Discovery of a novel series of α-terpineol derivatives as promising anti-asthmatic agents: Their design, synthesis, and biological evaluation.

A series of novel α-terpineol derivatives were designed and synthesized through structural derivatization of the tertiary hydroxyl moiety or reduction of the double bond. Of the resulting compounds, eight compounds enhanced relaxation of airway smooth muscle (ASM) compared to the α-terpineol precursor, and four compounds (4a, 4d, 4e, and 4i)were superior or comparable to aminophylline at a concentration of 0.75 mmol/L. Assays for 3'-5'-Cyclic adenosine monophpsphate (cAMP) activation revealed that some representative α-terpineol derivatives in this series were capable of upregulating the level of cAMP in ASM cells. Further in vivo investigation using the asthmatic rat model, illustrated that treatment with the compounds 4a and 4e resulted in significantly lowered lung resistance (RL) and enhanced dynamic lung compliance (Cldyn), two important parameters for lung fuction. Moreover, treatment with 4e downregulated the levels of both IL-4 and IL-17. Due to its several favorable physiological functions, including ASM relaxation activity, cAMP activation capability, and in vivo anti-asthmatic efficacy, 4e is a promising remedy for bronchial asthma, meriting extensive development.