Bioactive Natural Products from the Endophytic Fungus Ascochyta sp. from Meliotus dentatus – Configurational Assignment by Solid‐State CD and TDDFT Calculations

Abstract

Two new metabolites, (4S)‐(+)‐ascochin (1a) and (S,S)‐(+)‐ascodiketone (3), together with the known compounds (3R,4R)‐(–)‐4‐hydroxymellein (2), ent‐α‐cyperone (4) and (3S,4R)‐(–)‐dihydroxy‐(6S)‐undecyl‐α‐pyranone (5) were isolated from cultures of the of the endophytic fungus Ascochyta sp. The biologically active isocoumarin derivative, (4S)‐(+)‐ascochin (1a), has an unusual substitution pattern which was confirmed by X‐ray diffraction. Its absolute configuration was determined by our solid‐state TDDFT CD methodology using the X‐ray coordinates as input for the calculation. By catalytic hydrogenation, (4S)‐(+)‐ascochin was converted into the corresponding (3S,4S)‐dihydroisocoumarin derivative 1b. The measured and TDDFT calculated CD spectra enabled studies on the correlation between absolute configuration and n‐π* transition Cotton effect. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

New Massarilactones, Massarigenin E, and Coniothyrenol, Isolated from the Endophytic Fungus Coniothyrium sp. from Carpobrotus edulis

“…Part 26: Ref. [1] [a] Department of Chemistry, University of Paderborn, Warburger Straβe 100, 33098 Paderborn, Germany Fax: +49-5251-60-3245 E-mail: karsten.krohn@uni-paderborn. strain, has an unprecedented structural hexadecahydro-1H-benzo[a]xanthene skeleton, to date unknown as a natural product.…”

New Bioactive 2,3‐Epoxycyclohexenes and Isocoumarins from the Endophytic Fungus Phomopsis sp. from Laurus Azorica

“…[25] For example, (3S,4S)-dihydroascochin (12) (Figure 2), recently prepared by reduction of the natural product ascochin, had a positive n-π* CE at 267 nm, which derives from P helicity of its heteroring (Figure 7). [18] The n-π* CE of 4 at 262 nm is negative, and its high-energy CD transitions are also opposite to those of 12, which suggests that 4 has a heteroring with M helicity and hence (3R) absolute configuration (Figure 7, inset). Dihydroisocoumarin 5 showed the same -/+/-/+ CD pattern from the low-energy (n-π* CE) to the high-energy region as 4, which allowed its assignment as (3R) as well (Figure 8).…”

Metabolic Products of the Endophytic Fungus Microsphaeropsis sp. from Larix decidua

“…[15][16][17] In the case of compound 4, whose Xray structure was available, we applied our recently developed solid-state TDDFT/CD approach. [1,[18][19][20][21] In this method, the experimental solid-state CD spectrum is compared with that computed by the TDDFT method, [22,23] using the X-ray coordinates as input structure. Since the calculation and experiment are based on the same conformation of the compound in question, a very good agreement is usually observed.…”