Chemical Composition and Antimicrobial Activity of Monechma ciliatum (Jacq.) Milne-Redhead Stem

Abstract

Monechma ciliatum (Jacq.) Milne-Redhead is an annual plant of the Acanthaceae family and locally known as "black mahlab" growing in some African and Asian countries. It was chosen for this study because of its uses as an old remedy and cosmetic agent in Sudanese folk medicine. In Gibal Alnuba (Southem Kurdofan) it is used for treatment of vomiting and diarrhea in children and further used in traditional Sudanese fragrances, lotion and cosmetics in wedding and childbirth rituals and ceremonies. Phytochemical screening was "carried out seperately on petroleum ether, methanol, and aqueous extracts of the plant stem which revealed the presence of fatty acids, volatile oils, sterols and triterpenes, basic alkaloids, carotenoids, cournarins, flavone aglycone, emodols, tannins, polyuronides, alkaloid salts, reducing compounds and saponins. Antimicrobial screening of the three extracts showed that the petroleum ether and the methanolic extracts were the most active and further were subjected to column chromatographic fractionation and monitoring of their antibacterial activity ' The petroleum ether extract was investigated by GC-MS technique and resulted in identification of 60.52% of the extract as hydrocarbons, alcohols, ethers, ketones, free acids and esters of acyclic, alicyclic or aromatic nature as well as lignans. It was proposed that the activity may well be due to the high content of sterols (~ 30%) and phthalic acid esters (5.25%). The active column fiactions F4 and F5 of the methanolic extract were further investigated by analytical and preparative TLC and afforded seven compounds which were identified and characterized by spectroscopic methods.

Three compounds were not previously described in the literature namely: F4-I characterized as: 4-(3',4‘- methylenedioxy-6‘-methoxyphenyl)-5,6- methylenedioxy-2,3-naphthalide. F5-I characterized as: Tet1'ahydro-1-acetoxy-4-(3',4‘,5'-trimethoxyphenyl)- 6,7-dimethoxy-2,3-naphthalide. F5-IV characterized as: 8-(4,5-Dimethoxybenzyl)-8'-(4',5'- dimcthoxybenzyl)-7'-hydroxy-7-butyrolactone. The other four known compounds were identified as: F4-II: B-Sitosteryl glucoside. ' F4-III: Meamsetin. F5-II: Tetrahydro-2—(3,4-dimethoxyphenyl) -4- [(3,4-dimethoxyphenyl) methyl]-3-furanomethanol. F5-III: Magnolin. Compound F6-I has been isolated fiom column fiaction F6 and identified as sucrose by comparison of its MS and NMR-spectra with those of authentic samples. It is noteworthy that the stem of M. ciliatum was not previously investigated and the results of chemical composition of the petroleum ether and methanol extracts were reported for the first time in the present thesis.