LC-MS- and NMR-Guided Isolation of Monoterpene Dimers from Cultivated Thymus vulgaris Varico 3 Hybrid and Their Antityrosinase Activity.

Targeted isolation based on a combination of NMR and HPLC-PDA-MS of a dichloromethane extract of Thymus vulgaris Varico 3 aerial parts afforded one new p-cymene dimer, 6,3',4'-trihydroxy-5,5'-diisopropyl-2,2'-dimethylbiphenyl (1: ), together with two known p-cymene derivatives (2: and 3: ), as well as five known compounds, namely, thymol (4: ), oleanolic acid (5: ), ursolic acid (6: ), cirsimaritin (7: ), and xanthomicrol (8: ). The structural elucidation of all compounds was performed by spectroscopic analyses, including 1D and 2D NMR, and HRESIMS experiments. The biphenyls were assayed for their inhibitory activity on tyrosinase. Compounds 2: and 3: showed negligible activity on tyrosinase, while compound 1: effectively inhibited the enzyme with 35% (± 0.3) inhibitory activity, higher than the inhibition of the reference compound kojic acid (18.6 ± 0.02).