Leonidah Kerubo Omosa

Leonidah Kerubo Omosa
University of Nairobi | UON · Department of Chemistry

Doctor of Philosophy in Natural Products Chemistry

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81
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Publications

Publications (81)
Chapter
Isoflavonoids are a class of flavonoids also referred to as phytoestrogens, due to their biological effects via the estrogenic receptor. They possess interesting biological properties including antifungal, antibacterial, antiviral, anticancer, and antioxidant amongst others. In the present review, we have reported the cytotoxicity of 24 isoflavonoi...
Article
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Natural products (NPs) are essential in the search for new drugs to treat a wide range of diseases, including infectious and malignant disorders. However, despite the discovery of many bioactive NPs, they often do not make it to market as drugs due to toxicity and other challenges. The development of NPs into drugs is a long and expensive process,...
Article
The root extract of Suregada zanzibariensis Baill. afforded six previously described ent-abietane diterpenoids, namely 7-oxo-ent-abieta-5(6),8(14),13(15)-trien-16,12-olide (1), mangiolide (2), 8,14β:11,12α-diepoxy-13(15)-abietane-16,12-olide (3), 7β,11β,12β-trihydroxy-ent–abieta-8(14),13(15)-diene-16,12-olide (4), 8α,14-dihydro-7-oxo-jolkinolide E...
Article
The antibacterial potency of thirteen compounds reported from two distinct genera, Zanthoxylum (Rutaceae) and Dracaena (Asparagaceae) against a panel of sensitive and multi-drug resistant Gram-positive and Gram-negative bacteria is described. The minimal inhibitory concentrations (MICs) and minimal bactericidal concentrations (MBCs) determinations...
Article
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To overcome the negative impacts of invasive fall armyworm (FAW), this study assessed the laboratory and field efficacy of aqueous and oil-based formulations of Metarhizium anisopliae ICIPE 41 as an alternative source for FAW management. Three oil formulations, including canola, corn, olive and an aqueous formulation of ICIPE 41, were assessed agai...
Article
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Background of the Study: Tropical plants of the Ficus genus (Moraceae) are among the earliest fruit trees that humans have cultivated. Since ancient times, many folk medicines have used species of this genus to treat a variety of ailments. Evidence from earlier investigations has shown these plants contain abundant secondary metabolites with a vari...
Chapter
The present chapter highlights the antibacterial potential of nine highly active compounds isolated from the African medicinal plants: 8,8-bis-(dihydroconiferyl)-diferulate, buesgenine, candidone, diospyrone, ferruginin A, isobavachalcone, neobavaisoflavone, neocyclomorusin, and plumbagin. Their botanical source as well as their hypothetical biosyn...
Chapter
Species of the genus Garcinia (Clusiaceae) have been used for centuries in different folk medicine for the treatment of several ailments, as well as food supplements. Evidence from previous studies has demonstrated a rich depository of structurally diverse secondary metabolites with a wide array of biological activities. The present chapter summari...
Article
Background Leukemia is the most common type of childhood cancer. Numerous flavonoids isolated from plants have been reported as potential chemotherapeutic agents against malignant growth while taking care of healthy cells. Purpose To discover new anticancer agents from the seeds of Dracaena steudneri Engl for their potential uses as candidate comp...
Article
A new prenylated kaempferol, conglomeratin (1), alongside 7 known compounds including flavonoids (2 and 3), ellagic acid derivatives (4 and 5), triterpenoids (6 and 7), and a coumarin (8) were isolated from the leaves (1 − 5) and stem bark (6 − 8) of Macaranga conglomerata. Their structures were elucidated using spectroscopic and spectrometric tech...
Article
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Endophytic fungal isolates Hypocrea lixii F3ST1 and Beauveria bassiana G1LU3 were evaluated for their potential to endophytically colonize and induce active compounds in Phaseolus vulgaris, as a defense mechanism against pea leafminer (Liriomyza huidobrensis) and fall armyworm (Spodoptera frugiperda). Endophytic colonization was achieved through se...
Article
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Purification of the aerial parts of Vernonia auriculifera Hiern afforded steroids (1-2), flavonoids (3-5), and polyalcohol (6). Their structures were determined using spectral evidences as well as by comparison with reported data. Iodonitrotetrazolium chloride (INT) colorimetric assay was used to assess the antibacterial activity of the extract and...
