Structural Modification of Selected Essential Oil Components for Potential Anticancer Applications: A Review

Monoterpenes (thymol, carvacrol, menthol) and phenylpropanoids (eugenol and cinnamaldehyde) and their related derivatives are naturally occurring bioactive compounds found in essential oils (EOs) and have attracted considerable interest as anticancer agents; however, their direct therapeutic use in cancer treatment is often limited by factors such as low bioavailability, moderate potency, and lack of target specificity. Recent studies have demonstrated that rational structural modification of these EO scaffolds can substantially enhance their anticancer potential. This review critically evaluates the different structural modification strategies applied to EO components, including pharmacophore hybridization, heterocycle incorporation (e.g., triazoles, oxadiazoles, chalcones), esterification, halogenation, metal complexation, and nanoparticle conjugation. The review compares these approaches across the selected EO components, highlighting their impact on anticancer potency, and mechanistic relevance. However, the current evidence base is heterogeneous, with considerable variability in experimental conditions, selectivity assessments, and reliance on in vitro or in silico findings, which limits direct cross-study comparisons and translational interpretation. Overall, structural modification of EO components represents a promising strategy for generating novel anticancer lead compounds, but future progress will depend on standardized biological evaluation, rigorous in vivo validation, and comprehensive pharmacokinetic and toxicity profiling to realistically define their clinical potential.