Simon G. Mathenge

Neurotrophic and Antileukemic Daphnane Diterpenoids from Synaptolepis kirkii

Biological assay guided fractionation of a dichloromethane extract of Synaptolepis kirkii led to the isolation of four new and five known daphnane-type diterpene orthoesters, whose structure was established by spectroscopic data. Full spectroscopic data of the new and known natural products are reported here for the first time. Pronounced neurotrophic and substantial antileukaemia activities of these compounds were found in in vitro assays.

Acyclic triterpenoids from Ekebergia capensis

Abstract From the dried bark of Ekebergia capensis, two novel acyclic triterpenoids, 2,3,22,23-tetrahydroxy-2,6,10,15,19,23-hexamethyl-6,10,14,18-tetracosatetraene and 2-hydroxymethyl-2,3,22,23-tetrahydroxy-6,10,15,19,23-pentamethyl-6,10,14,18-tetracosatetraene were isolated, along with known cyclic triterpenoids. The structures of these two new triterpenoids were determined by spectroscopic and chemical methods.

Activity of 6-Pentadecylsalicylic Acid from Ozoroa insignis Against Marine Crustaceans

Bioassay-guided fractionation of the dichloromethane extract from twigs of Ozoroa insignis using Artemia salina larvae as a model led to the isolation of 6-pentadecylsalicylic acid as the active principle. This is the first report of this so-called antifouling activity for this compound. In addition, this compound may relate to the traditional use of this plant as a herbal remedy for the treatment of urinary schistosomiasis in Africa.

Chemical studies on the roots of Uvaria welwitschii

A chemical investigation of the chloroform extract of the roots of Uvaria welwitschii (Annonaceae), an African traditional medicine taken for stomach ache, led to the isolation of eight new compounds, named welwitschins A–H (1–8), together with five known compounds (9–13). The structural elucidation by spectroscopic studies of the compounds isolated is described. All new compounds were flavonoids having a 2-hydroxy-3,4,6-trimethoxyphenyl moiety in the A-ring, and unsubstituted phenyl in the B-ring. Four of them (1–4) were monomeric flavonoids while the others (5–8) were dimeric flavonoids. The cytotoxicity of the isolated compounds against human promyelocytic leukemia HL-60 cells was investigated.

Tropane alkaloids from Erythroxylum emarginatum

A tropane alkaloid, anhydroecgonine methyl ester N-oxide (2), was isolated for the first time as a naturally occurring compound, with anhydroecgonine methyl ester (1) from the bark of Erythroxylum emarginatum. Compound 1 was also isolated from the twigs. Their structures were elucidated mainly by spectroscopic methods.

Antifouling substances of natural origin : Activity of benzoquinone compounds from Maesa lanceolata against marine crustaceans

A screening of antifouling activity from plants extracts led to selection and further study of Maesa lanceolata Forssk. Two p‐benzoquinone compounds were isolated from the fruits and found to be active against Artemia salina. The anti‐crustacean activity of both p‐benzoquinones is reported for the first time.

The principal alkaloid of Senecio schweinfurthii

Air-dried epigeal parts of Senecio schweinfurthii, collected from two sites in Kenya, yielded 7β-hydroxy-1-methylene-8α-pyrrolizidine N-oxide, as the predominant alkaloid.

Structure revision of isoline (ruwenine), bisline and isolinecic acid.

X-ray crystallography of bisline, and the chemical interconversion of bisline and isoline (ruwenine), revealed that the structures previously assigned to these alkaloids required revision; as did that of isolinecic acid.

Absolute configurations of two acyclic triterpenoids from Ekebergia capensis

Abstract The absolute configurations of two acyclic triterpenoids 1 and 2, previously isolated from the bark of Ekebergia capensis (Meliaceae) have been determined by the modified Moshers method.

Mitogenic activities in African traditional herbal medicines (Part II).

Mitogenic activities in African traditional herbal medicines were examined on human peripheral blood lymphocytes and mouse spleen cells using protein fractions obtained from their extracts by precipitation with ammonium sulfate. Target specificity for these mitogens was investigated by using isolated T cells and lymphocytes from athymic nude mice. Among 20 plants investigated, potent mitogenic activities for both human and mouse lymphocytes were found in 7 plants: Monanthotaxis sp. (Annonaceae), Uvaria lucida (Annonaceae), Maytenus buchananii (Celastraceae), Lonchocarpus bussei (Leguminosae), Phytolacca dodecandra (Phytolaccaceae), Phytolacca octandra (Phytolaccaceae), and Toddalia asiatica (Rutaceae). The U. lucida stem demonstrated the highest activity among all and induced mitogenesis both in human and mouse isolated T cells, but not in lymphocytes from athymic nude mice.