Aliphatic side chains

When an aromatic compound having an aliphatic side chain is subjected to oxidation, fission of the side chain occurs between the first and second carbon atoms from the benzene ring, the first carbon atom thus becoming part of a carboxyl ( -COOH) group. For example ... 

Similar ligand-ligand interactions have been reported for a large number of ternary -amino acid complexes, built up of two different amino acid.s. A compilation of 72 examples is presented in reference 39. The extra stabilisation due to ligand-ligand interactions in these complexes depends on the character of the amino-acid side chains and amounts to 0.34 - 0.57 kJ/mole for combinations of aromatic and aliphatic side chains and 0.11 - 6.3 kJ/mole when arene - arene interactions are possible. ... 

Sterols and Cholesterol. Natural sterols are crystalline steroid alcohols containing an aliphatic side chain at C17. Sterols were first... 

Fluorosilicones consist of PDMS backbones with some degree of fluoro-aliphatic side chains. The fluorinated group can be trifluoropropyl, nonafluorohexylmethyl, or fluorinated ether side group [78,28,79]. These polymers differ not only in substituent group, but also in the amount of fluoro-substitution relative to PDMS, the overall molecular weight and crosslink density, and the amount of branching. In most commercially available cases, these polymers are addition cure systems and the reactions are those discussed previously for silicone networks. 

A saturated ring with an aliphatic side chain favors cleavage at the bond connecting the ring to the rest of the molecule. Compounds containing cyclohexyl rings fragment at m/z 83, 82, and 81, corre-... 

Elastase-like proteinases are serine proteinases that recognized peptide residues with linear aliphatic side chains (alanyl, valyl, leucyl or isoleucyl residues) and that effect hydrolysis of the polypeptide chain on the carboxy-terminal side of these residues. Examples of elastase-like proteinase are pancreatic elastase, neutrophil elastase and proteinase-3. 

More recently, Beckwith demonstrated that intramolecular Meerwein reactions are also possible if one uses an arenediazonium salt with an aliphatic side-chain in the ortho position containing a double or triple CC bond in 8-position. We will discuss them in Section 10.11. 

There are some reactions in which an aryl radical reacts with an sp2-carbon atom of an aliphatic side chain. In such reactions a carbo- or heteroalicyclic ring fused with a benzene ring is formed (Scheme 10-80). They may be called intramolecular Meerwein reactions. Techniques for these syntheses were developed by Beckwith s group in the 1980s. The majority of Beckwith s investigations were made with 2-(2 -propenyloxy)- and 2[(2 -methyl-2 -propenyl)oxy]benzenediazonium tetrafluoro-... 

An interesting example of regioselective CM with ethylene as a tool in natural product degradation was recently disclosed by Hawaiian authors [149]. Thus, CM using catalyst C and ethylene gas was used to degrade the plant polyacetylene oxylipin (+)-falcarindiol (342) with uncertain stereochemistry at C3. As the reaction provided a meso product (343) in 81% yield by regioselective attack at the aliphatic side chain, the natural compound 342, isolated from a Hawaiian endemic plant, had the 3R,8S configuration shown in Scheme 66. 

The mobile phase was an aqueous solution containing 50 mM sodium phosphate and 150 mM sodium chloride at a pH 7.0. Although ionic interactions are likely to constitute the major contribution to retention and selectivity, there would also be significant polar interactions and some dispersive interactions between the aromatic nuclei of the solutes and the aromatic nuclei and the aliphatic side chains of resin respectively. Under these circumstances, without considerable experimental work, it is impossible to identify the relative magnitude of the different contributions from each type of interaction. 

Lipase-catalyzed methanolysis of racemic N-benzyloxycarbonyl (Cbz) amino acid trifluoroethyl esters carrying aliphatic side chains afforded the L-methyl esters and the D-trifluoromethyl esters (Figure 6.16). The released alcohol (CF3CH2OH) is a weak nucleophile that cannot attack the ester product. The nucleophilidty of the leaving group is depleted by the presence of an electron-withdrawing group [63]. 

If a target aminodicarboxyl units bears an aryl group in one of its side chains, retrosynthetic analysis indicates that a bromoamide synthon 12, bearing an aliphatic side-chain, should react with a nucleophilic partner carrying the aromatic side chain. In the alternative bromoamide 21, HBr elimination to cinnamic derivatives competes with the desired bromine substitution. 