Article
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Chemical investigation of the root of Zanthoxylum paracanthum afforded 1 new alkamide derivative, (2E,4E)-6-oxo-N-isobutyldeca-2,4-dienamide (1) together with 10 known congeners including one phenolic amide (2), four benzophenanthridines (3 − 6), three indolonaphthyridines (7 − 9) and two lignans (10 and 11). Their structures were elucidated by a c...
Article
Aim: Certain edible plant sources contain vegetable oils that have been under-exploited both commercially and in research. This study aimed to determine the physicochemical properties, fatty acids composition, and antioxidant potential of the oil from the seed kernels of Telfairiapedata, which are used as food by the local population of Tharaka-Nit...
Research
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Aim: Certain edible plant sources contain vegetable oils that have been under-exploited both commercially and in research. This study aimed to determine the physicochemical properties, fatty acids composition, and antioxidant potential of the oil from the seed kernels of Telfairiapedata, which are used as food by the local population of Tharaka-Nit...
Article
The leaves of Dracaena steudneri yielded 6 new flavonoids–3,5,7-trihydroxy-6-methyl-3′,4′-methylenedioxyflavone (1), 5,7-dihydroxy-3-methoxy-6-methyl-3′,4′-methylenedioxyflavone (2), 3,5,7-trihydroxy-6-methoxy-3′,4′-methylenedioxyflavone (3), (2S,3S)-3,7-dihydroxy-6-methoxy-3′,4′-methylenedioxyflavanone (4), 4′,5,7-trihydroxy-3,3′,8-trimethoxy-6-me...
Article
Four new steroidal sapogenins, dracaenogenins CF (1–4), a new conjugated chalcone-stilbene, 3′′-methoxycochinchinenene H (5) together with eight known compounds namely, (25S)-spirosta-1,4-dien-3-one (6), trans-resveratrol (7), 4,4′-dihydroxy-3′-methoxychalcone (8), N-trans-coumaroyltyramine (9), N-trans-p-coumaroyloctopamine (10), N-trans-feruloylo...
Article
Two new norhopane derivatives namely 3β,6β,22-trihydroxy-7β,11α-di[(4-hydroxybenzoyl)oxy]-21αH-24-norhopa-4(23)-ene (1) and 3β,6β,22-trihydroxy-7β-[(4-hydroxybenzoyl)oxy]-21αH-24-norhopa-4(23)-ene (2) together with two previously reported compounds, including a norhopane, 3β,6β,11α-trihydroxy-7β-[(4-hydroxybenzoyl)oxy]-24-norhopa-4(23),17(21)-diene...
Article
Investigations of the root extract of Dracaena usambarensis Engl. for anticancer principles led to the characterization of one new homoisoflavonoid, (3S)-3,4ʹ,5,6-tetrahydroxy-7-methoxyhomoisoflavanone (1) and a new retrodihydrochalcone, 4ʹ,4-dihydroxy-2,3-dimethoxydihydrochalcone (2) along with six previously reported compounds, including two homo...
Article
Background: Cancer treatment failure is majorly attributed to the emergency of multi-drug resistance of cancer cells towards most conventional drugs used in chemotherapy hence the need for more active principles with less side effective from natural sources. Methods: Characterization of isolated compounds was achieved using NMR spectroscopy and com...
Article
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Pharmacogn. Commn. 2019; 9(2):59-74 A multifaceted peer reviewed journal in the field of Pharmacognosy and Natural Products www.phcogcommn.org Pharmacognosy Communications, Vol 9, Issue 2, Apr-Jun, 2019 59 Rapid Screening using GIBEX Screens-to-nature System of Ethnomedicinal Plants from Ngong Forest, Kenya for Potency against Infectious Diseases...
Article
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In our continuous search for cytotoxic compounds from the genus Zanthoxylum, chromatographic separation of the MeOH/CH2Cl2 (1:1) extract of Z. chalybeum yielded one new alkamide; 4-(isoprenyloxy)-3-methoxy-3,4-deoxymethylenedioxyfagaramide (1) and a known one; fagaramide (2). Similarly, from the MeOH/CH2Cl2 (1:1) extract of the stem bark of Z. para...
