Bioactive Compounds of Plectranthus scutellarioides: Extraction, Phytochemical Characterization and Biological Activities

Background: Plectranthus scutellarioides is an ornamental and medicinal species of the Lamiaceae family characterized by substantial phytochemical diversity and variability. This review critically synthesizes current evidence on its bioactive compounds, factors determining phytochemical composition, extraction efficiency, analytical characterization, and biological activity, with particular emphasis on relationships between plant material, extraction conditions, metabolite profiles, and experimentally determined bioactivity. Methods: A narrative review of the available scientific literature was conducted using studies addressing the phytochemical composition of P. scutellarioides, cultivar and cultivation-related variability, extraction procedures, analytical characterization, and biological activities of extracts and isolated metabolites. Particular attention was given to quantitative phytochemical and biological data and to methodological factors limiting direct comparison among studies. Results: P. scutellarioides contains phenolic acids, flavonoids, anthocyanins, abietane-type diterpenoids, and volatile constituents, with rosmarinic acid representing a major phytochemical marker. Substantial quantitative variability is associated with cultivar, geographical origin, cultivation conditions, plant material, and extraction procedure. Optimized ultrasound-assisted extraction yielded 110.8 ± 4.5 mg g−1 DW of rosmarinic acid after 45 min, approximately twice the recovery obtained by conventional heat-reflux extraction over the same period. Quantitative profiling also demonstrated marked cultivation-dependent changes in volatile metabolites. Biological studies revealed assay- and compound-dependent antioxidant, antimicrobial, anti-inflammatory, and cytotoxic/antiproliferative activities. In particular, isolated diterpenoids inhibited NF-κB activity with IC50 values of 4.5–11.2 µM, providing compound-specific quantitative evidence of anti-inflammatory potential. However, differences in extract composition, experimental models, and assay conditions, together with limited standardization and the predominance of in vitro studies, substantially restrict cross-study comparisons and assessment of translational relevance. Conclusions: The available evidence indicates that the biological potential of P. scutellarioides should be interpreted through an integrated extraction–composition–activity framework rather than from the simple presence of individual metabolites. Future studies should prioritize standardized and botanically characterized plant material, clearly defined harvesting conditions, quantitative phytochemical characterization, comparable biological endpoints, bioactivity-guided identification of active constituents, and in vivo validation. Establishing reproducible relationships between plant material, extraction conditions, chemical composition, and biological effects will be essential for assessing the pharmaceutical, cosmetic, and functional potential of this species.