Putrescine Transaminases for the Synthesis of Saturated Nitrogen Heterocycles from Polyamines

Putrescine transaminase (pATA; EC 2.6.1.82) catalyzes the transfer of an amino group from terminal diamine donor molecules to keto acid acceptors by using pyridoxal-5′-phosphate as a cofactor. The ygjG genes from Escherichia coli K12, Bacillus megaterium, and Bacillus mycoides were successfully cloned and expressed in E. coli BL21(DE3) cells. The three putrescine transaminases were all shown to prefer diaminoalkanes as substrates and thereby generated cyclic imines from the ω-amino aldehyde intermediates. The addition of a mild chemical reducing agent rapidly reduced the imine intermediate in situ to furnish a range of N-heterocycle products. We applied pATA in a biomimetic synthesis of 2,3-dihydro-1H-indolizinium-containing targets, notably the bioactive alkaloid ficuseptine.