The reaction of 6,8-disubstituted E,E-germacra-1(10),4-diene 4-epoxides with oxyphilic reagents

Discovery of diversified cassane diterpenoids as potent antibacterial agents from Caesaplinia pulcherrima and their mechanisms

BACKGROUND

Natural products play a significant role in the development of novel bactericide candidates. Caesalpinia pulcherrima, a traditional medicine, had anti-inflammatory, antimicrobial, and antifeedant activities, therefore the previous bioassay results of C. pulcherrima implied that its main active ingredients may have potential to be used as botanical bactericides.

RESULTS

Bio-guided isolation of C. pulcherrima was conducted to obtain 11 novel cassane diterpenoids (capulchemins A-K) and 10 known sesquiterpenes. Their structures were established by extensive spectroscopic methods and single-crystal X-ray diffraction analyses. Capulchemins A-F possess a rare aromatic C ring, while capulchemin K with a 15,16-degradative carbon skeleton represents a rare group of cassane diterpenes. Capulchemin A exhibited remarkable antibacterial activity against four phytopathogenic bacteria, particularly against Pseudomonas syringae pv. actinidae and Bacillus cereus, with minimal inhibitory concentration values of 3.13 μM. Meanwhile, capulchemin A showed significant control effect on kiwifruit canker in vivo. Further investigation of its mechanism of antibacterial activity revealed that compound 1 was closely related to destroy cell membrane to cause cell death. Additionally, some of those cassane diterpenoids showed potential antifeedant against Mythimna separate walker and Plutella xylostella. Consequently, capulchemin A could have the potential to be used as a template for the development for new eco-friendly NP-based bactericides.

CONCLUSION

These data contribute to a better understanding of the antibacterial activity of cassane diterpenes. Cassane diterpenes have been discovered to be leading to broad application prospects in the development as novel botanical bactericides. © 2023 Society of Chemical Industry.

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.

Structural diversity from the transannular cyclizations of natural germacrone and epoxy derivatives: a theoretical-experimental study

Treatment of germacrone (1) with different electrophiles, and of its epoxy derivatives germacrone-4,5-epoxide (2), germacrone-1,10-epoxide (3) and isogermacrone-4,5-epoxide (4) with Brönsted/Lewis acids and Ti(III), gives rise to a great structural diversity. Thus, by using a maximum of two steps, the production of more than 40 compounds corresponding to 14 skeletons is described. Computational calculations rationalizing the structural divergence produced are also described. Finally, since some of the compounds generated are bioactive natural sesquiterpenes, the mechanisms of formation of these substances will provide new insights in their biosynthesis.

Genepolide, a sesterpene gamma-lactone with a novel carbon skeleton from mountain wormwood (Artemisia umbelliformis)

The sesterpene gamma-lactone genepolide (5) has been isolated from a Swiss horticultural variety of mountain wormwood (Artemisia umbelliformis) developed as a thujones-free alternative to native Western Alps wormwoods for the production of liqueurs. Genepolide is the formal Diels-Alder adduct of the exomethylene-gamma-lactone costunolide (2) and the diene myrcene (6), two poorly reactive partners in cycloaddition reactions, and its structure was elucidated through a combination of spectroscopic methods. An investigation on the thermal stability of mixtures of 2 and 6, as well as considerations on the sensitivity of 2 to Brønsted and Lewis acids, suggests that 5 is a genuine natural product and that the Swiss chemotype of A. umbelliformis contains Diels-Alderase enzymatic activity that is lacking in native mountain wormwoods from Western Alps. Remarkable differences in thermal and acid-catalyzed reactions of the cyclodecadiene moiety of 2 and 5 suggest that quaternarization at C-11 has far-reaching effects on the reactivity of their homoconjugated medium-sized diene system. The wide occurrence of this structural motif in sesquiterpenoids makes this issue worth a systematic investigation.

Macrocyclic diterpenoids from Euphorbia hyberna L. subsp. insularis and their reaction with oxyphilic reagents

The aerial parts of Euphorbia hyberna subsp. insularis from Sardinia contain large amounts of macrocyclic diterpenoids of the jatrophane type, while phorboids could not be isolated. Treatment of the major constituent (1a) with various acidic and oxyphilic reagents was investigated, showing the surprising reluctance of the macrocyclic system to undergo transannular reactions. Dehydration, isomerization of the exocyclic double and acyl rearrangement were, however, observed after reduction of the 9-keto group.

Unnatural natural products from the transannular cyclization of lathyrane diterpenes

The potential of macrocyclic diterpenoids to afford natural product-like polycyclic compounds was demonstrated by the conversion of two lathyrane Euphorbia factors into a series of densely functionalized diterpenoids of unnatural skeletal type. Apparently, Nature is far from having fully exploited the built-in reactivity of these compounds to generate chemical diversity.

Oxygenated sesquiterpenoids from a nonpoisonous sardinian chemotype of giant fennel (Ferula communis)

The roots of the nonpoisonous chemotype of giant fennel (Ferula communis) from Sardinia afforded a novel cadinanetriol (1), whose structure was established by spectroscopic data and confirmed by synthesis from the E,E-Delta (1(10),5) germacradiene allohedycariol. A number of known compounds were also identified. Despite the lack of morphological differences, a broad chemical diversity exists within giant fennel, underlying the contrasting data on its poisonous properties.