Biosynthesis of aromatic isoprenoids. Part I. The role of 3-prenylquinolines and of platydesmine in the biosnthesis of the furuquinoline alkaloid, dictamnine

Abstract

Tracer feeding experiments show that quinoline-2,4-diol and 4-methoxy-2-quinolone are involved in the biosynthesis of the furoquinoline alkaloid, dictamnine (4) and of the hydroxyisopropyldihydrofuroquinoline alkaloid, platydesmine metho-salt (5) in Skimmia japonica Thunb., and that 4-hydroxy- and 4-methoxy-3-(3-methyl-[1-¹⁴C]but-2-enyl)-2-quinolone are incorporated specifically (3·6–4·8%) into the two alkaloids. Platydesmine (3) also is an efficient specific precursor of dictamnine (18·8% incorporation) in S. japonica, and trapping experiments indicate that it is a biosynthetic intermediate. There was no significant incorporation of dihydrodictamnine or of platydesmine metho-salt into dictamnine. The precursors were utilised to a small extent in the formation of 7,8-dimethoxydictamnine (skimmianine) in S. japonica, suggesting that aromatic hydroxylation can occur at a late stage of biosynthesis. A convenient preparation of 1-bromo-3-methyl[1-¹⁴C]but-2-ene is described.