Amphiphilic Guanidinocalixarenes Inhibit Lipopolysaccharide (LPS)- and Lectin-Stimulated Toll-like Receptor 4 (TLR4) Signaling.

We recently reported on the activity of cationic amphiphiles in inhibiting TLR4 activation and subsequent production of inflammatory cytokines in cells and in animal models. Starting from the assumption that opportunely designed cationic amphiphiles can behave as CD14/MD-2 ligands and therefore modulate the TLR4 signaling, we present here a panel of amphiphilic guanidinocalixarenes whose structure was computationally optimized to dock into MD-2 and CD14 binding sites. Some of these calixarenes were active in inhibiting, in a dose-dependent way, the LPS-stimulated TLR4 activation and TLR4-dependent cytokine production in human and mouse cells. Moreover, guanidinocalixarenes also inhibited TLR4 signaling when TLR4 was activated by a non-LPS stimulus, the plant lectin PHA. While the activity of guanidinocalixarenes in inhibiting LPS toxic action has previously been related to their capacity to bind LPS, we suggest a direct antagonist effect of calixarenes on TLR4/MD-2 dimerization, pointing at the calixarene moiety as a potential scaffold for the development of new TLR4-directed therapeutics.

Phosphoryl Transfer Processes Promoted by a Trifunctional Calix[4]arene Inspired by DNA Topoisomerase I.

The cone-calix[4]arene derivative (1H3)2+, decorated at the upper rim with two guanidinium units and a phenolic hydroxyl in an ABAH functionalization pattern, effectively promotes the cleavage of the DNA model compound bis(p-nitrophenyl) phosphate (BNPP) in 80% DMSO solution at pH values in the range 8.5-12.0. The pH dependence of the kinetics was found to be fully consistent with the results of the potentiometric titration of the triprotic acid (1H3)2+. At pH 9.5, the rate enhancement of p-nitrophenol liberation from BNPP relative to background hydrolysis is 6.5 × 104-fold at 1 mM concentration of the calix[4]arene derivative. Experimental data clearly point to the effective cooperation of the three active units and to the involvement of the phenolate moiety as a nucleophile in the phosphoryl transfer step. Subsequent liberation of a second equivalent of p-nitrophenol from the phosphorylated calixarene intermediate is conceivably promoted by the "built-in" guanidine/guanidinium catalytic dyad.

Novel cinchona carbamate selectors with complementary enantioseparation characteristics for N-acylated amino acids.

The synthesis and chromatographic evaluation of the enantiomer separation capabilities of covalently immobilized calix[4]arene-cinchona carbamate hybrid type receptors derived from quinine (QN) and its corresponding C9-epimer (eQN) in different solvents are reported. The receptors display complementary enantiomer separation profiles in terms of elution order, chiral substrate specificity, and mobile phase characteristics, indicating the existence of two distinct chiral recognition mechanisms. The QN-derived receptor binds the (S)-enantiomers of N-acylated amino acids more strongly, shows preferential recognition of open-chained amino acids, and superior enantioselectivity in polar media such as methanol/acetic acid. In contrast, the eQN congener preferentially recognizes the corresponding (R)-enantiomers, displays good enantioselectivity (alpha up to 1.74) for cyclic amino acids, and enhanced stereodiscriminating properties in apolar mobile phases, e.g., chloroform/acetic acid. A comparison of the enantiomer separation profiles with those of the corresponding QN and eQN tert-butyl carbamate congeners indicates no significant level of cooperativity between the calix[4]arene module and the cinchona units in terms of overall chiral recognition, most probably as a consequence of residual conformational flexibility of the calixarene module and the carbamate linkage.