Studies on Noricumazole A derivatives and their HCV p7 inhibitory activity

Abstract

Noricumazoles A is a natural product isolated for the first time from myxobacterium Sorangium celluloum, So ce399. Noricumazole A has been found to have hepatitis C specific antiviral activity by directly effecting the virus life-cycle while maintaining low cytotoxicity towards the host cell ([IC50] = 8.6 nM, [CC50] = 12.8 nM). Furthermore, Noricumazole A has shown above average inhibitory activity of the voltage-sensitive sodium channel NaV1.7 as well as stabilizing and inhibitory effect on the pH and voltage-dependent potassium ion channel KcsA. In this work, different strategies towards new Noricumazole A derivatives have been investigated. Initially a convergent approach to synthesize a derivative that constitutes of all activity relevant structural elements has been followed. The envisioned structure contained a thiazole ring that has been observed to decrease cytotoxicity as well as the acylated hydroxyl groups at C3 and C11 that have shown to inhibit above average increase of activity. The key coupling step between the two final fragments has been unsuccessful due to the initial oxidation step of the western fragment that has given none-reproducible results. A different strategy towards structurally different Noricumazole derivative has also been pursued – a derivative lacking the hydroxilic group at C13. The convergent synthesis was directed towards two key fragments that would be brought together in an o-lithiation end-game reaction. Furthermore, an optical transport test was developed to study the effect of Noricumazole A derivatives on the viroporin HCV p7. For this purpose, the fluorescent dye PBFI was used as an optical potassium sensor of detecting the HCV p7 mediated potassium transport activity of potassium ions into the liposomes. The transport capacity was reconstituted with PBFI and purified HCV p7 ion channel in liposomes. This made it possible to observe the transport activity of HCV p7 as a function of time. The change in the fluorescence intensity is interpreted as transport activity and is generated by injecting a concentrated potassium chloride solution into the current kinetics. The absence of HCV p7 ion channels in the control liposomes generates little response to the potassium chloride injection, while the presence of HCV p7 shows a drastic increase in the fluorescence signal. In the presence of Noricumazole A, the transport activity is reduced depending on the concentration and results in a dose-response dependence of an IC50 of 4 µM.