Amide NH proton

The catenane shown bears one furane dicarboxylic acid building BLOCK instead OF THE ISOPHTHALIC ACID ANALOGUE. SIMILAR TO PYRIDINE, THE FURANE FORMS INTRAMOLECULAR HYDROGEN BONDS WITH THE ADJACENT AMIDE NH PROTONS. 

Exhaustive NMR spectral studies have been reported for ceanothine-B(i9, 24-26), for pandamine (17), for americine (20), for aralionine-A (31), and their derivatives. The number and type of NMe and OMe groups can be learned as can the number and position of the amide NH protons even though exchange with deuterium is not always straightforward. In examples in which mass spectra do not differentiate between leucine and isoleucine the NMR spectra sometimes can do so. 

In the first reaction there are two nucleophilic substitutions and you must decide which nucleophile attacks first. The amine is a better nucleophile than the alcohol and the cyclization occurs because it is an equilibrium with two equal leaving groups (both alcohols) but one (EtOH) goes away when it leaves while the other is attached and cannot escape. The second reaction is more straightforward. The product is used to control the stereochemistry of new molecules as you will see in Chapter 45. For the first time we are using shorthand mechanisms. Note the double-headed arrow on the carbonyl group and the omission of proton transfer steps. If you drew the full mechanism, you did a better job. If you removed the amide (NH) proton before reaction with the acid chloride in the second step you also did a better job. 

Figure 5.67. The time-dependent propagation of magnetisation along a proton spin system as illustrated for the ornithine residue of Gramicidin-S. Traces are extracted from 2D MLEV-17 TOCSY spectra at the amide NH proton shift and show progressive transfer along the sidechain as the mixing time increases.

In the H spectrum, the peak from trace amounts of DMSO-ds is seen at about 2.6 ppm. The peak at 3.4 ppm is probably due to water or another impurity in the sample. Note the two small peaks located equidistant to the taU singlet near 2.0 ppm. The small "satellite" peaks are the result of the 1.1% of the methyl groups that have instead of and thus here coupling between the carbon and the protons is observed. The two doublets for the aromatic protons are observed near 7.5 ppm. The amide NH proton, which is probably hydrogen bonded to the basic (Lewis) sulfoxide functional group in DMSO-de/... 

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