Scheme 38. Use of putrescine transaminase in alkaloid synthesis: (a) biocatalytic formation of cyclic imines 294 from linear diamines 293 and decarboxylative Mannich reaction with in situ generated β-ketoacids 296 affords racemic pyrrolidine and piperidine alkaloids 297. (b) 1-Pyrroline (294a) formed by transaminase catalysis reacts with two molecules of aldehyde 303 to give the 2,3-dihydroindolizinium alkaloid ficuseptine (304).