Preparation and Metabolism of 2-(¹⁴C)-cis,trans-Xanthoxin

2-[14C]-cis, trans-xanthoxin (specific activity 0.26 μCi/μmol) has been synthesized from4-(1', 2'-epoxy-4'-hydroxy-2', 6',6'-trimethyl-l'-cyclohexyl)-trans-3-buten-2-one and methyl 2-[14C]-bromoacetate. When 2-[14C]-cis, trans-xanthoxin was fed to cut shoots of tomato and dwarf bean, it was converted within 8 h to (+)-abscisic acid in yields of 10.8 and 7.0 per cent respectively. Pea seeds and tomato fruits gave much smaller conversions. A second major metabolic product extracted from treated tomato and bean shoots was shown to be a metabolite of abscisic acid and has been tentatively identified as phaseic acid. These results, together with the earlier finding that xanthoxin is present in the extracts of many seedlings, suggest that xanthophylls and xanthoxin may be precursors in the biosynthesis of ( + )-abscisic acid