Diastereomeric Bis Research Articles

Stereoselective metabolism of the optical isomers of trans-1,2-dihydroxy-1,2-dihydrophenanthrene to bay-region diol epoxides by rat liver microsomes

Enantiomerically pure isomers of trans-1,2-dihydroxy-1,2-dihydrophenanthrene have been obtained by chromatographic separation of their diastereomeric bis esters with (−)-α-methoxy-α-trifluoromethylphenylacetic acid. Liver microsomes from control rats, as well as rats treated with phenobarbital or 3-methylcholanthrene, metabolize these dihydrodiols to a pair of diastereomerically related bay-region 1,2-diol-3,4-epoxides in which the benzylic hydroxyl group and the epoxide oxygen are either cis (isomer-1) or trans (isomer-2) to each other. In general, diol epoxide-1 was the major metabolite of the (+)-(1S,2S)-dihydrodiol, whereas diol epoxide-2 was the major metabolite of the (−)-(1R-2R)-dihydrodiol. The extent of this stereoselectivity is dependent on the source of the microsomes and is greatest for liver microsomes from 3-methylcholanthrene-treated rats; the ratio of diol epoxide-1 relative to diol epoxide-2 was 5.6 : 1 with the (+)-enantiomer as substrate and 1 : 5.5 with the (−)-enantiomer as substrate. For a given microsomal preparation, rates of metabolism were independent of the enantiomer composition of the substrate. Relative to microsomes from control animals, treatment of rats with 3-methylcholanthrene enhanced rates of metabolism by about 40%, whereas treatment with phenobarbital decreased rates to a similar extent when the amounts of metabolites formed per nanomole of cytochrome P−450 were compared. The failure of treatment by 3-methylcholanthrene to enhance markedly the rate of metabolism of a polycyclic aromatic hydrocarbon substrate is unusual.

Organometallic derivatives of the transition elements : II. Proton magnetic resonance spectra of substituted bis(arene)chromium(0) complexes

The proton magnetic resonance spectra of a series of bis(arene)chromium(0) complexes have been investigated. Simple first order spectra are obtained in most cases, for which chemical shift assignments are reported. A significant reduction in J(HH)-values, relative to the free ligand, are observed for the complexed arenes; HH coupling is limited to adjacent hydrogen atoms. In fluorobenzene complexes, HF coupling is so diminished as not to be observed in the majority of our spectra. Meta disubstituted arenes, in which the substituents are not identical, yield two diastereomeric bis(arene)chromium(0) complexes from the metal atom synthesis which can be distinguished on the basis of their PMR spectra.

Epimerization of the diastereomers of bis-(N-salicylidene-?-hydroxyalaninato)cobalt (III) under the action of bases and the thermodynamic stereoselectivity in these complexes

1. The diastereomers of bis-(N-salicylidene-α-hydroxyalaninato)-cobalt(III) undergo epimerization under the effect of bases. A mechanism has been proposed for this process. 2. The equilibrium relationships for the three diastereomers of bis-(N-salicylidene-α-hydroxyalaninato) cobalt(III) have been determined in water and acetonitrile. In both solvents the isomer containing ligands with opposite configurations is relatively unfavorable. This demonstrates the need to take into account the interaction between the distant asymmetric centers of the ligands.

Synthesis, separation, and some chemical properties of diastereomers of bis-(N-salicylidene-?-hydroxyalaninato)cobalt (III)

1. bis-(N-Salicylidene-α-hydroxyalaninato)cobalt (III) was synthesized by the oxidation of bis-(N-salicylidenealaninato)cobalt (III). Three possible diastereomers of this product were isolated. 2. Theα-hydroxy group of bis-(N-salicylidene-α-hydroxyalaninato)cobalt (III) undergoes exchange in dilute acid solutions, which leads to the epimerization of the diastereomers in water, and to a mixture of the diastereomers of bis-(N-salicylidene-α-ethoxyalaninato)cobalt (III) in ethanol. 3. It was shown that theoretically bis-(N-salicylidene-α-hydroxyalaninato)cobalt (III) can be synthesized by the reaction of pyruvate and salicylaldehyde with Co(OH)3 in the presence of excess ammonium salt.

Stereochemistry of the diastereomers of bis(oxalato)-N,N′-dimethyl-ethylenediaminecobaltate(III)

Stereochemistry of the diastereomers of bis(oxalato)-N,N′-dimethyl-ethylenediaminecobaltate(III)