99 生合成におけるDiels-Alder反応の証明 : 植物毒素solanapyrone Aの生合成(ポスター発表の部)

概要

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Involvement of Diels-Alder reaction in biosynthesis of secondary metabolites has been proposed in many instances. However the presence of the enzyme responsible for this biological unusual reaction has never been proved. In order to examine this possibility, we choose a phytotoxin, solanapyrone A (1) whose skeleton was presumably constructed via intramolecular Diels-Alder reaction. Here, we describe results of successful incorporation of precursors (7a) and (7b) prior to [4+2]cycloaddition. The specification of precursor of [4+2]cycloaddition were made as follows. From the incorporation experiments of [S-CD_3]methionine and [^2H]-labeled 8 suggested that oxidations of methyl group at C-14 occurs prior to [4+2] cycloaddition. Since polyenepyrones such as citreomontanine (6) are frequently occurred in natural products, we speculate that formation of pyrone ring and introduction of two C1-units take place before cyclization and that trienes (5) and (7) must be actual intermediates. The deuterium labeled plausible precursors (7a) and (7b) of Diels-Alder reaction were synthesized and incorporated. In ^2H-NMR spectra of 1 and 2 obtained from feeding experiments, the signals originated from OCH_3 and CHO and/or CH_2OH were observed. These data clearly indicated that less oxidized precursor, triene (7) was oxidized to aldehyde (5) which was subsequently cyclized to give solanapyrone A (1).
天然有機化合物討論会の論文
1993-09-10