C-O Natural Products: DihomoIsoF (Lee/Galano), Pyrenolide D (Gracza), Clavilactone A (Li), Psoracorylifol A (Tong), Bermudenynol (Kim), Aspercyclide C (Hirama)

Dihomo-Isofurans, produced in vivo by oxidation of adrenic acid, are potential markers of neuronal oxidative damage. Jetty Chung-Yung Lee of the University of Hong Kong and Jean-Marie Galano of Université de Montpellier I and II described (Angew. Chem. Int. Ed. 2014, 53, 6249. DOI: 10.1002/anie.201402440) the cyclization of 1 to 2, opening what should be a general route to these furans, exemplified by 10-epi-17(R,S)-SC-Δ¹⁵-11-dihomo-IsoF (3).

The cytotoxic lactone Pyrenolide D (6) was isolated from the phytogenic fungus Pyrenophora teres. Tibor Gracza of the Slovak University of Technology prepared (Synthesis 2014, 46, 817. DOI: 10.1055/s-0033-1338584) 6 by the Pd-mediated cyclization of 4 to 5.

The clavilactones, isolated from cultures of the Basidomycetous fungus Clitocybe clavipes, are potent tyrosine kinase inhibitors. Zhiping Li of Renmin University of China assembled (Angew. Chem. Int. Ed. 2014, 53, 4164. DOI: 10.1002/anie.201400326) the epoxy lactone 10 by the oxidative combination of the aldehyde 7 with the unsaturated ester 8 to give 9. Cyclization led to Clavilactone A (11).

The psoracorylifols, isolated from the traditional Chinese medicinal herb Psorlea corylifolia, are potent inhibitors of Heliobacter pylori. Rongbiao Tong of the Hong Kong University of Science and Technology used (Org. Lett. 2014, 16, 2986. DOI: 10.1021/ol501120m) the Achmatowicz oxidative rearrangement of 11 followed by acid treatment to construct 12, which was carried on to Psoracorylifol B (13).

Bermudenynol (16) was isolated from the red algae Laurencia intricata. Deukjoon Kim of Seoul National University closed (Angew. Chem. Int. Ed. 2014, 53, 272. DOI: 10.1002/anie.201308077) the eight-membered ring of 16 by intramolecular alkylation, cyclizing 14 to 15.

The aspercyclides, isolated from Aspergillus sp., show potential against allergy disorders. Building on previous work from his group, Masahiro Hirama of Tohoku University devised (Chem. Lett. 2014, 43, 349. DOI: 10.1021/ol3019727) a route to Aspercyclide C (19) based on the regioselective oxidative macrocyclization of 17 to 18.