Microwave assisted Westphal condensation and its application to synthesis of sempervirine and related compounds

Recent progress in chemistry and bioactivity of monoterpenoid indole alkaloids from the genus gelsemium: a comprehensive review

Monoterpenoid indole alkaloids (MIAs) represent a major class of active ingredients from the plants of the genus Gelsemium. Gelsemium MIAs with diverse chemical structures can be divided into six categories: gelsedine-, gelsemine-, humantenine-, koumine-, sarpagine- and yohimbane-type. Additionally, gelsemium MIAs exert a wide range of bioactivities, including anti-tumour, immunosuppression, anti-anxiety, analgesia, and so on. Owing to their fascinating structures and potent pharmaceutical properties, these gelsemium MIAs arouse significant organic chemists' interest to design state-of-the-art synthetic strategies for their total synthesis. In this review, we comprehensively summarised recently reported novel gelsemium MIAs, potential pharmacological activities of some active molecules, and total synthetic strategies covering the period from 2013 to 2022. It is expected that this study may open the window to timely illuminate and guide further study and development of gelsemium MIAs and their derivatives in clinical practice.

Selection of Natural Compounds with HMGA-Interfering Activities and Cancer Cell Cytotoxicity

HMGA proteins are intrinsically disordered (ID) chromatin architectural factors characterized by three DNA binding domains (AT-hooks) that allow them to bind into the DNA minor groove of AT-rich stretches. HMGA are functionally involved in regulating transcription, RNA processing, DNA repair, and chromatin remodeling and dynamics. These proteins are highly expressed and play essential functions during embryonic development. They are almost undetectable in adult tissues but are re-expressed at high levels in all cancers where they are involved in neoplastic transformation and cancer progression. We focused on identifying new small molecules capable of binding into the minor groove of AT-rich DNA sequences that could compete with HMGA for DNA binding and, thus, potentially interfere with their activities. Here, a docking-based virtual screening of a unique high diversity in-house library composed of around 1000 individual natural products identified 16 natural compounds as potential minor groove binders that could inhibit the interaction between HMGA and DNA. To verify the ability of these selected compounds to compete with HMGA proteins, we screened them using electrophoretic mobility shift assays. We identified Sorocein C, a Diels-Alder (D-A)-type adducts, isolated from Sorocea ilicifolia and Sorocea bonplandii with an HMGA/DNA-displacing activity and compared its activity with that of two structurally related compounds, Sorocein A and Sorocein B. All these compounds showed a cytotoxicity effect on cancer cells, suggesting that the Sorocein-structural family may provide new and yet unexplored chemotypes for the development of minor groove binders to be evaluated as anticancer agents.

Synthesis of Fluorescent, DNA-Binding Benzo[b]indolonaphthyridinium Derivatives by a Misguided Westphal Condensation

A novel type of azoniahetarene, namely, benzo[b]indolonaphthyridinium, was unexpectedly formed by the reaction of N-alkylated β-carbolinium derivatives and the enolizable 1,2-cyclohexadione under typical conditions of a Westphal reaction. The products exhibit high fluorescence intensities in polar solvents (Φ_fl = 0.52-0.67) and bind to DNA by intercalation with high affinity (K_b = 1.5 × 10⁶ M^-1). Furthermore, under the same conditions, DNA-binding sempervirine derivatives were synthesized in a Westphal reaction from 1,2-diketones that have at least one non-enolizable α-carbon atom, which shows that the reaction pathway is determined by the substrate structure.

Direct 3-Acylation of Indolizines by Carboxylic Acids for the Practical Synthesis of Red Light-Releasable Caged Carboxylic Acids

To enhance the practicality of photouncaging system using 3-acyl-2-methoxyindolizines, direct acylation of indolizines with carboxylic acids was developed using condensation reagents, generally used for peptide coupling. This method allowed for caging a broad range of carboxylic acids with indolizines. The method enabled a facile synthesis of water-soluble caged bioactive carboxylic acids having an intramolecular photosensitizer. The efficient release of carboxylic acids from the synthesized caged compounds upon red light irradiation was confirmed in neutral buffered solutions.

Fischer indole synthesis applied to the total synthesis of natural products

In this review, we are trying to underscore the application of FIS in one of the crucial step of indole construction in the total synthesis of biologically active natural products.

