Coleus aromaticus (Roxb.) Benth. (Lamiaceae) is a species of semi-succulent perennial plant with recognized medicinal and nutritional relevance, widely employed in traditional medicine. While its aromatic fraction and essential oils have been extensively investigated, the non-volatile secondary metabolism of the plant remains poorly characterized. In particular, the free amino acids have never been investigated.
In this study, fresh leaves of C. aromaticus were treated with liquid nitrogen, ground, and subjected to different extraction procedures: hydroalcoholic maceration, maceration in ethyl acetate, and liquid–liquid partitioning yielding an organic phase in dichloromethane and a hydroalcoholic phase. The resulting fractions were analyzed by HPTLC and HPLC to define their metabolic profiles. In addition, the Bligh–Dyer method was applied to extract polar and non-polar metabolites, which were subsequently characterized by NMR spectroscopy.
Chromatographic and spectroscopic analyses revealed the presence of organic acids, polyphenols (notably flavonoids), and proteinogenic amino acids. The detection of both polar and non-polar metabolites provided a detailed chemical fingerprint of C. aromaticus leaves. In particular, the organic acids rosmarinic acid and caffeic acid were found to be the most abundant compounds, with concentrations of 88.89 mg/100 g and 49.66 mg/100 g, respectively. The flavonoids apigenin, luteolin and quercetin were also clearly identified, together with the free proteinogenic amino acids alanine, arginine, asparagine, aspartic acid, glutamic acid, glutamine, and serine. The most abundant amino acid was asparagine, with a concentration of 7.51 mg/100 g of matrix. This integrated approach offered a broader compositional overview of C. aromaticus, expanding its phytochemical profile beyond the well-documented essential oils.
These findings contribute to a deeper understanding of the non-volatile secondary metabolism of C. aromaticus and emphasize its potential as a source of bioactive metabolites with possible nutraceutical and pharmaceutical applications.
