418. Flavanones in Angophora lanceolata

Journal of the Chemical Society (Resumed)
1960.0

Abstract

The kino of Angophora lanceolata contains a small proportion of flavanones, among which (-)-farrerol (I; R = R' = H) and (±)-angophorol (I; R = H, R' = Me) have been recognised. Some Australian Myrtaceae (Angophora and Eucalyptus) kinos were previously examined and thought to contain aromadendrin based on colour reactions, but Eucalyptus maculata kino was shown to contain naringenin and aromadendrin 7-methyl ether. Due to interest in the biosynthesis of chromone derivatives, other kinos were examined. Angophora lanceolata kino, consisting chiefly of tannins, yielded a small proportion of ether-soluble material which was fractionated into lower fatty acid, crystalline (-)-farrerol (m.p. 212-220°C) and angophorol (m.p. 150°C), with their proportions varying by geographical source. (-)-Farrerol was identified via comparison with Arthur's sample, dimethyl ether preparation, and alkali-fusion products (4-hydroxycinnamic acid, 2,4-dimethylphloroglucinol) as (I; R = R' = H). (±)-Angophorol (C₁₈H₁₆O₅) was structurally determined via spectral data, alkali-fusion (3-hydroxybenzoic acid, 4-hydroxycinnamic acid), methylated product (methylmatteucinol), and partial synthesis from (-)-farrerol, confirming its structure as (I; R = H, R' = Me) and suggesting racemisation during extraction and purification. The presence of two methyl groups on the phloroglucinol ring reinforces the idea that methyl groups may be biosynthetically introduced into such substances at a stage distinct from ring formation.

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