Synthesis and Antihistaminic Potential of Some Novel Substituted Dinitrophenothiazine Derivatives

Background: Phenothiazine consists of a three-ring structure compound in which two benzene rings are connected with nitrogen and sulfur atoms at nonadjacent sides. Phenothiazine and its substituted derivatives are abundantly able to produce a variety of important pharmacological and valuable therapeutic effects, and till now, these are under profound investigational processes. 
Objective: To synthesize and evaluate the antihistaminic potential of some newly synthesized dinitrophenothiazine derivatives. 
Materials and Methods: Different derivatives have been synthesized by the appropriate chemical scheme using dinitrophenothiazine as a basic nucleus. The completion of the chemical reactions has been monitored by thin-layer chromatography. The chemical structures of the newly synthesized products (P1–P25) were affirmed by elemental analysis and by spectral (infra-red, 1H nuclear magnetic resonance, and mass spectroscopy) findings and further examined for antihistaminic potential in guinea pigs. The synthesized products were also evaluated for their acute toxicity study and were found nontoxic. 
Results: The majority of the synthesized products of the dinitrophenothiazine series, namely, P07, P11, P12, P13, P15, P16, P17, P18, P19, and P20, have shown antihistaminic activity and compared with mepyramine (standard drug) at 0.8 μg/mL. Among the synthesized products, P18 was found to exhibit maximum antihistaminic activity. However, all the synthesized compounds were found to elicit a significant antihistaminic effect when compared with the standard drug.
Conclusion: Therefore, dinitrophenothiazine compounds could be a good starting point to develop efficacious and potent analogues, as an antihistaminic agent in the treatment of allergic disorders.