Original article
Synthesis, structure–activity relationship and in vitro anti-mycobacterial evaluation of 13-n-octylberberine derivatives

https://doi.org/10.1016/j.ejmech.2012.03.012Get rights and content

Abstract

Twenty-eight new 13-n-octylberberine derivatives were synthesized and evaluated for their activities against drug-susceptible Mycobacterium tuberculosis (M. tuberculosis) strain H37Rv. Among these compounds, compound 16e was the most effective anti-tubercular agent with a MIC value of 0.125 μg/mL. Importantly, compound 16e exhibited more potent effect against rifampicin (RIF)- and isoniazid (INH)-resistant M. tuberculosis strains than both RIF and INH, suggesting a new mechanism of action. Therefore, it has been selected as a drug candidate for further investigation, or as a chemical probe for identifying protein target and studying tuberculosis biology. We consider 13-n-octylberberine analogs to be a promising novel class of antituberculars against multi-drug-resistant (MDR) strains of M. tuberculosis.

Graphical abstract

A novel series of 13-substituted berberine derivatives have been identified as potent antimytobacterial agents against both drug-susceptible and MDR strains of Mycobacterium tuberculosis.

  1. Download : Download full-size image

Highlights

► 13-n-Octylberberine analogs are a promising novel class of antituberculars. ► n-Octyl group at position 13 might be essential for the activity. ► Compound 16e exhibited a potential activity against MDR strains of M. tuberculosis.

Introduction

Tuberculosis (TB) is more prevalent in the world today than at any other time in human history. It is anticipated that there will be about 9.8 million new TB cases this year, more than in any other year in history [1], [2]. Five percent of all TB cases are now estimated to be multi-drug-resistant TB (MDR-TB), which is resistant to at least rifampin (RIF) and isoniazid (INH), the two most important first-line drugs used currently in clinic [3], [3](a), [3](b). The overall incidence of TB in HIV positive patients is 50 times that of the rate for HIV negative individuals [4], [5], [6]. In recent years, the emergence of MDR-TB and extensively-drug-resistant TB (XDR-TB) becomes one of the biggest challenges in the treatment of this disease. Although some TB drug candidates are being currently evaluated in clinical trials, there have been no approved new chemical entities for treatment of TB in the past 40 years [7], [7](a), [7](b). Therefore, there is an urgent need to discover the novel scaffold of anti-TB candiates with new mechanism of action, or without cross-resistance with current anti-mycobacterial drugs [7b].

In search for new chemical classes of anti-mycobacterial agents, the compound libraries constructed in our laboratories were screened against drug-susceptible Mycobacterium tuberculosis (M. tuberculosis) strain H37Rv with RIF and INH as reference drugs [8]. 13-n-Octylberberine (1, Fig. 1), identified from the library of berberines, appeared to show a moderate anti-tubercular activity with a MIC of 2.0 μg/mL (Table 1). In particular, compound 1 demonstrated a mild antimycobaterial activity (Table 2) against RIF- and INH-resistant strains isolated from patients in China (MIC = 4.0 μg/mL), suggesting a new mechanism of action [9]. Therefore, the new chemical entity and ideal actitity with no cross resistance of hit 1 provoked our strong interest to explore the structure–activity relationship (SAR) so as to discover candidates with novel mode of action for treatment of TB, especially MDR-TB.

Among the 13-substituted berberine analogs, compounds 29 (Fig. 1) showed no anti-mycobacterial activities against M. tuberculosis H37Rv in comparison with 1. The primary SAR analysis revealed that n-octyl side-chain at the 13-position of 1 might be essential for the bactericidal activity. Therefore, in the present study we retained the n-octyl group at position 13, and focused our SAR study on the variation of substituents at positions 2-, 3- and/or 9-position(s) with 1 as the lead. On the basis of this strategy, 28 new 13-n-octylberberine analogs were designed, synthesized and evaluated for their in vitro anti-tubercular activities against drug-susceptible and drug-resistant stains of M. tuberculosis.

Section snippets

Chemistry

Twenty-eight 13-n-octylberberine analogs were synthesized with commercially available berberine (2) as the starting material as described in Scheme 1, which includes three synthetic methods (Route A, B and C). The intermediate 10 was obtained via a selective reduction reaction, in which NaBH4 was used as a reducing agent and methanol as the solvent [10]. Then, the intermediate 10 reacted with n-octyl aldehyde in the solvent mixture of EtOH (80%) and HOAc, and then acidified with 2 N HCl to yield

SAR analysis for anti-mycobacterial activity

Twenty-eight 13-substituted berberine derivatives were first evaluated for their anti-tubercular activities against the multiplication of drug-susceptible M. tuberculosis strain H37Rv with the microplate alamar blue assay (MABA). RIF and INH were used as reference drugs. Structures of 28 analogs and their anti-mycobacterial activities are shown in Table 1.

