Long range HETCOR

Using HMBC (or long-range HETCOR) and NOE difference spectra, connect the fragments that this procedure has created. 

NMR spectra were obtained using a Varian VXR-200 (200 MHz) spectrometer. In order to obtain unambiguous proton and carbon assignments, two different solvents (DMSO-d6 and CDCI3) and several different NMR experiments (DEPT, COSY, HETCOR and long-range HETCOR) were required. 

The carbon and DEPT (distortionless enhanced polarization transfer) spectra are shown in Figure 10. The HETCOR (heteronuclear two-dimensional proton-carbon correlation) spectrum is shown in Figure 11. The carbon assignments are listed in Table 5. Long-range HETCOR experiments were used to make the assignments for the thiophene carbons. 

A. Kumar, Bull. Magn. Reson., 10, 96-118 (1988). Long-range HETCOR... 

For APT, COSY and C/ H HETCOR experiments, standard pidses sequence were used. (9-11) For the long-range HETCOR experiment, J(C,C,H) was assumed to be 8 Hz. NOE Difference spectra (homonuclear decoupling experiments ) were recorded using the cyclenoe sequence. 1024 scans were recorded for each spectrum. 

C/ H chemkal sidft correlation eicperiment permits the assignment of the protonated carbons, while the non protonated carbons cormectivity is obUmed from the long-range HETCOR diagram. 

Identification of all directly bonded and long range heteronuclear pairs HETCOR, HMQC... 

In order to determine the structure and stereochemistry of compounds 36 and 37, standard H- HCOSY, H- C shift correlation (HETCOR), DEPT, and H NOE NMR experiments were performed. The 13C NMR spectrum of compound 36 is based on DEPT, HETCOR, and long-range H- C shift correlation experiments, which allowed the correct assignment of most of the carbon signals <1997MI328>. 

Proton-carbon HETCOR experiment has recently been done on a liquid crystal97 to observe long-range proton-carbon correlations. In this... 

This is the simple heteronuclear -X COSY (or HETCOR) pulse sequence adapted to long-range correlations simply by adjustment of the Ai and A2 delays. Small coupling constants rule out the use of broad-band proton decoupling during evolution time t by BIRD, and thus the correlation cross-peaks display the structure of proton multiplets, which reduces further the sensitivity of the experiment. 

More recently, reverse detection HETCOR (25) and long range, constant time HETCOR (26) methods have been successfully applied to the P assignment problem. Because of these methods, assignment of the P resonances of modest-size oligonucleotide duplexes is now quite feasible (19, 27). Thus the assignment problems that initially held back the use of P NMR have now been solved. 

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