Abstract
The preparation of 7R-HMR (allo-hydroxymatairesinol) is reported by: (a) NaBH4 kinetic reduction of 7R/7S diastereomeric mixture; and (b) epimerization of the C7 hydroxyl group by Mitsunobu reaction and subsequent ester hydrolysis. The availability of highly pure target compound (7R-HMR) made it possible to confirm the structure of the target compound and to complete the full spectroscopic characterization.
Highlights
Lignans are a large group of low molecular weight polyphenols, derived by oxidative coupling of monolignols
Its presence in cereals was not detected in previous studies because of inadequate analytical methods using either acidic or alkaline treatment steps where 7S-HMR is converted primarily to conidendrin or conidendric acids, respectively [3]
Two approaches to the obtainment of pure 7R-HMR are presented: the first is an enrichment of 7R-HMR taking advantage of the different kinetic of reduction of the two diastereomers, while the second is an epimerization of the hydroxylic group in the two diastereomers, while the second is an epimerization of the hydroxylic group in position C7, de facto converting 7S-HMR into 7R-HMR by Mitsunobu reaction
Summary
Lignans are a large group of low molecular weight polyphenols, derived by oxidative coupling of monolignols They are plant secondary products and present many different biological activities including anticancer, antioxidant, antimicrobial, anti-inflammatory, and immunosuppressive [1]. Norway spruce (Picea abies) branch stubs (or knots) have been shown to be extremely rich in them [3] They contain on average about 10% by weight of lignans of which (−)-7Shydroxymatairesinol (7S-HMR) makes up 70–85% [4]. Two approaches to the obtainment of pure 7R-HMR are presented: the first is an enrichment of 7R-HMR taking advantage of the different kinetic of reduction of the two diastereomers, while the second is an epimerization of the hydroxylic group in the two diastereomers, while the second is an epimerization of the hydroxylic group in position C7, de facto converting 7S-HMR into 7R-HMR by Mitsunobu reaction.
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