Hydroxy-neo-Clerodanes and 5,10-seco-neo-Clerodanes from Salvia decora.

ABSTRACT

Preliminary analysis of the mass spectrometric (MS) and NMR spectroscopic data of the primary fractions from the biologically active extract of Salvia decora revealed spectra that are characteristic for neo-clerodane-type diterpenoids. MS-guided isolation of the bioactive fractions led to the isolation of three new chemical entities, including two hydroxy-neo-clerodanes (1 and 2) and one acylated 5,10-seco-neo-clerodane (3), along with three known diterpenoids (4-6), ursolic acid (7), and eupatorin (8). The structures of the new compounds were established by analysis of the 1D and 2D NMR and MS data, whereas their absolute configuration was deduced using a combination of experimental and theoretical ECD data and confirmed by X-ray crystallography (1 and 4). Furthermore, compounds 1, 3, 4, and 6-8 were evaluated as hPTP1B1-400 (human protein tyrosine phosphatase) inhibitors, where 7 showed the best activity, with an IC50 value in the lower µM range. Additionally, compound 7 was evaluated as an α-glucosidase inhibitor. The affinity constant of the 7-hPTP1B1-400 complex was determined by quenching fluorescence experiments (ka = 1.3 × 104 M-1), while the stoichiometry ratio (11 protein-ligand) was determined by a continuous variation method.