Alex K. Machocho

Flavonoids from Tephrosia aequilata.

From the roots of the plant Tephrosia aequilata Baker, five flavonoids were isolated of which, 3,4:8,9-dimethylenedioxypterocarpan is reported for the first time. Its structure and those of the already known flavonoids were established by physical and spectroscopic analysis. Application of 2D NMR techniques was useful for complete characterization of the new pterocarpan as well as the other known flavonoids.

Alkaloids from Narcissus angustifolius subsp. transcarpathicus (Amaryllidaceae)

Seven alkaloids have been isolated from fresh bulbs of Narcissus angustifolius subsp. transcarpathicus (Amaryllidaceae). Nangustine, reported here for the first time, is the first 5,11-methanomorphanthridine alkaloid with a C-3/C-4 substitution. The structure and stereochemistry of this new alkaloid, as well as those previously known, have been determined by physical and spectroscopic methods. Spectroscopic data of pancracine have been completed. The in vitro assay activity against the parasitic protozoa Trypanosoma brucei rhodesiense, Trypanosoma cruzi, Leishmania donovani and Plasmodium falciparum was carried out with the compounds nangustine and pancracine.

Alkaloids from Crinum macowanii

Eleven alkaloids have been isolated from fresh bulbs of Crinum macowanii (Amaryllidaceae). Macowine is reported here for the first time. The structure and stereochemistry of this new alkaloid as well as of the known ones were determined by physical and spectroscopic methods.

Alkaloids from Cyrtanthus elatus

The alcoholic extract of the fresh bulbs of Cyrtanthus elatus yielded zephyranthine (1) and 1,2-O-diacetylzephyranthine (2), together with three other known alkaloids. Complete assignment of 1H and 13C NMR spectra of compounds 1 and 2 was done by employment of two-dimensional NMR techniques.

Pentacyclic triterpenoids from Embelia schimperi.

Five oleanane-type pentacyclic triterpenoids were isolated by chromatographic separation of a chloroform extract of the stem bark of Embelia schimperi. Three of these compounds have a methyleneoxy bridge. Two compounds, embelinone and schimperinone, are reported here for the first time from a natural source (they have been synthesized previously during chemical transformations). Their structures were determined by spectroscopic techniques, among which 2-D NMR was useful for complete characterization. Three of the triterpenoids exhibited mild antibacterial properties against the gram-positive bacterial strain Rhodococcus sp.

Reaction of benzoquinones and naphthoquinones with 1,8-diamino-3,6-dioxanonane and with 1,11-diamino-3,6,9-trioxaundecane

Reaction of 1,4-naphthoquinone or 2,3-dichloro-1,4-naphthoquinone with α,ω-diamino-derivatives of poly(alkylenoxides) leads to the formation of α,ω-bis(quinonyl) amines. A similar reaction with chloranil, bromanil, dichlorodicyanobenzoquinone, S-phenylbenzoquinone and 1,4-benzoquinone itself, leads to the formation of quinoid crown ethers.

Alkaloids from Ammocharis tinneana

Abstract Sixteen alkaloids have been isolated from fresh bulbs of Ammocharis tinneana (Amaryllidaceae), seven of which contain a 1,2β-epoxide group. 6α-Hydroxycrinamidine and 6α-hydroxyundulatine are reported here for the first time from a natural source. The structures and stereochemistry of these new alkaloids have been determined by physical and spectroscopic methods. 1 H and 13 C NMR spectra of flexinine, 1,2β-epoxyambelline and 11- O -acetyl-1,2β-epoxyambelline were completely assigned by means of 2D NMR techniques.

Bisbenzylisoquinoline and hasubanane alkaloids from Stephania abyssinica (Dillon & A. Rich) (Menispermeceae).

Two bisbenzylisoquinoline and one hasubanane alkaloids: (-)-pseudocurine (1), (-)-pseudoisocurine (2) and (-)-10-oxoaknadinine (3), were isolated from leaf extract of Stephania abyssinica, a plant used in traditional medicine in South Nyanza region of Kenya. They were characterized using 1D ((1)H, (13)C and DEPT) and 2D (COSY, NOESY, HMQC and HMBC) NMR techniques. (-)-Pseudocurine (1) and (-)-pseudoisocurine (2) exhibited strong to moderate anti-plasmodial activity while (-)-10-oxoaknadinine (3) showed moderate to mild activity.

Biflavonoids from an Ethno-Medicinal Plant Ochna holtzii Gilg

Ochna holtzii Gilg is a medicinal plant used extensively at the Kenya Coast for the treatment of various ailments. From solvent extracts of the root and stem barks of O. holtzii, seven constituents were isolated by standard chromatographic techniques (CC, VLC, prep-TLC and Sephadex LH-20). Their structures were analyzed by MS, UV,IR,1D and 2D NMR spectroscopy. All were found to be biflavonoids, including three novel compounds: dehydrate of lophirone C, hotzinol, and tri-O-methyl lophirone A. Crude methanol extracts of O. holtzii and the isolated biflavonoids were tested for antimicrobial activities against two Gram-positive bacteria, Staphylococcus aureus and Bacillus subtilis, two Gram-negative bacteria, Salmonella typhi and Pseudomonas aeruginosa, and the diploid fungus Candida albicans. The extracts and the isolated constituents showed varying levels of activities against the microbes. Afzelone D, lophirone A and the novel tri-O-methyl lophirone A showed strong activities against P. aeruginosa and S. aureus, with the latter being more susceptible. Calodenin B and the novel dehydrolophirone C also showed strong activities against these bacteria, but were more active against P. aeruginosa. However, none of these matched those of the antibiotic Chloramphenicol or the antifungal Fluconazole. This represents the first study on phytochemical and antimicrobial profiles of O. holtzii.

Plant Extracts as Solutions to Multi Drug Resistant, Indigofera hombleiBak.f and Martin, Fabaceae, a Plant used in Kenya against MicrobialRelated Conditions

Multi drug resistance of pathogens to drugs has become a universal problem. The aim the study was to investigate if plants’ natural products could offer alternative solutions to the problems. Roots of the plant were collected from Keiyo District; air dried in the shade then ground into fine powder and extracted with methanol, analytical grade, which eventually evaporated using a rotor evaporator. Known amount of the resultant material was measured and dissolved using 1 ml of dimethyl sulphoxide and topped with deionized water to form a known concentration. Serial dilutions of the drug were further made. Disc diffusion methods was used in the microbial studies with registered microorganisms at the National Public Health Laboratory, Nairobi. There were indications that the plant’s extracts possessed reasonable antimicrobial activities. The other portion of the extracts was subjected to wet bench studies which revealed the presence of several classes of compounds that are known to have curative properties. It was evident that the local inhabitants are justified to use the plant in the management of various that inflict them and it was recommended that the plants extracts cytotoxicity in higher animals be evaluated so as to justify its continued used in folklore medicine. It was also recommended that the compounds in the plant be further elucidated to assess their potential as sources of new compounds that could be used by the pharmaceutical concerns in new drugs development.