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

• Published in: Chemistry : a European journal 2008-05, Vol.14 (16), p.4913-4923
• Main Authors: Zhang, Wen, Krohn, Karsten, Zia-Ullah, Flörke, Ulrich, Pescitelli, Gennaro, Di Bari, Lorenzo, Antus, Sándor, Kurtán, Tibor, Rheinheimer, Joachim, Draeger, Siegfried, Schulz, Barbara
• Format: Article
• Language: English
• Subjects: absolute stereochemistry; antifungal agents; Bacillus megaterium; blennolides A-G; Carpobrotus edulis; Chlorella fusca; Circular Dichroism; Dimerization; Escherichia coli; Fungi - chemistry; Microbotryum violaceum; Models, Molecular; natural products; Spectrum Analysis - methods; total synthesis; Xanthones - chemistry; Xanthones - isolation & purification
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.200800035

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 (β‐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. Natural products: The monomeric units of the dimeric secalonic acids (see graphic), the existence of which had long been postulated, have been isolated for the first time, together with other unusual chromanones, from the Blennoria sp. The absolute configurations of all compounds were established by an X‐ray diffraction study and by TDDFT calculations of CD spectra.