A series of para-substituted alkyl aryl sulphides has been transformed stereoselectively to the sulphoxide by incubation with the fungus Mortierella isabellina. The enantiorneric purity of the products was dependent on the nature of substitution in the aromatic ring and at sulphur. Comparisons of the enantiomeric purities obtained from sulphides with para substituents of the same steric size but different electronic properties indicate that the stereoselectivity of S oxidation is susceptible to electron withdrawing or donating factors. This conclusion lends credence to a stepwise oxidation mechanism involving an electron deficient sulphur intermediate. 18 (1985).Par incubation avec des champignons Mortierella isabellina, on a transform6 stCrCosClectivement en sulfoxydes une sCrie de sulfures d'alkyles et d'aryles substituCs en para. La puretC CnantiomCrique des produits dCpend de la nature des substituants sur le noyau aromatique et au niveau du soufre. En se basant sur une comparaison des puretCs CnantiomCriques obtenues avec des sulfures portant des substituants en para qui ont des encombrernents stCriques sernblables rnais des propriCtCs Clectroniques differentes, on peut dCduire que la stCrCosClectivitC de l'oxydation du soufre est susceptible aux factuers Clectro-affinitaires ou Clectro-donneurs des substituants. Cette conclusion supporte le concept d'un mCcanisme par Ctape irnpliquant un intermediaire sulfur6 dkficient en Clectrons.[Traduit par le journal]In spite of the continued interest in chiral sulphoxides, both in the study of sulphur stereochemistry (1) and as intermediates in asymmetric synthesis (2), the best direct chemical methods for their generation from sulphides (3) have not yet achieved the high degree of enantiomeric purity desirable in modem asymmetric synthesis. High enantiomeric excesses (>35%) are routinely available for p-tolyl alkyl sulphoxides (only) by a modification (4) of the Anderson synthesis (5) using sulfinate esters, or by the use of biological oxidizing agents employing sulphides as substrates.In the latter area, the use of actively growing or resting cultures of fungi has been the most widely used technique for the production of sulphoxides of good optical purity (6-8).Other methods of biotransformation, using enzymes of mammalian origin (9,lO) or peroxide oxidation in the presence of enzyme templates (1 l), are not generally applicable to preparative scale work.In an extension of our earlier work on the mechanism of alkyl aryl sulphide oxidation by the fungus Mortierella isabellina (12), in which we proposed that cytochrome P-450 dependent mono-oxygenase enzymes of the fungus were responsible for oxidation at sulphur, we have now studied the effects of substitution at the para position of the aromatic ring, and at sulphur, on the degree of enantiomeric enrichment of the resultant sulphoxide. The sulphides used in this study, 1 and 4, gave the corresponding sulphoxides, 2 and 5, respectively, as major products on incubation with M. isabellina; this is summarized in Table ...

. Can. J. Chem. 65, 502 (1987). The fungus Mortierella isabellina can convert ethylbenzene and a number of para-substituted derivatives to the corresponding optically active I -phenylethanols with enantiomeric excesses between 5 and 40% and chemical yields up to 45%. 2-Ethylnaphthalene, 2-ethylthiophene, and n-propylbenzene were similarly converted, as were the bicyclic compounds indane and tetralin. In most cases, the R absolute configuration of product predominated. The fungi Cunninghamella echinulata var. elegans and Helminthosporium species are also capable of performing some of these transformations. M. isabellina and C. elegans also produce 2-phenylethanols as products in some cases. The highest enantiomeric excesses during benzylic hydroxylation were obtained with Helminthosporium and are attributable, at least in part, to further stereoselective oxidation of the alcohol. Cross induction experiments with M. isabellina indicate that the same enzyme may be responsible for the benzylic hydroxylation of ethylbenzene, 2-ethylthiophene, and 2-ethylnaphthalene.

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