Frederick Nartey's research while affiliated with IT University of Copenhagen and other places

Aspergillus flavus Link ex Fries was grown on cassava (Manihot utilissima) and Czapek-Dox media at 31±1°C and 90 per cent relative humidity for 8 weeks. Isolation and purification of the toxic and carcinogenic metabolic products of the mould by paper and thin layer chromatography are described. High concentrations of aflatoxin B1, B2, G1 and G2 were synthesized by the mould grown on cassava for 4 weeks. In addition to these four major toxic components, 9 other fluorescent materials were observed on the chromatograms of crude products from cassava. It is concluded that the high moisture, high polysaccharide and low nitrogen content of cassava constitute a favourable nutritional condition at high temperatures and high relative humidity for the growth of A. flavus and the synthesis of relatively high concentrations of aflatoxin. This conld represent a serious health hazard in the moist tropics.

Seeds and seedlings of Manihot utilissima were analysed for cyanogenic glycosides und free amino acids, with special reference to valine and isoleucine which serve as precursors of the aglycone moieties of linamarin and lotaustralin. Seeds contained traces of valine and isoleucine but no glycosides, whereas seedlings contained high concentrations of these amino acids and glycosides. Illumination of seedlings led to a steep increase in the concentration of glycosides followed by a decrease without excretion of detectable HCN. Seeds accumulated asparagine, while seedlings accumulated both asparagine and glutamine in the storage and transport of nitrogen. Seedlings incorporated 13.2 per cent of label from valine-14C(U) and 2.4 per cent of label from isoleucine-14C(U)into linamarin and lotaustralin, respectively. In both cases, appreciable amounts of label were also incorporated into asparagine. 49 per cent of label from H14CN was incorporated inio asparagine in which ca. 98 per cent of total radioactivity was located in the amide-carbon atom. The different patterns of labelling which occurred during the assimilation of H14CN and 14CO2 showed that cyanide metabolism did not proceed via CO2, and that M. utilissima contains an efficient enzyme-system which catalyses the conversion on high concentrations of HCN into asparagine, which subsequently enters different metabolic pools involved with respiration, protein and carbohydrate syntheses. Cyanogenesis in M. utilissima appears lo be directly influenced by available pools of valine and isoleucine, and the metabolism of HCN released from linamarin and lotaustralin by the action of linamarase may be directly related to respiratory and synthetic processes by way of the incorporation of HCN as a unit into asparagine.

A densitometric method for the quantitative determination of cyanogenic glycosides is described. The method is based on the release of HCN catalyzed by the enzyme preparation β-glucuronidase from Helix pomatia and subsequent direct detection of HCN on hydrophobic, picrate-impregnated, transparent, ion-exchange sheets. The sheets are placed directly on the enzyme-wetted chromatogram, and the intensities of the obtained spots are determined. No significant changes in intensities of spots occur over a period of 28 days, if the sheets are protected from corrosive vapors. If a densitometer is not available, or when a rapid field test is required, a semiquantitative determination is possible by visual inspection. The method was found suitable for the separate estimation of cyanogenic principles in cassava meal, lima beans, and linseed meal.

A new diol glucoside, 2-β-d-glucopyranosyloxy-2-methylpropanol, the first reported naturally occurring monoglucoside of an aliphatic dihydric alcohol, was isolated from pods of Acacia sieberana var. woodii. Structure elucidation was based on 1 H and 13C NMR spectroscopy, and enzymatic analyses. The compound was hydrolysed very slowly by almond β-glucosidase, but cleaved by a β-glucuronidase enzyme complex from Helix pomatia.

A new cyanogenic glucoside, isolated from pods of Acacia sieberiana var. woodii, was shown to be (2R)-2- (β-d-glucopyranosyloxy)-3-hydroxy-3-methylbutanenitrile by spectroscopic and chemical methods. The absolute configuration of this glucoside was correlated with that of proacacipetalin by oxymercuration of the latter, followed by borohydride reduction of the product.

A new cyanogenic glycoside isolated from pods of Acacia sieberiana var. woodii has been shown by chemical and spectroscopic methods to be (2S)-2-[(6-O-α-l-arabinopyranosyl-β-d-glucopyranosyl)oxy]-3-methylbut-3-enenitrileo. Acid-catalysed hydrolysis of the glycoside afforded arabinose and proacacipetalin, and base-catalysed double-bond migration gave 2- [(6-O-α-l-arabinopyranosyl-β- d-glucopyranosyl)oxy ]-3-methylbut-2-enenitrile.

The long-known cyanogenic glucoside acacipetalin, confirmed to be 2- (b-D-glucopyranosyloxy-)3 -methylbut-2-enenitrile, can be produced from a natural b-D-glucopyranoside of 2-hydroxy-3-methylbut-3-enenitrile, which is distinguished from its epimer and named proacacipetalin.