The Furan Shuffling Hypothesis: A Biogenetic Proposal for Eremophilane Sesquiterpenoids

Abstract

Based on the structural similarities of the recently isolated eremophilane-type sesquiterpenoids microsphaeropsisin Ba nd Ca nd the iso-eremophilane periconianone C, ar evised biogenetic hypothesis for C8-C11-connected isoeremophilanes is presented and corroborated by strong experimental evidence.The first enantioselective total syntheses of microsphaeropsisin Ba nd Cw ere achieved starting from ak nowni ntermediate,w hose synthesis was elaborated previously in the total synthesis of periconianone A, and in atotal of 15 steps starting from g-hydroxy carvone.M ild reaction conditions for the subsequent a-ketol rearrangement not only resulted in the herein proposed conversion of microsphaeropsisin Bi nto periconianone C, but also in the conversion of microsphaeropsisin Ci nto 4-epi-periconianone C.

Eremophilane Sesquiterpenoids with Antibacterial and Anti-inflammatory Activities from the Endophytic Fungus Septoria rudbeckiae

“…Eremophilane sesquiterpenes, consisting of three isoprenes, possess the identical decalin framework with the eudesmanes and probably belong to a small group of sesquiterpenes. , Eremophilane sesquiterpenoids widely existed in numerous medicinal plants, especially in the Asteraceae family. − Subsequently, the metabolites of eremophilanes produced by theendophytic and marine fungi have increased remarkably, with some exhibiting multiple bioactivities including antifungal, anti-inflammatory, antivirus, antibacterial, and insecticidal activities. − Owing to the structural diversiform and unique biological activities of eremophilane sesquiterpenes, extensive phytochemical and biological investigations have been carried out by numerous scientists. − Consequently, further studies toward the development of novel and medicinally valuable sesquiterpenoids are essential.…”

Paraconulones A–G: Eremophilane Sesquiterpenoids from the Marine-Derived Fungus Paraconiothyrium sporulosum DL-16

“…The 13 C NMR and HSQC spectra disclosed 17 carbons (Table ), including three carbonyl carbons, one non-hydrogenated sp 2 carbon, two non-hydrogenated sp 3 carbons [δ C 74.4 (monooxygenated) and 40.3], three sp 2 methines, two sp 3 methines, two sp 3 methylenes [δ C 64.9 (monooxygenated) and 35.1), and four methyl carbons. The NMR data recorded for 3 were similar to those of the furan-open form of microsphaeropsisin B, with the major differences being the presence of an additional methyl group at δ H 2.03 (3H, s)/δ C 20.8 and an ester carbonyl at δ C 170.6, suggesting the presence of an acetoxy group in 3 . HMBC correlations from the oxymethylene H 2 -12 and the acetate methyl H 3 -17 to the ester carbonyl carbon C-16 established an O -acetyl group substituted at C-12 (Figure ).…”

“…Eremophilane sesquiterpenoids are a series of secondary metabolites structurally characterized by a decalin core bearing two one-carbon residues at C-4 and C-5 and a three-carbon moiety (isopropyl or isopropenyl) at C-7 . Around half of them feature an additional oxygen-containing ring (furan or lactone) that is fused across positions C-7 and C-8 to form the corresponding furanoeremophilanes or eremophilenolides.…”

“…1,6,7 Eremophilane sesquiterpenoids are a series of secondary metabolites structurally characterized by a decalin core bearing two one-carbon residues at C-4 and C-5 and a three-carbon moiety (isopropyl or isopropenyl) at C-7. 8 Around half of them feature an additional oxygen-containing ring (furan or lactone) that is fused across positions C-7 and C-8 to form the corresponding furanoeremophilanes or eremophilenolides. Eremophilane sesquiterpenoids have been discovered from a variety of sources including higher plants and fungi, and they have been described as exhibiting cytotoxic, antimalarial, antimicrobial, phytogrowth-inhibitory, NO production-inhibitory, host-selective phytotoxic, entomotoxic, and phytohormone activities.…”

The Furan Shuffling Hypothesis: A Biogenetic Proposal for Eremophilane Sesquiterpenoids

“…[6] However,weidentified additional minor signals in the 1 Ha nd 13 CNMR spectra. [17] Analysis of the reaction mixture by 1 HNMR spectroscopy showed the presence of 14 and 13 with hardly any side products.A fter purification by flash column chromatography, 14 and 13 were isolated in almost equal quantities. Optical rotation values of both synthesized natural products were measured and compared with those reported in the literature for the isolated material to confirm that their absolute configurations are identical:t he measured value of a ½ 25 D ¼À20.28 8 (c = 0.60, MeOH) for 1 was in agreement with that reported in the literature ( a ½ 20 D ¼À16.08 8, c = 0.10, MeOH).…”