Synthesis, DNA-binding And Cleaving Activitives Of Functionalized Berberine Derivatives

Berberine is the main active ingredient of Chinese herb Huanglian. Recent studies show that berberine’s antitumor activity is attributed to its interaction with DNA in cancer cells. In order to gain further insight into the interaction between berberine and DNA, and to extend its application, two series of berberine derivatives were synthesized and their interactions with DNA were studied.This thesis mainly comprises the following three parts:Recent progress on the interaction between berberine and DNA is reviewed in Chapter One.In Chapter Two, trehalose-tethered monomeric berberine Ⅱ-1 and dimeric berberine II-2 (Fig.1) were synthesized, and their interaction with calf thymus (CT) DNA was studied by means of spectroscopic techniques. Compounds Ⅱ-1 and Ⅱ-2 were synthesized from the reaction of berberrubine with 6-O-(p-tosyl)-trehalose and 6,6’-O-(p-tosyl)-trehalose, respectively. Their structures were confirmed on the basis of ESI-MS, HR-MS and NMR (1H-,13C-and 2D) data.Secondly, the interaction between the two compounds and CT-DNA was studied by means of spectrophotometric and spectrofluorimetric titrations. Spectrophotomeric titrations suggest that compound Ⅱ-1 and Ⅱ-2 are capable of forming stable complexes with CT-DNA. The fact that compound Ⅱ-1 showed similar hypochromicity and bathochromic shift with berberine, whereas compound Ⅱ-2 exhibited larger hypochromicity and bathochromic shift suggests that compound Ⅱ-1 had comparable DNA-binding affinity with berberine, whereas compound Ⅱ-2 exhibited higher affinity. On the other hand, during the titratons with CT-DNA, two well-resolved isosbestic points were observed for both compound Ⅱ-1 and Ⅱ-2, revealing the existence of one preferential, almost exclusive binding mode of compound Ⅱ-1 and Ⅱ-2 with CT-DNA. Spectrofluorimetric experiments indicate that upon the addition of CT-DNA, the fluorescence intensities of compound II-1 and II-2 were greatly enhanced. Their association constants were calculated from the non-linear fitting of the relative fiuorescent intensity to the concentrations of each compound. Compared with berberine, compound Ⅱ-1 had comparable DNA-binding affinity, whereas compound Ⅱ-2 exhibited 7-fold higher affinity.In Chapter Three, a polyether-tethered dimeric berberine Ⅲ-1 (Fig.2) was synthesized. Compound Ⅲ-1 was synthesised from the reaction of berberrubine with tetraethylene glycol ditosylate, and fully charaterized on the basis of ESI-MS, HR-MS and 1H-NMR. Agarose gel electrophoresis experiments indicate that compound Ⅲ-1 was capable of efficiently cleaving plasmid pBR322 DNA under physiological conditions in the prescence of Cu(II) ion, most probably via an oxidative mechanism. Approximately 3.5×109-fold rate acceleration over uncatalyzed cleavage of supercoiled DNA was observed. The fact that its corresponding polyether-appended monomeric analog II-2 and n-propyl-tethered dimeric berberine Ⅲ-3 showed no cleaving activity supported a mode of action that the two covalently-linked berberine subunits bisintercalate into DNA to compel the polyether chain to form a podand that is capable of forming a catalytically active complex with Cu(Ⅱ) ion.