Adjacent side chains

The amplitude and correlation time tc of the libration in the stacked state were estimated by using the diffusion in a cone model. The semiangle of the cone 6c at 20° C were obtained to be 22° and 26° for the TiL component and PBG- d2 and PBLG- d2, respectively. The tc values were obtained to be about 10 12 s at 19°C in both states. The 6C of r1L component is 4° smaller than that of PBLG- d2, showing that the amplitude of the libration in the stacked state is smaller than that in the free state due to the steric hindrance between the adjacent side chains forming the stacking... 

The hydroxyiamino group will react with an adjacent side chain carbonyl function. Thus, 2-nitrobenzyl ketones 17 are reduced to the N-hydroxyindole [92]. Side... 

Symbol for the bond angle beween the C2 (that is, a) carbon and the adjacent side-chain carbon of an amino acid in a peptide or protein. 2. Symbol for surface electric potential. 3. A parameter associated with a distribution in statistics, more commonly referred to as chi-squared distributions ( -distribution). Chi-square is a sum of terms in which each term is a quotient obtained by dividing the square of the difference between the observed and the theoretical value of a quantity by the theoretical value. 

Sequentially adjacent side chains may or may not be near each other as seen in the plot of the distances between successive terminal reference points, T, in Fig. 5e. For carboxyl, amide, valine, leucine, and arginine side chains, T was defined as the center between the two terminal atoms. In proline Cy was chosen, in methionine the sulfur, in threonine the oxygen, and in histidine the point between C2 and N3. 

The absolute configuration of the /r -4-dicyanovinylthiochroman derivative 49 has been confirmed as, V at C-3 and R at the adjacent side-chain C atom <2006CC1563> and the (/. (-geometry of the alkene moiety of the heteroarotinoid 50 was established from a single-crystal analysis <2005PS(180)67>. 

The auto-hydrolytic effect of boiling an aqueous solution was also investigated by following changes in the sedimentation and diffusion constants and the intrinsic viscosity. Although the measurements were complicated by the fact that the insoluble portion dissolved as boiling proceeded, the results indicated that the gum molecules were long chains with small adjacent side chains, and that hydrolysis attacked the weaker side chains. 

The electrophilic nature of sulfuryl chloride is validated in a study on the chlorination of anthracene derivatives the observed substituent effects conform well with molecular orbital modeling859. Chlorination of ethyl 3,4,5-trialkylpyrrole-2-carboxylates results in a substantial amount of / -side-chain chlorinated products in addition to the expected a-side-chain chlorination860. This has been ascribed to the electrophilic nature of the reagent861 and the mechanism proposed involves an allylic migration of the halogen from the a-sigma adduct to the adjacent / -side chain. 

Pleated sheet structures are parallel or antiparallel. In the local minimum in the Ramachandran qt/y/ plot (Fig. 19.3) of y3-pleated sheet structures, two configurations are possible, with parallel and antiparallel orientation of the polypeptide strands (Fig. 19.6). The strands are linked by mferchain N-H 0=C hydrogen bonds, which run both ways between the strands and produce a characteristically different pattern in parallel and antiparallel sheets. It is a particular stereochemical feature of the /7-pleated sheets that amino acid side-chains point alternately up and down, and adjacent side-chains interact sterically to produce a right-handed twist [597, 5981 (see Fig. 19.7 a). The regular pattern of a /7-sheet can be interrupted locally by insertion of an extra amino acid, giving rise to a so-called /7-bulge [599]. 

Cho et al. described the synthesis and polymerization of 4,8-cyclododeca-dien-l-yl-(4 -methoxy-4-biphenyl) terephthalate VIII [54,55]. Polymerization was carried out with WCl4(OAr)2/PbEt4. The double bonds in the polymer backbone were subsequently hydrogenated with H2/Pd(C), leading to a SCLCP with a fully saturated hydrocarbon backbone. This polymer system had a very flexible polymer backbone but a stiff connection between the main chain and the mesogenic unit. The distance between two adjacent side chains was about 12 methylene units. This very flexible main chain allowed the polymer to organize into a LC mesophase. Both polymers - the unsaturated and the saturated -showed smectic liquid crystalline mesophases with almost the same transition temperatures (see Table 5). 

Fig. 6 Partial NOESY spectrum of tetramer 3 in water containing 5% D20 (10 mM, 500 MHz, 297 K, mixing time 0.5 s). The NOEs between the protons of the amide groups and those of the adjacent side chains are indicated by arrows...

Perhydropyrrolo[l,2-c][l,3]oxazines are derivatives of formaldehyde, and are cleaved by acid, the formaldehyde being trapped by dimedone <60JOC2028>. With a suitable adjacent side chain, as in (179), acid cleavage, iodine promoted, in the presence of formaldehyde, gives, after recyclization, an indolizidine (180) (Equation (53)) <92JA368>. Lithal has been used to prepare ( )pseudohygroline from oxazine (181) (Equation (54)) <60CCC483>. An indolizine is also produced from lactone (182) by treatment with base (Equation (55)) <90H(302)885>, a pyrrolizidine from lactone (183) via an... 

Prostaglandins are fatty acids of 20 carbon atoms having a cyclopentane ring with two adjacent side chains. Their chemical structure was elucidated in the early 1960s as a result of ultramicroanalysis and mass spectrometry together with various degradations of the small amounts of material then available [18]. A detailed review of the methods used has been published by Samuelsson [19]. The absolute stereochemistry was finally decided upon in 1966 [20] some papers published before then show the side chains in the positions now known to represent the mirror image of the natural forms. 

Our group additivity methods underestimate the stability of these molecules. On the other hand, several large alkanes with vicinal, or adjacent side chains have errors in the opposite direction (stability overestimated) ... 

Aminoheterocycle bioisosteric approaches to amide groupings are exemplified in a report on soluble epoxide hydrolase inhibitors [5j. The replacement of the amide grouping in 1 by adoption of the tethering strategy of linking the carbonyl to adjacent side chains or benzene rings produced 2 (Figure 3.2). 

One of the most studied classes of enzymes that cleave the peptide bond is the peptidases, of which chymotrypsin is one of the best known. The nucleophile in the reaction catalysed by this enzyme is from the alcohol group on the side chain of serine-195. The reaction is base-catalysed from the adjacent side chain, histidine-57. A stable intermediate is formed due to the hydrogen bonding occurring in the cavity, known as the oxy-anion packet. The leaving-group departure occurs from an acid-catalysed reaction (Scheme 2.21). 

Two independent ring-closing metathesis reactions between two adjacent side chains of 11c gave bicyclic alkene 37 in 46 % yield and with an E Z = 3 1 ratio. Such a relatively low yield was attributed to a co-occurring ADMET-like polymerization, which, although under unfavourable conditions, gave an oligomer product... 

Thus, in the synthesis of bislactone lignans such as 335 the aldol addition to succinic anhydrides has been employed [108]. Anhydride 331 is deprotonated and treated with aldehyde 333. The primary adducts 334 and 336 spontaneously open the anhydride ring and rearrange to the lactones 335 and 337. The on-ring stereogenic center is controlled by the adjacent side chain. A crucial diastereo differentiation... 

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