Abstract
Resolution of erythro-7-hydroxy-3′,5′-dimethoxy-3,4-methylenedioxy-8.4′-oxyneolign-8′-ene 1c was achieved by preparing the diastereomeric esters with (–)-(R)-α-methoxyphenylacetic acid. The correlation of its CD properties with the absolute configuration established a general CD method for the configurational assignment of erythro-8.4′-oxyneolignenes: positive Cotton effects of the two low-energy CD transitions derive from 7R,8S configuration while the negative ones from 7S,8R. This rule allows the configurational assignment of erythro-8.4′-oxyneolignenes with different aromatic substitution pattern by a CD measurement.
Highlights
The optical properties of these erythro-neolignenes were characterized by their optical rotation, these data can not be used for direct comparison if the substitution patterns of the aromatic rings are different or a glycoside residue is present
Effective enantiomeric separations of rac-erythro-8.4′-oxyneolign-8′-enes 1a–g with different aromatic substitution pattern were achieved on a Chiralcel OD column which allowed the LC/circular dichroism (CD) analysis of the enantiomers.[13]
The erythro-8.4′-oxyneolign-8′-ene 1c, isolated from the seeds of Myristica fragrans Houtt. by Forrest et al.,[18] was obtained in racemic form according to a known procedure.[6]
Summary
Within the great structural variety of neolignans, the 8.O.4′-type represents a small subgroup whose members were isolated exclusively from the plants of Myristicaceae species and studied for a wide range of biological activities such as antifungal,[1,2] antileukemic,[3] anti-leishmanial,[4] and antioxidant activity.[5,6] While the erythro and threo-isomers of 8.4′-oxyneolign-8′-enes were found to exhibit significantly different activities in pharmacological assays,[1,5,6] the differences in the activities of the enantiomers of the erythro or threo series have not been studied yet.The absolute configurations of erythro-8.4′-oxyneolign-8′-enes were determined by Horeau’s7,8 and Mosher’s8,9 methods or on the basis of the transition state of the asymmetric reduction if an enantioselective synthesis was achieved.[7,8] the optical properties of these erythro-neolignenes were characterized by their optical rotation, these data can not be used for direct comparison if the substitution patterns of the aromatic rings are different or a glycoside residue is present. The absolute configurations of erythro-8.4′-oxyneolign-8′-enes were determined by Horeau’s7,8 and Mosher’s8,9 methods or on the basis of the transition state of the asymmetric
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