Hosni Khalaf

High-performance liquid chromatographic separation of some naturally occurring naphtoquinones and anthraquinones

Abstract A high-performance liquid chromatographic method is described which allows the separation of thirteen naturally occuring naphthoquinones and anthraquinones as well as a pyranonaphthalene derivative on a reversed-phase column. The separation was achieved under isocratic and gradient conditions. The compounds are known as constituents of the heartwood of Tabebuia avellanedae (Bignoniaceae). Their chromatographic behaviour is compared to that of furanonaphthoquinones known from the inner bark of T. avellanedae.

HPLC separation and determination of naphtho[2,3-b]furan-4,9-diones and related compounds in extracts of Tabebuia avellanedae (Bignoniaceae)

Abstract A HPLC method for the separation of some naturally occurring naphtho[2,3-b]furan-4,9-diones and related compounds on a RP column is reported. These compounds were determined in aqueous and various non-aqueous extracts of the inner bark of Tabebuia avellanedae (Bignoniaceae). 8-Hydroxy-2-hydroxyethyl-naphtho[2,3-b]furan-4,9-dione, 2-hydroxyethyl-naphtho[2,3-b]furan-4,9-dione and 2,3-dihyldro- 2-(1-methylethenyl-)naphtho[2,3-b]furan-4,9-dione were predominating in all extracts investigated. Lapachol could not be detected in aqueous extracts known as “lapacho tea”.

Determination of secondary amines as highly fluorescent formamidines by high-performance liquid chromatography

Aliphatic secondary amines were derivatized with the non-fluorescent reagent, 5-isothiocyanato-1,3-dioxo-2-p-tolyl-2,3-dihydro-1H-benz[de]isoquinoline in a simple and fast two step reaction via thioureas to highly fluorescent formamidines. Derivatives were separated by reversed phase liquid chromatography by using acetonitrile/phosphate buffer as the mobile phase. The limits of detection (S:N = 3) ranged from 200 to 300 fmol (20 μl injected). A method for the determination of dimethylamine, piperidine and diethanolamine in spiked acidic aqueous samples is given, after the decomposition of their N-nitroso derivatives.

Sensitive liquid chromatograhic determination of hydrophobic primary and secondary amines by derivatization to form highly fluorescent thiazoles

Abstract Thioureas formed by addition of primary and secondary amines to the non-fluorescent 5-isothiocyanato- l ,3-dioxo-2- p -tolyl-2,3-dihydro-1 H -benz[de]isoquinoline were oxidized to the corresponding stable and highly fluorescent thiazoles with large Stokes shifts. The structure of the thiazoles was deduced. Liquid Chromatographic separation of the thiazoles in both normal phase (NP) and reversed phase (RP) systems was achieved. Fluorescence detection limits ranged from 2 to 8 f mol in the RP and NP systems. The fluorescence properties (maximal wavelengths and intensities) of the thiazoles are dependent on the solvent. An application to the determination of 2-phenylethylamine in cocoa powder is given.

[2-Chloro-1-methylpyridinium iodide. A suitable reagent for peptide synthesis]

2-Chloro-1-methylpyridinium iodide is a coupling reagent for peptide synthesis. By its use different peptides were synthesized with protected di- and trifunctional amino acids. While urethan-protected amino acids react free of racemization, the fragment condensation needs N-Hydroxysuccinimide, as shown by the Young test.