Enantiomeric Lignans and Neolignans from Phyllanthus glaucus: Enantioseparation and Their Absolute Configurations

Abstract

Eight pairs of enantiomeric neolignans, norlignans, and sesquineolignans (1a/1b–8a/8b), together with five known neolignans (9a/9b and 10–12), have been isolated from 70% acetone extract of the whole plants of Phyllanthus glaucus Wall. (Euphorbiaceae). The racemic or partial racemic mixtures were successfully separated by chiral HPLC using different types of chiral columns with various mobile phases. Their structures were elucidated on the basis of extensive spectroscopic data. The absolute configurations of 2a/2b were determined by computational analysis of their electronic circular dichroism (ECD) spectrum, and the absolute configurations of other isolates were ascertained by comparing their experimental ECD spectra and optical rotation values with those of structure-relevant compounds reported in literatures. Compounds 4a/4b featured unique sesquineolignan skeletons with a novel 7-4′-epoxy-8′-8′′/7′-2′′ scaffold, consisting of an aryltetrahydronaphthalene and a dihydrobenzofuran moiety. The planar structures of compounds 2, 3, 7, and 8 were documented previously; however, their absolute configurations were established for the first time in this study. The antioxidant activities of 1a/1b–8a/8b were evaluated using DPPH free radical scavenging assay, and the results demonstrated that compounds 1b and 3b showed potent DPPH radical scavenging activities with IC50 values of 5.987 ± 1.212 and 9.641 ± 0.865 μg/mL, respectively.

Chemical Constituents from Ethanoic Extracts of the Aerial Parts of Leea aequata L., a Traditional Folk Medicine of Myanmar

“…The absolute configurations of dihydrobenzofuran neolignans are usually determined by the signs of the band 1 L b (270–300 nm) or 1 L a (220–240 nm) in their ECD spectra. The positive signs of the 1 L b band in the ECD spectra predict the absolute configuration of 7,8- trans -3-methoxydihydrobenzofuran neolignans to be 7 S ,8 R [ 21 – 23 ]. The ECD spectrum of 1 showed a positive Cotton effect at 294 nm (Δ ε + 0.52).…”

Chemical Components and Biological Activities of the Genus Phyllanthus: A Review of the Recent Literature

“…Phenylpropanoids constitute the most prevalent class of compounds in the genus Phyllanthus . Thirty seven compounds ( Figure 1 , Table 1 ) were identified from P. glaucus [ 23 ], P. amarus [ 24 , 25 , 26 ], P. urinaria [ 24 ] and P. brasiliensis [ 27 ]. Among these compounds lignans such as neolignan, norlignan and sesquineolignan were the most prominent.…”

Lignans from Lepidium meyenii and Their Anti‐Inflammatory Activities

“…( Figure S12 ) In this way, the planar structure of 2 was assigned. The large coupling constant between H‐7 and H‐8 ( J 7,8 =7.5) indicates that the relationship between H‐7 and H‐8 is tran s [16] . Of note, chiral HPLC analysis indicates that compound 2 contains its enantiomers, corresponding to small value of optical rotation.…”