Article
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Bioassay-guided screening of Hypoestes verticillaris whole plant CH2Cl2:MeOH (1:1) extract for anti-plasmodial activity yielded four new compounds: two lignans 2, 6-dimethoxysavinin (1), 2,6-dimethoxy-(7E)-7,8-dehydroheliobuphthalmin (2); and two fusicoccane diterpenoids: 11(12)-epoxyhypoestenone (3) and 3(11)-epoxyhypoestenone (4). The chemical st...
Article
Abstract Background Practices of biopiracy to use genetic resources and indigenous knowledge by Western companies without benefit-sharing of those, who generated the traditional knowledge, can be understood as form of neocolonialism. Hypothesis : The One-World Medicine concept attempts to merge the best of traditional medicine from developing coun...
Article
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Background: Cancer constitutes a major hurdle worldwide and its treatment mainly relies on chemotherapy. Objectives: The present study was designed to evaluate the cytotoxicity of eleven naturally occurring compounds including six phenolics amongst them were 4 chalcones and 2 flavanones as well as 5 terpenoids (3 clerodane and 2 trachylobane dit...
Article
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Background: Drug resistance is one of the major hurdles in the treatment of cancer. Rather than single factors, drug resistance is caused by multiple mechanisms making it even more complex. In the present study, the cytotoxicity of six compounds isolated from Zanthoxylum gilletii were screened against drug-sensitive leukemia CCRF-CEM cells. The mos...
Chapter
Curcuma longa L. (Zingiberaceae), commonly known as turmeric, is native to Southwest India with its rhizomes being the source of a bright yellow spice with various medicinal applications. It is widely cultivated throughout the tropics and similarly used for it medicinal value, in the cosmetic industry, and as a dye. Herein, the medicinal potentials...
Article
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Infections caused by Mycoplasma species belonging to the ‘mycoides cluster’ negatively affect the agricultural sector through losses in livestock productivity. These Mycoplasma strains are resistant to many conventional antibiotics due to the total lack of cell wall. Therefore, there is an urgent need to develop new antimicrobial agents from altern...
Article
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A set of seven diterpenes, three kauranes and four trachylobanes, isolated from the African plant Psiadia punctulata were assayed against Mycobacterium tuberculosis and reached activity comparable with cycloserine, a second line drug used to treat tuberculosis (TB). Several structural properties of those diterpenes, such as lipophilicity, HOMO and...
Article
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This paper describes the semi-synthesis and anti-microbial activity of novel pyrazoline derivatives of Polygonum senegalense chalcones. The study was carried out on the understanding that heterocycles with pyrazoline ring systems are known to possess a broad spectrum of biological activities. The derivatives were afforded by refluxing mixtures of c...
Article
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Introduction: Multidrug resistance remains a major obstacle hindering successful antimalarial chemotherapy. In the current study, 50% methanol in dichloromethane extract and six compounds from the stem bark of Zanthoxylum gilletii were explored for their antiplasmodial potential against three strains of Plasmodium falciparum. Materials and Methods:...
Article
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Currently, researchers have given special attention to the synthesis of heterocyclic compounds with nitrogen and oxygen five in five- or six-membered ring systems. This is mainly due to their wide range of biological activities. Hence, in this study, isoxazoline, pyrazole and bypyrimidine derivatives were synthesized from flavonoids, previously iso...
Article
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Background Cancer is a major public health concern globally and chemotherapy remains the principal mode of the treatment of various malignant diseases. Methods This study was designed to investigate the cytotoxicity of 14 naturally occurring quinones including; 3 anthraquinones, 1 naphthoquinone and 10 benzoquinones against 6 human carcinoma cell l...
Article
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Ethnopharmocological relevance: Members of 'Mycoplasma mycoides cluster' are important ruminant pathogens in Africa. Diseases caused by these Mycoplasma negatively affect the agricultural sector especially in developing countries through losses in livestock productivity, mortality and international trade restrictions. There is therefore urgent nee...
