NMR Spectra of Nitrobenzanthrones Obtained by Using Double-Pulsed Field-Gradient Spin Echo

Abstract

We have synthesized several nitrobenzanthrones (NBAs) and investigated their structures in solution using NMR spectroscopy. In our study, however, low solubility of NBAs in organic solvents always became a serious problem and led to NMR spectra with low signal-to-noise ratios. To solve this problem, we adopted a new method of conventional coherence transfer pathway selection using pulsed field-gradients. The double-pulsed field-gradient spin echo (DPFGSE) sequence was used for selecting natural-abundance carbon-13 isotopomers by using a bilinear rotation decoupling (BIRD) sequence and a so-called gradient-BIRD pulse for the excitation sculpting technique. We performed NMR measurements on 3,9-dinitro-7 H -benz[ d,e ]anthracene-7-one (compound 1), 3,9,11-trinitro-7 H -benz[ d,e ]anthracene-7-one (compound 2), and 2-nitro-7 H -benz[ d,e ]anthracene-7-one (compound 3) by this method and obtained spectra of high quality. Combining the results from phase-sensitive 2D NOESY, HOHAHA, and DPFGSE-HMQC, DPFGSE-HMQC TOCSY, and phase-sensitive FG-HMBC permitted us to complete NMR assignments. It was confirmed that the present method enables us to improve the sensitivity and to assign the NMR signal readily, even for compounds with low solubility.