Tryptanthrin(indolo[2,1-b]quinazoline-6,12-dione) Isolation from Leaves of Couroupita guianensis and Its Characterization by NMR Experimental and GIAO-DFT Data

摘要

3 showed a total of 15 carbon signals consistent with the proposed structure. The theoretical chemical shifts calculations were performed in 5 different levels of theory. Our results are in very good agreementwith empirical data. Moreover the mPW1PW91/6-31G(d)//mPW1PW91/6-31G(d) level of theory was superior to the B3LYP/6-311 + (2d,p)//B3LYP/6-31G(d) regarding calculation accuracy. Thus, we effectively isolated tryptanthrin from leaves of Couroupita guianensis. Furthermore the present findingsindicate that the current 13C NMR chemical shift calculation methodology was very adequate for support tryptanthrin NMR experimental data. The present findings indicate that the current 13C NMR chemical shift calculation methodology was very adequate for support tryptanthrinNMR experimental data. So, we consider that GIAO-mPW1PW91/6-31G(d)//mPW1PW91/6-31G(d) NMR chemical shifts scaling factors protocols 13C calculations are useful tools to help structural elucidation of natural products.]]>