Guaiane-type sesquiterpenes from Carciofo Bianco di Pertosa, a cultivar of Cynara cardunculus subsp. scolymus (L.), leaf: Isolation and evaluation of tyrosinase inhibitory activity

Cynara cardunculus subsp. scolymus (L.) Benth. (Asteraceae) is a medicinal and food plant traditionally used in phytotherapy for its hepatoprotective, digestive, and antioxidant properties. While the edible bracts are widely consumed, artichoke leaf—recognized in herbal medicine as a valuable source of bioactive compounds—is largely discarded during industrial processing. “Carciofo Bianco di Pertosa”, a traditional artichoke cultivar from Campania region (Italy), also known as “white” artichoke, remains poorly investigated from a phytochemical and pharmacological point of view. The present study aimed at characterizing the phytochemical profile of its leaf and to explore their potential relevance for nutraceutical and cosmetic applications. A 75% ethanolic extract obtained by Solid–Liquid Dynamic Extraction (Naviglio method) was analyzed by Liquid Chromatography coupled with High-Resolution Mass Spectrometry (LC-ESI/LTQOrbitrap/MS/MS) in negative ion mode. Structural elucidation of the main constituents was performed by 1D- and 2D-NMR spectroscopy and Flow Injection Analysis–Mass Spectrometry (FIA-MS). The analysis revealed the presence of caffeoyl-, dicaffeoyl quinic acid derivatives and flavonoids, along with sesquiterpene lactones. A chlorinated guaiane-type sesquiterpene lactone, pertosin A ( 17 ), is here described for the first time. Based on the ability to prevent skin photoaging processes reported for cynaropicrin, the tyrosinase inhibitory activity of the 75% ethanolic extract and isolated sesquiterpenes was evaluated by a spectrophotometric assay. The extract inhibited tyrosinase activity with an IC₅₀ value of 55 μg/mL, while the isolated compounds showed IC₅₀ values between 139 and 312 μM. Pertosin A ( 17 ) displayed inhibitory activity (IC₅₀ = 139 μM) comparable to that of kojic acid (IC₅₀ = 134 μM).