A modular approach to the bisbenzylisoquinoline alkaloids tetrandrine and isotetrandrine.

An efficient racemic total synthesis of the bisbenzylisoquinoline alkaloids tetrandrine and isotetrandrine in four different routes is reported herein. Key steps of the synthesis include N-acyl Pictet-Spengler condensations to access the tetrahydroisoquinoline moieties, as well as copper-catalyzed Ullmann couplings for diaryl ether formation. Starting from commercially available building blocks tetrandrine and isotetrandrine are accessed in 12 steps. Depending on the sequence of the four central condensation steps, equimolar mixtures of both diastereomers or predominantly tetrandrine or its diastereomer isotetrandrine are obtained. Through computational analysis we were able to rationalize the differences in the observed diastereomeric specificities.

Racemic total synthesis and evaluation of the biological activities of the isoquinoline-benzylisoquinoline alkaloid muraricine.

The first racemic total synthesis of the isoquinoline-benzylisoquinoline alkaloid muraricine is reported herein. Pharmacological characterization identified muraricine as a moderate inhibitor of P-glycoprotein, a crucial factor of multidrug resistance in cancer. When combined with vincristine, muraricine partly reversed the chemoresistance of vincristine-resistant leukemia cells at a nontoxic concentration. Furthermore, no cytotoxic effects on noncancerous human cells in therapeutically relevant concentrations were observed.

Synthesis, biological evaluation and toxicity of novel tetrandrine analogues.

In this work, we present the design and synthesis of novel fully synthetic analogues of the bisbenzylisoquinoline tetrandrine, a molecule with numerous pharmacological properties and the potential to treat life-threatening diseases, such as viral infections and cancer. Its toxicity to liver and lungs and the underlying mechanisms, however, are controversially discussed. Along this line, novel tetrandrine analogues were synthesized and biologically evaluated for their hepatotoxicity, as well as their antiproliferative and chemoresistance reversing activity on cancer cells. Previous studies suggesting CYP-mediated toxification of tetrandrine prompted us to amend/replace the suspected metabolically instable 12-methoxy group. Of note, employing several in vitro models showed that the proposed CYP3A4-driven metabolism of tetrandrine and analogues is not the major cause of hepatotoxicity. Biological characterization revealed that some of the novel tetrandrine analogues sensitized drug-resistant leukemia cells by inhibition of the P-glycoprotein. Interestingly, direct anticancer effects improved in comparison to tetrandrine, as several compounds displayed a markedly enhanced ability to reduce proliferation of drug-resistant leukemia cells and to induce cell death of liver cancer cells. Those enhanced anticancer properties were linked to influences on activation of the kinase Akt and mitochondrial events. In sum, our study clarifies the role of CYP3A4-mediated toxicity of the bisbenzylisoquinoline alkaloid tetrandrine and provides the basis for the exploitation of novel synthetic analogues for their antitumoral potential.