Baker’s yeast (Saccharomyces cerevisiae) mediated transformations of C-aryl-N-phenylnitrones Ananda S. Amarasekara, * Wendy Hernandez and Paul Bonham Department of Chemistry, Prairie View A&M University, Prairie View, TX 77446, USA Received 21 November 2005; accepted 8 May 2006 Available online 30 May 2006 Abstract—C-Aryl-N-phenylnitrones are transformed to a mixture of azoxybenzene and aryl aldehydes when treated with a mixture of Baker’s yeast and sucrose in pH = 6.0 phosphate buffer medium at 32 °C. Ó 2006 Elsevier Ltd. All rights reserved. Baker’s yeast (Saccharomyces cerevisiae) mediated enzy- matic transformations of organic compounds are well known reactions in organic chemistry. 1–6 The most widely studied of these is the Saccharomyces cerevisiae promoted enzymatic reduction of the carbonyl com- pounds 1 like keto esters and ketones. Advantages in these reactions are the production of essentially enantio- pure alcohols under mild and economical reaction conditions. Reactions of nitrogen containing functional groups 2–6 are relatively less explored, and a survey in the current literature showed that selective and efficient reduction of nitro groups, 2 nitroso groups 4 and deoxygenation of N-oxides 6 have been achieved by these Saccharomyces cerevisiae mediated enzymatic processes. Further it was found that two types of reaction conditions have been employed in the reduction of nitrogen containing func- tionalities. The first type 2a–d,3b,5,6a involved the reactions carried out at room temperature or 25–32 °C range and in the pH 5.5–6.0 buffered medium, with or without an added sugar such as glucose or sucrose. The second type of reaction conditions 2e,f,3a,6b involved the reactions car- ried out at 70–80 °C or sometimes under reflux condi- tions and in the presence of a high concentration of sodium hydroxide in the medium with pH >12. Presum- ably different mechanisms are operating under these two different reaction conditions and the yeast is unlikely to be stable at high pH and temperature used in the type II conditions. Aromatic nitroso compounds 4 containing halogens and other labile substituents are known to reduce selectively to their corresponding amines under neutral conditions at 80 °C. On the other hand nitro aromatics 2e could be efficiently reduced to amines only in the strongly basic conditions employing aqueous sodium hydroxide medium and at temperatures in the range of 70–80 °C. Aromatic and heteroaromatic N-oxides 6 have been deoxygenated using the same type II conditions. Our interest 7 in the synthesis and chemistry of the nitrone functional group have revealed that there are no reports of any Saccharomyces cerevisiae promoted enzymatic transformations of the nitrone function. Nitrones are known for their properties as free radical scavengers as they can form stable free radicals in combining with hydroxyl and other radicals, and there are attempts to explore this radical trapping ability to develop nitrone based pharmaceuticals 8 as well. During these metabolic studies, 9 it has been reported that phenyl t butylnitrone hydrolyzes to a mixture of benzaldehyde and t butylhydr- oxylamine when incubated with human epithelial fibroblasts cells and t butylhydroxyl amine further oxidizes to t butyl nitroxide as well. We have under taken to study the possible enzymatic transformations of C-aryl-N-phenylnitrones, when trea- ted with Baker’s yeast–sucrose mixture in the pH = 6.0 phosphate buffer medium at room temperature. These nearly neutral conditions were chosen for the study, as nitrones are known 10 to hydrolyze to hydroxylamines and aldehydes in strongly acidic or basic conditions. 0040-4039/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.tetlet.2006.05.035 Keywords: Baker’s yeast (Saccharomyces cerevisiae); C,N-Diarylnitrones; Azoxybenzene. * Corresponding author. Tel.: +1 936 857 2616; fax: +1 936 857 2095; e-mail: asamarasekara@pvamu.edu Tetrahedron Letters 47 (2006) 4893–4895