Browsing by Author "Jacobs, Ayesha"

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    Antimycobacterial, Cytotoxic, and Antioxidant Activities of Abietane Diterpenoids Isolated from Plectranthus madagascariensis
    (2021-01-19) Ndjoubi, Kadidiatou O; Sharma, Rajan; Badmus, Jelili A; Jacobs, Ayesha; Jordaan, Audrey; Marnewick, Jeanine; Warner, Digby F; Hussein, Ahmed A
    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.
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    Desorption kinetics of a xanthenol-dioxane clathrate
    (International Union of Crystallography, 2004) Jacobs, Ayesha; Nassimbeni, Luigi R; Taljaard, Benjamin
    The host xanthenol compound forms a 1:1 clathrate with dioxane, namely 9-(1-naphthyl)-9H-xanthen-9-ol–1,4-dioxane, C23H16O2·C4H8O2. The structure of this clathrate is reported, along with a study of the kinetics of desolvation and the determination of an activation energy. The guest mol­ecules are stabilized by Ohost—H⋯Oguest hydrogen bonds [O—H = 0.968 (2) Å, O⋯O = 2.7532 (13) Å and O—H⋯O = 151.9 (4)°].
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    Structure and reactivity of selected organic inclusion compounds
    (2002) Jacobs, Ayesha; Nassimbeni, Luigi R; Caira, Mino R
    The inclusion behaviour of the two host compounds 1,1 ,6,6-tetraphenylhexa-2,4- diyne-l,6-diol and cyclotriveratrylene (2,3,7,8,12,13-hexamethoxy-5,lO-dihydro- 15H-tribenzo[ a,d,g]cyclononene) was studied. Small organic guests were complexed with these hosts and their crystal structures determined. The stability and reactivity of these inclusion compounds were investigated. Kinetics of desolvation were determined for some of the inclusion compounds using both isothermal and non-isothermal methods. Rate laws were proposed and activation energies established. The selectivity of the host 1,1 ,6,6-tetraphenylhexa-2,4-diyne- 1,6-diol for certain guests was determined by competition experiments. Lattice energies were calculated in some cases. Solid state reactions were performed with the host 1,1 ,6,6-tetraphenylhexa-2,4-diyne-1 ,6-diol and selected solid guests. The resultant complexes were analysed using X-ray powder diffraction. Guest exchange reactions were also performed and the reactions were monitored either by differential scanning calorimetry or thermogravimetry. The structures of the inclusion compounds were reconciled with their physico-chemical properties.