Abstract
A complete and unambiguous assignment of 1H and 13C nuclear magnetic resonance (NMR) signals of 29 naphthoquinones is reported on the basis of one- and two-dimensional NMR techniques (1H, 13C, 1H-1H correlated spectroscopy (COSY) and 1H-13C heteronuclear multiple-bond correlation (HMBC)). This is the first report distinguishing data between para-naphthoquinones, ortho- and para-furanonaphthoquinones isomers.
Highlights
Quinones are conjugated cyclic diones oxidatively derived from aromatic compounds
Signals assignments were based on chemical shifts (d, ppm) of 1H and 13C, on the multiplicity patterns of proton resonances depicted by the J couplings (Hz), and on data of homonuclear 1H-1H COSY and heteronuclear
The nuclear magnetic resonance (NMR) experiments and the signals assignments were made for all compounds (1, 4a-h, 5a-h and 6a-h), and the naphthoquinones 4d, 5d and 6d were focused for illustrating the 1H and 13C assignments
Summary
Quinones are conjugated cyclic diones oxidatively derived from aromatic compounds. Natural quinones are widespread as plant and microorganisms secondary metabolites disclosing several biological effects such as antitumor, trypanocidal, anti-inflamatory, antifungal and leishmanicidal.[1,2,3,4,5,6,7] Lapachol (1, Figure 1), a hydroxy prenylnaphthoquinone, was first isolated from Tabebuia avellanedae, in 1882, by Paternó.[8]. The furanonaphthoquinones (FNQs) were highlighted as interesting new hits of interest for antimalarial drug development.[17] Spectral analysis of this naphthoquinones were explored aiming to distinguish between the three structural classes: NQs, ortho- and para-FNQs as well as the distinction between the two groups of isomeric furanonaphthoquinones. The 1H spectra were acquired using the spectrometer frequency of 400 MHz, spectrum resolution of 0.12 Hz, zg 30 pulse program with ns 16, d1 1s, acquisition time 4.0894465 s and spectral width 20.0264 ppm. The 13C spectra were acquired using the spectrometer frequency of 100 MHz, spectrum resolution of 0.73 Hz, zgpg 30 pulse program with ns 1024, d1 2s, acquisition time 0.6815744 s and spectral width 238.9086 ppm. The 1H-1H COSY contour maps were obtained with a 2 s relaxation delay, acquisition time 0.1024000 s and spectral width 24.9930 ppm. The 1H-13C HMBC contour maps were recorded with a 1.5 s relaxation delay in a 24.9930 ppm spectral width in F2 and 260.0000 ppm in F1 and acquisition time 0.1024000 s (F2) and 0.0048928 s (F1)
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