Phloroglucinol α-Pyrones from Helichrysum: A Review on Structural Diversity, Plant Distribution and Isolation

Helichrysum species (Asteraceae) are renowned for their diverse phytochemical profiles and traditional medicinal applications. Among their specialized metabolites, phloroglucinol-α-pyrone derivatives represent a structurally unique and pharmacologically significant class of compounds. This review consolidates over five decades of phytochemical research, documenting 52 distinct compounds isolated from 11 Helichrysum species across the Mediterranean, African, and Iranian regions. The compounds are organized into structural subclasses, including monopyrones, dipyrones, and various phloroglucinol derivatives distinguished by their molecular scaffolds. Isolation yields reported in the literature range from trace amounts to relatively abundant constituents (0.48% w/w), with arzanol emerging as the most extensively studied compound. Bioactivity profiles reveal anti-inflammatory, antimicrobial, antioxidant, and antiparasitic properties, with arzanol demonstrating potent dual inhibition of mPGES-1 and 5-LOX. This review provides comprehensive reference data for future investigations into the chemistry and therapeutic potential of α-pyrone secondary metabolites from Helichrysum species.