Alpha-Glucosidase and Alpha-Amylase Inhibitory Activities of Novel Abietane Diterpenes from .

The re-investigation of a methanolic extract of collected from the Cape Floristic Region, South Africa (SA), afforded four new abietane diterpenes, namely 19-acetoxy-12-methoxycarnosic acid (), 3β-acetoxy-7α-methoxyrosmanol (), 19-acetoxy-7α-methoxyrosmanol (), 19-acetoxy-12-methoxy carnosol (), and two known named clinopodiolides A (), and B (), in addition to four known triterpenes, oleanolic, and ursolic acids (, ), 11,12-dehydroursolic acid lactone () and β-amyrin (). The chemical structural elucidation of the isolated compounds was determined on the basis of one and two dimensional nuclear magnetic resonance (1D and 2D NMR), high-resolution mass spectrometry (HRMS), ultra violet (UV), fourier transform infrared (IR), in comparison with literature data. The in vitro bio-evaluation against alpha-glucosidase showed strong inhibitory activities of , , and , with the half inhibitory concentration (IC) values of 11.3 ± 1.0, 17.1 ± 1.0 and 22.9 ± 2.0 µg/mL, respectively, while demonstrated the strongest in vitro alpha-amylase inhibitory activity among the tested compounds with IC of 12.5 ± 0.7 µg/mL. Additionally, some of the compounds showed significant antioxidant capacities. In conclusion, the methanolic extract of is a rich source of terpenoids, especially abietane diterpenes, with strong antioxidant and anti-diabetic activities that can be helpful to modulate the redox status of the body and could therefore be an excellent candidate for the prevention of the development of diabetes, a disease where oxidase stress plays an important role.