Hydrochloric Acid → 6,8-Bisbenzoylmercaptooctanoic benzoic anhydride

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Reaction Steps

In overview, 6,8-Bisbenzoylmercaptooctanoic acid was prepared by a three step procedure from commercially available α-lipoic acid. The lipoic acid was first reduced to 6,8-bismercaptooctanoic acid with sodium borohydride in water under slightly alkaline conditions. The product was benzoylated with three equivalents of benzoyl chloride in the presence of triethylamine to scavenge the HCl byproduct to produce 6,8-bisbenzoylmercaptooctanoic benzoic anhydride. The anhydride was selectively hydrolyzed with dioxane/water to produce 6,8-bisbenzoylmercaptooctanoic acid without any undesired hydrolysis of the benzoylthio ester groups. The product was purified by column chromatography on Silica Gel. The purified acid was dissolved in methanol and converted to the sodium salt by the slow addition of an aqueous solution containing one mole equivalent of sodium bicarbonate.

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