This thesis presents a new approach for the biotransformation of hydrophobic molecules using a membrane bioreactor for biotransformations (MBB) and polyimide organic solvent nanofiltration (OSN) membranes. The reaction occurs in the aqueous phase from which the product is in-situ extracted to the organic phase by diffusion through the membrane. Two model biotransformations were used to asymmetrically synthesise: R-citronellol by Saccharomices cerevisiae (Bio-I)'S-phenylethanol by Rhodotorula glutinis (Bio-II). The proposed reactor avoids the formation of emulsions and mitigates the solvent toxicity observed in direct contact biphasic (DCB) reactors, thus expanding the range of solvents that can be used in biotransformations. Additionally, the use of OSN membranes overcomes the problems of phase breakthrough and poor membrane organic solvent resistance, previously observed in microporous and non-porous MBBs, respectively.