J.M. te Koppele

On the mechanism of the formation of s(−)-(1, 1'-binaphthalene)-2,2'-diol via copper(II)amine complexes

Abstract The oxidative dimerization of 2-naphthol is studied by means with several copper(II)amine complexes as oxidants. Using primary amines a chemical yield of 95%–98% is obtained. Using (+)amphetamine as complexing amine a 94%–96% optically pure product is obtained It is established that this stereoselectivity is a result of selective precipitation of the copper(II)-(+)amphetamine-(−)binaphthol complex with a simultaneous racemization of the (+)binaphthol

Enzyme kinetics and substrate selectivities of rat glutathione S-transferase isoenzymes towards a series of new 2-substituted 1-chloro-4-nitrobenzenes

1. Four different rat glutathione S-transferase (GST) isoenzymes, belonging to three different classes, were examined for their GSH conjugating capacity towards 11 2-substituted 1-chloro-4-nitrobenzene derivatives. Significant differences were found in their enzyme kinetic parameters Km, kcat and kcat/Km. 2. Substrates with bulky substituents on the ortho-position appeared to have high affinities (low Kms) for the active site of the GST-isoenzymes, suggesting that there is sufficient space in this area of the active site. A remarkably high Km (low affinity) was found for 2-chloro-5-nitropyridine towards all GST-isoenzymes examined. 3. GST 3-3 catalysed the reaction between GSH and the substrates most efficiently (high kcat) compared with the other GST-isoenzymes. Moreover, GST 3-3 showed clear substrate selectivities towards the substrates with a trifluoromethyl-, chlorine- and bromine-substituent. 1-Chloro-2,4-dinitrobenzene and 2-chloro-5-nitrobenzonitrile were most efficiently conjugated by all four GST-isoenzymes examined. 4. When the rate of the conjugation reactions was followed, a linear increase of formation of GS-conjugate could be seen for 2-chloro-5-nitrobenzonitrile during a much longer period of time than for 1-chloro-2,4-dinitrobenzene with all GST-isoenzymes examined. Therefore, it is suggested that 2-chloro-5-nitrobenzonitrile might be recommended as an alternative model substrate in GST-research.

Mutagenicity of halogenated and other substituted dinitrobenzenes in Salmonella typhimurium TA100 and derivatives deficient in glutathione (TA100/GSH−) and nitroreductase (TA100NR)

In a previous study, it was shown that 1-chloro-2,4-dinitrobenzene (CDNB) was less mutagenic in a glutathione (GSH)-deficient derivative of Salmonella typhimurium TA100 (TA100/GSH-) than in TA100 itself, suggesting that the mutagenicity of the compound is dependent on GSH, possibly mediated by the action of a bacterial nitroreductase(s) on the CDNB-GSH conjugate. In the present study a series of mutagenicity tests were performed to determine how CDNB could be activated after reaction with GSH. In liquid preincubation assays, strains TA100, TA100/GSH- and TA100NR, a nitroreductase-deficient derivative of TA100, were treated with CDNB and its fluoro and bromo analogues (FDNB and BDNB), further with its GSH conjugate (S-GSH-DNB) and possible metabolic products, such as S-cysteine-dinitrobenzene (S-Cys-DNB) and S-methyl-dinitrobenzene (S-methyl-DNB), and with 2 more analogues, O-methyl-dinitrobenzene (O-methyl-DNB) and dinitrobenzene (DNB). CDNB, FDNB and BDNB were found to be mutagenic in TA100 and TA100NR, while TA100/GSH- was much less sensitive to the mutagenic action of these halogenated dinitrobenzenes. DNB, O-methyl-DNB, S-methyl-DNB and S-Cys-DNB induced equal numbers of His+ revertants in TA100 and TA100/GSH-, but were not mutagenic in TA100NR. S-GSH-DNB showed no mutagenic activity in any of the 3 strains under the present experimental conditions. These results suggest that the halogenated aromatics may react with bacterial DNA and produce pre-mutagenic alterations according to 2 mechanisms: direct attack on the DNA through nucleophilic substitution (SN2) of the halogen atoms; activation through GSH conjugation and subsequent nitroreduction of the conjugate or its metabolic products to more reactive intermediates.

Synthesis of reduced collagen crosslinks

A new synthetic route to reduced collagen crosslinks (LNL and HLNL) is described in this report. It enables an enantioselective synthesis of LNL. HLNL was obtained as a mixture of two diastereoisomers. This method also provides the possibility to introduce radio-labels during the synthesis.

Pharmacokinetics and stereoselectivity of glutathione conjugation

Pharmacokinetics and stereoselectivity of glutathione conjugation S t u d i e s w i t h t h e m o d e l s u b s t r a t e s c z b r o m o i s o v a l e r y l u r e a a n d c~ -b romoi sova l e r i c a c i d J.M. te Koppele, Leiden: Leiden University, 11 May 1988. Promoter: Prof. Dr. G.J. Mulder (Leiden).