Abstract
The re-investigation of a methanolic extract of Salvia africana-lutea collected from the Cape Floristic Region, South Africa (SA), afforded four new abietane diterpenes, namely 19-acetoxy-12-methoxycarnosic acid (1), 3β-acetoxy-7α-methoxyrosmanol (2), 19-acetoxy-7α-methoxyrosmanol (3), 19-acetoxy-12-methoxy carnosol (4), and two known named clinopodiolides A (5), and B (6), in addition to four known triterpenes, oleanolic, and ursolic acids (7, 8), 11,12-dehydroursolic acid lactone (9) and β-amyrin (10). 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 8, 10, and 7, with the half inhibitory concentration (IC50) values of 11.3 ± 1.0, 17.1 ± 1.0 and 22.9 ± 2.0 µg/mL, respectively, while 7 demonstrated the strongest in vitro alpha-amylase inhibitory activity among the tested compounds with IC50 of 12.5 ± 0.7 µg/mL. Additionally, some of the compounds showed significant antioxidant capacities. In conclusion, the methanolic extract of S. africana-lutea 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.
Highlights
Diabetes mellitus (DM) is one of the most common metabolic disorders with significant morbidity and mortality rates around the world
Chromatographic purification of a methanolic extract of S. africana-lutea was done using different techniques, including semi prep-HPLC yielded pure terpenoids (Figure 1), four of which were reported for the first time
S. africana-lutea were investigated by evaluating their ferric-ion reducing antioxidant power (FRAP), trolox equivalent absorbance capacity (TEAC), and oxygen radical absorbance capacity (ORAC)
Summary
Diabetes mellitus (DM) is one of the most common metabolic disorders with significant morbidity and mortality rates around the world It is caused either by deficiency in insulin secretion or degradation of secreted insulin [1], which is the result of cell alterations caused by many internal and external factors, such as obesity, sedentary lifestyle, and oxidative stress [2,3]. Oxidative stress occurs when the production of free radicals, such as reactive oxygen species (ROS), overwhelms the detoxification capacity of the cellular antioxidant system, resulting in biological damages [4]. It plays a central role in the development of diabetes, such as microvascular and cardiovascular complications [5]. This work primarily examines the phytochemical isolation of different constituents present in the methanolic extract of S. africana-lutea as well as the anti-diabetic and the antioxidant activities of its isolated compounds
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