Design, synthesis and biological activity evaluation of desloratadine analogues as H1 receptor antagonists.

A series of N-substituted desloratadine analogues were designed and synthesized. They were tested for H1 antihistamine activity by inhibiting histamine-induced contraction of isolated ileum muscles of guinea-pigs in vitro and inhibiting histamine-induced asthmatic reaction in guinea-pigs in vivo. All the evaluated compounds exhibited significant antihistamine activity compared with desloratadine. Five active compounds induced no sedative effects on mouse and four of them exhibited lower anticholinergic side effects than desloratadine. Among these analogues, compound 10, (1S,4S)-4-chlorocyclohexyl desloratadine displayed the highest activity and best safety profile. And it was believed to be a potential candidate as the 3rd generation antihistamine.

Design, synthesis and antihistamine evaluations of several N-hydroxyalkyl desloratadine analogues.

Several N-hydroxyalkyl desloratadines and N-methoxyl ethyl desloratadine were prepared and evaluated for H1 antihistamine activity. The effects on isolated ileum smooth muscle tension in guinea pigs in vitro and asthma-relieving effects on the histamine-induced asthmatic reaction in guinea-pigs in vivo were examined. Most of them exhibited satisfactory H1 antihistamine activity and were obviously more potent than loratadine. Among these, Compound 3, N-(3-hydroxy)propyl desloratadine was the most active one. And it was chosen as a candidate for evaluation of acute toxicity (LD(50)= 0.876(0.784-0.980) g/kg), significantly superior to that of desloratadine (LD(50)=0.353 g/kg). Meanwhile, the experimental results demonstrated that the oxygen atom in the side carbon chain is crucial for enhancing the antihistamine activities.