Proposed biosynthetic pathway for rosmarinic acid in cell cultures of Coleus blumei Benth

A biosynthetic pathway for rosmarinic acid is proposed. This pathway is deduced from studies of the enzymes detectable in preparations from suspension cells of Coleus blumei. Phenylalanine is transformed to 4-coumaroyl-CoA by the enzymes of the general phenylpropanoid pathway: phenylalanine ammonia-lyase (EC 4.3.1.5), cinnamic acid 4-hydroxylase (EC 1.14.13.11) and hydroxycinnamic acid:CoA ligase (EC 6.2.1.12). Tyrosine is metabolized to 4-hydroxyphenyllactate by tyrosine aminotransferase (EC 2.6.1.5) and hydroxyphenylpyruvate reductase. The ester can be formed from 4-coumaroyl-CoA and 4-hydroxyphenyllactate by the catalytic activity of rosmarinic acid synthase with concomitant release of CoA. Microsomal hydroxylase activities introduce the hydroxyl groups at positions 3 and 3 of the aromatic rings of the ester 4-coumaroyl-4-hydroxyphenyllactate giving rise to rosmarinic acid.Abbreviations Caf-pHPL caffeoyl-4-hydroxyphenyllactate - DHPL 3,4-dihydroxyphenyllactic acid - pC-DHPL 4-coumaryl-3,4-dihydroxyphenyllactate - pC-pHPL 4-coumaryl-4-hydroxyphenyllactate - pHPL 4-hydroxyphenyllactic acid - RA rosmarinic acid The financial support of the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie is gratefully acknowledged.