Non-natural Elemane as the “Stepping Stone” for the Synthesis of Germacrane and Guaiane Sesquiterpenes

Expanding Natural Diversity: Tailored Enrichment of the 8,12-Sesquiterpenoid Lactone Chemical Space through Divergent Synthesis

The divergent synthesis of a non-natural 8,12-sesquiterpenoid lactone collection is described. The synthesis relies on a rationally designed guaianolide scaffold bearing a tertiary hydroxyl as the pinpoint for inducing its selective diversification. Key reactions include an unprecedented Suarez-type CH lactonization and a highly diastereoselective oxy-Cope/ene cascade that allows the introduction of three stereocenters in a single operation. Selective oxidative/reductive and redox neutral transformations follow to highlight the synthesis of naturally unpresented highly substituted 8,12-guaianolides.

Structurally diverse rearranged sesquiterpenoids, including a pair of rare tautomers, from the aerial parts of Daphne penicillata

Eight structurally diverse rearranged sesquiterpenoids, including seven undescribed sesquiterpenoids (1a/1b and 3-8) were obtained from the aerial parts of Daphne penicillata. 1a/1b, 3, 5 and 6 possess rare rearranged guaiane skeletons and 4 represents the first example of rearranged carotene sesquiterpenoids. Their structures and absolute configurations were determined by extensive spectroscopic analyses, NMR and ECD calculations. Interestingly, 1a and 1b were a pair of magical interconverting epimers that may interconvert by retro-aldol condensation. The mechanism of interconversion has been demonstrated indirectly by 9-OH derivatization of 1a/1b and a hypothetical biogenetic pathway was proposed. All compounds were evaluated for anti-inflammatory and cytotoxic activities. Among them, 1a/1b and 2 exhibited potential inhibitory activities on the production of NO against LPS-induced BV2 microglial cells.

Short Scalable Route to Apiaceae Sesquiterpene Scaffolds: Total Synthesis of 4-epi-Epiguaidiol A

The oxy-Cope/ene reaction cascade to form a locked elemane conformer allows the short scalable synthesis of versatile Apiaceae scaffolds. The divergent fate of the obtained macrocyclic germacrane is surveyed under cationic and dioxygen-induced Prins-type reaction conditions to allow the diastereoselective synthesis of oxidized Apiaceae guaiane congeners and the total synthesis of 4-epi-epiguaidiol A. Additionally, the unprecedented reduction of a hydrogen-bond-biased guaiane substrate permits the chemoselective synthesis of desoxo-jungiaguaiane.

A multifunctional divergent scaffold to access the formal syntheses of various sesquiterpenoids

The development of a divergent scaffold able to access an array of diverse natural sesquiterpenoids is described. The route unifies the scope of previously reported plans of our group to allow the scalable synthesis of 8,12-furo and lactone sesquiterpenoid carbocyclic cores of elemanes, germacranes, guaianes, cadinanes, lindenanes and myliols. The formal syntheses of furogermenone, methyl-curdionolide, zedoarol, qweicurculactone, lindenene and sarcandralactone A are reported.

Selectfluor-Enabled C(sp3)-H Alkoxylation of 3-Methylfuranocoumarins

A facile and metal-free method for the direct C(sp³)-H bond alkoxylation of 3-methylfuranocoumarins with alcohols has been disclosed. Selectfluor enabled the (hetero)benzylic C-H etherification by tuning the reaction temperature and solvent. Various alcohols were compatible in this transformation with suitable yields. The mechanistic studies revealed that the reaction might undergo the double addition process of alcohols, as well as the departure of a fluoride anion and the formation of an oxonium ion.

In(OTf)3-Catalyzed Cascade Cyclization for Construction of Oxatricyclic Compounds

A highly diastereoselective cascade cyclization reaction has been developed for establishing a series of oxatricyclic compounds using Chan's diene and simple keto alkynal substrates with only 1 mol % of In(OTf)₃ as the catalyst in 82-92% yields. The potential utility of this synthetic strategy has been demonstrated in model studies for the construction the core structures of 1α,8α:4α,5α-diepoxy-4,5-dihydroosmitopsin and cortistatin A.

