New Austalides from the Sponge‐Associated Fungus Aspergillus sp.

Abstract

Keywords: Natural products / Fused-ring systems / Circular dichroism / Density functional calculations / Structure elucidation / CytotoxicityChromatographic separation of a crude extract obtained from the fungus Aspergillus sp., isolated from the Mediterranean sponge Tethya aurantium, yielded five new meroterpenoid metabolites, austalides M-Q (1-5), together with nine known compounds (6-13). The structures of the new compounds were unambiguously elucidated on the basis of extensive 1D and 2D NMR methods and by mass spectral analysis. Furthermore, the absolute configurations of 1 and 4 were determined by time-dependent density functional theory electronic circular dichroism (TDDFT ECD) calculations, allowing the assignment of the absolute configuration of analo-

Alkaloids from the Sponge‐Associated Fungus Aspergillus sp.

“…Moreover, 18-H and both cyclopropane methylene groups (29-CH 2 and 30-CH 2 ) were correlated with the downfield-resonating quaternary carbon C-20, as well as with the amide carbonyl carbon at C-21, thus verifying the 1-aminocyclopropane-1-carboxylic acid residue detected in 1. The remaining correlations of 3-H and 18-H with C-16, together with the downfield chemical shift of 16-CH 2 , indicating a neighboring nitrogen (N- 19), suggested that N-19 was linked to C-3 through 16-CH 2 .…”

“…Consequently, 2 was found to be structurally related to the fumiquinazolines A-J [19,31] previously isolated from A. fumigatus. More specifically, 2 represents an analogue of the known fumiquinazoline A, [34] differing in the presence of a methyl group at N-2, and the replacement of the methyl Table 3. 13 C NMR spectroscopic data of 2-7 (δ in ppm).…”

“…[19] Extraction and Isolation: The culture media were extracted with ethyl acetate, extracts were combined and evaporated under reduced pressure to yield a dry residue (35 g), which was then partitioned between n-hexane and 90 % aqueous MeOH. The 90 % aqueous MeOH-soluble material (18.0 g) was subjected to vacuum liquid chromatography (VLC) on silica gel, using a step gradient of dichloromethane/methanol to yield ten fractions (F1-F10).…”

“…[18] Recently, we identified new austalides from a marine-derived Aspergillus strain isolated from a specimen of the Mediterranean sponge Tethya aurantium. [19] A more intensive investigation of the same strain has now led to the isolation and identification of seven new alkaloids, tryptoquivaline K (1) and fumiquinazolines K-P (2-7), along with six known compounds 8-13. Previously known compounds were mainly identified by comparing their spectroscopic and physical data ( 1 H and 13 C NMR, MS, and [α] D ) with literature data.…”

Nuclear Magnetic Resonance Spectroscopy for Structural Characterization of Bioactive Compounds

“…For example, the correlations observed between 24-Me with H-21 and of 31-OMe with H-21 and 24-Me, indicates that rings C and D of austalide M 28 are cis-fused. The trans-configuration of 24-Me and 27-Me is due to the correlation between 27-Me and H-22 but not with H-21, establishing the (11S*, 13R*,14R*, 20R*, 21S*, 22S*)-relative configuration of 28 [30]. An extensive investigation on the same strain led to the isolation of seven new alkaloids.…”