4- Hydroxy-mercuri-benzoate

Thiols at a concentration of 10 to 40 mM also act as antagonists to the action of neuropeptides on rat uterus, but not to their pressor effect Such a difference could be due to a difference in the receptors. Thioglycollate (10 mM) and cysteine (10 mM) inhibit the permeability response of the toad bladder to oxytocin or vasopressin. Gluthathione has a similar effect These actions of the peptides are also inhibited after incubation of the tissues in the presence of either N-ethyl- or N-phenylaleimide which form covalent bonds with sulphydryl groups or complex mercury mercaptides (p-hydroxy-mercury-benzoate, p-chloro-mercury-benzoate). These results show that the receptor presents in its constitution some functional sulphydryl groups. 

Reduction of 2-bromo-3-pentanone at mercury affords a mixture of 3-pentanone and l-hydroxy-3-pentanone, whereas electrolysis of Q ,Q -dibromoacetone in the presence of benzoate gives a mixture of products arising from both a carbon-bromine bond cleavage and an Sn2 displacement of bromide by benzoate [94]. In an acetic acid-acetate buffer, branched dibromo ketones, such as 2,4-dibromo-2,4-dimethyl-3-pentanone, are reduced to a-acetoxy ketones however, less highly substituted compounds, such as 4,6-dibromo-5-nonanone, undergo simple cleavage of both carbon-bromine bonds [95]. Other work dealing with the reduction of Q, Q -dibromoketones has been described [96]. 

The hydroxy-group of cholesterol is protected either as the acetate or benzoate. Bromination in the allylic position by Karl Zieglers method using N-hro-mosuccinimide or l,3-dibromo-5,5-dimethylhydantoin, then dehydrobromina-tion with 2,4,6-collidine and hydrolysis gives 7-dehydrocholesterol. Photolysis of 7-dehydrocholesterol and ergosterol, respectively, with a mercury vapour lamp in an inert solvent (e.g. peroxide-free diethyl ether, methanol, cyclohexane... 

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