Novel 1,4 substituted piperidine derivatives. Synthesis and correlation of antioxidant activity with structure and lipophilicity

Natural-product-inspired bioactive alkaloids agglomerated with potential antioxidant activity: Recent advancements on structure-activity relationship studies and future perspectives

Alkaloids derived from natural sources have been shown to have substantial antioxidant activity, suggesting that these natural-product-inspired bioactive entities may have major beneficial influence on human health and food processing sector. The primary process intricates in the etiology of several disorders such as neurodegenerative, inflammatory cardiovascular, and other chronic diseases appear to be either oxidative injury or a cellular damage caused by reactive oxygen species (ROS) or free-radicals. The alkaloid class of bio-heterocycles have been divided into numerous groups based on their biosynthetic precursor and heterocyclic ring systems i.e., piperidine, imidazole, purine, pyrrolizidine, indole, quinolozidine, isoquinoline, tropane, and pyrrolidine alkaloids. Distinct biological properties have been attributed to various compounds belonging to this chemical groups, including antirheumatic, cardiovascular, antispasmodic, anti-ulcer, anti-inflammatory, antibacterial, antinociceptive etc. For many years, natural products and their analogs have been recognized as a possible source of medicinal agents. Recently, research has been concentrated on the synthesis, separation/purification, and identification of new alkaloids derived from a variety of natural sources. This book chapter aims to summarize on the latest developments on the current knowledge on the relationship between the structural features of promising class of bioactive alkaloids with their antioxidant activities.

Antioxidant activity of guaiazulene and protection against paracetamol hepatotoxicity in rats

The effect of guaiazulene, a lipophilic azulene derivative widely found in nature, on radical-mediated processes is examined. The ability of guaizulene to inhibit rat hepatic microsomal membrane lipid peroxidation and to scavenge hydroxyl radicals, as well as to interact with 1,1-diphenyl-2-picrylhydrazyl radical (DPPH), was estimated. It was found that guaiazulene can inhibit lipid peroxidation very significantly, having an IC50 value of 9.8 microM. It can also scavenge hydroxyl radicals and interact with DPPH. The protection afforded by guaiazulene to rats with paracetamol-induced liver injury was also investigated. Paracetamol hepatotoxicity is caused by the reactive metabolite N-acetyl-p-benzoquinone imine (NAPQI), which causes oxidative stress and glutathione (GSH) depletion. Hepatic cytosolic protein, GSH, glutathione transferase and glutathione reductase levels are determined as indices of hepatic injury with or without the administration of guaiazulene. It was found that all parameters affected by paracetamol are restored to normal by guaiazulene treatment, while the administration of guaiazulene alone has no effect on the performed tests compared with the control values. It was concluded that the significant protection against paracetamol-induced GSH depletion and hepatic damage afforded by guaiazulene is probably connected with its antioxidant activity. A molecular mechanism of action of guaiazulene is suggested.

Novel piperidine derivatives: inhibitory properties towards cytochrome P450 isoforms, and cytoprotective and cytotoxic characteristics

The ability of a series of eight piperidine derivatives, substituted at positions 1, 3 and 4, to inhibit P450-dependent metabolism of specific substrates, is reported. Five different P450 isoforms (1A1, 1A2, 2B1, 2E1 and 3A1) in differentially induced rat liver microsomes were used for this purpose. From the results it is concluded that compound 2 was the most potent and moreover, highly selective inhibitor for P4502B1 with an IC(50) of 2.5 μM. Compound 3 appeared to have high selectivity for P4501A1 but not for P4501A2 (IC(50)s 80 and > 1000 μM, respectively). P4502B1 was found to be the most susceptible P450 isoform for inhibition by compounds 2, 3 and 6, while P4502E1 was largely insensitive to the inhibitory properties of all piperidine derivatives. A preliminary SAR study for the cytotoxicity, cytoprotective and P450 inhibitory properties of the piperidine derivatives, was also attempted. Using freshly isolated rat hepatocytes, the toxicity of the compounds was estimated and expressed as lactate dehydrogenase (LDH) leakage, lipid peroxidation (LPO) levels and GSH depletion. Considering the P450 inhibition and cytotoxicity results, compounds 2 and 3 were tested for possible protective activity against paracetamol-induced cytotoxicities. It was found that compound 2 protects completely against LDH leakage and LPO caused by paracetamol in rat hepatocytes isolated from β-naphthoflavone (β-NF) pretreated rats. It is concluded that the piperidine structures studied proved to be potentially valuable lead compounds for the design of potent and selective P450 inhibitors and for non-toxic cytoprotective agents as well.