Medicinal plants of the Plectranthus genus (Lamiaceae) are well known for their ethnomedicinal applications. Plectranthus madagascariensis, which is native to South Africa, is traditionally used in the treatment of respiratory conditions, scabies, and cutaneous wounds. The phytochemical studies of P. madagascariensis led to the isolation of five known royleanone abietanes, namely, 6β,7α-dihydroxyroyleanone (1), 7α-acetoxy-6β-hydroxyroyleanone (2), horminone (3), coleon U quinone (4), and carnosolon (5). The relative configuration of compound 2 was established by X-ray analysis. Compounds 1–4 showed antimycobacterial activity (Minimum inhibitory concentration for 90% inhibition, MIC₉₀ = 5.61–179.60 μM) against Mycobacterium tuberculosis H₃₇Rv. Compound 4 and 5 showed comparable toxicity (Concentration for 50% inhibition, IC₅₀ 98.49 μM and 79.77 μM) to tamoxifen (IC₅₀ 22.00 μg/mL) against HaCaT cells. Compounds 1–5 showed antioxidant activity through single-electron transfer (SET) and/or hydrogen-atom transfer (HAT) with compound 5 being the most active antioxidant agent. Compounds 3 and 5 were isolated for the first time from P. madagascariensis. The observed results suggest P. madagascariensis as an important ethnomedicinal plant and as a promising source of diterpenoids with potential use in the treatment of tuberculosis and psoriasis.

The prevalence of diabetes mellitus (DM), considered one of the most common metabolic disorders, has dramatically increased and resulted in higher rates of morbidity and mortality around the world in the past decade. It is well known that insulin resistance in target tissues and a deficiency in insulin secretion from pancreatic β-cells are the main characteristics of type 2 diabetes. The aim of this study was the bio-evaluation of compounds isolated from three selected plant species: namely, Salvia africana-lutea, Leonotis ocymifolia, and Plectranthus madagascariensis, for their glucose-uptake ability. Methanolic extracts were produced from the aerial parts of each plant. Compounds were identified using different spectroscopic techniques. The glucose-uptake ability of each compound was then evaluated in mammalian cells using 2-deoxyglucose-6-phosphate. The cytotoxicity of each compound was established via the MTT assay. Chromatographic purification of the three plant species yielded sixteen pure terpenoids. Compounds 1 (p = 0.0031), 8 (p = 0.0053), and 6 (p = 0.0086) showed a marked increase in glucose uptake, respectively. Additionally, 1, 4, and 6 exhibited cytotoxicity toward mammalian tissue with a decrease in cell viability of ~70%, ~68%, and ~67%, respectively. The results suggested that several compounds demonstrated a marked increase in glucose uptake, while two of the compounds exhibited signs of cytotoxicity. It may, therefore, be suggested that these compounds be considered as potential candidates for novel plant-derived alternative therapies in the treatment of type 2 diabetes.

Every year, 10 million people are affected by tuberculosis (TB). Despite being a preventable and curable disease, 1.5 million people die from TB each year, making it the world’s top infectious disease. Many of the frontline antibiotics cause painful and disagreeable side effects. To mitigate the side effects from the use of chemically synthesized or clinical anti-tubercular drugs, there are many research studies focussed on natural products as a source of potential anti-tuberculosis drugs. Among different phytoconstituents, several classes of diterpenoids exert significant antimicrobial effects. This review explores diterpenoids as potential anti-tubercular drugs from natural sources. A total of 204 diterpenoids isolated from medicinal plants and marine species are discussed that inhibit the growth of Mycobacterium tuberculosis. The literature from 1994-2018 is reviewed, and 158 diterpenoids from medicinal plants, as well as 40 diterpenoids from marines, are alluded to have antituberculosis properties. The antitubercular activities discussed in the review indicate that the type of diterpenoids, the Mtb strains, substituents attached to diterpenoids and their position in the diterpenoids general skeleton can change the compounds antimycobacterial inhibitory effects.

