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K Heyns

Publications and source records attributed to K Heyns.

18 recordsLinked to original sources
PubMed1978

Possible nitrosodimethylamine formation in comparative in vitro nitrosation experiments with six different tetracycline antibiotics.

The hydrochlorides of tetracycline, minocycline, chlorotetracycline, anhydrochlorotetracycline, desmethylchlorotetracycline, oxytetracycline and doxycycline were reacted with sodium nitrite for two hours at 37 degrees C in aqueous buffer solutions at pH 2 and 4 under simulated stomach conditions. NDMA formation was detected from minocycline, doxycycline, oxytetracycline and anhydrochlorotetracycline by GLC and GLC-MS analysis. NDMA formation from minocycline and dodxycycline was blocked by ascorbic acid. The catalytic effect of sodium thiocyanate for NDMA formation from minocycline and nitrite was investigated. The different reactivities of the tested tetracyclines towards nitrite in acidic solutions (NDMA formation from minocycline, doxycycline, oxytetracycline and no NDMA formation from tetracycline, chlorotetracycline and desmethylchlorotetracycline) may be understood from stereochemical considerations. The failure of dealkylative nitrosation reactions in the latter tetracyclines is explained by the formation of intramolecular hydrogen bridge linkages between epidimethylamino groups at C-4 and OH groups at C-6. This hypothesis was proved by the observations of NDMA formation from anhydrochlortetracycline and sodium nitrite at pH 2.

Ascorbic Acid↗
PubMed1976

Mass spectrometry of nitrosamines: rearrangement of nitrosobenzylmethylamine molecular ions with loss of OH-radicals investigated by deuterated derivatives.

Nitrosamines (R1R2NO) containing a certain R groups yield mass spectra with M+-OH fragments which can be accounted for by intramolecular hydrogen shift with subsequent cleavage of OH-radicals. As can be shown with mass spectra of specifically deuterated derivatives of nitrosobenzylmethylamine - nitrosobenzyltrideuteriomethylamine, alpha,alpha-nitrosodideuteriobenzylmethylamine and o,o',p-nitrosotrideuteri0-benzylmethylamine - hydrogen transfer within the molecular ion of nitrosobenzylmethylamine occurs selectively onto the oxygen of the nitroso group from the benzylethylene group, probably via a five-membered cyclic transition state. Cleavage of OH radicals leads to formation of M+-17 ions, the stability of which can be explained by mesomerically stabilized cyclic diazirinium ions.

Chemical Phenomena↗
PubMedDate not supplied

[On the problem of dimethylnitrosamine formation from tetracycline-derivatives by nitrosation reaction in acidic medium (author's transl)].

The hydrochlorides from tetracycline and six tetracycline derivatives -- 7-dimethylamino-6-des-methyl-6-desoxytetracycline [minocycline], 7-chlorotetracycline [chlorotetracycline], 7-chloro-anhydrotetracycline [anhydrochlorotetracycline, 7-chloro-6-desmethyltetracycline [demethylchlorotetracycline], 5-hydroxytetracycline [oxytetracycline] and 6-desoxy-5-hydroxytetracycline [doxycycline] -- were reacted with different amounts of sodium nitrite at 37 degrees C for two hours in aqueous buffer solutions at pH 2 and 4. Dimethylnitrosamine formation was confirmed by gas-liquid chromatography and by combined gas-liquid chromatography/mass-spectrometry from minocycline, doxycycline, oxytetracycline and anhydrochlorotetracycline. Dimethylnitrosamine formation from minocycline and doxycycline was blocked by ascorbic acid. The catalytic effect of sodium thiocyanate for the dimethylnitrosamine formation from minocycline and nitrite was investigated. The different reactivity of the investigated tetracycline derivatives towards nitrite in acidic solutions is discussed by stereochemical considerations in connection with the formation of hydrogen bridge linkages. This hypothesis was confirmed by dimethylnitrosamine formation from anhydrochlorotetracycline and sodium nitrite at pH 2.

Ascorbic Acid↗