title: Secondary metabolites from Tetracera potatoria stem bark with anti-mycobacterial activity.
abstract: BACKGROUND
  Tetracera potatoria Afzel. Exg. Don (Dilleniaceae) is a medicinal plant used traditionally in Africa for the treatment of tuberculosis related ailments and respiratory infections. The antibacterial activity of the medium polar extracts of T. potatoria leaves and stem bark was recently reported against Mycobacterium smegmatis (MIC 25µg/mL) and M. aurum (65µg/mL), two fast-growing Mycobacterium strains used as model micro-organisms for the more pathogenic strain Mycobacterium tuberculosis (Fomogne-Fodjo et al., 2014). The aim of this study was consequently to isolate the compounds possibly contributing to this activity, and which may therefore be promising precursors to be used for the development of novel anti-TB drugs.
  
  
  METHODS
  T. potatoria medium polar extract [MeOH/DCM (1:1, v/v)] was fractionated sequentially with petroleum ether to which EtOAC and MeOH were gradually added to increase the polarity. The examination of T. potatoria extract and its fractions was guided by bioassays for anti-mycobacterial activity against M. smegmatis (ATCC 23246) and M. aurum (NCTC 10437) using the minimum inhibitory concentration (MIC) method. All the isolated compounds were structurally elucidated using spectroscopic techniques and evaluated for their anti-mycobacterial activity.
  
  
  RESULTS
  Two novel secondary metabolites (1, 2) named tetraceranoate and N-hydroxy imidate-tetracerane, together with five known compounds [β-stigmasterol (3), stigmast-5-en-3β-yl acetate (4), betulinic acid (5), betulin (6) and lupeol (7)] were isolated and identified. Tetraceranoate exhibited the best activity against M. smegmatis with a minimum inhibitory concentration (MIC) of 7.8µg/mL, while β-stigmasterol, betulinic acid and betulin showed appreciable anti-mycobacterial activity against both strains (MIC 15µg/mL).
  
  
  CONCLUSIONS
  Seven compounds were isolated from the medium polar extract [MeOH/DCM (1:1, v/v)] of T. potatoria stem bark. Only tetraceranoate one of the isolated compounds showed antibacterial activity against M. smegmatis having efficacy as high as rifampicin (one of a three drug regimen recommended in the initial phase short-course anti-tuberculosis therapy). Thus, tetraceranoate might be an interesting target for systematic testing of anti-TB treatment and management. This research supports the use of T. potatoria in African traditional medicine for the treatment of tuberculosis related symptoms.
authors.affiliation: Department of Chemistry, Rhodes University, PO Box 94, Grahamstown 6140, South Africa. Electronic address: cy.fomogne@gmail.com.
authors.forename: M C Y
authors.initials: MC
authors.lastname: Fomogne-Fodjo
authors.affiliation: Department of Applied Chemistry, University of Johannesburg, PO Box 17011, Doornfontein, Johannesburg 2028, South Africa.
authors.forename: D T
authors.initials: DT
authors.lastname: Ndinteh
authors.affiliation: Department of Pharmacy and Pharmacology, Faculty of Health Sciences, University of the Witwatersrand, 7 York Road, Parktown 2193, South Africa.
authors.forename: D K
authors.initials: DK
authors.lastname: Olivier
authors.affiliation: Department of Chemistry, Rhodes University, PO Box 94, Grahamstown 6140, South Africa.
authors.forename: P
authors.initials: P
authors.lastname: Kempgens
authors.affiliation: Department of Pharmacy and Pharmacology, Faculty of Health Sciences, University of the Witwatersrand, 7 York Road, Parktown 2193, South Africa.
authors.forename: S
authors.initials: S
authors.lastname: van Vuuren
authors.affiliation: Department of Chemistry, Rhodes University, PO Box 94, Grahamstown 6140, South Africa. Electronic address: R.Krause@ru.ac.za.
authors.forename: R W M
authors.initials: RW
authors.lastname: Krause
mesh_terms: D000995:Antitubercular Agents / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D005591:Chemical Fractionation; D045466:Dilleniaceae / Q000378:metabolism*; D008826:Microbial Sensitivity Tests; D015394:Molecular Structure; D020102:Mycobacterium smegmatis / Q000187:drug effects* / Q000254:growth & development; D009169:Mycobacterium tuberculosis / Q000187:drug effects* / Q000254:growth & development; D008517:Phytotherapy; D024301:Plant Bark / Q000378:metabolism*; D018547:Plant Stems / Q000378:metabolism*; D010946:Plants, Medicinal; D012293:Rifampin / Q000494:pharmacology; D012997:Solvents / Q000737:chemistry; D013329:Structure-Activity Relationship
chemical_list: D000995:Antitubercular Agents; D012997:Solvents; D012293:Rifampin
keywords: Anti-microbial; Compounds; Dilleniaceae; N-hydroxy imidate-tetracerane; Stem bark; Tetraceranoate; Tuberculosis