Lipophilic exploration

Tarzia et al. [69, 70] have recently reported the FAAH inhibitory activity of a series of alkylcarbamic acid aryl esters. The starting point for their studies was the known serine hydrolase inhibitor carbamyl (51) that had no activity at FAAH. Replacement of the small methyl group of carbamyl (51) with more lipophilic groups and, in particular, bulky lipophilic groups resulted in increased affinity at FAAH (Table 6.6). Exploration of replacements of the naphthyl moiety revealed that replacement with a biphenyl group resulted in improved affinity and in particular, the 3-biphenylyl group proved effective... 

In the bulk of this chapter we will focus on the rapidly emerging new in vitro technology based on the use of immobilized artificial membranes, constructed of phospholipid bilayers supported on lipophilic filters. One objective is to complete the coverage of the components of the transport model explored in Chapter 2, by considering the method for determining the top curve (horizontal fine) in the plots... 

Sugano et al. [561,562] explored the lipid model containing several different phospholipids, closely resembling the mixture found in reconstituted brush border lipids [433,566] and demonstrated dramatically improved property predictions. The best-performing lipid composition consisted of a 3% wt/vol lipid solution in 1,7-octadiene (lipid consisting of 33% wt/wt cholesterol, 27% PC, 27% PE, 7% PS, 7% PI). The donor and acceptor compartments were adjusted in the pH interval between 5.0 and 7.4 [562]. With such a mixture, membrane retention is expected to be extensive when lipophilic drugs are assayed. The use of 1,7-octadiene in the assay was noted to require special safety precautions. 

The method for creating acceptor sink condition discussed so far is based on the use of a surfactant solution. In such solutions, anionic micelles act to accelerate the transport of lipophilic molecules. We also explored the use of other sink-forming reagents, including serum proteins and uncharged cyclodextrins. Table 7.20 compares the sink effect of 100 mM (5-cyclodextrin added to the pH 7.4 buffer in the acceptor wells to that of the anionic surfactant. Cyclodextrin creates a weaker sink for the cationic bases, compared to the anionic surfactant. The electrostatic binding force between charged lipophilic bases and the anionic surfactant micelles... 

Therefore, a continued interest exists in the role of pKa in absorption, which often is related to its effect on lipophilicity and solubility. New methods to measure pKa values are being explored [36], e.g., using electrophoresis [37], and an instrument for high-throughput pKa measurement has recently been announced [38]. 

Although the simple hydroxamate analogues of arachidonic acid showed no anti-inflammatory activity, the concept prompted a number of research groups to explore hydroxamic acids with more stable lipophilic residues. This approach has yielded some of the most interesting anti-inflammatory 5-LO inhibitors reported to date. 

The orientation of the j8-polypeptide has been explored by the use of lipophilic affinity labelling reagents generated photochemically inside the membrane. This shows the region of the polypeptide embedded in the lipid bilayer. The probe 0-hexanoyl-3,5-diiodo-JV- 4-azido-2-nitro-phenyl)tyramine undergoes photochemical conversion into the reactive nitrene, and has been used to label the (Na+, K+)-ATPase from Bufo marinus toad kidney. This shows that the j8-polypeptide is also a transmembranous polypeptide,49 a view that is in accord with immunochemical evidence.50... 

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