Lawrence Onyango Arot Manguro’s research while affiliated with Maseno University and other places

A new oleanane type triterpene characterized as 3α, 24-diacetoxy-12-oleanene (1) together with known compounds 2-10, were isolated from Annona mucosa leaf extracts. Their structural elucidation was accomplished using physical and spectroscopic methods. The compounds showed weak to moderate insecticidal activities against stored maize insect pests Sitophilus zeamais and Prostephanus truncatus.

The plant species Elaeodendron buchananii Loes is widely used in folklore medicine to manage microbial infections in Kenya. Previous studies on the plant fruits and root bark revealed the presence of steroids and terpenoids. The present phytochemical analysis of the plant stem bark has led to the isolation of four new triterpenes characterized as methyl 3β-acetoxy-11α, 19α, 28-trihydroxyurs-12-en-23-oic acid (1), 3β, 11α, 19α-trihydroxyurs-12-en-23, 28-dioic acid (2), 3β-acetoxy-19α, 23, 28-trihydroxyurs-12-ene (3) and 3-oxo-19α, 28-dihydroxyurs-12-en-24-oic acid (4), together with ten known ones (5–14), whose structures were elucidated using spectroscopic techniques. The isolate canophyllol (8) showed promising antibacterial activity against N. meningitides with MIC value of 31.25 μg/ml.

Nitrogen fertilisation influences tea yields, quality and pests infestation levels. Red spider mites reduce tea production in western Kenya during prolonged droughts. Nitrogen fertiliser use maybe an agronomic practice that may influence infestation levels by mites. Overhead volatile compounds (OVOCs) composition also influences infestations of tea by mites. Influence of nitrogenous fertiliser rates on red spider mite infestations and OVOCS levels was determined. Mites populations varied (pd>0.05) with nitrogenous fertiliser rates. High infestations were at 0 and 300 kg N/ha/year, and sharp decline between 150 and 225 kg N/ha/year. Green leaf volatiles increased while some aromatic and terpenoid compounds decreased with increasing nitrogenous fertiliser rates. Significant (pd>0.05) direct linear regressions between 1-penten-3-ol, 3-penten- 2-ol, E-2-hexenal, Z-3-hexenyl acetate and inverse relationship between 2-phenyl ethanol, ethyl benzene, -methyl styrene, longifolene and ß-cedrene and nitrogenous fertiliser rates were observed. Most aromatic and terpenoid compounds, which are repellents of mites, were highest between 150 and 225 kg N/ha/year where infestations by mites were lowest. The recommended fertiliser rates of 100 to 225 kg N/ha/year in Kenya also produce most repellents of mites, protecting tea plants against infestations. Use of recommended nitrogen rates can protect tea from infestations by mites.

A new β-carboline alkaloid named sacleuximine A (1) together with known compounds palmatine (2), isotetrandrine (3), trans-N-feruloyltyramine (4), trans-N-caffeoyltyramine (5), yangambin (6), syringaresinol (7), sesamin (8), (+) epi-quercitol (9), 4-hydroxybenzaldehyde (10), β-sitosterol (11), quercetin 3-O-rutinoside (12) and myricetin 3-O-β-glucose (1→6) α-rhamnoside (13) have been isolated from methanol extract of Triclisia sacleuxii aerial parts. Compounds 1–10 were evaluated for their cytotoxicity against human adenocarcinoma (HeLa), human hepatocarcinoma (Hep3B) and human breast carcinoma (MCF-7) cells lines and also for antibacterial activities against both Gram-positive and Gram-negative bacteria. The cytotoxicity (IC50) values ranged between 0.15 and 36.7 μM while the minimum inhibitory concentrations were found to be in the range of 3.9 and 125 μM, respectively. This is the first report of antibacterial compounds and the isolation of lignans together with a β-carboline alkaloid from T. sacleuxii.

Two new ursane-type triterpenes characterized as 3-oxo-24-acetoxy-11α-hydroxy-urs-12-ene (1) and methyl 3α-acetoxy-11α-methoxy-urs-12-en-24-oate (2), together with known compounds 3-11, were isolated from Boswellia rivae oleo-gum resin exudate. Their structural elucidation was accomplished using physical, chemical, and spectroscopic methods. The compounds exhibited weak to moderate antibacterial activities against some Gram-positive and Gram-negative bacteria.

Agricultural production is constrained by insect pests, which cause serious post-harvest losses of up to 43% in developing countries. Maize weevil (Sitophilus zeamais Motschulsky.) is one of the most destructive pests of maize. Synthetic chemicals have been used to protect stored grain from damage by insects. The increasing knowledge about the harm derived from the indiscriminate use of synthetic insecticides has prompted research aimed at finding safe methods of pest control. Efficacy of extractives and isolates from Warburgia ugandensis (Canellaceae) were evaluated for maize grain protection against S. zeamais. The oil extract was the most repellent (P<0.05) with repellence distance of 6.37 within 2-hour exposure duration followed by n-hexane extract (6.20 cm). The most repellent compounds were mukaadial (6) and polygodial (1) (5.43 and 4.83 cm, respectively). Essential oil was the most toxic (P<0.05) to the weevils and showed 100% mortality at 21 days. The toxicity levels of the organic extracts ranged from 18.3 to 78.0% with n-hexane exhibiting the highest toxicity followed by ethyl acetate extract. Polygodial (1) and warburganal (2) were the most toxic compounds (70.0 and 65.0% respectively). The oil extract was as active as the Actellic dust and completely inhibited the emergence of the insect adults. Polygodial (1), ugandensolide (3) and warbuganal (2) had the best growth inhibition activity. The results from the present study indicate that W. ugandensis could be a useful alternative in stored grain protection against maize weevil and the isolated compounds could be good candidates as phytoinsecticidal agents against insect pests.

In this study, comparative analysis of Sesamum indicum L. oil synergized and non-synergized methanol extract of the T. minuta were assayed against P. americana collected from households within Maseno Division, Kenya. The mortality and LC50 for both synergized and non-synergized extracts were determined. The synergized extract had cockroach mortality of 60 (n = 60) (100%) while non-synergized showed mortality of 52 (n = 60) (86.1 ± 1.2%) at 22 μg/ml after 36 h using contact toxicity method. On the other hand, with fumigation method, 100% mortality of the pest was achieved within 30 h using synergized extract while the non-synergized extract afforded 84.0 ± 1.1% mortality at the same concentration after the same period of time. The LC50 for the synergized extract was observed to be 6.31 μg/ml while the non-synergized was found to be 8.91 μg/ml. Thus, T. minuta extract may be used alone or synergized with S. indicum oil for effective management of cockroaches within households.

Chemical investigation of CH2Cl2 and MeOH extracts of Conyza floribunda have led to the isolation of (24S)-ethylcholesta-5,22E, 25-trien-3-0-glucosy(l"→ 4')-rhamnoside (1), (24S)-ethylcholesta-5,25- dien-3-0-/3-glucoside (2), cyasterone (3), stigmasta 5,22-dien-3-acetate (4), stigmasta 5,22-dien-3-ol (5), spinasta 7,22-dien-3-ol (6), 3-oxofriedooleanane (7), 3-hydroxyfriedooleanane (8), 3-acetoxyfriedooleanane (9), betullinic acid (10), quercetin 3-0-/3-glucoside (11), quercetin (12), myricetin (13) and kaempferol (14). Their structures were determined using spectroscopic and physical methods as well as comparison with data available in the literature.