SAR study was first focused on the substituents at the 9-position on the aromatic ring D of 1. Replacement methoxyl at the 9-position with

Conclusion

In conclusion, 28 new 13-n-octylberberines with different substituents on the ring A and D were synthesized and evaluated for their anti-mycobacterial activities against M. tuberculosis H37Rv with 1 as the lead. SAR analysis revealed that (i) n-octyl group at position 13 might be essential for the activity; (ii) introduction of substituents at the 2-, 3- and/or 9-positions, especially an ethoxyl, might significantly enhance the activity. Among the test compounds, compound 16e exhibited a

Chemistry

Melting point (mp) was obtained with CXM-300 melting point apparatus and uncorrected. The 1H NMR spectra was performed on a Varian Inova 400 MHz spectrometer (Varian, San Francisco, CA) and 13C NMR on a Bruker Avance III 400 spectrometer in CD3OD or DMSO-d6, with Me4Si as the internal standard. ESI high-resolution mass spectra (HRMS) were recorded on an Autospec UItima-TOF mass spectrometer (Micromass UK Ltd, Manchester, UK). Flash chromatography was performed on CombiflashRf 200 (Teledyne,

Biological activity

RIF and INH were purchased from Sigma Company. All of 13-n-octylberberine analogs were examined for their activities against the multiplication of drug-susceptible M. tuberculosis strain H37Rv with MABA at different concentration. Subsequent two-fold dilutions were performed in 100 μL of 7H9 media in the 48-well microplates, then added 100 μL of bacterial suspension to wells. The amount of bacteria to each well is 4 × 10−4 mg/mL. Plates were incubated at 37 °C. At optimal time, alamar blue

Acknowledgments

This work was supported by the National Natural Science Fundation for Young Scientists (81102312) and the National S&T Major Special Project on Major New Drug Innovation (2012ZX09301002−001−017).

References (21)

  • K. Iwasa et al.

    Planta Med.

    (1997)
  • T. Ikekawa et al.

    J. Pharmacobiodyn

    (1982)
  • J.F. Pan, C. Yu, D.Y. Zhu, H. Zhang, J.Y. Ren, CN Patent 1314347...
  • L.J. Wang et al.

    Planta Med.

    (2008)
  • J.M. Cullen et al.

    Antimicrob. Agents Chemother.

    (2001)
  • C. Dye et al.

    Science

    (2010)
  • A. Koul et al.

    Nature

    (2011)
  • World Health Organization

    Tuberculosis

    World Health Organization

    Tuberculosis

  • P.G. Smith et al.

    Epidemiology of tuberculosis

  • P.C. Hopewell

    Overview of clinical tuberculosis

There are more references available in the full text version of this article.

Cited by (39)

  • A novel berberine-based colorimetric and fluorometric probe for Hg<sup>2+</sup> detection and its applications in water samples

    2021, Inorganic Chemistry Communications
    Citation Excerpt :

    Therefore, the fluorescent probes for detecting Hg2+ based on “turn-on” mechanism have attracted more and more attentions [19–22]. Berberine is a kind of typical isoquinoline alkaloids extracted from huanglian (Rhizoma coptidis) [23], and its derivatives were widely used as anti-bacterial agent [24], antiviral agent [25–27], antioxidant and anticancer [28,29]. In addition, it is a valuable researching direction of fluorescence-based theranostics based on berberine for effective diagnosis and therapy in cancer cells [30].

  • A novel turn-on fluorescent probe based on berberine for detecting Hg<sup>2+</sup> and ClO<sup>−</sup> with the different fluorescence signals

    2021, Microchemical Journal
    Citation Excerpt :

    Recently, some organic fluorescent probes have been reported for detecting Hg2+ [26–31] and HClO/ClO− [32–41]. As an isoquinoline alkaloids extracted from huanglian (Rhizoma coptidis) [42], berberine [43] plays an important role in anti-bacterial agent [44], antiviral agent [45–49], antioxidant and anticancer [50,51]. In addition, berberine also has a special and potential for fluorescence function [52–56].

  • The cell division protein FtsZ as a cellular target to hit cystic fibrosis pathogens

    2020, European Journal of Medicinal Chemistry
    Citation Excerpt :

    Nevertheless, through a combination of structure-assisted drug design and in vitro assays, Sun and co-workers synthesized a series of phenoxy alkyl derivatives of (20), in which the introduction of a hydrophobic function in position 9 of the isoquinoline significantly improved the properties, with the best compound (21) showing low micromolar Minimal Inhibitory Concentration (MIC) against MRSA strains (Table 1) [69]. Starting from an in-house isoquinoline alkaloid library, Song and colleagues identified 13-n-octylberberine derivatives as well as cycloberberines with promising antimicrobial activities [70,71]. In particular, the two 13-phenyl derivative (22) and the cycloberberine (23) were exploited to design and synthesize a novel series of 13-substituted cycloberberines.

  • Synthesis and biological evaluation of berberine derivatives as a new class of broad-spectrum antiviral agents against Coxsackievirus B

    2020, Bioorganic Chemistry
    Citation Excerpt :

    Berberine (BBR, Fig. 1), bearing special quaternary ammonium salt in the benzylisoquinoline alkaloid core, is a major active component of the Chinese herbal medicines Rhizoma Coptidis, Cortex Phellodendri, and Cortex Berberidis, and has been prescribed for the treatment of diarrhea for decades. Multiple therapeutic actions of BBR have been continuously reported including anti-microbial [15], anti-diarrhea [7], anti-inflammatory [8], anti-tumor effects [16], anti-tuberculosis activities [17], and so on. Recently, we and other group identified that BBR could suppress CVB3 replication with IC50 value of 6.41 µM by the inhibition of JNK and p38 activation [2,18].

  • Design, synthesis and biological evaluation of berberine-benzimidazole hybrids as new type of potentially DNA-targeting antimicrobial agents

    2016, European Journal of Medicinal Chemistry
    Citation Excerpt :

    Azoles are currently the most popular class of antimicrobial agents used in medicine. The development of azole based drugs has achieved much advance in medicinal chemistry [9–11]. Benzimidazole derivatives are structural isosteres of naturally occurring purine.

View all citing articles on Scopus
1

These authors made equal contributions to the work.

View full text