Synthesis and Superpotent Anticancer Activity of Tubulysins Carrying Non-hydrolysable N-Substituents on Tubuvaline.

Synthetic tubulysins 24 a-m, containing non-hydrolysable N-substituents on tubuvaline (Tuv), were obtained in high purity and good overall yields using a multistep synthesis. A key step was the formation of differently N-substituted Ile-Tuv fragments 10 by using an aza-Michael reaction of azido-Ile derivatives 8 with the α,ß-unsaturated oxo-thiazole 5. A structure-activity relationship study using a panel of human tumour cell lines showed strong anti-proliferative activity for all compounds 24 a-m, with IC50 values in the sub-nanomolar range, which were distinctly lower than those of tubulysin A, vinorelbine and paclitaxel. Furthermore, 24 a-m were able to overcome cross-resistance to paclitaxel and vinorelbine in two tumour cell lines with acquired resistance to doxorubicin. Compounds 24 e and 24 g were selected as leads to evaluate their mechanism of action. In vitro assays showed that both 24 e and 24 g interfere with tubulin polymerization in a vinca alkaloid-like manner and prevent paclitaxel-induced assembly of tubulin polymers. Both compounds exerted antimitotic activity and induced apoptosis in cancer cells at very low concentrations. Compound 24 e also exhibited potent antitumor activity at well tolerated doses on in vivo models of diffuse malignant peritoneal mesothelioma, such as MESOII peritoneal mesothelioma xenografts, the growth of which was not significantly affected by vinorelbine. These results indicate that synthetic tubulysins 24 could be used as standalone chemotherapeutic agents in difficult-to-treat cancers.

Tetracycline sensing using novel doxycycline derivatives immobilized on different surface plasmon resonance biosensor surfaces.

BACKGROUND: This article aims to explore novel doxycycline derivatives for analyzing low concentrations of tetracyclines in biological matrices and food in competitive assays. RESULTS: Surface plasmon resonance (SPR) was employed in an indirect competitive format using a bacterial tetracycline-dependent regulatory protein as receptor. Three doxycycline derivatives were synthesized and covalently bound to the surface of four different sensor chips. Parameters that influence the immobilization of the doxycycline derivatives and subsequent binding of the receptor protein were studied. CONCLUSION: The novel doxycycline derivatives were successfully used as competitors in an indirect SPR assay.

Click-chemistry-derived tetracycline-amino acid conjugates exhibiting exceptional potency and exclusive recognition of the reverse tet repressor.

A click-chemistry-based synthesis of biologically active doxycycline-amino acid conjugates is described. Starting from 9-aminodoxycycline derivatives and complementary functionalized amino acids, ligation was accomplished by copper(I)-catalyzed azide-alkyne [3+2] cycloaddition (CuAAC). The final products were tested in a variety of TetR and revTetR systems, and the C-terminally linked phenylalanine conjugate 12 c exhibited high selectivity for revTetR over TetR. Besides the unique property of the specific effector 12 c to effectively differentiate TetR and its reverse phenotype, the test compound proved to be almost devoid of any antibacterial activity; this will be highly beneficial for future applications to control gene expression in bacterial systems.