Complete assignments in 1H and 13C NMR Spectra of uraphine and 6-oxocorumdephine using 2D NMR spectroscopy
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We reported earlier on the isolation from the aerial part of Delphinium uralense Nevski of the unreported norditerpene alkaloids uraphine (1) and 6-oxocorumdephine (2) [1, 2]. The structures of these alkaloids were determined based on PMR, 13C NMR, and IR spectroscopy and mass spectrometry in addition to a comparison with the corresponding literature data on closely related compounds.
We performed a series of DEPT, 2D COSY, 2D HSQC, 2D HMBC, and 2D NOESY experiments in order to assign more reliably resonances in the PMR and 13C NMR spectra.
The starting point for solving 2D spectra of 1 were resonances of methylenedioxy protons (δH 5.12, 5.09 ppm), which had cross peaks in the 2D HMBC spectrum with resonances of quaternary C atoms C-7/C-8. Of these C atoms, only one had a cross peak with proton H-14. This fact enabled the resonances of C-7 and C-8 to be differentiated.
KeywordsCross Peak Methoxyl Methylenedioxy Characteristic Triplet Principal Correlation
The work was supported financially by the Basic Research Program of the RAS Presidium No. 7, Federal Targeted Program “Scientific and Scientific-Pedagogical Departments of Innovation Russia” for 2009–2013 (State Contract No. 14.740.11.0367), and a grant of the RF President for support of leading scientific schools (No. NSh-7014.2012.3).