Phytochemical and biological activities of Plectranthus Madagascariensis

Abstract

Tuberculosis is the leading cause of mortality and morbidity in South Africa due to its association with several chronic illnesses such as psoriasis, diabetes mellitus, and HIV. These chronic diseases weaken the patients resulting in a high risk of progressing from latent to active tuberculosis. Because of side effects associated with synthetic drugs, the attention of the scientific community has shifted to natural products for their use as therapeutic agents to develop effective modern medicines with less adverse effects for treating infectious as well as chronic diseases. Less than 10% of medicinal plant species have been thoroughly investigated and therefore this project focused on exploring one such under-studied medicinal plant namely Plectranthus madagascariensis. Phytochemical investigation of P. madagascariensis have led to the isolation of five royleanones abietanes and a mixture of two abietane dimers. The five royleanones were identified as; 6β,7α-dihydroxyroyleanone (I), 7α-acetoxy-6β-hydroxyroyleanone (II), horminone (III) and coleon U quinone (IV) and carnosolon (V) and the two the dimers as; grandidone A and 7-epimer grandidone A (VI & VII). All compounds were evaluated for their antitubercular, antidiabetic, antioxidant and cytotoxic activities. Compounds I-IV showed activity against the mycobacterial strain H37Rv in 7H9/CAS/Glu/Tx medium only except for compound II which showed activity in both 7H9/CAS/Glu/Tx and 7H9/ADC/Glu/Tw medium. Compound I, II, IV, and VI &VII displayed inhibitory effects against the intestinal enzyme α-glucosidase with the mixture of VI & VII giving the most promising result as an IC50 value twenty-one times lower than the positive control acarbose. All compounds exhibited cytotoxic effects against HacaT cell line with compound V being the most toxic. Furthermore, the compounds have antioxidant activity through single electron transfer and/or hydrogen atom transfer.