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Ten pentacyclic triterpenes (1-10) were isolated from Lavandula coronopifolia. We evaluated their α-glucosidase inhibitory activity, and found that the aglycones, 1, 2, 3, 4, 7 and 10 showed superior IC50 values to the positive control. In order to explain the structural requirements for α-glucosidase inhibitory activity, eleven derivatives were prepared, including one new compound, 2-formyl-(A)1-19α-hydroxy-1-norursane-2, 12-dien-28-oic acid 10c. The results demonstrated that a free hydroxyl at ring-A and a free carboxylic group at position 28 are key structural features for the α-glucosidase inhibitory activity, also that an ursane skeleton is optimum for the activity. Additionally, enzyme kinetic analysis of pomolic acid 2, the most potent compound, revealed that it inhibited α-glucosidase in a mixed-type manner. The molecular docking simulation validated this type of inhibition and highlighted the role of the C-3 hydroxyl and C-28 carboxylic groups in interaction with the enzyme in silico.

We report the isolation and anti-allergic activity (degranulation reduction) of six polyphenolic compounds, one of them being novel, from olive mill wastes (OMW). Additionally, we evaluated their ability to reduce; intracellular Ca2+ levels and expression of calcium channel proteins in RBL-2H3 cells, to assist the possible characterization of the mechanisms involved. The novel compound, new hemialdehydic decarboxymethylated oleuropein aglycone, HDOA 1 (IC50 = 108.3 µM), hydroxytyrosol acetate 3 (IC50 = 40.2 µM) and 1-acetoxypinoresinol 4 (IC50 = 43.8 µM) reduced intracellular Ca2+ levels after challenging by both A23187 and DNP-BSA, suggesting a mechanism beyond just blockage of extracellular Ca2+ influx. While luteolin 2, despite its strongest activity (IC50 = 3.9 µM), reduced Ca2+ levels only after challenging by A23187, suggesting its main mechanism is by blocking extracellular Ca2+ influx. We confirmed further, that, each compound decreased the expression of, two or more, calcium channel proteins suggesting that they act as ‘mast cell stabilizers’ by reducing the expression of calcium channel proteins. This work attracts more attention to OMW as a potential source of lead compounds for structural modification to improve and develop new anti-allergic drugs.