Synthesis of praziquantel derivatives and their in vitro activity against adult Clonorchis sinensis

The anthelminthic drug praziquantel is a selective agonist of the sensory transient receptor potential melastatin type 8 channel

Praziquantel is the most effective anthelminthic drug for the treatment of schistosomiasis, an infectious disease caused by the platyhelminth Schistosoma mansoni. While praziquantel is known to trigger calcium influx into schisostomes, followed by spastic paralysis of the worms and tegumental disruption, the mechanism of action of the drug is not completely understood. Although relatively well tolerated, praziquantel has been reported to cause mild adverse effects, including nausea, abdominal pain and headaches. As a number of putative Transient Receptor Potential (TRP) channel genes have recently been predicted in S. mansoni, we sought to investigate the effect of praziquantel on three mammalian TRP channels, TRP melastatin type 8 (TRPM8), TRP vanilloid type 1 (TRPV1) and TRP ankyrin type 1 (TRPA1). Using calcium microfluorimetry and the patch clamp technique, we recorded the effect of praziquantel on HEK293T cells expressing recombinant TRPM8, TRPV1 or TRPA1, as well as on cultured dorsal root ganglion (DRG) neurons from wild type and TRPM8 null mutant mice. We discovered that praziquantel is a relatively potent and selective partial agonist of the mammalian and avian cold and menthol receptor TRPM8. The activation of cultured DRG neurons by clinically relevant concentrations of praziquantel is predominantly mediated by TRPM8. Our results may provide clues to a better understanding of praziquantel's mechanism of action and its adverse effects.

Brønsted acid-mediated cyclization-dehydrosulfonylation/reduction sequences: An easy access to pyrazinoisoquinolines and pyridopyrazines

An efficient and alternative synthetic approach has been developed to prepare various N-(arylethyl)piperazine-2,6-diones from 4-benzenesulfonyliminodiacetic acid and primary amines using carbonyldiimidazole in the presence of a catalytic amount of DMAP at ambient temperature. Piperazine-2,6-diones are successfully transformed to pharmaceutically useful pyridopyrazines or pyrazinoisoquinolines and ene-diamides via an imide carbonyl group activation strategy using a Brønsted acid. Subsequent dehydrosulfonylation reactions of the ene-diamides, in a one pot manner, smoothly transformed them to substituted pyrazinones. A concise synthesis of praziquantel (1) has also been achieved through this method.

Praziquantel derivatives I: Modification of the aromatic ring

Several analogues of the potent anthelmintic praziquantel were prepared with variation in the aromatic ring. The biological activity of these analogues was evaluated and compared against known analogues. Amination of the ring was tolerated while other variations were not. These results have important implications for drug development for schistosomiasis.