BIOSYNTHESIS OF DIELS-ALDER TYPE ADDUCTS IN MORUS ALBA L. CELL CULTURES

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Callus and cell suspension cultures of high Diels-Alder type adducts productivity have been obtained through the selection of callus tissues induced from the seedlings or the leaves of Morus alba L. Experiments with [1-^<13>C]-, [2-^<13>]-, and [1,2-^<13>C_2]-acetates administered to the cell suspension induced from the leaves revealed that both optically active Diels-Alder type adducts chalcomoracin and kuwanon J, main components in the cell cultures, are formed through the condensation of two molecules of cinnamoy1-polkkeide-derived skeletons. In the ^<13>C-acetate labeled chalcomoracins, which is regarded as adduct of a dehydropreny1-2-arylbenzofuran derivative and a prenylchalcone derivative, the 2-arylbenzofuran skeleton is formed by a aldol type cyclization of the cinnamoylpolyketide, followed by decarboxylation, and the chalcone moiety is formed by a Claisen type cyclization of the precursor. The ^<13>C-labeling pattern in kuwanon J, which is regarded as a adduct of a dehydroprenylchalcone and a prenylchalcone, indicating the incorporation of three successive acetate units into the aromatic rings corroborates that kuwanon J is composed of two cinnamoylpolketide-derived chalcone skeletons, and that the possibility as a member of retrochalcone has been ruled out. On the other hand, in the ^<13>C-aceate labeled chalcomoracins, the [2-^<13> C]acetate was barely incorporated into the starter acetate carbons in the biosynthesis of the preny1 moieties, while the [1-^<13> C] acetate was not incorporated into the preny1 moieties. This may be due to the participation of the tricarboxylic acid (TCA) cycle. These labeling patterns clearly demonstrated that mixed biosynthesis of mulberry prenylchalcones from different origins. From the above results, the Diels-Alder type adducts, chalcomoracin and kuwanon J in the Morus alba cell cultures could be cycloaddition products of the , -double bond of the chalcone and the preny1 portion.