The biotransformations of triphenyl phosphite and of triphenyl-, tri-n.-butyl-, diethylphenyl-, and ethylmethylphenyl-phosphines by the fungi Mortierella isabellina ATCC 42613, Helminthosporium species NRRL 4671, and Aspergillus foetidus ATCC 10254, have been examined. 2. The triaryl and tri-n.-butyl substrates underwent oxidation at phosphorus in low yield, a process attributed largely to auto-oxidation under the experimental conditions used. 3. The alkyl aryl phosphines were enzymically oxidized at phosphorus, but concurrent auto-oxidation also occurred. 4. Incubation of ethylmethylphenyl phosphine with M. isabellina gave the corresponding S(-) phosphine oxide in a 92% yield with an enantiomeric purity of 13%.
