Dach effect

FIGU RE 6.1 The Dach effect showing how the outer legs ofthe doublets from two spins lose intensity as the separation between the two chemical shifts... 

Dach effect, intensity skewing. The deviation of the intensity of the individual peaks in a multiplet from those intensities predicted using Pascal s triangle. 

Dach effect. Syn. roof effect. The skewing of the intensities of the individual peaks (legs) of a multiplet caused by the close proximity (in the spectrum) of another resonance to which the resonance in guestion is coupled. The Dach effect is due to nonfirst-order coupling behavior. 

In the absence of Dach effects, we can predict the appearance of multiplets by counting the number of nearby NMR-active spins. Consider the molecule ethanol (Figure 6.2) with its methyl group... 

Clearly, upon using the enantiomeric catalyst [(S,S) instead of (R,R)] the opposite enantioselectivity of the overall process results. However, this effect is also seen with catalysts that are of analogous configuration, but not derived from trans-1,2-diaminocyclohexane (DACH). For example, the pseudo-ephedrine derived catalyst shown in Scheme 5, having (5)-configuration at the centers of chirality, shows some preference for the (5)-azlactone kinetically favors the (5)-azlactone in alcoholytic ring opening [37]. 

Potency. As might be expected, the DACH compounds with more labile leaving groups tend to be more potent as measured both by LDS0 value and optimum dose level in tumour inhibition studies [44,48, 82]. For example, the aquo sulphato and carboxyphthalato analogues of (7) and (8) require about 1.5-to 2-times the dose of cisplatin to achieve maximum antitumour effects on multidose schedules. 

The literature procedures were followed initially to separate cis-and trans-DACH (10) and to resolve the latter. Variations of the published procedure (8) were studied to determine the effect on optical yield of the (— ) -antipode. The best results were obtained when the reaction was run with no special precautions. Purification of the DACH was found to be unnecessary. 

Sedimentation of phytoplankton biomass is an effective pump for contaminants to sediments. Several studies have shown that phytoplankton biomass can significantly influence POP distributions in the water column (e.g., Baker et al., 1991 Dachs et al., 1997 Dachs etal., 1999). In general, high biomass results in lower concentrations of POPs in phytoplankton (Chung et al., 1999) and water (Larsson et al., 1992) and high rates of phytoplankton biomass production result in rapid depletion of POPs in the water column (Axelman et al., 1997). This, in turn, affects air-water gas exchange (eq. 4) by altering Cw. Lake trophic status thus impacts the flux of PCBs and other POPs across the air-water interface, and thus will affect the deposition of POPs in sediments when nutrient availability and phytoplankton dynamics are altered. 

Complex 14 recognizes the estradiol receptor reasonably well (RBA = 6.4%) but the antiproliferative effect observed in vitro on MCF7 cells, derived from hormone-dependent breast cancers, this time appears to be essentially anti-hormonal, with (DACH)PtCl2 itself showing only slight cytoxic activity on these cells. 

Table 4 lists representative data for the oxidation of several substrates by the bimetallic catalyst. Runs 1-3 demonstrate the relative effectiveness of the three chiral ligands studied. In all cases smdied the BINAP or Tol-BINAP ligands gave the highest enantiomeric selectivity with DIOP next and DACH last. The similarity of the enantiose-lectivities for runs 5-7 indicates electronic factors do not play an important role. 

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