Ionophore synthesis

Design and synthesis of crown ethers and other macroheterocycles as highly selective ionophores for chemical ion sensors 98YGK291. 

J.-P. Bourgeois, P. Seiler, M. Fibbioli, E. Pretsch, F. Diederich, L. Echegoyen, Cyclophane-Type Fullerene-dibenzo [18] crown-6 Conjugates with trans-1, trans-2, and trans-3 Addition Patterns Regioselective Templated Synthesis, X-ray Crystal Structure, Ionophoric Properties, and Cation-Complexation-Dependent Redox Behavior , Helv. Chim Acta 1999, 82,1572-1595. 

Very recently Bethell et al. (1995) have published the synthesis and electrochemical properties of ionophoric calix[4]arenes which are bridged at the lower rim by an anthraquinone group [58a-d] (Fig. 31). 

While ionophore-stimulated 5-LO product release from neutrophils is often used as an indication of 5-LO inhibition, one must interpret these results cautiously. For example, halothane, an inhalation anaesthetic which may cause membrane perturbation [26], and colchicine, a microtubule disrupter [27], both were active, but presumably not because of 5-LO inhibition. A23187 is assumed to stimulate 5-LO by raising the intracellular calcium level, but this agent causes many other effects which may or may not be related to 5-LO activation, including changes in membrane potential, protein phosphorylation, phospholipid turnover, cyclic nucleotide levels, and DNA and protein synthesis [28]. Also, the effects of some putative 5-LO inhibitors on product release from neutrophils has been shown to vary with the stimulant used [29]. 

For a synthesis of the anti-cancer drug taxol TPAP/NMO was used in three steps, two for oxidation of primary alcohols to aldehydes (by TPAP/NMO/PMS/ CHjClj) and one for a secondary alcohol to ketone (by TPAP/NMO/PMS/CHjClj-CHjCN) [66], cf. also [111] and for the SERCA inhibitor thapsigargin (two primary alcohol and one secondary alcohol oxidation steps) [112], This system was also used during synthesis of the cholesterol biosynthesis inhibitor 1233A [52], the antibiotic and anti-parasitic ionophore tetronasin [113, 114] and for the cytotoxic sponge alkaloids motopuramines A and B [115]. 

Recently, Nicolaou et al.167) reported an elegant asymmetric synthesis of the ionophore antibiotic X-14547 A (153) isolated at Hoffmann-La Roche from Strepto-myces antibioticus NRRL 8167. The key step in this synthesis was an enantioselective a-alkylation of n-butanal via its SAMP-hydrazone (151) to produce the intermediate (152). The asymmetric induction as determined by NMR-spectra of the product SAMP-hydrazone, was 95 % e.e. 

The a-pyrone (635) undergoes an exothermic Diels-Alder reaction with 1-diethylamino-1-propyne to afford the cycloadduct (636) (77JOC2930). Only a single regioisomer is produced, which is in line with the expected polarization of these reagents (Scheme 144). A Diels-Alder reaction of the same a-pyrone with 1-dibenzylamino-l-propyne affords an aniline derivative which has been employed in a chiral synthesis of the aromatic portion of the ionophore antibiotic lasalocid (80JA6178). 

Viewed (and drawn) in a terpene-like perspective, C-glycosyl compounds are in fact functionalized tetrahydrofurans and tetrahydropyrans. As such, they can be considered as versatile chirons for the synthesis of a variety of natural products containing cyclic ether motifs, such as in the ionophores. 

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