All-£ - amides

In addition to General Reactions i and 2, all amides react with nitrous acid evolving nitrogen ... 

Examine the structure of the short strand of Nylon 6 in which all amide bonds are Z. What is the monomer unit How many monomers are in the strand Note Each end of the polymer strand has been capped by one or more atoms. Do not count these caps as monomers. Compare the strand to that of a simple polypeptide, for example, polyglycine (see also Chapter 16, Problem 9), and point out any obvious similarities. Pay particular attention to hydrogen bonds. 

Examine the structure of a strand of Nylon 6 in which all amide bonds are E. Describe how this differs from the strand in which the amide linkages are Z. In particular, are the same hydrogen-bond patterns found ... 

The problem of the nucleophilicity of amides in glycosylation reactions is not limited to the sulfoxide method and has been shown to result in the formation of glycosyl imidates from intermolecular reaction with activated donors. It appears that this problem may be suppressed by the prior silylation of the amide [348,349]. Accordingly, it may be sufficient to operate the sulfoxide method with an excess of triflic anhydride when amides are present so as to convert all amides into O-triflyl imidates, which are then hydrolyzed on work-up. Despite these problems, several examples have been published of successful sulfoxide glycosylation reactions with acceptors carrying remote peptide bonds [344,345] and with donors coupled to resins via amide-based linkages [346,347], with no apparent problems reported. Sulfonamides and tertiary amides appear to be well tolerated by the sulfoxide method [340,350],... 

Another feature of the kinetics of acid-catalysed hydrolysis of amides may be of relevance in connection with the nature of the protonated cation, that is the rate maximum which is found at 3-6 M acid for all amides. The usual interpretation of this is that increasing... 

Of all the local anaesthetics available, levobupivacaine and ropivacaine have the most favourable pharmacological characteristics for use in obstetrics. They have the lowest potential for cardiotoxicity and, unlike lidocaine and prilocaine, there is little risk of cumulation when they are administered by epidural infusion at effective doses. Elimination of all amides is prolonged in the neonate, exceeding 20 h in the case of bupivacaine. 

All amides show a carbonyl absorption band known as the amide I band. Its position depends on the degree of hydrogen bonding and, thus, on the physical state of the compound. 

The steric bulk of the thioamide sulfur results in conformational changes that have been documented in cyclopentapeptide and cyclohexapeptide model systems (for more details see Vol. E22b, Section 6.8.5.2.1). For example, in c[-Proi(>[C(=S)-NH]Gly-Pro-Gly-D-Phe-], the first synthetic cyclic thiopeptide, an intramolecular y-turn seen in the all-amide parent compound by NMR methods was perturbed by the putative interaction of sulfur with the adjacent Pro s (3-protons.[9 On the other hand, in a cyclic hexapeptide, the enhanced H-bond donor capacity of the thioamide NH led to the formation of a relatively strong intramolecular H-bond stabilized (3-turn, which was frame shifted compared to that found in its all-amide parent peptide. 10 ... 

ANTIBIOTICS PEPTIDES. Peptide antibiotics are classified according to their overall shape, which can be linear or cyclic, and by the nature of the bonds joining the constituent amino acids and other carboxylic acids, which can be all amide bonds or amide plus ester bonds. Most peptide antibiotics are cyclic peptides that do not contain disulfide linkages. 

A strong carbonyl absorption is evident in the spectra of all amides, although the frequency of absorption varies somewhat with the structure of the amide. Thus primary amides generally absorb near 1680 cm 1, whereas secondary and tertiary amides absorb at slightly lower frequencies. The N—H stretching frequencies of amides are closely similar to those of amines and show shifts of 100 cm-1 to 200 cm 1 to lower frequencies as the result of hydrogen bonding. Primary amides have two N—H bands of medium intensity near 3500 cm 1 and 3400 cm 1, whereas secondary amides, to a first approximation, have only one N—H band near 3440 cm 1. However, a closer look reveals that the number, position, and intensity of the N—H bands of mono-substituted amides depend on the conformation of the amide, which can be either cis or trans ... 

Amides. All amides are characterised by a strong carbonyl absorption band, referred to as the amide I band. Primary and secondary amides additionally show bands arising from N—H stretching and bending vibrations. The N—H... 

Amides Basic (reflux) hydrolysis All amides yield ammonia or the corresponding amine detected by odor or by placing wet blue litmus paper on top of the condenser... 

Similar procedures might turn out to be necessary in the case of 2D vibrational spectroscopy. The spectroscopy demonstrated so far essentially reflects the first step of the procedure in NMR spectroscopy (COSY). So far, we have investigated only the amide I subspace. However, all amide vibrations (N-H, amide II, etc.) might turn out to be equally important in revealing the required information, each of them giving different and hopefully complementary pieces of information. Couplings between different amide subspaces need to be explored. Incoherent population transfer out of the amide I transition appears to be very efficient (Ti = 1.2 ps), and the mechanism and the course of this transfer is completely unknown. 

Figure 20 Part of the four-fold interpenetrated 3D diamondoid network formed by [Cu(L)4]+ [L = 3-cyano-6-methylpyrid-2(l//)-one] as its PF6 salt [58], Hydrogen-bonded links are provided by R2(8) synthons involving all amide groups. Oxygen, nitrogen and key hydrogen atoms are shaded.

The individual amino acids of a protein can be liberated by hydrolyzing the peptide (amide) bonds (-CO-NH-) that link them. The usual procedure is to dissolve the peptide or protein in 6 N HC1 and heat the solution in a sealed, evacuated tube at 100°C for 8 to 72 hr (or for shorter times at higher temperatures). All amide linkages (including the side chain amides of glutamine and asparagine) are cleaved under these conditions. Certain amino acids are entirely (tryptophan) or partially (serine, threonine, tyrosine, cysteine) destroyed, so that special precautions are required for the quantitative determination of these amino acids. 

List the systems perturbed by all amides (CONH2) having log P values of 2 . 5. 

Write line formulas for all amides that are isomers of dimethylmethanamide. 

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