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Computer Assisted Structure Elucidation of Two Biflavonoids from the Leaves of Ochna Mauritiana
EP26498
Poster Title: Computer Assisted Structure Elucidation of Two Biflavonoids from the Leaves of Ochna Mauritiana
Submitted on 02 Oct 2017
Author(s): G.A. Dziwornu1, N.R. Toorabally2, M.G Bhowon2, S. Jhaumeer-Laulloo2, S. Sunassee1,3, A. Moser4, D. Argyropoulos5
Affiliations: 1Chemistry Department, University of Cape Town, Rondebosch 7701, South Africa, 2Department of Chemistry, University of Mauritius, RĂ©duit, Mauritius, 3South African Medical Research Council Drug Discovery and Development Research Unit, University of Cape Town, Rondebosch 7701, South Africa, 4Advanced Chemistry Development, Inc., Toronto, ON, Canada, 5Advanced Chemistry Development UK Ltd., Bracknell, UK
This poster was presented at SMASH 2017 - Small Molecule NMR Conference
Poster Views: 558
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Poster Information
Abstract: As part of a phytochemical investigation of the leaves of O.mauritiana we have isolated, using a combination of silica gel flash chromatography and preparative layer chromatography (PLC), two biflavonoid compounds (1 and 2) from the organic extract of this plant. Approximately 12.5 mg of 1 and 2.5 mg of 2 were placed in NMR tubes and dissolved with DMSO-d6 in order to elucidate their structures. High-resolution mass spectra were also recorded in order to establish the molecular formulae.

Both compounds were relatively proton deficient resulting in few correlations in long range 2D NMR experiments. The repeated ring structure made some of the 13C peaks appear very close together, which also limited the usefulness of conventional 2D experiments (Fig. 1). Together with the presence of many exchangeable protons, the elucidation of the structures proved to be rather challenging. Here we describe the advanced computation method used for elucidating the structures using a series of 1D and 2D NMR experiments.

Initially, a search was performed on a database with predicted 13C spectra, or ca. 92 million compounds in search of a spectrum similar to the 13C spectra of 1 and 2. The spectrum of 1 matched that of a previously reported structure, while there was no match for the spectrum of 2.

Computer Assisted Structure Elucidation (CASE), together with band-selective versions of the HMBC experiment were employed to assign the NMR data and unequivocally determine the structures and thus confirming the molecules. Additionally, several closely related structures were ruled out either by poor agreement between predicted and experimental 13C chemical shifts, or by additional derivatization experiments.

Summary: Computer Assisted Structure Elucidation (CASE), together with band-selective versions of the HMBC experiment were employed to assign the NMR data and unequivocally determine the structures and thus confirming the molecules of biflavonoids extracted from the leaves of Ochna Mauritiana References: Neergheen, V.S. , et al. (2007). Pharm. Biol., 45: 9-17.
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De Oliveira, M.C.C., et al. (2002). J. Braz. Chem. Soc., 13: 119-123.
Likhitwitayawuid, K., et al. (2001). Phytochemistry, 56, 353-357.
Elyashberg, M.E. , et al. Prog. NMR Spectr. 2008, 53, 1-104.
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