Long-range COSY coupling

CH COLOC Correlation via long-range CH coupling, detects CH connectivities through two or three (more in a few cases) bonds in the CH COSY format, permits localisation of carbon nuclei two or three bonds apart from an individual proton... 

The exocyclic olefinic methylene protons show obvious COSY correlations to one another. In addition, we note weak cross peaks between the olefinic protons at 4.86 and 4.97 ppm and an apparent diastereotopic methylene group (2.11 and 2.37 ppm) and a quartet at 2.60 ppm, respectively. These interactions are reminiscent of the long-range allylic coupling that we saw in ipsenol we could assign these correlations to the diastereotopic methylene C-7 and the methine at C-9. For now, we will be cautious and conservative, and return to this point later in the chapter. 

Luy et al. have described a sensitive X-filtered-E.COSY-type method that measures both the sign and magnitude of long-range dipolar couplings... 

Figure 5.55. The delayed (or long-range) COSY sequence. Additional fixed delays are inserted into the basic COSY sequence to enhance the appearance of correlations from small couplings (see text).

Long-range COSY experiment for detection of small coupling constants... 

Kozmiriski and Nanz" reported the development of the HECADE experiment that allowed the determination of heteronuclear coupling constants from E-COSY-type crosspeaks. A sensitivity improved HSQC-HECADE pulse sequence has since been developed by the same authors." The HSQC-based GSQMBC experiment reported in 1997 by Sklenaf and coworkers,and discussed in Section 3.3.3, has also been used for the measurement of small, long-range heteronuclear coupling constants. 

Delayed COSY Correlating coupled homonuclear spins through small couplings. Often used to identify proton correlations over many bonds (>3), hence also known as long-range COSY... 

T. pittieri (A. pittieri) also provided three new bisindoles constituted from 11-methoxyvincamajinyl (367) and vincorine (368) units, viz., ll-[10-(ll-methoxy-17-epi-vincamajinyl)]-vincorine (369), ll-[10-(ll-methoxyvincamajinyl)]-vincorine (370), and 11-[10-(1 l-methoxyvincamedinyl)]-vincorine (371). All three bisindoles are branched from C(IO ) of the vincamajine half to C(11) of the vincorine unit, which was determined based on long-range COSY and NOESY experiments. The C(12) hydrogens were identified from their coupling with the NMe groups, and only one, H(12 ), coupled with an aromatic methoxy. These observations, coupled with the observed NOE between NMe and H(2 ) of the vincamajinyl unit, allowed assignment of the C(IO ) to C(ll) bond (24S). 

The addition of delays before and after the mixing pulse in the COSY sequence gives a relative enhancement to correlations arising from small coupling constants. This technique is called "delayed COSY" (or "small J COSY") it should be noted that the term "long-range COSY" is inappropriate for homonuclear proton experiments because use of it can encourage people to overlook the... 

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