Specifically, in the PS-HSQC experiment presented, the resolution attainable in the direct dimension is not limited by the sample heating of X-decoupling during detection, but simply by the number of t2 increments. Thus spectra with large numbers of t2 increments, offering high resolution in F2, can be collected even under the action of broadband heteronuclear decoupling. An additional advantageous side-product of the BIRD(d) filter employed in the acquisition scheme presented is the efficient suppression of undesired long-range cross peaks

arising from strong coupling effects, as demonstrated in Fig. 6. The strong coupling artifacts, marked by asterisk (*) in the standard EX 527 nmr HSQC spectrum (Fig. 6a) and the corresponding carbon traces at F4, F5, are almost entirely suppressed in the PS-HSQC spectrum (Fig. 6b), yielding a high quality pure shift correlation map for further spectral analysis. Note that this beneficial purging feature Selleck Fluorouracil of the BIRD module has been utilized earlier in the standard HSQC experiment [33] and [34]. To compare the sensitivity and robustness of the present pure shift HSQC

experiment and the earlier method of Sakhaii et al. [24], HSQC spectra were recorded using the two pulse sequences with identical experimental parameters, but employing the same data acquisition scheme and processing, to ensure comparability. The signal intensities measured in the correlation spectra of Fig. 7 and illustrated by representative carbon traces at the right show that the sensitivity of the two experiments is comparable. Interestingly, the HSQC

spectra recorded with intentionally mismatched INEPT/BIRD delays corresponding to 1JXH = 100 Hz show significant dissimilarity in the appearance of artifacts. The purging and coherence selection gradient scheme employed in the broadband proton-decoupled HSQC sequence of Fig. 5 seem to suppress the effects of the proportion of magnetization that does not experience perfect rotation by the BIRD(d) module with high efficiency, yielding clean and artifact-free spectra even for a wide range of BIRD delays and hence for a wide range of one-bond coupling constants. As noted earlier, the basic Cyclooxygenase (COX) BIRD approach to broadband homonuclear decoupling is not able to suppress the effects of geminal couplings. Thus in Fig. 3 and Fig. 4 the F2 multiplets corresponding to CH2 groups with non-equivalent (diastereotopic) geminal protons are doublets of doublets, with both 1JCH and 2JHH splittings. Example traces extracted at carbon C7 for compound 2 in Fig. 3 also illustrate this characteristic multiplet structure of CH2 moieties. A method for the suppression of these undesired splittings will be the subject of a later publication.