Biosynthesis of parasorbic acid (hex-2-en-5-olide) by the rowan berry (Sorbus aucuparia L.)
The biosynthetic incorporation of [1-14C], [2-14C], and [6-14C]-D-glucose, sodum [1-14C] and [2-14C]-acetate, and sodium [1-14C]malonate into parasorbic acid has been studied by use of ripening rowanberries attached to the tree. The distribution of labelling in parasorbic acid has been investigated by extraction and counting of C-1, C-5, and C-6. Results show that formation by alteration of the oxidation level of glucose, with stereochemical amendment but retention of the integrity and congruence of the chain (as occurs in macrolide carbohydrates), could at most be a minor pathway. An acetate–malonate pathway is supported and there is evidence of ‘starter’ and ‘extender’ effects. Comment is made on the absolute configuration of certain related lactones.