Antimicrobial phenolics and unusual glycerides from Helichrysum italicum subsp. microphyllum.

During a large-scale isolation campaign for the heterodimeric phloroglucinyl pyrone arzanol (1a) from Helichrysum italicum subsp. microphyllum, several new phenolics as well as an unusual class of lipids named santinols (5a-c, 6-8) have been characterized. Santinols are angeloylated glycerides characterized by the presence of branched acyl- or keto-acyl chains and represent a hitherto unreported class of plant lipids. The antibacterial activity of arzanol and of a selection of Helichrysum phenolics that includes coumarates, benzofurans, pyrones, and heterodimeric phloroglucinols was evaluated, showing that only the heterodimers showed potent antibacterial action against multidrug-resistant Staphylococcus aureus isolates. These observations validate the topical use of Helichrysum extracts to prevent wound infections, a practice firmly established in the traditional medicine of the Mediterranean area.