Document Type : Original Article
Authors
1
Department of Natural Compounds Chemistry, National Research Centre, 33 El-Bohouth St., Dokki, Giza 12622, Egypt
2
Chemistry of Medicinal Plants Department, National Research Centre, 33 El-Bohouth St., Dokki, Giza 12622, Egypt
Abstract
Eight stereoisomers of the lignan type were produced from the gum resin of Commiphora myrrha in this investigation and their characterisation is provided. These stereoisomers are (+)-epi-excelsin (1), (+)-5′-demethoxyepiexcelsin (2), (+)-epi-methoxypiperitol (3), (+)-epi-syringaresinol (4), (+)-methoxypiperitol (5), (+)-piperitol (6), (+)-syringaresinol (7) and (+)-dia-syringaresinol (8). The isolated and recognised secondary metabolites exhibited a wide range of structural features, including lignans. Correlations between the 1H and 13C NMR spectra of 7,7'-diaryl-7,9':7',9-dioxabicyclo[3.3.0]octane and those of other recognised lignans can be used to predict the arrangement in an unsymmetric (1-4) and symmetrical (5-8) substitution. We use techniques including 1H-1H COSY, HMQC, HMBC, and NOESY to characterise the 1H and 13C NMR spectra of three lignans: (+)-epi-excelsin (1), (+)-5′-demethoxyepiexcelsin (2) and (+)-epi-syringaresinol (4). We also propose updated structural NMR data for (+)-5′-demethoxyepiexcelsin (2) and (+)-epi-syringaresinol (4). To the best of our knowledge, (+)-epi-excelsin (1) its 13C NMR assignment has never been published with its absolute configuration through CD spectrum. They were isolated from the genus Commiphora (1–8) for the first time. With IC50 values of 27.6, 29.5, and 31.8 M, respectively, compounds 1, 2, and 4 showed tremendous inhibitory action against NO release, but compounds 3, 5, and 8 had weak activity > 50 M.
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