Abstract
A novel hybrid PKS–NRPS alkaloid, xylarialoid A (1), containing a 13-membered macrocyclic moiety and [5,5,6] fused tricarbocyclic rings, together with ten known cytochalasins (2–11), was isolated from a plant-derived endophytic fungus, Xylaria arbuscula. The chemical structures of all compounds were elucidated using 1D and 2D NMR, HR ESIMS spectroscopic analyses, and electronic circular dichroism (ECD) calculation. Compounds 1–3 and 10 exhibited significant antitumor activities against A549 and Hep G2 cell lines, with IC50 values of 3.6–19.6 μM. In addition, compound 1 showed potent anti-inflammatory activity against LPS-induced nitric oxide (NO) production in macrophage RAW 264.7 cells (IC50, 6.6 μM).
Highlights
The Xylaria genus belongs to the family of Xylariaceae, which is commonly found among saprophytic and endophytic fungi [1]
The biosynthesis pathway of the PKS–NRPS hybrid alkaloids was through P450-catalyzed cyclization to form paracyclophane, and all of the ring system was constructed from a PK–NRP product via oxidation [11]
Cytochalasins are a class of PKS–NRPS hybrids and have been isolated from the fungi of Chaetomium, Xylaria, Rosellinia, and Zygosporium [12,13,14,15]
Summary
The Xylaria genus belongs to the family of Xylariaceae, which is commonly found among saprophytic and endophytic fungi [1]. In the past ten years, a class of polyketide synthase–nonribosomal peptide synthetase (PKS–NRPS) alkaloids has attracted the attention of scientists due to their unique structure These alkaloids have 12- or 13-membered ring systems, γ-lactams, and fused [6,5,6] tricarbocyclic or [6,5,6,5] tetracarbocyclic cores, which were isolated from different fungal species and showed antitumor, antifungal, and antituberculosis biological activities [5,6,7,8,9,10]. Cytochalasins are a class of PKS–NRPS hybrids and have been isolated from the fungi of Chaetomium, Xylaria, Rosellinia, and Zygosporium [12,13,14,15] They have tricyclic core structures, which are in turn each composed of a perhydroisoindole moiety and a macrocyclic ring.
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