Reporter substrates

Catalysts prepared either from VAPOL (109) or from VANOL (110) ligands and triphenylborate were found to catalyze the asymmetric aziridination efficiently. Good to high yields, excellent enantioselectivities, and cis diastereoselectivities were observed with all the reported substrates, which included aromatic, heteroaromatic and aliphatic imines (Table 1.14). 

Ruano has reported substrate-controlled asymmetric ylide aziridination by treatment of enantiopure sulfinyl imines 117 with dimethyloxosulfonium methylide 118 to form terminal aziridines [63], The chiral tert-butylsulfinyl group was shown... 

Kaneda et al. reported substrate-specific hydrogenation of olefins using the tri-ethoxybenzamide-terminated polypropylene imine) dendrimers (PPI) as nanoreactors encapsulating Pd nanoparticles (mean diameter 2-3 nm) [59]. The catalytic tests were performed in toluene at 30 °C under dihydrogen at atmospheric pressure (Table 9.3). The hydrogenation rates were seen to decrease with increasing generation of dendrimers, from G3 to G5. 

Ligand 19 performs excellently with the wide variety of l,l -disubstituted olefins reported. Substrates 61a-m are efficiently reduced at 1 bar of hydrogen in high enantioselectivity with very little dependence on the bulk of the alkyl substituents. Strongly coordinating olefins such as 611 and 61m tyqrically perform poorly in iridium-catalyzed hydrogenations, but reduction with 19 clearly breaks this rule and the substrates are reduced in excellent selectivity and yield. 

Ligand 84 gave excellent enantioselectivity for most of the reported substrates but some sensitivity to steric hindrance was also clear. Changing from a-naphthyl... 

Related systems were later developed for transaldolases 10-12 (Scheme 1.3) [12]. The fructo/tagato stereoselectivity of various transaldolases was determined by fluorescence for the stereoisomeric substrate pair 11/12. However, the reactivity of the substrates towards transaldolases is much lower than with the natural substrate due to the replacement of the phosphate group at position 6 of the natural fructose-6-phosphate substrate with the neutral, aromatic coumarin ether, which is not well recognized by the enzyme. Sevestre et al. [13] reported substrate 13 as a fluorogenic substrate for transketolases, based on a similar fluorescence release mechanism. 

As a first step in determining the kinetics of mechanism-based enzyme inactivation, the time-dependence of the reaction is typically studied. In these experiments, the effects of preincubation (primary incubation) with increasing concentrations of the inactivator over various time intervals is studied for their effects on catalytic activity of the enzyme toward the reporter substrate. This typically results in a plot similar to that represented in Figure 4.11. 

A metabolomic search for endogenous substrates for P450 2W1 revealed lysolecithins [1236], Hydrojgrlation and epoxidation at the internal carbons of the fatly acids were observed, and the reaction occurred with other monoacyl (but not diacyl) glycerophosphohpids [1236]. Other reported substrates are indole, 3-methylin-... 

The only reported substrate for P450 4X1 is anan-damide (A-arachidonylethanolamine) [1656], with the reaction yielding the 14,15-epoxide. Ar-achidonic acid was also slowly converted to its 8,9- and 14,15-epoxides. A stucfy with a battery of carcinogens [350] yielded no positive results for the activation of any carcinogen [350] by bac-ulovims-expressed P450 4X1 (Y. Xiao, and E P. Guengerich, unpublished results). 

As indicated previously, the only reported substrate for P450 llBl is deoxycortisol, which undergoes lljff-hydroxylation to yield cortisol (Fig. 9.12). 

Detection and spatial localization of the reporter are other important considerations for in vivo imaging. For example, reporter substrates that are radiopharmaceuticals formulated with either PET or SPECT radionuclides can be detected readily deep within the body, and well-developed technologies already exist to tomographic ally map the location of the signal source (the radio-tracer) within cross-sections of body tissue. The emitted radiation particles are for all practical purposes minimally attenuated by overlying tissues in mice and other small animals, and can be detected and directly mapped to specific deep body... 

---