New insights into structure-activity relationship of ipomoeassin F from its bioisosteric 5-oxa/aza analogues

Progress in the total synthesis of resin glycosides

Resin glycosides, mainly distributed in plants of the family Convolvulaceae, are a class of novel and complex glycolipids. Their structural complexity and significant biological activities have received much attention from synthetic chemists, and a number of interesting resin glycosides have been synthesized. The synthesized resin glycosides and their analogues not only helped in structural verification, structural modification, and further biological activity exploration but also provided enlightenment for the synthesis of glycoside compounds. Herein, the present review summarizes the application of various efforts toward the synthesis of resin glycosides in the last decade.

Synthesis, Biological Evaluation and Docking Studies of Ring-Opened Analogues of Ipomoeassin F

The plant-derived macrocyclic resin glycoside ipomoeassin F (Ipom-F) binds to Sec61α and significantly disrupts multiple aspects of Sec61-mediated protein biogenesis at the endoplasmic reticulum, ultimately leading to cell death. However, extensive assessment of Ipom-F as a molecular tool and a therapeutic lead is hampered by its limited production scale, largely caused by intramolecular assembly of the macrocyclic ring. Here, using in vitro and/or in cellula biological assays to explore the first series of ring-opened analogues for the ipomoeassins, and indeed all resin glycosides, we provide clear evidence that macrocyclic integrity is not required for the cytotoxic inhibition of Sec61-dependent protein translocation by Ipom-F. Furthermore, our modeling suggests that open-chain analogues of Ipom-F can interact with multiple sites on the Sec61α subunit, most likely located at a previously identified binding site for mycolactone and/or the so-called lateral gate. Subsequent in silico-aided design led to the discovery of the stereochemically simplified analogue 3 as a potent, alternative lead compound that could be synthesized much more efficiently than Ipom-F and will accelerate future ipomoeassin research in chemical biology and drug discovery. Our work may also inspire further exploration of ring-opened analogues of other resin glycosides.

Chemistry and biological activity of resin glycosides from Convolvulaceae species

Carbohydrate-based drug discovery has gained more and more attention during the last few decades. Resin glycoside is a kind of novel and complex glycolipids mainly distributed in plants of the family Convolvulaceae. Over the last decade, a number of natural resin glycosides and derivatives have been isolated and identified, and exhibited a broad spectrum of biological activities, such as cytotoxic, multidrug-resistant reversal on both microbial pathogens and mammalian cancer cells, antivirus, anticonvulsant, antidepressant, sedative, vasorelaxant, laxative, and α-glucosidase inhibitory effects, indicating their potential as lead compounds for drug discovery. A systematic review of the literature studies was carried out to summarize the chemistry and biological activity of resin glycosides from Convolvulaceae species, based on various data sources such as PubMed, Web of Science, Scopus, and Google scholar. The keyword "Convolvulaceae" was paired with "resin glycoside," "glycosidic acid," "glycolipid," or "oligosaccharide," and the references published between 2009 and June 2021 were covered. In this article, we comprehensively reviewed the structures of 288 natural resin glycoside and derivatives newly reported in the last decade. Moreover, we summarized the biological activities and mechanisms of action of the resin glycosides with pharmaceutical potential. Taken together, great progress has been made on the chemistry and biological activity of resin glycosides from Convolvulaceae species, however, more exploratory research is still needed, especially on the mechanism of action of the biological activities.

Ring Expansion Leads to a More Potent Analogue of Ipomoeassin F

Two new ring-size-varying analogues (2 and 3) of ipomoeassin F were synthesized and evaluated. Improved cytotoxicity (IC₅₀: from 1.8 nM) and in vitro protein translocation inhibition (IC₅₀: 35 nM) derived from ring expansion imply that the binding pocket of Sec61α (isoform 1) can accommodate further structural modifications, likely in the fatty acid portion. Streamlined preparation of the key diol intermediate 5 enabled gram-scale production, allowing us to establish that ipomoeassin F is biologically active in vivo (MTD: ∼3 mg/kg).

An Overview on Glyco-Macrocycles: Potential New Lead and their Future in Medicinal Chemistry

Macrocycles cover a small segment of molecules with a vast range of biological activity in the chemotherapeutic world. Primarily, the natural sources derived from macrocyclic drug candidates with a wide range of biological activities are known. Further evolutions of the medicinal chemistry towards macrocycle-based chemotherapeutics involve the functionalization of the natural product by hemisynthesis. More recently, macrocycles based on carbohydrates have evolved a considerable interest among the medicinal chemists worldwide. Carbohydrates provide an ideal scaffold to generate chiral macrocycles with well-defined pharmacophores in a decorated fashion to achieve the desired biological activity. We have given an overview on carbohydrate-derived macrocycle involving their synthesis in drug design and discovery and potential role in medicinal chemistry.

Ipomoeassin F Binds Sec61α to Inhibit Protein Translocation

Ipomoeassin F is a potent natural cytotoxin that inhibits growth of many tumor cell lines with single-digit nanomolar potency. However, its biological and pharmacological properties have remained largely unexplored. Building upon our earlier achievements in total synthesis and medicinal chemistry, we used chemical proteomics to identify Sec61α (protein transport protein Sec61 subunit alpha isoform 1), the pore-forming subunit of the Sec61 protein translocon, as a direct binding partner of ipomoeassin F in living cells. The interaction is specific and strong enough to survive lysis conditions, enabling a biotin analogue of ipomoeassin F to pull down Sec61α from live cells, yet it is also reversible, as judged by several experiments including fluorescent streptavidin staining, delayed competition in affinity pulldown, and inhibition of TNF biogenesis after washout. Sec61α forms the central subunit of the ER protein translocation complex, and the binding of ipomoeassin F results in a substantial, yet selective, inhibition of protein translocation in vitro and a broad ranging inhibition of protein secretion in live cells. Lastly, the unique resistance profile demonstrated by specific amino acid single-point mutations in Sec61α provides compelling evidence that Sec61α is the primary molecular target of ipomoeassin F and strongly suggests that the binding of this natural product to Sec61α is distinctive. Therefore, ipomoeassin F represents the first plant-derived, carbohydrate-based member of a novel structural class that offers new opportunities to explore Sec61α function and to further investigate its potential as a therapeutic target for drug discovery.

Constrained saccharides: a review of structure, biology, and synthesis

Review primarily covers from 1995-2018Carbohydrate function, recognized in a multitude of biological processes, provides a precedent for developing carbohydrate surrogates that mimic the structure and function of bioactive compounds. In order to constrain highly flexible oligosaccharides, synthetic tethering techniques like those exemplified by stapled peptides are utilized to varying degrees of success. Naturally occurring constrained carbohydrates, however, exist with noteworthy cytotoxic and chemosensitizing properties. This review highlights the structure, biology, and synthesis of this intriguing class of molecules.