Indolo-pyrido-isoquinolin based alkaloid inhibits growth, invasion and migration of breast cancer cells via activation of p53-miR34a axis

The tumor suppressor p53 plays a critical role in suppressing cancer growth and progression and is an attractive target for the development of new targeted therapies. We synthesized several indolo-pyrido-isoquinolin based alkaloids to activate p53 function and examined their therapeutic efficacy using NCI-60 screening. Here, we provide molecular evidence that one of these compounds, 11-methoxy-2,3,4,13-tetrahydro-1H-indolo[2',3':3,4]pyrido[1,2-b]isoquinolin-6-ylium-bromide (termed P18 or NSC-768219) inhibits growth and clonogenic potential of cancer cells. P18 treatment results in downregulation of mesenchymal markers and concurrent upregulation of epithelial markers as well as inhibition of migration and invasion. Experimental epithelial-mesenchymal-transition (EMT) induced by exposure to TGFβ/TNFα is also completely reversed by P18. Importantly, P18 also inhibits mammosphere-formation along with a reduction in the expression of stemness factors, Oct4, Nanog and Sox2. We show that P18 induces expression, phosphorylation and accumulation of p53 in cancer cells. P18-mediated induction of p53 leads to increased nuclear localization and elevated expression of p53 target genes. Using isogenic cancer cells differing only in p53 status, we show that p53 plays an important role in P18-mediated alteration of mesenchymal and epithelial genes, inhibition of migration and invasion of cancer cells. Furthermore, P18 increases miR-34a expression in p53-dependent manner and miR-34a is integral for P18-mediated inhibition of growth, invasion and mammosphere-formation. miR-34a mimics potentiate P18 efficacy while miR-34a antagomirs antagonize P18. Collectively, these data provide evidence that P18 may represent a promising therapeutic strategy for the inhibition of growth and progression of breast cancer and p53-miR-34a axis is important for P18 function.

Synthesis and Cytoxicity of Sempervirine and Analogues

Sempervirine and analogues were synthesized using a route featuring Sonogashira and Larock Pd-catalyzed reactions. Structure-activity relationships were investigated using three human cancer cell lines. 10-Fluorosempervirine is the most potently cytotoxic member of the family yet described.

Natural Product Inhibitors of Ubiquitin Conjugation and Deconjugation

The ubiquitin–proteasome system has been recognized as fundamental toward protein turnover in eukaryotic cells. The system comprises the ubiquitin conjugation machinery consisting of an enzyme cascade of E1, E2, and E3 enzymes, the deubiquitinases (DUBs) and the proteasome, a multisubunit protease complex acting through an N-terminal threonine protease mechanism. A number of natural product inhibitors of the proteasome have been studied in detail and these inhibitors and their derivatives have been highly valuable in developing our understanding of this system. These efforts culminated in the successful development of bortezomib as a pharmacological agent used clinically as a cancer therapeutic in the treatment of multiple myeloma.

This review is focused on natural product inhibitors of the enzymes involved in intracellular ubiquitin conjugation (ubiquitin-activating enzyme E1, ubiquitin-conjugating enzyme E2, ubiquitin ligase E3) and ubiquitin deconjugation (DUBs). Members of both of these enzyme systems have been proposed as pharmacological targets for cancer therapy and several other diseases. Furthermore compounds with activities toward enzymes from the analogous ubiquitin-like (Ubl) protein families have been identified for SUMO and NEDD8. To date natural product inhibitors have been described for members of each of these protein families and were isolated from plant, fungal, animal, and microbial sources. Insights into the mechanism of action of natural products and their derivatives will enhance our understanding of this complex system and will improve our ability to rationally design novel inhibitors. The increased availability of assays and research tools for the study of protein ubiquitination, deubiquitination, and Ubl proteins will contribute to the discovery of more potent and selective compounds. We expect that these studies will stimulate development of further potential pharmacological agents in this area.

A convenient synthesis of quinolizinium salts through Rh(III) or Ru(II)-catalyzed C-H bond activation of 2-alkenylpyridines

An efficient synthesis of quinolizinium salts from 2-vinylpyridines and alkynes via Rh(III) or Ru(II)-catalyzed C-H activation and annulation reaction is described. A possible mechanism involving pyridine assisted vinylic ortho-C-H activation, alkyne insertion and reductive elimination is proposed.