New Mono‐ and Dimeric Members of the Secalonic Acid Family: Blennolides A–G Isolated from the Fungus Blennoria sp.

Abstract

Blennolides A-G (2-8), seven unusual chromanones, were isolated together with secalonic acid B (1) from Blennoria sp., an endophytic fungus from Carpobrotus edulis. This is the first reported isolation of the blennolides 2 and 3 (hemisecalonic acids B and E), the existence of which as the monomeric units of the dimeric secalonic acids had long been postulated. A compound of the proposed structure 4 (beta-diversonolic ester) will need to be revised, as its reported data do not fit those of the established structure of blennolide C (4). Other monomers, the blennolides D-F (5-7) seem to be derived from blennolides A (2) and B (3) by rearrangement of the hydroaromatic ring. The heterodimer 8, composed of the monomeric blennolide A (2) and the rearranged 11-dehydroxy derivative of blennolide E (6), extends the ergochrome family with an ergoxanthin type of skeleton. The structures of the new compounds were elucidated by detailed spectroscopic analysis and further confirmed by an X-ray diffraction study of a single crystal of 2. The absolute configurations were determined by TDDFT calculations of CD spectra, including the solid-state CD/TDDFT approach. Preliminary studies showed strong antifungal and antibacterial activities of these compounds against Microbotryum violaceum and Bacillus megaterium, respectively. They were also active against the alga Chlorella fusca and the bacterium Escherichia coli.

Antifungal Polyketides and Other Compounds from Amazonian Endophytic Talaromyces Fungi

“…26 The cis relationship between H-9 and H-10 in the γ-butyrolactone moiety was supported by its typical coupling constant ( 3 J H-5, H-6 = 7.1 Hz). 18,26 Additionally, nuclear Overhauser effect spectroscopy (NOESY) experiments confirmed the a-orientations of H-9 and H-10 ( Figure 2b).…”

“…After careful analysis of spectroscopic and spectrometric data, 13 compounds were identified. From T. stipitatus DgCr2 2.1b, the new compound 1 was identified, in addition to the polyketides: secalonic acid A (2), 16 blennolide G (3), versixanthone A (4), 18 penicillixanthone A (5), 16 and paecillin B (6). 19 Talaromyces sp.…”

“…(Figure 2a). The relative configuration of the chromanone monomers was readily established to be the same as that of versixanthone A 18 and previously described synthetic analogues. 26 The cis relationship between H-9 and H-10 in the γ-butyrolactone moiety was supported by its typical coupling constant ( 3 J H-5, H-6 = 7.1 Hz).…”

Xanthones and Oxepino[2, 3‐b]chromones from Three Endophytic Fungi

“…[12,22] The tetrahydroxanthones occur as monomers, for example, as aand b-diversonolic esters, [23,24] monodictysins, [25] or blennolides, the recently isolated monomeric units of secalonic acids. [26] Other examples of highly active anticancer dihydroxanthones are globosuxanthone A (11), [27] nidulalin A, xanthoquinodins, and parnafungins. [28] Symmetrical or asymmetrical coupling of identical or slightly different monomeric units is very common and often increases the bioactivity and toxicity.…”

The first total synthesis of nidulalin A, a dihydroxanthone possessing multiple bioactivities

“…1 In the later studies, nidulalin A (1) was found to possess potent inhibitory activity against DNA topoisomerase II and immunomodulatory activity. 2,3 Although natural products having the dihydroxanthone skeleton have been seen to be widespread, [4][5][6][7][8] only a few total syntheses have been achieved. 9,10 Interested in the structure and bioactivities of nidulalin A, we embarked on the synthetic studies of the natural product.…”