Enzymatic, stereoselective synthesis of (S)-norcoclaurine.

An efficient, stereoselective, synthesis of (S)-norcoclaurine has been developed using the recombinant (S)-norcoclaurine synthase (NCS) enzyme, starting from tyrosine and dopamine substrates in a one-pot, two steps process1-3. The first step of the biotransformation consists in the oxidative decarboxylation of tyrosine (1) by stoichiometric amounts of sodium hypochlorite in order to generate 4-hydroxyphenylacetadehyde (2). In the second step NCS and dopamine (3) substrate are added in the reaction mix in the presence of ascorbate (necessary to prevent oxidation of the catechol moiety). Quantitative extraction of the newly formed (S)-norcoclaurine (4) from the aqueous solution was achieved by adsorption on active charcoal, dispersed in the reaction mixture. The optimized process afforded enantiomerically pure (S)-norcoclaurine (93 %) with a yield higher than 80% and allowed good recovery of the enzyme for recycling.