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Multidrug resistance (MDR) is a widespread phenomenon exhibited by many cancers and represents a fundamental obstacle for successful cancer treatments. Tumour cells commonly achieve MDR phenotype through overexpression and/or increased activity of ABC transporters. P-glycoprotein transporter (P-gp, ABCB1) is a major cause of MDR and therefore represents a valuable target for MDR reversal. Several naturally occurring potassium ionophores (e.g. salinomycin) were shown to inhibit P-gp effectively. We have previously shown antitumour activity of a number of 18-crown-6 ether compounds that transport potassium ions across membranes. Here we present data on P-gp inhibitory activity of 16 adamantane-substituted monoaza- and diaza-18-crown-6 ether compounds, and their effect on MDR reversal in model cell lines. We show that crown ether activity depends on their lipophilicity as well as on the linker to adamantane moiety. The most active crown ethers were shown to be more effective in sensitising MDR cells to paclitaxel and adriamycin than verapamil, a well-known P-gp inhibitor. Altogether our data demonstrate a novel use of crown ethers for inhibition of P-gp and reversal of MDR phenotype.

We have demonstrated that quinone methide (QM) precursors can be introduced in the peptide structure and used as photoswitchable units for peptide modifications. QM precursor 1 was prepared from protected tyrosine in the Mannich reaction, and further used as a building block in peptide synthesis. Moreover, peptides containing tyrosine can be transformed into a photoactivable QM precursor by the Mannich reaction which can afford monosubstituted derivatives 2 or bis-substituted derivatives 3. Photochemical reactivity of modified tyrosine 1 and dipeptides 2 and 3 was studied by preparative irradiation in CHOH where photodeamination and photomethanolysis occur. QM precursors incorporated in peptides undergo photomethanolysis with quantum efficiency Φ = 0.1-0.2, wherein the peptide backbone does not affect their photochemical reactivity. QMs formed from dipeptides were detected by laser flash photolysis (λ ≈ 400 nm, τ = 100 μs-20 ms) and their reactivity with nucleophiles was studied. Consequently, QM precursors derived from tyrosine can be a part of the peptide backbone which can be transformed into QMs upon electronic excitation, leading to the reactions of peptides with different reagents. This proof of principle showing the ability to photochemically trigger peptide modifications and interactions with other molecules can have numerous applications in organic synthesis, materials science, biology and medicine.

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Abstract. New dipeptide derivatives 1 and 3 were synthesized and their reactivity in the photochemical reaction of decarboxylation was investigated. The photodecarboxylation of N-adamantyl derivatives 1a and 1b and N-phenylphthalimide derivatives 3a and 3b probably takes place from the triplet excited state. The triplet excited state of 1a, 3a and 3b was characterized by laser flash photolysis. N-phenylphthalimides 3a and 3b undergo 2−5 times more efficient photodecarboxylation than N-adamantylphthalimides 1a and 1b. The aminoacid residue (Phe or Gly) at the C-terminus of the dipeptide does not influence the photodecarboxylation efficiency. Product selectivity in the photoreactions is determined by the conformation of the molecules. N-phenylphthalimides with the separated electron donor (carboxylate) and acceptor moiety (phthalimide) give only simple decarboxylation products, whereas N-adamantyl derivatives also give cyclization products.

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Abstract. A series of adamantane functionalized diaza-lariat ethers 1-6 have been prepared and alkali metal picrate extraction profiles determined. The ability of aza-crown ethers 1-6 to extract the alkali metal picrates was compared with that of diaza-18-crown-6 (7) and N,N '-dibenzodiaza-18-crown-6 (8). Na + and K + transport across bulk liquid membrane was also measured. The results of alkali metal cation extraction experiments showed that lariat ethers 2 and 3, in which the adamantane molecule is linked to the diaza-18-crown-6 by amine bond, have better complexation abilities for all cations compared to the parent crown ethers 7 and 8, as well as a significantly higher selectivity for K + than diaza-18-crown-6. However, diazalariat ether 1 showed reduced, and 4-6 negligible extractability towards any of the alkali cations. Monte Carlo conformational analysis pointed to the importance of conformational flexibility of the investigated compounds for their extraction ability of alkali cations.(doi: 10.5562/cca2100)

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