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The biosynthetic incorporation of [I -14C], [2-14C], and [6-14C]-~-glucose, sodum [I -14C] and [2-14C] -acetate, and sodium [I -laC]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-I, C-5, and C-6. Results show that formation by alteration of the oxidation level of glucose, with stereochernical amendment but retention of the integrity and congruence of the chain (as occurs in macrolide carbohydrates), could a t 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.FOR more than a century it has been known that the berries of the mountain ash, or rowan (Sorbus aucuparia L., family Rosaceae),2-5 contain a dextrorotatory hex-2-en-5-olide (parasorbic acid) .6-9 Its (5s)-configuration (I) has been established by degradation to (+)-(S)-hexane-1,5-diol lo and to (+)-(S)-3-hydroxybutyric acid.ll The structurally related (-)-massoia lactone l2 (11) from Cryptocarya massoia (family Lauraceae) is enantiomeric (R) at C-5 as shown by the 0.r.d. curves (see Figure ). Also enantiomeric is an unsaturated 8-lactone (111) recently isolated from Cryptocarya caloneuya (Scheff.) and shown to be the (+)-(Cis) form by degradation to (-)-malic acid.13 Kawain (IV) and methysticin (V) (Piperaceae) are (5R) according to c.d. information.14 The base-catalysed elmination reaction leading to cis-2,trans-4-[(22: 4E)] l5 sorbic acid has been studied: l6 more strongly basic conditions lead to stereomutation to the trarzs-2,trans-4[(2E : 4E)] f0rrn.l

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