Article
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Phytochemical investigation of surface exudates of the leaves of Gardenia ternifolia resulted to characterization of four flavonoids; 3,5,3′-trihydroxy-7,4′-dimethoxyflavone (1), 5,7-trihydroxy-4′-methoxyflavone (2), 5,7-dihydroxy-3,4′-dimethoxyflavone (3), 5,4′-dihydroxy-7-methoxyflavanone (4) and two tritepenoids; β-sitosterol (6) and stigmastero...
Article
From the surface exudates of Senecio roseiflorus fourteen known methylated flavonoids and one phenol were isolated and characterized. The structures of these compounds were determined on the basis of their spectroscopic analysis. The surface exudate and the flavonoids isolated showed moderate to good antiplasmodial activity with 5,4′-dihydroxy-7-di...
Article
Full-text available
In the current study forty eight compounds belonging to anthraquinones, naphthoquinones, benzoquinones, flavonoids (chalcones and polymethoxylated flavones) and diterpenoids (clerodanes and kauranes) were explored for their antimicrobial potential against a panel of sensitive and multi-drug resistant Gram-negative and Gram-positive bacteria. The mi...
Article
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Dodonaea angustifolia L.f is a medicinal plant used in the Kenyan traditional system of medicine to cure human diseases. The secondary metabolites present in the surface exudates, showed phytochemical diversity of this plant from different geographical conditions in Kenya. There was great geographical variability in the composition of the surface e...
Article
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The current study was undertaken to validate the traditional use and determine the safety profiles of Moringa oleifera and Rauwolfia caffra used in Kenya to manage tumors and related ailments. This was achieved by determining the anti-proliferative activities of the active antioxidant extracts (50% methanol in dichloromethane) of Moringa oleifera l...
Article
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Background: Biopiracy mainly focuses on the use of biological resources and/or knowledge of indigenous tribes or communities without allowing them to share the revenues generated out of economic exploitation or other non-monetary incentives associated with the resource/knowledge. Methods: Based on collaborations of scientists from five continent...
Article
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Background In the present study, the methanol extracts from the leaves, as well as compounds namely sigmoidin I (1), atalantoflavone (2), bidwillon A (3), neocyclomorusin (4), 6α-hydroxyphaseollidin (5) and neobavaisoflavone (6) (from the bark extract) were tested for their activities against a panel of Gram-negative bacteria including multi-drug r...
Article
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Ethnopharmacological relevance: Plants from Kenyan flora are traditionally used against many ailments, including cancer and related diseases. Cancer is characterized as a condition with complex signs and symptoms. Recently there are recommendations that ethnopharmacological usages such as immune and skin disorders, inflammatory, infectious, parasi...
Article
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The root extract of Thespesia garckeana yielded three known oxidatively coupled sesquiterpenoids, namely (-)-gossypol (1) and two of its derivatives (-)-6-methoxygossypol (2) and (+)-6,6'-dimethoxygossypol (3), and the stem bark afforded (E)-docosy1-3-(3,4-dihydroxyphenyl) acrylate (4), stigmasterol (5) and betulinic acid (6). The structures of the...
Article
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Kenyan Croton sylvaticus Hochst. ex Krauss gave four clerodane diterpenoids, the new ent-3,13E-clerodadiene-15-formate (1), the known 15-acetoxy-ent- 3,13E-clerodadiene (2), ent-3,13E-clerodadien-15-ol (3) and hardwickiic acid (4), two known halimane diterpenoids, penduliflaworosin (5) and crotohalimaneic acid (6) and one labdane diterpenoid, labda...
Article
Full-text available
The root extract of Thespesia garckeana yielded three known oxidatively coupled sesquiterpenoids, namely (-)-gossypol (1) and two of its derivatives (-)-6-methoxygossypol (2) and (+)-6,6′-dimethoxygossypol (3), and the stem bark afforded (E)-docosyl-3-(3,4-dihydroxyphenyl) acrylate (4), stigmasterol (5) and betulinic acid (6). The structures of the...
Article
Three novel compounds; two polymethoxylated flavonoids, 5,7,4′-trihydroxy-3,8,3′,5′-tetramethoxyflavone (1), 5,7,3′-trihydroxy-3,8,4′,5′-trimethoxyflavone (2), and a clerodane diterpenoid; 8-acetoxyisochiliolide lactone (3) were characterized from the leaf exudates of Microglossa pyrifolia. In addition, three known polymethoxylated flavonoids inclu...
