Feedback regulation of β-thujaplicin production and formation of its methyl ether in a suspension culture of Cupressus lusitanica

Suspension cell cultures of Cupressus lusitanica produce β-thujaplicin, a tropolone found mostly in Cupressaceae heartwood. The factors controlling β-thujaplicin accumulation in this cell culture system were investigated. Initial cell density of the cultures did not affect β-thujaplicin levels, though initial addition of β-thujaplicin suppressed its de novo production. When β-thujaplicin accumulation reached a certain level (ca. 40 mg/l) in the medium, the cultures seemed to cease β-thujaplicin production. However, β-thujaplicin productivity was restored when the β-thujaplicin-containing medium was exchanged for fresh medium; the formation of 2-methoxy-6-(methylethyl)cyclohepta-2,4,6-trien-1-one, an isomer of methylated β-thujaplicin, in medium was also observed. These results suggest that β-thujaplicin synthesis was regulated by product feedback mechanism in this cell line, and that excess accumulation of β-thujaplicin is relieved by conversion of β-thujaplicin to its methyl ether.