Stilbene oxide hydration

The hydration of stilbene oxide also demonstrates unusual stereochemical characteristics [175][182][183]. Indeed, stilbene oxide exists as two /ranx-stilbene oxide enantiomers ((R,R) and (S,S)-10.121) and as the meso,... 

Fig. 10.28. The stereochemistry of enzymatic hydrolysis of stilbene oxide. The achiral (meso) r/.v-sli Ibene oxide (10.7) yields only one of the two enantiomers of IhreoA,2-diphcnylethane-1,2-diol (10.122). In contrast, the chiral trans-stilbene oxide (10.121) is hydrated exclusively to meso-l -diphenylethane-l -diol [182][183]. 

Resistance to hydration was elucidated with tricyclic model compounds that lack the side chain and, hence, pharmacological activity. In this context, a useful comparison has been made between two meso compounds, namely 5W-dibenz.oja, dIcycloheplene 10,11-oxide (10.130, X = CH2) and d.v-slilbcnc oxide (10.7) [195]. The former compound proved to be a very poor substrate for rabbit liver microsomal EH, with a Km value comparable to that of cis-stilbene oxide, but Emax ca. 100-fold lower. This indicates that the two compounds have a comparable affinity for the enzyme, but that nucleophilic attack in the catalytic step is much less efficient for dibcnzo[ // cycloheplcnc 10,11-oxide than for d.v-slilbcnc oxide. This implies that the former compound acts better as an inhibitor than as a substrate of microsomal EH. Furthermore, there was also a fundamental steric difference in the reaction course of the two substrates, since the predominant stereoisomer formed from dibenzo //]cyclohep(ene 10,11-oxide had the (I OS, 11. -configuration,... 

Acid-catalyzed hydration of a-methyl-lruTw-stilbene oxide W been reported by Tiffeneau and Levy,1 and more recently by Brewster, 49 to give a 1,2-diol whose structure likewise suggest ... 

Stilbenes that are used as fluorescent whitening agents are photolytically degraded by reactions involving cis-trans isomerization followed by hydration of the double bond, or oxidative fission of the double bond to yield aldehydes (Kramer et al. 1996). 

The metabolism of stilbenes has been studied in the rat and in vitro with rat liver microsomes. Aromatic ring hydroxylation and reduction of the double bond are known to occur (35, 36). The following sequence has been established (37) for the vitro metabolism of trans-stilbene epoxidation of the internal double bond, hydration of the epoxide to the diol which can be oxidized to the benzoin and this in turn can be oxidatively cleaved to give the benzoic acid. 

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