CRAPT: an improved version of APT with compensation for variations in JCH.

A modified version of the attached proton test (APT) sequence for C-13 spectral editing, which we call CRisis-APT (CRAPT), is developed and tested on representative organic compounds. CRAPT incorporates C-13 compensation for refocusing inefficiency with synchronized inversion sweeps (CRISIS) pulses in combination with H-1 broadband inversion pulses to give improved compensation for variations in (1)J(CH) along with improved refocusing efficiency. It is shown that CRAPT gives edited C-13 spectra with only small losses in sensitivity (between 8% and 15% for strychnine, 1, menthol, 2, cholecalciferol, 3, and isotachysterol, 4), compared with basic C-13 spectra obtained on the same compounds. CRAPT also gives significantly better signal/noise than DEPTQ for nonprotonated carbons. Therefore, we conclude that CRAPT is an improvement over APT or DEPTQ or a combination of DEPT135 with a full C-13 spectrum for routine C-13 spectral editing of organic compounds. Copyright (c) 2014 John Wiley & Sons, Ltd.