Article
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The CH2Cl2/MeOH (1: 1) extract of the roots of Tephrosia villosa showed good antiplasmodial activity against the chloroquine-sensitive (D6) and chloroquine-resistant (W2) strains of Plasmodium falciparum with IC50 values of 3.1 +/- 0.4 and 1.3 +/- 0.3 mu g/mL, respectively. Chromatographic separation of the extract yielded a new rotenoid, 6 alpha-h...
Article
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Five locally known plants, Solanum aculeastrum, Erythrina abyssinica, Carissa edulis, Croton megalocarpus and Myrica salicifolia used by Maasai traditional healers for treatment of bacterial infections were extracted using chloroform, ethanol and water. The extracts obtained were then tested for in-vitro antibacterial activity on clinical isolates...
Article
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The surface exudates of the leaves of Dodonaea angustifolia from Ngong forest population (6 km from Nairobi city center, Kenya) demonstrated antimicrobial activity against Gram-negative (Escherichia coli), Gram-positive (Staphylococcus aureus and Bacillus pumilus) bacteria and the fungus Sacchromyces cerevisiae. Chromatographic separation of the ex...
Article
Full-text available
Five locally known plants, Solanum aculeastrum, Erythrina abyssinica, Carissa edulis, Croton megalocarpus and Myrica salicifolia used by Maasai traditional healers for treatment of bacterial infections were extracted using chloroform, ethanol and water. The extracts obtained were then tested for in-vitro antibacterial activity on clinical isolates...
Article
Two novel compounds, alienusolin, a 4α-deoxyphorbol ester (1), crotonimide C, a glutarimide alkaloid derivative (2), and ten known compounds, julocrotine (3), crotepoxide (4), monodeacetyl crotepoxide (5), dideacetylcrotepoxide, (6), β-senepoxide (7), α-senepoxide (8), (+)-(2S,3R-diacetoxy-1-benzoyloxymethylenecyclohex-4,6-diene (9), benzyl benzoat...
Article
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The Quinine tree (Rauvolfia caffra) is used as a medicinal plant among traditional communities in many countries to manage tumors and other diseases associated with oxidative stress. To validate indigenous knowledge and possibly position this herb for technology uptake and utilization, we established the level of antioxidant activity in R. caffra,...
Article
Full-text available
From the surface exudates of Senecio roseiflorus fourteen known methylated flavonoids and one phenol were isolated and characterized. The structures of these compounds were determined on the basis of their spectroscopic analysis. The surface exudate and the flavonoids isolated showed moderate to good antiplasmodial activity with 5,4'-dihydroxy-7-di...
Article
Full-text available
Alectra sessiliflora (Vahl) Kuntze (Scrophulariaceae) is traditionally used in western Kenya in the management of microbial infections. The water, chloroform and methanol extracts of A. sessiliflora whole plant exhibited antimicrobial activity against a range of bacteria (Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Shigella dys...
Article
Phytochemical investigation of the leaf surface exudate of Dodonaea angustifolia L.f. yielded two new neo-clerodane diterpenes, neo-clerodan-3,13-dien-16,15:18,19-diolide (mkapwanin) and 15-methoxy-neo-clerodan-3,13-dien-16,15:18,19-diolide (15-methoxymkapwanin). In addition, ten known compounds were identified. The structures were determined on th...
Article
Quercetin shows structural features that have been related to the antioxidant potency of flavonoids and also shows neuroprotection in different models of oxidative death. Because only a few studies have focused on the flavonoid structural requirements for neuroprotection, this work evaluated the protective capacity of 13 flavones structurally relat...
Conference Paper
Full-text available
There are more than 1200 described medicinal plants in Kenya from a flora of approximately 10,000 members. Strong cross-medical information from the 42 ethnic groups points to the high potential of some of these species. The Myrsinaceae are well established ethno-anthelmintics and anti-bacterials. They are harbingers of long alkyl side chain benzoq...
Article
Full-text available
There are more than 1200 described medicinal plants in Kenya from a flora of approximately 10,000 members. Strong cross-medical information from the 42 ethnic groups points to the high potential of some of these species. The Myrsinaceae are well established ethno-anthelmintics and anti-bacterials. They are harbingers of long alkyl side chain benzoq...

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