An enzymatic, stereoselective synthesis of (S)-norcoclaurine

Abstract

An efficient, stereoselective, green synthesis of (S)-norcoclaurine (higenamine) has been developed using the recombinant (S)-norcoclaurine synthase (NCS) enzyme, starting from the cheap tyrosine and dopamine substrates in a one-pot, two step process. Key steps in the biotransformation consist of the oxidative decarboxylation of tyrosine by stoichiometric amounts of sodium hypochlorite in order to generate 4-hydroxyphenylacetadehyde, followed by the addition of enzyme and dopamine substrate in the presence of ascorbate, a necessary ingredient in order to avoid oxidation of the catechol moiety. Quantitative extraction of the product from an aqueous solution was achieved by adsorption onto active charcoal dispersed in the reaction mixture. The optimized process afforded enantiomerically pure (S)-norcoclaurine (93%) in a yield higher than 80% and allowed good recovery of the enzyme for recycling. The process thus developed represents the first example of a green Pictet-Spengler synthesis, which may pave the way to novel strategies in benzylisoquinoline alkaloid synthesis

Enzyme catalysed Pictet-Spengler formation of chiral 1,1’-disubstituted- and spiro-tetrahydroisoquinolines

“…The plant enzymes have a central role in engineered microbial systems for the production of alkaloids1819202122. Furthermore, the wide substrate promiscuity of these enzymes has led to their use in biocatalytic syntheses, but the carbonyl substrates employed have always been aldehydes23242526272829303132. The only example of a Pictet–Spenglerase accepting non-aldehyde carbonyl substrates was the report of a norcoclaurine synthase (NCS) from Coptis japonica ( Cj NCS2, also known as Cj PR10A) turning over 4-hydroxyphenylpyruvate and pyruvic acid, activated α-keto acids10.…”

Genes encoding norcoclaurine synthase occur as tandem fusions in the Papaveraceae

“…The stereoselective activity of NCS has prompted applications of the enzyme in both in vitro biocatalysis151617 and in vivo metabolic engineering for the purpose of synthesizing high-value BIAs18192021222324. However, measured kinetic parameters for NCS suggest an enzyme that is catalytically inefficient67142526.…”

Asymmetric synthesis of tetrahydroisoquinolines by enzymatic Pictet–Spengler reaction

“…3,4) TfNCS was shown to recognize phenylacetaldehydes that are substituted with various electron-withdrawing or donating groups, heteroaromatic moieties, aromatic bicyclics, aliphatic cycles, and aliphatic open-chained compounds. In that study, however, the stereoselectivity of the reactions was not established, for example, enantiomeric excess was not determined (note that the Pictet-Spengler reaction occurs spontaneously in aqueous solution).…”