Phenanthrene extraction, mechanism

Several inhibitors of AChE have been developed for use in treating Alzheimer s disease, which requires that the drugs readily enter the CNS. These inhibitors are structurally unrelated and vary in their mechanism of inhibition, although all are reversible inhibitors. Tacrine (Cognex) is a monoamine acridine. Donepezil (Aricept) is a piperidine derivative that is a relatively specific inhibitor of AChE in the brain, with little effect on pseudo-ChE in the periphery. Galanthamine (Reminyl) is a tertiary alkaloid and phenanthrene derivative extracted from daffodil bulbs that is a reversible competitive inhibitor of AChE it also acts on nicotinic receptors. 

If reactions of the above type occur during extraction, one would expect that gradually less hydrogen exchange takes place as the extraction proceeds because the number of reactive groups decreases. This assumption was tested in the last experiment shown in Table V. The coal was heated for 6 hours at 340°C. with nontritiated phenanthrene prior to extraction with tritiated phenanthrene. When this pretreated coal was extracted, the tritium content of the product was only 15.6% as compared with 21.4%, in the nonpretreated product. This decreased tritium content supports the above assumption and agrees with the proposed reaction mechanism. 

The latest results on imprinted chiral footprints [154] have shown that enantioselective catalysis (hydrolysis) does occur, and based on kinetic measurement the authors believe that this is due to an enantioselective mechanism. Kaiser and Andersson also chose aluminium doped silica as a polymeric material to obtain phenanthrene imprints and their work has been discussed earlier [52]. No selectivity towards the template was observed when imprinted silica was used as stationary phase. Only relative retention and capacity factors increased. Furthermore, even after careful extraction in a Soxhlet, the polymer still leaked phenanthrene. They also found that diazomethane yields a side reaction forming long alkyl chains. Finally they attempted to rej at the work of Morihara et al. [150-155]. but were not able to detect any selectivity using dibenzamide as the template and instead found that the template decomposes into at least five different products when adsorbed on the silica. Clearly further work is required on these systems. 

---