Synthesis of Cinnamyl and Caffeoyl Derivatives of Cucurbitacin-Eglycoside Isolated from Citrullus colocynthis Fruits and their Structures Antioxidant and Anti-inflammatory Activities Relationship

Abstract

Background: Citrullus colocynthis (L.) Schrad is an important medicinal plant belonging to the family Cucurbitaceae. Cucurbitacin E glucoside (1) was isolated from Citrullus colocynthis fruits. A novel mono-ester of cucurbitacin-E and cinnamyl and caffeoyl-β-D-glucoside (2 and 3) was synthesized by reaction of cucurbitacin E glucoside with cinnamic and/or caffeic acid in the presence of CHCl2 and K2CO3 with constant stirring with an ice-cooling state for 24h. Mass analyses of the isolated and purified compounds were determined.

Methods: The elemental analysis (C, H, N) suggesting the molecular formulae of the compounds (1-3) to be C38H54O13, C47H60O14, and C47H60O16; respectively. I.R., 1H-NMR, and 13C-NMR analyses were recorded. The median lethal doses (LD50s) of compounds (1-3) in rats were 1262.5, 2500 and 2350 mg/kg b.w., respectively. The anti-inflammatory, total antioxidant, reducing power, anti-reactive oxygen species (ROS) and anti-reactive nitrogen species (RNS) were more pronounced in compound 3 compared to compounds (1-2). This study provides the scientific basis for the anti-inflammatory effects of the isolated cucurbitacin E glucoside (1) and its derivatives (2 and 3) in a t-BHP (tert-butyl hydrogen peroxide)-induced liver damage model.

Results: Injection of rats with t-BHP (1.8 mmol/kg) showed a significant increase in plasma alanine transaminases (ALT), aspartate transaminases (AST), alkaline phosphatase (ALP), lactate dehydrogenase (LDH) and malondialdehyde (MDA) as well as hepatic tumor Necrosis Factor-α (TNF-α), interleukin- 6 (IL-6) and interleukin-23 (IL-23) when compared with control group. Also, injection of rats with t-BHP showed a significant increase in a liver level of reduced glutathione (GSH), superoxide dismutase (SOD), catalase (CAT) and glutathione-S-transferase (GST) as compared with control group. Oral administration of cucurbitacin E glucoside (1) and its derivatives (2 and 3) at a concentration of 25 and 50 mg/kg b.wt daily for 5 days showed a significant protection against-induced alteration in liver GSH, SOD, CAT and GST as well as plasma ALT, AST, ALP, LDH and MDA levels. Furthermore, Cucurbitacin E glucoside (1) and its derivatives (2 and 3) inhibited the elevation of proinflammatory cytokines (TNF-α, IL-6, and IL-23) in the livers of t-BHP-treated rat models.

Conclusion: These results suggested that mechanistic-based evidence substantiating the traditional claims of cucurbitacin E glucoside (1) and its derivatives (2 and 3) to be applied for the treatment of inflammation-related disorders, such as oxidative liver damage and inflammation diseases.

Keywords: Antioxidant; cinnamic and caffeic acids; cucurbitacin E glucoside; oxidative stress biomarkers; pro-inflammatory cytokines; structure activity relationship.