Clinal

In order to think about the nature and consequences of cell wall polymer phenolic cross-linking, we need a working model of the mode of assembly and the final structure of the primary cell wall. Unfortunately, there is no universally acceptable model that proposed by Albersheim and co-workers (3) is not now widely accepted because the postulated interpolysaccharide glycosidic bonds have not been demonstrated (4) and the warp-weft model of Lamport (5) rests on the assumptions that extensin (i) forms a defined-porosity network (not proven) (ii) is orientated anti-clinally to the cell surface [some evidence against (6)] and (iii) is a major component of all primary cell walls (not true). 

The same authors have also studied compounds 86 and 87 having a methoxy group (Fig. 15). These compounds could exist either in the chair form with an axial (88) or an equatorial methoxy group (89), or in the twist-boat 90. Conformer 88 is disfavored sterically but is favored electronically, whereas the twist boat 90 with a syn clinal methoxy group is favored electronically and does not suffer from severe steric hindrance. It was found... 

Bannister R. 1992. Brain and Bannister s Clinal Neurology. 7th edn. ELBS with Oxford University press, Oxford, pp 622. 

The vicinal coupling Jl 9 of 3-4-4-3 Hz in the spectra of adlumine [124], hydrastine [125], and narcotine [126] implies a syn clinal relationship between C(l)-H and C(9)-H. Considering conformation consonant with this, together with the chemical shifts of the aromatic protons which are related to the mutual orientation of the two aromatic rings, it is possible to assign the threo-configuration to adlumine and the... 

The assumption of a definite location for the negative charge on the j8-carbon requires that 59a and 60a both be on the lowest energy path for substitution and isomerization. That this location should be formed anti derives from orbital symmetry, i.e. microscopic reversibility suggests that anti entry of one halide and syw-departure of the other are improbable. We deduce, therefore, that the substitutions in (142) require at least three elementary steps, e.g. cis-1 - 59a -> 60b -v cis-2 isomerizations with exchange require at least three steps, e.g. cis-l 59a —> 59b - trans-2 isomeriza-... 

Fig. 26. Scale diagram of 1,2-dibromoethane and -ethone. cc, ethane CC c c ethene CC bb, syn BrBr b b, syn BrBr hh, syn HH bbg, Si/ra-clinal (60°) BrBr.

The [3 + 2] reaction of an allylsilane with an enone was proposed to proceed via a regiospecific electrophilic substitution (cf 80) of the enone at C-3 of the allylsilane followed by a cationic 1,2-silyl migration (equation 57). At the yyw-clinal transition state (81), the carbonyl group of the unsaturated ketone was assumed to occupy an endo orientation in relation to the allylsilane142. The transition state was thought to be favorable due to minimization of the charge separation and to possible secondary orbital stabilization. 

It is worth noting here that in contrast to the enantiomeric propanediols used in the dioldehydratase reaction, the two migrating groups here (1-H and -NH2) should have a syn-clinal arrangement if the coenzyme is to abstract and deliver the hydrogen atom on the same side of the molecule. 

The variation ranges of all the torsion angles are very wide from 145 ° for T5-T8, through 172°-180° for T3, T4 up to 225 °-228 ° for T2 and Tl. This means that individual enamine fragments may adopt, in respect of particular torsion angles, any conformation from syn-c ina through sjw-periplanar to anti-clinal, obviously, some of these conformations are observed more frequently than others. 

The molecular structure of the parent compound was investigated in the vapor and in the solid phase using X-ray, XN and GED methods. The reported data are shown in Table i6. In both phases a clear bond length separation could be detected with a localized three-membered ring and its three adjacent double bonds. The symmetry-equivalent cyclopropane bonds are rather long in Csv-symmetric BUL (1.533-1,542 A), which can be explained by the common electron-withdrawing effect of the r-systems in a syn-clinal conformation. For comparison, the unaffected bonds in unsubstituted cyclopropane are 1.499 A in the crystal and 1.5l0 A in the gas phase. Therefore, the bond lengths in BUL... 

Following the usual convention in this type of study in pharmacology, the torsion angle r of the bonded atomsA-5-C-i3 is the angle between the planes A5C and BCD. Viewed from the direction of A, t is positive for clockwise and negative for anticlockwise rotations. The value 7 = 0° corresponds to the planar-cir arrangement of the bonds AB and CD. Values of 7=0°, 60°, 120° and 180° are termed ryn-planar, jj n-clinal, anti-clinal and anri-planar, respectively. 

However, in the discussion Russell (1985) put his findings in the context of the knowledge about physiological dines in macroalgae in general (e.g., Bolton, 1979, 1983 Sheath and Cole, 1984) and came to the conclusion that the observed shift in salinity tolerance is clinal in character as well. On a broader point of view, he doubts the existence of endemic Baltic species in general because... 

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