3'-Hydroxyacetaminophen, a catechol metabolite of N-acetyl-p-aminophenol (acetaminophen) and N-acetyl-m-aminophenol (a structural analogue of acetaminophen and considered as a possible alternative because it is not hepatotoxic), is enzymatically synthesized for the first time using mushroom tyrosinase. Although reported to be weakly hepatotoxic in vivo, this catechol derivative of acetaminophen is not commercially available. This compound was obtained from its monophenolic precursor, acetaminophen, using the enzyme tyrosinase in the presence of an excess of ascorbic acid, thus reducing back the o-quinone product of catalytic activity to the catechol acetaminophen derivative. A mathematical model of the system is proposed, which is also applicable to the tyrosinase-mediated synthesis of any o-diphenolic compound from its corresponding monophenol. This synthesis procedure is continuous, easy to perform and control, and adaptable to a bioreactor with the immobilized enzyme for industrial purposes in a nonpolluting way.
Short chain citronellyl esters were synthesized by a new microbial lipase from Rhizopus sp strain isolated and lipase produced at UNICAMP, Brazil. Direct esterification and transesterification reactions have been performed to produce citronellyl acetate and butyrate in a free-solvent system and with n-hexane in reaction medium. Reaction mixture for direct esterification and transesterification was carried out at 45ºC in equimolar concentration of substrates: acid or ester and alcohol. Only citronellyl butyrate was synthesized by direct esterification with yields from 95 to 100% after 24 hrs. of reaction time, with or without n-hexane. Citronellyl acetate was synthesized by transesterification with ethyl acetate and cytronellol, with yield of 58% after 48 hrs. and 48% of conversion for reaction butyl acetate and cytronellol. The results suggest that the size of the aliphatic chain from acyl donor was importance to conversion rate. Acids with more than two carbons showed to be better substrate for Rhizopus sp lipase. Transesterification reaction showed different behaviour, ester substrate with four carbons was better than six carbon for citronellyl acetate synthesis.
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