Stereochemical assignment of prolycopene and other poly-Z-isomeric carotenoids in fruits of the tangerine tomato Lycopersicon esculentum var. ‘Tangella’

Abstract

The acyclic carotenoid pigments phytoene, phytofluene, ζ-carotene, neurosporene, and lycopene found in fruits of the Tangerine tomato Lycopersicon esculentum var. ‘ Tangella ’, were separated by chromatography and characterised. Spectroscopic data and comparison with synthetic model compounds established that the pigments have the stereochemistries 15Z-(1), 15Z,9′Z-(2), 9Z,9′Z-(3),9Z, 7′Z, 9′Z-(4), and 7Z, 9Z, 7′Z, 9′Z-(5) respectively; the remaining double bonds in the pigments have the E-geometry.

The data suggest that phytoene (1), rather than the widely accepted ζ-carotene (3), is the clear branch point for poly-Z-carotene formation in the Tangerine tomato. In addition, the data established that: (a) during the desaturation of phytoene (1) to phytofluene (2) in the Tangerine tomato, at the same time as the 11′E-double bond is introduced, the 9′-double bond undergoes specific E-to-Z isomerisation, (b) as the E-disubstituted double bond at C-11 is introduced during the formation of ζ-carotene (3) from phytofluene (2), the double bonds at C-15 and C-9 in the phytofluene undergo Z-to-E and E-to-Z isomerisation, respectively, and (c) during the biosynthesis of prolycopene (5) from ζ-carotene (3)via proneurosporene (4) in the Tangerine tomato fruit, the C-7 and C-7′ double are bonds are each introduced specifically with Z-geometry.