Donald E. U. Ekong

Spectral studies on coumarins and the determination of the constitution of ekersenin by total synthesis

Abstract During the determination of the constitution of ekersenin isolated from Ekererbegia senegalensis , eight isomeric monomethoxy-monomethylcoumarins were synthesised. These studies proved that ekersenin was 4-methoxy-5-methylcoumarin, a constitution with novel biosynthetic implications. Apparently ekersenin is the first example of natural coumarin biosynthesis involving only the polyketide route. Comparative spectral correlations on substituted coumarins are summarised.

Extracts from the fruits of Piper guineense schum. and thonn

Extraction of the fruits of P. guineense with petroleum has yielded the isobutylamides of 13-(3,4-methylenedioxy-phenyl)-2,4,12-tridecatrienoic, 13-(3,4-methylenedioxyphenyl)undeca-2,4,12-trienoic, eicosa-2,4-dienoic, octadeca-2,4-dienoic, and hexadeca-2,4-dienoic acids, as well as the known amides piperine, trichostachine, and piperlonguminine, and a mixture of unidentified sterols.

GC-MS identification of abscisic acid and abscisic acid metabolites in seed of Vigna unguiculata

Abscisic acid, phaseic acid and 4′-dihydrophaseic acid were identified by GC-MS of derivatized (Me, MeTMSi) extracts from immature fruits of Vigna unguiculata. The fruits also contained some other ABA-related compounds, one of which might be epi-4′-dihydrophaseic acid while another was tentatively identified as 6′-hydroxymethylabscisic acid.

The meliacins (limonoids): minor constituents of Khaya anthotheca: reduction of the meliacins with zinc–copper couple

The residues collected after isolation of anthothecol from Khaya anthotheca have afforded a new meliacin for which the structure (2b)(11β-acetoxyazadirone) is proposed. In addition, deacetylanthothecol and a sterol mixture shown by g.l.c. to consist of stigmasterol, β-sitosterol, campesterol, cycloeucalenol, and 24-methylenecycloartanol, were isolated. In the course of model experiments with anthothecol aimed at structural correlation with the new compound, zinc–copper couple was found to be a convenient and superior reagent for reduction of epoxides to olefins, αβ-unsaturated ketones to saturated ketones, and ketols and their acetates to ketones, in the meliacin series. By using this reagent new reduction products of anthothecol have been prepared and characterised.

Chemistry of the meliacins (limonoids). The structure of melianin A, a new protomeliacin from Melia azedarach

Evidence is presented for the structures of a new protomeliacin (melianin A) and the related melianin B, which co-occur with gedunin (or 7-deacetoxy-7-oxogedunin), nimbolin A, fraxinellone, and cycloeucalenone in the wood extracts of Melia azedarach.

X-Ray Crystal Structure Analysis of Deacetyldehydroeuphorianin: The Correct Structure of the Novel Pentacyclic Macrocyclic Diterpene, Euphorianin

Abstract The conversion of euphorianin to deacetyldehydroeuphorianin which was used in an X-ray crystal structure analysis is described. A new pentacyclic structure related to ingol tetraacetate is described for euphorianin.

Hormonal Aspects of the Fruit Abscission Problem in Cowpea (Vigna unguiculata L.)

Summary A comparative study of some of the hormones in acidic extracts obtained from fruits of cowpea was undertaken in relation to premature fruit abscission. Extracts were obtained from 6-day and 2-day old fruits from the lowest and upper racemes of the cowpea inflorescence, respectively. In the cultivar New Era, only growth inhibitors were detected in 2-day old fruits whereas inhibitors as well as gibberellins and auxins were detected in 6-day old fruits. In the cultivar Adzuki, gibberellin activity was detected in both 2-day old and 6-day old fruits. The results are discussed in relation to the abscission problem in cowpea.