Lessertia frutescens (L.) Goldblatt & J.C.Manning (synonym Sutherlandia frutescens), commonly known as cancer bush, is one of the most prominently used South African medicinal plants, with a rich history of traditional uses among indigenous communities. Its phytochemical profile showed different metabolites such as amino acids, fatty acids, sugars, flavonoid glycosides, cycloartenol glycosides, and oleanane-type saponins. Moreover, several research studies have highlighted the promising therapeutic effects of L. frutescens in combating various cancer cell lines. Additionally, the plant demonstrated potent immunomodulatory, antioxidant, anti-inflammatory, antidiabetic, neuroprotective, antistress, and antimicrobial activities. These research findings highlight L. frutescens as a promising candidate for the development of new or complementary therapies for a range of diseases and conditions. This review analyses the chemical and biological properties of L. frutescens based on 154 articles identified through SciFinder. Of these, 78 articles, including two patents, met the inclusion criteria and were reviewed. Studies focused on agriculture and horticulture were excluded as they fell outside the scope of this research.

The prevalence of diabetes mellitus (DM), considered one of the most common metabolic disorders, has dramatically increased and resulted in higher rate of morbidity and mortality around the world, in the past decade. It is well known that insulin resistance in target tissues and a deficiency in insulin secretion from pancreatic β-cells are the main characteristic of type 2 diabetes. The aim of this study was the bio-evaluation of compounds isolated from three selected plant species; namely, Salvia africana-lutea, Leonotis ocymifolia and Plectranthus madagascariensis, for their glucose uptake ability. Methanolic extracts were produced from the arterial part of each plant. Compounds were identified using different spectroscopic techniques. The glucose uptake ability of each compound was then evaluated in mammalian cells using 2-deoxyglucose-6-phosphate. The cytotoxicity of each compound was established via the MTT assay. Chromatographic purification of the three plant species yielded fifteen pure terpenoids. Compounds 1 (p = 0.0031), 8 (p = 0.0053), and 6 (p = 0.0086), showed a marked increase in glucose uptake, with p values of p=0.0031, p=0.0053 and p=0.0086, respectively. Additionally, 1, 4 and 6 exhibited cytotoxicity toward mammalian tissue with a decrease in cell viability of ~70%, ~68% and ~67%, respectively. The results suggested that several compounds demonstrated a marked increase in glucose uptake while two of the compounds exhibited signs of cytotoxicity. It may, therefore, be suggested that these compounds be considered as potential candidates for novel plant-derived alternative therapies in the treatment of type 2 diabetes.

Lessertia frutescens (synonym Sutherlandia frutescens) is an important South African medicinal plant used traditionally to treat different human pathologies and is considered an adaptogenic plant. This study sought to isolate compounds from the plant and determine their protective potentials using SH-SY5Y cells and MPP⁺ (1-methyl-4-phenylpyridinium) to mimic Parkinson’s disease. The phytochemical analysis of a 70% aqueous methanolic extract of L. frutescens leaves resulted in the isolation and identification of 11 pure compounds (1–11), among which compounds 1 and 2 were identified as new metabolites. The new compounds were characterised using IR, UV, NMR, and HRESIMS and were given the trivial names lessertiosides A (1) and B (2). Additionally, the flavonoids 8-methoxyvestitol (7) and mucronulatol (8) were isolated for the first time from the plant. The biological actions show that the isolated compounds had negligible toxicity on SH-SY5Y cells and improved cell viability in the cells exposed to MPP⁺. Furthermore, as a mechanism of action, the compounds could sustain cellular ATP generation and prevent MPP⁺-induced apoptotic cell death. Our findings provide evidence for the neuroprotective properties of compounds isolated from L. frutescens in MPP⁺-induced neuronal damage for the first time and create an avenue for these compounds to be further investigated to elucidate their molecular targets.