Gated Decoupling 13C NMR Application to Determine Conformation and Unambiguous Chemical Shift of Arylidene Barbiturates

Chemical shift assignment and conformational structure of small molecules are fundamental for their study of interaction with biological targets, like proteins and nucleic acids. Chemical shift assignments are usually obtained with the very efficient nuclear magnetic resonance (NMR) methods COSY, HSQC, HMBC, TOCSY and NOESY. When these NMR methods do not afford all information or need the results confirmation to determine the complete molecular chemical shift assignment, it is necessary to use other procedures, especially for determination of long range H-1-C-13 coupling constants and C-13 multiplicity. In this work, it is demonstrated that Gated decoupling C-13 NMR spectrum, which is a simple and easy to use method, is very appropriate to complete the unambiguous chemical shift assignment and the conformational condition of arylidene barbiturates. The NMR conformational results were also confirmed by molecular modeling.