Uncovering the pharmacological response of novel sesquiterpene derivatives that differentially alter gene expression and modulate the cell cycle in cancer cells

The present study aimed to assess the pharmacological anticancer profile of three natural and five synthetic sesquiterpenes developed by total chemical synthesis. To this end, their properties at the cellular and molecular level were evaluated in a panel of normal and cancer cell lines. The results obtained by performing cytotoxicity assays and gene expression analysis by reverse transcription-quantitative polymerase chain reaction showed that: i) Among the sesquiterpene derivatives analyzed, VDS58 exhibited a notable anticancer profile within attached (U-87 MG and MCF-7) and suspension (K562 and MEL-745) cancer cell cultures; however, U-87 MG cells were able to recover their proliferation capacity rapidly after 48 h of exposure; ii) gene expression profiling of U-87 MG cells, in contrast to K562 cells, showed a transient induction of cyclin-dependent kinase inhibitor 1A (CDKN1) expression; iii) the expression levels of transforming growth factor β1 (TGFB1) increased after 12 h of exposure of U-87 MG cells to VDS58 and were maintained at this level throughout the treatment period; iv) in K562 cells exposed to VDS58, TGFB1 expression levels were upregulated for 48 h and decrease afterwards; and v) the re-addition of VDS58 in U-87 MG cultures pretreated with VDS58 resulted in a notable increase in the expression of caspases (CASP3 and CASP9), BCL2‑associated agonist of cell death (BAD), cyclin D1, CDK6, CDKN1, MYC proto-oncogene bHLH transcription factor (MYC), TGFB1 and tumor suppressor protein p53. This upregulation persisted only for 24 h for the majority of genes, as afterwards, only the expression of TGFB1 and MYC was maintained at high levels. Through bioinformatic pathway analysis of RNA-Seq data of parental U-87 MG and K562 cells, substantial variation was reported in the expression profiles of the genes involved in the regulation of the cell cycle. This was associated with the differential pharmacological profiles observed in the same cells exposed to VDS58. Overall, the data presented in this study provide novel insights into the molecular mechanisms of action of sesquiterpene derivatives by dysregulating the expression levels of genes associated with the cell cycle of cancer cells.

Regioselective Ene-Type Allylic Chlorination of Electron-Rich Alkenes by Activated DMSO

A simple protocol involving the activation of DMSO by chlorotrimethysilane is described for the chemoselective chlorination of polyprenoids. The proposed protocol provides a versatile and scalable alternative to existing routes for accessing useful synthetic synthons for the synthesis of complex terpenoids.

Platinum-catalyzed cycloisomerizations of a common enyne: a divergent entry to cyclopropane sesquiterpenoids. Formal synthesis of sarcandralactone A

A common enyne scaffold, resembling the structures of natural elemanes was found to be an excellent substrate for highly regioselective cycloisomerizations to produce diverse cyclopropane sesquiterpenoids. Platinum-catalysis was utilized to produce either lindenane or myliol cores, found in natural products, starting from enyne acetate 10 and its corresponding allene 12 respectively. Based on this concept, a second generation strategy allows the formal synthesis of sarcandralactone A.

Divergent pathways to furosesquiterpenes: first total syntheses of (+)-zedoarol and (Rac)-gweicurculactone

Divergent transformation of a non-natural elemane to furo-guaiane and furo-cadinane cores.

Investigations into an anionic oxy-cope/transannular conjugate addition approach to 7,20-diisocyanoadociane

An anionic oxy-Cope/transannular conjugate addition approach to the potent antimalarial 7,20-diisocyanoadociane is presented. The unexpected formation of undesired diastereomers in the key reaction led to the structural reassignment of previous products of this type of cascade and a reevaluation of the reversibility of the transannular ring closure. During efforts to coax the reaction toward the desired product, a transannular ene reaction provided tricyclic compounds relevant to the kempane diterpenoids.

Furans and singlet oxygen – why there is more to come from this powerful partnership

Using the reaction of furans with singlet oxygen as a means to rapidly access huge structural diversity in a green & sustainable way.