Variecolortins A–C, Three Pairs of Spirocyclic Diketopiperazine Enantiomers from the Marine-Derived Fungus Eurotium sp. SCSIO F452

Abstract

Three pairs of spirocyclic diketopiperazine enantiomers, variecolortins A-C (1-3), were isolated from marine-derived fungus Eurotium sp. SCSIO F452. Compound 1 possesses an unprecedented highly functionalized seco-anthronopyranoid carbon skeleton featuring a 2-oxa-7-azabicyclo[3.2.1]octane core. Compounds 2 and 3 represent rare examples of a 6/6/6/6 tetracyclic cyclohexene-anthrone carbon scaffold. Their structures were determined by spectroscopic analyses, X-ray diffraction, and ECD calculations. Their enantiomers exhibited different antioxidative and cytotoxic activities, and their modes of action were investigated.

Three Pairs of New Spirocyclic Alkaloid Enantiomers From the Marine-Derived Fungus Eurotium sp. SCSIO F452

“…Motivated by the fascinating secondary metabolites produced by the fungi Eurotium spp., we have launched a chemical investigation on a marine-derived fungus isolated from a South China Sea sediment sample, Eurotium sp. SCSIO F452, and found a series of prenylated DKPs, prenyl benzaldehyde derivatives, especially three pairs of spirocyclic diketopiperazine-anthraquinone enantiomers variecolortins A–C (Wang et al, 2013; Zhong W. et al, 2018; Zhong W.-M. et al, 2018). In order to enrich and improve the chemical diversity of this fungus, we carried out a further chemical study on the Eurotium sp.…”

Spirocyclic Motifs in Natural Products

“…Referring back to the chemical investigation of the marine-derived fungus Eurotium sp. SCSIO F452 discussed above in connection with compounds belonging to the [5.5.0] spirocyclic system, an intriguing [5.6.0] spirocyclic compound 166 (Figure 79) was also isolated from the same species [109]. This is a case of one species giving rise to a diversity of spirocyclic frameworks, underscoring the significance of spirocycles in the natural product realm.…”

“…The compound exhibited different antioxidative and cytotoxic activities. Interestingly, the same species gave rise to a compound possessing an even more seldomly-occurring spirocyclic moiety; namely, [5.6.0] (vide infra) [109].…”

Marine-derived fungi as a source of bioactive indole alkaloids with diversified structures

“…Compound 215 showed significant radical scavenging activity against DPPH with an IC 50 value of 58.4 μmol/L, which was comparable to that of the positive control ascorbic acid (Vc) (IC 50 = 45.8 μmol/L) and nearly three times stronger than 216 (IC 50 = 159.2 μmol/L). Meanwhile, compound 217 showed moderate cytotoxicities against SF-268 and HepG2 cell lines with IC 50 values of 12.5, 15.0 μmol/L, respectively, while those of 219 were 30.1, 37.3 μmol/L (Zhong et al 2018b), respectively.…”