The present invention provides novel methods for the synthesis of racemic and enantiomers of modafinil via microbial oxidation-amidation transformation. The methods include the successive oxidation-amidation of benzhydrylsulfanyl carboxylic acid to produce racemic and enantiomers of modafinil using at least one microorganism of yeast, bacteria, or fungus. Also disclosed are pharmaceutical compositions of racemic and enantiomers of modafinil along with their use in the treatment of diseases, including attention deficit hyperactivity disorder and drug addiction.