Structure–Activity Relationships of Natural and Synthetic Anthraquinones: Relevance for Pharmacology and Nutritional Supplementation

Anthraquinones constitute an extensive class of natural and synthetic derivatives. Natural anthraquinones are widely utilized as active ingredients in dietary supplements and traditional medicine. However, their inherent polypharmacology frequently complicates their biomedical application; while a broad spectrum of biological activities is advantageous in defined clinical settings, it often triggers off-target or adverse reactions under other conditions. Consequently, standardizing both chemical composition and biological efficacy remains a critical challenge for drug development and supplement formulation. Although extensive research has focused on the chemistry and pharmacology of anthraquinones, the underlying structure–activity relationships (SARs) remain fragmented across individual studies, lacking a unified framework that correlates substituent effects and electronic properties with specific biological endpoints. This review systematically evaluates the relationship between the chemical structure of anthraquinones and their biological properties. Specifically, we analyze how the pharmacological profiles and toxicity of anthraquinones are governed by three levels of structural modification: simple monomers, dimeric systems, and hybrid architectures, ultimately providing structure-guided principles for designing optimized therapeutics and safer dietary supplements.