Herbarone, a Rearranged Heptaketide Derivative from the Sea Hare Associated Fungus Torula herbarum

Abstract

Herbarone (1), a novel heptaketide with a tetrahydro-5,9-methanobenzo[8]annulen-10(5H)-one skeleton, together with the new ent-astropaquinones B (2) and C (3) and four known pyranonaphthoquinones (4-7), was isolated from the sea hare associated fungus Torula herbarum. The structures of the new compounds were elucidated by detailed spectroscopic analysis, and the absolute configurations were determined by solution TDDFT/ECD calculations. Absolute configurations of the known compounds were studied by ECD measurements and calculations. The isolation of heptaketide 1 suggests that an intramolecular aldol reaction takes place to form the tricyclic scaffold.

Bioactive Polyoxygenated Steroids from the South China Sea Soft Coral, Sarcophyton sp.

“…In the course of our ongoing screening for bioactive secondary metabolites from marine sources [7,8,9,10,11], we have made a collection of Sarcophyton sp. off Weizhou Island, Guangxi Province, China.…”

Ruthmycin, a New Tetracyclic Polyketide from Streptomyces sp. RM-4-15

“…Herbarone (Figure 4), a tricyclic polyketide isolated from the sea hare associated fungus Torula herbarum , shares structural similarities with the A-B-D ring system of 1 . 10 Biosynthetically, the fused Cring of herbarone has been proposed to derive from a rearrangement of the polyketide core culminating in an intramolecular aldol reaction to provide the key C5/C6 C ring connection. While metabolic labeling and/or shunt metabolites in support of the proposed herbarone biosynthetic pathway are lacking, invoking an analogous putative rearrangement en route to 1 is implausible.…”

Pseudonectrins A–D, heptaketides from an endophytic fungus Nectria pseudotrichia

“…The low specic rotation value of 6 {[a] 25 D +3.7 (c 0.1, MeOH)} was consistent with the reported one {[a] 25 D +4.8 (c 0.06, CHCl 3 )}, 6 suggesting that the sample is racemic due to the labile cyclic hemiacetal moiety. 5 Compounds 1-8 were tested for cytotoxicity against the human tumor cell lines, MCF-7 (breast cancer), HepG2 (hepatocellular carcinoma), SH-SY5Y (glioma), and ACHN (rental cell carcinoma). Compound 1-3, 6, and 7 showed moderate cytotoxic effects, with IC 50 values of 11.6-45.9 mM (the positive control cisplatin showed IC 50 values of 11.7-18.3 mM).…”

“…Heptaketides are a subgroup of polyketides showing diverse structural features and biological effects. To date, a variety of heptaketides including pyranonaphthoquinones, [1][2][3] naphthoquinones, 4 and other rearranged, 5 ring-opened, 6,7 or dimeric 8 derivatives, have been encountered as fungal secondary metabolites, and showed a broad spectrum of biological activities, such as antibacterial, antifungal, and antitumor effects. [1][2][3][4] Natural products incorporating a quinone moiety have been the subject of intensive investigations due to their potent antitumor activity.…”