Selective One-Dimensional Analogs of HMBC - SIMBA

Berger (1989) anticipated the solution to the problem of needing experimental access to selective heteronuclear shift connectivities with the development of a selective ID analog of the HMQC experiment to which he gave the acronym SELINCOR. Simply, SELINCOR replaces the final 90° carbon pulse of the HMQC experiment (see Fig. 1) with a selective Gaussian 90° pulse applied to the C resonance of interest. SELINCOR has had no practical applications but was certainly of interest in a developmental sense. 

The initial demonstration of the SIMBA experiment utilized the simple alkaloid norharmane (5) as a model compound. Comparison spectra showing 

As noted above, one implicit impediment to the utilization of SIMBA is the requirement of an accurate chemical shift for the resonance to be pulsed selectively. The problem is exacerbated rather than ameliorated when Gaussian 270° pulses are employed. The need for an accurate chemical shift is circumvented by utilizing the recently reported E-BURP-2 pulse of Geen and Freeman (1991) for the final 90° pulse of the SIMBA experiment. Since the E-BURP-2 pulse gives uniform phase and excitation across a relatively wide bandwidth, in contrast to the Gaussian 270° pulse which provides uniform phase and excitation across only a relative narrow 

The application of SIMBA to cryptospirolepine (1) highlights another very important usage of selective one-dimensional experiments. While it 

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