ELECTROCHEMICAL BEHAVIOUR AND VOLTAMMETRIC DETERMINATION OF GESHOIDIN AND ITS SPECTROPHOTOMETRIC AND ANTIOXIDANT PROPERTIES IN AQUEOUS BUFFER SOLUTIONS

The electrochemical behaviour of Geshoidin was investigated at a glassy carbon electrode in mixtures of citric acid and di-sodium hydrogen orthophosphate aqueous buffer system over a wide pH range (pH 2-11) using cyclic voltammetry. Chemically irreversible single oxidation and reduction peaks were obtained in the potential and pH range investigated. Variations in the peak potential and peak current of the oxidation peak have been observed as function of pH. The wave characteristics, the reversibility of the reactions, the diffusion coefficient and the number of electrons transferred have been studied. Linear sweep voltammetry was applied for the voltammetric determination of Geshoidin and a linear calibration curve over the range 1.00 x 10-6 - 1.00 x 10-4 M Geshoidin was achieved. The detection limit was found to be 5.00 x 10-7 M Geshoidin. For eight successive determinations of 1 x 10-5 M Geshoidin, a relative standard deviation (RSD) of 3.2 % was obtained. The voltammetric method was applied to the direct determination of Geshoidin in Gesho. The absorption spectra of Geshoidin are interpreted in terms of structural changes caused by protonation and deprotonation of the molecule as a result of changes in pH. The pKa values of the compound have been determined from the voltammetry and spectrophotometry measurements. The superoxide anion scavenging ability of Geshoidin was examined by differential pulse voltammetry and its antioxidant activity has been compared with natural antioxidants. KEY WORDS: Gesho, Geshoidin, Rhamnus prionoides, Electrochemical behaviour, Voltammetric determination, Spectrophotometry, Antioxidant activity Bull. Chem. Soc. Ethiop. 2007, 21(2), 189-204

Ent-kaurene and ent-beyerene diterpenoids and other constituents of Thecacoris batesii

Two novel diterpenoids, thecacorins A (1) and B (2), were isolated from Thecacoris batesii and their structures were established as ent-3b,20-epoxy-16-kaurene-3a,12b-diol and ent-15-beyerene-2b,3b-diol, respectively, on the basis of extensive spectroscopic analysis, especially, 1D NMR spectra, in conjunction with 2D experiments, COSY, NOESY, HMQC and HMBC. KEY WORDS: Diterpenoids, Thecacorin A, Thecacorin B, Ent-3b,20-epoxy-16-kaurene-3a,12b-diol, Ent-15-beyerene-2b,3b-diol, Thecacoris batesii  Bull. Chem. Soc. Ethiop. 2007, 21(1), 89-94

<b><i>Ent</i>-kaurene and <i>ent</i>-beyerene diterpenoids and other constituents of <i>Thecacoris batesii</i></b>

Two novel diterpenoids, thecacorins A (1) and B (2), were isolated from Thecacoris batesii and their structures were established as ent-3&beta;,20-epoxy-16-kaurene-3&alpha;&alpha;,12&beta;-diol and ent-15-beyerene-2&beta;,3&beta;-diol, respectively, on the basis of extensive spectroscopic analysis, especially, 1D NMR spectra, in conjunction with 2D experiments, COSY, NOESY, HMQC and HMBC

<b>Antiparasitic prenylated isoflavonoids from seeds of <i>Millettia griffoniana</i></b>

Two new prenylated isoflavonoids, namely 7-methoxyebenosin and griffonianone E along with the known calopogonium isoflavone B and 7,2'-dimethoxy-4',5'-methylenedioxy isoflavone were isolated from the seeds of <i>Millettia griffoniana</i>. Their structures were assigned on the basis of spectroscopic data. The new compounds exhibit moderate trypanocidal and anti-plasmodial activities

ANTIPARASITIC PRENYLATED ISOFLAVONOIDS FROM SEEDS OF MILLETTIA GRIFFONIANA

Two new prenylated isoflavonoids, namely 7-methoxyebenosin and griffonianone E along with the known calopogonium isoflavone B and 7,2\'-dimethoxy-4\',5\'-methylenedioxy isoflavone were isolated from the seeds of Millettia griffoniana. Their structures were assigned on the basis of spectroscopic data. The new compounds exhibit moderate trypanocidal and anti-plasmodial activities. KEY WORDS: Millettia griffoniana, Fabaceae, Papilionoideae, Isoflavones, Trypanocidal, Anti-plasmodial Bull. Chem. Soc. Ethiop. 2005, 19(1), 75-80

Virtualizing the p-ANAPL Library: A Step towards Drug Discovery from African Medicinal Plants

<div><p>Background</p><p>Natural products play a key role in drug discovery programs, both serving as drugs and as templates for the synthesis of drugs, even though the quantities and availabilities of samples for screening are often limitted.</p><p>Experimental approach</p><p>A current collection of physical samples of > 500 compound derived from African medicinal plants aimed at screening for drug discovery has been made by donations from several researchers from across the continent to be directly available for drug discovery programs. A virtual library of 3D structures of compounds has been generated and Lipinski’s “Rule of Five” has been used to evaluate likely oral availability of the samples.</p><p>Results</p><p>A majority of the compound samples are made of flavonoids and about two thirds (2/3) are compliant to the “Rule of Five”. The pharmacological profiles of thirty six (36) selected compounds in the collection have been discussed.</p><p>Conclusions and implications</p><p>The p-ANAPL library is the largest physical collection of natural products derived from African medicinal plants directly available for screening purposes. The virtual library is also available and could be employed in virtual screening campaigns.</p></div