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The terpenoid (−)‐Istanbulin A is a natural product isolated from Senecio filaginoides DC, one of the 270 species of Senecio (Asteraceae) which occurs in Argentina. The structure and absolute configuration of this compound [9a‐hydroxy‐3,4a,5‐trimethyl‐4a,6,7,8a,9,9a‐hexahydro‐4H,5H‐naphtho[2,3‐b]‐furan‐2,8‐dione or (4S,5R,8R,10S)‐1‐oxo‐8β‐hydroxy‐10βH‐eremophil‐7(11)‐en‐12,8β‐olide, C15H20O4] were determined by single‐crystal X‐ray diffraction studies. It proved to be a sesquiterpene lactone showing an eremophilanolide skeleton whose chirality is described as 4S,5R,8R,10S. Structural results were also in agreement with the one‐ and two‐dimensional (1D and 2D) NMR and HR–ESI–MS data, and other complementary spectroscopic information. In addition, (−)‐Istanbulin A is a polymorph of the previously reported form of (−)‐Istanbulin A, form I; thus, the title compound is denoted form II or polymorph II. Structural data and a literature search allowed the chirality of Istanbulin A to be revisited. The antimicrobial and antifungal activities of (−)‐Istanbulin A, form II, were evaluated in order to establish a reference for future comparisons and applications related to specific crystal forms of Istanbulins. [ABSTRACT FROM AUTHOR]

Abstract: The investigation of the ethanol extract of fresh aerial parts of the Patagonian shrub Nardophyllum bryoides collected in the province of Chubut, Argentina, yielded eleven terpenoids. These include: three seco-ent-halimane diterpenoids (1–3), two ent-halimanes (4–5) and six pentacyclic oleanane and ursane triterpenoids (6–11). Four of these compounds (2, 6, 8 and 11) are hitherto unknown, while two others (1 and 4) have been previously reported but only as synthetic products. Several of these compounds showed moderate cytotoxicity against a human pancreatic adenocarcinoma cell line while compounds 4 and 5 were active at micromolar concentrations. The main component, seco-chiliolidic acid (1), could be isolated from this extract in large amounts, turning N. bryoides into a sustainable source of this bioactive compound. [Copyright &y& Elsevier]