Jacareubin Derivatives Increase Their Anti-Allergic Activity.

Jacareubin (2), nujiangexanthone A, and α-mangostin display the highest anti-allergic effects among the active xantones through still not well-known mechanisms. This study investigates the SAR of jacareubin, its precursor xanthone V (1) and their peracetylated (1a and 2a), permethylated (1b and 2b) derivatives and their anti-allergic and anti-inflammatory effects. To characterize the inhibitory effect of jacareubin, 2a and 2b on the anaphylactic reaction, we first utilized in vitro models of bone marrow derived mast cells (BMMCs), determining their capacity of inhibiting the IgE/Antigen-induced degranulation, myeloperoxidase (MPO), and xanthine oxidase (XO) activation. Also, we utilized in vivo models of passive cutaneous anaphylaxis (PCA) and TPA-induced ear edema. In vitro tests showed that the compound 2b was more effective than jacareubin in the inhibition of BMMCs degranulation. Besides, in vivo models of PCA revealed that the fourth cyclized ring of jacareubin is the critical structural element for anti-allergic efficacy, as compound 1 was less effective. Additionally, hydroxyl groups were found to be essential for inhibiting MPO. Jacareubin was the only tested xanthone that directly inhibited XO, a result supported by molecular docking. Overall, jacareubin represents a promising multi-target scaffold that could be used for developing new treatments for inflammatory and allergic diseases.