Biosynthesis of tylophorine and tylophorinine

Abstract

Administration of 3,4-dihydroxyphenyl[2-¹⁴C] alanine to young Tylophora asthmatica plants revealed that ring B and carbon atoms C₉ and C₇ of tylophorine and tylophorinine are derived from dopa. Tracer experiments with 6,7-diphenylhexahydroindolizines (1-7) and (26) demonstrated that compound 1 is efficiently and specifically incorporated into tylophorine (13) and tylophorinine (16). Compounds (3), (4) and (26) were not metabolized by the plants to form (13) and (16) whereas (5) and (6) were utilized to yield (13) and (16). Compound (2) was very poorly converted into (13) and (16) and thus is not on the major biosynthetic pathway of (13) and (16).