economy. Considering the importance of synthesizing organic molecules rapidly, I recently proposed adding the concept of time economy.In a multisep synthesis, each step has to be completed within a short period of time to make the desired molecule rapidly. The development of rapid reactions is important but also insufficient. After each step, frequent and repetitive workup operations such as quenching the reaction, extraction, separation of water and organic phases, drying the organic phase, filtration, evaporation, and purification may be required, and the time necessary for these processing operations must be taken into account. Indeed, some of the most time-consuming operations in most syntheses are the purification stages.On the other hand, one-pot reactions are processes in which several sequential reactions are conducted in a single reaction vessel, which avoids the need to purify intermediates. One-pot reactions are a useful way to shorten the total synthesis time, and the approach generally leads to an increase in the yield and a reduction in the amount of chemical waste formed. Thus, I also propose the importance of pot economy.On the basis of these concepts of time and pot economy, we have accomplished efficient syntheses of several natural products and medicines. The key to the success of these syntheses is the use of diphenylprolinol silyl ether as an effective catalyst in a one-pot reaction, in which it does not disturb the subsequent reactions. Our strategy is (1) to construct the chiral key skeletons and/or key components of natural products and medicines directly using organocatalyst-mediated one-pot reactions and (2) to conduct the subsequent transformations to the final molecules in a small number of pots utilizing the internal quench method. By means of this strategy, PGE₁ methyl ester, estradiol methyl ether, and clinprost were synthesized in three, five, and seven pots, respectively. Furthermore, (-)-oseltamivir, ABT-341, baclofen, and Corey lactone were synthesized in a single reaction vessel. Further optimization of the reactions in terms of time economy allowed (-)-oseltamivir and Corey lactone to be synthesized within 60 and 152 min, respectively. These syntheses will be highlighted as case studies. Although the organocatalyst is a key compound in this Account, pot- and time-economical syntheses can be expanded to organometallic chemistry and, indeed, to organic chemistry in general.

Total Synthesis of the Cardiotonic Steroid (+)-Cannogenol

The total synthesis of (+)-cannogenol, an aglycon common to various biologically important cardiotonic glycosides, has been achieved. Synthesis of the versatile intermediate involves Mizoroki-Heck and intramolecular Diels-Alder reactions from the enantiomerically pure CD-ring segment, newly prepared in a multidecagram scale this time. Total synthesis by the site-selective transformations of the versatile intermediate demonstrated the applicability of our synthetic approach.

Synthesis of Oxy-Functionalized Steroidal Skeletons via Mizoroki-Heck and Intramolecular Diels-Alder Reactions

Estrogenic and cardiotonic steroidal skeletons were concisely constructed via Mizoroki-Heck and intramolecular Diels-Alder (IMDA) reactions. Simple modification of the dienophile unsaturation of the IMDA precursor enabled representative AB-ring systems of both steroid classes to be accessed from the same intermediate. The diastereoselectivity of the IMDA reaction used to access the cardiotonic steroidal skeleton was found to be significantly enhanced by performing the reaction in water.

Steroidal dimer by001 inhibits proliferation and migration of esophageal cancer cells via multiple mechanisms

OBJECTIVE

To investigate the potential inhibitory effects of structurally novel steroidal dimer by001 in esophageal cancer in vitro.

METHODS

The cytotoxicity of by001 on esophageal, gastric, neuroblastoma and prostate cancer cells was examined MTT assay and colony formation assay. By001 induced apoptosis and production of intracellular reactive oxygen species on esophageal cancer cells Ec109, TE-1 and human normal gastric epithelial cells GES-1 was detected by flow cytometry. The effect of by001 on mitochondrial membrane potential was detected by fluorescence microscope through JC-1 staining. The level of intracellular reactive oxygen species was measured by fluorescence microscope and flow cytometry via DCFH-DA staining. The effect of by001 on members of Bcl-2 family, Fas, LC3, PARP and caspases was determined by Western blot. The effect of by001 on migration was measured by transwell assay.

RESULTS

By001 effectively inhibited proliferation of esophageal, gastric, neuroblastoma and prostate cancer cells in a time- and concentration-dependent manner in vitro. By001 reduced the number and the size of colonies at low micromolar concentrations, elevated cellular ROS levels and caused mitochondrial dysfunction in esophageal cancer cells. Molecular mechanistic studies showed that by001 triggered apoptosis through regulating members of Bcl-2 family and Fas.

CONCLUSIONS

These findings suggested that by001 may inhibited proliferation of esophageal cancer cells through mitochondria and death receptor-mediated apoptotic pathways, autophagy induction, as well as suppressed migration of esophageal cancer cells.

De Novo Synthesis of Possible Candidates for the Inagami-Tamura Endogenous Digitalis-like Factor

De novo synthesis of possible candidates for the Inagami-Tamura endogenous digitalis-like factor (EDLF) was achieved to validate a previously proposed structure. Our synthetic approach involves a highly regio- and diastereoselective Mizoroki-Heck reaction and a Friedel-Crafts-type cyclodehydration to construct steroidal tetracycle 14 as a versatile common intermediate leading to seven 2,14β-dihydroxyestradiol analogues 1a-c, 2a-c, and 3 as possible candidates. By comparing the potency of inhibitory activity against Na⁺/K⁺-ATPase between the synthesized candidates and the EDLF, it was found that the proposed structure is not likely to be a true structure of the Inagami-Tamura EDLF.

Pot Economy in the Total Synthesis of Estradiol Methyl Ether by Using an Organocatalyst

Enantioselective total synthesis of estradiol methyl ether has been accomplished in a pot-economical manner using five reaction vessels and four purifications. The key reaction is a diphenylprolinol silyl ether mediated domino Michael/aldol reaction to afford bicyclo[4.3.0]nonane derivatives, containing the A, C, and D rings of steroids, as a single isomer with excellent enantioselectivity. Six reactions such as oxidation, hydrogenation, formation of acid chloride, Friedel-Crafts reaction, deprotection, and reduction can be carried out in the last one-pot sequence.

Structurally novel steroidal spirooxindole by241 potently inhibits tumor growth mainly through ROS-mediated mechanisms

Cancer cells always have increased ROS levels, thus making them more vulnerable to persistent endogenous oxidative stress. The biochemical difference between cancer and normal cells could be exploited to achieve selective cancer cell killing by exogenous ROS-producing agents. Herein we described a structurally novel steroidal spirooxindole by241 and its anticancer efficacy. By241 exhibited potent inhibition against human cancer cells and less toxic to normal cells. By241 concentration-dependently induced apoptosis of MGC-803 and EC9706 cells, accompanied with the mitochondrial dysfunction and increased ROS levels. NAC can completely restore the decreased cell viability of MGC-803 cells caused by by241, suggesting ROS-mediated mechanisms. The expression levels of proteins involved in the mitochondrion-related pathways were detected, showing increased expression of proapoptotic proteins and decreased expression of anti-apoptotic proteins, and activation of caspases-9/-3, but without activating caspase-8 expression. Pretreatment with Z-VAD-FMK partially rescued by241-induced apoptosis of MGC-803 cells. Additionally, by241 inhibited mTOR, activated p53 and its downstream proteins, cleaved MDM2 and PI3K/AKT as well as NF-κB signaling pathway. In vivo experiments showed that by241 did not have significant acute oral toxicity and exerted good anticancer efficacy against MGC-803 bearing mice models. Therefore, by241 may serve as a lead for further development for cancer therapy.