Abstract
Context: Thymus alternans Klokov (Lamiaceae) is a neglected species of the genus Thymus (Sect. Serpyllum) endemic to Carpathian area, where it is used as a flavouring agent and for medicinal purposes. Objective: The aim of the work was to identify antiproliferative constituents from the flowering aerial parts of this plant. Materials and methods: Thymus alternans extracts were analyzed by HPLC-MSn and subjected to extensive chromatographic separations. The isolated compounds (phenolics and triterpenes) were structurally elucidated by MS and 1D and 2D NMR experiments. Essential oil (EO) composition was determined by GC-FID and GC-MS. Six purified triterpenes and EO were assayed for in vitro antiproliferative activity against a panel of human cancer cells, namely, breast (MDA-MB 231), colon (HCT-15 and HCT116), lung (U1810), pancreatic (BxPC3), melanoma (A375) and cervical carcinoma (A431) cells. Results: The structures of the isolated compounds were achieved on the basis of H-NMR and MS experiments. Luteolin-4′-O-β-d-glucopyranoside (P1), chrysoeriol-7-O-β-d-glucopyranoside (P2), chrysoeriol-5-O-β-d-glucopyranoside (P3), apigenin-7-O-β-d-glucopyranoside (P4), rosmarinic acid (P5), rosmarinic acid-3′-O-β-d-glucopyranoside (P6), caffeic acid-3-O-β-d-glucopyranoside (P7), 3α-hydroxy-urs-12,15-diene (T1), α-amyrin (T2), β-amyrin (T3), isoursenol (T4), epitaraxerol (T5), and oleanolic acid (T6). GC-MS analysis revealed that the EO of T. alternans was devoid of phenols and belonged to the nerolidol-chemotype, that is typical of the Sect. Serpyllum. The six purified triterpenes (T1-T6) were active with IC50 ranging from 0.5 to 5 μM being comparable or better than those of reference compounds betulinic acid and cisplatin. The EO exhibited significant effects on A375, MDA-MB 231 and HCT116 cell lines with IC50 in the range of 5–8 μg/mL. Conclusion: The reported results suggest that T. alternans can be considered as a good source of phytoconstituents with possible importance in the pharmaceutical field.
Highlights
The genus Thymus L. (Lamiaceae) includes 215 species divided in 8 sections, with the evolutionary centres in the Mediterranean area from where it spreads to Europe, Asia, Northern America and Abyssinia, as well as to Greenland (Morales 2002)
Chromatographic separations starting from flash chromatography and using semi-preparative HPLC allowed the isolation of seven phenolic derivatives whose structures were elucidated by 1D and 2D NMR and mass spectrometric analyses (Figure 2)
Glycosidation position was deduced from HMBC correlations observed from H-1glc (d 4.88) and C-40 (d 145.2) and from the NOESY correlation observed from H-1glc and H-30 (d 6.56); the compound P1was assigned to luteolin-40 -O-b-D-glucopyranoside
Summary
The genus Thymus L. (Lamiaceae) includes 215 species divided in 8 sections, with the evolutionary centres in the Mediterranean area from where it spreads to Europe, Asia, Northern America and Abyssinia, as well as to Greenland (Morales 2002). (Lamiaceae) includes 215 species divided in 8 sections, with the evolutionary centres in the Mediterranean area from where it spreads to Europe, Asia, Northern America and Abyssinia, as well as to Greenland (Morales 2002). Many species of this genus are used throughout the world in the traditional medicine and are nowadays important species in food, cosmetics and pharmaceutics (Nabavi et al 2015). For this reason, the evaluation of the phytochemical composition of different.
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