Structural Studies of Peptoids with Aliphatic Side Chains by CD, NMR, and X-ray Crystallography... 

Peptoids based on a-chiral aliphatic side chains can form stable helices as well [43]. A crystal of a pentameric peptoid homooligomer composed of homochiral N-(1-cyclohexylethyl)glycine residues was grown by slow evaporation from methanol solution, and its structure determined by X-ray crystallographic methods. In the crystalline state, this pentamer adopts a helical conformation with repeating cis-... 

Examination of the top view of the helix indicates that side-chains of residues i and i-t3 are located almost on top of each other (Fig. 2.12 B and D) and suggest that hydrophobic interactions between overlapping aliphatic side-chains could play a significant role in stabiUzing the overall structure. The distance between facing C(a) atoms at positions i and i-i-3 is approximately 4.8 A. The helix is compact with a diameter of ca. 4.7 A, shghtly larger than that of the a-hehx (4.3 A). 

Crucial to this class of inhibitors was the discovery of (1 J ,25)-l-amino-2-vinylcyclopropane carboxylic acid (vinyl-ACC A) as a PI residue [99]. Initially, several reports appeared describing chemically stable replacements for the cysteine residue at the PI position of all tra i-cleaved substrates. An aliphatic side chain with two (aminobutanoic acid) or three (nor-valine) carbon atoms seemed to be an acceptable replacement, with only a moderate loss in potency and improved chemical stability [96, 100]. An improved PI... 

Serine proteases usually show primary specificity (occupation of subsite Si) for positively charged arginine or lysine (trypsin, plasmin, plasminogen activators, thrombin), large hydrophobic side chains of phenylalanine, tyrosine, and tryptophan (chymotrypsin, cathepsin G, chymase, and subtilisin), or small aliphatic side chains (elastases). Nevertheless, there are a large number of variations and in many cases, other subsites like S2 and S3 are more discriminating while maintaining the... 

One of the few successful analogues in the p-1act am series with an aliphatic side chain is ceph-ac trile (23). It was made by reacting 7-amino-cephalosporanic acid with cyanoacetyl chloride in the... 

The solvent-range product was not separately analysed as it was not able to be separated from the recovered solvent in the distillate. However, GLC examination of the distillate indicated that the solvent-range product was derived mainly from aliphatic side chains in the coal (9). Note that virtually no solvent-range product was derived from fraction D. 

Ladik, J., A. Sutjianto, and P. Otto. 1991. Improved Band Structures of Some Homopolypeptides with Aliphatic Side Chains and of the Four Nucleotide Base Stacks Estimation of Their Fundamental Gap. J. Mol. Struct. (Theochem) 228, 271-276. 

Figure 18A shows the overlaid multiplicity-edited GHSQC and 60 Hz 1,1-ADEQUATE spectra of posaconazole (47). As will be noted from an inspection of the overlaid spectra, there is an overlap of the C46 and C47 resonances of the aliphatic side chain attached to the triazolone ring that can be seen more clearly in the expansion shown in Figure 18B. In contrast, when the data are subjected to GIC processing with power = 0.5, the overlap between the C46 and C47 resonances is clearly resolved (Figure 18C). In addition, the weak correlation between the C3 and C4 resonances of the tetrahydrofuryl moiety in the structure is also observed despite the fact that this correlation was not visible in the overlaid spectrum shown in A. This feature of the spectrum can be attributed to the sensitivity enhancement inherent to the covariance processing method.50...

The high viscosity of heavy crude oils is essentially due to the high levels of asphaltene content. Asphaltene is the highest MW component of crude oil, is a friable, amorphous dark solid, which is colloidally dispersed, in the oily portion of the crude. Asphaltenes are considered to be heavily condensed aromatic molecules with aliphatic side chains and with high heteroatom content (S, N, and O) as well as high-metal content. The asphaltene fraction is physically defined as that fraction insoluble in n-alkanes, but soluble in toluene and is the most polar fraction of oil. 

Several factors related to chemical structure are known to affect the glass transition tempera lure. The most important factor is chain stiffness or flexibility of the polymer. Main-chain aliphatic groups, ether linkages, and dimethylsiloxane groups build flexibility into a polymer and lower Tg Aliphatic side chains also lower Tg, (he effect of the length of aliphatic groups is illustrated by the methacrylate series (4,38) ... 

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